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

Abstract

To detect the amount of electric charges on an electrified sheet or perform control according to the amount of electric charges on the electrified sheet, with a simpler configuration.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 the voltage to be applied to the static eliminating member or a current flowing in the static eliminating member; and control means that controls the voltage application means. The control means detects the amount of electric charges on an electrified sheet on the basis of a result of detection performed by the detection means when the sheet passes through the static eliminating member.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 distribution on 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 non-contact type static eliminator of the corotron method. Patent Document 2 describes a charging device that performs charging (static elimination) of a sheet, having a surface potential sensor that detects the surface potential of the sheet, and adjusting the voltage applied to the charging roll based on the measurement value of 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] In Patent Document 2, the number of parts increases due to the additional arrangement of a surface potential sensor for the purpose of detecting the surface potential of the sheet. Therefore, it has been desired to be able to detect the charged charge amount or surface potential of the sheet, or to perform control according to the charged charge amount or surface potential of the sheet with a simpler configuration.

[0005] Therefore, an object of the present invention is to provide a static eliminator, an image forming system, and a charge adjusting device that can detect the charged charge amount of a sheet or perform control according to the charged charge amount with a simpler configuration.

Means for Solving the Problems

[0006] One aspect of the present invention includes a static elimination member that contacts a sheet and eliminates static electricity from the sheet, a voltage application means that applies a voltage to the static elimination member, a detection means that detects the voltage applied to the static elimination member or the current flowing through the static elimination member, and a control means that controls the voltage application means. The control means detects the amount of charged electricity of the sheet based on the detection result of the detection means when the sheet passes through the static elimination member. The static elimination device is characterized by this.

[0007] Another aspect of the present invention includes a static elimination member that contacts a sheet and eliminates static electricity from the sheet, a voltage application means that applies a voltage to the static elimination member, a detection means that detects the voltage applied to the static elimination member or the current flowing through the static elimination member, and a control means that controls the voltage application means. The control means determines the value of the voltage that the voltage application means applies to the static elimination member in order to eliminate static electricity from the sheet based on the detection result of the detection means when the sheet passes through the static elimination member. The static elimination device is characterized by this.

[0008] Another aspect of the present invention includes a charge supply member that contacts a sheet and supplies charge to the sheet, a voltage application means that applies a voltage to the charge supply member, a detection means that detects the voltage applied to the charge supply member or the current flowing through the charge supply member, and a control means that controls the voltage application means. The control means detects the amount of charged electricity of the sheet based on the detection result of the detection means when the sheet passes through the charge supply member. The charge adjustment device is characterized by this.

Advantages of the Invention

[0009] According to the present invention, it is possible to provide a static elimination device, an image forming system, and a charge adjustment device that can detect the amount of charged electricity of a sheet or perform control according to the amount of charged electricity with a simpler configuration.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments 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 static eliminator 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 of different sizes and materials, such as paper such as plain paper and cardboard, sheet materials with surface treatment such as coated paper, sheet materials with special shapes such as 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 removing device 300 is a device (static eliminator) having a charge removing function for removing (reducing) the charge of the sheet S discharged from the image forming system 400. The charge removing device 300 can also be said to be a charge adjusting device for adjusting the charged state of the sheet S discharged from the image forming system 400. The charge removing device 300 may have functions other than the charge removing function (for example, a decurler function for correcting the curl of the sheet S). Further, although the charge removing device 300 of the present embodiment is arranged as a device independent of the image forming device 100, the charge removing device 300 may be incorporated in the housing of the image forming device 100.

[0014] The image forming system 400 may include optional devices other than the charge removing device 300. Examples of the optional devices are a high-capacity feeder (optional feeder) for supplying the sheet S to the image forming device 100, and a sheet processing device (finisher) for performing processing such as binding processing on the sheet S on which an image is formed by the image forming device 100.

[0015] <Image forming device> The schematic configuration of the image forming device 100 is shown in FIG. 1. The image forming device 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, and 1K is rotationally driven in a predetermined rotational direction A. The process units 11Y, 11M, 11C, and 11K have substantially the same configuration except that the toner as the developer accommodated in the developing devices 4Y, 4M, 4C, and 4K is different.

[0018] The transfer unit 15 includes an intermediate transfer belt 6 as an intermediate transfer member, a secondary transfer roller 9 as transfer means (secondary transfer means), primary transfer rollers 5Y, 5M, 5C, and 5K, a plurality of rollers 20, 21, 22, 23, 24, and 25, and a belt cleaner 12. The intermediate transfer belt 6 is stretched over the plurality of rollers 20, 21, 22, 23, 24, and 25. The primary transfer rollers 5Y, 5M, 5C, and 5K are disposed on the inner surface side of the intermediate transfer belt 6 and at positions corresponding to the photosensitive drums 1Y, 1M, 1C, and 1K, respectively. A primary transfer portion is formed between the primary transfer rollers 5Y, 5M, 5C, and 5K and the corresponding photosensitive drums 1Y, 1M, 1C. 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 rotational direction G. The secondary transfer roller 9 is in contact with the outer surface of the intermediate transfer belt 6 and is disposed 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 supply 10 as voltage application means for forming a bias electric field for transferring the toner image to the secondary transfer portion T2. In this embodiment, the secondary transfer roller 9, which is the outer roller of the secondary transfer portion T2, is electrically connected to the transfer power supply 10, and a predetermined transfer voltage is applied from the transfer power supply 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 supply 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 portion T2, a fixing device 40 for fixing the toner image to the sheet S, and a discharge roller pair 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 separation roller pair 66 that conveys the fed-out sheet S while separating it one by one. The separation roller pair includes a conveyance roller that sends the uppermost sheet S in the sheet feeding direction, and a separation roller that abuts against 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 a 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 separation member for separating the sheet S, and for example, a pad-shaped elastic member (rubber pad) may be used as the separation member.

