Voltage supply device, developer recovery device, and image formation device

Abstract

To stably supply two types of voltages which have different polarities.SOLUTION: A first voltage generation circuit 51 outputs a first output voltage of a first polarity of a level corresponding to a first adjustment signal to a first output line. A first control circuit 53 executes a first feedback control that outputs the first adjustment signal to the first voltage generation circuit. A second voltage generation circuit 54 generates a second output voltage of a second polarity of a level corresponding to a second adjustment signal, and outputs the second output voltage to a second output line with reference to a second reference line electrically connected to the first output line. A second control circuit 56 selectively executes processing to execute a second feedback control that outputs the second adjustment signal to the second voltage generation circuit and processing to cause the second voltage generation circuit to stop the output of the second output voltage. The first control circuit executes the first feedback control at a responce speed slower than the speed in the second feedback control.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a voltage supply device capable of supplying two types of voltages with different polarities, a developer recovery device including the voltage supply device, and an image forming device including the voltage supply device.

Background Art

[0002] In an electrophotographic image forming apparatus, a charging device, an exposure device, and a developing device form an image of a developer on the surface of an image carrier, and a transfer device transfers the image of the developer from the image carrier to a sheet. Generally, the developer is toner, and the image carrier is a photoreceptor.

[0003] The charging device, the developing device, and the transfer device each include a high-voltage power supply device that outputs a high voltage.

[0004] For example, in the high-voltage power supply device, it is known that a pair of first voltage output lines of a first voltage generation circuit and a pair of second voltage output lines of a second voltage generation circuit are connected in series (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] By the way, the image forming apparatus includes a developer recovery device that executes a recovery process for recovering the developer remaining on the surface of the image carrier. The developer recovery device includes a recovery member and a voltage supply device.

[0007] The recovery member rotates while contacting the surface of the image carrier. The voltage supply device supplies a recovery voltage to the recovery member. The recovery voltage is a voltage having a polarity different from the charging polarity of the developer.

[0008] The developer recovery device executes the recovery process by supplying the recovery voltage to the recovery member.

[0009] The developer recovery device also executes a discharge process of discharging the recovered developer to the image carrier. The voltage supply device can selectively supply a discharge voltage having a polarity different from the polarity of the recovery voltage and the recovery voltage to the recovery member.

[0010] The developer recovery device executes the discharge process by supplying the discharge voltage having the same polarity as the charging polarity of the developer to the recovery member. The developer discharged to the image carrier is recovered by another device.

[0011] In the voltage output device of the developer recovery device, two voltage generation circuits for generating the recovery voltage and the discharge voltage may be employed.

[0012] In the two voltage generation circuits of the developer recovery device, it is required to be able to supply the stable recovery voltage.

[0013] An object of the present invention is to provide a voltage supply device capable of stably supplying two types of voltages having different polarities, a developer recovery device including the voltage supply device, and an image forming device.

Means for Solving the Problems

[0014] A voltage supply device according to one aspect of the present invention includes a first voltage generation circuit, a first control circuit, a second voltage generation circuit, and a second control circuit. The first voltage generation circuit generates a first output voltage of a first polarity at a level corresponding to a first adjustment signal input thereto, and outputs the first output voltage to a first output line with reference to a grounded first reference line. The first control circuit executes first feedback control for outputting the first adjustment signal to the first voltage generation circuit according to a comparison result between a level of a first target signal input thereto and a level of a first feedback signal representing the level of the first output voltage. The second voltage generation circuit generates a second output voltage of a second polarity at a level corresponding to a second adjustment signal input thereto, and outputs the second output voltage to a second output line with reference to a second reference line electrically connected to the first output line. The second control circuit executes second feedback control for outputting the second adjustment signal to the second voltage generation circuit according to a comparison result between a level of a second target signal input thereto and a level of a second feedback signal representing a level of a third output voltage generated between a ground line and the second output line, thereby causing the second voltage generation circuit to generate the second output voltage having an absolute value larger than the absolute value of the first output voltage, and selectively executing a process of stopping the output of the second output voltage from the second voltage generation circuit. The first control circuit executes the first feedback control at a response speed slower than that of the second feedback control. The voltage supply device supplies the third output voltage to a voltage supply target.

[0015] A developer recovery device according to another aspect of the present invention includes a rotating member and the voltage supply device. The rotating member rotates while contacting the surface of a rotating image carrier. The voltage supply device selectively supplies two types of voltages having different polarities to the rotating member. When one of the two types of voltages is supplied, the rotating member recovers the developer remaining on the surface of the image carrier, and when the other of the two types of voltages is supplied, the rotating member discharges the developer to the image carrier.

[0016] An image forming apparatus according to another aspect of the present invention includes a rotating image carrier, an exposure device, a developing device, and the developer recovery device. The exposure device forms an electrostatic latent image on the surface of the image carrier by exposing the surface of the image carrier. The developing device develops the electrostatic latent image by supplying a developer to the surface of the image carrier.

Advantages of the Invention

[0017] According to the present invention, it is possible to provide a voltage supply device capable of stably supplying two types of voltages having different polarities, a developer recovery device including the voltage supply device, and an image forming apparatus.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following embodiments are an example of embodying the present invention and do not limit the technical scope of the present invention.

[0020] The image forming apparatus 10 according to the embodiment is an apparatus that executes print processing by an electrophotographic method. The print processing is processing for forming an image on the sheet 9. The sheet 9 is an image forming medium such as paper or a sheet-like resin member.

