Image forming device

Abstract

To suppress occurrence of incomplete loading of a sheet and conveyance failure of a sheet when discharging static electricity-removed sheets separately into multiple discharge trays.SOLUTION: When removing static electricity by a contact-type static electricity removing device, a voltage applied to the contact-type static electricity removing device is changed according to whether a conveyance destination is a lower tray or an upper tray. Although the contact-type static electricity removing device removes static electricity from a sheet by applying a voltage, a voltage to be applied when the conveyance destination is the lower tray is made larger than a voltage applied when the conveyance destination is the upper tray when a length of a conveyance path reaching the lower tray is longer than a length of a conveyance path reaching the upper tray. A voltage applied to the contact-type static electricity removing device is a voltage in which a reference voltage corresponding to a type of the sheet is corrected based on an adjustment value determined according to the conveyance destination. Accordingly, although static electricity is removed excessively from the sheet, an amount of electrification of the sheet from which static electricity is removed excessively until the lower tray is reached is reduced, thus suppressing occurrence of incomplete loading of the sheet and conveyance failure of the sheet.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus equipped with a static eliminator that eliminates static electricity from a sheet. [Background technology]

[0002] In electrophotographic image forming apparatuses, a high transfer voltage is applied when a toner image is transferred to a sheet, which can cause the sheet to become charged after transfer. If the sheet is not neutralized after transfer, it may electrostatically adhere to a sheet previously stacked on the discharge tray when it is discharged onto the discharge tray, resulting in stacking problems, or it may electrostatically adhere to a sheet being transported toward the discharge tray, resulting in transport problems. To address this issue, image forming apparatuses are provided with a neutralization device that neutralizes the sheet after transfer (see Patent Document 1). To achieve a high neutralization effect on the sheet using the neutralization device, it is necessary to apply an optimal voltage for neutralization, and this voltage is set, for example, depending on the type of sheet. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-167169 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the past, when neutralized sheets were discharged separately onto a plurality of discharge trays, even if the voltage described above was applied, improper sheet loading or sheet transport sometimes occurred depending on the discharge tray.

[0005] The present invention has been made in consideration of the above problems, and aims to provide an image forming apparatus that can prevent sheet stacking errors and sheet transport errors from occurring when sheets that have been neutralized by a neutralization device are discharged onto multiple discharge trays. [Means for solving the problem]

[0006] an image forming apparatus according to one embodiment of the present invention, comprising: an image carrier that carries a toner image; an image forming unit that forms a toner image on the image carrier; a transfer member that contacts the image carrier to form a transfer nip and transfers the toner image on the image carrier to a sheet that passes through the transfer nip by applying a transfer voltage; a discharge unit that is arranged downstream of the transfer nip in the sheet transport direction and discharges electric charges that have accumulated on the sheet that has passed through the transfer nip by applying a voltage; a first transport path along which the sheet that has passed through the discharge unit is transported; a first discharge unit that discharges the sheet that has been transported through the first transport path; a second transport path along which the sheet that has passed through the discharge unit is transported; a second discharge unit that discharges the sheet that has been transported through the second transport path; and a control unit that controls the voltage applied to the discharge unit, wherein the control unit changes the voltage applied to the discharge unit depending on whether the sheet is discharged to the first discharge unit or the second discharge unit. [Effects of the Invention]

[0007] According to the present invention, when sheets neutralized by a neutralization unit are separately discharged to a first discharge unit and a second discharge unit, it is possible to prevent improper sheet stacking and sheet transport. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a block diagram showing a control system of the image forming apparatus. [Figure 3] FIG. 1 is a schematic diagram showing a contact-type static eliminator. [Figure 4] (a) is a schematic diagram showing the non-contact static eliminator before the sheet passes, and (b) is a schematic diagram showing the non-contact static eliminator after the sheet passes. [Figure 5] 10 is a flowchart showing a static elimination voltage adjustment process. [Figure 6] FIG. 10A is a diagram showing an adjustment value display screen, and FIG. 10B is a diagram showing an adjustment value input screen. [Figure 7] 1A is a diagram showing a seat type selection screen, FIG. 1B is a diagram showing a seat setting screen, FIG. 1C is a diagram showing an adjustment value display screen, and FIG. 1D is a diagram showing an adjustment value input screen. DETAILED DESCRIPTION OF THE INVENTION

