JP2014224930A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to suppress color misregistration correction error.SOLUTION: An image forming apparatus includes: multiple pieces of image forming means each of which comprises a rotated conductive image carrier and a photoreceptor, forms a developer image on the photoreceptor, and transfers the developer image formed on the photoreceptor to the image carrier in a transfer position; application means which applies a voltage to the image carrier; detection means which detects a current flowing between the photoreceptor and the image carrier; and correction means which forms a detection image for color-misregistration correction on the photoreceptor, to correct color misregistration by means of changes in current detected by the detection means.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine that forms an image by electrophotography.

  In an electrophotographic image forming apparatus, in order to support higher-speed printing, an image forming unit for each color is provided, images are sequentially transferred from the image forming unit for each color to an intermediate transfer member, and further recorded from the intermediate transfer member. A configuration is known in which images are collectively transferred to a material. In such an image forming apparatus, a position shift (color shift) of each color toner image transferred to the intermediate transfer member may occur. For this reason, for example, a detection pattern for detecting the positional deviation of the toner image is formed on the intermediate transfer member, and the detection pattern is detected by an optical sensor to measure and correct the positional deviation amount. Such a technique for correcting the positional deviation of each color toner image is generally called registration.

  Here, Patent Document 1 discloses that a current that flows between the image carrier and the ground when a pattern latent image for color misregistration adjustment is formed on each image carrier and the pattern latent image is transferred to the intermediate transfer member. A configuration is disclosed in which color misregistration is corrected by detecting the color shift.

Japanese Patent Laid-Open No. 10-039571

  The configuration described in Patent Document 1 requires a circuit for detecting a current flowing between each image carrier and ground. In addition, since it is necessary to form the intermediate transfer member with a high-resistance member, the waveform of the detection current becomes dull, and thus the color misregistration correction error may increase. Further, only the color misregistration in the sub-scanning direction can be corrected, and the inclination with respect to the main scanning direction and the color misregistration in the main scanning direction cannot be corrected.

  In view of the above problems, the present invention provides an image forming apparatus capable of suppressing a color misregistration correction error.

  According to one aspect of the present invention, an image forming apparatus includes a conductive image carrier that is rotationally driven and a photoconductor, and forms a developer image on the photoconductor, and the developer image formed on the photoconductor A plurality of image forming means for transferring the image to the image carrier at the transfer position, an application means for applying a voltage to the image carrier, and a detection means for detecting a current flowing between the photoconductor and the image carrier. And a correcting unit that forms a detection image for color misregistration correction on the photosensitive member and performs color misregistration correction by a change in current detected by the detecting unit.

  It is possible to correct not only the sub-scanning direction but also the inclination with respect to the main scanning direction and the color misregistration in the main scanning direction, and suppress the color misregistration correction error.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. 1 is a block diagram showing a control configuration of an image forming apparatus according to an embodiment. The figure which shows the measuring method of the resistance of the electroconductive belt by one Embodiment. The figure which shows the difference in the characteristic of an electroconductive belt and a high resistance belt. Explanatory drawing of the primary transfer to a conductive belt. FIG. 4 is a diagram illustrating a relationship between a secondary transfer bias and an intermediate transfer belt potential. The figure which shows the relationship between the toner image formed in the electroconductive belt, and the electric current which an electric current detection part detects. The figure which shows the relationship between the toner image formed in the high resistance belt, and the electric current which a current detection part detects. 9 is a flowchart of tilt correction processing with respect to a main scanning direction according to an embodiment. Explanatory drawing of the correction process of the inclination with respect to the main scanning direction by one Embodiment. 9 is a flowchart of sub-scanning direction correction processing according to an embodiment. Explanatory drawing of the correction process of the shift | offset | difference of the subscanning direction by one Embodiment. 9 is a flowchart of main-scanning direction correction processing according to an embodiment. Explanatory drawing of the correction process of the shift | offset | difference of the main scanning direction by one Embodiment.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings. Further, the following embodiments are for the purpose of explanation, and do not limit the scope of the invention. Furthermore, in the following embodiments, specific values are presented to facilitate the understanding of the invention, but these values are examples and other values can be used.

<First embodiment>
FIG. 1 is a schematic configuration diagram of the image forming apparatus according to the present embodiment. The image forming apparatus includes an image forming unit 1a that forms a yellow image, an image forming unit 1b that forms a magenta image, an image forming unit 1c that forms a cyan image, and an image forming unit that forms a black image. Four image forming units 1d are provided. These four image forming units 1a to 1d are arranged in a line at regular intervals.

