JP2019008262A - Image forming apparatus - Google Patents

Abstract

To make it possible to accurately detect images for detection on a secondary transfer body.SOLUTION: An image forming apparatus 100 according to the present invention comprises: an intermediate transfer body 310 to which images for detection T1 are transferred from image carriers 2Y to 2K; a secondary transfer body 404 that is wound around a plurality of rotating bodies 401 to 403 including a driving rotating body 36 and in contact with the intermediate transfer body to form a transfer part N2, and to which the images for detection are transferred from the intermediate transfer body at the transfer part; and a detection member 407 that detects the images for detection transferred to the secondary transfer body. The distance L2 from the transfer part N2 to a detection position Z2 on the secondary transfer body at which the detection member detects the images for detection is set to an integral multiple of the outer circumferential length of the driving rotating body.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus.

  In the image forming apparatus, a toner pattern, which is a detection image formed on an image carrier, is transferred to a secondary transfer member via an intermediate transfer member in contact with the image carrier, and the toner transferred to the secondary transfer member There is known a technique in which a pattern is detected by a sensor serving as a detection unit, and an image forming unit is controlled according to the detection result to adjust a color shift or a position shift (for example, Patent Document 1).

When adjusting the color shift or position shift by detecting on the secondary transfer member, the secondary transfer from the position of the primary transfer nip where the image carrier and the intermediate transfer member are in contact with each other is compared to the method of detecting on the intermediate transfer member. Between the sensor detection unit that detects the toner pattern transferred to the transfer body, there is a secondary transfer nip where the intermediate transfer body and the secondary transfer body come into contact with each other to transfer the toner pattern. This may cause a decrease in detection accuracy.
An object of the present invention is to make it possible to accurately detect a detection image on a secondary transfer member.

  In order to achieve the above object, an image forming apparatus according to the present invention is wound around an intermediate transfer member that is wound around a plurality of rotating members including an intermediate transfer member to which a detection image is transferred from an image carrier and a driving rotating member. A secondary transfer body on which the detection image is transferred from the intermediate transfer body at the transfer section, a detection member that detects the detection image transferred to the secondary transfer body, and a transfer The distance from the detection part to the detection position on the secondary transfer body by the detection member is an integral multiple of the outer peripheral length of the drive rotator.

  According to the present invention, the speed variation of the secondary transfer body can be suppressed by setting the distance from the transfer portion to the detection position on the secondary transfer body by the detection member to be an integral multiple of the outer peripheral length of the drive rotating body. Therefore, even if an intermediate transfer member or a secondary transfer member is interposed between the image forming unit and the detection position, the detection image on the secondary transfer member can be accurately detected.

1 is a schematic configuration diagram illustrating a first embodiment of an image forming apparatus according to the present invention. FIG. 2 is a perspective view illustrating a configuration of a secondary transfer unit in the image forming apparatus illustrated in FIG. 1. FIG. 2 is a diagram illustrating a configuration of a secondary transfer unit in the image forming apparatus illustrated in FIG. 1. The enlarged view explaining the example of 1 structure of the tape-shaped to-be-detected part provided in the intermediate transfer body. The figure explaining the arrangement structure of the optical detection means which detects a tape-shaped to-be-detected part. (A)-(c) is a figure explaining the structure of an optical detection means. The figure explaining the speed variation of a secondary transfer body, and the position shift of the image for a detection. The figure explaining the speed nonuniformity of the secondary transfer body containing the eccentricity of a drive system. The schematic block diagram explaining the structure of the modification 1 of 1st Embodiment. The schematic block diagram explaining the structure of the modification 2 of 1st Embodiment. FIG. 3 is a schematic configuration diagram illustrating a second embodiment of an image forming apparatus according to the invention. The perspective view which shows one form of the rotational drive mechanism of a rotational drive body.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In the embodiment, components having the same function and the same configuration are denoted by the same reference numerals, and redundant description will be omitted as appropriate. The drawings may be partially omitted to facilitate understanding of the configuration. In the figure, Y, M, C, and K are subscripts attached to components corresponding to yellow, magenta, cyan, and black, and will be omitted as appropriate.

An embodiment of an electrophotographic color printer (hereinafter referred to as “printer”) 100 as an image forming apparatus according to the present invention will be described.
A basic configuration of the printer 100 will be described. FIG. 1 is a schematic configuration diagram illustrating a printer 100 according to the present embodiment. In FIG. 1, a printer 100 includes four image forming units 1 (Y, M, C, K) for forming yellow (Y), magenta (M), cyan (C), and black (K) toner images. Is provided. The printer 100 includes an intermediate transfer unit 30 as a transfer device, a secondary transfer unit 41 as a secondary transfer device, a cassette 66 for storing a recording material P, a fixing device 90, and a control unit 300.
The four image forming units 1 (Y, M, C, and K) are powders and use different colors of Y, M, C, and K toners as developers, but the other configurations are the same. It will be replaced when it reaches the end of its service life. That is, the four image forming units 1 (Y, M, C, K) are detachably provided to the printer main body 100A as the main body of the image forming apparatus, and can be exchanged. Four image forming units 1 (Y, M, C, K) are arranged adjacent to each other.
The image forming units 1Y, 1M, 1C, and 1K are drum-shaped photoconductors 2Y, 2M, 2C, and 2K that are image carriers, drum cleaning devices 3Y, 3M, 3C, and 3K, static eliminators, and charging devices 6Y, 6M, and 6C. , 6K, developing devices 8Y, 8M, 8C, 8K and the like. The image forming units 1Y, 1M, 1C, and 1K constitute a process cartridge unit in which these plural devices are held by a common holding body and can be integrally attached to and detached from the printer main body 100A. It is possible.

  The photoreceptors 2Y, 2M, 2C, and 2K are rotationally driven in a counterclockwise direction in the drawing by a driving unit such as a motor. The charging devices 6Y, 6M, 6C, and 6K are configured such that a charging roller that serves as a charging member to which a charging bias is applied is in contact with or close to the photosensitive members 2Y, 2M, 2C, and 2K, and the charging rollers and the photosensitive members 2Y, 2M, and 2C. The surfaces of the photoreceptors 2Y, 2M, 2C, and 2K are uniformly charged by generating a discharge between them and 2K. Instead of a method in which a charging member such as a charging roller is brought into contact with or close to the photoreceptors 2Y, 2M, 2C, and 2K, a method using a charging charger may be adopted.

The surfaces of the photoreceptors 2Y, 2M, 2C, and 2K uniformly charged by the charging devices 6Y, 6M, 6C, and 6K are optical writing units 101 disposed above the image forming units 1Y, 1M, 1C, and 1K. An electrostatic latent image for each color is formed by optical scanning with exposure light such as laser light emitted from. The electrostatic latent image is developed by the developing devices 8Y, 8M, 8C, and 8K having toners of the respective colors to become toner images T as the images of the respective colors. A toner image is formed on the photoreceptor 2.
The toner images T of the photoreceptors 2Y, 2M, 2C, and 2K are primarily transferred and carried on the front surface 31a of the intermediate transfer belt 31 as an intermediate transfer member made of an endless belt member.
The drum cleaning devices 3Y, 3M, 3C, and 3K remove transfer residual toner that has adhered to the surfaces of the photoreceptors 2Y, 2M, 2C, and 2K after the primary transfer process (primary transfer nip described later). is there. The static eliminator is a well-known device that neutralizes residual charges on the photoreceptors 2, 2M, 2C, and 2K after being cleaned by the drum cleaning devices 3, 3M, 3C, and 3K. The surfaces of the photoreceptors 2Y, 2M, 2C, and 2K are initialized by this static elimination and are prepared for the next image formation.

