JP4427975B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to an image forming apparatus that selectively transfers toner to a latent image due to a difference in charging potential to form a toner image, and transfers the toner image onto a recording sheet to form a fixed image. The present invention relates to an image forming apparatus that applies an appropriate transfer voltage during transfer.
[0002]
[Prior art]
  Image forming apparatuses that form a visible image by selectively transferring toner to a latent image due to a difference in electrostatic potential are widely used as copying machines, printers, facsimiles, and the like. In these image forming apparatuses, a step of directly transferring a toner image on a latent image carrier on which an electrostatic latent image is formed to a recording sheet, a step of transferring to an intermediate transfer member, or a step of transferring from an intermediate transfer member to a recording sheet In general, a method is used in which a transfer voltage is applied between both members to transfer a charged toner within a formed electric field. One widely used apparatus for performing such transfer is a member carrying a toner image (generally called an image carrier, a member on which a toner image is formed on the surface of a photosensitive drum, and the like, and A transfer roll, a transfer brush, a transfer belt, and the like are disposed so as to face a toner image (including an intermediate transfer member to which a toner image is temporarily transferred), and a transfer material (including an intermediate transfer member and a recording sheet) is interposed between these members. And a toner image is electrically transferred by forming a transfer electric field between both members.
[0003]
  In such an apparatus, transfer members such as transfer rolls, transfer brushes, and transfer belts form resistors (10) to form a stable transfer electric field and prevent current leakage and the like.^FiveΩ or more) is often used. For example, when a transfer roll is used as the transfer member, conductive rubber is used. However, the resistance value of such a material is likely to fluctuate due to applied voltage, manufacturing variation, temperature change, deterioration during use, and the like. For this reason, the impedance when the transfer voltage is applied to the transfer portion where the image carrier and the transfer member face each other fluctuates, and proper transfer may not be performed if a constant voltage is always applied. For this reason, in Patent Document 1 below, when the toner image is not transferred, a predetermined voltage as a reference is applied to the transfer portion, the current value at that time is read, and the impedance is detected. An apparatus for setting an applied voltage based on impedance has been proposed. Patent Document 2 below discloses an apparatus for detecting an impedance, detecting a size of a transfer material, and determining an appropriate transfer voltage in consideration of the detection result.
[0004]
[Patent Document 1]
      JP-A-5-313522
[Patent Document 2]
      JP 2001-83816 A
[0005]
[Problems to be solved by the invention]
  However, the techniques described in the above patent documents have the following problems.
  As shown in FIG. 9, the intermediate transfer belt 102 and the transfer roll 103 that are stretched around the opposing roll 101 are arranged so as to face each other, and on the recording sheet 104 that passes between them, the intermediate transfer belt 102 is placed on the intermediate transfer belt 102. When a toner image is transferred, a transfer voltage is applied between the opposing roll 101 and the transfer roll 103, whereby the surface of the transfer roll 103 made of a resistor is charged. For example, when a negative voltage is applied to the opposing roll 101 that supports the intermediate transfer belt 102 in order to transfer the negatively charged toner on the intermediate transfer belt 102 onto the recording sheet 104, the surface of the transfer roll 103 is negatively charged. Become. Then, after the toner image is transferred, when the reference voltage is applied and the impedance of the transfer portion is measured when sufficient time has not passed, the impedance of the transfer portion is caused by the charge on the surface of the transfer roll 103. The problem arises that it cannot be measured accurately. That is, in the case shown in FIG. 9, since the surface of the transfer roll 103 is negatively charged, the current value when the reference voltage is applied to the opposite roll 101 is smaller than when the surface of the transfer roll is not charged. Thus, the impedance is detected to be larger than actual. If the transfer voltage is determined based on this detected value, an excessive voltage is applied during transfer.
[0006]
  The above problem will be described in detail with reference to FIG.
  FIG. 10 shows the monitoring result of the current value in the transfer portion and the surface potential of the transfer roll over time.
