JP3526356B2 - Image forming apparatus and color image forming apparatus - Google Patents

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 such as a copying machine, a facsimile and a printer, and a color image forming apparatus.

[0002]

2. Description of the Related Art Heretofore, a color image forming apparatus using an intermediate transfer member as a belt-shaped image carrier has been known. In this color image forming apparatus, a drum-shaped or belt-shaped photosensitive member is rotationally driven by a motor, the intermediate transfer member is disposed so as to face the photosensitive member and abuts against the photosensitive member, and the intermediate transfer member has the same circumference as the photosensitive member. It is driven to rotate at high speed. A mark is provided on a part of the intermediate transfer member, and a mark detection sensor provided in a predetermined passage area through which the mark passes detects the mark.

The image forming process is started after a lapse of a certain time from the mark detection by the mark detecting sensor, and the photosensitive member is uniformly charged by the charging means, and thereafter the optical writing is performed by the exposure of the exposing means to the photosensitive member and the static operation is performed. A latent image is formed. This electrostatic latent image is developed by the developing means to become a toner image of a predetermined color, and this toner image is transferred to the intermediate transfer body by the primary transfer means.

The above-described image forming process of a predetermined color is repeated for each color, and the toner images of a plurality of colors are superimposed and transferred onto the intermediate transfer member to form a color image, and the color image is formed on the intermediate transfer member. The color image is collectively transferred onto the transfer paper by the secondary transfer means, and the transfer paper is separated from the intermediate transfer body, and then the color image on the transfer paper is fixed by the fixing means. As the intermediate transfer member, a drum-shaped intermediate transfer member and an intermediate transfer belt as a belt-shaped intermediate transfer member are known, but an intermediate transfer belt having a large degree of freedom in layout may be used in order to downsize the machine. Many.

Incidentally, as the secondary transfer means, there are a roller transfer method using a bias roller and a corona transfer method using a charger. The roller transfer method requires a contact / separation mechanism for contacting / separating the bias roller with respect to the intermediate transfer member and a cleaning device for cleaning the vice-a roller, but the corona transfer method does not require such a contact / separation mechanism or cleaning device and is small in size. And the cost can be reduced.

However, in the corona transfer method, since the transfer paper is brought into close contact with the intermediate transfer member by electrostatic force, the transfer nip width and the transfer pressure are smaller than those in the roller transfer method. Therefore, in the corona transfer method in which the toner image on the intermediate transfer belt is transferred onto the transfer paper, the intermediate transfer belt is stretched between two rollers at the transfer position in order to secure a sufficient transfer nip width and transfer pressure. A method of forming a flat portion on a belt at a transfer position has been proposed. In this method, a flat portion is formed on the intermediate transfer belt, and a small diameter roller having a diameter of 16 mm or less is required so that separation of the transfer paper on the intermediate transfer belt is advantageous. In addition, due to the layout of the entire machine, a roller having a small diameter may be used as a roller for spanning the intermediate transfer belt.

This color image forming apparatus is used in a color copying apparatus or the like. In a digital color copying apparatus, for example, a reading section (scanner) scans and reads an original, and an image processing section reads a color image signal from the reading section. Then, a predetermined process is performed on the above, and optical writing is performed in real time on the photoconductor by the image signal of each color from the image processing unit by the exposure unit. Therefore, it does not require memory etc.,
The control of each unit by the control unit is also relatively simple.

Further, in the digital color copying apparatus having the variable magnification function, the speed of the reading section in the sub-scanning direction is changed in proportion to the variable magnification. When the reading unit rises from the home position at a constant acceleration and reaches a predetermined speed corresponding to each scaling ratio, the reading unit passes through the white reference plate at the constant speed and advances to the front end of the original to read the original.

[0009]

In the above-mentioned color image forming apparatus, the intermediate transfer belt stops at a position where it is not in use, and a portion of the intermediate transfer belt which is in contact with a roller having a small diameter (large curvature) is It causes plastic deformation. In particular, the degree of plastic deformation of the intermediate transfer belt deteriorates when the intermediate transfer belt is left to stand overnight and is used the next day or when it is not used for many days. The plastically deformed position of the intermediate transfer belt becomes apparent in the toner image as a transfer failure, resulting in an image failure. This is particularly likely to occur in a halftone toner image and is noticeable in a color image having many halftones. Specifically, this is because plastic deformation of the intermediate transfer belt causes a slight gap between the photoconductor and the intermediate transfer belt at the primary transfer portion to cause gap discharge, and also at the secondary transfer portion. This is because a small gap is generated between the intermediate transfer belt and the transfer paper due to the plastic deformation of the belt, and a gap discharge is generated.

Further, in the digital color copying apparatus having the variable magnification function, the speed of the reading unit in the sub-scanning direction is changed in proportion to the variable magnification so that the reading unit rises from the home position at a constant acceleration and each variable magnification is increased. When the speed reaches a predetermined speed according to the speed, the document passes through the white reference plate at the same speed and advances to the document front edge, so the document is read. Differently, the image forming position on the photoconductor with respect to the mark differs depending on the magnification.

Therefore, even if an image defect due to plastic deformation of the intermediate transfer belt does not occur at a certain scaling factor, an image defect due to plastic deformation of the intermediate transfer belt occurs at other scaling factors. SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus and a color image forming apparatus capable of preventing image defects due to deformation of a belt-shaped image carrier.

[0012]

In order to achieve the above object, the invention according to claim 1 is an image forming apparatus having a belt-shaped image carrier that is rotated by being spanned by a plurality of rollers. The region where the carrier is in contact with the roller having the smallest diameter among the plurality of rollers at the time of standby stop is located in the non-image part region of the belt-shaped image carrier.
It is equipped with a means to make it.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the plurality of rollers have a plurality of rollers having the smallest diameter. The region of the plurality of rollers having the smallest diameter that is in contact with the roller having the smallest wrap angle is located in the non-image portion region of the belt-shaped image carrier.
It is those that.

According to a third aspect of the present invention, a belt-shaped image carrier, which is partially provided with a mark, is stretched over a plurality of rollers and rotates, and the mark is detected in a predetermined passage area through which the mark passes. In the color image forming apparatus for forming a color image on a transfer material by forming an image of each color on the basis of a mark detection signal from the mark detecting sensor, When the rotation of the body is stopped, the belt-shaped image carrier is always stopped at a fixed position after the mark detection sensor detects the mark, and when the image is formed, the belt-shaped image carrier is in a standby position among the plurality of rollers. The area that is in contact with the roller having the smallest diameter is positioned in the non-image area corresponding to the maximum transfer material size in the belt-shaped image carrier.

