JP2017083754A - Applied voltage control device, image forming apparatus, applied voltage control method, and applied voltage control program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus of a two-component AC development system comprising an applied voltage control device that has improved the quality of an image to be formed.SOLUTION: There is provided an applied voltage device for controlling an AC voltage to be applied to develop an electrostatic latent image, wherein a main control part acquires the state of deterioration of a developer for developing the electrostatic latent image, determines a duty that is a ratio of time to apply the maximum voltage value in one cycle of the AC voltage according to the acquired state of deterioration, and controls the AC voltage to achieve the determined duty.SELECTED DRAWING: Figure 14

Description

  The present invention relates to an applied voltage control device, an image forming apparatus, an applied voltage control method, and an applied voltage control program.

  2. Description of the Related Art In recent years, image forming apparatuses such as printers used for outputting computerized information, facsimiles, and copying machines used for document copying have become indispensable devices. Among such image forming apparatuses, an image forming apparatus using an electrophotographic method is known.

  Among such electrophotographic image forming apparatuses, a two-component developer composed of toner and carrier is used, and a DC (Direct Current) voltage, which is a direct current voltage, is used as a developing bias when developing an electrostatic latent image. On the other hand, there is an image forming apparatus of a two-component AC developing system that uses an AC (Alternating Current) voltage that is an alternating voltage.

  In such a two-component AC developing type image forming apparatus, when an electrostatic latent image is developed, toner is transferred from the carrier to the photosensitive drum when the AC voltage, which is an alternating current component of the developing bias, is a minimum voltage value. A portion of the toner that has moved and once adhered to the photosensitive drum at the maximum voltage value is drawn back to the carrier.

  In such an image forming apparatus of the two-component AC developing system, there is a problem that the quality of the formed image is lowered when the carrier is deteriorated.

  Therefore, in order to solve such a problem, the potential difference (hereinafter referred to as “Vpp”) between the maximum voltage value and the minimum voltage value of the AC voltage, which is the AC component of the developing bias, is changed in accordance with carrier deterioration. An image forming apparatus that performs control is proposed and already known (see, for example, Patent Document 1).

  However, in the image forming apparatus described in Patent Document 1, when Vpp is lowered in accordance with the deterioration of the carrier, the force for moving the toner between the photosensitive drum and the carrier is reduced, and the toner is transferred to the carrier. It will be biased toward either the adhesion to the side or the adhesion to the photosensitive drum side. Therefore, the image forming apparatus described in Patent Document 1 has a problem in that the quality of the formed image is deteriorated.

  The present invention has been made in view of the above circumstances, and an object thereof is to improve the quality of an image formed in an image forming apparatus of a two-component AC developing system.

  In order to solve the above-described problem, an applied voltage control device that controls an alternating voltage applied to develop an electrostatic latent image, and acquires a deterioration state of a developer for developing the electrostatic latent image A deterioration state acquisition unit that performs, a duty determination unit that determines a duty that is a ratio of application time of the maximum voltage value in one cycle of the AC voltage, according to the acquired deterioration state, and the determined duty And an applied voltage control unit for controlling the AC voltage.

  According to the present invention, the quality of an image to be formed can be improved in an image forming apparatus of a two-component AC developing system.

1 is a block diagram schematically illustrating a hardware configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram schematically illustrating a functional configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a cross-sectional view from the main scanning direction of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a cross-sectional view from the main scanning direction of the image forming unit attached to the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a perspective view from above of an image forming unit attached to the image forming apparatus according to the embodiment of the present invention. 1 is a cross-sectional view from the main scanning direction of an image forming apparatus according to an embodiment of the present invention. FIG. 6 is a diagram illustrating a change with time of a developing bias applied to a developing roller by the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a diagram illustrating a toner movement locus in the vicinity of a developing nip when a low-frequency AC voltage is applied as a developing bias. FIG. 7 is a diagram illustrating a toner movement locus in the vicinity of a developing nip when a high-frequency AC voltage is applied as a developing bias. FIG. 7 is a diagram illustrating a toner movement locus in the vicinity of a developing region when only a DC voltage is applied as a developing bias. It is a figure which shows the distance between the developing roller in a reciprocating terminal position, and a photoconductive drum. FIG. 6 is a diagram illustrating a toner movement locus in the vicinity of a developing nip when an AC voltage is applied as a developing bias. FIG. 6 is a diagram illustrating a toner movement locus in the vicinity of a developing nip when an AC voltage is applied as a developing bias. 6 is a flowchart for explaining processing when the image forming apparatus according to the embodiment of the present invention optimizes the developing bias condition in accordance with carrier deterioration. 6 is a flowchart for explaining processing when the image forming apparatus according to the embodiment of the present invention optimizes the developing bias condition in accordance with carrier deterioration. 6 is a flowchart for explaining processing when the image forming apparatus according to the embodiment of the present invention optimizes the developing bias condition in accordance with carrier deterioration.

Embodiment 1 FIG.
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this embodiment, a two-component developer composed of a toner and a carrier is used, and an AC voltage that is an AC voltage with respect to a DC (Direct Current) voltage that is a DC voltage is used as a developing bias when developing an electrostatic latent image. (Alternating Current) An image forming apparatus of a two-component AC developing system using a superimposed voltage will be described as an example.

  First, a hardware configuration of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG. FIG. 1 is a block diagram schematically illustrating a hardware configuration of the image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 includes an engine for realizing a printer, a scanner, and a facsimile in addition to the hardware configuration shown in FIG.

  As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment includes a configuration similar to that of a general server, a PC (Personal Computer), or the like. That is, the image forming apparatus 1 according to the present embodiment includes a CPU (Central Processing Unit) 10, a RAM (Random Access Memory) 20, a ROM (Read Only Memory) 30, an HDD (Hard Disk Drive) 40, and an I / F 50. 90 is connected. In addition, a display unit 60, an operation unit 70, and a dedicated device 80 are connected to the I / F 50.

  The CPU 10 is a calculation unit and controls the operation of the entire image forming apparatus 1. The RAM 20 is a volatile storage medium capable of reading and writing information at high speed, and is used as a work area when the CPU 10 processes information. The ROM 30 is a read-only nonvolatile storage medium and stores a program such as firmware. The HDD 40 is a non-volatile storage medium capable of reading and writing information, and stores an OS (Operating System), various control programs such as an applied voltage control program, application programs, and the like.

  The I / F 50 connects and controls the bus 90 and various hardware and networks. The display unit 60 is a visual user interface for the user to check the state of the image forming apparatus 1 and is realized by a display device such as an LCD (Liquid Crystal Display). The operation unit 70 is a user interface such as a keyboard and a mouse for the user to input information to the image forming apparatus 1. The dedicated device 80 is hardware for realizing a dedicated function in the printer, scanner, and facsimile.

  In such a hardware configuration, a program stored in a storage medium such as the ROM 30, the HDD 40, or an optical disk (not shown) is read into the RAM 20, and the CPU 10 performs an operation according to the program loaded into the RAM 20, whereby the software control unit Is configured. A functional block that realizes the functions of the image forming apparatus 1 according to the present embodiment is configured by a combination of the software control unit configured as described above and hardware.

