JP4613647B2 - Image forming apparatus and image output apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile, and more particularly to an image forming apparatus that forms a final image by superimposing a plurality of color images.

  2. Description of the Related Art Conventionally, image forming apparatuses such as color printers and color copiers that form a full-color image by superimposing a plurality of color images on a recording medium such as paper have been widely used. In this type of image forming apparatus, color misregistration (positional misregistration) of each color image superimposed on the recording medium becomes a problem. For example, when the so-called tandem system in which a plurality of image forming units provided for each color is arranged in parallel facing the transfer belt is adopted, the color misregistration is caused by an error in the mounting position of each image forming unit, and each image forming unit. This occurs due to a peripheral speed error of a part, a difference in exposure position with respect to the transfer belt, a change in speed of the transfer belt, and the like. That is, for example, in a tandem type image forming apparatus, the alignment and mechanical error of each image forming unit directly becomes a positional shift on the recording medium. Therefore, in an image forming apparatus that employs such a method, it is indispensable to perform misregistration control (registration control) for measuring these misregistration amounts in advance and suppressing the occurrence of misregistration.

  As this misregistration control, for example, before actual image formation is started, such as when the power is turned on, each image forming unit marks Y (yellow), M (magenta), C (cyan), and K (black). Are sequentially formed on the transfer belt, the position of each color mark is read by a sensor, the amount of misregistration of each color is calculated from the result read by the sensor, and the image formation timing of each color is feedback controlled. (See Patent Document 1).

  Further, in an image forming apparatus such as a printer or a copier that employs a so-called electrophotographic system, the obtained image quality is easily affected by fluctuations in the environment (temperature and humidity), deterioration of parts over time, and the like. In particular, in the case where a plurality of image forming units are provided as in the tandem type image forming apparatus described above, the degree to which the image forming units are affected by environmental fluctuations and deterioration with time varies. For this reason, even when a full-color image is formed based on the same image data, the density or the like of the formed toner image may differ for each color. As a result, the color reproducibility and gradation of a full color image obtained by superimposing these color toner images are significantly changed. Therefore, in an image forming apparatus that employs such a method, density shift control (process control) for measuring the density shift amount of each color in advance and suppressing the occurrence of density shift is indispensable.

  As this density deviation control, for example, before actual image formation is started, such as when the power is turned on, high density and low density marks of each color of YMCK are formed on the transfer belt by each image forming unit, and the density is measured by a sensor. In addition to reading, a method has been proposed in which a density deviation amount from a reference density is calculated for each color from a reading result by a sensor, and feedback control is performed on a development contrast potential difference or the like when an image of each color is formed (Patent Document 2). reference.).

  Recently, a technique for reading the marks for performing these regicons (hereinafter referred to as regicon marks) and the marks for performing procons (hereinafter referred to as procon marks) with the same sensor has also been proposed (patents). Reference 3).

Japanese Patent No. 2765626 (page 4, FIG. 6) JP-A-6-102734 (page 6-8, FIG. 9) JP 2001-22227 A (page 4, FIG. 2)

  However, in Patent Document 3 described above, since the register control mark and the process control mark are separately formed, it is necessary to sequentially read the register control mark and the process control mark by the same sensor. For this reason, the time required for executing the registration control and the process control is increased, and the waiting time until the image forming operation can be executed becomes long.

  In order to solve such a problem, for example, it is conceivable that only the process control mark is formed on the transfer belt, and the process control and the registration control are performed based on the reading result of the process control mark by the sensor. Here, the mark for the process control includes a high density mark and a low density mark as described above. For this reason, for example, in a low-density mark, the boundary between the part where the mark exists and the part where the mark does not exist easily becomes ambiguous. As a result, not only the positional deviation of each color cannot be corrected, but also the positional deviation amount is increased. There was a risk of it.

The present invention has been made to solve such technical problems, and an object of the present invention is to provide an image forming apparatus capable of performing more accurate positional deviation correction and density deviation correction with a simple configuration. Is to provide etc.
It is another object of the present invention to provide an image forming apparatus and the like that can shorten the time for performing the positional deviation correction and the density deviation correction.

  For this purpose, the present invention is an image forming apparatus that has a plurality of image forming portions that form images of respective colors, and that superimposes and transfers images formed by the plurality of image forming portions. On the other hand, for each color including a misregistration correction mark used for misregistration correction and a density misregistration correction mark that exists in a rectangular area specified by the misregistration correction mark and is used for density misalignment correction. The control marks are sequentially formed by the control mark forming means using a plurality of image forming units, the control marks formed by the control mark forming means are read by the reading means, and the correcting means are read by the reading means. Based on the misalignment correction mark obtained by reading the control mark, misalignment correction is performed in a plurality of image forming units, and the control mark is read by the reading means. The density deviation correction in the plurality of image forming units based on the density deviation correction mark obtained by taking.

  Here, the control mark forming means forms the positional deviation correction mark as a high density image, and forms the density deviation correction mark as a predetermined density image selected from a range from low density to high density. Can be characterized. Further, the correction means can perform density deviation correction based on a position deviation correction mark obtained by reading the control mark by the reading means.

  From another point of view, the present invention is an image forming apparatus that includes a plurality of image forming units that form images of respective colors, and that superimposes and transfers images formed by the plurality of image forming units. Existing on the upstream side and downstream side of the transfer body in the sub-scanning direction of the transfer body, and in the intermediate part of the position-shift correction mark used for position-shift correction and the position-shift correction mark, A control mark for each color including a density deviation correction mark used in density deviation correction is sequentially formed by a control mark forming unit using a plurality of image forming units, and is formed by the control mark forming unit. The control mark is read by the reading means, and the correction means corrects the misalignment in the plurality of image forming units using the misalignment correction marks obtained by reading the control mark by the reading means. And, the density deviation correction in a plurality of image forming portions with a density deviation correction mark obtained by reading the control marks by reading means.

  Here, the correction means may be characterized in that the density deviation correction is not performed when there is an abnormality in the position deviation correction mark obtained by reading the control mark by the reading means. Further, the correction means may be characterized in that the position deviation correction is not performed when there is an abnormality in the density deviation correction mark obtained by reading the control mark by the reading means.

Further, from another point of view, the present invention is an image forming apparatus that includes a plurality of image forming units that form images of respective colors, and that superimposes and transfers images formed by the plurality of image forming units. Control images for each color including a misregistration correction mark used for misregistration correction and a density misregistration correction mark used for density deviation correction are transferred to a plurality of images by a control mark forming unit. The control mark formed by the forming portion is sequentially formed, the control mark formed by the control mark forming means is read by the reading means, and the position deviation correction mark and the density deviation correction mark in the control mark read by the reading means are read. Is determined by the determining unit, and based on the determination result by the determining unit, the correcting unit corrects misalignment in the plurality of image forming units based on the misalignment correction marks, and , The density deviation correction in a plurality of image forming section based on the mark for the density deviation correction.
Here, the discriminating means can discriminate between the position deviation correction mark and the density deviation correction mark based on the position occupied in the control mark.