According to a fourth aspect of the present invention, in the color image forming apparatus according to the third aspect, the belt-shaped image carrier is used only when the means is in a mode for forming a color image by superposing toner images of a plurality of colors. There are those which are positioned in the non-image area of the region where most small diameter roller in contact with respect to the maximum transfer material size in the belt-shaped image carrier of the plurality of rollers in the standby stop.

According to a fifth aspect of the present invention, in the color image forming apparatus according to the third aspect, the zooming function of varying the rotational direction image forming position on the belt-shaped image carrier with respect to the mark for each scaling factor. The means has a belt-shaped image bearing member, in which the belt-shaped image bearing member is in contact with a roller having the smallest diameter of the plurality of rollers when the belt-shaped image bearing member is stopped in a standby state, with priority given to a predetermined scaling factor. position of the non-image area to the maximum transfer material size in the predetermined magnification ratio in the body
It is something that can be made.

According to a sixth aspect of the present invention, a belt-shaped image carrier that is provided with a plurality of marks along the rotation direction and is stretched over a plurality of rollers, and a rotation direction image on the belt-shaped image carrier. In an image forming apparatus having a variable magnification function for changing the forming position with respect to the mark for each variable magnification,
A mark to be detected by the mark detection sensor at the time of image formation is defined for each magnification from the plurality of marks, and an image is formed on the belt-shaped image carrier based on a mark detection signal from the mark detection sensor for this mark. With the position kept substantially constant, the region where the belt-shaped image carrier is in contact with the roller having the smallest diameter among the plurality of rollers at the time of standby stop is positioned as the non-image part region of the belt-shaped image carrier.
And a means for stopping the rotation of the belt-shaped image carrier on the basis of the mark detection signal from the mark detecting sensor for one of the plurality of marks when the belt-shaped image carrier is stopped.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION FIG. 5 shows a first embodiment of the present invention. The first embodiment is an embodiment of the invention described in claim 1, and is an example of a color image forming apparatus including a color copying apparatus. A color image reading device (hereinafter, referred to as a color scanner) 11 illuminates a document 13 on a document table 12 made of contact glass with an illumination lamp 14, and the reflected light is reflected by mirrors 15 to 17 and a lens 18.
An image is formed on the color sensor 19 through the color image information of the original 13 and color-separated into, for example, blue (hereinafter referred to as B), green (hereinafter referred to as G), and red (hereinafter referred to as R) to be read, and an electrical image Convert to signal.

The color sensor 19 is composed of B, G, and R color separation means and a CCD (solid-state image pickup device composed of a charge-coupled device) as a photoelectric conversion element, and simultaneously reads three colors. An image processing unit (not shown) performs image processing such as color conversion processing based on the intensity levels of the B, G, and R image signals from the color scanner 11, and black (hereinafter referred to as BK), cyan (hereinafter referred to as C). ), Magenta (hereinafter referred to as M), and yellow (hereinafter referred to as Y) recording color data.

A color image recording device (hereinafter referred to as a color printer) 20 uses the color image data from the image processing section to form a full-color image of four colors as described below. In this case, the color scanner 11 for obtaining the image data of each color of BK, C, M, and Y has a movable optical system including an illumination lamp 14 and mirrors 15 to 17 according to a scanner start signal in time with the operation of the color printer 20. Moves in the direction of the left arrow to scan the original 13 and obtain color image data.

Next, the color printer 20 will be described. Photoconductor drum 2 as a latent image carrier made of a photoconductor
2 is rotated by a drive motor to rotate in a counterclockwise direction as indicated by an arrow, and a charger 2 as a charging unit is provided.
8 is uniformly charged. The writing optical unit 21 as an exposing unit converts the image data of each color input from the color scanner 11 through the image processing unit into an optical signal, and the optical signal causes the optical writing corresponding to the original image on the photoconductor drum 22. To form an electrostatic latent image.

The optical writing optical unit 21 drives the light emitting means 23, which is a laser diode, by a light emission drive control section (not shown) driven by image data from the image processing section, and a polygon mirror 25 rotationally driven by a motor 24 to cause the laser diode 23 to rotate. The laser light from the laser is deflected and scanned, and the laser light from the polygon mirror 25 is applied to the photoconductor drum 22 via the fθ lens 26 and the reflection mirror 27.

The photoconductor drum 22 is rotationally driven by a drive motor and rotates in a counterclockwise direction as shown by an arrow, around which the photoconductor cleaning unit 2 is provided.
9, a charge eliminating lamp 30, a charger 28, a potential sensor 31 for detecting the latent image potential on the photosensitive drum 22, a developing device selected in the rotary developing device 32, and a developing density pattern detector 3
3. An intermediate transfer member 34 including an intermediate transfer belt as a belt-shaped image carrier is arranged.

The rotary developing device 32 is a BK developing device 32.
K, C developing device 32C, M developing device 32M, Y developing device 32Y
And each of the developing devices 32K to 32Y is rotated in a counterclockwise direction as indicated by an arrow, and includes a rotation drive unit (not shown). These developing units 32K to 32Y are used for the photosensitive drum 2
In order to develop the electrostatic latent image on 2, the developing sleeves 32KS, 32CS, 32MS, 32YS that rotate by bringing the brush of the developer into contact with the surface of the photosensitive drum 22 at the developing position.
And a developing paddle that rotates to assemble and stir the developer.

Now, in the standby state, the rotary developing device 32
Is set to the developing position where the BK developing device 32BK develops the electrostatic latent image on the photosensitive drum 22, and when the copying operation is started, the color scanner 11 obtains BK image data from a predetermined timing. The reading of the original is started, the image data from the color scanner 11 is processed by the image processing section and is input to the optical writing optical unit 21 as BK image data, and the optical writing optical unit 21 is exposed based on the BK image data. Body drum 22
An optical latent image is formed by performing optical writing on. Hereinafter, the electrostatic latent image based on the BK image data is referred to as a BK latent image, and C, M, Y
The electrostatic latent images based on the respective image data are referred to as C latent image, M latent image, and Y latent image, respectively.