[0022] The fixing device 40 is a heat fixing device that has a fixing nip and heats the toner image on the sheet S while sandwiching and conveying the sheet S in 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 roller member having rigidity 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 that is a user interface of the image forming system 400. The user operation unit 102 includes a display unit such as a liquid crystal panel that displays information to the user, and an input unit such as a physical button that receives 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 condition of the image forming operation is, 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 the products. 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 an electrostatic latent image 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 toners to the photosensitive drums 1Y, 1M, 1C, and 1K, respectively, and develop the electrostatic latent image into a toner image of each color.

[0026] In addition, in this embodiment, the reversal 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 unit. A transfer voltage having a polarity opposite 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 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 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 speeds 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 onto the toner image transferred at the primary transfer unit on the upstream side, thereby forming a full-color toner image on the intermediate transfer belt 6. The full-color toner image is carried by the intermediate transfer belt 6 and conveyed toward the secondary transfer unit T2.

[0030] In parallel with the creation of the toner image in the image forming unit 101, the feeding unit 64 feeds the sheets S one by one toward the image forming unit 101. The fed sheet S is conveyed to the secondary transfer unit 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 unit T2. Then, in the secondary transfer unit T2, the toner image is transferred (secondary 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 having 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 as transfer rollers can be used. The secondary transfer roller 9 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.

[0032] Further, the opposing roller 21 is a conductive rubber roller having a core metal and an elastic layer of an electron-conductive foamed rubber formed on the outer peripheral side of the core metal. 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, materials known as transfer rollers can be used. The opposing 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 under 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 opposing 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 the toner image is transferred to the sheet S.

[0034] Note that, immediately before the secondary transfer portion T2, a conveyance guide 11 for improving the positional accuracy of the sheet S with respect to the intermediate transfer belt 6 is provided. Further, 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 the fixing process of the toner image by the fixing device 40. The fixing process is a process of heating and pressurizing 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. Further, 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 eliminator 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 eliminator> FIG. 2 is a schematic diagram of the static eliminator 300 in this embodiment. The static eliminator 300 includes a static elimination roller pair 51 as a contact type static eliminator, an ionizer unit 52 as a non-contact type static eliminator, and a high voltage power supply 55.

[0039] The charge-removing roller pair 51 includes a charge-removing opposing roller 51a (second opposing roller) that contacts the first surface Sa of the sheet S, and a charge-removing roller 51b that contacts the second surface Sb of the sheet S opposite to the first surface Sa. The charge-removing roller 51b is a contact-type charge-removing member that contacts the conveyed sheet S and removes charge from the sheet S. The charge-removing opposing roller 51a is abutted against the charge-removing roller 51b, and a charge-removing nip is formed as a nip portion between the charge-removing roller 51b and the charge-removing opposing roller 51a. The charge-removing roller pair 51 removes charge from the sheet S while sandwiching and conveying the sheet S at the charge-removing nip.

[0040] The charge-removing opposing roller 51a is connected to the ground potential GND. The charge-removing opposing roller 51a is electrically connected to, for example, the metal frame of the charge-removing device 300. The charge-removing roller 51b is connected to the high-voltage power supply 55. The high-voltage power supply 55 is a voltage application means that applies a voltage (charge-removing voltage) for removing charge from the sheet S to the charge-removing roller 51b.

[0041] Note that the charge-removing roller 51b may be arranged to contact the first surface Sa of the sheet S, and the charge-removing opposing roller 51a may be arranged to contact the second surface Sb of the sheet S. In that case, the voltage applied to the charge-removing roller 51b has a reverse polarity to the voltage applied to the charge-removing 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 that exhibits ion conductivity is dispersed. As the conductive agent and the foamed rubber material, known materials can be used. As the charge-removing roller 51b, for example, a roller 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 can be preferably used. The charge-removing opposing roller 51a is made of stainless steel (SUS) and uses a roller having 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, a corona discharge is generated from the needle tip, and the air around the needle tip is ionized. Then, the generated ions neutralize the charges on the surface of the sheet S, thereby discharging the sheet S.

[0044] In this embodiment, the ionizer unit 52 is arranged above and below the sheet conveyance path with bar type ionizers IZS40 (manufactured by SMC Corporation) 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 an example of a non-contact type discharger, and other non-contact type dischargers may be used. For example, a corotron type or scorotron type discharger that discharges the sheet by corona discharge from a discharge wire may be used. Further, the non-contact type discharger does not necessarily have to be provided on both sides of the conveyance path. For example, the discharging device 300 may be configured to have only the first ionizer 52a as a non-contact type discharger. Also, when the sheet S can be sufficiently discharged by the discharge roller 51b, the non-contact type discharger may be omitted.

