JP2017134273A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a variation in image density before and after a new developer is supplied to a developing device and a reduction in image quality.SOLUTION: An image forming apparatus comprises: image carriers; developer carriers; a developing voltage control part 62 that controls a developing voltage; a transfer device that includes a belt member and transfers developer images formed on the image carriers to a medium; and a printing control part 50 that, when a developer is supplied to the developing device 17, forms an image of a density detection pattern on the belt member, detects a pattern image density of the density detection pattern, and adjusts the developing voltage according to the detected pattern image density. Since the developing voltage is adjusted according to the pattern image density, the charging state of the developer can be stabilized.SELECTED DRAWING: Figure 1

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 copying machine, a facsimile machine, or a multifunction machine, for example, a printer, includes an image forming unit, an LED head, a transfer roller, a fixing device, and the like. Further, a developing device and the like are 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, the electrostatic latent image is developed by a developing device, and a toner image is formed. It is formed. The toner image is transferred onto a sheet by a transfer roller and fixed on the sheet by a fixing device, and 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. Toner as a developer in the image forming unit is supplied to the developing roller by the toner supplying roller, and the developing blade has a certain thickness on the developing roller. A toner layer is formed, and the toner of the toner layer is attached to the electrostatic latent image and development is performed to form a toner image.

  By the way, of the toner on the developing roller, the toner that is not used for development remains on the developing roller and deteriorates due to friction while repeatedly contacting the toner supply roller, the developing blade, and the like. The deteriorated toner has less charge control agent present on the surface, and the polarity of charging due to friction tends to change.

  Therefore, when new toner is supplied to the developing device in the presence of deteriorated toner, the charged state of the toner becomes unstable, and the deteriorated toner is opposite to the normal polarity due to friction with the new toner. May be charged to polarity.

  As a result, the density of the image formed on the paper, that is, the density of the image fluctuates, or the toner charged to the opposite polarity adheres to the portion other than the electrostatic latent image on the photosensitive drum, and the background is formed on the paper. Dirt is generated and image quality is deteriorated.

  Therefore, the charging state of the toner is increased by increasing at least one of the frequency component and the amplitude of the AC component of the developing voltage applied to the developing roller until a predetermined period elapses after the developing device is replenished with new toner. There is provided a printer that stabilizes (see, for example, Patent Document 1).

JP 2001-75341 A

  However, in the conventional printer, as the AC component of the developing voltage applied to the developing roller changes, the image density may fluctuate before and after new toner is supplied to the developing device. In this case, the image quality is degraded.

  The present invention solves the problems of the conventional printer, and the image density does not fluctuate before and after a new developer is supplied to the developing device, and the image quality can be prevented from deteriorating. An object is to provide a forming apparatus.

  Therefore, in the image forming apparatus of the present invention, an image carrier for carrying a latent image and a developing device are disposed in contact with the image carrier, carry a developer, and A developer carrying member that forms a developer image on the image carrying member by developing; a developing voltage control unit that controls a developing voltage applied to the developer carrying member; and a belt member that is movably disposed. And a transfer device that transfers the developer image formed on the image carrier to a medium as the belt member travels, and the developer is replenished with the developer at a predetermined timing. And a print control unit that forms an image of a density detection pattern on the belt member, detects the pattern image density of the density detection pattern, and adjusts the development voltage in accordance with the detected pattern image density.

  According to the present invention, in the image forming apparatus, an image carrier for carrying a latent image, and in the developing device, the image carrier is disposed in contact with the image carrier, carrying the developer, and A developer carrying member that forms a developer image on the image carrying member by developing; a developing voltage control unit that controls a developing voltage applied to the developer carrying member; and a belt member that is movably disposed. And a transfer device that transfers the developer image formed on the image carrier to a medium as the belt member travels, and the developer is replenished with the developer at a predetermined timing. And a print control unit that forms an image of a density detection pattern on the belt member, detects the pattern image density of the density detection pattern, and adjusts the development voltage in accordance with the detected pattern image density.

  In this case, when a new developer is supplied to the developing device, an image of the density detection pattern is formed on the belt member at a predetermined timing, the pattern image density of the density detection pattern is detected, and the detected pattern image density is obtained. Since the developing voltage is adjusted accordingly, the charged state of the developer can be stabilized even if a deteriorated developer and a new developer are mixed. Therefore, the deteriorated developer is not charged to a polarity opposite to the normal polarity due to friction with the new developer.

