Static eliminator, and image forming apparatus

Abstract

To provide a static eliminator capable of performing an operation of reaching a contact position from a separation position of a static elimination roller, without expanding a paper sheet interval between a preceding sheet for which static elimination is unnecessary and a following sheet for which the static elimination is necessary.SOLUTION: When plain paper sheets are continuously conveyed at paper sheet intervals (T1, time t0 to time t1), the plain paper sheets are statically eliminated only by a non-contact type static eliminator. After a front end of a preceding paper sheet reaches a nipping area at a static elimination nipping part (time t1), a reaching operation of a contact / separation mechanism 150 is started at time t10 after elapsing of a reaching operation start time "400 msec". In this manner, before a rear end of the preceding plain paper passes through the nipping area (time t2), movement of a static elimination roller is started from a separation position to a contact position; and before a front end of a following synthetic paper sheet reaches the nipping area (time t31), the movement of the static elimination roller to the contact position is completed. Thus, the movement of the static elimination roller from the separation position to the contact position can be completed without expanding a paper sheet interval (T1).SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a static eliminator that eliminates static electricity from a sheet, and an image forming apparatus including the static eliminator. [Background technology]

[0002] In an electrophotographic image forming apparatus, a high transfer voltage is applied when a toner image is transferred to a sheet, so the sheet after transfer may become charged. If the sheet after transfer is not neutralized, when the sheet is discharged onto the discharge tray, it may electrostatically adhere to a sheet previously stacked on the discharge tray, causing a stacking error, or a sheet being conveyed toward the discharge tray may electrostatically adhere to the sheet midway through the conveyance, causing a conveyance error. Therefore, the image forming apparatus is provided with a neutralization device that neutralizes the sheet after transfer (Patent Document 1).

[0003] The static eliminator described in Patent Document 1 has a contact type static eliminator capable of eliminating static electricity by contacting a sheet, and a non-contact type static eliminator capable of eliminating static electricity without contacting a sheet. In the static eliminator described in Patent Document 1, static electricity is eliminated from the sheet by using either the contact type static eliminator or the non-contact type static eliminator, or by using both the contact type static eliminator and the non-contact type static eliminator, depending on the difference in surface resistance of the sheet. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-167169 A Summary of the Invention [Problem to be solved by the invention]

[0005] Conventionally, when a contact type static elimination device is not used, in order to prevent wear of a pair of static elimination rollers of a contact type static elimination device, one of the static elimination rollers is moved from a contact position where it is in contact with the other static elimination roller to a separated position where it is not in contact with the other static elimination roller. Therefore, when a sheet that does not require static elimination by a contact type static elimination device is conveyed following a sheet that requires static elimination by a contact type static elimination device, it is necessary to move one of the static elimination rollers from the separated position to the contact position in order to perform static elimination by the contact type static elimination device. Conventionally, in order to allow the sheet that requires static elimination to arrive after the static elimination roller moves to the contact position, the distance from the leading edge of the preceding sheet to the leading edge of the succeeding sheet (called the paper distance) is widened, but this can cause a problem that the productivity of the image forming apparatus is reduced.

[0006] The present invention has been made in consideration of the above-mentioned problems, and aims to provide an electrostatic elimination device and an image forming apparatus that can perform the electrostatic elimination roller moving from the separation position to the contact position without widening the gap between the preceding sheet that does not require electrostatic elimination and the following sheet that requires electrostatic elimination. [Means for solving the problem]

[0007] A static elimination device according to one embodiment of the present invention has a first static elimination member and a second static elimination member that comes into contact with the first static elimination member to form a static elimination nip portion, and includes a contact type static elimination section that eliminates electric charges on a sheet that passes through the static elimination nip portion by application of a voltage, a transport section that transports the sheet to the static elimination nip portion, a contact and separation mechanism that can move the first static elimination member between a contact position where it comes into contact with the second static elimination member and a spaced position where it is spaced from the second static elimination member, and a contact and separation mechanism that, when a first type of sheet does not require static elimination by the contact type static elimination section, the first static elimination member is positioned at the spaced position so as not to perform static elimination, and when a second type of sheet requires static elimination by the contact type static elimination section, the first static elimination member is positioned at the spaced position so as not to perform static elimination, and a control unit that positions the first charge removal member at the abutment position to remove charge when the first type of sheet and the second type of sheet following the first type of sheet are transported by the transport unit, and the control unit is capable of executing a mode in which, in the sheet transport direction, when the first type of sheet and the second type of sheet are transported by the transport unit, the control unit starts moving the first charge removal member from the separation position to the abutment position by the contact / separation mechanism before the rear end of the first type of sheet passes through the nip area of ​​the charge removal nip section, and completes moving the first charge removal member to the abutment position before the leading edge of the following second type of sheet reaches the nip area. Effect of the Invention

[0008] According to the present invention, the first discharge member can be attached from the separated position to the abutment position without widening the gap between the preceding first type sheet that does not require discharge and the following second type sheet that requires discharge. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic diagram showing an image forming apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a block diagram showing a control system of the image forming apparatus. [Diagram 3] FIG. 2 is a schematic diagram showing a contact type static eliminator. [Figure 4] (a) is a schematic diagram showing the non-contact static electricity removing device before the sheet passes, and (b) is a schematic diagram showing the non-contact static electricity removing device after the sheet passes. [Diagram 5]5A and 5B are schematic diagrams showing a contact / separation mechanism when the static electricity removal roller is in a contact position and when the static electricity removal roller is in a separated position; [Figure 6] 5 is a flowchart showing a discharge operation process of the charge removing roller. [Figure 7] 6 is a flowchart showing a process of attaching an electricity removing roller. [Figure 8] 4 is a flowchart showing a charge removal control process according to the embodiment. [Figure 9] 5 is a timing chart for explaining the attachment operation of the charge removing roller in the embodiment. [Figure 10] FIG. [Figure 11] FIG. 13 is a diagram showing a setting input screen on which settings can be input for each type of sheet. [Figure 12] 11 is a timing chart for explaining a fastening operation of a discharging roller in a conventional example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] <Image forming device> The present embodiment will be described below. First, the schematic configuration of the image forming apparatus of the present embodiment will be described with reference to FIG. 1. The image forming apparatus 101 shown in FIG. 1 is a tandem-type full-color printer of an electrophotographic system. As shown in FIG. 1, the image forming apparatus 101 includes a printing apparatus 102, a static eliminator 103, and a finisher 104. Note that, in this example, the printing apparatus 102, the static eliminator 103, and the finisher 104 are configured in separate housings and are connected to each other, but the present invention is not limited to this. For example, the printing apparatus 102 and the static eliminator 103 may be provided in the same housing.

