JP2016018045A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can suppress a reduction in detection accuracy due to a curve of electrostatic latent images for correction in performing color shift correction by using the electrostatic latent images for correction.SOLUTION: An image forming apparatus includes control means for causing light irradiation means to form a plurality of latent image marks that are electrostatic latent images for correction on a photoreceptor along the direction of rotation of the photoreceptor, and detection means for detecting the plurality of latent image marks. The control means determines a formation range of the plurality of latent image marks in the main scanning direction orthogonal to the direction of rotation on the basis of the shape of a scan line of the light irradiation means for scanning the photoreceptor, and thereby causing the light irradiation means to form the plurality of latent image marks so as to prevent two or more latent image marks from simultaneously entering a detection area where the detection means detects the latent image marks.SELECTED DRAWING: Figure 12

Description

  The present invention relates to a color misregistration correction technique in an image forming apparatus using an electrophotographic system.

  As an electrophotographic image forming apparatus, a so-called tandem system in which an image forming unit for each color is provided independently is known. In this tandem image forming apparatus, an image is sequentially transferred from an image forming portion of each color to an intermediate transfer belt, and further, an image is transferred collectively from the intermediate transfer belt to a recording material. 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 having a scanner unit and a photoconductor for each color, color misregistration occurs because the positional relationship between the scanner unit and the photoconductor is different for each color.

  Accordingly, the color misregistration correction needs to be periodically executed even during continuous printing. However, while the color misregistration correction is being performed, printing by the user cannot be performed, which results in downtime for the user. For this reason, it is required to provide an image forming apparatus with reduced downtime and high usability.

  Japanese Patent Application Laid-Open No. 2004-228561 discloses a configuration in which color misregistration correction is performed by detecting an electrostatic latent image for correction formed on a photoconductor in order to shorten downtime.

JP 2012-032777 A

  When performing color misregistration correction using a plurality of latent image marks as a correction electrostatic latent image as in Patent Document 1, for example, a plurality of latent image marks are curved due to the curvature of the scanner unit. Sometimes. In such a case, there is a possibility that the next latent image mark enters the detection region before a certain latent image mark is completely removed from the detection region, resulting in a decrease in detection accuracy.

  The present invention provides an image forming apparatus capable of suppressing a decrease in detection accuracy due to curvature of a correcting electrostatic latent image when performing color misregistration correction using the correcting electrostatic latent image. is there.

  According to one aspect of the present invention, there is provided a photosensitive member that is rotationally driven, and a light irradiation unit that forms an electrostatic latent image on the photosensitive member by irradiating light, and the light irradiation unit is configured to form an image. An image forming apparatus capable of forming a correcting electrostatic latent image for controlling conditions, wherein a plurality of latent image marks as the correcting electrostatic latent image are arranged on the photosensitive member in a rotation direction of the photosensitive member. And a detection unit that detects the plurality of latent image marks, and the control unit scans the photoconductor with the light irradiation unit. By determining the formation range of the plurality of latent image marks in the main scanning direction orthogonal to the rotation direction based on the shape of the image, two or more latent images are detected in the detection area where the detection unit detects the latent image marks. The plurality of latent image marks so that the image marks do not enter simultaneously. To characterized thereby formed.

  When performing color misregistration correction using the electrostatic latent image for correction, it is possible to suppress a decrease in detection accuracy due to the curvature of the electrostatic latent image for correction.

1 is a configuration diagram of an image forming apparatus according to an embodiment. The figure which shows the supply structure of the bias by one Embodiment, and the structure of a charging power supply circuit. 1 is a control configuration diagram of an image forming apparatus according to an embodiment. FIG. The flowchart of the reference value acquisition process by one Embodiment. The figure which shows the detection pattern and latent image mark for color misregistration detection by one Embodiment. Explanatory drawing of the latent image mark detection by the charging current by one Embodiment. 5 is a flowchart of color misregistration correction control according to an embodiment. 5 is a flowchart of color misregistration correction control according to an embodiment. The block diagram of the charging power supply circuit by one Embodiment. 6 is a timing chart of color misregistration correction control according to an embodiment. The figure which shows the relationship between the shape of a latent image mark, and a detection voltage. Explanatory drawing of the formation method of the latent image mark by one Embodiment. Explanatory drawing of the formation method of the latent image mark by one Embodiment. 1 is a configuration diagram of a primary transfer power supply circuit and a development power supply circuit according to an embodiment. FIG.

  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 an intermediate transfer belt 30 that is driven by rollers 31, 32, and 33. 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.

  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 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 perform color misregistration correction control by forming a conventional developer image.

