JP6475149B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, an image forming apparatus such as a printer, a copier, a facsimile machine, a multifunction machine, for example, a printer, includes an image forming unit, an LED head, a transfer roller, a fixing device, etc., and the image forming unit includes a photosensitive drum, a charging roller, A developing device or the like is arranged.

  In the image forming unit, the surface of the photosensitive drum is charged by a charging roller, exposed by an LED head to form an electrostatic latent image on the surface of the photosensitive drum, and the electrostatic latent image is developed by a developing device. As a result, a toner image is formed. The toner image is transferred to a sheet as a medium by a transfer roller, and the toner image on the sheet is fixed by a fixing device, so that an image is formed on the sheet, that is, printing is performed.

  The developing device includes a developing roller, a toner supply roller, a developing blade, and the like. The toner as a developer in the image forming unit is supplied to the developing roller by the toner supplying roller, and the toner having a certain thickness is supplied to the developing roller by the developing blade. A layer is formed, and the toner in the toner layer is attached to the electrostatic latent image to form a toner image.

  By the way, in a printer, if printing is continuously performed in a state where the amount of toner in the image forming unit, that is, the amount of remaining toner is low, blurring occurs in the formed image and image quality is degraded. .

  Therefore, a sensor for detecting the remaining amount of toner is provided in the image forming unit, and when the remaining amount of toner falls below a predetermined value, the developing bias applied to the developing roller is reduced by an absolute value or the developing bias is set to be absolute. In addition to decreasing the value, the differential voltage between the developing bias and the supply bias applied to the toner supply roller is increased (for example, see Patent Document 1).

JP 2009-3313 A

  However, in the conventional printer, when printing with a low print duty is continuously performed, the toner layer on the developing roller becomes thick, and the area on the photosensitive drum that is not exposed by the LED head, that is, non-exposed. Toner adheres to the area, stains such as fogging occur on the paper, and the image quality deteriorates.

  The present invention solves the problems of the conventional printer and prevents the image quality from deteriorating even when printing with a low print duty is continuously performed with a small amount of developer remaining. It is an object of the present invention to provide an image forming apparatus that can be used.

  For this purpose, in the image forming apparatus of the present invention, an image carrier, a charging member for charging the surface of the image carrier, and the image carrier are exposed to form a latent image on the surface of the image carrier. An exposure device, a developer carrier that develops the latent image and forms a developer image on the surface of the image carrier, a developer supply member that supplies the developer to the developer carrier, and the number of printed sheets The number of printed sheets to be measured, the developer remaining amount calculating unit for calculating the remaining amount of developer, the print density calculating unit for calculating the print density, and the voltage for applying a voltage to the developer carrier and the developer supply member And a control unit.

  The voltage control unit prints a difference voltage between a voltage applied to the developer carrier and a voltage applied to the developer supply member when image formation for a predetermined print job is completed. The number is changed according to the number of sheets, the print density, and the remaining amount of developer.

  According to the present invention, in the image forming apparatus, an image carrier, a charging member for charging the surface of the image carrier, and the image carrier are exposed to form a latent image on the surface of the image carrier. An exposure device, a developer carrier that develops the latent image and forms a developer image on the surface of the image carrier, a developer supply member that supplies the developer to the developer carrier, and the number of printed sheets The number of printed sheets to be measured, the developer remaining amount calculating unit for calculating the remaining amount of developer, the print density calculating unit for calculating the print density, and the voltage for applying a voltage to the developer carrier and the developer supply member And a control unit.

  The voltage control unit prints a difference voltage between a voltage applied to the developer carrier and a voltage applied to the developer supply member when image formation for a predetermined print job is completed. The number is changed according to the number of sheets, the print density, and the remaining amount of developer.

  In this case, when the voltage control unit finishes forming the image for the predetermined print job, the voltage control unit calculates the difference voltage between the voltage applied to the developer carrier and the voltage applied to the developer supply member. Since the printing density is changed according to the printing density and the remaining amount of the developer, it is possible to suppress an increase in the amount of the developer attached to the developer carrying member.

  Therefore, even when printing with a low developer duty and a low print duty is continuously performed, the developer layer on the developer carrier does not become thick and the image carrier is not exposed. It is possible to prevent the developer from adhering to the surface.

  As a result, it is possible to prevent the medium from being contaminated and to prevent the image quality from deteriorating.

FIG. 3 is a control block diagram of the printer in the embodiment of the present invention. 1 is a conceptual diagram of a printer in an embodiment of the present invention. FIG. 2 is a conceptual diagram of an image forming unit in the embodiment of the present invention. FIG. 6 is a reference diagram illustrating a change in the amount of toner attached to the developing roller when continuous printing is performed. FIG. 6 is a reference diagram illustrating a change in the degree of smearing occurring on a sheet when continuous printing is performed. FIG. 10 is a diagram for explaining the influence of the remaining amount of toner in the process unit on the amount of toner attached to the developing roller in the embodiment of the present invention. 3 is a first flowchart showing the operation of the printer control apparatus according to the embodiment of the present invention. It is a 2nd flowchart which shows operation | movement of the control apparatus of the printer in embodiment of this invention. 6 is a time chart for explaining the operation of the printer control apparatus according to the embodiment of the present invention. It is a figure which shows the example of the printing rate coefficient table in embodiment of this invention. FIG. 10 is a diagram illustrating an example of a remaining toner coefficient table in the embodiment of the present invention. It is an image figure of the difference voltage in embodiment of this invention. It is a figure which shows the change of the toner adhesion amount to the developing roller when continuous printing is performed in the embodiment of the present invention. It is a figure which shows the change of the degree of the stain | pollution | contamination which generate | occur | produced on the paper when performing continuous printing in embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this case, a printer as an image forming apparatus will be described.

  FIG. 2 is a conceptual diagram of a printer in the embodiment of the present invention, and FIG. 3 is a conceptual diagram of an image forming unit in the embodiment of the present invention.

  In the figure, 10 is a printer, Cs is a housing, 11Bk, 11Y, 11M, and 11C are black, yellow, magenta, and cyan image forming units (image drum units) disposed adjacent to each other, and 13 is each image. A photosensitive drum 23 as an image carrier that is disposed in the forming units 11Bk, 11Y, 11M, and 11C and forms a toner image as a developer image of each color on the surface, and 23 is provided in each of the image forming units 11Bk, 11Y, and 11M. , 11C, and an LED head u1 as an exposure device disposed adjacent to the photoconductive drum 13 above the photoconductive drum 13 and the image forming units 11Bk, 11Y, 11M, and 11C. A toner image of each color formed on the surface of the photosensitive drum 13 disposed below is superimposed on a sheet P as a medium and transferred. And, a transfer unit that forms a toner image of a color, 17 fixing unit as a fixing unit, 18 is a paper cassette as a medium accommodating portion for accommodating the paper P.