[0011] The printing device 102 forms a toner image on a sheet based on image data sent from an external device, such as a document reading device connected to the printing device 102 or a personal computer (not shown). Sheets are supplied to the printing device 102 from cassettes 111 and 112 capable of accommodating various sheets. Only the topmost sheet among the sheets accommodated in the cassettes 111 and 112 is transported to a transport path 113. Examples of the sheet include sheet materials such as thin paper, plain paper, thick paper, rough paper, textured paper, and coated paper.

[0012] The printing device 102 has image forming stations 114, 115, 116, and 117 that form images of yellow, magenta, cyan, and black. In the image forming stations 114, 115, 116, and 117, a toner image is formed on the photosensitive drum of each station. The toner image formed on the photosensitive drum is primarily transferred to an intermediate transfer belt 118 as an image carrier in response to a primary transfer voltage being applied to the primary transfer roller. Then, the intermediate transfer belt 118 rotates clockwise, so that the toner image reaches a secondary transfer portion N2. The secondary transfer portion N2 is a transfer nip portion formed by abutting a secondary transfer inner roller 119 and a secondary transfer outer roller 120, and in response to a secondary transfer voltage being applied to the secondary transfer inner roller 119 as a transfer member by a power source (not shown), the toner image on the intermediate transfer belt 118 (on the image carrier) is secondarily transferred to a sheet conveyed through a conveying path 113. The image forming stations 114 , 115 , 116 , and 117 and the primary transfer roller constitute an image forming section 190 that forms a toner image on the intermediate transfer belt 118 .

[0013] The toner image secondarily transferred to the sheet is fixed to the sheet by applying heat and pressure by the first fixing unit 121. The first fixing unit 121 includes a pressure roller and a heating roller, and when the sheet is sandwiched and conveyed through a fixing nip portion formed by these rollers, the toner is melted by the heat, and the melted toner image is pressed onto the sheet by pressure.

[0014] The sheet that has passed through the first fixing unit 121 is conveyed to a conveying path 125 through a conveying path 122. However, depending on the type of sheet, further melting and pressure bonding may be required for fixing, and such a sheet is conveyed to a second fixing unit 123. The second fixing unit 123 has the same configuration as the first fixing unit 121 described above, and fixes the toner image to the sheet by applying heat and pressure. The sheet that has passed through the second fixing unit 123 is conveyed to a conveying path 125 through a conveying path 124. Here, in the case of a double-sided image forming mode in which a toner image is formed on both sides of a sheet, after the toner image is formed on the first side, the sheet is conveyed from the conveying paths 122 and 124 to a reversing path 126, where the leading edge and the trailing edge in the conveying direction are swapped. Thereafter, the sheet is conveyed to a conveying path 113 through a double-sided conveying path 127, and the toner image on the intermediate transfer belt 118 is secondarily transferred to the second side of the sheet at a secondary transfer section N2.

[0015] The sheet conveyed to the conveying path 125 is delivered from the printing device 102 to the static eliminator 103 disposed downstream of the secondary transfer unit N2 in the sheet conveying direction via the conveying path 128. The conveying path 128 is provided with conveying rollers 170 as a conveying section that conveys the sheet delivered from the printing device 102 toward the contact-type static eliminator 129.

[0016] In the image forming apparatus 101, a high secondary transfer voltage is applied when a toner image is secondarily transferred to a sheet, so that the sheet becomes charged after the transfer. If the sheet is charged, the sheet may electrostatically adhere to a conveyance guide or the like during conveyance, causing a conveyance failure, or when the sheet is discharged to the discharge tray (135, 136), it may electrostatically adhere to a sheet already stacked on the discharge tray (135, 136), causing a stacking failure. In order to remove the charge from the charged sheet, the image forming apparatus 101 of this embodiment is provided with a charge removing device 103. The charge removing device 103 has a contact charge removing device 129 and a non-contact charge removing device 131, and a charge removing voltage is applied to the contact charge removing device 129 and the non-contact charge removing device 131 as described later, thereby removing the charge from the sheet after the secondary transfer.

[0017] The finisher 104 is capable of stacking a large volume of sheets, and is provided with an upper tray 135 as a second discharge section and a lower tray 136 as a first discharge section as discharge trays for discharging sheets. The upper tray 135 is disposed vertically above the lower tray 136. A sheet transported from the printing device 102 to the finisher 104 is discharged to the upper tray 135 via a transport path 132 and a transport path 133, or is discharged to the lower tray 136 via a transport path 132 and a transport path 134. The transport path (132, 133) leading to the upper tray 135 and the transport path (132, 134) leading to the lower tray 136 share the same route as the transport path 132, and the routes of the transport paths 133 and 134 beyond the transport path 132 are different. The transport paths 132, 133, and 134 are formed by guide members (180, 181) that guide the sheet P toward the upper tray 135 and the lower tray 136. The guide members (180, 181) are molded from, for example, resin.

[0018] Transport sensors 137, 138, and 139 that detect the passage of a sheet are disposed along the transport paths 132, 133, and 134, respectively, and the detection results are sent to the printing device 102. If the printing device 102 (CPU 203 for details, see FIG. 2 described later) does not detect the passage of the leading or trailing end of the sheet in the transport direction after a predetermined time has elapsed based on the detection results, it detects that a transport jam, in which the sheet is stuck during transport, has occurred in the finisher 104.

[0019] <Image forming device control system> Next, the control system of the image forming apparatus 101 will be described using Fig. 2 with reference to Fig. 1. First, the control system of the printing apparatus 102 will be described. As shown in Fig. 2, the printing apparatus 102 includes a communication interface (I / F) 201, a hard disk drive (HDD) 202, a central processing unit (CPU) 203, a memory 204, an operation unit 205, and a display 206. Furthermore, the printing apparatus 102 includes a laser exposure unit 207, an image creating unit 208, a fixing unit 209, a feeding unit 210, and an image reading unit 211. Each of the components is connected via a system bus 213.

