JPS6125118A - Laser printer - Google Patents

Abstract

PURPOSE:To maintain the linearity of a scanning line and to make a spot interval constant by allowing a beam which has its optical axis off a plane of polarization to strike a polygon mirror through a mirror, and varying the angle of the mirror according to the scanning angle of the beam. CONSTITUTION:When a plane containing the optical axis of the light beam B1 is a plane of deflection scanning, the optical axis of a light beam B2 deviates from the plane of deflection scanning and the beam is incident on the polygon mirror 3 through the mirror 5. The optical axis of a laser light source 12 or the light beam B2 is so arranged that a laser beam spot projected on a photosensitive drum 4 is at right angles to a laser spot of a laser light source 11, and the direction of polarization of the light beam B2 is varied by varying the angle of the mirror 5 to adjust the interval of those spots. Further, the nonlinearity of a scanning line formed by the light beam B2 is corrected by adjusting the angle of the mirror 5 according to the scanning angle of the light beam B2.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention horizontally scans a light beam spot emitted from a laser light source on a photoreceptor to form an image to be recorded in dots (
This relates to a laser printer that displays and records information using a set of pixels (pixels).

[Conventional technology]

Conventionally, in such laser printers, the photoreceptor is generally scanned with a single light beam, but in order to increase the recording speed, multiple light beams are scanned simultaneously. Beam-type laser printers have also been put into practical use.

FIG. 3 is a block diagram showing an example of a conventional multi-beam laser printer. The laser printer shown in the figure is configured to scan two light beams at once. That is, a laser light source such as a semiconductor laser 1. ,1
．． The light beam Bl, 82 emitted from the focusing lens 2. , 2. The laser beam enters the polygon mirror 3 via the polygon mirror 3, is reflected by the polygon mirror 3, is projected onto the photosensitive drum 4, and is horizontally scanned (main scan) on the photosensitive drum 4 as a laser beam spot. In addition, laser light source 1. , 1.
is controlled on and off according to the image information to be recorded, and the photosensitive drum 4 rotates in a direction perpendicular to the horizontal scanning direction of the laser beam spot (this is called sub-scanning). An electrostatic latent image corresponding to image information is formed by a collection of dots. Although not shown, this electrostatic latent image is obtained as a recorded image on recording paper through a development process and a transfer process.

Here, the interval between the laser beam spots obtained on the photosensitive drum 4 is determined according to the resolution of the image, and the laser beam 1t1. , 1. The optical system including the laser beam spot is positioned such that the laser beam spots are aligned at predetermined intervals and perpendicularly to the main scanning direction.

[Problem that the invention seeks to solve]

However, as shown in the figure, the light beam Bl.

If B2 has different optical axes, and if the photosensitive drum 4 is simultaneously scanned with these light beams Bl and B2, the light beams Bl and B2 to the polygon mirror 3 are
Because of the angle of incidence of B2, the scanning lines formed by the two laser beam spots cannot both be accurately straight. For example, if the direction of the reflective surface of the polygon mirror 3 is adjusted in order to make the scanning line by the light beam B1 linear, then the plane on the same plane as the plane containing the optical axis of the light beam B1 (deflection scanning plane) For a light beam having an optical axis at , the scanning line can be made straight; however, for a light beam B2 whose optical axis is off this deflection scanning plane, the deflection direction is determined by the scanning angle. Accordingly, the light beam B1 differs from the light beam B1, and the linearity of the scanning line is impaired. Therefore, the spacing between these laser beam spots changes depending on the scanning angle, resulting in a significant deterioration in image quality.

The present invention eliminates the drawbacks of the conventional device as described above, and even when a photoreceptor is scanned by multiple light beams with different optical axes, multiple laser beams can be used without impairing the linearity of each scanning line. The purpose of this invention is to realize a laser printer with a simple configuration that can scan a beam spot at regular intervals.

[Means for solving problems]

The laser printer of the present invention includes a plurality of laser light sources and a polygon mirror that reflects the light beams emitted by the laser light sources and projects them onto the photoreceptor, so that the photoreceptor is simultaneously scanned by the plurality of light beams. In a laser printer that uses a laser printer, for a light beam whose optical axis is off the deflection scanning plane, the light beam is incident on a polygon mirror via a mirror, and the angle of this mirror is adjusted according to the scanning angle of the light beam. It was designed to change.

[For production]

In this way, for a light beam whose optical axis is outside the deflection scanning plane, the light beam is incident on the polygon mirror via the mirror, and the angle of the second mirror is set to the scanning angle of the light beam. By changing the scanning line non-linearity that appears depending on the scanning angle, it is possible to correct the nonlinearity of the scanning line that appears depending on the scanning angle by changing the incident angle to the polygon mirror, and the interval between the laser beam spots is always maintained at m-, resulting in a high image quality. Accuracy can be obtained.

〔Example〕

FIG. 1 is a configuration diagram showing an embodiment of a laser printer of the present invention. In the figure, the same parts as in FIG. 3 are designated by the same reference numerals. 5 is a mirror for reflecting the light beam B2 and making it incident on the polygon mirror 3; 6 is an actuator, such as a galvanometer, which adjusts the angle of the mirror 5; 7 is an actuator for detecting the rotation angle of the polygon mirror 3; This is a drive circuit that drives the actuator 6 according to the scanning angles of Bl and B2. The apparatus shown in the figure includes a laser light source 1. Based on the light beam B1 emitted from the
The arrangement of the polygon mirror 3 and the like are adjusted so that the scanning line formed by this light beam B1 becomes a straight line.

