JPH11272031A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device appropriately correcting color slurring in the case of forming a color image by plurally juxtaposing image forming means for forming different color toner images on transfer paper along a transfer belt. SOLUTION: In this image forming device, a toner mark 94 is formed on the transfer belt 21 by the respective color image forming parts and detected by a color slurring detection part 50 at the time of detecting the color slurring. In the detection part 50, a light emitting element 91 and a light receiving element 92 are disposed while putting the transfer belt 21 in between and a soiling preventing sheet 86b is disposed between the light emitting element 91 on the side of the belt 21 where the toner mark 94 is formed and the belt 21. The sheet 86b is carried by sheet carrying rollers 85a and 85b and cleaned by a sheet cleaner 88b. Therefore, scattered toner is prevented from adhering to the light emitting element 91, and the color slurring is always accurately and exactly detected by the detection part 50, so that the color slurring is exactly corrected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more particularly, to a method of forming a plurality of image forming means for forming toner images of different colors on transfer paper along a transfer belt to form toner images of different colors. The present invention relates to an electrophotographic image forming apparatus that appropriately corrects a color shift when a color image is formed by superimposing.

[0002]

2. Description of the Related Art Conventionally, as a so-called tandem type image forming apparatus for forming a color image by superposing images by arranging a plurality of writing units of an electrophotographic system and an image forming cartridge, for example, There is a copying machine. Such a color copying machine includes an image forming station that forms images of cyan, magenta, yellow, and black. The image forming station of each color includes a writing unit and an image forming cartridge, and stores image data of each color. The latent image is formed by irradiating the laser modulated by the writing unit to the photosensitive member of the image forming cartridge from the writing unit, and the image forming cartridge of each color supplies toner of each color to the photosensitive member on which the latent image is formed. Develop the toner image. The image forming cartridge of each color transfers the toner image on the photoconductor to the transfer paper conveyed on the transfer belt, and forms a color image by superimposing the toner image of each color on the transfer paper.

In an image forming apparatus having a plurality of image forming stations as described above, each image forming station is compared with an image forming apparatus having only one photosensitive member called a one-drum type and forming a color image. Then, different toner images are sequentially superimposed on the same surface of the same transfer paper,
Since a color image is formed, if the transfer image position on the transfer paper in each image forming station shifts, the image interval formed in each image forming station shifts or overlaps, and in the case of a color image, This causes a difference in color and a color shift, and deteriorates image quality.

[0004] The color misregistration may be caused by an assembling error in the writing optical system, an error in mounting each unit to the image forming apparatus main body, an error in mounting the photosensitive member to the image forming apparatus main body, or the like. There are two types of color shift: tilt color shift caused by the occurrence of color shift, and parallel color shift caused by shifting the position of the scanning line in parallel with respect to the reference position and shifting the image of four colors as a whole in the vertical or horizontal direction. Of these color shifts, the tilt color shift is
Correction can be performed by finely adjusting the position of the reflection mirror of the writing device, and parallel color shift can be corrected by adjusting the writing start timing in the main scanning direction or the sub-scanning direction. Further, the length of the image in the main scanning direction can be adjusted by changing the frequency of the writing pixel, that is, by adjusting the magnification error.

Conventionally, in an image forming apparatus provided with such a plurality of image forming stations, for example, a positional deviation of each color image is detected by a plurality of image forming stations on a transport belt for sequentially transporting a transfer sheet. Forming a toner mark, and detecting the toner mark by detecting means including a light emitting element and a light receiving element, detecting a position shift based on the detection result, and detecting an image by each image forming station based on the detection result. (See Japanese Patent Application Laid-Open No. 8-286458).

[0006]

However, in such a conventional image forming apparatus, a toner mark for detecting a displacement is formed on a transport belt for transporting a transfer sheet.
Since the color misregistration was corrected by detecting the toner mark by the detecting means including the light emitting element and the light receiving element, the light emitting element and the light receiving element, which are parts of the detecting means, were contaminated by the toner of the toner mark, and the positional displacement of the image was reduced. It is no longer possible to detect accurately, and it is no longer possible to correct color misregistration,
There is a problem that image quality deteriorates.

That is, since the toner mark formed on the transport belt is an unfixed toner image on which no fixing processing has been performed, the detection means of the detecting means provided on the side facing the toner image due to the scattering of the toner. The light emitting element or the light receiving element, which is a component, becomes dirty, so that it is impossible to accurately detect the positional shift of the image, and it is not possible to correct an appropriate color shift, thereby deteriorating the image quality.

