JPH1195575A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an excellent image having no irregularity nor misalignment by preventing a photoreceptor drum and an intermediate transfer body from being mutually slipped during temporary transfer by preventing a load caused by the speed difference between them from being accumulated. SOLUTION: As for an image forming device by which a color image is obtained by forming a superimposed toner image on an intermediate transfer belt 415 by repeating a process where an image formation process is started at a prescribed timing by detecting a mark 451 on the intermediate transfer belt 415 by a sensor 452 and the toner image of an arbitrary color is formed by executing developing with colored toner after forming a latent image by radiating image light to the electrifying area of the photoreceptor drum 414 and then it is transferred on the belt 415 by a primary transferring part 500 for each different color, and also executing the batch transfer of the superimposed image on transfer paper, the drum 414 and the belt 415 are mutually slipped by reducing electrostatic attractive force between them after transferring the toner image from the drum 414 to the belt 415 and before starting a next image formation process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic color image forming apparatus such as a color copying machine, a color printer, a color facsimile, or a digital multifunction machine having these functions, and more particularly, to a photoconductor drum. The present invention relates to an image forming apparatus of a type in which toner images of respective colors are sequentially transferred to an intermediate transfer member to form a superimposed toner image, and the superimposed toner images are collectively transferred onto transfer paper.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus provided with an intermediate transfer member, a mark is provided on a part of the intermediate transfer member, a mark detecting sensor is provided in a region where the mark passes, and a photosensitive drum and an intermediate transfer member are provided. A charging unit is provided at a charging position on the upstream side in the rotation direction of the photosensitive drum from the position of the primary transfer unit formed of a contact part with the body. An image forming process is started at a certain timing by detecting the mark by the sensor during rotation of the photosensitive drum and the intermediate transfer body, and the charged area of the photosensitive drum charged by passing through the charging position is started. To form a toner image of an arbitrary color by performing optical writing and development processing, and then transfer the toner image of the arbitrary color to the intermediate transfer member in the primary transfer unit, for each of the different colors, A color image is obtained by forming a color superimposed toner image on the intermediate transfer body, and transferring the superimposed toner image on a transfer sheet at a time. By the way, in the primary transfer portion of such an image forming apparatus, the photosensitive drum and the intermediate transfer member are in close contact to form a nip portion, and when both are charged, an electrostatic force, that is, a Coulomb force is applied. Adhesion has increased. In such a state, if the speeds of the photosensitive drum and the intermediate transfer member are completely the same, the two rotate completely in synchronization, and accurate toner image alignment is possible.

[0003]

However, since the photosensitive drum and the intermediate transfer member, and furthermore, the rotating means of the intermediate transfer member are industrial products, it is impossible that there is no dimensional error. There is always a certain range of dimensional variation, and the peripheral length ratio of each part often does not become an integer. Due to this dimensional variation, the peripheral speeds of the photosensitive drum and the intermediate transfer member slightly differ. for that reason,
This difference in convergence must be absorbed by a slight slip between the photosensitive drum and the intermediate transfer member in the primary transfer section, and the alignment by the mark detection must always be performed under the same relative conditions. However, as described above, in the primary transfer portion, the adhesion between the photosensitive drum and the intermediate transfer member is increased due to the electrostatic attraction force, so that a slip occurs almost at the contact portion between the photosensitive drum and the intermediate transfer member. Without trying to rotate only the surface synchronously. For this reason, the detected position of the mark and the relative position between the rotating means are shifted, and the reaction of the small peripheral speed causes the driven side of the photosensitive drum or the intermediate transfer body to be driven from the driven side to the driven side. Since the rotation is performed quickly, a slip occurs at a load change and a primary transfer nip portion. As a result, the transferred image during the primary transfer is disturbed or misaligned, and it becomes impossible to accurately superimpose the toner images of a plurality of colors to obtain a superimposed toner image. To solve the above problem, the contact force between the photosensitive drum and the intermediate transfer body in the primary transfer unit is constantly reduced, and the photosensitive drum and the intermediate transfer body are rotated while always allowing a slight speed difference. As long as an electrostatic force acts between the photoconductor drum and the intermediate transfer body, the photoconductor drum and the intermediate transfer body will come into close contact with each other in the primary transfer unit, so the same as the above case A slight slip occurs at the nip portion at the primary transfer portion. The present invention has been made in view of the above circumstances, and a problem thereof is to control an electrostatic attraction force between a photosensitive drum and an intermediate transfer body so that the primary transfer is performed while the primary transfer is performed. By causing the intermediate transfer members to be in a suction state and weakening the suction force between the photosensitive drum and the intermediate transfer member at a timing that does not affect the image formation, and slipping each other,
An object of the present invention is to provide an image forming apparatus capable of obtaining a good image without image disturbance or misalignment by preventing a load from being accumulated between the two.

