JP7771135B2 - 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. Therefore, image forming apparatuses are equipped with a neutralization device that neutralizes the sheet after transfer (Patent Document 1). The neutralization device described in Patent Document 1 includes a contact-type neutralization device that can neutralize the sheet by contacting it, and a non-contact neutralization device that can neutralize the sheet without contacting it. The neutralization device described in Patent Document 1 neutralizes the sheet using a contact-type neutralization device, a non-contact neutralization device, or both a contact-type and a non-contact neutralization device, depending on the surface resistance of the sheet.

To achieve a high level of sheet static elimination effectiveness using a contact-type static eliminator or a non-contact-type static eliminator, it is necessary to apply the optimal voltage for static elimination to each device (hereafter referred to as the static elimination voltage). Because the surface resistance of a sheet varies depending on the type of sheet, the static elimination voltage of a contact-type static eliminator or a non-contact-type static eliminator is determined based on the type of sheet. However, the amount of charge on the sheet after transfer can vary depending on the value of the transfer voltage applied to transfer the toner image to the sheet and the environment at the time (for example, humidity). Therefore, users need to measure the amount of charge on the sheet on which an image has been formed and adjust the static elimination voltage based on the measured amount of charge on the sheet.

JP 2019-167169 A

However, the method in which the user actually measures the amount of charge on the sheet and adjusts the neutralization voltage has the problem that the user's operations are cumbersome and it takes a long time to adjust the neutralization voltage.

The present invention was made in consideration of the above problems, and aims to provide a static elimination device and image forming apparatus that allow users to set an appropriate static elimination voltage through a simple process.

A static elimination device according to one embodiment of the present invention is characterized by comprising: a static elimination unit that eliminates charges that have been applied to sheets by applying a voltage; a control unit that is capable of executing a predetermined process , when outputting a sample sheet , to apply a first voltage to the static elimination unit to discharge a first sheet stack from which a set number of sheets have been neutralized, and, following the discharge of the first sheet stack, to apply a second voltage different from the first voltage to the static elimination unit to discharge a second sheet stack from which the set number of sheets have been neutralized; and an input unit that, after the predetermined process has been executed, accepts input to set either the first voltage or the second voltage as the voltage to be applied to the sheets by the static elimination unit.

This invention allows users to set an appropriate static elimination voltage through a simple process.

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. 4 is a flowchart showing a static elimination voltage adjustment process according to the first embodiment. 1A is a diagram showing an adjustment mode screen, and FIG. 1B is a diagram showing a screen for inputting the number of sheets per copy. FIG. 10 is a diagram showing a sample sheet to be output. 1A is a diagram showing an adjustment value input screen, and FIG. 1B is a diagram showing an adjustment value confirmation screen. 10 is a flowchart showing a static elimination voltage adjustment process according to a second embodiment. FIG. 10 is a diagram showing a sample confirmation screen.

[First embodiment]
<Image forming apparatus>
The image forming apparatus of this embodiment will be described below. First, the schematic configuration of the image forming apparatus of 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 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. As the intermediate transfer belt 118 rotates clockwise, the toner image reaches the secondary transfer unit T2. The secondary transfer unit T2 is a transfer nip formed by the contact between an inner secondary transfer roller 119 and an outer secondary transfer roller 120. When a secondary transfer voltage is applied to the inner secondary transfer roller 119 (transfer member) by a power source (not shown), 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, and such sheets are 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 T2.

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 located 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, it may electrostatically adhere to the transport guide or other device during transport, resulting in transport problems, or it may electrostatically adhere to sheets already stacked on the discharge tray (135, 136) when the sheet is discharged onto the discharge tray (135, 136), resulting in stacking problems. Therefore, the image forming device 101 of this embodiment is equipped with the static eliminator 103 to remove the charge from the charged sheet. The static eliminator 103 has a contact static eliminator 129 and a non-contact static eliminator 131, and as described below, 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.

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 that detect the passage of sheets are located along transport paths 132, 133, and 134, respectively, and these detection results 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 after a predetermined time has elapsed, it determines that a transport jam has occurred in the finisher 104, where the sheet has become stuck during 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 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 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, data, and the like between the printing device 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 types of data to and from the external device. The HDD 202, which serves as a storage unit, is a storage device that stores control programs and data. The CPU 203, which serves as a control unit, executes, for example, an image formation process (second mode) and a static elimination voltage adjustment process (first mode, see Figure 5 described below), not shown, based on the control programs 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 by the CPU 203 when performing various processes, and also functions as a temporary data work area.

