JP2011232414A - Image formation device and image formation method - Google Patents

Abstract

In an apparatus for forming a color image by transferring images formed by a plurality of image forming units to an image carrier, a high-quality color image is formed by adjusting the writing position of each image with high accuracy. .
A delayed vertical synchronization signal is output with a delay from the timing T1 by a waiting time corresponding to the rotational position of the photosensitive drum 21 at the timing T1 at which the color-specific vertical synchronization signal Vsync is received. The exposure is started. For this reason, the time from the reception timing T1 of the color-specific vertical synchronization signal Vsync to the primary transfer start timing T3 is constant without being affected by the rotation unevenness, and the leading edge of the image formed at each image forming station. The positions coincide with each other and the color misalignment at the front end of the image is suppressed.
[Selection] Figure 9

Description

  The present invention relates to an image forming apparatus and an image forming method for forming a color image by transferring images formed by a plurality of image forming units to an image carrier.

  As an image forming apparatus that forms a color image by an electrophotographic system, for example, so-called tandem apparatuses described in Patent Documents 1 to 3 are known. Among these, the image forming apparatus described in Patent Document 1 is provided with four image forming stations. In each image forming station, a latent image carrier such as a photosensitive drum is rotated in the sub-scanning direction, and a line head is disposed facing the photosensitive drum. In each line head, a plurality of light emitting elements are arranged in a row in the main scanning direction substantially orthogonal to the sub-scanning direction, and ON / OFF control corresponding to video data is executed based on the horizontal synchronization signal. As a result, a line latent image corresponding to the video data is formed on the photosensitive drum.

  In this way, the line latent image is written by driving and controlling the light emitting element corresponding to the video data while rotating the photosensitive drum. As a result, a two-dimensional latent image is formed on the photosensitive drum. Therefore, when the moving speed of the surface of the photosensitive drum fluctuates, the latent image forming position is shifted in the sub-scanning direction, and it is sometimes impossible to execute good latent image formation. Therefore, in the apparatus described in Patent Document 1, the moving speed (circumferential speed) of the surface of the photosensitive drum is detected, and the light emission timing of the light emitting element is adjusted based on the detection result, so that the surface of the photosensitive drum surface is adjusted. Occurrence of the shift of the latent image forming position due to the movement speed fluctuation is suppressed. The two-dimensional latent image is developed with toner to form an image, and the image formed at each image forming station is superimposed on the intermediate transfer belt to form a color image.

JP 2009-160917 A (paragraphs 0081 to 0083) JP 2002-108041 A JP 2006-349847 A

  By the way, in the apparatus described in Japanese Patent Application Laid-Open No. H10-228707, although the shift of the latent image forming position due to the fluctuation of the moving speed of the surface of the photosensitive drum, so-called image pitch unevenness is adjusted, special consideration is given to the exposure start timing. Is not paid. Therefore, there is a problem that the entire image is shifted in the sub-scanning direction for each color.

  In order to solve this problem, for example, it is conceivable to apply the correction technique described in Patent Document 2 or Patent Document 3 to the apparatus described in Patent Document 1. That is, in the apparatuses described in Patent Document 2, Patent Document 3, and the like, the reference image on the transfer belt is detected, and the exposure start timing is determined based on the detection result. However, the exposure start timing is disturbed due to the detection error of the reference image, and color misregistration may occur. In other words, it was impossible to write out a highly accurate image, and a reduction in image quality was inevitable.

  In some embodiments according to the present invention, in an apparatus for forming a color image by transferring an image formed by a plurality of image forming units to an image carrier, the writing position of each image is adjusted with high accuracy. The object is to form a quality color image.

  In order to solve the above problems, an image forming apparatus according to the present invention has an image carrier that carries an image, a first latent image carrier that is rotationally driven in a first direction, and a second direction that is different from the first direction. A plurality of first light emitting elements provided; a first exposure unit that exposes the first latent image carrier to form a first latent image; and a first latent image formed by exposure of the first exposure unit. A first image forming unit that has a first developing unit for developing, transfers a first image developed in the first developing unit to an image carrier, and a second latent image carrier that is rotationally driven in a first direction. A plurality of second light emitting elements arranged in the second direction, and a second exposure unit that exposes the second latent image carrier to form a second latent image, and is formed by exposure of the second exposure unit. A second image forming unit for developing the second latent image and transferring the second image developed by the second developing unit to the image carrier to which the first image is transferred. And a first exposure start signal for instructing start of exposure of the first latent image by the first exposure unit, and a second exposure start signal for instructing start of exposure of the second latent image by the second exposure unit. The first light emitting element emits light after a first delay time delay corresponding to the rotation position of the first latent image carrier when the exposure command unit and the first exposure start signal are received and the first exposure start signal is received. The first light emitting element light emission signal for controlling the timing is output to the first exposure unit, the second exposure start signal is received, and the second latent image carrier when the second exposure start signal is received corresponds to the rotational position of the second latent image carrier And an exposure control unit that outputs a second light emitting element light emission signal for controlling a timing at which the second light emitting element emits light after the second delay time delay to the second exposure unit.

  In order to solve the above-described problem, the image forming method according to the present invention outputs a first exposure start signal for instructing start of exposure of the first latent image carrier from the exposure command unit to the exposure control unit. The second exposure start signal for instructing the start of exposure to the two latent image carrier is output from the exposure command unit to the exposure control unit, and the rotation position of the first latent image carrier when the first exposure start signal is output. Detecting, calculating a first delay time corresponding to the detected rotation position of the first latent image carrier, delaying the calculated first delay time from the first exposure start signal, and then sending the first delay time from the exposure control unit. The output of the light emitting element light emission signal is started, the first latent image carrier is exposed based on the outputted first light emitting element light emission signal, the exposed first latent image carrier is developed, and the developed first The above image is transferred to an image carrier.

  In the invention configured as described above (image forming apparatus and image forming method), a first exposure start signal for instructing start of exposure to the first latent image carrier is output, and the first image forming unit outputs the first image. And transferred to the image carrier. Therefore, when the time until the exposure start of the first latent image carrier is fixed with respect to the output of the first exposure start signal, the tip of the first image formed by the first image forming unit is the surface of the image carrier. As will be described in detail later, the position transferred to the first latent image carrier varies in the first direction as the surface speed of the first latent image carrier varies. Thus, one of the main factors that cause the first image to shift in the first direction is the rotation unevenness of the latent image carrier, and the surface speed varies depending on the rotational position of the latent image carrier, so that the first image on the image carrier is the first. The image transfer position fluctuates in the first direction.

