JP2008032762A - Optical scanner and image forming apparatus equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an optical scanner capable of preventing occurrence of jitters that shake a writing start position, and to obtain an image forming apparatus equipped with the same. <P>SOLUTION: A write timing to start exposing a photoreceptor is determined on the basis of timing of detection in which an SOS sensor detects one beam of a light beam group as synchronous light for each deflection plane 99. In this instance, a synchronous light detecting means detects one beam that is deflected in the center in the main scanning direction of the deflection plane 99 of a polygon mirror 98 and in the center in the vertical scanning direction, as the synchronous light. As compared with deflection at the end of a deflection plane of inferior plane accuracy, the center has a better plane accuracy, reducing variance of the deflecting direction of the synchronous light and also of the detection timing thereof for each deflection plane 99. As a result, the occurrence of what is called jitters is prevented in which a write timing varies for each deflection plane 99 to shake a writing start position. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical scanning apparatus that forms an electrostatic latent image by irradiating a photosensitive member with a plurality of light beams, and an image forming apparatus including the optical scanning apparatus.

Some electrophotographic printing apparatuses scan a photosensitive member by emitting a plurality of light beams from a light source provided in an optical scanning apparatus. (Patent Document 1)
This optical scanning device is provided with a reflection mirror that irradiates the synchronization light detection member with one of the plurality of light beams as synchronization light. Any one synchronizing light is reflected by this reflecting mirror, and the synchronizing light detecting member detects this synchronizing light, thereby determining the writing timing on the photosensitive member.
JP 2004-053856 A

  However, if this arbitrarily selected one sync light is deflected at the end of the deflecting surface with poor surface accuracy, the deflection direction of the sync light varies, and the detection timing varies from one deflecting surface to another.

  Due to this variation in detection timing, the write timing varies from scan to scan, and so-called jitter occurs in which the write position fluctuates.

  An object of the present invention is to prevent the occurrence of jitter in which the writing position fluctuates in consideration of the above facts.

  An optical scanning device according to claim 1 of the present invention includes a deflector that exposes a photosensitive member by deflecting a plurality of light beams emitted from a light source on the same deflection surface, and one beam of the light beams is synchronized light. The synchronizing light detecting means detects the light beam deflected at the center side in the main scanning direction of the deflecting surface as the synchronizing light. .

  According to the above configuration, a plurality of light beams emitted from the light source are deflected by the same deflecting surface of the deflector to expose the photosensitive member.

  The writing timing at which the photosensitive member starts to be exposed is determined based on the detection timing when the detecting unit detects one beam of the light beam group as the synchronization light for each deflection surface.

  Here, the synchronizing light detection means detects one beam deflected on the center side in the main scanning direction of the deflecting surface of the deflector as synchronizing light. Compared with the case where deflection is performed at the end of the deflection surface with poor surface accuracy, the center side has good surface accuracy, so the variation in the direction of synchronization light deflection is reduced, and the detection timing of the synchronization light for each deflection surface also varies. Less. As a result, the writing timing varies for each deflection surface, and so-called jitter that causes the writing position to fluctuate can be prevented.

  An optical scanning device according to a second aspect of the present invention includes a deflector for exposing a photosensitive member by deflecting a plurality of light beams emitted from a light source on the same deflecting surface, and one beam of the light beams is synchronized light. The synchronizing light detecting means detects the light beam deflected on the center side in the sub-scanning direction of the deflecting surface as the synchronizing light. .

  According to the above configuration, a plurality of light beams emitted from the light source are deflected by the same deflecting surface of the deflector to expose the photosensitive member.

  The writing timing at which the photosensitive member starts to be exposed is determined based on the detection timing when the detecting unit detects one beam of the light beam group as the synchronization light for each deflection surface.

  Here, the synchronization light detection means detects one beam deflected on the center side in the sub-scanning direction of the deflection surface of the deflector as the synchronization light. Compared with the case where deflection is performed at the end of the deflection surface with poor surface accuracy, the center side has good surface accuracy, so the variation in the direction of synchronization light deflection is reduced, and the detection timing of the synchronization light for each deflection surface also varies. Less. As a result, the writing timing varies for each deflection surface, and so-called jitter that causes the writing position to fluctuate can be prevented.

  According to a third aspect of the present invention, there is provided a deflector for exposing a photosensitive member by deflecting a plurality of light beams emitted from a light source on the same deflecting surface, and synchronizing one beam of the light beams. The synchronizing light detecting means detects the light beam deflected at the center side in the main scanning direction and at the center side in the sub-scanning direction of the deflection surface. It is detected as light.

  According to the above configuration, a plurality of light beams emitted from the light source are deflected by the same deflecting surface of the deflector to expose the photosensitive member.

