GB2146461A

GB2146461A - Vacuum holddown system

Info

Publication number: GB2146461A
Application number: GB08419867A
Authority: GB
Inventors: Joseph Herman Cohen
Original assignee: Gerber Garment Technology Inc
Current assignee: Gerber Technology LLC
Priority date: 1983-08-16
Filing date: 1984-08-03
Publication date: 1985-04-17
Also published as: IT8467819A1; IT1179049B; JPS6052299A; ES533685A0; ES8600997A1; DE3430201A1; FR2550725A1; IT8467819A0; GB8419867D0

Abstract

An automatically controlled cutting machine for cutting limp sheet material includes a vacuum holddown system 22 for holding the material in place on a support surface during a cutting operation. The level of vacuum holding the material is regulated during the cutting operation to ensure adequate holding forces, to prevent damage to the material, and to improve cutting performance. Control is accomplished by sensing the level of vacuum applied to the material and regulating the vacuum generator at a desired vacuum level. Sensor 60 operates lobe 82 to move servomotor 84 to operate regulating lobe 62. <IMAGE>

Description

SPECIFICATION Method and apparatus for regulating vacuum holddown Background of the invention The present invention relates to vacuum holddown systems of the type used to hold and compress limp sheet materials during cutting operations.

Vacuum systems for holding limp sheet materials, such as woven and non-woven fabrics, cardboard, paper, leather, rubber, expanded foam, fluffed fibers, and synthetics, are well known in the art and have been used commercially in the manufacture of garments, upholstery, and other items for many years. Typically, the sheet material is placed in a multi-ply layup on a support surface and then covered with an air impermeable overlay. Vacuum is then applied to the material and atmospheric pressure operating on the overlay compresses the material against the support surface. A cutting tool in the form of a reciprocating cutting blade or cutting wheel is then guided through the material along a desired line of cut. Numerous products, such as garment pieces and upholstery panels, can be prepared in a wide variety of shapes and sizes through numerical control.

Generally, cutting operations as described above are performed on a relatively large expanse of material, such as 25 square feet or more. The cutting operation inherently produces slits or holes in the material through which air leaks into the vacuum generator of the system. The generator must accordingly have a relatively large capacity for moving air and maintaining an adequate vacuum level from the beginning to the end of the cutting operation. The large volume of leakage also results in significant power consumption. In orderto minimize the volume of leakage air that passes through cut material, cutting tables in the past have been divided into zones with control valves that energize only that portion of the surface over which the cutting tool is operating. U.S.Patents 3,495,492 and 3,765,289, having the same assignee as the present application, disclose cutting tables which are zoned in this fashion.

To further minimize the capacity of the vacuum holddown system and reduce the power consumed, an air permeable sheet is spread over the cut material to seal the cuts after the cutting tool has moved on. U.S. Patents, 3,495,492; 3,682,750; and 3,742,802 show various techniques for sealing cuts in this manner.

In the prior art cutting machines described in the patents referenced above, the vacuum generator in the holddown system in typically a high volume centrifugal pump or turbine that is driven art a substantially constant speed regardless of the leakage airflow being drawn from the material. As a result, the material is subjected to high vacuum levels intended for a worst case situation at the beginning of a cutting operation, and the vacuum levels weaken as the cutting operation is carried out.

It has been learned, however, that certain materials are adversely affected by high vacuum levels, and either the materials themselves may be damaged or cutting performance is adversely affected.

For example, delicate materials can be impaled on bristles which are typically employed to support the materials during cutting by a cutting blade unless a protective layer of paper or cardboard is interposed between the material and the bristles. Materials with relatively long fibers, such as fur liners for coats and the like, can be crushed or matted under high vacuum which adversely affects their insulating qualities and appearance. Resilient expanded foam materials do not compress uniformly and are sometimes distorted by high vacuum forces so that the pieces cut from the material do not conform to a desired pattern cut into the compressed material after the material is released from the cutting table and returns to its normally expanded condition.

It is accordingly a general object of the present invention to provide a vacuum holddown system that can be regulated at various vacuum levels as the cutting operation is carried out so that neither the materials nor cutting performance is adversely affected.

Summary of the invention The present invention resides in a vacuum holddown system in which the level of vacuum produced by a vacuum generator is regulated during the course of a cutting operation. The apparatus which carries out the method includes a cutting table defining a support surface on which the limp sheet material is placed in a spread condition for cutting.

