JP2016004140A - Power supply device to be used for image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus configured to control a primary transfer voltage to be applied to a primary transfer member, while reducing the size and cost of a high-voltage power supply to be mounted on the apparatus and simplifying device configuration.SOLUTION: An image forming apparatus executes a first image-forming mode in which a toner image is transferred from all image carriers 1a, 1b, 1c, 1d to an intermediate transfer body 7, and a second image-forming mode in which the toner image is transferred from only a specific one of the image carriers 1a, 1b, 1c, 1d to the intermediate transfer body 7. Voltage output means 60 includes: a first voltage output section 61 which outputs a voltage of characteristics opposite to a regular charging polarity of toner, to all primary transfer means 6a, 6b, 6c, 6d; and a second voltage output section 62 which outputs a voltage of the same characteristics as the regular charging polarity of the toner, to the primary transfer means other than the primary transfer means 6d relating to the second image-forming mode. The first voltage output section 61 is connected between the second voltage output section 62 and a ground potential.

Description

  The present invention relates to an image forming apparatus using an electrophotographic system or an electrostatic recording system. More specifically, the present invention arranges four single-color image forming portions on which toner images are respectively formed by electrophotography, and arranges them in contact with the four photoconductors constituting each unit. The present invention relates to an image forming apparatus having a full-color mode and a mono-color mode.

  Conventionally, as an image forming apparatus capable of outputting a full-color image, a so-called in-line that has a plurality of image forming portions that form a toner image by charging, exposure, development, and transfer processes along the moving direction of the intermediate transfer member. A type of image forming apparatus is known.

  In an in-line image forming apparatus, a full color mode for forming a full color image using all the image forming units as described above, and a mono color mode for forming an image using only a single image forming unit such as a K single color. (See Patent Document 1).

  In general, in a mono color mode in which K single-color image formation is performed, a system in which a primary transfer voltage is not applied to primary transfer members corresponding to Y, M, and C is employed. In this case, an example of setting the primary transfer voltage applied to each primary transfer member in the mono color mode will be described below. Here, it is assumed that the charging polarity of the toner is negative. In the mono-color mode when using plain paper in a room temperature and humidity environment, the primary transfer voltage when the intermediate transfer belt passes through each primary transfer member is 0V, 0V, 0V in order from the first image forming unit. , Set a constant voltage of + 1000V. In order to perform the above setting, a plurality of output voltage portions are provided on the primary transfer member.

  In the K mono-color mode, the image forming unit for each color of Y, M, and C is subject to fogging (non-imaged part) by separating the developing roller from the photosensitive member or stopping its driving. In general, toner adhesion is prevented.

JP 2008-309904 A

  By the way, in order to reduce the cost and size of the apparatus, it is conceivable to supply primary transfer voltages to be applied to a plurality of primary transfer members from a common high-voltage power source. Thereby, the high voltage power source required for the primary transfer member can be minimized.

  However, with such a configuration, the high voltage power source mounted in the apparatus can be reduced in size and cost, but a primary transfer voltage is applied to a plurality of primary transfer members from a common high voltage power source. Therefore, as described above, in the mono color mode, the primary transfer voltage applied to the primary transfer member not involved in image formation cannot be set to 0V. For this reason, an unnecessary charge-up of the intermediate transfer member due to the primary transfer voltage of the primary transfer member not involved in monocolor image formation occurs, and a higher primary transfer voltage is required. In addition, a monocolor toner image is reversely transferred to a photoconductor that is not involved in monocolor image formation, causing image defects.

  Therefore, in view of the above problems, the present invention can control the primary transfer voltage applied to the primary transfer member while simplifying the apparatus configuration and reducing the size and cost of the high-voltage power supply mounted on the apparatus. An object is to provide a forming apparatus.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the first invention is
A movable intermediate transfer member, a plurality of image carriers that carry toner images disposed in a moving direction of the intermediate transfer member, and the toner images provided corresponding to each of the plurality of image carriers. A plurality of primary transfer means for sequentially transferring onto the intermediate transfer body; a voltage output means for outputting a voltage for transferring the toner image to the plurality of primary transfer means; and a toner on the intermediate transfer body In an image forming apparatus having secondary transfer means for collectively transferring an image to a transfer material,
A first image forming mode in which toner images are transferred from all of the plurality of image carriers to the intermediate transfer member;
A second image forming mode in which a toner image is transferred from only a specific image carrier among the plurality of image carriers to the intermediate transfer member; and
The voltage output unit includes a first voltage output unit that outputs a voltage having a characteristic opposite to a normal charging polarity of toner to all of the plurality of primary transfer units, and the primary that is involved in the second image forming mode. In addition to the transfer means, the second voltage output unit outputs a voltage having the same characteristic as the normal charging polarity of the toner, and the first voltage output unit is between the second voltage output unit and the ground potential. An image forming apparatus that is connected.

