Image forming device

Abstract

To reduce the interference between a current flowing in primary transfer units and a current flowing in a secondary transfer unit without causing transfer failure during image formation, and prevent increases in size and cost of a device.SOLUTION: A transfer device 2 executes secondary transfer ATVC control processing of, based on a result of detection performed by a voltage detection unit 42 when a secondary transfer bias is applied or current is supplied to a secondary transfer inner roller 62, determining the secondary transfer bias to be applied to the secondary transfer inner roller 62 during image formation, and stops application of a primary transfer bias to primary transfer rollers 54 during the execution of the secondary transfer ATVC control processing.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention , turn The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile machine that includes a copying device. [Background technology]

[0002] Conventionally, as an image forming apparatus such as a printer, a copier, or a facsimile, an intermediate transfer type image forming apparatus is known in which a belt-like intermediate transfer member is provided facing each of a plurality of photosensitive drums serving as image carriers. The intermediate transfer type image forming apparatus is equipped with a transfer device having a plurality of primary transfer units that transfer the toner images carried on each of the plurality of photosensitive drums to the intermediate transfer member, and a secondary transfer unit that transfers the toner images transferred to the intermediate transfer member to a recording medium. The intermediate transfer member is also stretched over a plurality of support rollers and passes through the plurality of primary and secondary transfer units.

[0003] Conventionally, elastic rollers such as sponge rollers having an elastic layer such as a sponge-like foam layer on a metal roller or a core metal have been widely used as transfer rollers for transfer devices. Such elastic rollers are made conductive by dispersing conductive powder such as carbon black in the elastic layer.

[0004] The elastic layer with dispersed conductive powder experiences resistance fluctuations due to environmental and durability variations. For this reason, it has traditionally been necessary to use high-voltage control, such as Active Transfer Voltage Control (hereinafter referred to as "ATVC"), to ensure that the current flowing through the transfer roller during image formation is at a desired value. Here, ATVC refers to applying a predetermined voltage to the secondary transfer roller and controlling the voltage applied to the secondary transfer roller during image formation based on the detection results of the current flowing through the secondary transfer roller.

[0005] In addition, in the above-described transfer device, the polarities of the transfer biases applied to the primary transfer unit and the secondary transfer unit may be different. For example, a positive bias may be applied to the transfer roller of the primary transfer unit, and a negative bias may be applied to the transfer roller of the secondary transfer unit. In this case, there is a risk that the currents flowing through the primary transfer unit and the secondary transfer unit may interfere with each other.

[0006] In response to this, Patent Document 1 discloses a transfer device and an image forming apparatus that are provided with at least two grounding points between a primary transfer unit and a secondary transfer unit, where an intermediate transfer body is connected to a ground directly or via a resistor. This makes it possible to prevent interference between currents flowing through the primary transfer unit and the secondary transfer unit when biases of different polarities are applied to the transfer roller of the primary transfer unit and the transfer roller of the secondary transfer unit. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-153398 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in Patent Document 1, when ATVC is performed, the current that should flow to the secondary transfer roller flows into a grounded roller, making it impossible to supply an appropriate current to the secondary transfer roller, which can lead to a decrease in ATVC accuracy. This can cause a problem of poor toner image transfer during image formation. Furthermore, Patent Document 1 also has the problem of increasing the size and cost of the device by providing a grounded location between the primary transfer unit and the secondary transfer unit.

[0009] The object of the present invention is to reduce interference between currents flowing in a primary transfer unit and a secondary transfer unit without causing transfer defects during image formation, and to prevent the device from becoming larger and more expensive. Ru pictureAn image forming apparatus is provided. [Means for solving the problem]

[0010] an image forming apparatus according to the present invention, comprising: an image forming unit that forms a toner image on an image carrier; a belt onto which the toner image is transferred from the image carrier; a primary transfer member that performs primary transfer of the toner image from the image carrier to the belt; a first application unit that applies a voltage to the primary transfer member; a secondary transfer member that contacts the inner surface of the belt to stretch the belt and performs secondary transfer of the toner image from the belt to a recording material; a second application unit that applies a voltage to the secondary transfer member; a detection unit that detects a current flowing through or a voltage applied to the secondary transfer member; and a control unit that executes an operation to determine a transfer voltage to be applied to the secondary transfer member during secondary transfer based on a detection result of the detection unit when a test voltage is applied to the secondary transfer member during non-image formation, wherein the control unit controls the first application unit and the second application unit so as not to apply a voltage to the primary transfer member during a period when the test voltage is applied to the secondary transfer member during the operation. At the same time, the application period of the test voltage when forming a monochrome image is made shorter than the application period of the test voltage when forming a full-color image. , characterized by: [Effects of the Invention]