  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 setting value 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 this embodiment, the scanner unit 20 can form a latent image mark, which is an electrostatic latent image for color misregistration correction, on the photosensitive member 22 and corrects color misregistration using the latent image mark. 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, allows the detection voltage 56 when the latent image mark is not at the position facing the charging roller 23 and the position of the latent image mark to pass through the position of 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. The actuator 331 functions as, for example, a drive source that drives a cam for separating the developing sleeve 24 described later.

  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 developer image for correcting color misregistration on the intermediate transfer belt 30 described later. As will be described later, the process control unit 328 controls the operation / setting of each process unit when a latent image mark is detected. The color misregistration correction control unit 329 performs color misregistration correction described later from the timing detected by the binarized voltage 561.

  The outline of the color misregistration correction control in the present embodiment will be described below. First, the engine control unit 54 forms a color misregistration detection pattern based on the developer image on the intermediate transfer belt 30 and measures the relative position of other colors with respect to the reference color by the detection sensor 40 to determine the color misregistration amount. . Then, the engine control unit 54 adjusts image forming conditions, for example, the timing at which the scanner unit 20 irradiates the photosensitive member 22 with laser light so as to reduce the determined color misregistration amount.

  In a state where the color shift after the color shift correction using the developer image is small, the engine control unit 54 acquires a reference value for the color shift correction by the latent image mark. Specifically, the engine control unit 54 forms a plurality of latent image marks on each photoconductor 22 and obtains a reference value at a timing at which the formed latent image marks are detected. Thereafter, in color misregistration correction control performed when the temperature in the apparatus changes due to continuous printing or the like, color misregistration correction is performed by determining the color misregistration amount based on the detection timing of the formed latent image mark and the reference value. . In the following, correction of color misregistration is performed by controlling the irradiation timing of the laser beam. For example, even if the speed of the photosensitive member 22 is controlled, the reflection mirror included in the scanner unit 20 is controlled. The mechanical position may be controlled. Details of the color misregistration correction control will be described below with reference to FIG.

  In S <b> 1 of FIG. 4, the engine control unit 54 forms a detection pattern for detecting color misregistration on the intermediate transfer belt 30 with a developer. FIG. 5A is an example of a detection pattern for detecting color misregistration. In FIG. 5A, marks 400 and 401 are patterns for detecting the amount of color misregistration in the conveyance direction (sub-scanning direction) of the intermediate transfer belt 30. Marks 402 and 403 are patterns for detecting the amount of color misregistration in the main scanning direction orthogonal to the sub-scanning direction. 5A corresponds to the conveyance direction of the intermediate transfer belt 30, that is, the sub-scanning direction. In the example of FIG. 5A, the marks 402 and 403 are inclined by 45 degrees with respect to the main scanning direction. Note that the last characters of the reference numerals of marks 400 to 403, Y, M, C, and Bk indicate that the corresponding marks are formed of yellow, magenta, cyan, and black developers, respectively. Further, tsf1 to 4, tmf1 to 4, tsr1 to 4, and tmr1 to 4 of each mark indicate detection timings of the corresponding marks detected by the detection sensor 40. The detection of the marks by the detection sensor 40 can be performed using a known technique such as, for example, using reflected light when the mark is irradiated with light.

Hereinafter, the correction of the position of magenta will be described by using yellow as a reference color. However, the same applies to correction of other cyan and black positions. The moving speed of the intermediate transfer belt 30 is v (mm / s), and the theoretical distance between the yellow marks 400 and 401 and the magenta marks 400 and 401 is dsM. In this case, the color misregistration amount δesM in the sub-scanning direction of magenta is
δesM = v × {(tsf2−tsf1) + (tsr2−tsr1)} / 2−dsM
It is represented by

Further, regarding the main scanning direction, for example, the magenta color shift amount δemfM on the left side is
δemfM = v × (tmf2−tsf2) −v × (tmf1−tsf1)
It is represented by The same applies to the magenta color misregistration amount δemrM on the right side. The sign of δemfM and δemrM represents the direction of deviation in the main scanning direction. The engine control unit 54 corrects the writing position of the magenta color from δemfM, and corrects the width in the main scanning direction, that is, the main scanning magnification, from δemrM−δemfM. When there is an error in the main scanning magnification, the writing position is calculated not only by δemfM but also by taking into account the amount of change in the image frequency (image clock) that has changed as the main scanning magnification is corrected. For example, the engine control unit 54 changes the emission timing of the laser light by the scanner unit 20b so as to eliminate the calculated color misregistration amount. For example, if the amount of color misregistration in the sub-scanning direction is an amount corresponding to four lines, the engine control unit 54 changes the emission timing of the laser beam that forms the magenta electrostatic latent image by four lines. In this manner, the subsequent reference value acquisition process can be performed with the color misregistration amount reduced by the process of step S1.

