JP2007052125A - Potential measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a potential measuring device capable of setting an AC voltage or an AC current to an optimum value by a simple circuit configuration. <P>SOLUTION: The potential measuring device includes: an electrode 11 disposed close to a photoreceptor 2 that is rotary-driven, and a voltage detection section 12 that detects the surface potential of the photoreceptor 2 induced by the electrode 11. The electrode 11 and the voltage detecting section 12 are set so that a potential difference between the photoreceptor 2 and each of them is not greater than Paschen voltage at which discharge is caused. Accordingly, since the electrode 11 and the voltage detecting section 12 are set so that the potential difference between the photoreceptor 2 and each of them is not greater than the Paschen voltage, the discharge is not caused even when the electrode 11 is brought into close contact with the photoreceptor 2. Thus, the surface potential of the photoreceptor 2 can be detected at high resolution. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a potential measuring apparatus that measures a surface potential distribution on a member to be charged and controls a charging voltage based on the measured potential distribution.

  Conventionally, as a method for measuring the surface potential on a photoconductor, a method of measuring an induced current using an electrode or the like is known. An electrode is disposed close to the photoreceptor, and the electrode is moved relative to the photoreceptor by rotation of the photoreceptor. As a result, the electric charge detected by the electrode changes with time, and the surface potential is measured by detecting the induced current value at that time.

  In the measurement of electrostatic latent images using electrodes placed close to the photoconductor, a technique for reducing the size of the electrodes in order to increase resolution and a method for providing a plurality of electrodes and narrowing the pitch between these electrodes have been proposed. ing.

  Patent Document 1 discloses a method of increasing the discharge start voltage by filling an inert gas having a high discharge start voltage near the measurement electrode. In order to suppress the discharge phenomenon, a method is disclosed in which the common voltage of a circuit for measuring the potential induced in the electrode is set to an intermediate potential between the maximum and minimum values of the measured value, thereby reducing the potential difference.

Japanese Patent No. 03917979

  However, a device for injecting an inert gas and a device for exhausting the injected gas must be provided separately, which causes a problem that the device becomes large. Even when the common voltage of the circuit is set to an intermediate potential, there is a potential difference of about several hundred volts between the photoconductor and the electrode, and discharge occurs when approached to increase measurement accuracy. Can not.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a potential measuring device that can accurately measure the surface potential of an object to be charged.

  In order to achieve such an object, the potential measuring device of the present invention detects a measurement electrode arranged in the vicinity of a member to be rotated and driven, and a surface potential of the member to be charged guided to the measuring electrode. The measurement electrode and the detection circuit have a configuration in which a potential difference from the charged body is set to be equal to or lower than a Paschen voltage at which discharge occurs. As described above, according to the present invention, the measurement electrode and the detection circuit are set so that the potential difference from the charged body is equal to or less than the Paschen voltage. Therefore, no discharge occurs even when the measuring electrode is brought close to the charged body. For this reason, the surface potential of the member to be charged can be detected with high resolution.

  The potential measuring apparatus may include a power supply unit that supplies power to the detection circuit so that a common voltage that is a reference for the operation of the detection circuit becomes a saturation voltage of the charged body. Therefore, the potential of the detection circuit and the measurement electrode can be set to a value close to the potential of the charged object.

  In the potential measuring apparatus, the power supply unit may also serve as a power supply for supplying a voltage to the charging member. Without providing a new power source, the potential of the detection circuit and the measurement electrode can be set to a value close to the potential of the member to be charged.

  In the potential measurement device, the power supply unit may include a floating power supply that generates a voltage higher than a saturation voltage of the charged body by a predetermined value and supplies the voltage to the detection circuit. Therefore, it is possible to supply power for operating the detection circuit normally.

  The potential measurement device may include a voltage level conversion unit that converts the level of the output voltage of the detection circuit. Therefore, the output of the detection circuit can be input to another circuit, for example, a control unit and processed.

  In the potential measuring device, the detection circuit may be surrounded by a shield box for protecting from a noise source. Therefore, the detection circuit can be protected from the noise source.

  In the potential measurement device, the voltage level conversion unit may convert the level of the output voltage by optical coupling or magnetic coupling. Therefore, the voltage level can be converted with a simple configuration.

  The present invention can accurately measure the surface potential of an object to be charged.

  Preferred embodiments of the present invention will be described with reference to the accompanying drawings.

  First, the configuration of the present embodiment will be described with reference to FIG. The photoconductor 2 as an image carrier is a cylindrical OPC photoconductor, and is driven to rotate at a predetermined process speed (circumferential speed) in the clockwise direction indicated by an arrow about a central axis perpendicular to the paper surface.

  A charging roll 3 serving as a charging member is disposed around the photoreceptor 2. The charging roll 3 is rotated by the rotation of the photosensitive member 2, and a predetermined voltage is applied from the AC power source 21 and the DC power source 20, and the peripheral surface of the rotating photosensitive member 2 is uniformly set to a predetermined polarity and potential. Is charged (negatively charged in this example).

