JP2016021043A - Application voltage control apparatus, imaging apparatus, image forming apparatus, and application voltage control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrophotographic image forming apparatus configured to improve quality of an image to be formed.SOLUTION: An application voltage control apparatus operates as follows: deciding a frequency of an AC voltage so that developer having been moved to an electrostatic latent image is returned to a developer carrying section when controlling the AC voltage to be applied for electrostatically moving the developer from the developer carrying section toward the electrostatic latent image, in a facing area where the developer carrying section carrying charged developer faces an image carrying section carrying a developer image formed by developing an electrostatic latent image with developer; deciding a potential difference between the maximum voltage value and the minimum voltage value of the AC voltage, and a ratio between a period of time in which the maximum voltage value is applied and a period of time in which the minimum voltage value is applied, on the basis of the amount of developer in a developer storage section storing the developer to be carried on the developer carrying section, and transferability of the developer to be moved to the electrostatic latent image, respectively; and controlling the AC voltage to be applied so as to satisfy the decided frequency, potential difference, and ratio.SELECTED DRAWING: Figure 16

Description

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

  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.

  When forming an image, an electrophotographic image forming apparatus first forms an electrostatic latent image by charging the surface of a rotating image carrier such as a photosensitive drum, and is charged as a developer. A toner image is formed on the surface of the image carrier by developing the toner by adhering it along the electrostatic latent image. Then, the electrophotographic image forming apparatus is attached by transferring the toner image formed on the surface of the image carrier onto the transfer paper and pressing the transfer paper on which the toner image is transferred while heating. The toner is fixed on the transfer paper to form an image.

  In addition, such an electrophotographic image forming apparatus rotates while carrying toner on the surface by an electrostatic attraction generated by an internal magnetic force, so that an area facing the image carrier, that is, an electrostatic latent image is formed. A developing roller is provided that conveys toner to an area for developing an image (hereinafter referred to as “developing area”).

  In addition, when developing an electrostatic latent image, the electrophotographic image forming apparatus first transports the toner to the developing area by rotating the developing roller with the toner carried on the surface, A developing bias is applied to the developing roller in the developing region. The electrophotographic image forming apparatus has an image carrier that rotates the released toner by releasing the toner from the surface of the developing roller when the developing bias exceeds the electrostatic attractive force between the toner and the surface of the developing roller. It is moved electrostatically toward the electrostatic latent image formed on the surface. Thus, the electrophotographic image forming apparatus develops an electrostatic latent image (see, for example, Patent Document 1 and Patent Document 2).

  Incidentally, the distance between the surface of the developing roller and the surface of the image carrier (hereinafter referred to as “development gap”) in the development region is usually determined by the eccentricity of the developing roller and the image carrier, and the like. It fluctuates periodically with rotation. When the developing gap fluctuates in such an electrophotographic image forming apparatus, the magnetic field due to the developing bias applied to the developing roller becomes strong when the developing gap is small, and weak when the developing gap is large.

  Therefore, in a conventional electrophotographic image forming apparatus, when the development gap is small, the amount of toner that moves to the electrostatic latent image increases, and the density of the image corresponding to the portion increases. On the other hand, when the development gap is large A phenomenon occurs in which the amount of toner that moves to the electrostatic latent image decreases and the density of the image corresponding to that portion becomes lighter. As a result, in such a conventional electrophotographic image forming apparatus, there is a problem that periodic image density unevenness occurs due to fluctuations in the development gap.

  The present invention has been made in consideration of the above circumstances, and an object thereof is to improve the quality of an image formed in an electrophotographic image forming apparatus.

  In order to solve the above problems, a developer carrying unit carrying a charged developer, and an image carrying unit carrying a developer image formed by developing an electrostatic latent image with the developer. Is an applied voltage control device that controls an alternating voltage applied to electrostatically move the developer from the developer carrying portion toward the electrostatic latent image in an opposing region. A frequency determining unit for determining the frequency of the AC voltage so that the developer once moved to the electrostatic latent image is pulled back to the developer-carrying unit, and for carrying the developer on the developer-carrying unit. A maximum voltage value of the AC voltage based on the amount of the developer in the developer accommodating portion that accommodates the developer and the ease of movement of the developer to the electrostatic latent image; The potential difference from the minimum voltage value, the time during which the maximum voltage value is applied, and the minimum voltage A voltage characteristic determining unit that determines a ratio to the time during which the voltage is applied, and an applied voltage control unit that controls the AC voltage applied so that the determined frequency, the potential difference, and the ratio are obtained. It is characterized by that.

  According to the present invention, the quality of an image to be formed can be improved in an electrophotographic image forming apparatus.

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. 6 is a graph showing the toner adhesion amount per unit area of the surface of the photosensitive drum in the vicinity of the development region when a bias at the time of development and at the time of pulling is applied to the development roller in the image forming apparatus according to the embodiment of the present invention. . In an image forming apparatus that develops an electrostatic latent image by DC development according to an embodiment of the present invention, per unit area of the surface of the photosensitive drum near the development region when a DC voltage is applied to the development roller as a development bias. 6 is a graph showing a toner adhesion amount. In an image forming apparatus that develops an electrostatic latent image by AC development according to an embodiment of the present invention, toner per unit area of the surface of the photosensitive drum in the vicinity of the development area when a bias at the time of development is applied to the development roller It is a graph which shows the adhesion amount. In an image forming apparatus that develops an electrostatic latent image by AC development according to an embodiment of the present invention, toner per unit area of the surface of the photosensitive drum in the vicinity of the developing region when a bias at the time of pulling back is applied to the developing roller It is a graph which shows the adhesion amount. 6 is a graph showing the toner adhesion amount per unit area of the surface of the photosensitive drum in the vicinity of the development region when a bias at the time of development is applied to the development roller in the image forming apparatus according to the embodiment of the present invention. 6 is a graph showing a toner adhesion amount per unit area on the surface of a photosensitive drum in the vicinity of a developing region when a bias at the time of pulling is applied to the developing roller in the image forming apparatus according to the embodiment of the present invention. In the case where an electrostatic latent image is developed by each method according to an embodiment of the present invention, the development gap of the toner adhesion amount per unit area on the surface of the photosensitive drum when a bias at the time of development is applied to the development roller It is a graph which shows the change by the fluctuation | variation of. In the case where an electrostatic latent image is developed by the image forming apparatus according to the embodiment of the present invention, the development of the toner adhesion amount per unit area of the surface of the photosensitive drum when the developing bias is applied to the developing roller It is a graph which shows the change by the fluctuation | variation of a gap for every combination of Duty and Vpp. It is a figure which shows an example of the Duty-Vpp determination table which concerns on embodiment of this invention. 5 is a graph showing a change in toner adhesion amount per unit area on the surface of a photosensitive drum due to a developing bias in the image forming apparatus according to the embodiment of the present invention. It is a figure which shows an example of the toner charge amount determination table which concerns on embodiment of this invention. It is a figure which shows an example of the Duty-Vpp determination table which concerns on embodiment of this invention. It is a figure which shows an example of the Duty-Vpp determination table which concerns on embodiment of this invention. FIG. 6 is a cross-sectional view from the main scanning direction of an image forming apparatus according to another embodiment of the present invention. It is a figure which simplifies and shows the structure of the toner adhesion amount measuring sensor which concerns on embodiment of this invention. FIG. 6 is a diagram illustrating a 1-dot horizontal line image and a 1-dot vertical line image formed on a conveyance belt by an image forming apparatus according to another embodiment of the present invention. It is a figure which shows the relationship between 1 dot line aspect ratio and Duty. It is a figure which shows the relationship between the grade of image density nonuniformity, and Duty. It is a block diagram which shows typically the function structure of the image forming apparatus which concerns on other embodiment of this invention.