[0046] The sheet S conveyed from the image forming apparatus 100 to the static eliminator 300 first has most of its charges removed (rough removal) at the static elimination nip of the static elimination roller pair 51. Specifically, the static elimination voltage is set to the opposite polarity of 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.

[0047] 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 static elimination voltage of the opposite polarity to the transfer voltage to the static elimination roller 51b, a current flows between the static elimination roller 51b and the static elimination opposing 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 the static elimination voltage to the static elimination roller 51b, a current flows through the sheet S at the static elimination nip, reducing the amount of charged charges on the sheet S, which is the amount of charges carried on the first surface Sa and the second surface Sb of the sheet S.

[0048] The sheet S that has passed through the static elimination roller pair 51 is further static eliminated in the ionizer section 52. Specifically, the ions irradiated from the first ionizer 52a and the second ionizer 52b neutralize the charges remaining on the first surface Sa and the second surface Sb of the sheet S, further reducing the amount of charged charges on the sheet S. The sheet S that has passed through the ionizer section 52 is discharged to the outside of the static eliminator 300.

[0049] <Method for Detecting Charge Amount and Method for Controlling Static Elimination Voltage> In this embodiment, it is possible to execute a detection mode for detecting the amount of charged charges using the static elimination roller 51b. In other words, the control circuit 200 can execute a normal mode (first mode) for static eliminating the sheet S (the sheet S that becomes the product) and a mode (second mode) for detecting the amount of charged charges. The detection mode is a mode for detecting the amount of charged charges on 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 (static elimination member).

[0050] Also, in the detection mode of the present embodiment, the value of the static elimination voltage applied to the static elimination roller 51b to eliminate the charge of the sheet S is determined so as to be a value corresponding to the charged amount of the sheet. In other words, the control circuit 200 can execute a normal mode (first mode) for eliminating the charge of the sheet S (the sheet S that becomes the product) and a mode (second mode, adjustment mode) for automatically determining the value of the static elimination voltage. In the detection mode of the present embodiment, 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), the value of the static elimination voltage applied by the high-voltage power supply 55 (voltage application means) to the static elimination roller 51b in the normal mode is determined.

[0051] Note that the charged amount of the sheet S and the surface potential of the sheet S usually are proportional. Also, the charged amount of the sheet S may be represented by the amount of charge per unit area of the sheet surface (surface charge density). Therefore, the "charged amount" 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.

[0052] The detection mode is automatically executed, for example, when an image formation job is input, before forming an image on the sheet S that becomes the product. Alternatively, the detection mode may be executed based on an operation of the user operation unit 102 by the user as an operation independent of the image formation job.

[0053] Hereinafter, the voltage applied from the high-voltage power supply 55 to the static elimination roller 51b in the detection mode is referred to as "detection high voltage" to distinguish it from the static elimination voltage applied from the high-voltage power supply 55 to the static elimination roller 51b in the normal mode.

[0054] A block diagram of the control circuit 200 according to the present embodiment is shown in FIG. 4. The control circuit 200 is an example of control means for controlling the operation of the static elimination device 300. The control circuit 200 may be mounted inside the static elimination device 300, or a part or all of the functions of the control circuit 200 may be mounted on the image forming apparatus 100.

[0055] 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 discharge eliminating device 300. Further, the control circuit 200 is connected to the user operation unit 102, the discharge eliminating operation unit 54, the high-voltage power supply 55, and the transfer power supply 10. The discharge eliminating operation unit 54 will be described in detail in the second embodiment.

[0056] More specifically, the CPU 201 acquires information such as information related to an image forming job (job information), the value of the current (referred to as the discharge eliminating current) flowing through the discharge eliminating roller 51b when a discharge eliminating voltage is applied, and the value of the transfer voltage output by the transfer power supply 10, and stores the information in the RAM 210. Here, the job information is, for example, 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 discharge eliminating nip (during paper feeding), the value of the discharge eliminating current corresponds to the amount of charge supplied from the discharge eliminating roller 51b to the sheet S per unit time.

[0057] The CPU 201 causes the high-voltage power supply 55 to apply a detection high voltage to the discharge eliminating roller 51b during the period when the detection sheet S passes through the discharge eliminating nip and the periods before and after that. The CPU 201 determines the voltage (discharge eliminating voltage) applied by the high-voltage power supply 55 to the discharge eliminating roller 51b when the discharge eliminating roller 51b discharges the sheet based on the detection result of the current detection circuit 55A or the voltage detection circuit 55V when the detection sheet S passes through the discharge eliminating roller 51b.

[0058] In this embodiment, the high-voltage power supply 55 is capable of 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 high-voltage power supply 55 is provided with a voltage detection circuit 55V capable of detecting the voltage value applied from the high-voltage power supply 55 to the discharge eliminating roller 51b, and a current detection circuit 55A capable of detecting the current flowing through the discharge eliminating roller 51b due to the voltage application from the high-voltage power supply 55.

[0059] The voltage detection circuit 55V and the current detection circuit 55A are examples of detection means for detecting the voltage applied to the charge removal member or the current flowing through the charge removal member. As will be described below, in this embodiment, control mainly using the voltage detection result by the voltage detection circuit 55V is performed.

[0060] (Control Flow) The procedure of the control 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.