The present invention can also be understood as an image output device. That is, the present invention is an image output apparatus used in an image forming apparatus that has a plurality of image forming units that form images of respective colors and that superimposes and transfers images formed by the plurality of image forming units. Image data of a control mark including a misregistration correction mark used for correction and a density misregistration correction mark that exists in a rectangular area specified by the misregistration correction mark and is used for density misalignment correction. The image processing apparatus includes a storage unit for storing, and an image output unit that outputs the control mark image data read from the storage unit to a plurality of image forming units.
Here, the image data of the control mark stored in the storage section intersects obliquely with respect to both the sub-scanning direction and the main scanning direction, and the first side and the second side that function as a positional deviation correction mark And a third side that extends in the main scanning direction from the intersection of the first side and the second side in the main scanning direction and functions as a density deviation correction mark. Can be characterized.

According to the present invention, for example, the density deviation correction mark is formed in a rectangular region where the position deviation correction mark is formed, or the position deviation correction mark and the density deviation correction mark included in the control mark, for example. Since the mark is discriminated and used for position deviation correction and density deviation correction, more accurate position deviation correction and density deviation correction can be performed with a simple configuration.
Further, according to the present invention, for example, the position deviation correction mark and the density deviation correction mark are formed in the control mark of the same color. Compared with a mode in which the is formed at a completely different position, it is possible to shorten the time for performing the positional deviation correction and the density deviation correction.

The best mode for carrying out the present invention (hereinafter referred to as an embodiment) will be described below in detail with reference to the accompanying drawings.
<Embodiment 1>
FIG. 1 is a view showing a tandem type and intermediate transfer type image forming apparatus to which the present embodiment is applied, and FIG. 2 is an enlarged perspective view of a main part of the image forming apparatus. The image forming apparatus includes, for example, a plurality (four in the present embodiment) of image forming units 10 (specifically, 10K, 10Y, 10M, and 10C) on which each color component toner image is formed by electrophotography. Each color component toner image formed by each image forming unit 10 is sequentially transferred (primary transfer) and held, and the superimposed image transferred to the intermediate transfer belt 20 is collectively transferred (secondary transfer) to the paper P. A secondary transfer device 30 and a fixing device 50 for fixing the secondary transferred image on the paper P are provided. Further, the image forming apparatus is provided with a control unit 70 for controlling an image forming operation and alignment and density adjustment of each color toner image described later. In this embodiment, the plurality of image forming units 10K, 10Y, 10M, and 10C function as a plurality of image forming units.

  Here, the image forming unit 10 for each color component includes a photosensitive drum 11, a charging device 12 that charges the photosensitive drum 11 to a predetermined potential, and a laser exposure device that writes an electrostatic latent image on the charged photosensitive drum 11. 13 is provided. Further, the image forming unit 10 for each color component includes a developing device 14 that develops an electrostatic latent image on the photosensitive drum 11 in which each color component toner is stored, and a toner image carried on the photosensitive drum 11 as an intermediate transfer belt. A primary transfer roll 15 for transferring to a drum 20 and a drum cleaner 16 for removing residues on the photosensitive drum 11 after the primary transfer are provided.

  The intermediate transfer belt 20 as a transfer member is rotatable by a drive roll 21 that drives the intermediate transfer belt 20, a driven roll 22 that is driven by the intermediate transfer belt 20, and a backup roll 23 of a secondary transfer device 30 that will be described later. It is stretched. Further, a belt cleaner 24 for removing residues on the intermediate transfer belt 20 after the secondary transfer is disposed at a position facing the drive roll 21 with the intermediate transfer belt 20 interposed therebetween. On the other hand, a position / density detection sensor 25 is arranged on the upstream side in the moving direction of the intermediate transfer belt 20 as viewed from the secondary transfer device 30 (secondary transfer roll 31) and downstream of the black image forming unit 10K. It is installed. This position / density detection sensor 25 reads an image quality adjustment pattern (toner image) for alignment and density adjustment formed on the intermediate transfer belt 20, and as shown in FIG. Two portions are provided on both end sides in the direction orthogonal to the moving direction of the belt 20. Details of this image quality adjustment pattern will be described later.

  Further, the secondary transfer device 30 includes a secondary transfer roll 31 disposed in pressure contact with the toner image carrying surface side of the intermediate transfer belt 20, and a counter electrode of the secondary transfer roll 31 disposed on the back surface side of the intermediate transfer belt 20. And a backup roll 23 that constitutes A power supply roll 32 for applying a secondary transfer bias having the same polarity as the toner charging polarity is disposed in contact with the backup roll 23. On the other hand, the secondary transfer roll 31 is grounded.

  The paper transport system transports the paper P stacked on the paper tray 40 by the transport roll 41, temporarily stops it by the registration roll (registration roll) 42, and then stops the second transfer in the secondary transfer device 30 at a predetermined timing. It is fed to the next transfer position. Further, the sheet P after the secondary transfer is conveyed to the fixing device 50 via the conveyance belt 43, and the sheet P discharged from the fixing device 50 is discharged outside the apparatus by a discharge roll (not shown). Yes.

  Next, an image forming process of the image forming apparatus will be described. Now, when a start switch (not shown) is turned on, a predetermined image forming process is executed. More specifically, for example, when the image forming apparatus is configured as a digital color copying machine, a document set on a document table (not shown) is read by a color image reading device, and the read signal is converted into a digital image signal by a processing circuit. And temporarily stored in the memory, and toner images of each color are formed based on the stored digital image signals of four colors (Y, M, C, K). That is, the image forming unit 10 (specifically, 10Y, 10M, 10C, 10K) is driven in accordance with the digital image signal of each color. In each image forming unit 10, an electrostatic latent image corresponding to the digital image signal is written by the laser exposure device 13 on the photosensitive drum 11 uniformly charged by the charging device 12. Then, the electrostatic latent image formed on the photosensitive drum 11 is developed by the developing device 14 to form toner images of each color. In the case where the image forming apparatus is configured as a printer, toner images of each color may be formed based on a digital image signal input from the outside.

The toner image formed on each photosensitive drum 11 is sequentially transferred from the photosensitive drum 11 to the surface of the intermediate transfer belt 20 by the primary transfer roll 15 at the primary transfer position where the photosensitive drum 11 and the intermediate transfer belt 20 are in contact with each other. Is done. On the other hand, the toner remaining on the photosensitive drum 11 after the transfer is cleaned by the drum cleaner 16.
The toner image primarily transferred to the intermediate transfer belt 20 in this way is superimposed on the intermediate transfer belt 20 and conveyed to the secondary transfer position as the intermediate transfer belt 20 rotates. On the other hand, the paper P is conveyed to the secondary transfer position at a predetermined timing, and the secondary transfer roll 31 nips the paper P against the backup roll 23.
Then, at the secondary transfer position, the toner image carried on the intermediate transfer belt 20 is secondarily transferred to the paper P by the action of a transfer electric field formed between the secondary transfer roll 31 and the backup roll 23. . The sheet P on which the toner image is transferred is conveyed to the fixing device 50 by the conveying belt 43, and after the toner image on the sheet P is heated and pressure-fixed in the fixing device 50, the sheet is provided outside the apparatus. It is discharged to a tray (not shown). On the other hand, the toner remaining on the intermediate transfer belt 20 after the transfer is cleaned by the belt cleaner 24.