The operation unit 205, which serves as an input unit, accepts various setting inputs and operation instructions from the user. The display 206, which serves as a display unit, 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 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 component 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, etc.

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 the communication cable 229. The static elimination high-voltage control unit 222 controls the static elimination voltage of the contact static elimination device 129 from 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 the static elimination roller 130b of the contact static elimination device 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/detachment mechanism (not shown). The non-contact static elimination high-voltage control unit 224 controls the static elimination voltage of the non-contact static elimination device 131 from the non-contact static elimination high-voltage power supply 240 (see Figure 4(a) described below).

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, with each component 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 performs various controls necessary 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 control the separation and transport of sheets conveyed from the static eliminator 103 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 T2, 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 sticking together 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.

<Contact static eliminator>
As shown in Figure 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. When the static eliminator roller 130a is in contact with the front surface of the sheet and the static eliminator roller 130b is in contact with the back surface of the sheet, a negative static eliminator voltage is applied by the static eliminator 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. The contact-type static eliminator 129 can achieve 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>
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.

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." 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."

However, in the past, even when a reference voltage was applied to neutralize the sheet P, there were cases where a sufficient neutralization effect was not achieved. This is because the amount of charge on the sheet P after secondary transfer varies depending on the voltage value of the secondary transfer voltage and the environment at the time (e.g., humidity, temperature, etc.). In light of this, in this embodiment, multiple sample sheets (sheet stacks) are output by applying different neutralization voltages to sheets that have passed through the secondary transfer unit T2 under the same image formation conditions, and the user can adjust the neutralization voltage by comparing the multiple sheet stacks that have actually been output. The "neutralization voltage adjustment process" of this embodiment that achieves this will be described below using Figures 5 to 8(b) with reference to Figures 1 and 2.

<Static elimination voltage adjustment process>
5 is a flowchart showing the static elimination voltage adjustment process according to the first embodiment. The static elimination voltage adjustment process (mode) is executed by the CPU 203 in response to, for example, the user selecting the "adjustment mode."

As shown in FIG. 5, the CPU 203 displays an "adjustment mode screen" on the display 206 (S1). The "adjustment mode screen" is shown in FIG. 6(a). As shown in FIG. 6(a), a "cassette selection button" is displayed on the "adjustment mode screen." By operating the "cassette selection button," the user can specify which of cassettes 111 and 112 contains the sheet P to be sample output. For example, when the "cassette 1" button is operated, cassette 111 is specified, and when the "cassette 2" button is operated, cassette 112 is specified. Note that cassettes 111 and 112 may be assigned in advance a corresponding type of sheet that they can contain; in that case, the type of sheet is automatically determined when cassettes 111 and 112 are specified.

When the user presses the "Next" button, the screen on the display 206 transitions from the "Adjustment Mode Screen" to the "Number of Sheets per Copy Input Screen" shown in FIG. 6(b). As shown in FIG. 6(b), the "Number of Sheets per Copy Input Screen" displays a numeric keypad. The user can input the number of samples per copy by operating the number buttons "0-9" on the numeric keypad. FIG. 6(b) shows an example in which the number button "5" is operated, displaying the number of samples "5." Here, the number of samples per copy (set number) is the number of sample sheets to be output under the same image formation conditions without changing the static elimination voltage. The input number of samples per copy is stored in memory 204 by the CPU 203.

The "Number of Sheets per Copy Input Screen" also displays a "Start Adjustment" button. When the user operates the "Start Adjustment" button, the CPU 203 proceeds to step S2 shown in FIG. 5 to start sample output. The CPU 203 sets the variable "Step" to "1" (S2). The variable "Step" is used to output sample sheets with different static elimination voltages under the same image formation conditions, and a sample number of sample sheets (sheet stack) per copy is output for each variable "Step." The CPU 203 then acquires page information to be used for sample output (S3). The page information includes the sheet type. The CPU 203 determines the static elimination voltage of the contact static elimination device 129 and the static elimination voltage of the non-contact static elimination device 131 (S4). Note that the method of acquiring the sheet type is not limited to acquiring page information.

The method for determining the neutralization voltage of the contact-type neutralization device 129 will now be described. The CPU 203 determines the reference voltage of the contact-type neutralization device 129 in accordance with the "reference voltage table" in Table 1, based on the type of sheet included in the page information. The CPU 203 also determines the "adjustment value" in accordance with the "adjustment table" shown in Table 2, based on the value of the variable "Step." The adjustment table is stored in advance in the printing device 102, for example, in the HDD 202 (see FIG. 2).

