JP2019104186A - Optical writing device and image forming apparatus - Google Patents

Abstract

To provide an optical writing device which, even when the amount of a temperature rise in a sub-scan direction is different in any of a plurality of positions in the main scan direction, can appropriately correct the displacement in the sub-scan direction in that position.SOLUTION: A temperature difference calculation unit 4, when a light-emitting element group 400 repeats light emission operation, calculates how much temperature difference is caused by placement in a different position in the sub-scan direction with respect to an imaging lens 301e which belongs to one imaging lens group 301. A main scan direction distribution processing unit 5 identifies, as correction objects, the imaging lens groups 301 in which the amount of deformation in the sub-scan direction is equal to or greater than the pixel diameter, according to a temperature difference distribution indicating how temperature differences in the sub-scan direction in each of the plurality of imaging lens groups 301 are distributed in a plurality of positions in the main scan direction.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an optical writing device, and more particularly, to a technique for suppressing deterioration in image quality caused by thermal expansion of a lens array.

  In recent years, in the field of optical writing devices, development of OLED-PH (OLED Print Head) is highlighted as a new technological trend. The OLED-PH includes a light source substrate on which an organic light emitting diode (OLED: Organic Light Emitting Diode) is disposed, and an imaging lens for imaging the light emitted from the organic LED on the photosensitive surface of the photosensitive drum. It is comprised with the lens array arranged in a dimension. The lens array has a long shape, and the long side corresponds to the main scanning direction, and the short side corresponds to the sub-scanning direction. At one of the short sides, the lens array is fixed to one end of the light source substrate.

  The light emitting elements are densely arranged at a position directly under each imaging lens in the light source substrate. When the optical axes of all the imaging lenses coincide with the normal direction of the light emitting element, the spot diameter of the beam formed on the circumferential surface of the photosensitive member is minimized, and a clear image is formed. However, when the light emission of the light emitting element continues for a long time due to the execution of the print job, a temperature rise occurs in the imaging lens and the light emitting element. The light source substrate is expanded when the mounted light emitting element itself generates heat, while the lens array is expanded due to the radiation heat from the light source substrate. Since there is an expansion difference between the light source substrate and the lens array, the positional relationship between the two varies due to the temperature rise.

  The optical writing device described in Patent Document 1 executes correction processing regarding positional deviation in order to eliminate positional deviation accompanying expansion of the imaging lens. In FIG. 22A, assuming that the lens array and the light source substrate are fixed by the short side e11 at the upstream end in the main scanning direction, the lens array is fixed to the short side e11 of the fixed end when the light emitting element is lit. Extend relative to the opposite free end. At the time of expansion of the lens array, the optical writing described in Patent Document 1 is performed under the assumption that the central position of each imaging lens moves toward the free end as shown by arrows mv1, 2, 3. The device defines correction data for each light emitting element and the imaging lens for each of a plurality of temperature ranges. Based on the correction data, the amount of light emitted by the light emitting element is corrected.

JP 2008-155458 A

  When the lens array is heated from the light emitting element for a long time, even though the lens array as a whole expands in the main scanning direction, the expansion amount in each part in the main scanning direction and the sub scanning direction is not uniform. Specifically, the temperature increase amount may be different in each part in the main scanning direction (e.g., r1 and r30 in FIG. 22B). Further, even at the same position in the main scanning direction, the temperature increase amount in the sub-scanning direction may be different (for example, a set of r21 and r1 in FIG. 22B, a set of r30 and r10). This is because the amount of heat received from the light emitting element and the drive circuit differs in each part of the lens array. In particular, when a difference occurs in the temperature rise amount in the sub scanning direction, as shown in FIG. 22C, the long side lg11 of the lens array bulges out in the sub scanning direction (Y axis direction), The center position also moves in the sub-scanning direction as shown by mv11 and mv12 in FIG. In the correction data of the prior art, since the correction value is defined under the assumption that the center position of the imaging lens moves from the fixed end to the opposite side, such positional deviation of the center position in the sub scanning direction There is a problem that correction can not be properly made.

  When the normal direction of the light emitting element deviates from the optical axis of the imaging lens due to the fluctuation of the positional relationship in the sub scanning direction, the print quality deterioration becomes remarkable in the tandem type image forming apparatus. In the tandem type image forming apparatus, many optical writing devices exist for each color such as yellow, magenta, cyan and black, and if the optical axis for optical writing for each color is deviated, the circumference of the photosensitive member This is because the image forming positions on the surface are not aligned in the sub-scanning direction, which causes color deviation of the toner image.

  An object of the present invention is to provide a light capable of appropriately correcting the positional deviation in the sub scanning direction of the portion even if the temperature increase amount in the sub scanning direction is different at any of a plurality of positions in the main scanning direction. It is providing a writing device.

An optical writing device that can solve the above problems includes a lens array in which a plurality of imaging lens groups are disposed at a plurality of positions in the main scanning direction, a light source substrate on which a plurality of light emitting element groups are disposed, a lens array And a supporting member for supporting the light source substrate, wherein each of the imaging lens groups is premised to be constituted by a plurality of imaging lenses arranged in the sub scanning direction, and the plurality of imaging lenses When the light emitting element groups facing each other repeat the light emitting operation, a temperature difference caused by a pair of imaging lenses belonging to the same imaging lens group and disposed at different positions in the sub scanning direction is Calculating means for calculating
According to the temperature difference distribution of how the temperature difference in the sub scanning direction in each of the plurality of imaging lens groups is distributed at a plurality of positions in the main scanning direction, the displacement amount in the sub scanning direction is the diameter of the pixel Specifying means for specifying an imaging lens group having the above characteristics;
And correction means for performing correction regarding positional deviation of a plurality of pixel data following the pixel data for causing the light emitting element group corresponding to the specified imaging lens group to perform the light emission operation. It is characterized by

  The processing in the main scanning direction by the specifying unit may be specific as follows. That is, of the plurality of positions in the main scanning direction in the lens array, the temperature difference calculated by the calculation means from the position closest to the fixed position where the light source substrate and the lens array are fixed to the target position. A process of performing integration is performed for each of a plurality of positions in the main scanning direction, and displacement of the lens array in the sub-scanning direction at the position based on the integration value obtained at one position in the main scanning direction by the integration. The amount may be calculated.

  The calculation of the temperature difference by the calculation means can be made specific as follows. That is, among the plurality of imaging lenses constituting the imaging lens group, the pixel position corresponding to the imaging lens located at the upstream end in the sub scanning direction and the pixel position corresponding to the imaging lens located at the downstream end Then, calculation is made as to how much light emission by positionally corresponding pixel data continues from the start of the job, and the temperature difference in the sub-scanning direction of the imaging lens group is calculated It may be configured to calculate.

  The following may be comprised as a component of the said calculation means. That is, in the image data to be subjected to image formation, light emission is performed at the row position corresponding to the imaging lens located at the upstream end in the sub scanning direction and the row position corresponding to the imaging lens located at the downstream end A plurality of counters may be provided to count how many pieces of pixel data for causing the element group to emit light are arranged, and the duration of light emission by the pixel data may be calculated based on the count values of the plurality of counters.

  In the case where light receiving sensors are attached to a plurality of imaging lenses constituting the imaging lens group, which are located at the upstream end in the sub scanning direction and those located at the downstream end, the calculation means is You may comprise the component which utilizes the detected value of a light reception sensor. In other words, positional relationship between the light receiving sensor attached to the location corresponding to the imaging lens located at the upstream end in the sub scanning direction and the light receiving sensor attached to the location corresponding to the imaging lens located at the downstream end And a plurality of counters for counting how long light emission by pixel data corresponding to the number of pixels continues from the start of the job, and calculating the duration of light emission by the pixel data based on the count values of the plurality of counters It is also good.

  The calculation means may calculate the duration based on pixel data. Specifically, among the plurality of imaging lenses constituting the imaging lens group, a light emitting element group corresponding to the imaging lens located at the upstream end in the sub scanning direction, and the imaging lens located at the downstream end The calculation of how much power consumption by the light emitting element group corresponding to the light emission from the start of the job is performed based on the pixel data that is the basis of light emission by the light emitting element group, and based on the difference of the power consumption by the calculation The temperature difference in the sub scanning direction of the imaging lens unit may be calculated.

  When a drive circuit for driving the light emitting element groups is provided in the vicinity of each light emitting element group in the light source substrate, the calculation means may consider temperature rise by the drive circuit. That is, according to the drive condition of the drive circuit, the temperature rise amount of the drive circuit is calculated, weighting according to the reciprocal of the distance from the drive circuit to the light emitting element group is performed, and the temperature difference in the sub scanning direction is calculated. You may add.

  When a light receiving sensor is attached to each of the plurality of imaging lens groups, a specific means may be used to improve the accuracy of the light receiving sensor. Specifically, when the image forming lens group whose displacement amount in the sub scanning direction exceeds the diameter of the pixel is specified by the specifying means, the correction means is attached to the image forming lens group The detection value of the light receiving sensor may be used as an observation value to perform correction regarding positional deviation.

  The specifying means may use the amount of change in temperature difference in the main scanning direction for correction. Specifically, a change amount is calculated which indicates how much the temperature difference in the sub scanning direction has changed between the object of the plurality of imaging lens groups and the one adjacent in the main scanning direction. The amount of change in temperature difference between the two adjacent imaging lens groups may be used to determine whether the amount of displacement of each imaging lens group in the sub scanning direction is equal to or greater than the diameter of the pixel.

  The optical writing device may further include, as an additional component, interpolation means for performing linear interpolation on the detection results of two or more of the plurality of light receiving sensors. When the correction means calculates the displacement amount in the sub scanning direction for the imaging lens group not specified by the specifying means, the linear interpolation result by the interpolation means is used as the displacement amount between the light source substrate and the lens array. You may use.

The optical writing device may perform processing for errors. Specifically, the specifying means calculates the temperature calculated by the calculating means from the position closest to the fixed position where the light source substrate and the lens array are fixed among the plurality of positions in the lens array to the target position A process of integrating differences is performed for each of a plurality of positions in the main scanning direction to determine the temperature difference, and an integrated value obtained at one position in the main scanning direction in the determined temperature difference distribution, and a lens array And calculating the displacement amount of the lens array in the sub scanning direction at the position based on the thermal expansion coefficient of
The displacement amount based on the integrated value may be adjusted based on an error between the displacement amount calculated based on the integrated value and the positional displacement amount detected by the light receiving sensor.

