JP5317497B2 - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device for correctly controlling a transfer voltage applied to a transfer member, with simple structure. <P>SOLUTION: This image forming device includes a movable belt 21, a first image carrier 1a which carries a toner image, a first transfer member 5a which transfers the toner image on the first image carrier to the belt 21 in a first transfer region, a second image carrier 1d which carries the toner image located downstream of the moving direction of the belt 21, a second transfer member 5d which transfers the toner image on the second image carrier 1d overlapping with the toner image transferred on the belt 21 from the first image carrier 1a in a second transfer region, a power source 33d which applies a voltage to the second transfer member 5d, and a detection member 52 which detects current or voltage output from the power source 33d. The image forming device sets a second transfer voltage based on the detection result of the detection means 52 obtained from the detection voltage of the power source 33d when the voltage is applied to the first transfer member 5a and the region of the belt 21 being in the first transfer region enters the second transfer region. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to an image forming apparatus that uses an electrophotographic recording system such as a laser printer, a copying machine, or a facsimile.

2. Description of the Related Art In recent years, image forming apparatuses using an electrophotographic system are required to be able to output a color image with a high level of image quality as the size, function, and color become widespread. In addition, with the widespread use of image forming apparatuses, image forming apparatuses have been used in various environments, and it is required that stable image formation is possible even under various conditions. In response to these demands, various controls and functions have been developed, and are introduced and installed in image forming apparatuses.

  As an image forming apparatus capable of outputting a full-color image, there is an intermediate transfer system that forms a color image (multiple image) on a transfer material such as paper by a primary transfer process and a secondary transfer process. Further, for example, an intermediate transfer type image forming apparatus has a plurality of image forming portions that form images of different colors along the moving direction of the surface of the intermediate transfer member, and is formed in each image forming portion. It is known to superimpose an image on an intermediate transfer member. An image forming apparatus provided with a plurality of image forming units arranged in this way is called a tandem type or an inline type.

  In an intermediate transfer tandem image forming apparatus, first, a toner image is formed on an electrophotographic photosensitive member (photosensitive member) as an image carrier provided in each image forming unit. The toner image formed on each photoconductor is transferred onto an intermediate transfer belt as an intermediate transfer body at the primary transfer portion by the action of a primary transfer means provided corresponding to each photoconductor (1). Next transfer process). As the primary transfer means, a roller, a pad, a brush, or the like that is a transfer member for a primary transfer process to which a transfer voltage is applied (hereinafter referred to as “primary transfer member”) is used. This primary transfer process is sequentially performed in primary transfer units of a plurality of image forming units (for example, image forming units for yellow, magenta, cyan, and black colors). As a result, the toner images of the respective colors are superimposed on the intermediate transfer belt, and a multiple toner image is formed on the intermediate transfer belt. Next, the multiple toner images formed on the surface of the intermediate transfer belt are collectively transferred onto the surface of a transfer material such as paper by the action of the secondary transfer means (secondary transfer step). As the secondary transfer means, a roller, a pad, a brush, or the like which is a transfer member for a secondary transfer process to which a transfer voltage is applied (hereinafter referred to as “secondary transfer member”) is used. The toner image transferred onto the transfer material is fixed on the transfer material by fixing means. Thereby, a full-color output image is formed.

  Here, in the primary transfer process, by applying an optimal transfer voltage to the primary transfer member, the toner image on the photoreceptor is efficiently transferred to the intermediate transfer belt. That is, by selecting a transfer voltage having a high transfer efficiency and a low retransfer rate, it is possible to output a high-quality color image in which transfer defects and hue changes are suppressed. The optimum transfer voltage is obtained by calculation using, for example, a current detection unit and an output voltage detection unit provided for each transfer member (for example, Patent Document 1).

  That is, for example, a constant-current controlled voltage is applied to the primary transfer member at a preset value during multiple pre-rotation performed during warm-up after power-on of the image forming apparatus or pre-rotation performed before image formation. . Then, the voltage value generated at that time is detected, and the fluctuation of the electric resistance in the primary transfer portion is detected based on the fluctuation (electric resistance detection step). Then, at the time of image formation, the primary transfer process is performed by applying, to the primary transfer member, a voltage that has been subjected to constant voltage control with a value (for example, an average value of the generated voltage) obtained by calculating the previous generated voltage. .

By such a control method, it is possible to select an optimum transfer voltage and to output a high-quality color image in which transfer failure and color change are suppressed.
JP 2001-228680 A

  By the way, in order to reduce the cost and size of the apparatus, current detection is performed only for the primary transfer member of the most downstream image forming unit in the moving direction of the intermediate transfer belt among the plurality of image forming units. It is conceivable to provide means and output voltage detection means. Thereby, the current detection means and the output voltage detection means can be reduced to a minimum number.

  However, with such a configuration, it has been found that although the cost and size of the apparatus can be reduced, an appropriate transfer voltage may not be applied to the primary transfer member during image formation depending on conditions.

For example, when the intermediate transfer belt has a high resistance (for example, a volume resistivity of 1 × 10 ¹¹ Ωcm or more), the intermediate transfer belt is charged up under the influence of voltage application to the primary transfer member. Therefore, the surface potential of the intermediate transfer belt may be different between the upstream and downstream primary transfer portions in the moving direction of the intermediate transfer belt. As a result, the relationship of the transfer current with respect to the transfer voltage, that is, the VI characteristic may be greatly different between the upstream and downstream primary transfer portions in the moving direction of the intermediate transfer belt.

  As described above, when the current detection unit and the output voltage detection unit are provided only for the primary transfer member of the fourth image forming unit, the average voltage detected during constant current control in the electrical resistance detection step The value is calculated from the VI characteristic related to the primary transfer member of the fourth image forming unit. Then, when a transfer voltage at the time of image formation is obtained based on the calculated average voltage value and the obtained transfer voltage is applied to the primary transfer members of the first to third image forming units, it is greatly different from the optimum value. Current may flow. Since such a phenomenon greatly depends on the use environment of the apparatus, it is difficult to determine the transfer voltage to be applied at the time of image formation by predicting the charge-up of the intermediate transfer belt in advance.

  When a primary transfer process is performed by applying a transfer voltage that causes a current that is significantly different from the optimum value to the primary transfer member, the transfer efficiency is reduced and the retransfer rate is increased, and a defective image is generated. The possibility increases.

  Although the conventional problems have been described above with respect to the intermediate transfer type tandem type image forming apparatus, the direct transfer type tandem type image forming apparatus has the same problem.

  That is, the direct transfer type image forming apparatus uses a transfer belt as a transfer material conveying member that carries and conveys a transfer material such as paper instead of the intermediate transfer belt as an intermediate transfer body in the intermediate transfer type image forming apparatus. Have In the direct transfer type image forming apparatus, the toner image on the photoconductor is transferred to the transfer belt by the action of a transfer member provided corresponding to the photoconductor as an image carrier provided in each image forming unit. Transfer is performed on a transfer material carried thereon (transfer process). The transfer process is sequentially performed in the transfer units of the plurality of image forming units, so that the toner images of the respective colors are superimposed on the transfer material on the transfer belt, and a multiple toner image is formed on the transfer material.

  Also in such a direct transfer type image forming apparatus, the transfer voltage applied to each transfer member at the time of image formation can be controlled in the same manner as described above. However, when the current detection unit and the output voltage detection unit are provided only for the transfer member of the most downstream image forming unit in the moving direction of the conveyance belt in the same manner as described above, the same problem as described above occurs. There is.

  Accordingly, an object of the present invention is to provide an image forming apparatus that can control a transfer voltage applied to a transfer member more accurately with a simpler configuration.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the first invention provides a movable belt, a first image carrier for carrying a toner image, and the first image carrier in a first transfer region upon receiving a first transfer voltage. the first transfer member and said second image bearing member carrying the position and the toner image on the downstream of the moving direction of the belt with respect to a first image carrier for transferring the toner image on the body to the belt side When a second transfer member for transferring the toner image on the front Stories second image carrier Te second transfer region odor receiving second transfer voltage to the belt side, the second transfer member in the image forming apparatus having a power source for applying a voltage, and a detectable detection means a current or voltage the power supply output, the first transfer region when a voltage is applied to the first transfer member When the area of the belt entering into the second transfer area later enters the second transfer area, Setting the second transfer voltage in accordance with a detection result of said detecting means obtained by outputting the source or al voltage, region of the belt which is not charged by the first transfer member, said first The image forming apparatus is characterized in that the first transfer voltage is set in accordance with a detection result of the detection means obtained by outputting a voltage from the power supply when entering the second transfer region .