  According to the present invention, there is provided an image forming apparatus capable of controlling the primary transfer voltage applied to the primary transfer member while simplifying the apparatus configuration and reducing the size and cost of the high-voltage power source mounted on the apparatus. can do.

1 is a configuration diagram illustrating an image forming apparatus according to Embodiment 1 of the present invention. 1 is a configuration diagram of a high-voltage power supply device according to Embodiment 1 of the present invention. 1 is a circuit diagram of a primary transfer high-voltage power supply according to Embodiment 1 of the present invention. The current flow of the primary transfer high voltage power supply when performing impedance detection according to the first embodiment of the present invention. FIG. 6 is a circuit diagram of a primary transfer high-voltage power supply according to Embodiment 2 of the present invention. FIG. 6 is a circuit diagram of a primary transfer high-voltage power supply according to Embodiment 2 of the present invention.

  Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the drawings. However. The components described in this embodiment are merely examples, and the scope of the present invention is not limited to them.

(First embodiment)
A first embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a configuration diagram illustrating an image forming apparatus according to the present exemplary embodiment. An image forming apparatus 100 according to the present embodiment is an image forming apparatus using an electrophotographic method, and each color toner image formed according to image information separated into yellow, magenta, cyan, and black color components is an intermediate transfer member. An intermediate transfer method is employed in which the primary transfer is performed on the recording material, and the image is once superimposed and then secondarily transferred to a recording material. First, the overall configuration and operation of the image forming apparatus of this embodiment will be described.

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

  The station S includes a drum-type electrophotographic photosensitive member that is an image carrier, that is, a photosensitive drum 1. The photosensitive drum 1 is driven in a direction indicated by an arrow by a driving unit (not shown) and is uniformly charged by a primary charger 2 which is a charging unit. Subsequently, the exposure device 3 irradiates the photosensitive drum 1 with laser light L according to the image information, and a latent image is formed on the photosensitive drum 1. When the photosensitive drum 1 further advances in the direction of the arrow, the developing sleeve 4 and the developing device 5 develop and visualize the latent image formed on the photosensitive drum 1 according to the image information as a toner image.

  An intermediate transfer belt 7 as an intermediate transfer member is disposed downstream of the developing position in the rotational direction of the photosensitive drum 1. The intermediate transfer belt 7 is a cylindrical and endless belt-like film stretched around the drive roller 11, the secondary transfer counter roller 13, and the tension roller 12, and moves in the direction indicated by the arrow at substantially the same peripheral speed as the photosensitive drum 1. (Rotate. Here, the above-described 1, 2, 4, and 5 are constituted by an integral process cartridge P, and are detachable from the image forming apparatus main body.

  A primary transfer roller 6 is disposed as a primary transfer unit at a position facing the photosensitive drum 1 with the intermediate transfer belt 7 interposed therebetween to form a primary transfer nip portion. As the photosensitive drum 1 and the intermediate transfer belt 7 rotate, a primary transfer voltage is applied to the primary transfer roller 6 so that the toner image formed and carried on the photosensitive drum 1 is applied to the outer peripheral surface of the intermediate transfer belt 7. Perform primary transfer. By performing the above steps for yellow, magenta, cyan, and black colors, in the case of a multi-color toner image on the intermediate transfer belt 7, for example, a full-color image, yellow, magenta, cyan, and black colors. The four color toner images are overlaid. In this embodiment, from the upstream of the intermediate transfer belt, Pa is the first station (Sa), Pb is the second station (Sb), Pc is the third station (Sc), and Pd is the fourth station (Sd). In each order, yellow toner, magenta toner, cyan toner, and black toner are included.

  For example, a secondary transfer roller 8 is disposed as a secondary transfer means for transferring a toner image from the intermediate transfer belt 7 to the recording material 17 at a position facing the secondary transfer counter roller 13 with the intermediate transfer belt 7 interposed therebetween. Is done. The recording material 17 fed out by the pickup roller 14 is supplied at a predetermined timing to a secondary transfer nip portion where the intermediate transfer belt 7 and the secondary transfer roller 8 are in contact with each other by the conveying roller pair 15. At the same time, a secondary transfer voltage is applied to the secondary transfer roller 8, and the toner image is transferred from the intermediate transfer belt 7 to the recording material 17.

  Thereafter, the toner image of the recording material 17 is heated and fixed by the fixing roller pair 16, and then the recording material 17 is output to the outside of the apparatus. Here, toner that has not been transferred from the intermediate transfer belt 7 to the recording material 17 by the secondary transfer roller 8 (hereinafter referred to as “waste toner”) is collected in the waste toner container 10 by the cleaning blade 9.