Therefore, the invention according to claim 1 is to provide a full-color image by sequentially transferring toner images of different colors onto transfer paper by a plurality of image forming means arranged along a transfer belt, and at a predetermined timing. Then, a predetermined toner mark is formed on the transfer belt by each image forming means,
Light is emitted from the light emitting element to the toner mark and the reflected light or transmitted light of the light from the toner mark is received by the light receiving element. When correcting color misregistration at the time of full-color image formation by the image forming means, based on the light emitting element and the light receiving element, the element disposed on the side of the transfer belt on which the toner mark is formed and the transfer belt By arranging a dustproof sheet having a predetermined transparency so as to be movable by a predetermined amount, the toner of the unfixed toner mark scatters and adheres to the light emitting element and the light receiving element of the color misregistration detecting means, It is possible to prevent the detection accuracy of the toner mark of the color shift detecting unit from deteriorating, accurately detect a color shift of the toner image, correct an appropriate color shift, and improve the image quality. And its object is to provide an image forming apparatus.

According to the second aspect of the present invention, the dustproof sheet is cleaned by the cleaning means, so that the color misregistration detecting means always detects the toner mark with high accuracy, and detects the color shift of the toner image more accurately. It is another object of the present invention to provide an image forming apparatus capable of correcting color misregistration more appropriately and further improving image quality.

According to a third aspect of the present invention, there is provided a dustproof sheet,
By forming it into an endless sheet shape, stretching it over at least a pair of rollers, and making it movable through the rollers, the color misregistration detecting means always detects the toner mark with high accuracy, and further reduces the color shift of the toner image. It is an object of the present invention to provide an image forming apparatus capable of accurately detecting, correcting a more appropriate color shift, and further improving image quality.

[0011]

According to the first aspect of the present invention, there is provided an image forming apparatus which forms an electrostatic latent image by a writing scanning line scanned on a photosensitive member which is driven to rotate, and forms the electrostatic latent image. Image forming means for supplying and developing a toner of a predetermined color on the formed photoreceptor and transferring the toner image formed on the photoreceptor onto transfer paper to form a toner image is arranged along a plurality of transfer belts. Established
Each of the image forming means sequentially transfers a different color toner image onto the transfer paper to form a full-color image,
At a predetermined timing, a predetermined toner mark is formed on the transfer belt by the respective image forming means, and the toner mark is irradiated with light from a light emitting element to receive reflected light or transmitted light from the toner mark. An image forming apparatus that detects the toner mark by a color shift detecting unit that receives light by an element, and corrects a color shift during the full-color image formation by the image forming unit based on a detection result of the color shift detecting unit, The color misregistration detecting means includes a predetermined transparent member between the transfer belt and one of the light emitting element and the light receiving element which is disposed on a side of the transfer belt on which the toner mark is formed. The above object is achieved by arranging the dustproof sheet having a property to be movable by a predetermined amount.

According to the above-described configuration, a plurality of image forming means arranged along the transfer belt sequentially transfer toner images of different colors onto transfer paper to form a full-color image, and at the same time, form each color image at a predetermined timing. A color shift detecting unit that forms a predetermined toner mark on a transfer belt by an image unit, irradiates the toner mark with light from a light emitting element, and receives reflected light or transmitted light of the light from the toner mark by a light receiving element. When correcting the color misregistration at the time of full-color image formation by the image forming means based on the detection result of the color misregistration detecting means, the toner mark of the transfer belt is formed of the light emitting element and the light receiving element. Since a dust-proof sheet having a predetermined transparency is movably disposed between the element disposed on the side facing the surface and the transfer belt, a predetermined amount Adhering to the light emitting element and the light receiving element of the color shift detecting means not the toner mark toner is scattered,
It is possible to prevent the detection accuracy of the toner mark of the color shift detecting means from deteriorating, accurately detect a color shift of the toner image, correct an appropriate color shift, and improve the image quality.

In this case, for example, the image forming apparatus may further include a cleaning unit for cleaning the dustproof sheet of the color misregistration detecting unit.

According to the above construction, since the dust-proof sheet is cleaned by the cleaning means, the color misregistration detecting means can always detect the toner mark with high accuracy, and can more accurately detect the color shift of the toner image. It is possible to correct color misregistration more appropriately and to further improve image quality.

