JP5103967B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus using, for example, an electrophotographic system.

  2. Description of the Related Art An electrophotographic color image forming apparatus such as a printer or a copying machine is known in which a photosensitive drum and an exposure device are arranged for each color. In such a color image forming apparatus, each exposure apparatus exposes each photosensitive drum with a laser beam modulated in accordance with image data for each color. However, each exposure apparatus has variations in optical characteristics and the like. In some cases, the color toner images may be misaligned. Therefore, the exposure position is adjusted in each exposure apparatus (see, for example, Patent Document 1).

JP 2006-31290 A (pages 12-14)

  An object of the present invention is to perform exposure position adjustment in an exposure apparatus with high accuracy.

The invention according to claim 1 includes a plurality of image carriers , a belt member that conveys a predetermined pattern image transferred from each of the plurality of image carriers, and a surface having light reflectivity, and the belt member. A roll member composed of a first region extending in a contact state and a second region extending in a non-contact state the region to which the pattern image of the belt member is transferred; and the second member of the roll member. Detecting means for detecting the position of the pattern image on the surface of the belt member stretched in the area of the belt member, and the detection means spans the belt member stretched in the second area of the roll member. In the image forming apparatus, the position of the pattern image is detected based on the amount of movement of the reflected light from the belt member of the emitted light .

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the roll member includes a base material and a surface layer formed on the base material surface. The region 2 is composed of the base material .
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect , the detection unit emits the light toward a width direction of the belt member with respect to a surface of the belt member. To do.

According to a fourth aspect of the present invention, in the image forming apparatus according to the second aspect , the roll member has a frictional force with the belt member of the surface layer formed in the first region. It is characterized by being formed larger than the frictional force with the belt member.
The invention according to claim 5, in the image forming apparatus according to claim 2, wherein the roller member is that the second surface layer of the thin layer than the surface layer on the second region is further formed Features.

In the invention according to claim 6, a plurality of image carriers and a predetermined pattern image formed on each of the plurality of image carriers are transferred, the pattern images are conveyed, and the surface has light reflectivity. A belt member, a first region disposed at an end of the belt member and extending the belt member in a contact state, and a second region extending the region on which the pattern image is transferred in a non-contact state. And a detection means for detecting the position of the pattern image on the surface of the belt member stretched over the second region of the roll member, the belt member comprising: The roll member is configured to be separable from the plurality of image holding members in a fixed position, and the detection means is configured to be arranged on the belt member stretched in the second region of the roll member. Light against the surface The emitted, an image forming apparatus and detecting the position of the pattern image based on the moving amount of the reflected light from the belt member of the emitted the light.

According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, the roll member includes a base material and a surface of the base material, and the friction force between the belt member and the base member The surface layer is larger than the material, and the second region is formed of the base material.
According to an eighth aspect of the present invention, in the image forming apparatus according to the sixth aspect, the roll member includes a base material and a surface of the base material, and the friction force between the belt member and the base member A surface layer larger than the material is formed, and the second region is formed of the base material and a second surface layer that is thinner than the surface layer.

According to a ninth aspect of the present invention, in the image forming apparatus according to the sixth aspect , the detecting means emits the light toward the width direction of the belt member with respect to the surface of the belt member. To do.

According to the first aspect of the present invention, the position of the pattern image can be detected with high accuracy using a belt member whose surface has light reflectivity as compared with the case where the present invention is not adopted.
According to the second aspect of the present invention, exposure position adjustment in the exposure apparatus can be performed with high accuracy when a belt member having a light reflecting surface is used as compared with the case where the present invention is not adopted .
According to the third aspect of the present invention, the position of the pattern image in the sub-scanning direction can be stably measured as compared with the case where the present invention is not adopted.
According to the fourth aspect of the present invention, the belt member can be stably conveyed as compared with the case where the present invention is not adopted.
According to the fifth aspect of the present invention, the second region can be easily formed by polishing the surface layer as compared with the case where the present invention is not adopted.