  The LED head 23 includes an LED array composed of LEDs as a plurality of light emitting elements, a driving circuit that selectively drives each LED to emit light, a lens array that images the light of the LED on the surface of the photosensitive drum 13, and the like. The photosensitive drum 13 is exposed based on dot data sent from an exposure control unit 52 (FIG. 1) described later, and an electrostatic latent image as a latent image is formed on the surface of the photosensitive drum 13.

  Since the image forming units 11Bk, 11Y, 11M, and 11C all have the same structure, only the image forming unit 11Bk will be described with reference to the members.

  In each of the image forming units 11Bk, 11Y, 11M, and 11C, the toner image is formed by an electrophotographic process. Therefore, each of the image forming units 11Bk, 11Y, 11M, and 11C is detachable from the process unit (developer) 11a that constitutes the main body of the image forming units 11Bk, 11Y, 11M, and 11C, and the process unit 11a. A toner cartridge 28 is provided as a developer accommodating portion that is disposed and accommodates toner T of each color as a developer. The toner cartridge 28 includes a discharge port 28a for discharging the stored toner T and supplying the toner T to the process unit 11a. In this embodiment, the process unit 11a and the toner cartridge 28 are formed separately, but a toner storage unit as a developer storage unit is integrally formed above the process unit 11a. To be able to.

  In this embodiment, the toner T is a non-magnetic one-component toner, and is formed by adding an external additive such as silica, PMMA, melamine or the like to a toner base having an average particle diameter of 6 [μm].

  The process unit 11a includes a housing C1 that supports the toner cartridge 28, and is in contact with the photosensitive drum 13 and the photosensitive drum 13 that are rotatably disposed in an arrow direction in the housing C1. The charging roller 22 as a charging member that is rotatably arranged in the direction of the arrow, and in contact with the photosensitive drum 13 on the downstream side of the charging roller 22 in the rotational direction of the photosensitive drum 13, is rotatable in the direction of the arrow. The developing roller 24 as a developer carrying member and the charging roller 22 in the rotation direction of the photosensitive drum 13 are disposed on the downstream side of the photosensitive drum 13 and remain on the photosensitive drum 13 after the toner image is transferred. The toner C, that is, the first cleaning device 27 for removing residual toner, and the developing roller 24 are brought into contact with the housing C1. A developing blade 26 as a developer regulating member attached at a fixed location, and in contact with the developing roller 24 on the upstream side of the developing blade 26 in the rotational direction of the developing roller 24, is rotatably arranged in the direction of the arrow. The toner supply roller 25 as a developer supply member, and stirring members 29, 30 and the like disposed rotatably above the toner supply roller 25 in the housing C1. The developing roller 24, the toner supply roller 25, the developing blade 26, the stirring members 29 and 30 and the like constitute a developing device.

  The photosensitive drum 13 has an outer diameter of 30 [mm], and includes a conductive support and a photoconductive layer formed on the surface of the conductive support, and is driven by a drive motor (not shown) as a drive unit. Rotated. The conductive support is made of an aluminum metal pipe, and the photoconductive layer is made of an organic photoreceptor formed by laminating a charge generation layer and a charge transport layer.

  The charging roller 22 is composed of a metal shaft and a semiconductive rubber layer formed on the surface of the metal shaft, and the surface of the photosensitive drum 13 is made uniform by applying a charging voltage, that is, a charging bias. To charge.

The developing roller 24 has an outer diameter of 16 mm, and is composed of a metal shaft and a semiconductive member having an appropriate elasticity, such as a semiconductive urethane rubber material, formed on the surface of the metal shaft. By applying a developing voltage, that is, a developing bias, the toner T is attached to the photosensitive drum 13, the electrostatic latent image is developed, and a toner image is formed on the surface of the photosensitive drum 13. The developing roller 24 is brought into contact with the photosensitive drum 13 with a pressing force of 50 to 150 [g / cm ² ].

  The toner supply roller 25 has an outer diameter of 15.5 [mm] and is formed of a foamed elastic body such as silicone rubber or urethane rubber. A plurality of unillustrated cells including recesses are formed on the surface and supplied. The toner T supplied from the toner cartridge 28 is supplied to the developing roller 24 by applying a supply voltage, that is, a supply bias.

  In the present embodiment, the charging roller 22 has a negative polarity of −1000 [V], the developing roller 24 has a −200 [V], and the toner supply roller 25 has a negative polarity of −300 [V]. A voltage is applied.

  The developing blade 26 has a thickness of 0.08 [mm] and is formed such that the length in the longitudinal direction (the axial direction of the developing roller 24) matches the width of the semiconductive member of the developing roller 24. And a regulation voltage, that is, a regulation bias, is applied to regulate the amount of toner T supplied from the toner supply roller 25 to the development roller 24, thereby A toner layer as a developer layer having a certain thickness is formed on the surface.

  The first cleaning device 27 is disposed with its front end in contact with the photosensitive drum 13, and includes a cleaning blade 27a as a cleaning member for scraping off the residual toner, and a recovery toner (not shown) that is scraped off. A conveyance spiral 27b as a conveyance member to be conveyed to the unit is provided.

  The agitating members 29 and 30 agitate the toner T supplied from the toner cartridge 28 and stored in the housing C 1, and send it to the toner supply roller 25.

  The transfer unit u1 is stretched by a driving roller 15a as a first roller, a driven roller 15b as a second roller, a driving roller 15a and a driven roller 15b, and is moved in the direction of the arrow to thereby transfer the paper P An endless transfer belt 14 that conveys the toner, a transfer roller 12 that is rotatably disposed inside the transfer belt 14 so as to face the respective photosensitive drums 13 and transfers the toner images of the respective colors onto the paper P. And a second cleaning device 16 for removing the toner T adhering to the transfer belt 14. The second cleaning device 16 includes a cleaning blade 16 a as a cleaning member that is disposed with its tip in contact with the transfer belt 14 and scrapes off the toner T adhering to the transfer belt 14.

  The fixing device 17 is a heating roller R1 as a first fixing member that is rotatably arranged, and a second fixing member that is rotatably arranged in contact with the heating roller R1. A pressure roller R2 is provided, and a color toner image on the paper P is heated and pressed to form a color image on the paper P.

  The paper cassette 18 includes a feeding roller 19 which is rotatably disposed at the front end, feeds the paper P one by one, and supplies the paper P to the medium transport path Rt1.

  In the medium conveyance path Rt1, the conveyance roller 20 that conveys the sheet P fed from the sheet cassette 18 by the feeding roller 19, and the sheet P is temporarily stopped on the downstream side of the conveyance roller 20 in the medium conveyance path Rt1, A pair of registration rollers 21 for correcting the skew of the paper P, a pair of discharge rollers 31 for discharging the paper P on which a color image is formed outside the main body of the printer 10, that is, the apparatus main body at the downstream end of the medium conveyance path Rt 1. Is rotatably arranged.

