JP4730239B2 - Laser scanning optical device - Google Patents

Description

  The present invention relates to a laser scanning optical apparatus, and more particularly to a laser scanning optical apparatus used in an image forming apparatus that forms a desired image by combining images formed on a plurality of photoconductors.

  In a laser scanning optical apparatus used in an image forming apparatus such as a copying machine or a printer that forms an image by electrophotography, a casing for storing a polygon motor or an optical member is vibrated by vibration generated from the polygon motor. As a result, there has been a problem that pitch unevenness and jitter occur in an image obtained in the image forming apparatus.

  As a solution to the above problem, a scanning optical unit described in Patent Document 1 is known. In the scanning optical unit, a fixing portion for fixing a polygon motor serving as a vibration source to the housing is provided outside an area obtained by connecting a plurality of fixing points for fixing the scanning optical unit to the image forming apparatus. Thereby, the place where the polygon motor is fixed becomes the free end. At the free end, vibrations tend to damp and are difficult to sustain. For this reason, other optical members mounted on the housing are not easily affected by vibration, and occurrence of pitch unevenness and jitter in an image obtained by the image forming apparatus is suppressed.

Incidentally, in recent years, image forming apparatuses that form color images have become widespread. In the laser scanning optical device of the image forming apparatus, a plurality of light sources are provided. Since the plurality of light sources generate laser beams in different directions, in the laser scanning optical device, the laser beams are incident on the polygon mirror at the same angle when viewed in plan from the sub-scanning direction. An optical element that changes the traveling direction of the laser beam is required. In such a laser scanning optical apparatus, there is a problem of where to place the optical element in order to suppress pitch unevenness and jitter of an image generated by vibration from a polygon motor.
Japanese Patent No. 3305450

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to suppress the occurrence of image pitch unevenness and jitter caused by vibration from a deflecting device in a laser scanning optical device having a plurality of light sources.

  A laser scanning optical apparatus according to the present invention is used in a laser scanning optical apparatus used in an image forming apparatus that forms a desired image by combining images formed on a plurality of photosensitive members, and generates a plurality of laser beams. And at least one optical element that changes the traveling direction of the laser beam generated by the light source when aligned in a plan view from the sub-scanning direction, and the optical element A deflecting device that deflects a laser beam whose traveling direction has been changed, and a housing that holds the light source, the optical element, and the deflecting device and is fixed to the image forming apparatus by a plurality of fixing units, A housing is provided outside an area surrounded by a straight line connecting the fixed parts, and is provided with a first holding part that holds the deflection device, and is provided in the area and holds the optical element. That includes a second holding portion.

  Since the first holding part for holding the deflection device is provided outside the area surrounded by the straight line connecting the fixed parts, and the second holding part for holding the optical element is provided in the area, the deflection apparatus is generated. The vibration to be transmitted is difficult to be transmitted to the optical element. As a result, the optical element is less likely to be displaced, and the occurrence of image pitch unevenness and jitter is suppressed.

  In the present invention, all of the laser beams generated by the plurality of light sources may be incident on the optical element.

  Embodiments of a laser scanning optical device according to the present invention will be described below with reference to the drawings. In addition, in each figure of 1st, 2nd, and 3rd embodiment demonstrated below, the same code | symbol is attached | subjected about the same member and part, and the overlapping description is abbreviate | omitted.

(First embodiment)
FIG. 1 is a configuration diagram when the laser scanning optical device 1 according to the first embodiment of the present invention is viewed in plan view from above in the sub-scanning direction. The sub-scanning direction refers to a direction perpendicular to the main scanning direction in which the laser beam is scanned, and particularly in this embodiment, refers to a direction perpendicular to the plane formed by the scanned laser beam.

  The laser scanning optical device 1 is mounted on an image forming apparatus (not shown) that combines images formed on four photosensitive drums (not shown) to form a desired image. The four photosensitive drums Each is irradiated with a laser beam to form a latent image of each color (yellow, magenta, cyan, black). Specifically, the laser scanning optical device 1 includes laser diodes 2 to 5, mirrors 6 to 8, a deflection device 9, scanning lenses 10 and 11, and a housing 15. The housing 15 includes fixing portions 21 to 23 for fixing to the image forming apparatus.

