JP2006267288A - Optical scanner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To promote downsizing and cost reduction. <P>SOLUTION: Expansion and contraction of an image in the main scanning direction S are performed together with image data correction (total magnification correction in the main scanning direction), and also each laser beam L emitted from each light emitting element 102 is adjusted to a laser beam of an optimum diameter in each area 81 to 88 on a photoreceptor drum 38, so as to uniformalize the laser beam diameter on the photoreceptor drum 38 by selecting a light emitting element 102 to be turned on. The laser beam L scanned at an equal angle by a rotary polygon mirror is thereby formed into almost the same normal image as the image data without arranging a scan image-forming optical lens group such as an Fθ lens and the like. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an optical scanning device.

  As shown in FIG. 15, an optical scanning device 1010 used in an image forming apparatus such as a digital copying machine or a laser beam printer reflects and deflects a laser beam L emitted from a light source (not shown) by a rotating polygon mirror 1024. After passing through the scanning imaging optical system lens group 1000 such as an Fθ lens, the light is reflected by the reflecting mirrors 1030 and 1034 and emitted. Then, it is imaged and scanned on the photosensitive drum 1038.

  In recent years, the optical scanning device 1010 uses the scanning imaging optical system lens group 1000 as a spherical lens, reduces the number of lenses to be used, reduces the number of reflecting mirrors 1030 and 1034, and the optical scanning device 1010. The total number of parts is reduced, and miniaturization and cost reduction are progressing. (For example, refer to Patent Document 1).

However, it is desired to further advance miniaturization and cost reduction.
JP 2002-31373 A

  The present invention has been made to solve the above-described problems, and aims to further advance the reduction in size and cost.

  The image forming apparatus according to claim 1 is an optical scanning device that scans a scanning target with a plurality of light beams emitted from a light source having a plurality of light emitting points, and is an image in a main scanning direction. Correction means for inserting / decimating data; light beam diameter adjusting means for adjusting the light beam diameter of each of the plurality of light emitting points; selection means for selecting at least one light emitting point of the light source; And control means for controlling the selection means so as to select the predetermined light emitting point according to the position on the scanning body.

  According to another aspect of the present invention, a plurality of light beams emitted from a light source having a plurality of light emitting points are scanned on a scanning object by a deflecting unit.

  When the scanning object is scanned, the scanning speed and the light beam diameter on the scanning object change.

  Accordingly, the correction means inserts / decimates image data in the main scanning direction, and corrects image distortion (expansion / contraction of the image) due to change in the scanning speed of the light beam.

  Further, the light beam diameter adjusting means adjusts the light beam diameter corresponding to each of the plurality of light emitting points, and the control means controls the selecting means so as to select a predetermined light emitting point according to the position on the scanned object. By controlling, the light beam diameter is made substantially uniform, and the change of the light beam diameter on the main scanning line is corrected.

  Therefore, for example, a scanning imaging optical system lens group such as an Fθ lens, which has been conventionally arranged on the optical path between the deflecting means and the scanned object, is not necessary. Therefore, the optical scanning device is small and low cost.

  According to a second aspect of the present invention, there is provided the optical scanning device according to the first aspect, wherein the scanning object is divided into a plurality of areas in the main scanning direction, and the light beam diameter adjusting means is configured to emit light for each area. The beam diameter is adjusted, and the selection means selects the light emitting point that emits the light beam for each area.

  In the optical scanning device according to the second aspect, the light beam diameter is adjusted to the optimum light beam diameter for each area by the light beam diameter adjusting means. Then, the selection means selects and emits the light emission point of the light beam having the optimum light beam diameter for each area.

  Therefore, the light beam diameter on the main scanning line becomes substantially uniform, and the light beam diameter change on the main scanning line is corrected.

  According to a third aspect of the present invention, in the configuration of the first or second aspect, the light beam diameter adjusting unit controls a light emission amount of the light beam emitted from each light emitting point. The light beam diameter is adjusted.

