JP5043524B2 - Image forming apparatus - Google Patents

Description

  The present invention employs an intermediate transfer method in which a toner image formed on an image carrier using an electrophotographic method or an electrostatic recording method is primarily transferred to an intermediate transfer member and then secondarily transferred to a transfer material. The present invention relates to an image forming apparatus such as a printer or a printer.

  Conventionally, an image forming apparatus using an intermediate transfer member is known as an image forming apparatus such as a copying machine or a laser beam printer. This image forming apparatus forms a color image (multiple image) or the like on a transfer material by a primary transfer process and a secondary transfer process.

  That is, first, as a primary transfer step, a toner image as a transferable image formed on the surface of a photosensitive member as a first image carrier is transferred to an intermediate transfer member as a second image carrier. This primary transfer process is repeatedly performed for a plurality of color toner images, thereby forming a plurality of color toner images on the surface of the intermediate transfer member.

  Thereafter, as a secondary transfer step, the toner images of a plurality of colors formed on the surfaces of these intermediate transfer members are collectively transferred onto the surface of a transfer material such as paper.

  The plurality of color toner images transferred to the transfer material at a time are then melted and mixed by the fixing means and fixed to the transfer material, thereby forming, for example, a full-color image as a recorded image on the transfer material.

  On the other hand, as a method for recovering toner (residual toner) remaining on the intermediate transfer member after the secondary transfer step, the residual toner is charged to a polarity opposite to the normal charging polarity by a charging means, and is exposed in the primary transfer step. A method of reverse transcription to the body and recovery is known.

  Patent Document 1 proposes the following method for removing the residual toner on the intermediate transfer member. Specifically, the image forming apparatus described in Patent Document 1 has a configuration as shown in FIG. That is, the image forming apparatus described in Patent Document 1 includes a plurality of process cartridges 214a to 214d, each of which forms an image forming unit Sa to Sd. Each of the process cartridges 214a to 214d includes photosensitive drums 201a to 201d that carry a toner image, cleaning devices 271a to 271d that remove residual toner, and waste toner containers 272a to 272d that collect residual toner. The capacity of the waste toner containers 272a and 272d of the process cartridge 214a for the first color transferred first to the intermediate transfer member 206 and the process cartridge 214d for black color with the highest use frequency is set to the other waste toner container 272b. The capacity is larger than the capacity of 272c.

  With the above-described configuration, the image forming apparatus described in Patent Document 1 reduces the frequency of replacing the infrequently used color cartridges, and reduces unnecessary cartridge replacement, so that unnecessary cartridge replacement can be performed even when using a single color. It is possible to suppress the cost.

  On the other hand, Patent Document 2 proposes a method in which a CPU selects a photoconductor on which residual toner on a transfer belt is to be collected based on image data. Specifically, in the image forming apparatus described in Patent Document 2, when the integrated value of the used toner amount obtained from the image data exceeds a certain amount, the process cartridge uses the remaining toner on the transfer belt. Do not collect.

With the above-described configuration, the image forming apparatus described in Patent Document 2 can prevent residual toner from being biased and collected in a waste toner tank in a specific process cartridge, and can effectively use a plurality of waste toner tanks.
JP 2004-021134 A JP 2001-175047 A

  However, the above-described conventional image forming apparatus has problems that it is difficult to reduce the size of the entire apparatus or that color misregistration deteriorates.

  More specifically, according to the method of Patent Document 1, since the residual toner is collected in a specific process cartridge, the sizes of the individual process cartridges are different.

  Conventionally, in a so-called in-line type color image forming apparatus in which a plurality of image forming units are juxtaposed, as a method for reducing the color misregistration of each color, the circumference of the driving roller and the distance between each process cartridge (1 In general, the pitch between the next transfer) is approximately an integer multiple. This is performed for the purpose of canceling fluctuations in the belt peripheral speed due to shake of the driving roller by matching the image writing position of each color with a certain point of the driving roller.

  In the method described in Patent Document 1, since the sizes of the individual process cartridges are different, it is difficult to employ the configuration for reducing the color shift as described above, and thus the color shift is likely to deteriorate. Also, when collecting residual toner in a specific process cartridge, the process cartridge becomes unnecessarily large, and the entire apparatus tends to be large.

  Furthermore, according to the method of Patent Document 2, the number of high-voltage power supplies is large, the apparatus main body is complicated, and the entire apparatus becomes large.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of collecting the toner on the intermediate transfer member by reverse transfer to the image carrier with a configuration advantageous for simplifying the apparatus configuration and reducing the size of the apparatus main body. That is.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides a plurality of image carriers that carry toner images, a movable intermediate transfer member to which toner images on the plurality of image carriers are primarily transferred, and the plurality of image carriers. A plurality of primary transfer means provided corresponding to each of the plurality of primary transfer means for primarily transferring toner images on the plurality of image carriers onto the intermediate transfer body, and a voltage applied to the plurality of primary transfer means. A plurality of voltage output means for outputting, and a secondary transfer means for secondary transfer of the toner image on the intermediate transfer member to a transfer material, each of which includes a plurality of the image carrier and the primary transfer means. An image forming unit is disposed along the moving direction of the intermediate transfer member, and the primary transfer and the toner on the intermediate transfer member are generated by a voltage output from the voltage output unit and applied to the primary transfer unit. In an image forming apparatus that performs reverse transfer to the image carrier. The voltage output unit includes a first voltage output unit that outputs a voltage of a first polarity to the primary transfer unit of at least one of the plurality of image forming units, and the plurality of the plurality of image forming units. A second voltage output unit that outputs the voltage of the first polarity to the primary transfer unit of at least two image forming units different from the at least one image forming unit, A third voltage output section that is connected in series to both the first voltage output section and the second voltage output section and outputs a voltage having a second polarity that is opposite to the first polarity. And an image forming apparatus.

  According to the present invention, the toner on the intermediate transfer member can be reversely transferred to the image carrier and recovered with a configuration advantageous for simplifying the device configuration and reducing the size of the device main body.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
FIG. 1 is a schematic diagram of an overall configuration of an embodiment of an image forming apparatus according to the present invention. The image forming apparatus 100 of this embodiment is a laser beam printer using an electrophotographic system. The image forming apparatus 100 according to the present exemplary embodiment temporarily superimposes the toner images of the respective colors formed according to the image information decomposed into the color components of yellow, magenta, cyan, and black onto the intermediate transfer member by primary transfer. An intermediate transfer method is used in which the image is later transferred to a transfer material. First, the overall configuration and operation of the image forming apparatus of this embodiment will be described.

