JP6493304B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a tandem color image forming apparatus in which a plurality of image forming units including a photoconductor are arranged in parallel along an intermediate transfer member.

  Conventionally, a tandem that forms a color image by primary transfer of toner images of different colors onto an endless intermediate transfer belt by a plurality of image forming units and sequentially superimposing them, followed by secondary transfer and fixing on a recording medium A color image forming apparatus of the type is known.

  In the tandem type color image forming apparatus, when the toner images of the respective colors formed on the photosensitive drum are superimposed on the intermediate transfer belt, the primary image is first formed on the intermediate transfer belt in the image forming unit on the upstream side in the belt traveling direction. When the transferred toner image passes through the primary transfer electric field in the downstream image forming unit, discharge and charge injection to the toner image occur, and the charge amount of the toner increases. Toner having a high charge amount has a strong electrostatic adhesion to the intermediate transfer belt. In such a case, if a strong secondary transfer electric field is generated in order to ensure the secondary transfer efficiency of the toner image, the non-charged toner that is primarily transferred in the image forming section upstream in the belt traveling direction is discharged. As a result, reverse charging is facilitated, and the secondary transfer efficiency is lowered. In addition, a strong secondary transfer electric field tends to cause a discharge phenomenon between the recording medium and the intermediate transfer belt, and causes a reduction in quality of the secondary transfer image.

  The above-described primary transfer electric field control methods include constant current control and constant voltage control. Constant current control is almost unaffected by the impedance change between the primary transfer roller and the photosensitive drum, which varies depending on the durability and environment, and can stabilize the primary transfer electric field against the gap between the intermediate transfer belt and the photosensitive drum. On the other hand, the transfer electric field changes depending on the print pattern. Specifically, when forming a small print pattern (Short Solid Image) in the longitudinal direction, the resistance of the solid part increases and the transfer current leaks outside the solid part, so it is necessary to increase the current. There is. As a result, when a large print pattern (Long Solid Image) is formed in the longitudinal direction, an excessive transfer current (electric field) is generated, and the toner charge amount on the intermediate transfer belt is increased, so that an image is transferred at the secondary transfer portion. There is a problem that (transfer image quality) deterioration occurs.

  On the other hand, the constant voltage control has the advantage that the transfer electric field does not change depending on the print pattern, but is affected by the impedance change between the primary transfer roller and the photosensitive drum. Therefore, when performing constant voltage control of the primary transfer electric field, it is necessary to apply a voltage that matches the resistance of a member such as a transfer roller or an intermediate transfer belt.

  Therefore, in Patent Document 1, a circuit for measuring a current value is provided in a high-voltage power supply that applies a voltage to the transfer roller, and the current value when the voltage is applied is detected to determine the resistance (impedance) of the transfer roller. The correct voltage is determined. Further, since the resistance values of the transfer roller and the intermediate transfer belt are highly temperature dependent, in Patent Document 2, the resistance of the secondary transfer member is detected based on the detection result of the temperature detection means, and the secondary transfer voltage is corrected and controlled. A method is disclosed.

JP-A-5-313522 JP 2004-62086 A

  However, in a tandem type color image forming apparatus having four color image forming units, it takes time to detect the impedance between the primary transfer roller disposed in each image forming unit and the photosensitive drum. There was a problem that the formation efficiency was lowered. In addition, if a circuit for detecting impedance is provided in each image forming unit, there is a problem that the cost is increased.

  In view of the above problems, the present invention is capable of applying an appropriate primary transfer voltage to each primary transfer member with a simple configuration when controlling the primary transfer electric field at a constant voltage, and forming an image that can shorten the set time of the primary transfer voltage. An object is to provide an apparatus.