The second of the present invention, the move can be belt, a first image bearing member for bearing a toner image, first the first the first image bearing member in the transfer region of the receiving transfer voltage a first transfer member which transfers the toner image on to the belt side, a second image bearing member for bearing a location toner image downstream of the moving direction of the belt with respect to the first image bearing member a second transfer member to be transferred to the second transfer voltage receiving by the second transfer area smell the previous SL toner image on the second image bearing member Te belt side, voltage to the second transfer member a power source for applying an, in the image forming apparatus having a detectable detection means a current or voltage the power supply outputs, to the first transfer region when a voltage is applied to the first transfer member when the area of the belt which enters enters the second transfer region after the power supply or al Setting the second transfer voltage in accordance with a detection result of said detecting means obtained by outputting the pressure, and enters the first transfer region when a voltage is applied to the first transfer member The image forming apparatus is characterized in that the first transfer voltage is set in accordance with a detection result detected by the detection means before the belt area entering the second transfer area .
According to a third aspect of the present invention, there is provided a movable belt, a first image carrier that carries a toner image, and a first transfer region that receives a first transfer voltage on the first image carrier. A first transfer member that transfers the toner image to the belt side, a second image carrier that is located downstream in the moving direction of the belt with respect to the first image carrier and carries a toner image; In response to the second transfer voltage, a voltage is applied to the second transfer member that transfers the toner image on the second image carrier to the belt side in the second transfer region, and the second transfer member. In the image forming apparatus having a power source and a detection unit capable of detecting a current or voltage output from the power source, the first transfer voltage is an area of the belt that is not charged by the first transfer member. Outputs a voltage from the power source when entering the second transfer area It is set according to a detection result of said detecting means obtained Te which is an image forming apparatus according to claim.
According to a fourth aspect of the present invention, there is provided a movable belt, a first image carrier that carries a toner image, and a first transfer region that receives a first transfer voltage on the first image carrier. A first transfer member that transfers the toner image to the belt side, a second image carrier that is located downstream in the moving direction of the belt with respect to the first image carrier and carries a toner image; In response to the second transfer voltage, a voltage is applied to the second transfer member that transfers the toner image on the second image carrier to the belt side in the second transfer region, and the second transfer member. In the image forming apparatus having a power source and a detection unit capable of detecting a current or voltage output from the power source, the first transfer voltage is the first transfer voltage when a voltage is applied to the first transfer member. The belt area entering the first transfer area enters the second transfer area. It said sensing means is an image forming apparatus, wherein a set according to a detection result of detecting.

  According to the present invention, the transfer voltage applied to the transfer member can be more accurately controlled with a simpler configuration.

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

Example 1
1. 1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention. The image forming apparatus 100 according to the present exemplary embodiment is an intermediate transfer type tandem type image forming apparatus.

  The image forming apparatus 100 according to the present exemplary embodiment includes first, second, third, and fourth stations 10a, 10b, 10c, and 10d as a plurality of image forming units. In this embodiment, the first to fourth stations 10a to 10d are for forming toner images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K). .

  In the present embodiment, the configurations and operations of the stations 10a to 10d have many common parts. Therefore, in the following, unless there is a particular distinction, the subscripts a, b, c, and d given to the reference numerals in the drawings are omitted to indicate that they are elements provided for any color, and are summarized Explained.

  The station 10 is provided with a drum-type electrophotographic photosensitive member, that is, a photosensitive drum 1 as an image carrier. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 (counterclockwise) in the drawing. Around the photosensitive drum 1, a charging roller 2 as a charging means, an exposure device 3 as an exposure means, a developing device 4 as a developing means, a primary transfer member 5 as a primary transfer means, and the photosensitive drum 1 are cleaned. A cleaning device 6 is disposed as a cleaning means.

  In this embodiment, the photosensitive drum 1 is an OPC (organic photoconductor) photosensitive member. The photosensitive drum 1 is formed by laminating a plurality of functional organic materials including a carrier generation layer that generates charges upon exposure to light and a charge transport layer that transports generated charges on a metal cylinder. In this embodiment, the predetermined charging polarity of the photosensitive drum 1 is negative.

  The charging roller 2 is in contact with the photosensitive drum and uniformly charges the surface of the photosensitive drum 1 while being driven to rotate as the photosensitive drum 1 rotates.

  In this embodiment, the exposure apparatus 3 is a laser scanner unit that scans laser light with a polygonal mirror. The exposure device 3 irradiates the photosensitive drum 1 with a scanning beam L modulated based on the image signal. In addition to this, for example, an LED array can be used as the exposure apparatus 3.

  In the present embodiment, the developing device (developing unit) 4 uses a non-magnetic one-component developer, that is, toner, as the developer. Further, the developing device 4 includes a developing roller 41 as a developer carrying member, a developer application blade 42 as a developer amount regulating means, and the like.

  A cleaning device (cleaning unit) 6 cleans toner (primary transfer residual toner) remaining on the surface of the photosensitive drum 1 after the primary transfer process. The cleaning device 6 is disposed in contact with the surface of the photosensitive drum 1 and has a cleaning blade formed of an elastic body such as a plate-like urethane rubber as a cleaning member that removes toner from the surface of the photosensitive drum 1. As the cleaning member, a fur brush or the like can be used in addition to the blade. Further, the cleaning device 6 has a collected toner container that collects the toner removed from the surface of the photosensitive drum 1 by the cleaning blade.

  The primary transfer member 5 is provided in the intermediate transfer device 20. The intermediate transfer device 5 includes an endless belt as an intermediate transfer body, that is, an intermediate transfer belt 21 provided so as to face the photosensitive drums 1a to 1d of all the stations 10a to 10b. The intermediate transfer device 20 includes primary transfer members 5 a to 5 d at positions facing the respective photosensitive drums 1 a to 1 d on the inner peripheral surface side of the intermediate transfer belt 21. That is, the primary transfer members 5a to 5d are disposed on the opposite side of the photosensitive drums 1a to 1d with the intermediate transfer belt 21 interposed therebetween. The primary transfer members 5a to 5d are pressed against the photosensitive drums 1a to 1d via the intermediate transfer belt 21, and the primary transfer unit (primary transfer unit) where the intermediate transfer belt 21 and the photosensitive drums 1a to 1d come into contact with each other. Transfer nip portion) N1a to N1d are formed. In addition, the intermediate transfer device 20 performs secondary transfer at a position facing the secondary transfer counter roller 24 that is one of a plurality of support members that support the intermediate transfer belt 21 on the outer peripheral surface side of the intermediate transfer belt 21. It has a secondary transfer roller 7 as a secondary transfer member as means. The secondary transfer roller 7 is pressed against the secondary transfer counter roller 7 via the intermediate transfer belt 21, and a secondary transfer portion (secondary transfer nip portion) where the intermediate transfer belt 21 and the secondary transfer roller 7 are in contact with each other. ) N2 is formed.

  The intermediate transfer belt 21 is supported by three rollers, ie, a driving roller 22, a tension roller 23, and a secondary transfer counter roller 24, as a stretching member (supporting member) so that an appropriate tension is maintained. It has become. The intermediate transfer belt 21 rotates (circulates) in the direction of the arrow R3 (clockwise) in the figure by driving the drive roller 22 in the direction of the arrow R2 (clockwise) in the figure. The intermediate transfer belt 21 moves in a forward direction with respect to the surface of the photosensitive drum 1 at the primary transfer portion (contact portion) N1 at substantially the same speed as the moving speed (circumferential speed) of the surface of the photosensitive drum 1.

In this embodiment, a general-purpose engineering plastic sheet having a thickness of 100 μm and a volume resistivity of 10 ¹¹ Ωcm was used as the intermediate transfer belt 21. In this specification, the volume resistivity refers to the volume resistivity measured as follows. Mitsubishi Chemical Corporation's Hiresta-UP (MCP-HT450) is used as the measurement device, UR is used as the measurement probe, the room temperature during measurement is set to 23 ° C., the room humidity is set to 50%, the applied voltage is 500 V, and the measurement time is The volume resistivity is measured under the condition of 10 sec.

As the driving roller 22, in this embodiment, an aluminum cored bar is covered with EPDM (ethylene / propylene / diene) rubber having an electric resistance of 10 ⁴ Ω and a wall thickness of 1.0 mm in which carbon is dispersed as a conductive agent. The one with an outer diameter of 25 mm was used.

  In this embodiment, an aluminum metal rod having an outer diameter of 25 mm is used as the tension roller 23, and the tension is 19.6 N on one side and a total pressure of 39.2 N on both ends in the longitudinal direction of the tension roller 23.

As the secondary transfer counter roller 24, in this embodiment, an aluminum cored bar is coated with EPDM rubber having an electric resistance value of 10 ⁴ Ω and a wall thickness of 1.5 mm in which carbon is dispersed as a conductive agent. The thing of was used.

  In this embodiment, the primary transfer member 5 is a pad-like member that comes into contact with the inner peripheral surface of the intermediate transfer belt 21 and rubs the inner peripheral surface as the intermediate transfer belt 21 moves. It was. However, the primary transfer member 5 is not limited to a pad-like member, and a roller-like member, a brush-like member, or the like can also be used.

As the secondary transfer roller 7, in this embodiment, a nickel-plated steel rod having an outer diameter of 8 mm was covered with a foamed sponge of NBR (nitrile butadiene rubber) adjusted to have an electric resistance of 10 ⁸ Ω and a thickness of 5 mm. An outer diameter of 18 mm was used. The secondary transfer roller 7 was brought into contact with the intermediate transfer belt 21 with a linear pressure of about 5 to 15 g / cm. Further, the secondary transfer roller 7 was rotated such that the surface of the secondary transfer portion N2 moved at a substantially constant speed in the forward direction with respect to the moving direction of the surface of the intermediate transfer belt 21 in the secondary transfer portion N2.

  In this embodiment, the photosensitive drum 1 and the charging roller 2, the developing device 4, and the cleaning device 6 as process means acting on the photosensitive drum 1 are detachable from the main body of the image forming apparatus 100. The process cartridge 11 is configured.

