JP2011164476A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can suppress the occurrence of transfer failures. <P>SOLUTION: A copying machine includes a transfer roller 71 for transferring a toner image formed on an intermediate transfer belt 64 to a recording sheet; a destaticizing member 72 for destaticizing the recording sheet to which the toner image is transferred; and an HV power source 75 for controlling second current flowing through a transfer roller 71, based on a first current flowing through the destaticizing member 72. It is preferable that the HV power source 75 control the second current so that the difference between the first current and the second current becomes constant. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus such as an electrophotographic copying machine, a printer, or a facsimile machine.

  In general, an image forming apparatus forms a toner image on an image carrier, and transfers the toner image to a transfer material (paper) and presses the image to form an image on the transfer material. In particular, the contact transfer unit in the image forming apparatus transfers a toner image formed on the image carrier to a transfer material by causing a transfer current to flow from the transfer roller to the image carrier. Further, a neutralizing member is provided in the vicinity of the contact transfer means, and the neutralizing member performs neutralization of the transfer material after transfer and separation of the transfer material from the conveyance path.

Here, Japanese Patent Application Laid-Open No. 2002-365923 (Patent Document 1) discloses an image forming apparatus that can prevent paper separation failure regardless of the moisture absorption state of the paper and the operating environment. The image forming apparatus disclosed in Patent Document 1 measures a current flowing from a transfer roller to a static elimination needle through a sheet, and controls a voltage applied from the static elimination bias control unit to the static elimination needle according to the current value.
JP 2002-365923 A

  However, in the conventional electrophotographic field (especially an image forming apparatus), when the resistance of the transfer material is at a level within an assumed range, a desired transfer performance can be obtained (image performance is guaranteed), but resistance is assumed. In the case of a transfer material that is low beyond the range (for example, humidity-controlled paper in a high humidity environment), transfer defects such as blurring are likely to occur. That is, when an image is formed on humidity control paper in a high humidity environment, a part of the transfer current flowing from the transfer roller to the image carrier leaks from the static eliminator adjacent to the transfer roller and passes through the transfer material. It becomes easier for current to flow. As a result, the transfer current was insufficient, and transfer defects were likely to occur.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of transfer failure.

  An image forming apparatus according to one aspect of the present invention includes a transfer unit that transfers a toner image formed on an image carrier to a transfer material, and a charge removal member that discharges the transfer material onto which the toner image is transferred. And a current control unit that controls the second current flowing through the transfer unit based on the first current flowing through the charge removal member.

  Preferably, in the image forming apparatus, the current control unit controls the second current so that a difference between the first current and the second current is constant.

  Preferably, in the image forming apparatus, the neutralizing member includes a plurality of electrodes for neutralizing, and each of the plurality of electrodes is arranged in parallel with each other.

  According to the image forming apparatus of the present invention, it is possible to suppress the occurrence of transfer failure.

1 is a cross-sectional view schematically showing a configuration of a tandem type color digital copying machine according to an embodiment of the present invention. FIG. 2 is a cross-sectional view schematically illustrating configurations of an intermediate transfer unit, a secondary transfer unit, a fixing unit, and the like in FIG. 1. FIG. 2 is a diagram schematically illustrating a configuration near a secondary transfer unit in a copying machine according to an embodiment of the present invention. FIG. 6 is a diagram schematically illustrating another configuration in the vicinity of the secondary transfer unit in the copying machine according to the embodiment of the present invention. FIG. 6 is a diagram schematically illustrating an example of temporal changes in current It and current Ie when a toner image is transferred to humidity control paper in an HH (high temperature and high humidity) environment in the copying machine according to the embodiment of the present invention. is there. It is a figure which shows typically an example of a structure of a static elimination member. FIG. 6 is a diagram schematically showing a structure near a secondary transfer portion in a copying machine of a comparative example. FIG. 6 is a diagram schematically illustrating an example of temporal changes in current It and current Ie when a toner image is transferred to humidity control paper in an HH environment in a copying machine of a comparative example.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

  [Configuration of the entire copier]

  FIG. 1 is a cross-sectional view schematically showing a configuration of a tandem color digital copying machine (hereinafter referred to as “copying machine”) according to an embodiment of the present invention. FIG. 2 is a cross-sectional view schematically illustrating the configuration of the intermediate transfer unit, the secondary transfer unit, the fixing unit, and the like in FIG.