Further, for example, the dust-proof sheet is formed in an endless sheet shape, is stretched over at least a pair of rollers, and is moved by rotating the rollers. May be performed.

According to the above construction, the dust-proof sheet is formed in an endless sheet shape, stretched over at least a pair of rollers, and is movable via the rollers. With good detection, the color misregistration of the toner image can be more accurately detected, and more appropriate color shift can be corrected, so that the image quality can be further improved.

[0017]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. It should be noted that the embodiments described below are preferred embodiments of the present invention, and therefore, various technically preferable limitations are added. However, the scope of the present invention is not limited to the following description. The embodiments are not limited to these embodiments unless otherwise specified.

FIGS. 1 to 6 show an embodiment of the image forming apparatus of the present invention. FIG. 1 shows an image forming apparatus 1 to which the embodiment of the image forming apparatus of the present invention is applied. It is a schematic block diagram.

In FIG. 1, an image forming apparatus 1 includes a paper feeding unit 10 and a transfer belt mechanism 2 in a main body housing (not shown).
0, image forming units 30Y, 30M, 30C, 30 of each color of yellow (Y), magenta (M), cyan (C), and black (K) disposed along the transfer belt mechanism unit 20
K, a fixing unit 40, a color shift detecting unit 50, and the like.
In addition to these, although not shown, a control unit that controls each unit of the image forming apparatus 1, a motor, and a drive mechanism unit that transmits a drive source to each unit driven by the motor are provided.

The paper supply section 10 includes a paper supply cassette 12, in which a plurality of transfer papers 11 are loaded, a paper supply roller 13, a pair of registration rollers 14, and the like. The paper feed unit 10 separates the paper 11 in the paper feed cassette 12 one by one by a separation member (not shown) from the paper feed roller 13 and
4, the registration roller pair 14 is provided with a paper feed clutch and the like, and adjusts the timing of the paper 11 sent from the paper feed cassette 12 by the paper feed roller 13 and the separating member, thereby setting the paper 11 at a predetermined timing. To send it to the transfer belt mechanism 20.

The transfer belt mechanism 20 includes a transfer belt 2
1, a driving roller 22, a driven roller 23, a charge removing section 24, a cleaning section 25, and the like.
Are spread over the driving roller 22 and the driven roller 23. When the drive roller 22 is driven to rotate by a drive mechanism such as a motor (not shown) under the control of the control unit, the drive roller 22 is driven to rotate counterclockwise in FIG.
The paper 11 sent from the image forming unit 30 is sent to the image forming unit 30 for each color.
Y, 30M, 30C, and 30K, and the image forming units 30Y, 30M, 30C, and 3 of respective colors are applied to the conveyed paper 11.
0K, the yellow toner image, the magenta toner image, the cyan toner image, and the black toner image
1 is formed. The charge removing unit 24 removes the charge of the transfer belt 21, and the cleaning unit 25 removes toner and the like remaining on the transfer belt 21 to clean the transfer belt 21. The transfer belt 21 is formed of a predetermined transparent sheet material.

Image forming units (image forming means) 30Y, 30 for each color
M, 30C, and 30K are photosensitive members 31Y to 31K, respectively.
, Charging units 32Y to 32K, writing unit 33Y
~ 33K, developing units 34Y ~ 34K, transfer units 35Y ~ 35
K, cleaning units 36Y to 36K, a charge removing unit (not shown), and the like.

Each of the image forming units 30Y to 30K is driven by a driving mechanism (not shown) to rotate clockwise in FIG.
To 31K are uniformly charged by the charging units 32Y to 32K, and the writing units 33Y to 33K irradiate the lasers modulated with image data to the photoconductors 31Y to 31K to form electrostatic latent images. The developing units 34Y to 34K respectively apply yellow (Y), magenta (M), and cyan (C) to the photoconductors 31Y to 31K on which the electrostatic latent images are formed.
And toner of each color of black (K) is adhered to form a toner image of each color. And the image forming units 30Y to 30K
When the paper 11 is conveyed between the transfer belt 21 and the photoconductors 31Y to 31K, the transfer units 35Y to 35K disposed on the back surface of the transfer belt 21 apply a transfer potential, and The toner images of yellow (Y), magenta (M), cyan (C), and black (K) on 31Y to 31K are sequentially transferred to the sheet 11. The photoconductors 31Y to 31K for which the toner images have been completed are cleaned by the cleaning unit 36Y.
After the residual toner is cleaned at ~ 36K and the charge is removed by the charge removing unit, the charged toner is charged again by the charging units 32Y to 32K to perform the next image forming operation.