  Next, the functional configuration of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG. FIG. 2 is a block diagram schematically illustrating a functional configuration of the image forming apparatus 1 according to the present embodiment. In FIG. 2, the electrical connection is indicated by solid arrows, and the flow of the transfer paper or document bundle is indicated by broken arrows.

  As shown in FIG. 2, the image forming apparatus 1 according to the present embodiment includes a controller 100, a paper feed table 200, a print engine 300, a print paper discharge tray 400, an ADF (Auto Document Feeder) 500, It has a scanner engine 600, a scanning discharge tray 700, a display panel 800, and a network I / F 900. The controller 100 includes a main control unit 110, an engine control unit 120, an image processing unit 130, an operation display control unit 140, an input / output control unit 150, and a storage unit 160.

  The paper feed table 200 feeds transfer paper to the print engine 300 that is an image forming unit. The print engine 300 is an image forming unit that draws an image by executing an image forming output on the transfer paper conveyed from the paper feed table 200. A specific aspect of the print engine 300 according to the present embodiment is an electrophotographic image forming mechanism. The image-formed transfer sheet on which an image is drawn by the print engine 300 is discharged to the print discharge tray 400. The print engine 300 is realized by the dedicated device 80 shown in FIG.

  The ADF 500 automatically conveys a document to a scanner engine 600 that is a document reading unit. The scanner engine 600 is a document reading unit including a photoelectric conversion element that converts optical information into an electrical signal, and optically scans a document automatically conveyed by the ADF 500 or a document set on a platen glass (not shown). This is a document reading unit that reads and generates image information. A document automatically conveyed by the ADF 500 and read by the scanner engine 600 is discharged to a scanning discharge tray 700. The ADF 500 and the scanner engine 600 are realized by the dedicated device 80 shown in FIG.

  The display panel 800 is an output interface that visually displays the state of the image forming apparatus 1 and is an input when the user directly operates the image forming apparatus 1 or inputs information to the image forming apparatus 1 as a touch panel. It is also an interface. That is, the display panel 800 includes a function for displaying an image for receiving an operation by the user. The display panel 800 is realized by the display unit 60 and the operation unit 70 illustrated in FIG.

  A network I / F 900 is an interface through which the image forming apparatus 1 communicates with other devices such as an administrator terminal and a PC (Personal Computer) via the network, and is an Ethernet (registered trademark) or a USB (Universal Serial Bus). ) Interface, Bluetooth (registered trademark), Wi-Fi (Wireless Fidelity) (registered trademark), FeliCa (registered trademark), and other interfaces are used. As described above, the image forming apparatus 1 according to the present embodiment receives image data for a print request and various control commands such as a print request from a terminal connected via the network I / F 900. The network I / F 900 is realized by the I / F 50 shown in FIG.

  The controller 100 is configured by a combination of software and hardware. Specifically, a software control unit and an integrated circuit configured by loading a control program such as firmware stored in a non-volatile storage medium such as the ROM 30 or the HDD 40 into the RAM 20 and performing an operation by the CPU 10 according to the program. The controller 100 is configured by hardware such as the above. The controller 100 functions as a control unit that controls the entire image forming apparatus 1. Therefore, in this embodiment, the controller 100 functions as an applied voltage control device.

  The main control unit 110 plays a role of controlling each unit included in the controller 100, and gives a command to each unit of the controller 100. Further, the main control unit 110 controls the input / output control unit 150 and accesses other devices via the network I / F 900 and the network. The engine control unit 120 controls or drives driving units such as the print engine 300 and the scanner engine 600.

  The image processing unit 130 outputs drawing information based on image information described by PDL (Page Description Language), for example, document data or image data included in an input print job, under the control of the main control unit 110. Generate as information. This drawing information is information such as CMYK bitmap data, and is information for drawing an image to be formed in the image forming operation by the print engine 300 as an image forming unit.

  Further, the image processing unit 130 processes image data input from the scanner engine 600 and generates image data. The image data is information stored in the image forming apparatus 1 as a result of the scanner operation or transmitted to another device via the network I / F 900 and the network. Note that the image forming apparatus 1 according to the present embodiment can directly input drawing information instead of image information, and can execute image forming output based on the directly input drawing information.

  The operation display control unit 140 displays information on the display panel 800 or notifies the main control unit 110 of information input via the display panel 800. The input / output control unit 150 inputs signals and commands input via the network I / F 900 and the network to the main control unit 110.

  The storage unit 160 stores the usage status of the image forming apparatus 1 such as the accumulated number of printed sheets (hereinafter referred to as “accumulated number of printed sheets”) and the history of the image area ratio. The image area ratio is calculated by the main control unit 110 and stored independently for each color image forming unit.

  The accumulated number of printed sheets is counted by the main control unit 110 and stored independently for each color image forming unit. The accumulated number of prints is reset to zero when the image forming unit is replaced. If not, the accumulated number of printed sheets at the time of replacing the image forming unit is separately stored, and the job is executed after the image forming unit is replaced. Is obtained by subtracting the separately stored cumulative number of printed sheets from the updated number of printed sheets.

  In addition, the storage unit 160 stores table A, table B, and table C. Table A is a table in which the accumulated number of printed sheets and the developer resistance value are associated with each other, and is a table for obtaining the developer resistance value from the accumulated number of printed sheets. Here, the developer resistance value is a developer deposition resistivity or the like.

  Table B is a table in which the cumulative number of printed sheets and the pumping amount are associated with each other, and is a table for obtaining the pumping amount from the cumulative number of printed sheets. The table C is a table in which the developer resistance value, the pumping amount, and the developing bias duty are associated with each other, and is a table for obtaining the optimum developing bias duty from the developer resistance value and the pumping amount.

  Tables A and B are prepared in advance by experimentally measuring the developer resistance value and the pumping amount for each cumulative number of printed sheets. Table C is a system in which the pumping amount is fixed and an image forming output is executed with a different duty for each developer resistance value, and an experiment in which the duty having the best image quality is set to the optimum duty is changed. It is created in advance by performing.

  In this embodiment, an example of using Table A, Table B, and Table C to associate the cumulative number of printed sheets and developer resistance, the cumulative number of printed sheets and pumping amount, and the cumulative developer resistance value and pumping amount and Duty, respectively. However, they may be configured to be associated with each other using mathematical formulas. Alternatively, the table A, the table B, and the table C may be combined into one so that the duty can be obtained directly from the cumulative number of printed sheets.

  Next, a detailed configuration of the print engine 300 according to the present embodiment will be described with reference to FIGS. FIG. 3 is a cross-sectional view from the main scanning direction of the image forming apparatus 1 according to the present embodiment. FIG. 4 is a cross-sectional view from the main scanning direction of the image forming unit 320 attached to the image forming apparatus 1 according to the present embodiment. FIG. 5 is a transparent view from above of the image forming unit 320 attached to the image forming apparatus 1 according to the present embodiment.

  As shown in FIG. 3, the image forming apparatus 1 according to the present embodiment forms an image on the transfer paper 2 fed from the paper feed table 200 by the print engine 300, and then places the image on the print paper discharge tray 400. It has a configuration for discharging paper.

