Image forming apparatus including charge eliminating device and image forming apparatus including charge applying device

Abstract

To perform static elimination with a polarity suitable for the polarity of the surface of a charged sheet.SOLUTION: An image printing unit configured to print an image on a sheet, a reverse conveyance path configured to reverse a conveyance direction of the sheet printed by the image printing unit and conveyed, a double-sided conveyance path configured to convey the sheet conveyed from the reverse conveyance path to the image printing unit again, a discharge tray on which the discharged sheet is stacked, a conveyance control unit configured to control conveyance of the sheet, a discharging unit configured to apply a voltage to a discharging member and discharge the sheet printed by the image printing unit, and a discharge control unit configured to control a polarity of the voltage applied to the discharging member, the image forming apparatus according to claim 1, wherein the discharge control unit performs control to apply a voltage to the discharge member with a first polarity when first single-sided printing discharge is executed, apply a voltage to the discharge member with a second polarity when second single-sided printing discharge is executed, and apply a voltage to the discharge member with the second polarity when double-sided printing discharge is executed.SELECTED DRAWING: Figure 12

Description

[Technical Field]

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

[0002] In electrophotographic and electrostatic printers, a high voltage is applied to the rollers when forming an image on a sheet. In such printers, the sheet may become charged due to the characteristics of the sheet or the environmental conditions in which the printer is installed.

[0003] During image formation, sheets may become charged, and the static electricity generated between discharged sheets may cause the sheets to stick together, resulting in stacking problems. Patent Document 1, therefore, proposes an image forming apparatus equipped with a static eliminator that eliminates static electricity from sheets. The static eliminator described in Patent Document 1 includes a contact-type static eliminator (static eliminator roller) that contacts the conveyed sheets to eliminate static electricity, and a non-contact-type static eliminator that eliminates static electricity without contacting the sheets. Also known is a charge applying device that applies a voltage to every other sheet being conveyed, charging the sheets so that their surfaces have the same polarity when stacked, thereby improving stacking problems (see Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-167169 [Patent Document 2] Japanese Patent Publication No. 2022-171206 Summary of the Invention [Problem to be solved by the invention]

[0005] In the cited documents 1 and 2, a voltage of either positive or negative polarity is applied. In an image forming apparatus, depending on the setting of single-sided printing / double-sided printing and the setting of the image-forming surface upside down when the sheet is ejected, the sheet is inverted within the image forming apparatus. Depending on whether the sheet is inverted or not, the polarity of the charge on the side to which the voltage is applied when the sheet is transported to the static elimination unit or charge adjustment unit differs. If a voltage of the same polarity as the polarity of the surface of a charged sheet is applied, the charge on the sheet will deteriorate. Therefore, it is necessary to apply a voltage of the appropriate polarity to the charged sheet.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an image forming apparatus that performs charge removal or charge adjustment with an appropriate polarity on a charged sheet. [Means for solving the problem]

[0007] One aspect of the present invention is a printing system including an image printing unit that prints an image on a sheet, a reversing conveying path that reverses the conveying direction of a sheet printed by the image printing unit and conveyed, a double-sided conveying path that conveys the sheet conveyed from the reversing conveying path back to the image printing unit, an output tray on which the discharged sheets are stacked, a conveying control unit that controls the conveyance of the sheet, a static elimination unit that applies a voltage to a static elimination member to eliminate static electricity from the sheet printed by the image printing unit, and a static elimination control unit that controls the polarity of the voltage applied to the static elimination member, wherein the reversing conveying path is disposed downstream of the image printing unit and upstream of the static elimination unit in the sheet conveyance direction, and when performing a first single-sided printing output in which the sheet is output to the output tray with the side printed on one side facing up, the conveying control unit conveys the sheet to the static elimination unit without passing through the reversing conveying path and the double-sided conveying path, and outputs the sheet to the output tray with the side printed on one side facing down. When performing a second single-sided printing output in which the sheet is discharged so that the second side of the double-sided printed sheet faces up, the sheet is transported to the de-electrification unit via the reverse transport path but not via the double-sided transport path; when performing a double-sided printing output in which the sheet is discharged to the output tray so that the second side of the double-sided printed sheet faces up, the sheet on which the first side is printed by the image printing unit is transported again to the image printing unit via the reverse transport path and the double-sided transport path, and the sheet on which the second side, the reverse side of the first side, is printed by the image printing unit, is transported to the de-electrification unit; and the de-electrification control unit controls to apply a voltage to the de-electrification member with a first polarity when the first single-sided printing output is performed, to apply a voltage to the de-electrification member with a second polarity when the second single-sided printing output is performed, and to apply a voltage to the de-electrification member with the first polarity when the double-sided printing output is performed.

[0008] Another aspect of the present invention is a printing apparatus including an image printing unit that prints an image on a sheet, a reversing conveying path that reverses the conveying direction of a sheet that has been printed by the image printing unit and conveyed, a double-sided conveying path that conveys the sheet conveyed from the reversing conveying path back to the image printing unit, an ejection tray on which ejected sheets are stacked, a conveying control unit that controls the conveyance of the sheets, a charge applying unit that applies a voltage to a charge applying member to every other sheet so that the surface potential of the sheet on which the image has been printed by the image printing unit is reversed, and a charge applying control unit that controls the polarity of the voltage applied to the charge applying member, wherein the reversing conveying path is disposed downstream of the image printing unit and upstream of the charge applying unit in the sheet conveyance direction, and the conveying control unit conveys the sheet to the charge applying unit without passing through the reversing conveying path and the double-sided conveying path when performing a first single-sided printing ejection in which the sheet is ejected onto the ejection tray with the side that has been printed on one side facing up. When performing a second single-sided printing output in which the sheet is discharged to the output tray with the side printed on one side facing downwards, the sheet is transported to the charge applying unit via the reverse transport path but not via the double-sided transport path, and when performing a double-sided printing output in which the sheet is discharged to the output tray with the second side printed on both sides facing upwards, the sheet on which the first side has been printed by the image printing unit is transported again to the image printing unit via the reverse transport path and the double-sided transport path, and the sheet on which the second side, the reverse side of the first side, has been printed by the image printing unit is transported to the charge applying unit, and the charge applying unit is controlled to apply a voltage to the charge applying member with a first polarity when the first single-sided printing output is performed, apply a voltage to the charge applying member with a second polarity when the second single-sided printing output is performed, and apply a voltage to the charge applying member with the first polarity when the double-sided printing output is performed.

