JP2009014753A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of prolonging service life that is shortened due to problems arising when constant current control or constant voltage control of a diffusing member is performed. <P>SOLUTION: The image forming apparatus 100 with a diffusing brush 15 for diffusing toner remaining on the surface of a photoreceptor drum 10 after a transfer process includes: a constant voltage application circuit 35 for applying a constant voltage to the diffusing brush 15; a constant current application circuit 36 for applying a constant current to the diffusing brush 15; and a current detection part 37 for detecting a value capable of estimating diffusion efficiency of the diffusing brush 15, for example, the amount of the current flowing into the diffusing brush 15 when the constant voltage is applied to the diffusing brush 15. When the value detected by the current detection part 37 is below a normal value, an application means to the diffusing brush 15 is switched from the constant voltage application circuit 35 to the constant current application circuit 36. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a facsimile machine, and a copying machine, and more particularly to an image forming apparatus provided with a diffusion member that diffuses toner remaining on the surface of a photoreceptor after transfer.

  Image forming apparatuses for recording characters and graphics on paper include printers, facsimiles, and multifunction machines. As such an image forming apparatus, there is a cleaningless type that includes a diffusion member that diffuses toner remaining on the surface of the photoreceptor after transfer.

For example, Patent Document 1 describes that a brush is provided to disperse toner remaining on the surface of the photoreceptor after transfer, a constant current power source is connected to the brush, and a constant amount of current is applied to the brush. ing. Further, Patent Document 2 is provided with a memory removal brush that removes the toner image remaining on the surface of the photoconductor after transfer, and a current detector that detects the amount of current flowing into the memory removal brush. It is described that the time or frequency for executing the cleaning sequence of the toner adhering to the memory removal brush is changed according to the amount of current flowing into the memory removal brush when it is applied.
JP-A-9-152773 JP 2002-156881 A

  However, as in Patent Document 1, when performing control (constant current control) to apply a constant current amount to the diffusing member, the voltage applied to ensure the application of a constant current amount becomes very large, There has been a problem in that the photosensitive member charged to the opposite polarity to the diffusing member is sunk by reverse charging, and the charging performance of the photosensitive member is lowered.

  On the other hand, as in Patent Document 2, when performing control (constant voltage control) to apply a constant voltage to the diffusing member, there is a problem in that the effective voltage to the photosensitive member decreases and the diffusion efficiency of the diffusing member decreases. It was.

  The present invention has been made in view of such a problem, and provides an image forming apparatus capable of extending the lifetime caused by a problem caused when constant current control or constant voltage control is performed on a diffusion member. For the purpose.

  In order to achieve the above object, an image forming apparatus according to claim 1 is an image forming apparatus provided with a diffusing member for diffusing toner remaining on the surface of a photoconductor after transfer. A constant voltage applying means for applying a voltage; a constant current applying means for applying a constant current to the diffusing member; and a detecting means for detecting a value capable of estimating a diffusion efficiency of the diffusing member, wherein the detecting means comprises When the detected value detected reaches a specified value, the means for applying to the diffusing member is changed from the constant voltage applying means to the constant current applying means.

  The image forming apparatus according to claim 2, wherein the detection unit flows into the diffusion member when the constant voltage application unit applies a constant feedback voltage to the diffusion member. It is characterized in that the amount of current to be detected is detected.

  According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the detecting means detects the number of sheets on which the image forming apparatus has formed an image.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, the detection unit detects a driving time during which the image forming apparatus performs image formation.

  6. The image forming apparatus according to claim 5, wherein the image forming apparatus according to claim 1 is applied to the diffusion member when the image forming apparatus is not performing image formation. It is characterized by changing.