Below the image forming units 1Y, 1M, 1C, and 1K are belt units that endlessly move (rotate) in the clockwise direction in the figure while stretching the intermediate transfer belt 31, and an intermediate transfer unit that is a primary transfer device 30 is disposed. The intermediate transfer unit 30 is also referred to as a primary transfer unit or an intermediate transfer unit. In this embodiment, the rotational movement direction of the intermediate transfer belt 31 is a belt movement direction a.
The intermediate transfer unit 30 is detachable (replaceable) together with the printer main body 100A. The intermediate transfer unit 30 is a belt-like image carrier and an intermediate transfer belt 31 that is also an intermediate transfer member, as well as a driving roller 32, a secondary transfer back roller 33, a cleaning backup roller 34, and a four-wheel rotating roller. Primary transfer rollers 35Y, 35M, 35C, and 35K, a pre-transfer roller 37, and the like. The drive roller 32 constitutes an intermediate drive rotating body that is rotationally driven by the drive motor M1.

  The intermediate transfer belt 31 includes a driving roller 32, a secondary transfer back roller 33, a cleaning backup roller 34, primary transfer rollers 35Y, 35M, 35C, and 35K, and a pre-transfer roller 37, which are rotating bodies disposed inside the loop. It is wrapped around and supported and stretched. Then, it is transported endlessly in the same direction by the rotational force of the driving roller 32 that is driven to rotate clockwise in the drawing by a driving means such as a driving motor. In the present embodiment, the intermediate transfer belt 31 is formed of an elastic endless elastic belt in which a plurality of layers are laminated, and the toner images on the photoreceptors 2Y, 2M, 2C, and 2K are primarily transferred. Intermediate transfer member.

  The primary transfer rollers 35Y, 35M, 35C, and 35K sandwich the intermediate transfer belt 31 that is moved endlessly between the photoreceptors 2Y, 2M, 2C, and 2K, and form a front surface that forms an image carrying surface of the intermediate transfer belt 31. A primary transfer nip N1 is formed as a primary transfer portion for Y, M, C, and K where 31a and the surfaces of the photoreceptors 2Y, 2M, 2C, and 2K abut. A primary transfer bias is applied to the primary transfer rollers 35Y, 35M, 35C, and 35K from a known transfer bias power source. As a result, a transfer electric field is formed between the Y, M, C, and K toner images on the photoreceptors 2Y, 2M, 2C, and 2K and the primary transfer rollers 35Y, 35M, 35C, and 35K.

The Y toner image formed on the surface of the yellow photoconductor 2Y enters the yellow primary transfer nip N1 as the yellow photoconductor 2Y rotates. Then, the image is primarily transferred from the yellow photoreceptor 2Y onto the intermediate transfer belt 31 by the action of the transfer electric field and nip pressure. The intermediate transfer belt 31 onto which the Y toner image has been primarily transferred in this way then passes sequentially through the primary transfer nip N1 for M, C, and K. Then, the M, C, and K toner images on the photoreceptors 2M, 2C, and 2K are sequentially superimposed and superimposed on the Y toner image. A four-color superimposed toner image is formed on the intermediate transfer belt 31 by the primary transfer of the superposition.
The image forming process so far has been described on the assumption that a four-color full-color image is formed. However, the printer 100 may form a single color toner image of yellow, magenta, cyan, or black, or a toner image using toner of at least two of the colors, and transfer the toner image to the intermediate transfer belt 31. Is possible.

Below the outer loop of the intermediate transfer belt 31, a secondary transfer having a secondary transfer belt 404 formed of a material harder than the resin intermediate transfer belt 31 (for example, a polyimide resin belt (PI belt)). A belt-type secondary transfer device 40 including a unit 41 is disposed, and the secondary transfer belt 404 is a belt member, a transfer member, and a secondary transfer member. The intermediate transfer belt 31 is sandwiched between the secondary transfer back roller 33 and the secondary transfer belt 404 disposed inside the loop of the belt 31 so that the front surface 31a of the intermediate transfer belt 31 and the secondary transfer belt 404 are in contact with each other. A secondary transfer nip N2 is formed as a transfer portion in contact therewith.
In this embodiment, a secondary transfer bias is applied to the secondary transfer back roller 33 by a power source 39 as a transfer bias output unit. Thus, the negatively charged toner is electrostatically moved between the secondary transfer back roller 33 and the secondary transfer belt 404 from the secondary transfer back roller 33 side toward the secondary transfer belt 404 side. A secondary transfer electric field is formed. In the present embodiment, the toner image on the intermediate transfer belt 31 is secondarily transferred to the recording material P in the secondary transfer nip N2 serving as the transfer portion. The intermediate transfer belt 31 is an image carrier that forms a secondary transfer nip N2 with the secondary transfer belt 404, which is a conveyance belt, and the toner images on the photoreceptors 2Y, 2M, 2C, and 2K are primarily transferred. It is also an intermediate transfer member. The toner image transferred to the secondary transfer belt 404 is a toner image used for image density measurement.

In this embodiment, a bias used for secondary transfer (secondary transfer bias) is applied from the power source 39 to the secondary transfer back surface roller 33. The secondary transfer bias is a bias in which an AC voltage is superimposed on a DC voltage, and the time average value (time average voltage) of the voltage is negative. The secondary transfer back roller 33 is a roller to which a secondary transfer bias is applied, and a secondary transfer bias having a negative time average voltage is applied to this roller. Since the secondary transfer bias gives a repulsive force to the negatively charged toner, the secondary transfer back roller 33 may be called a repulsive roller.
In this embodiment, the secondary transfer back roller 33 is configured to apply a bias (secondary transfer bias) used for secondary transfer from the power source 39, but is disposed opposite to the secondary transfer back roller 33. A bias may be applied from the power source 39 to the secondary transfer roller 36. When a secondary transfer bias is applied to the secondary transfer roller 36, a secondary transfer bias whose time average voltage is opposite to that of the toner is applied, and a secondary transfer bias is applied to the secondary transfer back roller 33. In this case, a secondary transfer bias whose time average voltage has the same polarity as that of the toner is applied. The secondary transfer roller 36 is also referred to as a nip forming roller.
In this embodiment, a bias in which an AC voltage is superimposed on a DC voltage is used as the secondary transfer bias. However, a bias consisting of only a DC voltage may be used.

  Below the transfer device 40, a cassette 66 is provided that serves as a storage unit that can store a plurality of recording materials P such as various papers and resin sheets in a stacked state. In this cassette 66, a roller 66a is brought into contact with the top recording material P of the bundle, and the recording material P is moved from the cassette 66 to the secondary transfer nip N2 by being driven to rotate at a predetermined timing. It sends out toward the conveyance path 65. The recording material P sent to the conveyance path 65 is sent to the secondary transfer nip N2 by the registration roller pair 61 at a timing synchronized with the toner image on the front surface 31a of the intermediate transfer belt 31 in the secondary transfer nip N2. It is. The recording material P is a transported object.

  The toner image on the front surface 31a of the intermediate transfer belt 31 is secondarily transferred onto the recording material P at the secondary transfer nip N2 by the action of the secondary transfer electric field or nip pressure, and is combined with the white color of the recording material P to be full color. It becomes a toner image. Untransferred toner that has not been transferred to the recording material P adheres to the front surface 31a of the intermediate transfer belt 31 after passing through the secondary transfer nip N2. The transfer residual toner is cleaned from the belt surface by the intermediate belt cleaning device 38 that is in contact with the front surface 31 a of the intermediate transfer belt 31.

