JP2020046453A - Image formation apparatus - Google Patents

Abstract

To provide an image formation apparatus which can recover sheet powder by electrifying the unelectrified sheet powder.SOLUTION: An image formation apparatus 1 includes: a recovery part 100 having a primary recovery roller 110 which is arranged at a recovery position on the downstream side with respect to a transfer part 63 and on the upstream side with respect to an electrifier 62 in the rotation direction of a photoreceptor 61, recovers sheet powder from the photoreceptor 61 and a secondary recovery roller 120 which recovers the sheet powder recovered by the primary recovery roller 110; and a voltage application part 50 which applies the first voltage to the primary recovery roller 110 and applies the second voltage to the secondary recovery roller 120. The first voltage varies periodically, and the average value of the first voltage has the positive polarity, is lower than the average value of the second voltage and is higher than the surface potential of a portion where an electrostatic latent image is not formed at the recovery position of the photoreceptor 61.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a positive charging type image forming apparatus including a primary collection roller and a secondary collection roller.

2. Description of the Related Art Conventionally, in a positive charging type image forming apparatus, there has been known an image forming apparatus employing a cleanerless system in which a residual toner remaining on a photoconductor after transfer is collected by a developing device (for example, see Patent Document 1).
The image forming apparatus includes a cleaning unit (collection unit) having a primary cleaning roller for collecting paper dust from a photoconductor and a secondary cleaning roller for collecting paper dust collected by the primary cleaning roller. . The primary cleaning roller is applied with a positive voltage, and the secondary cleaning roller is applied with a positive voltage having an absolute value larger than the voltage applied to the primary cleaning roller, thereby being negative. The charged paper powder can be collected.

JP 2013-97151A

  However, the amount of charge of the paper dust varies, and paper dust that is not sufficiently charged (hereinafter referred to as “uncharged paper dust”) may not be collected by the cleaning unit in some cases.

  In an image forming apparatus adopting the cleanerless system, paper powder not collected by the cleaning unit may enter the developing device, which causes a reduction in the charge amount of the toner in the developing device.

  Accordingly, it is an object of the present invention to provide an image forming apparatus capable of charging and collecting uncharged paper powder.

In order to solve the above-described problems, an image forming apparatus according to the present invention includes a photoconductor, a charger that charges the photoconductor to a positive polarity, and an exposure unit that exposes the photoconductor to form an electrostatic latent image. A developer that supplies a developer to the electrostatic latent image to form a developer image, a transfer unit that transfers the developer image to a sheet, and a charging unit that is downstream of the transfer unit in the rotation direction of the photoconductor and that is charged. A collection unit disposed at a collection position upstream of the container and having a primary collection roller for collecting paper dust from the photoreceptor, and a secondary collection roller for collecting paper dust collected by the primary collection roller; A voltage application unit that applies a first voltage to the primary collection roller and applies a second voltage to the secondary collection roller.
The first voltage changes periodically, the average value of the first voltage is positive, lower than the average value of the second voltage, and the portion of the photoreceptor where the electrostatic latent image is not formed at the collection position. It is characterized by being higher than the surface potential.

  According to this configuration, the periodically charged first voltage is applied to the primary collection roller to move the negatively charged paper powder between the photoconductor and the primary collection roller. Uncharged paper powder can be charged. Then, the charged paper dust can be collected by the primary collection roller and the secondary collection roller in the collection section arranged at the collection position, so that the paper dust on the surface of the photoconductor can be collected.

  In the above-described image forming apparatus, the first voltage has a rectangular or trapezoidal waveform, and the time during which a voltage higher than the average of the first voltage is applied is determined by the time when the voltage lower than the average of the first voltage is changed. It can be longer than the time being applied.

  According to this, sufficient time for moving the paper powder to the secondary collection roller can be secured.

  In the above-described image forming apparatus, the first voltage has a sawtooth waveform, and the slope on the rising side can be made larger than the slope on the falling side.

  According to this, in the section where the first voltage rises steeply, the charged paper dust can be moved to the primary collection roller side, and the uncharged paper dust can be charged as the paper dust moves. Further, by making the section where the first voltage falls relatively gentle, it is possible to lengthen the time for moving the paper dust held by the primary collection roller to the secondary collection roller due to the potential difference.

  In the above-described image forming apparatus, the maximum value of the first voltage can be lower than the average value of the second voltage.