[0020] The communication interface 201 is connected to the static eliminator 103 via a communication cable 229, and input / output of control instructions, data, and the like is performed between the printing apparatus 102 and the static eliminator 103. The communication interface 201 is also connected to an external device such as a computer (not shown), and input / output of various data is performed between the printing apparatus 102 and the static eliminator 103. The HDD 202 is a storage device in which control programs and data are stored. The CPU 203 executes, for example, an image forming process and a static elimination control process (see FIG. 8 described later) (not shown) based on the control program and the like stored in the HDD 202, and controls the entire image forming apparatus 101 accordingly. The CPU 203 mainly controls the printing apparatus 102, but manages the control performed by the static eliminator 103 and the finisher 104 by sending control instructions to the static eliminator 103 and the finisher 104. The memory 204 stores control programs and image data required when the CPU 203 performs various processes, and also functions as a temporary work area for data.

[0021] An operation unit 205 accepts various setting inputs and operation instructions from a user. A display 206 can display setting information of the image processing apparatus, the processing status of an image forming job, various screens described later, etc. This display 206 may be a touch panel that allows a user to execute various operations that are assigned in advance to a software key on the screen by touching the software key.

[0022] The laser exposure unit 207 is a device that performs primary charging and laser exposure to irradiate the photosensitive drum with laser light in order to transfer a toner image. In the laser exposure unit 207, first, primary charging is performed to charge the surface of the photosensitive drum to a uniform negative potential. Next, the laser light emitted from the laser driver is irradiated onto the photosensitive drum while the reflection angle is adjusted by a polygon mirror, whereby the negative charge at the portion of the photosensitive drum surface irradiated with the laser light is neutralized, and an electrostatic latent image is formed on the photosensitive drum.

[0023] The image forming unit 208 is a device for transferring toner onto a sheet, and is composed of a developing unit, a transfer unit, a toner supply unit, etc., and transfers the toner on the photosensitive drum onto a sheet. In the developing unit, negatively charged toner from a developing cylinder is attached to the electrostatic latent image on the surface of the photosensitive drum to make it visible. In the transfer unit, a primary transfer is performed by applying a positive voltage to the primary transfer roller to transfer the toner on the surface of the photosensitive drum onto the intermediate transfer belt 118, and a secondary transfer is performed by applying a negative voltage to the secondary transfer inner roller 119 to transfer the toner on the intermediate transfer belt 118 onto the sheet. The fixing unit 209 is a device for melting and fixing the toner on the sheet to the sheet by heat and pressure, and is composed of a heater, a heating roller, a pressure roller, etc. The feeding unit 210 is a device for transporting the sheet, and the sheet feeding and transporting operations are controlled by rollers and various sensors.

[0024] Next, the control system of the static eliminator 103 will be described. The static eliminator 103 has a communication interface (I / F) 221 and a static elimination control unit 227. The communication interface 221 as an acquisition unit is connected to the printing device 102 via a communication cable 229, and acquires, for example, control instructions and setting inputs input by a user from the operation unit 205 between the CPU 203 of the printing device 102 and the static elimination control unit 227. The static elimination control unit 227 controls the static eliminator 103 in accordance with control instructions from the CPU 203, and has a static elimination high voltage control unit 222, an attachment / detachment control unit 223, a non-contact static elimination high voltage control unit 224, and a transport control unit 226, which are connected via a system bus 225.

[0025] The static elimination high voltage control unit 222 controls the static elimination voltage of the contact static elimination device 129 by the static elimination high voltage power supply 230 (see FIG. 3 described later). The attachment / detachment control unit 223 controls the movement between a contact position where the static elimination roller 130a and the static elimination roller 130b of the contact static elimination device 129 are in contact with each other by a contact / detachment mechanism (not shown) and a non-contact position (also called a separated position) where they are not in contact. The non-contact static elimination high voltage control unit 224 controls the static elimination voltage of the non-contact static elimination device 131 by the non-contact static elimination high voltage power supply 240 (see FIG. 4(a) described later). The transport control unit 226 controls the transport roller 170 that delivers the sheet to the static elimination device 103. When the transport control unit 226 controls the transport of the sheet, the CPU 203 controls the transport of the sheet in the printing device 102.

[0026] In this embodiment, the static elimination control unit 227 controls the static elimination device 103 in accordance with a control instruction from the CPU 203, but the present invention is not limited to this. For example, the CPU 203 may have the function of the static elimination control unit 227 and directly control the static elimination device 103.

[0027] Next, the control system of the finisher 104 will be described. The finisher 104 is composed of a communication interface (I / F) 231, a CPU 232, a memory 233, and a discharge control unit 234, and each of the components is connected via a system bus 235. The communication interface 231 is connected to the static eliminator 103 via a communication cable 239, and communication is performed between the finisher 104 and the static eliminator 103 to transmit and receive control instructions and data. The CPU 232 controls the finisher 104 according to a control instruction from the CPU 203 of the printing apparatus 102. Here, various controls required for sheet discharge are performed according to a control program stored in the memory 233. The memory 233 is a storage device in which the control program is saved. The discharge control unit 234 can perform control to separate and transport the sheet conveyed from the static eliminator 103 to the upper tray 135 and the lower tray 136 based on the control instruction from the CPU 232.

[0028] Next, the contact type static eliminator 129 and the non-contact type static eliminator 131 provided in the static eliminator 103 as a static eliminator will be described with reference to Fig. 1 and Fig. 3 to Fig. 4(b). Fig. 3 is a schematic diagram showing the contact type static eliminator 129. Fig. 4(a) is a schematic diagram showing the non-contact type static eliminator 131 before the sheet passes, and Fig. 4(b) is a schematic diagram showing the non-contact type static eliminator 131 after the sheet passes.

[0029] In this embodiment, a negative voltage is applied to the inner secondary transfer roller 119 as a secondary transfer voltage. Therefore, when the sheet passes through the secondary transfer portion N2, the surface of the sheet on the side of the inner secondary transfer roller 119 is negatively charged, and the reverse surface of the sheet on the opposite side is positively charged by dielectric polarization. If the sheet is transported to the finisher 104 while still being charged, the sheet may be electrostatically attracted to a transport guide or the like during transport, causing a transport failure. Alternatively, when the sheet is discharged to the discharge tray (135, 136), the sheet may be electrostatically attracted to sheets already stacked on the discharge tray (135, 136), causing a stacking failure, or the stacked sheets may stick to each other due to electrostatic force. Therefore, in this embodiment, the charge is removed from the sheet by the static eliminator 103 to eliminate static electricity. The static eliminator 103 has two static eliminators, a contact static eliminator 129 and a non-contact static eliminator 131, and these static eliminators are arranged side by side in the sheet transport direction.

