JP4438484B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that forms an image by scanning an image carrier with a light beam.

  2. Description of the Related Art Conventionally, a tandem type image forming apparatus that includes a plurality of image carriers that are scanned and exposed by a light beam such as a laser beam and forms a color image is known.

  In such an image forming apparatus, it is necessary to form an image on an image carrier and to transfer the image to a recording medium with accuracy for each color so as not to cause a tilt or color shift of the color image. For this reason, a method is known in which a mark for correcting deviation (hereinafter referred to as a “registon mark”) is transferred to a transfer belt, a recording medium or the like, and the position of the transferred resister mark is read to perform correction (see FIG. For example, see Patent Document 1, Patent Document 2, and Patent Document 3.)

  According to this technology, with the position based on the rotation of the image carrier and the start of conveyance of the conveyance belt as a reference, the position of the transferred registration mark is read by the light detection unit, and the amount of deviation from the predetermined specified position is determined. To detect. Furthermore, the deviation from the specified position is corrected by changing the exposure timing of the image carrier based on the detected deviation amount. As this light detection unit, a CCD sensor is used in Patent Document 1, a photo interrupter is used in Patent Document 2, and an optical Doppler device is used in Patent Document 3.

  However, in the above technique, since the position of the transferred regicon mark is read by a photodetection unit such as a CCD sensor, a photo interrupter, or an optical Doppler device, the reading accuracy of the position of the regicon mark may be reduced due to contamination of the photodetection unit. was there.

  Therefore, in order to solve the above technique, a technique for electrically detecting the position of the registration control mark is known (see, for example, Patent Document 4).

According to the technique of Patent Document 4, a conductive portion made of a conductive material is provided on a part of the conveyance belt, and a predetermined color misregistration adjustment is provided on each of the positions facing the conductive portions on a plurality of image carriers. An electrostatic latent image of a pattern is formed, and the movement of charges from the image carrier to the conductive portion of the conveyor belt is detected. Then, the time when the movement of the charge with reference to the rotation start time of the image carrier is detected as the position of each registration control mark.
JP-A-7-32656 Japanese Patent Laid-Open No. 7-104547 JP-A-7-229911 Japanese Patent Laid-Open No. 10-123791

  However, in the technique of Patent Document 4, since it is necessary to separately provide a conductive portion on the conveyor belt, there is a possibility that the enlargement of the image forming apparatus becomes a problem due to the formation of the conductive portion. In any of the techniques disclosed in Patent Documents 1 to 4, the position of the registration control mark is detected with reference to the position based on the rotation of the image carrier and the start of conveyance of the conveyor belt, so the image carrier is rotated. In consideration of the individual difference in the rotation response for the rotation motor and the conveyance roller activation response for conveying the conveyance belt, an error may occur in the reference position.

  The present invention has been made to solve the above-described problems. With a simple configuration, the skew amount indicating the inclination of the image formed on the image carrier with respect to the direction of the axis of the image carrier is accurately obtained. An object of the present invention is to provide an image forming apparatus that can be obtained.

An image forming apparatus according to the present invention includes a light beam scanning unit that scans a light beam in a main scanning direction, and a scanning exposure in the main scanning direction by the light beam scanning unit in a precharged state, and a sub-scanning direction. and control means for controlling said light beam scanning means such that the image bearing member is rotated at a predetermined speed, a long pattern image in the main scanning direction is formed on the image bearing member to be scanned exposing the A current value detecting means for detecting a current value flowing between the image carrier and a precharged transfer means for transferring the pattern image formed on the image carrier to a transfer body; The time required for the current value detected by the value detection means to return to the current value before the start of transfer after the current value before the transfer of the pattern image to the transfer body changes is changed to the pattern image. Of the above Detection means for detecting a time from the start of transcription of the body to the end transfer, in the state skew is not showing the inclination of the pattern image formed on the image bearing member relative to the axis direction of the image carrier, the pattern Based on the difference between the reference time and the storage means that stores in advance the time from the start of transfer of the image to the end of transfer as a reference time, and the time from the start of transfer of the pattern image to the end of transfer detected by the detection means Calculating means for calculating a value indicating the skew.

  The light beam scanning unit of the image forming apparatus of the present invention scans the light beam in the main scanning direction based on the image data. The image carrier is uniformly charged in advance, and in the charged state, the image carrier is scanned and exposed in the main scanning direction by the light beam scanning unit. The image carrier is scanned and exposed in the sub-scanning direction by the light beam scanning unit by rotating at a predetermined speed in the sub-scanning direction. The control means controls the light beam scanning means so that a pattern image long in the main scanning direction is formed on the image carrier by the light beam scanning means. Therefore, a long pattern image in the main scanning direction is formed on the image carrier by the light beam scanning unit. When the pattern image on the image carrier reaches the transfer position, the transfer means charged in advance transfers the pattern image formed on the image carrier. The pattern image is transferred to an object to be transferred such as an intermediate body, a conveyor belt, or a recording medium on the conveyor belt.

The detection means is the time required for the current value detected by the current value detection means to change from the current value before the transfer of the pattern image to the transfer target to the current value before the transfer starts. This is detected as the time from the start of transfer of the pattern image to the transfer target to the end of transfer . The storage means stores in advance as a reference time the time from the start of transfer of the pattern image formed on the image carrier to the end of transfer so that there is no skew indicating the inclination of the image carrier relative to the axial direction.

  When the pattern image is formed in a state tilted in the axial direction of the image carrier, the time from the start of transfer of the pattern image formed on the image carrier to the end of transfer is not inclined on the image carrier. The value is larger than the time from the start of transfer to the end of transfer of the formed pattern image.

  The computing means includes a time from the start of transfer of the pattern image detected by the detecting means to the end of transfer, and a reference time indicating a time from the start of transfer of the pattern image to the end of transfer in a state where there is no skew stored in the storage means in advance. Based on the difference, a value indicating a skew indicating the inclination of the pattern image formed on the image carrier with respect to the axial direction of the image carrier is calculated.

  As described above, the image forming apparatus of the present invention stores in advance, as a reference time, the time from the start of transfer of the pattern image to the end of transfer in a state where there is no skew indicating the inclination of the image carrier with respect to the axial direction in the storage unit. When a pattern image long in the scanning direction is formed on the image carrier by scanning exposure in the main scanning direction and sub-scanning direction by the light beam scanning means, and the pattern image formed on the image carrier is transferred by the transfer means The time from the start of transfer of the pattern image to the end of transfer is detected, and the difference between the detected time and the reference time is calculated as a value indicating the skew indicating the inclination of the pattern image with respect to the axial direction of the image carrier.

