JP2010085422A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the displacement of an image transferred to a conveying member, even if a skewing state of the conveying member changes while forming an image. <P>SOLUTION: The image forming apparatus 1 includes an intermediate transfer belt 15 to which images formed by a plurality of image forming units 10 are transferred. Prior to forming the image, respective color patch images formed by the respective image forming units 10 and transferred to the intermediate transfer belt 15 are read, and a main scanning exposure correction value and a subscanning exposure correction value for correcting displacement of the respective color images are generated, and then a skewing amount of the intermediate transfer belt 15 at this point is acquired as a first skewing amount. In the image forming operation, a skewing amount of the intermediate transfer belt 15 when the images formed by the respective image forming units 10 whose exposure positions are corrected according to the respective correction values are transferred to the intermediate transfer belt 15 is acquired as a second skewing amount, and the main scanning exposure correction value is corrected by using the second skewing amount and the first skewing amount already acquired. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image.

  Conventionally, as an image forming apparatus such as a copying machine or a printer, a color image forming apparatus that forms a multicolor image using an endless intermediate transfer belt, a photoreceptor belt, or a paper conveyance belt is known.

  In the image forming apparatus in which an image is formed by a plurality of image forming units with respect to an endless belt member that is stretched and conveyed by a plurality of rolls, the endless belt member conveys the endless belt member. A skew detecting means for detecting that the sheet is conveyed while being inclined with respect to the direction, and an endless shape detected by the skew detecting means when the skew detecting means detects the skew of the endless belt member. An image correcting unit that corrects image distortion by an image forming unit based on a skew amount of a belt member is disclosed (see Patent Document 1).

JP 2006-276427 A

  By the way, in an image forming apparatus including a plurality of image forming units, for example, when a power is turned on, a test image formed in each image forming unit is transferred to a conveying member such as a belt member, and the transferred image is read. Based on the positional deviation information of each image, the image formation timing in each image forming unit is adjusted. In actual image formation, an image is formed while adjusting the image formation timing in each image forming unit, thereby suppressing the positional deviation of the image transferred from each image forming unit to the conveying member.

  However, in the above-described operation, when skew feeding in which the posture of the conveying member changes occurs, accurate positional deviation information may not be obtained. In such a case, the position of the image in the actual image formation may not be obtained. Deviation occurs.

  An object of the present invention is to suppress misalignment of an image transferred to a conveying member even when the skew state of the conveying member changes during image formation.

  According to the first aspect of the present invention, a plurality of image forming units that form images, a conveying member that conveys images transferred from the plurality of image forming units, and a test image from the plurality of image forming units to the conveying member A first acquisition means for acquiring a first skew state with respect to the conveying direction of the conveying member in an alignment operation for determining an alignment correction value for correcting misalignment between images by transferring Second acquisition means for acquiring a second skew state in the transport direction of the transport member in an image forming operation for transferring the main image from the image forming unit to the transport member; the first skew state; An image forming apparatus including a correction unit that corrects the misregistration correction value based on a second skew state.

According to a second aspect of the present invention, the conveying member is configured by a rotating endless belt member, and the second acquisition unit is configured to perform the second skewing according to an increase in the number of rotations of the conveying member. 2. The image forming apparatus according to claim 1, wherein a state acquisition interval is lengthened.
According to a third aspect of the present invention, each of the plurality of image forming units includes a rotating image carrier and an image writing unit that writes an image on the image carrier, and the image writing unit includes the positional deviation correction value. The image forming apparatus according to claim 1, wherein an image writing position with respect to the image holding member is set based on the image forming unit.

  According to a fourth aspect of the present invention, there are provided a plurality of photoconductors, an exposure device that writes an electrostatic latent image on the photoconductor, and a developer that develops the electrostatic latent image written on the photoconductor. An image forming unit, a belt member that is rotatably supported and onto which the image formed on the photoreceptor provided in each of the plurality of image forming units is transferred, and a displacement in the width direction of the rotating belt member. A measuring unit to measure, a correction value of a writing position of the exposure device in each image forming unit determined based on a reading result of a test image transferred from the plurality of image forming units to the belt member, and A storage unit that associates and stores the first displacement amount of the belt member measured by the measurement unit when reading a test image, the first displacement amount, and a plurality of the image forming units. Belt member An image forming apparatus including: a correction unit that corrects a writing position of the exposure unit in each of the image forming units based on the second displacement amount measured by the measurement unit when transferring the main image; is there.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the correction unit lengthens the correction interval of the writing position of the exposure device in accordance with an increase in the rotational speed of the belt member. is there.
According to a sixth aspect of the present invention, the first displacement amount and the second displacement amount are acquired for each transfer position where the image forming unit and the belt member face each other. Item 6. The image forming apparatus according to Item 4 or 5.

