JP2022138353A - Image forming apparatus and image forming method - Google Patents

Abstract

To provide an image forming apparatus and an image forming method that can prevent the occurrence of a difference in surface potential of an image carrier without reducing productivity.SOLUTION: An image forming apparatus comprises: a transfer unit 25 that is provided opposite to a photoreceptor drum 21 electrified to have a positive polarity, and upon receiving application of voltage having a negative polarity, transfers a toner image formed on the photoreceptor drum 21 to a sheet; an electrode unit 26 that is provided opposite to the photoreceptor drum 21 with a path of movement R1 of the sheet from a nip position P1 therebetween; and an application control unit that, when the size in a width direction of the sheet is less than the maximum size in which the apparatus can form an image, applies a specific voltage having a positive polarity to the electrode unit 26 from a first timing at which a leading end of the sheet passes through a separation position P2 until a second timing at which a rear end of the sheet passes through the separation position P2.SELECTED DRAWING: Figure 3

Description

The present invention relates to an electrophotographic image forming apparatus and an image forming method executed by the image forming apparatus.

A transfer unit, such as a transfer roller, is provided in contact with an image carrier such as a photosensitive drum and transfers a toner image formed on the image carrier to a sheet passing through a nip portion between the image carrier. image forming apparatuses are known.

In this type of image forming apparatus, when the size of the sheet passing through the nip portion in the width direction is smaller than the maximum size that can be formed by the apparatus, the non-contact area outside the contact area with the sheet on the image carrier is prevented. A current may flow between the area and the transfer section, creating a difference between the potential of the contact area and the non-contact area. In this case, the toner supplied from the developing device adheres to the non-contact area, and the toner adheres to the widthwise end of the sheet passing through the nip, causing a problem called edge fogging. .

On the other hand, an image forming apparatus that executes a surface potential equalization mode when the size of a sheet passing through the nip portion in the width direction is smaller than the maximum size is known as a related technology (see Japanese Patent Application Laid-Open No. 2002-200033). ). In the surface potential equalization mode, after the trailing edge of the sheet has passed through the nip portion, the surface of the image carrier is charged with toner using at least one of the charging device and the transfer portion while the static elimination device is turned off. A charging step of charging to the same polarity as the polarity is performed, and then a static elimination step of turning on the static elimination device is performed.

JP 2015-106103 A

However, since image formation cannot be performed while the surface potential equalization mode is being executed, the productivity of the image forming apparatus according to the related art described above is lowered.

SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus and an image forming method capable of suppressing a difference in surface potential of an image carrier without lowering productivity.

An image forming apparatus according to one aspect of the present invention includes an image carrier, a transfer section, an electrode section, and an application control section. The image carrier is charged to a first polarity. The transfer section is provided to face the image carrier, and receives a voltage having a second polarity opposite to the first polarity, and transfers a toner image formed on the image carrier to the image carrier. transfer to a sheet passing through a first position between The electrode portion is provided so as to face the image bearing member across a moving path of the sheet from the first position. When the size of the sheet in the width direction perpendicular to the movement path is smaller than the maximum size of the sheet capable of forming an image, the application control unit is configured so that the leading edge of the sheet is positioned between the image carrier and the electrode unit. The specific voltage of the first polarity is applied to the electrode portion from the first timing when the sheet passes through the second position between the second positions to the second timing when the trailing edge of the sheet passes the second position.

An image forming method according to another aspect of the present invention includes: an image carrier charged to a first polarity; a transfer unit for transferring a toner image formed on the image carrier by receiving an application onto a sheet passing through a first position between the image carrier and a moving path of the sheet from the first position; and an electrode portion provided to face the image carrier, and includes the following determination step and application step. In the determination step, it is determined whether or not the size of the sheet in the width direction orthogonal to the movement path is smaller than the maximum image-formable size of the apparatus. In the applying step, when it is determined in the determining step that the size of the sheet in the width direction is smaller than the maximum size, the leading edge of the sheet is located at a second position between the image carrier and the electrode section. The specific voltage of the first polarity is applied to the electrode portion from the first timing when the sheet passes the position to the second timing when the trailing edge of the sheet passes the second position.

According to the present invention, it is possible to suppress the occurrence of a difference in surface potential of the image carrier without lowering productivity.

FIG. 1 is a block diagram showing the system configuration of an image forming apparatus according to an embodiment of the invention. FIG. 2 is a diagram showing the internal configuration of the housing of the image forming apparatus according to the embodiment of the present invention. FIG. 3 is a diagram showing the configuration of the transfer section and the electrode section of the image forming apparatus according to the embodiment of the present invention. FIG. 4 is a timing chart showing application timings of the transfer bias voltage and the specific voltage in the image forming apparatus according to the embodiment of the present invention. FIG. 5 is a flowchart showing an example of application control processing executed by the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a flowchart showing an example of first control processing executed by the image forming apparatus according to the embodiment of the invention. FIG. 7 is a flowchart showing an example of second control processing executed by the image forming apparatus according to the embodiment of the invention. FIG. 8 is a flowchart showing an example of third control processing executed by the image forming apparatus according to the embodiment of the invention.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. It should be noted that the following embodiment is an example that embodies the present invention, and does not limit the technical scope of the present invention.