[0021] [Configuration of Image Forming Apparatus 10] As shown in FIG. 1, the image forming apparatus 10 includes a sheet storage unit 2, a sheet conveyance path 30, a sheet conveyance device 3, and a printing device 4. Further, the image forming apparatus 10 also includes an operation device 801, a display device 802, and a control device 8.

[0022] The sheet conveyance path 30, the sheet conveyance device 3, the printing device 4, and the control device 8 are housed in the housing 1.

[0023] The sheet storage unit 2 stores sheets 9. The sheet conveyance device 3 feeds out the sheet 9 from the sheet storage unit 2 to the sheet conveyance path 30, and further conveys the sheet 9 along the sheet conveyance path 30.

[0024] The sheet conveyance device 3 includes a sheet feeding mechanism 31 and a plurality of sets of conveyance roller pairs 32.

[0025] The sheet feeding mechanism 31 feeds out the sheet 9 in the sheet storage unit 2 to the sheet conveyance path 30. The plurality of sets of conveyance roller pairs 32 convey the sheet 9 along the sheet conveyance path 30. Further, one set of the plurality of sets of conveyance roller pairs 32 discharges the sheet 9 onto the discharge tray 101 from the sheet conveyance path 30.

[0026] The printing device 4 performs the printing process on the sheet 9 conveyed along the sheet conveyance path 30. In the present embodiment, the printing device 4 is a tandem type color printing device.

[0027] The printing device 4 forms a toner image on the sheet 9 conveyed along the sheet conveyance path 30. The toner image is an image using toner as a developer. The toner is an example of the granular developer.

[0028] The printing device 4 includes a plurality of single-color image forming units 4x, an optical scanning device 40, a transfer device 44, and a fixing device 46. In the present embodiment, the printing device 4 includes four single-color image forming units 4x corresponding to four colors of yellow, cyan, magenta, and black.

[0029] Each monochromatic image forming unit 4x includes a drum-shaped photoreceptor 41, a charging device 42, a developing device 43, a drum cleaning device 45, and the like.

[0030] In each monochromatic image forming unit 4x, the photoreceptor 41 rotates, and the charging device 42 performs a charging process. The charging process is a process of charging the surface of the photoreceptor 41. Further, the optical scanning device 40 forms an electrostatic latent image on the charged surface of the photoreceptor 41 by scanning laser light.

[0031] The optical scanning device 40 is an example of an exposure device that forms the electrostatic latent image on the surface of the photoreceptor 41 by exposing the surface of the charged photoreceptor 41.

[0032] The developing device 43 develops the electrostatic latent image into the toner image by supplying the toner to the surface of the photoreceptor 41. The developing device 43 supplies the toner to the photoreceptor 41 at the developing position on the outer periphery of the photoreceptor 41. The toner image is an example of an image of the developer.

[0033] The charging device 42 includes a charging roller 421 and a charging voltage output device 422. The charging roller 421 is disposed to face the photoreceptor 41 at the charging position on the outer periphery of the photoreceptor 41. The charging voltage output device 422 applies a charging bias voltage to the charging roller 421. The charging bias voltage is the bias voltage applied in the charging process.

[0034] The charging bias voltage is applied from the charging voltage output device 422 to the photoreceptor 41 through the charging roller 421. Thereby, the surface of the photoreceptor 41 is charged.

[0035] The developing device 43 includes a developing roller 431 and a developing voltage output device 432. The developing roller 431 is disposed to face the photoreceptor 41 at the developing position. The developing roller 431 rotates while carrying the toner.

[0036] The developing voltage output device 432 applies a developing bias voltage to the developing roller 431. In the present embodiment, the developing bias voltage is a voltage in which an AC voltage is superimposed on a DC voltage.

[0037] The developing roller 431 is disposed to face the photoreceptor 41 and rotates while carrying toner. The developing roller 431 supplies the toner to the surface of the photoreceptor 41 at the developing position. The toner carried on the developing roller 431 migrates to the portion of the electrostatic latent image on the surface of the photoreceptor 41 due to the electric field generated between the developing roller 431 and the photoreceptor 41.

[0038] At the developing position, the toner migrates from the developing roller 431 to the portion of the electrostatic latent image on the surface of the photoreceptor 41. Thereby, the electrostatic latent image is developed into the toner image. Each of the photoreceptors 41 is an example of an image carrier that carries and rotates the toner image.

[0039] In the present embodiment, the developing device 43 performs development by a two-component development method. That is, the developing device 43 charges the toner by stirring a two-component developer containing the toner and the magnetic carrier. Further, the developing device 43 supplies the charged toner to the photoreceptor 41.

[0040] The magnetic carrier is a granular material having magnetism. For example, the magnetic carrier is a granular magnetic body whose surface is coated. The coating is made of a synthetic resin such as an epoxy resin, for example.

[0041] The transfer device 44 includes an intermediate transfer belt 441, four primary transfer devices 442 corresponding to the four single-color image forming units 4x, a secondary transfer device 443, and a belt cleaning device 444.

[0042] The intermediate transfer belt 441 is supported by a plurality of support rollers 440. One of the plurality of support rollers 440 rotates by power received from a motor (not shown). Thereby, the intermediate transfer belt 441 rotates.

