JP5690755B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine equipped with these functions, and in particular, charging means for charging each image carrier corresponding to each different toner color to a predetermined potential. A plurality of image forming units each including a latent image forming unit that forms an electrostatic latent image on the charged image carrier and a developing unit that attaches toner to the electrostatic latent image to form a toner image on the image carrier. And a primary transfer means for transferring the toner images formed on the image carrier of the plurality of image forming portions on an intermediate transfer belt, and transferring the toner images transferred onto the intermediate transfer belt to a recording material. And an image forming apparatus including a secondary transfer unit.

  2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine equipped with these functionally, an image carrier such as a photosensitive drum is charged to a predetermined potential by a charger, 2. Description of the Related Art An image forming apparatus that forms a toner image by attaching toner to an electrostatic latent image formed on an image carrier and transfers the toner image to an intermediate transfer belt is well known.

  In this case, when a plurality of development / transfer devices are arranged along the rotational movement direction of the intermediate transfer belt and a toner image composed of a plurality of colors (for example, full color) is transferred onto the intermediate transfer belt, the color shift is caused. May be a problem.

  As a method of reducing such color misregistration, the amount of deviation between the mark position transferred to the intermediate transfer belt and the ideal position is determined depending on whether the recording material is in contact with the intermediate transfer belt or not. A device that detects and corrects the toner transfer position based on these is known (for example, see Patent Document 1).

JP 2004-139037 A

  By the way, when the recording material is not in contact with the intermediate transfer belt, when the rotational movement speed of the intermediate transfer belt is stable, the color shift is reduced by performing the above-described correction.

  However, even when such a correction method is used, color misregistration may occur when printing is performed after printing has not been performed for a certain period.

  This is because sagging occurs in the intermediate transfer belt between the image carrier and the driving roller or between the image carriers during periods when printing is not performed, and the sagging of the intermediate transfer belt occurs when printing is started. This is due to the gradual elimination.

  That is, as the slack is eliminated, the speed of the intermediate transfer belt also varies so as to become gradually constant. However, color misregistration due to fluctuations in the speed of the intermediate transfer belt occurs until it becomes constant. Such color misregistration is particularly likely to occur in the first recording material immediately after the start of printing. Further, the first color in the most upstream direction in the rotational movement direction of the intermediate transfer belt (the first color in the actual printing order). The color shift is remarkable.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of color misregistration when an intermediate transfer belt is used.

  In order to solve the above problems, the image forming apparatus of the present invention includes an image forming unit capable of forming and superimposing different color toner images, and the image forming unit is rotationally driven at a predetermined speed. In addition, a plurality of image carriers that form toner images of different colors, a charging unit that charges each of the plurality of image carriers to a predetermined potential, and an electrostatic latent image on each of the plurality of charged image carriers. A latent image forming means for forming, a developing means for attaching toner to the electrostatic latent image to form toner images of different colors on the plurality of image carriers, and a surface contacting the surfaces of the plurality of image carriers. An intermediate transfer belt that is rotationally driven in a direction, and a primary transfer unit that primarily nips the intermediate transfer belt between the image carrier and the toner image formed on the image carrier to the intermediate transfer belt. With In the image forming apparatus, at the start of the image forming process, the primary transfer unit is not applied with a voltage immediately after driving the intermediate transfer belt and the image carrier, and the image is formed in at least one of the image forming units. A predetermined voltage having the same polarity as the predetermined potential is applied to the corresponding primary transfer unit from a substantially timing when the charged portion of the carrier starts to contact the intermediate transfer belt.

  According to the image forming apparatus of the first aspect, since the electrostatic adsorption force between the intermediate transfer belt and the image carrier is weakened from the approximate timing at which the image carrier starts to be charged to a predetermined potential, the intermediate transfer belt is slack. Therefore, the intermediate transfer belt can be quickly returned to the predetermined linear velocity, and color misregistration can be reduced from the first sheet.

  The image forming apparatus according to claim 2, wherein an initial voltage of a predetermined voltage is applied to at least one of the primary transfer units at the start of image forming processing immediately after the start of driving the intermediate transfer belt and the image carrier. The initial voltage is a voltage smaller than the absolute value of the predetermined voltage applied with the same polarity as the predetermined potential from the approximate timing when the charged portion of the image carrier starts to contact the intermediate transfer belt. And

  According to the image forming apparatus of the second aspect, since the electrostatic adsorption force between the intermediate transfer belt and the image carrier is weakened from the approximate timing at which the image carrier starts to be charged to a predetermined potential, the intermediate transfer belt is slack. Therefore, the intermediate transfer belt can be quickly returned to the predetermined linear velocity, and color misregistration can be reduced from the first sheet.

