JP2008304828A - Optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical scanner which can prevent deterioration in image quality by eliminating variation in synchronization detection signals without incurring a large scale/a heavy weight of a deflector. <P>SOLUTION: The optical scanner comprises: a light source unit which radiates a plurality of luminous fluxes simultaneously; a polygon mirror 10 which deflects the plurality of luminous fluxes in a main scanning direction Y; scanning lenses which focus the luminous fluxes deflected with the polygon mirror 10 on a face to be scanned (photoreceptor drum); and a synchronization detection means for detecting the write-in position (write-in beginning and/or write-in terminating position) of an image. The synchronization detection means detects the write-in beginning position of the image in the main scanning direction Y by using one of the luminous fluxes Ba, Bb and Bc except the luminous flux Bd which is reflected at a position which is the remotest position from the center in the main scanning direction Y on the reflection face 11 of the polygon mirror 10. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an optical scanning device, and more particularly to an optical scanning device that is mounted on an electrophotographic image forming apparatus and forms an electrostatic latent image on a photoreceptor.

  Conventionally, in this type of optical scanning device, in order to detect the writing position (writing start position and / or writing end position) of the image written line by line in the main scanning direction, the deflector deflects in the main scanning direction. A sensor (hereinafter also referred to as a synchronization sensor) that receives the emitted light beam is disposed. On the other hand, in recent years, there has been a demand for high-speed and high-density optical scanning devices, and multi-beam scanning that simultaneously scans a plurality of light beams has been realized. Further, regarding the deflector, it is required to reduce the load on the deflector by miniaturizing and reducing the reflection surface as much as possible.

  As described in Patent Document 1, when scanning with a multi-beam, an LD array is generally used as a light source. In order to expose the photosensitive member at a predetermined interval in the sub scanning direction, it is necessary to arrange the light emitting points of the LD array at a predetermined angle with respect to the sub scanning direction. When such a configuration is adopted, each light beam is incident on the reflecting surface of the deflector at a different position in the main scanning direction. Therefore, there is a possibility that synchronous detection of the writing position is performed by the light beam reflected at the position farthest from the center in the main scanning direction on the reflecting surface of the deflector.

When synchronous detection is performed using a light beam reflected at a position farthest from the center in the main scanning direction, the light beam may protrude from the reflecting surface of the deflector, so that the synchronization detection signal varies, resulting in image quality. It had the problem of inviting deterioration. In order to store a plurality of light beams on one reflecting surface, the reflecting surface may be enlarged in the main scanning direction. However, this increases the size and weight of the deflector, which increases the load. It is not a measure.
JP 11-326799 A

  SUMMARY OF THE INVENTION An object of the present invention is to provide an optical scanning device that can eliminate variations in synchronization detection signals and prevent image quality deterioration without increasing the size and weight of a deflector.

In order to achieve the above object, the present invention provides:
A light source unit that emits a plurality of light beams simultaneously, a deflector that deflects the light beams emitted from the light source unit in the main scanning direction, and scanning optics that forms an image of the light beams deflected by the deflector on the surface to be scanned In an optical scanning device comprising an element and a synchronization detection means for detecting a writing position in the main scanning direction of an image,
A plurality of light beams are emitted from the light source unit at a predetermined angle with respect to the sub-scanning direction,
The synchronization detection means detects an image writing position using a light beam other than a light beam reflected at a position farthest from the center in the main scanning direction on the reflecting surface of the deflector;
It is characterized by.

  In the optical scanning device according to the present invention, light beams other than the light beam reflected at the position farthest from the center in the main scanning direction on the reflecting surface of the deflector are not likely to protrude from the reflecting surface of the deflector. There is no variation. Therefore, it is possible to always detect an accurate image writing position and to prevent image quality from deteriorating. Further, in order to eliminate the variation in the synchronization detection signal, it is not necessary to increase the size and weight of the deflector more than necessary, and an increase in load can be suppressed.

  In the optical scanning device according to the present invention, the synchronization detecting means may detect at least one of the writing start position and the writing end position in the main scanning direction of the image. It is preferable that the synchronization detection means detects the writing start position and / or writing end position of the image in the main scanning direction using a light beam reflected at a position closest to the center in the main scanning direction on the reflecting surface of the deflector. The light source unit may include at least one LD array.