[0011] According to the present invention, it is possible to reduce interference between currents flowing through the primary transfer unit and the secondary transfer unit without causing transfer defects during image formation, and also to prevent the device from becoming larger and more expensive. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention. [Figure 2] 1 is a block diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention; [Figure 3] 1 is a block diagram showing a configuration of a transfer device according to an embodiment of the present invention; [Figure 4] 5A to 5C are schematic diagrams illustrating the operation of the transfer device according to the embodiment of the present invention. [Figure 5]10A and 10B are diagrams illustrating application timings of a primary transfer bias and a secondary transfer bias when the transfer device according to the embodiment of the present invention is operating in a full-color mode. [Figure 6] 10A and 10B are diagrams illustrating application timings of a primary transfer bias and a secondary transfer bias when the transfer device according to the embodiment of the present invention is in a monochrome mode. [Figure 7] 5 is a diagram showing the relationship between the potential difference and leakage current in the transfer device according to the embodiment of the present invention. FIG. [Figure 8] 10A and 10B are diagrams illustrating the relationship between leakage current and an image in the transfer device according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, embodiments will be described in detail with reference to the drawings.

[0014] <Configuration of image forming device> The configuration of an image forming apparatus 1 according to an embodiment of the present invention will be described in detail with reference to FIGS.

[0015] The image forming apparatus 1 includes a transfer device 2, an image forming unit 57, a registration roller 66, a fixing unit 67, and an operation unit 81. The image forming apparatus 1 is exemplified here as a full-color image forming apparatus having a so-called tandem intermediate transfer system.

[0016] The transfer device 2 primarily transfers the toner image formed by the image forming unit 57 onto the intermediate transfer belt 56, and then secondarily transfers the toner image primarily transferred onto the intermediate transfer belt 56 onto the sheet P conveyed by the registration rollers 66. The transfer device 2 conveys the sheet P onto which the toner image has been secondarily transferred to a fixing unit 67. The configuration of the transfer device 2 will be described in detail later.

[0017] Image forming unit 57 as an image forming means is composed of multiple image forming units 57a, 57b, 57c, and 57d. Image forming units 57a, 57b, 57c, and 57d are arranged in the order of yellow (Y), magenta (M), cyan (C), and black (K) from the upstream side in the rotation direction of intermediate transfer belt 56. Image forming units 57a, 57b, 57c, and 57d form toner images of each color component by electrophotography under the control of a controller 80 (described later) of transfer device 2.

[0018] Specifically, the image forming units 57a, 57b, 57c, and 57d include photosensitive drums 50a, 50b, 50c, and 50d, charging rollers 51a, 51b, 51c, and 51d, respectively, and also include exposure devices 52a, 52b, 52c, and 52d, developing devices 53a, 53b, 53c, and 53d, respectively, and cleaning devices 55a, 55b, 55c, and 55d.

[0019] The photosensitive drums 50a, 50b, 50c, and 50d, which serve as image carriers, rotate clockwise in FIG.

[0020] The charging rollers 51a, 51b, 51c, and 51d charge the photosensitive drums 50a, 50b, 50c, and 50d.

[0021] The exposure devices 52a, 52b, 52c, and 52d form electrostatic latent images on the photosensitive drums 50a, 50b, 50c, and 50d.

[0022] The developing devices 53a, 53b, 53c, and 53d supply toner to the electrostatic latent images on the photosensitive drums 50a, 50b, 50c, and 50d to form toner images on the photosensitive drums 50a, 50b, 50c, and 50d, thereby making the electrostatic latent images visible.

[0023] Cleaning devices 55a, 55b, 55c and 55d remove residual toner from the photoreceptor drums 50a, 50b, 50c and 50d.

[0024] The registration rollers 66 convey the sheet P conveyed by a pickup roller (not shown) to the transfer device 2 at a predetermined timing.

[0025] The fixing section 67 performs a fixing process on the toner image that has been secondarily transferred onto the sheet P transported from the transfer device 2, fixing the image onto the sheet P, and then transports the sheet P with the fixed image toward a discharge section not shown.

[0026] The operation unit 81 outputs an electrical signal corresponding to an operation by a user to the controller 80. The operation unit 81 outputs an electrical signal corresponding to an operation by a user specifying, for example, the paper type of the sheets P accumulated in a tray (not shown) to the controller 80.

[0027] <Configuration of transfer device> The configuration of a transfer device 2 according to an embodiment of the present invention will be described in detail with reference to FIGS.

