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 eliminates static electricity on a sheet; voltage application means that applies voltage to the static eliminating member; and control means that, when a voltage applied to the static eliminating member by the voltage application means in eliminating static electricity on a sheet having an image formed only on a single side of the sheet is defined as a first voltage, and a voltage applied to the static eliminating member by the voltage application means in eliminating static electricity on a sheet having images formed on both sides of the sheet as a second voltage, automatically sets the value of the second voltage to a value different from that of the first voltage.SELECTED DRAWING: Figure 9

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 adjustment device for adjusting the charging state 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] In the above document, there is no description of changing the set value of the voltage applied to the static elimination roll depending on whether the image forming apparatus performs single-sided printing or double-sided printing. However, as a result of investigations conducted by the inventor, there were cases where the appropriate voltage value for adjusting the static elimination or charging state of the sheet differed between a singly printed sheet and a doubly printed sheet.

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

Means for Solving the Problems

[0006] One aspect of the present invention is 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 when eliminating static electricity from a sheet having an image formed on only one side of the sheet, the voltage applied by the voltage application means to the static elimination member is a first voltage, and when eliminating static electricity from a sheet having images formed on both sides of the sheet, the voltage applied by the voltage application means to the static elimination member is a second voltage. In this case, a control means for setting the value of the second voltage to a value different from the first voltage is provided, and the static elimination device is characterized by this.

[0007] Another aspect of the present invention is a charge supply member for supplying charge to a sheet, a voltage application means for applying a voltage to the charge supply member, and when adjusting the charging state of a sheet having an image formed on only one side of the sheet, the voltage applied by the voltage application means to the charge supply member is a first voltage, and when adjusting the charging state of a sheet having images formed on both sides of the sheet, the voltage applied by the voltage application means to the charge supply member is a second voltage. In this case, a control means for setting the value of the second voltage to a value different from the first voltage is provided, and the charge adjustment device is characterized by this.

Advantages of the Invention

[0008] According to the present invention, it is possible to provide a static elimination device, an image forming system, and a charge adjustment device that can more appropriately perform static elimination or adjustment of the charging 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 charge removing apparatus 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 (printing product). The sheet S, which is a recording material (recording medium), can use various sheet materials with different sizes and materials, such as paper like plain paper and thick paper, sheet materials with surface treatment like coated paper, sheet materials with special shapes like envelopes and index paper, plastic sheet materials, cloth, etc. Examples of plastic sheet materials are synthetic paper mainly made of synthetic resin and sheets for overhead projectors (OHT).

[0012] The charge removal device 300 is a device (static eliminator) that removes (reduces) the charge of the sheet S discharged from the image forming system 400. The charge removal device 300 can also be said to be a charge adjustment device for adjusting the charged state of the sheet S discharged from the image forming system 400. The charge removal device 300 may have functions other than the charge removal function (for example, a decurler function for correcting the curl of the sheet S). Further, although the charge removal device 300 of the present embodiment is arranged as an independent device from the image forming device 100, the charge removal device 300 may be incorporated in the housing of the image forming device 100.

[0013] The image forming system 400 may include optional devices other than the charge removal device 300. Examples of the optional devices are a high-capacity feeder (optional feeder) that supplies the sheet S to the image forming device 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 device 100.

[0014] <Image forming device> The schematic configuration of the image forming device 100 is shown in FIG. 1. The image forming device 100 includes an image forming unit 101 which is an intermediate transfer type electrophotographic mechanism. The image forming unit 101 includes four process units 11Y, 11M, 11C, 11K each having a photosensitive drum 1Y, 1M, 1C, 1K, and a transfer unit 15 having an intermediate transfer belt 6 and a secondary transfer roller 9.

[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 photosensitive drum 1Y, 1M, 1C, 1K is rotationally driven in a predetermined rotational direction A. The process units 11Y, 11M, 11C, 11K have substantially the same configuration except that the toner as the developer accommodated in the developing devices 4Y, 4M, 4C, 4K is different.

[0017] The transfer unit 15 includes an intermediate transfer belt 6 as an intermediate transfer member, a secondary transfer roller 9 as transfer means (secondary transfer means), primary transfer rollers 5Y, 5M, 5C, 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 disposed 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 rotational direction G. The secondary transfer roller 9 is in contact with the outer surface of the intermediate transfer belt 6 and is disposed so as to sandwich the intermediate transfer belt 6 together with the opposing roller 21 (secondary transfer opposing roller). A secondary transfer portion T2 as a transfer portion where the toner image is transferred to the sheet S is formed as a nip portion between the secondary transfer roller 9 and the intermediate transfer belt 6.

[0018] The image forming apparatus 100 includes a transfer power source 10 as voltage application means for forming a bias electric field for transferring a toner image to the secondary transfer portion T2. In this embodiment, the secondary transfer roller 9, which is the outer roller of the secondary transfer portion T2, is electrically connected to the transfer power 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 portion T2, a fixing device 40 for fixing the toner image to the sheet S, and a discharge roller pair 42 as a discharge unit for discharging the sheet S to the outside of the image forming apparatus 100.

[0020] The feeding unit 64 includes, for example, a pickup roller 65 that feeds out the uppermost sheet S from the storage unit 63 in the sheet feeding direction, and a separation roller pair 66 that conveys the fed-out sheet S while separating it one by one. The separation roller pair includes a conveyance roller that sends the uppermost sheet S in the sheet feeding direction, and a separation roller that abuts against the conveyance roller and forms a separation nip together with the conveyance roller. The separation roller prevents double feeding of the sheet S by applying a frictional force to the sheet S at the separation nip, thereby preventing the sheets S other than the uppermost sheet S from passing through the separation nip. The separation roller is an example of a separating member for separating the sheet S, and for example, a pad-shaped elastic member (rubber pad) may be used as the separating member.