The rotary developing device 32 develops the BK latent image from the leading end thereof, so that the developing sleeve 32 of the BK developing device 32K is provided before the leading end of the BK latent image reaches the developing position.
The rotation of KS is started, and the BK latent image on the photoconductor drum 22 is developed into a BK toner image by the developer containing BK toner by the BK developing device 32K. After that, the BK developing device 32K continues to develop the BK latent image, but when the rear end of the BK latent image passes the developing position, the rotary developing device 32 immediately develops the next C latent image. The developing device 32C is rotated until it reaches the developing position. This rotational movement is at least
The process is completed before the leading edge of the next C latent image reaches the developing position.

When the image forming cycle is started, the photosensitive drum 22 rotates counterclockwise as indicated by the arrow, and the intermediate transfer belt 34 rotates clockwise by the drive motor. As the intermediate transfer belt 34 rotates, the BK toner image is formed on the photoconductor drum 22 as described above, and similarly, the C toner image, the M toner image, and the Y toner image are sequentially formed. Toner image, M toner image, Y
The toner images are transferred in order on the intermediate transfer belt 34.

In the formation of the BK toner image as described above, the charger 28 uses corona discharge in the dark to cause the photosensitive drum 2 to move.
2 is uniformly charged with a negative charge to about -700V. continue,
The photoconductor drum 22 is raster-exposed by the optical writing optical unit 21 based on the image data of BK to form an electrostatic latent image. In the BK developing device 32K of the rotary developing device 32, the toner is negatively charged by stirring with the ferrite carrier, and the developing bias potential in which the negative DC potential and the AC potential are superposed is applied to the BK developing sleeve 32KS. BK develops the BK latent image on the photoconductor drum 22
Toner image.

The intermediate transfer belt 34 includes a driving roller 35,
It is stretched around the paper transfer facing rollers 36, 37, the cleaning facing roller 38, and the driven rollers 39, 40, and is driven and controlled by a drive motor (not shown). The BK toner image on the photosensitive drum 22 is transferred to the surface of the intermediate transfer belt 34, which is driven at a constant speed in contact with the photosensitive drum 22, as a belt transfer corona discharger (hereinafter referred to as a belt transfer device) as a primary transfer unit. 41 is transferred. Hereinafter, the toner image transfer from the photoconductor drum 22 to the intermediate transfer belt 34 is referred to as belt transfer.

The photoconductor drum 22 is cleaned by the photoconductor cleaning unit 29 after the BK toner image is transferred on the belt, and the charge is removed by the charge removing lamp 30 so that it can be reused. The toner collected by the photoconductor cleaning unit 29 is stored in an exhaust toner tank (not shown) via the collection pipe. By the way, the process proceeds to the C toner image forming process after the BK toner image forming process, and the photoconductor drum 22 is uniformly charged by the charger 28.

Further, the color scanner 11 starts reading an original for obtaining C image data at a predetermined timing, and the image data from the color scanner 11 is processed by the image processing section to be converted into C image data, which is converted into an optical image. The optical writing optical unit 21 is input to the writing optical unit 21, and the optical writing optical unit 21 receives the photosensitive drum 22 based on the C image data.
Optical writing is performed to form a C latent image.

The rotary developing device 32 has a C on the photosensitive drum 22 after the rear end of the previous BK latent image has passed the developing position.
Before the leading edge of the latent image reaches the developing position, the C developing device 32C rotates so as to reach the developing position.
Develops the C latent image on the photosensitive drum 22 into a C toner image.

Thereafter, the C developing device 32C continues to develop the C latent image, but when the rear end of the C latent image passes the developing position,
The rotary developing device 32 rapidly rotates until the developing device 32M that develops the next M latent image reaches the developing position. This rotation operation is completed at least before the leading end of the next M latent image reaches the developing position.

The C toner image on the photosensitive drum 22 is transferred onto the intermediate transfer belt 34 by the belt transfer device 41 so as to be superimposed on the BK toner image. The photoconductor drum 22 is cleaned by the photoconductor cleaning unit 29 after the transfer of the C toner image on the belt, and is neutralized by the static elimination lamp 30 to be reusable. After the C toner image forming step, the M toner image forming step is performed, and the photoconductor drum 22 is uniformly charged by the charger 28.

Further, the color scanner 11 starts reading a document for obtaining M image data at a predetermined timing, and the image data from this color scanner 11 is processed by the image processing section to become M image data and is converted into an optical image. The optical writing optical unit 21 is input to the writing optical unit 21, and the optical writing optical unit 21 receives the photosensitive drum 22 based on the M image data.
Optical writing is performed to form an M latent image.

In the rotary developing device 32, the M developing device 32M develops after the trailing edge of the C latent image has passed the developing position and before the leading edge of the M latent image on the photosensitive drum 22 reaches the developing position. The M developing device 32M develops the M latent image on the photoconductor drum 22 to form an M toner image by rotating so as to reach the position.

After that, the M developing device 32M continues to develop the M latent image, but when the rear end of the M latent image passes the developing position,
The rotary developing device 32 rapidly rotates until the developing device 32Y for developing the next Y latent image reaches the developing position. This rotation operation is completed at least before the leading end of the next Y latent image reaches the developing position.

The M toner image on the photosensitive drum 22 is transferred onto the intermediate transfer belt 34 by the belt transfer device 41 so as to be superimposed on the BK toner image and the C toner image. Photoconductor drum 22
Is cleaned by the photoconductor cleaning unit 29 after the transfer of the M toner image on the belt, and is neutralized by the static elimination lamp 30 so that it can be reused. After the M toner image forming step, Y
Proceeding to the toner image forming process, the photosensitive drum 22 is charged by the charger 2.
8 is uniformly charged.

Further, the color scanner 11 starts reading a document for obtaining Y image data at a predetermined timing, and the image data from this color scanner 11 is processed by the image processing section to become Y image data and is optically converted. The optical writing optical unit 21 is input to the writing optical unit 21, and the optical writing optical unit 21 receives the image data based on the Y image data.
Optical writing is performed to form a Y latent image.