[0009] <Image forming device> An image forming apparatus according to this embodiment will be described below. First, the schematic configuration of the image forming apparatus according to this embodiment will be described with reference to FIG. 1. The image forming apparatus 101 shown in FIG. 1 is a tandem-type electrophotographic full-color printer. As shown in FIG. 1, the image forming apparatus 101 includes a printing device 102, a static eliminator 103, and a finisher 104. Note that, while an example in which the printing device 102, the static eliminator 103, and the finisher 104 are each configured in separate housings and then connected together has been shown here, this is not limiting. For example, the printing device 102, the static eliminator 103, and the finisher 104 may be provided in the same housing.

[0010] The printing device 102 forms a toner image on a sheet based on image data sent from an external device, not shown, such as a document reading device connected to the printing device 102 or a personal computer. Sheets are supplied to the printing device 102 from cassettes 111 and 112 that can accommodate various types of sheets. Only the topmost sheet stored in the cassettes 111 and 112 is transported to a transport path 113. Examples of sheets include thin paper, regular paper, thick paper, rough paper, textured paper, and coated paper.

[0011] The printing device 102 has image forming stations 114, 115, 116, and 117 that form images in yellow, magenta, cyan, and black. In the image forming stations 114, 115, 116, and 117, toner images are formed on the photosensitive drums of the respective stations. The toner images formed on the photosensitive drums are primarily transferred to an intermediate transfer belt 118, which serves as an image carrier, in response to a primary transfer voltage being applied to the primary transfer roller. Then, as the intermediate transfer belt 118 rotates clockwise, the toner images reach a secondary transfer portion T2. ​​The secondary transfer portion T2 is a transfer nip formed by the contact between an inner secondary transfer roller 119 and an outer secondary transfer roller 120. In response to a secondary transfer voltage being applied to the inner secondary transfer roller 119, which serves 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 along a conveyance 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 .

[0012] The toner image secondarily transferred onto 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 nipped and conveyed through the fixing nip formed by these rollers, the toner is melted by the heat, and the melted toner image is pressed onto the sheet by the pressure.

[0013] After passing through the first fixing unit 121, the sheet is transported to a transport path 125 via a transport path 122. However, depending on the type of sheet, further melting and pressure bonding may be required for fixing. In such cases, the sheet is transported 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. After passing through the second fixing unit 123, the sheet is transported to a transport path 125 via a transport path 124. In a double-sided image formation 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 transported from the transport paths 122 and 124 to a reversing path 126, where the leading and trailing ends in the transport direction are swapped. The sheet is then transported to a transport path 113 via a double-sided transport path 127, where the toner image on the intermediate transfer belt 118 is secondarily transferred to the second side of the sheet at a secondary transfer unit T2.

[0014] The sheet transported to the transport path 125 is handed over from the printing device 102 via the transport path 128 to the static eliminator 103, which is disposed downstream of the secondary transfer unit T2 in the sheet transport direction. In the image forming device 101, a high secondary transfer voltage is applied when a toner image is secondarily transferred to the sheet, causing the sheet to become charged after transfer. If the sheet is charged, the sheet may electrostatically adhere to a transport guide or the like during transport, resulting in transport problems, or when the sheet is discharged onto the discharge trays (135, 136), the sheet may electrostatically adhere to sheets already stacked on the discharge trays (135, 136), causing stacking problems. Therefore, the image forming device 101 of this embodiment is provided with the static eliminator 103 to remove the charge from the charged sheet and eliminate the charge. The static eliminator 103 has a contact static eliminator 129 and a non-contact static eliminator 131, and as will be described later, a static elimination voltage is applied to the contact static eliminator 129 and the non-contact static eliminator 131 to remove charge from the sheet after secondary transfer.

[0015] The finisher 104 is capable of stacking a large number of sheets, and is provided with an upper tray 135 as a second discharge unit and a lower tray 136 as a first discharge unit 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 are different.

[0016] The conveying paths 132, 133, 134 are formed by guide members (180, 181) that guide the sheet P toward the upper tray 135 or the lower tray 136. The guide members (180, 181) are molded from, for example, resin. In the example shown in FIG. 1, the lengths of the conveying paths 132 and 134 from the sheet discharge outlet of the static eliminator 103 to the lower tray 136 are longer than the lengths of the conveying paths 132 and 133 from the sheet discharge outlet of the static eliminator 103 to the upper tray 135. The guide members (180, 181) are arranged so that this is the case.