  Therefore, in the present invention, the first image forming unit adjusts the exposure start timing according to the rotational position of the first latent image carrier at the time when the first exposure start signal is given. That is, the first image forming unit controls the timing at which the first light emitting element emits light after the first delay time delay corresponding to the rotational position of the first latent image carrier when the first exposure start signal is output. One light emitting element light emission signal is output, and exposure of the first latent image carrier is started based on the first light emitting element light emission signal. For this reason, in spite of the occurrence of rotation unevenness, it is possible to effectively prevent a change in the position where the first image is transferred to the image carrier and to obtain a high-quality color image.

  Here, the rotation position of the second latent image carrier when the second exposure start signal is output is detected, and the second delay time corresponding to the detected rotation position of the second latent image carrier is calculated and calculated. After the delayed second delay time is delayed from the second exposure start signal, output of the second light emitting element light emission signal is started from the exposure control unit, and the second latent image is carried based on the output second light emitting element light emission signal. The body may be exposed, the exposed second latent image carrier may be developed, and the developed second image may be transferred to the image carrier to which the first image has been transferred. In this case, despite the occurrence of rotational unevenness, the leading edge of the second image can be superimposed with high precision on the leading edge of the first image, and the image leading edge color shift is effectively prevented. A high-quality color image can be obtained.

  In addition, the exposure control unit outputs a plurality of first light emitting element light emission signals to the first exposure unit, and adjusts the timing at which the first light emitting element light emission signal is output according to fluctuations in the rotation speed of the first latent image carrier. As a result, the pitch in the first direction of the exposure spots formed on the first latent image carrier by the light emitted from the first light emitting element is made uniform. As a result, even if rotation unevenness of the first latent image carrier occurs, it is possible to suppress the pitch unevenness of the first image and to form a higher quality image. The first delay time is preferably adjusted within a range of time longer than twice the average time interval of the plurality of first light emitting element light emission signals to be output and shorter than the rotation period of the first latent image carrier. . These points are the same in the second image forming unit. That is, the exposure control unit outputs a plurality of second light emitting element light emission signals to the second exposure unit, and adjusts the timing at which the second light emitting element light emission signal is output according to the fluctuation of the rotation speed of the second latent image carrier. As a result, the pitch in the first direction of the exposure spots formed on the second latent image carrier by the light emitted from the second light emitting element is made uniform. As a result, even if rotation irregularity of the second latent image carrier occurs, it is possible to suppress the pitch irregularity of the second image and to form a higher quality image. In addition, it is desirable to adjust the second delay time within a range of time longer than twice the average time interval of the output light emission signal of the second light emitting element and shorter than the rotation period of the second latent image carrier.

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. The block diagram which shows the electric constitution of the apparatus of FIG. The block diagram which shows the structure of a horizontal synchronizing signal generation part. FIG. 3 is a schematic diagram showing a relationship between rotation unevenness of a photosensitive drum and an image leading end position. FIG. 4 is a schematic diagram showing the occurrence of a position error and color misregistration at the front end of an image. The figure which shows the relationship between a paper feed direction image position and an image position error. The figure which shows the outline | summary of exposure start timing control typically. The flowchart which shows exposure start timing control. The graph which shows the operation | movement of exposure start timing control. The figure which shows an example of the content memorize | stored in LUTa. The figure which shows an example of the content memorize | stored in LUTb. The figure which shows the other example of the content memorize | stored in LUTa. The figure which shows the other example of the content memorize | stored in LUTb.

  FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a block diagram showing an electrical configuration of the apparatus of FIG. The image forming apparatus 1 includes four image forming stations 2Y (for yellow), 2M (for magenta), 2C (for cyan), and 2K (for black) that form images of different colors. The image forming apparatus 1 includes a color mode in which four color toners of yellow (Y), magenta (M), cyan (C), and black (K) are overlapped to form a color image, and black (K). A monochrome mode in which a monochrome image is formed using only toner can be selectively executed. In this image forming apparatus, when an image formation command (print information) is given from an external device such as a host computer to a main controller (not shown) having an image processing unit 81, a mechanical control unit is based on a control signal from the main controller. 82 controls each part of the apparatus to execute a predetermined image forming operation, and forms an image corresponding to the image forming command on a sheet as a recording material RM such as copy paper, transfer paper, paper, and an OHP transparent sheet.

  Each of the image forming stations 2Y, 2M, 2C, and 2K has the same structure and function except for the toner color. Therefore, in FIG. 1, in order to make the drawing easier to see, reference numerals are given only to the components constituting the image forming station 2 </ b> C, and description of reference numerals to be attached to the other image forming stations 2 </ b> Y, 2 </ b> M, and 2 </ b> K is omitted. Further, in the following description, the structure and operation of the image forming station 2C will be described with reference to the reference numerals attached to FIG. 1. However, the structure of the other image forming stations 2Y, 2M, and 2K is also different in toner color. It is the same except.

  The image forming station 2C is provided with a photosensitive drum 21 on which a cyan toner image is formed. The photosensitive drum 21 is arranged so that the rotation axis thereof is parallel or substantially parallel to the main scanning direction (direction perpendicular to the paper surface of FIG. 1). The direction of the arrow D21 in FIG. (Corresponding to the “first direction”). Further, in order to detect the rotation position and rotation state of the photosensitive drum 21, in this embodiment, a photosensitive encoder 211 (FIG. 2) is attached to the rotation shaft (not shown) of the photosensitive drum 21, An encoder signal is output in accordance with the rotation of the photosensitive drum 21. Accordingly, the surface moving speed (circumferential speed), rotational position, and the like of the photosensitive drum 21 can be accurately obtained based on the encoder signal output from the photosensitive encoder 211.

  Around the photosensitive drum 21, a charger 22 that is a corona charger that charges the surface of the photosensitive drum 21 to a predetermined potential, and an electrostatic latent image is formed by exposing the surface of the photosensitive drum 21 according to an image signal. An exposure head 23 that forms a toner image, a developing unit 24 that visualizes the electrostatic latent image as a toner image, a first squeeze portion 25, a second squeeze portion 26, and an intermediate transfer of the toner image to the transfer unit 3. A primary transfer unit for primary transfer to the belt 31, a cleaning unit for cleaning the surface of the photosensitive drum 21 after transfer, and a cleaner blade are arranged in the order of rotation D21 of the photosensitive drum 21 (in FIG. Around).

