JP5539944B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to a direct transfer type image forming apparatus that directly transfers a toner image formed on an image carrier onto a sheet.

  A photosensitive drum on which an electrostatic latent image is formed by irradiating the peripheral surface with a laser beam; and a developing device that supplies toner to the peripheral surface of the photosensitive drum to convert the electrostatic latent image into a toner image. 2. Description of the Related Art An image forming apparatus that forms an image on a sheet by directly transferring a toner image formed on a body drum onto the sheet is known.

  Such a direct transfer type transfer device forms a nip portion in contact with the peripheral surface of the photosensitive drum, conveys the sheet toward the nip portion, and the photosensitive drum sandwiching the conveying belt. A transfer roller is provided opposite to the transfer roller. Then, by applying a voltage having a polarity opposite to the charging polarity of the toner to the transfer roller as a transfer voltage, the toner image is electrostatically moved to the sheet carried by the conveying belt to perform the transfer.

  In such an apparatus, if there is a portion where current easily flows on the conveyor belt, that is, a defective portion such as a hole, a leakage current flows from the transfer roller to the photosensitive drum or the like when a transfer voltage is applied. If image formation is continued with leakage current flowing, dielectric breakdown tends to occur on the peripheral surface of the photosensitive drum. A toner image is not normally formed in the part where the dielectric breakdown occurred, and printing defects such as image omission occurred, resulting in a decrease in image quality.

  Therefore, in Patent Document 1, the transfer voltage electrode member has at least a two-layer structure, and the volume resistivity of the surface layer of one layer on the side in contact with the belt is made higher than the volume resistivity of the other layer. A belt transfer apparatus is described in which the current of the transfer belt electrode member is prevented from concentrating and flowing to a defective portion of the transfer belt due to the resistance of the surface layer of the transfer voltage electrode member, thereby preventing abnormal leakage.

JP-A-8-152789

  However, in the case of Patent Document 1, the configuration of the transfer voltage electrode member is complicated, and there is a concern that the transfer voltage electrode member cannot be completely handled when there is a large environmental change.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to provide an image forming apparatus that prevents dielectric breakdown of a photosensitive drum due to a leak current and thereby prevents printing defects.

  An image forming apparatus according to the present invention includes an image carrier that carries a toner image on a peripheral surface thereof, and a conveying unit that forms a nip portion in contact with the peripheral surface of the image carrier and conveys a sheet toward the nip portion. A transfer means for transferring the toner image carried by the image carrier onto the paper conveyed to the nip portion, and a voltage applied to the transfer means. An application means for applying a predetermined first voltage as a transfer voltage when transferring a toner image carried by the image carrier onto a sheet at the nip portion; and from the application means to the transfer means. A detecting means for detecting a flowing current; and a control means for controlling an applied voltage of the applying means. The control means is lower than the first voltage when the conveying means is not conveying a sheet, Defects exist in the transport means In this case, a second voltage in which a leakage current flows between the transfer unit and the image carrier through the defect portion is applied to the application unit, and during this period, the detection unit has a current value higher than a predetermined value. Is detected, the transfer voltage is changed to a third voltage lower than the second voltage.

  When the detection means detects that a current higher than a predetermined value has flowed between the transfer means and the image carrier, it means that a leakage current has flowed through a defect such as a hole in the conveyance means. Indicates. That is, the defect | deletion part of a conveyance means is detectable with the said structure.

  When the detection unit detects that a current higher than a predetermined value has flowed from the applying unit to the transfer unit, that is, when a defective part of the conveying unit is detected, the control unit detects a leakage current via the defective part. By changing the transfer voltage to a third voltage lower than the second voltage at which the current begins to flow, the occurrence of a leakage current can be suppressed. That is, dielectric breakdown of the image carrier can be prevented, and printing defects due to dielectric breakdown can also be prevented.

  In the above configuration, the control means performs control to intermittently apply the second voltage to the application means.

  If there is a defect in the conveying means, if the second voltage at which a leak current starts to flow is continuously applied to the conveying means, a discharge occurs and it becomes a dangerous state, which may cause component damage. Therefore, the application means intermittently applies the second voltage, so that the defective portion can be detected by detecting the leakage current while avoiding or minimizing the discharge.

