Static eliminator, image forming system, and electric charge adjustment device

Abstract

To more stably perform control according to the amount of electric charges on an electrified sheet.SOLUTION: A static eliminator comprises: a static eliminating member that comes into contact with a sheet to eliminate static electricity on the sheet; voltage application means that applies voltage to the static eliminating member; detection means that detects a voltage to be applied to a contact member in contact with the sheet or a current flowing in the contact member on the downstream of a transfer unit in a sheet conveyance direction; and control means that controls the voltage application means. The control means causes the voltage application means to apply voltage to the contact member under the control of voltage different from the voltage applied to the static eliminating member by the voltage application means when the static eliminating member eliminates static electricity on the sheet, and on the basis of a result of detection performed by the detection means when the sheet passes through the contact member, determines the value of the voltage applied to the static eliminating member by the voltage application means when the static eliminating member eliminates static electricity on the sheet.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a static eliminator for eliminating static electricity from a sheet, an image forming system for forming an image on the sheet, and a charge adjusting device for adjusting the charge of the sheet.

Background Art

[0002] Patent Document 1 describes a static eliminator that eliminates static electricity from a sheet using a static elimination roll (contact type static eliminator) that contacts the sheet and a corotron type non-contact static eliminator. Patent Document 2 describes a charging device that performs charging treatment (static elimination) of a sheet, has a surface potential sensor that detects the surface potential of the sheet, and adjusts the voltage applied to the charging roll based on the measured value of the surface potential sensor. Patent Document 2 also describes estimating the surface potential of a sheet based on the transfer bias voltage applied to the secondary transfer roll instead of detection by the surface potential sensor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] A configuration capable of performing control according to the charged charge amount of a sheet by detecting a physical quantity that changes according to the charged charge amount or surface potential of the sheet has been desired. However, in the case of a non-contact type surface potential sensor, when waves or curls are generated on the sheet to be detected, the detection accuracy may decrease due to fluctuations in the distance to the sheet. Further, in the method of estimating the surface potential of a sheet based on the transfer bias voltage applied to the secondary transfer roll, the accuracy of the estimation decreases due to attenuation of the charged charge amount in the conveyance process after passing through the secondary transfer unit.

[0005] An object of the present invention is to provide a charge removing device, an image forming system, and a charge adjusting device that can more stably perform control according to the amount of charged electricity of a sheet.

Means for Solving the Problems

[0006] One aspect of the present invention is a charge removing device for removing charge from a sheet onto which a toner image has been transferred in a transfer unit, the charge removing device including: a charge removing member that contacts the sheet and removes charge from the sheet; voltage applying means for applying a voltage to the charge removing member; detection means for detecting a voltage applied to a contact member that contacts the sheet downstream of the transfer unit in the sheet conveyance direction or a current flowing through the contact member; and control means for controlling the voltage applying means, wherein the control means applies a voltage to the contact member by voltage control different from the voltage applied by the voltage applying means to the charge removing member when the charge removing member removes charge from the sheet, and determines the value of the voltage applied by the voltage applying means to the charge removing member when the charge removing member removes charge from the sheet based on the detection result of the detection means when the sheet passes through the contact member. The charge removing device is characterized by this.

[0007] Another aspect of the present invention is a charge removing device for removing charge from a sheet onto which a toner image has been transferred in a transfer unit, the charge removing device including: a charge removing member that contacts the sheet and removes charge from the sheet; voltage applying means for applying a voltage to the charge removing member; detection means for detecting a voltage applied to a contact member that contacts the sheet downstream of the transfer unit in the sheet conveyance direction or a current flowing through the contact member; control means for controlling the voltage applying means; display means for displaying information; and input means through which a user can input the value of the voltage applied by the voltage applying means to the charge removing member, wherein the control means applies a voltage to the contact member by voltage control different from the voltage applied by the voltage applying means to the charge removing member when the charge removing member removes charge from the sheet, and causes the display means to display information regarding the amount of charged electricity of the sheet based on the detection result of the detection means when the sheet passes through the contact member. The charge removing device is characterized by this.

[0008] Another aspect of the present invention is a charge adjustment device that adjusts the charging state of a sheet on which a toner image has been transferred in a transfer unit, including a charge supply member that contacts the sheet and supplies charge to the sheet, voltage application means for applying a voltage to the charge supply member, detection means for detecting a voltage applied to a contact member that contacts the sheet downstream of the transfer unit in the sheet conveyance direction or a current flowing through the contact member, and control means for controlling the voltage application means. The control means applies a voltage to the contact member by voltage control different from the voltage applied to the charge supply member by the voltage application means when the charge supply member adjusts the charging state of the sheet, and determines the value of the voltage applied to the charge supply member by the voltage application means when the charge supply member adjusts the charging state of the sheet based on the detection result of the detection means when the sheet passes through the contact member. This is a charge adjustment device characterized by the above.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a charge removal device, an image forming system, and a charge adjustment device that can more stably perform control according to the amount of charged charge of a sheet.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 12

Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings.

[0012] 《Example 1》 FIG. 1 shows a schematic diagram of an image forming system 400 according to Example 1. The image forming system 400 includes an image forming apparatus 100 (printer) and a charge removal device 300 connected to the image forming apparatus 100. The image forming system 400 forms an image on a sheet S and discharges it as a product (printed product). The sheet S, which is a recording material (recording medium), can use various sheet materials with different sizes and materials, such as paper like plain paper and thick paper, sheet materials with surface treatment like coated paper, special-shaped sheet materials like envelopes and index paper, plastic sheet materials, cloth, etc. Examples of plastic sheet materials are synthetic paper mainly made of synthetic resin and sheets for overhead projectors (OHT).

[0013] The charge removal device 300 is a device (static eliminator) having a charge removal function for removing (reducing) the charge of the sheet S discharged from the image forming system 400. The charge removal device 300 can also be said to be a charge adjustment device for adjusting the charged state of the sheet S discharged from the image forming system 400. The charge removal device 300 may have functions other than the charge removal function (for example, a decurler function for correcting the curl of the sheet S). Also, although the charge removal device 300 of the present example is arranged as an independent device from the image forming apparatus 100, the charge removal device 300 may be incorporated in the housing of the image forming apparatus 100.

[0014] The image forming system 400 may include optional devices other than the static eliminator 300. Examples of the optional devices are a high-capacity feeder (optional feeder) that supplies the sheet S to the image forming apparatus 100, and a sheet processing apparatus (finisher) that performs processing such as binding processing on the sheet S on which an image is formed by the image forming apparatus 100.

[0015] <Image forming apparatus> The schematic configuration of the image forming apparatus 100 is shown in FIG. 1. The image forming apparatus 100 includes an image forming unit 101 which is an intermediate transfer type electrophotographic mechanism. The image forming unit 101 includes four process units 11Y, 11M, 11C, 11K each having a photosensitive drum 1Y, 1M, 1C, 1K, and a transfer unit 15 having an intermediate transfer belt 6 and a secondary transfer roller 9.

[0016] Each process unit includes a photosensitive drum as an image carrier (latent image carrier), and a charging device, an exposure device, and a developing device as process parts that act on the photosensitive drum to perform each step of the electrophotographic process. That is, the process unit 11Y includes the photosensitive drum 1Y, the charging device 2Y, the exposure device 3Y, and the developing device 4Y. The process unit 11M includes the photosensitive drum 1M, the charging device 2M, the exposure device 3M, and the developing device 4M. The process unit 11C includes the photosensitive drum 1C, the charging device 2C, the exposure device 3C, and the developing device 4C. The process unit 11K includes the photosensitive drum 1K, the charging device 2K, the exposure device 3K, and the developing device 4K.

[0017] Each of the photosensitive drums 1Y, 1M, 1C, 1K is rotationally driven in a predetermined rotation direction A. The process units 11Y, 11M, 11C, 11K have substantially the same configuration except that the toners as developers accommodated in the developing devices 4Y, 4M, 4C, 4K are different.

[0018] The transfer unit 15 includes an intermediate transfer belt 6 as an intermediate transfer member, a secondary transfer roller 9 as a transfer means (secondary transfer means), primary transfer rollers 5Y, 5M, 5C, 5K, a plurality of rollers 20, 21, 22, 23, 24, 25, and a belt cleaner 12. The intermediate transfer belt 6 is stretched over the plurality of rollers 20, 21, 22, 23, 24, 25. The primary transfer rollers 5Y, 5M, 5C, 5K are arranged on the inner surface side of the intermediate transfer belt 6 and at positions corresponding to the photosensitive drums 1Y, 1M, 1C, 1K, respectively. A primary transfer portion is formed between the primary transfer rollers 5Y, 5M, 5C, 5K and the corresponding photosensitive drums 1Y, 1M, 1C, 1K. The roller 20 is a tension roller that applies an appropriate tension to the intermediate transfer belt 6. The roller 22 is a drive roller that rotationally drives the intermediate transfer belt 6 in a predetermined rotation direction G. The secondary transfer roller 9 is in contact with the outer surface of the intermediate transfer belt 6 and is arranged so as to sandwich the intermediate transfer belt 6 together with the opposing roller 21 (secondary transfer opposing roller). A secondary transfer portion T2 as a transfer portion where the toner image is transferred to the sheet S is formed as a nip portion between the secondary transfer roller 9 and the intermediate transfer belt 6.

[0019] The image forming apparatus 100 includes a transfer power source 10 as a voltage application means for forming a bias electric field for transferring the toner image to the secondary transfer portion T2. In the present embodiment, the secondary transfer roller 9, which is the outer roller of the secondary transfer portion T2, is electrically connected to the transfer power source 10, and a predetermined transfer voltage is applied from the transfer power source 10. The transfer voltage is a voltage having a polarity opposite to the normal charging polarity of the toner used for image formation. On the other hand, the opposing roller 21, which is the inner roller of the secondary transfer portion T2, is electrically connected to the ground potential (such as a metal frame) of the image forming apparatus 100. Note that the inner roller of the secondary transfer portion T2 may be connected to the transfer power source 10, and the outer roller of the secondary transfer portion T2 may be connected to the ground potential GND. In this case, a transfer voltage having the same polarity as the normal charging polarity of the toner is applied to the inner roller.