  As a result, the image density of the image formed on the medium may fluctuate, or the developer charged to the opposite polarity may adhere to a portion other than the latent image on the image carrier to cause background staining on the medium. Therefore, it is possible to prevent the image quality from deteriorating.

  Further, since the development voltage is adjusted according to the pattern image density of the density detection pattern, the image density does not fluctuate before and after the new developer is supplied.

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. It is a figure which shows the example of the density | concentration detection pattern in embodiment of this invention. It is a figure which shows transition of the pattern image density | concentration of the development voltage and a density | concentration detection pattern in the conventional printer and the printer of this invention. It is a figure for demonstrating the method to determine the image quality of the image in embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In this case, an electrophotographic color 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, reference numeral 10 denotes a printer, and Cs denotes a housing of the printer 10. In the printer 10, image forming units 11Y, 11M, 11C, and 11Bk of yellow, magenta, cyan, and black colors are the main body of the printer 10, That is, it is detachably disposed on the apparatus main body. Then, LED heads 15Y, 15M, 15C, and 15Bk as exposure apparatuses are disposed corresponding to the image forming units 11Y, 11M, 11C, and 11Bk. Since the image forming units 11Y, 11M, 11C, and 11Bk have the same structure, only members of the image forming unit 11Y will be described in detail with reference to the drawings.

  Further, 31 is rotatably disposed in the image forming units 11Y, 11M, 11C, and 11Bk, and a photosensitive drum as an image carrier for carrying an electrostatic latent image as a latent image, and u0 is an image forming unit. A transfer unit as a transfer device disposed below the units 11Y, 11M, 11C, and 11Bk. The transfer unit u0 is a developer image of each color under the image forming units 11Y, 11M, 11C, and 11Bk. The toner image is formed on the intermediate transfer belt 24 and the first transfer unit u1 for primary transfer for sequentially superimposing and transferring the toner image on an endless intermediate transfer belt 24 as a belt member to form a color toner image. The second transfer unit u2 for secondary transfer for transferring the color toner image onto the paper P as a medium.

  The first transfer unit u1 includes a driving roller R1 as a first roller for primary transfer, a driven roller R2 as a second roller for primary transfer, and a tension roller 82 as a third roller for primary transfer. The intermediate transfer belt 24 stretched by the drive roller R1, the driven roller R2 and the tension roller 82 and run in the direction of the arrow, and the primary transfer for facing the photosensitive drum 31 via the intermediate transfer belt 24. The transfer roller 25 is provided as a transfer member. A primary transfer portion is formed between each photosensitive drum 31 and the transfer roller 25.

  The second transfer unit u2 is a secondary transfer unit that is rotatably disposed so as to face the tension roller 82 via the tension roller 82 as a secondary transfer roller and the intermediate transfer belt 24. For example, a transfer roller 27 as a transfer member. A secondary transfer portion is formed between the tension roller 82 and the transfer roller 27.

  Between the tension roller 82 and the driven roller R2 in the running direction of the intermediate transfer belt 24, a density sensor 39 (spectral densitometer X-Rite 500 series) is disposed as a density detector. The density sensor 39 includes an LED (not shown) as a light emitting unit and two light receiving photodiodes (not shown) as a light receiving unit, and each photodiode can receive specular reflection light and diffuse reflection light. It is arranged.

  Under the casing Cs, a paper cassette 20 serving as a medium accommodating portion for storing the paper P is disposed, and a hopping roller 21 serving as a feeding member is disposed at the front end of the paper cassette 20, and the hopping roller 21 , The sheets P in the sheet cassette 20 are separated one by one and fed out to the medium transport path Rt.

  In the medium transport path Rt, a transport roller unit 22 for transporting the fed paper P, and a paper position detection sensor 23 as a medium position detection unit that detects the front end of the paper P on the downstream side of the transport roller unit 22. The secondary transfer unit for transferring the toner image onto the paper P is disposed downstream of the paper position detection sensor 23.

  Further, a fixing device 14 as a fixing device is disposed on the downstream side of the secondary transfer portion in the medium transport path Rt. The fixing device 14 includes a heating roller 14a as a first fixing member and a pressure roller 14b as a second fixing member, and heats and presses the color toner image on the paper P to thereby change the paper. Fix to P to form a color image.