According to the first aspect of the present invention, as compared with the case where the present configuration is not adopted, even when the skew state of the conveying member changes during image formation, the positional deviation of the image transferred to the conveying member is suppressed. can do.
According to the second aspect of the present invention, as compared with the case where the present configuration is not adopted, the positional deviation of the image transferred to the conveying member is suppressed even in a situation where the skew state of the conveying member is likely to change. Can do.
According to the third aspect of the present invention, it is possible to more easily correct the position of the image formed in each image forming unit as compared with the case where this configuration is not adopted.
According to the fourth aspect of the present invention, compared to the case where this configuration is not adopted, even when the skew state of the belt member changes during image formation, the positional deviation of the image transferred to the belt member is suppressed. can do.
According to the fifth aspect of the present invention, it is possible to suppress the positional deviation of the image transferred to the belt member even in a situation where the skew state of the belt member is likely to change.
According to the sixth aspect of the present invention, it is possible to suppress misalignment in each image forming unit as compared with the case where this configuration is not adopted.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram showing an image forming apparatus 1 according to the present embodiment. An image forming apparatus 1 shown in FIG. 1 is a so-called tandem type image forming apparatus, and a plurality of image forming units 10 (10Y, 10M, 10C, 10K) on which toner images of respective color components are formed by, for example, electrophotography. ). In addition, the image forming apparatus 1 sequentially transfers (primary transfer) and holds each color component toner image formed by each image forming unit 10 and a superimposed image transferred onto the intermediate transfer belt 15. And a secondary transfer device 20 that collectively transfers (secondary transfer) to the paper P. In addition, the image forming apparatus 1 includes a fixing device 30 that fixes the second-transferred image on the paper P, a control unit 40 that controls the operation of each device (each unit), and a storage unit that stores various types of information. 41. Here, the first acquisition unit, the second acquisition unit, the correction unit, and the control unit 40 as an example of the correction unit are configured by, for example, a CPU, and the storage unit 41 is configured by, for example, a memory.

  In the present embodiment, each image forming unit 10 as an example of an image forming unit charges these photosensitive drums 11 around a photosensitive drum 11 as an example of an image carrier that rotates in the direction of arrow A. A charger 12 for exposing the photosensitive drum 11 to write an electrostatic latent image, and an electrostatic beam on the photosensitive drum 11 containing each color component toner. A developing device 14 that visualizes the latent image with toner, a primary transfer roll 16 that transfers each color component toner image formed on the photosensitive drum 11 to the intermediate transfer belt 15, and residual toner on the photosensitive drum 11 are removed. The electrophotographic devices such as the drum cleaner 17 are sequentially arranged. In the present embodiment, the charger 12, the laser exposure device 13, and the developing device 14 function as an image writing unit. These image forming units 10 are arranged substantially linearly in the order of yellow (Y color), magenta (M color), cyan (C color), and black (K color) from the upstream side in the moving direction of the intermediate transfer belt 15. ing.

As the intermediate transfer belt 15 as an example of a conveying member or a belt member, a material in which a suitable amount of a conductive agent such as carbon black is contained in a resin such as polyimide or polyamide is used, and its volume resistivity is 10 ⁶ to 10 ^14. It is formed to be Ω · cm. The intermediate transfer belt 15 is formed of a film-like endless belt having a thickness of, for example, about 0.08 mm, and is circulated and moved in the direction of arrow B (conveying direction) shown in FIG. 1 by various rolls. . The various rolls include a drive roll 31 that is driven by a motor (not shown) to rotate the intermediate transfer belt 15, and an idler roll 32 that maintains the flatness of the intermediate transfer belt 15 with respect to an image detection sensor 42 described later. There are a steering roll 33 for correcting meandering in a direction intersecting the moving direction of the intermediate transfer belt 15 (main scanning direction to be described later), and a backup roll 22 provided in a secondary transfer portion to be described later.

  Here, the meandering correction of the intermediate transfer belt 15 by the steering roll 33 will be briefly described. When a change in the position of the intermediate transfer belt 15 in the main scanning direction is detected by a second belt position sensor 44 described later, a steering motor (not shown) is driven based on the detection result. An eccentric cam (not shown) is connected to the steering motor. Further, a steering roll 33 is connected to the eccentric cam, and the inclination of the steering roll 33 with respect to the main scanning direction changes according to the eccentric amount of the eccentric cam. For this reason, when the steering motor is driven, the eccentric cam rotates, and the steering roll 33 is tilted accordingly. By controlling the inclination of the steering roll 33, the position fluctuation of the intermediate transfer belt 15, that is, the meandering is corrected.

  In the intermediate transfer module 18 provided to face each photoconductor drum 11, each primary transfer roll 16 provided inside the intermediate transfer belt 15 extending substantially linearly has a voltage having a polarity opposite to the charging polarity of the toner. It is to be applied. As a result, the toner images on the respective photosensitive drums 11 are sequentially electrostatically attracted to the intermediate transfer belt 15, and a superimposed toner image is formed on the intermediate transfer belt 15.

  The secondary transfer device 20 includes a secondary transfer roll 21 disposed on the toner image holding surface side of the intermediate transfer belt 15 and a backup roll 22 as an opposite roll. That is, the secondary transfer roll 21 is disposed in pressure contact with the backup roll 22 with the intermediate transfer belt 15 interposed therebetween. By the secondary transfer device 20 configured as described above, the visible image that has been multiplex-transferred onto the intermediate transfer belt 15 is transferred to a sheet P conveyed from a sheet tray 50 described later. A power supply roll 23 is disposed in pressure contact with the backup roll 22.

  Here, on the downstream side of the backup roll 22, a belt cleaner 34 that removes residual toner and paper dust on the intermediate transfer belt 15 after the secondary transfer and cleans the surface of the intermediate transfer belt 15 is provided.

An image detection sensor 42 that detects the toner images of the respective colors transferred onto the intermediate transfer belt 15 is provided on the downstream side of the black image forming unit 10K as viewed from the direction of the arrow B along which the intermediate transfer belt 15 moves. . The image detection sensor 42 is used for an alignment operation of each color image, which will be described later, and positions of toner images for alignment of each color (referred to as patch images in the following description) formed on the intermediate transfer belt 15. Detect deviation. The image detection sensor 42 detects the density of the toner image for adjusting the image quality of each color formed on the intermediate transfer belt 15. Note that the image detection sensor 42 is constituted by, for example, a CCD image sensor.
A first belt position sensor 43 is disposed upstream of the yellow image forming unit 10Y as viewed from the direction of the arrow B along which the intermediate transfer belt 15 moves, and a second belt position downstream of the black image forming unit 10K. A belt position sensor 44 is provided. In the present embodiment, the first belt position sensor 43 and the second belt position sensor 44 function as a measurement unit that measures the displacement in the width direction of the intermediate transfer belt 15 rotating in the arrow B direction.

