JP7743473B2 - Static eliminator and image forming apparatus - Google Patents

Description

The present invention relates to a static eliminator that eliminates static electricity from a sheet, and an image forming apparatus equipped with the same.

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. For this reason, image forming apparatuses are equipped with a neutralization device that neutralizes the sheet after transfer (Patent Document 1).

The static eliminator described in Patent Document 1 includes a contact-type static eliminator that can eliminate static electricity by contacting the sheet, and a non-contact-type static eliminator that can eliminate static electricity without contacting the sheet. The static eliminator described in Patent Document 1 uses either a contact-type static eliminator or a non-contact-type static eliminator, or both a contact-type static eliminator and a non-contact-type static eliminator, depending on the surface resistance of the sheet.

JP 2019-167169 A

Conventionally, when a contact-type static eliminator is not used, one of the static eliminator rollers is moved from a contact position where it contacts the other static eliminator roller to a spaced position where it does not contact the other static eliminator roller to prevent wear on the pair of static eliminator rollers. Therefore, when a sheet that does not require static elimination by a contact-type static eliminator is transported following a sheet that does require static elimination by a contact-type static eliminator, one of the static eliminator rollers must be moved from the spaced position to the contact position in order to perform static elimination by the contact-type static eliminator. Conventionally, the distance between the leading edge of the preceding sheet and the leading edge of the succeeding sheet (called the paper gap) is widened to allow the sheet that requires static elimination to arrive after the static eliminator roller has moved to the contact position, but this can result in a problem of reduced productivity in the image forming device.

The present invention was made in consideration of the above-mentioned problems, and aims to provide a static elimination device and an image forming apparatus that can move the static elimination roller from its separation position to its contact position without widening the gap between a preceding sheet that does not require static elimination and a succeeding sheet that does require static elimination.

A static eliminator according to one embodiment of the present invention has a first static eliminator and a second static eliminator that contacts the first static eliminator to form a static elimination nip portion, and includes a contact-type static eliminator that eliminates static on a sheet that passes through the static elimination nip portion by applying a voltage, a power supply unit that applies a voltage to the contact-type static eliminator, a conveying unit that conveys the sheet to the static elimination nip portion, a contact-separation mechanism that can move the first static eliminator between a contact position where it contacts the second static eliminator and a spaced position where it is spaced from the second static eliminator, and a mechanism that, when neutralizing a second sheet that is conveyed following a first sheet that does not require static elimination , moves the first sheet so that the trailing edge of the first sheet passes through the nip region of the static elimination nip portion in the sheet conveying direction by the conveying unit. The device is characterized in that it comprises a control unit capable of executing a first mode in which the contact/separation mechanism starts moving the first de-ionization member from the separation position to the contact position before the trailing end of the first sheet passes through the nip area, and a second mode in which the contact/separation mechanism starts moving the first de-ionization member from the separation position to the contact position after the trailing end of the first sheet passes through the nip area, and an input unit that allows a user to input whether the first mode or the second mode is to be executed depending on the type of the first sheet, and when de-ionizing the second sheet, the control unit executes either the first mode or the second mode in accordance with user input via the input unit .

According to the present invention, the first static elimination member can be moved from the separated position to the contact position without increasing the distance between the preceding first-type sheet that does not require static elimination and the following second-type sheet that requires static elimination.

1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a block diagram showing a control system of the image forming apparatus. FIG. 1 is a schematic diagram showing a contact-type static eliminator. 1A is a schematic diagram showing a non-contact static eliminator before a sheet passes through, and FIG. 1B is a schematic diagram showing the non-contact static eliminator after a sheet passes through. 5A and 5B are schematic diagrams showing the contact/separation mechanism when the charge removal roller is in the contact position and when the charge removal roller is in the separated position; 10 is a flowchart showing a discharge operation process of the charge eliminating roller. 10 is a flowchart showing the process of attaching the charge removal roller. 4 is a flowchart showing a static elimination control process according to the present embodiment. 5 is a timing chart for explaining the attaching operation of the charge removal roller in the present embodiment. FIG. FIG. 10 is a diagram showing a setting input screen on which settings can be input for each type of sheet. 10 is a timing chart for explaining the attachment operation of the static elimination roller in a conventional example.