  Further, the charging roller 2, the developing roller 41, and the primary transfer member 5 are respectively a charging power source 31 that is a voltage supply unit to the charging roller 2, a developing power source 32 that is a voltage supply unit to the developing roller 41, and primary transfer. It is connected to a primary transfer power supply 33 that is a means for supplying voltage to the member 5. The secondary transfer roller 7 is connected to a secondary transfer power supply 34 that is a voltage supply means to the secondary transfer roller 7.

  At the time of image formation, first, the photosensitive drum 1 and the intermediate transfer belt 21 of each station 10 start rotating at a predetermined process speed.

  The surface of the photosensitive drum 1 is uniformly charged to a predetermined polarity (negative polarity in this embodiment) by applying a predetermined charging voltage from the charging power source 31 to the charging roller 2. Subsequently, the surface of the charged photosensitive drum 1 is scanned and exposed by the scanning beam L from the exposure means 3. Thereby, an electrostatic latent image (electrostatic image) according to the image information is formed on the photosensitive drum 1.

  The electrostatic latent image formed on the photosensitive drum 1 is developed by the developing device 4. That is, the toner in the developing device 4 is charged to the negative polarity by the developer application blade 42 and applied to the developing roller 41. A predetermined developing bias is supplied to the developing roller 41 from the developing power source 32. Then, when the photosensitive drum 1 rotates and the electrostatic latent image formed on the photosensitive drum 1 reaches a portion (developing portion) facing the developing roller 41, toner charged negatively on the electrostatic latent image. Adhere to. As a result, the electrostatic latent image formed on the photosensitive drum 1 is visualized, and a toner image is formed on the photosensitive drum 1.

  The toner image formed on the photosensitive drum 1 is transferred (primary transfer) onto the intermediate transfer belt 21 at the primary transfer portion N1. At this time, the primary transfer member 5 is applied with a transfer voltage (primary transfer voltage) having a polarity (positive in this embodiment) opposite to the normal charging polarity of the toner by the primary transfer power source 33. In this embodiment, a DC voltage is applied as the transfer voltage. In the primary transfer process, an electric field is formed in the primary transfer portion (transfer area) N1 in a direction in which the toner charged to the normal charging polarity is moved from the photosensitive drum 1 side to the intermediate transfer belt 21 side.

  For example, when a full-color image is formed, the above-described operations are performed in the first to fourth stations 10a to 10d. At this time, according to the distance between the primary transfer positions of the stations 10a to 10d, the electrostatic latent images obtained by the exposure are put on the photosensitive drums 1a to 1d while delaying the writing signal from the controller 50 at a constant timing for each color. Form. Then, the electrostatic latent image is developed, and the toner images formed on the respective photosensitive drums 1a to 1d are sequentially superimposed and transferred onto the intermediate transfer belt 21 (primary transfer), and the intermediate transfer is performed. A multiple toner image is formed on the belt 21.

  Toner remaining on the surface of the photosensitive drum 1 after the primary transfer process (primary transfer residual toner) is cleaned by the cleaning device 6. That is, the cleaning device 6 removes the primary transfer residual toner on the surface of the photosensitive drum 1 with the cleaning blade and collects it in a recovery toner container.

  The transfer material P is supplied from the transfer material supply unit 8 to the secondary transfer unit N2 in accordance with the electrostatic latent image formed by the exposure. That is, in the transfer material supply 8, the transfer material P loaded on the transfer material cassette 81 is picked up by the transfer material supply roller 82 and conveyed to the registration roller 83 by a conveyance roller (not shown). Thereafter, the transfer material P is synchronized with the toner image on the intermediate transfer belt 21, and a secondary transfer portion (contact portion) N <b> 2 formed by the registration roller 83 between the intermediate transfer belt 21 and the secondary transfer roller 7. It is conveyed to.

  Thereafter, the four-color multiple toner images carried on the intermediate transfer belt 21 are collectively transferred (secondary transfer) onto the transfer material P in the secondary transfer portion N2. At this time, a transfer voltage (secondary transfer voltage) having a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied to the secondary transfer roller 7 by the secondary transfer power source 34. In this embodiment, a DC voltage is applied as the transfer voltage. In the secondary transfer process, an electric field is formed in the secondary transfer portion (transfer area) N2 in a direction to move the toner charged to the normal charging polarity from the intermediate transfer belt 21 side to the transfer material P side.

  After the secondary transfer is completed, toner remaining on the intermediate transfer belt 21 (secondary transfer residual toner) or paper dust generated by the transfer of the transfer material P is transferred by the belt cleaning device 25 to the intermediate transfer. It is removed from the surface of the belt 21 and collected. That is, for example, the belt cleaning device 25 uses an elastic cleaning blade formed of urethane rubber or the like as a cleaning member disposed in contact with the intermediate transfer belt 21 to perform secondary transfer residual from the intermediate transfer belt 21. Remove toner etc. The secondary transfer residual toner and the like removed by the cleaning blade are collected in a collected toner container.

  On the other hand, the transfer material P after the completion of the secondary transfer is conveyed to a fixing device 9 as a fixing unit, where the toner image is fused and fixed to the transfer material P and fixed to the transfer material P. Thereafter, the transfer material P is discharged to the outside of the image forming apparatus 100 as an image formed product (print, copy).

2. Transfer Voltage Control Next, transfer voltage control in the primary transfer process will be described.

  In the present embodiment, primary transfer power sources 33a to 33d are connected to the primary transfer members 5a to 5d of the first to fourth stations 10a to 10d. Each primary transfer power source 33a to 33d can output a constant voltage controlled voltage to each primary transfer member 5a to 5d.

  Further, the image forming apparatus 100 of the present embodiment is used for controlling the transfer voltage only in the fourth station 10d which is the most downstream in the moving direction of the intermediate transfer belt 21 among the first to fourth stations 10a to 10d. It has the following means. That is, for the primary transfer member 5d of the fourth station 10d, a constant current control unit (constant current control circuit) 51 as a constant current control unit and a voltage detection unit (detection unit) as an output voltage detection unit (detection unit). Voltage detection circuit) 52. The constant current control unit 51 includes current detection means for detecting the current value of the voltage output from the primary transfer power supply 33d, and the output voltage of the primary transfer power supply 33d is set so that the detected current value becomes a predetermined value. Control. The voltage detection unit 52 detects an output voltage value when the primary transfer power supply 33d outputs a voltage controlled by the constant current control unit 51 and controlled by the constant current.

  Each of the primary transfer power supplies 33 a to 33 d, the constant current control unit 51, and the voltage detection unit 52 are connected to the controller 50. As will be described in detail later, the controller 50 determines and controls transfer voltages to be applied to the primary transfer members 5a to 5d during image formation based on the detection result input from the voltage detection unit 52. It has the function of voltage control means. In the present embodiment, the controller 50 of the control unit that comprehensively controls the operation of the image forming apparatus 100 also has the above function, but these may be provided individually.

  In this embodiment, in order to detect information relating to the electrical resistance of the primary transfer portion N1, a voltage controlled at a constant current is applied to the primary transfer member 5d, particularly in the fourth station 10d. The voltage detection unit 52 detects the output voltage value from the primary transfer power supply 33d. However, the present invention is not limited to such a configuration, and in order to determine and control an optimum transfer voltage, information on the electrical resistance of the primary transfer portion N1 is obtained during non-image formation, and an image is obtained. It is sufficient that an optimum transfer voltage corresponding to the electric resistance can be used at the time of formation. Therefore, even when an electric resistance detection process at the time of non-image formation is applied, a constant voltage controlled voltage is applied to the primary transfer member 5d to detect the output current value from the primary transfer power source at that time. Good.

  By the way, as described above, when the electric resistance detection means such as the constant current control unit 51 and the voltage detection unit 52 for controlling the transfer voltage are provided only in the fourth station 10d, the transfer voltages in the other stations 10a to 10c are set. Difficult to determine and control. If the transfer voltage is significantly different from the optimum value, the transfer efficiency is lowered and the retransfer rate is increased, and the possibility of generating a defective image is increased.

For example, when the intermediate transfer belt 21 has a high resistance (for example, a volume resistivity of 1 × 10 ¹¹ Ωcm or more), the intermediate transfer belt 21 is charged up under the influence of voltage application to the primary transfer member 5. . Therefore, the surface potential of the intermediate transfer belt 21 may be different between the upstream and downstream primary transfer portions N1 in the moving direction of the intermediate transfer belt 21. As a result, the relationship of the transfer current with respect to the transfer voltage, that is, the VI characteristic may be greatly different between the upstream and downstream primary transfer portions in the moving direction of the intermediate transfer belt 21.

  FIG. 7 shows the transfer of each primary transfer member in the image forming apparatus having the first, second, third, and fourth stations 10a, 10b, 10c, and 10d in this order along the moving direction of the intermediate transfer belt. The VI characteristic which is the relationship between voltage and transfer current is shown. Hereinafter, in the drawings and tables, 1st, 2st, 3st, and 4st indicate data related to the first, second, third, and fourth stations 10a, 10b, 10c, and 10d, respectively.

  According to FIG. 7, the primary transfer member 5 on the upstream side in the moving direction of the intermediate transfer belt 21 tends to flow current, and the primary transfer member 5 on the downstream side in the moving direction of the intermediate transfer belt 21 tends to hardly flow current. I understand that there is.