[0043] The surface of the intermediate transfer belt 441 is in contact with the surface of each of the photoreceptors 41 at the primary transfer position on the outer periphery of each of the photoreceptors 41. The intermediate transfer belt 441 rotates while contacting the surface of each of the photoreceptors 41.

[0044] Each of the primary transfer devices 442 is capable of executing a primary transfer process. The primary transfer process is a process of transferring the toner image on the surface of the photoreceptor 41 to the surface of the intermediate transfer belt 441 at the primary transfer position.

[0045] By executing the primary transfer process by a plurality of primary transfer devices 442, the toner images of a plurality of colors are formed on the surface of the intermediate transfer belt 441.

[0046] Each of the primary transfer devices 442 includes a primary transfer roller 4421 and a primary transfer voltage output device 4422. The primary transfer roller 4421 is disposed to face the photoreceptor 41 via the intermediate transfer belt 441.

[0047] The primary transfer voltage output device 4422 applies a primary transfer voltage to the primary transfer roller 4421. The toner image formed on the surface of the photoreceptor 41 is transferred to the surface of the intermediate transfer belt 441 by an electric field generated between the photoreceptor 41 and the primary transfer roller 4421. The polarity of the primary transfer voltage is the opposite polarity of the charging polarity of the toner.

[0048] The secondary transfer device 443 is capable of executing a secondary transfer process. The secondary transfer process is a process of transferring the toner image formed on the intermediate transfer belt 441 to the sheet 9 at the secondary transfer position in the sheet conveyance path 30.

[0049] The secondary transfer device 443 includes a secondary transfer roller 4431 and a secondary transfer voltage output device 4432. The secondary transfer roller 4431 is in contact with the intermediate transfer belt 441 at the secondary transfer position. The sheet 9 passes between the intermediate transfer belt 441 and the secondary transfer roller 4431.

[0050] The secondary transfer voltage output device 4432 applies a secondary transfer voltage to the secondary transfer roller 4431. The toner image formed on the surface of the intermediate transfer belt 441 is transferred to the sheet 9 by an electric field generated between the intermediate transfer belt 441 and the secondary transfer roller 4431. The polarity of the secondary transfer voltage is opposite to the charging polarity of the toner.

[0051] Note that the intermediate transfer belt 441 is an example of an intermediate transfer member.

[0052] The drum cleaning device 45 performs a recovery process. The recovery process is a process of recovering the toner remaining on the portion of the surface of the photoreceptor 41 that has passed through the primary transfer position.

[0053] The belt cleaning device 444 removes the toner remaining on the portion of the intermediate transfer belt 441 that has passed through the secondary transfer position.

[0054] For example, the belt cleaning device 444 scrapes off the toner on the surface of the intermediate transfer belt 441 with a cleaning blade or a cleaning brush that contacts the surface of the intermediate transfer belt 441.

[0055] Note that the belt cleaning device 444 may include a cleaning roller that contacts the surface of the intermediate transfer belt 441 and a brush that contacts the cleaning roller. In this case, the belt cleaning device 444 applies a cleaning voltage to the cleaning roller to electrostatically adsorb the toner on the surface of the intermediate transfer belt 441 to the surface of the cleaning roller. The brush scrapes off the toner from the surface of the cleaning roller.

[0056] The fixing device 46 applies pressure while heating the toner image on the sheet 9. Thereby, the fixing device 46 fixes the toner image to the sheet 9.

[0057] The operation device 801 is a device that receives human operations. For example, the operation device 801 includes operation buttons and a touch panel.

[0058] The display device 802 is a device for displaying information. For example, the display device 802 includes a panel display device such as a liquid crystal display unit.

[0059] [Configuration of the control device 8] As shown in FIG. 2, the control device 8 includes a CPU (Central Processing Unit) 81, a RAM (Random Access Memory) 82, a secondary storage device 83, a signal interface 84, a communication device 85, and the like.

[0060] The secondary storage device 83 is a computer-readable non-volatile storage device. The secondary storage device 83 can store and update computer programs and various data. For example, one or both of a flash memory and a hard disk drive are adopted as the secondary storage device 83.

[0061] The signal interface 84 converts signals output by various sensors into digital data and transmits the converted digital data to the CPU 81. Further, the signal interface 84 converts a control command output by the CPU 81 into a control signal and transmits the control signal to the device to be controlled.

[0062] The communication device 85 executes communication with other devices such as a host device (not shown). The CPU 81 communicates with the other devices through the communication device 85.

[0063] The CPU 81 is a processor that executes various data processing and controls by executing the computer program. The control device 8 including the CPU 81 controls the sheet conveyance device 3, the printing device 4, the display device 802, the communication device 85, and the like.

[0064] The RAM 82 is a computer-readable volatile memory device. The RAM 82 primarily stores the computer program executed by the CPU 81 and the data output and referenced by the CPU 81 during the execution of various processes.

[0065] The CPU 81 includes a plurality of processing modules realized by executing the computer program. The plurality of processing modules includes a main processing unit 8a, a print control unit 8b, and the like.

[0066] The main processing unit 8a executes processes such as starting various processes in response to operations on the operation device 801 and controlling the display device 802.

[0067] The print control unit 8b controls the sheet conveyance device 3. Thereby, the print control unit 8b controls the feeding of the sheet 9 from the sheet storage unit 2 and the conveyance of the sheet 9 in the sheet conveyance path 30.

