Image forming apparatus

Abstract

To provide an image forming apparatus that can efficiently execute maintenance.SOLUTION: According to an embodiment, an image forming apparatus has a plurality of photoreceptors, an exposure unit, developing units, and a processor. The exposure unit irradiates the surfaces of the plurality of photoreceptors with rays of light according to images formed on the plurality of photoreceptors. The developing units supply toner to the surfaces of the plurality of photoreceptors on which electrostatic latent images are formed by the irradiation of the rays of light from the exposure unit. The processor adjusts, for each of the photoreceptors, a contrast potential for supplying the toner from the developing units to the electrostatic latent images formed on the surfaces of the plurality of photoreceptors, and when a contrast potential having a difference from the other contrast potentials exceeding a reference value is present, notifies a warning.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] FIELD An embodiment of the present invention relates to an image forming apparatus. [Background technology]

[0002] Conventionally, maintenance of image forming apparatuses such as digital multifunction peripherals is performed by a serviceman who visits the installation site. For such image forming apparatuses, it is desirable that a serviceman visit at an appropriate time to perform maintenance efficiently.

[0003] On the other hand, electrophotographic image forming apparatuses form color images using developers containing toners of multiple colors (e.g., yellow, magenta, cyan, and black). Electrophotographic image forming apparatuses adjust the contrast potential for developing electrostatic latent images with toners of each color for each color so as to equalize the density (toner density) of the image for each color. In an image forming apparatus, if the developers for each color have roughly the same charging characteristics, the difference in contrast potential between the colors is unlikely to be large when the toner density of each color is equalized. In other words, in an electrophotographic image forming apparatus, if the difference in contrast potential is large, some kind of malfunction is often occurring.

[0004] However, conventional image forming devices cannot detect the possibility of a malfunction or abnormality based on the difference in contrast potential between the colors, and therefore cannot promote efficient maintenance by reporting the malfunction or abnormality suggested by the difference in contrast potential between the colors. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-204219 Summary of the Invention [Problem to be solved by the invention]

[0006] The problem to be solved by the present invention is to provide an image forming apparatus that allows efficient maintenance. [Means for solving the problem]

[0007] According to an embodiment, an image forming apparatus includes a plurality of photoconductors, an exposure unit, a developer, and a processor. The exposure unit irradiates the surfaces of the plurality of photoconductors with light corresponding to an image to be formed on each of the plurality of photoconductors. The developer supplies toner to the surfaces of the plurality of photoconductors on which electrostatic latent images are formed by the light irradiated by the exposure unit. The processor adjusts, for each photoconductor, a contrast potential for supplying toner from the developer to the electrostatic latent images formed on the surfaces of the plurality of photoconductors, and issues a warning when a contrast potential whose difference from other contrast potentials exceeds a reference value. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an example of the configuration of a digital multifunction peripheral as an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a diagram showing an example of the configuration of a printer in a digital multifunction peripheral as an image forming apparatus according to an embodiment. [Figure 3] FIG. 3 is a block diagram showing an example of the configuration of a control system in a digital multifunction peripheral as an image forming apparatus according to an embodiment. [Figure 4] FIG. 4 is a flowchart for explaining an example of an operation of adjusting image density in a digital multifunction peripheral as an image forming apparatus according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, this embodiment will be described with reference to the drawings. First, the configuration of a digital multi-functional peripheral (MFP) 1 as an image forming apparatus according to the embodiment will be described. FIG. 1 is a block diagram showing an example of the configuration of a digital multifunction peripheral 1 as an image forming apparatus according to an embodiment. As shown in FIG. 1, the digital multifunction peripheral 1 includes a printer 2, an operation panel 3, a scanner 4, a system controller 5, and the like.

[0010] The printer 2 is an image forming device that forms an image on a recording medium. The printer 2 included in the digital multifunction peripheral 1 is an image forming device that forms an image on a recording medium by electrophotography. The printer 2 forms an image (toner image) on a recording medium such as paper using toner. The recording medium on which the printer 2 forms an image may be any medium on which an image can be formed, and is not limited to paper, and may also be cloth, plastic film, sheet, or the like.

[0011] The scanner 4 is installed on the top of the main body of the digital multifunction peripheral 1. The scanner 4 is a device that optically reads an image of an original. For example, the scanner 4 reads an image of an original placed on a platen glass. The scanner 4 may also be configured to include a device that reads an image of an original conveyed by an automatic document feeder (ADF).

[0012] The operation panel 3 is a user interface. The operation panel 3 has a display unit (display), a touch panel, operation buttons, etc. The operation panel 3 displays operation guides and the like on the display unit. The operation panel 3 accepts operation instructions from the user via the touch panel and operation buttons, etc. For example, the operation panel 3 has a touch panel on the display screen of the display unit, and detects the area on the display screen of the display unit that the user touches.

