Image forming device

Abstract

The present invention provides an image forming device. The image forming device comprises: a rotating member that rotates while holding a toner image on its circumferential surface; a transfer member that clamps a conveyed recording medium and the rotating member via a clamping portion, and is applied with a voltage to transfer the toner image held by the rotating member to the recording medium; a grounded guide member that guides the recording medium toward the clamping portion and contacts the recording medium clamped by the clamping portion; and a control unit that applies a voltage to the transfer member with the recording medium clamped by the clamping portion, so that the printing resistance when the voltage is applied to the transfer member is less than the system resistance when the voltage is applied to the transfer member without the recording medium clamped by the clamping portion.

Description

Technical Field

[0001] The present disclosure relates to an image forming apparatus. Background Art

[0002] In the image forming apparatus described in Japanese Patent Application Laid-Open No. 2003-302846, in a system that determines the transfer voltage by PTVC control and applies a constant voltage, when the transfer current is detected at the end of the transfer material and compared with a threshold to determine the applied voltage, the threshold is changed by referring to paper feed port information. Summary of the Invention

[0003] In a conventional image forming apparatus, a transfer member to which a voltage is applied sandwiches a rotating member holding a toner image and a recording medium, thereby transferring the toner image on the rotating member to the recording medium.

[0004] In such image forming apparatuses, constant voltage control is used to transfer a toner image held by a rotating member to a recording medium. However, when a low-resistance medium with a low surface resistance is used as the recording medium, transfer failure may occur under constant voltage control.

[0005] An object of the present disclosure is to suppress the occurrence of transfer failure of a toner image to a low-resistance medium, compared to a case where a toner image is always transferred to a recording medium by constant voltage control.

[0006] According to the first scheme of the present disclosure, an image forming device is provided, which comprises: a rotating member that holds a colorant image on its circumferential surface and rotates; a transfer member that clamps a conveyed recording medium and the rotating member through a clamping portion, and is applied with a voltage to transfer the colorant image held by the rotating member to the recording medium; a guide member that is grounded, guides the recording medium toward the clamping portion, and contacts the recording medium clamped by the clamping portion; and a control portion that transfers the colorant image to the recording medium by constant current control when a printing resistance when a voltage is applied to the transfer member in a state where the recording medium is clamped by the clamping portion is less than a system resistance when a voltage is applied to the transfer member in a state where the recording medium is not clamped by the clamping portion.

[0007] According to the second aspect of the present disclosure, when the print resistance is larger than the system resistance, the control unit transfers the toner image to the recording medium through constant voltage control.

[0008] According to the third aspect of the present disclosure, the control unit derives the print resistance based on a voltage applied to the transfer member in a state where the recording medium is clamped by the clamping unit and a current flowing when the voltage is applied.

[0009] According to the fourth scheme of the present disclosure, the image forming device also has a detection component, which detects the image density of multiple detection images as colorant images transferred to the recording medium. The control unit changes the voltage applied to the transfer component to multiple values ​​when transferring the detection images to the recording medium, so that the multiple detection images are transferred to the recording medium, selects one of the detection images based on the image density of the multiple detection images detected by the detection component, and derives the printing resistance using the voltage when transferring the selected detection image and the current flowing when the voltage is applied.

[0010] According to the fifth aspect of the present disclosure, the control unit transfers the plurality of detection images to one recording medium.

[0011] According to the sixth embodiment of the present disclosure, the image forming device further includes an input unit for inputting information of a confirmation image selected by a user from a plurality of confirmation images as colorant images to be transferred to a recording medium, the control unit changes the voltage applied to the transfer member to a plurality of values ​​when the confirmation image is transferred to the recording medium, and transfers the plurality of confirmation images to the recording medium, and derives the printing resistance based on the information of the confirmation image input to the input unit and using the voltage when the input confirmation image is transferred and the current flowing when the voltage is applied.

[0012] According to the seventh aspect of the present disclosure, the control unit causes information on the confirmation image applied to the transfer member when transferring the confirmation image to the recording medium to be displayed on the recording medium.

[0013] (Effect)

[0014] According to the first aspect, compared to the case where the toner image is always transferred to the recording medium by constant voltage control, the occurrence of transfer failure of the toner image to the low-resistance medium can be suppressed.

[0015] According to the second aspect, compared with the case where the toner image is transferred to plain paper by constant current control, the occurrence of transfer failure of the toner image to plain paper can be suppressed.

[0016] According to the third aspect, the print resistance can be derived more easily than when the print resistance is derived using the surface resistivity of the recording medium.

[0017] According to the fourth aspect, compared with the case where the print resistance is derived without changing the applied voltage, the occurrence of transfer failure of the toner image to the low-resistance medium can be suppressed.

[0018] According to the fifth aspect, the time required to derive the print resistance can be shortened compared to the case where a plurality of detection images are transferred to each recording medium.

[0019] According to the sixth aspect, compared to the case where the print resistance is derived without changing the applied voltage, it is possible to suppress the occurrence of transfer failure of the toner image to the low-resistance medium.

[0020] According to the seventh aspect, the user can easily select and confirm an image. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a side view showing a transfer member and the like included in the image forming apparatus according to the first embodiment of the present disclosure.

[0022] Figure 2 It is a side view showing a transfer member and the like included in the image forming apparatus according to the first embodiment of the present disclosure.

[0023] Figure 3 It is a side view showing a transfer member and the like included in the image forming apparatus according to the first embodiment of the present disclosure.

[0024] Figure 4 It is a front view showing a transfer member and the like included in the image forming apparatus according to the first embodiment of the present disclosure.