  The image forming apparatus according to claim 3, wherein the plurality of image forming units are arranged on a straight line along the rotational movement direction of the intermediate transfer belt, and arranged on the most upstream side in the rotational movement direction of the intermediate transfer belt. The primary transfer means is not applied with a predetermined voltage having the same polarity as the predetermined potential regardless of the approximate timing at which the charged portion of the image carrier starts to contact the intermediate transfer belt, and the other primary transfer means. Is characterized in that the predetermined voltage is applied substantially at the timing when the corresponding charged portion of the image carrier starts to contact the intermediate transfer belt.

  According to the image forming apparatus of the third aspect, by increasing the suction force between the image carrier and the intermediate transfer belt for only the most upstream first color, the first color image carrier becomes the brake and driving force of the intermediate transfer belt. The sag of the intermediate transfer belt can be taken quickly, and color misregistration can be reduced from the first sheet.

  The image forming apparatus according to claim 4, wherein the predetermined voltage applied to the transfer unit from a substantially timing at which a charged portion of the image carrier starts to contact the intermediate transfer belt is equal to a surface potential of the image carrier. The voltage is applied so as to approach the predetermined potential stepwise in accordance with the increase.

  According to the image forming apparatus of the fourth aspect, the intermediate transfer belt can be slackened more quickly, and the color shift can be reduced from the first sheet.

  The image forming apparatus according to claim 5, further comprising: a belt driving roller that rotationally moves the intermediate transfer belt; and a driving auxiliary roller that is disposed so as to face the intermediate transfer belt between the belt driving roller. A potential difference is generated between the belt driving roller and the driving auxiliary roller at least until the image carrier is charged to a predetermined potential.

  According to the image forming apparatus of the fifth aspect, the driving force of the intermediate transfer belt by the belt driving roller can be increased, the slack of the intermediate transfer belt can be taken even faster, and color misregistration from the first sheet can be achieved. Can be reduced.

  7. The image forming apparatus according to claim 6, wherein the driving auxiliary roller is secondary transfer means for transferring the toner image transferred to the intermediate transfer belt onto a recording material, and the toner image on the intermediate transfer belt is transferred to the recording material. The belt driving roller and the secondary transfer means until at least the image carrier is charged to a predetermined potential from a potential difference or current flowing between the belt driving roller and the secondary transfer means when transferring to the belt. The potential difference or current flowing between the two is large.

  According to the image forming apparatus of the sixth aspect, the driving force of the intermediate transfer belt by the belt driving roller can be increased, the slack of the intermediate transfer belt can be taken even more quickly, and color misregistration from the first sheet can be achieved. Can be reduced.

  The image forming apparatus of the present invention can suppress the occurrence of color misregistration when an intermediate transfer belt is used.

1 is an explanatory diagram of an image forming apparatus according to an embodiment of the present invention. 2 is a block diagram of a main part of a control system of the image forming apparatus according to the embodiment of the present disclosure. FIG. 1 is an explanatory diagram illustrating a first embodiment of operation control of an image forming apparatus according to an embodiment of the present invention. FIG. FIG. 10 is an explanatory diagram illustrating a second embodiment of operation control of the image forming apparatus according to an embodiment of the present invention.

  Next, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. The following embodiments are preferred specific examples of the image forming apparatus of the present invention, and may have various technically preferred limitations. However, the technical scope of the present invention is particularly limited to the present invention. As long as there is no description which limits, it is not limited to these aspects. In addition, the constituent elements in the embodiments shown below can be appropriately replaced with existing constituent elements and the like, and various variations including combinations with other existing constituent elements are possible. Therefore, the description of the embodiment described below does not limit the contents of the invention described in the claims.

  FIG. 1 is an explanatory diagram of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a block diagram of a main part of a control system of the image forming apparatus according to an embodiment of the present invention, and FIG. 3 is an embodiment of the present invention. FIG. 4 is an explanatory diagram showing a second embodiment of the operation control of the image forming apparatus according to the embodiment of the present invention.