As described above, the toner image of each color of yellow (Y), magenta (M), cyan (C), and black (K) is transferred to the paper 11 on which the image of each color is formed.
Is further conveyed by the transfer belt 21 while being electrostatically attracted to the transfer belt 21, separated from the transfer belt 21, and conveyed to the fixing unit 40.

As shown in FIG. 2, the writing units 33Y to 33K for the yellow (Y) writing unit 33Y include a laser emitting unit 61, a polygon mirror 62, a polygon motor 63, an fθ lens 64, a folding mirror 65, The mirror adjusting mechanism 66 includes a mirror supporting member 68 fixed to a supporting frame 67 which is a frame of the writing units 33Y to 33K and attached to one longitudinal end of the folding mirror 65. ,
The pressure spring 69 and the eccentric cam 70 that hold the other end of the return mirror 65, a step motor 71 that rotationally drives the eccentric cam 70, and the rotation of the step motor 71 are reduced and transmitted to the eccentric cam 70. A worm speed reducer 72 and the like are provided. Note that the pressure spring 69 is supported by a support frame 67 that is a frame of the writing units 33Y to 33K.
It is fixed to.

The writing unit 33Y includes a laser emitting unit 61
Irradiates the polygon mirror 62 with the laser beam modulated by the image data, deflects the laser beam in the main scanning direction by the polygon mirror 62 rotated and driven by the polygon motor 63, and converts the laser beam into a constant-speed linear by the fθ lens 64. Is incident on the return mirror 65 and returns to the return mirror 6.
The laser beam reflected at 5 is irradiated on the photoconductor 31Y.

As described above, the folding mirror 65 is supported such that one end is attached to the mirror support member 68 and the other end is held between the spring 69 and the eccentric cam 70. ing. Mirror support member 68
Is formed of a flexible member, and a thin bridge portion 68a is formed between a fixed portion to the support frame 67 and a fixed portion to the folding mirror 65. The folding portion 65a is formed by the bridge portion 68a. Is supported so as to be rotatable by a small angle in the direction of both arrows in FIG. Further, the mirror adjustment mechanism 66 includes the pressure spring 6
9 and the eccentric cam 70 to hold the other end of the folding mirror 65 with the other end thereof interposed therebetween.
Is rotated by a small angle by the step motor 71, whereby the folding mirror 65 is rotated by a small angle in the direction indicated by the double-headed arrow in FIG. 2 around the bridge portion 68a of the support member 68 as the center of rotation. When the angle of the folding mirror 65 is adjusted in this way, the writing position of the laser beam on the photoreceptor 31Y moves only the front side without changing the back side, and corrects the direction of the image data of the writing line. It can be performed.

Although FIG. 2 shows only the writing unit 33Y for yellow (Y), the other writing units 33M to 33C have the same configuration.

The fixing section 40 includes a fixing roller 41, a pressure roller 42, and a pair of discharge rollers (not shown). The fixing roller 41 and the pressing roller 42 are pressed with a predetermined pressing force, and one of them is driven to rotate, and the other is rotated. The fixing roller 41 is heated to a predetermined fixing temperature by a built-in heater. Heating is controlled.

The fixing section 40 fixes the toner image of each color of yellow (Y), magenta (M), cyan (C) and black (K) and conveys the paper 11 conveyed by the transfer belt 21 to a fixing roller. The toner of each color is fixed on the paper 11 by heating and pressing by the pressure roller 41 and the pressure roller 42, and is discharged onto a discharge tray (not shown) by a pair of discharge rollers.