  In the image forming apparatus according to the present embodiment, during the rotation of the intermediate transfer belt 20, the intermediate transfer belt 20 is displaced in the direction (lateral direction) perpendicular to the rotation direction (movement direction) or the rotation thereof. There may be fluctuations in the dynamic speed. As a result, the color toner images primarily transferred from the image forming units 10Y, 10M, 10C, and 10K cannot be accurately superimposed on the intermediate transfer belt 20. As a result, a color shift (position shift) occurs in the full-color toner image secondarily transferred from the intermediate transfer belt 20 to the paper P, and the obtained image quality is significantly deteriorated. Further, the mounting positions of the laser exposure devices 13 provided in the image forming units 10Y, 10M, 10C, and 10K are shifted, and the mounting positions of the image forming units 10Y, 10M, 10C, and 10K with respect to the intermediate transfer belt 20 are shifted. In the same way, misalignment also occurs. Further, when environmental factors such as temperature and humidity fluctuate, the image forming units 10Y, 10M, 10C, and 10K, the intermediate transfer belt 20, and the like may be slightly expanded and contracted to cause misalignment.

  On the other hand, in the present embodiment, each of the image forming units 10Y, 10M, 10C, and 10K forms a corresponding color component toner image by an electrophotographic method, and primary transfer the formed color component toner image to the intermediate transfer belt 20. is doing. In the tandem image forming apparatus, since the respective photosensitive drums 11, the charging devices 12, and the primary transfer roll 15 are used, the degree of deterioration differs for each color. That is, the thickness of the photosensitive layer provided on the photosensitive drum 11 and the resistance values of the charging device 12 and the primary transfer roll 15 are different for each image forming unit 10. Also, the charging characteristics of the toner for each color are different. For this reason, even if the corresponding color component toner images are formed by the image forming units 10Y, 10M, 10C, and 10K to form images of the same density for each color and are primarily transferred onto the intermediate transfer belt 20, the The image density of each color component toner formed on the transfer belt 20 is not actually the same.

  Therefore, in the present embodiment, the image adjustment toner image created by each of the image forming units 10Y, 10M, 10C, and 10K is transferred onto the intermediate transfer belt 20, and the image adjustment of each color transferred onto the intermediate transfer belt 20 is performed. The toner image is read by the position / density detection sensor 25, and the position adjustment (registration control) and density adjustment (process control) of each color component toner image are performed based on the obtained reading result. Details of these registration control and process control in the present embodiment will be described below.

  FIG. 3 shows a cross-sectional view of the position / concentration detection sensor 25 as a reading means used in registration control and process control. FIG. 3 shows a cross section in which the position / density detection sensor 25 is cut in a direction perpendicular to the moving direction of the intermediate transfer belt 20. The position / density detection sensor 25 includes a first LED (Light Emitting Device) 61 and a second LED 62 that irradiate the toner image carrying surface of the intermediate transfer belt 20. Further, the position / density detection sensor 25 receives the reflected light from the image quality adjustment pattern T formed on the intermediate transfer belt 20 and the intermediate transfer belt 20 irradiated by the first LED 61 and the second LED 62. A PD (Photo Diode) 63 that outputs a current value having an intensity corresponding to the amount of received light is provided.

  The first LED 61, the second LED 62, and the PD 63 are accommodated in a case 64 having a downward opening. The light emitted from the first LED 61 passes through a first ejection slit 64a provided in the case 64, and illuminates the surface of the intermediate transfer belt 20 at an angle of 70 °, for example. The case 64 is also provided with a second exit slit 64b that guides the irradiation light from the second LED 62 to the surface of the intermediate transfer belt 20. Here, the light irradiated by the second LED 62 is configured to illuminate the intermediate transfer belt 20 at an angle of, for example, 135 °. Further, the case 64 has an incident slit 64c for allowing reflected light from the intermediate transfer belt 20 and the image quality adjustment pattern T (image quality adjustment toner image) formed on the surface of the intermediate transfer belt 20 to pass toward the PD 63. Is provided. Here, the entrance slit 64 c is provided in a direction of, for example, 110 ° with respect to the surface of the intermediate transfer belt 20. Therefore, the reflected light regularly reflected by the intermediate transfer belt 20 and the image quality adjustment pattern T out of the light emitted from the first LED 61 enters the PD 63. On the other hand, reflected light diffused by the intermediate transfer belt 20 and the image quality adjustment pattern T out of the light emitted from the second LED 62 enters the PD 63. For example, in a black toner image, the amount of light received by the toner is large, so that the amount of light received may be insufficient with only diffused light. For this reason, in the position / concentration detection sensor 25 according to the present embodiment, the first LED 61 and the second LED 62 having different attachment angles are used as light sources. A lens 65 for condensing incident light on the light receiving surface of the PD 63 is mounted inside the incident slit 64c. The opening of the entrance slit 64c is set to φ0.8.

  FIG. 4 is a block diagram for explaining the functions of the control unit 70 and the position / density detection sensor 25. FIG. 4 shows only blocks related to the above-described registration control and process control among the plurality of controls executed by the control unit 70. The control unit 70 includes a CPU (Central Processing Unit) 71 that controls an image forming operation, registration control, process control, and the like by the image forming apparatus. Further, the control unit 70 outputs image information for actual image forming operation or image information for forming the image quality adjustment pattern T based on a command from the CPU 71 or an image as an image output unit. The output circuit 72 includes an image quality adjustment pattern storage unit 73 as a storage unit that stores in advance image information (image data of control marks) for forming the image quality adjustment pattern T. The control unit 70 further includes a ROM (Read Only Memory) 74 that stores a software program for controlling image forming operations, registration control, process control, and the like executed by the CPU 71. From the image output circuit 72, the ROS (Raster Output Scanner: specifically, ROS for Y, ROS for M, ROS for C, ROS for K, K for the laser exposure apparatus 13 corresponding to each image forming unit 10Y, 10M, 10C, 10K. ROS) is output image information for an actual image forming operation and image information for forming an image quality adjustment pattern T. The control unit 70 also includes a RAM (Random Access Memory) 75 for storing various counter values and temporary data generated during program execution. Further, the control unit 70 includes an LED driver 76 that controls lighting of the first LED 61 and the second LED 62 provided in the position / concentration detection sensor 25. Furthermore, the control unit 70 includes a selection signal output circuit 77 that outputs a predetermined selection signal to the CPU 71. In the present embodiment, the CPU 71 functions as a determination unit and a correction unit.

  On the other hand, the position / concentration detection sensor 25 converts / amplifies the current value corresponding to the amount of received light output from the PD 63 into a voltage value corresponding to the magnitude, and outputs an amplifier (AMP) 66 that outputs it as a sensor output signal. Have. Further, the position / concentration detection sensor 25 detects the maximum value of the sensor output signal output from the AMP 66 and outputs a peak detection signal, and takes in the sensor output signal output from the AMP 66 and detects the peak. A sample hold circuit 68 for outputting a hold signal obtained by holding the sensor output signal when the peak detection signal is output from the circuit 67; The peak detection signal and the hold signal are output toward the control unit 70.

