HK1248184B - Method and system for rotational 3d printing - Google Patents

Description

Method and system for rotational three-dimensional printing

Related applications

This application claims priority to U.S. Provisional Patent Application No. 62/023,897, filed July 13, 2014, the contents of which are incorporated herein by reference in their entirety. This application is filed jointly with U.S. Provisional Patent Applications entitled “Waste Disposal for 3D Printing,” attorney docket no. 63080; “METHOD AND SYSTEM FOR 3D PRINTING,” attorney docket no. 63081; “Operation of Printing Nozzles in Additive Manufacture,” attorney docket no. 63083; and “LEVELING APPARATUS FOR A 3D PRINTER,” attorney docket no. 63084.

The contents of all of the above-mentioned documents are incorporated herein by reference as if fully set forth herein.

Technical Field

In some embodiments of the present invention, the present invention relates to three-dimensional printing, and more particularly, but exclusively, to rotational three-dimensional printing.

Background Art

Additive manufacturing (AM) is generally a process in which a three-dimensional (3D) object is manufactured using computer models of multiple objects. This process is used in various fields, such as design-related fields, for visualization, demonstration, and mechanical prototyping, as well as for rapid manufacturing purposes.

The basic operation of any additive manufacturing system involves slicing a three-dimensional computer model into thin sections, converting the results into two-dimensional positional data, and feeding the data into a control device that fabricates the three-dimensional structure in a layer-by-layer manner.

Additive manufacturing involves many different manufacturing methods, including 3D printing, such as three-dimensional inkjet printing, laminated object manufacturing, and fused deposition modeling.

In a 3D printing process, a build material is dispensed, for example, from a dispensing head having a plurality of nozzles, to deposit multiple layers onto a support structure. Depending on the build material, the layers can then be cured or solidified using a suitable device. The build material can include a modeling material, which forms the object, and a support material, which supports the object as it is being built. Various three-dimensional printing technologies exist and are disclosed in, for example, U.S. Patent Nos. 6,259,962, 6,569,373, 6,658,314, 6,850,334, 7,183,335, 7,209,797, 7,225,045, 7,300,619, 7,364,686, 7,500,846, 7,658,976, 7,962,237, and 9,031,680, and U.S. Published Application No. US20130040091, all by the same assignee, the contents of which are incorporated herein by reference.

For example, U.S. Patent No. 9,031,680 discloses a system comprising an additive manufacturing apparatus having a plurality of dispensing heads, a build material supply apparatus configured to supply a plurality of build materials to the manufacturing apparatus, and a controller for controlling the manufacturing and supplying. The system has several operating modes. In one mode, all dispensing heads operate during a single build scan cycle of the manufacturing apparatus. In another mode, one or more dispensing heads do not operate during a single build scan cycle or a portion thereof.

US Patent No. 7,291,002 discloses an apparatus for manufacturing a three-dimensional object. A rotating annular build drum receives a plurality of successive layers of a powdered build material, and a print head is disposed above the annular build drum and configured to selectively dispense droplets of a liquid binder onto the powder.

U.S. Patent No. 8,172,562 discloses an apparatus for manufacturing a three-dimensional object. The apparatus includes a construction container, a support member within the construction container, and a fixed material application device for applying a layer of construction material to the support member. A drive causes the container to move about a rotational axis, and a vertical drive causes the support member to move vertically.

U.S. Published Application No. 20080109102 discloses an apparatus for fabricating a three-dimensional object. The apparatus includes a computer controller, a build platform for supporting the object being fabricated, and a build station for forming a layer of material on the object. Either the build station or the build platform is mounted and driven to rotate about an axis so that the surface of the object being fabricated is repeatedly presented to the build station.

Summary of the Invention

According to one aspect of some embodiments of the present invention, a system for three-dimensional printing is provided. The system comprises: a rotating tray configured to rotate about a vertical axis; a print head, each having a plurality of separate nozzles; and a controller configured to control the inkjet print head to dispense a plurality of droplets of a build material in a plurality of layers during the rotation, thereby printing a three-dimensional object on the tray.

According to some embodiments of the present invention, a plurality of different nozzles of at least one head are positioned at a plurality of different distances from the axis and dispense the building material at a plurality of different dispensing rates.

According to some embodiments of the present invention, at least one of the tray and the inkjet print head is configured to move along a vertical direction parallel to the vertical axis to change a vertical distance between the tray and the inkjet print head, and wherein the controller is configured to continue the dispensing during the movement along the vertical direction.

According to some embodiments of the present invention, the inkjet print head is configured to reciprocate relative to the tray along a radial direction.

According to some embodiments of the invention, the movement along the radial direction is by a screw.

According to some embodiments of the present invention, the controller is configured to compensate for errors in a radial position of the head according to a compensation function.

According to some embodiments of the invention, the screw is a dual support screw, and the function is a linear function.

According to some embodiments of the invention, the screw is a cantilever screw, and the function is a nonlinear function.

According to some embodiments of the present invention, for at least two of the inkjet print heads, the reciprocating motion along the radial direction is independent and at a different azimuth angle.

According to some embodiments of the invention, the controller is configured to stop the dispensing during the reciprocating motion.

According to some embodiments of the invention, the controller is configured to resume the dispensing after the reciprocating motion at an azimuth coordinate that is offset from the azimuth coordinate at which the dispensing was stopped.

According to some embodiments of the invention, the controller is configured to resume the dispensing after the reciprocating motion at the same azimuth coordinate at which the dispensing was stopped.

According to some embodiments of the present invention, the controller is configured to continue the dispensing during the reciprocating motion while adjusting a print data in response to the reciprocating motion.

According to one aspect of some embodiments of the present invention, a system for three-dimensional printing is provided. The system includes: a rotating tray configured to rotate about a vertical axis at a rotational speed; a print head, each having a plurality of separate nozzles; and a controller configured to control the inkjet print head to dispense a plurality of droplets of a build material in a plurality of layers during the rotation to print a three-dimensional object on the tray, and to control the inkjet print head to reciprocate in a radial direction relative to the tray.

According to some embodiments of the present invention, the controller is configured to change a rotational speed of the tray in response to a radial position of the inkjet print head.

According to some embodiments of the invention, the controller is configured to stop the dispensing during the reciprocating motion and to resume the dispensing after the reciprocating motion at an azimuth coordinate that is offset from the azimuth coordinate at which the dispensing was stopped.

According to some embodiments of the present invention, the controller is configured to continue the dispensing during the reciprocating motion while adjusting a print data in response to the reciprocating motion.

According to some embodiments of the present invention, the controller is configured to control at least one of the inkjet print heads to dispense the plurality of droplets such that an azimuthal distance between a plurality of sequentially dispensed droplets varies as a function of the print head along the radial direction.

According to some embodiments of the invention, the variation of the azimuthal distance is a probability function according to the position along the radial direction.

According to one aspect of some embodiments of the present invention, a system for three-dimensional printing is provided. The system comprises: a rotating tray configured to rotate about a vertical axis; a print head, each having a plurality of separate nozzles; and a controller configured to automatically determine a plurality of positions on the tray and to control the inkjet print head to dispense a plurality of droplets of a build material in a plurality of layers during the rotation, so as to three-dimensionally print a plurality of objects at the plurality of positions on the tray, respectively; wherein the automatic determination is based on a predetermined criterion or a set of predetermined criteria, the predetermined criteria being selected from: a first criterion according to which the plurality of objects are arranged so as to balance the tray; and a second criterion according to which more objects are printed away from the axis than objects printed close to the axis.

According to one aspect of some embodiments of the present invention, a system for three-dimensional printing is provided. The system comprises: a rotating tray configured to rotate about a vertical axis; a print head, each having a plurality of separate nozzles; a controller configured to control the inkjet print head to dispense a plurality of droplets of a build material in a plurality of layers during the rotation to print a three-dimensional object on the tray; and a pre-heating element for heating the build material before entering the print head, the pre-heating element being spaced apart from the print head and in fluid communication with the head via a conduit.

According to one aspect of some embodiments of the present invention, a system for three-dimensional printing is provided. The system comprises: a rotating tray configured to rotate about a vertical axis; a print head, each having a plurality of separate nozzles; a controller configured to control the inkjet print head to dispense a plurality of droplets of a build material in a plurality of layers during the rotation to print a three-dimensional object on the tray; and a radiation source configured to reciprocate in a radial direction relative to the tray, wherein the print head is further configured to reciprocate in the radial direction relative to the tray and is not synchronized with the radiation source.

According to one aspect of some embodiments of the present invention, a system for three-dimensional printing is provided, comprising: a rotating tray configured to rotate about a vertical axis; a print head, each having a plurality of separate nozzles; a controller configured to control the inkjet print head to dispense a plurality of droplets of a build material in a plurality of layers during the rotation to print a three-dimensional object on the tray; and a radiation source configured to irradiate the plurality of layers such that energy is delivered at different rates to a plurality of locations at different distances from a center of the tray.

According to an aspect of some embodiments of the present invention, a system for three-dimensional printing is provided, the system comprising: a rotating tray configured to rotate about a vertical axis; a print head, each having a plurality of separate nozzles; a controller configured to control the inkjet print head to dispense a plurality of droplets of a build material in a plurality of layers during the rotation to print a three-dimensional object on the tray; and a radiation source, wherein an azimuthal angular separation between the radiation source and the print head is between about 0.3ω radians and about 0.75ω radians, where ω is an average angular velocity of the tray relative to the print head and the radiation source.

According to one aspect of some embodiments of the present invention, a system for three-dimensional printing is provided. The system comprises: a rotating tray configured to rotate about a vertical axis; a print head, each having a plurality of separate nozzles; and a controller configured to control the inkjet print head to dispense a plurality of droplets of a building material in a plurality of layers during the rotation to print a three-dimensional object on the tray; wherein the controller is further configured to terminate any dispensing of the building material when the print head is over a predetermined area of the tray; and to signal the print head to move in a radial direction relative to the tray when the print head is over the predetermined area.

According to some embodiments of the present invention, the controller is configured to signal at least one of the tray and the inkjet print head to move along a vertical direction parallel to the vertical axis when the head is above the predetermined area to change a vertical distance between the tray and the inkjet print head.

According to some embodiments of the present invention, the controller is configured to control at least one of the inkjet print heads to dispense the multiple droplets so that an azimuthal distance between multiple sequentially dispensed droplets varies as a function of a position of the print head along the radial direction.

According to some embodiments of the present invention, the controller is configured to perform a staggered dispensing of the plurality of droplets during at least one rotation of the tray.

According to some embodiments of the present invention, a stagger level of the stagger distribution varies as a function of a position of the print head along the radial direction.

According to some embodiments of the present invention, the controller accesses a computer-readable medium of a bitmap mask and acquires print data related to a shape of the object only for locations on the tray not masked by the bitmap mask.

According to some embodiments of the present invention, the system further comprises a conical roller for straightening the dispensed building material.

According to some embodiments of the present invention, the tray continuously rotates in the same direction during the process of forming the object.

According to some embodiments of the present invention, at least one of the tray and the inkjet print head is configured to move along a vertical direction parallel to the vertical axis to change a vertical distance between the tray and the inkjet print head, and wherein the controller is configured to continue the dispensing during the movement along the vertical direction.

According to some embodiments of the present invention, the movement along the vertical direction is performed such that the tray and the inkjet print head traverse at least two different vertical distances during a single rotation of the tray.

According to some embodiments of the invention, the movement along the vertical direction is performed such that, during a single rotation of the tray, the vertical distance increases by an amount approximately equal to a characteristic thickness of a single layer of the building material.

According to some embodiments of the invention, the movement along the vertical direction is performed substantially continuously.

According to some embodiments of the present invention, the plurality of inkjet print heads include: at least one supporting material head for dispensing a supporting material; and at least two modeling material heads for respectively dispensing two different modeling materials.

According to some embodiments of the present invention, the system further comprises a support structure positioned below the inkjet print head portion such that the tray is located between the support structure and the head, the support structure being in contact with the tray to prevent or reduce vibration of the tray.

According to some embodiments of the present invention, the tray is replaceable.

According to some embodiments of the present invention, the system further comprises a pallet replacing device configured to automatically replace the pallet.

According to some embodiments of the present invention, the head is configured to maintain a vacuum level within a predetermined range of vacuum levels.

According to some embodiments of the present invention, the system further comprises a pre-heating element for heating the building material before entering the print head.

According to some embodiments of the present invention, the pre-heating element is spaced apart from the head and is in fluid communication with the head via a conduit.

According to some embodiments of the present invention, the system further comprises a pump for withdrawing the construction material from the conduit into the pre-heating element.

According to some embodiments of the present invention, the system further comprises at least one level mounted at one or more locations on a housing of a chassis of the system for indicating a deviation of the chassis from a horizontal state.

According to some embodiments of the present invention, the controller is configured to calculate an amount of building material required to print the object, compare the amount with an available amount of building material, and issue an alarm when the amount required to print the object is greater than the available amount.

According to some embodiments of the present invention, the system further comprises a radiation source configured to reciprocate in a radial direction relative to the tray, wherein the print head is further configured to reciprocate in the radial direction relative to the tray and is not synchronized with the radiation source.

According to some embodiments of the present invention, the system further comprises a radiation source configured to irradiate the plurality of layers such that energy is delivered at different rates to a plurality of locations at different distances from a center of the tray.

According to some embodiments of the present invention, the system further comprises a radiation source, wherein an azimuthal angular separation between the radiation source and the head is between about 0.3ω radians and about 0.75ω radians, where ω is an average angular velocity of the tray relative to the head and the radiation source.

According to some embodiments of the present invention, when printing a plurality of objects simultaneously, the controller is configured to calculate a total printing time of an exception of the plurality of objects and display the calculated time on a display device.

According to some embodiments of the present invention, the controller is configured to calculate the total printing time for each object and display the total printing time for each object.

According to some embodiments of the present invention, the controller is configured to terminate any dispensing of the building material when the head is over a predetermined area of the tray. According to some embodiments of the present invention, the predetermined area has a shape of a circular sector.

According to some embodiments of the present invention, when the head is above the predetermined area, the controller is configured to send a signal to notify the head to move in a radial direction relative to the tray.

According to some embodiments of the present invention, the controller is configured to signal at least one of the tray and the inkjet print head to move in a vertical direction parallel to the vertical axis, thereby changing a vertical distance between the tray and the inkjet print head when the head is above the predetermined area.

According to some embodiments of the present invention, the system further comprises a roller for straightening the dispensed building material, wherein the controller is configured to signal at least one of the tray and the inkjet print head to move in a vertical direction parallel to the vertical axis so as to immediately change a vertical distance between the tray and the inkjet print head once the dispensed building material first reaches the roller.

According to some embodiments of the present invention, the system further comprises a roller for straightening the dispensed building material, wherein the controller is configured to signal at least one of the tray and the inkjet print head to move in a vertical direction parallel to the vertical axis to change a vertical distance between the tray and the inkjet print head so that the vertical movement is completed immediately once the dispensed building material first reaches the roller.

According to some embodiments of the present invention, the controller is configured to select a first printing mode and a second printing mode, wherein an azimuth scan is used in the first printing mode and a vector scan is used in the second printing mode, wherein the vector scan is along a path selected to form at least one structure, wherein the structure is selected from: (i) an elongated structure; (ii) a boundary structure that at least partially surrounds an area filled with the first building material; and (iii) a group consisting of an interlayer connecting structure.

According to some embodiments of the present invention, the system further comprises a radiation source configured to irradiate the plurality of layers, wherein the controller is configured to control the radiation source to ensure that, for at least one layer, the irradiation is initiated at least t seconds after the start of curing of a layer immediately preceding the at least one layer, wherein t is longer than a total time required for the formation.

According to one aspect of some embodiments of the present invention, a device is provided, comprising: a cassette configured to hold a building material, which is selectively dispensed by an additive manufacturing system, the cassette comprising a front end and a rear end, wherein the rear end comprises a fluid connection for connecting the cassette to a dispensing unit of the additive manufacturing system; and a cassette seat for storing the cassette, wherein the cassette is configured to be mounted in the cassette seat at an angle such that the front end of the cassette is raised relative to the rear end.

According to some embodiments of the present invention, the cassette includes a locking spring, and wherein the locking spring is configured to lock into the cassette seat at the angle.

