JP5173389B2 - Image forming apparatus and control method thereof - Google Patents

Description

  The present invention generally relates to an image forming apparatus, and more particularly to an image processing apparatus that forms a latent image by a multi-beam method.

  Space saving of digital composite copying machines tends to be more emphasized especially in low-end products. Conventionally, an oblique incidence system is known as an optical system for realizing space saving.

  FIG. 11 is a side view showing an example of the oblique incidence method. According to FIG. 11, the light emitting element 1101 that outputs a beam for forming a latent image, the photosensitive drum 1103 that holds the latent image, and the polygon mirror 1102 for scanning the beam are at different positions in the height direction. Has been placed. The beam output from the light emitting element 1101 is obliquely incident on a mirror surface (scanning plane) provided on the side surface of the polygon mirror 1102. Reference numeral 1102 ′ denotes the upper surface of the polygon mirror 1102.

  According to the oblique incidence method, the distance from the center position (rotation axis) of the polygon mirror 1102 is different between the center and the end of the mirror surface (distances a and b). This difference in distance causes the position of the beam irradiated on the photosensitive drum 1103 to fluctuate in the height direction.

  FIG. 12 is a diagram for explaining a difference between an actual scanning line formed on the photosensitive drum 1103 in the oblique incidence method and an ideal scanning line. A curve indicated by a solid line 1201 is an actual scanning line. A straight line indicated by a broken line 1202 is an ideal scanning line. In the oblique incidence method, the scanning line is curved in this way.

  In order to alleviate this bending, a correction lens may be disposed on the beam path. The correction lens is shaped so that the refractive index in the height direction differs depending on the scanning position. This correction lens alleviates the curvature to some extent and achieves high image quality.

  However, in order to effectively alleviate the bending, it is necessary to ensure the processing accuracy of the correction lens and adjust the optical system to a desired state. This is not suitable for low-end products because it increases production time and increases production costs.

  Incidentally, even in the vertical incidence method in which the beam is incident perpendicularly to the rotation axis of the polygon mirror 1102, the same fluctuation as in the oblique incidence method can occur. In an ideal vertical system, a beam trajectory exists in the rotation plane of the polygon mirror 1102.

  FIGS. 13A and 13B are diagrams illustrating an example of an ideal optical system having no significant shift in the rotation axis and an actual optical system having a significant shift in the rotation axis. FIG. 13A shows an ideal optical system. Since the rotation axis is not deviated, the height of the irradiation position of the beam on the photosensitive drum 1103 is kept constant even if the distance from the rotation axis to the mirror reflection position is changed by the rotation of the polygon mirror 1102. On the other hand, FIG. 13B shows a state in which the rotation axis is displaced due to an attachment error. For this reason, the distance from the rotation axis to the reflection position of the mirror surface is changed by the rotation of the polygon mirror 1102, and the height of the irradiation position is also shifted in conjunction therewith. Such a shift is not preferable because image quality is deteriorated. In particular, in high-end models, such a mounting error of the rotating shaft is a problem that cannot be ignored.

  FIG. 14 is a diagram illustrating an example of a method for correcting curvature by changing lines. Here, a conventionally proposed correction method (Patent Documents 1 to 4) will be described with reference to FIG. In FIG. 14, a broken line indicates an ideal scanning locus L0. Each solid line represents actual scanning trajectories L1, L2, and L3 that pass within ± 0.5 lines with respect to an ideal scanning trajectory.

