JP2009031785A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of preventing the occurrence of transfer dust due to release discharge stably for a long time without using a current detection means. <P>SOLUTION: This image forming device is provided with an intermediate transfer belt 61 carrying a toner image, a transfer unit 60 transferring the toner image carried by the intermediate transfer belt onto a recording paper P electrostatically, a discharging member 80 discharging the recording paper P having the toner image transferred by the transfer unit 60 on it electrostatically, and a discharging bias power supply circuit 81 applying an electrostatically discharging bias on the discharging member 80. The discharging bias power supply circuit 81 is constituted to count cumulative electrostatically discharging processing time by the discharging member 81 and control an output value of a discharging bias based on the results of counting the time. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, or a printer that discharges a recording member after a toner image on an image carrier has been transferred by a discharging member.

  2. Description of the Related Art Conventionally, there is known an image forming apparatus that transfers a toner image carried on an image carrier such as a photoreceptor or an intermediate transfer belt onto a recording sheet as a recording member as follows. That is, the toner image on the image carrier is electrostatically transferred to the recording paper while the recording paper is sandwiched in a transfer nip formed by the image carrier and an abutting member such as a transfer roller brought into contact therewith. Thereafter, when the recording paper to which the toner image has been transferred is separated from the image carrier, peeling discharge may occur between the image carrier and the recording paper to which electric charge is applied in the transfer nip. When such a peeling discharge occurs, a phenomenon called transfer dust that causes the toner in the image to scatter around the toner image on the recording paper occurs and the image is disturbed. Therefore, a neutralizing bias is applied to the neutralizing member while the neutralizing member is in contact with the recording paper near the exit of the transfer nip. This suppresses the occurrence of peeling discharge by discharging the recording paper when separated from the image carrier.

  In an image forming apparatus having such a configuration, foreign matters such as paper dust, discharge products, and toner adhere to the surface of the static elimination member over time, so that a discharge is gradually generated between the static elimination member and the recording paper. It becomes difficult. Then, with long-term use, the static elimination capability of the static elimination member will fall gradually.

  On the other hand, the image forming apparatus described in Patent Literature 1 or Patent Literature 2 measures a static elimination current flowing between the static elimination member and the static elimination object at a predetermined timing, and adjusts the static elimination bias based on the measurement result. It has become. In such a configuration, it is detected based on the decrease in the charge removal current that the charge removal capability of the charge removal member has decreased. And by raising the static elimination bias according to the detection result, it is possible to suppress the occurrence of the static elimination failure due to the adhesion of foreign matter to the static elimination member.

JP 2000-214690 A JP 2005-241947 A

  However, in such a configuration, current detection means for detecting the static elimination current is required, which increases the cost. The present invention has been made in view of the above background, and an object of the present invention is to stably suppress generation of transfer dust caused by peeling discharge over a long period of time without using a current detection means. It is an object of the present invention to provide an image forming apparatus capable of performing the above.

In order to achieve the above object, an invention according to claim 1 is directed to an image carrier that carries a toner image, a transfer unit that electrostatically transfers a toner image on the image carrier to a recording member, and the transfer unit. In the image forming apparatus, comprising: a charge eliminating member that neutralizes the recording member onto which the toner image has been transferred, and a charge eliminating bias applying unit that applies a charge eliminating bias to the charge eliminating member. The present invention is characterized in that there is provided time-counting means and static elimination bias control means for controlling the static elimination bias output from the static elimination bias applying means based on the time measurement result by the static elimination timing means.

According to a second aspect of the invention, an image carrier that carries a toner image, a transfer unit that electrostatically transfers the toner image on the image carrier to a recording member, and the toner image is transferred by the transfer unit. In addition, in an image forming apparatus including a static elimination member that neutralizes the recording member and a static elimination bias application unit that applies a neutralization bias to the static elimination member, the cumulative number of recording members that have been neutralized by the static elimination member is counted. It is characterized in that there is provided a static elimination counting means and a static elimination bias control means for controlling the static elimination bias output from the static elimination bias applying means based on a counting result by the counting means.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the static elimination bias control means is configured to perform a control to increase the static elimination bias as the timing result or the counting result increases. It is characterized by comprising.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the discharging member is a member in which an edge of a thin plate-like conductive member is brought into contact with the recording member. It is a feature.
According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, as the charge eliminating member, an edge of a thin plate-like conductive member is opposed to the recording member via a predetermined gap. , Is used.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects of the present invention, the neutralizing bias applying means that applies only a DC bias to the neutralizing member is used. .
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, a transfer time measuring means for measuring a cumulative transfer processing time by the transfer means is provided, in addition to the time measurement result or the count result. The static elimination bias control means is configured to control the static elimination bias on the basis of a timing result by the transcription timing means.
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, a transfer counting unit that counts a cumulative number of recording members transferred by the transfer unit is provided, and the timing result is Alternatively, the static elimination bias control means is configured to control the static elimination bias based on the count result by the transfer counting means in addition to the count result.
According to a ninth aspect of the present invention, in the image forming apparatus of the seventh or eighth aspect, control is performed to increase the static elimination bias as the time measurement result by the transfer time measuring means or the count result by the transfer counting means becomes longer. Thus, the static elimination bias control means is configured as described above.
According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the first to ninth aspects, an endless belt member is used as the image carrier, and the back surface of the belt member is used as the transfer means. While applying a transfer bias having the same polarity as the normal charging polarity of the toner to the contact transfer bias member, the recording is sandwiched in the transfer nip between the front surface of the belt member and the contact member in contact with the belt member A member that transfers a toner image on the front surface to a member, and a combination of the belt member, the transfer bias member, and the corresponding contact member, and an electric resistance value of the transfer bias member and the belt member The sum of the electrical resistance value and the contact resistance member is larger than the electrical resistance value of the corresponding contact member.