<Image forming apparatus>
The present embodiment will be described below. First, the schematic configuration of an image forming apparatus according to the present 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 the printing device 102, the static eliminator 103, and the finisher 104 are each configured in separate housings and then connected together, this is not a limitation. For example, the printing device 102 and the static eliminator 103 may be provided in the same housing.

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, which can accommodate various types of sheets. Only the topmost sheet stored in cassettes 111 and 112 is transported to transport path 113. Examples of sheets include thin paper, regular paper, thick paper, rough paper, textured paper, and coated paper.

The printing device 102 has image forming stations 114, 115, 116, and 117 that form images in yellow, magenta, cyan, and black. At each of the image forming stations 114, 115, 116, and 117, a toner image is formed on the photosensitive drum. The toner image formed on the photosensitive drum is primarily transferred to an intermediate transfer belt 118 (image carrier) in response to the application of a primary transfer voltage to the primary transfer roller. Then, as the intermediate transfer belt 118 rotates clockwise, the toner image reaches the secondary transfer unit N2. The secondary transfer unit N2 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 the application of a secondary transfer voltage from a power source (not shown) to the inner secondary transfer roller 119 (transfer member), the toner image on the intermediate transfer belt 118 (image carrier) is secondarily transferred to a sheet transported along the transport path 113. The image forming stations 114, 115, 116, and 117 and the primary transfer roller described above constitute an image forming unit 190 that forms a toner image on the intermediate transfer belt 118.

The toner image that has been secondarily transferred to the sheet is fixed to the sheet by applying heat and pressure by the first fixing unit 121. The first fixing unit 121 is equipped with 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.

After passing through the first fixing unit 121, the sheet is transported to conveying path 125 via conveying 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 the 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 conveying path 125 via conveying 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 conveying paths 122 and 124 to reversing path 126, where the leading and trailing ends in the conveying direction are swapped. The sheet is then transported to conveying path 113 via double-sided conveying path 127, where the toner image on the intermediate transfer belt 118 is secondarily transferred to the second side of the sheet at secondary transfer unit N2.

The sheet transported to the transport path 125 is handed over from the printing device 102 to the static eliminator 103, which is located downstream of the secondary transfer unit N2 in the sheet transport direction, via the transport path 128. The transport path 128 is provided with a transport roller 170, which serves as a transport unit that transports the sheet handed over from the printing device 102 toward the contact static eliminator 129.

In the image forming apparatus 101, a high secondary transfer voltage is applied when a toner image is secondarily transferred to a sheet, causing the sheet to become charged after transfer. If the sheet is charged, it may electrostatically adhere to a transport guide or other object during transport, resulting in transport problems, or when the sheet is discharged onto the discharge tray (135, 136), it may electrostatically adhere to sheets already stacked on the discharge tray (135, 136), resulting in stacking problems. Therefore, to remove the charge from the charged sheet, the image forming apparatus 101 of this embodiment is equipped with a charge removal device 103. The charge removal device 103 has a contact-type charge removal device 129 and a non-contact-type charge removal device 131. As described below, a charge removal voltage is applied to the contact-type charge removal device 129 and the non-contact-type charge removal device 131 to remove charge from the sheet after secondary transfer.

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

Transport sensors 137, 138, and 139 are located along transport paths 132, 133, and 134, respectively, to detect the passage of sheets, and the results of these detections are sent to the printing device 102. Based on these detection results, if the printing device 102 (CPU 203 for details, see Figure 2 described below) does not detect the passage of the leading or trailing edge of the sheet in the transport direction after a predetermined time has elapsed, it determines that a transport jam has occurred in the finisher 104, causing the sheet to get stuck mid-transport.

<Control system of image forming apparatus>
Next, the control system of the image forming apparatus 101 will be described using FIG. 2 with reference to FIG. 1. First, the control system of the printing apparatus 102 will be described. As shown in FIG. 2, the printing apparatus 102 includes a communication interface (I/F) 201, a hard disk drive (HDD) 202, a central processing unit (CPU) 203, memory 204, an operation unit 205, and a display 206. The printing apparatus 102 also 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 these components is connected via a system bus 213.

