JP6439459B2 - Transfer unit, image forming apparatus, image forming system, and transfer voltage control method - Google Patents

Description

  The present invention relates to a transfer unit, an image forming apparatus, an image forming system, and a transfer voltage control method.

  In general, an image forming apparatus (printer, copier, facsimile, etc.) using an electrophotographic process technology generates an electrostatic latent image by irradiating (exposing) a charged photoconductor with a laser beam based on image data. Form. Then, by supplying toner from the developing device to the photoconductor on which the electrostatic latent image is formed, the electrostatic latent image is visualized to form a toner image. Further, after the toner image is directly or indirectly transferred to the sheet, the toner image is formed on the sheet by fixing by heating and pressing at the fixing nip.

  In addition, a paper feeding device that feeds continuous paper (hereinafter referred to as “long paper”) such as continuous paper roll paper or folding paper to the image forming apparatus at the front stage and the rear stage of the image forming apparatus; 2. Description of the Related Art An image forming system in which a paper discharge device that stores a long sheet on which a toner image is formed by an apparatus is connected has been put into practical use.

  In the above image forming apparatus, the intermediate transfer member is passed between the photosensitive member and the transfer roller, and the toner image carried on the photosensitive member is transferred to the intermediate transfer member by the transfer voltage applied to the transfer roller at the time of the passage. doing. The power source for applying the transfer voltage to the transfer roller is generally controlled by constant voltage or constant current.

  By the way, when the power source is controlled at a constant current, the transfer rate may vary due to a change in the toner image pattern. Therefore, transferability is ensured by changing the toner image pattern by controlling the power source at a constant voltage. However, when the power supply is controlled at a constant voltage, the transfer current flowing between the photoconductor and the transfer roller changes due to the change in resistance of the transfer roller. For this reason, when the same transfer voltage is continuously applied to the transfer roller, the resistance value of the transfer roller and the transfer current change according to changes in the image forming environment (such as changes in ambient temperature after continuous printing of a large number of sheets). As a result, the density of the toner image transferred to the intermediate transfer member changes. In order to cope with this problem, ATVC (Active Transfer Voltage) is used to re-determine the transfer voltage to be applied by using the sheet interval (between the trailing edge of the preceding sheet and the leading edge of the succeeding sheet after the preceding sheet). Control) is known. In ATVC control, the transfer voltage applied to the transfer roller is determined so that the transfer current flowing through the transfer roller becomes a predetermined optimum transfer current. More specifically, the transfer voltage applied to the transfer roller is changed, and a transfer voltage in which a transfer current of a desired value flows between the transfer roller and the photoconductor is searched for.

  Note that Patent Document 1 includes a resistance detection unit that detects the electrical resistance of the primary transfer roller, or an electrical property detection unit that detects a predetermined electrical characteristic correlated with the electrical resistance. Discloses a technique for obtaining an appropriate value of the output current from the image sensor based on the detection result of the resistance detection means or the electrical characteristic detection means in addition to the image area ratio on the photosensitive member.

JP 2013-109070 A

  However, a certain amount of time is required to perform ATVC control. Therefore, depending on the image forming conditions, it may be difficult to perform ATVC control during the image forming process. For example, when a toner image is formed on a long sheet in an image forming system, it is difficult to execute ATVC control during the image forming process because there is no gap between sheets. Further, even when a toner image is formed on a sheet cut to a predetermined sheet size (also referred to as “cut sheet”), if the interval between sheets is set narrow in order to improve productivity, an image forming process is in progress. It is difficult to execute ATVC control.

  The technique described in Patent Document 1 is a technique for controlling a transfer voltage to be applied to a transfer member in accordance with a change in an image forming environment during an image forming process, regardless of image forming conditions. Therefore, it does not have a configuration for it.

  The present invention relates to a transfer unit, an image forming apparatus, and an image forming system capable of controlling a transfer voltage to be applied to a transfer member according to a change in an image forming environment during an image forming process regardless of image forming conditions. It is another object of the present invention to provide a transfer voltage control method.

The transfer unit according to the present invention comprises:
An intermediate transfer member;
A transfer member that forms a transfer nip with the photoreceptor via the intermediate transfer member;
A resistance member having electrical resistance and being pressed against the transfer member;
When a transfer voltage is applied between the photoconductor and the transfer member, a current value flowing between the transfer member and the resistance member is acquired, and the applied transfer voltage value is divided by the acquired current value. To calculate a combined resistance value of the transfer member and the resistance member, and based on a relational expression indicating a relationship between a combined resistance value of the transfer member and the resistance member and a transfer voltage to be applied to the transfer member, A control unit that determines a transfer voltage to be applied to the transfer member using the calculated combined resistance value as a combined resistance value in the relational expression;
Is provided.

An image forming apparatus according to the present invention includes:
A photoreceptor,
An intermediate transfer member;
A transfer member that forms a transfer nip with the photoreceptor via the intermediate transfer member;
A resistance member having electrical resistance and being pressed against the transfer member;
When a transfer voltage is applied between the photoconductor and the transfer member, a current value flowing between the transfer member and the resistance member is acquired, and the applied transfer voltage value is divided by the acquired current value. To calculate a combined resistance value of the transfer member and the resistance member, and based on a relational expression indicating a relationship between a combined resistance value of the transfer member and the resistance member and a transfer voltage to be applied to the transfer member, A control unit that determines a transfer voltage to be applied to the transfer member using the calculated combined resistance value as a combined resistance value in the relational expression;
Is provided.