[0021] The fixing device 40 is a heat fixing type device that has a fixing nip, sandwiches the sheet S at the fixing nip, and heats the toner image on the sheet S while conveying it. The fixing device 40 includes a heating member that contacts the surface of the sheet S on which the toner image is formed, a pressing member that forms the fixing nip together with the heating member, and a heat source that heats the heating member. As the heating member and the pressing member, for example, a belt member stretched over a plurality of rollers or a roller member having rigidity can be used. As the heat source, for example, a halogen lamp or an IH type induction heating mechanism can be used.

[0022] In addition, the image forming apparatus 100 includes a user operation unit 102 that is a user interface of the image forming system 400. The user operation unit 102 includes a display unit such as a liquid crystal panel that displays information to the user, and an input unit such as a physical button that receives input of information from the user and a touch panel function of the liquid crystal panel. The user can set setting information and execution conditions of the image forming operation for the image forming system 400 by operating the user operation unit 102. The setting information is, for example, attribute information such as the size, material, and brand of the sheet S stored in the storage unit 63. The execution condition of the image forming operation is, for example, the value of the transfer voltage.

[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 conveying the sheets S one by one and outputting a finished product. Hereinafter, a series of operations for forming an image on one sheet S by the image forming apparatus 100 is referred to as an image forming operation. The image forming job includes an image forming operation for at least one sheet S.

[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 an electrostatic latent image on the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K. The developing devices 4Y, 4M, 4C, and 4K supply yellow, magenta, cyan, and black toner to the photosensitive drums 1Y, 1M, 1C, and 1K respectively, and develop the electrostatic latent image into toner images of respective colors.

[0025] In addition, in this embodiment, a 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 each of 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 unit. A transfer voltage having a polarity opposite to the normal charging polarity of the toner is applied to the primary transfer rollers 5Y, 5M, 5C, and 5K by constant voltage control.

[0027] In this embodiment, the primary transfer rollers 5Y, 5M, 5C, and 5K are conductive rollers having a core metal and an elastic layer having conductivity formed on the outer peripheral side of the core metal. The elastic layer is formed of, for example, an ion conductive foamed rubber. The ion conductive foamed rubber is a foamed rubber material in which a conductive agent that exhibits ion conductivity is dispersed. As the conductive agent and the foamed rubber material, known materials for transfer rollers can be used. Each primary transfer roller 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 speeds of the photosensitive drums 1Y, 1M, 1C, and 1K. The peripheral speed in this embodiment is 150 to 470 mm / sec. As the intermediate transfer belt 6 rotates, toner images of other colors are transferred onto the toner image transferred at the primary transfer unit on the upstream side, thereby forming a full-color toner image on the intermediate transfer belt 6. The full-color toner image is carried on the intermediate transfer belt 6 and conveyed toward the secondary transfer unit T2.

[0029] In parallel with the creation of the toner image in the image forming unit 101, the feeding unit 64 feeds the sheets S one by one toward the image forming unit 101. The fed sheet S is conveyed to the secondary transfer unit T2 by the registration roller 8 in synchronization with the timing at which the toner image on the intermediate transfer belt 6 is conveyed to the secondary transfer unit T2. Then, in the secondary transfer unit T2, the toner image is transferred (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 having conductivity formed on the outer peripheral side of the core bar. The elastic layer is formed of, for example, an ion conductive foamed rubber. 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. The secondary transfer roller 9 can preferably be 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.

[0031] Further, the opposing roller 21 is a conductive roller having a core metal and an elastic layer of an electron-conductive foamed rubber formed on the outer peripheral side of the core metal. The electron-conductive foamed rubber is a foamed rubber material in which a conductive agent that exhibits electron conductivity is dispersed. As the conductive agent and the foamed rubber material, materials known as transfer rollers can be used. The opposing roller 21 is preferably used, for example, with 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.

[0032] 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 source 10 under constant voltage control. The transfer voltage is, for example, +1 to +7 kV, and is automatically adjusted so that a current of +40 to +120 μA flows from the secondary transfer roller 9 to the opposing roller 21. By applying the transfer voltage, a bias electric field is formed in the secondary transfer section T2 such that the potential of the secondary transfer roller 9 is opposite to the normal charging polarity of the toner with respect to the intermediate transfer belt 6. Due to this bias electric field, an electrostatic force in the 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 section T2 from the intermediate transfer belt 6, and thus the toner image is transferred to the sheet S.

[0033] In addition, immediately before the secondary transfer section T2, a conveyance guide 11 is provided to improve the positional accuracy of the sheet S with respect to the intermediate transfer belt 6. Further, the transfer residual toner remaining on the intermediate transfer belt 6 without being transferred to the sheet S is recovered by the belt cleaner 12 and reused for image formation.

[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 the 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, for example, an endless rubber belt. As the rubber belt, a belt made of ethylene propylene diene rubber (EPDM) with a width of 100 to 110 mm and a thickness of 1 to 3 mm can be used. Further, the rubber belt has holes with a diameter of 3 to 7 mm, and by generating a negative pressure inside the rubber belt using a fan, the sheet S can be stably carried on the rubber belt.

[0035] 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 by the discharge roller pair 42 toward the charge eliminating device 300.