  Therefore, when the pattern image is transferred by the transfer means, the time from the start of transfer of the pattern image to the end of transfer is detected, and based on the difference from the reference time when there is no skew, the pattern image image carrier Since it is possible to calculate an inclination with respect to the axial direction, that is, a value indicating skew, it is possible to easily obtain a value indicating the inclination with respect to the axial direction of the image carrier of an image formed on the image carrier with a simple configuration. it can.

  Since the image carrier and the transfer unit are charged in advance, the value of the current flowing between the image carrier and the transfer unit changes when the pattern image is transferred. The current value fluctuates from the current value before transfer at the start of transfer, and returns to the current value before start of transfer at the end of transfer. The energy required to transfer the pattern image to the intermediate transfer member is the amount of change from the current value before the start of transfer and the time required for the current value before the start of transfer to return to the current value before the start of transfer. Is proportional to the product of For this reason, the smaller the amount of change from the current value before the start of transfer, the longer it takes to return from the current value before the start of transfer to the current value before the start of transfer. The larger the current value, the shorter the time required to return to the current value before the start of transfer after the current value has changed.

For this reason, the detection means returns to the current value before the transfer start after the current value detected by the current value detection means changes from the current value before the transfer of the pattern image to the transfer target. The time required until the transfer is detected as the time from the start of transfer of the pattern image to the end of transfer.

In this way, by detecting the time required to return from the current value before the transfer of the pattern image to the transfer target to the current value before the transfer starts, the transfer of the pattern image to the transfer end is detected. Therefore, the time from the start of pattern image transfer to the end of transfer can be easily detected with a simple configuration without considering the toner contamination of the transfer means.

The current value detection means of the detection means is provided integrally with the transfer means, and detects the current value flowing between the image carrier and the transfer means. When the current value is detected by the current value detection unit, the calculation unit performs the transfer after the current value detected by the current value detection unit has changed from the current value before the transfer of the pattern image to the transfer target. The time required to return to the current value before the start is detected as the time from the start of pattern image transfer to the end of transfer. As described above, since the current value detection unit can be provided integrally with the transfer unit, the current value flowing between the image carrier and the transfer unit can be detected with high accuracy, and the size of the main body of the image forming apparatus can be increased. Can be suppressed.

  The pattern image is a line image that is long in the main scanning direction. By making the pattern image a line image that is long in the main scanning direction, the inclination of the pattern image with respect to the axial direction of the image carrier can be accurately detected.

  The pattern image is formed at both ends in the axial direction of the image carrier. By forming a pattern image at both ends in the axial direction of the image carrier, that is, at both ends in the main scanning direction of the light beam scanning unit and in the axial direction of the image carrier, the pattern image with respect to the axial direction of the image carrier. The inclination can be detected with high accuracy.

The other image forming apparatus is provided corresponding to each of a plurality of light beam scanning means for scanning a light beam in the main scanning direction and the plurality of light beam scanning means, and the corresponding light in a state of being charged in advance. A plurality of image carriers that are scanned and exposed in the main scanning direction by the beam scanning means and rotated at a predetermined speed so as to be scanned and exposed in the sub-scanning direction, and a pattern image that is long in the main scanning direction are each color of the color image. Control means for controlling each of the plurality of light beam scanning means so as to be formed on each image carrier corresponding to a component, and provided for each of the plurality of image carriers , and the image carrier It has a current value detecting means for detecting a current flowing between the body and a plurality of transfer means for the pattern image formed on the image bearing member is previously charged is transferred to a transfer member, the current By value detection means The time required for the known current value to change from the current value before the start of transfer of the pattern image to the transfer target to return to the current value before the start of transfer is determined as the time required for the transfer of the pattern image to the transfer target. The detection means for detecting the time from the start of transfer to the body to the end of transfer, and the transfer of different values when the time from the start of transfer of the pattern image to the end of transfer detected by each of the detection means is not the same. Judging means for judging that the inclination of the pattern image formed on the image carrier corresponding to the time from the start to the end of transfer is different from the inclination of the pattern image formed on another image carrier; I have.

Another image forming apparatus includes a control unit, a plurality of light beam scanning units, and a plurality of image carriers, a plurality of transfer units, and a detection unit provided corresponding to each of the plurality of light beam scanning units. I have. The control means controls each of the plurality of light beam scanning means so that a pattern image corresponding to each color component of the color image is formed on each image carrier in the main scanning direction. The transfer unit includes a current value detection unit that detects a current value that is charged in advance and flows between the image carrier and the pattern image formed on the image carrier. For this reason, a pattern image long in the main scanning direction is formed on each image carrier. The detection means is the time required for the current value detected by the current value detection means to change from the current value before the transfer of the pattern image to the transfer target to the current value before the transfer starts. This is detected as the time from the start of transfer of the pattern image to the transfer target to the end of transfer . The judging means compares the time from the start of transfer to the end of transfer of the plurality of pattern images detected by the detecting means, and when the times are not the same, the pattern images formed on the image carrier at different times are obtained. It is determined that the inclination of the pattern image formed on the transferred image carrier is different from the inclination of the pattern image formed on another image carrier.

Thus, the plurality of image bearing members each, identical, to form a long pattern image in the main scanning direction, when the pattern image is transferred by the transfer means corresponding to the image carriers, to said transfer means The time required for the current value detected by the provided current value detecting means to change back from the current value before the transfer of the pattern image to the transfer target to the current value before the transfer is returned to the pattern. Detected as the time from the start of transfer to the transfer object to the transfer end , and based on the difference in the detected time, a tilted pattern image is formed among the pattern images formed on each image carrier The image carrier can be determined. For this reason, it is possible to determine an image carrier on which pattern images having different inclinations are formed among the pattern images formed between the plurality of image carriers with a simple configuration.

  According to the image forming apparatus of the present invention, the time from the start of transfer of the pattern image to the end of transfer in a state without skew indicating the inclination of the image carrier with respect to the axial direction is stored in advance as a reference time, and the pattern is long in the main scanning direction. The pattern image is transferred when the image is formed on the image carrier by scanning exposure in the main scanning direction and the sub-scanning direction by the light beam scanning unit, and the pattern image formed on the image carrier is transferred by the transfer unit. Since the time from the start to the end of transfer is detected, and the difference between the detected time and the reference time is calculated as a value indicating a skew indicating the inclination of the pattern image with respect to the axial direction of the image carrier, with a simple configuration, There is an effect that it is possible to easily obtain a value indicating the inclination of the image formed on the image carrier with respect to the axial direction of the image carrier.

  An embodiment of a tandem type color image forming apparatus according to an image forming apparatus of the present invention will be described with reference to the drawings.

  FIG. 1 shows the main configuration of an image forming apparatus 10 according to the present embodiment.