  In each of the image forming units 1a to 1d, photoconductors 2a to 2d, which are image carriers, are arranged, respectively. In the present embodiment, the photoreceptors 2a to 2d have a photosensitive layer on a drum base such as aluminum, and are driven to rotate at a predetermined peripheral speed by a driving device. Around the photoreceptors 2a to 2d, charging rollers 3a to 3d for charging the surfaces of the photoreceptors 2a to 2d to a uniform potential are arranged. The exposure devices 7a to 7d respectively scan the corresponding photoreceptors 2a to 2d with light to form electrostatic latent images on the surfaces of the photoreceptors 2a to 2d. Each of the developing devices 4a to 4d has a corresponding color toner (developer), and develops the electrostatic latent images formed on the surfaces of the photoconductors 2a to 2d with the developing bias with the toner, thereby developing the toner image (developer). Image).

As an example, the surface potentials of the photoreceptors 2a to 2d are charged to −500 V by the corresponding charging rollers 3a to 3d, respectively. As an example, the surface potential of the photoreceptors 2a to 2d exposed by the exposure devices 7a to 7d is -100V. As an example, the developing bias can be set to −500V. Further, the peripheral speed of the photosensitive members 2a to 2d is set to 50 mm / second, the image forming width in the main scanning direction is set to 215 mm, the charge amount of the toner is set to −40 μC / g, and the solid portion of the image formed on the photosensitive members 2a to 2d The toner amount can be 0.4 mg / cm ² .

An endless intermediate transfer belt 8 that is an intermediate transfer member is installed at the opposing position of each of the image forming units 1a to 1d. Opposing members 5a to 5d are provided at positions facing the respective image forming units 1a to 1d via the intermediate transfer belt 8, and constitute a primary transfer unit. In the present embodiment, the opposing members 5a to 5d are configured to be electrically floated without applying a primary transfer voltage, that is, a transfer bias. The toner images formed on the photoreceptors 2 a to 2 d are transferred to the intermediate transfer belt 8 at a transfer position that is a nip portion between the photoreceptors 2 a to 2 d and the intermediate transfer belt 8. Note that toner remaining on the photoreceptors 2a to 2d without being transferred to the intermediate transfer belt 8 is removed by the cleaning devices 10a to 10d. The intermediate transfer belt 8 is stretched by a stretching member including a drive roller 11, a secondary transfer counter roller 12 and a tension roller 13, and is rotated (moved) in the direction of the arrow in the drawing as the drive roller 11 rotates. Hereinafter, the rotation direction of the intermediate transfer belt 8 is referred to as a circumferential direction of the intermediate transfer belt 8. The driving roller 11 is provided with a high friction rubber layer on the surface layer for driving the intermediate transfer belt 8. The volume resistivity of the rubber layer can be, for example, 10 ⁵ Ωcm or less. The secondary transfer counter roller 12 is in contact with the secondary transfer roller 15 via the intermediate transfer belt 8 to form a secondary transfer portion. The secondary transfer counter roller 12 has a rubber layer as a surface layer. The volume resistivity of the rubber layer can be, for example, 10 ⁵ Ωcm or less. The tension roller 13, which is a metal roller, applies a tension of about 60 N to the intermediate transfer belt 8 and is rotated by being driven by the intermediate transfer belt 8. In the secondary transfer portion, the toner image on the intermediate transfer belt 8 is transferred to the recording material conveyed through the conveyance path 18 by the secondary transfer bias applied by the secondary transfer roller 15. The driving roller 11, the secondary transfer counter roller 12 and the tension roller 13 are grounded via a Zener diode 14 and a current detector 39 which is an ammeter. The current value detected by the current detection unit 39 is converted from analog to digital and output to the control unit 100 of FIG.

For example, the secondary transfer roller 15 can be an elastic roller having a volume resistivity of 10 ⁷ to 10 ⁹ Ωcm and a rubber hardness of 30 ° (Asker C hardness meter). Further, the secondary transfer roller 15 may be configured to rotate following the rotation of the intermediate transfer belt 8 and to press the secondary transfer counter roller 12 via the intermediate transfer belt 8 at about 39.2N. it can. The transfer power supply 19 outputs a voltage of −2.0 to +7.0 kV in order to supply the secondary transfer bias applied by the secondary transfer roller. The transfer power source 19 also operates as a current supply unit for supplying a current that flows in the circumferential direction of the intermediate transfer belt 8.

  Outside the intermediate transfer belt 8, a belt cleaning device 75 that removes and collects transfer residual toner remaining on the surface of the intermediate transfer belt 8 is installed. Further, a fixing device including a fixing roller 17a and a pressure roller 17b for fixing the toner image transferred to the recording material to the recording material is installed on the downstream side of the secondary transfer portion of the conveyance path 18. .