[0009] Another aspect of the present invention is a printing apparatus including an image printing unit that prints an image on a sheet, a reversing conveying path that reverses the conveying direction of a sheet that has been printed by the image printing unit and conveyed, a double-sided conveying path that conveys the sheet conveyed from the reversing conveying path back to the image printing unit, an output tray on which the discharged sheets are stacked, a conveying control unit that controls conveyance of the sheet, a static elimination unit that eliminates static electricity from the sheet printed by the image printing unit at a nip formed by a first static elimination roller and a second static elimination roller, and a static elimination control unit that controls a voltage applied to the static elimination unit, wherein the reversing conveying path is disposed downstream of the image printing unit and upstream of the static elimination unit in the sheet conveying direction, and the conveying control unit conveys the sheet to the static elimination unit without passing through the reversing conveying path and the double-sided conveying path when performing a first single-sided printing output in which the sheet is discharged to the output tray with the side that has been printed on one side facing up, and when performing a second single-sided printing output in which the sheet is discharged to the output tray with the side that has been printed on one side facing down, and when performing double-sided printing and paper output, the image forming apparatus controls the discharge control unit to apply a voltage so that the electric field formed in the discharge unit is oriented from the second discharge roller to the first discharge roller when the first single-sided printing and paper output is performed, the discharge control unit controls the discharge control unit to apply a voltage so that the electric field formed in the discharge unit is oriented from the second discharge roller to the first discharge roller when the second single-sided printing and paper output is performed, the discharge control unit controls the discharge control unit to apply a voltage so that the electric field formed in the discharge unit is oriented from the first discharge roller to the second discharge roller when the second single-sided printing and paper output is performed, and the discharge control unit controls the discharge control unit to apply a voltage so that the electric field formed in the discharge unit is oriented from the second discharge roller to the first discharge roller when the second single-sided printing and paper output is performed, and the discharge control unit controls the discharge control unit to apply a voltage so that the electric field formed in the discharge unit is oriented from the first discharge roller to the second discharge roller when the double-sided printing and paper output is performed. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide an image forming system that performs charge removal or charging with an appropriate polarity on a charged sheet. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is an overall view of an image forming apparatus system. [Figure 2] FIG. 1 is a block diagram showing a system configuration of an image forming apparatus according to a first embodiment. [Figure 3] FIG. [Figure 4] FIG. 1 is a cross-sectional view of an image forming apparatus according to a first embodiment. [Figure 5] FIG. [Figure 6] FIG. 10 is an explanatory diagram of sheet adhesion in the loading section. [Figure 7] FIG. [Figure 8] FIG. [Figure 9] Transport guide for non-contact static elimination unit. [Figure 10] (a) A diagram showing face-up paper ejection. (b) A diagram showing face-down paper ejection. [Figure 11] FIG. 2 is an operational block diagram according to the first embodiment. [Figure 12] FIG. [Figure 13] FIG. 2 is a top view of an example of an operation unit of the static eliminator. [Figure 14] FIG. 10 is a block diagram showing the system configuration of an image forming apparatus according to a second embodiment. [Figure 15] FIG. 10 is a cross-sectional view of an image forming apparatus according to a second embodiment. [Figure 16] FIG. 10 is a schematic diagram of a charge-giving unit in Example 2. [Figure 17] FIG. 10 is an explanatory diagram of prevention of sticking at the loading section in the second embodiment. [Figure 18] 10 is a diagram showing double-sided printing paper output. [Figure 19] FIG. 10 is a diagram illustrating a paper output setting screen. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. The dimensions, materials, shapes, relative positions, and the like of the components described in the following embodiments are not intended to limit the scope of application of the present technology unless otherwise specified.

[0013] [Example 1] <Configuration of image forming system> 1 is a configuration diagram of an image forming system 100 including an image forming apparatus according to this embodiment. The image forming system 100 includes an image forming apparatus 101 and an external controller 105. The image forming apparatus 101 and the external controller 105 are communicably connected via an internal LAN 108 and a video cable 109. The external controller 105 is connected to a client PC via an external LAN 107. The external controller 105 acquires a print instruction (print job) from a client PC 106.

[0014] A printer driver that has the function of converting images into a print description language that can be processed by the external controller 105 is installed in the client PC 106. A user can issue a printing instruction via the printer driver using various applications. The printer driver transmits a print job including image data to the external controller 105 based on a job from the user. The external controller 105 accepts the print job from the client PC 106, performs data analysis and rasterization processing on the image data included in the print job, and instructs the image forming apparatus 101 to print (form an image) based on the image data.

[0015] The image forming apparatus 101 includes a printing device 102, a static eliminator 103, and a finisher 104. The printing device 102 forms an image on a sheet based on instructions from an external controller 105. The static eliminator 103, which is disposed downstream of the printing device 102, eliminates static electricity from the sheet on which the image has been formed by the printing device 102. The finisher 104, which is disposed downstream of the static eliminator 103, stacks the sheet on which the image has been formed by the printing device 102 onto a discharge tray 137.

[0016] Although the image forming system 100 is configured such that an external controller 105 is connected to the image forming apparatus 101, the external controller 105 is not necessarily required. For example, the image forming apparatus 101 may be configured to directly receive a print job including image data from a client PC 106 via an external LAN 107. In this case, the image forming apparatus 101 performs the data analysis and rasterization processes that are performed by the external controller 105. In other words, the image forming apparatus 101 and the external controller 105 may be configured as an integrated unit.

[0017] <System configuration of image forming device> FIG. 2 is a block diagram showing the system configuration of the image forming apparatus 101. First, the configuration of the printing apparatus 102 of the image forming apparatus 101 will be described. The printing apparatus 102 has a communication interface (I / F) 201 for communicating with other devices. The printing apparatus 102 has an HDD 202, a CPU 203, a memory 204, and an on-belt reading unit 212 for controlling the operation of the printing apparatus 102. The printing apparatus 102 has a laser exposure unit 207, an image creating unit 208, a fixing unit 209, a paper feed unit 210, and a conveying unit 211 for forming an image. The printing apparatus 102 has an operation unit 205 and a display 206 as a user interface. These components are connected to each other so that they can communicate with each other via a system bus 213.

[0018] The communication I / F 201 is connected to the static eliminator 103 via a communication cable 229 and controls communication between the printing device 102 and the static eliminator 103. When the printing device 102 and the static eliminator 103 operate in cooperation with each other, information and data are transmitted and received via the communication I / F 201.

[0019] The CPU 203 comprehensively performs image processing and image formation processing (print control) by executing computer programs stored in the HDD 202. The memory 204 provides a work area for the CPU 203 to execute various processes. When performing image formation processing, the CPU 203 controls a laser exposure unit 207, an image creation unit 208, a fixing unit 209, a paper feed unit 210, and a conveyance unit 211.

[0020] The laser exposure unit 207 includes a photoconductor, a charging wire for charging the photoconductor, and a light source for exposing the photoconductor to light to form an electrostatic latent image on the photoconductor. The photoconductor may be, for example, a photoconductor belt having a photosensitive layer formed on the surface of a belt-shaped elastic member, or a photoconductor drum having a photosensitive layer formed on the surface of a cylinder. A charging roller may be used instead of the charging wire. The laser exposure unit 207 charges the surface of the photoconductor to a uniform negative potential using the charging wire. The laser exposure unit 207 outputs laser light from a light source based on image data. The laser light scans the uniformly charged surface of the photoconductor. This changes the potential of the photoconductor at the position irradiated with the laser light, forming an electrostatic latent image on the surface. Four photoconductors are provided, one for each of the four colors: yellow (Y), magenta (M), cyan (C), and black (K). Electrostatic latent images corresponding to different color images are formed on the four photoconductors.

[0021] The image forming unit 208 transfers the toner image formed on the photosensitive member onto a sheet. The image forming unit 208, which serves as an image printing unit, includes a developing unit, a transfer unit, and a toner supply unit. The developing unit uses negatively charged toner to develop the image. Four developing units are provided, one for each of the four colors: yellow (Y), magenta (M), cyan (C), and black (K). The developing unit visualizes the electrostatic latent image on the photosensitive member using toner of the corresponding color. When the amount of toner inside the developing unit runs low due to the formation of a toner image, the toner supply unit replenishes the toner.

[0022] The transfer unit has an intermediate transfer belt 118 and transfers a toner image from each photosensitive member onto the intermediate transfer belt 118. Primary transfer rollers are provided at positions facing the photosensitive members across the intermediate transfer belt 118. By applying a positive potential to the primary transfer rollers, the toner images from each of the four photosensitive members are transferred onto the intermediate transfer belt 118 in a superimposed state. In this way, a full-color toner image is formed on the intermediate transfer belt 118. The full-color toner image formed on the intermediate transfer belt 118 is transferred from the intermediate transfer belt 118 to the sheet P by applying a bias of the same polarity as the toner from a secondary transfer inner roller 119a inside the intermediate transfer belt 118.