Embodiment 1 FIG.
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 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 that can read and write information, and stores an OS (Operating System), various control programs, 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, and an input / output control unit 150.

  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.

  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.

  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.

  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. That is, in this embodiment, the lubricant uniformizing blade 327 functions as a lubricant application part.

  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 remove the scraped lubricant. Apply to drum 321. That is, in this embodiment, the solid lubricant 326a is used as a lubricant lump, and the lubricant application roller 326b functions as a lubricant supply unit. 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 photoconductor drum 323C, and generates a magnetic field therein, thereby serving as a toner carrier that carries toner to adhere to the photoconductor drum 321C. At this time, the developing roller 323c generates a magnetic field so that the magnetic force reaches in the range of 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 by is conveyed while being stirred with the carrier so as to spread over the entire main scanning direction. 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 a magnetic 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 by the doctor blade, it is conveyed to a facing area facing the photosensitive drum 323C, that is, an area for developing an electrostatic latent image (hereinafter referred to as “developing area”). That is, in the present embodiment, the developing unit 323 functions as a developer accommodating portion, and the developing roller 323c functions as a developer carrying portion.

  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 this embodiment, the image forming unit 320 functions as an image forming device, and the photosensitive drum 321 functions as an image carrier.

  In this embodiment, an example of a two-component development method will be described, but a one-component development method may be used. In other words, the image forming apparatus 1 according to the present embodiment is not limited to a two-component developer including a toner and a carrier, but is an image forming apparatus that uses a one-component developer including a magnetic toner containing magnetic powder in the toner. May be.

  The C plate image forming unit 320C displays the toner image at a position where the photosensitive drum 321C and the transport belt 311 are in contact with or closest to each other (hereinafter referred to as “previous transfer position”), and the primary transfer roller 340C is not illustrated. By being pressed against the photosensitive drum 321C by the urging member, the image is transferred onto the conveying belt 311.

  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. That is, in the present embodiment, the cleaning blade 325a functions as an unnecessary material removing unit that removes unnecessary materials adhering to the surface of the photosensitive drum 321.

  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 developer that has been formed and charged, 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 superimposes an AC (Alternating Current) voltage, which is an AC voltage, on a DC (Direct Current) voltage, which is a DC voltage, and applies it as a developing bias to the developing roller 323c. The electrostatic latent image is developed by AC development.

  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 having the maximum voltage value P _a V and the minimum voltage value P _b V is 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 of the AC voltage is (α / 100) · P _a + (1−α / 100) · P _b (V).

  When the electrostatic latent image is developed using such an AC voltage as a developing bias, in the image forming apparatus 1 according to the present embodiment, the developing roller 323c to the photosensitive drum 321 when the developing bias is the minimum voltage value. On the other hand, when the developing bias is at the maximum voltage value, a part of the toner once adhered to the photosensitive drum 321 is pulled back to the developing roller 323c.

  As described above, in the image forming apparatus 1 according to the present embodiment, the electrostatic latent image is developed when the development bias is the minimum voltage value, and once attached to the photosensitive drum 321 when the development bias is the maximum voltage value. A part of the toner is pulled back to the developing roller 323c. 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”.

  FIG. 8 shows the toner adhesion amount per unit area on the surface of the photosensitive drum 321 in the vicinity of the development region when the electrostatic latent image is developed in this manner. FIG. 8 shows the toner adhesion amount per unit area on the surface of the photosensitive drum 321 in the vicinity of the developing region when the bias at the time of development and pullback is applied to the developing roller 323c in the image forming apparatus 1 according to the present embodiment. It is a graph which shows.

In FIG. 8, the toner adhesion amount per unit area on the surface of the photosensitive drum 321 during development is indicated by a solid line, and the toner adhesion amount per unit area on the surface of the photosensitive drum 321 during pullback is indicated by a broken line. . In FIG. 8, the horizontal axis represents the distance in the circumferential direction of the photosensitive drum 321 from the closest position between the surface of the photosensitive drum 321 and the surface of the developing roller 323c. In the horizontal axis of FIG. 8, the upstream side in the rotation direction of the photosensitive drum 321, that is, the entrance side to the development area is represented by − (minus), and the downstream side in the rotation direction, that is, the exit side from the development area. Represented by + (plus). Further, FIG. 8 shows the toner adhesion amount (mg / cm ² ) per 1 cm ^{2 on the} surface of the photosensitive drum 321.

  As shown in FIG. 8, in the image forming apparatus 1 according to this embodiment, the toner adhesion amount per unit area on the surface of the photosensitive drum 321 from the entrance side to the development area to the exit side from the development area is It tends to increase. This is because the surface of the photosensitive drum 321 is located on the entrance side to the development area before passing through the development area and on the exit side from the development area after passing through the development area. It is.

  Further, as shown in FIG. 8, in the image forming apparatus 1 according to the present embodiment, the toner adhesion amount per unit area on the surface of the photosensitive drum 321 when the bias at the time of pulling back is applied to the developing roller 323c is It is less than when the bias at the time of development is applied. This is because in the image forming apparatus 1 according to the present embodiment, when a bias at the time of pulling back is applied to the developing roller 323c, a part of the toner once attached to the photosensitive drum 321 is pulled back to the developing roller 323c. .

  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 magnetic field due to the development bias applied to the development roller 323c becomes strong when the development gap is small, and weak when the development gap is large.

  Therefore, in such an image forming apparatus in which the development gap fluctuates, when the development gap is small, the amount of toner that moves to the electrostatic latent image increases, and the density of the image corresponding to the portion increases, whereas the development gap When the value is large, the amount of toner moving to the electrostatic latent image decreases, and the density of the image corresponding to that portion becomes light. As a result, in the image forming apparatus in which the development gap varies as described above, there is a problem that periodic image density unevenness occurs due to the variation in the development gap.

  As shown in FIGS. 9, 10, and 11, the periodic image density unevenness that occurs due to such a change in the development gap is caused by applying only a DC voltage to the developing roller 323c as a developing bias rather than AC developing. DC development that develops an electrostatic latent image by applying the voltage appears more remarkably.

  FIG. 9 illustrates toner per unit area of the surface of the photosensitive drum 321 in the vicinity of the developing region when a DC voltage is applied to the developing roller 323c as a developing bias in an image forming apparatus that develops an electrostatic latent image by DC development. It is a graph which shows the adhesion amount. FIG. 10 shows an image forming apparatus that develops an electrostatic latent image by AC development, and toner adhesion per unit area on the surface of the photosensitive drum 321 in the vicinity of the development area when a bias at the time of development is applied to the development roller 323c. It is a graph which shows quantity. FIG. 11 shows an image forming apparatus that develops an electrostatic latent image by AC development, and toner adhesion per unit area on the surface of the photosensitive drum 321 in the vicinity of the developing region when a bias for pulling back is applied to the developing roller 323c. It is a graph which shows quantity.