  For example, the optimum current value at the time of image formation is set to 5 μA, and a voltage subjected to constant current control is applied to the primary transfer member 5d at the fourth station 10d at the time of non-image formation, and the average value of the output voltage at this time ( The average voltage value was calculated. At this time, a predetermined voltage under constant voltage control was applied to the primary transfer members 5a to 5c of the first to third stations 10a to 10c. The calculated average voltage value was 1000V. Table 1 shows a result of measuring a transfer current value when a transfer voltage of 1000 V is applied to each of the primary transfer members 5a to 5d.

  The measured transfer current values were 8 μA for the first station 10a, 7 μA for the second station 10b, 6 μA for the third station 10c, and 5 μA for the fourth station 10d. The primary transfer members 5a to 5c of the first to third stations 10a to 10c flowed an electric current larger than the optimum value of 5 μA.

  As described above, when the transfer voltage of the first to third stations 10a to 10c is controlled only by the result of the average voltage value detected by the fourth station 10d in the electrical resistance detection step, the transfer efficiency and the retransfer rate are achieved. This increases the possibility of generating defective images.

  One object of the present embodiment is to have an image forming apparatus 100 having a plurality of primary transfer members 5a to 5d and having a constant current control unit 51 and a voltage detection unit 52 for only one primary transfer member 5d. Is to obtain the following effects. That is, it is possible to more accurately determine and control the optimum transfer voltage for each primary transfer member 5a to 5d, and to output a high-quality color image with suppressed transfer failure and retransfer. It is to be.

  Therefore, in this embodiment, the state where the intermediate transfer belt 21 is actually charged up at the time of image formation is reproduced according to the position of each of the primary transfer portions N1a to N1d. The transfer voltage to be applied is determined. This will be described in more detail below.

  In this embodiment, the moving speed (rotational speed) V of the surface of the intermediate transfer belt 21 is 50 mm / sec, and the distance D between adjacent primary transfer members 5 in the moving direction of the intermediate transfer belt 21 is 50 mm. did. That is, in this embodiment, the intermediate transfer belt 21 moves the distance between the adjacent primary transfer members 5 in one second.

  In order to control the transfer voltage, first, an electrical resistance detection process for detecting the electrical resistance of the primary transfer portion N1 is performed at a predetermined timing during non-image formation. That is, rotation driving of all the photosensitive drums 1a to 1d and the intermediate transfer belt 21 is started before the primary transfer process. All the photosensitive drums 1a to 1d are negatively charged by the charging rollers 2a to 2d. This operation is defined as a pre-rotation operation.

  During this pre-rotation operation, a transfer current value that is output from the primary transfer power supply 33d to the primary transfer member 5d of the fourth station 10d and is optimal for the primary transfer process during image formation by the constant current control unit 51. A detection voltage under constant current control is applied at 5 μA in this embodiment. At the same time, the voltage detector 52 calculates the average value (average voltage value) of the output voltage of the primary transfer power supply 33d. The calculated average voltage value is input to the controller 50.

  Here, in the electrical resistance detection step, the average voltage value is determined for each of the primary transfer members 5a to 5d as described in detail later. These average voltage values are calculated as Vt (1st), Vt (2st), Vt (3st), and Vt (4st) for the primary transfer members 5a to 5d, respectively. Each average voltage value is stored in a storage unit (such as an electronic memory) built in the controller 50 or connected to the controller 50. These average voltage values are used as transfer voltage values applied to the primary transfer members 5a to 5d during image formation.

  In this embodiment, the controller 50 determines the average voltage value calculated by the voltage detection unit 52 as the transfer voltage value at the time of image formation, but the processing method of the detection result of the voltage detection unit 52 is limited to this. It is not a thing. For example, the controller 50 multiplies the detection result of the output voltage when the constant current control is performed with a predetermined current value (which may be obtained by averaging the result), adds or subtracts it, and forms the image. The process of calculating the transfer voltage value may be executed.

  FIG. 2 shows the photosensitive drum 1 and the intermediate transfer belt 21 driven from the pre-rotation operation to the end of printing in this embodiment, the voltage output state of the charging power source 31, and the voltage output states of the primary transfer power sources 33a to 33d. Show. Hereinafter, the elapsed time in the flow of FIG. 2 is expressed as an elapsed time with reference to the start shown in FIG. 2 (at the start of driving of the photosensitive drum 1 and the intermediate transfer belt 21).

  Simultaneously with the start of the operations of the photosensitive drum 1 and the intermediate transfer belt 21, the application of the charging voltage is started. After 1 second, application of voltage to the primary transfer member 5a of the first station 10a is started. After 3 seconds, application of voltage to the primary transfer member 5b of the second station 10b is started. After 5 seconds, voltage application to the primary transfer member 5c of the third station 10c is started. Simultaneously with the start of voltage application to the primary transfer member 5b of the second station 10b, transfer voltages Vt (1st), Vt (2st), Vt (3st), and Vt (4st) at the time of image formation are calculated. Are started in order. Each calculation time is 1 second.

  Note that when calculating the transfer voltages Vt (1st), Vt (2st), Vt (3st), and Vt (4st) at the time of image formation, the values of the voltages applied to the primary transfer members 5a to 5d are as follows. It is desirable to be close to the transfer voltage value used. For example, a transfer voltage used in the previous image formation can be applied to the primary transfer members 5a to 5c of the first to third stations 10a to 10c. As described above, the detection voltage that is constant-current controlled to the optimum transfer current value is applied to the primary transfer member 5d of the fourth station 10d.

  A (1) to A (4) in FIG. 2 indicate the same portion of the intermediate transfer belt 21. The numbers in parentheses indicate the elapsed time. For example, the location of the intermediate transfer belt 21 indicated by A (1) is indicated by A (2) after 1 second. Similarly, B (1) to B (4), C (1) to C (4), and D (1) to D (4) also indicate the same portion of the intermediate transfer belt 21, respectively.

(1) Regarding Vt (1st) Calculation In order to obtain the optimum transfer voltage Vt (1st), the average voltage is detected by the voltage detector 52 of the fourth station 10d in the state where there is no influence of the charge-up of the intermediate transfer belt 21. It is important to calculate the value.

  Vt (1st) is calculated using the location of the intermediate transfer belt 21 indicated by A (4). At the location of the intermediate transfer belt 21 indicated by A (4), the charge-up history due to the transfer voltage can be confirmed by looking at A (1), A (2), and A (3) shown in FIG. In the periods A (1), A (2), and A (3), the transfer voltages of the first, second, and third stations 10a, 10b, and 10d are all OFF. Accordingly, the portion A (4) of the intermediate transfer belt 21 is not affected by the transfer voltage.

  As a result, the transfer voltage Vt (1st) is not affected by the charge-up of the intermediate transfer belt 21, and is calculated in the state of the intermediate transfer belt 21 equivalent to that when the actual first station 10a is passed during image formation. can do.

(2) Regarding Vt (2st) calculation In order to obtain the optimum transfer voltage Vt (2st), the fourth transfer is performed in the state where the intermediate transfer belt 21 is only affected by the charge-up due to the transfer voltage of the first station 10a. It is important to calculate the average voltage value in the voltage detection unit 52 of the station 10d.

  Vt (2st) is calculated using the location of the intermediate transfer belt 21 indicated by B (4). At the location of the intermediate transfer belt 21 indicated by B (4), the charge-up history due to the transfer voltage can be confirmed by looking at B (1), B (2) and B (3) shown in FIG. The transfer voltage of the first station 10a is ON during the period B (1), and the transfer voltages of the second and third stations 10b and 10c are OFF during the periods B (2) and B (3), respectively. It is a state. Accordingly, the portion B (4) of the intermediate transfer belt 21 is affected only by the transfer voltage of the first station 10a.

  As a result, the transfer voltage Vt (2st) is only affected by the charge-up due to the transfer voltage of the first station 10a, and is equivalent to the intermediate transfer belt when passing through the actual second station 10b during image formation. It can be calculated in 21 states.

(3) Regarding Vt (3st) Calculation In order to obtain the optimum transfer voltage Vt (3st), the intermediate transfer belt 21 is only affected by the charge-up due to the transfer voltages of the first and second stations 10a and 10b. Thus, it is important to calculate the average voltage value in the voltage detection unit 52 of the fourth station 10d.

  Vt (3st) is calculated using the location of the intermediate transfer belt 21 indicated by C (4). In the portion of the intermediate transfer belt 21 indicated by C (4), the charge-up history due to the transfer voltage can be confirmed by looking at C (1), C (2) and C (3) shown in FIG. In the period C (1) and C (2), the transfer voltages of the first and second stations 10a and 10b are both ON, and in the period C (3), the transfer voltage of the third station 10c is OFF. It is a state. Accordingly, the portion C (4) of the intermediate transfer belt 21 is affected only by the transfer voltage of the first and second stations 10a and 10b.

  As a result, the transfer voltage Vt (3st) is affected only by the charge-up due to the transfer voltages of the first and second stations 10a and 10b, and passes through the actual third station 10c during image formation. It can be calculated in the state of the equivalent intermediate transfer belt 21.

(4) Regarding Vt (4st) calculation In order to obtain the optimum transfer voltage Vt (4st), the intermediate transfer belt 21 is affected by the charge-up caused by the transfer voltages of the first to third stations 10a to 10c. It is important to calculate the average voltage value in the voltage detector 52 of the fourth station 10d.

