JP3744670B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in an image forming apparatus such as a black and white electrophotographic copying machine, a color electrophotographic copying machine, a laser printer, a facsimile, or a composite machine thereof, and more particularly to an image forming apparatus provided with an intermediate transfer belt.
[0002]
[Prior art]
Conventionally, a color image forming apparatus using an intermediate transfer belt as an intermediate transfer member has been widely used. In this color image forming apparatus, an electrophotographic process is applied to a drum-shaped or belt-shaped photoconductor, and a toner image of a predetermined color is formed through charging, exposure, and development processes. Further, the intermediate transfer belt is disposed to face the photoconductor and is in contact with the photoconductor, and is driven to rotate at the same peripheral speed as the photoconductor. The above-described toner image on the photosensitive member is transferred to the intermediate transfer belt by primary transfer means using corona discharge or the like. Such an image forming process is repeated for each color after the alignment of the photoreceptor and the intermediate transfer belt, and a color image is formed by transferring a plurality of color toner images on the intermediate transfer belt. It is formed. Further, the color image formed on the intermediate transfer belt is collectively transferred to the transfer material by the secondary transfer unit, and further fixed by the fixing unit, and the image forming process is completed.
Here, when the color image forming apparatus is not used, the intermediate transfer belt is stopped, and the portion of the intermediate transfer belt that is in contact with the support roller having a small diameter (large curvature) undergoes large plastic deformation. In particular, when it is left overnight and used for the next day, or when it is suddenly operated after not being used for many days, the degree of plastic deformation of the intermediate transfer belt portion in contact with the roller is the worst. The plastically deformed portion of the intermediate transfer belt becomes apparent as a toner image transfer failure and appears as an image failure. This phenomenon is particularly likely to occur in a halftone toner image, and is conspicuous in a color image with many halftones. The cause is that the intermediate transfer belt is curled due to plastic deformation, and a slight gap is generated between the photosensitive member and the intermediate transfer belt at the position of the primary transfer means to generate gap discharge. As a method of preventing image defects caused by the curl of the intermediate transfer belt, a region that is in contact with the roller having the smallest wrapping angle of the roller diameter when the intermediate transfer belt is stopped is set as a non-image region, or the intermediate transfer belt is stopped. Sometimes, a separation / contact mechanism for separating a roller having a small diameter from the intermediate transfer belt is provided.
[0003]
[Problems to be solved by the invention]
However, in the former method, a non-image area can be avoided for the contact portion with the small-diameter roller in which the curl state is the most severe, so that an image defect can be avoided. And a defect such as a linear white-out image has occurred as usual. Further, the control of the transfer start position on the intermediate transfer belt is complicated, and there is a problem that the image forming processing efficiency is lowered because the transfer is performed by shifting only the non-image area. Furthermore, in the latter method, a complicated separating / connecting mechanism is required, so that the apparatus becomes large, costs are high, and the processing efficiency of image formation is reduced.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus that is free of linear whiteout images and has high image formation processing efficiency even if a plurality of curls occur in any region of the intermediate transfer belt. To do.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to the first claim transfers a toner image formed on an image carrier to an intermediate transfer belt, and transfers the toner image on the intermediate transfer belt to a transfer material. In an image forming apparatus to be formed, an image carrier that carries a toner image, an intermediate transfer belt that operates in contact with the image carrier, and a toner image that is formed on the image carrier is transferred to the intermediate transfer belt. A primary transfer unit, a belt state detection unit that detects a curl state of the intermediate transfer belt, and the belt state detection unit detects that the curl value of the intermediate transfer belt exceeds a predetermined value; Transfer condition changing means for changing the transfer condition of the primary transfer means.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the transfer condition changing unit operates the intermediate transfer belt again when the belt state detecting unit detects a curl state of the intermediate transfer belt. The transfer condition of the primary transfer unit is changed after the predetermined number of images are formed.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the belt state detecting unit detects that the intermediate transfer belt has been inactive for a predetermined time, thereby detecting the intermediate transfer. It is determined that curling has occurred on the belt.
The invention of claim 4 is the invention of claim 1. Or 2 In the image forming apparatus described above, the belt state detection unit is a reflection type photosensor provided to face the intermediate transfer belt.