The communication interface 201 is connected to the static eliminator 103 via a communication cable 229, and inputs and outputs control instructions and data between the printing apparatus 102 and the static eliminator 103. It is also connected to an external device, such as a computer (not shown), and inputs and outputs various 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, image formation processing and static elimination control processing (not shown, see FIG. 8 described below) based on the control programs stored in the HDD 202, and accordingly controls the entire image forming apparatus 101. The CPU 203 primarily controls the printing apparatus 102, but also manages the control performed by the static eliminator 103 and finisher 104 by sending control instructions to them. The memory 204 stores control programs and image data required by the CPU 203 when performing various processes, and also functions as a temporary data work area.

The operation unit 205 accepts various setting inputs and operation instructions from the user. The display 206 can display setting information for the image processing device, the processing status of an image formation job, and various screens described below. This display 206 may be a touch panel that allows the user to touch a software key on the screen to execute various operations that have been pre-assigned to the operated software key.

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. The laser exposure unit 207 first performs primary charging, charging the surface of the photosensitive drum to a uniform negative potential. Next, the laser light emitted from the laser driver is irradiated onto the photosensitive drum while the reflection angle is adjusted by a polygon mirror, thereby neutralizing the negative charge at the points on the photosensitive drum surface where the laser light was irradiated, and an electrostatic latent image is formed on the photosensitive drum.

The image-forming unit 208 is a device for transferring toner onto a sheet. It is composed of a development unit, transfer unit, toner supply unit, etc., and transfers toner from the photosensitive drum onto a sheet. In the development unit, negatively charged toner from a development cylinder is attached to the electrostatic latent image on the photosensitive drum surface, creating a visible image. In the transfer unit, primary transfer is performed by applying a positive voltage to the primary transfer roller to transfer the toner on the photosensitive drum surface to the intermediate transfer belt 118, and 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, heating roller, 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.

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

The static elimination high-voltage control unit 222 controls the static elimination voltage of the contact-type static eliminator 129, which is supplied by the static elimination high-voltage power supply 230 (see Figure 3, described below). The attachment/detachment control unit 223 controls the movement of the static elimination roller 130a and static elimination roller 130b of the contact-type static eliminator 129 between a contact position where they are in contact and a non-contact position (also called a separated position) where they are not in contact, using a contact/detachment 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, which is supplied by the non-contact static elimination high-voltage power supply 240 (see Figure 4(a), described below). The transport control unit 226 controls the transport roller 170, which delivers the sheet to the static eliminator 103. When the transport control unit 226 controls the sheet transport, the CPU 203 controls the sheet transport within the printing device 102.

Note that, although an example has been shown here in which the static elimination control unit 227 controls the static elimination device 103 in accordance with control instructions from the CPU 203, this is not limiting. For example, the CPU 203 may have the functions of the static elimination control unit 227 described above, and the CPU 203 may directly control the static elimination device 103.

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 component 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 carried out between the finisher 104 and the static eliminator 103 to send and receive control instructions and data. The CPU 232 controls the finisher 104 in accordance with control instructions from the CPU 203 of the printing apparatus 102. Here, various controls required for sheet discharge are performed 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 control the sheets conveyed from the static eliminator 103 to be conveyed separately to the upper tray 135 and the lower tray 136 based on control instructions from the CPU 232.

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

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 section N2, the surface of the sheet facing the inner secondary transfer roller 119 is negatively charged, and the reverse 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 the transport guide or other device 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 together due to electrostatic force. Therefore, in this embodiment, the static eliminator 103 is used to remove charge from the sheet. 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.

<Contact static eliminator>
As shown in FIG. 3 , the contact-type static eliminator 129 (contact-type static eliminator unit) has two opposing static eliminator rollers 130a and 130b. The static eliminator roller 130a is grounded, and a static eliminator voltage is applied to the static eliminator roller 130b by a static eliminator high-voltage power supply 230. The static eliminator rollers 130a and 130b contact each other to form a static eliminator nip J1. When a sheet passes through the static eliminator nip J1, the static eliminator roller 130a contacts the front surface of the sheet, and the static eliminator roller 130b contacts the back surface of the sheet. In this state, when a negative static eliminator voltage is applied by the static eliminator high-voltage power supply 230, the positive charge present on the back surface of the sheet is removed. This reduces the positive charge present on the back surface of the sheet, and accordingly, the negative charge present on the front surface of the sheet. The contact-type static eliminator 129 achieves a high static elimination effect because it contacts the sheet P and applies a voltage directly.