  FIG. 2 shows a control configuration of the image forming apparatus according to the present embodiment. The control unit 100 is for controlling the image forming apparatus shown in FIG. 1 and includes, for example, a CPU that executes a program stored in the storage unit 40. The image formation control unit 101 performs control to form a detection image for registration (to be described later) and an image to be printed, and the correction control unit 102 performs registration such as color misregistration correction. The image forming control unit 101 and the correction control unit 102 are realized by a CPU that executes an appropriate program, that is, realized by software, hardware, or a combination of software and hardware. You can also.

  The intermediate transfer belt 8 shown in FIG. 1 can have, for example, a base layer in which electric resistance is adjusted by dispersing carbon in a polyphenylene sulfide (PPS) resin having a thickness of 100 μm. Here, the difference between the conventional intermediate transfer belt and the intermediate transfer belt 8 of the present embodiment will be described. The conventional intermediate transfer belt corresponds to the opposing members 5a to 5d of the present embodiment, and the primary transfer roller transfers the toner images formed on the photoreceptors 2a to 2d to the intermediate transfer belt, that is, the primary transfer roller. Even if a bias is applied, it is configured not to interfere. That is, in the conventional intermediate transfer belt, the volume resistance and the surface resistance are increased so that almost no current flows in the circumferential direction. On the other hand, the intermediate transfer belt 8 in the present embodiment has conductivity, and a predetermined current flows in the circumferential direction. Hereinafter, the conventional intermediate transfer belt is referred to as a high resistance belt, and the intermediate transfer belt 8 of the present embodiment is referred to as a conductive belt.

  Hereinafter, the electrical resistance of the high resistance belt and the conductive belt will be described. Volume resistivity and surface resistivity were measured for each intermediate transfer belt using a resistivity meter. The surface resistivity is the resistance of the outer surface of the belt. Here, in the high resistance belt, if a voltage of 100 V or higher is not applied, the current value becomes too small to be measured, so measurement was performed with an applied voltage of 100 V. On the other hand, in the conductive belt in this embodiment, the resistance of the belt is low, and when 100V is applied, the current value becomes too large to be measured, so that the applied voltage is set to 10V. As a result of the measurement, the high resistivity belt had a volume resistivity of 1.0E10 (Ωcm) when 100 V was applied, and a surface resistivity of 1.0E10 (Ω / □). On the other hand, the conductive belt has a volume resistivity of 2.5E12 (Ωcm) when 10 V is applied, an outer surface resistivity of 5.0E12 (Ω / □), and an inner surface resistivity of 1.0E6. (Ω / □).

  FIG. 3 shows another method for measuring the resistance value of the intermediate transfer belt 8. In the configuration of FIG. 3, when a constant voltage is applied to the intermediate transfer belt 8 from the transfer power source 19 of the secondary transfer unit, the current flowing to the ammeter connected to the photosensitive drum 2d of the image forming unit 1d is detected and The electric resistance of the intermediate transfer belt is obtained. The image forming units 1a, 1b, and 1c are removed so that a current flows only through the photosensitive member 2d. Further, in order to eliminate the influence of the resistance other than the intermediate transfer belt 8, the secondary transfer roller 15 and the photoreceptor 2d are made of only metal. In this example, the distance between the secondary transfer portion and the photosensitive member 2 d is 370 mm in the path on the upper surface side of the intermediate transfer belt 8 and 420 mm in the path on the lower surface side of the intermediate transfer belt 8. FIG. 4A shows the relationship between the voltage applied by the transfer power source 19 and the resistance value of the conductive belt. In this measurement method, since the resistance in the circumferential direction of the intermediate transfer belt 8 is measured, it is referred to as circumferential resistance. From FIG. 4A, it can be seen that the resistance tends to decrease little by little as the applied voltage is increased. This is a characteristic of a belt in which carbon is dispersed in a resin.

  FIG. 4B is a diagram in which the horizontal axis is an applied voltage and the vertical axis is a current value flowing through the photoreceptor 2d in the same measurement method. In addition, as shown in FIG.4 (b), even if it applied 2000V in the high resistance belt which is a comparative example, the electric current did not flow. Therefore, the conventional high resistance belt does not interfere even if the primary transfer bias for transferring the toner images of the respective colors to the intermediate transfer belt is applied in parallel to the high resistance belt. Instead, in the conventional high resistance belt, it is not possible to maintain the surface of the intermediate transfer belt 8 at substantially the same potential by passing a current in the circumferential direction of the intermediate transfer belt 8 with a single power source, unlike the conductive belt. . For example, a current of 100 μA or more flows through the conductive belt used in this embodiment at an applied voltage of 500 V or less. Therefore, it is possible to maintain the surface of the intermediate transfer belt 8 at substantially the same potential by flowing current in the circumferential direction of the intermediate transfer belt 8 with one power source.