  In these inventions, with all of the invention specific matters of claim 1, the generation of transfer dust due to peeling discharge can be stabilized over a long period of time without using a current detecting means by the following action. Can be suppressed. That is, the amount of foreign matter such as paper dust adhered to the static elimination member gradually increases with the use of the static elimination member. Therefore, a correlation is established between the reduction amount of the static elimination capability of the static elimination member and the accumulated static elimination processing time by the static elimination member. The cumulative charge removal processing time referred to here is the cumulative time during which the charge removal member is brought into contact with the recording member while the charge removal bias is applied to the charge removal member. In the invention according to claim 1, in which the static elimination bias applied to the static elimination member is controlled based on the accumulated static elimination processing time, the static elimination bias is increased with time in accordance with a decrease in the capability of the static elimination member with time, thereby increasing the current. Generation of transfer dust due to peeling discharge can be stably suppressed over a long period of time without using a detection means.

  In addition, with all of the specific matters of the invention of claim 2, by the following action, generation of transfer dust due to peeling discharge is stably suppressed over a long period of time without using a current detecting means. be able to. That is, as the cumulative number of recording members that have been subjected to static elimination processing by the static elimination member increases, the above-described cumulative static elimination processing time increases. That is, a correlation is also established between the amount of reduction in the charge removal capability of the charge removal member and the cumulative number of recording members that have undergone charge removal processing. Also in the invention according to claim 2, which is controlled based on the cumulative number, peeling discharge can be performed without using a current detecting means by increasing the static elimination bias with time in accordance with the deterioration of the static elimination member over time. It is possible to stably suppress the generation of transfer dust due to the occurrence of a long period of time.

Hereinafter, a first embodiment of a copier that forms an image by an electrophotographic method will be described as an image forming apparatus to which the present invention is applied.
First, the basic configuration of the copier according to the first embodiment will be described. FIG. 1 is a schematic configuration diagram showing a copying machine according to the first embodiment. The copying machine includes a printer unit 1, a blank paper supply device 100, and a document conveyance reading unit 150. The document conveyance reading unit 150 includes a scanner 160 as a document reading device fixed on the printer unit 1 and an ADF 170 as a document conveyance device supported by the scanner 160.

  The blank paper supply apparatus 100 includes two paper feed cassettes 102 and 103, two pairs of separation roller pairs 104 and 105, a paper feed path 106, a plurality of transport roller pairs 107, and the like arranged in multiple stages in the paper bank 101. is doing. Each of the two paper feed cassettes 102 and 103 is housed in a paper bundle in which a plurality of recording papers (not shown) are stacked. Based on the control signal from the printer unit 1, the sending rollers 102 a and 103 a are driven to rotate, and the uppermost recording paper in the paper bundle is sent out toward the paper feed path 106. The fed recording paper is separated into one sheet by the pair of separation rollers 104 and 105 and then enters the paper feed path 106. Then, the sheet is fed to the first receiving branch path 30 of the printer unit 1 through the conveyance nips of the plurality of conveyance roller pairs 107 provided in the sheet feeding path 106.

  The printer unit 1 includes four process units 2Y, 2M, 2C, and 2K for forming yellow (Y), magenta (M), cyan (C), and black (K) toner images. Also, the first receiving branch path 30, the receiving conveyance roller pair 31, the manual feed tray 32, the manual separation roller pair 33, the second receiving branch path 34, the manual conveyance roller pair 35, the pre-transfer conveyance path 36, the registration roller pair 37, the conveyance A belt unit 39, a fixing unit 43, a switchback device 46, a discharge roller pair 47, a discharge tray 48, a switching claw 49, an optical writing unit 50, a transfer unit 60, and the like are also provided. The process units 2Y, 2M, 2C, and 2K have drum-shaped photoreceptors 3Y, 3M, 3C, and 3K that are latent image carriers arranged at a predetermined pitch.

  A pre-transfer conveyance path 36 for conveying a recording sheet immediately before a secondary transfer nip, which will be described later, is branched into a first reception branch path 30 and a second reception branch path 34 on the upstream side in the paper conveyance direction. The recording paper fed from the paper feed path 106 of the blank paper supply device 100 is received by the first receiving branch path 30 and then passed through the transport nip of the receiving transport roller pair 31 disposed in the first receiving branch path 30. Then, it is sent to the pre-transfer conveyance path 36.

  A manual feed tray 32 is disposed on the side surface of the housing of the printer unit 1 so as to be openable and closable with respect to the housing. The uppermost recording paper in the manually fed paper bundle is sent out toward the second receiving / branching path 34 by the feed roller 32 a of the manual feed tray 32. After being separated into one sheet by the manual feed separation roller pair 33 and sent to the second receiving branch path 34, it passes through the transport nip of the manual feed roller pair 35 disposed in the second receiving branch path 34. Then, it is sent to the pre-transfer conveyance path 36.

  The optical writing unit 50 includes a laser diode, a polygon mirror, various lenses (not shown), etc., and is based on image information read by a scanner 160 described later or image information sent from an external personal computer. Drive the laser diode. Then, the photoconductors 3Y, M, C, and K of the process units 2Y, M, C, and K are optically scanned. Specifically, the photoconductors 3Y, 3M, 3C, and 3K of the process units 2Y, 2M, 2C, and 2K are rotated in the counterclockwise direction in the drawing by driving means (not shown). The optical writing unit 50 performs an optical scanning process by irradiating the driven photosensitive members 3Y, 3M, 3C, and 3K while deflecting laser light in the direction of the rotation axis. Thereby, electrostatic latent images based on Y, M, C, and K image information are formed on the photoreceptors 3Y, 3M, 3C, and 3K.