When attention is paid to both ends of the scanning trajectory, among the three scanning trajectories L1, L2, and L3, L1 is closest to the ideal scanning trajectory L0. In the scanning region located at the center of the scanning locus, L3 is closest to the ideal scanning locus L0. In the region located between the end and the center, L2 is closest to the ideal scanning locus L0. Therefore, in order to realize an ideal straight line, it is almost ideal if the line is changed to a different line in the sub-scanning direction in order of L1 => L2 => L3 => L2 => L1 according to the scanning region. A straight line can be realized. In this way, dividing one scanning cycle into a plurality of regions and selecting an actual scanning line for each region to form a desired image is referred to as line transfer. Further, the partition between regions is called a transfer point.
Japanese Patent Laid-Open No. 02-050176 JP 2003-182146 A JP 2003-276235 A JP 2005-304011 A

  The line transfer described above can be realized by a light source such as a VCSEL in which a plurality of light emitting elements are arranged on the surface. VCSEL is a vertical cavity surface emitting laser.

  FIG. 15 is a diagram illustrating an example of an element arrangement of a VCSEL. This VCSEL has 16 elements and can scan 4 lines at a time. In addition, four elements are assigned to one line. The position of the four light emitting elements is adjusted in the sub-scanning direction by emitting light while switching during scanning.

  For example, the element A1 corresponds to the scanning locus L1 shown in FIG. Similarly, the element A2 corresponds to the scanning locus L2, and the element A3 corresponds to the scanning locus L3. The element A4 corresponds to a scanning locus (not shown) located below the scanning locus L3.

  As described above, it is possible to draw a substantially straight line on the photosensitive drum by changing the line (switching the light emitting elements). However, changing the line can create new challenges. In particular, it has been found that if the timing for switching the light emitting elements is inappropriate, the gradation of image density may be impaired, or stripe-like density unevenness may occur.

  FIG. 16 is a diagram for comparing the drum potential when the laser beam is emitted at the switching timing and the drum potential when the laser beam to be emitted is not switched. In FIG. 16, the first row shows the laser emission pattern and the corresponding drum potential when not switched. The second and third stages show the laser emission pattern and the corresponding drum potential when the laser is switched. In particular, the second row shows the light emission pattern of the light emitting element A1, and the third row shows the light emission pattern of the light emitting element A2.

  Comparing the case of not switching and the case of switching, it can be seen that the latter loses the light emission time by the rise characteristic. Since the waveform pulse indicating the drum potential is divided at the right and left of the switching position, there is an adverse effect on the gradation. Furthermore, if the density variation continuously occurs in the direction orthogonal to the scanning direction at the switching position, the division of the waveform pulse is likely to be visually detected as streaky irregularities.

  Therefore, an object of the present invention is to solve at least one of such problems and other problems. An object of the present invention is, for example, to provide an image quality with good gradation that does not cause streak-like unevenness and brings about merit in accuracy and simplification of an adjustment process.

The image forming apparatus of the present invention includes, for example, an image carrier, a main scanning unit, a sub-scanning unit, an irradiation position adjusting unit, and a density unevenness reducing unit. The image carrier carries an electrostatic latent image formed by the irradiation light of the light emitting element. The main scanning means scans the irradiation light in the main scanning direction of the image carrier. The sub-scanning unit moves the light receiving surface of the image carrier in the sub-scanning direction. The irradiation position adjusting means adjusts the irradiation position by switching the light emitting elements to emit light during one scanning period so that the irradiation position of the irradiation light in the sub-scanning direction is within the error range. The density unevenness mitigating means modifies the switching timing of the light emitting elements according to the density information of the image data , thereby reducing the density unevenness of the image formed on the image carrier before and after the switching timing.

  According to the present invention, for example, it is possible to obtain an image quality with good gradation characteristics that is advantageous in terms of accuracy and simplification of the adjustment process and that does not cause streaky irregularities.

  An embodiment of the present invention is shown below. Of course, the individual embodiments described below will be helpful in understanding various concepts such as the superordinate concept, intermediate concept and subordinate concept of the present invention. Further, the technical scope of the present invention is determined by the scope of the claims, and is not limited by the following individual embodiments.