  According to the image forming apparatus of claim 1, when the detection unit detects a value from which the diffusion efficiency of the diffusion member can be estimated, and the detection value detected by the detection unit reaches a specified value, it is applied to the diffusion member. The means is changed from the constant voltage applying means to the constant current applying means. Therefore, when the diffusion efficiency of the diffusion member is high, it can be applied from the constant voltage application means to the diffusion member, and when the diffusion efficiency of the diffusion member is low, it can be applied from the constant current application means to the diffusion member. Become. Therefore, even if the diffusion efficiency of the diffusing member is lowered by applying the voltage from the constant voltage applying unit to the diffusing member when the diffusion efficiency of the diffusing member is high, there is no problem. Further, by applying a constant current from the constant current applying means to the diffusing member, even if the diffusion efficiency of the diffusing member is low, a constant current flows into the diffusing member. Sufficient diffusion is possible. Further, when the diffusion efficiency of the diffusing member is low, foreign matter such as paper dust and toner adheres to the diffusing member, and the surface of the photosensitive member is lifted up. Even if a high voltage is applied to the diffusing member Since the voltage drops before reaching the surface of the photosensitive member due to the gap generated between the photosensitive member and the surface of the photosensitive member, it is difficult to cause subsidence due to charging, which is not a problem. Therefore, it is possible to extend the life of the diffusing member and thus the image forming apparatus.

  According to the image forming apparatus of the second aspect, the detection unit detects the amount of current flowing into the diffusion member when the constant voltage application unit applies a constant feedback voltage to the diffusion member. When the amount of current flowing into the diffusing member decreases when the constant voltage applying means applies a constant feedback voltage to the diffusing member, the resistance value of the diffusing member increases and the diffusion efficiency decreases. Therefore, the detecting means easily detects a value that can estimate the diffusion efficiency of the diffusing member by detecting the amount of current flowing into the diffusing member when the constant voltage applying means applies a constant feedback voltage to the diffusing member. be able to.

  According to the image forming apparatus of the third aspect, the detection unit detects the number of sheets on which the image forming apparatus has formed an image. When the number of sheets on which image formation has been performed by the image forming apparatus increases, foreign matters such as paper dust and toner adhere to the diffusion member, and the diffusion efficiency decreases. Therefore, the detection means can easily detect a value that can estimate the diffusion efficiency of the diffusion member by detecting the number of sheets on which the image forming apparatus has formed an image.

  According to the image forming apparatus of the fourth aspect, the detecting unit detects a driving time during which the image forming apparatus performs image formation. When the drive time during which the image forming apparatus performs image formation increases, foreign matters such as paper dust and toner adhere to the diffusion member, and the diffusion efficiency decreases. For this reason, the detection unit can easily detect a value by which the diffusion efficiency of the diffusion member can be estimated by detecting the drive time during which the image forming apparatus performs image formation.

  According to the image forming apparatus of the fifth aspect, the means applied to the diffusing member is changed when the image forming apparatus is not performing image formation. Therefore, when the image forming apparatus is performing image formation, the means for applying to the diffusing member is not changed, so that image formation can be performed satisfactorily.

  Hereinafter, an MFP (Multiple Functional Peripheral) 100 equipped with an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. As shown in the schematic diagram of the internal configuration in FIG. 1 with the upper portion omitted, the MFP 100 is based on image information read by a scanner arranged in an upper portion (not shown) or image information received by a facsimile apparatus. An image forming unit 101 that forms an image on a sheet is disposed. Further, the MFP 100 is provided with a paper feeding unit 102 that sequentially supplies paper to the bottom thereof, and the paper is conveyed from the paper feeding unit 102 to the image forming unit 101 through the conveyance path 103, and the image forming unit 101 performs image and image processing. Characters and the like are recorded on the paper and discharged to the paper discharge tray 104.

  The paper feed unit 102 includes a box-shaped paper feed cassette 102a capable of storing various sizes of paper so that it can be pulled out to the bottom of the MFP 100, and can be loaded with paper as needed. A guide 102b for holding a predetermined size of paper at the paper feed position is provided in the paper feed cassette 102a, and one end side of the uppermost paper of the plurality of papers held in a stacked state is set as the paper feed position. It is designed to be positioned at all times. A pickup roller 102c is provided at the paper feed position, and the uppermost sheet positioned at the paper feed position by the guide 102b is fed out by the pickup roller 102c. The fed paper is nipped by a pair of paper feed rollers 102 d and fed to the conveyance path 103.

  The image forming unit 101 includes a photosensitive drum 10 as a photosensitive member, a charging brush 11 disposed around the photosensitive drum 10, an LED printer head 12, a developing device 13, a transfer roller 14, and a diffusion brush as a diffusion member. (Memory removal brush) 15 and a fixing device 16 disposed in the conveyance path 103 on the downstream side of the photosensitive drum 10.

