JP6921611B2 - Process cartridge, image forming device, image forming method - Google Patents

Description

The present invention relates to an image forming apparatus including a charging device that charges an object to be charged via a charging member.

Conventionally, an image forming apparatus that employs an electrophotographic method includes a step of uniformly charging the surface of a drum-type electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum) to a predetermined potential.

As a charging means, for example, a contact charging method in which a roller charging member (hereinafter referred to as a charging roller) is brought into contact with the surface of a photosensitive drum and a voltage is applied to the charging roller to charge the photosensitive drum is currently the mainstream.

As a method of applying a voltage to the charging roller, there are a method of applying a DC voltage and a method of superimposing an AC voltage on the DC voltage and alternately causing discharge to the plus side and the minus side to make the charging uniform. In the latter method, the resistance load current flowing through the resistive load between the charging roller and the photosensitive drum, the capacitive load current flowing through the capacitive load between the charging roller and the photosensitive drum, and the discharge current between the charging roller and the photosensitive drum Flows, and the total current flows through the charging roller. At this time, it is empirically known that the amount of discharge current should be set to a predetermined value or more in order to obtain stable charging.

FIG. 18 shows the current Ic characteristics that flow through the charging roller when an AC voltage Vc is applied to the charging roller. The AC voltage Vc indicates the peak voltage value of the AC voltage, and the current Ic indicates the effective value of the AC current. From FIG. 18, when the amplitude of the AC voltage Vc is gradually increased, the charging current increases accordingly. When the voltage is 2 times or less of the predetermined voltage Vh, the amplitude of the AC voltage and the charging current are substantially proportional to each other. This is because the resistance load current and the capacitance load current are proportional to the voltage amplitude, and because the voltage amplitude is small, the discharge phenomenon does not occur and the discharge current does not flow. Then, when the AC voltage is further increased, the discharge phenomenon starts at twice the predetermined voltage Vh. At this time, the charging current Ic deviates from the proportional relationship and flows as much as the discharge current Is. Here, in order to stably charge the battery, it is necessary to set the AC voltage Vc so that the discharge current Is becomes a predetermined value or more.

However, when the amount of discharge to the photosensitive drum increases, deterioration of the photosensitive drum such as scraping of the photosensitive drum is promoted, and abnormal images such as image flow in a high temperature and high humidity environment due to the discharge product may occur. .. Therefore, in order to obtain stable charging and solve the above problems, it is necessary to control the application of the minimum necessary voltage while suppressing the amount of discharge as much as possible. However, the relationship between the voltage applied to the photosensitive drum and the amount of discharge is not always constant, and changes depending on the film thickness of the photosensitive layer and the dielectric layer of the photosensitive drum, the environmental changes of the charging member and the air, and the like. In addition to the above-mentioned causes of environmental fluctuations, defects due to changes in the amount of discharge are caused by variations in the manufacturing of charged members, fluctuations in resistance due to dirt, fluctuations in the capacitance of the photosensitive drum due to durability, and characteristics of the high-voltage generator of the image forming device. It is known that it also occurs due to variations.

In order to suppress such a change in the amount of discharge, a "discharge current control method" has been proposed (see, for example, Patent Document 1). In this method, a control method has been proposed in which the peak voltage of the AC applied voltage applied to the charging roller and the peak voltage of the differential waveform thereof are detected to calculate the discharge current value (see Patent Document 1).

Japanese Unexamined Patent Publication No. 2004-157501

However, with the recent progress in extending the life of image forming devices and diversifying the usage methods in the market, uneven stains in the direction perpendicular to the image forming process direction of the charging roller (hereinafter referred to as the longitudinal direction) and the longitudinal direction of the photosensitive drum In some cases, uneven film thickness may occur. This is, for example, continuing to output a print pattern with a bias in the printing portion in the longitudinal direction, or continuing to use a small-sized recording material such as an envelope or a postcard in an image forming apparatus in which the recording material comes into direct contact with the photosensitive drum. It may happen due to such things as.

If uneven film thickness in the longitudinal direction of the photosensitive drum or uneven stain in the longitudinal direction of the charging roller occurs, the impedance when the current flows from the charging roller to the photosensitive drum in the longitudinal direction differs, and there are parts that are easy to discharge and parts that are difficult to discharge. It ends up. In this case, since the discharge current control method detects the entire discharge amount in the longitudinal direction, there is a portion where the discharge amount is lower than the appropriate amount or a portion where the discharge amount is higher than the appropriate value and the scraping of the photosensitive drum is promoted. There is. The part that is difficult to discharge becomes unstable in charging, and an over-discharged part and an under-discharged part are locally generated, and this under-discharged part is developed by the developing part and appears as a black spot on a white background. As a result, there is a case where an image harmful effect called a so-called sandy area in which a large number of black spots appear on a white background occurs.

The amount of discharge may be determined by predicting in advance the unevenness of dirt on the charging roller and the unevenness of the film thickness of the photosensitive drum, but such a phenomenon is difficult to predict because it changes greatly depending on the usage conditions of the user.

Therefore, an object of the present invention is to provide an image forming apparatus, a process cartridge, and an image forming method capable of detecting discharge unevenness in the longitudinal direction and optimizing the amount of discharge.

The configuration of the present invention for achieving the above object is a rotatable image carrier that carries a latent image, an exposure means that exposes the image carrier, a charging member that charges the image carrier, and the charging. From the bias applying means for applying a bias voltage to the member, the discharge amount detecting means for detecting the amount of current discharged between the charged member and the image carrier, and the discharge current amount detected by the discharge amount detecting means. the includes a discharge current control means for determining a bias voltage applied to the charging member, a discharge information detecting means for detecting information relating to the discharge is a discharge information between said image bearing member and said charging member, the discharge The information detecting means sets a part of the printable area in the plane of the image carrier whose width in the direction perpendicular to the rotation direction is smaller than the width of the printable area as a partial measurement area. When the image carrier is charged to a constant potential by the charging member and then different potentials are formed between the partial measurement region and the region other than the partial measurement region by the exposure means, the partial measurement region and the charge are formed. The discharge current control means detects partial discharge information regarding discharge with a member, and corrects a bias voltage in image formation applied to the charged member based on the partial discharge information.