(Configuration of high-voltage power supply)
Next, the configuration of the high-voltage power supply device in the image forming apparatus 100 of FIG. 1 will be described with reference to FIG. The high-voltage power supply device includes a charging high-voltage power supply 20, a development high-voltage power supply 40 a to 40 d, a primary transfer high-voltage power supply 60, and a secondary transfer high-voltage power supply 80.

  The charging high-voltage power source 20 applies a voltage (negative polarity in this embodiment) to the charging rollers 2a to 2d to form a background potential on the surface of the photosensitive drums 1a to 1d, and irradiates the laser beams La to Ld. An electrostatic latent image can be formed.

The development high-voltage power supplies 40a to 40d can form a toner image by applying a voltage (negative polarity in this embodiment) to the development sleeves 4a to 4d so that the toner is placed on the electrostatic latent images on the photosensitive drums 1a to 1d. Put it in a state.
The primary transfer high-voltage power supply 60 can transfer the toner images on the photosensitive drums 1a to 1d to the intermediate transfer belt 7 by applying a voltage (positive polarity in this embodiment) to the primary transfer rollers 6a to 6d. To. Further, since the transfer performance of the toner image on the primary transfer rollers 6a to 6d changes according to the amount of current flowing through the primary transfer rollers 6a to 6d, the primary transfer high-voltage power supply 60 includes a current detection circuit 63. Yes. The primary transfer high-voltage power supply 60 adjusts the voltage applied to the primary transfer rollers 6a to 6d according to the detection result of the current detection circuit 63, so that the impedance of the primary transfer rollers 6a to 6d varies depending on the environment. However, the transfer performance is kept constant. During primary transfer, constant voltage control is performed with a voltage set so that the amount of current flowing through the primary transfer rollers 6a to 6d becomes a target value.

  The secondary transfer high voltage power supply 80 applies a voltage (positive polarity in this embodiment) to the secondary transfer roller 8 so that the toner image transferred onto the intermediate transfer belt 7 can be transferred to the recording material 17. To do.

(Circuit diagram of primary transfer high-voltage power supply)
Next, an example of the circuit configuration of the primary transfer high-voltage power supply 60, which is the most characteristic feature of this embodiment, will be described with reference to FIG. The primary transfer high-voltage power supply 60 includes a primary transfer high-voltage circuit 61, a primary transfer high-voltage circuit 62, and a current detection circuit 63.

  The primary transfer high voltage circuit 61 is a circuit that applies a voltage (positive polarity in this embodiment) to the primary transfer rollers 6a to 6d. The transformer 612 boosts the voltage of the AC signal generated by the drive circuit 611 to an amplitude several tens of times. A rectifier circuit 61a including diodes 614 and 615 and capacitors 613 and 616 rectifies and smoothes the boosted AC signal. The output terminal 65 outputs the DC voltage rectified and smoothed by the rectifier circuit 61a to the primary transfer roller 26d. On the other hand, the rectifier circuit 61a is also connected in series to a rectifier circuit 62a described later, and the output terminal 64 outputs a DC voltage rectified and smoothed by the rectifier circuit 61a via a resistor 627. The comparator 610 controls the AC signal of the drive circuit 611 so that the DC voltage of the output terminal 65 divided by the detection resistors 618 and 619 is equal to the set value 900 set by the control unit 90. A current flows through the primary transfer rollers 26a to 26d, the photosensitive drums 22a to 22d, and the ground according to the DC voltage of the output terminal 64 and the output terminal 65.

  Next, the current detection circuit 63 is connected between the secondary circuit of the transformer 612 and the ground point 80. Here, since the input terminal of the operational amplifier 630 has high impedance and almost no current flows, almost all of the direct current flowing from the ground point 80 to the output terminal 64 and the output terminal 65 through the secondary circuit of the transformer 612 flows to the resistor 631. It is configured to flow. Further, since the inverting input terminal of the operational amplifier 630 is connected to the output terminal via the resistor 631, it is virtually grounded to the reference voltage 632 connected to the non-inverting input terminal. Therefore, a detection voltage 902 proportional to the amount of current flowing through the output terminal 64 and the output terminal 65 appears at the output terminal of the operational amplifier 630. The capacitor 633 is for stabilizing the inverting input terminal of the operational amplifier 630.