According to the sixth aspect of the present invention, the exposure position adjustment in the exposure apparatus of the image forming apparatus having the belt retract function can be performed with higher accuracy than in the case where the present invention is not adopted.
According to the seventh aspect of the present invention, the belt member can be stably conveyed as compared with the case where the present invention is not adopted.
According to the eighth aspect of the present invention, the belt member can be stably conveyed as compared with the case where the present invention is not adopted.
According to the ninth aspect of the present invention, the position of the pattern image in the sub-scanning direction can be stably measured as compared with the case where the present invention is not adopted.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a diagram illustrating an example of a configuration of an image forming apparatus 1 to which the exemplary embodiment is applied. An image forming apparatus 1 shown in FIG. 1 is a so-called tandem type digital color printer using an electrophotographic system, and an image forming process unit 70 that forms an image corresponding to image data of each color, and the entire image forming apparatus 1. An image processing unit 81 that performs predetermined image processing on image data received from, for example, an image reading device 4 such as a personal computer (PC) 3 or a scanner, a processing program, and image data are stored. For example, a main storage unit 82 realized by a hard disk drive (Hard Disk Drive) is provided.

In the image forming process unit 70, four image forming units 10Y, 10M, 10C, and 10K (hereinafter also collectively referred to as “image forming unit 10”) are arranged in parallel in the vertical direction (substantially vertical direction) at regular intervals. . The image forming unit 10 includes a photosensitive drum 11 as an image holding member, a charging roll 12 that charges the surface of the photosensitive drum 11, and a developing device that develops the electrostatic latent image formed on the photosensitive drum 11 with toner of each color. 13. A drum cleaner 14 for cleaning the surface of the photosensitive drum 11 after transfer is provided.
Each image forming unit 10 is configured to be detachable from the main body of the image forming apparatus 1. For example, when the toner in the developing device 13 is consumed or the photosensitive drum 11 reaches the end of its life, the image forming unit 10 Exchanged in units of 10 forming units.

The charging roll 12 is composed of a roll member in which a conductive elastic layer and a conductive surface layer are sequentially laminated on a conductive core metal such as aluminum or stainless steel. Then, a charging bias voltage is supplied from a charging power source (not shown), and the surface of the photosensitive drum 11 is uniformly charged at a predetermined potential while being driven to rotate relative to the photosensitive drum 11.
The developing device 13 holds a two-component developer composed of yellow (Y), magenta (M), cyan (C), and black (K) toners and a magnetic carrier in each of the image forming units 10, and is photosensitive. The electrostatic latent image formed on the body drum 11 is developed with each color toner.
The drum cleaner 14 brings a plate-like member formed of a rubber material such as urethane rubber into contact with the surface of the photosensitive drum 11 to remove toner, paper dust, and the like attached on the photosensitive drum 11.

Further, the image forming apparatus 1 according to the present embodiment is provided with a laser exposure unit 20 as an example of an exposure unit that exposes the photosensitive drum 11 provided in each image forming unit 10. The laser exposure unit 20 acquires image data for each color from the image processing unit 81, and scans and exposes the photosensitive drum 11 of each image forming unit 10 with laser light whose lighting is controlled based on the acquired image data. To do.
Further, a sheet conveying belt 30 as an example of a belt member that conveys a sheet P that is a recording material (recording sheet) is arranged so as to move while being in contact with the photosensitive drum 11 of each image forming unit 10. The paper transport belt 30 is formed of a film-like endless belt that electrostatically attracts the paper P. Then, the paper conveyance is carried over the drive roll 32 and the idle roll 33 as an example of a roll member so as to circulate and the paper P is conveyed from the lower side to the upper side in the substantially vertical direction. A path M1 is formed.

