JP2005208323A - Optical writing apparatus and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent image fluctuation due to a local shift of a main scanning position caused by variation of each surface of a deflecting device.
In an optical writing apparatus for writing a latent image on a surface to be scanned of a photoconductor 10 by a polygon mirror 2 having a plurality of change surfaces and rotating an optical beam modulated in accordance with an image signal, the polygon mirror 2 A main scanning position deviation storage device 6 that stores in advance a main scanning position deviation amount in advance for each main scanning position within the effective scanning range for each deflection surface, and a deviation stored in the main scanning position deviation storage device 6. A phase change circuit 7 is provided for locally changing the beam writing position for each scanning plane in accordance with the amount.
[Selection] Figure 1

Description

  The present invention relates to an optical writing device that performs optical writing by scanning a light beam deflected by an optical deflecting device, and an image that forms a latent image on an image carrier by this optical writing device and forms a visible image on a recording medium. The present invention relates to a forming apparatus.

  An optical writing device that records an image by scanning a scanned surface of a photoconductor as an image carrier by a deflecting device such as a polygon mirror through an optical system with a light beam modulated in accordance with an image signal is a digital copy. Widely used in the writing section of a machine, a facsimile, or an optical printer. As such an optical writing apparatus, for example, as shown in Patent Document 1, two sets of optical scanning optical systems are combined, and the optical scanning optical systems are connected in the main scanning direction to form a wide scanning writing area. Developed with different color developers by scanning a plurality of photoconductors using independent laser beams as shown in, for example, Japanese Patent Application Laid-Open No. 2005-26883. Then, an optical writing device called a tandem method that forms a multicolor image by superimposing on a recording medium such as transfer paper, or, for example, as shown in Patent Document 3, separate laser beams are applied to a single photoconductor. There is an optical writing apparatus called a multi-scanning method using a single photoconductor that irradiates and obtains a multicolored image, and an image forming apparatus using these optical writing apparatuses has been put into practical use.

  In the three methods described above, the same problem is that the scanning magnification varies for each deflection surface due to the accuracy of the deflection surface of the polygon mirror, which is a deflection device, the error of the rotation center axis of the deflection device, and the like. There is. This variation in scanning magnification is less affected, particularly on the synchronization detection side at the leading edge of the image, but the effect increases as the distance from the synchronization detection side increases in the scanning direction. In particular, the influence becomes large at the rear end side in the scanning direction, which adversely affects image fluctuation. Further, depending on the surface accuracy of the scanning lens and the nonuniformity of the refractive index distribution, a local magnification error may occur for each lens not only at the leading and trailing edges of the image but also at the center of the image. In particular, in a writing optical system such as the above-described tandem method or the above-described multiple scanning method using a single photoconductor, a positional deviation occurs. When the positional deviation becomes remarkable, there is a drawback that color unevenness occurs and the image is deteriorated.

  On the other hand, as described in the above-mentioned Patent Document 1, the above-described divided scanning method is a type in which writing is started from the center of the image, and scanning is performed in opposite directions to perform long writing, and Patent Document As shown in FIG. 4, there are two types, that is, a type in which the scanning directions are the same, and one scanning end and the other scanning start end are connected. In either method, the amount of image fluctuation that occurs on each writing end side is the same, but the former is connected on the writing front side with relatively little fluctuation, whereas the latter type. In this case, since the image is connected at the writing rear end where the image fluctuation is the largest and the writing front where the fluctuation is relatively small, there is a drawback that the performance of the joint is worse than the former.

  Also, in the second tandem method described above, the type that is scanned in the opposite direction as in Patent Document 2 described above and the same writing unit for each color as shown in Patent Document 5 are the same. Some types scan in the direction. In an image forming apparatus of a type that obtains a multicolor image by scanning in the opposite direction of the former, since the synchronization side and the rear end side of the image are formed with different colors, the image fluctuation is relatively small and the image fluctuation is relatively small. As a result, the color lines of the thin lines and the color unevenness of the halftone portions are generated. In the latter case, since the synchronization detection side is the same for each color, an image with relatively little fluctuation can be obtained on the writing start side, but on the rear end side, fluctuations are randomly generated in each color, so that the comparison is made with the former. Therefore, an adverse effect of image fluctuation is likely to occur.