  Next, primary transfer in the present embodiment will be described with reference to FIG. FIG. 5A is an explanatory diagram of the potential relationship of the primary transfer portion. The surface potential of the photoconductors 2a to 2d in this example is, for example, −500V in a dark part that is not exposed and −100V in a light part that is exposed. Further, as shown in FIG. 5A, the potential of the intermediate transfer belt 8 is set to + 200V. The toner having the charge amount q on the photoconductors 2 a to 2 d receives a force F in the direction of the intermediate transfer belt 8 by the electric field E formed by the potential difference between the potential of the photoconductors 2 a to 2 d and the intermediate transfer belt 8. Next transferred.

  FIG. 5B is an explanatory diagram of multiple transfer. The multiple transfer is a primary transfer in which a toner of another color is superimposed on a toner of a certain color that is primarily transferred to the intermediate transfer belt 8. In FIG. 5B, the toner is negatively charged, and the toner surface potential of the intermediate transfer belt 8 is +150 V due to the already transferred toner. In this case, the toner on the photoreceptors 2 a to 2 d is subjected to a force F ′ in the direction of the intermediate transfer belt 8 by an electric field E ′ formed by a potential difference between the potential of the photoreceptors 2 a to 2 d and the surface potential of the toner on the intermediate transfer belt 8. The primary transfer is received.

  FIG. 5C shows a state where multiple transfer has been completed. As described above, the primary transfer of the toner is related to the charge amount of the toner and the potential difference between the photoreceptors 2a to 2d and the intermediate transfer belt 8, and the intermediate transfer belt 8 is used to perform the primary transfer. It is necessary to set the potential of the current to a predetermined value or more.

  FIG. 5D is a graph plotting the potential of the intermediate transfer belt on the horizontal axis and the transfer efficiency on the vertical axis. The transfer efficiency is an index of transferability, and in this example, the ratio of the toner amount transferred to the intermediate transfer belt 8 to the toner amount of the toner image developed on the photoreceptors 2a to 2d is expressed as a percentage. It is said. For example, normally, if the transfer efficiency is 95% or more, it can be determined that the transfer has been completed without any problem. From the graph of FIG. 5D, when the potential of the intermediate transfer belt 8 is 200V, the transfer efficiency is about 95%, and when the potential of the intermediate transfer belt 8 is 220V, the transfer efficiency is about 98%. . At this time, the potential difference between each of the photoreceptors 2a to 2d and the potential difference between the intermediate transfer belt 8 are all the same. In other words, 300 V, which is the difference between −100 V that is the potential of the photoconductor and +200 V that is the potential of the intermediate transfer belt 8, is a transfer contrast potential necessary for each primary transfer portion.

  Next, secondary transfer in the present embodiment will be described. In the secondary transfer, similarly to the primary transfer, the toner on the intermediate transfer belt 8 is moved onto the recording material by the Coulomb force. FIG. 6 shows the relationship between the secondary transfer bias and the potential of the intermediate transfer belt 8 in this embodiment. A dotted line A in FIG. 6 is a Zener potential of the Zener diode 14. A range B in FIG. 6 is a setting range of the secondary transfer bias. Thus, in the present embodiment, for example, the Zener potential of the Zener diode 14 is set to a potential necessary for the intermediate transfer belt 8 for primary transfer, and the secondary transfer bias is set so that the potential of the intermediate transfer belt 8 is Zener. It can be set within a range where the potential is obtained. By applying the secondary transfer bias in this manner, primary transfer and secondary transfer can be performed without providing a separate bias supply source in the primary transfer portion.

  As shown in FIG. 1, in this embodiment, the driving roller 11, the secondary transfer counter roller 12, and the tension roller 13 are grounded via a Zener diode 14 and a current detection unit 39. Therefore, when the potential applied to the intermediate transfer belt 8 exceeds the zener potential, a current flows, and the potential of the intermediate transfer belt 8 is kept at the zener potential. That is, even if the secondary transfer bias is increased, the potential of the intermediate transfer belt 8 does not rise above the Zener potential, and the Zener diode 14 operates as a voltage maintaining unit. By keeping the potential of the intermediate transfer belt 8 constant by such a method, the primary transfer property can be stabilized. Further, the setting range of the secondary transfer bias is wide, and the degree of freedom of setting is also large. For example, the Zener potential can be set to +200 V or more in consideration of environmental influences. With this configuration, it is possible to optimize the secondary transfer setting independently of the primary transfer while stabilizing the primary transfer property.