  According to this, the paper dust held by the primary collection roller can be stably collected by the secondary collection roller.

  In the above-described image forming apparatus, the minimum value of the first voltage can be made lower than the surface potential of the portion where the electrostatic latent image is not formed at the collection position of the photoconductor.

  According to this, by increasing the amplitude of the first voltage, the effect of charging the uncharged paper powder can be enhanced.

  In the above-described image forming apparatus, the minimum value of the first voltage can be set to 0V.

  According to this, the circuit for applying the first voltage can have a simple configuration.

  In the above-described image forming apparatus, the second voltage may be a DC voltage.

  In the above-described image forming apparatus, the primary collection roller may have a sponge layer having conductivity on the surface.

  According to this, the primary collection roller not only electrically collects the paper dust, but also can mechanically collect the paper dust by using the gap of the sponge layer. it can.

  In the above-described image forming apparatus, the peripheral speed of the primary collection roller and the peripheral speed of the photoconductor may be different.

  According to this, by providing the peripheral speed difference, the collection effect due to friction between the photoconductor and the primary collection roller can be enhanced.

  In the above-described image forming apparatus, the secondary collection roller may be made of metal.

  According to this, paper dust can be electrically collected on the surface of the secondary collection roller.

  In the above-described image forming apparatus, the collection unit may be configured to include a scraping member that comes into contact with the secondary collection roller and scrapes paper dust held by the secondary collection roller.

  According to this, it is possible to suppress the paper dust collected by the secondary collection roller from returning to the primary collection roller.

  In the above-described image forming apparatus, a configuration may be adopted in which a discharge lamp is disposed downstream of the transfer unit and upstream of the collection unit in the rotation direction, and discharges the photosensitive member.

  According to this, the residual potential on the photoreceptor surface can be reduced prior to the collection of the paper dust. Therefore, the potential difference between the photoreceptor surface after static elimination and the primary recovery roller to which the first voltage has been applied becomes large, and the paper dust moves greatly, so that the effect of charging uncharged paper dust can be enhanced. .

  According to the present invention, uncharged paper powder on the surface of the photoconductor can be charged and collected.

FIG. 1 is a side sectional view of an image forming apparatus according to an embodiment. FIG. 3 is a diagram illustrating a schematic configuration around a photoconductor. 5 is a graph illustrating a relationship between voltages applied to a primary collection roller and a secondary collection roller. FIG. 3A is a diagram illustrating a state in which an electrostatic latent image is formed on a photoconductor during image formation, and FIG. 3B is a diagram illustrating a state in which a developer is supplied to the electrostatic latent image on the photoconductor. . FIG. 7A is a diagram illustrating a state in which a developer on a photoconductor is transferred to a sheet, and FIG. 7B is a diagram illustrating a state in which a primary collection roller collects paper powder on the photoconductor. FIG. 7A is a diagram illustrating a state in which paper dust held by a primary collection roller is collected by a secondary collection roller, and FIG. 7B is a diagram illustrating a state in which developer remaining on a photoconductor is moved to a development roller. It is a graph regarding the modification which shows the relationship between the voltage applied to a primary collection roller and a secondary collection roller. 9 is a graph related to another modification showing a relationship between voltages applied to a primary collection roller and a secondary collection roller.

  An embodiment of the present invention will be described in detail with reference to the drawings as appropriate. In the following description, first, a schematic configuration of the image forming apparatus 1 will be described, and then, a characteristic portion of the present invention will be described. The image forming apparatus 1 is, for example, a laser printer.

  As shown in FIG. 1, the image forming apparatus 1 includes a paper feed unit 3 for supplying a sheet S into a housing 2, an exposure unit 4, and a process unit 5 for transferring a developer image onto the sheet S. And a fixing device 8 for thermally fixing the developer image transferred onto the sheet S. The sheet S is, for example, a sheet of thick paper, postcard, thin paper, or the like.

  The paper feeding unit 3 is provided at a lower portion in the housing 2 and mainly includes a paper feeding tray 31, a paper pressing plate 32, and a paper feeding mechanism 33. The sheet S accommodated in the sheet feed tray 31 is moved upward by the sheet pressing plate 32 and supplied to the process unit 5 by the sheet feed mechanism 33.