  The charger 22 does not come into contact with the surface of the photosensitive drum 21, and a conventionally well-known and commonly used corona charger can be used as the charger 22. When a scorotron charger is used as the corona charger, a wire current flows through the charge wire of the scorotron charger and a direct current (DC) grid charging bias is applied to the grid. When the photosensitive drum 21 is charged by corona discharge by the charger 22, the surface potential of the photosensitive drum 21 is set to a substantially uniform potential.

  As will be described later, the exposure head 23 generates a light beam based on video data provided from the head controller HC and exposes the surface of the photosensitive drum 21 with the light beam to form an electrostatic latent image corresponding to the image signal. is there. In this embodiment, the exposure head 23 includes a plurality of light emitting elements arranged in a longitudinal direction parallel to the main scanning direction, and the width direction of the exposure head 23 is parallel or substantially parallel to the rotation direction D21, that is, the sub-scanning direction. The photoconductor drum 21 is disposed so as to be parallel to each other. Further, the lens array is disposed to face the light emitting element. Therefore, the light beam emitted from the light emitting surface of the light emitting element is imaged by the lens array, and the surface of the photosensitive drum 21 is irradiated with the spot. The configuration of the head controller HC and the exposure control of the exposure head 23 by the head controller HC will be described in detail later.

  Toner is applied from the developing unit 24 to the electrostatic latent image formed on the surface of the photosensitive drum 21 by the exposure head 23 configured as described above, and the electrostatic latent image is developed with the toner. In the developing unit 24 of the image forming apparatus 1, toner development is performed using a liquid developer in which toner is dispersed in a carrier liquid in an approximate weight ratio of about 20%. In this image forming apparatus 1, a volatile liquid developer having a low concentration (1 to 2 wt%) and a low viscosity at room temperature, which is generally used conventionally, is Isopar (trademark: exon) as a carrier liquid. Rather, solid particles having an average particle diameter of 1 μm, in which a colorant such as a pigment is dispersed in a non-volatile resin having a high concentration and high viscosity at room temperature, liquid such as organic solvent, silicon oil, mineral oil, or edible oil A liquid developer having a high viscosity (about 30 to 10,000 mPa · s) added to the solvent together with the dispersant and having a toner solid content concentration of about 20% is used.

  The first squeeze unit 25 and the second squeeze unit 26 are provided with squeeze rollers, respectively. Each squeeze roller comes into contact with the surface of the photosensitive drum 21 to remove excess carrier liquid and fog toner from the toner image. In the present embodiment, the excess carrier liquid and fog toner are removed by the two squeeze portions 25 and 26. However, the number and arrangement of the squeeze portions are not limited to this, for example, one squeeze portion. May be arranged.

  The toner image that has passed through the squeeze portions 25 and 26 is primarily transferred to the intermediate transfer belt 31 by the primary transfer unit. This intermediate transfer belt 31 is an endless belt as an image carrier capable of carrying a toner image on its surface, more specifically, on its outer peripheral surface, and is stretched around a plurality of rollers 32, 33, 34 and 35. . Of these, the roller 32 is mechanically connected to the belt drive motor M3, and functions as a belt drive roller for driving the intermediate transfer belt 31 in the direction of the arrow D31 in FIG. Of the rollers 32 to 35 on which the intermediate transfer belt 31 is stretched, only the belt driving roller 32 is driven by the motor, and the other rollers 33, 34 and 35 are driven without a driving source. It is a roller.

  The primary transfer unit has a primary transfer backup roller 271, and the primary transfer backup roller 271 is disposed to face the photosensitive drum 21 with the intermediate transfer belt 31 interposed therebetween. At the primary transfer position TR1 where the photosensitive drum 21 and the intermediate transfer belt 31 abut, the toner image on the photosensitive drum 21 is transferred to the outer peripheral surface of the intermediate transfer belt 31 (the lower surface at the primary transfer position TR1). Thus, the cyan toner image formed by the image forming station 2 </ b> C is transferred to the intermediate transfer belt 31. Similarly, the toner images are transferred at the other image forming stations 2Y, 2M, and 2K, so that the toner images of the respective colors are sequentially superimposed on the intermediate transfer belt 31 to form a full-color toner image. On the other hand, when a monochrome toner image is formed, the toner image is transferred to the intermediate transfer belt 31 only in the image forming station 2K corresponding to the black color.

  The toner image thus transferred to the intermediate transfer belt 31 is conveyed to the secondary transfer position TR2. At the secondary transfer position TR2, the secondary transfer roller 4 is disposed opposite to the roller 34 around which the intermediate transfer belt 31 is wound, with the intermediate transfer belt 31 interposed therebetween, and the surface of the intermediate transfer belt 31 and the transfer roller 4 are disposed. The surface is in contact with each other to form a transfer nip NP. That is, the roller 34 functions as a secondary transfer backup roller. The rotation shaft 421 of the secondary transfer roller 4 is supported elastically by a pressing portion 45 that is an elastic member such as a spring and so as to be movable toward and away from the intermediate transfer belt 31.

  At the secondary transfer position TR2, the single-color or multi-color toner images formed on the intermediate transfer belt 31 are transferred from the pair of gate rollers 51 to the recording material RM conveyed along the conveyance path PT. In this embodiment, since the toner image is formed by a wet development method in which a toner image is formed using a liquid developer, in order to obtain good transfer characteristics, the intermediate transfer belt 31 is used in the transfer nip. It is desired that the recording material RM is pressed with a high pressing force. Further, since the liquid developer is interposed, there is a high possibility that the recording material RM sticks to the intermediate transfer belt 31 and is jammed. Therefore, in this image forming apparatus 1, a secondary transfer roller 4 having a grip portion is used.