  A fixing device 90 is disposed downstream of the secondary transfer nip N2 in the recording material conveyance direction b. A recording material P onto which a toner image has been transferred is sent to the fixing device 90. The fed recording material P is sandwiched between fixing nips in which a fixing roller 91 having a heat source and a pressure roller 92 are in contact with each other, and the toner in the full-color toner image is softened and fixed by heating and pressing. The The recording material P after fixing is discharged from the fixing device 90 and discharged outside the apparatus.

  The printer 100 has an image adjustment mode for adjusting the image density. When the image adjustment mode is set, the printer 100 issues an image formation signal and detects the color misregistration correction with the corresponding color toner outside the image formation areas of the photoreceptors 1Y, 1M, 1C, and 1K. A pattern image (registration mark) T1 which is a toner image of each color is developed as an image, transferred to the intermediate transfer belt 31 at the primary transfer nip N1, and not the recording medium P at the secondary transfer nip N2 but the secondary transfer belt 404. The image is transferred onto the outer side surface 404a which becomes an image carrying surface. In the image adjustment mode, the image position of the pattern image T1 transferred onto the outer surface 404a of the secondary transfer belt 404 is detected by a pattern detection sensor 407 serving as a detection member. In the image adjustment mode, feedback control is performed so that the image position of the pattern image T1 becomes a predetermined position according to the image position information detected by the pattern detection sensor 407 by the control unit 300. Specifically, the control unit 300 sets each color on the photoreceptors 2Y, 2M, 2C, and 2K so that the pattern image T1 of each color is at a predetermined position according to the image position information detected by the pattern detection sensor 407. The position where the electrostatic latent image is formed is adjusted. This prevents color misregistration between the colors.

Next, the configuration of the secondary transfer unit 41 and the configuration and arrangement of the guide member 63 will be described.
As shown in FIGS. 1 and 3, the secondary transfer unit 41 is detachably supported by the pressure frame 49 and can be replaced in units. The secondary transfer unit 41 includes a secondary transfer roller 36 that is a rotating body and a transfer member that are disposed to face the secondary transfer back surface roller 33 via the intermediate transfer belt 31. The secondary transfer unit 41 includes rollers 401, 402, and 403 as three rotating bodies, a secondary transfer roller 36, a secondary transfer belt 404 wound around the rollers 401, 402, and 403, and a belt cleaning member. A cleaning blade 405 is provided. In the present embodiment, the cleaning blade 405 constitutes a cleaning unit. The secondary transfer unit 41 is an image carrier, and is a secondary transfer belt 404 composed of an endless belt member. The secondary transfer unit 41 includes a plurality of secondary transfer rollers 36 and rollers 401, 402, and 403 that are rotating bodies. This is a belt unit that winds, supports and conveys the secondary transfer belt 404. The secondary transfer roller 36 is also referred to as a nip forming roller.

The secondary transfer roller 36 is grounded and performs secondary transfer of the toner image T on the front surface 31 a of the intermediate transfer belt 31 to the recording material P. That is, the secondary transfer roller 36 is provided in the secondary transfer belt 404 and is disposed to face the secondary transfer back roller 33. The secondary transfer roller 36 sandwiches the intermediate transfer belt 31 and the secondary transfer belt 404 between the secondary transfer back surface roller 33. The secondary transfer roller 36 is in contact with the secondary transfer belt 404 by being biased, and forms a secondary transfer nip N <b> 2 between the intermediate transfer belt 31 and the secondary transfer belt 404.
As the secondary transfer belt 404, a belt member made of a resin material such as polyimide (PI), polyamideimide (PAI), or polyvinylidene fluoride (PVDF) can be selected and used. As the secondary transfer belt 404, a belt member made of an elastic material may be used instead of these materials.

The roller 401 peels off the recording material P attached on the secondary transfer belt 404 by electrostatic attraction force from the secondary transfer belt 404 by the curvature separation of the roller 401. The roller 403 constitutes a tension roller by urging the secondary transfer belt 404 from the inside to the outside by a tension spring 406 as urging means.
The secondary transfer roller 36 is driven to rotate counterclockwise in the figure by a drive motor M2 (see FIG. 4) serving as a drive unit, so that the secondary transfer belt 404 is independent of the intermediate transfer belt 31. Rotate. In the present embodiment, the contact portion between the secondary transfer belt 404 and the intermediate transfer belt 31 is the secondary transfer nip N2. That is, the printer 100 includes a belt-type secondary transfer unit. In the drawing, an arrow c indicates the moving direction of the secondary transfer belt 404.
The tip of the cleaning blade 405 is in contact with the outer surface 404 a of the secondary transfer belt 404 facing the roller 403. The cleaning blade 405 is disposed downstream of the pattern detection sensor 407 in the moving direction c of the secondary transfer belt 404. The cleaning blade 405 forms a cleaning portion for cleaning the pattern image T <b> 1 that has been detected by the pattern detection sensor 407 by scraping it off from the secondary transfer belt 404.

In the secondary transfer unit 41, a pattern detection sensor 407 serving as an image position detection unit is disposed outside the secondary transfer belt 404 facing the roller 402. The pattern detection sensor 407 detects the image position of the pattern image T1, which is an image position correction toner image transferred onto the outer surface 404a of the secondary transfer belt 404 via the intermediate transfer belt 31, and outputs the detection result. .
As shown in FIG. 3, the pattern detection sensors 407 are supported by a sensor support 408 extending in the width direction W of the secondary transfer belt 404, and a plurality of pattern detection sensors 407 are arranged in the width direction W. In the present embodiment, six pattern detection sensors 407 are arranged at a distance from the pattern image T1 in a region G (see FIG. 5) where the pattern image T1 is formed. The pattern detection sensor 407 is located downstream of the secondary transfer nip N2 in the movement direction c and between the outer surface 404a of the secondary transfer belt 404 and a gap between the pattern detection sensor 407 and the outer surface 404a of the secondary transfer belt 404. Opposed.

When the pattern image (registration mark) T1 is detected on the secondary transfer belt 404 by the pattern detection sensor 407 as in the present embodiment, the pattern image (registration mark) T1 includes the primary transfer nip N1 and the secondary transfer nip. It is transferred onto the secondary transfer belt 404 via N2 and conveyed to the sensor detection unit Z2.
However, if an elastic belt is used as the endless intermediate transfer belt 31 in consideration of the transferability of the image onto the transfer material P, the intermediate transfer belt 31 is driven by a driving roller 32 as a driving rotating body, and thus driving. Strictly speaking, the intermediate transfer belt 31 is at a constant speed due to the eccentricity of the surface of the roller 32 with respect to the rotational axis and the eccentricity of a rotational transmission component such as a gear attached to the shaft of the driving roller 32 to transmit rotational force. Instead, it is moved while the speed fluctuates periodically. Similarly, the speed of the secondary transfer belt 404 also depends on the eccentricity of the surface of the secondary transfer roller 36 with respect to the rotational axis and the rotational transmission parts such as gears attached to the shaft of the secondary transfer roller 36 for transmission of rotational force. It moves while the speed fluctuates periodically due to eccentricity.

  For this purpose, the image is transferred from the photoreceptors 1Y to 1K to the intermediate transfer belt 31 at the primary transfer nip N1, which is the image transfer position, and further transferred to the secondary transfer belt 404 at the secondary transfer nip N2, which is the image transfer position. The pattern image (registration mark) T1 is formed with a deviation from the original position due to uneven conveyance speed of the conveyance belt 35 and the secondary transfer belt 404, and also at the detection position of the pattern image (registration mark) T1. Detected at a position shifted from the original position due to uneven conveyance speed, the amount of shift between colors may not be detected accurately.