For example, the sheet material may be a fabric that is placed in a multi-ply layup for cutting out pattern pieces for garments. A cutting tool, such as a reciprocating knife blade, is supported over the sheet material on the support surface for movement in cutting engagement with the material. The blade is advanced along a predetermined line of cut that is defined by the shape of the desired pattern piece.

Vacuum generating means are associated with the limp sheet material on the surface for evacuating the material and compressing the material for cutting. In one embodiment, the cutting table has a penetrable bed on which the material is placed, and the bed is formed by a plurality of bristles that are penetrated by the knife blade during a cutting operation. The vacuum generating means includes a vacuum pump which is placed in fluid communication with the sheet material through the penetrable bed, and an air impermeable sheet is overlaid on the material to aid the evacuation.

In accordance with the present invention, vacuum regulating means are connected in controlling relationship to the vacuum generating means for regulating the vacuum which compresses the material as the material is cut by the tool. The regulating means includes sensing means that measures the level of the vacuum produced in the material by the vacuum generating means. The vacuum level is regulated to maintain a uniform level within the capacity of the vacuum generating means or to restrict the level to which the material is exposed, so that the material is not damaged and cutting performance is not depreciated. Regulation can be carried out by throttling the flow of air removed by the vacuum generating means or by admitting additional airto lessen the effect of the generating means.

Brief description of the drawings Figure 1 is a perspective view of an automatically controlled cutting machine with a vacuum holddown system embodying the present invention.

Figure 2 is a schematic diagram of the cutting machine and controls for regulating the vacuum holddown system.

Figure 3 is a schematic diagram showing another embodiment of the controls for regulating the vacuum holddown system.

Figure 4 is a schematic diagram showing still another embodiment of the controls for regulating the vacuum holddown system.

Description of the preferred embodiments Figure 1 illustrates an automatically controlled cutting machine, generally designated 10, of the type shown and described in greater detail in U.S. Patent No. 3,495,492 having the same assignee as the present invention. Such cutting machine 10 is utilized to cut multi-ply layups L of sheet material such as woven and nonwoven fabrics, paper, cardboard, leather, rubber, synthetics, expanded foam, and fluffy fibrous materials. The illustrated machine 10 is a numerically controlled machine connected with a computer controller 12 by means of an electrical cable 14. The controller 12takes data from a program tape 16 and converts that data into machine commands for guiding a reciprocating that data into machine commands for guiding a reciprocating cutting blade 20 along a cutting path P defined by the program tape 16.The cutting path may, for example, be the periphery of a pattern piece forming part of a garment or a panel of upholstery.

The cutting machine 10 includes a table 22 having a penetrable bed 24 defining the support surface for the layup L during cutting. The bed 24 may be comprised of a Styrofoam material or preferably a bed of bristles which are easily penetrated by the reciprocating cutting blade 20 without damage to either while the cutting path P is traversed.

The cutting blade 20 in a preferred embodiment is a knife blade suspended above the support surface of the table 22 by means of an X-carriage 26 and a Y-carriage 28. The X-carriage 26 translates back and forth in the illustrated X coordinate direction on a set of racks 30 and 32 which are engaged by an X-drive motor 34 energized by command signals from the controller 12. The Y-carriage 28 is mounted on the X-carriage 26 for movement relative to the Xcarriage in the Y coordinate direction and is translated by the Y-drive motor 36 and a lead screw 38 connected between the motor and carriage. Like the drive motor 34, the drive motor 36 is also energized by command signals from the controller 12. Thus coordinated movements of the carriages 26 and 28 can translate the cutting blade 20 along a cutting path over any area of the table 22.

The cutting blade 20 is suspended in cantilever fashion from a platform 40 attached to the projecting end of the Y carriage 28 for elevating the sharp, leading cutting edge of the blade into and out of cutting engagement with the layup of sheet material on the table 22. The blade 20 is reciprocated by means of a drive motor 42 also supported on the platform 40.

The cutting table 22 is provided with a vacuum holddown system for holding the layup Lsheet material firmly on the penetrable bed 24 and for compressing the sheet material into a firm condition for cutting as described in U.S. Patent 3,495,492 and others mentioned above. The vacuum system includes a vacuum generator or pump 50 which, in the preferred embodiment, is a high volume centrifugal air pump. The pump 50 is connected to the vacuum table 22 through an evacuation duct 52 that is connected with a plenum chamber 54 in the base of the table 22, as shown in Figure 2. In Figure, the bed 24 is comprised of a plurality of bristle mats with the bristles projecting upwardly to define the support surface of the table on which the layup L rests.The bristled mats are in turn supported on a grating 56 extending across the top of the plenum chamber 54, and the mats are perforated or circumvented at the sides of the table so that vacuum within the plenum chamber 54 is also drawn within the bristles as well as the layup. Preferably, the layup L is overlaid with an air impermeable sheet S as shown in Figure 1 so that the permeability of the fabric comprising the layup does not interfere with vacuum generation by permitting more air than that which leaks through the cuts in the material to enter the vacuum system.