  The writing timing at which the photosensitive member starts to be exposed is determined based on the detection timing when the detecting unit detects one beam of the light beam group as the synchronization light for each deflection surface.

  Here, the synchronization light detection means detects one beam deflected on the center side in the main scanning direction and on the center side in the sub-scanning direction of the deflection surface of the deflector as the synchronization light. Compared with the case where deflection is performed at the end of the deflection surface with poor surface accuracy, the center side has good surface accuracy, so the variation in the direction of synchronization light deflection is reduced, and the detection timing of the synchronization light for each deflection surface also varies. Less. As a result, the writing timing varies for each deflection surface, and so-called jitter that causes the writing position to fluctuate can be prevented.

  According to a fourth aspect of the present invention, there is provided an optical scanning device that deflects a plurality of light beams emitted from a light source on the same deflection surface to expose a photosensitive member, and synchronizes one beam of the light beam group with a synchronous light. The light beam group includes two rows in the sub-scanning direction, and the synchronizing light detection unit is deflected below the deflection surface in the sub-scanning direction. The detected light beam is detected as the synchronization light.

  According to the above configuration, a plurality of light beams emitted from the light source and deflected by the same deflection surface of the deflector in the sub-scanning direction are exposed to the photosensitive member.

  The writing timing at which the photosensitive member starts to be exposed is determined based on the detection timing when the detecting unit detects one beam of the light beam group as the synchronization light for each deflection surface.

  Here, the synchronization light detection means detects one beam deflected on the lower side in the sub-scanning direction of the deflection surface of the deflector as the synchronization light. The deflector is attached to the optical box on the lower side in the sub-scanning direction, and the deflection surface on the lower side in the sub-scanning direction is not easily tilted. For this reason, the variation in the deflection direction of the synchronization light is reduced, and the variation in the detection timing of the synchronization light for each deflection surface is also reduced. As a result, the writing timing varies for each deflection surface, and so-called jitter that causes the writing position to fluctuate can be prevented.

  According to a fifth aspect of the present invention, there is provided an optical scanning device comprising: a deflector that exposes a photosensitive member by deflecting a plurality of light beams emitted from a light source on the same deflection surface; and one beam of the light beams is synchronized light. The light beam group is in two rows in the sub-scanning direction, and the synchronizing light detection unit is below the deflection surface in the sub-scanning direction, and The light beam deflected on the center side in the main scanning direction is detected as the synchronizing light.

  According to the above configuration, a plurality of light beams emitted from the light source and deflected by the same deflection surface of the deflector in the sub-scanning direction are exposed to the photosensitive member.

  The writing timing at which the photosensitive member starts to be exposed is determined based on the detection timing when the detecting unit detects one beam of the light beam group as the synchronization light for each deflection surface.

  Here, the synchronization light detecting means detects one beam deflected on the lower side in the sub-scanning direction and on the center side in the main scanning direction as the synchronization light. The deflector is attached to the optical box on the lower side in the sub-scanning direction, and the deflection surface on the lower side in the sub-scanning direction is not easily tilted. Compared with the case where the deflection is performed at the end of the deflecting surface with poor surface accuracy, the surface accuracy is better on the center side in the main scanning direction.

  For this reason, the variation in the deflection direction of the synchronization light is reduced, and the variation in the detection timing of the synchronization light for each deflection surface is also reduced. As a result, the writing timing varies for each deflection surface, and so-called jitter that causes the writing position to fluctuate can be prevented.

  An optical scanning device according to a sixth aspect of the present invention is the optical scanning device according to any one of the first to fifth aspects, wherein the light beam group from the light source is incident on the deflection surface after intersecting a main scanning direction. Or after crossing in the main scanning direction after being deflected by the deflection surface.

  According to the above configuration, the light beam group intersects with the main scanning direction and then enters the deflection surface, or after being deflected with the deflection surface, intersects with the main scanning direction. For this reason, the spread of the light beam group in the main scanning direction is suppressed, a deflector having a small deflection surface can be used, and the optical scanning device can be miniaturized.

  An optical scanning device according to a seventh aspect of the present invention is the optical scanning device according to the sixth aspect, wherein the light beam group from the light source is incident on the deflection surface from the scanning start side and is deflected by the deflection surface. The synchronizing light that intersects the scanning direction and is deflected on the center side of the deflecting surface precedes the main scanning direction, or enters the deflecting surface after intersecting the main scanning direction from the scanning end side, and The synchronizing light deflected on the center side of the surface precedes the main scanning direction.