  The laser diodes 2 to 5 serve as light sources, and each generates a laser beam. Each of the mirrors 6 to 8 is disposed so as to overlap in the sub-scanning direction. The mirror 6 reflects the laser beam generated by the laser diode 2 and guides it to the deflecting device 9. The mirror 7 reflects the laser beam generated by the laser diode 3 and guides it to the deflecting device 9. The mirror 8 reflects the laser beam generated by the laser diode 4 and guides it to the deflecting device 9. The laser beam generated by the laser diode 5 is directly incident on the deflecting device 9 without passing through a mirror. That is, the mirrors 6 to 8 serve to change the traveling direction of the laser beams so that the traveling directions of the laser beams generated by the laser diodes 2 to 5 are aligned.

  The deflecting device 9 includes a polygon mirror 9a and a polygon motor 9b. The polygon mirror 9a is rotationally driven by a polygon motor 9b (stepping motor or linear motor), and deflects and scans the laser beam reflected by the mirrors 6 to 8 and the laser beam generated by the laser diode 5. That is, each laser beam is deflected at a constant angular velocity in the main scanning direction based on the rotation of the polygon mirror 9a.

  The scanning lenses 10 and 11 are combined with a plurality of optical path folding mirrors (not shown) to serve as imaging optical elements that image the laser beam deflected by the polygon mirror 9a onto the photosensitive drum. Specifically, the scanning lenses 10 and 11 give fθ characteristics to the light deflected by the polygon mirror 9a and correct necessary aberrations. Since the plurality of optical path folding mirrors have a conventionally known configuration, the description and illustration thereof are omitted.

  The housing 15 serves to hold the laser diodes 2 to 5, the mirrors 6 to 8, the deflecting device 9, and the lenses 10 and 11, and is fixed to the image forming apparatus main body by the three fixing portions 21 to 23. Screws are used for the fixing portions 21 to 23. In the present embodiment, the fixing portions 21 to 23 are not arranged in a straight line but are arranged so as to form a triangular region 30. And the deflection | deviation apparatus 9 is arrange | positioned out of the triangular area | region 30 obtained by connecting the fixing | fixed parts 21-23 with a straight line. Specifically, as shown in FIG. 2, the bearing portion of the polygon motor 9 b of the deflection device 9 is fixed to the housing 15 by a screw 25 outside the region 30. The screw 25 is located outside the region 30. On the other hand, the mirrors 6 to 8 are arranged in the region 30. Specifically, as shown in FIG. 3, the mirror 6 is fixed to the housing 15 with an adhesive 26 in the region 30. The adhesive 26 is located in the region 30. Similarly, the mirror 7 is fixed on the mirror 6 with an adhesive, and the mirror 8 is fixed on the mirror 7 with an adhesive.

  As described above, according to the laser scanning optical device 1, the deflection device 9 serving as the vibration source is provided outside the region 30 obtained by connecting the fixing portions 21 to 23 with straight lines, and the mirrors 6 to 8 are provided in the region 30. Therefore, in the image forming apparatus using the laser scanning optical device 1, it is possible to suppress the occurrence of image pitch unevenness and jitter. This will be described below.

  The deflection device 9 is fixed to the housing 15 outside the region 30. In other words, the deflecting device 9 is in the same state as when it is disposed on the cantilever. Since the free end side of the cantilever, that is, the side in the direction of the arrow X with respect to the dotted line 30a connecting the fixed part 21 and the fixed part 22 is free to change, the vibration of the deflecting device 9 is easily damped and difficult to sustain. On the other hand, the mirrors 6 to 8 are fixed in the region 30 on the fixed end side of the cantilever, that is, the side in the arrow Y direction with respect to the dotted line 30a so that the influence of the vibration of the deflecting device 9 is reduced. ing. Since the area 30 is an area surrounded by the fixing portions 21 to 23 fixed to the image forming apparatus main body, large vibrations are not easily transmitted. Thereby, it is reduced that the vibration from the deflecting device 9 is transmitted to the mirrors 6 to 8, and the mirrors 6 to 8 are less likely to be displaced. As a result, the laser beam irradiation position is prevented from deviating from the position that should be irradiated, and the occurrence of image pitch unevenness, jitter, and the like is suppressed.

