JPH0488370A - Exposure scanning device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an exposure scanning device, and particularly relates to an exposure scanning device that changes the direction of travel of a laser beam by changing the attitude of a mirror that is irradiated with a laser beam. be.

2. Description of the Related Art An exposure scanning device that exposes and scans a photoreceptor by reflecting laser light emitted from a laser light source on a mirror and changing the attitude of the mirror to change the direction of travel of the laser light is used, for example, in a printer. and copy machines. In such an exposure scanning device, when performing exposure with a constant light intensity, such as when forming a black and white image, a laser beam of a constant intensity is emitted from the laser light source for exposure scanning, while when performing exposure scanning, such as when forming a grayscale image. When changing the light intensity during exposure scanning, the light intensity of the laser beam is controlled in accordance with the desired exposure intensity.

Problem to be Solved by the Invention However, the reflectance of the laser beam by the mirror is
The light intensity of the laser beam after being reflected by the mirror, that is, the exposure intensity, changes depending on the mirror's attitude because it changes according to the change in the incident angle of the laser beam due to the change in the mirror's attitude, which causes the problem of uneven exposure. Ta.

To explain specifically using the t-th point, the laser light emitted from the laser light source 10 is irradiated onto the mirror 12, and the mirror 1
2 is rotated in the direction shown by arrow C from the posture a shown by the solid line to the posture shown by the dashed-dotted line, the traveling direction of the laser beam reflected by the mirror 12 is as shown by the arrow d, and the surface of the photoreceptor 14 is exposed and scanned from left to right, but as the mirror 12 is rotated from the posture a to the posture, the laser beam The angle of incidence is the angle θ, from the angle θ
2, and depending on the change in the incident angle, the mirror 12
Since the reflectance of the photoreceptor 14 decreases, even if the laser light source 10 emits a laser beam of constant intensity, the exposure intensity I on the photoreceptor 14 becomes weaker from the left side to the right side.

Therefore, for example, in an electrophotographic apparatus, the amount of charge on the photoreceptor 14 after exposure increases toward the right side of the figure, causing density unevenness in the image after development.

The present invention has been made against the background of the above-mentioned circumstances, and its purpose is to prevent the exposure intensity to a photoreceptor from changing due to changes in reflectance of a mirror.

Means for Solving the Problems In order to achieve the object, the present invention reflects a laser beam emitted from a laser light source with a mirror, and also changes the attitude of the mirror to change the traveling direction of the laser beam. By doing so, in an exposure scanning device that exposes and scans a photoconductor, the light intensity of the laser beam is adjusted to the mirror so that the exposure intensity of the laser beam to the photoconductor does not change due to a change in reflectance due to a change in the attitude of the mirror. It is characterized by providing a correction means for correcting according to the posture.

By doing this, the light intensity of the laser beam is adjusted by the correction means according to the attitude of the mirror so that the exposure intensity of the laser beam on the photoconductor does not change due to the change in reflectance caused by the change in the attitude of the mirror. is corrected, the exposure intensity to the photoreceptor is controlled to a desired level regardless of changes in reflectance of the mirror during exposure scanning, and uneven exposure of the photoreceptor is prevented.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 shows a photosensitive drum 20 whose surface has been charged in advance.
FIG. 2 is a configuration diagram showing an exposure scanning device of an electrophotographic apparatus that forms a latent image by exposing and scanning an image using a laser beam and partially removing the electrical charge.

In the figure, 22 is a laser light source made of a semiconductor laser or the like, and the laser light emitted from this laser light source 22 is irradiated onto a rotating polygon mirror 24. The rotating polygon mirror 24 is a combination of mirrors facing outward in the shape of a polygonal prism, and is driven to rotate clockwise around the axis at a constant speed. As a result, the laser beam irradiated to the rotating polygon mirror 24 is reflected by each mirror, and as the rotating polygon mirror 24 rotates, that is, the attitude of each mirror changes,
The traveling direction of the laser beam is changed as shown by a solid line, a dashed-dotted line, and a dashed-double-dotted line, and the fθ lenses 26a, 26
The photoreceptor drum 20 is exposed and scanned in the upper and lower directions of the figure through the arrows b. In FIG. 1, the rotating polygon mirror 24 has a hexagonal prism shape, and exposure scans are performed six times in one rotation.
The photosensitive drum 20 is driven to rotate around its axis,
The exposure position is gradually shifted in the circumferential direction.

Light intensity 1 of the laser light emitted from the laser light source 22
．． The driving times! The exposure amount data B0 is supplied from the correction circuit 30 to the drive circuit 28. The correction circuit 30 is supplied with exposure position data A and exposure amount data B corresponding to the image to be formed from the image processing device 32, and is configured to adjust the exposure position data A in the main scanning direction, that is, the rotating polygon mirror. According to the exposure position X in the exposure scanning direction of the laser beam by rotation of 24,
The exposure amount data B is corrected to calculate the exposure amount data Be. Specifically, the correction circuit 30 includes a ROM (read only memory) 34 and a multiplication circuit 36 as shown in FIG. 2, and performs correction from the ROM 34 according to the exposure position By reading out the coefficient f (X) and multiplying the correction coefficient f (X) by the exposure data B in the East Army circuit 36, the exposure data B is obtained.
. =B-f(X) is calculated. Further, the light intensity (2) of the laser light is controlled according to the drive signal DI output from the drive circuit 28. is proportional to the above exposure amount data B0, and if its proportionality constant is k, then the light intensity is ■. is expressed by the following equation (1).