[0061] In this embodiment, by operating the user operation unit 102, the user can instruct the control circuit 200 to execute the detection mode as an operation independent of the image forming job. When an instruction to execute an image forming job or a detection 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 a detection mode.

[0062] If the current job is an image forming job (S11N), the CPU 201 operates the charge removal device 300 in the normal mode (S12). That is, the CPU 201 applies a charge removal voltage from the high-voltage power supply 55 to the charge removal roller 51b in order to remove the charge of the sheet formed by the image forming apparatus 100 with the charge removal nip. The value of the charge removal voltage is, for example, the value recorded in the RAM 210 in the previous detection mode. When the detection 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 removal 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 removal device 300.

[0063] When the current job is in the detection 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 a detection high voltage to be applied from the 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 charge removal 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).

[0064] 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 applying a voltage to the charge removal roller 51b by constant current control and subtracting the detected value of the voltage detection circuit 55V when the sheet S is not passing through the charge removal nip from the detected value of the voltage detection circuit 55V when the sheet S passes through the charge removal nip.

[0065] The CPU 201 records the detection voltage obtained in S14 in the RAM 210 as the detection result. Then, based on the detection voltage obtained in S14, the charge amount and the charge removal voltage value of the sheet S are calculated (S15, S16) using the charge conversion table and the charge removal voltage conversion table (Fig. 4) stored in the ROM 220.

[0066] 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 detection mode and the charge removal device 300 operates in the normal mode, the charge removal voltage is applied from the high voltage power supply 55 to the charge removal roller 51b using the adjusted charge removal voltage value recorded in the RAM 210 (S12).

[0067] 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) calculates the charged charge amount of the sheet 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 detection mode (second mode). Thereby, the charge removal device 300 can automatically detect the charged charge amount of the sheet S.

[0068] Further, 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 detection mode (second mode). Thereby, the charge removal voltage is automatically set to a value suitable for removing the charge of the sheet S according to the charged charge amount of the sheet S.

[0069] (Reason for being able to detect the charged charge amount) The reason for being able to obtain the charged charge amount of the sheet S based on the amount of change (detection voltage) in the voltage value of the detection high voltage when the sheet S passes through the charge removal nip will be explained. The sheet S is affected by the electric field in the secondary transfer portion T2. In the secondary transfer portion T2, an electric field is formed such that the potential of the secondary transfer roller 9 with respect to the intermediate transfer belt 6 is 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 portion T2, the sheet S is affected by an electric field where the side of the surface (first surface Sa, image surface) on which the toner image is transferred is negative and the side of its back surface (second surface Sb, non-image surface) is positive.

[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 section 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 the sheet S with a high resistance value are sheets made of synthetic resin such as plastic film and synthetic paper. These sheets are typical examples of sheets that require high-voltage discharge by the discharge device 300. In these sheets, if discharge 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 discharge nip with a voltage applied to the discharge roller 51b is different from the relationship between voltage and current when the uncharged sheet S passes through the discharge nip. That is, the applied voltage required to pass a current through the discharge roller 51b at a specific current value while the sheet S is passing through the discharge 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 charging roller 51b is supplied with a negative charge (a high voltage for detecting negative polarity is applied) while the sheet S is charged such 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 discharged 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 charging roller 51b. That is, if the applied voltage is constant, when the sheet S passes through the discharge nip, the current flowing through the charging roller 51b 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 charging roller 51b at a predetermined current value when the sheet S passes through the discharge nip changes according to the amount of charged charge of the sheet S. When a sheet S in which the first surface Sa is negatively charged and the second surface Sb is positively charged passes through the discharge nip, the applied voltage required to pass a current through the charging roller 51b at a predetermined current value (for example, -20 μA) is lower than the applied voltage required to pass a current through the charging roller 51b at the same current value when a non-charged sheet S passes through the discharge nip. Conversely, when a sheet S in which the first surface Sa is positively charged and the second surface Sb is negatively charged passes through the discharge nip, the applied voltage required to pass a current through the charging roller 51b at a predetermined current value is higher than the applied voltage required to pass a current through the charging roller 51b at the same current value when a non-charged sheet S passes through the discharge nip.

[0076] (Relationship between detection voltage and amount of charged charge) Fig. 6(a) shows the result of a preliminary study on the relationship between the amount of change (detection voltage) in the voltage value of the high voltage for detection when the sheet S passes through the discharge nip and the amount of charged charge of the sheet S. 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 discharge device 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 discharge 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 S14 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 discharge nip. In other words, the control circuit 200 (control means) has a ROM220 (storage unit) that stores information indicating the correspondence between the amount of voltage variation and the charged charge amount of the sheet. Further, the control circuit 200 detects the charged charge amount of the sheet based on the amount of voltage variation detected by the voltage detection circuit 55V (detection means) and the information in the ROM220.

[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 as a function with 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 preliminary study on the relationship between the amount of variation (detected voltage) of the voltage value of the high voltage for detection when the sheet S passes through the discharge 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 in advance 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 discharge 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 charge-removal voltage conversion table representing the correspondence between the detected voltage and the charge-removal voltage shown in FIG. 6(b) is stored in the ROM 220 (FIG. 4) within the control circuit 200. In S14 of the above-described flow (FIG. 5), the CPU 201 can determine the value of the charge-removal voltage by referring to the charge-removal voltage conversion table using the detected voltage obtained when the sheet S passes through the charge-removal nip. In other words, the control circuit 200 (control means) has a ROM 220 (storage unit) that stores information indicating the correspondence between the amount of voltage variation and the value of the voltage to be applied to the charge-removal roller 51b (charge-removal member). Further, the control circuit 200 determines the value of the voltage applied by the high-voltage power supply 55 (voltage application means) to the charge-removal roller 51b in the normal mode based on the amount of voltage variation detected by the voltage detection circuit 55V (detection means) and the information in the ROM 220.