[0023] The fixing unit 209 fixes the transferred toner image onto the sheet. The fixing unit 209 has a heater and a pair of rollers. The fixing unit 209 heats and presses the toner image on the sheet using the heater and the pair of rollers, melting and fixing the toner image to the sheet. This forms an image on the sheet. The paper feed unit 210 has a conveyance roller and various sensors on the conveyance path, and controls the sheet feeding operation. The conveyance unit 211 (conveyance control unit) controls the conveyance of sheets in the image forming apparatus 101. The conveyance unit 211 conveys the sheet fed from the paper feed unit 210 to the transfer unit in accordance with the timing of the toner image transfer, and conveys the sheet with the transferred toner to the fixing unit. After the sheet has the toner image fixed by the fixing unit 209, it is selected whether to head to the conveyance path 125 or the reverse conveyance path 126 after passing through the fixing unit, depending on the information of the input print data.

[0024] The on-belt reading unit 212 reads an image formed on the intermediate transfer belt of the transfer unit based on instructions from the CPU 203. For example, when adjusting image formation conditions, the CPU 203 reads an image for adjusting the image formation conditions formed on the intermediate transfer belt 118 using the on-belt reading unit 212. The operation unit 205 is an input device that accepts input of various settings and operation instructions from the user. The operation unit 205 is, for example, various input keys or a touch panel. The display 206 as a display unit is an output device that displays setting information of the image forming apparatus 101 and the processing status (status information) of a print job.

[0025] Next, a description will be given of the configuration of the static eliminator 103. The static eliminator 103 includes a communication I / F 221, a contact static elimination control unit 222, and a non-contact static elimination control unit 223. These components are connected via a system bus 225.

[0026] The communication I / F 221 is connected to the printing device 102 via a communication cable 229, and controls communication between the printing device 102 and the static eliminator 103. The communication I / F 221 is also connected to the finisher 104 via a communication cable 239, and controls communication between the static eliminator 103 and the finisher 104.

[0027] The contact static elimination control unit 222 and the non-contact static elimination control unit 223 perform various controls based on control instructions received from the CPU 203 via the communication cable 229. The contact static elimination control unit 222 includes a static elimination control switch unit 251 and a static elimination voltage adjustment unit 252, and controls the static elimination voltage of the contact static elimination unit 129, which will be described later. The static elimination control switch unit 251 acquires the state of a mode lever 141 shown in FIG. 3 and switches the contact static elimination unit 129 ON / OFF based on the state of the mode lever 141. The static elimination voltage adjustment unit 252 acquires a setting value set in a dial 142, which will be described later, and controls the magnitude of the voltage (voltage value, high voltage value) to be applied to the contact static elimination unit 129 based on the setting value and the polarity of the voltage to be applied to the static elimination roller 130b determined by the static elimination CPU 224. In this embodiment, the setting value set in the dial 142 is an absolute value. The non-contact static elimination control unit 223 controls static elimination by the non-contact static elimination unit 131, which will be described later. In this embodiment, the static eliminator 103 operates based on control instructions from a CPU 203 mounted on the image forming apparatus 101, but the operation of the static eliminator 103 is not limited to this, and control instructions may be given by a CPU mounted on the static eliminator 103, for example. A drive unit 226 controls the driving of a motor provided in the static eliminator 103 for conveying a sheet.

[0028] Next, a description will be given of the configuration of the finisher 104. The finisher 104 includes a communication I / F 231, a CPU 232, a memory 233, and a paper discharge control unit 234. These components are connected via a system bus 235.

[0029] The communication I / F 231 is connected to the static eliminator 103 via a communication cable 239, and controls communication between the static eliminator 103 and the finisher 104. The CPU 232 performs various controls required for paper discharge 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 paper discharge control unit 234 controls the transport of the transported sheet to the discharge tray 137 based on instructions from the CPU 232.

[0030] <Configuration of image forming device> 4 is a cross-sectional view of the image forming apparatus 101. A display 206 is provided on the top of the housing of the printing apparatus 102. The display 206 displays the printing status of the image forming apparatus 101 and information for settings.

[0031] The printing device 102 includes paper feed decks 111 and 112, transport paths 113, 122, 124, and 125, a reverse transport path 126, a duplex transport path 127, and various rollers. Each of the paper feed decks 111 and 112, which form a paper feed unit 210, can accommodate different types of sheets. The topmost sheet stored in the paper feed decks 111 and 112 is separated and fed to the transport path 113. The printing device 102 includes image forming units 114, 115, 116, and 117 as a laser exposure unit 207 for forming images, and forms color images on sheets. The image forming unit 114 forms a black (K) image (toner image). The image forming unit 115 forms a cyan (C) image. The image forming unit 116 forms a magenta (M) image. The image forming unit 117 forms a yellow (Y) image.

[0032] The printing device 102 includes, as an image creation unit 208, an intermediate transfer belt 118 and a secondary transfer roller 119 onto which toner images are transferred from the image forming units 114, 115, 116, and 117. The intermediate transfer belt 118 rotates clockwise in the figure, and toner images are transferred (primary transfer) onto the intermediate transfer belt 118 in the order of image forming units 117, 116, 115, and 114, superimposed on one another. As a result, a full-color toner image is formed on the intermediate transfer belt 118. As the intermediate transfer belt 118 rotates, it transports the toner image to the secondary transfer roller 119. In synchronization with the timing at which the toner image is transported to the secondary transfer roller 119, the transport unit 211 transports the sheet into the transport path 113 and sends it to the secondary transfer unit 214. A high voltage of the same polarity as the toner is applied to the inner secondary transfer roller 119a in order to transfer (secondary transfer) the toner image on the intermediate transfer belt 118 onto the transported sheet. The toner on the intermediate transfer belt 118 repels from the intermediate transfer belt 118 and is transferred onto the sheet in the transfer nip. In this embodiment, since the toner has a negative polarity, a negative voltage is applied to the inner secondary transfer roller 119a. Meanwhile, the outer secondary transfer roller 119b is electrically grounded. However, a bias of the opposite polarity to the toner may be applied to the outer secondary transfer roller 119b, and the inner secondary transfer roller 119a may be electrically grounded.

[0033] An on-belt reading sensor 120 serving as an on-belt reading unit 212 is provided near the intermediate transfer belt 118. The on-belt reading sensor 120 is located downstream of the image forming units 114, 115, 116, and 117 in the rotation direction of the intermediate transfer belt 118. The on-belt reading sensor 120 reads images transferred to the intermediate transfer belt 118 from the image forming units 114, 115, 116, and 117. The on-belt reading sensor 120 is, for example, an optical sensor, and reads the image by irradiating the image on the intermediate transfer belt 118 with light and receiving the reflected light. For example, the on-belt reading sensor 120 reads an adjustment image formed on the intermediate transfer belt 118 for adjusting image formation conditions. The CPU 203 analyzes the results of reading the adjustment image by the on-belt reading sensor 120 and performs calibration by feeding the results back to the image formation conditions.