  On the other hand, the primary transfer high-voltage circuit 62 is a circuit that applies a voltage having a reverse characteristic (negative polarity in this embodiment) to the primary transfer rollers 26a to 26c. The transformer 622 boosts the voltage of the AC signal generated by the drive circuit 621 to an amplitude several tens of times. A rectifier circuit 62a including diodes 624 and 625 and capacitors 623 and 626 rectifies and smoothes the boosted AC signal. Here, since the diodes 624 and 625 of the rectifier circuit 62a are connected to the diodes 614 and 615 of the rectifier circuit 61a in opposite directions of the anode and the cathode, the DC voltage rectified and smoothed by the rectifier circuit 62a. And the polarity of the DC voltage rectified and smoothed by the rectifier circuit 61a have opposite characteristics. The output terminal 64 outputs the DC voltage rectified and smoothed by the rectifier circuit 62a to the primary transfer rollers 26a to 26c. The comparator 620 controls the AC signal of the drive circuit 621 so that the DC voltage of the output terminal 64 divided by the detection resistors 628 and 629 is equal to the set value 901 set by the control unit 90.

  The primary transfer high-voltage circuit 62 is a circuit for applying different voltages between the primary transfer rollers 26a to 26c and the primary transfer roller 26d in a mono-color mode to be described later, and outputs a voltage only at the output terminal 64. Good. That is, the primary transfer high-voltage power source is configured such that the primary transfer high-voltage circuit 61 is connected between the primary transfer high-voltage circuit 62 and the ground point 80.

(Operation of primary transfer high-voltage power supply)
With the configuration described above, the operation of the primary transfer high-voltage power supply 60 during image formation will be described in detail. In this embodiment, the monochromatic image forming unit is disposed at the most downstream side (Sd) in the moving direction of the intermediate transfer belt 7. The primary transfer high-voltage power supply 60 performs different control in the full color mode and the mono color mode.

(I) Full Color Mode In image formation in the full color mode, the primary transfer high-voltage power source 60 applies a voltage (positive polarity in the present embodiment) to the primary transfer rollers 6a to 6d, so that the photosensitive drums 1a to 1d are applied. The toner image is transferred to the intermediate transfer belt 7. The setting state of the primary transfer high-voltage power supply 60 and the operation status at each station are as shown in Table 1 below. In the table, the column “positive voltage” 1 is a voltage value of a DC voltage rectified and smoothed by the rectifier circuit 61 a of the primary transfer high-voltage circuit 61. In the table, the column “negative voltage” is a voltage value of a DC voltage rectified and smoothed by the rectifier circuit 62 a of the primary transfer high voltage circuit 62. In the column of “primary transfer voltage” 1 in the table, the positive voltage and the negative voltage are superimposed and applied to the output terminal 64 and the output terminal 65 from the primary transfer high-voltage power supply 60. Indicates the voltage value. The same applies to Tables 2 to 7 described later.

(II) Mono-color mode In image formation in the mono-color mode, the primary transfer high-voltage power supply 60 applies a voltage (positive in this embodiment) to the primary transfer roller 26d, so that the toner on the photosensitive drum 1d. An image can be transferred to the intermediate transfer belt 7. The setting state of the primary transfer high-voltage power supply 60 and the operation status at each station at this time are as shown in Table 2 below.

In the mono color mode, an image forming unit that performs mono color image formation forms an image by the same process as the full color mode described above and transfers it to the recording material 17, and other image forming units form images. do not do. Thereby, a monocolor image is obtained. In this embodiment, the developing rollers 4a to 4c that are not involved in monocolor image formation are separated from the photosensitive drums 1a to 1c and stopped.

  Now, voltages applied to the primary transfer rollers 6a to 6c that are not involved in mono color image formation in the mono color mode will be described. In this embodiment, in the mono color mode, the primary transfer high-voltage power supply 60 applies a voltage of 0 V to the primary transfer rollers 6 a to 6 c located upstream of the mono color image forming unit in the moving direction of the intermediate transfer belt 7. Specifically, the polarity of the DC voltage rectified and smoothed by the rectifier circuit 61a of the primary transfer high voltage circuit 61 and the polarity of the DC voltage rectified and smoothed by the rectifier circuit 62a of the primary transfer high voltage circuit 61 are mutually different. Because of the reverse polarity, the absolute value of the DC voltage rectified and smoothed by the rectifier circuit 61a of the primary transfer high-voltage circuit 61 and the absolute value of the DC voltage rectified and smoothed by the rectifier circuit 62a of the primary transfer high-voltage circuit 61 And the AC signal of the drive circuit 621 of the primary transfer high-voltage circuit 62 may be controlled by the control unit 90 of the primary transfer high-voltage power supply 60. Thereby, unnecessary charge-up of the intermediate transfer belt 7 due to the voltage applied to the primary transfer rollers 6a to 6c not involved in monocolor image formation can be reduced. As a result, various image defects due to charge-up of the intermediate transfer belt 7 can be prevented, and a good monocolor image can be obtained.