[0081] In this embodiment, information representing the correspondence between the detected voltage and the charge-removal voltage is prepared in the form of a table. However, for example, a method may be used in which the charge-removal voltage is expressed as a function with the detected voltage as a variable, and the coefficients of the function are stored in the ROM 220 as control parameters.

[0082] (Difference between the detection high voltage and the charge-removal voltage) The voltage (detection high voltage) applied to the charge-removal roller 51b to obtain the charge amount and the charge-removal voltage of the sheet S is subject to different voltage controls from the voltage (charge-removal voltage) applied to the charge-removal roller 51b to remove the charge 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 a change in the voltage value according to the detection result of the detection means is different.

[0083] In this embodiment, the charge-removal voltage is controlled by constant voltage control. This is because it is easier to stably remove the charge 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 one hand, the detection high voltage is controlled by constant current control. Also, the detection high voltage is a preset value (a predetermined value stored in ROM220) regardless of the detection result of the voltage detection circuit 55V (detection means), whereas the value of the discharge voltage is changed based on the detection result of the voltage detection circuit 55V.

[0085] The discharge voltage is changed according to the amount of charged charge of the sheet S in order to appropriately discharge the sheet S. On the other hand, for the purpose of evaluating the amount of charged charge of the sheet S, the detection high voltage may be a predetermined value, and rather, it is possible to more easily perform prior consideration such as a charged charge conversion table by fixing the detection high voltage to a predetermined value.

[0086] If the detection high voltage is controlled by constant voltage control, for example, due to a change in the resistance value of the discharge roller 51b, etc., the detection result may change due to factors other than the amount of charged charge. That is, even if the relationship between the detection result (current value or its fluctuation amount) when applying the detection high voltage by constant voltage control and the amount of charged charge or the discharge voltage is obtained by prior consideration, there is a possibility that it will deviate from the result of prior consideration while the discharge device 300 is used for a long period of time.

[0087] Also, when the detection high voltage is controlled by constant voltage at the same voltage value as the discharge voltage, depending on the value of the discharge voltage, there may be a case where the current flowing through the discharge roller 51b becomes almost 0A when the sheet S passes through the discharge nip. In this case, the change in the current value according to the amount of charged charge of the sheet S is hidden by noise (the S / N ratio becomes low), and it may become difficult to appropriately evaluate the amount of charged charge of the sheet S and set the discharge voltage according to the amount of charged charge. Also, when the detection high voltage is controlled by constant voltage at the same voltage value as the discharge voltage, depending on the value of the discharge voltage, there may be a case where the current flowing through the discharge roller 51b becomes extremely large when the sheet S passes through the discharge nip. In this case, it may become difficult to perform appropriate control by exceeding the detectable range of the current detection circuit 55A.

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

[0089] <Image in Detection Mode> The test sheet S used in the detection mode (second mode) may be either a solid white sheet S on which no toner image has been transferred in the image forming apparatus 100 or a sheet S on which a test chart has been transferred in the image forming apparatus 100. The solid white sheet S is a sheet output when the image forming apparatus 100 performs a normal image forming operation based on image data with a printing rate (toner coverage rate) of 0%. The test chart is a preset toner image for testing (test pattern image). The test chart is output when the image forming apparatus 100 performs a normal image forming operation based on the image data for the test chart stored in advance in the ROM 220.

[0090] The advantage of using the solid white sheet S in the detection mode is that the charged charge amount in the state of only the sheet S on which no toner image has been transferred can be detected. Therefore, for example, when an image forming job for printing an image with a low printing rate is executed after the detection mode, the value of the discharging voltage can be made more accurate.

[0091] The advantage of using the sheet S on which the test chart has been transferred in the detection mode is that the charged charge amount of the sheet S in the state where a toner image with a printing rate close to that of an image output under general use conditions has been transferred can be detected. Therefore, for example, when an image forming job for printing a general image (for example, an image mainly composed of text) is executed after the detection mode, the value of the discharging voltage can be made more accurate.

[0092] In the detection mode, regardless of whether solid white or a test chart is used, when the test sheet S passes through the secondary transfer unit T2 in the image forming apparatus 100, a transfer voltage similar to that during normal image formation is applied to the secondary transfer roller 9. That is, in the detection mode (second mode), the control circuit 200 detects the charged amount of the sheet using the sheet that has passed through the transfer unit of the image forming apparatus in a state where the same bias electric field as when transferring the toner image is formed. As a result, it is possible to detect the charged amount of the sheet S charged under the same conditions as during normal image formation in the transfer unit, and the value of the discharge voltage can be made more accurate.

[0093] <Summary of this embodiment> As described above, in this embodiment, the charged amount of the sheet S is detected using the discharge roller 51b itself, which is a contact type discharge member. In other words, the control circuit 200 (control means) detects the charged amount of the sheet based on the detection result of the voltage detection circuit 55V (detection means) when the sheet passes through the discharge roller 51b (discharge member).