  As shown in FIG. 3, the print engine 300 according to the present embodiment includes a configuration in which the image forming units 320 of the respective colors are arranged along the endless conveying unit 310, and is referred to as a so-called tandem type. Is. That is, the print engine 300 according to this embodiment includes a plurality of image forming units in order from the upstream side in the transport direction of the transport belt 311 along the transport belt 311 spanned between the driving roller 312 and the driven roller 313. The C plate image forming unit 320C, the M plate image forming unit 320M, the Y plate image forming unit 320Y, and the K plate image forming unit 320K are arranged.

  The plurality of image forming units 320C, 320M, 320Y, and 320K have the same internal configuration except that the color of the toner image to be formed is different. The C plate image forming unit 320C forms a cyan image, the M plate image forming unit 320M forms a magenta image, the Y plate image forming unit 320Y forms a yellow image, and the K plate image forming unit 320K forms a black image. . In the following description, the C plate image forming unit 320C will be described in detail, but the other image forming units 320M, 320Y, and 320K are the same as the C plate image forming unit 320C, and therefore other image forming units. The constituent elements of 320M, 320Y, and 320K are replaced with C attached to the respective constituent elements of the C-plate image forming unit 320C, and only the symbols distinguished by M, Y, and K are displayed in the figure, and the description thereof is omitted. To do.

  The conveying belt 311 is made of a heat-resistant material such as polyimide or polyamide, and is an endless belt, ie, an endless belt, which is stretched between a driving roller 312 and a driven roller 313 that are rotationally driven. This is an intermediate transfer belt on which an intermediate transfer image is formed by the unit, the C plate image forming unit 320C, the M plate image forming unit 320M, the Y plate image forming unit 320Y, and the K plate image forming unit 320K. The drive roller 312 is driven to rotate by a drive motor (not shown), and the drive motor, the drive roller 312 and the driven roller 313 move the conveyor belt 311.

  The C-plate image forming unit 320 </ b> C forms a cyan intermediate transfer image on the transport belt 311. As shown in FIGS. 4 and 5, the C plate image forming unit 320C includes a photosensitive drum 321C as a photosensitive member, a charging unit 322C disposed around the photosensitive drum 321C, a developing unit 323C, and a static eliminator. 324C, a toner recovery unit 325C, a lubricant application unit 326C, and a lubricant uniformizing blade 327C. The C plate image forming unit 320C may be configured independently. However, the charging unit 322C, the developing unit 323C, the charge eliminator 324C, the toner collecting unit 325C, the lubricant applying unit 326C, and the lubricant uniformizing blade. At least one of 327 </ b> C and the photosensitive drum 321 </ b> C may be configured integrally, and may be configured as a process cartridge that is detachable from the image forming apparatus 1. 4 and 5 are diagrams in which the image forming unit 320 of each plate in FIG. 3 is cut out.

  The C-plate image forming unit 320C configured as described above applies a lubricant onto the surface of the photosensitive drum 321C by a lubricant application unit 326C prior to image formation, and applies the applied lubricant to a lubricant uniformizing blade. It is averaged and fixed on the surface of the photosensitive drum 321C by 327C so as to have a uniform thickness.

  As described above, the reason for applying the lubricant on the surface of the photosensitive drum 321C prior to image formation is to reduce the coefficient of friction between the surface of the photosensitive drum 321C and the mechanism portion in contact therewith, The wear of the contact portion between the photosensitive drum 321C and the mechanism portion is reduced, the efficiency when the toner recovery unit 325C recovers the toner remaining on the surface of the photosensitive drum 321C, or the image carrier is improved. This is to prevent the generation of frictional noise between the surface of the cleaning blade and the edge portion of the cleaning blade.

  In addition, the reason for applying the lubricant on the surface of the photosensitive drum 321C prior to image formation is that the charging unit 322C protects the surface from the current when the surface of the photosensitive drum 321C is charged. This is to prevent a problem that the surface of the photosensitive drum 321C is consumed due to the charging current at that time.

  The lubricant applied on the surface of the photosensitive drum 321C deteriorates and wears over time or with the driving of the photosensitive drum 321C. By applying from 326C, the effect of lubricant application can be continuously obtained.

  As shown in FIG. 4, the lubricant application unit 326C according to this embodiment is disposed on the downstream side of the toner recovery unit 325 in the rotational direction of the photosensitive drum 321C, and is disposed on the upstream side of the developing unit 323C. Has been. As shown in FIG. 4, the lubricant application unit 326C according to this embodiment includes a solid lubricant 326a, a lubricant application roller 326b, and a solid lubricant pressing spring 326c.

  The lubricant application roller 326b is disposed at a position facing the photoconductor drum 321C, and rotates while contacting the photoconductor drum 321C and the solid lubricant 326a to scrape off the solid lubricant 326a, and the scraped lubricant is removed from the photoconductor. Apply to drum 321. The solid lubricant pressing spring 326c is a compression spring that generates a pressing force for pressing the solid lubricant 326a against the lubricant application roller 326b.

  When the lubricant is applied onto the surface of the photosensitive drum 321C as described above, the C plate image forming unit 320C forms a cyan intermediate transfer image on the conveyor belt 311 during image formation. That is, the C-plate image forming unit 320C first charges the surface of the photosensitive drum 321C uniformly by the charging unit 322C in the dark when forming an image. Then, the C plate image forming unit 320C performs electrostatic writing by irradiating the uniformly charged photosensitive drum 321C with light corresponding to the cyan image from the optical writing device 330C, and the surface of the photosensitive drum 321C. Then, an electrostatic latent image corresponding to the cyan image is formed.

  As shown in FIG. 4, the charging unit 322C according to this embodiment includes a charging roller 322a and a charging roller cleaner 322b. When the charging roller 322a is applied with a charging bias and approaches the surface of the photosensitive drum 321C, the charging roller 322a uniformly charges the surface of the photosensitive drum 321C by the action of the applied charging bias.

  The charging roller cleaner 322b contacts the charging roller 322a to remove dirt on the surface of the charging roller 322a. As described above, as a reason for removing the dirt on the surface of the charging roller 322a, when the surface of the charging roller 322a is dirty, the charging ability of the part to which the dirt is attached is reduced, and the photosensitive drum 321C is charged to a target potential. This is to prevent the occurrence of abnormal images due to poor charging.

  When the electrostatic latent image corresponding to the cyan image is formed on the surface of the photosensitive drum 321C as described above, the C plate image forming unit 320C causes the developing unit 323C to convert the electrostatic latent image with cyan toner. By making the image visible, a cyan toner image is formed on the surface of the photosensitive drum 321C.

  As shown in FIGS. 4 and 5, the developing unit 323C according to this embodiment includes a first developer conveying screw 323a, a second developer conveying screw 323b, and a developing roller 323c. The developing roller 323c is disposed at a position facing the photoconductive drum 321C, and plays a role as a toner carrying body that carries toner to adhere to the photoconductive drum 321C by generating an electric field therein. At this time, the developing roller 323c generates an electric field so that the magnetic force reaches the magnetic flux densities in the five normal directions P1 to P5 indicated by broken lines in FIG.