As described above, according to the present invention, it is possible to detect discharge unevenness in the longitudinal direction and optimize the discharge amount.

Flow chart diagram according to the first embodiment Schematic diagram of the image forming apparatus according to the first embodiment Discharge current control block diagram according to the first embodiment Discharge current control circuit diagram according to the first embodiment The figure which shows the discharge current detection method which concerns on Example 1. Discharge current control detection waveform diagram according to the first embodiment DC bias discharge start voltage detection block diagram according to the first embodiment DC bias discharge start voltage detection circuit diagram according to the first embodiment Schematic diagram of VI characteristics when DC charging bias is applied according to Example 1. Conceptual diagram of the discharge start voltage detection method according to the first embodiment Longitudinal schematic view of the photosensitive drum potential according to the first embodiment Schematic diagram of partial discharge start voltage measurement according to Example 1. Conceptual diagram of the measurement area according to the first embodiment Conceptual diagram of Discharge Start Voltage Value Difference Detection of Multiple AC Bias in Longitudinal According to Example 1 Conceptual diagram of Discharge Start Voltage Value Difference Detection of Multiple AC Bias in Longitudinal According to Example 1 Relationship diagram of discharge amount and AC bias according to Example 1. Relationship diagram of discharge amount and AC bias according to Example 2 Current characteristics of the current flowing through the charging roller when an AC voltage is applied to the charging roller Conceptual diagram of the discharge start voltage detection method according to the third embodiment The relationship between the potential and the film thickness of the photosensitive drum according to the third embodiment. Conceptual diagram of the discharge start voltage detection method according to the fourth embodiment AC bias at the time of detecting the discharge start voltage according to the fourth embodiment

Hereinafter, embodiments for carrying out the present invention will be described in detail exemplarily based on examples with reference to the drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in this embodiment should be appropriately changed depending on the configuration of the apparatus to which the invention is applied and various conditions. That is, it is not intended to limit the scope of the present invention to the following embodiments.

In this embodiment, in a configuration in which the bias voltage applied to the charging member is controlled so that the discharge current flowing between the charging member and the image carrier is constant, a plurality of partial discharge information in the longitudinal direction is detected in the longitudinal direction. Then, the discharge amount is optimized by correcting the bias voltage output value from those values.

Hereinafter, the process cartridge and the image forming apparatus according to the present invention will be described by taking an electrophotographic method as an example.

<Outline of configuration and operation of image forming device and process cartridge>
FIG. 2 is a schematic view of the image forming apparatus 1 in a state where the process cartridge is attached. Reference numeral 3 denotes a photosensitive drum which is a rotatable image carrier, and reference numeral 4 denotes a laser scanner which is an exposure means for forming an electrostatic latent image by scanning a laser beam on the photosensitive drum 3 with a semiconductor laser 5. Reference numeral 2 is a replaceable process cartridge. The process cartridge 2 includes a charging roller 6 which is a charging member for uniformly charging the photosensitive drum 3, and a developing agent that develops an electrostatic latent image formed on the photosensitive drum 3 by a laser scanner 4 with a developing agent. It is composed of a carrier 7 and a developer 8 for storing a developer. Reference numeral 10 denotes a transfer roller for transferring the developer image developed on the photosensitive drum 3 to a predetermined recording material 11, and reference numeral 12 denotes a fixing device for fixing the developer transferred to the recording material 11 by heat and pressure. Reference numeral 13 denotes a temperature thermistor for controlling the temperature of the fuser. Reference numeral 14 denotes a paper feed roller for feeding the recording material. 15 is a top sensor that synchronizes with the transportation of the recording material, 16 is a paper ejection roller for ejecting the fixed recording material 11 to the paper ejection tray 17, and 18 is for detecting the presence or absence of the recording material 11 after fixing. It is a paper ejection sensor. Reference numeral 19 denotes an engine controller including a CPU 20 and controlling each part constituting the image forming apparatus 1. Reference numeral 21 denotes an environment sensor that detects the external environment of the image forming apparatus 1.

Further, this embodiment will be described using an environment of 23 ° C. 50% RH under the conditions of a resolution of 600 dpi, a process speed of 235 mm / sec, and an exposure amount of 0.2 μJ / cm2. Further, although the negative electrode toner is used in this embodiment, the positive electrode toner may be used. In this case, the configuration is the same as when the negative electrode toner is used, except that the signs such as bias are all reversed.

<Control of charged part>
Next, FIG. 3 shows a block diagram for controlling the charged portion of the image forming apparatus in this embodiment. The CPU 20 includes a calculation unit 30, a storage unit 31, and an AC voltage drive signal generation unit 32. Inside the discharge current control circuit (bias applying means) 33, a voltage is applied to the charging roller 6 while controlling the discharge current by sending a signal from the CPU 20. Here, the discharge control means includes a CPU 20 and a discharge current control circuit 33. Further, the CPU 20 detects the output value of the environment sensor 21 and controls the discharge current according to the output value. The detailed operation of the discharge current control circuit 33 will be described below.

<Discharge current control>
The discharge current control circuit 33 in this embodiment is shown in FIG. The AC high voltage of the sine wave generated by the sine wave voltage application unit 50 is superimposed on the DC voltage output by the DC high voltage circuit 51. The vibration voltage is supplied to the charging roller 6. Further, the AC current value is controlled so as to have a constant vibration voltage output level according to the detection output value of the AC current detection unit 52 as the AC current value detecting means. Further, the discharge current control circuit 33 includes a peak voltage detection circuit 53 which is a voltage amplitude value detection unit and a differential waveform peak voltage detection circuit 54 which is a differential amplitude value detection unit. As a result, the CPU 20 can detect the peak value of the output AC voltage and the peak value of the differential waveform. Here, the discharge amount detecting means includes a peak voltage detecting circuit 53, a differential waveform peak voltage detecting circuit 54, and a CPU 20.