[overall structure]
The image forming apparatus 100 includes four image forming units (stations) for forming toner images of yellow, magenta, cyan, and black as a plurality of image forming units, that is, first, second, and third. And fourth stations Sa, Sb, Sc, Sd. In this embodiment, the configuration and operation of each of the stations Sa to Sd are substantially the same except for the color of the toner image formed by each station and the details of the power supply to the primary transfer unit described later in detail. . Therefore, in the following description, if there is no particular need to distinguish, the subscripts a, b, c, and d given to the reference numerals are omitted to indicate that they are elements provided for any of the colors. I will explain it.

  The station S includes a drum-type electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum 1. The photosensitive drum 1 is rotationally driven in a direction indicated by an arrow (counterclockwise) by a driving unit (not shown). The station S has, around the photosensitive drum 1, a charging roller (primary charger) 2 as primary charging means, an exposure device (laser scanner) 3 as exposure means, and a developing device 4 as development means. Further, the station S includes a primary transfer roller 5 as a primary transfer unit and a cleaning device 7 as a cleaning unit around the photosensitive drum 1. The cleaning device 7 includes a cleaning blade 71 that scrapes and removes toner on the surface of the photosensitive drum 1 as a cleaning member, and a waste toner container 72 that collects toner removed by the cleaning blade 71.

  The surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. Next, the exposure device 3 irradiates the surface of the photosensitive drum 1 with laser light L according to the image information, and an electrostatic image (latent image) according to the image information is formed on the photosensitive drum 1. When the photosensitive drum 1 further advances in the direction of the arrow shown in the figure, the electrostatic image formed on the photosensitive drum 1 according to the image information is developed as a toner image by the developing device 4 and visualized.

  In this embodiment, the developing device 4 develops the electrostatic image by a reversal development method. In other words, the developing device 4 applies the toner charged to a normal polarity (negative polarity in this embodiment) that is the same as the charging polarity of the photosensitive drum 1 on the photosensitive drum 1 whose charge has been attenuated by exposure after being charged. A toner image is formed on the photosensitive drum 1 by being attached to the portion (bright portion). Although the developing device 4 is not limited to this, for example, a non-magnetic one-component developer, that is, a toner can be suitably used as the developer.

  An intermediate transfer belt 6 as an intermediate transfer member is disposed so as to face the photosensitive drum 1 of each station S on the downstream side of the developing position in the rotation direction of the photosensitive drum 1. In this embodiment, the intermediate transfer belt 6 has a cylindrical shape, that is, an endless belt shape, which is stretched around a driving roller 61, a secondary transfer counter roller 62 and a tension roller 63 as support rollers as a plurality of support members. It is a film. The intermediate transfer belt 6 moves (rotates) in the illustrated arrow direction (clockwise) at substantially the same peripheral speed (surface movement speed) as that of the photosensitive drum 1.

  A primary transfer roller 5 as a primary transfer unit is disposed at a position facing the photosensitive drum 1 with the intermediate transfer belt 6 interposed therebetween. The primary transfer roller 5 presses the intermediate transfer belt 6 toward the photosensitive drum 1 on the inner peripheral surface side of the intermediate transfer belt 6, and a primary transfer portion (primary transfer portion) where the intermediate transfer belt 6 and the photosensitive drum 1 are in contact with each other. A transfer nip portion N1 is formed. Then, the toner image carried on the photosensitive drum 1 is transferred to the photosensitive drum 1 and the intermediate transfer belt 6 by a primary transfer bias output from a primary transfer voltage output means 50 described later and applied to the primary transfer roller 5. With this rotation, the primary transfer is performed on the outer peripheral surface of the intermediate transfer belt 6. Due to the primary transfer bias, an electric field is formed in the primary transfer portion N1 in the direction (polarity) in which the toner charged to the normal charging polarity (negative polarity in this embodiment) is directed from the photosensitive drum 1 to the intermediate transfer belt 6. Is done.

  In the primary transfer process, toner (residual toner) remaining on the photosensitive drum 1 without being transferred to the intermediate transfer belt 6 is removed and collected by the cleaning device 7.

  The charging, exposure, development, and primary transfer processes as described above are performed for each color of yellow, magenta, cyan, and black in the first to fourth stations Sa to Sd. As a result, a plurality of color toner images (for example, four color toner images of yellow, magenta, cyan, and black in the case of a full color image) are formed on the intermediate transfer belt 6 in an overlapping manner.

  A secondary transfer roller 8 as a secondary transfer unit is disposed at a position facing the secondary transfer counter roller 62 with the intermediate transfer belt 6 interposed therebetween. The transfer material P is supplied at a predetermined timing to a secondary transfer portion (secondary transfer nip portion) N2 where the intermediate transfer belt 6 and the secondary transfer roller 8 abut. At the same time, the secondary transfer bias output from the secondary transfer voltage output means 80 is applied to the secondary transfer roller 8. As a result, the toner image is secondarily transferred from the intermediate transfer belt 6 to the transfer material P. Due to the secondary transfer bias, an electric field is formed in the secondary transfer portion N1 in the direction (polarity) in which the toner charged to the normal charging polarity (negative polarity in this embodiment) is directed from the intermediate transfer belt 6 to the transfer material P. Is done.

  The transfer material P is supplied from the cassette 12 as a transfer material storage unit to the secondary transfer unit N2 at a predetermined timing by a supply roller 11 as a transfer material supply unit, a registration roller 10, and the like.

  In the secondary transfer process, toner (residual toner) that is not transferred to the transfer material P and remains on the intermediate transfer belt 6 is reversely transferred to the photosensitive drum 1 of the station S, as will be described in detail later. It is removed and collected by the cleaning device 7 of the station S. Typically, the residual toner on the intermediate transfer belt 6 is charged by a cleaning roller 9 as an intermediate transfer member cleaning unit (toner charging unit), and is reversely transferred to the photosensitive drum 1 at the next primary transfer. . At this time, the residual toner adhering to the photosensitive drum 1 is removed and collected by a cleaning device 7 as a cleaning unit (photoconductor cleaning unit).

  In this embodiment, the photosensitive drum 1 and the charging roller 2, the developing device 4, and the cleaning device 7 as process means acting on the photosensitive drum 1 are integrally formed into a cartridge to form a process cartridge 14. The process cartridge 14 is detachable from the image forming apparatus main body (apparatus main body). Therefore, by exchanging the process cartridge 14, the waste toner container 72 from which residual toner and the like are collected can be exchanged together. The process cartridge is an image forming apparatus in which an electrophotographic photosensitive member and at least one of a charging unit, a developing unit, and a cleaning unit that act on the electrophotographic photosensitive member are integrally formed into a cartridge. It can be attached to and detached from the main body.

  In the present embodiment, the process cartridges 14a to 14d contain yellow toner, magenta toner, cyan toner, and black toner in order from the upstream in the moving direction of the intermediate transfer belt 6, respectively.