The color shift detecting section (color shift detecting means) 50 includes:
Transfer belt 21 from drive roller 22 to driven roller 23
And is configured as shown in FIGS. 3 and 4. That is, two light emitting unit holders 82 disposed on the light emitting unit support 81 extending in the width direction of the transfer belt 21 at predetermined intervals in the width direction of the transfer belt 21.
a, 82b; two light receiving unit holders 84a, 84b disposed on the light receiving unit support 83 extending in the width direction of the transfer belt 21 so as to face the light emitting unit holders 82a, 82b; Rollers 85a, 85b, a pair of dirt prevention sheets 86a, 86b stretched over the sheet conveying rollers 85a, 85b in a state of being located between the light emitting unit holders 82a, 82b and the light receiving unit holders 84a, 84b, and a cleaner support. 87, a pair of sheet cleaners 88a, 88b disposed so as to be in contact with the outer surfaces of the stain prevention sheets 86a, 86b at one of the sheet conveying rollers 85a, 85b.
The light-emitting unit support 81, the light-receiving unit support 83, and the cleaner support 87 provided at both ends in the width direction of the transfer belt 21 are fixed by screws or the like, and the sheet conveying rollers 85a and 85b can be rotated. A pair of side plates 89 to support
a, 89b and one of the shafts of the sheet conveying rollers 85a, 85b.
And a turning knob 90 for rotating. As shown in FIG. 4, the light emitting unit holders 82a and 82b
For example, a light emitting diode or the like is used as the light emitting element 91. Light receiving unit holders 84a, 84
4B, as shown in FIG. 4, while holding the light receiving element 92, a slit plate 93 is provided on the surface on the side of the light emitting unit holders 82a, 82b. Toner mark 94 formed on belt 21
Are formed (not shown) having a shape corresponding to the above shape. The dirt prevention sheets 86a and 86b are disposed on the side facing the toner mark 94 formed on the transfer belt 21, and are formed of, for example, a transparent sheet such as a polyester film. Through the light. The stain prevention sheets 86a and 86b are
When the sheet conveying rollers 85a and 85b are rotated in the direction indicated by the arrow in FIG. 3 by the turning unit 90, they are rotated in the direction indicated by the arrow in FIG. 4 and the sheet cleaners 88a and 88b are rotated.
To prevent toner marks 94 and the like from being scattered.
The toner attached to 6a and 86b is cleaned.

The color misregistration detection unit 50 applies light emitted from the light emitting element 91 to the transfer belt 21 on which the toner marks 94 are formed in each color by the image forming units 30Y, 30M, 30C, and 30K during color misregistration adjustment. Stain prevention sheets 86a, 86
b, passes through the transfer belt 21 and is incident on the light receiving element 92 to detect the toner mark 94. The color misregistration detection unit 50 outputs a detection result of the toner mark 94 of each color to a control unit of the image forming apparatus 1 (not shown).

The image forming apparatus 1 is controlled by the control unit based on the detection result of the color shift detection unit 50 to determine whether there is a color shift.
By detecting the direction of the color shift and the shift amount, as described above,
The writing start timing by the image forming units 30Y, 30M, 30C, and 30K is adjusted, and the image forming units 30Y, 30C, and 30K are adjusted.
The color shift is corrected by adjusting the angles of the turning mirrors of the writing units 33Y to 33K of M, 30C, and 30K.

Next, the operation of the present embodiment will be described. The image forming apparatus 1 is characterized in that the color shift of each color is reliably and appropriately detected, and the color shift of each color is accurately corrected.

That is, the image forming apparatus 1 sequentially forms images of each color on the paper 11 by the image forming units 30Y, 30M, 30C, and 30K of each color, and forms a color image on the paper 11, so that each color The image position is in the main scanning direction, sub-scanning direction,
If the magnification and the inclination do not match, a color shift or the like occurs, and the image quality deteriorates.

The main scanning direction, the sub-scanning direction, and the magnification among the elements related to the image displacement are adjusted by controlling the write signals of the image forming units 30Y, 30M, 30C, and 30K. Although it is possible to tilt, only by mechanically adjusting the angle of the photoconductors 31Y to 31K and the conveyance direction of the paper 11 with respect to the inclination,
Elimination is possible.

In the image forming apparatus 1 of the present embodiment, the inclination is adjusted by adjusting the optical axis of the laser light emitted from the writing units 33Y to 33K to the photoconductors 31Y to 31K, and adjusting the inclination of the return mirror 65 by mirror adjustment. The adjustment is performed by the mechanism 66.