  According to the above configuration, the light beam group from the light source is incident on the deflection surface from the scanning start side, is deflected by the deflection surface, intersects the main scanning direction, and is deflected on the center side of the deflection surface. Precedes the main scanning direction. Alternatively, the light beam group from the light source is incident on the deflecting surface from the scanning end side, is deflected by the deflecting surface, intersects the main scanning direction, and the synchronized light deflected on the center side of the deflecting surface is the main scanning direction. Precedes.

  Since the synchronization light is detected by the synchronization light detection means in the light beam group in the main scanning direction, a separation margin between the image area on the photoconductor and the synchronization light, that is, a time margin is secured as compared with the subsequent configuration. it can.

  An image forming apparatus according to an eighth aspect of the present invention includes the optical scanning device according to any one of the first to seventh aspects.

  According to the above configuration, since the image forming apparatus includes the optical scanning device according to any one of the first to seventh aspects, jitter can be prevented and a high-quality output image can be obtained.

  According to the image forming apparatus of the present invention, it is possible to prevent the occurrence of jitter in which the writing position fluctuates.

  The image forming apparatus 10 employing the optical scanning device 36 of the first embodiment will be described with reference to FIGS.

  As shown in FIG. 12, the image forming apparatus 10 includes four process cartridges 13Y, 13M, 13C, and 13K of yellow (Y), magenta (M), cyan (C), and black (K) in the horizontal direction. Are arranged in parallel at regular intervals. In addition, when it is necessary to distinguish YMCK, it demonstrates by attaching | subjecting any one of Y, M, C, and K after a code | symbol, and when it is not necessary to distinguish YMCK, YMCK is abbreviate | omitted.

  These four process cartridges 13Y, 13M, 13C, and 13K are all configured in the same manner, and a photoreceptor 16 that is rotationally driven at a predetermined speed, and a charging roll that uniformly charges the surface of the photoreceptor 16 44 (see FIG. 11) and a cleaning device 18 for cleaning the surface of the photosensitive member 16. The process cartridge 13 is integrally formed as a unit, and is configured to be individually replaceable from the main body 10 </ b> A of the image forming apparatus 10.

  Further, the optical scanning device 36 disposed below the process cartridge 13 exposes an image corresponding to a predetermined color on the surface of the photoconductor 16 to form an electrostatic latent image. Details of the optical scanning device 36 will be described later.

  As shown in FIG. 11, the electrostatic latent image formed on the surface of the photoreceptor 16 is yellow (Y), magenta (M), cyan (C), black by the developing roll 17A provided in the developing unit 17, respectively. It is developed as a toner image of each color of (K).

  Also, as shown in FIG. 12, the toner images of the respective colors formed on the surface of the photoconductor 16 are transferred to the four primarys on the surface of the intermediate transfer belt 25 of the transfer unit 22 disposed above each process cartridge 13. The images are sequentially transferred by the transfer rolls 26Y, 26M, 26C, and 26K. These primary transfer rolls 26Y, 26M, 26C, and 26K are disposed on the back side of the intermediate transfer belt 25 corresponding to the photosensitive member 16 of each process cartridge 13Y, 13M, 13C, and 13K.

  Further, the intermediate transfer belt 25 is wound around the drive roll 27, the tension roll 24, and the backup roll 28 with a constant tension, and is predetermined in the direction of the arrow by the drive roll 27 that is rotated by a motor (not shown). It is designed to circulate at a speed of.

  Further, the yellow (Y), magenta (M), cyan (C), and black (K) toner images transferred to the surface of the intermediate transfer belt 25 are full-color, and a secondary transfer roll 29 that is in pressure contact with the backup roll 28. Thus, the sheet material P transferred to the sheet material P as a recording medium and transferred with the toner images of these colors is conveyed to the fixing device 31 disposed above. The secondary transfer roll 29 is in pressure contact with the side of the backup roll 28 and is configured to secondary-transfer toner images of each color onto the sheet material P conveyed from below to above. Thereafter, the sheet material P to which the toner image has been transferred is fixed by the fixing device 31 and then discharged by a discharge roll 32 to a discharge tray 33 provided on the upper portion of the main body 10A.

  The sheet material P is a sheet conveyance path 37 in a state in which sheets of a predetermined size are separated one by one by a nudger roll 35 and a separation conveyance feed roll 30 from a sheet feeding device 34 disposed inside the main body 10A. Then, it is conveyed to the registration roll 38 and stopped. The sheet material P fed from the paper feeding device 34 is sent to the secondary transfer position of the intermediate transfer belt 25 by a registration roll 38 that rotates at a predetermined timing.