  Further, the above-described multiple scanning method using a single photoconductor also has a forward scanning type and an opposite scanning type, and has the same problems as in the tandem method.

Therefore, in order to prevent the fluctuation of the image, the above-described Patent Document 5 describes the frequency of the clock signal according to the partial recording magnification of the designated image with reference to the frequency according to the recording magnification of the designated image. It has been proposed to specify the recording position of an image while changing the width of the image. Further, in order to prevent image fluctuation, Patent Document 6 proposes to divide a high-frequency clock and generate a pixel clock whose phase is changed for each deflection surface, and Patent Document 7 proposes a PLL loop. It is proposed to prevent this by using a direct synthesizer that uses a synthesizer. Patent Document 8 proposes changing the frequency of the pixel clock to be changed according to the magnification and setting the writing start position for each magnification. Has proposed that a laser light detection device is arranged at an exposure start position and an end position, and the pixel frequency is changed in accordance with the measurement value.
JP 2000-267027 A JP-A-6-18796 Japanese Patent Laid-Open No. 6-1002 JP-A-3-163477 Japanese Patent Laid-Open No. 11-198435 JP 2002-36626 A Japanese Patent No. 3166311 JP-A-9-109446 JP 2002-160398 A

  However, the method described in Patent Document 6 requires a high-frequency clock having double the resolution for changing the phase. For example, when it is desired to change the phase by 1 / n of one pixel, a high-frequency clock that is n times the pixel clock is required. Specifically, when the phase is made variable by 1/8 of one pixel with a 50 MHz pixel clock, the frequency of the high frequency clock needs to be 50 × 8 = 400 MHz, and radio waves are likely to be emitted in terms of EMI. Therefore, the circuit is inevitably large and the cost is high. Further, in order to increase the resolution of the phase change, a higher frequency clock is required, and the circuit becomes complicated and the cost is increased.

  In the method described in Patent Document 7, in order to increase the resolution, it is necessary to increase the frequency of the master clock, and it is difficult to realize one chip. In addition, it is necessary to convert the phase error into an analog voltage by an AD converter, add it in an analog manner, and supply it to the PLL loop, which is easily affected by noise and increases the correction error.

  Further, the invention described in Patent Document 5 is an improvement of the optical writing apparatus in the tandem method, and the inventions described in Patent Documents 8 and 9 are improvements in the optical writing apparatus of the divided scanning method. Is not applicable.

  The present invention has been made in view of such a state of the prior art, and an object of the present invention is to prevent image fluctuation due to a local main scanning position shift caused by variations in each surface of the deflecting device.

  In order to achieve the above object, the first means is the optical writing apparatus for deflecting and scanning the optical beam modulated in accordance with the image signal by the optical deflection scanning means having a plurality of optical deflection surfaces and rotating. Reference position detection means for detecting a reference position within one rotation of the light deflection scanning means, synchronization detection means for synchronizing the writing position of the light beam, and each light deflection surface of the light deflection scanning means Storage means for storing in advance each main scanning position a deviation amount of a local main scanning position within each effective scanning range, and writing out a beam for each scanning surface in accordance with the deviation amount stored in the storage means. And changing means for locally changing the position for each main scanning position.

  The second means is characterized in that, in the first means, the storage means records a scanning magnification and / or a positional deviation amount of the light beam.

  A third means is characterized in that, in the first means, the changing means locally changes at least one of a light beam writing position, a pixel frequency and a phase for each scanning plane.

  The fourth means is characterized in that, in the first means, the changing means changes the phases of the image clock and the image data.

  A fifth means is characterized in that, in the fourth means, the phase is changed by changing a delay amount in accordance with a main scanning position.

  The sixth means includes an optical writing device according to any one of the first to fifth means, and an image forming means for outputting an image written on the image carrier by the optical writing device as a visible image on a recording medium. And an image forming apparatus.