[0025] Figure 5 It is a front view showing a transfer member and the like included in the image forming apparatus according to the first embodiment of the present disclosure.

[0026] Figure 6 This is a diagram showing a portion of the user interface of the image forming apparatus according to the first embodiment of the present disclosure.

[0027] Figure 7 This is a flowchart showing a control flow of each component controlled by the control unit of the image forming apparatus according to the first embodiment of the present disclosure.

[0028] Figure 8 This is a block diagram illustrating a control system of a control unit of the image forming apparatus according to the first embodiment of the present disclosure.

[0029] Figure 9 This is a graph showing the voltage required to transfer a toner image to a sheet member P for each paper type in the image forming apparatus according to the first embodiment of the present disclosure.

[0030] Figure 10 1 is a diagram showing the configuration of a toner image forming section of the image forming apparatus according to the first embodiment of the present disclosure.

[0031] Figure 11 1 is a diagram showing the configuration of an image forming unit of an image forming apparatus according to a first embodiment of the present disclosure.

[0032] Figure 12 This is a diagram schematically illustrating the configuration of an image forming apparatus according to a first embodiment of the present disclosure.

[0033] Figure 13 This is a block diagram illustrating a control system of a control unit of an image forming apparatus according to a comparative embodiment of the first embodiment of the present disclosure.

[0034] Figure 14 This is a flowchart showing a control flow of each component controlled by a control unit of the image forming apparatus according to the second embodiment of the present disclosure.

[0035] Figure 15 This is a block diagram illustrating a control system of a control unit of an image forming apparatus according to a second embodiment of the present disclosure.

[0036] Figure 16 It is a diagram showing a detection image output by the image forming apparatus according to the second embodiment of the present disclosure.

[0037] Figure 17 This is a flowchart showing a control flow of each component controlled by a control unit of the image forming apparatus according to the third embodiment of the present disclosure.

[0038] Figure 18 This is a block diagram illustrating a control system of a control unit of an image forming apparatus according to a third embodiment of the present disclosure.

[0039] Figure 19 This is a diagram showing a portion of a user interface of an image forming apparatus according to a third embodiment of the present disclosure.

[0040] Figure 20 This is a diagram showing a confirmation image output by the image forming apparatus according to the third embodiment of the present disclosure. DETAILED DESCRIPTION

[0041] <First embodiment>

[0042] according to Figures 1 to 12 An example of an image forming apparatus according to the first embodiment of the present disclosure will be described. Arrow H in each figure indicates the vertical direction and the apparatus up-down direction, arrow W indicates the horizontal direction and the apparatus width direction, and arrow D indicates the horizontal direction and the apparatus depth direction.

[0043] (Overall Structure of Image Forming Apparatus)

[0044] like Figure 12 As shown, the image forming apparatus 10 includes an image forming unit 12 for forming an image by electrophotography, and a conveying device 18 including a plurality of conveying rollers (reference numerals omitted) for conveying a sheet member P (an example of a recording medium) along a conveying path 16 thereof.

[0045] The image forming apparatus 10 also includes a cooling unit 20 for cooling the sheet member P on which an image is formed; a straightening unit 22 for correcting curvature of the sheet member P; an image inspection unit 24 for inspecting the image formed on the sheet member P; and a control unit 36 ​​for controlling each unit. The image inspection unit 24, the control unit 36, and the conveying device 18 will be described in detail later.

[0046] Furthermore, the image forming apparatus 10 includes a reversing path 26 for reversing the sheet P having an image formed on the front surface thereof so as to form images on both sides of the sheet P and conveying the sheet P toward the image forming unit 12 again.

[0047] In this configuration, in the image forming apparatus 10, an image (toner image) formed by the image forming section 12 is formed on the front surface of a sheet member P conveyed along a conveyance path 16. The sheet member P on which the image is formed then passes sequentially through a cooling section 20, a straightening section 22, and an image inspection section 24 before being discharged to the outside of the apparatus.

[0048] On the other hand, when an image is formed on the back side of the sheet P, the sheet P with the image formed on the front side is conveyed along the reversing path 26 , and an image is formed on the back side of the sheet P again by the image forming unit 12 .

[0049] [Image forming unit 12]

[0050] The image forming section 12 includes a plurality of toner image forming sections 30 that form toner images of respective colors, and a transfer section 14 that includes a transfer belt 50 that holds the toner images and transfers the toner images to a sheet member P. Furthermore, the image forming section 12 includes a fixing device 34 that fixes the toner images transferred to the sheet member P by the transfer section 14 to the sheet member P. The transfer section 14 will be described in detail later.

[0051] In order to form toner images for each color, a plurality of toner image forming units 30 are provided. In this embodiment, the toner image forming units 30 for four colors, namely yellow (Y), magenta (M), cyan (C), and black (K), are provided. Figure 12The colors (Y), (M), (C), and (K) shown here represent the aforementioned colors. In the following description, when there is no need to distinguish between yellow (Y), magenta (M), cyan (C), and black (K), Y, M, C, and K are omitted from the reference numerals.

[0052] The toner image forming units 30 of various colors have basically the same structure except for the toner used. Figure 10 As shown, the toner image forming unit 30 includes a rotating cylindrical image holder 40 and a charger 42 for charging the image holder 40. Furthermore, the toner image forming unit 30 includes an exposure device 44 for irradiating the charged image holder 40 with exposure light to form an electrostatic latent image, and a developing device 46 for developing the electrostatic latent image into a toner image using a developer G containing toner. The developer G used in this embodiment is a two-component developer containing toner and carriers.