  The image forming apparatus 10 includes an intermediate transfer body 24 that is transported in the transport direction Y of the intermediate transfer body 24. The intermediate transfer member 24 is for electrostatically attracting the recording medium and transporting it in the transport direction Y. Further, the image forming apparatus 10 is arranged in a tandem shape from the upstream side to the downstream side along the transport direction Y of the intermediate transfer body 24, and the Y image forming unit 30Y, the M image forming unit 30M, and the C image forming unit. A unit 30C and a K image forming unit 30K are provided.

  The Y image forming unit 30Y, the M image forming unit 30M, the C image forming unit 30C, and the B image forming unit 30K respectively transfer a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image to an intermediate transfer member. Transfer to 24.

  The Y image forming unit 30Y includes a light beam scanning device 14Y, a charging device 18Y, an image carrier 20Y, a developing device 22Y, and a transfer device 26Y. Similar to the Y image forming unit 30Y, the M image forming unit 30M includes a light beam scanning device 14M, a charging device 18M, an image carrier 20M, a developing device 22M, and a transfer device 26M. The C image forming unit 30C includes a light beam scanning device 14C, a charging device 18C, an image carrier 20C, a developing device 22C, and a transfer device 26C. The K image forming unit 30K includes a light beam scanning device 14K, a charging device 18K, an image carrier 20K, a developing device 22K, and a transfer device 26K.

  In addition, the image forming apparatus 10 includes an image processing unit 12. The image processing unit 12 converts the input image data as a laser modulation signal for each of four colors (K (black), C (cyan), M (magenta), and Y (yellow)), and the light beam scanning device 14K. Output to the device 14C, the light beam scanning device 14M, and the light beam scanning device 14Y, respectively.

  The light beam scanning device 14Y includes a laser diode driver (hereinafter referred to as LDD) 16Y, modulates a light beam emitted from the LDD 16Y by a laser modulation signal output from the image processing unit 12, and controls the image carrier 20Y. Scan in the main scanning direction.

  The image carrier 20Y rotated at a predetermined speed in the rotation direction B of the image carrier is uniformly charged by the charging device 18Y and then scanned and exposed by the light beam scanning device 14Y. Specifically, the image carrier 20Y is scanned and exposed in the main scanning direction by the light beam scanning device 14Y and rotated at a predetermined speed so as to be scanned and exposed in the sub-scanning direction. Scan exposure in the direction. As a result, an electrostatic latent image corresponding to the yellow component image of the image data input to the image processing unit 12 is formed on the image carrier 20Y. The electrostatic latent image on the image carrier 20Y is developed by the developing machine 22Y, and then the toner image on the image carrier 20Y is transferred to the intermediate transfer member 24 by the transfer device 26Y.

  Each configuration included in each of the M image forming unit 30M, the C image forming unit 30C, and the K image forming unit 30K has the same function as each configuration included in the Y image forming unit 30Y.

  That is, in the M image forming unit 30M, the C image forming unit 30C, and the K image forming unit 30K, similarly to the Y image forming unit 30Y, each of the light beam scanning device 14M, the light beam scanning device 14C, and the light beam scanning device 14K. As a result, the image carrier 20M, the image carrier 20C, and the image carrier 20K are scanned and exposed in the main scanning direction and at the predetermined speed so as to be scanned and exposed in the sub-scanning direction. By rotating, scanning exposure is performed in the main scanning direction and the sub-scanning direction to form an electrostatic latent image. Further, the electrostatic latent images formed on the image carriers 20M, 20C, and 20K are developed by the developing machine 20M, the developing machine 20C, and the developing machine 20K, respectively. The magenta, cyan, and black toner images on the image carrier 20M, image carrier 20C, and image carrier 20K are transferred to the intermediate transfer member 24 by the corresponding transfer device 26M, transfer device 26C, and transfer device 26K. Sequentially transferred. In this way, a color image is formed on the intermediate transfer member 24.

  The light beam scanning by each of the light beam scanning device 14Y, the light beam scanning device 14M, the light beam scanning device 14C, and the light beam scanning device 14K depends on the conveyance speed of the intermediate transfer member 24, each image carrier 20Y, and the image carrier. The exposure is performed at intervals of a predetermined time determined according to the distance between the body 20M, the image carrier 20C, and the image carrier 20K. At this time, when the image data corresponding to each image carrier 20Y, image carrier 20M, image carrier 20C, and image carrier 20K is the same, it is formed on the intermediate transfer member 24 in an ideal state. The image formation position and the image inclination are the same. However, in practice, the mounting position shift of the optical components constituting each light beam scanning device, the error of the characteristics of the optical components, the mounting position shift of each light beam scanning device, the mounting position shift of each image carrier, Due to distortion or the like of the entire forming apparatus 10, the deviation between the main scanning direction of the light beam and the axial direction of the image carrier, the inclination between images formed on each image carrier, and the scanning of each image carrier. Misalignment may occur.

  Therefore, the image processing unit 12 calculates a value indicating the inclination of the pattern image formed on each of the plurality of image carriers with respect to the axial direction Z of the image carrier, and pattern images having different inner inclinations of the pattern images for each color. The image processing unit 12 includes a light beam scanning device 14Y, a light beam scanning device 14M, a light beam scanning device 14M, and a light beam scanning device 14M. Each of the light beam scanning device 14C and the light beam scanning device 14K is preliminarily attached to each of the corresponding image carrier 20Y, image carrier 20M, image carrier 20C, and image carrier 20K as shown in FIG. Control is performed to form a predetermined pattern image 40Y. The pattern image 40Y is a pattern image that is long in the main scanning direction of each of the image carrier 20Y, the image carrier 20M, the image carrier 20C, and the image carrier 20K. In the present embodiment, description will be made assuming that a line image in which the main scanning direction is the longitudinal direction is adopted as the pattern image that is long in the main scanning direction.

  In the present embodiment, the pattern image 40Y is described as a line image. However, the pattern image 40Y may be a pattern image that is long in the main scanning direction, and is not limited to such a shape.

  The pattern image 40Y is a laser modulation signal for forming the pattern image 40Y from the image processing unit 12 to each of the light beam scanning device 14Y, the light beam scanning device 14M, the light beam scanning device 14C, and the light beam scanning device 14K. By being output, each image carrier 20Y, image carrier 20M, image carrier 20C, and light beam scanner 14Y, light beam scanner 14M, light beam scanner 14C, and light beam scanner 14K A pattern image 40Y which is a long line image in the main scanning direction of each image carrier 20Y, image carrier 20M, image carrier 20C, and image carrier 20K is formed on each image carrier 20K.