[0028] The transfer device 2 includes a high-voltage power supply 30, a transfer transformer 40, a primary transfer roller 54, an intermediate transfer belt 56, a tension roller 60, and an idler roller 61. The transfer device 2 also includes a secondary inner transfer roller 62, a drive roller 63, a secondary outer transfer roller 64, an intermediate transfer belt cleaning device 65, a primary transfer roller separation mechanism 70, and a controller 80.

[0029] The high voltage power supply 30 applies a primary transfer bias to the primary transfer roller 54 or stops applying the primary transfer bias under the control of the controller 80 .

[0030] The transfer transformer 40 applies or stops application of the secondary transfer bias to the inner secondary transfer roller 62 under the control of the controller 80. Specifically, the transfer transformer 40 includes a transfer bias output unit 41 and a voltage detection unit 42.

[0031] The transfer bias output unit 41 applies the secondary transfer bias to the inner secondary transfer roller 62 or stops applying the secondary transfer bias under the control of the controller 80 .

[0032] The voltage detection unit 42 as a detection means detects the secondary transfer bias applied to the inner secondary transfer roller 62, and outputs an electric signal according to the detection result to the controller 80.

[0033] A plurality of primary transfer rollers 54 are provided as primary transfer members, and are arranged inside the intermediate transfer belt 56, facing the photosensitive drums 50 across the intermediate transfer belt 56. The primary transfer rollers 54 are composed of a plurality of primary transfer rollers 54a, 54b, 54c, and 54d corresponding to the image forming units 57a, 57b, 57c, and 57d.

[0034] The primary transfer roller 54d is provided at the most downstream position of the primary transfer rollers 54 in the rotation direction of the intermediate transfer belt 56, and is closest to the inner secondary transfer roller 62 among the primary transfer rollers 54. The photosensitive drums 50a, 50b, 50c, and 50d are collectively referred to as photosensitive drum 50, and the primary transfer rollers 54a, 54b, 54c, and 54d are collectively referred to as primary transfer rollers 54.

[0035] The primary transfer roller 54 is a metal roller that is straight in the longitudinal direction and made of stainless steel (SUS) or sulfur and sulfur-composite free-cutting steel (SUM). The diameter of the primary transfer roller 54 is 8 mm in this example. A high-voltage power supply 30 is connected to the primary transfer roller 54, and a primary transfer bias of a polarity opposite to the charge polarity of the toner is applied from the high-voltage power supply 30 during image formation. By applying the primary transfer bias, the primary transfer roller 54 performs a primary transfer process in which the toner image formed on the photosensitive drum 50 is electrostatically attracted and superimposed onto the intermediate transfer belt 56 in sequence.

[0036] The primary transfer roller 54 is disposed so that a perpendicular line drawn from the central axis of the primary transfer roller 54 to the intermediate transfer belt 56 is a predetermined distance downstream in the movement direction of the intermediate transfer belt 56 from a perpendicular line drawn from the central axis of the photosensitive drum 50 to the intermediate transfer belt 56. In this example, the predetermined distance is 5 mm. The primary transfer roller 54 is displaceable in the vertical direction in FIG. 1 by a primary transfer roller separation mechanism 70. The primary transfer roller 54 can be pressed against the intermediate transfer belt 56 by displacing it downward in FIG. 1, and presses down the intermediate transfer belt 56 by 0.1 to 0.3 mm on the downstream side of the photosensitive drum 50 in the movement direction of the intermediate transfer belt 56.

[0037] The intermediate transfer belt 56 is disposed opposite the photosensitive drums 50, extends along the arrangement direction of the photosensitive drums 50, and moves in a predetermined rotational direction. In the case of FIG. 1, the intermediate transfer belt 56 moves in a counterclockwise rotational direction.

[0038] The intermediate transfer belt 56 is an endless film belt having a thickness of, for example, about 40 μm to 60 μm. The intermediate transfer belt 56 is made of a resin material such as polyimide or polyamide, a compound of this resin material, or rubber containing an appropriate amount of an antistatic agent such as carbon black. The intermediate transfer belt 56 is formed so as to have a surface resistivity of 1E+10 Ω / sq to 1E+11 Ω / sq.

[0039] Toner images of each color component formed on the photosensitive drums 50a, 50b, 50c and 50d by the image forming units 57a, 57b, 57c and 57d are sequentially primarily transferred onto the intermediate transfer belt 56.

[0040] The tension roller 60 applies a constant tension to the intermediate transfer belt 56. The tension roller 60 is configured so that the tension of the intermediate transfer belt 56 is approximately 3 kgf to 12 kgf.

[0041] The idler roller 61 supports the intermediate transfer belt 56. The idler roller 61 is electrically floated.