[0034] The printing apparatus 102 includes a first fuser 121 and a second fuser 123 as a fuser unit 209. The first fuser 121 and the second fuser 123 have the same configuration and fuse a toner image onto a sheet. To fuse a toner image onto a sheet, the first fuser 121 and the second fuser 123 each include a pressure roller and a heating roller. The sheet is heated and pressurized as it passes between the pressure roller and the heating roller, melting and bonding the toner image. After passing through the second fuser 123, the sheet is transported to a transport path 124. The second fuser 123 is located downstream of the first fuser 121 in the sheet transport direction and is used to add gloss to the image on the sheet that has been fused by the first fuser 121 and to ensure fixation. For this reason, the second fuser 123 may not be used depending on the type of sheet or the content of the print job. A conveying path 122 is provided to convey the sheet that has undergone the fixing process in the first fixing device 121 without passing through the second fixing device 123.

[0035] A conveyance path 125 and a reversing conveyance path 126 are provided after the conveyance path 124 and the conveyance path 122 merge. When there is an instruction for double-sided printing or for the sheet to be stacked on the discharge tray 137 with the image formed side facing downwards (hereinafter referred to as face-down discharge), the sheet is conveyed to the reversing conveyance path 126. When there is an instruction for double-sided printing, the sheet conveyed to the reversing conveyance path 126 has its conveyance direction reversed by the reversing conveyance path 126 and is conveyed to the double-sided conveyance path 127. The sheet is reversed by the reversing conveyance path 126 and the double-sided conveyance path 127 so that the side on which the image is formed (the first side) is turned over. The sheet is conveyed again to the conveyance path 113 by the double-sided conveyance path 127, and passes through the secondary transfer unit 214 again, where an image is formed on the second side. In the case of face-down discharge, the sheet drawn into the reversing conveyance path 126 is switched back and directed toward the conveyance path 160, allowing the sheet to be discharged with the image formed side facing downwards. In the case of single-sided printing, or in the case of double-sided printing with images formed on both sides, the sheet is transported to the static eliminator 103 via the transport path 125 and the transport path 160. In the case of a single-sided printing job, an image is formed only on the first side of the sheet, and in the case of a double-sided printing job, an image is formed on both the first and second sides of the sheet. The transport of these sheets is controlled by the transport unit 211 (transport control unit).

[0036] <Explanation of the secondary transfer unit> As described above in the description of the <Configuration of the Image Forming Apparatus>, in the secondary transfer unit 214, the toner image on the intermediate transfer belt 118 is transferred (secondary transfer) to the sheet at the transfer nip formed by the secondary transfer roller 119 and the intermediate transfer belt 118. As shown in FIG. 5 , in this embodiment, a high voltage is applied from the secondary transfer high-voltage board 138 to the inner secondary transfer roller 119a inside the intermediate transfer belt 118 to transfer the toner image. Therefore, it is necessary to apply a polarity in the direction in which the toner image is peeled from the transfer belt 118, and a high voltage of the same polarity as the toner is applied. In this embodiment, since the toner has a characteristic of being negatively charged, a high voltage of negative polarity is applied to the inner secondary transfer roller 119a. The upper surface of the sheet that has passed through the secondary transfer unit 214 is negatively charged, and the lower surface of the sheet is positively charged due to dielectric polarization.

[0037] <Configuration of static eliminator> The static eliminator 103 includes a conveying path 128, a contact static eliminator 129, a non-contact static eliminator 131, and a plurality of conveying rollers 256. As described above, in this embodiment, a sheet that has passed through the secondary transfer unit 214 is negatively charged on the upper surface of the sheet and positively charged on the lower surface of the sheet due to dielectric polarization. Therefore, as shown in FIG. 6, if sheets are stacked on the discharge tray 137 without undergoing static elimination, the contact surfaces of the stacked sheets may have opposite polarities, which may cause the sheets to stick together due to electrostatic force. In this embodiment, the static eliminator 103 removes charges from the sheet surfaces using the contact static eliminator 129 and the non-contact static eliminator 131 to prevent the sheets from sticking together due to electrostatic force. The non-contact static eliminator 131 (non-contact static eliminator), located downstream of the contact static eliminator 129, eliminates static charges from the conveyed sheet without contacting the sheet (in a non-contact state). A top surface 103a constituting the top surface of the exterior of the static eliminator 103 is provided with a static elimination operation unit 132 that allows an operator to set the ON / OFF of the contact-type static eliminator 129 and the voltage value (static elimination voltage). A sheet transported from the printing device 102 to the static eliminator 103 passes through a transport path 128 and is neutralized by the contact-type static eliminator 129 and the non-contact static eliminator 131. The sheet that has undergone static elimination processing is then transported to the finisher 104.

[0038] <Finisher configuration> The finisher 104 stacks sheets delivered from the printing device 102. The finisher 104 is equipped with a conveyance path 135 and a discharge tray 137 on which sheets are stacked. The conveyance path 135 is provided with conveyance sensors 133, 134, and 136. Sheets conveyed from the printing device 102 are discharged to the discharge tray 137 via the conveyance path 135. The conveyance sensors 133, 134, and 136 detect the passage of the sheet conveyed along the conveyance path 135. If the conveyance sensors 133, 134, and 136 do not detect the leading or trailing edge of the sheet in the conveyance direction even after a predetermined time has elapsed since the start of sheet conveyance, the CPU 232 determines that a conveyance jam (conveyance abnormality) has occurred in the finisher 104. In this case, the CPU 232 notifies the printing device 102 that a conveyance jam has occurred.

[0039] <Configuration of contact-type static eliminator> 7 is a cross-sectional view showing the configuration of the contact-type charge eliminating unit 129. The contact-type charge eliminating unit 129 is composed of a charge eliminating opposing roller 130a and a charge eliminating roller 130b as a pair of charge eliminating rollers that come into contact with the sheet P. The charge eliminating roller 130b is made of an elastic layer of ion-conductive foamed rubber and a core metal, has an outer diameter of 20 to 25 mm, and a resistance of 1×10 when measured in an environment at 23°C and 50% RH with a voltage of 2 kV applied. 5 ~1×10 8 The static elimination counter roller 130a is made of stainless steel (SUS) and is electrically grounded (connected to ground). A roller with an outer diameter of 20 to 25 mm is used, and is positioned opposite the static elimination roller 130b to form a static elimination nip. The static elimination counter roller 130a is driven by a static elimination drive motor (not shown) to rotate and transport the sheet held in the static elimination nip. Furthermore, the contact-type static elimination unit 129 is provided with a static elimination high-voltage board 230. Specifically, the static elimination high-voltage board 230 applies a voltage to the static elimination roller 130b, which serves as a static elimination member. In this embodiment, the static elimination high-voltage board 230 is configured to apply voltages of both positive and negative polarities with approximately the same absolute value. In this embodiment, the static elimination roller 130b is positioned below the sheet, but the static elimination roller 130b and the static elimination counter roller 130a may be positioned in reverse. In this embodiment, the static elimination high-voltage board 230 is capable of applying both positive and negative polarities with a single board, but the high-voltage board may be provided with two built-in high-voltage boards, one for positive and one for negative. The polarity of the voltage applied to the static elimination member by the high-voltage board 230 is determined according to the polarity of the charge on the surface of the sheet transported to the contact-type static elimination unit 129. In this embodiment, the first static elimination roller is static elimination roller 130b, and the second static elimination roller is static elimination opposing roller 130a.

[0040] The contact-type static eliminator 129 of this embodiment has a high static elimination effect because it contacts the sheet P and applies a voltage directly. On the other hand, the contact-type static eliminator 129 has a characteristic that the surface potential of the neutralized sheet P varies greatly, making static elimination uneven. Therefore, in the static eliminator of this embodiment, a non-contact-type static eliminator 131 is provided downstream of the contact-type static eliminator 129 in the conveyance direction.

