JP2005062488A - Electrifying device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrifying device which electrifies a surface of a photoreceptor before the formation of an electrostatic latent image to a stable potential without an AC voltage and prevents failure in electrification of the surface of the photoreceptor. <P>SOLUTION: The electrifying device electrifies the surface of the photoreceptor before the formation of an electrostatic latent image. In the electrifying device, a first contact electrifying member to which a DC voltage is applied and a second contact electrifying member to which an AC voltage by a DC pulse is applied are disposed so as to come into contact with the surface of the photoreceptor in the direction of the rotation of the photoreceptor. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a charging device, and more particularly to a charging device that uniformly charges the surface of a photoreceptor before an electrostatic latent image is formed using a contact charging brush.

  In an electrophotographic image forming apparatus, the surface of the photosensitive drum is positively or negatively charged by a contact charging brush disposed so as to be in contact with the surface of the photosensitive drum, and image data is transferred to the surface of the charged photosensitive drum. An electrostatic latent image is formed by irradiating the corresponding light, and a toner image is formed by attaching toner to the electrostatic latent image, and the toner image is transferred to a predetermined sheet, thereby transferring the image onto the sheet. It is recorded. As described above, the toner image on the surface of the photosensitive drum is transferred to a predetermined sheet, but not all of the toner is transferred to the sheet, and a part of the toner image is not transferred to the sheet. Remains on the surface. The so-called residual toner remaining on the surface of the photosensitive drum is collected and reused by a developing device that supplies toner to the surface of the photosensitive drum.

  However, since the contact charging brush is disposed in contact with the surface of the photosensitive drum, a part of the toner to be collected by the developing unit adheres to the contact charging brush. Thus, if residual toner adheres to the contact charging brush, charging failure occurs when charging the surface of the photosensitive drum. In order to prevent the occurrence of this charging failure, as shown in FIG. 5, two contact charging brushes 51 and 52 are arranged along the rotation direction of the photosensitive drum 50, and a DC voltage is applied to the contact charging brush 51. There is a contact charging device 53 that charges the surface of the photosensitive drum 50 with two contact charging brushes 51 and 52 by applying and applying a voltage obtained by superimposing an AC voltage on a DC voltage to the contact charging brush 52 (for example, , See Patent Document 1).

According to the contact charging device 53, by applying a voltage in which an AC voltage is superimposed on a DC voltage, the valley of the surface potential of the photosensitive drum 50 is relaxed and the surface potential can be stabilized. Further, a part of the residual toner remaining on the surface of the photosensitive drum 50 without being transferred onto the sheet is captured by the contact charging brush 51, thereby preventing the residual toner from adhering to the contact charging brush 52. Even if the contact charging brush 51 is contaminated with residual toner, it is possible to prevent the contact charging brush 52 from causing a charging failure.
JP 2001-35669 A

  However, when a voltage obtained by superimposing an AC voltage on a DC voltage as described above is used, it is necessary to increase the frequency of the AC voltage in order to increase the resolution of the image recorded on the paper, but the frequency is too high. When the frequency is set too low, cycle unevenness occurs. As described above, when a voltage obtained by superimposing an AC voltage on a DC voltage is used, there is a problem that a frequency to be used is limited.

  The present invention has been made in view of such a problem, and can charge the surface of the photoreceptor before the formation of the electrostatic latent image to a stable potential without using an AC voltage. An object of the present invention is to provide a charging device capable of preventing the occurrence of charging failure on the surface of the battery.

  In order to achieve the above object, the charging device according to claim 1 is a charging device for charging the surface of the photosensitive member before the electrostatic latent image is formed, wherein the first contact is applied with a DC voltage. A charging member and a second contact charging member to which an alternating voltage by a direct current pulse is applied are disposed so as to be in contact with the surface of the photoconductor along the rotation direction of the photoconductor. .

