JP2016173488A - Image formation apparatus and control method of image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a positional deviation caused by time-division light emission and prevent a density variation due to a difference in a rotation speed of a photoreceptor when performing the time-division light emission.SOLUTION: Time-division driving is performed by respectively controlling light emission of LED devices by group in a predetermined light emission period. In response to a determination of linear velocity according to a sheet, a pattern for density correction is drawn and a density correction value is generated.SELECTED DRAWING: Figure 16

Description

  The present invention relates to an image forming apparatus and a method for controlling the image forming apparatus.

  In recent years, there has been a tendency to digitize information, and image processing apparatuses such as printers and facsimiles used for outputting digitized information and scanners used for digitizing documents have become indispensable devices. Such an image processing apparatus is often configured as a multifunction machine that can be used as a printer, a facsimile, a scanner, or a copier by providing an imaging function, an image forming function, a communication function, and the like.

  Among such image processing apparatuses, electrophotographic image forming apparatuses are widely used in image forming apparatuses used for outputting digitized documents. In an electrophotographic image forming apparatus, an electrostatic latent image is formed by exposing a photoreceptor, and the electrostatic latent image is developed using a developer such as toner to form a toner image. Paper output is performed by transferring the toner image onto paper.

  In such an electrophotographic image forming apparatus, a linear light source such as an LEDA (LED Array) in which LED (Light Emitting Diode) elements are arranged in the main scanning direction is used as a light source for exposing a photosensitive member. Sometimes. In such a linear light source, when performing exposure for one line, time division driving is used in which each LED element is divided into a plurality of groups, and each group emits light in order.

  This time-division driving can reduce the power required at one time compared to the case where all the light sources are driven to emit light at the same timing. On the other hand, since the photosensitive member is always rotating, when the LED elements arranged linearly in the direction parallel to the rotation axis are driven in a time-sharing manner, the exposure position for one line that should be aligned linearly is There is a problem that it is shifted according to the light emission timing.

  In order to solve such a problem, a method of shifting image data in accordance with a shift caused by time-division driving has been proposed (see, for example, Patent Document 1). In the technique disclosed in Patent Document 1, the level difference is made inconspicuous by shifting the image line in the sub-scanning direction in the vicinity of the main scanning position where the level difference is generated by time-division driving.

  In the technique disclosed in Patent Document 1, the shift in the time-division driving is eliminated by line-shifting the image in the sub-scanning direction. However, since the time-division driving is to emit each group at different timings in the light emission control for one line as described above, the resulting shift amount is in the range of one line or less. Therefore, the shift due to the time division drive cannot be eliminated by the line shift.

  In order to suppress the deviation caused by the time-division driving described above, it is possible to shorten the exposure time corresponding to one pixel as much as possible and to allow the light emission control interval when the LED elements of each group emit light sequentially. It needs to be as short as possible. Therefore, it is required that the exposure time and the light emission cycle when the LED elements of each group are sequentially emitted in time-division driving be a minimum period in which necessary exposure energy can be obtained.

  On the other hand, in the control of the electrophotographic image forming apparatus, for example, the sheet conveyance speed in the apparatus is changed according to the thickness or quality of the sheet to be transferred, and the rotation speed of the photosensitive member is changed accordingly. There is. Here, when the exposure time per pixel when exposing the photosensitive member is set to a fixed value as the minimum period as described above, when changing the rotational speed of the photosensitive member, per unit area according to the rotational speed. The exposure energy will fluctuate. As a result, the density of the image is affected.

  The present invention has been made in consideration of the above circumstances, and divides the light emitting elements included in the linear light source into a plurality of groups, and performs time division light emission in which light emission for one line is performed at different timings for each group. In the case of performing, it is an object to reduce the amount of misalignment caused by time-division emission and to prevent density fluctuation due to the difference in the rotation speed of the photoconductor.

  In order to solve the above problems, one embodiment of the present invention provides an electrostatic latent image on a photosensitive member by controlling light emission of a light source device including a plurality of light sources configured by linearly arranging a plurality of light emitting elements. An image forming apparatus including an optical writing device to be formed, and generated based on the acquired image information and an image information acquiring unit that acquires image information that is information on an image to be formed as the electrostatic latent image A light source control unit that controls light emission of the light source on the basis of information on the detected pixels, and detects the image in a conveyance path on which an image in which an electrostatic latent image formed on the photosensitive member is developed is transferred and conveyed. A detection signal acquisition unit for acquiring a detection signal of the sensor and a correction pattern for correcting the density of the developer image obtained by developing the electrostatic latent image formed on the photosensitive member are detected by the sensor. Based on the detection signal, A correction value generation unit that generates a correction value for correcting the recording density, and the light source control unit performs light emission control on the plurality of light emitting elements divided into a plurality of groups in order for each group. One light emission control of the light source is performed to form an electrostatic latent image corresponding to an image for one line, and the light emitting elements of each group are controlled to emit light during a predetermined light emission period, and By controlling the light emission of the light source so that the correction pattern for correcting the density is drawn according to the determination of the rotation speed of the photoconductor according to the recording medium to which the colorant image is transferred, The photosensitive member rotating at the determined rotation speed is exposed, and the correction value generating unit calculates the density based on a detection signal of the correction pattern drawn according to the determination of the rotation speed of the photosensitive member. Correct And generating a correction value for.

  According to the present invention, when the light emitting elements included in the linear light source are divided into a plurality of groups and the time division light emission is performed by performing light emission for one line at different timings for each group, the position generated by the time division light emission It is possible to reduce the amount of deviation and prevent the density fluctuation due to the difference in the rotation speed of the photoconductor.