  A discharge roller pair 28 is disposed in the vicinity of the discharge port of the printer 10 on the downstream side of the fixing device 14 in the medium conveyance path Rt, and the paper P on which a color image is formed by the discharge roller pair 28 is provided in the apparatus. It is discharged out of the main unit.

  The image forming unit 11Y is rotatably disposed in contact with the photosensitive drum 31, which is rotated in the direction of an arrow by a drum motor 45 (FIG. 1) as a driving unit described later. A charging roller 32 serving as a charging device for uniformly charging the photosensitive drum 31 by applying a predetermined voltage, that is, a charging voltage under the control of a charging voltage control unit 65 (FIG. 1) described later, the photosensitive drum 31, is rotatably disposed in contact with the toner 31, carries toner as a developer, and the toner adheres to the electrostatic latent image formed when the LED head 15 </ b> Y exposes the photosensitive drum 31. A developing roller 33 as a developer carrying member for developing a latent image, a toner tank 34 as a developer container for storing toner, and the developing roller 33 are in contact with the developing roller 33 and are rotatable. A toner supply roller 35 as a developer supply member for supplying the toner supplied from the toner tank 34 to the developing roller 33, and a predetermined portion in the vicinity of the tip thereof is disposed in pressure contact with the developing roller 33; A developing blade 36 as a developer regulating member that regulates a toner layer as a developer layer on the developing roller 33, and a toner remaining on the photosensitive drum 31 after the transfer of the toner image, that is, a residual toner is scraped off. A cleaning blade 37 or the like is provided as a first cleaning member to be removed by taking.

  The LED heads 15Y, 15M, 15C, and 15Bk selectively expose light to the surface of the photosensitive drum 31 based on the print data to form an electrostatic latent image.

  Reference numeral 50 denotes a print controller, and 62 denotes a voltage applied to the developing roller 33, that is, a developing voltage controller that controls the developing voltage.

  The toner used in the present embodiment is composed of a polyester resin, a colorant, a charge control agent, and a release agent. Hydrophobic silica is added as an external additive, formed by a pulverization method, and an average particle size of 8 [ μm].

  The developing roller 33 includes a metal shaft and an elastic body that covers the outer periphery of the shaft. As the elastic body, urethane rubber having semiconductivity with a rubber hardness of 70 ° (Asker C) is used.

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

  FIG. 1 is a control block diagram of a printer according to an embodiment of the present invention.

  The printer 10 includes a print control unit 50, an interface unit 51, an operation input unit 52, a memory 53 as a storage device, a CPU 54 as a main control unit and an arithmetic device, various sensors 55 as various detection elements, The density sensor 39, the process control unit 61, the development voltage control unit 62, the voltage applied to the toner supply roller 35, that is, the supply voltage control unit 63 that controls the supply voltage, and the voltage applied to the development blade 36, that is, the layer A layer forming voltage control unit 64 that controls the forming voltage, a voltage applied to the charging roller 32, that is, a charging voltage control unit 65 that controls the charging voltage, a motor control unit 66 that controls the drum motor 45, LED heads 15Y and 15M, An exposure control unit 67 for controlling 15C and 15Bk is provided.

  The developing device 17 is constituted by the developing roller 33, the toner supply roller 35, the developing blade 36, and the like.

  The interface unit 51 receives print data and a control command (control command) from the host computer 40 as an information input unit and as a host device.

  The print control unit 50 controls the printing operation of the printer 10 based on print data and control commands received via the interface unit 51.

  The operation input unit 52 includes an operation unit including operation buttons that are operation elements for an operator to input various instructions, and a display unit including a display.

  The memory 53 includes a ROM 41 as a first recording unit and a RAM 42 as a second recording unit. The ROM 41 has a control program (software) and control data for controlling and processing the operation of the entire printer 10. Etc. are recorded, and various information generated as the control program is executed is temporarily recorded in the RAM 42. In the present embodiment, a rewritable flash ROM is used as the ROM 41.

  The CPU 54 controls and processes the operation of the entire printer 10 based on a control program recorded in the ROM 41.

  The various sensors 55 include the paper position detection sensor 23 (FIG. 2) and the like, and detect the paper P.