[0017] Transport sensors 137, 138, and 139 that detect the passage of a sheet are arranged along the transport paths 132, 133, and 134, respectively, and the detection results are sent to the printing device 102. Based on these detection results, the printing device 102 (CPU 203 for details, see FIG. 2 described later) detects that a transport jam has occurred in the finisher 104, where the sheet has become stuck during transport, if the printing device 102 does not detect the passage of the leading or trailing edge of the sheet after a predetermined time has elapsed.

[0018] <Image forming device control system> Next, the control system of the image forming apparatus 101 will be described using FIG. 2 while referring to FIG. 1. First, the control system of the printing apparatus 102 will be described. As shown in FIG. 2, the printing apparatus 102 is composed of a communication interface (I / F) 201, an HDD (Hard Disk Drive) 202, a CPU (Central Processing Unit) 203, memory 204, an operation unit 205, and a display 206. The printing apparatus 102 further includes a laser exposure unit 207, an image creation 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.

[0019] The communication interface 201 is connected to the static eliminator 103 via a communication cable 229, and inputs and outputs control instructions, data, and the like 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 inputs and outputs various types of data to and from the external device. The HDD 202 is a storage device that stores control programs and data. The CPU 203 executes, for example, an image formation process (not shown) and a static elimination voltage adjustment process (see FIG. 5, described below) based on the control program and the like stored in the HDD 202, and accordingly controls the entire image forming apparatus 101. The memory 204 stores the control programs and image data required when the CPU 203 performs various processes, and also functions as a temporary data work area.

[0020] An operation unit 205 serving as an input unit accepts various setting inputs and operation instructions from the user. A display 206 serving as a display unit can display setting information of the image processing apparatus, the processing status of an image forming job, and various screens (described later). This display 206 may be a touch panel that enables the user to execute various operations pre-assigned to the software keys on the screen by touching the software keys.

[0021] 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, primary charging is first performed to charge the surface of the photosensitive drum to a uniform negative potential. Next, laser light emitted from a laser driver is irradiated onto the photosensitive drum while the reflection angle is adjusted by a polygon mirror, thereby neutralizing the negative charge at the point on the photosensitive drum surface where the laser light was irradiated, and an electrostatic latent image is formed on the photosensitive drum.

[0022] 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, creating a visible image. 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 to 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 to the sheet. The fixing unit 209 is a device for melting and fixing the toner on the sheet to the sheet using heat and pressure, and is composed of a heater, a heating roller, a pressure roller, etc. The feed unit 210 is a device for transporting sheets, and the sheet feeding and transport operations are controlled by rollers and various sensors.

[0023] Next, we will explain the control system of the static eliminator 103. The static eliminator 103 is composed of a communication interface (I / F) 221, a static elimination high voltage control unit 222, an attachment / detachment control unit 223, and a non-contact static elimination high voltage control unit 224, and each of these components is connected via a system bus 225. The communication interface 221 is connected to the printing device 102 via a communication cable 229, and communication is carried out between the printing device 102 and the static eliminator 103 to send and receive control instructions, data, and the like.

[0024] The static elimination high voltage control unit 222, the attachment / detachment control unit 223, and the non-contact static elimination high voltage control unit 224 perform various controls based on control instructions received from the CPU 203 via a communication cable 229. The static elimination high voltage control unit 222 controls the static elimination voltage of the contact static eliminator 129 by the static elimination high voltage power supply 230 (see FIG. 3 described later). The attachment / detachment control unit 223 controls the movement of the static elimination roller 130a and the static elimination roller 130b of the contact static eliminator 129 between a contact position where they come into contact and a non-contact position where they do not come into contact, using a contact / separation mechanism not shown. The non-contact static elimination high voltage control unit 224 controls the static elimination voltage of the non-contact static eliminator 131 by the non-contact static elimination high voltage power supply 240 (see FIG. 4(a) described later).

[0025] 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 these 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 send and receive control instructions, data, and the like. The CPU 232 performs various controls required for sheet discharge in accordance with 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 sheets conveyed from the static eliminator 103 to an upper tray 135 and a lower tray 136, based on a control instruction from the CPU 232.