  The exposure unit 4 is a laser scanner that is disposed in the upper part of the housing 2 and includes a laser emission unit (not shown), a polygon mirror, a lens, a reflection mirror, and the like. The exposure unit 4 emits a laser beam (see a two-dot chain line) based on image data from the laser emission unit, and scans the surface of the photoconductor 61 to expose the surface of the photoconductor 61.

  The process unit 5 is disposed below the exposure unit 4, and is configured to be detachably attached to the housing 2 from an opening formed when the front cover 21 provided on the housing 2 is opened. The process unit 5 includes a drum cartridge 6 and a developing device 7. The developing device 7 is, for example, a developing cartridge.

  The drum cartridge 6 mainly includes a photoreceptor 61, a charger 62, and a transfer unit 63. The developing device 7 is configured to be detachably attached to the drum cartridge 6. The developing device 7 mainly includes a developing roller 71, a supply roller 72, a layer thickness regulating blade 73, and a developer accommodating section 74 for accommodating a developer. The photoconductor 61 is, for example, a photosensitive drum. The transfer unit 63 is, for example, a transfer roller. The developer is a non-magnetic one-component positively chargeable toner.

  In the process unit 5, after the surface of the photoconductor 61 is uniformly positively charged by the charger 62, the surface is exposed to the laser beam from the exposure unit 4. As a result, an electrostatic latent image based on the image data is formed on the photoconductor 61. Further, the developer in the developer container 74 is supplied to the developing roller 71 via the supply roller 72. At this time, the developer is positively frictionally charged between the supply roller 72 and the developing roller 71. The developer supplied onto the developing roller 71 enters between the layer thickness regulating blades 73 with the rotation of the developing roller 71, and is further charged on the developing roller 71 as a thin layer having a constant thickness while being triboelectrically charged. It is carried on.

  The developer carried on the developing roller 71 is supplied from the developing roller 71 to an electrostatic latent image formed on the photoconductor 61. Thus, the electrostatic latent image is visualized, and a developer image is formed on the photoconductor 61. Thereafter, the sheet S is conveyed between the photoconductor 61 and the transfer unit 63, so that the developer image on the photoconductor 61 is transferred onto the sheet S.

  The fixing device 8 is disposed behind the process unit 5, and holds the fixing belt between a heating unit 81 having a halogen heater, a fixing belt, a nip plate, and the like, which are omitted from reference numerals, and a nip plate of the heating unit 81. And a pressurizing roller 82 which operates. In the fixing device 8, the developer image transferred onto the sheet S is thermally fixed while the sheet S passes between the heating unit 81 and the pressure roller 82. The sheet S on which the developer image has been thermally fixed is discharged onto a discharge tray 22 by discharge rollers 23.

  Further, the image forming apparatus 1 employs a so-called cleaner-less system in which the developer remaining on the photoconductor 61 without being transferred to the sheet S is collected by the developing device 7. Specifically, when collecting the developer, the surface of the photoconductor 61 is charged by the charger 62. Then, by making the surface potential of the photoconductor 61 higher than the potential of the developing roller 71, the developer remaining on the photoconductor 61 moves to the developing roller 71 and is returned to the developer accommodating section 74.

  As shown in FIG. 2, the process unit 5 includes a photoreceptor 61, a charger 62, a transfer unit 63, a discharging lamp 65, a developing roller 71, and a collection unit 100.

  As described above, the developing roller 71 is a roller that supplies the developer T to the electrostatic latent image on the photoconductor 61, and the laser emitted from the exposure unit 4 of the photoconductor 61 in the rotation direction of the photoconductor 61. On the downstream side of the light exposure position, the photosensitive member 61 rotates in contact with the peripheral surface thereof.

  The transfer unit 63 is disposed downstream of the developing roller 71 in the rotation direction of the photoconductor 61. When transferring the developer image onto the sheet S, a negative transfer bias is applied to the transfer unit 63.

  The charger 62 is configured to apply a charging bias and charge the surface of the photoconductor 61 to a positive polarity. The charger 62 is disposed upstream of the developing roller 71 in the rotation direction of the photoconductor 61.

  The collection unit 100 is disposed at a collection position downstream of the transfer unit 63 and upstream of the charger 62 in the rotation direction of the photoconductor 61. The collection unit 100 mainly includes a primary collection roller 110, a secondary collection roller 120, a scraping member 130, and a case 140.