(Primary transfer roller impedance detection)
Next, impedance detection of the primary transfer roller 6 that is a primary transfer member will be described. The primary transfer high-voltage power supply 60 obtains information related to the impedance of the primary transfer roller 6 during non-image formation or image formation in order to determine and control the optimum primary transfer voltage, Control is performed so that an optimal primary transfer voltage corresponding to the impedance can be applied to the primary transfer roller 6.

  The impedance of the primary transfer roller 6 varies depending on environmental factors such as the degree of deterioration of various members and the in-machine temperature. Therefore, as a method of detecting the impedance of the primary transfer roller 6, the primary transfer high-voltage power supply 60 applies a constant-current controlled voltage to the primary transfer roller 6 during non-image formation, and an output terminal at that time. 64 and a method of detecting the voltage value of the output terminal 65. In this embodiment, a method for detecting the impedance of the primary transfer roller 26d will be described in detail with reference to FIG.

  First, the primary transfer high-voltage circuit 61 applies a voltage to the output terminal 64 and the output terminal 65 so that the detection voltage 902 generated by the current detection circuit 63 has a certain value (constant current control). On the other hand, the primary transfer high-voltage circuit 62 applies a voltage having characteristics opposite to those of the primary transfer high-voltage circuit 61 to the output terminal 64 so that the voltage of the output terminal 64 becomes 0 V (constant voltage control). The primary transfer high-voltage circuit 62 preferably has faster response characteristics than the primary transfer high-voltage circuit 61. This is because by quickly setting the voltage of the output terminal 64 to 0V, a current i3 flowing through a primary transfer roller 26d described later can be detected with high accuracy. By performing the above-described control, the primary transfer high-voltage power supply 60 applies a constant current controlled voltage to the primary transfer roller 26d, and as shown in FIG. A current i3 flows through the drum 22d and the ground. Further, since the current i3 flows through the resistor 631 of the current detection circuit 63 and the detection voltage 902 proportional to the current i3 appears at the output terminal of the operational amplifier 630, the primary transfer is performed based on the detection voltage 902 and the voltage value of the output terminal 65. The impedance of the roller 26d can be calculated.

  As described above, the primary transfer high-voltage circuit 61 and the primary transfer high-voltage circuit 62 having different polarities are arranged in series while minimizing the number of primary transfer high-voltage circuits constituting the primary transfer high-voltage power supply 60. Also in monomode image formation, the primary transfer voltage applied to each primary transfer member can be controlled by performing the above-described control.

(Second embodiment)
Next, another embodiment according to the present invention will be described with reference to the drawings. Only differences from the first embodiment will be described. In the first embodiment, the waste toner remaining on the intermediate transfer belt 7 is collected in the waste toner container 10 by the cleaning blade 9. However, in this embodiment, with the same configuration as the primary transfer high-voltage power supply 60 in the first embodiment, waste toner remaining on the intermediate transfer belt 7 is distributed as evenly as possible, and is transferred back to the photosensitive drum for recovery. Features.

  FIG. 5 is a configuration diagram of the entire image forming apparatus of the present embodiment. In this embodiment, the arrangement of the monochromatic image forming unit is preferably set in consideration of the following. First, when the monocolor image forming unit is arranged at the most upstream position (Sa) in the moving direction of the intermediate transfer belt 7, the photosensitive drums for collecting waste toner by reverse transfer in the monocolor mode and the full color mode, which will be described later, overlap. It is not preferable. Further, in order to increase the time (first printout speed) until the first image is output in the mono color mode, the mono color image forming unit is most downstream in the moving direction of the intermediate transfer belt 7 (Sd ) Is preferable. In view of these matters, as a configuration in which the waste toner of the intermediate transfer belt 7 is collected as uniformly as possible on each photosensitive drum, the monocolor image forming unit is configured in the moving direction of the intermediate transfer belt 7 as in this embodiment. It is preferable to arrange in the most downstream (Sd).

(overall structure)
The image forming apparatus 200 includes a cleaning roller 18 that charges the waste toner on the intermediate transfer belt 7. Waste toner that has not been transferred from the intermediate transfer belt 7 to the recording material 17 by the secondary transfer roller 8 is reversely transferred to the photosensitive drum 1 of the station S and then incorporated into the process cartridge P, as will be described in detail later. Are removed and collected by the cleaning devices 9 and 10. Typically, the waste toner on the intermediate transfer belt 7 is charged by a cleaning roller 18 as an intermediate transfer member cleaning unit (toner charging unit), and is reversely transferred to the photosensitive drum 1 at the next primary transfer. . At this time, the waste toner adhering to the photosensitive drum 1 is removed and collected by the cleaning devices 9 and 10 as cleaning means (photoconductor cleaning means).