[0013] The system controller 5 controls the entire digital multifunction peripheral 1. The system controller 5 receives operation instructions input to the operation panel 3 and controls the operation of each unit. The system controller 5 also receives operation instructions from external devices connected via an interface and controls the operation of each unit. For example, when an instruction to form an image on a recording medium is received, the system controller 5 controls the printer 2 to cause the printer 2 to form an image on the recording medium.

[0014] The configuration of the printer 2 will be described below. As shown in FIG. 1, the printer 2 includes a medium supply mechanism 13, a conveying mechanism 15, multiple image forming stations SY, SM, SC, and SK, an intermediate transfer belt 21, a secondary transfer roller 22, a support roller 23, a toner adhesion sensor 24, a transfer belt cleaner 25, and a fixing unit 26.

[0015] The medium supply mechanism 13 has multiple paper feed cassettes 321, 322, and 323. Any number of paper feed cassettes may be used. Each paper feed cassette 321, 322, and 323 stores paper as recording media M. The paper as recording media M stored in each paper feed cassette may be of different sizes or types. Pickup rollers 341, 342, and 343 are disposed in each paper feed cassette 321, 322, and 323, respectively. The pickup rollers 341, 342, and 343 pick up sheets of paper as recording media one by one from the paper feed cassettes 321, 322, and 323, respectively. The pickup rollers 341, 342, and 343 supply the picked-up recording media M to the transport mechanism 15.

[0016] The conveying mechanism 15 conveys the recording medium M. The conveying mechanism 15 has first conveying rollers 521, 522, and 523, a second conveying roller 54, and a registration roller 56 in a conveying path before an image is formed on the recording medium M. The conveying mechanism 15 conveys the recording medium M supplied by the pickup rollers 341, 342, and 343 from the first conveying rollers 521, 522, and 523 to the second conveying roller 54. In the conveying mechanism 15, the second conveying roller 54 further conveys the recording medium M to the registration roller 56.

[0017] Registration rollers 56 of the transport mechanism 15 transport the recording medium M to a secondary transfer position, which will be described later, in accordance with the timing at which an image is transferred from the intermediate transfer belt 21 to the recording medium M at the secondary transfer position. The transport mechanism 15 configures a transport path so as to transport the recording medium M, onto which the image has been transferred from the intermediate transfer belt 21, to the fixing device 26. The transport mechanism 15 further includes a third transport roller 58 for discharging the paper to a paper discharge section, and a transport mechanism for transporting the recording medium M to an inversion section that inverts the recording medium M.

[0018] Each of the image forming stations SY, SM, SC, and SK forms an image using toner. In this embodiment, the image forming station SY forms a yellow image. The image forming station SM forms a magenta image. The image forming station SC forms a cyan image. The image forming station SK forms a black image. Each of the image forming stations SY, SM, SC, and SK transfers the image formed using toner onto the intermediate transfer belt 21.

[0019] The intermediate transfer belt 21 is a medium that holds the images transferred by each of the image forming stations SY, SM, SC, and SK. The intermediate transfer belt 21 is an endless belt as shown in FIG. 1. The intermediate transfer belt 21 moves in the direction indicated by the arrow a in FIG. 1. The intermediate transfer belt 21 moves the images transferred by each of the image forming stations SY, SM, SC, and SK to a position where the secondary transfer roller 22 and the support roller 23 face each other.

[0020] The secondary transfer roller 22 and the support roller 23 constitute a transfer section (secondary transfer section) that transfers an image from the intermediate transfer belt 21 to the recording medium. The position where the secondary transfer roller 22 and the support roller 23 face each other is the secondary transfer position where an image is transferred from the intermediate transfer belt 21 to the recording medium. The secondary transfer roller 22 and the support roller 23 sandwich the intermediate transfer belt 21 and the recording medium at the secondary transfer position.

[0021] The support roller 23 supports the intermediate transfer belt 21. The support roller 23 is a drive roller that drives the intermediate transfer belt 21. The secondary transfer roller 22 faces the support roller 23 across the intermediate transfer belt 21. The secondary transfer roller 22 transfers (secondary transfer) an image formed with toner on the transfer surface of the intermediate transfer belt 21 onto the surface of a recording medium.

[0022] The toner adhesion amount sensor 24 is a sensor that detects the amount (density) of toner. The toner adhesion amount sensor 24 detects the amount of toner adhesion on the intermediate transfer belt 21. The toner adhesion amount sensor 24 is disposed facing the transfer surface of the intermediate transfer belt 21. The toner adhesion amount sensor 24 is provided between the image transfer position (primary transfer position) by each image forming station and the secondary transfer position in the movement direction a of the intermediate transfer belt 21. The toner adhesion amount sensor 24 outputs the detected amount of toner adhesion to the system controller 5.