An image forming system according to the present invention includes:
A paper feeder for feeding long paper,
The image forming apparatus for forming a toner image on a long sheet fed by the sheet feeding apparatus;
A paper discharge device for storing the long paper on which a toner image is formed by the image forming device;
Is provided.

The transfer voltage control method according to the present invention includes:
When a transfer voltage is applied between the transfer member that forms a transfer nip with the photosensitive member via the intermediate transfer member and the photosensitive member, the transfer member has an electrical resistance and is pressed against the transfer member. Obtain the value of the current flowing between the
Calculate the combined resistance value of the transfer member and the resistance member by dividing the applied transfer voltage value by the acquired current value,
Based on the relational expression indicating the relation between the combined resistance value of the transfer member and the resistance member and the transfer voltage to be applied to the transfer member, the combined resistance value in the relational expression is used as the calculated combined resistance value. A transfer voltage to be applied to the transfer member is determined.

  According to the present invention, it is possible to control the transfer voltage to be applied to the transfer member in accordance with the change in the image forming environment during the image forming process, regardless of the image forming conditions.

1 is a diagram schematically showing an overall configuration of an image forming system in the present embodiment. FIG. 2 is a diagram illustrating a main part of a control system of the image forming apparatus according to the present embodiment. FIG. 3 is a diagram illustrating a configuration of an intermediate transfer unit in the present embodiment. 5 is a flowchart showing a control operation during image formation in the present embodiment. 5 is a flowchart showing a transfer voltage control operation in the present embodiment. FIG. 10 is a diagram showing a modification of the configuration of the intermediate transfer unit in the present embodiment. FIG. 10 is a diagram showing a modification of the configuration of the intermediate transfer unit in the present embodiment.

  Hereinafter, the present embodiment will be described in detail with reference to the drawings. FIG. 1 is a diagram schematically showing an overall configuration of an image forming system 100 according to the present embodiment. FIG. 2 shows a main part of a control system of the image forming apparatus 2 provided in the image forming system 100 according to the present embodiment. The image forming system 100 uses a long paper P indicated by a thick line in FIG. 1 or a paper (also referred to as “cut paper”) S cut to a predetermined paper size as a recording medium. This is a system for forming a toner image on the top. Here, the long paper P is a paper having a length exceeding the width of the main body of the image forming apparatus 2 in the transport direction, for example.

  As shown in FIG. 1, the image forming system 100 includes a paper feeding device 1, an image forming device 2, and a paper discharge from the upstream side along the transport direction of the long paper P (hereinafter also referred to as “paper transport direction”). The apparatus 3 is connected and configured. The paper feeding device 1 and the paper discharge device 3 are used when a toner image is formed on the long paper P.

  The paper feeding device 1 is a device that feeds the long paper P to the image forming apparatus 2. In the casing of the paper feeding device 1, as shown in FIG. 1, a roll-shaped long paper P is wound around a support shaft and held rotatably. The sheet feeding device 1 conveys the long paper P wound around the support shaft to the image forming apparatus 2 at a constant speed via a plurality of pairs of conveying rollers (for example, a feeding roller, a sheet feeding roller, etc.). To do. The sheet feeding operation of the sheet feeding apparatus 1 is controlled by the control unit 101 provided in the image forming apparatus 2.

  In the paper feeding device 1, the long paper P is not necessarily held in a roll shape, and a plurality of long papers P of a predetermined size (for example, 210 [mm] × 1200 [mm]) are held. May be.

  The image forming apparatus 2 is an intermediate transfer type color image forming apparatus using electrophotographic process technology. That is, the image forming apparatus 2 primarily transfers Y (yellow), M (magenta), C (cyan), and K (black) toner images formed on the photosensitive drum 413 to the intermediate transfer belt 421. After the four color toner images are superimposed on the intermediate transfer belt 421, the secondary transfer is performed on the long paper P fed from the paper feeding device 1 or the paper S sent from the paper feed tray units 51a to 51c. As a result, a toner image is formed.

  In the image forming apparatus 2, photosensitive drums 413 corresponding to four colors of YMCK are arranged in series in the running direction of the intermediate transfer belt 421, and each color toner image is sequentially transferred to the intermediate transfer belt 421 in one procedure. Tandem system is adopted.

  As shown in FIG. 2, the image forming apparatus 2 includes an image reading unit 10, an operation display unit 20, an image processing unit 30, an image forming unit 40, a paper transport unit 50, a fixing unit 60, and a control unit 101.

  The control unit 101 includes a CPU (Central Processing Unit) 102, a ROM (Read Only Memory) 103, a RAM (Random Access Memory) 104, and the like. The CPU 102 reads out a program corresponding to the processing content from the ROM 103 and develops it in the RAM 104, and centrally controls the operation of each block of the image forming apparatus 2 in cooperation with the developed program. At this time, various data stored in the storage unit 72 is referred to. The storage unit 72 includes, for example, a nonvolatile semiconductor memory (so-called flash memory) or a hard disk drive.

  The control unit 101 transmits and receives various data to and from an external device (for example, a personal computer) connected to a communication network such as a LAN (Local Area Network) or a WAN (Wide Area Network) via the communication unit 71. Do. For example, the control unit 101 receives image data transmitted from an external device, and forms an image on the long paper P or the paper S based on the image data (input image data). The communication unit 71 is composed of a communication control card such as a LAN card, for example.

  The image reading unit 10 includes an automatic document feeder 11 called an ADF (Auto Document Feeder), a document image scanning device 12 (scanner), and the like.

  The automatic document feeder 11 transports the document D placed on the document tray by a transport mechanism and sends it out to the document image scanning device 12. The automatic document feeder 11 can continuously read images (including both sides) of a large number of documents D placed on the document tray all at once.