According to some embodiments of the present invention, the cassette includes a well proximate the fluid connection, the well being configured to accumulate a portion of the building material contained in the cassette.

According to some embodiments of the present invention, the angle is 2 to 5 degrees.

According to some embodiments of the present invention, the cassette holder is configured to store a plurality of cassettes.

According to an aspect of some embodiments of the present invention, there is provided a system for three-dimensional printing, the apparatus as described above and optionally as described below.

According to an aspect of some embodiments of the present invention, there is provided a method for manufacturing an object, the method comprising the steps of receiving three-dimensional printing data corresponding to a shape of an object, sending the data to a system for three-dimensional printing, and operating the system to print the object based on the data, wherein the system is the system described above and optionally as described below.

Unless otherwise defined, all technical and/or scientific terms used herein have the same meaning as understood by those of ordinary skill in the art to which the present invention belongs. Although methods or materials similar or identical to those described herein can be used to practice or test embodiments of the present invention, exemplary methods and/or materials are described below. In the event of a conflict, the definitions contained in the patent specification shall prevail. In addition, materials, methods, and examples are for illustration only and are not intended to necessarily limit the respective embodiments.

Implementation of the method and/or system of embodiments of the present invention may involve performing or completing selected tasks manually, automatically, or a combination thereof. Furthermore, according to actual apparatus and devices of embodiments of the method and/or system of the present invention, several selected tasks may be implemented by hardware, software, firmware, or a combination thereof using an operating system.

For example, according to an embodiment of the present invention, the hardware for performing the selected task can be implemented as a chip or circuit. As software, the selected task according to an embodiment of the present invention can be implemented as multiple software instructions, which are executed by a computer using any suitable operating system. In an exemplary embodiment of the present invention, one or more tasks according to the exemplary embodiments of the method and/or system described herein are performed by a data processor, such as a computing platform for executing multiple instructions. Optionally, the data processor includes a volatile memory for storing instructions and/or data and/or a non-volatile memory for storing instructions and/or data, such as a magnetic hard disk and/or a removable medium. Optionally, a network connection is also provided. A display and/or user input device, such as a keyboard or a mouse, is also optionally provided.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is described herein by way of example only, with reference to the accompanying drawings. With specific and detailed reference now to the drawings, it is important to note that the details shown are by way of example only and are intended to illustrate and discuss embodiments of the present invention. In this regard, it will become apparent to those skilled in the art how the embodiments of the present invention may be practiced when this description is taken in conjunction with the accompanying drawings.

In the attached figure:

1A to 1D are schematic diagrams of a system for three-dimensional printing in a top view ( FIG. 1A and FIG. 1D ), a side view ( FIG. 1B ), and an isometric view ( FIG. 1C ) according to some embodiments of the present invention;

2A to 2C are schematic diagrams of multiple print heads according to some embodiments of the present invention;

3A to 3F are schematic diagrams illustrating coordinate transformation according to some embodiments of the present invention;

4A and 4B are schematic diagrams illustrating an embodiment of the present invention according to which a distance along an azimuth angle between sequentially dispensed droplets varies as a function of a position of the print head along the radial direction;

5A to 5H are schematic diagrams illustrating radial motion of the print head portion according to some embodiments of the present invention;

FIG6 is a schematic diagram showing a plurality of print heads mounted on a plurality of different radial axes, arranged such that an azimuthal separation angle exists between adjacent axes;

FIG7 is a schematic diagram illustrating staggering along the radial direction according to some embodiments of the present invention;

8A and 8B are schematic diagrams of a plurality of objects arranged on a tray of a system for three-dimensional printing ( FIG. 8A ), and the expected printing time as a function of the number of objects ( FIG. 8B ), according to some embodiments of the present invention;

9A to 9C are schematic diagrams illustrating a technique for reducing or eliminating resolution variation along an azimuth direction as a function of the radial coordinate according to some embodiments of the present invention;

10 is a schematic diagram of a platform having a screw for establishing reciprocating motion of a print head portion according to some embodiments of the present invention;

11A to 11C show radial position errors of a print head obtained through calculations and experiments performed according to some embodiments of the present invention;

12 is a schematic diagram of a pre-heater element located in a fluid path between a material supply and a print head according to some embodiments of the present invention;

FIG13 shows an experimental setup used in a number of experiments performed according to some embodiments of the present invention;

14A to 14I show experimental results obtained during experiments performed according to some embodiments of the present invention;

15A to 15D are schematic diagrams of multiple structures formed in a layer by vector scanning according to some embodiments of the present invention;

FIG16 is an exemplary cartridge according to some embodiments of the present invention;

FIG. 17 is an exemplary rotary 3D printing system including a cassette according to some embodiments of the present invention; and

18 is an exemplary cartridge housing and a plurality of cartridges according to some embodiments of the present invention.

DETAILED DESCRIPTION

Some embodiments of the present invention relate to three-dimensional printing, and more particularly, but not exclusively, to rotational three-dimensional printing.

Before describing at least one embodiment of the present invention in detail, it should be understood that the present invention is not limited to the details of the construction and configuration of the multiple components and/or multiple methods described in the following description and/or shown in the figures and/or examples. The present invention is capable of other embodiments and being practiced in various ways.

Referring now to the accompanying drawings, Figures 1A to 1D are schematic diagrams of a top view (Figures 1A and 1D), a side view (Figure 1B), and an isometric view (Figure 1C) of a system 10 for three-dimensional printing according to some embodiments of the present invention. The system 10 includes a tray 12 and a plurality of inkjet print heads 16, each having a plurality of separate nozzles. Material for three-dimensional printing is supplied to the head 16 by a build material supply system 42. Typically, the nozzle dispenses a drop of build material in response to an activation pulse having sufficient activation energy. A nozzle receiving energy from an activation pulse that is insufficient to dispense a drop is said to be "tickled." The tray 12 can have a disc shape or can be annular in shape. Non-circular shapes are also conceivable as long as it can be rotated about a vertical axis.

The tray 12 and the plurality of heads 16 are mounted to allow for relative rotational movement between the tray 12 and the plurality of heads 16. This can be achieved by (i) configuring the tray 12 to rotate about a vertical axis 14 relative to the plurality of heads 16, (ii) configuring the heads 16 to rotate about the vertical axis 14 relative to the tray 12, or (iii) configuring the tray 12 and the plurality of heads 16 to rotate about the vertical axis 14, but at different rotational speeds (e.g., directions). Although the following embodiments are described with particular emphasis on configuration (i), in which the tray is configured as a rotating tray that rotates about the vertical axis 14 relative to the heads 16, it should be understood that configurations (ii) and (iii) are also contemplated by the present application. Any of the embodiments described herein can be adjusted to be applicable to either of configurations (ii) and (iii), and one of ordinary skill in the art will know how to make such adjustments.

In the following description, the direction parallel to the tray 12 and pointing outward from the axis 14 is referred to as the radial direction r, the direction parallel to the tray 12 and perpendicular to the radial direction r is referred to herein as the azimuthal direction, and the direction perpendicular to the tray 12 is referred to herein as the vertical direction z.

As used herein, the term "radial position" refers to a position on or above the tray 12 that is a specific distance from the axis 14. When the term is used in conjunction with the print head, the term refers to a position of the head that is a specific distance from the axis 14. When the term is used in conjunction with a point on the tray 12, the term corresponds to any point that belongs to a locus of points, the locus being a circle whose radius is the specific distance from the axis 14 and whose center is at the axis 14.

As used herein, the term "azimuthal position" refers to a position at a specific azimuthal angle relative to a predetermined reference point on or above the tray 12. Thus, a radial position refers to any point that belongs to a locus of points that is a straight line that forms a specific azimuthal angle relative to the reference point.

As used herein, the term "vertical position" refers to a position on a plane that intersects the vertical axis 14 at a particular point.

Tray 12 serves as a support structure for three-dimensional printing. The working area for printing one or more objects is typically (but not necessarily) smaller than the total area of tray 12. In some embodiments of the present invention, the working area is annular. The working area is shown at 26. In some embodiments of the present invention, tray 12 rotates continuously in the same direction throughout the object formation process. In some embodiments of the present invention, the tray reverses its rotation direction at least once during the object formation process (e.g., in an oscillating manner). Tray 12 is optionally and preferably removable. Removing tray 12 can be used for maintenance of system 10 or, if necessary, to replace the tray before printing a new object. In some embodiments of the present invention, system 10 is provided with one or more different replacement trays (e.g., a kit of multiple replacement trays), where two or more trays are designated for different types of objects (e.g., different weights), operating modes (e.g., different rotation speeds), etc. Tray 12 replacement can be manual or automatic, as desired. When automatic replacement is used, system 10 includes a tray replacement device 36 configured to remove tray 12 from its position below head 16 and replace it with a replacement tray (not shown). In the representative illustration of FIG. 1 , the tray exchanger 36 of FIG. 1A is shown as a drive 38 having a movable arm 40 configured to pull the tray 12 , although other types of tray exchangers are contemplated.

In some embodiments of the present invention, the plurality of heads 16 are configured to reciprocate relative to the tray in a radial direction r. These embodiments are useful when the length of the nozzle array of the plurality of heads 16 is shorter than the radial width of the working area 26 on the tray 12. The movement of the plurality of heads 16 in the radial direction is optionally and preferably controlled by the controller 20. A representative diagram of a mechanism suitable for moving the plurality of heads 16 in the radial direction is shown in FIG2. As shown in FIG1D, a head 16 is mounted on a platform 52 (FIG. 10) configured to establish reciprocating motion of the head 16 in the radial direction. The head 16 can communicate with the power supply 42 and the controller 20 (not shown in FIG1D) via a flexible communication line shown at 54.

Several exemplary embodiments of the print head 16 are shown in Figures 1 and 2. Figures 2A and 2C show a print head 16 having one (Figure 2A) and two (Figure 2B) nozzle arrays 22. The nozzles in the arrays are preferably aligned linearly along a straight line. In embodiments where a particular print head has two or more linear nozzle arrays, the nozzle arrays may optionally and preferably be parallel to each other.

Typically (but not necessarily) all print heads 16 are oriented radially (parallel to the radial direction) with their azimuth positions offset from one another. Thus, in these embodiments, the multiple nozzle arrays of different print heads are not parallel to one another, but are angled relative to one another, the angle being approximately equal to the azimuth offset between the heads. For example, one head may be oriented radially and positioned at an azimuth position, and another head may be oriented radially and positioned at an azimuth position. In this example, the azimuth offset between the two heads is , and the angle between the linear nozzle arrays of the two heads is also .

In some embodiments, two or more printheads may be assembled as a block of printheads, in which case the printheads of the block are generally parallel to each other. Figure 2C shows a block comprising several inkjet printheads 16a, 16b, 16c.

In some embodiments of the present invention, a predetermined sub-atmospheric pressure of air is maintained above the liquid level in the head 16. To prevent gravity leakage of the nozzle, a certain vacuum level relative to the surrounding atmosphere, for example, 60 mm water pressure, can be continuously maintained within the head 16. In practice, the mechanism for maintaining the pressure differential can provide a tolerance of, for example, ±5%. In another example, the mechanism for maintaining the pressure differential can provide a tolerance of ±5 mm water pressure.

To maintain the desired vacuum level, a bidirectional pump (not shown) can be placed between the material chamber of the head 16 and the atmosphere. The pump can move air from the chamber of the head 16 to the atmosphere, thereby increasing the vacuum within the head. Conversely, the bidirectional pump can move air from the atmosphere into the head 16, thereby increasing the pressure within the head, that is, reducing the vacuum within the head. Preferably, the head 16 includes a pressure sensor (not shown) that measures the pressure difference between the interior of the head 16 and the external atmosphere. The controller 20 receives current pressure data from the pressure sensor and can activate the pump to maintain a predetermined vacuum level within the head.

In operation, the pressure difference between the pressure inside the head and a reference ambient atmospheric pressure is measured. The pressure difference is optionally and preferably compared to a desired relative pressure or pressure range. The comparison can be performed, for example, by the controller 20. If the measured pressure difference is lower than the desired relative pressure or desired pressure difference range, the pump is preferably started to add air to the chamber. If the measured pressure difference is higher than the desired relative pressure or desired pressure difference range, the pump can be started to remove air from the chamber. If the measured pressure difference is found to be equal to or sufficiently close (within a predetermined pressure difference range) to the desired relative pressure, the pump is optionally and preferably kept inactive, thereby effectively causing the pump to act as a valve to block the air passage between the ambient atmosphere and the interior of the head.

In some embodiments of the present invention, the build material is preheated to a temperature suitable for the build material and the print head prior to entering the print head portion. This preheating is preferably performed as additional heating within the print head, as is known in the art. Preheating can be achieved by a preheating element 160 located in the fluid path between the material supply source 42 and the print head 16, as shown in FIG12 . Preheating element 160 is preferably spaced apart from the print head 16 and is in fluid communication with the supply source 42 via conduit 162 and with the print head 16 via conduit 164. This differs from conventional 3D printing systems, in which the preheater is mounted within the print head portion. Conduit 162 is optionally and preferably provided with a pump 170 configured to generate a flow of build material from the supply source 42 to the preheater 160, and from there into the print head 16. Pump 170 is preferably controlled by controller 20.

In various exemplary embodiments of the present invention, preheating element 160 is stationary, i.e., it is not allowed to move with head 16. Preheating element 160 can employ any type of heating technology, including, but not limited to, resistive heating, radiant heating, and convection heating. Preferably, system 10 includes a fluid recovery loop 166 for controllably recovering construction material from conduit 164, and optionally and preferably from head 16, to preheating element 160 or supply source 42. Fluid recovery loop 166 can include a pump 168 for controlling flow within loop 166. Pump 168 is preferably controlled by controller 20. Alternatively, pump 170 can be a bidirectional pump, in which case recovery of construction material into preheating element 160 can be achieved by reversing the operation of pump 170. In these embodiments, system 10 need not include pump 168.

FIG12 shows that fluid recovery loop 166 has a conduit separate from conduit 164. In these embodiments, when construction material flows back through loop 166, it is preferably prevented from entering preheater element 160, for example, by a controllable valve (not shown) that may be mounted on conduit 164, such as at outlet 172 of preheater 160. However, in some embodiments, the construction material may not necessarily be recovered through a separate conduit. For example, when pump 170 is bidirectional, loop 166 may be implemented as a reverse flow in conduit 164. In such embodiments, a separate conduit for recovery is not necessary, and valve 164 mounted on the conduit is not required.

When head 16 is operating, pump 170 (or pump 168, if used) generally does not allow build material to be withdrawn from conduit 164. When pump 170 is not operating, such as when an operator or controller 20 temporarily interrupts the printing process (e.g., to replace a material cartridge), head 16 is idle. If the idle interval is long enough, build material already in conduit 164 may lose heat to the surroundings, causing the temperature of the build material to drop below the operating temperature. At the end of the idle interval, and before reactivating head 16, controller 20 preferably activates pump 168 or reverses the direction of operation of pump 170 to withdraw build material from conduit 164 into preheater 160. The withdrawn build material is reheated in preheater 160. The withdrawal process preferably continues until no build material remains in conduit 164. Controller 20 may thereafter again reverse the direction of operation of pump 170 (or if recovery is being performed by pump 168 , resume its operation and terminate operation of pump 168 ), and the reheated building material is fed into head 16 via conduit 164 .

In some embodiments, system 10 includes a support structure 30 positioned beneath head 16 such that tray 12 is positioned between support structure 30 and head 16. Support structure 30 may be used to prevent or reduce vibrations that may occur in tray 12 during operation of inkjet printhead 16. In configurations in which printhead 16 rotates about axis 14, support structure 30 preferably also rotates such that support structure 30 is always directly beneath head 16 (with tray 12 between head 16 and tray 12).

In operation, the system 10 is preferably placed on a surface so that the tray 12 is substantially level (e.g., with a deviation of less than 10°, or less than 5°, or less than 4°, or less than 3°, or less than 2°, or less than 1°, or less than 0.5°, or less). In some embodiments, the system 10 further comprises a level 44 mounted at one or more locations on a housing of a chassis 46 of the system 10. Optionally and preferably, the level(s) 44 are electronic devices that communicate with the controller 20. In these embodiments, the controller 20 can issue an alarm signal when the housing or chassis 46 deviates from the horizontal direction above a predetermined threshold. Also contemplated are embodiments in which the controller 20, in response to a signal received from the level device 44, transmits a signal to the actuator 48 to automatically level the housing or chassis 46 when a deviation from the horizontal direction is detected.