[Cleaning of intermediate transfer belt]
Next, a method for cleaning the intermediate transfer belt 6 will be described in detail with reference to FIG. FIG. 2 is a schematic configuration diagram of a main part showing in more detail the primary transfer voltage output means in the image forming apparatus 100 of the present embodiment.

A. Primary transfer roller The primary transfer roller 5 which is a primary transfer member (rotating member) as a primary transfer means has a volume resistivity of 10 ⁵ to 10 ⁹ Ωcm and a rubber hardness of 30 ° (Asker C hardness meter). An elastic roller was used. The primary transfer roller 5 is pressed against the photosensitive drum 1 through the intermediate transfer belt 6 with a total pressure of about 9.8 N. The primary transfer roller 5 is driven to rotate as the intermediate transfer belt 6 rotates. The primary transfer roller 5 is configured to be able to apply a voltage of −2.0 to 3.5 kV output from a primary transfer voltage output device 50 as a primary transfer voltage output unit.

  Here, in this embodiment, as shown in FIG. 2, the primary transfer voltage output device 50 has a common voltage output unit (high voltage power supply).

  That is, in the primary transfer voltage output device 50 that applies a voltage to the primary transfer roller 5, a high voltage power source that generates a positive bias voltage and a high voltage power source that generates a negative bias voltage are arranged in series. The number of high-voltage power supplies that generate a positive bias voltage and the number of high-voltage power supplies that generate a negative bias voltage are smaller than the number of image forming units, respectively.

  More specifically, in this embodiment, first, the primary transfer voltage output device 50 outputs (generates) a positive polarity (first polarity) voltage having a polarity opposite to the normal charging polarity of the toner. Voltage output section (positive bias generating high voltage power supply) 51. The first voltage output unit 51 is an independent voltage output unit of the first station Sa.

  The primary transfer voltage output device 50 outputs a second voltage output unit (positive bias generation high voltage) that outputs (generates) a positive polarity (first polarity) voltage having a polarity opposite to the normal charging polarity of the toner. Power source) 52. The second voltage output unit 52 is shared by the second, third, and fourth stations Sb, Sc, Sd. In the second, third, and fourth stations Sb, Sc, and Sd, there are cases where a plurality of colors are superimposed at the time of primary transfer, and usually a setting different from that of the first station Sa is required. The output unit is separated from the first station Sa.

  Further, the primary transfer voltage output device 50 outputs a third voltage output unit (negative bias generation high-voltage power supply) that outputs (generates) a negative polarity (second polarity) voltage having the same polarity as the normal charging polarity of the toner. ) 53. The third voltage output unit 53 is shared by all the first to fourth stations Sa to Sd.

  The high-voltage power source for generating the positive polarity bias voltage and the high-voltage power source for generating the negative polarity bias voltage are connected in series, and the positive polarity bias voltage and the negative polarity bias voltage are superimposed to be the primary. The transfer roller 5a to 5d can be applied. That is, the third voltage output unit 53 is connected in series to both the first voltage output unit 51 and the second voltage output unit 52.

  As a result, the apparatus configuration can be simplified and the apparatus main body can be reduced in size, and various residual toners as described later can be collected in the waste toner containers 72 of the process cartridges 14 as uniformly as possible. A recovery operation can be realized. Since each process cartridge 14 does not need to have a different size, a configuration for reducing the color misregistration as described above, which is common in an in-line image forming apparatus, can be easily adopted to achieve good image quality. Can be maintained.

B. Intermediate transfer belt The intermediate transfer belt 6 as an intermediate transfer member is an endless belt made of polyvinylidene fluoride (PVDF) having a thickness of 100 μm and a volume resistivity adjusted to 10 ¹¹ Ωcm by mixing a conductive agent. Shaped film was used. The intermediate transfer belt 6 is stretched around three axes of a drive roller 61, a secondary transfer counter roller 62, and a tension roller 63, and is urged by the tension roller 63 with a total pressure of about 60N.

C. Secondary transfer roller The secondary transfer roller 8 which is a secondary transfer member (rotating member) as a secondary transfer means has a volume resistivity of 10 ⁵ to 10 ⁹ Ωcm and a rubber hardness of 30 ° (Asker C hardness meter). An elastic roller was used. The secondary transfer roller 8 is pressed against the secondary transfer counter roller 62 via the intermediate transfer belt 6 with a total pressure of about 39.2N. The secondary transfer roller 8 is driven to rotate as the intermediate transfer belt 6 rotates. The secondary transfer roller 8 is configured to be able to apply a voltage of −2.0 to 4.0 kV output from a secondary transfer voltage output device (positive bias generation high voltage power supply) 80 as a secondary transfer voltage output means. It has become. More specifically, in this embodiment, the secondary transfer voltage output device 80 has a positive voltage output unit (positive bias generation high voltage power source) 81 and a negative voltage output as a DC voltage output unit that outputs (generates) a DC voltage. Part (negative bias generation high voltage power supply) 82. The positive voltage output unit 81 generates a positive (first polarity) voltage having a polarity opposite to the normal charging polarity of the toner. The negative polarity voltage output unit 82 generates a negative polarity (second polarity) voltage having the same polarity as the normal charging polarity of the toner. The secondary transfer voltage output device 80 includes a switching unit 83 that switches the polarity of the DC voltage output from the DC voltage output unit.

D. Cleaning roller An elastic roller having a volume resistivity of 10 ⁵ to 10 ⁹ Ωcm was used as the cleaning roller 9 which is a toner charging member (rotating member) as toner charging means. The cleaning roller 9 is pressed against the driving roller 61 via the intermediate transfer belt 6 and is rotated following the rotation of the intermediate transfer belt 6. Further, the cleaning roller 9 can be applied with a voltage obtained by superimposing an AC voltage and a DC voltage output from a toner charging voltage output device 90 serving as a toner charging voltage output unit, or a DC voltage. ing. In this embodiment, the toner charging voltage output device 90 is configured to be able to apply an AC voltage (rectangular wave in this embodiment) having a frequency of 1000 Hz and a peak-to-peak voltage of 2000 V and a DC voltage of -2.0 to +2.0 kV. It has become. More specifically, in this embodiment, the toner charging voltage output device 90 includes a positive voltage output unit (positive bias generation high-voltage power supply) 91 and a negative voltage output unit as a DC voltage output unit that outputs (generates) a DC voltage. (Negative bias generation high voltage power source) 92 is provided. The positive voltage output unit 91 generates a positive (first polarity) voltage having a polarity opposite to the normal charging polarity of the toner. The negative polarity voltage output unit 92 generates a negative polarity (second polarity) voltage having the same polarity as the normal charging polarity of the toner. In addition, the toner charging voltage output device 90 includes switching means 93 that switches the polarity of the DC voltage output from the DC voltage output unit. Further, the toner charging voltage output device 90 includes an AC voltage output unit (AC bias generating high voltage power source) 94 that outputs an AC voltage.

