JP2016224351A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation device that can generate a sufficiently required AC discharge in a charging processing in accordance with a charging member or a state of an image carrier when implementing the charging processing of the image carrier in an AC charging method.SOLUTION: An image formation device 10 includes: an image carrier 1; a charging member 2 that is arranged in contact with or proximity to the image carrier 1; a power source SP1 that can apply a voltage having a DC voltage and AC voltage overlapped to the charging member 2; a measurement unit 14 that measures an AC current flowing into the charging member 2; and an adjustment unit 11 that adjusts the voltage to be applied to the charging member 2 by the power source SP1. The adjustment unit 11 is configured to: cause the measurement unit 14 to measure the AC current flowing into the charging member 2 when the power source SP1 applies at least the AC voltage to the charging member 2 over a prescribed period upon non-image formation; and adjust the AC voltage in the voltage having the overlapped DC voltage and AC voltage to be applied to the charging member 2 by the power source SP1 upon image formation on the basis of a size of amplitude of the measured AC current.SELECTED DRAWING: Figure 11

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile machine using an electrophotographic system.

  Conventionally, for example, an electrophotographic apparatus or an electrostatic recording apparatus that forms an image by applying an image forming process such as an electrophotographic process or an electrostatic recording process including a charging process to an image carrier such as a photosensitive member or a dielectric. There is an image forming apparatus. As a means for charging an image carrier when forming an image in such an image forming apparatus, a non-contact charging method using a corona discharge phenomenon such as a scorotron charger has been widely used. The corona discharge device is effective as means for uniformly charging the surface of an object to be charged such as an image carrier to a predetermined potential, but has problems such as generation of ozone due to corona discharge.

  For such a corona discharge device, recently, a conductive charging member is brought into contact with or close to an image carrier such as a photoconductor, and a charging voltage (charging bias) is applied to the charging member. A method (hereinafter referred to as “contact charging method”) is used. For example, in a configuration in which a conductive rubber roller (charging roller) as a charging member is brought into contact with a photosensitive drum as an image carrier and is driven to rotate along with the rotation of the photosensitive drum, a voltage is supplied to a core metal that serves as a shaft of the charging roller. By doing so, the photosensitive drum is charged almost uniformly.

  In the contact charging method using a charging roller, the charging roller is brought into pressure contact with the photosensitive drum, and a voltage is applied to the charging roller, so that the photosensitive drum is discharged by a discharge in a minute gap between the charging roller and the photosensitive drum. Is charged. Specifically, there is a DC charging method in which charging processing is performed by applying a DC voltage (DC bias) obtained by adding a required surface potential Vd of the photosensitive drum to the discharge start voltage Vth. In order to improve fluctuations in the potential of the photosensitive drum due to environmental fluctuations and durability fluctuations, the following AC charging method is available. In the AC charging method, a oscillating voltage obtained by superimposing a DC bias corresponding to the required surface potential Vd of the photosensitive drum and an AC voltage (AC bias) having a peak-to-peak voltage Vpp more than twice the discharge start voltage Vth. Is applied to the charging roller to perform a charging process. The oscillating voltage may be a superimposed voltage of an AC component (AC component) and a DC component (DC component), and a sine wave, a rectangular wave, a triangular wave, or the like can be appropriately used as the AC component waveform. It may be a rectangular wave voltage formed by periodically turning on and off a DC power supply.

  Compared with the AC charging method, the DC charging method has a narrower discharge area and does not have the effect of leveling the AC discharge current, resulting in streak-like image defects due to charging defects due to minute uneven resistance values of the charging roller. There is a problem that it is easy to do. On the other hand, the AC charging method can perform uniform charging (static elimination) processing and is effective for improving the image quality, and is therefore widely used as a charging unit in recent image forming apparatuses.

  However, in the AC charging method, compared with the DC charging method, an AC discharge is generated in the charging process, so that a discharge current is increased, which promotes deterioration of the photosensitive drum and the charging roller, and “image flow caused by discharge products”. There is a problem that an image defect called “is likely to occur”. In the image flow, the discharge product adhering to the surface of the photosensitive drum adsorbs moisture in the atmosphere to cause a decrease in the electric resistance of the surface of the photosensitive drum, and the electrostatic latent image formed at the time of image output is the photosensitive drum. It is generated by spreading in the surface direction. As a result, the latent image is distorted and the output image is blurred or the density is lowered. In order to improve this problem, it is desirable to minimize the AC discharge generated in the charging process by applying the minimum necessary AC bias.

  On the other hand, when the AC bias is minimized as a countermeasure against the above-described image flow, the AC discharge current is reduced, but the discharge becomes unstable, and it is called “sandy ground” due to local excessive discharge (abnormal discharge). There is a problem that a defective image tends to occur. The sandy ground is caused by abnormal discharge by locally forming an abnormally high potential portion or an abnormally low potential portion on the photosensitive drum as follows. In other words, no toner image is formed on any part where the potential is abnormally high even if any image output is performed. In addition, a toner image is formed in any portion where the potential is abnormally low even if any image output is performed. For this reason, spots and toner missing due to toner are scattered throughout the image, and a sandy image is output.

  Therefore, a technique (discharge current optimization control) that optimizes the AC discharge current is known. For example, the relationship between the AC bias applied to the charging roller and the AC current flowing through the charging roller at that time is obtained, and AC is adjusted so that the optimum AC discharge current (minimum AC discharge current) is obtained based on this relationship. There is control for determining a bias (Patent Document 1).

  Here, the target AC discharge current in the discharge current optimization control as described above, that is, the target value of the AC discharge current (hereinafter also referred to as “target current value”) reliably prevents charging defects such as sandy ground. In order to do this, it is set in advance. In principle, if an AC bias that causes AC discharge is applied to the charging roller, the surface potential of the photosensitive drum is charged substantially uniformly. Therefore, if the AC bias at which AC discharge starts is calculated by the above-described discharge current optimization control and the AC bias is applied to the charging roller, an ideal setting is obtained in which excessive discharge does not occur.

  However, during the period until the next discharge current optimization control is performed, AC discharge does not occur even if the same AC bias is applied due to the electrical resistance of the photosensitive drum and the charging roller changing due to repeated use of the apparatus. It may become a state. In that case, an image defect due to a charging defect such as the above-mentioned sandy ground occurs. Therefore, it is general to set a target current value corresponding to an AC bias larger than the AC bias at which the AC discharge starts in consideration of a margin for such fluctuation.

JP-A-10-232534

  Here, when determining the above-described target current value, in addition to the margin for the usage status (endurance fluctuation) of the apparatus and the usage environment (environment fluctuation), due to uneven electrical resistance in the circumferential direction of the charging roller and the photosensitive drum. Generally, a margin for fluctuation of the measured current value is set.

