Intermediate transfer unit, image forming apparatus, and method for manufacturing intermediate transfer unit

Abstract

To adjust all the values of current flowing in primary transfer members to be a target value.SOLUTION: An intermediate transfer unit comprises an intermediate transfer belt, a plurality of primary transfer members, and a plurality of power supply sections that apply transfer voltage to the corresponding primary transfer members. The power supply sections each have a power supply line that is connected to a supply source of the transfer voltage, and a resistance part that is arranged between the corresponding primary transfer member and the power supply line. The resistance part includes a plurality of resistance elements. The primary transfer member is connected to the power supply line through one or more resistance elements selected in advance, of the plurality of resistance elements of the corresponding power supply section.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an intermediate transfer unit, an image forming apparatus, and a method for manufacturing the intermediate transfer unit. [Background technology]

[0002] A conventional image forming apparatus includes four image forming units, one for each of the colors cyan, magenta, yellow, and black. The image forming apparatus also includes an intermediate transfer unit with an intermediate transfer belt. Each image forming unit forms a toner image using toner of the corresponding color and performs primary transfer onto the intermediate transfer belt. The intermediate transfer unit then performs secondary transfer of the toner image onto a sheet.

[0003] Each image forming section has an image carrier that carries a toner image. The intermediate transfer unit has four primary transfer members that correspond to each image carrier. Each primary transfer member faces the corresponding image carrier with the intermediate transfer belt sandwiched between them. A transfer voltage is applied to each primary transfer member. This causes the toner image to be primarily transferred from each image carrier to the intermediate transfer belt. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2017-26872 Summary of the Invention [Problem to be solved by the invention]

[0005] In a configuration with four primary transfer members, variations in the current values ​​flowing through each primary transfer member can occur. For example, excessive current may flow through a primary transfer member. This can cause problems such as a decrease in image quality.

[0006] The present invention has been made to solve the above-mentioned problems, and aims to provide an intermediate transfer unit, an image forming apparatus, and a method for manufacturing an intermediate transfer unit in a configuration having multiple primary transfer members, in which the current values ​​flowing through each primary transfer member can all be set to target values. [Means for solving the problem]

[0007] To achieve the above object, an intermediate transfer unit according to a first aspect of the present invention includes an intermediate transfer belt that is rotatably supported and has an outer peripheral surface onto which a toner image is transferred from each of a plurality of image carriers, the intermediate transfer belt carrying the toner image and rotating; a plurality of primary transfer members that are assigned to the plurality of image carriers, respectively, sandwiching the intermediate transfer belt between the image carriers and the corresponding image carriers, and that perform a primary transfer of the toner image to the intermediate transfer belt; and a plurality of power supply units that are assigned to the plurality of primary transfer members, respectively, and apply a transfer voltage to the corresponding primary transfer member. The power supply units have a power supply line connected to a transfer voltage supply source and a resistor unit disposed between the corresponding primary transfer member and the power supply line. The resistor unit includes a plurality of resistor elements having the same or different resistance values. The primary transfer member is connected to the power supply line via one or more preselected resistor elements from the plurality of resistor elements of the corresponding power supply unit.

[0008] An image forming apparatus according to a second aspect of the present invention includes the above-mentioned intermediate transfer unit, a plurality of image carriers, and a secondary transfer member that is pressed against the outer peripheral surface of the intermediate transfer belt to form a transfer nip between the intermediate transfer belt and the secondary transfer member, and that performs a second transfer of the toner image on the intermediate transfer belt to a sheet passing through the transfer nip.