  The primary collection roller 110 is a roller having a sponge layer having conductivity on its surface, rotates while being in contact with the peripheral surface of the photoconductor 61, and collects paper dust attached on the photoconductor 61. I have. The first voltage V1 is applied to the primary collection roller 110 by the voltage application unit 50 provided in the housing 2 during image formation.

  As a result, the primary collection roller 110 uses the gap formed on the sponge surface to collect the negatively charged paper powder attached to the photoconductor 61 while attracting the powder.

As shown in FIG. 3, the first voltage V1 has a trapezoidal waveform and is a voltage that changes periodically. The average value Vave of the first voltage V1 is positive and lower than the average value of a second voltage V2 described later applied to the secondary collection roller 120, and an electrostatic latent image is formed at the collection position of the photoconductor 61. It is higher than the surface potential Vel of the portion where there was not. Further, the minimum value Vmin of the first voltage V1 is lower than the surface potential Vel of a portion where the electrostatic latent image is not formed at the collection position of the photoconductor 61. The frequency of the first voltage V1 is, for example, 2 kHz.
Note that the average value Vave of the voltage V1 can be obtained by the following equation.

Ｔ：周期

T: Period

  More specifically, the first voltage V1 has a minimum value Vmin of 0 V, a maximum value Vmax of 500 V, a duty ratio of 70%, and an average value Vave of 350 V. The time T1 during which a voltage higher than the average value Vave of the first voltage V1 is applied is longer than the time T2 during which a voltage lower than the average value Vave of the first voltage V1 is applied. Further, the maximum value Vmax of the first voltage V1 is lower than an average value of a second voltage V2 described later.

  The secondary collection roller 120 is a metal roller, rotates while contacting the peripheral surface of the primary collection roller 110, and collects the paper dust collected by the primary collection roller 110. More specifically, the second voltage V2 is applied by the voltage application unit 50 to the secondary collection roller 120 during image formation, so that the paper dust held by the primary collection roller 110 is attracted and held. .

  Specifically, the secondary collection roller 120 is disposed obliquely above the primary collection roller 110 and opposed to the primary collection roller 110. The second voltage V2, which is a positive voltage whose absolute value is larger than the voltage applied to the primary recovery roller 110, is applied to the secondary recovery roller 120.

  As shown in FIG. 3, the second voltage V2 is a DC voltage of 600 V, which is higher than the average value Vave of the first voltage V1 and higher than the maximum value Vmax of the first voltage V1.

  The scraping member 130 is a member that scrapes the paper powder adsorbed on the surface of the secondary collection roller 120, and is provided above the secondary collection roller 120 so as to slide on the surface of the secondary collection roller 120. . The scraping member 130 is formed of sponge, and is configured to scrape off the paper dust held by the secondary collection roller 120 by being pressed by the secondary collection roller 120.

  The case 140 houses the primary collection roller 110 and the secondary collection roller 120. The case 140 has a bottomed storage section 141 for storing the paper dust scraped by the scraping member 130 below the secondary collection roller 120.

  The static elimination lamp 65 is arranged downstream of the transfer unit 63 and upstream of the collection position where the collection unit 100 is arranged in the rotation direction of the photoconductor 61. The discharging lamp 65 is for exposing the photoconductor 61 after the photoconductor 61 has passed through the transfer unit 63 to lower the surface potential of the photoconductor 61.

Next, the operation of the process unit 5 configured as described above will be described with reference to FIGS.
During image formation, the photoconductor 61 rotates at a higher peripheral speed than the primary collection roller 110 and the secondary collection roller 120.

  As shown in FIG. 4A, at the time of image formation, in the process unit 5, first, the surface of the photoconductor 61 is positively charged by the charger 62, and the surface potential becomes 850V. Next, exposure is performed by laser light from the exposure unit 4 to form an electrostatic latent image. When the portion where the electrostatic latent image is formed reaches a position facing the developing roller 71, as shown in FIG. 4B, the positively charged developer T carried by the developing roller 71 is moved to the photosensitive member 61. Is supplied to the portion where the electrostatic latent image is formed.

  As the photoconductor 61 further rotates, the developer T on the photoconductor 61 is transferred to the sheet S conveyed between the photoconductor 61 and the transfer unit 63, as shown in FIG. . At this time, the negatively charged paper dust D1 and the uncharged paper dust D2 adhere to the photosensitive member 61 from the sheet S. Further, the developer T that has not been transferred to the sheet S and remains on the photosensitive member 61 is also attached. The surface potential of the photoreceptor 61 is reduced by passing through the transfer unit 63, and the surface potential Vel of the portion where the electrostatic latent image is not formed becomes about 150 V by being exposed to the discharging lamp 65.