  The document image scanning device 12 optically scans a document conveyed on the contact glass from the automatic document feeder 11 or a document placed on the contact glass, and reflects light from the document to a CCD (Charge Coupled Device). ) An image is formed on the light receiving surface of the sensor 12a, and an original image is read. The image reading unit 10 generates input image data based on the reading result by the document image scanning device 12. The input image data is subjected to predetermined image processing in the image processing unit 30.

  The operation display unit 20 is configured by, for example, a liquid crystal display (LCD) with a touch panel, and functions as a display unit 21 and an operation unit 22. The display unit 21 displays various operation screens, image states, operation states of functions, and the like according to a display control signal input from the control unit 101. The operation unit 22 includes various operation keys such as a numeric keypad and a start key, receives various input operations by the user, and outputs an operation signal to the control unit 101.

  The image processing unit 30 includes a circuit that performs digital image processing on input image data according to initial settings or user settings. For example, the image processing unit 30 performs gradation correction based on the gradation correction data (gradation correction table) under the control of the control unit 101. Further, the image processing unit 30 performs various correction processes such as color correction and shading correction, a compression process, and the like on the input image data in addition to the gradation correction. The image forming unit 40 is controlled based on the image data subjected to these processes.

  The image forming unit 40 is based on the input image data, and image forming units 41Y, 41M, 41C, 41K, and an intermediate transfer unit 42 for forming an image using colored toners of Y component, M component, C component, and K component. (Corresponding to the “transfer unit” of the present invention).

  The Y component, M component, C component, and K component image forming units 41Y, 41M, 41C, and 41K have the same configuration. For convenience of illustration and description, common constituent elements are denoted by the same reference numerals, and when distinguished from each other, Y, M, C, or K is appended to the reference numerals. In FIG. 1, only the components of the Y-component image forming unit 41Y are denoted by reference numerals, and the constituent elements of the other image forming units 41M, 41C, and 41K are omitted.

  The image forming unit 41 includes an exposure device 411, a developing device 412, a photosensitive drum 413, a charging device 414, a drum cleaning device 415, and the like.

  The photosensitive drum 413 has an undercoat layer (UCL) and a charge generation layer (CGL) on the peripheral surface of an aluminum conductive cylinder (aluminum tube) having a drum diameter of 80 mm, for example. It is a negatively charged organic photoconductor (OPC) in which a generation layer (CTL) and a charge transport layer (CTL) are sequentially stacked. The charge generation layer is made of an organic semiconductor in which a charge generation material (for example, phthalocyanine pigment) is dispersed in a resin binder (for example, polycarbonate), and generates a pair of positive charges and negative charges by exposure by the exposure device 411. The charge transport layer consists of a material in which a hole transport material (electron donating nitrogen-containing compound) is dispersed in a resin binder (for example, polycarbonate resin), and transports positive charges generated in the charge generation layer to the surface of the charge transport layer. To do.

  The control unit 101 rotates the photosensitive drum 413 at a constant peripheral speed by controlling a driving current supplied to a driving motor (not shown) that rotates the photosensitive drum 413.

  The charging device 414 uniformly charges the surface of the photoconductive drum 413 to a negative polarity. The exposure device 411 is composed of, for example, a semiconductor laser, and irradiates the photosensitive drum 413 with laser light corresponding to the image of each color component. A positive charge is generated in the charge generation layer of the photosensitive drum 413 and is transported to the surface of the charge transport layer, whereby the surface charge (negative charge) of the photosensitive drum 413 is neutralized. An electrostatic latent image of each color component is formed on the surface of the photosensitive drum 413 due to a potential difference from the surroundings.

  The developing device 412 is a two-component developing type developing device, and attaches toner of each color component to the surface of the photosensitive drum 413 to visualize the electrostatic latent image to form a toner image.

  The drum cleaning device 415 includes a drum cleaning blade that is slidably contacted with the surface of the photosensitive drum 413, and removes transfer residual toner remaining on the surface of the photosensitive drum 413 after primary transfer.

  The intermediate transfer unit 42 includes an intermediate transfer belt 421, a primary transfer roller 422 (corresponding to the “transfer member” of the present invention), a plurality of support rollers 423, a secondary transfer roller 424, a belt cleaning device 426, and the like.

  The intermediate transfer belt 421 is an endless belt, and is stretched around a plurality of support rollers 423 in a loop shape. At least one of the plurality of support rollers 423 is configured by a driving roller, and the other is configured by a driven roller. For example, it is preferable that the roller 423A disposed downstream of the K component primary transfer roller 422 in the belt traveling direction is a drive roller. This makes it easy to keep the belt running speed constant in the primary transfer portion. As the driving roller 423A rotates, the intermediate transfer belt 421 travels in the direction of arrow A at a constant speed.

  The intermediate transfer belt 421 is a belt having conductivity and elasticity, and has a high resistance layer having a volume resistivity of 8 to 11 [log Ω · cm] on the surface. The intermediate transfer belt 421 is rotationally driven by a control signal from the control unit 101. Note that the material, thickness, and hardness of the intermediate transfer belt 421 are not limited as long as they have conductivity and elasticity.

  The primary transfer roller 422 is disposed on the inner peripheral surface side of the intermediate transfer belt 421 so as to face the photosensitive drum 413 of each color component. The primary transfer roller 422 is pressed against the photosensitive drum 413 with the intermediate transfer belt 421 interposed therebetween, thereby forming a primary transfer nip for transferring a toner image from the photosensitive drum 413 to the intermediate transfer belt 421.