[Embodiment 1]
FIG. 1 is a schematic cross-sectional view of an image forming apparatus that forms a multicolor image by superimposing a plurality of colors according to the embodiment. This image forming apparatus is a four-drum color copying machine in which four photoconductors are arranged in tandem. Note that the image forming apparatus may be realized as, for example, a printing apparatus, a printer, a multifunction peripheral, or a facsimile. The number of colors may be two or more. Therefore, it is sufficient that the number of photoconductors is two or more. In the following, an outline of a color image reading apparatus (hereinafter referred to as “color scanner”) 1 and a color image recording apparatus (hereinafter referred to as “color printer”) 2 constituting the color copying machine 100 will be described.

The color scanner 1 forms an image of the document 13 on the color sensor 17 through the illumination lamp 14, the mirror groups 15 </ b> A, B, C, and the lens 16. Further, the color scanner 1 reads the color image information of the document for each color separation light of, for example, blue (hereinafter referred to as B), green (hereinafter referred to as G), and red (hereinafter referred to as R), and converts it into an electrical image signal. To do. The color scanner 1 performs color conversion processing based on the intensity levels of the B, G, and R image signals. As a result, color image data of black (K), cyan (C), magenta (M), and yellow (Y) is obtained.


Next, the color printer 2 will be described. One writing optical unit 28M (for magenta), 28Y (for yellow), 28C (for cyan), 28K (for black) is provided for each color toner. Note that the suffix MYCK attached to the reference number indicates the color of the toner. These writing optical units are examples of main scanning means for scanning the irradiation light in the main scanning direction of the image carrier. The writing optical unit is sometimes called an exposure device or a scanner device.

  The writing optical unit converts the color image data from the color scanner 1 into an optical signal and performs optical writing. Thereby, electrostatic latent images are formed on the photoreceptors 21M, 21Y, 21C, and 21K provided for the respective colors. These photoreceptors are examples of an image carrier that carries an electrostatic latent image formed by light emitted from a light emitting element. Note that the photoconductor rotates itself during the formation of the latent image to operate the irradiation light in the sub-scanning direction. Therefore, the photoconductor is an example of a sub-scanning unit that moves the light-receiving surface of the image carrier in the sub-scanning direction.

  These photoconductors 21M, 21Y, 21C, and 21K rotate counterclockwise as indicated by arrows. Chargers 27M, 27Y, 27C, and 27K for uniformly charging the photoconductor are provided around the photoconductor. Further, an M developing unit 213M, a C developing unit 213C, a Y developing unit 213Y, and a Bk developing unit 213K for developing an electrostatic latent image using a developer (eg, toner) are also provided. Further, the intermediate transfer belt 22 as an intermediate transfer member is stretched around a driving roller 220 and driven rollers 219 and 237. In addition, first transfer bias blades 217M, 217Y, 217C, and 217K, which are first transfer units, are also provided so as to face the respective photoconductors.

  The second transfer bias roller 221 is disposed at a position facing the driven roller 219. The second transfer bias roller 221 is separated from or in contact with the intermediate transfer belt 22 by a separation / contact mechanism (not shown).

  In the color printer 2, image formation is first started from magenta. Thereafter, cyan image formation is started at a timing delayed with respect to the rotational speed of the intermediate transfer belt 22 corresponding to the separation distance between the photoconductor 21M and the photoconductor 21C. Next, yellow image formation is started at a timing delayed with respect to the rotational speed of the intermediate transfer belt 22 corresponding to the separation distance between the photosensitive member 21C and the photosensitive member 21CY. Finally, black image formation is started at a timing delayed with respect to the rotational speed of the intermediate transfer belt 22 corresponding to the distance between the photosensitive member 21Y and the photosensitive member 21K. Thus, on the intermediate transfer belt 22, the developer images of the respective colors are superimposed to form a multicolor image. This multicolor image is transferred to the recording material conveyed by the conveying rollers 228, 227, 226, and 225 at the secondary transfer position formed by the driven roller 219 and the second transfer bias roller 221. Thereafter, a color image is fixed on the surface of the recording material in the fixing device 25. Note that the recording material may be called, for example, a recording medium, paper, sheet, transfer material, or transfer paper.