<Non-contact static eliminator>
Although the contact-type static eliminator 129 described above provides a high static elimination effect, variations in the potential (hereinafter referred to as surface potential) of the front and back surfaces of the sheet P after static elimination are likely to occur. Therefore, in order to substantially uniform the surface potential of the sheet P that has become uneven due to static elimination by the contact-type static eliminator 129, a 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, in a non-contact state, the remaining charge on the sheet after static elimination by the contact-type static eliminator 129. In this embodiment, an AC corotron type non-contact static eliminator 131 is used.

As shown in Figure 4(a), the non-contact static elimination device 131 (non-contact static elimination 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 Figure 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 neutralized by being attracted to the earth electrode 141, which is grounded and has a potential of "0". The effect of eliminating static electricity from the sheet P using this non-contact static eliminator 131 is smaller than that of the contact static eliminator 129, but the non-contact static eliminator 131 can reduce the variation in the surface potential of the sheet P after static elimination, so the surface potential of the sheet P after passing through the non-contact static eliminator 131 becomes approximately uniform.

<Static elimination voltage>
However, 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.

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

<Contact/separation mechanism>
The contact-type static eliminator 129 described above eliminates static electricity by bringing the static eliminator roller 130a and the static eliminator roller 130b into contact with the sheet, and therefore the static eliminator roller 130a and the static eliminator roller 130b wear out each time the sheet is conveyed, which can reduce the static elimination capability of the sheet. Therefore, when static elimination of a sheet is performed using the non-contact static eliminator 131 alone, the static eliminator roller 130a and the static eliminator roller 130b are not brought into contact with each other in the contact-type static eliminator 129, which does not eliminate static electricity from the sheet. To achieve this, the contact-type static eliminator 129 is provided with a contact/separation mechanism 150 that moves one static eliminator roller 130a toward and away from the other static eliminator roller 130b, as shown in Figures 5(a) and 5(b).

As shown in Figures 5(a) and 5(b), the contact/separation mechanism 150 is attached to the charge removal roller 130a, which serves as a first charge removal member, and can move the charge removal roller 130a between a contact position where it contacts the charge removal roller 130b and a spaced position where it is spaced apart from the charge removal roller 130b. The contact/separation mechanism 150 has a swing arm 151 that swings around a swing fulcrum 152, and the swing arm 151 is swung counterclockwise or clockwise by a detachable motor 160. The charge removal roller 130a is rotatably supported on the tip of the swing arm 151, away from the swing fulcrum 152. When the detachable motor 160 is driven counterclockwise, as shown in Figure 5(a), the swing arm 151 swings counterclockwise around the swing fulcrum 152, and the charge removal roller 130a is moved to a contact position where it contacts the charge removal roller 130b, which serves as a second charge removal member.

Conversely, when the attachment/detachment motor 160 is driven clockwise, as shown in FIG. 5(b), the swing arm 151 swings clockwise around the swing fulcrum 152, and the charge removal roller 130a is moved to a separated position away from the charge removal roller 130b (detachment operation). Then, as the charge removal roller 130a moves from the contact position to the separated position, it presses the attachment/detachment sensor 153 located on the top of the contact/detachment mechanism 150, causing the attachment/detachment motor 160 to stop, and the charge removal roller 130a to stop at the separated position. The attachment/detachment sensor 153 is, for example, a push switch that is on when pressed by the charge removal roller 130a and off when not pressed by the charge removal roller 130a.

