Static elimination device, image forming system, and charge adjusting device

Abstract

This static elimination device includes: a static elimination member for eliminating static electricity on a sheet; a voltage application means for applying a voltage to the static elimination member; and a control means that automatically sets a second voltage to a value different from the value of a first voltage, the first voltage being a voltage that the voltage application means applies to the static elimination member when a sheet having an image formed only on one side thereof is subjected to static elimination, and the second voltage being a voltage that the voltage application means applies to the static elimination member when a sheet having an image formed on both sides thereof is subjected to static elimination.

Description

Discharger, image forming system, and charge adjustment device

[0001] The present invention relates to a static eliminator that eliminates static electricity from a sheet, an image forming system that forms an image on a sheet, and a charge adjusting device that adjusts the charge state of a sheet.

[0002] Japanese Patent Application Laid-Open No. 2019-167169 describes a static eliminator that eliminates static from paper using a static eliminator roll (contact static eliminator) that comes into contact with the paper and a corotron-type non-contact static eliminator.

[0003] The above-mentioned Japanese Patent Application Laid-Open No. 2019-167169 does not disclose that the set value of the voltage applied to the static elimination roll is changed depending on whether the image forming apparatus performs single-sided printing or double-sided printing. However, as a result of investigations conducted by the inventors, it was found that the voltage value suitable for eliminating static electricity or adjusting the charged state of a sheet may differ between single-sided printed sheets and double-sided printed sheets.

[0004] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a static eliminator, an image forming system, and a charge adjustment device that are capable of more appropriately eliminating static from a sheet or adjusting the charged state of the sheet.

[0005] One aspect of the present invention is a static elimination device comprising: a static elimination member that eliminates static electricity from a sheet; a voltage application means that applies a voltage to the static elimination member; and a control means that automatically sets the value of the second voltage to a value different from the first voltage, where the voltage that the voltage application means applies to the static elimination member when eliminating static electricity from a sheet having an image formed on only one side of the sheet is a first voltage, and the voltage that the voltage application means applies to the static elimination member when eliminating static electricity from a sheet having an image formed on both sides of the sheet is a second voltage.

[0006] Another aspect of the present invention is a charge adjustment device comprising: a charge supply member that supplies charge to a sheet; a voltage application means that applies a voltage to the charge supply member; and a control means that automatically sets the value of the second voltage to a value different from the first voltage when adjusting the charge state of a sheet having an image formed on only one side of the sheet, where the voltage that the voltage application means applies to the charge supply member is a first voltage, and when adjusting the charge state of a sheet having images formed on both sides of the sheet, the voltage that the voltage application means applies to the charge supply member is a second voltage.

[0007] According to the present invention, it is possible to provide a static eliminator, an image forming system, and a charge adjustment device that can more appropriately eliminate static electricity from a sheet or adjust the charged state of the sheet.

[0008] FIG. 1 is a schematic diagram of an image forming system according to the first embodiment.

[0009] FIG. 2 is a schematic diagram of the static eliminator according to the first embodiment.

[0010] FIG. 3 is a schematic diagram of a conveying guide according to the first embodiment.

[0011] FIG. 4 is a schematic diagram of the static elimination operation unit according to the first embodiment.

[0012] FIG. 5 is a schematic diagram showing the charged state of a single-sided printed sheet before and after passing through the charge removal nip.

[0013] FIG. 6 is a schematic diagram showing the charged state of a double-sided printed sheet before passing through the secondary transfer portion.

[0014] FIG. 7 is a diagram showing the relationship between the thickness of the sheet and the appropriate value of the static elimination voltage.

[0015] FIG. 8 is a block diagram of a control system according to the first embodiment.

[0016] FIG. 9 is a flowchart showing a control method according to the first embodiment.

[0017] FIG. 10 is a flowchart showing a control method according to the second embodiment.

[0018] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0019] FIG. 1 shows a schematic diagram of an image forming system 400 according to a first embodiment. 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 the sheet S as a finished product (printed product). The sheet S, which is a recording medium, can be a variety of sheet materials of different sizes and materials, including paper such as plain paper and cardboard, surface-treated sheet materials such as coated paper, specially shaped sheet materials such as envelopes and index paper, plastic sheet materials, and cloth. Examples of plastic sheet materials include synthetic paper made primarily of synthetic resin and overhead projector sheets (OHT).

[0020] The static eliminator 300 is a device (static eliminator) that removes (reduces) the charge on the sheet S discharged from the image forming system 400. The static eliminator 300 can also be considered a charge adjustment device that adjusts the charge state of the sheet S discharged from the image forming system 400. The static eliminator 300 may be provided with a function other than the static elimination function (for example, a decurler function that corrects curling of the sheet S). Furthermore, although the static eliminator 300 in this embodiment is disposed as a device independent of the image forming apparatus 100, the static eliminator 300 may also be incorporated into the housing of the image forming apparatus 100.

[0021] The image forming system 400 may include optional devices other than the static eliminator 300. Examples of the optional devices include a large-capacity feeding device (optional feeder) that supplies sheets S to the image forming apparatus 100, and a sheet processing device (finisher) that performs processing such as binding on sheets S on which images have been formed by the image forming apparatus 100. <Image Forming Apparatus>

[0022] 1 shows a schematic configuration of an image forming apparatus 100. The image forming apparatus 100 includes an image forming section 101, which is an intermediate transfer type electrophotographic mechanism. The image forming section 101 includes four process units 11Y, 11M, 11C, and 11K, each having a photosensitive drum 1Y, 1M, 1C, and 1K, and a transfer unit 15 having an intermediate transfer belt 6 and a secondary transfer roller 9.

[0023] Each process unit includes a photosensitive drum as an image carrier (latent image carrier) and a charging device, an exposure device, and a developing device as process parts that act on the photosensitive drum to perform each step of the electrophotographic process. Specifically, process unit 11Y includes a photosensitive drum 1Y, a charging device 2Y, an exposure device 3Y, and a developing device 4Y. Process unit 11M includes a photosensitive drum 1M, a charging device 2M, an exposure device 3M, and a developing device 4M. Process unit 11C includes a photosensitive drum 1C, a charging device 2C, an exposure device 3C, and a developing device 4C. Process unit 11K includes a photosensitive drum 1K, a charging device 2K, an exposure device 3K, and a developing device 4K.

[0024] Each of the photosensitive drums 1Y, 1M, 1C, and 1K is rotated in a predetermined rotation direction A. The process units 11Y, 11M, 11C, and 11K have substantially the same configuration, except that the toners contained as developers in the developing devices 4Y, 4M, 4C, and 4K are different.

[0025] The transfer unit 15 includes an intermediate transfer belt 6 as an intermediate transfer body, a secondary transfer roller 9 as a transfer means (secondary transfer means), primary transfer rollers 5Y, 5M, 5C, and 5K, multiple rollers 20, 21, 22, 23, 24, and 25, and a belt cleaner 12. The intermediate transfer belt 6 is stretched over the multiple rollers 20, 21, 22, 23, 24, and 25. The primary transfer rollers 5Y, 5M, 5C, and 5K are disposed on the inner surface of the intermediate transfer belt 6 at positions corresponding to the photosensitive drums 1Y, 1M, 1C, and 1K, respectively. A primary transfer portion is formed between the primary transfer rollers 5Y, 5M, 5C, and 5K and the corresponding photosensitive drums 1Y, 1M, and 1C. Roller 20 is a tension roller that applies an appropriate tension to the intermediate transfer belt 6. Roller 22 is a drive roller that rotates 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 disposed so as to sandwich the intermediate transfer belt 6 together with an opposing roller 21 (secondary transfer opposing roller). A nip portion between the secondary transfer roller 9 and the intermediate transfer belt 6 forms a secondary transfer portion T2, which serves as a transfer portion where a toner image is transferred onto the sheet S.

