JP2016053694A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of shortening the length in a sub-scan direction of a detection pattern for color shift.SOLUTION: The image forming apparatus which includes a rotationally driven photoreceptor, light irradiation means for forming an electrostatic latent image on the photoreceptor by irradiation with light, and an image carrier to which a developer image obtained by developing the electrostatic latent image is transferred and can form a latent image pattern which is an electrostatic latent image for correction and a detection pattern which is a developer image for correction includes first detection means for detecting the latent image pattern formed on the photoreceptor, second detection means for detecting the detection pattern formed on the image carrier, and correction means for correcting a second detection result with a first detection result on the basis of the first detection result by the first detection means and the second detection result by the second detection means.SELECTED DRAWING: Figure 12

Description

  The present disclosure relates to a color misregistration correction technique in an image forming apparatus.

  As an electrophotographic image forming apparatus, each color image forming unit is provided, and an image is transferred from the image forming unit of each color to an intermediate transfer belt, and further, the image is transferred from the intermediate transfer belt to a recording material in a batch. It has been known. In such an image forming apparatus, color misregistration (positional misregistration) may occur when the images are overlapped due to mechanical factors in the image forming unit of each color. In particular, in a configuration in which a laser scanner and a photoconductor are provided for each color image forming unit, color misregistration occurs because the positional relationship between the laser scanner and the photoconductor is different for each color. Therefore, color misregistration correction control is performed in the image forming apparatus. Patent Document 1 discloses a configuration in which a detection pattern for color misregistration detection, which is a developer image, is formed on an intermediate transfer belt, a detection pattern is detected by an optical sensor to obtain a color misregistration amount, and color misregistration correction is thereby performed. doing. The detection pattern is formed according to a predetermined condition in order to suppress the influence of uneven rotation of the driving roller for driving the photosensitive member and the intermediate transfer belt.

JP 2006-350320 A

  In order to suppress the influence of rotation unevenness of the photoconductor and the driving roller that drives the intermediate transfer belt, it is necessary to form each developer image included in the detection pattern so as to cancel the influence of the rotation unevenness. The length of the pattern in the sub-scanning direction was long. Here, the sub-scanning direction corresponds to the rotation direction of the photoconductor and the intermediate transfer belt.

  The present invention provides an image forming apparatus that can shorten the length of the color misregistration detection pattern in the sub-scanning direction.

  According to one aspect of the present invention, a photosensitive member that is rotationally driven, a light irradiation unit that forms an electrostatic latent image on the photosensitive member by irradiating light, and a developer image obtained by developing the electrostatic latent image And an image carrier that can transfer a latent image pattern that is an electrostatic latent image for correction and a detection pattern that is a developer image for correction. First detection means for detecting the latent image pattern formed on the photoconductor, second detection means for detecting the detection pattern formed on the image carrier, and first detection by the first detection means And correcting means for correcting the second detection result with the first detection result based on the result and the second detection result by the second detection means.

  According to the present invention, the length of the color misregistration detection pattern in the sub-scanning direction can be shortened.

1 is a configuration diagram of an image forming apparatus according to an embodiment. 1 is a diagram illustrating a bias supply system and a charging power supply circuit of an image forming apparatus according to an embodiment. The functional block diagram of the engine control part by one Embodiment. Explanatory drawing of the color shift detection pattern by one Embodiment. The figure which shows the conventional color misregistration detection pattern. 6 is a timing chart of color misregistration correction according to an embodiment. The figure which shows the latent-image mark by one Embodiment. Explanatory drawing of the detection principle of the latent image mark by one Embodiment. Explanatory drawing of the rotational speed fluctuation | variation detection of the photoreceptor by one Embodiment. The figure which shows the detection pattern by one Embodiment. Explanatory drawing of the calculation principle of the shift | offset | difference of the detection timing of the latent image mark by the rotational speed fluctuation | variation of the photoreceptor by one Embodiment. 6 is a flowchart of color misregistration correction according to an embodiment. The block diagram of the primary transfer power supply circuit by one Embodiment.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In addition, the following embodiment is an illustration and does not limit this invention to the content of embodiment. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings.