[0030] <Contact static eliminator> As shown in FIG. 3, the contact-type static elimination device 129 (contact-type static elimination section) has two opposing static elimination rollers 130a and 130b. The static elimination roller 130a is grounded, and a static elimination voltage is applied to the static elimination roller 130b by a static elimination high-voltage power supply 230. The static elimination rollers 130a and 130b come into contact with each other to form a static elimination nip section J1. When the sheet passes through the static elimination nip section J1, the static elimination roller 130a comes into contact with the front surface of the sheet, and the static elimination roller 130b comes into contact with the rear surface of the sheet. In this state, when a negative static elimination voltage is applied by the static elimination high-voltage power supply 230, the positive charge present on the rear surface of the sheet is removed. As a result, the positive charge present on the rear surface of the sheet is reduced, and the negative charge present on the front surface of the sheet is also reduced accordingly. The contact-type static elimination device 129 comes into contact with the sheet P and applies a voltage directly, so that a high static elimination effect can be obtained.

[0031] <Non-contact static eliminator> Although the contact type static eliminator 129 described above provides a high static elimination effect, the potentials of the front and back surfaces of the sheet P after static elimination (hereinafter referred to as surface potential) are prone to variation. In order to make the surface potential of the sheet P, which has become uneven due to static elimination by the contact type static eliminator 129, approximately uniform, the non-contact type static eliminator 131 is disposed downstream of the contact type static eliminator 129 in the conveying direction of the sheet P. The non-contact type static eliminator 131 can generally eliminate the remaining charge of the sheet after static elimination by the contact type static eliminator 129 in a non-contact state. In this embodiment, an AC corotron type is used as the non-contact type static eliminator 131.

[0032] As shown in FIG. 4(a), the non-contact static electricity removal device 131 (non-contact static electricity removal section) has a discharge wire 140 and an earth electrode 141, and a positive static electricity removal voltage is applied to the discharge wire 140 by a non-contact static electricity removal high-voltage power supply 240. When a positive static electricity removal voltage is applied to the discharge wire 140, a corona discharge occurs in the discharge wire 140, and a positive charge is generated. Then, as shown in FIG. 4(b), the positive charge generated in the discharge wire 140 is attracted to the negative charge on the sheet surface by electrostatic force. As a result, the negative charge on the sheet surface is removed. On the other hand, the positive charge on the back surface of the sheet is attracted to the earth electrode 141, which is grounded and has a potential of "0", and is thereby removed. The effect of eliminating static electricity on sheet P by such a non-contact static eliminator 131 is smaller than that by the contact static eliminator 129; however, since the non-contact static eliminator 131 can reduce the variation in the surface potential of sheet P after static elimination, the surface potential of sheet P after passing through the non-contact static eliminator 131 becomes approximately uniform.

[0033] <Static charge removal voltage> However, the amount of charge on the sheet P after the secondary transfer differs depending on the type of sheet. Therefore, in this embodiment, in order to obtain a charge removal effect on the sheet P, a predetermined reference voltage to be applied to each of the contact-type charge removal device 129 and the non-contact-type charge removal device 131 can be set according to the type of sheet in accordance with a reference voltage table shown in Table 1. The reference voltage table is stored in advance in the printing device 102, for example, in the HDD 202 (see FIG. 2). [Table 1]

[0034] As shown in Table 1, the reference voltage table sets the reference voltage of the contact-type static eliminator 129 and the reference voltage of the non-contact-type static eliminator 131 for each type of sheet (paper type). In the reference voltage table of Table 1, the reference voltage of the contact-type static eliminator 129 is set to "0 volts" for "plain paper" and "thick paper", "-100 volts" for "coated paper", and "-800 volts" for "synthetic paper". That is, "plain paper" and "thick paper" are sheets of a first type that do not require static elimination by the contact-type static eliminator 129, and "coated paper" and "synthetic paper" are sheets of a second type that require static elimination by the contact-type static eliminator 129. On the other hand, the reference voltage of the non-contact-type static eliminator 131 is set to "800 volts" for all of "plain paper", "thick paper", "coated paper", and "synthetic paper". In this specification, a sheet that does not require static elimination refers to a sheet that does not require static elimination by the contact-type static eliminator 129, and a sheet that requires static elimination refers to a sheet that requires static elimination by the contact-type static eliminator 129. Both sheets that do not require static elimination and sheets that require static elimination are subjected to static elimination by the non-contact static eliminator 131.

[0035] <Contact / separation mechanism> The contact type static eliminator 129 described above eliminates static electricity by bringing the static eliminator roller 130a and the static eliminator roller 130b into contact with the sheet, so that the static eliminator roller 130a and the static eliminator roller 130b wear out each time the sheet is conveyed, and the static elimination ability of the sheet may decrease. Therefore, when the non-contact type static eliminator 131 alone eliminates static electricity from the sheet, the static eliminator roller 130a and the static eliminator roller 130b are not brought into contact with each other in the contact type static eliminator 129 that does not eliminate static electricity from the sheet. To achieve this, the contact type static eliminator 129 is provided with a contact / separation mechanism 150 that brings one static eliminator roller 130a into contact with the other static eliminator roller 130b, as shown in Figs. 5(a) and 5(b).

[0036] As shown in Fig. 5(a) and Fig. 5(b), the contact / separation mechanism 150 is attached to the charge removing roller 130a as a first charge removing member, and can move the charge removing roller 130a between a contact position where the charge removing roller 130a contacts the charge removing roller 130b and a spaced position where the charge removing roller 130a is spaced from the charge removing roller 130b. The contact / separation mechanism 150 has a swing arm 151 that swings around a swing fulcrum 152, and the swing arm 151 is swung counterclockwise or clockwise by the attachment / detachment motor 160. The charge removing roller 130a is rotatably supported on the tip side of the swing arm 151 away from the swing fulcrum 152. When the attachment / detachment motor 160 is driven counterclockwise, as shown in Fig. 5(a), the swing arm 151 swings counterclockwise around the swing fulcrum 152, and the charge removing roller 130a is moved to a contact position where the charge removing roller 130a contacts the charge removing roller 130b as a second charge removing member.