The CPU 203 then calculates the neutralization voltage of the contact-type neutralization device 129 from the reference voltage determined based on the sheet type and the adjustment value determined based on the value of the variable "Step." For example, if the sheet type is "coated paper," the reference voltage of the contact-type neutralization device 129 is determined to be "-100 volts" (see Table 1). If the variable "Step" is "1," the adjustment value is determined to be "-10" (first adjustment value) (see Table 2). As shown in the "Adjustment Table" in Table 2, in this embodiment, the voltage is offset by "-25 V" per adjustment value of "1." Therefore, when the variable "Step" is "1," the neutralization voltage of the contact-type neutralization device 129 is "+150 volts (-100 + (+250))" (first voltage), which is obtained by offsetting the reference voltage of "-100 volts" by the voltage adjustment amount of "+250 V (-10 x -25)."

The following describes how to determine the neutralization voltage of the non-contact static eliminator 131. In this embodiment, the reference voltage determined based on the type of sheet is used as the neutralization voltage for the non-contact static eliminator 131, without using an adjustment value determined based on the value of the variable "Step". 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), and therefore the neutralization voltage of the non-contact static eliminator 131 will be "800 volts" regardless of the value of the variable "Step".

Returning to the explanation of Figure 5, the CPU 203 sets the variable "Number of Prints" to "1" (S5). The variable "Number of Prints" is used to output sample sheets under the same image forming conditions without changing the neutralization voltage, so as not to exceed the input number of sample sheets per copy.

The CPU 203 executes sample output using the sheet P (S6). At this time, the printing device 102 operates under the same image formation conditions as in normal image formation processing. The static eliminator 103, to which the sheet P is then handed over from the printing device 102, applies the static elimination voltage of the contact static eliminator 129 and the static elimination voltage of the non-contact static eliminator 131 to eliminate static electricity from the sheet P. After static elimination, the sheet P is transported to the finisher 104 and discharged to the discharge trays (135, 136) as a sample sheet.

The CPU 203 determines whether the variable "number of prints" is equal to or greater than the number of sample sheets per copy (e.g., 5 sheets) stored in the memory 204 (S7). If the variable "number of prints," i.e., the number of sample sheets output under the same image forming conditions without changing the neutralization voltage, is less than the number of sample sheets per copy (NO in S7), the CPU 203 increments the variable "number of prints" (S8) and returns to the processing of step S6. The CPU 203 then repeats the processing of steps S6 to S8 until the variable "number of prints" is equal to or greater than the number of sample sheets per copy, and performs sample output using multiple sheets P. As a result, multiple sample sheets (the number of sample sheets per copy) neutralized with the same neutralization voltage under the same image forming conditions are stacked on the upper tray 135 or the lower tray 136 as a first sheet stack, a second sheet stack, etc.

On the other hand, if the variable "Number of Prints" is equal to or greater than the number of samples per copy (YES in S7), the CPU 203 determines whether the variable "Step" is equal to or greater than the threshold "Number of Output Copies" (S9). In this embodiment, as shown in the adjustment table in Table 2, the adjustment value is changed in 21 steps from "-10 to +10," so the number of output copies is set to "21 copies." If the variable "Step" is less than the threshold "Number of Output Copies" (NO in S9), the CPU 203 increments the variable "Step" (S13) and returns to the processing of step S4.

As described above, the CPU 203 determines the "adjustment value" in accordance with the "adjustment table" shown in Table 2 based on the value of the variable "Step." Therefore, each time the variable "Step" is incremented by one, the neutralization voltage of the contact-type neutralization device 129 is offset by "-25 V." For example, when the variable "Step" is "2," the adjustment value is determined to be "-9" (second adjustment value) (see Table 2). Therefore, when the variable "Step" is "2," the neutralization voltage of the contact-type neutralization device 129 becomes "+125 volts (-100 + (+225))" (second voltage), which is obtained by offsetting the voltage adjustment amount of "+250 V (-9 x -25)" from the reference voltage of "-100 volts." In this way, by executing sample output, for example, 21 copies (number of output copies) of sample sheets with a sample number of "5" per copy are output under the same image formation conditions but with different neutralization voltages. That is, the CPU 203 can execute a predetermined process to output multiple sheet stacks that have been neutralized with different neutralization voltages.