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

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

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

When the attachment/detachment control unit 223 receives an instruction to start the attachment/detachment operation from the CPU 203, it starts driving the attachment/detachment motor 160 counterclockwise at a predetermined speed (S11). The attachment/detachment control unit 223 determines whether 600 msec has elapsed since the attachment/detachment sensor 153 started to be driven (S12). The attachment/detachment control unit 223 moves the charge removal roller 130a toward the separation position until 600 msec has elapsed (No in S12). If 600 msec has elapsed since the attachment/detachment sensor 153 started to be driven (Yes in S12), the attachment/detachment control unit 223 stops the attachment/detachment motor 160 (S13). As a result, the charge removal roller 130a stops at the abutment position. After stopping the attachment/detachment motor 160, the attachment/detachment control unit 223 sends a notification of the end of the attachment/detachment operation to the CPU 203 via the communication interface 201.

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

As described above, when the contact-type static eliminator 129 is not discharging a sheet, it moves the static eliminator roller 130a to the separated position so that the static eliminator rollers 130a and 130b are not in contact with each other, thereby preventing unnecessary wear on the static eliminator rollers 130a and 130b. Therefore, when a continuous image formation job (not shown) is being executed in which images are formed continuously on multiple sheets, if a sheet that requires static elimination is to be discharged after a sheet that does not require static elimination, it is necessary to move the static eliminator roller 130a from the separated position to the contact position and have the contact-type static eliminator 129 discharge the sheet.

Figure 12 shows a conventional example of the timing of the discharge roller 103a's attachment operation when discharging a sheet that requires static elimination following a sheet that does not require static elimination. Figure 12 is a timing chart for explaining the attachment operation of the discharge roller 103a in a conventional example. Figure 12 shows an example in which a "synthetic paper" sheet that requires static elimination is transported immediately after a "plain paper" sheet that does not require static elimination. The non-contact static elimination device 131 applies a reference voltage of 800 volts to both the "plain paper" and the "synthetic paper" from the non-contact static elimination high-voltage power supply 240 (discharge voltage on).

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

In this specification, the term "paper gap" refers to the distance between the leading edge of the preceding sheet and the leading edge of the succeeding sheet. Furthermore, the nip region of the discharge nip J1 refers to the region of the discharge nip J1 itself in the sheet conveyance direction when the discharge roller 103a is in the contact position, and refers to the region of the discharge roller 103b in the sheet conveyance direction that corresponds to the discharge nip J1 when the discharge roller 103a is in the separated position (see region Z in Figure 5(b)).

For example, when switching from plain paper to synthetic paper, the synthetic paper requires static elimination by the contact-type static elimination device 129, so the contact mechanism 150 must start a contact operation to move the static elimination roller 103a from the separated position to the contact position. Conventionally, the contact mechanism 150 would start the contact operation after the trailing edge of the preceding plain paper passes through the nip area of the static elimination nip J1 (time t2). Then, after the contact operation starts, the static elimination voltage is switched to "-800 volts" (static elimination voltage ON) by the static elimination high-voltage power supply 230.

The synthetic paper is then transported so that it enters the nip region of the discharge nip J1 after the discharge roller 130a reaches the contact position, so that the contact-type discharge device 129 can properly discharge the synthetic paper. As mentioned above, it takes 600 msec for the discharge roller 130a to move from the separation position to the contact position.

Consequently, in the past, a paper interval "T2" was left, which was calculated by adding the above-mentioned "600 msec" to the time (time t1 to time t2) it takes from the leading edge of the plain paper entering the nip area of the discharge nip J1 until the trailing edge of the plain paper passes through the nip area of the discharge nip J1. Thus, in the past, the interval between the preceding plain paper and the following synthetic paper was wider than "T1" to allow the synthetic paper requiring discharge to arrive after the discharge roller 103a moves to the contact position. Therefore, in the past, when performing continuous image formation jobs in which the contact/separation mechanism 150 repeatedly performs the attachment operation, the productivity of the image forming apparatus 101 could decrease.

In light of this, in this embodiment, when switching from a sheet that does not require static elimination to a sheet that does, the contact operation by the contact/separation mechanism 150 begins while the preceding sheet is passing through the nip area of the static elimination nip J1, without waiting for the trailing edge of the preceding sheet to pass through the nip area of the static elimination nip J1. The "static elimination control process" of this embodiment that achieves this will be described below using FIGS. 8 and 9, with reference to FIGS. 1 and 2. FIG. 8 is a flowchart showing the static elimination control process of this embodiment. FIG. 9 is a timing chart for explaining the contact operation of the static elimination roller 103a in this embodiment.