1 is a block diagram illustrating a hardware configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating a functional configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a diagram illustrating a configuration of a print engine according to an embodiment of the present invention. It is a figure which shows the structure of the optical writing apparatus which concerns on embodiment of this invention. It is a figure which shows the structure of the LEDA print head which concerns on embodiment of this invention. It is a figure which shows the problem of the time division drive which concerns on embodiment of this invention. It is a figure which shows the problem of the time division drive which concerns on embodiment of this invention. It is a figure which shows the problem of the time division drive which concerns on embodiment of this invention. It is a figure which shows the problem of the time division drive which concerns on embodiment of this invention. It is a figure which shows the relationship between the line period and strobe period which concern on embodiment of this invention. It is a figure which shows the fluctuation | variation of the exposure area by the change of a linear velocity. It is a figure which shows the fluctuation | variation of the exposure energy by the change of a linear velocity. It is a figure which shows the function structure of the optical writing control part which concerns on embodiment of this invention. It is a figure which shows the setting value of the strobe period which concerns on embodiment of this invention, and a strobe space | interval. It is a figure which shows the example of the mark for density correction which concerns on embodiment of this invention. It is a flowchart which shows operation | movement of the optical writing control part which concerns on embodiment of this invention. It is a figure which shows the example of the reading density according to a developing bias. It is a figure which shows the example of the reading density according to a transfer bias. It is a figure which shows the example in case the reading density according to a transfer bias is less than a reference value. It is a figure which shows the example of the table which shows the correspondence of an insufficient density value and the correction value of exposure intensity.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the present embodiment, an image forming apparatus as an MFP (Multi Function Peripheral) will be described as an example. The image forming apparatus according to the present embodiment is an electrophotographic image forming apparatus, and a linear light source in which light emitting elements are arranged in the main scanning direction is used as a light source for exposing a photosensitive member.

  In the image forming apparatus according to the present embodiment, in order to reduce the instantaneous peak value of power consumption, the light emitting elements included in the linear light source are divided into a plurality of groups and driven to emit light sequentially in time series. Time division driving is performed. As the light emission timing is shifted by this time-division driving, the exposure position of each pixel included in the same line is shifted in the rotation direction of the photosensitive member.

  In order to reduce such a shift, it is required to shorten the period when the light emitting elements of each group are sequentially driven to emit light in time division driving as much as possible. Therefore, it is preferable to fix the exposure time for one time when the light emitting element is driven to emit light in the shortest period within a range in which sufficient exposure energy can be given to the photoreceptor.

  On the other hand, in an electrophotographic image forming apparatus, the rotational speed of a rotating photosensitive member may be changed depending on the type of paper as a recording medium. In such a case, as described above, when a fixed value is adopted as the exposure time for one time, the exposure energy per unit area changes as the rotational speed of the photoconductor changes, and as a result, the image Concentration will fluctuate. Such a control for solving the problem of the deviation of the exposure position by the time-division driving and the fluctuation of the density is one of the gist according to the present embodiment.

  FIG. 1 is a block diagram illustrating a hardware configuration of an image forming apparatus 1 according to the present embodiment. As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment includes an engine that executes image formation in addition to the same configuration as an information processing terminal such as a general server or a PC (Personal Computer). That is, the image forming apparatus 1 according to the present embodiment includes a CPU (Central Processing Unit) 10, a RAM (Random Access Memory) 11, a ROM (Read Only Memory) 12, an engine 13, an HDD (Hard Disk Drive) 14, and an I / O. F15 is connected via the bus 18. Further, an LCD (Liquid Crystal Display) 16 and an operation unit 17 are connected to the I / F 15.

  The CPU 10 is a calculation unit and controls the operation of the entire image forming apparatus 1. The RAM 11 is a volatile storage medium capable of reading and writing information at high speed, and is used as a work area when the CPU 10 processes information. The ROM 12 is a read-only nonvolatile storage medium, and stores programs such as firmware. The engine 13 is a mechanism that actually executes image formation in the image forming apparatus 1.

  The HDD 14 is a nonvolatile storage medium capable of reading and writing information, and stores an OS (Operating System), various control programs, application programs, and the like. The I / F 15 connects and controls the bus 18 and various hardware and networks. The LCD 16 is a visual user interface for the user to check the state of the image forming apparatus 1. The operation unit 17 is a user interface for the user to input information to the image forming apparatus 1 such as a touch panel configured on the screen and various hard keys.

  In such a hardware configuration, the software control unit is configured by the CPU 10 performing calculations in accordance with a program stored in the ROM 12 or a program read to the RAM 11 from a recording medium such as the HDD 14 or an optical disk (not shown). . A functional block that realizes the functions of the image forming apparatus 1 according to the present embodiment is configured by a combination of the software control unit configured as described above and hardware.

  Next, the functional configuration of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG. FIG. 2 is a block diagram illustrating a functional configuration of the image forming apparatus 1 according to the present embodiment. As shown in FIG. 2, the image forming apparatus 1 according to the present embodiment includes a controller 20, an ADF (Auto Document Feeder) 21, a scanner unit 22, a paper discharge tray 23, a display panel 24, and a paper feed table. 25, a print engine 26, a paper discharge tray 27, and a network I / F 28.

  The controller 20 includes a main control unit 30, an engine control unit 31, an input / output control unit 32, an image processing unit 33, and an operation display control unit 34. As shown in FIG. 2, the image forming apparatus 1 according to the present embodiment is configured as a multifunction machine having a scanner unit 22 and a print engine 26. In FIG. 2, the electrical connection is indicated by solid arrows, and the flow of paper is indicated by broken arrows.

  The display panel 24 is an output interface that visually displays the state of the image forming apparatus 1 and is an input when the user directly operates the image forming apparatus 1 or inputs information to the image forming apparatus 1 as a touch panel. It is also an interface (operation unit). Accordingly, the display panel 24 includes the LCD 16 and the operation unit 17 shown in FIG. The network I / F 28 is an interface for the image forming apparatus 1 to communicate with other devices via the network, and uses an Ethernet (registered trademark) or a USB (Universal Serial Bus) interface.

  The controller 20 is configured by a combination of software and hardware. Specifically, as described above, the controller 20 is configured by the software control unit configured by the calculation of the CPU 10 and hardware such as an integrated circuit. The controller 20 functions as a control unit that controls the entire image forming apparatus 1.

  The main control unit 30 plays a role of controlling each unit included in the controller 20 and gives a command to each unit of the controller 20. The engine control unit 31 serves as a drive unit that controls or drives the print engine 26, the scanner unit 22, and the like. The input / output control unit 32 inputs a signal or a command input via the network I / F 28 to the main control unit 30. The main control unit 30 controls the input / output control unit 32 and accesses other devices via the network I / F 28.

  The image processing unit 33 generates drawing information based on the print information included in the input print job under the control of the main control unit 30. The drawing information is information for drawing an image to be formed in the image forming operation by the print engine 26 as an image forming unit. The print information included in the print job is image information converted into a format that can be recognized by the image forming apparatus 1 by a printer driver installed in an information processing apparatus such as a PC. The operation display control unit 34 displays information on the display panel 24 or notifies the main control unit 30 of information input via the display panel 24.