Figure 7 shows an example of a sample sheet output by the sample output described above. As shown in Figure 7, for each variable "Step" (1 to 21), sample sheets are output under the same image formation conditions without changing the static elimination voltage, resulting in "21 copies" of "5 sheets" per copy, for a total of "105 copies (21 copies x 5 copies)" of sample sheets. Once the sample sheets corresponding to the number of samples per copy have been discharged onto the discharge trays (135, 136), the user removes the stack of sample sheets from the discharge trays (135, 136). When removing the stack of sample sheets from the discharge trays (135, 136), the user checks the stacking status of the sample sheets on the discharge trays (135, 136) and the transport status of the sample sheets.

It is preferable that the sample sheets be stacked in sets of one copy on each of the upper tray 135 and the lower tray 136. It is also preferable that a toner image of information related to the static elimination voltage is formed on the sample sheets by the printing device 102. In the example shown in Figure 7, a toner image of the same adjustment value is formed on each set of sample sheets as an example of information related to the static elimination voltage.

Returning to the explanation of FIG. 5, if the variable "Step" is equal to or greater than the threshold "Number of Output Copies" (YES in S9), the CPU 203 displays an "Adjustment Value Input Screen" on the display 206 (S10). The CPU 203 then determines whether the user has input an adjustment value (S11). The CPU 203 waits until the user inputs an adjustment value (NO in S11). By displaying the "Adjustment Value Input Screen" on the display 206, the CPU 203 prompts the user to input an adjustment value for adjusting the reference voltage described above, allowing the user to set the static elimination voltage to be applied to the sheet by the contact-type static eliminator 129 after the specified process is executed. If an adjustment value has been input by the user (YES in S11), the CPU 203 stores the user-inputted adjustment value in the HDD 202 in response to the user's confirmation of the adjustment value (S12), and terminates processing.

Figure 8(a) shows the "Adjustment Value Input Screen." As shown in Figure 8(a), the "Adjustment Value Input Screen" displays a numeric keypad. The user can enter an adjustment value by operating the number buttons "0-9" on the numeric keypad. Figure 8(a) shows an example in which the number button "8" is operated, displaying an adjustment value of "8." The user checks the sample sheets for each set discharged to the output tray (135, 136) (see Figure 7), and inputs an adjustment value on the "Adjustment Value Input Screen" based on the adjustment value for the image formed on the sample sheet determined to have the greatest static elimination effect. After inputting the adjustment value, the user operates the "Next" button to confirm the adjustment value.

The adjustment value determined in this way is used to determine the neutralization voltage of the contact-type neutralization device 129 when neutralizing a sheet P that has undergone normal image formation processing. For example, if the sheet type is "synthetic paper" and the adjustment value is "-9," the neutralization voltage of the contact-type neutralization device 129 will be "-575 volts (-800 + (+225))," which is the reference voltage of "-800 volts" offset by the voltage adjustment amount of "+250 V (-9 x -25)."

In this embodiment, the user can display the "adjustment value confirmation screen" shown in Figure 8(b) on the display 206 and confirm the confirmed adjustment values. As shown in Figure 8(b), the "adjustment value confirmation screen" displays the adjustment values entered by the user on the above-mentioned "adjustment value input screen" and stored in HDD 202.

Furthermore, if a sheet transport error or sheet stacking error occurs during normal image formation processing, the user can display the "adjustment value confirmation screen" on the display 206 and check the adjustment values stored in the HDD 202. Then, by performing the above-mentioned "neutralization voltage adjustment process" and changing the adjustment value on the "adjustment value input screen," the user can adjust the neutralization voltage to a voltage value that is less likely to cause a sheet transport error or sheet stacking error during normal image formation processing. In addition to the adjustment values, the "adjustment value confirmation screen" may also display image formation conditions stored in the HDD 202, such as image position adjustment values, secondary transfer voltage adjustment values, and gloss adjustment values.

As described above, in this embodiment, the static elimination voltage adjustment process is performed, and multiple sample sheets, each consisting of a set of sheets output by applying the same static elimination voltage, are stacked on the output tray (135, 136). In the static elimination voltage adjustment process, the same static elimination voltage is applied under the same image formation conditions to output the sample sheets one by one, allowing the user to actually check the sample sheet stacking status and sample sheet transport status. Furthermore, the static elimination voltage adjustment process outputs multiple sample sheets at different static elimination voltages. Therefore, the user can compare multiple sample sheets output at different static elimination voltages and identify sample sheets that achieve a better sheet static elimination effect. By inputting information (adjustment value) regarding the static elimination voltage applied when the identified sample sheets were output, the user can adjust the static elimination voltage to a voltage value that achieves a better sheet static elimination effect. In this way, this embodiment allows the user to set the optimal static elimination voltage according to the amount of charge on the sheets after transfer through a simple process.

