JP2012210751A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of satisfactorily suppressing the occurrence of density unevenness while suppressing increase in costs.SOLUTION: This image forming apparatus includes: an exposure device 5 forming an electrostatic latent image on a photoreceptor drum 1 by performing exposure scanning using light emitted from a semiconductor laser element 51; and an exposure control part 150 generating a pulse signal and controlling turning on/off of the semiconductor laser element 51. The exposure control part 150 performs first correction of adjusting a light emission time of the semiconductor laser element 51 for each dot by modulating the width of the pulse signal to correct density in a main scanning direction and second correction of further correcting the light emission time of the semiconductor laser element 51 about predetermined dots in each block obtained by dividing the main scanning line into a plurality of pieces.

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, as an image forming apparatus, an apparatus in which an electrostatic latent image is formed on a photosensitive drum and a toner image is obtained by developing the electrostatic latent image formed on the photosensitive drum is known. Such an image forming apparatus includes, for example, an exposure apparatus having a semiconductor laser element. The exposure apparatus forms an electrostatic latent image on the photosensitive drum by performing exposure scanning on the photosensitive drum with the rotation axis direction of the photosensitive drum as the main scanning direction.

  By the way, if exposure scanning is performed with the light emission time of the semiconductor laser element made uniform for each dot, the density in the main scanning direction should ideally be uniform, but the transfer characteristics and the photosensitive film thickness of the photosensitive drum are not satisfactory. Density unevenness in the main scanning direction occurs due to unevenness in sensitivity due to uniformity. Further, uneven density in the main scanning direction may appear due to variations in the beam diameter of the semiconductor laser element. Such density unevenness in the main scanning direction can be reduced by increasing the manufacturing accuracy of the photosensitive drum and optical system components, but if so, the manufacturing cost increases.

  For this reason, generally, a technique for electrically correcting density unevenness in the main scanning direction is used (see, for example, Patent Document 1). For example, as a technique for electrically correcting density unevenness in the main scanning direction, a method of adjusting a light emission time (pulse width) of a semiconductor laser element with respect to 1-dot image data with a predetermined resolution, or a current to a semiconductor laser element A method for adjusting the amount of light by control has been proposed.

JP 2006-17774 A

  However, when the former method of the conventionally proposed methods is adopted, in order to make it difficult for the density change point to be visually recognized, the emission time of the semiconductor laser element with respect to 1-dot image data is set to a high resolution (for example, 1 It is necessary to control at a resolution of 1/100 of the scanning time per dot. In order to realize such control, it is necessary to make the minimum time change width (one step) of light emission extremely short and to accurately manage the signal delay. A decrease in manufacturing yield and an increase in cost are inevitable.

  When the latter method is employed, a high-speed type D / A converter that can change the current to the semiconductor laser element during one line exposure scanning is required. Therefore, even in this case, an increase in cost is inevitable.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of satisfactorily suppressing the occurrence of density unevenness while suppressing an increase in cost. .

  In order to achieve the above object, an image forming apparatus of the present invention has an image carrier that is rotatably supported and a light emitting element, and the rotation axis direction of the image carrier is a main scanning direction. An exposure device that performs exposure scanning using light emitted from the light emitting element to form an electrostatic latent image on the image carrier, and generates a pulse signal that indicates whether the light emitting element is turned on or off, and controls turning on and off of the light emitting element An exposure control unit. The exposure control unit modulates the width of the pulse signal to adjust the light emission time of the light emitting element for each dot to correct the density in the main scanning direction, and the main scanning line extending in the main scanning direction. In each of the blocks divided into a plurality of, the second correction for further correcting the light emission time of the light emitting element for a predetermined dot is performed.

  According to the configuration of the present invention, the exposure control unit adjusts the light emission time of each light emitting element for each dot by modulating the width of the pulse signal, and corrects the density in the main scanning direction. In each block obtained by dividing the main scanning line extending in the direction into a plurality, a second correction for further correcting the light emission time of the light emitting element for a predetermined dot is performed. Here, since there is a limit to the minimum change width (one step) of the pulse width, it is difficult to perfectly match the light emission time of the light emitting element in each dot with the ideal light emission time. For this reason, a slight error occurs between the actual light emission time and the ideal light emission time for each dot, and when a small error is accumulated in each dot, it may be visually recognized as uneven density in blocks. However, in the configuration of the present invention, the second correction is performed so as to eliminate the error accumulated in each dot. As a result, it is possible to perform appropriate correction of density without degrading the image due to human eye resolution or toner drawing errors, even with low resolution pulse width modulation instead of high resolution pulse width modulation. Therefore, even if the exposure control unit does not have an expensive high-resolution pulse width modulation function, it is possible to perform density correction that satisfactorily suppress the occurrence of density unevenness in the main scanning direction, thereby suppressing an increase in cost. it can.

  In the above configuration, the exposure control unit sets the positions of the predetermined dots for the second correction for each main scanning line so that the positions of the predetermined dots for the second correction are not aligned in the sub-scanning direction orthogonal to the main scanning direction. It is preferable to shift to When the positions of the predetermined dots for performing the second correction are aligned in the sub-scanning direction, vertical stripe-like density unevenness may occur in the sub-scanning direction. However, according to this configuration, since the position of the predetermined dot for intentionally performing the second correction is shifted for each main scanning line, the vertical stripe-shaped density unevenness does not occur.

  In the above configuration, it is preferable that the exposure control unit sets the same number of dots in each block and shifts the block boundary position in the main scanning direction for each main scanning line. With this configuration, it is difficult for a density step to occur at the block boundary position in the main scanning direction. For this reason, even if the second correction is performed on each block obtained by dividing the main scanning line into a plurality of blocks, the density uniformity is not impaired.

  In the above configuration, it is preferable that the exposure control unit performs the second correction using a dot at the same position as a predetermined dot among the dots included in each block. With this configuration, when the block boundary position in the main scanning direction is shifted for each main scanning line, the position of the predetermined dot for performing the second correction is shifted for each main scanning line.

  In the above configuration, the exposure control unit preferably shifts the block boundary position in the main scanning direction for each main scanning line so that periodicity does not occur. With this configuration, it is possible to suppress the occurrence of an inconvenience that the block boundaries interfere with each other and interference fringes appear.