  Returning to FIG. 4, in S <b> 2, the engine control unit 54 sets the rotation phase between the photoconductors 22 to a predetermined state in order to suppress the influence when the rotation speed (surface speed) of the photoconductor 22 varies. Match. Specifically, under the control of the engine control unit 54, the phase of the photoconductor 22 of the reference color is adjusted to have a predetermined relationship with the phase of the photoconductor 22 of the reference color. Further, in the case where the drive gear of the photoconductor 22 is provided on the rotation shaft of the photoconductor 22, the phase relationship of the drive gear of each photoconductor 22 is adjusted so as to be a predetermined relationship.

  The engine control unit 54 adjusts the phase of each photoconductor 22 in S <b> 2, and then in S <b> 3, a predetermined number, for example, 20 latent image marks in each photoconductor 22, along the rotation direction of the photoconductor 22, respectively. Form. When forming a plurality of latent image marks, the developing sleeve 24 is separated from the photosensitive member 22 so that the developer does not adhere to the photosensitive member 22, and the primary transfer roller 26 is also separated from the photosensitive member 22. For the primary transfer roller 26, the applied voltage may be set to off (zero) so that the action on the photosensitive member 22 is smaller than that during normal image formation. Further, the developer sleeve 24 may be prevented from adhering to the photosensitive member 22 by applying a bias voltage having a polarity opposite to that of the normal one. Further, when using the jumping development method in which the photosensitive member 22 and the developing sleeve 24 are brought into a non-contact state and the voltage application is performed by superimposing the AC bias on the DC bias, the voltage application to the developing sleeve 24 is turned off. You just need to.

  FIG. 5B shows a state in which the latent image mark 80 is formed on the photosensitive member 22. For example, the latent image mark 80 can be formed to have the maximum width in the image forming area in the main scanning direction, and can be formed to have a width of about 30 scanning lines in the sub-scanning direction. . In the main scanning direction, the length may exceed the image forming area (printing area on the recording material).

  Next, the engine control unit 54 detects each edge of each latent image mark 80 formed on each photoconductor 22 based on the binarized voltage 561 in S4. FIG. 6A shows the temporal variation of the detection voltage 56 when the latent image mark 80 passes the position facing the charging roller 23. As shown in FIG. 6A, when the latent image mark 80 passes through a position facing the charging roller 23, the detection voltage 56 is lowered accordingly and then changes so as to return. Here, the reason why the detection voltage 56 varies as shown in FIG. 6B and 6C 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. 6C, even if the developer adheres to the latent image mark 80, the potential on the surface of the photoreceptor 22 is different between the position where the latent image mark 80 is formed and the 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. 3 rises and falls when one latent image mark 80 passes the position facing the charging roller 23. Are output. Therefore, for example, when 20 latent image marks 80 are formed for each color, the engine control unit 54 detects 40 edges for each color. The engine control unit 54 stores the detection times ty (k), tm (k), tc (k) tbk (k) of the respective edges of yellow, magenta, cyan, and black in the RAM 323.

  Thereafter, the engine control unit 54 calculates the reference values esYM, esYC, and esYBk for magenta, cyan, and black, respectively, based on yellow in S5, using the following equations.

各基準値は、対応する色の各潜像マーク８０で検出する２つのエッジの中心の平均値と、基準色であるイエローの各潜像マーク８０で検出する２つのエッジの中心の平均値との差分に相当する。なお、基準値は、ＣＰＵ３２１がプログラムに基づき演算を行っても良いし、ハードウェア回路やテーブルを用いて行っても良い。エンジン制御部５４は、計算した各基準値を、感光体２２の回転周期の成分をキャンセルした色ずれ量を示すデータとしてＥＥＰＲＯＭ３２４に保存する。

Each reference value includes an average value of the centers of the two edges detected by each latent image mark 80 of the corresponding color, and an average value of the centers of the two edges detected by each latent image mark 80 of yellow, which is the reference color. It is equivalent to the difference. The reference value may be calculated by the CPU 321 based on a program, or may be performed using a hardware circuit or a table. The engine control unit 54 stores the calculated reference values in the EEPROM 324 as data indicating the color misregistration amount in which the rotation period component of the photoconductor 22 is canceled.

  Next, color misregistration correction control according to the present embodiment will be described with reference to FIG. In S11, the engine control unit 54 forms the same number of latent image marks 80 on each photoconductor 22 as when obtaining the reference values described in FIG. 4, and in S12, the latent image marks 80 on the respective photoconductors 22 are formed. The time is detected and stored in the RAM 323. Thereafter, in S13, the engine control unit 54 calculates ΔesYM, ΔesYC, and ΔesYBk by the following equations and stores them in the RAM 323.