[0036] In the case of an image forming operation (double-sided printing) in which images are formed on both sides of the sheet S, the sheet S that has passed through the fixing device 40 with a toner image transferred to the first side (front surface) is reversely conveyed. The image forming apparatus 100 includes a reversing unit 43 that reverses the sheet S and a double-sided conveyance unit 44 that conveys the reversed sheet S back toward the secondary transfer unit T2. The reversing unit 43 is a roller pair capable of normal and reverse rotation. The reversing unit 43 switches back the sheet S and feeds it into the double-sided conveyance unit 44. Then, the sheet S in a state where the first side (front surface) and the second side (back surface) are reversed is conveyed back to the secondary transfer unit T2 via the double-sided conveyance unit 44, and a toner image is transferred to the back surface of the sheet S. Then, the sheet S that has passed through the fixing device 40 with a toner image transferred to the back surface is discharged by the discharge roller pair 42 toward the charge eliminating device 300.

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

[0038] <Charge removing device> FIG. 2 is a schematic view of the charge removing device 300 in the first embodiment. In the present embodiment, the charge removing device 300 is connected to the downstream side of the image forming apparatus 100. The charge removing device 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 removing the charge of the sheet S (reducing the electrostatic charge on the sheet surface). By removing the charge of the sheet S, it is possible to prevent the sheets discharged from and stacked in the image forming system 400 from sticking to each other due to electrostatic adsorption force, and to reduce the likelihood of a decrease in the alignment of the sheet S due to the sticking of the sheets to each other. The charge removing device 300 includes a charge removing roller pair 51 as a contact type charge remover and an ionizer unit 52 as a non-contact type charge remover.

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

[0040] The charge removal counter roller 51a is connected to the ground potential GND. The charge removal counter roller 51a is electrically connected to, for example, the metal frame of the charge removal device 300 and is electrically grounded. The charge removal roller 51b is connected to the high-voltage power supply 55. The high-voltage power supply 55 is a voltage application means for applying a voltage (charge removal voltage) for removing charges from the sheet S to the charge removal roller 51b. In the present embodiment, the high-voltage power supply 55 applies a DC voltage having a polarity opposite to the transfer voltage applied by the transfer power supply 10 to the secondary transfer roller 9 to the charge removal roller 51b.

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

[0042] In the present embodiment, the charge removal roller 51b is a conductive roller having a core metal and an elastic layer having conductivity formed on the outer peripheral side of the core metal. The elastic layer is formed of, for example, an ion-conductive foamed rubber. The ion-conductive foamed rubber is a foamed rubber material in which a conductive agent that exhibits ion conductivity is dispersed. As the conductive agent and the foamed rubber material, known materials can be used. As the charge removal roller 51b, for example, 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 can be preferably used. The charge removal counter roller 51a is made of stainless steel (SUS) and uses a roller having an outer diameter of 20 to 25 mm. Note that as the charge removal roller 51b, a roller formed of a metal such as stainless steel may be used.

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

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

[0045] The above-described first ionizer 52a and second ionizer 52b are examples of non-contact static eliminators, and other non-contact static eliminators may be used. For example, a corotron type 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 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.

[0046] The sheet S conveyed from the image forming apparatus 100 to the static elimination device 300 first has most of its charges removed (rough removal) by the static elimination nip of the static elimination roller pair 51. Specifically, the static elimination voltage is set to the opposite polarity to the transfer voltage applied to the secondary transfer roller 9. The value of the static elimination voltage is set in the range of -1 kV to -6 kV.

[0047] In the secondary transfer unit T2 (Fig. 1), normally, 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 charge removal voltage having a polarity opposite to that of the transfer voltage to the charge removal roller 51b, a current flows between the charge removal roller 51b and the charge removal counter roller 51a so that positive charges are supplied to the first surface Sa of the sheet S and positive charges are supplied to the second surface Sb. In this way, by applying a charge removal voltage to the charge removal roller 51b and causing a current to flow through the sheet S in the charge removal nip, the amount of charged charges of the sheet S, which is the amount of charges carried on the first surface Sa and the second surface Sb of the sheet S, is reduced.

[0048] The sheet S that has passed through the charge removal roller pair 51 is further discharged 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 the ions irradiated from the first ionizer 52a and the second ionizer 52b, and the amount of charged charges of the sheet S is further reduced. The sheet S that has passed through the ionizer unit 52 is discharged to the outside of the charge removal device 300.

[0049] Incidentally, the amount of charged charges of the sheet S and the surface potential of the sheet S usually are proportional. Also, the amount of charged charges of the sheet S may be represented by the amount of charges per unit area of the sheet surface (surface charge density). For this reason, the "amount of charged charges" of the sheet S in the following description may be replaced with the surface potential of the sheet S or the surface charge density of the sheet S.

[0050] <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) that enables a user to input (set) the value of the voltage applied by the high-voltage power supply 55 (voltage application means) to the charge removal roller 51b (charge removal member).

[0051] The charge removal operation unit 54 includes a changeover switch 54a and voltage adjustment switches 54b and 54c. By operating the changeover switch 54a, the user can switch between the output (ON) and 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 switches 54b and 54c enable the user to adjust the value of the charge removal voltage.

[0052] 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 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 charge on the sheet S tends to increase. Therefore, when using plastic film or synthetic paper as the sheet S, it is conceivable to preset the value of the charge removal voltage according to the category of the sheet S 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, and environmental conditions of the environment where the charge removal device 300 is installed, 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.

[0053] In this embodiment, as the charge removal voltage setting, two types of voltage values can be set: a voltage value for single-sided printing (referred to as the first charge removal voltage) and a voltage value for double-sided printing (referred to as the second charge removal voltage). The first charge removal voltage (first voltage) is the charge removal voltage applied to the charge removal roller 51b when the image forming system 400 executes an image forming job (single-sided printing job) that forms an image on only one side of the sheet. The second charge removal voltage (second voltage) is the charge removal voltage applied to the charge removal roller 51b when the image forming system 400 executes an image forming job (double-sided printing job) that forms images on both sides of the sheet.