The operation of the inkjet print head 16, and optionally and preferably, one or more other components of the system 10 (e.g., movement of the tray 12), is controlled by a controller 20. The controller may include an electronic circuit and a non-volatile memory medium readable by the circuit, wherein the memory medium stores program instructions that, when read by the circuit, cause the circuit to perform control operations as described in further detail below.

The controller 20 can also communicate with a host computer 24, which transmits digital data regarding manufacturing instructions based on computer object data, such as in Standard Tessellation Language (STL) or Stereo Lithography Contour (SLC) format, Virtual Reality Modeling Language (VRML), Additive Manufacturing File (AMF) format, Drawing Exchange Format (DXF), Polygon File Format (PLY), or any other format suitable for computer-aided design (CAD). Object data formats are typically structured according to a Cartesian coordinate system. In such cases, the computer 24 preferably executes a program for transforming the coordinates of each slice in the computer object data from a Cartesian coordinate system to a polar coordinate system. The computer 24 optionally and preferably transmits the manufacturing instructions in terms of the transformed coordinate system. Alternatively, the computer 24 may transmit the manufacturing instructions according to a native coordinate system provided by the computer object data, in which case the coordinate transformation is performed by circuitry of the controller 20 .

In some embodiments of the present invention, when the system 10 prints two or more objects (or two or more separate parts of the same object) on the tray 12, the computer 24 or the circuitry of the controller 20 can automatically determine a plurality of locations on the tray 12. The controller 20 can then instruct the print head 16 to print the objects at the determined plurality of locations. The plurality of locations at which the objects are printed on the tray 12 can be determined by executing an optimization program that simulates different configurations of the objects on the tray 12 and selects one of the plurality of configurations (typically the best possible configuration) based on a predetermined criterion or a set of multiple criteria.

For example, according to a standard, the objects are arranged on the tray 12 so as to balance the tray. This standard is particularly applicable when the objects to be printed are relatively heavy, so that their weight can affect the balance of the tray 12. As a representative example, when the system 10 prints two relatively heavy objects of similar weight, the controller 20 or computer 24 may determine that their positions are approximately opposite relative to the center of the tray, and are generally at the same radial position (i.e., similar distance from the axis 14), and are preferably close to the periphery of the working area; and when the system 10 prints three relatively heavy objects of similar weight, the controller 20 or computer 24 may determine that their positions are at three azimuth positions approximately 120° apart from each other, and are generally at the same radial position, and are preferably close to the periphery of the working area.

According to another criterion, more objects are printed farther from the axis 14 than closer to it. This criterion is particularly applicable when the number of objects to be printed is greater than two, but it can also be applied to the case of two objects. As a representative example, when the system 10 prints n objects, the controller or computer first attempts to arrange all objects around the working area without overlapping and with sufficient distance between adjacent objects. If not all objects can occupy the perimeter of the working area with sufficient distance between adjacent objects, the controller or computer attempts to arrange n-1 objects around the working area (again without overlapping and with sufficient distance between adjacent objects), with one object closer to the axis 14, and so on.

The optimization process optionally and preferably assigns one or more optimization weights (not to be confused with physical weights due to gravity) to each object, simulates different configurations of the multiple objects, calculates an overall optimization score for each simulated configuration, and selects a configuration based on its optimization score. Typically, but not necessarily, the weights have numerical values that quantify a preference for a particular object to be printed at the periphery of the work area. For each specific configuration, an object optimization score can be calculated for each object, and then all object optimization scores can be combined (e.g., added, multiplied). The optimization score for a particular configuration can be calculated at least in part based on the multiple combined object optimization scores, and optionally also based on other criteria (e.g., the spatial relationship between the positions of different objects).

For a particular configuration, the object optimization score can be calculated by combining (e.g., adding or multiplying) the numerical weight of the corresponding object with a parameter representing the distance of the object from the axis 14. Thus, when, in some simulation configurations, objects with high weights (indicating a desire to print the object around the working area) are placed around the working area, the object optimization score of the object is high. On the other hand, when, in some simulation configurations, objects with high weights are not placed around the working area, the object optimization score of the object is low.

In some embodiments of the present invention, computer 24 or the circuitry of controller 20 may also execute an optimization process that receives data regarding the total amount of building material in the system (e.g., in supply source 42) and calculates the amount of material required to print the object. Controller 20 of this embodiment issues an alarm when the amount of material required to print the object exceeds the amount of material available in supply source 42.

The transformation of coordinates allows three-dimensional printing on a rotating tray. In conventional three-dimensional printing, the print head moves back and forth along a straight line above a fixed tray. In such a conventional system, as long as the distribution rate of the head is uniform, the printing resolution is the same at any point on the tray. Unlike conventional three-dimensional printing, not all of the multiple nozzle points of the head cover the same distance on the tray 12 at the same time. Coordinate transformation is optionally and preferably performed to ensure that equal amounts of excess material are at different radial positions. Representative examples of coordinate transformation according to some embodiments of the present invention are provided in Figures 3A to 3F, showing three slices of an object (each slice corresponding to the manufacturing instructions for a different layer of the object), wherein Figures 3A, 3C and 3E show the slices in a Cartesian coordinate system, and Figures 3B, 3D and 3F show the same slices after the coordinate program has been converted to the corresponding slices.

Controller 20 generally controls the voltages applied to the respective components of system 10 according to manufacturing instructions and according to stored program instructions as described below.

Typically, controller 20 controls print head 16 to dispense droplets of build material in multiple layers during rotation of tray 12 to print a three-dimensional object on tray 12 .

Inkjet printheads dispense build materials using inkjet technology. Each printhead can be configured to dispense a different build material. When a particular printhead includes two or more nozzle arrays, each nozzle array can be configured to dispense a different build material. Thus, different build materials can occupy different target locations. Build material types can be divided into two main categories: modeling materials and support materials.

The support material serves as a supporting matrix for supporting an object or part of an object during the manufacturing process and/or other purposes, such as providing a hollow or porous object. The support material is preferably water-dispersible to facilitate its removal once the object is constructed. The support material is preferably dispensed in liquid form and can be cured by radiation, such as, but not limited to, electromagnetic radiation (e.g., ultraviolet radiation, visible radiation, infrared radiation) and electron beam radiation. Conceivable support materials also encompass materials comprising a wax component and, optionally, a viscosity modifying component. These types of support materials are in liquid form at the inkjet printing temperature of the system 10, solidify upon cooling after dispensing, and do not require curing by radiation.

The modeling material is typically a composition formulated for inkjet technology that is capable of forming a three-dimensional object on its own, i.e., without being mixed or combined with any other substances. The modeling material is preferably dispensed in liquid form and is curable by radiation, such as, but not limited to, electromagnetic radiation (e.g., ultraviolet radiation, visible radiation, infrared radiation) and electron beam radiation.

In some embodiments of the present invention, both the support material and the modeling material may be cured using the same type of radiation.

The final three-dimensional object produced by the system 10 is made of the modeling material or a combination of the modeling material and the support material or a modified combination thereof (eg, after curing).

Preferably, but not necessarily, the total number of dispensing nozzles or nozzle arrays is selected so that half of the dispensing nozzles are designated for dispensing support material, and half of the dispensing nozzles are designated for dispensing modeling material. In the representative example of FIG2C , head 16a and head 16b each have one nozzle array, while head 16c has two nozzle arrays. In this embodiment, heads 16a and 16b can be designated for modeling material, and head 16c can be designated for support material. Thus, head 16a can dispense a first modeling material, head 16b can dispense a second modeling material, and head 16c can dispense support material. In an alternative embodiment, for example, head 16c can include two physically separate structures, each having a single nozzle array. In this embodiment, each of the two structures can be physically similar to heads 16a and 16b.

The number of building heads, the number of support heads, and the number of nozzles in each head are typically selected to provide a predetermined ratio, a, between the maximum dispensing rate of the support material and the maximum dispensing rate of the building material. The value of the predetermined ratio, a, is preferably selected to ensure that the height of the building material is equal to the height of the support material at each build layer. Typical values for a range from about 0.6 to about 1.5.

For example, for a=1, the total dispensing rate of support material is typically the same as the total dispensing rate of modeling material when all styling heads and support heads are operating.

In a preferred embodiment, there are M modeling heads, each having m arrays of p nozzles, and S support heads, each having s arrays of q nozzles, such that M×m×p=S×s×q. Each of the M×m modeling arrays and each of the S×s support arrays can be manufactured as a separate physical unit that can be assembled and disassembled from the array group. In this embodiment, each such array optionally and preferably includes a temperature controller and its own material level sensor, and receives a separate control voltage for its own operation.

The type of material delivered to each nozzle array of each print head section for dispensing is optionally and preferably controlled by the controller 20. For example, the controller 20 may signal the build material supply system 42 to supply a first modeling material to the nozzle array of the first head and a support material to another nozzle array of the first head. The controller 20 may also signal the system 42 to supply the first modeling material to the nozzle array of the first head, the support material to another nozzle array of the first head, and a second modeling material to the nozzle array of the second head. Alternatively, the controller 20 may signal the system 42 to supply the support material to one nozzle array of the other head. The controller 20 may also signal the system 42 to supply the first modeling material to the nozzle array of the first head, the support material to another nozzle array of the first head, the second modeling material to one nozzle array of the second head, and the third modeling material to another nozzle array of the second head.

The tray 12 and/or print head 16 are configured to move in a vertical direction z parallel to the vertical axis 14 to change the vertical distance between the tray 12 and the print head 16. In a configuration where the vertical distance is changed by moving the tray 12 in the vertical direction, the support structure 30 preferably also moves vertically with the tray 12. In a configuration where the vertical distance is changed by moving the print head 16 in the vertical direction while maintaining a fixed vertical position of the tray 12, the support structure 30 also remains in a fixed vertical position.

Vertical motion can be established by a vertical drive 28. Once a layer is completed, the vertical distance between the tray 12 and the head 16 can be increased (e.g., the tray 12 is lowered relative to the head 16) by a predetermined vertical step, depending on the desired thickness of the subsequently printed layer. The process is repeated to form a three-dimensional object layer by layer.

The system of this embodiment can select modeling materials from a specific number of modeling materials and/or from materials used to comprise a portion of the object being manufactured to define the desired combination of the selected materials and define the "spatial location" (combined or separate) of their deposition within the layer, thereby enabling a wide range of materials (i.e., material combinations) to be formed, with a certain range of material properties or properties, and enabling the manufacture of an object composed of a combination of multiple different modeling materials, with different parts of the object being characterized by the desired properties.

A three-dimensional object can be constructed using appropriate software, such as CAD software, which outputs the virtual object to system 10 in a portable file format suitable for CAD, as described in further detail above. The user can divide or segment the virtual object to be created into multiple separate parts or regions. Thus, a region in the object is a sub-volume of the object, confined to one or more adjacent surfaces that do not intersect each other.

The virtual object is divided so that different modeling materials, combinations of modeling materials, or structures can be assigned to different regions. In some embodiments, the different regions are stored as separate data files or multiple different parts of a data file, all of which refer to the same axis system and source. The division into multiple separate regions and their conversion into data files are generally performed as known in the art, for example, as described in U.S. Patent No. 5,768,134 assigned to Materialise N.V. Thus, a group of multiple regions or a group of multiple data files can constitute the entire object or an entire part thereof.

In some embodiments of the present invention, the deposition of modeling materials is determined based on the regions thus defined, for example the specific modeling materials to be used and their combination and/or spatial deposition within the regions is determined in the software, as well as the spatial definition of the regions themselves within the object layer, based on the predefined properties desired for the parts of the final object. Typically, the definition of multiple region properties (for example the type of modeling materials and their combination in a given region) can be defined by the software when the virtual object is divided into regions or thereafter. In a preferred embodiment, for any given region, a user or operator of the system 10 can introduce the definition, for example via a user interface. For example, the operator can select a specific region based on the properties desired for each corresponding region and select a modeling material and/or material combination for the region thus defined. An example of this is to define one modeling material or material combination for the perimeter or boundary of the region and a different material or material combination for the remainder. A useful example is to print the bulk of the object in a hard substance, but to print the surface of the object in a soft substance.

Combinations of different modeling materials having different properties can be selected for deposition in different regions to produce a composite material having properties that differ from those of the materials dispensed, or exhibiting a combination of their properties. The resulting properties can vary depending on the combination and/or relative amounts of the materials dispensed. The various materials can be used in a variety of different combinations and their configurations, such as spatial/relative deposition, can be predetermined, depending on the desired properties to be achieved in the final composite material that forms the object or portion thereof.

Thus, according to some embodiments of the present invention, the resulting object can have properties that vary within the object itself, such as properties that increase or decrease from one side of the object to the other, or properties that alternate within the object. For example, selecting one modeling material that is rigid after curing and another that is flexible or elastic after curing can produce a composite object in which some parts of the object are more rigid than others and some parts are more flexible than others. Or, for example, the object can be rigid at the exterior and center but flexible elsewhere. For example, if a greater amount of rigid material is dispensed than a more flexible material, the resulting object material is less rigid than the selected rigid material, but also less flexible than the selected flexible material. Thus, different regions of the resulting object can have different material properties, where a region can be a layer, a portion of a layer, or multiple layers, such as horizontal blocks or other structural configurations of multiple layers, so that material properties can vary within a layer or between different blocks of multiple layers. Composite materials can also have multiple colors that differ from the overall composite material, depending on the relative amounts and spatial distribution of the multiple different colored materials.

Different types of modeling materials can remain separate and distinct within the manufactured object, or they can be mixed during the manufacturing process. In a single-material mode, if, for example, two modeling materials are used, the materials themselves can be combined into a single material, or they can be deposited such that each material remains distinct, yet they are deposited uniformly in adjacent droplets of material to form a uniform, homogenous mixture. In a multi-material mode, two or more modeling materials can be selected to be distributed individually in multiple parts or multiple areas, and/or in other combinations, where the combinations can be generated by distributing relative amounts of each material to multiple different specific target locations or multiple groups of target locations, or by distributing two or more types of modeling materials within the same group of target locations.

During the fabrication of the object, particularly when it is desired to fabricate an object having non-uniform or anisotropic properties, the relative amounts of the different modeling materials dispensed into each layer or portion of each layer can be dynamically varied by the controller 20. The controller 20 preferably receives digital data describing the relative amounts from the computer 24 and controls the respective dispensing rates based on the data. The relative amounts can be varied in a continuous or discrete manner.

The system of this embodiment utilizes the ability of two or more different modeling materials to make it possible to use a wider variety of materials in solid free form fabrication than has heretofore been possible with existing solid free form fabrication techniques, providing many different possibilities for combining multiple materials depending on the desired end goal and/or object properties.

For example, building materials that have a significant tendency to shrink due to the polymerization process are generally not suitable for use in traditional solid freeform fabrication devices. The system of the present embodiment effectively provides a solution to this problem. For example, the system of the present embodiment can produce multiple parts or objects, where the outer surface of the part or object is made of one material, while the rest of the part or object comprises a different material. In such examples, the interior region can be made of a material that lacks mechanical strength, such as a gel or liquid, but has other desirable properties, such as ease of removal, such as to produce a hollow object, or easy burning without leaving ash or other traces.

In some embodiments of the present invention, two or more modeling materials may be dispensed, one or both of which may not have the properties required to construct the desired object. The combination of the two materials can provide a functional building material. For example, one of the materials may not be solidified during the manufacturing process, but may remain in a liquid, gel, paste, or other non-solid or semi-solid form, while the other material is solidified during the manufacturing process. The solidified material may "contain" the non-solidified material, or, once the process is complete, the unsolidified material may be drained, burned, or otherwise removed to provide a hollow or porous model.

In some embodiments of the present invention, two or more modeling materials may be dispensed, one of which may have too low a reactivity as a modeling material in a particular system, resulting in poor precision and low print quality if used alone, while the other material has appropriate reactivity. In this example, it can be noted that a fundamental property of a UV-curable formulation is its reactivity to UV radiation. Reactivity is typically achieved through an appropriate combination of monomers, oligomers, photoinitiators, and photoinitiator concentrations. Acrylic monomers and oligomers (relative to methacrylic acid) are particularly suitable because they have a relatively high intrinsic reactivity, which means that acrylic formulations can use relatively low concentrations of photoinitiators. Due to the relatively low intrinsic reactivity of the methacrylic acid component, its use in the preparation of the formulation is quite difficult. The lack of reactivity of the formulation directly affects its print quality. Using formulations with low reactivity will produce objects with imprecise and unreliable edges and/or surfaces.