In the rotary developing device 32, the Y developing device 32Y develops after the rear end of the previous M latent image has passed the developing position and before the tip of the Y latent image on the photosensitive drum 22 reaches the developing position. The Y developing device 32Y develops the Y latent image on the photoconductor drum 22 to form a Y toner image by rotating the Y developing device 32Y so as to reach the position. The Y toner image on the photoconductor drum 22 is transferred to the belt transfer device 4.
1, the BK toner image, the C toner image, and the M toner image are transferred onto the intermediate transfer belt 34 in an overlapping manner, and a full-color toner image is obtained. The photoconductor drum 22 is cleaned by the photoconductor cleaning unit 29 after the transfer of the Y toner image on the belt, and the charge is removed by the charge removing lamp 30.

The belt cleaning device 42 comprises an inlet seal, a rubber blade, a discharge coil, and a contact / separation mechanism for contacting / separating the inlet seal and the rubber blade with respect to the intermediate transfer belt 34. The belt cleaning device 42 transfers the belt of the BK image of the first color,
While the toner images of the second, third, and fourth colors are being transferred onto the belt, the entrance seal, the rubber blade, etc. are separated from the intermediate transfer belt 34 by the contact / separation mechanism.

Transfer paper cassettes 44 to 47 in the paper supply bank
Transfer paper of various sizes is stored in the transfer paper cassette that stores the paper of the specified size.
Paper is fed and conveyed to the registration roller pair 52 by any one of .about.51. Further, transfer paper such as OHP paper and thick paper is manually fed from the paper feed tray 53 to the registration roller pair 52. The registration roller pair 52 is a paper transfer corona discharger (hereinafter referred to as a paper transfer device) 4 serving as a secondary transfer unit according to the full-color toner image on the intermediate transfer belt 34.
The transfer sheet is sent between the sheet 3 and the intermediate transfer belt 34.

When this transfer paper passes between the paper transfer device 43 and the intermediate transfer belt 34, it is charged with a positive charge by the corona discharge current from the paper transfer device 43, and a full color image on the intermediate transfer belt 34 is obtained. The toner image is transferred. This transfer paper is destaticized by a destaticizing brush (not shown) arranged on the left side of the paper transfer device 43, separated from the intermediate transfer belt 34, and conveyed by the paper conveyance belt 54.

Further, on the transfer paper, the toner image is melted and fixed at the nip portion between the fixing roller 55A and the pressure roller 55B whose temperature is controlled by the fixing device 55, and a full color copy is made outside the main body by the discharge roll pair 56. Sent out. Further, the surface of the intermediate transfer belt 34 is cleaned after the color toner image is transferred onto the transfer paper and then the blade of the belt cleaning device 42 is pressed by the contact / separation mechanism of the belt cleaning device 42.

In the case of repeat copying, on the side of the color scanner 11 and the photoconductor drum 22, the first color toner image forming process for the second sheet is carried out at a predetermined timing subsequent to the first color toner image forming process for the first sheet. Further, the intermediate transfer belt 34 has a belt cleaning device 42 following the batch transfer process of the first full-color toner image onto the transfer paper.
The belt transfer of the second BK toner image is performed on the area cleaned by. After that, the same operation as the copying operation for the first sheet is performed.

The above is the description of the copy mode for obtaining a four-color full color copy. In the case of the three-color copy mode and the two-color copy mode, the same operation as described above is performed for the designated color and the number of times. Further, in the single color copy mode, only the developing device of the predetermined color of the rotary developing device 32 is placed in the developing position to be in the developing operation state until the copying of the predetermined number of sheets is completed, and the belt cleaning device 42
The copying operation is continuously performed while the blade of No. 1 is pressed against the intermediate transfer belt 34.

Position detecting marks are provided on the outer peripheral surface or the inner peripheral surface of the intermediate transfer belt 34. However, on the outer peripheral surface side of the intermediate transfer belt 34, it is necessary to devise a position detection mark so as to avoid the passage area of the belt cleaning device 42, which may cause difficulty in arrangement. The position detection mark is attached to the intermediate transfer belt 3
It is provided on the inner peripheral surface side of No. 4. The optical sensor S as a mark detection sensor is provided at a position between the drive roller 35 and the support roller 39 on which the intermediate transfer belt 34 is stretched.

FIG. 1 is an enlarged view of a part of the first embodiment. The photosensitive drum 22 and the intermediate transfer belt 34 rotate at the same linear velocity as indicated by an arrow at the primary transfer position by the belt transfer device 41 as the primary transfer means. A mark MC is provided on the back side of the intermediate transfer belt 34. The mark MC moves together with the intermediate transfer belt 34, and an optical sensor S is attached to an immovable member in a predetermined passage area where the mark MC passes.

As the optical sensor S, a reflection type photo sensor or a transmission type photo sensor is used. When a reflection type photo sensor is used as the optical sensor S, the intermediate transfer belt 3
A member such as a reflective tape is attached to 4 and a place where the surface of the intermediate transfer belt 34 having a low reflectivity is changed to the mark MC by a reflective photosensor, or the mark MC has a low reflectivity on the intermediate transfer belt 34. You can read the changes on the surface.

At the time of image formation, the mark MC is detected by the optical sensor S while the photosensitive drum 22 and the intermediate transfer belt 34 are rotating, and the control unit (not shown) detects the mark MC by the optical sensor S based on the mark detection signal of the optical sensor S. The image forming process described above is started after a lapse of a certain time from the detection of the mark MC. Therefore, the photosensitive drum 2
2 is uniformly charged by the charger 28 and is optically written by the writing optical unit 21 to form a BK latent image, and the BK developing device 32K of the rotary developing device 32.
As a result, the BK latent image is developed into a BK toner image.

Next, this BK toner image is transferred onto the intermediate transfer belt 34 by the belt transfer device 41. In the full-color image forming mode, as described above, the C toner image, the M toner image, and the Y toner image are formed on the photosensitive drum 22 and then transferred to the intermediate transfer belt 34 in an overlapping manner. A four-color superposed full-color toner image is formed, and this full-color toner image is transferred to the intermediate transfer belt 3.
After being collectively transferred to the transfer paper by the paper transfer device 43 at the position of the plane portion by the paper transfer facing rollers 36 and 37 of 4, the transfer paper is separated from the intermediate transfer belt 34. A positive DC voltage is applied from the power sources 57 and 58 to the belt transfer device 41 and the paper transfer device 43.