[0020] The image forming apparatus 100 further includes a storage unit 63 (storage, cassette) for storing the sheet S, a feeding unit 64 for feeding the sheet S, and a registration roller 8 for performing registration (alignment) of the sheet S. The image forming apparatus 100 also includes a pre-fixing conveyance device 41 for conveying the sheet S that has passed through the secondary transfer unit T2, a fixing device 40 for fixing the toner image on the sheet S, and a pair of discharge rollers 42 as a discharge unit for discharging the sheet S to the outside of the image forming apparatus 100.

[0021] The feeding unit 64 includes, for example, a pickup roller 65 that feeds out the uppermost sheet S from the storage unit 63 in the sheet feeding direction, and a pair of separation rollers 66 that convey the fed-out sheet S one by one while separating it. The pair of separation rollers includes a conveyance roller that sends the uppermost sheet S in the sheet feeding direction, and a separation roller that contacts the conveyance roller and forms a separation nip together with the conveyance roller. The separation roller prevents double feeding of the sheet S by applying frictional force to the sheet S at the separation nip, thereby preventing the sheets S other than the uppermost sheet S from passing through the separation nip. The separation roller is an example of a separating member for separating the sheet S, and for example, a pad-shaped elastic member (rubber pad) may be used as the separating member.

[0022] The fixing device 40 is a heat fixing type device that has a fixing nip and heats the toner image on the sheet S while sandwiching and conveying the sheet S at the fixing nip. The fixing device 40 includes a heating member that contacts the surface of the sheet S on which the toner image is formed, a pressing member that forms the fixing nip together with the heating member, and a heat source that heats the heating member. As the heating member and the pressing member, for example, a belt member stretched over a plurality of rollers or a rigid roller member can be used. As the heat source, for example, a halogen lamp or an IH type induction heating mechanism can be used.

[0023] In addition, the image forming apparatus 100 includes a user operation unit 102 which is a user interface of the image forming system 400. The user operation unit 102 has a display unit such as a liquid crystal panel for displaying information to the user, and an input unit such as physical buttons for receiving input of information from the user and a touch panel function of the liquid crystal panel. The user can set setting information and execution conditions of the image forming operation for the image forming system 400 by operating the user operation unit 102. The setting information is, for example, attribute information such as the size, material, and brand of the sheet S stored in the storage unit 63. The execution conditions of the image forming operation are, for example, the value of the transfer voltage.

[0024] When an execution instruction for image formation is input from the user, the control unit of the image forming apparatus 100 starts an image forming job which is a series of tasks of forming an image while conveying the sheets S one by one and outputting a product. Hereinafter, a series of operations for forming an image on one sheet S by the image forming apparatus 100 is referred to as an image forming operation. The image forming job includes an image forming operation for at least one sheet S.

[0025] In the image forming operation, toner images of respective colors are created in the process units 11Y, 11M, 11C, and 11K. Specifically, the photosensitive drums 1Y, 1M, 1C, and 1K are rotationally driven, and the charging devices 2Y, 2M, 2C, and 2K uniformly charge the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K. The exposure devices 3Y, 3M, 3C, and 3K expose the photosensitive drums 1Y, 1M, 1C, and 1K based on the image information input together with the execution instruction, and form electrostatic latent images on the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K. The developing devices 4Y, 4M, 4C, and 4K supply yellow, magenta, cyan, and black toner to the photosensitive drums 1Y, 1M, 1C, and 1K respectively, and develop the electrostatic latent images into toner images of respective colors.

[0026] In addition, in this embodiment, a reverse development method is used. That is, after the charging device charges the surface of the photosensitive drum to the same polarity as the normal charging polarity of the toner, the potential of the exposed area exposed by the exposure device decays, and toner adheres to the exposed area during development.

[0027] The toner images created in the respective process units 11Y, 11M, 11C, and 11K are primarily transferred from the photosensitive drums 1Y, 1M, 1C, and 1K to the intermediate transfer belt 6 in the primary transfer section. A transfer voltage of the opposite polarity to the normal charging polarity of the toner is applied to the primary transfer rollers 5Y, 5M, 5C, and 5K by constant voltage control.

[0028] In this embodiment, the primary transfer rollers 5Y, 5M, 5C, and 5K are conductive rollers having a core bar and an elastic layer with conductivity formed on the outer peripheral side of the core bar. The elastic layer is formed of, for example, an ion conductive foamed rubber. An ion conductive foamed rubber is a foamed rubber material in which a conductive agent that exhibits ion conductivity is dispersed. As the conductive agent and the foamed rubber material, known materials for transfer rollers can be used. Each primary transfer roller preferably has an outer diameter of 15 to 20 mm and a resistance value of 1E+5 to 1E+8 Ω when a voltage of 2 kV is applied under environmental conditions of 23°C and 50% RH.

[0029] The intermediate transfer belt 6 is rotationally driven at a predetermined peripheral speed (process speed) equal to the peripheral speed of the photosensitive drums 1Y, 1M, 1C, and 1K. The peripheral speed in this embodiment is 150 to 470 mm / sec. As the intermediate transfer belt 6 rotates, toner images of other colors are transferred on top of the toner image transferred in the upstream primary transfer section, thereby forming a full-color toner image on the intermediate transfer belt 6. The full-color toner image is carried on the intermediate transfer belt 6 and conveyed toward the secondary transfer section T2.

[0030] In parallel with the creation of the toner image in the image forming section 101, the feeding unit 64 feeds the sheets S one by one toward the image forming section 101. The fed sheet S is conveyed to the secondary transfer section T2 by the registration roller 8 in synchronization with the timing at which the toner image on the intermediate transfer belt 6 is conveyed to the secondary transfer section T2. Then, in the secondary transfer section T2, the toner image is transferred (secondarily transferred) from the intermediate transfer belt 6 to the sheet S.

[0031] In this embodiment, the secondary transfer roller 9 is a conductive roller having a core bar and an elastic layer with conductivity formed on the outer peripheral side of the core bar. The elastic layer is formed of, for example, an ion conductive foamed rubber. The ion conductive foamed rubber is a foamed rubber material in which a conductive agent that exhibits ion conductivity is dispersed. As the conductive agent and the foamed rubber material, known materials for transfer rollers can be used. The secondary transfer roller 9 is preferably one having an outer diameter of 20 to 25 mm and a resistance value of 1E+5 to 1E+8 Ω when a voltage of 2 kV is applied under environmental conditions of 23°C and 50% RH, for example.

[0032] Further, the counter roller 21 is a conductive rubber roller having a core bar and an elastic layer of an electron conductive foamed rubber formed on the outer peripheral side of the core bar. The electron conductive foamed rubber is a foamed rubber material in which a conductive agent that exhibits electron conductivity is dispersed. As the conductive agent and the foamed rubber material, known materials for transfer rollers can be used. The counter roller 21 is preferably one having an outer diameter of 20 to 22 mm and a resistance value of 1E+5 to 1E+8 Ω when a voltage of 50 V is applied under environmental conditions of 23°C and 50% RH, for example.

[0033] During secondary transfer, a transfer voltage having a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 9 from the transfer power source 10 by constant voltage control. The transfer voltage is, for example, +1 to +7 kV, and is automatically adjusted so that a current of +40 to +120 μA flows from the secondary transfer roller 9 to the counter roller 21. By applying the transfer voltage, a bias electric field is formed in the secondary transfer portion T2 such that the potential of the secondary transfer roller 9 is opposite to the normal charging polarity of the toner with respect to the intermediate transfer belt 6. Due to this bias electric field, an electrostatic force in a direction approaching the secondary transfer roller 9 acts on the toner on the intermediate transfer belt 6. Then, the toner is transferred to the sheet S passing through the secondary transfer portion T2 from the intermediate transfer belt 6, and thus the toner image is transferred to the sheet S.

[0034] Prior to the secondary transfer unit T2, a conveyance guide 11 is provided to improve the positional accuracy of the sheet S with respect to the intermediate transfer belt 6. Also, the transfer residual toner remaining on the intermediate transfer belt 6 without being transferred to the sheet S is recovered by the belt cleaner 12 and reused for image formation.

[0035] The sheet S that has passed through the secondary transfer unit T2 is conveyed to the fixing device 40 by the pre-fixing conveyance device 41 and undergoes a fixing process of the toner image by the fixing device 40. The fixing process is a process of heating and pressing the toner image on the sheet S while sandwiching and conveying the sheet S at the nip portion of the fixing device 40. The pre-fixing conveyance device 41 conveys the sheet S by carrying it on an endless rubber belt, for example. As the rubber belt, a belt made of ethylene propylene diene rubber (EPDM) with a width of 100 to 110 mm and a thickness of 1 to 3 mm can be used. Also, the rubber belt has holes with a diameter of 3 to 7 mm, and by generating a negative pressure inside the rubber belt using a fan, the sheet S can be stably carried on the rubber belt.

[0036] The sheet S that has passed through the fixing device 40 is discharged toward the static elimination device 300 by the discharge roller pair 42.

[0037] The above-described intermediate transfer type image forming unit 101 is an example of an image forming means for forming an image on the sheet S, and the image forming means may be, for example, a direct transfer type electrophotographic unit. In this case, the toner image formed on the photosensitive drum as the image carrier is directly transferred from the photosensitive drum to the sheet S at the transfer nip (transfer unit) where the photosensitive drum and the transfer roller face each other. At the transfer nip, a bias electric field is formed in which the potential of the transfer roller is opposite to the normal charging polarity of the toner with respect to the photosensitive drum.

[0038] <Static elimination device> FIG. 2 is a schematic diagram of the static eliminator 300 in the first embodiment. In this embodiment, the static eliminator 300 is connected to the downstream side of the image forming apparatus 100. The static eliminator 300 receives the sheet S formed with an image by the image forming apparatus 100 and conveys it in the sheet conveyance direction Cv, while performing static elimination of the sheet S (reducing the electrostatic charge on the sheet surface). By performing static elimination of the sheet S, it is possible to prevent the sheets discharged from and stacked on the image forming system 400 from sticking to each other due to electrostatic attraction force, and to make it difficult for the alignment of the sheet S to deteriorate due to the sticking of the sheets to each other. The static eliminator 300 includes a pair of static elimination rollers 51 as a contact type static eliminator, an ionizer unit 52 as a non-contact type static eliminator, a pair of detection rollers 56, a first high voltage power supply 55, and a second high voltage power supply 58.