  According to a third aspect of the present invention, the light emission amount of the light beam emitted from each light emitting point is controlled and adjusted to an optimum light beam diameter.

  Then, a light emitting point for emitting a light beam having an optimum light beam diameter is selected and emitted, the light beam diameter on the main scanning line is made substantially uniform, and the change in the light beam diameter on the main scanning line is corrected.

  According to a fourth aspect of the present invention, in the configuration of the first or second aspect, the light beam diameter adjusting unit controls a light emission time of the light beam emitted from each light emitting point. The light beam diameter is adjusted.

  The optical scanning device according to claim 4 controls the light emission time of the light beam emitted from each light emitting point and adjusts the light beam diameter to an optimum value.

  Then, a light emitting point for emitting a light beam having an optimum light beam diameter is selected and emitted, the light beam diameter on the main scanning line is made substantially uniform, and the change in the light beam diameter on the main scanning line is corrected.

  According to a fifth aspect of the present invention, in the configuration of the first or second aspect, the optical beam diameter adjusting unit is configured to scan the light beam emitted from the light emitting points. It is an optical path length changing means for changing the optical path length up to.

  The optical scanning device according to claim 5 adjusts the optical beam diameter to the optimum by changing the optical path length of the light beam emitted from each light emitting point.

  Then, a light emitting point for emitting a light beam having an optimum light beam diameter is selected and emitted, the light beam diameter on the main scanning line is made substantially uniform, and the change in the light beam diameter on the main scanning line is corrected.

  According to a sixth aspect of the present invention, in the configuration of the fifth aspect, the optical path length changing unit is configured to change the incident angle of each light beam to the scanned object. It is characterized in that it is configured to be incident with an inclination with respect to the normal line.

  The optical scanning device according to claim 6, wherein the light beam is made incident by tilting the incident angle of each light beam to the scanned body with respect to the normal line of the scanned body, thereby emitting the light beam from each light emitting point. The optical path length is changed to an optimum light beam diameter.

  Then, a light emitting point for emitting a light beam having an optimum light beam diameter is selected and emitted, the light beam diameter on the main scanning line is made substantially uniform, and the change in the light beam diameter on the main scanning line is corrected.

  According to a seventh aspect of the present invention, in the configuration of the fifth aspect, the optical path length changing unit is configured such that an optical path length of the light beam to the scanned object is varied depending on a transmission position through which the light beam is transmitted. It is characterized by a changing prism.

  According to a seventh aspect of the present invention, the optical path length of the light beam emitted from each light emitting point is changed by the prism that changes the optical path length of the light beam to the scanning object depending on the transmission position through which the beam is transmitted. Adjust to the optimal light beam diameter.

  Then, a light emitting point for emitting a light beam having an optimum light beam diameter is selected and emitted, the light beam diameter on the main scanning line is made substantially uniform, and the change in the light beam diameter on the main scanning line is corrected.

  According to an eighth aspect of the present invention, in the configuration according to the fifth aspect, the optical path length changing means is arranged at a different distance from the collimating lens for each of a plurality of light emitting points of the light source. The optical scanning device according to claim 5.

  In the optical scanning device according to the eighth aspect, the focal lengths of the respective light beams can be made different by arranging the respective light emitting points of the light source at different distances with respect to the collimating lens.

  Then, the light emitting point for emitting the light beam having the optimum light beam diameter is selected and emitted, the light beam diameter on the main scanning line is made substantially uniform, and the change of the light beam diameter on the main scanning line is corrected.

  As described above, according to the present invention, a scanning imaging optical system lens group such as an Fθ lens is not necessary, and thus a small and low-cost optical scanning device can be provided.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. The present embodiment can be applied to an image forming apparatus such as a laser printer, a copying machine, or a multi-function machine that forms an image by an electrophotographic process.

  As shown in FIG. 2, the image forming apparatus 1 includes a paper tray 200, a registration roller 202, a paper conveyance path 204, a photosensitive drum 38, an intermediate transfer belt 222, a fixing device 240, an optical scanning device 10, a primary transfer device 221, A secondary transfer device 223, a control device unit 500, and the like are provided. Further, based on image data input from an external device such as a personal computer, the control device unit 500 controls the entire image forming apparatus 1 to form an image on the recording paper P.