  In S14, the engine control unit 54 determines whether or not the difference between ΔesYM and esYM, which is the magenta reference value, is 0 or more. If the difference is greater than or equal to 0, this indicates that the magenta detection timing when yellow is used as a reference is delayed. Therefore, in S15, the engine control unit 54 determines the irradiation timing of the laser light from the scanner unit 20b in S15. Advance. The amount to be advanced can be specified by the difference value. On the other hand, when the difference is less than 0, this indicates that the detection timing of magenta when yellow is used as a reference is early. Therefore, in S16, the engine control unit 54 determines the irradiation timing of the laser light from the scanner unit 20b. Delay. When the difference is 0, there is no change in the irradiation timing because the color misregistration amount is also 0. Thereby, the amount of color misregistration between yellow and magenta can be suppressed. At this time, since laser emission is performed in units of one line, the difference is converted into units of one line, and the emission timing of the laser beam is controlled so that the color misregistration amount is minimized. The engine control unit 54 performs the same process as described above for cyan in steps S17 to S19, and performs the same process as described above for black in steps S20 to S22. In this way, the color misregistration state at that time can be returned to the reference color misregistration state (reference state).

  In the above embodiment, the relative positions of other colors with respect to the reference color are corrected. However, as described below, each color can be controlled independently. Hereinafter, a modified example in which each color is controlled independently will be described. The engine control unit 54 executes the following procedure independently for each color. In this example, the detection time t (k) of each edge of the latent image mark 80 is detected and stored for each color in S4 of FIG. 4, and the reference value es for each color is calculated by the following formula in S5. .

基準値ｅｓは、対応する色の潜像マーク８０の中心の検出時刻の平均値に相当する。

The reference value es corresponds to the average value of the detection times at the center of the latent image mark 80 of the corresponding color.

  Next, color misregistration correction control according to this modification will be described with reference to FIG. In S31, the engine control unit 54 forms the same number of latent image marks 80 on each photoconductor 22 as when each reference value is acquired. In S32, the engine control unit 54 detects the latent image marks 80 on each photoconductor 22 and detects the time. Is stored in the RAM 323. Thereafter, in S33, the engine control unit 54 calculates Δes for each color according to the following equations, and stores them in the RAM 323.

  In S34, the engine control unit 54 determines whether or not the difference between Δes and the reference value es is 0 or more for each color. If the difference is 0 or more, this indicates that the detection timing of the corresponding color is delayed, and therefore the engine control unit 54 advances the irradiation timing of the laser beam of the corresponding color in S35. The amount to be advanced can be specified by the difference value. On the other hand, when the difference is less than 0, this indicates that the detection timing of the latent image mark 80 of the corresponding color is early, and therefore the engine control unit 54 delays the irradiation timing of the corresponding laser beam in S36. As a result, the color misregistration amount can be returned to the reference state. When the difference is 0, the color misregistration amount is also 0, and there is no need to change the irradiation timing.

  In the present embodiment, the charging power supply circuits 43a to 43d corresponding to the charging rollers 23a to 23d are provided, and the current detection circuit 50 is provided to each of the charging power supply circuits 43a to 43d. However, as will be described below, a configuration in which one current detection circuit 50 common to the charging rollers 23a to 23d may be provided.

  FIG. 9 shows a circuit configuration when the charging power supply circuits 43a to 43d and the current detection circuit 50 common to the charging power supply circuits 43a to 43d are provided. For simplification, reference numerals of individual components in the secondary side circuits 500a to 500d of the charging power supply circuits 43a to 43d are omitted. In FIG. 9, the engine control unit 54 controls the drive circuits 61a to 61d based on the voltage setting values 55a to 55d set for the operational amplifiers 60a to 60d, and outputs desired voltages to the output terminals 53a to 53d. . The charging currents in the charging power supply circuits 43a to 43d flow to the current detection circuit 50, respectively. Therefore, a voltage corresponding to a value obtained by superimposing the charging currents of the output terminals 53a to 53d appears in the detection voltage 56. Note that the configuration of the current detection circuit 50, the configuration related to the comparator 74, and the configuration of the engine control unit 54 are the same as those in FIG.

  Hereinafter, color misregistration correction control in the case of the configuration described with reference to FIG. 9 will be described with reference to the timing chart of FIG. First, the engine control unit 54 outputs a drive signal for driving a cam for separating the developing sleeves 24a to 24d at time T1. At the timing T2, the developing sleeves 24a to 24d are separated from the photosensitive members 22a to 22d. The engine control unit 54 controls the primary transfer bias from the on state to the off state at time T3. In the period from time T4 to time T6, the engine control unit 54 forms the latent image mark 80 on the photosensitive member 22 of each color. In the drawing, the latent image marks 80 are formed in the order of laser signals 90a, 90b, 90c, 90d, 91a, 91b, 91c, 91d, 92a, 92b, 92c, and 92d.