  Therefore, in the present embodiment, the position of the pattern image (registration mark) T1 is detected with high accuracy so as to improve the detection accuracy of the shift amount between the colors.

(First embodiment)
As shown in FIG. 1, the first embodiment includes transfer pressure changing means 50 for changing the transfer pressure acting on the secondary transfer nip N2 serving as a transfer portion, and an intermediate transfer belt 31 shown in FIG. Is provided with a scale tape 200 serving as a detected portion. The scale tape 200 is detected by a scale sensor 60 serving as a detecting portion, and the operation of a drive motor M1 that rotationally drives the drive roller 32 is controlled to control the intermediate transfer belt 31. It is assumed that the moving speed of is stabilized.

As shown in FIG. 4, the intermediate transfer belt 31 according to the present embodiment is opposed to each roller at an end portion 31 c that is at least one side in the belt width direction that is in the axial direction W of the roller and intersects the belt moving direction a. A scale tape 200 serving as a detected portion is disposed on the inner surface 31b serving as the side to be detected over the entire belt in the longitudinal direction.
The scale tape 200 has an uneven portion 202c. As shown in FIGS. 4 and 5A, the concavo-convex portions 202c have the same length, are arranged at equal intervals in parallel to each other, and are arranged at an extremely small pitch along the belt moving direction a. Is provided on the entire circumference, thereby constituting a scale mark M serving as a detection portion for reading by the optical detection means as a whole.
In the present embodiment, the scale tape 200 is provided on the entire circumference of the intermediate transfer belt 31, but instead, the scale tape 200 may be provided on a part of the moving direction of the intermediate transfer belt 31. The scale mark M may be either a concave portion or a convex portion of the concave and convex portion 202c.

  A scale mark sensor (hereinafter referred to as “scale sensor”) 60 as optical detection means is arranged to face the scale mark M as shown in FIG. The scale sensor 60 is connected to the drive control device 71 via a signal line. The scale sensor 60 sequentially detects the scale marks M on the intermediate transfer belt 31 and outputs a detection signal to the drive control device 71. That is, the scale sensor 60 has a function of detecting the scale tape 200 that is a detected portion and reading the scale tape 200. The drive control device 71 is connected to the drive motor M1 via the motor drive circuit 81, and has a function of controlling the belt moving speed by controlling the operation of the drive motor M1. As will be described later, the drive control device 71 acquires position data and the like for correcting the pitch of the scale mark M from the detection signal from the scale sensor 60, and inputs the target position data to the motor drive circuit 81. The belt moving speed of the intermediate transfer belt 31 is controlled. As described above, the drive control device 71 appropriately outputs a signal to the motor drive circuit 81 based on the position information of the intermediate transfer belt 31 detected by the scale sensor 60, and drives the drive motor M1 by the motor drive circuit 81. The belt moving speed of the intermediate transfer belt 31 is feedback controlled.

The detection of the scale mark M by the scale sensor 60 will be described with reference to FIG.
6A is a plan view of the scale mark M on the scale tape, FIG. 6B is a side perspective view showing the configuration and optical path of the optical system of the scale sensor 60, and FIG. 6C is the detection of the scale sensor 60. It is a top view of a surface. The scale mark M is a reflection type mark, and as shown in the figure, scale marks M and light shielding portions S as reflection portions are alternately formed on the outer peripheral surface of the intermediate transfer belt 31 along the belt moving direction a. ing.
The scale sensor 60 includes a light emitting element 111 such as an LED, a collimating lens 112, a slit mask 113 (see FIG. 6B), a light receiving window 114 made of a transparent cover such as glass or a transparent resin film, and a light receiving element such as a phototransistor. 115, which are fixed to each part of the housing 110.

  When the light emitting element 111 that is the light source of the scale sensor 60 emits light, the light passes through the collimating lens 112 and becomes a parallel light flux, and as shown in FIG. The slit 113a passes through the slit 113a, is divided into a plurality of light beams LB, and is irradiated onto the scale tape 200 on the intermediate transfer belt 31. A part of the plurality of light beams LB is reflected by the scale mark M, the reflected light is received by the light receiving element 115 through the light receiving window 114, and the light receiving element 115 detects the change (intensity) of the brightness of the reflected light as an electric signal. Convert to As described above, the scale sensor 60 detects the scale mark M by detecting the intensity of the reflected light by the light receiving element 115, and the presence / absence of the scale mark M accompanying the movement of the intermediate transfer belt 31 is continuously modulated to the analog. Output as an alternating signal.

  Based on the detection result obtained by detecting the scale tape 200 with the scale sensor 60, the back-up control is applied to the drive of the drive motor M1, thereby suppressing the speed variation of the intermediate transfer belt 31 and stabilizing the drive.

As shown in FIG. 1, the secondary transfer device 40 is mounted on a pressure frame 49 that is swingably supported on a printer main body 100 a by a support shaft 48, and can swing integrally with the pressure frame 49. It is configured. The pressure frame 49 urges the secondary transfer belt 404 in a direction to contact the intermediate transfer belt 31 by a tension coil spring 55 that is a pressure spring. As a result, the secondary transfer belt 404 is in pressure contact with the intermediate transfer belt 31.
The transfer pressure changing unit 50 includes a cam 51 and a drive motor M3 serving as a cam drive source that rotationally drives the cam 51. The cam 51 is composed of an eccentric cam and is disposed below the pressure frame 49. A cam surface 51 a formed on the peripheral surface of the cam 51 is in contact with a lower portion 49 a of the pressure frame 49. The cam 51 is rotationally driven by the operation of the cam drive motor M3. The pressure frame 49 is swung by the rotation of the cam 51, whereby the transfer pressure at the secondary transfer nip N2 is adjusted. For example, when the recording material P is thin paper, the cam 51 remains at the home position in FIG. 1, and when the recording material P is thick paper, the cam 51 is rotated counterclockwise here in order to increase the transfer pressure. Thus, by moving the pressure frame 49 counterclockwise in the drawing, the operation of the drive motor M3 can be controlled by the control unit 300 so as to raise the entire secondary transfer device 40 and increase the transfer pressure. .

The plurality of rollers 401, 402, 403 and the secondary transfer roller 36 around which the secondary transfer belt 404 is wound are secondary transferred with reference to the secondary transfer roller 36 that forms the secondary transfer nip N2. In the moving direction of the belt 404, the secondary transfer roller 36 and the rollers 401, 402, and 403 are arranged in this order. The plurality of rollers 401, 402, 403 and the secondary transfer roller 36 are mounted on a pressure frame 49 serving as the same support frame.
The secondary transfer roller 36 is configured as a drive roller that is rotationally driven by a drive motor M2 via a drive transmission means. That is, the secondary transfer nip N2 serving as a transfer portion is disposed opposite to the secondary transfer roller 36 as a driving rotary body, and the secondary transfer back roller 33 as a rotary body around which the intermediate transfer belt 31 is wound, and the secondary transfer nip N2 It is formed between the transfer roller 36. The secondary transfer belt 404 moves in the counterclockwise direction in FIG. 1 when the drive motor M operates. The roller 403 functions as a tension roller serving as a tension applying member that applies the secondary transfer belt 404 from the inside to the outside.