[0023] 1, the transfer belt cleaner 25 is disposed between the secondary transfer position and the primary transfer position in the movement direction a of the intermediate transfer belt 21. The transfer belt cleaner 25 removes toner from the intermediate transfer belt 21. For example, the transfer belt cleaner 25 removes toner remaining on the transfer surface of the intermediate transfer belt 21 after an image is transferred from the intermediate transfer belt 21 to a recording medium.

[0024] The fixing device 26 fixes the image formed with the toner transferred to the recording medium onto the recording medium. The fixing device 26 is disposed on the transport path of the recording medium after it has passed the secondary transfer position. The fixing device 26 has a pressure roller and a heating roller that face each other. The fixing device 26 applies heat and pressure to the recording medium by transporting the recording medium between the opposing heating roller and pressure roller. The fixing device 26 fixes the toner image transferred to the recording medium by applying heat under pressure.

[0025] Next, the configuration of each of the image forming stations SY, SM, SC, and SK in the printer 2 as the image forming apparatus according to the embodiment will be described in detail. FIG. 2 is a diagram showing an example of the configuration of each of the image forming stations SY, SM, SC, and SK in the printer 2. 2, each of the image forming stations SY, SM, SC, and SK includes an exposure unit 100, a developing unit 110, a photosensitive drum 122, a charger 126, a primary transfer roller 128, a photosensitive cleaner 130, and a static eliminator 132. In this embodiment, each of the image forming stations SY, SM, SC, and SK has the configuration shown in FIG.

[0026] The photosensitive drum 122 is an image carrier having a photosensitive layer 124 on its surface. The photosensitive drum 122 rotates in a direction (indicated by arrow b in FIG. 2) that matches the movement of the intermediate transfer belt 21 in the moving direction a. Around the photosensitive drum 122, a charger 126, an exposure unit 100, a developing unit 110, a primary transfer roller 128, the intermediate transfer belt 21, a photosensitive cleaner 130, and a static eliminator 132 are arranged.

[0027] The charger 126 uniformly charges the photosensitive layer 124 on the surface of the photosensitive drum 122. The charger 126 uniformly charges the photosensitive layer 124 on the surface of the photosensitive drum 122 to a negative polarity, for example.

[0028] The exposure unit 100 forms an electrostatic pattern (electrostatic latent image) corresponding to an image on the surface of the photosensitive drum 122. The exposure unit 100 irradiates the surface of the photosensitive drum 122 with light L, the emission of which is controlled based on image data. For example, the exposure unit 100 irradiates the surface of the photosensitive drum 122 with light L, which is emitted based on the image data, via an optical system such as a polygon mirror. The exposure unit 100 may be configured to include a device that emits multiple laser beams that are guided to the photosensitive drums 122 of multiple image forming stations. Alternatively, the exposure unit 100 may be a light emitting device provided for each of the multiple image forming stations.

[0029] The developing unit 110 develops the electrostatic latent image formed on the surface of the photoconductor drum 122 with developer. The developing unit 110 supplies developer D to the surface of the photoconductor drum 122 exposed by the exposure unit 100. The developing unit 110 of each image forming station develops an image in its corresponding color. For example, the developing unit 110 of the image forming station SY develops the electrostatic latent image on the photoconductor drum 122 with yellow toner. The developing unit 110 of the image forming station SM develops the electrostatic latent image on the photoconductor drum 122 with magenta toner. The developing unit 110 of the image forming station SC develops the electrostatic latent image on the photoconductor drum 122 with cyan toner. The developing unit 110 of the image forming station SK develops the electrostatic latent image on the photoconductor drum 122 with black toner.

[0030] In the configuration example shown in FIG. 2, the developing device 110 has a developer container 112, a developing roller 114, a first mixer 116, a second mixer 118, and a toner concentration sensor 120. The developer container 112 is a container that contains developer D. The developer D is a mixture of toner and a carrier made of magnetic fine particles. When the developer D is stirred, the toner becomes frictionally charged. As a result, the toner adheres to the surface of the carrier by electrostatic force. Inside the developer container 112, a developing roller 114, a first mixer 116, a second mixer 118, and a toner concentration sensor are arranged.

[0031] The toner concentration sensor 120 is disposed inside the developer container 112. The toner concentration sensor 120 detects the toner concentration in the developer D contained in the developer container 112. The toner concentration is expressed, for example, as the ratio of toner to carrier (toner / carrier) of the developer D contained in the developer container 112. The system controller 5 controls the toner concentration detected by the toner concentration sensor 120 to a predetermined value.