  However, the margin is often set as a constant value obtained experimentally, and individual differences between the charging roller and the photosensitive drum are not considered. For this reason, for example, when the unevenness of the electrical resistance in the circumferential direction of the charging roller or the photosensitive drum is larger than expected, no discharge occurs in the portion where the electrical resistance in the circumferential direction is high, and sand or a poor charging may occur. There is a risk of doing. On the other hand, even when the unevenness of the electrical resistance in the circumferential direction is smaller than expected and the margin may be reduced, the target current value is set uniformly, so that excessive current flows and the photosensitive drum or charging roller There is a risk of promoting deterioration.

  Accordingly, an object of the present invention is to provide an image capable of generating necessary and sufficient AC discharge in the charging process depending on the state of the charging member and the image carrier when the image carrier is charged by the AC charging method. A forming apparatus is provided.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention applies an image carrier, a charging member disposed in contact with or close to the image carrier, and a vibration voltage in which a DC voltage and an AC voltage are superimposed on the charging member. The image forming apparatus includes: a power source capable of power supply; a measurement unit that measures a current flowing through the charging member; and an adjustment unit that adjusts a voltage applied to the charging member by the power source. Sometimes, when the power source applies at least an alternating voltage to the charging member over a predetermined period of time, the measurement unit measures the current flowing through the charging member, and the magnitude of the current fluctuation measured in the control is executed. The image forming apparatus is characterized in that an AC voltage in the oscillating voltage applied to the charging member by the power source during image formation is adjusted.

  According to the present invention, when the image carrier is charged by the AC charging method, necessary and sufficient AC discharge can be generated in the charging process according to the state of the charging member or the image carrier.

1 is a schematic sectional view of an image forming apparatus. 6 is an explanatory diagram of an operation sequence of the image forming apparatus. FIG. FIG. 2 is a block diagram illustrating a schematic control mode of a main part of the image forming apparatus. It is a graph for demonstrating discharge current optimization control. It is a graph which shows the example of AC current waveform. It is a graph for demonstrating the discharge state when a target electric current value is 35 microamperes (comparative example 1). It is a graph for demonstrating the discharge state in case a target electric current value is fixed at 22 microamperes (comparative example 2). It is a flowchart figure of target current value change mode. It is a graph which shows the AC current waveform in unit A, and the power spectrum by a Fourier transform. It is a graph which shows the AC current waveform in the unit B, and the power spectrum by a Fourier transform. It is a graph for demonstrating the discharge state at the time of changing a target current value by target current value change mode. It is a block diagram which shows the general | schematic control aspect of the principal part of the other example of an image forming apparatus. It is a graph for demonstrating the other example of discharge current optimization control.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

[Example 1]
1. FIG. 1 is a schematic cross-sectional view of an image forming apparatus 10 according to an embodiment of the present invention. The image forming apparatus 10 according to the present exemplary embodiment is an electrophotographic laser beam printer that employs a contact charging method.

  The image forming apparatus 10 includes a photosensitive drum 1 that is a rotatable drum type (cylindrical) electrophotographic photosensitive member as an image carrier. In this embodiment, the photosensitive drum 1 is an organic photoconductor (OPC) having a negative charging property. This photosensitive drum 1 has an outer diameter of 30 mm, and is driven to rotate in the direction of arrow R1 in the figure at a process speed (circumferential speed) of 200 mm / sec around the center support shaft. The photosensitive drum 1 is configured by coating a photocharge generation layer and a charge transport layer (thickness of about 20 μm) on the surface of an aluminum cylinder (conductive drum base) in order from the bottom.

  The image forming apparatus 10 includes a charging roller 2 as a charging unit that charges the surface of the photosensitive drum 1 substantially uniformly. The charging roller 2 charges the photosensitive drum 1 using a discharge phenomenon that occurs in a small gap (gap) between the charging roller 2 and the photosensitive drum 1. In this embodiment, the charging roller 2 has a length in the longitudinal direction (rotation axis direction) of 320 mm and a diameter of 14 mm. The charging roller 2 is a rubber roller having a metal core (core material) 2a and an elastic layer (rubber layer) 2b formed of rubber as an elastic body around the metal core 2a. The charging roller 2 is brought into contact with the surface of the photosensitive drum 1 with a predetermined pressing force, and is rotated by the rotation of the photosensitive drum 1. A charging voltage (charging bias) under a predetermined condition is applied to the cored bar 2a of the charging roller 2 by a charging power source (high voltage power source) PS1 as a charging voltage applying means. In this embodiment, the charging power source PS1 includes a DC power source 12 and an AC power source 13 as shown in FIG. The surface of the rotating photosensitive drum 1 is charged to a predetermined potential having a predetermined polarity (negative polarity in this embodiment) by a charging roller 2 to which a charging bias is applied. In this embodiment, a vibration voltage in which a DC bias of −600 V and an AC bias of a peak-to-peak voltage that discharges sufficiently stably are superimposed on the charging roller 2 as a charging bias. As a result, the surface potential of the photosensitive drum 1 is substantially uniformly charged to −600V. Specific AC bias setting will be described in detail later. A charging portion (charging position) a is a position where the charging roller 2 on the photosensitive drum 1 is charged in the rotation direction of the photosensitive drum 1.

  The image forming apparatus 10 includes an exposure device 3 as an exposure unit (information writing unit) that forms an electrostatic latent image on the surface of the charged photosensitive drum 1. In this embodiment, the exposure apparatus 3 is a laser beam scanner using a semiconductor laser. The exposure device 3 outputs a laser beam L that is modulated in response to an image signal sent from the host processing device such as an image reading device (not shown) to the image forming device 10 and performs a substantially uniform charging process. The surface of the rotated photosensitive drum 1 is subjected to laser scanning exposure. By this laser scanning exposure, the absolute value of the potential of the portion irradiated with the laser light L on the surface of the photosensitive drum 1 is reduced, and an electrostatic latent image (static image) corresponding to image information is displayed on the surface of the rotating photosensitive drum 1. (Image) is formed (image portion exposure). In the rotation direction of the photosensitive drum 1, the position where the exposure apparatus 3 on the photosensitive drum 1 is irradiated with the laser light L is an exposure portion (exposure position) b.

  The image forming apparatus 10 includes a developing device 4 as a developing unit that supplies toner to the electrostatic latent image on the photosensitive drum 1 and develops the electrostatic latent image as a toner image (developer image). In this embodiment, the developing device 4 performs development while bringing a magnetic brush made of a two-component developer containing non-magnetic toner particles (toner) and magnetic carrier particles (carrier) into contact with the photosensitive drum 1. The method is adopted. The developing device 4 includes a non-magnetic developing sleeve 4a as a developer carrying member and a developing container 4b that stores the developer. A developing voltage (developing bias) under a predetermined condition is applied to the developing sleeve 4a by a developing power source (high voltage power source) PS2 as a developing voltage applying means. The developer supplied from the inside of the developing container 4b onto the developing sleeve 4a is conveyed to a portion facing the photosensitive drum 1 when the developing sleeve 4a is rotationally driven. Then, the toner of the developer selectively adheres to the photosensitive drum 1 corresponding to the electrostatic latent image on the surface of the photosensitive drum 1 by the electric field due to the developing bias, and the electrostatic latent image is developed as a toner image. In this embodiment, the developing device 4 forms a toner image by a reversal development method. That is, the same polarity as the charged polarity of the photosensitive drum 1 (in this embodiment) is applied to the exposed portion (image portion) on the photosensitive drum 1 where the absolute value of the potential is reduced by being exposed after being charged substantially uniformly. Negatively charged toner adheres. A position on the photosensitive drum 1 that faces the developing sleeve 4a of the developing device 4 and is supplied with toner from the developing sleeve 4a in the rotation direction of the photosensitive drum 1 is a developing portion (developing position) c.