  When images are formed on both sides of the sheet material P, the sheet material P on which the image is fixed on one side is not discharged as it is to the discharge tray 33 by the discharge roll 32, but the conveyance direction is changed by a switching gate (not shown). It is switched and conveyed to the duplex conveying unit 40 via the sheet conveying roll 39. In the double-sided conveyance unit 40, the sheet material P is conveyed again to the resist roll 38 in a state where the front and back of the sheet material P are reversed by a conveyance roll pair (not shown) provided along the conveyance path 41. After the image is transferred and fixed on the back surface of the paper, it is discharged to the discharge tray 33.

  Residual toner, paper dust, and the like are removed from the surface of the photoreceptor 16 after the toner image transfer process is completed by a cleaning device 18 shown in FIG. 11 to prepare for the next image forming process. The cleaning device 18 is provided with a cleaning blade 42 to remove residual toner, paper dust and the like on the surface of the photoconductor 16. Further, residual toner and the like are removed from the surface of the intermediate transfer belt 25 after the toner image transfer process is completed by the cleaning device 43 shown in FIG. The cleaning device 43 includes a cleaning brush 43A and a cleaning blade 43B.

  Next, the optical scanning device 36 will be described in detail.

  As shown in FIGS. 9 and 10, the optical scanning device 36 irradiates the four photoconductors 16Y, 16M, 16C, and 16K with the light beam groups LY, LM, LC, and LK, respectively, on the photoconductor 16. An electrostatic latent image is formed.

  The optical scanning device 36 includes light sources 90 and 92, pre-deflection optical systems 94 and 96, a polygon mirror 98 as a deflector, and a scanning optical system 100. The light source 90 emits two color light beam groups LY and LM, and the light beam groups LY and LM are separated into light beam groups of each color in the scanning optical system 100 and scanned on the two photoconductors 16Y and 16M. Is done. Similarly, the light source 92 emits two color light beam groups LC and LK, and the light beam groups LC and LK are separated into light beam groups of the respective colors in the scanning optical system 100, and the two photoconductors 16C, Scan to 16K.

  The deflection scanning direction due to the rotation of the polygon mirror 98 is referred to as a main scanning direction, and the direction orthogonal to the deflection scanning direction is referred to as a sub-scanning direction.

  As shown in FIG. 5, the light source 90 has two light emitting points 90 </ b> A arranged on a straight line inclined with respect to the main scanning direction (Y direction in the drawing). In other words, the light beam can be scanned at a time, and the increase in speed can be accommodated.

  The light emitting points 90A for each color are arranged at a predetermined pitch on the same straight line, and are arranged on the same straight line in the sub-scanning direction as the light emitting points 90A for other colors. For this reason, if each of the light emitting points 90A is turned on with a predetermined delay time, the writing position in the main scanning direction is aligned, and a color image without color misregistration can be formed.

  Further, in the present embodiment, the light beam group LY imaged on the yellow (Y) photoreceptor 16Y is emitted from the light emitting point 90A which is inclined upward in the main scanning direction and arranged on the lower side. From the light emitting point 90A, the light beam group LM imaged on the magenta (M) photoconductor 16M emits light. The light source 92 has the same structure as the light source 90 and emits light beam groups LC and LB that form images on the cyan (C) and black (K) photoreceptors 16C and 16B.

  6 and 8, in the optical path from the light source 90 to the polygon mirror 98, the first collimator lens 108 and the first TAN cylindrical lens 110 (hereinafter, the main scanning direction is described as TAN). A first reflection mirror 102, a second TAN cylindrical lens 112, a first SAG cylindrical lens 114, a second reflection mirror 104 (hereinafter referred to as SAG) and a third reflection mirror 106 are arranged. Thereby, the light beam groups LY and LM emitted from the light source 90 are a first collimator lens 108 having a collimator function, a first TAN cylindrical lens 110, a second TAN cylindrical lens 112, and a first SAG cylindrical lens having a condensing function. By passing through 114, the light is focused in the sub-scanning direction and is incident on the deflecting surface 99 of the polygon mirror 98.

  Further, in the optical path from the light source 92 to the polygon mirror 98, the second collimator lens 122, the third TAN cylindrical lens 124, the fourth reflection mirror 116, the fourth TAN cylindrical lens 126, the second SAG cylindrical lens 128, and the fifth reflection. A mirror 118 and a sixth reflecting mirror 120 are arranged. Thereby, the light beam groups LC and LK emitted from the light source 92 are used for the second collimator lens 122, the third TAN cylindrical lens 124, the fourth TAN cylindrical lens 126 having a collimator function, and the second SAG cylindrical lens having a condensing function. By passing through 128, the light is focused in the sub-scanning direction and is incident on the deflection surface 99 of the polygon mirror 98.

  Further, the polygon mirror 98 including the six deflecting surfaces 99 rotates at a predetermined rotation speed, and scans the light beam groups LY, LN, LC, and LK at a predetermined speed.