  FIG. 2 is a partially enlarged configuration diagram illustrating a part of the internal configuration of the printer unit 1 in an enlarged manner. The process units 3K, Y, M, and C for the respective colors support the photosensitive member as a latent image carrier and various devices arranged around it on a common support as a unit. It is detachable from the printer unit main body. The configuration is the same except that the colors of the toners used are different. Taking the process unit 2Y for Y as an example, this has a developing device 4Y for developing an electrostatic latent image formed on the surface of the photoreceptor 3Y into a Y toner image in addition to the photoreceptor 3Y. Further, it also includes a drum cleaning device 18Y that cleans transfer residual toner adhering to the surface of the photoreceptor 3Y after passing through a Y primary transfer nip described later. This copying machine has a so-called tandem configuration in which four process units 2Y, 2M, 2C, and 2K are arranged along an endless movement direction with respect to an intermediate transfer belt 61 described later.

  FIG. 3 is an enlarged configuration diagram showing the Y process unit 2Y. As shown in the figure, the process unit 2Y includes a developing device 4Y, a drum cleaning device 18Y, a charge eliminating lamp 17Y, a charging roller 16Y, and the like around the photoreceptor 3Y.

  As the photoreceptor 3 </ b> Y, a drum-like member is used in which a photosensitive layer is formed by applying a photosensitive organic photosensitive material to a raw tube such as aluminum. However, an endless belt may be used.

  The developing device 4Y develops a latent image using a two-component developer (hereinafter simply referred to as developer) containing a magnetic carrier (not shown) and non-magnetic Y toner. And it has the stirring part 5Y which conveys the developer accommodated in the inside while stirring, and the developing part 9Y which develops the electrostatic latent image on the photoreceptor 3Y. The developing device 4Y may be of a type that performs development with a one-component developer that does not include a magnetic carrier, instead of the two-component developer.

  The agitating unit 5Y is provided at a position lower than the developing unit 9Y. The first conveying screw 6Y and the second conveying screw 7Y are arranged in parallel to each other, a partition plate provided between these screws, and the bottom surface of the casing. The toner density sensor 8Y and the like provided in the printer.

  The developing unit 9Y includes a developing roll 10Y that faces the photoreceptor 3Y through the opening of the casing, a doctor blade 13Y that makes its tip close to the developing roll 10Y, and the like. The developing roll 10Y includes a cylindrical developing sleeve 11Y made of a nonmagnetic material, and a magnet roller 12Y provided inside the developing roll 11Y so as not to rotate. The magnet roller 12Y has a plurality of magnetic poles arranged in the circumferential direction. Each of these magnetic poles applies a magnetic force to the developer on the sleeve at a predetermined position in the rotational direction. As a result, the developer sent from the stirring unit 5Y is attracted and carried on the surface of the developing sleeve 11Y, and a magnetic brush along the magnetic field lines is formed on the sleeve surface.

  The magnetic brush is transported to a developing region facing the photoreceptor 3Y after being regulated to an appropriate layer thickness when passing through a position facing the doctor blade 13Y as the developing sleeve 11Y rotates. Then, Y toner is transferred onto the electrostatic latent image by the potential difference between the developing bias applied to the developing sleeve 11Y and the electrostatic latent image on the photoreceptor 3Y, thereby contributing to development. Further, as the developing sleeve 11Y rotates, the developing sleeve 9Y returns to the developing portion 9Y again, and after the release from the sleeve surface due to the influence of the repulsive magnetic field formed between the magnetic poles of the magnet roller 12Y, the developing sleeve 11Y returns to the stirring portion 5Y. An appropriate amount of toner is supplied to the developer in the stirring unit 5Y based on the detection result of the toner density sensor 8Y.

  As the drum cleaning device 18Y, a system that presses the cleaning blade 20Y made of polyurethane rubber against the photoreceptor 3Y is used, but another system may be used. For the purpose of improving the cleaning property, this copying machine employs a system having a fur brush 19Y whose outer peripheral surface is in contact with the photoreceptor 3Y so as to be rotatable in the direction of the arrow in the figure. The fur brush 19Y also serves to apply the lubricant to the surface of the photoreceptor 3Y while scraping the lubricant from a solid lubricant (not shown) into a fine powder.

  The toner attached to the fur brush 19Y is transferred to the electric field roller 21Y to which a bias is applied while rotating in contact with the fur brush 19Y in the counter direction. And after scraping off from the electric field roller 21Y by the scraper 22Y, it falls on the collection | recovery screw 23Y.

  The collection screw 23Y conveys the collected toner toward the end of the drum cleaning device 18Y in the direction perpendicular to the drawing surface, and delivers it to an external recycling conveyance device. A recycle conveyance device (not shown) sends the delivered toner to the developing device 4Y for recycling.

  The neutralization lamp 17Y neutralizes the photoreceptor 3Y by light irradiation. The surface of the photoreceptor 3Y that has been neutralized is uniformly charged by the charging roller 16Y, and then subjected to optical scanning by the optical writing unit described above. The charging roller 16Y is rotationally driven while receiving a charging bias from a power source (not shown). Instead of the charging method using the charging roller 16Y, a scorotron charger method in which charging processing is performed in a non-contact manner on the photoreceptor 3Y may be employed.

  In FIG. 2 described above, Y, M, C, and K toner images are formed on the surfaces of the photoreceptors 3Y, M, C, and K of the four process units 2Y, 2M, 2C, and 2K by the processes described above. Is formed.

