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

Abstract

To more appropriately eliminate static electricity on a sheet or adjust an electrification state.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; current detection means that detects a current flowing in the static eliminating member; and control means that, on the basis of a result of detection performed by the current detection means when the sheet passes through the static eliminating member, controls the value of the voltage applied to the static eliminating member by the voltage application means, so that the current flowing in the static eliminating member when the sheet passes through the static eliminating member falls within a predetermined range relative to a target value.SELECTED DRAWING: Figure 6

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 adjuster 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 non-contact type static eliminator of the corotron method.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The above document describes determining the voltage (static elimination bias) applied to the static elimination roll based on the actually measured surface potential of the sheet. However, when the resistance value of the static elimination roll changes due to continuous energization of the static elimination roll or when environmental conditions change, it may be difficult to appropriately perform static elimination or adjustment of the charging state of the sheet.

[0005] Therefore, an object of the present invention is to provide a static eliminator, an image forming system, and a charge adjuster capable of more appropriately performing static elimination or adjustment of the charging state of a sheet.

Means for Solving the Problems

[0006] One aspect of the present invention is a static eliminator device comprising: 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 current detection means that detects a current flowing through the static elimination member; and a control means that controls the value of the voltage applied by the voltage application means to the static elimination member based on the detection result of the current detection means when the sheet passes through the static elimination member, such that the current flowing through the static elimination member when the sheet passes through the static elimination member falls within a predetermined range with respect to a target value.

[0007] Another aspect of the present invention is a charge adjustment device comprising: 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 current detection means that detects a current flowing through the charge supply member; and a control means that controls the value of the voltage applied by the voltage application means to the charge supply member based on the detection result of the current detection means when the sheet passes through the charge supply member, such that the current flowing through the charge supply member when the sheet passes through the charge supply member becomes a value within a predetermined range.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a static eliminator device, an image forming system, and a charge adjustment device capable of more appropriately performing static elimination or adjustment of the charged state of a sheet.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments according to the present disclosure will be described with reference to the drawings.

[0011] 《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 (print product). The sheet S, which is a recording material (recording medium), can use various sheet materials with different sizes and materials, such as paper such as plain paper and thick paper, sheet materials with surface treatment such as coated paper, special-shaped sheet materials 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).

[0012] The static eliminator 300 is a device (static eliminator) that removes (reduces) the charge of the sheet S discharged from the image forming system 400. The static eliminator 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 static eliminator 300 may have functions other than the static elimination function (for example, a decurler function for correcting the curl of the sheet S). In addition, although the static eliminator 300 of the present embodiment is arranged as an apparatus independent of the image forming apparatus 100, the static eliminator 300 may be incorporated in the housing of the image forming apparatus 100.

[0013] The image forming system 400 may include optional devices other than the charge removing device 300. Examples of the optional devices include a high-capacity sheet feeding device (optional feeder) that supplies the sheet S to the image forming apparatus 100, and a sheet processing device (finisher) that performs processing such as binding processing on the sheet S on which an image is formed by the image forming apparatus 100.

[0014] <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 that is an intermediate transfer type electrophotographic mechanism. The image forming unit 101 includes four process units 11Y, 11M, 11C, and 11K each having a photosensitive drum 1Y, 1M, 1C, and 1K, respectively, and a transfer unit 15 having an intermediate transfer belt 6 and a secondary transfer roller 9.

[0015] 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 units 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.

[0016] Each of the photosensitive drums 1Y, 1M, 1C, and 1K is rotationally driven in a predetermined rotation direction A. The process units 11Y, 11M, 11C, and 11K have substantially the same configuration except that the toners as developers accommodated in the developing devices 4Y, 4M, 4C, and 4K are different.

[0017] 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. 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.

[0018] 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 in 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 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.

[0019] 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.

[0020] The feeding unit 64 includes, for example, a pickup roller 65 that feeds out the topmost 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 while separating it one by one. The pair of separation rollers includes a conveyance roller that sends the topmost 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 frictional force to the sheet S at the separation nip to prevent the sheets S other than the topmost 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.

[0021] 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 pressure member that forms the fixing nip together with the heating member, and a heat source that heats the heating member. For the heating member and the pressure 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.

[0022] The image forming apparatus 100 also 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.

[0023] 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 transporting 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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 can preferably be one having 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.

[0028] 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 onto 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.

[0029] 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.

[0030] 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.

[0031] Further, the counter roller 21 is a conductive 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.

[0032] 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 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 has a polarity 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, whereby the toner image is transferred to the sheet S.

[0033] Before reaching 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 collected by the belt cleaner 12 and reused for image formation.

[0034] 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.

[0035] The sheet S that has passed through the fixing device 40 is discharged toward the static eliminator 300 by the discharge roller pair 42.

[0036] 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.

[0037] <Static eliminator> 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 on which an image is formed 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 attractive 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 and an ionizer unit 52 as a non-contact type static eliminator.

[0038] The pair of static elimination rollers 51 includes a static elimination counter roller 51a that contacts the first surface Sa of the sheet S and a static elimination roller 51b that contacts the second surface Sb opposite to the first surface Sa of the sheet S. 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.

[0039] 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 and is electrically grounded. The static elimination roller 51b is connected to a high-voltage power source 55. The high-voltage power source 55 is a voltage application means for applying a voltage (static elimination voltage) for performing static elimination of the sheet S to the static elimination roller 51b.

[0040] 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.

[0041] In this embodiment, the static eliminator 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. The static eliminator roller 51b is preferably 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 static elimination counter roller 51a is made of stainless steel (SUS) and uses a roller with an outer diameter of 20 to 25 mm. Incidentally, as the static eliminator roller 51b, a roller made of a metal such as stainless steel may be used.

[0042] 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 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 eliminating the static electricity of the sheet S.

[0043] 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 that form 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.

[0044] The above-described first ionizer 52a and second ionizer 52b are examples of non-contact static eliminators, and other non-contact static eliminators may also 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 sheet S can be sufficiently static-eliminated by the static elimination roller 51b, the non-contact static eliminator may be omitted.

[0045] The sheet S conveyed from the image forming apparatus 100 to the static elimination device 300 first has most of its charges removed (roughly removed) 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.

[0046] In 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 becomes negatively charged, and the second surface Sb that was in contact with the secondary transfer roller 9 becomes positively charged, so that the sheet S is charged. By applying a static elimination voltage having a polarity opposite to the transfer voltage to the static elimination roller 51b, a current flows between the static elimination roller 51b and the static elimination 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. Thus, by applying a static elimination voltage to the static elimination roller 51b and causing a current to flow through the sheet S at the static elimination nip, 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.

[0047] 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, 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 static elimination device 300.

[0048] Generally, the amount of charged electricity of the sheet S and the surface potential of the sheet S are proportional. Also, the amount of charged electricity of the sheet S may be represented by the amount of charge per unit area of the sheet surface (surface charge density). Therefore, in the following description, the "amount of charged electricity" of the sheet S may be replaced with the surface potential of the sheet S or the surface charge density of the sheet S.