[0041] <Configuration of non-contact static eliminator> FIG. 8 is a cross-sectional view showing the configuration of the non-contact static eliminator 131. FIG. 9 is a plan view of the conveying guide 260. The non-contact static eliminator 131 of this embodiment is capable of uniformly adjusting the surface potential of the sheet P that has become uneven due to the static elimination process by the contact static eliminator 129 described above. The non-contact static eliminator 131 is composed of an ionizer 240 and a conveying guide 260. The ionizer is a bar type IZS40 (SMC Corporation) that is arranged above and below the sheet P to form an ionizer irradiation section. The conveying guide 260 arranged in the ionizer irradiation section uses an insulating resin that is a composite of PC (polycarbonate) and ABS (acrylonitrile-butadiene-styrene). The volume resistivity of the conveying guide in this embodiment is 1×10 14Ω·cm. Furthermore, as shown in FIG. 9 , holes are provided in the conveying guides 260 arranged on the upper and lower sides of the sheet to prevent ions generated from the ion irradiation unit from being physically blocked by the sheet conveying member. An AC bias is applied to the ionizer 240, and positive and negative ions are alternately emitted by corona discharge. Therefore, residual charge can be eliminated regardless of the polarity of the residual charge at the contact-type static eliminator 129. The static elimination effect of the non-contact static eliminator 131 on the sheet P in this embodiment is smaller than that of the contact-type static eliminator 129, but the surface potential of the sheet P after static elimination is less variable. Therefore, the non-contact static eliminator 131 can even out the surface potential of the sheet P that has become uneven due to the contact-type static eliminator 129. Note that, although an ionizer is used as the non-contact static eliminator 131 in this embodiment, this is not limited thereto. For example, the non-contact static eliminator 131 may be an AC corotron type that applies a high voltage to a wire. In addition, in this embodiment, the ionizers are arranged on the upper and lower surfaces of the sheet in the non-contact static eliminator 131, but this is not limiting. For example, the non-contact static eliminator 131 may be arranged only on one side of the sheet, either the upper or lower side. Furthermore, the high voltage applied may be a DC voltage instead of an AC voltage.

[0042] <Configuration of the static eliminator operation unit> As shown in FIG. 3, the static elimination device 103 is provided with a static elimination operation unit 132 for setting the operation of the contact-type static eliminator 129. The static elimination operation unit 132 is disposed on a top surface 103a (top surface of the device) of the exterior of the static eliminator 103. The static elimination operation unit 132 includes a mode lever 141 and a dial 142. The mode lever 141 is a selector switch for manually switching between "ON" and "OFF" (enabled and disabled) the application of voltage to the static elimination roller 130b by the static elimination high-voltage board 230. The state of the mode lever 141 is acquired by a static elimination control switching unit 251. The static elimination control switching unit 251 switches the contact-type static eliminator 129 between ON and OFF based on the state of the mode lever 141. The non-contact static eliminator 131 is always in the ON state, regardless of the settings of the mode lever 141 and the dial 142. Note that the sheet is transported even when the mode lever 141 is in the OFF state. The dial 142 is composed of a button 142a and a display unit 142b, and when the operator presses the button 142a, the number displayed on the display unit 142b changes. The set value set on the dial 142 is acquired by the static elimination voltage adjustment unit 252. In this embodiment, the value displayed on the dial 142 multiplied by 0.1 kV becomes the absolute value of the voltage to be applied to the contact-type static elimination unit 129. However, instead of displaying the first two digits of the absolute value of the voltage to be applied, the absolute value of the voltage to be applied itself may be displayed, or the level of the voltage to be applied may be expressed in, for example, 10 stages and a numerical value may be displayed.

[0043] <Bias polarity setting according to the paper ejection side> As described above, the secondary transfer unit 214 in this embodiment causes the upper surface (image-forming surface) of the sheet to have a negative charge, and the lower surface (rear surface) of the sheet to have a positive charge. The user also uses the client PC 106 or the operation unit 205 to select one of face-up output for single-sided printing, face-down output for single-sided printing, and double-sided output, as shown in FIG. 19 . Note that face-up output for single-sided printing and face-down output for single-sided printing are sheet output methods for single-sided print jobs. The sheet P is transported to the selected output method based on the user's printing information, and is output to the output tray 137. In the case of face-up output for single-sided printing, the sheet is output to the output tray 137 with the side with the printed image on the single side facing up. In the case of face-down output for single-sided printing, the sheet is output to the output tray 137 with the side with the image on the bottom facing down. In the case of double-sided printing, the sheet is output to the output tray 137 with the second side, which is the back side of the first side, facing up. In a double-sided printing job, the first side of a sheet refers to the side on which the first image is formed, and the second side refers to the side on which the second image is formed. As shown in Fig. 4, when the reverse conveyance path 126 is provided upstream of the static eliminator 103 in the conveyance direction, the polarity of the charge on the surface of the sheet conveyed to the static eliminator 103 differs depending on the setting for single-sided printing / double-sided printing and the setting for the front / back orientation of the sheet when it is discharged. Therefore, the static elimination high-voltage board 230 of the static eliminator 103 switches to an appropriate polarity and applies a voltage to the static elimination roller 130b.

[0044] FIG. 10(a) shows face-up discharge of one side, and FIG. 10(b) shows face-down discharge of one side. As shown in FIG. 10, when face-up discharge of one side is specified, the sheet is not inverted, and therefore is transported to the static elimination device 103 with the top surface of the sheet negatively charged and the bottom surface of the sheet positively charged. In other words, the sheet is transported to the static elimination device 103 with the top and bottom surfaces of the sheet still charged to the polarities charged by the secondary transfer unit 214. To eliminate static electricity from a sheet in this state, the static elimination roller 130b arranged on the bottom side of the sheet must apply a negative charge to the sheet. For this reason, the static elimination high-voltage board 230 applies a negative voltage to the static elimination roller 130b.

[0045] On the other hand, when face-down discharge of one side is specified, the sheet is transported to the static eliminator 103 via the reversing transport path 126. At this time, the sheet is reversed by the reversing transport path 126, so that the image-forming side faces down and the non-image-forming side faces up. In other words, because the sheet is reversed, the top side of the sheet is positively charged and the bottom side of the sheet is negatively charged before being transported to the static eliminator 103. For this reason, the static elimination roller 130b arranged on the bottom side of the sheet must apply a positive charge to the sheet. For this reason, the static elimination high-voltage board 230 applies a positive voltage to the static elimination roller 130b.