E. Cleaning operation of the intermediate transfer belt The optimal cleaning operation of the intermediate transfer belt 6 greatly depends on the polarity and amount of toner on the intermediate transfer belt 6 and is a special method in various situations during image formation (printing). Can be used. In this embodiment, the cleaning operation of the intermediate transfer belt 6 is roughly classified into the following four types.

(1-1) Cleaning during normal image formation During normal image formation, a superposition of a rectangular wave having a frequency of 1000 Hz and a peak-to-peak voltage of 2000 V and a DC voltage of 1.3 kV is applied to the cleaning roller 9 from the toner charging voltage output device 90. Apply voltage. As a result, a positive charge is imparted to the residual toner remaining on the intermediate transfer belt 6 without being subjected to secondary transfer. Further, during normal image formation, a positive bias voltage is applied to the primary transfer roller 5. Accordingly, the residual toner on the intermediate transfer belt 6 charged to the positive polarity by the cleaning roller 9 is reversely transferred to the photosensitive drum 1 at the next primary transfer.

(1-2) Toner Cleaning from the Cleaning Roller The toner on the intermediate transfer belt 6 before the secondary transfer process is normally charged to a negative polarity which is a normal charging polarity of the toner. However, since a positive bias voltage is applied in the secondary transfer step, both positive and negative polarities are exerted on the intermediate transfer belt 6 after the secondary transfer step due to the influence of the positive bias voltage. Toner is present. Further, since a positive bias voltage is applied to the cleaning roller 9, the negative residual toner easily adheres to the cleaning roller 9. For this reason, as a predetermined timing at the time of non-image formation, when one print job (a series of image forming operations on one or a plurality of transfer materials according to one image formation start instruction) is completed, the cleaning roller 9 The remaining toner adhering to the toner is discharged to the intermediate transfer belt 6.

  Specifically, as a predetermined timing at the time of non-image formation, the toner charging voltage output device 90 to −1 is applied to the cleaning roller 9 during a post-rotation operation that is a rearranging operation after the image forming operation in one print job is completed. Apply a voltage of .5 kV. As a result, the negative toner is discharged from the cleaning roller 9 onto the intermediate transfer belt 6. The residual toner discharged on the intermediate transfer belt 6 is applied with a negative polarity bias voltage having a reverse polarity (that is, the same polarity as the normal charging polarity of the toner) to the primary transfer roller 5 at the time of image formation. Thus, it is possible to reversely transfer to the photosensitive drum 1 and collect it.

(1-3) Cleaning during Jam (Paper Jam) When a jam occurs, there are many cases where untransferred toner remains on the intermediate transfer belt 6 without passing through the secondary transfer process. Further, this toner is usually much larger than the amount of residual toner remaining on the intermediate transfer belt 6 after the secondary transfer process. For this reason, during the jam cleaning, the intermediate transfer belt 6 is cleaned by rotating the intermediate transfer belt 6 a plurality of times.

  Specifically, in the present embodiment, the toner on the intermediate transfer belt 6 is cleaned by rotating the intermediate transfer belt 6 three times at the time of non-image formation until the image can be formed after the jam processing.

  In the first round, a negative bias voltage is applied to the cleaning roller 9 and the secondary transfer roller 8, and the toner on the intermediate transfer belt 6 passes through the secondary transfer roller 8 and the cleaning roller 9. Thereafter, when this toner comes to the image forming section (station), a negative bias voltage is applied to the primary transfer roller 5 to electrostatically collect it on the photosensitive drum 1.

  In the second round, a positive bias voltage is applied to the cleaning roller 9 to charge the toner on the intermediate transfer belt 6 to a positive polarity, and then a positive bias voltage is applied to the primary transfer roller 5. Then, it is reversely transferred to the photosensitive drum 1 and collected.

  On the third round, the discharge process of the toner adhering to the cleaning roller 9 is performed in the same manner as the operation (1-2).

(1-4) Regular cleaning If the number of image formations increases during continuous image formation, charging of the residual toner on the intermediate transfer belt 6 occurs due to the influence of toner adhering to the cleaning roller 9, and gradually becomes intermediate. The residual toner remaining on the transfer belt 6 without being cleaned increases. In this embodiment, as a predetermined timing at the time of non-image formation, cleaning is forcibly performed when a predetermined number of images are continuously formed (in this embodiment, when 50 images are continuously formed). Do. The periodical cleaning operation is the same as the above-described operation (1-3).

F. Specific Example In the present example, the cleaning operation of the above-described four types of intermediate transfer belt 6 was performed with the settings shown more specifically below in order to collect toner as uniformly as possible with the four process cartridges 14a to 14d. . And the effect was confirmed in a normal environment.

(1-1) Cleaning during normal image formation (full color) During normal image formation, all residual toner on the intermediate transfer belt 6 is collected at the first station Sa. This is because it is preferable to collect the residual toner at the first station Sa because the method of collecting the residual toner by reverse transfer at the same time as the primary transfer is adopted.

  The setting of the bias voltage output from the primary transfer voltage output device 50 to the primary transfer roller 5 at each station S and the operation status at each station S are as shown in Table 1 below.

  The column “Positive Bias” in Table 1 indicates the set value of the positive bias voltage output by the first voltage output unit 51 for the first station Sa, and the second to fourth stations Sb to Sd. Indicates the set value of the positive bias voltage output by the second voltage output unit 52. In addition, the “negative bias” column in Table 1 indicates a set value of the negative polarity bias voltage output from the third voltage output unit 53. In the column of “primary transfer output” in Table 1, the positive transfer bias voltage and the negative bias voltage of each setting described above are superimposed and output from the primary transfer voltage output device 50. The setting value of the bias voltage applied to the primary transfer roller 5 of the station S is shown. The same applies to Tables 2 to 4 below. In this embodiment, it is assumed that the photosensitive drum 1 is charged to the same potential (negative polarity in this embodiment) as that during normal image formation in any case.

  In this case, in the primary transfer portions N1a to N1d of the first to fourth stations Sa to Sd, the toner charged to a polarity opposite to the normal charging polarity is directed from the intermediate transfer belt 6 to the photosensitive drums 1a to 1d ( Polarity) electric field is formed.

  It was confirmed that the residual toner on the intermediate transfer belt 6 can be collected only by the first station Sa with the above setting.

(1-2) Cleaning of toner discharged from the cleaning roller The toner discharged from the cleaning roller 9 passes through the first station Sa and is collected almost evenly at the second, third, and fourth stations Sb to Sd.