[0026] 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 using Fig. 3 to Fig. 4(b) with reference to Fig. 1. 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.

[0027] In this embodiment, a negative voltage is applied to the inner secondary transfer roller 119 as the secondary transfer voltage. Therefore, when a sheet passes through the secondary transfer portion T2, the surface of the sheet facing the inner secondary transfer roller 119 is negatively charged, and the back surface of the sheet on the opposite side is positively charged due to dielectric polarization. If the charged sheet is transported to the finisher 104, the sheet may electrostatically adhere to a transport guide or the like during transport, resulting in transport problems. Alternatively, when the sheet is discharged onto the discharge tray (135, 136), the sheet may electrostatically adhere to sheets already stacked on the discharge tray (135, 136), resulting in stacking problems, or the stacked sheets may stick to each other due to electrostatic force. Therefore, in this embodiment, the static eliminator 103 is used to remove charge from the sheet and eliminate static electricity. The static eliminator 103 has two static eliminators: a contact static eliminator 129 and a non-contact static eliminator 131. These static eliminators are arranged side by side in the sheet transport direction.

[0028] <Contact static eliminator> As shown in FIG. 3, contact-type static eliminator 129 (contact-type static eliminator unit) has two opposing static eliminator rollers 130a and 130b. Static eliminator roller 130a is grounded, and static eliminator roller 130b has a static elimination voltage applied thereto by static elimination high-voltage power supply 230. When static eliminator roller 130a is in contact with the front surface of the sheet and static eliminator roller 130b is in contact with the back surface of the sheet, a negative static elimination voltage is applied by static elimination high-voltage power supply 230, and the positive charge present on the back surface of the sheet is removed. As a result, when the positive charge present on the back surface of the sheet decreases, the negative charge present on the front surface of the sheet also decreases accordingly. Contact-type static eliminator 129 applies a voltage directly to contact sheet P, thereby achieving a high static elimination effect.

[0029] <Non-contact static eliminator> Although the contact-type static eliminator 129 described above has a high static elimination effect, variations tend to occur in the electric potential (hereinafter referred to as surface potential) on the front and back surfaces of the sheet P after static elimination. Therefore, in order to substantially uniform the surface electric potential of the sheet P that has become uneven due to static elimination by the contact-type static eliminator 129, the non-contact static eliminator 131 is disposed downstream of the contact-type static eliminator 129 in the conveyance direction of the sheet P. The non-contact static eliminator 131 can generally eliminate residual charges on the sheet in a non-contact state after static elimination by the contact-type static eliminator 129. In this embodiment, an AC corotron type non-contact static eliminator 131 is used.

[0030] As shown in FIG. 4(a), the non-contact static eliminator 131 (non-contact static eliminator unit) has a discharge wire 140 and an earth electrode 141, and a positive static elimination voltage is applied to the discharge wire 140 by a non-contact static elimination high-voltage power supply 240. When a positive static elimination voltage is applied to the discharge wire 140, a corona discharge occurs in the discharge wire 140, generating a positive charge. 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. This eliminates the negative charge on the sheet surface. 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 eliminated. Although the effect of such a non-contact type static eliminator 131 on the sheet P is smaller than that of the contact type static eliminator 129, the non-contact type static eliminator 131 can reduce the variation in the surface potential of the sheet P after static elimination, so that the surface potential of the sheet P after passing through the non-contact type static eliminator 131 becomes approximately uniform.

[0031] <Static elimination voltage> Incidentally, the amount of charge on the sheet P after secondary transfer differs depending on the type of sheet. Therefore, in this embodiment, in order to obtain a neutralization effect on the sheet P, a predetermined reference voltage to be applied to each of the contact-type static eliminator 129 and the non-contact-type static eliminator 131 can be set according to the type of sheet in accordance with the reference voltage table shown in Table 1. The reference voltage table is stored in advance in, for example, the HDD 202 (see FIG. 2) of the printing apparatus 102. [Table 1]

[0032] 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 "cardboard," "-100 volts" for "coated paper," and "-800 volts" for "synthetic paper." 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," "cardboard," "coated paper," and "synthetic paper."