[0046] FIG. 18 is a diagram illustrating duplex printing and paper ejection. As shown in FIG. 18, in the case of duplex printing, an image is first formed on the first side of the sheet by the secondary transfer unit 214. Then, the sheet's conveyance direction is reversed by the reversing conveyance path 126, and the sheet is conveyed to the duplex conveyance path 127. At this time, the sheet is reversed by the reversing conveyance path 126, so that when an image is formed on the second side of the sheet, the sheet is conveyed to the secondary transfer unit 214 with the top side positively charged and the bottom side negatively charged. At this time, the amount of charge on the sheet attenuates during conveyance due to friction with the grounded conveyance guide while being conveyed through the reversing conveyance path 126 and the duplex conveyance path 127. Note that, compared to low-resistance sheets, the amount of charge attenuates less during conveyance through the reversing conveyance path 126 and the duplex conveyance path 127, and therefore the charge on the sheet remains even when the image is transferred to the second side. The magnitude of the transfer current (current flowing from the secondary transfer roller to the sheet S) required to achieve good transfer performance is essentially the same during single-sided printing and during the secondary transfer of the first and second sides in double-sided printing. During the transfer of the second side in double-sided printing, a portion of the negative charge supplied to the sheet surface from the inner secondary transfer roller 119a is consumed to offset the positive charge on the sheet surface that was generated during the secondary transfer of the first side and remains until the transfer of the second side. As a result, the amount of charge on the sheet immediately after the secondary transfer to the second side in double-sided printing is smaller than the amount of charge on the sheet immediately after the secondary transfer in single-sided printing. That is, the amount of charge on a double-sided printed sheet transported to the static eliminator 103 is smaller than the amount of charge on a single-sided printed sheet transported to the static eliminator 103. In other words, in double-sided printing, the sheet is transported to the static eliminator 103 with a negative charge on the top side and a positive charge on the bottom side. In this case, the static eliminator roller 130b, located on the bottom side of the sheet, must impart a negative charge to the sheet. Therefore, the static elimination high-voltage board 230 applies a negative voltage to the static elimination roller 130b. The amount of charge when a double-sided printed sheet is transported to the static elimination device 103 is smaller than the amount of charge when a single-sided printed sheet is transported to the static elimination device 103, so the optimum value of the static elimination voltage for double-sided printing is a value whose absolute value is smaller than the static elimination voltage value for single-sided printing.

[0047] In this embodiment, the static elimination high-voltage board 230 can select either polarity to apply voltage. Therefore, the static elimination roller 130b can apply a negative charge to the sheet during face-up discharge for single-sided printing and during face-down discharge for double-sided printing, and the static elimination roller 130b can apply a positive charge to the sheet during face-down discharge for single-sided printing. In other words, during face-up discharge for single-sided printing and during face-down discharge for double-sided printing, the static elimination CPU 224 determines the polarity of the voltage that the static elimination high-voltage board 230 applies to the static elimination roller 130b to be negative (first polarity), and during face-down discharge for single-sided printing, the static elimination CPU 224 determines the polarity of the voltage that the static elimination high-voltage board 230 applies to the static elimination roller 130b to be positive (second polarity).

[0048] That is, in the case of face-up discharge of single-sided printing and double-sided printing, a voltage is applied to the discharge roller so that the electric field is oriented from the discharge roller 130a (second discharge roller) to the discharge roller 130b (first discharge roller). Furthermore, in the case of face-down discharge of single-sided printing, a voltage is applied to the discharge roller so that the electric field is oriented from the discharge roller 130b (first discharge roller) to the discharge roller 130a (second discharge roller). In this case, since the voltage is applied so as to achieve the above-mentioned electric field orientation, it is not necessary for the discharge high-voltage board 230 to be capable of applying both polarities, and only one polarity may be applied. For example, a negative high-voltage power supply may be connected to each of the discharge roller 130b and the discharge roller 130a, and the connection to the negative high-voltage power supply may be switched depending on the discharge method. Specifically, when the direction of the electric field is changed from the discharge roller 130a to the discharge roller 130b, a negative voltage is applied to the discharge roller 130b, and when the direction of the electric field is changed from the discharge roller 130b to the discharge roller 130a, a negative voltage is applied to the discharge roller 130a. However, in this embodiment, whether or not to discharge a sheet passing through the discharge device 103 is determined by the state of the mode lever 141 described above, and the magnitude (absolute value) of the voltage used for discharge is set by the dial 142. In this embodiment, the first single-sided printed sheet discharge is a face-up discharge of a single-sided printed sheet, and the second single-sided printed sheet discharge is a face-down discharge of a single-sided printed sheet.

[0049] FIG. 11 is a block diagram illustrating the operation of this embodiment. Print data is input directly from a PC 106 connected externally to the printing apparatus 102 or via an external controller 105 (not shown in FIG. 11). The user may specify print data stored in the HDD inside the printing apparatus 102 by operating the operation unit 205. The CPU 203 in the printing apparatus 102, upon receiving the print data, determines the necessary image creation and transport conditions from the print data. At this time, the CPU 203 determines sheet ejection side information from information input from the operation unit 205 or the PC 106. The CPU 203 passes the sheet information, image information, and ejection side information specified in the print data to the static elimination CPU 224. Based on the received ejection side information, the static elimination CPU 224 determines the polarity to be applied to the static elimination member to eliminate static electricity from the sheet. Whether or not to actually apply a static elimination high voltage and the magnitude of the static elimination high voltage are determined based on the settings of a static elimination control switching unit 251 and a static elimination voltage adjusting unit 252 connected to the contact static elimination control unit 222. Specifically, the static elimination voltage adjustment unit 252 acquires the setting value (absolute value) set on the dial 142 and the polarity determined by the static elimination CPU 224. Then, the static elimination voltage adjustment unit 252 sets the magnitude of the voltage (voltage value, high voltage value) based on the acquired absolute value and polarity to the high-voltage board 230. The high-voltage board 230 applies a voltage to the static elimination roller 130b at the set voltage magnitude. Furthermore, the static elimination CPU 224 outputs static elimination setting information to the non-contact static elimination control unit 223, and the non-contact static elimination control unit 223 controls the voltage to drive the ionizer 240. Furthermore, the static elimination CPU 224 outputs a drive command to the static elimination motor driver 253, and the driver drives various motors to transport the sheet. The static elimination roller motor 254 is driven to rotate the static elimination opposing roller 130a, and the transport roller motor 255 is driven to rotate multiple transport rollers 256, thereby transporting the sheet.

[0050] FIG. 12 is a flowchart illustrating the operation of this embodiment. First, in S001, the user transmits print data, and printing begins. In S002, the print data specified by the user is acquired, and the discharge CPU 224 obtains the information specifying the discharge side. In S003, it is confirmed whether the print is single-sided or double-sided. If it is single-sided, the process proceeds to S004. If the discharge side specification for single-sided printing is face-down discharge in S004, the sheet is inverted, so the polarity of the voltage applied to the discharge roller 130b is set to positive (S005). If it is face-up discharge for single-sided printing or double-sided printing, the polarity of the applied voltage is determined to be negative (S013). Next, the discharge CPU 224 checks whether the mode lever 141 is ON (S006). If it is ON, it determines the magnitude of the discharge voltage from the dial 142 (S007). If the mode lever 141 is OFF in S006, no discharge voltage is applied (S014). Once the static elimination settings are determined, the motor in the static eliminator is driven in S008 and S015 to rotate the rollers. Thereafter, if static elimination is ON, high voltage is applied to static elimination roller 130b (S009). If it is determined that the submitted print job has ended (Y in S010 and S016), if static elimination is ON, the high voltage to static elimination roller 130b is turned OFF (S011), the rollers in the static eliminator are stopped (S012), and printing is completed (S017).

[0051] By implementing the invention described above, it is possible to neutralize a charged sheet with an appropriate polarity.