  FIG. 2A is a schematic cross-sectional view of the writing optical unit according to the embodiment. FIG. 2B is a schematic plan view of the writing optical unit according to the embodiment. The light emitting element array 281 includes four light emitting elements, and can irradiate four beams (laser light) at the same time. The light emitting element array 281 is an example of a light emitting element unit having M light emitting elements for forming an image.

  Each beam is applied to the mirror surface of the rotating polygon mirror 283 via the lens 282. The polygon mirror 283 is rotationally driven by a polygon motor. When the polygon mirror 283 rotates once, the photosensitive member can be scanned six times. This is because the polygon mirror 283 has six mirror surfaces. The beam deflected by the polygon mirror 283 is first detected by the BD element 286. BD is an abbreviation for beam detection (beam detection). The BD signal output from the BD element 286 serves as a trigger for starting exposure for each main scan. That is, pixel data included in the corresponding four lines are sequentially read out and applied to the four light emitting elements, respectively. The scanning speed is corrected by the fθ lens 284 so that the scanning speed of the beam on the photosensitive member is constant. Thereafter, the beam is deflected by a plane mirror 285 to expose and scan the photoreceptor.

  FIG. 3 is an exemplary block diagram of a control system and an image processing system according to the embodiment. The reading system image processing unit 301 applies image processing such as shading correction to the image signal output from the color scanner 1 and passes the image signal to the central image processing unit 305. The central image processing unit 305 stores the image signal in the image memory 304, and passes the image signal to the output system image processing units 306 to 309 at an appropriate timing reflecting the distance between the photoconductors.

  The output system image processing unit 306 is an image processing unit for yellow (Y). The output system image processing unit 307 is an image processing unit for magenta (M). The output system image processing unit 308 is an image processing unit for cyan (C). The output system image processing unit 309 is an image processing unit for black (K). The output system image processing units 306 to 309 execute correction processing and interpolation processing according to each color of Y, M, C, and K, respectively. The line converter 313 converts the input image density data into image data (PWM data) for driving the laser, and distributes the image data according to the number of light emitting elements (lines) to be scanned simultaneously. For example, if the light emitting element unit as shown in FIG. 15 is used, the number of lines is four. The sub-scanning correction units 316 to 319 adjust the irradiation position of the laser light in the sub-scanning direction for the input image data, and the irradiation position of the irradiation light in the sub-scanning direction falls within the error range. Thereby, the bending of the scanning locus is corrected. Therefore, the sub-scan correction units 316 to 319 are an example of an irradiation position adjusting unit that adjusts the irradiation position by switching the light emitting elements to emit light during one scanning cycle.

  Further, the sub-scanning correction units 316 to 319 correct the switching timing of the light emitting elements according to the density information of the image to be formed. Thereby, density unevenness that can occur on the image carrier before and after the switching timing is alleviated. Therefore, the sub-scanning correction units 316 to 319 are an example of density unevenness reducing means.

  The central image processing unit 305 transmits and receives data via an external interface 303 connected to a telephone line, a network, and the like. If the received data is data described in PDL (page description language), the PDL processing unit 302 develops the image information.

  FIG. 4 is a block diagram illustrating an example of the sub-scanning correction unit according to the embodiment. The sub-scanning correction unit 316 receives image data (density information) output from the line conversion unit 313, a synchronization signal, and a clock signal. The counter 401 counts the position in the main scanning direction (main scanning position) and passes the counter value to the sub-scanning position control unit 402.