  When the image forming apparatus 1 operates as a printer, first, the input / output control unit 32 receives a print job via the network I / F 28. The input / output control unit 32 transfers the received print job to the main control unit 30. When receiving the print job, the main control unit 30 controls the image processing unit 33 to generate drawing information based on the print information included in the print job.

  When drawing information is generated by the image processing unit 33, the engine control unit 31 controls the print engine 26 based on the generated drawing information, and executes image formation on the paper conveyed from the paper supply table 25. To do. That is, the print engine 26 functions as an image forming unit. A document on which an image has been formed by the print engine 26 is discharged to a discharge tray 27.

  When the image forming apparatus 1 operates as a scanner, the operation display control unit 34 or the input / output unit is operated in accordance with a user operation on the display panel 24 or a scan execution instruction input from an external PC or the like via the network I / F 28. The control unit 32 transfers a scan execution signal to the main control unit 30. The main control unit 30 controls the engine control unit 31 based on the received scan execution signal.

  The engine control unit 31 drives the ADF 21 and conveys the document to be imaged set on the ADF 21 to the scanner unit 22. Further, the engine control unit 31 drives the scanner unit 22 and images a document conveyed from the ADF 21. If no original is set on the ADF 21 and the original is directly set on the scanner unit 22, the scanner unit 22 takes an image of the set original under the control of the engine control unit 31. That is, the scanner unit 22 operates as an imaging unit.

  In the imaging operation, an imaging element such as a CCD included in the scanner unit 22 optically scans the document, and imaging information generated based on the optical information is generated. The engine control unit 31 transfers the imaging information generated by the scanner unit 22 to the image processing unit 33. The image processing unit 33 generates image information based on the imaging information received from the engine control unit 31 according to the control of the main control unit 30. Image information generated by the image processing unit 33 is stored in a storage medium attached to the image forming apparatus 1 such as the HDD 14. That is, the scanner unit 22, the engine control unit 31, and the image processing unit 33 work together to function as a document reading unit.

  The image information generated by the image processing unit 33 is stored in the HDD 14 or the like as it is according to a user instruction or transmitted to an external device via the input / output control unit 32 and the network I / F 28. That is, the ADF 21 and the engine control unit 31 function as an image input unit.

  Further, when the image forming apparatus 1 operates as a copying machine, the image processing unit 33 generates drawing information based on the imaging information received by the engine control unit 31 from the scanner unit 22 or the image information generated by the image processing unit 33. To do. Based on the drawing information, the engine control unit 31 drives the print engine 26 as in the case of the printer operation.

  Next, the configuration of the print engine 26 according to the present embodiment will be described with reference to FIG. As shown in FIG. 3, the print engine 26 according to the present embodiment includes a configuration in which image forming units 106 of respective colors are arranged along a conveyor belt 105 that is an endless moving unit, which is a so-called tandem type. It is what is said. That is, along the transport belt 105, which is an intermediate transfer belt on which an intermediate transfer image for transfer onto a sheet (an example of a recording medium) 104 that is separated and fed by the sheet feed roller 102 from the sheet feed tray 101 is formed. A plurality of image forming units (electrophotographic process units) 106Y, 106M, 106C, and 106K (hereinafter collectively referred to as image forming units 106) are arranged in order from the upstream side in the transport direction of the transport belt 105.

  Further, the sheet 104 fed from the sheet feeding tray 101 is stopped once by the registration roller 103 and is sent out to the image transfer position from the conveying belt 105 according to the image forming timing in the image forming unit 106.

  The plurality of image forming units 106Y, 106M, 106C, and 106K have the same internal configuration except that the colors of the toner images to be formed are different. The image forming unit 106K forms a black image, the image forming unit 106M forms a magenta image, the image forming unit 106C forms a cyan image, and the image forming unit 106Y forms a yellow image. In the following description, the image forming unit 106Y will be described in detail. However, since the other image forming units 106M, 106C, and 106K are the same as the image forming unit 106Y, the image forming units 106M, 106C, and 106K. For each of these components, instead of Y added to each component of the image forming unit 106Y, only the symbols distinguished by M, C, and K are displayed in the figure, and the description is omitted.

  The conveying belt 105 is an endless belt, that is, an endless belt that is stretched between a driving roller 107 and a driven roller 108 that are rotationally driven. The drive roller 107 is driven to rotate by a drive motor (not shown), and the drive motor, the drive roller 107, and the driven roller 108 function as a drive unit that moves the conveyance belt 105 that is an endless moving unit. .

  At the time of image formation, the first image forming unit 106Y transfers a yellow toner image to the conveyance belt 105 that is driven to rotate. The image forming unit 106Y includes a photoconductor drum 109Y as a photoconductor, a charger 110Y disposed around the photoconductor drum 109Y, an optical writing device 111, a developing device 112Y, a photoconductor cleaner (not shown), and a static eliminator. 113Y and the like. The optical writing device 111 is configured to irradiate light to each of the photosensitive drums 109Y, 109M, 109C, and 109K (hereinafter collectively referred to as “photosensitive drum 109”).

  In the image formation, the outer peripheral surface of the photosensitive drum 109Y is uniformly charged by the charger 110Y in the dark, and then writing is performed by light from the light source corresponding to the yellow image from the optical writing device 111. An electrostatic latent image is formed. The developing device 112Y which is a developing device visualizes the electrostatic latent image with yellow toner, thereby forming a yellow toner image on the photosensitive drum 109Y.

  This toner image is transferred onto the conveyance belt 105 by the action of the transfer unit 115Y at a position (transfer position) where the photosensitive drum 109Y and the conveyance belt 105 are in contact with or closest to each other. By this transfer, an image of yellow toner is formed on the conveyance belt 105. After the transfer of the toner image is completed, the photosensitive drum 109Y is wiped away with unnecessary toner remaining on the outer peripheral surface by the photosensitive cleaner, and then is neutralized by the static eliminator 113Y and waits for the next image formation.

  As described above, the yellow toner image transferred onto the conveying belt 105 by the image forming unit 106Y is conveyed to the next image forming unit 106M by driving the rollers of the conveying belt 105. In the image forming unit 106M, a magenta toner image is formed on the photosensitive drum 109M by the same process as the image forming process in the image forming unit 106Y, and the toner image is superimposed and transferred onto the already formed yellow image. Is done.