[0049] <Charge removal voltage adjustment switch> The charge removal device 300 includes a charge removal operation unit 54 that enables 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. 4. 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).

[0050] The charge removal 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 charge removal voltage by the high-voltage power supply 55 (FIG. 2) that applies the charge removal voltage to the charge removal roller 51b. The voltage adjustment switch 54b enables the user to adjust the value of the charge removal voltage.

[0051] The value of the charge removal 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 amount of charged electricity 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 charge removal voltage so that the charge removal 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 charge removal 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 value of the charge removal voltage can be adjusted.

[0052] The voltage adjustment switch 54b in this embodiment includes a display unit that displays the value of the discharge voltage in two digits, and buttons (+ button and - button) for increasing and decreasing the value of the discharge voltage. When the + button is pressed, the digit corresponding to it increases, and when the - button is pressed, the digit corresponding to it decreases.

[0053] The value displayed on the display unit is the absolute value of the discharge 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 discharge voltage. For example, when "45" is displayed on the display unit of the voltage adjustment switch 54b, the set value of the discharge 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 discharge voltage is set to -3.7 kV.

[0054] In addition, when the display on the voltage adjustment switch 54b is set to "00", the set value of the discharge voltage is 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 first high-voltage power supply 55 applies 0 V to the discharge roller 51b.

[0055] In addition, the display method and input method of the discharge voltage value are not limited to the above. Instead of displaying the upper two digits of the discharge voltage value, the discharge voltage value itself may be displayed, or a numerical value representing the discharge voltage level in, for example, 10 levels may be displayed. The discharge 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 discharge voltage value, a numeric keypad for numerical input may be provided on the discharge operation unit 54, or it may be a touch panel operation of the user operation unit 102, or input may be received 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 high-voltage power supply 55 (voltage application means) to the discharge roller 51b (discharge member).

[0056] <Correction control of discharge voltage> Incidentally, when a voltage is continuously applied to the charge removing roller 51b, the resistance value of the charge removing roller 51b may change. For example, when a conductive roller containing an ion conductive agent is used as the charge removing roller 51b as in the present embodiment, the distribution of the conductive agent in the roller may be biased by continuous energization, resulting in a change in the resistance value. In this case, if the set value of the charge removing voltage set through the charge removing operation unit 54 is continuously used in the state before the resistance value of the charge removing roller 51b changes, the charge removing roller 51b may not be able to appropriately remove the charge from the sheet S due to the change in the resistance value of the charge removing roller 51b. That is, due to the change in the resistance value of the charge removing roller 51b, the charge supply ability from the charge removing roller 51b to the sheet S is affected, resulting in an excess or deficiency in the amount of charge actually supplied with respect to the amount of charge required for removing the charge from the sheet S.

[0057] Note that although the ion conductive agent is less likely to cause resistance fluctuations compared to the electron conductive agent, as described above, resistance value fluctuations may occur due to continuous energization. Also, although the change in the resistance value in the case where the charge removing roller 51b is a conductive roller containing an ion conductive agent has been described here, the resistance value of the charge removing roller 51b (charge removing member) may also change for other reasons. For example, the resistance value of the charge removing roller 51b may change due to the adhesion of dirt such as paper dust (paper fibers and fillers) and toner generated from the sheet S to the surface of the charge removing roller 51b.

[0058] Therefore, in the present embodiment, feedback control is performed to automatically correct the charge removing voltage based on the detection result of the charge removing current during paper feeding.

[0059] A block diagram of the control circuit 200 related to the control of the charge removing voltage is shown in FIG. 5. The control circuit 200 is an example of control means for controlling the operation of the charge removing device 300. The control circuit 200 may be mounted inside the main body of the charge removing device 300, or part or all of the functions of the control circuit 200 may be mounted on the image forming apparatus 100.

[0060] As shown in FIG. 5, 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 a user operation unit 102, a discharge eliminating operation unit 54, a high-voltage power supply 55, and a transfer power supply 10. Inside the high-voltage power supply 55, a current detection circuit 55a for detecting the current supplied from the high-voltage power supply 55 to the discharge eliminating roller 51b is provided. The current detection circuit 55a functions as current detection means for detecting the current flowing through the discharge eliminating roller 51b (discharge eliminating member).

[0061] The CPU 201 acquires information such as information related to an image forming job (job information), a set value of the discharge eliminating voltage, a value of the current flowing through the discharge eliminating roller 51b (referred to as the discharge eliminating current) when the discharge eliminating voltage is applied, and a value of the transfer voltage output by the transfer power supply 10, and stores them 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 attribute information of the sheet S used in the current image forming job. The set value of the discharge eliminating voltage is a value set by the user by operating the discharge eliminating operation unit 54. The value of the discharge eliminating current is a value detected by the current detection circuit 55a. 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. The CPU 201 calculates the corrected discharge eliminating voltage based on these pieces of information stored in the RAM 210 and the control conditions described later stored in the ROM 220, and performs feedback control for controlling the output of the high-voltage power supply 55 based on the corrected discharge eliminating voltage.

[0062] The control circuit 200 is also connected to an environment sensor 13 for detecting the environmental conditions of the installation environment (the surrounding space where the device is installed) of the static elimination device 300 (image forming system 400). The control using the environment sensor 13 will be described in the second embodiment. Further, the ROM 220 stores control parameters and various tables used for controlling the static elimination voltage.

[0063] The procedure for controlling the static elimination voltage performed by the control circuit 200 will be described with reference to the flowchart of FIG. 6. Hereinafter, unless otherwise specified, the execution subject of each step of this flow is the CPU 201.

[0064] 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 acquires a set value of the static elimination voltage from the static elimination operation unit 54 in preparation for the static elimination process in the static elimination device 300 (S1). The CPU 201 determines the acquired set value of the static elimination voltage as the value of the static elimination voltage output by the high-voltage power supply 55 immediately after the start of the image forming job (initial static elimination voltage) (S2).

[0065] Hereinafter, the current value detected by the current detection circuit 55a from when the leading edge of the sheet S enters the charge removal nip in the sheet conveyance direction Cv until the trailing edge of the sheet S passes through the charge removal nip is referred to as the charge removal current during paper passage for the sheet S. For the first several sheets S in an image forming job, it is considered that by applying an initial charge removal voltage (a predetermined voltage value) to the charge removal roller 51b, the charge removal current during paper passage becomes a value capable of appropriately removing the charge from the sheet S. However, for example, during the execution of an image forming job that outputs a very large number of sheets S, due to the reasons described above, the resistance value of the charge removal roller 51b may vary, and there is a possibility that the sheet S cannot be appropriately charge-removed. In this embodiment, although charge removal is also performed by the ionizer unit 52 disposed downstream of the charge removal roller 51b, the amount of charged charge that the ionizer unit 52 can remove is less than that of the charge removal roller 51b. Therefore, when the charge removal roller 51b cannot appropriately remove the charge from the sheet S, there is a possibility that the sheet S is not appropriately charge-removed before being discharged from the charge removal device 300.