  The photoconductive drum 10 has a cylindrical shape, and a photoconductive film made of an organic photoconductor is formed on the outer peripheral surface thereof. The photoconductive drum 10 is rotated about its own axis at a predetermined speed by a motor (not shown). The charging brush 11 is a so-called contact-type charging device, and the surface of the rotating photosensitive drum 10 is uniformly charged by bringing the tip of the brush into contact with the surface of the photosensitive drum 10 with a charging voltage applied. Act on. Note that other charging devices such as a non-contact charging method and a contact-type roller charging method may be employed.

  The LED printer head 12 is a so-called self-luminous printer head in which LED arrays are arranged in parallel for the number of recording pixels, and light emitted from the LED array is imaged on the surface of the photosensitive drum 10 by a Selfoc lens array. The exposure device selectively exposes the surface of the photosensitive drum 10 based on image information to the photosensitive drum 10 to form an electrostatic latent image on the surface. Note that an exposure device of a scanning optical system using a semiconductor laser may be adopted.

  The developing device 13 is a developing device including a supply roller 13a, a developing roller 13b, and a regulating blade 13c. Due to the difference in bias voltage applied to the supply roller 13a and the developing roller 13b, the toner in the toner container is supplied to the developing roller 13b through the supply roller 13a. The toner layer formed on the surface of the developing roller 13b is made uniform by pressing a regulating blade 13c to which a predetermined bias voltage is applied. In this way, the developing roller 13b having a uniform toner layer formed on the surface is rotated at a position close to the photosensitive drum 10, and the toner on the developing roller 13b is caused by a potential difference from the electrostatic latent image on the photosensitive drum 10. Moves to the photosensitive drum 10, and a toner image is formed on the surface of the photosensitive drum 10 based on the electrostatic latent image.

  Further, the developing roller 13b serves as a developing unit and also serves as a so-called cleaning unit. That is, the developing roller 13b serves as a developing unit when performing the first rotation after the photosensitive drum 10 starts rotating during image formation, and when the photosensitive drum 10 performs the second rotation. In this case, the toner remaining on the surface of the photosensitive drum 10 without being completely transferred to the paper and acting on the surface of the photosensitive drum 10 by the action of the diffusion brush 15 is removed. As described above, the developing roller 13b serves as both a developing unit and a cleaning unit, and the MFP 100 is configured as a cleanerless system.

  The transfer roller 14 includes a shaft and a foam using a carbon conductive material or an ionic conductive material, and is disposed so as to be in pressure contact with the surface of the photosensitive drum 10 at a position opposite to the conveyance path 103. When the transfer bias voltage is applied, the transfer roller 14 is charged. When the sheet is fed into the nip portion between the photosensitive drum 10 and the transfer roller 14, the sheet is sandwiched between the photosensitive drum 10 and the transfer roller 14, that is, the sheet is transferred to the outer peripheral surface of the photosensitive drum 10. It is made to adhere by. As a result, the toner image on the photosensitive drum 10 is transferred to the sheet.

  The diffusion brush 15 is a cleaning device that is provided in contact with the surface of the photoconductive drum 10 and plays a role of lifting the toner remaining without being transferred onto the paper from the surface of the photoconductive drum 10. The toner floating from the surface of the photosensitive drum 10 by the diffusion brush 15 is removed by the developing roller 13b.

  The fixing device 16 heats and presses and fixes the paper on which the toner image has been transferred by a heating roller 16a and a pressure roller 16b, which are arranged at positions opposed to the conveyance path 103, respectively. It is a fixing device for fixing on paper. The surface of the heating roller 16a is heated by a heater disposed therein, and a pressure roller 16b is pressed against the heating roller 16a with a predetermined pressure. The sheet on which the toner image is transferred is nipped between the heating roller 16a and the pressure roller 16b, so that the toner on the sheet is melted and fixed. An image or the like is recorded on a sheet by the image forming unit 101 configured as described above.