<First embodiment>
FIG. 1 is a configuration diagram of an image forming apparatus according to the present embodiment. Note that the English letters a, b, c, and d at the end of the reference numerals form the developer images of the members in yellow (Y), magenta (M), cyan (C), and black (Bk), respectively. It shows that it is a thing. In addition, when it is not necessary to distinguish colors, reference numerals excluding the last alphabetic characters a, b, c, and d are used. The photoreceptor 22 is an image carrier and is driven to rotate during image formation. The charging roller 23 charges the surface of the corresponding photoconductor 22 to a uniform potential. As an example, the charging bias output from the charging roller 23 is −1200 V, and thereby the surface of the photosensitive member 22 is charged to a potential of −700 V (dark potential). The scanner unit 20 is a light irradiation unit that forms an electrostatic latent image on the photosensitive member 22 by scanning and exposing the surface of the photosensitive member 22 with a laser beam corresponding to image data of an image to be formed. As an example, the potential of the portion where the electrostatic latent image is formed becomes −100 V (bright potential) by exposure with laser light. Each of the developing devices 25 has a corresponding color developer, and the developing sleeve 24 supplies the developer to the electrostatic latent image on the photosensitive member 22 to develop the electrostatic latent image on the photosensitive member 22. . As an example, the developing bias output from the developing sleeve 24 is −350 V, and the developing unit 25 attaches the developer to the electrostatic latent image by this potential. The primary transfer roller 26 is an image carrier that transfers the developer image formed on the photosensitive member 22 to the intermediate transfer belt 30 stretched by rollers 31, 32, and 33. The intermediate transfer belt 30 is driven to rotate in accordance with the rotation of the driving roller 33 during image formation. As an example, the primary transfer bias output from the primary transfer roller 26 is +1000 V, and the primary transfer roller 26 transfers the developer image to the intermediate transfer belt 30 by this potential. At this time, a color image is formed by transferring the developer images of the respective photosensitive members 22 onto the intermediate transfer belt 30 in a superimposed manner. As described above, the image forming apparatus is configured to be able to form an electrostatic latent image on the photoreceptor 22 and a developer image on the intermediate transfer belt 30.

  The secondary transfer roller 27 transfers the developer image on the intermediate transfer belt 30 to the recording material 12 conveyed through the conveyance path 18. The fixing roller pairs 16 and 17 heat and press the recording material 12 to fix the developer image transferred to the recording material 12 to the recording material 12. The recording material 12 is also an image carrier. The cleaning blade 35 collects the developer that has not been transferred from the intermediate transfer belt 30 to the recording material 12 into the container 36. In addition, a detection sensor 40 is provided to face the intermediate transfer belt 30 in order to detect a detection pattern for color misregistration correction formed on the intermediate transfer belt 30. The detection sensor 40 emits light toward the intermediate transfer belt 30 and detects a detection pattern based on the reflected light.

  The scanner unit 20 may be configured to expose the photosensitive member 22 by an LED array or the like instead of a laser. Further, instead of providing the intermediate transfer belt 30, an image forming apparatus that directly transfers the developer image of each photoconductor 22 to the recording material 12 may be used.

  FIG. 2A illustrates a high-voltage power supply system to each process unit of the image forming unit. Here, the process unit is a member that acts on the photosensitive member 22 for image formation, including at least one of the charging roller 23, the developing device 25, and the primary transfer roller 26. The charging power supply circuit 43 applies a voltage to the corresponding charging roller 23. Further, the developing power supply circuit 44 applies a voltage to the developing sleeve 24 of the corresponding developing device 25. Further, the primary transfer power supply circuit 46 applies a voltage to the corresponding primary transfer roller 26. In this manner, the charging power supply circuit 43, the development power supply circuit 44, and the primary transfer power supply circuit 46 function as a voltage application unit for the process unit.