  A seventh means is the sixth means, wherein the optical writing device deflects and scans a plurality of light beams emitted from a plurality of laser light sources, and connects the light beams on the image carrier in the main scanning direction. It is characterized by matching.

  The eighth means is characterized in that in the seventh means, there are two laser light sources, and the light beams from these laser light sources are connected in the forward direction.

  According to a ninth means, in the seventh means, there are two laser light sources, and light beams from these laser light sources are scanned in directions opposite to each other from a substantially central portion in the main scanning direction. .

  A tenth means is the tandem type optical writing apparatus according to the sixth means, wherein the optical writing device deflects and scans the plurality of light beams emitted from the plurality of laser beams in parallel in an arbitrary distance in the sub-scanning direction. It is characterized by comprising.

  In the following embodiments, the reference position detection means is a reference position detection circuit for detecting a reference signal (polygon rotation reference position signal) for each rotation provided in the polygon motor, and the synchronization detection means is the tip synchronization detection unit 4. The storage means corresponds to the main scanning position shift storage device 6 and the change means corresponds to the phase change circuit 7.

  According to the present invention, the surface fluctuation of each surface of the light deflecting means, the image fluctuation at the rear end of the image and the positional deviation of the beam due to the variation of the central axis are locally changed for each surface. The occurrence of image fluctuations can be prevented with a simple circuit configuration at low cost.

  The best mode for carrying out the present invention will be described below with reference to the drawings.

<First Embodiment>
FIG. 1 is a diagram illustrating an overall configuration of an optical writing device according to a first embodiment of the present invention, and FIG. 2 is a diagram illustrating an example of a relationship between an image height and a delay amount when the phase is changed by a phase change circuit. FIG. 3 is a diagram showing a change in the pixel clock frequency when the phase is changed by the phase change circuit.

  The optical writing apparatus according to the first embodiment includes a laser light source 1, a polygon mirror 2 including a rotating polygon mirror, a scanning lens 3, a tip synchronization detection unit 4, a scanning surface selection circuit 5, a main scanning position shift storage device 6, and a phase change. The circuit 7 includes a modulation drive circuit 8 and an image control circuit (video board) 9. The light beam emitted from the laser light source 1 is made into substantially parallel light by a coupling lens (not shown) and further imaged linearly on the polygon mirror 2 by a cylinder lens (not shown). Next, scanning is performed in the main scanning direction by the rotation of the polygon mirror 2, and the surface to be scanned of the photosensitive member 10 which is an image carrier is scanned through the scanning lens 3 and the like. At this time, the leading edge synchronization detection unit 4 detects the scanning timing of the light beam, and synchronizes the leading edge of the image. A polygon motor (not shown) that rotationally drives the polygon mirror 2 generates a polygon rotation reference position signal (also called a Z-phase pulse) every rotation, and detects this reference position signal by a reference position detection circuit (not shown). It is configured. The positional relationship between the generation position of the polygon rotation reference position signal and the surface of the polygon mirror 2 is preferably generated at a rotation position other than the effective scanning width in terms of the circuit configuration. It can be generated at the rotational position.

  The polygon rotation reference position signal from the polygon motor is connected so as to be input to the scanning plane selection circuit 5, and when this signal is input, the counter inside the scanning plane selection circuit 5 is reset and a synchronization detection signal is input. Then it is counted up. Thereby, the current scanning plane can be specified. The specified scanning plane values are sequentially read out by a writing position changing circuit (not shown).

  The main scanning position deviation storage device 6 stores a local main scanning position deviation amount for each surface of the polygon mirror 2 measured in advance in the manufacturing stage as a value obtained by inverting the sign. An example of this value is shown in FIG. FIG. 7 shows the main scanning dot shift at each image height of one scanning lens in an example of the type having one scanning lens for each color of the tandem optical writing apparatus. In the example of FIG. 7, the dot position deviation amount is stored separately for each of the 1 to 4 scanning lenses, and further stored according to the image height (−1 to +1). Further, for each scanning lens, each surface of the polygon mirror is stored. FIG. 8 is a diagram showing the relationship between the image height and the main scanning dot shift at that time. In this example, since the variation caused by each scanning lens 3 is larger than the variation of the main scanning position on the mirror surface of the polygon mirror 2, a large tendency is brought about by the scanning lens 3, and the polygon mirror is further formed thereon. The variation due to the mirror surface 2 is added.