[0026] The image forming apparatus 100 includes a transfer power supply 10 as a voltage application means for forming a bias electric field at the secondary transfer portion T2 for transferring a toner image. In this embodiment, the secondary transfer roller 9, which is the outer roller of the secondary transfer portion T2, is electrically connected to the transfer power supply 10, and a predetermined transfer voltage is applied from the transfer power supply 10. The transfer voltage has a polarity opposite to the normal charging polarity of the toner used in image formation. Meanwhile, the counter roller 21, which is the inner roller of the secondary transfer portion T2, is electrically connected to the ground potential (metal frame, etc.) of the image forming apparatus 100. Alternatively, the inner roller of the secondary transfer portion T2 may be connected to the transfer power supply 10, and the outer roller of the secondary transfer portion T2 may be connected to the ground potential GND. In this case, a transfer voltage of the same polarity as the normal charging polarity of the toner is applied to the inner roller.

[0027] The image forming apparatus 100 further includes a storage section 63 (storage cabinet, cassette) that stores the sheets S, a feeding unit 64 that feeds the sheets S, and registration rollers 8 that register (align) the sheets S. The image forming apparatus 100 also includes a pre-fixing conveying device 41 that conveys the sheets S that have passed through the secondary transfer section T2, a fixing device 40 that fixes the toner image on the sheets S, and a pair of discharge rollers 42 as a discharge unit that discharges the sheets S to the outside of the image forming apparatus 100.

[0028] The feeding unit 64 includes, for example, a pickup roller 65 that feeds the top sheet S from the storage section 63 in the sheet feeding direction, and a separation roller pair 66 that separates and conveys the fed sheets S one by one. The separation roller pair includes a conveying roller that feeds the top sheet S in the sheet feeding direction, and a separation roller that abuts against the conveying roller and forms a separation nip together with the conveying roller. The separation roller applies friction to the sheet S at the separation nip, thereby preventing sheets S other than the top sheet S from passing through the separation nip, thereby preventing double feeding of sheets S. The separation roller is an example of a separating member that separates sheets S, and a pad-shaped elastic member (rubber pad), for example, may be used as the separating member.

[0029] The fixing device 40 is a thermal fixing device that has a fixing nip and heats the toner image on the sheet S while sandwiching and transporting the sheet S in the fixing nip. The fixing device 40 has 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. The heating member and pressure member can be, for example, a belt member stretched over multiple rollers or a rigid roller member. The heat source can be, for example, a halogen lamp or an induction heating mechanism.

[0030] The image forming apparatus 100 also includes a user operation unit 102, which is a user interface for the image forming system 400. The user operation unit 102 includes a display unit, such as a liquid crystal panel, that displays information to the user, and an input unit, such as physical buttons and a touch panel function of the liquid crystal panel, that receives information input from the user. The user can set setting information and execution conditions for 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 sheets S stored in the storage unit 63. The execution conditions for the image forming operation are, for example, the value of the transfer voltage.

[0031] When a user inputs an instruction to perform image formation, the control unit of the image forming apparatus 100 starts an image formation job, which is a series of tasks for forming an image on sheets S while transporting the sheets S one by one and outputting a product. Hereinafter, a series of operations for forming an image on one sheet S by the image forming apparatus 100 will be referred to as an image forming operation. The image forming job includes an image forming operation on at least one sheet S.

[0032] During image formation, toner images of each color are formed in process units 11Y, 11M, 11C, and 11K. Specifically, photosensitive drums 1Y, 1M, 1C, and 1K are rotated, and charging devices 2Y, 2M, 2C, and 2K uniformly charge the surfaces of photosensitive drums 1Y, 1M, 1C, and 1K. Exposure devices 3Y, 3M, 3C, and 3K expose photosensitive drums 1Y, 1M, 1C, and 1K to light based on image information input along with execution instructions, thereby forming electrostatic latent images on the surfaces of photosensitive drums 1Y, 1M, 1C, and 1K. Developing devices 4Y, 4M, 4C, and 4K supply yellow, magenta, cyan, and black toner to photosensitive drums 1Y, 1M, 1C, and 1K, respectively, to develop the electrostatic latent images into toner images of each color.

[0033] In this embodiment, a reverse development method is used, in which the charging device charges the surface of the photosensitive drum to the same polarity as the normal charging polarity of the toner, and then the potential of the exposed area exposed by the exposure device is attenuated, and the toner adheres to the exposed area during development.

[0034] The toner images created in the 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 a polarity opposite to the normal charging polarity of the toner is applied to the primary transfer rollers 5Y, 5M, 5C, and 5K by constant voltage control.

[0035] In this embodiment, the primary transfer rollers 5Y, 5M, 5C, and 5K are conductive rollers having a core and a conductive elastic layer formed on the outer periphery of the core. The elastic layer is formed, for example, from ion-conductive foam rubber. Ion-conductive foam rubber is a foam rubber material in which a conductive agent that exhibits ionic conductivity is dispersed. The conductive agent and foam rubber material can be made of materials known for use in transfer rollers. Each primary transfer roller preferably has an outer diameter of 15 to 20 mm and a resistance of 1E+5 to 1E+8 Ω when a voltage of 2 kV is applied under environmental conditions of 23°C and 50% RH.

[0036] The intermediate transfer belt 6 is rotated at a predetermined peripheral speed (process speed) equal to the peripheral speed of the photosensitive drums 1Y, 1M, 1C, and 1K. In this embodiment, the peripheral speed is 150 to 470 mm / sec. As the intermediate transfer belt 6 rotates, toner images of other colors are transferred onto the toner image transferred at the upstream primary transfer unit, 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 transported toward the secondary transfer unit T2.

[0037] In parallel with the creation of the toner image in the image forming unit 101, the feeding unit 64 feeds the sheet S one by one toward the image forming unit 101. The fed sheet S is transported to the secondary transfer unit T2 by the registration rollers 8 in synchronization with the timing at which the toner image on the intermediate transfer belt 6 is transported to the secondary transfer unit T2. Then, at the secondary transfer unit T2, the toner image is transferred (secondary transfer) from the intermediate transfer belt 6 to the sheet S.

[0038] In this embodiment, the secondary transfer roller 9 is a conductive roller having a core and a conductive elastic layer formed on the outer periphery of the core. The elastic layer is formed, for example, from ion-conductive foam rubber. Ion-conductive foam rubber is a foam rubber material in which a conductive agent that exhibits ionic conductivity is dispersed. Materials known for transfer rollers can be used for the conductive agent and foam rubber material. A suitable secondary transfer roller 9 is, for example, one with an outer diameter of 20 to 25 mm and a resistance of 1E+5 to 1E+8 Ω when a voltage of 2 kV is applied under environmental conditions of 23°C and 50% RH.

