JP2009288454A - Image forming apparatus and method of controlling the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce cost for replacing a charger in an image forming apparatus that uses the charger. <P>SOLUTION: The image forming apparatus includes: a photoreceptor; and a charger including a power-supply member for charging the photoreceptor, and a grid. In particular, the image forming apparatus includes: a detection unit for detecting the occurrence of tracking based on at least one of a bias voltage of the grid and a power-supply voltage of the power-supply member; and a reporting unit for reporting that the charger should be replaced, when the detection unit detects the occurrence of the tracking. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using a charger.

Conventionally, a scorotron charger has been proposed as a charger for charging a photoreceptor of an image forming apparatus (Patent Document 1).
JP 2002-132023 A.

  FIG. 1 is a schematic cross-sectional view of a general scorotron charger. The power supply wire 101 of the charger 104 is provided along the length direction of the cylindrical photosensitive drum 105 (direction parallel to the rotation axis of the photosensitive drum). Similarly, shields 102 a and 102 b are arranged in parallel with the feeding wire 101. Further, a grid 103 is attached between the power supply wire 101 and the photosensitive drum 105. The grid 103 is realized by a grid-like wire or a plate provided with a large number of holes by etching or the like in order to allow charges to pass through.

  When a high voltage is applied to the power supply wire 101, corona discharge is generated between the power supply wire 101 and the grid 103 and between the power supply wire 101 and the shields 102a and 102b. This corona discharge causes a current to flow between the power supply wire 101 and the shields 102 a and 102 b or the grid 103. Note that the charge passing through the grid 103 charges the photosensitive drum 105.

  By the way, an insulator is provided to insulate the power supply wire 101 and the shields 102a and 102b. If the insulation performance of the insulator deteriorates due to a change over time or the like, corona discharge cannot be maintained by tracking. Tracking is creeping discharge that occurs due to a drop in impedance on the surface of the insulator. When tracking occurs, the photosensitive drum cannot be charged as expected, and the quality of the formed image is degraded.

  Conventionally, since tracking was not detected, the charger was replaced before its original life reached. Accordingly, an object of the present invention is to efficiently replace the charger, reduce the number of replacements, and reduce costs in the long term.

  The image forming apparatus of the present invention includes a photoconductor and a charger including a power feeding member and a grid for charging the photoconductor. In particular, the image forming apparatus has a detection unit that detects the occurrence of tracking based on at least one of the bias voltage of the grid and the supply voltage of the power supply member, and that the charger should be replaced when the detection unit detects the occurrence of tracking. A notification unit for notification.

  According to the present invention, by detecting the tracking that occurs when the life of the charger is exhausted, it is possible to prevent the charger from being replaced before the lifetime is exhausted. That is, since the charger can be used longer than before, the cost due to the replacement of the charger can be reduced.

  An embodiment of the present invention is shown below. The individual embodiments described below will help to understand various concepts, such as the superordinate concept, intermediate concept and subordinate concept of the present invention. Further, the technical scope of the present invention is determined by the scope of the claims, and is not limited by the following individual embodiments.

[Embodiment 1]
FIG. 2 is a schematic cross-sectional view of the image forming apparatus. The present invention can be applied to an image forming apparatus that uses a single color toner. Here, an image forming apparatus that uses a plurality of toners having different colors will be described. Although four image forming units are shown in FIG. 2, it is assumed that each image forming unit adopts a common configuration except for the color of the toner.

  The photosensitive drum 105 is an example of an image bearing member and a photosensitive member, and the surface (image forming surface) thereof is uniformly charged by the charger 104. The charger 104 is, for example, a scorotron charger. An electrostatic latent image is formed on the image forming surface of the photosensitive drum 105 by the light beam output from the exposure device 202. The electrostatic latent image is visualized by the developing device 204 and becomes a visible image (developer image).

  The visible images formed in each image forming unit are sequentially primary-transferred to the intermediate transfer member 208. Further, the visible image is secondarily transferred from the intermediate transfer member 208 to the recording material by the secondary transfer roller 209. Thereafter, the fixing device 212 fixes the multicolor visible image onto the recording material.