  In this embodiment, the dot position deviation amount is directly stored in the main scanning position deviation storage device 6, but one dot may be stored at a phase of 360 degrees, or may be stored as a local magnification. May be.

  The phase change circuit 7 reads out the amount of positional deviation for each image height from the main scanning positional deviation storage device 6 according to the selected surface of the polygon mirror 2, and can shift the phase of the clock according to the pixel clock. . In the example of FIG. 7, seven locations are stored between the image heights −1 and +1. However, the total scan width may be divided into eight to set the phase shift amount, or the intermediate value is complemented by spline interpolation or the like. Processing may be performed to set the phase shift amount for each pixel.

  The phase change circuit 7 is constituted by a delay circuit, for example, and can linearly delay digital data. When the scanning selection surface is changed by the synchronization detection signal from the leading edge synchronization detection unit 4, the delay value sent from the main scanning position shift storage device 6 to the phase change circuit 7 is switched, and the pixel clock and the image control circuit 9 The phase of the image data can be changed. Here, since the phase is changed using a delay element, there is no need to divide the phase by dividing the high-frequency clock as in Patent Document 6 described above, and the writing position can be very easily made at a level of one pixel or less. Can be shifted.

  FIG. 2 is a diagram showing an example of the delay amount for each image height at that time. The delay amount can be moved not in a straight line but in a curve with respect to the scanning position, and a local positional deviation due to a variation in the refractive index of the scanning lens can be corrected. FIG. 3 shows how the frequency of the pixel clock changes at this time.

<Second Embodiment>
FIG. 4 is a diagram showing an overall configuration of the optical writing device according to the second embodiment. The optical writing apparatus according to the second embodiment is a forward scanning optical writing apparatus in which light beams scanned by two writing systems are connected in the main scanning direction to form a wide optical writing apparatus. FIG. 5 is a diagram for explaining image fluctuation at the joint between the first and second light beams, and FIG. 6 is a diagram for explaining a state in which the fluctuation at the joint between the first and second light beams is corrected. is there.

  As shown in FIG. 4, the first and second writing systems having exactly the same configuration are configured to scan the surface to be scanned of the photoreceptor 10 in half in the main scanning direction. The scanning is configured to be connected in the forward direction by polygon mirrors 2a and 2b rotating in the same direction. In FIG. 4, a rear end synchronization detection sensor for detecting the rear end side, which is the end of writing in the scanning direction, provided to connect the polygon mirror 2, the scanning lens 3, the front end synchronization detection unit 4, and the two sets of writing systems. Although two sets of 11 are illustrated, the scanning plane selection circuit 5, which is an image correction circuit, the main scanning position shift storage device 6, the phase change circuit 7, the modulation drive circuit 8, and the image control circuit 9 are complicated. In order to prevent this, only the first writing system is shown as 5a, 6a, 7a, 8a, 9a, and the image correcting circuit for the second writing system is omitted, but the same one is actually provided. These image correction circuits and the like that can be shared by the first and second writing systems may be shared. Reference numeral 12a denotes a magnification calculation / average processing circuit.

  Since the front end side of the image on the first writing system side is relatively close to synchronous detection as shown in FIG. 5, the influence of image fluctuations due to variations in the surface of the polygon mirror 2a is relatively small. At the rear end of the image, which is the joint portion of the two-writing system, the displacement due to scanning of each surface of the polygon mirror (one line scan) is periodically repeated for one rotation, and the image fluctuation increases at the joint. On the other hand, in the second writing system, there is little fluctuation at the leading edge of the image, which is the joint, but the fluctuation of the image becomes large at the trailing edge of the image. In the optical writing device of the type connected in the forward direction, the image fluctuation at the joint becomes white stripes or black stripes at the joint as shown in FIG. The occurrence of such white stripes or black stripes is a major cause of image quality deterioration and becomes fatal in terms of image quality.