[0039] The opposing roller 21 is a conductive roller having a core and an elastic layer of electronically conductive foamed rubber formed on the outer periphery of the core. The electronically conductive foamed rubber is a foamed rubber material in which a conductive agent that exhibits electronic conductivity is dispersed. The conductive agent and foamed rubber material may be materials known for use in transfer rollers. For example, the opposing roller 21 may preferably have an outer diameter of 20 to 22 mm and a resistance of 1E+5 to 1E+8 Ω when a voltage of 50 V is applied under environmental conditions of 23°C and 50% RH.

[0040] During secondary transfer, a transfer voltage of a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 9 from the transfer power supply 10 under constant voltage control. The transfer voltage is, for example, +1 to +7 kV, and is automatically adjusted so that a current of +40 to +120 μA flows from the secondary transfer roller 9 to the opposing roller 21. The application of the transfer voltage forms a bias electric field at the secondary transfer portion T2, in which the potential of the secondary transfer roller 9 has a polarity opposite to the normal charging polarity of the toner relative to the intermediate transfer belt 6. This bias electric field acts on the toner on the intermediate transfer belt 6 with an electrostatic force in a direction that draws it closer to the secondary transfer roller 9. The toner is then transferred from the intermediate transfer belt 6 to the sheet S passing through the secondary transfer portion T2, thereby transferring a toner image to the sheet S.

[0041] Incidentally, a conveying guide 11 is provided immediately before the secondary transfer portion T2 to improve the positional accuracy of the sheet S with respect to the intermediate transfer belt 6. Furthermore, residual toner that is not transferred to the sheet S and remains on the intermediate transfer belt 6 is collected by a belt cleaner 12 and reused for image formation.

[0042] After passing through the secondary transfer portion T2, the sheet S is transported by the pre-fixing conveying device 41 to the fixing device 40, where the toner image is fixed. The fixing process involves heating and pressurizing the toner image on the sheet S while the sheet S is nipped and conveyed in the nip of the fixing device 40. The pre-fixing conveying device 41 conveys the sheet S, for example, on an endless rubber belt. The rubber belt may be an ethylene propylene diene rubber (EPDM) belt with a width of 100 to 110 mm and a thickness of 1 to 3 mm. The rubber belt has holes with a diameter of 3 to 7 mm, and a fan can be used to generate negative pressure inside the rubber belt, allowing the sheet S to be stably supported on the rubber belt.

[0043] In the case of an image forming operation (single-sided printing) in which an image is formed on only one side of the sheet S, the sheet S that has passed through the fixing device 40 is discharged toward the static eliminator 300 by a pair of discharge rollers 42 .

[0044] In an image forming operation (double-sided printing) in which images are formed on both sides of a sheet S, the sheet S, which has passed through the fixing device 40 with a toner image transferred to its first side (front side), is reversed and conveyed. The image forming apparatus 100 has an inverting unit 43 that inverts the sheet S, and a double-sided conveying unit 44 that conveys the inverted sheet S again toward the secondary transfer unit T2. The inverting unit 43 is a pair of rollers that can rotate forward and backward. The inverting unit 43 switches back the sheet S and sends it to the double-sided conveying unit 44. Then, the sheet S, with its first side (front side) and second side (rear side) reversed, is conveyed again to the secondary transfer unit T2 via the double-sided conveying unit 44, where the toner image is transferred to the rear side of the sheet S. Then, the sheet S, which has passed through the fixing device 40 with the toner image transferred to its rear side, is discharged toward the static eliminator 300 by a pair of discharge rollers 42.

[0045] The intermediate transfer type image forming unit 101 described above is an example of an image forming means for forming an image on a sheet S, and the image forming means may be, for example, a direct transfer type electrophotographic unit. In this case, a toner image formed on a photosensitive drum serving as an image carrier is directly transferred from the photosensitive drum to the sheet S at a transfer nip (transfer portion) where the photosensitive drum and a transfer roller face each other. At the transfer nip, a bias electric field is formed in which the potential of the transfer roller has a polarity opposite to the normal charging polarity of the toner relative to the photosensitive drum. <Discharger>

[0046] 2 is a schematic diagram of a static eliminator 300 in Example 1. In this example, the static eliminator 300 is connected downstream of the image forming apparatus 100. The static eliminator 300 receives a sheet S on which an image has been formed by the image forming apparatus 100 and conveys the sheet S in the sheet conveying direction Cv while eliminating static from the sheet S (reducing static charge on the sheet surface). By eliminating static from the sheet S, it is possible to prevent stacked sheets discharged from the image forming system 400 from sticking to each other due to electrostatic attraction, and to prevent deterioration in the integrity of the sheets S due to sticking to each other. The static eliminator 300 includes a pair of static eliminators 51 as a contact static eliminator and an ionizer unit 52 as a non-contact static eliminator.

[0047] The discharge roller pair 51 includes a discharge opposing roller 51a that contacts a first surface Sa of the sheet S, and a discharge roller 51b that contacts a second surface Sb opposite the first surface Sa of the sheet S. The discharge roller 51b is a contact-type discharge member that contacts the sheet S being conveyed and discharges the sheet S. The discharge opposing roller 51a abuts against the discharge roller 51b, and a discharge nip is formed as a nip portion between the discharge roller 51b and the discharge opposing roller 51a. The discharge roller pair 51 discharges the sheet S while conveying it by nipping the sheet S in the discharge nip.

[0048] The discharge opposing roller 51a is connected to the ground potential GND. The discharge opposing roller 51a is electrically connected to, for example, a metal frame of the discharge device 300 and is electrically grounded. The discharge roller 51b is connected to a high-voltage power supply 55. The high-voltage power supply 55 is a voltage application unit that applies a voltage (discharge voltage) to the discharge roller 51b to discharge the sheet S. In this embodiment, the high-voltage power supply 55 applies a DC voltage of opposite polarity to the transfer voltage that the transfer power supply 10 applies to the secondary transfer roller 9 to the discharge roller 51b.

[0049] The discharge roller 51b may be disposed so as to contact the first surface Sa of the sheet S, and the discharge opposing roller 51a may be disposed so as to contact the second surface Sb of the sheet S. In this case, the voltage applied to the discharge roller 51b has a polarity opposite to that of the voltage applied to the discharge roller 51b in this embodiment.

[0050] In this embodiment, the static elimination roller 51b is a conductive roller having a core and a conductive elastic layer formed on the outer periphery of the core. The elastic layer is formed, for example, from ion-conductive foam rubber. Ion-conductive foam rubber is a foam rubber material in which a conductive agent that exhibits ionic conductivity is dispersed. Known materials can be used for the conductive agent and foam rubber material. For example, the static elimination roller 51b preferably has an outer diameter of 20 to 25 mm and a resistance 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 opposing roller 51a is made of stainless steel (SUS) and has an outer diameter of 20 to 25 mm. Note that the static elimination roller 51b may also be formed from a metal such as stainless steel.

[0051] The ionizer unit 52 includes a first ionizer 52a facing the first side of the sheet S and a second ionizer 52b facing the second side of the sheet S. Each of the first ionizer 52a and the second ionizer 52b has an electrode needle, and by applying a voltage to the electrode needle, a corona discharge is generated from the tip of the needle, ionizing the air around the needle tip. The generated ions then neutralize the charge on the sheet surface, thereby de-electrifying the sheet S.