[0066] Therefore, in this embodiment, control is performed to store the measured value of the charge removal current for the first predetermined number N of sheets S in an image forming job as the initial charge removal current, and correct the value of the subsequent charge removal voltage based on the initial charge removal current.

[0067] The number of sheets S (predetermined number N) for measuring the initial charge removal current is preferably two or more in order to reduce the influence of variations for each sheet S. In this embodiment, the predetermined number N is set to 3, but it may be set to other values.

[0068] The CPU 201 counts the number of the current sheet S conveyed to the static eliminator 300, starting from the first sheet S conveyed to the static eliminator 300 at the start of the image forming job, and acquires the static elimination current during sheet passage for each sheet S (S3). Then, when the current sheet S corresponds to a predetermined number of sheets from the start of the job (S4Y), an initial static elimination current I0 is calculated based on the values of the static elimination currents of the sheets S from the first sheet to the predetermined number of sheets (S5). In this embodiment, the average value of the values of the static elimination currents of the sheets S from the first sheet to the predetermined number of sheets is set as the initial static elimination current I0.

[0069] The initial static elimination current I0 is the target value (target current value) of the static elimination current (controlled variable, control amount) during the execution of the image forming job. In other words, in this embodiment, the target value of the static elimination current is determined based on the detection result of the current detection circuit 55a (current detection means) when the sheet S passes through the static elimination roller 51b while the high-voltage power supply 55 (voltage application means) applies a voltage to the static elimination roller 51b (static elimination member) at a predetermined voltage value after the start of the job.

[0070] Subsequently, following the calculation of the initial static elimination current I0, the CPU 20 calculates a threshold Ith for determining whether to correct the static elimination voltage (S6). The threshold Ith is a quantity (unit: μA) that determines by how much the static elimination current during sheet passage deviates from the initial static elimination current I0 before the static elimination voltage correction is performed.

[0071] In this embodiment, the value of the threshold Ith is determined by the following method. Let the set value of the static elimination voltage set via the static elimination operation unit 54 be V0 (kV). Let the initial static elimination current be I0. Let the fluctuation range of the static elimination voltage when the numerical value of the units place is changed by 1 using the voltage adjustment switch 54b be ΔV (kV). In this case, the threshold Ith is calculated by the following formula. Ith = | I0 / V0 ×ΔV |

[0072] In other words, the threshold Ith in this embodiment is defined as the absolute value of the value obtained by dividing the initial discharging current I0 by the set value V0 of the discharging voltage and then multiplying the result by the variation width ΔV of the discharging voltage corresponding to the minimum adjustment unit of the voltage adjustment switch 54b. For example, when the initial discharging current I0 is -40 μA, the set value V0 of the initial voltage is -4.0 kV, and the variation width ΔV of the discharging voltage is -0.1 kV, the threshold Ith is 1.0 μA.

[0073] When the current sheet S is a sheet after a predetermined number of sheets from the start of the job, the CPU 201 acquires the discharging current I during the passage of the current sheet S (S7). Then, the CPU 201 compares the absolute value of the difference between the discharging current I during the passage of the sheet and the initial discharging current I0 with the above-described threshold Ith (S8). When the absolute value of the difference between I and I0 is greater than the threshold Ith (S8Y), the CPU 201 determines that it is necessary to correct the value of the discharging voltage, and corrects the value of the discharging voltage so that the discharging current approaches the target value (I0) (S9). When the absolute value of the difference between I and I0 is equal to or less than the threshold Ith (S8N), the CPU 201 determines that it is not necessary to correct the value of the discharging voltage, and maintains the value of the discharging voltage.

[0074] For example, consider a case where the initial discharging current I0 is -40 μA, the set value V0 of the initial voltage is -4.0 kV, the variation width ΔV of the discharging voltage is -0.1 kV, and the threshold Ith is 1.0 μA. In this case, when the discharging current I during the passage of the current sheet S is a value less than -41 μA or greater than -39 μA, the correction of the discharging voltage (S9) is performed. Suppose that the discharging current I is -42 μA at the fourth sheet S. Since the absolute value of the difference from the initial discharging current I0 is 2 (μA), which is greater than the threshold Ith, the discharging voltage is corrected so that the absolute value of the discharging current I becomes smaller. The correction width of the discharging voltage is, for example, the variation width ΔV of the discharging voltage corresponding to the minimum adjustment unit of the voltage adjustment switch 54b. That is, the value of the discharging voltage applied by the high-voltage power supply 55 to the discharging roller 51b is corrected from the set value V0 of the initial voltage, which is -4.0 kV, to -3.9 kV, which is 0.1 kV lower.

[0075] Further, in this embodiment, the correction width of the charge-removing voltage is set to a fixed value (0.1 kV) regardless of the magnitude of the absolute value of the difference between the detected charge-removing current I and the initial charge-removing current I0. However, the correction width may be changed according to the absolute value of the difference between I and I0.

[0076] Thereafter, the CPU 201 determines whether the current sheet S is the last sheet in the image forming job. If it is not the last sheet (S10N), the process returns to S7 and the same process is repeated for the subsequent sheet S. If the current sheet S is the last sheet (S10Y), the CPU 201 ends the process of this flow.

[0077] (Examples of transitions of charge-removing voltage and charge-removing current) An example of the transitions of the charge-removing voltage and the charge-removing current when the above control is performed is shown in FIG. 7. For several sheets S immediately after the start of the image forming job, the initial charge-removing voltage is applied at the set value V0 of the charge-removing voltage, and the charge-removing current during paper feeding is the initial charge-removing current I0. However, as time passes, the value of the charge-removing current deviates from the initial charge-removing current I0.

[0078] In the example of FIG. 7, for the m-th sheet S from the start of the job, the absolute value of the charge-removing current I_m during paper feeding becomes larger than the absolute value of the initial charge-removing current I0, and the difference becomes larger than the threshold Ith. In this case, after the m-th sheet S passes through the charge-removing nip and before the (m + 1)-th sheet S enters the charge-removing nip, the correction of the charge-removing voltage (S9 in FIG. 6) is performed. The charge-removing voltage is corrected to a voltage value lower than the initial charge-removing voltage (V0) so that the charge-removing current approaches the initial charge-removing current I0, that is, so that the absolute value of the charge-removing current becomes smaller in this case. As a result, the charge-removing current I_m+1 of the (m + 1)-th sheet S becomes a value close to the initial charge-removing current I0.

[0079] (Modification example of method for determining target value of charge-removing current) In this embodiment, as described above, assuming that the static elimination voltage adjustment operation is completed before the start of the image forming job, the initial static elimination current I0, which is the static elimination current immediately after the start of the image forming job, is used as the target value of the static elimination current when controlling the static elimination voltage. However, the target value of the static elimination current when controlling the static elimination voltage may be determined by other methods.