  The controller 214 controls the charging bias in the charger 104 via the charger high-voltage board 201. Note that a mechanism for detecting tracking is added to the high-voltage board 201 for charger, whereby the controller 214 recognizes the occurrence of tracking. When the tracking occurs, the controller 214 determines that the charger 104 is abnormal, that is, the lifetime has expired, and outputs a message prompting the replacement of the charger 104 to the display device 215.

  FIG. 3 is a schematic cross-sectional view of the charger and a part of the photosensitive drum according to the embodiment. The shields 102a and 102b of the charger 104 and the grid 103 are electrically insulated. A power supply wire 101, which is an example of a power supply member, is connected to a constant current source 301 of the charger high-voltage board 201. The power supply wire 101 is an example of a power supply member, but is not necessarily a wire. In other words, the power supply wire 101 may be replaced with a power supply member having another shape intended for power supply.

  The shields 102a and 102b are connected to GND. That is, the shields 102a and 102b are grounded. The grid 103 is connected to a variable resistor 302 that generates a constant voltage based on a current from the power supply wire 101. The variable resistor 302 is controlled so that the voltage at both ends becomes a constant voltage by an external signal. The voltage across the variable resistor 302 is called a so-called grid bias voltage (hereinafter referred to as grid voltage). The grid voltage is detected by the grid voltage detection unit 303. Thus, the variable resistor 302 is an example of a constant voltage source that generates a constant voltage from the current flowing from the power supply member to the grid. The grid voltage detection unit 303 is an example of a first detection unit that detects a constant voltage as a grid bias voltage.

The constant current source 301 supplies a constant current to the power feeding member. A current flowing from the constant current source 301 to the feeding wire 101 is _defined as I _pri . I _pri is the total of the current I _ws toward the shields 102 a and 102 b, the current I _wg toward the grid 103, and the current I _wd toward the photosensitive drum 105.

There is a lower limit to the voltage generated across the variable resistor 302. The lower limit voltage (minimum value) is determined depending on I _pri . The grid voltage is usually greater than or equal to this minimum value (within a predetermined value) and never falls below this minimum value. Therefore, if the grid voltage is outside the predetermined range, that is, less than the minimum value, the grid voltage indicates an abnormality.

That is, when tracking occurs in the directions of the shields 102a and 102b, the impedance between the power supply wire 101 and the shields 102a and 102b decreases. In this case, I _ws increases and I _wg and I _wd decrease. As a result, no matter how much the variable resistor 302 connected to the grid 103 increases its resistance value, no grid voltage is generated.

At this time, if the grid voltage detected by the grid voltage detection unit 303 is lower than the minimum value of the voltage corresponding to the value of I _pri at that time, the controller 214 detects an abnormality (the occurrence of tracking / the life of the charger is Recognize what has been done. Then, the controller 214 stops the image forming process, and notifies the user of a message prompting the replacement through the display device 215 because the charger is abnormal. Note that an output device that outputs a voice message instead of a visual message may be employed.

  FIG. 4 is a flowchart illustrating a method for controlling the image forming apparatus with tracking detection processing. In step S <b> 401, the controller 214 instructs the charger high-voltage board 201 to start supplying power to the power supply wire 101. The charger high-voltage board 201 that has received this instruction supplies power to the power supply wire 101.

  In step S <b> 402, the controller 214 sets the value of the current flowing through the power supply wire 101 in the charger high-voltage board 201. Note that the execution order of step S401 and step S402 may be reversed, or may be substantially simultaneous.

  In step S404, the controller 214 detects the grid voltage using the grid voltage detection unit 303 provided in the high-voltage board 201 for charger. Note that the controller 214 may detect the grid voltage after waiting until a time (eg, about 100 ms) during which the grid voltage is stabilized elapses.

  In step S405, the controller 214 determines whether or not the grid voltage is outside a predetermined range. For example, the controller 214 compares the detected value (measured value) of the grid voltage with a predetermined steady value, and determines whether or not the detected value is smaller than the predetermined steady value. That is, the controller 214 determines whether tracking has occurred. The predetermined steady value is a minimum value of the grid voltage determined depending on the supply current. For example, the memory provided in the controller 214 may store a table in which the value of the feeding current and the minimum value of the grid voltage are associated with each other. The controller 214 can read out the minimum value of the grid voltage corresponding to the set value of the feeding current from the table.