  The predetermined predetermined pattern image 40Y forming process is an image forming process in which a recording medium is attracted to the intermediate transfer member 24 and an image based on image data input from the outside to the image processing unit 12 is formed on the recording medium. Before execution of processing, calculation of a value indicating the inclination (hereinafter referred to as skew for each color) of the pattern image formed on each of the plurality of image carriers with respect to the axial direction Z of the image carrier, and the pattern image for each color Is performed before image formation processing based on image data in order to discriminate an image carrier that has formed pattern images having different inner inclinations and to discriminate an image carrier that has undergone an internal color shift in the pattern image for each color. The

  Hereinafter, in order to simplify the description, the Y image forming unit 30Y will be described. The M image forming unit 30M, the C image forming unit 30C, and the B image forming unit 30K are also processed in the same manner as the Y image forming unit 30Y.

  The light beam scanning device 14Y is controlled by the control of the image processing unit 12, and the image carrier 20Y in which the pattern image 40Y long in the main scanning direction is formed on the image carrier 20Y is rotated in the rotation direction B of the image carrier. Then, after being developed by the developing device 22Y, when the formation position of the pattern image 40Y on the image carrier 20Y reaches a position where the intermediate transfer member 24 is pressed against the image carrier 20Y by the transfer device 26Y. The pattern image 40Y is transferred to the intermediate transfer member 24.

  In order to detect the pattern image 40Y formed on the image carrier 20Y, the transfer unit 26Y includes a detection unit 28Y. The detection unit 28Y is connected to the image processing unit 12, and detects a current value flowing between the image carrier 20Y and the transfer unit 26Y based on a potential difference between the image carrier 20Y and the transfer unit 26Y. The time from the start of transfer of the pattern image 40Y to the end of transfer when the pattern image 40Y is transferred to the intermediate transfer member 24 by the transfer device 26Y is detected.

  Here, the current that flows due to the potential difference between the image carrier 20Y and the transfer device 26Y will be described. The image carrier 20Y rotates in the rotation direction B of the image carrier at a predetermined speed. After the image carrier 20Y on which the pattern image 40Y is formed rotates in the rotation direction B of the image carrier and is developed by the developing device 22Y, the formation position of the pattern image 40Y on the image carrier 20Y is the transfer unit 26Y. After the intermediate transfer member 24 reaches a position where the intermediate transfer member 24 is pressed against the image carrier 20Y, the image carrier 20Y continues to rotate, so that the pattern image 40Y on the image carrier 20Y and the intermediate transfer member While the transfer unit 26Y is in contact with the image forming unit 24, the potential difference between the image carrier 20Y and the transfer unit 26Y changes.

  In the present embodiment, the image carrier 20Y is substantially uniformly charged to about −800 V by the charging device 18Y, and then is scanned and exposed in the main scanning direction by the light beam scanning device 14Y to be statically matched to the pattern image 40Y. When the electrostatic latent image is formed, the potential of the exposed portion where the electrostatic latent image is formed is -200V, and the potential of the non-exposed portion is -800V. Furthermore, the bias potential of the developing device 22Y is set to be −400 V, and the negatively charged toner adheres to the electrostatic latent image forming position, so that the toner image to which the charged toner of −200 V is attached. The pattern image 40Y is developed on the image carrier 20Y.

  Here, a voltage of +700 V having a polarity opposite to that of the toner is applied in advance to the transfer device 26Y. The image carrier 20Y on which the pattern image 40Y in which the toner charged to -200V is attached to the non-exposed portion of -800V is further rotated at a predetermined speed in the rotation direction B of the image carrier, and the pattern image 40Y Since the formation position of -200V pattern image 40Y reaches the installation position of the transfer device 26Y from the -800V non-exposed portion, the image carrier 20Y and the transfer device reach the installation position of the transfer device 26Y. The potential difference between the image carrier 26Y and the electric current flowing between the image carrier 20Y and the transfer device 26Y changes. Further, when the image carrier 20Y continues to rotate in the rotation direction B of the image carrier and the non-exposed portion charged to −800 V reaches the installation position of the transfer device 26Y again, the image carrier 20Y and the transfer member 20Y are transferred. The potential difference between the image transfer device 26Y and the electric current flowing between the image carrier 20Y and the transfer device 26Y changes, and the original, that is, the non-exposed portion reaches the installation position of the transfer device 26Y. And the current value returns to the original value. In this way, the current value before the start of transfer is changed by the start of transfer of the pattern image 40Y formed on the image carrier 20Y to the intermediate transfer body 24, and further, the current value before the start of transfer is completed by the end of the transfer. Therefore, the detection waveform indicating the formation state of the pattern image 40Y formed on the image carrier 20Y is detected. When the detection unit 28Y detects the current flowing between the image carrier 20Y and the transfer unit 26Y and detects the detection waveform indicating the pattern image 40Y, the detected detection waveform is output to the image processing unit 12. Is done.

  For example, as shown in FIGS. 2 and 3A, the image carrier 20Y is scanned and exposed in the main scanning direction so that the axial direction Z of the image carrier 20Y is the same as the main scanning direction of the light beam. When the pattern image 40Y having no inclination with respect to the axial direction Z of the image carrier 20Y is formed on the image carrier 20Y, the detection unit 28Y detects the detection waveform 42 shown in FIG. 12 is output. This detected waveform 42 indicates that the current value before the start of transfer flowing between the image carrier 20Y and the transfer device 26Y changes, and the changed current until the formation position of the pattern image 40Y passes the installation position of the transfer device 26Y. The detected waveform is detected by returning to the current value before the start of transfer after the value continues. For this reason, between the image carrier 20Y and the transfer device 26Y at a time corresponding to the width of the pattern image 40Y in the rotation direction B of the image carrier 20Y, that is, a time t1 from the start of transfer of the pattern image 40Y to the end of transfer. Changes in the potential difference. The time t1 is obtained based on the pulse width of the detection waveform 42.

  Here, when the image carrier 20Y is scanned and exposed to form a pattern image 40Y in a state where the main scanning direction of the light beam is inclined with respect to the axial direction Z of the image carrier 20Y, FIGS. As shown in A), the pattern image 40Y is a pattern image 40A inclined with respect to the axial direction Z.

  Since the pattern image 40Y is a line image that is long in the main scanning direction, as shown in FIG. 4A, when the pattern image 40Y is formed on the image carrier 20Y as a pattern image 40A inclined with respect to the axial direction Z, the image The width of the pattern image 40A in the rotation direction B of the carrier 20Y is a value different from the width in the rotation direction B of the pattern image 40Y in a state where there is no inclination. Therefore, when the pattern image 40A on the image carrier 20Y reaches the installation position of the transfer device 26Y and is transferred to the intermediate transfer member 24, the time from the start of transfer to the end of transfer is in a state where there is no inclination. The time from the start of transfer of the pattern image 40Y to the end of transfer is a different value.