  As shown in FIG. 7, the fθ lens 130 is provided in the optical path of the light beam groups LY, LM, LC, and LK deflected by the polygon mirror 98, and each light beam group passes through the fθ lens 130. Then, the light enters the first plane mirror 132. Note that the fθ lens 130 is configured to have a characteristic of causing the light beam group scanned at an equal angle by the polygon mirror 98 to scan at a constant speed on the photosensitive member 16.

  The light beam group that has passed through the fθ lens 130 and entered the first plane mirror 132 is folded back in the opposite direction, and the folded light beam group is further disposed below by the second plane mirror 134. Folded toward the cylindrical mirror 136. Further, the light beam group is folded back by the first cylindrical mirror 136 and forms an image on the photosensitive member 16 disposed above through the dust-proof glass 144 fixed to the housing (not shown) of the optical scanning device 36. Is done. As a result, each photoconductor 16 is exposed to form an electrostatic latent image.

  Next, a method for synchronizing the writing timing of the light beam group scanned for each deflection surface 99 of the polygon mirror 98 to the photosensitive member 16 will be described.

  As shown in FIG. 8, one beam of sync light in the light beam group is transmitted through the fθ lens 130 and then folded back toward the SOS lens 140 by the first plane mirror 132C, and further in the main scanning direction by the SOS mirror 138. The SOS lens 140 disposed on the opposite side is focused on the SOS sensor 142 disposed outside the image area as a synchronization light detection unit. A control unit (not shown) controls the timing of image writing on the photoconductor 16 based on the timing detected by the SOS sensor 142.

  Here, as shown in FIG. 3, the surface accuracy of the end portion of the deflecting surface 99 is poor due to the influence of processing. For this reason, when the synchronization light is deflected at the end of the deflection surface 99, the deflection direction varies, and the detection timing of the synchronization light for each deflection surface 99 also varies. Further, the write timing of the light beam group deflected for each deflection surface varies, and so-called jitter in which the write position fluctuates occurs in the output image as shown in FIG. Note that FIG. 4 illustrates an example in which one color is simultaneously scanned with four light beams.

  However, as shown in FIG. 1A, the synchronization light detected by the SOS sensor 142 (see FIG. 8) is on the center side in the main scanning direction on the deflection surface 99 of the polygon mirror 98 and on the center side in the sub scanning direction. This is a single light beam deflected by. For this reason, the variation in the deflection direction of the synchronization light is reduced, and the detection timing of the synchronization light for each deflection surface 99 is also reduced. As a result, as shown in FIG. 4A, the occurrence of jitter can be prevented. In FIG. 1, the length of the deflecting surface 99 in the sub-scanning direction is increased in order to make the reflection direction of each light beam understandable and cheap.

  In the first embodiment, as shown in FIG. 2, the light beam group in the main scanning direction emitted from the light sources 90 and 92 by adjusting the emission direction of the light beam is deflected from the scanning start side. After entering the beam 99 and being deflected by the deflection surface 99, it intersects the main scanning direction. Further, the synchronization light deflected on the center side of the deflection surface 99 precedes the main scanning direction.

  Therefore, as shown in FIG. 1B, the deflecting surface 99 can be made smaller than in the case where they do not intersect, and the optical scanning device 36 can be downsized.

  Further, when the synchronizing light is deflected by the polygon mirror 98, it precedes in the light beam group in the main scanning direction, so that it can be detected by the SOS sensor 142 in advance. Therefore, the width of the image area relative to the scannable width on the photosensitive member 16, that is, the effective scanning rate can be increased as compared with the following configuration.

  Further, as shown in FIG. 13A, since the synchronization light is deflected by the polygon mirror 98, it precedes in the light beam group in the main scanning direction, so that the separation margin up to the image region width (M range in the drawing) is obtained. Compared with the case where the following light is used as the synchronization light (see FIG. 13B), the (N range in the figure) can be secured longer. FIGS. 13A and 13B show the state where the synchronization light reaches the photosensitive member 16 in order to explain the separation margin. However, in actuality, the synchronization light is reflected by the SOS mirror 138. The photosensitive member 16 does not reach.

  Next, the image forming apparatus 10 employing the optical scanning device 36 of the second embodiment will be described with reference to FIG.

  In addition, about the same member as 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  In this embodiment, as in the first embodiment, the light beam group incident on the polygon mirror 98 does not enter from the scanning start side of the photoconductor 16 (SOS side incidence), but instead, it is shown in FIG. As shown, it is configured to enter from the scanning end side of the photoconductor 16 (EOS side incidence).

  Specifically, the light beam group from the light sources 90 and 92 is incident on the deflection surface 99 from the scanning end side, is deflected by the deflection surface 99, intersects the main scanning direction, and is deflected on the center side of the deflection surface 99. The synchronized light precedes the main scanning direction.