[0080] For example, when the static elimination voltage adjustment operation is performed separately from the image forming job, as a part of the process executed by the control circuit 200 of the static eliminator 300 in the adjustment operation, a process of writing the target value of the static elimination current into the RAM 210 may be performed.

[0081] Specifically, when the user determines that the charged amount of the sheet S is sufficiently small and instructs the apparatus to complete the static elimination voltage adjustment operation, the CPU 201 writes the value of the static elimination current during the previous sheet feeding as the target value of the static elimination current into the RAM 210. Then, when the image forming job is input, the CPU 201 corrects the static elimination voltage from the first sheet S in the image forming job using the target value of the static elimination current read from the RAM 210. That is, in the flow of FIG. 6, the target value of the static elimination current read from the RAM 210 may be used instead of I0 in S8. In this case, the target value of the static elimination current will be set in advance before the first sheet in the image forming job reaches the static elimination roller 51b (static elimination member). Incidentally, when the absolute value of the difference between the static elimination current during the sheet feeding of the first sheet S in the image forming job and the target value of the static elimination current is greater than the threshold Ith, the static elimination voltage is corrected before the second sheet S enters the static elimination nip.

[0082] (Advantages of performing control based on the static elimination current during sheet feeding) In both this embodiment and the above-described modified examples, the charge-removal voltage is corrected based on a comparison between the detection result of the charge-removal current during paper passage and the target value of the charge-removal current during paper passage. This is because by using the charge-removal current during paper passage, the current value for appropriately removing the charged sheet S can be uniquely determined. Thereby, even if the resistance value of the charge-removal roller 51b fluctuates, the charge-removal voltage can be corrected according to the resistance value of the charge-removal roller 51b so that the magnitude of the charge-removal current is maintained within an appropriate range.

[0083] On the other hand, instead of using the charge-removal current during paper passage, it is conceivable to correct the charge-removal voltage based on the relationship between the voltage applied to the charge-removal roller 51b when the sheet S is not passing through the charge-removal nip (when not passing paper) and the current flowing through the charge-removal roller 51b. However, in this method, for example, when using a plastic film or synthetic paper as the sheet S, it may be difficult to appropriately correct the charge-removal voltage.

[0084] The sheet S made of a synthetic resin such as a plastic film or synthetic paper is a typical example of a sheet S that highly requires charge removal by the charge-removal device 300. Since these sheets S have a very high resistance, the amount of charge when the sheet S is charged may become very large. That is, when the sheet S is exposed to the bias electric field in the secondary transfer portion T2, the surfaces of the front and back of the sheet S are charged with opposite polarities to each other due to dielectric polarization. The higher the resistance of the sheet S, the less likely the charged charge amount on the surface of the sheet S is to decay even after passing through the secondary transfer portion T2. The larger the charged charge amount on the surface of the sheet S, the more likely the sheets S are to stick to each other due to the electrostatic adsorption force, and thus the necessity of charge removal becomes higher.

[0085] Here, the amount of charge held by the sheet S immediately before entering the charge-removing nip affects the magnitude of the charge-removing current during paper passage. This is because when the sheet S is held between the charge-removing roller pair 51, the charge held by the sheet S functions as an electromotive force that causes a current to flow through a circuit including the charge-removing roller pair 51, the high-voltage power supply 55, and the ground potential GND (Figure 2). For this reason, the magnitude of the charge-removing current during paper passage is not determined solely by the value of the charge-removing voltage or the resistance value of the charge-removing roller 51b, and it is desirable to also consider the amount of charge held by the sheet S itself. That is, since the current value indicated by the current detection circuit 55a when the sheet S has not passed through the charge-removing nip does not reflect the amount of charge held by the sheet S itself, it is difficult to uniquely determine appropriate current conditions for charging the sheet S. The current conditions referred to here are the conditions that the current flowing through the charge-removing roller 51b should satisfy in relation to the voltage applied to the charge-removing roller 51b. Also, if appropriate current conditions are not determined, it is difficult to uniquely determine the value of the charge-removing voltage as a control value for flowing an appropriate current to charge the sheet S.

[0086] The above content will be further explained with reference to FIGS. 8(a) and 8(b). FIGS. 8(a) and 8(b) illustrate the relationship between the amount of charge (charged charge amount) when the synthetic paper is pre-charged and the magnitude of the charge-removing current required to remove the charged charge amount with the charge-removing nip, divided into the cases where the resistance value of the charge-removing roller 51b is large and low. The vertical axis in FIG. 8(a) is the value of the charge-removing current when the sheet S is passing through the charge-removing nip (during paper passage). In contrast, the vertical axis in FIG. 8(b) is the value of the charge-removing current when the sheet S is passing through the charge-removing nip (when not passing paper).

[0087] As shown in FIG. 8(a), it can be seen that the value of the charge-removing current during paper passage that enables appropriate charging of the sheet S is uniquely determined as a value approximately proportional to the charged charge amount regardless of the magnitude of the resistance value of the charge-removing roller 51b. That is, even if the resistance value of the charge-removing roller 51b fluctuates, the sheet S can be appropriately charged by performing control so that the charge-removing current during paper passage becomes an appropriate value.

[0088] On the other hand, as shown in FIG. 8(b), it can be seen that the value of the discharging current during non-sheet passage, which enables appropriate discharging of the sheet S, varies greatly depending on the resistance value of the discharging roller 51b and is not uniquely determined from the amount of charged charge. In other words, even if the discharging voltage is pre-adjusted so as to obtain a voltage value suitable for appropriately discharging the sheet S with a certain amount of charged charge, the value of the discharging current during non-sheet passage depends greatly on the resistance value of the discharging roller 51b rather than the amount of charged charge of the sheet S. If the discharging voltage is corrected based on the discharging current during non-sheet passage during the execution of an image forming job, the discharging current during sheet passage may deviate from a value suitable for discharging the sheet S.

[0089] <Summary of this embodiment> As described above, the control circuit 200 (control means) of this embodiment detects the discharging current during sheet passage, and controls the value of the voltage applied by the high-voltage power supply 55 (voltage applying means) to the discharging roller 51b (discharging member) so that the discharging current during sheet passage falls within a predetermined range with respect to the target value. Here, an example of the "target value" is the initial discharging current I0, and an example of the "predetermined range" is a range in which the absolute value of the difference from the initial discharging current I0 is equal to or less than a threshold Ith (predetermined threshold).

[0090] Thereby, even when the resistance value of the discharging roller 51b changes due to continuous voltage application or the like, the discharging voltage can be controlled so that a discharging current of an appropriate magnitude corresponding to the amount of charged charge of the sheet S flows. For this reason, a state in which the discharging roller 51b can more appropriately discharge the sheet S can be realized.

[0091] That is, according to this embodiment, it is possible to provide a discharging device capable of more appropriately discharging a sheet, and an image forming system including the same.

[0092] If this embodiment is not applied and the initial discharging voltage (V0) is maintained, the value of the discharging current during sheet passage may change during the execution of an image forming job due to a change in the resistance value of the discharging roller 51b. In this case, the discharging roller 51b may not be able to appropriately discharge the sheet S, and as a result, there may be adhesion between the sheets.