[0039] The pair of static elimination rollers 51 includes a static elimination counter roller 51a (second counter roller) that contacts the first surface Sa of the sheet S, and a static elimination roller 51b that contacts the second surface Sb of the sheet S opposite to the first surface Sa. The static elimination roller 51b is a contact type static elimination member that contacts the conveyed sheet S and eliminates static electricity from the sheet S. The static elimination counter roller 51a is abutted against the static elimination roller 51b, and a static elimination nip is formed as a nip portion between the static elimination roller 51b and the static elimination counter roller 51a. The pair of static elimination rollers 51 performs static elimination of the sheet S while sandwiching and conveying the sheet S at the static elimination nip.

[0040] The static elimination counter roller 51a is connected to the ground potential GND. The static elimination counter roller 51a is electrically connected to, for example, the metal frame of the static eliminator 300. The static elimination roller 51b is connected to the first high voltage power supply 55. The first high voltage power supply 55 is a voltage application means (first voltage application means) that applies a voltage (static elimination voltage) for performing static elimination of the sheet S to the static elimination roller 51b.

[0041] Note that the static elimination roller 51b may be arranged to contact the first surface Sa of the sheet S, and the static elimination counter roller 51a may be arranged to contact the second surface Sb of the sheet S. In that case, the voltage applied to the static elimination roller 51b has a reverse polarity to the voltage applied to the static elimination roller 51b in this embodiment.

[0042] In this embodiment, the charge removing roller 51b is a conductive roller having a core metal and an elastic layer having conductivity formed on the outer peripheral side of the core metal. The elastic layer is formed of, for example, an ion conductive foamed rubber. The ion conductive foamed rubber is a foamed rubber material in which a conductive agent for expressing ion conductivity is dispersed. As the conductive agent and the foamed rubber material, known materials can be used. The charge removing roller 51b can preferably be used, for example, with an outer diameter of 20 to 25 mm and a resistance value of 1E+5 to 1E+8 Ω when a voltage of 2 kV is applied under environmental conditions of 23°C and 50% RH. The charge removing counter roller 51a is made of stainless steel (SUS) and uses a roller with an outer diameter of 20 to 25 mm. Note that, as the charge removing roller 51b, a roller formed of a metal material such as stainless steel may be used.

[0043] The ionizer unit 52 includes a first ionizer 52a facing the first surface of the sheet S and a second ionizer 52b facing the second surface of the sheet S. Each of the first ionizer 52a and the second ionizer 52b has an electrode needle. By applying a voltage to the electrode needle, corona discharge is generated from the tip of the needle, and the air around the tip of the needle is ionized. Then, the generated ions neutralize the charges on the surface of the sheet S, thereby removing the charge from the sheet S.

[0044] In the ionizer unit 52 in this embodiment, bar type ionizers IZS40 (manufactured by SMC) are arranged above and below the sheet conveyance path as the first ionizer 52a and the second ionizer 52b. The conveyance guides 53a and 53b forming the sheet conveyance path of the ionizer unit 52 are made of, for example, a resin obtained by synthesizing PC (polycarbonate) and ABS (acrylonitrile-butadiene-styrene). The volume resistivity of the conveyance guides 53a and 53b is, for example, 1×10 14 Ω·cm. Further, as shown in FIG. 3, a plurality of holes 530 are formed in each of the conveyance guides 53a and 53b so that the ions emitted from the first ionizer 52a and the second ionizer 52b are not physically shielded. The plurality of holes 530 are arranged side by side in the sheet width direction orthogonal to the sheet conveyance direction Cv.

[0045] The above-described first ionizer 52a and second ionizer 52b are examples of non-contact static eliminators, and other non-contact static eliminators may be used. For example, a corotron or scorotron type static eliminator that eliminates static electricity from a sheet by corona discharge from a discharge wire may be used. Further, the non-contact static eliminator does not necessarily have to be provided on both sides of the conveyance path. For example, the static elimination device 300 may be configured to have only the first ionizer 52a as a non-contact static eliminator. Also, when the static elimination roller 51b can sufficiently eliminate static electricity from the sheet S, the non-contact static eliminator may be omitted.

[0046] The detection roller pair 56 is arranged upstream of the static elimination roller pair 51 in the sheet conveyance direction Cv. The detection roller pair 56 includes a detection roller 56b and a detection opposing roller 56a (first opposing roller) that faces the detection roller 56b. The detection opposing roller 56a is in contact with the detection roller 56b, and a detection nip is formed between the detection roller 56b and the detection opposing roller 56a. The detection opposing roller 56a sandwiches and conveys the sheet S together with the detection roller 56b. As the detection roller 56b, a roller (conductive roller) having the same configuration as the static elimination roller 51b can be used. As the detection opposing roller 56a, a roller having the same configuration as the static elimination opposing roller 51a can be used.

[0047] The detection opposing roller 56a is connected to the ground potential GND. The detection opposing roller 56a is electrically connected to, for example, the metal frame of the static elimination device 300 and is electrically grounded. The detection roller 56b is connected to the second high-voltage power supply 58. The second high-voltage power supply 58 is a voltage application means (voltage application means) that applies a voltage to the detection roller 56b. Hereinafter, the voltage applied from the second high-voltage power supply 58 to the detection roller 56b is referred to as "detection high voltage".

[0048] Note that the detection roller 56b may be arranged so as to contact the first surface Sa of the sheet S, and the detection opposing roller 56a may be arranged so as to contact the second surface Sb of the sheet S.

[0049] In this embodiment, the second high-voltage power supply 58 can perform output control by constant-voltage control in the range of 0 kV to -6 kV and constant-current control in the range of 0 μA to -100 μA. Further, the second high-voltage power supply 58 is provided with a voltage detection circuit 58V capable of detecting the voltage value of the detection high voltage applied from the second high-voltage power supply 58 to the detection roller 56b (FIG. 4). Further, the second high-voltage power supply 58 is provided with a current detection circuit 58A capable of detecting the current flowing through the detection roller 56b due to the voltage application from the second high-voltage power supply 58 (FIG. 4).

[0050] The detection roller pair 56 is used for detecting the charged charge amount of the sheet S conveyed to the static eliminator 300 and for control for setting the static elimination voltage applied by the first high-voltage power supply 55 to the sheet S. Details of these controls will be described later.

[0051] The detection roller 56b is an example of a contact member that contacts the sheet S downstream of the transfer portion (secondary transfer portion T2) in the sheet conveyance direction. That is, the contact member in this embodiment is a member different from the static elimination roller 51b (static elimination member). The voltage detection circuit 58V and the current detection circuit 58A are examples of detection means for detecting the voltage applied to the contact member or the current flowing through the contact member. As will be described below, in this embodiment, control mainly using the detection result of the voltage by the voltage detection circuit 58V is performed.

[0052] The sheet S conveyed from the image forming apparatus 100 to the static eliminator 300 first has most of its charges removed (rough removal) by the static elimination nip of the static elimination roller pair 51. Specifically, the static elimination voltage is set to the opposite polarity to the transfer voltage applied to the secondary transfer roller 9. The value of the static elimination voltage is set in the range of -1 kV to -6 kV.

[0053] Immediately after passing through the secondary transfer section T2 (FIG. 1), usually, the first surface Sa of the sheet S that was in contact with the intermediate transfer belt 6 is charged negatively, and the second surface Sb that was in contact with the secondary transfer roller 9 is charged positively. By applying a charge removal voltage having a polarity opposite to that of the transfer voltage to the charge removal roller 51b, a current flows between the charge removal roller 51b and the charge removal counter roller 51a so that positive charges are supplied to the first surface Sa of the sheet S and positive charges are supplied to the second surface Sb. In this way, by applying a charge removal voltage to the charge removal roller 51b, a current flows through the sheet S in the charge removal nip, and the amount of charged charge of the sheet S, which is the amount of charge carried on the first surface Sa and the second surface Sb of the sheet S, is reduced.

[0054] The sheet S that has passed through the charge removal roller pair 51 is further charge-removed in the ionizer section 52. Specifically, the charges remaining on the first surface Sa and the second surface Sb of the sheet S are neutralized by the ions irradiated from the first ionizer 52a and the second ionizer 52b, and the amount of charged charge of the sheet S is further reduced. The sheet S that has passed through the ionizer section 52 is discharged to the outside of the charge removal device 300.

[0055] <Method for Detecting Amount of Charged Charge and Method for Controlling Charge Removal Voltage> Hereinafter, the nip portion of the detection roller pair 56 is referred to as a detection nip. In the present embodiment, when the sheet S passes through the detection roller pair 56, a detection high voltage is applied from the second high voltage power source 58 to the detection roller 56b. Then, based on the applied voltage value to the detection roller 56b and / or the current value flowing through the detection roller 56b, the amount of charged charge of the sheet S is detected, and the charge removal voltage applied from the first high voltage power source 55 to the charge removal roller 51b when performing charge removal of the sheet S is controlled.

[0056] Note that the amount of charged charge of the sheet S and the surface potential of the sheet S usually are proportional. Also, the amount of charged charge of the sheet S may be represented by the amount of charge per unit area of the sheet surface (surface charge density). Therefore, the "amount of charged charge" of the sheet S in the following description may be replaced with the surface potential of the sheet S or the surface charge density of the sheet S.

[0057] The block diagram of the control circuit 200 according to this embodiment is shown in FIG. 4. The control circuit 200 is an example of a control means for controlling the operation of the static eliminator device 300. The control circuit 200 may be mounted inside the static eliminator device 300, or part or all of the functions of the control circuit 200 may be mounted in the image forming apparatus 100.