  The yellow and magenta toner images transferred onto the conveying belt 105 are further conveyed to the next image forming units 106C and 106K, and the cyan toner image formed on the photosensitive drum 109C and the photosensitive member are subjected to the same operation. The black toner image formed on the body drum 109K is superimposed and transferred on the already transferred image. Thus, a full-color intermediate transfer image is formed on the conveyance belt 105. Such a toner image is a developer image.

  The sheets 104 stored in the sheet feed tray 101 are sent out in order from the top, and the intermediate transfer image formed on the conveyance belt 105 is transferred at a position where the conveyance path is in contact with or closest to the conveyance belt 105. It is transferred onto the paper. As a result, an image is formed on the surface of the sheet 104. The sheet 104 on which the image is formed on the sheet surface is further conveyed, the image is fixed by the fixing device 116, and then discharged to the outside of the image forming apparatus.

  In such an image forming apparatus 1, the toner images of the respective colors do not overlap at positions where they should overlap, and there may be a positional shift between the colors. Causes include, for example, errors in the inter-axis distances of the photosensitive drums 109Y, 109M, 109C, and 109K, and parallelism errors in the photosensitive drums 109Y, 109M, 109C, and 109K. In addition, there is an installation error of the LEDA 132 in the optical writing device 111, an error in writing timing of the electrostatic latent image on the photosensitive drums 109Y, 109M, 109C, and 109K, an expansion / contraction of the conveyance belt due to a change in temperature in the apparatus or deterioration with time, and the like. .

  For the same reason, the image may be transferred to a range that is outside the range where the image is originally transferred on the paper to be transferred. As such misregistration components, skew, registration deviation in the sub-scanning direction, and the like are mainly known.

  Further, in the image forming apparatus 1, the density variation occurs due to various factors. Factors include, for example, variations in the exposure intensity of the light source included in the optical writing device 111 and variations in the developing bias of the developing device 112 that develops the electrostatic latent image formed on the photosensitive drum 109. The developing bias is a voltage applied between the photosensitive drum 109 and the developing device 112 when developing the electrostatic latent image. There is also a variation in transfer bias when the developed image is transferred onto the photosensitive drum 109. The transfer bias is a voltage having a polarity opposite to the charging polarity of the toner applied from the back side of the paper when the toner image is transferred to the paper.

  A pattern detection sensor 117 is provided in order to correct such positional deviation and density variation. The pattern detection sensor 117 is an optical sensor for reading the misregistration correction pattern and the density correction pattern transferred onto the conveyor belt 105 by the photosensitive drums 109Y, 109M, 109C, and 109K. Therefore, the pattern detection sensor 117 includes a light emitting element for irradiating a pattern drawn on the surface of the transport belt 105 and a light receiving element for receiving reflected light from the correction pattern. As shown in FIG. 3, the pattern detection sensor 117 is disposed on the downstream side of the photosensitive drums 109Y, 109M, 109C, and 109K.

  The image forming apparatus 1 corrects parameters when driving and controlling each part of the print engine 26 based on the reading result of the pattern detection sensor 117 of each pattern described above. Examples of parameters include drive parameters for the image forming units 106Y, 106M, 106C, and 106K, drive parameters for the optical writing device 111, and drive timing. Details of the pattern detection sensor 117 and the mode of positional deviation correction and density correction will be described in detail later.

  A belt cleaner 118 is provided to remove the toner of the correction pattern drawn on the conveyance belt 105 in such drawing parameter correction and the toner remaining on the conveyance belt 105 in the image forming output. As shown in FIG. 3, the belt cleaner 118 is a cleaning blade pressed against the transport belt 105 on the downstream side of the driving roller 107 and on the upstream side of the photosensitive drum 109. That is, the belt cleaner 118 is a developer removing unit that scrapes off the toner adhering to the surface of the conveyor belt 105.

  Next, the optical writing device 111 according to the present embodiment will be described. FIG. 4 is a diagram showing an arrangement relationship between the optical writing device 111 and the photosensitive drum 109 according to the present embodiment. As shown in FIG. 4, the light emitted to the photosensitive drums 109Y, 109M, 109C, and 109K of the respective colors is a light-emitting diode array (LEDA) print head 130Y, 130M, 130C, and 130K (hereinafter referred to as light sources). , Generally LEDA print head 130). This LEDA print head 130 is used as a light source device.

  FIG. 5 is a diagram illustrating the configuration of the LEDA print head 130. In FIG. 5, the irradiation surface of LEDA which is a light source included in the LEDA print head 130 is displayed from the front. As shown in FIG. 5, the LEDA print head 130 is configured by arranging a plurality of LEDAs 132 on a substrate 131. The direction in which the LEDA 132 is arranged corresponds to the main scanning direction of the photosensitive drum 109.

  Each LEDA 132 is a light emitting element array configured by arranging a plurality of LED elements as light emitting elements in the same direction as the direction in which each LEDA 132 is arranged. Each LED element included in each LEDA 132 performs irradiation for one pixel.

  In addition, a plurality of drive circuits 133 that drive each LEDA 132 to emit light are provided inside the substrate 131. Each drive circuit 133 has a one-to-one correspondence with each LEDA 132.

  The control unit included in the optical writing device 111 determines the ON / OFF state of each LED arranged in the main scanning direction in the LEDA print head 130 for each main scanning line based on the drawing information input from the controller 20. By controlling, the surface of the photosensitive drum 109 is selectively exposed to form an electrostatic latent image.

  As shown in FIG. 5, one LEDA print head 130 includes a plurality of LEDAs 132. Here, when all the LEDs A132 are driven to emit light simultaneously, the amount of power required at that moment is the sum of the amounts of power required to issue all the LEDs A132. On the other hand, if the LED elements included in each LEDA 132 are divided into a plurality of groups and driven at different timings for each group, the amount of power required at one time can be reduced. Therefore, the optical writing device 111 according to the present embodiment employs such time division driving.

Here, a problem caused by time-division driving will be described. FIG. 6 is a diagram showing the timing of light emission driving of each group when the LED elements are divided into four groups, and the position on the photosensitive drum 109 exposed as a result. As shown in FIG. 6 top, the period of the light emission drive of the LED elements of each group are strobe period t _c.