[0093] Also, in order to avoid the sticking of sheets to each other, if the user interrupts the image forming job or performs the static elimination voltage adjustment operation at regular intervals within a day, the user's load will increase. The static elimination voltage adjustment operation is, for example, a series of operations in which (1) the image forming system 400 outputs a test sheet, (2) the user manually measures the amount of charged charge of the discharged test sheet using a surface electrometer, and (3) the value of the static elimination voltage of the voltage adjustment switch 54b (FIG. 4) is increased or decreased according to the measurement result, and this series of operations is repeated until the amount of charged charge of the test sheet becomes sufficiently small.

[0094] On the other hand, in this embodiment, during the execution of the image forming job, the static elimination current during paper feeding is detected, and the static elimination voltage is automatically corrected so that the static elimination current during paper feeding approaches the target value. In other words, when the control circuit 200 executes a job of performing static elimination while continuously transporting a plurality of sheets, based on the detection result of the current detection circuit 55a (current detection means) when the preceding sheet passes through the static elimination roller 51b (static elimination member), during the execution of the job, the value of the voltage applied by the high voltage power supply 55 (voltage application means) to the static elimination roller 51b is corrected so that the current flowing through the static elimination roller 51b when the subsequent sheet transported after the preceding sheet passes through the static elimination roller 51b falls within a predetermined range.

[0095] According to this embodiment, it is possible to maintain a state in which the static elimination roller 51b can more appropriately eliminate static electricity from the sheet S without increasing the user's load, and it is possible to make it difficult for the sheets to stick to each other.

[0096] <Modification Example> In the present embodiment, it has been described that the user can set the value of the charge removal voltage applied by the high-voltage power supply 55 to the charge removal roller 51b by operating the charge removal operation unit 54 (FIG. 4). However, the present invention is not limited to this, and the user may set the set value V0 of the charge removal voltage by operating the user operation unit 102. Further, the charge removal device 300 may have a sensor that measures the amount of charged electric charge (surface potential) of the sheet S, and the control circuit 200 may automatically set the set value V0 of the charge removal voltage based on the detection result of the sensor.

[0097] In the present embodiment, it has been described that the charge removal voltage is automatically corrected based on the detection result of the charge removal current during the passage of the sheet during the execution of the image forming job. However, the present invention is not limited to this, and the same control may be applied to a mode (adjustment mode) in which the charge removal voltage is adjusted as a job independent of the image forming job. The CPU 201 starts the adjustment mode when, for example, the execution of the adjustment mode is instructed by the user via the user operation unit 102. In the adjustment mode, a test image is formed by the same process as normal image formation, and charge removal is performed by the charge removal device 300. At this time, the voltage applied to the charge removal roller 51b is set to a value preset according to conditions such as the type and size of the sheet. Further, the target value of the charge removal current is set to a value preset according to conditions such as the type and size of the sheet. When the absolute value of the difference between the detection result of the charge removal current when the test sheet passes through the charge removal roller 51b (corresponding to S7 in FIG. 6) and the target value of the charge removal current is greater than the threshold value Ith, the charge removal voltage is corrected (S9). The output of the test sheet is repeated until the absolute value of the difference between the detection result of the charge removal current and the target value becomes equal to or less than the threshold value Ith, and when it becomes equal to or less than the threshold value Ith, the adjustment mode may be terminated assuming that the adjustment of the charge removal voltage is completed. Thus, the control method described in the present embodiment may be applied as the control of the charge removal voltage in the adjustment mode.

[0098] <<Embodiment 2>> Embodiment 2 will be described. The content of the control of the charge removal voltage in Embodiment 2 is different from that in Embodiment 1. Hereinafter, elements denoted by the same reference numerals as those in Embodiment 1 have basically the same configuration and operation as those described in Embodiment 1 unless otherwise specified, and the parts different from Embodiment 1 will be mainly described.

[0099] The charge-removing device 300 of this embodiment includes a detection means (environmental detection means) for detecting the environmental conditions in which the charge-removing device 300 (image forming system 400) is placed, and has a function of automatically changing the target value of the charge-removing current used for controlling the charge-removing voltage according to the environmental conditions. The "environmental conditions" referred to here may be any of humidity (either relative humidity or absolute humidity), temperature, or a combination of temperature and humidity.

[0100] In Example 1, the target value of the charge-removing current during paper feeding is the initial charge-removing current I0 (or the value determined by the method described in the modified example), and the target value is constant during the execution of the image forming job. This configuration can appropriately control the charge-removing voltage in a simple manner in a case where the resistance value of the charge-removing roller 51b changes due to continuous voltage application and the amount of charged charge of the sheet S does not change much.

[0101] On the other hand, when the environmental conditions in which the charge-removing device 300 or the image forming system 400 is placed change, the amount of charged charge of the sheet S conveyed to the charge-removing device 300 may also change. As described above, if the amount of charged charge of the sheet S changes, the charge-removing current suitable for removing the charge from the sheet S also changes.

[0102] As a factor for the amount of charged charge of the sheet S to change according to the environmental conditions, the current value for efficiently transferring the toner image in the secondary transfer portion T2 of the image forming apparatus 100 is changed according to the environmental conditions. Another factor is that the attenuation amount of the charged charge during the conveyance of the sheet S from the secondary transfer portion T2 to the charge-removing roller 51b changes according to the environmental conditions.

[0103] Therefore, in this embodiment, while changing the target value of the charge-removing current during paper feeding according to the environmental conditions, the charge-removing voltage is corrected so that the charge-removing current during paper feeding approaches the target value.

[0104] The charge removal device 300 includes an environmental sensor 13 (Fig. 5) as environmental detection means. As the environmental sensor 13 in this embodiment, a known temperature and humidity sensor can be used. The control circuit 200 can acquire information (environmental information) on the surrounding environment where the charge removal device 300 or the image forming system 400 is placed based on the detection result of the environmental sensor 13. Note that the environmental sensor 13 may be disposed outside the housing of the charge removal device 300 (for example, inside the image forming apparatus 100).

[0105] The procedure for controlling the charge removal voltage 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 in this flow is the CPU 201.

[0106] When an image forming job is input to the image forming system 400, the processing of this flow starts. First, the CPU 201 acquires job information set via the user operation unit 102 (S20). In the image forming apparatus 100, an image forming operation is started based on the job information. On the other hand, the CPU 201 acquires a set value of the charge removal voltage from the charge removal operation unit 54 in preparation for the charge removal process in the charge removal device 300 (S21). The CPU 201 determines the acquired set value of the charge removal voltage as the value of the charge removal voltage (initial charge removal voltage) output by the high-voltage power supply 55 immediately after the start of the image forming job (S22).

[0107] For the same reason as in the first embodiment, control is performed to store the measured value of the charge removal current for the first predetermined number N of sheets S in the image forming job as the initial charge removal current, and correct the value of the charge removal voltage thereafter based on the initial charge removal current.