[0042] The inner secondary transfer roller 62, which serves as a secondary transfer member, is disposed on the inner side of the intermediate transfer belt 56, contacts the inner surface of the intermediate transfer belt 56, and stretches the inner peripheral surface of the intermediate transfer belt 56. The inner secondary transfer roller 62 is made of ethylene propylene diene rubber (EPDM) or the like, and is formed to have a diameter of 14 mm, a thickness of 0.5 mm, and a hardness set to, for example, 70° (Asker C). A secondary transfer bias of the same polarity as the charging polarity of the toner is applied to the inner secondary transfer roller 62 from the transfer transformer 40.

[0043] Here, the secondary transfer bias applied to the secondary transfer inner roller 62 includes both the bias applied in the secondary transfer ATVC control process described below and the bias applied when the toner image is secondarily transferred from the intermediate transfer belt 56 to the sheet P during image formation.

[0044] The drive roller 63 is driven by a motor having excellent constant speed characteristics, and drives the intermediate transfer belt 56 to circulate in a predetermined direction.

[0045] The outer secondary transfer roller 64 is disposed opposite the inner secondary transfer roller 62 across the intermediate transfer belt 56, and is disposed on the toner image bearing surface side of the intermediate transfer belt 56. The outer secondary transfer roller 64 is composed of an elastic layer made of nitrile rubber (NBR), ethylene propylene diene rubber, or the like, and a grounded core metal, and is formed to have a diameter of 20 mm. The outer secondary transfer roller 64 is connected to ground.

[0046] The intermediate transfer belt cleaning device 65 is provided downstream of the inner secondary transfer roller 62 and the outer secondary transfer roller 64 in the rotation direction of the intermediate transfer belt 56. The intermediate transfer belt cleaning device 65 cleans the surface of the intermediate transfer belt 56 by removing residual toner or paper dust from the intermediate transfer belt 56 after the secondary transfer.

[0047] The primary transfer roller separation mechanism 70 displaces the primary transfer roller 54 in the vertical direction in FIG. 1 under the control of the controller 80, thereby bringing the intermediate transfer belt 56 into contact with or separating it from the photosensitive drum 50.

[0048] The controller 80 performs overall control of the image forming apparatus 1. The controller 80 includes a CPU 82, a ROM 83, and a RAM 84.

[0049] The CPU 82 as a control means reads and executes a control program stored in the ROM 83, thereby transferring or reading data between the ROM 83 and the RAM 84 and performing predetermined arithmetic processing, etc., to control the overall operation of the image forming apparatus 1. The CPU 82 receives an image formation signal including image data or control commands, etc., from an external host device (not shown), such as an image reading device or a personal computer. The CPU 82 executes the image formation operation in accordance with the image formation signal input from the external host device or a signal input from the operation unit 81.

[0050] For example, the CPU 82 performs appropriate control according to the paper type designated by the user, which is indicated by a signal input from the operation unit 81. Here, paper types are classified into multiple categories based on a combination of the material of the sheet P, such as fine paper or coated paper, the surface properties of the sheet P, and the basis weight of the sheet P. When the user does not designate a paper type, the CPU 82 selects one of the multiple paper type categories and performs appropriate control according to the paper type of the selected category.

[0051] Before image formation, the CPU 82 executes secondary transfer ATVC control processing as secondary transfer bias determination control processing for determining the secondary transfer bias to be applied from the transfer transformer 40 to the inner secondary transfer roller 62 during image formation. Specifically, the CPU 82 determines the secondary transfer bias to be applied to the inner secondary transfer roller 62 during image formation based on the current value of the current flowing through the inner secondary transfer roller 62 by constant current control and the secondary transfer bias indicated by the electrical signal input from the voltage detection unit 42.

[0052] The ROM 83 stores a control program or a pre-determined data table.

[0053] The RAM 84 is a rewritable memory that stores information input from the controller 80, calculation results from the controller 80, and the like.

[0054] <Transfer device operation> The operation of the transfer device 2 according to the embodiment of the present invention will be described in detail with reference to FIG.

[0055] In Figure 4, Figure 4(a) shows the primary transfer roller 54 in a fully detached state, Figure 4(b) shows the primary transfer roller 54 in a fully attached state, and Figure 4(c) shows the primary transfer roller 54 in a black attached state.

[0056] The CPU 82 of the controller 80 executes an image forming operation when a print job is input, and executes an appropriate image forming mode based on image data input from an external host device (not shown). When an image forming mode is designated by a user through an electrical signal input from the operation unit 81, the CPU 82 executes the image forming mode designated by the user. Specifically, the CPU 82 executes either a full-color mode for forming a color image or a monochrome mode for forming a monochrome image as the image forming mode.