  According to a second aspect of the present invention, in the charging device according to the first aspect, the first contact charging member is disposed downstream of the second contact charging member in the rotation direction of the photosensitive member. It is characterized by that.

The charging device according to claim 3 is the charging device according to claim 1 or 2, wherein an absolute value _VA of a DC voltage applied to the first contact charging member and an application to the second contact charging member are provided. The minimum value V _B1 in the absolute value and the maximum value V _{B2 in} the absolute value of the alternating voltage due to the DC pulse applied are set so as to satisfy the relationship of | V _B1 | ≦ | V _A | <| V _B2 | It is characterized by having.

  According to the charging device of the first aspect, even if a charging failure occurs on the surface of the photosensitive member due to the residual toner adhering to one of the contact charging members located on the upstream side in the rotation direction of the photosensitive member, The other charging contact member located on the downstream side in the rotation direction of the body drum can compensate for the charging failure. Further, since the voltage applied to the second contact charging member is an alternating voltage generated by a DC pulse, the frequency is not limited as in the case where an AC voltage is used. Further, since the duty can be easily changed as compared with the AC voltage, the toner on the surface of the photosensitive member is captured by one contact charging member, and the duty ratio is optimal to compensate for the charging failure by the other contact charging member. In addition, the voltage applied to the second contact charging member can be easily controlled.

  According to the charging device of the second aspect, since the residual toner on the surface of the photoreceptor is captured by the second contact charging member, it is possible to prevent the residual toner from adhering to the first contact charging member. Can do. Therefore, even when residual toner adheres to the second contact charging member and a charging failure occurs on the surface of the photoreceptor, the charging failure can be compensated for by the first contact charging member.

  According to the charging device of claim 3, since the surface potential of the photoconductor charged by one contact charging member and the surface potential of the photoconductor charged by the other contact charging member are substantially equal, the photoconductor The surface potential can be stabilized.

  Hereinafter, a charging device 1 according to the best mode for carrying out the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the configuration of the charging device 1. The charging device 1 is a device for uniformly charging a surface of a photosensitive drum (photosensitive body) 10 before forming an electrostatic latent image by a contact charging method by causing electrons or ions to act uniformly. Yes, as shown, the first charging brush (first contact charging member) 2, the switch 3, the first DC power supply 4, the second charging brush (second contact charging member) 5, the changeover switch 6, the second A DC power source 7 and a resistor 8 are provided.

  The first charging brush 2 is one in which conductive brushes are radially implanted on a conductive shaft, and a known charging brush can be used in this field. The first charging brush 2 is disposed so that the axes of the first charging brush 2 and the photosensitive drum 10 are parallel to each other, and in contact with the surface of the photosensitive drum 10. The first charging brush 2 rotates in the same direction as the photosensitive drum 10 around its own axis as indicated by an arrow in the figure, and the switch 3 is turned on based on a control signal (signal) from a control means (not shown). Then, the surface of the photosensitive drum 10 is charged to a predetermined potential by the DC voltage applied by the first DC power supply 4.

Similar to the first charging brush 2, the second charging brush 5 is configured such that a conductive brush is radially implanted on a conductive shaft, and the axes of the photosensitive drum 10 and the mutual brush are parallel to each other. In addition, it is disposed so as to be in contact with the surface of the photosensitive drum 10. Here, the first charging brush 2 is disposed so as to be located downstream of the second charging brush 5 in the rotation direction of the photosensitive drum 10. When the changeover switch 6 is switched to the short-circuit side, the second charging brush 5 is applied with a voltage substantially equal to the power supply voltage of the second DC power supply by the second DC power supply 7, and conversely the changeover switch 6 is a resistance When the switch is switched to the 8 side, a voltage having a voltage drop of 8 resistors is applied. By switching the switch 6 with a preset duty ratio, the absolute value of the amplitude is obtained. An alternating voltage is applied by a DC pulse having a minimum value of V _B1 and a maximum absolute value of V _B2 . Similar to the first charging brush 2, the second charging brush 5 rotates in the same direction as the photosensitive drum 10 around its own axis, and based on the alternating voltage of this DC pulse based on a control signal from the control means. The surface of the photoreceptor 10 is charged.