  The first developer conveying screw 323a and the second developer conveying screw 323b are disposed below the developing roller 323c, and rotate in directions opposite to each other, whereby a toner supply mechanism (not shown) from the toner bottle 350C. The cyan toner supplied in step 1 is conveyed so as to spread over the entire main scanning direction (screw rotation direction) while being stirred together with the carrier. At this time, the toner and carrier conveyed to the end of the developing unit 323C by the first developer conveying screw 323a are transferred to the other second developer conveying screw 323b, and the second developer conveying screw 323b. The toner and carrier conveyed to the other end of the developing unit 323C by the above are transferred to the other first developer conveying screw 323a so as to circulate in the developing unit 323C throughout the main scanning direction. Be transported.

  The developer conveyed by the second developer conveying screw 323b is pumped and adhered to the surface by the electric field generated inside the developing roller 323c, and is conveyed along with the rotation of the developing roller 323c. After being regulated to a predetermined layer thickness, the sheet is conveyed to a facing area facing the photosensitive drum 321C, that is, an area for developing an electrostatic latent image (hereinafter referred to as “developing area”).

  In this way, the toner in the developer that has been transported to the developing area is applied to the surface of the photosensitive drum 321C in the developing area by the action of the developing bias generated between the developing roller 323c and the photosensitive drum 321C. It electrostatically moves to an electrostatic latent image corresponding to the formed cyan image and adheres to the surface of the photosensitive drum 321C. In this way, the developing unit 323C forms a cyan toner image on the surface of the photosensitive drum 321C by visualizing the electrostatic latent image with cyan toner. That is, in the present embodiment, the photosensitive drum 321 functions as an image carrier.

  The C-plate image forming unit 320C urges the primary transfer roller 340C with the toner image at a position where the photosensitive drum 321C and the conveying belt 311 are in contact with or closest to each other (hereinafter referred to as “previous transfer position”). The material is transferred onto the conveyor belt 311 by being pressed against the photosensitive drum 321C.

  By this transfer, an image of cyan toner, that is, a cyan intermediate transfer image is formed on the conveyance belt 311. At this time, a transfer bias is applied to the primary transfer roller 340C, and a transfer electric field is formed between the photosensitive drum 321C and the primary transfer roller 340C at the preceding transfer position by the transfer bias. As a result, the toner image is transferred from the photosensitive drum 321C to the conveying belt 311.

  When the C plate image forming unit 320C finishes forming the cyan intermediate transfer image on the conveyance belt 311, the toner collecting unit 325C causes the toner remaining on the surface of the photosensitive drum 321C (hereinafter referred to as “residual toner”) to be generated. After the collection, the surface of the photosensitive drum 321C is discharged by the charge eliminator 324C, and preparation for the next image formation, for example, supply of cyan toner from the toner bottle 350C to the developing unit 323C by a toner supply mechanism (not shown), etc. And wait. The toner bottle 350 </ b> C is configured to be removable from the image forming apparatus 1 by opening a printing paper discharge tray 400 formed on the upper part of the image forming apparatus 1. It should be noted that the replenishment of toner from the toner bottle 350C to the developing unit 323C is performed as needed at a predetermined timing, not immediately after the image forming operation.

  As shown in FIG. 4, the toner recovery unit 325C according to this embodiment includes a cleaning blade 325a, a recovery toner transport screw 325b, and a recovery toner transport path 325c.

  The cleaning blade 325a is configured such that an edge portion made of an elastic material such as urethane rubber is pressed against the surface of the cleaning blade 325a from the direction facing the rotation direction of the photosensitive drum 321C. The toner remaining on the surface of the toner is scraped off, and the scraped toner is collected in the collected toner conveyance path 325c.

  The collected toner conveying screw 325b conveys the toner collected in the collected toner conveying path 325c (hereinafter referred to as “collected toner”) along the collected toner conveying path 325c. The collected toner transported in this manner is transported toward a waste toner storage container (not shown) that is a container for storing the discarded toner and discarded, or transported toward the developing unit 323C. Reused.

  As described above, the cyan toner image transferred onto the conveying belt 311 by the C-plate image forming unit 320C, that is, the cyan intermediate transfer image, is conveyed by the driving belt, the driving roller 312 and the driven roller 313. By moving 311, the image is conveyed to the next M-plate image forming unit 320 </ b> M. The M plate image forming unit 320M forms a magenta toner image on the photosensitive drum 321M by a process similar to the image forming process in the C plate image forming unit 320C, and the magenta toner image is formed on the cyan toner image already formed. The image is transferred onto the conveyance belt 311 so as to be superimposed on the intermediate transfer image. By this transfer, an image of magenta toner, that is, a magenta intermediate transfer image is formed on the conveyance belt 311. In this way, an intermediate transfer image of cyan and magenta is formed on the conveyance belt 311.

  The cyan and magenta intermediate transfer images formed on the conveying belt 311 are further sequentially conveyed to the next image forming unit, Y plate image forming unit 320Y, and K plate image forming unit 320K, and the photosensitive drum is similarly operated. The yellow toner image formed on 321Y and the black toner image formed on the photosensitive drum 321K are superimposed on the intermediate transfer image already formed and transferred onto the conveying belt 311. By this transfer, an image with yellow toner and an image with black toner, that is, an intermediate transfer image of yellow and black are formed on the conveyance belt 311. Thus, a full-color intermediate transfer image is formed on the conveyance belt 311.

  When a full-color intermediate transfer image is formed on the transport belt 311 in this way, the transfer paper 2 stored in the paper feed table 200 is separated by the paper feed roller 210 and the separation roller pair 220 in order from the top. The paper is fed and sent toward the registration roller pair 230. Then, after the skew of the transfer sheet 2 is corrected by the registration roller pair 230, the position at which the transfer sheet 2 and the transfer belt 311 contact on the transfer path in accordance with the transfer timing of the transfer belt 311 by the registration roller pair 230. Alternatively, the sheet is conveyed to the closest position (hereinafter referred to as “second-stage transfer position”).

  The transfer sheet 2 transported in this manner is a full color formed on the transport belt 311 by the secondary transfer roller 360 being pressed against the driven roller 313 by a biasing member (not shown) at the subsequent transfer position. The intermediate transfer image is transferred. As a result, an image is formed on the surface of the transfer paper 2. The transfer paper 2 on which the image is formed on the paper surface is further conveyed, and is sandwiched from the direction perpendicular to the image formation surface by the fixing unit 370 and is heated and pressed to fix the image, and then discharged. The paper is discharged to the print paper discharge tray 400 by the paper roller pair 410.

  Note that the fixing unit 370 according to the present embodiment includes a pair of fixing rollers 371 for rotating the transfer paper 2 while pressing the transfer paper 2 from a direction perpendicular to the image forming surface to convey and pressurize the transfer paper 2. Further, a heating element is provided on the fixing surface of the fixing roller pair 371, and the fixing unit 370 according to the present embodiment heats the transfer paper 2 by the fixing roller pair 371. As described above, the fixing unit 370 according to the present embodiment is configured to fix the image by heating and pressing the transfer paper 2 by sandwiching the transfer paper 2 from the direction perpendicular to the image forming surface by the fixing roller pair 371.

  The belt cleaner 380 scrapes off toner adhering to the surface of the conveyor belt 311 by the cleaning blade 325a pressed against the conveyor belt 311 at the downstream side of the post-transfer position and upstream of the C-plate image forming unit 320C. Then, the conveyor belt 311 is cleaned.