[0033] However, in the past, even when the reference voltage was applied to neutralize the charge on the same type of sheet P, improper sheet stacking or sheet transport could occur when the sheet P was discharged to the lower tray 136, which was not observed when the sheet P was discharged to the upper tray 135. This is because when the sheet P is conveyed through the conveying paths 132 and 134 or the conveying paths 132 and 133 (see FIG. 1), it can become recharged by rubbing against the conveying paths 132, 133, and 134. In the example shown in FIG. 1, the length of the conveying paths 132 and 134 as the first conveying paths leading to the lower tray 136 is longer than the length of the conveying paths 132 and 133 as the second conveying paths leading to the upper tray 135. Therefore, the sheet P conveyed toward the lower tray 136 is more likely to be charged than the sheet P conveyed toward the upper tray 135, which can result in improper sheet stacking or sheet transport.

[0034] In view of this, in this embodiment, a reference voltage set according to the type of sheet is applied to the contact-type static eliminator 129, which is different when the static-eliminated sheet P is discharged to the lower tray 136 and when the static-eliminated sheet P is discharged to the upper tray 135. The "static elimination voltage control process" of this embodiment that achieves this will be described below using FIGS. 5 to 6(b) with reference to FIGS. 1 and 2.

[0035] <Static elimination voltage control process> 5 is a flowchart showing the neutralization voltage control process of this embodiment. The neutralization voltage control process is executed by the CPU 203 in response to an input of an instruction to start a continuous image forming job in which images are formed continuously on a plurality of sheets P, for example.

[0036] 5, the CPU 203 applies a voltage to the non-contact static eliminator 131 (S1). The CPU 203 acquires page information to be used in the continuous image forming job, and determines the reference voltage of the non-contact static eliminator 131 in accordance with the reference voltage table of Table 1 based on the type of sheet included in the page information. For example, if the type of sheet is "coated paper," the reference voltage of the non-contact static eliminator 131 is determined to be "800 volts" (see Table 1). Then, the reference voltage is applied to the non-contact static eliminator 131, and static elimination of the sheet P is performed by the non-contact static eliminator 131.

[0037] Next, the CPU 203 determines whether or not to perform static elimination on the sheet P conveyed to the static eliminator 103 using the contact static eliminator 129 in addition to the non-contact static eliminator 131 (S2). The CPU 203 determines whether or not to perform static elimination on the sheet P using the contact static eliminator 129 based on the surface resistance of the sheet P. For example, if the surface resistance value of the sheet P is equal to or less than a threshold value, static elimination on the sheet P is performed using only the non-contact static eliminator 131, and if the surface resistance value of the sheet P is greater than the threshold value, static elimination on the sheet P is performed using both the non-contact static eliminator 131 and the contact static eliminator 129. The threshold value may be set to, for example, "10 13 Ω / □".

[0038] If static elimination by the contact-type static eliminator 129 is not to be performed (No in S2), the CPU 203 turns off the voltage to the contact-type static eliminator 129 (S7), and proceeds to the process of step S5. In other words, the voltage applied to the contact-type static eliminator 129 is changed to "0." On the other hand, if static elimination by the contact-type static eliminator 129 is to be performed (Yes in S2), the CPU 203 changes the voltage applied to the contact-type static eliminator 129 from the reference voltage depending on whether the conveyance destination is the lower tray 136 or the upper tray 135 (S3). Then, the CPU 203 applies the changed voltage to the contact-type static eliminator 129, thereby eliminating static from the sheet P by the contact-type static eliminator 129 (S4).

[0039] The method for determining the voltage to be applied to the contact-type static eliminator 129 will be described below. The CPU 203 determines the reference voltage of the contact-type static eliminator 129 in accordance with the reference voltage table in Table 1 based on the type of sheet. The CPU 203 then changes the reference voltage in accordance with the "adjustment value" in the voltage change table shown in Table 2. The voltage change table is stored in advance in, for example, the HDD 202 (see FIG. 2) of the printing apparatus 102, and as shown in Table 2, an "adjustment value" is set for each of the lower tray 136 and upper tray 135, which are the destinations for conveying the sheet P. [Table 2]

[0040] For example, if the sheet type is "coated paper," the reference voltage of the contact-type static eliminator 129 is determined to be "-100 volts" (see Table 1). Here, if the destination of the sheet P is the lower tray 136, the adjustment value is determined to be "+5," and if the destination of the sheet P is the upper tray 135, the adjustment value is determined to be "0." In this embodiment, the voltage is offset by "-25 V" per adjustment value of "1." Therefore, if the "adjustment value" is "+5," the voltage applied to the contact-type static eliminator 129 is changed to "-225 V (-100 + (-125))," which is corrected by offsetting the voltage adjustment amount "-125 V (+5 × -25)" from the reference voltage of "-100 volts." If the "adjustment value" is "0," the reference voltage of the voltage applied to the contact-type static eliminator 129 remains the reference voltage of "-100 volts" without being corrected.