[0009] A manufacturing method of an intermediate transfer unit according to a third aspect of the present invention is a manufacturing method of the above-mentioned intermediate transfer unit, and includes the steps of applying a predetermined voltage to each of a plurality of primary transfer members and measuring the value of the current flowing through each of the plurality of primary transfer members, and selecting, for each power supply unit, a resistance element to be connected to the power supply line so that the value of the current flowing through each of the plurality of primary transfer members becomes a predetermined current value. [Effects of the Invention]

[0010] In the present invention, in a configuration including a plurality of primary transfer members, the current values ​​flowing through the respective primary transfer members can all be set to the target value. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram of a primary transfer roller and its surroundings according to an embodiment. [Figure 3] FIG. 1 is a block diagram of an image forming apparatus according to an embodiment. [Figure 4] FIG. 2 is a schematic diagram showing the configuration of a resistance section according to an embodiment (a diagram in which three resistance elements are selected). [Figure 5] FIG. 2 is a schematic diagram showing the configuration of a resistance section according to an embodiment (a diagram in which two resistance elements are selected). [Figure 6] FIG. 2 is a schematic diagram showing the configuration of a resistance section according to an embodiment (a diagram in which one resistance element is selected). [Figure 7] 5A and 5B are diagrams for explaining a method for measuring the value of a current flowing through a primary transfer roller according to an embodiment. [Figure 8] 5A to 5C are diagrams illustrating a flow of a manufacturing process for an intermediate transfer unit according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] The image forming apparatus 100 of this embodiment will be described below with reference to Figs. 1 to 8. The image forming apparatus 100 executes a job (hereinafter simply referred to as a print job) to print an image on a sheet S. Normally, the image forming apparatus 100 is placed on a substantially flat floor surface FL. The direction perpendicular to the floor surface FL is the up-down direction of the image forming apparatus 100.

[0013] <Configuration of image forming device> As shown in Fig. 1, the image forming apparatus 100 includes a main transport path MP. The image forming apparatus 100 also includes a sheet cassette CA. The sheet cassette CA is detachable from the main body of the image forming apparatus 100. The sheet cassette CA stores sheets S used in a print job. The main transport path MP runs from the sheet cassette CA, passing through a transfer position and a fixing position in that order, to an output tray ET.

[0014] In a print job, a sheet S from a sheet cassette CA is supplied to a main transport path MP, and the sheet S is transported along the main transport path MP. An image is formed using toner. The image is then printed on the sheet S as it is being transported. In other words, a transfer process (specifically, a secondary transfer) of the image onto the sheet S as it is being transported is performed at the transfer position. At the fixing position, a fixation process of the image onto the sheet S is performed.

[0015] The image forming apparatus 100 includes four image forming units 1 assigned to the respective colors of cyan, magenta, yellow, and black. Each image forming unit 1 forms an image (i.e., a toner image) using toner of the corresponding color.

[0016] The following description focuses on one image forming unit 1 and explains its configuration, but the configurations of the image forming units 1 are the same. Therefore, the following description will be used to cite the configurations of the other image forming units 1 and will not be explained.

[0017] As shown in Fig. 2, the image forming unit 1 includes a photosensitive drum 11, a charging device 12, an exposure device 13, a developing device 14, and a cleaning device 15. The photosensitive drum 11 corresponds to an "image carrier." For example, the photosensitive drum 11, the charging device 12, the developing device 14, and the cleaning device 15 form a single unit. The exposure device 13 is a separate unit from the single unit.

[0018] The photosensitive drum 11 is supported so as to be rotatable about an axis extending in one direction (a direction perpendicular to the plane of the paper in FIG. 2). The outer peripheral surface of the photosensitive drum 11 serves as a toner image bearing surface. The photosensitive drum 11 rotates with the toner image carried on its outer peripheral surface.

[0019] The charging device 12 has a charging roller. The charging roller comes into contact with the outer peripheral surface of the photosensitive drum 11. In this way, the charging device 12 charges the outer peripheral surface of the photosensitive drum 11.

[0020] The exposure device 13 exposes the outer peripheral surface of the photosensitive drum 11 to light to attenuate the charge. The exposure device 13 exposes the outer peripheral surface of the photosensitive drum 11 to light to form an electrostatic latent image on the outer peripheral surface of the photosensitive drum 11.