  Step a shown in FIG. 10 is a preparatory stage for transferring a toner image, and positive and negative voltages are alternately applied between the transfer roll 103 and the opposing roll 101 to adhere to the transfer roll 103. The transfer toner is transferred to the intermediate transfer belt 102 and the transfer roll 103 is cleaned. In step b, a predetermined reference voltage (negative) is applied, and the impedance is detected from the current value. Thereafter, in step c, a patch for adjusting the density of the toner image, a patch for adjusting the superposition position of the toner image, and the like are transferred onto the intermediate transfer belt 102, and these toner images are used. A process of cleaning and removing the toner adhering to the transfer roll 103 is performed. In step d, a transfer voltage is applied between the opposing roll 101 and the transfer roll 103, and the toner image is transferred to a predetermined number (for example, 80 sheets) of recording sheets. The transfer voltage is set based on the impedance detected in step b. At this time, negative charges are gradually accumulated on the surface of the transfer roll 103 to be charged. In step e after the transfer of the predetermined number of sheets is completed, a predetermined reference voltage is applied again to detect the impedance. At this time, the surface of the transfer roll 103 is negatively charged and current does not easily flow, and the detected impedance is larger than the detected value in the step b. That is, it is detected to be larger than the actual impedance due to the charge on the surface of the transfer roll. When the transfer voltage is calculated from the detected value, an excessive voltage is applied in the next step f in which the toner image is transferred. When such an excessive transfer voltage is applied, a transfer failure occurs and a defect such as an image blank occurs.
[0007]
  The invention according to the present application has been made in view of such problems, and its purpose is to set a transfer voltage to be applied during transfer from an impedance detected by applying a reference voltage to the transfer portion. An object of the present invention is to provide an image forming apparatus capable of always detecting impedance under substantially the same conditions and setting an appropriate transfer voltage.
[0008]
[Means for Solving the Problems]
  In order to solve the above problems, the invention according to claim 1An image carrier that carries and conveys a toner image on an endless peripheral surface, a transfer member that includes a resistor and is provided to face the image carrier, and the image carrier and the transfer member A sheet conveying device that conveys a recording sheet so as to pass through an opposing transfer unit; and a toner image on the image carrier for transferring the toner image on the recording sheet between the image carrier and the transfer member. A power supply device that applies a transfer voltage, a voltage control device that controls a voltage applied from the power supply device to the transfer portion, a voltage applied to the transfer portion, and a current value that flows through the transfer portion. An impedance detector for measuring impedance;  Static elimination member supported so as to be in contact with the transfer memberThe voltage control device is configured to set a voltage to be applied from the power supply device to the transfer unit during toner image transfer based on the detection value of the impedance detection device.  The impedance detection device provides an image forming apparatus that detects an impedance after the charge removal member abuts on the transfer member to remove the charge of the transfer member.
[0009]
  In the above-described image forming apparatus, the image carrier can carry and carry a toner image, and the toner image can be transferred from the member to a transfer member such as a recording sheet. It includes both an image formed image and a toner image formed on another member. Specifically, it includes a photosensitive drum / photosensitive belt having a photosensitive layer on the surface, a dielectric on which a latent image is formed by an ion beam or the like, an intermediate transfer drum / intermediate transfer belt to which a toner image is temporarily transferred, and the like. .
[0010]
  In this image forming apparatus, the impedance of the transfer portion is detected at a predetermined time, and the applied voltage is set based on the detected value so that an appropriate current is generated in the transfer portion. Therefore, even if there is a temperature change or a change with time of the impedance, it is possible to maintain an appropriate current in the transfer portion.
AndSince the charge eliminating member that contacts the transfer member is provided, the charge of the transfer member is removed through the charge eliminating member before the impedance is detected. Therefore, the impedance of the transfer portion can always be detected under the same electrical conditions, and the voltage applied during transfer can be set appropriately.
[0011]
  Claim 2Such an image forming apparatusAn image carrier that carries and conveys a toner image on an endless peripheral surface, a transfer member that includes a resistor and is provided to face the image carrier, and the image carrier and the transfer member A sheet conveying device that conveys a recording sheet so as to pass through an opposing transfer unit; and a toner image on the image carrier for transferring the toner image on the recording sheet between the image carrier and the transfer member. A power supply device that applies a transfer voltage, a voltage control device that controls a voltage applied from the power supply device to the transfer portion, a voltage applied to the transfer portion, and a current value that flows through the transfer portion. An impedance detection device that measures impedance, and the voltage control device sets a voltage to be applied from the power supply device to the transfer unit during toner image transfer based on a detection value of the impedance detection device. Ri,  The impedance detection device detects an impedance after alternately applying a bipolar voltage from the power supply device to the transfer unit.An image forming apparatus is provided.