  In this way, the deflection surface 99 can be made smaller by crossing the light beam group in the main scanning direction before deflection by the deflection surface 99.

  Next, in the image forming apparatus 200 of the third embodiment, exposure is performed by two optical scanning devices 202 and 204.

  In addition, about the same member as 1st Embodiment, the same code | symbol is attached | subjected and the description is abbreviate | omitted.

  As shown in FIG. 20, the image forming apparatus 200 includes image forming units 180Y, 180M, 180C, which form yellow (Y), magenta (M), cyan (C), and black (K) toner images. It has 180K. In the following, when it is necessary to distinguish YMCK, description will be made by adding any of Y, M, C, and K after the reference. When YMCK does not need to be distinguished, Y, M, C, K is omitted.

  The image forming units 180Y, 180M, 180C, and 180K are in contact with the traveling direction of the endless intermediate transfer belt 186 that is stretched by the backup roll 182 and the plurality of stretch rolls 184. They are arranged in series in the order of 180K. The intermediate transfer belt 186 is in contact with the photoreceptors 188Y, 188M, 188C, and 188K of the image forming units 180Y, 180M, 180C, and 180K, respectively, and the primary transfer rolls 190Y, 190M, 190C, and 180C disposed on the inner side. The image is transferred from the photoreceptors 188Y, 188M, 188C, and 188K to the intermediate transfer belt 186 by 190K.

  Next, the image forming units 180Y, 180M, 180C, and 180K will be described by taking the image forming unit 180Y as an example.

  The surface of the photoreceptor 188Y is uniformly charged by a charging roll 192Y as a charging member. The surface of the charging roll 192Y is cleaned by a hollow cleaning member 194Y that rotates following the charging roll 192Y.

  Next, exposure corresponding to the yellow image is performed by the optical scanning device 202, and an electrostatic latent image corresponding to the yellow image is formed on the surface of the photoreceptor 188Y. Details of the optical scanning device 202 will be described later.

  The electrostatic latent image corresponding to the yellow image is developed with the toner carried on the developing roll 197Y to which the developing bias of the developing device 196Y is applied, and becomes a yellow toner image. The yellow toner image is primarily transferred onto the intermediate transfer belt 186 by the pressing force of the primary transfer roll 190Y and the electrostatic attraction force due to the transfer bias applied to the primary transfer roll 190Y.

  In this primary transfer, the entire yellow toner image is not transferred to the intermediate transfer belt 186, and a part thereof remains on the photosensitive member 188Y as transfer residual yellow toner. After the primary transfer, the photosensitive member 188Y passes through a position facing the cleaning device 198Y, and transfer residual toner and the like on the surface of the photosensitive member 188Y are removed. Thereafter, the surface of the photoreceptor 188Y is charged again by the charging roll 192Y for the next image forming cycle.

  Further, in the image forming apparatus 200, the image forming process similar to the above is performed at the timing considering the relative positions of the image forming units 180Y, 180M, 180C, and 180K. At 180K, toner images of Y, M, C, and K are sequentially superimposed on the intermediate transfer belt 186 to form a multiple toner image.

  Then, the multiple toner images are batched from the intermediate transfer belt 186 by the electrostatic attraction force of the secondary transfer roll 170 to which a transfer bias is applied to the sheet material P conveyed to the secondary transfer position A at a predetermined timing. Then, it is transferred to the sheet material P.

  The sheet material P to which the multiple toner images have been transferred is separated from the intermediate transfer belt 186 and then conveyed to the fixing device 172, where it is fixed to the sheet material P by heat and pressure, thereby forming a full color image.

  The transfer residual toner on the intermediate transfer belt 186 that has not been transferred to the sheet material P is collected by the intermediate transfer belt cleaner 174.

  Next, the optical scanning devices 202 and 204 will be described.

  As shown in FIG. 20, the optical scanning device 202 irradiates the two photoconductors 188Y and 188M with light beam groups LY and LM, respectively, to form an electrostatic latent image.

  As shown in FIG. 19, the optical scanning device 202 includes a light source 90, a pre-deflection optical system 208, a polygon mirror 210 as a deflector, and a scanning optical system 212. The light source 90 emits two color light beam groups LY and LM as in the first embodiment. The light beam groups LY and LM are separated into light beam groups of each color in the scanning optical system 212, and two light beam groups LY and LM are separated. The photoconductors 188Y and 188M are scanned.

  Specifically, in the optical path from the light source 90 to the polygon mirror 210, a collimator lens 216 as the pre-deflection optical system 208, a first TAN cylindrical lens 218, a SAG cylindrical lens 220, a reflection mirror 214, and a second TAN cylindrical lens. 222 is arranged.