[0005]
[Action]
In the first aspect of the present invention, the curl state of the intermediate transfer belt is detected by the belt state detecting means, and the transfer condition changing means causes the transfer condition of the primary transfer means to be exceeded when the curl value of the intermediate transfer belt exceeds a predetermined value. Therefore, the curl state in which the intermediate transfer belt is likely to be plastically deformed is detected at the start of the intermediate transfer belt, and the transfer condition changing means reduces the transfer current value of the primary transfer means from the reference set value. You can switch to a value.
According to the second aspect of the invention, in addition to the invention of the image forming apparatus configured as in the first aspect, the intermediate transfer belt is operated again by detecting the curl state at the time of starting by the belt state detecting means. Since the transfer conditions of the primary transfer unit are changed before the predetermined number of image formations are completed, the primary transfer is performed after the intermediate transfer belt is operated until the predetermined number of image formations are completed. The transfer current value of the means is switched from the reference set value to a smaller value, and when the predetermined number of images are formed, the original reference set value can be restored.
According to a third aspect of the invention, in addition to the invention of the image forming apparatus configured as in the first or second aspect, the belt state detecting means detects that the non-operation time of the intermediate transfer belt has continued for a predetermined time. Therefore, when the intermediate transfer belt has been inactive for a predetermined time, it is determined that the primary transfer means has been in operation until the predetermined number of images have been formed. When the transfer current value is switched from the reference set value to a smaller value and image formation for a predetermined number of images is completed, the original reference set value can be restored.
The invention of claim 4 is the invention of claim 1. Or 2 In addition to the invention of the image forming apparatus described above, since the belt state detecting means is a reflective sensor provided to face the intermediate transfer belt, the belt is inexpensive and has good controllability without touching the intermediate transfer belt. It becomes possible to detect the curl state.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a side view showing a main part of a color copying machine which is a typical example of an image forming 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 or the like with an illumination lamp 14, and reflects the reflected light through mirrors 15 to 17 and a lens 18. The color image information of the original 13 formed on the color sensor 19 is separated into, for example, blue (hereinafter referred to as “B”), green (hereinafter referred to as “G”), and red (hereinafter referred to as “R”), and is read into an electrical image signal. Convert.
The color sensor 19 is composed of B, G, and R color separation means and a CCD (solid-state imaging device including a charge coupled device) as a photoelectric conversion element, and performs simultaneous reading of 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 performs black (hereinafter referred to as BK) and cyan (hereinafter referred to as C). ), Magenta (hereinafter referred to as “M”), and yellow (hereinafter referred to as “Y”) recording color power image data.
A color image recording apparatus (hereinafter referred to as a color printer) 20 forms four full-color images as described below using color image data from the image processing unit. In this case, the color scanner 11 for obtaining the image data of each color of BK, C, M, and Y is constituted by an illumination lamp 14 and mirrors 15 to 17 by a scanner start signal taking the operation and timing of the color printer 20. As the movable optical system moves in the direction of the arrow, the original 13 is scanned to obtain color image data.
Next, the color printer 20 will be described. The photosensitive drum 1 as an image carrier is rotated by a drive motor and rotated counterclockwise as indicated by an arrow, and is uniformly charged by a charger 28 as a charging unit. A writing optical unit 21 as an exposure unit converts image data of each color input from the color scanner 11 via an image processing unit into an optical signal, and optical writing corresponding to the original image is performed on the photosensitive drum 1 by the optical signal. To form an electrostatic latent image.
[0007]
Further, the writing optical unit 21 drives the light emitting means composed of the laser diode 23 by image data from the image processing unit by a light emission drive control unit (not shown), and rotates from the laser diode 23 by a polygon mirror 25 driven to rotate by a motor 24. The laser beam is deflected and scanned, and the photosensitive drum 1 is irradiated with the laser beam from the polygon mirror 25 via the fθ lens 26 and the reflection mirror 27.