In this embodiment, the hardness of the surface of the secondary transfer roller 36 is larger (harder) than the hardness (JIS-A) of the surface of the secondary transfer back roller 33. In this embodiment, the surface hardness of the secondary transfer roller 36 is 70 (JIS-A), and the surface hardness of the secondary transfer roller 36 is 45 (JIS-A).
A roller 401 arranged between the secondary transfer roller 36 and the roller 402 separates the curvature of the recording material P conveyed by the movement of the secondary transfer belt 404 through the secondary transfer nip N2 from the secondary transfer belt 404. Function as a separation roller.
A roller 402 that is one of a plurality of rotating bodies around which the secondary transfer belt 404 is wound is a detecting rotating body that is disposed to face the pattern detection sensor 407 via the secondary transfer belt 404. .
A roller 401, which is another rotating body among the plurality of rotating bodies, is disposed between the secondary transfer nip N2 and the roller 402 serving as a detecting rotating body, and is a support rotation composed of a metal roller having no elastic layer. Is the body.

In the printer 100 having such a configuration, the pattern detection sensor 407 serving as a detection member is arranged to face the roller 402 and irradiates the surface of the secondary transfer belt 404 on which the roller 402 is positioned with detection light. In this embodiment, the position on the secondary transfer belt 404 irradiated with the detection light is set as a detection position Z2 on the secondary transfer belt 404 by the pattern detection sensor 407.
In this embodiment, the detection position Z2 (pattern detection sensor 407) is disposed between the secondary transfer nip N2 and the roller 403 serving as a tension applying member in the moving direction of the secondary transfer belt 404.

Next, the distance between each part will be described.
In this embodiment, the distance from the transfer unit to the detection position on the secondary transfer body by the detection member is the secondary transfer belt 404 from the center position Z1 of the secondary transfer nip N2 to the detection position Z2 of the pattern detection sensor 407. The upper distance L2.
Here, the distance from the intermediate transfer portion to which the detection image is transferred from the image carrier to the intermediate transfer member to the transfer portion is the center of the primary transfer nip N1 that transfers the black toner image closest to the drive roller 32. A distance L1 on the intermediate transfer belt 31 from the position Z3 to the center position Z1 of the secondary transfer nip N2. The center position Z3 is the position of the center portion of the nip width with respect to the belt moving direction a of the primary transfer nip N1. The center position Z1 of the secondary transfer nip N2 is the position of the center of the nip width with respect to the belt moving direction a. The distance between the image forming units is the distances L3, L4 between the central portions of the primary transfer nip N1 of each unit formed between the image forming units 1Y, 1M, 1C, and 1K and the intermediate transfer belt 31. L5. The distances L3, L4, and L5 have the same dimensions.

In the printer 100 having such a configuration, in the first embodiment, the distance L2 is set to be an integral multiple of the outer peripheral length D2π of the secondary transfer roller 36 serving as a driving rotating body.
That is, when there is an eccentricity in the surface position of the secondary transfer roller 36, the peripheral speed of the surface position is periodically changed by the rotation of the secondary transfer roller 36, and the secondary transfer belt driven by the secondary transfer roller 36. The conveyance speed 404 changes periodically according to the rotation of the secondary transfer roller 36.
FIG. 7A shows fluctuations in the conveyance speed of the secondary transfer belt 404 based on the eccentricity of the secondary transfer roller 36. The fluctuations in the speed center around the target conveyance speed V0. The speed variation Vd due to the speed fluctuation is expressed by the following [Equation 1] where A is the amplitude of the speed unevenness and ω is the angular speed of the secondary transfer roller 36. .

  Due to this speed unevenness Vd, a positional deviation ΔS from the target position occurs on the secondary transfer belt 404, which causes color misregistration during image formation. This positional deviation ΔS is obtained as shown in [Equation 2] by integrating [Equation 1].

  The positional deviation ΔS is as shown in FIG. 7B. In FIG. 7, the positive region has a positional deviation ΔS that precedes the target position, and the negative region has a positional deviation Δ that is delayed from the target position. It shows that S occurs. For example, when the transfer is performed at the position P1 in FIG. 7B, the speed unevenness Vd at the time tp1 at which the transfer is performed is 0, but due to the positive speed unevenness before that, the A / Transfer is performed in a state where the secondary transfer belt 404 is positioned at a position preceded by ω. Therefore, the pattern image (registration mark) T1 is formed at a position delayed by A / ω. Further, the pattern image (registration mark) T1 formed at the correct position on the secondary transfer belt 404 is converted into a downstream position P2 where the positional deviation ΔS of the secondary transfer belt 404 is in the same phase relationship as the position P1. When detected at, a detection signal of the pattern image (registration mark) T1 is detected before the target time tp2.

  Accordingly, two points having the same phase relationship of the positional deviation ΔS of the secondary transfer belt 404, such as the position P1 and the position P2, are selected, for example, a registration mark is transferred and formed at the position P1, and the positional deviation sensor at the position P2. When the pattern image (registration mark) T1 is detected by the lens 22, the delay of the mark formation position is compensated by the earlier detection time, and the pattern image (registration mark) T1 that is not affected by the speed variation of the secondary transfer belt 404 is compensated. Can be detected.

  On the other hand, when the transfer is performed at the position Q1 in FIG. 7B, the speed unevenness at the time tq1 at which the transfer is performed is 0, but due to negative speed unevenness before that, A / ω is more than the target position. A pattern image (registration mark) T1 is formed at the preceding position. When the pattern image (registration mark) T1 transferred on the secondary transfer belt 404 is detected at a downstream position Q2 where the positional deviation ΔS of the secondary transfer belt 404 is in the same phase relationship as the position Q1, The registration mark detection signal is detected later than the target time tq2.

  Accordingly, two points having the same phase relationship of the positional deviation ΔS of the secondary transfer belt 404, such as the position Q1 and the position Q2, are selected, for example, a registration mark is transferred and formed at the position Q1, and the pattern detection sensor at the position Q2. If the registration mark is detected by 407, the preceding deviation is compensated by the delay of the detection time, and the registration mark can be detected without being affected by the speed fluctuation of the secondary transfer belt 404.

  In the present embodiment, the distance L2 between the detection position Z2 of the pattern detection sensor 407 and the center position Z1 of the secondary transfer nip N2 is an integral multiple of the surface circumferential length D2π of the secondary transfer roller (drive roller) 36. Therefore, the phase relationship of the positional deviation ΔS of the secondary transfer belt 404 due to the eccentricity of the secondary transfer roller 36 is the same at the detection position Z2 and the transfer position of the registration mark, and the speed of the secondary transfer belt 404 is set. Without being affected by unevenness, it is possible to accurately detect the amount of color misregistration and correct color misregistration.

  Further, in the present embodiment, the rotation of the drive motor M2 is performed by rotating the secondary transfer roller 36 via a drive transmission means such as a motor gear, an intermediate gear, a gear, and a drive roller gear provided on the secondary transfer roller 36. Although it is transmitted to the next transfer roller 36, there is a dimensional error such as eccentricity of the pitch circle in each gear. By superimposing these dimensional errors, the speed unevenness curve in FIG. As shown in FIG. 8, a small period fluctuation due to the superposition error is superimposed.

  In the present embodiment, while the secondary transfer roller 36 rotates once, the drive motor M2, the motor gear constituting the drive transmission means, the intermediate gear, and the gear are configured to rotate an integral number of times. A plurality of cycles are included in one rotation of the secondary transfer roller 36. Thus, after the second rotation, the rotation unevenness state is exactly the same as the first rotation, and the color transfer amount is increased without being affected by the rotation unevenness of the motor of the drive transmission system of the secondary transfer roller 36 and the intermediate rotating body. It is possible to accurately detect and correct color misregistration.