Methacrylic acid components generally have valuable properties, such as lower shrinkage and higher Tg (glass transition temperature) than acrylic acid components, but they have lower reactivity than acrylic acid components. The problem can be solved using the system of the present invention, wherein a modeling material with high reactivity, such as an acrylic acid formulation, and another modeling material with low reactivity, such as a methacrylic acid formulation, are used. The high reactivity formulation can be used for the low reactivity formulation surrounded in each layer, so the surface of the object will be composed of the high reactivity formulation and the object core of the low reactivity formulation. Therefore, the quality of the object periphery is ensured, because the characteristics require high reactivity (the quality of the periphery includes wall smoothness and edge sharpness). Since the main body deformation caused by shrinkage is minimized, the accuracy of the object is also ensured. In this way, the valuable properties of the low reactivity component can be utilized. Other types of low reactivity formulations can be used, for example, including UV cationically initiated polymerizable formulations (UV cationically initiated polymerizable formulations).

In some embodiments of the present invention, the nozzle arrays of one or more print heads are configured so that nozzles at different distances from axis 14 dispense build material at different dispensing rates. Preferably, nozzles closer to axis 14 (or the center of tray 12) dispense build material at a lower dispensing rate than nozzles further from axis 14. This configuration is advantageous because it reduces or eliminates different linear velocities at different distances from axis 14.

Different allocation rates can be ensured in more than one way.

In some embodiments of the present invention, the diameter of the nozzle holes varies between different nozzles in the same nozzle array. For example, the diameter of the nozzle holes may be an increasing function of the distance of the nozzle from the axis 14, such that for any pair of nozzles in the same array, the nozzle hole closer to the axis 14 has a smaller diameter than the nozzle hole farther from the axis 14.

In some embodiments of the present invention, the diameter of the nozzle orifice is the same for all nozzles in the same nozzle array, but the nozzles are individually controlled by controller 20. In these embodiments, controller 20 applies different voltage levels to different nozzles in the same array to ensure different dispensing rates for different nozzles in the same array. Preferably, controller 20 selects the applied voltage so that nozzles closer to axis 14 dispense build material at a lower dispensing rate than nozzles further from axis 14.

In some embodiments of the present invention, the diameter of the nozzle orifice varies between different nozzles of the same nozzle array, and the nozzles are individually controlled by the controller 20. In these embodiments, different dispense rates are further ensured by the different sized orifices and by appropriate selection of the voltage applied by the controller 20.

The inventors have also devised a technique to address the problem of a constant dispensing rate when the relative motion between the priming head and the tray is not linear. The technique described below can be used when all nozzles in head 16 dispense build material at the same dispensing rate, but can be used when the printing rate varies. The technique can be used in any printing situation where the nozzles follow a trajectory that is not linear, particularly when operating all nozzles in a print head at the same frequency results in uneven resolution. The technique includes data masking, which will now be explained in more detail.

Each slice in the computer object data is typically, but not necessarily, in the form of a binary bitmap, or the slice data may be calculated on the fly from a three-dimensional computer representation of the object (eg, a 3D mesh).

Although the following embodiments are described with particular emphasis on the use of a bitmap, it should be understood that the operation of reading information from the bitmap can be replaced by the operation of calculating the value at a specific location within a three-dimensional computer representation of the object, and both are contemplated according to various exemplary embodiments of the present invention.

A nozzle activation bitmap is typically calculated from a bitmap of the computer object data. Each bitmap element (e.g., pixel) in the nozzle activation bitmap corresponds to a target location on the corresponding layer, where the value of the bitmap element determines whether a corresponding nozzle is activated upon reaching the corresponding physical location. For example, a "1" indicates a location occupied by build material in the final layer, while a "0" indicates a void in the final layer.

According to this embodiment, the operational bitmap is masked so that the resolution along the azimuth direction of all nozzles is the same, regardless of their position in the head and the trajectory of the head. A representative example of such masking is shown in FIG9A . It shows the nozzle array 22 of the head 16 . The first nozzle (furthest from the axis 14) is represented as nozzle 104 and the last nozzle (closest to the axis 14) is represented as nozzle 106 . FIG9A also shows two exemplary curved trajectories 102 and 108 following the nozzles 104 and 106 during the relative motion of the head 16 and the tray 12 . Six nozzles are shown in the array 22 , but the array 22 can have any number of nozzles. The multiple positions shown of the nozzles 104 and 106 on the trajectories 102 and 108 correspond to a point in time called T ₁ . At another time point T ₁ +dT, nozzle 104 reaches position 110 along trajectory 102 , and nozzle 106 reaches position 112 along trajectory 108 . At yet another time point T ₁ +2dT, nozzle 104 reaches position 114 along trajectory 102 , and nozzle 106 reaches position 116 along trajectory 108 .

Nozzles 104 and 106 mask different arc lengths on trajectories 102 and 108 over the same time interval. Specifically, the three locations traversed by nozzle 104 at time points _T1 , _T1 +dT, and _T1 +2dT are more spaced apart than the three locations traversed by nozzle 106 at these time points. In the example shown in FIG9A , the arc length masked by nozzle 106 between time points _T1 and _T1 +2dT is approximately the same as the arc length masked by nozzle 106 between time points _T1 and _T1 +dT or between time points _T1 +dT and _T1 +2dT. According to some embodiments of the present invention, nozzle 106 is activated at time points _T1 and time point _T1 +2dT, but not at time point _T1 +dT. In other words, the nozzle activation bitmap corresponding to the respective layer is masked so that material is not dispensed at location 112, regardless of whether the nozzle activation bitmap or the bitmap of the input computer object data specifies location 112 as a location for dispensing droplets of build material.

FIG9A shows an example of a 50% masking ratio, wherein for nozzle 106, 50% of the positions along trajectory 108 are masked so that nozzle 106 does not dispense material when reaching these positions. It should be understood that the masking ratio may be different from 50% for other trajectories. The masking ratio for each trajectory of each nozzle can be calculated based on the ratio between the arc lengths masked by different nozzles during the same time interval dT, or based on the ratio between the linear velocities of different nozzles. Based on the masking ratio, controller 20 optionally and preferably decides whether to activate the corresponding nozzle at the corresponding position. According to some embodiments of the present invention, when a nozzle is masked at a point in time, print data is not read from the input bitmap of the nozzle activation bitmap of the nozzle. Or such input is not calculated. These embodiments can be regarded as data dilution because they reduce the amount of data processed at the bitmap level. The advantage of the embodiments is that they save computing time and resources.

By considering the arc length of the trajectory masked by a nozzle that belongs to a group of multiple nozzles, such as a nozzle array, further savings in computing time and resources can be achieved. According to some embodiments of the present invention, the nozzle that masks the longest trajectory segment of the group during a time interval is identified. A binary mask value for the nozzle is then calculated at a time point within the time interval (e.g., "0" for masking and "1" otherwise). When the nozzle is masked, all other nozzles in the group are masked, without calculating individual mask values for these nozzles. Optionally and preferably, the nozzle activation bitmap is not accessed for a group of masked nozzles.

Figure 9B schematically shows the nozzle arrays 22a and 22b of the two heads 16a and 16b, respectively. The symbols corresponding to head 16a are the same as those for head 16 in Figure 9A above. The last nozzle in head 16b is indicated as 122, and the trajectory followed by the nozzle is indicated as 120.

The positions of nozzles 104, 106, and 122 along trajectories 102, 108, and 120 correspond to a point in time, referred to as _T1 . At time _T1 +dT, nozzle 104 reaches position 110 along trajectory 102, nozzle 106 reaches position 112 along trajectory 108, and nozzle 122 reaches position 124 along trajectory 120. For a given time interval (e.g., between time points _T1 and _T1 +dT), the arc length covered by nozzle 104 is the longest of the arc lengths covered by any other nozzle in array 22a.

In the example shown in FIG9B , the arc length covered by nozzle 122 between time points _T1 and _T1 +dT is approximately the same as the arc length covered by nozzle 104 between time points _T1 and _T1 +2dT. According to some embodiments of the present invention, nozzle 104 is activated at time points _T1 and _T1 +2dT, but not at time point _T1 +dT, and nozzle 106 is activated at time point _T1 , but not at time points _T1 +dT or _T1 +2dT. Furthermore, since the arc length covered by any nozzle in array 22a other than nozzle 104 is shorter than the arc length covered by nozzle 104 during the same time interval, no nozzle in array 22a needs to be activated at time point _T1 +dT. In other words, the nozzle activation bitmap corresponding to the corresponding layer is masked so that no material is dispensed by any nozzle in array 22a, at least until first nozzle 104 reaches position 114 along trajectory 102. This corresponds to a data thinning operation as described above, as it reduces the amount of data processed at the bitmap level.

The inventors have discovered that such a process significantly reduces processing time and required computing resources because there is no need to access the nozzle activation bitmap (or calculate its value) when the first nozzle 104 reaches position 114. This savings can be better understood from the illustration provided in Figure 9C.

FIG9C shows nozzle array 22 superimposed on an input bitmap, which in this example is defined on a rectangular grid. Each position on the grid represents an input bitmap element (e.g., a pixel). As shown in FIG9B , these are bitmap elements 130 and 132. Array 22 is shown at time _T1 , where the first nozzle 104 and the last nozzle 106 of array 22 are approximately superimposed on elements 130 and 132 of the input bitmap. Therefore, the values stored in elements 130 and 132 can result in the activation or deactivation of nozzles 104 and 106 at time _T1 .

Existing printing systems search for the location of the relevant nozzle at a specific time point ( _T1 in this example), search for the bitmap element that is at the same location as the nozzle at that specific time point, obtain the information contained in the corresponding bitmap element, and decide whether to activate the corresponding nozzle. The inventors have discovered that at least some of these steps are redundant and can be skipped using the masking technique of this embodiment. In other words, at the masked nozzle location, there is no need to process the bitmap, thus saving processing time.

In various exemplary embodiments of the present invention, the controller 20 or data processor 24 accesses a computer-readable medium storing a pre-calculated mask and applies the mask to the input bitmap or nozzle activation bitmap. The pre-calculated mask can be in the form of a rectangular Boolean matrix that indicates the locations where nozzle activation is masked (i.e., the nozzle locations where the nozzle does not dispense material regardless of the value at the corresponding bitmap element). The size of the mask is optionally and preferably equal to the number of nozzles in the head multiplied by the number of droplets that can be dispensed along the longest trajectory on the working area 26 (e.g., the outermost perimeter of the working area 26, or the outermost perimeter of the occupied area 90).

The calculation of the plurality of elements of the pre-calculated mask is optionally and preferably based on the aforementioned mask ratio. Optionally and preferably, the calculation includes applying a pseudo-random number generator using the mask ratio as input probability. Specifically, the position of each nozzle along a trajectory is masked with a probability equal to the mask ratio with respect to the position. The inventors have discovered that such application of the pseudo-random number generator significantly improves the quality of the printed object. Without being bound by any particular theory, it is hypothesized that the pseudo-random number generator improves quality due to a reduction in the number of interference events in the head 16 and, optionally, other components of the system 10.

When a nozzle covering the longest arc length is identified within a group of multiple nozzles (e.g., a nozzle array) within a time interval, the pseudo-random number generator is preferably applied only to the trajectory of that nozzle, with all other nozzles within the group being masked for the entire time interval. Referring again to FIG. 9B , according to this embodiment, the pseudo-random number generator is applied only to trajectory 102, and all other nozzles in array 22 a are masked for the entire time interval between time points T ₁ and T ₁ + dT. This process can be mathematically viewed as masking a nozzle (in this example, nozzle 104) with a probability less than 1, and when a given nozzle is masked, all other nozzles in the group (in this example, array 22 a) are masked with a probability of 1.

The inventors also contemplate calculating a plurality of binary mask values for each of at least some of the nozzle positions during the three-dimensional printing process. This can be accomplished, for example, based on a predetermined mask function of the arc lengths of the corresponding positions from the axis 14. In various exemplary embodiments of the present invention, the mask function is selected so that, for example, the positions of the nozzles closer to the axis 14 are masked more frequently than the positions of the nozzles further from the axis 14. For example, the mask function can calculate a masking ratio that is equal to the ratio between the linear velocities of the different nozzles along different trajectories. Once the masking ratio is calculated, the decision to mask a particular nozzle position along the trajectory is optionally and preferably made in a probabilistic manner as further described above. When the nozzle covering the longest arc length is identified in a group of multiple nozzles (e.g., a nozzle array) within a time interval, a decision is made (optionally and preferably in a probabilistic manner) only for the trajectory of the nozzle, as further described above.

The inventors also contemplate calculating binary mask values in situations where printing does not follow a circular segment. In these embodiments, data relating to the trajectory of the nozzles during printing is received, and a masking ratio is calculated based on the received trajectory (e.g., based on the arc length ratio as described in further detail above). The position of each nozzle is then optionally and preferably probabilistically masked based on the calculated masking ratio, as described in further detail above. When a nozzle covering the longest arc length is identified within a set of multiple nozzles (e.g., a nozzle array) within a time interval, a decision is then made (optionally and preferably probabilistically) only for the trajectory of that nozzle, as described in further detail above.

In any of the above embodiments, the nozzle activation bitmap is accessed, optionally and preferably only at unmasked nozzle positions, to decide whether to activate nozzles at these unmasked positions.

In any of the above embodiments, the non-activated nozzles (eg, masked nozzles) are optionally and preferably "tickled," ie, receive an activation energy that is less than the energy required to activate the nozzles to dispense build material.

The present inventors have discovered that, in certain circumstances, operating a nozzle at a specific frequency can be detrimental to the long-term health of the nozzle, as it can cause the nozzle to cease operation or change its operating characteristics, such as the weight or lift of emitted droplets. Therefore, in some embodiments of the present invention, specific frequencies are eliminated from the pseudo-random mask. For example, the highest frequency can be eliminated from the mask so that instead of an off-on-off sequence, an off-on-off-off sequence occurs.

The system 10 optionally and preferably includes one or more radiation sources 18, which may be, for example, ultraviolet light, visible light, infrared light, or other electromagnetic radiation sources or electron beam sources, depending on the modeling material being used. The radiation source 18 may include any type of radiation emitting device, including but not limited to a light emitting diode (LED), a digital light processing (DLP) system, a resistance lamp, etc. The radiation source 18 is used to cure or solidify the modeling material. In various exemplary embodiments of the present invention, the operation of the radiation source 18 is controlled by a controller 20, which can activate and deactivate the radiation source 18 and optionally also control the amount of radiation generated by the radiation source 18.

In some embodiments of the present invention, the radiation source 18 is configured to reciprocate relative to the tray in a radial direction r. These embodiments are useful when the length of the radiation source 18 is shorter than the radial width of the working area 26 on the tray 12. The movement of the radiation source 18 in the radial direction is optionally and preferably controlled by the controller 20. FIG1D shows a representative diagram of a mechanism suitable for moving the radiation source 18 in the radial direction. As shown in FIG1D, a radiation source 18 is mounted on a platform 56 and configured to generate reciprocating motion of the radiation source 18 in the radial direction. Therefore, this embodiment contemplates that the radiation source and the print head can each be independently controlled to move in the radial direction on a separate motion platform. This differs from conventional 3D printing systems, in which the print head and radiation source are mounted on the same print block and are therefore forced to move simultaneously. In some embodiments of the present invention, the controller 20 is configured to asynchronously move the radiation source 18 and the head 18 in the radial direction during operation of the system 10. In some embodiments of the present invention, the controller 20 is configured to independently move the radiation source 18 and the head(s) 18 in the radial direction during operation of the system 10. These embodiments are particularly useful when it is desired to select the start time of curing, such as to delay curing, as described in further detail below.