[0108] The CPU 201 counts the number of the current sheet S conveyed to the charge elimination device 300 starting from the first sheet S conveyed to the charge elimination device 300 first after the start of the image forming job, and acquires the charge elimination current during paper passage for each sheet S (S23). Then, when the current sheet S corresponds to a predetermined number of sheets from the start of the job (S24Y), an initial charge elimination current I1 is calculated based on the values of the charge elimination currents of the sheets S from the first sheet to the predetermined number of sheets (S25). In this embodiment, the average value of the values of the charge elimination currents of the sheets S from the first sheet to the predetermined number of sheets is set as the initial charge elimination current I1. The predetermined number of sheets is, for example, three sheets. The initial charge elimination current I1 is a target value to which the charge elimination current (controlled variable, control amount) should be approximated during the execution of the image forming job.

[0109] Subsequently to the calculation of the initial charge elimination current I1, the CPU 201 calculates a threshold Ith for determining whether to correct the charge elimination voltage (S26). The threshold Ith is a quantity (unit: μA) that determines by how much the charge elimination current during paper passage deviates from the initial charge elimination current I1 to perform the correction of the charge elimination voltage.

[0110] In this embodiment, the value of the threshold Ith is determined by the following method. Let the set value of the charge elimination voltage set via the charge elimination operation unit 54 be V0 (kV). Let the initial charge elimination current be I1. Let the variation width of the charge elimination voltage when the numerical value of the ones place is changed by 1 with the voltage adjustment switch 54b be ΔV (kV). In this case, the threshold Ith is calculated by the following formula. Ith = | I1 / V0 ×ΔV |

[0111] In other words, the threshold Ith of this embodiment is defined as the absolute value of the value obtained by dividing the initial charge elimination current I1 by the set value V0 of the charge elimination voltage and multiplying the result by the variation width ΔV of the charge elimination voltage corresponding to the minimum adjustment unit of the voltage adjustment switch 54b. For example, when the initial charge elimination current I1 is -40 μA, the set value V0 of the initial voltage is -4.0 kV, and the variation width ΔV of the charge elimination voltage is -0.1 kV, the threshold Ith becomes 1.0 μA.

[0112] Furthermore, at the same timing as the calculation of the initial discharge current I1, the CPU 201 acquires, as the detection result of the environment sensor 13, the environmental information of the environment where the discharge device 300 (or the image forming system 400) is placed. In this embodiment, the environmental information obtained from the environment sensor 13 is temperature and humidity (relative humidity). Based on the acquired temperature and humidity, the CPU 201 acquires the environmental moisture content (absolute humidity: the weight of moisture per 1 kg of dry air) around the discharge device 300 immediately after the start of the image forming job (S27). The environmental moisture content around the discharge device 300 immediately after the start of the image forming job is defined as the initial environmental moisture content H0 (g / kg).

[0113] When the current sheet S is a sheet after a predetermined number of sheets from the start of the job, the CPU 201 acquires the discharge current I during the paper passage of the current sheet S and the current environmental moisture content H (S28). Furthermore, the CPU 201 calculates a target current I2, which is a value obtained by correcting the initial discharge current I1, based on the current environmental moisture content H and the environmental table (FIG. 5) stored in the ROM 220 (S29). The target current I2 is, like the initial discharge current I1, a target value to which the discharge current (controlled variable, control amount) should be approximated during the execution of the image forming job. During the execution of the image forming job, the period in which the target current I2 is used as the target value is later than the period in which the initial discharge current I1 is used as the target value.

[0114] The environmental table is information representing the ratio of increase or decrease of the target value of the discharge current according to environmental conditions. As shown in FIG. 10, the environmental table of this embodiment defines the correspondence between the environmental moisture content and the target current ratio (the relative magnitude of the target value of the discharge current). In S29 of FIG. 9, the target current I2 is calculated by the following formula using the environmental table. I2 = (target current ratio corresponding to the current environmental moisture content H) / (target current ratio corresponding to the initial environmental moisture content H0) × I1

[0115] For example, assuming that the initial discharge current I1 is -40 μA and the initial environmental moisture content H0 is 0.88 g / kg, the target current ratio corresponding to the initial environmental moisture content H0 is 10 (Figure 10). On the other hand, assuming that the current environmental moisture content H is 8.9 g / kg, the target current ratio corresponding to this is 7 (Figure 10). In this case, the new target current I2 is (7 / 10) × (-40) = -28 μA.

[0116] In this embodiment, the higher the absolute humidity detected by the environmental sensor 13 (environmental detection means), the lower the target value of the discharge current (the smaller the amount of charge supplied to the sheet). In other words, the target value of the discharge current when the detected absolute humidity is the first value is greater than the target value when the detected absolute humidity is a second value greater than the first value. Here, an example of the "first value" is 0.88 g / kg as described above, and an example of the "second value" is 8.9 g / kg.

[0117] Then, the CPU 201 compares the absolute value of the difference between the discharge current I and the target current I2 during paper feeding with the aforementioned threshold Ith (S30). When the absolute value of the difference between I and I2 is greater than the threshold Ith (S30Y), the CPU 201 determines that it is necessary to correct the value of the discharge voltage, and corrects the value of the discharge voltage so that the discharge current approaches the target value (I2) (S31). When the absolute value of the difference between I and I2 is less than or equal to the threshold Ith (S30N), the CPU 201 determines that there is no need to correct the value of the discharge voltage and maintains the value of the discharge voltage.

[0118] For example, in the case where the initial charge-removal current I1 is -40 μA, the initial environmental moisture content H0 is 0.88 g / kg, and the target current I2 updated based on the current environmental moisture content H is -28 μA, assume that the charge-removal current I during the passage of the current sheet is -30 μA. In this case, the absolute value of the difference between I and I2 is 2 μA, which is greater than the threshold Ith of 1 μA. Therefore, the charge-removal voltage is corrected so that the absolute value of the charge-removal current I becomes smaller. The correction width of the charge-removal voltage is, for example, the fluctuation width ΔV of the charge-removal voltage corresponding to the minimum adjustment unit of the voltage adjustment switch 54b. That is, the value of the charge-removal voltage applied by the high-voltage power supply 55 to the charge-removal roller 51b is corrected from the set value V0 of the initial voltage, which is -4.0 kV, to -3.9 kV, which is 0.1 kV lower.

[0119] Note that in this embodiment, the correction width of the charge-removal voltage is set to a fixed value (0.1 kV) regardless of the magnitude of the absolute value of the difference between the detected charge-removal current I and the target current I2, but the correction width may be changed according to the absolute value of the difference between I and I2.

[0120] Thereafter, the CPU 201 determines whether the current sheet S is the last sheet in the image formation job. If it is not the last sheet (S32N), it returns to S28 and repeats the same process for the subsequent sheet S. If the current sheet S is the last sheet (S32Y), the CPU 201 ends the process of this flow.