  Embodiments of an optical scanning device according to the present invention will be described below with reference to the accompanying drawings. In addition, in each Example, the same code | symbol is attached | subjected to the same member and part, and the overlapping description is abbreviate | omitted.

(Refer 1st Example and FIGS. 1-7)
FIG. 1 is a plan view showing a schematic configuration of a first embodiment of an optical scanning device according to the present invention. This optical scanning device includes a light source unit 1, a polygon mirror 10, a first scanning lens 15, and a second scanning lens 16, which are housed in a housing 30. The light source unit 1 includes an LD (laser diode) array 2, a collimator lens 3, and a cylindrical lens 4. Further, two sets of synchronization detection means 20A and 20B for detecting the writing position (writing start position and writing end position) of the image in the main scanning direction Y are provided.

  In the first embodiment, the LD array 2 is a type that simultaneously emits four light beams, and the respective light emitting points 2a, 2b, 2c, and 2d are in the sub-scanning direction Z as shown in FIG. Are arranged with a predetermined angle θ. The light beam (diffused light) emitted from the LD array 2 is condensed into substantially parallel light by the collimator lens 3, passes through the cylindrical lens 4, and is condensed and imaged in the sub-scanning direction Z by the reflecting surface 11 of the polygon mirror 10. To do. These light beams are deflected in the main scanning direction Y at a constant angular velocity based on the rotation of the polygon mirror 10, imaged on the photosensitive drum 40 by the scanning lenses 15 and 16, and scanned at a constant speed.

  The synchronization detection means 20A and 20B are configured by condenser lenses 21A and 21B and optical sensors (photoelectric conversion elements) 22A and 22B, respectively. A part of the light beam transmitted through the first scanning lens 15 is received by the optical sensor 22A through the condenser lens 21A, and the image writing start position is detected. Further, a part of the light beam transmitted through the first scanning lens 15 is received by the optical sensor 22B through the condenser lens 21B, and the image writing end position is detected.

  FIG. 3 shows a state where the light beams Ba, Bb, Bc, and Bd for detecting the image writing start position are reflected by the reflecting surface 11 of the polygon mirror 10. FIG. 4 shows a state where the light beams Ba, Bb, Bc, and Bd for detecting the image writing end position are reflected by the reflecting surface 11 of the polygon mirror 10.

  Since the simultaneously emitted light beams Ba, Bb, Bc, Bd have an angle θ in the sub-scanning direction Z as shown in FIG. 2, each light beam is at a different position on the reflecting surface 11 in the main scanning direction Y. Reflected. In order to reduce the size and weight of the polygon mirror 10, the size of the reflecting surface 11 in the main scanning direction Y is made as small as possible, and the light beam Bd or Ba reflected at the position farthest from the center line 11a of the reflecting surface 11 is In some cases, the reflection surface 11 may protrude. When synchronous detection of the writing position is performed with such a light beam Bd or Ba, a temporal variation occurs in the synchronous detection signal.

  For example, the light amount signal detected by the optical sensor with the protruding light beam has the characteristic indicated by the curve A1 in FIG. 5, and the light amount signal detected by the optical sensor with the light beam having no protrusion is indicated by the curve A2 in FIG. Has characteristics. Both have a variation ΔD as a light quantity signal, and have a variation of ΔE in time. Therefore, when synchronous detection is performed with the protruding light flux, the image writing start position or the writing end position varies, leading to degradation of image quality.

  Therefore, in the first embodiment, when the image writing start position is detected, the light beam Ba other than the light beam Bd reflected at the position farthest from the center in the main scanning direction Y on the reflecting surface 11 of the polygon mirror 10. , Bb, or Bc is used (see FIG. 3). It is preferable to use a light beam Ba reflected at a position closest to the center. Further, when detecting the image writing end position, any one of the light beams Bb, Bc, and Bd other than the light beam Ba reflected at the position farthest from the center in the main scanning direction Y on the reflecting surface 11 is used (see FIG. 4). Also in this case, it is preferable to use a light beam Bd reflected at a position closest to the center. In order to use a specific light beam among the plurality of light beams as the synchronization detection signal, for example, only a specific light beam may be emitted.