[0058] As shown in FIG. 4, the control circuit 200 includes a CPU 201, a RAM 210, and a ROM 220. The CPU 201 is an execution means for reading and executing a control program. The RAM 210 serves as a work area when the CPU 201 executes the control program. The ROM 220 is an example of a storage unit that stores various types of information such as setting information related to the control of the static eliminator device 300. Further, the control circuit 200 is connected to the user operation unit 102, the static elimination operation unit 54, the high voltage power supply 55, and the transfer power supply 10.

[0059] More specifically, the CPU 201 acquires information such as information related to the image forming job (job information), the value of the current flowing through the static elimination roller 51b when the static elimination voltage is applied (referred to as the static elimination current), and the value of the transfer voltage output by the transfer power supply 10, and stores it in the RAM 210. Here, the job information is, for example, the attribute information of the sheet S input from the user via the user operation unit 102, and is the attribute information of the sheet S used in the current image forming job. When the sheet S is passing through the static elimination nip (during paper feeding), the value of the static elimination current corresponds to the amount of charge supplied from the static elimination roller 51b to the sheet S per unit time.

[0060] Further, the CPU 201 calculates the charged charge amount of the sheet S based on the detection results of the current detection circuit 58A and / or the voltage detection circuit 58V when applying a detection high voltage from the second high-voltage power supply 58 to the detection roller 56b. The CPU 201 performs feedback control to calculate the discharge voltage to be applied from the first high-voltage power supply 55 to the discharge roller 51b for discharging the sheet S based on the calculated charged charge amount. Further, the CPU 201 can display the calculated charged charge amount on the user operation unit 102. Also, in order to obtain these results, a process of determining a control signal to be sent to the second high-voltage power supply 58 to apply a detection high voltage to the detection roller 56b is also performed.

[0061] The CPU 201 applies a detection high voltage from the second high-voltage power supply 58 to the detection roller 56b during the period when the detection sheet S passes through the detection nip and the periods before and after that. The CPU 201 determines the voltage (discharge voltage) applied by the first high-voltage power supply 55 to the discharge roller 51b when the discharge roller 51b discharges the sheet based on the detection result of the current detection circuit 58A or the voltage detection circuit 58V when the detection sheet S passes through the detection roller 56b.

[0062] In this embodiment, the detection sheet S and the sheet S to be discharged may be the same sheet. That is, when an image formation job is input, the CPU 201 can use the sheet S on which an image is to be formed (the sheet S that is the result of the image formation job) as the detection sheet S. Hereinafter, a mode in which, when an image formation job is input, detection of the charged charge amount and setting of the discharge voltage using the detection roller 56b are performed as part of the image formation job will be described.

[0063] Further, as an operation independent of the image forming job, a mode (adjustment mode) for detecting the charged charge amount using the detection roller 56b and setting the discharging voltage may be executed. In that case, the detection sheet S used in the adjustment mode is a sheet S different from the sheet S on which an image is formed in the image forming job. Further, the CPU 201 starts the adjustment mode when instructed by the user to execute the adjustment mode via, for example, the user operation unit 102 or the like. The content of the adjustment mode may be the same as S1 to S3 of the flow of FIG. 5 described below.

[0064] (Control Flow) The control procedure performed by the control circuit 200 will be described with reference to the flowchart of FIG. 5. Hereinafter, unless otherwise specified, the execution subject of each step of this flow is the CPU 201.

[0065] When an image forming job is input to the image forming system 400, the processing of this flow is started. First, the CPU 201 acquires job information set via the user operation unit 102 (S0). In the image forming apparatus 100, an image forming operation is started based on the job information. On the other hand, the CPU 201 applies a detection high voltage from the second high voltage power supply 58 to the detection roller 56b during the period when the first sheet S in the image forming job passes through the detection nip and the periods before and after that (S1). In the present embodiment, the detection high voltage is applied by constant current control with a preset current value in the range of, for example, -10 to -30 μA. Then, the fluctuation of the voltage value when the sheet S passes through the detection nip during the application of the detection high voltage is measured (S2).

[0066] The amount of change in the voltage value of the detection high voltage when the sheet S passes through the detection nip is defined as the "detection voltage". That is, the detection voltage is obtained by subtracting the detection value of the voltage detection circuit 58V when the sheet S is not passing through the detection nip from the detection value of the voltage detection circuit 58V when the sheet S passes through the detection nip while the detection high voltage is being applied to the detection roller 56b by constant current control.

[0067] The CPU 201 records the detected voltage obtained in S2 in the RAM 210 as a detection result. Then, based on the detected voltage obtained in S2 and the charge conversion table and discharge voltage conversion table (Fig. 4) stored in the ROM 220, the CPU 201 calculates the values of the charge amount and discharge voltage of the sheet S (S3, S4). Further, the CPU 201 applies the discharge voltage to the discharge roller 51b at the value of the discharge voltage determined in S4 to the first high-voltage power supply 55, and discharges the sheet S by the discharge roller 51b (S5).

[0068] As described above, the voltage detection circuit 58V as a detection means detects the voltage applied to the detection roller 56b (contact member). The control circuit 200 (control means) determines the value of the discharge voltage based on the amount of change in the voltage detected by the voltage detection circuit 58V when the sheet passes through the detection roller 56b with a voltage applied to the detection roller 56b by constant current control. Thereby, according to the charge amount of the sheet S, the discharge voltage is automatically set to a value suitable for discharging the sheet S.

[0069] (Reasons for using the detection high voltage) The reason why the charge amount of the sheet S can be obtained based on the amount of change in the voltage value (detection voltage) of the detection high voltage when the sheet S passes through the detection nip will be explained. The sheet S is affected by the electric field in the secondary transfer section T2. In the secondary transfer section T2, an electric field is formed such that the potential of the secondary transfer roller 9 with respect to the intermediate transfer belt 6 has a polarity opposite to the normal charging polarity of the toner. Hereinafter, it is assumed that the normal charging polarity of the toner is negative. In the secondary transfer section T2, the sheet S is affected by an electric field in which the side of the surface (first surface Sa, image surface) where the toner image is transferred is negative and the side of the back surface (second surface Sb, non-image surface) is positive. When controlling the charge amount and discharge voltage using the detection roller 56b, it is assumed that the transfer voltage during normal image formation is applied in the secondary transfer section T2 regardless of whether it is an adjustment mode independent of the image formation job.

[0070] When the resistance value of the sheet S is low, for example, the positive charges supplied from the secondary transfer roller 9 to the second surface Sb of the sheet S can move in the thickness direction of the sheet S and escape from the first surface Sa to the intermediate transfer belt 6. As a result, when the resistance value of the sheet S is low, most of the positive charges supplied to the second surface Sb of the sheet S escape to the intermediate transfer belt 6, except for the amount of positive charges necessary for transferring the toner image. Therefore, when the resistance value of the sheet S is low, the amount of charged electric charges on the first surface Sa and the second surface Sb of the sheet S does not reach a large value.

[0071] However, when the resistance value of the sheet S is high, the positive charges supplied from the secondary transfer roller 9 to the second surface Sb of the sheet S tend to remain on the second surface Sb. On the first surface Sa of the sheet S, dielectric polarization occurs in response to the positive charges on the second surface Sb, and negative charges are distributed on the first surface Sa. Also, when the resistance value of the sheet S is high, even after the sheet S passes through the secondary transfer portion T2, the amount of charged electric charges on the first surface Sa and the second surface Sb is maintained without much attenuation.

[0072] Incidentally, examples of sheets S with a high resistance value are sheets made of synthetic resin such as plastic films and synthetic papers. These sheets are typical examples of sheets that require high-voltage static elimination by the static eliminator 300. In these sheets, if static elimination is not performed, the amount of charged electric charges on the sheet surface remains large and is discharged to the discharge tray or the like, and the sheets are likely to stick to each other due to electrostatic adsorption force.

[0073] The relationship between voltage and current when the charged sheet S passes through the detection nip with a voltage applied to the detection roller 56b is different from the relationship between voltage and current when the non-charged sheet S passes through the detection nip. That is, the applied voltage required to pass a current through the detection roller 56b at a specific current value while the sheet S is passing through the detection nip varies according to the resistance value of the sheet S, the amount of charged electric charges on the sheet S, and the polarity of the charge.

[0074] For example, consider a case where the detection roller 56b is supplied with a negative charge (a negative-polarity high voltage for detection is applied) in a state where the sheet S is charged so that the first surface Sa carries a negative charge and the second surface Sb carries a positive charge. In this case, the sheet S acts as a capacitor, and the charges stored on the first surface Sa and the second surface Sb are released when the sheet S passes through the transfer nip. As a result, more charges tend to move in the direction along the potential gradient generated by applying a voltage to the detection roller 56b. That is, if the applied voltage is constant, when the sheet S passes through the detection nip, the current flowing through the detection roller 56b increases by the amount of current induced by the charges on the sheet surface.

[0075] In other words, the applied voltage required to pass a current through the detection roller 56b at a predetermined current value when the sheet S passes through the detection nip changes according to the amount of charged charge of the sheet S. When a sheet S charged with the first surface Sa being negative-polar and the second surface Sb being positive-polar passes through the detection nip, the applied voltage required to pass a current through the detection roller 56b at a predetermined current value (for example, -20 μA) is lower than the applied voltage required to pass a current through the detection roller 56b at the same current value when an uncharged sheet S passes through the detection nip. Conversely, when a sheet S charged with the first surface Sa being positive-polar and the second surface Sb being negative-polar passes through the detection nip, the applied voltage required to pass a current through the detection roller 56b at a predetermined current value is higher than the applied voltage required to pass a current through the detection roller 56b at the same current value when an uncharged sheet S passes through the detection nip.

[0076] (Relationship between detection voltage and amount of charged charge) The result of a preliminary study on the relationship between the amount of variation in the voltage value (detection voltage) of the high voltage for detection when the sheet S passes through the detection nip and the amount of charged charge of the sheet S is shown in FIG. 6(a). Here, a sheet with a high resistance value (synthetic paper) was charged in advance with a specified amount of charged charge by a charging means prepared separately from the static eliminator 300. The horizontal axis in FIG. 6(a) represents the amount of charged charge of the sheet in terms of charge density (the amount of charge per unit area of the sheet surface). Then, the detection voltage (vertical axis) was measured when the charged sheet was passed through the detection nip.