[0121] (Modification example of the method for determining the target value of the charge-removal current) In this embodiment, as described above, the target current I2, which is the target value of the charge-removal current, is updated based on the initial charge-removal current (I1) and the initial environmental moisture content H0 immediately after the start of the image formation job, and the current environmental moisture content H. However, the method for determining the target value of the charge-removal current according to the environmental conditions is not limited to the above method.

[0122] For example, as part of the process executed by the control circuit 200 in an adjustment operation independent of the image formation job, a process of writing the initial environmental moisture content H0 and the target value of the static elimination current (corresponding to I1) at the initial environmental moisture content H0 into the RAM 210 may be performed. When starting the image formation job, the CPU 201 corrects the static elimination voltage from the first sheet S in the image formation job using the target value of the static elimination current (I0) read from the RAM 210, the initial environmental moisture content H0, and the current environmental moisture content H. That is, in the flow of FIG. 6, the target value of the static elimination current read from the RAM 210 may be used instead of the initial static elimination current I1 in the calculation of the threshold Ith and the target current I2 (S26, S29). In this case, when the absolute value of the difference between the static elimination current I and the target current I2 during the passage of the first sheet S in the image formation job is greater than the threshold Ith, the static elimination voltage is corrected before the second sheet S enters the static elimination nip.

[0123] Also, through preliminary consideration, values of the target current I2 (target value of the static elimination current) determined for each category of the environmental moisture content value may be stored in the reference table in the ROM 220. In this case, when starting the image formation job, the CPU 201 refers to the reference table in the ROM 220 and reads out the target current I2 corresponding to the current environmental moisture content H. Then, the CPU 201 determines whether correction of the static elimination voltage is necessary by comparing the absolute value of the difference between the static elimination current I during the passage of the current sheet S and the target current I2 corresponding to the current environmental moisture content H with the threshold Ith.

[0124] (Advantages of using the target value of the static elimination current according to environmental conditions) As described above, in this embodiment, while changing the target value of the static elimination current according to changes in environmental conditions, the static elimination voltage is corrected based on the comparison result between the detection result of the static elimination current and the target value of the static elimination current. Thereby, even when the charged charge amount of the sheet S changes due to changes in environmental conditions, a more appropriate static elimination voltage can be applied to the static elimination roller 51b, and a state where the static elimination roller 51b can more appropriately eliminate static electricity from the sheet can be maintained.

[0125] <Summary of this embodiment> As described above, the control circuit 200 (control means) of the present embodiment controls the value of the voltage applied by the high-voltage power supply 55 (voltage application means) to the charge removal roller 51b so that the current flowing through the charge removal roller 51b (charge removal member) falls within a predetermined range with respect to the target value based on the detection result of the current detection circuit 55a (current detection means). Further, the control circuit 200 changes the target value based on the detection result of the environmental sensor, the environmental detection means. Here, an example of the "target value" is the target current I2, and an example of the "predetermined range" is a range in which the absolute value of the difference from the target current I2 is equal to or less than the threshold Ith (predetermined threshold).

[0126] Thereby, even when the amount of charged charge of the sheet S changes due to a change in environmental conditions, the charge removal voltage can be controlled so that a charge removal current of an appropriate magnitude corresponding to the amount of charged charge of the sheet S flows. For this reason, a state in which the charge removal roller 51b can more appropriately remove charge from the sheet S can be realized.

[0127] That is, according to the present embodiment, it is possible to provide a charge removal device capable of more appropriately removing charge from a sheet, and an image forming system including the same.

[0128] Further, in the present embodiment, during the execution of a job of removing charge while continuously conveying a plurality of sheets, the target value of the charge removal current is changed based on the detection result of the environmental sensor 13 (environmental detection means). For this reason, for example, even when environmental conditions change during the execution of an image forming job, a state in which the charge removal roller 51b can more appropriately remove charge from the sheet S can be realized.

[0129] More specifically, at a first point in time during the job, an initial charge removal current I1 is determined as the target value of the charge removal current based on the detection result of a current detection circuit 55a (current detection means) when the sheet passes over a charge removal roller 51b (charge removal member) while a high-voltage power supply 55 (voltage application means) applies a voltage to the charge removal roller 51b at a predetermined voltage value. Also, at a second point in time after the first point in time during the job, the target value of the charge removal current is changed from the initial charge removal current I1 to a target current I2 based on the target value at the first point in time, the detection result of an environmental sensor 13 (environmental detection means) at the first point in time, and the detection result of the environmental sensor 13 at the second point in time. Thereby, the target value of the charge removal current can be updated to a more appropriate value according to changes in environmental conditions.

[0130] Also, similar to the first embodiment, a control circuit 200 (control means) of the present embodiment detects the charge removal current during sheet passage, and controls the value of the voltage applied by a high-voltage power supply 55 (voltage application means) to a charge removal roller 51b (charge removal member) so that the charge removal current during sheet passage falls within a predetermined range with respect to the target value. Thereby, even when the resistance value of the charge removal roller 51b changes due to continuous voltage application or the like, the charge removal voltage can be controlled so that an appropriate magnitude of charge removal current corresponding to the amount of charged charge of the sheet S flows. For this reason, a state in which the charge removal roller 51b can more appropriately remove charge from the sheet S can be realized.

[0131] <Modification> In addition, in the present embodiment, a configuration in which the charge removal voltage is controlled based on the detection result of the charge removal current during sheet passage, similar to the first embodiment, has been described. However, the present invention is not limited to this. In the present embodiment, the charge removal voltage may be controlled based on the detection result of the charge removal current when the sheet S is not passing over the charge removal roller 51b (when not passing the sheet) so that the charge removal current when not passing the sheet falls within a predetermined range with respect to the target value. In addition, when handling a sheet S with high resistance such as synthetic paper, it is preferable to perform control based on the detection result of the charge removal current during sheet passage for the reasons described in the first embodiment.

[0132] <<Embodiment 3>> In Example 2, a configuration was described in which the target value of the static elimination current is changed according to the environmental conditions of the environment where the static eliminator 300 is placed. However, the target value of the static elimination current may be changed according to other conditions. In this example, an example in which the target value of the static elimination current is changed according to the conveyance speed of the sheet S, the sheet width, and the type of the sheet S will be described. Hereinafter, elements denoted by the same reference numerals as those in Examples 1 and 2 have basically the same configurations and operations as those described in Examples 1 and 2 unless otherwise specified, and differences from Examples 1 and 2 will be mainly described.

[0133] In the ROM 220 of the control circuit 200 of this example, a table (speed ratio table) for converting the target value of the static elimination current according to the conveyance speed of the sheet S is stored (FIG. 5). Further, in the ROM 220, a table (paper type table) for converting the target value of the static elimination current according to the type of the sheet and a table (paper width table) for converting the target value of the static elimination current according to the sheet width are stored. These tables, like the environmental table (FIG. 10) of Example 2, enable conversion of the target value of the static elimination current based on the conditions before and after a certain condition changes. As long as the target value of the static elimination current can be converted according to the change in the condition, the information stored in the ROM 220 is not limited to the form of a table and may be parameters of a function representing a conversion formula.