  Vt (4st) is calculated using the location of the intermediate transfer belt 21 indicated by D (4). At the location of the intermediate transfer belt 21 indicated by D (4), the charge-up history due to the transfer voltage can be confirmed by looking at D (1), D (2) and D (3) shown in FIG. During the periods D (1), D (2), and D (3), the transfer voltages of the first, second, and third stations 10a, 10b, and 10c are all in an ON state. Accordingly, the portion D (4) of the intermediate transfer belt 21 is affected by all the transfer voltages of the first to third stations 10a to 10c.

  As a result, the transfer voltage Vt (4st) is affected by the charge-up caused by the transfer voltages of the first to third stations 10a to 10c, and is equivalent to when the actual voltage passes through the fourth station 10d during image formation. The intermediate transfer belt 21 can be calculated.

  As described above, the image forming apparatus 100 according to the present exemplary embodiment includes the movable belt (intermediate transfer belt 21). The image forming apparatus 100 includes a first image carrier (a photosensitive drum 1a, 1b, or 1c of the first, second, or third station 10a, 10b, or 10c) that carries a toner image. The image forming apparatus 100 receives a first transfer voltage and transfers a toner image on the first image carrier onto the belt in a first transfer region (first and second transfer members). A primary transfer member 5a, 5b or 5c) of the second or third station 10a, 10b or 10c. The image forming apparatus 100 also includes a second image carrier (photosensitive drum 1d of the fourth station 10d) that carries a toner image positioned downstream of the first image carrier in the moving direction of the belt. Have. The image forming apparatus 100 receives the second transfer voltage and overlaps the toner image transferred on the belt from the first image carrier in the second transfer region on the second image carrier. A second transfer member (primary transfer member 5d of the fourth station 10d) for transferring the toner image is included. The image forming apparatus 100 also includes a power source (primary transfer power source 33d of the fourth station 10d) that applies a voltage to the second transfer member. Further, the image forming apparatus 100 includes a detection unit (voltage detection unit 52) capable of detecting the current or voltage output from the power source.

  The image forming apparatus 100 according to the present embodiment forms the second transfer voltage (image formation on the primary transfer member 5d of the fourth station 10d) based on the detection result of the detection unit obtained as follows. Set the transfer voltage (sometimes applied). That is, the belt region (D (1), D (2) or D (3) in FIG. 2) entering the first transfer region when a voltage is applied to the first transfer member. Is a detection result obtained by outputting a detection voltage from the power source when the second transfer area is entered later.

  In this embodiment, the first transfer voltage (primary transfer of the first, second or third station 10a, 10b or 10c) is based on the detection result of the detection means obtained as follows. The transfer voltage to be applied to the members 5a, 5b or 5c during image formation is set. That is, a detection result obtained by outputting a detection voltage from the power supply when the belt region not charged by the first transfer member enters the second transfer region. In the belt region, A (1) to A (3) in FIG. 2 correspond to the first transfer voltage for the primary transfer member 5a of the first station 10a. Further, B (2) to B (3) in FIG. 2 correspond to the first transfer voltage for the primary transfer member 5b of the second station 10b. Furthermore, C (3) in FIG. 2 corresponds to the first transfer voltage for the primary transfer member 5c of the third station 10c.

  In other words, in the present embodiment, the first transfer voltage (first, second or third station 10a, 10b or 10c) is based on the detection result detected by the detection means as follows. The transfer voltage applied to the primary transfer member 5a, 5b or 5c during image formation is set. That is, when the voltage is applied to the first transfer member, the detection means detects before the belt area entering the first transfer area enters the second transfer area. It is a result. The belt area corresponds to B (1), C (1), and D (1) in FIG. 2 for the first transfer voltage for the primary transfer member 5a of the first station 10a. Further, C (2) and D (2) in FIG. 2 correspond to the first transfer voltage for the primary transfer member 5b of the second station 10b. Further, D (3) in FIG. 2 corresponds to the first transfer voltage for the primary transfer member 5c of the third station 10c.

  As described above, according to the control of this embodiment, the voltage detection unit 52 of the fourth station 10d detects the output voltage value in consideration of the charge-up of the intermediate transfer belt 21, and the average voltage value (image) Transfer voltage value at the time of formation) can be calculated. This charge-up of the intermediate transfer belt 21 is due to the influence of voltage application to the primary transfer members 5a to 5c of the first to third stations 10a to 10c. Therefore, according to the control method of this embodiment, the transfer voltage can be controlled with high accuracy.

  Table 2 shows the transfer voltage at the time of image formation of each of the stations 10a to 10d calculated according to the present embodiment and the transfer current value actually measured during the transfer process.

  According to this example, the transfer voltages Vt (1st), Vt (2st), Vt (3st), and Vt (4st) used at the time of image formation were calculated as 600 V, 650 V, 800 V, and 1000 V, respectively. This difference in the value of the calculation result means that the surface of the intermediate transfer belt 21 is charged up at the time of calculation, that is, the surface potential of the intermediate transfer belt 21 is different.

  The measured transfer current values when the transfer voltage calculated as described above is applied to the primary transfer members 5a to 5d during image formation are 5.2 μA, 5.1 μA, 5 μA, respectively. 5 μA. These actually measured transfer current values were almost equal to 5 μA, which is the optimum current value during image formation.

  As described above, according to this embodiment, the transfer voltage applied to the primary transfer members 5a to 5d at the time of image formation is increased in consideration of the effect of the charge-up of the intermediate transfer belt 21 which varies depending on the stations 10a to 10d. It is possible to calculate with accuracy. Therefore, according to this embodiment, it is possible to more accurately calculate the optimum transfer voltage for each of the primary transfer members 5a to 5d, and to apply the optimum transfer current during image formation. That is, according to the present embodiment, an optimal transfer voltage can be more accurately determined and controlled for each of the primary transfer members 5a to 5d, and a high-quality color image in which transfer failure or retransfer is suppressed. Can be output.

Example 2
Next, another embodiment of the image forming apparatus according to the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, elements having the same functions or configurations as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 3 shows the driving state of the photosensitive drum 1, the intermediate transfer belt 21, the voltage output state of the charging power source 31, and the voltage output states of the primary transfer power sources 33a to 33d from the pre-rotation operation to the end of printing in this embodiment. Show. Hereinafter, the elapsed time in the flow of FIG. 3 is expressed as an elapsed time based on the start shown in FIG. 3 (at the start of driving of the photosensitive drum 1 and the intermediate transfer belt 21).

  Three seconds after the driving of the photosensitive drum 1 and the intermediate transfer belt 21 is started, application of voltage to the primary transfer members 5a to 5c of the first to third stations 10a to 10c is started. Then, the calculation of the transfer voltages Vt (1st), Vt (2st), Vt (3st), and Vt (4st) at the time of image formation is started in order. Each calculation time is 1 second.

  In this embodiment, voltage application to the primary transfer members 5a to 5d of the first to fourth stations 10a to 10d is started simultaneously. Thereby, control can be simplified. However, since the voltages of the primary transfer members 5a to 5d of all the stations 10a to 10d are applied simultaneously, there is a possibility that a sudden load is applied to the drive roller 22 that rotates the intermediate transfer belt 21. As a result, the transfer voltage value calculation accuracy may be reduced. In particular, when a member having a large sliding resistance is used for the primary transfer member 5, sufficient care is required.

  Note that when calculating the transfer voltages Vt (1st), Vt (2st), Vt (3st), and Vt (4st) at the time of image formation, the values of the voltages applied to the primary transfer members 5a to 5d are as follows. It is desirable to be close to the transfer voltage value used.

  A (1) to A (4), B (1) to B (4), C (1) to C (4), and D (1) to D (4) in FIG. Has the same meaning as

(1) Regarding Vt (1st) Calculation In order to obtain the optimum transfer voltage Vt (1st), the average voltage is detected by the voltage detector 52 of the fourth station 10d in the state where there is no influence of the charge-up of the intermediate transfer belt 21. It is important to calculate the value.

  Vt (1st) is calculated using the location of the intermediate transfer belt 21 indicated by A (4). At the location of the intermediate transfer belt 21 indicated by A (4), the charge-up history due to the transfer voltage can be confirmed by looking at A (1), A (2) and A (3) shown in FIG. In the periods A (1), A (2), and A (3), the transfer voltages of the first, second, and third stations 10a, 10b, and 10d are all OFF. Accordingly, the portion A (4) of the intermediate transfer belt 21 is not affected by the transfer voltage.

  As a result, the transfer voltage Vt (1st) is not affected by the charge-up of the intermediate transfer belt 21, and is calculated in the state of the intermediate transfer belt 21 equivalent to that when the actual first station 10a is passed during image formation. can do.

(2) Regarding the Vt (2st) calculation In order to obtain the optimum transfer voltage Vt (2st), the fourth transfer is performed while the intermediate transfer belt 21 is only affected by the charge-up due to the transfer voltage of the third station 10c. It is important to calculate the average voltage value in the voltage detection unit 52 of the station 10d.

  Vt (2st) is calculated using the location of the intermediate transfer belt 21 indicated by B (4). At the location of the intermediate transfer belt 21 indicated by B (4), the charge-up history due to the transfer voltage can be confirmed by looking at B (1), B (2) and B (3) shown in FIG. The transfer voltage at the first and second stations 10a and 10b is OFF during the period B (1) and B (2), respectively, and the transfer voltage at the third station 10c is ON during the period B (3). It is. Accordingly, the portion B (4) of the intermediate transfer belt 21 is affected only by the transfer voltage of the third station 10c.