[0068] Furthermore, the print control unit 8b controls the printing device 4. The print control unit 8b causes the printing device 4 to execute the printing process in synchronization with the conveyance of the sheet 9 by the sheet conveyance device 3.

[0069] Furthermore, when causing the printing device 4 to execute the printing process, the print control unit 8b causes the drum cleaning device 45 to execute the recovery process.

[0070] Incidentally, the drum cleaning device 45 includes a recovery member 451 and a voltage supply device 452 for executing the recovery process (see FIG. 1).

[0071] The recovery member 451 rotates while contacting the surface of the photoreceptor 41. The recovery member 451 is an example of a rotating member. The voltage supply device 452 supplies a recovery voltage to the recovery member 451. The recovery voltage is a voltage having a polarity different from the charging polarity of the toner.

[0072] The recovery member 451 is a member capable of holding toner. For example, the recovery member 451 is a porous member such as a sponge.

[0073] The drum cleaning device 45 executes the recovery process by supplying the recovery voltage to the recovery member 451.

[0074] The drum cleaning device 45 also executes a discharge process of discharging the recovered toner onto the surface of the photoreceptor 41.

[0075] The drum cleaning device 45 executes the discharge process by supplying a discharge voltage having the same polarity as the charging polarity of the toner to the recovery member 451. The toner discharged onto the surface of the photoreceptor 41 is recovered by another device.

[0076] For example, when the charging polarity of the toner is positive, the recovery voltage is a negative voltage, and the discharge voltage is a positive voltage.

[0077] The voltage supply device 452 can selectively supply the recovery voltage and the discharge voltage to the recovery member 451. The drum cleaning device 45 is an example of a developer recovery device.

[0078] In the following description, the toner remaining on the portion of the surface of the photoreceptor 41 that has passed through the primary transfer position is referred to as residual toner. Also, the toner discharged onto the surface of the photoreceptor 41 by the discharge process is referred to as discharged toner.

[0079] The recovery member 451 is in contact with the surface of the photoreceptor 41 at a recovery position on the outer periphery of the photoreceptor 41. The recovery position is a position between the primary transfer position and the charging position on the outer periphery of the photoreceptor 41.

[0080] The drum cleaning device 45 selectively executes one of the recovery process and the discharge process by applying the recovery voltage or the discharge voltage to the recovery member 451.

[0081] The voltage supply device 452 applies the recovery voltage to the recovery member 451 in the recovery process. Thereby, the voltage supply device 452 electrically attracts the residual toner to the recovery member 451. The recovery member 451 holds the attracted toner.

[0082] That is, the voltage supply device 452 recovers the residual toner to the recovery member 451 by applying the recovery voltage to the recovery member 451. The toner recovered by the recovery member 451 is accumulated in a plurality of holes formed on the surface of the recovery member 451.

[0083] On the other hand, the voltage supply device 452 applies the discharge voltage to the recovery member 451 in the discharge process. Thereby, the toner recovered by the recovery member 451 is electrically repelled from the recovery member 451 and discharged onto the surface of the photoreceptor 41 from the recovery member 451.

[0084] When the printing process is executed, the drum cleaning device 45 executes the recovery process. By executing the recovery process, the toner that has not been transferred to the intermediate transfer belt 441 at the primary transfer position is recovered by the recovery member 451.

[0085] However, as the toner accumulates on the recovery member 451, the toner recovery performance of the recovery member 451 deteriorates.

[0086] On the other hand, when predetermined discharge conditions are satisfied under the condition that the printing process is not being executed, the discharge process is executed. By executing the discharge process, the toner recovery performance of the recovery member 451 is improved.

[0087] In the present embodiment, when the discharge process is executed, the primary transfer voltage output device 4422 transfers the discharged toner from the photoreceptor 41 to the intermediate transfer belt 441, and the secondary transfer device 443 does not transfer the discharged toner on the intermediate transfer belt 441 to the sheet 9.

[0088] That is, when the ejection process is executed, the primary transfer voltage output device 4422 applies the primary transfer voltage to the primary transfer roller 4421, and the secondary transfer voltage output device 4432 applies a non-transfer voltage having a polarity different from that of the secondary transfer voltage to the secondary transfer roller 4431.

[0089] The secondary transfer voltage output device 4432 can output the secondary transfer voltage or the non-transfer voltage to the secondary transfer roller 4431.

[0090] When the ejection process is executed, the belt cleaning device 444 removes the ejected toner from the surface of the intermediate transfer belt 441.

[0091] The print control unit 8b determines whether the ejection condition is satisfied in a situation where the print process is not being executed.

[0092] For example, the ejection condition is a condition that is satisfied every time the number of page prints reaches a predetermined number. The page print is the print process for one page of the sheet 9.

[0093] Furthermore, when the print control unit 8b determines that the ejection condition is satisfied, it executes reproduction control.

[0094] In the reproduction control, the print control unit 8b causes the drum cleaning device 45 to execute the ejection process.

[0095] Furthermore, in the reproduction control, the print control unit 8b does not output a voltage to the charging voltage output device 422 and does not cause the electrostatic latent image to be formed on the optical scanning device 40.

[0096] Furthermore, in the reproduction control, the print control unit 8b outputs the primary transfer voltage to the primary transfer voltage output device 4422 and outputs the non-transfer voltage to the secondary transfer voltage output device 4432. Thereby, the belt cleaning device 444 removes the ejected toner from the surface of the intermediate transfer belt 441.

