RU2297724C2 - Laser scanning method and device - Google Patents

Abstract

FIELD: office equipment; laser scanning devices.

SUBSTANCE: optical shaping system of device is designed for shaping light beam with parameters required for system operation from light beam produced by light source; horizontal deflector functions to deflect light beam coming from vertical deflector in horizontal direction thereby affording horizontal sweep; optical focusing system provides for focusing light beam deflected by vertical and horizontal deflectors on point of photosensitive surface; the latter can move in direction perpendicular to that of horizontal sweep afforded by horizontal deflector and project image thereon by light beam.

EFFECT: reduced scanning time, enhanced reliability.

9 cl, 2 dwg

Description

The invention relates to office equipment and can be used in the design of laser scanning devices.

Laser scanning devices (LLS) are used to form images on a photosensitive surface by creating a raster by the line-by-line scanning method with a laser beam. LPS are used in laser printers, digital copiers, laser fax machines, etc. In general terms, the principle of functioning of the LSP can be represented as follows. The laser beam, the intensity of which is modulated by the signal supplied to the laser source, after passing through the optical system forms an image on a photosensitive surface with which the image is in most cases transferred to paper.

Currently, most laser scanning devices used in laser printers, including the laser scanning device described in published application US No. 2002/0131138 [1], contains a laser diode, a collimator, a rotating polyhedron, forming a lens and a photosensitive screen. Projection of the image on the screen is carried out by the method of progressive scanning. Moreover, a horizontal scan is provided by a mechanical deflector, structurally made in the form of a rotating polygon, and a vertical scan is provided by translational movement of the screen.

The main parameters characterizing the quality of laser scanning devices are performance (ppm) and resolution (dpi).

The disadvantages of the known designs of scanning devices, including [1], is their low productivity due to the limited scanning speed. The main factor limiting the scanning speed is the maximum allowable rotation speed of the polyhedron. Moreover, a further increase in speed due to a number of technical problems entails a significant increase in the cost of the system or a decrease in its reliability.

The most promising direction in solving the above problem is the use of multi-beam laser scanning devices, in which several lines of the projected image are reproduced in one pass of the laser beam. This approach allows you to reduce the rotation speed of the polyhedron in proportion to the number of rays simultaneously projected onto the screen.

There are various methods for creating multi-beam laser scanning devices:

- use of several laser diodes;

- use of multi-beam laser diodes;

- dividing one beam into several beams using special optical devices with independent subsequent modulation of each beam, etc.

US Published Application No. 2004/0056185 [2] describes a multi-beam laser scanning device that uses four laser diodes for projecting an image, four collimators, a rotating polyhedron, a forming lens, and a photosensitive screen onto which the image is projected. This device is selected as a prototype of the claimed invention.

The disadvantage of the prototype and other multi-beam scanning devices is the complexity of their design, arising from the increase in the number of laser diodes and optical elements for each diode. In addition, the complexity of the design increases the requirements for precision manufacturing of device elements, reduces the reliability of devices and increases the cost of their manufacture. Moreover, the number of lines simultaneously reproduced in a single pass by a multi-beam scanning device is limited by its design and, as a rule, does not exceed four.

The problem to which the invention is directed, is to create a laser scanning device based on a new scanning method in order to reduce scanning time, increase the reliability of the device, simplify the optical part of the device, and expand the functionality of the device.

The technical result is achieved by increasing the number of lines of the projected image scanned in one horizontal passage along the screen at a constant speed of rotation of the polyhedron, through the use of a single single-beam light source and one forming optical system, by introducing a function to dynamically change the resolution of the scan at a constant speed of movement of the screen that is ensured by creating a laser scanning device that contains a monochromatic light source forming an optical system, a horizontal deflector, a focusing optical system, a photosensitive surface, and the scanning device further comprises a vertical deflector configured to perform a vertical scan by deflecting a light beam with a given amplitude and frequency in a direction perpendicular to the horizontal direction, and forming vertical raster, the height of which is equal to the height of several lines of the projected image, and

- the forming optical system is configured to form from the light beam created by the light source a light beam with the parameters required for the system to operate;

- the horizontal deflector is configured to deflect a beam of light emerging from the vertical deflector in the horizontal direction and, thereby, horizontal scanning;

- the focusing optical system is configured to focus a light beam deflected by a vertical deflector and a horizontal deflector to a point on a photosensitive surface;

- the photosensitive surface is arranged to move in a direction perpendicular to the horizontal direction provided by the horizontal deflector and to project the image onto it with a light beam.

For the operation of the device, it is essential that the monochromatic light source was made in the form of a laser.

For the operation of the device, it is important that the laser is made in the form of a semiconductor laser.

For the functioning of the device, it is necessary that the vertical deflector be made in the form of an electro-optical deflector, an acousto-optical deflector or a piezoelectric deflector.