  In order to achieve the above object, a first configuration of the present invention includes a plurality of image carriers, an intermediate transfer member, a plurality of primary transfer members, and a plurality of color toners formed on the surfaces of the plurality of image carriers. An image forming apparatus comprising an intermediate transfer body on which images are sequentially stacked, a conductive member, a first power supply device, a second power supply device, a first detection unit, a second detection unit, and a control unit. It is. The primary transfer member is pressed against each image carrier with the intermediate transfer member interposed therebetween, and primarily transfers the toner images of a plurality of colors developed on each image carrier onto the intermediate transfer member. The conductive member is disposed in contact with the intermediate transfer member. The first power supply device is connected to each of the plurality of primary transfer members, and applies a primary transfer voltage to each primary transfer member to form a predetermined primary transfer electric field between the intermediate transfer member and each primary transfer member. The second power supply device applies a voltage or current to the conductive member. The first detection unit detects a current value when a voltage is applied to the primary transfer member. The second detection unit detects a current value when a voltage is applied to the conductive member or a voltage value when a current is applied. The control unit controls the first power supply device and the second power supply device. The control unit uses the first voltage-current characteristic acquired using the voltage value applied to the primary transfer member from the first power supply device and the current value detected by the first detection unit to perform the primary transfer voltage. Set. The control unit includes a voltage value applied to the conductive member from the second power supply device and a current value detected by the second detection unit, or a current value applied to the conductive member from the second power supply device and the second detection unit. The voltage value at the time of acquiring the first voltage-current characteristic is set using the second voltage-current characteristic acquired using the voltage value detected by the above.

  According to the first configuration of the present invention, the voltage value for obtaining the first voltage-current characteristic is set using the second voltage-current characteristic of the conductive member in contact with the intermediate transfer member. As a result, the primary transfer voltage corresponding to the target value of the primary transfer current can be predicted using the second voltage-current characteristic of the conductive member, so that the primary transfer voltage can be easily set so that the primary transfer current becomes the target value. can do. Therefore, it is possible to acquire voltage-current characteristic data by applying a voltage at which a current close to the target value of the primary transfer current flows to each primary transfer member, thereby improving the setting accuracy of the primary transfer voltage and reducing the set time. Is also possible.

1 is a schematic cross-sectional view illustrating an overall configuration of an image forming apparatus 100 according to an embodiment of the present invention. 1 is a partially enlarged view around the intermediate transfer belt 8 in FIG. 1 is a block diagram illustrating an example of a control path of an image forming apparatus 100 according to the present invention. A graph showing the transition of voltage-current characteristics when the primary transfer voltage is applied to the primary transfer rollers 6a to 6d by changing the temperature in the apparatus under an environment of 10 ° C. and 10%. The graph which shows transition of the voltage-current characteristic when changing the internal temperature in 10 degreeC and 10% environment and applying a voltage to the prebrush 20 A pre-brush current detection unit 53 when a voltage of 300 V is applied to the pre-brush 20 in a state where the target value of the primary transfer current is set to −20 μA in a 10 ° C., 10% environment and the primary transfer voltage is applied. Graph showing the relationship with the pre-brush current detected by FIG. 1 is a partially enlarged view showing another configuration example around the intermediate transfer belt 8 in FIG.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic view showing a configuration of a tandem color image forming apparatus of the present invention, and FIG. 2 is an enlarged view of the vicinity of an intermediate transfer belt 8 in FIG. In the main body of the image forming apparatus 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (yellow, cyan, magenta, and black), and yellow, cyan, magenta, and the like are respectively performed by charging, exposure, development, and transfer processes. And black (hereinafter also referred to as Y, C, M, and BK) images are sequentially formed.

  These image forming portions Pa to Pd are respectively provided with photosensitive drums 1a to 1d for carrying visible images (toner images) of the respective colors, and further an intermediate transfer belt that rotates clockwise in FIG. 8 is provided adjacent to each of the image forming portions Pa to Pd. In this embodiment, the photosensitive drums 1a to 1d are formed by forming a photosensitive layer made of amorphous silicon (a-Si) on the outer peripheral surface of a drum base tube having a diameter of 40 mm.

  The paper P onto which the toner image is transferred is accommodated in a paper cassette 16 below the image forming apparatus 100 and is conveyed to the secondary transfer roller 9 via the paper feed roller 12a and the registration roller pair 12b.

  Next, the image forming units Pa to Pd will be described. There are charging devices 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. An exposure unit 4 that forms an electrostatic latent image by exposing the toner, and developing devices 3a, 3b, 3c, and 3d that develop the electrostatic latent images formed on the photosensitive drums 1a to 1d to form toner images, Cleaning devices 5a, 5b, 5c and 5d for removing the developer (toner) remaining on the photosensitive drums 1a to 1d are provided.

  Further, a belt cleaning device 19 having a belt cleaning brush 19a facing the driven roller 10 with the intermediate transfer belt 8 interposed therebetween is disposed on the upstream side in the rotation direction of the intermediate transfer belt 8 with respect to the photosensitive drum 1a. A cleaning bias power source 46 (see FIG. 3) is connected to the belt cleaning device 19, and the toner scraped off from the intermediate transfer belt 8 is collected electrically and mechanically by a belt cleaning brush 19a.