[0097] In the voltage supply device 452 of the drum cleaning device 45, two voltage generation circuits for generating the recovery voltage and the discharge voltage may be employed.

[0098] It is desirable that the voltage supply device 452 of the drum cleaning device 45 can stably supply two types of voltages with different polarities to the recovery member 451. The two types of voltages are the recovery voltage and the discharge voltage.

[0099] [Voltage supply device 452] Hereinafter, with reference to FIG. 3, the configuration of the voltage supply device 452 will be described. The voltage supply device 452 includes a configuration for stably outputting the two types of voltages. FIG. 3 shows an example when the charging polarity of the toner is the positive electrode.

[0100] The voltage supply device 452 includes a first voltage generation circuit 51, a first output level detection circuit 52, a first control circuit 53, a second voltage generation circuit 54, a second output level detection circuit 55, and a second control circuit 56.

[0101] The first voltage generation circuit 51 generates a first output voltage VO1 of a first polarity at a level corresponding to the input first adjustment signal SA1. The first voltage generation circuit 51 adjusts the level of the first output voltage VO1 according to the level of the first adjustment signal SA1. The first voltage generation circuit 51 outputs the first output voltage VO1 to the first output line 51b with reference to the grounded first reference line 51a.

[0102] The first reference line 51a and the first output line 51b are a pair of voltage output lines of the first voltage generation circuit 51.

[0103] In the present embodiment, the first voltage generation circuit 51 includes a first drive circuit 511, a first transformer 512, and a first rectifier circuit 513.

[0104] The first drive circuit 511 outputs a first AC voltage corresponding to the level of the first adjustment signal SA1 to the first transformer 512.

[0105] The first transformer 512 amplifies the first AC voltage supplied from the first drive circuit 511. The first rectifier circuit 513 rectifies the first AC voltage amplified by the first transformer 512 to generate a DC first output voltage VO1. The generated first output voltage VO1 is output to the first reference line 51a and the first output line 51b.

[0106] In the example shown in FIG. 3, the first rectifier circuit 513 outputs the first output voltage VO1 of the positive electrode to the first output line 51b with reference to the grounded first reference line 51a.

[0107] The first output voltage VO1 is a voltage having the same polarity as the charging polarity of the toner. The first output voltage VO1 is the discharge voltage output to the recovery member 451 when the discharge process is executed. The first adjustment signal SA1 is supplied from the first control circuit 53 to the first drive circuit 511.

[0108] The first output level detection circuit 52 detects the level of the first output voltage VO1 and outputs a first feedback signal FB1 representing the level of the first output voltage VO1 to the first control circuit 53. The first feedback signal FB1 is an example of a signal representing the level of the first output voltage VO1.

[0109] In the present embodiment, the first output level detection circuit 52 includes a first resistor element R11 and a second resistor element R12 connected in series, and is a voltage dividing circuit that divides the first output voltage VO1. The voltage level of the first feedback signal FB1 is the voltage level obtained by dividing the first output voltage VO1 by the first resistor element R11 and the second resistor element R12.

[0110] Therefore, the voltage level of the first feedback signal FB1 is proportional to the level of the first output voltage VO1. The proportional coefficient of the voltage level of the first feedback signal FB1 with respect to the level of the first output voltage VO1 is determined by the resistance values of the first resistor element R11 and the second resistor element R12.

[0111] The first control circuit 53 is a circuit that executes first feedback control. In the first feedback control, the first control circuit 53 outputs a first adjustment signal SA1 to the first voltage generation circuit 51 according to the comparison result between the level of the input first reference voltage VS1 and the level of the first feedback signal FB1.

[0112] The first control circuit 53 adjusts the level of the first adjustment signal SA1 to a higher level when the level of the first feedback signal FB1 is lower than the level of the first reference voltage VS1. On the other hand, the first control circuit 53 adjusts the level of the first adjustment signal SA1 to a lower level when the level of the first feedback signal FB1 is higher than the level of the first reference voltage VS1.

[0113] By executing the first feedback control, the level of the first output voltage VO1 is adjusted to the first target level by the first voltage generation circuit 51. In this embodiment, the first target level is the target level of the discharge voltage. The first reference voltage VS1 is an example of a first target signal.

[0114] Note that the first control circuit 53 selectively executes first feedback processing and first stop processing according to the level of the first control voltage VC1 supplied from the CPU 81. The first feedback processing is a process of causing the first voltage generation circuit 51 to generate the first output voltage VO1 by executing the first feedback control. The first stop processing is a process of stopping the output of the first output voltage VO1 to the first voltage generation circuit 51.

[0115] The second voltage generation circuit 54 generates a second output voltage VO2 of a second polarity at a level corresponding to the input second adjustment signal SA2. The second voltage generation circuit 54 adjusts the level of the second output voltage VO2 according to the level of the second adjustment signal SA2. The second voltage generation circuit 54 outputs the second output voltage VO2 to the second output line 54b with reference to the second reference line 54a.

[0116] The second reference line 54a is electrically connected to the first output line 51b. Specifically, the second reference line 54a is short-circuited with the first output line 51b.

[0117] In this embodiment, the second voltage generation circuit 54 includes a second drive circuit 541, a second transformer 542, a second rectification circuit 543, and a bleeder resistor element R21.

[0118] The second drive circuit 541 outputs a second AC voltage, whose amplitude is the reference AC voltage to be supplied, corresponding to the level of the second adjustment signal SA2, to the second transformer 542.