  Specifically, it is desirable that the correction regarding the positional deviation by the correction means be the following processing. That is, it is desirable that the light emission timing by the light emitting element group is changed based on the position in the image data of the pixel data to be corrected or the pixel data to be corrected.

  The above optical writing device may be a component of the image forming apparatus.

  In the individual imaging lens groups constituting the lens array, when there is a temperature difference in the sub-scanning direction, the area of the lens array corresponding to the individual imaging lens group is curved by a curvature according to this temperature difference. The calculating means calculates a temperature difference which is the basis of the curvature, and the specifying means specifies an imaging lens group to be corrected from the distribution of the temperature difference in the main scanning direction. Through the above process, it is possible to select, as a correction target, pixel data following pixel data for which the light emitting element group corresponding to the specified imaging lens group has caused the light emission operation. By performing correction of the pixel position and correction of the light emission timing by the light emitting element group on the selected pixel data, it is possible to eliminate the color misregistration of the toner image.

FIG. 2 shows a configuration of an image forming apparatus 1000. FIG. 2A is a cross-sectional view of the optical writing device 100. FIG. FIG. 2 (b) is a plan view and a cross-sectional view of the light source substrate 200. FIG. 3A is a cross-sectional view of the lens array 201, and FIG. 3B is a plan view of the G1 lens 301. FIG. 3C is a plan view of the diaphragm 302. FIG. FIG. 4A is a plan view on the light source substrate 200, and FIG. 4B is a view showing correspondence between the light emitting element group and the pixel position in the exposure pattern. FIG. 2 is a block diagram showing a functional configuration of an image forming apparatus main body. An example of the exposure pattern stored in exposure pattern memory 503Y, M, C, K is shown. It is a block diagram which shows the function structure of an optical writing device. FIG. 8A shows a rectangular shape to be an imaging lens group. FIG. 8B shows a minute region having a width in the main scanning direction of “Δx” and a length in the sub scanning direction of “h”. FIG. 8C shows a central angle Δθ which is the basis of the curvature of a minute area and a minute width Δx. FIG. 8 (d) shows the addition of micro areas. FIG. 9A shows an arrangement of a plurality of imaging lens groups, and FIG. 9B shows a temperature difference distribution in the main scanning direction. FIG. 9C shows the deflection amount distribution in the main scanning direction. FIG. 9D shows the accumulation of displacement in the main scanning direction. FIG. 10A is a flowchart showing a main routine of the optical writing procedure. FIG. 10B is a flowchart showing the procedure of generating a corrected exposure pattern. It is a flowchart which shows calculation procedure of deflection amount D (i) and elongation amount E (i) by the temperature difference of a subscanning direction. The temperature difference in the sub scanning direction, the integrated value distribution of the temperature difference in the main scanning direction, and the deflection amount distribution in the main scanning direction are shown. FIG. 13A shows a plurality of imaging lens groups in a bent state. FIG. 13B shows the bit values of the portion of the exposure pattern that corresponds to the imaging lens of FIG. FIG. 13C shows a state in which a portion of the exposure pattern corresponding to the imaging lens in FIG. 13A is corrected. FIG. 14A shows the light receiving sensor 304 attached to the lens array 201. FIG. FIG. 14B shows the G1 lens 301 to which the light receiving sensor 304 is attached. It is a block diagram showing functional composition of an optical writing device concerning a 2nd embodiment. It is a figure showing functional composition of an optical writing device concerning a 3rd embodiment. It is a flowchart which shows the variation | change_quantity calculation procedure of the temperature difference in a subscanning direction. 17 shows a variation distribution di21 of a temperature difference in the main scanning direction. The temperature difference distribution in the main scanning direction, which is the target of simplified processing, is shown. FIG. 20A shows an interpolation straight line ln1 obtained by applying linear interpolation to the amount of displacement detected by the light receiving sensor. FIG. 20 (b) shows a temperature difference distribution in the main scanning direction which is a target of prediction error calculation, and FIG. 20 (c) shows a deflection amount distribution which is a target of prediction error calculation. FIG. 20 (d) shows the prediction error. FIG. 21 (a) shows drive circuits 31, 32, 33 disposed on the same light source substrate as the light emitting element group. FIG. 21B shows a light receiving sensor 305 provided in the center of the three imaging lenses arranged in the sub scanning direction in the light emitting element group. FIG. 22A shows a lens array in which the light source substrate is fixed at the short side e11 at the upstream end in the main scanning direction. FIG. 22B shows the amount of temperature rise in the sub scanning direction in each part of the lens array. FIG. 22C shows the lens array in which the long side lg11 protrudes toward the sub scanning direction.

  Hereinafter, embodiments of an image forming apparatus according to the present invention will be described with reference to the drawings.

[1] First Embodiment [1-1] Configuration of Image Forming Apparatus First, the configuration of the image forming apparatus according to the present embodiment will be described.

  As shown in FIG. 1, the image forming apparatus 1000 is a so-called tandem type color printer, and an image for forming toner images of yellow (Y), magenta (M), cyan (C) and black (K) colors. The forming stations 110Y, 110M, 110C and 110K are provided. The image forming stations 110Y, 110M, 110C and 110K have photosensitive drums 101Y, 101M, 101C and 101K which rotate in the direction of arrow A.

  Around the photosensitive drums 101Y, 101M, 101C and 101K, charging devices 102Y, 102M, 102C and 102K, optical writing devices 100Y, 100M, 100C and 100K, and developing devices 103Y, 103M, 103C and 103K along the outer peripheral surface. The primary transfer chargers 104Y, 104M, 104C and 104K and the cleaning devices 105Y, 105M, 105C and 105K are disposed.

  The charging devices 102Y, 102M, 102C and 102K uniformly charge the outer peripheral surfaces of the photosensitive drums 101Y, 101M, 101C and 101K.

  The optical writing devices 100Y, 100M, 100C and 100K expose the outer peripheral surfaces of the photosensitive drums 101Y, 101M, 101C and 101K to form electrostatic latent images based on the exposure patterns of Y, M, C and K colors. .

  The developing devices 103Y, 103M, 103C, and 103K supply toners of Y, M, C, and K colors, develop electrostatic latent images, and form toner images of Y, M, C, and K colors. The primary transfer chargers 104Y, 104M, 104C and 104K electrostatically transfer the toner images carried by the photosensitive drums 101Y, 101M, 101C and 101K to the intermediate transfer belt 106 (primary transfer).

  The cleaning devices 105Y, 105M, 105C, and 105K remove charges remaining on the outer peripheral surfaces of the photosensitive drums 101Y, 101M, 101C, and 101K after primary transfer, and remove residual toner. In the following, when describing the configuration common to the image forming stations 110Y, 110M, 110C and 110K, the characters YMCK will be omitted.

  The intermediate transfer belt 106 is an endless belt and is stretched around the secondary transfer roller pair 107 and the driven rollers 108 and 109, and rotationally travels in the arrow B direction. By performing primary transfer in accordance with the rotational travel, toner images of Y, M, C, and K colors are superimposed on each other to form a color toner image. The intermediate transfer belt 106 conveys the color toner image to the secondary transfer nip of the secondary transfer roller pair 107 by rotating and traveling with the color toner image carried.

  The two rollers constituting the secondary transfer roller pair 107 form a secondary transfer nip by being pressed against each other. A secondary transfer voltage is applied between these rollers. When the recording sheet S is supplied from the paper feed tray 120 at the same timing as the conveyance of the color toner image by the intermediate transfer belt 106, the color toner image is electrostatically transferred onto the recording sheet S at the secondary transfer nip (secondary Transcription).

  The recording sheet S is conveyed to the fixing device 130 in a state of carrying a color toner image, thermally fixed on the color toner image, and then discharged onto the sheet discharge tray 140.

[1-2] Configuration of Optical Writing Device 100 Next, the configuration of the optical writing device 100 will be described.

  As shown in FIG. 2A, the optical writing device 100 is configured to hold the light source substrate 200 and the lens array 201 by the holding member 202, and the light L emitted from the light source substrate 200 is The light is condensed on the outer peripheral surface of the photosensitive drum 101. The cables and the like for connecting the optical writing device 100 and other devices of the image forming apparatus 1000 are not shown.

  As shown in FIG. 2B, the light source substrate 200 includes a glass substrate 210, a sealing plate 211, a driver IC (Integrated Circuit) 212, a spacer frame 213, and a TFT (Thin Film Transistor) circuit 214.

  The sealing plate 211 is attached to the glass substrate 210 with the spacer frame 213 interposed therebetween. The substrate surface on which the light emitting element 400e is disposed is sealed in a state in which dry nitrogen or the like is sealed so as not to be exposed to the outside air. In order to absorb moisture, a hygroscopic agent may be additionally sealed in the sealing region.

  The driver IC 212 is mounted outside the sealing region of the glass substrate 210, and converts the luminance signal in line units of the image output from the control circuit of the circuit substrate 220 into an analog luminance signal and outputs it.

  The TFT circuit 214 is formed on the surface of the light source substrate 200.

[1-3] Configuration of Lens Array 201 Next, the configuration of the lens array 201 will be described.

  As shown in FIG. 3A, the lens array 201 is a so-called telecentric optical system, and is configured by arranging the G1 lens 301, the diaphragm 302, and the G2 lens 303 in this order from the side closer to the light source substrate 200. The light source substrate 200 is covered by a dust-proof cover (not shown).

  The G1 lens 301 is configured by fixing two spherical plano-convex lenses to both principal surfaces of the flat plate-like member 301b, functions as a biconvex lens, and emits 100 light beams at overlapping positions when viewed from the optical axis direction The light emitted from the element 400e is refracted. As shown in FIG. 3B, the plano-convex lens is a 3-row × 50-column imaging lens 301e arranged in a staggered manner, and the whole is made of a resin material or a glass material.

  The diaphragm 302 is a flat member made of a light shielding material such as resin or metal as shown in FIG. 3C, and corresponds to each of the 150 imaging lenses 301 e in a one-to-one manner. At the positions, 150 through holes 302 h are provided. The light emitted from the light emitting element 400 e passes through the imaging lens 301 e of the G1 lens 301, and then only the part incident on the through hole 302 h by the diaphragm 302 proceeds to the imaging lens 303 e of the G2 lens 303.