  Specifically, as shown in FIGS. 2 and 4A, the image carrier 20Y is scanned and exposed in the main scanning direction so that the axial direction Z of the image carrier 20Y is different from the main scanning direction of the light beam. When the pattern image 40A having an inclination with respect to the axial direction Z of the image carrier 20Y is formed on the image carrier 20Y, the detection unit 28Y detects the detection waveform 44 shown in FIG. To the unit 12. As shown in the detection waveform 44, at a time corresponding to the width of the pattern image 40A in the rotation direction B of the image carrier 20Y, that is, a time t2 from the start of transfer of the pattern image 40A to the end of transfer, There is a change in the potential difference with the transfer device 26Y. This time t2 is obtained based on the pulse width of the detected waveform 44.

  As described above, the potential difference between the image carrier 20Y and the transfer device 26Y changes only in the rotation direction B of the image carrier 20Y for the time corresponding to the width of the pattern image 40A. The pulse width of 42 and the pulse width of the detected waveform based on the pattern image 40A show different values.

  Therefore, as shown in FIG. 3B and FIG. 4B, the pattern image 40Y in a state where the pattern image formed on the image carrier 20Y is not inclined with respect to the axial direction of the image carrier 20Y is intermediate transferred. The pattern in the state where there is no inclination with respect to the axial direction of the image carrier 20Y compared to the time t1 from the start of transfer to the end of transfer indicated based on the pulse width of the detection waveform 42 output when transferred to the body 24. The time t2 from the start of transfer to the end of transfer indicated based on the pulse width of the detection waveform 44, which is output when the image 40A is transferred to the intermediate transfer body 24, is a different value, and the amount of inclination of the pattern image Depending on the difference.

  Similarly, the M image forming unit 30M, the C image forming unit 30C, and the B image forming unit 30K perform the same processing as that of the Y image forming unit 30Y. Similarly to the Y image forming unit 30Y, the transfer device 26M, the transfer device 26C, and the transfer device 26K of each of the M image forming unit 30M, the C image forming unit 30C, and the B image forming unit 30K include a detection unit 28M and a detection unit, respectively. 28C and a detection unit 28K, and each detection unit 28M, detection unit 28C, and detection unit 28K are connected to the image processing unit 12, respectively. In the M image forming unit 30M, the C image forming unit 30C, and the B image forming unit 30K, the same processing as that of the Y image forming unit 30Y is performed, and each of the detection unit 28M, the detection unit 28C, and the detection unit 28K The current value due to the potential difference between the corresponding image carrier and the transfer device is detected, and the transfer from the start to the end when the pattern image formed on the corresponding image carrier is transferred to the intermediate transfer member 24. A detection waveform having a pulse width corresponding to the time until is output to the image processing unit 12.

  The image processing unit 12 includes a main calculation unit 30, a deviation correction amount calculation unit 32, a deviation amount calculation unit 34, and a storage unit 36.

  The storage unit 36 scans and exposes in the main scanning direction by the light beam scanning device 14Y so that the main scanning direction of the light beam scanning device 14Y is the same as the axial direction Z (see FIG. 2) of the image carrier 20Y. When this is done, a detection waveform having a pulse width corresponding to the detection time of the pattern image 40Y formed on the image carrier 20 is stored in advance as a reference waveform. That is, the detection waveform of the pattern image in a state where there is no skew indicating the inclination of the pattern image formed on the image carrier 20Y with respect to the axial direction Z of the image carrier 20Y is stored in advance as a reference waveform. Instead of the reference waveform, the time from the start of pattern image transfer to the end of transfer in a state without skew may be stored in advance.

  The deviation amount calculation unit 34 is configured to output the image of the pattern image formed on each of the plurality of image carriers based on the detection waveforms output from the detection unit 28Y, the detection unit 28M, the detection unit 28C, and the detection unit 28K. Calculation of a value indicating the inclination of the carrier with respect to the axial direction Z, determination of an image carrier that forms a pattern image having a different inclination among the pattern images for each color, and an image in which an internal color shift of the pattern image for each color occurs It is a functional part for discriminating a carrier. The deviation amount calculation unit 34 corresponds to a detection unit of the image forming apparatus of the present invention.

  Specifically, the deviation amount calculation unit 34 includes each pulse width of the detection waveform output from each of the detection units 28Y, 28M, 28C, and 28K, and a reference stored in the storage unit 36. By obtaining the difference from the pulse width of the waveform, the skew amount for each color is obtained. That is, the main beam scanning direction of the light beam for each color is calculated by calculating the difference in pulse width based on the detection waveforms output from each of the detection units 28Y, 28M, 28C, and 28K. Then, an amount indicating the inclination of the image carrier with respect to the axial direction Z is calculated to obtain a skew amount for each color.

  The processing for obtaining the skew amount for each color, which is executed by the deviation amount calculation unit 34, will be described with reference to the flowchart shown in FIG. In order to simplify the description, the case where the skew amount is obtained based on the detection waveform output from the detection unit 28Y will be described. However, the detection output from each of the detection unit 28M, the detection unit 28C, and the detection unit 28K. Similar processing is performed on the waveform.

  When the deviation amount calculation unit 34 obtains the skew amount for each color, the processing routine of FIG.

  In step 100, a negative determination is repeated until a detection signal is input from the detection unit 28Y.

  In step 102, the time from the start of pattern image transfer to the end of transfer is detected based on the pulse width of the detection signal received in step 100.

  Next, in step 104, based on the pulse width of the reference waveform stored in the storage unit 36, the time from the start of pattern image transfer to the end of transfer in the absence of skew indicating the inclination of the image carrier 20Y with respect to the axial direction Z. That is, read the reference time.

  Next, in step 106, based on the difference between the reference time read in step 104 and the time from the start of pattern image transfer to the end of transfer detected in step 102, the axial direction Z of the image carrier of the pattern image is determined. After calculating the amount indicating the inclination with respect to, this routine is terminated.

  By executing the processing from step 100 to step 104, the deviation amount calculation unit 34 causes the pattern image 40A formed to be inclined in the axial direction Z shown in FIG. 4 to reach the installation position of the transfer unit 26Y. Based on the difference between the pulse width of the detection waveform 44 output from the detection unit 28Y, that is, the detection time t2, and the pulse width of the reference waveform 42 (see FIG. 3B) stored in the storage unit 36, that is, the detection time t1. The amount indicating the inclination of the pattern image with respect to the axial direction Z of the image carrier 20Y can be calculated.

  Further, the deviation amount calculation unit 34 compares the pulse widths of the detection waveforms output from the detection units 28Y, 28M, 28C, and 28K, and determines whether or not they are the same. As a result, the image carrier on which the pattern images having different inclinations among the pattern images for the respective colors are determined.