Then, the paper dust D1 adhering to the photoreceptor 61 has a voltage Vmax higher than the surface potential Vel of the photoreceptor 61 applied to the primary collection roller 110 corresponding to the pulse width of the first voltage V1 (see FIG. 3). While the voltage is applied, it is attracted to the primary collection roller 110, and the operation of separating from the primary collection roller 110 is repeated while the voltage Vmin lower than the surface potential Vel of the photoconductor 61 is applied to the primary collection roller 110. Thus, a fine reciprocating motion is performed between the photoconductor 61 and the primary recovery roller 110.
The uncharged paper dust D2 is also negatively charged due to the friction caused by the movement of the negatively charged paper dust D1 between the photoconductor 61 and the primary collection roller 110.
As a result, as shown in FIG. 5B, the paper dusts D1 and D2 are attracted to the primary collection roller 110 and collected in the gap on the sponge surface of the primary collection roller 110.

Thereafter, as shown in FIG. 6A, the paper dusts D1 and D2 collected by the primary collection roller 110 are subjected to the second collection in which the second voltage V2 larger than the maximum value Vmax of the first voltage V1 is applied. Collected by the roller 120.
Further, the paper dusts D1 and D2 collected by the secondary collection roller 120 are scraped off by the scraping member 130 and collected in the storage section 141 (not shown in FIG. 6) of the case 140. As shown in FIG. 6B, when the photoconductor 61 further rotates, the positively charged developer T remaining on the photoconductor 61 is not collected by the primary collection roller 110 and It moves to the developing roller 71. Since the developer T is positively charged when passing through the charger 62, the developer T moves to the developing roller 71 and returns to the developer accommodating section 74.

According to the above, the following effects can be obtained in the present embodiment.
By applying a periodically varying first voltage V1 to the primary collection roller 110, the negatively charged paper dust D1 is moved between the photoconductor 61 and the primary collection roller 110, and the The charged paper dust D2 can be charged. The charged paper dusts D1 and D2 can be collected by the primary collection roller 110 and the secondary collection roller 120 in the collection unit 100 disposed at the collection position. , D2 can be recovered.

  The first voltage V1 has a trapezoidal waveform, and during the time T1 during which a voltage higher than the average value Vave of the first voltage V1 is applied, a voltage lower than the average value Vave of the first voltage V1 is applied. By making the time longer than the time T2, a time for moving the paper dusts D1 and D2 to the secondary collection roller 120 can be sufficiently secured.

  By setting the maximum value Vmax of the first voltage V1 lower than the average value of the second voltage V2, the paper dusts D1 and D2 held by the primary collection roller 110 can be stably collected by the secondary collection roller 120. Can be.

  By setting the minimum value Vmin of the first voltage V1 lower than the surface potential Vel of the portion where the electrostatic latent image is not formed at the collection position of the photoconductor 61, the amplitude of the first voltage V1 is increased, The effect of charging the uncharged paper powder D2 can be enhanced.

  By setting the minimum value Vmin of the first voltage V1 to 0 V, the circuit for applying the first voltage V1 can have a simple configuration.

  Since the primary collection roller 110 has a sponge layer having conductivity on the surface, the primary collection roller 110 not only electrically collects the paper dust D1 and D2, but also mechanically collects the paper powder D1 and D2 using the gap of the sponge layer. Therefore, the effect of collecting the paper dusts D1 and D2 can be enhanced.

  Since the peripheral speed of the primary recovery roller 110 and the peripheral speed of the photoconductor 61 are different, it is possible to increase the peripheral speed difference to enhance the recovery effect due to the friction between the photoconductor 61 and the primary recovery roller 110.

  Since the secondary collection roller 120 is made of metal, paper dusts D1 and D2 can be electrically collected on the surface of the secondary collection roller 120.

  The collection unit 100 includes the scraping member 130 that contacts the secondary collection roller 120 and scrapes the paper dusts D1 and D2 held by the secondary collection roller 120. It is possible to prevent the powders D1 and D2 from returning to the primary collection roller 110.