  FIG. 5 shows an example of an image quality adjustment pattern T read from the image quality adjustment pattern storage unit 73 by the image output circuit 72 and formed on the intermediate transfer belt 20 by the image forming units 10Y, 10M, 10C, and 10K. It is shown. The image quality adjustment pattern T is configured by arranging a plurality of control marks M for each color in the moving direction of the intermediate transfer belt 20. In the present embodiment, an arrow (→) -shaped control mark M is formed by each of the image forming units 10Y, 10M, 10C, and 10K.

  The control mark M substantially crosses both the moving direction of the intermediate transfer belt 20 (sub-scanning direction: process direction) and the direction orthogonal thereto (main scanning direction: lateral direction). It has a first side M1 and a second side M2 forming a “character”. The first side M1 and the second side M2 have an inclination angle of 45 ° with respect to the process direction and the lateral direction, respectively, and the angle formed by the first side M1 and the second side M2 Is 90 °. Further, the control mark M has a third side M3 extending in the lateral direction from the intersection of the first side M1 and the second side M2 to the inside of the first side M1 and the second side M2. Yes. The lateral width W of each control mark M is set to 3.5 mm, and the length X in the process direction is set to 7 mm. In the present embodiment, the third side M3 has a substantially rectangular shape. However, the present invention is not limited to this. For example, the third side M3 may have an elliptical shape.

  The image quality adjustment pattern T is arranged such that the yellow, magenta, and black control marks M are sandwiched between the two cyan control marks M. This is because the cyan control mark M is used as a reference, and the relative misregistration amount and density error of the other control marks M (yellow, magenta, black) are detected and the misregistration is facilitated. This is to increase the detection accuracy of the quantity and density error. In each control mark M, the first side M1 and the second side M2 function as a positional deviation correction mark used for registration control (positional deviation correction), as will be described later. For this reason, the first side M1 and the second side M2 are always created at a density of Cin = 100%. On the other hand, in the control mark M, the third side M3 functions as a density deviation correction mark used for process control (density deviation correction) as described later. For this reason, the third side M3 is created at a required density (from a low density to a high density) each time.

  In the present embodiment, in each control mark M, the third side M3 that functions as a density deviation correction mark is replaced by the first side M1 and the second side M2 that function as a position deviation correction mark. It exists in the specified rectangular area S (S ′). From another point of view, each control mark M exists on the upstream side and the downstream side in the process direction, and the first side M1 and the second side M2 used for positional deviation correction (for positional deviation correction). Mark) and a third side M3 (density correction mark) that exists in the middle of the process direction of the first side M1 and the second side M2 and is used for density deviation correction. I can say that.

  FIG. 6 shows an image forming example of the actual image quality adjustment pattern T. In this example, as the image quality adjustment pattern T, first, in each color of YMCK, the density of the first side M1 and the second side M2 is 100%, and the density of the third side M3 is 75%. A mark M is formed. Next, a control mark M is formed in which the density of the first side M1 and the second side M2 is 100% and the density of the third side M3 is 50%. Further, a control mark M is formed in which the density of the first side M1 and the second side M2 is 100% and the density of the third side M3 is 25%. Note that the density of the third side M3 does not necessarily have to be in the order of high density to low density, and the value of each density may be set as appropriate. Further, the density value of the third side M3 may be further finely shaken. Furthermore, the image quality adjustment pattern T as shown in FIG. 6 can be created a plurality of times during the same process.

FIG. 7 is a flowchart showing a processing procedure of output image density control (process control) and output image position adjustment control (registration control) in each imager forming unit 10Y, 10M, 10C, 10K.
In this process, first, an image quality adjustment pattern T including a plurality of control marks M as shown in FIG. 6 is formed on the intermediate transfer belt 20 by the image forming units 10Y, 10M, 10C, and 10K (step 101). . At this time, the density deviation amount correction value and the positional deviation amount correction value in each of the image forming units 10Y, 10M, 10C, and 10K are reset. Therefore, on the intermediate transfer belt 20, an image quality adjustment pattern T composed of a plurality of control marks M is formed at positions and densities corresponding to the characteristics of the image forming units 10Y, 10M, 10C, and 10K. Will be.

Next, the image quality adjustment pattern T composed of a plurality of control marks M formed on the intermediate transfer belt 20 is read by the position / density detection sensor 25 (step 102). Then, the control unit 70 calculates the image density of the control mark M for each color based on the reading result by the position / density detection sensor 25 (step 103), and obtains the predetermined density target value and step 103. An error from the obtained image density is calculated (step 104). Then, the control unit 70 calculates the correction amount of the laser power in each color laser exposure apparatus 13 (step 105), and sets the laser power based on the obtained correction amount (step 106). As a result, the density of the monochromatic toner image formed by each of the image forming units 10Y, 10M, 10C, and 10K can be made appropriate based on the influence of environmental conditions and the like at that time. Therefore, the color reproduction and gradation of a full color image formed by superimposing single color toner images can be made highly accurate.
As described above, the density adjustment (process control) in each of the image forming units 10Y, 10M, 10C, and 10K is performed by steps 103 to 106.

Next, based on the reading result by the position / density detection sensor 25, the control unit 70 determines the absolute positional deviation amount with respect to the lateral direction and target value in the process direction of the cyan control mark M serving as the reference color, and A relative positional shift amount in the lateral direction and process direction of the yellow, magenta, and black control marks M with respect to the cyan control mark M, which is the reference color, is calculated (step 107). Then, based on the lateral displacement amount and the process displacement amount obtained for each color, the toner images (electrostatic latent images) on the photosensitive drum 11 in the image forming units 10Y, 10M, 10C, and 10K are obtained. The image formation position, that is, the exposure timing of each laser drum 11 by each laser exposure device 13 is reset in both the lateral direction and the process direction (step 108). Thereby, the formation position of the monochromatic toner image in each of the image forming units 10Y, 10M, 10C, and 10K can be made appropriate. Therefore, it is possible to superimpose the single color toner images on the intermediate transfer belt 20 with high definition, and it is possible to obtain a high-quality full-color image in which color misregistration is suppressed.
As described above, the alignment (registration control) in each of the image forming units 10Y, 10M, 10C, and 10K is performed in steps 107 to 108.

Next, the operation of the position / concentration detection sensor 25 in the above-described process will be described. FIG. 8 is a diagram showing the relationship between the control mark M formed on the intermediate transfer belt 20 and the visual field region R on the intermediate transfer belt 20 of the PD 63 (see FIG. 3) with time. Further, a sensor output signal, a peak detection signal, and a hold signal output from the position / concentration detection sensor 25 based on the reading result by the PD 63 are also shown. Here, the thickness t1 of the first side M1, the second side M2, and the thickness t2 of the third side M3 in the control mark M are slightly smaller than the diameter d (0.8 mm) of the visual field region R. It is set to be smaller.
8A is a sensor output signal output from the AMP 66 (see FIG. 4) of the position / concentration detection sensor 25 at that time, and FIG. 8B is a peak detection circuit of the position / concentration detection sensor 25. 67 (see FIG. 4) and the peak detection signal output from the sample / hold circuit 68 (see FIG. 4) of the position / concentration detection sensor 25 are shown in FIG. Each is shown.