  The secondary transfer roller 424 is disposed on the outer peripheral surface side of the intermediate transfer belt 421 so as to face the backup roller 423B disposed on the downstream side in the belt traveling direction of the drive roller 423A. The secondary transfer roller 424 is pressed against the backup roller 423B with the intermediate transfer belt 421 interposed therebetween, thereby forming a secondary transfer nip for transferring the toner image from the intermediate transfer belt 421 to the long paper P or paper S. Is done.

  When the intermediate transfer belt 421 passes through the primary transfer nip, the toner images on the photoconductive drum 413 are primarily transferred onto the intermediate transfer belt 421 in sequence. Specifically, by applying a primary transfer voltage to the primary transfer roller 422 and applying a charge having a polarity opposite to that of the toner to the back side of the intermediate transfer belt 421 (the side in contact with the primary transfer roller 422), the toner image It is electrostatically transferred to the intermediate transfer belt 421.

  Thereafter, when the long paper P or paper S passes through the secondary transfer nip, the toner image on the intermediate transfer belt 421 is secondarily transferred to the long paper P or paper S. Specifically, a secondary transfer voltage is applied to the secondary transfer roller 424, and a charge having a polarity opposite to that of the toner is applied to the back side of the long paper P or the paper S (the side in contact with the secondary transfer roller 424). As a result, the toner image is electrostatically transferred onto the long paper P or the paper S. The long paper P or paper S to which the toner image is transferred is conveyed toward the fixing unit 60.

  The belt cleaning device 426 removes transfer residual toner remaining on the surface of the intermediate transfer belt 421 after the secondary transfer. Instead of the secondary transfer roller 424, a configuration (so-called belt-type secondary transfer unit) in which a secondary transfer belt is looped around a plurality of support rollers including the secondary transfer roller is adopted. Also good.

  The fixing unit 60 has an upper fixing unit 60A having a fixing surface side member disposed on the fixing surface (surface on which the toner image is formed) of the long paper P or paper S, and the back surface of the long paper P or paper S. A lower fixing portion 60B having a back surface side support member disposed on the (opposite surface to the fixing surface) side is provided. When the back surface side support member is pressed against the fixing surface side member, a fixing nip for nipping and transporting the long paper P or the paper S is formed.

  The fixing unit 60 fixes the toner image on the long paper P or the paper S by heating and pressurizing the long paper P or the paper S, to which the toner image is secondarily transferred and conveyed, at the fixing nip. The fixing unit 60 is disposed in the fixing device F as a unit. The fixing device F may be provided with an air separation unit that separates the long paper P or the paper S from the fixing surface side member or the back surface side support member by blowing air.

  The upper fixing unit 60A includes an endless fixing belt 61, a heating roller 62, and a fixing roller 63 which are fixing surface side members (belt heating method). The fixing belt 61 is stretched between the heating roller 62 and the fixing roller 63 with a predetermined belt tension (for example, 40 [N]).

  The fixing belt 61 contacts the long paper P or paper S on which the toner image is formed, and heat-fixes the toner image on the long paper P or paper S at a fixing temperature (for example, 160 to 200 [° C.]). To do. Here, the fixing temperature is a temperature at which the amount of heat necessary for melting the toner on the long paper P or the paper S can be supplied, and depends on the paper type of the long paper P or the paper S on which an image is formed. Different.

  The heating roller 62 includes a heating source (halogen heater) and heats the fixing belt 61. The heating roller 62 is heated by the heating source, and as a result, the fixing belt 61 is heated.

  The fixing roller 63 has, for example, an elastic layer (for example, thickness: 10 [mm]) made of silicon rubber or the like on a peripheral surface of a cylindrical cored bar made of aluminum or the like, and a surface layer (for example, made of fluorine resin such as PTFE). And a thickness of 70 [μm]) are sequentially stacked. Driving control of the fixing roller 63 (for example, rotation on / off, peripheral speed, etc.) is performed by the control unit 101. The control unit 101 rotates the fixing roller 63 in the clockwise direction. As the fixing roller 63 rotates, the fixing belt 61 and the heating roller 62 are driven to rotate clockwise.

  The lower fixing unit 60B includes a pressure roller 64 that is a back side support member (roller pressure method). The pressure roller 64 has a configuration in which, for example, an elastic layer made of silicon rubber or the like and a surface layer made of a PFA tube are sequentially laminated on the outer peripheral surface of a cylindrical cored bar made of iron or the like. The pressure roller 64 is pressed against the fixing roller 63 with a predetermined fixing load (for example, 1000 [N]) via the fixing belt 61 by a press-contacting / separating portion (not shown). The press contact / separation unit has a known configuration and presses or separates the fixing belt 61 and the pressure roller 64 from each other. In this way, a fixing nip is formed between the fixing belt 61 and the pressure roller 64 to hold the long paper P or the paper S and convey it. The control unit 101 performs drive control of the pressure roller 64 (for example, rotation on / off, peripheral speed, etc.) and drive control of the press contact / separation unit. The control unit 101 rotates the pressure roller 64 in the counterclockwise direction.

  The paper transport unit 50 includes a paper feed unit 51, a paper discharge unit 52, a transport path unit 53, and the like. In the three paper feed tray units 51a to 51c constituting the paper feed unit 51, paper S (standard paper, special paper) identified based on basis weight, size, etc. is stored for each preset type. . The conveyance path unit 53 includes a plurality of conveyance roller pairs including a registration roller pair 53a. The registration roller portion in which the registration roller pair 53a is disposed corrects the inclination and deviation of the paper S or the long paper P.