[0037] Conversely, when the attachment / detachment motor 160 is driven clockwise, as shown in Fig. 5(b), the swing arm 151 swings clockwise about the swing fulcrum 152, and the charge removal roller 130a is moved to a separated position separated from the charge removal roller 130b (detachment operation). Then, when the charge removal roller 130a moving from the contact position to the separated position presses the attachment / detachment sensor 153 arranged on the upper part of the contact / detachment mechanism 150, the attachment / detachment motor 160 stops, and the charge removal roller 130a is stopped at the separated position. The attachment / detachment sensor 153 is, for example, a push switch, which is in an on state when pressed by the charge removal roller 130a and is in an off state when not pressed by the charge removal roller 130a.

[0038] <Deactivation process> Next, the de-emission process for moving the charge removing roller 130a from the contact position to the separation position will be described with reference to Fig. 2, Fig. 5(a) and Fig. 5(b) and Fig. 6. Fig. 6 is a flowchart showing the de-emission process of the charge removing roller 130a. When the contact type charge removing device 129 does not remove static electricity from the sheet, the CPU 203 transmits an instruction to start the de-emission process to the attachment / detachment control unit 223 via the communication interface 201.

[0039] When the attachment / detachment control unit 223 receives an instruction to start the detachment operation from the CPU 203, it starts driving the attachment / detachment motor 160 in a clockwise direction at a predetermined speed (S1). The attachment / detachment control unit 223 determines whether the attachment / detachment sensor 153 is pressed and turned on by the charge removal roller 130a moving in a clockwise direction via the swing arm 151 (S2). If the attachment / detachment sensor 153 is off (No in S2), the attachment / detachment control unit 223 drives the attachment / detachment motor 160 in a clockwise direction at a predetermined speed until the attachment / detachment sensor 153 is turned on, and moves the charge removal roller 130a toward the abutment position. If the attachment / detachment sensor 153 is turned on (Yes in S2), the attachment / detachment control unit 223 stops the attachment / detachment motor 160 (S3) to stop the charge removal roller 130a at the separation position. When the attachment / detachment control unit 223 stops the attachment / detachment motor 160, it transmits a notification of the end of the detachment operation to the CPU 203 via the communication interface 201.

[0040] <Attachment process> Next, the attaching operation process for moving the charge removing roller 130a from the separated position to the contact position will be described with reference to Fig. 2, Fig. 5(a) and Fig. 5(b) and Fig. 7. Fig. 7 is a flowchart showing the attaching operation process of the charge removing roller 130a. When the contact type charge removing device 129 is used to remove static electricity from a sheet, the CPU 203 transmits an instruction to start the attaching operation to the attachment / detachment control unit 223 via the communication interface 201.

[0041] When the attachment / detachment control unit 223 receives an instruction to start the attachment / detachment operation from the CPU 203, it starts driving the attachment / detachment motor 160 counterclockwise at a predetermined speed (S11). The attachment / detachment control unit 223 judges whether or not "600 msec" has elapsed since the attachment / detachment sensor 153 started to be driven (S12). The attachment / detachment control unit 223 moves the charge removal roller 130a toward the separation position until "600 msec" has elapsed (No in S12). If "600 msec" has elapsed since the attachment / detachment sensor 153 started to be driven (Yes in S12), the attachment / detachment control unit 223 stops the attachment / detachment motor 160 (S13). As a result, the charge removal roller 130a stops at the abutment position. When the attachment / detachment control unit 223 stops the attachment / detachment motor 160, it transmits a notification of the end of the attachment operation to the CPU 203 via the communication interface 201.

[0042] In this embodiment, the above-mentioned "600 msec" is the time required for the charge removal roller 130a to move from the separated position to the contact position when the attachment / detachment motor 160 is driven counterclockwise at a predetermined speed. Therefore, depending on the configuration of the contact / detachment mechanism 150 and the driving speed of the attachment / detachment motor 160, the time is not limited to "600 msec".

[0043] As described above, when the contact-type static eliminator 129 does not eliminate static electricity from a sheet, the static eliminator roller 130a is moved to the separated position so that the static eliminator roller 130a and the static eliminator roller 130b are not brought into contact with each other, thereby suppressing unnecessary wear of the static eliminator roller 130a and the static eliminator roller 130b. If this is the case, when a continuous image forming job (not shown) in which images are continuously formed on a plurality of sheets is executed, if a sheet requiring static elimination is to be eliminated following a sheet requiring static elimination, it is necessary to move the static eliminator roller 130a from the separated position to the contact position and have the contact-type static eliminator 129 eliminate static electricity from the sheet.

[0044] FIG. 12 shows a conventional example of the timing of the static elimination roller 103a's attachment operation when a sheet requiring static elimination is to be neutralized following a sheet not requiring static elimination. FIG. 12 is a timing chart for explaining the attachment operation of the static elimination roller 103a in the conventional example. FIG. 12 shows an example in which a "synthetic paper" sheet requiring static elimination is transported immediately after a "plain paper" sheet not requiring static elimination. A reference voltage of "800 volts" is applied to both the "plain paper" and the "synthetic paper" by the non-contact static elimination high-voltage power supply 240 in the non-contact static elimination device 131 (static elimination voltage on).

[0045] First, when "plain paper" that does not require static elimination is continuously transported, static elimination by the contact-type static eliminator 129 is not required, so the static elimination voltage is set to "0 volts" (static elimination voltage off) by the static elimination high-voltage power supply 230, and the static elimination roller 103a is in the separated position by the contact / separation mechanism 150. At this time, the preceding plain paper and the succeeding plain paper are transported to the nip area of ​​the static elimination nip J1 with a paper interval T1 (from time t0 to time t1). In this embodiment, the paper interval T1 is, for example, "1000 msec." The preceding synthetic paper and the succeeding synthetic paper are also transported to the nip area of ​​the static elimination nip J1 with a paper interval T1 (from time t3 to time t4).

[0046] In this specification, the paper gap refers to the gap between the leading edge of the preceding sheet and the leading edge of the succeeding sheet. The nip region of the discharge nip J1 refers to the region of the discharge nip J1 itself in the sheet conveying direction when the discharge roller 103a is in the contact position, and refers to the region of the discharge roller 103b in the sheet conveying direction corresponding to the discharge nip J1 when the discharge roller 103a is in the separated position (see region Z in FIG. 5(b)).

[0047] For example, when switching from plain paper to synthetic paper, the synthetic paper requires static elimination by the contact type static elimination device 129, so the contact operation must be started to move the static elimination roller 103a from the separated position to the contact position by the contact / separation mechanism 150. Conventionally, the contact operation by the contact / separation mechanism 150 was started after the trailing edge of the preceding plain paper passed through the nip area of ​​the static elimination nip J1 (time t2). Then, after the contact operation has started, the static elimination voltage is switched to "-800 volts" (static elimination voltage ON) by the static elimination high voltage power supply 230.