  Here, as shown in FIG. 5A, the pulse widths of the detection waveform 46, the detection waveform 48, the detection waveform 50, and the detection waveform 52 for each color are the same, that is, the detection time of the pattern image for each color is the same. Thus, for example, when all are t3, the main scanning direction when the pattern image is formed on the image carrier between the colors is the same between the image carriers, and the inclination of the pattern image between the colors is determined. The indicated value “0” is calculated. For this reason, the deviation amount calculation unit 34 determines that all the pattern images for each color have the same inclination.

  However, as shown in FIG. 5B, the deviation amount calculation unit 34 compares the pulse widths of the detection waveform 54, the detection waveform 56, the detection waveform 58, and the detection waveform 60 for each color, That is, when a detection waveform indicating a different detection time (pulse width t4 of the detection waveform 58 in FIG. 5B) is included, it is determined that the inclinations of the pattern images between the colors do not match and different pulse widths are used. The image bearing member on which the pattern image corresponding to the detected waveform indicating is formed is discriminated. In this discrimination of the image carrier, for example, identification information that can identify the image carrier corresponding to each detector is stored in the storage unit 36 in advance in correspondence with the detection waveform detected from each detector. The image carrier may be discriminated based on identification information corresponding to the detection order of detection waveforms indicating different pulse widths.

  In addition, in the deviation amount calculation unit 34, the pulse widths of the detection waveforms indicating different pulse widths and a plurality of other detection waveforms indicating the same pulse width are set so that the inclinations of the pattern images between the colors are the same. The difference from the pulse width may be calculated as a value indicating the inclination of the pattern image between the colors with respect to the image carrier corresponding to the detection unit that outputs the detection waveform indicating the different pulse width.

  Further, the deviation amount calculation unit 34 calculates the difference between the detection timings of the pattern images calculated based on the detection waveforms output from the detection units 28Y, 28M, 28C, and 28K, that is, By obtaining and comparing the detection intervals of each pattern image, an image carrier in which color misregistration has occurred among the pattern images for each color is determined.

  For example, the image processing unit 12 forms an image of a pattern image so that a pattern image is formed at a predetermined interval in each of the Y image forming unit 30Y, the M image forming unit 30M, the C image forming unit 30C, and the B image forming unit 30K. A pattern image is formed on the image carrier of each color by controlling the output timing of the laser modulation signal based on the data. Then, as shown in FIG. 5A, each detection unit 28Y, detection unit 28M, detection based on the detection waveform output from each detection unit 28Y, detection unit 28M, detection unit 28C, and detection unit 28K. The detection intervals of the pattern images detected by the unit 28C and the detection unit 28K are calculated. The pattern image detection interval corresponds to, for example, the adjacent downstream image carrier 20M from the output of the detection waveform 46 output by the detector 28Y provided corresponding to the most upstream image carrier 20Y. The time until the output of the detection waveform 48 output by the provided detection unit 28Y is calculated as the pattern image detection interval. Similarly, the detection interval of the pattern image between each detection unit is calculated from the detection waveforms detected by each detection unit 28M, detection unit 28C, and detection unit 28K, and color misregistration is performed based on the calculated detection interval. The image bearing member on which the image is generated is discriminated.

  The determination of the image carrier in which the color misregistration has occurred is performed, for example, by storing in advance a predetermined interval for forming a pattern image on each image carrier in the storage unit 36 and storing it in the storage unit 26 among the calculated detection intervals. A detection interval having a value different from the predetermined interval is specified. Further, it is determined that the image carrier corresponding to the detection unit that outputs the two detection waveforms from which the specified detection interval is calculated is an image carrier in which color misregistration has occurred. Note that the image carrier corresponding to the detection unit that outputs the two detection waveforms that are the basis of calculation of the detection intervals for the detection intervals indicating different values by comparing the calculated detection intervals, You may make it discriminate | determine that it is an image carrier in which the shift | offset | difference generate | occur | produced.

  For example, as shown in FIG. 5A, each calculated based on the detection waveforms output from the detection unit 28Y and the detection unit 28M, between the detection unit 28M and the detection unit 28C, and between the detection unit 28C and the detection unit 28K. When the differences in the detection timing of the pattern image by the detection unit are all the same time, for example, t5, the scanning position of the light beam for each color is the same, indicating that no color shift occurs between the colors. . However, when the difference in the detection timing of the pattern image by each detection unit is different, it indicates that color misregistration has occurred. As shown in FIG. 5B, the difference in the detection timing of the pattern image by each detection unit calculated from the detection waveforms among the adjacent detection units 28Y, 28M, 28C, and 28K is different. When the values are, for example, t5, t6, and t5, respectively, the difference in detection timing of the pattern image between the detection unit 28M and the detection unit 28C is compared with the difference in detection timing output from the other detection units. Long or short. In this case, it is indicated that a color misregistration occurs due to a scanning position deviation of the light beam in the C image forming unit 30C. That is, it is determined that the scanning position deviation, that is, the positional deviation has occurred in the image carrier 20M and the image carrier 20C corresponding to the detection waveform 56 and the detection waveform 58, which are the basis of detection of the detection intervals at different times t6. .

  Further, the shift amount calculator 34 may calculate the color shift amount of the image carrier in which the color shift has occurred. The amount of color misregistration may be calculated based on a detection interval having a value different from the predetermined interval stored in advance in the storage unit 26, and a difference between the predetermined interval, or a different value among a plurality of detection intervals. It may be calculated based on the difference between the detection interval that indicates and the detection interval that indicates the same value.

  The deviation correction amount calculation unit 32 calculates the skew for each color calculated from the deviation amount calculation unit 34 based on the detection waveforms output from the detection unit 28Y, the detection unit 28M, the detection unit 28C, and the detection unit 28K. When a value, a value indicating the inclination of the pattern image between the colors, and a color misregistration amount are input, a value indicating the skew for each input color, a value indicating the inclination of the pattern image between the colors, and the color misregistration amount This is for calculating the shift correction amount for each image forming unit. The misregistration correction amount is based on image data in which each skew, tilt, and color misregistration is suppressed based on, for example, a value indicating the skew for each color, a value indicating the tilt of the pattern image between the colors, and the color misregistration amount. In order to correct the input image data in order to output a laser modulation signal from the image processing unit 12 to each of the Y image forming unit 30Y, the M image forming unit 30M, the C image forming unit 30C, and the B image forming unit 30K. Indicates the value of.

  When the shift correction amount calculation unit 32 obtains the shift correction amount for each image forming unit, the main calculation unit 30 obtains data obtained by performing a predetermined calculation on the input image data based on the shift correction amount. Is output to a line memory (not shown), and a laser modulation signal modulated in accordance with data input from the line memory is output to the LDD 16Y, LDD 16M, LDD 16C, and LDD 16K for each color. Accordingly, a value indicating the skew for each color, a value indicating the inclination of the pattern image between the colors, and a laser modulation signal based on the image data corrected based on the amount of color misregistration are received from the image processing unit 12. Output to forming unit.