  In this embodiment, 1, 2, 4, 5, 9, and 10 are constituted by an integral process cartridge P, and are detachable from the main body of the image forming apparatus.

(Configuration of high-voltage power supply)
Next, the configuration of the high-voltage power supply device in the image forming apparatus 200 of FIG. 5 will be described with reference to FIG. The high-voltage power supply device includes a charging high-voltage power supply 20, development high-voltage power supplies 40 a to 40 d, a primary transfer high-voltage power supply 60, a secondary transfer high-voltage power supply 80, and toner charging high-voltage power supplies 180 and 181.

  The toner charging high-voltage power supplies 180 and 181 apply a voltage (positive polarity and negative polarity in the present embodiment) to the cleaning roller 18 so that the waste toner is removed during the cleaning operation of the intermediate transfer belt 7 as will be described in detail later. An operation of discharging negatively charged waste toner that is charged or attached to the cleaning roller 18 is performed.

(Intermediate transfer member cleaning operation)
In the configuration described above, a method for cleaning the intermediate transfer belt 7 will be described in detail. The cleaning of the intermediate transfer belt 7 greatly depends on the polarity and amount of toner on the intermediate transfer belt 7, and a special method is used in various situations during printing. ).

(I) Cleaning in Full Color Mode In image formation in the full color mode, the toner charging high voltage power supplies 180 and 181 apply a positive voltage to the cleaning roller 18 so that the waste toner is charged with a positive polarity. The image is reversely transferred to the photosensitive drum 1a during the primary transfer.

(II) Cleaning in Mono Color Mode In image formation in the mono color mode, the toner charging high-voltage power supplies 180 and 181 apply a positive voltage to the cleaning roller 18 so that the waste toner is charged with a positive polarity. The image is reversely transferred to the photosensitive drum 1d at the next primary transfer.

(III) Cleaning of toner discharged from the cleaning roller The toner before the secondary transfer usually has a negative polarity on the intermediate transfer belt 7, but the positive polarity 2 in the secondary transfer step. Since the next transfer voltage is applied and transferred, there are both positive and negative toner polarities. Further, since a positive voltage is used during cleaning, the negative waste toner tends to adhere to the cleaning roller 18. For this reason, the waste toner adhering to the cleaning roller 18 is discharged when one print job is completed. Specifically, the negative polarity toner is discharged by applying a negative polarity voltage to the cleaning roller 18 from the toner charging high-voltage power supplies 180 and 181 by rotation after the print operation of one job is completed. The discharged waste toner can be collected on the photosensitive drum 1 by applying a negative voltage opposite to that at the time of image formation to the primary transfer roller 6.

(IV) Cleaning at Jam (Paper Jam) Cleaning at the time of jam often has untransferred toner remaining on the intermediate transfer belt 7 without being secondarily transferred. Further, these toners are much larger than the amount of waste toner that is secondarily transferred and remains on the intermediate transfer belt. Therefore, cleaning is performed by rotating the intermediate transfer belt 7 a plurality of times. Specifically, in this embodiment, the intermediate transfer belt 7 is rotated three times. First, a negative voltage is applied to the cleaning roller 18 to pass the toner on the intermediate transfer belt 7. Thereafter, when a negative voltage is applied to the primary transfer roller 6 when it comes to the image forming station, it is electrostatically collected on the photosensitive drum. Second, a positive voltage is applied to the cleaning roller 18 to charge the toner on the intermediate transfer belt 6 to a positive polarity, and a positive voltage is applied to the primary transfer roller 6 to the photosensitive drum. to recover. On the third round, a process of discharging the toner adhering to the cleaning roller 18 (same as (II) above) is performed.

(V) Regular cleaning If the number of prints increases during continuous printing, the toner adhering to the cleaning roller 18 causes a charging failure of the waste toner and gradually remains on the intermediate transfer belt 7 without being cleaned. Waste toner increases. In this embodiment, the main cleaning is forcibly performed when 50 sheets are continuously printed. The cleaning operation is the same as (III).

(Operation of the primary transfer high-voltage power supply during cleaning)
In this embodiment, the primary transfer high-voltage power supply 60 performs the following operations (I) to (V) in order to collect the waste toner as evenly as possible with the process cartridges Pa to Pd. In this embodiment, it is assumed that the photosensitive drum 1 is charged to the same potential (negative polarity in this embodiment) as in the image formation in any case.

(I) Cleaning in Full Color Mode In image formation in the full color mode, all waste toner on the intermediate transfer belt 7 is collected with Sa. This is because it is preferable to collect waste toner with Sa since a method of collecting waste toner by reverse transfer at the same time as primary transfer is adopted. The setting state of the primary transfer high-voltage power supply 60 and the operation status at each station at this time are as shown in Table 3 below.

