JP2010175593A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for separating a sheet from an image carrier as if it naturally separates. <P>SOLUTION: The image forming apparatus 100 includes an exposure device 33, a developing device 34, a transfer unit 35, a discharging lamp 39 and a controller 50. The discharging lamp 39 is configured to discharge a photoreceptor drum 31 before transfer of a developer image and decrease potential on a surface of the photoreceptor drum 31. The controller 50 is configured to control at least the transfer unit 35 and the discharging lamp 39. The controller 50 controls the discharging lamp 39 to discharge at least an area corresponding to a non-image area located at the leading edge of paper 40 on the photoreceptor drum 30. Simultaneously, the controller 50 controls the transfer unit 35 so that the potential is lower than ordinary transfer potential when the non-image area of the paper 40 passes. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus that executes a transfer process for transferring a developer image from an image carrier to a sheet.

  In an electrophotographic image forming apparatus, a transfer process for transferring a developer image from a photoreceptor to a sheet is performed. During this transfer process, since the paper may be adsorbed to the photoconductor, various contrivances for preventing the paper from adsorbing to the photoconductor or peeling the paper adsorbed to the photoconductor are conventionally performed. I have been.

  For example, conventionally, there has been a case where a static elimination lamp is provided in the vicinity of the developing device in order to improve the peelability of the sheet from the photoreceptor. Among the technologies that employ this static elimination lamp, switching of the static elimination lamp so that the amount of light of the static elimination lamp is high at the leading edge of the image on the photosensitive member and low at the trailing edge of the image may interfere with image forming processing. However, there is one that attempts to improve the peelability of the paper (for example, see Patent Document 1).

JP-A-1-169478

  However, as described in Patent Document 1, even when the surface of the photosensitive member is neutralized by increasing the light amount of the pre-transfer neutralization lamp with respect to the leading end region of the sheet, there is a sheet to be transferred. There has been a case in which the toner is attracted to the photosensitive member side. The reason for this is that even if the adsorption force of the photoconductor is reduced by removing the charge from the photoconductor, the force still acts on the paper from the photoconductor and the paper is peeled off from the photoconductor in a state close to natural peeling. Is not formed.

  An object of the present invention is to provide an image forming apparatus capable of peeling a sheet from an image carrier in a state close to natural peeling.

  The image forming apparatus according to the present invention includes a transfer unit, a pre-transfer charge eliminating unit, and a control unit. The transfer unit is configured to transfer the developer image formed on the image carrier to a sheet. The pre-transfer charge removing unit is configured to discharge the image carrier before transferring the developer image and to reduce the surface potential of the image carrier. As an example of the pre-transfer charge eliminating means, a charge eliminating lamp including an LED or the like can be given.

  The control means is configured to control at least the transfer means and the pre-transfer charge eliminating means. The control unit controls the pre-transfer neutralization unit so as to neutralize at least a region corresponding to the non-image region located at the leading edge of the sheet in the image carrier, and a normal transfer potential when the non-image region of the sheet passes. The transfer means is controlled so as to have a lower potential.

  In this configuration, the portion of the image carrier that comes into contact with the non-image area at the leading edge of the sheet is neutralized by the pre-transfer neutralizing means, so that the leading edge of the sheet is hardly attracted to the image carrier.

  Furthermore, for the non-image area at the leading edge of the sheet, the transfer means is set to a potential smaller than the normal transfer potential, thereby canceling the influence of the residual potential on the image carrier acting on the sheet. It becomes easy.

  According to the applicant's experiment with respect to the non-image area at the leading edge of the sheet, the transfer potential by the transfer means is required to be as high as the remaining potential on the photoreceptor. For example, even if the image carrier is neutralized, if the transfer potential by the transfer means is high, the probability that the sheet will go to the image carrier is high. On the other hand, the sheet may be adsorbed to the image carrier even when the transfer potential by the transfer means is reduced to near zero.

  By setting the transfer potential of the transfer means to the non-image area at the leading edge of the sheet so as not to be defeated by the residual potential on the photoconductor, the sheet naturally peels from the photoconductor using its stiffness. Therefore, the peelability of the sheet is improved.

  In the above-described configuration, the control means equalizes the potential of the area neutralized by the pre-transfer neutralization means in the image carrier and the potential of the contact portion with the sheet in the transfer means when the non-image area of the sheet passes. Thus, it is preferable to control the transfer means. By adopting such control, the sheet can be easily peeled from the image carrier in a situation closer to natural peeling.

  According to the present invention, an image forming apparatus capable of peeling a sheet from an image carrier in a state close to natural peeling is provided.

  FIG. 1 is a schematic front sectional view showing the configuration of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus 100 includes an image reading unit 200, an image forming unit 300, and a paper feeding unit 400.