The strobe period t _c includes a strobe period t _{a for} driving the LED element to emit light and a strobe interval t _b which is a waiting period until the next issue. In other words, the strobe period t _a is the light emission period, t _b are off period. Then, as shown in the figure, the light emission control is performed for each group in sequence, that is, the light emission control for one line is performed.

As shown in the middle of FIG. 6, in the example of FIG. 6, each LED element is divided into groups 1 to 4 so that groups 1 to 4 are sequentially repeated in the main scanning direction. Under such grouping, when the LED elements of groups 1 to 4 are sequentially controlled to light in the strobe cycle shown in the upper part, the exposure position by the adjacent LED elements is Lt in the sub-scanning direction as shown in the lower part of FIG. _The state is shifted by _c . Here, Lt _c is Lt _c = V _d × t _c where the linear velocity of the photosensitive drum 109 is V _d .

As shown in FIG. 6 the lower part, the time-division driving, the exposure position of the one line of pixels should be arranged in a linear state in the original main scanning direction, so that the distorted depending on the strobe period t _c.

On the other hand, FIG. 7 is a diagram showing an example in which the strobe period tc is half that of FIG. As shown in the lower part of FIG. 7, the exposure position shift Lt _c due to the adjacent LED elements becomes half that in FIG. 6, and the distortion of the exposure position that should originally be linear is reduced compared to the state of FIG. 6. That is, in order to suppress the distortion of the exposure position of a pixel by time division driving, it is preferable strobe period t _c is shorter as possible.

FIG. 8 is a diagram illustrating an example in which the arrangement of the light emission timings of each group in the time division drive is changed. In the example of FIG. 8, the arrangement of 1 to 4, 4 to 1 is repeated along the main scanning direction. In the case of FIG. 1, a large step is generated between the “4” group and the “1” group. However, in the case of the arrangement as shown in FIG. 8, the adjacent shift amount is always suppressed to Lt _c . I can do it.

Figure 9 is similar to FIG. 7 for 6 illustrates a case where the half strobe period t _c in FIG. As in FIG. 7, the distortion of the exposure position of the pixels on one line is reduced by reducing the strobe period by half.

  As described above, when time-division driving is performed, the exposure position on the photosensitive drum 109 of each pixel that should be in a straight line is distorted in the sub-scanning direction. This amount of distortion is determined by the strobe period, and increases as the strobe period becomes longer as described above. Therefore, it is preferable to shorten the strobe cycle in the time division drive as much as possible.

  FIGS. 10A and 10B are timing charts showing the relationship between the line period and the strobe period, which are the light emission timings for each main scanning line. As shown in FIG. 10A, the strobe periods of groups 1 to 4 need to be completed during one line period.

  Here, for example, when the linear speed of the photosensitive drum 109, that is, the rotational speed is halved, the line period is doubled in order to form an image with the same resolution in the sub-scanning direction. Further, when the linear velocity is the same, the line period is also doubled when the resolution in the sub-scanning direction is reduced to half.

  FIG. 10B is a timing chart when the line period is doubled. When the line period is doubled as shown in FIG. 10B, there is a margin in the period for completing the strobe periods 1 to 4. Therefore, the strobe cycle can be at least doubled.

  However, as described above, the longer the strobe period, the greater the distortion in the sub-scanning direction of the exposure position of the pixels on one line. Therefore, it is preferable to maintain the strobe period as it is. In other words, the strobe period is preferably the minimum period that can always be taken regardless of the line period.

To the strobe period t _c and the minimum, it is necessary to make people strobe period t _a and strobe interval t _b respectively minimized. Strobe period t _a, it is necessary to secure a period that can provide sufficient exposure energy to the photosensitive drum 109. In addition, the strobe interval t _b needs to ensure an interval necessary for the purpose of time-division driving, that is, to reduce the instantaneous peak value of power consumption. Therefore, the strobe period t _c can be a fixed value in consideration of the minimum period required for each of t _a and t _b .

  On the other hand, the paper transport speed in the apparatus may be changed according to the type of paper supplied from the paper feed table 25. This is due to a transfer accuracy problem when transferring the toner image from the transport belt 105 to the paper and a transport problem in the transport path. When the paper transport speed is changed, the transport speed of the transport belt 105 is changed accordingly. As a result, the rotational speed of the photosensitive drum 109 is also adjusted accordingly.

Here, consider the exposure energy given to the photosensitive drum 109 when the strobe period ta is _a fixed value as described above. FIGS. 11A and 11B are diagrams showing the range of the surface of the photosensitive drum 109 exposed by light emission driving of one LED element.

11 (a) shows, when the strobe period t _a rotational speed and the LED elements of the photosensitive drum 109 is a predetermined value, indicating a range of the photosensitive drum 109 surface to be exposed by one of the light emission drive FIG. As shown in FIG. 11 (a), the position of the arrows shown as "exposure start", the process advances to the position of the arrows shown as "end of exposure" during the strobe period t _a. That is, the range from “exposure start” to “exposure end” is exposed.

On the other hand, FIG. 11B is a diagram showing an example where the rotational speed of the photosensitive drum 109 is half that in the state of FIG. In this case, the same strobe duration t _a, the distance which the surface of the photosensitive drum 109 moves is halved. As a result, as shown in FIG. 11B, the range from “exposure start” to “exposure end” is half that in FIG. 11A.

  FIGS. 12A and 12B are diagrams showing the distribution of exposure energy according to the position of the surface of the photosensitive drum 109 in each of FIGS. 11A and 11B. FIG. 12A shows the distribution of exposure energy in the case of FIG. 11A, and the exposure energy is distributed in the range from “exposure start” to “exposure end” shown in FIG. 11A. It becomes.

  On the other hand, FIG. 12B shows the exposure energy distribution in the case of FIG. In the case of FIG. 11B, the surface of the photosensitive drum 109 moves slowly at half speed during the same exposure period as in FIG. For this reason, a narrow section on the surface of the photosensitive drum 109 is slowly exposed. As a result, as shown in FIG. 12B, high exposure energy is concentrated and distributed in a narrower section than that in FIG.

Thus, in the same strobe duration t _a, the rotational speed of the photosensitive drum 109 is changed, the exposure energy per unit area of the photosensitive drum 109 surface changes. The intensity of the exposure energy is a value that affects the charge on the surface of the photosensitive drum 109, and consequently affects the density of the developed image. Therefore, when the exposure energy per unit area changes, the density of the image is affected.