  In the above configuration, it is preferable that the image processing apparatus further includes a random number generation unit that generates a random number, and the exposure control unit shifts the boundary position of the block in the main scanning direction for each main scanning line using the random number generated by the random number generation unit. . With this configuration, the block boundary position in the main scanning direction can be easily shifted for each main scanning line so that periodicity does not occur.

  In the above configuration, the random number generation unit preferably generates a random number based on a density correction curve indicating a relationship between a position in the main scanning direction and the density. With this configuration, the block boundary position in the main scanning direction can be easily shifted for each main scanning line based on the density correction curve.

  In the above configuration, the exposure control unit selects a delay circuit that delays an input signal by connecting delay elements in a plurality of stages in series, and selects an output signal from the delay elements in a plurality of stages and outputs it as a delay signal. It is preferable to include a selector and a logic circuit that performs a logical operation of the input signal and the delay signal, and modulate the width of the pulse signal. With this configuration, the width of the pulse signal can be modulated in units of delay time by providing a plurality of delay elements. As a result, the width of the pulse signal can be modulated without using a high multiplying type PLL (Phase Locked Loop) or the like in order to modulate the width of the pulse signal, and an increase in cost can be suppressed.

  In this case, when performing the second correction, the exposure control unit sets one dot included in each block as a predetermined dot, and emits light from the light emitting element for the delay time of one of the delay elements in the plurality of stages. More preferably, the time is corrected. With this configuration, the density correction of each block can be performed within a range that does not significantly affect the density.

  In the above configuration, the exposure control unit performs magnification correction after dividing the main scanning line into a plurality of magnification correction blocks, and performs second correction using the magnification correction block as a second correction block. It is preferable. With this configuration, appropriate density correction can be performed on the magnification correction block.

  As described above, according to the present invention, it is possible to easily obtain an image forming apparatus capable of satisfactorily suppressing the occurrence of density unevenness while suppressing an increase in cost.

1 is an overall configuration diagram of an image forming apparatus according to a first embodiment of the present invention. 1 is a schematic diagram of an image forming unit of an image forming apparatus according to a first embodiment of the present invention. 1 is a schematic view of an exposure apparatus provided in an image forming apparatus according to a first embodiment of the present invention. 1 is a block diagram showing a hardware configuration of an image forming apparatus according to a first embodiment of the present invention. 1 is a block diagram showing a hardware configuration of an exposure apparatus provided in an image forming apparatus according to a first embodiment of the present invention. The figure for demonstrating an example of the pulse width modulation performed in the exposure control part shown in FIG. The figure for demonstrating the outline | summary of the density correction performed in the exposure control part shown in FIG. The figure for demonstrating the outline | summary of the density correction performed in the exposure control part shown in FIG. The figure for demonstrating the outline | summary of the density correction performed in the exposure control part shown in FIG. The figure for demonstrating the outline | summary of the density correction performed in the exposure control part shown in FIG. The figure for demonstrating the outline | summary of the magnification correction performed in the image forming apparatus by 2nd Embodiment of this invention.

  The multi-function device 100 according to the first embodiment of the present invention will be described below.

  As shown in FIG. 1, the multifunction peripheral 100 according to the first embodiment includes an operation panel 101, an image reading unit 102, a paper feeding unit 103, a conveyance path 104, an image forming unit 105, an intermediate transfer unit 106, a fixing unit 107, and both sides. At least a conveyance path 108 is provided.

  The operation panel 101 is indicated by a broken line in FIG. 1 and includes a liquid crystal display unit 11 and a touch panel unit 12 that covers the liquid crystal display unit 11. The operation panel 101 is also provided with hard keys such as a start key 13 and a numeric keypad 14 for instructing start of execution of various functions.

  The image reading unit 102 reads a document and forms image data of the document. Although not shown, the image reading unit 102 is provided with optical system members such as an exposure lamp, a mirror, a lens, and an image sensor. The image reading unit 102 irradiates a document placed on the placement reading contact glass 21 with a beam, and A / D converts the output value of each pixel of the image sensor that receives the reflected beam of the document. , Generate image data. Further, when the original is read by the image reading unit 102, the original placed on the placement contact glass 21 is pressed by the original cover 22.

  The paper feed unit 103 stores paper P as a recording medium and supplies the paper P to the conveyance path 104. The paper feed unit 103 is provided with a pickup roller 31 for pulling out the stored paper P, a separation roller 32 for suppressing double feeding of the paper P, and the like.

  The conveyance path 104 conveys the paper P inside the multifunction peripheral 100. More specifically, the paper P supplied from the paper supply unit 103 passes through the intermediate transfer unit 106 and the fixing unit 107 in this order by the conveyance path 104 and is guided to the discharge tray 109. The conveyance path 104 is provided with a registration roller 41 that waits for the paper P in front of the intermediate transfer unit 106 and feeds the paper P to the intermediate transfer unit 106 in time.

  The image forming unit 105 forms a toner image based on image data. The image forming unit 50 for four colors (an image forming unit 50Bk that forms a black toner image, an image that forms a yellow toner image) The image forming unit 50Y includes an image forming unit 50C that forms a cyan toner image, an image forming unit 50M that forms a magenta toner image, and the exposure device 5. The image forming units 50Bk, 50Y, 50C, and 50M form toner images of different colors, but all have basically the same configuration. Therefore, in the following description, symbols (Bk, Y, C, and M) representing each color are omitted.

  As shown in FIG. 2, each image forming unit 50 includes a photosensitive drum 1, a charging device 2, a developing device 3, and a cleaning device 4. Each image forming unit 50 uses, for example, the exposure apparatus 5 in common.

  Each photosensitive drum 1 carries a toner image on its outer peripheral surface, has a photosensitive layer on its outer peripheral surface, and is supported so as to be rotatable in the circumferential direction. Each charging device 2 charges the corresponding photosensitive drum 1 with a constant potential. Each developing device 3 stores a developer of a corresponding color and supplies toner to the corresponding photosensitive drum 1. Each cleaning device 4 cleans the corresponding photosensitive drum 1. The exposure device 5 performs scanning exposure on each photoconductor 1 to form an electrostatic latent image.

  As shown in FIG. 3, the exposure apparatus 5 includes a semiconductor laser element 51, a polygon mirror 52, a polygon motor 53, an Fθ lens 54, a reflection mirror 55, and the like. In FIG. 3, for the sake of convenience, only the configuration for one color is shown. For example, in the configuration for four colors, the polygon mirror 52 and the polygon motor 53 are shared, and the semiconductor laser element 51, the Fθ lens 54, and the reflection mirror 55 are provided for each color. Alternatively, the polygon mirror 52 and the polygon motor 53 may be provided for each color.