(overall structure)
As shown in FIG. 1, a tandem color printer 11 as an image forming apparatus according to an embodiment of the present invention includes a paper feed cassette 13 for storing a transfer material (not shown) inside a printer body 12. A sheet feeding section 14 for taking out a transfer material from the sheet feeding cassette 13, an image forming processing section 15 for performing an image forming process on a transfer material supplied from the sheet feeding cassette 13 or a manual feed tray (not shown), and a sheet feeding cassette. 13 or a secondary transfer unit 17 that transfers the toner image image-formed by the image forming processing unit 15 while guiding the transfer material supplied from the manual feed tray 16 through the conveyance path 16, and fixing that fixes the toner image after transfer. And a paper discharge section 19 for discharging the transfer material after fixing.

(Configuration of the image forming processing unit 15)
For example, the image forming processing unit 15 employs a tandem system that performs image forming processing using toner (developer) of four colors of yellow (Y), magenta (M), cyan (C), and black (K). ing. In the following description, only in the case of color designation, the symbol of each arithmetic numeral is attached with a color (Y, M, C, K) in parentheses, and in the common case, only the arithmetic numeral is included. A description will be given with reference numerals. In the present embodiment, the image forming processor 15 corresponds to each color (Y, M, C, K) and a plurality of toner containers 20 (Y, M, C, K) containing supply toner. A plurality of photosensitive drums 21 (Y, M, C, K) made of amorphous silicon that form toner images based on image data included in print data transmitted from a personal computer (not shown) for each color toner; A plurality of developing units 22 (Y, M, C, K) for supplying toner to each photosensitive drum 21 and an endless intermediate transfer belt (image carrier) to which a toner image formed on the photosensitive drum 21 is transferred 23).

(Configuration of Photosensitive Drum 21)
The photosensitive drum 21 as an image carrier is for carrying the toner image of each color on the surface thereof based on the beam of light emitted from the exposure unit 24 and transferring the toner image to the intermediate transfer belt 23. The developing unit 22 is disposed below the intermediate transfer belt 23. Further, around each photosensitive drum 21 (Y, M, C, K), a charger 25 that applies a charging voltage to the photosensitive drum 21 in order of the transfer process to charge the surface to a predetermined potential, and the photosensitive drum. An exposure unit 24 that exposes the surface of 21 to form an electrostatic latent image on the surface; a developing unit 22 that supplies toner to the electrostatic latent image to form a toner image on the photosensitive drum 21; A transfer roller 26 that applies a transfer voltage to transfer the toner image on the photosensitive drum 21 to the intermediate transfer belt 23, a photosensitive member cleaning device 27 that removes toner remaining on the photosensitive drum 21, and the surface of the photosensitive drum 21. A static eliminator 28 that removes the charged charges by irradiating the static elimination light is disposed.

(Configuration of charger 25)
The charger 25 applies a charging voltage while being in contact with the surface of the photosensitive drum 21 to charge to a predetermined polarity / potential. For example, the charging device 25 has a charging bias in which an AC voltage (Vac) is superimposed on a DC voltage (Vdc). Applied.

(Configuration of exposure unit 24)
For example, the exposure unit 24 processes image data included in print data transmitted from a personal computer (PC) (not shown) and irradiates the surface of the photosensitive drum 21 with the laser beam P. In addition to the above-described image data, the print data here includes, for example, data relating to various settings such as the number of image forming processing copies, enlargement / reduction ratio, and image density. In the present embodiment, the exposure unit 24 outputs each beam flux emitted from a plurality of light sources 32 (Y, M, C, K) corresponding to the respective photosensitive drums 21 (Y, M, C, K). Polarizers 33 (YM) and 33 (CK) such as polygon mirrors that share a pair of units, that is, light sources 32 (Y) and (M) and light sources 32 (C) and (K), respectively. ) Irradiates the photosensitive drum 21 (Y, M, C, K) with the laser beam P while performing polarization scanning.

(Developer 22)
The developing units 22 having basically the same configuration are disposed adjacent to each other below the intermediate transfer belt 23 along the rotational movement direction. A detailed description of the configuration of the developing device 22 is omitted.

(Configuration of transfer roller 26)
A transfer voltage having a polarity opposite to that of the toner is applied to the transfer roller 26, and the toner image formed on the surface of the photosensitive drum 21 is transferred to the intermediate transfer belt 23 by the applied voltage.