  Reference numeral 33 denotes a stacker that is formed on the top surface of the housing Cs and for stacking the paper P discharged outside the apparatus main body.

  Next, the control device of the printer 10 will be described.

  FIG. 1 is a control block diagram of the printer in this embodiment.

  In the figure, 50 is connected to the printer 10 via a network Nt as a connection member, and is a host computer as a host device that transmits print data to the printer 10, and 51 is a main control unit that controls the entire printer 10. The printer control unit 52 is an exposure control unit that controls each LED head 23 (FIG. 3) and selectively emits each LED of the LED head 23.

  When the printer control unit 51 receives print data from the host computer 50, the printer control unit 51 edits the print data, converts it into image data, and sends it to the exposure control unit 52. The exposure control unit 52 selects each color based on the image data. Are generated and sent to each LED head 23.

Reference numeral 53 denotes an operation time after the printing operation is started in the printer 10, that is, a time measuring unit that measures the elapsed time Tp, and 54 measures the number of prints ε after the printing operation of the printer 10 is started. The number-of-printing-number measuring unit 55 performs the printing operation while measuring the number of dots (the number of light emitting dots) formed by causing each LED to emit light based on the dot data sent to the LED head 23 as a dot count. The dot count measuring unit 56 calculates a cumulative dot count ΣNd that is a cumulative value of the dot count since the start of the toner count, and the consumption of toner T based on the cumulative dot count ΣNd calculated by the dot count measuring unit 55 The amount of toner T is calculated, and the remaining amount of toner T in the process unit 11a, that is, toner -Toner remaining amount calculation unit as a developer remaining amount calculation unit for calculating the remaining amount γ, 57 is a memory as a storage unit for recording information such as various values and data, and 58 is the number of printed sheets ε. And the print duty cumulative value σ as the print density, which represents the cumulative value of the print duty δ from the start of the printing operation based on the cumulative dot count ΣNd.
σ = a · ΣNd / ε (a is a constant)
A print duty calculation unit 59 serving as a print density calculation unit for calculating the print density 59 calculates a print rate coefficient k1 as a first coefficient, which is a degree representing the ease with which the toner T adheres to the developing roller 24. The rate coefficient calculation unit 60 is connected to a voltage power source (not shown), and is applied to the charging roller 22, the LED head 23, the developing roller 24, the toner supply roller 25, and the developing blade 26 based on instructions from the printer control unit 51. A voltage control unit 61 for controlling each voltage, a difference voltage calculation unit 61 for calculating a difference voltage (bias difference) Δv between the development bias applied to the development roller 24 and the supply bias applied to the toner supply roller 25; A driver control unit 62 drives the drive motor based on an instruction from the printer control unit 51.

  In the present embodiment, the elapsed time Tp is measured by the time measuring unit 53, or the number of printed sheets is based on the drum counter disposed adjacent to the predetermined photosensitive drum 13 by the printed number measuring unit 54. In order to measure ε or to measure the number of dots as a dot count in the dot count measurement unit 55, a common counter is provided, and based on the count value of the common counter, the elapsed time Tp, printing The number ε and the dot count are measured.

  Next, the operation of the printer 10 will be described.

  In each of the image forming units 11Bk, 11Y, 11M, and 11C, when a charging bias is applied to the charging roller 22 by the voltage control unit 60, the surface of the photosensitive drum 13 is uniformly charged.

  When the driver controller 62 drives the drive motor based on an instruction from the printer controller 51, the photosensitive drum 13, the charging roller 22, the developing roller 24, the toner supply roller 25, and the like are rotated.

  When the charged portion on the surface of the photosensitive drum 13 reaches the position facing the LED head 23 as the photosensitive drum 13 rotates, the exposure control unit 52 sends the dot data to each LED head 23. And each LED is caused to emit light corresponding to the dot data. Along with this, light corresponding to the dot data is irradiated onto the photosensitive drum 13, and an electrostatic latent image is formed in the portion irradiated with the light on the surface of the photosensitive drum 13.

  Subsequently, when the photosensitive drum 13 is further rotated and the portion where the electrostatic latent image is formed reaches a position facing the developing roller 24, a developing bias is applied to the developing roller 24 by the voltage control unit 60, and A potential difference between the surface of the developing roller 24 and the surface of the photosensitive drum 13 is formed, and the toner T on the developing roller 24 is adhered to the surface of the photosensitive drum 13 by Coulomb force, frictional force, or the like. As a result, the electrostatic latent image is developed and a toner image of each color is formed on each photosensitive drum 13.

  At this time, a supply bias is applied to the toner supply roller 25 by the voltage controller 60, whereby a differential voltage Δv between the development roller 24 and the toner supply roller 25 is formed, and the development roller 24 and the toner supply roller 25 are Are rotated in the same direction at a constant peripheral speed ratio. As a result, the toner T is charged, and the charged toner T is supplied from the toner supply roller 25 to the developing roller 24.

  Further, a regulation bias is applied to the developing blade 26 by the voltage control unit 60, and a predetermined portion of the developing blade 26 is brought into contact with the developing roller 24, whereby a toner layer having a certain thickness is formed on the developing roller 24. Is done. As a result, the toner T on the developing roller 24 is further charged by the charge injection from the developing blade 26 and the friction with the developing blade 26.

  On the other hand, the paper P accommodated in the paper cassette 18 is fed out by the feed roller 19 and supplied to the medium transport path Rt1, transported by the transport roller 20, and after the skew feeding is corrected by the registration roller pair 21, each image is corrected. It is sent between the forming units 11Bk, 11Y, 11M, and 11C and the transfer unit u1, and is conveyed as the transfer belt 14 travels. When a voltage for transfer is applied to each LED head 23 by the voltage control unit 60 when the paper P passes between the photosensitive drums 13 and the transfer rollers 12, the toner images of the respective colors are transferred to the paper P. And a color toner image is formed on the paper P.

  As described above, the residual toner on each photosensitive drum 13 after the toner image of each color is transferred to the paper P is removed and collected by the first cleaning device 27. Further, the toner T adhering to the transfer belt 14 during the printing operation is removed by the second cleaning device 16.

  Subsequently, the paper P on which the color toner image is formed is conveyed to the fixing device 17 where it is heated by the heating roller R1 and pressed by the pressure roller R2. At this time, the toner constituting the toner image is melted by the heat of the heating roller R1, and the melted toner is pressed against the paper P by the pressure roller R2 and penetrates between the fibers of the paper P. As a result, a color toner image is fixed on the paper P, and a color image is formed on the paper P.