  The process control unit 61 controls the image forming process of the image forming units 11Y, 11M, 11C, and 11Bk, and the print control unit 50 includes a development voltage control unit 62, a supply voltage control unit 63, and a layer formation voltage control unit. 64, the charging voltage control unit 65, the motor control unit 66, the exposure control unit 67, and the like are controlled to apply a voltage to each of the charging roller 32, the developing roller 33, the toner supply roller 35, the transfer roller 25, and the developing blade 36. It is applied, the drum motor 45 is driven, and the LED heads 15Y, 15M, 15C, 15Bk are driven.

  The development voltage control unit 62 controls the development voltage applied to the development roller 33, the supply voltage control unit 63 controls the supply voltage applied to the toner supply roller 35, and the layer formation voltage control unit 64 develops. The layer forming voltage applied to the blade 36 is controlled, and the charging voltage controller 65 controls the charging voltage applied to the charging roller 32.

  The motor controller 66 controls the drum motor 45 to rotate the photosensitive drum 31 (FIG. 2). A gear (not shown) serving as a rotation transmission element for transmitting the drive of the drum motor 45 is disposed at one end of the photosensitive drum 31, the developing roller 33, and the toner supply roller 35. The gear of the roller 35 is engaged with the gear of the photosensitive drum 31, and the rotation of the photosensitive drum 31 is transmitted to the developing roller 33 and the toner supply roller 35 via the gear, whereby the developing roller 33 and the toner supply roller 35 are transmitted. Is rotated.

  The exposure control unit 67 controls the exposure of the LED heads 15Y, 15M, 15C, and 15Bk according to the print data.

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

  When the print control unit 50 receives print data from the host computer 40, the print control unit 50 sends an instruction to the motor control unit 66, drives the drum motor 45, and rotates the photosensitive drum 31 in the direction of the arrow. Accordingly, the charging roller 32, the developing roller 33, the toner supply roller 35, and the like are rotated.

  Further, the print control unit 50 sends an instruction to the charging voltage control unit 65 and applies a charging voltage to the charging roller 32 to uniformly charge the surface of the photosensitive drum 31. Subsequently, the print control unit 50 sends an instruction to the exposure control unit 67, causes each LED of the LED heads 15Y, 15M, 15C, and 15Bk to emit light according to the print data, exposes the surface of the photosensitive drum 31, and An electrostatic latent image is formed.

  Then, the print control unit 50 sends an instruction to the supply voltage control unit 63 to apply the supply voltage to the toner supply roller 35. As a result, the toner in the toner tank 34 is supplied to the developing roller 33 by the toner supply roller 35. The toner supplied to the developing roller 33 is thinned by the developing blade 36.

  When the portion where the electrostatic latent image is formed on the photosensitive drum 31 reaches a position facing the developing roller 33, the print control unit 50 sends an instruction to the developing voltage control unit 62, and the developing voltage is supplied to the developing roller 33. Apply. As a result, the toner on the developing roller 33 is attached to the photosensitive drum 31, the electrostatic latent image is developed, and a toner image is formed on each photosensitive drum 31.

  The toner images on the respective photosensitive drums 31 are sequentially transferred onto the intermediate transfer belt 24 by the transfer roller 25 in the primary transfer portion. Residual toner on the photosensitive drum 31 is removed by the cleaning blade 37.

  Then, the paper P stored in the paper cassette 20 is separated one by one by the hopping roller 21 and sent to the medium transport path Rt, and sent to the secondary transfer unit by the transport roller unit 22. In the secondary transfer portion, the color toner image on the intermediate transfer belt 24 is transferred onto the paper P by the transfer roller 27.

  The paper P on which the color toner image has been transferred is sent to the fixing device 14, where the toner image is heated by the heating roller 14 a and pressurized by the pressure roller 14 b to be fixed on the paper P. And a color image is formed.

  The paper P on which the color image is formed is discharged out of the apparatus main body by the discharge roller pair 28.

  By the way, of the toner on the developing roller 33, toner that is not used for development remains on the developing roller 33 and deteriorates due to friction while repeatedly contacting the toner supply roller 35, the developing blade 36, and the like. The deteriorated toner has less charge control agent present on the surface, and the polarity of charging due to friction tends to change.

  Then, when new toner is supplied from the toner tank 34 (FIG. 2) to the developing device 17 in a state where the deteriorated toner exists, the charged state of the toner becomes unstable, and the deteriorated toner is replaced with the new toner. Friction may cause the battery to be charged to a polarity opposite to the normal polarity. In that case, the image density of the image formed on the paper P fluctuates, or the toner charged with the opposite polarity adheres to the portion other than the electrostatic latent image on the photosensitive drum 31 and the background stains on the paper P. Or the image quality deteriorates.