  Next, the charging power supply circuit 43 in this embodiment will be described with reference to FIG. The transformer 62 boosts the voltage of the AC signal generated by the drive circuit 61 to an amplitude several tens of times. The rectifier circuit 51 including the diodes 1601 and 1602 and the capacitors 63 and 66 rectifies and smoothes the boosted AC signal. The rectified and smoothed signal is output as a DC voltage from the output terminal 53 to the charging roller 23. The operational amplifier 60 controls the output voltage of the drive circuit 61 so that the voltage obtained by dividing the voltage at the output terminal 53 by the detection resistors 67 and 68 is equal to the voltage 55 set by the engine control unit 54. Then, according to the voltage of the output terminal 53, a current flows through the charging roller 23, the photosensitive member 22, and the ground. In the following description, a current that flows between the charging roller 23 and the photosensitive member 22 when the charging roller 23 outputs a charging bias is referred to as a charging current.

  The current detection circuit 50 is provided for outputting a detection voltage 56 corresponding to the charging current. The detection voltage 56 is input to the negative input terminal of the comparator 74. A reference voltage (Vref) 75 is input to the positive input terminal of the comparator 74. The comparator 74 outputs a binarized voltage 561 corresponding to the detected voltage 56 and the reference voltage 75 to the engine control unit 54. Specifically, the comparator 74 outputs “high” when the detection voltage 56 falls below the reference voltage 75, and outputs “low” otherwise.

  As will be described later, in the present embodiment, the scanner unit 20 forms a latent image pattern on the photosensitive member 22 in order to detect the amount of detection timing shift of the detection pattern caused by uneven rotation of the photosensitive member 22. The latent image pattern is a pattern in which a plurality of latent image marks that are electrostatic latent images are formed along the rotation direction of the photosensitive member 22. As will also be described later, when the latent image mark passes through the position facing the charging roller 23, the detection voltage 56 temporarily decreases. The reference voltage 75, which is a threshold value, is detected voltage 56 when the latent image mark is not at the position facing the charging roller 23 and the latent image mark passes the position facing the charging roller 23 so that the passage of the latent image mark can be detected. Is set to a value between the detection voltage 56 and the minimum value. With this configuration, when the latent image mark passes the position facing the charging roller 23, the comparator 74 outputs a binarized voltage 561 having one rising edge and one falling edge thereafter to the engine control unit 54. For example, the engine control unit 54 uses the midpoint between the rise and fall of the binarized voltage 561 as the latent image mark detection timing. Note that the engine control unit 54 can detect only one of the rising edge and the falling edge of the binarized voltage 561 and set it as the detection timing of the latent image mark.

  Next, the current detection circuit 50 in FIG. 2B will be described. The current detection circuit 50 is inserted between the secondary circuit 500 of the transformer 62 and the ground 57. The non-inverting input terminal of the operational amplifier 70 is connected to the reference voltage 73, and the inverting input terminal is connected to the output terminal 53 via resistors 67 and 68. Since the input impedance of the operational amplifier 70 is very high, almost all of the charging current flows through the resistor 71. Accordingly, the detection voltage 56 corresponding to the charging current appears at the output terminal of the operational amplifier 70. More specifically, when the charging current increases, the detection voltage 56 decreases, and when the charging current decreases, the detection voltage 56 increases. The capacitor 72 is for stabilizing the inverting input terminal of the operational amplifier 70.

  The engine control unit 54 comprehensively controls the operation of the image forming apparatus. The CPU 321 uses the RAM 323 as a main memory and work area, and controls the image forming apparatus according to various control programs stored in the EEPROM 324. In addition, the ASIC 322 performs control of each motor, high voltage power supply control such as a developing bias, and the like in image formation under the instruction of the CPU 321. Note that part or all of the functions of the CPU 321 may be performed by the ASIC 322, and conversely, part or all of the functions of the ASIC 322 may be performed by the CPU 321 instead. A part of the function of the engine control unit 54 may be assigned to hardware corresponding to another control unit.

  Next, the operation of the engine control unit 54 will be described with reference to FIG. 3 collectively represents actuators such as a drive motor for the photosensitive member 22 and a separation motor for the developing unit 25. 3 collectively represents sensors such as a registration sensor, a current detection circuit 50, and the like. The engine control unit 54 performs various processes based on information acquired from each sensor 330. For example, the actuator 331 functions as a drive source that drives a cam for separating the developing sleeve 24.