  The sheets S stored in the sheet feed tray units 51 a to 51 c are sent one by one from the top and are conveyed to the image forming unit 40 by the conveyance path unit 53. In the image forming unit 40, the toner image on the intermediate transfer belt 421 is secondarily transferred onto one surface of the sheet S at once, and a fixing process is performed in the fixing unit 60. Further, the long paper P fed from the paper feeding device 1 to the image forming device 2 is conveyed to the image forming unit 40 by the conveyance path unit 53. In the image forming unit 40, the toner image on the intermediate transfer belt 421 is secondarily transferred to one side of the long paper P at a time, and a fixing process is performed in the fixing unit 60. The long paper P or paper S on which an image has been formed is transported to the paper discharge device 3 by a paper discharge unit 52 having a pair of transport rollers (a pair of paper discharge rollers) 52a.

  The paper discharge device 3 is a device that winds and stores the long paper P conveyed from the image forming apparatus 2. In the housing of the paper discharge device 3, for example, as shown in FIG. 1, the long paper P is wound around a support shaft and held in a roll shape. For this purpose, the paper discharge device 3 supports the long paper P conveyed from the image forming apparatus 2 at a constant speed via a plurality of pairs of conveyance rollers (for example, feeding rollers and paper discharge rollers). Take up around. The winding operation of the paper discharge device 3 is controlled by the control unit 101 provided in the image forming device 2.

  In the image forming apparatus 2, as described above, the intermediate transfer belt 421 is passed between the photosensitive drum 413 and the primary transfer roller 422, and the photosensitive drum is exposed by the primary transfer voltage applied to the primary transfer roller 422 during the passage. The toner image carried on the body drum 413 is transferred to the intermediate transfer belt 421. A power source (voltage application unit 80) that applies a transfer voltage to the primary transfer roller 422 is generally controlled by constant voltage or constant current.

  By the way, when the voltage application unit 80 is controlled at a constant current, there is a possibility that the transfer rate varies due to the change in the toner image pattern. Therefore, it is conceivable to ensure transferability by changing the toner image pattern by controlling the voltage application unit 80 at a constant voltage. However, when the voltage application unit 80 is controlled at a constant voltage, the transfer current flowing between the photosensitive drum 413 and the primary transfer roller 422 changes due to the change in the resistance of the primary transfer roller 422. Therefore, when a transfer voltage having the same value is continuously applied to the primary transfer roller 422, the resistance value of the primary transfer roller 422 and the transfer in accordance with changes in the image forming environment (such as changes in ambient temperature after continuous printing of a large number of sheets). As the current changes, the density of the toner image transferred to the intermediate transfer belt 421 changes. In order to cope with this problem, ATVC control is known in which a transfer voltage to be applied is re-determined using a gap between sheets. The ATVC control determines a transfer voltage applied to the primary transfer roller 422 so that the transfer current flowing through the primary transfer roller 422 becomes a predetermined optimum transfer current. More specifically, the control unit 101 changes the transfer voltage applied to the primary transfer roller 422 and searches for a transfer voltage in which a transfer current having a desired value flows between the primary transfer roller 422 and the photosensitive drum 413.

  However, a certain amount of time is required to perform ATVC control. Therefore, depending on the image forming conditions, it may be difficult to perform ATVC control during the image forming process. For example, when a toner image is formed on the long paper P, it is difficult to execute ATVC control during the image forming process because there is no paper space in the first place. Even when a toner image is formed on the sheet S (cut sheet), it is difficult to perform ATVC control during the image forming process when the sheet interval is set narrow in order to improve productivity. .

  Therefore, in this embodiment, the transfer voltage to be applied to the primary transfer roller 422 is controlled in accordance with the change in the image forming environment during the image forming process regardless of the image forming conditions (hereinafter, this control is referred to as the transfer voltage). The intermediate transfer unit 42 is provided with a configuration that enables control. The configuration of the intermediate transfer unit 42 will be described with reference to FIG. As shown in FIG. 3, the primary transfer roller 422 is arranged on the inner peripheral surface side of the intermediate transfer belt 421 so as to face the photosensitive drum 413 of each color (K (black) in FIG. 3) component.

  A voltage application unit 80 is connected to the primary transfer roller 422. The voltage application unit 80 applies a transfer voltage to the primary transfer roller 422 under the control of the control unit 101.

  The intermediate transfer unit 42 is provided with a metal roller 110 that can be pressed against the primary transfer roller 422 as indicated by an arrow B. The outer peripheral surface of the metal roller 110 is covered with a resistance material 112 made of the same material as the intermediate transfer belt 421 and the photosensitive drum 413. The metal roller 110 and the resistance material 112 correspond to the “resistance member” of the present invention.

  The metal roller 110 is brought into pressure contact with the primary transfer roller 422 by a predetermined pressure contact force by a pressure contact separation portion 84 (see FIG. 2). The press contact / separation unit 84 has a known configuration, and receives the control of the control unit 101 to press the metal roller 110 against the primary transfer roller 422 or to separate the metal roller 110 from the primary transfer roller 422.

  A current detection unit 82 is connected to the metal roller 110. When the metal roller 110 is pressed against the primary transfer roller 422 and a transfer voltage is applied to the primary transfer roller 422 by the voltage application unit 80, the current detection unit 82 includes the primary transfer roller 422, the metal roller 110, and the resistance material 112. The detected current value is output to the control unit 101.

  FIG. 4 is a flowchart showing the control operation during image formation in the present embodiment. The processing in each step in FIG. 4 is executed after the image forming system 100 is turned on. Note that the metal roller 110 is separated from the primary transfer roller 422 in the previous stage of step S100.