Typically, a sheet of polyethylene is employed as the overlay material, and the polyethylene as well as the fabric forming the layup, is cut during the cutting operation. The cutting table 22 may also be zoned as described in the above referenced patent 3,495,492 to restrict the application of vacuum to that section of the material over which the cutting blade operates.

In accordance with the present invention, means are provided for regulating the level of vacuum generated in the cutting table during the cutting operation. The regulating means includes a pressure sensor 60 that is connected into the plenum chamber 54 by a vacuum or pressure sensing line 61 and measures the level of vacuum that exists in the chamber at any point in time. An adjustable flow control valve 62 is mounted in the evacuation duct 52 and is adjusted by means of an actuator 64 in response to signals derived from the pressure sensor 60. The control valve 62 is preferably a butterfly valve having a large vane member mounted to rotate in the conduit 52 between a fully opened and closed position. The adjustment of the valve 62 throttles the flow of air evacuated from the layup Lthrough the duct 52 and, accordingly, controls the level of vacuum existing at any point in time in the layup L. Various modes of control are possible, and in the preferred embodiment of the invention illustrated in Figure 2, the pressure or vacuum level existing within the plenum 54 is maintained between upper and lower limits, provided that the capacity of the vacuum pump 50 is not exceeded.

The pressure sensor 60 illustrated in Figure 2 is a photohelic gauge of a type manufactured by Dwyer Instruments, Inc. The pressure or the vacuum level sensed through the line 61 is applied to the gauge and moves an indicating needle 70 relative to a graduated face 72. Two adjustable supports 74,76 hold photocells 78, 80 respectively at opposite sides of the indicating needle 70 and respond to the needle when the needle is adjacent one or the other of the cells at upper and lower vacuum levels respectively to provide an electrical control signal that is transmitted to a four-way solenoid valve 82 in the actuator 64. The supports 74,76 are manually adjustable so that the upper and lower vacuum levels can be set by the machine operator. Typical settings for the supports would be four and six inches of mercury respectively.

The solenoid valve is a pneumatic valve that controls the flow of pressurized air to the piston and cylinder assembly 84. The valve 82 has three basic positions. When the needle 70 is at a position between the photocells 78,80, no signal is supplied from the pressure gauge 60, the solenoid valve assumes a centered, closed position, and the piston and cylinder assembly and the flow control valve do not move from the established positions. When the vacuum level is low (absolute pressure is high) in the plenum 54, the indicating needle 70 of the sensor 60 moves adjacent to the photocell 78 and causes the cell to send a signal to the solenoid valve 82, move the piston in the assembly 84 and the flow control valve 62 toward the open position to permit more air to be evacuated from the plenum by the pump 52.

When vacuum level is high (absolute pressure is correspondingly low) in the plenum 54, the indicating needle 70 moves adjacent to the photo cell 80 and energizes the solenoid valve 82 to move the piston of the assembly 84 in the opposite direction, which moves the flow control 62 toward the closed position. Consequently, the position of the photocells 78, 80 represents the upper and lower control limits of the vacuum level as long as the capacity of the vacuum pump 50 is not exceeded. The maintain stability within the system, the control ports in the valve 82 and the piston and cylinder assembly 84 are designed so that the adjustment of the valve 62 is slow and the valve movement between fully open and fully closed positions requires lotto 15 seconds.

In this manner, rapid fluctuations of the vacuum level within the plenum chamber 54 are avoided.

Of course, other control systems which provide proportional and other control processes may also be employed.

It will be understood that throttling the flow of air evacuated from the layup L with the valve 62 positioned as shown in Figure 2 minimizes the quantity of air that must be handled by the pump 50 and thus results in minimum energy consumption.

At the beginning of a cutting operation when the pump is energized and the layup L is uncut, there is minimum leakage of air into the plenum 54 due to small holes or slits that invariably exist in the cutting table. When the pump 50 has lowered the vacuum pressure to a desired level in the plenum 54, the flow control valve 62 is moved towards its closed position, and the pump 50 has a minimum load demand.