  The secondary transfer roller 4 has a roller base 42 provided with a recess 41 formed by cutting out a part of the outer peripheral surface of the cylinder. In this roller base material 42, a rotation shaft 421 that is rotatable in the direction D4 about the rotation axis is disposed in parallel or substantially parallel to the rotation axis of the secondary transfer backup roller 34, and the secondary transfer backup roller is pressed by the pressing portion 45. A predetermined load (60 kgf in this embodiment) is applied by being biased to the 34 side. When a rotational driving force is applied to the rotary shaft 421 from a motor not shown, the secondary transfer roller 4 rotates in the rotational direction D4. Further, the secondary transfer roller 4 is provided with a vertical synchronization sensor 46 (FIG. 2), and a vertical synchronization signal Vsync is output when the secondary transfer roller 4 passes a predetermined reference position. In this embodiment, image formation (printing) is started based on the vertical synchronization signal Vsync thus obtained. The vertical synchronization signal Vsync is generated based on the rotating operation of the intermediate transfer belt 31, or the mechanical control unit 82 is based on the reference clock. For example, the vertical synchronization signal Vsync may be generated.

  An elastic layer (not shown) such as rubber or resin is formed on the outer peripheral surface of the roller base material 42, that is, on the surface region excluding the region corresponding to the inside of the recess 41. This elastic layer forms a transfer nip NP so as to face the intermediate transfer belt 31 wound around the backup roller 34. In addition, a grip 44 for gripping the recording material RM is disposed inside the recess 41. The grip portion 44 includes a gripper support member that is erected on the outer peripheral surface of the roller base material 42 from the inner bottom portion of the recess 41, and a gripper member that is supported so as to be able to contact with and separate from the distal end portion of the gripper support member. is doing. The recording material RM can be gripped and released by controlling the gripper member.

  The recording material RM on which the toner image is secondarily transferred is sent from the secondary transfer roller 4 to the fixing unit 7 provided on the transport path PT. In the fixing unit 7, heat or pressure is applied to the toner image transferred to the recording material RM to fix the toner image on the recording material RM. As described above, in this embodiment, the moving direction D31 of the intermediate transfer belt 31 corresponds to a “paper feeding direction” described later.

  Next, the configuration and operation of the head controller HC that controls the exposure head 23 in the image forming apparatus configured as described above will be mainly described. In the image forming apparatus according to the present embodiment, when an image forming command (printing information) is given from an external device such as a host computer, the image processing unit 81 provided in the main controller responds to the image data included in the image forming command. Then, data processing such as screen processing is performed to generate video data of each toner color. These video data are transferred from the image processing unit 81 to the video data control unit 83 of the head controller HC.

  In addition to the video data control unit 83 described above, the head controller HC includes a RAM (Random Access Memory) 84, a horizontal synchronization signal generation unit 85, a LUTa (look-up table a) 86a, and a LUTb (look-up). An uptable b) 86b and a head control signal generator 87 are provided. Of these, the horizontal synchronization signal generator 85, LUTs 86a and 86b, and head control signal generator 87 are provided for each toner color as shown in FIG.

  FIG. 3 is a block diagram showing the configuration of the horizontal synchronizing signal generator. Each horizontal synchronization signal generation unit 85 includes a horizontal synchronization signal output control circuit 851, a dynamic horizontal synchronization signal generation circuit 852, a dynamic horizontal synchronization number counter 853, a vertical synchronization signal delay circuit 854, and a storage circuit 855. The horizontal synchronization signal Hsync is output based on the color-specific vertical synchronization signal Vsync corresponding to the toner color, the encoder signal from the photoconductor encoder 211, the number of Hsyncs in the LUTa 86a, and the standby time in the LUTb 86b.

  In the present embodiment, as described above, the vertical synchronization signal Vsync is output based on the vertical synchronization sensor 46. Based on the vertical synchronization signal Vsync, the mechanical control unit 82 generates four color-specific vertical synchronization signals Vsync. This is output to the vertical synchronization signal delay circuit 854 of the horizontal synchronization signal generator 85. The reason why the four color vertical synchronizing signals are generated in this way is that the four image forming stations 2Y, 2M, 2C, and 2K are arranged apart from each other and the primary transfer positions TR1 are different from each other. Based on the distance between the image forming stations for each color, four types of vertical sync signals Vsync for each color are generated and transmitted to the vertical sync signal delay circuit 854 for the corresponding color.

  The dynamic horizontal sync signal generation circuit 852 is a circuit that outputs an Hsync signal. As described below, the cycle of the Hsync signal can be varied according to the rotation unevenness of the photosensitive drum 21. That is, the dynamic horizontal synchronizing signal generation circuit 852 is electrically connected to the photoconductor encoder 211 and the LUTa 86a, receives the encoder signal output from the photoconductor encoder 211, and receives the encoder number (that is, the encoder signal). The number of Hsyncs corresponding to the rotation position of the photosensitive drum 21 is read from the LUTa 86a. More specifically, in the LUTa 86a, as shown in later specific examples (FIGS. 10 and 12), data indicating the relative relationship between the encoder number indicating the rotational position of the photosensitive drum 21 and the number of Hsyncs is stored. . Then, the dynamic horizontal synchronization signal generation circuit 852 synchronizes with the encoder signal, the Hsync number corresponding to the encoder number of the encoder signal, and the count value (hereinafter referred to as the Hsync signal output from the dynamic horizontal synchronization signal generation circuit 852). "Dynamic horizontal synchronization count"). In this embodiment, a dynamic horizontal synchronization number counter 853 is provided to obtain the dynamic horizontal synchronization number, and the Hsync signal output from the dynamic horizontal synchronization signal generation circuit 852 is counted up and the encoder In synchronization with the signal, the count value is output to the horizontal synchronization signal output control circuit 851 and the dynamic horizontal synchronization signal generation circuit 852 as the number of dynamic horizontal synchronizations.

  In response to the number of dynamic horizontal synchronizations, the dynamic horizontal synchronization signal generation circuit 852 feedback-controls the cycle of the Hsync signal and adjusts the cycle to a value corresponding to the rotation unevenness of the photosensitive drum 21. That is, when the surface speed of the photosensitive drum 21 varies due to uneven rotation of the photosensitive drum 21, the number of dynamic horizontal synchronizations does not match the number of Hsyncs. Therefore, each time an encoder signal is received, the Hsync signal having a variable period is supplied to the horizontal synchronization signal output control circuit 851 while controlling the period of the Hsync signal so that the number of dynamic horizontal synchronizations matches the number of Hsyncs.