[0012]
  In this image forming apparatus, since a bipolar voltage is alternately and repeatedly applied from the power supply device to the transfer portion, even if the surface of the transfer member is charged, it is quickly discharged and the surface potential converges to a substantially constant value. Can be made. Therefore, the impedance of the transfer portion can always be detected under substantially constant conditions, and the applied voltage at the time of transfer can be set appropriately.
[0013]
  Claim 3The invention concernedAn image carrier that carries and conveys a toner image on an endless peripheral surface;
A transfer member made of a resistor and provided so as to face the image carrier, and a sheet conveying device that conveys a recording sheet so that the image carrier and the transfer member pass through a transfer part opposite to the image carrier. A power supply device for applying a transfer voltage for transferring a toner image on the image carrier onto the recording sheet between the image carrier and the transfer member; and applied from the power supply device to the transfer unit. A voltage control device that controls a voltage to be transferred, and an impedance detection device that measures an impedance of the transfer portion from a voltage applied to the transfer portion and a current value flowing through the transfer portion, and the voltage control device includes: Based on the detection value of the impedance detection device, a voltage to be applied from the power supply device to the transfer portion during toner image transfer is set.  The impedance detection device detects an impedance after applying a predetermined voltage from the power supply device for a predetermined time, and the predetermined time is set to be equal to or longer than a time at which the fluctuation of the surface potential of the transfer member converges. ingAn image forming apparatus is provided.
[0014]
  Also,Claim 4The invention concernedClaim 3In the image forming apparatus described above, the predetermined voltage applied from the power supply device before the impedance is detected has a polarity opposite to the transfer voltage applied when the toner image is transferred.
[0015]
  In such an image forming apparatus, the transfer member is charged by applying a constant voltage to the transfer portion, and reaches a saturated state after a sufficient time has elapsed. That is, the surface potential of the transfer member converges to a value having a correlation with the applied voltage and becomes constant. Thereafter, the reference voltage is applied to the transfer portion to detect the impedance of the transfer portion, thereby enabling accurate detection.
  In addition, by applying a voltage having a polarity opposite to that at the time of transfer to the transfer member so that the surface of the transfer member has a potential opposite to the charged potential at the time of transfer, and detecting the impedance of the transfer portion in this state, Impedance fluctuations can be detected significantly,
More appropriate control is possible.
[0016]
  Claim 5The invention according to claim 1 starts from claim 1.Until claim 4The image forming apparatus according to claim 1, further comprising: a potential sensor that measures a surface potential of the transfer member, wherein the impedance detection device detects that the surface of the transfer member has a predetermined potential by the potential sensor. After that, the impedance is detected.
[0017]
  Since this image forming apparatus includes a potential sensor that measures the surface potential of the transfer member, the impedance can be detected after confirming the surface potential of the transfer member. Therefore, the impedance is detected under the condition that the potential of the transfer member is made constant, and the applied voltage at the time of transfer can be set appropriately. In addition, impedance can be detected immediately after detecting that the potential of the transfer member is within a predetermined range, and impedance can be detected quickly and reliably.
[0018]
  Claim 6The invention concernedAn image carrier that carries and conveys a toner image on an endless peripheral surface;
A transfer member made of a resistor and provided so as to face the image carrier, and a sheet conveying device that conveys a recording sheet so that the image carrier and the transfer member pass through a transfer part opposite to the image carrier. A power supply device for applying a transfer voltage for transferring a toner image on the image carrier onto the recording sheet between the image carrier and the transfer member; and applied from the power supply device to the transfer unit. A voltage control device that controls a voltage to be transferred, and an impedance detection device that measures an impedance of the transfer portion from a voltage applied to the transfer portion and a current value flowing through the transfer portion, and the voltage control device includes: Based on the detection value of the impedance detection device, a voltage to be applied from the power supply device to the transfer portion during toner image transfer is set.  The impedance detection device detects impedance when the image carrier is started and the rotation is stabilized after the device has been stopped for a long time.An image forming apparatus is provided.