  Below the four process units 2Y, 2M, 2C, and 2K, a transfer unit 60 as transfer means is disposed. The transfer unit 60 rotates in the clockwise direction in the drawing by rotating one of the rollers while contacting an intermediate transfer belt, which is an image carrier stretched by a plurality of rollers, with the photoreceptors 3Y, 3M, 3C, and 3K. Move endlessly in the direction. As a result, primary transfer nips for Y, M, C, and K in which the photoreceptors 3Y, 3M, 3C, and 3K contact the intermediate transfer belt 61 are formed.

  In the vicinity of the primary transfer nips for Y, M, C, and K, the intermediate transfer belt 61 is moved to the photosensitive members 3YY, M, C, and K by primary transfer rollers 62Y, M, C, and K disposed inside the belt loop. Pressing toward K. A primary transfer bias is applied to the primary transfer rollers 62Y, 62M, 62C, 62K by a power source (not shown). As a result, a primary transfer electric field for electrostatically moving the toner images on the photoreceptors 3Y, 3M, 3C, and 3K toward the intermediate transfer belt 61 is formed in the primary transfer nips for Y, M, C, and K. Has been.

  In the drawing, a toner image is formed on each of the primary transfer nips on the front surface of the intermediate transfer belt 61 that sequentially passes through the primary transfer nips for Y, M, C, and K with endless movement in the clockwise direction. Are sequentially superimposed and primarily transferred. By this primary transfer of superposition, a four-color superposed toner image (hereinafter referred to as a four-color toner image) is formed on the front surface of the intermediate transfer belt 61.

  A secondary transfer counter roller 72 as a contact member is disposed below the intermediate transfer belt 61 in the drawing, and the belt is placed at a place where the intermediate transfer belt 61 is wound around the secondary transfer roller 68. A secondary transfer nip is formed in contact with the surface. As a result, a secondary transfer nip is formed in which the front surface of the intermediate transfer belt 61 and the secondary transfer counter roller 72 abut.

  In the loop of the intermediate transfer belt 61, a secondary transfer roller 68 as a transfer bias member is subjected to secondary transfer having the same polarity as the normal charging polarity of the toner (negative polarity in this example) by a secondary transfer power supply circuit (not shown). A bias is applied. On the other hand, the secondary transfer counter roller 72 that forms the secondary transfer nip while being in contact with the front surface of the belt is grounded. As a result, a secondary transfer electric field is formed in the secondary transfer nip for electrostatically moving negative toner from the belt side toward the secondary transfer counter roller 72 side.

  On the right side of the secondary transfer nip in the drawing, the above-described registration roller pair (not shown) is disposed, and the recording paper sandwiched between the rollers can be synchronized with the four-color toner image on the intermediate transfer belt 61. Send to the secondary transfer nip. In the secondary transfer nip, the four-color toner image on the intermediate transfer belt 61 is secondarily transferred onto the recording paper under the influence of the secondary transfer electric field and the nip pressure, and becomes a full color image combined with the white color of the recording paper.

  The transfer residual toner that has not been transferred to the recording paper at the secondary transfer nip adheres to the front surface of the intermediate transfer belt 61 that has passed through the secondary transfer nip. This transfer residual toner is cleaned by a belt cleaning device 75 in contact with the intermediate transfer belt 61.

  In FIG. 1 described above, the recording paper that has passed through the secondary transfer nip is separated from the intermediate transfer belt 61 and transferred to the transport belt unit 39. The transport belt unit 39 moves the endless transport belt 40 endlessly in the counterclockwise direction in the figure by the rotational drive of the drive roller 41 while being stretched by the drive roller 41 and the driven roller 42. The recording paper delivered from the secondary transfer nip is conveyed along with the endless movement of the belt while being held on the belt upper tension surface, and delivered to the fixing unit 43.

  In the fixing unit 43, a fixing belt stretched by a driving roller and a heating roller containing a heat generation source is moved endlessly in the clockwise direction in the drawing as the driving roller is driven to rotate. The pressure roller 45 disposed below the fixing belt is brought into contact with the lower tension surface of the fixing belt to form a fixing nip. The recording paper received by the fixing unit 43 is pressed or heated in the fixing nip, whereby the full-color image on the surface is fixed. Then, it is sent out from the fixing unit 43 toward the switching claw 49.

  The switching claw 49 is swung by a solenoid (not shown), and the recording paper conveyance path is switched between the paper discharge path and the reversing path with the swing. When the paper discharge path is selected by the switching claw 49, the recording paper fed out from the fixing unit 43 passes through the paper discharge path and the paper discharge roller pair 47 and is then discharged to the outside of the apparatus and discharged to the paper discharge tray. 48 is stacked.

  A switchback device 46 is disposed below the fixing unit 43 and the conveyor belt unit 39. When the switchback path is selected by the switching claw 49, the recording paper fed out from the fixing unit 43 is turned upside down via the reversing path and then sent to the switchback device 46. Then, the image enters the secondary transfer transfer nip again, and the secondary transfer processing and fixing processing of the image are performed on the other surface.

  The scanner 160 fixed on the printer unit 1 has a fixed reading unit 161 and a moving reading unit 162 as reading means for reading an image of a document (not shown). A fixed reading unit 161 having a light source, a reflection mirror, an image reading sensor such as a CCD, and the like is disposed immediately below a first contact glass (not shown) fixed to the upper wall of the casing of the scanner 160 so as to contact the document. . Then, when the document conveyed by the ADF 170 passes over the first contact glass, the light emitted from the light source is sequentially reflected by the document surface and is received by the image reading sensor via the plurality of reflection mirrors. Thus, the original is scanned without moving the optical system including the light source and the reflecting mirror.