For the operation of the device, it is advisable that the horizontal deflector be made in the form of a rotating multifaceted reflector, a rotating mirror, an acousto-optical deflector or a piezoelectric deflector.

For the functioning of the device, it is important that the vertical scan is provided with pulses of a triangular, sawtooth or step shape.

For the operation of the device, it is important that the photosensitive surface is made in the form of a rotating photosensitive drum.

For the functioning of the device, it is essential that the forming optical system is made in the form of a collimator.

For the functioning of the device, it is necessary that the focusing optical system is made in the form of an f-Θ lens.

The technical result is also achieved by creating a method of functioning of a laser scanning device, which includes the following operations:

- a light beam is supplied from a monochromatic source through a forming optical system to a vertical deflector;

- they reject the light beam with a given amplitude and vertical frequency by a vertical deflector in a direction perpendicular to the horizontal direction, while forming a vertical raster with a light beam whose height is equal to the height of several lines of the projected image;

- scan the beam of light emerging from the vertical deflector in the horizontal direction with a horizontal deflector, while deflecting the light beam along the photosensitive surface;

- focus the light beam exiting from the horizontal deflector by means of a focusing optical system to a point on the photosensitive surface, and at that one pixel of the projected image is illuminated at the same time, while several lines of the projected image are formed in one horizontal passage of the light beam along the photosensitive surface;

- move the photosensitive surface in the direction perpendicular to the horizontal direction, the width of several lines of the projected image, and then repeat all the above operations of the method until the projection of the entire image on the photosensitive surface.

This ensures the creation of a laser scanning device and a method of its operation, which allows to reduce the scanning time, increase the reliability of the device, simplify the optical part of the device and expand its functionality.

For a better understanding of the present invention, the following is a detailed description thereof with corresponding drawings.

Figure 1 is a simplified diagram of a laser scanning device with additional vertical scan according to the invention.

Figure 2 - a method of creating multiple raster lines in a single pass of a light beam along a photosensitive surface according to the invention.

The laser scanning device contains a monochromatic light source 1, forming an optical system 2, a horizontal deflector 3, a focusing optical system 4, a photosensitive surface 5. Moreover, the scanning device further comprises a vertical deflector 6, configured to perform a vertical scan by deflecting the light beam with a given amplitude and frequency in the direction perpendicular to the horizontal direction, and the formation of a vertical raster, height Otori equal to the height of several lines of the projected image. The forming optical system 2 is configured to form from the light beam created by the light source 1 a light beam with the parameters required for the operation of the system. The horizontal deflector 3 is configured to deflect the beam exiting the vertical deflector 6 in the horizontal direction along the photosensitive surface 5 and, thereby, sweep in the horizontal direction. The focusing optical system 4 is configured to focus the light beam deflected by the vertical deflector 6 and the horizontal deflector 3 to a point on the photosensitive surface 5. The photosensitive surface 5 is configured to move in the direction perpendicular to the horizontal direction provided by the horizontal deflector 6 and project onto her images with a beam of light.

Consider the claimed scanning method using the example of a laser scanning device in which the monochromatic light source 1 is made in the form of a semiconductor laser, and the horizontal deflector 3 is made in the form of a horizontal rotating multifaceted reflector, i.e. polygon (figure 1, 2).

First, the light beam is sent to the forming optical system 2, made in the form of a collimator, passing through which the beam is focused. Then the beam is directed to the vertical deflector 6. In the vertical deflector 6, a light beam is deflected with an amplitude and a vertical frequency in the direction perpendicular to the horizontal direction, while a vertical raster is formed by the light beam, the height of which is equal to the height of several lines of the projected image. It should be noted that the vertical pulses can have a different shape: triangular, sawtooth, step, etc. Figure 2 shows an example of vertical pulses having a sawtooth shape. The light beam emerging from the vertical deflector 6 is directed to a horizontal deflector 3, with which a light beam is deflected in a horizontal direction along the photosensitive surface 5. The light beam emerging from the horizontal deflector 3 is focused by a focusing optical system to a point on the photosensitive surface, in each moment of time illuminating one pixel of the projected image, while several lines of the projected image are formed in one horizontal pass of the beam that along the photosensitive surface 5. Move the photosensitive surface 5 in the direction perpendicular to the horizontal scanning lines on the multiple width of the projected image, then repeating all the above process steps until the total projection image on the photosensitive surface 5.

The following is a calculation of the parameters of a laser scanning device.

If the number of horizontal lines of the projected image reproduced in a single pass of the light beam through the drum is N, then the required polyhedron rotation frequency, or horizontal frequency, is given by:

where N _{facets is the} number of faces of the polygon, which is equal to the number of passes of a light beam through the drum in one rotation of the polygon; M = R _V H is the number of lines on the page, R _V and H are the vertical resolution and height of the scanned area, respectively, and V is the productivity of the laser scanning device (speed of rotation of the polyhedron).