Radiation source 18 and/or controller 20 are optionally and preferably configured to ensure that the solidification rate of the build material of the droplets dispensed at different radial locations is approximately the same (e.g., within 20%, within 10%, within 5%, or within 1%). Typically, this is achieved by configuring or controlling radiation source 18 to deliver energy at different rates to locations at different distances from axis 14. Preferably, the rate delivered by energy source 18 decreases linearly with distance from axis 14. Specifically, denoting the energy rate delivered to a location at a distance r1 from axis ₁₄ as _P1 and the energy rate delivered to a location at a distance r2 from axis ₁₄ as _P2 , rates _P1 and _P2 preferably satisfy _the relationship _P1 / _P2≈r1 / _r2 .

Delivering different energy doses to locations at different distances from axis 14 can be accomplished in more than one manner. In some embodiments of the present invention, radiation source 18 has a tapered shape such that its width, generally along the azimuthal direction, is narrower at its inner end (proximal to axis 14) than at its outer end (farther from axis 14). In some embodiments of the present invention, the radiation-emitting elements (e.g., LEDs, etc.) within radiation source 18 are not characterized by the same emission power. In these embodiments, the emitting elements are preferably distributed radially along radiation source 18 such that elements with lower emission power are closer to the inner end and elements with higher emission power are closer to the outer end. Preferably, the emitting elements are distributed such that the emission power decreases linearly with distance from the inner end. In some embodiments of the present invention, the radiation-emitting elements within radiation source 18 (e.g., LEDs, etc.) are all characterized by the same emission power, but controller 20 individually controls each radiation-emitting element or group of radiation-emitting elements to emit radiation at different powers. This can be achieved by generating different electric fields within different plurality of radiation-emitting elements or different groups of radiation-emitting elements. Combinations of the above-described embodiments are also conceivable (eg the conical radiation source and the radiation emitting elements do not all emit with the same emission power).

The present inventors have discovered that the time interval between the event of dispensing build material and the event of exposing the newly dispensed material to radiation from radiation source 18 can affect the accuracy, surface finish, and general print quality of the printed object. Generally, a shorter time interval between these events results in dot gain and better quality of the printed object. On the other hand, the present inventors have discovered that placing radiation source 18 near head 16 can have an adverse effect on the jet stream dispensed by head 16. Without wishing to be bound by any particular theory, it is believed that these effects are due to radiation being reflected from tray 12 or from the build material on tray 12 in the direction of the nozzle of head 16.

The present inventors conducted experiments to determine a preferred geometric configuration of the source 18 and head 16 that achieves adequate print quality while reducing or minimizing nozzle damage. The experiments are described in the Examples section below. According to experimental data obtained in accordance with some embodiments of the present invention, adequate print quality is achieved when the curing time is about 0.5 seconds, preferably no more than 0.75 seconds. Therefore, the azimuthal separation between the radiation source 18 and head 16 is preferably between 0.3ω radians and 0.75ω radians, where ω is the average angular velocity of the tray 12 relative to the head 16 and the radiation source 18. Typically, but not necessarily, the azimuthal separation between the head 16 and the radiation source 18 is about 30° to about 120°, more preferably about 40° to about 110°, more preferably about 45° to about 100°, more preferably about 45° to about 90°, and more preferably about 55° to about 90°.

In some embodiments of the present invention, system 10 further includes one or more leveling devices 32, which can be implemented as rollers or blades. Leveling devices 32 are used to straighten a newly formed layer before forming a subsequent layer. In some embodiments, leveling device 32 has the shape of a conical roller positioned so that its axis of symmetry 34 is inclined relative to the surface of pallet 12 and its surface is parallel to the surface of the pallet. This embodiment is shown in a side view of system 10 ( FIG. 1B ).

The conical roller can have a conical or conical frustum shape. The opening angle of the conical roller is preferably selected so that the ratio between the radius of the cone at any position along its axis 34 and the distance between that position and the axis 14 is constant. This embodiment allows the roller 32 to effectively smooth the multiple layers because, as the roller rotates, any point p on the roller surface has a linear velocity that is proportional to (e.g., the same as) the linear velocity of the tray at a point vertically below point p. In some embodiments, the roller has a conical frustum shape with a height h, a radius r ₁ at the closest distance from the axis 14, and a radius r ₂ at the farthest distance from the axis 14, where the parameters h, r ₁ , and r ₂ satisfy the relationship r ₁ /r ₂ = (Rh)/h, and where R is the farthest distance of the roller from the axis 14 (e.g., R can be the radius of the tray 12).

The operation of the leveling device 32 is optionally and preferably controlled by the controller 20, which can activate and deactivate the leveling device 32 and optionally also control its position in the vertical direction (parallel to the axis 14) and/or radial direction (parallel to the pallet and pointing towards or away from the axis 14).

As described above, the head 16 can reciprocate relative to the tray in a radial direction. In some embodiments of the present invention, the controller 20 independently controls the movement of the head 16 in a radial direction for each print head. Preferably, each such independent movement is at a different azimuth angle. For example, two or more heads can be mounted on a plurality of different radial axes, and the plurality of radial axes are configured so that there is an azimuthal separation angle (azimuthal separation angle) between adjacent axes. The embodiment is shown in Figure 6, which shows three heads 16a, 16b and 16c mounted on three radial axes 62a, 62b and 62c, respectively. As shown, the azimuthal separation angle between axis 62a and axis 62b is and the azimuthal separation angle between axis 62b and axis 62c is. Any number of heads and any number of axes can be used.

The present inventors have found that when the tray 12 rotates continuously in the same direction, the expected total printing time increases with the number of passes of the multiple heads 16 in the radial direction, and not necessarily with the number of multiple objects being printed.

For example, assume that N objects can be printed at a similar distance from the axis 14 so that the head 16 can form all of these objects without moving in the radial direction, for example, all N objects are printed on the outermost area of the tray. Further assume that M additional objects can also be printed at a similar distance from the axis 14, but the distance of the M objects is different from the distance of the N objects. This situation is shown in Figure 8A. Therein, the N objects are represented by squares and the additional M objects are represented by triangles. The expected overall printing time as a function of the number of objects in the described situation is shown in Figure 8B. For any number of objects, N or less, the overall printing time is generally the same because they are printed without moving the head in the radial direction. For any number of objects from N+1 to M, the overall printing time is generally the same, but is longer than the time required to print N objects.

In some embodiments, the computer 24 or the circuitry of the controller 20 calculates the expected total printing time for all objects and displays the calculated time on a display device. In various exemplary embodiments of the present invention, the computer 24 or the circuitry of the controller 20 performs an optimization process that calculates the number of objects that can be printed without significantly increasing the total printing time. The calculated number of objects can be displayed, and the system 10 can print the calculated number of objects based on the optimization process. In some embodiments of the present invention, the computer 24 or the circuitry of the controller 20 calculates the total printing time for each object for several printing scenarios and displays the calculation results. The number of objects to be printed can be selected based on the calculation results (e.g., by selecting the number of objects with the shortest total printing time). As a representative example, assume that the expected total printing time for a particular configuration _N1 objects is _T1 , such that the total printing time for each object is _T1 / _N1 . Further assume that for _N2 < _N1 , the expected total printing time is _T2 . When T ₁ /N ₁ <T ₂ /N ₂ , the system 10 is used to simultaneously print N ₁ objects, and when T ₁ /N ₁ >T ₂ /N ₂ , the system 10 is used to simultaneously print N ₂ objects.

The optimization program that calculates the number of objects to be printed may also receive data regarding the overall build material present in the system (e.g., in supply 42). Controller 20 may issue an alarm when the amount of material required to print an object is greater than the amount of material present in supply 42. Alternatively or additionally, controller 20 may generate an output regarding a reduced number of objects that can be printed using the material available in supply 42, in which case system 10 may be used to print a reduced number of objects, even if that number is suboptimal from the perspective of the exemplary graph shown in FIG8B .

The present inventors have found that repositioning of a print head portion along a radial direction may affect print resolution because repositioning of the print head along a radial direction causes a number of distances between the axis of rotation and each nozzle in the nozzle array of the head to change.

The inventors of the present invention have discovered that there is more than one solution to this problem.

In some embodiments, controller 20 changes the rotational speed of tray 12 in response to the radial position of print head 16. Preferably, when print head 16 is repositioned closer to axis 14, controller 20 increases the rotational speed of tray 12, as shown in FIG. 12, and when print head 16 is repositioned farther from axis 14, controller 20 decreases the rotational speed of tray 12. The amount of change in rotational speed is preferably selected so that, when print head 16 operates at the same dispensing rate, the print resolution of head 16 before and after radial repositioning is the same. As a representative example, consider a print head initially dispensing build material at a distance _r1 from axis 14 while tray 12 rotates at a speed _ω1 . The print head is then radially repositioned to dispense build material at a distance _r2 from axis 14, and the controller changes the rotational speed of tray 12 to _ω2 ≠ _ω1 . In various exemplary embodiments of the present invention, ω ₂ is selected to satisfy the relationship ω ₁ /ω ₂ =r ₂ /r ₁ .

In some embodiments, controller 20 varies the dispense rate of print head portion 16 in response to the radial position of print head portion 16. Preferably, controller 20 decreases the dispense rate when print head 16 is repositioned closer to axis 14, and increases the dispense rate when print head 16 is repositioned further from axis 14. The amount of change in dispense rate is preferably selected so that the print resolution of print head 16 before the radial repositioning is the same as the print resolution after the radial repositioning.

In some embodiments, the controller 20 controls one or more print heads 16 to dispense droplets such that the azimuthal distance between sequentially dispensed droplets varies as a function of the position of the print head along the radial direction. These embodiments are shown in FIG4A and FIG4B. As shown in FIG4A,

Several droplets (solid circles) are dispensed onto tray 12 while a print head (not shown) is positioned at three different distances Δr ₁ , Δr ₂ , and Δr ₃ from axis of rotation 14 . Four droplets are shown for each distance. At the shortest distance Δr ₁ from axis 14 , the droplets are azimuthally closer to one another. At the next shortest distance Δr ₂ , the droplets are azimuthally farther apart. At the longest distance Δr ₃ , the droplets are azimuthally furthest apart. This distribution pattern can be ensured by signaling the print head to leave one or more gaps between successively deposited droplets during rotation of tray 12 .

The above distribution scheme can be implemented in a staggered distribution mode. This embodiment is shown in FIG4B . As shown in FIG4B , during additional time periods of the tray, additional droplets are distributed to corresponding positions of the print head. The droplets are shown as solid circles, hollow circles, and intersecting circles. Some droplets are staggered along the azimuth direction.

Specifically, FIG4B shows additional droplets dispensed when the print head portion is at distances Δr ₂ and Δr ₃ (open circles), and even more additional droplets dispensed when the print head portion is at distance Δr ₃ (crossed circles). When the print head is at distance Δr ₁ , it dispenses all droplets during a single pass of the tray (solid circles). When the print head is at distance Δr ₂ , it dispenses a first droplet during the first pass of the tray (solid circles), and a second droplet during the second pass of the tray (open circles). When the print head is at distance Δr ₃ , it dispenses a first droplet during the first pass of the tray (solid circles), a second droplet during the second pass of the tray (open circles), and a third droplet during the third pass of the tray (crossed circles). Thus, in these embodiments, the print head

Controlled by the controller 20 to perform staggered dispenses, wherein at least one droplet is dispensed between two previously dispensed drops and at the same vertical position therewith.

Interlaced dispensing is typically characterized by an interlacing level, which indicates how many passes are required to fill a profile. In the exemplary embodiment shown in FIG. 4B , but not to be construed as limiting, three profiles are printed, each profile shaped as an arc. Profiles at a distance Δr ₁ are dispensed without interlacing. Profiles at a distance Δr ₂ are referred to as having a 2-pass interlacing level (indicating that two passes through the tray are required to fill the profile) or, equivalently, a 50% interlacing level (indicating that 50% of the profile is filled with each pass). Profiles at a distance Δr ₃ are referred to as having a 3-pass interlacing level (indicating that three passes through the tray are required to fill the profile) or, equivalently, a 30% interlacing level (indicating that 30% of the profile is filled with each pass). Often, the term "interlaced dispensing" is generalized to also include situations where a profile is filled during a single pass. Using this generalization of the term, a profile at a distance Δr ₁ is referred to as having a 1-pass interlacing level or, equivalently, a 100% interlacing level.

Therefore, this embodiment contemplates a stagger level that varies as a function of a position of the print head along the radial direction.

The present embodiments also contemplate staggered dispensing, in which the dispensed droplets are staggered along a radial direction. In these embodiments, the head dispenses droplets such that gaps exist between simultaneously dispensed droplets, wherein the length of the gaps along the radial direction (referred to herein as radial gaps) is at least the diameter of a dispensed droplet, and preferably an integer multiple of the diameter of a dispensed droplet. Thereafter, the head moves in the radial direction so that, on subsequent passes of the tray, the head dispenses droplets to fill or partially fill the radial gaps. An advantage of staggered dispensing along the radial direction is that it allows for increased resolution along the radial direction beyond that dictated by the spacing between nozzles in the nozzle array of the head.

When the system 10 includes two or more modeling material print heads, staggering along the radial direction can also be achieved by appropriately aligning the multiple print heads. In these embodiments, the two or more modeling material print heads are aligned so that their nozzle arrays are arranged in a staggered manner. A representative example of these embodiments is shown in FIG7 . FIG7 shows a staggered arrangement of two circles 72 and 74 on the tray 12 using two nozzle arrays, each corresponding to a different inkjet print head (not shown), wherein the distance between the circles 72 and 74 along the radial direction is less than the distance between the nearest adjacent nozzles in each array.

In some embodiments of the present invention, the controller 20 stops dispensing during the reciprocating motion of the print head in the radial direction. After the print head becomes stationary at a new radial position, the controller 20 controls the print head portion to resume dispensing. This can be accomplished in a variety of ways.

In some embodiments, controller 20 resumes dispensing at the same azimuthal coordinate at which dispensing was stopped. In these embodiments, dispensing is stopped for a period equal to a rotation of tray 12 or an integer multiple thereof. Thus, the dispensing scheme causes the controller 20 to wait until the same azimuthal position is directly below the print head after the print head becomes stationary at a new radial position before resuming printing.

In some embodiments, the controller 20 resumes the dispensing at an azimuth coordinate that is offset from the azimuth coordinate at which the dispensing was stopped. This can be done in more than one way, as will now be explained with reference to Figures 5A to 5F.

FIG5A illustrates a situation in which the print head 16 (shown as a black bar for simplicity) reciprocates between a first radial position _r1 and a second radial position _r2 . During this reciprocating motion in the radial direction, the tray 12 continues to rotate, causing the tray 12 to assume different azimuthal orientations. In a representative example, when the tray 12 assumes the azimuthal orientations denoted by and , the head 16 is in the first radial position _r1 , and when the tray 12 assumes the azimuthal orientations denoted by and , the head 16 is in the second radial position _r2 . Each azimuthal orientation corresponds to the azimuthal position of the tray beneath the head 16. According to this embodiment, when the head 16 first reaches _r2 , it resumes the dispensing at the azimuthal position relative to the offset; when the head 16 returns to _r1 , it resumes the dispensing at the azimuthal position relative to the offset; and when the head 16 second reaches _r2 , it resumes the dispensing at the azimuthal position relative to the offset.

FIG5B illustrates a preferred embodiment in which the printing of the plurality of objects occupies a predetermined range of azimuth angles on tray 12. The predetermined range is preferably at least 5° but less than 350°, or less than 340°, or less than 330°, or less than 320°, or less than 310°, or less than 300°, or less than 290°, or less than 280°, for example, 270°. FIG5B illustrates a first region 90 and a second region 92 on tray 12, where region 90 represents the predetermined range of azimuth angles at which objects are printed. Regions 90 and 92 each have a circular sector shape. Preferably, the arc length of region 92 is shorter than the arc length of region 90. Thus, one or more objects are printed on region 90 of tray 12, while region 92 remains free of printed objects, preferably at all times. Region 90 is referred to as the occupied region, while region 92 is referred to as the unoccupied region. Using occupied and unoccupied regions is useful for timing the movement of head 16 along a radial direction. In these embodiments, controller 20 signals heads 16 only when they are moving in a radial direction when over an unoccupied area (eg, area 92).