[0021] The developing device 14 contains a developer containing toner. The developer is a two-component developer containing toner and a carrier. The developing device 14 has a developing roller. The developing roller is supported so as to be rotatable about an axis extending in one direction (a direction perpendicular to the plane of the paper in FIG. 2). The developing roller carries a developer (i.e., toner) on its outer circumferential surface. A magnetic brush is formed on the outer circumferential surface of the developing roller. The developing roller rotates while bringing the magnetic brush into contact with the outer circumferential surface of the photosensitive drum 11. As a result, the toner adheres to the outer circumferential surface of the photosensitive drum 11, and a toner image is formed on the outer circumferential surface of the photosensitive drum 11.

[0022] The cleaning device 15 removes residual toner from the outer circumferential surface of the photosensitive drum 11 downstream in the rotation direction of the photosensitive drum 11 from a contact position between the intermediate transfer belt 21 (described later) and the photosensitive drum 11. Toner that has not been transferred to the intermediate transfer belt 21 remains on the outer circumferential surface of the photosensitive drum 11.

[0023] As shown in FIG. 1 , the image forming apparatus 100 also includes an intermediate transfer unit 2. The intermediate transfer unit 2 is disposed below each image forming section 1. The components of the intermediate transfer unit 2 are supported by a frame (not shown) of the intermediate transfer unit 2 (hereinafter, this frame will be referred to as a unit frame). The unit frame is detachable from the main body of the image forming apparatus 100. This allows the intermediate transfer unit 2 to be detachable from the main body of the image forming apparatus 100.

[0024] The intermediate transfer unit 2 includes an intermediate transfer belt 21. The intermediate transfer belt 21 is an endless belt. The intermediate transfer belt 21 is stretched by a plurality of tension rollers (reference numbers for other tension rollers are omitted) including a drive roller 210. Each tension roller is supported by a unit frame and is rotatable around an axis extending in one direction (a direction perpendicular to the plane of the paper in FIG. 2).

[0025] The drive roller 210 rotates by power transmitted from a belt motor (not shown). The intermediate transfer belt 21 rotates in response to the rotation of the drive roller 210. In other words, the intermediate transfer belt 21 is rotatably supported. The four photosensitive drums 11 are arranged in a row below the intermediate transfer belt 21 at intervals along the rotation direction of the intermediate transfer belt 21.

[0026] The intermediate transfer belt 21 is disposed so that its outer circumferential surface contacts the outer circumferential surface of each photosensitive drum 11. That is, each photosensitive drum 11 is disposed on the outer circumferential side of the intermediate transfer belt 21. The toner image on each photosensitive drum 11 is primarily transferred onto the outer circumferential surface of the intermediate transfer belt 21. The intermediate transfer belt 21 rotates while carrying the toner image on its outer circumferential surface. This transports the toner image on the intermediate transfer belt 21 toward the transfer position.

[0027] The intermediate transfer unit 2 includes primary transfer rollers 22. The primary transfer rollers 22 correspond to the "primary transfer members." There are four primary transfer rollers 22, one for each photosensitive drum 11. In other words, the intermediate transfer unit 2 includes four primary transfer rollers 22, one for each of the colors cyan, magenta, yellow, and black.

[0028] Each primary transfer roller 22 is supported by a unit frame and is rotatable around an axis extending in one direction (a direction perpendicular to the plane of the paper in FIG. 2). Each primary transfer roller 22 is disposed on the inner circumferential side of the intermediate transfer belt 21. Each primary transfer roller 22 is pressed against the photosensitive drum 11 carrying a toner image of the corresponding color via the intermediate transfer belt 21. A transfer voltage is applied to each primary transfer roller 22. The transfer voltage has a polarity opposite to that of the toner.