  Thus, according to the present embodiment, the distance L2 between the detection position Z2 of the pattern detection sensor 407 and the center position Z1 of the secondary transfer nip N2 is an integral multiple of the surface circumferential length Dπ of the secondary transfer roller 36. Further, while the secondary transfer roller 36 rotates once, the drive motor M2, the motor gear, the intermediate gear and the gear are configured to rotate an integer number of times. The phase relationship of the positional deviation ΔS of the secondary transfer belt 404 is the same at the detection position Z2 of the pattern detection sensor 407 and the transfer position of the pattern image (registration mark), and is not affected by the speed unevenness of the secondary transfer belt 404. In addition, it is possible to accurately detect and correct the color misregistration without being affected by the rotation unevenness of the drive motor M2 of the drive transmission system of the secondary transfer roller 36. .

  That is, in the first embodiment, the speed of the intermediate transfer belt 31 is feedback-controlled by the scale sensor 60, and the cam 51 serving as a transfer pressure changing unit that changes the transfer pressure at the secondary transfer nip N2 is provided. In the nip N2, the hardness of the support roller (secondary transfer roller 36) on the secondary transfer belt side is higher than the hardness of the support roller (secondary transfer back roller 33) on the intermediate transfer belt 31 side. For this reason, even if the external shape of the secondary transfer belt 404 is subjected to transfer pressure, it is difficult to change. For this reason, the distance L2 hardly changes even if the transfer pressure varies. That is, the distance L2 is stable regardless of the transfer pressure.

In this embodiment, in the configuration on the secondary transfer device 40 side, a roller 401 disposed between the secondary transfer roller 36 and the roller 402 is disposed between the secondary transfer nip N2 and the roller 402 serving as a detection rotating body. The metal roller is arranged and does not have an elastic layer. For this reason, the circumferential length fluctuation of the secondary transfer belt 404 between the secondary transfer nip N2 and the detection position Z2 can be suppressed to be extremely small, so that the distance L2 is stabilized.
The detection position Z2 by the pattern detection sensor 407 is set upstream of the roller 403 and the secondary transfer nip N2 in the moving direction of the secondary transfer belt 404 with respect to the roller 403 as a tension roller. Therefore, the distance L2 hardly changes even when the load on the secondary transfer belt 404 fluctuates and the roller 403 is displaced. That is, the distance L2 is stable regardless of the tension force of the roller 403.
Further, since the secondary transfer roller 36 and the rollers 401 to 403 constituting the secondary transfer device 40 are mounted on the pressure frame 49 that is the same frame, the tolerance in the secondary transfer device 40 can be suppressed. Therefore, the distance L2 can be set with high accuracy.

With such a configuration, the intermediate transfer belt 31 is driven with high accuracy without performing control based on distance. Further, the transfer pressure at the secondary transfer nip N2 is set when the magnitude of the hardness of the secondary transfer roller 36 and the secondary transfer back surface roller 33 that is the counter-rotating body is set, thereby changing the transfer pressure by the cam 51. The variation of the distance L2 is made smaller than the variation of the distance L1 due to the transfer pressure. Specifically, the hardness of the secondary transfer roller 36 is larger than the hardness of the secondary transfer back roller 33. Thereby, the accuracy of the driving speed of the secondary transfer belt 404 can be ensured.
That is, the pattern image (registration mark / toner pattern) T1 on the secondary transfer belt 404 can be accurately detected.

(Modification 1)
FIG. 9 shows a first modification of the first embodiment.
In the first modification, the transfer pressure changing means 50 for changing the transfer pressure (secondary transfer pressure) acting on the secondary transfer nip N2 serving as a transfer portion is not provided in the configuration of the first embodiment. . Thus, the configuration of the printer 100 is not limited to the one provided with the transfer pressure changing means 50.
Even if there is no transfer pressure changing means 50 for changing the transfer pressure (secondary transfer pressure) acting on the secondary transfer nip N2, the secondary transfer pressure fluctuates not a little. For example, the transfer pressure may fluctuate due to deterioration of the tension coil spring 55, tolerance, fluctuations in the temperature and humidity environment, and the like. Even if there is such deterioration or fluctuation, the magnitude relationship between the hardness of the secondary transfer back roller 33 and the secondary transfer roller 36 is set as described above (specifically, the hardness of the secondary transfer roller 36 is set to 2). By making it larger than the hardness of the secondary transfer back roller 33), it is possible to ensure the accuracy of the moving speed of the secondary transfer belt 404 regardless of the fluctuation of the transfer pressure (secondary transfer pressure).

(Modification 2)
FIG. 10 shows a second modification of the first embodiment.
In the second modification, the intermediate transfer belt 310 that does not include the scale tape 200 as an intermediate transfer body is replaced with the intermediate transfer belt 31 and the feedback control is performed by detecting the scale tape 200 in contrast to the configuration of the first embodiment. It is the structure which does not implement. The intermediate transfer belt 310 and the intermediate transfer belt 31 have the same configuration except that the scale tape 200 is different. Therefore, a pattern image (registration mark) T1 that is a toner image of each color developed outside the image forming areas of the photoreceptors 1Y, 1M, 1C, and 1K is transferred onto the front surface 310a of the intermediate transfer belt 310. The
In the second modification, the secondary transfer nip N2 serving as a transfer portion is formed between the intermediate transfer belt 310 and the secondary transfer belt 404, and the object to which the secondary transfer belt 404 is pressed is the intermediate transfer belt. The belt 310 is formed. Thus, the configuration of the printer 100 is not limited to that using the intermediate transfer belt 31 including the scale tape 200.

  By setting the distance L2 of the secondary transfer belt 404 from the center position Z1 of the secondary transfer portion N2 to the detection position Z2 on the secondary transfer belt to an integral multiple of the outer peripheral length D2π of the secondary transfer roller 36, The pattern detection sensor 407 can accurately detect the speed at which the image is transferred to the actual recording material P at the secondary transfer nip N2. Thereby, at least the driving accuracy of the secondary transfer belt 404 is ensured. In the second modification, the driving accuracy of the intermediate transfer belt 31 may be lower than that in the first embodiment, because the intermediate transfer belt 31 is not provided with the scale belt 200. However, in this case as well, the driving accuracy of the intermediate transfer belt 31 can be ensured by using a motor (M1 having small tolerance and eccentricity) having a small periodic fluctuation as the driving motor M1 and the driving roller 32 of the intermediate transfer belt 31. Can do.

(Second Embodiment)
In the present embodiment, as shown in FIG. 11, the variable control of the transfer pressure of the secondary transfer nip N2 by the transfer pressure changing unit 50 described in the first embodiment and the feedback control by detecting the scale tape 200 are performed. In addition, the distance L1 is an integral multiple of the outer peripheral length D2π of the secondary transfer roller (drive roller) 36, and the distance L2 is an integral multiple of the outer peripheral length D2π of the secondary transfer roller (drive roller) 36. It is what.

  With such a configuration, the distance from the primary transfer portion to the detection position of the pattern image (registration mark) T1 by the pattern detection sensor 407 (the sum of the distances on the intermediate transfer belt 31 and the secondary transfer belt 404) L1 + L2 Is an integral multiple of the outer peripheral length D2π of the secondary transfer roller (drive roller) 36. The eccentricity of the secondary transfer roller (drive roller) 36 causes periodic speed fluctuations in the intermediate transfer belt 31 and the secondary transfer belt 404 that are in contact with the eccentricity. Both the pattern image (registration mark) T1 at the primary transfer portion and the pattern image (registration mark) T1 at the detection position of the pattern image (registration mark) T1 by the pattern detection sensor 407 are affected by this periodic speed fluctuation. Move on the belt. In this embodiment, since the distance L1 + L2 is an integral multiple of the outer peripheral length D2π of the secondary transfer roller (drive roller) 36, the phase of the speed fluctuation waveform at the primary transfer portion and the phase of the speed fluctuation waveform at the detection position are the same. Be the same. Therefore, the periodic speed fluctuation due to the eccentricity of the secondary transfer roller 36 does not affect the pattern image (registration mark) T1 detection result by the pattern detection sensor 407. That is, the pattern detection sensor 407 can detect the transfer timing (transfer position) of the pattern image (registration mark) T1 at the primary transfer portion with high accuracy. There is a possibility that the distance L1 and the distance L2 slightly vary due to the variation of the secondary transfer pressure. However, compared with the case where the distance L1 and the distance L2 are not set to an integral multiple of the outer peripheral length D2π of the secondary transfer roller 36, it is expected that the detection accuracy of the pattern image (registration mark) T1 by the pattern detection sensor 407 is improved.