[0052] In this embodiment, the non-contact static eliminator 131 is supplied with an AC voltage, which alternately emits positive and negative ions through corona discharge. Therefore, the non-contact static eliminator 131 is always ON regardless of whether the paper is ejected face-up for single-sided printing, face-down for single-sided printing, or double-sided printing. However, the polarity of the static eliminator can be switched depending on the paper ejection method not only by the contact static eliminator 129 but also by the non-contact static eliminator 131. If the non-contact static eliminator 131 can switch between positive and negative DC voltages, it is better to apply a voltage with a polarity corresponding to the polarity of the charge on the top and bottom surfaces of the sheet when it is transported to the static eliminator. For example, an ionizer located below the sheet may impart a negative charge to the sheet when ejected face-up for single-sided printing and double-sided printing, and a positive charge to the sheet when ejected face-down for single-sided printing. In this embodiment, the ON / OFF and magnitude of the static elimination high voltage can be manually set using the mode lever 141 and dial 142 provided on the static eliminator 103. However, the embodiment is not limited to this. The static elimination CPU 224, which receives sheet information and image information from the CPU 203 of the printing apparatus 102, may automatically set the ON / OFF of static elimination and the magnitude of the static elimination high voltage based on a static elimination setting table stored in the memory 250, while determining the polarity according to the discharged paper surface. The static elimination setting table determines the static elimination voltage based on the type and size of the sheet, such as the material and thickness, the temperature and humidity at which the image forming apparatus is installed, and sensing information within the image forming apparatus and static eliminator. Furthermore, the above determination may be made by the CPU 203 in the image forming apparatus, rather than the static elimination CPU 224.

[0053] 13, the mode lever 141 may be configured to switch between automatic and manual rather than to set the static elimination voltage ON / OFF. When automatic is selected, as described above, the static elimination CPU 224 or CPU 203 automatically determines whether to eliminate static and the static elimination voltage setting value based on the sheet information linked to the print data, inversion information, and environmental information about the main body. When manual is selected, if a value has been input into the dial 142, the static elimination voltage is applied, and the polarity of the applied voltage is determined from the inversion information in the print data.

[0054] The print data input from the client PC 106 or the operation unit 205 to the CPU 203 is not limited to output side information such as single-sided face-up output, single-sided face-down output, or double-sided output, but may also include other job information. In other words, the output method may be automatically determined based on the job information. For example, for a job in which different images are printed on one side of multiple sheets, the CPU 203 may output face-down output as output side information to the static elimination CPU 224, while for a job in which the same image is printed on one side of multiple sheets, face-up output may be output. For a job in which different images are printed on one side of multiple sheets, associating face-down output with the job allows the printed sheets to be arranged in page order. Furthermore, for a job in which the same image is printed on one side of multiple sheets, associating face-up output with the job shortens the distance the sheets must be transported compared to face-down output, thereby shortening the job time. As another example, an appropriate output setting may be associated based on the function settings of an optional unit. For example, if an inner tri-fold function is set in the optional unit, the CPU 203 may output a single-sided print face-up to the static elimination CPU 224. In other words, the sheet discharge method is not limited to the orientation of the image-formed side of the sheet when discharged to the discharge tray 137, as long as it corresponds to the charged state of the top and bottom surfaces of the sheet conveyed to the static elimination device 103.

[0055] [Example 2] In the second embodiment, a charge applying device 800 will be described. The charge removing device 103 in the first embodiment applied a voltage to the charge removing roller 130b so that the surface potential of the sheet approached approximately zero, thereby removing the charge from the sheet. The charge applying device 800 in the second embodiment applies a voltage to the charge applying roller 830b so that the polarity of the surface of every other sheet being continuously conveyed is reversed. The basic configuration of the image forming apparatus and the like is the same as in the first embodiment, and only the differences from the first embodiment will be described. Components with the same reference numerals as in the first embodiment have the same functions, so their description will be omitted.

[0056] <Configuration of image forming system> Fig. 14 shows the system configuration of the image forming apparatus in Example 2, and Fig. 15 shows a cross-sectional view of the image forming apparatus in Example 2. The image forming apparatus 101 is composed of a printing device 102, a charge applying device 800, and a finisher 104. The static eliminator 103 in Example 1 has a non-contact static eliminator, but the charge adjusting device in Example 2 does not have a non-contact static eliminator.

[0057] <Configuration of the charge applying device> 15, the charge applying device 800 includes a conveying path 828, a charge applying unit 829, and a plurality of conveying rollers 856 that receive and convey a sheet from the printing device 102. A charge applying operation unit 832 is provided on a top surface 803a that forms the top surface of the exterior of the charge applying device 800. That is, the static eliminator 103 of the first embodiment includes a non-contact static eliminator 131, but the charge applying device 800 of the second embodiment does not include a non-contact static eliminator.

[0058] 14 shows the system configuration of the image forming apparatus in Example 2. The configuration of the charge applying device 800 will be described. The charge applying device 800 includes a communication I / F 821, a charge applying control unit 822, a charge applying CPU 824, and a drive unit 826. These components are connected via a system bus 825. The charge applying control unit 822 includes a control switching unit 851 and a voltage adjusting unit 852, and controls the voltage applied to the roller of the charge applying unit 829.

[0059] In this embodiment, the upper surface of a sheet that has passed through the secondary transfer unit 214 is negatively charged, and the lower surface of the sheet is positively charged due to dielectric polarization. Therefore, as shown in FIG. 6, when sheets are stacked on the discharge tray 137, the contact surfaces of the stacked sheets have opposite polarities, and there is a risk that the sheets will stick together due to electrostatic force. In this embodiment, the charge applying device 800 performs the following control to prevent the sheets from sticking together due to electrostatic force.

[0060] FIG. 16 shows a schematic diagram of the charge applying unit in the second embodiment. The charge applying unit 829 includes a charge applying roller 830b and a charge applying counter roller 830a as charge applying members that contact the sheet. The charge applying counter roller 830a and the charge applying roller 830b constitute a pair of charge applying rollers as the charge applying unit 829 that apply a charge to the sheet while in contact with the sheet. The charge applying counter roller 830a is electrically grounded (connected to ground). Furthermore, the charge applying roller 830b is provided with a high-voltage board 831. Next, the case of face-up paper ejection will be described. When multiple sheets are successively image-formed, the charge applying control unit 822 controls the high-voltage board 831 to apply a negative voltage to the charge applying roller 830b for every other sheet, so that the electrostatic polarity of the sheet surface is reversed and charged. In other words, the pair of charge applying rollers applies a charge to the sheet with a polarity opposite to the surface potential of the image-formed sheet. This reverses the surface potential of the sheet before and after passing through the pair of charge applying rollers. That is, the charge applying unit performs a charge applying process of applying a charge to every other sheet so that the surface potential of the sheets on which an image is formed is reversed.

[0061] For the sheet following the sheet with the reversed polarity, the charge applying unit 829 turns off the high voltage and does not apply a charge. For the sheet following that, the charge applying unit again applies a charge of the opposite polarity to that of the sheet, reversing the polarity. In this way, the charge application is turned on and off for every other sheet, and when it is turned on, the polarity is reversed.

[0062] When sheets controlled as described above are stacked, the result is as shown in Figure 17. When stacking, the opposing surfaces of the sheets repel each other with the same polarity, creating a repulsive force that prevents the sheets from sticking together.