[0119] The second transformer 542 amplifies the second AC voltage supplied from the second drive circuit 541. The second rectification circuit 543 rectifies the second AC voltage amplified by the second transformer 542 to generate a DC second output voltage VO2. The generated second output voltage VO2 is output to the second reference line 54a and the second output line 54b.

[0120] In the example shown in FIG. 3, the second rectification circuit 543 outputs the second output voltage VO2 with a negative electrode to the second output line 54b with the second reference line 54a as a reference. The bleeder resistor element R21 is connected to the second reference line 54a and the second output line 54b.

[0121] The second reference line 54a and the second output line 54b are a pair of voltage output lines of the second voltage generation circuit 54. The recovery member 451 is electrically connected to the second output line 54b and the ground line.

[0122] That is, the voltage supply device 452 supplies the third output voltage VO3 generated between the ground line and the second output line 54b to the recovery member 451. The recovery member 451 is an example of a voltage supply target to which voltage is supplied by the voltage supply device 452.

[0123] The second output voltage VO2 is a voltage with a polarity different from the charging polarity of the toner. The second output voltage VO2 is the recovery voltage output to the recovery member 451 when the recovery process is executed. The second adjustment signal SA2 is supplied from the second control circuit 56 to the second drive circuit 541.

[0124] The second output level detection circuit 55 detects the level of the second output voltage VO2 and outputs a second feedback signal FB2 representing the level of the second output voltage VO2 to the second control circuit 56. The second feedback signal FB2 is an example of a signal representing the level of the second output voltage VO2.

[0125] In the present embodiment, the second output level detection circuit 55 includes a third resistor element R22, a first diode D21, a fourth resistor element R23, and a second diode D22. The third resistor element R22 is connected to the second output line 54b.

[0126] The third resistor element R22, the first diode D21, and the fourth resistor element R23 are connected in series, and the third resistor element R22 and the second diode D22 are connected in series.

[0127] The first diode D21 is connected between the third resistor element R22 and the fourth resistor element R23, and the fourth resistor element R23 is connected between the first diode D21 and the supply line of the second control voltage VC2. The second diode D22 is connected between the third resistor element R22 and the ground line.

[0128] The first diode D21 blocks the current flowing from the second output line 54b toward the supply line side of the second control voltage VC2. When the second control voltage VC2 drops while the negative-polarity third output voltage VO3 is output from the second output line 54b, the second diode D22 blocks the current flowing toward the ground line, thereby preventing the polarity of the second feedback signal FB2 from becoming negative.

[0129] The voltage of the line between the fourth resistor R23 and the first diode D21 is input to the second control circuit 56 as the second feedback signal FB2. Further, a second reference voltage VS2 is input to the second control circuit 56.

[0130] Here, the voltage obtained by adding the third output voltage VO3 and the forward voltage VD1 of the first diode D21 is referred to as the feedback voltage. The level of the second feedback signal FB2 is the level of the voltage obtained by weighted-averaging the second control voltage VC2 and the feedback voltage with the voltage division ratio of the third resistor R22 and the fourth resistor R23.

[0131] Therefore, in a situation where the second control voltage VC2 is constant, the level of the second feedback signal FB2 has a positive correlation with the level of the third output voltage VO3. The second feedback signal FB2 is an example of a signal representing the level of the third output voltage VO3.

[0132] The second control circuit 56 is a circuit that executes second feedback control. In the second feedback control, the second control circuit 56 outputs a second adjustment signal SA2 to the second voltage generation circuit 54 according to the comparison result between the level of the input second reference voltage VS2 and the level of the second feedback signal FB2.

[0133] The second control circuit 56 adjusts the level of the second adjustment signal SA2 to a higher level when the level of the second feedback signal FB2 is smaller than the level of the second reference voltage VS2. On the other hand, the second control circuit 56 adjusts the level of the second adjustment signal SA2 to a lower level when the level of the second feedback signal FB2 is larger than the level of the second reference voltage VS2.

[0134] By executing the second feedback control, the level of the third output voltage VO3 is adjusted to the second target level by the second voltage generation circuit 54. In the present embodiment, the second target level is the target level of the recovery voltage at the negative electrode. The second reference voltage VS2 is an example of a second target signal.

[0135] When the first feedback control and the second feedback control are being executed, the absolute value of the second output voltage VO2 is greater than the absolute value of the first output voltage VO1. As a result, the third output voltage VO3 of the negative electrode is supplied to the recovery member 451.

[0136] On the other hand, when the voltage output by the second voltage generation circuit 54 has stopped, the level of the second output voltage VO2 is 0. Therefore, when the first feedback control is being executed and the output of the second output voltage VO2 by the second voltage generation circuit 54 has stopped, the third output voltage VO3 of the positive electrode is supplied to the recovery member 451.

[0137] The second control circuit 56 selectively executes the second feedback process and the second stop process according to the level of the second control voltage VC2 supplied from the CPU 81. The second feedback process is a process of causing the second voltage generation circuit 54 to generate a second output voltage VO2 by executing the second feedback control. The second stop process is a process of stopping the output of the second output voltage VO2 to the second voltage generation circuit 54.

