JP2010102262A - Image forming apparatus and method of controlling the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately derive the value of a discharge current without using a differential operation. <P>SOLUTION: A charging member is abutted with an image carrier and charges the image carrier. A voltage application means applies an AC voltage to the charging member. A current detecting means applies an AC voltage to the charging member, thereby detecting the value of an AC current flowing in the charging member. An integrating means integrates the values of AC currents, which are detected by the current detecting means, for a predetermined integration period. A voltage command value control means creates a voltage command value so that the integrating value obtained by the integrating means approaches a target value, and outputs the voltage command value to the voltage application means. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a charging voltage control technique in an electrophotographic image forming apparatus.

  In general, an electrophotographic image forming apparatus includes a charging device that charges a transfer roller and a photosensitive drum in order to promote transfer of a toner image. In recent years, the contact charging method is becoming mainstream as the charging method of the charging device. This is because the contact charging method is more advantageous than the conventional non-contact charging method in terms of lowering the process voltage, reducing the amount of ozone generated, and reducing costs.

  In the contact charging method, generally, the surface of the photosensitive drum is uniformly charged by bringing a charging roller to which a voltage is applied into contact with the surface of the photosensitive drum. The voltage applied to the charging roller may be only a DC voltage, but an AC voltage may be applied in addition to the DC voltage. This is because the alternating voltage causes the discharge to the plus side and the minus side to occur alternately, so that the charging can be made uniform.

  When a sinusoidal AC voltage is applied to the charging roller, a resistive load current, a capacitive load current, and a discharge current flow through the charging roller. The resistive load current is a current that flows through a resistive load between the charging roller and the photosensitive drum. The capacitive load current is a current that flows through the capacitive load between the charging roller and the photosensitive drum. The discharge current is a current resulting from a discharge phenomenon generated between the charging roller and the photosensitive drum.

  By the way, in order to obtain stable charging, it has been empirically known that the value of the discharge current should be set to a predetermined value or more. However, if the discharge current is too large, deterioration of the photosensitive drum is likely to proceed. Further, the toner image may be disturbed by the discharge product. Therefore, it is important how accurately the appropriate value of the discharge current is set.

  The value of the discharge current can be controlled by the voltage applied to the charging roller. However, the relationship between the value of the discharge current and the voltage applied to the charging roller is not always constant. This is because the relationship changes depending on the film thickness of the photosensitive layer and dielectric layer of the photosensitive drum, environmental variation of the charging member and air, and the like. For example, the resistance value of the charging roller is low in a high temperature and high humidity environment, and conversely, the resistance value of the charging roller is high in a low temperature and low humidity environment. Therefore, the applied voltage for obtaining a constant discharge current is different. In addition, a change in the value of the discharge current also occurs due to variations in the resistance value due to manufacturing variations and contamination of the charging member, variations in the capacitance of the photosensitive drum due to durability, and variations in the characteristics of the high voltage generator of the image forming apparatus main body.

  In order to suppress such a change in the amount of discharge current, a “discharge current control method” has been proposed. In the discharge current control method, an alternating current value flowing through the charging member is detected, and an alternating voltage applied to the charging member is adjusted according to the detected alternating current value. However, the AC current value must be detected by the current detection means at at least two points in each of the voltage level lower than Vh where the discharge phenomenon does not occur and the voltage level higher than Vh where the discharge phenomenon occurs. Vh is referred to as a discharge start voltage.

  FIG. 10 is a diagram showing the relationship between the charging AC voltage applied to the charging member and the charging AC current flowing through the charging member. The horizontal axis represents the charging AC voltage value, and the vertical axis represents the charging AC current value. In FIG. 10, A, B, C, and D indicate detection points of alternating current. When the AC voltage becomes Vh or more, a discharge current amount Is corresponding to the AC voltage is generated. For example, when V_tar is applied as an AC voltage, the AC current value is I_tar, and Is_tar corresponds to the discharge current. Thus, since the relationship between the charging AC voltage and the charging AC current is not constant, it is necessary to measure the characteristics before and after the discharge start voltage Vh.

  For example, two points A and B are sampled at a voltage lower than Vh. Thereby, the characteristics of the alternating voltage V and the alternating current I in a region where no discharge current is generated are measured. When the voltage is Vh or higher, two points C and D are sampled. Thereby, the characteristics of V and I in the region where the discharge current is generated are measured. In the figure, Vd indicates the AC voltage value at point D, and Id indicates the AC voltage value at point D.