[0052] In this embodiment, the ionizer unit 52 is configured with bar-type ionizers IZS40 (manufactured by SMC Corporation) arranged above and below the sheet transport path as the first ionizer 52a and the second ionizer 52b. The transport guides 53a and 53b forming the sheet transport path of the ionizer unit 52 are made of a resin obtained by compounding PC (polycarbonate) and ABS (acrylonitrile-butadiene-styrene). The volume resistivity of the transport guides 53a and 53b is, for example, 1×10 １４ 3, each of the conveying guides 53a and 53b has a plurality of holes 530 formed therein to prevent the ions emitted from the first ionizer 52a and the second ionizer 52b from being physically blocked. The holes 530 are arranged side by side in the sheet width direction perpendicular to the sheet conveying direction Cv.

[0053] The first ionizer 52a and the second ionizer 52b described above are examples of non-contact static eliminators, and other non-contact static eliminators may be used. For example, a corotron or scorotron static eliminator that eliminates static electricity from a sheet by corona discharge from a discharge wire may be used. Furthermore, non-contact static eliminators do not necessarily need to be provided on both sides of the conveyance path. For example, the static eliminator 300 may be configured to include only the first ionizer 52a as a non-contact static eliminator. Furthermore, if the static eliminator roller 51b can sufficiently eliminate static electricity from the sheet S, the non-contact static eliminator may be omitted.

[0054] The sheet S conveyed from the image forming apparatus 100 to the static eliminator 300 first has most of the charge removed (roughly removed) in the static elimination nip of the static elimination roller pair 51. Specifically, the static elimination voltage is set to a polarity opposite to that of the transfer voltage applied to the secondary transfer roller 9. The value of the static elimination voltage is set in the range of -1 kV to -6 kV.

[0055] At the secondary transfer portion T2 (FIG. 1), the sheet S is typically charged so that the first surface Sa of the sheet S, which has been in contact with the intermediate transfer belt 6, becomes negatively charged and the second surface Sb of the sheet S, which has been in contact with the secondary transfer roller 9, becomes positively charged. When a discharge voltage of a polarity opposite to the transfer voltage is applied to the discharge roller 51b, a current flows between the discharge roller 51b and the discharge opposing roller 51a so that a positive charge is supplied to the first surface Sa of the sheet S and a positive charge is supplied to the second surface Sb. In this way, the application of the discharge voltage to the discharge roller 51b causes a current to flow through the sheet S at the discharge nip, thereby reducing the amount of charge carried on the first surface Sa and the second surface Sb of the sheet S.

[0056] The sheet S that has passed through the pair of charge-removing rollers 51 is further neutralized in the ionizer unit 52. Specifically, the charges remaining on the first surface Sa and the second surface Sb of the sheet S are neutralized by ions irradiated from the first ionizer 52a and the second ionizer 52b, thereby further reducing the amount of charge on the sheet S. The sheet S that has passed through the ionizer unit 52 is discharged to the outside of the charge removal device 300.

[0057] The amount of charge on the sheet S is usually proportional to the surface potential of the sheet S. The amount of charge on the sheet S may be expressed as the amount of charge per unit area of ​​the sheet surface (surface charge density). Therefore, the "amount of charge" on the sheet S in the following description may be replaced with the surface potential or the surface charge density of the sheet S. <Static Neutralization Voltage Adjustment Switch>

[0058] The static eliminator 300 includes a static elimination operation unit 54 that can be operated to change the operating conditions of the static eliminator 300. An enlarged view of the static elimination operation unit 54 is shown in Fig. 4. The static elimination operation unit 54 is an example of an input unit (setting unit) that allows a user to input (set) the value of the voltage that the high-voltage power supply 55 (voltage application unit) applies to the static elimination roller 51b (static elimination member).

[0059] The static elimination operation unit 54 includes a selector switch 54a and voltage adjustment switches 54b and 54c. By operating the selector switch 54a, the user can switch between outputting (ON) and stopping (OFF) the static elimination voltage from the high-voltage power supply 55 (FIG. 2), which applies the static elimination voltage to the static elimination roller 51b. The voltage adjustment switches 54b and 54c allow the user to adjust the value of the static elimination voltage.

[0060] The value of the neutralization voltage can also be fixed at a value that is preset according to the category of the sheet S. For example, it is known that plastic film or synthetic paper tends to experience stronger dielectric polarization at the secondary transfer portion than plain paper, and the amount of charge on the sheet S tends to be large. Therefore, when using plastic film or synthetic paper as the sheet S, it is possible to set the neutralization voltage value in advance according to the category of the sheet S so that the neutralization 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 neutralization voltage value varies due to differences in electrical resistance caused by differences in the specific materials, differences in thickness, differences in the environmental conditions in the environment where the neutralization device 300 is installed, and so on. Therefore, in this embodiment, the neutralization voltage value is configured to be adjustable.

[0061] In this embodiment, two types of voltage values ​​can be set as the static elimination voltage: a voltage value for single-sided printing (referred to as a first static elimination voltage) and a voltage value for double-sided printing (referred to as a second static elimination voltage). The first static elimination voltage (first voltage) is a static elimination voltage that is applied to the static elimination roller 51b when the image forming system 400 executes an image forming job (single-sided printing job) in which an image is formed on only one side of a sheet. The second static elimination voltage (second voltage) is a static elimination voltage that is applied to the static elimination roller 51b when the image forming system 400 executes an image forming job (double-sided printing job) in which an image is formed on both sides of a sheet.

[0062] One of the voltage adjustment switches, 54b, is used by the user to set (input) the value of the first static elimination voltage. The other voltage adjustment switch, 54c, is used by the user to set (input) the value of the second static elimination voltage. Different values ​​can be input for the first static elimination voltage and the second static elimination voltage. This is because, as will be described below, the value appropriate for elimination of static electricity from a sheet S (referred to as the appropriate value of the static elimination voltage) may differ between elimination of static electricity from a sheet S printed on one side (during single-sided printing) and elimination of static electricity from a sheet S printed on both sides (during double-sided printing).

[0063] Each of the voltage adjustment switches 54b and 54c in this embodiment includes a display unit that displays the value of the static elimination voltage (first static elimination voltage or second static elimination voltage) in two digits, and buttons (+ button and − button) for increasing or decreasing the value of the static elimination voltage. Pressing the + button increases the number in the corresponding digit, and pressing the − button decreases the number in the corresponding digit.

[0064] The value displayed on the display is the absolute value of the static elimination voltage, displayed as a two-digit number in 0.1 kV increments. In other words, the set value of the static elimination voltage is obtained by multiplying the value displayed on the display of the voltage adjustment switches 54b and 54c by -0.1 kV. For example, when "45" is displayed on the display of the voltage adjustment switch 54b, the set value of the first static elimination voltage is -4.5 kV. From this state, if the - button for the tens digit is pressed once and the + button for the ones digit is pressed twice, the display will change to "37," and the value of the first static elimination voltage will be set to -3.7 kV.