  FIG. 1 shows a main part of the image forming apparatus 1. As shown in FIG. 1, the photosensitive drum 38 has a substantially cylindrical shape that is elongated along the direction of the rotation axis. (See FIG. 1) The longitudinal direction (rotating axis direction) of the photosensitive drum 38 is the main scanning direction S, and the rotating direction of the photosensitive drum 38 is the sub-scanning direction F.

  The optical scanning device 10 includes a semiconductor laser 12 as a light source that emits laser light L. The semiconductor laser 12 includes a surface-emitting laser array 100 as a multi-beam light source in which the light-emitting elements 102 shown in FIG. 3 are two-dimensionally arranged in a lattice pattern (4 columns × 8 rows = 32). Each laser beam L emitted from each light emitting element 102 of the laser array 100 is emitted from the optical scanning device 10 as beam light having substantially uniform spread angles in the main scanning direction S and the sub-scanning direction F, respectively.

  Each light emitting element 102 of the laser array 100 emits laser light having a substantially Gaussian distribution when driven. The light emitting elements 102 are arranged in a staggered manner in order to increase the resolution. In FIG. 1, only one laser beam L is shown for easy understanding.

  As shown in FIG. 1, a collimator lens 14, a slit member 16, a cylindrical lens 18, and a half mirror 20 are arranged in order from the semiconductor laser 12 side in the optical path of the laser light L.

  The collimator lens 14 is disposed so that the distance from the laser array 100 matches the focal length of the collimator lens 14. As a result, the laser light L transmitted through the collimator lens 14 becomes substantially parallel light. The laser light L that has passed through the collimator lens 14 passes through the slit 16A of the slit member 16, and is shaped by a predetermined cross-sectional shape of the slit 16A. Then, the laser light L is condensed in the sub-scanning direction F by the cylindrical lens 18.

  The half mirror 20 transmits about 30% of the total amount of the laser light L transmitted through the cylindrical lens 18 and reflects the remaining about 70% toward the rotating polygon mirror 24.

  The back side of the half mirror 20 has a curvature along the main scanning direction S and has a function as a cylindrical lens. Therefore, the laser light L transmitted through the half mirror 20 is condensed in the sub-scanning direction and the main scanning direction, respectively, and forms a light spot of a predetermined size on the light quantity monitoring photodiode 22 (hereinafter referred to as MPD 22). Incident.

  On the other hand, the laser beam L reflected by the half mirror 20 is reflected by the rotary polygon mirror 24 and deflected and scanned. The scanning direction scanned by the rotary polygon mirror 24 is the main scanning direction S described above. The laser beam L reflected by the rotating polygon mirror 24 is reflected by the first cylindrical mirror 30 and the second cylindrical mirror 34. The first cylindrical mirror 30 and the second cylindrical mirror 34 have optical power for converging the laser light L in the sub-scanning direction F.

  Then, as shown in FIG. 4, the light is emitted from the dust-proof glass 36 of the optical box 11 of the optical scanning device 10, is imaged on the photosensitive drum 38 that is a scanning target, and is scanned in the main scanning direction S.

  As shown in FIG. 1, the rotary polygon mirror 24 is formed in a substantially regular polygonal prism shape, and its outer peripheral surface is a reflection deflection surface 24a. In addition, a drive motor (not shown) composed of a stepping motor or the like is connected to the rotary polygon mirror 24, and the rotary polygon mirror 24 is rotated in the rotation direction K (main scanning) by this drive motor (not shown). Direction) at a substantially equal angular speed. That is, the laser beam L reflected by the half mirror 20 is reflected by the reflection deflection surface 24a of the rotary polygon mirror 24 and moves at a constant angular velocity in the main scanning direction S.