[0094] Therefore, compared with the case of using a non-contact type surface potential sensor arranged separately from the discharge member, it is possible to provide a discharge device capable of detecting the charged amount of the sheet with a simpler configuration, and an image forming system including the same.

[0095] In this embodiment, it is not necessary to additionally arrange a surface potential sensor to detect the charged amount, and the cost and arrangement space associated with the addition of the surface potential sensor can be saved.

[0096] In this embodiment, the value of the static elimination voltage is determined based on the detection result of the voltage or current when a detection high voltage is applied, using the static elimination roller 51b itself which is a contact type static elimination member. In other words, 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), the control circuit 200 (control means) determines the value of the voltage (static elimination voltage) applied to the static elimination roller 51b by the high voltage power supply 55 (voltage application means) to eliminate the charge on the sheet.

[0097] Therefore, compared with the case of using a non-contact type surface potential sensor arranged separately from the static elimination member, it is possible to provide a static elimination device capable of determining the value of the static elimination voltage according to the charged charge amount of the sheet with a simpler configuration, and an image forming system including the same.

[0098] Also, in this embodiment, since the value of the static elimination voltage is determined based on the detection result of the voltage detection circuit 55V (detection means), the load of the operation for adjusting the static elimination voltage by the user can be reduced. The operation for adjusting the static elimination voltage by the user is, for example, a series of operations of (1) causing the image forming system 400 to output a test sheet, (2) the user manually measuring the charged charge amount of the discharged test sheet using a surface potentiometer, and (3) operating the user interface of the static elimination device 300 or the image forming system 400 according to the measurement result to increase or decrease the set value of the static elimination voltage, which is repeatedly performed until the charged charge amount of the test sheet becomes sufficiently small.

[0099] <Modification Example> In this embodiment, an example of controlling the detection high voltage with a constant current has been described, but the detection high voltage may be controlled with a constant voltage. That is, with a predetermined voltage preset to the static elimination roller 51b, the amount of change in the current value when the sheet S passes through the static elimination nip is used as the detection current, and the charged charge amount and the static elimination voltage of the sheet S may be obtained based on the detection current. In this case, a table or the like representing the relationship (corresponding to FIGS. 6(a) and 6(b)) between the detection current and the charged charge amount or the static elimination voltage of the sheet S is obtained through prior consideration and stored in the ROM 220.

[0100] In addition, the relationship between the detected voltage detected using the charge removal roller 51b and the charge amount or 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 charge amount and charge removal voltage based on the detected voltage may be changed according to at least one of the material and thickness of the sheet S. Thereby, the charge amount and charge removal voltage can be obtained with higher accuracy. Specifically, a conversion table (paper type table and paper thickness table in FIG. 4) of the charge amount corresponding to the material and thickness of the sheet S 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 charge amount corresponding to the material and thickness of the sheet S may be prepared. Also, a table (charge amount conversion table, charge removal voltage conversion table) representing the relationship between the detected voltage, the charge amount, and the charge removal voltage may be prepared for each type and thickness of the sheet S.

[0101] 《Example 2》 In Example 1, the configuration in which the control circuit 200 automatically determines the value of the charge removal voltage was described. In Example 2, a configuration will be described in which the result of obtaining the charge amount of the sheet S is presented to the user, and the adjustment of the charge removal voltage is entrusted to the user. Hereinafter, elements with the same reference numerals as those in Example 1 have basically the same configuration and operation as those described in Example 12 unless otherwise specified, and the parts different from Example 12 will be mainly described.

[0102] <Charge removal voltage adjustment switch> The charge removal device 300 of this embodiment includes a charge removal operation unit 54 capable of performing an operation for changing the operating conditions of the charge removal device 300. An enlarged view of the charge removal operation unit 54 is shown in FIG. 7. The charge removal operation unit 54 is an example of an input means (setting means) by which a user can input (set) the value of the voltage applied by the high-voltage power supply 55 (voltage application means) to the charge removal roller 51b (charge removal member).

[0103] 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 the output stop (OFF) of the static elimination voltage by the 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.

[0104] The value of the static elimination voltage can also be fixed to 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 with 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 according to the category of the sheet S so that the static elimination voltage is higher (the absolute value is larger) than when using plain paper as the sheet S. However, even for sheets S of the same category, there are cases where the appropriate value of the static elimination voltage fluctuates 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.

[0105] 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 number in the corresponding digit increases, and when the - button is pressed, the number in the corresponding digit decreases.

[0106] The value displayed on the display unit is the absolute value of the static elimination voltage displayed as 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 becomes "37", and the value of the static elimination voltage is set to -3.7 kV.

[0107] Also, when the display is set to "00" by the voltage adjustment switch 54b, the value of the static elimination voltage is set to 0 V (0.0 kV). In this case, the state of the 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 high-voltage power supply 55 applies 0 V to the static elimination roller 51b.

[0108] Also, the display method and input method of the value of the static elimination voltage are not limited to the above. Instead of displaying the upper two digits of the value of the static elimination voltage, the value of the static elimination voltage 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 value of the static elimination voltage 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 value of the static elimination voltage, a numeric keypad for numeric 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) by which a user can 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).