  As described above, in this embodiment, printing is performed by the endless conveyance unit 310, the image forming unit 320, the optical writing device 330, the primary transfer roller 340, the toner bottle 350, the secondary transfer roller 360, the fixing unit 370, and the belt cleaner 380. An engine 300 is configured.

  As shown in FIG. 3, in this embodiment, an intermediate transfer image is formed on the conveyance belt 311 and the intermediate transfer image is transferred onto a transfer sheet, that is, an indirect transfer type image forming apparatus. However, the present invention can also be applied to a method in which an image is directly formed on a transfer sheet, that is, an image forming apparatus of a direct transfer method as shown in FIG.

  As described with reference to FIGS. 3 to 5, the image forming apparatus 1 according to the present embodiment first forms an electrostatic latent image by charging the surface of the photosensitive drum 321 when forming an image. Development is performed by adhering a toner, which is a charged developer, along the electrostatic latent image. As a result, the image forming apparatus 1 according to the present embodiment forms a toner image that is a developer image on the surface of the photosensitive drum 321. Then, the image forming apparatus according to the present embodiment is attached by transferring the toner image formed on the surface of the photosensitive drum 321 onto the transfer paper and pressurizing the transfer paper on which the toner image is transferred while heating. The toner is fixed on the transfer paper to form an image.

  Further, as described with reference to FIGS. 3 to 5, the image forming apparatus 1 according to the present embodiment rotates while carrying toner on the surface by electrostatic attraction due to the magnetic force generated inside. A developing roller 323c that transports toner to a region facing the photosensitive drum, that is, a region (development region) for developing the electrostatic latent image is provided.

  In addition, when developing the electrostatic latent image, the image forming apparatus 1 according to the present embodiment first transports the toner to the developing region by rotating the developing roller 323c with the toner carried on the surface. At the same time, a developing bias is applied to the developing roller 323c in the developing region. The image forming apparatus 1 according to the present embodiment causes the toner to be detached from the surface of the developing roller 323c and rotate the separated toner when the developing bias exceeds the electrostatic attractive force between the toner and the surface of the developing roller 323c. Electrostatically moving toward the electrostatic latent image formed on the surface of the photosensitive drum 321. In this manner, the image forming apparatus 1 according to the present embodiment develops an electrostatic latent image.

  At this time, the image forming apparatus 1 according to the present embodiment uses an AC (Alternating Current) voltage (rectangular wave, sawtooth wave, etc.) that is an AC voltage with respect to a DC (Direct Current) voltage that is a DC voltage as a developing bias. The electrostatic latent image is developed by AC development (AC development) applied to the developing roller 323c in a superimposed manner.

  Here, the principle of AC development when the image forming apparatus 1 according to the present embodiment develops the electrostatic latent image formed on the photosensitive drum 321 will be described with reference to FIG. FIG. 7 is a diagram illustrating a change with time of the developing bias applied to the developing roller 323c by the image forming apparatus 1 according to the present embodiment.

At this time, the image forming apparatus 1 according to this embodiment, the potential difference between the maximum voltage and minimum voltage values of the AC voltage (hereinafter referred to as "Vpp") are formed so that P _a -P _b volts (V) The AC voltage and DC voltage having the maximum voltage value P _a V and the minimum voltage value P _b V are applied to the developing roller 323c as a developing bias.

Further, at this time, the image forming apparatus 1 according to the present embodiment has an AC frequency of 1 / A kHz so that the maximum voltage value (P _a V) and the minimum voltage value (P _b V) are repeated in an Ams cycle. The voltage is applied to the developing roller 323c as a developing bias. Ratio of application time of the maximum voltage value _(P a V) in the AC voltage one period of time (hereinafter referred to as "Duty"), when the maximum voltage value application time _(P a V) and BMS, B / Calculated by A, it is α% in FIG. Therefore, in FIG. 7, the average voltage V _{ave for} AC development is (α / 100) · P _a + (1−α / 100) · P _b (V). This average voltage is the DC voltage (component) of the developing bias in AC development, and the absolute value of the difference between this average voltage and the potential of the exposed portion of the photosensitive drum 321 is the developing potential described later.

When the electrostatic latent image is developed as the developing bias of such AC development, in the image forming apparatus 1 according to the present embodiment, the developing roller 323c is used when the developing bias is the minimum voltage value (P _b V). From the toner to the photosensitive drum 321, on the other hand, when the developing bias is at the maximum voltage value (P _a V), part of the toner once adhered to the photosensitive drum 321 is pulled back to the developing roller 323 c.

  As described above, in the image forming apparatus 1 according to the present embodiment, the electrostatic latent image is developed when the developing bias has the minimum voltage value. On the other hand, when the developing bias has the maximum voltage value, the photosensitive drum 321 is discharged from the carrier. A part of the toner that has moved once is returned to the carrier. Hereinafter, the minimum voltage value in the developing bias is referred to as “bias during development”, and the maximum voltage value is referred to as “bias during pullback”.

  Note that the image forming apparatus 1 according to the present embodiment is configured to use a low-frequency AC voltage, for example, an AC voltage of about 1 kHz, as the developing bias. Thus, when a low frequency AC voltage is used as the developing bias, the toner reciprocates between the photosensitive drum 321 and the carrier as described above. The state at this time is shown in FIG. FIG. 8 is a diagram showing a toner movement locus in the vicinity of the developing nip when a low-frequency AC voltage is applied as the developing bias. Here, the development nip is a range in which the electric field of the development bias acts on the toner.

  However, when only a high-frequency AC voltage or DC voltage is used as the developing bias, the toner once moved from the carrier to the photosensitive drum 321 remains on the photosensitive drum 321 and does not return to the carrier side. The situation at this time is shown in FIGS. FIG. 9 is a diagram illustrating a toner movement locus in the vicinity of the development nip when a high-frequency AC voltage is applied as the development bias. FIG. 10 is a diagram illustrating a toner movement locus in the vicinity of the developing region when only the DC voltage is applied as the developing bias.

  Incidentally, the amount of toner that moves from the carrier to the photosensitive drum 321, that is, the amount of toner attached to the photosensitive drum 321 (hereinafter referred to as “development amount”) is determined by the electric field acting on the toner. Therefore, the development amount becomes maximum at the closest portion between the developing roller 323c and the photosensitive drum 321 where the electric field is the strongest.

  When only a high frequency AC voltage or DC voltage is used as the developing bias, the toner once moved from the carrier to the photosensitive drum 321 remains on the photosensitive drum 321 as shown in FIGS. The development amount becomes the final development amount at the closest portion.

  Incidentally, the distance between the surface of the developing roller 323c and the surface of the photosensitive drum 321 in the developing region (hereinafter referred to as “development gap”) is usually determined by the eccentricity of the developing roller 323c and the photosensitive drum 321. And it fluctuates periodically with the rotation of the photosensitive drum 321. When the development gap fluctuates in this way, the electric field acting on the toner by the development bias becomes stronger when the development gap is small, and weaker when the development gap is large.