In this case, the Sa to Sd secondary transfer rollers 6a to 6d form an electric field in a direction (polarity) in which the toner charged with a characteristic opposite to the normal charging polarity is directed from the intermediate transfer belt 7 to the photosensitive drums 1a to 1d. The By setting the primary transfer high-voltage power supply 60 to the above setting, it is possible to collect waste toner on the intermediate transfer belt 7 using only Sa.

(II) Cleaning in Mono Color Mode In image formation in the mono color mode, the stations Sa to Sc are set to a voltage setting that allows the toner on the intermediate transfer belt 7 to pass. All the waste toner on the intermediate transfer belt 7 is collected by Sd. The setting state of the primary transfer high-voltage power supply 60 and the operation status at each station at this time are as shown in Table 4 below.

In this case, in the primary transfer rollers 6a to 6c of Sa to Sc, an electric field is formed in a direction (polarity) in which the toner charged with a reverse characteristic to the normal charging polarity is directed to the intermediate transfer belt 7. On the other hand, in the primary transfer roller 6d of Sd, an electric field is formed in a direction (polarity) in which the toner charged with a reverse characteristic to the normal charging polarity is directed from the intermediate transfer belt 7 to the photosensitive drum 1d. By setting the primary transfer high-voltage power supply 60 to the above setting, it becomes possible to collect waste toner on the intermediate transfer belt 7 using only Sd.

(III) Cleaning of toner discharged from cleaning roller Waste toner discharged from the cleaning roller 18 is collected almost evenly by Sa to Sc. The setting state of the primary transfer high-voltage power supply 60 and the operation status at each station at this time are as shown in Table 5 below.

In this case, in the primary transfer rollers 6a to 6c of Sa to Sc, an electric field is formed in a direction (polarity) in which the toner charged with a reverse characteristic to the normal charging polarity is directed from the intermediate transfer belt 7 to the photosensitive drum 1d. The On the other hand, in the Sd primary transfer roller 6d, an electric field is formed in a direction (polarity) in which the toner charged with a characteristic opposite to the normal charging polarity is directed to the intermediate transfer belt 7. By setting the primary transfer high-voltage power supply 60 to the above setting, it is possible to collect waste toner on the intermediate transfer belt 7 at Sa to Sc.

(IV) Cleaning at Jam (Paper Jam) In this case as well, the waste toner on the intermediate transfer belt 7 is collected almost evenly by Sa to Sd. The setting state of the primary transfer high-voltage power supply 60 and the operation status at each station at this time are as shown in Tables 6 and 7 below.

"First lap"
Negative waste toner on the intermediate transfer belt 7 is collected.

In this case, in the primary transfer rollers 6a to 6c of Sa to Sc, an electric field is formed in a direction (polarity) in which the toner charged with a reverse characteristic to the normal charging polarity is directed from the intermediate transfer belt 7 to the photosensitive drum 1d. The On the other hand, in the Sd primary transfer roller 6d, an electric field is formed in a direction (polarity) in which the toner charged with a characteristic opposite to the normal charging polarity is directed to the intermediate transfer belt 7.

"Second lap"
The waste toner on the intermediate transfer belt 7 is collected by being charged positively by the cleaning roller 18.

In this case, in the primary transfer rollers 6a to 6d of Sa to Sd, an electric field is formed in a direction (polarity) in which the toner charged with a reverse characteristic to the normal charging polarity is directed from the intermediate transfer belt 7 to the photosensitive drum 1d. The

"3rd lap"
Waste toner adhering to the cleaning roller 18 is discharged onto the intermediate transfer belt 7 and the operation of setting similar to the above (III) is performed.

  As described above, by setting the primary transfer high-voltage power supply 60 to the above setting, the waste toner on the intermediate transfer belt 7 can be collected at Sa to Sd.

(V) Periodic cleaning With the same setting as the above (IV), the waste toner on the intermediate transfer belt 7 can be collected into Sa to Sd.

  As described above, by performing the above-described control in the cleaning operation of various intermediate transfer belts 7, it becomes possible to collect the waste toner on the intermediate transfer belt 7 to each process cartridge Pa to Pd as evenly as possible. It was. According to this embodiment, the number of primary transfer high-voltage circuits constituting the primary transfer high-voltage power supply 60 is minimized, and the primary transfer high-voltage circuit 61 and the primary transfer high-voltage circuit 62 having different voltage polarities are generated in series. Such an effect can be acquired by arrange | positioning.

