JPH029503B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser printer, and more particularly to a laser printer whose scanning line density can be easily changed.

Conventional laser printers have been announced with various scanning line densities (hereinafter referred to as density) such as 12 lines/mm, 18 lines/mm, and 24 lines/mm, but each of these printers has only one line density. It could only be used as a single machine, and it was impossible to change the linear density to several types with one machine.

However, depending on the object to be printed, it may be better to have a faster printing speed even if the linear density is coarse.
On the other hand, even if the printing speed is slow, there are some images that require high quality images with fine line density, so it is desirable to have a single printer that can be used for different purposes.

An object of the present invention is to provide a laser printer that can meet such demands and can freely change linear density and printing speed over several types.

The details of the invention 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 for detecting the end of scanning, and 11 indicates the path of the laser beam.

To explain the operation of a laser printer using Figure 1,
A laser beam emitted from a light source 1 is turned into a parallel beam by a lens 2, the intensity of the light is modulated by a modulator 3, and the beam is sent to the left and right by a scanner 7 via a lens 4, a mirror 5, and a lens 6. The photosensitive paper is swung and scanned at the focal plane 8. Although not shown, the photosensitive paper moves in a direction perpendicular to the scanning direction of the laser beam.

The present invention adds special features to the conventional laser printer described above.

FIG. 2 shows a basic structural diagram of an embodiment of the laser printer of the present invention.

In Figure 2, 12 is a board with a vertically long rectangular window, 1
3 is a cylindrical lens; 14 is a photosensitive surface located at the focal plane 8; 15 is provided just before the photosensitive surface 14;
A slit plate with slits of several different widths,
16 is the slit, 17 is a motor that moves the slit plate 15 up and down, 18 is an optical image of the laser beam formed on the slit 16, and 19 is a motor that conveys the photosensitive surface 14 in a direction perpendicular to the longitudinal direction of the slit. It is a device that does

The light image 18 formed on the slit plate 15 in FIG. 2 is a rectangular image whose longitudinal direction is perpendicular to the scanning direction of the laser beam 11.

Creating such an image can be achieved by appropriately selecting the shape of the window of the window plate 12 and the shape of the lens 14.

The cylindrical lens 13 may be of any type as long as it forms an elongated image, and may include an elliptical distortion imaging optical system. The scanner 7 may use a polygon mirror, a galvanometer mirror, a hologon, or a pure electric polarizer.

In FIG. 2, the light from the laser light source 1 passes through the modulator 3, is made into a rectangle through the window of the window plate 12, is made into a rectangle by the cylindrical lens 14, and is made into a rectangle by the imaging lens 6 into the slit 16. A rectangular image 18 is formed on top.

FIG. 3 shows a light image 18 formed on the slit 16.
In the figure showing the pattern, A is a plan view and B is a side view.

As shown in FIG. 2, a plurality of slits 16 having different groove widths are formed on the slit plate 15. FIG. 3 shows a case where there are two slits 16.

(a) and (b) show that the slit plate 15 is moved by the motor 17.
We show two cases where the position of is changed.

(a) shows a case where a light image 18 is formed on a slit 16 having a narrow groove width, and a narrow light image limited by the slit having a narrow groove width is formed on the photosensitive surface 14.

(b) shows a case where the slit plate 15 is moved upward by the motor 17 and the optical image 18 is formed on the slit 16 with a wide groove width, and the photosensitive surface 14 is limited by the slit with a wide groove width. A thick optical image is formed.

That is, the thickness of the scanning laser beam, in other words the linear density, is changed depending on the type of slit 16 used. The shape and thickness of the laser beam 11 may be constant regardless of the linear density.

The laser beam 11 scans over the slit 16 and exposes the photosensitive surface 14 at a linear density determined by the thickness of the slit 16.

If we try to scan the photosensitive surface at a rate of 1000 times per second with a line density of 10 lines/mm, the optical image 18 will be
The slit plate 15 is moved by a motor 17 so as to scan over the 100 μm slit 16 and stopped at that position. The laser beam 11 is scanned at the position of the slit plate 15. The photosensitive surface 14 may then be transported by a transport device 19 at a speed of 100 mm per second in a direction perpendicular to the scanning direction of the laser beam 11.

Also, at a linear density of 40 lines/mm, the photosensitive surface 14 is
If you want to scan the light image 18 over the slit 16 with a line thickness of 25 μm, the slit plate 15 is moved by the motor 17 and fixed at that position, and the photosensitive surface 14 is scanned every second. It is sufficient to transport it by the transport device 19 at a speed of 40 mm.