  For example, when the counter value matches the initial switching timing read from the table 403, the sub-scanning position control unit 402 outputs a switching signal to the relaxation unit 404. The table 403 stores default switching timing (main scanning position) and the identification number of the light emitting element after switching in association with each other. The default switching timing and the identification number of the light-emitting element after switching are determined in advance so that the irradiation position of the irradiation light in the sub-scanning direction is within the error range by switching the light-emitting element to emit light during one scanning cycle. Is held in. The sub-scanning position control unit 402 is an example of an irradiation position adjusting unit that adjusts the irradiation position.

  The mitigating unit 404 is an example of density unevenness mitigating means for relieving density unevenness that may occur on the image carrier before and after the switching timing by correcting the switching timing according to the density information of the image to be formed. The selector 405 selects a light emitting element that should emit light in synchronization with the switching timing corrected in the relaxation unit 404 and sends a drive signal (PWM data) to the selected light emitting element.

  The irradiation period determination unit 406 determines the irradiation period of irradiation light from the density information. A light emission pattern is formed by the irradiation period and the non-irradiation period. The irradiation period determination unit 406 includes an irradiation period calculated from the concentration information, a first irradiation period of the first light emitting element that is the light emitting element before switching, and a second irradiation period of the second light emitting element that is the light emitting element after switching. Divide into For example, the irradiation period is divided into the first half and the second half with the switching signal as a boundary (FIG. 16).

  The comparison unit 407 compares the length of the first irradiation period (first half) and the length of the second irradiation period (second half). The relaxation unit 404 shifts the switching timing according to the comparison result so that one of the first irradiation period and the second irradiation period becomes longer. For example, the mitigation unit 404 may make the second irradiation period relatively longer by shifting the switching timing until the start time of the irradiation period. Alternatively, the relaxation unit 404 may make the first irradiation period relatively longer by shifting the switching timing until the end time of the irradiation period. Ultimately, the mitigation unit 404 may lengthen the other length so that one length of the first irradiation period and the second irradiation period is substantially zero. This is preferable in reducing density unevenness due to the division of the irradiation period.

  FIG. 5 is a diagram illustrating a modification example of the switching timing according to the embodiment. A light emission pattern 501 before correcting the switching timing and a light emission pattern 502 after correcting the switching timing are shown. The light emission pattern is determined by the image data density information.

  For example, the comparison unit 407 compares the length T2 from the initial switching timing determined by the sub-scanning position control unit 402 to the end time of one irradiation period and the length T1 to the start time. If the length T2 until the end time is shorter than the length T1 until the start time, the relaxation unit 404 shifts the switching timing to the end time (FIG. 5). In contrast to the example of FIG. 5, if the length T1 until the start time is shorter than the length T2 until the end time, it is preferable that the mitigation unit 404 shifts the switching timing to the start time.

  In this manner, density unevenness does not occur by lengthening one of the first half and the second half obtained by dividing the irradiation period according to the initial switching timing. In particular, if one length is sufficiently shorter than the other length (minimum is zero), division of the irradiation period can be avoided, and density unevenness due to the division is reduced. Furthermore, by shifting the switching timing in a direction where the shift amount is small, it is easy to maintain the irradiation position correction effect in the sub-scanning direction.

  Since the length of the irradiation period determined by the density information is basically a fixed length, if the first half is lengthened, the second half is shortened, and if the second half is lengthened, the first half is shortened. In addition, when the switching timing comes within the irradiation period, the switching timing needs to be corrected. However, when the switching timing comes within the non-irradiation period (outside the irradiation period), it is not necessary to correct the switching timing. This is because the problem of density unevenness does not occur.

  FIG. 6 is a diagram illustrating a modification example of the switching timing according to the embodiment. A light emission pattern 601 before the switching timing is corrected and a light emission pattern 602 after the switching timing is corrected are shown. The light emission pattern is determined by the image data density information.