  The intermediate transfer belt 8 is stretched around a driven roller 10, a driving roller 11, and a tension roller 12. The intermediate transfer belt 8 has a three-layer structure including a base layer, an elastic layer, and a coat layer. The base layer is in contact with the primary transfer rollers 6a to 6d, and the coat layer is in contact with the photosensitive drums 1a to 1d.

The base material layer becomes a basic material constituting the intermediate transfer belt 8 and imparts a predetermined rigidity, withstands the processing conditions when laminating the coat layer. Further, when the intermediate transfer belt 8 is manufactured, It is preferable that it is excellent in heat resistance, slipperiness, and other physical properties. As a material of such a base material layer, for example, a resin such as PI (polyimide), PAI (polyacrylimide), PVDF (polyvinylidene fluoride) which is difficult to expand and contract is used. Also, carbon black is dispersed as a conductive agent in the resin, and the volume resistivity when 500 V is applied is adjusted to about 10 ⁹ to 10 ¹² Ω · cm.

  When the toner image on the surface of the intermediate transfer belt 8 is secondarily transferred to the paper P, the elastic layer uniformly applies the pressure contact force of the intermediate transfer belt 8 and the secondary transfer roller 9 to the entire paper P, and the superimposed toner image. This is a layer for preventing the occurrence of a void image. As the material of the elastic layer, an elastic material such as CR (chloroprene rubber) or thermoplastic polyurethane elastomer (TPU) is used. The coat layer protects the elastic layer and imparts releasability to the intermediate transfer belt 8. As the material of the coating layer, a fluororesin such as PVDF (polyvinylidene fluoride) or PTFE (polytetrafluoroethylene) is used.

  In this embodiment, an ion conductive laminated elastic belt having a volume resistance value of 10.5 log Ω · cm in which an elastic layer formed of TPU is laminated on a PVDF base material layer and PTFE is coated as a coating layer is used. The linear speed of the intermediate transfer belt 8 is 350 mm / sec.

  The primary transfer rollers 6 a to 6 d are in contact with the photosensitive drums 1 a to 1 d with a predetermined pressure across the intermediate transfer belt 8, and the toner images formed on the photosensitive drums 1 a to 1 d are transferred onto the intermediate transfer belt 8. Primary transfer. First DC power supplies 44a to 44d are connected to the primary transfer rollers 6a to 6d, respectively. The first DC power supplies 44a to 44d flow between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d. One (common) current detector 50 that detects the primary transfer current is connected. In the present embodiment, as the primary transfer rollers 6a to 6d, electronically conductive rollers are used in which a roller body made of EPDM foam rubber having a resistance value of 6.8 logΩ is formed on the outer peripheral surface of a metal shaft having a diameter of 8 mm. The secondary transfer roller 9 is connected to a second DC power supply 45 for applying a secondary transfer voltage.

  A pre-brush 20 is disposed on the upstream side of the belt cleaning device 19 with respect to the moving direction of the intermediate transfer belt 8. The pre-brush 20 is connected to a pre-brush bias power source 47 and a pre-brush current detector 53 that detects a current flowing through the pre-brush 20, and charging the residual toner on the intermediate transfer belt 8 by applying a voltage to the pre-brush 20. Make the amount uniform. Thereby, the residual toner on the intermediate transfer belt 8 can be easily removed by the cleaning brush 19a. In this embodiment, the pre-brush 20 is formed of nylon brush fibers having a volume resistance value of 6 logΩ, a yarn density of 120 kF (kilofilament) per inch, and a yarn thickness of 6D (denier), and a voltage of 550 V is applied during image formation. Is done.

  When image data is input from a host device such as a personal computer (hereinafter referred to as a personal computer) connected to the image forming apparatus 100, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the charging devices 2a to 2d. Then, the exposure unit 4 irradiates the surfaces of the photosensitive drums 1a to 1d with light, and electrostatic latent images corresponding to the image signals are formed on the photosensitive drums 1a to 1d. Next, toner of each color of yellow, magenta, cyan, and black is supplied from the developing devices 3a to 3d onto the photosensitive drums 1a to 1d and adheres to the electrostatic latent image, thereby forming by exposure from the exposure unit 4. A toner image corresponding to the electrostatic latent image thus formed is formed.