[0048] Then, in order to properly perform static elimination by the contact-type static eliminator 129, the synthetic paper is transported so as to enter the nip region of the static elimination nip J1 after the static elimination roller 130a reaches the contact position. As described above, the time it takes for the static elimination roller 130a to move from the separated position to the contact position is "600 msec."

[0049] Therefore, in the past, at least a paper interval "T2" was provided by adding the above-mentioned "600 msec" to the time (time t1 to time t2) it takes from when the leading edge of the plain paper enters the nip area of ​​the discharge nip J1 until when the trailing edge of the plain paper passes through the nip area of ​​the discharge nip J1. Thus, in the past, the paper interval between the preceding plain paper and the succeeding synthetic paper was made wider than "T1" so that the synthetic paper requiring discharge can arrive after the discharge roller 103a moves to the contact position. Therefore, in the past, when continuous image forming jobs were performed in which the contact operation by the contact / separation mechanism 150 was repeated, the productivity of the image forming apparatus 101 could decrease.

[0050] In view of this, in this embodiment, when switching from a sheet not requiring static elimination to a sheet requiring static elimination, the contacting / separating mechanism 150 starts the contacting operation while the preceding sheet is passing through the nip area of ​​the static elimination nip J1, without waiting for the trailing end of the preceding sheet to pass through the nip area of ​​the static elimination nip J1. Hereinafter, the "static elimination control process" of this embodiment that realizes this will be described using Figs. 8 and 9 with reference to Figs. 1 and 2. Fig. 8 is a flowchart showing the static elimination control process of this embodiment. Fig. 9 is a timing chart for explaining the contacting operation of the static elimination roller 103a in this embodiment.

[0051] Here, as an example, a case will be described in which the static elimination control process (mode) is executed by the static elimination control unit 227 under the control of the CPU 203. When receiving an instruction to start a continuous image forming job and executing the continuous image forming job, the CPU 203 instructs the static elimination control unit 227 via the communication interface 201 to start the execution of the static elimination control process.

[0052] <Static charge removal control process> As shown in FIG. 8, the static elimination control unit 227 first starts applying a reference voltage to the non-contact static elimination device 131 by the non-contact static elimination high voltage power supply 240 (S21). Then, the static elimination control unit 227 judges whether or not the first sheet sent from the printing device 102 is a sheet that needs to be static eliminated (S22). If the first sheet is a sheet that does not need to be static eliminated (No in S22), the static elimination control unit 227 judges whether or not the leading edge of the first sheet has reached the nip area of ​​the static elimination nip J1 (S23). If the leading edge of the sheet has not reached the nip area of ​​the static elimination nip J1 (No in S23), the static elimination control unit 227 waits until the leading edge of the sheet reaches the nip area of ​​the static elimination nip J1. When the leading edge of the sheet reaches the nip area of ​​the static elimination nip J1 (Yes in S23), the static elimination control unit 227 judges whether or not there is a sheet to be subsequently conveyed (S24).

[0053] If there is no subsequent sheet (No in S24), the static elimination control unit 227 jumps to the process of step S40. In step S40, the static elimination control unit 227 stops the application of the reference voltage to the non-contact static elimination device 131 by the non-contact static elimination high-voltage power supply 240. Then, the static elimination control unit 227 ends this static elimination control process, and notifies the CPU 203 via the communication interface 221 that the static elimination control process has ended.

[0054] On the other hand, if there is a subsequent sheet (Yes in S24), the static elimination control unit 227 judges whether or not the sheet following the preceding sheet not requiring static elimination is a sheet requiring static elimination (S25). If the subsequent sheet does not require static elimination (No in S25), the static elimination control unit 227 returns to the process of step S23. When sheets not requiring static elimination are thus continuously conveyed, the static elimination roller 130a of the contact static eliminator 129 is in the separated position, so that these sheets are subjected to static elimination only by the non-contact static eliminator 131. As shown in FIG. 9, when plain papers are continuously conveyed with a paper interval (T1, time t0 to time t1), these plain papers are subjected to static elimination only by the non-contact static eliminator 131.

[0055] If the succeeding sheet is one that requires static elimination (Yes in S25), the static elimination control unit 227 determines the contact operation start time T at which the contact operation of the static elimination roller 130a by the contact / separation mechanism 150 starts based on the paper gap between the sheets being conveyed and the time it takes for the static elimination roller 130a to move from the separation position to the contact position (S26). As shown in Fig. 9, for example, if the paper gap (T1) between the sheets is "1000 msec" and the time it takes for the static elimination roller 130a to move from the separation position to the contact position is "600 msec," then the contact operation start time T is "400 msec (1000-600)."

[0056] The static elimination control unit 227 determines whether or not the contact operation start time T has elapsed since the leading edge of the preceding sheet not requiring static elimination reached the nip region of the static elimination nip J1 (S27). If the contact operation start time T has not elapsed (No in S27), the static elimination control unit 227 waits until the contact operation start time T has elapsed. If the contact operation start time T has elapsed (Yes in S27), the static elimination control unit 227 starts the contact operation of the static elimination roller 130a by the contact / separation mechanism 150 (S28).

[0057] In the example shown in FIG. 9, the time "t10" is the time after the leading edge of the preceding plain paper reaches the nip area of ​​the discharge nip J1 (time t1) and the contact operation start time T "400 msec" has elapsed. Therefore, the discharge control unit 227 determines the timing for starting the contact operation of the discharge roller 130a by the contact / separation mechanism 150 to be time t10, and starts the contact operation of the contact / separation mechanism 150 at time t10. In this way, before the rear end of the preceding plain paper passes through the nip area of ​​the discharge nip J1 (time t2), the contact / separation mechanism 150 starts moving the discharge roller 130a from the separation position to the contact position (time t10). The timing at which this contact operation starts (time t10) is the timing at which the movement of the discharge roller 130a to the contact position can be completed before the leading edge of the succeeding synthetic paper transported in the paper gap (T1) reaches the nip area of ​​the discharge nip J1 (time t31).