[0065] When the voltage adjustment switches 54b and 54c are set to "00," the set value of the static elimination voltage becomes 0 V (0.0 kV). In this case, the state of the high-voltage power supply 55 is the same as when the selector switch 54a is turned OFF. This state can also be said to be a state in which the high-voltage power supply 55 applies 0 V to the static elimination roller 51b.

[0066] The display and input methods for the neutralization voltage value are not limited to those described above. Instead of displaying the first two digits of the neutralization voltage value, the neutralization voltage value itself may be displayed, or a numeric value representing the neutralization voltage level, for example, on a 10-point scale, may be displayed. The neutralization voltage value may be displayed, for example, on the user operation unit 102 or on the screen of an external computer communicatively connected to the image forming system 400. The neutralization voltage value may be input by providing a numeric keypad on the neutralization operation unit 54 for numeric input, by operating a touch panel on the user operation unit 102, or by receiving input via an external computer. The user operation unit 102 is another example of an input unit (setting unit) that allows a user to input (set) the value of the voltage to be applied by the high-voltage power supply 55 (voltage application unit) to the neutralization roller 51b (neutralization member). Even when the neutralization voltage value is input via the user operation unit 102 or an external computer, two types of voltage values, the first neutralization voltage and the second neutralization voltage, can be set. <Automatic Setting of the Second Neutralization Voltage>

[0067] In this embodiment, when the user inputs the value of the first static elimination voltage for single-sided printing, the value of the second static elimination voltage for double-sided printing is automatically set. For example, the value of the second static elimination voltage is automatically set to a value that is -1 kV lower than the value of the first static elimination voltage. Note that the user can further change the value of the second static elimination voltage automatically set by the device by operating the voltage adjustment switch 54c of the static elimination operation unit 54.

[0068] First, the appropriate value of the static elimination voltage for double-sided printing will be described. １３ Sheets with a volume resistivity of 1×10 Ω cm or more are called "high resistance sheets." １３ Sheets with a resistivity of less than Ω·cm are called “low resistivity sheets.” An example of a high resistivity sheet is synthetic paper, and an example of a low resistivity sheet is plain paper.

[0069] In the case of a high-resistivity sheet, the amount of charge when a double-sided printed sheet S reaches the discharge nip is smaller than the amount of charge when a single-sided printed sheet S reaches the discharge nip. The reason why the amount of charge on the sheet S differs between single-sided printing and double-sided printing will be described later.

[0070] The smaller the amount of charge on the sheet S when it reaches the discharge nip, the smaller the amount of charge that the discharge roller 51b needs to supply to the sheet S in order to discharge the sheet S. In other words, in the case of a high-resistivity sheet, the optimum value of the discharge voltage (second discharge voltage) during double-sided printing is smaller in absolute value than the optimum value of the discharge voltage (second discharge voltage) during single-sided printing.

[0071] FIG. 7 shows an example of an appropriate value of the static elimination voltage for a high-resistivity sheet. The data in the figure indicates that the volume resistivity is 1×10 １３ ~1×10 １４ The graph shows the results for several types of synthetic paper in Ω cm. The horizontal axis represents the thickness of the synthetic paper. The vertical axis represents the appropriate values ​​of the neutralization voltages (first neutralization voltage, second neutralization voltage) when each sheet is neutralized by the neutralization roller 51b after single-sided or double-sided printing is performed on each sheet under preset conditions.

[0072] As can be seen from the figure, for all high-resistivity sheets of different thickness, the appropriate value of the static elimination voltage (second static elimination voltage) for double-sided printing is lower than the appropriate value of the static elimination voltage (first static elimination voltage) for single-sided printing. In other words, the appropriate value of the static elimination voltage for a sheet with images formed on both sides is lower (its absolute value is smaller) than the appropriate value of the static elimination voltage for a sheet with images formed on only one side of the sheet.

[0073] For this reason, it is preferable that the value of the second static elimination voltage is lower (its absolute value is smaller) than the value of the first static elimination voltage. If the value of the second static elimination voltage were equal to the first static elimination voltage, the second static elimination voltage would be greater than the appropriate value for the static elimination voltage, causing excessive charge to be supplied to the sheet S, resulting in poor static elimination (the sheet S being charged to a polarity opposite to that before passing through the static elimination nip), and making it more likely that the sheet S would stick. Furthermore, for example, when multiple levels of static elimination voltage are set according to the thickness of the sheet, it is preferable that the set value of the second static elimination voltage be set to a value lower (its absolute value is smaller) than the set value of the first static elimination voltage for each sheet of a different thickness.

[0074] Therefore, in this embodiment, the control means of the static elimination device 300 is configured to automatically set the value of the static elimination voltage (second static elimination voltage, second voltage) during double-sided printing to a value different from the static elimination voltage (first static elimination voltage, first voltage) during single-sided printing. More specifically, in this embodiment, when the first static elimination voltage is set in the static elimination operation unit 54, the value of the second static elimination voltage is automatically set to a value that has the same polarity as the first static elimination voltage and a smaller absolute value than the first static elimination voltage. "Automatically" means that the second static elimination voltage is set to a value different from the first static elimination voltage at the discretion of the control means when the user has not input a value different from the first static elimination voltage as the value of the second static elimination voltage. <Control Circuit>

[0075] 8 shows a block diagram of the control circuit 200 related to the control of the static elimination voltage. The control circuit 200 is an example of a control means for controlling the operation of the static eliminator 300. The control circuit 200 may be mounted in the main body of the static eliminator 300, or some or all of the functions of the control circuit 200 may be mounted in the image forming apparatus 100.

[0076] 5 , the control circuit 200 includes a CPU 201, a RAM 210, and a ROM 220. The CPU 201 is an execution unit that reads and executes a control program. The RAM 210 serves as a work area for the CPU 201 when executing the control program. The ROM 220 is an example of a storage unit that stores various information such as setting information related to the control of the static eliminator 300. The control circuit 200 is also connected to the user operation unit 102, the static elimination operation unit 54, the high-voltage power supply 55, and the transfer power supply 10.

[0077] The CPU 201 acquires information related to the image forming job (job information), the setting of the static elimination voltage, the value of the transfer voltage output by the transfer power supply 10, and stores it in the RAM 210. Here, the job information is, for example, attribute information of the sheet S input by the user via the user operation unit 102, and is attribute information of the sheet S used in the current image forming job. The setting of the static elimination voltage is the value of the first static elimination voltage and the second static elimination voltage set by the user by operating the static elimination operation unit 54. In addition, the ROM 220 stores control parameters and various tables used to control the static elimination voltage.

[0078] The control circuit 200 is connected to an environment sensor 13 for detecting the environmental conditions of the installation environment (the space surrounding the installation environment) of the static eliminator 300 (image forming system 400). The control circuit 200 can also obtain the value of the current (static elimination current) flowing through the static eliminator roller 51b based on the detection result of a current detection circuit 55a provided inside the high-voltage power supply 55. <Control Flow>

[0079] The procedure for controlling the static elimination voltage performed by the control circuit 200 will be described with reference to the flowchart in Fig. 9. Hereinafter, the CPU 201 executes each step of this flow unless otherwise specified. This flow is executed continuously while the user can set the value of the first static elimination voltage via the static elimination operation unit 54.