The photosensitive drum 1 is driven to rotate by a drive motor and rotates counterclockwise as indicated by an arrow. Around the photosensitive drum 1, a photosensitive member cleaning unit 29, a charge eliminating lamp 30, a charger 28, and the photosensitive drum 1 are provided. An electric potential sensor 31 for detecting the upper latent image potential, a selected developing device of the rotary developing device 32, a developing density pattern detector 33, an intermediate transfer belt 2 as an intermediate transfer member, and the like are arranged. The rotary developing device 32 rotates the BK developing device 32K, the C developing device 32C, the M developing device 32M, the Y developing device 32Y, and the developing devices 32K to 32Y in a counterclockwise direction as indicated by arrows. It consists of a drive unit.
The developing devices 32K to 32Y are developed by rotating a developing sleeve 32KS that rotates a developer ear in contact with the surface of the photosensitive drum 1 at a developing position in order to develop the electrostatic latent image on the photosensitive drum 1. , 32CS, 32MS, 32YS, and a developing paddle that rotates to assemble and stir the developer.
[0008]
In the standby state, the rotary developing device 32 is set at a developing position where the BK developing unit 32BK develops the electrostatic latent image on the photosensitive drum 1, and when the copying operation is started, the color scanner 11 Reading of an original for obtaining BK image data is started from a predetermined timing, and the image data from the color scanner 11 is processed by the image processing unit and input to the writing optical unit 21 as BK image data. However, optical writing is performed on the photosensitive drum 1 based on the BK image data to form an electrostatic latent image. Hereinafter, an electrostatic latent image based on BK image data is referred to as a BK latent image, and electrostatic latent images based on C, M, and Y image data are referred to as a C latent image, an M latent image, and a Y latent image, respectively.
Further, the rotary developing device 32 starts to rotate the developing sleeve 32KS of the BK developing device 32K before the leading end of the BK latent image reaches the developing position in order to develop the BK latent image from the leading end. The BK latent image on the photosensitive drum 1 is developed with a developer containing BK toner in the BK developing unit 32K to obtain a BK toner image. Thereafter, the BK developing unit 32K continues to develop the BK latent image. When the rear end of the BK latent image passes the developing position, the rotary developing device 32 quickly develops the next C latent image. The developing device 32C to be rotated rotates until it reaches the developing position. This rotation operation is completed at least before the leading edge of the next C latent image reaches the developing position.
[0009]
When the image forming cycle is started, the photosensitive drum 1 is rotated counterclockwise as indicated by an arrow, and the intermediate transfer belt 2 is rotated clockwise by the drive motor. As described above, the BK toner image is formed on the photosensitive drum 1 as the intermediate transfer belt 2 rotates, and similarly, the C toner image, the M toner image, and the Y toner image are sequentially formed, and the BK toner image, C A toner image, an M toner image, and a Y toner image are transferred onto the intermediate transfer belt 2 in this order.
In the formation of the BK toner image as described above, the charger 28 uniformly charges the photosensitive drum 1 to about −700 V with a negative charge by corona discharge in the dark. Subsequently, the photosensitive drum 1 is subjected to raster exposure based on the BK image data by the writing optical unit 21 to form an electrostatic latent image. The BK developing device 32K of the rotary developing device 32 charges the toner negatively by stirring with the ferrite carrier, and a developing bias potential in which a negative DC potential and an AC potential are superimposed is applied to the BK developing sleeve 32KS. The BK latent image on the photosensitive drum 1 is developed into a BK toner image.
Further, the intermediate transfer belt 2 is stretched around a drive roller 35, paper transfer counter rollers 36 and 37, a cleaning counter roller 38, a support roller 39, and a driven roller 40, and is driven and controlled by a drive motor (not shown). The BK toner image on the photosensitive drum 1 is transferred to the surface of the intermediate transfer belt 2 that is driven at a constant speed in contact with the photosensitive drum 1 by a belt transfer corona discharger 3 that is a primary transfer unit. Hereinafter, toner image transfer from the photosensitive drum 1 to the intermediate transfer belt 2 is referred to as primary transfer.