  As described above, according to the image forming apparatus of the present embodiment, on the image carrier that rotates at a predetermined speed, the other end of the image carrier in the axial direction Z extends from one end to the other. When the pattern image, which is a line image formed toward the surface, is scanned and exposed, and the pattern image formed on the image carrier is transferred to the intermediate transfer member by the transfer device, the detection unit provided in the transfer device A detection waveform indicating a change in current value caused by a potential difference between the transfer unit and the image carrier is output to the image processing unit 12.

  The pulse width of the detected waveform, that is, the time from the start to the end of transfer of the pattern image, and from the start to the end of transfer of the pattern image in a state where there is no inclination with respect to the axial direction Z of the image carrier of the pattern image stored in advance. Can be obtained as a skew amount indicating the inclination of the pattern image formed on the image carrier with respect to the axial direction of the image carrier, with a simple configuration, for each image carrier, A skew amount indicating the inclination of the pattern image formed on each image carrier with respect to the axial direction of the image carrier can be obtained.

  In addition, the pulse width of the detection waveform output from each of the plurality of detection units provided corresponding to each of the plurality of image carriers provided corresponding to each color in order to form a color image, that is, each detection unit By comparing the time from the start of transfer to the end of transfer of the detected pattern images, and obtaining the difference, a value indicating the inclination between the pattern images between the respective colors can be obtained. Therefore, it is possible to obtain a value indicating the inclination of the pattern image between the colors with a simple configuration.

  Further, with respect to the detection timing of the pattern image for each color calculated based on the detection waveform output from each of the detection units 28Y, 28M, 28C, and 28K, the detection timing between adjacent detection units By obtaining the difference, it is possible to calculate a color misregistration amount, that is, a color misregistration amount indicating a scan position misalignment between the colors. For this reason, the color misregistration amount can be obtained with a simple configuration.

  Further, in the image forming apparatus 10 of the present embodiment, each transfer device is provided so as to be pressed against the corresponding image carrier via the intermediate transfer member 24, so that the detection unit provided in the transfer device is used. The potential difference between the image carrier and the transfer device can be detected with high accuracy.

  The pattern image is scanned and exposed on the image carrier as a line image from one end to the other end in the axial direction Z of the image carrier, so that the main scanning direction of the light beam to be scanned and the image carrier The detection accuracy of the inclination with respect to the axial direction Z can be improved.

  As shown in FIGS. 3 and 4, the pattern image 40Y and the pattern image 40A formed on the image carrier 20Y have different inclinations with respect to the axial direction Z of the image carrier 20Y, but are based on the same image data. Since the pattern image is long in the main scanning direction, the energy at the time of transferring the pattern image is the same, and the integrated values of the detection waveform 42 and the detection waveform 44 output by the detection unit 28Y are the same. Therefore, in the present embodiment, the difference between the pulse widths of the detection waveform 42 and the detection waveform 44, that is, the time from the start of transfer to the end of transfer has been described as being obtained as an amount indicating the inclination with respect to the axial direction Z. The difference (h1 and h2) in the amount of change (h1 in FIG. 3B and h2 in FIG. 4B) from the current value before the start of transfer in the waveform 42 and the detected waveform 44, respectively. ) May be obtained as an amount indicating an inclination with respect to the axial direction Z.

  In the present embodiment, the image carrier 20Y is substantially uniformly charged to about −800V by the charging device 18Y, and the pattern image 40Y as a toner image to which the toner charged to −200V is adhered is the image carrier 20Y. It has been described that a voltage of +700 V having a polarity opposite to that of the toner is applied in advance to the transfer device 26Y. However, the potential of the image carrier 20Y, the potential of the pattern image by development, and the transfer device The applied voltage is not limited to such a value. For example, the image carrier 20Y and the transfer unit 26Y may be charged to the same voltage, and the pattern image area may be developed to have a voltage different from the voltage. With this configuration, the potential difference between the image carrier 20Y and the transfer device 26Y changes when the pattern image is transferred. Therefore, the amount is obtained as an amount indicating the inclination with respect to the axial direction Z based on the detected waveform due to the change in the potential difference. What should I do?

  In the present embodiment, the pattern image has been described as a long line image in the main scanning direction formed from one end to the other end in the axial direction Z of the image carrier. It is not limited. For example, as shown in FIG. 6, a pair of images formed at both ends in the axial direction Z of the image carrier may be formed as a pattern image (pattern image 40B).

  When the image carrier 20Y on which such a pattern image 40B is formed rotates in the rotation direction B and the formation position of the pattern image 40B on the image carrier 20Y reaches the transfer device 26Y, the image carrier 20Y is formed on the image carrier. When the pattern image 40B formed is a pattern image formed with no inclination with respect to the axial direction Z of the image carrier, for example, as shown in FIG. 7A, the axial direction Z of the image carrier. As shown in FIG. 7B, the detection unit 28Y outputs a detection waveform 62 composed of two detection waveforms 62A and a detection waveform 62B, based on a pattern image 40B composed of a pair of images formed at both ends of the image. To do.

  On the other hand, as shown in FIG. 8A, a pattern image consisting of a pair of images formed at both ends in the axial direction Z of the image carrier is formed on the image carrier in a state inclined with respect to the axial direction Z. When the pattern image is 40C, the detection unit 28Y outputs a detection waveform 64 including two detection waveforms 64A and 62B as shown in FIG. 8B.

  For example, the detection waveform 62 of the two detection waveforms 62 and 64 may be stored in the storage unit 36 as a reference waveform. Then, the difference between the detection times of the two detection waveforms included in each of the detection waveform 62 and the detection waveform 64, specifically, the time t9 shown in FIG. 7B and the time t10 shown in FIG. 8B. Is obtained as a skew amount indicating the inclination of the pattern image with respect to the axial direction Z of the image carrier.

  In this embodiment, the value indicating the inclination of the pattern image between the colors is obtained by comparing the pulse width of the detection waveform output from each detection unit, that is, the time from the start of transfer to the end of transfer. In the above description, the value indicating the inclination of the pattern image between the colors is obtained. However, the method for obtaining the value indicating the inclination of the pattern image between the colors is not limited to such a form.

  For example, the detection unit 28K may be provided only in the transfer unit 26K provided on the most downstream side in the transport direction Y of the intermediate transfer body 24, and the detection waveform may be output only from the detection unit 28K. In this case, the intermediate transfer member is controlled by the image processing unit 12 such that the pattern image is scanned and exposed to each image carrier so that the same pattern image is positioned in a different sub-scanning direction for each color. The pattern image for each color may be transferred so that the positions are different from each other in the transport direction Y on the image 24. In this way, a plurality of detection waveforms based on the pattern image formed by the image carrier for each color can be detected by the detection unit 28K provided in the most downstream transfer device 26K. For this reason, the configuration of the image forming apparatus 10 can be further simplified.