  Next, the image-modulated laser beam output from the exposure device 4 is irradiated (scanning exposure) to the charging processing surface of the rotating photoconductor 2, and the potential of the exposed portion is attenuated to form an electrostatic latent image.

  When the latent image arrives at the developing portion facing the developing device 5 as the photosensitive member 2 rotates, negatively charged toner is supplied from the developing device 5 and a toner image is formed by reversal development.

  An electroconductive transfer roll 6 is disposed in pressure contact with the photoconductor 2 on the downstream side of the developing device 5 when viewed in the rotation direction of the photoconductor 2, and a nip portion between the photoconductor 2 and the transfer roll 6 serves as a transfer site. Forming.

  When the toner image formed on the surface of the photoconductor 2 reaches the transfer site as the photoconductor 2 rotates, the paper is supplied to the transfer position at the same time, and a predetermined voltage is applied to the transfer roll 6 at the same time. As a result, the toner image is transferred from the surface of the photoreceptor 2 to the paper.

  The sheet that has received the toner image transfer at the transfer position is conveyed to the fixing device 7 where the toner image is fixed and discharged out of the apparatus.

  On the other hand, the untransferred toner remaining on the surface of the photoconductor 2 is scraped off by the cleaning blade 8, whereby the surface of the photoconductor 2 is cleaned and prepared for the next image formation.

  Here, a contact charging method in which the charging roll 3 is brought into contact with the photoreceptor 2 and a voltage obtained by superimposing a DC voltage on the AC voltage is applied to charge the photoreceptor 2 will be described. In general, even when a DC voltage is applied alone, a current flows only where the resistance on the photosensitive member 2 is low, so that uniform charging cannot be performed. Therefore, a voltage obtained by superimposing a DC voltage on an AC voltage is applied to uniformly charge the surface potential of the photoreceptor.

  However, if the AC voltage is too high, the photoreceptor is worn out. On the other hand, if it is too small, the uniformity of charging cannot be maintained, and unevenness occurs when printed. For this reason, it is necessary to set the AC voltage to the minimum necessary optimum value. Therefore, the AC voltage applied to the charging roll 3 is sequentially increased, the charged potential of the photosensitive member at that time is detected by a potential sensor, and the AC voltage or AC voltage is determined based on the AC voltage at which the photosensitive member is saturated. The current is set to an optimum value (for example, set to a voltage that is larger by a predetermined value than the voltage when the photosensitive member 2 is saturated, such as Vpp (α) shown in FIG. 2). By setting the AC voltage to such a value (Vpp (α)), it is possible to set the charging potential at which the surface potential of the photosensitive member 2 is locally stable and to a minimum value. Image quality and reliability can be improved. Note that the saturated voltage as shown in FIG. 2 is called a shoulder voltage. Further, it is known that when the photosensitive member 2 is saturated, the surface potential of the photosensitive member 2 matches the applied DC voltage.

  Further, the image forming apparatus 1 includes an electrode 11 disposed in the vicinity of the photoconductor 2 so as to face the photoconductor 2, and a voltage detection unit that measures an induced voltage or an induced current induced in the electrode 11 (detection of the present invention). (Corresponding to a circuit) 12, a voltage level conversion unit 13, and a control unit 14 are provided as the potential measuring device 10. As shown in FIG. 1, the electrode 11 is disposed after being charged by the charging roll 3 and before being exposed by the exposure device 4.

  The configuration of the voltage detection unit 12 will be described with reference to FIG. As shown in FIG. 3, the voltage detector 7 includes an operational amplifier 16, a detection capacitor 17, and a reset switch 18. As described above, the voltage detection unit 12 does not require a high voltage circuit and can be configured with a simple circuit, and thus can be realized at low cost. Further, the periphery of the voltage detection unit 12 is surrounded by a shield box 15 as shown in FIG. Since a high voltage is applied to the photoreceptor 2 and its peripheral members, the voltage detector 12 is surrounded by a low-potential shield box 15 in order to protect the voltage detector 12 from noise such as electromagnetic waves. The potential of the shield box 15 is connected so as to coincide with the common voltage of the circuit constituting the voltage detector 12.

  The operational amplifier 16 and the detection capacitor 17 constitute an integrator. The photoconductor 2 and the electrode 11 adjacent to the photoconductor 2 form a capacitor, and a change in the surface potential of the photoconductor 2 when the applied voltage of the charging roll 3 is changed is detected as an induced potential. The surface potential of the photoreceptor 2 is measured by integrating the current flowing through the electrode 11 with an integrator composed of an operational amplifier 16 and a detection capacitor 17. The reset switch 18 discharges the charge accumulated in the detection capacitor 172 and resets it.

  In addition, the operational amplifier 16 of the voltage detection unit 12 is driven by a floating power supply 30. The floating power supply 30 has a configuration in which a diode 31 is connected in parallel with a Zener diode 32 and a resistor 33 as shown in FIG. The ground of the floating power source 30 is connected to the DC output of a power source (AC power source 21 and DC power source 20) that applies a charging voltage to the charging roll 3. Further, the output of the AC power supply 21 is connected to the input of the floating power supply 30. The floating power supply 30 generates a voltage higher than the DC level connected to the ground by a predetermined value and supplies the voltage to the operational amplifier 16.

  In the case of a charging method in which a DC voltage is superimposed on an AC voltage, the final surface potential of the photoreceptor 2 matches the DC voltage. Therefore, in this embodiment, the ground side of the floating power source 30, the shield box 15, and the input terminal of the operational amplifier 16 are connected to the DC power source 20, and these are set to the DC level. As a result, the circuit of the voltage detection unit 12 can be set to operate on the basis of −750 V (DC level) which is the saturation voltage of the photosensitive member 2. Further, the potential of the shield box 15 can be set to the lowest potential of the circuit.

  It is assumed that the common potential of the circuit of the voltage detection unit 12 is set to a voltage that matches the average value of the surface potential of the photoreceptor 2. At this time, the potential difference between the voltage detection unit 12 and the photoreceptor 2 is approximately 0V. Even if the surface potential of the photoconductor 2 varies locally, this variation is about 100 V at most. Therefore, even if the electrode 9 is sufficiently close to the photoconductor 2, no discharge occurs, and as a result The surface potential can be detected with high resolution. That is, the difference between the surface potential of the photoreceptor 2 and the potential of the electrode 11 and the voltage detection unit 12 can be set to be equal to or lower than the Paschen discharge voltage, and the occurrence of discharge can be prevented.

  The voltage level conversion unit 13 converts the voltage level of the signal output from the voltage detection unit 12. As described above, the voltage detector 12 operates based on −750V. For this reason, it is necessary to convert the level of the output voltage of the voltage detection unit 12 into an electric signal of 0 to 5 V that can be input to the control unit 14. The voltage level conversion unit 13 optically couples the output side of the operational amplifier 16 and the control unit 14 using a photocoupler or the like. Therefore, the voltage level of the signal can be converted by optical coupling of the photocoupler. The operational amplifier 16 and the control unit 14 can be magnetically coupled using a transformer or the like. Therefore, signal level conversion is performed by magnetic coupling of the transformer.

  The control unit 8 controls each unit described above, and controls the AC + DC voltage applied to the charging roll 3 to an optimum value based on the photoreceptor surface potential detected by the voltage detection unit 7.

  As described above, in this embodiment, the electrode 11 and the voltage detection unit 12 are set so that the potential difference from the photoreceptor 2 is equal to or less than the Paschen voltage. Therefore, no discharge occurs even when the electrode 11 is brought close to the photoreceptor 2. Therefore, the surface potential of the photoreceptor 2 can be detected with high resolution.

  The above-described embodiment is a preferred embodiment of the present invention. However, the present invention is not limited to this, and various modifications can be made without departing from the scope of the present invention.

1 is a diagram illustrating a configuration of an image forming apparatus. It is a figure for demonstrating a shoulder voltage. It is a figure which shows the detailed structure of a voltage detection part.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Photoconductor 3 Charging roll 4 Exposure device 5 Developing device 6 Transfer roll 7 Fixing device 8 Cleaning blade 9 Static elimination lamp 10 Potential measuring device 11 Electrode 12 Voltage detection part 13 Voltage level conversion part 14 Control part 15 Shield box

Claims (7)

A measurement electrode arranged in proximity to the object to be rotated,
A detection circuit for detecting a surface potential of the charged body induced by the measurement electrode;
The potential measuring apparatus, wherein the measurement electrode and the detection circuit are set so that a potential difference from the charged body is equal to or less than a Paschen voltage at which discharge occurs.   The potential measuring apparatus according to claim 1, further comprising a power supply unit configured to supply power to the detection circuit so that a common voltage serving as a reference for the operation of the detection circuit becomes a saturation voltage of the charged body.   The potential measuring apparatus according to claim 2, wherein the power supply unit also serves as a power supply for supplying a voltage to the charging member.   The potential measuring apparatus according to claim 2, wherein the power supply unit includes a floating power supply that generates a voltage higher than a saturation voltage of the charged body by a predetermined value and supplies the voltage to the detection circuit.   5. The potential measuring device according to claim 1, further comprising a voltage level conversion unit that converts a level of an output voltage of the detection circuit.   6. The potential measuring device according to claim 1, wherein the detection circuit is surrounded by a shield box for protecting from a noise source. 6. The potential measuring device according to claim 5, wherein the voltage level conversion unit converts the level of the output voltage by optical coupling or magnetic coupling.

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