JP2007248831A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suitably judging the applied state of an overlap bias voltage. <P>SOLUTION: The image forming apparatus applies an overlap bias, obtained by overlapping an AC voltage and a DC voltage, to a charger 11 that charges a photoreceptor drum 10. The image forming apparatus has an AC charging current detecting means that detects an AC charging current flowing from the ground level of the photoreceptor drum 10 to the ground level of the apparatus. Based upon the output of the AC charging current detecting means, an abnormal state is discriminated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that applies a superimposed bias voltage formed by superimposing an AC voltage and a DC voltage to a charger that charges a photosensitive drum.

  Conventionally, a photosensitive drum undergoes a uniform charging process with a predetermined polarity and potential by a charging device during its rotation, and then undergoes image exposure by an exposure device.

  As a result, an electrostatic latent image is formed on the photosensitive drum surface. The developing means having a developing roller disposed opposite to the photosensitive drum conveys the toner to the developing means on the surface of the photosensitive drum on which the electrostatic latent image is formed, and further, the developing bias means uniformly supplies a predetermined polarity and potential. By applying a voltage, a potential difference from the latent image portion of the photosensitive drum is generated, and the toner is electrostatically adsorbed on the photosensitive drum.

  As a charging device, a contact charging method is widely used in which a photosensitive drum surface is charged using a charging member such as a roller type or a blade type.

  As for the output of the charging device, the charging bias voltage may be only a DC voltage, but generally an output in which an AC voltage is superimposed and applied to the DC voltage (hereinafter referred to as AC charging output or AC charging voltage) is made.

  This charging method is excellent for uniformly charging the photosensitive drum. By applying an alternating voltage to the direct current voltage and further setting the frequency of the alternating charging voltage suitable for the rotational speed of the photosensitive drum, Local potential unevenness on the photosensitive drum is eliminated, and the charged potential Vd on the surface of the photosensitive drum converges uniformly on the DC applied voltage value Vdc.

  Further, in the developing device, a system is widely employed in which toner is transported to a portion in contact with the surface of the photosensitive drum using a developing member such as a developing roller.

  The output of the developing device may be only a DC voltage, but in general, an AC voltage set to a frequency several times the AC charging voltage frequency superimposed on the DC voltage (hereinafter referred to as AC developing output or AC developing). (Denoted as voltage) increases the toner leaving the carrier and improves the developing ability.

  As the toner reciprocates according to the AC bias, the toner around the image area gathers in the image area and is developed. The AC development method is characterized by high image density and good dot reproducibility, such as the toner attached to the non-image area being rearranged in the image area. , Described as AC development output).

  However, the charging method of this apparatus is more likely to cause filming in which impurities such as NOx adhere to the surface of the photosensitive member because the discharge amount to the photosensitive drum increases compared to the case where only the DC component is applied as the charging bias voltage. Become.

  In order to remove this, there is a tendency that the photosensitive surface is likely to be deteriorated due to abrasion with the cleaning device, and in order to cope with this, the AC peak voltage Vpp of the charging bias voltage is suppressed as small as possible and charging is performed. It was necessary to prevent the roller from being excessively discharged to the photosensitive drum.

  Further, the relationship between the AC peak-to-peak voltage (Vpp) and the discharge amount is not always constant because it varies depending on the film thickness of the photosensitive layer on the surface of the photosensitive drum, the usage environment, and the like.

  For example, even if the same peak-to-peak voltage is applied to the charging device, the impedance of the charging device increases in a low-temperature and low-humidity environment, so that the amount of discharge is small.

  Even when the usage environment is the same, if the surface of the photoconductor is scraped off due to wear, the impedance is reduced as compared with the initial use, and the amount of discharge increases.

  For this reason, when a certain AC charging voltage is output, the AC charging current under the usage condition is detected and control is performed to output the necessary current of the AC charging current. However, the AC charging voltage becomes a high voltage. The AC charging current does not flow into the photoconductor, but flows through the charging output path and the stray capacitance around the path.

  An AC charging current, which is the sum of the AC current through the stray capacitance and the AC current flowing through the photosensitive member, is detected, and the correct current flowing through the photosensitive member cannot be detected.