[0041] Returning to the description of FIG. 5, the CPU 203 determines whether the trailing edge of the sheet P has passed the contact-type static eliminator 129 in the conveyance direction of the sheet P (S5). The CPU 203 waits until the trailing edge of the sheet P has passed the contact-type static eliminator 129 (No in S5). When the trailing edge of the sheet P has passed the contact-type static eliminator 129 (Yes in S5), the CPU 203 determines whether there is another sheet P following the sheet P that has passed (S6). If there is another following sheet P (Yes in S6), the CPU 302 returns to the process of step S2 and repeats the processes of steps S1 to S7 described above. If there is no other following sheet P (No in S6), that is, if the continuous image forming job has ended, the CPU 302 turns off the voltage to the contact-type static eliminator 129 and the voltage to the non-contact static eliminator 131 (S8 and S9), and ends the process.

[0042] In this embodiment, the user can input an "adjustment value" (see Table 2) in the voltage change table. FIG. 6(a) shows an "adjustment value display screen," and FIG. 6(b) shows an "adjustment value input screen." As shown in FIG. 6(a), the "adjustment value display screen" displays the adjustment value (first adjustment value) for the lower tray 136 and the adjustment value (second adjustment value) for the upper tray 135. By displaying the "adjustment value display screen" on the display 206, the user can check the current "adjustment value" in the voltage change table stored in the HDD 202. Here, an example is shown in which the adjustment value for the upper tray 135 is "0" and the adjustment value for the lower tray 136 is "+8."

[0043] The "adjustment value display screen" also displays a "change button" for each of the lower tray 136 and the upper tray 135. When the user operates the "change button," the screen of the display 206 transitions from the "adjustment value display screen" to the "adjustment value input screen" shown in FIG. 6(b). As shown in FIG. 6(b), a numeric keypad is displayed on the "adjustment value input screen." The user can input an adjustment value within the range of, for example, "-10 to +10" by operating the numeric buttons "0 to 9" on the numeric keypad. FIG. 6(b) shows an example in which the numeric button "8" is operated, resulting in the display of the adjustment value "8." After inputting the adjustment value using the numeric buttons, the user can confirm the adjustment value by operating the "next" button. The "adjustment value" in the voltage change table stored in the HDD 202 is updated to the adjustment value input by the CPU 203. In this manner, the user can input an "adjustment value" in the voltage change table for each of the lower tray 136 and the upper tray 135.

[0044] As described above, in this embodiment, the voltage applied to the static eliminator 103 that eliminates static electricity from the sheet P is changed depending on whether the destination of the neutralized sheet P is the lower tray 136 or the upper tray 135. As described above, if the length of the transport path (132, 134) from the static eliminator 103 to the lower tray 136 is longer than the length of the transport path (132, 133) from the static eliminator 103 to the upper tray 135, the voltage applied to the static eliminator 103 when the destination of the sheet P is the lower tray 136 is made higher than the voltage applied to the static eliminator 103 when the destination of the sheet P is the upper tray 135. The voltage applied to the static eliminator 103 is a voltage obtained by correcting a reference voltage according to the type of sheet P based on an adjustment value determined according to the destination.

[0045] In this way, by increasing the voltage applied to the static eliminator 103 in advance in consideration of the amount of charge that is applied to the sheet P as it is conveyed along the conveying path, the static eliminator 103 can eliminate more charge from the sheet P than when a reference voltage is applied. In other words, a voltage greater than the reference voltage is applied to the static eliminator 103 to eliminate charge from the sheet P so that the sheet P is conveyed along the conveying path (132, 134) in an over-discharged state. As a result, even when the sheet P is conveyed along the conveying path (132, 134) and discharged onto the lower tray 136, the amount of charge on the sheet P can be reduced before it reaches the lower tray 136. Therefore, even when the sheet P is discharged onto the lower tray 136, sheet stacking errors and sheet conveyance errors are less likely to occur.