[0010]
The photosensitive drum 1 is cleaned by the photosensitive member cleaning unit 29 after the transfer of the BK toner image to the belt, is neutralized by the neutralizing lamp 30, and can be reused. The toner collected by the photoconductor cleaning unit 29 is stored in a waste toner tank (not shown) via a collection pipe. By the way, the process proceeds to the C toner image forming process after the BK toner image forming process, and the photosensitive drum 1 is uniformly charged by the charger 28. Further, the color scanner 11 starts reading a document for obtaining C image data at a predetermined timing, and the image data from the color scanner 11 is processed by the image processing unit to become C image data. The writing optical unit 21 performs optical writing on the photosensitive drum 1 based on the C image data to form a C latent image.
In the rotary developing device 32, the C developing device 32C reaches the developing position after the trailing end of the previous BK latent image has passed the developing position and before the leading edge of the C latent image on the photosensitive drum 1 reaches the developing position. The C developing device 32C develops the C latent image on the photosensitive drum 1 to form a C toner image. Thereafter, the C developing device 32C continues to develop the C latent image, but when the rear end portion of the C latent image passes the developing position, the rotary developing device 32 immediately develops the next M latent image. The container 32M rotates until it reaches the developing position. This rotation operation is completed at least before the leading edge of the next M latent image reaches the development position. The C toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 2 by the belt transfer corona discharger 3 so as to overlap the BK toner image. The photosensitive drum 1 is cleaned by the photosensitive member cleaning unit 29 after the transfer of the C toner image to the belt, is discharged by the discharging lamp 30, and can be reused. After the C toner image forming process, the process proceeds to the M toner image forming process, and the photosensitive drum 1 is uniformly charged by the charger 28.
[0011]
Further, the color scanner 11 starts reading a document for obtaining M image data from a predetermined timing, and the image data from the color scanner 11 is processed by the image processing unit to become M image data, and the writing optical unit 21. The writing optical unit 21 performs optical writing on the photosensitive drum 1 based on the M image data to form an M latent image. In the rotary developing device 32, the M developing device 32M reaches the developing position after the rear end of the previous C latent image has passed the developing position and before the leading end of the M latent image on the photosensitive drum 1 reaches the developing position. Thus, the M developing device 32M develops the M latent image on the photosensitive drum 1 into an M toner image.
Thereafter, the M developing device 32M continues to develop the M latent image. When the rear end portion of the M latent image passes the developing position, the rotary developing device 32 immediately develops the next Y latent image. The container 32Y rotates until it 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 1 is transferred onto the intermediate transfer belt 2 by the belt transfer corona discharger 3 so as to overlap the BK toner image and the C toner image. The photosensitive drum 1 is cleaned by the photosensitive member cleaning unit 29 after the transfer of the M toner image to the belt, is neutralized by the neutralizing lamp 30, and can be reused. After the M toner image forming process, the process proceeds to the Y toner image forming process, and the photosensitive drum 1 is uniformly charged by the charger 28.
[0012]
Further, the color scanner 11 starts reading a document for obtaining Y image data from a predetermined timing, and the image data from the color scanner 11 is processed by the image processing unit to become Y image data, and the writing optical unit 21. The writing optical unit 21 performs optical writing on the photosensitive drum 1 based on the Y image data to form a Y latent image.
In the rotary developing device 32, the Y developing device 32Y reaches the developing position after the trailing end of the previous M latent image has passed the developing position and before the leading end of the Y latent image on the photosensitive drum 1 reaches the developing position. The Y developing device 32Y develops the Y latent image on the photosensitive drum 1 to form a Y toner image. The Y toner image on the photosensitive drum 1 is transferred onto the intermediate transfer belt 2 by the belt transfer corona discharger 3 so as to overlap the BK toner image, the C toner image, and the M toner image, thereby obtaining a full color toner image. The photosensitive drum 1 is cleaned by the photosensitive member cleaning unit 29 after the transfer of the Y toner image to the belt, and discharged by the discharging lamp 30.
The belt cleaning device 42 includes an inlet seal, a rubber blade, a discharge coil, and a contact / separation mechanism that contacts and separates the inlet seal and the rubber blade with respect to the intermediate transfer belt 2. The belt cleaning device 42 transfers the BK image of the first color after the belt transfer, and then transfers the toner images of the second, third, and fourth colors from the intermediate transfer belt 2 by the contact / separation mechanism to the entrance seal, rubber blade, etc. Are separated.