  Therefore, when only a high-frequency AC voltage or DC voltage is used as the development bias, when the development gap is small, the final development amount increases, and the density of the image corresponding to the portion increases, while the development gap is large. In some cases, the final development amount decreases and the density of the image corresponding to that portion becomes lighter. As a result, when only a high-frequency AC voltage or DC voltage is used as the developing bias, in an image forming apparatus in which the developing gap fluctuates, periodic image density unevenness occurs due to the fluctuation of the developing gap. There is a problem such as.

  On the other hand, when the low-frequency AC voltage is used as the developing bias as in the image forming apparatus 1 according to the present embodiment, the toner moved from the carrier to the photosensitive drum 321 returns to the carrier side again. Therefore, when the low-frequency AC voltage is used as the developing bias as in the image forming apparatus 1 according to the present embodiment, the final developing amount is not the closest portion between the developing roller 323c and the photosensitive drum 321. This is the developing amount at the position where the reciprocating motion of the toner ends (hereinafter referred to as “reciprocating motion end position”).

  Incidentally, the distance between the developing roller 323c and the photosensitive drum 321 at the end position of the reciprocating motion is constant regardless of the developing gap. The state at this time is shown in FIG. FIG. 11 is a diagram showing the distance between the developing roller 323c and the photosensitive drum 321 at the reciprocating end position.

  Therefore, when a low-frequency AC voltage is used as the developing bias, if the strength of the electric field acting on the toner is the same, that is, if the developing bias applied to the developing roller 323c is the same, the reciprocating motion end position is The development amount is constant regardless of the development gap.

  Accordingly, when an AC voltage having a low frequency is used as the developing bias as in the image forming apparatus 1 according to the present embodiment, even if the developing gap varies with the rotation of the developing roller 323c and the photosensitive drum 321, the image density is changed. Unevenness can be reduced.

  However, in order to reduce such image density unevenness, a low-frequency AC voltage may be used as the developing bias. However, as shown in FIG. 8, the range in which the toner reciprocates is near the center of the developing nip. Thus, the developing bias conditions must be optimized.

  For example, if the time for applying the bias at the time of pulling back is too short, that is, the duty is too small, or the bias at the time of pulling back is too weak, the toner once moved to the photosensitive drum 321 in the developing nip is moved to the carrier side. The image cannot be returned, and the effect of reducing the image density unevenness cannot be obtained. The state at this time is shown in FIG. FIG. 12 is a diagram illustrating a toner movement locus in the vicinity of the developing nip when an AC voltage is applied as the developing bias.

  For example, if the time for applying the bias at the time of pulling back is too long, that is, the duty is too large, or the bias at the time of pulling back is too strong, the toner continues to reciprocate until the end of the developing nip. Then, toner that should originally adhere to the photosensitive drum 321 due to the bias at the time of development passes through the development nip while remaining on the carrier side, and therefore, toner peeling traces due to the bias at the time of pullback are on the photosensitive drum 321. The toner image remains and becomes a blurred image. The state at this time is shown in FIG. FIG. 13 is a diagram illustrating a toner movement locus in the vicinity of the developing nip when an AC voltage is applied as the developing bias.

  As described above, in order to reduce the unevenness of the image density and suppress the blur of the image, it is necessary to optimize the developing bias condition so that the range in which the toner reciprocates is near the center of the developing nip.

  However, the optimum conditions for the development bias change as the carrier deteriorates. For example, when the surface coat layer of the carrier is scraped and the developer resistance value is reduced, it is necessary to reduce the bias and duty at the time of pulling back in order to optimize the condition of the developing bias. In addition, for example, when a spent on which a toner-derived component adheres to the carrier surface and the developer resistance value increases, it is necessary to increase the bias and Duty at the time of pulling back in order to optimize the developing bias condition. is there.

  Further, for example, when the flowability of the developer changes due to the deterioration of the carrier, the amount of developer flowing into the development area, that is, the developer conveyed to the development area by the development roller 323c on the surface of the development roller 323c. The weight per unit area (hereinafter referred to as “pumping amount”) varies. When the pumping amount rises, it is necessary to reduce the bias and duty at the time of pulling back in order to optimize the developing bias condition. When the pumping amount decreases, the developing bias condition is optimized. It is necessary to increase the bias and duty at the time of pulling back.

  However, if Vpp is decreased in order to change the bias at the time of pulling back for the purpose of optimizing the developing bias conditions accompanying the deterioration of the carrier, the toner is pulled back from the photosensitive drum 321 to the carrier side by the bias at the time of pulling back. Therefore, the magnitude of the force is close to the magnitude of the adhesion force of the toner to the photosensitive drum 321.

  Then, the change in the area ratio of the printed image, that is, the change in toner consumption, the change in temperature and humidity, the change in the adhesion amount of the toner due to the change in the charge amount of the toner, and the like. The range of reciprocating movement between the drum 321 and the carrier is likely to change. As a result, the development amount becomes unstable, the difference in image density between pages deteriorates, or the image is blurred due to uneven adhesion of toner to the photosensitive drum 321, resulting in image quality. Decreases.

  Further, if Vpp is increased in order to change the bias at the time of pulling back for the purpose of optimizing the developing bias condition as the carrier deteriorates, electric discharge is likely to occur between the photosensitive drum 321 and the carrier. As a result, discharge marks are generated on the toner image on the photosensitive drum 321 and the image quality is deteriorated.

  In view of this, the image forming apparatus 1 according to the present embodiment is set to Vpp at which no discharge is generated between the photosensitive drum 321 and the carrier in order to optimize the condition of the developing bias accompanying the deterioration of the carrier, and then pulled back. The time for applying the time bias, that is, the duty is changed. With this configuration, the image forming apparatus 1 according to the present embodiment can prevent a decrease in image quality even when the carrier deteriorates.

  The image forming apparatus 1 according to the present embodiment is configured to estimate the carrier deterioration state based on the cumulative number of printed sheets.

  Next, processing when the image forming apparatus 1 according to the present embodiment optimizes the developing bias condition with carrier deterioration will be described with reference to FIG. FIG. 14 is a flowchart for explaining processing when the image forming apparatus 1 according to the present embodiment optimizes the developing bias condition as the carrier deteriorates. Note that the processing shown in FIG. 14 is performed before the image forming apparatus 1 starts image formation. This is to prevent the occurrence of a difference in image density between pages caused by changing the duty during image formation.

  As shown in FIG. 14, when the image forming apparatus 1 according to the present embodiment optimizes the developing bias condition as the carrier deteriorates, the main control unit 110 first stores the table A, the table A from the storage unit 160. B and Table C are read (S1401), and the cumulative number of printed sheets is read (S1402).

  As described above, the table A is a table in which the cumulative number of printed sheets is associated with the developer resistance value, and is a table for obtaining the developer resistance value from the cumulative number of printed sheets. Here, the developer resistance value is a developer deposition resistivity or the like.

  The table B is a table in which the cumulative number of printed sheets and the pumping amount are associated with each other, and is a table for obtaining the pumping amount from the cumulative number of printed sheets. The table C is a table in which the developer resistance value, the pumping amount, and the developing bias duty are associated with each other, and is a table for obtaining the optimum developing bias duty from the developer resistance value and the pumping amount. .