[0053] Furthermore, the image retaining bodies 40 of various colors are grounded and contact the rotating transfer belt 50 (described in detail later). Figure 12 As shown, the toner image forming units 30 of yellow (Y), magenta (M), cyan (C), and black (K) are arranged in order horizontally from the upstream side in the rotation direction of the transfer belt 50 (the direction of arrow A in the figure).

[0054] like Figure 12 As shown, the fixing device 34 includes a fixing belt 60 that is wound around a plurality of rollers (reference numerals omitted) and heated, and a pressure roller 62 that presses the sheet member P toward the fixing belt 60 .

[0055] In this configuration, the sheet member P to which the toner image has been transferred is conveyed while being sandwiched between the rotating fixing belt 60 and the pressure roller 62 , whereby the toner image is fixed to the sheet member P.

[0056] (Main structure)

[0057] Next, the transfer section 14 , the image inspection section 24 , the transport device 18 , the control section 36 , and the like will be described.

[0058] [Transfer unit 14]

[0059] like Figure 11 As shown, the transfer unit 14 includes: a transfer belt 50; a plurality of rollers 32 around which the transfer belt 50 is wound; and a primary transfer roller 52 that transfers the toner image on the image holder 40 to the transfer belt 50. The transfer unit 14 also includes: a secondary transfer roller 54 that transfers the toner image transferred to the transfer belt 50 to the sheet member P; and a high-voltage power supply 68 (see FIG. 1 ). Figure 1 ) The transfer belt 50 is an example of a rotating member.

[0060] -Transfer belt 50-

[0061] like Figure 11 As shown, the transfer belt 50 is annular and wound around multiple rollers 32. Furthermore, when viewed from the depth of the device, the transfer belt 50 assumes an inverted obtuse triangle shape that is elongated in the width direction of the device. In this embodiment, as an example, the transfer belt 50 is formed from a material obtained by dispersing carbon in polyimide. Furthermore, the volume resistivity of the transfer belt 50 is 12.5 logΩcm.

[0062] - Roller 32 -

[0063] like Figure 11 As shown, a plurality of rollers 32 are provided. Among the plurality of rollers 32, the roller 32d arranged on one side in the width direction of the device (right side in the figure) receives rotational force from a motor (not shown), which rotates the transfer belt 50 in the direction of arrow A (counterclockwise in the figure).

[0064] Furthermore, among the multiple rollers 32, the top roller 32b, which forms the lower end of the obtuse angle and around which the transfer belt 50 is wound in an obtuse triangle shape, is located on the opposite side of the transfer belt 50 from the secondary transfer roller 54 (described later). A voltage is applied to this roller 32b. In this embodiment, as an example, the roller 32b is an elastic roller with an outer diameter of 28 mm. Furthermore, the surface resistance of the roller 32b is 7.3 logΩ / sq, and the surface hardness of the roller 32b is 53 degrees on the Asker C hardness scale.

[0065] Among the plurality of rollers 32 , the roller 32 t located upstream of the roller 32 b in the rotation direction of the transfer belt 50 (hereinafter referred to as “belt rotation direction”) applies tension to the transfer belt 50 .

[0066] -Primary transfer roller 52-

[0067] like Figure 11 As shown, the primary transfer rollers 52 are respectively arranged on the opposite side of the image holding members 40 of the respective colors with the transfer belt 50 interposed therebetween.

[0068] In this structure, a transfer current flows through the primary transfer rollers 52 of each color, forming a transfer electric field between the primary transfer rollers 52 and the image holder 40. The toner image on the image holder 40 is then transferred to the transfer belt 50 by this transfer electric field.

[0069] -Secondary transfer roller 54-

[0070] like Figure 1As shown, the secondary transfer roller 54 is grounded, and the transfer belt 50 is sandwiched between the secondary transfer roller 54 and the roller 32b. In this embodiment, as an example, the secondary transfer roller 54 is an elastic roller with an outer diameter of 28 mm and a resistance of 6.3 logΩ.

[0071] -High voltage power supply 68-

[0072] The high voltage power supply 68 has a function of applying a DC voltage to the roller 32b to cause current to flow. Figure 1 As shown, the high-voltage power supply 68 includes an ammeter 68a capable of monitoring the current flowing through the roller 32b and a voltmeter 68b capable of monitoring the voltage applied to the roller 32b.

[0073] In this configuration, a sheet member P is conveyed while being nipped by the secondary transfer portion NT between the transfer belt 50 and the secondary transfer roller 54, and is pressed against the transfer belt 50. Then, by applying a voltage to the roller 32b, a current flows between the roller 32b and the secondary transfer roller 54, forming a transfer electric field. This transfer electric field causes the toner image held on the transfer belt 50 to be transferred to the conveyed sheet member P via the secondary transfer portion NT. The secondary transfer portion NT is an example of a nip.

[0074] In this manner, the secondary transfer roller 54 and the roller 32 b sandwich the conveyed sheet member P and the transfer belt 50 , thereby forming a transfer member 56 that transfers the toner image held by the transfer belt 50 to the sheet member P.

[0075] [Image inspection unit 24]

[0076] like Figure 12 As shown, the image inspection unit 24 is located downstream of the fixing device 34 in the conveyance direction of the sheet member P (hereinafter referred to as the "sheet conveyance direction"). The image inspection unit 24 irradiates light toward the sheet member P on which a toner image is formed, receives reflected light, and detects the density of the toner image ("toner image density") based on the intensity of the received light. The image inspection unit 24 is an example of a detection unit.