From formula (1) it follows that if the productivity of the laser scanning device has reached a technological maximum, the height of the scanned area is equal to the height of the page, i.e. standard, and the vertical resolution is set, the productivity of the laser scanning device can be increased due to the parameter N:

From the formula (1) it also follows that if the performance of the scanning device is limited for any technical reason, then the vertical resolution can be increased due to the parameter N:

Moreover, the maximum number of lines N projected in one horizontal scan (passage) of the light beam is limited by the resolution of the vertical deflector.

We calculate the required vertical frequency for a laser scanning device with the following parameters:

- Productivity - 200 ppm.

- Resolution - 1200 × 1200 dpi.

- The size of the printed page is 8.5 × 11 inches.

The vertical resolution of R _V is related to the N ratio

where f _H is the horizontal frequency,

V is the performance

H is the height of the scanned area.

The horizontal resolution is set by the ratio

where W is the width of the scanned area.

From relations (2) and (3) it follows that the required vertical frequency is given by

where R _H is the horizontal resolution [dpi],

W is the width of the scanned area [inch],

R _V - vertical resolution [dpi],

N is the height of the scanned area [inch],

V - productivity (print speed) [ppm],

N is the number of lines in one pass.

At N = 32, the vertical frequency is

and period

Based on a comparative analysis of various types of optical deflectors, we can conclude that electro-optical deflectors satisfy the given conditions.

Moreover, the estimated number of lines reproduced in one pass should not exceed the optical resolution of the electro-optical deflector. The practicable maximum resolution of the electro-optical deflector is about 100, which is the upper limit on the number of lines in one pass.

Based on the foregoing, it can be argued that the claimed invention makes it possible to create laser printers, significantly superior to existing on the market in terms of print performance / resolution.

The claimed laser scanning device can be used:

- in high-performance laser printing devices;

- in devices of high-quality laser printing;

- in laser photo printers;

- in laser printers with increased reliability requirements;

- in laser digital copying devices.

Since the above embodiment of the invention was set forth only to illustrate the claimed invention, it is clear to those skilled in the art that various modifications, additions and substitutions are possible without departing from the scope and meaning of the present invention reflected in the attached claims.

Claims (9)

1. A laser scanning device containing a monochromatic light source, forming an optical system, a horizontal deflector, a focusing optical system, a photosensitive surface and further comprising a vertical deflector configured to perform a vertical scan by deflecting a focused light beam with a given amplitude and frequency in a direction perpendicular to horizontal direction, and the formation of a vertical raster whose height is equal to the heights a few lines of the projected image, and the forming optical system is configured to form from the light beam created by the light source a light beam with the parameters required for the system to operate, the horizontal deflector is configured to deflect a beam of light emerging from the vertical deflector in the horizontal direction and thereby perform horizontal scanning, a focusing optical system is configured to focus a light beam deflected by a vertical deflector and a horizontal deflector to a point on a photosensitive surface, the photosensitive surface is arranged to move in a direction perpendicular to the horizontal scan direction provided by the horizontal deflector and to project the image onto it with a light beam. 2. The device according to claim 1, characterized in that the monochromatic light source is made in the form of a laser. 3. The device according to claim 2, characterized in that the laser is made in the form of a semiconductor laser. 4. The device according to claim 1, characterized in that the vertical deflector is made in the form of an electro-optical deflector, or an acousto-optical deflector, or a piezoelectric deflector. 5. The device according to claim 1, characterized in that the horizontal deflector is made in the form of a rotating multifaceted reflector, a rotating mirror, an acousto-optical deflector or a piezoelectric deflector. 6. The device according to claim 1, characterized in that the vertical scan has pulses of a triangular, sawtooth or step shape. 7. The device according to claim 1, characterized in that the photosensitive surface is made in the form of a rotating photosensitive drum. 8. The device according to claim 1, characterized in that the forming optical system is made in the form of a collimator. 9. The method of operation of the laser scanning device, comprising the following operations: directing a light beam from a monochromatic light source through a forming optical system to a vertical deflector, deflect a light beam with a given amplitude and vertical frequency by a vertical deflector in a direction perpendicular to the horizontal direction, while forming a vertical light beam with a beam of light, the height of which is equal to the height of several lines of the projected image, scan the beam of light emerging from the vertical deflector in the horizontal direction with a horizontal deflector, while deflecting the light beam along the photosensitive surface, focusing the light beam emerging from the horizontal deflector by means of a focusing optical system to a point on the photosensitive surface, and at a time, one pixel of the projected image is illuminated, while several lines of the projected image are formed in one horizontal passage of the light beam along the photosensitive surface, the photosensitive surface is moved in the direction perpendicular to the horizontal direction, to the width of several lines of the projected image, after which all the above operations of the method are repeated until the entire image is projected onto the photosensitive surface.

Images