  First, the control unit 101 confirms whether or not the execution of a print job is instructed by a user operation on the operation unit 22, for example, and determines whether or not it is time to start execution of the image forming process (step S100). ). If the result of this determination is that it is not time to start execution of the image forming process (step S100, NO), the process returns to before step S100.

  On the other hand, when it is time to start executing the image forming process (step S100, YES), the control unit 101 executes transfer voltage control (step S120). FIG. 5 is a flowchart showing the transfer voltage control operation in the present embodiment.

  First, the control unit 101 controls the press contact / separation unit 84 to press the metal roller 110 against the primary transfer roller 422 (step S300). Next, the control unit 101 controls the voltage application unit 80 to perform primary transfer of a transfer voltage having a transfer voltage value used when transferring the toner image carried on the photosensitive drum 413 to the intermediate transfer belt 421. It is made to apply to the roller 422 (step S320). At that time, the current detection unit 82 detects the current value that flows through the primary transfer roller 422, the metal roller 110, and the resistance material 112, and outputs the detected current value to the control unit 101. As described above, the material of the resistance material 112 is the same material as the intermediate transfer belt 421 and the photosensitive drum 413. That is, the combined resistance value of the primary transfer roller 422, the metal roller 110, and the resistance material 112 is substantially equal to the combined resistance value of the primary transfer roller 422, the intermediate transfer belt 421, and the photosensitive drum 413. That is, when a transfer voltage is applied to the primary transfer roller 422, the current that flows to the primary transfer roller 422, the metal roller 110, and the resistance material 112, and the current that flows to the primary transfer roller 422, the intermediate transfer belt 421, and the photosensitive drum 413 are It is almost equivalent.

  Next, the control unit 101 acquires the current value output from the current detection unit 82 (step S340). Next, the control unit 101 calculates the combined resistance value of the primary transfer roller 422, the metal roller 110, and the resistance material 112 by dividing the transfer voltage value applied in step S320 by the current value acquired in step S320. (Step S360). The combined resistance value calculated in step S360 is substantially equal to the combined resistance value of the primary transfer roller 422, the intermediate transfer belt 421, and the photosensitive drum 413.

Next, when the controller 101 transfers the combined resistance value of the primary transfer roller 422, the metal roller 110 and the resistance material 112 and the toner image carried on the photosensitive drum 413 to the intermediate transfer belt 421, the primary transfer roller 421. Based on the following relational expression (1) indicating the relation with the transfer voltage to be applied to 422, the primary transfer roller using the combined resistance value calculated in step S360 as the combined resistance value in the relational expression (1). A transfer voltage to be applied to 422 is calculated (step S380).
V = A × R + B (1)
V: transfer voltage, A, B: coefficient R: combined resistance value of the primary transfer roller 422, the metal roller 110, and the resistance material 112 The coefficients A, B are experiments performed in advance to obtain the relational expression (1). Determined from the results. In the present embodiment, the coefficients A and B are 50.4 × 10 ⁻⁶ and 390, respectively.

  The control unit 101 updates the transfer voltage value used when the toner image carried on the photosensitive drum 413 is transferred to the intermediate transfer belt 421 to the calculated transfer voltage value. This update is performed at the timing between images if the image forming process is being executed. Further, when the difference between the transfer voltage value before the update and the transfer voltage value after the update exceeds a predetermined value (for example, 500 [V]), the transfer voltage value to be updated is set at the timing between the first images. It is preferable to change the voltage by 500 [V] and change the rest at the timing between the next images. This is to prevent the transfer voltage value and hence the transfer current value from fluctuating greatly in a short time, and to suppress a sudden change in the density of the toner image transferred to the intermediate transfer belt 421.

  Finally, the control unit 101 controls the press contact / separation unit 84 to separate the metal roller 110 from the primary transfer roller 422 (step S400). When the process of step S400 is completed, the transfer voltage control in FIG. 5 ends.

  Returning to the flowchart of FIG. 4, in step S140, the control unit 101 starts execution of the image forming process. Next, the control unit 101 determines whether or not the transfer voltage control execution condition is satisfied (step S160). When the resistance value of the primary transfer roller 422 is likely to change in response to a change in the image forming environment (for example, the ambient temperature has changed by 1 [° C.] after 30 sheets are continuously printed), the control unit 101 performs transfer. It is determined that the voltage control execution condition is satisfied. As a result of the determination, if the execution condition of the transfer voltage control is not satisfied (step S160, NO), the process transitions to step S200.

  On the other hand, when the execution condition of the transfer voltage control is satisfied (step S160, YES), the control unit 101 executes the transfer voltage control similar to step S120 (step S180). Thereafter, the process proceeds to step S200.

  In step S200, the control unit 101 determines whether or not the image forming process being executed has ended. If the result of this determination is that the image forming process being executed has not been completed (step S200, NO), the process returns to before step S160. On the other hand, when the image forming process being executed is completed (step S200, YES), the process returns to before step S100.

  In the flowcharts of FIGS. 4 and 5, the example in which the metal roller 110 is pressed against the primary transfer roller 422 is described only when the transfer voltage control is executed. However, the transfer is not limited to the case where the transfer voltage control is executed. The metal roller 110 may be pressed against the roller 422. However, when the metal roller 110 is brought into pressure contact with the primary transfer roller 422 under constant voltage control, the current flows in two directions, ie, the photosensitive drum 413 direction and the metal roller-110 direction, that is, the current is doubled and voltage is applied. The power consumption of the unit 80 increases. Therefore, from the viewpoint of suppressing the load (power consumption) of the voltage application unit 80 so that current flows only in the direction of the photosensitive drum 413 when the transfer voltage control is not executed, only when the transfer voltage control is executed. It is preferable to press the metal roller 110 against the primary transfer roller 422.