[0054] One of the voltage adjustment switches 54b is for the user to set (input) the value of the first static elimination voltage. The other voltage adjustment switch 54c is for the user to set (input) the value of the second static elimination voltage. The first static elimination voltage and the second static elimination voltage can have different values inputted. This is because, as will be described below, the values suitable for statically eliminating the sheet S (referred to as the appropriate values of the static elimination voltage) may be different between the case of statically eliminating the one-sided printed sheet S (during one-sided printing) and the case of statically eliminating the double-sided printed sheet S (during double-sided printing).

[0055] 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 (the first static elimination voltage or the second static elimination voltage) in two digits, and buttons (+ button and - button) for increasing and decreasing the value of the static elimination voltage. When the + button is pressed, the digit corresponding to it increases, and when the - button is pressed, the digit corresponding to it decreases.

[0056] The value displayed on the display unit is the absolute value of the static elimination voltage displayed as two digits in units of 0.1 kV. That is, the value obtained by multiplying the value displayed on the display units of the voltage adjustment switches 54b and 54c by -0.1 kV is the set value of the static elimination voltage. For example, when "45" is displayed on the display unit of the voltage adjustment switch 54b, the set value of the first static elimination voltage is -4.5 kV. From this state, if the - button in the tens place is pressed once and the + button in the units place is pressed twice, the display becomes "37", and the value of the first static elimination voltage is set to -3.7 kV.

[0057] In addition, when the display on the voltage adjustment switches 54b and 54c is 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 changeover switch 54a is turned off. This state can also be said to be a state where the high-voltage power supply 55 applies 0 V to the static elimination roller 51b.

[0058] Furthermore, the display method and input method of the static elimination voltage value are not limited to those described above. Instead of displaying the upper two digits of the static elimination voltage value, the static elimination voltage value itself may be displayed, or a numerical value representing the static elimination voltage level in, for example, 10 levels may be displayed. The static elimination voltage value may be displayed, for example, on the user operation unit 102 or on the screen of an external computer communicably connected to the image forming system 400. As an input method for the static elimination voltage value, a numeric keypad for numerical input may be provided on the static elimination operation unit 54, or it may be a touch panel operation of the user operation unit 102, or input may be accepted via an external computer. The user operation unit 102 is another example of an input means (setting means) that enables the user to input (set) the value of the voltage applied by the high-voltage power supply 55 (voltage application means) to the static elimination roller 51b (static elimination member). Even when the static elimination voltage value is input via the user operation unit 102 or an external computer, two types of voltage values, namely the first static elimination voltage and the second static elimination voltage, can be set respectively.

[0059] <Automatic Setting of the Second Static Elimination Voltage> 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 set to a value - 1 kV lower than the value of the first static elimination voltage. Furthermore, 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.

[0060] First, the appropriate value of the static elimination voltage during double-sided printing will be described. In the following description, a sheet with a volume resistivity of 1×10 13 Ω·cm or more is referred to as a "high-resistance sheet", and a sheet with a volume resistivity of less than 1×10 13 Ω·cm is referred to as a "low-resistance sheet". An example of a high-resistance sheet is synthetic paper, and an example of a low-resistance sheet is plain paper.

[0061] In the case of a high-resistance sheet, the amount of charged electricity when the sheet S printed on both sides reaches the charge-removing nip is less than the amount of charged electricity when the sheet S printed on one side reaches the charge-removing nip. The reason why the amount of charged electricity of the sheet S differs between single-sided printing and double-sided printing will be described later.

[0062] And, the less the amount of charged electricity of the sheet S at the time of reaching the charge-removing nip, the less the amount of charge that the charge-removing roller 51b needs to supply to the sheet S for charge removal of the sheet S. That is, in the case of a high-resistance sheet, the appropriate value of the charge-removing voltage (second charge-removing voltage) at the time of double-sided printing is a value with an absolute value smaller than the appropriate value of the charge-removing voltage (second charge-removing voltage) at the time of single-sided printing.

[0063] FIG. 7 shows an example of the appropriate value of the charge-removing voltage for a high-resistance sheet. The data in the figure represents the results for multiple types of synthetic papers with a volume resistivity of 1×10 13 ~1×10 14 Ω·cm. The horizontal axis is the thickness of the synthetic paper. The vertical axis represents the appropriate values of the charge-removing voltage (first charge-removing voltage, second charge-removing voltage) when each sheet is printed on one side or both sides under preset conditions and the sheet is charge-removed by the charge-removing roller 51b.

[0064] As can be seen from the figure, for any high-resistance sheet with different thicknesses, the appropriate value of the charge-removing voltage (second charge-removing voltage) at the time of double-sided printing is lower than the appropriate value of the charge-removing voltage (first charge-removing voltage) at the time of single-sided printing. That is, the appropriate value of the charge-removing voltage for a sheet with an image formed on both sides of the sheet is lower (has a smaller absolute value) than the appropriate value of the charge-removing voltage for a sheet with an image formed on only one side of the sheet.

[0065] Therefore, it is preferable that the value of the second discharge voltage is lower (has a smaller absolute value) than the value of the first discharge voltage. If the value of the second discharge voltage is equal to the first discharge voltage, the second discharge voltage becomes a value larger than the appropriate value of the discharge voltage, excessive charges are supplied to the sheet S, and discharge failure (charging with the opposite polarity before passing through the discharge nip) occurs, making it easier for the sheet S to stick. Also, for example, when setting multiple levels of discharge voltage according to the thickness of the sheet, for each sheet with a different thickness, the set value of the second discharge voltage is preferably set to a value lower (with a smaller absolute value) than the set value of the first discharge voltage.