[0029] As shown in FIG. 2, the intermediate transfer unit 2 also includes a power supply unit 23. There are four power supply units 23, one for each primary transfer roller 22. Each power supply unit 23 is connected to a transfer voltage power supply 200. The transfer voltage power supply 200 supplies a transfer voltage to each primary transfer roller 22. Each power supply unit 23 applies a transfer voltage to the corresponding primary transfer roller 22. For convenience, FIG. 2 illustrates only the image forming unit 1 corresponding to one primary transfer roller 22, and does not illustrate the image forming units 1 corresponding to the other primary transfer rollers 22.

[0030] Each power supply unit 23 has a power supply line 20. Unit-side contacts are provided on the unit frame. The power supply line 20 of each power supply unit 23 is connected to the unit-side contacts. The power supply line 20 of each power supply unit 23 branches off and extends from the unit-side contacts.

[0031] Meanwhile, a main body contact is provided on the main body of the image forming apparatus 100. The transfer voltage power supply 200 is connected to the main body contact. The main body contact is disposed at a position where it can come into contact with the unit contact when the intermediate transfer unit 2 is attached to the main body of the image forming apparatus 100.

[0032] In this configuration, when the intermediate transfer unit 2 is attached to the main body of the image forming apparatus 100, the unit-side contacts come into contact with the main body-side contacts. That is, each power supply 23 is connected to the transfer voltage power supply 200. As a result, even if the intermediate transfer unit 2 is detachable from the main body of the image forming apparatus 100, attaching the intermediate transfer unit 2 to the main body of the image forming apparatus 100 makes it possible to apply a transfer voltage to each primary transfer roller 22.

[0033] Here, each power supply unit 23 has a resistance unit 230. The resistance unit 230 of each power supply unit 23 is disposed between the corresponding primary transfer roller 22 and the power supply line 20. The resistance unit 230 of each power supply unit 23 is disposed on the current path between the corresponding primary transfer roller 22 and the unit-side contact. In other words, the power supply line 20 of each power supply unit 23 is connected to the corresponding primary transfer roller 22 via the resistance unit 230.

[0034] As shown in FIG. 1, the image forming apparatus 100 also includes a secondary transfer roller 3. The secondary transfer roller 3 corresponds to a "secondary transfer member." The secondary transfer roller 3 is pressed against the outer circumferential surface of the intermediate transfer belt 21 at the transfer position. The secondary transfer roller 3 sandwiches the intermediate transfer belt 21 between itself and the drive roller 210, forming a transfer nip between itself and the intermediate transfer belt 21. This forms a transfer nip at the transfer position. The main transport path MP passes through the transfer nip.

[0035] In a print job, the sheet S is transported toward a transfer position (i.e., a transfer nip). During transport, the sheet S passes through the transfer nip. The outer circumferential surface of the intermediate transfer belt 21 contacts the sheet S downstream of the contact position with each photosensitive drum 11 in the belt rotation direction.

[0036] Each image forming unit 1 forms a toner image using toner of the corresponding color. Each primary transfer roller 22 primarily transfers the toner image onto the outer circumferential surface of the intermediate transfer belt 21. The intermediate transfer belt 21 rotates while carrying the toner image. In other words, the intermediate transfer belt 21 transports the toner image toward the transfer position. The direction of arrow D in the figure is the transport direction of the toner image. The secondary transfer roller 3 secondarily transfers the toner image onto the sheet S passing through the transfer nip.

[0037] In color printing, toner images are formed in all of the image forming units 1. Of the four image forming units 1, toner images are formed in order starting from the image forming unit 1 whose contact position between the photosensitive drum 11 and the intermediate transfer belt 21 is more upstream in the belt rotation direction, and the toner images are primarily transferred to the intermediate transfer belt 21. At this time, the toner images of each color are superimposed on each other on the intermediate transfer belt 21. As a result, a full-color toner image is formed on the intermediate transfer belt 21. The full-color toner image is secondarily transferred to the sheet S.

[0038] The image forming apparatus 100 also includes a fixing unit 4. The fixing unit 4 includes a heating roller and a pressure roller. The heating roller has a built-in heater. The pressure roller is in pressure contact with the heating roller. The heating roller and the pressure roller are in pressure contact with each other to form a fixing nip at the fixing position.