[0032] The developing roller 114 has a magnetic material (e.g., a magnet) in which positive and negative poles are alternately arranged along a circumference. The developing roller 114 rotates counterclockwise. The first mixer 116 and the second mixer 118 agitate the developer D in the developer container 112. The first mixer 116 and the second mixer 118 also transport the developer D. The second mixer 118, which is disposed below the developing roller 114, supplies the developer D to the surface of the developing roller 114.

[0033] Developer D adheres to the surface of the developing roller 114 in the form of spikes in accordance with the magnetic field distribution generated by the magnetic material of the developing roller 114. The developing roller 114 rotates while carrying the developer D. The layer of developer D adhering to the developing roller 114 is limited to a predetermined thickness by a blade provided so as to maintain a predetermined distance from the surface of the developing roller 114. The developer D carried by the developing roller 114, limited to a predetermined thickness by the blade, moves to a position (developing position) facing the surface of the photosensitive drum 122.

[0034] A developing bias is applied to the developing roller 114 that carries the developer D. The potential of the surface of the developing roller 114 is controlled by the developing bias. The toner in the developer D carried by the developing roller 114 adheres to the electrostatic latent image due to the potential difference between the potential of the surface of the developing roller 114 and the potential of the electrostatic latent image formed on the surface of the photosensitive drum 122. As the developing roller 114 rotates in a predetermined direction, the developer D carried by the developing roller 114 approaches the surface of the photosensitive drum 122 on which the electrostatic latent image is formed. When the toner contained in the developer D carried by the developing roller 114 approaches the surface of the photosensitive drum 122, it develops the electrostatic latent image on the photosensitive drum 122. As a result, a toner image obtained by developing the electrostatic latent image with toner is formed on the photosensitive drum 122.

[0035] Here, the potential difference between the potential of the surface of the developing roller 114 and the potential of the electrostatic latent image formed on the surface of the photosensitive drum 122 is referred to as the contrast voltage. The contrast voltage is related to the density of toner that moves from the developing roller 114 to the electrostatic latent image on the photosensitive drum 122. In other words, the density of the toner image formed on the photosensitive drum 122 is adjusted by controlling the contrast voltage. The contrast voltage is adjusted by controlling the developing bias. Alternatively, the contrast voltage may be adjusted by controlling the potential of the electrostatic latent image.

[0036] An image (toner image) developed with toner on the surface of the photosensitive drum 122 moves to a position corresponding to the primary transfer roller 128 as the photosensitive drum 122 rotates. The primary transfer roller 128 faces the photosensitive drum 122 with the intermediate transfer belt 21 sandwiched between them. The primary transfer roller 128 abuts against the surface of the photosensitive drum 122 with the intermediate transfer belt 21 sandwiched between them. The primary transfer roller 128 transfers the toner image on the surface of the photosensitive drum 122 to the intermediate transfer belt 21 (primary transfer).

[0037] The photosensitive drum cleaner 130 is disposed downstream, in the circumferential direction of the photosensitive drum 122, of the position where the toner image on the surface of the photosensitive drum 122 is transferred onto the intermediate transfer belt 21. The photosensitive drum cleaner 130 removes toner from the surface of the photosensitive drum 122. That is, the photosensitive drum cleaner 130 removes toner remaining on the surface of the photosensitive drum 122 after the primary transfer of the toner image from the photosensitive drum 122 to the intermediate transfer belt 21 has been performed.

[0038] The static eliminator 132 is disposed downstream of the photosensitive drum cleaner 130 in the circumferential direction of the photosensitive drum 122. The static eliminator 132 irradiates the surface of the photosensitive drum 122 with light. As a result, the static eliminator 132 removes any charge remaining on the photosensitive layer 124 on the surface of the photosensitive drum 122.

[0039] Next, the configuration of a control system in the digital multifunction peripheral 1 as the image forming apparatus according to the embodiment will be described. FIG. 3 is a block diagram showing an example of the configuration of a control system in a digital multifunction peripheral 1 as an image forming apparatus according to an embodiment. 3, the system controller 5 includes a processor 101, a ROM 102, a RAM 103, a storage device 104, and a communication interface (I / F) 105. The processor 101 of the system controller 5 is connected to each unit in the digital multifunction peripheral 1 via various interfaces.

[0040] The processor 101 executes programs to perform various processes. The processor 101 is, for example, a CPU. The processor 101 is connected to a ROM 102, a RAM 103, a storage device 104, a communication interface (I / F) 105, and the like. The processor 101 is also connected to each part in the printer 2, the operation panel 3, and the scanner 4 via the interfaces.

[0041] The ROM 102 is a non-volatile memory that cannot be rewritten. The ROM 102 operates as a program memory that stores programs. The RAM 103 operates as a working memory or a buffer memory. The processor 101 executes various processes by using the RAM 103 to execute programs stored in the ROM 102 or the storage device 104.