[0004]

According to a first aspect of the present invention, there is provided a photosensitive drum driven to rotate, and an intermediate transfer member driven at substantially the same peripheral speed as the photosensitive drum. A primary transfer portion comprising a contact portion between the photoconductor drum and the intermediate transfer member; a charging unit provided at a charging position on the rotation direction upstream side of the photoconductor drum with respect to the primary transfer portion; A mark provided on a part of the transfer body, and a mark detection sensor provided facing the passing position of the mark, and the sensor is used by the sensor during rotation of the photosensitive drum and the intermediate transfer body. An image forming process is started at a predetermined timing by detecting a mark, and a latent image is formed by irradiating image light to a charged area of the photosensitive drum charged by the charging unit, and then the latent image is colored. No Forming a toner image of an arbitrary color, and then transferring the toner image of the arbitrary color to the intermediate transfer body in the primary transfer unit for each of the different colors. An image forming apparatus for forming a superimposed toner image formed by superimposing toners of a plurality of colors on a transfer body and collectively transferring the superimposed toner image onto transfer paper in a secondary transfer unit to obtain a color image, After the toner image is transferred from the drum to the intermediate transfer body, an attraction force control unit that reduces an electrostatic attraction force between the photosensitive drum and the intermediate transfer body is provided. According to a second aspect of the present invention, based on the apparatus configuration of the first aspect, the attraction force control unit determines whether or not the mark indicating the start timing of the next image forming process is detected by the sensor. It is characterized in that the attraction force is reduced. According to a third aspect of the present invention, based on the apparatus configuration of the second aspect, the attraction force control unit reduces the attraction force by forming a non-charged area on the photosensitive drum. It is characterized by having According to a fourth aspect of the present invention, based on the apparatus configuration of the second aspect, the attraction force control unit switches the bias voltage applied to the intermediate transfer member of the primary transfer unit to thereby perform the attraction. It is characterized by reduced power. According to a fifth aspect of the present invention, on the premise of the device configuration of the second aspect, the attraction force control unit switches the bias voltage to apply a bias voltage opposite to that at the time of primary transfer. It is characterized in that the attraction force is reduced. Further, the invention according to claim 6 is based on the premise of the apparatus configuration according to claim 2 or 3, wherein the attraction force control means forms a non-charged area by irradiating light on the photosensitive drum. It is characterized in that the attraction force is reduced. According to a seventh aspect of the present invention, on the premise of the apparatus configuration according to any one of the first to sixth aspects, the attraction force control unit controls the attraction force control unit from the photosensitive drum every image forming process for one color. After transferring the toner image to the intermediate transfer member, the attraction force is reduced. According to an eighth aspect of the present invention, on the premise of the apparatus configuration according to any one of the first to sixth aspects, the attraction force control unit forms the overlaid toner image on the intermediate transfer body, It is characterized in that the attraction force is reduced.