[0039] During a print job, the sheet S passes through the fixing position. That is, the sheet S is sandwiched in the fixing nip. The fixing unit 4 heats the sheet S as it passes through the fixing position. Also, pressure is applied to the sheet S at the fixing position. The fixing unit 4 applies heat and pressure to the sheet S to fix the toner image to the sheet S. The sheet S that has undergone the fixing process is discharged onto the discharge tray ET.

[0040] The image forming apparatus 100 includes a transport unit, the reference numeral of which is omitted. The transport unit includes a transport roller pair. The transport roller pair includes a pair of rollers. The pair of rollers has a transport nip between them. The transport roller pair rotates to transport the sheet S that has entered the transport nip. The transport unit transports the sheet S along a main transport path MP. The transport unit also transports the sheet S along a double-sided printing transport path DP, which will be described later.

[0041] The image forming apparatus 100 is capable of executing a single-sided print job in which an image is printed on only one side of a sheet S, as well as a double-sided print job in which an image is printed on both sides of a sheet S. To execute a double-sided print job, the image forming apparatus 100 is provided with a double-sided printing transport path DP.

[0042] The double-sided printing transport path DP branches off from the main transport path MP at a branching position downstream of the fixing position in the sheet transport direction, and merges with the main transport path MP at a merging position upstream of the transfer position in the sheet transport direction.

[0043] If the job to be executed is a single-sided print job, the sheet S passes through the transfer nip only once, and a single transfer process is performed on the sheet S while it is passing through the transfer nip. After the first transfer process, the sheet S is discharged directly onto the discharge tray ET.

[0044] If the job being executed is a double-sided printing job, the sheet S passes through the transfer nip twice, with one transfer process performed on each of the front and back sides of the sheet S. Specifically, the first time the sheet S passes through the transfer nip, the transfer process is performed on one side of the sheet S. After the first transfer process, the sheet S is switched back after the rear end of the sheet S passes the branch position but before the sheet S is completely discharged onto the discharge tray ET. This causes the rear end of the sheet S to be drawn into the double-sided printing transport path DP.

[0045] Thereafter, the sheet S is transported along the double-sided printing transport path DP. Then, the sheet S on the double-sided printing transport path DP is returned to the main transport path MP from the junction position. The sheet S returned to the main transport path MP is transported along the main transport path MP and passes through the transfer nip again. At this time, the orientation of the front and back surfaces of the sheet S is reversed to the orientation when it passed through the transfer nip the previous time. As a result, when the sheet S passes through the transfer nip for the second time, the transfer process is performed on the other side of the sheet S, which is opposite to the one side.

[0046] 3, the image forming apparatus 100 also includes a control unit 5. The control unit 5 includes processing circuits such as a CPU and an ASIC. The control unit 5 also includes storage devices such as a ROM and a RAM. The control unit 5 controls print jobs executed by the image forming apparatus 100. The control unit 5 controls image formation using toner, primary transfer of a toner image, and secondary transfer of a toner image.

[0047] The image forming apparatus 100 includes a communication unit 101. The communication unit 101 includes a communication circuit, a communication memory, a communication connector, and the like. The communication unit 101 is communicably connected to an external device via a network such as a LAN. The external device may be a user terminal. A personal computer (PC), a smartphone, a tablet computer, or the like may serve as the user terminal.

[0048] Control unit 5 communicates with external devices using communication unit 101. For example, print data of a print job is transmitted from an external device (user terminal) to image forming apparatus 100. The print data includes image data to be printed in the print job.

[0049] The control unit 5 adds a print job corresponding to the received print data to a queue. The control unit 5 executes the print jobs in the queue in the order in which they are received. If there are multiple print jobs in the queue, these multiple print jobs are executed consecutively.

[0050] The image forming apparatus 100 includes an operation unit 102. The operation unit 102 is an operation panel and includes a touch screen. The operation unit 102 receives settings, instructions, and the like from a user. The operation unit 102 is connected to a control unit 5. The control unit 5 detects the settings, instructions, and the like received by the operation unit 102 from the user.