[0019]
  When the driving of the apparatus is stopped for a long time, the electric charge accumulated in the transfer member or the like is dissipated, and the electric potential becomes close to zero. If the rotation of the image carrier or the like is stable in this state, the impedance of the transfer portion is detected without being affected by the potential of the transfer member, and the transfer voltage applied during transfer can be set appropriately.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments of the invention according to the present application will be described with reference to the drawings.
  FIG.Claim 1It is a schematic block diagram which shows the image forming apparatus which is one Embodiment of described invention.
  The image forming apparatus includes four image forming units 10a, 10b, 10c, and 10d that form yellow, magenta, cyan, and black toner images, and is endless so as to face each of these image forming units 10. A belt-like intermediate transfer member 11 is supported, and the peripheral surface is driven to rotate. On the downstream side of the position where the image forming unit faces the intermediate transfer body 11, a transfer roll 12 is disposed so as to face the intermediate transfer body, and the secondary transfer section is provided with a conveyance path 14 from the sheet tray 13. After that, the recording sheet is conveyed. A fixing device 15 that heats and pressurizes the toner image to press the toner image onto the recording sheet is provided downstream of the secondary transfer portion in the recording sheet conveyance path, and the toner image is fixed further downstream. A paper discharge tray 16 for storing the recorded sheet is provided. On the other hand, on the downstream side of the secondary transfer portion in the circumferential direction of the intermediate transfer body 11, the intermediate transfer is performed in order to collect the toner remaining without being transferred to the recording sheet in the secondary transfer portion and the patches that are not secondary transferred. A cleaning device 17 is provided to face the body 11.
[0021]
  Each of the image forming units 10a, 10b, 10c, and 10d has a photoconductive drum 1 on which an electrostatic latent image is formed, and around the photoconductive drum 1, the surface of the photoconductive drum is provided. A charging device 2 that charges the surface of the photosensitive drum approximately uniformly, an optical scanning device 3 that scans the surface of the photosensitive drum with a laser beam and writes an electrostatic latent image, and a toner that selectively forms a latent image formed on the photosensitive drum. And a transfer charger 5 for primary transfer of the toner image on the photosensitive drum 1 onto the intermediate transfer member 11.
[0022]
  The intermediate transfer body 11 is made of a resin film having a thickness of about 10 to 300 μm, and a polyimide film or the like is used. Further, in order to electrostatically transfer the toner image from the photosensitive drum 1 to the intermediate transfer body 11 without disturbing the image, powder of a conductive material such as carbon black is mixed and the volume resistivity is set to 10.^TenIt is adjusted to about Ωcm.
[0023]
  Inside the intermediate transfer body 11, a drive roll 21, an opposing roll 22 arranged in the transfer section, and support rolls 23, 24, and 25 are arranged, and the intermediate transfer body 11 is stretched around these. It moves around in the direction of the arrow shown in the figure.
[0024]
  The transfer roll 12 is provided at a position facing the opposing roll 22 and is pressed against the opposing roll 22 via the intermediate transfer body 11. The transfer roll 12 is a roll formed by forming an outer peripheral portion of a metal core material with a conductive rubber material, and the core material is electrically grounded. The outer peripheral portion made of a conductive rubber material has a thickness of 10 when the resistance value between the outer peripheral portion and the core material is measured by bringing a conductive plate into contact with the peripheral surface.^FiveIt is made to be Ω or more.
[0025]
  On the other hand, a power supply device 18 is connected to the opposing roll 22 as shown in FIG. 2, and the voltage applied to the opposing roll 22, the timing of voltage application, and the like are controlled by the voltage control device 19. . In addition, an impedance detection device 20 that detects an impedance by detecting a current value at the time of voltage application is inserted in a circuit that applies a voltage to the facing roll 22. The output of the impedance detection device 20 is input to the voltage control device 19, and the voltage control device 19 sets the applied voltage based on the detected impedance so that the current value of the transfer portion is appropriate. .
[0026]
  The transfer roll 12 is in contact with a static elimination brush 31 made of a conductive material as a static elimination member, and is grounded to remove charges on the surface of the transfer roll 12. Further, a potential sensor 32 that detects the potential of the surface of the transfer roll 12 is provided opposite to the transfer roll 12, and an output is input to the voltage control device 19.