  1 and 2, a copying machine as an image forming apparatus in the present embodiment includes an image reader unit 10 that reads a document image, and a printer unit that prints and reproduces the read image on a recording sheet S. 20 and a control unit 30 that controls the operation of the image forming apparatus by controlling each unit. The image reader unit 10, the printer unit 20, and the control unit 30 are electrically connected to each other.

  The image reader unit 10 is a portion that reads an image of a document placed on a document glass plate (not shown) by moving the scanner along the image of the document. The original image is color-separated into three colors of red (R), green (G), and blue (B), and is converted into an electric signal by a CCD (Charge Coupled Device) image sensor (not shown). Thereby, R, G, and B image data of the document are obtained. The image reader unit 10 further includes a panel unit 13 for displaying information such as a jam (JAM) and life of the printer unit 20.

  The control unit 30 includes an image memory 33 for storing programs, data, and the like for realizing the basic functions of the image forming apparatus. The image data of each color component obtained by the image reader unit 10 is subjected to various types of data processing in the control unit 30, and further reproduces each color of cyan (C), magenta (M), yellow (Y), and black (K). Converted to image data. Hereinafter, the reproduction colors of cyan, magenta, yellow, and black are represented as C, M, Y, and K, and the C, M, Y, and K are added as subscripts to the numbers of the components related to the reproduction colors. The image data converted by the image reader unit 10 is stored in the image memory 33 in the control unit 30 for each reproduction color. The image data is corrected by the control unit 30 to correct the misregistration, and then read out for each scanning line in synchronization with the supply of the recording sheet S (transfer material). The laser diode (LD) The drive signals are 46Y to 46K.

  The printer unit 20 forms an image by an electrophotographic method, and includes an image processing unit 40, a paper feeding unit 50, an intermediate transfer unit 60, a secondary transfer unit 70, and a fixing unit 80. Yes.

  The image processing unit 40 is a part for forming a toner image on the intermediate transfer belt 64, and is configured by image forming units 40Y to 40K for each color of Y, M, C, and K. Each of the image forming units 40Y to 40K faces the intermediate transfer belt 64 and extends from the intermediate transfer belt cleaner 66 side (hereinafter referred to as “upstream side”) to the recording sheet S conveyance side (hereinafter referred to as “downstream side”). Are arranged in this order at predetermined intervals. Each of the image forming units 40Y to 40K includes an image processing unit and exposure scanning units 47Y to 47K. Each of the exposure scanning units 47Y to 47K has laser diodes (LD) 46Y to 46K that emit light in response to the drive signal output from the control unit 30. The image processing unit includes photosensitive drums 41Y to 41K, charging chargers 42Y to 42K disposed around the photosensitive drums 41Y to 41K, developing units 43Y to 43K, cleaners 44Y to 44K, Transfer rollers 45Y to 45K that transfer the toner images on the photoconductive drums 41Y to 41K to the intermediate transfer belt 64 are included.

  The sheet feeding unit 50 is a part for supplying the recording sheet S as a transfer material to the secondary transfer unit 70, and is the most upstream side (see FIG. 1 on the lower side). The paper feeding unit 50 takes the timing of feeding the recording sheet S to the secondary transfer unit 70 and the paper feeding roller 51 for feeding the recording sheet S from the paper feeding cassette 51. And a registration roller 53. A sheet detection sensor SE1 for detecting the leading edge of the recording sheet S is provided immediately upstream of the registration roller 53.