  In this embodiment, in addition to the color-specific vertical synchronization signal Vsync described above, the dynamic horizontal synchronization signal generation circuit 852 supplies an Hsync signal to the vertical synchronization signal delay circuit 854. The vertical synchronization signal delay circuit 854 receives the Hsync signal, calculates the average period of the Hsync signal, and stores it in the storage circuit 855. The “average period” is an average of the periods of the Hsync signal output from the signal Vsync to the next signal Vsync. The vertical synchronization signal delay circuit 854 is also electrically connected to the photoconductor encoder 211, receives the encoder signal output from the photoconductor encoder 211, calculates the rotation cycle of the photoconductor drum 21, and stores the storage circuit 855. To remember. Further, the vertical synchronizing signal delay circuit 854 is also electrically connected to the LUTb 86b, and has a waiting time corresponding to the encoder number of the encoder signal output from the photosensitive encoder 211 (that is, information indicating the rotational position of the photosensitive drum 21). Read from LUTb 86b. More specifically, in the LUTb 86b, as shown in later specific examples (FIGS. 11 and 13), data indicating the relative relationship between the encoder number indicating the rotational position of the photosensitive drum 21 and the standby time is stored. .

  The vertical synchronization signal delay circuit 854 reads out the average period of the Hsync signal stored in the storage circuit 855 and the rotation period of the photosensitive drum 21 in synchronization with the encoder signal. Here, after confirming that the condition that the standby time corresponding to the encoder number of the encoder signal is longer than twice the average period of the Hsync signal and smaller than the rotation period of the photosensitive drum 21 is satisfied, the standby is performed. The color-specific vertical synchronization signal Vsync is delayed by the time and is provided to the horizontal synchronization signal output control circuit 851 as the delayed vertical synchronization signal Vsync. As described above, in this embodiment, the vertical synchronization signal delay circuit 854 delays and outputs the signal Vsync by the delay time corresponding to the rotational position of the photosensitive drum 21 when the color-specific vertical synchronization signal Vsync is received.

  As described above, in this embodiment, the Hsync signal corresponds to the “first light emitting element light emission signal” or the “second light emitting element light emission signal” of the present invention, and the average period of the Hsync signal is the “average time interval” of the present invention. It corresponds to. Further, the color-specific vertical synchronization signal Vsync input to the vertical synchronization signal delay circuit 854 corresponds to the “first exposure start signal” and the “second exposure start signal” of the present invention.

  The horizontal synchronization signal output control circuit 851 to which the delayed vertical synchronization signal Vsync, the Hsync signal from the dynamic horizontal synchronization signal generation circuit 852, and the number of dynamic horizontal synchronizations are input, generates the head control signal as follows. A horizontal synchronization signal Hsync to be supplied to the unit 87 is generated. Hereinafter, the operation of the head controller HC will be described with reference to FIGS. 4 to 13. In the present embodiment, the control of variably controlling the pitch of the horizontal synchronization signal Hsync (hereinafter referred to as “dynamic horizontal synchronization control”) and the output of the horizontal synchronization signal Hsync based on the delayed vertical synchronization signal Vsync. The control to adjust the exposure start timing by controlling the start (hereinafter referred to as “exposure start timing control”), but in order to deepen the understanding of them, the reason for the occurrence of positional error and color misalignment at the front edge of the image After the explanation, we compared the cases where both dynamic horizontal synchronization control and exposure start timing control are not executed, only when dynamic horizontal synchronization control is executed, and when both dynamic horizontal synchronization control and exposure start timing control are executed. While explaining.

  FIG. 4 is a schematic diagram showing the relationship between the rotation unevenness of the photosensitive drum and the position of the leading edge of the image. FIG. 5 is a schematic diagram showing the occurrence of a position error or color shift at the leading edge of the image. For example, when exposure by the exposure head 23 is started simultaneously with the reception of the color-specific vertical synchronization signal Vsync at the image forming station 2Y, as shown in FIG. 4, the leading edge position of the image formed at the image forming station 2Y (in FIG. The black circles (see black circles) vary in the paper feeding direction, that is, the moving direction D31 of the intermediate transfer belt 31 due to the influence of the rotation unevenness of the photosensitive drum 21. On the other hand, in an ideal state where no rotation unevenness occurs, the front end position of the image is moved to the primary transfer position TR1 after a lapse of a predetermined time from the start of exposure to the ideal position of the intermediate transfer belt 31 (see the hatched circles in the figure). Transcribed.

  However, when the surface speed (peripheral speed) of the photosensitive drum 21 is decreased, the leading edge of the image formed on the photosensitive drum 21 has not yet reached the primary transfer position TR1 even when a predetermined time has elapsed from the start of exposure. However, the image is primarily transferred onto the intermediate transfer belt 31 later than that. As a result, as shown in FIG. 5A, the image I (y) formed by the image forming station 2Y is upstream of the image primary transfer position (dashed line position in the figure) in the paper feed direction D31. First transfer is performed by shifting to the side, and a tip position error occurs. Conversely, when the surface speed (circumferential speed) of the photosensitive drum 21 increases, the leading edge of the image formed on the photosensitive drum 21 reaches the primary transfer position TR1 before a predetermined time has elapsed from the start of exposure. Then, the image is primarily transferred to the intermediate transfer belt 31. As a result, although illustration in FIG. 5A is omitted, the image I (y) formed by the image forming station 2Y is from the primary transfer position of the image in the ideal state (the broken line position in the figure). First transfer is performed by shifting to the downstream side in the paper feed direction D31, and a tip position error occurs. Such a front end position error is not limited to the yellow color, and an image front end error occurs due to rotation unevenness of the photosensitive drum 21 for other toner colors as well as the yellow color.

  Further, in the image forming apparatus shown in FIG. 1, since the color image is formed by superimposing the other color image on the yellow image I (y), the influence of the rotation unevenness of the photosensitive drum 21 in each color is the color at the leading edge of the image. Misalignment may be caused. For example, as shown in FIG. 5B, the leading edges of the yellow image I (y) and the magenta image I (m) are shifted from each other by the image leading edge color shift amount ΔY in the paper feed direction D31. May occur, which may degrade image quality.

  Further, the rotation unevenness of the photosensitive drum 21 not only causes an image front end position error and an image front end color shift, but also causes image pitch unevenness. That is, when the exposure processing is executed by outputting the horizontal synchronization signal Hsync at a constant period despite the occurrence of rotation unevenness of the photosensitive drum 21, for example, as shown in FIG. The image position error at fluctuates greatly depending on the image position in the paper feed direction D31. 6 indicates the relationship between the image position in the paper feed direction D31 and the image position error in an ideal state where the rotation unevenness of the photosensitive drum 21 does not occur. The image position error is constant. In this embodiment, the image position error is set to zero with this as a reference state. That is, the “paper feed direction image position error” in the figure means an amount of deviation from the image position in the ideal state, and the amplitude of each profile P (y), P (m) is the paper feed direction. The size of the image pitch unevenness is shown.