  The exposure device 5 exposes and scans the photosensitive drum 1 using laser light emitted from the semiconductor laser element 51 with the rotation axis direction of the photosensitive drum 1 as the main scanning direction. Thereby, an electrostatic latent image is formed on the photosensitive drum 1.

  Specifically, when laser light is emitted from the semiconductor laser element 51, the laser light is incident on the polygon mirror 52. At this time, the polygon mirror 52 is rotated by the driving force transmitted from the polygon motor 53. For this reason, the laser light incident on the polygon mirror 52 is reflected and deflected by the polygon mirror 52. That is, the polygon mirror 52 scans the laser beam in the main scanning direction. Thereafter, the laser light is incident on the Fθ lens 54.

  The Fθ lens 54 guides the laser light to the reflection mirror 55 so that the laser light scans in the main scanning direction at a constant speed. The reflection mirror 55 reflects the laser light toward the photosensitive drum 1. In this way, scanning exposure of the photosensitive drum 1 by the exposure device 5 is performed.

  The exposure apparatus 5 also includes a light receiving unit 56 that receives laser light. The light receiving unit 56 includes a photodiode, and is disposed within the laser beam irradiation range (scanning range) by the polygon mirror 52 and outside the irradiation range of the photosensitive drum 1. Thus, when laser light is emitted from the semiconductor laser element 51, the light receiving unit 56 receives the laser light, and the output current (output voltage) of the light receiving unit 56 changes. Based on the output current (output voltage) of the light receiving unit 56, the scanning exposure start timing (light emission start timing of the first dot of the main scanning line) to the photosensitive drum 1 is taken.

  Returning to FIG. 1, the intermediate transfer unit 106 performs the secondary transfer onto the paper P after receiving the primary transfer of the toner image from the image forming unit 105. The intermediate transfer unit 106 includes at least an intermediate transfer belt 61 and primary transfer rollers 62Bk, 62Y, 62C, and 62M assigned to the image forming units 50, respectively. The primary transfer rollers 62Bk, 62Y, 62C, and 62M sandwich the intermediate transfer belt 61 with the corresponding image forming unit 50 (specifically, the photosensitive drum 1) and also transfer voltage (transfer bias). ) Is applied.

  The intermediate transfer unit 106 also includes a driving roller 63 and a driven roller 64. The driving roller 63 and the driven roller 64 stretch the intermediate transfer belt 61 together with the primary transfer rollers 62Bk, 62Y, 62C, and 62M.

  Further, the intermediate transfer unit 106 includes a secondary transfer roller 65. The secondary transfer roller 65 sandwiches the intermediate transfer belt 61 between the drive roller 63 and a transfer voltage (transfer bias) is applied.

  The toner images formed by the image forming units 50 are sequentially superimposed on the intermediate transfer belt 61 by the primary transfer rollers 62Bk, 62Y, 62C, and 62M to which a transfer voltage is applied. Is done. Thereafter, the toner image primarily transferred to the intermediate transfer belt 61 is secondarily transferred to the paper P by the secondary transfer roller 65 to which a transfer voltage is applied.

  The intermediate transfer unit 106 also includes a belt cleaning device 66. The belt cleaning device 66 cleans the intermediate transfer belt 61 after the secondary transfer of the toner image from the intermediate transfer belt 61 to the paper P.

  The fixing unit 107 heats and presses the toner image secondarily transferred onto the paper P to fix it. The fixing unit 107 includes a fixing roller 71 having a built-in heat source, and a pressure roller 72 that is pressed against the fixing roller 71. Then, the sheet P on which the toner image is secondarily transferred passes between the fixing roller 71 and the pressure roller 72 and is heated and pressed. As a result, the toner image is fixed on the paper P.

  The paper P passes through the fixing unit 107 and is then discharged to the discharge tray 109. Thereby, the image forming process is completed.

  The duplex conveyance path 108 enables duplex printing. The double-sided conveyance path 108 branches off from the conveyance path 104 on the downstream side of the fixing unit 107 and merges with the conveyance path 104 on the upstream side of the registration roller 41. In the double-sided conveyance path 108, a switching valve 81 disposed at a branch point with the conveyance path 104, a discharge roller 82 disposed at a discharge port 109a connected to the discharge tray 109 and capable of switching between forward and reverse rotation, In addition, a transport roller 83 that transports the paper P is provided.

  When performing duplex printing, the switching valve 81 is in a position to close the duplex conveying path 108 and guides the paper P sent from the fixing unit 107 to the discharge tray 109. Further, the discharge roller 82 first rotates forward to discharge the paper P to the discharge tray 109. Thereafter, the discharge roller 82 rotates in the reverse direction before the paper P passes through the discharge roller 82. At this time, the switching valve 81 rotates in a direction to open the double-sided conveyance path 108. As a result, the sheet P printed on one side is guided to the duplex conveyance path 108.

  The paper P guided to the double-sided conveyance path 108 is conveyed by the conveyance roller 83 and reaches the upstream side of the registration roller 41. Then, it is sent again from the intermediate transfer unit 106 to the fixing unit 107. At this time, since the front and back of the paper P are reversed, the secondary transfer process and the fixing process are performed on the back surface (unprinted surface) of the paper P. Then, the paper P on which double-sided printing is completed is discharged to the discharge tray 109.

  Next, the hardware configuration of the multifunction peripheral 100 will be described with reference to FIG.

  The multifunction device 100 includes a control unit 110 inside. The control unit 110 includes a CPU 111 (central processing unit), an image processing unit 112, and the like, and controls each unit of the multifunction peripheral 100.

  The control unit 110 is connected to the storage unit 113. The storage unit 113 includes a combination of a nonvolatile storage device such as a ROM, a RAM, a flash ROM, and an HDD and a volatile storage device. For example, the storage unit 113 stores a control program and control data of the multifunction peripheral 100. Then, the CPU 111 performs control and calculation of each unit of the multifunction peripheral 100 based on a control program and control data stored in the storage unit 113.

  Further, the control unit 110 is connected to the I / F unit 114. The I / F unit 114 is a communication interface for performing communication with a computer 200 (for example, a personal computer) that is a transmission source of print data (image data to be printed and data that includes setting data for printing). It is. Further, a modem or the like may be incorporated in the I / F unit 114 so that image data and the like can be transmitted / received to / from an external FAX apparatus.