[0063] In this embodiment, as in the first embodiment, as shown in Fig. 10, in the case of face-down discharge in single-sided printing, the sheet is transported to the charging device 800 with its upper surface positively charged and its lower surface negatively charged. Then, as shown in Figs. 10 and 18, in the case of face-up discharge in single-sided printing and double-sided printing, the sheet is transported to the charging device 800 with its upper surface negatively charged and its lower surface positively charged. In the charging device 800, the high-voltage board 831 can also apply a voltage of either polarity. Therefore, during face-up discharge in single-sided printing and double-sided printing, the charging roller 830b can apply a negative charge to the sheet, and during face-down discharge in single-sided printing, the charging roller 830b can apply a positive charge to the sheet. In other words, in the case of face-up discharge in single-sided printing and double-sided printing, the charge applying CPU 824 determines the polarity of the voltage that the high-voltage board 831 applies to the charge applying roller 830b to be negative (first polarity), and in the case of face-down discharge in single-sided printing, the charge applying CPU 824 determines the polarity of the voltage that the high-voltage board 831 applies to the charge applying roller 830b to be positive (second polarity). In other words, in the second embodiment, as in the first embodiment, the charge applying CPU 824 selects an appropriate polarity from the print data, and the charge of the charged sheet can be adjusted to an appropriate polarity in the same way as in the first embodiment. [Explanation of symbols]

[0064] 100 Image forming system 102 Printing device 103 Static eliminator 126 Reversing conveyance path 127 Double-sided transport path 129 Contact-type static eliminator 211 Conveyor 224 Static elimination CPU 230 Antistatic high voltage board 800 Charge applying device

Claims

1. an image printing unit that prints an image on a sheet; a reversing conveying path that reverses the conveying direction of the sheet printed by the image printing unit and conveyed; a double-sided conveying path that conveys the sheet conveyed from the reversing conveying path back to the image printing unit; a discharge tray on which discharged sheets are stacked; a conveyance control unit that controls conveyance of the sheet; a static elimination unit that applies a voltage to a static elimination member to eliminate static electricity from the sheet printed by the image printing unit; a static elimination control unit that controls the polarity of the voltage applied to the static elimination member; and the reverse conveyance path is disposed downstream of the image printing unit and upstream of the static elimination unit in a sheet conveyance direction, when performing a first single-sided printing discharge in which the sheet is discharged onto the discharge tray with the single-sided printed side facing up, the conveyance control unit conveys the sheet to the static elimination unit without passing through the reversing conveyance path and the double-sided conveyance path; When a second single-sided printing discharge is performed in which the sheet is discharged onto the discharge tray with the single-sided printed side facing downward, the sheet is conveyed to the static elimination unit via the reversing conveyance path but not via the double-sided conveyance path, When performing double-sided printing and ejection in which a sheet printed on both sides is ejected onto the ejection tray with the second side facing up, the sheet on which the first side has been printed by the image printing unit is transported again to the image printing unit via the reversing transport path and the double-sided transport path, and the sheet on which the second side, which is the reverse side of the first side, has been printed by the image printing unit is transported to the static elimination unit, the charge removal control unit applies a voltage to the charge removal member with a first polarity when the first single-sided printed paper is discharged, applies a voltage to the charge removal member with a second polarity when the second single-sided printed paper is discharged, and controls the voltage to the charge removal member with the first polarity when the double-sided printed paper is discharged. An image forming apparatus characterized by:

2. the image forming apparatus has an operation unit into which information about a job is input; When a job for printing the same image on one side of a plurality of sheets is set by the operation unit, the conveyance control unit executes the first single-sided printing and ejection of sheets, and when a job for printing different images on one side of a plurality of sheets is set by the operation unit, the conveyance control unit executes the second single-sided printing and ejection of sheets.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

3. the static elimination control unit controls the magnitude of the voltage applied to the static elimination member, the static elimination control unit is set so that, in the case of a job in which double-sided printing and paper ejection are performed, the absolute value of the voltage to be applied to the static elimination member is smaller than that in the case of a job in which the first single-sided printing and paper ejection are performed.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

4. the static elimination member is a first static elimination roller, The sheet is neutralized in a state of contact with the sheet at a nip portion formed by the first and second neutralization rollers.

2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

5. an image printing unit that prints an image on a sheet; a reversing conveying path that reverses the conveying direction of the sheet printed by the image printing unit and conveyed; a double-sided conveying path that conveys the sheet conveyed from the reversing conveying path back to the image printing unit; a discharge tray on which discharged sheets are stacked; a conveyance control unit that controls conveyance of the sheet; a charge applying unit that applies a voltage to a charge applying member to every other sheet so that the surface potential of the sheet on which the image is printed by the image printing unit is reversed, thereby applying a charge to the sheet; a charge applying control unit that controls the polarity of the voltage applied to the charge applying member; and the reverse conveyance path is disposed downstream of the image printing unit and upstream of the charge applying unit in a sheet conveyance direction, when performing a first single-sided printing discharge in which the sheet is discharged onto the discharge tray with the single-sided printed side facing up, the conveyance control unit conveys the sheet to the charge applying unit without passing through the reversing conveyance path and the double-sided conveyance path; When a second single-sided printed sheet discharge is performed in which the sheet is discharged onto the discharge tray with the single-sided printed side facing downward, the sheet is conveyed to the charge applying unit via the reversing conveying path but not via the double-sided conveying path; When performing double-sided printing and ejection, in which a sheet printed on both sides is ejected onto the ejection tray with the second side facing up, the sheet on which the first side has been printed by the image printing unit is transported again to the image printing unit via the reversing transport path and the double-sided transport path, and the sheet on which the second side, which is the reverse side of the first side, has been printed by the image printing unit is transported to the charge applying unit, the charge applying unit applies a voltage to the charge applying member with a first polarity when the first single-sided printed paper is discharged, applies a voltage to the charge applying member with a second polarity when the second single-sided printed paper is discharged, and controls the charge applying unit to apply a voltage to the charge applying member with the first polarity when the double-sided printed paper is discharged. An image forming apparatus characterized by:

6. an image printing unit that prints an image on a sheet; a reversing conveying path that reverses the conveying direction of the sheet printed by the image printing unit and conveyed; a double-sided conveying path that conveys the sheet conveyed from the reversing conveying path back to the image printing unit; a discharge tray on which discharged sheets are stacked; a conveyance control unit that controls conveyance of the sheet; a static elimination unit that eliminates static electricity from a sheet printed by the image printing unit at a nip formed by a first static elimination roller and a second static elimination roller; a static elimination control unit that controls a voltage applied to the static elimination unit; and the reverse conveyance path is disposed downstream of the image printing unit and upstream of the static elimination unit in a sheet conveyance direction, when performing a first single-sided printing discharge in which the sheet is discharged onto the discharge tray with the single-sided printed side facing up, the conveyance control unit conveys the sheet to the static elimination unit without passing through the reversing conveyance path and the double-sided conveyance path; When a second single-sided printing discharge is performed in which the sheet is discharged onto the discharge tray with the single-sided printed side facing downward, the sheet is conveyed to the static elimination unit via the reversing conveyance path but not via the double-sided conveyance path, When performing double-sided printing and ejection in which a sheet printed on both sides is ejected onto the ejection tray with the second side facing up, the sheet on which the first side has been printed by the image printing unit is transported again to the image printing unit via the reversing transport path and the double-sided transport path, and the sheet on which the second side, which is the reverse side of the first side, has been printed by the image printing unit is transported to the static elimination unit, the discharge control unit applies a voltage so that the electric field formed in the discharge unit is oriented from the second discharge roller to the first discharge roller when the first single-sided printed paper is discharged, applies a voltage so that the electric field formed in the discharge unit is oriented from the first discharge roller to the second discharge roller when the second single-sided printed paper is discharged, and controls to apply a voltage so that the electric field formed in the discharge unit is oriented from the second discharge roller to the first discharge roller when the double-sided printed paper is discharged. An image forming apparatus characterized by:

7. a non-contact static elimination unit disposed downstream of the first static elimination roller in a sheet conveyance direction, the non-contact static elimination unit eliminating static electricity from the sheet without contacting the sheet; the non-contact static elimination unit emits ions of positive and negative polarities regardless of the polarity of the voltage applied to the first static elimination roller; 5. The image forming apparatus according to claim 4.

8. the image printing unit includes a transfer unit that transfers a toner image formed on an intermediate transfer belt onto a sheet; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is a recording medium.

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