JPH0576430B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser printer, and more particularly to a laser printer suitable for recording color images.

Normally, to print a color image, images of the three primary colors cyan, magenta, and yellow are superimposed using the subtractive color method, but by adding black, the quality of the image can be improved, and at the same time it can be printed like text. A method is known in which an image requiring high resolution is rendered by printing only black.

Color laser printers that perform such four-color printing by applying laser printer technology often have a structure that uses multiple photosensitive drums, each developing a different color tone, and transferring them onto a recording medium in a superimposed manner. known (for example, JP-A-56
-43659). In this type of apparatus, the number of drums and the number of laser light sources are equal, or a plurality of drums are sequentially recorded with one laser. However, in general, recording a color image requires superimposing three or four colors; in this case, the former requires three to four laser light sources and scanning devices, resulting in high costs; The disadvantage of this method was that even if multiple drums were installed, the recording speed was limited to the laser scanning speed, making it impossible to print at high speed.

The present invention has been made to eliminate the above-mentioned drawbacks of the conventional laser printer, and an object of the present invention is to provide a laser printer that can perform high-speed printing at a low cost.

That is, the present invention provides a laser beam generating section that is shared by a plurality of photosensitive drums, first and second photosensitive drums that are not adjacent to each other among the plurality of photosensitive drums, and generates a laser beam modulated by image information; a switching means capable of selectively directing the laser beam from the laser beam generating section to either the first or second photosensitive drum;
The switching means directs the laser beam from the laser beam generating section to the second photosensitive drum after outputting the laser beam modulated according to one page of image information from the laser beam generating section to the first photosensitive drum. The present invention provides a laser printer characterized in that the laser beam is switched so as to be directed to a photosensitive drum.

Hereinafter, details of the present invention will be explained based on embodiments shown in the drawings.

The figure shows one embodiment of the present invention. In the figure, the reference numeral 1 indicates a casing, and a rotating shaft is provided above the inside of the casing 1 to scan light from a first laser light source (not shown). A scanner 2 made of a polyhedron and a second scanner 3 that scans light from a second laser light source (not shown) are provided.

At a position between the first and second scanners and closer to the first scanner 2, the light from the first laser light source is switched to the first photosensitive drum 7 and the third photosensitive drum 9 for scanning. A switching mirror 4 is provided for this purpose. Further, on the side where the second scanner 3 is connected, the light from the second laser light source is transmitted to the second photosensitive drum 8 and the fourth photosensitive drum 10.
A switching mirror 5 is provided for switching between the two.

A fixed mirror 6 is provided near the first to fourth photosensitive drums 7 to 10 to align the directions of incidence of laser beams onto each drum.

A corona charger 1 is provided near each photosensitive drum 7 to 10 for charging each drum with electrostatic charge.
2. A developing device 11 is provided to develop the latent image formed on the drum, and a cleaner 13 is provided to remove residual toner from each drum.

A tray 14 for storing recording media such as printing paper is provided at the bottom of the casing 1.
The recording medium 14a in this tray 14 is connected to the pulley 15
-1, 15 Conveyor belt 1 stretched between -2
The toner-developed image is transferred by contacting each of the photosensitive drums 7 to 10 by the photosensitive drum 7, and this image is fixed by the fixing device 16.

Next, the operation of this embodiment configured as above will be explained.

In this embodiment, the first photosensitive drum 7 is developed with yellow toner, the second photosensitive drum 8 is developed with magenta, and the third and fourth photosensitive drums 9 and 1 are developed with magenta toner.
0, development is performed with cyan and black toners, respectively. It is also assumed that the image to be recorded has been separated into three colors and black by a known method and stored in an electrical image memory as scanning information.

By the way, when drawing a color image, the switching mirrors 4 and 5 each occupy the positions indicated by solid lines in the figure, and the light from the first laser light source passes through the fixed mirror 6 to the first photosensitive drum 7. To,
Similarly, the light from the second laser light source is made to enter the second photosensitive drum 8 via the fixed mirror 6, and the first laser light source is modulated by yellow image information. The image is recorded on the recording medium, developed using a normal electrostatic photographic method, and transferred from the tray 14 to a recording medium fed out in synchronization with the rotation of the first photosensitive drum 7.