  The image forming apparatus 10 includes a transfer roller 5 that is a roller-type transfer member as a transfer unit. The transfer roller 5 is pressed against the photosensitive drum 1 with a predetermined pressing force, and is rotated by the rotation of the photosensitive drum 1. A position where the photosensitive drum 1 and the transfer roller 5 are in contact with each other in the rotation direction of the photosensitive drum 1 (pressure nip portion) is a transfer portion (transfer position) d. The recording material P is fed to the transfer portion d from the recording material feeding portion (not shown) at a predetermined control timing. The recording material P fed to the transfer part d is nipped and conveyed between the rotating photosensitive drum 1 and the transfer roller 5. At this time, the transfer roller 5 is supplied to the transfer roller 5 by a transfer power source PS3 serving as a transfer voltage application unit. The transfer voltage (transfer in the present embodiment is positive) opposite to the toner charging polarity (normal charging polarity) during development. Bias) is applied. In this embodiment, the transfer bias is a DC voltage of + 600V. Thereby, in the transfer part d, the toner image on the photosensitive drum 1 is electrostatically transferred onto the surface of the recording material P that is nipped and conveyed between the photosensitive drum 1 and the transfer roller 5.

  Note that the configuration of the image forming apparatus 10 is not limited to the configuration in which the toner image is directly transferred from the photosensitive drum 1 to the recording material P, and an intermediate transfer body that temporarily holds and conveys the toner image from the photosensitive drum 1. In other words, the recording medium P may be transferred to the recording material P from the intermediate transfer member.

  The recording material P onto which the toner image has been transferred is separated from the surface of the photosensitive drum 1 and conveyed to a heat roller fixing device 6 as fixing means. The recording material P is subjected to a toner image fixing process by the fixing device 6, and is discharged (output) to the outside of the main body of the image forming device 10 as an image formed product (print, copy).

  The toner (transfer residual toner) remaining on the surface of the photosensitive drum 1 after the transfer process is removed from the surface of the photosensitive drum 2 by the cleaning device 7 and collected. The cleaning device 7 includes a cleaning blade 7a as a cleaning member disposed in contact with the photosensitive drum 1, and a collected toner container 7b.

  In this embodiment, the cleaning device 7 is used as a means for removing the transfer residual toner. However, for example, a cleaner-less system that has a charge optimization means for the transfer residual toner and that simultaneously collects the development with the developing device 4 is adopted. May be.

  The image forming apparatus 10 is provided with a control circuit 11 (FIG. 3) that comprehensively controls the operation of the image forming apparatus 10. The control circuit 11 includes a CPU as an arithmetic control unit and a memory as a storage unit. The control circuit 11 controls driving of each part of the image forming apparatus 10, outputs of the power supplies PS 1, PS 2, PS 3, image information processing, discharge current optimization control operation described later, target current value change control operation described later, and the like. Is done.

  FIG. 2 is a schematic diagram illustrating an operation sequence of the image forming apparatus 10.

  (1) Initial rotation operation (pre-multi-rotation process): The initial rotation operation is an operation during a start-up operation period (start-up operation period, warming period) when the image forming apparatus 10 is started up. In the initial rotation operation, when the power switch of the image forming apparatus 10 is turned on, rotation driving of the photosensitive drum 1 is started, and a preparatory operation for a predetermined process device such as starting up the fixing device 6 to a predetermined temperature is performed. Executed.

  (2) Print preparation rotation operation (pre-rotation process): The print preparation rotation operation is performed after an image formation start instruction (print signal) is input to the image forming apparatus 10 until a print process described later is actually started. This is a preparatory operation for the period. When a print signal is input to the image forming apparatus 10 during the initial rotation operation, the print preparation rotation operation is executed following the initial rotation operation. When the print signal is not input during the initial rotation operation, the drive of the main motor is temporarily stopped after the initial rotation operation is finished, the rotation drive of the photosensitive drum 1 is stopped, and the image forming apparatus 10 receives the print signal. It is kept in the standby (standby) state until When a print signal is input, a print preparation rotation operation is executed. In this embodiment, in this print preparation rotation operation, a program for calculating and determining an AC bias in the charging process of the printing process described later is executed.

  (3) Printing process (image forming process, image forming process): The printing process is a period during which toner image formation and toner image transfer are actually performed. When the predetermined print preparation rotation operation is completed, the toner image is formed on the rotating photosensitive drum 1, the toner image is transferred to the recording material P, and the toner image is fixed on the recording material P. Is output. In the case of the continuous printing (continuous printing) mode, the above printing process is repeatedly executed for a predetermined set number of prints n (3 in the illustrated example).

  (4) Inter-sheet process: In the inter-sheet process, in the continuous printing mode, after the trailing end of one recording material P passes through the transfer portion d, the leading end of the next recording material P reaches the transfer portion d. This is a period during which the recording material P is not present in the transfer portion d.

  (5) Post-rotation operation: In the post-rotation operation, after the printing process of the last recording material P is completed, the main motor is continuously driven for a while and the photosensitive drum 1 is continuously rotated. This is a period during which operations (organization operation, preparation operation) are executed.

  (6) Standby (standby): When the predetermined post-rotation operation ends, the drive of the main motor is stopped and the rotation of the photosensitive drum 1 is stopped, and the image forming apparatus 10 sends the next print signal to the image forming apparatus 10. It is kept in a standby state until it is input. In the case of printing only one sheet, after the printing is completed, the image forming apparatus 10 goes into a standby state through a post-rotation operation. When a print signal is input to the image forming apparatus 10 in the standby state, the image forming apparatus 10 starts a print preparation rotating operation.

  Here, the time of the printing process of (3) is the time of image formation, the time of the initial rotation operation of (1), the time of printing preparation rotation operation of (2), the time of paper interval of (4), (5) The post-rotation operation is during non-image formation.