[0066] Therefore, in this embodiment, the control means of the discharge device 300 is configured to be able to automatically set the value of the discharge voltage (the second discharge voltage, the second voltage) during double-sided printing to a value different from the discharge voltage (the first discharge voltage, the first voltage) during single-sided printing. More specifically, in this embodiment, when the first discharge voltage is set in the discharge operation unit 54, the value of the second discharge voltage is automatically set to a value having the same polarity as the first discharge voltage and a smaller absolute value than the first discharge voltage. "Automatically" means that the second discharge voltage is set to a value different from the first discharge voltage based on the judgment of the control means in a state where the user has not input a value different from the first discharge voltage as the value of the second discharge voltage.

[0067] <Control circuit> A block diagram of the control circuit 200 related to the control of the discharge voltage is shown in FIG. 8. The control circuit 200 is an example of the control means for controlling the operation of the discharge device 300. The control circuit 200 may be mounted inside the discharge device 300, or part or all of the functions of the control circuit 200 may be mounted in the image forming apparatus 100.

[0068] 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 information such as setting information related to the control of the static eliminator 300. Further, the control circuit 200 is connected to the user operation unit 102, the static elimination operation unit 54, the high-voltage power supply 55, and the transfer power supply 10.

[0069] The CPU 201 acquires information such as information related to the image forming job (job information), the setting of the static elimination voltage, and the value of the transfer voltage output by the transfer power supply 10, and stores it in the RAM 210. Here, the job information is, for example, 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 setting of the static elimination voltage is the values of the first static elimination voltage and the second static elimination voltage set by the user by operating the static elimination operation unit 54. Further, control parameters and various tables used for controlling the static elimination voltage are stored in the ROM 220.

[0070] In addition, the control circuit 200 is 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 eliminator 300 (image forming system 400). Further, the control circuit 200 can acquire the current value (static elimination current) flowing through the static elimination roller 51b based on the detection result of a current detection circuit 55a provided inside the high-voltage power supply 55.

[0071] <Control Flow> The procedure for controlling the static elimination 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 of this flow is the CPU 201. Further, this flow is continuously executed while the user can set the value of the first static elimination voltage via the static elimination operation unit 54.

[0072] 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). Further, the CPU 201 calculates the value of the second static elimination voltage in 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). That is, the control circuit 200 (control means) sets the value of the second static elimination voltage (second voltage value) based on the value of the first static elimination voltage (first voltage value) input via the static elimination operation unit 54 (input means).

[0073] The preset method is, for example, a table representing the correspondence between the value of the first static elimination voltage and the value of the second static elimination voltage, and it is assumed that the result obtained through prior consideration is stored in the ROM 220. Further, the conversion method may be a function for obtaining the value of the second static elimination voltage with the value of the first static elimination voltage as a variable. In this case, the coefficients and constants of the function are obtained through prior consideration and stored in the ROM 220 as control parameters.

[0074] As a result of the above control, when a duplex printing job is input after the operation of inputting the first static elimination voltage is performed in the static elimination operation unit 54, the CPU 201 automatically applies the second static elimination voltage from the high-voltage power supply 55 to the static elimination roller 51b at the set value of the second static elimination voltage. Therefore, when the appropriate value of the static elimination voltage is different between duplex printing and single-sided printing, the static elimination voltage with a value suitable for the duplex-printed sheet can be automatically applied.

[0075] Further, according to the present embodiment, compared with the case where the user inputs the first static elimination voltage and the second static elimination voltage individually, the input operation can be made simpler, and the usability can be improved.

[0076] On the one hand, when the user inputs the value of the second discharging voltage by operating the discharging operation unit 54 (S0N→S4Y), the CPU 201 stores the input value in the RAM 210 and resets the value of the second discharging voltage (S5). In other words, when the value of the second discharging voltage (second voltage) is automatically set and then the value of the second discharging voltage is input via the discharging operation unit 54 (input means), the control circuit 200 (control means) resets the second discharging voltage to the input value.

[0077] Therefore, even when the value of the second discharging voltage is automatically set based on the input value of the first discharging voltage, the user can arbitrarily change the value of the second discharging voltage.

[0078] <Reasons for the difference in the amount of charged electricity> The reasons for the difference in the amount of charged electricity of the sheet S between single-sided printing and double-sided printing for the high-resistance sheet will be explained. Hereinafter, the surface of the sheet S on which the image is formed during single-sided printing and the surface of the sheet S on which the image is formed first during double-sided printing are referred to as "front surface Sf", and the opposite surface of the sheet S (the surface on which the image is formed later during double-sided printing) is referred to as "back surface Sr". On the other hand, the surface of the sheet S that contacts the discharging counter roller 51a when passing through the discharging nip is referred to as "first surface Sa", and the surface of the sheet S that contacts the discharging roller 51b is referred to as "second surface Sb", which is distinguished from the front surface Sf and the back surface Sr.

[0079] Common to both single-sided printing and double-sided printing, the sheet S is subjected to the action of a bias electric field in the secondary transfer unit T2. The bias electric field is formed such that the potential on the secondary transfer roller 9 (outer roller) side has the same polarity as the opposite polarity of the normal charging polarity of the toner with respect to the potential on the counter roller 21 (inner roller) side. Hereinafter, for the sake of explanation, it is assumed that the normal charging polarity of the toner is negative. As described above, the electrostatic force generated by the bias electric field acts on the charged toner, so that the toner is transferred from the intermediate transfer belt 6 to the sheet S, and the transfer of the toner image is performed.

[0080] When the sheet S is a high-resistance sheet, when the sheet S passes through the secondary transfer unit T2, a positive charge is supplied from the secondary transfer roller 9 to one surface of the sheet S (the surface in contact with the secondary transfer roller 9), while a negative charge is generated on the other surface of the sheet S due to dielectric polarization. As a result, both surfaces of the sheet S are in a charged state. Since the sheet S is of high resistance, the amount of charged charge does not easily decay even after passing through the secondary transfer unit T2.