According to the first aspect of the present invention, the electrostatic attraction force between the photosensitive drum and the intermediate transfer member is controlled so that the photosensitive transfer is performed during the primary transfer. The suction between the photosensitive drum and the intermediate transfer body is reduced at a timing that does not affect image formation by causing the body drum and the intermediate transfer body to be in an attraction state and slipping each other, so that no load is accumulated between the two. As a result, a good image free from image distortion such as white spots or misalignment can be obtained. According to the second aspect of the present invention, in the first aspect, before the mark for starting the image forming process is detected, the attraction force is reduced so that the photosensitive drum and the intermediate transfer body slip from each other. By doing so, it is possible to prevent a slip from occurring when an image is formed on the photosensitive drum, so that it is possible to obtain a good image without image disturbance such as white spots or misalignment. According to the third aspect of the present invention, in the first or second aspect, a non-charged area is formed on the photoconductor drum to reduce a potential difference between the photoconductor drum and the intermediate transfer body, thereby reducing the potential difference between the two. The electrostatic attraction force can be effectively reduced. According to the fourth aspect of the present invention, the potential difference between the photosensitive drum and the intermediate transfer body is reduced by switching the bias voltage applied to the intermediate transfer body of the primary transfer unit in the first or second aspect. As a result, the electrostatic attraction between the two can be effectively reduced. According to a fifth aspect of the present invention, in the first or second aspect, the potential difference between the photosensitive drum and the intermediate transfer body is reduced by switching the bias voltage and applying a bias voltage opposite to that at the time of the primary transfer. This can effectively reduce the electrostatic attraction between the two. According to a sixth aspect of the present invention, in the first or second aspect, the potential difference between the photosensitive drum and the intermediate transfer member is reduced by irradiating the photosensitive drum with light to form an uncharged area. This can effectively reduce the electrostatic attraction between the two. According to a seventh aspect of the present invention, in any one of the first to sixth aspects, after transferring a toner image from the photosensitive drum to the intermediate transfer body for each image forming process for one color, By reducing the attraction force, the load caused by the speed difference between the photosensitive drum and the intermediate transfer member increases and the two can be slipped with each other before the load adversely affects, thereby eliminating the load. According to an eighth aspect of the present invention, in any one of the first to sixth aspects, after forming a superimposed toner image for a previous color on the intermediate transfer body, that is, all colors on the intermediate transfer body. After the primary transfer operation is completed, the photosensitive drum and the intermediate transfer member are slipped to each other by performing an operation of reducing the suction force without significantly lowering the printing or copying speed. Can be eliminated.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the embodiments shown in the drawings. FIG. 1 is an overall view showing a configuration of an image forming apparatus according to the present invention. The image forming apparatus 100 includes a color image reading unit (hereinafter, referred to as a scanner unit) 200, a color image forming unit (hereinafter, referred to as a printer unit) 300, a paper feed bank 400, and the like. The scanner unit 200 converts the image of the original 180 on the contact glass 202 into an illumination lamp 205 and a mirror group 204.
An image is formed on the color sensor 207 via the lens 206 and the color image information of the original is, for example, blue (hereinafter, referred to as B), green (hereinafter, referred to as G), and red (hereinafter, referred to as R). It is read for each color separation light and converted into an electrical image signal. The color sensor 207 is
In this example, B, G, and R color separation means and a photoelectric conversion element such as a CCD (solid-state imaging device) are used to perform simultaneous reading of three colors. Based on the B, G, and R color separation image signal intensity levels obtained by the scanner unit 200,
A color conversion process is performed by an image processing unit (not shown), 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). To obtain color image data including the color information. At this time, the illumination lamp 205 receives a scanner start signal that is timed with the operation of the printer unit 300.
An illumination / mirror optical system including mirror groups 204A, 204B, and 204C scans the document in the direction of the left arrow, and obtains one color image data for each scan. By repeating this operation a total of four times, sequential four-color image data is obtained. Then, each time, while sequentially visualizing the images in the printer unit 300, the images are superimposed to form a full-color image of four colors. Next, an outline of the printer unit 300 will be described. The printer unit 300 includes a writing optical unit 401 as an exposure unit, a photosensitive drum 414, and a revolver developing device 420. The writing optical unit 401 converts color image data from the scanner unit 200 into an optical signal, Optical writing corresponding to the original image is performed to form an electrostatic latent image on the photosensitive drum 414. The optical writing optical unit 401 includes a laser emission unit 441, an emission drive control unit (not shown) for driving the laser emission unit 441, and a polygon mirror 44.
3. Rotating motor 444 for driving the same, fθ lens 4
42, a reflection mirror 446 and the like. The photoconductor drum 414 rotates counterclockwise as indicated by the arrow. Around the photoconductor drum 414, a photoconductor cleaning unit 421, a neutralization lamp 414M, a charger 419 as a charging unit, a potential sensor 414D for detecting a latent image potential on the photoconductor drum 414, and a revolver developing device 420 are selected. A developing device, a developing density pattern detector 414P, an intermediate transfer belt 415 as an intermediate transfer member according to the present invention, and the like are arranged. The revolver developing device 420 includes a BK developing device 420K, a C developing device 420C,
It comprises a developing unit 420M, a Y developing unit 420Y, a developing unit holder 420A for holding these, a revolver rotation drive unit (not shown) for rotating the developing unit holder 420A counterclockwise as indicated by an arrow. In order to develop the electrostatic latent image, each of these developing units rotates developing sleeves 420KS, 420CS, 420MS, and 420YS which rotate by contacting the ears of the developer with the surface of the photosensitive drum 414;
It is composed of a developing paddle that rotates to pump up and agitate the developer.