[0134] Note that the type of the sheet is, for example, a category of sheets classified at least by the material of the sheet, such as synthetic paper and plain paper. The sheet width is the length of the sheet in the sheet width direction orthogonal to the sheet conveyance direction.

[0135] When other conditions are constant and only the conveyance speed of the sheet S changes, the target value of the static elimination current is inversely proportional to the conveyance speed. That is, when the target current when the conveyance speed is v1 is I1, the target current I2 when the conveyance speed changes to v2 is expressed as I2 = I1 × v2 / v1. In other words, as the conveyance speed increases, the target value of the static elimination current increases.

[0136] The direction of increase or decrease in the target value of the static elimination current with respect to changes in the type of the sheet S and the sheet width varies depending on specific conditions. This is because the value of the static elimination current suitable for eliminating static electricity from the sheet S varies depending on a plurality of factors such as the resistance value of the sheet, the resistance value of the static elimination roller 51b, the difference between the sheet width and the longitudinal width of the static elimination roller 51b, and the amount of charged electricity of the sheet S.

[0137] In this embodiment, in the same manner as the change in the target value of the static elimination current according to environmental conditions in Embodiment 2, the target value of the static elimination current is changed according to at least one of the conveyance speed of the sheet S, the sheet width, and the material of the sheet. Thereby, the target value of the static elimination current can be set to a more appropriate value according to the situation when the static elimination roller 51b eliminates static electricity from the sheet S.

[0138] 《Other Embodiments》 In each of the above-described embodiments, the static elimination device 300 for eliminating static electricity from the sheet S has been described. However, the static elimination device 300 has a function as a charge adjustment device that adjusts the charged state of the sheet S by supplying charges to the sheet S via the static elimination roller 51b as a charge supply member. The charge adjustment device does not necessarily reduce (eliminate static electricity) the amount of charged electricity of the sheet S. For example, in a state where the sheet S is stacked after being processed by the charge adjustment device, the charge adjustment device may adjust the amount of charged electricity on each surface of the sheet S so that the surfaces of the overlapping sheets facing each other 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 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. Further, by applying the control described in each embodiment to the control of the voltage applied to the static elimination roller 51b as a charge supply member, the charged state of the sheet S can be adjusted more appropriately.

[0139] In addition, in each of the above-described embodiments, as an example of the contact-type static eliminator member that contacts the sheet S, the static elimination roller 51b, which is a roller member, has been described. The contact-type static eliminator 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.

[0140] In addition, in each of the above-described embodiments, it has been mainly described that the charging of the sheet S 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, the charging of the sheet S can 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, the present technology may be applied to an image forming system other than the electrophotographic method.

[0141] (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 device via a network or a storage medium, and having one or more processors in the computer of the system or device read and execute the program. It can also be realized by a circuit (for example, an ASIC) that realizes one or more functions.

Explanation of Reference Numerals

[0142] 13... Environment detection means (environment sensor) / 51b... Static eliminator member, charge supply member (static elimination roller) / 55... Voltage application means (high voltage power supply) / 55a... Current detection means (current 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, current detection means for detecting a current flowing through the static eliminator member, control means for controlling the value of the voltage applied by the voltage application means to the static eliminator member so that the current flowing through the static eliminator member when the sheet passes through the static eliminator member falls within a predetermined range with respect to a target value, based on the detection result of the current detection means when the sheet passes through the static eliminator member; A static eliminator device comprising the above.

2. When the control means executes a job of eliminating static electricity while continuously conveying a plurality of sheets, based on the detection result of the current detection means when the preceding sheet passes through the static eliminator member, the current flowing through the static eliminator member when the subsequent sheet conveyed after the preceding sheet passes through the static eliminator member falls within the predetermined range, during the execution of the job, the control means corrects the value of the voltage applied by the voltage application means to the static eliminator member. The static eliminator device according to claim 1, characterized in that.

3. The target value is determined based on the detection result of the current detection means when the sheet passes through the static eliminator member in a state where the voltage application means applies a voltage to the static eliminator member at a predetermined voltage value after the start of the job. The static eliminator device according to claim 2, characterized in that.

4. The voltage application means further comprises input means through which a user can input the value of the voltage applied to the static eliminator member, The predetermined voltage value is a value input via the input means before the start of the job. The static eliminator device according to claim 3, characterized in that.

5. The predetermined range is a range in which the absolute value of the difference between the current value detected by the current detection means and the target value is equal to or less than a predetermined threshold value. The static eliminator device according to claim 3, characterized in that.

6. The target value is preset before the first sheet in the job passes through the static eliminator member. The static eliminator device according to claim 2, characterized in that.

7. The target value is changed according to at least one of the conveyance speed of the sheet, the length of the sheet in the sheet width direction orthogonal to the sheet conveyance direction, and the material of the sheet. The static eliminator device according to claim 1, characterized in that.

8. The static eliminator member is a roller member having an elastic layer in which an ion-conductive conductive agent is dispersed. The static eliminator device according to claim 1, characterized in that.

9. Further comprising an opposing roller that contacts the static elimination member and forms a nip portion that sandwiches the sheet together with the static elimination member, The opposing roller is electrically grounded, The static elimination device according to claim 8, characterized in that.

10. Further comprising an environment detection means for detecting the environmental conditions of the environment in which the static elimination device is installed, The target value is changed based on the detection result of the environment detection means, The static elimination device according to claim 1, characterized in that.

11. The environment detection means is configured to be able to detect the absolute humidity of the environment in which the static elimination device is installed, When the absolute humidity detected by the environment detection means is a first value, the target value is larger than the target value when the absolute humidity detected by the environment detection means is a second value larger than the first value, The static elimination device according to claim 10, characterized in that.

12. During the execution of a job of eliminating static electricity while continuously conveying a plurality of sheets, the control means changes the target value based on the detection result of the environment detection means, The static elimination device according to claim 11, characterized in that.

13. At a first point in time during the execution of the job, based on the detection result of the current detection means when the sheet passes through the static elimination member while the voltage application means applies a voltage to the static elimination member at a predetermined voltage value, the target value is determined, At a second point in time after the first point in time during the execution of the job, the target value is changed based on the target value at the first point in time, the detection result of the environment detection means at the first point in time, and the detection result of the environment detection means at the second point in time, The static elimination device according to claim 12, characterized in that.

14. Further comprising an input means by which a user can input the value of the voltage applied by the voltage application means to the static elimination member, The predetermined voltage value is a value input via the input means before the start of the job, The static elimination device according to claim 13, characterized in that.

15. An image forming apparatus that forms an image on a sheet, The static elimination device according to any one of claims 1 to 14, 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.

16. 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, Current detection means for detecting a current flowing through the charge supply member; Based on the detection result of the current detection means when the sheet passes through the charge supply member, the voltage application means controls the value of the voltage applied to the charge supply member so that the current flowing through the charge supply member when the sheet passes through the charge supply member becomes a value within a predetermined range; A charge adjustment device characterized by comprising the above.

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