JPS6313169B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a printer using a laser beam.

Traditionally, a thin beam of laser light is swung horizontally using a galvanometer or polygon mirror, and the photosensitive surface is moved perpendicularly to the thin beam of laser light, and the laser beam is scanned finely over the photosensitive surface to print characters and figures. Laser printers were put into practical use. In any of these cases, the printed figure may be distorted due to the beam being swayed due to the vibration of the light source or the vibration of the mirror, or due to errors in the surface tilt of the polygon mirror, so in order to remove this distortion, A complex mechanism was devised. Also, it was extremely difficult to manufacture a printer with high density.

The present invention provides a method that can easily solve the problems of light source vibration and polygon mirror tilt error at the same time, instead of the conventional complicated method.

This will be explained below with reference to the drawings.

FIG. 1 shows the basic structure of a laser printer.

In Figure 1, 1 is a laser light source, 2 is a lens, 3 is a modulator, 4 is a lens, 5 is a mirror, 6 is an imaging lens, 7 is a scanner, 8 is a focal plane, and 9 detects the beginning of scanning. An SOS detector, 10 is an EOS detector that detects the end of scanning, and arrows indicate the path of the laser beam.

The biggest problem with the mechanism shown in FIG. 1 is the mirror tilt error when a polygon mirror is used in the scanner. This error causes one scanning line to overlap with an adjacent scanning line, or causes screen distortion in a direction perpendicular to the scanning direction.

In order to solve this problem, a method has been proposed in which a distortion optical system, such as a cylindrical lens, is installed between the polygon mirror and the image line on the photoresist film.

FIG. 2 shows a method for correcting errors in polygon mirror surface tilt using a cylindrical lens. In FIG. 2, 11 is a cylindrical lens, and 12 is an image line. In this way, the surface inclination error is reduced. However, when the laser 1 as the light source vibrates due to mechanical vibration, the image position on the polygon mirror becomes erroneous, and this cannot be corrected by the cylindrical lens 11. This is not a problem for office-use laser printers with a resolution of about 12 lines/mm, but it becomes a problem for printers with a resolution of 50 lines/mm or more used for printing plates.

The present invention provides a method for simultaneously solving both the surface tilt error of a polygon mirror and the error caused by laser vibration.

FIG. 3 is a diagram showing an embodiment of the present invention.

13 is a window with a rectangular hole, 14 is a cylindrical lens,
15 is a photosensitive surface, 16 is a slit provided just in front of the photosensitive surface, 17 is a light image formed on the slit 16, and 18 is a slit plate.

The optical image 17 formed on the photosensitive surface in FIG. 3 is a rectangular image whose longitudinal direction is perpendicular to the scanning line.

Creating such an image is achieved by appropriately choosing the shapes of window 13 and lens 14. still,
The cylindrical lens 14 may be of any type as long as it can form an elongated image, and may include an elliptical distortion imaging optical system.

The scanner 7 may be a polygon mirror, a carbanometer mirror, a hologon or a pure electric polarizer.

In FIG. 3, the light from the laser 1 passes through the modulator 3, is rectangularized by the window 13, and is rectangularized by the cylindrical lens 14.
A rectangular image is formed on the slit 16 by the imaging lens 6.

Suppose that this image is now swung in a direction perpendicular to the scanning direction due to laser vibration or the like. The situation at that time is shown in the 4th page.
As shown in the figure.

In FIG. 4, 17 is a light image formed on the slit, A is a plan view of the light image 17 formed on the slit 16,
B is a side view. a, b, c indicate the case where the optical image is swung up and down by vibration etc., and a is the optical image 17.
When b is located at the center of the slit 16, b is when the optical image 17 is located at the bottom of the slit 16,
c is a case where the optical image 17 is located above the slit 16. The light image on the photosensitive surface in this case corresponds to the blacked-out area in FIG. 4A, but when these three light images 17 move as shown,
The size of the light image formed on the photosensitive surface 15 is limited by the width of the slit and is constant, and the linearity of its scanning depends only on the linearity of the slit 16, so it is necessary to improve the linearity of the slit 16. If this is done, even if the optical image 17 moves up and down due to vibration, the size and linearity of the optical image formed on the photosensitive surface can be maintained well.

The distance between the slit 16 and the photosensitive surface 15 is selected to be as small as possible in order to reduce the influence of diffraction caused by the slit 16.