[0077] In this embodiment, a charge conversion table representing the correspondence between the detected voltage and the charged charge amount shown in FIG. 6(a) is stored in the ROM220 (FIG. 4) in the control circuit 200. In S3 of the above-described flow (FIG. 5), the CPU 201 can obtain the charged charge amount of the sheet S by referring to the charge conversion table using the detected voltage acquired when the sheet S passes through the detection nip.

[0078] In this embodiment, information representing the correspondence between the detected voltage and the charged charge amount is prepared in the form of a table. However, for example, a method of expressing the charged charge amount by a function using the detected voltage as a variable and storing the coefficients of the function in the ROM220 as control parameters may also be used.

[0079] (Relationship between detected voltage and discharge voltage) FIG. 6(b) shows the result of a prior study on the relationship between the amount of change (detected voltage) in the voltage value of the detection high voltage when the sheet S passes through the detection nip and the value of the discharge voltage suitable for discharging the sheet S. Similar to the case of FIG. 6(a), a sheet with a high resistance value (synthetic paper) was charged with a specified charged charge amount by a charging means prepared separately from the discharge device 300. The horizontal axis in FIG. 6(b) represents the detected voltage when the charged sheet is passed through the detection nip. The vertical axis in FIG. 6(b) indicates the value of the discharge voltage corresponding to the charged charge amount of the sheet S.

[0080] In this embodiment, a discharge voltage conversion table representing the correspondence between the detected voltage and the discharge voltage shown in FIG. 6(b) is stored in the ROM220 (FIG. 4) in the control circuit 200. In S4 of the above-described flow (FIG. 5), the CPU 201 can determine the value of the discharge voltage by referring to the discharge voltage conversion table using the detected voltage acquired when the sheet S passes through the detection nip.

[0081] In this embodiment, information representing the correspondence between the detected voltage and the discharge voltage is prepared in the form of a table. However, for example, a method of expressing the discharge voltage by a function using the detected voltage as a variable and storing the coefficients of the function in the ROM220 as control parameters may also be used.

[0082] <Difference between Detection High Voltage and Static Elimination Voltage> The voltage (detection high voltage) applied to the detection roller 56b to obtain the charged amount of the sheet S and the static elimination voltage is subjected to different voltage controls from the voltage (static elimination voltage) applied to the static elimination roller 51b for static elimination of the sheet S. Here, "different voltage controls" means that at least one of the voltage control method (constant current control or constant voltage control) and the presence or absence of change in the voltage value according to the detection result of the detection means is different.

[0083] In this embodiment, the static elimination voltage is controlled by constant voltage control. That is, the voltage applied to the static elimination member is controlled by constant voltage control. This is because it is easy to stably perform static elimination of the sheet S. For example, in constant voltage control, it is not necessary to vary the output value according to the width of the sheet S (the length of the sheet in the sheet width direction orthogonal to the sheet conveyance direction Cv).

[0084] On the other hand, the detection high voltage is controlled by constant current control. That is, the voltage applied to the contact member is controlled by constant current control. Also, the detection high voltage is a preset value (a predetermined value stored in the ROM 220) regardless of the detection result of the voltage detection circuit 58V (detection means), while the value of the static elimination voltage is changed based on the detection result of the voltage detection circuit 58V.

[0085] The static elimination voltage is changed according to the charged amount of the sheet S in order to appropriately perform static elimination of the sheet S. On the other hand, for the purpose of evaluating the charged amount of the sheet S, the detection high voltage may be a predetermined value. Rather, fixing the detection high voltage to a predetermined value can more easily perform prior studies such as a charged amount conversion table.

[0086] When the detection high voltage is controlled by constant voltage control, for example, due to a change in the resistance value caused by aging deterioration of the detection roller 56b or the like, the detection result may change due to factors other than the charged charge amount. That is, even if the relationship between the detection result (current value or its fluctuation amount) when the detection high voltage is applied by constant voltage control and the charged charge amount or the discharge voltage is obtained through prior consideration, there is a possibility that the result of the prior consideration will deviate during the long-term use of the discharge device 300.

[0087] Also, when the detection high voltage is controlled at a constant voltage equal to the discharge voltage, depending on the value of the discharge voltage, there may be a case where the current flowing through the detection roller 56b becomes almost 0 A when the sheet S passes through the detection nip. In this case, the change in the current value corresponding to the charged charge amount of the sheet S is hidden by noise (the S / N ratio becomes low), and it may be difficult to appropriately evaluate the charged charge amount of the sheet S and set the discharge voltage according to the charged charge amount. Also, when the detection high voltage is controlled at a constant voltage equal to the discharge voltage, depending on the value of the discharge voltage, there may be a case where the current flowing through the detection roller 56b becomes extremely large when the sheet S passes through the detection nip. In this case, it may be difficult to perform appropriate control by exceeding the detectable range of the current detection circuit 58A.

[0088] By controlling the detection high voltage with constant current control, the above-mentioned inconveniences are less likely to occur.

[0089] <Summary of this embodiment> As described above, in this embodiment, a detection voltage is applied to the detection roller 56b (contact member) by a voltage control different from the static elimination voltage, and the value of the static elimination voltage applied to the static elimination roller 51b is determined based on the detection voltage when the detection high voltage is applied to the detection roller 56b. That is, the control circuit 200 (control means) applies a voltage (detection high voltage) to the detection roller 56b (contact member) by a voltage control different from the voltage (static elimination voltage) applied to the static elimination roller 51b (static elimination member) by the first high voltage power supply 55 (voltage application means) when the static elimination roller 51b eliminates static electricity from the sheet. Then, the control circuit 200 determines the value of the voltage (static elimination voltage) applied to the static elimination roller 51b by the first high voltage power supply 55 when the static elimination roller 51b eliminates static electricity from the sheet based on the detection result of the voltage detection circuit 58V (detection means) when the sheet passes through the detection roller 56b.

[0090] Thereby, the value of the static elimination voltage can be automatically determined according to the charge amount of the charged sheet S, and the work load of the user can be reduced compared with a configuration that requires the user to adjust the static elimination voltage.

[0091] The operation of adjusting the static elimination voltage by the user is, for example, a series of operations in which (1) a test sheet is output to the image forming system 400, (2) the user manually measures the charge amount of the discharged test sheet using a surface potentiometer, and (3) the voltage adjustment switch 54b (FIG. 4) is operated according to the measurement result to increase or decrease the value of the static elimination voltage, which is repeated until the charge amount of the test sheet becomes sufficiently small.

[0092] Also, in this embodiment, the charged amount of the sheet S and the static elimination voltage are obtained using the detection roller 56b located downstream of the secondary transfer portion T2 (transfer portion) in the sheet conveyance direction Cv. For this reason, compared with the case of obtaining the charged amount of the sheet S from the relationship between the transfer voltage and the current in the secondary transfer portion T2, the charged amount of the sheet S after passing through the secondary transfer portion T2 is less likely to be affected by attenuation, and the charged amount of the sheet S and the static elimination voltage can be obtained more appropriately.

[0093] In addition, in this embodiment, the detection roller 56b that contacts the sheet S is used to obtain the charged amount of charge and the charge elimination voltage of the sheet S. Although it is also conceivable to use a non-contact type surface potential sensor instead of the detection roller 56b, the measurement result of the non-contact type surface potential sensor varies depending on the distance to the measurement target. For this reason, a member for stabilizing the distance to the measurement target may be additionally required. Further, when waves or curls occur in the sheet S due to image formation, the measurement accuracy is deteriorated. In this embodiment, since the detection roller 56b that contacts the sheet S is used to obtain the charged amount of charge and the charge elimination voltage of the sheet S, these inconveniences can be avoided.

[0094] As described above, according to this embodiment, it is possible to provide a charge elimination device capable of more stably performing control according to the charged amount of charge of the sheet, and an image forming system including the same.

[0095] Further, the detection roller pair 56 of this embodiment functions as a conveyance roller pair that sandwiches and conveys the sheet S. For this reason, it is not necessary to additionally arrange a surface potential sensor for detecting the charged amount of charge, and the cost and arrangement space associated with the addition of the surface potential sensor can be saved.

[0096] Further, the detection roller 56b of this embodiment is arranged upstream of the charge elimination roller 51b in the sheet conveyance direction Cv. For this reason, after the detection voltage is acquired when the sheet S passes through the detection nip, the charge elimination voltage determined based on the acquired detection voltage can be started to be applied to the charge elimination roller 51b before the sheet S passes through the charge elimination nip. That is, the control circuit 200 (control means) determines the value of the charge elimination voltage applied to the charge elimination roller 51b (charge elimination member) for eliminating the charge of the sheet based on the detection result of the voltage detection circuit 58V (detection means) when the sheet passes through the detection roller 56b (contact member). Thereby, the charge elimination voltage can be controlled with higher accuracy according to the charged amount of charge of each sheet.

[0097] <Modification Example> In this embodiment, an example of constant current control of the detection high voltage has been described, but the detection high voltage may be controlled at a constant voltage. That is, in a state where a predetermined voltage set in advance is applied to the detection roller 56b, the amount of change in the current value when the sheet S passes through the detection nip is used as the detection current, and the charged charge amount and the charge removal voltage of the sheet S may be obtained based on the detection current. In this case, a table or the like representing the relationship between the detection current and the charged charge amount or the charge removal voltage of the sheet S (corresponding to FIGS. 6(a) and 6(b)) is obtained through preliminary consideration and stored in the ROM 220.

[0098] Also, the relationship between the detection voltage detected using the detection roller 56b and the charged charge amount or the charge removal voltage of the sheet S may vary depending on the material (type) and thickness (basis weight) of the sheet S. Therefore, the calculation method of the charged charge amount and the charge removal voltage based on the detection voltage may be changed according to at least one of the material and thickness of the sheet S. Thereby, the charged charge amount and the charge removal voltage can be obtained with higher accuracy. Specifically, a conversion table of the charged charge amount according to the material and thickness of the sheet S (paper type table and paper thickness table in FIG. 4) may be stored in the ROM 220, and the CPU 201 may refer to the conversion table based on the information of the sheet S included in the job information. Instead of the conversion table, parameters (coefficients of calculation formulas) enabling conversion of the charged charge amount according to the material and thickness of the sheet S may be prepared. Also, a table (charged charge conversion table, charge removal voltage conversion table) representing the relationship between the detection voltage and the charged charge amount and the charge removal voltage may be prepared for each type and thickness of the sheet S.