  The paper P on which the color image is formed is discharged out of the apparatus main body by the discharge roller pair 31 and is stacked on the stacker 33.

  By the way, when the toner layer on the developing roller 24 becomes thick as printing with a low print duty δ is continuously performed, a non-exposed area where the photosensitive drum 13 is not exposed (area where an electrostatic latent image is not formed). The toner T may adhere to the paper P and stains such as fog may occur on the paper P.

  Therefore, the amount of toner T adhering to the developing roller 24 when continuous printing was performed, that is, the amount of toner adhering, and the degree of contamination generated on the paper P were observed.

  FIG. 4 is a reference diagram showing a change in the amount of toner adhering to the developing roller when continuous printing is performed, and FIG. 5 is a reference diagram showing a change in the degree of dirt generated on the paper when continuous printing is performed. In FIG. 4, the horizontal axis represents the number of printed sheets ε, the vertical axis represents the toner adhesion amount, the horizontal axis represents the number of printed sheets ε, and the vertical axis represents the stain level Lv.

  In this case, continuous printing of 3000 sheets per day was performed. The number of printed sheets ε was measured by the drum counter.

The amount of toner adhering to the developing roller 24 is set such that a probe having an end face of 1 [cm ² ] at the tip is placed on the developing roller 24 with the developing roller 24 stopped every time a predetermined number of prints ε are printed. The toner T adhering to the developing roller 24 is sampled by applying a DC voltage of 300 [V] to the probe from a measuring power source, and the difference in the weight of the probe before and after sampling is measured. Measured and calculated based on the difference.

  Further, the level Lv of the stain generated on the paper P is determined by the color of the printing area (white background portion) of 1 [sheet] of paper P and the density of 10 levels on the white paper in advance every time a predetermined number of prints ε are printed. The color was calculated by visually comparing the color formed with the standard color.

  In FIG. 4, L1 is a line indicating the amount of toner adhering to the developing roller 24 when continuous printing is performed with the print duty δ being increased to 60%, and L2 is a print duty δ being decreased to 0 .3 [%] is a line indicating the amount of toner adhering to the developing roller 24 when continuous printing is performed.

In forming an image in a predetermined area (for example, 1 [sheet] of paper P), the number of dots formed by causing the LED to emit light in the predetermined area is Ny, and in the predetermined area The total number Nd of dots that can form an image in the predetermined area when the number of dots that are not emitted by the LED and are not formed is Nn.
Nd = Ny + Nn
And the printing duty δ is
δ = (Ny / Nd) × 100 [%]
Can be expressed as

As shown in the figure, when continuous printing is performed with a high printing duty δ, the amount of toner adhesion hardly changes even when the number of printed sheets ε increases, whereas continuous printing is performed with a low printing duty δ. In this case, the amount of toner adhesion increases as the number of printed sheets ε increases. That is, when the printing duty δ is lowered, the toner adhesion amount when the number of printed sheets ε is 0 [sheets] is 0.5 [mg / cm ² ], whereas the number of printed sheets ε is 1000 [sheets]. ], The toner adhesion amount gradually increases, and when the number of printed sheets ε reaches 3000 [sheets], the toner adhesion amount becomes 0.9 [mg / cm ² ].

  Further, when the toner adhesion amount increases, most of the toner T on the developing roller 24 is not used for developing the electrostatic latent image, but remains on the developing roller 24, and is caused by friction between the toner supply roller 25 and the developing blade 26. It continuously deteriorates due to external force and electrostatically aggregates. As a result, the toner layer on the developing roller 24 becomes thick, and the toner T on the developing roller 24 adheres to the non-exposed area on the photosensitive drum 13, thereby causing stain on the paper P.

  In FIG. 5, L3 is a line indicating the level Lv of the stain generated on the paper when the application duty δ is set to 0.3 [%], and in this case, the stain level Lv is 1 to 10 are represented by 10 levels, 1 represents that the dirt is the largest, and 10 represents the smallest dirt. When the dirt level Lv is 7 or less, it is out of the specification range of the printer 10, and there is a problem with the image quality. When the dirt level Lv is higher than 7, the specification range of the printer 10 is used. It is assumed that there is no problem in image quality.

  As shown in the figure, the stain level Lv is approximately 10 when the number of printed sheets ε is about 0 [sheets] to about 1000 [sheets], gradually decreases from about 1000 [sheets], and the number of printed sheets ε is 2500. The number of sheets is almost 8, and the number of printed sheets ε is 7 when the number is 3000 [sheets], which is out of the specification range of the printer 10.

  Next, the effect of the remaining amount of toner γ in the process unit 11a on the toner adhesion amount when the number of printed sheets ε increases as continuous printing is performed will be described.

  FIG. 6 is a diagram for explaining the influence of the remaining amount of toner in the process unit on the toner adhesion amount on the developing roller in the embodiment of the present invention. In the figure, the horizontal axis represents the number of printed sheets ε, and the vertical axis represents the toner adhesion amount.

  In this case, continuous printing of 3000 [sheets] was performed with an applied duty δ of 0.3 [%].

  In the figure, L4 is a line indicating the amount of toner adhering to the developing roller 24 when the remaining amount of toner γ in the process unit 11a is sufficiently large and the process unit 11a is in a toner full state, and L5 is a process unit 11a. This is a line indicating the amount of toner adhering to the developing roller 24 when the toner remaining amount γ is small and the process unit 11a is in a toner empty state.

  As shown in the figure, when the process unit 11a is in a toner empty state, the amount of toner attached to the developing roller 24 is greater with respect to the number of printed sheets ε than when the process unit 11a is in a toner full state. This is because when the process unit 11a is in a toner empty state, the process unit 11a is less likely to replace the new toner T with the deteriorated toner T, and the toner T is easily subjected to external force and is likely to deteriorate. This is because the deteriorated toner T increases and electrostatic aggregation tends to occur.

  As described above, when printing with a low printing duty δ is continuously performed, the amount of toner adhering to the developing roller 24 increases, and the paper P is likely to be smeared. The amount of toner T supplied from the toner supply roller 25 to the developing roller 24 is reduced by changing the differential voltage Δv according to the number of sheets ε and the print duty accumulated value σ.

  In addition, in the present embodiment, the amount of toner adhering to the developing roller 24 increases when the process unit 11a continuously performs printing in a toner empty state. By changing the difference voltage Δv, the amount of toner T supplied from the toner supply roller 25 to the developing roller 24 is reduced.

  Next, the operation of the control device of the printer 10 will be described.