[0057] The CPU 82 controls the primary transfer roller separation mechanism 70 to set the primary transfer roller 54 of the transfer device 2 in an appropriate state according to the determined image formation mode, and determines whether or not to perform image formation operations in the image forming units 57a, 57b, 57c, and 57d. The primary transfer roller 54 of the transfer device 2 can be in one of three states: a fully detached state, a fully attached state, or a black attached state, depending on whether the primary transfer roller separation mechanism 70 is driven.

[0058] Specifically, when the image formation mode is not being executed, the CPU 82 does not control image formation in any of the image forming units 57a, 57b, 57c, and 57d. Furthermore, when the image formation mode is not being executed, the primary transfer rollers 54a, 54b, 54c, and 54d are in a fully detached state. At this time, the primary transfer rollers 54a, 54b, 54c, and 54d separate the intermediate transfer belt 56 from all of the photosensitive drums 50a, 50b, 50c, and 50d, as shown in FIG. 4(a).

[0059] When the full-color mode is executed, the CPU 82 controls image formation in all image forming units 57a, 57b, 57c, and 57d. As a result, image formation operations are initiated in order, starting with the image forming units 57a, 57b, 57c, and 57d located upstream in the rotation direction of the intermediate transfer belt 56. Furthermore, when the full-color mode is executed, the primary transfer rollers 54a, 54b, 54c, and 54d are in a full-transfer state. At this time, the primary transfer rollers 54a, 54b, 54c, and 54d bring the intermediate transfer belt 56 into contact with all of the photosensitive drums 50a, 50b, 50c, and 50d, as shown in FIG. 4(b).

[0060] When the CPU 82 executes the monochrome mode, it controls image formation in the black image forming unit 57d and does not control image formation in the yellow, magenta, and cyan image forming units 57a, 57b, and 57c. As a result, only the image forming unit 57d, which is located most downstream in the rotation direction of the intermediate transfer belt 56, performs image formation. Furthermore, the primary transfer rollers 54a, 54b, 54c, and 54d are in a black-on state in the monochrome mode.

[0061] At this time, the primary transfer rollers 54a, 54b, and 54c separate the intermediate transfer belt 56 from the photosensitive drums 50a, 50b, and 50c, as shown in Figure 4(a), and the primary transfer roller 54d brings the intermediate transfer belt 56 into contact with the photosensitive drum 50d.

[0062] Next, after the driving of the intermediate transfer belt 56 is stabilized and before the sheet P is conveyed to the inner secondary transfer roller 62 and the outer secondary transfer roller 64, the CPU 82 starts the execution of the primary transfer process and the secondary transfer ATVC control process.

[0063] In the primary transfer process, when the image formation mode is not being executed, the CPU 82 does not apply the primary transfer bias to the primary transfer rollers 54a, 54b, 54c, and 54d from the high-voltage power supply 30. When the full-color mode is being executed, the CPU 82 applies the primary transfer bias to the primary transfer rollers 54a, 54b, 54c, and 54d from the high-voltage power supply 30. When the monochrome mode is being executed, the CPU 82 does not apply the primary transfer bias to the primary transfer rollers 54a, 54b, and 54d from the high-voltage power supply 30, and applies the primary transfer bias to the primary transfer roller 54d from the high-voltage power supply 30.

[0064] <Secondary transfer ATVC control processing> The secondary transfer ATVC control process according to the embodiment of the present invention will be described in detail below.

[0065] The secondary transfer ATVC control process starts to be executed after the driving of the intermediate transfer belt 56 is stabilized and before the sheet P is conveyed to the secondary transfer inner roller 62 and the secondary transfer outer roller 64.

[0066] First, the CPU 82 executes constant current control to apply a secondary transfer bias corresponding to a preset target current Itg to the inner secondary transfer roller 62 from the transfer bias output unit 41 in the transfer transformer 40 .

[0067] Next, the voltage detection unit 42 in the transfer transformer 40 detects the voltage generated in the transfer bias output unit 41 and the inner secondary transfer roller 62 for a predetermined time. Here, the predetermined time is exemplified as the time required for the outer secondary transfer roller 64 to make one rotation. Then, the CPU 82 sets the average value of the voltages detected by the voltage detection unit 42 for the predetermined time as the base voltage Vb.

[0068] Next, the CPU 82 starts the image forming operation and calculates a voltage value Vtr (Vtr=Vb+Vp) by adding the paper assigned voltage Vp set based on the paper type and environmental information. At this time, the CPU 82 acquires environmental information detected by a temperature and humidity sensor (not shown) provided in the image forming apparatus 1. The CPU 82 also sets the paper assigned voltage Vp associated with the paper type and the acquired environmental information in a paper assigned voltage table that is stored in advance in the ROM 83 and associates the paper type, environmental information, and paper assigned voltage Vp.