The light from the second laser light source is modulated by magenta image information and recorded on the second photosensitive drum. Here, the light from the second laser light source is emitted only by the time required for the recording medium to be transferred from the transfer position of the first photosensitive drum 7 to the transfer position of the second photosensitive drum 8 relative to the light from the first laser light source. The delayed information is recorded, and the superimposed image is controlled so as not to be misaligned.

After the first laser light source records an image for one page of the recording medium on the first photosensitive drum 7, the switching mirror 4 is switched from the position shown by the solid line to the position shown by the broken line in the figure. It is desirable that this switching be performed electromagnetically and quickly.

After the mirrors are switched, the first laser light source is modulated with cyan image information and recorded on the third photosensitive drum 9. In this case as well, the image information is accurately delayed and synchronously controlled by the time the recording medium is conveyed from the first photosensitive drum 7 to the third photosensitive drum 9.

On the other hand, a magenta image is recorded on the second photosensitive drum 8 by the second laser light source, and when the magenta image is recorded on the second photosensitive drum 8, the switching mirror 5 is switched from the position shown by the solid line to the position shown by the broken line in the figure, and the magenta image is recorded on the second photosensitive drum 8 by the second laser light source. is the fourth
The light enters the drum 10, is modulated by black information, and records an image. At this time, the recording medium 14a
from the first photosensitive drum 7 to the fourth photosensitive drum 10
This is controlled by delaying the yellow image information by the amount of time it is conveyed.

Since the laser printer according to the present invention is configured to sequentially draw images using four photosensitive drums and two laser light sources, many specific effects as described below can be obtained.

1) Record the distance between the first and third drums and the distance between the second and fourth drums at a distance slightly longer than the length of the recording medium in the feeding direction, which is essentially the time required to switch the switching mirror. By arranging the drums apart from each other by the distance that the medium travels, the recording medium can run in a straight line, and stable running of the recording medium can be realized.

2) The switching mirror used to switch the optical path of the laser beam requires high precision in its holding position in order to align the image, but since it only switches between two positions, it is easy to press the stopper at each position. Highly stable structure.

3) Transfer can be performed while conveying the recording medium at a constant speed, and since four colors are sequentially superimposed, the printing speed can be increased.

4) Immediately after the light from the first laser light source finishes recording on the third drum, the switching mirror 4 is switched to enable recording on the first drum, so the number of prints per hour can be increased.

5) Cost can be reduced by reducing the number of relatively expensive laser light sources and scanners to two.

6) Since each photosensitive drum uses toner of one color, residual toner can be easily collected.

7) The four photosensitive drums can have exactly the same shape, allowing for stable image quality, high-speed printing, and cost reduction.

As is clear from the above description, according to the laser printer of the present invention, the laser beam generating section that generates the laser beam modulated by image information is connected to the first and second photosensitive drums that are not adjacent to each other among the plurality of photosensitive drums. After a laser beam that is shared by the drum and modulated according to one page of image information is directed from the laser beam generating section to the first photosensitive drum, the laser beam from the laser beam generating section is directed to the second photosensitive drum. Since the switching is performed so as to derive the information, the number of parts can be reduced with a simple configuration and the cost can be reduced, and printing can be performed at high speed.

[Brief explanation of drawings]

The figure is a schematic configuration diagram illustrating an embodiment of the present invention. 1...Casing, 2, 3...Sukiyana, 4,
5...Switching mirror, 7...First photosensitive drum, 8...Second photosensitive drum, 9...Third photosensitive drum, 10...Fourth photosensitive drum, 11...Developer, 12... ...Corona charger, 13...Cleaner, 14...Tray.

Claims (1)

[Scope of Claims] 1: a plurality of photosensitive drums; a laser beam generating section that is shared by first and second photosensitive drums that are not adjacent to each other among the plurality of photosensitive drums, and that generates a laser beam modulated by image information; , switching means capable of selectively directing the laser beam from the laser beam generating section to either the first or second photosensitive drum, the switching means being configured to direct the laser beam from the laser beam generating section to one page. After the laser beam modulated according to the image information is directed to the first photosensitive drum, the laser beam from the laser beam generating section is switched to be directed to the second photosensitive drum. printer.