[Configuration of Image Forming Apparatus 100]
First, the configuration of an image forming apparatus 100 according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2. FIG. Here, FIG. 2 is a sectional view showing the internal configuration of the housing 6. As shown in FIG.

The image forming apparatus 100 is a printer that forms an image using an electrophotographic method. Note that the image forming apparatus of the present invention may be a facsimile machine, a copier, a multifunction machine, or the like.

As shown in FIG. 1, the image forming apparatus 100 includes an image forming section 1, a paper feeding section 2, an operation display section 3, a storage section 4, and a control section 5. As shown in FIG. Further, as shown in FIG. 2 , the image forming apparatus 100 includes a housing 6 that accommodates each component of the image forming apparatus 100 .

The image forming section 1 forms an image based on image data.

The paper feeding unit 2 supplies sheets to the image forming unit 1 . As shown in FIG. 2 , the paper feeder 2 includes a paper feed cassette 31 , a first pickup roller 32 , a paper feed roller 33 , a manual feed tray 34 , a second pickup roller 35 and registration rollers 36 .

The operation display section 3 is a user interface of the image forming apparatus 100 . The operation display unit 3 includes a display unit such as a liquid crystal display for displaying various information according to control instructions from the control unit 5, and operation keys or a touch panel for inputting various information to the control unit 5 according to user operations. It has an operation part such as

The storage unit 4 is a nonvolatile storage device. For example, the storage unit 4 is a storage device such as non-volatile memory such as flash memory and EEPROM (registered trademark), SSD (Solid State Drive), or HDD (Hard Disk Drive).

The control unit 5 controls the image forming apparatus 100 as a whole. As shown in FIG. 1, the control unit 5 includes a CPU 11, a ROM 12, and a RAM 13. The CPU 11 is a processor that executes various kinds of arithmetic processing. The ROM 12 is a non-volatile storage device in which information such as control programs for causing the CPU 11 to execute various processes is stored in advance. The RAM 13 is a volatile or nonvolatile storage device used as a temporary memory (work area) for various processes executed by the CPU 11 . In the control unit 5 , various control programs pre-stored in the ROM 12 are executed by the CPU 11 . Thereby, the control unit 5 controls the image forming apparatus 100 in an integrated manner.

[Configuration of Image Forming Unit 1]
Next, the configuration of the image forming section 1 will be described with reference to FIGS. 1 to 3. FIG. In FIG. 3, the movement path R1 from the nip position P1 of the sheet supplied from the sheet feeding unit 2 is indicated by a dashed line with an arrow. Further, in FIG. 3, the power supply path between the first power supply 41 and the transfer section 25 and the power supply path between the second power supply 42 and the electrode section 26 are indicated by dashed lines.

As shown in FIG. 2, the image forming section 1 includes a photosensitive drum 21, a charging device 22, an optical scanning device 23, a developing device 24, a transfer section 25, an electrode section 26, a cleaning device 27, a neutralizing device 28, and a fixing device. A device 29 is provided. Further, as shown in FIGS. 1 and 3, the image forming section 1 includes a first power source 41 and a second power source 42 .

The photoreceptor drum 21 carries a toner image. The photoreceptor drum 21 receives a rotational driving force supplied from a motor (not shown) and rotates about a rotating shaft 21A (see FIG. 3) in the direction of the arrow shown in FIGS. For example, photoreceptor drum 21 is an organic photoreceptor (OPC) drum having an organic photoreceptor layer. The photoreceptor drum 21 is an example of the image carrier of the present invention.

The charging device 22 charges the surface of the photosensitive drum 21 . As shown in FIG. 2 , the charging device 22 includes a charging roller 22A provided in contact with the surface of the photoreceptor drum 21 . A positive charging voltage is applied to the charging roller 22A from a power source (not shown). Thereby, the charging roller 22A charges the surface of the photoreceptor drum 21 to a positive polarity. A positive polarity is an example of the first polarity of the present invention.

The optical scanning device 23 emits light based on image data toward the charged surface of the photosensitive drum 21 . Thereby, an electrostatic latent image is formed on the surface of the photosensitive drum 21 .

The developing device 24 uses toner to develop the electrostatic latent image formed on the surface of the photosensitive drum 21 . As shown in FIG. 2, the developing device 24 includes a developing roller 24A provided facing the surface of the photoreceptor drum 21. As shown in FIG. The developing roller 24</b>A conveys the positively charged toner in the developing device 24 to a region facing the photosensitive drum 21 . A developing bias voltage in which a positive DC voltage and an AC voltage are superimposed is applied to the developing roller 24A from a power source (not shown). As a result, the developing roller 24A supplies the toner conveyed to the area facing the photoreceptor drum 21 to the exposure area of the surface of the photoreceptor drum 21 irradiated with the light from the optical scanning device 23 . Toner is supplied to the developing device 24 from a toner container 24B shown in FIG.