  The forming unit 327 controls the scanner unit 20 to form a latent image mark described later on each photoconductor 22. The forming unit 327 also performs processing for forming a detection pattern for correcting color misregistration on the intermediate transfer belt 30 described later. The process control unit 328 controls the operation / setting of each process unit when a latent image mark is detected or when an image is formed. The color misregistration correction control unit 329 performs later-described color misregistration correction based on the detection pattern detection result and the latent image mark detection result.

FIG. 4 is a diagram showing a part of a detection pattern formed on the intermediate transfer belt 30 for detecting the color misregistration amount in the present embodiment. Note that the characters Y, M, C, and K on the right side of the detection pattern in FIG. 4 indicate that the colors of the corresponding developer images are yellow, magenta, cyan, and black, respectively. A dotted line passing through the developer image is a detection position of the detection sensor 40, and ty1 on the left side of each developer image indicates a detection time of the corresponding developer image by the detection sensor 40. In FIG. 4, the detection pattern includes a pattern 110 including a developer image rising to the right and a pattern 111 including a developer image falling to the right. Each developer image has a line shape inclined by 45 degrees with respect to the moving direction of the intermediate transfer belt 30. For example, if the reference color for color misregistration is yellow, the color misregistration amount Δms in the magenta sub-scanning direction (moving direction of the intermediate transfer belt 30) will be expressed as follows.
Δms = V × ((tm1−ty1) + (tm2−ty2)) / 2
It can be asked. Further, the color misregistration amount Δmm in the main scanning direction of magenta (direction orthogonal to the sub-scanning direction) is defined as YM as a reference distance between yellow and magenta.
Δmm = V × ((tm1-ty1-YM) − (tm2-ty2 + YM))
It can be asked.

  First, conventional color misregistration correction will be described. FIG. 5 shows a detection pattern according to the prior art. The detection pattern of FIG. 5 is formed by continuously forming the pattern 110 of FIG. 4 four times in the sub-scanning direction, and then forming the pattern 111 of FIG. 4 continuously four times in the sub-scanning direction. Two identical detection patterns are formed in the vicinity of both ends of the image forming area in the main scanning direction of the intermediate transfer belt 30, and each is detected by the corresponding detection sensor 40. In the following description, as an example, it is assumed that the driving roller 33 and the photosensitive member 22 have uneven cycles. Further, as a specific numerical example, the circumferential length of the photosensitive member 22 is 48 mm, and the circumferential length of the drive roller 33 is 40 mm.

  In the detection pattern of FIG. 5, in order to cancel out the two period unevenness of the driving roller 33 and the photosensitive member 22, the distance in the sub-scanning direction of the developer image of the same color is determined based on the two period unevenness. Hereinafter, as a representative, a method for determining this distance will be described based on the yellow developer images 112, 113, 114, and 115 of the left detection pattern.

  First, in order to cancel out the period unevenness caused by the drive roller 33, the distance between the developer images 112 and 113 and the distance between the developer images 114 and 115 are set to 20 mm, which is half the circumferential length of the drive roller 33, respectively. That is, the developer images 112 and 113 and the developer images 114 and 115 are formed so as to be in opposite phases of the drive roller 33, respectively. Therefore, the deviation amounts due to the non-uniformity of the developer images 112 and 113 due to the driving roller 33 have the same absolute value and opposite signs, and the influence of the non-uniformity of the driving roller 33 is offset. The same applies to the developer images 114 and 115.

  Further, in order to cancel out the period unevenness due to the photosensitive member 22, the distance between the developer images 112 and 114 and the distance between the developer images 113 and 115 are respectively (3/2) times the circumferential length of the photosensitive member 22. It is set to 72 mm. That is, the developer images 112 and 114 and the developer images 113 and 115 are formed so as to be in opposite phases of the photoconductor 22. Therefore, the deviation amounts due to the nonuniformity of the developer images 112 and 114 due to the nonuniformity of the photoconductor 22 are opposite to each other with the same absolute value, and the influence of the nonuniformity of the photoconductor 22 is offset. The same applies to the developer images 113 and 115.