9, 10, and 11, the development gap is 0.2 mm is indicated by a solid line, the case of 0.225 mm is indicated by a dotted line, the case of 0.26 mm is indicated by a broken line, and the 0.3 mm The case is indicated by a long broken line. In FIGS. 9, 10 and 11, the horizontal axis represents the distance in the circumferential direction of the photosensitive drum 321 from the closest position between the surface of the photosensitive drum 321 and the surface of the developing roller 323c. Further, in the horizontal axes of FIGS. 9, 10 and 11, the upstream side in the rotation direction of the photosensitive drum 321, that is, the entrance side to the development area is represented by − (minus), and the downstream side in the rotation direction, that is, development. The exit side from the region is represented by + (plus). 9, FIG. 10 and FIG. 11 show the toner adhesion amount (mg / cm ² ) per 1 cm ^{2 on the} surface of the photosensitive drum 321.

  As shown in FIGS. 9, 10, and 11, in an image forming apparatus that develops an electrostatic latent image by DC development, the toner adhesion amount per unit area of the surface of the photosensitive drum 321 near the exit from the development area. Changes due to fluctuations in the development gap are larger than in AC development. On the other hand, as shown in FIGS. 9, 10, and 11, in an image forming apparatus that develops an electrostatic latent image by AC development, toner adhesion per unit area on the surface of the photosensitive drum 321 near the exit from the development area. The change due to variation in the development gap of the amount is larger than that in DC development.

  As described above, the periodic image density unevenness generated due to the fluctuation of the development gap appears in the AC development as shown in FIGS. 9, 10 and 11, but the DC development is more remarkable. appear. For this reason, the image forming apparatus 1 according to the present embodiment develops an electrostatic latent image by AC development.

  However, the problem of periodic image density unevenness due to fluctuations in the development gap occurs only when an AC voltage having a high frequency exceeding a predetermined frequency is applied to the development roller as a development bias. As in the image forming apparatus 1 according to the present embodiment, this does not occur when a low-frequency AC voltage having a frequency equal to or lower than a predetermined frequency is applied to the developing roller 323c as a developing bias.

  The reason will be described. The magnetic field due to the developing bias applied to the developing roller 323c is strong when the developing gap is small, and is weak when the developing gap is large.

  Therefore, when the development gap is small, the amount of toner (hereinafter referred to as “development amount”) that moves from the developing roller 323c to the photosensitive drum 321 increases while the bias at the time of development is applied, but at the time of pullback. The amount of toner that adheres once to the photosensitive drum 321 and is pulled back to the developing roller 323c (hereinafter referred to as “the pullback amount”) increases while the bias is applied. Therefore, even when the development gap is small, an excessive amount of toner does not adhere to the photosensitive drum 321 and an appropriate amount of toner adheres.

  On the other hand, when the development gap is large, the development amount decreases while the bias at the time of development is applied, but the pull back amount decreases while the bias at the time of withdrawal is applied. Therefore, even when the development gap is large, there is no case where only a small amount of toner adheres to the photosensitive drum 321 and an appropriate amount of toner adheres.

  As described above, when the development amount and the pullback amount are well balanced, it is possible to attach an appropriate amount of toner to the photosensitive drum 321 regardless of the change in the development gap.

  However, this is a case where a low-frequency AC voltage is applied to the developing roller 323c as a developing bias, and when a high-frequency AC voltage is applied to the developing roller as a developing bias, the photosensitive drum is once applied. The adhered toner is not pulled back to the developing roller even when a bias at the time of pulling is applied, and only hops on the surface of the photosensitive drum. Therefore, in such a case, the balance between the development amount and the pullback amount is not well balanced, and periodic image density unevenness occurs due to fluctuations in the development gap.

  Therefore, as described with reference to FIGS. 7 and 8, the image forming apparatus 1 according to the present embodiment is configured to apply a low-frequency AC voltage as a developing bias to the developing roller 323c. However, if the frequency of the AC voltage applied as the developing bias is too low, image density unevenness that can be visually recognized occurs in the switching cycle between the bias at the time of development and the bias at the time of pulling back. A frequency is preferred.

  Here, the reason why the image density unevenness that can be visually recognized occurs in the switching period between the bias at the time of development and the bias at the time of pulling back when the frequency of the AC voltage applied as the development bias is too low will be described. This image density unevenness is defined as indicating how much distance the photosensitive drum 321 is rotated while the bias at the time of development and the bias at the time of pulling are switched, and image density unevenness (mm) = photosensitive body. It is calculated from the rotational linear velocity (mm / s) of the drum 321 / developing bias frequency (Hz). For this reason, the image density unevenness (mm) defined as described above becomes shorter as the frequency of the AC voltage applied as the developing bias becomes higher and becomes less visible. However, the lower the frequency, the longer the image density unevenness (mm). Become.

  For this reason, the image forming apparatus 1 according to this embodiment is configured to apply a low-frequency AC voltage that is not too low to the developing roller 323c as a developing bias. However, since the image density unevenness (mm) depends on the rotational linear velocity of the photosensitive drum 321 as described above, the image forming apparatus 1 according to the present embodiment responds to the rotational linear velocity of the photosensitive drum 321. Thus, the frequency of the AC voltage applied to the developing roller 323c as the developing bias can be changed.

  As described so far, the image forming apparatus 1 according to the present embodiment has a low-frequency AC voltage that is not too low in order to suppress periodic image density unevenness caused by fluctuations in the development gap. Is applied to the developing roller 323c as a developing bias.

  However, when the AC voltage applied to the developing roller 323c as a developing bias is a low frequency, if the duty and Vpp of the developing bias are not appropriate values, a bias at the time of pulling back is applied to the developing roller 323c and applied to the photosensitive drum 321. When the toner once adhered is pulled back to the developing roller 323c, the image is likely to be blurred. For this reason, in an image forming apparatus that applies a low-frequency AC voltage as a developing bias to the developing roller 323c, the duty and Vpp of the developing bias must be appropriate values.

  Specifically, in an image forming apparatus that applies a low-frequency AC voltage as a developing bias to the developing roller 323c, both the duty of the developing bias and the bias at the time of pulling back are reduced in order to suppress image blurring. There must be. However, the optimum duty of the developing bias for suppressing image blur and the bias at the time of pulling back vary depending on the toner charge amount. Therefore, the fact that both the duty of the developing bias and the bias at the time of pulling back must be reduced can be applied to the case where the same toner charge amount is compared.

  Thus, by reducing both the duty of the developing bias and the bias at the time of pulling back, the toner once attached to the photosensitive drum 321 is pulled back only at the closest portion between the photosensitive drum 321 and the developing roller 323c in the developing region. Therefore, it is possible to suppress the blur of the image. However, if the Duty is too small, the toner once attached to the photosensitive drum 321 is not pulled back even at the closest portion, so that it is preferable that the Duty is equal to or greater than a predetermined value.