A method of detecting the discharge current in this embodiment will be described with reference to FIG. FIG. 5 shows the charging current flowing through the charging roller 6 when an AC voltage is applied to the charging roller 6. The horizontal axis shows the peak voltage value of the AC voltage, and the vertical axis shows the effective value of the AC current. As shown in FIG. 5, in the region where the charged AC voltage is twice or less the discharge start voltage (Vh), the relational expression of the charged current value with respect to the charged AC voltage is represented by a straight line substantially proportional to the origin. In this region, a current flows between the charging roller 6 and the photosensitive drum 3 according to the resistive load and the capacitive load. On the other hand, in the region where the charged AC voltage is twice or more the discharge start voltage (Vh), a discharge current is generated between the charging roller 6 and the photosensitive drum 3, and the charging current to which this discharge current value is added is added. The value Ic flows. In the discharge start region, the characteristic when discharging is represented by 500, and the characteristic when not discharging is represented by 501. Here, the discharge current value can be calculated from the relationship between the characteristic 500 and the characteristic 501. Further, in the case of the peak value Va when discharging, the peak value Va ′ when not discharging, and the charging current Ic, the discharge current value Is can be obtained by the following equation (1).
Is = Ic × (Va'-Va) / Va'... Equation (1)
That is, if (Va'-Va) / Va'can be known, the amount of discharge with respect to the charging current can be detected. A method of obtaining (Va'-Va) / Va'will be described with reference to FIG. FIG. 6A shows the charged AC voltage output waveform applied to the charging roller 6, and FIG. 6B shows the differential waveform of the charged AC voltage output. The output waveform of the charged AC voltage has a shape in which the level near the peak is lowered by ΔV (= (Va'-Va)) due to the influence of the discharge. Further, since the phase of the differential voltage waveform is delayed by 90 °, the peak value is not affected by the discharge. Therefore, the peak value (Vb) of the differential voltage corresponds to the peak level (Va') of the output voltage when no discharge is performed. Therefore, (Va'-Va) / Va'can be obtained. The discharge current value Is is detected by the method shown in FIGS. 5 and 6, and the charge current value Ic is set so as to be the discharge current value Is.
Is being adjusted.

In this embodiment, in order to solve the problem of uneven discharge in the longitudinal direction, in addition to the discharge current control described above, partial discharge information in the longitudinal direction (hereinafter referred to as partial discharge information) is detected, and the charge bias is obtained from those values. The amount of discharge was optimized by correcting the output value. Further, in this embodiment, a partial discharge start voltage (hereinafter referred to as a partial discharge start voltage) was measured as partial discharge information.

In the following, first, the discharge start voltage detection required to detect the partial discharge start voltage as partial discharge information and the method of performing uniform charging will be described, and then the partial discharge start voltage detection method as partial discharge information will be described. Will be explained.

<Discharge start voltage detection>
In this embodiment, in order to detect partial discharge information in the longitudinal direction, a DC bias discharge start voltage detection circuit (discharge information detection means) 34 is provided as shown in FIG. The DC bias discharge start voltage detection circuit 34 detects the discharge start voltage while applying the DC voltage to the charging roller 6 by sending a signal from the CPU 20. FIG. 8 shows a schematic configuration of the DC bias discharge start voltage detection circuit 34 in the present invention. In 100, the voltage setting circuit unit changes the bias value according to the PWM signal. Reference numeral 101 is a transformer drive circuit unit, and 102 is a high voltage transformer unit. Reference numeral 103 denotes a circuit provided in which the feedback circuit unit monitors the output voltage via R61 so that the output voltage value corresponds to the setting of the PWM signal. Reference numeral 104 denotes a current detection circuit unit (current detection means). The current value I63, which is the sum of the current value I62 flowing through the charging roller 6 and the current value I61 flowing from the feedback circuit, is detected by R63 and transmitted from J110 to the CPU 20 as an analog value. Will be done. Until the discharge starts between the photosensitive drum 3 and the charging roller 6, the photosensitive drum 3 and the charging roller 6 are insulated from each other. Therefore, until the discharge is started, the current flowing through the detection resistor R63 is only I61 flowing from the feedback circuit unit 103. I61 is determined by Vpwm and Vref, R64, and R65 set by the PWM signal.
I61 = (Vref-Vpwm) / R64-Vpwm / R65

Further, when the current value I61 flows through the feedback resistor R61, the output voltage Vout is also set as follows.
Vout = I61 x R61 + Vpwm ≒ I61 x R61
That is, as shown in the straight line (1) of FIG. 9, until the discharge is started, only the current of I61 corresponding to the PWM signal flows to R63 of the current detection circuit unit, so that the current value becomes a straight line.

However, when the discharge is started between the photosensitive drum 3 and the charging roller 6, I63, which is the sum of the current value I62 flowing through the charging roller 6 and the current value I61 flowing from the feedback circuit, flows through R63 of the current detection circuit unit. That is, as shown in the curve (2) of FIG. 9, the current value becomes a curve having a branch point when the discharge starts. From this, the current flowing through the charging roller 6 can be calculated by Isd obtained by subtracting the straight line (1) from the curve (2).

In this embodiment, a plurality of Isds are measured while operating the DC bias, and the time when a certain Isd reaches a predetermined current value is determined as the DC bias discharge start voltage. However, the method for determining the DC bias discharge start voltage is not limited to this. For example, as shown in FIG. 10, the discharge amount for two different DC biases is measured, an approximate straight line is drawn from the approximate straight line, and the point where this straight line becomes the discharge amount 0 (D in FIG. 10) is determined as the DC bias discharge start voltage. The method may be used. Further, from the viewpoint of accuracy, the number of measurement points is not limited to two and may be increased.