  Further, in the above configuration, when the detection unit detects a current value higher than the predetermined value while the application unit intermittently applies the second voltage, a notification unit that notifies that fact. It is desirable to further comprise.

  In general, the conveying means is made of a heat-resistant synthetic resin material such as a polyimide resin whose surface is coated with silicone or the like, a rubber material, or the like. Furthermore, the conveying means is likely to change over time due to heat in the apparatus. Therefore, when the detection unit detects a current higher than a predetermined value between the transfer unit and the image carrier, that is, when a missing portion of the conveyance unit is detected, the notification unit notifies the fact, The user can immediately check the state of the conveying means and deal with maintenance. Since the conveying means can be replaced before the dielectric breakdown of the image carrier occurs, it is possible to prevent the image carrier from being damaged.

  According to the present invention, it is possible to detect the missing portion of the conveying means. Furthermore, after the detection, the control unit changes the transfer voltage to a fourth voltage lower than the third voltage at which the leakage current starts to flow, whereby the leakage current flowing through the defective portion of the transport unit can be suppressed. That is, dielectric breakdown of the image carrier can be prevented, and printing defects due to dielectric breakdown can also be prevented.

1 is a diagram schematically showing an internal configuration of an image forming apparatus. FIG. 3 is a diagram simply illustrating the configuration of a photosensitive drum and a transfer conveyance unit. 5 is a flowchart showing a flow of processing for detecting leakage current and changing transfer voltage by a control unit. The figure which showed the waveform of the 1st voltage.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In this embodiment, a direct transfer type printer is described as an example of the image forming apparatus. However, the present invention can also be applied to a copying machine, a facsimile machine, and a multifunction machine having various functions.

  FIG. 1 is a diagram schematically showing an internal configuration of an image forming apparatus 1 according to the present embodiment. The image forming apparatus 1 includes a housing 18, a main body unit 12 that prints an image on a sheet, and a paper discharge unit 14 that is disposed above the main body unit 12 and discharges a sheet on which an image is printed by the main body unit 12. It consists of In addition, a display unit (notification unit) 61 including a liquid crystal display or the like is provided on the front surface of the image forming apparatus 1. The display unit 61 displays various messages according to control by a control unit described later.

  The main body 12 includes a paper feed cassette 20 disposed in the lower portion of the housing 18, an image forming portion 22 disposed in the upper portion of the housing 18, and a lower portion of the image forming portion 22 in the housing 18. Between the sheet feeding cassette 20 and the transfer transport unit 24, the transfer transport unit 24 disposed in the housing 18, the fixing unit 26 disposed on the downstream side of the transfer transport unit 24 in the transport direction of the paper in the housing 18. A first transport path 28 is provided, and a second transport path 30 is provided between the fixing unit 26 and the paper discharge unit 14.

  The paper feed cassette 20 stores a large number of sheets P on which images are printed in a stacked state, and the paper P can be replenished by being pulled out of the housing 18. The paper P in the paper feed cassette 20 is fed to the first transport path 28 side by sheet by a paper feed roller (not shown).

  The image forming unit 22 includes a photosensitive drum (image carrier) 225 that rotates in the clockwise direction, a charging unit 226 that is disposed to face the peripheral surface of the photosensitive drum 225, and a downstream side in the rotation direction of the charging unit 226. An exposure unit 227 disposed to face the circumferential surface of the photosensitive drum 225, and a developing unit 228 disposed on the downstream side of the exposure unit 227 and opposed to the circumferential surface of the photosensitive drum 225. And a cleaning unit 229 disposed on the downstream side of the developing unit 228 and facing the peripheral surface of the photosensitive drum 225. Further, a transfer roller 244 is disposed opposite to the lower surface of the peripheral surface of the photosensitive drum 225 with the transfer belt 243 interposed therebetween, and a nip portion 230 is formed.

  The transfer conveyance unit 24 includes a driven roller 241, a driving roller 242, an endless transfer belt (conveying means) 243 disposed across the driven roller 241 and the driving roller 242, and a transfer belt at a position below the photosensitive drum 225. A transfer roller (transfer means) 244 disposed so as to be in pressure contact with the photosensitive drum 225 with the 243 interposed therebetween, and a blade 246 disposed downstream of the nip portion 230 in the rotation direction (arrow A direction) of the transfer belt 243. Yes.