[0109] The configurations of the image forming system 400 and the static elimination device 300 in this embodiment are the same as those in the first embodiment. That is, 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. 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 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.

[0110] (Control Flow) Regarding the control procedure performed by the control circuit 200 of this embodiment, it will be described with reference to the flowchart of FIG. 8. Since the processes up to S10 to S15 are the same as those in the first embodiment, the description thereof will be omitted. When the charged charge amount of the sheet S is obtained in S15, the CPU 201 causes the charged charge 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. 9. On the screen 102a as the display unit of the user operation unit 102, information 102b representing the charged charge amount of the sheet S and information 102c prompting the input of the discharge voltage value are displayed. The user operates the discharge operation unit 54 based on the screen display and inputs a discharge voltage value corresponding to the charged charge amount (S17). The CPU 201 stores the value input from the user in the RAM 210 as a new discharge voltage value (S18) and ends the adjustment mode.

[0111] Incidentally, 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 of FIG. 9 may be displayed on an external computer communicably connected to the control circuit 200. The external computer may be a smartphone or tablet owned by the user.

[0112] Also, the information displayed on the screen in S16' is not limited to the numerical value of the charged charge amount of the sheet S itself, and may be other information related to the charged charge amount of the sheet S. For example, since the charged charge amount (surface charge density) of the sheet S is proportional to the surface potential of the sheet S, the value displayed on the screen in S16' may be the surface potential of the sheet.

[0113] <Summary of this embodiment> As described above, in this embodiment, the charged charge amount of the sheet S is detected using the discharge roller 51b itself, which is a contact-type discharge member. In other words, the control circuit 200 (control means) detects 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 discharge roller 51b (discharge member).

[0114] Therefore, similar to Example 1, when using a non-contact type surface potential sensor arranged separately from the charge removal member, for example, a charge removal device with a simpler configuration capable of detecting the charged charge amount of the sheet, and an image forming system including the same can be provided.

[0115] Further, in this embodiment, the charged charge amount detected using the charge removal roller 51b is displayed on the screen 102a of the user operation unit 102. That is, the charge removal device 300 further includes a screen 102a (display means) for displaying information. The control circuit 200 (control means) causes the screen 102a to display information regarding the charged charge amount of the sheet detected based on the detection result of the voltage detection circuit 55V (detection means) in the detection mode (second mode).

[0116] Thereby, without using a surface potential sensor, the user can be notified of the charged state of the sheet S. Further, since the user can input the value of the charge removal voltage via the charge removal operation unit 54 (input means) based on the screen display, the load of the user's adjustment work can be reduced as compared with the case of manually measuring the charged charge amount using a surface potentiometer.

[0117] <Modification Example> In this embodiment, the charged charge amount of the sheet S before charge removal by the charge removal roller 51b is detected in the adjustment mode, but the charged charge amount of the sheet S after charge removal by the charge removal roller 51b may be detected. For example, the charge removal device 300 may be provided with a circulation conveyance path for conveying the sheet S that has passed through the charge removal nip again toward the charge removal nip. When the sheet S passes through the charge removal nip for the first time, a charge removal voltage is applied to the charge removal roller 51b to perform charge removal of the sheet S. When the sheet S passes through the charge removal nip for the second time, a detection high voltage is applied to the charge removal roller 51b to acquire a detection voltage. In this configuration, the information S102b displayed on the screen at S16' is the charged charge amount of the sheet S after charge removal by the charge removal roller 51b. Further, the processes of S13 to S18 may be automatically (or based on an instruction from the user) repeated until the charged charge amount of the sheet S after charge removal becomes a sufficiently low value.

[0118] "Other Embodiments" In each of the above-described embodiments, the charge removing device 300 for removing charge from the sheet S has been described. However, the charge removing device 300 has a function as a charge adjusting device that adjusts the charged state of the sheet S by supplying charge to the sheet S via the charge removing roller 51b as a charge supply member. The charge adjusting device does not necessarily reduce (discharge) the amount of charged charge on the sheet S. For example, in a state where the sheets S are stacked after being processed by the charge adjusting device, the amount of charged charge on each surface of the sheet S may be adjusted so that the surfaces of the overlapping sheets facing each other are charged with the same polarity. Specifically, the charge adjusting 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 surfaces of the overlapping sheets facing each other are charged with the same polarity, the sticking of the sheets due to electrostatic force can be reduced. Also, by applying the control described in each embodiment to the control of the voltage applied to the charge removing roller 51b as a charge supply member, the charged state of the sheet S can be adjusted more appropriately.

[0119] Also, in each of the above-described embodiments, as an example of the contact-type charge removing member that contacts the sheet S, the charge removing roller 51b which is a roller member has been described. The contact-type charge removing member is not limited to this, and for example, it may be a brush member in which conductive fibers or long and narrow conductive sheet pieces contact the sheet S.

[0120] Also, in each of the above-described embodiments, it has been described that 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 the inkjet method, charging of the sheet S can occur due to triboelectric charging or peeling charging caused by rubbing or peeling with a conveyance guide, conveyance roller, conveyance belt, etc. Therefore, this technology may be applied to an image forming system other than the electrophotographic method.