In order to cope with the above-mentioned problems, by providing a means for detecting an AC charging current flowing from the photoreceptor ground level to the apparatus ground level, the flowing AC current can be ignored by the stray capacitance, and the photoreceptor can be more accurately detected. There has been proposed a method capable of detecting the AC charging current flowing through the.
Japanese Patent Laid-Open No. 08-202218

  However, in such a conventional apparatus, an abnormal image is generated when the photoreceptor ground level is separated from the apparatus ground level.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can appropriately determine an application state of a superimposed bias voltage.

  The present invention relates to an alternating current that flows between a ground level of a photosensitive drum and a ground level of the device in an image forming apparatus that applies a superimposed bias voltage formed by superimposing an alternating voltage and a direct current voltage to a charger that charges the photosensitive drum. An AC charging current detecting means for detecting a charging current is provided, and an abnormal state is discriminated based on the output of the AC charging current detecting means.

  Further, when the output of the superimposed bias voltage is short-circuited, an abnormality is detected based on the abnormality detection signal of the DC voltage output.

  Further, when the superimposed bias voltage is released, an abnormality is detected based on a current detection signal of AC voltage output.

  The determination of the abnormal state is performed while the photosensitive drum is rotating.

  Therefore, according to the present invention, since the abnormal state is determined based on the detection output of the AC charging current flowing between the ground level of the photosensitive drum and the apparatus ground level, it is possible to appropriately determine the abnormality. The effect is obtained.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 shows an example of a schematic configuration of an image forming apparatus according to an embodiment of the present invention.

  In the figure, a control unit 1 controls the operation of each part of the image forming apparatus to appropriately form and output an image. An external interface unit 2 is connected to an external apparatus such as a host apparatus. In addition, various information is exchanged with the external device.

  The transport unit 3 is for separating and transporting the transfer paper from the paper feed table, the charging unit 4 is for charging a photosensitive drum (described later), and the writing unit 5 is charged. This is for forming an electrostatic latent image of a written image on the surface of the photosensitive drum, and is composed of, for example, a laser beam writing device.

  The developing unit 6 is for developing the electrostatic latent image formed on the photosensitive drum with toner and developing it, and the fixing unit 7 is transferred onto the transfer paper by a transfer unit (not shown). The operation display unit 8 constitutes a user interface of the image forming apparatus, and is used by the user to operate the image forming apparatus.

  FIG. 2 shows an example of an image forming system.

  In the figure, the surface of the photosensitive drum 10 is charged by a charger 11, and a laser beam 12 output from the writing unit 5 is scanned to form an electrostatic latent image of a printed image on the surface.

  This electrostatic latent image is developed with toner by the developing device 13, transferred to the surface of the transfer paper DP by the transfer device 14, and then thermally fixed by a fixing device (not shown). Further, the toner remaining on the surface of the photosensitive drum 10 is removed by the cleaning unit 15.

  As described above, when the surface of the photosensitive drum 10 is charged, a superimposed bias voltage in which an AC voltage is superimposed on a DC voltage is applied. FIG. 3 shows an example of the configuration of the superimposed bias voltage generator.

  In the figure, an AC output control circuit 21 forms an AC voltage having a predetermined frequency and a predetermined voltage value on the basis of a DC voltage 24 (volts). Applied to the charger 11.

  The DC output control circuit 23 forms a DC voltage having a predetermined voltage value based on the DC voltage 24 (volts), and the output is applied to the charger 11 via the output circuit 23. .

  In this way, the AC voltage output from the AC output control circuit 21 and the DC voltage output from the DC output control circuit 23 are applied to the charger 11 in a superimposed state.

  Further, the voltage value of the AC voltage output from the AC output control circuit 21 is controlled by the signal S1 output from the control unit 1, and the frequency of the AC voltage output from the AC output control circuit 21 is controlled by the signal S3.

  Further, the voltage value of the DC voltage output from the DC output control circuit 23 is controlled by the signal S2 output from the control unit 1.

  The AC charging current detection circuit 25 detects a current Ia flowing through the photosensitive member ground level (photosensitive member GND) of the photosensitive drum 10, and the detection signal S 4 is output to the control unit 1.

  Reference sign Cp represents a stray capacitance generated between the charger 11 and the apparatus ground level (apparatus GND).