As the cutting operation takes place and more and more holes or slits are cut in the layup L, a large volume of air leaks through these slits into the plenum 54, and the pressure level rises. The pressure rise is detected by the pressure sensor 60 and through the actuator 64 causes the control valve 62 to open so that the higher flow of air through the layup is matched through the conduit 52 by the pump 50 to maintain a substantially uniform vacuum level. If the layup L is cut extensively, the full capacity of the vacuum pump 50 can be reached or exceeded, and in that event, the flow control valve 62 is moved towards its fully opened position to remove air at the maximum capacity of the pump.

Figure 3 illustrates a further embodiment of the invention in which the reference numerals corresponding to components in the embodiment of Figures 1 and 2 are the same.

In Figure 3, the vacuum pump 50 has an inlet port 90 that is connected directly with the plenum chamber 54 through an evacuation conduit 92, and a discharge port 94 is connected to the flow control valve 62. Air is evacuated from the layup Land the plenum 54 by means of the pump 50 and is discharged from the pump through the control valve 62. The control valve is operated in response to the signal from the pressure sensor 60 by the actuator 64 and throttles the air flow through the pump at the discharge of the pump. In operation, the system is basically the same as the embodiment shown in Figures 1 and 2, except that the control valve throttles the air flow from the layup by controlling the discharge pressure of the pump.

Figure 4 illustrates still a furthe embodiment of the invention in which the same reference numerals are used to identify components described in the embodiments above.

In Figure 4, the vacuum pump 50 is connected directly to the plenum chamber 54 of the cutting table through a conduit 100, and air evacuated from the layup and the table is discharged directly into the ambient environment. The flow control valve 62 is connected in series with the plenum 54 through a separate conduit 102 and is connected with the ambient environment to admit air to the plenum chamber by means o a conduit 104. Consequently, when the valve 62 is open, air can flow serially through the conduits 104, 102, the plenum chamber 54, and the duct 100 to the pump 50.

The vacuum level in the layup Land the plenum 54 is regulated by the pressure sensor 60 and the actuator 64 by throttling the flow of air into the plenum chamber when the vacuum pump 50 is evacuating air from the plenum chamber. A uniform vacuum level is maintained in the chamber by the pressure sensor 60 and the actuator 64 by opening the valve 62 when the level is too high and closing the valve when the level is too low. It will be understood that this method of regulation inherently introduces air into the plenum and causes the vacuum pump 50 to operate with substantially higher energy consumption, but the vacuum regulation system in this embodiment can be readily applied to prior art vacuum holddown systems without interfering with the existing plumbing between the cutting table and the pump.

Accordingly, a method and apparatus have been disclosed for regulating the level of vacuum in a cutting machine to achieve a controlled vacuum level during a cutting operation. It should be understood that numerous modifications and substitutions can be made to the disclosed embodiments without departing from the spirit of the invention.

For example, the controlled vacuum level within the cutting table may not be held uniform throughout the cutting operation, and can be adjusted up or down to permit removal of cut material or to perform other operations, such as indexing of the layup L between different segments of the cutting operation.

The level at which the vacuum is initially set may be adjusted in accordance with the characteristics of the material, such as its strength to withstand the vacuum level. For example, the vacuum level may be initially set at a low level to avoid crushing long fibers of fluffy materials, such as felts or simulated fur liners, orto avoid deforming the material, such as expanded foam, in a non-uniform manner. The vacuum level can also be adjusted to provide the most satisfactory cutting performance. For example, reducing the vacuum to low levels on high strength, hard-to-cut materials, such as denim, facilitates movement of the cutting blade through the material in a cutting operation. Accordingly, the pressure level can be set to any desired level depending upon the goals to be achieved. The pressure gauge 60 described in detail is merely one example of the pressure gauge that can be used to measure the vacuum level within the chamber, and other sensors and controls for changing or maintaining the vacuum level can be employed. Regulation of the vacuum generator may be accomplished by adjusting the speed or power at which the vacuum pump is operated, and in this event, the flow control valve for throttling the evacuated air may be eliminated.

According, the present invention is described in a preferred embodiment by way of illustration rather than limitation.

Claims

1. An apparatus for cutting limp sheet material including a cutting table defining a support surface on which limp sheet material is placed in a spread condition for cutting; a cutting tool for cutting the material spread on the support surface; means for supporting the cutting tool and the support surface with the sheet material spread on the surface for movement relative to one another to advance the cutting tool along a predetermined line of cut whereby the tool can cut the material in selected shapes; and vacuum generating means associated with the limp sheet material on the support surface of the table for evacuating the material and compressing the material for cutting, the improvement comprising vacuum regulating means connected in controlling relationship to the vacuum generating means for regulating the vacuum compressing the material as the material is cut by the tool, and including sensing means measuring the level of vacuum produced by the vacuum generating means.