In each of the above-described embodiments and modifications, the distance L2 from the secondary transfer nip N2 (transfer portion) to the detection position Z2 on the secondary transfer belt 404 by the pattern detection sensor 407 is the secondary transfer roller (drive roller). Although described as an integral multiple of the outer peripheral length D2π of 36, it is not limited to such a form. For example, the speed fluctuations of the intermediate transfer belt 31 and the secondary transfer belt 404 are caused by the eccentricity of the outer periphery of the secondary transfer roller 36, but are also caused by the drive motor M2 that is a drive system for driving the secondary transfer roller 36. There is a case. For this reason, even if the distances L1 and L2 are set to an integral multiple of the length equivalent to one rotation of the drive motor M2, which is a drive source for rotationally driving the drive rotator such as the secondary transfer roller 36, the secondary transfer roller 36 is It can be inferred that the same effect can be obtained as when the outer peripheral length is an integral multiple.

One form of the rotation drive mechanism 420 that rotates the secondary transfer roller 36 will be described.
The rotation drive mechanism 420 includes a secondary transfer gear 421 fixed to the end of the shaft 360 of the secondary transfer roller 36, a toothed tension belt 423 wound around the secondary transfer gear 421 and the drive pulley 422, A drive motor M2 is provided. A motor output gear 425 is fixed to the output shaft M2a of the drive motor M2. The drive pulley 422 includes a small-diameter tension pulley 422a around which the tension belt 423 is wound, and a motor pulley 422b around which a toothed drive belt 426 wound around the motor output gear 425 has a larger diameter than the tension pulley 422a. On the same axis. Reference numeral 424 in the drawing denotes a tension roller that applies tension to the tension belt 423. The tension roller 424 may be provided as necessary.
According to such a configuration of the rotation drive mechanism 420, when the drive motor M2 is operated and the motor output gear 425 is rotated, the rotation is transmitted via the drive belt 426, the drive pulley 422, the tension belt 423, and the secondary transfer gear 421. As a result, the secondary transfer roller 36 is driven to rotate.
When such a rotation drive mechanism 420 is used, the length equivalent to one rotation of the drive motor M2 is the movement distance of the surface of the secondary transfer roller 36 when the drive motor M2 is rotated once in FIG.

The inventors of the present application experimented on the speed fluctuation of the intermediate transfer belt 31 and the secondary transfer belt 404 using a drive motor with different output torque as the drive motor M2. As the output torque of the drive motor increased, the roller outer peripheral length increased. Even if the distances L1 and L2 are set to integral multiples of the above, the speed fluctuations of the intermediate transfer belt 31 and the secondary transfer belt 404 are not improved or the improvement rate tends to be low.
Therefore, the distances L1 and L2 are set to an integral multiple of the length equivalent to one rotation of the drive motor M2, the output torque of the drive motor is changed, and the speed fluctuations of the intermediate transfer belt 31 and the secondary transfer belt 404 are tested. It has been found that as the output torque of the motor increases, the speed fluctuation tends to be suppressed as compared with the case where the distances L1 and L2 are set to integer multiples of the roller outer peripheral length.
That is, when the driving torque of the driving motor M2 is large and the resistance and inertial force of the motor are large, the factor that affects the speed fluctuation of the intermediate transfer belt 31 and the secondary transfer belt 404 is the driving rather than the eccentricity of the roller outer periphery. It can be assumed that the load of the motor M2 contributes greatly.
It is more preferable that the distances L1 and L2 be an integral multiple of the outer peripheral length D1π of the drive roller 32. Further, it is more preferable to make it an integral multiple of the length equivalent to one rotation of the drive motor M1.

(Third embodiment)
In the first embodiment, the relationship between the distance L2 and the outer peripheral length D2π of the secondary transfer roller (drive roller) 36 will be described. In the second embodiment, the distance L2 and the secondary transfer roller (drive roller) 36 are changed. In the present embodiment, the relationship between the rotationally driven drive motor M2 has been described. In this embodiment, the distance L2 and the outer peripheral length D2π of the secondary transfer roller (drive roller) 36, the distances L3 to L5 between the primary transfer portions, and the drive roller ( The relationship between the outer peripheral length D1π of the intermediate drive rotator 32 and the outer peripheral length D2π of the secondary transfer roller (drive roller) 36 and the outer peripheral length D1π of the drive roller (intermediate drive rotator) 32 will be described. The configuration of the image forming apparatus is the same as in FIG.
That is, the image forming apparatus according to this embodiment includes a plurality of photoconductors 2Y, 2M, 2C, and 2K that are image carriers, and a pattern image (registration mark) T1 that is a toner image of each color that becomes a detection image. The images are transferred from the photoreceptors 2Y, 2M, 2C, and 2K to an intermediate transfer belt 31 that is an intermediate transfer member at a primary transfer nip N1 that is a primary transfer portion. The distances L3, L4, and L5 between the central portions of the primary transfer nips N1 are set to integral multiples of the outer peripheral length D1π of the driving roller (intermediate driving rotating body) 32, and the outer peripheral length D1π of the driving roller 32 is driven. The length is set to an integral multiple of the length equivalent to one rotation of the drive motor M1 for rotationally driving the roller 32.
With such a configuration, periodic speed fluctuations occur in the intermediate transfer belt 31 with the eccentricity of the driving roller 32 and the rotation of the driving motor M1. If the photosensitive member pitch (distances L3, L4, L5 of the primary transfer nip N1) does not coincide with an integral multiple of the outer peripheral length D1π of the driving roller 32, this speed variation will cause a phase shift between the photosensitive members (between each color). And appears as a color shift. According to the present embodiment, periodic speed fluctuations on the intermediate transfer belt 31 are caused by setting the distances L3, L4, and L5 of the photoreceptor pitch (between each station) to an integral multiple of the outer peripheral length D1π of the driving roller 32. It does not appear as a color shift between colors. Therefore, when the color shift of each color is corrected based on the pattern image (registration mark) T1 of each color transferred from the intermediate transfer belt 31 to the secondary transfer belt 404 and detected by the pattern detection sensor 407, the intermediate transfer is performed. The influence of periodic speed fluctuations of the belt 31 can be eliminated. Thereby, color shift can be suppressed (corrected) with high accuracy. In the present embodiment, the outer peripheral length D1π of the drive roller 32 is set to an integral multiple of the length equivalent to one rotation of the drive motor M1 that rotationally drives the drive roller 32. Thereby, when correcting the color misregistration of each color based on the pattern image (registration mark) T1 of each color detected by the pattern detection sensor 407, the intermediate transfer belt 31 caused by the periodic drive unevenness of the drive motor M1. The influence of periodic speed fluctuations can be eliminated. Thereby, color shift can be suppressed (corrected) with high accuracy.