[0042] The storage device 104 is a rewritable non-volatile memory. For example, the storage device 104 is configured with a storage device such as an HDD (hard disk drive) or an SSD (solid state drive). The storage device 104 stores data such as control data, control programs, and setting information. The storage device 104 also stores image data and the like.

[0043] The communication I / F 105 is an interface for performing data communication with an external device. For example, the communication I / F 105 communicates with a user terminal such as a PC or a mobile terminal via a network. The communication I / F 105 may also input an image print request (print job) from a user terminal such as a PC.

[0044] As shown in FIG. 3, the printer 2 includes a power supply 140 in addition to the components shown in FIGS. The power supply 140 supplies voltage to the developing device 110, the charger 126, the primary transfer roller 128, and the secondary transfer roller 22. As shown in Fig. 3, the power supply 140 has a high-voltage power supply 141, a developing bias transformer 142, a charging bias transformer 143, a primary transfer bias transformer 144, and a secondary transfer bias transformer 145. However, the developing bias transformer 142, the charging bias transformer 143, and the primary transfer bias transformer 144 are provided for each of the image forming stations SY, SM, SC, and SK.

[0045] High voltage power supply 141 supplies high voltage to various transformers 142, 143, 144, and 145. The high voltage is, for example, a voltage of several hundred volts to several kilovolts. High voltage power supply 141 generates the high voltage from an input voltage of, for example, several tens of volts.

[0046] The developing bias transformer 142 supplies a developing bias voltage to the developing device 110. The developing bias transformer 142 converts the high voltage generated by the high-voltage power supply 141 into a developing bias voltage of a voltage value set by the system controller 5. The developing bias transformer 142 supplies the developing bias voltage specified by the system controller 5 to the developing device 110.

[0047] The charging bias transformer 143 supplies a charging bias voltage to the charger 126. The charging bias transformer 143 converts the high voltage generated by the high-voltage power supply 141 into a charging bias voltage of a voltage value set by the system controller 5. The charging bias transformer 143 supplies the charging bias voltage specified by the system controller 5 to the charger 126.

[0048] The primary transfer bias transformer 144 supplies a primary transfer bias voltage to the primary transfer roller 128. The primary transfer bias transformer 144 converts the high voltage generated by the high voltage power supply 141 into a primary transfer bias voltage of a voltage value set by the system controller 5. The primary transfer bias transformer 144 supplies the primary transfer bias voltage specified by the system controller 5 to the primary transfer roller 128.

[0049] The secondary transfer bias transformer 145 supplies a secondary transfer bias voltage to the secondary transfer roller 22. The secondary transfer bias transformer 145 converts the high voltage generated by the high voltage power supply 141 into a secondary transfer bias voltage of a voltage value set by the system controller 5. The secondary transfer bias transformer 145 supplies the secondary transfer bias voltage of a value specified by the system controller 5 to the secondary transfer roller 22.

[0050] Next, the operation of the image forming process in the printer 2 as the image forming apparatus according to the embodiment will be described. The digital multifunction peripheral 1 acquires an image to be formed on a recording medium M, and executes an image forming process in which the acquired image is printed on the recording medium M by the printer 2. For example, when a copy command is issued on the operation panel 3, the processor 101 of the system controller 5 executes a process in which the image of the document read by the scanner 4 is printed on the recording medium M by the printer 2.

[0051] When executing image forming processing, the processor 101 of the system controller 5 takes in the recording medium M stored in the storage unit by the medium supply mechanism 13. The processor 101 then causes the conveying mechanism 15 to convey the recording medium M supplied from the medium supply mechanism 13 to just before the registration rollers 56 in the printer 2.

[0052] Furthermore, the processor 101 of the system controller 5 generates images to be formed by each of the image forming stations SY, SM, SC, and SK based on an image to be printed (print image) on the recording medium M. For example, the processor 101 generates images of each color (yellow, magenta, cyan, and black) to be formed by each of the image forming stations SY, SM, SC, and SK from the print image. After generating images of each color from the print image, the processor 101 causes each image forming station to form the generated image of each color.

[0053] In each of the image forming stations SY, SM, SC, and SK, a charger 126 receives a charging bias voltage from a charging bias transformer 143 and charges a photosensitive layer 124 of a photosensitive drum 122. An exposure unit 100 irradiates the photosensitive drum 122 of each of the image forming stations SY, SM, SC, and SK with light to form an electrostatic latent image corresponding to an image of each color. In each of the image forming stations SY, SM, SC, and SK, an electrostatic latent image is formed on the photosensitive layer 124 of the photosensitive drum 122 by the light irradiated from the exposure unit 100.