[0081] Therefore, when performing single-sided printing on a high-resistance sheet, as shown in FIG. 5, the sheet S reaches the charge removal nip in a state where the front surface Sf (the first surface Sa) is negatively charged and the back surface Sr (the second surface Sb) is positively charged, and the amount of its charged charge is large. In the charge removal nip, a first charge removal voltage is applied to the charge removal roller 51b so that a current flows in the direction opposite to the current during transfer (that is, a negative charge is supplied to the back surface Sr of the sheet S). Even after passing through the charge removal nip, the charges remaining on each surface of the sheet S are further removed by the ionizer unit 52 (FIG. 2) in this embodiment.

[0082] On the other hand, when performing double-sided printing on a high-resistance sheet, for the same reason as during single-sided printing, when transferring the toner image to the front surface Sf (during front surface transfer), the front surface Sf (the first surface Sa) of the sheet S is negatively charged and the back surface Sr (the second surface Sb) is positively charged. Since the sheet S is of high resistance, the decay of the amount of charged charge during conveyance through the inversion unit 43 and the double-sided conveyance unit 44 is relatively small. Therefore, as shown in FIG. 6, when transferring the toner image to the back surface Sr of the sheet S (during back surface transfer), the sheet S enters the secondary transfer unit T2 with the surface charge remaining on the sheet S.

[0083] Here, between the front surface transfer and the back surface transfer, the front surface Sf and the back surface Sr of the sheet S are interchanged. Therefore, immediately before the back surface transfer, the sheet S has a positive charge remaining on the back surface Sr (the first surface Sa) facing the intermediate transfer belt 6 and a negative charge remaining on the front surface Sf (the second surface Sb) facing the secondary transfer roller 9. On the other hand, in the secondary transfer unit T2, a positive charge is supplied from the secondary transfer roller 9 to the front surface Sf (the first surface Sb) of the sheet S.

[0084] Therefore, a part of the positive charge supplied from the secondary transfer roller 9 to the surface Sf of the sheet S during backside transfer neutralizes (consumes) the negative charge on the surface Sf of the sheet S that was generated during frontside transfer and remains until backside transfer. On the other hand, the magnitude of the transfer current (the current flowing from the secondary transfer roller 9 to the sheet S) for obtaining good transfer performance is basically the same between single-sided printing and during frontside and backside transfers in double-sided printing. As a result, in the case of a high-resistance sheet, the amount of charged charge of the sheet S immediately after toner image transfer to the backside Sr in double-sided printing is smaller than the amount of charged charge of the sheet S immediately after toner image transfer in single-sided printing. And in the case of a high-resistance sheet, the amount of charged charge when the double-sided printed sheet S reaches the charge elimination nip is less than the amount of charged charge when the single-sided printed sheet S reaches the charge elimination nip.

[0085] In addition, in the case of a high-resistance sheet, the transfer voltage during backside transfer is lower than the transfer voltage during single-sided printing. For example, when the transfer voltage during single-sided printing for a high-resistance 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 in a direction to strengthen the bias electric field in the secondary transfer section T2 during backside transfer. That is, in order to make the intensity of the bias electric field uniform between frontside transfer and backside transfer, the transfer voltage during backside transfer should be made lower than that during frontside transfer.

[0086] <Differences due to sheet type> In the above description, the case of using a high-resistance sheet such as synthetic paper has been described, but in the case of a low-resistance sheet, different behaviors may be shown.

[0087] In the case of a low-resistance sheet, dielectric polarization is less likely to occur, and most of the charges supplied from the secondary transfer roller 9 pass through the sheet in the thickness direction. Therefore, the amount of charged charges on the sheet S immediately after passing through the secondary transfer section T2 is relatively small. Also, while the sheet S that has passed through the secondary transfer section T2 for the first time is being conveyed by the inversion section 43 and the duplex conveyance section 44 (Fig. 1), the charged charge amount of the sheet S decays by rubbing against the grounded conveyance guide. Therefore, there is little negative charge on the surface Sf of the sheet S that remains until the backside transfer occurs during the surface transfer, and it is difficult for the positive charges supplied from the secondary transfer roller 9 to the sheet S during the backside transfer to be offset. Furthermore, in common for both single-sided printing and double-sided printing, in the process from when the sheet S passes through the secondary transfer section T2 until it is conveyed to the static elimination nip, the charged charge amount of the sheet S further decays by rubbing against the grounded conveyance guide or the like.

[0088] As a result, in the case of a low-resistance sheet, there is often little difference in the charged charge amount of the sheet S when reaching the static elimination nip between single-sided printing and double-sided printing. In this case, the second static elimination voltage may be the same value as the first static elimination voltage. When the charged charge amount of the sheet S does not cause inconveniences such as sticking of the sheets, both the first static elimination voltage and the second static elimination voltage may be set to 0V.

[0089] That is, according to the type of the sheet S, 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. Specifically, for a high-resistance sheet (e.g., synthetic paper), the second static elimination voltage is automatically set to a value with an absolute value 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.

[0090] Thereby, when automatically setting the value of the second static elimination voltage, a more appropriate value can be set according to the type of the sheet S.

[0091] Although it has been explained that the transfer voltage during backside transfer is lower than the transfer voltage during single-sided printing for a high-resistance sheet, for a low-resistance sheet, the transfer voltage during backside transfer may rather be higher than the transfer voltage during single-sided printing. For example, when the moisture content of the sheet S decreases due to heating in the fixing device 40, the resistance value of the sheet S during backside transfer becomes higher than that during frontside transfer. Also, setting the transfer voltage during backside transfer to be higher than the transfer voltage during frontside transfer is, for example, when toner with a higher resistance than the material of the sheet S adheres to the surface of the sheet S, and the resistance value of the sheet S during backside transfer becomes higher than that during frontside transfer.