[0077] [Conveying device 18]

[0078] like Figure 12 As shown, the conveying device 18 has: a storage portion 70 for storing the sheet member P; a plurality of conveying rollers (omitted reference numerals) for conveying the sheet member P stored in the storage portion 70 along the conveying path 16; and a guide member 64 for guiding the conveyed sheet member P toward the secondary transfer portion NT.

[0079] like Figure 1As shown, the guide member 64 is grounded and is arranged to contact the sheet member P in a state where the upstream side and the end side of the secondary transfer portion NT in the sheet conveying direction are sandwiched by the secondary transfer portion NT (see Figure 2 ). Specifically, the guide member 64 is bent by the conveying posture of the sheet member P and contacts the sheet member P. The guide member 64 is formed of a conductive material and has: a plate-shaped guide plate 64a that covers the sheet member P from above; and a plate-shaped guide plate 64b that supports the sheet member P from below. In this way, the guide member 64 functions as a charge removal unit that removes the charge of the sheet member P. In addition, the conductive material refers to a material with a conductivity of 10 6 Materials above S / m.

[0080] 〔other〕

[0081] And, as Figure 6 As shown, the user interface 72 of the image forming apparatus 10 is provided with an input device 70 (refer to FIG. Figure 12 ) is an input unit 74 for inputting information of the sheet member P therein.

[0082] The input unit 74 is provided with a paper type input unit 74a for inputting the paper type of the sheet member P accommodated in the accommodating unit 70, and a sample output unit 74b for outputting a toner image of a sample image onto the sheet member P accommodated in the accommodating unit 70. As will be described in detail later, when a user touches the sample output unit 74b, a toner image of the sample image is formed on the sheet member P accommodated in the accommodating unit 70. This determines the control of the high-voltage power supply 68 by the control unit 36, as will be described in detail later.

[0083] [Control Unit 36]

[0084] like Figure 8 As shown, the control unit 36 ​​controls the high-voltage power supply 68 based on information input by the user to the input unit 74. The control of the high-voltage power supply 68 by the control unit 36 ​​will be described together with the operation described later.

[0085] (Function of the main structure)

[0086] Next, the main configuration and operation of the image forming apparatus 510 will be described in comparison with the comparative image forming apparatus 510. The configuration and operation of the comparative image forming apparatus 510 will be described primarily with respect to the portions that differ from the image forming apparatus 10.

[0087] [Structure of Image Forming Device 510]

[0088] like Figure 13 As shown, the image forming apparatus 510 includes a control unit 536 , and the control unit 536 controls the high-voltage power supply 68 .

[0089] [Functions of Image Forming Apparatuses 10 and 510]

[0090] In cutting Figure 12 In the state of the main power supply of the image forming apparatus 10 shown in FIG. 1 (the state of being turned off), the operation of all components is stopped. Therefore, when the user turns on the main power supply of the image forming apparatus 10 (conduction), Figure 1 The control unit 36, 536 shown controls the high-voltage power supply 68 to flow a predetermined current value through the roller 32b. Furthermore, the control unit 36, 536 obtains the voltage when the current is flowing through the roller 32b from the voltmeter 68b, and derives the system resistance based on the current flowing through the roller 32b and the voltage obtained from the voltmeter 68b.

[0091] The “system resistance” refers to the combined resistance of the roller 32 b , the transfer belt 50 , and the secondary transfer roller 54 when the current required to transfer the toner image to the sheet member P flows through the roller 32 b and the sheet member P is not nipped by the secondary transfer portion NT.

[0092] -Control Unit 536 of Image Forming Apparatus 510-

[0093] In the image forming apparatus 510 according to the comparative embodiment, the control unit 536 applies a predetermined voltage to the roller 32b based on the aforementioned system resistance and the paper type information input by the user into the paper type input unit 74a when transferring a toner image to the sheet member P. The control unit 536 then continuously transfers the toner image to the sheet member P using constant voltage control.

[0094] Specifically, the control unit 536 determines the voltage applied to the roller 32b using the print resistance of the sheet member P, which is plain paper, when it is nipped by the secondary transfer unit NT. Furthermore, the print resistance is determined by paper type information pre-stored in the image forming apparatus 510 and input to the paper type input unit 74a.

[0095] "Constant voltage control" refers to control intended to make the output voltage value consistent with the target voltage value. In addition, "plain paper" refers to a recording medium generally used in image forming apparatuses and has a surface resistivity (JIS K 6911) of less than 10 6 The "print resistance" refers to the combined resistance of the roller 32b, the transfer belt 50, the secondary transfer roller 54, the sheet P, and the guide member 64 when the current required to transfer the toner image to the sheet P flows through the roller 32b, and the combined resistance when the sheet P is nipped by the secondary transfer unit NT.

[0096] Here, in Figure 9Graph 1 shows a graph with the vertical axis representing the voltage applied to roller 32b when the current required to transfer a toner image to sheet P flows through roller 32b, and the horizontal axis representing the system resistance. A solid line L01 represents the voltage when sheet P is not nipped by secondary transfer section NT, and a dashed line L02 represents the voltage when plain paper is nipped by secondary transfer section NT as sheet P.

[0097] When voltage is applied to the roller 32b in a state where the plain paper as the sheet member P is nipped by the secondary transfer portion NT, Figure 2 As shown, current flows from the roller 32b toward the secondary transfer roller 54 (see arrow E01 in the figure). Therefore, the printing resistance in a state where the sheet member P of plain paper is nipped by the secondary transfer portion NT is higher than the system resistance.

[0098] Therefore, by Figure 9 As can be seen from the graph shown, when transferring the colorant image to plain paper as the sheet member P (see dotted line L02), a higher voltage must be applied to the roller 32b than when the sheet member P is not clamped by the secondary transfer portion NT (see solid line L01).