FIG. 2 shows the operation timing of the first embodiment. In FIG. 2, the "belt & drum MT" column is
The operating state of the drive motor that drives the intermediate transfer belt 34 and the photosensitive drum 22 is shown. The column of “charge CH” shows the operating state of the charger 28. The “image signal writing” column shows the operating state of the writing optical unit 21,
It shows that optical writing is performed in the rising state of the image signal waveform of each color of K, C, M, and Y. In this example, BK → C
Optical writing is performed in the order of → M → Y. The "primary transfer" column shows the operating state of the belt transfer device 41, and the transfer charging voltage is applied from the photosensitive drum 22 to the intermediate transfer belt 34 in synchronization with the main switch of the image forming apparatus being turned on. It will be in the state of being.

The column of "secondary transfer" shows the operating state of the paper transfer unit 43, and shows the timing of batch transfer of the four-color superposed toner images of BK, C, M, and Y onto the transfer paper with a rising waveform. ing. In the "mark detection" column, the vertical line indicates the timing at which the optical sensor S detects the mark MC.
Further, in FIG. 2, the point of time indicates the point of time when the leading end of the charging area charged by the charger 28 on the photosensitive drum 22 reaches the primary transfer position by the belt transfer unit 41.
Further, at the point of time B, which is the first color B after a certain period of time has passed since the mark MC was detected by the optical sensor S.
The time point when the optical writing by the image data of K is started is shown.

Thus, the mark M by the optical sensor S is
After a certain period of time from the detection of C, the photosensitive drum 22
The leading end of the charging area charged by the upper charger 28 reaches the primary transfer position, and optical writing is performed using BK image data. Similarly, the mark MC is detected by the optical sensor S every time the intermediate transfer belt 34 makes one revolution, and BK
At the same timing as the optical writing by the image data, that is, after a certain time after the detection of the mark MC by the optical sensor S, the optical writing by the C image data, the optical writing by the M image data, and the optical writing by the Y image data are performed. Done.

In the first embodiment, as shown in FIG. 1, the intermediate transfer belt 34 is stretched over six rollers 35 to 40, and among these rollers 35 to 40, paper transfer facing rollers 36 and 37. Has the smallest diameter. Intermediate transfer belt 34
Has a problem that when curl curl marks of the paper transfer opposing rollers 36 and 37 are generated and enter the image area where the toner image is transferred from the photoconductor drum 22, transfer failure occurs and an image defect occurs. .

Therefore, the two paper transfer opposing rollers 36, 3
Since the position of 7 is close and the length of the intermediate transfer belt 34 in contact with the paper transfer facing rollers 36 and 37 in the rotation direction is about 30 mm in total, the intermediate position of the intermediate transfer belt 34 is intermediate from the stop position at the time of standby stop. The above problem is solved by calculating a region of the transfer belt 34 which is in contact with the paper transfer facing rollers 36 and 37 and setting the region as a non-image portion region in the rotation direction of the intermediate transfer belt 34.

That is, the control unit (not shown) is based on the input signals from the start switch, the optical sensor S, etc.
A drive motor for rotating the photosensitive belt 22 and the intermediate transfer belt 34, a charger 28, and an optical writing optical unit 2
1, the load of the rotary developing device 32, the belt transfer device 41, the paper transfer device 43, the color scanner 11 and the like is controlled to perform the above-mentioned copying operation, but the intermediate transfer belt 34 is moved from the stop position. Paper transfer facing roller 36,
The area in contact with 37 at the time of standby stop is the intermediate transfer belt 3
Each load is controlled so as to be the non-image area in the rotation direction of No. 4.

As described above, the first embodiment is characterized by claim 1.
4 is an example embodiment of the described invention, comprising a plurality of rollers 35-35.
In the image forming apparatus having the intermediate transfer belt 34 as a belt-shaped image carrier that is stretched around 40 and rotates, the belt-shaped image carrier 34 has a plurality of rollers 35 to 35 when the standby is stopped.
Since a control unit is provided as a unit for setting a region of 40, which is in contact with the rollers 36 and 37 having the smallest diameter, as a non-image region in the rotation direction of the belt-shaped image carrier 34,
Image defects due to deformation of the belt-shaped image carrier can be prevented.

In the first embodiment, if there is no margin in the circumferential length of the intermediate transfer belt 34, the intermediate transfer belt 34
Among the plurality of rollers 35 to 40, which have the smallest diameter, of the paper transfer facing rollers 36 and 37 having the smallest diameter, the winding angle is small and the pressure per unit area against the intermediate transfer belt 34 is strong. With respect to only the paper transfer counter roller 36, the area in contact with the paper transfer counter roller 36 of the intermediate transfer belt 34 at the time of standby stop is calculated from the stop position of the intermediate transfer belt 34, and the area is determined in the rotation direction of the intermediate transfer belt 34. If the non-image part area is set, the worst case of the above problems can be solved.

Therefore, in the second embodiment of the present invention, in the first embodiment, the control unit (not shown) causes the paper transfer counter roller of the intermediate transfer belt 34 to be stopped from the stop position of the intermediate transfer belt 34 during standby. The above problem is solved by calculating an area in contact with 36 and setting the area as a non-image portion area in the rotational direction of the intermediate transfer belt 34. That is, the control unit (not shown) controls the intermediate transfer belt 3
Each load is controlled so that the area of the intermediate transfer belt 34 which is in contact with the paper transfer facing roller 36 at the time of standby stop from the stop position of 4 is the non-image portion area in the rotation direction of the intermediate transfer belt 34.

The second embodiment is an embodiment of the invention described in claim 2, and the plurality of rollers 35 to 40 around which the intermediate transfer belt 34 is stretched are rollers 36 and 37 having the smallest diameter. There is a plurality of rollers, and the control unit as the means contacts the roller 36 having the smallest wrap angle among the rollers 36, 37 having the smallest diameter when the intermediate transfer belt 34 as the belt-shaped image carrier is in the standby stop state. Since the existing area is the non-image portion area in the rotation direction of the belt-shaped image carrier 34, it is possible to prevent image defects due to deformation of the belt-shaped image carrier.