5C to 5F illustrate a dispensing scheme in which heads 16 move radially only when they are over unoccupied areas. In FIG5C to 5F, solid arc arrows indicate trajectories that allow heads 16 to dispense building material without relative movement of heads 16 in the radial direction relative to tray 12. Solid circles mark the various swaths of the various trajectories. The movement of heads 16 along the radial position as tray 12 rotates is indicated by dashed arrows. The position coordinates corresponding to area 92 (and therefore also to area 90) are denoted by and

As shown in the figure. Figures 5C to 5F are six tracks, denoted as 94a to 98b. Each track within the same swath can correspond to a different nozzle of the head 16 or the same nozzle, but shifted in the radial direction to achieve staggered distribution along the radial direction, as described in further detail above. Therefore, when staggered distribution along the radial direction is used, the difference between the radial positions of adjacent tracks in the same swath (tracks 94a and 94b, tracks 96a and 96b, and tracks 98a and 98b, in this example) can be the diameter of a dispensed droplet, and when staggered distribution along the radial direction is not used, the difference between the radial positions of adjacent tracks in the same swath can be the distance between multiple adjacent nozzles in the array.

Different strips of trajectories generally correspond to radial displacements of head 16 by an amount that is an integer multiple of the nozzle array length. Thus, the difference between the radial positions of the trajectories corresponding to two adjacent strips may be, but is not necessarily, the nozzle array length of head 16 (e.g., in this example, between trajectories 94a and 96a, trajectories 96a and 98a, trajectories 94b and 96b, and trajectories 96b and 98b).

It should be understood that the reduced number of tracks in Figures 5C to 5F is not intended to limit the scope of the present invention to six tracks. Typically, the number of tracks is at most W/L, where W is the radial width of the working area 26 on the tray 12 and L is the length of the nozzle array of the head 16. When staggered distribution along the radial direction is used, the total number of tracks is preferably at most W/D, and the number of tracks in each strip is preferably about L/D, where D is the characteristic diameter of a dispensed droplet. When staggered distribution along the radial direction is not used, the number of tracks in each strip is preferably at most equal to the number of nozzles in the array. Preferably, there are at least two or at least three strips in the plurality of tracks, and at least two or at least three or at least four tracks.

Figures 5C and 5D illustrate a dispensing scheme employing staggered dispensing along the radial direction. Referring to Figure 5C , head 16 dispenses building material at a radial position corresponding to trajectory 94a. When the tray reaches the azimuth position, head 16 is above region 92 and temporarily ceases dispensing. While still above region 92, head 16 moves outward to a radial position corresponding to trajectory 94b. Dispensing does not resume until at least the tray reaches the azimuth position, i.e., when head 16 is above region 90. This process continues until the multiple heads have passed through all or some of the trajectories on strips 94. During the time period that head 16 is above region 92, radial movement from one strip to another is also performed, as illustrated by the dashed arrows, which represent radial movement of head 16 from a radial position corresponding to trajectory 94b to a radial position corresponding to trajectory 96a, and from a radial position corresponding to trajectory 96b to a radial position corresponding to trajectory 98a.

When staggered distribution along the radial direction is not employed, the distribution scheme does not include a radial displacement equal to the difference between the radial positions of adjacent tracks within the same strip. In these embodiments, the amount of radial displacement is equal to the length of the nozzle array of head 16. These embodiments are illustrated in Figures 5E and 5F. Referring to Figure 5E, head 16 distributes building material at a radial position corresponding to tracks 94a and 94b from two different nozzles. When the tray reaches the azimuth position, head 16 is above area 92 and dispensing is temporarily stopped. While still above area 92, head 16 moves outward to a radial position corresponding to track 96a. Head 16 does not resume dispensing until at least the tray reaches the azimuth position, i.e., when head 16 is above area 90. The process continues with strips 96 and 98.

5D and 5F depict a distribution scheme similar to that of FIG. 5C and FIG. 5E , except that the head moves inward over region 92. Combinations of the schemes depicted in FIG. 5C and FIG. 5D , or combinations of the schemes depicted in FIG. 5E and FIG. 5F , are conceivable. For example, these protocols can be performed alternately.

Also contemplated are embodiments in which the controller 20 resumes the dispensing at an azimuth coordinate that is substantially the same as the azimuth coordinate at which the dispensing was stopped (eg, within less than 1°, or less than 0.1°, or less than 0.01°).

Figures 5G and 5H illustrate multiple allocation scenarios, where allocation is resumed at the same position coordinates where it was stopped, as described in further detail above. Figure 5G depicts an allocation scenario with the head moving outward, while Figure 5H depicts an allocation scenario with the head moving inward. Combinations of the scenarios depicted in Figures 5G and 5H are also contemplated. For example, these scenarios can be performed alternately. The symbols in Figures 5G and 5H are the same as those in Figures 5C through 5E.

In an embodiment where the controller 20 restores the distribution at an offset azimuthal coordinate, the print data is adjusted so that the corresponding polar coordinates of the plurality of different portions of the object corresponding to different radial positions are also offset. This configuration of the data can be performed by the controller 20 or the computer 24.

From the perspective of print output, the allocation scheme according to the teaching of FIG. 5A is superior to the allocation scheme according to the teaching of FIG. 5B to FIG. 5H . From the perspective of data manipulation simplicity, the allocation scheme according to the teaching of FIG. 5B to FIG. 5F is superior to the allocation scheme according to the teaching of FIG. 5A . From the perspective of data manipulation simplicity, the allocation scheme according to the teaching of FIG. 5G to FIG. 5H is superior to the allocation scheme according to the teaching of FIG. 5A to FIG. 5F .

The inventors also contemplate embodiments in which controller 20 continues to dispense the build material during the reciprocating motion. In these embodiments, the print data is adjusted in response to the reciprocating motion of the head. This dispensing scheme allows for dispensing multiple droplets along multiple non-circular segments.

As described above, the vertical distance between tray 12 and head 16 can be varied to allow a three-dimensional object to be formed in a layered manner. In some embodiments, controller 20 stops the dispensing of building material during the vertical motion. These embodiments are preferred from the perspective of simplicity of the dispensing scheme.

The inventors have found that the timing of the vertical motion has an impact on the quality of the printed object. Therefore, the inventors have designed a three-dimensional printing solution that improves the quality of the printed object. Generally, during the production of a layer, there are several operations performed by the system 10. These operations include, for example,

The build material is dispensed by multiple heads 16, the newly printed layer is leveled by leveling device 32, and the layer is cured by radiation source 18. These operations are typically performed at different azimuth positions on tray 12 and are therefore sequential for a given object. In some embodiments of the present invention, the timing of the vertical movement is synchronized with the timing of these sequential operations. For example, the vertical movement can be initiated after the last operation applied to a newly formed layer (e.g., after curing the layer by radiation source 18) and before dispensing the subsequent layer.

In some embodiments of the present invention, vertical motion is initiated immediately (e.g., in less than 1 second) when a newly formed layer arrives at the leveling device 32. Alternatively, vertical motion can be initiated such that vertical motion is completed immediately (e.g., in less than 1 second) when a newly formed layer arrives at the leveling device 32. These embodiments are particularly useful in multiple printing situations where it is undesirable to leave unoccupied area on the tray 12 (e.g., when the area of multiple layers of an object to be printed is larger than the area of area 90 of FIG. 5B).

In various embodiments, in which multiple objects are printed to occupy a predetermined range of azimuth angles on the tray 12, wherein predetermined occupied and unoccupied areas are defined on the tray 12 (see FIG. 5B ), the vertical movement is optionally and preferably performed when the area 90 is below the leveling device 32 or below the head 16 or below the radiation source 18, most preferably below the leveling device 32.

In some embodiments of the present invention, controller 20 continues dispensing the build material during vertical movement of head 16 and/or tray 12. The head continues dispensing build material during vertical movement. These embodiments have the advantage of shortening overall printing time because the system spends less time not dispensing material. In embodiments in which dispensing is continued, the coordinate transformation preferably includes transforming the coordinates of at least a portion of the computer-physical data into a helical coordinate system.

Optionally and preferably, the motion is performed in a vertical direction such that, during the process of print head 16 dispensing build material, tray 12 and print head 16 experience at least two different vertical distances between them during a single rotation of the tray. In some embodiments of the present invention, the motion is performed in the vertical direction such that, during a single rotation of tray 12, the vertical distance increases by an amount approximately equal to the characteristic thickness of a single layer of build material. For example, when the thickness of the single layer is t microns and the angular velocity of tray 12 is ω radians per second, the vertical distance may increase at a rate of t×ω/2π microns per second, which is equivalent to t/360 microns per degree of tray 12 rotation. The motion in the vertical direction may be continuous or intermittent, as desired.

When the system 10 includes two or more print heads 16 for dispensing modeling material, these heads can be arranged on the tray 12 according to the printing mode. For example, when dispensing the same modeling material from two or more modeling material heads, these heads can be arranged at different radial positions, such as the radial positions r ₁ , r ₂ , and r ₃ shown in FIG6 for the case of three modeling material print heads 16 a , 16 b , and 16 c , thereby reducing the need to move these heads in the radial direction. The number of modeling material heads can be selected so that when they are arranged at different radial positions, they cover the entire width of the working area 26 in the radial direction.

When two or more different modeling material heads dispense two or more different modeling materials, the radial positions of these heads are independently controlled by the controller 20 depending on the positions on the tray to which the different modeling materials are dispensed.

As described above, in some embodiments, a plurality of heads 16 reciprocate relative to the tray in a radial direction r via a platform configured to establish reciprocating motion of the heads 16 in a radial direction. A representative example of a platform 52 suitable for this embodiment is shown in FIG10 . In this example, the radial motion of the heads 16 is achieved by a screw 130, which is driven by the rotational motion of a motor 132. The motor 132 is optionally and preferably mounted at the end of the platform 52 closest to the axis 14 (not shown, see, for example, FIG1D ). One end 134 of the screw 130 is connected to the motor 132. The other end 136 can be unsupported, in which case the screw 130 acts as a cantilever screw, or is supported by a screw support structure 138.

The present inventors have discovered that when the head 16 is moved along the platform 52, particularly by a rotating screw, the radial position of the head is susceptible to inaccuracies that vary as a function of radial position. Inaccuracies are interchangeably referred to herein as errors.

According to some embodiments of the present invention, a compensation function is applied to at least partially compensate for variations in inaccuracy as a function of radial position. Preferably, the compensation function is selected to at least partially compensate for non-oscillatory variations in inaccuracy. The compensation function can be applied by controller 20, wherein for any displacement of head 16 from one radial position to another, controller 20 calculates the expected inaccuracy at the destination point based on the compensation function and recalculates the radial position of the destination point to compensate for the calculated inaccuracy. Controller 20 then moves head 16 to the recalculated radial position. For example, when head 16 moves from radial position _r1 to radial position _r2 , controller 20 calculates the expected inaccuracy _Δr2 at _r2 using the compensation function and moves head 16 to radial position _r2 - _Δr2 , where _Δr2 can be positive, zero, or negative.

The compensation function is generally based on the mechanical properties of the screw 130 and the stiffness of the connection between the screw 130 and the platform 52 .

FIG11A illustrates the expected inaccuracy as a function of distance from end 134 when end 136 of screw 130 is supported by a support structure. In FIG11A , graph 140 depicts the variation in radial position error as a function of distance from end 134. As shown, the error exhibits an oscillatory behavior, with the mean value increasing as the distance from end 134 increases. The variation in the mean value is approximately linear. Therefore, in these embodiments, controller 20 employs a substantially linear compensation function (e.g., having a linear deviation of less than 20%, less than 10%, less than 5%, or less than 1%). The slope and intersection of the linear function can be calculated based on the mechanical properties of screw 130, such as its modulus of elasticity and its second moment of area. Alternatively, the slope and intersection can be calculated by measuring the error as a function of radial position to experimentally obtain line segment 140 and fitting the mean value of the experimentally obtained line segment to a linear function. A representative example of a compensation function suitable for this embodiment is shown at 142, and the result of the compensation (FIG. 11A) is shown at 144. As shown, the error is still oscillatory, but the average error is essentially zero.

FIG11B shows the expected inaccuracy 146 as a function of distance from end 134 when screw 130 is a cantilever screw, i.e., when end 136 is unsupported. For comparison, the expected inaccuracy 140 when end 136 is supported is also shown. As shown, the average value 146 of the inaccuracy increases nonlinearly as a function of distance from end 134 and is significantly higher than the average value of the inaccuracy 140 near end 136. In these embodiments, controller 20 preferably employs a nonlinear compensation function. The nonlinear compensation function may comprise an nth-degree polynomial function, where n>1. The coefficients of the polynomial function may be calculated by experimentally obtaining line segments 146 by measuring the error as a function of radial position and fitting the average value of the experimentally obtained line segments to an nth-degree polynomial function.

Theoretically, when a one-dimensional cylinder along direction x is supported at x = 0 and receives a concentrated load P at its free end at x = L, the cylinder exhibits a curved shape that can be approximated by a cubic polynomial, defined by y = Px ² (3L-x)/(6EI), where E and I are the modulus of elasticity and second moment of area of the cylinder, respectively, with y measured perpendicular to x. Therefore, the nonlinear compensation function preferably comprises a cubic polynomial.

A representative example of a cubic polynomial compensation function suitable for this embodiment is shown at 148 in FIG. 11C . The results of the compensation are shown at 150. As shown, the error still oscillates, but the average error is close to zero. In experiments conducted by the present inventors, the maximum error without compensation (line segment 146) was approximately 119 μm, while the maximum error after compensation (line segment 150) was approximately 30 μm.

Typically, building material is supplied to an additive manufacturing (AM) system, such as, but not limited to, system 10, with a pre-filled cassette. The cassette is installed in the AM system and connected to a delivery system, through which the building material is deposited for printing. Once the supply of building material is nearly depleted, the cassette is replaced. Desirably, removal and installation of the cassette can be performed easily and without the need for additional tools.

Typically, cartridges are disposable but require emptying for safe disposal before disposal. Emptying the entire contents of a cartridge during operation without disrupting the manufacturing process is often difficult. However, complete or nearly complete depletion of the cartridge is desirable because it maximizes the cartridge's printing capacity and minimizes waste of expensive build materials.

According to some embodiments of the present invention, a plurality of cassettes are mounted in a cassette housing at an angle that promotes flow of the contents toward a fluid connection for delivering building material during additive manufacturing, such as printing. In some exemplary embodiments, the cassette is formed with a well or recess in the wall of the cassette at or near the lowest area of the cassette, such that the outlet of the building material is near the lowest area, such as the lowest relative to gravity. Optionally, an angle of 2 to 10 degrees or 2 to 5 degrees is sufficient to promote flow toward the well. Optionally, the housing accommodates 4 to 10 housings, such as 6, and is configured so that it can be easily pulled out of the printer to allow maintenance of the building material delivery system connected to the plurality of cassettes during operation of an additive manufacturing system (e.g., system 10). According to some embodiments of the present invention, each cassette is mounted with a spring lock that holds the cassette in place after installation and is easily released when the cassette needs to be replaced.

Reference is now made to FIG. 16 , which illustrates an exemplary cassette according to some embodiments of the present invention. According to some embodiments of the present invention, a cassette 300 for use in an additive manufacturing system, such as, but not limited to, system 10, includes a housing 305 for storing building materials (e.g., building materials), a fluid connection 340 for connecting the cassette 300 to a delivery unit of the additive manufacturing system, one or more sensors 350 for sensing the presence of contents in the cassette 300 and/or for identifying the contents, and a vent 360 to the atmosphere. According to some embodiments of the present invention, the cassette 300 additionally includes a locking spring having a handle 330 for locking the cassette in the additive manufacturing system, thereby establishing a stable connection between the cassette and a dispensing unit of the additive manufacturing system. According to some embodiments of the present invention, when installed in the additive manufacturing system, the cassette 300 is angled at an angle "a." Adjusting the angle of the cassette 300 facilitates the flow of contents toward the fluid connection 340. Optionally, the angle "a" is between 2 and 10 degrees, for example, 2 degrees. According to some embodiments of the present invention, housing 305 forms a notch or depression 320 at the lowest point of the cartridge, and an output of fluid connection 340 is aligned proximate to notch 320 so that contents can accumulate near the outlet.