  A control mark M constituting the image quality adjustment pattern T formed on the intermediate transfer belt 20 by the image forming units 10Y, 10M, 10C, and 10K is a position / density detection sensor as the intermediate transfer belt 20 rotates. 25, and crosses the visual field region R of the PD 63. When the control mark M moves with the intermediate transfer belt 20 and the visual field region R of the PD 63 reaches the point A shown in FIG. 8, the first side M1 of the control mark M enters the visual field region R. Therefore, the sensor output signal starts to change. When the control mark M is further moved, the area of the control mark M included in the visual field region R, that is, the overlapping area between the visual field region R and the first side M1 of the control mark M is increased. As shown in a), the sensor output signal gradually increases. The sensor output signal is maximized at point B where the visual field region R is substantially covered by the first side M1. Since the first side M1 is created at a high density (100%) as described above, the corresponding sensor output signal is also large.

  The thickness t1 of the first side M1 constituting the control mark M is set slightly smaller than the diameter d of the visual field region R of the PD 63 as described above. For this reason, when the first side M1 of the control mark M passes the point B, the overlapping area of the visual field region R and the control mark M is decreased, and the sensor output signal gradually decreases. Then, at the point C where the first side M1 of the control mark M is completely removed from the visual field region R of the PD 63, the sensor output signal is minimized again.

  When the control mark M further moves and the visual field region R of the PD 63 passes through the point C, the third side M3 of the control mark M enters the visual field region R immediately after that, so that the sensor The output signal begins to change. When the control mark M further moves, the area of the control mark M included in the visual field region R, that is, the overlapping area between the visual field region R and the third side M3 of the control mark M increases, so that the sensor output signal Gradually rises. The sensor output signal is maximized at a point D where the visual field region R is substantially covered by the third side M3. However, unlike the first side M1 and the second side M2, the third side M3 is not always created at a high concentration, as described above. Therefore, when the third side M3 has a lower density than the first side M1 and the second side M2, the maximum value is lower as shown by the solid line in the figure. On the other hand, when the third side M3 has the same density (high density) as the first side M1 and the second side M2, the maximum value becomes high as shown by a one-dot chain line in the figure.

  The thickness t2 of the third side M3 constituting the control mark M is set slightly smaller than the diameter d of the visual field region R of the PD 63 as described above. For this reason, when the third side M3 of the control mark M passes the point D, the overlapping area between the visual field region R and the control mark M is decreased, and the sensor output signal gradually decreases. Then, at the point E where the third side M3 of the control mark M is completely removed from the visual field region R of the PD 63, the sensor output signal is minimized again.

  When the control mark M further moves and the visual field region R of the PD 63 passes through the point E, the second side M2 of the control mark M enters the visual field region R, so that the sensor output signal Begins to change. When the control mark M further moves, the area of the control mark M included in the visual field region R, that is, the overlapping area between the visual field region R and the second side M2 of the control mark M increases, so that the sensor output signal Gradually rises. The sensor output signal is maximized at point F where the visual field region R is substantially covered by the second side M2. Since the second side M2 is created at a high concentration (100%), like the first side M1, the corresponding sensor output signal is substantially the same as when the first side M1 passes. It becomes equivalent.

  The thickness t1 of the second side M2 constituting the control mark M is set slightly smaller than the diameter d of the visual field region R of the PD 63 as described above. For this reason, when the second side M2 of the control mark M passes the point F, the overlapping area between the visual field region R and the control mark M is decreased, and the sensor output signal gradually decreases. Then, at the point G where the second side M2 of the control mark M is completely removed from the visual field region R of the PD 63, the sensor output signal is minimized again.

  In this example, when the first side M1 of the control mark M passes through the visual field region R of the PD 63 (between points A and C), the overlapping area of the visual field region R and the first side M1 is increased. As the intermediate transfer belt 20 moves, it changes continuously. That is, the sensor output signals having the same intensity are not continuously output. Therefore, during this time, the maximum value is instantaneously generated in the sensor output signal. The waveform of the sensor output signal is such that the visual field region R of the PD 63 is formed in a circular shape, and the thickness t1 of the first side M1 constituting the control mark M is the same as the diameter d of the visual field region R. Or it can obtain easily by setting it as less than the diameter d.

In the image forming apparatus employing the electrophotographic system as in the present embodiment, when the control mark M is formed on the intermediate transfer belt 20, the first control mark M is configured according to the environmental conditions at that time. The thickness t1 of the side M1 and the second side M2 may change. For this reason, it is very difficult to completely match the thickness t1 of the first side M1 and the second side M2 with the visual field region R of the PD 63. Therefore, even when the thickness t1 of the first side M1 (second side M2) constituting the control mark M is smaller than the diameter d of the visual field region R, the waveform of the sensor output signal is instantaneous. The generation of the maximum value is advantageous when actually configuring a color printer or the like.
Note that the above is true when the third side M3 of the control mark M passes through the visual field region (between points C and E) and when the second side M2 of the control mark M is in the visual field region. The same applies when passing through R (between point E and point G).

Next, the peak detection signal output based on the reading result of the control mark M will be described. For example, the instantaneous maximum value in the sensor output signal corresponding to the first side M1 is when the center position in the thickness direction of the first side M1 matches the center position of the visual field region R of the PD 63 (point B). appear. In this embodiment, the peak detection circuit 67 (see FIG. 4) detects the maximum value (peak) of the sensor output signal, and as shown in FIG. 8 (b), the peak detection is performed at the moment when the maximum value occurs. The signal is configured to be at a high level (H) for a predetermined time. Thus, the rising edge portion of the peak detection signal indicates the center position of the first side M1 of the control mark M, and the position of the first side M1 can be accurately detected.
Further, for example, the instantaneous maximum value in the sensor output signal corresponding to the second side M2 is obtained when the center position in the thickness direction of the second side M2 matches the center position of the visual field region R of the PD 63 (point F). ). Therefore, the rising edge portion of the peak detection signal indicates the center position of the second side M2 of the control mark M, and the position of the second side M2 can be accurately detected.

  On the other hand, for example, the instantaneous maximum value in the sensor output signal corresponding to the third side M3 is obtained when the center position in the thickness direction of the third side M3 matches the center position of the visual field region R of the PD 63 (point D). ). The peak detection signal is output in the same manner as when the other first side M1 and second side M2 are read. Note that the reading result of the third side M3 is used for correcting the density deviation in each of the image forming units 10Y, 10M, 10C, and 10K, and is used for correcting the density deviation in each of the image forming units 10Y, 10M, 10C, and 10K. It is not used for correction of misalignment. For this reason, the high-level peak detection signal obtained by reading the third side M3 is excluded when detecting a displacement. Details of this will be described later.