Transfer rolls 31 are arranged at positions inside the paper conveyance belt 30 and facing the respective photosensitive drums 11. Each transfer roll 31 forms a transfer electric field with the photosensitive drum 11, so that each color toner image formed by each image forming unit 10 is formed on the paper P held and transported by the paper transport belt 30. Transfer sequentially. Further, on the outer side of the paper conveying belt 30 and on the downstream side of each transfer roll 31, a static elimination lamp 21 that neutralizes the photosensitive drum 11 after the transfer is provided.
An adsorption roll 34 that charges the paper transport belt 30 is disposed at the most upstream portion of the paper transport belt 30 on the photosensitive drum 11 side. The surface of the paper transport belt 30 is electrostatically attracted to the paper P by being charged to a predetermined potential by the suction roll 34.
A detection sensor 60 as an example of a detection unit used when adjusting the exposure position on the photosensitive drum 11 of the laser exposure device 20 described later is provided in an area where the paper conveying belt 30 is stretched over the drive roll 32. Is arranged. The detection sensor 60 detects the position on the paper conveyance belt 30 of the position correction pattern formed on the paper conveyance belt 30 and composed of each color toner image of a predetermined pattern, and the position data of the detected position correction pattern, etc. Is transmitted to the control unit 80.
A belt cleaner 36 for removing the position correction pattern held on the paper transport belt 30 is provided on the opposite side of the paper transport belt 30 from the area where the image forming units 10 are arranged.
A fixing device 40 is provided on the downstream side of the paper transport belt 30 along the paper transport path M1 to perform a fixing process using heat and pressure on an unfixed toner image on the paper P.

Further, as a paper transport system other than the paper transport belt 30, a paper storage unit 50 that stores the paper P on the paper feed side, and a pickup that picks up and transports the paper P stored in the paper storage unit 50 at a predetermined timing. A roll 51, a transport roll 52 that transports the paper P fed by the pickup roll 51, and a registration roll 53 that feeds the paper P to the paper transport belt 30 in accordance with the image forming operation are provided.
On the other hand, on the paper discharge side, a paper discharge roll 54 that conveys the paper P fixed by the fixing device 40, and in the case of single-sided printing, the paper P is directed toward a paper discharge unit 90 provided at the top of the apparatus main body. In the case of double-sided printing, the paper P on which one side is fixed by the fixing device 40 is directed to the double-sided conveyance path M2 by reversing from the rotation direction toward the paper discharge unit 90 at a predetermined timing. A reversing roll 55 that is fed out is disposed. In addition, the double-sided conveyance path M2 is provided with a plurality of conveyance rolls 56 along the double-sided conveyance path M2.

  In the image forming apparatus 1 of the present embodiment, the image forming process unit 70 performs an image forming operation under the control of the control unit 80. That is, the image data input from the PC 3 or the image reading device 4 is subjected to predetermined image processing by the image processing unit 81 and supplied to the laser exposure unit 20. For example, in the black (K) image forming unit 10 </ b> K, the surface of the photosensitive drum 11 uniformly charged at a predetermined potential by the charging roll 12 is based on the image data from the image processing unit 81 by the laser exposure unit 20. Then, scanning exposure is performed with the laser light whose lighting is controlled, and an electrostatic latent image is formed on the photosensitive drum 11. The formed electrostatic latent image is developed by the developing device 13, and a black (K) toner image is formed on the photosensitive drum 11. Similarly, in the image forming units 10Y, 10M, and 10C, yellow (Y), magenta (M), and cyan (C) toner images are formed.

On the other hand, when the formation of each color toner image in each image forming unit 10 is started, the paper P taken out from the paper storage unit 50 is supplied to the paper transport belt 30 by the registration roll 53 in accordance with the toner image formation timing. Is done. The surface of the paper transport belt 30 is charged to a predetermined potential by the suction roll 34. As a result, the paper P is electrostatically attracted onto the paper transport belt 30 and is transported along the paper transport path M1 by the paper transport belt 30 that circulates and moves in the direction of the arrow in FIG. In the middle of the process, the color toner images are sequentially transferred onto the paper P by the transfer electric field formed by the transfer roll 31.
The sheet P on which each color toner image is electrostatically transferred is peeled from the sheet conveying belt 30 downstream of the image forming unit 10K and conveyed to the fixing device 40. When the paper P is conveyed to the fixing device 40, the unfixed toner image on the paper P is fixed to the paper P by receiving a fixing process using heat and pressure. The paper P on which the color toner images are fixed is stacked on a paper discharge unit 90 provided in a discharge unit of the image forming apparatus 1. On the other hand, during double-sided printing, the same image forming operation is performed again via the double-sided conveyance path M2, and then the paper is stacked on the paper discharge unit 90.