  For example, the comparison unit 407 may compare the length T3 from the initial switching timing to the center of the irradiation period with the length T2 from the initial switching timing to the end time. If the initial switching timing is closer to the center, the relaxation unit 404 moves the switching timing to the center (FIG. 6). On the other hand, if the initial switching timing is closer to the end timing than the center, the mitigation unit 404 moves the switching timing to the end timing. In this way, if the shift amount to the center is relatively short, by shifting the switching timing to the center, the length of the first half and the length of the second half are substantially the same, and the density unevenness is less noticeable. In addition, since the shift amount is relatively small, the effect of correcting the irradiation position in the sub-scanning direction can be easily maintained.

  Note that the comparison unit 407 may compare the length T3 from the initial switching timing to the center with the length T1 from the initial switching timing to the start timing. If the initial switching timing is closer to the start timing than the center, the mitigation unit 404 moves the switching timing to the start timing. On the other hand, if the initial switching timing is closer to the center, the relaxing unit 404 moves the switching timing to the center. Note that the shortest of T1 to T3 may be determined, and the switching timing may be moved to the corresponding maintenance. For example, if T3 is the shortest, the relaxing unit 404 moves the switched ming to the center.

  In addition, by moving to the center, the lengths of the first half and the second half are substantially the same, but the relaxation unit 404 lengthens either one so that the difference in length between the first half and the second half is within a predetermined range. It will be. Within the predetermined range is a difference that is determined by the inconspicuousness of density unevenness, and is determined according to the image quality required by the image forming apparatus, for example.

  FIG. 7 is a block diagram illustrating another example of the sub-scanning correction unit according to the embodiment. In general, if the shift amount of the switching timing becomes too large, it may be difficult to obtain the effect of correcting the irradiation position in the original sub-scanning direction. Therefore, if the shift amount is equal to or greater than the critical amount at which a correction effect can be obtained, it is desirable to prohibit modification of the switching timing.

  The determination unit 701 determines whether or not the shift amount of the switching timing is a predetermined amount or more. The predetermined amount is, for example, a critical amount with which a shift amount can obtain a correction effect. If the shift amount is not equal to or greater than the predetermined amount, the control unit 702 causes the switching timing to be adjusted. On the other hand, if the shift amount is equal to or greater than the predetermined amount, the control unit 702 prohibits the adjustment of the switching timing. This would make it possible to achieve both the effect of correcting the irradiation position in the sub-scanning direction and the effect of reducing density unevenness.

  FIG. 8 is a block diagram illustrating an example of the sub-scanning correction unit according to the embodiment. The parts already described are given the same reference numerals. The sub-scanning position control unit 402 reads the first switching timing and the selection value indicating which light emitting element is selected and switched from the table 403 storing the switching timing. For example, the sub-scanning position control unit 402 reads the next switching timing and the next selector value from the table 403 before the counter value reaches the current switching timing. Then, the sub-scanning position control unit 402 outputs a switching signal indicating the switching timing and a selection signal indicating the selection value to the pattern matching unit 801.

  The delay unit 802 delays the image data by a predetermined time and outputs the delayed image data to the selector 405. The selector 405 switches the light emitting element to emit light according to the select signal output from the pattern matching unit 801. That is, the selector 405 outputs image data (PWM data) only to the light emitting element designated by the select signal.

  The pattern matching unit 801 performs pattern matching for detecting a specific pattern with respect to the image data input from the line conversion unit 313 and the switching signal input from the sub-scanning position control unit 402. The shift register 803 stores a detection target pattern.

9 and 10 are diagrams illustrating examples of detection target patterns. D0 to D3 in FIG. 9 and V0 to V3 in FIG. 10 indicate values output from the shift register 803. Note that these subscript values (0 to 3) indicate clock delay. DA to DP and VA to VE given to the left of the columns in FIGS. 9 and 10 are pattern names for distinguishing each detection target pattern name.
In particular, FIG. 9 shows a detection target pattern for image data. 1 indicates the case where the gradation data is not white (when the density is not 0). 0 indicates a case where the gradation data is white (density> 0).