[0051] The image forming apparatus 100 includes a storage unit 6. Various storage devices such as a flash memory, an HDD, and an SSD can be used as the storage unit 6. The storage unit 6 is connected to the control unit 5. The control unit 5 writes data to the storage unit 6 and reads data from the storage unit 6.

[0052] <Voltage application to the primary transfer roller> Each primary transfer roller 22 receives a transfer voltage via a power supply unit 23 having any of the configurations shown in Figures 4 to 6. This will be described in detail below.

[0053] Each power supply unit 23 has a plurality of resistive elements R as a resistance unit 230. That is, each resistance unit 230 includes a plurality of resistive elements R. This point is common to all power supply units 23. For example, each power supply unit 23 has three resistive elements R. Note that the resistance values ​​of the plurality of resistive elements R in each resistance unit 230 may be the same or different. Furthermore, the number of resistive elements R in each resistance unit 230 may be two or four or more as long as it is plural.

[0054] Here, in this embodiment, the power supply line 20 of each power supply unit 23 is connected only to one or more pre-selected resistance elements R out of the multiple resistance elements R of the corresponding power supply unit 23, and is not connected to unselected resistance elements R. In other words, each primary transfer roller 22 is connected to the power supply line 20 of the corresponding power supply unit 23 via one or more pre-selected resistance elements R out of the multiple resistance elements R of the corresponding power supply unit 23.

[0055] In the example shown in Figure 4, three (i.e., all) resistive elements R are selected. In the example shown in Figure 5, two resistive elements R are selected. In the example shown in Figure 6, one resistive element R is selected.

[0056] The power supply unit 23 having the configuration shown in Fig. 4 connects the corresponding primary transfer roller 22 and the power supply line 20 via all three resistance elements R. The power supply unit 23 having the configuration shown in Fig. 5 connects the corresponding primary transfer roller 22 and the power supply line 20 via two resistance elements R. The power supply unit 23 shown in Fig. 6 connects the corresponding primary transfer roller 22 and the power supply line 20 via one resistance element R.

[0057] With this configuration, the value of the current flowing through each primary transfer roller 22 can be adjusted individually. The current value can be adjusted simply by changing the connection method of the resistance element R for each primary transfer roller 22. This makes it easy to set all the current values ​​flowing through each primary transfer roller 22 to the target value. In other words, it is possible to prevent the current value flowing through each primary transfer roller 22 from deviating from the target value. As a result, it is possible to prevent degradation in image quality caused by the current value flowing through each primary transfer roller 22 deviating significantly from the target value.

[0058] In this embodiment, a process for adjusting the value of the current flowing through each primary transfer roller 22 is included as one of the manufacturing processes for the intermediate transfer unit 2. After the intermediate transfer unit 2 is assembled, the value of the current flowing through each primary transfer roller 22 is adjusted.

[0059] 7, in the process of adjusting the value of the current flowing through each primary transfer roller 22, a grounded roller member 110 is prepared, and the intermediate transfer unit 2 is held so that each primary transfer roller 22 faces the roller member 110 across the intermediate transfer belt 21. Then, the intermediate transfer belt 21 is rotated, and in this state, a predetermined voltage is applied to each primary transfer roller 22, and the value of the current flowing through each primary transfer roller 22 is measured.

[0060] Next, a connection method for the resistance element R of each power supply unit 23 is determined based on the value of the current flowing through each primary transfer roller 22. At this time, the resistance element R to be connected to the power supply line 20 is selected for each power supply unit 23 so that the value of the current flowing through each primary transfer roller 22 becomes a predetermined current value (i.e., a target value). Then, the power supply line 20 is connected to each primary transfer roller 22 via one or more resistance elements R selected in this process. This makes it easy to set the value of the current flowing through each primary transfer roller 22 to the target value.