  Note that the reflection deflection surface 24a of the rotary polygon mirror 24 and the outer peripheral surface of the photosensitive drum 38 are in a substantially conjugate relationship, and the photosensitive drum is caused by variations in the deflection direction of the rotation polygon mirror 24 (such as surface tilt of the reflection deflection surface 24a). 38, the positional deviation in the sub-scanning direction F is corrected.

  Further, the curvature in the sub-scanning direction F of the collimator lens 14, the cylindrical lens 18, the first cylindrical mirror 30, and the second cylindrical mirror 34 is determined based on the interval between the laser beam L in the sub-scanning direction F on the photosensitive drum 38 and the photosensitivity. The distance between the laser beams L at a position several millimeters away from the body drum 38 is set to be equal to each other in a telecentric relationship.

  The photosensitive drum 38 has a substantially cylindrical shape elongated along the rotation axis direction, and a photosensitive layer (not shown) whose outer peripheral surface is sensitive to the laser beam L is formed. Then, it is uniformly charged by a charging device (not shown).

  The laser beam L emitted from the optical scanning device 10 is converged as a light spot having a predetermined light beam diameter on the photosensitive drum 38 whose surface is uniformly charged, and linear main scanning on the photosensitive drum 38. The line SS is scanned in the main scanning direction S.

  The photosensitive drum 38 is rotated (moved in the sub-scanning direction F) by a driving mechanism (not shown). Then, while rotating the photosensitive drum 38 (moving in the sub-scanning direction F), the two-dimensional latent image is formed on the photosensitive drum 38 by scanning the laser light L in the main scanning direction S as described above. It is formed.

  As shown in FIG. 2, the latent image formed on the photosensitive drum 38 becomes a toner image by a developing device (not shown). The toner image formed on the photosensitive drum 38 is transferred to the intermediate transfer belt 222 by the primary transfer device 221 and then transferred to the recording paper P by the secondary transfer device 223. The recording paper P to which the toner image has been transferred is fixed to the recording paper P by the fixing device 240 and then discharged to a paper discharge tray (not shown).

  As shown in FIG. 1, the laser beam LL reflected by the end portion of the first cylindrical mirror 30 to the outside of the scanning to the photosensitive drum 38 is reflected by the plane mirror 40 and enters the cylindrical lens 42. The laser beam LL that has passed through the cylindrical lens 42 forms an image on the synchronization sensor 44.

  Based on the SOS signal output from the synchronization sensor 44, the writing timing in the main scanning direction S and the rotation timing (movement in the sub-scanning direction F) of the photosensitive drum 38 are determined.

  As shown in FIG. 5, the laser beam L scanned at the same angle by the rotary polygon mirror 24 has a scanning speed in the main scanning direction S on the photosensitive drum 38 (on the imaging surface) is not constant. The image expands and contracts in the main scanning direction S. Specifically, as schematically shown in FIG. 5B, the center portion becomes a slow and narrow image, and both end portions become a fast and wide image. Also, since the optical path lengths are different, the light beam diameter on the photosensitive drum 38 is also different. Specifically, as schematically shown in FIG. 5A, the central portion is small and both end portions are large. Therefore, as it is, the input image data becomes a distorted image, and a normal image (an image equivalent to the input image data) is not formed.

  For this reason, normally, as shown in FIG. 15, a scanning imaging optical system lens group 1000 such as an Fθ lens is arranged on the optical path between the rotary polygon mirror 1024 and the photosensitive drum 1038 for correction. The Fθ lens has a function of scanning a beam scanned at an equal angle by a rotating polygon mirror at a constant speed on the image plane. When the image height is Y, the focal length of the lens is f, and the incident angle to the lens is θ, it is expressed as Y = fθ, and thus is named “Fθ lens”.

  However, the optical scanning device 10 of the image forming apparatus 1 of the present embodiment does not include a scanning imaging optical system lens group such as an Fθ lens (compare FIGS. 4 and 15).

  Therefore, a normal image (an image substantially equivalent to the input image data) is formed by performing the following correction and control of the image data. This will be described below.