[0069] Then, when the sheet P is conveyed to the inner secondary transfer roller 62 and the outer secondary transfer roller 64, the CPU 82 causes the transfer bias output unit 41 to output the determined voltage value Vtr as a constant voltage to the inner secondary transfer roller 62. This makes it possible to apply an appropriate secondary transfer bias to the inner secondary transfer roller 62 even if the resistance of the outer secondary transfer roller 64 changes due to temperature and humidity environments or endurance use.

[0070] <Execution timing of primary transfer process and secondary transfer ATVC control process> The execution timing of the primary transfer process and the secondary transfer ATVC control process according to the embodiment of the present invention will be described in detail with reference to FIGS.

[0071] When the primary transfer bias is applied while the secondary transfer ATVC control process is being executed, current interference may occur between the primary transfer roller 54d and the inner secondary transfer roller 62 while the secondary transfer ATVC control process is being executed, which may affect the accuracy of the secondary transfer ATVC control process.

[0072] Specifically, when a secondary transfer bias corresponding to the target current Itg is applied to the inner secondary transfer roller 62 during the secondary transfer ATVC control process, a negative current (hereinafter referred to as "leakage current") may flow from the inner secondary transfer roller 62 to the primary transfer roller 54d. In this case, the negative current flowing from the inner secondary transfer roller 62 to the outer secondary transfer roller 64 via the intermediate transfer belt 56 becomes smaller than the target current Itg, reducing the accuracy of the secondary transfer ATVC control process. The accuracy of the secondary transfer ATVC control process decreases as the leakage current increases. As a result, a sufficient current cannot be supplied to the inner secondary transfer roller 62 during image formation, deteriorating secondary transfer performance and causing transfer defects.

[0073] Furthermore, the leakage current is highly dependent on the electrical resistance of the intermediate transfer belt 56 and the potential difference ΔV between the primary transfer roller 54d and the inner secondary transfer roller 62. Therefore, in executing the secondary transfer ATVC control process, it is desirable that the potential difference ΔV be small. Specifically, as shown in FIG. 7, the value of the leakage current increases as the potential difference ΔV increases.

[0074] Figure 8 shows a summary of the leakage current and the occurrence of defective transfer images when the target current Itg was set to -20 μA. In Figure 8, the image evaluation was a subjective visual evaluation, with no defective transfer occurring marked with a circle, slight defective transfer occurring marked with a triangle, and clear defective transfer occurring marked with an cross.

[0075] The image evaluation level is preferably O or A. Therefore, as shown in Figure 8, it is desirable to keep the leakage current below 3 μA.

[0076] The polarity of the primary transfer bias applied to the primary transfer roller 54d and the polarity of the secondary transfer bias applied to the inner secondary transfer roller 62 are opposite. Therefore, when the primary transfer bias and the secondary transfer bias are applied simultaneously, the potential difference ΔV increases, resulting in a large leakage current. Therefore, it is desirable to avoid applying the primary transfer bias to the primary transfer roller 54d while the secondary transfer ATVC control process is being executed. Based on this, the execution timing of the primary transfer process and the secondary transfer ATVC control process when executing the full-color mode and when executing the monochrome mode will be specifically described below.

[0077] First, the execution timing of the primary transfer process and the secondary transfer ATVC control process when the full-color mode is executed will be described in detail with reference to FIG.

[0078] At time t1, the driving of the intermediate transfer belt 56 becomes stable.

[0079] At time t2, the CPU 82 starts the execution of the secondary transfer ATVC control process, and applies the secondary transfer bias from the transfer bias output unit 41 of the transfer transformer 40 to the inner secondary transfer roller 62.

[0080] At time t3, the CPU 82 ends the execution of the secondary transfer ATVC control process and stops the application of the secondary transfer bias from the transfer bias output unit 41 to the inner secondary transfer roller 62.

[0081] At time t4, the CPU 82 starts the execution of the primary transfer process, and causes the high-voltage power supply 30 to apply a primary transfer bias to the primary transfer roller 54.

[0082] Furthermore, until time t4 has elapsed, the CPU 82 stops the application of the primary transfer bias from the high-voltage power supply 30 to the primary transfer roller 54. As a result, the application of the primary transfer bias to the primary transfer roller 54 is stopped during the execution of the secondary transfer ATVC control process.

[0083] At time t5, the CPU 82 starts the execution of the secondary transfer process and causes the transfer bias output unit 41 to apply the secondary transfer bias to the inner secondary transfer roller 62 based on the voltage value Vtr set in the secondary transfer ATVC control process.