  Therefore, in the present embodiment, in the image forming unit in which new toner is supplied to the developing device 17, a toner image of a corresponding color is formed in a predetermined pattern and transferred to the intermediate transfer belt 24 at a predetermined timing. Thus, an image of the density detection pattern is formed, the density of the image, that is, the pattern image density is detected, and the developing voltage applied to the developing roller 33 is adjusted based on the detection result.

  Next, the operation of the printer 10 when new toner is supplied to the developing device 17 will be described.

  FIG. 4 is a diagram showing an example of the density detection pattern in the embodiment of the present invention.

  When printing is performed in the printer 10 and a color image is formed, any one of the image forming units 11Y, 11M, 11C, and 11Bk (FIG. 2), for example, cyan image formation is performed. In the unit 11C, when the toner in the developing device 17 is low and new toner is supplied from the toner tank 34 to the developing device 17, the print control unit 50 (FIG. 1) counts the number of rotations of the photosensitive drum 31. When the count value of a drum counter (not shown) is reset and the number of rotations of the photosensitive drum 31 is counted by the drum counter in the subsequent printing, the count value is set to the photosensitive member after new toner is supplied to the developing device 17. Read as the number of revolutions of the drum 31.

  Then, after the new toner is replenished to the developing device 17, the print control unit 50 sets the predetermined number of timings, in this embodiment, the rotational speed of the photosensitive drum 31 to a preset density correction rotational speed. 10, 600, and 1200, a cyan toner image is formed using only the cyan image forming unit 11 </ b> C in which new toner is supplied to the developing device 17, and transferred to the intermediate transfer belt 24. To form an image of a cyan density detection pattern. For example, as shown in FIG. 4, the density detection pattern image is formed as a solid image with an area ratio of 100 [%] in an area of 30 [mm] × 90 [mm].

  Subsequently, in the cyan image forming unit 11C, the print control unit 50 detects the pattern image density of the density detection pattern formed on the intermediate transfer belt 24 by the density sensor 39, and develops according to the detected pattern image density. An instruction is sent to the voltage control unit 62 to adjust the developing voltage applied to the developing roller 33 so that the pattern image density of the density detection pattern is higher than the pattern image density when new toner is supplied to the developing device 17. To do.

  For this purpose, a table created in advance in correspondence with the pattern image density detected by the density sensor 39 and the developing voltage applied to the developing roller 33 is generated in the ROM 41. The print control unit 50 reads the pattern image density detected by the density sensor 39, refers to the table, reads the development voltage corresponding to the pattern image density, and applies the development voltage to the development roller 33.

  Further, the print control unit 50 sends an instruction to the motor control unit 66 so that the linear speed of the photosensitive drum 31 indicating the printing speed in the printer 10 (the sheet P is transferred to the secondary transfer unit while an image is being formed on the sheet P). The sheet passing speed) is 86 [mm / s] or less.

  The developing voltage applied to the developing roller 33 is set to a constant value, in this embodiment, −120 [V] until new toner is supplied to the developing device 17, and new toner is supplied to the developing device 17. Then, the density is adjusted according to the pattern image density of the density detection pattern formed on the intermediate transfer belt 24. Thereafter, the developing voltage is the same until the rotational speed of the photosensitive drum 31 becomes the next density correction rotational speed and the pattern image density of the density detection pattern newly formed on the intermediate transfer belt 24 is detected by the density sensor 39. Valued.

  The charging voltage applied to the charging roller 32 is set to −900 [V] and the supply voltage applied to the toner supply roller 35 is set to −200 [V] before and after the new toner is supplied to the developing device 17. The

  In the first transfer unit u1 (FIG. 2), in the present embodiment, downstream of the density sensor 39 in the traveling direction of the intermediate transfer belt 24 and upstream of the driven roller R2. A cleaning blade (not shown) serving as a second cleaning member is disposed opposite the intermediate transfer belt 24, and the density detection pattern formed on the intermediate transfer belt 24 after the image density is detected by the cleaning blade. The image (toner image) is scraped off and removed.

  By the way, when new toner is supplied to the developing device 17, even if there is no deteriorated toner in the developing device 17, if the linear velocity of the photosensitive drum 31 is low, the old toner and the new toner are evenly distributed. It takes time for the toner charge amount and image density to stabilize after stirring. Therefore, in this embodiment, as described above, when new toner is supplied to the developing device 17, the linear velocity of the photosensitive drum 31 is set to 86 [mm / s] or less.