(Configuration of Photoconductor Cleaning Device 27)
The photoreceptor cleaning device 27 uses, for example, a rotating brush to which a cleaning voltage having a polarity opposite to that of the toner is applied, and adsorbs and removes toner remaining on the photoreceptor drum 21. A detailed description of the configuration of the photoconductor cleaning device 27 is omitted.

(Configuration of static eliminator 28)
For example, an LED light source is used as the static eliminator 28, and the surface of the photosensitive drum 21 is irradiated with static elimination light to remove charged charges (static elimination).

(Configuration of secondary transfer unit 17)
The secondary transfer unit 17 is applied with a secondary transfer voltage having a polarity opposite to that of the toner, and secondarily transfers the toner image from the surface of the intermediate transfer belt 23 onto the transfer material that has been conveyed.

(Configuration of the fixing unit 18)
The fixing unit 18 includes a pair of a fixing roller 34 and a pressure roller 35 that are disposed to face each other with the conveyance path 16 therebetween, and a heating source 36 such as a halogen heater that is disposed inside the fixing roller 34 and directly heats the fixing roller 34. And. The toner image transferred to the transfer material by the secondary transfer unit 17 is fixed to the transfer material by the heating of the fixing roller 34 and the pressure of the pressure roller 35.

(Configuration of the intermediate transfer belt 23)
The intermediate transfer belt 23 is an endless belt disposed in the printer body 12 so as to extend in the horizontal direction, and is circulated and driven in accordance with an image forming operation. Further, the toner image transferred onto the intermediate transfer belt 23 is transferred by the secondary transfer unit 17 to the transfer material conveyed through the conveyance path 16 from the paper feed cassette 13 or the manual feed tray. Further, the intermediate transfer belt 23 is installed so as to be rotatable between a pair of rollers 29, 30. One of the rollers 29 is a driving roller, and the other roller 30 is a tension roller that also serves as a driven roller. Maintained. Further, on the side of the intermediate transfer belt 23 (on the left side facing the roller 30 via the intermediate transfer belt 23 in the figure), the residual toner after transferring the toner image to the transfer material in the secondary transfer unit 17 is intermediate. A cleaning device 31 is provided to remove from the surface of the transfer belt 23.

  The transfer material onto which the toner image has been transferred by the secondary transfer unit 17 is fixed by the fixing unit 18 through the conveyance path 16 and then guided to the paper discharge unit 19 disposed at the end of the conveyance path 16. The paper is discharged and stacked toward a paper discharge tray portion 12 a that is also used as the upper surface of the printer main body 12. The tension mechanism of the roller 30 employs a known technique, and maintains the tensioned state of the intermediate transfer belt 23 by displacing the intermediate transfer belt 23 in the rotational movement direction (directions of arrows a and b in the drawing).

(Cleaning device 31)
The cleaning device 31 extends in the width direction of the intermediate transfer belt 23 (the depth direction perpendicular to the paper surface of FIG. 1 and the transfer material width direction), and is disposed to face the roller 30 via the intermediate transfer belt 23.

(Control circuit part)
As shown in FIG. 2, a color printer 11 according to an embodiment of the present invention includes a receiving unit 51 such as a USB port that receives print data including image data transmitted from a personal computer (not shown), and print data. In addition to the operation unit 52 for various operations including manual selection operation of various modes, a touch panel display unit 53 such as a liquid crystal monitor, and a printer including a program settable on the operation unit 52 and the display unit 53 11 ROM 54 that stores general control programs, RAM 55 that temporarily stores image forming processing conditions and the like that have been changed in the operation unit 52 and display unit 53, and relatively large-capacity data such as received print data A hard disk drive (HDD) 56 for storing the image and an image forming process based on a control program stored in the ROM 54 And a control circuit section 57, the.

  Accordingly, the control circuit unit 57 executes image forming processing from the print data received by the receiving unit 51 based on the control program stored in the ROM 54. Specifically, the control circuit unit 51 includes, for example, a charger 25 that uniformly charges the photosensitive drum 21, an exposure unit 24 that exposes the photosensitive drum 21 to form an electrostatic latent image, and an electrostatic latent image. The developer 22 for visualizing the toner image, the control of the potential and bias of the transfer roller 26 for transferring the visualized toner image to the transfer medium, and the calibration of the erase light quantity of the static eliminator 28 are executed. Further, the control circuit unit 57 functions as a function according to the present invention, as a drum driving motor 58 for rotationally driving the photosensitive drum 21 and a belt 29 for rotationally driving the driving-side roller 29 for rotating the intermediate transfer belt 23. Various devices such as a drive motor 59, peripheral devices (Y, M, C, K) of the photosensitive drum 21 for each color and a secondary transfer unit 17 related to the primary transfer process are controlled. In FIGS. 1 and 2, the peripheral devices (Y, M, C, K) of the photosensitive drum 21 are not shown for the sake of convenience.