  The G2 lens 303 is configured by fixing a plano-convex lens to the main surface of the flat member 303b on the light source substrate 200 side. The imaging lenses 303e, which are plano-convex lenses, are arranged in a 3 × 50 staggered arrangement, and each imaging lens 303e emits light from 100 light emitting elements 400e at overlapping positions when viewed from the optical axis direction. Refract. In FIG. 3A, a set of the G1 lens 301e and the G2 lens 303e, which receive light emitted from the light emitting element 400e from the same position, is collectively called "imaging lens 301e". Further, as shown in FIG. 3B, a group of three imaging lenses 300e arranged in the sub scanning direction from the upstream end e1 to the downstream end e2 is called "imaging lens group 301", and such an imaging lens group Let 301 be the target of the subsequent processing.

[1-4] Configuration of Light Source Substrate 200 Next, the configuration of the light source substrate 200 will be described.

  As shown in FIG. 4A, on the surface of the light source substrate 200, a light emitting element group 400 is disposed inside a circular area 401 corresponding to the individual imaging lenses 301e of the lens array 201 when viewed from the optical axis direction. It is set up. In the light emitting element group 400, the individual light emitting elements 400e are arranged in a matrix of 10 rows by 10 columns. The diameter of the light emitting element group 400 is about 300 μm, and one light emitting element group 400 records a dot corresponding to one pixel.

  “K” in FIG. 4A is a light emitting element group number, and “j” is a number of an imaging lens group corresponding to the light emitting element group. In the light source substrate, a light emitting element group having a light emitting element group number corresponding to a value obtained by subtracting 2 from a multiple of 3 such as k = 1, 4, 7, 10, 13 ... at the upstream end e1 in the sub scanning direction 400 are placed. At the downstream end e2 in the sub scanning direction, a light emitting element group 400 having a light emitting element group number corresponding to a multiple of 3, such as k = 3, 6, 9, 12, 15,.

  FIG. 4B shows the first, second, fourth, seventh,... Second, fifth, eighth,... First pixels in one line of any of the Y, M, C, and K exposure patterns. Indicates the pixel located at the third, sixth, ninth,... As shown in FIG. 4B, the light emitting element group 400 present at the upstream end e1 in the sub scanning direction emits light. The first, fourth, seventh,... Pixels located at the downstream end e2 in the sub scanning direction The third, sixth, ninth,... Pixels which cause the light emitting element group 400 to emit light are separated by one pixel in the sub scanning direction.

[1-5] Configuration of Image Forming Apparatus Main Body FIG. 5 is a block diagram showing a functional configuration of a portion (hereinafter referred to as an image forming apparatus main body) of the image forming apparatus shown in FIG. is there. As shown in the figure, the image forming apparatus main body includes a print job data processing unit 501, an image memory 501m, an image developing unit 502, and exposure pattern memories 503Y, M, C, and K.

(Print job data processing unit 501)
The print job data processing unit 501 takes out page image data (page image data pa1, pa2, pa3 in the figure) from the print job data transmitted from the external terminal, and associates the image data 501m with the respective page numbers. , And each of the page image data pa1, pa2, pa3... Is an object of image formation by the image forming apparatus 1000 shown in FIG.

(Image development unit 502)
The image developing unit 502 applies error diffusion by color separation or dithering to the image data to be processed among the page image data pa1, pa2, pa3... Written in the image memory 501m. , K color exposure patterns YP1, YP2, YP3 ..., MP1, MP2, MP3 ..., CP1, CP2, CP3 ..., KP1, KP2, KP3 ... , And write in exposure pattern memories 503Y, M, C, K.

(Exposure pattern memory 503 Y, M, C, K)
Exposure patterns YP1, YP2,... Obtained by expanding each of the plurality of page image data pa1, 2, 3, 4 ... contained in the job data in the exposure pattern memories 503Y, M, C, K. ..., MP1, MP2, ..., CP1, CP2, ..., KP1, KP2, ... are stored. FIG. 6 shows a part of the exposure pattern for one page. As shown in FIG. 6, the horizontal direction is the main scanning direction, and the vertical direction is the sub-scanning direction. In this exposure pattern, the column bit pattern in which the first row L1 in the main scanning direction is aligned in the sub-scanning direction is the k = 1th light emitting element group of all the light emitting element groups 400 shown in FIG. Supplied to 400 A column bit pattern in which the second row L2 in the main scanning direction is aligned in the sub-scanning direction is supplied to the k = 2nd light emitting element group 400. A column bit pattern in which the third row L3 in the main scanning direction is aligned in the sub-scanning direction is supplied to the k = 3th light emitting element group 400. Similarly, a column bit pattern existing in the order of arrangement in the main scanning direction is supplied to the light emitting element group 400 indicated by k in the next order. The light emitting element group 400 emits light when the value of the supplied column bit pattern is the bit value “1”.

[1-6] Functional Configuration of Optical Writing Device On the circuit board 220 shown in FIG. 2B, a logic circuit for controlling the optical writing device is integrated. The functional configuration of such a logic circuit is shown in FIG. As shown in FIG. 7, the optical writing device includes counter circuits 1 a, b, c, d, e..., Counter circuits 2 a, b, c, d, e. Temperature difference calculation unit 4, main scanning direction distribution processing unit 5, pixel position correction unit 6, processing target memory 6m, line readout unit 7, current DAC group 8, drive circuit blocks 9a, b, c, d,. The selection circuit 10 is configured. The main work performed by the functional configuration of the optical writing device in FIG. 7 is in the sub-scanning direction generated by the thermal expansion of the lens array 201 in the sub-scanning direction for the exposure patterns stored in the exposure pattern memories 503Y, M, C, and K. The correction exposure pattern YA1 corrected based on the magnitude of the shift amount of the exposure position is created in the processing target memory 6m. Here, it should be pointed out that the exposure pattern which is the basis of the correction is the exposure pattern of the image which has already been subjected to the image forming process and which precedes by one page. On the other hand, the exposure pattern YA1 after correction is data of a subsequent page read from this and subjected to an image forming process. The reason is that the thermal expansion of the imaging lens 301e is caused by the image data actually subjected to image formation, and the thermal expansion caused thereby affects printing of the image data of the next page.

(Counter circuit)
The counter circuits 1a, 1b, 1c,... Are the columns of L1, L4, L7... In FIG. 6 in the exposure pattern from the top page of the job data to the page immediately before the page to be processed. It is counted how many bit values of “1” are supplied to the row corresponding to the light emitting element group number k = 1, 4, 7... On the upstream end e1 side in the sub scanning direction.

  On the other hand, the counter circuits 2a, b, c... Are columns existing in the columns L3, L6, L9... Of FIG. 6 in the exposure pattern from the page at the head of the job data to the page immediately before the page to be processed. It is counted how many "1" bit values are supplied to the row corresponding to the light emitting element group number k = 3, 6, 9, ... at the downstream end e2 in the sub scanning direction shown in FIG. 4A. The total count number of column bit patterns corresponding to the light emitting element group numbers k = 1, 4, 7..., 3, 6, 9... In the sub scanning direction upstream end e 1 and downstream end e 2 as a counter circuit Is the expansion amount of the imaging lens 301e corresponding to both sides in the sub-scanning direction when the image formation from the page at the head of the job data to the page immediately before the page to be processed is completed. This is to calculate based on the number of times of light emission of the light emitting element group 400. In the present embodiment, since the imaging lens group 301 for one column is three as shown in FIG. 3B, the expansion in the sub-scanning direction is performed by the imaging lens 301e at both ends of that direction. It is obtained by the amount of expansion. When the number of imaging lenses 301e for one column is four or more, it is necessary to obtain the amount of expansion for each imaging lens 301e except for the imaging lens 301e at the center in the sub scanning direction.

(Time difference calculation unit 3)
The time difference calculation unit 3 calculates bit values “1” at the first, fourth, seventh,... Row positions of the exposure pattern of the immediately preceding page counted by the counter circuits 1a, b, c, d. 1 and the number of bit values “1” at the third, sixth, ninth... Column positions of the immediately preceding page counted by the counter circuits 2a, b, c, d. The time difference between the light emission time by the fourth light emission element group 400 and the light emission time by the third light emission element group 400 is calculated. Here, the counter circuits 1a, b, c, d,..., And the counter circuits 2a, b, c, d,... Continue counting from the first page of the job data to the page immediately before the page to be processed. By doing this, it is assumed that count values c1 and c2 are obtained. Then, assuming that the light emission time of the light emitting element 400e for writing a pixel of 1 dot is tu, the counter circuits 2a, b, c, d ··· from the count value c1 of the counter circuits 1a, b, c, d. The time difference calculation unit 3 obtains the time difference (c1−c2) · tu of the light emission time by subtracting the count value c2 according to ··· and multiplying by tu.

(Temperature difference calculation unit 4)
The temperature difference calculating unit 4 determines the positions of the first, fourth, seventh,..., And the third, sixth, ninth, and so on imaging lenses from the time differences calculated by the time difference calculating unit 3. The temperature difference with the position of 301e is calculated. Assuming that the power of the light emitting element group 400 is a fixed amount P [w], the amount of power generated when light emission is continued by c1 · tu with the power of P [w] is “P [w] · c1 · tu [Second]]. Assuming that the thermal capacity of the light emitting element group 400 and the lens array 201 is C [cal / ° C.], the first, fourth, seventh, and tenth imaging lenses are emitted by the light emitting element group 400 emitting light for c1 · tu [seconds]. The amount of temperature rise T1 occurring in 301e can be calculated, for example, by the following equation (1).

(Expression 1) T1 = 4.19 · P [w] · c1 · tu [seconds] / C [cal / ° C.]
Similarly, when the light emitting element group 400 corresponding to the third, sixth, ninth ... imaging lens 301e emits light for c2 [seconds], the third, sixth, ninth, 12 ...... imaging lens 301e The difference T1−T2 between the temperature rise amount of the light source and the temperature rise amount of the first, fourth, seventh,... Second imaging lens 301e can be derived by the following equation (2).

(Formula 2) T1-T2 = 4.19P [w] (c1-c2) tu / C [cal / ° C]
The temperature difference calculation unit 4 performs the calculation of multiplying the time difference tu · (c1-c2) calculated by the time difference calculation unit 3 by the fixed value 4.19 · P / C according to the equation 2 to obtain a temperature rise. Obtain the quantity difference T1-T2. The temperature difference calculated by the temperature difference calculation unit 4 is a signed numerical value because it is calculated from the subtraction of subtracting T2 from T1. The positive sign of the temperature difference indicates that the temperature of the upstream end e1 of the imaging lens group 301 is higher than the temperature of the downstream end e2. Conversely, the negative sign of the temperature difference indicates that the temperature of the upstream end e1 of the imaging lens group 301 is lower than the temperature of the downstream end e2.