[0080] When the user inputs the value of the first static elimination voltage by operating the static elimination operation unit 54 (S0Y), the CPU 201 stores the input value in the RAM 210 and resets the value of the first static elimination voltage (S1). The CPU 201 also calculates the value of the second static elimination voltage using a preset method based on the reset first static elimination voltage (S2), stores the calculated value in the RAM 210, and resets the value of the second static elimination voltage (S3). In other words, the control circuit 200 (control means) automatically sets the value of the second static elimination voltage (value of the second voltage) based on the value of the first static elimination voltage (value of the first voltage) input via the static elimination operation unit 54 (input means).

[0081] The predetermined method is, for example, a table showing the correspondence relationship between the value of the first static elimination voltage and the value of the second static elimination voltage, and the result obtained through advance study is stored in the ROM 220. The conversion method may also be a function for obtaining the value of the second static elimination voltage using the value of the first static elimination voltage as a variable. In this case, the coefficients and constants of the function are obtained through advance study and stored in the ROM 220 as control parameters.

[0082] As a result of the above control, when a double-sided printing job is submitted after the operation to input the first static elimination voltage is performed in the static elimination operation unit 54, the CPU 201 applies the second static elimination voltage to the static elimination roller 51b at the automatically set value of the second static elimination voltage from the high-voltage power supply 55. Therefore, when the appropriate value of the static elimination voltage differs between double-sided printing and single-sided printing, a static elimination voltage of a value appropriate for double-sided printed sheets can be automatically applied.

[0083] Furthermore, according to this embodiment, the input work can be simplified compared to when the user inputs the first static elimination voltage and the second static elimination voltage separately, thereby improving usability.

[0084] On the other hand, when the user inputs the value of the second static elimination voltage by operating the static elimination operation unit 54 (S0N→S4Y), the CPU 201 stores the input value in the RAM 210 and resets the value of the second static elimination voltage (S5). In other words, if the value of the second static elimination voltage (second voltage) is input via the static elimination operation unit 54 (input means) after the control circuit 200 (control means) automatically sets the value of the second static elimination voltage (second voltage), the control circuit 200 resets the second static elimination voltage to the input value.

[0085] Therefore, even if the value of the second static elimination voltage is automatically set based on the input value of the first static elimination voltage, the user can further change the value of the second static elimination voltage at will.

[0086] The reason why the amount of charge on a high-resistivity sheet S differs between single-sided printing and double-sided printing will be explained below. Hereinafter, the surface of the sheet S on which an image is formed during single-sided printing and the surface of the sheet S on which an image is formed first during double-sided printing will be referred to as the "front surface Sf," and the opposite surface of the sheet S (the surface on which an image is formed later during double-sided printing) will be referred to as the "rear surface Sr." Meanwhile, the surface of the sheet S that contacts the discharge opposing roller 51a when passing through the discharge nip will be referred to as the "first surface Sa," and the surface of the sheet S that contacts the discharge roller 51b will be referred to as the "second surface Sb," to distinguish between the front surface Sf and the rear surface Sr.

[0087] In both single-sided and double-sided printing, the sheet S is subjected to the action of a bias electric field at the secondary transfer portion T2. ​​The bias electric field is formed so that the potential on the side of the secondary transfer roller 9 (outer roller) is the same polarity as the potential on the side of the opposing roller 21 (inner roller), which is the opposite polarity to the normal charging polarity of the toner. For the sake of explanation, the normal charging polarity of the toner is assumed to be negative. As described above, the electrostatic force generated by the bias electric field acts on the charged toner, causing the toner to transfer from the intermediate transfer belt 6 to the sheet S, thereby transferring the toner image.

[0088] If the sheet S is a high-resistivity sheet, when the sheet S passes through the secondary transfer portion T2, a positive charge is supplied from the secondary transfer roller 9 to one side of the sheet S (the side in contact with the secondary transfer roller 9), while a negative charge is generated on the other side of the sheet S due to dielectric polarization. As a result, both sides of the sheet S become charged. Because the sheet S has high resistance, the amount of charge does not easily attenuate even after it passes through the secondary transfer portion T2.

[0089] For this reason, when single-sided printing is performed on a high-resistivity sheet, as shown in Fig. 5, the sheet S reaches the discharge nip with its front surface Sf (first surface Sa) negatively charged and its back surface Sr (second surface Sb) positively charged, resulting in a large amount of charge. In the discharge nip, a first discharge voltage is applied to the discharge roller 51b so that a current flows in the opposite direction to the current during transfer (i.e., so that a negative charge is supplied to the back surface Sr of the sheet S). In this embodiment, the charge remaining on each surface of the sheet S after passing through the discharge nip is further discharged by the ionizer unit 52 (Fig. 2).

[0090] On the other hand, when double-sided printing is performed on a high-resistivity sheet, for the same reason as single-sided printing, when a toner image is transferred to the front surface Sf (front surface transfer), the front surface Sf (first surface Sa) of the sheet S is negatively charged and the back surface Sr (second surface Sb) is positively charged. Because the sheet S has high resistance, attenuation of the charge amount while being transported through the reversing unit 43 and the double-sided transport unit 44 is relatively small. Therefore, as shown in FIG. 6 , when a toner image is transferred to the back surface Sr of the sheet S (reverse surface transfer), the sheet S enters the secondary transfer unit T2 with the surface charge remaining on the sheet S.

[0091] Here, the front surface Sf and back surface Sr of the sheet S are switched between the time of front surface transfer and the time of back surface transfer. Therefore, immediately before back surface transfer, a positive charge remains on the back surface Sr (first surface Sa) of the sheet S that faces the intermediate transfer belt 6, and a negative charge remains on the front surface Sf (second surface Sb) that faces the secondary transfer roller 9. Meanwhile, at the secondary transfer portion T2, a positive charge is supplied from the secondary transfer roller 9 to the front surface Sf (first surface Sb) of the sheet S.

[0092] Therefore, a portion of the positive charge supplied from the secondary transfer roller 9 to the front surface Sf of the sheet S during back surface transfer is consumed (neutralized) to offset the negative charge on the front surface Sf of the sheet S that was generated during front surface transfer and remains until back surface transfer. Meanwhile, the magnitude of the transfer current (current flowing from the secondary transfer roller 9 to the sheet S) required for good transfer performance is essentially the same during single-sided printing and during front and back surface transfer in double-sided printing. As a result, in the case of a high-resistivity sheet, the amount of charge on the sheet S immediately after a toner image is transferred to the back surface Sr in double-sided printing is smaller than the amount of charge on the sheet S immediately after a toner image is transferred in single-sided printing. Furthermore, in the case of a high-resistivity sheet, the amount of charge on the double-sided printed sheet S when it reaches the discharge nip is smaller than the amount of charge on the single-sided printed sheet S when it reaches the discharge nip.

[0093] In addition, in the case of a high-resistivity sheet, the transfer voltage during backside transfer is lower than the transfer voltage during single-sided printing. For example, if the transfer voltage during single-sided printing for a high-resistivity sheet is +5 kV, the transfer voltage during backside transfer in double-sided printing is set to about +4 kV. This is because the surface charge of the sheet S generated during frontside transfer acts to strengthen the bias electric field at the secondary transfer section T2 during backside transfer. In other words, to make the strength of the bias electric field during frontside transfer and backside transfer uniform, the transfer voltage during backside transfer should be lower than that during frontside transfer. <Differences depending on sheet type>

[0094] In the above explanation, a case where a high resistance sheet such as synthetic paper is used has been described, but a low resistance sheet may exhibit different behavior.