[0084] As described above, the CPU 82 executes the secondary transfer ATVC control process from time t1, when the drive of the intermediate transfer belt 56 stabilizes, to time t4, when the primary transfer bias is applied to the primary transfer roller 54d. At this time, the time from time t1 to time t4 is longer than the time it takes for the outer secondary transfer roller 64 to make one rotation. Therefore, the CPU 82 sets the time for executing the secondary transfer ATVC control process to the time it takes for the outer secondary transfer roller 64 to make one rotation.

[0085] Next, the execution timing of the primary transfer process and the secondary transfer ATVC control process when the monochrome mode is executed will be described in detail with reference to FIG.

[0086] At time t11, the driving of the intermediate transfer belt 56 becomes stable, and the CPU 82 starts the execution of the secondary transfer ATVC control process, and causes the transfer bias output unit 41 of the transfer transformer 40 to apply the secondary transfer bias to the inner secondary transfer roller 62.

[0087] At time t12, the CPU 82 ends the execution of the secondary transfer ATVC control process and stops the application of the secondary transfer bias from the transfer bias output unit 41 to the inner secondary transfer roller 62.

[0088] At time t13, the CPU 82 starts the execution of the primary transfer process, and causes the high-voltage power supply 30 to apply a primary transfer bias to the primary transfer roller 54.

[0089] Furthermore, until time t13 has elapsed, the CPU 82 stops the application of the primary transfer bias from the high-voltage power supply 30 to the primary transfer roller 54. As a result, the application of the primary transfer bias to the primary transfer roller 54 is stopped during the execution of the secondary transfer ATVC control process.

[0090] At time t14, the CPU 82 starts the execution of the secondary transfer process and causes the transfer bias output unit 41 to apply the secondary transfer bias to the inner secondary transfer roller 62 based on the voltage value Vtr set in the secondary transfer ATVC control process.

[0091] The CPU 82 executes the secondary transfer ATVC control process from time t11, when the drive of the intermediate transfer belt 56 stabilizes, to time t13, when the primary transfer bias is applied to the primary transfer roller 54d. At this time, the time from time t11 to time t13 is shorter than the time required for the outer secondary transfer roller 64 to rotate once, but longer than the time required for the outer secondary transfer roller 64 to rotate half a revolution. Therefore, the CPU 82 sets the time for executing the secondary transfer ATVC control process to the time required for the outer secondary transfer roller 64 to rotate half a revolution.

[0092] As described above, the CPU 82 shortens the time required for the secondary transfer ATVC control process when executing the monochrome mode compared to when executing the full color mode. This makes it possible to suppress a decrease in the accuracy of the secondary transfer ATVC control process without delaying the print job when executing the monochrome mode.

[0093] Furthermore, the CPU 82 starts and completes the secondary transfer ATVC control process before the start of the primary transfer process, i.e., before starting to apply the primary transfer bias. As a result, according to this embodiment, the potential difference ΔV can be made smaller than when the primary transfer bias is applied during execution of the secondary transfer ATVC control process, thereby reducing leakage current and preventing a decrease in the accuracy of the secondary transfer ATVC control process.

[0094] Furthermore, when executing the monochrome mode, the execution time of the secondary transfer ATVC control process can be extended by starting the execution of the secondary transfer ATVC control process at the timing when the driving state of the intermediate transfer belt 56 is stabilized.

[0095] Furthermore, by stopping the application of the primary transfer bias to the primary transfer roller 54d, which is the closest to the inner secondary transfer roller 62 among the primary transfer rollers 54, during the execution of the secondary transfer bias determination control process, leakage current can be reliably reduced.

[0096] Here, the influence on the image when a secondary transfer bias corresponding to the target current Itg-20 μA is applied to the inner secondary transfer roller 62 by constant current control was confirmed.

[0097] First, when the secondary transfer ATVC control process was started with 1500 V applied as the primary transfer bias, the base voltage Vb was 2500 V, the potential difference ΔV was 4000 V, the leakage current was approximately -4 μA, and poor image transfer was observed.

[0098] In contrast, when the application of the primary transfer bias is stopped during the execution of the secondary transfer ATVC control process as in this embodiment, the base voltage Vb is 2800 V, the potential difference ΔV is 2800 V, and the leakage current is approximately -2 μA, resulting in a good image. This confirms that the present embodiment can suppress a decrease in the accuracy of the secondary transfer ATVC control process.