(Main scanning direction distribution processing unit 5)
The main scanning direction distribution processing unit 5 includes an integration circuit 5a, a multiplication circuit 5b, and a comparison circuit 5c, calculates the deflection amount by the curvature of the imaging lens group 301, integrates the deflection amount in the main scanning direction, and integrates the deflection amount. And the comparison of whether or not the integration result according to. The main scanning direction distribution processing unit 5 has a rectangular shape as shown in FIG. 8A, that is, the width of the main scanning direction is “l”, when calculating the deflection amount. And the rectangular shape in which the length in the sub scanning direction is "h". Further, in the rectangular shape of the imaging lens group 301, as shown in FIG. 8B, a set of minute regions having a width in the main scanning direction of ".DELTA.x" and a length in the subscanning direction of "h". Suppose it is a body.

  When a temperature difference of (T1-T2) calculated by the temperature difference calculation unit 4 occurs in the sub scanning direction in such a micro area, each micro area is deformed into a fan shape as shown in FIG. The upstream end e1 in the sub scanning direction is displaced in the sub scanning direction by a minute amount Δy. As shown in FIG. 8D, the sum of the displacement amount Δy in the sub-scanning direction of the fan-shaped small area is the deflection amount of the imaging lens group 301 when heat is radiated from the light source substrate. become.

  The amount of displacement Δy in the subscanning direction of the micro area is based on a value obtained by multiplying the curvature φ of the imaging lens group area in the sub scanning direction by the width dx of the micro area. The curvature φ is a ratio dθ / Δx of the minute fan-shaped central angle dθ shown in FIG. 8B and the minute amount Δx. Assuming that the temperature difference T1-T2 in the sub scanning direction calculated by the temperature difference calculation unit 4 is ΔT, the mathematical expression of Equation 3 below using the thermal expansion coefficient α and the length h of the small rectangular shape in the sub scanning direction It can be calculated by

(Expression 3) φ = α · ΔT / h
The sum of the displacement amount Δy as shown in FIG. 8C is obtained by multiplying the moment of the minute unit in the main scanning direction of the lens array by the curvature φ and the range occupied by one imaging lens group 301 in the main scanning direction It is calculated by performing an integration operation. Since the imaging lens group 301 has a rectangular shape, it is possible to calculate the amount of deflection of the imaging lens group 301 by approximation calculation using a square value of the fixed length l. For example, the amount of deflection can be calculated by the approximate calculation of Equation 4 below.

(Equation ^{4) α · ΔT · l 2} / 2h
In Equation 4, α, l, and h are common to all the imaging lens groups 301, and therefore, the object of integration may be only ΔT. That is, when the integration circuit 5a of the main scanning direction distribution processing unit 5 calculates the deflection amount with the imaging lens group 301 positioned second and subsequent in the main scanning direction as the calculation target, the first to the immediately preceding calculation target The integration of the temperature difference ΔT in the sub-scanning direction calculated for the imaging lens group 301 is calculated, and the multiplication circuit 2b calculates that the integration result is multiplied by α · l ² / 2h, and the first image formation is performed. The deflection amount by the imaging lens group 301 from the lens group 301 to immediately before the calculation target is calculated. Since the temperature difference calculated by the temperature difference calculation unit 4 is a numerical value with a sign, when the temperature difference of the positive sign is continuously calculated at the positions of the plurality of light emitting element groups 400, the integrated value is monotonous To increase. When the temperature difference of the negative sign is continuously calculated at the positions of the plurality of light emitting element groups 400, the integrated value monotonously decreases. When the temperature difference between the positive and negative signs appears with the same degree of frequency, the increase and decrease of the integrated value is small, and a substantially constant value is maintained. Since such an integrated value with a sign is used as the basis of the deflection amount, the deflection amount of the content largely bent at the upstream end e1 in the sub scanning direction is calculated when the integrated value of the temperature difference has a positive sign. . In the case of having a negative sign, the amount of deflection of the content that largely bends at the downstream end e2 in the sub-scanning direction is calculated.

  The comparison circuit 5 c compares the integration result of the deflection amount in the sub scanning direction with the diameter of the pixel corresponding to one light emitting element group 400, and the integration result of the calculated deflection amount corresponds to one light emitting element group 400. If the diameter of the pixel corresponding to 以上 or more is exceeded, the imaging lens group 301 is specified as the correction target, and the pixel position correction unit 6 is notified. FIG. 9B is a main scanning direction in which a temperature difference appears in every other light emitting element group (light emitting element group 400 having light emitting element group numbers 1, 3 and 5) in FIG. 9A. The temperature difference distribution di1 of In the temperature difference distribution di1, the temperature differences DT1, DT2, and DT3 appear in the imaging lens unit 301 with the numbers 1, 3, and 5, respectively. As described above, the lens array 200 is fixed to the optical substrate at the leading end side in the main scanning direction, and the other end side is a free end, so in FIG. The occurrence of the temperature difference DT1 causes the first deflection DB1 to be seen from the leading end in the main scanning direction as shown in FIG. 9C. The imaging lens group 301 of imaging lens group number = 1 is bent by its deflection amount DB1. Further, as a temperature difference DT2 (FIG. 9B) occurs in the imaging lens group 301 of No. 3, the second deflection (deflection of DB2) is the No. 3 as shown in FIG. 9C. It occurs in the imaging lens group 301 of three. As the temperature difference DT3 is generated in the imaging lens group 301 of No. 5, the third deflection (deflection of DB3) is in the imaging lens group 301 of No. 5, as shown in FIG. 9C. Occur. Any of the deflection amounts DB1, DB2 and DB3 generated at the three deflection points shown in FIG. 9C is equal to or exceeds the diameter of the pixel by the light emitting element group 400. I assume. If the amount of bending of each bending portion is equal to or larger than the diameter of the pixel, the amount of bending of each bending portion will not be cut off as a fractional part smaller than the diameter of the pixel. The second and subsequent imaging lens groups 301 are affected by the amount of deflection produced in the other imaging lens groups 301. Since the imaging lens group 301 of No. 3 which is the second bending point is affected by the first bending, the first bending amount DB1 and the second bending as shown in FIG. 9D. The deflection amount (DB1 + DB2) in addition to the amount DB2 is to be deflected. Similarly, as shown in FIG. 9 (d), the imaging lens group 301 of No. 5 which is the third bending point is also affected by the first, second and third bending points, and the amount of bending is The total value of (DB1 + DB2 + DB3) is bent.

  The imaging lens group (the imaging lens group with the number 2) located between the first and second bending points propagates the first bending even if they are not bent by themselves. It will bend by the amount of bending (DB1).

  The deflection amount (DB2) of the second deflection point also affects the imaging lens group (the imaging lens group of No. 4) located between the second and third deflection points, so the first and second The total amount of bending (DB1 + DB2) is bent. After all, as it goes to the free end of the main scanning direction end, it is bent by the added value (DB1 + DB2 + DB3) of the amount of bending from the start side.

(Pixel position correction unit 6)
The pixel position correction unit 6 shown in FIG. 7 calculates the temperature difference in the sub-scanning direction of the imaging lens group 301 for the exposure pattern from the page at the beginning of the job to the page immediately before the processing target. When the image lens group 301 is specified by the main scanning direction distribution processing unit 5, pixel data corresponding to the specified image forming lens group 301 in the exposure pattern of the page to be processed next is corrected. The correction by the pixel position correction unit 6 is divided into correction in the main scanning direction and correction in the sub scanning direction. In the present embodiment, the correction in the main scanning direction is performed by adjusting the light emission amount, and the correction in the sub scanning direction is performed according to the shift of the pixel position. The amount of extension of the imaging lens group in the main scanning direction can be calculated by multiplying the lower end e1 and the upper end e2 by the thermal expansion coefficient. Thus, the amount of expansion is obtained, and the amount of light emitted by the light emitting element group 400 is corrected according to the amount of expansion.

  The correction in the subscanning direction is performed as follows. That is, as shown in FIG. 7, based on the exposure pattern of the page to be processed next, processing of the corrected exposure pattern YA1 in which the positions of some pixel data are shifted as shown in sf1 and sf2 of FIG. It generates in target memory 6m. By providing the processing by the line reading unit 7 generated in this way, correction in the sub-scanning direction is performed.

(Line reading unit 7)
The line reading unit 7 reads pixels (hereinafter, referred to as line pixels) aligned in the main scanning direction among the exposure patterns stored in the processing target memory 6 m and outputs the read pixels to the current DAC group 8.

(Current DAC group 8)
The current DAC group 8 is a digital-controllable variable current source, and from a current DAC (Digital to Analogue Converter) circuit corresponding to the driving circuit blocks 9a, b, c, d,. Become. Each current DAC circuit converts the luminance of each line pixel of the exposure pattern stored in the processing target memory 6m from a digital value to an analog value, and the drive circuit blocks 9a, b, c, d,. It outputs to the 100 light emitting elements 400e placed under it. The light emitting elements 400 e of 10 horizontal rows × 10 vertical rows correspond to one current DAC belonging to the current DAC group 8 and are driven by − current DACs.

(Drive circuit block 9a, b, c, d,...)
The drive circuit blocks 9a, 9b, 9c, 9d,... Correspond to the image forming lens 301e constituting the lens array 201, and the light emitting element group 400, and are constituted by 100 light emitting pixel circuits. . Each light-emitting pixel circuit corresponds to each of the light-emitting elements 400e, and includes a drive TFT and a capacitor. The capacitor of the light emitting pixel circuit accumulates the charge in response to the current application by the current DAC group 8. The drive TFT supplies a drive current corresponding to the accumulated charge to the light emitting element 400e.

(Selection circuit 10)
The selection circuit 10 includes a selection TFT for setting whether to apply the current by the current DAC to the capacitor corresponding to each light emitting element 400e, and a shift register for selectively driving the selection TFT corresponding to the light emitting element 400e. The operations of the reset period, the sample period, and the hold period are performed on the individual light emitting elements 400e. The reset period is a period in which the capacitor of the driving circuit corresponding to the light emitting element 400 e is discharged in a state where the light emitting element 400 e is turned off. The sample period is a period in which charge is accumulated in a capacitor of a driver circuit corresponding to the light emitting element 400 e in a state where the light emitting element 400 e is turned off. The hold period is a period during which lighting of the light emitting element 400 e is continued by the charge stored in the capacitor.