  First, image distortion in the main scanning direction S due to the scanning speed of the laser light L in the main scanning direction S on the photosensitive drum 38 being not constant (main scanning direction S expansion / contraction) can be dealt with by correcting the image data. is doing.

  Specifically, the image correction technique (full-scanning direction full magnification correction) described in Japanese Patent Application Laid-Open No. 2003-274143 is used. Hereinafter, correction of distortion (expansion / contraction) of the image in the main scanning direction S using this image correction technique (correction of all magnifications in the main scanning direction) will be described. Further, the following correction of image data is all performed by the control unit 50 (see FIG. 10) of the control device unit 500.

  First, the reduction and enlargement of the output image on the main scanning line SS due to the scanning speed of the laser light L of the photosensitive drum 38 in the main scanning direction S being not uniform are calculated. Next, with respect to the image data on the memory 502 (see FIG. 2), coordinates (correction coordinates) for inserting correction data and coordinates (correction coordinates) for thinning out the data are calculated.

  Further, as shown in FIG. 6A, the address used when reading out the image data from the memory 502 is controlled, and the image data to be inserted into or thinned out from the correction coordinates calculated as described above is subjected to main scanning. An anti-phase correction with respect to the direction S is performed.

  Then, based on the image data subjected to the reverse phase correction, the laser beam L of the optical scanning device 10 is controlled to form an image, so that the output image of the output image due to the non-constant scanning speed in the main scanning direction S is obtained. An output image in which distortion (reduction and enlargement) in the main scanning direction S is canceled can be obtained.

  FIG. 6A is a diagram showing data insertion / thinning positions in an image as described above. However, when data is simply inserted into the same position in the main scanning direction S (on the main scanning line SS) as described above, it becomes visually noticeable. In addition, when data thinning is simply performed on the same position in the main scanning direction S (on the main scanning line SS), if a thin line overlaps the thinned position, the thin line is It disappears and the amount of information in the image is significantly reduced.

  Therefore, in the actual processing, as shown in FIG. 6B, or although not shown, the position where the data insertion / thinning operation is performed is changed for each main scanning line SS in a more random manner. In this way, the above-mentioned problems are solved.

  Next, control for making the light beam diameter on the main scanning line SS on the photosensitive drum 38 substantially uniform will be described.

  The light beam diameter on the photosensitive drum 38 is made different for each light emitting element 102 of the laser array 100 shown in FIG. Details of the method of changing the light beam diameter will be described later. In addition, hereinafter, for the sake of clarity, description will be made only with respect to the light emitting element 102A, the light emitting element 102B, the light emitting element 102C, and the light emitting element 102D illustrated in FIG.

  As described above, the laser light LA to laser light LD emitted from the light emitting element 102A, the light emitting element 102B, the light emitting element 102C, and the light emitting element 102D are deflected and scanned by the reflection deflecting surface 24a of the rotary polygon mirror 24, and then the photosensitive member. The main scan line SS is scanned on the drum 38.

As shown in FIG. 7, the image width of the photosensitive drum 38 in the main scanning direction S is divided into eight areas 81 to 88, and the light emitting element 102A, the light emitting element 102B, the light emitting element 102C, and the light emitting element 102D respectively. Each of the emitted laser light LA, laser light LB, laser light LC, and laser light LD has an optimum light beam diameter in each of the areas 81 to 88. Then, as shown in FIG. The light emitting element 102B, the light emitting element 102C, and the light emitting element 102D are selected. In other words, the light beams are turned on in order from the light emitting element 102A to the light emitting element 102D, and then from the light emitting element 102D to the light emitting element 102A, so that the light beam diameter on the main scanning line SS is substantially uniform.