[0092] That is, for a low-resistance sheet, the amount of charged charge of the sheet S during double-sided printing may be larger than the amount of charged charge of the sheet S during single-sided printing. Therefore, for a low-resistance sheet, the second charge removal voltage may be set to a value with an absolute value larger than that of the first charge removal voltage.

[0093] 《Example 2》 Example 2 will be described. Hereinafter, elements denoted by the same reference numerals as those in Example 1 have basically the same configuration and operation as those described in Example 1 unless otherwise specified, and the parts different from Example 1 will be mainly described.

[0094] The control circuit 200 of this example is capable of executing a mode (adjustment mode) for adjusting the charge removal voltage. The configuration of the control circuit 200 may be the same as that of Example 1 (FIG. 8).

[0095] The adjustment mode is executed when the value of the charge removal voltage to be applied to the charge removal roller 51b is unknown in order to remove the charge of the sheet S used for the image formation job. The adjustment mode is automatically executed, for example, when an image formation job is input, before forming an image on the sheet S that becomes the product. Alternatively, the adjustment mode may be executed as a job independent of the image formation job based on an operation of the user operation unit 102 by the user.

[0096] The control procedure performed by the control circuit 200 will be described below with reference to the flowchart of FIG. 10. Hereinafter, unless otherwise specified, the execution entity of each step of this flow is the CPU 201.

[0097] When starting the adjustment mode, the CPU 201 acquires the 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 for the current job, and is preset 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, with a resistance value (volume resistivity) of 1×10 13 Ω·cm as the threshold, if the resistance value is equal to or greater than the threshold, it is determined to be a high-resistance sheet, and if the resistance value is less than the threshold, it is determined to be a low-resistance sheet.

[0098] Furthermore, the CPU 201 determines whether the image forming operation mode in the current job is single-sided printing or double-sided printing (S12a, S12b), and sets the value of the charge removal voltage according to the result. That is, the control circuit 200 (control means) automatically sets the value of the first charge removal voltage (first voltage) and the value of the second charge removal voltage (second voltage) based on the sheet information regarding the sheet and the information on whether the image is formed on only one side of the sheet or on both sides of the sheet.

[0099] In the case of a high-resistance sheet and single-sided printing, the CPU 201 determines the set value of the charge removal voltage used for the current job as the value of the first charge removal voltage for high-resistance sheets (S13a). In the case of a high-resistance sheet and double-sided printing, the CPU 201 determines the set value of the charge removal voltage used for the current job as the value of the second charge removal voltage for high-resistance sheets (S13b). In the case of a low-resistance sheet and single-sided printing, the CPU 201 determines the set value of the charge removal voltage used for the current job as the value of the first charge removal voltage for low-resistance sheets (S13c). In the case of a low-resistance sheet and double-sided printing, the CPU 201 determines the set value of the charge removal voltage used for the current job as the value of the second charge removal voltage for low-resistance sheets (S13d).

[0100] The first and second charge-removing voltages for the high-resistance sheet, and the first and second charge-removing voltages for the low-resistance sheet may be values that are preset and stored in the ROM 220 in the form of a table (paper type table in FIG. 8), for example, according to the sheet information. Further, when a value of any of the charge-removing voltages has been input from the user by an operation of the charge-removing operation unit 54 or the like, the input value may be used as the value of each of the charge-removing voltages. Further, the values of the respective charge-removing voltages may be set to different values according to other conditions such as environmental conditions (for example, temperature and / or humidity) detected by the environmental sensor 13.

[0101] Compared with the case of the high-resistance sheet, the absolute value of the second charge-removing voltage is set to a value smaller than the value of the first charge-removing voltage. As an example, the second charge-removing voltage is set to be 1 kV lower than the first charge-removing voltage. Further, compared with the case of the low-resistance sheet, the second charge-removing voltage is set to the same value as the value of the first charge-removing voltage or a value having an absolute value larger than the first charge-removing voltage.

[0102] Next, the CPU 201 causes the image forming apparatus 100 to execute double-sided printing, and uses the second charge-removing voltage set in S12 or S13 to charge-remove the sheet S by the charge-removing device 300 (S14). At this time, the same voltage value as that in a normal image forming job is applied as the transfer voltage to the secondary transfer roller 9.

[0103] The user measures the amount of charged charge of the discharged sheet S using a surface potential sensor or the like, and if it is determined that adjustment of the charge-removing voltage is necessary, the user inputs the value of the second charge-removing voltage to the charge-removing operation unit 54 (S15N). In this case, the CPU 201 re-sets the second charge-removing voltage with the value input by the user (S16), and returns to S14 to continue the adjustment mode. On the other hand, if it is determined as a result of the measurement that the sheet S is sufficiently charge-removed, 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 after the adjustment mode is ended, a double-sided printing job may be started continuously.

[0104] Also in this embodiment, the control means of the static eliminator 300 sets 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. Thereby, when the appropriate value of the static elimination voltage is different between double-sided printing and single-sided printing, the static elimination voltage with a value suitable for the sheet printed on both sides can be automatically applied.

[0105] Further, according to this embodiment, starting from the first static elimination voltage or the second static elimination voltage automatically set by the control means, the adjustment of the first static elimination voltage or the second static elimination voltage can be started. Therefore, the load of the adjustment work of the first static elimination voltage and the second static elimination voltage can be reduced.