  As described above, the surface of the photosensitive drum 10 is charged by the second charging brush 5 to which an alternating voltage by a DC pulse is applied and then charged by the first charging brush 2 to which a DC voltage is further applied. It is like that. FIG. 2 is a cross-sectional view illustrating a configuration of the image forming apparatus 11 when the charging device 1 is applied to the image forming apparatus 11. The image forming apparatus 11 records an image of image data on a sheet in a multi-function peripheral equipped with a copy function, a facsimile function, a (network) printer function, and the like. Specifically, the image forming apparatus 11 is read by a copy function. An image of the original image data, an image of the image data received from another G3 facsimile apparatus (not shown), and an image of the image data received from the client PC (not shown) via a LAN (not shown) are predetermined. Record on paper. As shown in FIG. 1, the image forming apparatus 11 includes a charging device 1, a photosensitive drum 10, an exposure device 12, a developing device 13, a transfer device 14, an ERS brush 15, a paper feed cassette 16, a registration roller 17, a heat roller 18, A press roller 19, a paper discharge roller 20, and a paper discharge tray 21 are provided.

  The photosensitive drum 10 is configured by forming a photosensitive layer of OPC (Organic Photo Conductor), amorphous silicon, selenium or the like on the surface of a conductive support such as aluminum formed in a drum shape. An electrostatic latent image is formed on the surface of the drum 10. The exposure device 12 irradiates the surface of the photosensitive drum 10 uniformly charged to a constant potential by the charging device 1 to remove the charged charges, thereby forming an electrostatic latent image on the surface of the photosensitive drum 10. Specifically, an LED (Light Emitting Diode) optical system, a semiconductor laser optical system, or the like is used as an exposure optical system for this purpose. The developing device 13 is a device for attaching a toner to the electrostatic latent image formed on the surface of the photosensitive drum 10 to form a visible toner image, and includes a supply roller 24 and a supply roller 24 for charging the toner. The developing roller 25 that adheres the supplied toner to the surface of the photosensitive drum 10, the blade 26 that uniformizes the layer thickness of the toner that adheres to the outer peripheral surface of the developing roller 25, etc. The three steps of conveying the toner to the photosensitive drum 10 side and attaching the toner to the electrostatic latent image on the surface of the photosensitive drum 10 are performed.

  The transfer unit 14 transfers a toner image formed on the surface of the photosensitive drum 10 onto the paper 30. Specifically, a conductive roller, a corona charger, or the like to which a voltage is applied is used. The ERS brush 15 is for dispersing residual toner remaining on the surface of the photosensitive drum 10 without being transferred to the paper 30. The residual toner dispersed by the ERS brush 15 is Accompanying the rotation, it is collected by the developing device 13 and then reused. A large number of sheets of a predetermined size are stored in the sheet feed cassette 16, and the sheets 30 stored in the sheet feed cassette 16 are separated one by one by a sheet feed roller 27 and supplied to a sheet transport path 28. The registration roller 17 conveys the sheet 30 supplied from the sheet feeding cassette 16 along the sheet conveyance path 28 between the photosensitive drum 10 and the transfer unit 14. The heat roller 18 and the press roller 19 heat the toner image by heat from a heat source provided inside the heat roller 18 while pressing the paper 30 from above and below to fix the toner image on the paper 30. The paper discharge roller 20 discharges the recording paper (paper 30) on which the image is fixed to the paper discharge tray 21.