  The transfer conveyance unit 24 electrostatically attracts the sheet P conveyed from the first conveyance path 28 onto the transfer belt 243 rotated in the direction of arrow A by a drive motor (not shown) and conveys the sheet P downstream. At this time, the toner image carried by the photosensitive drum 225 is transferred onto the paper P at the position of the nip portion 230. The transfer belt 243 is made of a heat-resistant synthetic resin material such as a polyimide resin whose surface is coated with silicone or the like, a rubber material, or the like.

  The blade 246 is for scraping off adhering matter such as residual toner on the transfer belt 243, and has a length substantially the same as the width direction dimension of the transfer belt 243, and its tip is always on the surface of the transfer belt 243. It arrange | positions in the state contact | abutted.

  The fixing unit 26 performs a process of fixing the toner image on the paper P by heating the paper P on which the toner image is transferred. The fixing unit 26 includes a fixing roller 262 with a built-in heater, and a pressure roller 263 disposed in pressure contact with the fixing roller 262.

  The first conveyance path 28 conveys the sheet P fed from the paper feed cassette 20 to the transfer conveyance unit 24 side, and includes a plurality of conveyance roller pairs 281 disposed at predetermined positions and the transfer conveyance unit 24. And a registration roller pair 282 for taking a timing between an image forming operation of the image forming unit 22 and a paper feeding operation. The plurality of transport roller pairs 281 and the registration roller pairs 282 are respectively rotated by a drive motor (not shown).

  The second conveyance path 30 conveys the sheet fixed by the fixing unit 26 to the sheet discharge unit 14, and a plurality of conveyance roller pairs 301 are disposed at predetermined positions, and the discharge roller pair is disposed on the exit side. 302 is arranged. The transport roller pair 301 and the discharge roller pair 302 are rotated by a drive motor (not shown). The paper discharge unit 14 is formed by providing a recess in the upper surface of the casing 18, and the paper P after the fixing process conveyed from the second conveyance path 30 is sequentially discharged.

  The image forming apparatus 1 configured as described above includes a print instruction signal including various print information such as paper size information and print number information from an external device such as an externally connected personal computer, and job data indicating an image to be printed. When is sent, it operates as follows.

  First, the charging unit 226 forms an electrostatic region on the peripheral surface of the photosensitive drum 225, and the electrostatic region is exposed by laser light emitted from the exposure unit 227, whereby an electrostatic latent image based on job data is formed. It is formed. The developing unit 228 supplies toner to develop the electrostatic latent image and form a toner image. In addition, the fixing roller 262 is energized by applying a voltage to a built-in heater by a voltage supply circuit (not shown), and is heated and controlled so that the surface of the fixing roller 262 reaches a fixable temperature.

  On the other hand, the designated size paper P is fed out from the paper feed cassette 20, transported to the front of the registration roller pair 282 through the first transport path 28, and temporarily stopped. The paper P is transported to the transfer transport unit 24 after timing with the image forming operation of the image forming unit 22, and the image forming unit 22 transfers the toner image onto the paper P.

  The sheet P on which the toner image has been transferred is conveyed into the fixing unit 26, is sandwiched between the fixing roller 262 and the pressure roller 263 while being heated by the fixing roller 262, and is conveyed downstream, and is conveyed by the second conveyance path 30. The paper is discharged to the paper discharge unit 14. The toner remaining on the surface of the photosensitive drum 225 on which the toner image is transferred to the paper P is removed by the cleaning unit 229. This operation is sequentially repeated, and printing on a predetermined number of sheets P is executed.

  FIG. 2 is a diagram simply showing the configuration of the photosensitive drum 225 and the transfer conveyance unit 24. As described above, the transfer roller 244 is in contact with the transfer belt 243 so that the transfer belt 243 is pressed against the photosensitive drum 225. The transfer roller 244 rotates depending on the endless rotation of the transfer belt 243 while being in contact with the transfer belt 243.