Next, adjustment of the exposure position on the photosensitive drum 11 of the laser exposure device 20 in the image forming apparatus 1 of the present embodiment will be described.
The laser exposure unit 20 includes a semiconductor laser as an example of a light source, for example, a scanning optical system including a rotating polygon mirror (polygon mirror) formed of a regular octahedron, various lenses, various mirrors, and the like. Then, the laser exposure device 20 exposes the photosensitive drums 11 provided in the respective image forming units 10 via different optical paths. Since these optical elements constituting the laser exposure device 20 are affected by the environmental temperature and the like, the dimensions and the arrangement position thereof vary, so that the exposure position on the photosensitive drum 11 is set between the image forming units 10. Deviation may occur. Therefore, in the image forming apparatus 1 of the present embodiment, the exposure position of the laser exposure unit 20 is adjusted at a predetermined interval (time interval, number of printed sheets, etc.) when the apparatus is started up or during the image forming operation.

The exposure position adjustment of the laser exposure device 20 in the image forming apparatus 1 according to the present embodiment is performed by adjusting each color toner of a predetermined pattern on the sheet conveying belt 30 during the non-image forming operation between the image forming operation and the image forming operation. A position correction pattern consisting of an image is formed. Then, the position of the position correction pattern on the paper transport belt 30 is detected by the detection sensor 60 in the region where the paper transport belt 30 is stretched over the drive roll 32.
FIG. 2 is a diagram showing a position where the position correction pattern held on the paper transport belt 30 is detected by the detection sensor 60. The detection sensor 60 of the present embodiment is configured to optically detect the position of the position correction pattern (see the subsequent stage), and the light emitted from the detection sensor 60 is applied to the drive roll 32 by the paper transport belt 30. It is set so as to be emitted toward the stretched area. As described above, the detection sensor 60 of the present embodiment is configured such that light is emitted from the detection sensor 60 toward the surface of the sheet conveying belt 30 in the region supported by the drive roll 32 and is received. Thus, the position of the position correction pattern held on the paper transport belt 30 is detected.

FIG. 3 is a diagram showing an example of the configuration of the detection sensor 60 of the present embodiment. As shown in FIG. 3, the detection sensor 60 emits light along the width direction of the paper transport belt 30 (direction perpendicular to the moving direction of the paper transport belt 30), for example, a light emitting element 61 such as an LED, and the light emitting element. A light receiving element 63 configured to receive, for example, a photodiode, and the like, and a condenser lens 62 that condenses the light reflected from the paper transport belt 30 on the light receiving element 63. Has been. In other words, in the detection sensor 60 of the present embodiment, light is emitted from the light emitting element 61 along the width direction of the paper conveyance belt 30 and from the position correction pattern held on the paper conveyance belt 30 along the width direction. The reflected light is condensed on the light receiving element 63 by the condenser lens 62. Then, the position of the position correction pattern on the paper transport belt 30 is detected by the light received by the light receiving element 63. The detected position of the position correction pattern is transmitted to the control unit 80 as position data of the position correction pattern.
As the light receiving element 63, besides a photodiode or the like, a position detecting element (PSD: Position Sensitive Detector) can also be used. PSD performs measurement in units of several μm with a high-speed response of about 0.1 μsec, and is suitable for detecting a position correction pattern.

FIG. 4 is a diagram illustrating an example of a position correction pattern. Each image forming unit 10 of the present embodiment forms a position correction pattern as shown in FIG. 4 when adjusting the exposure position of the laser exposure device 20.
As shown in FIG. 4, the image forming unit 10 </ b> Y forms a yellow parallel pattern PY and a 45 ° inclined pattern LY, which are reference colors when performing exposure position adjustment in the present embodiment. The image forming unit 10M forms a magenta parallel pattern PM and a 45 ° inclined pattern LM. The image forming unit 10C forms a cyan parallel pattern PC and a 45 ° inclined pattern LC. The image forming unit 10K forms a black parallel pattern PB and a 45 ° inclined pattern LB.
Here, the parallel patterns PY, PM, PC, and PB are used when adjusting the exposure position in the sub-scanning direction. The 45 ° inclined patterns LY, LM, LC, and LB are used when adjusting the exposure position in the main scanning direction.