  As described above in detail, in the present embodiment, the image forming apparatus 2 has a primary transfer nip between the photosensitive drum 413, the intermediate transfer belt 421, and the photosensitive drum 413 via the intermediate transfer belt 421. A transfer voltage between the primary transfer roller 422 to be formed, a resistance member (metal roller 110 and resistance material 112) having electrical resistance and pressed against the primary transfer roller 422, and the photosensitive drum 413 and the primary transfer roller 422. Is applied, a current value flowing between the primary transfer roller 422 and the resistance member is acquired, and the applied transfer voltage value is divided by the acquired current value to thereby combine the resistance of the primary transfer roller 422 and the resistance member. Value is calculated, and the relationship between the combined resistance value of the primary transfer roller 422 and the resistance member and the transfer voltage to be applied to the primary transfer roller 422 is calculated. Based on the relational expression indicating the as combined resistance value in the equation, using the calculated combined resistance value, and a control unit 101 which determines the transfer voltage to be applied to the primary transfer roller 422.

  According to the present embodiment configured as described above, when the toner image is formed on the long paper P, that is, when there is no paper space, or when the toner image is formed on the paper S, the paper space is set narrow. Even when the image forming condition is such that the transfer voltage to be applied to the primary transfer roller 422 can be controlled according to the change in the image forming environment during the image forming process in which the voltage applying unit 80 is controlled at a constant voltage. Therefore, even if the resistance value of the primary transfer roller 422 changes according to the change of the image forming environment during the image forming process, the primary current is set so that the transfer current flowing through the primary transfer roller 422 becomes a predetermined optimum transfer current. The transfer voltage applied to the transfer roller 422 can be determined again. That is, it is possible to prevent the density of the toner image transferred to the intermediate transfer belt 421 from changing during the image forming process.

  In this embodiment, since the resistance material 112 is coated on the outer peripheral surface of the metal roller 110, the combined resistance value of the primary transfer roller 422, the metal roller 110, and the resistance material 112 is the primary transfer roller 422, the intermediate transfer. The combined resistance value of the belt 421 and the photosensitive drum 413 is almost equal. As a result, in the transfer voltage control, it is possible to improve the accuracy of the transfer voltage value calculated so that the transfer current flowing through the primary transfer roller 422 becomes a predetermined optimum transfer current.

  In the above embodiment, the example in which the outer peripheral surface of the metal roller 110 is coated with the resistance material 112 has been described. However, the present invention is not limited to this. For example, instead of covering the outer peripheral surface of the metal roller 110 with the resistance material 112, a variable resistor 120 connected to the metal roller 110 may be provided as shown in FIG. In this case, the metal roller 110 and the variable resistance 120 correspond to the “resistance member” of the present invention. When the metal roller 110 is pressed against the primary transfer roller 422 and a transfer voltage is applied to the primary transfer roller 422 by the voltage application unit 80, the current detection unit 82 includes the primary transfer roller 422, the metal roller 110, and the variable resistor 120. The detected current value is output to the control unit 101.

  The control unit 101 calculates the combined resistance value of the primary transfer roller 422, the metal roller 110, and the variable resistor 120 by dividing the transfer voltage value applied to the primary transfer roller 422 by the current value acquired from the current detection unit 82. To do. As in the above embodiment, the calculated combined resistance value is preferably substantially equal to the combined resistance values of the primary transfer roller 422, the intermediate transfer belt 421, and the photosensitive drum 413. Therefore, the control unit 101 sets the resistance value of the variable resistor 120 to be equal to the resistance value of the photosensitive drum 413 before the execution of the image forming process is started (step S120 in FIG. 4). More specifically, the control unit 101 applies a voltage of a predetermined value (for example, 1000 [V]) to the primary transfer roller 422 in a state where the metal roller 110 is pressed against the primary transfer roller 422. At that time, the control unit 101 changes the variable resistance so that the current flowing through the primary transfer roller 422, the intermediate transfer belt 421, and the photosensitive drum 413 is equal to the current flowing through the primary transfer roller 422, the metal roller 110, and the variable resistor 120. A resistance value of 120 is set.

  Thereafter, the controller 101 transfers the combined resistance value of the primary transfer roller 422, the metal roller 110, and the variable resistor 120 and the toner image carried on the photosensitive drum 413 to the intermediate transfer belt 421. The transfer voltage to be applied to the primary transfer roller 422 is calculated using the calculated combined resistance value as the combined resistance value in the relational expression based on the relational expression indicating the relationship with the transfer voltage to be applied to. When the resistance value of the variable resistor 120 is set, the primary transfer roller 422 and the photosensitive drum 413 are changed by changing the pressure contact force of the metal roller 110 according to the magnitude of the surface charge (surface potential) of the photosensitive drum 413. It is preferable to change the width of the primary transfer nip formed between the two. For example, when the surface charge of the photosensitive drum 413 is larger than usual, that is, when the resistance value of the photosensitive drum 413 is higher than the actual value, the pressure contact force of the metal roller 110 is increased and the surface charge is increased. The apparent resistance value of the photosensitive drum 413 is lowered by the amount corresponding to this. On the other hand, when the surface charge of the photosensitive drum 413 is smaller than usual, that is, when the resistance value of the photosensitive drum 413 is lower than the actual value, the pressure contact force of the metal roller 110 is decreased, and the surface The apparent resistance value of the photosensitive drum 413 is increased by an amount corresponding to the smaller charge. As described above, the apparent resistance fluctuation of the photosensitive drum 413 can be corrected by changing the pressure contact force of the metal roller 110 in accordance with the magnitude of the surface charge of the photosensitive drum 413.