[0027]
  Next, the operation of the image forming apparatus, the current value due to voltage application to the secondary transfer unit, and the potential of the transfer roll surface will be described.
  Black, yellow, magenta, and cyan toner images are formed by the four image forming units 10a, 10b, 10c, and 10d provided to face the intermediate transfer member 11, respectively. The toner image is formed by the following process.
  Each of the photosensitive drums 1 is charged almost uniformly by the charging device 2, and a laser beam that is turned on / off in accordance with an image signal is scanned on the peripheral surface of the photosensitive drum 1 by the optical scanning device 3 to form an electrostatic latent image. It is formed. The electrostatic latent image on each photoconductor drum 1 is developed by the developing device 4 containing black, yellow, magenta, and cyan toners, and each color toner image is formed on each photoconductor drum 1.
[0028]
  The respective color toner images formed in this way are sequentially transferred onto the intermediate transfer body 11 by the transfer charger 6, and a color image in which a plurality of color toner images are superimposed on the intermediate transfer body 11 is formed. Is done. The toner images of a plurality of colors formed on the intermediate transfer body 11 are transferred onto the recording sheet P conveyed from the sheet tray 13 at a position where the intermediate transfer body 11 faces the transfer roll 12 and pass through the fixing device 15. When heated, it is heated and pressurized to form a fixed image. Then, the recording sheet P on which the toner image is fixed is discharged to the paper discharge tray 16.
[0029]
  In the secondary transfer portion where the toner image is transferred to the recording sheet P, a transfer voltage is applied between the opposing roll 22 and the transfer roll 12 from the power supply device 18. In the secondary transfer portion, voltage application is started before the toner image transferred to the recording sheet arrives. As shown in FIG. 3, first, positive and negative voltages are alternately applied for a predetermined time (step A 1), and the toner adhering to the transfer roll 12 is transferred onto the intermediate transfer body 11. Thereafter, the transfer roll 12 and the intermediate transfer body 11 circulate without voltage being applied, and the charge on the transfer roll 12 is removed by the contact of the charge eliminating brush 31 (step A2).
[0030]
  When it is detected by the potential sensor 32 that the surface potential of the transfer roll 12 has become substantially zero potential and the detection result is input to the voltage control device 19, a predetermined reference voltage (for example, −− 1000V) is applied to the opposing roll 22 from the power supply device 18, and the impedance is detected from the current value of the transfer portion in the impedance detection device 20 (step A3). Based on this detection value, the transfer voltage at the time of transferring the toner image is determined.
[0031]
  Thereafter, a transfer voltage determined using the detected impedance value is applied to the transfer portion, and the toner image is transferred to the recording sheet (step A4). If there is a patch transferred to the intermediate transfer body 12 for image alignment or density adjustment before the toner image transfer step (A4 step), this patch cleaning step (not shown). Is done. In addition, before the toner image transfer step, a large voltage may be temporarily applied to the transfer portion, and the surface potential of the transfer roll may be raised as shown by the alternate long and short dash line in FIG. By increasing the surface potential at the beginning of toner image transfer in this way, the surface potential of the transfer roll changes and the current value of the transfer section gradually decreases while transferring multiple images continuously. Can be prevented.
[0032]
  When a predetermined number of images are formed and transferred, the temperature of the apparatus fluctuates, and the characteristic values of the materials constituting the transfer roll 12 also fluctuate. For this reason, the image formation is stopped once and the impedance is detected again. At this time, before applying the reference voltage from the power supply device 18, the transfer roll 12 and the intermediate transfer body 11 are driven to rotate, and the surface potential of the transfer roll 12 is removed by the charge eliminating brush 31 (step A <b> 5). Then, the impedance is detected again by applying the reference voltage, and the transfer voltage to be applied when the next toner image is transferred is set based on the detected value (step A6). After the transfer of a predetermined number of sheets, the surface of the transfer roll 12 is charged as shown in FIG. 3, but the surface of the transfer roll 12 is brought to a substantially zero potential by abutting the neutralizing brush 31 and driving around. It becomes. Therefore, when the impedance is detected by applying the reference voltage, almost the same electrical condition is always maintained, and the impedance can be detected appropriately. As a result, the transfer voltage is set appropriately and good secondary transfer is performed.