  Further, as viewed from the direction of the arrow B along which the intermediate transfer belt 15 moves, the image forming timing in each image forming unit 10 is a reference upstream of the yellow image forming unit 10Y and inside the intermediate transfer belt 15. A belt home sensor 45 that generates a mark detection signal is disposed. When the belt home sensor 45 recognizes a belt home mark (not shown) provided on the back side of the intermediate transfer belt 15, the belt home sensor 45 outputs a mark detection signal to the control unit 40. In addition, each image forming unit 10 starts an image forming operation in response to an instruction from the control unit 40 based on recognition of the mark detection signal.

  The image forming apparatus 1 includes a paper tray 50 that stores the paper P and a pickup roll 51 that takes out and transports the paper P accumulated in the paper tray 50 as a paper transport system. Also, as a paper transport system, a transport roll 52 that transports the paper P fed out by the pickup roll 51, and a registration roll that transports the paper P transported by the transport roll 52 to the secondary transfer unit after being temporarily stopped. 53.

  Next, a basic image forming process of the image forming apparatus 1 according to the present embodiment will be described. Image data output from an image reading device (not shown) or a computer device (not shown) is input to the image forming apparatus 1. In the image forming apparatus 1, image processing is performed by the image forming units 10 </ b> Y, 10 </ b> M, 10 </ b> C, and 10 </ b> K after image processing is performed by an image processing apparatus (not shown). In an image processing apparatus (not shown), input reflectance data is subjected to image processing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color editing, and movement editing. The image data subjected to the image processing is converted into color material gradation data of four colors of yellow (Y), magenta (M), cyan (C), and black (K), and image forming units 10Y, 10M, and 10C. Is output to the laser exposure unit 13 provided in each of 10K.

  In the laser exposure device 13, the photosensitive drum 11 of each of the image forming units 10Y, 10M, 10C, and 10K is irradiated with, for example, an exposure beam Bm emitted from a semiconductor laser according to the input color material gradation data. ing. The photosensitive drums 11 of the image forming units 10Y, 10M, 10C, and 10K are rotated in the direction of the arrow A, and the surface is charged by the charger 12, and then the surface is scanned and exposed by the laser exposure unit 13, thereby electrostatic latent images. Is formed. The electrostatic latent image formed on the photosensitive drum 11 is developed as a toner image of each color of yellow, magenta, cyan, and black by using the developing device 14 in each of the image forming units 10Y, 10M, 10C, and 10K. The Here, the writing start timing of scanning exposure of the laser exposure device 13 in the circumferential direction (sub-scanning direction) of the photosensitive drum 11 is determined based on the mark detection signal output from the belt home sensor 45. In addition, the scanning exposure start timing of the laser exposure device 13 in the axial direction (main scanning direction) of the photosensitive drum 11 is determined based on information obtained by detecting the behavior of the intermediate transfer belt 15 described later.

  The toner images formed on the respective photoconductive drums 11 of the image forming units 10Y, 10M, 10C, and 10K are transferred to the intermediate transfer unit at the primary transfer portion where the photoconductive drums 11 and the intermediate transfer belt 15 are in contact with each other. Transferred onto the transfer belt 15.

  Here, the primary transfer portion will be further described. A primary transfer power source 19 controlled by the control unit 40 is connected to the primary transfer roll 16, while the photosensitive drum 11 is grounded. The primary transfer power source 19 supplies a primary transfer bias (primary transfer current) to the primary transfer roll 16 by performing constant current control. A primary transfer current flows from the primary transfer power source 19 through the primary transfer roll 16, the intermediate transfer belt 15, and the photosensitive drum 11, whereby a transfer electric field is formed between the photosensitive drum 11 and the intermediate transfer belt 15. . As a result, the toner image on the photosensitive drum 11 is transferred to the intermediate transfer belt 15.

  As described above, in the primary transfer portion, the primary transfer roll 16 applies a voltage having a polarity opposite to the toner charging polarity to the base material of the intermediate transfer belt 15, and the toner image on the photosensitive drum 11 is transferred to the intermediate transfer belt 15. Primary transfer is performed by sequentially superimposing on the surface. The primarily transferred toner image is conveyed to the secondary transfer device 20 as the intermediate transfer belt 15 rotates in the arrow B direction.

  On the other hand, in the paper transport system, the pickup roll 51 rotates in accordance with the image formation timing, and the paper P is supplied from the paper tray 50. For example, the paper P supplied by the pickup roll 51 is transported by the transport roll 52 and reaches the secondary transfer device 20. At that time, the position of the sheet P and the position of the toner image are aligned on the sheet P by rotating the registration roll 53 in accordance with the movement timing of the intermediate transfer belt 15 on which the toner image is held.

  In the secondary transfer device 20, the secondary transfer roll 21 is pressed against the backup roll 22 in accordance with the timing of the secondary transfer onto the paper P. At this time, the sheet P conveyed at the same timing is sandwiched between the intermediate transfer belt 15 and the secondary transfer roll 21. At this time, when a secondary transfer voltage (normal transfer bias) having the same polarity as the toner charging polarity is applied to the power supply roll 23, a transfer electric field is formed on the secondary transfer roll 21 as a counter electrode, and the secondary transfer. The unfixed toner image held on the intermediate transfer belt 15 is electrostatically transferred onto the paper P at the secondary transfer position pressed by the roll 21 and the backup roll 22.