  A sheet is conveyed from the sheet cassette 102 along the conveyance path 103 to the image forming unit 101, and the sheet on which the image is recorded is conveyed to the paper discharge tray 104. The conveyance path 103 is one end of the sheet cassette 102a. After extending from the side and extending upward, it is curved in a substantially horizontal direction to reach the image forming unit 101, and further extended in a substantially horizontal direction, and then communicated with the paper discharge tray 104. The conveyance path 103 is appropriately provided with a pair of conveyance rollers 103 a in the middle thereof, and the sheet is nipped between the conveyance rollers 103 a and conveyed along the conveyance path 103.

  As shown in the block diagram of FIG. 2, the MFP 100 includes an MPU (Microprocessing Unit) 20, an NCU (Network Control Unit) 21, a modem 22, a ROM (Read Only Memory) 23, a RAM (Random Access Memory) 24, an image memory. 25, a CODEC (Coder and Decoder) 26, an operation unit 27, a scanner 28, a printer interface 29, and a printer controller 30. The units 20 to 30 are communicably connected via a bus.

  The MPU 20 controls the operation of each unit of the MFP 100. The NCU 21 is a line network control device that controls a telephone line to make or cut a call, and is connected to a PSTN (Public Switched Telephone Network) (not shown). The modem 22 is an ITU-T (International Telecommunication Union Telecommunication Standardization Sector) recommendation V.3. The transmission data is modulated and the received data is demodulated according to the 34 standard or a similar standard.

  The ROM 23 stores various programs for the MPU 20 to control the operation of each unit of the MFP 100. The RAM 24 stores various data such as processing setting information and operation information used for processing operations of the MFP 100 in a readable and writable state. The image memory 25 stores image information such as image information read by the scanner 28 and image information received by facsimile. The CODEC 26 encodes (encodes) and decodes (decodes) image information.

  The operation unit 27 includes a start key for instructing start of image reading of a document, image formation such as copying, and transmission, a numeric keypad for inputting the number of copies and a transmission destination number, and a cursor for inputting various settings. Various operation keys such as keys and button keys are provided. The operation unit 27 receives an input of an operation for instructing to start copying a document and sends a print signal to the printer controller 30.

  The scanner 28 reads an image of a document and performs image processing on the image information of the document obtained by reading. Specifically, although not shown in detail, the scanner 28 reads an image of a document by a CCD (Charge Coupled Device) disposed on a scanning carriage equipped with a light source, a reflection mirror, and the like. When the CCD reads an image of an original as an FBS (Flat Bed Scanner), it scans the original placed on the platen glass while the scanning carriage moves horizontally from a predetermined position to read the image of the original. When reading an image of a document conveyed by an ADF (Automatic Document Feeder), the CCD waits at a predetermined position and reads an image of the document passing through the reading position. Then, image processing is performed on the image information of the original obtained by reading by the CCD. Specifically, image processing such as shading correction and γ correction is performed as necessary.

  The printer interface 29 receives print signals and image information from an external computer or the like (PC) and sends them to the printer controller 30.

  Based on the image information received by the facsimile, the image information obtained by reading by the scanner 28, and the image information received via the printer interface 29, the printer controller 30 is configured to form an image on a sheet by a print signal. 101 is controlled.

  The MFP 100 is provided in a mechanism controlled by the printer controller 30, as schematically shown in FIG. A printer controller 30 that controls the overall operation of the image forming unit 101 applies a charging voltage to the charging brush 11, applies a developing voltage to the developing roller 13 b, and applies predetermined voltages to the supply roller 13 a and the regulating blade 13 c. A control signal is transmitted to the developing device voltage application circuit 32 that applies the voltage of 1 and the transfer voltage circuit 33 that applies the transfer voltage to the transfer roller 14 to perform voltage control.

  The printer controller 30 transmits a control signal to the switching circuit 34 to perform switching control for connecting either the constant voltage application circuit 35 or the constant current application circuit 36 to the diffusion brush 15. The constant voltage application circuit 35 applies a constant diffusion voltage, for example, 300 V to the diffusion brush 15, and the constant current application circuit 36 applies a constant diffusion current, for example, 3 μA to the diffusion brush 15. A current detection unit 37 as detection means is connected to the diffusion brush 15, and when a diffusion voltage or a diffusion current is applied to the diffusion brush 15 from the constant voltage application circuit 35 or the constant current application circuit 36, the diffusion brush 15 is applied. Detect the inflowing current value. The current value detected by the current detection unit 37 is transmitted to the printer controller 30 as a detection signal.