  As described above, in this embodiment, for example, the photoreceptors 2a to 2d are charged to -500V (dark part) by the charging rollers 3a to 3d, and the potential of the intermediate transfer belt 8 is maintained at + 200V. Therefore, the potential difference between the dark portions of the photoreceptors 2a to 2d and the surface of the intermediate transfer belt 8 is 700V. Here, since the discharge start voltage in a normal environment (1 atm) is about 600 V, when the dark part of the photoconductors 2a to 2d approaches the intermediate transfer belt 8 to a dischargeable distance, discharge occurs, and the photoconductor. Negative charges 2 a to 2 d move to the intermediate transfer belt 8. However, for example, when a toner image is present on the intermediate transfer belt 8 and the potential of the toner on the intermediate transfer belt 8 is lowered by 150 V on the surface of the intermediate transfer belt 8, the potential difference from the bright portions of the photoreceptors 2a to 2d. Becomes 550V and no discharge occurs. The same applies to the case where toner images are present not on the intermediate transfer belt 8 but on the photoreceptors 2a to 2d. As described above, the discharge current fluctuates depending on the potential difference between the photoconductors 2a to 2d and the intermediate transfer belt 8 depending on the presence or absence of the toner image on the photoconductors 2a to 2d or the intermediate transfer belt 8, and passes through the primary transfer portion. It is possible to detect the timing and distribution of toner. In the present embodiment, a current detector 39 shown in FIG. 1 is provided to detect this current fluctuation. As shown in FIG. 1, in this embodiment, it is not necessary to provide the current detection unit 39 for each image forming unit, and by providing one between the intermediate transfer belt 8 and the ground, the photoconductors 2a to 2d are provided. The current flowing between the intermediate transfer belt 8 can be detected.

  7 and 8 illustrate a case where a toner image including a plurality of lines in the main scanning direction formed on the intermediate transfer belt 8 by the image forming unit 1a passes through the primary transfer unit of the most downstream image forming unit 1d. It is a graph which shows the fluctuation | variation of the electric current which the electric current detection part 39 detects. The discharge current from the photoreceptor 2d is detected by the current detection unit 39 when it flows to the ground via the intermediate transfer belt 8 and the rollers 11, 12, 13 for stretching the intermediate transfer belt 8. 7 and FIG. 8 shows the formed toner image for reference at the top of the current waveform. As shown in FIG. 7, when there is no toner image (toner layer) on the intermediate transfer belt 8, the value of the discharge current is about 20 μA on average, and the error fluctuation amount including variation is about 2 μA. When the toner image passes through the primary transfer portion, the potential difference between the photosensitive member 2d and the intermediate transfer belt 8 is reduced below the discharge start voltage due to the potential of the toner layer, and the current amount is reduced to about 2 μA. The current value varies depending on the thickness and potential of the photosensitive members 2a to 2d and the intermediate transfer belt 8, but in the example of FIG. It can be seen that it is sufficient to detect the timing of passing through the next transfer portion. FIG. 8 shows a case where a conventional high resistance belt is used, and it can be seen that it is difficult to detect the passage of the toner image from the change in the current.

<Registration>
Subsequently, registration according to the present embodiment, that is, detection and adjustment of the color misregistration amount will be described. Registration, as described above, corrects the relative misalignment of each toner image that occurs when the toner images of the respective colors formed by the image forming units 1a to 1d are transferred to the intermediate transfer belt 8. It is. It should be noted that the components of the positional deviation can be roughly divided into three types: (1) inclination deviation with respect to the main scanning direction, (2) deviation in the sub-scanning direction, and (3) deviation in the main scanning direction. it can.

<(1) Deviation of tilt with respect to main scanning direction>
The deviation of the inclination with respect to the main scanning direction is a deviation of the angle of the image with respect to the direction orthogonal to the moving direction of the intermediate transfer belt 8. The deviation of the inclination with respect to the main scanning direction is mainly caused by a positional deviation at the time of assembling the optical system or an optical path deviation due to the thermal expansion of the optical system accompanying the temperature rise of the main body. Therefore, other than the initial adjustment, it is often performed under conditions of temperature relationship and operation time, such as when the temperature of the fixing device exceeds a certain value or when the printing time exceeds a certain time. A specific procedure for correcting the deviation of the inclination with respect to the main scanning direction will be described below.