  For this reason, in an image forming apparatus that applies a low-frequency AC voltage as a developing bias to the developing roller 323c, the duty and Vpp of the developing bias must be appropriate values. However, the appropriate values of Duty and Vpp vary according to the toner charge amount in the developing unit 323.

  Therefore, the image forming apparatus 1 according to the present embodiment is configured to determine appropriate values of Duty and Vpp based on the toner charge amount in the developing unit 323 in order to suppress image blurring.

  As described above, the image forming apparatus 1 according to this embodiment is configured to apply a low-frequency AC voltage to the developing roller 323c as a developing bias, and based on the toner charge amount in the developing unit 323, The gist is that it is configured to determine an appropriate value of Vpp. For this reason, the image forming apparatus 1 according to the present embodiment can suppress periodic image density unevenness caused by fluctuations in the development gap, and can suppress image blurring. Become. As a result, the image forming apparatus 1 according to the present embodiment can improve the quality of the formed image.

  12 and 13 show the toner adhesion amount per unit area on the surface of the photosensitive drum 321 in the vicinity of the developing region at this time. FIG. 12 is a graph showing the toner adhesion amount per unit area on the surface of the photosensitive drum 321 in the vicinity of the development region when a bias at the time of development is applied to the development roller 323c in the image forming apparatus 1 according to the present embodiment. It is. FIG. 13 is a graph showing the toner adhesion amount per unit area on the surface of the photosensitive drum 321 in the vicinity of the development region when the pull-back bias is applied to the development roller 323c in the image forming apparatus 1 according to the present embodiment. It is.

In FIG. 12 and FIG. 13, a solid line indicates the development gap of 0.2 mm, a dotted line indicates the case of 0.225 mm, a broken line indicates the case of 0.26 mm, and a long case of 0.3 mm. It is indicated by a broken line. 12 and 13, the horizontal axis represents the distance in the circumferential direction of the photosensitive drum 321 from the closest position between the surface of the photosensitive drum 321 and the surface of the developing roller 323c. 12 and 13, the upstream side in the rotation direction of the photosensitive drum 321, that is, the entrance side to the development area is represented by − (minus), and the downstream side in the rotation direction, that is, from the development area. The exit side is represented by + (plus). 12 and 13 show the toner adhesion amount (mg / cm ² ) per 1 cm ^{2 on the} surface of the photosensitive drum 321.

  As shown in FIGS. 12 and 13, in the image forming apparatus 1 according to the present embodiment, as shown in FIGS. 10 and 11, when a high frequency AC voltage is applied to the developing roller 323c as a developing bias. In comparison, periodic image density unevenness resulting from fluctuations in the development gap is suppressed.

As a result, as shown in FIG. 14, the image forming apparatus 1 according to the present embodiment has a period derived from fluctuations in the development gap, as compared with DC development and AC development using a high-frequency AC voltage as a development bias. Image density unevenness is suppressed. FIG. 14 shows the development gap of the toner adhesion amount per unit area of the surface of the photosensitive drum 321 when a bias at the time of development is applied to the developing roller 323c when the electrostatic latent image is developed by each method. It is a graph which shows the change by a fluctuation | variation. In FIG. 14, the toner adhesion amount (mg / cm ² ) per 1 cm ^{2 on the} surface of the photosensitive drum 321 is shown.

  In FIG. 14, when the electrostatic latent image is developed by AC development using a low frequency AC voltage as a development bias, that is, the electrostatic latent image is developed by the image forming apparatus 1 according to the present embodiment. The case is indicated by a solid line, the case where an electrostatic latent image is developed by AC development using a low frequency AC voltage as a development bias is indicated by a dotted line, and the case where an electrostatic latent image is developed by DC development is indicated by a broken line. Yes.

  Next, a method in which the image forming apparatus 1 according to the present embodiment determines appropriate values of Duty and Vpp based on the toner charge amount will be described with reference to FIG. FIG. 15 shows a case where the electrostatic latent image is developed by the image forming apparatus 1 according to the present embodiment, and a unit area on the surface of the photosensitive drum 321 when a developing bias is applied to the developing roller 323c. 6 is a graph showing a change in toner adhesion amount due to a change in a development gap for each combination of Duty and Vpp.

FIG. 15 shows a case where the toner density in the developing unit 323 is S ₃ (wt%). In FIG. 15, the case where the toner charge amount is E ₂ μC / g is indicated by a line connecting ♦, the case where the toner charge amount is E ₄ μC / g is indicated by a line connecting ■, and the toner charge amount is E The case of ₈ μC / g is indicated by a line connecting x. In FIG. 15, the toner adhesion amount per unit area on the surface of the photosensitive drum 321 is indicated by M / A (mg / cm ² ). In FIG. 15, the development gap is indicated by GAP (mm). Further, in FIG. 15 _is a _{E 2 <E 4 <E 8} . In FIG. 15, α ₁ <α ₂ <α ₅ <α ₇ <α ₈ is satisfied. Further, in FIG. 15 _is a _{P 1 <P 3 <P 5} <P 6.

  As shown in FIG. 15, the change due to the change in the development gap of the toner adhesion amount per unit area on the surface of the photosensitive drum 321 varies according to the toner charge amount in the development unit 323, and further, a combination of Duty and Vpp. Fluctuates depending on

  Therefore, in the image forming apparatus 1 according to the present embodiment, a combination of Duty and Vpp that minimizes a change due to a change in the development gap of the toner adhesion amount per unit area on the surface of the photosensitive drum 321 is set according to the toner charge amount. Is configured to select. As described above, the gist of the image forming apparatus 1 according to the present embodiment is that the appropriate values of Duty and Vpp are determined based on the toner charge amount in the developing unit 323.

For example, in FIG. 15, when the toner charge amount is E ₂ μC / g, the change in the toner adhesion amount per unit area on the surface of the photosensitive drum 321 due to the change in the development gap is Duty = α ₇ %, Vpp. = P ₃ V is the smallest. In FIG. 15, when the toner charge amount is E ₄ μC / g, the change in the toner adhesion amount per unit area on the surface of the photosensitive drum 321 due to the change in the development gap is Duty = α ₅ %, Vpp. = P ₃ V is the smallest. In FIG. 15, when the toner charge amount is E ₈ μC / g, the change in the toner adhesion amount per unit area on the surface of the photosensitive drum 321 due to the change in the development gap is Duty = α ₂ %, Vpp. = P ₃ V is the smallest.

Therefore, in the image forming apparatus 1 according to the present embodiment, when the toner density is S ₃ % and the toner charge amount is E ₂ μC / g, Duty = α ₇ % and Vpp = P ₃ V are appropriate values. When the toner charge amount is E ₄ μC / g, it is determined as Duty = α ₅ % and Vpp = P ₃ V. When the toner charge amount is E ₈ μC / g, Duty = α ₂ %, Vpp = P ₃ V is determined as an appropriate value.

In FIG. 15, for example, when the toner charge amount is E ₈ μC / g, Duty = α ₅ % and Vpp = P ₆ V are determined as optimal as described above. Duty = α ₂ %, Vpp The change due to the change in the development gap of the toner adhesion amount per unit area on the surface of the photosensitive drum 321 is smaller than P ₃ V. However, the image forming apparatus 1 according to this embodiment does not determine Duty = α ₅ % and Vpp = P ₆ V as appropriate values when the toner charge amount is E ₈ μC / g.