  As a result, the transfer voltage Vt (2st) is only affected by the charge-up due to the transfer voltage of the third station 10c, and is equivalent to the intermediate transfer belt when passing the actual second station 10b during image formation. It can be calculated in 21 states.

(3) Regarding Vt (3st) calculation In order to obtain the optimum transfer voltage Vt (3st), the intermediate transfer belt 21 is only affected by the charge-up due to the transfer voltages of the second and third stations 10b and 10c. Thus, it is important to calculate the average voltage value in the voltage detection unit 52 of the fourth station 10d.

  Vt (3st) is calculated using the location of the intermediate transfer belt 21 indicated by C (4). At the location of the intermediate transfer belt 21 indicated by C (4), the charge-up history due to the transfer voltage can be confirmed by looking at C (1), C (2) and C (3) shown in FIG. The transfer voltage of the first station 10a is OFF during the period C (1), and the transfer voltages of the second and third stations 10b and 10c are both ON during the period C (2) and C (3). It is a state. Accordingly, the portion C (4) of the intermediate transfer belt 21 is affected only by the transfer voltage of the second and third stations 10b and 10c.

  As a result, the transfer voltage Vt (3st) is only affected by the charge-up due to the transfer voltages of the second and third stations 10b and 10c, and passes through the actual third station 10c during image formation. It can be calculated in the state of the equivalent intermediate transfer belt 21.

(4) Regarding Vt (4st) calculation In order to obtain the optimum transfer voltage Vt (4st), the intermediate transfer belt 21 is affected by the charge-up caused by the transfer voltages of the first to third stations 10a to 10c. It is important to calculate the average voltage value in the voltage detector 52 of the fourth station 10d.

  Vt (4st) is calculated using the location of the intermediate transfer belt 21 indicated by D (4). At the location of the intermediate transfer belt 21 indicated by D (4), the charge-up history due to the transfer voltage can be confirmed by looking at D (1), D (2), and D (3) shown in FIG. During the periods D (1), D (2), and D (3), the transfer voltages of the first, second, and third stations 10a, 10b, and 10c are all in an ON state. Accordingly, the portion D (4) of the intermediate transfer belt 21 is affected by all the transfer voltages of the first to third stations 10a to 10c.

  As a result, the transfer voltage Vt (4st) is affected by the charge-up caused by the transfer voltages of the first to third stations 10a to 10c, and is equivalent to when the actual voltage passes through the fourth station 10d during image formation. The intermediate transfer belt 21 can be calculated.

  As described above, according to the control of this embodiment, the voltage detection unit 52 of the fourth station 10d detects the output voltage value in consideration of the charge-up of the intermediate transfer belt 21, and the average voltage value (image) Transfer voltage value at the time of formation) can be calculated. This charge-up of the intermediate transfer belt 21 is due to the influence of voltage application to the primary transfer members 5a to 5c of the first to third stations 10a to 10c. Therefore, according to the control method of this embodiment, the transfer voltage can be controlled with high accuracy.

  Table 3 shows the transfer voltage at the time of image formation of each of the stations 10a to 10d calculated according to the present embodiment and the transfer current value actually measured during the transfer process.

  According to this example, the transfer voltages Vt (1st), Vt (2st), Vt (3st), and Vt (4st) used at the time of image formation were calculated as 600 V, 650 V, 800 V, and 1000 V, respectively. This difference in the value of the calculation result means that the surface of the intermediate transfer belt 21 is charged up at the time of calculation, that is, the surface potential of the intermediate transfer belt 21 is different.

  The measured transfer current values when the transfer voltage calculated as described above is applied to the primary transfer members 5a to 5d during image formation are 5.2 μA, 5.1 μA, 5 μA, respectively. 5 μA. These actually measured transfer current values were almost equal to 5 μA, which is the optimum current value during image formation. Further, it was almost the same as the result of Example 1.

  As described above, according to the present embodiment, the transfer voltage applied to the primary transfer members 5a to 5d at the time of image formation is increased in consideration of the effect of the charge-up of the intermediate transfer belt 21 which varies depending on the stations 10a to 10d. It is possible to calculate with accuracy. Therefore, according to the present embodiment, as in the first embodiment, the optimum transfer voltage value can be accurately calculated for each of the primary transfer members 5a to 5d, and the optimum transfer current can be applied during image formation. Is possible. That is, according to the present embodiment, as in the first embodiment, the optimum transfer voltage can be more accurately determined and controlled for each of the primary transfer members 5a to 5d, and transfer defects and retransfer can be prevented. A suppressed high-quality color image can be output. Furthermore, this embodiment is advantageous in that the control can be further simplified.

Example 3
Next, another embodiment of the image forming apparatus according to the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the image forming apparatus of the first embodiment. Therefore, elements having the same functions or configurations as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  FIG. 4 shows the photosensitive drum 1 and intermediate transfer belt drive state, voltage output state of the charging power source 31, and voltage output states of the primary transfer power sources 33a to 33d from the pre-rotation operation to the end of printing in this embodiment. ing. Hereinafter, the elapsed time in the flow of FIG. 4 is expressed as an elapsed time with reference to the start shown in FIG. 4 (at the start of driving of the photosensitive drum 1 and the intermediate transfer belt 21).

  Driving of the photosensitive drum 1 and the intermediate transfer belt 21 is started simultaneously. Three seconds later, the transfer voltages Vt (1st), Vt (2st), Vt (3st), and Vt (4st) are calculated in order. Each calculation time is 2 seconds. That is, in this embodiment, each calculation time is longer than that in the first embodiment. Then, after 4 seconds, application of voltage to the primary transfer member 5c of the third station 10c is started. After 5 seconds, application of voltage to the primary transfer member 5b of the second station 10b is started. After 6 seconds, voltage application to the primary transfer member 5a of the first station 10a is started.

  In the present embodiment, a longer pre-rotation time is required than in the first and second embodiments. Accordingly, in this embodiment, the calculation time of each of the transfer voltages Vt (1st), Vt (2st), Vt (3st), and Vt (4st) is also 1 second as compared with the first and second embodiments. long. For this reason, in this embodiment, the calculation time has a sufficient margin, and the transfer voltage can be calculated with higher accuracy.

  Note that when calculating the transfer voltages Vt (1st), Vt (2st), Vt (3st), and Vt (4st) at the time of image formation, the values of the voltages applied to the primary transfer members 5a to 5d are as follows. It is desirable to be close to the transfer voltage value used.

  A (1) to A (4), B (1) to B (4), C (1) to C (4), and D (1) to D (4) in FIG. 4 are those described with reference to FIG. Has the same meaning as The transfer voltage Vt (1st), Vt (2st), Vt (3st), and Vt (4st) calculation methods in this embodiment are described in Example 1 except that the transfer voltage calculation time is long. The detailed description is omitted because it is almost the same as that described above.

  Table 4 shows the transfer voltage at the time of image formation of each of the stations 10a to 10d calculated according to the present embodiment, and the transfer current value actually measured during the transfer process.

  According to this example, the transfer voltages Vt (1st), Vt (2st), Vt (3st), and Vt (4st) used at the time of image formation were calculated as 580 V, 630 V, 800 V, and 1000 V, respectively. This difference in the value of the calculation result means that the surface of the intermediate transfer belt 21 is charged up at the time of calculation, that is, the surface potential of the intermediate transfer belt 21 is different.

  The measured transfer current values when the transfer voltage calculated as described above is applied to the primary transfer members 5a to 5d at the time of image formation are 5.1 μA, 5 μA, 5 μA, and 5 μA, respectively. there were. These actually measured transfer current values were almost equal to 5 μA, which is the optimum current value during image formation. Further, an effect substantially equal to or higher than the results of Examples 1 and 2 was confirmed.

  As described above, according to this embodiment, the transfer voltage applied to the primary transfer members 5a to 5d at the time of image formation is increased in consideration of the effect of the charge-up of the intermediate transfer belt 21 which varies depending on the stations 10a to 10d. It is possible to calculate with accuracy. Therefore, according to the present embodiment, as in the first and second embodiments, the optimum transfer voltage value is accurately calculated for each primary transfer member 5a to 5d, and the optimum transfer current is applied during image formation. It is possible. That is, according to the present embodiment, as in the first and second embodiments, it is possible to more accurately determine and control the optimum transfer voltage for each of the primary transfer members 5a to 5d. A high-quality color image with suppressed transfer can be output. Furthermore, in this embodiment, the control accuracy can be further increased.

Example 4
Next, another embodiment of the image forming apparatus according to the present invention will be described. In the image forming apparatus of the present embodiment, elements having the same or equivalent functions and configurations as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

1. Overall Configuration and Operation of Image Forming Apparatus FIG. 5 shows a schematic cross section of an image forming apparatus 200 of this embodiment. The image forming apparatus 200 of this embodiment is a direct transfer tandem type image forming apparatus that uses a transfer belt 61 as a transfer material carrier that carries and conveys a transfer material P such as paper.

  The image forming apparatus according to the present exemplary embodiment includes first, second, third, and fourth stations 10a, 10b, 10c, and 10d as a plurality of image forming units. The configurations and operations of the stations 10a to 10d are substantially the same as those in the first embodiment.