  Hereinafter, the image forming process performed in the image forming apparatus 11 will be described with reference to FIGS. When a control signal for recording an image of image data on a sheet is input from a control unit (not shown), each unit of the image forming apparatus 11 performs a predetermined operation. That is, when the main motor (not shown) starts to rotate, the photosensitive drum 10, the first charging brush 2, the second charging brush 5, the developing roller 25, and the transfer roller of the transfer unit 14 rotate in the directions of the arrows shown in FIG. To do. The surface of the photosensitive drum 10 is charged with an alternating voltage generated by a DC pulse applied to the second charging brush 5 and then further charged with a DC voltage applied to the first charging brush 2.

Here, the absolute value _{VA of the} DC voltage applied to the first charging brush 2, the minimum value _VB1 of the absolute value of the alternating voltage due to the DC pulse applied to the second charging brush 5, and the maximum of the absolute value. The value V _B2 is set so as to satisfy the relationship of | V _B1 | ≦ | V _A | <| V _B2 |. Therefore, since the surface potential of the photosensitive drum 10 charged by the second charging brush 5 and the surface potential of the photosensitive drum 10 after being charged by the first charging brush 2 are substantially equal, the photosensitive drum can be stably provided. Ten surfaces can be charged.

  In this manner, the surface of the photosensitive drum 10 is charged to a predetermined potential by the second charging brush 5 and the first charging brush 2, and the surface of the photosensitive drum 10 is cleaned. The cleaning process performed here is a process of removing residual toner remaining on the surface of the photosensitive drum 10 without being transferred to the paper 30 from the surface of the photosensitive drum 10. That is, the residual toner adhering to the surface of the photosensitive drum 10 is diffused by the ERS brush 15 to which a predetermined voltage is applied, and then sent to the developing device 13 as the photosensitive drum 10 rotates, and the developing device. 13 is collected. At this time, as shown in FIG. 3, in order to prevent the residual toner on the surface of the photosensitive drum 10 from adhering to the transfer roller of the transfer unit 14, a voltage (in this case, a positive polarity) is used. Is applied).

  As described above, after the photosensitive drum 10 is charged to a predetermined potential and the surface of the photosensitive drum 10 is cleaned, light corresponding to image data is irradiated to the surface of the photosensitive drum 10 by the exposure device 12. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 10. When the photosensitive drum 10 rotates while the electrostatic latent image is formed, toner (here, positively charged toner) is supplied from the developing device 13, and the electrostatic latent image formed on the surface of the photosensitive drum 10. A visible toner image is formed on top. Accordingly, the paper 30 is supplied from the paper supply cassette 16 to the paper conveyance path 28 by the paper supply roller 27, and the supplied paper 30 is transferred between the photosensitive drum 10 and the transfer roller of the transfer device 14 by the registration roller 17. It is conveyed. The toner image formed on the surface of the photoconductive drum 10 is transferred onto the paper 30 by the photoconductive drum 10 and the transfer roller of the transfer unit 14. At this time, a voltage (in this case, a negative voltage) having a polarity opposite to that of the toner image is applied to the transfer roller of the transfer device 14. It is transcribed into. The paper 30 on which the toner image has been transferred is conveyed between the heat roller 18 and the press roller 19 along the paper conveyance path 28, and the paper 30 is heated by the pressing force of the press roller 19 and the heat roller 18 and the heat of the heat roller 18. 30 is fixed. The recording paper (paper 30) on which the image is formed in this way is discharged from the paper transport path 28 to the paper discharge tray 21 by the paper discharge roller 20. When the transfer of the toner image onto the paper 30 is completed, a voltage having the same polarity as the residual toner (in this case, a positive voltage) is again applied to the transfer roller of the transfer unit 14 for a predetermined time. A surface cleaning process is performed, and the image forming process ends.

  In this embodiment, the surface of the photosensitive drum 10 is charged to a positive potential by the second charging brush 5 and the first charging brush 2, and the charged charge is removed by irradiating the image portion with light by the exposure device 12. In this way, an electrostatic latent image is formed, and a positively charged toner is supplied from the developing device 13 to form a toner image on the surface of the photosensitive drum 10, but the second charging brush 5 and the first charging brush are used. 2, the surface of the photosensitive drum 10 is charged to a negative potential, and the exposure unit 12 irradiates light to a portion other than the image area to remove the charged charge, thereby forming an electrostatic latent image. The toner image may be formed by supplying the positively charged toner to the image portion on the surface of the photosensitive drum 10.