  On the other hand, the moving reading unit 162 is disposed directly below a second contact glass (not shown) fixed to the upper wall of the casing of the scanner 160 so as to come into contact with the document, and an optical system including a light source, a reflection mirror, and the like. It can be moved in the left-right direction in the figure. Then, in the process of moving the optical system from the left side to the right side in the figure, the light emitted from the light source is reflected by a document (not shown) placed on the second contact glass and then passed through a plurality of reflecting mirrors. The image is received by an image reading sensor fixed to the scanner body. Accordingly, the original is scanned while moving the optical system.

  Since this copying machine having the above basic configuration employs a so-called tandem method, it is important to prevent the occurrence of color misregistration by accurately superimposing the toner images of the respective colors on the intermediate transfer belt 61. It is.

Next, a characteristic configuration of the copying machine will be described.
In FIG. 2 shown above, near the outlet of the secondary transfer nip due to the contact between the front surface of the intermediate transfer belt 61 and the secondary transfer counter roller 72 (near the downstream end in the belt moving direction in the nip), A neutralizing member 80 is provided in contact with the recording paper P coming out of the secondary transfer nip. The static eliminating member 80 is made of a thin metal plate with sharp edges. The static elimination member 80 is electrically connected to a static elimination bias power supply circuit 81 which is a static elimination bias applying means and is a static elimination bias control means.

  The static elimination bias power supply circuit 81 includes a high voltage power supply circuit for outputting a static elimination bias consisting only of a high DC voltage, an output voltage control circuit consisting of an AISC (Application Specific Integrated Circuit), an IC memory for data storage, and the like. Have. Then, in anticipation of the timing when the leading edge of the recording paper P is discharged from the secondary transfer nip, application of a static elimination bias consisting only of a DC voltage to the static elimination member 80 starts. In addition, the application of the neutralizing bias is stopped at the timing when the trailing edge of the recording paper P passes through the contact position with the neutralizing member 80. The timing at which the leading edge of the recording paper P is discharged from the secondary transfer nip and the timing at which the trailing edge of the recording paper P passes through the contact position with the charge eliminating member 80 are obtained based on the detection result by a resist sensor (not shown). Specifically, a registration sensor (not shown) for detecting the recording paper conveyed in the pre-transfer conveyance path 36 is disposed in the vicinity of the registration roller pair 37 shown in FIG. This registration sensor is connected to the main control unit of the copying machine. Based on the timing at which the registration sensor starts to detect the leading edge of the recording paper P, the main control unit stops driving the registration roller pair 37 and sends a leading edge detection signal to the static elimination bias power supply circuit 81. Further, based on the timing at which the registration sensor no longer detects the trailing edge of the recording paper P, a trailing edge passing signal is sent to the static elimination bias 81. The output voltage control circuit of the static elimination bias power supply circuit 81 calculates the timing at which the leading edge of the recording paper P is discharged from the secondary transfer nip based on the leading edge detection signal sent from the main controller. Further, the timing at which the trailing edge of the recording paper P passes through the position facing the neutralization member 80 is calculated based on the trailing edge passage signal sent from the main control unit.

  The neutralizing member 80 is disposed at a position where the leading end of the recording paper P faces the recording paper P through a predetermined gap when the recording paper P that has passed through the secondary transfer nip passes directly above the neutralizing member 80. At this time, when a charge removal bias is applied to the charge removal member 80, a discharge is generated between the charge removal member 80 and the recording paper P. As a result, the recording paper P that has received the secondary transfer current in the secondary transfer nip is neutralized. In the copying machine, the recording paper P is charged in the secondary transfer nip with a polarity opposite to the normal charging polarity (negative polarity in this example) of the toner. Therefore, the neutralization bias power supply circuit 81 applies a neutralization bias having the same polarity (negative polarity) as the normal charging polarity of the toner to the recording paper P.

  By eliminating the charge of the recording paper P in this way, it is possible to suppress the occurrence of peeling discharge when the recording paper P is separated from the intermediate transfer belt 61 as an image carrier. However, if foreign matter such as paper dust, discharge products, and toner adheres to the charge removal member 80 with long-term use, the discharge between the charge removal member 80 and the recording paper P cannot be performed satisfactorily. come. As a result, a peeling discharge due to the charge removal failure of the recording paper P is generated, and transfer dust is generated in the toner image on the recording paper P.

  FIG. 4 is an enlarged schematic view showing the vicinity of the edge of the toner image causing transfer dust. In the figure, reference numeral E denotes an edge portion of the toner image. Reference numeral F denotes a boundary between the edge portion of the toner image and the solid recording paper surface (non-image portion). Reference numeral G denotes a transfer dust due to the toner scattered from the edge portion of the toner image to the surrounding non-image area. When such transfer dust occurs, the edge of the toner image is blurred, and the image quality is significantly deteriorated.

  The inventors attached a current measuring device for measuring a static elimination current flowing between the static elimination member 80 and the recording paper P to the test machine having the same configuration as the printer unit 1 shown in FIG. Then, while printing out a predetermined test image, the relationship between the static elimination current and the transfer dust caused by the peeling discharge was examined. Then, it was found that when the charge removal current became 1.5 [μA] or less due to deterioration of the charge removal member 80 (foreign matter adhesion), noticeable transfer dust was generated.