  By calculating the level of the AC voltage V_tar (AC current I_tar) for setting the discharge current to the predetermined level Is_tar from the two characteristics obtained by such a method, and controlling this as a target value, the value of the discharge current is obtained. Fluctuations can be suppressed.

  However, the conventional discharge current control method has the following problems.

  (1) If the detected value detected by the current detection circuit includes an error, the control accuracy of the discharge current is greatly deteriorated. Since the difference in current level is large between the points A and B and the points C and D described above, if an error occurs in the detected value, a large error also occurs in the calculated value of the discharge current.

  (2) The value of the discharge current changes before and after the continuous printing operation. When printing is performed continuously, a temperature rise occurs around the photosensitive drum. Therefore, the relationship between the voltage applied to the charging roller and the discharge current also changes, and the value of the discharge current varies.

  (3) The high-voltage power supply is required to be able to output an adjustment output (Vd, Id) larger than an image output (eg, V_tar, I_tar). Therefore, the cost and size of the high-voltage power supply are increased.

Techniques for solving these problems are described in Patent Document 1 and Patent Document 2. In Patent Document 1, the difference between the amplitude when the discharge does not occur and the amplitude when the discharge actually occurs, obtained by differentiating the output voltage drop due to the discharge phenomenon, is calculated as the value of the discharge current. Yes. In Patent Document 2, by differentiating the voltage waveform, a current waveform when no discharge is generated is simulated, and the value of the discharge current is calculated from the difference between the simulated current waveform and the actual current waveform. .
JP 2004-157501 A JP 2006-276273 A

  As described above, in Patent Document 1 and Patent Document 2, the value of the discharge current is derived by calculating the differential value of the applied AC voltage. However, the differential operation tends to be less stable against noise and variations from the theoretical waveform.

  Therefore, an object of the present invention is to solve at least one of such problems and other problems. For example, an object of the present invention is to derive a value of a discharge current with high accuracy without using a differential operation. Other issues can be understood throughout the specification.

  The image forming apparatus of the present invention includes, for example, an image carrier, a charging member, a voltage application unit, a current detection unit, an integration unit, and a voltage command value control unit. The charging member is disposed so as to contact the image carrier, and charges the image carrier. The voltage applying means applies an alternating voltage to the charging member. The current detection means detects the value of the alternating current flowing through the charging member by applying an alternating voltage to the charging member. The integrating means integrates the value of the alternating current detected by the current detecting means over a predetermined integration period. The voltage command value control means generates a voltage command value so that the integration value of the integration means approaches the target value, and outputs the voltage command value to the voltage application means.

  According to the present invention, the value of the discharge current can be derived with high accuracy without using a differential operation. Therefore, the image carrier can be more uniformly charged, and high image quality and high quality can be maintained over a long period of time.

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

[First Embodiment]
FIG. 1 is a block diagram illustrating a charging device according to the first embodiment. The arithmetic device 101 is a digital arithmetic unit such as a CPU or a DSP, for example. The voltage command value V_tar output from the arithmetic unit 101 is converted into an analog signal V_tar ′ through the DA converter 102. An analog signal V_tar ′ indicating a voltage command value is input to the AC voltage application circuit 103 of the high-voltage power supply unit.

  The AC voltage application circuit 103 includes a signal amplifier 104, a low-pass filter 105, and the like. The AC voltage application circuit 103 is an example of a voltage application unit that applies an AC voltage to the charging member. The signal amplifier 104 includes resistors R1, R2, and R3 and an operational amplifier OP1, and amplifies the input analog signal. The amplified analog signal passes through resistor R4. Further, the analog signal is chopped by the transistor Q1 with a built-in resistor in accordance with the sine wave PWM signal (eg, carrier wave 1 kHz, modulation wave 50 kHz) output from the arithmetic unit 101. As a result, the analog signal is converted into a rectangular wave. Thus, the resistor built-in transistor Q1 and the like function as a rectangular wave converter. Thereafter, an AC component is extracted from the analog signal by the capacitor C1. That is, the direct current component is removed. The extracted AC component is input to the resistor R5 of the low-pass filter 105.

  The low-pass filter 105 includes resistors R5, R6, R7, R8, R9, capacitors C2, C3, and an operational amplifier OP2. The low-pass filter 105 passes a rectangular fundamental wave based on the sine wave PWM signal among the input signals input to the resistor R5. That is, the cutoff frequency of the low-pass filter 105 is set so as to cut off the harmonics. Vcc in the figure is a DC power supply voltage for offsetting the AC signal to a positive voltage.