[0099] During image formation, the CPU 82 applies a voltage value Vtr obtained by adding the base voltage Vb to the paper voltage Vp using constant voltage control as the secondary transfer bias. As a result, the potential difference ΔV becomes larger by the amount of the paper voltage Vp than when the secondary transfer ATVC control process is executed, and the leakage current increases. However, when the secondary transfer bias determined by the secondary transfer ATVC control process is applied using constant voltage control, the current flowing through the inner secondary transfer roller 62 does not decrease even if the leakage current increases, and no transfer failure occurs.

[0100] In this embodiment, while the secondary transfer ATVC control process is being executed, the application of the primary transfer bias to the primary transfer roller 54 is stopped. This makes it possible to reduce interference between the currents flowing through the primary transfer roller 54 and the inner and outer secondary transfer rollers 62 and 64 without causing transfer defects during image formation, and also to prevent the device from becoming larger and more expensive.

[0101] The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications are possible without departing from the spirit and scope of the present invention.

[0102] Specifically, in the above embodiment, the execution time of the secondary transfer ATVC control process is the time required for the outer secondary transfer roller 64 to make one rotation or a half rotation, but the execution time of the secondary transfer ATVC control process can be set to any predetermined time, provided that this predetermined time is shorter than the time from when the drive of the intermediate transfer belt 56 becomes stable to when the primary transfer bias is applied to the primary transfer roller 54d.

[0103] Furthermore, in the above embodiment, a plurality of primary transfer rollers 54 are provided, but this is not limiting, and a single primary transfer roller may be provided.

[0104] In the above embodiment, the application of the primary transfer bias to the primary transfer roller 54d is stopped during the execution of the secondary transfer ATVC control process. However, this is not limiting, and the application of the primary transfer bias to any number of primary transfer rollers 54 from the downstream side in the rotation direction of the intermediate transfer belt 56 may be stopped during the execution of the secondary transfer ATVC control process.

[0105] In the above embodiment, constant current control is used as the test bias in the secondary transfer ATVC control process. However, this is not limiting. In the secondary transfer ATVC control process, the current supplied to the inner secondary transfer roller 62 and the outer secondary transfer roller 64 when a constant voltage controlled test bias is applied may be detected by a detection unit. The secondary transfer bias may then be set based on the current value detected by the detection unit. [Explanation of symbols]

[0106] 1. Image forming device 2. Transcription device 30 High voltage power supply 40 Transfer transformer 41 Transfer bias output unit 42 Voltage detection section 50 Photosensitive drum 54 Primary transfer roller 56 Intermediate transfer belt 57 Image forming unit 60 Tension roller 61 Idler Roller 62 Secondary transfer inner roller 63 Drive roller 64 Secondary transfer outer roller 65 Intermediate transfer belt cleaning device 66 Registration roller 67 Fixing section 70 Primary transfer roller separation mechanism 80 Controller 81 Operation section 82 CPU 83 ROM 84 RAM

Claims

1. an image forming unit that forms a toner image on an image carrier; a belt onto which a toner image is transferred from the image carrier; a primary transfer member that primarily transfers a toner image from the image carrier to the belt; a first applying unit that applies a voltage to the primary transfer member; a secondary transfer member that contacts the inner surface of the belt to stretch the belt and secondarily transfers a toner image from the belt to a recording material; a second applying unit that applies a voltage to the secondary transfer member; a detection unit that detects a current flowing through or a voltage applied to the secondary transfer member; a control unit that executes an operation of determining a transfer voltage to be applied to the secondary transfer member during secondary transfer based on a detection result of the detection unit when a test voltage is applied to the secondary transfer member during non-image formation; and The control unit In the operation, the first application unit and the second application unit are controlled so as not to apply a voltage to the primary transfer member during a period in which the test voltage is applied to the secondary transfer member, and the application period of the test voltage when forming a monochrome image is made shorter than the application period of the test voltage when forming a full-color image. An image forming apparatus characterized by:

2. The control unit a first time is a time period from the start of driving the belt to the start of the operation when performing the operation in forming a monochrome image, and a second time is a time period when performing the operation in forming a full-color image, the second time being longer than the first time period; the drive start timing is a timing at which the belt starts to drive in response to the start of image formation; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. The primary transfer member is including a metal roller, 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. The surface resistivity of the belt is 1E+10 Ω / sq or more and 1E+11 Ω / sq or less.

4. The image forming apparatus according to claim 3, wherein the image forming apparatus is a recording medium.

5. The primary transfer member is a first contact portion and a second contact portion are arranged so as not to overlap with each other in the moving direction of the belt, the image carrier is in contact with the belt at the first contact portion, and the image carrier is in contact with the belt at the second contact portion; 4. The image forming apparatus according to claim 3, wherein the image forming apparatus is a recording medium.

Images