[0058] After the contact / separation mechanism 150 starts the attachment operation, the static elimination control unit 227 determines whether or not the trailing end of the preceding sheet that does not require static elimination has passed through the nip area of ​​the static elimination nip J1 (S29). If the trailing end of the preceding sheet has not reached the nip area of ​​the static elimination nip J1 (No in S29), the static elimination control unit 227 waits until the trailing end of the preceding sheet passes through the nip area of ​​the static elimination nip J1. If the trailing end of the preceding sheet reaches the nip area of ​​the static elimination nip J1 (Yes in S29), the static elimination control unit 227 starts applying a static elimination voltage to the static elimination roller 130b by the static elimination high-voltage power supply 230 (S31).

[0059] As shown in FIG. 9, the charge removal control unit 227 starts applying a charge removal voltage to the charge removal roller 130b at time t2. This is because if a charge removal voltage is applied to the charge removal roller 130b while a preceding plain paper that does not require charge removal is passing through the nip area of ​​the charge removal nip J1, an unnecessary voltage is applied to the plain paper, causing the plain paper to become charged. In that case, there is a risk of sheet stacking failure or sheet conveyance failure. To prevent this, the charge removal voltage is started to be applied to the charge removal roller 130b after the plain paper passes through the nip area of ​​the charge removal nip J1. In addition, the voltage applied by the charge removal high voltage power supply 230 is set to reach a reference voltage (see Table 1) corresponding to the type of sheet before the leading edge of the succeeding synthetic paper conveyed at the paper interval (T1) reaches the nip area of ​​the charge removal nip J1 (time t31).

[0060] After starting application of a discharge voltage to the discharge roller 130b (S31), the discharge control unit 227 judges whether or not the leading edge of the succeeding sheet that needs to be discharged has reached the nip area of ​​the discharge nip J1 (S32). If the leading edge of the succeeding sheet that needs to be discharged has not reached the nip area of ​​the discharge nip J1 (No in S32), the discharge control unit 227 waits until the leading edge of the succeeding sheet reaches the nip area of ​​the discharge nip J1. If the leading edge of the succeeding sheet reaches the nip area of ​​the discharge nip J1 (Yes in S32), the discharge control unit 227 judges whether or not there is a succeeding sheet to be conveyed (S33).

[0061] If there is no subsequent sheet (No in S33), the static elimination control unit 227 ends the application of static elimination voltage to the static elimination roller 130b by the static elimination high-voltage power supply 230 (S38). Then, the static elimination control unit 227 starts the release operation of the static elimination roller 130a by the contact / separation mechanism 150 (S39), and moves the static elimination roller 130a from the contact position to the separation position. In addition, the static elimination control unit 227 stops the application of the reference voltage to the non-contact static elimination device 131 by the non-contact static elimination high-voltage power supply 240 (S40), and ends this static elimination control process.

[0062] On the other hand, if there is a subsequent sheet (Yes in S33), the static elimination control unit 227 judges whether or not the subsequent sheet also requires static elimination (S34). If the subsequent sheet also requires static elimination (Yes in S34), the static elimination control unit 227 returns to the process of step S32. In this way, when sheets requiring static elimination are continuously transported between sheets (T1), the static elimination roller 130a of the contact static eliminator 129 is in the contact position, so that these sheets are static eliminated by the contact static eliminator 129 and the non-contact static eliminator 131. As shown in FIG. 9, when synthetic paper is continuously transported between sheets (T1, from time t31 to time t41) after time t31, these synthetic papers are static eliminated by the contact static eliminator 129 and the non-contact static eliminator 131.

[0063] If the succeeding sheet does not require static elimination (No in S34), the static elimination control unit 227 judges whether or not the trailing end of the preceding sheet requiring static elimination has passed through the nip area of ​​the static elimination nip J1 (S35). If the trailing end of the preceding sheet has not reached the nip area of ​​the static elimination nip J1 (No in S35), the static elimination control unit 227 waits until the trailing end of the preceding sheet passes through the nip area of ​​the static elimination nip J1. When the trailing end of the preceding sheet reaches the nip area of ​​the static elimination nip J1 (Yes in S35), the static elimination control unit 227 ends the application of static elimination voltage to the static elimination roller 130b by the static elimination high voltage power source 230 (S36). Then, the static elimination control unit 227 starts the release operation of the static elimination roller 130a by the contact / separation mechanism 150 (S37), moves the static elimination roller 130a from the contact position to the separation position, and returns to the process of step S23.

[0064] In the process of step S22 described above, if the first sheet is a sheet that requires static elimination (Yes in S22), the static elimination control unit 227 starts the contact operation of the static elimination roller 130a by the contact / separation mechanism 150 (S30) and moves the static elimination roller 130a from the separation position to the contact position. After that, the static elimination control unit 227 proceeds to the process of step S31 and performs the processes after step S31.

[0065] As described above, in this embodiment, the charge removal roller 130a starts moving to the contact position before the trailing end of the preceding sheet that does not require charge removal passes through the nip area of ​​the charge removal nip J1, and the charge removal roller 130a completes moving from the separation position to the contact position before the leading end of the succeeding sheet that requires charge removal reaches the nip area of ​​the charge removal nip J1. This allows the charge removal roller 130a to complete moving from the separation position to the contact position without widening the paper gap (T1) between the preceding sheet that does not require charge removal and the succeeding sheet that requires charge removal. Therefore, the productivity of the image forming apparatus 101 does not decrease.

[0066] As described above, the timing for starting the contact operation of the charge removal roller 130a is such that the movement of the charge removal roller 130a to the contact position can be completed before the leading edge of the succeeding synthetic paper reaches the nip area of ​​the charge removal nip J1 (time t31). In that case, if the paper interval (T1) is shorter, for example, at "500 msec," than the time (for example, 600 msec) it takes for the charge removal roller 130a to move from the separation position to the contact position, the contact operation of the charge removal roller 130a can be started "100 msec" before time t1 when the leading edge of the preceding plain paper reaches the nip area of ​​the charge removal nip J1.

[0067] <Other embodiments> In addition, when the movement of the charge removal roller 130a to the contact position is completed before the trailing end of the preceding sheet not requiring charge removal passes through the nip area of ​​the charge removal nip portion J1 (time t2 in FIG. 9), wrinkles or the like may occur in the preceding sheet not requiring charge removal (e.g., thin paper, etc.) depending on the type of sheet. Therefore, in order to prevent wrinkles or the like from occurring in the preceding sheet not requiring charge removal, it is preferable that the user is allowed to input a setting as to whether or not to execute the above-mentioned "charge removal control process". FIG. 10 shows a "setting input screen" displayed on the display 206 to allow the user to input a setting as to whether or not to execute the "charge removal control process". As shown in FIG. 10, the "setting input screen" displays a message prompting the user to input a setting as to whether or not to execute the "charge removal control process", and displays an "execute" button 1201 and a "not execute" button 1202.