In a standby state, the revolver developing device 420 is set at a position where development is performed by the BK developing device 420K.
At 00, the reading of the BK image data starts at a predetermined timing, and based on this image data, optical writing / latent image formation by laser light starts (hereinafter, an electrostatic latent image based on the BK image data is referred to as a BK latent image). , M, and Y image data). In order to enable development from the leading end of the BK latent image, before the leading end of the latent image reaches the developing position of the BK developing unit 420K, the rotation of the developing sleeve 420KS is started to transfer the BK latent image to the BK toner. Develop with. Thereafter, the developing operation of the BK latent image area is continued. When the trailing edge of the latent image passes the BK latent image position, the developing position of the BK developing unit 420K is immediately changed from the developing position of the next color developing unit. Until then, the revolver developing device 420 is driven to rotate. This rotation operation is completed at least before the leading end of the latent image based on the next image data arrives. When the image forming cycle is started, the photosensitive drum 414 rotates counterclockwise as shown by an arrow, and the intermediate transfer belt (intermediate transfer body) 415 is rotated clockwise by a drive motor (not shown). To rotate. Intermediate transfer belt 415
BK toner image formation, C toner image formation, M toner image formation, and Y toner image formation are sequentially performed with the rotation of the intermediate transfer belt 415 in the order of BK, C, M, and Y.
A toner image is formed on top of the toner image.

The formation of a BK image is performed as follows. The charger 419 causes the photosensitive drum 414 to have a negative charge of about -400 V to -600 V in the dark by corona discharge.
To be uniformly charged. Subsequently, the laser diode 44
1 performs raster exposure based on the BK signal. When the raster image is exposed in this manner, in the initially exposed portion of the photosensitive drum 414 that is uniformly charged, the charge proportional to the amount of exposure light disappears, and an electrostatic latent image is formed.
The toner in the revolver developing device 420 is negatively charged by stirring with the ferrite carrier, and the BK developing sleeve 420 KS of the developing device is a photosensitive drum 4.
The negative direct current potential and the alternating current are biased by a power source (not shown) to the fourteen metal base layers. As a result, no toner adheres to the portion of the photosensitive drum 414 where the charge remains, and the BK toner is adsorbed to the portion having no charge, that is, the exposed portion.
A BK visible image similar to the latent image is formed. The intermediate transfer belt 415 is stretched around drive rollers 415D and 415T, an earth roller 415C, a bias roller 415F, and a group of driven rollers, and is driven and controlled by a drive motor (not shown).

The BK toner image formed on the photosensitive drum 414 is transferred onto the surface of an intermediate transfer belt 415, which is rotationally driven (circularly running) at substantially the same speed as the photosensitive drum 414, by a belt transfer corona. The image is transferred by an electric device (hereinafter, referred to as a belt transfer unit) 416. Hereinafter, the transfer of the toner image from the photosensitive drum 414 to the intermediate transfer belt 415 is referred to as belt transfer. Some untransferred residual toner on the photoconductor drum 414 is cleaned by the photoconductor cleaning unit 421 in preparation for reuse of the photoconductor drum 414. The collected toner is stored in a waste toner tank (not shown) via a collection pipe. The intermediate transfer belt 415 sequentially aligns the BK, C, M, and Y toner images formed on the photosensitive drum 414 on the same surface to form a four-color superimposed belt transfer image. And collective transfer to a transfer paper by a corona discharge transfer device. On the photosensitive drum 414 side, the process proceeds to the C image forming process after the BK image forming process. Reading of the C image data by the scanner starts at a predetermined timing, and the C light is written by the image data. A latent image is formed. The C developing device 420C rotates the revolver developing device 420 with respect to the developing position after the rear end of the previous BK latent image has passed and before the leading end of the C latent image has arrived. The latent image is developed with C toner. Since then
The development of the C latent image area is continued, but when the rear end of the latent image has passed, the revolver developing device 420 is driven as in the case of the BK developing device, and the C developing device 420C is sent out. The M developing device 420M is located at the developing position. This operation is also performed before the leading end of the next M latent image reaches the developing unit. Note that the steps of reading the respective image data, forming the latent image, and developing the M and Y images are the same as those of the above-described BK image and C image steps, and thus the description thereof is omitted.