  The AC component output from the low-pass filter 105 is the primary winding (for example, the turn ratio is 120) of the high-voltage transformer T1 via the resistors R10 and R11 and the capacitors C4 and C5. The AC voltage V output from the secondary winding of the high-voltage transformer T1 through the limiting resistor R16 is variable (eg, variable with an amplitude from 0 V to 1250 V) according to the voltage command value. The AC voltage V is superimposed on the DC voltage Vdc output from the DC voltage application unit 106 and applied to the charging roller 107. Here, the applied voltage is referred to as a charging AC voltage, but hereinafter referred to as an AC voltage. The charging roller 107 is an example of a charging member, and may have another shape such as a charging blade or a charging brush. The charging roller 107 is disposed so as to contact the photosensitive drum 108.

  Every time the AC voltage V increases and reaches a discharge start voltage (discharge start threshold value) Vh, a discharge phenomenon occurs between the charging roller 107 and the photosensitive drum 108. As a result, the surface potential of the photosensitive drum 108 becomes the DC voltage Vdc. In this way, the surface of the photosensitive drum 108 is uniformly charged. The photosensitive drum 108 is an example of an image carrier.

  The alternating current detection circuit 109 includes resistors R12, R13, R14, R15, capacitors C6, C7, and an operational amplifier OP3. The alternating current detection circuit 109 is an example of a current detection unit that detects the value of the alternating current flowing through the charging member by applying an alternating voltage to the charging member. Capacitor C6 blocks the DC component and allows only the AC component to pass. The alternating current flowing through the high-voltage transformer T1 is converted into a voltage by the resistor R12. This voltage is detected as a current value voltage Isns' through the capacitor C7, resistors R13, R14, R15, and the operational amplifier OP3. The current value voltage is a voltage indicating the current value of the alternating current, and the amplitude of the voltage corresponds to the current value. Compared to the load impedance formed by the charging roller 107 and the photosensitive drum 108, the impedance of the capacitor C7 and the resistors R13, R14, and R15 is designed to be sufficiently large.

  Since the detected current value voltage Isns ′ is an analog signal, it is converted into a digital signal (current value voltage Isns) by the AD converter 110. The current value voltage Isns is input to the arithmetic unit 101. The sampling frequency of the AD converter 110 is assumed to be sufficiently faster than the frequency of the current value voltage Isns' (eg, 200 kHz).

  The arithmetic device 101 includes a waveform pulse generator 111, an integral calculator 112, and a voltage command value controller 113. The waveform pulse generator 111 outputs a sine wave PWM signal to the resistor built-in transistor Q1. The integral calculation unit 112 integrates the detected current value voltage Isns. The integration calculation unit 112 is an example of an integration unit that integrates the value of the alternating current detected by the current detection unit over a predetermined integration period. The voltage command value control unit 113 generates a voltage command value V_tar based on the integration result and outputs it to the DA converter 102. The voltage command value control unit 113 is an example of a voltage command value control unit that generates a voltage command value so that the integration value of the integration unit approaches a target value, and outputs the voltage command value to the voltage application unit.

  FIG. 2 is a flowchart showing detection and control of the discharge current in the first embodiment. In step S201, the waveform pulse generation unit 111 outputs a rectangular wave (sine wave PWM signal) generated by pulse width modulation (PWM) of the sine wave to the transistor Q1 with a built-in resistor.

  In step S202, the integration calculation unit 112 determines the length of the integration period (time width). For example, the integration calculation unit 112 calculates a time width corresponding to a half cycle of the sine wave PWM signal as the time width of the integration period. Note that if the length of the integration period is fixed, step S202 can be omitted.

  In step S203, the integration calculation unit 112 determines an integration start timing and an integration end timing. The integration calculation unit 112 determines the time when the phase has advanced by 90 ° from the time when the detected charging AC current becomes zero cross as the integration start timing of the current value voltage Isns. For example, if the frequency of the sine wave is 1 kHz, the integration start timing is the time when 0.25 ms has elapsed from the time of zero crossing. Note that 90 ° corresponds to a time width of a quarter cycle. The phase difference between the sine wave PWM signal and the charging alternating current is 90 °. Therefore, the time when the sine wave PWM signal becomes zero crossing coincides with the integration start timing.