  7 is a first flowchart showing the operation of the printer control apparatus according to the embodiment of the present invention, FIG. 8 is a second flowchart showing the operation of the printer control apparatus according to the embodiment of the present invention, and FIG. FIG. 10 is a diagram showing an example of a printing rate coefficient table according to the embodiment of the present invention, and FIG. 11 is a diagram according to the embodiment of the present invention. 7 is a diagram illustrating an example of a toner remaining coefficient table. FIG.

  When the printer 10 is turned on and print data of a predetermined print job is sent from the host computer 50 to the printer 10, the printer control unit 51 drives (turns on) the drive motor via the driver control unit 62 at timing t0. Then, the voltage control unit 60 controls the charging bias, the developing bias, and the supply bias in each of the image forming units 11Bk, 11Y, 11M, and 11C, and starts a print job printing operation with values set in advance.

  In this embodiment, the charging bias is a negative polarity voltage of −1000 [V] in the on state, is a voltage of 0 [V] in the off state, and the developing bias is in the on state. The positive polarity voltage is +100 [V] and the negative polarity voltage is −200 [V]. The voltage is 0 [V] in the off state, and the supply bias is −300 in the on state. [V] is a negative polarity voltage, and is 0 [V] in the off state.

  When the photosensitive drum 13, the charging roller 22, the developing roller 24, the toner supply roller 25, and the like are rotated as the drive motor is driven, the voltage control unit 60 causes the toner T on the developing roller 24 to be rotated. In order to prevent the toner from adhering to the photosensitive drum 13, a developing bias of +100 [V] is applied to the developing roller 24, and a charging bias of -1000 [V] is applied to the charging roller 22 at timing t1. The surface of the photosensitive drum 13 is uniformly charged.

  Subsequently, the exposure control unit 52 starts image formation for the print job, exposes the surface of the photosensitive drum 13 with the LED head 23, and forms an electrostatic latent image on the surface of the photosensitive drum 13. Then, the voltage control unit 60 applies a developing bias of 0 [V] to the developing roller 24 at timing t <b> 2, and then applies a developing bias of −200 [V] to the developing roller 24 at timing t <b> 3. Is applied with a supply bias of −300 [V], thereby forming a difference voltage Δv of 100 [V] in absolute value between the development bias and the supply bias. As a result, the toner supply roller 25 supplies the toner T to the developing roller 24, and a toner layer having a predetermined thickness is formed on the developing roller 24 by the developing blade 26.

  Thereafter, when the paper P passes between the photosensitive drums 13 and the transfer rollers 12, a voltage for transfer is applied to the LED heads 23 by the voltage control unit 60, and the toner images of the respective colors are superimposed on the paper P. Thus, a color toner image is formed on the paper P. Subsequently, when the color toner image is fixed on the paper P in the fixing device 17, the formation of the color image on the 1 [sheet] paper P is completed.

  In this way, an image is formed for the print job.

  By the way, when printing with a low print duty δ is continuously performed in the print job, as described above, the amount of toner adhering to the developing roller 24 increases, and the paper P is likely to be stained.

  Therefore, in the present embodiment, the printing operation for the print job is performed every time a predetermined time, in the present embodiment, 30 [minutes] elapses while the image is formed for the print job. In another process (parallel processing), the printing rate Px as an index for changing the differential voltage Δv is calculated, and when the image formation is completed, the differential voltage Δv is changed based on the printing rate Px. It has become so.

  For this reason, as shown in FIG. 9, when the section in which the printing operation is performed is set as the printing operation section τ, the image formation for the printing job is started at the timing t0 in the printing operation section τ. The drive motor, the charging bias, the developing bias, and the supply bias are turned off at the image forming section τ1 until the end of the image formation for the print job at the timing t4 and at the timing t5 after the image formation is completed at the timing t4. The non-image forming section τ2 until the printing operation is completed is set.

  In the image forming section τ1, an image is formed on each sheet P in a state where the difference voltage Δv is formed for the print job. During that time, the printer control unit 51 performs a printing rate by another process. Px is calculated and recorded in the memory 57.

  Subsequently, when the image formation for all the sheets P is completed for the print job, in the present embodiment, in the present embodiment, the voltage control unit 60 performs the difference in the non-image formation section τ2 at the timing t4 immediately after the image formation is completed. The voltage Δv is changed based on the printing rate Px.

  For this purpose, the printer control unit 51 reads the printing rate Px from the memory 57 and sends it to the printing rate coefficient calculation unit 59 at timing t4, and the printing rate coefficient for correcting the difference voltage Δv from the printing rate coefficient calculation unit 59. The coefficient k1 is read. For this purpose, when the printing rate Px is sent, the printing rate coefficient calculation unit 59 refers to the printing rate coefficient table shown in FIG. 10 formed in the memory 57, and each image forming unit 11Bk, 11Y, 11M, It is calculated by reading the printing rate coefficient k1 corresponding to the printing rate Px set for every 11C and sent to the printer control unit 51.

  The printing rate coefficient k1 is larger as the printing rate Px is lower, and is smaller as the printing rate Px is higher. In the present embodiment, when the printing rate Px is 1, the printing rate coefficient k1 is set to 1.0, and when the printing rate Px is 10, the printing rate coefficient k1 is set to 0.1.

  Subsequently, the printer control unit 51 reads the accumulated dot count ΣNd calculated by the dot count measurement unit 55 and sends it to the toner remaining amount calculation unit 56. The remaining toner amount calculation unit 56 calculates the consumption amount of the toner T based on the accumulated dot count ΣNd, calculates the remaining toner amount γ in the process unit 11a based on the consumption amount, and sends it to the printer control unit 51. send. The printer control unit 51 then reads the remaining toner amount γ and sends it to the voltage control unit 60.

  In the voltage controller 60, the differential voltage calculator 61 is set for each of the image forming units 11Bk, 11Y, 11M, and 11C with reference to the remaining toner coefficient table shown in FIG. Further, the calculation is performed by reading out the toner remaining amount coefficient k2 as the second coefficient corresponding to the toner remaining amount γ.

  Note that the remaining toner coefficient k2 increases as the remaining toner amount γ increases, and decreases as the remaining toner amount γ decreases. In the present embodiment, when the toner remaining amount γ is 100% to 70%, the toner remaining amount coefficient k2 is set to 1.0, and when the toner remaining amount γ is 10%, The toner remaining coefficient k2 is set to 0.5.

Then, the difference voltage calculation unit 61 calculates the difference voltage Δv ′ in the non-image forming section τ2 based on the difference voltage Δv, the printing rate coefficient k1, and the remaining toner coefficient k2.
Δv ′ = Δv · k1 · k2
Is calculated. In this case, the difference voltage Δv ′ is Δv ≧ Δv ′ ≧ 0 [V].
To be.

  The printing rate coefficient k1 is a correction coefficient for correcting the difference voltage Δv according to the number of printed sheets ε and the print duty cumulative value σ, and the toner remaining amount coefficient k2 is a difference voltage according to the remaining toner amount γ. This is a correction coefficient for correcting Δv.