The photosensitive surface 14 is preferably a photosensitive paper or a photosensitive plastic for plate making when handling items with a fine linear density, and an electrostatic photosensitive drum or the like when handling items with a coarse linear density.

These two photosensitive materials are selected based on a linear density of approximately 25 lines/mm. That is, if the number is 25 lines/mm or more, photosensitive paper or photosensitive plastic is selected, and if it is less than 25 lines/mm, an electrostatic photosensitive drum or the like is preferable.

In other words, 25 lines/mm, 30 lines/mm, 40 lines/mm, 50
When changing book/mm, use photosensitive paper, 8
An electrostatic photosensitive drum is suitable when changing the number of lines/mm, 12 lines/mm, 16 lines/mm, 25 lines/mm, etc.

The scanning speed may be constant regardless of the linear density,
Further, the size of the optical image 18 may also be constant.

However, it is necessary to move the slit plate 15 to use the appropriate slit 16, and in conjunction with this, the photosensitive surface 1
By simply changing the transport speed of 4 and the modulation speed of the modulator, it is possible to freely use several types of linear densities.

For example, if the size of one pixel is 100 μm x 100 μm, the scanning speed is 1000 times/second and the scanning width is 200 mm.
The operation of the modulator is set to repeat ON/OFF in 0.5 μs, and the speed of the photosensitive surface 14 is set to 100 mm per second.

Also, when the size of one pixel is 25μm x 25μm,
When the scanning speed and width are respectively 1000 times/second and 200 mm, the modulator is turned on and off at 0.125 μs, and the speed of the photosensitive surface 14 is 25 mm/second. In order to change the linear density while keeping the modulation period of the modulator for one pixel the same, it is necessary to increase the scanning speed as the width of the slit 16 increases, but this method is also a good idea if the output of the light source 1 has a margin. It is.

The vertical to horizontal ratio of the optical image 18 of the laser beam changes depending on how the thickness of the scanning line is changed, but the length in the vertical direction is at least the maximum groove of the plurality of slits 16. It is desirable that the width in the lateral direction be a fraction of the minimum width of the plurality of slits 16.

The distance between the slit plate 15 and the photosensitive surface 14 is preferably as small as possible in order to avoid adverse effects due to light diffraction. This interval is preferably about 0.1 mm or less.
The slit plate 15 can be made by gluing a thin metal foil onto a glass plate and etching it using a photo-etching method.

As mentioned above, the slit plate 1 is placed just before the photosensitive surface 14.
5, it is possible to minimize the effects of light diffraction, surface tilt error of the scanner 7, vibration of the laser light source 1, etc., and a very good effect can be obtained.

As described above, in the present invention, a slit plate 15 provided with a plurality of slits 16 having several types of groove widths is placed in front of the photosensitive surface 14, and the slit plate 15 is moved to an appropriate position to select an appropriate slit. However, by changing the modulation speed of the laser beam and the moving speed of the photosensitive surface, it is possible to obtain laser printers with a plurality of types of linear densities using one laser beam scanning device.

In other words, it is possible to finish printing within a short time for applications that require a coarse line density, and it is also possible to print items with a high line density, although it takes time.
It is convenient because one laser printer can be used for multiple purposes depending on the purpose, and its effects are great.

[Brief explanation of drawings]

FIG. 1 is a diagram for explaining the basic structure of a laser printer, FIG. 2 is a diagram showing an embodiment of the present invention, FIG. 3 is a diagram showing the relationship between the optical image and the slit in the present invention, and A is a plan view. , b are side views. DESCRIPTION OF SYMBOLS 1...Laser light source, 3...Modulator, 7...Scanner, 12...Window plate, 13...Cylindrical lens, 14...
... Photosensitive surface, 15 ... Slit plate, 16 ... Slit, 17 ... Motor, 18 ... Optical image, 19 ... Photosensitive surface conveying device.

Claims (1)

[Claims] 1. In a laser printer that is composed of a laser light source and an optical system, the laser beam is modulated by a modulator and scanned by a scanner, and the photosensitive surface is conveyed in a direction perpendicular to the scanning direction to print characters and figures. a slit plate disposed immediately in front of a surface and provided with a plurality of slits having different groove widths formed in the same direction as the scanning direction; a device for moving the slit plate in a direction perpendicular to the scanning direction; means for forming an elongated optical image on the slit so that the longitudinal direction is perpendicular to the slit, and the length thereof is longer than the maximum groove width of the plurality of slits;
By moving the slit plate, a slit with an appropriate groove width is selected from among the plurality of slits,
A laser printer characterized by being able to print at multiple types of linear density by changing the conveyance speed of the photosensitive surface.