  Further, a hold signal output based on the result of reading the control mark M will be described. In the sample hold circuit 68 (see FIG. 4), as shown in FIG. 8C, the sensor output signal when the peak detection signal becomes high level, that is, the maximum value is output until the next peak detection signal is output. Hold and output as a hold signal. As a result, the maximum value of the sensor output signal, that is, the density of the target control mark M can be accurately detected at an appropriate timing.

The operation of the control unit 70 in the above-described process, specifically, process control and registration control will be described in detail. FIG. 9 is a timing chart for explaining the operation of the control unit 70 (CPU 71). Here, (a) shows a sensor output signal in the position / concentration detection sensor 25, (b) shows a peak detection signal output from the position / concentration detection sensor 25, and (c) shows a hold signal. Further, (d) is a selection signal output from a selection signal output circuit 78 provided in the control unit 70. Here, the selection signal is a binary signal of high level (H) and low level (L). The selection signal is, for example, in a period in which the first side M1 and the second side M2 of the control mark M can exist, that is, in a period in which a signal necessary for positional deviation correction is output. Set to low level. On the other hand, the selection signal is set to a high level during a period in which the third side M3 of the control mark M can exist, that is, a period during which a signal necessary for correcting the density deviation is output. Further, (e) is a density deviation correction hold signal in which only a hold signal generated during a period in which the selection signal shown in (d) is at a low level among the hold signals shown in (c) is output. Therefore, the density deviation correction hold signal corresponds to the sensor output signal of the third side M3 of the control mark M. Furthermore, (f) is a position detection correction peak detection signal in which only the peak detection signal generated during the period when the selection signal shown in (d) is at a high level among the peak detection signals shown in (b) is output. is there. Therefore, the misregistration correction peak detection signal corresponds to the sensor output signals of the first side M1 and the second side M2 of the control mark M.
In other words, in the present embodiment, the CPU 71 discriminates a signal necessary for positional deviation correction and a signal necessary for density deviation correction based on the selection signal. In the present embodiment, density deviation correction (process control) is executed by the program executed by the CPU 71 using the density deviation correction hold signal obtained in this way. Further, using the obtained positional deviation correction peak detection signal, positional deviation correction (registration control) is executed by a program executed by the CPU 71.

First, density deviation correction (process control) will be described. In the control unit 70, the voltage values Vc (cyan), Vy (yellow), and Vy (yellow) of the density deviation correction hold signal obtained by reading the third side M 3 of the control mark M for each color by the position / density detection sensor 25 Density deviation correction is performed using Vm (magenta) and Vk (black). The position / density detection sensor 25 reads a reference reflector (not shown) for the voltage values Vc (cyan), Vy (yellow), Vm (magenta), and Vk (black) of the hold signal for density deviation correction. Assuming that the reference output voltage obtained by the above is Vref, the image density Dn of each color can be defined as follows.
Dn = Vn / Vref
However, n = toner color (Y, M, C, K), and Vn is preferably the average value of the reading results of the third side M3 in the same color and a plurality of control marks M. The reason why the relative value with respect to the output reference voltage Vref is used as the image density is that the characteristics change due to contamination, deterioration with time, temperature change, etc. of the first LED 61, the second LED 62, or the PD 63. Even so, this is because the density of the third side M3 in the control mark M is measured with high accuracy. In step 70, the control unit 70 calculates the image density according to the above-described procedure.

Then, the control unit 70 calculates a density error ΔDn which is a difference between the density target value stored in advance in the ROM 74 or the like and the obtained image density as step 104.
Next, as step 105, the control unit 70 calculates the correction amount (ΔLP) of the laser power in each laser exposure apparatus 13 for each color as follows.
ΔLP = ΔDn / An
However, n = toner color (Y, M, C, K), and An is a coefficient indicating the correspondence between the laser power and the image density of the control mark M. This coefficient An is obtained in advance by experiments or the like.
When the correction amount ΔLP for each color is obtained in this way, the control unit 70 subtracts the correction amount ΔLP from the laser power when the third side M3 of the control mark M is formed as step 106 described above. The laser power setting value is corrected for each color. Then, such calculation and correction operations are executed for each density (for example, 75%, 50%, and 25% in the example shown in FIG. 6).
Thus, the process control ends.

  Next, positional deviation correction (registration control) will be described. The control unit 70 uses the positional deviation correction peak detection signal obtained by reading the first side M1 and the second side M2 of the control mark M for each color by the position / density detection sensor 25, and uses the position detection sensor 25 for each color. Misalignment correction is performed for the lateral direction and the process direction. In the present embodiment, as described above, cyan is determined as the reference color. In step 107, the absolute displacement amount of the reference color cyan with respect to the lateral target value and the yellow for the reference color cyan are set. , Magenta and black relative displacement amounts (lateral direction, process direction) are obtained.

  In the control unit 70, a misregistration correction peak detection signal is captured, and a misregistration correction peak detection signal is detected by detecting the first side M1 and the second side M2 constituting each control mark M from a predetermined reference time. Measures the elapsed time from when the signal rises from the low level (L) to the high level (H). In this description, as shown in FIG. 9, the time point when the misalignment correction peak detection signal rises from L to H corresponding to the first side M1 of the first cyan control mark M is defined as tA1. The point in time when the positional deviation correction peak detection signal rises from L to H corresponding to the side M2 of 2 is defined as tA2. Further, the time point when the misalignment correction peak detection signal rises from L to H corresponding to the first side M1 of the yellow control mark M is set to tT1, and the misalignment correction is performed corresponding to the second side M2. The time point when the peak detection signal for the signal rises from L to H is defined as tT2. Furthermore, the time point when the position detection correction peak detection signal rises from L to H corresponding to the first side M1 of the cyan control mark M formed next to the yellow control mark M is defined as tB1. The point in time when the misalignment correction peak detection signal rises from L to H corresponding to the side M2 of 2 is defined as tB2.

First, the absolute positional shift amount of the reference color cyan control mark (toner image) M with respect to the lateral direction can be calculated by the following equation.
Lateral absolute displacement amount = {(tA2−tA1) −target value} / 2

Next, the relative positional deviation amount of the yellow control mark (toner image) M with respect to the reference color cyan can be calculated by the following equation.
Process direction displacement: ΔEp
= {(TT2 + tT1) / 2-((tA2 + tA1) / 2 + (tB2 + tB1) / 2) / 2} × PS
= {(TT2 + tT1) / 2- (tA2 + tA1) / 4- (tB2 + tB1) / 4} × PS
Lateral displacement: ΔEl
= {((TB1 + tA1) / 2-tT1 + ΔEp + tT2- (tB2 + tA2) / 2-ΔEp) / 2} × PS
= {((TB1 + tA1) / 2-tT1 + tT2- (tB2 + tA2) / 2)} * PS
However, PS is a process speed (mm / s). Further, the relative positional deviation amount of the magenta and black control marks M with respect to the reference color cyan can be obtained in the same manner as for yellow.

When the absolute displacement amount of cyan and the relative displacement amounts of yellow, magenta, and black are obtained, the control unit 70 forms each image in step 108 according to the obtained displacement amount. The exposure timing by the laser exposure device 13 of the units 10Y, 10M, 10C, and 10K is corrected.
Thus, the registration control ends.