  Subsequently, the differential voltage calculation unit 61 changes the differential voltage Δv to Δv ′, and resets the elapsed time Tp, the number of printed sheets ε, and the print duty accumulated value σ.

Therefore,
Δv ≧ Δv ′ ≧ 0 [V]
In this range, the larger the number of printed sheets ε and the lower the print duty cumulative value σ, the smaller the difference voltage Δv ′ and the smaller the amount of toner adhering to the developing roller 24. On the other hand, the smaller the number of printed sheets ε and the higher the print duty cumulative value σ, the larger the difference voltage Δv ′ and the larger the amount of toner adhering to the developing roller 24.

  Further, the smaller the remaining amount of toner γ, the smaller the difference voltage Δv ′ becomes, and the smaller the amount of toner adhering to the developing roller 24 becomes. The larger the remaining amount of toner γ, the larger the difference voltage Δv ′ becomes. The amount of adhesion increases.

  In this way, the differential voltage Δv is changed to Δv ′ in the non-image forming period τ2, and the printing operation is ended at the timing t5.

  Thereafter, when print data is sent from the host computer 50 to the printer 10 for another print job, a print operation is started, and the print rate Px is calculated while an image is being formed for the print job, and at timing t4. The difference voltage Δv is changed to the difference voltage Δv ′ based on the printing rate Px.

  Note that the non-image forming section τ2 is a section for changing the differential voltage Δv while the image is not formed. Therefore, in this embodiment, the non-image forming section τ2 is on the last photosensitive drum 13 of the print job. The time point when the toner image is transferred to the paper P is set to the timing t4 when the image formation is completed, but the image formation is completed when the toner image transferred onto the last paper P is fixed. It can also be set to timing t4.

  The timing t5 is set to be after the developing roller 24 has rotated at least one rotation after the toner image on the photosensitive drum 13 at the end of the print job is transferred to the paper P. The roller 24 is rotated at a difference voltage Δv by at least one rotation.

  Next, the operation of the printer control unit 51 for calculating the printing rate Px while an image is being formed for a print job will be described. Note that the process of calculating the printing rate Px is performed in parallel by a process different from the process of forming an image for a print job.

  First, when the printer 10 is turned on, the printer control unit 51 sends an instruction to the time measurement unit 53, starts time measurement by the time measurement unit 53, and sends an instruction to the print number measurement unit 54 to perform printing. Measurement of the number of printed sheets ε by the number measuring unit 54 is started. The time measurement unit 53 sends the elapsed time Tp since the start of measurement to the printer control unit 51, and the print number measurement unit 54 sends the print number ε after the start of measurement to the printer control unit 51.

  Then, the printer control unit 51 reads the elapsed time Tp from the time measurement unit 53, waits for the elapsed time Tp to become a predetermined time, which is 30 [minutes] or more in this embodiment, and the elapsed time Tp. Is 30 [minutes] or more, the number of printed sheets [epsilon] is read, and it is determined whether the number of printed sheets [epsilon] is a predetermined number, in this embodiment, 200 [sheets] or more.

When the number of printed sheets ε is 200 [sheets] or more, the printer control unit 51 reads the print duty accumulated value σ from the print duty calculating unit 58, and the print duty accumulated value σ is a predetermined value. It is judged whether it is 20 [%] or less. When the print duty cumulative value σ is 20% or less, the printer control unit 51 increases (increments) the print rate Px, which is an index indicating the frequency of continuous printing with a low print duty δ,
Px ← Px + 1
To.

  That is, the printing rate Px is increased by +1 when printing of 200 [sheets] or more is performed with a print duty cumulative value σ of 20 [%] or less.

  Then, the printer control unit 51 determines whether or not the printing rate Px is greater than 10, and when the printing rate Px is greater than 10, sets the printing rate Px to 10.

In addition, when the number of printed sheets ε is less than 200 [sheets], and when the print duty cumulative value σ is higher than 20 [%] even when the number of printed sheets ε is 200 [sheets] or more, the printer controller 51 sets the printing rate Px. Decrease (decrement),
Px ← Px-1
To.

  In other words, the print rate Px is set so that the print duty cumulative value σ is 20 [%] even when 200 [sheets] or more is not printed or 200 [sheets] or more is printed. If it is higher, it is reduced by +1.

  Then, the printer control unit 51 determines whether the printing rate Px is 0 or less. If the printing rate Px is 0 or less, the printer control unit 51 sets the printing rate Px to 0. Therefore, the printing rate Px takes a value from 0 to 10.

  As described above, the printer control unit 51 performs printing with a print duty accumulation value σ of whether or not 200 [sheets] or more are printed and 20 [%] or less every 30 [minutes]. The print rate Px is updated according to the number of printed sheets ε and the print duty accumulated value σ and recorded in the memory 57.

  Subsequently, the printer control unit 51 determines whether or not the printer 10 is turned off. If the printer 10 is turned off, the process is terminated. If the printer 10 is not turned off, the common counter is reset, Start measurement. When the common counter is reset, the count value becomes 0, and the elapsed time Tp, the number of printed sheets ε, and the dot count are all reset to 0.

  In this case, as printing is repeated, the printing rate Px increases as the number of prints ε at the elapsed time Tp increases, and as the print duty cumulative value σ decreases, and as the number of prints ε in each print job decreases. Further, the higher the print duty accumulated value σ, the lower the print rate Px.

  In the present embodiment, the voltage control unit 60 changes the supply bias voltage from −300 [V] to a supply bias having a small absolute value corresponding to the difference voltage Δv ′ at the timing t4, and in the non-image forming section τ2. Then, a supply bias is applied to the toner supply roller 25. In the non-image forming section τ2, the voltage controller 60 applies a charging bias of −1000 [V] to the charging roller 22 as in the image forming section τ1, and applies to the developing roller 24 as in the image forming section τ1. A charging bias of 200 [V] is applied. That is, the difference voltage Δv ′ is calculated so that the absolute value is smaller than 100 [V] of the difference voltage Δv.

  Incidentally, the difference voltage Δv ′ is a parameter for controlling the thickness of the toner layer on the developing roller 24. If the difference voltage Δv ′ is too large in absolute value, the thickness of the toner layer on the developing roller 24 is decreased. The paper P becomes excessively large, and the paper P is likely to be stained. On the other hand, when the difference voltage Δv ′ approaches 0 [V], the thickness of the toner layer on the developing roller 24 decreases, fading to the paper P, and an afterimage or the like is likely to occur.

  Therefore, in the present embodiment, the thickness of the toner layer on the developing roller 24 is set to an appropriate value by reducing the difference voltage Δv ′ in absolute value only in the non-image forming period τ2.