[0013]
The transfer paper cassettes 44 to 47 in the paper supply bank store transfer papers of various sizes. From the transfer paper cassette in which the paper of the specified size is stored, the registration rollers 48 to 5l can be used to register rollers. Paper is fed to the pair 52. Further, transfer paper such as OHP paper or thick paper is manually fed from the paper feed tray 53 to the registration roller pair 52. The registration roller pair 52 sends the transfer paper between the intermediate transfer belt 2 and the paper transfer device 7 serving as a secondary transfer unit in accordance with the full-color toner image on the intermediate transfer belt 2.
When the transfer paper passes between the paper transfer device 7 and the intermediate transfer belt 2, it is charged with a positive charge by the corona discharge current from the paper transfer device 7, and the full-color toner image on the intermediate transfer belt 2 is charged. Transcribed. The transfer paper is neutralized by a neutralizing brush (not shown) disposed on the left side of the paper transfer unit 7, peeled off from the intermediate transfer belt 2, and conveyed by the paper conveying belt 54. Further, the toner image is fused and fixed at the nip portion between the fixing roller 55A and the pressure roller 55B, which is controlled to a predetermined temperature by the fixing device 55, and the transfer paper is sent out as a full-color copy to the outside of the main body by the discharge roller pair 56. Further, after the color toner image is transferred to the transfer paper, the surface of the intermediate transfer belt 2 is cleaned by pressing the blade of the belt cleaning device 42 by the contact / separation mechanism of the belt cleaning device 42.
[0014]
In the case of repeat copying, the color scanner 11 and the photosensitive drum 1 side proceed to the second color toner image forming process at a predetermined timing following the first color toner image forming process of the first sheet. Further, the intermediate transfer belt 2 performs belt transfer of the second BK toner image to the area cleaned by the belt cleaning device 42 following the batch transfer process of the first full color toner image to the transfer paper. Thereafter, an operation similar to the copying operation for the first sheet is performed.
The above is a description of a 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 case of the single color copy mode, until the predetermined number of copies are completed, only the predetermined color developing device of the rotary developing device 32 is placed in the developing position to be in the developing operation state, and the belt cleaning device The copying operation is continuously performed while the blade 42 is pressed against the intermediate transfer belt 2.
[0015]
A position detection mark is provided on the outer peripheral surface or the inner peripheral surface of the intermediate transfer belt 2. However, on the outer peripheral surface side of the intermediate transfer belt 2, it is necessary to devise a position detection mark that avoids the passing area of the belt cleaning device 42, which may be difficult to arrange. Position detection marks are provided on the inner peripheral surface side of the intermediate transfer belt 2. The optical sensor 41 as a mark detection sensor is provided at a position between the driving roller 35 and the support roller 39 where the intermediate transfer belt 2 is bridged.
Further, a positive DC voltage or DC current is applied to the belt transfer corona discharger 3 by the transfer condition changing unit 5, and the transfer condition changing unit 5 is connected to the control unit 9 (see FIG. 2). . Further, a belt state detection sensor 4 which is a belt state detection means for detecting a singular state at the start of the intermediate transfer belt 2 is attached to face the intermediate transfer belt 2. Further, the output of the belt state detection sensor 4 is connected to a control unit 9 constituted by a microprocessor or the like. That is, the belt state detection sensor 4 detects a singular state at the start of the intermediate transfer belt 2 and notifies the transfer condition changing unit 5 of the singular state via the control unit 9. Therefore, the transfer condition changing unit 5 informed of the singular state changes the DC voltage or DC current value of the belt transfer corona discharger 3.