  As a representative, the four yellow developer images in the pattern 110 have been described, but the same applies to the developer images of other colors in the pattern 110 and the developer images in the pattern 111. As described above, in the related art, the arrangement positions of the developer images of the same color are limited so that the period unevenness can be offset, and thus the length of the entire detection pattern is increased. In this embodiment, as will be described in detail below, a detection pattern shift in the detection pattern due to the non-uniformity of the photosensitive member 22 is detected by the latent image mark. Therefore, in the detection pattern, it is not necessary to consider the period variation of the photoconductor 22, and the length of the detection pattern can be shortened.

  FIG. 6 is a timing chart of color misregistration correction according to the present embodiment. The engine control unit 54 changes the primary transfer bias from the on state to the off state at time T1. Instead of turning off, the primary transfer roller 26 may be separated to a position that does not affect the intermediate transfer belt 30 and the photosensitive member 22. Subsequently, at times T <b> 2 to T <b> 4, the engine control unit 54 forms a latent image pattern, which is an electrostatic latent image for detecting periodic unevenness, on each photoconductor 22. The latent image pattern includes a plurality of latent image marks 80 shown in FIG. Note that the period from time T2 to time T4 is the time required for the photoreceptor 22 to make one revolution. That is, the engine control unit 54 forms a latent image pattern on each photoconductor 22 over one circumference of the photoconductor 22.

  FIG. 7A representatively shows a state in which one latent image mark 80 is formed on the photoreceptor 22a related to the formation of the yellow developer image. The same applies to other colors. For example, the latent image mark 80 is formed to have a length over the entire image area in the main scanning direction, and to have a width of about 30 scanning lines in the sub-scanning direction. It should be noted that the length in the main scanning direction can be set to more than half the length of the image forming area in order to obtain a good detection result. Further, the main scanning direction may be formed so as to extend outside the image area. The engine control unit 54 forms a latent image pattern by forming the latent image marks 80 at predetermined time intervals.

  Returning to FIG. 6, when the latent image mark 80 reaches the position facing the charging roller 23 at time T <b> 3, the engine control unit 54 starts a timer. This time T3 is a reference timing. At times T3 to T5, the engine control unit 54 detects each latent image mark 80 by the charging current.

  Here, the principle of detection of the latent image mark 80 will be described with reference to FIG. FIG. 8A shows the time variation of the detection voltage 56 of FIG. 2 when one latent image mark 80 passes the position facing the charging roller 23. As shown in FIG. 8A, when the latent image mark 80 passes through the position facing the charging roller 23, the detection voltage 56 is lowered correspondingly and then changed so as to return. Here, the reason why the detection voltage 56 varies as shown in FIG. 8B and 8C show the surface potential of the photosensitive member 22 when the developer is not attached to the latent image mark 80 and when it is attached. In these drawings, the horizontal axis indicates the surface position of the photosensitive member 22 in the rotation direction, and the region 93 indicates the position where the latent image mark 80 is formed. The vertical axis indicates the potential. The dark potential of the photosensitive member 22 is VD (for example, −700 V), the bright potential is VL (for example, −100 V), and the charging bias potential of the charging roller 23 is VC (for example, −1000 V).

  In the region 93 where the latent image mark 80 is formed, the potential differences 96 and 97 between the charging roller 23 and the photosensitive member 22 are larger than the potential difference 95 in other regions. For this reason, when the latent image mark 80 reaches the position facing the charging roller 23, the charging current increases. When the charging current increases, the detection voltage 56 decreases as described above. As described above, the detection voltage 56 reflects the surface potential of the photosensitive member 22. As shown in FIG. 8C, even if the developer adheres to the latent image mark 80, the potential on the surface of the photoconductor 22 is different between the position where the latent image mark 80 is formed and other positions. . Therefore, even if the developer adheres to the latent image mark 80, the charging current changes, and the latent image mark 80 can be detected by the charging current. Accordingly, the latent image mark 80 in the present invention includes not only the case where the developer is not attached but also the case where the developer is attached.