  FIG. 5 is a graph showing the relationship between the static elimination bias application time and the static elimination current measured value confirmed by the inventors' experiment. This static elimination bias application time is the same as the cumulative static elimination processing time described above. The figure shows the result of continuous printing while applying a static elimination bias consisting of a DC voltage of −3 [kV] until the static elimination bias application time reaches 50 hours, and −1.5 [kV]. It shows the result when continuous printing is performed while applying a static elimination bias comprising a DC voltage. It can be seen that in any static elimination bias, the static elimination current decreases as the static elimination bias application time, that is, the cumulative static elimination processing time increases. This is because, as the cumulative charge removal time increases, the amount of foreign matter adhered to the surface of the charge removal member 80 gradually increases, so that the charge removal capability of the charge removal member 80 gradually decreases.

  FIG. 6 is a graph showing the relationship between the transfer bias application time and the measured static elimination current value confirmed by the inventors' experiment. This transfer bias application time is the accumulated time when the secondary transfer bias is applied to the secondary transfer roller 68, and this is the same as the accumulated transfer processing time. This figure shows the result when continuous printing is performed while applying the secondary transfer bias to the secondary transfer roller 68 until the transfer bias application time reaches 50 hours. It can be seen that the static elimination current decreases as the transfer bias application time, that is, the cumulative transfer processing time increases. This is for the reason described below. That is, the secondary transfer roller 68 as a transfer bias member is formed by covering a peripheral surface of a metal cored bar with a conductive elastic layer made of a conductive elastic member. This conductive elastic layer is formed by dispersing carbon, an ionic conductive agent, or the like in an insulating elastic material such as rubber so as to exert a predetermined electric resistance. In such a secondary transfer roller 68, the conductive elastic layer (particularly due to the ionic conductive agent) gradually increases its own electrical resistance value as the voltage application time increases. That is, the secondary transfer roller 68 gradually increases the electrical resistance value as it deteriorates. Then, since the electric resistance of the path through which the charge removal current flows increases, the charge removal current hardly flows from the charge removal member 80 to the recording paper P. For this reason, the static elimination current decreases as the transfer bias application time increases.

  In view of the above experimental results, in this copying machine, the output voltage control circuit of the static elimination bias power supply circuit 81 is configured so as to perform the following control. That is, when the output voltage control circuit of the static elimination bias power supply circuit 81 starts the output of the static elimination bias from the high voltage power supply circuit, it starts measuring the static elimination bias application time (cumulative static elimination processing time). Further, when the output voltage control circuit stops the output of the static elimination bias from the high voltage power supply circuit, the output voltage control circuit stops counting the static elimination bias application time. Next, when the output of the static elimination bias from the high-voltage power supply circuit is started again, the timing of the static elimination bias application time is started with the timing of the static elimination bias application time so far as the initial value. Thus, the output voltage control means of the static elimination bias power supply circuit 81 functions as static elimination timing means for timing the static elimination bias application time (cumulative static elimination processing time) by the static elimination member 80.

  On the other hand, when the secondary transfer bias power supply circuit (not shown) that outputs the secondary transfer bias to the secondary transfer roller 68 starts the output of the secondary transfer bias, it measures the secondary transfer bias application time (cumulative transfer processing time). Start. When the output of the secondary transfer bias is stopped, the time measurement of the secondary transfer bias application time is stopped. Next, when the output of the secondary transfer bias is started again, the measurement of the secondary transfer bias application time is started with the measurement result of the secondary transfer bias application time so far as the initial value. In this way, the secondary transfer bias power supply circuit functions as a transfer timing unit that measures the secondary transfer bias application time, which is the cumulative transfer processing time by the transfer unit. The time measurement result of the secondary transfer bias application time is appropriately transferred to the output voltage control means of the static elimination bias power supply circuit 81.

The output voltage control means of the static elimination bias power supply circuit 81 controls the value of the static elimination bias output from the high voltage power supply circuit. Specifically, a data table as shown in the following Table 1 is stored in the IC memory of the static elimination bias power supply circuit 81.

  In Table 1, the bias correction value is for correcting a predetermined static elimination bias basic value. Specifically, a predetermined static elimination bias basic value is stored in the IC memory, and the output voltage control circuit applies the static elimination bias having the same value as the result obtained by multiplying the static elimination bias basic value by the bias correction value to the high voltage. Output from the power circuit. As the bias correction value, those corresponding to the time measurement result of the static elimination bias application time and the time measurement result of the secondary transfer bias application time sent from the secondary transfer bias power supply circuit are specified from Table 1 and used. For example, when both the static elimination bias application time and the secondary transfer bias application time are less than 35 hours, a bias correction value of “1.5” is selected as shown in Table 1. From Table 1, it can be seen that a larger bias correction value is selected as the static elimination bias application time increases. It can also be seen that a larger bias correction value is selected as the secondary transfer bias application time increases. Therefore, a larger value of the neutralization bias is applied as the neutralization bias application time and the secondary transfer bias application time increase.

  In such a configuration, the static elimination bias is increased with time in accordance with an increase in the static elimination bias application time (cumulative static elimination processing time), that is, in accordance with a decrease in the capability of the static elimination member 81 over time. Thereby, generation | occurrence | production of the transfer dust resulting from peeling discharge can be stably suppressed over a long period of time, without using an electric current detection means.

  Further, as the secondary transfer bias application time (cumulative transfer processing time) increases, that is, as the resistance of the secondary transfer roller 68 increases with time, the static elimination bias is increased with time. As a result, it is possible to suppress the occurrence of transfer dust due to a decrease in the charge removal capability due to the deterioration of the secondary transfer roller.