As described above, by forming an optical system so as to form a rod-shaped rectangular or long circular optical image 17 having a length longer than the width of the slit 16 on the slit 16, surface tilting and vibration of the polygon mirror 7 can be prevented. light source 1
Disturbances in the scanning line due to vertical movement of the optical image 17 due to vibration or the like are corrected.

The width of the slit as described above is, for example, about 20 μm when the scanning line density is 50 lines/mm, and 100 μm.
When setting it to lines/mm, set it to about 10 μm. The length of the slit is determined by the required width of the photosensitive surface 15.
Usually around 100-300mm.

Such slits can be made by gluing a thin metal foil onto a glass plate and etching it using a photo-etching method.

It can also be done by using a photographic plate and creating an inverted image of the slit image on it. It can also be made by fixing two precisely straight plates separated by, for example, 20 μm.

If the joint between the support of the slit 16 and the support of the photosensitive surface 15 is made mechanically strong, displacement of the relative positions of the two due to vibration can be minimized.

The effect of the vibration given to the light source 1 is magnified by its optical magnification ratio, but the slit 16
The main reason for the advantage of this method is that the distance between the photosensitive surface 15 and the photosensitive surface 15 is small and there is no such enlarging effect.

The unavoidable non-linear distortion of the optical image 17 caused by a motor etc. can be avoided by forming the slit 16 immediately before the photosensitive surface 15 and the optical image 17 longer and narrower at right angles to the scanning direction than the width of the slit 16. can be avoided by

When the width of the slit 16 is about 20 μm, it is preferable to construct the optical system so that the optical image 17 is about 100 to 200 μm in the longitudinal direction and about 10 to 20 μm in the width direction.

The influence of the optical image 17 being swayed in the scanning direction by mechanical vibrations etc. cannot be removed by the method of the present invention; For example, several thousand vibrations occur several times during this single scan.
Mechanical vibrations above Hertz usually do not exist, and even if they do, they are easy to eliminate.

Also, for slow vibrations, for example, vibrations of several hundred hertz or less, the vibration amplitude of the optical image 17 generated in the scanning direction is 100μ.
Even if it is about 300mm, the effect on the amplitude is small and the effect on linearity is 300mm/100μm ≒ 0.3%.
It is as follows.

In addition, since the amplitude in the scanning direction is controlled by the SOS detector and the EOS detector, the influence of the optical image 17 in the scanning direction can be ignored.

On the other hand, the moving speed of the photosensitive surface 15 in the direction perpendicular to the scanning line is extremely slow, on the order of several mm/second, so the optical image 1
7 vibrations perpendicular to the scanning direction cause significant distortion.

The present invention solves this problem.

As described above, according to the present invention, a slit plate with a very small groove width is provided just before the photosensitive surface, and a long and narrow scanning plate having a length longer than the slit groove width is placed on the slit at right angles to the scanning direction. It has a simple structure that forms an optical image, and it has a 1mm diameter, which was previously considered very difficult.
We were able to obtain a laser printer with a high density of more than 50 lines per unit, and its practical effects are very large.

[Brief explanation of the drawing]

Fig. 1 is a diagram for explaining the basic structure of a laser printer, Fig. 2 is an explanatory diagram of an optical system showing a method for correcting errors in surface tilt of a polygon mirror, and Fig. 3 is a diagram showing an embodiment of the present invention. FIG. 4 is a top view and a side view showing the relationship between the scanning optical image and the slit in the present invention. 1...Laser light source, 7...Scanner, 14...Cylindrical lens, 15...Photosensitive surface, 16...Slit,
17...Scanning optical image, 18...Slit plate.

Claims (1)

[Claims] 1 In a laser printer, which is composed of a laser light source and an optical system, and which prints characters and figures by scanning a laser beam horizontally with a scanner and moving a photosensitive surface in a direction perpendicular to the scanning direction, it forms a long and narrow optical image. An optical system for imaging is provided, and a slit plate having a slit with an extremely small groove width formed in the same direction as the scanning direction of the laser beam is provided just in front of the photosensitive surface, and a slit plate is provided on the slit in a direction perpendicular to the scanning direction. A laser printer characterized in that the optical system forms an elongated scanning optical image having a length longer than a groove width.