  The control unit 110 is connected to the operation panel 101, the image reading unit 102, the paper feeding unit 103, the conveyance path 104, the image forming unit 105, the intermediate transfer unit 106, the fixing unit 107, the double-side conveyance path 108, and the like. Based on the control program and control data of the unit 113, the operation of each unit is controlled.

  Further, the control unit 110 is connected to the exposure apparatus 5. The exposure apparatus 5 is provided with an exposure control unit 150 that controls the light emission (turning on and off) of each semiconductor laser element 51 based on the image data.

  Then, the image processing unit 112 converts the image data after the image processing into image data that can be used for exposure by the exposure device 5. For example, for each color component (black, yellow, cyan, and magenta), the image processing unit 112 converts the image data having the pixel value of each dot into image data that indicates gradation or turning on / off of the semiconductor laser element 51, Output to the exposure apparatus 5. The exposure control unit 150 receives this image data and controls the light emission of each semiconductor laser element 51.

  Next, the hardware configuration of the exposure apparatus 5 will be described with reference to FIG.

  First, the exposure control unit 150 that controls the exposure scanning of the exposure apparatus 5 is configured by, for example, an ASIC (Application Specific Integrated Circuit).

  The exposure control unit 150 is provided with a receiving unit 151 as an I / O part that receives image data subjected to image processing for exposure by the image processing unit 112. Further, for example, the exposure control unit 150 may be provided with an image memory 152 that stores image data for at least several lines. Note that the receiving unit 151 and the image memory 152 may be provided externally to the exposure control unit 150. The exposure control unit 150 controls turning on / off of the semiconductor laser element 51 and rotation of the polygon motor 53 based on the image data received by the receiving unit 151.

  For example, the exposure control unit 150 is provided with a controller 153 that actually controls turning on and off of the semiconductor laser element 51. The controller 153 receives a signal received by the light receiving unit 56, sets the exposure (writing) timing from the first dot in the main scanning direction, and matches the writing position of each line in the main scanning direction. Prior to the start of exposure, the polygon motor 53 is rotated, and the polygon motor 53 is rotated at a speed suitable for exposure scanning.

  A controller 153, a reference pulse signal generation unit 154, a pulse signal modulation unit 155, and the like are provided as portions that generate a pulse signal for controlling turning on and off of the semiconductor laser element 51.

  First, the reference pulse signal generation unit 154 generates a reference pulse signal that serves as a reference for instructing turning on and off of the one-dot semiconductor laser element 51. The reference pulse signal generation unit 154 sets High at the start position (time) of one dot and changes to Low at a position (time) slightly before the end position (end time) of one dot for the dot on which toner is placed. For a dot that outputs a pulse signal and does not carry toner, it is maintained low. In this case, High means that the semiconductor laser element 51 is turned on, and exposure is performed on the dots on which the toner is placed.

  In addition, the exposure control unit 150 controls the lighting time of the semiconductor laser element 51 for each dot to change the density gradation of one dot (for example, 16 gradations, 8 gradations, etc.). The image data given to 150 includes a value indicating the gradation of each dot). In other words, the reference pulse signal generation unit 154 sets the time obtained by dividing the High time of the reference pulse signal per dot by the number of gradations as a unit, and matches the gradation value with the unit time × the time of the gradation value. A pulse signal is generated.

  In order to generate a pulse signal having a pulse width matched to the gradation of each dot, the exposure control unit 150 is provided with a pulse signal modulation unit 155 including a delay circuit 156, a selector 157, and a logic circuit 158. The output of the reference pulse signal generation unit 154 is input to the pulse signal modulation unit 155. The delay circuit 156 of the pulse signal modulation unit 155 includes a plurality of delay elements 159. The delay elements 159 are connected in series by the number obtained by dividing the drawing time per dot by the time delayed by the delay element 159 (83 in the example of FIG. 5).

  For example, if the drawing time per dot is about 25 ns and the delay time of the delay element 159 is about 300 ps, then 25 ns ÷ 300 ps≈83. Therefore, for example, 83 delay elements 159 are connected in series. Thereby, the pulse width can be modulated in units of drawing time per dot / 83.

  The selector 157 is a circuit for selecting one of the delayed output signals of each delay element 159 as described above. The controller 157 causes the selector 157 to select one of the delayed output signals of each delay element 159 based on the tone value of each dot. The logic circuit 158 calculates a logical product of the reference pulse signal and the delay signal and outputs the logical product to the driver 160. The driver 160 turns on the semiconductor laser element 51 if it is High, and turns off the semiconductor laser element 51 if it is Low.

  An example of pulse width modulation using the pulse signal modulation unit 155 is shown in FIG. When a reference pulse signal corresponding to a certain dot is input from the reference pulse signal generator 154 to the delay circuit 156, the output signals D1 to D83 at each stage are delayed by a predetermined time (for example, about 300 ps). At this time, for example, if the selector 157 selects the output signal D5, the logic circuit 158 calculates the logical product of the reference pulse signal and the output signal D5. Thereby, the pulse corresponding to a certain dot becomes narrow. The corrected pulse corresponding to a certain dot is output to the driver 160, thereby shortening the light emission time of the semiconductor laser element 51 at a certain dot.

  For example, when the gradation of one dot is 16 gradations (gradation value 0 to 15), the darkest dot (for example, the dot of gradation value 15) takes a long time to turn on the semiconductor laser element 51. As described above, the controller 153 causes the selector 157 to output the output signal of the first-stage delay element 159 (for example, the output signal D1 of the first-stage delay element 159) among the delay elements 159 connected in series. In addition, in the case of dots with gradation values 7 and 8, the controller 153 uses the delay elements per middle stage among the delay elements 159 connected in series in order to make the time to turn on the semiconductor laser element 51 about half of the reference pulse signal. The selector 157 outputs the output signal 159 (for example, the output signal of the delay element 159 per 40th stage). In the thinnest dot (for example, a dot having a gradation value of 1) while the toner is placed, the last time among the delay elements 159 connected in series is set to shorten the time for turning on the semiconductor laser element 51 to be significantly shorter than the reference pulse signal. The selector 157 outputs the output signal of the delay element 159 at the stage (for example, the output signal D83 of the delay element 159 at the 83rd stage).