<Method of performing uniform charging in the longitudinal direction>
Next, a method of performing uniform charging in the longitudinal direction will be described. In order to detect the partial discharge start voltage in the longitudinal direction, it is necessary to charge the photosensitive drum 3 uniformly in the longitudinal direction, that is, to a constant potential. Since the DC bias discharge start voltage changes depending on the potential of the charging roller 6, discharge unevenness cannot be detected from the DC bias discharge start voltage unless the potential is uniform in the longitudinal direction. Sufficient charging AC voltage must be applied for uniform charging in the longitudinal direction. In this embodiment, the maximum value of the charged AC bias in the current configuration is applied. Further, it may have a mechanism for confirming that the charging potential is uniform at that time.

The mechanism for confirming the uniform charging potential will be described below. First, a predetermined DC bias and the maximum AC bias are applied, and the DC bias discharge start voltage detection circuit 34 detects the DC bias discharge start voltage Vdcth1 (ave) in the entire longitudinal direction at that time. Next, the AC bias (PWM) is stepped down by one, and a predetermined DC bias and its AC bias are similarly applied, and the DC bias discharge start voltage detection circuit 34 at that time causes the DC bias discharge start voltage Vdcth2 in the entire longitudinal direction. (Ave) is detected. At this time, the DC bias discharge start voltage in the entire longitudinal direction can be written as Vdcth1 (ave) = (1 + C / Cd) Vpa + Vd1 (ave), Vdcth2 (ave) = (1 + C / Cd) Vpa + Vd2 (ave), respectively. Here, the capacitance of the photosensitive drum 3 is Cd, and the capacitance between the charging roller 6 and the photosensitive drum 3 is C.

Then, the relational expression of Vdcth1 (ave) -Vdcth2 (ave) = Vd1 (ave) -Vd2 (ave) is obtained. Here, Vd1 (ave) is the average potential in the longitudinal direction of the photosensitive drum 3 charged with the maximum AC bias, and Vd2 (ave) is the photosensitive drum 3 charged with the AC bias whose set value is one step down from the maximum. Is the average potential in the longitudinal direction of. Vpa is the Paschen voltage, which is a function of the atmospheric pressure and the distance between discharges.

FIG. 11 shows the relationship between the electric potential of the photosensitive drum 3 in the longitudinal direction and the AC bias. Vac1, Vac2, and Vac3 are values between the peaks of the AC bias applied to the charging roller 6, respectively, and Vac1 <Vac2 <Vac3. Charging by AC bias stabilizes at a constant charging potential by repeating forward discharge and reverse discharge, but if the AC bias is low, it causes longitudinal unevenness of the charging potential when there is longitudinal unevenness of the discharge (FIG. 11). (A)). However, if the AC bias is increased, the amount of discharge increases in the entire longitudinal direction, and the charging potential of the photosensitive drum 3 becomes uniform ((b) in FIG. 11). And the average potential rises accordingly. When the AC bias is further increased and the charging potential becomes uniform in the entire longitudinal direction, the average potential remains a constant value ((c) in FIG. 11).

From this, the uniformity of the charging potential of the photosensitive drum 3 can be confirmed by comparing Vdcth1 (ave) and Vdcth2 (ave). Specifically, if Vdcth1 = Vdcth2, then Vd1 = Vd2, and it can be determined that the longitudinal direction is uniform. On the contrary, if Vdcth1 ≠ Vdcth2, Vd1 ≠ Vd2, and it is determined that the battery is not sufficiently charged. In this case, it is not possible to provide a quality-stable image at any voltage, so it is necessary to take measures such as notifying the user of the life of the process cartridge.

In this embodiment, the maximum AC bias is applied to the charging bias, but the present limitation is not limited to this, and the bias that can be charged sufficiently uniformly may be clarified in advance by examination or the like and the value may be used.

<Detection of partial discharge information>
The detection of the partial discharge start voltage as the partial discharge information in the longitudinal direction will be described with reference to FIG. The horizontal direction of FIG. 12 represents the position in the longitudinal direction, and the vertical direction represents the potential.

First, as shown in FIG. 12A, the photosensitive drum 3 is uniformly charged (charging potential: Vd) by applying the maximum AC bias as described above. Next, as shown in FIG. 12B, a measurement region (hereinafter, partial measurement region) D (i) having a width smaller in the longitudinal direction than the printable region is set in a part of the printable region of the photosensitive drum 3. Only the partial measurement area D (i) is exposed by the laser scanner 4 to obtain the exposure potential (Vl). The partial measurement areas may be provided at a plurality of locations in the longitudinal direction. At this time, the partial measurement region D (i) exposed by the laser scanner 4 and the region excluding this partial measurement region have different potentials. Further, as shown in FIG. 12C, a DC bias (Vdc) is applied to the charging roller 6 using the DC bias discharge start voltage detection circuit 34, and the DC bias discharge start voltage is measured with a partial exposure potential. .. At this time, since only the partial measurement region D (i) starts to discharge, the DC bias partial discharge start voltage Vdcth (i) of the partial measurement region D (i) can be obtained. Consider an equivalent circuit where the capacitance of the photosensitive drum in the partial measurement area D (i) is Cd (i) and the capacitance between the charging roller 6 and the photosensitive drum 3 is C (i). Then, the magnitude of the DC bias partial discharge start voltage becomes Vdcth (i) = (1 + C (i) / Cd (i)) Vpa + | Vl |.