[0033]
  next,Claim 2The voltage applied to the secondary transfer portion and the surface potential of the transfer roll in the image forming apparatus which is an embodiment of the described invention will be described.
  FIG. 4 shows the result of monitoring the current value in the secondary transfer portion of this image forming apparatus and the result of detecting the potential of the transfer roll surface, following the image forming process.
  In this image forming apparatus, as the apparatus starts driving, positive and negative voltages are alternately applied to the secondary transfer portion for a predetermined time, and the toner charged in either positive or negative polarity on the transfer roll is transferred to the intermediate transfer body. And removed by a cleaning device. Then, the application of alternating voltage is continued until a predetermined time has elapsed after the transfer of the toner, and the surface potential of the transfer roll is converged to around 0 V (step B1). After confirming that the surface potential is a predetermined value, a predetermined reference voltage is applied to the secondary transfer portion, and the impedance is determined based on the current value detected at the secondary transfer portion at that time. Measured (step B2). Based on this impedance, the transfer voltage for transferring the toner image is determined, and the toner image is transferred to the recording sheet that is applied to the secondary transfer portion and fed from the sheet tray (step B3).
[0034]
  When the toner images are transferred for a predetermined number of sheets, the transfer of the toner images is stopped once, and positive and negative voltages are alternately applied again (step B4), the potential on the surface of the transfer roll is removed, and then a reference voltage is applied. Then, the impedance of the secondary transfer portion is measured (step B5). The transfer voltage is reset based on the detected value, the image forming operation is restarted, and the color image formed on the intermediate transfer member is transferred onto the recording sheet (step B6).
[0035]
  In this way, an appropriate transfer voltage is set by detecting the impedance each time a predetermined number of transfers are performed, and the impedance is detected without being affected by the charge amount of the transfer roll. Is set. Accordingly, even when a large number of images are formed, it is possible to perform stable and stable transfer.
[0036]
  In the image forming apparatus, the positive and negative polarities are alternately applied for a predetermined time, and then the reference voltage is applied to detect the impedance. However, as shown in FIG. It is also possible to continuously apply a certain voltage for a predetermined time (C1 step) and then apply a reference voltage to detect the impedance (C2 step). The image forming apparatus controlled in this way isClaim 3 or claim 4It is one Embodiment of the invention which concerns.
  In the image forming apparatus, it is desirable that the voltage applied to the secondary transfer unit prior to the impedance detection is a voltage having a polarity opposite to that applied when the toner image is transferred. For example, when a negatively charged toner is used, a negative voltage is applied to the opposite roll during transfer, but a positive voltage is applied before the reference voltage is applied.
[0037]
  By applying the voltage to the secondary transfer portion, the surface potential of the transfer roll is charged to a constant potential corresponding to the applied voltage and stabilized. Thus, by detecting the impedance by applying the reference voltage after adjusting the surface potential of the transfer roll, the impedance can always be detected in the same electrical state. Accordingly, when the impedance of the transfer roll fluctuates with a change in temperature, an appropriate transfer voltage can be set without being affected by the charged state of the transfer roll.
[0038]
  Further, by setting the voltage applied prior to the detection of the impedance to a polarity opposite to the transfer voltage applied at the time of transferring the toner image, it is possible to significantly detect the fluctuation of the impedance of the transfer roll or the like.
[0039]
  FIG. 6 is a diagram showing the relationship between the surface potential of the transfer roll and the current value detected at the transfer portion for three transfer rolls having different impedances (resistance values: 8.1 logΩ, 8.5 logΩ, and 8.9 logΩ). is there.
  When a negative voltage is applied to the opposite roll in a state where the surface potential of the transfer roll is positive, the current value (absolute value) increases as the surface potential of the transfer roll increases. If the surface potential of the transfer roll is negative, the current value observed decreases as the absolute value increases. Then, as the surface of the transfer roll is positively charged and the charged potential increases, the difference in current value due to the difference in impedance of the transfer roll appears more remarkably. Therefore, as shown in FIG. 5, when a constant voltage is applied to the transfer portion in advance and the impedance is detected with the transfer roll surface charged to a predetermined potential, the transfer roll surface is charged positively. It is possible to obtain an accurate value by setting it to the state.