  The intermediate transfer unit 60 includes a driving roller 61 for rotationally driving the intermediate transfer belt 64, a driven roller 62 that rotates according to the rotation of the intermediate transfer belt 64, and a driven roller 62 for stretching the intermediate transfer belt 64. It includes a tension spring 63 provided, and an intermediate transfer belt 64 that is stretched around a driving roller 61 and a driven roller 62. The intermediate transfer unit 60 further includes an intermediate transfer belt cleaner 66 for removing residual toner on the intermediate transfer belt 64, a screw 67, a joint 68, and a waste toner box 69.

  The secondary transfer portion 70 (contact transfer means) is a portion for secondary transfer of the toner image formed on the intermediate transfer belt 64 to the recording sheet S, and is disposed so as to face the intermediate transfer belt 64. The image forming apparatus includes a next transfer roller 71 and a charge removal member 72 for removing charge from the recording sheet S on which the toner image is transferred. The neutralizing member 72 is disposed on the downstream side of the secondary transfer roller 71 in the conveyance path of the recording sheet S. As the secondary transfer roller 71, for example, an electronic conductive type in which carbon is dispersed in EPDM (ethylene-propylene-diene rubber), an ion conductive NBR (nitrile rubber) having a large environmental dependency, or the like is used. May be used. In addition to NBR, urethane rubber, hydrin rubber, or the like may be used as the transfer roller having ion conductivity in the secondary transfer roller 71. Further, a voltage may be applied to the charge removal member 72.

  The fixing unit 80 is a part for fixing the toner image transferred onto the recording sheet S. The fixing unit 80 is disposed on the downstream side of the secondary transfer unit 70 in the conveyance path of the recording sheet S.

  [Image printing method on copier]

  With reference to FIGS. 1 and 2, when the recording sheet S is fed from the sheet feeding cassette 51 by the sheet feeding roller 52 and the leading edge of the recording sheet S reaches the registration roller 53, the recording sheet S is moved by the sheet detection sensor SE1. Detected. Upon receiving the detection signal from the sheet detection sensor SE1, the control unit 30 issues a leading edge registration roller signal to the driving unit (not shown) of the registration roller 53 to start feeding by the registration roller 53 while taking a timing. The recording sheet S is sent to the secondary transfer unit 70 (upward in FIG. 1).

  Each of the LDs 46Y to 46K in the exposure scanning units 47Y to 47K emits light in response to a drive signal from the control unit 30, and each of these lights exposes and scans the surfaces of the photosensitive drums 41Y to 41K. . Each of the photoconductive drums 41Y to 41K is subjected to charge removal by removing residual toner on the surface by each of the cleaners 44Y to 44K before being exposed and scanned, and further irradiating an eraser lamp (not shown). Each of the photosensitive drums 41Y to 41K is exposed to light from the LDs 46Y to 46K in a state where the photosensitive drums 41Y to 41K are uniformly charged by the supply of electric charges from the charging chargers 42Y to 42K. As a result, electrostatic latent images are formed on the surfaces of the photosensitive drums 41Y to 41K. The electrostatic latent images on the surfaces of the photosensitive drums 41Y to 41K are developed by the developing units 43Y to 43K for the respective colors, and thereby toner images of Y, M, C, and K are formed on the respective surfaces of the photosensitive drums 41Y to 41K. Is formed. The toner images on the photoconductive drums 41Y to 41K are attracted to the transfer rollers 45Y to 45K to which a voltage is applied, and are sequentially transferred onto the intermediate transfer belt 64. At this time, the transfer operation of each color on the intermediate transfer belt 64 is performed from the upstream side to the downstream side of the intermediate transfer belt 64 so that the toner images of the respective colors are transferred to the same position of the intermediate transfer belt that is conveyed. It is executed at different timings.