  For example, when forming a thin line having a diameter of one light beam in the main scanning direction S, as shown in FIG. 8, the light emitting element 102A is turned on by the fourth scanning surface of the reflection deflection surface 24a of the rotary polygon mirror 24, and the third scanning is performed. The light emitting element 102B is lit on the surface, the light emitting element 102C is lit on the second scanning plane, the light emitting element 102D is lit on the first scanning plane, the light emitting element 102D is lit on the first scanning plane, and the light emitting element 102C is lit on the second scanning plane. The substantially uniform line width is formed by turning on the light emitting element 102B on the third scanning plane and lighting the light emitting element 102A on the fourth scanning plane.

  In some cases, the divided portions (lighting switching portions of the light emitting elements 102A, 102B, 102C, and 102D) are visually noticeable. In such a case, the defects (streaks in the sub-scanning direction F) can be made inconspicuous by overlapping each laser beam LA, laser beam LB, laser beam LC, and laser beam LD as shown in FIG.

  Next, a method for adjusting the laser beam LA to the laser beam LD to the optimum light beam diameter in each of the areas 81 to 88 on the photosensitive drum 38 (method for adjusting the light beam diameter) will be described.

  First, the first method for changing the light beam diameter will be described.

  The first method adjusts the amount of light emitted from each of the light emitting elements 102A, 102B, 102C, and 102D to change the light beam diameter. In other words, the light emission amount is increased in the central area in the main scanning direction S, the light emission intensity is decreased in the areas at both ends in the scanning direction S, and the light beam diameter is substantially uniform.

  FIG. 10 is a block diagram illustrating a configuration of the control device unit 500 of the image forming apparatus 1, which includes a control unit 50, a detection unit 52, and a laser drive circuit 60.

  The control unit 50 corrects the image data and outputs the image data to the synchronization circuit 61 of the laser drive circuit 60. Further, the MPD signal of the detection result of an ESV (Electro-Static Voltage) sensor (not shown) which is a latent image potential sensor for detecting the potential of the electrostatic latent image formed on the photosensitive drum is used as a target of the laser drive circuit 60. This is output to the light amount calculation circuit 62.

  The detection unit 52 outputs the SOS signal that is the detection result of the synchronization sensor 44 (see FIG. 1) to the synchronization circuit 61, and outputs the MPD signal that is the detection result of the MPD 22 (see FIG. 1) to the target light amount calculation circuit 62. .

  The target light amount calculation circuit 62 of the laser drive circuit 60 determines the light amount of each light emitting element 102 using the MPD signal and the ESV signal described above and the output signal from the synchronization circuit 54 as a timing reference, and controls the drive current. Is output to a light amount control circuit 64 (hereinafter referred to as APC circuit 64).

  On the other hand, the synchronization circuit 54 is displaced in the main scanning direction S due to the design of each light emitting element 102 (interval of staggered arrangement in FIG. 3) based on the SOS signal that is the detection result of the synchronization sensor 44 (see FIG. 1). Minutes, the image data sent from the controller 50 and the laser light LA to laser light LD are synchronized, and the data is output to the data converter 66 as serial data.

  The data converter 66 distributes the image data input as serial data to the light emitting elements 102A, 102B, 102C, and 102D, and outputs them to the APC circuit 64.

  The APC circuit 64 inputs the input synchronized image data and the intensity signal determined from the drive current 48 to the laser driver (LDD) 68, and is set in each light emitting element 102A, 102B, 102C, 102D. By turning on the light emitting elements 102A, 102B, 102C, and 102D with the amount of emitted light, the optimum light beam diameter is obtained for each of the areas 81 to 88, and the light beam diameter in the main scanning direction S is substantially uniform.

  Next, a second method for changing the light beam diameter will be described.

  In the second method, the light beam diameter is changed by adjusting the light emission time (lighting time) of each laser beam LA to laser beam LD of each light emitting element 102A, 102B, 102C, 102D. That is, the light emission time is made longer for the area at the center in the main scanning direction S, the light emission time is made shorter for the areas at both ends in the scanning direction S, and the light beam diameter is made substantially uniform.

  From the APC circuit 64 of FIG. 10 to the LDD 68, as indicated by the dotted arrows, the light emitting elements 102A, 102B, 102C, and 102D have the light emission times (lighting times) set for the light emitting elements 102A, 102B, 102C, and 102D. Is turned on so that the optimum light beam diameter is obtained in each area, and the light beam diameter in the main scanning direction S is substantially uniform.