The transfer section 25 is provided to face the photosensitive drum 21 . As shown in FIG. 3 , the transfer section 25 is a roller-shaped member provided in contact with the photosensitive drum 21 . For example, the transfer portion 25 is made of conductive sponge rubber. The transfer unit 25 rotates integrally with a metallic rotating shaft 25A (see FIG. 3). The rotating shaft 25A is elongated in the same direction as the rotating shaft 21A of the photoreceptor drum 21 . The transfer unit 25 receives a negative transfer bias voltage, and transfers the toner image formed on the photoreceptor drum 21 to a sheet passing through the nip position P1 (see FIG. 3) between the photoreceptor drum 21 and the transfer unit 25 . to transcribe. Negative polarity is an example of the second polarity of the present invention. Also, the nip position P1 is an example of the first position of the present invention.

The electrode portion 26 is provided so as to face the photosensitive drum 21 across the sheet movement path R1 (see FIG. 3) from the nip position P1. As shown in FIG. 3, the electrode portion 26 includes metal needle-like members 26A arranged at equal intervals along the extending direction of the rotating shaft 25A, and the needle-like members 26A supporting the respective needle-like members 26A. is provided with an elongated support portion 26B. The electrode part 26 receives the application of the positive first voltage, and separates the leading edge of the sheet electrostatically attracted to the surface of the photoreceptor drum 21 from the surface. Specifically, the electrode portion 26 generates a discharge between the needle member 26A and the sheet negatively charged by the transfer portion 25, thereby reducing the amount of charge on the sheet. The first voltage is a preset voltage that can separate the sheet from the photosensitive drum 21 .

The cleaning device 27 removes toner remaining on the surface of the photosensitive drum 21 after the toner image is transferred by the transfer unit 25 .

The neutralization device 28 neutralizes the surface of the photoreceptor drum 21 after the toner image has been transferred by the transfer unit 25 . As shown in FIG. 2 , the neutralization device 28 is provided downstream of the cleaning device 27 in the rotation direction of the photosensitive drum 21 and upstream of the charging device 22 in the rotation direction. Specifically, the static elimination device 28 irradiates the surface of the photoreceptor drum 21 with light to eliminate static electricity from the surface of the photoreceptor drum 21 .

The fixing device 29 fixes the toner image transferred onto the sheet by the transfer unit 25 onto the sheet. The sheet on which the toner image is fixed by the fixing device 29 is transferred to the paper discharge tray 39 ( 2).

The first power supply 41 applies the transfer bias voltage to the transfer section 25 . The first power supply 41 is electrically connected to the rotary shaft 25A (see FIG. 3) of the transfer section 25. As shown in FIG. For example, the first power supply 41 is configured such that the output current X1 (see FIGS. 3 and 4) flowing between the transfer unit 25 and the transfer unit 25 has a current value A0 (see FIG. 4) or a current value A1 (see FIG. 4). Constant current control is performed to control the voltage applied to the transfer unit 25 . The transfer bias voltage is a voltage applied to the transfer section 25 when constant current control is performed so that the output current X1 becomes the current value A1.

The second power supply 42 applies the first voltage to the electrode section 26 . The second power supply 42 is electrically connected to the plurality of needle-like members 26A (see FIG. 3). For example, the output current Y1 (see FIGS. 3 and 4) flowing between the second power supply 42 and the electrode portion 26 is the current value B0 (see FIG. 4), the current value B1 (see FIG. 4), or the current value B2. (See FIG. 4). The first voltage is the voltage applied to the electrode section 26 when constant current control is performed so that the output current Y1 becomes the current value B1.

Note that the first power supply 41 may perform constant voltage control instead of constant current control. In this case, the first power supply 41 may apply a predetermined voltage value corresponding to the current value A0 or a predetermined voltage value corresponding to the current value A1 to the transfer section 25 .

Further, the second power supply 42 may perform constant voltage control instead of constant current control. In this case, the second power supply 42 provides a predetermined voltage value corresponding to the current value B0, a predetermined voltage value corresponding to the current value B1, or a predetermined voltage value corresponding to the current value B2. is applied to the electrode section 26 .

By the way, when the size of the sheet passing through the nip position P1 in the width direction orthogonal to the movement path R1 is smaller than the maximum size that can be image-formed by the image forming apparatus 100, the area of the photosensitive drum 21 outside the contact area with the sheet A current may flow between the non-contact area and the transfer portion 25, causing a potential difference between the contact area and the non-contact area. In this case, the toner supplied from the developing device 24 adheres to the non-contact area, and the toner adheres to the widthwise end of the sheet passing through the nip position P1, causing a problem called edge fogging. Occur.