The image forming apparatus 1 divides the paper 11 in the paper feed cassette 12 by a paper feed roller 13 and a separating member (not shown).
The sheet 11 is separated and sent to the registration roller pair 14, the timing of the sheet 11 sent from the sheet feeding cassette 12 is adjusted by the registration roller pair 14, and the sheet 11 is sent to the transfer belt mechanism 20 at a predetermined timing. . The transfer belt mechanism 20 is a transfer belt 21 that is driven to rotate counterclockwise in FIG.
The paper 11 sent from the printer is converted into an image forming unit 30 for each color.
Y, 30M, 30C, and 30K, and the image forming units 30Y, 30M, 30C, and 30 of the respective colors are formed on the conveyed paper 11.
K, yellow toner image, magenta toner image,
A cyan toner image and a black toner image are sequentially formed on the sheet 11. That is, the image forming units 30Y to 30K uniformly charge the photoconductors 31Y to 31K, which are rotationally driven clockwise in FIG. When an electrostatic latent image is formed by irradiating the photoconductors 31Y to 31K with laser beams modulated by image data by the 33Y to 33K, the developing units are attached to the photoconductors 31Y to 31K on which the electrostatic latent images are formed. 34Y-34K
Then, toner of each color of yellow (Y), magenta (M), cyan (C) and black (K) is adhered to form a toner image of each color. Then, the image forming unit 30Y
When the paper 11 is conveyed between the transfer belt 21 and the photoconductors 31Y to 31K, the transfer units 35Y to 35K disposed on the back surface of the transfer belt 21 apply a transfer potential, Yellow (Y) on the photoconductors 31Y to 31K,
Magenta (M), cyan (C), and black (K) toner images are sequentially transferred to the sheet 11. The photoconductors 31Y to 31K for which the toner images have been completed are cleaned of residual toner by the cleaning units 36Y to 36K, are discharged by the discharging unit, and are charged again by the charging units 32Y to 32K to perform the next image forming operation. Do.

As described above, the toner image of each color of yellow (Y), magenta (M), cyan (C), and black (K) is transferred to the sheet 11 on which the image of each color is formed.
Is further conveyed by the transfer belt 21 while being electrostatically attracted to the transfer belt 21, separated from the transfer belt 21, and conveyed to the fixing unit 40.

The fixing section 40 transfers toner 11 of each color of yellow (Y), magenta (M), cyan (C) and black (K), and fixes the paper 11 conveyed by the transfer belt 21 to a fixing roller 41. Then, the toner of each color is fixed on the sheet 11 by heating and pressing by the pressure roller 42 and is discharged onto a discharge tray (not shown) by a pair of discharge rollers.

In the image forming process, each image forming unit 30
If there is a misalignment of the image formed on the transfer paper 11 at Y, 30M, 30C, and 30K, a color shift occurs in the color image formed on the transfer paper 11.

The color misregistration is, for example, as shown by a solid line and a broken line in the case of two colors for simplicity in FIG. 6, in the main scanning direction of the image formed by the image forming units 30Y, 30M, 30C and 30K. And color misregistration due to misregistration in the sub-scanning direction (see FIG. 6A), and the image forming units 30Y, 30M, 30
C and 30K, there is a color shift due to an angle shift of the image formed (see FIG. 6B).

Therefore, the image forming apparatus 1 performs a color shift detection process at a predetermined timing, and when a color shift is detected, performs a process of correcting the color shift.

That is, the image forming apparatus 1 applies, for example, a toner mark 94 as shown in FIG. 5 to each of the image forming units 30Y, 30M, 30C and 30K when detecting a color shift.
1 are formed at both ends in the width direction, and the color misregistration detection unit 50 detects the toner marks 94 formed on the transfer belt 21 to detect the color misregistration.

As shown in FIGS. 3 and 4, the color misregistration detecting section 50 interposes the transfer belt 21 with the transfer belt 21 therebetween.
Light-emitting unit holders 82a and 82b and light-receiving unit holders 84a and 84b at positions corresponding to toner marks 94 formed on
A light emitting element 91 and a light receiving element 92 housed in the transfer belt 2 are provided in the light receiving section holders 84a and 84b.
The slit plate 93 in which a slit having a shape corresponding to the shape of the toner mark 94 formed in the light emitting element 91 is formed.
It is disposed at the position where light from the light passes. Color shift detection unit 5
0 is the light emitting unit holders 82a and 82b and the light receiving unit holder 84
a, 84b, the toner mark 9 on the transfer belt 21
The dirt prevention sheets 86a and 86b are disposed at positions corresponding to the surface on which the dirt prevention sheet 4 is formed.
6a and 86b are stretched over the sheet conveying rollers 85a and 85b, and rotate when the sheet conveying rollers 85a and 85b are rotated by the turning knob 90. Sheet cleaners 88a and 88b attached to the cleaner support 87 are disposed in contact with the stain prevention sheets 86a and 86b, and the stain prevention sheets 86a and 86b are cleaned by the sheet cleaners 88a and 88b. . Then, the transfer belt 21 and the stain prevention sheet 86
a and 86b are formed of a predetermined transparent member.