  Next, a third method for changing the light beam diameter will be described.

  As shown in FIG. 11, a prism 15 is disposed between the collimator lens 14 (see FIG. 1) and the semiconductor laser 12 (see FIG. 1). The prism 15 changes the optical path length to the photosensitive drum 38 depending on the position through which the laser light L passes. That is, by making the optical path lengths of the central area and the end areas in the main scanning direction S substantially coincide with each other, an optimal light beam diameter is obtained for each of the areas 81 to 88, and the light beam diameter in the main scanning direction S is set. It is almost uniform.

  Next, a fourth method for changing the light beam diameter will be described.

  As shown in FIG. 12, by arranging the optical scanning device 10 so that the laser beams LA to LD are incident at an angle θ with respect to the normal G of the photosensitive drum 38, up to the photosensitive drum 38. The optical path length is changed. That is, by making the optical path lengths of the central area and the end areas in the main scanning direction S substantially coincide with each other, an optimal light beam diameter is obtained for each of the areas 81 to 88, and the light beam diameter in the main scanning direction S is set. It is almost uniform.

  Next, a fifth method for changing the light beam diameter will be described.

  As shown in FIG. 16, the semiconductor laser 12 (see FIG. 1) is tilted and fixed to the collimator lens 14 (see FIG. 1), and the light emitting elements 102 </ b> A, 102 </ b> B, 102 </ b> C, 102 </ b> D reach the collimator lens 14. The distances are different. As described above, when the distance to the collimator lens 14 is different, the focal lengths at which the laser beams LA, LB, LC, and LD can be reduced can be made different. That is, by making the optical path lengths of the central area and the end areas in the main scanning direction S substantially coincide with each other, an optimal light beam diameter is obtained for each of the areas 81 to 88, and the light beam diameter in the main scanning direction S is set. It is almost uniform.

  Two or more of the first to fifth methods for changing the light beam diameter described above may be combined.

  In addition, as described above, for the sake of simplicity, only four of the light emitting element 102A, the light emitting element 102B, the light emitting element 102C, and the light emitting element 102D are described for convenience. Therefore, the area is divided into eight areas 81 to 88. However, in reality, it can be divided into a maximum of 64 (32 × 2) areas. That is, the light beam diameter in the main scanning direction S of the photosensitive drum 38 becomes substantially uniform.

  In the above embodiment, the light emitting elements 102 are arranged in a staggered manner as shown in FIG. 3 in order to increase the resolution (in order to increase the resolution), but as shown in FIGS. As such, they may be arranged in a line.

  Next, the operation of this embodiment will be described.

  As described so far, the expansion and contraction of the output image in the main scanning direction S is corrected using the image correction technology (full magnification correction in the main scanning direction) described in Japanese Patent Laid-Open No. 2003-274143, and each light emitting element 102 is corrected. The laser beam L emitted from the laser beam L is adjusted to the optimum light beam diameter in each area 81 to 88 on the photosensitive drum 38, the light emitting element 102 to be lit is selected, and the light beam diameter on the photosensitive drum 38 is adjusted. It is almost uniform.

  Therefore, it is possible to form a normal image substantially the same as the image data without providing a scanning imaging optical system lens group such as an Fθ lens with the laser light L scanned at an equal angle by the rotary polygon mirror 24. That is, since there is no scanning imaging optical system lens group such as an Fθ lens that is expensive and needs to be positioned with high accuracy, the optical scanning device 10 is small and inexpensive.