2. Control Mode FIG. 3 is a block diagram showing a schematic control mode of the main part of the image forming apparatus 10 of the present embodiment. As shown in FIG. 3, in this embodiment, the charging power source PS1 includes a DC power source 12, an AC power source 13, and an AC ammeter 14 as a measurement unit. The AC ammeter 14 can measure the AC current that flows through the charging roller 2 when the charging power supply SP1 applies at least an AC bias to the charging roller 2. The charging power supply PS1 applies an oscillating voltage in which a predetermined DC bias and an AC bias having a predetermined frequency are applied to the charging roller 2 through the cored bar 2a, so that the periphery of the rotating photosensitive drum 1 is rotated. The surface is charged to a predetermined potential having a predetermined polarity. The control circuit 11 has a function of controlling the DC voltage value output from the DC power supply 12 and the peak-to-peak voltage value of the AC voltage output from the AC power supply 13. Further, the control circuit 11 has a function of reading the measurement result of the AC ammeter 14 and storing a current value and a current waveform of the AC current, and a function of executing a program for calculating and determining an AC bias in the charging process of the printing process. Have.

3. Discharge Current Optimization Control In this embodiment, control (discharge current optimization control) that optimizes the discharge current in the charging process of the printing process is executed, as in Patent Document 1. In the present embodiment, this discharge current optimization control is executed in the print preparation rotation operation during non-image formation. In this embodiment, the case where the discharge current optimization control is performed in an environment of a temperature of 23 ° C. and a humidity of 50% will be described.

  FIG. 4A shows the relationship between the applied AC bias (peak-to-peak voltage) and the measured AC current (current value after the average processing) acquired in the discharge current optimization control. In the discharge current optimization control, first, the slope of the baseline for calculating the discharge current is calculated as follows. That is, an approximate straight line is created by the least square method from the relationship between the applied AC bias in the undischarged region and the measured AC current (square plot in FIG. 4A), and this approximate straight line is used as a baseline (see FIG. The slope is calculated as a straight line in 4 (a). This baseline represents a current that does not participate in the discharge that flows from the contact surface between the photosensitive drum 1 and the charging roller 2 due to the application of an AC bias. In the discharge current optimization control, next, the relationship between the AC bias (voltage between peaks) of the applied discharge region and the measured AC current (current value after average processing) (circle plot in FIG. 4A). And the difference from the baseline. This difference is defined as “discharge current”. FIG. 4 (b) shows the relationship between the difference between the measured AC current (circled plot in FIG. 4 (a)) and the current not involved in the discharge predicted from the above-mentioned baseline with respect to the AC bias of the applied discharge region. Indicates. The vertical axis in FIG. 4B represents the discharge current. In the discharge current optimizing control, next, an AC bias corresponding to the target current value is obtained based on the relationship of FIG. The target current value is determined so that a desired AC discharge can be generated in accordance with the usage status (endurance fluctuation) of the apparatus and the usage environment (environment fluctuation). In the discharge current optimization control, the obtained AC bias (peak-to-peak voltage) is set as an AC bias in the charging process of the printing process. A conventional method for determining a target current value and a method for determining a target current value in the present embodiment will be described in detail later.

  The AC current measurement method in the discharge current optimization control will be further described. When measuring the current when a certain voltage is applied to the charging roller 2, it is desirable to sample the current over substantially one turn of the charging roller 2 and average the obtained values for processing. By this processing, it is possible to cancel the uneven electrical resistance in the circumferential direction of the charging roller 2. In this embodiment, the control circuit 11 detects the AC current flowing through the charging roller 2 at every predetermined measurement cycle (read from the AC ammeter 14). Therefore, in this embodiment, the number of times of detection (number of times of reading) is set to a number corresponding to the time required for one rotation of the charging roller 2 calculated from the outer diameter of the charging roller 2 and the process speed. However, one cycle of the charging roller 2 may not be an integral multiple of the AC current detection cycle (reading cycle). In this case, the number of detections can be determined by moving the calculated value below the decimal point. Specifically, in this embodiment, the AC current is detected every 8 msec, and the time required for the charging roller 2 to make one revolution is about 220 msec. Therefore, from the following equation, 220/8 = 27.5, the number of AC current detections is 28, and the average value is the sampling current. In this case, it is assumed that the traveling distance of the charging roller 2 that travels while detecting the AC current 28 times corresponds to approximately one turn of the charging roller 2.

  As described above, it is desirable that the error range of substantially one round of the charging roller 2 for obtaining the sampling current is within a range of ± 10% with respect to the circumferential length of the charging roller 2. More desirably, the range is ± 5%. The number of AC current detections is preferably 10 or more.

4). Setting of Target Current Value and Issues As described above, when determining the target current value, in addition to the margin for the usage status (endurance fluctuation) and usage environment (environment fluctuation) of the apparatus, the charging roller 2 and the photosensitive drum 1 Generally, a margin is set for fluctuations in the measured current value due to uneven electrical resistance in the circumferential direction.

  However, the margin is often set as a constant value obtained experimentally, and individual differences between the charging roller 2 and the photosensitive drum 1 are not considered. For this reason, for example, when the unevenness of the electrical resistance in the circumferential direction of the charging roller 2 or the photosensitive drum 1 is larger than expected, no discharge occurs in a portion where the electrical resistance in the circumferential direction is high, and sand or a poor charging occurs. There is a risk of becoming. On the other hand, even when the unevenness of the electrical resistance in the circumferential direction is smaller than expected and the margin may be reduced, the target current value is set uniformly, so that excessive current flows and deterioration of the photosensitive drum 1 is caused. There is a risk of promoting.

  FIG. 5A shows an AC current waveform when an AC bias is applied to the charging roller 2 in a unit in which a certain photosensitive drum 1 and the charging roller 2 are combined (this is referred to as “unit A”). Is. Similar to the AC current measurement method in the discharge current optimization control described above, the AC current waveform is detected a plurality of times (28 times in the present embodiment) while the charging roller 2 makes one round, and the AC current waveform is also described above. Can be obtained by not performing the average processing. In addition, it has been found in advance that the charging roller 2 having relatively large unevenness in electrical resistance in the circumferential direction is incorporated in the unit A. Here, X in the figure represents the time (cycle) required for the charging roller 2 to make one rotation, which is obtained from the circumferential length of the charging roller 2 and the process speed of the apparatus. Compared with the period X, it can be seen that the AC current waveform in FIG. 5A has AC current fluctuation (periodic unevenness) due to the uneven electrical resistance in the circumferential direction of the charging roller 2. Further, in the AC current waveform of FIG. 5A, it can be seen that the fluctuation of the AC current due to the AC current periodic unevenness is relatively large, for example, at the Ya point and the Za point.

  Next, FIG. 5B is the same as the case of the unit A in the charging roller 2 in a unit (this unit is referred to as “unit B”) in which the photosensitive drum 1 and the charging roller 2 different from the unit A are combined. 2 shows an AC current waveform when an AC bias is applied. It can be seen that the unit B also has an AC current fluctuation (period irregularity) as in the AC current waveform in the unit A (FIG. 5A). However, in the AC current waveform of FIG. 5B, it can be seen that the fluctuation of the AC current due to the AC current periodic unevenness is relatively small, for example, at the Yb point and the Zb point.