[0099] Also, instead of the detection roller 56b, other contact members that come into contact with the sheet S may be used to obtain the charged charge amount and the charge removal voltage. The contact member does not necessarily have to be a dedicated member for obtaining the charged charge amount and the charge removal voltage. For example, an arbitrary conveyance roller downstream of the secondary transfer portion T2 may be used instead of the detection roller 56b. Also, not limited to the conveyance roller, for example, a guide member or a brush member that comes into contact with the sheet S may be used instead of the detection roller 56b.

[0100] However, if there are other members (especially grounded members) that come into contact with the sheet S between the contact member used in place of the detection roller 56b and the static elimination roller 51b, the amount of charged electricity of the sheet S may change. For this reason, as in this embodiment, it is preferable that no other rollers for conveying the sheet S are arranged between the detection roller pair 56 (first roller pair) and the static elimination roller pair 51 (second roller pair). Further, for example, when using a conveyance roller inside the image forming apparatus 100 in place of the detection roller 56b, it is preferable to use the most downstream conveyance roller in the sheet conveyance direction (the discharge roller that discharges the sheet S from the image forming apparatus 100).

[0101] <<Example 2>> In Example 1, a configuration for obtaining the amount of charged electricity and the static elimination voltage of the sheet S using the detection roller 56b provided separately from the static elimination roller 51b was described. In Example 2, a configuration for obtaining the amount of charged electricity and the static elimination voltage of the sheet S using the static elimination roller 51b will be described. Hereinafter, elements denoted by the same reference numerals as those in Example 1 have basically the same configuration and operation as those described in Example 1 unless otherwise specified, and differences from Example 1 will be mainly described.

[0102] FIG. 7 is a schematic diagram of the static elimination device 300 in Example 2. The static elimination device 300 includes a static elimination roller pair 51 as a contact type static eliminator and an ionizer unit 52 as a non-contact type static eliminator. The configurations of the static elimination roller pair 51 and the ionizer unit 52 may be the same as those in Example 1.

[0103] In this embodiment, it is possible to execute a mode (adjustment mode) for detecting the amount of charged electricity using the static elimination roller 51b and setting the static elimination voltage. In other words, the control circuit 200 can execute a normal mode (first mode) for eliminating static electricity from the sheet S (the sheet S that becomes the product) as part of an image forming job by the image forming system 400, and an adjustment mode (second mode) for performing adjustments such as the static elimination voltage. The adjustment mode is a mode for determining the value of the voltage (static elimination voltage) applied by the first high voltage power supply 55 to the static elimination roller 51b in the normal mode (first mode) based on the detection result of the voltage detection circuit 55V (detection means) when the sheet passes through the static elimination roller 51b (static elimination member).

[0104] The adjustment mode is executed when the value of the static elimination voltage to be applied to the static elimination roller 51b for eliminating static electricity from the sheet S used in the image forming job is unknown. The adjustment mode is automatically executed, for example, when an image forming job is input, before forming an image on the sheet S that becomes the product. Alternatively, the adjustment mode may be executed as an operation independent of the image forming job based on an operation of the user operation unit 102 by the user.

[0105] Hereinafter, the voltage applied from the first high voltage power supply 55 to the static elimination roller 51b in the adjustment mode is referred to as "detection high voltage" to distinguish it from the static elimination voltage applied from the first high voltage power supply 55 to the static elimination roller 51b in the normal mode.

[0106] A block diagram of the control circuit 200 according to this embodiment is shown in FIG. 8. In this embodiment, the first high voltage power supply 55 can perform output control by constant voltage control in the range of 0 kV to -6 kV and constant current control in the range of 0 μA to -100 μA. Further, the first high voltage power supply 55 is provided with a voltage detection circuit 54V capable of detecting the voltage value applied from the first high voltage power supply 55 to the static elimination roller 51b, and a current detection circuit 55A capable of detecting the current flowing through the static elimination roller 51b due to the voltage application from the first high voltage power supply 55.

[0107] The charge-removing roller 51b is an example of a contact member that contacts the sheet S downstream of the transfer unit (secondary transfer unit T2) in the sheet conveyance direction. That is, the contact member in this embodiment is the charge-removing member itself. The voltage detection circuit 55V and the current detection circuit 55A are examples of detection means for detecting the voltage applied to the contact member or the current flowing through the contact member. As will be described below, in this embodiment, control mainly using the voltage detection result by the voltage detection circuit 55V is performed.

[0108] (Control Flow) The procedure of the control performed by the control circuit 200 will be described with reference to the flowchart of FIG. 9. Hereinafter, unless otherwise specified, the execution subject of each step of this flow is the CPU 201.

[0109] In this embodiment, by operating the user operation unit 102, the user can instruct the control circuit 200 to execute the adjustment mode as an operation independent of the image forming job. When an execution instruction for an image forming job or an adjustment mode is input to the image forming system 400, the processing of this flow is started. First, the CPU 201 acquires job information set via the user operation unit 102 (S10). The job information includes information indicating whether the current job is an image forming job or an adjustment mode.

[0110] If the current job is an image forming job (S11N), the CPU 201 operates the charge-removing device 300 in the normal mode (S12). That is, the CPU 201 applies a charge-removing voltage from the first high-voltage power supply 55 to the charge-removing roller 51b in order to remove the charge of the sheet formed with an image by the image forming apparatus 100 with the charge-removing nip. The value of the charge-removing voltage is, for example, the value recorded in the RAM 210 in the adjustment mode performed previously. When the adjustment mode has not been executed or when an operation to reset the value recorded in the RAM 210 has been performed, the value of the charge-removing voltage uses the value stored in advance in the table in the ROM 220. The operation to reset the value recorded in the RAM 210 is, for example, turning off the power of the charge-removing device 300.

[0111] When the current job is in the adjustment mode (S11Y), the CPU 201 causes the image forming apparatus 100 to form an image (test image) on the sheet S in the same process as the normal image forming operation. On the other hand, the CPU 201 causes the detection high voltage to be applied from the first high voltage power supply 55 to the charge removal roller 51b during the period when the first sheet S in the image forming job passes through the detection nip and the periods before and after that (S13). In this embodiment, for example, the detection high voltage is applied by constant current control with a preset current value in the range of -10 to -30 μA. Then, the fluctuation of the voltage value when the sheet S passes through the charge removal nip during the period when the detection high voltage is applied is measured (S14).

[0112] The amount of fluctuation of the voltage value when the sheet S passes through the charge removal nip is defined as the "detection voltage". That is, the detection voltage is obtained by subtracting the detection value of the voltage detection circuit 55V when the sheet S has not passed through the charge removal nip from the detection value of the voltage detection circuit 55V when the sheet S passes through the charge removal nip when a voltage is applied to the charge removal roller 51b by constant current control.

[0113] The CPU 201 records the detection voltage obtained in S14 in the RAM 210 as the detection result. Then, the CPU 201 calculates the value of the charged charge amount and the charge removal voltage of the sheet S based on the detection voltage obtained in S14, the charged charge conversion table and the charge removal voltage conversion table (Fig. 8) stored in the ROM 220 (S15, S16).

[0114] The value of the charge removal voltage obtained in S16 is recorded in the RAM 210 as the adjusted charge removal voltage value. When an image forming job is input after the execution of the adjustment mode and the charge removal device 300 operates in the normal mode, the charge removal voltage is applied from the first high voltage power supply 55 to the charge removal roller 51b using the adjusted charge removal voltage value recorded in the RAM 210 (S12).

[0115] In this way, the voltage detection circuit 55V as the detection means detects the voltage applied to the charge removal roller 51b (charge removal member). The control circuit 200 (control means) determines the value of the charge removal voltage in the normal mode (first mode) based on the amount of change in the voltage detected by the voltage detection circuit 55V when the sheet passes through the charge removal roller 51b while a voltage is applied to the charge removal roller 51b in the adjustment mode (second mode). Thereby, according to the amount of charged charge of the sheet S, the charge removal voltage is automatically set to a value suitable for removing the charge of the sheet S.

[0116] The reason why the amount of charged charge of the sheet S can be obtained based on the amount of change in the voltage value (detected voltage) when the sheet S passes through the charge removal nip is the same as in the first embodiment. That is, when the sheet S is charged, since the sheet S itself functions as a capacitor, the relationship between the applied voltage of the charge removal roller 51b and the current flowing through the charge removal roller 51b when the sheet S passes through the charge removal nip changes according to the amount of charged charge of the sheet S. Therefore, the applied voltage required to flow a current through the charge removal roller 51b at a predetermined current value when the sheet S passes through the charge removal nip changes according to the amount of charged charge of the sheet S.

[0117] The relationship between the detected voltage, the amount of charged charge, and the value of the charge removal voltage (corresponding to FIGS. 6(a) and 6(b)) is obtained through preliminary study and stored in the ROM 220 in the form of a table or the like. In S15 and S16 of the above-described flow (FIG. 9), the CPU 201 can obtain the amount of charged charge and the value of the charge removal voltage by referring to the charged charge conversion table and the charge removal voltage conversion table using the detected voltage acquired in S14.

[0118] Also in this embodiment, the detection high voltage applied to the charge removal roller 51b to obtain the amount of charged charge and the charge removal voltage of the sheet S in the adjustment mode is subject to different voltage control from the charge removal voltage applied to the charge removal roller 51b to remove the charge of the sheet S in the normal mode. Here, "the voltage control is different" between the detection high voltage and the charge removal voltage means that at least one of the voltage control method (constant current control or constant voltage control, etc.) and the presence or absence of change in the voltage value according to the amount of charged charge of the sheet S is different.