Further, in the third embodiment of the present invention, in the above first embodiment, the control unit (not shown) is used when the rotation of the intermediate transfer belt 34 as a belt-shaped image carrier is stopped. Mark detection sensor S
After the detection of the mark, it is always stopped at a fixed position, and the position where the curl blemishes are generated by the paper transfer facing rollers 36 and 37 of the intermediate transfer belt 34 is set to a fixed position. Then, the controller controls the paper transfer facing roller 36 of the intermediate transfer belt 34 as shown in FIG. 3 from the positional relationship between the mark MC and the curl mark formed by the paper transfer facing rollers 36 and 37 of the intermediate transfer belt 34 during image formation. , 37 are contacted with each other at the time of stand-by stop, and the above-mentioned problem is solved by calculating the area 59 as a non-image portion area with respect to the maximum transfer paper size 60 in the rotation direction of the intermediate transfer belt 34.

That is, the control unit (not shown) controls the paper transfer facing rollers 36, 3 of the intermediate transfer belt 34 during image formation.
From the positional relationship between the curl mark and the mark MC by 7,
Based on the mark detection signal from the optical sensor S, the area 59 which is in contact with the paper transfer facing rollers 36 and 37 of the intermediate transfer belt 34 at the time of standby stop is determined, and the area 59 is the maximum in the rotation direction of the intermediate transfer belt 34. Transfer paper size 60
Each load is controlled so as to be a non-image part area for.

The third embodiment is an embodiment of the invention described in claim 3, and is a belt-shaped image carrier that is provided with a mark MC on a part thereof and is stretched around a plurality of rollers 35 to 40 to rotate. Intermediate transfer belt 34 as a body and mark MC
An optical sensor S as a mark detecting sensor for detecting the mark MC in a predetermined passage area through which the image passes, and forms an image of each color based on a mark detection signal from the mark detecting sensor S and transfers the image. In a color image forming apparatus for forming a color image on a material, a belt-shaped image carrier 34
When the rotation of the belt-shaped image carrier 34 is stopped, the belt-shaped image carrier 34 is always stopped at a fixed position after the mark detection sensor S detects the mark. Since the area contacting the rollers 36 and 37 having the smallest diameter among them is a non-image area for the maximum transfer material size in the rotation direction of the belt-shaped image carrier 34, the controller is provided. It is possible to prevent image defects due to deformation of the image carrier.

Further, in the fourth embodiment of the present invention, in the third embodiment, the control unit (not shown) has the intermediate transfer belt 34 facing the paper transfer only in the copy mode for obtaining a full color copy with many halftone images. Rollers 36, 3
From the positional relationship between the curl mark and the mark MC by 7,
Based on the mark detection signal from the optical sensor S, the area of the intermediate transfer belt 34 that is in contact with the paper transfer facing rollers 36 and 37 at the time of standby stop is determined, and the area is determined.
Each load is controlled so as to be a non-image portion area with respect to the maximum transfer paper size in the rotation direction of No. 4.

Then, the control unit forms an image mainly composed of a character image such as BK single color, and in a mode which does not require the alignment of the toner images of the respective colors by the mark MC, the paper transfer of the intermediate transfer belt 34 is performed. Opposing rollers 36, 37
The image formation is performed without the control to avoid the curl trace due to, and the copy speed is prioritized.

The fourth embodiment is an embodiment of the invention described in claim 4, and in the third embodiment, the control unit as the means superimposes toner images of a plurality of colors to form a color image. Only in the mode of forming an image, the intermediate transfer belt 34 as a belt-shaped image bearing member is the roller 3 having the smallest diameter among the plurality of rollers 35 to 40 when the standby is stopped.
Since the areas in contact with 6, 37 are the non-image portion areas with respect to the maximum transfer material size in the rotation direction of the belt-shaped image carrier 34, it is possible to prevent image defects due to deformation of the belt-shaped image carrier. In addition, the copy speed can be prioritized in a mode other than the mode in which toner images of a plurality of colors are overlapped to form a color image.

Further, in the fifth embodiment of the present invention, in the third embodiment, the intermediate transfer belt 34 is 502.
A curl trace is formed by the paper transfer facing rollers 36 and 37 with a length of 30 mm in the rotational direction with respect to a peripheral length of mm. Further, a scaling function is provided for scaling the original image with a scaling factor of 25 to 400% to obtain a full-color toner image, and the dotted line in FIG. 4 shows how much the image position actually shifts during scaling.
At the time of changing the magnification, the changing function changes the speed of the color scanner 11 as the reading unit in the sub-scanning direction in proportion to the changing magnification.

When reading an original, the color scanner 11 moves at a constant speed when the movable optical systems 14 to 17 rise from the home position at a constant acceleration and reaches a predetermined speed corresponding to each magnification ratio, and then moves at a constant speed to obtain a white reference. It passes through the plate 61 and advances to the leading edge of the document 13. Then, the image data from the color scanner 11 is input to the optical writing optical unit 21 via the image processing section, and the optical writing optical unit 21 causes the photoconductor drum 22 based on the image data.
Optical writing in real time.

Therefore, the image forming position on the intermediate transfer belt 34 is displaced by 30 mm for a magnification of 100%. Therefore, the control unit controls the respective loads so that the front end of the toner image at the time of the 25% scaling is immediately after the curl blemishes by the paper transfer facing rollers 36 and 37 on the intermediate transfer belt 34. %, The front end of the toner image on the intermediate transfer belt 34 shifts to the rear side in the rotation direction,
Up to a variable magnification of about A3 size (rotation direction 420 mm), the curl blemishes by the paper transfer facing rollers 36 and 37 become a non-image area. Therefore, the control unit gives priority to a scaling factor of about 250% or less and sets the area in contact with the paper transfer facing rollers 36 and 37 having the smallest diameter in the intermediate transfer belt 34 at the time of standby stop in the rotation direction of the intermediate transfer belt 34. Is a non-image area for the maximum transfer paper size at a scaling factor of about 250% or less.

The fifth embodiment is an embodiment of the present invention as defined in claim 5, wherein the rotational direction image forming position on the intermediate transfer belt 34 as a belt-shaped image bearing member is marked with a mark M.
C has a variable power function that varies for each variable power ratio, and the control unit as the means gives priority to a predetermined variable power ratio (about 250% or less), and when the belt-shaped image carrier 34 is in the standby stop state. Of the plurality of rollers 35 to 40, the area in contact with the roller 36, 37 having the smallest diameter is a non-image area corresponding to the maximum transfer material size at the predetermined scaling ratio in the rotation direction of the belt-shaped image carrier 34. Therefore, even if it has a variable magnification function, it is possible to prevent an image defect due to the deformation of the belt-shaped image carrier at a predetermined variable magnification.