  Thereafter, the sheet P on which the toner image has been electrostatically transferred is peeled off from the intermediate transfer belt 15 and conveyed to a fixing device 30 provided downstream of the secondary transfer roll 21 in the sheet conveying direction. The unfixed toner image on the paper P is fixed on the paper P by being subjected to a fixing process with heat and pressure by the fixing device 30. Further, the paper P on which the fixed image is formed is discharged outside the image forming apparatus 1 by a discharge roll (not shown). On the other hand, after the transfer to the paper P is completed, the residual toner remaining on the intermediate transfer belt 15 is conveyed to the cleaning unit as the intermediate transfer belt 15 rotates, and is removed from the intermediate transfer belt 15 by the belt cleaner 34. Removed.

  By the way, in the image forming apparatus 1 shown in FIG. 1, full-color images are obtained by superimposing on the intermediate transfer belt 15 toner images of different colors created by the image forming units 10Y, 10M, 10C, and 10K. . Therefore, it is required to superimpose the toner images of the respective colors on the intermediate transfer belt 15 with high accuracy. When the overlay accuracy of the toner images of the respective colors is low, a color shift (position shift) in the main scanning direction (arrow B direction) and the sub-scanning direction (direction intersecting the arrow B direction) occurs in the full color image. Image quality is reduced.

  Therefore, in this image forming apparatus 1, before performing the above-described image forming operation, an alignment operation for accurately superimposing the respective color toner images on the intermediate transfer belt 15 is executed. In the image forming apparatus 1, the above-described alignment operation is started before the traveling posture of the intermediate transfer belt 15 is stabilized in order to shorten the waiting time of the user.

FIG. 2 is a plan view of the intermediate transfer belt 15 as viewed from the image forming unit 10 side. 2 shows the near side in FIG. 1 as OUT and the back side as IN.
As shown in FIG. 2, the first belt position sensor 43 is positioned adjacent to the drive roll 31 wound around the intermediate transfer belt 15, and the second belt position sensor 44 is positioned adjacent to the idler roll 32. positioned. The first belt position sensor 43 and the second belt position sensor 44 detect the position of the belt edge 15 a that is the same side edge of the intermediate transfer belt 15. And the detection result in the 1st belt position sensor 43 and the 2nd belt position sensor 44 is output to the control part 40 shown in FIG.

  Note that, between the first belt position sensor 43 and the second belt position sensor 44 in the arrow B direction of the intermediate transfer belt 15, a yellow image forming unit 10Y, a magenta image forming unit 10M, and a cyan image forming unit 10C. Y-color primary transfer position Ty, M-color primary transfer position Tm, and C-color primary transfer position where the photosensitive drum 11 (see FIG. 1) provided in each of the black image forming unit 10K and the intermediate transfer belt 15 are in contact with each other. Tc and K-color primary transfer position Tk are sequentially arranged.

FIG. 3 is a time chart showing ON / OFF timing of the primary transfer power source 19 in each of the image forming units 10Y, 10M, 10C, and 10K when performing the alignment operation and the image forming operation.
When a mark detection signal is input from the belt home sensor 45 at time t0, the control unit 40 switches the primary transfer power source 19 in each of the image forming units 10Y, 10M, 10C, and 10K from OFF to ON in order. . That is, the control unit 40 first turns on the primary transfer power source 19 of the image forming unit 10Y at time t01, turns on the primary transfer power source 19 of the image forming unit 10M at time t02, and turns on the primary transfer power source 19 of the image forming unit 10C at time t03. The primary transfer power source 19 is turned on, and the primary transfer power source 19 is turned on at time t04. When the alignment operation or the image forming operation is completed and time t11 is reached, the control unit 40 switches off the primary transfer power source 19 of the image forming unit 10Y. Thereafter, the primary transfer power source 19 of the image forming unit 10M is turned off at time t12, the primary transfer power source 19 of the image forming unit 10C is turned off at time t13, and the primary transfer power source 19 of the image forming unit 10K is turned off at time t14. Turn off. As described above, in this embodiment, the primary transfer power source 19 is not switched on and off at the same time in each of the image forming units 10Y, 10M, 10C, and 10K, but on the upstream side in the arrow B direction in which the intermediate transfer belt 15 moves. In turn, switching from OFF to ON and switching from ON to OFF are performed.

  When executing the alignment operation and the image forming operation, the control unit 40 turns on the primary transfer power source 19 after receiving the mark detection signal in each of the image forming units 10Y, 10M, 10C, and 10K. In the meantime, an instruction is output to each device so as to start charging by the charger 12, start writing by the laser exposure device 13, and start development by the developing device 14.

  Incidentally, the axial direction of the photosensitive drum 11 provided in each of the image forming units 10 </ b> Y, 10 </ b> M, 10 </ b> C, and 10 </ b> K is preferably orthogonal to the arrow B direction that is the moving direction of the intermediate transfer belt 15. However, in reality, there is a limit to the processing accuracy and attachment accuracy of each of the photosensitive drums 11 and the intermediate transfer belt 15, so that the axial directions of the photosensitive drums 11 are all orthogonal to the moving direction of the intermediate transfer belt 15. It is very difficult to arrange in the state of being made to be.