  The image formed on the intermediate transfer belt 64 is conveyed to the secondary transfer unit 70 where the secondary transfer is performed on the recording sheet S by the secondary transfer roller 71. The recording sheet S on which the toner image of each color has been transferred is subjected to removal (discharge) of excess charges from the back side (right side in FIG. 1) by the charge removal member (charge removal needle) 72 immediately after the transfer. Next, the recording sheet S is guided upward in FIG. 1 by the conveyance guide 83 and the fixing rush guide 82, and is pressed by the fixing unit 80 with high heat. As a result, the toner particles on the surface of the recording sheet S are fused and fixed on the sheet surface. The fixed recording sheet S is then discharged onto a paper discharge tray (not shown).

  Residual toner remaining on the intermediate transfer belt 64 after the secondary transfer is collected by an intermediate transfer belt cleaner 66, and the collected residual toner is conveyed to the front side of the apparatus by a screw 67, and is used as waste toner through a joint 68. Housed in a box 69.

  [Method of controlling transfer current in secondary transfer section]

  FIG. 3 is a diagram schematically showing a configuration in the vicinity of the secondary transfer unit in the copying machine according to the embodiment of the present invention.

  Referring to FIG. 3, secondary transfer unit 70 in the copying machine of the present embodiment includes an HV (high voltage) power supply 75 in addition to the configuration shown in FIGS. The HV power supply 75 is electrically connected to each of the transfer roller 71 and the charge removal member 72. A predetermined voltage is applied to the transfer roller 71 by an HV power supply 75. In this state, when the recording sheet S passes between the intermediate transfer belt 64 and the transfer roller 71 in the direction indicated by the arrow from the bottom to the top in FIG. 3, the toner image on the intermediate transfer belt 64 is transferred to the recording sheet S. A transfer current Ic flows between the transfer roller 71 and the intermediate transfer belt 64.

  When the transfer current Ic flows between the transfer roller 71 and the intermediate transfer belt 64, the leakage current Ie also flows between the transfer roller 71 and the charge removal member 72 through the recording sheet S. As a result, a current It that is the sum of the transfer current Ic and the leakage current Ie flows through the transfer roller 71. The leakage current Ie flowing through the charge removal member 72 is input to the HV power supply 75. The HV power supply 75 controls the current It based on the leakage current Ie. Specifically, the HV power supply 75 adds the leakage current Ie input from the static elimination member 72 to the reference current (here, the current corresponding to the transfer current Ic), thereby setting it as the current It. That is, the HV power supply 75 outputs the current It so that the relationship It = Ic + Ie is established. Thereby, control is performed so that the transfer current Ic becomes constant.

  Further, the control method of the transfer current in the secondary transfer portion may be, for example, a control method having the following configuration in addition to the control method having the configuration shown in FIG. FIG. 4 is a diagram schematically showing another configuration in the vicinity of the secondary transfer portion in the copying machine according to the embodiment of the present invention.

  Referring to FIG. 4, secondary transfer unit 70 in the copying machine of the present embodiment includes a current measurement unit 73, a current measurement unit 74, an HV power supply 75, in addition to the configuration shown in FIGS. Is included. The current measurement unit 73 is electrically connected to the transfer roller 71, the current measurement unit 74 is electrically connected to the charge removal member 72, and the HV power source 75 is electrically connected to each of the current measurement units 73 and 74. It is connected. In this configuration, the current It is measured by the current measuring unit 73, and the leakage current Ie is measured by the current measuring unit 74. Then, the current It is controlled by the HV power supply 75 based on the value of the leakage current Ie measured by the current measuring unit 74 while the value of the current It measured by the current measuring unit 73 is monitored. The current It is controlled so that the transfer current Ic (= It−Ie) becomes constant, for example.

  FIG. 5 is a diagram schematically showing an example of temporal changes in each of the current It and current Ie when a toner image is transferred to humidity control paper in an HH environment in the copying machine according to the embodiment of the present invention. . In FIG. 5, the horizontal axis indicates the passage of time, and the vertical axis indicates the current. In FIG. 5, arrows with arrows at the left and right ends in the horizontal direction indicate a time period during which the A3 size transfer material passes through the secondary transfer portion.