[0138] In the present embodiment, when the second control voltage VC2 is greater than the second reference voltage VS2, the second voltage generation circuit 54 outputs a second output voltage VO2 at a level determined by equation (1). Equation (1) is an equation indicating that the second output voltage VO2 is determined based on the second control voltage VC2, the second reference voltage VS2, the resistance value R1 of the bleeder resistor element R21, the resistance value R2 of the third resistor element R22, the resistance value R3 of the fourth resistor element R23, and the forward voltage VD1 of the first diode D21.

[0139]

Equation

[0140] That is, when the second control circuit 56 is supplied with a second control voltage VC2 greater than the second reference voltage VS2, the second feedback process is executed.

[0141] When the first feedback control and the second feedback control are being executed, the third output voltage VO3 of negative polarity determined by Equation (2) is supplied to the recovery member 451.

[0142]

Number

[0143] On the other hand, when the second control voltage VC2 is smaller than the second reference voltage VS2, the state where the level of the second feedback signal FB2 is lower than the level of the second reference voltage VS2 is maintained. In this case, the second control circuit 56 stops the voltage output by the second voltage generation circuit 54 by reducing the level of the second adjustment signal SA2 to 0.

[0144] That is, the second control circuit 56 executes the second stop process when a second control voltage VC2 smaller than the second reference voltage VS2 is supplied.

[0145] When the first feedback control is being executed and the voltage output by the second voltage generation circuit 54 has stopped, the third output voltage VO3 of positive polarity determined by Equation (3) is supplied to the recovery member 451. Equation (3) indicates that the third output voltage VO3 is a voltage at a level corresponding to the first output voltage VO1, the resistance value R1 of the bleeder resistor element R21, and the load current I1 flowing through the recovery member 451.

[0146]

Number

[0147] (3) indicates that the third output voltage VO3 at the same level as the first output voltage VO1 is supplied to the recovery member 451.

[0148] Furthermore, equation (3) indicates that when the voltage output by the second voltage generation circuit 54 has stopped, the third output voltage VO3 is affected by the load. On the other hand, equation (2) indicates that when the second voltage generation circuit 54 is outputting the second output voltage VO2, the third output voltage VO3 is not affected by the load.

[0149] When the recovery process is executed, the print control unit 8b executes recovery control. In the recovery control, the print control unit 8b outputs a first control voltage VC1 at a predetermined level to the first control circuit 53 and outputs a second control voltage VC2 greater than the second reference voltage VS2 to the second control circuit 56. In the present embodiment, the print control unit 8b outputs the second control voltage VC2 to the second control circuit 56 through the fourth resistor element R23.

[0150] The second voltage generation circuit 54 executes a voltage output operation when the recovery process is executed.

[0151] When the recovery control is executed, the third output voltage VO3 of the negative electrode is output to the recovery member 451 as the recovery voltage. At that time, the third output voltage VO3 at the level determined by equation (2) is supplied to the recovery member 451 as the recovery voltage.

[0152] As shown in equation (2), the third output voltage VO3 output in the recovery process is not affected by the load.

[0153] However, if the output state of the voltage by the first voltage generation circuit 51 fluctuates under the condition that the second voltage generation circuit 54 is operating, the second output voltage VO2 may fluctuate significantly.

[0154] In the voltage supply device 452, the first control circuit 53 executes the first feedback control at a response speed slower than the second feedback control by the second control circuit 56. This is synonymous with the second control circuit 56 executing the second feedback control at a response speed faster than the first feedback control by the first control circuit 53.

[0155] In other words, the sensitivity of the first feedback control by the first control circuit 53 is lower than the sensitivity of the second feedback control by the second control circuit 56. This is synonymous with the fact that the sensitivity of the second feedback control by the second control circuit 56 is higher than the sensitivity of the first feedback control by the first control circuit 53. Thereby, the fluctuation speed of the output state of the voltage by the first voltage generation circuit 51 is alleviated, and the convergence of the voltage fluctuation by the second voltage generation circuit 54 is accelerated, so that the fluctuation of the third output voltage VO3 is suppressed.

[0156] For example, the change speed of the first control voltage VC1 is slower than the change speed of the second control voltage VC2. Thereby, the first feedback control is executed at a response speed slower than that of the second feedback control.

[0157] Also, the time constant of the output circuit of the first adjustment signal SA1 in the first control circuit 53 may be set larger than the time constant of the output circuit of the second adjustment signal SA2 in the second control circuit 56.

[0158] When the third output voltage VO3 shown in the formula (2) is output to the recovery member 451 as the recovery voltage, the recovery voltage is stabilized regardless of the load situation.

[0159] On the other hand, when the discharging process is executed, the print control unit 8b executes discharging control. In the discharging control, the print control unit 8b outputs a first control voltage VC1 at a predetermined level to the first control circuit 53 and outputs a second control voltage VC2 smaller than the second reference voltage VS2 to the second control circuit 56. That is, the second voltage generation circuit 54 stops the voltage output operation when the discharging process is executed.

[0160] In the present embodiment, the print control unit 8b outputs the second control voltage VC2 to the second control circuit 56 through the fourth resistor element R23.

[0161] When the discharge control is executed, a third output voltage VO3 at the same level as the first output voltage VO1 of the positive electrode is output to the recovery member 451 as the discharge voltage. At this time, the third output voltage VO3 at the level determined by equation (3) is supplied to the recovery member 451 as the recovery voltage.

[0162] As shown in equation (3), the third output voltage VO3 output in the discharge process is affected by the load. However, in the discharge process, some fluctuations in the voltage output to the recovery member 451 are not a problem.