  Further, the printer controller 30 performs exposure control of the LED printer head 12 based on the image information. A paper passage sensor 37 is provided on the upstream side of the photosensitive drum 10 and transmits a detection signal to the printer controller 30 while detecting the passage of paper. The printer controller 30 rotates the photosensitive drum 10, the supply roller 13a, the developing roller 13b, the transfer roller 14, the heating roller 16a, and the pressure roller 16b via a driving mechanism including a motor and a clutch (not shown). Control. Further, the printer controller 30 controls the rotation of the pickup roller 102c, the paper supply roller 102d, and the transport roller 103a of the paper supply unit 102 via a drive mechanism including a motor and a clutch (not shown).

  Hereinafter, an example of the processing operation of each unit relating to image formation in MFP 100 according to the present embodiment will be described mainly based on the flowchart shown in FIG.

  First, it is determined whether the printer controller 30 has received a print signal (S1). The printer controller 30 receives the print signal when the print signal is transmitted from the operation unit 27 or the printer interface 29 or when image information is received by facsimile.

  If the printer controller 30 determines that a print signal has been received (S1: YES), it starts drive control as a preparation for image formation (S2). First, the printer controller 30 rotates the photosensitive drum 10, the supply roller 13a, the developing roller 13b, the transfer roller 14, the heating roller 16a, and the pressure roller 16b via the driving mechanism. At the same time, the printer controller 30 transmits a control signal to the charging voltage application circuit 31, the developing device voltage application circuit 32, and the transfer voltage application circuit 33 to apply a voltage necessary for preparation for image formation. Start each one.

  Further, the printer controller 30 transmits a control signal to the switching circuit 34, connects the constant voltage circuit 35 and the diffusion brush 15, and applies a constant diffusion voltage to the diffusion brush 15 (S21). Then, the current detection unit 37 detects the amount of current flowing into the diffusion brush 15 (S22), and transmits a detection signal indicating the detected current value to the printer controller 30. Then, the printer controller 30 determines whether or not the current value detected by the current detector 37 is a predetermined value, for example, 3 μA or more, by the current circuit comparison circuit 39 provided therein (S23). . When the current value detected by the current detection unit 37 is less than the specified value (S23: NO), the printer controller 30 transmits a control signal to the switching circuit 34 to connect the constant current circuit 36 and the diffusion brush 15. .

  Thereafter, the printer controller 30 starts drive control for image formation (S3). First, the printer controller 30 rotates the pickup roller 102c, the paper feed roller 102d, and the transport roller 103a to start transporting the paper. When the paper passage sensor 38 detects that the leading edge of the paper has passed a predetermined position on the upstream side of the photosensitive drum 10, the paper passage sensor 38 transmits a detection signal indicating that fact to the printer controller 30. Upon receiving this detection signal, the printer controller 30 controls each mechanism so as to perform image formation. At this time, when the current value detected by the current detection unit 37 is equal to or greater than the specified value (S23: YES), a constant diffusion voltage is applied from the constant voltage circuit 35 to the diffusion brush 15. On the other hand, when the current value detected by the current detection unit 37 is less than the specified value (S23: NO), a constant diffusion current is applied from the constant current circuit 36 to the diffusion brush 15.

  After the image formation is completed, the printer controller 30 ends the drive control for image formation (S4), and the MPF 100 returns to the standby state.