  The primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d are arranged by primary transfer rollers 6a to 6d arranged so as to be in pressure contact with the photosensitive drums 1a to 1d with the intermediate transfer belt 8 interposed therebetween. An electric field is applied at a predetermined transfer voltage during the interval (primary transfer portion), and the toner images of yellow, magenta, cyan and black on the photosensitive drums 1 a to 1 d are primarily transferred onto the intermediate transfer belt 8. The toner remaining on the surfaces of the photosensitive drums 1a to 1d after the primary transfer is removed by the cleaning devices 5a to 5d.

  When the intermediate transfer belt 8 starts to rotate counterclockwise in FIG. 1 as the drive roller 11 is rotated by a belt drive motor (not shown), the sheet P is transferred from the registration roller 12b to the intermediate transfer belt 8 at a predetermined timing. The toner image is conveyed to a nip portion (secondary transfer nip portion) between the secondary transfer roller 9 and the intermediate transfer belt 8 provided close to each other, and the toner image is secondarily transferred from the intermediate transfer belt 8 onto the paper P at the nip portion. . The paper P on which the toner image is transferred is conveyed to the fixing unit 7.

  The sheet P conveyed to the fixing unit 7 is heated and pressurized when passing through the nip portion (fixing nip portion) of the pair of fixing rollers 13 to fix the toner image on the surface of the sheet P, and a predetermined color image is formed. It is formed. The sheet P on which the color image is formed is discharged to the discharge tray 17 by the discharge roller pair 15 as it is (or after being distributed to the reverse conveyance path 18 by the branching unit 14 and the image is formed on both sides).

  Next, the control path of the image forming apparatus 100 of the present invention will be described. FIG. 3 is a block diagram showing an example of a control path used in the image forming apparatus of the present invention. It should be noted that since various control of each part of the apparatus is performed when the image forming apparatus 100 is used, the control path of the entire image forming apparatus 100 becomes complicated. Therefore, here, a portion of the control path that is necessary for the implementation of the present invention will be mainly described.

  The control unit 90 includes a central processing unit (CPU) 91 as a central processing unit, a read only memory (ROM) 92 that is a read-only storage unit, a random access memory (RAM) 93 that is a read / write storage unit, A plurality of (two in this case) that transmit control signals to and receive input signals from the operation unit 60, such as a temporary storage unit 94 that stores image data and the like, a counter 95, and each device in the image forming apparatus 100. The I / F (interface) 96 is provided. Further, the control unit 90 can be arranged at an arbitrary location inside the apparatus main body.

  The ROM 92 stores a control program for the image forming apparatus 100, data necessary for control, and the like that are not changed during use of the image forming apparatus 100. The RAM 93 stores necessary data generated during the control of the image forming apparatus 100, data temporarily required for controlling the image forming apparatus 100, and the like. For example, when determining the target value of the primary transfer current flowing between the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d by changing the voltage applied to the primary transfer rollers 6a to 6d, the primary transfer roller 6a. A reference value of a plurality of levels of voltages applied to ˜6d is stored. The counter 95 adds up the number of printed sheets and counts it.

  In addition, the control unit 90 transmits a control signal from the CPU 91 to the respective units and apparatuses in the image forming apparatus 100 through the I / F 96. In addition, a signal indicating the state and an input signal are transmitted from each part or device to the CPU 91 through the I / F 96. As each part and device controlled by the control unit 90, for example, the image forming units Pa to Pd, the exposure unit 4, the primary transfer rollers 6a to 6d, the intermediate transfer belt 8, the secondary transfer roller 9, the image input unit 40, the bias Examples include the control circuit 41, the operation unit 60, and the like.

  The image input unit 40 is a receiving unit that receives image data transmitted from the personal computer or the like to the image forming apparatus 100. The image signal input from the image input unit 40 is converted into a digital signal and then sent to the temporary storage unit 94.

  The bias control circuit 41 is connected to the charging bias power source 42, the developing bias power source 43, the first DC power sources 44 a to 44 b, the second DC power source 45, and the belt cleaning bias power source 46, and these signals are output by an output signal from the control unit 90. Each power source is operated, and according to a control signal from the bias control circuit 41, each of these power sources is charged by the charging bias power source 42 to the charging roller 21 in the chargers 2a to 2d and the developing bias power source 43 by the developing device 3a. -3d, magnetic roller 27 and developing roller 29, first DC power supplies 44a-44d to primary transfer rollers 6a-6d, second DC power supply 45 to secondary transfer roller 9, and belt cleaning bias power supply 46 to belt cleaning. The pre-brush bias power supply 47 is applied to the brush 19a, and the pre-brush 20 is applied to the predetermined A voltage is applied.