When a color shift is detected, the color shift detecting unit 50 projects light from the light emitting element 91 toward the light receiving element 92 and emits light emitted from the light emitting element 91 to the stain prevention sheet 86a.
After passing through 86b, the transfer belt 21 is irradiated. When the color shift is detected, the image forming units 30Y and 30
The toner marks 94 are formed by M, 30C, and 30K, and are conveyed to the color misregistration detection unit 50.

When the toner mark 94 formed on the transfer belt 21 is conveyed between the light emitting element 91 and the light receiving element 92, a slit plate 93 provided in front of the light receiving element 92 is provided.
Since the slit corresponding to the shape of the toner mark 94 is formed in the toner mark 94,
Color misregistration is properly and reliably detected.

The color misregistration detecting section 50 includes the image forming sections 3.
0Y, 30M, 30C, 30K indicate toner mark 94
Is transferred, the toner mark 94 is not subjected to the fixing process, and the toner mark 9 of the transfer belt 21 conveyed to the color misregistration detection unit 50 is transferred.
4 is scattered, and the scattered toner adheres to the light emitting element 91 facing the side where the toner mark 94 of the transfer belt 21 is formed, and the light emission intensity of the light emitting element 91 is reduced. The detection accuracy of the color misregistration 94 decreases.

However, the image forming apparatus 1 of the present embodiment
The light-emitting element 91 of the transfer belt 21 on the side where the toner mark 94 is formed and the transfer belt 21
The dirt prevention sheets 86a and 86b are disposed between the two. Therefore, it is possible to prevent the scattered toner from adhering to the light emitting element 91, prevent the color shift detection unit 50 from lowering the color shift detection accuracy, and always detect the color shift with high accuracy. Further, the color misregistration detection unit 50 detects that the stain prevention sheets 86a and 86b
a, 85b, and the sheet cleaners 88a, 88b are disposed in contact with the dirt prevention sheets 86a, 86b at the position of the sheet conveying roller 85b, and the turning knob 90 is turned. Then, the sheet conveying rollers 85a and 85b rotate, and the sheet cleaner 8 rotates.
The stain prevention sheets 86a and 86b are cleaned by 8a and 88b, and the clean stain prevention sheets 86a and 86b can be positioned between the light emitting element 91 and the light receiving element 92.

Therefore, the image forming apparatus 1 can always detect the color misregistration with high accuracy by the color misregistration detection unit 50, and can appropriately correct the color misregistration and improve the image quality.

Although the invention made by the inventor has been specifically described based on the preferred embodiments, the present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the invention. It goes without saying that it is possible.

For example, in the above embodiment, the light emitting element 91 is disposed at a position facing the side where the toner mark 94 of the transfer belt 21 is formed, and the toner mark 94 of the transfer belt 21 is not formed. The light receiving element 92 is disposed at a position facing the side, but the position at which the light emitting element 91 and the light receiving element 92 are disposed is not limited to the above-described embodiment. The light receiving element 92 may be provided at a position facing the side where the mark is formed, and the light emitting element 91 may be provided at a position facing the side where the toner mark 94 of the transfer belt 21 is not formed.

Further, in this embodiment, the dirt prevention sheets 86a and 86b are rotated manually by the knob 90. However, using a motor or the like,
The stain prevention sheets 86a and 86b may be automatically rotated.

Further, in the present embodiment, the transmission type in which the light emitting element 91 and the light receiving element 92 are disposed at the positions opposed to each other in the color misregistration detecting section 50 is adopted, but the present invention is not limited to the transmission type. The same applies to the case where a reflection type optical sensor is used. In this case, dirt prevention sheets 86a and 86b are provided between the transmission type optical sensor and the transfer belt 21.

[0055]

According to the image forming apparatus of the present invention, a full-color image is formed by sequentially transferring toner images of different colors onto transfer paper by image forming means arranged along a transfer belt. At the same time, a predetermined toner mark is formed on the transfer belt by each image forming means at a predetermined timing, and the toner mark is irradiated with light from a light emitting element to reflect or transmit the light from the toner mark. When the color misregistration detecting means for receiving the toner mark detects the toner mark, and correcting the color misregistration at the time of full-color image formation by the image forming means based on the detection result of the color misregistration detecting means, A dust-proof sheet having a predetermined transparency can be moved by a predetermined amount between the transfer belt and an element disposed on the side of the transfer belt on which the toner mark is formed; The arrangement prevents the toner of the unfixed toner mark from scattering and adhering to the light emitting element and the light receiving element of the color misregistration detecting means, thereby preventing the accuracy of the color misregistration detecting means from detecting the toner mark from deteriorating. This makes it possible to accurately detect a color shift of a toner image, correct an appropriate color shift, and improve image quality.