  As a result, the detected light amount signal has the characteristic indicated by the curve A2 in FIG. 5, and no temporal variation ΔE occurs. That is, without causing an increase in size and weight of the polygon mirror 10, it is possible to eliminate variations in the synchronization detection signal and prevent deterioration in image quality.

(Refer to the second embodiment, FIG. 6)
FIG. 6 is a plan view showing a schematic configuration of a second embodiment of the optical scanning device according to the present invention. In this optical scanning device, only the writing start position in the main scanning direction Y of the image is detected by the synchronization detection means 20A. In the second embodiment, as shown in FIG. 3, light beams Ba, Bb, and Bc other than the light beam Bd farthest from the center of the reflecting surface 11 of the polygon mirror 10 are used (the light beam Ba closest to the center is (It is preferable to use) The writing start position is detected. Therefore, the same effect as the first embodiment can be obtained.

(Refer to the third embodiment, FIG. 7)
FIG. 7 is a plan view showing a schematic configuration of a third embodiment of the optical scanning device according to the present invention. In this optical scanning device, the light source unit 1 is provided with LD arrays 2 a and 2 b having two light emitting points, the collimator lenses 3 a and 3 b and the beam splitter 5 are provided, and the cylindrical lens 4 is disposed after the beam splitter 5. Is. The manner in which each light beam enters the reflecting surface 11 of the polygon mirror 10 is as shown in FIGS. 3 and 4, and the operation and effect thereof are the same as in the second embodiment.

(Other examples)
The optical scanning device according to the present invention is not limited to the above-described embodiments, and can be variously modified within the scope of the gist.

  In particular, the configuration of the light source unit and the configuration and shape of the scanning lens are arbitrary. Further, the optical path of the synchronization detecting means may be arbitrarily bent, and a mirror or a prism can be used for bending the optical path.

1 is a schematic configuration diagram illustrating a first embodiment of an optical scanning device according to the present invention. It is a perspective view which shows LD array which has four light emission points. It is a perspective view which shows a mode that the light beam for detecting a writing start position is reflected by the reflective surface of a polygon mirror. It is a perspective view which shows a mode that the light beam for detecting the write end position is reflected by the reflective surface of a polygon mirror. It is a graph which shows the light quantity signal for a synchronous detection. It is a schematic block diagram which shows 2nd Example of the optical scanning device based on this invention. It is a schematic block diagram which shows 3rd Example of the optical scanning device based on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Light source unit 2, 2a, 2b ... LD array 10 ... Polygon mirror 11 ... Reflecting surface 15, 16 ... Scanning lens 20A, 20B ... Synchronous detection means 40 ... Photosensitive drum (scanned surface)
Ba, Bb, Bc, Bd ... luminous flux X ... optical axis direction Y ... main scanning direction Z ... sub-scanning direction

Claims (4)

A light source unit that emits a plurality of light beams simultaneously, a deflector that deflects the light beams emitted from the light source unit in the main scanning direction, and scanning optics that forms an image of the light beams deflected by the deflector on the surface to be scanned In an optical scanning device comprising an element and a synchronization detection means for detecting a writing position in the main scanning direction of an image,
A plurality of light beams are emitted from the light source unit at a predetermined angle with respect to the sub-scanning direction,
The synchronization detection means detects an image writing position using a light beam other than a light beam reflected at a position farthest from the center in the main scanning direction on the reflecting surface of the deflector;
An optical scanning device characterized by the above.   2. The optical scanning device according to claim 1, wherein the synchronization detection unit detects a writing start position and / or a writing end position in the main scanning direction of the image.   The synchronization detecting means detects a writing start position and / or a writing end position in the main scanning direction of an image using a light beam reflected at a position closest to the center in the main scanning direction on the reflecting surface of the deflector. The optical scanning device according to claim 1 or 2.   The optical scanning device according to claim 1, wherein the light source unit includes at least one LD array.

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