Here, the density deviation correction hold signal (the reading result of the third side M3 as the density deviation correction mark) shown in FIG. 9 (e) and the position deviation correction peak detection signal (position) shown in FIG. 9 (f). Processing in the case where an abnormality has occurred in the reading result of the first side M1 and the second side M2 as the deviation correction marks will be described.
For example, the density deviation correction hold signal may have no output or an abnormally high output. Here, as the cause of the former, for example, a case where the image quality adjustment pattern T is not created on the intermediate transfer belt 20 or a case where the position / density detection sensor 25 is broken can be considered. On the other hand, as the cause of the latter, a case where the control mark M having an abnormal density exceeding the allowable range is formed. Although the actual allowable range differs depending on the device, for example, if the device is in a normal state, the concentration fluctuation from the previous time is generally within 10%, for example.
Further, for example, there is a case where there is no output or a case where an abnormally high output is made in the position detection correction peak detection signal. Here, as the cause of the former, for example, a case where the image quality adjustment pattern T is not created on the intermediate transfer belt 20 or a case where the position / density detection sensor 25 is broken can be considered. On the other hand, as the cause of the latter, there may be a case where an abnormal position shift of the control mark M exceeding the allowable range occurs. Although the actual allowable range differs depending on the device, for example, if the device is in a normal state, the position fluctuation from the previous time is generally within, for example, 0.2 mm.

In this embodiment, for example, when it is found that there is an abnormality in the density deviation correction hold signal, not only the density deviation correction but also the position deviation correction is not performed. Alternatively, when the previous density deviation correction amount and the positional deviation correction amount are stored, the density deviation correction and the positional deviation correction are performed using the previous correction amount.
On the other hand, for example, when it is determined that there is an abnormality in the positional deviation correction peak detection signal, not only the positional deviation correction but also the density deviation correction is not performed. Alternatively, when the previous density deviation correction amount and the positional deviation correction amount are stored, the density deviation correction and the positional deviation correction are performed using the previous correction amount.

  In the present embodiment, density deviation correction and position deviation correction are performed based on the reading result of the image quality adjustment pattern T by the position / density detection sensor 25. That is, the sensor used for position shift correction and density shift correction is shared. Therefore, when there is an abnormality in one data, there is a high possibility that an abnormality exists in the other data, and thus such control is performed. It should be noted that even if the density deviation correction and the position deviation correction are stopped, there is little problem in image quality immediately, so it is not necessary to stop the image forming operation itself. However, as the deviation in density and position increases over time, for example, the message “Image quality cannot be adjusted” is displayed on the user interface, or the occurrence of abnormality is non-volatile so that the occurrence of abnormality can be transmitted during maintenance. It is preferable to store it in a memory.

As described above, in the present embodiment, the position / density detection sensor 25 is used to read the image quality adjustment pattern T (a plurality of control marks M) formed to perform the positional deviation correction and the density deviation correction. I made it. As a result, it is not necessary to provide dedicated sensors for correcting the positional deviation and for correcting the density deviation, so that a simple configuration can be achieved, and the size and cost of the image forming apparatus can be reduced.
Further, in the present embodiment, when the image quality adjustment pattern T is formed on the intermediate transfer belt 20, the first used for correcting misalignment on the control mark M constituting the image quality adjustment pattern T. Side M1 and second side M2, and a third side M3 used to perform density deviation correction. Further, the third side M3 is arranged between the first side M1 and the second side M2 when viewed from the process direction. Then, the control unit 70 corrects misalignment corresponding to the first side M1 and the second side M2 based on the peak detection signal obtained from the sensor output signal obtained by reading such a control mark M. The peak signal for discrimination is discriminated and acquired, and the misalignment correction (registration control) is executed using the peak signal for misalignment correction. On the other hand, the control unit 70 determines the density deviation correction hold signal corresponding to the third side M3 based on the hold signal obtained from the sensor output signal obtained by reading the control mark M. The density deviation correction (process control) is executed based on the acquired density deviation correction hold signal. As a result, it is possible to shorten the overall length of the image quality adjustment pattern T as compared with the case where the correction is made for each of the positional deviation correction and the density deviation correction, thereby shortening the reading time and consequently the positional deviation correction and the density deviation correction. It is possible to shorten the time required for the operation. For this reason, a user's waiting time can be shortened at the time of power-on.

In particular, in the present embodiment, the first side M1 and the second side M2 used for the positional deviation correction in the control mark M are always created with a high density. For this reason, the situation where the boundary of the 1st edge | side M1 and the 2nd edge | side M2 blurs is avoided, and the position detection accuracy and also the correction | amendment accuracy of position shift can be improved.
In the present embodiment, the third side M3 used for density deviation correction among the control marks is created with the required density. For this reason, good reproducibility can be obtained from a low density to a high density. In this way, the third side M3 is created with various densities. However, since the reading result of the third side M3 is not used for misalignment correction, there is no particular problem. However, since the first side M1 and the second side M2 are formed at 100% density, for example, when correcting the density deviation of 100% density, the first side M1 and / or the second side M2 are formed. The reading result of the side M2 can be used.

<Embodiment 2>
Although the present embodiment is substantially the same as the first embodiment, the shape of the control mark M constituting the image quality adjustment pattern T is different. In the present embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.
FIG. 10 shows the image quality adjustment read from the image quality adjustment pattern storage unit 73 by the image output circuit 72 and formed on the intermediate transfer belt 20 by the image forming units 10Y, 10M, 10C, and 10K in this embodiment. The pattern T for use is shown. In the present embodiment, the control marks M each having a shape in which a “−” character is added to a “Z” character are formed by the image forming units 10Y, 10M, 10C, and 10K.

The control mark M includes a first side Ma extending in the lateral direction on the most upstream side in the moving direction (process direction) of the intermediate transfer belt 20, a second side Mb extending in the lateral direction on the most downstream side, and a first side Mb. There is a third side Mc that obliquely connects one end of the side Ma (for example, the IN side) and one end of the opposite side of the second side Mb (for example, the OUT side). A “Z” character is formed by the first side Ma, the second side Mb, and the third side Mc. Further, the control mark M has a fourth side Md extending in the lateral direction between the first side Ma and the second side Mb and on the second side Mb side when viewed from the process direction. The fourth side Md forms a “−” character.
Here, the first side Ma, the second side Mb, and the third side Mc are formed with high density (100%), and are used for positional deviation correction. On the other hand, the fourth side Md is formed at a desired density (low density to high density) and is used for density deviation correction.

Also in the present embodiment, in each control mark M, the fourth side Md that functions as a density deviation correction mark has the first side Ma and the second side Mb that function as a position deviation correction mark. , And the rectangular region S "specified by the third side Mc. From another viewpoint, each control mark M exists on the upstream side and the downstream side in the process direction. The first side Ma, the second side Mb, and the third side Mc (positional deviation correction mark) used in the positional deviation correction, the first side Ma, the second side Mb, and It can be said that it has a fourth side Md (density correction mark) that exists in the middle of the process direction of the third side Mc and is used for density deviation correction.
Also in the present embodiment, by performing the same control as in the first embodiment, the positional deviation correction is performed based on the reading results of the first side Ma, the second side Mb, and the third side Mc. The density deviation correction can be performed based on the reading result of the fourth side Md.