  In FIG. 5, the current It is controlled so that the substantial transfer current Ic (= It−Ie) becomes a constant current of 10 μA. Since the transfer current Ic is controlled at a constant current, even if the leakage current Ie increases in the humidity-controlled paper in the HH environment, the image transfer on the transfer material is less likely to be blurred due to insufficient transfer current, and transfer defects can be suppressed. is there.

  The control of the current It based on the current Ie is performed by an electric circuit electrically connected to the HV power supply, software installed in the HV power supply, or software installed in a computer electrically connected to the HV power supply. It may be done. In particular, when the current It is controlled by software, the control may be performed based on the B / W (black / white) ratio of the image formed on the transfer material. Further, the current It may be controlled based on the environment such as temperature and humidity inside and / or outside the copying machine detected by the sensor, the type of paper, and the like.

  [Configuration of static elimination member]

  FIG. 6 is a diagram schematically illustrating an example of the configuration of the charge removal member.

  Referring to FIG. 6, the charge removal member 72 is for ensuring sheet separation and charge removal, and includes a plurality of electrodes 72 a for discharging the recording sheet S. The electrodes 72a are arranged at equal intervals and are arranged in parallel with each other. Each of the electrodes 72a extends from the main body 72b in the direction of the recording sheet S (upward in FIG. 6). In addition, as a static elimination member, the thing of the shape of a brush type or a plate type other than the structure where the sawtooth-shaped electrode shown in FIG. 6 arranged in a line as a static elimination needle may be used.

  [Effects of the present embodiment]

  Hereinafter, the effect of the present embodiment will be described in comparison with the transfer current control method in the comparative example.

  FIG. 7 is a diagram schematically showing the structure in the vicinity of the secondary transfer portion in the copying machine of the comparative example.

  Referring to FIG. 7, in the configuration of the secondary transfer unit 70 in the comparative example, the voltage applied from the HV power supply 75 to the transfer roller 71 is constant, whereby the current It flowing through the transfer roller 71 is constant-current controlled. This is different from the configuration of the secondary transfer portion of the present embodiment shown in FIG.

  FIG. 8 is a diagram schematically illustrating an example of temporal changes in each of the current It and the current Ie when a toner image is transferred to humidity control paper in an HH environment in the copying machine of the comparative example. In FIG. 8, the horizontal axis indicates the passage of time, and the vertical axis indicates the current. In FIG. 8, arrows with arrows at the left and right ends in the horizontal direction indicate a time period during which the A3 size transfer material passes through the secondary transfer portion.

  The current It applied to the transfer roller as a transfer current for plain paper is controlled at a constant current of 10 μA. When an image is formed on humidity control paper under this constant current control, the leakage current Ie is small because the resistance decrease of the humidity control paper (recording sheet S) is small in an NN (normal) environment or an LL (low temperature, low humidity) environment. The transfer current Ic is substantially the same as the current It. For this reason, the influence due to insufficient transfer current is very small. However, in the HH environment, the resistance of the humidity control paper is greatly reduced, and the surface resistance ρs (1 ΩΩ) is as low as 10 or less. For this reason, the leakage current Ie increases. In FIG. 8, the current Ie increases to about 3 μA, and the value of the substantial transfer current Ic (current flowing into the image carrier) (= It−Ie) decreases to about 7 μA. As a result, blurring of the image on the transfer material due to insufficient transfer current occurs. In general, a charge eliminating member is installed after transfer for the purpose of paper separation and charge removal, and the charge of the paper is released. However, the current for releasing the charge of the paper is a small amount in a normal environment. Specifically, this current is related to the system speed and is about 0.5 to 1 μA at 100 mm / sec.