  In S <b> 1 of FIG. 9, the image forming unit 1 a forms a detection image for registration on the intermediate transfer belt 8 under the control of the control unit 100. As shown in the upper part of FIG. 10, the detection image for correction (first detection image) includes five lines whose directions are different from each other in this embodiment. The line length can be made equal to the maximum image width in the sub-scanning direction. In the example of FIG. 10, one line has its right end inclined in the positive direction by a width of two lines in the sub-scanning direction with respect to its left end. Note that the positive direction is the moving direction of the intermediate transfer belt 8 in the present embodiment. Also, one line has its right end inclined by a width of one line in the positive direction with respect to the sub-scanning direction, one line is also inclined by a width of one line in the negative direction, and one line is also negative It is inclined in the direction by the width of two lines. Further, one line has no inclination in the sub-scanning direction and is a line in the main scanning direction. In FIG. 10, the inclination is displayed on each line. Note that the inclination here is an inclination to be formed by the image forming unit 1a, and is not a result of adding the inclination of the actually formed line. For example, the middle line of the five lines shown in FIG. 10 is formed in the same direction as the main scanning direction of the image forming unit 1a, but the actually formed line has an inclination with respect to the main scanning direction. Can be a thing.

  Returning to FIG. 9, in S <b> 2, the control unit 100 detects the value of the discharge current when the formed detection image passes through the primary transfer unit of the image forming unit 1 d by the current detection unit 39. The control unit 100 stores the detected current value in the storage unit 40 illustrated in FIG. The lower part of FIG. 10 is a graph of the current values recorded in the storage unit 40. The position of the current graph is aligned with the passage time of the primary transfer portion of the detection image line shown in the upper part of FIG. Note that Is (k) in FIG. 10 is a current value when a line having an inclination k passes through the primary transfer unit of the image forming unit 1d.

  In the present embodiment, the higher the parallelism between the detected image line and the primary transfer portion of the image forming portion 1d, the greater the change in the discharge current when passing through the line. This is because the higher the degree of parallelism, the longer the range of simultaneous discharge in the sub-scanning direction. In FIG. 10, the change in the discharge current when the line with the slope 0 passes is the largest. This indicates that the inclination of the image formed by the image forming unit 1a with respect to the main scanning direction is very small when the direction of the primary transfer unit of the image forming unit 1d is set as the main scanning direction. On the other hand, for example, when the change in the discharge current is largest when the inclination is +1, this is because the image forming unit 1a forms an image when the image is inclined by +1 with respect to the main scanning direction. It shows that the inclination with respect to the main scanning direction with respect to the portion 1d is the smallest. In other words, the amount of inclination of the image formed by the image forming unit 1a with respect to the direction of the primary transfer unit of the image forming unit 1d, which is the reference direction, is determined, and thus the deviation is corrected by forming the image so as to cancel this inclination. be able to. The control unit 100 determines the line with the largest change in the discharge current in S3 of FIG. 9, determines the correction amount in S4, and controls the image forming unit 1a so as to reduce the inclination amount. Further, the control unit 100 performs the processing of FIG. 9 on the other image forming units 1b, 1c, and 1d, and thereby, the inclination of all the image forming units 1a to 1d with respect to the main scanning direction is changed. Correction is performed by approaching the direction of the primary transfer portion of the forming portion 1d.

<(2) Deviation in sub-scanning direction>
The shift in the sub-scanning direction is a positional shift of the image in the moving direction of the intermediate transfer belt 8. Since the photosensitive members 2a to 2d are rigid bodies, the moving speed is basically constant, but the sub-scanning is caused by the speed fluctuation due to the eccentricity of the driving roller 11 that stretches the intermediate transfer belt 8 from the inside. Directional image shift occurs. A specific procedure for correcting the shift in the sub-scanning direction will be described. The detection image for correcting the deviation in the sub-scanning direction includes one line whose length is equal to the maximum writing width in the main scanning direction in the main scanning direction, that is, the direction orthogonal to the sub-scanning direction. It is an image.

  In S11 of FIG. 11, the control unit 100 forms an electrostatic latent image to form a correction detection image (second detection image) on the photoreceptor 2a of the image forming unit 1a on the most upstream side, The time Ta0 is stored. Here, upstream and downstream are based on the moving direction of the surface of the intermediate transfer belt 8. Thereafter, in S12, the control unit 100 develops the electrostatic latent image with yellow toner by the developing device 4a. The formed yellow detection image reaches the primary transfer portion of the image forming portion 1a in S13 and is transferred to the intermediate transfer belt 8. The control unit 100 detects and stores this time Ta1 based on the change in the discharge current. Thereafter, the detected images transferred to the intermediate transfer belt 8 reach the primary transfer portions of the image forming units 1b, 1c, and 1d in S14, S15, and S16, respectively, and the control unit 100 determines the time Ta2, Save Ta3 and Ta4 respectively.