On the other hand, an image forming apparatus that executes a surface potential equalization mode when the size of the sheet passing through the nip position P1 in the width direction is smaller than the maximum size is known as a related art. In the surface potential equalization mode, after the trailing edge of the sheet passes through the nip position P1, the surface of the photosensitive drum 21 is flattened by using at least one of the charging device 22 and the transfer unit 25 while the neutralization device 28 is turned off. A charging step of charging the toner to the same polarity as the charging polarity of the toner is performed, and then a static elimination step of turning on the static eliminator 28 is performed.

However, since image formation cannot be performed while the surface potential equalization mode is being executed, the productivity of the image forming apparatus according to the related art described above is lowered.

On the other hand, in the image forming apparatus 100 according to the embodiment of the present invention, it is possible to suppress the difference in the surface potential of the photoreceptor drum 21 without lowering productivity, as described below.

[Configuration of control unit 5]
Next, the controller 5 will be described with reference to FIG.

As shown in FIG. 1 , the control unit 5 includes a determination processing unit 51 , a setting processing unit 52 and an application control unit 53 .

Specifically, the ROM 12 of the control unit 5 stores in advance an application control program for causing the CPU 11 of the control unit 5 to execute an application control process (see the flowchart of FIG. 5), which will be described later. The CPU 11 of the control unit 5 functions as a determination processing unit 51 , a setting processing unit 52 and an application control unit 53 by executing the application control program stored in the ROM 12 .

The application control program is recorded on a computer-readable recording medium such as a CD, DVD, and flash memory, and may be read from the recording medium and stored in a storage device such as the storage unit 4. Further, the determination processing unit 51, the setting processing unit 52, and the application control unit 53 may be configured by an electronic circuit such as an integrated circuit (ASIC).

The determination processing unit 51 determines whether or not the size of the sheet in the width direction is smaller than the maximum size.

Specifically, when image forming processing for forming an image on a sheet based on image data is executed, the determination processing unit 51 determines the width direction of the sheet on which an image is formed by the image forming processing. is smaller than the maximum size.

For example, in the image forming apparatus 100 , the size of a sheet on which an image is formed in the image forming process is set in advance by a user's operation on the operation display section 3 . In this case, the determination processing unit 51 determines whether or not the size of the sheet in the width direction is smaller than the maximum size, based on a preset size of the sheet.

A sensor capable of detecting the size of the sheets supplied to the image forming section 1 may be provided in the paper feed cassette 31 or the manual feed tray 34 . In this case, the determination processing unit 51 may determine whether the size of the sheet in the width direction is less than the maximum size based on the size of the sheet detected by the sensor.

The setting processing unit 52 sets a positive second voltage based on the size of the sheet in the width direction. The second voltage is the voltage applied to the electrode section 26 when constant current control is performed so that the output current Y1 becomes the current value B2. In other words, the setting processing unit 52 sets the current value B2 based on the size of the sheet in the width direction.

Here, the current value B2 is the value of the output current Y1 that can change the potential of the non-contact area of the photosensitive drum 21 . Specifically, the current value B2 is the value of the output current Y1 that can reduce the difference between the potential of the non-contact region and the potential of the contact region.

For example, in the image forming apparatus 100, table data indicating the correspondence relationship between the size of the sheet in the width direction and the current value B2 is stored in the storage unit 4 in advance. In the table data, the correspondence relationship between the size and the current value B2 is defined such that the smaller the size of the sheet in the width direction, the larger the corresponding current value B2. This is based on the following reasons.

When a sheet whose size in the width direction is smaller than the maximum size passes through the nip position P1, current flows between the transfer portion 25 and the contact area, and current flows between the transfer portion 25 and the non-contact area. flows. Here, a current is less likely to flow between the transfer portion 25 and the contact area than between the transfer portion 25 and the non-contact area due to the presence of the sheet. Therefore, the contact area has a lower density in the width direction of the current flowing between it and the transfer section 25 than the non-contact area. This decrease in density increases as the size of the sheet in the width direction decreases.

On the other hand, in the image forming apparatus 100, the current value A1 is set so that the density in the width direction of the current flowing between the transfer portion 25 and the contact area is constant regardless of the size of the sheet in the width direction. is set. That is, in the image forming apparatus 100, the smaller the size of the sheet in the width direction, the larger the current value A1 is set. As the value of the current value A1 increases, the current flowing between the transfer portion 25 and the non-contact area increases, and the potential fluctuation amount in the non-contact area increases. That is, the difference between the potential of the contact area and the potential of the non-contact area increases. Therefore, in the table data, the smaller the size of the sheet in the width direction, the larger the current value B2 for canceling the potential fluctuation in the non-contact area. is defined.

The setting processing unit 52 sets the current value B2 using the table data.

The table data may be prepared for each predetermined sheet type. For example, the sheet type is determined based on one or more combinations of sheet thickness, basis weight, and material. In this case, the setting processing unit 52 may set the current value B2 based on the size of the sheet in the width direction and the sheet type.