  In the above configuration, the photosensitive drum 21 is rotationally driven at a predetermined process speed (circumferential speed) by a drum drive motor 58 (not shown), and the surface thereof is charged by the charger 25.

  An electrostatic latent image is formed on the surface of the charged photosensitive drum 21 by the exposure unit 24. Here, the exposure unit 24 irradiates the surface of the photosensitive drum 21 with the laser beam P based on the image data included in the print data output from the personal computer or the like, and the laser beam on the surface of the photosensitive drum 21. The electrostatic charge image corresponding to the image information is formed by removing the charge of the irradiated portion.

  The electrostatic latent image formed on the surface of the photosensitive drum 21 is developed as an unfixed toner image by electrostatically attaching toner having a charge supplied from the toner container 20 by the developing unit 22. Further, the unfixed toner image is transferred to the transfer material as a transfer image by the transfer roller 26.

  At this time, the photosensitive drum 21 on which the unfixed toner image is transferred to the transfer material is subjected to a removal process of residual toner and the like by the cleaning device 34, and then is neutralized by the static eliminator 28 for charging at the next image formation. Processing is performed.

  Further, the transferred transfer material is fixed by the fixing unit 18, and is then discharged from the paper discharge unit 24 after the normal nip conveyance of the switchback roller pair.

(Example)
Examples of the present invention will be described below. When the receiving unit 51 receives print data from a PC or the like (not shown), the control circuit unit 57 drives the drum driving motor 58 and the belt driving motor 59 at a predetermined timing to rotate the intermediate transfer belt 23 and the photosensitive drum 21. Let

  Here, if the printing is left without printing for a certain period (for example, one week or more), the roller 29 and the photosensitive drum 21 (K), the photosensitive drum 21 (K) and the photosensitive drum 21 (C), The slack of the intermediate transfer belt 23 occurs between the photosensitive drum 21 (C) and the photosensitive drum 21 (M), and between the photosensitive drum 21 (M) and the photosensitive drum 21 (Y), and the roller 29 is moved. Even if it is rotated, the intermediate transfer belt 23 does not immediately reach a predetermined linear velocity. In addition, the linear velocity may vary depending on the location. As a result, color misregistration occurs.

  For example, it is assumed that the surface linear velocity of the intermediate transfer belt 23 at the contact portion between the intermediate transfer belt 23 and the photosensitive drum 21 is set faster than the surface linear velocity of the photosensitive drum 21. In this case, the intermediate transfer belt 23 is pulled by the roller 29 so that the intermediate transfer belt 23 can be easily slackened between the roller 29 and the photosensitive drum 21 (K). It may take time to get it. If there is a potential difference between the surface potential of the photosensitive drum 21 (K) and the transfer roller 26, an attractive force acts between the photosensitive drum 21 (K) and the intermediate transfer belt 23, and the roller 29 is moved to the intermediate transfer belt. This is because the force pulling the belt 23 is less easily transmitted to the upstream side in the rotational movement direction of the intermediate transfer belt 21 than the photosensitive drum 21 (K). Naturally, the sag of the intermediate transfer belt 21 is less likely to be eliminated as the intermediate transfer belt 21 becomes upstream in the rotational movement direction.

(First embodiment)
Therefore, in order to weaken the attractive force, the control circuit unit 57 performs control as shown in FIG. In FIG. 3, the surface potential of the photoconductor drum 21 indicates the surface potential of the photoconductor drum 21 in a portion in contact with the intermediate transfer belt 23.

  First, the initial voltage T1a applied to the transfer roller 26 (Y) from the time t1 at which the drum drive motor 58 and the belt drive motor 59 start to the time t2 at which the photosensitive drum 21 (Y) starts to be charged is the potential V1a. Make it near. Most preferred is T1a = V1a. The potential V1a is an expected surface potential of the photosensitive drum 21 (Y) before the start of charging, and in most cases is about 0 V, so no voltage is applied to the transfer roller 26 (Y).