Further, when an image is actually formed, a DC + AC bias is applied, and the AC bias partial discharge start voltage Vacts (i) in the partial measurement region D (i) at that time is Vacts (i) = 2Vpa (1 + C (i)). / Cd (i)) can be written. Here, the AC bias partial discharge start voltage is not the voltage at which the partial measurement region D (i) starts discharging from the charging roller 6 to the photosensitive drum 3, but the back discharge also starts from the photosensitive drum 3 to the charging roller 6, and the DC bias. It is the voltage that begins to converge to. The AC bias partial discharge start voltage is a value between the peaks of the AC bias. Therefore, the relational expression of the equation (2) is satisfied.
Vacts (i) = 2 (Vdcth (i)-| Vl |) ... Equation (2)
Assuming that the DC bias discharge start voltage in the entire longitudinal direction is Vdcth (ave) and the AC bias discharge start voltage in the entire longitudinal direction is Vact (ave), the equation (3) can be obtained from this relational expression.
Vacts (i) -Vacts (ave) = 2 (Vdcth (i) -Vdcth (ave)) ... Equation (3)
The AC bias partial discharge start voltage in the partial measurement region D (i) can be detected by this equation (3). Actually, the correction is performed using this AC bias partial discharge start voltage difference Vacts (i) -Vacts (ave). Here, Vdcth (ave) is actually used to obtain the DC bias discharge start voltage in the entire longitudinal direction from the detection of the DC bias discharge start voltage. However, the present invention is not limited to this, and the average value of Vdcht (1), Vdcth (2) ... Vdcht (N) may be obtained and used.

Next, the partial measurement area for detecting the partial discharge start voltage will be described. FIG. 13A shows a partial measurement area of this embodiment. The lateral direction of FIG. 13 indicates the longitudinal direction (direction perpendicular to the rotation direction) of the photosensitive drum 3. In this embodiment, the longitudinal direction of the printable region in the surface of the photosensitive drum 3 is uniformly divided into 7 equal parts, and the partial discharge start voltage is detected in each region. However, the method of setting the partial measurement area is not limited to this, and it does not have to be divided into equal parts. Further, as shown in FIG. 13B, the partial measurement area may be determined according to the size of the paper. In this case, since the measurement can be performed in consideration of the scraping of the photosensitive drum 3, the accuracy is improved. Further, the paper usage history may be stored in the CPU 20 or the like, and the partial measurement area may be changed according to the paper usage history.

Further, when the region where the discharge start voltage becomes large is known in advance from the prediction of scraping of the photosensitive drum 3 and the prediction of dirt on the charging roller 6, it is effective to measure the partial discharge start voltage only in that region. In this case, it is necessary to obtain the entire DC bias discharge amount start voltage Vdcth (ave) from the discharge start voltage detecting means for the entire longitudinal direction.

<Correction method>
Next, a method of correcting the charge bias output value from the AC bias partial discharge start voltage will be described.
In FIG. 14A, the horizontal axis is the longitudinal direction and the vertical axis is the image forming process progress direction, and represents a partial measurement region of the photosensitive drum 3. In this embodiment, the partial discharge start voltage is detected in order from D (1) as shown in FIG. 14 (a). However, the method is not limited to this, and for example, the order of measurement may be changed, or there may be intervals in the detection of the partial measurement area as shown in FIG. FIG. 14B shows the difference between the AC bias partial discharge start voltage and the AC bias discharge start voltage of the entire length in each partial measurement region. The largest region of Vact (i) -Vact (ave) is the most difficult to discharge portion, and the smallest region is the most easily discharged portion. In the detection result shown in FIG. 14B, D (6) is the most difficult part to discharge, and D (1) is the most easily discharged part. Correction is performed from the AC bias partial discharge start voltage in the partial measurement region obtained above.

FIG. 16 shows the relationship between the discharge amount and the AC bias. In FIG. 16, the relationship between the discharge amount of the entire photosensitive drum 3 and the AC bias is shown by a solid line. The relationship between the discharge amount and the AC bias in the region of the photosensitive drum 3 that is most likely to be discharged (D (1) in the example of FIG. 14 (b)) is shown by a coarse broken line. Further, the relationship between the discharge amount and the AC bias in the region of the photosensitive drum 3 that is most difficult to discharge (D (6) in the example of FIG. 14B) is shown by a fine broken line. AC bias is the voltage value between peaks. As shown in FIG. 16, the discharge characteristic shifts the discharge start voltage difference in the portion that is most difficult to discharge. Therefore, even if the total discharge amount reaches the target discharge amount, the discharge amount does not reach the target discharge amount in the portion where the discharge is difficult (A in FIG. 16). In FIG. 16A, the AC bias at the intersection of the broken line and the solid line graph passing through the target value on the vertical axis and horizontal to the horizontal axis shows the AC bias when the total discharge amount of the photosensitive drum 3 becomes the target value. The intersection A of the broken line passing through the above-mentioned intersection and parallel to the vertical axis and the fine broken line is the region where the discharge is most difficult when an AC bias having a value such that the discharge amount of the entire photosensitive drum 3 becomes a target value is applied. Indicates the amount of discharge. As can be seen from FIG. 16A, the amount of discharge in this case is less than the target value. In such a case, sandy areas may be generated as described in the above problem.

Further, as shown in FIG. 16, even in the portion most easily discharged, the discharge characteristic shifts to the side where the discharge starting voltage difference is easy to flow. Therefore, the amount of discharge flows excessively in the portion that is easily discharged. If the amount of discharge is large, the amount of local scraping to the photosensitive drum 3 increases, which may cause local scratches on the photosensitive drum 3.