  The detection voltage 56 is once decreased by the latent image mark 80 and returns to the original value. Therefore, the comparator 74 in FIG. 2 rises and falls when one latent image mark 80 passes the position facing the charging roller 23. Are output as a binarized voltage 561. For example, the engine control unit 54 can set the detection timing of the rising or falling of the binarized voltage 561 as the detection timing of the latent image mark 80. Further, the engine control unit 54 can set, for example, an intermediate timing between rising and falling of the binarized voltage 561 as the detection timing of the latent image mark 80.

  9A and 9B show the detection results of the latent image pattern formed on a certain photoconductor 22. 9A shows the detection result when the photosensitive member 22 has no periodic unevenness, and FIG. 9B shows the detection result when the photosensitive member 22 has uneven periodicity. 9A to 9C, the time T is the time required for the photoreceptor 22 to make one revolution. When the photosensitive member 22 has no periodic variation, the surface speed of the photosensitive member 22 is a constant value Vref. Accordingly, a period ta (k) from detection of a certain latent image mark 80 to detection of the next latent image mark 80 (k = 1 to n is an integer, where n is 1 from the number of latent image marks formed. The number obtained by subtracting is the same.

On the other hand, when the unevenness of the photoconductor 22 occurs, the surface speed of the photoconductor 22 periodically varies due to the nonuniformity. Therefore, as shown in FIG. 9B, the period tb (k) between the detection timings of the two adjacent latent image marks 80 also periodically varies. For example, the fluctuation amount of the surface speed of the photosensitive member 22 can be obtained from the time interval at which the latent image mark 80 is formed and the detection timing period tb (k) of the two latent image marks 80. FIG. 9C is a plot of the speed variation obtained in this way against time, and a curve C is obtained by interpolating each point. The curve C can be approximated by the following equation.
C = a × sin (2πt / T + Ψ) + Vref (1)
Note that a is the maximum fluctuation value of the surface speed of the photosensitive member 22 with respect to Vref, and Ψ is the initial phase.

  Returning to FIG. 6, after time T <b> 5, the engine control unit 54 outputs the charging bias to the charging roller 23 to charge the photoconductor 22 in order to form a detection pattern based on the developer image. Thereafter, the developing sleeve 24 is brought into contact with the photosensitive member 22 to form a detection pattern on the photosensitive member 22, and a primary transfer bias is output to the primary transfer roller 26, and the detection pattern of the photosensitive member 22 is applied to the intermediate transfer belt 30. Transfer. Thereafter, from time T6, the detection pattern of the intermediate transfer belt is detected by the detection sensor 40 to obtain the amount of color misregistration, and image forming conditions such as the electrostatic latent image formation timing by the scanner unit 20 are reduced so as to reduce color misregistration. Adjust etc.

  FIG. 10 shows a detection pattern according to this embodiment. The detection pattern in FIG. 10 is different from the detection pattern in FIG. 5 in that the pattern 110 and the pattern 111 are each repeated twice in the sub-scanning direction. In FIG. 10, developer images of the same color in the pattern 110 and the pattern 111 are arranged at intervals of half the circumferential length of the drive roller 33 in order to cancel out the period unevenness of the drive roller 33. For example, when the photosensitive member 22 has no periodic unevenness, the developer image of the detection pattern formed by the scanner unit 20 at the point X of the photosensitive member 22 in FIG. Transferred to the point Y of the transfer belt 30. However, if period irregularity occurs in the photosensitive member 22, the moving time from the formation of the electrostatic latent image to the transfer position of the developer image obtained by developing the electrostatic latent image to the intermediate transfer belt 30 changes. Therefore, the image is transferred to a point Z on the intermediate transfer belt 30 different from the point Y. Therefore, the distance between the point Z and the point Y becomes a color misregistration amount due to the non-uniformity of the photosensitive member 22 and is added to the actual color misregistration amount.