Further, in the sixth embodiment of the present invention, in the fifth embodiment, two marks MC1 and MC2 are provided on the intermediate transfer belt 34 as shown in FIG. The individual marks MC1 and MC2 are detected, and the mark MC1 is the same as the mark MC. The mark MC2 is provided at a position 50 mm away from the mark MC1 in the traveling direction. In FIG. 4, the solid line shows the relationship between the scaling ratio of the sixth embodiment and the image position on the intermediate transfer belt 34, and the dotted line shows the scaling ratio of the fifth embodiment and the image position on the intermediate transfer belt 34. Show the relationship.

When the rotation of the intermediate transfer belt 34 as the belt-shaped image bearing member is stopped, the control section always keeps the intermediate transfer belt 34 constant after the mark MC1 of the mark detecting sensor S is detected, as in the third embodiment. Stop at the position. Here, the control unit distinguishes the marks MC1 and MC1 from the width of the mark detection signal from the optical sensor S by making the lengths of the marks MC1 and MC2 different in the traveling direction, or as shown in FIG. MC1 and one of the mark detection signals from the optical sensor S for MC1 are masked at a timing of about 20 mm before and after the timing so that the scaling ratio of the scaling function is 2
When it is 5 to 200%, only the mark detection signal from the optical sensor S for the mark MC1 is read, and when the magnification of the magnification changing function is 201 to 400%, only the mark detection signal from the optical sensor S to the mark MC2 is read.

In the control unit, the scaling ratio of the scaling function is 25 to 20.
At 0%, as in the third embodiment, the mark detection signal from the optical sensor S for the mark MC1 is determined from the positional relationship between the mark MC1 and the curl traces of the intermediate transfer belt 34 caused by the paper transfer facing rollers 36 and 37. The area of the intermediate transfer belt 34 which is in contact with the paper transfer facing rollers 36 and 37 at the time of standby stop is determined based on the above, and the area is the maximum transfer paper with a scaling ratio of 25 to 200% in the rotation direction of the intermediate transfer belt 34. Each load is controlled so as to be a non-image area corresponding to the size.

In addition, the control unit changes the magnification of the magnification function to 20.
When the ratio is 1 to 400%, the curl curl mark and the mark MC2 by the paper transfer facing rollers 36 and 37 of the intermediate transfer belt 34
From the positional relationship with the optical sensor S for the mark MC2
The area in contact with the paper transfer facing rollers 36, 37 of the intermediate transfer belt 34 at the time of standby stop is judged based on the mark detection signal from the above, and the area has a scaling factor of 201 to 400% in the rotation direction of the intermediate transfer belt 34. Each load is controlled so as to be a non-image portion area with respect to the maximum transfer paper size.

The sixth embodiment is an embodiment of the invention described in claim 6 and comprises a plurality of marks MC1 and MC2.
Is provided along the rotation direction and is laid across a plurality of rollers 35 to 40 to rotate, and an intermediate transfer belt 34 as a belt-shaped image carrier, and a rotation direction image forming position on the belt-shaped image carrier 34 are marked. In an image forming apparatus having a variable magnification function for varying magnifications with respect to MC1 and MC2, marks detected by an optical sensor S as a mark detection sensor at the time of image formation from a plurality of marks MC1 and MC2 at each magnification. Based on the mark detection signal from the mark detection sensor S for this mark, the image forming position on the belt-shaped image carrier 34 is made substantially constant, and when the belt-shaped image carrier 34 is on standby, a plurality of rollers 35 to 35 are provided. A region of 40, which is in contact with the rollers 36 and 37 having the smallest diameter, is set as a non-image portion region in the rotation direction of the belt-shaped image carrier 34, and when stopped, Since the control unit is provided as a means for stopping the rotation of the belt-shaped image carrier 34 with reference to the mark detection signal from the mark detection sensor S for one of the plurality of marks MC1 and MC2, the variable magnification function is provided. As a result, it is possible to prevent an image defect due to the deformation of the belt-shaped image carrier at an arbitrary magnification.

The present invention is not limited to the above-mentioned embodiment, and toner images of respective colors are formed by using, for example, a belt-shaped image carrier, which is a belt-shaped photosensitive member which is stretched around a plurality of rollers. By overlapping and forming on the belt-shaped photoconductor, it is possible to be similarly applied to a color image forming apparatus that forms a full-color toner image and transfers it to a transfer material such as paper.

[0078]

As described above, according to the first aspect of the present invention, in the image forming apparatus having the belt-shaped image carrier which is stretched over the plurality of rollers, the belt-shaped image carrier is stopped by waiting. Since there is provided means for making a region, which is in contact with the roller having the smallest diameter among the plurality of rollers, a non-image portion region in the rotation direction of the belt-shaped image carrier, the belt-shaped image carrier may be deformed. Image defects can be prevented.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the plurality of rollers have a plurality of rollers having the smallest diameter, and the means is that the belt-shaped image carrier is stopped by waiting. Sometimes, the region of the plurality of rollers having the smallest diameter, which is in contact with the roller having the smallest wrap angle, is set as the non-image portion region in the rotation direction of the belt-shaped image bearing member, so that the belt-shaped image bearing member is deformed. It is possible to prevent an image defect due to.

According to the third aspect of the present invention, the belt-shaped image carrier, which is partially provided with a mark and which is stretched over a plurality of rollers, and the mark, is provided in a predetermined passage area through which the mark passes. In the color image forming apparatus for forming a color image on a transfer material by forming an image of each color on the basis of a mark detection signal from the mark detection sensor, When the rotation of the image carrier is stopped, the belt-shaped image carrier is always stopped at a fixed position after the mark detection sensor detects the mark, and when the image is formed, the belt-shaped image carrier is in a standby state and the plurality of rollers are stopped. And a means for making the area in contact with the roller having the smallest diameter of the non-image area with respect to the maximum transfer material size in the rotation direction of the belt-shaped image carrier. Since, it is possible to prevent image defect due to deformation of the belt-shaped image carrier.