  The engine control unit 54 detects each latent image mark between times T5 and T7. Reference numerals 95a to 95d in FIG. 10 indicate the detection timing of the latent image mark 80 formed by the laser signals 90a to 90d. Similarly, reference numerals 96a to 96d are detection timings of the latent image mark 80 formed by the laser signals 91a to 91d, and reference numerals 97a to 97d are detection timings of the latent image mark 80 formed by the laser signals 92a to 92d. Is shown. In this way, the engine control unit 54 forms each latent image mark 80 so that the detection timing of the latent image mark 80 does not overlap. Thereby, a common current detection circuit 50 can be applied to the plurality of charging rollers 23. When each latent image mark 80 is detected during the period of time T5 to T7, the engine control unit 54 performs a reference value calculation process.

  In the case of the configuration described with reference to FIG. 9, the processes other than sequentially detecting the latent image marks 80 corresponding to the respective colors are the same as in the case of using the configuration of FIG. That is, the calculation of the reference value and the color misregistration correction control are the same as described with reference to FIGS.

  Next, formation of the latent image mark 80 will be described. In the present embodiment, a change in the charging current when the latent image mark 80 passes the position facing the charging roller 23 is detected as the detection voltage 56. The charging current flows in a region (nip portion) where the charging roller 23 and the photosensitive member 22 are in contact with each other. When a discharge occurs between the charging roller 23 and the photosensitive member 22, a charging current flows in the nip portion and the region including the discharge region. Hereinafter, a region where a charging current flows between the charging roller 23 and the photoconductor 22 is referred to as a detection region. When a plurality of latent image marks 80 pass through the detection area, charging occurs when a state in which all of the detection areas are covered with the latent image mark 80 and a state in which no latent image mark has entered the detection area 81 occur alternately. The amount of change in current is maximized. FIG. 11A shows an example in which the latent image mark 80 is formed such that a state where all the detection areas 81 are covered with the latent image mark 80 and a state where it is not covered alternately occur. In FIG. 11A, W is the width of the detection region 81 in the sub-scanning direction, and L is the shortest distance in the sub-scanning direction between adjacent latent image marks 80. In this example, the width of the latent image mark 80 in the sub-scanning direction is the same W as that of the detection area 81. However, the width of the latent image mark 80 in the sub-scanning direction may be larger than the width W of the detection area 81. FIG. 11B shows a change over time of the detection voltage 56 when the latent image mark 80 is formed as shown in FIG. The length of the latent image mark 80 in the main scanning direction is equal to or longer than the length of the detection region 81 in the main scanning direction. As shown in FIG. 11B, the latent image mark 80 can be correctly detected with the reference voltage 75 (Vref).

  On the other hand, FIG. 11C shows a case where the latent image mark 80 is formed to be curved. In FIG. 11C, L is the shortest distance between adjacent latent image marks 80, and Lref is the formation interval of adjacent latent image marks 80. More specifically, Lref is an interval between the latent image marks 80 that the engine control unit 54 tries to form, and the engine control unit 54 controls the image forming unit so that the interval between adjacent latent image marks 80 becomes Lref. Thus, the latent image mark 80 is formed. However, since the scanning line on the photosensitive member 22 by the scanner unit 20 is curved, FIG. 11C shows the case where the shortest distance between the latent image marks 80 that are actually formed is L shorter than Lref. ing. In the example of FIG. 11C, the distance L is shorter than the width W of the detection area 81. When the latent image mark 80 is formed as shown in FIG. 11C, the next latent image mark 80 enters the detection region 81 before a certain latent image mark 80 is completely removed from the detection region 81. That is, the latent image mark 80 always enters the detection area 81, and the change in the detection voltage 56 becomes small. Here, when the change of the detection voltage 56 becomes small and the reference voltage 75 that is the threshold value is not straddled as shown in FIG. 11D, the latent image mark 80 cannot be detected correctly. In order to prevent this, the distance Lref may be increased, but the detection time of the plurality of latent image marks 80 becomes longer.

  Therefore, in the present embodiment, the range in the main scanning direction in which the latent image mark 80 is formed is adjusted so that two adjacent latent image marks 80 do not enter the detection area 81 at the same time. In FIG. 11E, when the scanning line is curved as shown in FIG. 11C, the range in the main scanning direction for forming the latent image mark 80 is adjusted, and two adjacent latent image marks 80 are detected simultaneously. In this example, the latent image mark 80 is formed so as not to enter the area 81. FIG. 11F shows the change over time of the detection voltage 56 when the latent image mark 80 is formed as shown in FIG. Although the time change of the amplitude of the detection voltage 56 shown in FIG. 11 (F) is smaller than that shown in FIG. 11 (B), each latent image mark 80 can be detected correctly because it crosses the reference voltage 75.