  Note that it is determined in advance which output signal of the delay element 159 is output from the selector 157 for the dot gradation value, and which output signal of the delay element 159 is the selector for the dot gradation value. Data indicating whether to output from 157 is stored in the memory 161. The controller 153 refers to the memory 161 and modulates the pulse width of the reference pulse signal based on the dot gradation value. In other words, the pulse signal modulation unit 155 is a PWM circuit using signal delay.

  Next, a first correction for correcting the density in the main scanning direction by adjusting the light emission time of the semiconductor laser element 51 for each dot by modulating the width of the pulse signal will be described. First, even if an image having a uniform density in the main scanning direction is formed due to transfer characteristics, sensitivity variations in the main scanning direction of the photosensitive drum 1, processing accuracy of various lenses or mirrors, etc., the main scanning direction In some cases, uneven density may occur. More specifically, when exposure scanning is performed with the light emission time of the semiconductor laser element 51 uniform for each dot, the density in the main scanning direction should ideally be uniform, but due to the above factors, Density unevenness may occur in the main scanning direction.

  FIG. 7 is a graph showing an example of such density unevenness in the main scanning direction. The density curve in FIG. 7 is actually measured at the time of factory shipment, for example. The horizontal axis in FIG. 7 indicates the position of the photosensitive drum 1 in the main scanning direction. The photosensitive drum 1 is a photosensitive drum (the peripheral surface of the photosensitive drum is about 300 mm) corresponding to the short side of A3 paper (the long side of A4 paper), and is in the main scanning direction of the photosensitive drum 1. The center of is 0. Further, the vertical axis in FIG. 7 is a relative density difference (color difference) depending on the position of the photosensitive drum 1 in the main scanning direction based on the reading value of the density sensor. The smaller the color difference, the smaller the color change. Show.

  In the density curve shown in FIG. 7, the density tends to be lighter toward the end portion in the main scanning direction than the central portion of the photosensitive drum 1. In such a photosensitive drum 1, even if exposure scanning is performed with the light emission time of the semiconductor laser element 51 of each dot being the same, density unevenness such as “thin → dark → thin” occurs in the main scanning direction.

  Therefore, it is necessary to correct the density in the main scanning direction so that such density unevenness does not occur. For example, in the memory 161 (see FIG. 5), the light emission time (pulse width) of the semiconductor laser element 51 is based on a density correction curve indicating the relationship between the position in the main scanning direction and the density in the main scanning range (image forming range). ) Is stored in dot units. In the example shown in FIG. 7, the dots at the end of the photosensitive drum 1 in the main scanning direction are corrected in the direction of increasing the density by increasing the light emission time of the semiconductor laser element 51, and the dots at the center are corrected by the semiconductor laser. The light emission time of the element 51 is shortened and correction is performed in the direction of decreasing the density.

  As described above, in the present embodiment, the density correction is performed by adjusting the High and Low widths of the pulse signal for each dot (first correction). For example, when the concentration is increased, the delay element 159 that is one or two stages ahead of the delay element 159 selected based on the gradation value is set so that the light emission time of the semiconductor laser element 51 becomes longer. An output signal is output from the selector 157, and adjustment is performed to increase the High time in one dot. When the density is decreased, the output signal of the delay element 159 that is one or two stages later than the delay element 159 selected based on the gradation value so that the light emission time of the semiconductor laser element 51 is shortened. Is output from the selector 157 and adjustment is performed to shorten the High time in one dot.

  In the above description, generation and correction of pulse signals for one color have been described. However, the driver 160 and the semiconductor laser elements 51 are provided for a plurality of colors. Therefore, the pulse signal modulator 155 is also provided for a plurality of colors. The memory 161 stores correction data for a plurality of colors (one photoconductor drum), and the controller 153 controls the selector 157 of the pulse signal modulator 155 for each color to generate and correct a pulse signal for each color. (The same applies to the second correction below).

  Next, the second correction for further correcting the light emission time of the semiconductor laser element 51 for a predetermined dot in each block obtained by dividing the main scanning line extending in the main scanning direction into a plurality of blocks will be described.

  As an example, as described above, it is assumed that the drawing time per dot is about 25 ns and the propagation delay of the delay element 159 is about 300 ps under the longest condition. In this case, the light emission time of the semiconductor laser element 51 for 1-dot image data can be corrected with a resolution of about 1/83.

  However, considering the sensitivity of the photosensitive drum 1 and the like, even if correction is performed with a resolution of 1/83, the light emission time after correction of the semiconductor laser element 51 for each dot is ideal light emission time in view of the density correction curve. On the other hand, a slight deviation occurs. For this reason, when viewed in block units (for example, 20 dot units), the density of each of the plurality of blocks may also deviate from the ideal density.

  In general, when correcting the light emission time of the semiconductor laser element 51 and performing density correction, the light emission time of the semiconductor laser element 51 is controlled by 100 divisions or more per dot in order to make it difficult to see the change point of the density. It is said that it is necessary to do. In other words, in the correction of the light emission time of the semiconductor laser element 51, the smaller the change width (one step) of the light emission time, the less the change in density is visually recognized. For example, if the specification is 16 gradations per pixel, a resolution of (1/16) × (1/100) = 1/1600 is required, and a resolution of 1/83 requires an additional 20 times higher resolution. .

  Therefore, in the present embodiment, in order to realize correction at a desired resolution (for example, resolution of 1/1600), the main scan line extending in the main scan direction is divided into a plurality of parts at the same time as performing the first correction described above. In each block (each block having 20 dots), the light emission time of the semiconductor laser element 51 is further corrected for a predetermined dot. Here, in the present embodiment, the emission time of the semiconductor laser element 51 with respect to 1-dot image data can be adjusted with a resolution of 1/83. Therefore, the emission time of the semiconductor laser element 51 with respect to 1 block of image data is 1/1660. It will be finally adjusted with the resolution.

  Specifically, as shown in FIG. 8A, the exposure control unit 150 divides the main scanning line extending in the main scanning direction into a plurality of blocks (divided every 20 dots), and each of the blocks in each block. The light emission time of the semiconductor laser element 51 is further corrected for the predetermined one dot. For example, in consideration of the sensitivity of the photosensitive drum 1 and the like, in a block at a position to be darkened, the light emission time of a predetermined dot is increased by 1/83 dots. On the other hand, for example, in a block at a position to be thinned, the light emission time of a predetermined dot is shortened by 1/83 dots. In FIG. 8, in order to make the drawing easier to see, each dot is outlined and each block is separated by a thick line. Further, in FIG. 8, “◯” is given to a predetermined dot.