  Table 2 below shows the setting of the bias voltage output from the primary transfer voltage output device 50 to the primary transfer roller 5 at each station S and the operation status at each station S at this time.

  In this case, in the primary transfer portion N1a of the first station Sa, an electric field is formed in a direction (polarity) in which the toner charged to the normal charging polarity is directed from the photosensitive drum 1a to the intermediate transfer belt 6. On the other hand, in the primary transfer portions N1b to N1d of the second to fourth stations Sb to Sd, an electric field in a direction (polarity) that directs the toner charged to the normal charging polarity from the intermediate transfer belt 6 to the photosensitive drums 1b to 1d. It is formed.

  With the above setting, it was confirmed that the toner discharged from the cleaning roller 9 can pass through the first station Sa and be collected almost evenly at the second, third, and fourth stations Sb to Sd. .

(1-3) Cleaning at Jam (Paper Jam) In this case as well, the toner on the intermediate transfer belt 6 passes through the first station Sa and is almost evenly distributed at the second, third, and fourth stations Sb to Sd. to recover. It should be noted that individual control is performed according to the number of rotations of the intermediate transfer belt 6, and collection is performed with the following settings.

[First lap]
The negative toner on the intermediate transfer belt 6 is collected.

  In this case, in the primary transfer portion N1a of the first station Sa, an electric field is formed in a direction (polarity) in which the toner charged to the normal charging polarity is directed from the photosensitive drum 1a to the intermediate transfer belt 6. On the other hand, in the primary transfer portions N1b to N1d of the second to fourth stations Sb to Sd, an electric field in a direction (polarity) that directs the toner charged to the normal charging polarity from the intermediate transfer belt 6 to the photosensitive drums 1b to 1d. It is formed.

[Second lap]
The toner on the intermediate transfer belt 6 is collected by being charged positively by the cleaning roller 9.

  In this case, in the primary transfer portion N1a of the first station Sa, an electric field is formed in a direction (polarity) in which the toner charged to a polarity opposite to the normal charging polarity is directed from the photosensitive drum 1a to the intermediate transfer belt 6. On the other hand, in the primary transfer portions N1b to N1d of the second to fourth stations Sb to Sd, the direction (polarity) in which the toner charged to a polarity opposite to the normal charging polarity is directed from the intermediate transfer belt 6 to the photosensitive drums 1b to 1d. ) Is formed.

[3rd lap]
The toner adhering to the cleaning roller 9 is discharged onto the intermediate transfer belt 6, and the setting operation similar to (1-2) is performed.

  With the above settings, it is confirmed that the toner on the intermediate transfer belt 6 at the time of jam can pass through the first station Sa and be collected almost evenly at the second, third, and fourth stations Sb to Sd. did it.

(1-4) Regular Cleaning With the same setting as the above (1-3), the toner on the intermediate transfer belt 6 can be collected to the second, third and fourth stations Sb to Sd.

G. Control Mode In this embodiment, the operation of the image forming apparatus 100 is comprehensively controlled by a controller 150 (FIG. 2) as a control unit provided in the apparatus main body. In particular, in connection with the present embodiment, the controller 150 starts / stops and outputs the voltage output of the primary transfer voltage output device 50, the secondary transfer voltage output device 80, and the toner charging voltage output device 90 as described above. Controls the voltage value (including polarity switching). The controller 150 performs control according to a program stored in a storage unit built in the controller 150 or connected to the controller 150.

  As described above, the image forming apparatus 100 includes a plurality of photosensitive drums 1 that carry toner images and a movable intermediate transfer belt on which the toner images on the plurality of photosensitive drums 1 (on the image carrier) are primarily transferred. 6. Further, the image forming apparatus 100 is provided corresponding to each of the plurality of photosensitive drums 1, and a plurality of primary transfer rollers 5 that primarily transfer the toner images on the plurality of photosensitive drums 1 onto the intermediate transfer belt 6. Have The image forming apparatus 100 includes a primary transfer voltage output device 50 that outputs a voltage to the plurality of primary transfer units 5. Further, the image forming apparatus 100 includes a secondary transfer roller 8 that secondarily transfers the toner image on the intermediate transfer belt 6 to the transfer material P. A plurality of image forming portions S each having a photosensitive drum 1 and a primary transfer roller 5 are arranged along the moving direction of the intermediate transfer belt 6. Then, the image forming apparatus 100 performs primary transfer and reverse rotation of the toner on the intermediate transfer belt 6 to the photosensitive drum 1 by the voltage output from the primary transfer voltage output device 50 and applied to the primary transfer roller 5. Copying is performed.

  Here, the primary transfer voltage output device 50 outputs a first voltage output to the primary transfer roller 5 of at least one image forming unit S among the plurality of image forming units S. Part 51. Further, the primary transfer voltage output device 50 has the first transfer roller 5 of at least two image forming portions S different from the at least one image forming portion S among the plurality of image forming portions S with respect to the first transfer roller 5. It has the 2nd voltage output part 52 which outputs a voltage of polarity. Further, the primary transfer voltage output device 50 is connected in series to both the first voltage output unit 51 and the second voltage output unit 52 and has a polarity opposite to the first polarity. A third voltage output unit 53 that outputs a voltage having a polarity of 2; Preferably, the at least one image forming unit S is set so as to include the image forming unit S arranged on the most upstream side in the moving direction of the intermediate transfer belt 6. With such a configuration, the voltage output unit having the first polarity and the voltage output unit having the second polarity are smaller than the number of the plurality of image forming units S, respectively. In this embodiment, in particular, the at least one image forming unit S is a first station Sa, and the at least two image forming units S are second to fourth stations Sb to Sd.

  According to the image forming apparatus 100 of this embodiment having such a configuration, the apparatus configuration can be simplified and the apparatus main body can be reduced in size, and the residual toner can be uniformly distributed in the waste toner containers of the respective image forming units as much as possible. Control can be performed to recover. Thereby, since it is not necessary to change the size of the process cartridge 14 of each image forming unit S, the configuration for reducing color misregistration as described above can be easily adopted.

  That is, typically, in the image forming apparatus 100, the image forming unit S that collects residual toner by reverse transfer has a cleaning mode different from that at the time of image formation. In one embodiment, in the cleaning mode, the polarity of the voltage applied to the primary transfer roller 5 of the at least one image forming unit S and the primary transfer roller 5 of the at least two image forming units S are applied. The polarity of the voltage is reversed. In particular, in this embodiment, the cleaning mode is different from the image forming unit S in which the toner discharged from the cleaning roller 9 and the toner on the intermediate transfer belt 6 at the time of jam are collected from the remaining toner at the time of image formation. Collecting in part S.