  6A and 6B show AC current waveforms when the AC bias in the discharge region is applied to the charging roller 2 with the target current value set to 35 μA in the unit A and the unit B, respectively. 7A and 7B show AC current waveforms when the AC bias of the discharge region is applied to the charging roller 2 with the target current value set to 22 μA in the unit A and the unit B, respectively. The vertical axis of FIGS. 6 and 7 is a scale of the discharge current.

  As shown in FIGS. 6 and 7, in an environment of a temperature of 23 ° C. and a humidity of 50%, the target current value has a margin of 20 μA. This margin (hereinafter also referred to as “resistance variation margin”) is a fluctuation in the discharge current due to fluctuations in the electrical resistance of the charging roller 2 and the photosensitive drum 1 depending on the usage status (endurance variation) of the apparatus and the usage environment (environmental variation). This is a predetermined margin.

  As shown in FIG. 6A, when the target current value is 35 μA, the AC current waveform in the unit A shows a fluctuation of the AC current in the range of about 19 μA centering on the discharge current of about 35 μA. Therefore, the lower limit of the AC current fluctuation is about 25.5 μA. That is, there is an additional margin of about 5.5 μA for a resistance variation margin of 20 μA. Therefore, it can be seen that a slightly excessive discharge current is set.

  As shown in FIG. 6B, when the target current value is 35 μA, the AC current waveform in unit B shows a fluctuation of AC current in the range of about 4 μA centering on the discharge current of about 35 μA. It is done. Therefore, the lower limit of the AC current fluctuation is about 33 μA. That is, there is a margin of about 13 μA for the resistance variation margin of 20 μA. Therefore, it can be seen that a considerably excessive discharge current is set.

  Next, as shown in FIG. 7A, when the target current value is 22 μA, the AC current waveform in unit A has a fluctuation of AC current in the range of about 19 μA centering on the discharge current of about 22 μA. It can be seen. Therefore, the lower limit of the AC current fluctuation is about 12.5 μA. That is, about 7.5 μA is insufficient for a resistance variation margin of 20 μA. Therefore, depending on the electrical resistance of the photosensitive drum 1 and the charging roller 2 which varies depending on the usage status and usage environment of the apparatus, the discharge current may be insufficient, which may cause sand and poor charging.

  As shown in FIG. 7B, when the target current value is 22 μA, the AC current waveform in unit B shows a fluctuation of AC current in the range of about 4 μA centering on the discharge current of about 22 μA. It is done. Therefore, the lower limit of the AC current fluctuation is about 20 μA. That is, for the resistance fluctuation margin of 20 μA, the lower limit of the AC current fluctuation is almost the same value. Therefore, it can be seen that an ideal discharge current is set.

  Thus, the AC current fluctuation may vary greatly depending on the combination of the photosensitive drum 1 and the charging roller 2. Therefore, it can be seen that if the target current value is determined uniformly, the margin may be excessively large or conversely insufficient.

  Therefore, in this embodiment, control (target current value change mode) for changing the target current value of the discharge current optimization control is executed prior to the above-described discharge current optimization control. In the target current value change mode, the AC current fluctuation is measured, and the target current value of the discharge current optimization control is changed according to the measured magnitude of the AC current fluctuation. The target current value change mode will be described in detail below.

5. Target Current Value Change Mode FIG. 8 is a flowchart of operations including the target current value change mode and the discharge current optimization control in the present embodiment.

  First, the control circuit 11 determines whether it is time to perform the target current value change mode during non-image formation (in the present embodiment, during the pre-rotation process) (S1). In the present embodiment, when the unit (drum cartridge) that includes the photosensitive drum 1 and the charging roller 2 and is detachable from the apparatus main body of the image forming apparatus 10 is replaced, the target current value change mode is set. did. In this embodiment, when the unit is inserted into the image forming apparatus 10 and the image forming apparatus 10 is turned on, the unit is replaced by a unit detection mechanism such as a memory tag attached to the unit A as a replacement detection unit. Is detected. Based on the detection result of the unit detection mechanism, the control circuit 11 can determine whether it is time to perform the target current value change mode.

  The target current value change mode is not limited to being performed when the photosensitive drum 1 and the charging roller 2 are simultaneously replaced as in the present embodiment. For example, the target current value change mode may be set in at least one of the case where only the charging roller 2 is replaced or the case where only the photosensitive drum 1 is replaced. Alternatively, the target current value change mode may be set to be performed when the power of the image forming apparatus 10 is turned on or when the usage environment of the image forming apparatus 10 fluctuates more than a certain level. Furthermore, it is good also as a setting which performs target current value change mode according to the use condition of an apparatus. For example, the target current value change mode can be performed each time the usage amount (rotation time, rotation speed, etc.) of the photosensitive drum 1 or the charging roller 2 exceeds a predetermined threshold. Further, the target current value change mode is not limited to being executed at the time of the pre-rotation process, and can be executed at any timing as long as it is during non-image formation.

  If the control circuit 11 determines in S1 that it is not the timing for performing the target current value change mode (No in S1), it does not change the target current value, performs discharge current optimization control (S5), and performs the process. finish.

  On the other hand, if the control circuit 11 determines that it is time to perform the target current value change mode in S1 (Yes in S1), the control circuit 11 captures an AC current waveform (S2). That is, while rotating the photosensitive drum 1 and the charging roller 2, an AC bias is applied to the charging roller 2 by the charging power source SP 1, and the AC current at that time is measured by the AC ammeter 14. Then, the AC current waveform as the measurement result is stored in a memory provided in the control circuit 11. The AC current waveform is preferably obtained by measuring the AC current during a period in which the charging roller 2 and the photosensitive drum 1 rotate a plurality of times. However, in the general system, since the outer diameter of the photosensitive drum 1 is larger than the outer diameter of the charging roller 2, in that case, the AC current during the period in which the photosensitive drum 1 rotates a plurality of times is measured. do it. In this embodiment, the AC current is measured for about 2 seconds, and this time corresponds to the time required for the photosensitive drum 1 to rotate about 4.2 and the time for the charging roller 2 to rotate about 9.1. Note that the time for measuring the AC current is typically less than the time for which the charging roller 2 and the photosensitive drum 1 each rotate 10 times so that the time required for control does not become longer than necessary.

  In this embodiment, when the AC current waveform is acquired, the discharge start voltage Vth, which is predicted to generate a stable AC discharge in any combination of the photosensitive drum 1 and the charging roller 2, is obtained. It is preferable to apply an AC bias sufficiently larger than twice. In the configuration of this embodiment, the discharge start voltage Vth is about 550 V in an environment with a temperature of 23 ° C. and a humidity of 50%. For example, an AC bias corresponding to a target current value of 35 μA shown in FIG. 6 can be used. In this embodiment, when an AC current waveform is acquired, a DC bias equivalent to that at the time of image formation is also superimposed and applied. However, when the AC current waveform is captured, the DC bias need not be superimposed and applied.