  Further, the exposure control unit 150 shifts the predetermined one dot for each main scanning line so that the predetermined one dot is not adjacent in the sub-scanning direction.

  For example, as shown in FIG. 8B, when a predetermined dot is adjacent in the sub-scanning direction, the position of the dot for performing the second correction is fixed in the sub-scanning direction, and vertical stripes extending in the sub-scanning direction are visually recognized. It becomes easy. Therefore, the exposure control unit 150 shifts the predetermined one dot for each main scanning line so that the predetermined one dot is not adjacent in the sub-scanning direction. For example, the exposure control unit 150 holds the relative position between the block boundary position in the main scanning direction and the position of a predetermined one dot without being changed. Then, the block boundary position in the main scanning direction is shifted for each main scanning line while maintaining the relative position. In this way, inevitably, one predetermined dot is not adjacent in the sub-scanning direction. In FIG. 8A, the boundary position of the second line block is shifted to the right by 2 dots with respect to the first line, and the boundary position of the third line block is shifted to the left by 4 dots. Yes.

  Further, for example, a plurality of division position setting data for setting block boundary positions in the main scanning direction are stored in the memory 161. Further, the plurality of division position setting data indicate different division positions. Then, the exposure control unit 150 randomly selects the division position setting data to be used from the plurality of division position setting data for each main scanning line. Thereby, the boundary position of the block in the main scanning direction is shifted for each main scanning line.

  Hereinafter, an example of the above-described density correction will be described with reference to FIG. Each drawing in FIG. 9 is an enlarged view of a part of a line in the main scanning direction. In the following description, it is assumed that a gray image having a uniform density is formed.

  Further, when the light emission time of the semiconductor laser element 51 is made uniform for each dot and exposure scanning for a plurality of lines is performed in the sub-scanning direction, the density on the left side in the main scanning direction becomes high as shown in the lower diagram of FIG. Assume that an image having a low density on the right side is formed. Note that black in each figure in FIG. 9 means a light emission section (a section on which toner is placed) of the semiconductor laser element 51, and white in each figure in FIG. 9 means a light-off section of the semiconductor laser element 51.

  Under the above-described conditions, the exposure control unit 150 makes the density gradually higher from the left side toward the right side in order to make the density uniform in the main scanning direction (the density is decreased toward the left side, Density correction is performed so as to increase the density. For example, as illustrated in FIG. 9B, the exposure control unit 150 shortens the light emission time of the semiconductor laser element 51 at a rate of 1 dot per several dots among the dots in the block where the density is high. Thinning density correction (first correction) is performed. Note that the light emission time of the semiconductor laser element 51 may be increased for the block of the portion where the concentration is low. Further, the exposure control unit 150 further adjusts the light emission time of the semiconductor laser element 51 for a predetermined one dot in the block for density correction in units of blocks (second correction).

  However, when the first correction is performed, the thinned portion continues in the sub-scanning direction, and the vertical stripes extending in the sub-scanning direction are easily visible. Further, when one predetermined dot subjected to the second correction continues in the sub-scanning direction, the portion subjected to the second correction appears in a streak shape and is recognized as density unevenness.

  The reason why such an inconvenience occurs is that, as described above, the change width (one step) of the light emission time of the semiconductor laser element 51 is large, and the light emission time of the semiconductor laser element 51 cannot be finely adjusted. Therefore, the exposure control unit 150 shifts the block boundary position in the main scanning direction for each main scanning line.

  However, even if this is done, interference fringes will appear if the deviation is periodic. Therefore, the exposure control unit 150 blocks the block in the main scanning direction when the boundary position of the block in the main scanning direction is shifted for each main scanning line (when the division position setting data to be used is selected from a plurality of division position setting data). Prevent periodicity from occurring at the boundary position. If it does in this way, as shown in FIG.9 (c), it will become difficult to visually recognize stripe-shaped density | concentration unevenness. In FIG. 9C, a gray solid line indicates a block boundary position.

  Note that random numbers may be used in order to prevent periodicity at the block boundary positions in the main scanning direction. For example, a random number for preventing periodicity from occurring in the block boundary position in the main scanning direction is generated by the random number generation unit 162 (see FIG. 5). The random number generator 162 generates a random number based on the density correction curve. FIG. 10 is a conceptual diagram of random number generation. Based on this concept, the random number generation unit 162 generates random numbers.

  For example, in the density correction curve of FIG. 10A, the density is gradually increased from the left side to the right side in the main scanning direction. In this case, the random number average position is taken near the density change point in the main scanning direction, and the random number variation (spreading of the divided positions) is made relatively large.

  In the density correction curve of FIG. 10B, the change in density in the main scanning direction is steeper than that of FIG. In this case, the random number variation (spreading of divided positions) is made smaller than in FIG.

  In the density correction curve of FIG. 10C, the density change point in the main scanning direction is shifted to the right as compared with FIG. In this case, the random number average position is shifted to the right as compared with FIG.

  As described above, in the first embodiment, the photosensitive drum 1 (image carrier) that is rotatably supported and the semiconductor laser element 51 (light emitting element) are provided, and the rotation shaft of the photosensitive drum 1 is provided. The exposure apparatus 5 that performs exposure scanning using light emitted from the semiconductor laser element 51 with the direction as the main scanning direction and forms an electrostatic latent image on the photosensitive drum 1, and shows whether the semiconductor laser element 51 is turned on or off. And an exposure control unit 150 that generates a pulse signal and controls turning on and off of the semiconductor laser element 51. Then, the exposure control unit 150 adjusts the emission time of the semiconductor laser element 51 for each dot by modulating the width of the pulse signal, and extends in the main scanning direction, and corrects the density in the main scanning direction. In each block obtained by dividing the main scanning line into a plurality of pieces, a second correction is performed to further correct the light emission time of the semiconductor laser element 51 for a predetermined dot.