  Therefore, in the present embodiment, pitch unevenness is suppressed by executing dynamic horizontal synchronization control. That is, when the photoconductor encoder 211 detects the reference position of the photoconductor drum 21, it outputs a signal corresponding to this (Z phase detection). Further, the number of Hsyncs is read from the LUTa 86a based on the encoder number corresponding to the encoder signal output from the photoconductor encoder 211 after the detection of the Z phase. Then, the number of Hsyncs is compared with the number of dynamic horizontal synchronizations output from the dynamic horizontal synchronization signal generation circuit 852, and the Hsync signal is supplied to the horizontal synchronization signal output control circuit 851 while controlling the cycle of the Hsync signal. More specifically, when the surface speed (peripheral speed) of the photosensitive drum 21 is decreased, the cycle of the Hsync signal is shortened. On the other hand, when the surface speed (peripheral speed) of the photosensitive drum 21 is increased, the cycle of the Hsync signal is increased. become longer. Accordingly, it is possible to suppress image pitch unevenness due to rotation unevenness of the photosensitive drum 21. As a result, as is apparent from comparing the profiles P (y) shown in FIG. 6 or comparing the profiles P (m), the variation amount of the image position error in the paper feed direction D31 is suppressed. Thus, the image pitch unevenness of each color is reduced, and the image quality can be improved.

  However, since the image forming stations 2Y, 2M, 2C, and 2K operate independently from each other, the surface speed of the photosensitive drum 21 at the exposure start timing may be different for each color. As described above, the image position error at the leading edge of the image may be greatly different for each color. This means that the image leading edge color deviation amount ΔY (see FIG. 5B) is large, and the color deviation at the leading edge of the image becomes more noticeable even though the pitch unevenness is suppressed, leading to a decrease in image quality. I mean. Further, as is apparent from the comparison between FIGS. 6B and 6C, the image leading edge color shift amount ΔY varies with the number of printed sheets. Therefore, in the present embodiment, exposure start timing control is executed in addition to dynamic horizontal synchronization control, and for example, as shown in FIG.

  FIG. 7 is a diagram schematically showing an outline of exposure start timing control. FIG. 8 is a flowchart showing exposure start timing control. FIG. 9 is a graph showing the operation of exposure start timing control. Further, FIGS. 10 and 12 are diagrams illustrating the stored contents of the LUTa, and FIGS. 11 and 13 are diagrams illustrating the stored contents of the LUTb. Here, first, the outline of the exposure start timing control will be described with reference to FIG. 7, and then the operation of the exposure start timing control will be described with reference to FIGS.

  The exposure start timing control in this embodiment starts exposure with a delay from the color-specific vertical synchronization signal Vsync, and the vertical synchronization signal delay circuit 854 adjusts the delay time (standby time DT) from the color-specific vertical synchronization signal Vsync. To do. In the present embodiment, in the ideal state where the rotation unevenness of the photosensitive drum 21 is not generated, exposure by the exposure head 23 is started at “Vsync timing” when the color-specific vertical synchronization signal Vsync is received, as shown in the upper part of FIG. Instead, exposure is started based on the delayed vertical synchronization signal Vsync output from the vertical synchronization signal delay circuit 854 after a predetermined standard standby time DT0 (exposure start timing). The leading edge position of the image formed at the image forming station (see the black circle in the figure) is moved to the primary transfer position TR1 after a predetermined movement time (hereinafter referred to as “standard movement time”) has elapsed from the Vsync timing. Then, the image is transferred to the ideal position of the intermediate transfer belt 31 (see the hatched circles in the figure). Note that the broken-line circles in the figure indicate the surface position of the photosensitive drum 21 facing the exposure head 23 at the Vsync timing.

  Here, when rotation irregularity occurs in the photosensitive drum 21, the surface speed (peripheral speed) of the photosensitive drum 21 varies, and the time required for the image leading edge position to reach the primary transfer position TR1 varies. Therefore, in consideration of the time variation, in this embodiment, the standby time is adjusted by the variation time. That is, when the surface speed of the photosensitive drum 21 at the Vsync timing to which the color-specific vertical synchronization signal Vsync is given is slower than the surface speed in the ideal state, as shown in the middle of FIG. After waiting from the reception timing of the color-specific vertical synchronization signal Vsync for a short standby time DTs, the vertical synchronization signal delay circuit 854 outputs the delayed vertical synchronization signal Vsync. In response to the delayed vertical synchronization signal Vsync, exposure of the photosensitive drum 21 at the image forming station is started. As a result, the leading edge position of the image formed by the image forming station is moved to the primary transfer position TR1 and transferred to the ideal position of the intermediate transfer belt 31 at the timing when the standard movement time has elapsed from the Vsync timing. On the other hand, when the surface speed of the photosensitive drum 21 at the Vsync timing to which the vertical sync signal Vsync for each color is given is faster than the surface speed in the ideal state, as shown in the lower part of FIG. The exposure is started after waiting from the Vsync timing for a longer standby time DTf. As a result, the leading edge position of the image formed by the image forming station is moved to the primary transfer position TR1 and transferred to the ideal position of the intermediate transfer belt 31 at the timing when the standard movement time has elapsed from the Vsync timing.

  As described above, the surface speed of the photosensitive drum 21 varies depending on the rotational position of the photosensitive drum 21 at the time when the color-specific vertical synchronization signal Vsync is given due to the occurrence of rotation unevenness in the photosensitive drum 21. The exposure start timing is adjusted accordingly. As a result, in any of the image forming stations 2Y, 2M, 2C and 2K, the image leading edge position coincides with the ideal position of the intermediate transfer belt 31, and the images formed at the image forming stations 2Y, 2M, 2C and 2K, respectively. Can be superimposed on the intermediate transfer belt 31 with high accuracy, and a high-quality color image can be obtained.

  Next, the operation of the exposure start timing control will be described with reference to FIGS. In FIG. 9, a profile Cd indicating the change in the number of dynamic horizontal synchronizations (left graph in the figure) and a profile indicating the image transfer position on the intermediate transfer belt 31 (right graph in the figure). Is described. In addition, the vertical axis on the left side of the figure shows not only the above-described dynamic horizontal synchronization number but also the Hsync number indicating the rotational position of the photosensitive drum 21. Reference numeral Cr is a profile showing a change in the number of horizontal synchronizations in an ideal state where no rotation unevenness occurs, and is shown for reference.