[0016]
FIG. 2 is an enlarged view of a part of the embodiment of the present invention. The photosensitive drum 1 and the intermediate transfer belt 2 rotate at the same linear velocity in the direction indicated by the arrow at the primary transfer position by the belt transfer corona discharger 3. A mark MC for setting a timing for starting the image forming process is provided on the back side of the intermediate transfer belt 2. The mark MC moves together with the intermediate transfer belt 2, and an optical sensor 41 is attached to a non-moving member in a predetermined passing region through which the mark MC passes. As the optical sensor 41, a reflection type photo sensor or a transmission type photo sensor is used, and a signal detecting the mark MC is transmitted to a control unit 9 constituted by a microprocessor or the like. When a reflection type photosensor is used as the optical sensor 41, a member such as a reflective tape is attached to the intermediate transfer belt 2, and the reflection type photosensor is used to reflect from the surface having low reflectivity on the intermediate transfer belt 2. A location (time) at which the mark MC changes to a high mark MC or a location (time) at which the mark MC changes to the surface of the intermediate transfer belt 2 may be detected.
[0017]
At the time of image formation, the mark MC is detected by the optical sensor 41 while the photosensitive drum 1 and the intermediate transfer belt 2 are rotated, and the control unit 9 detects a certain time from the detection of the mark MC based on the mark detection signal of the optical sensor 41. After the elapse of time, the above-described image forming process is started. Therefore, the photosensitive drum 1 is uniformly charged by the charger 28 and optically written by the writing optical unit 21 to form a BK latent image. The BK latent image is formed by the BK developing device 32K of the rotary developing device 32. Is developed into a BK toner image.
Next, the BK toner image is transferred to the intermediate transfer belt 2 by the belt transfer corona discharger 3. In the mode for forming a full-color image, a C toner image, an M toner image, and a Y toner image are formed on the photosensitive drum 1 after the BK toner image and transferred onto the intermediate transfer belt 2 as described above. A full-color toner image of four colors is formed, and this full-color toner image is collectively transferred to the transfer paper P by the paper transfer device 7 at the position of the flat surface by the paper transfer opposing rollers 36 and 37 of the intermediate transfer belt 2. After that, the transfer paper P is separated from the intermediate transfer belt 2. The belt transfer corona discharger 3 is applied with a positive DC voltage or DC current having a predetermined positive reference value by the transfer condition changing unit 5 and the paper transfer unit 7 by the power source 8.
[0018]
In the present invention example, a belt state detection sensor (belt state detection means) 4 for detecting a singular state at the start of the intermediate transfer belt 2 is attached to face the intermediate transfer belt 2. Further, the output of the belt state detection sensor 4 is transmitted to a control unit 9 constituted by a microprocessor or the like, and the result is a value of the DC voltage or DC current of the belt transfer corona discharger 3 via the transfer condition changing unit 5. Is configured to change. Further, the belt state detection sensor 4 is a singular state at the time of starting when the intermediate transfer belt 2 is in an inoperative state for a predetermined time at the start of starting or when the curl value of the belt exceeds a predetermined value. Can be detected.
Further, in this example of the invention, the intermediate transfer belt 2 is stretched over six rollers 35 to 40, and among these rollers, the paper transfer counter rollers 36 and 37 have the smallest diameter. Therefore, when the intermediate transfer belt 2 has been inactive for a long time and stopped, an excessive force is applied to the portions pressed against the paper transfer opposing rollers 36 and 37, and curling is most likely to occur. I can say that.
[0019]
FIG. 3 is a diagram showing a case where the belt state detection sensor 4 described with reference to FIG. 2 is a belt curl detection sensor 4 a which is a belt curl detection means for detecting the curl of the intermediate transfer belt 2. The belt curl detection sensor 4a is configured by a non-contact type sensor such as an optical sensor in which a light emitting element and a light receiving element are combined. Similar to the belt state detection sensor 4 in FIG. 2, the output of the belt curl detection sensor 4 a is transmitted to the control unit 9, and the result is a DC voltage or DC of the belt transfer corona discharger 3 via the transfer condition changing unit 5. It is configured to change the current value.
That is, at the start of the operation of the intermediate transfer belt 2, it is detected by the belt curl detection sensor 4a whether or not the belt curl value exceeds a predetermined value. If the curl value of the belt exceeds a predetermined value, it is transmitted to the control unit 9, and in the control unit 9, the primary transfer current value or the primary transfer voltage applied to the belt transfer corona discharger 3 via the transfer condition changing unit 5. Switch the value from the reference set value to a smaller value.