  Next, in the conventional printer, the pattern image density of the density detection pattern detected by setting the developing voltage in the cyan image forming unit 11C to a constant value, and the pattern image density of the density detection pattern in the printer 10 of the present invention. The pattern image density of the density detection pattern detected by adjusting the development voltage will be described.

  FIG. 5 is a graph showing changes in the pattern image density of the development voltage and the density detection pattern in the conventional printer and the printer of the present invention.

  In the conventional printer, when new toner is supplied to the developing device 17 of the cyan image forming unit 11C, that is, when the rotational speed of the photosensitive drum 31 is 0, the pattern image density is 1.40. When the rotational speed of the photosensitive drum 31 reaches 10, the pattern image density becomes 1.30, and then the rotational speed of the photosensitive drum 31 reaches 200, 400, 600, 800, 1000, 1200. The pattern image density was 1.31, 1.35, 1.37, 1.37, 1.37, 1.42. During this time, the development voltage was set to -120 [V] without being changed.

  On the other hand, in the printer 10 of the present invention, the pattern image density when the rotational speed of the photosensitive drum 31 is 0 is 1.40, and the pattern image density when the rotational speed of the photosensitive drum 31 is 10. Is 1.37 and the pattern image density is low, so the development voltage is adjusted from -120 [V] to -180 [V]. As a result, the pattern image density when the rotational speed of the photosensitive drum 31 reached 200 was increased to 1.41.

  In the printer 10 of the present invention, if the developing voltage of −180 [V] is continuously applied, the pattern image density when the rotational speed of the photosensitive drum 31 reaches 400 becomes 1.45, which is excessive. It became high. Therefore, when the rotational speed of the photosensitive drum 31 reached 600, the developing voltage was adjusted from -180 [V] to -150 [V], and thereby the pattern image density became 1.42. Thereafter, the developing voltage when the rotational speed of the photosensitive drum 31 reached 800 was kept at −150 [V], and the pattern image density was 1.45, which was excessively high. Therefore, when the rotational speed of the photosensitive drum 31 is 1200, the developing voltage is set to −120 [V], and the pattern image density is 1.42.

  As described above, in the conventional printer, the developing voltage applied to the developing roller 33 is set to a constant value. Therefore, when new toner is supplied to the developing device 17, deteriorated toner and new toner are mixed. As a result, the charge amount of the toner fluctuates and the charged state becomes unstable. In the printer 10 of the present invention, after the new toner is supplied to the developing device 17, the rotational speed of the photosensitive drum 31 is increased. At 10, 600, and 1200, the development voltage is adjusted according to the detected pattern image density of the density detection pattern, so that the pattern image density can be stabilized and the charged state of the toner can be stabilized.

  Next, a method for determining the image quality when a cyan image is formed on the paper P with the development voltage adjusted will be described.

  FIG. 6 is a diagram for explaining a method of determining the image quality of an image according to the embodiment of the present invention.

  In this case, the linear velocity of the photosensitive drum 31 (FIG. 2) is set to 86 [mm / s], and A4 standard paper (Excellent White Paper manufactured by Oki Data) is used as the paper P. Then, printing was performed on the printable range 80 of the paper P with a print duty of 5% or less, and it was visually determined whether or not the background stain on the paper P occurred. The print duty represents the area ratio of an image when the area ratio when solid printing is performed is 100 [%].

  Thus, in this embodiment, when new toner is supplied to the developing device 17, an image of the density detection pattern is formed on the intermediate transfer belt 24 at a predetermined timing, and the pattern image density of the density detection pattern is Since the developing voltage is detected by the density sensor 39 and adjusted according to the pattern image density, the charged state of the toner is unstable even when new toner is supplied to the developing device 17 in the presence of deteriorated toner. Thus, the deteriorated toner is not charged to a polarity opposite to the normal polarity due to friction with the new toner.

  As a result, the image density does not fluctuate, and the toner charged to the opposite polarity does not adhere to a portion other than the electrostatic latent image on the photosensitive drum 31 to cause background stain on the paper P. Therefore, it is possible to prevent the image quality from deteriorating.