  In S <b> 17, the control unit 100 calculates the difference between the time Ta <b> 0 and the times Ta <b> 1 to Ta <b> 4, and obtains and corrects the shift amount in the sub-scanning direction with respect to the reference image forming unit. Note that the amount of color misregistration in the sub-scanning direction is the time when the detected image reaches the primary transfer portion of one of the image forming portions serving as a reference, and the detected image reaches the primary transfer portion of the image forming portion to be corrected. It can also be obtained as a difference from the time to be. FIG. 12 shows the relationship between the electrostatic latent image formation timing in the image forming section 1a, that is, the exposure timing, and the time variation of the current detected by the current detection section 39. In the present embodiment, the detection image is formed in the image forming unit 1a at the most upstream. This is because correction is performed on all image forming units by forming the detected image once. However, when the image forming unit to be corrected is specified, any image forming unit upstream from the image forming unit can form the detected image.

<(3) Deviation in main scanning direction>
The deviation in the main scanning direction is a position deviation of the image in the main scanning direction orthogonal to the moving direction of the intermediate transfer belt 8. This also occurs mainly due to a positional shift at the time of assembling the optical system, an optical shift due to thermal expansion of the optical system accompanying a temperature rise of the main body, and the like, similar to the shift in the sub-scanning direction. Hereinafter, a specific procedure for correcting a shift in the main scanning direction will be described. In order to correct a deviation in the main scanning direction, the image forming units 1a to 1c to be corrected include detections for correction including a plurality of broken lines (dotted lines) parallel to the main scanning direction and equivalent to the maximum writing width. An image (third detected image) is formed. In addition, the image forming units 1a to 1c to be corrected form a detected image by shifting a plurality of broken lines with their formation start positions one dot at a time. In addition, the image forming unit 1d located on the most downstream side as a reference in this example forms a detection image (fourth detection image) including a plurality of broken lines with the same writing start point. It should be noted that the number of broken lines in the detection image formed by the image forming units 1a to 1c to be corrected and the reference image forming unit 1d is the same, and the length of the solid line portion of the broken line and the portion where there is no line. Same length. In the following description, it is assumed that the broken line is a solid line corresponding to the length of 5 dots and a gap corresponding to the length of 5 dots alternately arranged, and the image forming unit to be corrected sets the writing start position to 1 dot. It is assumed that five lines shifted from each other are formed.

  After correcting the inclination with respect to the main scanning direction and the deviation in the sub-scanning direction already described, the control unit 100 controls the image forming unit to be corrected, for example, the image forming unit 1a in S21 of FIG. The detected image including the five broken lines is formed on the intermediate transfer belt 8. Thereafter, the control unit 100 waits for a predetermined time in S22, and in S23, controls the image forming unit 1d as a reference to form a detection image including five broken lines so as to be transferred to the intermediate transfer belt 8. Note that the standby time in S22 is the time when each broken line transferred by the image forming unit 1a to the intermediate transfer belt 8 reaches the primary transfer unit of the image forming unit 1d and each of the photosensitive members 2d formed in the image forming unit 1d. The time when the broken line reaches the primary transfer portion of the image forming portion 1d is set to coincide with the time. That is, each detection image is formed such that each broken line formed by the image forming unit to be corrected and each broken line formed by the reference image forming unit 1d are overlapped in the primary transfer unit of the image forming unit 1d. .

  The control unit 100 stores the current value detected by the current detection unit 39 in the storage unit 40 in S24. FIG. 14 is a graph of current values stored in the storage unit 40. In the upper part of FIG. 14, five broken lines formed by the image forming unit 1a and five broken lines formed by the image forming unit 1d are shown together with their numbers. Since the color misregistration control in the sub-scanning direction has already been performed, the five broken lines formed by the image forming unit 1a and the image forming unit 1d almost overlap each other. However, in FIG. 14, the broken line formed by the image forming unit 1 d is displayed shifted to the right with respect to the broken line formed by the image forming unit 1 a in order to make the drawing easier to see.

  As described above, the image forming unit 1d forms five broken lines at the same writing position, and the image forming unit 1a changes the writing position to form five broken lines. Different for each broken line. For example, in FIG. 14, the position of the gap between the third broken line and the third broken line is substantially the same, and the second and fourth broken lines are larger than the third broken line. The broken line is the largest. As the overlapping of the position of the broken line formed by the image forming unit 1a and the solid line part of the broken line formed by the image forming unit 1d increases, the discharge region becomes smaller. Therefore, as shown in the lower part of FIG. Get smaller. That is, the shift amount with respect to the image forming unit 1d serving as the reference in the main scanning direction can be obtained based on the timing when the broken line with the smallest change in the discharge current is formed. In FIG. 14, If (k) is a current value when the kth broken line passes through the primary transfer portion of the image forming portion 1d. In S25, the control unit 100 determines a color shift amount based on the writing position in the main scanning direction when the broken line with the smallest change in discharge current is formed in the image forming unit to be corrected. In S26, the control unit 100 determines the shift amount. The image forming unit is set so as to correct.