The change from the charge potential to the exposure potential due to exposure occurs due to the generation of carriers (holes if the charge is negative, electrons if the charge is positive) on the photosensitive drum 3 due to the exposure and the neutralization of the surface charge by the carriers. However, the exposure potential depends not only on the neutralized surface charge but also on the capacitance of the drum. The simple formula is as follows.
Vl = Vd + qd / ε …… Equation (4)
Here, q is the carrier charge per unit area, d is the film thickness of the photosensitive drum 3, and ε is the dielectric constant. Strictly speaking, q also depends on the film thickness, and the equation (4) becomes a little more complicated, but the relationship itself does not change significantly, and as the film thickness decreases, Vl approaches Vd. That is, in a scratched portion with a small film thickness, the exposure potential may not be sufficiently lowered even when exposed, and when solid black or the like is printed, the scratched portion is not printed and vertical white streaks may appear in the image. ..

The correction method of this embodiment is a correction method of reducing sandy areas while suppressing the amount of scraping of the photosensitive drum and suppressing the occurrence of vertical white streaks in the image.

As a specific method, V0- (Vact (ave) -Vact (min)) is set to the scrap amount allowable threshold (Vth) with respect to the AC bias (V0) at the time of the discharge amount (I0) that causes the allowable limit of scraping amount. ). Here, Vact (min) is the AC bias partial discharge start voltage in the region where discharge is most likely to occur. I0 is obtained in advance by examination or the like and stored in the CPU 20 or the like. In FIG. 16A, the AC bias at the intersection of the alternate long and short dash line passing through the discharge amount I0 and parallel to the horizontal axis and the solid line showing the relationship of the entire photosensitive drum 3 is V0. Then, as shown in FIG. 16A, the Vth defined as described above with respect to this V0 is a alternate long and short dash line showing the relationship between the regions most likely to be discharged, passing through I0 and parallel to the horizontal axis. It is the AC bias at the point where it intersects with. At this time, the intersection of the broken line passing through Vth and parallel to the vertical axis and the fine chain line showing the relationship between the regions most difficult to discharge is C. That is, when the AC bias is set so that the discharge amount (I0) causes the allowable limit of scraping amount in the region where the discharge is most likely to occur, the relationship between the regions where the discharge is most difficult is shown by C. As for the AC bias value at the intersection B of the broken line that passes through the target value of the discharge amount and is parallel to the horizontal axis and the coarse broken line that shows the relationship between the regions that are most likely to be discharged, the discharge amount in the region that is the most difficult to discharge is the target value. It is a value of AC bias such that. Then, if the AC bias at the intersection B is smaller than the AC bias at the intersection C as shown in FIG. 16A, the AC bias is corrected from the intersection A to the intersection B. That is, only Vact (max) -Vact (ave), which is the difference between the AC bias value at the intersection B and the AC bias value at the intersection A, is added to the AC bias that reaches the target discharge amount as a whole. Here, Vacts (max) is the AC bias partial discharge start voltage in the region where discharge is most likely to occur, and Vacts (max) -Vacts (ave) can be obtained from the above equation 3. As a result, the target amount of discharge flows even in the part that is most difficult to discharge. Further, since the AC bias at the intersection B is smaller than the AC bias at the intersection C, even if the AC bias is corrected from the intersection A to the intersection B, the amount of scraping that is the allowable limit is not exceeded even in the region where the discharge is most likely to occur. ..

If the AC bias at the intersection B is larger than the AC bias at the intersection C as shown in FIG. 16B, the AC bias is set to Vth and controlled so that the discharge amount does not increase any more. This is because when the AC bias is corrected from the intersection A to the intersection B as in FIG. 16A, the AC bias at the intersection B is larger than the AC bias at the intersection C, so that the limit is acceptable in the region where the discharge is most likely to occur. This is because the amount of discharge (I0) that causes the amount of scraping is exceeded. As a result, even the portion most easily discharged can be limited to the allowable limit of scraping amount.

By this correction method, it is possible to suppress the amount of scraping of the photosensitive drum, suppress the occurrence of vertical white streaks in the image, and suppress the sandy ground.

<Confirmation of effect>
In order to confirm the effect of this example, the image adverse effect of poor charging was confirmed in the above correction method and the comparative example which is the conventional discharge current control method. In the configuration of the comparative example, the conventional discharge current control is performed without correcting the charge bias output value with respect to the configuration of the present embodiment. Others are the same as in this embodiment, so the explanation is omitted. The measurement was performed by passing 30,000 sheets of Canon CS680 paper B5 size intermittently at a 4% printing rate, and printing one solid white image and one solid black image on Canon CS680 paper A3 size every 5,000 sheets. .. The paper was passed so that the paper passed through the central portion of the photosensitive drum 3. As for the harmful effects of poorly charged images, the presence or absence of sand on the solid white image and its level were confirmed. As for the harmful image of the scraping of the photosensitive drum, it was confirmed whether or not white streaks were generated on solid black and at that level.

＜フローチャート＞ The results are shown in Table 1. ○ in the sandy area of the table indicates that no sandy area has occurred. Δ indicates that sandy areas are generated, but 5 or less are generated per 1 cm2, and × indicates that more than 5 are generated per 1 cm2. The circles in the vertical white streaks in the table indicate that no vertical white streaks occur. Δ indicates the degree to which the streaks can be seen faintly, and × indicates the degree to which the streaks can be clearly seen. Looking at the results, it can be seen that in the comparative example, the sandy area was Δ at 25,000 sheets, whereas in this example, there was no occurrence. It can also be seen that no vertical white streaks have occurred. From this, it was found that in this example, sandy ground can be suppressed while suppressing the amount of scraping of the photosensitive drum 3.

<Flowchart>

Next, using the flowchart of FIG. 1, an image forming method including a detection flow of partial discharge information in the longitudinal direction in this embodiment will be described.