[1-7] Description of Operation of Image Forming Apparatus 1000 The operation of the image forming apparatus 1000 configured as described above will be described.

  First, it is assumed that print job data is sent that causes two or more page image data to be printed in the color mode. In this case, the print job data of the print job data processing unit 501 is received, and each page image data included in the print job data is expanded into exposure patterns YP1, MP1, CP1, KP1 of Y, M, C, K colors.

  Hereinafter, the operation of the optical writing apparatus will be described with reference to the flowcharts of FIGS. 10 (a) and 10 (b) and FIG.

  In the flowcharts of FIGS. 10A and 10B, a variable p is a variable that indicates an individual page in a job. In this flowchart, the variable p is initialized to 1 (step S1), and thereafter, it is determined whether or not correction by the pixel position correction unit 6 is necessary (step S2). Specifically, by determining whether the variable p indicating the page number of the page image data is “1 (indicating that it is page image data of one page)”, the pixel position correction unit 6 needs correction. Decide no. If the page number p is "1" and it is determined that the correction is not necessary (No in step S2), step S3 is skipped and the electrostatic latent image is written based on the exposure pattern of the p-th page . Thereafter, it is determined whether the loop continuation requirement is met or not, whether p is less than the page number n of image data in the job (step S5). If it is less than, the variable p is incremented (step S6), and the process returns to step S2.

  Since the variable p becomes 2 and it is determined that the correction is necessary (Yes in step S2), the temperature difference in the subscanning direction of the exposure pattern of the previous page stored in the exposure pattern memories 503Y, M, C, K , Correct the pixel position of the p-th exposure pattern (step S3).

  The flowchart of FIG. 10B shows the details of the correction procedure of the pixel position in step S3. This flowchart constitutes a subroutine that receives a variable p that specifies page image data to be subjected to image correction, and returns a corrected exposure pattern corresponding to the variable p.

  “I” in this flowchart specifies the imaging lens group 301 to be processed in processing the main scanning direction. As an array variable subscripted with this variable i, there are an expansion amount E (i) and a deflection amount D (i), and E (i) is the temperature increase amount of the upstream end e1 in the i-th imaging lens 301e 6 shows the amount of elongation according to the integrated value of the temperature difference from the temperature rise amount of the downstream end e2. D (i) represents a deflection amount according to the integrated value of the temperature difference between the temperature rise amount of the upstream end e1 and the temperature rise amount of the downstream end e2.

  In this flowchart, after the variable i is initialized (step S11), the extension amount E (i) and the deflection amount D (i) are calculated for the exposure pattern of the previous page for the i-th imaging lens group 301. (Step S12).

  It is the flowchart of FIG. 11 which represented the detail of the process of step S12 of FIG.10 (b). This flowchart constitutes a subroutine that receives the variable i as an argument, and returns the amount of deflection D (i) and the amount of extension E (i) for the i-th imaging lens group 301. T1 (i) in this flowchart is a variable for storing the temperature rise amount at the upstream end e1 of the i-th imaging lens group 301, and T2 (i) is the downstream of the i-th imaging lens group 301 It is a variable for storing the temperature rise amount at the end e2. Sum is a variable for storing the integrated value in the main scanning direction. First, it is determined whether or not the variable i is 1 (step S21). Since no integrated value exists for the first imaging lens group 301 (Yes in step S21), the variable Sum is set to an initial value "0" (step S22). When the variable i is 2 or more and the second and subsequent imaging lens groups 301 are designated (No in step S21), the initialization of the variable Sum is skipped.

  Subsequently, the temperature increase amount based on the lighting time of the first, fourth, seventh,... Light emitting element group 400 counted by the counter circuits 1a, b, c, d. (Step S23), and the temperature increase amount based on the lighting time by the third, sixth, ninth... Light emitting element group 400 counted by the counter circuits 2a, b, c, d. , T2 (i) (step S24). “K” in the Σ operator in steps S23 and S24 is a variable that specifies an arbitrary line of any page. “M” is the number of lines included in one page. The Σ operator is the first, fourth, seventh, and so on bits from the first line of the first page of the job to the last line (m · (p−1)) of the immediately preceding page, p−1. It means the operation of adding the bit values of "1" in the position.

  If T1 (i) and T2 (i) are calculated, the integrated value Sum is updated by adding the integrated value Sum to the value obtained by subtracting T2 (i) from T1 (i) (step S25). , And Sum are calculated and set to D (i) (step S26). Further, the expansion amount in the main scanning direction based on Sum is calculated and set to E (i) (step S27). The deflection amount D (i) and the elongation amount E (i) thus obtained are set as return values, and the process returns to the flowchart of FIG. By this return, the process shown in the flowchart of FIG. 10B is restarted from the step following step S12 (step S13).

  In step S13, the displacement amount in the sub-scanning direction of the pixels formed on the peripheral surfaces of the photosensitive drums 101Y, M, C, and K by the light emitting element group 400 according to the deflection amount D (i) is at least the diameter of one pixel. Determine if it will be If it is equal to or larger than the diameter of the pixel (Yes in step S13), the x coordinate of the pixel data (bit of value "1") corresponding to the center position of the imaging lens 301e in the exposure pattern is the elongation amount E (i) Accordingly, the pixel value is corrected (step S14), and the y-coordinate of the same pixel data is updated to the shifted value according to the deflection amount D (i) (step S15).

  The correction of the pixel value in step S14 is performed, for example, by obtaining a correction value by multiplying the pixel value by a correction coefficient according to the expansion amount E (i) obtained in advance.

  Subsequently, in step S16, it is determined whether to continue the loop for steps S12 to S15. Specifically, it is determined whether or not the variable i is smaller than the number Hm of imaging lens groups in the main scanning direction. If the value is smaller (Yes at step S16), the variable i is incremented (step S17), the adjacent imaging lens group 301 is set as a processing target, and the process returns to step S12. By repeating the processing in steps S12 to S16, each of the imaging lens groups 301 aligned in the main scanning direction in the lens array 201 is subjected to the calculation of the amount of deflection and the calculation of the amount of elongation in steps S14 and S15.

  The operation in the case where the lens array 201 has the temperature difference distribution di11 as shown in FIG. 12 will be described.

  For the imaging lens group 301 with i = 1, a small temperature difference (about -2) in the negative direction is calculated. Since the position of i = 1 is close to the fixed position and Sum = 0, a small temperature difference in the negative direction is added to Sum, and the amount of deflection based on this small temperature difference is calculated. Since the integrated value of the temperature difference is small, the deflection amount D (1) calculated according to the integrated value becomes a small value (step S26 in FIG. 11). Since it is determined that the deflection amount D (1) is smaller than the diameter of the pixel formed by the light emitting element group 400 (No in step S13 of FIG. 10B), the pixel data shift is not performed.

  For the imaging lens group 301 with i = 2, a large temperature difference (+6) in the positive direction is calculated. At the time of setting i = 1, since Sum is a temperature difference in the negative direction, a temperature difference in the positive direction is obtained in Sum (2) (step S25 in FIG. 11). Since the integrated value of the temperature difference is small, the amount of deflection D (2) calculated according to the integrated value becomes a small value (step S26 in FIG. 11). Since it is determined that the deflection amount D (i) is smaller than the diameter of the pixel formed by the light emitting element group 400 (No in step S13 of FIG. 10B), the position shift of the pixel data is not performed.

  Since a small temperature difference in the negative direction is calculated at the position of i = 3, the integrated value Sum is reduced, but a temperature difference in the positive direction is calculated at the position of i = 4 and i = 5. The integrated value monotonously increases, and Sum (5) becomes approximately "+10" as shown in the main scanning direction distribution di11 of the integrated value. However, as shown in the main scanning direction distribution di12 of the deflection amount, the deflection amount D (5) based on Sum (5) is less than the diameter of the pixel formed by the light emitting element group 400 (FIG. No) in step S13)), position shift of pixel data is not executed.

  As the temperature difference (+4) of a relatively large value is calculated in the imaging lens group 301 of i = 6, as shown in the main scanning direction distribution di11 of the integrated value, Sum (6) is relatively high. It becomes a value (step S25 of FIG. 11).

  Here, as shown in FIG. 13A, the y-coordinate of the central position MP3 of the imaging lens 301e where the imaging lens group 301 is curved along the curve cv1 and the imaging lens group number = 6 is the original position It is assumed that it is deviated from Oc3 by dy. As the predicted value of this dy, the amount of deflection D (6) based on the integrated value of the temperature difference of the imaging lens group 301 from No. 1 to No. 5 is calculated, and the amount of deflection D (6) becomes a correspondingly large value. Thus, the deflection amount D (6) calculated based on Sum (6) is determined to be equal to or larger than the diameter of the pixel corresponding to the light emitting element group 400 (Yes in step S13 of FIG. 10B).

  The center positions MP1, MP2, MP3 of the imaging lens 301e of the imaging lens group number = 6 correspond to the bit values r61, r62, r63 in the exposure pattern in FIG. 13B. Since the deflection amount exceeding the diameter of the pixel group is calculated, as shown in FIG. 13C, the positions of the bit values r61, r62, and r63 are shifted by one pixel in the Y axis negative direction (downward direction).

  The temperature difference calculated at the position of imaging lens group number = 7, = 8 in FIG. 12 is very small, the integrated value Sum does not change, and the deflection calculated at the position of imaging lens group number = 7, 8 The quantities D (7), D (8) also exceed the diameter of the pixel. Therefore, the correction is performed as in the case of the position of number = 6 (steps S14 and S15).

  Thereafter, when the temperature difference in the negative direction is made in the imaging lens group 301 of No. 9, the integrated value becomes low, and the deflection amount D (9) falls below the threshold value. In the imaging lens group 301 of No. 10, a low temperature difference in the positive direction is calculated, and the amount of deflection is less than the diameter of the pixel. However, when the temperature difference in the positive direction is calculated for the imaging lens unit with the number = 11 (step S26), the deflection amount D (11) exceeds the diameter of the pixel (Yes in step S13) Is done.