  The in-machine temperature sensor 51 detects the temperature inside the image forming apparatus 100, particularly the temperature around the primary transfer rollers 6a to 6d, and is arranged in the vicinity of the image forming portions Pa to Pd.

  The operation unit 60 is provided with a liquid crystal display unit 61 and LEDs 62 indicating various states. The user operates the stop / clear button of the operation unit 60 to stop image formation, and operates the reset button to operate the image. Various settings of the forming apparatus 100 are set to a default state. The liquid crystal display unit 61 displays the state of the image forming apparatus 100, and displays the image forming status and the number of copies to be printed. Various settings of the image forming apparatus 100 are performed from a printer driver of a personal computer.

  By the way, when the yellow toner image primarily transferred to the intermediate transfer belt 8 in the image forming portion Pa passes through the primary transfer electric field in the image forming portions Pb to Pd on the downstream side in the traveling direction of the intermediate transfer belt 8, the yellow toner image is transferred to the toner image. Discharge and charge injection occur, and the charged state of the toner changes. Further, when the magenta toner image primarily transferred in the image forming portion Pb passes the primary transfer electric field in the downstream image forming portions Pc and Pd, or the cyan toner image primarily transferred in the image forming portion Pc is downstream. A similar phenomenon also occurs when passing through the primary transfer electric field in the image forming unit Pd on the side. Due to the change in the charged state of the toner, a highly charged toner that is difficult to be secondarily transferred or a toner having a reverse polarity is generated. It has become.

  In order to solve the above problem, it is necessary to apply an appropriate primary transfer reverse voltage to the primary transfer rollers 6a to 6d. Specifically, the voltage-current characteristics (first voltage-current characteristics) of each of the primary transfer rollers 6a to 6d are acquired, and the primary transfer in which the primary transfer current becomes a target value based on the acquired voltage-current characteristics. It is necessary to set the reverse voltage. Here, when the first DC power supplies 44a to 44d for applying the primary transfer voltage to the primary transfer rollers 6a to 6d are controlled at a constant voltage, it is necessary to acquire the voltage-current characteristics of the four primary transfer rollers 6a to 6d. There is a drawback that it takes time to obtain the voltage-current characteristics.

  FIG. 4 is a graph showing the transition of voltage-current characteristics when the primary transfer voltage is applied to the primary transfer rollers 6a to 6d with the temperature inside the machine changed at 10 ° C. and 10%. In FIG. 4, the voltage-current characteristics when the in-machine temperature is 10 ° C. and 20 ° C. and the surface potential V0 (white background portion potential, +250 V) of the photosensitive drums 1a to 1d are indicated by ▪ and ◆, respectively. The voltage-current characteristics when the internal temperature is 10 ° C. and 20 ° C. and the surface potential VL (exposure portion potential, +30 V) of the photosensitive drums 1a to 1d are indicated by ▲ and ×, respectively.

  Since the intermediate transfer belt 8 has ionic conductivity, the resistance value changes when the in-machine temperature changes. Therefore, as shown in FIG. 4, the voltage-current characteristics also change according to the change in the in-machine temperature. The appropriate value of the primary transfer current in an environment of 10 ° C. and 10% is −20 μA at the surface potential VL. From FIG. 4, the voltage-current characteristic in the vicinity of −20 μA is not linear (linear). For this reason, if the primary transfer voltage is determined by linear interpolation from the voltage-current characteristics at a point away from −20 μA, the primary transfer current value deviates from the target value.

  As described above, when acquiring voltage-current characteristic data for setting the primary transfer voltage, it is possible to acquire voltage-current characteristic data by applying a voltage at which a current close to the target value of the primary transfer current is applied. It turns out that it leads to the improvement of the voltage setting accuracy.

  Here, an appropriate value of the primary transfer current necessary for actual printing is that the toner is present in the entire longitudinal direction of the photosensitive drums 1a to 1d, that is, the surface potential of the photosensitive drums 1a to 1d is VL. This is an appropriate value. Therefore, the primary transfer voltage needs to be set in the VL state, but if the VL state is set during printing, it is necessary to make the condition that the developing bias and the like are not developed (the toner does not shift to the photosensitive drums 1a to 1d). Therefore, there is a drawback that it takes time to return to the steady state during printing again.