1 is a schematic configuration diagram of an image forming apparatus. FIG. 3 is an image diagram illustrating a configuration of an image carrier, an intermediate transfer member, and a transfer device on which a pattern image as a diagram extending from one end to the other end in the main scanning direction of the image carrier is formed. FIG. 3A is a plan view showing an image carrier on which the pattern image shown in FIG. 2 is formed in a state where there is no inclination of the pattern image with respect to the axial direction of the image carrier. FIG. 3B is a diagram showing a detection waveform corresponding to the pattern image shown in FIG. 2 in a state where there is no inclination of the pattern image with respect to the axial direction of the image carrier. FIG. 3A is a plan view showing an image carrier on which the pattern image shown in FIG. 2 is formed in a state where the pattern image has an inclination with respect to the axial direction of the image carrier. (B) is a diagram showing a detection waveform corresponding to the pattern image shown in FIG. 2 in a state where the pattern image is inclined with respect to the axial direction of the image carrier. It is an image figure which shows the detection waveform of the pattern image formed on the image carrier for every color, (A) is when the inclination of the pattern image for every color is the same, and the color shift between each color has not arisen It is a diagram which shows an example of the detection waveform output from the detection part for every color. (B) is a diagram showing an example of a detection waveform output from the detection unit for each color when the inclination of the pattern image for each color is different and color misregistration occurs. FIG. 3 is an image diagram illustrating configurations of an image carrier, an intermediate transfer member, and a transfer device in which pattern images are formed at both ends in the main scanning direction of the image carrier. FIG. 7A is a plan view showing an image carrier on which the pattern image shown in FIG. 6 is formed in a state where there is no inclination of the pattern image with respect to the axial direction of the image carrier. FIG. 7B is a diagram showing a detection waveform corresponding to the pattern image shown in FIG. 6 in a state where there is no inclination of the pattern image with respect to the axial direction of the image carrier. FIG. 7A is a plan view showing an image carrier on which the pattern image shown in FIG. 6 is formed in a state where the pattern image has an inclination with respect to the axial direction of the image carrier. FIG. 7B is a diagram showing a detection waveform corresponding to the pattern image shown in FIG. 6 in a state in which the pattern image is inclined with respect to the axial direction of the image carrier. It is a flowchart which shows the process which calculates the value which shows the inclination with respect to the axial direction of the image carrier of a pattern image performed by the deviation | shift amount calculating part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Image processing part 14Y, 14M, 14C, 14K Light beam scanning device 20Y, 20M, 20C, 20K Image carrier 24 Intermediate transfer body 26Y, 26M, 26C, 26K Transfer device 28Y, 28M, 28C, 28K Detection Unit 30 main calculation unit 34 deviation amount calculation unit 36 storage unit

Claims (5)

A light beam scanning means for scanning the light beam in the main scanning direction;
An image carrier that is pre-charged and scanned and exposed in the main scanning direction by the light beam scanning means, and rotated at a predetermined speed so as to be scanned and exposed in the sub-scanning direction;
Control means for controlling the light beam scanning means so that a pattern image long in the main scanning direction is formed on the image carrier;
A current value detecting means for detecting a current value flowing between the image carrier and a precharged transfer means for transferring the pattern image formed on the image carrier to a transfer target;
The time required for the current value detected by the current value detecting means to return to the current value before the start of transfer after the current value before the transfer of the pattern image to the transfer body is changed, Detecting means for detecting the time from the start of transfer of the pattern image to the transfer target to the end of transfer;
Memory stored in advance as a reference time, the time from the start of transfer of the pattern image to the end of transfer in the absence of skew indicating the inclination of the pattern image formed on the image carrier relative to the axial direction of the image carrier Means,
A computing means for computing a value indicating the skew based on a difference between a time from the start of transfer of the pattern image detected by the detecting means to the end of transfer and the reference time;
An image forming apparatus. A light beam scanning means for scanning the light beam in the main scanning direction;
An image carrier that is pre-charged and scanned and exposed in the main scanning direction by the light beam scanning means, and rotated at a predetermined speed so as to be scanned and exposed in the sub-scanning direction;
Control means for controlling the light beam scanning means so that a pattern image long in the main scanning direction is formed on the image carrier;
A current value detecting means for detecting a current value flowing between the image carrier and a precharged transfer means for transferring the pattern image formed on the image carrier to a transfer target;
Detecting means for detecting an amount of change from the current value before the transfer of the pattern image to the transfer object based on the current value detected by the current value detecting means;
In the absence of skew indicating the inclination of the pattern image formed on the image bearing member relative to the axis direction of the image bearing member, flows between the image carrier and the transfer means, the object of the pattern image Storage means for storing in advance the amount of change from the current value before the start of transfer to the transfer body ;
The difference between the amount of change from the current value of the pattern image detected before the transfer to the transfer object and the amount of change stored in the storage means detected by the detection means is a value indicating the skew. Computing means for computing as
An image forming apparatus. The image forming apparatus according to claim 1, wherein the pattern image is a line image that is long in a main scanning direction. The image forming apparatus according to any one of claims 1 to 3, wherein the pattern image is formed at both ends of the image carrier in the axial direction. A plurality of light beam scanning means for scanning the light beam in the main scanning direction;
Provided in correspondence with each of the plurality of light beam scanning means, and in a precharged state, the corresponding light beam scanning means performs scanning exposure in the main scanning direction and scanning exposure in the sub scanning direction. A plurality of image carriers rotated at a predetermined speed;
Control means for controlling each of the plurality of light beam scanning means so that a pattern image long in the main scanning direction is formed on each image carrier corresponding to each color component of a color image;
Current value detecting means is provided corresponding to each of the plurality of image carriers, and detects a current value flowing between the image carriers, and the pattern image formed on the image carrier is covered A plurality of pre-charged transfer means for transferring to a transfer body;
The time required for the current value detected by each of the current value detection means to change from the current value before the transfer of the pattern image to the transfer body before returning to the current value before the transfer start, Detecting means for detecting each current value detecting means as a time from the start of transfer of the pattern image to the transfer body to the end of transfer ;
The detected in the detection means depending on each of said current value detection means, when the time to end transcription from the transcription start of the pattern image is not identical to each other, corresponding to the time from the start of transcription of different values to the end transfer Determining means for determining that the inclination of the pattern image formed on the image carrier is different from the inclination of the pattern image formed on another image carrier;
An image forming apparatus.

Images