  In the above embodiment, as shown in FIG. 7, a cleaning device 130 having a cleaning blade 132 (corresponding to the “cleaning member” of the present invention) for cleaning the surface of the resistance material 112 (resistance member) may be provided. good. For example, the resistance value of the resistance material 112 fluctuates due to the toner or the like floating around the intermediate transfer unit 42 adhering to the resistance material 112, and the accuracy of the transfer voltage value calculated by the transfer voltage control decreases. This is to prevent this. In the configuration shown in FIG. 6, a cleaning device 130 having a cleaning blade 132 for cleaning the surface of the metal roller 110 (resistive member) may be provided.

  In the above embodiment, a plurality of resistance members (metal roller 110 and resistance material 112) that are pressed against each of a plurality of primary transfer rollers 422 provided corresponding to each of a plurality of colors are provided, and a plurality of primary transfers are performed. Transfer voltage control may be performed for each of the rollers 422. This is because the resistance value is not always the same for each of the plurality of primary transfer rollers 422 due to a change in the image forming environment. However, it is considered that the resistance value of the primary transfer roller 422 (for example, K component) closest to the heat source (for example, the fixing unit 60) is most likely to fluctuate. Therefore, if the variation in the resistance value of the K component primary transfer roller 422 is so small that it hardly affects the density change of the toner image, it is not always necessary to perform the transfer voltage control for the other primary transfer rollers 422.

  In addition, each of the above-described embodiments is merely an example of actualization in carrying out the present invention, and the technical scope of the present invention should not be construed as being limited thereto. That is, the present invention can be implemented in various forms without departing from the gist or the main features thereof.

DESCRIPTION OF SYMBOLS 1 Paper feeder 2 Image forming apparatus 3 Paper discharge apparatus 10 Image reading part 20 Operation display part 21 Display part 22 Operation part 30 Image processing part 40 Image formation part 42 Intermediate transfer unit 50 Paper conveyance part 60 Fixing part 71 Communication part 72 Memory | storage Unit 80 voltage application unit 82 current detection unit 84 pressure contact separation unit 100 image forming system 101 control unit 102 CPU
103 ROM
104 RAM
DESCRIPTION OF SYMBOLS 110 Metal roller 112 Resistance material 120 Variable resistance 130 Cleaning apparatus 132 Cleaning blade 413 Photosensitive drum 421 Intermediate transfer belt 422 Primary transfer roller P Long paper

Claims (7)

An intermediate transfer member;
A transfer member that forms a transfer nip with the photoreceptor via the intermediate transfer member;
A resistance member having electrical resistance and being pressed against the transfer member;
When a transfer voltage is applied between the photoconductor and the transfer member, a current value flowing between the transfer member and the resistance member is acquired, and the applied transfer voltage value is divided by the acquired current value. To calculate a combined resistance value of the transfer member and the resistance member, and based on a relational expression indicating a relationship between a combined resistance value of the transfer member and the resistance member and a transfer voltage to be applied to the transfer member, A control unit that determines a transfer voltage to be applied to the transfer member using the calculated combined resistance value as a combined resistance value in the relational expression;
A transfer unit comprising: A pressure contacting / separating portion that presses the resistance member against the transfer member or separates the resistance member from the transfer member;
When a transfer voltage is applied between the photoconductor and the transfer member, the control unit presses the resistance member against the transfer member, while a transfer voltage is applied between the photoconductor and the transfer member. If not applied, the transfer member is separated from the resistance member;
The transfer unit according to claim 1 . A plurality of resistance members pressed against each of a plurality of transfer members provided corresponding to each of a plurality of colors;
The transfer unit according to claim 1 or 2 . A cleaning member for cleaning the surface of the resistance member;
The transfer unit according to any one of claims 1 to 3 . A photoreceptor,
An intermediate transfer member;
A transfer member that forms a transfer nip with the photoreceptor via the intermediate transfer member;
A resistance member having electrical resistance and being pressed against the transfer member;
When a transfer voltage is applied between the photoconductor and the transfer member, a current value flowing between the transfer member and the resistance member is acquired, and the applied transfer voltage value is divided by the acquired current value. To calculate a combined resistance value of the transfer member and the resistance member, and based on a relational expression indicating a relationship between a combined resistance value of the transfer member and the resistance member and a transfer voltage to be applied to the transfer member, A control unit that determines a transfer voltage to be applied to the transfer member using the calculated combined resistance value as a combined resistance value in the relational expression;
An image forming apparatus comprising: A paper feeder for feeding long paper,
The image forming apparatus according to claim 5 , wherein a toner image is formed on the long paper fed by the paper feeding device;
A paper discharge device for storing the long paper on which a toner image is formed by the image forming device;
Comprising
Image forming system. When a transfer voltage is applied between the transfer member that forms a transfer nip with the photosensitive member via the intermediate transfer member and the photosensitive member, the transfer member has an electrical resistance and is pressed against the transfer member. Obtain the value of the current flowing between the
Calculate the combined resistance value of the transfer member and the resistance member by dividing the applied transfer voltage value by the acquired current value,
Based on the relational expression indicating the relation between the combined resistance value of the transfer member and the resistance member and the transfer voltage to be applied to the transfer member, the combined resistance value in the relational expression is used as the calculated combined resistance value. Determining a transfer voltage to be applied to the transfer member;
Transfer voltage control method.

Images