  From time t2 to time t3 when the photosensitive drum 21 (Y) starts to be charged by applying a voltage to the charger 25 (Y), transfer is performed in accordance with the increase in the surface potential of the photosensitive drum 21 (Y). The voltage applied to the roller 26 (Y) also increases. At this time, the predetermined voltage T2a when the surface potential of the photosensitive drum 21 (Y) becomes the predetermined potential V2a is preferably V2a = T2a. For example, V2a = T2a = 600V. Alternatively, the predetermined voltage T2a may be applied to the transfer roller 26 (Y) at a stretch before and after the time t2 or the time t3. When applying the predetermined voltage T2a at once, it is preferable to be simultaneously with the time t3.

  The predetermined voltage T2a applied to the transfer roller 26 (Y) is set near the predetermined potential V2a from the time t3 to the time t4 when the surface potential of the photosensitive drum 21 (Y) becomes the predetermined potential V2a. For example, it is kept at 600V.

  At time t4, a transfer voltage T3a is applied to the transfer roller 26 (Y) in order to transfer the toner developed on the photosensitive drum 21 (Y) to the intermediate transfer belt 23. For example, -1000V.

  By doing so, until the transfer voltage T3a for transferring the toner to the intermediate transfer belt 23 is applied to the transfer roller 26 (Y), the gap between the photosensitive drum 21 (Y) and the intermediate transfer belt 23 is increased. Electrostatic adsorption power can be weakened.

  Thereafter, the transfer rollers 26 (M) to 26 (K) are similarly controlled according to the surface potential of the photosensitive drums 21 (M) to 21 (K).

  As a result, the slack of the intermediate transfer belt 23 between the roller 29 and the photosensitive drum 21 (Y) can be taken before the toner is transferred to the intermediate transfer belt 23, and the linear velocity is also stabilized. An image with little color misregistration can be obtained from the first sheet.

(Second Embodiment)
Next, a second embodiment of control in the control circuit unit 57 is shown in FIG. Conditions such as potentials V1a to V1d, V2a to V2d, voltages Ta1 to T1d, T2a to T2d, and times t1 to t3 are the same as those in FIG. As shown in FIG. 4, depending on the characteristics of the photosensitive layer, the surface potential of the photosensitive drum 21 (Y) may not rise to V2a by one charge, but may gradually increase to V2a by several turns of charging. is there. In this case, the voltage T2a applied to the transfer roller 26 (Y) during that time is also raised stepwise in accordance with the surface potential of the photosensitive drum 21 (Y). By doing so, the potential difference between the transfer roller 26 (Y) and the photosensitive drum 21 (Y) can be reduced, and the electrostatic adsorption force can be kept weak.

  In the embodiment of FIG. 4, the application is applied to the transfer roller 26 (Y) from the time t1 when the drum driving motor 58 and the belt driving motor 59 start to the time t2 when the photosensitive drum 21 (Y) starts charging. The initial voltage T1a to be applied is not zero but a voltage having an absolute value of about 100V, which is considerably lower than the absolute value 600V of T2a, is applied. The initial voltages Ta1 and T1c of the transfer rollers 26 (Y) and 26 (C) have the same polarity as Ta2, and the initial voltages T1b and T1d of the transfer rollers 26 (M) and 26 (K) have voltages opposite to those of T2a. is there. While the initial voltages T1a to T1d are applied, the surface potential of the photosensitive drum is almost zero, and the absolute value is small, so that the electrostatic adsorption force of the intermediate transfer belt is maintained in a relatively weak state. On the other hand, by applying the initial voltages T1a to T1d, the residual toner charged on the intermediate transfer belt and charged to the positive polarity or reverse polarity can be reversely transferred to the photosensitive drum by electrostatic force and removed. . This makes it possible to form a good image without fogging.

  In the control shown in FIGS. 3 and 4, only the uppermost transfer roller 26 (Y) in the rotational movement direction of the intermediate transfer belt 21 is not subjected to such control, and the photosensitive drum 21 (Y) in that portion. The same effect can be obtained by making the suction force of the intermediate transfer belt 23 work, using the brake as a brake, and pulling the intermediate transfer belt 23 with the roller 29 to take a slack.

  Further, when this control is performed, the current or potential difference between the secondary transfer unit 17 and the roller 29 is made larger than when the toner is transferred to the recording material, so that the intermediate transfer belt 23 is driven by the roller 29. As the force increases, the slack of the intermediate transfer belt 23 between the roller 29 and the photosensitive drum 21 (Y) can be quickly removed, and the linear velocity is also stabilized. An image with little color misregistration can be obtained from the first sheet.