[0061] 8, the manufacturing process of the intermediate transfer unit 2 (adjusting the value of the current flowing through each primary transfer roller 22) includes a current value measurement process #1 and a resistance element selection process #2. The current value measurement process #1 is a process of applying a predetermined voltage to each primary transfer roller 22 and measuring the value of the current flowing through each primary transfer roller 22. The resistance element selection process #2 is a process of selecting a resistance element R to be connected to the power supply line 20 for each power supply unit 23 so that the value of the current flowing through each primary transfer roller 22 becomes a predetermined current value.

[0062] For example, the resistance value (when 1000 V is applied) of each primary transfer roller 22 is 500 kΩ or more. In each power supply unit 23, a resistance element R connected to the power supply line 20 is selected so that the resistance value is 10 times or more the upper tolerance limit of the resistance value of the primary transfer roller 22. In other words, the resistance value of the resistance unit 230 of each power supply unit 23 is higher than the resistance value of the corresponding primary transfer roller 22.

[0063] Furthermore, in this embodiment, the resistance unit 230 of each power supply unit 23 includes at least one resistance element R with a resistance value of 100 MΩ or more. This allows for efficient adjustment of the value of the current flowing through each primary transfer roller 22. For example, of the three resistance elements R of each power supply unit 23, one may be 100 MΩ or more and the rest may be less than 100 MΩ. Alternatively, the resistance values ​​of the three resistance elements R of each power supply unit 23 may be the same.

[0064] Furthermore, in this embodiment, the resistance elements R connected to the power supply line 20 are selected so that the resistance value of the resistance unit 230 connected to the primary transfer roller 22 further downstream in the transport direction of the toner image carried and transported by the intermediate transfer belt 21 (hereinafter simply referred to as the image transport direction) becomes lower. In other words, the resistance elements R connected to the power supply line 20 are selected so that the resistance value of the resistance unit 230 connected to the downstream primary transfer roller 22 is equal to or lower than the resistance value of the resistance unit 230 connected to the upstream primary transfer roller 22. For example, the more downstream the resistance unit 230 connected to the primary transfer roller 22, the fewer the number of resistance elements R connected to the power supply line 20.

[0065] For example, in the image transport direction (the direction of arrow D in the figure), starting from the most upstream primary transfer roller 22 toward the downstream side, if the resistance value of the resistor unit 230 connected to the first primary transfer roller 22 is R1, the resistance value of the resistor unit 230 connected to the second primary transfer roller 22 is R2, the resistance value of the resistor unit 230 connected to the third primary transfer roller 22 is R3, and the resistance value of the resistor unit 230 connected to the fourth primary transfer roller 22 is R4, then the following equation (1) is satisfied. R1 ≥ R2 ≥ R3 ≥ R4 (1)

[0066] By configuring the roller 22 so as to satisfy the above formula (1), the value of the current flowing through the primary transfer roller 22 on the most downstream side in the image transport direction becomes larger. Here, at the most downstream side in the image transport direction, it is preferable to increase the value of the current flowing through the primary transfer roller 22 in order to perform primary transfer of another toner image onto the toner image that has already been primarily transferred. In other words, it is preferable to configure the roller 22 so as to satisfy the above formula (1). This can improve image quality.

[0067] In this embodiment, unselected resistance elements R among the plurality of resistance elements R of each power supply unit 23 are kept in a state of being unconnected to the power supply line 20. This makes it easy to keep only the selected resistance elements R connected to the power supply line 20.

[0068] In this embodiment, roller information 60 indicating the results when a predetermined voltage is applied to each primary transfer roller 22 and the current value is measured is stored in the storage unit 6 (see FIG. 3). That is, the manufacturing process of the intermediate transfer unit 2 further includes an information storage step #3, as shown in FIG. 8. The information storage step #3 is a step of storing roller information 60 indicating the current value and predetermined voltage flowing through each primary transfer roller 22 in the storage unit 6. This makes it possible, for example, to control image formation by each image forming unit 1 based on the roller information 60 stored in the storage unit 6. The roller information 60 corresponds to "information."