  In the present embodiment, the main scanning position for each surface is corrected by changing the phase of the pixel clock and the image data as described above for the optical writing apparatus of such a system. Thereby, as shown in FIG. 6, the beam positions at the leading and trailing edges of the image are constant, and the occurrence of white stripes or black stripes due to image fluctuations at the joints can be prevented. In addition, the non-uniformity of the refractive index of the lens in the center of the image and the fluctuation of the beam position due to the temperature gradient can be corrected for each image height by the phase change circuit, and the fluctuation can be prevented.

  Other parts that are not particularly described are configured in the same manner as the first embodiment and function in the same manner.

<Third Embodiment>
FIG. 9 is a diagram illustrating an overall configuration of an optical writing device according to the third embodiment. As described above, in the second embodiment, two polygon mirrors are used. However, in this third embodiment, there is one polygon mirror 2 and two surfaces thereof are used, and the writing optical system has two. By using the system, a wide-width optical writing device for forward scanning is configured.

  In other words, this optical writing apparatus includes one polygon mirror 2, a laser light source 1a for irradiating the polygon mirror 2 with a laser beam for scanning substantially half of the surface to be scanned of the photoconductor 10, a coupling lens 21a, and a cylinder lens. A first writing system I comprising a lens 22a and lenses 23a, 24a constituting an fθ lens as an imaging means, a laser light source 1b for scanning the remaining half of the scanned surface of the photosensitive member 10, and a coupling lens 21b, a cylinder lens 22b, and a second writing system II comprising lenses 23b, 24b constituting an fθ lens as an imaging means, and a beam from these first and second writing systems I, II. And 10 reflecting mirrors 25 for reflecting the surface to be scanned. This optical writing apparatus is the same as that of the second embodiment described above except that scanning is performed by one polygon mirror 2, and the first writing system is provided by providing the image correction circuit in the second embodiment. It is possible to prevent image fluctuations that occur at the joint between the rear end portion of the image due to I and the front end portion of the image of the second writing system II.

<Fourth Embodiment>
FIG. 10 is a diagram illustrating an overall configuration of an optical writing device according to the fourth embodiment. This embodiment relates to an optical writing apparatus that scans in opposite directions from the center of a surface to be scanned of a photoreceptor.

  This optical writing apparatus also has a first writing system I and a second writing system II. Explaining the first writing system I, the laser light source 1a emits a laser beam whose intensity is modulated in accordance with an image signal. The emitted laser beam is made into a parallel beam by the collimating action of the collimating lens 21a, is given a tendency to converge only in the sub-scanning direction by the cylinder lens 22a, and is mainly near one deflecting reflecting surface of the polygon mirror 2 as the deflecting means. An image is formed as a long line image in the scanning direction. The beam deflected at a constant angular velocity by the rotation of the polygon mirror 2 passes through the lens 23a, is sequentially reflected by the mirrors 31a and 32a and the folding mirror 33a, and forms a beam spot on half of the surface to be scanned of the photoreceptor 10. The second writing system II is disposed at a position obtained by rotating the first writing system I by 180 degrees about the rotation axis of the polygon mirror 2, and similarly to the first writing system I, the laser light source 1b, the collimating lens 21b, the cylinder The lens 22b, the lenses 23b and 24b, the mirrors 31b and 32b, and the folding mirror 33b are formed to form a beam spot on the remaining half of the scanned surface of the photoconductor 10. The laser beam from the laser light source 1b is converted into a parallel beam by the collimator lens 21b, and is given a tendency to converge only in the sub-scanning direction by the cylinder lens 22b. It is formed as a long line image. The beam deflected at a constant angular velocity by the rotation of the polygon mirror 2 passes through the lenses 23b and 24b constituting the fθ lens as the image forming means, and is sequentially reflected by the mirrors 31b and 32b and the folding mirror 33b to be photoreceptor 10. A beam spot is formed on the photosensitive surface, and the second scanning region of the photosensitive member 10 is scanned at a constant speed. The first and second writing systems I and II have tip synchronization detection units 4a and 4b, respectively. Each tip synchronization detection unit 4a and 4b is provided outside the image area of each scanning beam, and is a scanning beam written for each scanning. The scanning start timing is determined. Also in this embodiment, an image control circuit and an image correction circuit are provided as in the second embodiment described above. The scanning start timing follows the timing determined by the image control circuit, writing is started from the writing start position, and the next portion of each scanning beam in the main scanning direction is well aligned. This optical writing apparatus is also provided with the image correction circuit in the second embodiment, so that the image fluctuation generated at the joint between the rear end portion of the image by the first writing system I and the front end portion of the image of the second writing system II. Can be prevented.