  In one embodiment, the image forming apparatus 100 includes a cleaning roller 9 that charges the toner on the intermediate transfer belt 6. The cleaning roller 9 is located downstream of the secondary transfer roller 8 (secondary transfer portion) in the moving direction of the intermediate transfer belt 6 and the most upstream image forming portion Sa (the primary transfer thereof) among the plurality of image forming portions S. The toner is applied to the toner on the intermediate transfer belt 6 on the upstream side of the portion. Further, the image forming apparatus 100 includes a toner charging voltage output device 90 that outputs a voltage to the cleaning roller 9. The toner charging voltage output device 90 outputs voltages having different polarities between the image forming time and the cleaning mode to the cleaning roller 9, and the toner is transferred from the cleaning roller 9 to the intermediate transfer belt 6 in the cleaning mode. Can be exhaled.

  As described above, according to this embodiment, by performing the above-described control in the cleaning operation of various intermediate transfer belts 6, it becomes possible to collect the toner on the intermediate transfer belt 6 to each process cartridge 14 as evenly as possible. It was. According to the present embodiment, although the number of high-voltage power supplies is small, such an effect can be obtained by arranging the positive power supply and the negative power supply in series. Since each process cartridge 14 has the same configuration, a configuration advantageous for reducing color misregistration, that is, a circumferential length of the driving roller 61 of the intermediate transfer belt 6 and a pitch between the process cartridges (between primary transfer) are provided. It is possible to easily adopt a configuration that is an integer multiple.

  That is, according to the present embodiment, the residual toner on the intermediate transfer belt 6 can be distributed and collected as evenly as possible to the plurality of process cartridges 14 with a smaller number of high-voltage power supplies. Further, the configuration of each process cartridge 14 can be made the same, and the pitch between the process cartridges 14 can be made the same.

Example 2
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Accordingly, in the image forming apparatus and the image forming method according to the present embodiment, portions common to those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, the image forming apparatus 100 forms a single color image as the second image forming mode in addition to the normal image forming mode (full color image forming mode) similar to that in the first embodiment as the first image forming mode. Mode (monocolor image forming mode). In particular, in this embodiment, only the black color image is formed in the monochromatic image forming mode.

  FIG. 3 is a schematic configuration diagram of a main part of the image forming apparatus 100 of the present embodiment.

  In this embodiment, the arrangement of the process cartridge (black station) containing black toner is preferably set in consideration of the following. First, when the black station is arranged at the first station on the most upstream side in the moving direction of the intermediate transfer belt 6, the stations for collecting the residual toner by reverse transfer overlap in the monocolor image forming mode and the full color image forming mode. Therefore, it is not preferable. Further, in order to increase the time (first printout speed) until the first image is output in the mono-color image forming mode, the black station is the fourth most downstream in the moving direction of the intermediate transfer belt 6. It is preferable to arrange in the station. In view of the above, it is preferable that the black station is arranged at the fourth station as in this embodiment as a configuration for collecting the residual toner on the intermediate transfer belt 6 as uniformly as possible in each process cartridge. However, if the specific image forming unit that forms an image in the mono-color image forming mode is not arranged at the most upstream in the moving direction of the intermediate transfer belt 6, the remaining toner on the intermediate transfer belt 6 is evenly distributed to each process cartridge as much as possible. The effect of recovering is obtained.

A. Primary transfer roller In this embodiment, as in the first embodiment, a roller transfer system is adopted as the configuration of the primary transfer means. The configuration of the primary transfer roller 5 is the same as that of the first embodiment. However, in this embodiment, the configuration of the primary transfer voltage output device 50 is different from that of the first embodiment.

  In this embodiment, first, the primary transfer voltage output device 50 includes a first voltage output unit (positive bias) that outputs a positive polarity (first polarity) voltage having a polarity opposite to the normal charging polarity of the toner. Generation high voltage power source) 51. The first voltage output unit 51 is an independent voltage output unit of the first station Sa as in the first embodiment.

  The primary transfer voltage output device 50 outputs a second voltage output unit (positive bias generation high voltage) that outputs (generates) a positive polarity (first polarity) voltage having a polarity opposite to the normal charging polarity of the toner. Power source) 52. In the present embodiment, the second voltage output unit 52 is shared by the second and third stations Sb and Sc.

  The primary transfer voltage output device 50 is a third voltage output unit (negative bias generating high-voltage power supply) that outputs (generates) a negative polarity (second polarity) voltage having the same polarity as the normal charging polarity of the toner. ) 53. In the present embodiment, the third voltage output unit 53 is shared by the first, second, and third stations Sa, Sb, and Sc. In other words, in the present embodiment, the third voltage output unit 53 is connected in series to both the first voltage output unit 51 and the second voltage output unit 52, so that a positive bias voltage and a negative polarity are connected. The bias voltage is superimposed and applied to the primary transfer rollers 5a to 5c.

  In this embodiment, the primary transfer voltage output device 50 further includes a fourth voltage output unit (positive polarity) that outputs a positive polarity (first polarity) voltage having a polarity opposite to the normal charging polarity of the toner. A bias generating high voltage power source) 54. The fourth voltage output unit 54 is an independent voltage output unit of the fourth station Sd.

  In this embodiment, the fourth station Sd can be limited so as to collect the residual toner on the intermediate transfer belt 6 only at the time of monochromatic image formation. Therefore, a negative voltage output unit is not required for the fourth station Sd. For this reason, the black station is preferably arranged at the fourth station. However, if desired, a negative voltage output unit may also be provided for a specific image forming unit used during monocolor image formation.

B. Intermediate Transfer Belt Cleaning Operation In addition to the four types of intermediate transfer belt 6 cleaning operations described in the first embodiment, the following intermediate transfer belt 6 cleaning operation is added in this embodiment.

(2-5) Cleaning at the time of mono-color image formation At the time of mono-color image formation, a rectangular wave having a frequency of 1000 Hz and a peak-to-peak voltage of 2000 V and a DC voltage of 1.3 kV are applied to the cleaning roller 9 from the toner charging voltage output device 90. Apply the superimposed voltage. As a result, a positive charge is imparted to the residual toner remaining on the intermediate transfer belt 6 without being subjected to secondary transfer. Further, when forming a monocolor image, a positive bias voltage is applied to the primary transfer roller 5d of the fourth station Sd. Accordingly, the residual toner on the intermediate transfer belt 6 charged to the positive polarity by the cleaning roller 9 is reversely transferred to the photosensitive drum 1d at the next primary transfer at the fourth station Sd.

C. Specific Example In this example, the cleaning operation of the above-described five types of intermediate transfer belt 6 was performed with the settings shown in more detail below in order to collect toner as uniformly as possible with the four process cartridges 14a to 14d. . And the effect was confirmed in a normal environment.