[0040]
  Further, when a voltage is applied to the transfer portion as described above, the potential on the surface of the transfer roll gradually increases, and a saturation state is reached in which the charging potential does not fluctuate over time. FIG. 7 shows the relationship between the saturated surface potential and the voltage applied to the transfer portion at this time. From the relationship between the voltage applied to the transfer portion and the saturated surface potential, it is possible to appropriately determine the voltage to be applied to the transfer portion before impedance detection in the process shown in FIG.
[0041]
  On the other hand, in the image forming apparatus shown in FIG. 1, a potential sensor is provided opposite to the transfer roll, and the timing for detecting the impedance by applying a reference voltage can be set while monitoring the surface potential of the transfer roll. . However, when detecting the impedance after adjusting the surface potential of the transfer roll by applying a predetermined voltage as shown in FIG. 5, the time until the saturated surface potential is reached together with the saturated surface potential (static time). By measuring in advance, the impedance detection timing can be set appropriately without using a potential sensor.
[0042]
  FIG. 8 shows the results of measuring the relationship between the saturation surface potential and the time to reach the surface potential (static time) for three transfer rolls having different impedances. As shown in this figure, as the impedance of the transfer roll increases and as the saturation surface potential increases, the time until the saturation state is reached increases.
[0043]
  In the embodiment described above, the transfer roll impedance is detected and the set value of the transfer voltage is changed every time a predetermined number of images are transferred in addition to when the image forming apparatus is activated. When only the influence of environmental fluctuations is reflected in the transfer voltage setting value, the surface potential of the transfer roll is not forcibly set to a predetermined potential. Can also be done. In other words, if the rotation of the intermediate transfer member and the transfer roll is stabilized when the device is started after being left unused for a long time, the impedance is detected by immediately applying the reference voltage to the transfer portion. . When the device is not driven for a long time, the charge of the transfer roll is dissipated and becomes almost zero potential, and the impedance can be detected in a stable state by detecting the impedance immediately after driving. .
  An apparatus for setting the transfer voltage in this way isClaim 6It is one Embodiment of the invention which concerns.
[0044]
【The invention's effect】
  As described above, the image forming apparatus according to the present invention detects the impedance of the transfer portion when the surface potential of the transfer member arranged to face the image carrier becomes a predetermined value. Regardless of the detection time, the impedance is detected under substantially the same electrical conditions. For this reason, the reliability of the detected value is improved, and the transfer voltage to be applied to the transfer portion is set based on the detected value, so that the transfer voltage is always set appropriately and good transfer is performed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic diagram illustrating a configuration of a secondary transfer unit of the image forming apparatus illustrated in FIG.
FIG. 3 is a diagram illustrating an image forming process of a monitoring result of a current value and a detection result of a surface potential of a transfer roll in a secondary transfer unit of the image forming apparatus illustrated in FIG. 1;
FIG. 4 is a diagram illustrating another example of the current value monitoring result and the detection result of the surface potential of the transfer roll in the secondary transfer unit.
FIG. 5 is a diagram illustrating another example of the current value monitoring result and the surface potential detection result of the transfer roll in the secondary transfer unit.
FIG. 6 is a diagram showing the relationship between the surface potential of a transfer roll and a monitor current value for three transfer rolls having different impedances.
FIG. 7 is a diagram showing a relationship between a voltage applied to a transfer portion and a saturated surface potential for three transfer rolls having different impedances.
FIG. 8 is a diagram showing the relationship between the saturation surface potential of a transfer roll and the settling time for three transfer rolls having different impedances.
FIG. 9 is a schematic diagram illustrating a configuration of a transfer unit in a conventional image forming apparatus.
FIG. 10 is a diagram illustrating a monitoring result of a current value of a secondary transfer unit and a detection result of a surface potential of a transfer roll in a conventional image forming apparatus, following an image forming process.