  In this embodiment, while rotating the photosensitive drum 21 having a diameter of 40 (mm) with a rotation period of 0.84 (sec), the average period of the horizontal synchronization signal Hsync is set to 141.1 (μsec) and sub-scanning is performed. When an image is formed with a resolution in the direction (Y direction) of 1200 (dpi), the configuration is as follows. One circumference of the photosensitive drum 21 is divided into 5937. That is, the position where the photosensitive drum 21 is rotated by 0.06 ° (= 360 ° / 5937) from the reference rotation position (rotation position at the time of detecting the Z phase) is set to Hsync number = 1. In this way, the rotational position of the photosensitive drum 21 during one rotation of the photosensitive drum 21 is indicated by the Hsync number, and the rotational position of the photosensitive drum 21 when the Hsync number is M is (0) from the reference position. .06 ° × M). Further, the number of encoder signals output from the photoconductor encoder 211 during one rotation of the photoconductor drum 21 is set to 1024, that is, the number of pulses of the photoconductor encoder 211 is set to 1024 (Plus / rev). ing. Therefore, the correlation between the encoder number of the encoder signal output from the photoconductor encoder 211 and the number of Hsyncs is as shown in FIG. 10, and this correlation is stored in the LUTa 86a. In this embodiment, the standard standby time DT0 is set to 3000 (μsec), and data indicating the relative relationship between the encoder number indicating the rotational position of the photosensitive drum 21 and the standby time DT is obtained in advance, for example, FIG. Is stored in the LUTb 86b.

  In this embodiment, the average period of the horizontal synchronization signal Hsync is set to 52.9 (μsec) while rotating the photosensitive drum 21 having a diameter of 80 (mm) at a rotation period of 1.26 (sec). When an image is formed at a resolution of 2400 (dpi) in the sub-scanning direction (Y direction), the following configuration is used. One circumference of the photosensitive drum 21 is divided into 23747. That is, the position where the photosensitive drum 21 is rotated by 0.015 ° (= 360 ° / 23747) from the reference rotation position (rotation position at the time of Z-phase detection) is set to Hsync number = 1. Therefore, the rotational position of the photosensitive drum 21 when the Hsync number is M is a position rotated by (0.015 ° × M) from the reference position. Further, the number of encoder signals output from the photoconductor encoder 211 during one rotation of the photoconductor drum 21 is set to 3600, that is, the number of pulses of the photoconductor encoder 211 is set to 3600 (Plus / rev). ing. Therefore, the correlation between the encoder number of the encoder signal output from the photoconductor encoder 211 and the number of Hsyncs is as shown in FIG. 12, and this correlation is stored in the LUTa 86a. In the present embodiment, the standard standby time DT0 is 2500 (μsec), and data indicating the relative relationship between the encoder number indicating the rotational position of the photosensitive drum 21 and the standby time DT is obtained in advance, for example, FIG. Is stored in the LUTb 86b.

  Then, the vertical synchronizing signal delay circuit 854 executes the following steps S1 to S4. First, when the vertical synchronizing signal delay circuit 854 detects the color-specific vertical synchronizing signal Vsync (step S1), the encoder number corresponding to the encoder signal, that is, the rotational position of the photosensitive drum 21 is acquired (step S2). The vertical synchronization signal delay circuit 854 reads the standby time DT corresponding to the encoder number from the LUTb 86b (step S3), and further delays the color-specific vertical synchronization signal Vsync by the standby time DT acquired in step S3. The vertical synchronization signal Vsync is output to the horizontal synchronization signal output control circuit 851 (step S4).

  Upon receiving the delayed vertical synchronization signal Vsync, the horizontal synchronization signal output control circuit 851 uses the Hsync signal output from the dynamic horizontal synchronization signal generation circuit 852 as the horizontal synchronization signal Hsync and starts output to the head control signal generation unit 87. (Step S5). As a result, exposure is started with a delay from the color-specific vertical synchronization signal Vsync. For example, at the timing T1 in FIG. 9, when the surface speed of the photosensitive drum 21 is slower than the ideal state as shown in the middle part of FIG. 7, dynamic horizontal synchronization control is performed to suppress image pitch unevenness. For this reason, the cycle of the Hsync signal is shorter than the ideal state, and as a result, the number of dynamic horizontal synchronizations is counted up in a state exceeding the standard number of horizontal synchronizations. Therefore, the cycle of the Hsync signal is shorter than the ideal state. Therefore, in the present embodiment, the standby time DTs read from the LUTb 86b is shorter than the standard standby time DT0, and as a result, the photosensitive drum 21 rotates in an ideal state with no rotation unevenness (in other words, the photosensitive drum 21). Exposure is started at a timing T2s that is earlier than the standard exposure start timing T20.

  On the other hand, although illustration in FIG. 9 is omitted, if the surface speed of the photosensitive drum 21 is higher than the ideal state as shown in the lower part of FIG. The Hsync signal cycle is longer than the ideal state in order to suppress image pitch unevenness by performing dynamic horizontal synchronization control. As a result, the dynamic horizontal synchronization frequency is counted up below the standard horizontal synchronization frequency. To go. Therefore, the cycle of the Hsync signal is longer than the ideal state. Therefore, in this embodiment, the standby time DTs read from the LUTb 86b is longer than the standard standby time DT0, and as a result, exposure is started at a timing later than the standard exposure start timing T20. When the surface speed of the photosensitive drum 21 is the same as the ideal state at the timing T1, the exposure is started at the standard exposure start timing T20.

  As described above, in this embodiment, in any of the image forming stations 2Y, 2M, 2C, and 2K, the standby time corresponding to the rotational position of the photosensitive drum 21 at the timing T1 when the color-specific vertical synchronization signal Vsync is received. (Delay time) Delayed vertical synchronization signal Vsync is output delayed from timing T1 by DT, and exposure of the photosensitive drum 21 is started based on the signal Vsync. Therefore, the time from the reception timing T1 of the color-specific vertical synchronization signal Vsync to the primary transfer start timing T3 can be made constant without being affected by the rotation unevenness. As a result, the leading end positions of the images formed by the image forming stations 2Y, 2M, 2C, and 2K can be matched with each other, and the image leading end color shift can be effectively suppressed.