  The detection sensor 60 detects the positions of the parallel patterns PY, PM, PC, and PB on the paper transport belt 30 by the light receiving element 63, and sends the detected positions to the control unit 80 as sub-scanning direction position data. For example, using the timing at which the sub-scanning direction position data is transmitted, the control unit 80 calculates the time interval of the timing at which the other color parallel patterns PM, PC, and PB pass the detection sensor 60 using the parallel pattern PY as a reference. . That is, as shown in FIG. 4, the time interval P1 between the passage timing of the parallel pattern PY and the passage timing of the parallel pattern PM, the time interval P2 between the passage timing of the parallel pattern PY and the passage timing of the parallel pattern PC, and the parallel pattern A time interval P3 between the passage timing of PY and the passage timing of parallel pattern PB is calculated. Then, the control unit 80 adjusts the exposure position in the sub-scanning direction of the laser exposure device 20 in each image forming unit 10 based on the calculated time intervals.

The detection sensor 60 detects the positions of the 45 ° inclined patterns LY, LM, LC, and LB in the width direction of the paper transport belt 30 by the light receiving element 63, and controls the detected positions as position data in the main scanning direction. Send to part 80. The controller 80 calculates the amount of positional deviation of each of the 45 ° inclination patterns LM, LC, and LB with reference to the position in the width direction of the 45 ° inclination pattern LY. That is, as shown in FIG. 4, the positional deviation amount L1 between the 45 ° inclination pattern LY and the 45 ° inclination pattern LM, the positional deviation amount L2 between the 45 ° inclination pattern LY and the 45 ° inclination pattern LC, and the 45 ° inclination pattern. A positional deviation amount L3 between LY and the 45 ° inclined pattern LB is calculated. Then, the control unit 80 adjusts the exposure position in the main scanning direction of the laser exposure unit 20 in each image forming unit 10 based on the calculated amount of misregistration.
After that, the position correction pattern used for adjusting the exposure position is transported to a belt cleaner 36 provided on the downstream side of the driving roll 32 in the transport direction of the paper transport belt 30 and removed from the paper transport belt 30 by the belt cleaner 36. Is done.

  By the way, in the detection sensor 60 of the present embodiment, the light emitted from the light emitting element 61 along the width direction of the paper transport belt 30 is reflected on the paper transport belt 30 and along the width direction of the paper transport belt 30. The reflected light is condensed on the light receiving element 63 by the condenser lens 62, and the position of the light received by the light receiving element 63 is detected. Here, FIG. 5 is a diagram for explaining the principle of detecting the position correction pattern by the light receiving element 63. As shown in FIG. 5, in the light receiving element 63, the light reflection position varies depending on the position correction pattern formed on the paper conveyance belt 30, and the light receiving position on the light receiving element 63 changes accordingly. As a result, the position on the sheet conveying belt 30 in the position correction pattern is detected.

Specifically, as shown in FIG. 5, when there is no position correction pattern on the paper transport belt 30, the light emitted from the light emitting element 61 along the width direction of the paper transport belt 30 is the paper. Reflected on the surface of the conveyor belt 30. Therefore, the reflected light from the paper transport belt 30 passes through the reflected light path 1 (solid line in the figure) and enters the light receiving element 63.
On the other hand, when the position correction pattern exists, the light emitted from the light emitting element 61 along the width direction of the paper transport belt 30 is reflected by the surface of the position correction pattern on the paper transport belt 30. For this reason, the reflected light from the paper transport belt 30 moves along the reflected light path depending on the thickness of the position correction pattern, passes through the reflected light path 2 (broken line in the figure), and enters the light receiving element 63. For this reason, the light receiving position of the light receiving element 63 moves by the amount of optical path movement. As a result, an output change corresponding to the amount of optical path movement occurs in the output from the light receiving element 63, and the position on the paper transport belt 30 in the position correction pattern is detected.