  In the present embodiment, both rollers are configured such that the outer peripheral length D1π of the drive roller (intermediate drive rotor) 32 and the outer peripheral length D2π of the secondary transfer roller (drive roller) 36 are integral multiples of each other. . The integral multiples include a case where the outer peripheral length D1π is an integral multiple of the outer peripheral length D2π, a case where the outer peripheral length D2π is an integral multiple of the outer peripheral length D1π, and a case where the outer peripheral length D1π is equal to the outer peripheral length D2π. . By configuring both rollers in this way, even if the periodic fluctuation of the secondary transfer roller (drive roller) 36 affects the driving speed of the intermediate transfer belt 31, the speed fluctuation is between each color. Will not appear as a color shift. Therefore, it is possible to suppress (correct) the color shift with higher accuracy.

  In the embodiment for carrying out the invention, the “integer multiple” is not limited to a numerical value such as double or triple that does not include a decimal point in the numerical value. There may be. The deviation from the integer multiple is preferably within ± 5% (eg, 1.95 to 2.05 times), and more preferably within ± 2% (eg, 1.98 to 2.02 times).

As mentioned above, although preferable embodiment of this invention was described, this invention is not limited to this specific embodiment, Unless it is specifically limited by the above-mentioned description, this invention described in the claim is described. Various modifications and changes are possible within the scope of the gist of the invention.
For example, the image forming apparatus may be a copying machine, a facsimile alone, or a multifunction machine having at least two functions of a copying machine, a printer, a facsimile, and a scanner, instead of a printer.

In the above-described embodiment, the image forming apparatus has been described using the transfer unit (secondary transfer nip N2) that transports the recording material P in the horizontal direction. However, the transfer unit transfers the recording material P upward, downward, and diagonally upward. The present invention can also be applied to an image forming apparatus configured to convey in a direction or obliquely downward.
In the above embodiment, the recording material P made of paper is exemplified as the transported object, but the transported object is a resin sheet material such as a prepreg sheet, recording paper, recording paper, film, cloth, and the like. Of course.
In the above embodiment, the image forming apparatus including a plurality of image carriers 2Y, 2M, 2C, and 2K has been described. However, an image forming apparatus having only one image carrier, that is, a monochrome image forming apparatus may be used. Absent.

The monochrome image forming apparatus is, for example,
An intermediate transfer belt as an intermediate transfer member to which a pattern image (registration mark) as a detection image is transferred from a drum-shaped photosensitive member as one image carrier;
A secondary transfer nip is wound around a roller that is a plurality of rotary bodies including a secondary transfer roller as a driving rotary body and abuts against an intermediate transfer belt to form a secondary transfer nip as a transfer portion, and the intermediate transfer is performed at the secondary transfer nip. A secondary transfer belt as a secondary transfer body to which a pattern image (registration mark) is transferred from the belt;
And a pattern detection sensor as a detection member for detecting a pattern image (registration mark) transferred to the secondary transfer belt.
Then, the distance L2 from the secondary transfer nip to the detection position on the secondary transfer belt by the pattern detection sensor is set to an integral multiple of the outer peripheral length of the drive rotor, or the drive motor that rotationally drives the secondary transfer roller Is an integral multiple of the length equivalent to one rotation.
Even with a monochrome image forming apparatus having such a configuration, it is possible to accurately detect a detection image on the secondary transfer member. Then, the control unit adjusts the image forming position (position of the electrostatic latent image) on the image carrier based on the detection result, whereby the position of the image transferred onto the recording material P, particularly the recording material P, is adjusted. A positional shift in the transport direction can be reliably prevented, and an image can be transferred to a desired position on the recording material P.

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

1Y, 1M, 1C, 1K Distance between image forming units 2Y, 2M, 2C, 2K Image carrier 31 Intermediate transfer member 33 Opposite rotating member 36 Drive rotating member 49 Support frame 50 Transfer pressure changing means 100 Image forming apparatus 401 Support Rotating body 402 Rotating body for detection 403 Tension applying member 404 Secondary transfer body 407 Detection member c Moving direction of secondary transfer body D2π Outer peripheral length of driving rotary body D1π Outer peripheral length of intermediate driving rotor L1 From intermediate transfer section to transfer section Distance L2 Distance from transfer section to detection position L3 to L5 Distance between primary transfer sections M2 Drive motor N1 Primary transfer section N2 Transfer section T1 Detection image Z2 Detection position

Japanese Patent No. 3694143

Claims (12)

An intermediate transfer body onto which an image for detection is transferred from the image carrier;
A secondary transfer member that is wound around a plurality of rotating members including a driving rotating member, abuts against the intermediate transfer member to form a transfer portion, and the detection image is transferred from the intermediate transfer member at the transfer portion; ,
A detection member for detecting a detection image transferred to the secondary transfer member;
An image forming apparatus in which a distance from the transfer unit to a detection position on the secondary transfer body by the detection member is an integral multiple of an outer peripheral length of the drive rotating body.   2. The image forming apparatus according to claim 1, wherein a distance from a primary transfer portion to which the detection image is transferred from the image carrier to the intermediate transfer member to the transfer portion is an integral multiple of an outer peripheral length of the drive rotating member. . A plurality of the image carrier,
The detection images are respectively transferred from the plurality of image carriers to the intermediate transfer member in a primary transfer unit,
3. The image forming apparatus according to claim 1, wherein a distance between the primary transfer portions on the intermediate transfer member is an integral multiple of an outer peripheral length of an intermediate drive rotating member that rotationally drives the intermediate transfer member.   The image forming apparatus according to claim 3, wherein an outer peripheral length of the intermediate drive rotator is an integral multiple of a length equivalent to one rotation of a drive motor that rotationally drives the intermediate drive rotator.   5. The image forming apparatus according to claim 3, wherein an outer peripheral length of the intermediate driving rotator and an outer peripheral length of the driving rotator are integral multiples of each other. An intermediate transfer body onto which an image for detection is transferred from the image carrier;
A secondary transfer member that is wound around a plurality of rotating members including a driving rotating member, abuts against the intermediate transfer member to form a transfer portion, and the detection image is transferred from the intermediate transfer member at the transfer portion; ,
A detection member for detecting a detection image transferred to the secondary transfer member;
An image forming apparatus in which a distance from the transfer unit to a detection position on the secondary transfer body by the detection member is an integral multiple of a length corresponding to one rotation of a drive motor that rotationally drives the drive rotary body. The transfer unit is disposed between the drive rotator and the counter rotator, which is disposed to face the drive rotator and is wound with the intermediate transfer member,
The image forming apparatus according to claim 1, wherein a hardness of the driving rotator is larger than a hardness of the counter rotator. The transfer unit is disposed between the drive rotator and the counter rotator, which is disposed to face the drive rotator and is wound with the intermediate transfer member,
A transfer pressure changing means for changing the transfer pressure acting on the transfer portion;
The image forming apparatus according to claim 1, wherein a hardness of the driving rotator is larger than a hardness of the counter rotator. One of the plurality of rotating bodies around which the secondary transfer body is wound is a tension applying member that applies tension to the secondary transfer body,
9. The image forming apparatus according to claim 1, wherein the detection position on the secondary transfer body is located between the transfer portion and the tension applying member in the moving direction of the secondary transfer body. . One of the plurality of rotators around which the secondary transfer body is wound is a detection rotator disposed opposite to the detection member via the secondary transfer body, and among the plurality of rotators The other rotating body is a supporting rotating body that is disposed between the transfer portion and the detecting rotating body and does not have an elastic layer.
The image according to any one of claims 1 to 8, wherein the detection position on the secondary transfer body is disposed between the transfer portion and the counter rotating body in the moving direction of the secondary transfer body. Forming equipment.   The image forming apparatus according to claim 1, wherein the plurality of rotating bodies are mounted on the same support frame.   The image forming apparatus according to claim 1, wherein the intermediate transfer member is an elastic belt.

Images