This is because, as described above, in an image forming apparatus that applies a low-frequency AC voltage to the developing roller 323c as a developing bias, both the duty of the developing bias and the bias at the time of pulling back are suppressed in order to suppress image blurring. Although it must be reduced, the value Vpp = P ₆ V is because Vpp is too large to suppress image blur.

Further, in FIG. 15, for example, when the toner charge amount is E ₂ μC / g, Duty = α ₈ % and Vpp = P ₃ V are determined as optimal as described above. Duty = α ₄ %, Vpp The change due to the change in the development gap of the toner adhesion amount per unit area on the surface of the photosensitive drum 321 is smaller than P ₃ V. However, the image forming apparatus 1 according to this embodiment does not determine Duty = α ₈ % and Vpp = P ₃ V as appropriate values when the toner charge amount is E ₂ μC / g.

This is because, as described above, in an image forming apparatus that applies a low-frequency AC voltage to the developing roller 323c as a developing bias, both the duty of the developing bias and the bias at the time of pulling back are suppressed in order to suppress image blurring. This is because the value of Duty = α ₈ % is too large to suppress the blurring of the image.

  As described above, the image forming apparatus 1 according to the present embodiment is configured to determine appropriate values of Duty and Vpp based on the toner charge amount in the developing unit 323, but the toner charging in the developing unit 323 is performed. Even if the amount is the same, if the toner density in the developing unit 323 is different, the appropriate values of Duty and Vpp are also different.

  Therefore, the image forming apparatus 1 according to the present embodiment is configured to determine appropriate values of Duty and Vpp based not only on the toner charge amount in the developing unit 323 but also on the toner density in the developing unit 323. Yes.

  For this purpose, the image forming apparatus 1 according to the present embodiment measures the toner concentration and the toner charge amount in the developing unit 323, and then determines the toner concentration and the toner charge amount in the developing unit 323 as shown in FIG. By referring to a Duty-Vpp determination table in which appropriate values of Duty and Vpp are associated with each combination, the appropriate values of Duty and Vpp are determined. FIG. 16 is a diagram showing an example of the Duty-Vpp determination table according to the present embodiment.

Therefore, the image forming apparatus 1 according to the present embodiment, when the toner density and the toner charge amount in the developing unit 323 are known, refers to the duty-Vpp determination table as shown in FIG. The value can be determined. Since the image forming apparatus 1 according to the present embodiment stores the Duty-Vpp determination table as shown in FIG. 16 in a nonvolatile storage medium such as the ROM 30 or the HDD 40, it can be referred to at any time. In FIG. 16, S ₁ <S ₂ <S ₃ <S ₄ <S ₅ . Further, in FIG. 16 _is a _{E 1 <E 2 <E 3} <E 4 <E 5 <E 6 <E 7 <E 8. In FIG. 16, α ₁ <α ₂ <α ₃ <α ₄ <α ₅ <α ₆ <α ₇ <α ₈ . Further, in FIG. 16 _is a _{P 1 <P 2 <P 3} <P 4 <P 5 <P 6 <P 7.

Note that the image forming apparatus 1 according to the present embodiment includes a toner concentration detection sensor (not shown) for detecting the toner concentration in the developing unit 323. Therefore, the toner concentration (wt%) in the developing unit 323 is set. Can be measured directly. However, the image forming apparatus 1 according to the present embodiment cannot directly measure the toner charge amount in the developing unit 323. Therefore, the image forming apparatus 1 according to the present embodiment is configured to predict the toner charge amount in the development unit 323 based on the development γ (mg / cm ² · V) and the toner density in the development unit 323. ing.

Therefore, the image forming apparatus 1 according to the present embodiment first measures the development γ (mg / cm ² · V) when measuring the toner charge amount in the developing unit 323. Here, the development γ (mg / cm ² · V) is a change amount of the toner adhesion amount per unit area of the photosensitive drum 321 due to a change in the developing bias, and the toner is applied to the photosensitive drum 321. It is an index indicating the ease of adhesion. The developing bias at this time is only a DC voltage.

  In the image forming apparatus 1 according to this embodiment, in order to measure the development γ, first, the toner adhesion amount per unit area of the photosensitive drum 321 is measured at each development bias by changing the development bias. As described above, since the image forming apparatus 1 according to the present embodiment needs to measure the toner adhesion amount per unit area of the photosensitive drum 321, the image forming apparatus 1 includes a toner adhesion amount detection sensor (not illustrated) for that purpose.

  As shown in FIG. 17, the image forming apparatus 1 according to the present embodiment has each developing bias on a graph in which the horizontal axis represents the developing bias and the vertical axis represents the toner adhesion amount per unit area of the photosensitive drum 321. 3 plots the toner adhesion amount per unit area of the photosensitive drum 321 measured in step. FIG. 17 is a graph showing a change in the toner adhesion amount per unit area on the surface of the photosensitive drum 321 due to the developing bias in the image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 according to the present embodiment calculates the slope of the approximate line based on the plotted points by the least square method, and sets the calculation result as development γ.

  In the present embodiment, the amount of toner adhesion per unit area of the photosensitive drum 321 is defined as a change amount due to a change in the developing bias. However, the toner amount per unit area of the intermediate transfer image formed on the transport belt 311 is used. The amount of change due to the change in the development bias may be the development γ. In this case, in order to measure the development γ, the image forming apparatus 1 according to the present embodiment first measures the toner amount per unit area of the intermediate transfer image at each development bias while changing the development bias. As described above, since the image forming apparatus 1 according to the present embodiment needs to measure the toner amount per unit area of the intermediate transfer image formed on the conveyance belt 311, a toner amount detection sensor (not illustrated) for that purpose is required. It has.

  In the image forming apparatus 1 according to the present embodiment, the intermediate transfer image measured at each development bias is plotted on a graph in which the horizontal axis represents the development bias and the vertical axis represents the toner amount per unit area of the intermediate transfer image. The amount of toner per unit area is plotted. The image forming apparatus 1 according to the present embodiment calculates the slope of the approximate line based on the plotted points by the least square method, and sets the calculation result as development γ.

When the development γ is measured in this way, the image forming apparatus 1 according to the present embodiment uses the combination of the development γ and the toner density as shown in FIG. 18 based on the measured development γ and the toner density. The toner charge amount in the developing unit 323 is determined by referring to the toner charge amount determination table associated with the toner charge amount for each time. FIG. 18 is a diagram illustrating an example of a toner charge amount determination table according to the present embodiment. In FIG. 18, γ ₁ > γ ₂ > γ ₃ > γ ₄ > γ ₅ is satisfied.

  When the toner charge amount is determined in this way, the image forming apparatus 1 according to the present embodiment, based on the measured toner density and the determined toner charge amount, as described with reference to FIG. The appropriate values of Duty and Vpp are determined by referring to the Duty-Vpp determination table.