  Then, the main control unit 110 obtains a developer resistance value from the cumulative number of printed sheets and the table A (S1403), obtains a pumping amount from the cumulative number of printed sheets and the table B (S1404), and determines the developer resistance value and the pumping amount. The optimum duty is obtained from the table C (S1405). That is, in the present embodiment, the main control unit 110 functions as a deterioration state acquisition unit and a duty determination unit.

  Then, the main control unit 110 changes the development bias Dtuy to the optimum duty determined in S1405 (S1406). Then, the engine control unit 120 starts image formation by controlling the development bias so that the duty of the development bias becomes the duty changed in S1406 (S1407). That is, in the present embodiment, the engine control unit 120 functions as an applied voltage control unit.

  As described above, the image forming apparatus 1 according to the present embodiment is set to Vpp at which no discharge is generated between the photosensitive drum 321 and the carrier in order to optimize the developing bias condition as the carrier deteriorates. In addition, the time for applying the bias at the time of pulling back, that is, the duty is changed. With this configuration, the image forming apparatus 1 according to the present embodiment can prevent a decrease in image quality even when the carrier deteriorates.

  Note that the image forming apparatus 1 according to the present embodiment is configured to estimate the deterioration state of the carrier based on the cumulative number of printed sheets. In addition, for example, between the developing roller 323c and the doctor blade. Since the current that flows when voltage is applied and the pressure applied to the doctor blade change due to carrier deterioration, the deterioration state of the carrier may be estimated by measuring this.

  However, the configuration that counts the cumulative number of printed sheets is a configuration that is provided in an electrophotographic image forming apparatus for recording the durability of consumables and determining the replacement time. If they are estimated based on the above, they can be used mutually and no additional cost is required.

  In addition, the image forming apparatus 1 according to the present embodiment is configured to estimate the deterioration state of the carrier based on the cumulative number of printed sheets. However, the cumulative driving distance of the driving unit related to the developer transport is as follows. Further, it may be configured to estimate based on a cumulative driving amount such as a cumulative driving time and a cumulative driving number. Even if the image forming apparatus 1 according to the present embodiment is configured as described above, an existing configuration can be used, and no additional cost is required.

Embodiment 2. FIG.
In the first embodiment, the image forming apparatus 1 configured to estimate the carrier deterioration state based on the cumulative number of printed sheets has been described. On the other hand, in the present embodiment, an image forming apparatus 1 configured to estimate the carrier deterioration state based on the history of the image area ratio will be described.

  Carrier degradation includes a scraping mode in which the surface coat layer of the carrier is scraped, and a spent mode in which a spent with toner-derived components adhering to the surface of the carrier is generated. There are differences in gender changes. The developer resistance value decreases in the scraping mode and increases in the spent mode. Further, the fluidity of the developer is deteriorated in either mode, but is worse in the spent mode.

  Further, when the scraping mode is entered after the spent mode, the spent material is peeled off from the carrier, and the fluidity of the developer is increased. When the amount of toner supplied to the developer is large, a large amount of external additives and fine powders released from the toner adhere to the carrier. Therefore, since the image area ratio history is used to determine which mode is likely to be inclined, the cumulative number of printed sheets is used by calculating the developer resistance value and the pumping amount using the image area ratio history. Duty can be optimized with higher accuracy.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, about the structure which attaches | subjects the code | symbol similar to Embodiment 1, it shall show the same or an equivalent part, and abbreviate | omits detailed description.

  First, a process when the image forming apparatus 1 according to the present embodiment optimizes the developing bias condition as the carrier deteriorates will be described with reference to FIG. FIG. 15 is a flowchart for explaining processing when the image forming apparatus 1 according to the present embodiment optimizes the condition of the developing bias as the carrier deteriorates. The process shown in FIG. 15 is performed by the image forming apparatus 1 before the start of image formation, as in the process of FIG. This is to prevent the occurrence of a difference in image density between pages caused by changing the duty during image formation.

  When the image forming apparatus 1 according to the present embodiment optimizes the developing bias condition as the carrier deteriorates, first, the main control unit 110 reads the image area ratio and the cumulative number of printed sheets from the storage unit 160 (S1501). ).

  Then, the main control unit 110 uses a calculation formula to calculate the scraping speed, which is the speed at which the surface coat layer of the carrier is scraped from the image area ratio, and the spent speed, which is the speed at which the spent on which the toner-derived components adhere to the carrier surface (S1502).

  Then, the main control unit 110 multiplies the scraping speed and the spent speed respectively by the cumulative number of printed sheets, and the scraping amount, which is the total amount of scraping of the carrier surface coat layer, and the spent where the toner-derived component adheres to the carrier surface. The spent amount, which is the total amount generated, is calculated using a calculation formula (S1503).

  The main control unit 110 calculates the developer resistance value and the pumping amount from the scraping amount and the spent amount (S1504, S1505), and obtains the optimum duty from the developer resistance value, the pumping amount, and the table C (S1506). ).

  Then, the main control unit 110 changes the development bias Dtuy to the optimum duty obtained in S1506 (S1507). Then, the engine control unit 120 starts image formation by controlling the development bias so that the duty of the development bias becomes the duty changed in S1507 (S1508). Each calculation formula is experimentally obtained in advance.

  As described above, the image forming apparatus 1 according to the present embodiment is configured to estimate the carrier deterioration state based on the history of the image area ratio. Therefore, the image forming apparatus 1 according to the present embodiment can optimize the duty with higher accuracy.

  The image forming apparatus 1 according to the present embodiment has been described with respect to the example in which the history of the image area ratio is stored and the optimum duty is obtained using the history. In addition, every time printing is performed, the image forming apparatus 1 according to the present embodiment updates the current carrier deterioration state, that is, the scraping amount and spent amount, or the developer resistance value and the pumping amount from the image area. You may memorize | store and it may be comprised so that optimal Duty may be calculated | required using it.

  In addition to this, the image forming apparatus 1 according to the present embodiment can more easily obtain the optimum duty, but the accuracy decreases, but the cumulative number of printed sheets and the average image area ratio from the start of use of the developer are reduced. And may be used. In this case, the image forming apparatus 1 according to the present embodiment has an average image area ratio higher than the image area ratio at the time of creating the tables A and B with respect to the developer resistance value and the pumping amount calculated in the first embodiment. A positive correction is applied to the calculated developer resistance value, and a negative correction is applied to the pumping amount. Conversely, if the average image area ratio is low, the reverse correction may be applied.

  In addition, the image forming apparatus 1 according to the present embodiment supplies a toner consumption amount that changes in accordance with the image area ratio, that is, the amount of toner consumed, instead of the image area ratio. The amount of toner supplied to the agent may be used.

Embodiment 3 FIG.
In the first and second embodiments, in order to optimize the developing bias condition in accordance with the deterioration of the carrier, the bias at the time of pulling back is set after setting to Vpp at which no discharge occurs between the photosensitive drum 321 and the carrier. The image forming apparatus 1 configured to change the application time, that is, the duty has been described.

  On the other hand, in the present embodiment, when a lower limit value is set in advance for the duty and the duty is calculated to optimize the developing bias condition as the carrier deteriorates, the duty falls below the lower limit. An image forming apparatus 1 configured to perform correction to lower Vpp after correcting the value to the lower limit will be described.