  The image forming apparatus 200 according to the present exemplary embodiment includes a transfer device 60 instead of the intermediate transfer device 20 of the image forming apparatus 100 according to the first exemplary embodiment. The transfer device 60 is provided with an endless belt as a transfer material carrier, that is, a transfer belt (electrostatic adsorption conveyance belt) 61 provided so as to face the photosensitive drums 1a to 1d of all the stations 10a to 10d. Have. The transfer device 60 includes transfer members 5 a to 5 d at positions facing the respective photosensitive drums 1 a to 1 d on the inner peripheral surface side of the transfer belt 61. That is, the transfer members 5a to 5d are disposed on the opposite side of the photosensitive drums 1a to 1d with the transfer belt 61 interposed therebetween. The transfer members 5a to 5d are pressed against the photosensitive drums 1a to 1d via the transfer belt 61, and transfer portions (transfer nip portions) Na to Nd where the transfer belt 61 and the photosensitive drums 1a to 1d come into contact with each other. Form.

Transfer belt 61 is, as its stretching members (supporting member), the driving roller 6 2 for driving the transfer belt 61 is supported by the tension rollers 6 3 to apply tension to the transfer belt 61. The transfer belt 61 rotates (circulates) in the direction of the arrow R3 (counterclockwise) in the figure when the drive roller 62 is driven to rotate in the direction of the arrow R2 (counterclockwise) in the figure. The transfer belt 61 carries the transfer material P on its surface and sequentially conveys it to the transfer portions Na to Nd of the stations 10a to 10d.

In this embodiment, the configuration of the transfer belt 61 is the same as that of the intermediate transfer belt 21 included in the image forming apparatus 100 of the first embodiment. That is, as the transfer belt 61, a general-purpose engineering plastic sheet having a thickness of 100 μm and a volume resistivity of 10 ¹¹ Ωcm was used. The configuration of the transfer member 5 is the same as that of the primary transfer member 5 in the image forming apparatus 100 of the first embodiment. A transfer power source 33, which is a voltage supply means for the transfer member 5, is connected to the transfer member 5.

  The operation of each station 10 during image formation of the image forming apparatus 200 of the present embodiment is the same as that of the image forming apparatus 100 of the first embodiment. However, in this embodiment, the toner image formed on each photosensitive drum 1 of each station 10 is transferred onto the transfer material P carried on the transfer belt 61 and conveyed.

  In other words, in this embodiment, the transfer material P picked up from the transfer material cassette 81 by the transfer material supply roller 82 and transported to the registration roller 83 is synchronized with the toner image on the photosensitive drum 1. Is conveyed onto the transfer belt 61.

  The toner image on the photosensitive drum 1 is transferred onto the transfer material P carried on the transfer belt 61 at the transfer portion N. At this time, a transfer voltage having a polarity opposite to the normal charging polarity of the toner (positive polarity in this embodiment) is applied to the transfer member 5 by the transfer power source 33. In this embodiment, a DC voltage is applied as the transfer voltage. During the transfer process, an electric field is formed in the transfer portion (transfer region) N in a direction in which the toner charged to the normal charging polarity is moved from the photosensitive drum 1 side to the transfer material P side on the transfer belt 61.

  For example, when a full-color image is formed, the toner images formed on the photosensitive drums 1a to 1d are sequentially transferred onto the transfer material P on the transfer belt 61 as the transfer material P is conveyed by the transfer belt 61. Overlaid and transferred. Thereafter, the transfer material P onto which the toner image has been transferred is separated from the transfer belt 61 and sent to the fixing device 9. Here, the toner image on the transfer material P is melted and fixed to the transfer material P, and a color image is obtained.

2. Transfer Voltage Control Next, transfer voltage control in the transfer process will be described.

In this embodiment, transfer power sources 33a to 33d are connected to the transfer members 5a to 5d of the first to fourth stations 10a to 10d. Each of the transfer power sources 33a to 33d can output a constant voltage controlled voltage to each of the transfer members 5a to 5d.

  The image forming apparatus 200 according to the present embodiment further controls the transfer voltage only in the fourth station 10d which is the most downstream in the moving direction of the transfer belt 61 among the first to fourth stations 10a to 10d. It has the following means. That is, for the transfer member 5d of the fourth station 10d, a constant current control unit (constant current control circuit) 51 as a constant current control unit and a voltage detection unit (voltage detection unit) as an output voltage detection unit (detection unit). Circuit) 52. Functions and configurations of the constant current control unit 51 and the voltage detection unit 52 are the same as those of the image forming apparatus 100 of the first embodiment.

  In this embodiment, the moving speed (rotational speed) V of the surface of the transfer belt 61 is 50 mm / sec, and the distance D between the adjacent transfer members 5 in the moving direction of the transfer belt 61 is 50 mm. That is, in this embodiment, the transfer belt 61 moves the distance between the adjacent transfer members 5 in one second.

  In order to control the transfer voltage, first, an electrical resistance detection process for detecting the electrical resistance of the transfer portion N is performed at a predetermined timing during non-image formation. That is, the rotational drive of all the photosensitive drums 1a to 1d and the transfer belt 61 is started before the primary transfer process. All the photosensitive drums 1a to 1d are negatively charged by the charging rollers 2a to 2d. This operation is defined as a pre-rotation operation.

  At the time of this pre-rotation operation, the transfer power source 33d outputs the transfer member 5a of the fourth station 10d, and the transfer current value optimum for the transfer process at the time of image formation by the constant current control unit 51 (5 μA in this embodiment). ) Is applied with a constant current controlled detection voltage. At the same time, the voltage detector 52 calculates the average value (average voltage value) of the output voltage of the transfer power supply 33d. The calculated average voltage value is input to the controller 50.

  Here, in the electrical resistance detection step, the average voltage value is determined for each of the transfer members 5a to 5d as described in detail later. These average voltage values are calculated as Vt0 (1st), Vt0 (2st), Vt0 (3st), and Vt0 (4st) for the respective transfer members 5a to 5d. Each average voltage value is stored in a storage unit (such as an electronic memory) built in the controller 50 or connected to the controller 50.

  However, at the time of image formation, there is a transfer material P such as paper on the transfer belt 61, and it is preferable to correct the transfer voltage in consideration of the type (paper type) of the transfer material P and the electric resistance value. Therefore, in this embodiment, the average voltage value as described above is not used as it is as the value of the transfer voltage applied to the transfer member 5 during image formation, but is calculated as the transfer voltage before correction.

  In this embodiment, the temperature and humidity detection sensor 53 detects and monitors the temperature t [° C.] and the humidity h [%]. The detection result of the temperature / humidity detection sensor 53 is input to the controller 50. The controller 50 predicts the electric resistance value of the transfer material P based on the detected values of temperature and humidity and the type of the transfer material P. Based on the prediction result, the above-mentioned pre-correction transfer voltages Vt0 (1st), Vt0 (2st), Vt0 (3st), and Vt0 (4st) are corrected.

  The post-correction transfer voltage value after the predictive correction is used as transfer voltages Vt (1st), Vt (2st), Vt (3st), and Vt (4st) applied to the transfer member 5 during image formation.

  FIG. 6 shows the photosensitive drum 1 and the transfer belt 61 in the driving state, the voltage output state of the charging power source 31, and the voltage output states of the transfer power sources 33a to 33d from the pre-rotation operation to the end of printing in this embodiment. . Hereinafter, the elapsed time in the flow of FIG. 6 is expressed as an elapsed time with reference to the start (when driving of the photosensitive drum 1 and the transfer belt 61 is started) shown in FIG.

  Simultaneously with the start of the operation of the photosensitive drum 1 and the transfer belt 61, application of the charging voltage is started. After 1 second, application of voltage to the transfer member 5a of the first station 10a is started. After 3 seconds, application of voltage to the transfer member 5b of the second station 10b is started. After 5 seconds, application of voltage to the transfer member 5c of the third station 10c is started. Simultaneously with the start of voltage application to the transfer member 5b of the second station 10b, calculation of the pre-correction transfer voltages Vt0 (1st), Vt0 (2st), Vt0 (3st), and Vt0 (4st) is started in order. The Each calculation time is 1 second.

  Note that when calculating the pre-correction transfer voltages Vt0 (1st), Vt0 (2st), Vt0 (3st), and Vt0 (4st), the values of the voltages applied to the transfer members 5a to 5d are the transfer values used during image formation. It is desirable to be close to the voltage value.

A of FIG. 6 (1) ~A (4) , B (1) ~B (4), C (1) ~C (4), D (1) ~D (4) is, instead of the intermediate transfer belt 21 2 has the same meaning as described with reference to FIG. Since the calculation method of the pre-correction transfer voltages Vt0 (1st), Vt0 (2st), Vt0 (3st), and Vt0 (4st) in this embodiment is the same as that described in the first embodiment, detailed description thereof is omitted. To do.

  As described above, the image forming apparatus 100 according to the present exemplary embodiment includes the belt (transfer belt 61) that is movable while carrying the transfer material P. The image forming apparatus 200 includes a first image carrier (a photosensitive drum 1a, 1b, or 1c of the first, second, or third station 10a, 10b, or 10c) that carries a toner image. The image forming apparatus 200 receives a first transfer voltage and transfers a toner image on the first image carrier to a transfer material P in a first transfer region (first and second transfer members). 2 or a third station 10a, 10b or 10c of a transfer member 5a, 5b or 5c). In addition, the image forming apparatus 200 includes a second image carrier (photosensitive drum 1d of the fourth station 10d) that carries a toner image positioned downstream of the first image carrier in the moving direction of the belt. Have. The image forming apparatus 200 receives the second transfer voltage and overlaps the toner image transferred from the first image carrier to the transfer material P in the second transfer region on the second image carrier. A second transfer member (transfer member 5d of the fourth station 10d) for transferring the toner image is included. Further, the image forming apparatus 200 has a power supply (transfer power supply 33d of the fourth station 10d) for applying a voltage to the second transfer member. Further, the image forming apparatus 200 includes a detection unit (voltage detection unit 52) capable of detecting the current or voltage output from the power source.