The belt cleaning device 415U includes an inlet seal, a rubber blade, a discharge coil, and a mechanism for contacting and separating the inlet seal and the rubber blade. 1
After the BK image of the color is transferred to the belt, while the second, third, and fourth colors are being transferred to the belt, the blade seal mechanism separates the entrance seal, the rubber blade, and the like from the intermediate transfer belt surface. . The paper transfer roller 417 applies AC + DC or a DC component to the transfer paper and the intermediate transfer belt by a corona discharge method in order to transfer the superimposed toner image on the intermediate transfer belt 415 to the transfer paper.
The transfer paper cassette 482 in the paper supply bank 400 stores transfer papers of various sizes. The paper supply roller 483 is moved from a storage cassette storing paper of a designated size.
Is fed and conveyed in the direction of the pair of registration rollers 418R. Reference numeral 412B2 indicates a paper feed tray for manually feeding OHP paper, thick paper, and the like. At the time when the image formation is started, the transfer paper is fed from any one of the above-mentioned paper feed trays, and is waiting at the nip portion of the registration roller pair 418R. When the leading end of the toner image on the intermediate transfer belt 415 reaches the paper transfer roller 417,
The registration roller pair 418R is driven so that the leading edge of the transfer paper coincides with the leading edge of the image, and the registration between the paper and the image is performed. In this way, the transfer paper P is superimposed on the color superimposed image on the intermediate transfer belt and passes over the paper transfer roller 417 connected to a positive potential. At this time, the transfer paper is charged with a positive charge by the corona discharge current, and most of the toner image is transferred onto the transfer paper. Subsequently, when the transfer paper passes through a separation and static eliminator by a static elimination brush (not shown) disposed on the left side of the paper transfer roller 417, the transfer paper is discharged, separated from the intermediate transfer belt 415 and moved to the paper transport belt 422.

The transfer paper on which the four-color superimposed toner image is collectively transferred from the intermediate transfer belt surface is conveyed to a fixing device 423 by a paper conveyance belt 422, and a nip between a fixing roller 423A and a pressure roller 423B controlled to a predetermined temperature. The toner image is fused and fixed in the section, sent out of the main body by a discharge roll pair 424, and stacked face up on a copy tray (not shown) to obtain a full-color copy. The surface of the photoconductor drum 414 after the belt transfer is cleaned by a photoconductor cleaning unit 421 including a brush roller, a rubber blade, and the like, and is uniformly discharged by a discharge lamp 414M. Further, the intermediate transfer belt 415 after the transfer of the toner image onto the transfer paper is again put into the cleaning unit 41.
The surface is cleaned by pressing the blade with a 5U blade contact / separation mechanism. In the case of repeat copying, the operation of the scanner and the image formation on the photosensitive member follow the fourth-color image process of the first sheet, and the first sheet is printed at a predetermined timing.
Proceed to the color image process. In the case of the intermediate transfer belt 415, the second BK toner image is transferred to a region where the surface of the intermediate transfer belt 415 is cleaned by the belt cleaning device, following the batch transfer process of the first four-color superimposed image onto the transfer paper. Be transferred. After that, the operation is the same as that of the first sheet. The above is the description of the copy mode for obtaining the four-color full-color copy. However, 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. Become. Further, in the case of the single-color copy mode, until the predetermined number of sheets is completed, only the developing device of the revolver developing device 420 of the predetermined color is located at the developing position of the predetermined color, the developing operation is performed, and the belt cleaning device 415U The copying operation is continuously performed while the blade is pressed against the belt.