In the present embodiment, in terms of the strobe period t _a and strobe interval t _b is fixed to the minimum value in order to suppress the deviation by time division driving, is one aspect to prevent variations in concentration, as described above . Control for achieving such an object will be described below.

  FIG. 13 is a block diagram illustrating a control configuration of the optical writing control unit 201 according to the present embodiment. As illustrated in FIG. 13, the optical writing control unit 201 according to the present embodiment includes an LEDA writing control circuit 210, an optical writing controller 220, a line memory 231, and a line memory 232.

  The LED writing control circuit 210 includes a frequency conversion unit 211, an image processing unit 212, a skew correction unit 213, and an LEDA control unit 214. The LEDA write control circuit 210 is configured as hardware.

  The optical writing controller 220 includes an operation setting unit 221, a sensor control unit 222, a correction value generation unit 223, a reference value storage unit 224, and a correction value storage unit 225. Similar to the hardware configuration described in FIG. 1, the optical writing controller 220 is configured by linking software and hardware. That is, the CPU is configured to perform calculations according to a program stored in the ROM or a program loaded in the RAM.

  In the following description, the configuration and function of the optical writing control unit 201 for the LEDA print head 130 will be described. As described with reference to FIGS. 3 and 4, the LEDA print head 130 includes the photosensitive drums 109K, 109M, 109C and 109Y are provided correspondingly. Therefore, the optical writing control unit 201 has a function of controlling each LEDA print head 130 and each photosensitive drum 109 for each color.

  The LEDA writing control circuit 210 is a control circuit that controls the light emission of the LEDA print head 130 based on the drawing information input from the controller 20, and is configured by hardware such as an integrated circuit. The LEDA write control circuit 210 operates according to parameter settings by the optical write controller 220.

  The frequency conversion unit 211 outputs the drawing information input from the controller 20 in association with the operating frequency of the LEDA write control circuit 210. Therefore, the frequency conversion unit 211 temporarily stores the drawing information input from the controller 20 in the line memory 231 provided for frequency conversion, and outputs it according to the operating frequency of the LEDA write control circuit 210. The frequency conversion unit 211 also functions as an image information acquisition unit that acquires image information input from the controller 20.

  The image processing unit 212 performs various kinds of image processing on the image data output after frequency conversion. Image processing performed by the image processing unit 212 includes image size change, trimming processing, and addition of an internal pattern. Further, by controlling the output timing of the image data to the skew correction unit 213 which is the processing module at the next stage, the positional deviation correction in the main scanning direction is performed in units of resolution input from the controller 20. This misalignment correction in the main scanning direction is performed according to register settings in the LEDA write control circuit 210.

  Further, the image processing unit 212 converts drawing information input as multi-gradation image information from the frequency conversion unit 211 into two-colored / colorless gradations, and finally controls the LEDA print head 130 to emit light. A binarization process for generating pixel information is performed.

  The skew correction unit 213 corrects image skew caused by various factors such as an error due to the arrangement of the LEDA print head 130 and the photosensitive drum 109. Parameter values relating to skew correction are set by the optical writing controller 220.

  The skew correction unit 213 stores the image data input from the image processing unit 212 in the line memory 232 for each main scanning line, and executes skew correction by reading out the image data from the line memory 232 according to the set parameter value. .

  The skew correction unit 213 reads out pixel data at a predetermined position on the main scanning line in accordance with the inclination of the image to be corrected in a state where pixel data for a plurality of main scanning lines is stored in the line memory 232. To shift. For example, when pixel data is read from the first line, the main scan line from which pixel data is read is switched to the second line at a predetermined position on the main scan line (hereinafter referred to as “shift position”). By such processing, it is possible to correct the inclination of the image.

The LEDA control unit 214 controls the light emission of the LEDA print head 130 according to the operating frequency based on the pixel information output from the skew correction unit 213. That is, the LEDA control unit 214 functions as a light source control unit. As described above, the LEDA control unit 214 controls the strobe period t _a , the strobe interval t _b, and the strobe period t _c when the LED element is driven to emit light according to the setting by the optical writing controller 220.

  The optical writing controller 220 performs parameter setting of the LEDA writing control circuit 210 based on a command input from the controller 20 and control of adjustment operations using the various adjustment patterns described above.

  The operation setting unit 221 sets parameters for driving the LEDA 132 by the LEDA write control circuit 210 based on a command input from the engine control unit 31 of the controller 20. In addition, the adjustment operation is controlled by the various patterns described above, and the adjustment value obtained by the adjustment operation is set for each part of the print engine 26.

As described above, the strobe period t _a and strobe interval t _b according to the present embodiment, the minimum period is used as a fixed value. Accordingly, operation setting unit 221, as shown in FIG. 14, holds the information of the strobe period t _a and strobe interval t _b is a fixed value, the value is set with respect LEDA writing control circuit 210. That is, the strobe period t _a and strobe interval t _b shown in FIG. 14, a predetermined light emission period and the light emitting interval determined in advance.

  The sensor control unit 222 is a control unit that controls the pattern detection sensor 117, and generates a reading result of the pattern formed on the conveyance belt 105 based on the output signal of the pattern detection sensor 117. For example, in the case of a misalignment correction pattern, the sensor control unit 222 generates information indicating the timing at which the misalignment correction pattern formed on the transport belt 105 is transported and reaches the detection position of the pattern detection sensor 117.

  On the other hand, in the case of the density correction pattern, the sensor control unit 222 acquires the signal intensity of the output signal of the pattern detection sensor 117 when the density correction pattern is read by the pattern detection sensor 117, and generates information indicating the density. To do. The sensor control unit 222 inputs these pieces of information to the correction value generation unit 223.

  The correction value generation unit 223 generates correction values based on the reference values for positional deviation correction and density correction stored in the reference value storage unit 224 based on the information of the read result acquired from the sensor control unit 222. The correction value generation unit 223 stores the correction value information generated in this way in the correction value storage unit 225.

The operation setting unit 221 sets parameters of the LEDA write control circuit 210 based on the correction value information generated in this way and stored in the correction value storage unit 225. Particularly, in the present embodiment, FIG. 11, in order to meet the challenges described in FIG. 12, except the strobe period t _a, setting parameters for correcting the image density.