  In such a configuration, in a normal operation, an alternating current “Ia + Ib” flows from the photoconductor GND through the alternating charging current detection circuit 25 to the device GND.

  When an AC charging current is detected and a charging current suitable for the current environment and the state of the photosensitive member is set, the output of the developing unit 6 is turned off, and the current flowing from the developing unit 6 to the photosensitive drum 10 Is set so that only the alternating current Ia can be accurately detected.

  The constant of the AC charging current detection circuit is taken into consideration so that the voltage of the photoconductor GND when the AC current flows is sufficiently small so that the AC charging current does not flow from the portion of the photoconductor GND to the stray capacitance. In the normal printing operation, it is set so that there is no image defect.

  A method for setting an AC charging current according to the environment of the apparatus and the state of the photosensitive member will be described with reference to FIG.

  When an AC charging current is passed, the AC charging current detection circuit 25 detects a DC voltage proportional to the AC charging current flowing through the photosensitive member. For example, assume that a 1 V voltage is output from the AC charging current detection circuit 25 when an AC current of 1 mA flows.

  In this case, constants and the like of the AC charging current detection circuit are set in advance. When the AC charging current: X is desired to flow, the AC charging currents a and b at the time of the AC charging voltage A and the AC charging voltage B are detected (processing 101, 102, 103, 104).

From this relationship, the amount of increase in current with respect to voltage can be found. Increase amount of current: ΔI = (ab) / (AB) From this, the AC charging voltage: Y when the AC charging current: X is to flow is
Y = A + (X−a) ÷ {(ab) / (AB)}
(Process 105). The calculated AC charging voltage: Y is held until the next AC charging voltage setting control (process 106), and is output during printing.

  In the case of constant voltage output, detection of the short-circuit mode can be easily configured as a circuit as abnormality detection.

  As DC charging, a constant voltage output is generally used because a stable voltage is required even if the load fluctuates.

  The AC charging output is controlled by a constant voltage as described above, but has a configuration capable of detecting a current.

  That is, when the output terminal portion is short-circuited to the AC charging current detection portion without passing through the device GND or the charging roller and the photosensitive member, the load becomes extremely small compared to the load of the normal device, and the DC charging output is The output voltage cannot be maintained, and the abnormality detection circuit operates.

  On the contrary, when it is opened, the load becomes infinitely large, so that the voltage can be maintained and the abnormality detection circuit does not operate.

  In this way, the DC charging voltage abnormality detection circuit can detect the short-circuit state of the output terminal portion but cannot detect the abnormality of the open state.

  A method for detecting an abnormality in the AC charging output will be described.

  In order to maintain the image quality, a means for detecting and adjusting the AC charging current is provided, and if the current value of the AC charging current does not become a specified value, it can be determined that there is an abnormality.

  When it is in an open state, it can be detected because the AC charging current stops flowing. In addition, even when the photoconductor GND and the device GND are short-circuited, the AC charging current cannot be detected because it does not pass through the AC charging current detection circuit, but the load is sufficiently large only by not passing through the AC charging current detection circuit. Can be distinguished because it is output normally.

  As described above, it is possible to determine an abnormal state and an abnormal part. The above abnormality detection is performed while the photoconductor is rotating, because the photoconductor is rotating and becomes a normal load of the apparatus.

  FIG. 5 is a diagram for explaining a process when an abnormality in the charging voltage is detected during the printing operation.

  First, when a print request is received from an external device (process 201), rotation of the photosensitive drum 10 is started (process 202), and signals S1, S2, and S3 are output, and an AC output control circuit 21 and a DC output control circuit are output. 23 is operated to generate a superimposed bias voltage (process 203).

  Then, the detection signal S4 of the AC charging current detection circuit 25 is input to check whether the AC charging voltage is normal (determination 204). When the result of determination 204 is YES, it is checked whether the DC charging voltage is normal (determination 205). When the result of determination 205 is YES, the printing operation is started (process 206).

  Here, when the DC charging voltage is not normal and the result of determination 205 is NO, it is a case where the output terminal and the AC charging current detection circuit 25 are short-circuited without passing through the photosensitive drum 10, so that the DC charging abnormality is detected. The information is retained (process 207), and this operation is terminated.