As an example, the following describes a case where the discharge control process (mode) is executed by the discharge control unit 227 under the control of the CPU 203. When the CPU 203 receives an instruction to start a continuous image formation job and executes the continuous image formation job, it instructs the discharge control unit 227 via the communication interface 201 to start the discharge control process.

<Static Charge Elimination Control Process>
As shown in FIG. 8 , the static elimination control unit 227 first starts applying a reference voltage to the non-contact static elimination device 131 using the non-contact static elimination high-voltage power supply 240 (S21). The static elimination control unit 227 then determines whether the first sheet sent from the printing apparatus 102 requires static elimination (S22). If the first sheet does not require static elimination (No in S22), the static elimination control unit 227 determines whether the leading edge of the first sheet has reached the nip area of the static elimination nip J1 (S23). If the leading edge of the sheet has not yet reached the nip area of the static elimination nip J1 (No in S23), the static elimination control unit 227 waits until the leading edge of the sheet reaches the nip area of the static elimination nip J1. If the leading edge of the sheet has reached the nip area of the static elimination nip J1 (Yes in S23), the static elimination control unit 227 determines whether there is a subsequent sheet to be conveyed (S24).

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

On the other hand, if there is a subsequent sheet (Yes in S24), the static elimination control unit 227 determines whether the sheet following the preceding sheet that does not require static elimination requires static elimination (S25). If the subsequent sheet does not require static elimination (No in S25), the static elimination control unit 227 returns to the processing of step S23. When sheets that do not require static elimination are continuously conveyed in this manner, the static elimination roller 130a of the contact static eliminator 129 is in the separated position, so these sheets are neutralized only by the non-contact static eliminator 131. As shown in Figure 9, when plain paper is continuously conveyed with a gap between sheets (T1, time t0 to time t1), these plain papers are neutralized only by the non-contact static eliminator 131.

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

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

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

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

As shown in FIG. 9 , the discharge control unit 227 begins applying a discharge voltage to the discharge roller 130b at time t2. This is because if a discharge voltage is applied to the discharge roller 130b while a preceding sheet of plain paper that does not require discharge is passing through the nip area of the discharge nip J1, an unnecessary voltage will be applied to the plain paper, causing it to become charged. This could result in sheet stacking errors or sheet transport errors. To prevent this, the discharge voltage begins to be applied to the discharge roller 130b after the plain paper has passed through the nip area of the discharge nip J1. Furthermore, the voltage applied by the discharge high-voltage power supply 230 reaches a reference voltage (see Table 1) corresponding to the sheet type before the leading edge of the succeeding synthetic paper being transported at the paper gap (T1) reaches the nip area of the discharge nip J1 (time t31).

After starting to apply a discharge voltage to the discharge roller 130b (S31), the discharge control unit 227 determines whether the leading edge of the subsequent sheet that requires discharge has reached the nip area of the discharge nip J1 (S32). If the leading edge of the subsequent sheet that requires discharge has not reached the nip area of the discharge nip J1 (No in S32), the discharge control unit 227 waits until the leading edge of the subsequent sheet reaches the nip area of the discharge nip J1. If the leading edge of the subsequent sheet has reached the nip area of the discharge nip J1 (Yes in S32), the discharge control unit 227 determines whether there is a subsequent sheet to be conveyed (S33).

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

On the other hand, if there is a subsequent sheet (Yes in S33), the static elimination control unit 227 determines whether the subsequent sheet also requires static elimination (S34). If the subsequent sheet also requires static elimination (Yes in S34), the static elimination control unit 227 returns to the processing of step S32. When sheets requiring static elimination are continuously transported between sheets (T1), the static elimination roller 130a of the contact static eliminator 129 is in the abutting position, and these sheets are neutralized by the contact static eliminator 129 and the non-contact static eliminator 131. As shown in FIG. 9, when synthetic paper is continuously transported between sheets (T1, times t31 to t41) after time t31, these synthetic papers are neutralized by the contact static eliminator 129 and the non-contact static eliminator 131.