The correction parameters the density of the image other than the strobe period t _a, for example, a developing bias when developing an electrostatic latent image, a charging bias, transfer bias, etc. at the time of transferring the developed toner image to a conveyor belt 105 There is. Therefore, in the above-described density correction process using the density correction pattern, an optimum parameter is determined by forming a pattern with various parameters.

  Here, the density correction pattern according to the present embodiment and the density correction operation using the pattern will be described with reference to FIG. FIG. 15 is a diagram showing a density correction pattern 500 drawn on the transport belt 105 in the density correction operation according to the present embodiment. As shown in FIG. 15, the density correction pattern 500 according to the present embodiment includes a black gradation pattern 501, a cyan gradation pattern 502, a magenta gradation pattern 503, and a yellow gradation pattern 504.

  As shown in FIG. 15, the pattern detection sensor 117 has a plurality (two in the present embodiment) of sensor elements 170 in the main scanning direction. Each pattern included in the density correction pattern 500 is drawn at a main scanning position corresponding to one of the sensor elements 170.

  In the present embodiment, the gradation patterns of the respective colors included in the density correction pattern 500 are configured by four rectangular patterns having different densities, and these rectangular patterns are arranged in the sub-scanning direction in the order of density. Configured. The gradation pattern of each color is drawn separately for black and magenta and cyan and yellow. In FIG. 15, the density of each pattern is shown by the number of hatches applied to each square pattern.

  In the density correction using the density correction pattern 500 shown in FIG. 15, the correction value generation unit 223 displays information indicating the density based on the intensity of the read signal of the gradation pattern of each color by the pattern detection sensor 117. 222. Then, by comparing with the reference value of the density of each gradation stored in the reference value storage unit 224, the quality of the parameter value used in forming the gradation pattern is determined.

  In the density correction operation according to the present embodiment, when a print job is executed, a conveyance speed and a rotation speed of the photosensitive drum 109 (hereinafter, generally referred to as “linear speed”) according to the thickness and quality of the paper used are set. Will be executed after. The timing at which the density correction operation according to this embodiment is to be executed will be described with reference to FIG.

  As shown in FIG. 16, first, the main control unit 30 receives a print job (S1601), and determines the linear velocity based on the paper type specified in the print job (S1602). The main control unit 30 notifies the determined linear velocity to the print engine 26 via the engine control unit 31. Thereby, each part of the print engine 26 operates at the determined linear velocity.

  When the linear velocity is set in the print engine 26, the optical writing controller 220 starts the density correction operation. In the density correction operation, the operation setting unit 221 first sets the development bias and transfer bias described above to specific values (S1603). Then, the operation setting unit 221 controls the LEDA writing control circuit 210 to execute the output of the density correction pattern 500 as described with reference to FIG. 15 (S1604).

  When the density correction pattern is output in S1604, the linear velocity determined in S1602 is used. As a result, the density correction operation including the problem with the density fluctuation as described with reference to FIGS. 11 and 12 is executed.

  When the density correction pattern 500 is formed on the transport belt 105 and the transport belt 105 rotates, the sensor control unit 222 acquires the detection result of the density correction pattern 500 (S1605). That is, the sensor control unit 222 functions as a detection signal acquisition unit. The operation setting unit 221 repeats the processing from S1603 until the processing from S1603 is completed for all the parameter values that are candidates for application in the density correction operation (S1606 / NO).

  When the processing is completed for all candidates (S1606 / YES), the correction value generation unit 223 first determines a development bias value as a parameter correction value (S1607). In the processing of S 1607, the correction value generation unit 223 compares the pattern reading result acquired from the sensor control unit 222 with the reference value stored in the reference value storage unit 224. Then, the bias setting value used in the closest reading result is determined as a correction value. The correction value generation unit 223 stores the determined correction value in the correction value storage unit 225.

  In addition, as shown in FIG. 17, the reading density tendency according to the developing bias may be compared with a reference value, and an optimum developing bias corresponding to the reference value may be obtained by linear interpolation. The development bias has a great influence on the image density of a relatively high gradation. Therefore, in S1607, only the reading result of the high gradation patch among the reading results of the patches included in the gradation pattern of each color may be used.

  When the development bias is determined, the correction value generation unit 223 next determines a transfer bias value (S1608). Also in the processing of S1608, the correction value generation unit 223 compares the pattern reading result acquired from the sensor control unit 222 with the reference value stored in the reference value storage unit 224. Then, the bias setting value used in the closest reading result is determined as a correction value. The correction value generation unit 223 stores the determined correction value in the correction value storage unit 225.

  Similarly to the development bias, as shown in FIG. 18, the reading density tendency according to the transfer bias may be compared with a reference value, and an optimum transfer bias corresponding to the reference value may be obtained by linear interpolation. The transfer bias has a great influence on the image density of a relatively low gradation. Therefore, in S1607, only the reading result of the low gradation patch among the reading results of the patches included in the gradation pattern of each color may be used.

  Here, in determining the transfer bias, there may be a case where a desired density cannot be realized with a bias setting value within a settable range. For example, as shown in FIG. 19, the reading results of the density correction patterns formed at various transfer bias settings are all less than the reference density.

  If it is not in such an unadjustable range (S1609 / NO), the optical writing controller 220 completes the density correction operation. On the other hand, when it is out of the adjustable range (S1609 / YES), the correction value generation unit 223 generates a correction value for adjusting the light emission intensity when the LEDA control unit 214 drives the LEDA 132 to emit light, that is, the exposure intensity. In step S1610, the density correction operation is completed.

  When generating the correction value of the exposure intensity in S1610, for example, adjustment values corresponding to the insufficient density value with respect to the reference value are tabulated as shown in FIG. A correction value can be selected. In addition, an optimal value may be determined in the same manner as the bias setting value by repeating the processing of S1603 to S1605 using various exposure intensities as parameters.

As described above, in the image forming apparatus 1 according to the present embodiment, the density correction operation using the density correction pattern is performed after the linear velocity is determined when the print job is executed, and the development bias and the transfer bias are determined. Therefore, even when the fixed strobe time t _a and strobe interval t _b in order to minimize the distortion due to time-division driving, it is possible to prevent density variations due to linear velocity.

  In the above embodiment, as described with reference to FIG. 16, the correction of the transfer bias is performed first in the correction of the low gradation density, and the exposure intensity is corrected when the correction cannot be completed. However, this is only an example, and the transfer bias may be corrected after the exposure intensity is corrected first.