  The image reading unit 200 includes an automatic document feeder (hereinafter referred to as ADF) 201, a first document table 202, a second document table 203, a first mirror base 204, a second mirror base 205, a lens 206, and a charge coupled device (hereinafter referred to as “charge coupled device”). CCD) 207.

  The ADF 201 sequentially conveys documents from the document tray 211 to the second document table 203. The ADF 201 functions as a document cover that covers the first document table 202 and the second document table 203. Both the first platen 202 and the second platen 203 are made of hard glass plates.

  The first mirror base 204 and the second mirror base 205 are disposed below the first document table 202 and the second document table 203. The first mirror base 204 and the second mirror base 205 are supported so as to be reciprocally movable in the horizontal direction. The moving speed of the second mirror base 205 is ½ of the moving speed of the first mirror base 204. The first mirror base 204 is equipped with a light source and a first mirror. The second mirror base 205 is equipped with a second mirror and a third mirror.

  When reading an image of a document conveyed by the ADF 201, the first mirror base 204 is stopped below the second document table 203. On the other hand, when reading an image of a document placed on the first document table 202, the first mirror base 204 and the second mirror base 205 move horizontally below the first document table 202.

  Reflected light from the image surface of the document enters the CCD 207 via the first mirror base 204, the second mirror base 205, and the lens 206. The CCD 207 outputs an electrical signal corresponding to the amount of reflected light on the image surface of the document. This electrical signal is input to the image forming unit 300 as image data.

  The image forming unit 300 includes an image forming unit 30. The image forming unit 30 includes a photosensitive drum 31, a charger 32, an exposure device 33, a developing device 34, a static elimination lamp 39, a transfer unit 35, a cleaner 36, and a fixing device 37.

  The photosensitive drum 31 has a photosensitive layer formed on the surface thereof, and rotates in a direction indicated by an arrow in FIG. The charger 32 uniformly charges the surface of the photosensitive drum 31 to a predetermined potential. The charger 32 may be a non-contact type such as a charger or a contact type such as a roller or a brush.

  The exposure device 33 irradiates the surface of the photosensitive drum 31 with light based on image data. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 31. Here, a laser scanning unit is used as the exposure device 33. However, as the exposure device 33, a writing unit in which light emitting elements such as EL and LEDs are arranged in an array can be used. The developing device 34 forms a toner image on the surface of the photosensitive drum 31 by supplying toner to the surface of the photosensitive drum 31. The neutralizing lamp 39 is configured to expose the surface of the photosensitive drum 31 in order to reduce the surface potential of the photosensitive member. In this embodiment, an LED is used as the static elimination lamp, but the configuration of the static elimination lamp 39 is not limited to this.

The transfer unit 35 is disposed below the photosensitive drum 31 and includes a transfer belt 354. The transfer belt 354 is stretched around a plurality of rollers. The transfer belt 354 has a resistance value of about 1 × 10 ⁹ to 1 × 10 ¹³ Ω · cm. Inside the loop formed by the transfer belt 354, a transfer roller 352 for transferring the toner image on the surface of the photosensitive drum 31 to a sheet is disposed. The transfer roller 352 is in pressure contact with the photosensitive drum 31 with the transfer belt 354 interposed therebetween. A predetermined transfer voltage is applied to the transfer roller 352 when the toner image is transferred.

  The cleaner 36 removes residual toner from the surface of the photosensitive drum 31 after the transfer of the toner image to the paper. A separation claw 41 is disposed between the transfer roller 352 and the cleaner 36 for separating the paper adsorbed on the surface of the photosensitive drum 31.

  The fixing device 37 includes a heating roller 372 and a pressure roller 374. The heating roller 372 includes a heater for heating the surface of the heating roller 372 inside. The pressure roller 374 is in pressure contact with the heating roller 372 with a predetermined pressure. By passing between the heating roller 372 and the pressure roller 374, the toner image attached to the paper is fixed on the paper. The paper that has passed through the fixing device 37 is discharged to a paper discharge tray 38 mounted on the side surface of the image forming apparatus 100, or is transported to the image forming position again via the switchback transport path.

  The paper feed unit 400 is a paper feed unit of the present invention, and includes paper feed cassettes 401, 402, 403, 404 and a manual feed tray 405. The paper feed unit 400 sequentially supplies paper to the image forming unit 30 from any one of the paper feed cassettes 401 to 404 or the manual feed tray 405.

  FIG. 2 is a block diagram illustrating an outline of the image forming apparatus 100. The image forming apparatus 100 includes a control unit 50 that comprehensively controls each unit. The control unit 50 is connected to the image reading unit 200, the image forming unit 300, the paper feeding unit 400, the transport unit 56, the ROM 52, the RAM 54, the image processing unit 58, the interface unit 60, and the hard disk 62.