[Explanation of symbols]
    1 Photosensitive drum
    2 Charging device
    3 Optical scanning device
    4 Development device
    5 Transfer charger
  10 Image forming unit
  11 Intermediate transfer member
  12 Transfer roll
  13 Sheet tray
  14 Transport path
  15 Fixing device
  16 Output tray
  17 Cleaning device
  18 Power supply
  19 Voltage controller
  20 Impedance detection device
  21 Drive roll
  22 Opposite roll
  23, 24, 25 Support roll
  31 Static elimination brush
  32 Potential sensor

Claims (6)

An image carrier that carries and conveys a toner image on an endless peripheral surface;
A transfer member made of a resistor and provided to face the image carrier;
A sheet conveying apparatus that conveys a recording sheet so that the image carrier and the transfer member pass through opposing transfer portions;
A power supply device for applying a transfer voltage for transferring a toner image on the image carrier onto the recording sheet between the image carrier and the transfer member;
A voltage control device for controlling a voltage applied to the transfer unit from the power supply device;
An impedance detection device that measures the impedance of the transfer portion from the voltage applied to the transfer portion and the current value flowing through the transfer portion;
A static elimination member supported so as to contact the transfer member ,
The voltage control device is configured to set a voltage to be applied from the power supply device to the transfer unit during toner image transfer based on a detection value of the impedance detection device,
The image forming apparatus according to claim 1, wherein the impedance detection device detects impedance after the charge removal member abuts on the transfer member to remove the charge of the transfer member. An image carrier that carries and conveys a toner image on an endless peripheral surface;
A transfer member made of a resistor and provided to face the image carrier;
A sheet conveying apparatus that conveys a recording sheet so that the image carrier and the transfer member pass through opposing transfer portions;
A power supply device for applying a transfer voltage for transferring a toner image on the image carrier onto the recording sheet between the image carrier and the transfer member;
A voltage control device for controlling a voltage applied to the transfer unit from the power supply device;
An impedance detection device that measures the impedance of the transfer portion from the voltage applied to the transfer portion and the current value flowing through the transfer portion;
The voltage control device is configured to set a voltage to be applied from the power supply device to the transfer unit during toner image transfer based on a detection value of the impedance detection device,
The image forming apparatus according to claim 1, wherein the impedance detection device detects impedance after alternately applying bipolar voltages from the power supply device to the transfer unit. An image carrier that carries and conveys a toner image on an endless peripheral surface;
A transfer member made of a resistor and provided to face the image carrier;
A sheet conveying apparatus that conveys a recording sheet so that the image carrier and the transfer member pass through opposing transfer portions;
A power supply device for applying a transfer voltage for transferring a toner image on the image carrier onto the recording sheet between the image carrier and the transfer member;
A voltage control device for controlling a voltage applied to the transfer unit from the power supply device;
An impedance detection device that measures the impedance of the transfer portion from the voltage applied to the transfer portion and the current value flowing through the transfer portion;
The voltage control device is configured to set a voltage to be applied from the power supply device to the transfer unit during toner image transfer based on a detection value of the impedance detection device,
The impedance detection device detects impedance after applying a predetermined voltage from the power supply device for a predetermined time,
The image forming apparatus according to claim 1, wherein the predetermined time is set to be equal to or longer than a time at which a change in surface potential of the transfer member converges.     The image forming apparatus according to claim 3, wherein the predetermined voltage applied from the power supply device before the impedance is detected has a polarity opposite to that of the transfer voltage applied when the toner image is transferred. Having a potential sensor for measuring the potential of the surface of the transfer member;
The impedance detection device, according to claim 1, wherein the surface of the transfer member by the potential sensor is for detecting the impedance after detecting that a predetermined potential to claim 4 Image forming apparatus. An image carrier that carries and conveys a toner image on an endless peripheral surface;
A transfer member made of a resistor and provided to face the image carrier;
A sheet conveying apparatus that conveys a recording sheet so that the image carrier and the transfer member pass through opposing transfer portions;
A power supply device for applying a transfer voltage for transferring a toner image on the image carrier onto the recording sheet between the image carrier and the transfer member;
A voltage control device for controlling a voltage applied to the transfer unit from the power supply device;
An impedance detection device that measures the impedance of the transfer portion from the voltage applied to the transfer portion and the current value flowing through the transfer portion;
The voltage control device is configured to set a voltage to be applied from the power supply device to the transfer unit during toner image transfer based on a detection value of the impedance detection device,
The image forming apparatus according to claim 1, wherein the impedance detection device detects impedance when the image carrier is started and the rotation is stabilized after the device has been stopped for a long time.

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