  On the other hand, the integration calculation unit 112 determines a time (for example, after 0.75 ms) when the phase is advanced by 270 ° from the time when the charging AC current becomes zero cross as the integration end timing. Note that the period between the time when the phase advances 90 ° and the time when the phase advances 270 ° from the time when the charging AC current reaches zero crossing is a time width corresponding to a half cycle of the sine wave PWM signal. . The arithmetic unit 101 monitors the waveform of a sine wave PWM signal (charging AC voltage) and a current value voltage (charging AC current), and particularly monitors whether or not a zero cross has occurred. Then, when detecting the zero cross, the arithmetic unit 101 waits for the integration start timing to arrive by a timer. When the integration start timing arrives, the process proceeds to step S204. Thus, the arithmetic unit 101 is an example of a timing determining unit that determines the timing at which the alternating current reaches the zero cross as the integration start timing.

  In step S <b> 204, the integration calculation unit 112 integrates the current value voltage Isns input from the AD converter 110. The arithmetic unit 101 waits for the integration end timing to arrive, and stops the integration processing of the integration arithmetic unit 112 when the integration end timing arrives. As described above, the integration calculation unit 112 is an example of a timing determination unit that determines, as the integration end timing, the timing at which the 270 ° phase has advanced from the timing at which the alternating current reaches the zero cross. The integration calculation unit 112 outputs the integration result (discharge current amount Is) to the voltage command value control unit 113.

  In step S205, the voltage command value control unit 113 compares the discharge current amount Is with the target discharge current amount Is_tar, generates a voltage command value V_tar such that the discharge current amount Is approaches the target discharge current amount Is_tar, and performs DA conversion. Output to the device 102.

  3 and 4 are diagrams showing the concept of discharge current amount calculation. The upper row shows the AC voltage V applied to the charging roller. The middle row shows the alternating current I flowing through the charging roller. The lower part shows the discharge current amount Is. Each horizontal axis indicates time.

  As regards the load between the charging roller 107 and the photosensitive drum 108 as viewed from the AC voltage application circuit 103, a capacitive load is dominant. Therefore, the phase of the AC current I is advanced by 90 ° with respect to the phase of the AC voltage V to be applied. Further, since the AC voltage V is a sine wave, the AC current I is also a sine wave.

  As shown in FIG. 4, when the AC voltage V applied between the charging roller 107 and the photosensitive drum 108 increases and exceeds the discharge start voltage (discharge start threshold value) Vh, a discharge phenomenon occurs. Therefore, discharge occurs over a time corresponding to the amplitude of the AC voltage in the vicinity of 0 ° and 180 ° with respect to the phase of the AC voltage. When the discharge occurs, the alternating current I increases by the amount of the discharge current Is. For example, in FIG. 4, the alternating current I increases from the value indicated by the dotted line portion to the value indicated by the solid line portion.

  As can be seen from FIG. 4, in the vicinity of 0 ° and 180 ° with respect to the phase of the AC voltage V, there is a region where no discharge occurs regardless of the amplitude. Therefore, when the alternating current I is integrated from 90 ° to 270 °, the current flowing through the capacitive load is canceled out. That is, the integral value of the capacitive load current is 0 A · s.

  In this way, the length of the integration period is set to the AC voltage waveform (sine wave) ½ cycle. That is, the integration calculation unit 112 can derive the discharge current amount Is for one time by integrating the alternating current I from 90 ° to 270 °. The arithmetic unit 101 is an example of an integration period determination unit that determines an integration period so that an integration value for a current flowing through a capacitive load formed by a charging member and an image carrier is zero.

  The voltage command value control unit 113 calculates the absolute value of the discharge current amount Is. Further, the voltage command value control unit 113 calculates an average value Is_ave for the absolute value of the discharge current amount Is for 10 discharges. The voltage command value control unit 113 does not take the absolute value, but instead calculates the average value from the discharge current amount Is for the integration period of only one of the zero crossing from negative to positive or the zero crossing from positive to negative. May be calculated. The voltage command value control unit 113 generates the voltage command value V_tar so that the difference between the target discharge current amount Is_tar and the discharge current amount average value Is_ave input from a host computer (not shown) approaches zero, and DA conversion is performed. Output to the device 102. Thereby, feedback control is realized.

  As described above, according to the present embodiment, the value of the discharge current can be derived with high accuracy without using the differential operation. As a result, it is possible to generate a fixed amount of discharge with high accuracy regardless of environmental conditions and variations in characteristics of the charging member due to manufacturing. Thereby, since uniform charging is realized, problems such as deterioration of the image carrier, toner fusion, and image defects may be reduced. In the present invention, since the value of the discharge current can be finely adjusted during printing, the printing speed can be maintained even during continuous printing. In addition, uniform charging can be realized regardless of contamination of the charging member and environmental changes. This makes it possible to maintain high image quality and high quality over a long period of time.