FIG. 4A shows the positional relationship between each photosensitive drum 11 and the intermediate transfer belt 15 during non-image formation. Here, during non-image formation, each photosensitive drum 11 and intermediate transfer belt 15 stop rotating, and a primary transfer current is supplied between each primary transfer roll 16 and each photosensitive drum 11. The state that is not. In the following description, the photosensitive drum 11 provided in the yellow image forming unit 10Y is referred to as a photosensitive drum 11 (Y). This is also expressed as photosensitive drums 11 (M), 11 (C), and 11 (K) for the photosensitive drums 11 of other colors, respectively.
In the example shown in FIG. 4A, a yellow photosensitive drum 11 (Y), a magenta photosensitive drum 11 (M), and a black photosensitive drum 11 (K) are attached to be inclined in the same direction. The cyan photosensitive drum 11 (C) is attached in a direction opposite to these.

On the other hand, FIG. 4B shows the positional relationship between each photosensitive drum 11 and the intermediate transfer belt 15 during image formation. Here, during image formation, each photosensitive drum 11 and intermediate transfer belt 15 rotate, and a primary transfer current is supplied between each primary transfer roll 16 and each photosensitive drum 11. Say. However, FIG. 4B shows a state in which a considerable time has elapsed from the start of image formation and the posture of the intermediate transfer belt 15 is stable (for example, the state after the intermediate transfer belt 15 has rotated several times or more). .
In the example shown in FIG. 4B, compared to the state shown in FIG. 4A, the intermediate transfer belt 15 is inclined, that is, the intermediate transfer belt 15 is skewed. Understood.

The reason is considered as follows.
During image formation, the primary transfer current is supplied as described above. As a result, an electrostatic attraction force due to electric charges acts between the photosensitive drums 11 and the intermediate transfer belt 15. Here, when the axial direction of each photosensitive drum 11 is not orthogonal to the arrow B direction, which is the moving direction of the intermediate transfer belt 15, the direction in which each photosensitive drum 11 intersects the intermediate transfer belt 15 with the arrow B direction. As a result, the intermediate transfer belt 15 is skewed to the IN side or the OUT side (IN side in the example shown in FIG. 4B).

  When the alignment operation or the image forming operation is started, the intermediate transfer belt 15 gradually shifts from the state shown in FIG. 4A to the state shown in FIG. After the intermediate transfer belt 15 has made several rotations (for example, three rotations), the posture of the intermediate transfer belt 15 is stabilized in the state shown in FIG.

Next, details of the alignment operation will be described.
FIG. 5 shows the main-scan exposure reference value and the sub-scan exposure reference value for each color used in the alignment operation. Here, the sub-scan exposure reference value for each color serves as a reference for the writing start timing of the scanning exposure in the laser exposure unit 13 for each color, and the main-scan exposure reference value for each color corresponds to the laser exposure unit 13 for each color. This is a reference for the timing of the start of scanning exposure. The main scanning exposure reference value and the sub-scanning exposure reference value for each color are stored in advance in the storage unit 41 shown in FIG. In the following description, the yellow main scanning exposure reference value is referred to as a Y main scanning exposure reference value Yy, and the sub scanning exposure reference value is referred to as a Y sub scanning exposure reference value Yx. The magenta main scanning exposure reference value is referred to as an M main scanning exposure reference value My, and the sub scanning exposure reference value is referred to as an M sub scanning exposure reference value Mx. Further, the cyan main scanning exposure reference value is referred to as a C main scanning exposure reference value Cy, and the sub scanning exposure reference value is referred to as a C sub scanning exposure reference value Cx. The black main scanning exposure reference value is called a K main scanning exposure reference value Ky, and the sub scanning exposure reference value is called a K sub scanning exposure reference value Kx.

FIG. 6 is a flowchart showing the flow of processing in the alignment operation.
When the control unit 40 receives an instruction to start the alignment operation (step 101), the control unit 40 reads the main scanning exposure reference value and the sub-scanning exposure reference value for each color from the storage unit 41, and outputs them to the laser exposure unit 13 for the corresponding color. (Step 102). In each laser exposure unit 13, the driver provided in each laser receives the main scanning exposure reference value and the sub scanning exposure reference value of the corresponding color, and uses the main scanning exposure reference value as the main scanning exposure set value to perform the sub scanning. The exposure reference value is set as the sub-scanning exposure setting value.

  Next, the control unit 40 instructs each of the image forming units 10Y, 10M, 10C, and 10K to start forming a patch image (step 103). Further, the control unit 40 rotates the photosensitive drum 11 provided in each of the image forming units 10Y, 10M, 10C, and 10K in the direction of arrow A, and rotates the intermediate transfer belt 15 in the direction of arrow B. Further, the control unit 40 turns on the primary transfer power sources 19 provided in the primary transfer rolls 16 in the order shown in FIG. 3, and sequentially starts supplying the primary transfer current.

  Each of the image forming units 10Y, 10M, 10C, and 10K receives a command from the control unit 40 and forms a patch image as an example of a test image on the photosensitive drum 11 through charging, exposure, and development processes. The patch images of the respective colors are sequentially transferred to the intermediate transfer belt 15 by the action of the primary transfer electric field acting between each primary transfer roll 16 and each photosensitive drum 11. At this time, each laser exposure unit 13 of each of the image forming units 10Y, 10M, 10C, and 10K emits an exposure beam Bm at a timing based on each main scanning exposure reference value and a timing based on the sub-scanning exposure reference value. An electrostatic latent image is formed.

  Subsequently, each color patch image transferred onto the intermediate transfer belt 15 passes through a portion facing the image detection sensor 42. Accordingly, the control unit 40 acquires the output of the image detection sensor 42, that is, the result of reading the patch images of the respective colors formed on the intermediate transfer belt 15 (step 104).