  At this time, in the image forming apparatus 1 according to the present embodiment, the main control unit 110 determines the frequency of the AC voltage, and the engine control unit 120 controls the AC voltage so that the determined frequency is obtained. In the image forming apparatus 1 according to the present embodiment, the main control unit 110 determines Duty and Vpp, and the engine control unit 120 controls the AC voltage so that the determined Duty and Vpp are obtained. That is, in the present embodiment, the main control unit 110 functions as a frequency determination unit and a voltage characteristic determination unit, and the engine control unit 120 functions as an applied voltage control unit. In the present embodiment, the controller 100 including the main control unit 110 and the engine control unit 120 functions as an applied voltage control device.

  Note that, as described with reference to FIG. 16, the image forming apparatus 1 according to the present embodiment measures the toner concentration and the toner charge amount in the developing unit 323, and then measures the toner concentration and the toner charge amount. The example configured to determine the appropriate values of Duty and Vpp by referring to the Duty-Vpp determination table has been described. In addition, the image forming apparatus 1 according to the present embodiment measures the development γ and the toner charge amount in the development unit 323, measures the development γ and the toner charge amount, and then develops the development γ as shown in FIG. The appropriate values of Duty and Vpp may be determined by referring to the Duty-Vpp determination table in which appropriate values of Duty and Vpp are associated with each combination of toner and toner charge amount. FIG. 19 is a diagram showing an example of the Duty-Vpp determination table according to the present embodiment.

  Therefore, when the image forming apparatus 1 according to the present embodiment is configured as described above, if the development γ and the toner charge amount in the development unit 323 are known, refer to the duty-Vpp determination table as shown in FIG. This makes it possible to determine appropriate values for Duty and Vpp.

  In addition, the image forming apparatus 1 according to the present embodiment measures the development γ and the toner density in the development unit 323, measures the development γ and the toner density, and then develops the development γ as shown in FIG. The appropriate values of Duty and Vpp may be determined by referring to a Duty-Vpp determination table in which appropriate values of Duty and Vpp are associated with each combination of toner density. FIG. 20 is a diagram showing an example of the Duty-Vpp determination table according to the present embodiment.

  Therefore, when the image forming apparatus 1 according to the present embodiment is configured as described above, if the development γ and the toner density in the development unit 323 are known, the image forming apparatus 1 refers to the Duty-Vpp determination table shown in FIG. This makes it possible to determine appropriate values for Duty and Vpp.

  In FIG. 16 and FIG. 19, the duty and Vpp tend to decrease as the toner charge amount increases. This is because the larger the toner charge amount, the easier the toner once attached to the photosensitive drum 321 is pulled back to the developing roller 323c even if the bias and duty at the time of pulling back are small. Because there is no.

  As described above, in the image forming apparatus that applies a low-frequency AC voltage to the developing roller 323c as the developing bias, both the duty of the developing bias and the bias at the time of pulling back are suppressed in order to suppress image blurring. Although it must be reduced, Vpp and Duty can be reduced as the toner charge amount is increased. Therefore, the image forming apparatus 1 according to the present embodiment can further suppress the image blur.

  As described above, the image forming apparatus 1 according to this embodiment is configured to apply a low-frequency AC voltage to the developing roller 323 c as a developing bias, and based on the toner charge amount in the developing unit 323. The gist of the invention is that the appropriate values of Duty and Vpp are determined. For this reason, the image forming apparatus 1 according to the present embodiment can suppress periodic image density unevenness caused by fluctuations in the development gap, and can suppress image blurring. Become. As a result, the image forming apparatus 1 according to the present embodiment can improve the quality of the formed image.

  Note that the image forming apparatus 1 according to the present embodiment determines an appropriate value of Duty and Vpp by referring to any of the Duty-Vpp determination tables illustrated in FIGS. 16, 19, and 20. The configured example has been described. In addition, the image forming apparatus 1 according to the present embodiment stores a plurality of Duty-Vpp determination tables shown in FIGS. 16, 19, and 20 according to the use environment such as temperature and humidity, and performs measurement. The Duty-Vpp determination table corresponding to the usage environment may be selected and used. This is because the development γ and the toner charge amount change according to the use environment.

  Therefore, when the image forming apparatus 1 according to the present embodiment is configured as described above, it is possible to determine appropriate Duty and Vpp regardless of the use environment. For this reason, the image forming apparatus 1 according to the present embodiment can suppress periodic image density unevenness caused by fluctuations in the development gap regardless of the use environment, and can also cause image blurring. It becomes possible to suppress. As a result, the image forming apparatus 1 according to the present embodiment can further improve the quality of the formed image.

  Further, the image forming apparatus 1 according to the present embodiment has been described with respect to the example in which the toner charge amount in the developing unit 323 is predicted based on the developing γ and the toner density in the developing unit 323. The toner charge amount in the unit 323 may be directly measured.

  Further, the image forming apparatus 1 according to the present embodiment has been described with respect to the example in which the appropriate value of Duty-Vpp is determined for all the colors C, M, Y, and K. It is possible to determine an appropriate value of Duty-Vpp only for a color that tends to be noticeable, and to perform DC development for a color that is less noticeable for image density unevenness and blur. With this configuration, the image forming apparatus 1 according to the present embodiment can reduce costs.

Embodiment 2. FIG.
In the first embodiment, the image forming apparatus 1 configured to determine the appropriate values of Duty and Vpp based on the toner charge amount in the developing unit 323 has been described as an example. With this configuration, the image forming apparatus 1 according to the first embodiment can suppress periodic image density unevenness caused by fluctuations in the development gap, and can also prevent image blurring. It becomes possible to suppress sticking. Thereby, the image forming apparatus 1 according to the first embodiment can improve the quality of the formed image.

  On the other hand, in the present embodiment, the image forming apparatus 1 configured to change the duty according to the one-dot line aspect ratio will be described as an example. With this configuration, the image forming apparatus 1 according to the present embodiment can achieve both improvement in line quality and suppression of periodic image density unevenness caused by fluctuations in the development gap. It becomes possible. As a result, the image forming apparatus 1 according to the present embodiment can improve the quality of the formed image.

  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 detailed configuration of the print engine 300 according to the present embodiment will be described with reference to FIG. FIG. 21 is a cross-sectional view from the main scanning direction of the image forming apparatus 1 according to the present embodiment. As shown in FIG. 21, the image forming apparatus 1 according to the present embodiment includes a toner adhesion amount measurement sensor 390 for measuring the toner adhesion amount on the conveyance belt 311.

  As shown in FIG. 22, the toner adhesion amount measuring sensor 390 includes a light emitting element 391, a first light receiving element 392, and a second light receiving element 393. FIG. 22 is a diagram showing a simplified configuration of the toner adhesion amount measuring sensor 390 according to the present embodiment.

  The light emitting element 391 irradiates the conveyor belt 311 with light. The first light receiving element 392 is a reflected light (hereinafter referred to as “diffuse reflected light”) in a direction perpendicular to the image forming surface of the conveyor belt 311 among the reflected light of the light emitted from the light emitting element 391 by the conveyor belt 311. And a detection signal corresponding to the amount of the received light is output to the controller 100.

  The second light receiving element 393 reflects the light emitted from the light emitting element 391 with the same reflection angle as the incident angle with respect to the direction perpendicular to the image forming surface of the conveyor belt 311 out of the reflected light from the conveyor belt 311. Light (hereinafter referred to as “regular reflection light”) is received, and a detection signal corresponding to the amount of the received light is output to the controller 100.