[0106] 《Other Embodiments》 In each of the above-described embodiments, the static eliminator 300 that eliminates static electricity from the sheet S has been described. However, the static eliminator 300 has a function as a charge adjustment device that adjusts the charged state of the sheet S by supplying charge to the sheet S via the 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 amount of charged electricity on each surface of the sheet S may be adjusted so that the mutually facing surfaces of the overlapping sheets are charged with the same polarity. Specifically, the charge adjustment device applies a voltage so that the electrostatic polarity on the surface of the sheet is reversed every other sheet among a plurality of sheets. In this case, since the mutually facing surfaces of the overlapping sheets are charged with the same polarity, the 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 the charge supply member, the charged state of the sheet S can be adjusted more appropriately.

[0107] Also, in each of the above-described embodiments, as an example of the contact-type static elimination member that contacts the sheet S, the static elimination roller 51b that is a roller member has been described. The contact-type static elimination member is not limited to this, and for example, a brush member in which a conductive fiber or an elongated conductive sheet piece contacts the sheet S may be used.

[0108] In addition, in each of the above-described embodiments, the method for setting the voltage applied to the charge removing roller 51b, which is a contact-type charge removing member, has been mainly described. However, the present invention is not limited thereto, and the method for setting the applied voltage described in each embodiment may be applied to a non-contact-type charge removing member. For example, when a corotron or scorotron charge remover is used instead of the charge removing roller 51b, the present technology may be applied to the control of the voltage applied to the discharge wire as the charge removing member.

[0109] In addition, in each of the above-described embodiments, it has been mainly described that charging of the sheet S occurs in the transfer section in the electrophotographic process. However, the present invention is not limited thereto, and in an image forming system other than the electrophotographic method, such as an inkjet method, charging of the sheet S may occur due to frictional charging or peeling charging caused by rubbing or peeling with a conveyance guide, conveyance roller, conveyance belt, or the like. Therefore, the present technology may be applied to an image forming system other than the electrophotographic method.

[0110] (Other Embodiments) The present invention can also be realized by supplying a program that realizes one or more functions of the above-described embodiments to a system or apparatus via a network or a storage medium, and causing one or more processors in a computer of the system or apparatus to read and execute the program. Further, it can also be realized by a circuit (for example, ASIC) that realizes one or more functions.

Description of Reference Numerals

[0111] 51b... Charge removing member, charge supply member (charge removing roller) / 54... Input means (charge removing operation section) / 55... Voltage application means (high voltage power supply 55) / 200... Control means (control circuit)

Claims

1. A static eliminator member for eliminating static electricity from a sheet, voltage application means for applying a voltage to the static eliminator member, When eliminating static electricity from a sheet with an image formed on only one side of the sheet, the voltage applied by the voltage application means to the static eliminator member is set as a first voltage, and when eliminating static electricity from a sheet with images formed on both sides of the sheet, the voltage applied by the voltage application means to the static eliminator member is set as a second voltage. Control means for setting the value of the second voltage to a value different from the first voltage, A static elimination device characterized by comprising the above.

2. The control means sets the value of the second voltage to a value with an absolute value smaller than the value of the first voltage. The static elimination device according to claim 1, characterized by the above.

3. When the control means eliminates static electricity from synthetic paper, it sets the value of the second voltage to a value with an absolute value smaller than the value of the first voltage. When eliminating static electricity from plain paper, it sets the value of the second voltage to the same value as the value of the first voltage or a value with an absolute value larger than the value of the first voltage. The static elimination device according to claim 1, characterized by the above.

4. When the control means eliminates static electricity from a sheet with a volume resistivity equal to or higher than a threshold value, it sets the value of the second voltage to a value with an absolute value smaller than the value of the first voltage. When eliminating static electricity from a sheet with a volume resistivity lower than the threshold value, it sets the value of the second voltage to the same value as the value of the first voltage or a value with an absolute value larger than the value of the first voltage. The static elimination device according to claim 1, characterized by the above.

5. It comprises input means provided so that the user can input the value of the first voltage. 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. The static elimination device according to claim 1, characterized by the above.

6. The input means is provided so that the user can input the value of the second voltage. After setting the value of the second voltage, when the value of the second voltage is input via the input means, the control means resets the second voltage to the input value. The static elimination device according to claim 5, characterized by the above.

7. The control means sets the value of the first voltage and the value of the second voltage based on sheet information regarding the sheet and information on whether an image is formed on only one side of the sheet or on both sides of the sheet. The static elimination device according to claim 1, characterized by the above.

8. When a job for discharging the sheet by the discharge member is input, the control means acquires the sheet information of the sheet used for the job and sets the value of the first voltage or the value of the second voltage used in the job. The static eliminator device according to claim 7, characterized in that.

9. The static eliminator member is arranged so as to contact the conveyed sheet. The static eliminator device according to claim 1, characterized in that.

10. The static eliminator device further includes an opposing roller facing the static eliminator member. The static eliminator member is a roller member that forms a nip portion that sandwiches the sheet together with the opposing roller. The static eliminator device according to claim 9, characterized in that.

11. The voltage application means applies a DC voltage to the static eliminator member. The static eliminator device according to claim 9, characterized in that.

12. An image forming apparatus that forms an image on a sheet; The static eliminator device according to any one of claims 1 to 11, which discharges the sheet on which an image is formed by the image forming apparatus; An image forming system, characterized by comprising.

13. A charge supply member that supplies charge to the sheet; Voltage application means for applying a voltage to the charge supply member; When adjusting the charging state of a sheet on which an image is formed on only one side of the sheet, the voltage applied by the voltage application means to the charge supply member is set as the first voltage, and when adjusting the charging state of a sheet on which images are formed on both sides of the sheet, the voltage applied by the voltage application means to the charge supply member is set as the second voltage. In this case, control means for setting the value of the second voltage to a value different from the first voltage; A charge adjustment device, characterized by comprising.

Images