  In the present embodiment, the discharge current amount can be controlled by detecting the discharge current amount during the image forming sequence. Therefore, it is not necessary to secure a special adjustment period for the charging AC voltage (AC voltage) separately from the image forming sequence. In addition, since the output range of the high-voltage board can be designed according to the actual usage range, the cost can be reduced.

[Second Embodiment]
In the first embodiment, the AC current integration period is controlled by the phase of the current waveform. On the other hand, the second embodiment includes an adjustment sequence in addition to the image forming sequence. In this adjustment sequence, the integration period is adjusted so that the current integration value in the undischarged region becomes zero.

  FIG. 5 is a block diagram illustrating a charging device according to the second embodiment. The parts that are the same as those in FIG. 1 are given the same reference numerals to simplify the description. A component different from that of the first embodiment is an integration period adjustment unit 501. The integration period adjustment unit 501 adjusts the integration period of the alternating current Isns.

  FIG. 6 is a flowchart showing detection and control of the discharge current in the second embodiment. In step S601, the voltage command value control unit 113 outputs a fixed voltage command value Vc_tar regardless of the integration result output by the integration calculation unit 112. The voltage command value Vc_tar is, for example, a voltage value that has been confirmed in advance that a discharge phenomenon does not occur even in various environments and member variations assumed in advance. Thus, the voltage command value control unit 113 is an example of a setting unit that sets a voltage command value in the voltage application unit that does not cause a discharge between the charging member and the image carrier.

  In step S602, the waveform pulse generator 111 starts outputting a sine wave PWM signal. In step S603, the integration period adjustment unit 501 calculates a time width corresponding to a quarter cycle of the sine wave PWM signal.

  In step S604, the integration period adjustment unit 501 determines an integration start timing and an integration end timing. The method for determining the integration start timing and the integration end timing is as described in the first embodiment. That is, the time when the 90 ° phase has advanced from the zero cross is the integration start timing. The time when the phase of 270 ° advances from the zero cross is the integration end timing.

  In step S605, the integration calculation unit 112 calculates the discharge current amount Is by integrating the current value voltage Isns from the integration start timing to the integration end start timing. Ideally, the discharge current amount Is, which is an integral value, becomes zero, but does not actually become zero.

  FIG. 7 is a diagram showing the concept of integration period and discharge current amount calculation. As shown in FIG. 7, when distortion (solid line) occurs in the load current, an error occurs in the discharge current amount (integrated value).

In step S606, the integration period adjustment unit 501 determines whether or not the following conditional expression is satisfied for the integration value Is_err.
| Is_err | <α
α is a discharge current amount adjustment constant, and a sufficiently small value allowable as an error with respect to the target discharge current amount Is_tar is used. In FIG. 7, | Is_err | <α means that the difference between the shaded area and the horizontal line area is less than or equal to α during the integration period.

  If the conditional expression is not satisfied, the process proceeds to step S607. In step S607, the integration period adjustment unit 501 shifts the integration start timing and the integration end timing by a predetermined adjustment amount. Thereafter, the process returns to step S604.

  On the other hand, when the conditional expression is satisfied in step S606, the integration period adjustment unit 501 determines the integration start timing and integration end timing at that time as timings to be used at the time of image formation. In this way, the adjustment integration period is determined. As can be seen from FIG. 7, the integration start timing and integration end timing of the adjustment integration period are offset from the integration start timing and integration end timing of the ideal integration period, respectively.

  The predetermined adjustment amount is determined as follows, for example. If | Is_err |> α, the integration period adjustment unit 501 calculates an average value of 10 times of the integration values corresponding to the integration period only during zero crossing from positive to negative among the detected integration values. If the average value is positive, the integration period adjustment unit 501 shifts the integration start timing and integration end timing in a direction that is advanced. Conversely, if the average value is negative, the integration period adjustment unit 501 shifts in a direction to delay the integration start timing and the integration end timing. Thus, the integration period adjustment unit 501 is an example of an adjustment unit that adjusts the integration period so that the integration value of the alternating current obtained when the voltage command value is set by the setting unit becomes zero.

  When the image forming sequence is started, the integration period adjustment unit 501 performs charge control similar to that in the first embodiment using the adjustment integration period determined in the adjustment sequence (FIG. 2).