  As described above, according to the MFP 100, the current detection unit 37 detects the amount of current flowing into the diffusion brush 15 when a certain diffusion voltage is applied to the diffusion brush 15, and the detected current amount is equal to or less than a specified value. If so, the means for applying to the diffusion brush 15 is changed from the constant voltage application circuit 35 to the constant current application circuit 36, that is, the diffusion brush 15 is changed from constant voltage control to constant current control. When the amount of current flowing into the diffusion brush 15 decreases when a certain diffusion voltage is applied to the diffusion brush 15, the resistance value of the diffusion brush 15 increases and the diffusion efficiency decreases. Therefore, when the diffusion efficiency of the diffusion brush 15 is high, it is applied from the constant voltage application circuit 35 to the diffusion brush 15, and when the diffusion efficiency of the diffusion brush 15 is low, the constant current application circuit 36 applies to the diffusion brush 15. It becomes possible to apply. Therefore, even when the diffusion efficiency of the diffusion brush 15 is reduced by applying the voltage from the constant voltage application circuit 35 to the diffusion brush 15 when the diffusion efficiency of the diffusion brush 15 is high, there is no problem. Further, by applying the constant current application circuit 36 to the diffusion brush 15, even if the diffusion efficiency of the diffusion brush 15 is low, a constant diffusion current flows into the diffusion brush 15. The toner remaining on the surface of the drum 10 can be sufficiently diffused. Further, when the diffusion efficiency of the diffusion brush 15 is low, foreign matter such as paper dust or toner adheres to the diffusion brush 15, and the surface of the photosensitive drum 10 is lifted, and a high voltage is applied to the diffusion brush 15. Even when a voltage is applied, the voltage drops before reaching the surface of the photoconductive drum 10 due to the gap formed between the photoconductive brush 15 and the submergence due to charging is less likely to occur, which does not cause a problem. Accordingly, it is possible to extend the life of the diffusion brush 15 and thus the MFP 100.

  Note that the configuration of MFP 100 described in this embodiment is merely one aspect of the image forming apparatus according to the present invention, and various modifications can be made without departing from the scope of the present invention. For example, the current detection unit 37 detects the amount of current flowing into the diffusion brush 15 when a certain diffusion voltage is applied to the diffusion brush 15, and the diffusion brush 15 depends on whether or not the detected current amount is a specified value or less. As an example, the case where the means for applying voltage to the constant voltage application circuit 35 is changed from the constant voltage application circuit 35 to the constant current application circuit 36 has been described. However, the present invention is not limited to this as long as a value that can estimate the diffusion efficiency of the diffusion brush 15 is detected and changed depending on whether or not the detected value reaches a specified value.

  For example, the printer controller 30 includes a cumulative number counter that detects the number of sheets on which the MFP 100 has formed an image, and the number counted by the cumulative number counter is a predetermined number, for example, a predetermined number of thousands to tens of thousands. When the number exceeds the number, the means for applying to the diffusion brush 15 may be changed from the constant voltage application circuit 35 to the constant current application circuit 36. In this case, as shown in the flowchart shown in FIG. 5, when the printer controller 30 determines that the print signal has been received (S1: YES), in drive control as preparation for image formation (S100), It is determined whether or not the number of sheets on which MFP 100 has formed an image is less than a predetermined specified number by using a cumulative number counter provided inside (S101). If the number counted by the cumulative number counter is equal to or greater than the specified number (S101: NO), the printer controller 30 transmits a control signal to the switching circuit 34 to connect the constant current circuit 36 and the diffusion brush 15 (see FIG. S102). Thereby, in the drive control for image formation (S3), when the number of sheets counted by the cumulative sheet counter is less than the specified number (S101: YES), the constant voltage circuit 35 applies a constant amount to the diffusion brush 15. The diffusion voltage is applied. On the other hand, when the number counted by the cumulative number counter is equal to or greater than the specified number (S101: NO), a constant current is applied from the constant current circuit 36 to the diffusion brush 15. When the number of sheets on which the MFP 100 has formed an image increases, foreign matter such as paper dust and toner adheres to the diffusion member, and the diffusion efficiency decreases. Therefore, when the diffusion efficiency of the diffusion brush is high, it is applied from the constant voltage application circuit 35 to the diffusion brush 15, and when the diffusion efficiency of the diffusion brush 15 is low, it is applied from the constant current application circuit 36 to the diffusion brush 15. It becomes possible to do. Accordingly, it is possible to extend the life of the diffusion brush 15 and thus the MFP 100.