  FIG. 10 shows a detection target pattern for the switching signal. For example, 1 means occurrence of switching and 0 means no switching. The switching signal has an interval of 4 clocks or more due to the frequency of sub-scan correction. Therefore, there are only five patterns VA to VE as detection target patterns.

  The pattern matching unit 801 corrects the switching timing that occurs between D1 and D2. The corresponding switching timing signal corresponds to the pattern VD. Timing adjustment is realized by shifting the initial switching timing one clock before or after one clock.

  For example, when the detection target pattern is VD & DG or VD & DH, the pattern matching unit 801 outputs a switching signal to the selector 405 with a delay of one clock from the normal. When the detection pattern is VD & DO, the pattern matching unit 801 outputs the switching signal to the selector 405 one clock earlier than normal.

  The delay unit 802 is provided to adjust a delay caused by the pattern matching unit 801. The selector 405 selects one of the four light emitting elements according to the select signal from the pattern matching unit 801. Furthermore, the selector 405 switches the light emitting element that should emit light in real time according to the switching signal.

  The output system image processing units 307 to 309 also have the same configuration as the output system image processing unit 306 and operate in the same manner. The sub-scanning correction units 316 to 319 have the same configuration as the sub-scanning correction unit 316 and operate in the same manner.

  In this way, by correcting the ming that has been switched using pattern matching, there is a merit in accuracy and simplification of the adjustment process, etc., and a high gradation image quality with no streak-like unevenness is produced. It will be obtained.

1 is a schematic cross-sectional view of an image forming apparatus that forms a multicolor image by superimposing a plurality of colors according to an embodiment. It is a schematic sectional drawing of the writing optical unit which concerns on embodiment. It is a schematic plan view of the writing optical unit according to the embodiment. It is an exemplary block diagram about a control system and an image processing system concerning an embodiment. It is the block diagram which showed an example of the subscanning correction | amendment part which concerns on embodiment. It is a figure which shows the example of correction of the switching timing which concerns on embodiment. It is a figure which shows the example of correction of the switching timing which concerns on embodiment. It is the block diagram which showed another example of the subscanning correction | amendment part which concerns on embodiment. It is the block diagram which showed an example of the subscanning correction | amendment part which concerns on embodiment. It is a figure which shows an example of a detection target pattern. It is a figure which shows an example of a detection target pattern. It is a side view which shows an example of an oblique incidence system. FIG. 10 is a diagram for explaining a difference between an actual scanning line formed on the photosensitive drum 1103 in the oblique incidence method and an ideal scanning line. It is a figure which shows an example of an ideal optical system without a significant shift | offset | difference in a rotating shaft, and an actual optical system with a significant shift | offset | difference in a rotating shaft. It is a figure which shows an example of an ideal optical system without a significant shift | offset | difference in a rotating shaft, and an actual optical system with a significant shift | offset | difference in a rotating shaft. It is a figure which shows an example of the method of correct | amending curvature by the transfer of a line. It is a figure which shows the element arrangement example of VCSEL. It is a figure for comparing the drum potential when the laser is emitted at the switching timing and the drum potential when the laser to be emitted is not switched.

Claims (12)