[0099] For example, when the system resistance is R01, and the current required to transfer a toner image to the sheet P is flowing through the roller 32b while the sheet P is not nipped by the secondary transfer section NT, the voltage applied to the roller 32b is V01. Furthermore, when the system resistance is R01, and the current required to transfer a toner image to the sheet P is flowing through the roller 32b while the sheet P is nipped by the secondary transfer section NT, the voltage applied to the roller 32b is V02. Voltage V02 is higher than voltage V01.

[0100] Thus, in the image forming apparatus 510, when the sheet member P is not clamped by the secondary transfer portion NT, a voltage higher than the voltage applied to the roller 32b when the current required to transfer the colorant image to the sheet member P flows through the roller 32b is applied to the roller 32b.

[0101] The applied voltage then causes a current to flow between the roller 32b and the secondary transfer roller 54, thereby forming a transfer electric field. This transfer electric field transfers the toner image held by the transfer belt 50 to the sheet member P. In this manner, the image forming apparatus 510 always transfers the toner image to the sheet member P under constant voltage control.

[0102] Here, the reason for executing constant voltage control is explained. Figure 5Figure 5 shows the current flowing from roller 32b toward secondary transfer roller 54 when voltage is applied to roller 32b while plain paper, serving as sheet P, is nipped by secondary transfer section NT. However, the current flowing through the portion where sheet P is nipped (see arrow E11 in the figure) has a different value than the current flowing through the portion where sheet P is not nipped (see arrow E12 in the figure). Therefore, it is difficult to control the current value of current E11 flowing through the portion where sheet P is nipped. Therefore, the control unit 536 of image forming apparatus 510 always uses constant voltage control to transfer the toner image to sheet P.

[0103] Here, the case of using a low-resistance medium as the sheet member P will be described. "Low-resistance medium" refers to a recording medium having a surface resistivity lower than that of ordinary paper, such as metal-deposited paper or black paper colored black with a pigment, and having a surface resistivity (JIS K 6911) of 10 6 Recording media with a resistance of Ω / sq or less.

[0104] Therefore, if a voltage is applied to the roller 32b in a state where the low-resistance medium as the sheet member P is sandwiched by the secondary transfer portion NT, as shown in FIG. Figure 3 As shown, since the surface resistivity of the sheet member P is low, current flows from the roller 32 b through the sheet member P and toward the guide member 64 formed of a conductive material (see arrow E02 in the figure).

[0105] Therefore, if Figure 4 As shown, current does not flow to the portion of the sheet P not clamped. Current flows from roller 32b through sheet P and toward guide member 64. Consequently, when the low-resistance medium, sheet P, is clamped by secondary transfer unit NT, the printing resistance is equal to or lower than the system resistance. Thus, guide member 64 functions as a control unit that controls the direction of current flow so that the current flows along the sheet surface of sheet P.

[0106] Figure 9 The single-dot chain line L03 in the diagram shows the voltage applied to the roller 32b when the current required to transfer the toner image to the sheet member P flows through the roller 32b in the state where the low-resistance medium as the sheet member P is clamped by the secondary transfer section NT. As mentioned above, the printing resistance in the state where the low-resistance medium is clamped by the secondary transfer section NT is equal to or lower than the system resistance. Therefore, when the toner image is transferred to the low-resistance medium (the case of the single-dot chain line), the current required to transfer the toner image to the sheet member P is passed through the roller 32b. Figure 9 As can be seen from the graph of , a lower voltage must be applied to the roller 32b than when the sheet member P is not clamped by the secondary transfer portion NT (see solid line L01). Figure 9The single dot chain line L03 is a line with a surface resistivity of 10 5 Ω / sq low resistance medium.

[0107] For example, when the system resistance is R01, the voltage applied to the roller 32b when the current required for transferring the toner image to the sheet member P flows through the roller 32b in a state where the low-resistance medium as the sheet member P is nipped by the secondary transfer portion NT is V03.

[0108] However, in the image forming apparatus 510 according to the comparative embodiment, the toner image is always transferred to the sheet member P by constant voltage control. Furthermore, in the image forming apparatus 510, a voltage higher than that in the case where the sheet member P is not nipped by the secondary transfer portion NT (see solid line L01) is always applied to the roller 32b.

[0109] Therefore, when a low-resistance medium is used as the sheet member P, the transfer rate of the toner in the image forming apparatus 510 decreases, and transfer failure may occur when the toner image is transferred to the sheet member P.

[0110] -Control Unit 36 ​​Included in Image Forming Apparatus 10-

[0111] Next, use Figure 7 The flowchart shown here explains the operation of the high-voltage power supply 68 by the control unit 36 ​​included in the image forming apparatus 10 according to this embodiment.

[0112] The user stores the sheet member P in the storage portion 70 and inputs the paper type information of the stored sheet member P into the paper type input portion 74a of the input portion 74. Then, if the user touches the sample output portion 74b of the input portion 74 to output a sample image as a black toner image, Figure 7 In step S100, the control unit 36 ​​rotates the transfer belt 50 and controls the toner image forming unit 30K and the primary transfer roller 52K to transfer the sample image to the transfer belt 50. Furthermore, the control unit 36 ​​controls the high-voltage power supply 68 to apply a predetermined voltage to the roller 32b. Furthermore, the control unit 36 ​​controls the conveying device 18 to convey the sheet member P accommodated in the accommodating portion 70 along the conveying path 16.