  The process of FIG. 10B is performed for all the imaging lens groups 301, and when the variable i reaches the number Hm of imaging lens groups in the main scanning direction (No in step S16), the processing target memory 6m is Since an exposure pattern after correction is obtained, the process returns to the flowchart of FIG. At the time of return, the process is resumed from the next step (step S4) of step S3.

  In step S4, the line reading unit 7 reads the correction page image data in which the position of the pixel data has been corrected, line by line, and causes the individual light emitting elements 400e in the light emitting element group 400 to emit light. Execute writing to M, C, K. Thereafter, it is determined whether or not the loop continuation requirement that the variable p is less than the page number n in the job is satisfied (step S5). If it is less than the variable p is incremented (step S6) and the process returns to step S2. While the process of steps S2 to S6 is repeated while step S5 is determined to be Yes, the exposure pattern of each of the plurality of pages of image data constituting the job data is subjected to the process of steps S3 to S4. .

[1-8] Summary The temperature difference calculation unit 4 calculates the thermal expansion of the lens array 201 according to the number of “1” bit values calculated by the counter circuits 1a, b, c, d, 2a, b, c, d. The deflection amount in the sub-scanning direction in the case of deflection is calculated, and the main scanning direction distribution processing unit 5 specifies the imaging lens group 301 to be corrected from the distribution of the temperature difference of the deflection amount in the main scanning direction. In this way, it is possible to identify the imaging lens 301e which is shifted by one or more pixels by the accumulation of the curvature in the main scanning direction with appropriate accuracy and to perform appropriate correction.

Second Embodiment
[2-1] Overview In the first embodiment, using the number of bit values “1” of the column bit pattern in the exposure pattern, the temperature at the first, fourth, seventh, tenth,... The difference in the amount of temperature increase in the third, sixth, ninth, twelfth,... Order imaging lens 301 e is calculated, but in the second embodiment, the difference in the amount of temperature increase in the sub scanning direction is calculated Implement an improvement using the amount of light received by the sensor. FIG. 14A and FIG. 14B show a cross-sectional view and a plan view of the lens array 201 to which the light receiving sensor 304 is attached. The light receiving sensor 304 in FIGS. 14A and 14B includes a photodiode (PD) and a charge coupled device (CCD), is a portion covered by the diaphragm 302, and is close to the imaging lens 301e. It is provided in the position.

[2-2] Configuration of Optical Writing Device in Second Embodiment FIG. 15 is a block diagram showing a functional configuration of the optical writing device according to the second embodiment.

  The following points are different as compared with the functional configuration of the optical writing device shown in the first embodiment. That is, in the optical writing device of the second embodiment, components (counter circuits 1a, b, c, d,..., 2a, b,..., 2a, b,. c, d · · · · ·, the time difference calculating section 3, the temperature difference calculating unit 4, there is no main scanning direction distribution processing unit 5), instead, as a target quantity of received light by the light receiving sensor 304, calculates the temperature difference , Components for processing (counter circuits 11a, b, c, d, ..., 12a, b, c, d, ..., time difference calculation unit 13, temperature difference calculation unit 14, main scanning direction The difference is that the distribution processing unit 15) is present.

  The counter circuits 11a, b, c..., The counter circuits 12a, b, c... Count the number of times of light emission of the light emitting element group 400, like the counter circuits 1a, b, c. The difference is the subject of counting. The counter circuits 1a, b, c..., The counter circuits 2a, b, c... Count the number of bit values “1” of the column bit pattern for the exposure pattern for which the image formation for one page is completed. The counter circuits 11a, 11b, 11c,... Are positioned in the vicinity of the imaging lens group k = 1, 4, 7,... The imaging lens 301e located on the upstream end e1 side in the sub scanning direction shown in FIG. The number of times of detection of the amount of light received by the light receiving sensor 304 is counted. Similarly, the counter circuits 12a, b, c... Are in the vicinity of the imaging lens group k = 3, 6, 9,..., The third imaging lens group 301e located on the upstream end e2 side in the sub scanning direction shown in FIG. The number of times of detection of the amount of light received by the light receiving sensor 304 located is counted.

  The time difference calculation unit 13 calculates the time difference between the light emission time of the first, fourth, seventh light emitting element group 400 and the light emitting time of the third light emitting element group 400. The difference from the time difference calculation unit 3 is a target of calculation. Specifically, while the time difference calculation unit 3 calculates the time difference from the number of bit values "1" in the column bit pattern, the time difference calculation unit 13 calculates the counter circuits 11a, b, c, d, ... The number of times of detection by the light receiving sensor 304 adjacent to the first, fourth, seventh,... Imaging lens group 301 counted by ... and counted by the counter circuits 12a, b, c, d. The light emitting time by the first, fourth, seventh light emitting element group 400 from the number of times of detection of the received light amount by the light receiving sensor 304 corresponding to the third, sixth, ninth ... imaging lens group 301; The time difference with the light emission time of the ninth light emitting element group 400 is calculated.

  The temperature difference calculation unit 14 determines the positions of the third, sixth, ninth image forming lenses 301 e and the first, fourth, seventh image forming lenses 301 e from the time differences calculated by the time difference calculating unit 3. Calculate the temperature difference.

  Like the main scanning direction distribution processing unit 5, the main scanning direction distribution processing unit 15 positions the third, sixth, ninth ... imaging lens 301e, and the first, fourth, seventh ... imaging lens 301e, and The deflection amount due to the curvature of the imaging lens group 301 is calculated from the temperature difference in the above, and the integration of the deflection amount in the main scanning direction and the comparison of the integration result with the threshold value are executed. By this comparison, the imaging lens group 301 whose integration result is determined to exceed the threshold is specified as the correction target. The pixel position correction unit 6 shifts the position of the pixel data corresponding to the imaging lens group 301 thus identified in the sub-scanning direction.

Third Embodiment
[3-1] Third Embodiment The third embodiment discloses a configuration in which the processing by the main scanning direction distribution processing unit 5 shown in the first embodiment and the processing by the light receiving sensor 304 are used in combination. In this embodiment, in the present embodiment, among the light receiving sensors 304 attached to the lens array 201, the imaging lens group closest to the fixed end, that is, the imaging lens group with number 1 in FIG. The detection value of the light receiving sensor attached to the reference numeral 301 is used as a reference value in positional deviation correction.

[3-2] Configuration of Third Embodiment FIG. 16 is a diagram showing a functional configuration of the optical writing device according to the third embodiment. Comparing FIG. 16 with the functional configuration of the optical writing device shown in FIG. 7 of the first embodiment, the main scanning direction distribution processing unit 5 is replaced with the main scanning direction distribution processing unit 20, and the pixel position correction unit 6 is The difference is that the geometry correction unit 21 is replaced.

(Main scanning direction distribution processing unit 20)
Similar to the main scanning direction distribution processing unit 5, the main scanning direction distribution processing unit 20 integrates the calculated temperature difference for each of the plurality of imaging lens groups 301 aligned in the main scanning direction, a multiplication circuit, and a comparison Including circuits. The difference from the main scanning direction distribution processing unit 5 is an object of comparison by the comparison circuit. Specifically, while the comparison circuit of the main scanning direction distribution processing unit 5 compares the deflection amount with the diameter of the pixel corresponding to the light emitting element group 400, the comparison circuit of the main scanning direction distribution processing unit 20 The comparison of the integrated value of the temperature difference calculated for the sub-scanning direction with the threshold value is performed. Threshold here is a diameter of a pixel by the light emitting element group 400 is divided by the coefficient (α · l ² / 2h) for deflection amount calculation. That is, in the equation for calculating the amount of deflection, α · l ² / 2h is a fixed value, and the variable value is only the integrated value. Therefore, the diameter of the pixel by the light emitting element group 400 is a coefficient for calculating the amount of deflection ( If the value divided by α · l ² / 2h) is used as a threshold value for comparison with the integrated value of the temperature difference, a comparison equivalent to the main scanning direction distribution processing unit 5 can be performed by simple calculation. . By this comparison, the imaging lens group 301 whose integrated value exceeds the threshold is specified as the correction target.

(Geometry correction unit 21)
The geometric correction unit 21 performs geometric correction based on the geometric characteristics of the light receiving sensor 304. Geometric correction is performed through procedures such as determination of a coordinate conversion equation, rearrangement of pixels based on the coordinate conversion equation, and interpolation of pixels. When the optical writing device 100 is considered to be one optical system having the light receiving sensor 304, such optical system may include internal distortion related to the mechanism of the light receiving sensor 304, and the position and posture of the imaging lens group 301 and the light receiving sensor 304. There is an external distortion about. A change in position and posture due to the imaging lens group 301 receiving radiant heat from the light emitting element group 400 can be said to be an external distortion.

  In general geometric correction, parameters relating to internal distortion and external distortion are determined from a reference point, and based on these parameters, a coordinate transformation equation for transformation of an input image is generated. In this embodiment, the light receiving sensor 304 located in the vicinity of the imaging lens group 301 near the fixed end is used as a reference point, and the light receiving sensor 304 located in the vicinity of the imaging lens group 301 specified by the scanning direction distribution processing unit 20. The parameters relating to the internal strain and the external strain are generated according to the detection values of the light receiving sensor 304 which is the reference point and the light receiving sensor 304 which is the observation point, with the observation point as an observation point. Then, the amount of positional deviation for the pixel group corresponding to the imaging lens group specified by the main scanning direction distribution processing unit 20 is calculated by the coordinate conversion formula based on such parameters, and the amount of positional deviation is corrected.

[3-3] Summary In the optical writing device configured as described above, in the exposure pattern, the pixel position corresponding to the third, sixth, ninth ... imaging lens 301 e, the 1, 4, 7th ... imaging The temperature difference in the sub-scanning direction is calculated from the number of bit values "1" of the pixel position corresponding to the lens 301e, and the imaging lens group 301 to be subjected to geometric correction is calculated based on the integrated value of this temperature difference. Since the identification is performed, the correction accuracy can be enhanced while reducing the amount of processing applied to the detection value of the light receiving sensor.