(2-1) Cleaning during normal image formation (full color) During normal image formation, all residual toner on the intermediate transfer belt 6 is collected at the first station Sa. This is because it is preferable to collect the residual toner at the first station Sa because the method of collecting the residual toner by reverse transfer at the same time as the primary transfer is adopted.

  Table 5 below shows the setting of the bias voltage output from the primary transfer voltage output device 50 to the primary transfer roller 5 at each station S and the operation status at each station S at this time.

  The column of “positive bias” in Table 5 indicates the set value of the positive bias voltage output by the first voltage output unit 51 for the first station Sa. The “positive bias” column indicates the set value of the positive bias voltage output by the second voltage output unit 52 for the second and third stations Sb and Sc. The column “positive bias” indicates the set value of the positive bias voltage output by the fourth voltage output unit 54 for the fourth station Sd. The column “Negative Bias” in Table 5 shows the set value of the negative bias voltage output from the third voltage output unit 53. In the column of “primary transfer output” in Table 5, for the first to third stations Sa to Sc, the positive polarity bias voltage and the negative polarity bias voltage are superimposed and the primary transfer roller. The setting value of the bias voltage applied to 5a-5c is shown. On the other hand, the column of “primary transfer output” indicates the set value of the positive bias voltage because the negative bias voltage is not superimposed on the fourth station Sd. The same applies to Tables 6 to 9 below. In this embodiment, it is assumed that the photosensitive drum 1 is charged to the same potential (negative polarity in this embodiment) as that during normal image formation in any case.

  In this case, in the primary transfer portions N1a to N1d of the first to fourth stations Sa to Sd, the toner charged to a polarity opposite to the normal charging polarity is directed from the intermediate transfer belt 6 to the photosensitive drums 1a to 1d ( Polarity) electric field is formed.

  It was confirmed that the residual toner on the intermediate transfer belt 6 can be collected only by the first station Sa with the above setting.

(2-2) Cleaning of toner discharged from the cleaning roller The toner discharged from the cleaning roller 9 passes through the first and fourth stations Sa and Sd and is collected almost evenly at the second and third stations Sb and Sc. .

  Table 6 below shows the setting of the bias voltage output from the primary transfer voltage output device 50 to the primary transfer roller 5 at each station S and the operation status at each station S at this time.

  In this case, in the primary transfer portions N1a and N1d of the first and fourth stations Sa and Sd, an electric field in a direction (polarity) in which the toner charged to the normal charging polarity is directed from the photosensitive drums 1a and 1b to the intermediate transfer belt 6 is used. Is formed. On the other hand, in the primary transfer portions N1b and N1c of the second and third stations Sb and Sc, an electric field in the direction (polarity) that directs the toner charged to the normal charging polarity from the intermediate transfer belt 6 to the photosensitive drums 1b and 1c. It is formed.

  With the above setting, it is possible that the toner discharged from the cleaning roller 6 can pass through the first and fourth stations Sa and Sd and can be collected almost uniformly at the second and third stations Sb and Sc. It could be confirmed.

(2-3) Cleaning at Jam (Paper Jam) In this case as well, the toner on the intermediate transfer belt 6 passes through the first and fourth stations Sa and Sd and is almost at the second and third stations Sb and Sc. Collect evenly. The collection is performed with the following settings according to the number of rotations of the intermediate transfer belt 6.

[First lap]
The negative toner on the intermediate transfer belt 6 is collected.

  In this case, in the primary transfer portions N1a and N1d of the first and fourth stations Sa and Sd, the electric field in the direction (polarity) in which the toner charged to the normal charging polarity is directed from the photosensitive drums 1a and 1d to the intermediate transfer belt 6 is used. Is formed. On the other hand, in the primary transfer portions N1b and N1c of the second and third stations Sb and Sc, an electric field in the direction (polarity) that directs the toner charged to the normal charging polarity from the intermediate transfer belt 6 to the photosensitive drums 1b and 1c. It is formed.

  With the above setting, the toner on the intermediate transfer belt 6 at the time of jam is passed through the first station Sa, collected at the second and third stations Sb, Sc, and toner collected at the fourth station Sd is seen. There wasn't.

[Second lap]
The toner remaining on the intermediate transfer belt 6 is collected by being charged positively by the cleaning roller 9.

  In this case, in the primary transfer portions N1a and N1d of the first and fourth stations Sa and Sd, the toner charged to a polarity opposite to the normal charging polarity is directed from the photosensitive drums 1a and 1d to the intermediate transfer belt 6 ( Polarity) electric field is formed. On the other hand, in the primary transfer portions N1b to N1d of the second and third stations Sb and Sc, a direction (polarity) in which the toner charged to a polarity opposite to the normal charging polarity is directed from the intermediate transfer belt 6 to the photosensitive drums 1b and 1c. ) Is formed.

  With the above setting, the toner on the intermediate transfer belt 6 at the time of jam is passed through the first station Sa, collected at the second and third stations Sb, Sc, and toner collected at the fourth station Sd is seen. There wasn't.

[3rd lap]
The toner adhering to the cleaning roller 9 is discharged onto the intermediate transfer belt 6 and the same setting operation as in (2-2) is performed.

  With the above settings, the toner on the intermediate transfer belt 6 at the time of jam can pass through the first and fourth stations Sa and Sd and be collected almost evenly at the second and third stations Sb and Sc. Was confirmed.

(2-4) Periodic Cleaning With the same setting as the above (2-3), the toner on the intermediate transfer belt 6 can be collected to the second and third stations Sb and Sc.

(2-5) Cleaning during mono-color image formation During mono-color image formation, the first, second, and third stations Sa, Sb, and Sc are set to voltages that allow the toner on the intermediate transfer belt 6 to pass therethrough. Then, all the toner on the intermediate transfer belt 6 at the time of monochromatic image formation is collected at the fourth station Sd.

  The setting of the bias voltage output from the primary transfer voltage output device 50 to the primary transfer roller 5 at each station S and the operation status at each station S are as shown in Table 1 below.

  In this case, in the primary transfer portions N1a to N1d of the first to third stations Sa to Sd, the toner charged to a polarity opposite to the normal charging polarity is directed from the photosensitive drums 1a to 1d to the intermediate transfer belt 6 ( Polarity) electric field is formed. On the other hand, in the primary transfer portion N1d of the fourth station Sd, an electric field is formed in a direction (polarity) in which the toner charged to a polarity opposite to the normal charging polarity is directed from the intermediate transfer belt 6 to the photosensitive drum 1d.