[0095] In the case of a low-resistivity sheet, dielectric polarization is unlikely to occur, and most of the charge supplied from the secondary transfer roller 9 passes through the sheet in the thickness direction. Therefore, the amount of charge on the sheet S immediately after passing through the secondary transfer unit T2 is relatively small. Furthermore, the amount of charge on the sheet S is attenuated by rubbing against a grounded transport guide while the sheet S, which has passed through the secondary transfer unit T2 for the first time, is transported by the inverting unit 43 and the duplex transport unit 44 ( FIG. 1 ). Therefore, the negative charge on the front surface Sf of the sheet S, which is generated during front surface transfer and remains until back surface transfer, is small, and the positive charge supplied to the sheet S from the secondary transfer roller 9 during back surface transfer is less likely to be offset. Furthermore, in both single-sided and double-sided printing, the amount of charge on the sheet S is further attenuated by rubbing against a grounded transport guide, etc., during the process from when the sheet S passes through the secondary transfer unit T2 until when it is transported to the discharge nip.

[0096] As a result, with a low-resistivity sheet, there is often no significant difference in the amount of charge on the sheet S when it reaches the discharge nip between single-sided printing and double-sided printing. In this case, the second discharge voltage may be the same as the first discharge voltage. If the amount of charge on the sheet S is low enough not to cause problems such as sheets sticking to each other, both the first and second discharge voltages may be set to 0 V.

[0097] That is, the magnitude relationship between the absolute value of the second static elimination voltage and the absolute value of the first static elimination voltage may be changed depending on the type of sheet S. Specifically, for a high-resistance sheet (e.g., synthetic paper), the second static elimination voltage is automatically set to a value whose absolute value is smaller than that of the first static elimination voltage. For a low-resistance sheet (e.g., plain paper), the second static elimination voltage is automatically set to the same value as the first static elimination voltage.

[0098] This allows a more appropriate value to be set depending on the type of sheet S when the value of the second static elimination voltage is automatically set.

[0099] While it has been explained that the transfer voltage during backside transfer is lower for high-resistivity sheets than for single-sided printing, there are cases where the transfer voltage during backside transfer is higher for low-resistivity sheets than for single-sided printing. For example, this occurs when the moisture content of the sheet S decreases due to heating in the fixing device 40, causing the resistance value of the sheet S during backside transfer to be higher than that during frontside transfer. Furthermore, the transfer voltage during backside transfer is set higher than the transfer voltage during frontside transfer when, for example, toner with a higher resistance than the material of the sheet S adheres to the surface of the sheet S, causing the resistance value of the sheet S during backside transfer to be higher than that during frontside transfer.

[0100] That is, with a low resistance sheet, the amount of charge on the sheet S during double-sided printing may be greater than the amount of charge on the sheet S during single-sided printing. Therefore, for a low resistance sheet, the second static elimination voltage may be set to a value having an absolute value greater than that of the first static elimination voltage.

[0101] A description will be given of Example 2. Hereinafter, elements with the same reference numerals as those in Example 1 will be considered to have basically the same configurations and functions as those described in Example 1 unless otherwise specified, and differences from Example 1 will be mainly described.

[0102] The control circuit 200 of this embodiment can execute a mode (adjustment mode) for adjusting the static elimination voltage. The configuration of the control circuit 200 may be the same as that of the first embodiment (FIG. 8).

[0103] The adjustment mode is executed when the value of the static elimination voltage to be applied to the static elimination roller 51b to eliminate static electricity from the sheet S used in the image forming job is unknown. The adjustment mode is automatically executed when, for example, an image forming job is input and before an image is formed on the sheet S that will be the result. Alternatively, the adjustment mode may be executed based on the user's operation of the user operation unit 102 as a job independent of the image forming job.

[0104] The control procedure performed by the control circuit 200 will be described below with reference to the flowchart of Fig. 10. Unless otherwise specified, the CPU 201 executes each step in this flow.

[0105] When the adjustment mode is started, the CPU 201 acquires sheet information included in the job information (S10). The sheet information is attribute information such as the type (material and thickness), size, and brand of the sheet S used in the current job, and is set in advance via the user operation unit 102 or the like. The CPU 201 determines whether the sheet S is a high-resistance sheet or a low-resistance sheet based on the sheet information (S11). In this embodiment, the resistance value (volume resistivity) is 1×10 １３ A resistance value equal to or greater than the threshold value (Ω·cm) is determined to be a high resistance sheet, and a resistance value less than the threshold value is determined to be a low resistance sheet.

[0106] Furthermore, the CPU 201 determines whether the image forming operation mode for the current job is single-sided printing or double-sided printing (S12a, S12b), and sets the value of the neutralization voltage according to the result. That is, the control circuit 200 (control means) automatically sets the value of the first neutralization voltage (first voltage) and the value of the second neutralization voltage (second voltage) based on sheet information related to the sheet and information on whether an image is formed on only one side of the sheet or on both sides.

[0107] In the case of a high-resistance sheet and single-sided printing, the CPU 201 determines the set value of the static elimination voltage to be used for the current job as the value of the first static elimination voltage for the high-resistance sheet (S13a). In the case of a high-resistance sheet and double-sided printing, the CPU 201 determines the set value of the static elimination voltage to be used for the current job as the value of the second static elimination voltage for the high-resistance sheet (S13b). In the case of a low-resistance sheet and single-sided printing, the CPU 201 determines the set value of the static elimination voltage to be used for the current job as the value of the first static elimination voltage for the low-resistance sheet (S13c). In the case of a low-resistance sheet and double-sided printing, the CPU 201 determines the set value of the static elimination voltage to be used for the current job as the value of the second static elimination voltage for the low-resistance sheet (S13d).

[0108] The first and second static elimination voltages for the high-resistivity sheet and the first and second static elimination voltages for the low-resistivity sheet may be values ​​that are set in advance in the form of a table (paper type table in FIG. 8 ) according to sheet information and stored in the ROM 220. Furthermore, if the value of any of the static elimination voltages is input by the user through operation of the static elimination operation unit 54 or the like, the input value may be used as the value of each static elimination voltage. Furthermore, the value of each static elimination voltage may be set to a different value depending on other conditions such as environmental conditions (e.g., temperature and / or humidity) detected by the environmental sensor 13.

[0109] In the case of a high-resistivity sheet, the second static elimination voltage is set to a value smaller in absolute value than the first static elimination voltage. For example, the second static elimination voltage is set to a voltage 1 kV lower than the first static elimination voltage. In the case of a low-resistivity sheet, the second static elimination voltage is set to a value equal to or larger in absolute value than the first static elimination voltage.

[0110] Next, the CPU 201 causes the image forming apparatus 100 to perform double-sided printing, and causes the static eliminator 300 to neutralize the sheet S using the second static elimination voltage set in S12 or S13 (S14). At this time, the transfer voltage is applied to the secondary transfer roller 9 at the same voltage value as that of a normal image forming job.