According to the image forming apparatus of the present invention, the dust-proof sheet is cleaned by the cleaning means, so that the color misregistration detecting means always detects the toner mark with high accuracy, thereby reducing the color shift of the toner image. Detection can be performed more accurately, color shift can be corrected more appropriately, and image quality can be further improved.

According to the image forming apparatus of the present invention, the dust-proof sheet is formed into an endless sheet, stretched over at least a pair of rollers, and is movable via the rollers. The detection means can always detect the toner mark with high accuracy, detect the color shift of the toner image more accurately, correct the color shift more appropriately, and further improve the image quality. .

[Brief description of the drawings]

FIG. 1 is a schematic configuration front view of an image forming apparatus to which an embodiment of the image forming apparatus of the present invention is applied.

FIG. 2 is a perspective view of a yellow (Y) writing unit of the image forming apparatus of FIG. 1;

FIG. 3 is an enlarged exploded perspective view of a color misregistration detection unit in FIG. 1;

FIG. 4 is a front sectional view of a main part of a color misregistration detection unit in FIG. 3;

5 is a perspective view of a main part showing a state where toner marks are formed on a transfer belt of the image forming apparatus of FIG. 1;

FIG. 6 is an explanatory diagram of a case where a color shift occurs in the main scanning direction and the sub-scanning direction (FIG. 6A) and a case where a color shift occurs in an oblique direction (FIG. 6B).

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 image forming apparatus 10 paper feed unit 11 paper 12 paper feed cassette 13 paper feed roller 14 registration roller pair 20 transfer belt mechanism unit 21 transfer belt 22 drive roller 23 driven roller 24 static elimination unit 25 cleaning unit 30Y, 30M, 30C, 30K Image unit 31Y to 31K Photoreceptor 32Y to 32K Charging unit 33Y to 33K Writing unit 34Y to 34K Developing unit 35Y to 35K Transfer unit 36Y to 36K Cleaning unit 40 Fixing unit 50 Color shift detecting unit 61 Laser emitting unit 62 Polygon mirror 63 Polygon Motor 64 fθ lens 65 Folding mirror 66 Mirror adjustment mechanism 67 Support frame 68 Mirror support member 68a Bridge section 69 Pressure spring 70 Eccentric cam 71 Step motor 72 Worm reducer 81 Light emitting unit support 82a, 82b Light emitting unit Holder 83 Light receiving unit support 84a, 84b Light receiving unit holder 85a, 85b Sheet transport roller 86a, 86b Stain prevention sheet 87 Cleaner support 88a, 88b Sheet cleaner 89a, 89b Side plate 90 Turning knob 91 Light emitting element 92 Light receiving element 93 Slit plate 94 Toner mark

Claims (3)

[Claims] An electrostatic latent image is formed by a writing scanning line scanned on a photoreceptor that is rotationally driven, and a toner of a predetermined color is formed on the photoreceptor and developed on the photoreceptor to develop the image. Image forming means for transferring a toner image formed on a photoreceptor onto transfer paper to form a toner image is disposed along a plurality of transfer belts, and each image forming means forms a different color toner image. A full-color image is formed by sequentially transferring images onto transfer paper, and at a predetermined timing, a predetermined toner mark is formed on the transfer belt by the image forming means, and light is emitted from the light emitting element to the toner mark. The color misregistration detecting means for receiving the reflected light or transmitted light of the light from the toner mark by a light receiving element detects the toner mark, and the full-color image forming by the image forming means based on the detection result of the color misregistration detecting means. An image forming apparatus that corrects the color misregistration, wherein the color misregistration detection unit is disposed to face a side of the transfer belt on which the toner mark is formed, of the light emitting element and the light receiving element. An image forming apparatus, wherein a dustproof sheet having a predetermined transparency is movably disposed between the element and the transfer belt by a predetermined amount. 2. The image forming apparatus according to claim 1, wherein said image forming apparatus further comprises a cleaning means for cleaning said dustproof sheet of said color misregistration detecting means. 3. The dustproof sheet is formed in an endless sheet shape, stretched over at least a pair of rollers, and moved by rotating the rollers. The image forming apparatus according to claim 2.