  As described above, in the present embodiment, the primary transfer voltage output device 50 further outputs the voltage having the first polarity to the specific image forming unit S among the plurality of image forming units S. A voltage output unit; The specific image forming unit S is applied with the voltage output from the above-described at least one image forming unit S and the second voltage output unit to which the voltage output from the first voltage output unit is applied. The image forming unit S is different from the at least two image forming units S described above.

  Typically, the specific image forming unit S is an image forming unit other than the image forming unit arranged at the most upstream in the moving direction of the intermediate transfer belt 6. Further, the specific image forming unit S is preferably an image forming unit Sd disposed on the most downstream side in the moving direction of the intermediate transfer belt 6.

  In this embodiment, the image forming apparatus 100 includes a first image forming unit that can form an image using all of the at least one image forming unit, the at least two image forming units, and the specific image forming unit. Has a mode. In this embodiment, the image forming apparatus 100 can form an image using only the specific image forming unit among the at least one image forming unit, the at least two image forming units, and the specific image forming unit. A second image forming mode. Preferably, the first image forming mode and the second image forming mode differ in the image forming portion S where the toner is reversely transferred from the intermediate transfer belt 6 to the photosensitive drum 1.

  As described above, according to the present embodiment, by performing the above-described control in the cleaning operation of various intermediate transfer belts 6, it is possible to collect the toner on the intermediate transfer belt 6 to each process cartridge 14 as uniformly as possible. became. According to the present embodiment, although the number of high-voltage power supplies is small, such an effect can be obtained by arranging the positive power supply and the negative power supply in series. Since each process cartridge 14 has the same configuration, a configuration advantageous for reducing color misregistration, that is, a circumferential length of the driving roller 61 of the intermediate transfer belt 6 and a pitch between the process cartridges (between primary transfer) are provided. It is possible to easily adopt a configuration that is an integer multiple.

  It should be understood that the present invention is not limited to the embodiments 1 and 2 described above.

  For example, the order of the colors of the toner images formed by the plurality of image forming units may be different from those in the above-described embodiments, and the configuration of the primary transfer voltage output unit differs depending on the difference in the order of the colors. It may be. For example, consider a case where the station that forms an image in the mono-color image forming mode described in the second embodiment is not the fourth station but the second station or the third station. In this case, the second voltage output unit described in the second embodiment outputs a voltage to the third and fourth stations, or outputs a voltage to the second and fourth stations, respectively. And it is sufficient.

  Further, in each of the above embodiments, the regular charging polarity of the toner is described as having a negative polarity, but the regular charging polarity of the toner may be positive. In that case, the various output bias settings described in the above embodiments may generally be reversed in polarity.

1 is a schematic configuration diagram of an embodiment of an image forming apparatus according to the present invention. 1 is a schematic configuration diagram of a main part of an embodiment of an image forming apparatus according to the present invention. It is a principal part schematic block diagram of the other Example of the image forming apparatus which concerns on this invention. It is a schematic block diagram of an example of the conventional image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 5 Primary transfer roller 8 Secondary transfer roller 9 Cleaning roller 50 Primary transfer voltage output device 80 Secondary transfer voltage output device 90 Toner charge voltage output device

Claims (11)

A plurality of image carriers that carry toner images, a movable intermediate transfer member to which toner images on the plurality of image carriers are primarily transferred, and a plurality of image carriers are provided corresponding to each of the plurality of image carriers. A plurality of primary transfer means for primarily transferring toner images on the plurality of image carriers onto the intermediate transfer body; a voltage output means for outputting a voltage to the plurality of primary transfer means; Secondary transfer means for secondary transfer of the toner image on the intermediate transfer body onto a transfer material, and a plurality of image forming units each including the image carrier and the primary transfer means include the intermediate transfer body. And the reverse transfer of the toner on the intermediate transfer member to the image carrier by the voltage output from the voltage output unit and applied to the primary transfer unit. In an image forming apparatus in which copying is performed,
The voltage output unit includes a first voltage output unit that outputs a voltage having a first polarity to the primary transfer unit of at least one of the plurality of image forming units, and the plurality of images. A second voltage output unit that outputs the voltage of the first polarity to the primary transfer unit of at least two image forming units different from the at least one image forming unit among the forming units; A third voltage output section that is connected in series to both the voltage output section and the second voltage output section and outputs a voltage having a second polarity that is opposite to the first polarity, An image forming apparatus comprising:   2. The image forming apparatus according to claim 1, wherein the at least one image forming unit includes an image forming unit disposed at a most upstream position in a moving direction of the intermediate transfer member.   The voltage output means further outputs a voltage having a first polarity to a specific image forming unit different from the at least one image forming unit and the at least two image forming units among the plurality of image forming units. The image forming apparatus according to claim 1, further comprising a fourth voltage output unit.   The image forming apparatus according to claim 3, wherein the specific image forming unit is an image forming unit other than the image forming unit arranged at the most upstream in the moving direction of the intermediate transfer member.   The image forming apparatus according to claim 4, wherein the specific image forming unit is an image forming unit arranged on the most downstream side in the moving direction of the intermediate transfer member.   A first image forming mode capable of forming an image using all of the at least one image forming unit, the at least two image forming units, and the specific image forming unit, and only the specific image forming unit among them A second image forming mode capable of forming an image using the image forming unit, and the first image forming mode and the second image forming mode are different in an image forming unit where the reverse transfer is performed. The image forming unit according to claim 3, wherein the image forming unit is a part of the image forming unit.   The plurality of image forming units include four image forming units that form toner images of yellow, magenta, cyan, and black, and the specific image forming unit forms a black toner image. The image forming apparatus according to claim 3, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 1, wherein the first polarity is a polarity opposite to a normal charging polarity of the toner.   The polarity of the voltage output from the voltage output unit and applied to the primary transfer unit of the at least one image forming unit, and the primary transfer of the at least two image forming units output from the voltage output unit 9. The image forming apparatus according to claim 1, wherein the image forming apparatus has a cleaning mode in which the polarity of the voltage applied to the means is opposite to that of the voltage.   Charging that imparts a charge to the toner on the intermediate transfer member on the downstream side of the secondary transfer unit in the moving direction of the intermediate transfer member and on the upstream side of the most upstream image forming unit among the plurality of image forming units. The image forming apparatus according to claim 1, further comprising a charging unit and a charging voltage output unit that outputs a voltage to the charging unit.   The polarity of the voltage output from the voltage output unit and applied to the primary transfer unit of the at least one image forming unit, and the primary transfer of the at least two image forming units output from the voltage output unit A charging mode in which the polarity of the voltage applied to the means is opposite to the polarity; and the charging voltage output means outputs to the charging means a voltage having a different polarity during image formation and in the cleaning mode. The image forming apparatus according to claim 10, wherein the image forming apparatus can perform the operation.

Images