  The transport unit 56 is configured to transport a sheet according to a set procedure along a transport path formed inside the image forming apparatus 100. The ROM 52 stores a plurality of programs necessary for the operation of the control unit 50. The RAM 54 is a memory that can be directly accessed from the control unit 50 and is a volatile memory that can temporarily record data. The image processing unit 58 is configured to perform image processing according to a procedure set for image data input via the image reading unit 200 or the interface unit 60. The interface unit 60 has a function of performing communication with an external device. The hard disk 62 is configured to be able to record data such as image data and setting information.

  FIG. 3 is a diagram showing an outline of a configuration for controlling the transfer roller 352 and the charge removal lamp 39. As shown in FIG. 3, the transfer roller 352 is connected to a transfer current control unit 356 that controls a current value applied to the transfer roller 352. The static elimination lamp 39 is connected to a lamp control unit 392 for controlling the voltage value applied to the static elimination lamp 39.

  The control unit 50 includes a determination unit 64 that determines the start position of the image region of the image data. The control unit 50 determines the range of the non-image region on the sheet based on the determination result of the determination unit 64, and the transfer current control unit 356 and A control signal is output to the lamp controller 392. On the other hand, the transfer current control unit 356 and the lamp control unit 392 operate based on control signals from the control unit 50, respectively.

  FIG. 4 is a diagram illustrating a charged state of the photosensitive drum 31 when the transfer roller 352 and the charge removal lamp 39 are operated. As shown in FIG. 4, the surface potential of the photosensitive drum 31 is lowered by being exposed to the charge removal lamp 39. At this time, if the light emission output of the static elimination lamp 39 exceeds a predetermined value, the surface potential of the photosensitive drum 31 will not be completely 0V even if the light emission output is increased further, and it is about several tens of volts ( For example, a residual potential of about -80 V remains.

  For this reason, the control unit 50 applies a slight current to the transfer roller 352 so as to cancel the influence from the residual potential on the photosensitive drum 31, so that the conveyed paper 40 is attracted to the photosensitive drum 31. I try to prevent that.

  FIG. 5A to FIG. 5C are timing charts for explaining control of the charge removal lamp 39 and the transfer roller 352. As shown in FIG. 5B, the control unit 50 causes the static elimination lamp 39 to execute the static elimination process on at least the area corresponding to the non-image area located at the leading edge of the sheet in the photosensitive drum 31.

  Further, as shown in FIG. 5C, when the control unit 50 comes into contact with a portion corresponding to the region exposed by the static elimination lamp 39, that is, the non-image region located at the leading end of the paper 40, the control unit 50 The transfer current control unit 356 is controlled such that a current (T2) lower than the transfer current value (T3) is applied to the transfer roller 352.

  FIG. 6 shows the relationship between the voltage applied to the static elimination lamp 39 and the current applied to the transfer roller 352, and the peelability of the paper 40 at that time. In FIG. 6, the circled result indicates that the sheet 40 has not been attracted to the photosensitive drum 31 even when 1000 sheets are continuously conveyed. In this experiment, it is determined that the paper 40 is attracted to the photosensitive drum 31 when it is confirmed that there is a scratch or a black spot at a position corresponding to the arrangement position of the peeling claw 41 on the paper 40.

  As shown in FIG. 6, when a transfer current is not applied to the transfer roller 352, the sheet 40 may be attracted to the photosensitive drum 31 regardless of whether or not exposure is performed by the charge removal lamp 39. Further, the paper 40 may be attracted to the photosensitive drum 31 even when a transfer current similar to that during normal transfer is applied to the transfer roller 352.

  On the other hand, when the pre-transfer static elimination is not performed or when the voltage applied to the static elimination lamp 39 is lower than a predetermined value, the paper 40 may be attracted to the photosensitive drum 31. Here, the predetermined value indicates an applied voltage value that can reduce the residual potential on the surface of the photosensitive drum 31 to the lowest level (for example, about −80 V).

  As a result of the above experiment, the sheet 40 is prevented from being attracted to the photosensitive drum 31 when a voltage of 40 V or more is applied to the static elimination lamp 39 and a current value of 10 μA is applied to the transfer roller 352. I understood that. By applying a voltage of 40 V or more to the static elimination lamp 39, the residual potential on the surface of the photosensitive drum 31 is reduced to the lowest level (for example, about −80 V). Further, by applying a current value of 10 μA to the transfer roller 352, it is presumed that the potential of the portion of the transfer belt 354 that contacts the paper 40 becomes equal to the remaining potential of the surface of the photosensitive drum 31. For this reason, the force acting on the paper 40 from the photosensitive drum 31 and the force acting on the paper 40 from the transfer belt 354 are almost balanced, so that the paper 40 naturally peels from the photosensitive drum 31 by its own stiffness. It is assumed that

  In the above example, an example in which a current value of 10 μA is applied to the transfer roller 352 has been described. However, the current value applied to the transfer roller 352 may be appropriately changed depending on the resistance values of the transfer roller 352 and the transfer belt 354. . What is important is to adjust the value of the current applied to the transfer roller 352 so that the potential of the portion of the transfer belt 354 that contacts the paper is equal to the minimum value of the remaining potential on the surface of the photosensitive drum 31. . Since the current value applied to the transfer roller 352 is influenced by the environment such as temperature and humidity, it is preferable to finely adjust the current value applied to the transfer roller 352 according to the environment around the transfer roller 352.