  As described above, in the image forming apparatus according to the present embodiment, by using the conductive belt, it is possible to correct the inclination with respect to the main scanning direction, the deviation in the sub-scanning direction, and the main scanning direction, and suppress the correction error of the color deviation. it can.

[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, etc.) of the system or apparatus reads the program. It is a process to be executed.

Claims (13)

A conductive image carrier that is driven to rotate;
A plurality of image forming means including a photoreceptor, forming a developer image on the photoreceptor, and transferring the developer image formed on the photoreceptor to the image carrier at a transfer position;
Applying means for applying a voltage to the image carrier;
Detection means for detecting a current flowing between the photoconductor and the image carrier;
A correction unit that forms a detection image for color misregistration correction on the photoconductor and performs color misregistration correction by a change in current detected by the detection unit;
An image forming apparatus comprising:   The correction unit forms a first detection image including a plurality of lines having different inclinations with respect to the main scanning direction on the image forming unit to be corrected in order to correct the inclination of the developer image with respect to the main scanning direction. The image forming apparatus according to claim 1, wherein the image forming apparatus is transferred to an image carrier.   The correction unit is a developer image formed by the image forming unit to be corrected by a change in current detected by the detection unit while the first detection image passes through the transfer position of the image forming unit serving as a reference. The image forming apparatus according to claim 2, wherein a tilt with respect to the main scanning direction is corrected.   The correction unit determines, for each line of the first detection image, a change in current detected by the detection unit when the first detection image passes through the transfer position of the reference image forming unit. The image forming apparatus according to claim 3, wherein the amount of inclination of the developer image formed by the image forming unit to be corrected with respect to the main scanning direction is determined.   The correction unit forms a second detection image including a line in the main scanning direction on one of the plurality of image forming units and transfers the second detection image to the image carrier, and the second detection image is The time for reaching the transfer position of the image forming means on the downstream side in the rotation direction of the image carrier from the position where the second detection image is transferred is detected from the change in the current of the detection means, and the second The developer image formed by the remaining image forming means with respect to the developer image formed by the image forming means serving as a reference among the image forming means for transferring the detection image to the image carrier and the image forming means on the downstream side. The image forming apparatus according to claim 1, wherein a shift in the sub-scanning direction is corrected.   The image forming apparatus according to claim 5, wherein the second detection image is formed by an image forming unit on a most upstream side in a rotation direction of the image carrier.   The correction unit forms a third detection image including a plurality of broken lines having different formation start positions in the main scanning direction on the image forming unit to be corrected in order to correct a deviation in the main scanning direction of the developer image. And a fourth detection image including a plurality of broken lines having the same formation start position in the main scanning direction is formed on a reference image forming unit and transferred to the image carrier. The image forming apparatus according to any one of claims 1 to 6.   The correction unit detects the third detection so that each broken line of the third detection image and a position of each broken line of the fourth detection image overlap each other at the transfer position of the reference image forming unit. An image and the fourth detection image are formed on the correction target image forming unit and the reference image forming unit, and the third detection image passes through the transfer position of the reference image forming unit. The image forming apparatus according to claim 7, wherein a deviation in a main scanning direction of a developer image formed by the image forming unit to be corrected is corrected by a change in current detected by the detecting unit.   The correction unit determines, for each broken line of the third detection image, a change in current detected by the detection unit when the third detection image passes through the transfer position of the reference image forming unit. The image forming apparatus according to claim 8, wherein an amount of deviation in a main scanning direction of a developer image formed by the image forming unit to be corrected is determined.   The image forming apparatus according to claim 1, wherein the correction unit corrects the deviation in the main scanning direction after correcting the inclination with respect to the main scanning direction and the deviation in the sub-scanning direction. . Voltage maintaining means for maintaining the potential of the image carrier at a predetermined potential;
11. The developer image formed on the photosensitive member by the image forming unit is transferred to the image bearing member by a potential difference between the potential of the photosensitive member and the image bearing member. The image forming apparatus according to claim 1.   When the surface of the photoconductor is not covered with the developer, a discharge occurs between the photoconductor and the image carrier, and the surface of the photoconductor is covered with the developer. The image forming apparatus according to claim 11, wherein the potential is such that no discharge occurs between the photosensitive member and the image carrier.   The image forming apparatus according to claim 1, wherein the detection unit is provided between the image carrier and ground.

Images