Further, the table data may be prepared for each predetermined temperature and humidity condition of the housing 6 . For example, the temperature and humidity conditions are a combination of multiple stages of temperature conditions and multiple stages of humidity conditions. For example, the temperature conditions are two stages of high temperature and low temperature. Also, the humidity conditions are two stages of high humidity and low humidity. In this case, the setting processing unit 52 may set the current value B2 based on the size of the sheet in the width direction and the temperature and humidity conditions.

Note that the control unit 5 does not have to include the setting processing unit 52 .

When the size of the sheet in the width direction is less than the maximum size, the application control unit 53 allows the leading edge of the sheet to pass through the separation position P2 (see FIG. 3) between the photosensitive drum 21 and the electrode unit 26. A positive specific voltage is applied to the electrode portion 26 from the first timing when the rear end of the sheet passes through the separation position P2 to the second timing when the trailing edge of the sheet passes through the separation position P2. The separation position P2 is an example of the second position of the invention.

Here, the specific voltage is a voltage that can change the potential of the non-contact area of the photosensitive drum 21 . The specific voltage includes the first voltage and the second voltage.

For example, when the second voltage is equal to or higher than the first voltage, the application control section 53 applies the second voltage to the electrode section 26 from the first timing to the second timing. The application control unit 53 determines that the second voltage is equal to or higher than the first voltage when the current value B2 is equal to or higher than the current value B1.

Further, when the second voltage is less than the first voltage, the application control unit 53 applies the first voltage to the electrode unit 26 from the first timing to an intermediate timing before the second timing. Thus, the second voltage is applied to the electrode portion 26 from the intermediate timing to the second timing.

For example, the first timing is the timing before the leading edge of the sheet reaches the separation position P2. The second timing is the timing before the trailing edge of the sheet reaches the separation position P2. The arrival of the first timing and the second timing is determined based on the detection result of a sheet sensor provided on the upstream side of the nip position P1 in the sheet conveying direction. The first timing may be the timing after the leading edge of the sheet reaches the separation position P2. Also, the second timing may be a timing after the trailing edge of the sheet reaches the separating position P2.

Here, the application timing of the transfer bias voltage, the first voltage, and the second voltage in the image forming apparatus 100 will be described with reference to FIG. FIG. 4 shows application timings of the transfer bias voltage, the first voltage, and the second voltage when the second voltage set by the setting processing unit 52 is less than the first voltage. there is

Note that t1 in FIG. 4 indicates the timing when the leading edge of the sheet reaches the nip position P1. t2 in FIG. 4 indicates the timing when the leading edge of the sheet reaches the separation position P2. Also, t3 in FIG. 4 indicates an arbitrary timing between timing t2 and timing t4. t4 in FIG. 4 indicates the timing when the trailing edge of the sheet reaches the nip position P1. t5 in FIG. 4 indicates the timing when the trailing edge of the sheet reaches the separation position P2.

As shown in FIG. 4, in the image forming apparatus 100, the transfer bias voltage is applied after timing t1. That is, a voltage is applied to the transfer section 25 so that the output current X1 becomes the current value A1. Specifically, in the image forming apparatus 100, the transfer bias voltage is applied after the timing t1 and before the leading edge of the image forming area onto which the toner image is transferred on the sheet reaches the nip position P1.

Further, as shown in FIG. 4, in the image forming apparatus 100, application of the transfer bias voltage is stopped before timing t4. That is, a voltage is applied to the transfer section 25 so that the output current X1 becomes the current value A0. For example, in the image forming apparatus 100, application of the transfer bias voltage is stopped before timing t4 and after the trailing edge of the image forming area on the sheet reaches the nip position P1.

Further, as shown in FIG. 4, in the image forming apparatus 100, the first voltage is applied before timing t2. That is, a voltage is applied to the electrode section 26 so that the output current Y1 becomes the current value B1. For example, in the image forming apparatus 100, the first voltage is applied before timing t1. The first voltage may be applied after timing t2. Specifically, the first voltage may be applied until the tip of the contact area of the sheet with the transfer section 25 to which the transfer bias voltage is applied reaches the separation position P2.

Further, as shown in FIG. 4, in the image forming apparatus 100, the second voltage is applied at timing t3. That is, a voltage is applied to the electrode section 26 so that the output current Y1 becomes the current value B2. The timing t3 is determined to be the timing after the leading edge of the sheet is separated from the photosensitive drum 21 by applying the first voltage to the electrode section 26 .

Further, as shown in FIG. 4, in the image forming apparatus 100, application of the specific voltage is stopped before timing t5. That is, a voltage is applied to the electrode section 26 so that the output current Y1 becomes the current value B0. For example, in the image forming apparatus 100, application of the specific voltage is stopped after timing t4. The application of the specific voltage may be stopped at an arbitrary timing after the rear end of the contact area of the sheet with the transfer section 25 to which the transfer bias voltage is applied reaches the separation position P2.