  As described above, the image of the image data is recorded on the paper, and the residual toner remaining on the surface of the photosensitive drum 10 is diffused by the ERS brush 15 and then collected by the developing unit 13 and reused. However, since the second charging brush 5 and the first charging brush 2 are disposed so as to be in contact with the surface of the photosensitive drum 10, a part of the residual toner to be collected by the developing device 13 is the second charging brush. Although it is predicted that the toner adheres to the brush 5 or the first charging brush 2, the residual toner on the surface of the photosensitive drum 10 is a second toner positioned upstream of the first charging brush 2 in the rotation direction of the photosensitive drum 10. Since the toner is captured by the charging brush 5, it is possible to prevent the residual toner from adhering to the first charging brush 2. Therefore, even when residual toner adheres to the second charging brush 5 and charging failure occurs on the surface of the photosensitive drum 10, the charging failure is eliminated by the first charging brush 2 to which no residual toner is attached. And stable charging treatment can be performed over a long period of time.

  Since the voltage applied to the second charging brush 5 is not a voltage obtained by superimposing an AC voltage on a DC voltage as conventionally used, but an alternating voltage based on a DC pulse, the duty can be easily changed. Therefore, a stable charging operation can be performed over a long period of time by capturing the residual toner with one charging brush and changing the optimum duty in order to prevent charging failure with the other charging brush. .

  In addition, as shown in FIG. 4, the first charging brush 2 may be disposed on the upstream side in the rotation direction of the photosensitive drum 10 with respect to the second charging brush 5. In this case, since the residual toner is captured by the first charging brush 2, it is possible to prevent the residual toner from adhering to the second charging brush 5. Further, even if the surface potential of the photosensitive drum 10 after being charged by the first charging brush 2 becomes low due to the residual toner adhering to the first charging brush 2, it is applied to the second charging brush 5. The surface of the photosensitive drum 10 can be charged to an appropriate potential by changing the duty of the alternating voltage by the DC pulse.

  The present invention can be applied to a charging device that charges a surface of a photoreceptor before an electrostatic latent image is formed with a contact-type charging brush.

1 is a cross-sectional view illustrating a configuration of a charging device according to the best mode for carrying out the present invention. 1 is a cross-sectional view illustrating a configuration of an electrophotographic image forming apparatus to which a charging device is applied. FIG. 6 is a diagram illustrating an operation sequence of each unit in the image forming apparatus. FIG. 7 is a cross-sectional view illustrating a configuration of an image forming apparatus to which a modification of the charging device according to the best mode for carrying out the invention is applied. It is the figure which showed the structure of the conventional contact charging device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Charging apparatus 2 1st charging brush (1st contact charging member)
4 First DC power supply 5 Second charging brush (second contact charging member)
6 switch 7 second DC power supply 8 resistance 10 photoconductor drum (photoconductor)

Claims (3)

A charging device for charging the surface of a photoreceptor before an electrostatic latent image is formed,
A first contact charging member to which a DC voltage is applied and a second contact charging member to which an alternating voltage by a DC pulse is applied are in contact with the surface of the photoconductor along the rotation direction of the photoconductor. A charging device characterized by being arranged.   2. The charging device according to claim 1, wherein the first contact charging member is disposed downstream of the second contact charging member in the rotation direction of the photoconductor. The absolute value _{VA of the} DC voltage applied to the first contact charging member and the absolute value of the absolute value of the alternating voltage due to the DC pulse applied to the second contact charging member V _B1 The charging device according to claim 1, wherein the maximum value V _B2 is set so as to satisfy a relationship of | V _B1 | ≦ | V _A | <| V _B2 |.

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