If the succeeding sheet does not require static elimination (No in S34), the static elimination control unit 227 determines whether the trailing edge of the preceding sheet requiring static elimination has passed through the nip area of the static elimination nip J1 (S35). If the trailing edge of the preceding sheet has not yet reached the nip area of the static elimination nip J1 (No in S35), the static elimination control unit 227 waits until the trailing edge of the preceding sheet passes through the nip area of the static elimination nip J1. When the trailing edge of the preceding sheet reaches the nip area of the static elimination nip J1 (Yes in S35), the static elimination control unit 227 terminates the application of static elimination voltage to the static elimination roller 130b by the static elimination high-voltage power supply 230 (S36). The static elimination control unit 227 then initiates the release operation of the static elimination roller 130a by the contact/separation mechanism 150 (S37), moves the static elimination roller 130a from the contact position to the separation position, and returns to step S23.

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

As described above, in this embodiment, the discharge roller 130a begins to move to the contact position before the trailing edge of the preceding sheet that does not require discharge passes through the nip area of the discharge nip J1, and the discharge roller 130a completes its movement from the separation position to the contact position before the leading edge of the succeeding sheet that requires discharge reaches the nip area of the discharge nip J1. This allows the discharge roller 130a to complete its movement from the separation position to the contact position without increasing the paper gap (T1) between the preceding sheet that does not require discharge and the succeeding sheet that requires discharge. Therefore, the productivity of the image forming apparatus 101 does not decrease.

As mentioned above, the timing for starting the contact operation of the discharge roller 130a should be such that the discharge roller 130a can complete its movement to the contact position before the leading edge of the succeeding synthetic paper reaches the nip area of the discharge nip J1 (time t31). If this is the case, and the paper interval (T1) is shorter, such as 500 msec, than the time it takes for the discharge roller 130a to move from the separation position to the contact position (e.g., 600 msec), the discharge roller 130a can start its contact operation 100 msec before time t1, when the leading edge of the preceding plain paper reaches the nip area of the discharge nip J1.

<Other Embodiments>
If the movement of the discharge roller 130a to the contact position is completed before the trailing edge of the preceding sheet that does not require discharge passes through the nip area of the discharge nip J1 (time t2 in FIG. 9 ), wrinkles or the like may occur in the preceding sheet that does not require discharge (e.g., thin paper, etc.) depending on the type of sheet. Therefore, to prevent wrinkles or the like from occurring in the preceding sheet that does not require discharge, it is preferable to allow the user to input a setting as to whether or not to execute the above-described "discharge control process." FIG. 10 shows a "setting input screen" displayed on the display 206 to prompt the user to input a setting as to whether or not to execute the "discharge control process." As shown in FIG. 10 , the "setting input screen" prompts the user to input a setting as to whether or not to execute the "discharge control process," and displays a "Execute" button 1201 and a "Do Not Execute" button 1202.

When the user operates the "Execute" button 1201, the "discharge control process" described above is executed. In this case, the discharge roller 130a begins moving to the contact position before the trailing edge of the preceding sheet that does not require discharge passes through the nip area of the discharge nip J1. The discharge roller 130a completes its movement from the separation position to the contact position before the leading edge of the succeeding sheet that requires discharge reaches the nip area of the discharge nip J1 (first mode). On the other hand, when the user operates the "Do Not Execute" button 1202, the "discharge control process" described above is not executed. In this case, as in the conventional example (see FIG. 12), the discharge roller 130a begins moving from the separation position to the contact position after the trailing edge of the preceding sheet that does not require discharge passes through the nip area of the discharge nip J1 (second mode). The first mode improves productivity, while the second mode reduces the occurrence of wrinkles and other problems.

The user's setting input for whether or not to perform the "static elimination control process" may be set for each sheet type. Figure 11 shows a "setting input screen" that allows the user to set whether or not to perform the "static elimination control process" for each sheet type. The "setting input screen" shown in Figure 11 displays the sheet type, as well as a "productivity priority" button 1301 and a "wrinkle suppression priority" button 1302.