Hereinafter, conditions for preventing two adjacent latent image marks 80 from entering the detection area 81 at the same time will be described. As shown in FIG. 11E, if the shortest distance L between two adjacent latent image marks 80 is equal to or larger than the width W of the detection area 81, the two adjacent latent image marks 80 enter the detection area 81 at the same time. Never do. Therefore,
L ≧ W (1)
Should be satisfied. In order to shorten the detection time of the plurality of latent image marks 80, it is better that L is short. Therefore, in the following description, L = W. However, if the expression (1) is satisfied, two adjacent latent image marks 80 do not cover the detection area 81 at the same time. Hereinafter, description will be made with a specific example.

  First, for example, it is assumed that the latent image mark 80 is formed as shown by a dotted line in FIG. In FIG. 12A, positions XL, XC, and XR respectively indicate the left end, center, and right end of the electrostatic latent image formation region in the main scanning direction. The distance between the position XL and the position XR, that is, the length of the electrostatic latent image formation region in the main scanning direction is M. Note that the hatched area is obtained by approximating the formed latent image mark 80 with a straight line connecting the positions XL, XC, and XR. That is, the straight line XL-XC and the straight line XC-XR are approximations of the scanning lines on the photosensitive member 22 by the scanner unit 20 with straight lines, and hereinafter, the straight lines XL-XC and XC-XR with respect to the main scanning direction. The inclination is called the inclination of the scanning line. In FIG. 12A, the amount of inclination of the straight line XL-XC with respect to the main scanning direction is α, and the amount of inclination of the straight line XC-XR with respect to the main scanning direction is β. In the figure, the inclination is positive when moving from the left side to the right side in the main scanning direction and moving upward in the sub-scanning direction. That is, in FIG. 12A, the inclination amount α is positive and the inclination amount β is negative. It should be noted that the data regarding the inclination amounts α and β of the scanning lines are measured in advance and stored in the engine control unit 54.

Next, how to determine the range in the main scanning direction for forming the latent image mark 80 will be described. FIGS. 12B and 12C are diagrams illustrating a method for determining the formation range of the latent image mark 80 when the inclination amounts α and β of the scanning lines are the same. In the examples of FIGS. 12B and 12C, the inclination amounts α and β are both negative. 12B shows an example in which the inclination is large and the range in the main scanning direction for forming the latent image mark 80 is half or less of the length M, and FIG. 12C shows the latent image. This is an example in which the range in the main scanning direction for forming the mark 80 is larger than half of the length M. In the present embodiment, when the inclination amounts α and β are the same, the latent image mark 80 is formed from the side with the smaller absolute value of the inclination. In FIGS. 12B and 12C, the absolute value of the tilt amount is smaller in α than in β, so that the latent image mark 80 is formed from the position XL. First, in the example of FIG. 12B, the interval Lref between adjacent latent image marks 80 is defined as m when the formation length of the latent image marks 80 in the main scanning direction is m.
Lref = W + | α | m (2)
It becomes. Therefore, the formation width m is
m = (Lref−W) / | α | (3)
It becomes.

In the example of FIG. 12C, the interval Lref between adjacent latent image marks 80 is
Lref = W + 0.5 | α | M + | β | (m−0.5M) (4)
It becomes. Therefore, the formation width m is
m = (Lref−W−0.5 | α | M + 0.5 | β | M) / | β | (5)
It becomes.

FIG. 12D shows an example where the signs of the scan line inclination amounts α and β are different. When the left and right inclinations of the latent image mark 80 are different from each other, the latent image mark is inclined to the same side in the sub-scanning direction with the central position XC as the center, so that the latent image mark is located on both sides of the position XC so as to include the position XC. Form. In the example of FIG. 12D, if the length in the main scanning direction of the latent image mark 80 on the left side from the position XC is m1, and the length in the main scanning direction of the latent image mark 80 on the right side from the position XC is m2. The formation interval Lref of the image mark 80 is as follows.
Lref = W + | α | m1 (6)
Lref = W + | β | m2 (7)
From the equations (6) and (7), the following equations (8) and (9) are obtained.
m1 = (Lref−W) / | α | (8)
m2 = (Lref−W) / | β | (9)
Therefore, the length m of the latent image mark 80 in the main scanning direction is expressed by the following formula (10).
m = m1 + m2 = (| α | + | β |) (Lref−W) / | α || β | (10)
As described above, in the present embodiment, the formation range of the latent image mark 80 in the main scanning direction is determined based on the shape of the scanning line so that the two adjacent latent image marks 80 do not enter the detection region 81 at the same time. With this configuration, it is possible to correctly detect the plurality of latent image marks 80 while suppressing an increase in the length of the plurality of latent image marks 80 in the sub-scanning direction. Therefore, with this configuration, the time required for color misregistration correction can be shortened.