[0113] Next, in step S200, the control unit 36 ​​transfers the sample image to the sheet P in the secondary transfer unit NT and obtains the current value of the current flowing when the sheet P is nipped by the secondary transfer unit NT from the ammeter 68a. The control unit 36 ​​then derives the print resistance based on the obtained current value and the voltage value applied to the roller 32b.

[0114] Next, in step S300, the control unit 36 ​​determines whether the acquired print resistance is less than or equal to the system resistance. If the print resistance is less than or equal to the system resistance, the sheet member P is determined to be low-resistance medium, and the process proceeds to step S400. On the other hand, if the print resistance is greater than the system resistance, the sheet member P is determined to be plain paper, and the process proceeds to step S410. In this way, the control unit 36 ​​functions as a determination unit for determining whether the sheet member P held by the secondary transfer unit NT is low-resistance medium or plain paper.

[0115] Next, in step S400, when transferring the toner image to the sheet member P determined to be a low-resistance medium, the control unit 36 ​​controls the high-voltage power supply 68 to flow a predetermined current through the roller 32b. Specifically, the control unit 36 ​​transfers the toner image to the sheet member P through constant current control. In other words, the control unit 36 ​​controls the voltage applied to the roller 32b so that the current reaches a predetermined value. The current value used is the current value required to transfer the toner image to the sheet member P and, in this embodiment, the current value for low-resistance media pre-stored in the image forming apparatus 10. "Constant current control" refers to control intended to ensure that the output current value matches the target current value.

[0116] As previously mentioned, due to the low surface resistivity of the low-resistance medium, current does not flow to the portion of the sheet member P that is not clamped. Most of the current flows from roller 32b through the sheet member P toward guide member 64. In other words, this majority of the flowing current forms a transfer electric field that transfers the toner image to the sheet member P. Therefore, with the low-resistance medium, constant current control is possible. This concludes the series of operations.

[0117] On the other hand, if the print resistance is greater than the system resistance and the process proceeds to step S410, the control unit 36 ​​applies a predetermined voltage to the roller 32b based on the paper type information input by the user into the paper type input unit 74a. Specifically, the control unit 36 ​​applies a higher voltage to the roller 32b than when the sheet P is not nipped by the secondary transfer unit NT. In this way, the control unit 36 ​​transfers the toner image to the sheet P through constant voltage control. This completes the series of operations.

[0118] (Summarize)

[0119] As described above, in the image forming apparatus 10, when the printing resistance is less than or equal to the system resistance, the control unit 36 ​​determines that the medium is a low-resistance medium and transfers the toner image to the sheet member P through constant current control. Specifically, the control unit 36 ​​causes the current required to transfer the toner image to the sheet member P to flow through the roller 32b. Therefore, compared to the image forming apparatus 510, which always transfers the toner image to the sheet member P through constant voltage control, transfer defects caused by toner image transfer to the low-resistance medium can be suppressed.

[0120] Furthermore, in the image forming apparatus 10, when the print resistance is greater than the system resistance, the control unit 36 ​​determines that the sheet is plain paper and transfers the toner image to the sheet member P through constant voltage control. Therefore, compared to the case of transferring the toner image to plain paper through constant current control, transfer defects of the toner image to plain paper can be suppressed.

[0121] Furthermore, in the image forming apparatus 10, the control unit 36 ​​derives the print resistance from the voltage applied to the roller 32b when the sheet P is nipped by the secondary transfer unit NT and the current flowing during the voltage application. Therefore, compared to deriving the print resistance based on the surface resistivity of the sheet P, the print resistance can be derived more easily.

[0122] <Second embodiment>

[0123] according to Figures 14 to 16 An example of an image forming apparatus according to a second embodiment of the present disclosure will be described. The second embodiment will be described mainly focusing on differences from the first embodiment.

[0124] like Figure 15 As shown, the image forming apparatus 210 according to the second embodiment includes a control unit 236 for controlling various components.

[0125] Next, the control of the high-voltage power supply 68 by the control unit 236 will be described.

[0126] The user stores the sheet member P in the storage portion 70 and touches the sample output portion 74b (see Figure 6 ). In this way, Figure 14 In step S1100, the control unit 236 rotates the transfer belt 50 and controls the toner image forming unit 30K and the primary transfer roller 52K to transfer the detection image to the transfer belt 50. Furthermore, the control unit 236 controls the high-voltage power supply 68 to apply voltage to the roller 32b. Furthermore, the control unit 236 controls the conveying device 18 to convey the sheet member P accommodated in the accommodating portion 70 along the conveying path 16.

[0127] Then, if Figure 16 As shown, in step S1200, the control unit 236 forms a plurality of detection images K01 having different voltage values ​​applied to the roller 32b on a single sheet member P in the secondary transfer unit NT. Specifically, the control unit 236 controls the high-voltage power supply 68 to change the voltage value applied to the roller 32b, and forms a plurality of black detection images K01 on a single sheet member P according to each voltage value. Thus, a plurality of black detection images K01 having different toner image densities are formed on a single sheet member P.

[0128] Next, in step S1300 , the image inspection section 24 detects the toner image density for each of the plurality of detection images K01 , and the control section 236 receives the detection result from the image inspection section 24 .

[0129] Next, in step S1400, the control unit 236 selects the detection image K01 having a toner image density closest to the target toner image density from among the plurality of detection images K01. In this manner, the control unit 236 functions as density selection means for selecting the detection image having a toner image density closest to the target toner image density from among the plurality of detection images.

[0130] The control unit 236 then obtains the voltage value applied to the roller 32b when transferring the selected detection image K01. Furthermore, the control unit 236 obtains the current value flowing through the roller 32b when this voltage is applied from the ammeter 68a. The control unit 236 then derives the print resistance based on the obtained current and voltage values.