I0=-B-f(X) (1) On the other hand, the light intensity ■. The laser beam is reflected by the rotating polygon mirror 24, and its reflectance corresponds to the incident angle of the laser beam with respect to the mirror of the rotating polygon mirror 24, as well as the exposure position X, which is the traveling direction of the laser beam after reflection. , its exposure position
It can be expressed as a function g (X) with a variable.

Therefore, the light intensity of the laser beam after being reflected by the rotating polygon mirror 24, that is, the exposure intensity I to the photosensitive drum 20 is expressed by the following equation (2).

1=g (X)・I.

=g (X) ・k-B-f(X) ・ ・
・(2) Here, the correction coefficient f (X) is 1/g (
X). As a result, the exposure intensity I becomes -B, and the light intensity is always proportional to the exposure amount data B corresponding to the image to be formed, regardless of changes in the reflectance g (X) due to the rotation of the rotating polygon mirror 24. Exposure is performed. The ROM 34 stores a correction coefficient f (X) = 1/g(X) determined in advance through experiments or the like using a look-up table or the like.

Note that the rotating polygon mirror 24 is rotationally driven in synchronization with the output of the drive signal DI, or the rotating polygon mirror 24 is rotated in synchronization with the output of the drive signal DI so that the exposure value IX of the exposure position data A matches the actual exposure position of the laser beam. The drive signal DI is output based on a signal output from a sensor that detects the rotational position of the rotor 24.

That is, the exposure position X corresponds to the rotational position 1 of the rotating polygon mirror 24 and also to the attitude of each mirror of the rotating polygon mirror 24, and the correction circuit corrects the exposure amount data B based on the exposure value Wx. 30 corresponds to a correction means for correcting the light intensity I0 of the laser beam according to the attitude of the mirror.

As described above, according to the exposure scanning device of this embodiment, the exposure amount data B is corrected according to the rotational position of the rotating polygon mirror 24, that is, the exposure position X, and the reflectance g (X ), the light intensity of the laser beam after being reflected by the rotating polygon mirror 24, that is, the exposure intensity I, is proportional to the exposure amount data B, so that the reflectance change of the rotating polygon mirror 24 Uneven exposure of the photoreceptor drum 20 caused by this can be prevented.

Although one embodiment of the present invention has been described above in detail based on the drawings, the present invention can also be implemented in other embodiments.

For example, in the embodiment described above, the rotating polygon mirror 24 is rotated around the axis, but the traveling direction of the laser beam can be changed by rotating or swinging one mirror back and forth around the axis. You may also let them do so.

Furthermore, in the embodiment described above, the exposure amount data B is corrected according to the exposure position X, and the light intensity I0 of the laser beam is controlled according to the corrected exposure amount data B0.
The light intensity of the laser light emitted from the laser light source 22 is corrected using a filter device or the like that can control the light transmittance, or a filter whose light transmittance changes continuously is used to correct the light intensity of the laser light emitted from the laser light source 22. It is also possible to correct the light intensity by disposing it between the rotating polygon mirror 24 and the rotary polygon mirror 24.

Further, in the embodiment described above, the exposure amount data B is corrected based on the exposure position X, but the rotational position of the rotating polygon mirror 24 is detected and the drive signal DI etc. is corrected according to the rotational position. Also good.

Further, in the above embodiment, an exposure scanning device used in an electrophotographic apparatus was described, but the present invention is applicable to other exposure scanning devices such as one that exposes and scans a photosensitive pressure-sensitive sheet coated with a photosensitive pressure-sensitive capsule. can be applied to

Although other examples are not provided, the present invention can be implemented with various modifications and improvements based on the knowledge of those skilled in the art.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the configuration of an exposure scanning device that is an embodiment of the present invention. FIG. 2 is a block diagram illustrating the contents of the correction circuit of the apparatus shown in FIG. 1. FIG. 3 is a diagram illustrating changes in exposure intensity due to changes in mirror posture. 20: Photoreceptor drum (photoreceptor) 22: Laser light source 24: Rotating polygon mirror (mirror) 30: Correction circuit (correction means)

Claims (1)

[Claims] In an exposure scanning device that exposes and scans a photoreceptor by reflecting laser light emitted from a laser light source on a mirror and changing the attitude of the mirror to change the traveling direction of the laser light, the attitude of the mirror is An exposure scanning device comprising a correction means for correcting the light intensity of the laser light according to the attitude of the mirror so that the exposure intensity of the laser light to the photoreceptor does not change due to a change in reflectance accompanying the change. .