[0068] When the "Execute" button 1201 is operated by the user, the above-mentioned "discharge control process" is executed. In this case, the discharge roller 130a starts moving to the contact position before the trailing end of the preceding sheet that does not need to be discharged passes through the nip area of ​​the discharge nip J1, and the discharge roller 130a completes moving from the separation position to the contact position before the leading end of the succeeding sheet that needs to be discharged reaches the nip area of ​​the discharge nip J1 (first mode). On the other hand, when the "Do not execute" button 1202 is operated by the user, the above-mentioned "discharge control process" is not executed. In this case, as in the conventional example (see FIG. 12), the discharge roller 130a starts moving from the separation position to the contact position after the trailing end of the preceding sheet that does not need to be discharged passes through the nip area of ​​the discharge nip J1 (second mode). In the first mode, productivity can be improved, and in the second mode, wrinkles and the like can be prevented from occurring.

[0069] The user may be allowed to input the setting as to whether or not to execute the "static charge removal control process" for each type of sheet. Fig. 11 shows a "setting input screen" that allows the user to input the setting as to whether or not to execute the "static charge removal control process" for each type of sheet. The "setting input screen" shown in Fig. 11 displays the type of sheet, as well as a "productivity priority" button 1301 and a "wrinkle suppression priority" button 1302.

[0070] When the user operates the "productivity priority" button 1301, the above-mentioned "static elimination control process" is executed. In this case, the above-mentioned first mode is executed, which can improve productivity, but wrinkles may occur depending on the type of sheet. In contrast, when the user operates the "wrinkle suppression priority" button 1302, the above-mentioned second mode is executed, which cannot improve productivity, but can suppress the occurrence of wrinkles, etc., in any type of sheet.

[0071] In the above-described first and second embodiments, the printing device 102 is an intermediate transfer type in which the toner image of each color is primarily transferred from the photosensitive drum of each color to the intermediate transfer belt 118, and then the composite toner image of each color is secondary-transferred collectively to a sheet, but the present invention is not limited to this. For example, the printing device 102 may be a direct transfer type in which the toner image on the photosensitive drum is directly transferred to the sheet by applying a voltage to a transfer roller disposed opposite the photosensitive drum and the conveying belt, with the sheet being conveyed by a conveying belt having a nip formed between the photosensitive drum and the conveying belt. [Explanation of symbols]

[0072] 103...discharging device, 118...image carrier (intermediate transfer belt), 119...transfer member (secondary transfer inner roller), 129...contact type discharging section (contact type discharging device), 130a...first discharging member (discharging roller), 130b...second discharging member (discharging roller), 131...non-contact type discharging section (non-contact type discharging device), 150...contact and separation mechanism, 170...conveying section (conveying roller), 190...image forming section, 221...acquiring section (communication interface), 227...control section (discharging control section), J1...discharging nip section, N2...transfer nip section (secondary transfer section), P...sheet

Claims

1. a contact-type static elimination unit that includes a first static elimination member and a second static elimination member that contacts the first static elimination member to form a static elimination nip portion, and that eliminates electric charges on a sheet that passes through the static elimination nip portion by application of a voltage; a conveying section that conveys a sheet to the charge removing nip section; a contact / separation mechanism that can move the first charge removing member between a contact position where the first charge removing member contacts the second charge removing member and a spaced position where the first charge removing member is spaced from the second charge removing member; a control unit that, when a first type of sheet does not require static elimination by the contact-type static elimination unit, positions the first static elimination member at the separation position and does not perform static elimination, and, when a second type of sheet does require static elimination by the contact-type static elimination unit, positions the first static elimination member at the contact position and performs static elimination, the control unit is capable of executing a mode in which, when the conveying unit conveys the first type of sheet and the second type of sheet following the first type of sheet, the contact mechanism starts moving the first charge removal member from the separation position to the contact position in the sheet conveying direction before the trailing end of the first type of sheet passes through the nip area of ​​the charge removal nip portion, and completes the movement of the first charge removal member to the contact position before the leading end of the following second type of sheet reaches the nip area. A static eliminator characterized by the above.

2. the mode is a first mode, the control unit is capable of executing a second mode in which, when the first type of sheet and the second type of sheet are transported following the first type of sheet, the contact / separation mechanism starts moving the first static electricity removing member from the separation position to the contact position after the trailing end of the first type of sheet passes through the nip area in a sheet transport direction, an acquisition unit that acquires a setting input for determining whether the first mode or the second mode is to be executed; 2. The static eliminator according to claim 1 .

3. an acquisition unit that acquires a setting input as to whether to perform static elimination by the contact-type static elimination unit or not to perform static elimination by the contact-type static elimination unit according to a type of sheet; The control unit is When the type of sheet that is set and input to be subjected to static elimination by the contact-type static elimination unit is the first type of sheet, the first mode is executed; When the type of sheet for which the static elimination by the contact-type static elimination unit is not to be performed is the first type of sheet, the second mode is executed.

3. The static eliminator according to claim 2.

4. the control unit determines a timing for starting movement of the first discharge member from the separation position to the contact position by the contact-separation mechanism based on a time required for the leading edge of the first type of sheet to reach the nip region after the leading edge of the first type of sheet reaches the nip region in a sheet conveying direction and a time required for the first discharge member to be moved from the separation position to the contact position by the contact-separation mechanism.

2. The static eliminator according to claim 1 .

5. the control unit, when the first type of sheet is transported following the second type of sheet, starts moving the first charge removing member from the contact position to the separation position by the contact / separation mechanism after the trailing end of the second type of sheet passes through the nip area in a sheet transport direction.

2. The static eliminator according to claim 1 .

6. a non-contact type static electricity eliminating unit that is provided downstream of the contact type static electricity eliminating unit in a sheet conveying direction and is capable of eliminating residual charges of the sheet in a non-contact state after static electricity is eliminated by the contact type static electricity eliminating unit; 2. The static eliminator according to claim 1 .

7. an image carrier that carries a toner image; an image forming unit for forming a toner image on the image carrier; a transfer member that contacts the image carrier to form a transfer nip and transfers a toner image on the image carrier to a sheet passing through the transfer nip by application of a transfer voltage; and the static elimination device according to claim 1 , which is disposed downstream of the transfer nip portion in a sheet transport direction.

1. An image forming apparatus comprising:

Images