  If the detected value is equal to or greater than a predetermined steady value, tracking does not occur (not abnormal), and the processing according to this flowchart ends. Thus, the controller 214, the charger high-voltage board 201, and the like function as a detection unit that detects the occurrence of tracking based on the grid voltage.

  On the other hand, if it is determined in step S405 that the detected value is smaller than the steady value, the process proceeds to step S407. In step S407, the controller 214 instructs the high-voltage board 201 for charger to stop energizing the power supply wire 101. As a result, the charging high-voltage board 201 stops energizing the power supply wire 101.

  In step S408, the controller 214 displays a message on the display device 215 indicating that the charger needs to be replaced. As described above, the display device 215 is an example of a notification unit that notifies the abnormality of the charger when the detection unit detects the occurrence of tracking.

  According to the present embodiment, since the tracking that occurs when the life of the charger is exhausted based on the grid voltage can be detected and notification that the charger should be replaced can be made, the charger is replaced before the lifetime ends. Can be suppressed. That is, since the charger can be used longer than before, the cost due to the replacement of the charger can be reduced.

  The content of the message displayed in step S408 may be a message indicating that the charger is abnormal.

[Embodiment 2]
FIG. 5 is a schematic cross-sectional view of the charger and a part of the photosensitive drum according to the second embodiment of the present invention. In addition, the description is simplified by giving the same reference number to the already demonstrated location.

As can be seen by comparing FIG. 3 and FIG. 5, in the second embodiment, a power supply voltage detection unit 501 that detects the voltage (power supply voltage) of the constant current source 301 is added. When tracking occurs, the impedance between the feed wire 101 and the location where the tracking occurs (for example, a sheet metal connected to the shields 102a and 102b, the grid 103, or other GND) decreases. For example, if the tracking locations are shields 102a and 102b, I _ws increases and I _wg and I _wd decrease. On the other hand, if the tracking location is the grid 103, _Iwg increases and _Iws and _Iwd decrease. If the tracking location is another sheet metal connected to GND, I _ws , I _wg and I _{wd all} decrease.

Thus, if the tracking point shield 102a, 102b or grid _103, although either _{I ws} and _{I wg} increases, the total current _{(I ws + I wg + I} wd) is not changed. For this reason, the grid voltage is a controllable value. However, since the impedance between the power supply wire 101 and the shields 102a, 102b or the grid 103 is reduced, the potential (power supply voltage) of the power supply wire 101 is reduced and corona discharge does not occur.

Incidentally, there is a certain relationship between the feeding current I _pri and the feeding voltage. This correspondence may also be stored as a table in the memory of the controller 214. However, when the corona discharge does not occur, the power supply voltage detected by the power supply voltage detection unit 501 becomes lower than the original voltage value determined by I _pri at that time. Therefore, if the supply voltage is monitored, the occurrence of tracking can be detected. The power supply voltage detection unit 501 is an example of a second detection unit that detects the voltage across the constant current source 301 as the power supply voltage of the power supply member.

Note that if the location where the tracking occurs is another sheet metal connected to GND, I _ws and I _wg decrease, and no matter how much the variable resistor 302 connected to the grid 103 increases the resistance value, the voltage Will not occur. At this time, if the grid voltage detected by the grid voltage detection unit 303 is smaller than the minimum value determined by I _pri at that time, the controller 214 can recognize that tracking has occurred.

  FIG. 6 is a flowchart illustrating a method for controlling the image forming apparatus with tracking detection processing. Note that the same reference numerals are assigned to the processes common to the processes described in FIG. Here, step S405 is replaced with steps S601 to S603, as can be seen when compared with FIG. When the grid voltage is detected in step S404, the process proceeds to step S601.

  In step S601, the controller 214 determines whether or not the detection value of the grid voltage is within a predetermined range. The predetermined range is, for example, a range based on the control value of the grid voltage (eg, 700 V ± 50 V when the control value is 700 V). If the detected value is not within the predetermined range, tracking has occurred, and the process proceeds to step S407.