When the user operates the "Productivity Priority" button 1301, the above-mentioned "Discharge Control Process" is executed. In this case, the first mode described above is executed, which can improve productivity, but wrinkles may occur depending on the type of sheet. In contrast, when the user operates the "Wrinkle Suppression Priority" button 1302, the above-mentioned second mode is executed, which cannot improve productivity, but can prevent wrinkles and other problems from occurring on any type of sheet.

In the first and second embodiments described above, an intermediate transfer type printing device 102 is described as an example 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. However, this is not limited to this. For example, the printing device 102 may be a direct transfer type printing device 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 conveyance belt, while the sheet is conveyed on a conveyance belt that forms a nip between the photosensitive drum and the sheet.

103... de-ionization device, 118... image carrier (intermediate transfer belt), 119... transfer member (secondary transfer inner roller), 129... contact-type de-ionization unit (contact-type de-ionization device), 130a... first de-ionization member (de-ionization roller), 130b... second de-ionization member (de-ionization roller), 131... non-contact de-ionization unit (non-contact de-ionization device), 150... contact-separation mechanism, 170... transport unit (transport roller), 190... image forming unit, 221... acquisition unit (communication interface), 227... control unit (de-ionization control unit), J1... de-ionization nip, N2... transfer nip (secondary transfer unit), P... sheet

Claims (6)

a contact-type static elimination unit including a first static elimination member and a second static elimination member that contacts the first static elimination member to form a static elimination nip portion, and that eliminates static electricity from a sheet that passes through the static elimination nip portion by applying a voltage;
a power supply unit that applies a voltage to the contact-type static eliminator;
a conveying unit that conveys a sheet to the charge removal nip portion;
a contact/separation mechanism that can move the first charge-removing member between a contact position where the first charge-removing member contacts the second charge-removing member and a spaced position where the first charge-removing member is spaced from the second charge-removing member;
a control unit that is capable of executing , in the case of neutralizing a second sheet that is conveyed following a first sheet that does not require neutralization , a first mode in which, with respect to the sheet conveyance direction by the conveyance unit, the contact/separation mechanism starts moving the first neutralization member from the separation position to the contact position before the trailing end of the first sheet passes through the nip area of the neutralization nip portion, and a second mode in which the contact/separation mechanism starts moving the first neutralization member from the separation position to the contact position after the trailing end of the first sheet passes through the nip area ;
an input unit that allows a user to input whether the first mode or the second mode is to be executed depending on the type of the first sheet,
the control unit executes either the first mode or the second mode in accordance with a user input via the input unit when neutralizing the second sheet.
A static eliminator characterized by: the control unit, in the first mode, starts applying a voltage to the contact-type static elimination unit at a timing when the trailing edge of the first sheet passes through the nip area in the conveying direction, and applies a reference voltage according to the type of the second sheet before the leading edge of the second sheet reaches the nip area.
2. The static eliminator according to claim 1. In the first mode, the control unit determines a timing for starting movement of the first discharge member from the separation position to the contact position by the contact-separation mechanism based on a time required for the leading edge of the first sheet to reach the nip area in the conveying direction and a time required for the leading edge of the second sheet to reach the nip area and a time required for the contact-separation mechanism to move the first discharge member from the separation position to the contact position, and completes movement of the first discharge member to the contact position before the leading edge of the second sheet reaches the nip area.
2. The static eliminator according to claim 1. when a third sheet that does not require static elimination is conveyed following the second sheet, the control unit starts moving the first static elimination member from the contact position to the separation position by the contact/separation mechanism after the trailing edge of the second sheet passes through the nip area in the conveyance direction.
2. The static eliminator according to claim 1. a non-contact static elimination unit that is provided downstream of the contact static elimination unit in the conveyance direction and that can neutralize static on the sheet in a non-contact state after static elimination by the contact static elimination unit;
the control unit causes the non-contact static eliminator to neutralize the first sheet and the second sheet so as to uniformize the surface potentials of the first sheet and the second sheet.
2. The static eliminator according to claim 1. 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 passing through the transfer nip by application of a transfer voltage;
the static elimination device according to claim 1 , which is disposed downstream of the transfer nip portion in a sheet conveyance direction.
An image forming apparatus characterized by: