JP2006276054A - Image forming apparatus and application voltage control method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of keeping a photoreceptor in a good charged state by a simple configuration. <P>SOLUTION: The image forming apparatus includes a rotationally driven photoreceptor 2, a charging roller 3 which is disposed in contact with or in proximity to the photoreceptor 2 and charges the photoreceptor 2, a current detection resistance 12 for detecting an amount of DC current flowing from the charging roller 3 to the photoreceptor 2, and a control part 13 which applies a DC voltage being within a range of the DC voltage flowing to the photoreceptor 2, and an AC voltage to the charging roller in a plurality of conditions and computes an AC voltage to be applied to the charging roller 3, from the amount of the DC current. Consequently, the AC voltage to be applied to a charging member is computed from the amount of the DC current to be able to keep the photoreceptor in a good charged state even in the image forming apparatus having no electric charge removing functions. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an applied voltage control method for uniformly charging a photoconductor by applying an AC bias and a DC bias by a contact or proximity charging method based on a charging principle.

  Conventionally, as a charging device, there is a contact type charging device in which a charging member such as a roller or a blade to which a voltage is applied is brought into contact with a surface of a charged body such as a photoconductor to charge the surface of the charged body to a predetermined polarity and potential. It is used.

  In this contact-type charging device, a method of applying a DC voltage and an AC voltage for charging to the charging device is employed. Only by applying a DC voltage, a current flows only at a low resistance on the photoconductor, so that it cannot be uniformly charged. Further, when the surface of the photosensitive member is locally soiled, there arises a problem that only that portion is not charged. Therefore, both the DC voltage and the AC voltage are applied to the charging device to charge the surface of the photoreceptor.

  However, if the AC voltage is too large, the photoreceptor wear will be affected. On the other hand, if the size is reduced, the uniformity of charging cannot be maintained, and unevenness occurs when printing. For this reason, it is necessary to set the AC voltage to the minimum necessary optimum value.

  In Patent Document 1, the AC voltage applied to the charging roller is sequentially increased as shown in FIG. 1, and the charged potential of the photosensitive member at that time is detected by a potential sensor, and the AC voltage is determined based on the saturated AC voltage. The amplitude (AC current or AC voltage) is determined. Hereinafter, the saturated voltage is referred to as a shoulder voltage.

  Patent Document 2 is also a technique related to a shoulder voltage detection method, in which the AC voltage is sequentially increased to detect the shoulder voltage, and the DC current at that time is detected. The AC voltage when the slope of the DC current with respect to the AC voltage stops changing is determined as the voltage to be applied to the charging member.

JP-A-9-185219 JP 7-239603 A

  However, in Patent Documents 1 and 2, since the shoulder voltage is detected while the AC voltage is sequentially increased, there is a problem that it takes a detection time. In addition, the photoconductor and the charging member have eccentricity and variations in film thickness. However, the DC current flowing due to these factors also varies with the rotation of the photoconductor. If a potential sensor or erase lamp is installed, the cost of the machine will increase.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image forming apparatus that can keep a photosensitive member in a favorable charged state with a simple configuration.

  In order to achieve the above object, an image forming apparatus of the present invention includes a rotationally driven photoconductor, a charging member that is disposed in contact with or in proximity to the photoconductor, and charges the photoconductor. A direct current detecting unit for detecting a direct current amount flowing into the photosensitive member; and a direct current voltage and an alternating current voltage within a range in which the direct current flows through the photosensitive member are applied to the charging member under a plurality of conditions, and the direct current current And a control unit that determines an AC voltage to be applied to the charging member based on a change in the amount. Therefore, even an image forming apparatus that does not have a charge eliminating function can calculate the AC voltage applied to the charging member from the amount of DC current, and keep the photosensitive member in a good charged state.

  In the image forming apparatus, the control unit may switch a DC voltage applied to the charging member so that the photoconductor is charged and discharged at a predetermined interval. Therefore, even an image forming apparatus that does not have a charge eliminating function can calculate the AC voltage applied to the charging member from the amount of DC current, and keep the photosensitive member in a good charged state.

  In the image forming apparatus, the control unit may apply the DC voltage and the AC voltage of the plurality of conditions at 1 / N (N is an arbitrary natural number) of the rotation period of the photoconductor. Therefore, a plurality of measurements can be performed during one rotation of the photoconductor, and the optimum value of the AC voltage applied to the charging member can be quickly detected.

  In the image forming apparatus, the control unit may determine values of the DC voltage and the AC voltage to be next applied to the charging member from the amount of DC current detected by the DC current detection unit. Therefore, the optimum value of the AC voltage applied to the charging member can be quickly detected.

  In the image forming apparatus, the control unit detects when the photoconductor is saturated based on a change in the amount of DC current detected by the DC current detection unit, and applies the AC voltage applied at that time to the film of the photoconductor. The AC voltage applied to the charging member may be determined by multiplying or adding a coefficient corresponding to the thickness. Therefore, the AC voltage applied to the charging member can be set to an optimum value.

  The applied voltage control method of the present invention applies a DC voltage and an AC voltage within a range in which a direct current flows to the photosensitive member to the charging member under a plurality of conditions, and the current of the direct current that flows from the charging member to the photosensitive member. The AC voltage applied to the charging member may be calculated from the amount. Therefore, even an image forming apparatus that does not have a charge eliminating function can calculate an AC voltage applied to the charging member based on a change in the amount of DC current, and keep the photosensitive member in a good charged state.

  The present invention can keep a photosensitive member in a good charged state with a simple configuration.

  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. Reference numeral 2 denotes a photoconductor as an image carrier. The photoconductor 2 of this example is a cylindrical OPC photoconductor, and is rotationally driven at a predetermined process speed (circumferential speed) in the clockwise direction indicated by an arrow about a central axis perpendicular to the paper surface.

  Reference numeral 3 denotes a charging roller (hereinafter referred to as BCR (Bias Charge Roll)) as a charging member brought into contact with the photosensitive member 2, and the charging roller 3 is rotated by the rotation of the photosensitive member 2 and AC. A predetermined voltage is applied from the power supply 10 and the DC power supply 11, and the peripheral surface of the rotating photosensitive member 2 is uniformly charged to a predetermined polarity and potential (in this example, negatively charged).

  Next, an image-modulated laser beam output from a ROS (Raster Optical Scanner) 4 is irradiated (scanning exposure) on the charging surface of the rotating photoconductor 2, and the potential of the exposed portion is attenuated to form an electrostatic latent image. It is formed.

  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.

  A conductive transfer roller 6 is disposed in pressure contact with the photosensitive drum 2 on the downstream side of the developing device 5 when viewed in the rotation direction of the photosensitive member 2, and the nip portion between the two 1 and 6 forms a transfer portion. Yes.

  When the toner image formed on the surface of the photoconductor drum 2 reaches the transfer portion as the photoconductor 2 rotates, the paper is supplied to the transfer position in synchronization with this, and a predetermined voltage is simultaneously applied to the transfer roller 6. 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 9 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 photosensitive member 2 is scraped off by the cleaning blade 7, whereby the surface of the photosensitive member 2 is cleaned and prepared for the next image formation.

  Further, in this embodiment, as shown in FIG. 2, an AC power source 10 and a DC power source 11 that apply a voltage to the charging member, a current detection resistor 12 inserted into the current flow, and a DC current detected by the current detection resistor 12 And a control unit 13 for controlling the AC voltage and the DC voltage applied to the charging roller 3.

  The AC power supply 10 and the DC power supply 11 apply a voltage obtained by superimposing an AC voltage on a DC voltage to the charging roller 3. The current detection resistor 12 detects a direct current flowing from the charging roller 3 to the photosensitive member 2 as a voltage by applying a voltage to the charging roller 3.

  The image forming apparatus 1 according to the present exemplary embodiment performs control so that the AC voltage applied to the charging roller 3 becomes an optimum value. First, an AC + DC voltage that becomes a reference charging potential state is applied, and then an AC + DC voltage for detection is applied to detect a DC current repeatedly.

  If the static elimination lamp is not installed, once the photosensitive member 2 is charged, static elimination cannot be performed, so that the direct current that has flowed in when the photosensitive member 2 is charged does not flow. Therefore, in this embodiment, as shown in FIG. 3A, the DC voltage of 0 V and −750 V is switched and applied at regular intervals. By applying a DC voltage of 0 V to the charging roller, the charge charged on the photoconductor 2 can be discharged. Even in the configuration without the charge-removing lamp, the DC voltage is always applied from the charging roller 3 to the photoconductor 2. Control can be performed so that current flows.

  Further, in order to detect the shoulder voltage, the amplitude of the AC voltage is changed stepwise as shown in FIG. 3B, and at this time, the direct current flowing from the charging roller 3 to the photosensitive member 2 is detected.

  The operation procedure of this embodiment will be described with reference to the flowchart of FIG. In this embodiment, as shown in FIG. 3B, first, a DC voltage as a reference condition is applied at 0 V and an AC voltage at 1.5 KVpp) (step S1). Note that AC of 1.5 kVpp indicates that the peak-to-peak voltage is 1.5 kV. Next, as a detection condition for detecting the DC current, the DC voltage is detected by setting the DC voltage to −750 V and the AC voltage to 1.3 kVpp (step S2). Next, a DC voltage of 0 V and an AC voltage of 1.5 kVpp are applied as reference conditions, a DC voltage as a measurement condition is −750 V, an AC voltage is 1.1 kVpp, and a DC current is detected.

  When such a procedure is repeated and the value of the detected DC current (FIG. 3C) is plotted, the result is as shown in FIG. The value immediately before the value of the DC current that has greatly changed is the voltage at which the photoreceptor is saturated (step S3), and by adjusting the applied voltage applied to the charging roller 3 based on this voltage, The voltage applied to the charging roller 3 can be set to the minimum necessary value (step S4). Since the detected AC voltage is a minimum state in which the charged state is stable, it is applied by performing arithmetic processing such as addition and multiplication on the value during actual drawing. Further, the coefficient at that time is not fixed but is changed depending on the film thickness. As a result, the amount of generated discharge products and the stress on the photoreceptor are drastically reduced at an extremely low cost, and an image forming apparatus that can withstand long-term continuous use without causing image quality defects can be obtained.

  FIG. 4 shows the positional relationship between the applied voltage switching timing and the photosensitive member 2 according to the present invention. In this embodiment, the photosensitive member 2 is divided into three, and a plurality of measurements are realized by one rotation of the photosensitive member 2. First, as shown in FIG. 4A, the area A on the photoreceptor 2 is set as a reference condition. Here, the reference conditions are described assuming that the DC voltage is ground and the AC voltage is 1.5 kVpp. Next, when the photosensitive member 2 rotates and the charging roller 3 comes over the area B as shown in FIG. 4B, a predetermined detection condition is applied to the area B by the charging roller 3, Measure. It is assumed that the region B is set as a reference condition when approaching the charging roller 3 last time (not shown). From this state, the charging roller 3 applies a DC voltage of −750 V and an AC voltage of 1.3 kVpp as detection conditions. Then, the DC current in region B is measured.

  Next, when the photosensitive member 2 rotates and the charging roller 3 comes over the area C as shown in FIG. 4C, the area C is set as a reference condition by the charging roller 3. In the area C, it is assumed that the DC current is measured by applying the voltage of the detection condition when approaching the charging roller 3 last time. Therefore, this time, the region C is set as a reference condition.

  Next, when the photosensitive member 2 rotates and the charging roller 3 comes over the area A as shown in FIG. 4D, a predetermined detection condition is applied to the area A by the charging roller 3, and Measure. Since the area A is set as a reference condition when it approaches the charging roller 3 last time, a detection condition such as a DC voltage of −750 V and an AC voltage of 1.1 kVpp is applied. Then, the DC current in region A is measured.

  As described above, since the area on the photosensitive member 2 is divided into a plurality of parts and the DC current is measured, the measurement time can be shortened. For example, in Patent Documents 1 and 2, it takes 6 rotations to detect 6 points, but in this example, 4 rotations can be performed without reducing accuracy. Further, if the photosensitive member is divided into five parts, it can be completed in 2.4 rounds. Further, the number of divisions of the photosensitive member 2 has been described as an odd number division, but even the even number division can be achieved by changing the way of giving a signal. For example, in the case of two divisions, it can be realized by repeating the applied voltage in the order of the reference condition, the reference condition, the detection condition, and the detection condition. Therefore, it does not occur. Therefore, the number of divisions of the photosensitive member can be arbitrarily determined in consideration of time and other influences.

  Further, by measuring the time required for one rotation of the photosensitive member 2 and performing measurement at the same positions on the areas A, B, and C by the time control of the control unit 13, the eccentricity of the photosensitive member 2 and the charging roller 3, It is possible to eliminate errors caused by variations in the photoreceptor film thickness.

  Next, a method for efficiently detecting the point where the detected value changes will be described. The applied AC voltage is sequentially decreased in FIG. 3B, but as shown in FIG. 4, the first AC voltage (1.5 kVpp in the above description) is increased to +1, −1/2, + 1 / 4 and −1/8 may be integrated to control the AC voltage to be applied. As described above, the next application value is determined based on the first detection value, so that time-effective detection can be performed.

  The embodiment described above 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.

It is a figure for demonstrating a shoulder voltage. 1 is a diagram illustrating a configuration of an image forming apparatus. It is a figure which shows the DC voltage and AC voltage which are applied to a charging roller, and the measured DC current. It is a figure which shows the measurement position in a photoconductor. It is a figure which shows the AC voltage at the time of a measurement. It is a flowchart which shows an operation | movement procedure.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 Photoconductor 3 Charging roller 4 ROS
5 Developing Device 6 Transfer Roller 7 Cleaning Blade 9 Fixing Device 10 AC Power Supply 11 DC Power Supply 12 Current Detection Resistor 13 Control Unit

Claims (6)

A rotationally driven photoreceptor;
A charging member disposed in contact with or in proximity to the photoconductor to charge the photoconductor;
A direct current detector for detecting the amount of direct current flowing from the charging member into the photosensitive member;
A DC voltage and an AC voltage within a range where the DC current flows through the photoconductor are applied to the charging member under a plurality of conditions, and an AC voltage applied to the charging member based on a change in the amount of the DC current is applied. An image forming apparatus comprising: a control unit for determining.   The image forming apparatus according to claim 1, wherein the controller switches a DC voltage applied to the charging member so that the photosensitive member is charged and discharged at predetermined intervals.   2. The controller according to claim 1, wherein the controller applies the DC voltage and the AC voltage under the plurality of conditions at 1 / N (N is an arbitrary natural number) of the rotation period of the photoconductor. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the control unit determines a value of the DC voltage and the AC voltage to be next applied to the charging member from a DC current amount detected by the DC current detection unit. apparatus.   The control unit detects when the photoconductor is saturated based on a change in the amount of DC current detected by the DC current detection unit, and applies a coefficient corresponding to the film thickness of the photoconductor to the applied AC voltage at that time. The image forming apparatus according to claim 1, wherein an AC voltage applied to the charging member is determined by multiplication or addition. The charging member is applied based on a change in the amount of the DC current flowing from the charging member into the photosensitive member by applying a DC voltage and an AC voltage within a range in which a direct current flows to the photosensitive member to the charging member under a plurality of conditions. An applied voltage control method, comprising: determining an alternating voltage to be applied to the power supply.

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