[0119] In this embodiment, the static elimination voltage in the normal mode is under constant voltage control, while the detection high voltage in the adjustment mode is under constant current control. In other words, the voltage applied by the voltage application means to the static elimination member in the first mode is under constant voltage control, and the voltage applied by the voltage application means to the static elimination member in the second mode is under constant current control.

[0120] Also, the static elimination voltage in the normal mode is changed based on the detection voltage in the adjustment mode, while the detection voltage in the adjustment mode is preset regardless of the situation. In other words, the value of the voltage applied by the voltage application means to the static elimination member in the first mode is changed based on the detection result of the detection means in the second mode. Also, the value of the voltage applied by the voltage application means to the static elimination member in the second mode is preset regardless of the detection result of the detection means.

[0121] The advantages of the different voltage controls for the detection high voltage and the static elimination voltage are the same as those in Embodiment 1. That is, by controlling the static elimination voltage under constant voltage, there is an advantage that it is easy to stably perform static elimination of the sheet S without the need to vary the output value according to the width of the sheet S. Also, by fixing the detection high voltage to a predetermined value, it is possible to more easily conduct prior considerations such as a charged charge conversion table. Also, by controlling the detection high voltage under constant current, it becomes less susceptible to the influence of changes in the resistance value of the static elimination roller 51b due to aging deterioration. Also, by controlling the detection high voltage under constant current, it is possible to make it less likely to cause inconveniences (such as a decrease in the S / N ratio or excessive current flowing) that may occur when the detection high voltage is set to the same value as the static elimination voltage.

[0122] <Summary of this embodiment> As described above, in this embodiment, using the static elimination roller 51b itself, based on the detection voltage when a voltage is applied to the static elimination roller 51b by a voltage control different from the static elimination voltage, the value of the static elimination voltage applied to the static elimination roller 51b is determined. Thereby, the value of the static elimination voltage can be automatically determined according to the charged charge amount of the sheet S, and the work load of the user can be reduced compared to a configuration that requires the user to adjust the static elimination voltage.

[0123] Further, in this embodiment, the charging amount and the charge removal voltage of the sheet S are obtained by using the charge removal roller 51b itself. Therefore, compared with the first embodiment, it is less affected by the attenuation of the charging amount between the detection nip and the charge removal nip, and the charging amount and the charge removal voltage of the sheet S can be obtained more appropriately.

[0124] Further, in this embodiment, the charging amount and the charge removal voltage of the sheet S are obtained by using the charge removal roller 51b that contacts the sheet S. Therefore, similar to the first embodiment, the inconvenience in the case of using a non-contact type surface potential sensor can be avoided.

[0125] As described above, according to this embodiment, it is possible to provide a charge removal device capable of more stably performing control according to the charging amount of the sheet, and an image forming system including the same.

[0126] Further, in this embodiment, it is not necessary to additionally arrange a surface potential sensor for detecting the charging amount, and the cost and the arrangement space associated with the addition of the surface potential sensor can be saved. Furthermore, in this embodiment, the detection roller pair 56 can be omitted compared with the first embodiment. That is, since it is not necessary to arrange a dedicated member for detecting the charging amount, the cost and the arrangement space can be further saved.

[0127] <<Embodiment 3>> In the first and second embodiments, the configuration in which the control circuit 200 obtains the charging amount of the sheet S and automatically determines the value of the charge removal voltage has been described. In the third embodiment, a configuration in which the result of obtaining the charging amount of the sheet S is presented to the user and the adjustment of the charge removal voltage is entrusted to the user will be described. Hereinafter, elements denoted by the same reference numerals as those in the first and second embodiments have basically the same configuration and operation as those described in the first and second embodiments unless otherwise specified, and differences from the first and second embodiments will be mainly described.

[0128] <Charge removal voltage adjustment switch> The static eliminator 300 of this embodiment includes a static elimination operation unit 54 that enables an operation for changing the operating conditions of the static eliminator 300. An enlarged view of the static elimination operation unit 54 is shown in FIG. 10. The static elimination operation unit 54 is an example of an input means (setting means) that enables a user to input (set) the value of the voltage applied by the high-voltage power supply 55 (voltage application means) to the static elimination roller 51b (static elimination member).

[0129] The static elimination operation unit 54 includes a changeover switch 54a and a voltage adjustment switch 54b. By operating the changeover switch 54a, the user can switch between the output (ON) and output stop (OFF) of the static elimination voltage by the first high-voltage power supply 55 (FIG. 2) that applies the static elimination voltage to the static elimination roller 51b. The voltage adjustment switch 54b enables the user to adjust the value of the static elimination voltage.

[0130] The value of the static elimination voltage can also be fixed at a preset value according to the category of the sheet S. For example, in the case of a plastic film or synthetic paper, it is known that compared to plain paper, dielectric polarization is stronger in the secondary transfer section, and the charge amount of the sheet S tends to increase. Therefore, when using a plastic film or synthetic paper as the sheet S, it is conceivable to preset the value of the static elimination voltage so that the static elimination voltage is higher (the absolute value is larger) than when using plain paper as the sheet S according to the category of the sheet S. However, even for sheets S of the same category, there are cases where the appropriate value of the static elimination voltage varies due to differences in electrical resistance, thickness, usage environment, etc. caused by differences in specific materials. Therefore, in this embodiment, the configuration is such that the user can adjust the value of the static elimination voltage.

[0131] The voltage adjustment switch 54b of this embodiment includes a display unit that displays the value of the static elimination voltage in two digits, and buttons (+ button and - button) for increasing and decreasing the value of the static elimination voltage. When the + button is pressed, the digit corresponding number increases, and when the - button is pressed, the digit corresponding number decreases.

[0132] The value displayed on the display unit is the absolute value of the static elimination voltage, represented by two digits in units of 0.1 kV. That is, the value obtained by multiplying the value displayed on the display unit of the voltage adjustment switch 54b by -0.1 kV is the set value of the static elimination voltage. For example, when "45" is displayed on the display unit of the voltage adjustment switch 54b, the set value of the static elimination voltage is -4.5 kV. From this state, if the "-" button in the tens place is pressed once and the "+" button in the units place is pressed twice, the display will show "37", and the static elimination voltage value will be set to -3.7 kV.

[0133] In addition, when the display on the voltage adjustment switch 54b is set to "00", the static elimination voltage value is set to 0 V (0.0 kV). In this case, the state of the first high-voltage power supply 55 is the same as when the changeover switch 54a is turned off. This state can also be said to be a state where the first high-voltage power supply 55 applies 0 V to the static elimination roller 51b.

[0134] In addition, the display method and input method of the static elimination voltage value are not limited to the above. Instead of displaying the upper two digits of the static elimination voltage value, the static elimination voltage value itself may be displayed, or a numerical value representing the level of the static elimination voltage in, for example, 10 steps may be displayed. The static elimination voltage value may be displayed, for example, on the user operation unit 102 or on the screen of an external computer communicably connected to the image forming system 400. As an input method for the static elimination voltage value, a numeric keypad for numerical input may be provided on the static elimination operation unit 54, or it may be by touch panel operation of the user operation unit 102, or input may be accepted via an external computer. The user operation unit 102 is another example of an input means (setting means) that enables the user to input (set) the value of the voltage applied by the first high-voltage power supply 55 (voltage application means) to the static elimination roller 51b (static elimination member).

[0135] The configurations of the image forming system 400 and the static eliminator 300 in this embodiment are the same as those in Embodiment 2. That is, in this embodiment, the user can instruct the control circuit 200 to execute the adjustment mode as an operation independent of the image forming job by operating the user operation unit 102. However, after obtaining the charged amount of the sheet S, the value of the static elimination voltage is not automatically determined, but the obtained charged amount of the sheet is displayed on the screen of the user operation unit 102, and the user is requested to input the value of the static elimination voltage.

[0136] (Control Flow) The control procedure performed by the control circuit 200 in this embodiment will be described with reference to the flowchart of FIG. 11. Since the processes from S10 to S15 are the same as those in Embodiment 2, the description thereof will be omitted. When the charged amount of the sheet S is obtained in S15, the CPU 201 causes the charged amount to be displayed on the screen of the user operation unit 102 (S16'), and waits for an input from the user. An example of the screen display in S16 is shown in FIG. 12. On the screen 102a as the display unit of the user operation unit 102, information 102b representing the charged amount of the sheet S and information 102c prompting the input of the value of the static elimination voltage are displayed. The user operates the static elimination operation unit 54 based on the screen display and inputs the value of the static elimination voltage corresponding to the charged amount (S17). The CPU 201 stores the value input from the user in the RAM 210 as the new value of the static elimination voltage (S18), and ends the adjustment mode.

[0137] Note that the screen 102a of the user operation unit 102 is an example of a display means for displaying information to the user. For example, information corresponding to the screen display in FIG. 12 may be displayed on an external computer communicably connected to the control circuit 200. The external computer may be a smartphone or a tablet owned by the user.

[0138] Also, the information displayed on the screen in S16' is not limited to the numerical value of the charged amount of the sheet S itself, and may be other information related to the charged amount of the sheet S. For example, since the charged amount (surface charge density) of the sheet S and the surface potential of the sheet S are proportional, the value displayed on the screen in S16' may be the surface potential of the sheet.

[0139] <Summary of this embodiment> In this embodiment, using the static elimination roller 51b itself, based on the detected voltage when a voltage different from the static elimination voltage is applied to the static elimination roller 51b by voltage control, the charged charge amount of the sheet S is displayed on the display unit of the user operation unit 102. That is, the control circuit 200 (control means) applies a voltage to the static elimination roller 51b (contact member) by voltage control different from the voltage (static elimination voltage) applied to the static elimination roller 51b by the first high-voltage power supply 55 (voltage application means) when the static elimination roller 51b (static elimination member) eliminates static electricity from the sheet. Further, the control circuit 200 causes the screen 102a (display means) to display information 102b regarding the charged charge amount of the sheet based on the detection result of the voltage detection circuit 55V (detection means) when the sheet passes through the static elimination roller 51b (contact member).

[0140] Thereby, in the operation of adjusting the static elimination voltage, the work load of the user can be reduced as compared with the case where the user manually measures the charged charge amount using a surface electrometer. Also, compared with a method of detecting or estimating the surface charge amount of the sheet S based on a non-contact type surface potential sensor or the transfer voltage in the secondary transfer unit, control according to the charged charge amount of the sheet can be performed more stably.