Then, the control unit 40 performs main scanning exposure on the laser exposure unit 13 of each color as a correction value for aligning the formation position of each color image on the intermediate transfer belt 15 based on the read result of the obtained patch image of each color. A correction value and a sub-scanning exposure correction value are created (step 105). Here, the main scanning exposure correction value as an example of the alignment correction value or the writing position correction value is used to correct the main scanning exposure reference value, and the sub scanning exposure correction value is the sub scanning exposure reference value. It is used for the correction.
The main-scan exposure correction value and the sub-scan exposure correction value for each color are obtained as a result of reading, that is, the formation position of each color patch image on the intermediate transfer belt 15 and a predetermined patch image color image on the intermediate transfer belt 15. The main scanning direction deviation and the sub-scanning direction deviation from the ideal formation position are each set to be eliminated.

  On the other hand, the control unit 40 acquires the respective outputs of the first belt position sensor 43 and the second belt position sensor 44 during the period in which the image detection sensor 42 is reading the patch images of the respective colors (step 106). Then, the control unit 40 uses the acquired outputs of the first belt position sensor 43 and the second belt position sensor 44 to perform primary transfer positions (Y color primary transfer positions Ty and M colors) during the alignment operation. A first skew amount that is the skew amount of the intermediate transfer belt 15 at the primary transfer position Tm, the C color primary transfer position Tc, and the K color primary transfer position Tk (see FIG. 2) is determined (step 107).

  After that, the control unit 40 determines the first skew state determined as step 107 or the first skew amount as an example of the first displacement amount, the main scanning exposure correction value and the sub scanning exposure correction created in step 105. The value is stored in the storage unit 41 in association with each color (step 108), and the process is completed. After the image forming operation is finished, the supply of each primary transfer current is finished in the order shown in FIG. 3, and then the driving of each photosensitive drum 11 and the intermediate transfer belt 15 is stopped.

  FIG. 7 is a diagram showing the relationship between the first skew amount of each color and the main scanning exposure correction value and sub-scanning exposure correction value of each color stored in the storage unit 41 in step 108. In the following description, the first skew amount of each color is defined as Y first skew amount Sy1, M first skew amount Sm1, C first skew amount Sc1, and K first skew amount Sk1, respectively. Call. The main scanning exposure correction values for each color are referred to as a Y main scanning exposure correction value Ryy, an M main scanning exposure correction value Rmy, a C main scanning exposure correction value Rcy, and a K main scanning exposure correction value Rky, respectively. Further, the sub-scan exposure correction values for the respective colors are referred to as a Y sub-scan exposure correction value Ryx, an M sub-scan exposure correction value Rmx, a C sub-scan exposure correction value Rcx, and a K sub-scan exposure correction value Rkx, respectively.

  FIG. 8 is a diagram for explaining a method for determining the skew amount (the first skew amount described above and the second skew amount described later) at the primary transfer position of each color in step 107. Here, a specific description will be given of a method of determining the Y first skew amount Sy1 at the Y color primary transfer position Ty. However, the first skew amount of all other colors and all the second skew amounts are also described. The same procedure is used.

  Now, it is assumed that the intermediate transfer belt 15 is skewed in a state as shown in FIG. 8 at time t = T1. Further, at time t = T1, it is assumed that the output of the first belt position sensor 43 is the first measured value W43 (T1), and the output of the second belt position sensor 44 is the second measured value W44 (T1). Suppose there was. Further, it is assumed that the distance from the first belt position sensor 43 to the Y color primary transfer position Ty is Ly1, and the distance from the Y color primary transfer position Ty to the second belt position sensor 44 is Ly2. The distances Ly1 and Ly2 are stored in the storage unit 41 in advance, and the control unit 40 reads the distances Ly1 and Ly2 from the storage unit 41 as necessary. The storage unit 41 also stores a distance from the primary transfer position of the other color to the first belt position sensor 43 and a distance from the primary transfer position of the other color to the second belt position sensor 44.

  Then, the control unit 40 reads the distances Ly1 and Ly2 from the storage unit 41 and also reads from the storage unit 41 an arithmetic expression for obtaining the Y first skew amount Sy (t) at the Y color primary transfer position Ty. The control unit 40 substitutes the distances Ly1 and Ly2, the first measurement value W43 (T1), and the second measurement value W44 (T1) into the read arithmetic expression, and uses the Y first skew feed amount Sy1 (T1). Ask. Specifically, the control unit 40 obtains the Y first skew amount Sy1 by one of the following arithmetic expressions.

  Here, in the present embodiment, the first measurement value W43 (t) and the second measurement value W44 (t) are obtained 50 times at equal intervals while the intermediate transfer belt 15 makes one revolution, and Y The calculation of the first skew amount Sy1 is also performed 50 times. Then, the control unit 40 averages the values of the obtained 50 Y first skew feed amounts Sy (T1) to Sy (T50), and stores the obtained average value as the Y first skew feed amount Sy1. 41 is stored.

FIG. 9 is a flowchart showing a flow of exposure timing correction processing in the image forming operation of the main image.
When the control unit 40 receives an instruction to start an image forming operation (step 201), the main scanning exposure reference value, the main scanning exposure correction value, the sub scanning exposure reference value, and the sub scanning exposure correction value for each color are stored from the storage unit 41. Are output to the corresponding laser exposure devices 13 (step 202). In each laser exposure unit 13, the driver provided in each receives the main scanning exposure reference value and the main scanning exposure correction value, the sub scanning exposure reference value and the sub scanning exposure correction value for the corresponding color. A value obtained by adding the main scanning exposure correction value to the scanning exposure reference value is set as the main scanning exposure setting value, and a value obtained by adding the sub scanning exposure correction value to the sub scanning exposure reference value is set as the sub scanning exposure setting value.