  By providing a static elimination lamp 65 that is disposed downstream of the transfer unit 63 and upstream of the collection unit 100 in the rotation direction of the photoconductor 61 and that eliminates the charge of the photoconductor 61, the paper dusts D1 and D2 are collected. Prior to this, the potential remaining on the surface of the photoconductor 61 can be reduced. Therefore, the potential difference between the surface of the photoreceptor 61 after static elimination and the primary recovery roller 110 to which the first voltage V1 has been applied increases, and the paper dust D1 largely moves, so that the uncharged paper dust D2 is charged. The effect can be enhanced.

  As mentioned above, although the embodiment of the present invention was described, the present invention is not limited to the embodiment. The specific configuration can be appropriately changed without departing from the spirit of the present invention.

For example, as shown in FIG. 7, a first voltage V1 and a second voltage V2 may be set.
Specifically, as in the embodiment shown in FIG. 3, the second voltage V2 is a DC voltage of 600 V, and the first voltage V1 is a voltage having a trapezoidal waveform and periodically changing. The maximum value Vmax of one voltage V1 is set to 750 V, which is higher than the second voltage V2. Even when the maximum value Vmax of the first voltage V1 is higher than the second voltage V2, the first voltage Vave is set to be positive so that the average value Vave of the first voltage V1 does not exceed the average value of the second voltage V2. V1 is set to have a duty ratio of 60% and a minimum value of 0V. Note that the frequency of the first voltage V1 is 1 kHz.
More specifically, the average value Vave of the first voltage V1 is 450 V, lower than the second voltage V2, and higher than the surface potential Vel of the portion where the electrostatic latent image is not formed at the collection position of the photoconductor 61. Has become. Further, the minimum value Vmin of the first voltage V1 is lower than the surface potential Vel of the portion where the electrostatic latent image is not formed at the collection position of the photoconductor 61. Further, the time T3 during which a voltage higher than the average value Vave of the first voltage V1 is applied is longer than the time T4 during which a voltage lower than the average value Vave of the first voltage V1 is applied.

According to such an image forming apparatus 1, the maximum value Vmax of the first voltage V1 is temporarily set higher than the second voltage V2, so that the negatively charged paper dust D1 on the photoconductor 61 is increased. By exercise, the uncharged paper powder D2 can be reliably charged.
Further, when the average value Vave of the first voltage V1 is set to be positive and lower than the average value of the second voltage V2, the maximum value Vmax of the first voltage V1 temporarily becomes higher than the second voltage V2. However, the paper dusts D1 and D2 collected by the primary collection roller 110 can be collected by the secondary collection roller 120.

In each of the above-described embodiments, in the rotation direction of the photoconductor 61, the static elimination lamp 65 is disposed downstream of the transfer unit 63 and upstream of the collection position where the collection unit 100 is arranged. A configuration without the static elimination lamp may be adopted.
Note that, even when the static elimination lamp is not provided, the average value Vave of the first voltage V1 is set to be higher than the surface potential of the portion where the electrostatic latent image is not formed at the collection position of the photoconductor 61. I do.

In each of the embodiments described above, the second voltage V2 is a DC voltage. However, the second voltage V2 is not limited to a DC voltage, and may be, for example, a voltage that changes periodically. In this case, the average value of the second voltage V2 is set to be higher than the average value Vave of the first voltage V1.
The surface potential of the photoconductor 61, the transfer bias of the transfer unit 63, the frequencies of the first voltage V1 and the second voltage V2, the maximum value, the minimum value, the average value, the duty ratio, and the like can be appropriately changed. It is.
Further, the peripheral speed of the primary collection roller 110 can be set faster than the peripheral speed of the photoconductor 61. Further, the primary collection roller 110 and the secondary collection roller 120 can have a peripheral speed difference.
Further, the second recovery roller may be formed of a conductor having a smooth surface instead of a metal.

In each of the above-described embodiments, the first voltage V1 has a trapezoidal waveform, but may have a rectangular waveform.
Further, as shown in FIG. 8, the first voltage V1 has a sawtooth waveform, and can be set so that the rising slope is larger than the falling slope.
Specifically, the first voltage V1 is a voltage that periodically changes, including a section T5 that rises sharply and a section T6 that gradually falls compared to the section T5. The second voltage V2 is a DC voltage. The average value Vave of the first voltage V1 is positive, lower than the second voltage V2, and higher than the surface potential Vel of the portion where the electrostatic latent image is not formed at the collection position of the photoconductor 61.
Further, the minimum value Vmin of the first voltage V1 is lower than the surface potential Vel of the portion where the electrostatic latent image is not formed at the collecting position of the photoconductor 61, and the maximum value Vmax of the first voltage V1 is the second voltage Vmax. It is higher than V2.