[0046] <Other embodiments> The "adjustment value" of the voltage change table described above may be input by the user for each of the lower tray 136 and the upper tray 135 according to the type of sheet. Fig. 7(a) shows a "sheet type selection screen" on which the type of sheet can be selected, and Fig. 7(b) shows a "sheet setting screen" for the selected sheet type. Fig. 7(c) shows an "adjustment value display screen" for the selected sheet type, and Fig. 7(d) shows an "adjustment value input screen."

[0047] As shown in FIG. 7(a), the "sheet type selection screen" displays sheet types such as "user-defined paper 1" and "user-defined paper 2." Specifically, for example, "user-defined paper 1" displays "coated paper" as the sheet type, and "user-defined paper 1" displays "synthetic paper" as the sheet type. The sheet types displayed on the "sheet type selection screen" are, for example, sheets P for which a reference voltage is set in the reference voltage table (see Table 1) stored in the HDD 202. By displaying the "sheet type selection screen" on the display 206, the user can select the sheet type for which they want to change the "adjustment value" of the voltage change table for each of the lower tray 136 and the upper tray 135.

[0048] When the user selects a sheet type such as "user-defined sheet 1" or "user-defined sheet 2," the screen of the display 206 transitions from the "sheet type selection screen" to the "sheet setting screen" shown in FIG. 7B. The "sheet setting screen" displays output conditions for forming and outputting an image on the selected type of sheet P for each of several items. One of the items displayed is the "static neutralization adjustment" item.

[0049] When the user selects the "Static Charge Adjustment" item, the screen on the display 206 transitions from the "Sheet Setting Screen" to the "Adjustment Value Display Screen" shown in FIG. 7(c). The "Adjustment Value Display Screen" shown in FIG. 7(c) displays the adjustment values ​​for the lower tray 136 and the upper tray 135 for the selected sheet type. By displaying the "Adjustment Value Display Screen" on the display 206, the user can check the current "Adjustment Value" in the voltage change table stored in the HDD 202 for each sheet type. In this embodiment, the voltage change table shown in Table 2 is stored in the HDD 202 for each type of sheet P.

[0050] The "adjustment value display screen" displays a "change button" for each of the lower tray 136 and the upper tray 135. When the user operates the "change button," the screen of the display 206 transitions from the "adjustment value display screen" to the "adjustment value input screen" shown in FIG. 7(d). As shown in FIG. 7(d), the "adjustment value input screen" displays a numeric keypad. The user can input an adjustment value within the range of, for example, "-10 to +10" by operating the number buttons "0 to 9" on the numeric keypad. After inputting the adjustment value using the number buttons, the user can confirm the adjustment value by operating the "next" button. The "adjustment value" in the voltage change table stored in the HDD 202 is updated to the adjustment value input by the CPU 203. In this way, the user may be able to input the "adjustment value" for the lower tray 136 and the "adjustment value" for the upper tray 135 according to the type of sheet.

[0051] In the above-described embodiment, the voltage applied to the static eliminator 103 is changed depending on the length of the transport path from the static eliminator 103 to each tray (136, 135), but this is not limiting. For example, even if the length of the transport path from the static eliminator 103 to each tray (136, 135) is the same, the voltage applied to the static eliminator 103 may be changed depending on the material of the guide members that form the transport paths 132, 133, and 134.

[0052] 1, a first guide portion 181 serving as a first guide member forming a conveying path 134 leading to a lower tray 136 is made of resin, and a second guide portion 180 serving as a second guide member forming a conveying path (132, 133) leading to an upper tray 135 is made of metal and has the same length as the conveying path 134. In this case, the voltage applied to the static eliminator 103 when the sheet P is conveyed along the conveying path 134 is set to be higher than the voltage applied to the static eliminator 103 when the sheet P is conveyed along the conveying path 133. This is because resin is more likely to charge the sheet P than metal when conveyed the same distance.