  In the above embodiment, the case where the developing bias is determined in S1607 and the transfer bias is determined in S1608 has been described as an example. In addition, for example, as described above, a charging bias value, which is a voltage applied by the charger 110 to the photosensitive drum 109 in order to charge the photosensitive drum 109 before the electrostatic latent image is formed, is used as a correction value. It may be used.

  In particular, the charging bias has a great influence on the image density of low gradation. Therefore, instead of the transfer bias described above, the charging bias is used as a parameter to be corrected. At that time, only the reading result of the low gradation patch among the reading results of the patches included in the gradation pattern of each color may be used. good.

1 Image forming apparatus 10 CPU
11 RAM
12 ROM
13 Engine 14 HDD
15 I / F
16 LCD
17 Operation unit 18 Bus 20 Controller 21 ADF
22 Scanner unit 23 Paper discharge tray 24 Display panel 25 Paper feed table 26 Print engine 27 Paper discharge tray 28 Network I / F
30 Main control unit 31 Engine control unit 32 Input / output control unit 33 Image processing unit 34 Operation display control unit 101 Paper feed tray 102 Paper feed roller 103 Registration roller 104 Paper 105 Conveying belts 106K, 106C, 106M, 106Y Image forming unit 107 Drive Roller 108 Driven roller 109K, 109C, 109M, 109Y Photoconductor drum 110K Charger 111 Optical writing device 112K, 112C, 112M, 112Y Developer 113K, 113C, 113M, 113Y Charger 115K, 115C, 115M, 115Y Transfer device 116 Fixing 117 Pattern detection sensor 131 Substrate 132 LEDA
133 Drive circuit 201 Optical write control unit 210 LEDA write control circuit 211 Frequency conversion unit 212 Image processing unit 213 Skew correction unit 214 LEDA control unit 220 Optical write controller 221 Operation setting unit 222 Sensor control unit 223 Correction value generation unit 224 Reference value storage Unit 225 correction value storage units 231 and 232 line memory

Japanese Patent Laid-Open No. 9-17437

Claims (8)

An image forming apparatus including an optical writing device that forms an electrostatic latent image on a photoreceptor by controlling light emission of a light source device including a plurality of light sources configured by arranging a plurality of light emitting elements in a linear form,
An image information acquisition unit that acquires image information that is information of an image to be formed as the electrostatic latent image;
A light source control unit that controls emission of the light source based on pixel information generated based on the acquired image information;
A detection signal acquisition unit that acquires a detection signal of a sensor that detects the image in a conveyance path in which an image obtained by developing the electrostatic latent image formed on the photosensitive member is transferred and conveyed;
A correction pattern for correcting the density of the developer image developed from the electrostatic latent image formed on the photoreceptor is corrected for correcting the density based on the detection signal detected by the sensor. A correction value generation unit for generating a value,
The light source controller is
By performing light emission control of the light emitting elements divided into a plurality of groups in order for each group, light emission control for one time of the light source is performed to form an electrostatic latent image corresponding to an image for one line. ,
Light emission control is performed for each of the light emitting elements for each group in a predetermined light emission period,
Controlling light emission of the light source so that a correction pattern for correcting the density is drawn according to determination of a rotation speed of the photoconductor according to a recording medium to which the developer image is to be transferred. To expose the photoconductor rotating at the determined rotational speed,
The correction value generation unit generates a correction value for correcting the density based on a detection signal of the correction pattern drawn according to the determination of the rotation speed of the photoconductor. apparatus.   The image according to claim 1, wherein the correction value generation unit generates a value related to a voltage applied between the photoconductor and a developing device as the correction value when the electrostatic latent image is developed. Forming equipment. The correction pattern is a pattern composed of a plurality of patches having different densities,
The correction value generation unit relates to a voltage applied between the photosensitive member and the developing device when developing the electrostatic latent image based on a detection signal when a high gradation patch is detected among the plurality of patches. The image forming apparatus according to claim 2, wherein a value is generated as the correction value. The correction pattern is a pattern composed of a plurality of patches having different densities,
The correction value generation unit is applied to charge the photoconductor before the electrostatic latent image is formed based on a detection signal when a low gradation patch is detected among the plurality of patches. The image forming apparatus according to claim 1, wherein a value related to a voltage is generated as the correction value.   The correction value generation unit emits the light source when a value related to a voltage to be set based on a detection signal in which a low gradation patch is detected among the plurality of patches is out of a settable range. The image forming apparatus according to claim 4, wherein a value related to light emission intensity at the time of control is generated as the correction value.   The image forming apparatus according to claim 1, wherein the correction value generation unit generates a value related to light emission intensity when the light source is controlled to emit light as the correction value. The correction pattern is a pattern composed of a plurality of patches having different densities,
The correction value generation unit generates, as the correction value, a value related to light emission intensity when the light source is controlled to emit light based on a detection signal in which a low gradation patch is detected among the plurality of patches. The image forming apparatus according to claim 6. A control method for an image forming apparatus including an optical writing device that forms an electrostatic latent image on a photosensitive member by controlling light emission of a light source device including a plurality of light sources configured by linearly arranging a plurality of light emitting elements. And
The image forming apparatus includes:
An image information acquisition unit that acquires image information that is information of an image to be formed as the electrostatic latent image;
A light source control unit that controls emission of the light source based on pixel information generated based on the acquired image information;
A detection signal acquisition unit that acquires a detection signal of a sensor that detects the image in a conveyance path in which an image obtained by developing the electrostatic latent image formed on the photosensitive member is transferred and conveyed;
A correction pattern for correcting the density of the developer image developed from the electrostatic latent image formed on the photoreceptor is corrected for correcting the density based on the detection signal detected by the sensor. A correction value generation unit for generating a value,
By performing light emission control of the light emitting elements divided into a plurality of groups in order for each group, light emission control for one time of the light source is performed to form an electrostatic latent image corresponding to an image for one line. ,
Light emission control is performed for each of the light emitting elements for each group in a predetermined light emission period,
Controlling light emission of the light source so that a correction pattern for correcting the density is drawn according to determination of a rotation speed of the photoconductor according to a recording medium to which the developer image is to be transferred. To expose the photoconductor rotating at the determined rotational speed,
A control method for an image forming apparatus, comprising: generating a correction value for correcting the density based on a detection signal of the correction pattern drawn in accordance with determination of a rotation speed of the photoconductor.