  According to the configuration of the first embodiment, the exposure control unit 150 adjusts the light emission time of the semiconductor laser element 51 for each dot by correcting the width of the pulse signal to correct the density in the main scanning direction. Correction and second correction for further correcting the light emission time of the semiconductor laser element 51 for a predetermined dot are performed in each block obtained by dividing the main scanning line extending in the main scanning direction into a plurality of blocks. Here, since the minimum change width (one step) of the pulse width is limited, it is difficult to completely match the light emission time of the semiconductor laser element 51 in each dot with the ideal light emission time. For this reason, a slight error occurs between the actual light emission time and the ideal light emission time for each dot, and when a small error is accumulated in each dot, it may be visually recognized as uneven density in blocks. However, in the configuration of the first embodiment, the second correction is performed so as to eliminate the error accumulated in each dot. As a result, it is possible to perform appropriate correction of density without degrading the image due to human eye resolution or toner drawing errors, even with low resolution pulse width modulation instead of high resolution pulse width modulation. Therefore, even if the exposure controller 150 does not have an expensive high-resolution pulse width modulation function, density correction can be performed to satisfactorily suppress the occurrence of density unevenness in the main scanning direction, thereby suppressing an increase in cost. Can do.

  In the first embodiment, the exposure control unit 150 determines the position of the predetermined dot for performing the second correction so that the position of the predetermined dot for which the second correction has been performed is not aligned in the sub-scanning direction orthogonal to the main scanning direction. Shift every main scan line. When the positions of the predetermined dots for performing the second correction are aligned in the sub-scanning direction, vertical stripe-like density unevenness may occur in the sub-scanning direction. However, according to this configuration, since the position of the predetermined dot for intentionally performing the second correction is shifted for each main scanning line, the vertical stripe-shaped density unevenness does not occur.

  In the first embodiment, the exposure control unit 150 sets the same number of dots in each block and shifts the block boundary position in the main scanning direction for each main scanning line. With this configuration, it is difficult for a density step to occur at the block boundary position in the main scanning direction. For this reason, even if the second correction is performed on each block obtained by dividing the main scanning line into a plurality of blocks, the density uniformity is not impaired.

  In the first embodiment, the exposure control unit 150 performs the second correction by setting the dot at the same position among the dots included in each block as a predetermined dot. With this configuration, when the block boundary position in the main scanning direction is shifted for each main scanning line, the position of the predetermined dot for performing the second correction is shifted for each main scanning line.

  In the first embodiment, the exposure control unit 150 shifts the block boundary position in the main scanning direction for each main scanning line so that periodicity does not occur. With this configuration, it is possible to suppress the occurrence of an inconvenience that the block boundaries interfere with each other and interference fringes appear.

  The first embodiment further includes a random number generation unit 162 that generates random numbers, and the exposure control unit 150 uses the random numbers generated by the random number generation unit 162 to determine the block boundary position in the main scanning direction as the main scanning line. Shift every time. With this configuration, the block boundary position in the main scanning direction can be easily shifted for each main scanning line so that periodicity does not occur.

  In the first embodiment, the random number generation unit 162 generates a random number based on a density correction curve indicating the relationship between the position in the main scanning direction and the density. With this configuration, the block boundary position in the main scanning direction can be easily shifted for each main scanning line based on the density correction curve.

  In the first embodiment, the exposure control unit 150 selects one of the output signals from the delay circuit 156 that delays the input signal by connecting the delay elements 159 in a plurality of stages in series, and the delay elements 159 in a plurality of stages. And a selector 157 that outputs the delayed signal and a logic circuit 158 that performs a logical operation of the input signal and the delayed signal, and modulates the width of the pulse signal. With this configuration, it is possible to modulate the width of the pulse signal in units of delay time only by providing a plurality of delay elements 159. Thereby, in order to modulate the width of the pulse signal, the width of the pulse signal can be modulated without using a high multiplication type PLL or the like, and an increase in cost can be suppressed.

  In this case, when performing the second correction, the exposure control unit 150 sets one dot included in each block as a predetermined dot, and performs the semiconductor laser for the delay time of one delay element among the delay elements 159 in a plurality of stages. The light emission time of the element 51 is corrected. With this configuration, the density correction of each block can be performed within a range that does not significantly affect the density.

(Second Embodiment)
In the second embodiment, a case will be described in which partial equality correction (position shift correction) as magnification correction and density correction of the first embodiment described above are performed as a set.

  First, partial equality correction will be described. First, in the formed image, the start position and the end position of the image formation are aligned in the main scanning direction, but there may be a deviation between the start position and the end position (image formation start position). And the end positions may not even be aligned). The shift in the main scanning direction is caused by a shift of the optical system member in the image reading unit 102 or the exposure apparatus 5. This shift is particularly important when color images are superimposed, and can be a factor that degrades the quality of the formed image.

  Here, if the start position of image formation in the main scanning direction is deviated, the timing at which the semiconductor laser element 51 starts emitting in the entire main scanning direction may be adjusted. If the end position is deviated, the emission time of laser light per dot may be adjusted in the entire main scanning direction.

  However, if the start position and end position of toner image formation match, but they deviate between them, the above adjustment method cannot cope. Therefore, the correction corresponding to the deviation between the start position and the end position in the main scanning direction is partial equality correction. Specifically, the main scanning line is divided into a plurality of magnification correction blocks, and the deviation in the main scanning direction is corrected for each of the plurality of magnification correction blocks. As a result, it is possible to form an image having no deviation as a whole, and it is possible to form a high-quality image particularly for a color image.

  Here, partial equality correction will be described more specifically with reference to FIG. Note that the broken lines in FIG. 11 are ideal lines i1 to i8, and are arranged at equal intervals in the main scanning direction. Therefore, the widths of the blocks divided by the ideal lines i1 to i8 are equal. On the other hand, the solid lines shown in FIG. 11A are actual lines t1 to t8 that have been printed out, although printing has been attempted at the positions of the ideal lines i1 to i8. And the solid line arrow shown below Fig.11 (a) is a shift | offset | difference direction.

  As shown in FIG. 11A, there is a shift in each block. Here, FIG. 11A shows only one color among black, yellow, cyan, and magenta. In this case, misregistration occurs in the other colors as well, and the misregistration method is usually different for each color. Therefore, when the toner images of the respective colors are overlapped, a large misalignment may occur. is necessary.

  Therefore, an example of a method for correcting the shift in each block will be described. First, a pattern image for correcting deviation is printed out with the highest resolution. Image data of this pattern image is stored in the storage unit 113. The pattern image only needs to be able to determine the deviation in the formation of each color toner image. For example, a plurality of line-shaped pattern image blocks extending in the sub-scanning direction as shown in FIG. 11A are arranged in the main scanning direction. Can be considered. Further, since four color toner images are formed, it is conceivable to arrange each color in the sub-scanning direction.