  The inventor of the present application performed analysis by a computer in order to confirm the effect exhibited by the laser scanning optical device 1. Specifically, a predetermined vibration is generated from the deflecting device 9, and the amplitude at the point A in the region 30 is compared with the amplitude at the point B outside the region 30. The point A and the point B are in a line-symmetric relationship with respect to a dotted line 30 b that connects the fixed portion 21 and the fixed portion 23. According to this analysis, it was found that the amplitude at point B was 7.3 times the amplitude at point A. That is, it can be understood that the region 30 is less susceptible to vibration from the deflecting device 9 than the region 30 outside. Therefore, this analysis makes it difficult for the mirrors 6 to 8 to be misaligned in the laser scanning optical device 1, and the laser beam irradiation position is prevented from deviating from the position to be originally irradiated, thereby causing image pitch unevenness, jitter, and the like. It can be understood that the occurrence is suppressed.

(Second Embodiment)
In the laser scanning optical device 1, the mirrors 6, 7, and 8 are used as optical elements for reflecting the laser beams generated by the laser diodes 2, 3, and 4 and guiding them to the deflecting device 9. As the element, prisms 56 to 58 may be used like the laser scanning optical device 41 according to the second embodiment shown in FIG. The prisms 56 to 58 are disposed so as to overlap in the sub-scanning direction within the region 30, and the deflection device 9 is disposed outside the region 30. Thereby, there exists an effect similar to 1st Embodiment.

(Third embodiment)
In the laser scanning optical device 1, the laser beam generated by the laser diode 5 is directly incident on the polygon mirror 9a without passing through the mirror, but the laser scanning optical device 61 according to the third embodiment shown in FIG. As described above, the laser beam generated by the laser diode 5 may be reflected by the mirror 69 and incident on the polygon mirror 9a. That is, the laser beams generated by all the laser diodes 2 to 5 may be reflected by the mirrors 6 to 8 and 69. The mirrors 6 to 8 and 69 are disposed so as to overlap in the sub-scanning direction within the region 30, and the deflecting device 9 is disposed outside the region 30. Thereby, there exists an effect similar to 1st Embodiment.

(Other embodiments)
In the first to third embodiments, a mirror or a prism is used as an optical element for reflecting the laser beam generated by the laser diodes 2, 3, 4, and 5 to the deflecting device 9. Although it is used, a beam splitter or a half mirror can be used for the optical element.

It is a block diagram when the laser scanning optical apparatus according to the first embodiment of the present invention is viewed from above in the sub-scanning direction. It is the figure which showed a mode that the deflection | deviation apparatus was fixed to a housing | casing. It is the figure which showed a mode that a mirror was fixed to a housing | casing. It is a block diagram when the laser scanning optical apparatus concerning the 2nd Embodiment of this invention is planarly viewed from the upper direction of a subscanning direction. It is a block diagram when the laser scanning optical apparatus concerning the 3rd Embodiment of this invention is planarly viewed from the upper direction of a subscanning direction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,41,61 Laser scanning optical apparatus 2,3,4,5 Laser diode 6,7,8,69 Mirror 9 Deflector 9a Polygon mirror 9b Polygon motor 10,11 Scan lens 15 Case 21,22,23 Fixed part 25 Screw 26 Adhesive 30 Area 56, 57, 58 Prism

Claims (2)

In a laser scanning optical device used in an image forming apparatus that forms a desired image by combining images formed on a plurality of photoconductors,
A plurality of light sources for generating a laser beam;
At least one optical element that changes the traveling direction of the laser beam so that the traveling direction of the laser beam generated by the light source is aligned when viewed in plan from the sub-scanning direction;
A deflecting device for deflecting a laser beam whose traveling direction is changed by the optical element;
A housing that holds the light source, the optical element, and the deflection device, and is fixed to the image forming apparatus by a plurality of fixing portions;
The housing is
A first holding part that is provided outside a region surrounded by a straight line connecting the fixed parts and holds the deflection device;
A second holding unit provided in the region and holding the optical element;
A laser scanning optical device comprising: The laser beams generated by the plurality of light sources are all incident on the optical element;
The laser scanning optical apparatus according to claim 1.

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