  In the present invention, the order of the colors of the toner images forming the plurality of image forming units may be different from those in the above-described embodiments, and the configuration of the output terminal differs depending on the order of the colors. It may be. For example, let us consider a case where the mono-color image forming station in the mono-color mode described in the first embodiment is Sc instead of Sd. In this case, the output terminal 64 may be connected to the primary transfer rollers 6a, 6b and 6d, and the output terminal 65 may be connected to the primary transfer roller 6c. At this time, by applying a voltage of 0 V to the voltage of the primary transfer roller not involved in monocolor image formation, reverse transfer to a photosensitive drum not involved in monocolor image formation can be reduced, which is favorable. A monocolor image is obtained.

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

  In each of the above embodiments, the configuration of the electromagnetic transformer has been described as the transformer. However, the transformer may be a piezoelectric transformer. In that case, a circuit disclosed in Japanese Patent Application Laid-Open No. 2006-91757 may be applied.

1a, 1b, 1c, 1d photosensitive drum, 2a, 2b, 2c, 2d charging roller,
4a, 4b, 4c, 4d developing sleeve, 6a, 6b, 6c, 6d primary transfer roller,
7 Intermediate transfer belt, 8 Secondary transfer roller

Claims (9)

A movable intermediate transfer member, a plurality of image carriers that carry toner images disposed in a moving direction of the intermediate transfer member, and the toner images provided corresponding to each of the plurality of image carriers. A plurality of primary transfer means for sequentially transferring onto the intermediate transfer body; a voltage output means for outputting a voltage for transferring the toner image to the plurality of primary transfer means; and a toner on the intermediate transfer body In an image forming apparatus having secondary transfer means for collectively transferring an image to a transfer material,
A first image forming mode in which toner images are transferred from all of the plurality of image carriers to the intermediate transfer member;
A second image forming mode in which a toner image is transferred from only a specific image carrier among the plurality of image carriers to the intermediate transfer member; and
The voltage output unit includes a first voltage output unit that outputs a voltage having a characteristic opposite to a normal charging polarity of toner to all of the plurality of primary transfer units, and the primary that is involved in the second image forming mode. In addition to the transfer means, the second voltage output unit outputs a voltage having the same characteristic as the normal charging polarity of the toner, and the first voltage output unit is between the second voltage output unit and the ground potential. An image forming apparatus that is connected. A movable intermediate transfer member, a plurality of image carriers that carry toner images disposed in a moving direction of the intermediate transfer member, and the toner images provided corresponding to each of the plurality of image carriers. A plurality of primary transfer means for sequentially transferring onto the intermediate transfer body; a voltage output means for outputting a voltage for transferring the toner image to the plurality of primary transfer means; and a toner on the intermediate transfer body A secondary transfer unit that collectively transfers an image to a transfer material, a charging unit that is disposed on the intermediate transfer member that imparts a charge to residual toner on the intermediate transfer member, and a voltage is output to the charging unit Charging voltage output means,
In the image forming apparatus for reversely transferring the residual toner onto the image carrier by the voltage output to the voltage output means,
A first image forming mode in which toner images are transferred from all of the plurality of image carriers to the intermediate transfer member;
A second image forming mode in which a toner image is transferred from only a specific image carrier among the plurality of image carriers to the intermediate transfer member; and
The voltage output unit includes a first voltage output unit that outputs a voltage having a characteristic opposite to a normal charging polarity of toner to all of the plurality of primary transfer units, and the primary that is involved in the second image forming mode. In addition to the transfer means, the second voltage output unit outputs a voltage having the same characteristic as the normal charging polarity of the toner, and the first voltage output unit is between the second voltage output unit and the ground potential. An image forming apparatus that is connected. The voltage output unit includes a current detection unit that detects a current flowing through the primary transfer unit, and sets the voltage of the first voltage output unit based on a detection result of the current detection unit. The image forming apparatus according to claim 1 or 2. 4. The voltage output means includes control means for equalizing the absolute value of the voltage of the first voltage output section and the absolute value of the voltage of the second voltage output section. The image forming apparatus according to any one of the above. The image forming apparatus according to claim 4, wherein the second voltage output unit includes a control unit having a response characteristic faster than that of the first voltage output unit. The image forming apparatus according to claim 2, wherein the specific image carrier is arranged on the most downstream side in the moving direction of the intermediate transfer member. The image forming apparatus according to claim 6, wherein the residual toner is reversely transferred onto the different image carriers in the first image forming mode and the second image forming mode. The image forming apparatus according to claim 6, wherein the voltage output unit has a cleaning mode in which only the voltage of the second voltage output unit is output to the primary transfer unit. The charging voltage output unit can output voltages having different polarities to the charging unit in the first image forming mode or the second image forming mode and the cleaning mode. The image forming apparatus according to any one of claims 6 to 8.