  The dynamic horizontal synchronization signal generation circuit 852 reads the Hsync count from the LUTa 86a based on the encoder number corresponding to the encoder signal output from the photoconductor encoder 211 after the detection of the Z phase. Then, the number of Hsyncs is compared with the number of dynamic horizontal synchronizations output from the dynamic horizontal synchronization signal generation circuit 852, and the Hsync signal is supplied to the horizontal synchronization signal output control circuit 851 while controlling the cycle of the Hsync signal. More specifically, when the surface speed (peripheral speed) of the photosensitive drum 21 is decreased, the cycle of the Hsync signal is shortened. On the other hand, when the surface speed (peripheral speed) of the photosensitive drum 21 is increased, the cycle of the Hsync signal is increased. become longer. Accordingly, it is possible to suppress image pitch unevenness due to rotation unevenness of the photosensitive drum 21. As a result, as is apparent from comparing the profiles P (y) shown in FIG. 6 or comparing the profiles P (m), the variation amount of the image position error in the paper feed direction D31 is suppressed. Thus, the image pitch unevenness of each color is reduced, and the image quality can be improved. Therefore, by executing the dynamic horizontal synchronization control while suppressing the color misalignment of the leading edge of the image as described above, the pitch unevenness of each image can be suppressed, and a high quality color image can be obtained.

  The present invention is not limited to the above-described embodiment, and various modifications can be made to the above-described one without departing from the spirit of the present invention. For example, in the above embodiment, the present invention is applied to an image forming apparatus provided with four image forming stations corresponding to the image forming unit of the present invention. The present invention can be applied to all tandem image forming apparatuses having an image forming unit. That is, among the plurality of image forming stations, the image forming station positioned on the upstream side in the paper feeding direction D31, that is, the sub-scanning direction Y corresponds to the “first image forming unit” of the present invention, while the downstream image forming station. Corresponds to the “second image forming unit” of the present invention.

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2Y, 2M, 2C, 2K ... Image forming station (image forming part), 21 ... Photosensitive drum (1st latent image carrier, 2nd latent image carrier), 23 ... Exposure head, 31 ... Intermediate transfer belt (image carrier) 46 ... Vertical synchronization sensor 81 ... Image processing section 82 ... Mechanical control section (exposure command section) 85 ... Horizontal synchronization signal generation section (exposure control section) 87 ... Head control Signal generation unit (exposure control unit), D31 ... paper feed direction, DT0, DTf, DTs ... standby time (delay time), Hsync ... horizontal synchronization signal (first light emitting element light emission signal, second light emitting element light emission signal), HC ... Head controller (exposure controller), Vsync ... Vertical sync signal for each color (first exposure start signal, second exposure start signal)

Claims (7)

An image carrier for carrying an image;
A first latent image carrier that is rotationally driven in a first direction; a plurality of first light emitting elements disposed in a second direction different from the first direction; and exposing the first latent image carrier to A first exposure unit that forms one latent image; and a first development unit that develops the first latent image formed by exposure of the first exposure unit. The first development unit that is developed by the first development unit A first image forming unit that transfers the image of the image to the image carrier;
A plurality of second latent image carriers that are driven to rotate in the first direction; and a plurality of second light emitting elements that are arranged in the second direction. The second latent image carrier is exposed to form a second latent image. A second exposure part to be formed; and a second development part for developing the second latent image formed by exposure of the second exposure part, wherein the second image developed by the second development part is A second image forming unit for transferring to the image carrier onto which the first image has been transferred;
A first exposure start signal for instructing start of exposure of the first latent image by the first exposure unit; and a second exposure start signal for instructing start of exposure of the second latent image by the second exposure unit. An exposure command section to output,
The timing at which the first light emitting element emits light after receiving the first exposure start signal and after a first delay time delay corresponding to the rotational position of the first latent image carrier when the first exposure start signal is received. The first light emitting element light emission signal for controlling the light is output to the first exposure unit, the second exposure start signal is received and the second latent image carrier is rotated when the second exposure start signal is received. An exposure control unit that outputs a second light emitting element light emission signal for controlling the timing at which the second light emitting element emits light after the second delay time delay according to
An image forming apparatus comprising:   The exposure control unit outputs a plurality of the first light emitting element light emission signals to the first exposure unit, and outputs the first light emitting element light emission signal in accordance with a change in the rotation speed of the first latent image carrier. The image forming apparatus according to claim 1, wherein the timing is adjusted.   The exposure control unit includes the first delay within a range of time longer than twice the average time interval of the plurality of first light emitting element light emission signals to be output and shorter than the rotation period of the first latent image carrier. The image forming apparatus according to claim 2, wherein the time is adjusted.   The exposure control unit outputs a plurality of the second light emitting element light emission signals to the second exposure unit, and outputs the second light emitting element light emission signals in accordance with fluctuations in the rotation speed of the second latent image carrier. The image forming apparatus according to claim 1, wherein the timing is adjusted.   The exposure control unit sets the second delay time within a range that is longer than twice the average time interval of the output light emitting signal of the second light emitting element and shorter than the rotation period of the second latent image carrier. The image forming apparatus according to claim 4, which is adjusted. A first exposure start signal for instructing start of exposure on the first latent image carrier is output from the exposure command unit to the exposure control unit, and a second exposure start signal for instructing start of exposure on the second latent image carrier is provided. Output from the exposure command unit to the exposure control unit,
Detecting a rotational position of the first latent image carrier when the first exposure start signal is output;
Calculating a first delay time corresponding to the detected rotational position of the first latent image carrier;
After delaying the calculated first delay time from the first exposure start signal, starting the output of the first light emitting element light emission signal from the exposure control unit,
Exposing the first latent image carrier based on the outputted first light emitting element emission signal,
Developing the exposed first latent image carrier,
An image forming method comprising transferring a developed first image to an image carrier. Detecting the rotational position of the second latent image carrier when the second exposure start signal is output;
Calculating a second delay time corresponding to the detected rotational position of the second latent image carrier,
After delaying the calculated second delay time from the second exposure start signal, starting the output of the second light emitting element light emission signal from the exposure control unit,
Exposing the second latent image carrier based on the output light emitting signal of the second light emitting element,
Developing the exposed second latent image carrier,
The image forming method according to claim 6, wherein the developed second image is transferred to the image carrier on which the first image is transferred.

Images