According to a fourth aspect of the present invention, in the color image forming apparatus according to the third aspect, the belt-shaped image is formed only in a mode of forming a color image by superposing toner images of a plurality of colors. The belt-shaped image carrier is in the non-image portion region with respect to the maximum transfer material size in the rotation direction of the belt-shaped image carrier because the region in which the carrier is in contact with the roller having the smallest diameter among the plurality of rollers at the time of standby stop Image defects due to deformation of the image carrier can be prevented, and the copy speed can be prioritized in a mode other than the mode in which toner images of a plurality of colors are overlapped to form a color image.

According to a fifth aspect of the invention, in the color image forming apparatus according to the third aspect, the rotational direction image forming position on the belt-shaped image bearing member is varied with respect to the mark for each magnification. The unit has a doubling function, and the means prioritizes a predetermined scaling factor, and the belt-shaped image bearing member is in contact with a roller having the smallest diameter among the plurality of rollers when the belt-shaped image bearing member is in a standby state. Since it is a non-image portion area with respect to the maximum transfer material size at the above-mentioned predetermined scaling ratio in the rotation direction of the image bearing member, even if it has a scaling function, the belt-shaped image bearing member is deformed at a predetermined scaling factor. Image defects can be prevented.

According to the sixth aspect of the present invention, a belt-shaped image carrier which is provided with a plurality of marks along the rotation direction and is stretched over a plurality of rollers, and a rotation on the belt-shaped image carrier. In an image forming apparatus having a magnification changing function of changing the direction image forming position with respect to the mark for each magnification change, a mark to be detected by the mark detection sensor at the time of image formation is determined for each magnification change from the plurality of marks. , The image forming position on the belt-shaped image carrier is made substantially constant on the basis of a mark detection signal from the mark detection sensor for this mark, and the belt-shaped image carrier is in a standby state among the plurality of rollers. An area in contact with the roller having the smallest diameter is defined as a non-image area in the rotation direction of the belt-shaped image bearing member, and is set to one of the plurality of marks when stopped. Since the means for stopping the rotation of the belt-shaped image bearing member on the basis of the mark detection signal from the mark detecting sensor is provided, the image defect due to the deformation of the belt-shaped image bearing member at an arbitrary scaling factor by the scaling function. Can be prevented.

[Brief description of drawings]

FIG. 1 is a schematic view showing a part of a first embodiment of the present invention in an enlarged manner.

FIG. 2 is a timing chart showing the operation timing of the first embodiment example.

FIG. 3 is a diagram for explaining a first embodiment example of the present invention.

FIG. 4 is a diagram showing a relationship between a scaling ratio and an image position on an intermediate transfer belt in a fifth embodiment example and a sixth embodiment example of the present invention.

FIG. 5 is a cross-sectional view showing the first embodiment example.

FIG. 6 is a waveform diagram for explaining the sixth embodiment example.

[Explanation of symbols]

21 Optical writing optical unit 22 Photosensitive drum 35-40 rollers 41 Belt transfer device 43 Paper transfer device S optical sensor MC, MC1, MC2 mark

Continuation of the front page (56) Reference JP-A-3-106736 (JP, A) JP-A-6-115755 (JP, A) JP-A-5-289542 (JP, A) JP-A-61-11974 (JP , A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/00

Claims (6)

(57) [Claims] 1. An image forming apparatus having a belt-shaped image bearing member which is stretched around a plurality of rollers and rotates, wherein the belt-shaped image bearing member is the roller having the smallest diameter among the plurality of rollers when waiting and stopped. An image forming apparatus comprising means for locating a contact area in a non-image portion area of the belt-shaped image carrier. 2. The image forming apparatus according to claim 1, wherein the plurality of rollers have a plurality of rollers having the smallest diameter, and the means includes a plurality of rollers having the smallest diameter when the belt-shaped image carrier is stopped in a standby mode. An area of the roller, which has the smallest winding angle, is in contact with the belt-shaped image carrier.
Image forming apparatus, characterized in that to position the definitive non-image area. 3. A belt-shaped image carrier, which is partially provided with a mark and which is stretched around a plurality of rollers to rotate, and a mark detection sensor which detects the mark in a predetermined passage region through which the mark passes. In the color image forming apparatus, which forms an image of each color on the basis of the mark detection signal from the mark detecting sensor to form a color image on the transfer material, the rotation of the belt-shaped image carrier is stopped. Sometimes, the belt-shaped image carrier is always stopped at a fixed position after the mark detection sensor detects the mark, and during image formation, the belt-shaped image carrier is the smallest roller among the plurality of rollers when the standby is stopped. a color image forming instrumentation, characterized in that it comprises means for positioning in the non-image area to the maximum transfer material size is the region in the belt-shaped image carrier which is in contact . 4. The color image forming apparatus according to claim 3, wherein the means is configured to provide the plurality of toner images when the belt-shaped image carrier is in a standby stop only in a mode in which toner images of a plurality of colors are overlapped to form a color image. Of the above rollers, the area in contact with the roller having the smallest diameter is positioned in the non-image portion area for the maximum transfer material size in the belt-shaped image carrier. Image forming apparatus. 5. The color image forming apparatus according to claim 3, further comprising a variable magnification function for changing the rotational direction image forming position on the belt-shaped image carrier with respect to the mark for each variable magnification. Priority is given to a predetermined scaling factor, the region in which the belt-shaped image carrier is in contact with the roller having the smallest diameter among the plurality of rollers at the time of the stand-by stop is set to the predetermined scaling in the belt-shaped image carrier. A color image forming apparatus characterized in that the color image forming apparatus is positioned in a non-image portion area with respect to a maximum transfer material size at a magnification. 6. A belt-shaped image carrier, which is provided with a plurality of marks along the rotation direction and is stretched over a plurality of rollers, and a rotation direction image forming position on the belt-shaped image carrier is defined by the marks. On the other hand, in an image forming apparatus having a magnification changing function for changing the magnification for each magnification, a mark to be detected by the mark detecting sensor at the time of image formation is determined for each magnification from the plurality of marks, Based on the mark detection signal from the sensor, the image forming position on the belt-shaped image carrier is made substantially constant, and the belt-shaped image carrier comes into contact with the roller having the smallest diameter among the plurality of rollers when the standby is stopped. the regions are then located in the non-image area of the belt-shaped image carrier, from the mark detection sensor for one mark of the plurality of marks on stop Color image forming apparatus characterized by comprising a means for stopping the rotation of the belt-shaped image carrier, based on the over click detection signal.