FIGS. 2A and 2B show an intermediate transfer belt 41.
5 and the configuration of the periphery thereof. As illustrated, the intermediate transfer belt 415 has a mark 451 for position detection on a part of the inner peripheral surface thereof. An optical sensor 452 for mark detection is arranged near the inner peripheral surface of the intermediate transfer belt 415 so as to face the position where the mark 451 passes. The intermediate transfer belt 415 forms the primary transfer portion 500 by a portion of the intermediate belt 415F that is bridged between the bias roller 415F and the ground roller 415C partially contacts the photosensitive drum 414. During normal image formation, a bias voltage of 1000 V is applied to the bias roller 415F. Further, since the earth roller 415C is grounded, the potential is always kept at 0V. The photosensitive drum 414 is charged by a charger 419 with a voltage of -400V to -400V.
It is charged to 600V. Therefore, at the time of the primary transfer, the potential of the intermediate transfer belt 415 in the primary transfer section 500 is about +500 V, and the potential between the intermediate transfer belt 415 and the photosensitive drum 414 is 9
Since a potential difference of 00V to 1100V is generated, the photosensitive drum 414 and the intermediate transfer belt 415 are attracted to each other by an electrostatic force. Also, the photosensitive drum 4
14 and the intermediate transfer belt 415 are originally mechanically pressed against each other, so that the photosensitive drum 414 and the intermediate transfer belt 41
At the contact portion with 5, the frictional force causes almost no slip, and only the surface tries to rotate in synchronization. Therefore, if there is a speed difference between the two, a load is applied to one of the driving belts 415E on the side of the intermediate transfer belt 415, which is usually the driving force which is weaker, or a motor for driving the driving belt. The body drum 414 and the intermediate transfer belt 415 slip with each other. The timing at which this slip occurs is random, which causes horizontal band-shaped white spots in the image and misregistration of the images of each color. Therefore, in the image forming apparatus according to the present embodiment, while the primary transfer is performed, the photosensitive drum 414 is not used.
The intermediate transfer belt 415 and the intermediate transfer belt 415 are set in an attraction state, and at a timing that does not affect image formation, the attraction force between the photosensitive drum 414 and the intermediate transfer belt 415 is weakened and slipped with each other so that no load is accumulated between the two. In addition, a suction force control unit is provided in order to obtain a good image without image distortion or misalignment. The function of the attraction force control unit is performed by a control unit (not shown) that controls the entire image forming apparatus 100. In the first embodiment shown in FIG. 3, the output of the charger 419 is temporarily turned off, and the non-charged region R, that is, the negative charge is not applied at a timing that does not affect image formation. The region is formed over the entire length of the photosensitive drum 414 in the axial length direction (horizontal direction) and a predetermined length in the circumferential direction. That is, in this case, the non-charged area R of the photosensitive drum 414
Is about 0 V to -150 V, the potential difference from the intermediate transfer belt 415 is reduced to about 500 V to 650 V. For this reason, a large amount of toner adheres to the photosensitive drum 414 during development, but the electrostatic charge between the photosensitive drum 414 and the intermediate transfer belt 415 when that part passes through the primary transfer unit 500 Attractive force is reduced.
As a result, the photosensitive drum 414 and the intermediate transfer belt 415
Are slipped with each other and no load is accumulated between them, so that it is possible to prevent the occurrence of slip during the primary transfer. (Corresponding to claim 3) In the second embodiment shown in FIG.
The bias voltage applied to 5F is temporarily turned off at a timing that does not affect image formation. In this case, the potential difference between the photosensitive drum 414 and the intermediate transfer belt 415 is
As shown in FIG.
The voltage drops to about 0 V, and the attraction force between them decreases. As a result, the photoconductor drum 414 and the intermediate transfer belt 415 slip with each other and no load is accumulated between them, so that it is possible to prevent the slip from occurring during the primary transfer. (Claim 4
In the third embodiment shown in FIG. 6, the bias roller 41
By switching the bias voltage applied to 5F to a reverse bias voltage at the time of not affecting the image formation at the time of the primary transfer, as shown in FIG. 7, the potential of the intermediate transfer belt 415 in the primary transfer portion is changed to the photosensitive drum. 414
, That is, 0 V potential difference. In this case, there is no substantial electric field between the photosensitive drum 414 and the intermediate transfer belt 415, and the attraction force between them is greatly reduced. As a result, the photosensitive drum 414
And the intermediate transfer belt 415 slip with each other, and no load is accumulated between them, so that it is possible to prevent a slip from occurring during the primary transfer. (Corresponding to claim 5) In the fourth embodiment shown in FIG.
The exposure means 550 is provided so as to face the surface of the primary transfer section 5.
By irradiating the surface of the photosensitive drum 414 immediately before entering the position 00 with light at a timing that does not affect image formation, a non-charged region R similar to that of the first embodiment is formed. Also in this case, since the potential of the non-charged area R of the photosensitive drum 414 is about 0 V to -150 V, the potential difference with the intermediate transfer belt 415 is 500 V to 65 V.
The photosensitive drum 414 and the intermediate transfer belt 415 when the voltage is reduced to about 0 V and the portion passes through the primary transfer unit 500
And the electrostatic attraction force between them decreases. As a result, the photoconductor drum 414 and the intermediate transfer belt 415 slip with each other and no load is accumulated between them, so that it is possible to prevent the slip from occurring during the primary transfer. (Corresponding to claim 6) In the fifth embodiment shown in FIG. 9, a grounded earth roller 415G is used in place of the bias roller 415F, and a primary charger 415H disposed between the earth rollers 415C and 415G is used. Intermediate transfer belt 41 of transfer section
In the apparatus of the type for charging the transfer belt 5, the output of the charger 415 H is switched at a timing that does not affect the image formation to switch the charging potential of the intermediate transfer belt 415, as in the third embodiment. As shown, the potential of the intermediate transfer belt 415 in the primary transfer portion is equal to the potential of the photosensitive drum 414, that is, the potential difference is 0.
V. Also in this case, the photosensitive drum 4
No substantial electric field exists between the transfer belt 14 and the intermediate transfer belt 415, and the attraction force between the two greatly decreases. As a result, the photosensitive drum 414 and the intermediate transfer belt 415 slip with each other, and no load is accumulated between them.
Slip can be prevented from occurring during the primary transfer. (Corresponding to claim 5) In each of the above embodiments, the operation of reducing the electrostatic attraction force between the photosensitive drum 414 and the intermediate transfer belt 415 is performed for each color image forming process. Photoconductor drum 4
This is performed when the transfer of the toner image from the transfer belt 14 to the intermediate transfer belt 415 is completed. As a result, during the primary transfer, the photosensitive drum 414 and the intermediate transfer belt 415 can be stuck to each other by electrostatic attraction force and mechanical pressure force to perform a stable primary transfer operation. In this case, the electrostatic attraction force is weakened, and the load due to the difference in speed between the photosensitive drum 414 and the intermediate transfer belt 415 can be released by slipping each other. (Corresponding to claim 7) However, the mark 451 attached to the intermediate transfer belt 415
Since the image forming process for the photosensitive drum 414 is started based on the detection of the image, if the slip is performed after the mark detection for starting the next image forming process is performed, the primary transfer position of the image in the next image forming process is changed. It deviates from the normal position. Therefore, the operation of reducing the attraction force is performed before the mark detection for starting the next image forming process.
If the operation of reducing the suction force is performed for each color image forming process, the copying or printing speed may be reduced. If the slip which causes the image quality to be reduced does not occur during the operation, the superimposed toner images of all the colors are transferred to the intermediate transfer belt 4.
It is efficient to perform the belt cleaning after the transfer (secondary transfer) from 15 to the transfer paper. However, also in this case, it is necessary to be before the mark detection for starting the next image forming process. (Corresponding to claim 8) In the above embodiment, the photosensitive drum 414
By not only performing the operation of reducing the electrostatic attraction force between the intermediate transfer belt 415 and the intermediate transfer belt 415, but also applying a lubricity imparting agent to the surface of the intermediate transfer belt 414 and the photosensitive drum 415, It is possible to reduce the frictional force between them and make it easy to cause a slip for releasing the load.