11. Color printer (image forming apparatus)
17 ... secondary transfer section (secondary transfer means)
21 ... Photosensitive drum (image carrier)
22. Developing device (developing means)
23 ... Intermediate transfer belt 24 ... Exposure unit (latent image forming means)
26: Transfer roller (primary transfer means)
29 ... Roller (belt drive roller)

Claims (6)

Each has an image forming unit capable of forming and superposing different color toner images,
A plurality of image carriers that form toner images of different colors while being rotationally driven at a predetermined speed, a charging unit that charges each of the plurality of image carriers to a predetermined potential, and a plurality of charged units A latent image forming unit that forms an electrostatic latent image on each of the image carriers, and a developing unit that attaches toner to the electrostatic latent images to form toner images of different colors on the plurality of image carriers, respectively. An intermediate transfer belt that is in contact with the surfaces of the plurality of image carriers and is rotationally driven in the same direction, and a toner image formed on the image carrier by niping the intermediate transfer belt with the image carrier. In an image forming apparatus comprising a primary transfer means for primary transfer to the intermediate transfer belt,
At the start of the image forming process, the primary transfer unit is not applied with a voltage immediately after the start of driving the intermediate transfer belt and the image carrier, and at least one charged portion of the image carrier in the image forming unit. An image forming apparatus, wherein a predetermined voltage having the same polarity as the predetermined potential is applied to the corresponding primary transfer unit from a substantially timing when the toner starts to contact the intermediate transfer belt. An image forming unit capable of forming and superimposing different color toner images,
A plurality of image carriers that form toner images of different colors while being rotationally driven at a predetermined speed, a charging unit that charges each of the plurality of image carriers to a predetermined potential, and a plurality of charged units A latent image forming unit that forms an electrostatic latent image on each of the image carriers, and a developing unit that attaches toner to the electrostatic latent images to form toner images of different colors on the plurality of image carriers, respectively. An intermediate transfer belt that is in contact with the surfaces of the plurality of image carriers and is rotationally driven in the same direction, and a toner image formed on the image carrier by niping the intermediate transfer belt with the image carrier. In an image forming apparatus comprising a primary transfer means for primary transfer to the intermediate transfer belt,
An initial voltage of a predetermined voltage is applied to at least one of the primary transfer units at the start of the image forming process immediately after the start of driving the intermediate transfer belt and the image carrier, and the initial voltage is applied to the image carrier. images forming device you wherein the charged portion is less voltage than the absolute value of the predetermined voltage applied at the predetermined potential of the same polarity from substantially the timing to start contact with the intermediate transfer belt.   A plurality of the image forming units are arranged on a straight line along the rotational movement direction of the intermediate transfer belt, and the primary transfer unit disposed on the most upstream side in the rotational movement direction of the intermediate transfer belt includes the image Regardless of the timing at which the charged portion of the carrier starts to contact the intermediate transfer belt, a predetermined voltage having the same polarity as the predetermined potential is not applied, and the other charged portions of the image carrier are not applied to the primary transfer means. 3. The image forming apparatus according to claim 1, wherein the predetermined voltage is applied substantially at a timing when the toner starts to contact the intermediate transfer belt.   The predetermined voltage applied to the transfer means from substantially the timing when the charged portion of the image carrier starts to contact the intermediate transfer belt is gradually increased to the predetermined potential as the surface potential of the image carrier increases. The image forming apparatus according to claim 1, wherein the image forming apparatus is applied so as to approach the image forming apparatus. A belt driving roller for rotating the intermediate transfer belt;
A drive assisting roller disposed oppositely to sandwich the intermediate transfer belt with the belt drive roller,
5. The image formation according to claim 1, wherein a potential difference is generated between the belt driving roller and the driving auxiliary roller at least until the image carrier is charged to a predetermined potential. apparatus. The driving auxiliary roller is secondary transfer means for transferring the toner image transferred to the intermediate transfer belt onto a recording material, and when transferring the toner image of the intermediate transfer belt to the recording material, The potential difference or current to be generated between the belt driving roller and the secondary transfer means is at least until the image carrier is charged to a predetermined potential rather than the potential difference or current to be generated between the secondary transfer means and the secondary transfer means. The image forming apparatus according to claim 5, wherein the image forming apparatus is large.

Images