  Next, the control circuit 11 performs a process of obtaining the magnitude of the AC current fluctuation in the acquired AC current waveform (S3). In this embodiment, the acquired AC current waveform is converted into a power spectrum by Fourier transform, and the relationship between the frequency as information on the AC current fluctuation period and the fluctuation amount as information on the magnitude of the AC current fluctuation is shown. Ask. Here, the amount of AC current fluctuation as information on the magnitude of AC current fluctuation corresponds to the peak-to-peak magnitude in the AC current waveform. Note that the analysis method used here is not limited to the Fourier transform, and any method may be used as long as information on the AC current fluctuation period and amplitude can be obtained.

Next, the control circuit 11 performs a process of changing the target current value of the subsequent discharge current optimization control based on the relationship between the obtained AC current fluctuation frequency and fluctuation amount (S4). In the present embodiment, the amount of shake (hereinafter also referred to as “maximum amount of shake”) when the amount of shake of the AC current is maximum in the above relationship is obtained, and the discharge current optimum thereafter is determined according to the maximum amount of shake. Change the target current value for control. More specifically, in the present embodiment, the target current value is calculated by the following formula (1) representing the relationship between the maximum shake amount Iamp [μA] and the target current value Itgt [μA], and the calculated value is Change the target current value for discharge current optimization control. In the following formula (1), α is a coefficient of the relationship between the maximum shake amount Iamp [μA] and the target current value Itgt [μA]. In the image forming apparatus 10 of the present embodiment, α = 0.5. It is. Further, Ienv in the following formula (1) is a correction value (corresponding to the resistance fluctuation margin) in a predetermined environment. For example, in the environment of the present embodiment at a temperature of 23 ° C. and a humidity of 50%, 20 [μA]. It is.
Itgt = α × Iamp + Ienv (1)

  Then, the control circuit 11 performs discharge current optimization control with the setting of the target current value calculated in S4 (S5), and ends the process. The processing of S2 to S4 corresponds to the target current value change mode.

  The target current value is not limited to being calculated by the above formula. For example, a target current value is set in advance for each range of magnitudes of AC current fluctuations in a plurality of stages, and one of the target current values is selectively selected according to the measured magnitude of AC current fluctuation. You may make it use for.

  Here, the case where the target current value change mode of the present embodiment is applied to the above-described unit A and unit B will be described.

  In the unit A, an AC current waveform as shown in FIG. 9A is obtained. The AC current waveform is converted into a power spectrum as shown in FIG. 9B by Fourier transform processing. Here, the horizontal axis of the power spectrum is the frequency, and the vertical axis is the fluctuation amount of the AC current. In FIG. 9B, the peak frequency at which the amount of fluctuation of the AC current is maximum is 4.55 Hz, and this value corresponds to a period of about one turn of the charging roller 2. That is, in unit A, it can be seen that the AC current fluctuation caused by the charging roller 2 is the largest. Incidentally, the frequency of the peak with the second largest amount of AC current fluctuation is 2.12 Hz, and this value corresponds to a period of about one round of the photosensitive drum 1. As described above, when the AC current is detected while the charging roller 2 and the photosensitive drum 1 are rotated a plurality of times, the fluctuation of the AC current may increase corresponding to the respective rotation cycles of the photosensitive drum 1 and the charging roller 2. It is common. According to the Fourier transform, such AC current fluctuation can be detected more clearly. When the value of the maximum shake amount is read in FIG. 9B, it is 19 μA. Therefore, the target current value is obtained as Itgt = 29.5 [μA] by substituting α = 0.5, Ienv = 20 [μA], and Iamp = 19 [μA] into the above formula (1).

  Further, in the unit B, an AC current waveform as shown in FIG. This AC current waveform is converted into a power spectrum as shown in FIG. 10B by Fourier transform processing. In FIG. 10B, the peak frequency at which the amount of fluctuation of the AC current is maximum is 4.55 Hz, and this value corresponds to a period of about one turn of the charging roller 2. That is, it can be seen that the unit B has the largest current fluctuation caused by the charging roller 2 as in the case of the unit A. When the value of the maximum shake amount is read in FIG. 10B, it is 4 μA. Therefore, the target current value is obtained as Itgt = 22 [μA] by substituting α = 0.5, Ienv = 20 [μA], and Iamp = 4 [μA] into the above formula (1).

  FIGS. 11A and 11B show AC current waveforms when an AC bias is applied so as to output the target current value determined by the target current value change control in this embodiment in Unit A and Unit B, respectively. Show. The vertical axis of FIGS. 11A and 11B is a discharge current scale. As described above, in unit A, the determined target current value is 29.5 μA, and in unit B, the determined target current value is 22 μA. Note that, as shown in FIGS. 11A and 11B, a margin of 20 μA is provided as a resistance variation margin in an environment where the temperature is 23 ° C. and the humidity is 50%.

  As shown in FIG. 11A, the AC current waveform in the unit A has a fluctuation of AC current in the range of about 19 μA centering on the discharge current of about 29.5 μA corresponding to the determined target current value. It can be seen. Therefore, the lower limit of the AC current fluctuation is about 20 μA. That is, for the resistance fluctuation margin of 20 μA, the lower limit of the AC current fluctuation is almost the same value. Therefore, it can be seen that an ideal discharge current is set.

  Further, as shown in FIG. 11B, the AC current waveform in the unit B has an AC current fluctuation in the range of about 4 μA centering on the discharge current of about 22 μA corresponding to the determined target current value. It can be seen. Therefore, the lower limit of the AC current fluctuation is about 20 μA. That is, for the resistance fluctuation margin of 20 μA, the lower limit of the AC current fluctuation is almost the same value. Therefore, it can be seen that an ideal discharge current is set.

  On the other hand, the case where the discharge current optimization control is performed with the fixed target current value described with reference to FIGS. 6 and 7 is referred to as Comparative Example 1 and Comparative Example 2, respectively. Specifically, as described above, discharge current optimization control was performed with the target current value fixed at 35 μA in Comparative Example 1 and the target current value fixed at 22 μA in Comparative Example 2. Since the results of Comparative Example 1 and Comparative Example 2 shown in FIGS. 6 and 7 are as described above, repeated description is omitted here.

  The above results are summarized as shown in Table 1.

  In Comparative Example 1, a relatively large target current is set, and even when the amount of fluctuation of the AC current is large, the minimum discharge current does not fall below the resistance fluctuation margin, so that no sand or charging failure occurs. However, since the discharge current is large, the discharge damage to the photosensitive drum 1 and the charging roller 2 is large, and the life of the apparatus and members tends to be shortened. In addition, due to the discharge product, there is a tendency that image flow, or a peeling of the cleaning blade 7a due to an increase in the frictional force between the photosensitive drum 1 and the cleaning blade 7a is likely to occur. As a countermeasure against the image flow and the removal of the cleaning blade 7a, it is conceivable to send toner or an external additive of toner as a polishing agent or a lubricant to the cleaning unit e. Thereby, discharge products can be removed, and the frictional force between the photosensitive drum 1 and the cleaning blade 7a can be reduced. However, this may lead to an increase in toner consumption.