1 is a diagram schematically illustrating a configuration of an image forming apparatus including an optical scanning device according to the present invention. 1 is a diagram schematically illustrating a configuration of an image forming apparatus. (A) is a figure which shows a semiconductor laser, (B) is an enlarged view of the laser array 100 part of a semiconductor laser, (C) is an enlarged view of the round part of (B). 1 schematically shows a configuration of an optical scanning device included in an image forming apparatus according to the present invention, (A) is a view seen from the side, and (B) is a plan view. FIG. (A) is a figure explaining the change of the light beam diameter in the main scanning direction on the photosensitive drum, (B) is a figure explaining the scanning speed change in the main scanning direction on the photosensitive drum, (C) FIG. 4 is a diagram schematically showing scanning of a light beam on the photosensitive drum in the main scanning direction. The data insertion / decimation position in the image is shown, (A) is a diagram in the case where data insertion / decimation is simply performed at the same position in the main scanning direction, and (B) is a random mode. It is a figure which shows an example in the case of changing and changing the position which inserts and thins data for every scanning line. (A) is an explanatory view for explaining that the image width of the photosensitive drum in the main scanning direction is divided into eight areas, each of which is an optimum light beam diameter, and (B) is an explanation for explaining a light emitting element to be lit. FIG. It is explanatory drawing explaining the light emitting element lighted when forming the thin line of 1 light beam diameter in the main scanning direction. It is explanatory drawing explaining the overlap of a laser beam. It is a block diagram which shows the structure of a control apparatus part. It is the schematic diagram which has arrange | positioned the prism between the collimator lens and the semiconductor laser. It is a schematic diagram explaining how each laser beam is incident on the normal line G of the photosensitive drum with an angle θ. It is the figure which arranged each light emitting element in a line in the main scanning direction. It is the figure which arranged each light emitting element in a line in the subscanning direction. The structure of the conventional optical scanning device is schematically shown. (A) is a view seen from the side, and (B) is a plan view. FIG. 3 is a schematic view in which a semiconductor laser is tilted and fixed so that each light emitting element has a different distance from a collimating lens.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Optical scanning apparatus 14 Collimator lens (collimating lens)
15 Prism 24 Rotating polygon mirror 50 Control unit (correction means)
81 area 82 area 83 area 84 area 85 area 86 area 87 area 88 area 100 laser array (light source)
102 Light emitting element (light emitting point)
500 Control unit (selection means, light beam diameter adjustment means, control means)
L Laser light (light beam)
S main scanning direction SS main scanning line
P Recording paper

Claims (8)

An optical scanning device that scans a plurality of light beams emitted from a light source having a plurality of light emitting points onto a scanned object by a deflection unit,
Correction means for performing insertion / decimation in image data in the main scanning direction;
A light beam diameter adjusting means for adjusting a light beam diameter of each of the plurality of light emitting points;
Selecting means for selecting at least one light emitting point of the light source;
Control means for controlling the selection means so as to select the predetermined light emitting point according to the position on the scanned object;
An optical scanning device comprising: Dividing the object to be scanned into a plurality of areas in the main scanning direction;
The light beam diameter adjusting means adjusts the light beam diameter for each area,
The optical scanning apparatus according to claim 1, wherein the control unit controls the selection unit so as to select the predetermined light emitting point for each area.   3. The light according to claim 1, wherein the light beam diameter adjusting means controls a light emission amount of the light beam emitted from each of the light emitting points to adjust the light beam diameter. 4. Scanning device.   3. The light according to claim 1, wherein the light beam diameter adjusting means controls a light emission time of the light beam emitted from each of the light emitting points to adjust the light beam diameter. 4. Scanning device.   3. The optical beam length adjusting means is optical path length changing means for changing an optical path length of each light beam emitted from each light emitting point to the scanned body. The optical scanning device according to 1.   6. The optical path length changing means is configured to cause the light source to be incident with an incident angle of each light beam to the scanned body being inclined with respect to a normal line of the scanned body. The optical scanning device according to 1.   6. The optical scanning device according to claim 5, wherein the optical path length changing unit is a prism in which an optical path length of the light beam to the scanned object is changed depending on a transmission position through which the light beam is transmitted.   The optical scanning device according to claim 5, wherein the optical path length changing unit is arranged at a different distance from the collimating lens for each of a plurality of light emitting points of the light source.

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