  According to such an image forming apparatus 1, in the section T5 where the first voltage V1 rises sharply, the charged paper dust D1 is moved to the primary collection roller 110 side, and the uncharged paper dust D1 is moved with the movement of the paper dust D1. Can be charged. In addition, by making the section T6 where the first voltage V1 falls relatively gentle, the time for moving the paper dusts D1 and D2 held by the primary collection roller 110 toward the secondary collection roller 120 by the potential difference is reduced. Can be longer.

  In the above embodiment, the photosensitive drum is used as an example of the photosensitive member 61, but the present invention is not limited to this, and for example, a belt-like photosensitive member may be adopted.

  In the above-described embodiment, a laser scanner is used as an example of the exposure unit 4. However, the present invention is not limited to this. For example, an exposure unit that exposes the photoconductor 61 using a light emitting element such as an LED is used. A head may be employed.

  In the above-described embodiment, a laser printer is described as an example of the image forming apparatus 1. However, the present invention is not limited to this. For example, another image forming apparatus such as a copying machine or a multifunction peripheral may be used.

  The components described in the above embodiments and modifications can be implemented in any combination.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 4 Exposure part 7 Developing device 50 Voltage application part 61 Photoreceptor 62 Charger 63 Transfer part 100 Collection part 110 Primary collection roller 120 Secondary collection roller 130 Scraping member S Sheet T Developer D1 Paper dust D2 Paper Powder V1 First voltage V2 Second voltage

Claims (12)

A photoreceptor,
A charger for charging the photoconductor to a positive polarity,
Exposure unit that exposes the photoconductor to form an electrostatic latent image,
A developing device that supplies a developer to the electrostatic latent image to form a developer image;
A transfer section for transferring the developer image to a sheet,
A primary collection roller disposed at a collection position downstream of the transfer unit and upstream of the charger in the rotation direction of the photoconductor, and configured to collect paper powder from the photoconductor; A collection unit having a secondary collection roller for collecting the paper dust collected by the roller,
A voltage application unit that applies a first voltage to the primary collection roller and applies a second voltage to the secondary collection roller,
The first voltage changes periodically, the average value of the first voltage is positive, lower than the average value of the second voltage, and no electrostatic latent image is formed at the collection position of the photoconductor. An image forming apparatus characterized in that the surface potential is higher than the surface potential of the portion.   The first voltage has a rectangular or trapezoidal waveform, and a voltage lower than the average value of the first voltage is applied while the voltage higher than the average value of the first voltage is applied. The image forming apparatus according to claim 1, wherein the time is longer than the time.   2. The image forming apparatus according to claim 1, wherein the first voltage has a saw-tooth waveform, and a slope on an ascending side is larger than a slope on a descending side. 3.   The image forming apparatus according to claim 1, wherein a maximum value of the first voltage is lower than an average value of the second voltage.   5. The device according to claim 1, wherein the minimum value of the first voltage is lower than a surface potential of a portion of the photoconductor at which the electrostatic latent image is not formed at the collection position. 6. An image forming apparatus according to claim 1.   The image forming apparatus according to claim 5, wherein a minimum value of the first voltage is 0V.   The image forming apparatus according to claim 1, wherein the second voltage is a DC voltage.   The image forming apparatus according to any one of claims 1 to 7, wherein the primary collection roller has a sponge layer having conductivity on a surface.   The image forming apparatus according to claim 1, wherein a peripheral speed of the primary collection roller is different from a peripheral speed of the photoconductor.   The image forming apparatus according to any one of claims 1 to 9, wherein the secondary collection roller is made of metal.   The said collection | recovery part has a scraping member which contacts the said secondary collection roller and scrapes off the paper powder which the said secondary collection roller holds, The Claim 1 characterized by the above-mentioned. The image forming apparatus as described in the above.   12. The apparatus according to claim 1, further comprising: a discharge lamp that is disposed downstream of the transfer unit and upstream of the collection unit in the rotation direction, and that discharges the photosensitive member. 13. An image forming apparatus according to claim 1.

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