  According to the above embodiment, the sheet 40 is less affected by the force acting from the photosensitive drum 31 and the force acting from the transfer roller 352 (or the transfer belt 354), so the sheet 40 is attracted to the photosensitive drum 31. Even when the photosensitive drum 31 is attracted to the photosensitive drum 31, it is naturally peeled off from the photosensitive drum 31 by its own stiffness.

  FIG. 7A to FIG. 7C are timing charts showing another example of a control method for the charge removal lamp and the transfer roller. In this example, as shown in FIG. 7B, after exposure is performed on a portion of the photosensitive drum 31 corresponding to the non-image area of the paper 40, the portion corresponding to the image area of the paper is further neutralized. Exposure by the lamp 39 is performed. At this time, the value of the voltage applied to the static elimination lamp 39 is a lower value (for example, a value halved) than the value in the case of exposing the portion corresponding to the non-image area.

  Whether to perform the control shown in FIG. 7B may be determined according to the type of paper 40. For example, when the image forming process is performed on paper (for example, thin paper) that is weak and easily attracted to the photosensitive drum 31, the control shown in FIG. When the image forming process is performed on a sheet that is difficult to be attracted to the body drum 31, the control shown in FIG.

  Further, whether or not to perform the control shown in FIG. 7B may be determined according to input image data. For example, when the amount of toner used during the image forming process is large, such as a black solid image, the control shown in FIG. 7B is performed, while when the amount of toner used during the image forming process is small, The control shown in FIG. 5B may be performed. Furthermore, whether or not to perform the control shown in FIG. 7B may be determined in consideration of both the type of paper 40 and the input image data.

  In the above-described embodiment, the case where the image carrier is a photoconductor has been described. However, the application range of the present invention is not limited to the photoconductor. For example, the present invention can be applied to peel off the paper adsorbed on the intermediate transfer belt in the vicinity of the intermediate transfer belt and the secondary transfer roller.

  The above description of the embodiment is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown not by the above embodiments but by the claims. Furthermore, the scope of the present invention is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.

1 is a diagram schematically illustrating an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram illustrating an outline of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the outline of the structure for controlling a transfer roller and a static elimination lamp. FIG. 6 is a diagram illustrating a charged state of a photosensitive drum when a transfer roller and a charge removal lamp are operated. 6 is a timing chart for explaining control of the charge removal lamp and the transfer roller. It is a figure which shows the relationship between the voltage applied to a static elimination lamp, the electric current applied to a transfer roller, and the peelability of the paper at that time. 6 is a timing chart for explaining control of the charge removal lamp and the transfer roller.

31-photosensitive drum 39-static discharge lamp 50-control unit 100-image forming apparatus 352-transfer roller 354-transfer belt 356-transfer current control unit 392-lamp control unit

Claims (6)

Transfer means for transferring a developer image formed on the image carrier to a sheet;
A pre-transfer charge eliminating unit configured to neutralize the image carrier before transferring the developer image, and to reduce the surface potential of the image carrier;
Control means configured to control at least the transfer means and the pre-transfer charge eliminating means;
With
The control unit controls the pre-transfer neutralization unit so as to neutralize at least a region corresponding to a non-image region located at the leading edge of the sheet in the image carrier, and when the non-image region of the sheet passes. An image forming apparatus for controlling the transfer unit so as to have a potential lower than a normal transfer potential.   The control means is configured such that the potential of the area neutralized by the pre-transfer neutralization means on the image carrier is equal to the potential of the contact portion of the transfer means with the sheet when the non-image area of the sheet passes. The image forming apparatus according to claim 1, wherein the transfer unit is controlled.   The image forming apparatus according to claim 1, wherein the control unit includes a determination unit that determines a start position of an image region of image data, and specifies the non-image region based on a determination result of the determination unit.   The control unit controls the charge removal process of the pre-transfer charge eliminating unit for a region other than a region corresponding to a non-image region located at the leading edge of the sheet in the image carrier according to the type of the sheet. The image forming apparatus according to any one of the above.   5. The control unit according to claim 1, wherein the control unit controls a charge removal process of the pre-transfer charge removing unit for a region other than a region corresponding to a non-image region located at a front end of a sheet in the image carrier according to image data. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 1, further comprising a peeling claw configured to peel the sheet from the image carrier.

Images