  In the toner adhesion amount measuring sensor 390 configured as described above, the smaller the toner adhesion amount on the conveyance belt 311, the more regular reflection by the second light receiving element 393 with respect to the received light amount Ra of the diffusely reflected light by the first light receiving element 392. The ratio Rb / Ra of the received light amount Rb is increased.

  Therefore, the image forming apparatus 1 according to the present embodiment uses the toner adhesion amount measuring sensor 390 configured as described above, and the second light receiving element 393 with respect to the light receiving amount Ra of the diffuse reflected light by the first light receiving element 392. By measuring the ratio Rb / Ra of the received light amount Rb of regular reflection light by the toner, it becomes possible to measure the toner adhesion amount on the conveyor belt 311. That is, in the present embodiment, the toner adhesion amount measurement sensor 390 functions as an adhesion amount measurement unit.

  Then, as shown in FIG. 23, the image forming apparatus 1 according to the present embodiment forms a 1-dot horizontal line image and a 1-dot vertical line within a predetermined range on the conveyor belt 311, and the toner adhesion amount The toner adhesion amount in the predetermined range of each line image is measured by the measurement sensor 390.

  Here, the 1-dot horizontal line image is a line image in the main scanning direction having a width of 1 dot in the predetermined range, and the 1-dot vertical line image is a sub-pixel having a width of 1 dot in the predetermined range. It is a line image in the scanning direction.

  In this way, when the image forming apparatus 1 according to the present embodiment measures the toner adhesion amount of each line image, the main control unit 110 calculates a 1-dot line aspect ratio that is difference information. That is, in the present embodiment, the main control unit 110 functions as a difference information acquisition unit.

  Here, the 1-dot line aspect ratio is an index representing a difference in toner adhesion amount between the 1-dot horizontal line image and the 1-dot vertical line image in the predetermined range, and any one of the toner adhesion amounts is represented by A. When the other is B, it is defined by | (B−A) / A | × 100 (%) or | (A−B) / B | × 100 (%).

  Therefore, the smaller the one-dot line aspect ratio is, the smaller the difference in toner adhesion amount between the one-dot horizontal line image and the one-dot vertical line image in the predetermined range is, and the line quality is better. Means that.

  Further, as shown in FIG. 24, the 1-dot line aspect ratio tends to increase as the duty increases. That is, the line quality tends to deteriorate as the duty increases. This is because when the duty is large, the scavenging effect in which a part of the toner once attached to the photosensitive drum 321 is pulled back to the developing roller 323c is increased. In such a case, the 1-dot horizontal line image is relatively thinner than the 1-dot vertical line image.

  Therefore, in order to improve the line quality, that is, to reduce the one-dot line aspect ratio, it is necessary to set the duty to be small.

  On the other hand, as shown in FIG. 25, the periodic image density unevenness caused by the change in the development gap tends to be reduced as the duty increases. This is because the scavenging effect increases as the duty increases.

  Therefore, in order to suppress periodic image density unevenness that occurs due to a change in the development gap, it is necessary to set the duty to be large.

  As described above, the improvement in line quality and the suppression of the periodic image density unevenness caused by the change in the development gap are in a trade-off relationship with respect to the duty setting.

  Therefore, the gist of the image forming apparatus 1 according to the present embodiment is to change the duty according to the calculated 1-dot line aspect ratio. Therefore, the image forming apparatus 1 according to the present embodiment can achieve both improvement in line quality and suppression of periodic image density unevenness that occurs due to fluctuations in the development gap. As a result, the image forming apparatus 1 according to the present embodiment can improve the quality of the formed image.

  In particular, image forming apparatuses used for PP (Products Printing) tend to be required to prioritize suppression of periodic image density unevenness that occurs due to development gap fluctuations rather than line quality. is there. However, even in an image forming apparatus used for PP, the line quality is excellent.

  For this reason, even in an image forming apparatus used for PP, the line quality is ensured to a certain level or more by changing the duty according to the calculated 1-dot line aspect ratio, and this occurs due to fluctuations in the development gap. Periodic image density unevenness can be suppressed.

  On the contrary, for example, depending on the image such as a CAD drawing, the line quality may be required to be given priority over the suppression of the periodic image density unevenness caused by the fluctuation of the development gap. In such a case, the effect of improving the line quality is great by changing the duty according to the calculated 1-dot line aspect ratio.

  As described above, in the image forming apparatus 1 according to the present embodiment, when priority is given to line quality, the duty is set to be low, and periodic image density unevenness generated due to fluctuations in the development gap is suppressed. When priority is given, the duty is set higher.

  In the image forming apparatus 1 according to the present embodiment, the user can select which of the line quality and the suppression of the periodic image density unevenness generated due to the change in the development gap is prioritized. It may be configured as follows.

  In the present embodiment, the duty is changed in accordance with the 1-dot line aspect ratio that is an index of the difference in toner adhesion amount between the 1-dot horizontal line image and the 1-dot vertical line image in the predetermined range. The image forming apparatus 1 thus described has been described. In addition, the image forming apparatus 1 according to the present embodiment is not limited to one dot, and is configured to use a line aspect ratio of 2 dots or more if the horizontal line image and the vertical line image have the same dot width. May be.

Embodiment 3 FIG.
In the second embodiment, the image forming apparatus 1 configured to calculate the one-dot line aspect ratio using the toner adhesion amount measuring sensor 390 has been described as an example. On the other hand, in the present embodiment, an image forming apparatus 1 configured to calculate a one-dot line aspect ratio using the toner adhesion amount measurement sensor 390 will be described as an example.

  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, 2, it shall show the same or an equivalent part, and detailed description is abbreviate | omitted.

  First, the functional configuration of the image forming apparatus 1 according to the present embodiment will be described with reference to FIG. FIG. 26 is a block diagram schematically illustrating a functional configuration of the image forming apparatus 1 according to the present embodiment. As shown in FIG. 26, the image forming apparatus 1 according to the present embodiment includes a development power supply 101 and a current detection unit 102.

  The development power source 101 applies a development bias to the development roller 323 c under the control of the controller 100. The voltage value of the developing bias at this time is variable by the controller 100. Further, the developing bias at this time may be a DC voltage or an AC voltage.

  The current detector 102 detects the current value of the developing current when the developing power source 101 applies a developing bias to the developing roller 323c, and outputs a detection signal corresponding to the current value to the controller 100.

  The image forming apparatus 1 according to the present embodiment forms a 1-dot horizontal line image and a 1-dot vertical line image as shown in FIG. 23 in a predetermined range with respect to the conveyance belt 311, and performs main control. In the unit 110, the current value at that time is acquired by the current detection unit 102. That is, in the present embodiment, the main control unit 110 functions as a current value measurement unit.

  Since the development current of the development bias applied at this time is due to the movement of the toner (charge), the current value of the development current is regarded as the toner adhesion amount in the 1-dot horizontal line image and the 1-dot vertical line image. Can be tricked.

  Therefore, the image forming apparatus 1 according to the present embodiment can calculate the 1-dot line aspect ratio by acquiring the development current when the 1-dot horizontal line image and the 1-dot vertical line image are formed. .