In addition, the specific voltage does not have to include the second voltage. In this case, the application control section 53 may apply the first voltage to the electrode section 26 from the first timing to the second timing when the size of the sheet in the width direction is less than the maximum size.

Also, the specific voltage may not include the first voltage. In this case, the application control section 53 may apply the second voltage to the electrode section 26 from the first timing to the second timing when the size of the sheet in the width direction is less than the maximum size.

[Application control processing]
The image forming method of the present invention will be described below with reference to FIG. Here, steps S11, S12, . The application control process is executed when the image forming process is executed.

<Step S11>
First, in step S11, the control unit 5 determines whether or not the size of the sheet in the width direction is less than the maximum size. Here, the process of step S<b>11 is an example of the determination step of the present invention, and is executed by the determination processing section 51 of the control section 5 .

Here, the control unit 5 switches the next process according to the determination result as to whether or not the size of the sheet in the width direction is less than the maximum size. Specifically, when the control unit 5 determines that the size of the sheet in the width direction is smaller than the maximum size (Yes in step S11), the control unit 5 shifts the process to step S12. When the control unit 5 determines that the size of the sheet in the width direction is not less than the maximum size (No side of step S11), the control unit 5 shifts the process to step S16.

<Step S12>
In step S12, the control unit 5 sets the second voltage based on the size of the sheet in the width direction. Here, the processing of step S<b>12 is executed by the setting processing section 52 of the control section 5 .

Specifically, the control unit 5 sets the current value B2 of the output current Y1 based on the size of the sheet in the width direction.

<Step S13>
In step S13, the control unit 5 determines whether or not the second voltage set in step S12 is less than the first voltage.

Specifically, the control unit 5 determines that the second voltage is less than the first voltage when the current value B2 set in step S12 is less than the current value B1.

Here, the control unit 5 switches the next process according to the determination result as to whether or not the second voltage is less than the first voltage. Specifically, when the control unit 5 determines that the second voltage is less than the first voltage (Yes in step S13), the process proceeds to step S14. When the control unit 5 determines that the second voltage is not less than the first voltage (No in step S13), the control unit 5 shifts the process to step S15.

<Step S14>
In step S14, the control unit 5 executes a first control process, which will be described later.

<Step S15>
In step S15, the control unit 5 executes a second control process, which will be described later.

<Step S16>
In step S16, the control unit 5 executes a third control process, which will be described later.

[First control process]
Next, the first control process executed in step S14 of the application control process will be described with reference to FIG.

<Step S21>
First, in step S21, the control unit 5 determines whether or not the first timing has arrived.

Here, the control unit 5 switches the next process according to the determination result as to whether or not the first timing has arrived. Specifically, when the control unit 5 determines that the first timing has arrived (Yes in step S21), the process proceeds to step S22. Further, when the control unit 5 determines that the first timing has not arrived (No side in step S21), it waits for the arrival of the first timing in step S21.

<Step S22>
In step S<b>22 , the control section 5 applies the first voltage to the electrode section 26 . Here, the process of step S22 is an example of the application step of the present invention, and is executed by the application control section 53 of the control section 5. FIG.

Specifically, the control unit 5 causes the second power supply 42 to perform constant current control so that the output current Y1 becomes the current value B1. As a result, it is possible to reduce the amount of charge on the sheet by generating a discharge between the electrode portion 26 and the sheet. Therefore, it is possible to separate the leading edge of the sheet electrostatically attracted to the surface of the photoreceptor drum 21 from the surface. Further, it is possible to generate a discharge between the electrode portion 26 and the non-contact area of the photosensitive drum 21 to increase the potential of the non-contact area (change to the positive polarity side). Therefore, it is possible to cancel part or all of the potential drop in the non-contact region due to the current flowing between the non-contact region and the transfer section 25 .

<Step S23>
In step S23, the control unit 5 determines whether or not the intermediate timing has arrived.

Here, the control unit 5 switches the next process according to the determination result as to whether or not the intermediate timing has arrived. Specifically, when the control unit 5 determines that the intermediate timing has arrived (Yes in step S23), the process proceeds to step S24. Further, when the control unit 5 determines that the intermediate timing has not arrived (No in step S23), it waits for the intermediate timing in step S23.

<Step S24>
In step S<b>24 , the control section 5 applies the second voltage to the electrode section 26 . Here, the process of step S24 is executed by the application control section 53 of the control section 5. FIG.

Specifically, the control unit 5 causes the second power supply 42 to perform constant current control so that the output current Y1 becomes the current value B2. As a result, it is possible to generate a discharge between the electrode portion 26 and the non-contact area of the photosensitive drum 21, thereby increasing the potential of the non-contact area (fluctuation to the positive polarity side). Therefore, it is possible to cancel part or all of the potential drop in the non-contact region due to the current flowing between the non-contact region and the transfer section 25 .