  As described above, the image forming apparatus 1 according to the present embodiment is easily affected by the change in the toner adhesion force when Vpp is lowered. However, since the duty is preferentially changed up to the lower limit value, the Vpp is changed from the beginning. Compared with the case where the toner is applied, it is less affected by the toner adhesion. Thereby, the image forming apparatus 1 according to the present embodiment can improve the image quality in consideration of the AC power supply performance.

  The image forming apparatus 1 according to the present embodiment sets the correction magnification of Vpp to the square of the reciprocal of the correction magnification of Duty, that is, corrected Vpp = original Vpp × (calculated duty / lower limit value) ^ 2. It is configured. This is to prevent the distance that the toner moves from the photosensitive drum 321 toward the carrier side before and after correction while the bias for pulling is applied.

  Also, the reason why the lower limit is set for the duty is that if the duty is too small, the bias at the time of retraction is switched to the bias at the time of development before the toner is stably returned to the carrier side. This lower limit is a value determined by the response performance of the AC bias power supply.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, about the structure which attaches | subjects the code | symbol similar to Embodiment 1, it shall show the same or an equivalent part, and abbreviate | omits detailed description.

  First, the processing when the image forming apparatus 1 according to the present embodiment optimizes the developing bias condition as the carrier deteriorates will be described with reference to FIG. FIG. 16 is a flowchart for explaining processing when the image forming apparatus 1 according to the present embodiment optimizes the developing bias condition as the carrier deteriorates. Note that the processing shown in FIG. 16 is performed by the image forming apparatus 1 at the start of a job. This is to prevent the occurrence of a difference in image density between pages caused by changing the duty during job execution.

  When the image forming apparatus 1 according to the present embodiment optimizes the developing bias condition as the carrier deteriorates, first, the main control unit 110 performs the same processing as S1401 to S1405 in FIG. 14 (S1601 to S1601). S1605).

  Then, the main control unit 110 determines whether or not the duty calculated in S1605 is greater than or equal to a lower limit value (S1606).

  When determining that the calculated duty is less than the lower limit value in the determination process in S1606 (S1606 / NO), the main control unit 110 changes the development bias Dtuy to the lower limit value (S1607) and sets Vpp to the original value. Change to Vpp × (calculated duty / lower limit) ^ 2 (S1608). Then, the engine control unit 120 starts image formation by controlling the development bias so that the development bias duty becomes the duty changed in S1607 and the development bias Vpp becomes the Vpp changed in S1608 (S1609). .

  On the other hand, if the main control unit 110 determines in the determination processing in S1606 that the calculated duty is equal to or greater than the lower limit (S1606 / YES), the main control unit 110 changes the development bias Dtuy to the duty calculated in S1605 (S1610). The engine control unit 120 starts image formation by controlling the development bias so that the duty of the development bias becomes the duty changed in S1605 (S1609).

  As described above, when the image forming apparatus 1 according to this embodiment sets a lower limit value for the Duty in advance and calculates the Duty to optimize the developing bias condition as the carrier deteriorates, the Duty is calculated. Is set to be lower than the lower limit value, the duty is corrected to the lower limit value and then the correction for lowering Vpp is performed. Thereby, the image forming apparatus 1 according to the present embodiment can improve the image quality in consideration of the AC power supply performance.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Transfer paper 10 CPU
20 RAM
30 ROM
40 HDD
50 I / F
DESCRIPTION OF SYMBOLS 60 Display part 70 Operation part 80 Dedicated device 90 Bus 100 Controller 101 Developing power supply 102 Current detection part 110 Main control part 120 Engine control part 130 Image processing part 140 Operation display control part 150 Input / output control part 160 Storage part 200 Paper feed table 210 Paper feed roller 220 Separating roller pair 230 Registration roller pair 300 Print engine 310 Endless conveying means 311 Conveying belt 312 Driving roller 313 Followed roller 314 First tension roller 315 Second tension roller 320 Image forming unit 321 Photosensitive drum 322 Charging Unit 322a Charging roller 322b Charging roller cleaner 323 Development unit 323a First toner conveying screw 323b Second toner conveying screw 323c Developing roller 324 Electric device 325 Toner recovery unit 325a Cleaning blade 325b Collected toner transport screw 325c Collected toner transport path 325d Cleaning blade position control roller 326 Lubricant coating unit 326a Solid lubricant 326b Lubricant coating roller 326c Solid lubricant pressing spring 327 Lubricant equalizing blade 330 Optical Writing Device 340 Primary Transfer Roller 350 Toner Bottle 360 Secondary Transfer Roller 370 Fixing Unit 371 Fixing Roller Pair 380 Belt Cleaner 400 Print Discharge Tray 410 Discharge Roller Pair 500 ADF
600 Scanner engine 700 Output tray for scanning 800 Display panel 900 Network I / F

JP-A-11-65244

Claims (10)

An applied voltage control device for controlling an alternating voltage applied to develop an electrostatic latent image,
A deterioration state acquisition unit for acquiring a deterioration state of a developer for developing the electrostatic latent image;
A duty determining unit that determines a duty that is a ratio of an application time of a maximum voltage value in one cycle of the alternating voltage according to the acquired deterioration state;
An applied voltage control unit that controls the AC voltage so as to be the determined Duty;
An applied voltage control apparatus comprising:   The applied voltage control apparatus according to claim 1, wherein the deterioration state acquisition unit acquires, as the deterioration state, a cumulative driving amount of a driving unit related to transport of the developer.   The applied voltage control apparatus according to claim 1, wherein the deterioration state acquisition unit acquires an image area ratio as the deterioration state.   The applied voltage control apparatus according to claim 1, wherein the deterioration state acquisition unit acquires a supply amount of toner supplied to the developer as the deterioration state.   5. The applied voltage control apparatus according to claim 1, wherein the deterioration state acquisition unit acquires a developer resistance value of the developer as the deterioration state. 6.   The applied voltage control apparatus according to claim 1, wherein the deterioration state acquisition unit acquires an inflow amount of the developer into a developing region as the deterioration state. The duty determining unit re-determines the duty as the lower limit value when the determined duty is less than a predetermined lower limit value, and is Vpp which is a potential difference between the maximum voltage value and the minimum voltage value of the alternating voltage. Change the value of
The applied voltage control unit according to any one of claims 1 to 6, wherein the applied voltage control unit controls the AC voltage so that the determined Duty and the changed Vpp are obtained. .   An image forming apparatus comprising the applied voltage control device according to claim 1. An applied voltage control method for controlling an alternating voltage applied to develop an electrostatic latent image, comprising:
Obtaining a deterioration state of a developer for developing the electrostatic latent image;
According to the acquired deterioration state, determine the duty which is the ratio of the application time of the maximum voltage value in one cycle of the AC voltage,
The applied voltage control method, wherein the AC voltage is controlled so as to be the determined duty. An applied voltage control program for controlling an alternating voltage applied to develop an electrostatic latent image,
Obtaining a deterioration state of a developer for developing the electrostatic latent image;
Determining a duty, which is a ratio of an application time of a maximum voltage value in one cycle of the alternating voltage, according to the acquired deterioration state;
Controlling the AC voltage to be the determined Duty;
An applied voltage control program characterized by causing