  In the present embodiment, as described below, the detection result of the detection pattern is corrected based on the detection result of the latent image mark 80 to obtain the color misregistration amount. FIG. 11A shows the case where no periodic unevenness occurs in the photoconductor 22, and FIG. 11B shows the surface speed and time of the photoconductor 22 when the nonuniformity occurs in the photoconductor 22. Showing the relationship. In FIGS. 11A and 11B, time Sy (i) is the time when an electrostatic latent image for forming a developer image having a detection pattern starts to be formed on the photosensitive member 22. Furthermore, the time Sy (i) + Tref in FIG. 11A is the time when the developer image starts to be transferred to the intermediate transfer belt 30 when the period unevenness does not occur. Further, the time Sy (i) + t in FIG. 11B is the time when the developer image starts to be transferred to the intermediate transfer belt 30 when the period unevenness occurs. Note that time 0 in FIGS. 11A and 11B is the same as time 0 in FIG. 9C.

11A and 11B, the area of the hatched portion is the moving distance of the surface of the photosensitive member 22 from the point X in FIG. 7B to the transfer position of the developer image onto the intermediate transfer belt 30. There is equal. Here, the area of the hatched portion in FIG. 11A is Tref × Vref. On the other hand, the time change V of the moving speed of the surface of the photosensitive member at the transfer position to the intermediate transfer belt 30 is expressed by Expression (2) when time 0 is the same as time 0 in FIG.
V = a × sin (2πt / T + Ψ−φ) + Vref (2)
Here, φ is a phase difference between the charging roller 23 for which the speed fluctuation is obtained and the intermediate transfer belt 30 as shown in FIG. Therefore, the area of the hatched portion in FIG. 11B is obtained by integrating equation (2) from time Sy (i) to time Sy (i) + t. Therefore, the period t can be obtained by solving the equation that the areas of the hatched portions in FIGS. 11A and 11B are equal for t. The period Tref is an ideal period when the photosensitive member has no period unevenness, that is, a reference period. Therefore, the engine control unit 54 can obtain the detection pattern shift amount ΔY of the detection pattern due to the non-uniformity of the photosensitive member period by ΔY = t−Tref. Then, the engine control unit 54 corrects the detection timing Dy (i) of each developer image of the detection pattern of the detection pattern by the detection sensor 40 with the corresponding detection timing shift amount ΔY, thereby detecting the detection timing due to the non-uniformity of the photoconductor. Can be offset.

  FIG. 12 is a flowchart of color misregistration correction according to this embodiment. The engine control unit 54 forms a latent image pattern over the circumference of the photosensitive member 22 in S10, and detects each latent image mark 80 of the latent image pattern based on the charging current in S11. In step S <b> 12, the engine control unit 54 determines the speed fluctuation of the surface speed of the photoconductor 22 due to the non-uniformity of the photoconductor 22 from the detection timing of each latent image mark 80. Thereafter, the engine control unit 54 forms the detection pattern shown in FIG. 10 on the intermediate transfer belt 30 in S13, and detects the detection pattern by the detection sensor 40 in S14. The engine control unit 54 corrects the detection timing of each developer image of the detection pattern based on the speed fluctuation of the photosensitive member in S15, obtains the color misregistration amount of each color from the corrected detection timing in S16, and this color misregistration amount. The image formation timing and the like are adjusted so as to reduce the image quality.

  As described above, in the present embodiment, it is not necessary to consider the period unevenness of the photosensitive member 22 in the arrangement of the developer images of the detection pattern, and thus the length of the detection pattern in the sub-scanning direction can be shortened. Therefore, the time required for color misregistration correction control can be shortened. Furthermore, the number of developer images constituting the detection pattern can be reduced, so that the amount of toner consumed in color misregistration correction can be reduced.