  The power source (applying unit) 51 applies a transfer voltage having a polarity opposite to the charging polarity of the toner T to the transfer roller 244. As a result, the toner T on the peripheral surface of the photosensitive drum 225 is electrostatically moved to the paper P at the nip portion 230 between the photosensitive drum 225 and the transfer roller 244. That is, the toner image formed on the photosensitive drum 225 is transferred to the paper P conveyed by the transfer belt 243 that circulates in the direction of arrow A.

  The current detection unit (detection unit) 52 is connected in series with the power supply 51 between the power supply 51 and the transfer roller 244, and when a voltage is applied from the power supply 51 to the transfer roller 244, the current detection unit (detection unit) 52 is provided between the transfer roller 244 and the photosensitive drum 225. Detects the current flowing through Further, the current detection unit 52 outputs the detection result to the control unit 41 described later.

  The control unit (control unit) 41 is configured by a CPU (Central Processing Unit) or the like, and outputs an instruction signal to each functional unit configuring the image forming apparatus 1, performs data transfer, and the like to perform the image forming apparatus. 1 is centrally controlled. In addition, the control unit 41 takes in the detection result from the current detection unit 52 and controls the power supply 51 to change the transfer voltage according to the detection result. Further, display control such as displaying a predetermined message or the like on the display unit 61 is performed.

  When a defective portion such as a hole is formed on the transport belt 243 due to secular change, electric discharge, or the like, a leak current flows between the transport roller 224 and the photosensitive drum 225 through the defective portion. If image formation is continued in this state, dielectric breakdown may occur on the peripheral surface of the photosensitive drum 225. A toner image is not normally formed in the part where the dielectric breakdown occurred, and printing defects such as image omission occurred, resulting in a decrease in image quality.

  Therefore, when the conveyance belt 243 before image formation or the like is not conveying the paper P, the power supply 51 is lower than a predetermined first voltage that is applied to the transfer roller 244 when the conveyance belt 243 has no defective portion. The second voltage is applied intermittently. At this time, the current detection unit 52 detects the current flowing between the transfer roller 244 and the photosensitive drum 225. When the current detection unit 52 detects a current value that is equal to or greater than a predetermined value, it is determined that a leak current is flowing, and the control unit 41 controls the power supply 51 to vary the transfer voltage during image formation. .

  FIG. 3 is a flowchart showing a flow of processing for detecting leakage current and changing transfer voltage by the control unit 41. First, when the conveyance belt 243 is not conveying the paper P (before and after image formation, when the power is turned on, etc.), the control unit 41 is continuously applied to the transfer roller 244 at a voltage lower than a predetermined first voltage that is normally used. When this occurs, a second voltage in which a leakage current flows in the missing portion of the conveyor belt 243 is intermittently applied (step S11). The second voltage is a voltage at which dielectric breakdown does not occur on the peripheral surface of the photosensitive drum 225 even when a leak occurs from the transfer roller 244 to the peripheral surface of the photosensitive drum 225.

FIG. 4 is a diagram showing the waveform of the second voltage V1, where the vertical axis represents voltage and the horizontal axis represents time. In general, the first voltage V _TC = 3 kV, the second voltage V 1 = about 2.5 kV, and the leakage voltage V 2 = about 2.1 kV. The controller 41 causes the power supply 51 to intermittently generate a voltage V1 having a pulse interval of 1 ms. When the voltage V1 is continuously applied, a discharge occurs when a defect portion exists on the transport belt 243, which may cause destruction of peripheral components such as the photosensitive drum 225. In order to avoid or minimize this discharge, the control unit 41 intermittently applies the second voltage V1.

  Note that the leakage voltage V <b> 2 at which the leakage current starts to flow through the missing portion of the conveyance belt 243 varies depending on the installation environment (temperature, humidity, and atmospheric pressure) of the image forming apparatus 1. Therefore, it is preferable to change the second voltage V1 as the leakage voltage V2 changes. For example, the control unit 41 stores a plurality of combinations of the second voltage V <b> 1 and the leakage voltage V <b> 2 in association with a plurality of different environmental conditions, and the service person installs the second voltage V <b> 1 and the leakage voltage when the image forming apparatus 1 is installed. You may make it set whether voltage V2 is employ | adopted.