[0054] Each of the image forming stations SY, SM, SC, and SK develops the electrostatic latent image on the photosensitive drum 122 with toner of the color contained in the corresponding developing device 110. In each of the image forming stations SY, SM, SC, and SK, the developing roller 114 rotates while carrying developer containing toner of the corresponding color supplied from the developer container 112. A developing bias voltage is applied to the developing roller 114 carrying the developer from a developing bias transformer 142. The developing device 110 supplies the toner in the developer carried by the developing roller 114 to the electrostatic latent image due to the potential difference (contrast potential) between the potential on the developing roller 114 and the electrostatic latent image on the photosensitive drum 122.

[0055] In each of the image forming stations SY, SM, SC, and SK, the photosensitive drum 122 moves the image (toner image) developed by the developer 110 to a position (primary transfer position) opposite the primary transfer roller 128. At the primary transfer position, the photosensitive drum 122 faces the primary transfer roller 128 with the intermediate transfer belt 21 sandwiched therebetween. A primary transfer bias voltage is applied to the primary transfer roller 128 from a primary transfer bias transformer 144. The toner image on the photosensitive drum 122 is transferred to the intermediate transfer belt 21 by the primary transfer roller to which the primary transfer bias voltage is applied at the primary transfer position. When forming a color image, each of the image forming stations SY, SM, SC, and SK transfers toner images of each color onto the intermediate transfer belt 21 in an overlapping manner. As a result, a color image in which the toner images of each color are overlapped is transferred onto the intermediate transfer belt 21.

[0056] The intermediate transfer belt 21 moves the transferred toner image to a position (secondary transfer position) opposite the secondary transfer roller 22. The registration roller 56 sends the recording medium M to the secondary transfer position in synchronization with the position of the image transferred onto the intermediate transfer belt 21. As a result, the secondary transfer roller 22 and the support roller 23 convey the overlapping intermediate transfer belt 21 and recording medium M in a sandwiched state at the secondary transfer position. A secondary transfer bias voltage is applied to the secondary transfer roller 22 from a secondary transfer bias transformer 145. The toner image on the intermediate transfer belt 21 is transferred to the recording medium M by the secondary transfer roller 22 to which the secondary transfer bias voltage is applied at the secondary transfer position.

[0057] The recording medium M that has passed the secondary transfer position is transported to the fixing device 26. The fixing device 26 fixes the toner image transferred from the intermediate transfer belt 21 to the recording medium M at the secondary transfer position onto the recording medium M. The fixing device 26 applies heat and pressure to the recording medium M onto which the toner image has been transferred, fixing the toner image to the recording medium M. The recording medium M that has passed through the fixing device 26 is discharged from the paper discharge section with the toner image fixed thereon.

[0058] Next, image density adjustment in the printer 2 as the image forming apparatus according to the embodiment will be described. The printer 2 of the digital multifunction peripheral 1 adjusts the density of the image formed on the recording medium M through the image forming process described above. The density of the image formed on the recording medium M varies depending on the amount (density) of toner supplied from the developing roller 114 to the electrostatic latent image on the photosensitive drum 122 when the electrostatic latent image is developed.

[0059] The density of the toner supplied from the developing roller 114 to the electrostatic latent image is adjusted by the contrast potential, which is the potential difference between the electrostatic latent image on the photosensitive drum 122 and the developing roller 114. The processor 101 of the system controller 5 performs image density adjustment, which adjusts the density of the image of each color formed on the recording medium M, by controlling the contrast potential for each color. The image density adjustment may be performed periodically or at any timing.

[0060] The processor 101 of the system controller 5 in the digital multifunction peripheral 1 according to this embodiment detects the difference in contrast potential between each color after performing image density adjustment. The processor 101 issues a warning when there is a contrast potential whose difference from another contrast potential exceeds a reference value.

[0061] FIG. 4 illustrates an example of the operation of adjusting image density in the printer 2 as the image forming apparatus according to the embodiment. The processor 101 of the system controller 5 performs image density adjustment to equalize the toner density of the images of each color formed by each image forming station SY, SM, SC, and SK. As the image density adjustment, the processor 101 transfers the toner images formed by each image forming station SY, SM, SC, and SK onto the intermediate transfer belt 21 (ACT11).

[0062] The toner images formed by each image forming station SY, SM, SC, and SK in the image density adjustment may be images of a predetermined test pattern or any other image. The toner images of each color formed by each image forming station SY, SM, SC, and SK are transferred to the intermediate transfer belt 21 at their respective primary transfer positions.