Reference is now made to FIG. 17 , which shows an exemplary rotary 3D printing system having multiple cassettes, and FIG. 18 , which shows exemplary cassette receptacles according to some embodiments of the present invention. In some exemplary embodiments, cassettes 300 are mounted in a rotary lamination system 400. The principles and operation of system 400 can be similar to those of system 10 , with cassettes and cassette receptacles added as needed as follows. Alternatively, cassettes 300 can be used in other lamination systems, such as linear lamination systems. Typically, rotary lamination system 400 includes a print chamber 420 in which objects are manufactured by distributing material in a layered manner on a build tray 12, and a cassette chamber 455 for accommodating one or more cassettes 300.

Typically, the cassette 300 is connected to a dispensing unit for selectively dispensing material onto the tray 12 as the tray 12 rotates. According to some embodiments of the present invention, a plurality of cassettes, for example 4 to 10 cassettes, are housed in a cassette seat 420 and locked in place by a locking spring 410. As shown in Figure 16, when the cassette body is installed in the seat 420, the locking spring 410 is forcibly pressed down by the cassette body. When the cassette is fully installed, a locking member pops up behind the cassette to lock it in place. This allows the cassette to be installed in the printer with one hand. To release the lock, the locking spring can be depressed and the cassette can be pulled out of the seat 420. Each cassette can be replaced independently of the other cassettes. The cassette 300 is locked in place to establish a fluid connection between the cassette 300 and the dispensing head (e.g., head 16) of the lamination system.

The following are several printing modes contemplated in any of the above embodiments.

As used herein, "azimuthal scan" refers to a printing mode in which the relative motion between head 16 and tray 12 is always parallel to the azimuthal direction. In this scanning mode, build material is preferably dispensed only along a path equidistant from axis 14 during the relative motion. This path is referred to herein as an arc.

A representative example of azimuthal scanning is as follows. The head is stationary while the tray rotates. As the tray rotates, each nozzle moves along an arc past a previously formed layer or multiple target locations on the tray surface. A controller determines, for each target location or group of target locations, whether the target location or group of target locations is occupied by build material and what type of build material is to be delivered thereto. This determination is made based on a computer image of the surface. Optionally, the dispensing head then moves in a radial direction without dispensing build material.

As used herein, "vector scan" refers to a scanning pattern in which the relative motion between the head 16 and the tray is along a path that is dynamically selected by the controller based on a computer image of the layer. Optionally, the path is not a circular arc. Optionally, at least a portion of the path is not parallel to the boundary of the work surface where the dispense is to be made.

Therefore, unlike azimuth scanning, where any movement of the head is parallel to the r or direction, movement in vector scanning can follow any path, not necessarily parallel to the r or direction.

In some embodiments of the present invention, a controller selects a scanning mode based on two-dimensional position data corresponding to the layer being built. In vector scanning, the output for a particular layer is determined by the size of the area that will be covered by the support material or modeling material, so non-bulky objects are built faster than bulky objects. On the other hand, in azimuth scanning, the output is not necessarily determined by the area where the material needs to be deposited, but by the number of scanning passes that the head needs to make in order to deposit the material. For example, if printing using azimuth scanning mode, it takes the same time to build a rod parallel to the Z axis as it does to build a tube of the same length and diameter; if printing using vector scanning mode, it takes longer to build the same rod than it does to build the same tube.

Therefore, in some embodiments, azimuth scanning is used when the output obtained is similar to or greater than that obtained by alternative vector scanning. This depends on system characteristics such as rotation speed, radial motion speed, layer thickness, etc.

In some embodiments, azimuthal deposition is used to deposit one or more materials, and vector deposition is used to deposit one or more different materials, depending on the properties or attributes of the deposited material and/or the properties or attributes desired to be present in the final object, by selecting the purpose and/or specific location of the particular material for deposition.

Vector scanning is advantageous for printing conductive "tracks," such as continuous, elongated structures, because the vector deposition head can continuously deposit conductive material as it moves parallel to the plate. Vector scanning optionally and preferably follows a path selected to form at least one structure in the layer. The structure can, for example, be an elongated structure.

The term "elongated structure" refers to a three-dimensional body in which one dimension is at least 2 times, more preferably at least 10 times, more preferably at least 100 times, for example at least 500 times, greater than any of the other two dimensions. The largest dimension of an elongated solid structure is referred to herein as the longitudinal dimension, and the dimensions are referred to herein as the transverse dimensions.

A representative example of a plurality of elongated structures 262 formed in layer 260 by vector scanning is shown in FIG15A. The structure may also be a boundary structure that at least partially surrounds an area filled with the first building material. A representative example of boundary structure 266 formed in layer 260 by vector scanning is shown in FIG15B. The structure may also be an interlayer connecting structure. In these embodiments, the structure is preferably small relative to the overall size of the layer (e.g., less than 1%). FIG15C shows a representative example of an interlayer structure 268 connecting two layers 260 and 270. The structure shown in FIG15C may also be embedded within an area formed by azimuthal scanning. For example, referring again to FIG15A, a primary area 272 of layer 260 may be formed by azimuthal scanning, wherein structure 262 may be embedded within area 272. The structure may also be relative to the perimeter of a layer. Such an embodiment is shown in FIG15D, which shows layer 260 and structure 274 at its perimeter.

The combination of azimuth scanning and vector scanning can be performed on any layer forming the object. Specifically, in some embodiments, the combination of azimuth scanning and vector scanning is performed on an inner layer among the multiple layers, in some embodiments, the combination of azimuth scanning and vector scanning is performed on the topmost layer, and in some embodiments, the combination of azimuth scanning and vector scanning is performed on the bottommost layer. The combination of azimuth scanning and vector scanning can also be performed on multiple layers as needed.

The inventors have found that exposing low viscosity solvents to high temperatures while the building material is still in the dispensing head can be problematic due to premature solvent evaporation. The inventors have also found that high temperatures can also damage the substrate on which the object is built, for example when the substrate is a polymer.

The present inventors have therefore discovered that dispensing a UV-curable material that is too viscous at low temperatures and a build material containing volatile solvents at the same temperature can cause problems.

The above problems can be creatively solved by a technology that distributes one construction material at a high temperature (e.g., above 60°C, or above 65°C, or above 70°C, or above 75°C, or at least 80°C) and distributes the other construction material at a low temperature (e.g., below 40°C, or below 35°C, or below 30°C).

This can be accomplished by individually controlling the temperature of each building material when loaded into its corresponding dispensing head. Thus, in various exemplary embodiments of the present invention, a controller maintains at least two dispensing heads at different temperatures. Optionally and preferably, the controller implements azimuthal scanning for dispensing building material at a higher temperature and vector scanning for dispensing building material at a lower temperature.

The present inventors have found that some modeling materials, particularly UV polymerizable materials, exhibit undesirable deformations, such as curling, during the manufacture of an object. This curling tendency has been found to be a result of the material shrinking during the phase transition from liquid to solid.

The degree of curl is a measurable quantity. A suitable procedure for measuring the degree of curl may include fabricating an object of a predetermined shape, such as an elongated cylinder having a rectangular or square cross-section, on a flat and level surface, applying a predetermined load to one end of the object, and measuring the height of the opposite end above the surface.

In their research into solutions to the curling problem, the present inventors discovered that the degree of curling is proportional to the degree of volumetric shrinkage experienced by the material during polymerization, as well as the temperature difference between the material's heat distortion temperature (HDT) and the temperature within the system during manufacturing. The present inventors discovered that curling is particularly pronounced for materials with relatively high volumetric shrinkage and relatively high HDT (e.g., within the polymerization temperature range). The present inventors also discovered a monotonic relationship between HDT and curling tendency. Without wishing to be bound by any theory, it is hypothesized that materials that develop during curing at HDT (which is close to the temperature within the system during manufacturing) can undergo stress relaxation or plastic deformation during the lamination process more easily than materials with similar shrinkage but that develop a higher HDT.

As used herein, the term "heat deflection temperature" (HDT) refers to the temperature at which a material or combination of materials deforms under a predetermined load at a specific temperature. A suitable test procedure for determining the HDT of a material or combination of materials is the ASTM D-648 series, particularly ASTM D-648-06 and ASTM D-648-07 methods.

For example, the PolyJet ^™ system sold by Stratasys Ltd. of Israel uses formulations that produce cross-linked polymer materials under UV irradiation. Objects manufactured using these materials have relatively high rigidity and a HDT above room temperature, for example, approximately 50°C or higher. This elevated HDT has been found to result in low dimensional accuracy (high curling). High HDT and low curling have therefore been found to be conflicting properties. The present inventors have conducted experimental research, specifically to provide a technique for providing the additive manufacturing of three-dimensional objects with both high dimensional accuracy (low curling) and high HDT immediately after fabrication.

The inventors have found that the presence or absence of a curling effect depends on the time elapsed between the solidification of a plurality of successive layers. Specifically, it has been found that by setting a sufficiently long time interval between initiating the solidification of a plurality of successive layers, the curling effect of the final object can be reduced or eliminated.

In various exemplary embodiments of the present invention, the controller 20 is configured to operate the head 16 and the radiation source 18 so that for at least one, at least two, or at least three layers, such as most or all of the layers, forming the object, curing of the corresponding layer begins at least t seconds after the layer immediately preceding the corresponding layer begins curing. Typically, but not necessarily, the corresponding layer has a thickness of about 15 microns. In some embodiments, each layer has a thickness of at least 5 microns, such as about 5 microns, or about 10 microns, or about 15 microns, or about 30 microns. Other thicknesses are not excluded from the scope of the present invention.

In various exemplary embodiments of the present invention, t is longer than the total time to form a single layer, including the time for dispensing and curing combined. For example, when the total formation time for a particular layer is 5 seconds, t is greater than 5. The difference between the total formation time and t is defined as the "delay." Thus, unlike conventional systems, in which each layer is deposited and cured immediately after the curing of the previous layer, controller 20 delays the deposition and/or curing of the layer until t seconds or more have passed since the curing of the immediately preceding layer began.

Typical values for t include, but are not limited to, at least 6, or at least 7, or at least 8, or at least 9, or at least 10. In some embodiments of the invention, t is at most 25. In some embodiments of the invention, t is less than 6.

The value of t may also depend on the properties of the respective material used to manufacture the object and optionally also on the temperature at which the object is manufactured.

In some embodiments of the present invention, controller 20 receives HDT data, which characterizes the building material being used. The HDT data typically corresponds to the HDT achieved by the material once cured. Such data may be provided, for example, by an operator via data processor 24. It should be understood that the operator need not literally enter the HDT data (although this is contemplated). In some embodiments of the present invention, the controller or data processor accesses a database of HDT values, which may be stored on a storage medium (not shown), and selects an HDT value based on other types of operator input. For example, such a database may include multiple entries, each with a building material type and a corresponding HDT value. In these embodiments, the operator may enter the type of building material or select it from a list of options, and the controller or data processor obtains the corresponding HDT value from the database. Embodiments are also contemplated in which the controller or data processor obtains the corresponding HDT value from the database based on the type of building material loaded into supply system 42.

Once the controller receives the HDT data, it optionally selects a t-value in response to the HDT. This can be done in a variety of ways. In some embodiments, a lookup table is used. This lookup table can be stored in a storage medium accessible by the controller. The lookup table can include multiple entries, each with an HDT value and a corresponding t-value. The controller can search the table for the entry that best matches the received HDT value and select a corresponding t-value or approximate t-value based on the best-matching entry. In some embodiments, the controller can use a pre-programmed function t(HDT) to determine the t-value for a specific value of HDT. This function is preferably a monotonically increasing function of HDT (e.g., a linear function with a positive slope). Preferably, the return value of the function for HDT=50°C is at least 6.

It should be understood that controller 20 does not necessarily select a t-value based on the HDT value. In some embodiments of the present invention, controller 20 selects a t-value directly from the type of building material used to make the object. This is typically performed by a lookup table, which, in some embodiments of the present invention, is stored on a storage medium accessible to controller 20. Such a lookup table may include multiple entries, each with a building material type or building material family and a corresponding t-value. Controller 20 may search the table for the entry that best matches the building material type or building material family and select the corresponding t-value.

Embodiments are also contemplated in which the value of t is also based on the operating temperature of the manufacturing process, preferably but not necessarily on the difference between the HDT value and the operating temperature.

The value of t can, and preferably does, depend at least in part on the energy dose delivered to the most recently formed layer. The energy dose per unit volume depends, in principle, on the intensity of the radiation emitted by radiation source 18 and the rate at which the material is dispensed. The dispensing rate, in turn, depends on the relative rotational speed of tray 12 and the flow of the build material from the nozzle of head 16. For example, for a particular modeling material, a particular flow of the build material from the nozzle, and a particular radiation intensity, the rotational speed results in a lower degree of polymerization of the layers during formation, wherein the layers continue to polymerize during the curing of subsequent layers thereon. The inventors have discovered that this polymerization of previously formed layers increases the curling effect.

Thus, in various exemplary embodiments of the present invention, the value of t is calculated based on one or more of the following parameters: (i) layer thickness, (ii) dispense rate, (iii) radiation intensity, (iv) energy dose, and (v) HDT of the material being cured. In some embodiments, the value of t is calculated based on at least two of the aforementioned parameters, in some embodiments of the present invention, the value of t is calculated based on at least three of the aforementioned parameters, and in some embodiments of the present invention, the value of t is calculated based on all of the aforementioned parameters.

The methods and systems of the present embodiments can utilize many types of build materials. Representative examples include, but are not limited to, a variety of build materials having a post-cure HDT (measured by one or more ASTM D-648 series procedures, particularly by ASTM D-648-06 and ASTM D-648-07 methods, and optionally by both ASTM D-648-06 and ASTM D-648-07 methods) at a pressure of about 0.45 MPa above the temperature at which the multiple layers are formed, preferably with an HDT of about 50°C or greater.

Suitable building materials may include compositions comprising acrylic or methacrylic functional groups that can be UV-polymerized via a free radical mechanism (e.g., an addition reaction of the acrylic functional groups). Further examples include, but are not limited to, UV-polymerizable compositions comprising at least 30% by weight of monoacrylic or monomethacrylic functional monomers, wherein the corresponding polymers of the monomers have a glass transition temperature (Tg) greater than about 50°C. In some embodiments, the Tg is greater than 60°C or greater than 70°C.

As used herein, "Tg" refers to the glass transition temperature, which is defined as the location of the local maximum of the E" curve, where E" is the loss modulus of the material as a function of temperature.

Some representative types of materials suitable for this embodiment include VeroBlue RGD840, VeroGrey RGD850, VeroBlack RGD870 and RGD525, which are commercially available modeling materials from Stratasys, Inc.

As used herein, the term "about" refers to ±10%, and the symbol "≈" indicates equality with a tolerance of up to 10%.

The word “exemplary” is used herein to mean “serving as an example, instance, or illustration.” Any embodiment described as “exemplary” is not necessarily to be construed as preferred or advantageous over other embodiments and/or to exclude the incorporation of features from other embodiments.

The word “optionally” is used herein to mean “provided in some embodiments and not provided in other embodiments.” Any particular embodiment of the present invention may include a number of “optional” features, unless such features are incompatible.

The terms "comprises," "comprising," "includes," "including," "having" and their conjugations mean "including but not limited to."

The term "consisting of" means "including and limited to."

The term “essentially consisting of” means that the composition, method, or structure may include additional ingredients, steps, and/or components, but only if the additional ingredients, steps, and/or components do not materially alter the basic and novel characteristics of the claimed composition, method, or structure.

As used herein, the singular forms "a," "an," and "at least one" include plural references unless the context clearly dictates otherwise. For example, the term "a compound" or "at least one compound" may include a plurality of compounds, including mixtures thereof.

Throughout this application, various embodiments of the present invention may be presented in the form of a range. It should be understood that descriptions in the form of a range are merely for convenience and brevity and should not be construed as rigid limitations on the scope of the invention. Therefore, the description of a range should be considered to have specifically disclosed all possible subranges and single numbers within that range. For example, the description of a range from 1 to 6 should be considered to have specifically disclosed subranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range.

Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integer) within the indicated range. The terms "range between" a first indicated numeral and a second indicated numeral and "range from" a first indicated numeral to" a second indicated numeral" are used interchangeably herein and are meant to include the first and second indicated numerals, and all fractions and integers therebetween.

It will be appreciated that certain features of the present invention, which for clarity are described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the present invention, which for brevity are described in the context of a single embodiment, may also be provided separately, in any suitable subcombination, or in any other described embodiment applicable to the present invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

Various embodiments and aspects of the present invention as delineated hereinabove and as claimed in the claims section below find experimental support in the following examples.