<Step S25>
In step S25, the control unit 5 determines whether or not the second timing has arrived.

Here, the control unit 5 switches the next process according to the determination result as to whether or not the second timing has arrived. Specifically, when the control unit 5 determines that the second timing has arrived (Yes in step S25), the process proceeds to step S26. Further, when the control unit 5 determines that the second timing has not arrived (No side in step S25), it waits for the arrival of the second timing in step S25.

<Step S26>
In step S<b>26 , the control section 5 stops applying the specific voltage to the electrode section 26 . Here, the process of step S26 is an example of the application step of the present invention, and is executed by the application control section 53 of the control section 5. FIG.

Specifically, the control unit 5 causes the second power supply 42 to perform constant current control so that the output current Y1 becomes the current value B0.

<Step S27>
At step S27, the controller 5 determines whether or not the image forming process has ended.

Here, the control unit 5 switches the next process according to the determination result as to whether or not the image forming process has ended. Specifically, when the control unit 5 determines that the image forming process has ended (Yes in step S27), it ends the first control process. If the control unit 5 determines that the image forming process has not ended (No side of step S27), the process proceeds to step S21.

[Second control process]
Next, the second control process executed in step S15 of the application control process will be described with reference to FIG.

<Step S31>
First, in step S31, the control unit 5 determines whether or not the first timing has arrived.

Here, the control unit 5 switches the next process according to the determination result as to whether or not the first timing has arrived. Specifically, when the control unit 5 determines that the first timing has arrived (Yes in step S31), the process proceeds to step S32. Further, when the control unit 5 determines that the first timing has not arrived (No side in step S31), it waits for the arrival of the first timing in step S31.

<Step S32>
In step S<b>32 , the control section 5 applies the second voltage to the electrode section 26 . Here, the process of step S32 is executed by the application control section 53 of the control section 5. FIG.

Specifically, the control unit 5 causes the second power supply 42 to perform constant current control so that the output current Y1 becomes the current value B2. As a result, it is possible to reduce the amount of charge on the sheet by generating a discharge between the electrode portion 26 and the sheet. Therefore, it is possible to separate the leading edge of the sheet electrostatically attracted to the surface of the photoreceptor drum 21 from the surface. Further, it is possible to generate a discharge between the electrode portion 26 and the non-contact area of the photosensitive drum 21 to increase the potential of the non-contact area (change to the positive polarity side). Therefore, it is possible to cancel part or all of the potential drop in the non-contact region due to the current flowing between the non-contact region and the transfer section 25 .

<Step S33>
In step S33, the controller 5 determines whether or not the second timing has arrived.

Here, the control unit 5 switches the next process according to the determination result as to whether or not the second timing has arrived. Specifically, when the control unit 5 determines that the second timing has arrived (Yes in step S33), the process proceeds to step S34. Further, when the control unit 5 determines that the second timing has not arrived (No side in step S33), it waits for the arrival of the second timing in step S33.

<Step S34>
In step S<b>34 , the control section 5 stops applying the specific voltage to the electrode section 26 . Here, the process of step S34 is executed by the application control section 53 of the control section 5. FIG.

Specifically, the control unit 5 causes the second power supply 42 to perform constant current control so that the output current Y1 becomes the current value B0.

<Step S35>
At step S35, the control unit 5 determines whether or not the image forming process has ended.

Here, the control unit 5 switches the next process according to the determination result as to whether or not the image forming process has ended. Specifically, when the control unit 5 determines that the image forming process has ended (Yes in step S35), it ends the second control process. Further, when the control section 5 determines that the image forming process has not ended (No in step S35), the process proceeds to step S31.

[Third control process]
Next, the third control process executed in step S16 of the application control process will be described with reference to FIG.

<Step S41>
First, in step S41, the control unit 5 determines whether or not the first timing has arrived.

Here, the control unit 5 switches the next process according to the determination result as to whether or not the first timing has arrived. Specifically, when the control unit 5 determines that the first timing has arrived (Yes in step S41), the process proceeds to step S42. Further, when the control unit 5 determines that the first timing has not arrived (No side in step S41), it waits for the arrival of the first timing in step S41.

<Step S42>
In step S<b>42 , the control section 5 applies the first voltage to the electrode section 26 . Here, the process of step S42 is executed by the application control section 53 of the control section 5. FIG.

Specifically, the control unit 5 causes the second power supply 42 to perform constant current control so that the output current Y1 becomes the current value B1. As a result, it is possible to reduce the amount of charge on the sheet by generating a discharge between the electrode portion 26 and the sheet. Therefore, it is possible to separate the leading edge of the sheet electrostatically attracted to the surface of the photoreceptor drum 21 from the surface.

<Step S43>
In step S43, the control unit 5 determines whether or not the intermediate timing has arrived.