  The neutralizing bias application time stored in the IC memory of the neutralizing bias power supply circuit 81 is reset to zero by an operation of a service person or the like when the neutralizing member 80 is replaced with a new one. The secondary transfer bias application time stored in the IC memory of the secondary transfer bias power supply circuit is reset to zero by the operation of a service person or the like when the secondary transfer roller 68 is replaced with a new one. The

  As described above, the static elimination bias power supply circuit 81 that outputs a static elimination bias consisting only of a DC voltage is used. As the charge removal capability, AC charge removal using an AC voltage or AC superimposed DC charge removal is higher, but a high-voltage power supply for outputting an AC voltage is more expensive than a DC power supply. In this copying machine, since it is possible to stably remove the recording paper P over a long period of time even with a DC voltage by controlling the discharging bias, the cost is reduced by using an inexpensive DC power supply. .

FIG. 7 is a graph showing the relationship between the static elimination current and the image density confirmed by the experiments of the present inventors. In this experiment, as the combination of the secondary transfer roller 68, the intermediate transfer belt 61, and the secondary transfer counter roller 72, two types described below are used. That is, the first combination is a combination in which the sum of the electric resistance R1 of the secondary transfer roller 68 and the electric resistance R3 of the intermediate transfer belt 61 is larger than the electric resistance R2 of the secondary transfer counter roller 72 as a contact member. (R1 + R3> R2). In this combination, the sum of the electrical resistance R1 of the secondary transfer roller 68 and the n electrical resistance R3 of the intermediate transfer belt 61 is 10 ⁸ [Ω], whereas the electrical resistance of the secondary transfer counter roller 72 is R2 is 10 ⁶ [Ω]. The second type is a combination in which the sum of the electric resistance R1 of the secondary transfer roller 68 and the electric resistance R3 of the intermediate transfer belt 61 is smaller than the electric resistance R2 of the secondary transfer counter roller 72 (R1 + R3). <R2). In this combination, the sum of the electrical resistance R1 of the secondary transfer roller 68 and the electrical resistance R3 of the intermediate transfer belt 61 is 10 ⁷ [Ω], whereas the electrical resistance R2 of the secondary transfer counter roller 72 is 10 ⁷ [Ω]. Is 10 ⁸ [Ω].

  In any combination, there is a tendency that the image density decreases as the neutralization bias is increased. This is because when the charge removal bias is increased, a part of the charge removal current flows toward the secondary transfer roller 68 and a part of the toner on the recording paper P is reversely transferred to the intermediate transfer belt 61.

  From the graph, it can be seen that the combination of “R1 + R3> R2” has a lower reduction rate of the image density with respect to the increase of the static elimination bias. If “R1 + R3” is smaller than R2, the static elimination current is more likely to flow to the secondary transfer roller 68 than the secondary transfer counter roller 72, whereas if “R1 + R3” is greater than R2, the static elimination current is secondary transferred. This is because it becomes easier to flow toward the secondary transfer counter roller 72 than the roller 68.

  Therefore, in the present copying machine, a combination of the secondary transfer roller 68, the intermediate transfer belt 61, and the secondary transfer counter roller 72 having a relationship of “R1 + R3> R2” is used. Even if the condition “R1 + R3> R2” is satisfied, if the static elimination current is excessively increased, the image density is significantly reduced. According to the experiments by the present inventors, when the static elimination current is 5 [μA] or more, the image density is significantly reduced. In addition, it was confirmed that problems due to abnormal discharge occurred when the static elimination current was further increased. Therefore, it is desirable to keep the static elimination current within the range of 1.5 to 4 [μA].

  Next, a modification of the copier according to the first embodiment will be described. Unless otherwise specified below, the configuration of the copying machine according to the modification is the same as that of the first embodiment. In the copying machine according to the modification, the neutralizing member 80 is disposed at a position where the leading end of the neutralizing member 80 is brought into contact with the recording paper P that has passed through the secondary transfer nip. With this configuration, the recording paper P can be neutralized with a small neutralization bias as compared with the copying machine according to the first embodiment. On the other hand, in the copying machine according to the first embodiment, since the charge removal member 80 is disposed in a non-contact manner with respect to the recording paper P, the charge removal from the recording paper P compared to the copying machine according to the modified example. The amount of paper powder transferred to the member 80 is reduced. Thereby, the fall of the static elimination function of the static elimination member 80 by the adhering of paper dust can be suppressed.

Next, a copying machine according to a second embodiment to which the present invention is applied will be described. Unless otherwise specified below, the configuration of the copying machine according to the second embodiment is the same as that of the first embodiment.
Each time the main control unit of the printer unit 1 performs printing on one recording sheet P, the main control unit adds 1 to the accumulated transfer number and transmits a print count-up signal to the static elimination bias power supply circuit 81. That is, the main control unit functions as a transfer counting unit that counts the cumulative number of transfer sheets that is the cumulative number of recording sheets P that have been transferred by the transfer unit.

  When the output voltage control circuit of the static elimination bias power supply circuit 81 receives the print count-up signal sent from the main control unit, the time count result of the cumulative static elimination number, which is the cumulative number of the recording paper P that has undergone static elimination processing, is 1 Count up. That is, the output voltage control circuit functions as a static elimination counter that counts the cumulative static elimination number.

The output voltage control means of the static elimination bias power supply circuit 81 controls the value of the static elimination bias output from the high voltage power supply circuit. Specifically, a data table as shown in the following Table 2 is stored in the IC memory of the static elimination bias power supply circuit 81.

  In Table 2, when both the cumulative charge removal number and the cumulative transfer number are less than 80000, a bias correction value of “1.5” is selected. From Table 2, it can be seen that a larger bias correction value is selected as the cumulative number of static elimination sheets increases. It can also be seen that a larger bias correction value is selected as the cumulative number of transferred sheets increases. Therefore, as the cumulative charge removal number and the cumulative transfer number increase, a larger value of charge removal bias is applied.