  Other parts that are not particularly described are configured in the same manner as the first and third embodiments described above, and function in the same manner.

<Fifth Embodiment>
FIG. 11 is a diagram showing an overall configuration of an optical writing device according to the fifth embodiment. This embodiment relates to a writing apparatus that scans modulated optical beams on independent photosensitive members by four independent optical systems as shown in FIG.

  That is, this embodiment is an example of a tandem optical writing apparatus as can be seen from FIG. This tandem optical writing apparatus is of a type that scans two of the four optical beams from the opposite scanning direction.

  The optical writing device is disposed obliquely above an image forming unit in which four photosensitive drums 51, 52, 53, and 54 are arranged in parallel. The optical writing device includes four laser light sources 55, 56, 57, and 58, a polygon mirror 59 that deflects and scans light beams from the laser light sources in two symmetrical directions, and the polygon mirror 59 as a center. An fθ lens 61 for guiding a plurality of light beams arranged symmetrically in two directions and deflected by a polygon mirror 59 onto the scanned surfaces of the corresponding photosensitive drums 51, 52, 53, and 54, respectively. , 62, imaging lenses 63, 64, 65, 66, optical path folding mirrors 67, 68, 69, 71, 72, 73, 74, 75, 76, 77, 78, 79, and the like. These components are housed in a housing 80. The housing 80 is provided with openings for allowing the light beam to pass through, and a dustproof glass 81 is attached to these openings. The fθ lenses 61 and 62 have a two-layer structure so that the fθ lens 61 forms an image of the light beam from the laser light sources 55 and 56 and the fθ lens 62 forms an image of the light beam from the laser light sources 57 and 58. Yes.

  This optical writing device converts color-separated image data input from an image data output device such as a document reading device, a personal computer, a word processor, or a facsimile reception unit into a signal for driving a light source, and accordingly each laser light source The light beams emitted from 55, 56, 57, and 58 reach the polygon mirror 59, and are deflected and scanned by the polygon mirror 59 in two symmetrical directions by two beams. In the structure shown in FIG. 11, the polygon mirror 59 is divided into two upper and lower stages for the light beams of the laser light sources 56 and 57 and for the light beams of the laser light sources 55 and 58. A configuration may be adopted in which four light beams are deflected and scanned by a polygon mirror that is thick in the direction. The light beam deflected and scanned in two directions by the polygon mirror 59 in two directions is the first imaging lens, passes through the fθ lenses 61 and 62 having the upper and lower two-layer structures, and is folded back by the folding mirror. After passing through the section, it passes through imaging lenses 63, 64, 65, and 66, which are second imaging lenses composed of, for example, a long toroidal lens, and passes through the folding mirror and dust-proof glass 81 for each color. The photosensitive drums 51, 52, 53, and 54 are irradiated onto the scanned surface, and an electrostatic latent image is written.

  The four 52, 53, 54 and 55 of the optical writing device 5 are each composed of a semiconductor laser (LD) as a light source and a collimating lens for collimating the emitted light beam of the semiconductor laser, which are not shown. The structure is integrated into the holder. Further, a synchronization detection mirror (not shown) is provided in the optical path of the four light beams to extract a light beam at the scanning start position in the main scanning direction, and the light beam reflected by the synchronization detection mirror is not shown in the figure. Light is received by the detector and a scanning start synchronization signal is output.