  The image forming apparatus 200 according to the present exemplary embodiment applies the second transfer voltage (applied to the transfer member 5d of the fourth station 10d at the time of image formation based on the detection result of the detection unit obtained as follows. Transfer voltage). That is, the belt region (D (1), D (2) or D (3) in FIG. 6) entering the first transfer region when a voltage is applied to the first transfer member. Is a detection result obtained by outputting a detection voltage from the power source when the second transfer area is entered later.

  Table 5 shows the transfer voltage at the time of image formation of each of the stations 10a to 10d calculated according to the present embodiment and the transfer current value actually measured during the transfer process.

  According to this example, the pre-correction transfer voltages Vt0 (1st), Vt0 (2st), Vt0 (3st), and Vt0 (4st) were calculated as 600 V, 650 V, 800 V, and 1000 V, respectively. The difference in the value of the calculation result means that the charge-up state of the surface of the transfer belt 61 at the time of calculation, that is, the surface potential of the transfer belt 61 is different.

  The monitoring result of the temperature / humidity detection sensor 53 at this time was 25 ° C./50%, and the transfer material P used was plain paper (color laser copier paper A4 manufactured by Canon Inc.). The correction was calculated to be +200 V from the temperature and humidity and the paper type. Therefore, the transfer voltages Vt (1st), Vt (2st), Vt (3st), and Vt (4st) used at the time of image formation were determined as 800 V, 850 V, 1000 V, and 1200 V, respectively.

  The measured transfer current values when the transfer voltage values calculated as described above are applied to the transfer members 5a to 5d at the time of image formation are 5.3 μA, 5.2 μA, 5.1 μA, and 5 μA, respectively. Met. These actually measured transfer current values were almost equal to 5 μA, which is the optimum current value during image formation.

  Thus, according to the present embodiment, the image forming apparatus 100 using the intermediate transfer belt 21 according to the first embodiment is used in the image forming apparatus 200 using the transfer belt 61 that carries and conveys the transfer material P such as paper. The same effect as in can be obtained. That is, according to the present embodiment, the transfer voltage applied to the transfer members 5a to 5d at the time of image formation is calculated with high accuracy in consideration of the effect of the charge-up of the transfer belt 61 that varies depending on the stations 10a to 10d. It is possible. Therefore, according to the present embodiment, it is possible to more accurately calculate an optimum transfer voltage for each of the transfer members 5a to 5d, and to apply an optimum transfer current during image formation. That is, according to this embodiment, the optimum transfer voltage can be more accurately determined and controlled for each of the transfer members 5a to 5d, and a high-quality color image that suppresses transfer failure and retransfer is output. can do.

  In the present exemplary embodiment, the case where the transfer voltage control method similar to that in the first exemplary embodiment is employed in the tandem image forming apparatus 200 of the direct transfer method has been described. However, the present invention is not limited to this, and in the tandem image forming apparatus 200 of the direct transfer method, the transfer voltage control methods described in the second embodiment and the third embodiment may be employed. The same effect can be obtained.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention. It is a chart figure which shows an example of the control flow of the transfer voltage according to this invention. It is a chart figure which shows the other example of the control flow of the transfer voltage according to this invention. It is a chart figure which shows the other example of the control flow of the transfer voltage according to this invention. It is a schematic sectional drawing of the other Example of the image forming apparatus which concerns on this invention. It is a chart figure which shows the other example of the control flow of the transfer voltage according to this invention. It is a graph which shows an example of VI characteristic for demonstrating the control of the conventional transfer voltage.

Explanation of symbols

1 Photosensitive drum (image carrier)
5 Primary transfer member 21 Intermediate transfer belt 33 Primary transfer power source 51 Constant current control unit 52 Voltage detection unit (detection means)
53 Temperature / Humidity Sensor 61 Transfer Belt

Claims (12)

A movable belt, a first image carrier for carrying a toner image, and a toner image on the first image carrier in a first transfer region upon receiving a first transfer voltage to the belt side a first transfer member, receiving a second image bearing member for bearing a location toner image downstream of the moving direction of the belt with respect to the first image bearing member, a second transfer voltage first to a second transfer member for transferring the pre-Symbol toner image on the second image carrier to the belt side on 2 of the transfer area smell, a power source for applying a voltage to the second transfer member, wherein the power supply output in the image forming apparatus having a detectable detection means a current or voltage, the,
When entering the second transfer region after region of the belt which enters the said first transfer region when a voltage is applied to the first transfer member, it outputs the power supply or al voltage And setting the second transfer voltage according to the detection result of the detection means obtained by,
According to the detection result of the detection means obtained by outputting a voltage from the power supply when the belt region not charged by the first transfer member enters the second transfer region. An image forming apparatus, wherein the first transfer voltage is set . A move possible belt, a first image bearing member for bearing a toner image, the toner image on the first image bearing member at a first transfer region receives the first transfer voltage the belt side receiving a first transfer member which transfers a second image carrier for carrying a position to the toner image on the downstream of the moving direction of the belt with respect to the first image bearing member, a second transfer voltage a power source for applying a second transfer member for transferring the pre-Symbol toner image on the second image carrier to the belt side Te second transfer region odor, a voltage to the second transfer member, wherein the power source in the image forming apparatus having a detectable detection means a current or voltage output,
When entering the second transfer region after region of the belt which enters the said first transfer region when a voltage is applied to the first transfer member, it outputs the power supply or al voltage And setting the second transfer voltage according to the detection result of the detection means obtained by,
When the voltage is applied to the first transfer member, the detection result detected by the detection means before the belt region entering the first transfer region enters the second transfer region. The image forming apparatus is characterized in that the first transfer voltage is set accordingly .   A movable belt, a first image carrier for carrying a toner image, and a toner image on the first image carrier in a first transfer region upon receiving a first transfer voltage to the belt side A first transfer member, a second image carrier that is positioned downstream of the first image carrier in the moving direction of the belt and carries a toner image, and receives a second transfer voltage and receives a second transfer voltage. A second transfer member that transfers the toner image on the second image carrier to the belt side in the second transfer region, a power source that applies a voltage to the second transfer member, and a current that the power source outputs. Or an image forming apparatus having detection means capable of detecting voltage,
  The first transfer voltage is obtained by outputting the voltage from the power source when the belt area not charged by the first transfer member enters the second transfer area. An image forming apparatus that is set in accordance with the detection result.   A first power source that applies a voltage to the first transfer member; a power source that applies a voltage to the second transfer member is a second power source; and the detection unit includes the first power source. The image forming apparatus according to claim 3, wherein the image forming apparatus is not connected but connected to the second power source.   The belt region that is not charged by the first transfer member passes through the first transfer region when no voltage is applied from the first power source to the first transfer member. The image forming apparatus according to claim 4, wherein the image forming apparatus is an area of the image forming apparatus.   A plurality of image carriers that carry toner images other than the first and second image carriers, and the first image carrier, the second image carrier, and the other plurality of images. A carrier is arranged along the moving direction of the belt, and the second image carrier is arranged at the most downstream position in the moving direction of the belt among all the image carriers. The image forming apparatus according to any one of claims 3 to 5.   A movable belt, a first image carrier for carrying a toner image, and a toner image on the first image carrier in a first transfer region upon receiving a first transfer voltage to the belt side A first transfer member, a second image carrier that is positioned downstream of the first image carrier in the moving direction of the belt and carries a toner image, and receives a second transfer voltage and receives a second transfer voltage. A second transfer member that transfers the toner image on the second image carrier to the belt side in the second transfer region, a power source that applies a voltage to the second transfer member, and a current that the power source outputs. Or an image forming apparatus having detection means capable of detecting voltage,
  The first transfer voltage is applied before the belt region entering the first transfer region enters the second transfer region when a voltage is applied to the first transfer member. An image forming apparatus, wherein the image forming apparatus is set according to a detection result detected by a detection unit.   A first power source that applies a voltage to the first transfer member; a power source that applies a voltage to the second transfer member is a second power source; and the detection unit includes the first power source. The image forming apparatus according to claim 7, wherein the image forming apparatus is not connected but connected to the second power source.   The belt region entering the first transfer region when a voltage is applied to the first transfer member is charged by the first transfer member to which a voltage is applied from the first power source. The image forming apparatus according to claim 8, wherein the image forming apparatus is an area of the belt that has been subjected to printing.   A plurality of image carriers that carry toner images other than the first and second image carriers, and the first image carrier, the second image carrier, and the other plurality of images. A carrier is arranged along the moving direction of the belt, and the second image carrier is arranged at the most downstream position in the moving direction of the belt among all the image carriers. The image forming apparatus according to any one of claims 7 to 9.   The image forming apparatus according to claim 1, wherein the belt is an intermediate transfer belt to which a toner image is transferred from the first and second image carriers.   11. The belt according to claim 1, wherein the belt is a conveyance belt that conveys a transfer material onto which a toner image is transferred from the first and second image carriers. Image forming apparatus.

Images