  Further, when the AC charging voltage is not normal and the result of determination 204 is NO, AC charging abnormality information is held (processing 208). Next, it is examined whether or not the DC charging voltage is normal (decision 209). When the result of determination 209 is YES, DC charging normal information is held (processing 210), and the operation at this time is terminated.

  If the result of determination 205 is NO, the DC charging abnormality information is held (processing 211), and this operation is terminated.

  FIG. 6 is a diagram for explaining a process when detecting abnormality of the charging voltage during the process adjustment operation.

  First, when a process adjustment request is received from an external device (process 301), rotation of the photosensitive drum 10 is started (process 302), and signals S1, S2, and S3 are output, and the AC output control circuit 21 and DC output control are output. The circuit 23 is operated to generate a superimposed bias voltage (process 303).

  Then, the detection signal S4 of the AC charging current detection circuit 25 is input to check whether the AC charging voltage is normal (decision 304). When the result of determination 304 is YES, it is checked whether the DC charging voltage is normal (determination 305). When the result of determination 305 is YES, a process adjustment operation is started (process 306).

  Here, when the DC charging voltage is not normal and the result of the determination 305 is NO, it is a case where the output terminal and the AC charging current detection circuit 25 are short-circuited without passing through the photosensitive drum 10, so that the DC charging abnormality is detected. The information is retained (process 307), and this operation is terminated.

  Further, when the AC charging voltage is not normal and the result of determination 304 is NO, AC charging abnormality information is held (processing 308). Next, it is examined whether or not the DC charging voltage is normal (decision 309). When the result of determination 309 is YES, the DC charging normal information is held (processing 310), and the operation at this time is terminated.

  If the result of determination 305 is NO, DC charging abnormality information is held (processing 311), and this operation is terminated.

  FIG. 7 shows an example of the operation when an error is detected.

  By the above processing, AC charging abnormality information or DC charging abnormality information is held, and when an abnormality is detected (processing 401), an error sound is output by the operation display unit 8 (processing 402) and an error occurrence is displayed. (Process 403).

  Here, it is checked whether or not the execution of printing is instructed by the user (determination 404). When the result of determination 404 is YES, the printing operation is started (process 405).

  In this way, in the present embodiment, it is possible to appropriately determine the abnormality of AC charging and the abnormality of DC charging, so that a highly reliable printing operation can be realized.

  In addition, since the detection operation is performed while the photoconductive drum is rotating, for example, it is possible to prevent the photoconductive drum from being unduly high impedance and to perform normal detection of abnormality.

  In the above-described embodiments, the case where the present invention is applied to an apparatus capable of monochrome printing has been described. However, the present invention can also be applied to an apparatus capable of color printing in the same manner.

1 is a block diagram showing an example of a schematic configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic configuration diagram illustrating an example of an image forming system. The block diagram which showed an example of the structure of a superimposition bias voltage generation part. 6 is a flowchart for explaining a method of setting an AC charging current according to the environment of the apparatus and the state of the photosensitive member. 6 is a flowchart for explaining processing when abnormality of charging voltage is detected during a printing operation. The flowchart for demonstrating the process at the time of performing abnormality detection of a charging voltage during process adjustment operation | movement. The flowchart which showed an example of the operation | movement at the time of an error detection.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Control unit 4 Charging unit 10 Photosensitive drum 11 Charger 21 AC output control circuit 23 DC output control circuit 25 AC charging current detection circuit

Claims (4)

In an image forming apparatus that applies a superimposed bias voltage formed by superimposing an AC voltage and a DC voltage to a charger that charges a photosensitive drum,
AC charging current detection means for detecting AC charging current flowing between the ground level of the photosensitive drum and the apparatus ground level,
An image forming apparatus characterized in that an abnormal state is determined based on an output of the AC charging current detecting means.   2. The image forming apparatus according to claim 1, wherein when the output of the superimposed bias voltage is short-circuited, an abnormality is detected based on an abnormality detection signal of a DC voltage output.   2. The image forming apparatus according to claim 1, wherein when the superimposed bias voltage is released, an abnormality is detected based on a current detection signal of an AC voltage output.   The image forming apparatus according to claim 1, wherein the abnormal state is determined while the photosensitive drum is rotating.

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