[0069] The embodiments disclosed herein should be considered to be illustrative in all respects and not restrictive. The scope of the present invention is defined by the claims rather than the description of the above embodiments, and further includes all modifications within the meaning and scope of the claims. [Explanation of symbols]

[0070] 2 Intermediate transfer unit 3 Secondary transfer roller (secondary transfer member) 6 Memory section 11 Photosensitive drum (image carrier) 20 Power supply line 21 Intermediate transfer belt 22 Primary transfer roller (primary transfer member) 23 Power supply section 60 Roller Information (Information) 100 Image forming device 200 Transfer voltage power supply (supplier) 230 Resistance section R resistive element S seat

Claims

1. an intermediate transfer belt that is rotatably stretched, has an outer peripheral surface onto which toner images are transferred from each of a plurality of image carriers, and rotates while carrying the toner images; a plurality of primary transfer members that are assigned to the plurality of image carriers, respectively, and that sandwich the intermediate transfer belt between the primary transfer members and the corresponding image carriers, and that primarily transfer the toner images onto the intermediate transfer belt; a plurality of power supply units assigned to the plurality of primary transfer members, respectively, for applying a transfer voltage to the corresponding primary transfer members; The power supply unit a power supply line connected to a source of the transfer voltage; a resistor portion disposed between the corresponding primary transfer member and the power supply line, the resistor section includes a plurality of resistor elements having the same or different resistance values, an intermediate transfer unit, wherein the primary transfer member is connected to the power supply line via one or more preselected resistor elements from among the plurality of resistor elements of the corresponding power supply unit;

2. 2. The intermediate transfer unit according to claim 1, wherein the resistance portion includes at least one resistance element having a resistance value of 100 M[Omega] or more.

3. 2. The intermediate transfer unit according to claim 1, wherein the resistance element connected to the power supply line is selected so that the resistance value of the resistance section connected to the downstream primary transfer member is equal to or less than the resistance value of the resistance section connected to the upstream primary transfer member in the transport direction of the toner image carried and transported by the intermediate transfer belt.

4. the number of primary transfer members is four, 2. The intermediate transfer unit according to claim 1, wherein, in the transport direction of the toner image carried and transported on the intermediate transfer belt, the resistance value of the resistor unit connected to the first of the four primary transfer members is R1, the resistance value of the resistor unit connected to the second of the four primary transfer members is R2, the resistance value of the resistor unit connected to the third of the four primary transfer members is R3, and the resistance value of the resistor unit connected to the fourth of the four primary transfer members is R4, and wherein R1 ≧ R2 ≧ R3 ≧ E4 is satisfied.

5. 2. The intermediate transfer unit according to claim 1, wherein a total resistance value of the selected resistor elements of the resistor section is higher than a resistance value of the primary transfer member.

6. The intermediate transfer unit according to claim 1 , wherein the unselected resistor elements of the resistor section are kept in a state of being unconnected to the power supply line.

7. an intermediate transfer unit according to any one of claims 1 to 6; A plurality of the image carriers; a secondary transfer member that is pressed against the outer peripheral surface of the intermediate transfer belt to form a transfer nip between the intermediate transfer belt and the secondary transfer member, and that performs a second transfer of the toner image on the intermediate transfer belt to a sheet that passes through the transfer nip.

8. A method for manufacturing the intermediate transfer unit according to any one of claims 1 to 6, comprising the steps of: applying a predetermined voltage to each of the plurality of primary transfer members and measuring a current value flowing through each of the plurality of primary transfer members; and selecting the resistance element to be connected to the power supply line for each power supply unit so that the current value flowing through each of the plurality of primary transfer members is a predetermined current value.

9. The method for manufacturing an intermediate transfer unit according to claim 8 , further comprising the step of storing information indicating the current values ​​and the predetermined voltages flowing through the plurality of primary transfer members in a storage unit.

Images