That is, the plane containing the optical axis of the light beam B1 is the deflection scanning plane. Therefore, the laser beam 1i1. The optical axis of the light beam B2 emitted from the polygon mirror 3 is deviated from this deflection scanning plane, and is incident on the polygon mirror 3 via the mirror 5. Here, laser light source 1. Alternatively, the optical axis of the light beam B2 is such that the laser beam spot projected onto the photosensitive drum 4 is the laser light source 1. By changing the angle of the mirror 5, the deflection direction of the light beam B2 can be changed and the interval between these laser beam spots can be adjusted. Also,
By utilizing this property, by adjusting the angle of the mirror 5 according to the scanning angle of the light beam B2, it is possible to correct the nonlinearity of the scanning line caused by the light beam B2.

FIG. 2 shows how this nonlinearity is corrected. In the figure, a is a linear scanning line by the light beam B1, which is a mirror 5.
This is a scanning line by the light beam B2 when the angle of . Here, the angle of the mirror 5 is adjusted and fixed so that the distance between the two laser beam spots at the center of the photosensitive drum 4 is a predetermined distance. As shown in the figure, if the angle of the mirror 5 is constant, the optical axis of the light beam B2 is off the deflection scanning plane, so the scanning line is not a straight line and goes to both ends of the photosensitive drum 4. The distance from the scanning line a of the light beam Bl increases.

Therefore, if the angle of the mirror 5 is controlled in accordance with the scanning angle of the light beam B2 so as to provide a reflection characteristic as shown by the broken line C, the actual scanning line can be corrected as shown by d and made straight.

A spot position detector 8 is arranged in a part of the scanning range of the laser beam spot and detects the interval between the laser beam spots. The spot position detector 8 is composed of, for example, a COD line sensor or a photodiode array, and detects the interval between two laser beam spots at all times or at any time, such as during startup, and the drive circuit 7 receives this detection output. The angle of the mirror 5 is adjusted so as to maintain the interval between the laser beam spots constant, and the angle of the mirror 5 is controlled in accordance with the rotation of the polygon mirror 3 using this as a reference state.

Therefore, if the reflection angle of the mirror 5 changes slightly due to changes in ambient temperature or changes over time, the interval between the laser beam spots will change, which will directly affect the image quality. Position detector 8
By detecting this and adjusting the angle of the mirror 5 via the drive circuit 7 and the actuator 6, the interval between the laser beam spots can always be maintained constant.

Note that although the above description has exemplified the case where scanning is performed using two light beams, the number of light beams used for scanning is not limited to two. Furthermore, the arrangement of the laser beam spots projected onto the photosensitive drum 4 is
In addition to arranging them perpendicularly to the main scanning direction, any arrangement can be selected as long as the positional relationship is constant. In this case, the state of the arrangement of the laser beam spots can be monitored by the spot position detector 8, and based on this, the state of the arrangement of the laser beam spots can be monitored by the laser light sources 11.1. can be controlled. Furthermore, although the mirror 5 is illustrated as a means for reflecting the light beam B2, this is not limited to the mirror 5, and any device that can arbitrarily change the direction of the light beam B2 may be used. There may be.

【Effect of the invention〕

As explained above, the laser printer of the present invention includes a plurality of laser light sources and a polygon mirror that reflects the light beam emitted by the laser light source and projects it onto the photoreceptor, and a plurality of light beams are directed onto the photoreceptor. In a laser printer that scans at the same time, when the optical axis of the light beam is off the deflection scanning plane, the light beam is incident on a polygon mirror via a mirror, and the angle of this mirror is adjusted to change the angle of the light beam. Since the non-linearity of the scanning line that appears depending on the scanning angle can be corrected by changing the angle of incidence on the polygon mirror, it is possible to correct the non-linearity of the scanning line that appears depending on the scanning angle. It is possible to realize a laser printer with a simple configuration that can scan multiple laser beam spots at regular intervals without impairing the linearity of each scanning line even when scanning on a photoreceptor. .

[Brief explanation of drawings]

1 and 2 are block diagrams showing one embodiment of a laser printer of the present invention, and FIG. 3 is a block diagram showing an example of a conventional multi-beam type laser printer. 1, ,1. ...Laser light source, 2. , 2. ...Focusing lens, 3...Polygon mirror, 4...Photosensitive drum, 5...Mirror, 6...Actuator, 7...
- Drive circuit, 8... spot position detector. Kano 1 figure Tsume 2 figure Atsushi 3 figure

Claims (1)

[Claims] In a laser printer that has a plurality of laser light sources and a polygon mirror that reflects the light beam emitted by the laser light source and projects it onto the photoreceptor, the photoreceptor is simultaneously scanned by the plurality of light beams. For a light beam whose axis is off the deflection scanning plane, the light beam is incident on a polygon mirror via a mirror, and the angle of this mirror is changed according to the scanning angle of the light beam. printer.