  In particular, in the present embodiment, the linear velocity of the photosensitive drum 31 when printing is performed is 86 [mm / s] or less, and the printable range 80 of the paper P is 5 [%] or less. When printing is performed with a duty (that is, when the average printing duty of an image formed until the rotational speed of the photosensitive drum 31 is 0 to 10 which is the density correction rotational speed is 5% or less. When the average print duty of an image formed until the rotational speed of the photosensitive drum 31 reaches 0, which is 600, which is the density correction rotational speed, is 5% or less, and the rotational speed of the photosensitive drum 31 is The development voltage is adjusted in accordance with the pattern image density when the average print duty of the image formed from 0 to the density correction rotational speed of 1200 is 5% or less. ing

  This is because, when the linear speed of the photosensitive drum 31 is low or the printing duty is low, the toner is uniformly stirred after the developing device 17 is replenished with new toner, so that the toner charge amount and image density are reduced. This is because it takes time to stabilize, and the effect of adjusting the development voltage becomes more remarkable.

  In this embodiment, when the linear velocity of the photosensitive drum 31 is 86 [mm / s] or less and printing is performed with a print duty of 5 [%] or less, the development voltage is reduced. Although the adjustment is performed, the development voltage can be adjusted regardless of the linear velocity of the photosensitive drum 31 and the printing duty. Further, when the linear velocity of the photosensitive drum 31 is 86 [mm / s] or less, the development voltage is adjusted regardless of the printing duty, or printing is performed with a printing duty of 5 [%] or less. In this case, the development voltage can be adjusted regardless of the linear velocity of the photosensitive drum 31.

  In the present embodiment, since the development voltage is adjusted according to the pattern image density, the image density does not fluctuate before and after new toner is supplied to the developing device 17.

  In the present embodiment, a toner image formed on each photosensitive drum 31 is transferred to the intermediate transfer belt 24 to form a color toner image, and the color toner image formed on the intermediate transfer belt 24 is transferred to the paper P However, the present invention can be applied to a printer in which the toner image formed on each photosensitive drum 31 is directly transferred to the paper P. In this case, a transfer belt for conveying the paper P is provided as a belt member, and an image of the density detection pattern is formed on the transfer belt.

  In the above embodiment, the printer 10 has been described. However, the present invention can be applied to an image forming apparatus such as a copying machine, a facsimile machine, or 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 17 Developing device 24 Intermediate transfer belt 31 Photosensitive drum 33 Developing roller 50 Print control unit 62 Development voltage control unit P Paper u0 Transfer unit

Claims (9)

(A) an image carrier for carrying a latent image;
(B) a developer carrier disposed in contact with the image carrier in the developing device, carrying a developer, and developing a latent image to form a developer image on the image carrier;
(C) a development voltage controller for controlling a development voltage applied to the developer carrying member;
(D) a transfer device that includes a belt member that is movably disposed, and that transfers the developer image formed on the image carrier to a medium as the belt member travels;
(E) When the developer is supplied to the developing device, an image of a density detection pattern is formed on the belt member at a predetermined timing, the pattern image density of the density detection pattern is detected, and the detected pattern image density And a print control unit that adjusts the development voltage in accordance with the image forming apparatus.   The print control unit forms an image of the density detection pattern at a plurality of timings when the developer is supplied to the developing device, detects the pattern image density of the density detection pattern, and adjusts the development voltage. Item 2. The image forming apparatus according to Item 1.   The image forming apparatus according to claim 1, wherein the print control unit adjusts the developing voltage so that a pattern image density of the density detection pattern is higher than a value when the developer is supplied to the developing apparatus.   The image forming apparatus according to claim 1, wherein the developer image formed on the image carrier is transferred to the medium after being transferred to the belt member.   The image forming apparatus according to claim 1, wherein the developer image formed on the image carrier is transferred to a medium conveyed by the belt member.   The image forming apparatus according to claim 1, wherein a linear velocity of the image carrier is set to 86 mm / s or less.   The image processing apparatus according to claim 1, wherein the predetermined timing is a timing at which a rotational speed of the image carrier becomes a preset density correction rotational speed.   The image processing apparatus according to claim 7, wherein the print control unit adjusts the development voltage when a printing speed until the rotation speed of the image carrier reaches a density correction rotation speed is 86 mm / s or less. .   The image processing apparatus according to claim 7, wherein the printing control unit adjusts the developing voltage when a printing duty until the rotation speed of the image carrier reaches a density correction rotation speed is 5% or less.

Images