  As shown in FIG. 18, the light beam groups LY and LM emitted from the light source 90 include a collimator lens 216 having a collimator function, a first TAN cylindrical lens 218, a second TAN cylindrical lens 222, and a SAG having a condensing function. By passing through the cylindrical lens 220, the light is focused in the sub-scanning direction and enters the deflection surface 211 of the polygon mirror 210.

  Further, the polygon mirror 210 including the six deflecting surfaces 211 rotates at a predetermined rotation speed, and scans the light beam groups LY and LN at a predetermined speed.

  In addition, as shown in FIG. 17, in the optical path from the polygon mirror 210 to the photoconductors 188M and 188Y, an fθ lens 224 through which the light beam groups LY and LM pass, and a light beam group of each color are provided. The first cylindrical mirrors 226Y and 226M, the plane mirrors 228Y and 228M, and the second cylindrical mirrors 230Y and 230M are arranged as the scanning optical system 212.

  The light beam groups LY and LM deflected by the polygon mirror 210 pass through the fθ lens 224 and enter the first cylindrical mirrors 226Y and 226M. Note that the fθ lens 224 is configured to have a characteristic of causing the light beam group scanned at the same angle by the polygon mirror 210 to scan at a constant speed on the photosensitive member 188.

  The light beam group incident on the first cylindrical mirror 226 is folded back in the opposite direction toward the plane mirror 228, and the folded light beam group is folded back toward the second cylindrical mirror 230 by the plane mirror 228. The light beam group is folded downward by the second cylindrical mirror 230 and imaged on the photoreceptor 188 disposed below. As a result, the photosensitive members 188Y and 188M are exposed to form an electrostatic latent image.

  Next, a method for synchronizing the writing timing of the light beam group scanned for each deflection surface 211 of the polygon mirror 210 to the photosensitive member 16 will be described.

  As shown in FIG. 19, one synchronized light beam of the light beam group passes through the fθ lens 224 and is reflected by the SOS mirror 232 shown in FIG. 19 toward the SOS lens 234 disposed on the opposite side in the main scanning direction. Is done. The reflected synchronization light is condensed on the SOS sensor 236 by the SOS lens 234. Based on the timing detected by the SOS sensor 236, a control unit (not shown) controls the timing for writing an image on the photosensitive member 188.

  Here, as shown in FIG. 15, the synchronous light detected by the SOS sensor 142 is a single light deflected on the deflection surface 211 of the polygon mirror 210 on the center side in the main scanning direction and on the lower side in the sub-scanning direction. It is a beam. In FIG. 15, the length of the deflecting surface 211 in the sub-scanning direction is increased in order to make the reflection direction of each light beam understandable and cheap.

  For this reason, as compared with the case where the deflection surface 211 is deflected at the end in the main scanning direction where the surface accuracy is poor, the variation in the deflection direction of the synchronization light is reduced.

  Further, a cylindrical concave shape 210 </ b> A that opens upward is provided inside the polygon mirror 210 for weight reduction. For this reason, as shown in FIG. 16, the polygon mirror 210 is attached to the main body on the lower side of the deflection surface 211 in the sub-scanning direction, and the lower side in the sub-scanning direction has higher rigidity than the upper side in the sub-scanning direction. . Therefore, since the synchronization light is deflected on the lower side in the sub-scanning direction of the highly rigid deflection surface 211, the variation in the deflection direction of the synchronization light is further reduced, and the detection variation of the synchronization light is also reduced.

  Therefore, it is possible to prevent the occurrence of so-called jitter in which the writing position fluctuates.

  The optical scanning device 204 forms an electrostatic latent image on the two photoconductors 188C and 188K in the same manner as the optical scanning device 202.

  This embodiment is an example of solving a problem in an underfilled optical system in which a deflection surface includes a beam group.