[0141] As described above, according to this embodiment, it is possible to provide a static elimination device capable of more stably performing control according to the charged charge amount of the sheet, and an image forming system including the same.

[0142] <Modification example> In this embodiment, what is detected in the adjustment mode is the charged amount of the sheet S before static elimination by the static elimination roller 51b. However, the charged amount of the sheet S after static elimination by the static elimination roller 51b may be detected. For example, in a configuration where the charged amount of the sheet S is detected using a detection roller 56b different from the static elimination roller 51b as in the first embodiment, the detection roller 56b may be arranged downstream of the static elimination roller 51b. In this case, the information S102b displayed on the screen at S16' is the charged amount of the sheet S after static elimination by the static elimination roller 51b. Also, the processes of S13 to S18 may be automatically repeated (or based on an instruction from the user) until the charged amount of the sheet S after static elimination reaches a sufficiently low value.

[0143] Further, a circulation conveyance path for conveying the sheet S that has passed through the static elimination nip back toward the static elimination nip may be provided in the static elimination device 300. When the sheet S passes through the static elimination nip for the first time, a static elimination voltage is applied to the static elimination roller 51b to perform static elimination of the sheet S. When the sheet S passes through the static elimination nip for the second time, a detection high voltage is applied to the static elimination roller 51b to obtain a detection voltage. Even with this configuration, the information S102b displayed on the screen at S16' is the charged amount of the sheet S after static elimination by the static elimination roller 51b. Also, the processes of S13 to S18 may be automatically repeated (or based on an instruction from the user) until the charged amount of the sheet S after static elimination reaches a sufficiently low value.

[0144] 《Other Embodiments》 In each of the above-described embodiments, the charge eliminator 300 for eliminating the charge of the sheet S has been described. However, the charge eliminator 300 has a function as a charge adjustment device that adjusts the charged state of the sheet S by supplying charge to the sheet S via the charge elimination roller 51b as a charge supply member. The charge adjustment device does not necessarily reduce (eliminate) the amount of charged charge of the sheet S. For example, in a state where the sheets S are stacked after being processed by the charge adjustment device, the charged charge amount of each surface of the sheet S may be adjusted so that the mutually facing surfaces of the overlapping sheets are charged with the same polarity. Specifically, the charge adjustment device applies a voltage so that the electrostatic polarity on the surface of the sheet is reversed every other sheet among a plurality of sheets. In this case, since the mutually facing surfaces of the overlapping sheets are charged with the same polarity, the adhesion between the sheets due to electrostatic force can be reduced. Further, by applying the control described in each embodiment to the control of the voltage applied to the charge elimination roller 51b as a charge supply member, the charged state of the sheet S can be adjusted more appropriately.

[0145] Also, in each of the above-described embodiments, as an example of the contact-type charge elimination member that contacts the sheet S, the charge elimination roller 51b which is a roller member has been described. The contact-type charge elimination member is not limited to this, and for example, a brush member in which conductive fibers or long and narrow conductive sheet pieces contact the sheet S may be used.

[0146] Also, in each of the above-described embodiments, it has been described that the charging of the sheet S mainly occurs in the transfer section in the electrophotographic process. However, it is not limited to this, and in an image forming system other than the electrophotographic method such as an inkjet method, charging of the sheet S may occur due to frictional charging or peeling charging caused by rubbing or peeling with a conveyance guide, a conveyance roller, a conveyance belt, or the like. Therefore, this technology may be applied to an image forming system other than the electrophotographic method.

[0147] (Other Embodiments) The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and causing one or more processors in a computer of the system or apparatus to read and execute the program. It can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

Explanation of Signs

[0148] 51b... charge removal member, contact member (charge removal roller) / 55... voltage application means (first high-voltage power supply) / 55A, 55V, 58A, 58V... detection means (current detection circuit, voltage detection circuit) / 56b... contact member (detection roller) / 200... control means (control circuit)

Claims

1. A static eliminator for eliminating static electricity from a sheet onto which a toner image has been transferred by a transfer unit, comprising: a static elimination member that contacts the sheet and eliminates static electricity from the sheet; voltage application means for applying a voltage to the static elimination member; detection means for detecting a voltage applied to a contact member that contacts the sheet downstream of the transfer unit in the sheet conveyance direction or a current flowing through the contact member; control means for controlling the voltage application means; wherein the control means applies a voltage to the contact member by voltage control different from the voltage applied by the voltage application means to the static elimination member when the static elimination member eliminates static electricity from the sheet, and determines the value of the voltage applied by the voltage application means to the static elimination member when the static elimination member eliminates static electricity from the sheet based on the detection result of the detection means when the sheet passes through the contact member. A static eliminator characterized by the above.

2. The contact member is a member different from the static elimination member. The static eliminator according to claim 1, characterized by the above.

3. The voltage applied to the static elimination member is controlled at a constant voltage. The voltage applied to the contact member is controlled at a constant current. The static eliminator according to claim 2, characterized by the above.

4. The detection means detects the voltage applied to the contact member. The control means determines the value of the voltage applied by the voltage application means to the static elimination member when the static elimination member eliminates static electricity from the sheet based on the amount of change in the voltage detected by the detection means when the sheet passes through the contact member while a voltage is applied to the contact member by constant current control. The static eliminator according to claim 3, characterized by the above.

5. The value of the voltage applied to the static elimination member is changed based on the detection result of the detection means. The value of the voltage applied to the contact member is preset regardless of the detection result of the detection means. The static eliminator according to claim 2, characterized by the above.

6. The contact member is disposed upstream of the static elimination member in the sheet conveyance direction. The control means determines the value of the voltage applied to the static elimination member for eliminating static electricity from the sheet based on the detection result of the detection means when the sheet passes through the contact member. The static eliminator according to claim 2, characterized by the above.

7. The contact member is a roller, and forms a first pair of rollers that sandwich and convey the sheet together with a first opposing roller. The charge removing member is a roller, and forms a second pair of rollers that sandwich and convey the sheet together with a second opposing roller. No other rollers for conveying the sheet are arranged between the first pair of rollers and the second pair of rollers. The charge removing device according to claim 2, characterized in that.

8. The contact member is the charge removing member. The charge removing device according to claim 1, characterized in that.

9. The control means A first mode in which a voltage is applied from the voltage applying means to the charge removing member in order to remove the charge of the sheet from the charge removing member, A voltage is applied from the voltage applying means to the charge removing member by voltage control different from the voltage in the first mode, and based on the detection result of the detection means when the sheet passes through the charge removing member, in the first mode Determining a value of the voltage applied by the voltage applying means to the charge removing member; a second mode; Execute The charge removing device according to claim 8, characterized in that.

10. The voltage applied by the voltage applying means to the charge removing member in the first mode is controlled at a constant voltage. The voltage applied by the voltage applying means to the charge removing member in the second mode is controlled at a constant current. The charge removing device according to claim 9, characterized in that.

11. The detection means detects the voltage applied to the charge removing member. The control means determines the value of the voltage applied by the voltage applying means to the charge removing member in the first mode based on the amount of change in the voltage detected by the detection means when the sheet passes through the charge removing member in the second mode. The charge removing device according to claim 10, characterized in that.

12. The value of the voltage applied by the voltage applying means to the charge removing member in the first mode is changed based on the detection result of the detection means in the second mode. The value of the voltage applied by the voltage applying means to the charge removing member in the second mode is preset regardless of the detection result of the detection means. The charge removing device according to claim 9, characterized in that.

13. The relationship between the value of the voltage applied by the voltage applying means to the charge removing member with respect to the detection result of the detection means is changed according to at least one of the thickness of the sheet and the material of the sheet. The charge removing device according to claim 1, characterized in that.

14. A charge removing device for removing charge from a sheet on which a toner image has been transferred in a transfer section, A charge removing member that contacts the sheet and removes charge from the sheet. voltage application means for applying a voltage to the static eliminator member; detection means for detecting a voltage applied to a contact member that contacts the sheet downstream of the transfer unit in the sheet conveyance direction or a current flowing through the contact member; control means for controlling the voltage application means; display means for displaying information; input means by which a user can input the value of the voltage applied by the voltage application means to the static eliminator member; comprising: the control means applies a voltage to the contact member by voltage control different from the voltage applied by the voltage application means to the static eliminator member when the static eliminator member eliminates static electricity from the sheet, and causes the display means to display information regarding the amount of charged charge of the sheet based on the detection result of the detection means when the sheet passes through the contact member; a static eliminator device characterized by the above.

15. the contact member is a member different from the static eliminator member; the static eliminator device according to claim 14, characterized by the above.

16. the contact member is the static eliminator member; the static eliminator device according to claim 14, characterized by the above.

17. the voltage applied to the static eliminator member to eliminate static electricity from the sheet is controlled at a constant voltage, the voltage applied to the contact member to cause the display means to display the information regarding the amount of charged charge of the sheet is controlled at a constant current; the static eliminator device according to claim 14, characterized by the above.

18. an image forming apparatus that forms an image on a sheet; the static eliminator device according to any one of claims 1 to 17, which eliminates static electricity from the sheet on which an image has been formed by the image forming apparatus; an image forming system characterized by comprising the above.

19. a charge adjustment device that adjusts the charged state of a sheet on which a toner image has been transferred in a transfer unit, a charge supply member that contacts the sheet and supplies charge to the sheet; voltage application means for applying a voltage to the charge supply member; detection means for detecting a voltage applied to a contact member that contacts the sheet downstream of the transfer unit in the sheet conveyance direction or a current flowing through the contact member; control means for controlling the voltage application means; comprising: The control means applies a voltage to the contact member by voltage control different from the voltage applied to the charge supply member by the voltage application means when the charge supply member adjusts the charging state of the sheet, and based on the detection result of the detection means when the sheet passes through the contact member, determines the value of the voltage applied to the charge supply member by the voltage application means when the charge supply member adjusts the charging state of the sheet. A charge adjustment device characterized by the above.

Images