[0020]
FIG. 4 shows the curled belt portion in contact with the photosensitive drum 1. In the drawing, a minute gap due to curling is generated at a portion indicated by an arrow between the photosensitive drum 1 and the intermediate transfer belt 2, and a discharge occurs between the photosensitive drum 1 and the intermediate transfer belt 2 due to the minute gap. A phenomenon occurs in which the toner on the transfer belt 2 is reversely transferred to the photosensitive drum 1 side. As a result, a linear white-out portion is generated on the belt, and a white-out portion is also generated on the transfer paper as it is. In order to prevent this linear void, it is only necessary to prevent the discharge of a minute gap portion due to curling. For this purpose, it is necessary to set the value as low as possible within the range of a good transfer voltage or transfer current.
[0021]
FIG. 5 shows a state in which white portions are generated on the transfer paper. That is, a line-shaped white spot portion is generated between normal images represented by oblique lines. The position of the linear white portion is not particularly defined.
FIG. 6 shows that the primary transfer current of the belt transfer corona discharger 3 in a state where the intermediate transfer belt 2 has been inactive for a long time and the belt portion is curled and a minute gap is generated as shown in FIG. This shows the state of occurrence of a linear blank level when the value is changed. A linear white-out state is easily manifested in a halftone image. Further, in the configuration example of the image forming apparatus of the present invention as shown in FIG. 1, the primary transfer current value at the time of monochromatic image formation is a standard setting value of 100 μA, but in a state where the belt portion is curled. The above-mentioned minute gap discharge occurred and linear white spots occurred. Therefore, when the value of the primary transfer current was reduced to 50 μA, a good image without linear white spots was obtained.
[0022]
FIG. 7 shows that the curling of the transfer belt is gradually recovered when copying is continuously performed from the state where the linear white spot occurs while the primary transfer current value is set to the standard setting value of 100 μA. It shows a state that returns to a state where can be taken normally. As can be seen from the figure, in this configuration example, it can be seen that the number of copies returns to normal from about 30 copies. Therefore, judging from the results of FIGS. 6 and 7, in the initial state in which curling occurs in the belt portion and minute gap discharge occurs, the primary transfer current value is lowered from the reference set value to 50 μA. By preventing linear white spots and returning the value of the primary transfer current to the standard setting value of 100 μA again after the number of copies reaches about the first 30 sheets, more preferably about 50 sheets, linear white areas are always obtained. An image without missing can be obtained.
Accordingly, for example, when the intermediate transfer belt has been inactive for a predetermined time, this is detected, and the transfer current value of the primary transfer unit is used as a reference from when the intermediate transfer belt is operated until the predetermined number of images have been formed. By switching from a set value to a smaller value and controlling to return to the original reference set value when a predetermined number of images have been formed, a good image free from linear white spots caused by belt curl is obtained. be able to.
When the belt curl detecting unit 4a detects that the predetermined curl value is exceeded, the transfer current value of the primary transfer unit is set as a reference until the predetermined number of image formations are completed after the intermediate transfer belt is operated. By switching from a lower value to a smaller value and returning to the original reference setting value when a predetermined number of image formations are completed, a good image free of linear white spots due to belt curl can be obtained, Further, since complicated control for determining the transfer start position on the transfer belt is not required, image formation with high processing efficiency is possible.
[0023]
【The invention's effect】
As described above, according to the first aspect of the present invention, the curling state of the intermediate transfer belt is detected by the belt state detecting unit, and the transfer condition changing unit is 1 when the curl value of the intermediate transfer belt exceeds a predetermined value. Since the transfer conditions of the secondary transfer means can be changed, a curl state in which the intermediate transfer belt is likely to be plastically deformed is detected at the start of the intermediate transfer belt, and the transfer current value of the primary transfer means is detected by the transfer condition changing means. The reference set value can be switched to a smaller value.
According to the invention of claim 2, in addition to the invention of the image forming apparatus configured as in claim 1, the intermediate transfer belt is operated again by detecting the curl state at the time of starting by the belt state detecting means. Since the transfer condition of the primary transfer unit is changed from the start of the intermediate transfer belt to the end of the predetermined number of image formations, the transfer condition of the primary transfer unit is changed. When the transfer current value of the next transfer unit is switched from the reference setting value to a smaller value and the formation of a predetermined number of images is completed, the original reference setting value can be restored.