  FIG. 5 is a graph showing the transition of the voltage-current characteristics when a voltage is applied to the pre-brush 20 by changing the in-machine temperature in an environment of 10 ° C. and 10%. Since the pre-brush 20 has ionic conductivity, the resistance value changes when the in-machine temperature changes. Therefore, as shown in FIG. 5, the voltage-current characteristics also change according to the change in the in-machine temperature.

  FIG. 6 shows the pre-brush 20 in a state where the primary transfer voltage applied to the primary transfer rollers 6a to 6d and the primary transfer voltage are applied when the target value of the primary transfer current is −20 μA in an environment of 10 ° C. and 10%. It is a graph which shows the relationship with the pre-brush current detected by the pre-brush current detection part 53 when the voltage of 300V is applied to this.

  As shown in FIGS. 4 and 5, since the primary transfer rollers 6a to 6d and the prebrush 20 both have voltage-current characteristics depending on the resistance value of the intermediate transfer belt 8, the primary transfer voltage and the prebrush as shown in FIG. The relationship of current has linearity (linearity). Therefore, it can be seen that the appropriate value of the primary transfer voltage can be predicted by detecting the pre-brush current.

  In the image forming apparatus 100 of the present invention, using the voltage-current characteristics (second voltage-current characteristics) of the pre-brush 20 that contacts the intermediate transfer belt 8, the primary transfer rollers 6a to 6d and the photosensitive drums 1a to 1d are used. A primary transfer voltage is set so that the primary transfer current flowing between them has an appropriate current value. Accordingly, since the primary transfer voltage corresponding to the target value of the primary transfer current can be predicted using the voltage-current characteristic of the prebrush 20, it is possible to easily set the primary transfer voltage so that the primary transfer current becomes the target value. it can.

  Specifically, a reference value (for example, two levels) close to the voltage predicted using the voltage-current characteristics of the pre-brush 20 is selected from the reference values for voltages of a plurality of levels (for example, five levels) stored in the RAM 93. Apply. Therefore, voltage-current characteristic data can be acquired by selectively applying a voltage at which a current close to the target value of the primary transfer current flows to the primary transfer rollers 6a to 6d, and the setting accuracy of the primary transfer voltage is improved. The setting time can be shortened.

  Since the intermediate transfer belt 8 used in the present embodiment is ionic conductive, the resistance varies depending on the temperature. Further, since the primary transfer rollers 6a to 6d are electronically conductive, the resistance change due to temperature is small, but the resistance changes depending on the degree of deterioration of the roller. Therefore, the voltage-current characteristics of the primary transfer rollers 6a to 6d and the intermediate transfer belt 8 change depending on the temperature and the degree of roller deterioration.

  Therefore, when the temperature detected by the in-machine temperature sensor 51 has changed by a predetermined temperature from the time of the previous primary transfer voltage correction, or the number of accumulated prints from the time of the previous primary transfer voltage correction counted by the counter 95 is predetermined. When the number of sheets has been reached (when the cumulative driving time of the intermediate transfer belt 8 has reached a predetermined time), a voltage is applied to the pre-brush 20 to acquire voltage-current characteristics, and the acquired voltage-current characteristics of the pre-brush 20 are used. It is preferable to correct the primary transfer voltage applied to the primary transfer rollers 6a to 6d so that the primary transfer current becomes a target value.

  In addition, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention. For example, in the above embodiment, as shown in FIG. 2, one current detection unit 50 that detects the primary transfer current flowing through the primary transfer rollers 6 a to 6 d is connected. However, as shown in FIG. You may provide separately the electric current detection part 50 which detects the primary transfer electric current which flows into the transfer rollers 6a-6d.

  In the above embodiment, the second voltage-current characteristic is acquired using the voltage value applied to the pre-brush 20 from the pre-brush bias power supply 47 and the current value detected by the current detection unit 50 when the voltage is applied. The primary transfer voltage applied to the primary transfer rollers 6a to 6d was corrected using the acquired second voltage-current characteristic. Instead of the above configuration, a voltage detection unit that detects a voltage value applied to the pre-brush 20 is provided, and a current value applied to the pre-brush 20 from the pre-brush bias power source 47 and the voltage detection unit when a current is applied. The second voltage-current characteristic may be acquired using the detected voltage value.