  In the above embodiment, the formation area of the electrostatic latent image is divided into two sections in the main scanning direction, but may be divided into three or more sections. In this case, the inclinations of the scanning lines in a plurality of sections are measured in advance and held in the EEPROM 324 or the like. Then, when the positive and negative inclination amounts of the plurality of sections are the same, the engine control unit 54 lies on either side of the two end portions in the main scanning direction of the electrostatic latent image formation region based on the inclination amount. Whether to form the image mark 80 is determined. Here, the determined side is the side on which the length in the main scanning direction for forming the latent image mark 80 becomes longer. Further, the engine control unit 54 starts from one end of a section having the smallest absolute value of the inclination amount as a starting point when the inclination amount of each of the plurality of sections is the same, and applies to the other end of the section having the smallest inclination amount. The formation range can also be determined in the direction. In addition, when there are a positive inclination amount and a negative inclination amount in the inclination amounts of the plurality of sections, the engine control unit 54 determines one of the boundaries where the positive and negative of the inclination amounts of the two sections are different among the boundaries of the plurality of sections. The formation range of the latent image mark 80 can be determined so as to include the two.

  In the present embodiment, the latent image mark 80 is detected by the charging current flowing between the charging roller 23 and the photosensitive member 22. However, the latent image mark 80 can be detected using the primary transfer roller 26 that outputs a bias toward the photosensitive member 22 and the developing sleeve 24. FIG. 14A shows the primary transfer power supply circuit 46 when the latent image mark 80 is detected by the primary transfer current flowing between the photosensitive member 22 and the primary transfer roller 26. Since the primary transfer bias has a polarity different from that of the charging bias, the direction of the diodes 1601 and 1602 in the primary transfer power supply circuit 46 is opposite to that of the charge power supply circuit 43 shown in FIG. The detection principle of the mark 80 is the same.

  FIG. 14B shows the developing power supply circuit 44 when the latent image mark 80 is detected by the developing current flowing between the photosensitive member 22 and the developing sleeve 24. The development power supply circuit 44 in FIG. 14B has two rectifier circuits so that both the negative development bias and the positive bias can be output from the output terminal 53. Note that which of the two rectifier circuits is operated is controlled by the engine control unit 54 using the signals CLK1 and CLK2. Specifically, a negative development bias is output during normal image formation, and a positive bias is output when the latent image mark 80 is detected. The reason why the positive polarity bias is output when the latent image mark 80 is detected is that the developer does not adhere to the photosensitive member 22. Therefore, the developer can be prevented from adhering to the photoconductor 22 as long as a bias having a potential higher than the light potential of the photoconductor 22 is output even with a negative polarity bias. In this case, the developing power supply circuit 44 does not need to be provided with a rectifier circuit for outputting a positive polarity bias. In the primary transfer power supply circuit 46 and the development power supply circuit 44 shown in FIGS. 14A and 14B, the current detection circuit 50 is provided separately. However, like the charging power supply circuit 43 shown in FIG. 9, the current detection circuit 50 may be provided in common for the plurality of photoconductors 22.

  Further, in the present embodiment, the bias output from the process unit is constant, and the latent image mark 80 is detected by a change in the current flowing between the photoconductor 22 and the process unit. However, in the system in which the bias output from the process unit is controlled to make the current flowing between the photosensitive member 22 and the process unit constant, the latent image mark 80 is detected by the change in the bias output from the process unit. be able to.

<Second embodiment>
Next, the second embodiment will be described focusing on the differences from the first embodiment. For example, as shown in FIG. 13A, when the inclination of the latent image mark 80 is large, the area of the latent image mark 80 that enters the detection region is reduced, and as shown in FIG. May not fall below the reference voltage 75. Note that W1 to W4 in FIG. 13A represent sections in the sub-scanning direction, and the length of each is the same as the width W of the detection region in the sub-scanning direction. In this embodiment, the width of the latent image mark 80 in the sub-scanning direction is adjusted in such a case. Hereinafter, adjustment of the width of the latent image mark 80 in the sub-scanning direction will be described.

  For example, as described in the first embodiment, the inclination of the latent image mark 80 is obtained, and the main scanning direction length M of the electrostatic latent image formation region is measured in the main scanning direction from the end portion on the small inclination side. The latent image mark 80 is formed by a predetermined length. The predetermined ratio is a ratio with respect to the total area of the detection area 81 that needs to cover the detection area 81 in order to detect the latent image mark 80. In the example of FIG. 13C, this ratio is 40%, that is, the length of the latent image mark 80 to be formed in the main scanning direction is 0.4M. In order for the latent image mark 80 to cover 40% of the detection region 81, as shown in FIG. 14C, the width of the latent image mark 80 in the sub-scanning direction is set so that the inclination of the latent image mark 80 is α. Then, it is necessary to set W + 0.4αM.