  Since the detection sensor 60 of the present embodiment detects the position of the position correction pattern based on the amount of movement of the reflected light path as described above, the paper transport belt 30 of the present embodiment is separated from the light receiving element 63. The light is reflected by the surface of the paper transport belt 30 that holds the position correction pattern. On the other hand, the reflectance of the surface that holds the position correction pattern of the paper transport belt 30 does not need to be high, and it is sufficient if the reflectance is comparable to that of the toner image constituting the position correction pattern. .

However, in the detection sensor 60 according to the present embodiment that detects the amount of movement of the reflected light path as described above, in the region that holds the position correction pattern formed by each image forming unit 10, other than the position correction pattern. When the convex portion due to the above factor is formed on the paper conveying belt 30, the reflected light path moves and the same output change occurs as in the case where the position correction pattern exists, as shown in FIG. Become. When such an output change occurs, it becomes difficult to set the exposure positions of the laser exposure device 20 in each image forming unit 10 in the main scanning direction and the sub-scanning direction with high accuracy.
Therefore, in the image forming apparatus 1 according to the present embodiment, a concave portion is formed in the circumferential direction on the drive roll 32 in a region including a region where the sheet conveyance belt 30 holds the position correction pattern. That is, a portion (small diameter) in which the outer diameter of the driving roll 32 including the area where the paper conveyance belt 30 holds the position correction pattern is smaller than the outer diameter of other areas of the driving roll 32. Part). As a result, the drive roller 32 in the region including the region where the sheet conveying belt 30 holds the position correction pattern holds the sheet conveying belt 30 while maintaining the sheet conveying belt 30 in a non-contact state.

6A and 6B are views for explaining the shape of the drive roll 32 according to the present embodiment. FIG. 6A is a sectional view in the longitudinal direction, and FIG. 6B is a perspective view. As shown in FIG. 6, the drive roll 32 according to the present embodiment includes the entire area of the area for holding the position correction pattern at the center in the longitudinal direction where the paper transport belt 30 holds the position correction pattern. Thus, for example, a small diameter portion (concave portion) having a width of 10 mm and a depth of 200 μm is formed.
Thereby, for example, even if a foreign matter adheres to the drive roll 32, the foreign matter does not contact the paper transport belt 30, so that the surface flatness in the region where the paper transport belt 30 holds the position correction pattern is maintained.

  The drive roll 32 that drives the paper transport belt 30 is configured to increase the frictional force with the paper transport belt 30 in order to stably transport the paper transport belt 30 at a constant speed. Specifically, the drive roll 32 has a structure in which, for example, a hollow roll (or solid roll) made of aluminum is used as a base material, and a surface layer made of a rubber material such as urethane foam is coated on the surface of the hollow roll. ing. Such a surface layer made of a rubber material increases the frictional force with the paper transport belt 30 and stably transports the paper transport belt 30, but on the other hand, for example, dust of 20 μm or less is attached at the time of manufacture. It may adhere as a kimono. For example, dust larger than 20 μm is relatively large and therefore hardly adheres to the surface layer, and once attached, it is relatively easily removed by air blow or the like. However, fine deposits of, for example, 20 μm or less are difficult to remove even by air blow or the like, and may remain on the surface of the drive roll 32 even after the paper transport belt 30 is assembled.

  In such a state where fine deposits of, for example, 20 μm or less remain on the surface (surface layer) of the drive roll 32, the influence on the normal conveyance of the paper conveyance belt 30 is extremely small, but the exposure position adjustment described above is performed. Inconvenience may occur. That is, it is assumed that a fine deposit of about 20 μm, for example, is attached to the surface of the drive roll 32 in the area in the width direction of the paper transport belt 30 where the position correction pattern formed by each image forming unit 10 is held. . In that case, the reflected light path on the paper transport belt 30 of the light emitted from the light emitting element 61 along the width direction of the paper transport belt 30 moves as shown in FIG. The same output change as in the case where the position correction pattern exists is generated in the rotation period of the drive roll 32. When such an output change occurs in the light receiving element 63, the control unit 80 regards the position correction pattern as a position correction pattern even though the position correction pattern does not exist, and thus accurately detects the position of the position correction pattern. This makes it difficult to adjust the exposure position of the laser exposure device 20 with high accuracy.