[Second embodiment]
Next, a second embodiment will be described using Fig. 9 and Fig. 10 with reference to Fig. 1 and Fig. 2. Fig. 9 is a flowchart showing the static elimination voltage adjustment process of the second embodiment. Fig. 10 is a diagram showing a "sample confirmation screen" displayed on the display 206. In the static elimination voltage adjustment process shown in Fig. 9, the same steps as those in the static elimination voltage adjustment process of the first embodiment (see Fig. 5) are assigned the same step numbers, and their descriptions will be simplified or omitted.

As shown in Figure 9, in the static elimination voltage adjustment process of the second embodiment, sample output is performed using multiple sheets P in the same manner as in the static elimination voltage adjustment process of the first embodiment (steps S1 to S8). As a result, multiple sample sheets (the number of sample sheets per copy) output under the same image formation conditions without changing the static elimination voltage are stacked on the output tray (135, 136). The user can input the number of sample sheets per copy (e.g., 5 sheets) using the "Number of sheets per copy input screen" shown in Figure 6(b) described above.

If the variable "Number of Prints" is equal to or greater than the number of sample sheets per copy (YES in S7), that is, each time a copy of sample sheets is discharged onto the discharge tray (135, 136), the CPU 203 temporarily suspends the sample output (S6) and displays a "Sample Confirmation Screen" on the display 206 (S21). As shown in FIG. 10, the "Sample Confirmation Screen" displays a message prompting the user to confirm the copy of sample sheets stacked on the discharge tray (135, 136). The "Sample Confirmation Screen" also displays an "OK button" and an "NG button."

The CPU 203 determines whether either the "OK button" or the "NG button" on the "Sample Confirmation Screen" has been operated (S22). The CPU 203 waits for processing until either the "OK button" or the "NG button" is operated by the user (NO in S22). If either the "OK button" or the "NG button" has been operated by the user (YES in S22), the CPU 203 determines whether the operated button was the "OK button" (S23).

If the user operates the "OK button" (YES in S23), the CPU 203 stores the adjustment value (see Table 2) corresponding to the value of the variable "Step" at that time in the HDD 202 (S24), and ends the process. In other words, each time a set of sample sheets is discharged onto the discharge tray (135, 136), the user can check whether there are any transport or stacking errors with those sheets, and input the adjustment value by operating the "OK" button.

On the other hand, if the user operates the "NG button" (NO in S23), the CPU 203 determines whether the variable "Step" is equal to or greater than the threshold "Number of copies to be output" (S25). In this embodiment, as shown in the adjustment table in Table 2, the adjustment value is changed in 21 steps from "-10 to +10," so the number of copies to be output is set to "21 copies." If the variable "Step" is equal to or greater than the threshold "Number of copies to be output" (YES in S25), the CPU 203 ends processing. In this case, the CPU 203 displays an error on the display 206 indicating that the adjustment value cannot be set.

If the variable "Step" is less than the threshold "Number of Output Copies" (NO in S25), the CPU 203 increments the variable "Step" (S26). As described above, the CPU 203 determines the "adjustment value" in accordance with the "adjustment table" shown in Table 2 based on the value of the variable "Step." Therefore, each time the variable "Step" is incremented by 1, the static elimination voltage of the contact static eliminator 129 is offset by -25 V. The CPU 203 then returns to the processing of step S4, resumes the paused sample output (S6), and outputs one copy of a new sample sheet count of five sheets based on the offset static elimination voltage.

The user can adjust the neutralization voltage to a better level by comparing the sheet stacks. Therefore, it is preferable to output at least two sets of sheet stacks as samples for comparison, and then allow the user to operate the "OK button" and "NG button" on the "Sample Confirmation Screen" described above. That is, when executing the neutralization voltage adjustment process of the second embodiment, if the "NG button" is operated after the second set of sheet stack is discharged, an incremented voltage (third voltage) is applied to the contact-type neutralization device 129, and a new sample of "five sheets" (one copy of the third sheet stack) is output.