A light emitting element unit having a plurality of light emitting elements that form an image by irradiating light according to image data ;
An image carrier for carrying an electrostatic latent image formed by the light emitted from the light emitting element;
Main scanning means for scanning the irradiation light in the main scanning direction of the image carrier;
Sub-scanning means for moving the light receiving surface of the image carrier in the sub-scanning direction;
An irradiation position adjusting means for adjusting the irradiation position by switching light emitting elements to emit light so that the irradiation position of the irradiation light in the sub-scanning direction is within an error range;
Density unevenness mitigating means for relieving density unevenness of an image formed on the image carrier before and after the switching timing by correcting the switching timing of the light emitting element according to the density information of the image data ;
An image forming apparatus comprising: One irradiation period of the irradiation light determined by the density information is a first irradiation period of the first light emitting element which is the light emitting element before the switching and a second light emitting element after the switching, with the switching timing as a boundary. is divided into a second irradiation period of the light emitting element,
The density unevenness alleviating means is:
The image forming apparatus according to claim 1, wherein the switching timing is shifted so that one of the first irradiation period and the second irradiation period becomes longer. The density unevenness alleviating means is:
3. The image forming apparatus according to claim 2, wherein the second irradiation period is relatively lengthened by shifting the switching timing until a start time of one irradiation period of the irradiation light. The density unevenness alleviating means is:
3. The image forming apparatus according to claim 2, wherein the first irradiation period is relatively lengthened by shifting the switching timing until an end time of one irradiation period of the irradiation light. 4. The density unevenness alleviating means is:
3. The image forming apparatus according to claim 2, wherein one of the first irradiation period and the second irradiation period is lengthened so that one length is substantially zero. 4. Comparing means for comparing the length from the initial switching timing determined by the irradiation position adjusting means to the end time of the one irradiation period with the length from the initial switching timing to the start timing of the one irradiation period Further comprising
The density unevenness alleviating means is:
If the length to the end time is shorter than the length to the start time, the switching timing is shifted to the end time, and if the length to the start time is shorter than the length to the end time, the switching The image forming apparatus according to claim 2, wherein the timing is shifted to the start time. Comparison means for comparing the length from the initial switching timing determined by the irradiation position adjusting means to the center of the one irradiation period and the length from the initial switching timing to the end timing of the one irradiation period. In addition,
If the initial switching timing is closer to the end timing than the center, the switching timing is moved to the end timing, and if the initial switching timing is closer to the center, the switching timing is moved to the center. The image forming apparatus according to claim 1, wherein: Comparison means for comparing the length from the initial switching timing determined by the irradiation position adjusting means to the center of the one irradiation period and the length from the initial switching timing to the start timing of the one irradiation period. In addition,
If the initial switching timing is closer to the start timing than the center, the switching timing is moved to the start timing, and if the initial switching timing is closer to the center, the switching timing is moved to the center. The image forming apparatus according to claim 1, wherein: One irradiation period of the irradiation light with the switching timing as a boundary is a first irradiation period of the first light emitting element which is the light emitting element before the switching and a second irradiation of the second light emitting element which is the light emitting element after the switching. It has been divided into a period,
The density unevenness alleviating means is:
2. The method according to claim 1, wherein one of the first irradiation period and the second irradiation period is lengthened so that a difference between the first irradiation period and the second irradiation period is within a predetermined range. The image forming apparatus described. The density unevenness alleviating means is:
10. The image according to claim 9, wherein one of the first irradiation period and the second irradiation period is lengthened so that the first irradiation period and the second irradiation period are substantially the same. Forming equipment. Determining means for determining whether or not a shift amount of the switching timing is a predetermined amount or more;
Control means for executing adjustment of the switching timing when the shift amount is not equal to or greater than the predetermined amount, and prohibiting adjustment of the switch timing when the shift amount is equal to or greater than the predetermined amount. The image forming apparatus according to any one of claims 1 to 10. A light emitting element unit having a plurality of light emitting elements that form an image by irradiating light according to image data ;
An image carrier for carrying an electrostatic latent image formed by the light emitted from the light emitting element;
Main scanning means for scanning the irradiation light in the main scanning direction of the image carrier;
A method of controlling an image forming apparatus comprising: a sub-scanning unit that moves a light receiving surface of the image carrier in a sub-scanning direction;
Adjusting the irradiation position by switching a light emitting element to emit light during one scanning period so that the irradiation position of the irradiation light in the sub-scanning direction is within an error range;
Correcting the switching timing of the light emitting elements according to the density information of the image data , thereby reducing density unevenness of the image formed on the image carrier before and after the switching timing. And a control method of the image forming apparatus.

Images