  In such a configuration, the static elimination bias is increased with time in accordance with an increase in the cumulative number of static elimination sheets, that is, in accordance with a decrease in the capability of the static elimination member 81 over time. Thereby, generation | occurrence | production of the transfer dust resulting from peeling discharge can be stably suppressed over a long period of time, without using an electric current detection means.

  Further, the neutralization bias is increased with time in accordance with the increase in the cumulative number of transferred sheets, that is, according to the increase in resistance of the secondary transfer roller 68 with time. As a result, it is possible to suppress the occurrence of transfer dust due to a decrease in the charge removal capability due to the deterioration of the secondary transfer roller.

  Note that the accumulated static elimination number stored in the IC memory of the static elimination bias power supply circuit 81 is reset to zero by an operation of a service person or the like when the static elimination member 80 is replaced with a new one. In addition, the cumulative number of sheets stored in the main control unit is reset to zero by an operation of a service person or the like when the secondary transfer roller 68 is replaced with a new one.

  So far, the copying machine for transferring the toner image on the intermediate transfer belt, which is an image carrier, to the recording paper has been described. However, the present invention is also applied to an image forming apparatus for transferring the toner image on the photosensitive body, which is an image carrier, to the recording paper. The invention can be applied. Further, although a copying machine that forms a full-color image has been described, the present invention can also be applied to an image forming apparatus that forms only a single-color image.

1 is a schematic configuration diagram showing a copier according to a first embodiment. FIG. 3 is a partially enlarged configuration diagram illustrating a part of an internal configuration of a printer unit in the copier. FIG. 2 is an enlarged configuration diagram illustrating a process unit for Y in the printer unit. FIG. 3 is an enlarged schematic diagram showing the vicinity of an edge of a toner image causing transfer dust. The graph which shows the relationship between the static elimination bias application time and the static elimination current measured value which were confirmed by experiment of the present inventors. The graph which shows the relationship between the transfer bias application time and the static elimination current measured value which were confirmed by our experiment. The graph which shows the relationship between the static elimination current confirmed by the inventors' experiment, and image density.

Explanation of symbols

60: Transfer unit (transfer means)
61: Intermediate transfer belt (image carrier, belt member)
68: Secondary transfer roller (transfer bias member)
72: Secondary transfer opposing roller (contact member)
80: Static elimination member 81: Static elimination bias power supply circuit (static elimination bias application means, static elimination bias control means, static elimination metering means, static elimination counting means)

Claims (10)

An image carrier that carries a toner image, a transfer unit that electrostatically transfers the toner image on the image carrier to a recording member, and a charge removal member that neutralizes the recording member onto which the toner image has been transferred by the transfer unit And an image forming apparatus including a charge eliminating bias applying unit that applies a charge eliminating bias to the charge eliminating member.
There is provided a static elimination time measuring means for timing the cumulative static elimination processing time by the static elimination member, and a static elimination bias control means for controlling the static elimination bias output from the static elimination bias applying means based on the timing result by the static elimination time applying means. An image forming apparatus. An image carrier that carries a toner image, a transfer unit that electrostatically transfers the toner image on the image carrier to a recording member, and a charge removal member that neutralizes the recording member onto which the toner image has been transferred by the transfer unit And an image forming apparatus including a charge eliminating bias applying unit that applies a charge eliminating bias to the charge eliminating member.
Static elimination counting means for counting the cumulative number of recording members subjected to static elimination processing by the static elimination member, and static elimination bias control means for controlling the static elimination bias output from the static elimination bias applying means based on the counting result by the counting means And an image forming apparatus. The image forming apparatus according to claim 1 or 2,
An image forming apparatus, wherein the static elimination bias control means is configured to perform a control to increase the static elimination bias as the timing result or the counting result increases. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus comprising: a member having a thin plate-like conductive member brought into contact with the recording member as the charge eliminating member. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus comprising: a member having a thin plate-like conductive member facing the recording member with a predetermined gap as the charge eliminating member. 6. The image forming apparatus according to claim 1, wherein:
An image forming apparatus using the neutralizing bias applying means that applies only a DC bias to the neutralizing member. The image forming apparatus according to claim 1,
There is provided a transfer timing means for measuring the accumulated transfer processing time by the transfer means, and the static elimination bias is controlled so as to control the static elimination bias based on the timing result or the count result in addition to the timing result or the count result. An image forming apparatus comprising a control means. The image forming apparatus according to claim 1,
A transfer counting means for counting the cumulative number of recording members transferred by the transfer means is provided, and in addition to the timing result or the counting result, the static elimination bias is applied based on the counting result by the transfer counting means. An image forming apparatus characterized in that the static elimination bias control means is configured to control. The image forming apparatus according to claim 7 or 8,
An image forming apparatus, wherein the static elimination bias control means is configured to perform a control to increase the static elimination bias as the time measurement result by the transfer timing means or the count result by the transfer count means becomes longer. The image forming apparatus according to claim 1,
While using an endless belt member as the image carrier and applying a transfer bias having the same polarity as the normal charging polarity of the toner to the transfer bias member in contact with the back surface of the belt member as the transfer means, A transfer member that transfers a toner image on the front surface to a recording member sandwiched in a transfer nip formed by a front surface of the belt member and a contact member that is in contact with the front surface; and As a combination of the belt member, the transfer bias member, and the corresponding contact member, the sum of the electrical resistance value of the transfer bias member and the electrical resistance value of the belt member is larger than the electrical resistance value of the contact member. An image forming apparatus characterized by comprising:

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