  Note that the toner adhesion amount in the predetermined range of each line image depends on the toner charge amount. For this reason, the image forming apparatus 1 according to the present embodiment cannot directly measure the toner adhesion amount in the predetermined range of each line image, but can calculate the 1-dot line aspect ratio. .

  The gist of the image forming apparatus 1 according to the present embodiment is to change the duty according to the one-dot line aspect ratio calculated as described above. For this reason, the image forming apparatus 1 according to the present embodiment does not require the toner adhesion amount measurement sensor 390, and can improve the line quality and suppress the periodic image density unevenness caused by the change in the development gap. It is possible to achieve both. As a result, the image forming apparatus 1 according to the present embodiment can improve the quality of the formed image.

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 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 Developing unit 323a First toner conveying screw 323b Second toner conveying screw 323c Developing roller 324 Charger 325 G Toner recovery unit 325a cleaning blade 325b recovery toner transport screw 325c recovery toner transport path 325d cleaning blade position control roller 326 lubricant application unit 326a solid lubricant 326b lubricant application roller 326c solid lubricant pressure spring 327 lubricant equalization blade 330 light Writing device 340 Primary transfer roller 350 Toner bottle 360 Secondary transfer roller 370 Fixing unit 371 Fixing roller pair 380 Belt cleaner 390 Toner adhesion amount measuring sensor 391 Light emitting element 400 Output tray for printing 410 Output roller pair 500 ADF
600 Scanner engine 700 Output tray for scanning 800 Display panel 900 Network I / F

JP 2009-020281 A JP-A-5-257369

Claims (16)

In a facing region where a developer carrying portion carrying a charged developer and an image carrying portion carrying a developer image formed by developing an electrostatic latent image with the developer are opposed to each other, An applied voltage control device that controls an alternating voltage applied to electrostatically move the developer toward the electrostatic latent image from a developer carrier,
A frequency determining unit that determines the frequency of the AC voltage so that the developer once moved to the electrostatic latent image is pulled back to the developer carrying unit;
The amount of the developer in the developer accommodating portion that accommodates the developer to be carried on the developer carrying portion, and the ease of movement of the developer to the electrostatic latent image A voltage characteristic determining unit that determines a potential difference between a maximum voltage value and a minimum voltage value of the AC voltage, and a ratio between a time during which the maximum voltage value is applied and a time during which the minimum voltage value is applied;
An applied voltage control unit for controlling the applied AC voltage so as to be the determined frequency, the potential difference, and the ratio;
An applied voltage control apparatus comprising:   The applied voltage control apparatus according to claim 1, wherein the voltage characteristic determination unit determines the potential difference and the ratio based on a charge amount of the developer.   The voltage characteristic determination unit includes an amount of the developer in the developer storage unit that stores the developer for supporting the developer in the developer support unit, and the amount of the developer. The applied voltage control apparatus according to claim 2, wherein a charge amount of the developer is predicted based on ease of movement to the electrostatic latent image.   The voltage characteristic determination unit predicts the charge amount of the developer based on the amount of the developer in the developer storage unit and the ease of movement of the developer to the electrostatic latent image. 4. The potential difference and the ratio are determined based on the predicted charge amount of the developer and the amount of the developer in the developer accommodating portion. The applied voltage control apparatus described in 1.   The voltage characteristic determination unit predicts the charge amount of the developer based on the amount of the developer in the developer storage unit and the ease of movement of the developer to the electrostatic latent image. 5. The potential difference and the ratio are determined based on the estimated charge amount of the developer and ease of movement of the developer to the electrostatic latent image. The applied voltage control apparatus of any one of Claims.   The voltage characteristic determination unit determines the potential difference and the ratio so that the potential difference and the ratio become smaller as the charge amount of the developer increases. The applied voltage control apparatus described in 1.   The applied voltage control apparatus according to claim 1, wherein the voltage characteristic determination unit determines the potential difference and the ratio based on an environment near the facing region.   The voltage characteristic determination unit includes a developer adhesion amount in the developer image in the main scanning direction transferred from the image carrier, and a developer image in the sub-scanning direction transferred from the image carrier. The ratio between the time during which the maximum voltage value is applied and the time during which the minimum voltage value is applied is determined based on difference information relating to the difference between the developer adhesion amount and the developer amount. 7. The applied voltage control device according to any one of 7 above. A difference information acquisition unit for acquiring the difference information;
The applied voltage control apparatus according to claim 8, wherein the voltage characteristic determination unit determines the ratio based on the acquired difference information. An adhesion amount measuring unit for measuring the adhesion amount;
The applied voltage control apparatus according to claim 9, wherein the difference information acquisition unit acquires the difference information based on the measured adhesion amount.   The difference information acquisition unit is applied when the developer image in the main scanning direction and the developer image in the sub-scanning direction are imaged on the image carrier by the developer carrier. The applied voltage control device according to claim 9 or 10, wherein the difference information is acquired based on a current value of a current accompanying the AC voltage. A current value measuring unit for measuring the current value;
The applied voltage control apparatus according to claim 11, wherein the difference information acquisition unit acquires the difference information based on the measured current value.   The voltage characteristic determining unit is configured to detect the developer image generated by a change in a distance between the developer-carrying unit and the image-carrying unit in the facing region by driving the developer-carrying unit and the image-carrying unit. The application according to any one of claims 1 to 12, wherein the ratio is determined according to whether priority is given to suppression of density unevenness or improvement of image quality according to the difference information. Voltage control device. An AC voltage is applied in a facing region where a developer carrying portion that carries a charged developer and an image carrying portion that carries a developer image formed by developing an electrostatic latent image by the developer are opposed to each other. To develop the electrostatic latent image by electrostatically moving the developer from the developer carrying portion toward the electrostatic latent image. An imaging device for imaging,
An image forming apparatus comprising the applied voltage control apparatus according to claim 1. An AC voltage is applied in a facing region where a developer carrying portion that carries a charged developer and an image carrying portion that carries a developer image formed by developing an electrostatic latent image by the developer are opposed to each other. To develop the electrostatic latent image by electrostatically moving the developer from the developer carrying portion toward the electrostatic latent image. An image forming apparatus for forming an image,
An image forming apparatus comprising the applied voltage control device according to claim 1. In a facing region where a developer carrying portion carrying a charged developer and an image carrying portion carrying a developer image formed by developing an electrostatic latent image with the developer are opposed to each other, An applied voltage control method for controlling an AC voltage applied to electrostatically move the developer toward the electrostatic latent image from a developer carrying part,
The frequency of the AC voltage is determined so that the developer once moved to the electrostatic latent image is pulled back to the developer carrying part,
The amount of the developer in the developer accommodating portion that accommodates the developer to be carried on the developer carrying portion, and the ease of movement of the developer to the electrostatic latent image On the basis of the potential difference between the maximum voltage value and the minimum voltage value of the alternating voltage, and the ratio of the time during which the maximum voltage value is applied and the time during which the minimum voltage value is applied;
The applied voltage control method, wherein the applied AC voltage is controlled so that the determined frequency, the potential difference, and the ratio are obtained.