[0013]

As described above, according to the present invention, the following excellent effects can be exhibited. According to the first aspect of the present invention, the electrostatic attraction force between the photosensitive drum and the intermediate transfer member is controlled so that the photosensitive drum and the intermediate transfer member are in the suction state during the temporary transfer. By reducing the attraction force between the photosensitive drum and the intermediate transfer body at a timing that does not affect image formation and slipping each other, a load is not accumulated between the two, so that image disturbance such as white spots or the like can be prevented. A good image without any displacement can be obtained.
According to the second aspect of the present invention, the photosensitive drum and the intermediate transfer member are slipped with each other by reducing the attraction force before a mark for starting an image forming process is detected. Since it is possible to prevent a slip from occurring when an image is formed on the body drum, it is possible to obtain a good image free from image disturbances such as white spots and displacement. According to the third aspect of the present invention, by forming a non-charged area on the photosensitive drum, the potential difference between the photosensitive drum and the intermediate transfer member is reduced, and the electrostatic attraction between the two is reduced. It can be reduced effectively. According to the fourth aspect of the present invention, by switching the bias voltage applied to the intermediate transfer member in the primary transfer portion, the potential difference between the photosensitive drum and the intermediate transfer member is reduced, and the electrostatic potential between the two is reduced. Effective attraction force can be effectively reduced.