In this case, the interval Lref between the latent image marks 80 for preventing the adjacent latent image marks 80 from entering the detection area 81 at the same time is as follows from FIG.
Lref = W + 0.4 | α | M
The width of the latent image mark 80 in the sub-scanning direction is also W + 0.4 | α | M.

  In the above embodiment, the length of the latent image mark 80 in the main scanning direction is determined by the area of the latent image mark 80 that needs to cover the detection area 81 regardless of the inclination of the scanning line. However, when the formation range of the latent image mark 80 in the main scanning direction is determined as in the first embodiment, and the detection voltage 56 does not become lower than the reference voltage 75 in the determined formation range, the latent image mark 80 is sub-scanned. It can also be set as the structure which enlarges the width | variety of a direction. In the determined formation range, if the detection voltage 56 does not become lower than the reference voltage 75 even if the width of the latent image mark 80 in the sub-scanning direction is increased, the length of the latent image mark 80 in the main scanning direction is changed to the main scanning direction. It can also be set as the structure determined as demonstrated in embodiment.

  As described above, the length in the main scanning direction and the width in the sub-scanning direction in which the plurality of latent image marks 80 are formed based on the inclination of the scanning line so that the area of the detection region 81 covered with the latent image mark 80 becomes a predetermined value or more. To decide. With this configuration, it is possible to correctly detect the plurality of latent image marks 80 while suppressing the length in the sub-scanning direction in which the plurality of latent image marks 80 are formed.

[Other Embodiments]
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.

  22: photoconductor, 20: scanner unit, 54: engine control unit, 23: charging unit, 24: developing sleeve, 26: primary transfer roller

Claims (12)

A rotationally driven photoreceptor;
Light irradiating means for forming an electrostatic latent image on the photoreceptor by irradiating light;
Have
The light irradiation means is an image forming apparatus capable of forming an electrostatic latent image for correction for controlling image forming conditions,
A control unit that causes the light irradiation unit to form a plurality of latent image marks that are electrostatic latent images for correction on the photoconductor along a rotation direction of the photoconductor;
Detecting means for detecting the plurality of latent image marks;
With
The control means determines the formation ranges of the plurality of latent image marks in the main scanning direction orthogonal to the rotation direction based on the shape of a scanning line that the light irradiation means scans the photoconductor. An image forming apparatus, wherein the plurality of latent image marks are formed so that two or more latent image marks do not simultaneously enter a detection area where the detection unit detects the latent image marks. For each of the plurality of sections in the main scanning direction, it further comprises holding means for holding information indicating the amount of inclination of the scanning line by the light irradiation means with respect to the main scanning direction,
The image forming apparatus according to claim 1, wherein the control unit determines the formation range based on the inclination amount.   When the positive and negative inclination amounts of the plurality of sections are the same, the control means is arranged on either side of the two end portions in the main scanning direction of the formation area of the electrostatic latent image based on the inclination amount. The image forming apparatus according to claim 2, wherein whether to form a latent image mark is determined.   The image forming apparatus according to claim 3, wherein the control unit determines that a latent image mark is to be formed on a side where the formation range is larger, of two end portions in the main scanning direction.   In the direction to the other end of the section with the smallest amount of inclination, the control means starts from one end of the section with the smallest absolute value of the amount of inclination when the slope amounts of the plurality of sections are the same. The image forming apparatus according to claim 2, wherein the forming range is determined.   The control means, when there is a positive inclination amount and a negative inclination amount in the inclination amounts of the plurality of sections, is one of the boundaries where the positive and negative of the inclination amounts of the sections on both sides are different among the boundaries of the plurality of sections. The image forming apparatus according to claim 2, wherein the formation range is determined to include   The said control means determines the width | variety of the said rotation direction of the said latent image mark so that the area of the latent image mark which approachs into the said detection area may become larger than predetermined value. 2. The image forming apparatus according to item 1. Further comprising process means acting on the photoreceptor,
The image forming apparatus according to claim 1, wherein the detection unit detects the latent image mark based on a current flowing between the photosensitive member and the process unit.   The image forming apparatus according to claim 8, wherein the detection area is an area in which a current flows between the photoconductor and the process unit. The process means includes
Charging means for charging the photosensitive member, developing means for developing an electrostatic latent image on the photosensitive member to form a developer image, and transferring the developer image formed on the photosensitive member to another member or a recording material The image forming apparatus according to claim 8, wherein the image forming apparatus is any one of a transfer unit.   The image forming apparatus according to claim 1, wherein the image forming condition is a timing at which the light irradiation unit forms an electrostatic latent image on the photosensitive member. A plurality of the photoreceptors;
The image forming apparatus according to claim 1, wherein the control unit corrects color misregistration between a plurality of photosensitive members by controlling the image forming conditions.

Images