  Then, for example, the deviation amount and the deviation direction are visually confirmed and input from the operation panel 101 (note that if the deviation amount is input with a plus or minus sign, the direction and the amount can be expressed simultaneously). Alternatively, data transmission from the computer 200 connected to the multifunction peripheral 100 to the control unit 110 may be performed. The amount of shift and the direction of the shift can be checked by comparing an ideal pattern image prepared separately with a pattern image actually printed, or by checking the width of the interval between actually printed lines. Also good. Further, the shift amount and the shift direction of each pattern image of other colors (yellow, magenta, and cyan) may be confirmed with respect to the black pattern image using one color as a reference (for example, black as a reference). The inputted shift amount and shift direction in the main scanning direction are stored in the memory 161 as partial equality correction data.

  Then, the exposure control unit 150 performs partial equal magnification correction based on the partial equal magnification correction data. For example, when the exposure control unit 150 performs correction for expanding the magnification correction block in the main scanning direction, the exposure control unit 150 increases the pulse width of the reference pulse signal and reduces the magnification correction block in the main scanning direction. Reduce the pulse width of the reference pulse signal. As a result, as shown in FIG. 11B, the displacement in each magnification correction block is corrected.

  By the way, in the above-mentioned partial equality correction, the magnification is simply corrected, and the density correction is not performed. More specifically, since the emission energy of the semiconductor laser element 51 does not change during the exposure scan, the density of the block that shrinks in the main scan direction tends to increase because the scan speed is slow, and the main scan In the block spreading in the direction, the scanning speed is high and the density tends to be thin. When the same-magnification correction is applied thereto (that is, the contracted block is expanded and the expanded block is contracted), only the magnification is corrected while the dark block remains dark and the thin block remains thin.

  Therefore, in the second embodiment, the above-described density correction and partial equality correction of the first embodiment are performed as a set.

  For example, assume that partial equality correction is performed on a predetermined magnification correction block. In this case, the density of the predetermined magnification correction block remains dark (or even darker) only by performing partial equal magnification correction that expands the predetermined magnification correction block in the main scanning direction. Therefore, in the block for magnification correction that is expanded in the main scanning direction (currently reduced), the exposure control unit 150 performs semiconductor laser processing on one dot or two dots or more (including all dots) in the block for magnification correction. Correction for shortening the light emission time of the element 51 is performed. On the other hand, in the magnification correction block narrowed in the main scanning direction (currently widened), the light emission time of the semiconductor laser element 51 for one dot or two dots or more (including all dots) in the magnification correction block. Make a correction to lengthen.

  At the same time, the exposure control unit 150 performs the density correction of the first embodiment described above. That is, the exposure control unit 150 corrects the light emission time of the semiconductor laser element 150 in units of dots (first correction), and for each of a plurality of magnification correction blocks, a predetermined one in each magnification correction block. The light emission time of the semiconductor laser element 51 is further corrected (second correction) for the dots. In other words, in the second embodiment, the exposure control unit 150 performs magnification correction after dividing the main scanning line into a plurality of magnification correction blocks, and sets the magnification correction block as the second correction block. 2 Correction is performed.

  In the second embodiment, the exposure control unit 150 performs magnification correction after dividing the main scanning line into a plurality of magnification correction blocks, and uses the magnification correction block as a second correction block to perform second correction. To do. With this configuration, appropriate density correction can be performed on the magnification correction block.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

1 Photosensitive drum (image carrier)
5 Exposure equipment 51 Semiconductor laser element (light emitting element)
150 Exposure Control Unit 156 Delay Circuit 157 Selector 158 Logic Circuit 159 Delay Element 162 Random Number Generation Unit

Claims (10)

An image carrier that is rotatably supported;
A light-emitting element is included, and the rotation axis direction of the image carrier is a main scanning direction, and exposure scanning is performed using light emitted from the light-emitting element to form an electrostatic latent image on the image carrier. An exposure device;
An exposure control unit that generates a pulse signal indicating turning on or off of the light emitting element, and controls turning on and off of the light emitting element, and
The exposure control unit adjusts a light emission time of the light emitting element for each dot by modulating a width of the pulse signal, and corrects the density in the main scanning direction, and extends in the main scanning direction. An image forming apparatus comprising: a second correction for further correcting the light emission time of the light emitting element for a predetermined dot in each block obtained by dividing the main scanning line into a plurality of blocks.   The exposure control unit sets the position of the predetermined dot for performing the second correction for each main scanning line so that the position of the predetermined dot for which the second correction has been performed is not aligned in the sub-scanning direction orthogonal to the main scanning direction. The image forming apparatus according to claim 1, wherein the image forming apparatus is shifted to a first position.   The image forming apparatus according to claim 2, wherein the exposure control unit sets the same number of dots in each block and shifts a block boundary position in the main scanning direction for each main scanning line.   The image forming apparatus according to claim 3, wherein the exposure control unit performs the second correction using a dot at the same position as a predetermined dot among the dots included in each block.   The image forming apparatus according to claim 3, wherein the exposure control unit shifts a block boundary position in the main scanning direction for each main scanning line so that periodicity does not occur. A random number generator for generating random numbers;
The image forming apparatus according to claim 5, wherein the exposure control unit shifts a block boundary position in the main scanning direction for each main scanning line using a random number generated by the random number generating unit.   The image forming apparatus according to claim 6, wherein the random number generation unit generates a random number based on a density correction curve indicating a relationship between the position in the main scanning direction and the density.   The exposure control unit includes a delay circuit that delays an input signal by connecting a plurality of delay elements in series, a selector that selects any one of the plurality of delay elements and outputs it as a delay signal, and The image forming apparatus according to claim 1, further comprising a logic circuit that performs a logical operation of the input signal and the delay signal, and modulating a width of the pulse signal.   The exposure control unit, when performing the second correction, sets one dot included in each block as a predetermined dot, and the light emitting element for a delay time of one delay element among the plurality of stages of delay elements The image forming apparatus according to claim 8, wherein the light emission time is corrected.   The exposure control unit performs magnification correction after dividing the main scanning line into a plurality of magnification correction blocks, and performs the second correction using the magnification correction block as the second correction block. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.