  Therefore, in the image forming apparatus 1 according to the present embodiment, a region in the longitudinal direction including a region where the paper conveyance belt 30 in the driving roll 32 holds the position correction pattern is defined as another region (the paper conveyance belt 30). The first region extending in contact with the outer diameter of the first region) is smaller. Therefore, even if a fine deposit of, for example, about 20 μm is attached to the area where the position correction pattern on the surface of the drive roll 32 is held, the deposit is a small diameter portion as shown in FIG. Since it is inside the (concave portion) and does not come into contact with the paper transport belt 30, the surface of the paper transport belt 30 is maintained flat in the region where the position correction pattern is held. Thereby, an accurate output is generated from the light receiving element 63 when adjusting the exposure position.

As described above, the region where the concave portion is formed in the drive roll 32 (second region extending in a non-contact state with the paper conveyance belt 30) includes the region where the paper conveyance belt 30 holds the position correction pattern. Formed. As a result, an accurate output is generated from the light receiving element 63 at the time of adjusting the exposure position, regardless of which fine deposit adheres to any of the areas where the paper transport belt 30 holds the position correction pattern.
In the drive roll 32 according to the present embodiment, a concave portion (second region) is formed in the central portion in the longitudinal direction. However, the region for holding the position correction pattern in the paper transport belt 30 is, for example, the paper transport belt 30. In the case of both end regions in the width direction, correspondingly, concave portions are formed in both end portions in the longitudinal direction of the drive roll 32.

In addition, the recess formed in the drive roll 32 is difficult to remove even by air blow or the like, and is deep enough to cover fine deposits of, for example, 20 μm or less that easily remain on the surface of the drive roll 32 from both ends. That is, the outer diameter of the recess is formed to be 20 μm or more smaller than the outer diameter of other regions. Furthermore, it is preferable that the outer diameter is reduced by 50 μm or more in consideration of the allowance associated with the shape, size, attached state, and the like of the attached matter.
Specifically, for example, in order to form a recess in the surface layer made of urethane foam or the like on the surface of the drive roll 32, a surface layer as an example of a second surface layer thinner than the surrounding by 200 μm is formed to form the recess. Constitute. Further, for example, a surface layer of 200 μm is formed, and the surface layer is not covered on the portion where the recess is formed.
In addition, the width in the longitudinal direction of the concave portion is based on the premise that the paper transport belt 30 includes the region for holding the position correction pattern as described above, but the paper transport that is transported in a state where a predetermined tension is applied. The belt 30 is preferably 10 mm or less from the viewpoint of suppressing occurrence of distortion, wrinkles and the like in the recesses.

By the way, in the image forming apparatus 1 according to the present embodiment, as shown in FIG. 7, the transfer roll 31 disposed so as to face the image forming unit 10K has the sheet conveying belt 30 attached to the photosensitive drum 11K of the image forming unit 10K. A retract mechanism that separates the sheet conveying belt 30 from the other image forming units 10 while maintaining the state of being in pressure contact with each other is provided.
For example, when forming a monochrome image, no image forming unit 10 other than the image forming unit 10K is used. In this case, as in the case of forming a full-color image, if the image forming unit 10 other than the image forming unit 10K is set so that the sheet P passes through the sheet conveying belt 30, another image is formed. In the forming unit 10, wear of the photosensitive drum 11, wasteful consumption of toner, and the like occur. Therefore, when continuously forming monochrome images, the sheet conveying belt 30 is set to be separated from other image forming units 10 other than the image forming unit 10K.

  When the paper transport belt 30 is thus separated, the transport direction of the paper transport belt 30 changes by θ in the region upstream of the drive roll 32 as shown in FIG. However, in the image forming apparatus 1 according to the present embodiment, even when the sheet conveying belt 30 is set to be separated, the position of the driving roll 32 disposed at the top of the sheet conveying belt 30 is fixed and does not vary. That is, the portion including the drive roll 32 is set as a fulcrum of the retract mechanism that separates the paper transport belt 30. Therefore, when the detection sensor 60 detects the position of the position correction pattern, the position of the paper transport belt 30 does not vary. Thereby, in the image forming apparatus 1 of the present embodiment, the detection sensor 60 detects the position correction pattern even when the paper transport belt 30 is separated.