[0111] The user measures the amount of charge on the discharged sheet S using a surface potential sensor or the like, and if it is determined that adjustment of the neutralization voltage is necessary, inputs the value of the second neutralization voltage to the neutralization operation unit 54 (S15N). In this case, the CPU 201 resets the second neutralization voltage to the value input by the user (S16), returns to S14, and continues the adjustment mode. On the other hand, if it is determined as a result of the measurement that the sheet S has been sufficiently neutralized, the user instructs completion of the adjustment mode via the user operation unit 102 (S15Y), and the CPU 201 ends the adjustment mode. Note that a double-sided printing job may be started immediately after the adjustment mode ends.

[0112] In this embodiment as well, the control means of the static elimination device 300 automatically sets the static elimination voltage (second static elimination voltage, second voltage) during double-sided printing to a value different from the static elimination voltage (first static elimination voltage, first voltage) during single-sided printing. This makes it possible to automatically apply a static elimination voltage of a value appropriate for double-sided printed sheets when the appropriate static elimination voltage differs between double-sided printing and single-sided printing.

[0113] Furthermore, according to this embodiment, the adjustment of the first or second static elimination voltage can be started using the first or second static elimination voltage automatically set by the control means as a starting point, thereby reducing the load of the adjustment work for the first and second static elimination voltages. (Other Embodiments)

[0114] In the above-described embodiments, the static eliminator 300 that eliminates static electricity from the sheet S has been described. However, the static eliminator 300 also functions as a charge adjustment device that adjusts the charge state of the sheet S by supplying charge to the sheet S via the static eliminator roller 51b as a charge supply member. The charge adjustment device may not necessarily reduce the amount of charge on the sheet S (i.e., it does not eliminate static electricity). For example, the charge adjustment device may adjust the amount of charge on each surface of the sheets S so that the opposing surfaces of overlapping sheets S are charged to the same polarity when the sheets S are stacked after processing by the charge adjustment device. Specifically, the charge adjustment device applies a voltage to every other sheet so that the electrostatic polarity of the sheet surface is reversed. In this case, since the opposing surfaces of overlapping sheets are charged to the same polarity, sticking of the sheets due to electrostatic force can be reduced. Furthermore, by applying the control described in each embodiment to the control of the voltage applied to the static eliminator roller 51b as a charge supply member, the charge state of the sheets S can be more appropriately adjusted.

[0115] In the above-described embodiments, the static elimination roller 51b, which is a roller member, has been described as an example of a contact-type static elimination member that comes into contact with the sheet S. However, the contact-type static elimination member is not limited to this, and may be, for example, a brush member in which conductive fibers or elongated conductive sheet pieces come into contact with the sheet S.

[0116] In addition, in the above-described embodiments, the method for setting the voltage applied to the static elimination roller 51b, which is a contact-type static elimination member, has been mainly described, but the method for setting the applied voltage described in each embodiment may also be applied to a non-contact static elimination member. For example, when a corotron or scorotron static eliminator is used instead of the static elimination roller 51b, the present technology may be applied to control the voltage applied to a discharge wire as a static elimination member.

[0117] Furthermore, in the above-described embodiments, the sheet S is mainly charged at a transfer section in an electrophotographic process. However, this is not limiting. In an image forming system other than the electrophotographic system, such as an inkjet system, the sheet S may be charged by frictional charging or peeling charging due to rubbing or peeling with a conveying guide, a conveying roller, or a conveying belt. Therefore, the present technology may also be applied to image forming systems other than the electrophotographic system. (Other Embodiments)

[0118] The present invention can also be realized by supplying a program that realizes one or more of the 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.The present invention can also be realized by a circuit (e.g., an ASIC) that realizes one or more of the functions.

[0119] According to the present invention, there are provided a static eliminator for eliminating static electricity from a sheet, an image forming system for forming an image on a sheet, and a charge adjusting device for adjusting the charge state of a sheet.

[0120] The present invention is not limited to the above-described embodiments, and various modifications and variations can be made without departing from the spirit and scope of the present invention. Therefore, the following claims are appended to apprise the public of the scope of the present invention.

[0121] This application claims priority based on Japanese Patent Application No. 2023-212350, filed December 15, 2023, the entire contents of which are incorporated herein by reference.

Claims

1. A static elimination device comprising: a static elimination member for eliminating static electricity from a sheet; a voltage application means for applying a voltage to the static elimination member; and a control means for setting the value of the second voltage to a value different from the first voltage, wherein the voltage applied by the voltage application means to the static elimination member when eliminating static electricity from a sheet having an image formed on only one side of the sheet is a first voltage, and the voltage applied by the voltage application means to the static elimination member when eliminating static electricity from a sheet having an image formed on both sides of the sheet is a second voltage.

2. The static eliminator according to claim 1, wherein the control means sets the value of the second voltage to a value whose absolute value is smaller than the value of the first voltage.

3. The static elimination device according to claim 1, wherein the control means sets the second voltage value to a value smaller in absolute value than the first voltage value when eliminating static electricity from synthetic paper, and sets the second voltage value to the same value as the first voltage value or a value larger in absolute value than the first voltage value when eliminating static electricity from plain paper.

4. The static elimination device according to claim 1, wherein the control means sets the value of the second voltage to a value smaller in absolute value than the value of the first voltage when eliminating static electricity from a sheet whose volume resistivity is equal to or greater than a threshold value, and sets the value of the second voltage to the same value as the value of the first voltage or a value larger in absolute value than the value of the first voltage when eliminating static electricity from a sheet whose volume resistivity is less than the threshold value.

5. The static elimination device according to claim 1, further comprising an input means configured to allow a user to input the value of the first voltage, and when the value of the first voltage is input via the input means, the control means sets the value of the second voltage based on the input value of the first voltage.

6. The static elimination device according to claim 5, wherein the input means is configured to allow a user to input a value of the second voltage, and when the value of the second voltage is input via the input means after the value of the second voltage has been set, the control means resets the second voltage to the input value.

7. The static eliminator according to claim 1, wherein the control means sets the value of the first voltage and the value of the second voltage based on sheet information relating to the sheet and information on whether an image is formed on only one side of the sheet or on both sides.

8. The static elimination device according to claim 7, wherein when a job is submitted to eliminate static electricity from a sheet using the static elimination member, the control means acquires the sheet information of the sheet to be used in the job and sets the value of the first voltage or the value of the second voltage to be used in the job.

9. The static eliminator according to claim 1, wherein the static eliminator is disposed so as to come into contact with the sheet being transported.

10. The static eliminator according to claim 9, further comprising an opposing roller opposed to said static eliminator, said static eliminator being a roller member forming a nip portion that sandwiches the sheet together with said opposing roller.

11. The static eliminator according to claim 9, wherein the voltage application means applies a DC voltage to the static eliminator member.

12. An image forming system comprising: an image forming device that forms an image on a sheet; and a static elimination device according to any one of claims 1 to 11 that eliminates static electricity from the sheet on which an image has been formed by the image forming device.

13. A charge adjustment device comprising: a charge supplying member which supplies a charge to a sheet; a voltage application means which applies a voltage to the charge supplying member; and a control means which sets the value of the second voltage to a value different from the first voltage, where the voltage applied by the voltage application means to the charge supplying member is a first voltage when adjusting the charged state of a sheet having an image formed on only one side of the sheet, and the voltage applied by the voltage application means to the charge supplying member is a second voltage when adjusting the charged state of a sheet having images formed on both sides of the sheet.

Images