As described above, in the second embodiment, similar to the first embodiment, the static elimination voltage adjustment process is performed, and a set of sample sheets consisting of multiple sheets output by applying the same static elimination voltage is stacked on the output tray (135, 136). However, unlike the first embodiment, in the second embodiment, the user checks the sample sheet stacking state and sample sheet transport state, and when it determines that a sample sheet has achieved a higher sheet static elimination effect, the static elimination voltage used when outputting that sample sheet is stored. In other words, the user can input information (adjustment value) related to the static elimination voltage without waiting for multiple sample sheets to be output at different static elimination voltages. In this way, in the second embodiment, the user can set the optimal static elimination voltage according to the amount of charge on the sheets after transfer through a simple process. In addition, compared to the first embodiment, there is no need to output unnecessary sample sheets, and the user can reduce the time required to set the static elimination voltage.

<Other Embodiments>
In the first and second embodiments described above, the static elimination voltage of the contact static eliminator 129 is adjusted, but the present invention is not limited to this. For example, the static elimination voltage of the non-contact static eliminator 131 may be adjusted, or both the static elimination voltage of the contact static eliminator 129 and the static elimination voltage of the non-contact static eliminator 131 may be adjusted.

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...Discharge unit (discharge device), 118...Image carrier (intermediate transfer belt), 119...Transfer member (secondary transfer inner roller), 129...Contact discharge unit (contact discharge device), 131...Non-contact discharge unit (non-contact discharge device), 135...Second discharge unit (upper tray), 136...First discharge unit (lower tray), 190...Image forming unit, 202...Storage unit (HDD), 203...Control unit (CPU), 205...Input unit (operation unit), 206...Display unit (display), P...Sheet, T2...Transfer nip unit (secondary transfer unit)

Claims (10)

a charge removal unit that removes electric charges from the sheet by applying a voltage;
a control unit that is capable of executing a predetermined process of applying a first voltage to the static elimination unit to discharge a first sheet bundle from which a set number of sheets have been neutralized when outputting a sample sheet , and subsequently applying a second voltage different from the first voltage to the static elimination unit to discharge a second sheet bundle from which the set number of sheets have been neutralized;
an input unit that receives an input for setting either the first voltage or the second voltage as the voltage to be applied to the sheet by the static eliminator after the predetermined process is executed.
A static eliminator characterized by: a storage unit that stores a first adjustment value for adjusting a predetermined reference voltage determined for each type of sheet, and a second adjustment value that is different from the first adjustment value for adjusting the reference voltage;
When the control unit applies the first voltage to the static eliminator during the execution of the predetermined process, the control unit adjusts the reference voltage based on the first adjustment value and applies the adjusted reference voltage to the static eliminator, and when the control unit applies the second voltage to the static eliminator, the control unit adjusts the reference voltage based on the second adjustment value and applies the adjusted reference voltage to the static eliminator.
2. The static eliminator according to claim 1. the input unit is capable of accepting input of either the first adjustment value or the second adjustment value stored in the storage unit,
the control unit adjusts the reference voltage based on either the first adjustment value or the second adjustment value input by the input unit and applies the adjusted reference voltage to the static eliminator.
3. The static eliminator according to claim 2. a display unit capable of displaying either the first adjustment value or the second adjustment value input by the input unit,
4. The static eliminator according to claim 3. an input unit capable of inputting the set number of sheets;
2. The static eliminator according to claim 1. A first discharge section;
a second discharge section different from the first discharge section,
the control unit, when executing the predetermined process, discharges the first sheet bundle to the first discharge unit and discharges the second sheet bundle to the second discharge unit.
2. The static eliminator according to claim 1. the charge eliminating section includes a contact type charge eliminating section that comes into contact with the sheet being conveyed to eliminate charge, and a non-contact type charge eliminating section that is provided downstream of the contact type charge eliminating section in the sheet conveyance direction and that eliminates residual charge of the sheet in a non-contact state after the sheet has been neutralized by the contact type charge eliminating section,
The control unit controls a voltage applied to the contact-type static eliminator.
2. The static eliminator according to claim 1. when the control unit performs the predetermined process, if there is no input from the input unit to set either the first voltage or the second voltage after the second sheet bundle is discharged, the control unit applies a third voltage to the static eliminator to discharge the third sheet bundle from which the set number of sheets have been neutralized;
the input unit is capable of receiving an input for setting the third voltage as a voltage to be applied to the sheets by the static eliminator after the third sheet stack is discharged.
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: the control unit, during execution of the predetermined process, causes the image forming unit to form a toner image of information related to the first voltage and transfer it to a sheet of the first sheet bundle, and causes the image forming unit to form a toner image of information related to the second voltage and transfer it to a sheet of the second sheet bundle.
10. The image forming apparatus according to claim 9,