[0131] Next, in step S1500, the control unit 236 determines whether the acquired print resistance is less than or equal to the system resistance. If the print resistance is less than or equal to the system resistance, the sheet member P is determined to be low-resistance medium, and the process proceeds to step S1600. On the other hand, if the print resistance is greater than the system resistance, the sheet member P is determined to be plain paper, and the process proceeds to step S1610.

[0132] Next, in step S1600, when the toner image is transferred to the sheet member P, which is determined to be a low-resistance medium, the control unit 236 controls the high-voltage power supply 68 to flow a predetermined current through the roller 32b. In this way, the control unit 236 transfers the toner image to the sheet member P through constant current control. This completes the series of operations.

[0133] On the other hand, if the print resistance is greater than the system resistance and the process proceeds to step S1610, the control unit 236 applies a predetermined voltage to the roller 32b based on the paper type information input by the user into the paper type input unit 74a. In this way, the control unit 236 transfers the toner image to the sheet member P through constant voltage control. This completes the series of operations.

[0134] (Summarize)

[0135] As described above, in the image forming apparatus 210, the image inspection unit 24 detects the toner image density for each of the multiple detection images K01 formed by varying the voltage value. The control unit 236 then selects the detection image K01 with the toner image density closest to the target toner image density from the multiple detection images K01. Furthermore, the control unit 236 derives the print resistance based on the voltage and current values ​​when transferring this detection image K01. This improves the accuracy of the derived print resistance compared to deriving the print resistance without varying the voltage applied to the roller 32b, thereby minimizing transfer defects caused by the toner image being transferred to a low-resistance medium.

[0136] Furthermore, in the image forming apparatus 210 , a plurality of black detection images K01 are formed on one sheet member P. This shortens the time required to derive the print resistance compared to when a plurality of detection images are formed for each sheet member P.

[0137] <Third embodiment>

[0138] according to Figures 17 to 20 An example of an image forming apparatus according to a third embodiment of the present disclosure will be described. Regarding the third embodiment, the description will focus on the differences from the first embodiment. Figure 19 As shown, the input unit 374 of the image forming apparatus 310 in the third embodiment includes: a paper type input unit 74a; a sample output unit 74b for outputting a confirmation image as a sample image to the sheet member P; and a selection unit 374c. The selection unit 374c will be described later. Figure 18 As shown, the image forming apparatus 310 includes a control unit 336 for controlling various components.

[0139] Next, the control of the high-voltage power supply 68 by the control unit 336 will be described.

[0140] The user stores the sheet member P in the storage portion 70 and touches the sample output portion 74b of the input portion 74 to output a confirmation image. Figure 17 In step S2100, the control unit 336 rotates the transfer belt 50 and controls the toner image forming unit 30K and the primary transfer roller 52K to transfer the confirmation image to the transfer belt 50. Furthermore, the control unit 336 controls the high-voltage power supply 68 to apply voltage to the roller 32b. Furthermore, the control unit 336 controls the conveying device 18 to convey the sheet member P accommodated in the accommodating portion 70 along the conveying path 16.

[0141] Then, if Figure 20As shown, in step S2200, the control unit 336 forms a plurality of verification images K02 at the secondary transfer unit NT, each with a different voltage value applied to the roller 32b for each sheet member P. Specifically, the control unit 336 controls the high-voltage power supply 68 to change the voltage value applied to the roller 32b, and forms a plurality of black verification images K02 for each sheet member P at each voltage value. Consequently, a plurality of black verification images K02 having different toner image densities are formed for each sheet member P.

[0142] Here, the control unit 336 controls various components to form the value of the voltage applied to the roller 32b when transferring the confirmation image K02 to the sheet P and the number of each confirmation image K02. The voltage value and number are examples of information on the confirmation image K02.

[0143] Next, in step S2300 , the control unit 336 acquires the number of the confirmation image K02 input by the user to the selection unit 374 c .

[0144] Specifically, the user checks the confirmation image K02 on the sheet member P output in step S2200. The user then selects the confirmation image K02 that has the closest to the target toner image density and inputs the number of the confirmation image K02 into the selection portion 374c. The control portion 336 then receives the number of the confirmation image K02 input by the user into the selection portion 374c.

[0145] Next, in step S2400, the control unit 336 obtains the voltage value applied to the roller 32b when transferring the selected confirmation image K02. Furthermore, the control unit 336 obtains the current value flowing through the roller 32b when this voltage is applied from the ammeter 68a. The control unit 336 then derives the print resistance based on the obtained current and voltage values.

[0146] Next, in step S2500, the control unit 336 determines whether the acquired print resistance is less than or equal to the system resistance. If the print resistance is less than or equal to the system resistance, the sheet member P is determined to be low-resistance media, and the process proceeds to step S2600. On the other hand, if the print resistance is greater than the system resistance, the sheet member P is determined to be plain paper, and the process proceeds to step S2610.

[0147] Next, in step S2600, when the toner image is transferred to the sheet member P, which is determined to be a low-resistance medium, the control unit 336 controls the high-voltage power supply 68 to flow a predetermined current through the roller 32b. In other words, the control unit 336 transfers the toner image to the sheet member P through constant current control. This completes the series of operations.

[0148] On the other hand, if the print resistance is greater than the system resistance and the process proceeds to step S3610, the control unit 336 applies a predetermined voltage to the roller 32b based on the paper type information input by the user into the paper type input unit 74a. In this way, the control unit 336 transfers the toner image to the sheet member P through constant voltage control. This completes the series of operations.