Here, the control unit 5 switches the next process according to the determination result as to whether or not the intermediate timing has arrived. Specifically, when the control unit 5 determines that the intermediate timing has arrived (Yes in step S43), the process proceeds to step S44. If the control unit 5 determines that the intermediate timing has not arrived (No side in step S43), it waits for the intermediate timing in step S43.

<Step S44>
In step S<b>44 , the control section 5 stops applying the first voltage to the electrode section 26 . Here, the process of step S44 is executed by the application control section 53 of the control section 5. FIG.

Specifically, the control unit 5 causes the second power supply 42 to perform constant current control so that the output current Y1 becomes the current value B0.

<Step S45>
In step S45, the control section 5 determines whether or not the image forming process has ended.

Here, the control unit 5 switches the next process according to the determination result as to whether or not the image forming process has ended. Specifically, when the control unit 5 determines that the image forming process has ended (Yes in step S45), it ends the third control process. Further, when the control section 5 determines that the image forming process has not ended (No in step S45), the process proceeds to step S41.

Thus, in the image forming apparatus 100, the specific voltage is applied to the electrode section 26 from the first timing to the second timing when the size of the sheet in the width direction is less than the maximum size. As a result, it is possible to generate a discharge between the electrode portion 26 and the non-contact area of the photosensitive drum 21, thereby increasing the potential of the non-contact area (fluctuation to the positive polarity side). Therefore, it is possible to cancel part or all of the potential drop in the non-contact region due to the current flowing between the non-contact region and the transfer section 25 . Therefore, compared with the configuration in which the surface potential equalization mode is executed, it is possible to suppress the occurrence of a difference in the surface potential of the photosensitive drum 21 without lowering productivity.

Further, in the image forming apparatus 100, when the second voltage is equal to or higher than the first voltage, the second voltage is applied to the electrode section 26 from the first timing to the second timing, and the second voltage is If the voltage is less than the first voltage, the first voltage is applied to the electrode section 26 from the first timing to the intermediate timing, and the second voltage is applied to the electrode section 26 from the intermediate timing to the second timing. be done. As a result, both the sheet separation and the uniformity of the surface potential of the photosensitive drum 21 can be realized using the electrode portion 26 .

1 Image forming unit 2 Paper feeding unit 3 Operation display unit 4 Storage unit 5 Control unit 6 Housing 21 Photoreceptor drum 22 Charging device 23 Optical scanning device 24 Developing device 25 Transfer unit 26 Electrode unit 27 Cleaning device 28 Eliminating device 29 Fixing device 41 First power supply 42 Second power supply 51 Determination processing unit 52 Setting processing unit 53 Application control unit 100 Image forming apparatus

Claims (6)

an image carrier charged to a first polarity;
A toner image formed on the image carrier by receiving a voltage having a second polarity opposite to the first polarity is provided opposite to the image carrier and placed between the image carrier and the toner image. a transfer unit that transfers onto a sheet passing through the position;
an electrode portion provided facing the image carrier across a path of movement of the sheet from the first position;
When the size of the sheet in the width direction perpendicular to the movement path is smaller than the maximum image-formable size of the sheet, the leading edge of the sheet moves to the second position between the image carrier and the electrode section. an application control unit that applies the specific voltage of the first polarity to the electrode unit from a first timing of passage to a second timing of passage of the trailing edge of the sheet through the second position;
An image forming apparatus comprising: The specific voltage is a voltage that can vary the potential of a non-contact area of the image carrier that does not contact the sheet.
The image forming apparatus according to claim 1. The specific voltage includes a preset first voltage capable of separating the sheet from the image carrier,
The image forming apparatus according to claim 1 or 2. The specific voltage includes a preset second voltage,
The application control section applies the second voltage to the electrode section from the first timing to the second timing when the second voltage is equal to or higher than the first voltage, and the second voltage is applied to the electrode section from the first timing to the second timing. When the voltage is less than 1 voltage, the first voltage is applied to the electrode section from the first timing to an intermediate timing before the second timing, and the electrode section is applied with the voltage from the intermediate timing to the second timing. applying a second voltage;
The image forming apparatus according to claim 3. A setting processing unit that sets the second voltage based on the size of the sheet in the width direction,
The image forming apparatus according to claim 4. An image carrier charged to a first polarity, and a toner provided opposite to the image carrier and formed on the image carrier by receiving a voltage of a second polarity opposite to the first polarity. a transfer unit for transferring an image onto a sheet passing through a first position between the image carrier; and an electrode unit provided facing the image carrier across a movement path of the sheet from the first position. and an image forming method executed by an image forming apparatus comprising:
a determination step of determining whether the size of the sheet in the width direction orthogonal to the movement path is less than the maximum size capable of image formation by the device;
When the determining step determines that the size of the sheet in the width direction is smaller than the maximum size, the leading edge of the sheet passes through a second position between the image carrier and the electrode portion. an applying step of applying the specific voltage of the first polarity to the electrode unit from the first timing to the second timing when the trailing edge of the sheet passes the second position;
An imaging method comprising:

Images