  Further, the printer controller 30 includes an accumulated drive time counter that detects the drive time when the MFP 100 performs image formation. The drive time counted by the accumulated drive time counter is a specified drive time, for example, several hours to several hundred hours. The means for applying to the diffusion brush 15 may be changed from the constant voltage application circuit 35 to the constant current application circuit 36 when a predetermined time between the two is exceeded. In this case, as shown in the flowchart of FIG. 6, when the printer controller 30 determines that the print signal has been received (S1: YES), in drive control as preparation for image formation (S110), It is determined whether or not the driving time in which the MFP 100 has formed an image is less than a predetermined driving time determined in advance using an accumulated driving time counter provided inside (S111). When the driving time counted by the cumulative driving time counter is equal to or longer than the prescribed driving time (S111: NO), the printer controller 30 transmits a control signal to the switching circuit 34, and the constant current circuit 36 and the diffusion brush 15 are connected. Connect (S102). As a result, in the drive control for image formation (S3), if the drive time counted by the cumulative drive time counter is less than the specified drive time (S111: YES), diffusion from the constant voltage circuit 35 is performed. A constant diffusion voltage is applied to the brush 15. On the other hand, when the drive time counted by the cumulative drive time counter is equal to or longer than the specified drive time (S111: NO), a constant constant current is applied from the constant current circuit 36 to the diffusion brush 15. When the paper driving time during which the MFP 100 performs image formation increases, foreign matters such as paper dust and toner adhere to the diffusion member, and the diffusion efficiency decreases. Therefore, when the diffusion efficiency of the diffusion brush is high, it is applied from the constant voltage application circuit 35 to the diffusion brush 15, and when the diffusion efficiency of the diffusion brush 15 is low, it is applied from the constant current application circuit 36 to the diffusion brush 15. It becomes possible to do. Accordingly, it is possible to extend the life of the diffusion brush 15 and thus the MFP 100.

  Furthermore, the constant voltage application circuit 35 and the constant current application circuit 36 have been described by taking as an example the case of applying a constant diffusion voltage and diffusion current, respectively. However, the present invention is not limited to applying a constant value. For example, based on the current value detected by the current detection unit 37, the value of the constant diffusion voltage or constant diffusion current applied by the printer controller 30 by the constant voltage application circuit 35 or the constant current application circuit 36 may be set.

  Furthermore, in the present embodiment, the aspect in which the image forming apparatus is implemented as MFP 100 has been described. However, the image forming apparatus is not limited to this, and can be applied to a printer, a facsimile, a copying machine, and any of these multifunction devices. is there. Further, the image formed on the paper may be a monochrome image or a color image. In particular, in the case of a tandem machine that forms color images, the charging brushes arranged around the respective photosensitive drums are simultaneously controlled in the same manner, thereby extending the life of each charging brush and thus the image forming unit of each color. Is possible.

FIG. 3 is a schematic diagram showing an internal configuration in which an upper part of MFP 100 according to the embodiment of the present invention is omitted. 2 is a block diagram showing an electrical configuration of MFP 100. FIG. 2 is a schematic diagram showing a mechanism controlled by a printer controller 30. FIG. 5 is a flowchart showing processing operations of MFP 100. 10 is a flowchart showing another processing operation of MFP 100. 10 is a flowchart showing another processing operation of MFP 100.

Explanation of symbols

10 Photosensitive drum (photosensitive member)
15 Diffusion brush (Diffusion member)
30 Printer Controller 34 Switching Circuit 35 Constant Voltage Application Circuit 36 Constant Current Application Circuit 37 Current Detection Unit (Detection Means)
39 Current Value Comparison Circuit 100 MFP (Image Forming Apparatus)
101 Image forming unit

Claims (5)

An image forming apparatus including a diffusion member that diffuses toner remaining on the surface of a photoreceptor after transfer,
Constant voltage applying means for applying a constant voltage to the diffusion member;
Constant current applying means for applying a constant current to the diffusion member;
Detecting means for detecting a value from which the diffusion efficiency of the diffusion member can be estimated, and
An image forming apparatus characterized in that, when the detection value detected by the detection means reaches a specified value, the means for applying to the diffusing member is changed from the constant voltage applying means to the constant current applying means.   The image forming apparatus according to claim 1, wherein the detection unit detects the number of sheets on which the image forming apparatus has formed an image.   The image forming apparatus according to claim 1, wherein the detection unit detects an amount of current flowing into the diffusion member when the constant voltage application unit applies a constant feedback voltage to the diffusion member.   The image forming apparatus according to claim 1, wherein the detection unit detects a driving time during which the image forming apparatus performs image formation.   5. The image forming apparatus according to claim 1, wherein when the image forming apparatus is not performing image formation, the means applied to the diffusing member is changed. 6.

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