[0053] In the above-described first and second embodiments, the reference voltage of the contact-type static eliminator 129 is changed as the voltage to be applied to the static eliminator 103, but this is not limiting. For example, the reference voltage of the non-contact-type static eliminator 131 may be changed, or both the reference voltage of the contact-type static eliminator 129 and the reference voltage of the non-contact-type static eliminator 131 may be changed.

[0054] In the first and second embodiments described above, the printing device 102 is an intermediate transfer type in which a toner image of each color is primarily transferred from the photosensitive drum of each color to the intermediate transfer belt 118, and then a composite toner image of each color is secondarily transferred collectively to a sheet, but the present invention is not limited to this. For example, the printing device may be a direct transfer type in which a toner image on a photosensitive drum is directly transferred to a sheet by applying a voltage to a transfer roller disposed opposite the photosensitive drum and the conveying belt, with a nip formed between the sheet and the photosensitive drum. [Explanation of symbols]

[0055] 103...discharge unit (discharge device), 118...image carrier (intermediate transfer belt), 119...transfer member (secondary transfer inner roller), 129...contact type discharge unit (contact type discharge device), 131...non-contact type discharge unit (non-contact type discharge device), 132, 133...second conveying path (conveying path), 132, 134...first conveying path (conveying path), 135...second discharge unit (upper tray), 136...first discharge unit (lower tray), 180...second guide member (second guide portion), 181...first guide member (first guide portion), 190...image forming unit, 205...input unit (operating unit), 206...display unit (display), 222...control unit (discharge high voltage control unit), P...sheet, T2...transfer nip portion (secondary transfer unit)

Claims

1. 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; a charge removing section that is disposed downstream of the transfer nip section in a sheet conveying direction and removes electric charges from the sheet that has passed through the transfer nip section by applying a voltage; a first conveying path through which the sheet that has passed through the static electricity removing unit is conveyed; a first discharge section that discharges the sheet conveyed through the first conveying path; a second conveying path along which the sheet that has passed through the static electricity removing unit is conveyed, the second conveying path being a path different from the first conveying path; a second discharge portion that discharges the sheet conveyed through the second conveying path; A control unit that controls a voltage applied to the static eliminator, the control unit changes a voltage applied to the static electricity removing unit depending on whether the sheet is discharged to the first discharge unit or the second discharge unit.

1. An image forming apparatus comprising:

2. a length of the first transport path extending from the static electricity removing unit to the first discharge unit is longer than a length of the second transport path extending from the static electricity removing unit to the second discharge unit; a voltage applied to the static electricity removing unit when the sheet is discharged to the first discharge unit is greater than a voltage applied to the static electricity removing unit when the sheet is discharged to the second discharge unit; 2. The image forming apparatus according to claim 1,

3. the first conveying path is formed by a first guide member that is made of resin and guides a sheet; the second conveying path is formed by a second guide member that is made of metal and guides the sheet, a voltage applied to the static electricity removing unit when the sheet is discharged to the first discharge unit is greater than a voltage applied to the static electricity removing unit when the sheet is discharged to the second discharge unit; 2. The image forming apparatus according to claim 1,

4. an input unit capable of inputting a first adjustment value for adjusting a voltage applied to the static electricity removal unit when the sheet is discharged to the first discharge unit, and a second adjustment value for adjusting a voltage applied to the static electricity removal unit when the sheet is discharged to the second discharge unit, 2. The image forming apparatus according to claim 1,

5. the control unit corrects a reference voltage determined for each type of sheet based on the first adjustment value and the second adjustment value input by the input unit, and adjusts the voltage to be applied to the static electricity removing unit.

5. The image forming apparatus according to claim 4.

6. the input unit is capable of inputting the first adjustment value and the second adjustment value for each type of sheet.

6. The image forming apparatus according to claim 5,

7. a display unit capable of displaying the first adjustment value and the second adjustment value for each type of sheet; 7. The image forming apparatus according to claim 6,

8. The charge eliminating unit includes a contact type charge eliminating unit that eliminates charge by contacting the sheet being transported, and a non-contact type charge eliminating unit that is provided downstream of the contact type charge eliminating unit in the sheet transport direction and eliminates residual charge of the sheet after the charge has been eliminated by the contact type charge eliminating unit in a non-contact state.

2. The image forming apparatus according to claim 1,

9. The control unit changes a voltage applied to the contact-type static electricity removing unit.

9. The image forming apparatus according to claim 8,

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