(Modification 1)
The main scanning direction distribution processing unit 5 in the first embodiment calculates the integration of the temperature difference from the fixed position between the lens array and the light source substrate as processing for the temperature difference distribution in the sub scanning direction. . On the other hand, in this modification, the amount of change as to how the temperature difference in the sub scanning direction changes in the main scanning direction is calculated and used for determination of necessity of correction. The amount of change in the main scanning direction as described above is the difference between the temperature difference in the sub scanning direction for the imaging lens group 301 to be processed and the temperature difference in the sub scanning direction for the adjacent imaging lens group 301. . The fact that the absolute value of the amount of change is large means that the lens array 201 is greatly protruded in the corresponding imaging lens group 301. If the absolute value of the amount of change exceeds a threshold value corresponding to the diameter of the pixel corresponding to the light emitting element group 400, it is assumed that the imaging lens group 301 is bent to such an extent that the diameter of the pixel is exceeded. Make corrections to the pattern.

  In order to calculate the amount of change in the temperature difference in the sub-scanning direction, in this modification, in the optical writing device having the functional configuration shown in FIG. 7, the main scanning direction distribution processor 5 performs the processing shown in the flowchart in FIG. Run. “Ds” in this flowchart is a variable for storing the amount of change in temperature difference from the adjacent imaging lens group 301. “Prev” is a variable for storing the difference between the temperature difference of the i-th imaging lens group 301 and the temperature difference of the i−1-th imaging lens group 301 for calculation of the variable ds. is there.

  First, in step S30, from the count values for the first, fourth, seventh pixel positions calculated by the counter circuits 1a, b, c, d... Shown in FIG. .., D... By subtracting the count value for the third, sixth, ninth... In the following step S31, T1-T2 is calculated by performing the approximate calculation shown in the first embodiment based on the difference c1-c2 of the count value. Step S32 is a judgment as to whether or not the variable i is "1". If the variable i is “1”, there is no temperature difference in the sub-scanning direction with respect to the immediately preceding imaging lens group 301, so T1-T2 is set to ds (step S33) and set to the variable Prev At step S35, the processing of this flowchart is ended. If the variable i is not "1", the value obtained by subtracting the variable Prev from T1-T2 is set to ds (step S34), and T1-T2 is set to the variable Prev (step S35). Finish the process.

  By the above processing, the main scanning direction distribution di21 of the variation of the temperature difference as shown in FIG. 18 is obtained. In the main scanning direction distribution di21, for the position of i = 1, since the immediately preceding imaging lens group 301 does not exist, the temperature difference calculated for itself is set as the variable Prev, and the process is ended. For the imaging lens group 301 with i = 2, since the temperature difference for the imaging lens group 301 with i = 1 is set to the variable Prev, the temperature difference set to Prev from the temperature difference of itself Subtraction is performed to reduce the As a result, the obtained change amount ds2 is a positive value and a correspondingly high value (+8), and the difference from the previous value exceeds the threshold value.

  For the position of i = 3, a relatively large amount of change ds3 in the negative direction is calculated. Even if the temperature difference at the position of i = 2 set to Prev is reduced, it still falls below the negative direction threshold.

  If an imaging lens group 301 having a large amount of change in temperature difference from the adjacent imaging lens group 301 is identified, this imaging lens group 301 is set as the start point of the section in which the deflection amount becomes large. If an imaging lens group 301 in which the amount of change in temperature difference from the adjacent imaging lens group 301 is large and the sign of the difference is reversed is identified, a section in which the amount of deflection of this imaging lens group 301 becomes large End point of In this way, when the section in which the amount of deflection increases is identified, the position shift of the pixel data corresponding to the imaging lens 301e belonging to the section is executed.

(Modification 2)
In the first embodiment, the processing in the main scanning direction performed by the main scanning direction distribution processing unit 5 may be simplified. Specifically, among the exposure patterns shown in FIG. 6, the number of bit values “1” at column positions L1, L2, L3, L4, L5... Corresponds to the counter circuits 1a, b, c in FIG. , D,..., 2a, b, c, d,. When the temperature difference calculation unit 4 calculates the temperature difference in the sub-scanning direction of each imaging lens group 301 based on these count values, the main scanning direction distribution processing unit 5 according to this modification The deflection amount for each imaging lens group 301 is calculated from the above and compared with the diameter of the pixel. The pixel data corresponding to the imaging lens group 301 whose deflection amount calculated in this way becomes equal to or larger than the diameter of the pixel is specified as the correction target. For example, as shown in FIG. 19, when the temperature difference is calculated for each imaging lens group 301, the main scanning direction distribution processing unit 5 compares the temperature difference with a threshold as a simplified process. In the example of FIG. 19, in the imaging lens group 301 at the position of the imaging lens group number = 2, 5, 9, 11, 14, the temperature difference exceeds the threshold, so imaging at the imaging lens group 301 at such position The coordinates of the pixel corresponding to the center position of the lens 301e are corrected.

(Modification 3)
In the above embodiment, the integrated value of the temperature difference in the main scanning direction is calculated for each of the imaging lens groups 301, and the position where the integrated value is equal to or greater than the threshold value is set as the correction target. On the other hand, in this modification, linear interpolation is performed on the imaging lens group 301 located therebetween.

  Such linear interpolation is performed as follows. The detected values by the light receiving sensor 304 provided in the corresponding imaging lens group 301 are plotted in a coordinate system in which the number of the imaging lens group 301 is x coordinate and the temperature difference is y coordinate, and these x coordinates y Determine the interpolation curve passing through the coordinates, the coefficients of the interpolation formula defining the interpolation straight line, and the constants. If an interpolation formula is obtained by determining the coefficient and the constant, the number of the imaging lens group 301 which is not a target of detection by the light receiving sensor 304 is substituted into the interpolation formula, and the interpolation value at that number is calculated. Do.

  In FIG. 20A, when the amount of shift is detected in the imaging lens group 301 of No. 5 and No. 9, the numbers of these imaging lens groups 301 are taken as X coordinates, and the detected amount of deviation is taken as An equation defining the interpolation straight line ln1 passing through the position as the Y coordinate is determined. By substituting the imaging lens group numbers not detected by the light receiving sensor, that is, the imaging lens numbers 6, 7, 8 into the equation defining the interpolation straight line ln1, the interpolation values ip1, ip2, ip3 are obtained. You may get it.

(Modification 4)
In the second embodiment, the main scanning direction distribution processing unit 15 calculates the deflection amounts of the upstream end e1 and the downstream end e2 of the imaging lens group 301 in the main scanning direction based on the temperature difference in the sub scanning direction. However, the amount of deflection calculated in this way is only a predicted value. It is difficult to improve the correction accuracy when correcting the position of the pixel data because the actual measurement value of the deviation is not taken into consideration. On the other hand, in the present modification, the accuracy is improved by using the actual measurement value of the light receiving sensor 304.

  Specifically, in this modification, the correction value shown in the third embodiment, that is, the correction value calculated by the calculation by the geometric correction, and the deflection amount calculated based on the temperature difference in the sub-scanning direction Calculate the error. Such an error is used to correct the deflection amount calculated by the main scanning direction distribution processing unit 15.

  It is assumed that the main scanning direction distribution di41 of the temperature difference as shown in FIG. 20 (b) is obtained by the temperature difference calculation unit 4. By integrating the power in the main scanning direction distribution (the temperature difference in the sub scanning direction of the imaging lens group 301), a main scanning direction distribution di42 of the deflection amount as shown in FIG. 20C can be obtained. In this modification, as shown in FIG. 20D, correction values calculated by geometric correction of the geometric correction unit 21 are plotted as measured values ob1 and ob2 in the main scanning direction distribution di42 of the deflection amount in the sub scanning direction. Do. Then, interpolation is performed between the actual measurement positions ob1 and ob2 with the interpolation straight line ln1. Then, it becomes clear that the errors er1, 2, 3, 4 and 5 exist in the main scanning direction distribution of the deflection amount and the measured value. By using the error obtained in this manner for the correction of the deflection amount calculated by the main scanning direction distribution processing unit 15, the accuracy of the calculation processing by the main scanning direction distribution processing 15 can be enhanced.

(Modification 5)
In the optical writing device, a drive circuit for current drive may be disposed on the same light source substrate as the light emitting element group 400. FIG. 21A shows drive circuits 31, 32 and 33 disposed on the same light source substrate as the light emitting element group 400.

  The drive circuits 31, 32, 33 are arranged at a distance ds1 from the light emitting element group 400 in the sub scanning direction. Then, a drive cycle, a current amount, and the like of a drive circuit of the light emitting element 400e are set as drive conditions, and a drive current is applied to the light emitting element group 400 according to the drive condition. In this modification, the amount of temperature rise due to heat generation of these drive circuits is determined, and this is multiplied by a coefficient according to the reciprocal of the distance ds1 between the light emitting element group 400 and the drive circuits 31, 32 and 33. The amount of temperature rise due to heat generation is calculated, and this is added to the temperature difference in the sub-scanning direction.

(Modification 6)
In the third embodiment, the light receiving sensors 304 are provided for all the imaging lenses 301 e, but in the present modification, one light receiving sensor 305 is provided for each imaging lens group. Specifically, as shown in FIG. 21B, in the imaging lens group 301, among the three imaging lenses 301e aligned in the sub-scanning direction, one located at the center (3 · i−1 The light receiving sensor 305 is provided on the imaging lens. The amount of deflection in the sub-scanning direction is calculated from the difference between the amount of light received by the light receiving sensor and the amount of light received by the reference sensor to correct the pixel position of the exposure pattern, and the light emission timing by the light emitting element 400e in the light emitting element group 400 It may be used for the correction of In addition, the light emission amount of the light emitting element 400e may be changed.

(Modification 7)
Under the premise that the power supplied to the light emitting element 400e per unit time is constant and the temperature rise amount is simply proportional to the lighting time, the temperature rise at the upstream end e1 and the downstream end e2 of the imaging lens group 301 in the sub scanning direction The amount was calculated. The temperature rise amount at the upstream end e1 and the downstream end e2 may be calculated by calculating the power consumption of the drive circuit blocks 9a, 9b, 9c, 9d,. Specifically, the power consumption due to the capacitor of the drive circuit blocks 9a, 9b, 9c, 9d repeatedly charging and discharging current is calculated based on the capacity, time constant, and potential difference of the capacitor. , May be the basis of the amount of temperature rise. Alternatively, integral calculation based on the current waveform of the discharge current discharged by the capacitor may be performed to calculate the power consumption by the drive circuit.

(Modification 8)
The temperature difference calculation unit 4 and the main scanning direction distribution processing unit 5 shown in the first embodiment, the main scanning direction distribution processing unit 15 shown in the second embodiment, and the main scanning direction distribution processing unit shown in the third embodiment The geometric correction unit 21 may be configured by a logic operation circuit or may be configured by a ROM operation circuit. That is, the combination of a plurality of non-operators is associated with the address, and the operation result by those operands is stored in the storage area corresponding to the address. Then, various operations may be executed by reading out and outputting the operation result stored in each storage area according to the combination of the operands to be input.