[0163] [First Modified Example] Next, a second modified example of the image forming apparatus 10 will be described with reference to FIG. 4.

[0164] In this modified example, the charging polarity of the toner is the negative electrode. FIG. 4 shows the configuration of the recovery voltage output device 452X employed in this application example. The recovery voltage output device 452X is employed in place of the recovery voltage output device 452 in the image forming apparatus 10.

[0165] In FIG. 4, the components corresponding to the components shown in FIG. 3 are given the same reference numerals.

[0166] In the recovery voltage output device 452X, the first voltage generation circuit 51 generates the first output voltage VO1 of the negative electrode, and the second voltage generation circuit 54 generates the second output voltage VO2 of the positive electrode. When the recovery voltage output device 452X is employed, the same effects as when the recovery voltage output device 452 is employed can be obtained.

[0167] [Second Modified Example] Hereinafter, a second modified example of the image forming apparatus 10 will be described.

[0168] In the image forming apparatus 10, the belt cleaning device 444 recovers the discharged toner.

[0169] On the other hand, in this modified example, the developing device 43 recovers the discharged toner.

[0170] In this modified example, the developing voltage output device 432 can also apply an attracting bias voltage to the developing roller 431. The attracting bias voltage is a voltage different from the developing bias voltage applied to the developing roller 431 when development of the latent electrostatic image is performed. The attracting bias voltage is a voltage having a polarity different from the charging polarity of the toner.

[0171] When the discharging process is executed, the developing voltage output device 432 applies the attracting bias voltage to the developing roller 431. Thereby, the developing device 43 recovers the discharged toner discharged from the surface of the photoreceptor 41 to the recovery member 451 by the developing roller 431.

Explanation of Signs

[0172] 4: Printing device 8: Control device 10: Image forming device 40: Optical scanning device (exposure device) 41: Photoreceptor 42: Charging device 43: Developing device 44: Transfer device 45: Drum cleaning device (developer recovery device) 51a: First reference line 51b: First output line 52: First output level detection circuit 54a: Second reference line 54b: Second output line 55: Second output level detection circuit 441: Intermediate transfer belt 442: Primary transfer device 443: Secondary transfer device 444: Belt cleaning device 451: Recovery member 452: Recovery voltage output device 511: First drive circuit 512: First transformer 513: First rectifier circuit 541: Second drive circuit 542: Second transformer 543: Second rectifier circuit

Claims

1. A first voltage generation circuit that generates a first output voltage of a first polarity at a level corresponding to a first adjustment signal input thereto and outputs the first output voltage to a first output line with reference to a grounded first reference line; A first control circuit that executes first feedback control for outputting the first adjustment signal to the first voltage generation circuit according to a comparison result between a level of a first target signal input thereto and a level of a first feedback signal representing the level of the first output voltage; A second voltage generation circuit that generates a second output voltage of a second polarity at a level corresponding to a second adjustment signal input thereto and outputs the second output voltage to a second output line with reference to a second reference line electrically connected to the first output line; A second control circuit that selectively executes a process of causing the second voltage generation circuit to generate the second output voltage having an absolute value larger than the absolute value of the first output voltage by executing second feedback control for outputting the second adjustment signal to the second voltage generation circuit according to a comparison result between a level of a second target signal input thereto and a level of a second feedback signal representing the level of a third output voltage generated between a ground line and the second output line, and a process of stopping the output of the second output voltage from the second voltage generation circuit, and a voltage supply device that supplies the third output voltage to a voltage supply target. The first control circuit executes the first feedback control with a response speed slower than that of the second feedback control. A voltage supply device that supplies the third output voltage to a voltage supply target.

2. A rotating member that rotates while contacting the surface of a rotating image carrier; The voltage supply device according to claim 1, which selectively supplies two types of voltages having different polarities to the rotating member; The rotating member is a developer recovery device that recovers the developer remaining on the surface of the image carrier when one of the two types of voltages is supplied, and discharges the developer to the image carrier when the other of the two types of voltages is supplied.

3. A rotating image carrier; An exposure device that forms an electrostatic latent image on the surface of the image carrier by exposing the surface of the image carrier; A developing device that develops the electrostatic latent image by supplying a developer to the surface of the image carrier; An image forming apparatus comprising the developer recovery device according to claim 2.

4. An intermediate transfer body that rotates while contacting the surface of the image carrier; A primary transfer device that transfers the image of the developer on the surface of the image carrier to the surface of the intermediate transfer body; A secondary transfer device that transfers the image of the developer transferred to the surface of the intermediate transfer body to a sheet; A cleaning device that removes the developer remaining on the surface of the intermediate transfer body, comprising: When the developer recovery device discharges the developer from the recovery member to the image carrier, the primary transfer device transfers the developer discharged to the image carrier to the intermediate transfer body, the secondary transfer device does not transfer the developer transferred to the intermediate transfer body to the sheet, and the cleaning device removes the developer transferred to the intermediate transfer body. The image forming apparatus according to claim 3.

5. The developing device is disposed opposite to the image carrier and includes a developing roller that rotates while carrying the developer; When the developer recovery device discharges the developer from the recovery member to the image carrier, the developing device applies a voltage different from the developing bias voltage applied to the developing roller when the electrostatic latent image is developed to the developing roller, thereby recovering the developer discharged to the image carrier. The image forming apparatus according to claim 3.

Images