  Next, the control unit 40 instructs each of the image forming units 10Y, 10M, 10C, and 10K to start forming the main image (Step 203). Further, the control unit 40 rotates the photosensitive drum 11 provided in each of the image forming units 10Y, 10M, 10C, and 10K in the direction of arrow A, and rotates the intermediate transfer belt 15 in the direction of arrow B. Further, the control unit 40 turns on the primary transfer power sources 19 provided in the primary transfer rolls 16 in the order shown in FIG. 3, and sequentially starts supplying the primary transfer current.

  Each of the image forming units 10Y, 10M, 10C, and 10K receives an instruction from the control unit 40, forms a main image on the photosensitive drum 11 through charging, exposure, and development processes. The images of the respective colors are sequentially transferred to the intermediate transfer belt 15 by the action of the primary transfer electric field acting between the photosensitive drums 11 and the photosensitive drums 11. At this time, in each laser exposure unit 13 of each of the image forming units 10Y, 10M, 10C, and 10K, the timing of adding the main scanning exposure correction value to each main scanning exposure reference value and the sub scanning to each sub scanning exposure reference value. An exposure beam Bm is emitted at a timing taking the exposure correction value into consideration, and an electrostatic latent image is formed. The toner image primarily transferred onto the intermediate transfer belt 15 is then secondarily transferred onto the paper P and then output after fixing.

  During this time, the control unit 40 acquires the outputs of the first belt position sensor 43 and the second belt position sensor 44 (step 204). At this time, the intermediate transfer belt 15 rotates while holding the toner image that has been primarily transferred. The control unit 40 uses the acquired outputs of the first belt position sensor 43 and the second belt position sensor 44 to perform primary transfer positions (Y-color primary transfer positions Ty, M-color) during the image forming operation. A second skew amount, which is the skew amount of the intermediate transfer belt 15 at the primary transfer position Tm, the C color primary transfer position Tc, and the K color primary transfer position Tk (see FIG. 2), is determined (step 205). In the following description, the second skew amount of each color is defined as Y second skew amount Sy2, M second skew amount Sm2, C second skew amount Sc2, and K second skew amount Sk2, respectively. Call.

  Here, the procedure for determining the second skew amount as an example of the second skew state or the second displacement amount is basically the same as the procedure for determining the first skew amount described above. However, during the period from when the intermediate transfer belt 15 starts to rotate until the third turn has passed (referred to as a transition period), the second skew amount obtained 50 times per turn of the intermediate transfer belt 15. Among them, 10 consecutive data are averaged to obtain the second skew amount. This is because the posture of the intermediate transfer belt 15, that is, the skew state, changes suddenly from the state shown in FIG. 4A to FIG. 4B during the transition period. On the other hand, during the period after the fourth turn after the intermediate transfer belt 15 starts rotating (referred to as a stable period), the second skew feed amount acquired 50 times per turn of the intermediate transfer belt 15 is continuously. The second skew amount is obtained by averaging data for 100 times. This is because the posture of the intermediate transfer belt 15, that is, the skew state is settled in the state shown in FIG. 4B during the stable period.

  Next, the control unit 40 reads the Y first skew amount Sy1, the M first skew amount Sm1, the C first skew amount Sc1, and the K first skew amount Sk1 from the storage unit 41. The control unit 40 then includes the Y first skew amount Sy1, the M first skew amount Sm1, the C first skew amount Sc1, the K first skew amount Sk1, and the Y second skew obtained in step 205. Based on the line amount Sy2, the M second skew amount Sm2, the C second skew amount Sc2, and the K second skew amount Sk2, skew correction values for the laser exposure devices 13 of the respective colors are determined (step 206). Here, the skew correction value is a position in the main scanning direction due to the skew of the intermediate transfer belt 15 with respect to the result of correcting the main scanning exposure reference value with the main scanning exposure correction value in the laser exposure unit 13 of each color. It is used to correct the deviation. More specifically, in this embodiment, the difference between the first skew amount and the second skew amount of the same color is calculated (for example, in the case of yellow, the Y first skew amount Sy1-Y second The skew correction value for the color is determined based on the skew amount Sy2) and the magnitude of the difference. In the following description, the skew correction value of each color is referred to as a Y skew correction value Ey, an M skew correction value Em, a C skew correction value Ec, and a K skew correction value Ek, respectively.

  Thereafter, the control unit 40 reads the Y main scanning exposure correction value Ryy, the M main scanning exposure correction value Rmy, the C main scanning exposure correction value Rcy, and the K main scanning exposure correction value Rky from the storage unit 41. Then, the control unit 40 skews the Y main scanning exposure correction value Ryy, the M main scanning exposure correction value Rmy, the C main scanning exposure correction value Rcy, and the K main scanning exposure correction value Rky obtained in step 206. The correction value Ey, the M skew correction value Em, the C skew correction value Ec, and the K skew correction value Ek are respectively added, and the obtained addition results are used as new Y main scanning exposure correction values Ryy and M main scanning. The exposure correction value Rmy, the C main scanning exposure correction value Rcy, and the K main scanning exposure correction value Rky are determined (step 207). Next, the control unit 40 uses the obtained new Y main scanning exposure correction value Ryy, M main scanning exposure correction value Rmy, C main scanning exposure correction value Rcy, and K main scanning exposure correction value Rky to the corresponding color laser. The data is output to the exposure unit 13 (step 208). Each laser exposure unit 13 corrects the exposure timing using the received new main scanning exposure correction value.