[0149] (Summarize)

[0150] As described above, the image forming apparatus 310 forms multiple confirmation images K02 by varying the voltage value for each sheet member P. The control unit 336 then obtains the number of the confirmation image K02 input by the user into the selection unit 374c and derives the print resistance based on the voltage and current values ​​when transferring the confirmation image K02. This improves the accuracy of the derived print resistance compared to deriving the print resistance without changing the voltage applied to the roller 32b, thereby minimizing transfer failures of the toner image onto low-resistance media.

[0151] Then, in the image forming apparatus 310 , the voltage value of the voltage applied to the confirmation image K02 and the number of the confirmation image K02 are formed on the sheet member P. Therefore, the user can easily select the confirmation image K02.

[0152] Furthermore, in the image forming apparatus 310, multiple confirmation images K02 are formed by varying the voltage value for each sheet member P. Therefore, compared to the case of forming multiple confirmation images with different voltage values ​​on a single sheet member P, there is no need to vary the voltage value on a single sheet member P. As a result, the toner image density of the confirmation image K02 transferred to the sheet member P is stabilized, improving the accuracy of the derived print resistance.

[0153] While the present disclosure has been described in detail with respect to specific embodiments, the present disclosure is not limited to these embodiments. Those skilled in the art will readily appreciate that various other embodiments are possible within the scope of the present disclosure. For example, although not specifically described in the first embodiment, in step S200, the sample image may or may not be transferred to the sheet member P. The only requirement is that the value of the current flowing when the sheet member P is sandwiched between the secondary transfer unit NT can be determined.

[0154] Furthermore, in the second and third embodiments described above, constant current control is performed using the current value for the low-resistance medium pre-stored in the image forming apparatuses 210 and 310. However, the current value acquired in steps S1400 and S2400 may also be used. This allows constant current control to be performed on the low-resistance medium even when the current value for the low-resistance medium is not pre-stored.

[0155] Furthermore, in the second embodiment, multiple detection images K01 are formed on one sheet member P, but multiple detection images may be formed for each sheet member P. In this case, the effect obtained by forming multiple detection images K01 on one sheet member P cannot be obtained.

[0156] Furthermore, in the third embodiment described above, multiple confirmation images K02 are formed by varying the voltage value for each sheet member P. However, multiple confirmation images K02 may be formed on a single sheet member P. However, in this case, the effect obtained by forming multiple confirmation images K02 for each sheet member P cannot be achieved.

[0157] Furthermore, in the third embodiment, the voltage value applied to the roller 32b is displayed on the sheet P. However, the voltage value may not be displayed. However, in this case, the effect obtained by displaying the voltage value on the sheet P cannot be obtained.

Claims

1. An image forming apparatus, wherein: The image forming apparatus comprises: a rotating member that rotates while holding a toner image on its circumferential surface; a transfer member that sandwiches the conveyed recording medium and the rotating member with a sandwich portion and transfers the toner image held by the rotating member to the recording medium when a voltage is applied thereto; a guide member that is grounded, guides the recording medium toward the clamping portion, and contacts the recording medium clamped by the clamping portion; as well as a control unit that transfers the toner image to the recording medium by constant current control when a printing resistance when a voltage is applied to the transfer member in a state where the recording medium is clamped by the clamping unit is equal to or lower than a system resistance when a voltage is applied to the transfer member in a state where the recording medium is not clamped by the clamping unit; The image forming apparatus further includes a detecting section that detects image densities of a plurality of detection images that are toner images transferred to the recording medium. The control unit changes the voltage applied to the transfer component when transferring the detection image to the recording medium to multiple values, so that multiple detection images are transferred to the recording medium, selects one detection image based on the image density of the multiple detection images detected by the detection component, and derives the printing resistance based on the voltage when transferring the selected detection image and the current flowing when the voltage is applied.

2. The image forming apparatus according to claim 1, wherein When the print resistance is greater than the system resistance, the control unit transfers the toner image to the recording medium through constant voltage control.

3. The image forming apparatus according to claim 1 or 2, wherein: The control unit derives the print resistance based on a voltage applied to the transfer member in a state where the recording medium is clamped by the clamping unit and a current flowing when the voltage is applied.

4. The image forming apparatus according to claim 1, wherein The control unit transfers the plurality of detection images to one recording medium.

5. An image forming apparatus, wherein: The image forming apparatus comprises: a rotating member that rotates while holding a toner image on its circumferential surface; a transfer member that sandwiches the conveyed recording medium and the rotating member with a sandwich portion and transfers the toner image held by the rotating member to the recording medium when a voltage is applied thereto; a guide member that is grounded, guides the recording medium toward the clamping portion, and contacts the recording medium clamped by the clamping portion; as well as a control unit that transfers the toner image to the recording medium by constant current control when a printing resistance when a voltage is applied to the transfer member in a state where the recording medium is clamped by the clamping unit is equal to or lower than a system resistance when a voltage is applied to the transfer member in a state where the recording medium is not clamped by the clamping unit; The image forming apparatus further includes an input unit for inputting information of one confirmation image selected by a user from a plurality of confirmation images that are toner images transferred to a recording medium. The control unit changes the voltage applied to the transfer component to multiple values ​​when transferring the confirmation image to the recording medium, so that multiple confirmation images are transferred to the recording medium, and derives the printing resistance based on the information of the confirmation image input to the input unit and using the voltage when transferring the input confirmation image and the current flowing when the voltage is applied.

6. The image forming apparatus according to claim 5, wherein The control unit causes information of the confirmation image applied to the transfer member to be displayed on the recording medium when the confirmation image is transferred to the recording medium.

Images