(A) It is the perspective view which showed the polygon mirror of the optical scanner which concerns on 1st Embodiment of this invention, and showed the condition where the reflected light beam crossed. (B) The perspective view which showed the polygon mirror of the optical scanning device, and showed the case where the light beam compared with the reflected light of the polygon mirror of 1st Embodiment of this invention does not cross | intersect. It is the top view which showed the polygon mirror of the optical scanning device which concerns on 1st Embodiment of this invention, and showed the condition where synchronous light reflects and precedes the main scanning direction. It is the perspective view which showed the polygon mirror of the optical scanning device concerning 1st Embodiment of this invention. (A) It is the image output from the optical scanning device based on 1st Embodiment of this invention, It is drawing which showed that the jitter has not generate | occur | produced. (B) It is the output image, and is a drawing showing a case where jitter occurs as a comparative example of the first embodiment. 1 is a diagram illustrating a light source of an optical scanning device according to a first embodiment of the present invention. 1 is a plan view showing a pre-deflection optical system of an optical scanning device according to a first embodiment of the present invention. 1 is a side view showing an optical scanning device according to a first embodiment of the present invention. 1 is a plan view showing an optical scanning device according to a first embodiment of the present invention. It is the perspective view which showed the optical scanner which concerns on 1st Embodiment of this invention, and was seen from the side. It is the perspective view which showed the optical scanning device which concerns on 1st Embodiment of this invention, and was seen from the downward direction. 1 is a side view showing a photoreceptor and the like of an image forming apparatus according to a first embodiment of the present invention. 1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention. (A) The photoconductor which concerns on 1st Embodiment of this invention is shown, and it is the schematic diagram which showed the image area width | variety and the separation margin. (B) It is a comparison figure for comparing with the separation margin of the optical scanning device concerning a 1st embodiment of the present invention. It is the top view which showed the polygon mirror of the optical scanning device which concerns on 2nd Embodiment of this invention, and showed the condition where synchronous light reflects and precedes the main scanning direction. It is the perspective view which showed the polygon mirror of the optical scanner which concerns on 3rd Embodiment of this invention, and showed the condition where the reflected light beam crossed. It is the sectional view which showed the polygon mirror of the optical scanning device concerning a 3rd embodiment of the present invention, and looked at the polygon mirror from the side. It is the side view which showed the scanning optical system of the optical scanning device concerning 3rd Embodiment of this invention. It is the side view which showed the optical system before deflection | deviation of the optical scanner which concerns on 3rd Embodiment of this invention. It is the top view which showed the optical scanning device concerning 3rd Embodiment of this invention. FIG. 5 is a schematic configuration diagram illustrating an image forming apparatus according to a third embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 16 Photoconductor 36 Optical scanning device 90 Light source 90A Light emission point 92 Light source 98 Polygon mirror 99 Deflection surface 142 SOS sensor 188 Photoconductor 200 Image forming device 202 Optical scanning device 204 Optical scanning device 210 Polygon mirror 211 Deflection surface 236 SOS Sensor

Claims (8)

Optical scanning comprising: a deflector that deflects a plurality of light beams emitted from a light source on the same deflecting surface to expose a photosensitive member; and synchronization light detection means that detects one beam of the light beam group as synchronization light. In the device
The synchronizing light detecting means detects a light beam deflected at the center side in the main scanning direction of the deflection surface as the synchronizing light. Optical scanning comprising: a deflector that deflects a plurality of light beams emitted from a light source on the same deflecting surface to expose a photosensitive member; and synchronization light detection means that detects one beam of the light beam group as synchronization light. In the device
The synchronizing light detecting means detects a light beam deflected at the center side in the sub-scanning direction of the deflecting surface as the synchronizing light. Optical scanning comprising: a deflector that deflects a plurality of light beams emitted from a light source on the same deflecting surface to expose a photosensitive member; and synchronization light detection means that detects one beam of the light beam group as synchronization light. In the device
The synchronizing light detecting means detects a light beam deflected on the center side in the main scanning direction and on the center side in the sub-scanning direction of the deflection surface as the synchronizing light. Optical scanning comprising: a deflector that deflects a plurality of light beams emitted from a light source on the same deflecting surface to expose a photosensitive member; and synchronization light detection means that detects one beam of the light beam group as synchronization light. In the device
The light beam group has two rows in the sub-scanning direction, and the synchronization light detecting unit detects a light beam deflected below the deflection surface in the sub-scanning direction as the synchronization light. Scanning device. Optical scanning comprising: a deflector that deflects a plurality of light beams emitted from a light source on the same deflecting surface to expose a photosensitive member; and synchronization light detection means that detects one beam of the light beam group as synchronization light. In the device
The light beam groups are arranged in two rows in the sub-scanning direction, and the synchronization light detecting means applies the light beams deflected on the lower side of the deflection surface in the sub-scanning direction and on the center side in the main scanning direction. An optical scanning device characterized by detecting as follows.   The light beam group from the light source crosses the main scanning direction and then enters the deflection surface, or after being deflected by the deflection surface, crosses the main scanning direction. 6. The optical scanning device according to any one of 1 to 5.   The light beam group from the light source is incident on the deflection surface from the scanning start side, is deflected by the deflection surface, intersects the main scanning direction, and is deflected on the center side of the deflection surface. Precedes in the main scanning direction, or enters the deflection surface from the end of scanning, is deflected by the deflection surface, intersects the main scanning direction, and is deflected on the center side of the deflection surface An optical scanning device characterized in that light precedes the main scanning direction.   An image forming apparatus comprising the optical scanning device according to claim 1.

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