As described above, in the image forming apparatus 1 according to the present embodiment, a predetermined position correction pattern is formed on the paper transport belt 30 and the paper transport belt 30 is stretched over the drive roll 32 by the detection sensor 60. The exposure position of the laser exposure device 20 is adjusted by detecting the position of the position correction pattern in step. The drive roll 32 is formed with a recess that stretches the paper transport belt 30 in a non-contact state with the paper transport belt 30 in a longitudinal region including a region where the paper transport belt 30 holds the position correction pattern. Yes.
Thereby, even if a fine deposit adheres to any of the areas where the sheet conveying belt 30 holds the position correction pattern, the exposure position adjustment is performed with high accuracy.

1 is a diagram illustrating an overall configuration of an image forming apparatus to which the present invention is applied. It is the figure which showed the position where the pattern for position correction is detected by the detection sensor. It is the figure which showed an example of the structure of a detection sensor. It is the figure which showed an example of the pattern for position correction. It is a figure explaining the detection principle of the pattern for position correction by a light receiving element. It is a figure explaining the shape of a drive roll, (a) is sectional drawing of a longitudinal direction, (b) is a perspective view. FIG. 6 is a diagram illustrating a state in which the paper transport belt is separated from other image forming units other than the black image forming unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10Y, 10M, 10C, 10K ... Image forming unit, 11 ... Photosensitive drum, 20 ... Laser exposure device, 30 ... Paper conveyance belt, 32 ... Drive roll, 60 ... Detection sensor, 80 ... Control part

Claims (9)

A plurality of image carriers;
A belt member that conveys a predetermined pattern image transferred from each of the plurality of image carriers, and a surface having light reflectivity; and
A roll member composed of a first region that stretches the belt member in a contact state and a second region that stretches the region to which the pattern image of the belt member is transferred in a non-contact state;
Detecting means for detecting the position of the pattern image on the surface of the belt member stretched in the second region of the roll member;
The detection means emits light to the surface of the belt member stretched in the second region of the roll member, and is based on a movement amount of reflected light from the belt member of the emitted light. An image forming apparatus that detects the position of the pattern image . 2. The roll member, wherein the first region is composed of a base material and a surface layer formed on the surface of the base material, and the second region is composed of the base material. The image forming apparatus described. The detecting device, an image forming apparatus according to claim 1, characterized in that emits the light toward a width direction of the belt member against the surface of the belt member. The roll member is formed such that a frictional force between the surface layer formed in the first region and the belt member is larger than a frictional force between the base material and the belt member. 2. The image forming apparatus according to 2 . The image forming apparatus according to claim 2 , wherein the roll member further includes a second surface layer that is thinner than the surface layer in the second region. A plurality of image carriers;
A predetermined pattern image formed on each of the plurality of image carriers is transferred , conveys the pattern image, and a belt member whose surface has light reflectivity; and
A first region disposed at an end of the belt member and extending the belt member in a contact state; and a second region extending the region to which the pattern image of the belt member is transferred in a non-contact state. A roll member configured; and
Detecting means for detecting the position of the pattern image on the surface of the belt member stretched in the second region of the roll member;
The belt member is configured to be separable from a plurality of the image holding bodies in a state where the arrangement position of the roll member is fixed .
The detection means emits light to the surface of the belt member stretched in the second region of the roll member, and is based on a movement amount of reflected light from the belt member of the emitted light. An image forming apparatus that detects the position of the pattern image .   In the roll member, the first region is formed of a base material and the surface of the base material, and a frictional force between the belt member and the belt member is larger than the base material, and the second region is the base material. The image forming apparatus according to claim 6, wherein the image forming apparatus is made of a material.   In the roll member, the first region is formed of a base material and the surface of the base material, and a frictional force between the belt member and the belt member is larger than the base material, and the second region is the base material. The image forming apparatus according to claim 6, wherein the image forming apparatus is formed of a material and a second surface layer that is thinner than the surface layer. The image forming apparatus according to claim 6 , wherein the detection unit emits the light toward a surface of the belt member in a width direction of the belt member.

Images