First, when a print command is received by the image forming apparatus 1 (A101), discharge current control is started (A102), and a charging bias for producing a target discharge amount is determined. After that, it is determined whether or not to detect the partial discharge information (A103). Since the unevenness in the longitudinal direction of the discharge is caused by a change with time such as unevenness in the longitudinal direction of the photosensitive drum 3 and unevenness in dirt on the charging roller 6, it is not always necessary to measure the partial discharge information. In the configuration of this embodiment, it is known that it takes about 1000 sheets from the generation to the actualization. Therefore, in this embodiment, the partial discharge information is measured once in 1000 sheets, and when it is determined that the partial discharge information is not detected, the most recently performed data stored in the CPU 20 is corrected as a correction value. (A111). However, the frequency is not limited to this, and the frequency may be adjusted according to the configuration of the image forming apparatus. When it is determined that the partial discharge information is detected, the measurement of the first measurement area is started (A104). First, a sufficient bias is applied so that the photosensitive drum 3 can be uniformly charged by the charging roller 6 (A105). Then, the measurement region is exposed (A106), and the DC bias discharge start voltage is detected by the DC bias discharge start voltage detection 34 (A107). When the measurement is completed, it is determined whether all the regions have been measured (A108). If it is determined that the entire measurement area has not been measured yet, the area returned to (A109) A105 with the area not yet measured as the measurement area, and the measurement is started. If it is determined that the entire measurement area has been measured, the charge bias of the discharge current control is corrected (A110) based on the measured value, and printing is started (A112).

By carrying out the above flow, the partial discharge start voltage as the partial discharge information can be detected and the charging bias can be corrected.

A non-volatile memory may be installed in the process cartridge, and information used for determining a target discharge current value, a usage status, a bias voltage such as a usage environment, and the like may be stored in the non-volatile memory. Since the process cartridge is removable from the image forming apparatus main body and information can be given to each process cartridge by the non-volatile memory, an appropriate bias can be set for each process cartridge.

The configuration of this embodiment is not limited to this. The speed, exposure amount, etc. are only examples for carrying out this embodiment. Further, in this embodiment, the discharge start voltage is detected as the discharge information and the partial discharge start voltage is measured as the partial discharge information, but the present invention is not limited to this, for example, the discharge current is detected as the discharge information and a partial discharge current is detected. (Hereinafter, partial discharge current) may be measured. In the case of detecting the discharge current, for example, the discharge unevenness in the longitudinal direction can be detected by detecting the partial discharge current under a constant charging voltage.

The first embodiment was a correction method for suppressing sandy ground while suppressing the amount of scraping of the photosensitive drum 3 to suppress the occurrence of vertical white streaks in the image. The present embodiment is characterized by being a correction method for suppressing the generation of sand even in a configuration having a longer life. The description of the part that overlaps with the first embodiment will be omitted.

FIG. 17 shows the relationship between the discharge amount and the AC bias. As shown in FIG. 17, the discharge characteristic shifts the discharge start voltage difference in the portion that is most difficult to discharge. Therefore, even if the total discharge amount reaches the target discharge amount, the discharge amount does not reach the target discharge amount in the portion where the discharge is difficult (A in FIG. 17). In such a case, sandy areas may be generated as described in the above-mentioned problems of the prior art. In such a case, the correction method of Example 1 is effective, but when the number of printed sheets increases due to the extension of the service life, it may be difficult to control the sandy area.

Therefore, in this embodiment, the AC bias was corrected from A to B in FIG. 17 in order to eliminate the threshold value and eliminate the sandy area. That is, the AC bias was always added by Vacts (max) -Vacts (ave).

By this correction method, since the target discharge amount flows to the portion where the discharge is most difficult in the longitudinal direction, sandy ground can be suppressed.

<Confirmation of effect>
In order to confirm the effect of this example, the same effect confirmation as in Example 1 was performed. The confirmation targets were the present example, the first example, and the comparative example used in the first example. Moreover, since the effect of this example is the suppression of sandy areas, only sandy areas were confirmed. Since the measurement is the same as in Example 1, the description is omitted.

The confirmation results are shown in Table 2. Looking at the results, it can be seen that there is no sandy area in this example. From this, it was found that the sandy area can be suppressed in this example.

The configuration of this embodiment is not limited to this. The speed, exposure amount, etc. are only examples for carrying out this embodiment. Further, in this embodiment, the discharge start voltage is detected as the discharge information and the partial discharge start voltage is measured as the partial discharge information. However, the present invention is not limited to this, for example, the discharge current is detected as the discharge information and the partial discharge current is measured. You may.

In Examples 1 and 2, the partial discharge information was detected by using the partial measurement area for detecting the partial discharge information as an exposed portion. In this embodiment, the partial measurement area for detecting partial discharge information is a non-exposed area that is not exposed by the laser scanner 4, and the non-measurement area excluding the partial measurement area is an exposed area that is exposed by the laser scanner 4. In this embodiment, the partial measurement region and the region excluding the partial measurement region have different potentials in this way. As a result, the detection accuracy of the partial discharge information is improved with respect to Examples 1 and 2, and the occurrence of sandy ground is suppressed even in a configuration having a longer life. The description of the parts that overlap with Examples 1 and 2 will be omitted. Further, in this embodiment, the partial discharge start voltage was measured as the partial discharge information.

In Example 1, when the DC bias partial discharge start voltage Vdcth (i) was obtained, the term of the exposure potential Vl was included, and it was considered that the exposure potential Vl did not change significantly in the longitudinal direction. However, for example, when the film thickness of the photosensitive drum 3 becomes thinner, the exposure potential may change significantly depending on the film thickness of the photosensitive drum 3 even if the charging potential is made uniform in the longitudinal direction. FIG. 20 shows the change in the potential of the exposed portion and the non-exposed portion of the photosensitive drum 3 depending on the film thickness with a solid line. When the film thickness of the photosensitive drum 3 becomes thinner, the film thickness dependence of the exposure potential becomes large, and the exposure potential difference due to the film thickness difference becomes large. This is becoming more prominent due to the increasing life of the image forming apparatus, which has been progressing in recent years.