  Therefore, it is possible to prevent the paper P from being stained, and to prevent the paper P from being blurred and causing an afterimage or the like.

  The difference voltage Δva between the charging bias and the developing bias is also a parameter for controlling the contamination of the paper P, and the appropriate difference voltage Δva is 800 [V] in absolute value, but the charging bias is in absolute value. When the difference voltage Δva is made smaller than 800 [V] in absolute value, the surface potential of the photosensitive drum 13 becomes low, and the toner T on the developing roller 24 adheres to the non-exposed area on the surface of the photosensitive drum 13. As a result, the paper P becomes dirty.

  On the other hand, when the charging bias is increased in absolute value and the difference voltage Δva is greater than 800 [V] in absolute value, the surface potential of the photosensitive drum 13 is increased, and when the difference voltage Δva is decreased in absolute value, Since the charge on the surface of the photosensitive drum 13 charges the toner T on the developing roller 24 and increases the charge amount of the toner T on the developing roller 24, the paper P is soiled.

  Therefore, in the present embodiment, as described above, in the non-image forming section τ2, the charging bias of −1000 [V], which is the same as that in the image forming section τ1, is applied to the charging roller 22.

  Further, a developing bias of −200 [V], which is the same as the image forming section τ1, is applied to the developing roller 24. In this case, the developing bias is a parameter that determines the density of the image, and does not contribute to the occurrence of smearing on the paper P. Therefore, the developing bias is set to the same value in the image forming section τ1 and the non-image forming section τ2.

  Next, the influence of the remaining toner amount γ in the process unit 11a on the difference voltage Δv ′ will be described.

  FIG. 12 is an image diagram of the differential voltage in the embodiment of the present invention. In the figure, the horizontal axis represents the number of printed sheets ε, and the vertical axis represents the absolute value of the differential voltage Δv ′.

  In this case, the differential voltage Δv ′ when 3000 [sheets] was printed with the applied duty δ being 0.3 [%] was calculated.

  In the figure, L6 is a line indicating the absolute value of the difference voltage Δv ′ when the process unit 11a is in the toner full state, and L7 is the absolute value of the difference voltage Δv ′ when the process unit 11a is in the toner empty state. It is a line which shows.

  As shown in the figure, when the process unit 11a is in a toner empty state, the slope of the difference voltage Δv ′ is larger than when the process unit 11a is in a toner full state, and the process unit 11a is in a toner empty state. In some cases, when the difference voltage Δv ′ when the number of printed sheets ε is 0 [sheets] is V0 [V], when the number of printed sheets ε is 2000 [sheets], the difference voltage Δv ′ becomes V0 / 2 [V]. Become. It can be seen that the absolute value of the differential voltage Δv ′ decreases as the number of printed sheets ε increases.

  Further, when the process unit 11a is in a toner empty state, as shown in FIG. 6, as the number of printed sheets ε increases, the toner adhesion amount to the developing roller 24 gradually increases. By increasing the absolute value of the differential voltage Δv ′ by the amount of toner adhesion to the toner 24, it is possible to suppress the toner adhesion to the developing roller 24 from increasing.

  Note that if the absolute value of the differential voltage Δv ′ is set larger than an appropriate value with respect to the increase in the toner adhesion amount on the developing roller 24, it is not possible to suppress the toner adhesion amount from increasing. The paper P is smudged. On the other hand, when the absolute value of the differential voltage Δv ′ is set smaller than an appropriate value with respect to the increase in the toner adhesion amount on the developing roller 24, the toner adhesion amount is excessively suppressed. When the toner image is formed on the surface of the photosensitive drum 13, the thickness of the toner layer on the developing roller 24 cannot be optimized, and the paper P is faded, and an afterimage or the like is formed.

  Since it is desirable to make the toner adhesion amount to the developing roller 24 constant in the image forming section τ1 and the non-image forming section τ2, the difference voltage Δv ′ in the non-image forming section τ2 is the developing roller in the image forming section τ1. The absolute value is reduced by the amount of toner adhesion to 24.

Next, the flowchart of FIG. 7 will be described.
Step S 1 Print data is sent from the host computer 50 to the printer 10.
Step S2: The printer control unit 51 starts a printing operation.
Step S3 The printer control unit 51 waits for completion of image formation. When the image formation is completed, the process proceeds to step S4.
Step S4: The printer controller 51 reads the printing rate Px.
Step S5: The remaining toner amount calculation unit 56 calculates the remaining toner amount γ.
Step S6: The differential voltage calculation unit 61 calculates the differential voltage Δv ′ in the non-image forming section τ2.
Step S7: The differential voltage calculation unit 61 changes the differential voltage Δv.
Step S8: The differential voltage calculation unit 61 resets the elapsed time Tp, the number of printed sheets ε, and the print duty accumulated value σ, and ends the process.

Next, the flowchart of FIG. 8 will be described.
Step T1 The printer 10 is turned on.
Step T2 The time measuring unit 53 starts measuring time.
Step T3 The printed sheet number measuring unit 54 starts measuring the number of printed sheets ε. Step T4 The printer control unit 51 waits for the elapsed time Tp to be 30 minutes or more. When the elapsed time Tp becomes 30 [minutes] or more, the process proceeds to step T5.
Step T5: The printer control unit 51 determines whether the number of printed sheets ε is 200 [sheets] or more. If the number of printed sheets ε is 200 [sheets] or more, the process proceeds to step T6. If the number of printed sheets ε is less than 200 [sheets], the process proceeds to step T13.
Step T6 The printer controller 51 determines whether or not the print duty accumulated value σ is 20% or less. If the print duty accumulated value σ is 20% or less, the process proceeds to step T7, and if the print duty accumulated value σ is greater than 20%, the process proceeds to step T13.
Step T7 The printer control unit 51 increments the printing rate Px.
Step T8 The printer controller 51 determines whether the printing rate Px is greater than 10. If the printing rate Px is greater than 10, the process proceeds to step T9. If the printing rate Px is 10 or less, the process proceeds to step T10.
Step T9 The printer control unit 51 sets the printing rate Px to 10.
Step T10 The printer control unit 51 records the printing rate Px in the memory 57.
Step T11 The printer control unit 51 determines whether or not the printer 10 is turned off. If the printer 10 is turned off, the process ends. If the printer 10 is not turned off, the process proceeds to step T12.
Step T12 The printer control unit 51 resets the common counter and returns to Step T2.
Step T13 The printer control unit 51 decrements the printing rate Px.
Step T14 The printer controller 51 determines whether or not the printing rate Px is 0 or less. If the printing rate Px is 0 or less, the process proceeds to step T15. If the printing rate Px is greater than 0, the process proceeds to step T10.
Step T15 The printer control unit 51 sets the printing rate Px to 0 and proceeds to step T10.