In the first and second embodiments, a so-called tandem type and intermediate transfer type image forming apparatus has been described as an example. However, the present invention is not limited to this. For example, the present invention is also applied to a tandem type image forming apparatus in which a conveyance belt that conveys a sheet is opposed to a plurality of image forming units, and an image formed by each image forming unit is sequentially transferred to a sheet conveyed by the conveyance belt. be able to. In addition, an intermediate transfer device in which a plurality of color developing devices are arranged on one photosensitive drum, and an image formed on the photosensitive drum is sequentially superimposed on the intermediate transfer belt by causing the intermediate transfer belt to face the photosensitive drum. The present invention can also be applied to a type image forming apparatus. Furthermore, the present invention can also be applied to a so-called image-on-image (IOI) type image forming apparatus that sequentially superimposes each color component image on a photosensitive drum.
In addition to the control mark M described in the first and second embodiments, the shape of the control mark M can be appropriately selected as long as it satisfies the above-described requirements.

1 is a diagram illustrating an image forming apparatus to which the exemplary embodiment is applied. FIG. 3 is an enlarged perspective view of a main part of the image forming apparatus. It is sectional drawing of a position / concentration detection sensor. It is a block diagram explaining the function of a control part and a position / concentration detection sensor. FIG. 4 is a diagram illustrating an example of an image quality adjustment pattern formed on an intermediate transfer belt. It is a figure which shows the image formation example of the pattern for an actual image quality adjustment. 6 is a flowchart showing processing procedures of output image density control (process control) and output image position adjustment control (registration control) in each imager forming unit. FIG. 3 is a diagram showing the relationship between a control mark formed on an intermediate transfer belt and a visual field area of a PD (photodiode) on the intermediate transfer belt as time elapses. It is a timing chart for demonstrating operation | movement of the control part in process control and registration control. 6 is a diagram illustrating an image quality adjustment pattern formed on an intermediate transfer belt in Embodiment 2. FIG.

Explanation of symbols

10 (10Y, 10M, 10C, 10K) ... image forming unit, 11 ... photosensitive drum, 13 ... laser exposure apparatus, 20 ... intermediate transfer belt, 25 ... position / density detection sensor, 61 ... first LED (Light Emitting) Device), 62 ... second LED, 63 ... PD (Photo Diode), 65 ... Lens, 66 ... AMP, 67 ... Peak detection circuit, 68 ... Sample hold circuit, 70 ... Control unit, 71 ... CPU (Central Processing Unit) , 72 ... Image output circuit, 73 ... Image storage pattern storage section, 74 ... ROM (Read Only Memory), 75 ... RAM (Random Access Memory), 76 ... LED driver, 77 ... Selection signal output circuit, M ... Control Mark for M1, first side, M2 ... second side, M3 ... third side, P ... paper, R ... field of view, S ... rectangular region, T ... pattern for image quality adjustment

Claims (10)

An image forming apparatus that has a plurality of image forming units that form images of each color, and that superimposes and transfers images formed by the plurality of image forming units,
A misregistration correction mark that exists on the upstream side and the downstream side in the moving direction of the transfer body that moves along the plurality of image forming units and is used in the misregistration correction of each color image, and the upstream misregistration correction. For the control of each color including the density deviation correction mark that is present in the intermediate portion in the moving direction of the transfer body and used for density deviation correction of each color image as seen from the position deviation correction mark and the downstream position deviation correction mark Control mark forming means for sequentially forming marks using the plurality of image forming units so that the position deviation correction mark in each of the control marks has a higher density than the density deviation correction mark; ,
A reading means for reading the control mark formed on the transfer body by the control mark forming means;
The misregistration correction in the plurality of image forming units is performed using the misregistration correction mark obtained by reading the control mark by the reading unit, and the control mark is read by the reading unit. An image forming apparatus comprising: a correcting unit that performs density shift correction in the plurality of image forming units using the density shift correction mark obtained by the above. A discriminating unit for discriminating between the position deviation correction mark and the density deviation correction mark in the control mark read by the reading unit;
The correction unit performs position shift correction in the plurality of image forming units based on the position shift correction mark based on the determination result by the determination unit, and the plurality of the plurality of image shift portions based on the density shift correction mark. The image forming apparatus according to claim 1, wherein density deviation correction is performed in the image forming unit. 3. The discriminating unit discriminates between the position deviation correction mark and the density deviation correction mark based on a position in the control mark with respect to a moving direction of the transfer body. Image forming apparatus. The control mark forming means forms a plurality of the control marks for the same color and forms images having different densities as the density deviation correction marks in the control marks of the same color. The image forming apparatus according to any one of claims 1 to 3. The correction means includes the density deviation correction mark obtained by reading the control mark by the reading means and the density deviation correction mark obtained by reading the control mark by the reading means. The image forming apparatus according to claim 1, wherein density deviation correction is performed based on the position deviation correction mark having a higher density. The reading means is an optical sensor that is arranged facing the transfer body and sequentially reads the control marks formed on the moving transfer body for each color,
In the formation of the control mark for each color, the control mark forming unit includes a gap between the positional deviation correction mark and the density deviation correction mark on the upstream side in the movement direction of the transfer body, and the transfer The gap between the density deviation correction mark and the downstream position deviation correction mark in the body movement direction is set wider than a reading area on the transfer body by the optical sensor. The image forming apparatus according to any one of 1 to 5. Wherein the correction means, when there is abnormality in the positional deviation correction mark obtained by reading the mark the control by said reading means, according to claim 1, characterized in that it is carried out the density deviation correction the image forming apparatus according to any one of 6. Wherein the correction means, when there is abnormality in the density deviation correction mark obtained by reading the mark the control by said reading means, 1 to claim, characterized in that it is carried out the positional deviation correction the image forming apparatus according to any one of 7. An image output device used in an image forming apparatus that has a plurality of image forming units that form images of respective colors and that superimposes and transfers images formed by the plurality of image forming units,
A misregistration correction mark that is used in misregistration correction and exists on the upstream side and the downstream side in the moving direction of the transfer body with respect to the transfer body that moves along the plurality of image forming units, and the upstream position. A control mark for each color including a deviation correction mark and a density deviation correction mark used in density deviation correction, which is present in the intermediate portion in the moving direction of the transfer body as viewed from the downstream position deviation correction mark. A storage unit for storing the position deviation correction mark as image data having a higher density than the density deviation correction mark ;
An image output apparatus comprising: an image output unit that outputs image data of the control mark read from the storage unit to the plurality of image forming units. The image data of the control mark stored in the storage section intersects obliquely with respect to both the sub-scanning direction, which is the moving direction of the transfer body, and the main-scanning direction orthogonal to the sub- scanning direction. a first side and a second side that functions as a correction mark, the inside of the first side and the second of the first from the side of the intersection of the sides and the second side to the main scanning direction And a third side that functions as the density deviation correction mark, the first side and the second side are set to be higher in density than the third side, and the first side The image output apparatus according to claim 9, wherein the side and the second side are set to the same density .

Images