  Further, in Comparative Example 2, a relatively small target current is set, and discharge damage to the photosensitive drum 1 and the charging roller 2 is small, so that it is possible to extend the life of the apparatus and members. In addition, there is a tendency that image flow due to the discharge product, meklet of the cleaning blade 7a, and the like hardly occur. However, when the amount of AC current fluctuation is large, such as when the unit A is used, the minimum discharge current value may fall below the resistance variation margin. For this reason, if the electrical resistance of the photosensitive drum 1 or the charging roller 2 varies depending on the usage status or usage environment of the apparatus, a portion where the discharge current is locally short is formed, and there is a concern that sand or charging failure may occur.

  On the other hand, in the present embodiment, attention is paid to the maximum shake amount in the AC current waveform, and the target current value of the discharge current optimization control is changed according to the maximum shake amount. As a result, the target current value corresponding to the state of the photosensitive drum 1 and the charging roller 2 can be set to generate AC discharge that is not excessive or insufficient. Specifically, when the fluctuation of the AC current is relatively large, the target current value is relatively increased, thereby suppressing the occurrence of sand and poor charging due to local shortage of the discharge current. On the other hand, when the fluctuation of the AC current is relatively small, the life of the device or member can be extended by reducing the discharge damage by making the target current value relatively small and not discharging more than necessary. . In addition, it is possible to suppress an increase in toner consumption for the purpose of taking measures against the image flow and the peeling of the cleaning blade 7a.

  As described above, the image forming apparatus 10 according to the present exemplary embodiment includes the adjusting unit that adjusts the voltage applied to the charging member 2 by the power supply SP1. In the present embodiment, the control circuit 11 has the function of the adjustment unit. The adjustment unit 11 causes the measurement unit 14 to control the current flowing through the charging member 2 when the power supply SP1 applies at least an AC voltage to the charging member 2 over a predetermined period during non-image formation. Then, the adjusting unit 11 determines the AC voltage in the oscillating voltage in which the DC voltage and the AC voltage applied by the power source SP1 to the charging member 2 during image formation are superimposed based on the magnitude of the current fluctuation measured in the control. Adjust. In the present embodiment, the measurement unit 14 can measure the alternating current flowing through the charging member 2. In the present embodiment, the adjustment unit 11 performs alternating current at the oscillating voltage that the power supply SP1 applies to the charging member 2 during image formation based on the magnitude of the alternating current fluctuation measured by the measurement unit 14 during the control. Adjust the voltage. In particular, in the present embodiment, the adjustment unit 11 performs the above-described adjustment by changing the target value of the alternating current flowing through the charging member 2 when the power supply SP1 applies the vibration voltage to the charging member 2 during image formation. More specifically, the adjusting unit 11 increases the target value of the alternating current in the second case where the magnitude of the shake is larger than the first value than in the case where the magnitude of the shake is the first value. In particular, in the present embodiment, the adjustment unit 11 obtains a relationship between the shake period and the magnitude of the shake from the measurement result by the measurement unit 14 in the control, and is based on the magnitude of the shake that is the maximum in the relationship. To make the above adjustments.

  As described above, according to this embodiment, when the charging process of the photosensitive drum 1 is performed by the AC charging method, the necessary and sufficient AC discharge is generated in the charging process according to the state of the charging roller 2 and the photosensitive drum 1. it can.

[Example 2]
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the image forming apparatus of the first embodiment. Accordingly, in the image forming apparatus of the present embodiment, elements having the same or corresponding functions and configurations as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the present embodiment, the discharge current optimization control is different from that in the first embodiment. In the discharge current optimization control of this embodiment, the relationship between the applied AC bias (peak-to-peak voltage) and the DC current flowing through the charging roller 2 at that time is obtained. Further, based on the relationship, an AC bias (saturated AC bias) is obtained in which the DC current does not increase even when the AC bias is increased. Then, the AC bias in the charging process in the printing process is set to an AC bias equal to or higher than the saturated AC bias. Therefore, as shown in FIG. 12, in this embodiment, a direct current meter 15 is provided in the charging power source PS1 instead of the alternating current ammeter 14 in the first embodiment. The direct current ammeter 15 can measure the direct current flowing through the charging roller 2 when the charging power source SP1 applies at least a DC bias to the charging roller 2.

  With reference to FIG. 13, the discharge current optimization control in the present embodiment will be further described. FIG. 13 is a plot of the DC current flowing through the charging roller 2 against the AC bias applied to the charging roller 2. When the AC bias peak-to-peak voltage Vpp is small (Vpp ≦ 400 V in FIG. 13), the surface potential of the photosensitive drum 1 does not change before and after passing through the charging portion a, and thus the DC current flowing through the charging roller 2 is zero. When the AC bias peak-to-peak voltage Vpp is increased, no discharge occurs between the charging roller 2 and the photosensitive drum 1, but a region that changes the potential of the photosensitive drum 1 (400 V <Vpp ≦ V in FIG. 13). 1100V). Therefore, the DC current increases as the AC bias peak-to-peak voltage Vpp increases. When the AC bias peak-to-peak voltage Vpp is further increased (Vpp ≧ 1100 V in FIG. 13), the surface potential of the photosensitive drum 1 after passing through the charging portion a is a DC bias applied to the charging roller 2 ( Here, it is equivalent to −600 V). Even if the AC bias peak-to-peak voltage Vpp is further increased, the surface potential of the photosensitive drum 1 does not change, so that the DC current with respect to the AC bias peak-to-peak voltage Vpp is substantially constant. That is, at this time, it is considered that stable AC discharge has occurred. Therefore, an AC bias (saturated AC bias) in which the DC current is stable is obtained, and an AC bias (voltage between peaks) larger than the saturated AC bias by a certain amount is set as an AC bias in the charging process in the printing process.

  This fixed amount (hereinafter also referred to as “AC bias margin”) when set larger than the saturated AC bias by a fixed amount corresponds to the discharge current margin in the first embodiment. As described in the first embodiment, this margin is often a fixed value regardless of individual differences between the charging roller 2 and the photosensitive drum 1. Therefore, there is a problem similar to that described in the first embodiment.

  Therefore, in this embodiment, control (AC bias margin change mode) for changing the AC bias margin is executed prior to the above-described discharge current optimization control. In the AC bias margin change mode, the DC current fluctuation is measured, and the AC bias margin is changed according to the measured magnitude of the DC current fluctuation.

  More specifically, the AC bias margin change mode is the same as in the first embodiment, for example, when the unit including the photosensitive drum 1 and the charging roller 2 is replaced, for example, during non-image formation (for example, during the pre-rotation process). This is executed prior to the discharge current optimization control. First, while rotating the photosensitive drum 1 and the charging roller 2, a DC bias is applied to the charging roller 2 by the charging power supply SP1 to acquire a DC current waveform. When acquiring a DC current waveform, an AC bias can be superimposed and applied. When an AC bias is superimposed and applied when acquiring a DC current waveform, the DC bias can be set to the same DC bias as that during image formation. In this case, the AC bias is sufficiently larger than twice the discharge start voltage Vth, which is predicted to generate a stable AC discharge in any combination of the photosensitive drum 1 and the charging roller 2. A bias is preferable. However, the DC current waveform may be acquired by applying only the DC bias. The DC bias in this case is preferably a sufficiently large DC bias that generates a discharge between the photosensitive drum 1 and the charging roller 2. As in the first embodiment, it is preferable that the time for measuring the DC current is a time for each of the charging roller 2 and the photosensitive drum 1 to rotate a plurality of times.