  Then, the control unit 40 determines whether or not the image forming operation has ended (step 209). If it is determined that the image forming operation has not ended, the control unit 40 returns to step 204 and continues the processing. On the other hand, if it is determined in step 209 that the image forming operation has been completed, a series of processing is completed. After the image forming operation is finished, the supply of each primary transfer current is finished in the order shown in FIG. 3, and then the driving of each photosensitive drum 11 and the intermediate transfer belt 15 is stopped. As a result, the posture of the intermediate transfer belt 15 returns from the state shown in FIG. 4B to the state shown in FIG.

  In the present embodiment, the configuration in which images formed by the image forming units 10Y, 10M, 10C, and 10K are transferred to the intermediate transfer belt 15 has been described as an example. However, the present invention is not limited to this. For example, by providing a conveyance belt that is circulated and conveyed at positions opposed to the image forming units 10Y, 10M, 10C, and 10K, and holding the paper P on the conveyance belt, the image forming units 10Y, 10M, 10C, and 10K are provided. The image formed in (1) may be directly transferred onto the paper P. In this case as well, each color patch image is transferred to the transport belt.

  In this embodiment, the case where an image of each color is formed using an electrophotographic method has been described as an example, but the present invention is not limited to this. For example, an inkjet recording device that forms an image of each color may be arranged side by side, and an image may be sequentially recorded on a sheet on an intermediate transfer belt or a conveyance belt using each inkjet recording device.

1 is a diagram illustrating a schematic configuration of an image forming apparatus to which the exemplary embodiment is applied. FIG. 3 is a plan view of an intermediate transfer belt as viewed from the image forming unit side. 6 is a time chart showing the timing of turning on and off the primary transfer power supply in each image forming unit. (A) is a diagram showing the positional relationship between each photosensitive drum and the intermediate transfer belt during non-image formation, and (b) is a diagram showing the positional relationship between each photosensitive drum and the intermediate transfer belt during image formation. It is. It is a figure which shows the main scanning exposure reference value and sub-scanning exposure reference value of each color used by alignment operation. It is a flowchart which shows the flow of a process in the control part in position alignment operation | movement. It is a figure which shows the relationship between the 1st skew amount of each color, the main scanning exposure correction value of each color, and a sub-scanning exposure correction value. It is a figure for demonstrating the determination method of the skew feeding amount in the primary transfer position of each color. It is a flowchart which shows the flow of the process of exposure timing correction | amendment in image forming operation | movement.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Image forming unit, 11 ... Photoconductor drum, 12 ... Charger, 13 ... Laser exposure device, 14 ... Developing device, 15 ... Intermediate transfer belt, 15a ... Belt edge, 16 ... Primary transfer roll 18 ... Intermediate transfer module, 19 ... Primary transfer power source, 20 ... Secondary transfer device, 21 ... Secondary transfer roll, 22 ... Backup roll, 31 ... Drive roll, 32 ... Idler roll, 33 ... Steering roll, 34 ... Belt cleaner, 40 ... control unit, 41 ... storage unit, 42 ... image detection sensor, 43 ... first belt position sensor, 44 ... second belt position sensor, 45 ... belt home sensor

Claims (6)

A plurality of image forming units for forming an image;
A transport member for transporting images transferred from the plurality of image forming units;
A first skew with respect to the transport direction of the transport member in a positioning operation for determining a registration correction value for transferring a test image from a plurality of the image forming units to the transport member and correcting a positional deviation between the images. First acquisition means for acquiring a state;
Second acquisition means for acquiring a second skew state with respect to the transport direction of the transport member in an image forming operation for transferring the main image from the plurality of image forming units to the transport member;
An image forming apparatus comprising: a correction unit that corrects the misregistration correction value based on the first skew state and the second skew state. The conveying member is composed of a rotating endless belt member,
The image forming apparatus according to claim 1, wherein the second acquisition unit lengthens the acquisition interval of the second skew state in accordance with an increase in the rotation speed of the transport member. Each of the plurality of image forming units includes a rotating image carrier and an image writing unit that writes an image on the image carrier,
The image forming apparatus according to claim 1, wherein the image writing unit sets an image writing position with respect to the image holding body based on the misregistration correction value. A photoreceptor,
An exposure device for writing an electrostatic latent image on the photoreceptor;
A developing unit for developing the electrostatic latent image written on the photoreceptor;
A plurality of image forming units each having
A belt member rotatably supported and onto which an image formed on the photoconductor provided in each of the plurality of image forming units is transferred;
A measuring unit for measuring a displacement in the width direction of the rotating belt member;
When reading the test image and the correction value of the writing position of the exposure device in each image forming unit determined based on the reading result of the test image transferred from the plurality of image forming units to the belt member A storage unit that associates and stores the first displacement amount of the belt member measured by the measurement unit;
Based on the first displacement amount and the second displacement amount measured by the measurement unit when transferring the main image from the plurality of image forming units to the belt member, each of the image forming units. An image forming apparatus including a correction unit that corrects a writing position of the exposure device in the above.   The image forming apparatus according to claim 4, wherein the correction unit increases a correction interval of a writing position of the exposure device in accordance with an increase in the number of rotations of the belt member.   6. The image formation according to claim 4, wherein the first displacement amount and the second displacement amount are acquired for each transfer position where the image forming unit and the belt member face each other. apparatus.

Images