  In the above embodiment, the primary transfer voltage applied to the primary transfer rollers 6a to 6d is corrected using the second voltage-current characteristic of the pre-brush 20, but instead of the pre-brush 20, a second voltage-current characteristic is detected. A configuration in which a conductive member is separately provided and brought into contact with the intermediate transfer belt 8 may be employed. The set current value of the primary transfer current described above is merely an example, and may be set as appropriate according to the specifications of the image forming apparatus, the usage environment, and the like.

  The present invention is applicable to a tandem color image forming apparatus using an intermediate transfer system. By using the present invention, an appropriate primary transfer voltage can be applied to each primary transfer member with a simple configuration, and the image forming apparatus can shorten the set time of the primary transfer voltage.

1a to 1d Photosensitive drum (image carrier)
2a to 2d Charging device 3a to 3d Developing device 4 Exposure unit 5a to 5d Cleaning device 6a to 6d Primary transfer roller (primary transfer member)
8 Intermediate transfer belt (intermediate transfer member)
9 Secondary transfer roller 19 Belt cleaning device 19a Belt cleaning brush (cleaning member)
20 Pre-brush (conductive member)
44a-44d 1st DC power supply (1st power supply device)
45 Second DC power supply 47 Pre-brush bias power supply (second power supply device)
50 Current detector (first detector)
51 Air temperature sensor (temperature detector)
53 Pre-brush current detector (second detector)
90 control unit 100 image forming apparatus Pa to Pd image forming unit

Claims (5)

A plurality of image carriers;
An intermediate transfer body in which a plurality of color toner images formed on the surface of the plurality of image carriers are sequentially laminated;
A plurality of primary transfer members that are pressed against the respective image carriers with the intermediate transfer member interposed therebetween, and that primarily transfer a plurality of color toner images developed on the respective image carriers onto the intermediate transfer member;
A conductive member disposed in contact with the intermediate transfer member;
A primary transfer electric field is connected between each of the plurality of primary transfer members, and a primary transfer electric field having a polarity opposite to that of toner is applied to each primary transfer member so that a predetermined primary transfer electric field is generated between the intermediate transfer member and each primary transfer member. A plurality of first power supply devices to be formed;
A second power supply device for applying a voltage or current to the conductive member;
A first detection unit for detecting a current value flowing between each primary transfer member and each image carrier;
A second detection unit that detects a current value when a voltage is applied to the conductive member or a voltage value when a current is applied to the conductive member;
A control unit for controlling the first power supply device and the second power supply device;
In an image forming apparatus comprising:
The control unit uses a first voltage-current characteristic acquired using a voltage value applied to the primary transfer member from the first power supply device and a current value detected by the first detection unit. To set the primary transfer voltage,
The voltage value applied to the conductive member from the second power supply device and the current value detected by the second detection unit, or the current value applied to the conductive member from the second power supply device and the second An image forming apparatus, wherein a voltage value for acquiring the first voltage-current characteristic is set using a second voltage-current characteristic acquired using a voltage value detected by a detection unit. A cleaning member for cleaning the intermediate transfer member by electrostatic force;
2. The pre-brush, wherein the conductive member is a pre-brush that is disposed upstream of the cleaning member with respect to the moving direction of the intermediate transfer member, and controls a charge amount of toner on the intermediate transfer member. Image forming apparatus. It has a temperature detection unit that detects the temperature inside the image forming apparatus,
The control unit acquires the second voltage-current characteristic and acquires the first voltage-current characteristic when the temperature detected by the temperature detection unit changes more than a predetermined temperature from the previous setting of the primary transfer voltage. 3. The image forming apparatus according to claim 1, wherein a voltage value at the time of setting is set, and the primary transfer voltage is set using the acquired first voltage-current characteristic.   The control unit obtains the second voltage-current characteristic and obtains the first voltage-current characteristic when the cumulative driving time of the intermediate transfer body from the previous setting of the primary transfer voltage becomes a predetermined time or more. The image forming apparatus according to claim 1, wherein a voltage value at the time of acquisition is set, and the primary transfer voltage is set using the acquired first voltage-current characteristic.   5. The current value flowing between each primary transfer member and each image carrier is detected by one shared first detection unit. 6. Image forming apparatus.

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