  Next, the magnitude of the DC current fluctuation in the acquired DC current waveform is obtained. At this time, as in the first embodiment, the relationship between the period and the magnitude of the DC current fluctuation is obtained using Fourier transform, and the magnitude of the fluctuation when the magnitude of the DC current fluctuation is maximized ( Maximum runout amount) can be obtained. When the maximum shake amount is relatively large, in order to relatively increase the AC bias margin, a relatively large amount of AC bias is added to the saturation AC bias, so that the AC bias in the charging process of the printing process is increased. Set the bias. On the other hand, when the maximum shake amount is relatively small, the AC bias margin may be relatively small. Therefore, the AC bias is added to the saturation AC bias to a relatively small amount, so that the AC bias in the charging process of the printing process is increased. Set the bias.

  The DC current waveform acquired by the AC bias margin change control or the relationship between the AC current waveform and the margin when the determined AC bias is applied is the same as that related to the AC current waveform described in the first embodiment. Therefore, repeated description is omitted here.

  As described above, in this embodiment, the adjustment unit 11 causes the measurement unit 15 to measure the current flowing through the charging member 2 when the power supply SP1 applies at least an AC voltage to the charging member 2 over a predetermined period during non-image formation. Make control run. Then, the adjusting unit 11 determines the AC voltage in the oscillating voltage in which the DC voltage and the AC voltage applied by the power source SP1 to the charging member 2 during image formation are superimposed based on the magnitude of the current fluctuation measured in the control. Adjust. In the present embodiment, the measuring unit 15 can measure the direct current flowing through the charging member 2. In this embodiment, the adjusting unit 11 measures the direct current flowing through the charging member 2 when the power supply SP1 applies the vibration voltage to the charging member 2 during the control. At the same time, the adjusting unit 11 adjusts the AC voltage in the oscillating voltage applied to the charging member 2 by the power source SP1 during image formation based on the magnitude of the DC current fluctuation measured by the measuring unit 15 during the control. In particular, in the present embodiment, the adjustment unit 11 performs the above-described adjustment by changing the peak-to-peak voltage of the AC voltage in the oscillating voltage that the power supply SP1 applies to the charging member 2 during image formation. More specifically, the adjustment unit 11 increases the peak-to-peak voltage of the AC voltage in the second case in which the magnitude of the shake is larger than the first value than in the case of the first value. .

  As described above, according to the present embodiment, although the discharge current control is different from that of the first embodiment, the same effect as that of the first embodiment can be obtained.

[Others]
As mentioned above, although this invention was demonstrated according to the specific Example, this invention is not limited to the above-mentioned Example.

  In the above-described embodiments, the case where the charging member is in contact with the photosensitive member has been described. However, a charging member such as a charging roller does not necessarily need to be in contact with the surface of the photosensitive member that is a member to be charged, and has a gap (gap) of, for example, several tens of μm if discharge is possible in the vicinity. And you may arrange | position close to non-contact. In this way, the charging member is arranged close to the photoconductor, and the photoconductor is discharged by discharge at a proximity portion thereof (corresponding to the gap upstream and downstream of the contact portion between the charging roller and the photoconductor in the above-described embodiment). The present invention can also be applied to a configuration in which charging is performed.

  In the above-described embodiment, the case where the charging member is of a roller type has been described. However, the charging member may be, for example, an endless belt. In the above-described embodiments, the case where the image carrier is a drum type has been described. However, the image carrier may be an endless belt, for example. In particular, the present invention is effective when either the charging member or the image carrier is a rotatable rotating body.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 10 Image forming apparatus 11 Control circuit 14 AC ammeter

Claims (11)

An image carrier;
A charging member disposed in contact with or close to the image carrier;
A power source capable of applying an oscillating voltage in which a DC voltage and an AC voltage are superimposed on the charging member;
A measurement unit for measuring a current flowing through the charging member;
An adjustment unit for adjusting a voltage applied to the charging member by the power source;
In an image forming apparatus having
The adjustment unit executes control to cause the measurement unit to measure a current flowing through the charging member when the power source applies at least an AC voltage to the charging member over a predetermined period during non-image formation, and performs measurement in the control. An image forming apparatus that adjusts an alternating voltage in the oscillating voltage that the power source applies to the charging member during image formation based on the magnitude of the current fluctuation.   The measuring unit is capable of measuring an alternating current flowing through the charging member, and the adjusting unit is configured so that the power source is used during image formation based on the magnitude of the alternating current shake measured by the measuring unit during the control. The image forming apparatus according to claim 1, wherein an AC voltage in the oscillating voltage applied to the charging member is adjusted.   The measuring unit is capable of measuring a direct current flowing through the charging member, and the adjusting unit is configured to measure a direct current flowing through the charging member when the power source applies the vibration voltage to the charging member during the control. The adjusting unit adjusts the AC voltage in the oscillating voltage that the power source applies to the charging member during image formation based on the magnitude of the DC current fluctuation measured by the measuring unit during the control. The image forming apparatus according to claim 2.   The adjustment unit performs the adjustment by changing a target value of an alternating current flowing through the charging member by applying the vibration voltage to the charging member by the power source during image formation. The image forming apparatus according to 2.   The adjustment unit increases the target value of the alternating current in the second case in which the magnitude of the shake is larger than the first value than in the case of the first value. The image forming apparatus according to claim 4.   4. The image formation according to claim 3, wherein the adjustment unit performs the adjustment by changing a peak-to-peak voltage of an AC voltage in the oscillating voltage applied by the power source to the charging member during image formation. apparatus.   The adjusting unit increases the peak-to-peak voltage of the AC voltage in the second case in which the magnitude of the shake is larger than the first value than in the case of the first value. The image forming apparatus according to claim 6.   The adjustment unit obtains a relationship between the shake period and the magnitude of the shake from a measurement result by the measurement unit in the control, and performs the adjustment based on the magnitude of the shake that is the maximum in the relationship. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 1, wherein the adjustment unit performs the adjustment when at least one of the image carrier and the charging member is replaced.   10. The charging member according to claim 1, wherein the charging member is rotatable, and the adjustment unit performs the measurement of the current during the control over a period in which the charging member rotates a plurality of times. The image forming apparatus described in the item.   11. The image bearing member according to claim 1, wherein the image bearing member is rotatable, and the adjustment unit performs the measurement of the current during the control over a period in which the image bearing member rotates a plurality of times. The image forming apparatus according to claim 1.