  On the other hand, if the detected value is within the predetermined range, the process proceeds to step S602. In step S <b> 602, the controller 214 detects a power supply voltage using the power supply voltage detection unit 501 provided in the charger high-voltage board 201.

In step S603, the controller 214 determines whether or not the power supply voltage of the power supply member is outside a predetermined range. For example, the controller 214 compares the detected value of the power supply voltage with a predetermined steady value, and determines whether or not the detected value of the power supply voltage is smaller than the predetermined steady value. The predetermined steady value is determined from a table stored in a memory provided in the controller 214. As described above, the minimum value (steady value) of the supply voltage with respect to the supply current is registered in the table. Therefore, the controller 214 determines a steady value as a comparison target from the power supply current I _pri at that time and the table. If the detected value of the power supply voltage is not smaller than the predetermined steady value, tracking has not occurred (it is not abnormal), and the processing according to this flowchart is terminated. On the other hand, if the detected value of the power supply voltage is smaller than the predetermined steady value in step S603 (eg, the minimum value of the power supply voltage is 8 kV but the detected value is 2 kV), tracking occurs. Therefore, the process proceeds to step S407.

  According to this embodiment, the controller 214 and the charger high-voltage board 201 function as a detection unit that detects the occurrence of tracking based on at least one of the grid voltage and the power supply voltage of the power supply member. According to the present embodiment, the controller 214 recognizes that tracking has occurred if the grid voltage is abnormal. Even when the power supply voltage of the power supply member indicates an abnormality regardless of whether the grid voltage is abnormal or not, the controller 214 notifies the display device 215 that the charger should be replaced. Therefore, there is an advantage that the tracking can be detected even if the location where the tracking occurs is another sheet metal connected to the GND.

It is a schematic sectional drawing of a general scorotron charger. 1 is a schematic sectional view of an image forming apparatus. FIG. 3 is a schematic cross-sectional view of a charger and a part of the photosensitive drum according to the embodiment. 5 is a flowchart illustrating a method for controlling an image forming apparatus with tracking detection processing. FIG. 6 is a schematic cross-sectional view of a charger and a part of a photosensitive drum according to Embodiment 2 of the present invention. 5 is a flowchart illustrating a method for controlling an image forming apparatus with tracking detection processing.

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 ... Feed wire 102 ... Shield 103 ... Grid 104 ... Charger 105 ... Photosensitive drum 201 ... High voltage board 202 for chargers ... Exposure device 204 ... Developer 208 ..Intermediate transfer member 209 ... secondary transfer roller 212 ... fixing device 214 ... controller 215 ... display device 301 ... constant current source for power supply 302 ... variable resistor 303 ... Grid voltage detector 501... Power supply voltage detector

Claims (6)

An image forming apparatus,
A photoreceptor,
A charger including a power supply member and a grid for charging the photosensitive member;
A detection unit that detects occurrence of tracking based on at least one of the bias voltage of the grid and the power supply voltage of the power supply member;
An image forming apparatus comprising: a notification unit that notifies the abnormality of the charger when the detection unit detects the occurrence of tracking. A constant voltage source for generating a constant voltage from a current flowing from the power supply member to the grid;
A first detector that is provided in the detector and detects the constant voltage as a bias voltage of the grid;
The image forming apparatus according to claim 1, wherein the notification unit notifies an abnormality of the charger when a bias voltage of the grid is outside a predetermined range.   The image forming apparatus according to claim 2, wherein the constant voltage source includes a variable resistor. A constant current source for supplying a constant current to the power supply member;
A second detection unit that detects a voltage across the constant current source as the power supply voltage of the power supply member;
The image forming apparatus according to claim 1, wherein when the power supply voltage of the power supply member is outside a predetermined range, the notification unit notifies the abnormality of the charger.   The image forming apparatus according to claim 1, wherein the charger is a scorotron charger. A control method for an image forming apparatus, comprising: a photoconductor; and a charger including a power supply member and a grid for charging the photoconductor,
A detection step of detecting occurrence of tracking based on at least one of the bias voltage of the grid and the power supply voltage of the power supply member;
And a notifying step of notifying the abnormality of the charger when the occurrence of tracking is detected in the detecting step.

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