<Second embodiment>
Next, the second embodiment will be described focusing on the differences from the first embodiment. In the first embodiment, the current detection circuit 50 is provided in the charging power supply circuit 43, and the latent image mark 80 is detected by the charging current flowing between the charging roller 23 and the photosensitive member 22. In the present embodiment, a current detection circuit 50 is provided in the primary transfer power supply circuit 46, and the latent image mark 80 is detected by a transfer current flowing between the primary transfer roller 26 and the photosensitive member 22. FIG. 13 is a configuration diagram of the primary transfer power supply circuit 46 according to the present embodiment. Since the primary transfer bias is positive, the operation is the same as that of the charging power supply circuit 43 of FIG. 2B except that the direction of the rectifying diodes 1601 and 1602 is different from that of the charging power supply circuit 43 of FIG. Is the same. Further, the detection of the temporal change in the surface speed due to the unevenness of the period of the photoconductor 22 is the same except that the charging current of the first embodiment becomes the transfer current. In this embodiment, since the speed fluctuation is observed at the transfer position, the period t is obtained by integrating the equation (1) in the first embodiment as it is.

[Other Embodiments]
In the first embodiment, the latent image mark 80 is detected by a charging current, and in the second embodiment, the latent image mark 80 is detected by a transfer current. However, the latent image mark 80 may be detected by a developing current flowing between the developing sleeve 24 and the photosensitive member 22 based on the same principle. In the configuration in which the bias applied to the photosensitive member 22 is not constant and the bias is changed so that the current flowing between the photosensitive member 22 and the latent image mark 80 is detected. What is necessary is just composition. In this case, the time change V of the moving speed of the surface of the photosensitive member 22 at the transfer position to the intermediate transfer belt 30 is expressed by the following equation (3) when time 0 is the same as time 0 in FIG. .
V = a × sin (2πt / T + Ψ + β) + Vref (3)

  The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

  20: Scanner unit, 22: Photoconductor, 23: Charging roller, 25: Developer, 26: Primary transfer roller, 30: Intermediate transfer belt, 50: Current detection circuit, 40: Detection sensor, 54: Engine control unit, 329 : Color shift correction controller

Claims (10)

A rotationally driven photoreceptor;
Light irradiating means for forming an electrostatic latent image on the photoreceptor by irradiating light;
An image carrier to which a developer image obtained by developing the electrostatic latent image is transferred;
An image forming apparatus capable of forming a latent image pattern that is an electrostatic latent image for correction and a detection pattern that is a developer image for correction,
First detection means for detecting the latent image pattern formed on the photosensitive member;
Second detection means for detecting the detection pattern formed on the image carrier;
Correction means for correcting the second detection result with the first detection result based on the first detection result by the first detection means and the second detection result by the second detection means;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the correction unit performs color misregistration correction based on a result of correcting the second detection result with the first detection result.   The correction means obtains a periodic speed fluctuation of the photoconductor based on the first detection result, and corrects the second detection result based on the periodic speed fluctuation. The image forming apparatus described in 1. The detection pattern includes a plurality of developer images;
The second detection result is a detection timing of each of the plurality of developer images.
The image forming apparatus according to claim 3, wherein the correction unit corrects the detection timing of each of the plurality of developer images based on the first detection result.   The correction means obtains a deviation in detection timing of each of the plurality of developer images due to a periodic speed fluctuation of the photoreceptor, and corrects the deviation in detection timing of each of the plurality of developer images. The image forming apparatus according to claim 4. The latent image pattern includes a plurality of latent image marks that are electrostatic latent images,
The first detection result is a detection timing of each of the plurality of latent image marks,
6. The image forming apparatus according to claim 3, wherein the correction unit obtains a periodic speed fluctuation of the photoconductor based on a detection timing of each of the plurality of latent image marks.   The said correction | amendment means calculates | requires the periodic speed fluctuation | variation of the said photoconductor based on the period of the detection timing of two adjacent latent image marks among these several latent image marks. Image forming apparatus. Further comprising process means acting on the photoreceptor,
8. The image forming apparatus according to claim 1, wherein the first detection unit detects the latent image pattern based on a current flowing between the photoconductor and the process unit. 9. The process means includes
Charging means for charging the photoconductor, developing means for developing an electrostatic latent image on the photoconductor to form a developer image, and transfer means for transferring the developer image formed on the photoconductor to the image carrier The image forming apparatus according to claim 8, wherein the image forming apparatus is any one of the following. A drive roller for driving the image carrier;
The image forming apparatus according to claim 1, wherein the arrangement of the developer image included in the detection pattern is determined based on a periodic speed fluctuation of the driving roller.

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