According to the invention of claim 3, in addition to the invention of the image forming apparatus configured as in claim 1 or 2, the belt state detecting means detects that the non-operation time of the intermediate transfer belt has continued for a predetermined time. As a result, it is determined that curling has occurred in the intermediate transfer belt. If the intermediate transfer belt has been inactive for a predetermined time, the primary transfer is performed until the predetermined number of images have been formed after the intermediate transfer belt has been operated. The transfer current value of the means is switched from the reference set value to a smaller value, and when the predetermined number of images are formed, the original reference set value can be restored.
According to the invention of claim 4, claim 1 is provided. Or 2 In addition to the invention of the image forming apparatus described above, since the belt state detecting means is a reflective sensor provided to face the intermediate transfer belt, the belt is inexpensive and has good controllability without touching the intermediate transfer belt. It becomes possible to detect the curl state.
[Brief description of the drawings]
FIG. 1 is a side view of a main part of an image forming apparatus showing an embodiment of the present invention.
FIG. 2 is an enlarged side view of a main part of an image forming apparatus showing an embodiment of the present invention.
FIG. 3 is an enlarged side view of a main part of an image forming apparatus showing an embodiment of claim 4, claim 5, or claim 6 of the present invention.
FIG. 4 is an explanatory diagram illustrating a state where a curled intermediate transfer belt and a photosensitive drum are in contact with each other.
FIG. 5 is an explanatory diagram for explaining an example of a transfer sheet in which a linear white-out portion is generated.
FIG. 6 is an explanatory diagram for explaining the occurrence of a linear blank state with respect to a primary transfer current.
FIG. 7 is an explanatory diagram for explaining how a linear white-out state is recovered with respect to the number of copies.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Image carrier or photosensitive drum, 2 Intermediate transfer belt, 3 Primary transfer means, Belt transfer corona discharger, 4 Belt state detection means, or belt state detection sensor, 4a Belt curl detection means, or belt curl Detection sensor, 5 transfer condition changing means, or transfer condition changing section, 7 secondary transfer means, or paper transfer device, 8 power supply, 9 control section, 11 color image reading device or color scanner, 12 document table, 13 document, 14 illumination lamp, 19 color sensor, 20 color image recording device or color printer, 21 writing optical unit, 28 charger, 29 photoconductor cleaning unit, 30 static elimination lamp, 31 potential sensor, 32 rotary developing device, 33 development density Pattern detector, 35 Drive roller, 36 Paper transfer counter roller, 37 Transfer counter roller, 38 cleaning facing roller 39 support roller 40 driven roller 41 optical sensor

Claims (4)

  In an image forming apparatus for transferring a toner image formed on an image carrier onto an intermediate transfer belt, and transferring the toner image on the intermediate transfer belt to a transfer material to form an image, the image carrier carrying the toner image; An intermediate transfer belt operating in contact with the image carrier, a primary transfer means for transferring a toner image formed on the image carrier to the intermediate transfer belt, and a belt state for detecting a curl state of the intermediate transfer belt Detecting means; and a transfer condition changing means for changing the transfer condition of the primary transfer means by detecting that the curl value of the intermediate transfer belt exceeds a predetermined value by the belt state detecting means; An image forming apparatus comprising the image forming apparatus.   2. The image forming apparatus according to claim 1, wherein the transfer condition changing unit detects a predetermined number of images after the belt state detecting unit detects the curl state of the intermediate transfer belt so that the intermediate transfer belt is operated again. An image forming apparatus, wherein transfer conditions of the primary transfer unit are changed until formation is completed.   3. The image forming apparatus according to claim 1, wherein the belt state detection unit detects that the intermediate transfer belt has been curled by detecting that the intermediate transfer belt has been inactive for a predetermined time. An image forming apparatus characterized by determining. 3. The image forming apparatus according to claim 1, wherein the belt state detection unit is a reflective photosensor provided to face the intermediate transfer belt.

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