  Returning to FIG. While the power supply 51 intermittently applies the second voltage V1, the control unit 41 takes in the current detection result from the current detection unit 52 and determines whether or not a current equal to or greater than the threshold value has flowed (step S12). When a current value equal to or greater than the threshold is detected (step S12; YES), the control unit 41 controls the power supply 51 to change the transfer voltage used for transferring the toner image onto the paper P to a third voltage lower than the second voltage V1. This is performed (step S13). By changing the transfer voltage to a voltage equal to or lower than the second voltage V <b> 1 at which the leakage current flows in the missing portion of the transport belt 243, it is possible to prevent the leakage current from flowing in the missing portion.

  In addition, a fourth voltage that is lower than the leakage voltage V2 and does not extremely reduce the image density is stored in advance in a storage unit (not shown) of the control unit 41, and in step S13, the voltage V1 is changed to the fourth voltage. It may be changed. Similarly to the voltage V1 and the leak voltage V2, the control unit 41 stores a plurality of different fourth voltages, and the serviceman sets which fourth voltage to use when the image forming apparatus 1 is installed. May be. Accordingly, it is possible to more reliably prevent a leakage current from flowing from the transfer roller 244 in the defective portion of the conveyance belt 243.

  Further, the control unit 41 causes the display unit 61 to display an error message notifying that a defective portion has been detected on the conveyor belt 243 (step S14). In addition to displaying an error message on the display unit 61, the control unit 41 may notify the user of an abnormality in the conveyor belt 243 by lighting with a warning sound or a light emitting element such as a light emitting diode.

  As described above, when the transport belt 243 is not transporting the paper P, the control unit 41 causes the leak voltage V <b> 2 at which a leak current starts to flow in the missing portion of the transport belt 243 when continuously applied to the transfer roller 244. A voltage V1 that is higher and has almost no leakage current flowing to the conveying belt 243 in a normal state is intermittently applied to the power source 51, and the current detection unit 52 detects the current that flows toward the photosensitive drum 225 during this period. Thus, the missing portion of the conveyor belt 243 can be detected.

  If the current detection unit 52 detects a current equal to or greater than the threshold value while the power supply 51 intermittently applies the voltage V1 (there is a missing portion in the transport belt 243), the control unit 51 sets the transfer voltage to the leakage voltage V2. By setting the third voltage (or the fourth voltage) to be lower, the image current is reduced, but the leakage current flowing through the defective portion can be suppressed, and the dielectric breakdown of the photosensitive drum 225 can be prevented.

  Further, the control unit 51 causes the display unit 61 to display an error message indicating that there is a defective portion on the conveyor belt 243, so that the user can immediately confirm the state of the conveyor belt 243 and contact the maintenance. The conveyor belt 243 can be replaced before the dielectric breakdown of the photosensitive drum 225 occurs.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 225 Photosensitive drum 243 Conveyor belt 244 Transfer roller 41 Control part 51 Power supply 52 Current detection part 61 Display part

Claims (3)

An image carrier that carries a toner image on a peripheral surface;
A conveying means for forming a nip portion in contact with the peripheral surface of the image carrier and conveying a sheet toward the nip portion;
Transfer means for transferring the toner image carried by the image carrier onto the paper conveyed to the nip portion, facing the image carrier with the conveyance means interposed therebetween;
Applying voltage to the transfer means, and applying means that applies a predetermined first voltage as a transfer voltage when transferring a toner image carried by the image carrier onto a sheet at the nip portion;
Detecting means for detecting a current flowing from the applying means to the transferring means;
Control means for controlling the applied voltage of the applying means;
And the control means is lower than the first voltage when the transport means is not transporting paper, and the transfer means and the image via the defect portion when the transport means has a defect portion. When a second voltage in which a leakage current flows between the carriers is applied to the application unit, and the detection unit detects a current value higher than a predetermined value during this period, the transfer voltage is lower than the second voltage. Control means for changing to a third voltage;
An image forming apparatus.   The image forming apparatus according to claim 1, wherein the control unit controls the application unit to intermittently apply the second voltage.   2. The information processing apparatus according to claim 1, further comprising: an informing means for informing that when the detecting means detects a current value higher than the predetermined value while the applying means intermittently applies the second voltage. Or the image forming apparatus according to 2;

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