  As described above, in the present embodiment, when the difference voltage calculation unit 61 finishes forming an image for a predetermined print job, the difference voltage Δv between the development bias and the supply bias is set to the number of printed sheets ε and the number of prints. Since the duty is changed according to the cumulative duty value σ and the remaining toner amount γ, it is possible to suppress an increase in the amount of toner attached to the developing roller 24.

  Therefore, even if printing with a low printing duty δ is continuously performed, the toner layer on the developing roller 24 is not thickened, and the toner T is prevented from adhering to the non-exposed area on the surface of the photosensitive drum 13. Can do.

  As a result, it is possible to prevent the paper P from being stained and to prevent the image quality from deteriorating.

  Further, since the printing rate Px is calculated according to the number of printed sheets ε and the print duty accumulated value σ and the printing rate Px is updated every time a print job is performed, the difference voltage Δv can be changed stepwise. Accordingly, since the toner layer on the developing roller 24 can be prevented from suddenly becoming thicker or thinner, the image quality can be stabilized.

  Next, the amount of toner adhering to the developing roller 24 and the degree of stain generated on the paper P when continuous printing is performed in the embodiment of the present invention will be described.

  FIG. 13 is a diagram showing a change in the toner adhesion amount to the developing roller when continuous printing is performed in the embodiment of the present invention, and FIG. 14 is generated on a sheet when continuous printing is performed in the embodiment of the present invention. It is a figure which shows the change of the degree of the stain | pollution | contamination performed. In FIG. 13, the horizontal axis represents the number of printed sheets ε, the vertical axis represents the toner adhesion amount, the horizontal axis represents the number of printed sheets ε, and the vertical axis represents the dirt level Lv.

  In this case, continuous printing of 3000 sheets per day was performed.

  In FIG. 13, L11 is a line indicating the amount of toner adhering to the developing roller 24 when continuous printing is performed in the present invention, and L12 is a conventional technique in which the print duty δ is increased to 60%. L13, a line indicating the amount of toner adhering to the developing roller 24 when continuous printing is performed, is obtained when continuous printing is performed with the print duty δ reduced to 0.3% in the conventional technique. 4 is a line showing the amount of toner attached to the developing roller 24;

  As shown in the figure, in the conventional technique, when continuous printing is performed with a low printing duty δ, the toner adhesion amount increases as the number of printed sheets ε increases. Regardless of the printing duty δ, the toner adhesion amount hardly changes even when the number of printed sheets ε increases.

  In FIG. 14, L14 is a line indicating the stain level Lv when continuous printing is performed in the present invention, and L15 is continuous printing with an applied duty δ of 0.3% in the prior art. It is a line which shows the level Lv of dirt when it is performed.

  As shown in the figure, in the conventional technique, the level Lv of the stain decreases as the number of printed sheets ε increases. In contrast, in the present invention, the level of stains increases even when the number of printed sheets ε increases. The level Lv hardly changes.

  In the present embodiment, voltage values such as charging bias, developing bias, supply bias, and regulation bias, elapsed time Tp, number of printed sheets ε, set values such as cumulative average printing duty, printing rate coefficient k1, and toner remaining coefficient k2 Are set to predetermined values. However, since the optimum value differs depending on the printer 10, the voltage value, the set value, the parameter, etc. can be changed for each printer.

  In the present embodiment, the image forming units 11Bk, 11Y, 11M, and 11C include the process unit 11a and the toner cartridge 28. Therefore, the remaining amount of toner T in the process unit 11a is set as the remaining toner amount γ. In the image forming unit in which the process unit 11a and the toner storage unit are integrated, the remaining amount of toner in the image forming unit is defined as a remaining toner amount γ.

  Furthermore, in this embodiment, a printer is described. However, the present invention can be applied to an image forming apparatus such as a copying machine, a facsimile machine, and a multifunction machine.

  In addition, this invention is not limited to the said embodiment, It can change variously based on the meaning of this invention, and does not exclude them from the scope of the present invention.

DESCRIPTION OF SYMBOLS 10 Printer 13 Photosensitive drum 22 Charging roller 23 LED head 24 Developing roller 25 Toner supply roller 54 Print number measurement part 56 Dot count measurement part 58 Print duty calculation part 60 Voltage control part γ Toner remaining quantity ε Print sheets number Δv, Δv ′ Difference Voltage σ Print duty cumulative value

Claims (13)

(A) an image carrier;
(B) a charging member for charging the surface of the image carrier;
(C) an exposure device that exposes the image carrier to form a latent image on the surface of the image carrier;
(D) a developer carrier that develops the latent image and forms a developer image on the surface of the image carrier;
(E) a developer supply member for supplying a developer to the developer carrying member;
(F) a print number measurement unit for measuring the number of prints;
(G) a developer remaining amount calculating unit for calculating the remaining amount of developer;
(H) a print density calculation unit for calculating the print density;
(I) having a voltage controller for applying a voltage to the developer carrier and the developer supply member;
(J) The voltage control unit calculates a difference voltage between a voltage applied to the developer carrier and a voltage applied to the developer supply member when image formation for a predetermined print job is completed. An image forming apparatus that is changed according to the number of printed sheets, a printing density, and a remaining amount of developer.   The image forming apparatus according to claim 1, wherein the voltage control unit decreases the difference voltage as the number of printed sheets increases.   The image forming apparatus according to claim 1, wherein the voltage control unit decreases the difference voltage as the printing density is lower.   The image forming apparatus according to claim 1, wherein the voltage control unit decreases the difference voltage as the remaining amount of the developer is smaller. When the difference voltage when an image is formed for a predetermined print job is Δv and the changed difference voltage is Δv ′,
Δv ≧ Δv ′ ≧ 0
The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 1, wherein the voltage control unit calculates the difference voltage based on an index that changes according to the number of printed sheets and a printing density.   The image forming apparatus according to claim 6, wherein the voltage control unit corrects a differential voltage when an image is formed for a predetermined print job by a first coefficient set based on the index. .   The image forming apparatus according to claim 7, wherein the first coefficient is decreased as the number of printed sheets increases.   The image forming apparatus according to claim 7, wherein the first coefficient is made smaller as the printing density is lower.   The voltage controller corrects a difference voltage when an image is formed for a predetermined print job by a second coefficient set based on the remaining amount of the developer. The image forming apparatus according to any one of the above.   The image forming apparatus according to claim 10, wherein the second coefficient is made smaller as the remaining amount of developer is smaller.   The image forming apparatus according to claim 1, wherein the voltage control unit changes the differential voltage immediately after the image formation is completed.   12. The image forming apparatus according to claim 1, wherein the voltage control unit changes the differential voltage after image formation is completed and the developer carrying member rotates at least once or more.

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