Example:

Reference is now made to the following examples, which together with the above descriptions illustrate some embodiments of the invention in a non limiting fashion.

Experiments were conducted to determine the preferred geometric configuration of the radiation source and print head. The experimental setup is shown in Figure 13, which shows the head 16 and radiation source 18 mounted on a frame 180. The radiation source was an ultraviolet lamp.

The printing process was performed at a diameter of 352.8 mm, which allowed for an angular velocity of approximately 100 degrees per second. The angular separation between the radiation source and the head was approximately 52 degrees, and the corresponding time interval from material dispensing to curing was approximately 0.52 seconds.

Baseline tests were performed at different power levels. A UV radiometer was used to measure the power output of the UV lamp at different voltage inputs to the ballast. The UV lamp power as a function of applied voltage is shown in FIG14A and

Images of the resulting printed patterns for input voltages of 2.2 V, 3.2 V, and 4.5 V are shown in FIG14B, FIG14C, and FIG14D, respectively. The radiometer confirmed the increase in power output. The effect of power on the fill level of the printed pattern was not significant.

Another printing process was performed at a diameter of 497.8 mm, which allowed an angular velocity of approximately 80 degrees per second. The angular separation between the radiation source and the head was approximately 180°, and the corresponding time interval from material dispensing to curing was approximately 2.25 seconds. The resulting printed pattern had a significantly higher fill level compared to the baseline shown in Figures 14B to 14D. The surface finish of the model was significantly affected. Edges and corners were not sharp, resulting in a wavy finish. Dimensional accuracy was also reduced, with an error of approximately 2% in the nominal dimension. Images of the printed patterns obtained from these experiments are shown in Figures 14E and 14F.

To confirm that print quality was not affected by moving to a larger diameter, the UV lamp was moved to several alternative positions around the tray. Figures 14G and 14H show images of the resulting print patterns for angles of approximately 80° and 60° between the radiation source and the print head. As shown, the fill level decreased as the UV lamp was moved closer to the print head.

In another print run, dot gain increased. Surface finish improved, and dimensional accuracy was enhanced. Dimensional errors were reduced to less than 0.5% of the nominal size. A representative image of the resulting print pattern for an 80° angular separation is shown in FIG14I . This print quality is consistent with printing the baseline at a smaller diameter.

To confirm that fill level was less affected by UV lamp power, additional experiments were performed at different power levels at larger print diameters. No significant changes in fill level and dimensional accuracy were observed (data not shown).

Table 1 summarizes the experimental parameters and results.

Table 1:

Although the present invention has been described in conjunction with specific embodiments thereof, it is apparent that many alternatives, modifications and variations will be apparent to those skilled in the art. It is therefore intended to embrace all alternatives, modifications and variations that fall within the scope of the appended claims.

All publications, patents, and patent applications mentioned in this specification are hereby incorporated by reference in their entirety. This is to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. Furthermore, any reference cited or identified should not be construed as an admission that such reference is available as prior art to the present invention. Headings are used herein to facilitate understanding of the specification and should not be construed as necessarily limiting.

Claims (74)

1. A system for 3D printing, characterized in that the system comprises: A rotating tray configured to rotate about a vertical axis; An inkjet printhead, each with multiple separate nozzles; and A controller configured to control the inkjet printhead to dispense multiple droplets of building material in multiple layers during the rotation, so as to print a three-dimensional object on the tray; The controller also accesses a computer-readable medium with a bitmap mask and acquires print data relating to a shape of the object only for the positions on the tray not masked by the bitmap mask. 2. The system of claim 1, wherein for at least one inkjet printhead, a plurality of different nozzles are located at a plurality of different distances from the axis and dispense the building material at a plurality of different dispensing rates. 3. The system of claim 1, wherein the inkjet printhead is configured to reciprocate relative to the tray in a radial direction. 4. The system as claimed in claim 3, wherein the movement along the radial direction is carried out by a screw. 5. The system of claim 4, wherein the controller is configured to compensate for a plurality of errors in a radial position of the inkjet printhead according to a compensation function. 6. The system as claimed in claim 5, wherein the screw is a double-support screw and the function is a linear function. 7. The system as claimed in claim 5, wherein the screw is a cantilever screw and the function is a nonlinear function. 8. The system of claim 3, wherein for at least two of the inkjet printheads, the reciprocating motion along the radial direction is independent and at a different azimuth angle. 9. The system as claimed in any one of claims 4 to 7, characterized in that: for at least two of the inkjet printheads, the reciprocating motion along the radial direction is independent and at a different azimuth angle. 10. The system of claim 3, wherein the controller is configured to change a rotational speed of the tray in response to a radial position of the inkjet printhead. 11. The system as claimed in any one of claims 4 to 8, wherein the controller is configured to change a rotational speed of the tray in response to a radial position of the inkjet printhead. 12. The system of claim 3, wherein the controller is configured to stop the allocation during the reciprocating motion. 13. The system as claimed in any one of claims 4 to 8, wherein the controller is configured to stop the allocation during the reciprocating motion. 14. The system of claim 13, wherein the controller is configured to resume the assignment at an azimuth coordinate after the reciprocating motion, the azimuth coordinate being offset relative to the azimuth coordinate from which the assignment was stopped. 15. The system of claim 12, wherein the controller is configured to resume the assignment at an azimuth coordinate after the reciprocating motion, the azimuth coordinate being offset relative to the azimuth coordinate from which the assignment was stopped. 16. The system of claim 13, wherein the controller is configured to resume the allocation at the same azimuth coordinate as the one at which the allocation was stopped after the reciprocating motion. 17. The system of claim 3, wherein the controller is configured to continue the allocation during the reciprocating motion while adjusting a print data in response to the reciprocating motion. 18. The system of claim 11, wherein the controller is configured to continue the allocation during the reciprocating motion while adjusting a print data in response to the reciprocating motion. 19. The system of claim 3, wherein the controller is configured to control at least one of the inkjet printheads to dispense the plurality of droplets, such that an azimuth distance between the plurality of sequentially dispensed droplets varies as a function of the inkjet printhead along the radial direction. 20. The system of any one of claims 4 to 8, wherein the controller is configured to control at least one of the inkjet printheads to dispense the plurality of droplets, such that an azimuth distance between the plurality of sequentially dispensed droplets varies as a function of a position of the inkjet printhead along the radial direction. 21. The system of claim 20, wherein the change in the azimuth distance is based on a probability function of the position along the radial direction. 22. The system of claim 19, wherein the change in the azimuth distance is based on a probability function of the position along the radial direction. 23. The system of claim 20, wherein the controller is configured to perform an interleaved distribution of the plurality of droplets during at least one rotation of the tray. 24. The system of claim 23, wherein the stagger level of the staggered allocation varies as a function of a position of the inkjet printhead along the radial direction. 25. The system of claim 1, wherein the system further comprises a conical roller for straightening the dispensed building material. 26. The system according to any one of claims 2 to 8, characterized in that: the system further includes a conical roller for straightening the dispensed building material. 27. The system of claim 1, wherein the tray rotates continuously in the same direction during the formation of the object. 28. The system as claimed in any one of claims 2 to 8, wherein the tray rotates continuously in the same direction during the formation of the object. 29. The system of claim 1, wherein at least one of the tray and the inkjet printhead is configured to move along a vertical direction parallel to the vertical axis to change a vertical distance between the tray and the inkjet printhead, and wherein the controller is configured to continue the dispensing along the vertical direction during the movement. 30. The system of any one of claims 2 to 8, wherein at least one of the tray and the inkjet printhead is configured to move along a vertical direction parallel to the vertical axis to change a vertical distance between the tray and the inkjet printhead, and wherein the controller is configured to continue the dispensing along the vertical direction during the movement. 31. The system of claim 30, wherein the movement is performed along the vertical direction such that the tray and the inkjet printhead experience at least two different vertical distances during a single rotation of the tray. 32. The system of claim 29, wherein the movement is performed along the vertical direction such that the tray and the inkjet printhead experience at least two different vertical distances during a single rotation of the tray. 33. The system of claim 30, wherein the movement is performed along the vertical direction such that during a single rotation of the tray, the vertical distance increases by an amount approximately equal to a characteristic thickness of a single layer of the building material. 34. The system of claim 29, wherein the movement is performed along the vertical direction such that during a single rotation of the tray, the vertical distance increases by an amount approximately equal to a characteristic thickness of a single layer of the building material. 35. The system of claim 33, wherein the movement along the vertical direction is performed substantially continuously. 36. The system of claim 34, wherein the movement along the vertical direction is performed substantially continuously. 37. The system according to any one of claims 1 to 8, wherein the plurality of inkjet printing heads comprises: at least one support material head for dispensing a support material; and at least two modeling material heads for dispensing two different modeling materials respectively. 38. The system according to any one of claims 1 to 8, wherein the system further comprises a support structure positioned below the inkjet printhead portion, such that the tray is located between the support structure and the inkjet printhead, the support structure contacting the tray to prevent or reduce tray vibration. 39. The system as claimed in any one of claims 1 to 8, wherein the tray is replaceable. 40. The system of claim 39, wherein the system further comprises a tray replacement device configured to automatically replace the tray. 41. The system according to any one of claims 2 to 8, wherein the system further comprises a preheating element for heating the building material before it enters the inkjet printhead. 42. The system according to any one of claims 1 to 8, wherein the inkjet printhead is configured to maintain a vacuum level within a predetermined range of a plurality of vacuum levels. 43. The system of claim 1, wherein the system further comprises a preheating element for heating the building material before it enters the inkjet printhead. 44. The system of claim 41, wherein the preheating element is spaced apart from the inkjet printhead and is in fluid communication with the inkjet printhead via a conduit. 45. The system of claim 43, wherein the preheating element is spaced apart from the inkjet printhead and is in fluid communication with the inkjet printhead via a conduit. 46. The system of claim 44, wherein the system further comprises a pump for retracting the building material from the conduit into the preheating element. 47. The system according to any one of claims 1 to 8, wherein the system further comprises at least one level, mounted at one or more locations on a housing of a chassis of the system, for indicating a deviation of the chassis from a level state. 48. The system of claim 1, wherein the controller is configured to calculate an amount of building material required to print the object, compare the amount with an available amount of building material, and issue an alarm when the amount required to print the object is greater than the available amount. 49. The system as claimed in any one of claims 2 to 8, wherein the controller is configured to calculate an amount of building material required to print the object, compare the amount with an available amount of building material, and issue an alarm when the amount required to print the object is greater than the available amount. 50. The system of claim 1, wherein the system further comprises a radiation source configured to reciprocate relative to the tray in a radial direction, wherein the inkjet printhead is further configured to reciprocate relative to the tray in the radial direction and is not synchronized with the radiation source. 51. The system according to any one of claims 2 to 8, characterized in that: the system further includes a radiation source configured to reciprocate relative to the tray in a radial direction, wherein the inkjet printhead is further configured to reciprocate relative to the tray in the radial direction and is not synchronized with the radiation source. 52. The system of claim 1, wherein the system further comprises a radiation source configured to irradiate the plurality of layers such that energy is delivered at different rates to a plurality of locations, the plurality of locations being at a plurality of different distances from a center of the tray. 53. The system according to any one of claims 2 to 8, wherein the system further comprises a radiation source configured to irradiate the plurality of layers such that energy is delivered at different rates to a plurality of locations, the plurality of locations being at a plurality of different distances from a center of the tray. 54. The system of claim 1, further comprising a radiation source, wherein the system further comprises a radiation source, and the azimuth interval between the radiation source and the inkjet printhead is between approximately 0.3 ω radians and approximately 0.75 ω radians, wherein ω is an average angular velocity of the tray relative to the inkjet printhead and the radiation source. 55. The system according to any one of claims 2 to 8, characterized in that: the system further comprises a radiation source, the azimuth interval between the radiation source and the inkjet printhead being between about 0.3 ω radians and about 0.75 ω radians, where ω is an average angular velocity of the tray relative to the inkjet printhead and the radiation source. 56. The system of claim 1, wherein when multiple objects are printed simultaneously, the controller is configured to calculate the total printing time of an exception of the multiple objects and display the calculated time on a display device. 57. The system as claimed in any one of claims 2 to 8, characterized in that: when printing multiple objects simultaneously, the controller is configured to calculate the total printing time of an exception of the multiple objects, and display the calculated time on a display device. 58. The system of claim 57, wherein the controller is configured to calculate the total printing time for each object and display the total printing time for each object. 59. The system of claim 56, wherein the controller is configured to calculate the total printing time for each object and display the total printing time for each object. 60. The system of claim 1, wherein the controller is configured to terminate any dispensing of the building material when the inkjet printhead is above a predetermined area of the tray. 61. The system as claimed in any one of claims 2 to 8, wherein the controller is configured to terminate any dispensing of the building material when the inkjet printhead is above a predetermined area of the tray. 62. The system as claimed in claim 61, wherein the predetermined region has a circular fan-shaped form. 63. The system of claim 62, wherein when the inkjet printhead is above the predetermined area, the controller is configured to signal the inkjet printhead to move in a radial direction relative to the tray. 64. The system of claim 61, wherein when the inkjet printhead is above the predetermined area, the controller is configured to signal the inkjet printhead to move in a radial direction relative to the tray. 65. The system as claimed in any one of claims 62 to 63, wherein the controller is configured to signal at least one of the tray and the inkjet printhead to move along a vertical direction parallel to the vertical axis, thereby changing a vertical distance between the tray and the inkjet printhead when the inkjet printhead is above the predetermined area. 66. The system of claim 61, wherein the controller is configured to signal at least one of the tray and the inkjet printhead to move along a vertical direction parallel to the vertical axis, thereby changing a vertical distance between the tray and the inkjet printhead when the inkjet printhead is above the predetermined area. 67. The system of claim 1, wherein the system further comprises a roller for straightening the dispensed building material, wherein the controller is configured to signal at least one of the tray and the inkjet printhead to move in a vertical direction parallel to the vertical axis so as to immediately change a vertical distance between the tray and the inkjet printhead once the dispensed building material first reaches the roller. 68. The system of any one of claims 2 to 8, wherein the system further comprises a roller for straightening the dispensed building material, wherein the controller is configured to signal at least one of the tray and the inkjet printhead to move in a vertical direction parallel to the vertical axis so as to immediately change a vertical distance between the tray and the inkjet printhead once the dispensed building material first reaches the roller. 69. The system of claim 1, wherein the system further comprises a roller for straightening the dispensed building material, wherein the controller is configured to signal at least one of the tray and the inkjet printhead to move in a vertical direction parallel to the vertical axis to change a vertical distance between the tray and the inkjet printhead so that the vertical movement is completed immediately once the dispensed building material first reaches the roller. 70. The system of any one of claims 2 to 8, wherein the system further comprises a roller for straightening the dispensed building material, wherein the controller is configured to signal at least one of the tray and the inkjet printhead to move in a vertical direction parallel to the vertical axis to change a vertical distance between the tray and the inkjet printhead so that the vertical movement is completed immediately once the dispensed building material first reaches the roller. 71. The system as claimed in any one of claims 1 to 8, characterized in that: the controller is configured to select a first printing mode and a second printing mode, the first printing mode employing an azimuth scan and the second printing mode employing a vector scan along a path selected to form at least one structure, the structure being selected from: (i) an elongated structure; (ii) a boundary structure at least partially surrounding an area filled with the building material; and (iii) a group consisting of interlayer connection structures. 72. The system of claim 1, wherein the system further comprises a radiation source configured to irradiate the plurality of layers, wherein the controller is configured to control the radiation source to ensure that, for at least one layer, the irradiation is initiated at least t seconds after the curing of the layer immediately preceding the at least one layer, wherein t is longer than a total time required for the formation. 73. The system of any one of claims 2 to 8, wherein the system further comprises a radiation source configured to irradiate the plurality of layers, wherein the controller is configured to control the radiation source to ensure that, for at least one layer, the irradiation is initiated at least t seconds after the curing of the layer immediately preceding the at least one layer, wherein t is longer than a total time required for the formation. 74. A method for manufacturing an object, characterized in that the method comprises the following steps: Receive 3D printing data corresponding to the shape of an object. The data is sent to a system for 3D printing, and The system is operated according to the data to print the object, wherein the system is the system as claimed in any one of claims 1 to 8.