[0063] After transferring the toner images of each color onto the intermediate transfer belt 21, the processor 101 of the system controller 5 detects the toner density of each color using the toner adhesion sensor 24 (ACT12). The toner adhesion sensor 24 detects the density (toner density) of the toner images of each color transferred onto the intermediate transfer belt 21. The toner adhesion sensor 24 supplies the detection result indicating the toner density of each color to the processor 101.

[0064] The processor 101 determines whether to perform density adjustment for each image forming station based on the toner density of each color detected by the toner adhesion sensor 24 (ACT13). For example, the processor 101 determines whether the toner density of each color detected by the toner adhesion sensor 24 is a predetermined density (within a predetermined density range). The processor 101 determines to perform density adjustment for the image forming station of the color for which the processor 101 determines that the toner density is not the predetermined density.

[0065] If there is an image forming station for which density adjustment has been determined (ACT13, YES), the processor 101 adjusts the contrast potential of the image forming station for which density adjustment is to be performed (ACT14). For example, if the toner density of yellow (magenta, cyan, black) is not a predetermined density, the processor 101 adjusts the contrast potential at the image forming station SY (SM, SC, SK).

[0066] To adjust the density, the processor 101 changes (adjusts) the contrast potential so that the toner density of the toner image formed by the image forming station becomes a predetermined density. For example, the processor 101 changes the contrast potential by controlling the development bias voltage that the development bias transformer 142 applies to the development roller 114. Alternatively, the system controller 5 may change the contrast potential by controlling the charging bias voltage that the charging bias transformer 143 applies to the charger 126. Alternatively, the system controller 5 may change the contrast potential by controlling the light that the exposure unit 100 irradiates onto the photosensitive drum 122.

[0067] When image density adjustment is performed, the processor 101 stores the adjustment results of the contrast potential at each of the image forming stations SY, SM, SC, and SK in the storage device 104 (ACT15). For example, when the processor 101 adjusts the contrast potential at the image forming station SY, it stores the adjustment results of the yellow contrast potential (the contrast potential corresponding to the image forming station SY) in the storage device 104. Similarly, when the processor 101 adjusts the contrast potential at the image forming station SM (SC, SK), it stores the adjustment results of the magenta (cyan, black) contrast potential in the storage device 104.

[0068] Furthermore, when the contrast potential is adjusted, the processor 101 calculates the difference in contrast potential at each of the image forming stations SY, SM, SC, and SK (ACT 16). The processor 101 calculates the difference between the contrast potential of each color (the contrast potential corresponding to each image forming station) and the contrast potential of other colors (the contrast potential corresponding to other image forming stations).

[0069] After calculating the difference in contrast potential for each color, the processor 101 determines whether there is a contrast potential whose difference with the contrast potential of another color exceeds a reference value (ACT17). The reference value to be compared with the difference in contrast potential is a threshold value for determining whether a malfunction such as a breakdown or abnormality may have occurred in the digital multifunction peripheral 1. An image forming station including a device with a malfunction or abnormality may have a contrast potential whose difference is large compared to the contrast potential of other image forming stations.

[0070] For example, if a developing device has an abnormality in its toner concentration sensor, the toner concentration in the developer will not be maintained at a predetermined value. If the toner concentration in the developer is not maintained at a predetermined value in an image forming station, the contrast potential will be significantly changed to adjust the toner concentration to the predetermined value. The contrast potential of an image forming station that includes a developing device with an abnormality in its toner concentration sensor may differ greatly from the contrast potential of other image forming stations. Furthermore, the contrast potential of an image forming station whose charger, exposure device, or development roller is not operating normally may differ greatly from the other contrast potentials.

[0071] If there is no contrast potential whose difference with other contrast potentials exceeds the reference value (ACT17, NO), the processor 101 ends the image density adjustment. In other words, if the difference between the contrast potentials of each color is within the reference value, the processor 101 ends the series of operations for adjusting the image density.

[0072] If there is any contrast potential difference that exceeds the reference value (ACT17, YES), the processor 101 issues a warning that the contrast potential difference has exceeded the reference value (ACT18). The warning may be a warning that prompts inspection or maintenance of the malfunction indicated by the contrast potential difference exceeding the reference value. For example, the warning may be a guide for inspection or maintenance, or a message that notifies the user that there may be a malfunction or abnormality in the digital multifunction peripheral. The warning may also include a message indicating the image forming station or color whose difference from other contrast potentials has exceeded the reference value.

[0073] Furthermore, even if the difference in contrast potential exceeds the reference value, the digital multifunction peripheral 1 can form an image with normal density as long as the toner density of each color is adjusted to a normal value. Therefore, even if the processor 101 issues a warning indicating that the difference in contrast potential has exceeded the reference value, the digital multifunction peripheral 1 may continue the operation of the image formation process. This allows the digital multifunction peripheral to notify that the difference in contrast potential has increased while maintaining image formation process with normal density.