[0121] In addition, in Examples 1 and 2, as an example of control according to the charged amount of the sheet S, the determination of the value of the static elimination voltage and the screen display of the charged amount were described. Not limited to this, the charged amount of the sheet S detected using the static elimination roller 51b (or an amount correlated with the charged amount of the sheet S such as the detected voltage) may be used for other control. For example, a warning may be displayed to the user when the charged amount of the sheet S exceeds a predetermined threshold value.

[0122] (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.

Description of Reference Numerals

[0123] 51b... Static elimination member (static elimination roller) / 55... Voltage application means (high-voltage power supply) / 55A, 55V... Detection means (current detection circuit, voltage detection circuit) / 200... Control means (control circuit)

Claims

1. A static eliminator member that contacts the sheet and eliminates static electricity from the sheet, voltage application means for applying a voltage to the static eliminator member, detection means for detecting the voltage applied to the static eliminator member or the current flowing through the static eliminator member, control means for controlling the voltage application means, comprising: the control means detects the charged charge amount of the sheet based on the detection result of the detection means when the sheet passes through the static eliminator member, a static eliminator device characterized by this.

2. The control means is capable of executing a first mode in which a voltage is applied from the voltage application means to the static eliminator member to eliminate static electricity from the sheet, and a second mode in which the charged charge amount of the sheet is detected based on the detection result of the detection means, The static eliminator device according to claim 1, characterized by this.

3. The detection means detects the voltage applied to the static eliminator member, the control means detects the charged charge amount of the sheet based on the amount of change in the voltage detected by the detection means when the sheet passes through the static eliminator member in the second mode, The static eliminator device according to claim 2, characterized by this.

4. The control means has a storage unit that stores information indicating the correspondence between the amount of change in voltage and the charged charge amount of the sheet, and detects the charged charge amount of the sheet based on the amount of change in the voltage detected by the detection means and the information in the storage unit, The static eliminator device according to claim 3, characterized by this.

5. further comprising display means for displaying information, in the second mode, the control means causes the display means to display information regarding the charged charge amount of the sheet detected based on the detection result of the detection means, The static eliminator device according to claim 2, characterized by this.

6. further comprising input means by which a user can input the value of the voltage applied by the voltage application means to the static eliminator member, The static eliminator device according to claim 5, characterized by this.

7. in the second mode, the control means detects the charged charge amount of the sheet using a sheet on which no toner image has been transferred in the transfer unit of the image forming apparatus, The static eliminator device according to claim 2, characterized by this.

8. in the second mode, the control means detects the charged charge amount of the sheet using a sheet on which a test toner image has been transferred in the transfer unit of the image forming apparatus, The static eliminator device according to claim 2, characterized by this.

9. In the second mode, the control means detects the charged charge amount of the sheet using the sheet that has passed through the transfer unit in a state where the same bias electric field as when transferring the toner image is formed. The charge eliminating device according to claim 2, characterized in that.

10. The relationship between the charged charge amount of the sheet 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 eliminating device according to claim 1, characterized in that.

11. The charge eliminating member is a roller member. The charge eliminating device further includes an opposing roller that sandwiches and conveys the sheet together with the roller member and is electrically grounded. The charge eliminating device according to claim 1, characterized in that.

12. A charge eliminating member that contacts the sheet and eliminates the charge of the sheet; Voltage applying means for applying a voltage to the charge eliminating member; Detection means for detecting the voltage applied to the charge eliminating member or the current flowing through the charge eliminating member; Control means for controlling the voltage applying means; Comprising Based on the detection result of the detection means when the sheet passes through the charge eliminating member, the control means determines the value of the voltage that the voltage applying means applies to the charge eliminating member to eliminate the charge of the sheet. A charge eliminating device characterized in that.

13. The control means is capable of executing a first mode in which a voltage is applied from the voltage applying means to the charge eliminating member to eliminate the charge of the sheet by the charge eliminating member, and a second mode in which, based on the detection result of the detection means, the value of the voltage that the voltage applying means applies to the charge eliminating member in the first mode is determined. The charge eliminating device according to claim 12, characterized in that.

14. The detection means detects the voltage applied to the charge eliminating member. Based on the amount of change in the voltage detected by the detection means when the sheet passes through the charge eliminating member in the second mode, the control means determines the value of the voltage that the voltage applying means applies to the charge eliminating member in the first mode. The charge eliminating device according to claim 13, characterized in that.

15. The control means has a storage unit that stores information indicating the correspondence relationship between the amount of change in voltage and the value of the voltage to be applied to the charge eliminating member, and based on the amount of change in the voltage detected by the detection means and the information in the storage unit, determines the value of the voltage that the voltage applying means applies to the charge eliminating member in the first mode. The static eliminator device according to claim 14, characterized in that...

16. The static elimination member is a roller member, The static eliminator device further includes a counter roller that sandwiches and conveys a sheet together with the roller member and is electrically grounded. The static eliminator device according to claim 8, characterized in that...

17. An image forming apparatus that forms an image on a sheet, The static eliminator device according to any one of claims 1 to 16, which eliminates static electricity from the sheet on which the image has been formed by the image forming apparatus, An image forming system, characterized by comprising...

18. 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 the voltage applied to the charge supply member or the current flowing through the charge supply member, Control means for controlling the voltage application means, Comprising The control means detects the charged charge amount of the sheet based on the detection result of the detection means when the sheet passes through the charge supply member. A charge adjustment device, characterized in that...

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