  Further, the temperature difference calculation unit 4 and the main scanning direction distribution processing unit 5 shown in the first embodiment, the main scanning direction distribution processing unit 15 shown in the second embodiment, and the main scanning direction distribution processing shown in the third embodiment The unit 20 and the geometry correction unit 21 may be configured by a look-up table circuit. That is, a combination of a plurality of operands is associated with an index, and the operation result of the operands is stored in the record area corresponding to the index. Then, various operations may be executed by reading out and outputting the operation result stored in each record area according to the combination of the operands to be input.

(Modification 9)
In all the embodiments and all the modifications, the correction according to the positional deviation of the imaging lens group 301 is performed by executing the position shift of the pixel data in the exposure pattern, but the pixel position in the exposure pattern is corrected Instead, the correction according to the positional deviation of the imaging lens group 301 may be performed by advancing or delaying the lighting timing of the light emitting element 400 e by the number of lines according to the deflection amount. When the correction of lighting timing is set as the correction method, is the timing (the timing of the hold period) to light the light emitting element 400e in the light emitting element group 400 specified by the main scanning direction distribution processing unit 5 as the correction target? By delaying, the deviation amount in the main scanning direction and the sub scanning direction of the light emitting element group 400 is corrected.

(Other modifications)
As mentioned above, although this invention was demonstrated based on embodiment, it is needless to say that this invention is not limited to the above-mentioned embodiment, The following modifications can be implemented.
(1) In the above embodiment, although the main scanning direction distribution of the temperature difference in the sub scanning direction is calculated for each optical writing device 100 for forming toner images of Y, M, C, and K colors, the present invention is not limited thereto. It is needless to say that the invention is not limited to the above, and instead of this, the following may be performed.

Of the four optical writing devices 100 that form toner images of Y, M, C, and K colors, when there is an optical writing device 100 in which the deflection of the lens array 201 is similar, only one of the optical writing devices 100 is detected. Then, the main scanning direction distribution of the temperature difference in the sub scanning direction may be calculated, and the density reduction may be suppressed for the other optical writing devices 100 by using the main scanning direction distribution.
(2) The counter circuits 1a, b, c, d, 2a, b, c, d, the time difference calculation unit 3, the main scanning direction distribution processing unit 5, and the pixel position correction unit 6 are present in the optical writing device It may be present in the forming device body.
(3) In the above embodiment, although the case where the image forming apparatus 1000 is a tandem type color printer has been described as an example, it goes without saying that the present invention is not limited to this. It may be a printer. Also, the same effect can be obtained by applying the present invention to a copying machine equipped with a scanner, a facsimile machine equipped with a facsimile communication function, or a multi-function peripheral (MPF: Multi-Function Peripheral) having these functions. it can.

  Although the image forming apparatus 1000 receives a print job from an external terminal and forms an image, a scan unit (not shown) of the image forming apparatus 1000 optically reads an original, and an operation unit (not shown) By accepting an operation from the user, the image formation may be performed on the generated print job.

  The image forming apparatus according to the present invention is useful as an apparatus for suppressing deterioration in image quality caused by distortion of a microlens array mounted on a line optical type optical writing apparatus.

1a, b, c, d ······ Counter circuit 2a, b, c, d ····························································· Counter circuit 2 time difference calculation unit 4 temperature difference calculation unit 5 main scanning direction distribution processing unit 5a integration circuit 5b multiplier 5c Comparison circuit 6 Pixel position correction unit 6m Process target memory 7 Line readout unit 8 Current DAC group 9a, b, c, d ··· Drive circuit block 10 Selection circuit 11 Sensor value processing unit 15 Main scanning direction distribution processing unit 15a Integration circuit 15b Multiplication circuit 15c Comparison circuit 101Y, M, C, K Photosensitive drum 102Y, M, C, K Charging device 103Y, M, C, K Development device 104Y, M, C, K Primary transfer charger 105Y, M, C, K cleaning device 200 light source substrate 201 lens array 201 e imaging lens 202 holding member 210 glass substrate 211 sealing plate 21 Driver IC
213 spacer frame body 214 TFT circuit 220 circuit board 301b flat plate member 301e imaging lens 302h through hole 303b flat plate member 303e imaging lens 304 light receiving sensor 305 light receiving sensor 400 light emitting element group 400e light emitting element 503Y, M, C, K exposure Pattern memory 1000 Image forming apparatus

Claims (13)

An optical writing device including a lens array in which a plurality of imaging lens groups are disposed at a plurality of positions in a main scanning direction, a light source substrate on which a plurality of light emitting element groups are disposed, and supporting members that support the lens array and the light source substrate And
Each of the imaging lens groups is constituted by a plurality of imaging lenses arranged in the sub scanning direction,
A light emitting element group facing each of the plurality of imaging lenses is a set of imaging lenses belonging to the same imaging lens group when the light emitting operation is repeated, and is disposed at a different position in the sub scanning direction Calculating means for calculating a temperature difference caused by
According to the temperature difference distribution of how the temperature difference in the sub scanning direction in each of the plurality of imaging lens groups is distributed at a plurality of positions in the main scanning direction, the displacement amount in the sub scanning direction is the diameter of the pixel Specifying means for specifying an imaging lens group having the above characteristics;
And correction means for performing correction regarding positional deviation of a plurality of pixel data following the pixel data for which the light emitting element group corresponding to the specified image forming lens group is caused to perform the light emission operation. An optical writing device characterized by The identification means is
Of the plurality of positions in the main scanning direction in the lens array, the integration of the temperature difference calculated by the calculating means from the position closest to the fixed position where the light source substrate and the lens array are fixed to the target position Execute the process of performing for each of a plurality of positions in the main scanning direction,
The optical writing device according to claim 1, wherein the displacement amount in the sub scanning direction of the lens array at the position is calculated based on the integration value obtained at one position in the main scanning direction by the integration. The calculation means
Among the plurality of imaging lenses constituting the imaging lens group, the pixel position corresponding to the imaging lens located at the upstream end in the sub scanning direction and the pixel position corresponding to the imaging lens located at the downstream end Calculate how much light emission by pixel data corresponding in position continues from the start of the job, and calculate the temperature difference in the sub-scanning direction of the imaging lens group based on the difference of the duration by the calculation The optical writing device according to claim 1, The calculation means
Among the image data to be subjected to image formation, a row position corresponding to the imaging lens located at the upstream end in the sub scanning direction and a row position corresponding to the imaging lens located at the downstream end The multiple counters that count how many pieces of pixel data that cause the light emission are arranged,
The optical writing device according to claim 3, wherein a duration of light emission by the pixel data is calculated based on count values of the plurality of counters. Among the plurality of imaging lenses constituting the imaging lens group, light receiving sensors are attached to those located at the upstream end in the sub scanning direction and those located at the downstream end,
The calculation means includes a light receiving sensor attached to a position corresponding to an imaging lens located at the upstream end in the sub scanning direction, and a light receiving sensor attached to a position corresponding to an imaging lens located at the downstream end. , And includes a plurality of counters that count how many times light emission by positionally corresponding pixel data is performed from the start of the job,
The optical writing device according to claim 3, wherein a duration of light emission by the pixel data is calculated based on count values of the plurality of counters. The calculation means
Among the plurality of imaging lenses constituting the imaging lens group, a light emitting element group corresponding to the imaging lens located at the upstream end in the sub scanning direction, and a light emitting element group corresponding to the imaging lens located at the downstream end Calculation of how much power consumption occurs from the start of the job is performed based on pixel data that is the basis of light emission by the light emitting element group, and based on the difference in power consumption by the calculation, The optical writing device according to claim 1, wherein a temperature difference in the sub scanning direction is calculated. In the light source substrate, in the vicinity of each light emitting element group, a driving circuit for driving the light emitting element group is provided.
The calculation means
According to the drive condition of the drive circuit, the temperature rise amount of the drive circuit is calculated, weighting according to the reciprocal of the distance from the drive circuit to the light emitting element group is performed, and added to the temperature difference in the sub scanning direction The optical writing device according to any one of claims 1 to 6, wherein Each of the plurality of imaging lens groups is provided with a light receiving sensor for detecting a relative positional deviation between the light source substrate and the lens array,
When the image forming lens group whose displacement amount in the sub scanning direction exceeds the diameter of the pixel is specified by the specifying unit:
The correction means executes correction regarding positional deviation using an observation value detected by a light receiving sensor attached to the imaging lens group as an observation value. Optical writing device. The specifying means calculates a change amount indicating how much the temperature difference in the sub-scanning direction has changed between a target one among the plurality of imaging lens groups and an adjacent one in the main scanning direction;
In order to determine whether the displacement amount in the sub scanning direction for each of the imaging lens groups is equal to or larger than the diameter of the pixel, the variation amount of the temperature difference between the two adjacent imaging lens groups is used. The optical writing device according to claim 8. The optical writing device is
An interpolation unit configured to execute linear interpolation on detection results of two or more of the plurality of light receiving sensors;
The correction means is
The linear interpolation result by the interpolation means is used as the displacement amount between the light source substrate and the lens array in calculating the displacement amount in the sub scanning direction for the imaging lens group not identified by the identification means. The optical writing device according to claim 8. The identification means is
Among the plurality of positions in the lens array, the processing of integrating the temperature difference calculated by the calculating means from the position closest to the fixed position where the light source substrate and the lens array are fixed to the target position is mainly The above temperature difference is determined for each of a plurality of positions in the scanning direction, and the determined position is based on the integrated value obtained at one position in the main scanning direction in the determined temperature difference distribution and the thermal expansion coefficient of the lens array. Execute the process of calculating the displacement amount in the sub scanning direction of the lens array in
9. The optical writing device according to claim 8, wherein the amount of displacement based on the integrated value is adjusted based on an error between the amount of displacement calculated based on the integrated value and the amount of positional displacement detected by the light receiving sensor. . The correction regarding the positional deviation by the correction means is
The light emission timing is changed by the light emitting element group based on the position in the image data of the pixel data to be corrected or the pixel data to be corrected. The optical writing device according to any one of the above.   An image forming apparatus comprising the optical writing device according to claim 1.

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