[0074] Furthermore, the processor 101 may notify a service person or an administrator that the difference in contrast potential exceeds the reference value without notifying the user. This allows the digital multifunction peripheral 1 to provide normal image formation processing to the user, while urging the service person to perform maintenance on an abnormality or the like indicated by the difference in contrast potential.

[0075] For example, the processor 101 notifies a terminal device (external device) carried by a service person that the difference in contrast potential has exceeded a reference value via the communication I / F 105. The processor 101 may also notify a system that manages the operating state of the digital multifunction peripheral that the difference in contrast potential has exceeded a reference value via the communication I / F 105. The processor 101 may also display on the operation panel 3 that the difference in contrast potential has exceeded the reference value when a service person or an administrator logs in.

[0076] The processor 101 may execute the processes of ACT11-15 as image density adjustment, and may execute the processes of ACT16-18 in response to a request from a service technician, etc. This allows the digital multifunction peripheral 1 to notify the service technician of the possibility of a malfunction or abnormality based on the difference between the contrast potentials of each color in response to a request from the service technician.

[0077] As described above, the image forming apparatus according to the embodiment includes multiple photosensitive drums, multiple developing rollers, and a system controller. Each photosensitive drum carries an electrostatic latent image formed by light from an exposure device. Each developing roller faces a corresponding photosensitive drum. Each developing roller supplies toner to the electrostatic latent image carried by the opposing photosensitive drum using a contrast potential, which is the potential difference between the developing roller and the electrostatic latent image carried by the opposing photosensitive drum. The system controller adjusts the contrast potential corresponding to each photosensitive drum so that the density of the toner image developed on each photosensitive drum is uniform. The system controller issues a warning when the difference in contrast potential corresponding to each photosensitive drum exceeds a reference value.

[0078] With the above-described configuration, the image forming apparatus according to the embodiment can notify the user that a contrast potential difference that may indicate a malfunction or abnormality has occurred when image density adjustment is performed. As a result, the image forming apparatus according to the embodiment can enable a service technician to predict an area that may be malfunctioning or abnormal based on the contrast potential difference. Furthermore, by notifying the user that the contrast potential difference has exceeded a reference value, the image forming apparatus can promote prompt maintenance of areas where a malfunction or abnormality may have occurred.

[0079] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0080] 1...digital multifunction peripheral (image forming apparatus), 2...printer, 3...operation panel, 4...scanner, 5...system controller, 13...medium supply mechanism, 15...conveyance mechanism, 21...intermediate transfer belt (medium), 22...secondary transfer roller, 24...toner adhesion amount sensor, 100...exposure device, 101...processor, 104...storage device, 105...communication interface, 110...developer, 112...developer storage section, 114...developing roller, 120...toner concentration sensor, 122...photosensitive drum, 124...photosensitive layer, 126...charger, 128...primary transfer roller, 142...developing bias transformer, 143...charging bias transformer

Claims

1. A plurality of photoreceptors; an exposure device that irradiates the surfaces of the plurality of photoconductors with light corresponding to an image to be formed on the plurality of photoconductors; a developing unit that supplies toner to the surfaces of the plurality of photoconductors on which electrostatic latent images are formed by the light irradiated by the exposure unit; a processor that adjusts a contrast potential for supplying toner from the developing device to the electrostatic latent images formed on the surfaces of the plurality of photoconductors for each photoconductor, and issues a warning when a contrast potential exists whose difference with other contrast potentials exceeds a reference value; An image forming apparatus having the same.

2. The developing unit has a plurality of developing rollers facing the respective photosensitive members, the processor adjusts the contrast potential for each photoconductor by adjusting the voltage applied to the plurality of developing rollers; The image forming apparatus according to claim 1 .

3. a sensor for detecting a toner concentration on a medium onto which a toner image formed on the surface of each of the plurality of photosensitive members with the toner supplied from the developing device has been transferred; the processor adjusts the contrast potential corresponding to each photoconductor so that the toner density detected by the sensor becomes a desired density, and calculates the difference between the contrast potentials of all the photoconductors after the adjustment of the contrast potentials corresponding to all the photoconductors is completed.

3. The image forming apparatus according to claim 1.

4. having an interface for communicating with an external device; the processor notifies an external device via the interface of a warning when there is a contrast potential whose difference from other contrast potentials exceeds a reference value; The image forming apparatus according to claim 1 .

5. a memory for storing the result of adjusting the contrast potential for each of the photosensitive members; when there is a contrast potential whose difference from another contrast potential exceeds a reference value, the processor displays a warning on a display device indicating that there is a contrast potential whose difference from another contrast potential exceeds a reference value. The image forming apparatus according to claim 4 .

Images