2. An apparatus for cutting limp sheet material as defined in claim 1, the improvement wherein the vacuum regulating means regulates the vacuum generating means to maintain a substantially uniform level of vacuum measured by the sensing means as the sheet material is progressively cut.

3. In an apparatus for cutting sheet material as defined in claim 1, in which the cutting table has an air permeable support surface and the vacuum generating means communicates with the sheet material through the cutting table and the support surface, the improvement wherein the sensing means of the vacuum regulating means is connected for measuring the level of vacuum in the cutting table.

4. An apparatus for cutting sheet material as defined in claim 1, wherein the vacuum generating means includes a vacuum pump connected with the cutting table for evacuating and compressing the material on the support surface; and the vacuum regulating means further comprises a flow control valve connected in series with the vacuum pump and adjustable between open and closure positions to regulate flow through the pump.

5. In an apparatus for cutting sheet material as defined in claim 4, the improvement wherein the flow control valve is interposed between the cutting table and the vacuum pump.

6. An apparatus for cutting sheet material as defined in claim 4, the improvement wherein the vacuum pump has an inlet port connected with the cutting table and an outlet port discharging air evacuated from the table; and the flow control valve is connected with the outlet port.

7. In an apparatus for cutting sheet material as defined in claim 4, the improvement wherein the cutting table includes a plenum chamber in fluid communication with the sheet material on the support surface for evacuating the material, the vacuum pump is connected to the plenum chamber for evacuating the chamber and material; and the flow control valve is connected with the vacuum pump through the plenum chamber and regulates the vacuum level in the chamber.

8. In an apparatus for cutting limp sheet material as defined in claim 1, the improvement wherein the vacuum generating means includes a vacuum pump connected with the sheet material on the cutting table to evacuate air from the material; the sensing means in the vacuum regulating means comprises pressure sensing means providing a pressure signal indicative of the vacuum level in the material; and adjustable flow control valve means is connected with the sensing means and responsive to the pressure signal for adjusting the flow of air evacuated from the material by the pump.

9. An apparatus as defined in claim 8, the improvement wherein the adjustable flow control valve means has a controlled valve adjustable between an open and a closed position; the pressure sensing means provides a high pressure signal indicating a low vacuum level and a low pressure signal indicating a high vacuum level; and the controlled valve is adjusted toward one position in response to the high pressure signal to increase the vacuum level, and is adjusted toward the other position in response to the low pressure signal to decrease the vacuum level.

10. A method of controlling a vacuum holddown system employed in a cutting machineto hold limp sheet material on a support surface while the material is cut with a cutting tool, the vacuum holddown system including a vacuum generator connected with the sheet material on the support surface for withdrawing air from the material comprising the steps of: sensing the level of vacuum holding the sheet material on the surface as the cutting operation progresses and increases the amount of material cut and, correspondingly, the leakage of air through the cuts into the vacuum holddown system; and regulating the operation of the vacuum generator in response to the sensed level of vacuum to maintain a desired level of vacuum on the sheet material as the leakage increases.

11. A method of controlling a vacuum holddown system as defined in claim 10 including the additional steps of initially setting the desired level of vacuum on the sheet material in accordance with characteristics of the sheet material on the support surface.

12. A method of controlling a vacuum holddown system as defined in claim 10 wherein the vacuum is regulated at a level dependent upon the strength characteristics of the material under vacuum.

13. A method of controlling a vacuum holddown system as defined in claim 10 wherein the step of regulating the operation of the vacuum generator comprises throttling the flow of air drawn from the sheet material by the vacuum generator.

14. A method of controlling a vacuum holddown system as defined in claim 10 wherein the vacuum generator is connected with the sheet material through a plenum chamber and the step of sensing the level of vacuum comprises sensing the level of vacuum in the plenum chamber.

15. A method of controlling a vacuum holddown system as defined in claim 10 wherein the limp sheet material is positioned on an air permeable support surface; and the vacuum generator is connected with the sheet material through the air permeable surface to evacuate the material and compress the material against the surface.

16. A method of controlling a vacuum holddown system as defined in claim 15 wherein the air permeable support surface is defined by a bed of upwardly projecting bristles.

17. An apparatus for cutting limp sheet material substantially as herein described and shown in the accompanying drawings.

18. A method of controlling a vacuum holddown system substantially as herein described with reference to the accompanying drawings.