  The latent images formed on the photosensitive drums 51, 52, 53, and 54 by the optical writing device are respectively yellow (Y), magenta (M), cyan (C), and black (Bk) colors of the developing units. The toner images of each color Y, M, C, and Bk that have been developed and visualized with toner are sequentially superimposed and transferred onto a transfer material by a transfer device (not shown). By providing the image correction circuit according to the second embodiment for each writing optical system, an optical writing device is applied to obtain a color image free from image fluctuation and positional deviation over the front and rear ends of the image and the front surface of the scanning area. Can do.

  Other parts that are not particularly described are configured in the same manner as the first embodiment and function in the same manner.

1 is a diagram illustrating an overall configuration of an optical writing device according to a first embodiment of the present invention. It is a figure which shows an example of the delay amount for every image height when a phase is changed by a phase change circuit as a graph. It is a figure which shows the change of the pixel clock frequency when a phase is changed by a phase change circuit as a graph. It is a figure which shows the whole structure of the optical writer concerning the 2nd Embodiment of this invention. It is a figure for demonstrating the fluctuation of the image in the joint of the 1st and 2nd light beam in 2nd Embodiment. It is a figure for demonstrating the state which correct | amended the fluctuation | variation of the joint of the 1st and 2nd light beam. It is a figure which shows the main scanning dot shift | displacement which can be set | placed on each image height of each scanning lens in a tandem optical writing apparatus as a table | surface. It is a figure which shows the main scanning dot shift | offset | difference for every surface of each lens and each polygon mirror in a tandem optical writing apparatus as a graph. It is a figure which shows schematic structure of the optical writing apparatus which concerns on the 3rd Embodiment of this invention. It is a figure which shows schematic structure of the optical writing apparatus which concerns on the 4th Embodiment of this invention. It is a figure which shows schematic structure of the optical writing apparatus which concerns on the 5th Embodiment of this invention.

Explanation of symbols

1, 1a, 1b Laser light source 2, 2a, 2b Polygon mirror 3, 3a, 3b Scanning lens 4, 4a, 4b Tip synchronization detection sensor 5, 5a Scanning surface selection circuit 6.6a Main scanning position shift storage device 7, 7a, Phase change circuit 8, 8a Modulation drive circuit 10 Photoreceptor 11, 11a, 11b Rear end synchronization detection sensor

Claims (10)

In an optical writing apparatus that deflects and scans an optical beam modulated in accordance with an image signal by a rotating optical deflection scanning unit having a plurality of optical deflection surfaces,
A reference position detecting means for detecting a reference position within one rotation of the light deflection scanning means;
Synchronization detecting means for synchronizing the writing position of the light beam;
Storage means for preliminarily storing, for each main scanning position, a local main scanning position shift amount within an effective scanning range for each light deflection surface of the light deflection scanning means;
Changing means for locally changing the beam writing position for each scanning surface in accordance with the shift amount stored in the storage means for each main scanning position;
An optical writing device comprising:   The optical writing apparatus according to claim 1, wherein the storage unit records a scanning magnification and / or a positional deviation amount of the light beam.   The optical writing apparatus according to claim 1, wherein the changing unit locally changes at least one of a writing position, a pixel frequency, and a phase of a light beam for each scanning plane.   The optical writing apparatus according to claim 1, wherein the changing unit changes a phase of an image clock and image data.   The optical writing apparatus according to claim 4, wherein the phase is changed by changing a delay amount according to a main scanning position. The optical writing device according to any one of claims 1 to 5,
Image forming means for outputting an image written on the image carrier by the optical writing device as a visible image on a recording medium;
An image forming apparatus comprising:   The image forming apparatus according to claim 6, wherein the optical writing device deflects and scans a plurality of light beams emitted from a plurality of laser light sources, and joins the light beams in the main scanning direction.   8. The image forming apparatus according to claim 7, wherein the number of the laser light sources is two, and light beams from these laser light sources are connected in the forward direction.   8. The image forming apparatus according to claim 7, wherein there are two laser light sources, and light beams from these laser light sources are scanned in directions opposite to each other from a substantially central portion in the main scanning direction. 7. The image forming apparatus according to claim 6, wherein the optical writing device deflects and scans the plurality of light beams emitted from the plurality of laser beams in parallel in an arbitrary distance in the sub-scanning direction.

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