  On the other hand, the image forming apparatus according to the present embodiment transfers a toner image formed on an image carrier onto a transfer material by a contact transfer unit, and has a saw-tooth shape as a charge eliminating member for ensuring sheet separation / discharge characteristics. An image forming apparatus in which static elimination needles having electrodes arranged in a line are installed, and a difference (It−Ie) between a current It flowing through a transfer roller and a leakage current Ie flowing from a transfer material to a static elimination member becomes constant. Thus, it is characterized by constant current control. As a result, the leakage current Ie flowing through the charge removal member during printing is detected, and the current value of the current Ie is fed back to the current value of the current It flowing through the transfer roller. As a result, even if the transfer current leaks from the static eliminator on low resistance paper such as transfer materials conditioned in a high humidity environment, a substantial transfer current for transferring the toner is secured and the transfer current is kept constant. Can be controlled. Further, it is possible to suppress the occurrence of transfer failure such as image fading even in a low resistance paper such as a transfer material conditioned in a high humidity environment while securing the paper separation / static discharge performance. The control method according to the present embodiment is a control method that can suppress blurring of an image due to insufficient transfer current in an apparatus that controls the current that flows through the transfer roller due to leakage of the transfer current to the charge removal member in a high humidity environment. This is an inexpensive control method that does not require application of a voltage to the static elimination bias.

  In addition, according to the present embodiment, since it is not necessary to apply a bias to the static elimination member as in Patent Document 1, an expensive configuration such as an HV transformer can be omitted, and the configuration of the apparatus is simplified and the cost is reduced. Can be achieved. Further, in order to prevent blurring of the image on the transfer material, a control method for controlling the applied voltage of the neutralizing bias based on the current value flowing through the neutralizing member to prevent the transfer current from leaking from the neutralizing member more than necessary. This is a method for dealing with only a very rare case of humidity control paper in a high humidity environment. Nevertheless, a high voltage transformer for applying a voltage to the static elimination bias is required, leading to an increase in cost. In this embodiment, such an increase in cost can be suppressed.

  Furthermore, by adopting the charge eliminating member 72 having the configuration shown in FIG. 6, the charge removal of the recording sheet S is facilitated.

  In the above-described copying machine, the case where the image carrier is an intermediate transfer belt has been described. However, a photosensitive member, an intermediate transfer member, or the like may be used as the image carrier. Further, each component of the image forming apparatus can be changed as appropriate according to the apparatus. In the present embodiment, the current measurement unit 73 measures the current It and the current measurement unit 74 measures the current Ie. However, in the present invention, the current measurement unit 73 is based on the first current flowing through the charge removal member. Thus, the second current flowing through the transfer unit may be controlled.

  Furthermore, the image forming apparatus of the present invention is not limited to the above-described copying machine, and may be a monochrome / color copying machine, a printer, a facsimile, or a complex machine thereof.

  The above embodiment should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 10 Image reader part 13 Panel part 20 Printer part 30 Control part 33 Image memory 40 Image process part 40Y-40K Image formation part 41Y-41K Photosensitive drum 42Y-42K Charge charger 43Y-43K Developer 44Y-44K Cleaner 45Y-45K Transfer Roller 46Y-46K Laser diode 47C-47K Exposure scanning part 50 Paper feed part 51 Paper feed cassette 52 Paper feed roller 53 Registration roller 60 Intermediate transfer unit 61 Drive roller 62 Driven roller 63 Tension spring 64 Intermediate transfer belt 66 Intermediate transfer belt cleaner 67 Screw 68 Joint 69 Waste toner box 70 Secondary transfer part 71 Transfer roller 72 Static elimination member 72a Electrode 72b Main body part 73, 74 Current measurement part 75 HV power supply 80 Fixing part 82 Fixing inrush Id 83 conveying guide S recording sheet SE1 sheet detecting sensor

Claims (3)

Transfer means for transferring the toner image formed on the image carrier to a transfer material;
A charge removal member for discharging the transfer material onto which the toner image has been transferred;
An image forming apparatus comprising: a current control unit configured to control a second current flowing through the transfer unit based on a first current flowing through the charge eliminating member.   The image forming apparatus according to claim 1, wherein the current control unit controls the second current so that a difference between the first current and the second current is constant. The image forming apparatus according to claim 1, wherein the charge removal member includes a plurality of electrodes for discharging electricity, and each of the plurality of electrodes is arranged in parallel with each other.

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