  FIG. 8 is a diagram showing the concept of adjustment integration period and discharge current amount calculation. As can be seen from comparison with FIG. 4, in FIG. 8, the integration period is adjusted even if the phase of the AC voltage V and the AC current I is shifted due to distortion. Therefore, the current integration value in the undischarged region becomes 0, and the discharge current amount error can be reduced.

  As described above, according to the present embodiment, it is possible to accurately detect and control the discharge current amount even in an environment where distortion occurs in the alternating current.

  FIG. 9 is a diagram illustrating an example of an image forming apparatus to which the charging device of the present invention is applied. The image forming apparatus 900 is a multicolor image forming apparatus in which four image forming stations are juxtaposed. The present invention can also be applied to a monochrome image forming apparatus.

  The photoreceptors 1a to 1d are image carriers, and correspond to the above-described photosensitive drum 108. The charging devices 2a to 2d uniformly charge the surface of the corresponding photoconductor. The charging devices 2a to 2d include the above-described charging roller 107.

  The exposure devices 3a to 3d expose the surface of the corresponding photosensitive drum according to the image signal to form an electrostatic latent image. The developing devices 4a to 4d use different color toners to develop the corresponding electrostatic latent images to form toner images. The primary transfer devices 53 a to 53 d transfer the toner image on the photoconductor to the intermediate transfer belt 51. At this stage, a multicolor toner image is formed by superimposing toner images of different colors. The secondary transfer device 56 secondarily transfers a multicolor toner image from the intermediate transfer belt (intermediate transfer member) to the recording medium P. The fixing device 7 fixes the toner image on the recording medium P by pressurizing and heating the recording medium P and the toner image.

It is a block diagram which shows the charging device in 1st Embodiment. It is a flowchart which shows the detection and control of the discharge current in 1st Embodiment. It is the figure which showed the concept of discharge current amount calculation. It is the figure which showed the concept of discharge current amount calculation. It is a block diagram which shows the charging device in 2nd Embodiment. It is a flowchart which shows the detection and control of the discharge current in 2nd Embodiment. It is the figure which showed the concept of the integration period and discharge current amount calculation. It is the figure which showed the concept of an adjustment integration period and discharge current amount calculation. 1 is a diagram illustrating an example of an image forming apparatus to which a charging device of the present invention is applied. It is the figure which showed the relationship between the charging alternating voltage applied to a charging member, and the charging alternating current which flows into a charging member.

Claims (6)

An image forming apparatus,
An image carrier;
A charging member disposed so as to contact the image carrier;
Voltage applying means for applying an alternating voltage to the charging member;
Current detecting means for detecting a value of an alternating current flowing through the charging member by applying the alternating voltage to the charging member;
Integrating means for integrating the value of the alternating current detected by the current detecting means over a predetermined integration period;
An image forming apparatus comprising: a voltage command value control unit that generates a voltage command value so that an integrated value of the alternating current approaches a target value, and outputs the voltage command value to the voltage application unit.   2. The integration period according to claim 1, wherein the integration period is a period determined so that an integration value of a current flowing in a capacitive load formed by the charging member and the image carrier is zero. The image forming apparatus described.   2. The image forming apparatus according to claim 1, wherein the length of the integration period is a half cycle of a sine wave that is a waveform of the AC voltage.   Timing determining means for determining, as an integration start timing, a timing at which a 90 ° phase advances from a timing at which the AC current becomes zero cross, and a timing at which a 270 ° phase advances from the timing at which the AC current becomes zero cross as an integration end timing; The image forming apparatus according to claim 3, wherein the image forming apparatus is provided. Setting means for setting a voltage command value in the voltage application means so that no discharge occurs between the charging member and the image carrier;
2. The adjusting device according to claim 1, further comprising adjusting means for adjusting the integration period so that an integrated value of the alternating current obtained when the voltage command value is set by the setting means becomes zero. The image forming apparatus described in 1. A control method for an image forming apparatus, comprising: an image carrier; a charging member arranged to contact the image carrier; and a voltage applying unit that applies an alternating voltage to the charging member.
A current detection step of detecting a value of an alternating current flowing through the charging member by applying the alternating voltage to the charging member;
An integration step of integrating the value of the alternating current detected in the current detection step over a predetermined integration period;
And a voltage command value control step of generating a voltage command value so that the integral value of the alternating current approaches a target value and outputting the voltage command value to the voltage application means.

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