According to the fifth aspect of the present invention, the bias voltage is switched to apply a reverse bias voltage to that at the time of the temporary transfer, so that the potential difference between the photosensitive drum and the intermediate transfer member is reduced, and both of them are reduced. The electrostatic attraction force between them can be effectively reduced. According to the sixth aspect of the present invention, by irradiating light onto the photosensitive drum to form a non-charged area, the potential difference between the photosensitive drum and the intermediate transfer body is reduced, and static electricity between the two is reduced. The electric attraction force can be effectively reduced. Further, according to the present invention, the toner image is transferred from the photosensitive drum to the intermediate transfer body for each image forming process for one color, and thereafter, the attraction force is reduced, so that the photosensitive image is formed. Before the load caused by the speed difference between the body drum and the intermediate transfer member increases and adversely affects the load, the two can be slipped with each other to eliminate the load. According to the invention described in claim 8,
After forming a superimposed toner image for the previous color on the intermediate transfer body, that is, after the primary transfer operation for all colors on the intermediate transfer body is completed, by performing an operation of reducing the suction force. In addition, the photosensitive drum and the intermediate transfer member can be slipped with each other without significantly lowering the printing or copying speed, and the load between them can be eliminated.

[Brief description of the drawings]

FIG. 1 is an overall view showing a configuration of an image forming apparatus according to the present invention.

FIGS. 2A and 2B are diagrams illustrating a configuration of an intermediate transfer belt and a peripheral portion thereof.

FIG. 3 is an explanatory diagram of a main part showing the first embodiment.

FIG. 4 is an explanatory diagram of a main part showing a second embodiment.

FIG. 5 is an explanatory diagram showing a potential of each unit according to the second embodiment.

FIG. 6 is an explanatory diagram of a main part showing a third embodiment.

FIG. 7 is an explanatory diagram showing a potential of each unit according to the third embodiment.

FIG. 8 is an explanatory diagram of a main part showing a fourth embodiment.

FIG. 9 is an explanatory diagram of a main part showing a fifth embodiment.

[Explanation of symbols]

100 image forming apparatus, 200 color image reading unit, 3
00 color image forming unit, 400 paper supply bank, 401
Writing optical unit, 414 photosensitive drum, 41
5 Intermediate transfer belt (intermediate transfer member), 415C ground roller, 415F bias roller, 415G ground roller, 415H charger, 419 charger (charging means), 420 revolver developing device, 451 mark,
452 sensor, 500 primary transfer section, 550 exposure means, R non-charged area.

Claims (8)

[Claims] A photosensitive drum driven to rotate; an intermediate transfer member driven at substantially the same peripheral speed as the photosensitive drum;
A primary transfer portion comprising a contact portion between the photoconductor drum and the intermediate transfer member, and a charging unit provided at a charging position on the rotation direction upstream side of the photoconductor drum from the primary transfer portion,
A mark provided on a part of the intermediate transfer body, and a mark detection sensor provided facing a passing position of the mark, wherein the sensor is provided during rotation of the photosensitive drum and the intermediate transfer body. Starts the image forming process at a predetermined timing by detecting the mark, and irradiates the charged area of the photosensitive drum charged by the charging means with image light to form a latent image. Is formed with a colored toner to form a toner image of an arbitrary color, and then, the toner image of the arbitrary color is transferred to the intermediate transfer body in the primary transfer unit. In an image forming apparatus, a superimposed toner image formed by superimposing toners of a plurality of colors on the intermediate transfer body is formed, and the superimposed toner image is collectively transferred onto transfer paper in a secondary transfer unit to obtain a color image. And after transferring a toner image from the photoconductor drum to the intermediate transfer body, further comprising an attraction force control unit that reduces an electrostatic attraction force between the photoconductor drum and the intermediate transfer body. Characteristic image forming apparatus. 2. The image according to claim 1, wherein the attraction force control means reduces the attraction force before the mark indicating the start timing of the next image forming process is detected by the sensor. Forming equipment. 3. The image forming apparatus according to claim 1, wherein the attraction force control unit reduces the attraction force by forming a non-charged area on the photoconductor drum. 4. The image forming apparatus according to claim 1, wherein the attraction force control unit reduces the attraction force by switching a bias voltage applied to an intermediate transfer member of the primary transfer unit. apparatus. 5. The image forming apparatus according to claim 4, wherein the attraction force control unit reduces the attraction force by switching the bias voltage and applying a bias voltage opposite to that at the time of primary transfer. apparatus. 6. The attraction force control unit irradiates light onto the photosensitive drum to form a non-charged area,
The image forming apparatus according to claim 1, wherein the attraction force is reduced. 7. The attraction force control unit reduces the attraction force after transferring a toner image from the photosensitive drum to the intermediate transfer member for each image forming process for one color. The image forming apparatus according to claim 1. 8. The image according to claim 1, wherein the attraction force control unit reduces the attraction force after forming the superimposed toner image on the intermediate transfer member. Forming equipment.