In such a case, the exposure potential Vl is considered to be different in the measurement region (Vl = Vl (i)), and the equations (2) to (3) are not obtained, and the equation (5) is obtained.
Vact (i) -Vact (ave) = 2 (Vdcth (i) -Vdcth (ave)) + 2 (| Vl (ave) |-| Vl (i) |) ... Equation (5)

That is, an error corresponding to the second term on the right side of the equation (5) occurs. In such a state, if the correction is performed using the equation (3), the correction may be lowered by 2 (| Vl (ave) | − | Vl (i) |). For example, when discharge unevenness occurs due to a film thickness difference, even if an attempt is made to detect a region where the partial discharge start voltage is high, the region where the partial discharge start voltage is high is a region where the film thickness is thick. Vl (i) | That is, the correction is made lower by 2 (| Vl (ave) |-| Vl (i) |) (> 0), and a sufficient bias may not be applied and sandy areas may be generated.

Therefore, in this embodiment, the influence of the exposure potential is avoided by setting the partial measurement region as the non-exposed portion. Therefore, the partial discharge start voltage can be detected with high accuracy. Hereinafter, the detection of the partial discharge start voltage in the longitudinal direction in this embodiment will be described in detail with reference to FIG. The horizontal direction of FIG. 19 indicates the position in the longitudinal direction, and the vertical direction indicates the electric potential.

First, as shown in FIG. 19A, the photosensitive drum 3 is uniformly charged (charging potential: Vd). Next, as shown in FIG. 19B, the area other than the partial measurement area D (i) is exposed by the laser scanner 4 to obtain the exposure potential (Vl). Further, as shown in FIG. 19C, a DC bias discharge start voltage detection circuit 34 is used to apply a DC bias (Vdc) to the charging roller 6, and a DC bias discharge start is performed in a region where only the partial measurement region D (i) is discharged. Measure the voltage. As a result, the DC bias partial discharge start voltage Vdcth (i) in the partial measurement region D (i) is obtained. Assuming that the capacitance of the photosensitive drum 3 in the partial measurement region D (i) is Cd (i) and the capacitance between the charging roller 6 and the photosensitive drum 3 is C (i), the DC bias discharge start voltage is Vdcth ( i) = (1 + C (i) / Cd (i)) Vpa + Vd. Here, Vpa is the Paschen voltage, which is a function of the atmospheric pressure and the distance between discharges. As shown by the broken line in FIG. 20, since the charging potential is uniformly charged by the AC bias regardless of the film thickness, it does not greatly depend on the film thickness. Therefore, the equation (3) can be obtained in the same manner as in the first embodiment.
Vacts (i) -Vacts (ave) = 2 (Vdcth (i) -Vdcth (ave)) ... Equation (3)
That is, in this embodiment, the influence of the change in the exposure potential is avoided by setting the area to be measured as the non-exposed area. Therefore, the partial discharge start voltage can be detected with high accuracy.

<Confirmation of effect>
In order to confirm the effect of this example, the same effect confirmation as in Example 2 was performed. Four confirmation targets were used in this example, Example 1, Example 2, and Comparative Example used in Example 1. Since the measurement is the same as in Examples 1 and 2, the description thereof will be omitted. The confirmation results are shown in Table 3. Looking at the results, it can be seen that in this example, the occurrence of sandy ground can be further suppressed as compared with Examples 1 and 2.

It is considered that this is because in Examples 1 and 2, in the latter half of the number of sheets to be passed, sufficient bias correction could not be performed due to the measurement error due to the exposure voltage dependence due to the film thickness as described above. On the other hand, it can be seen that the correction is properly performed in this embodiment.

The configuration of this embodiment is not limited to this. The speed, exposure amount, photosensitive drum film thickness, etc. are only examples for performing this embodiment. Further, in this embodiment, the discharge start voltage is detected as the discharge information and the partial discharge start voltage is measured as the partial discharge information. However, the present invention is not limited to this, for example, the discharge current is detected as the discharge information and the partial discharge current is measured. You may.

In Examples 1 to 3, the DC bias discharge start voltage detection circuit 34 was used for the partial discharge start voltage detection as the partial discharge information detection. In this embodiment, a configuration will be described in which the same effect as that of the first embodiment can be obtained even if the discharge current control circuit 33 is used for detecting the partial discharge start voltage. That is, in this embodiment, the discharge current control circuit 33 constitutes the discharge information detecting means. The same reference numerals are used for the parts that overlap with those of the first embodiment, and the description thereof will be omitted. In this example, the partial discharge start voltage was measured as the partial discharge information.

The detection of the partial discharge start voltage in the longitudinal direction will be described with reference to FIG. In FIG. 21, the horizontal axis represents the position in the longitudinal direction, and the vertical axis represents the electric potential.

First, as shown in FIG. 21A, the photosensitive drum 3 is uniformly charged (charging potential: Vd). Next, as shown in FIG. 21B, only the partial measurement area D (i) is exposed by the laser scanner 4 to obtain the exposure potential (Vl). Then, as shown in FIG. 21C, a DC + AC bias is applied to the charging roller 6 using the discharge current control circuit 33. At this time, the bias is such that the peak on one side is fixed (Vt) and amplified to the other side as shown in FIG. 21 (c). Specifically, the DC bias is set to be Vt + Vac / 2 so as to be linked with the AC bias. Here, Vt is set to a bias in a region where discharge does not start. For example, it may be set to a value of Vd or its vicinity. FIG. 22 shows the time change of the applied AC charging bias. As shown in FIG. 22, the discharge start voltage is measured in a state where only the partial measurement region D (i) is discharged by gradually amplifying to one side. As a result, the partial measurement region D (i) starts discharging, and the discharge start voltage Voltage'(i) of the partial measurement region D (i) is obtained.

The magnitude of the discharge start voltage Voltage'(i) is
Vact'(i) = (1 + C (i) / Cd (i)) Vpa + | Vl |-| Vt |.

Further, the AC bias discharge start voltage Vacts (i) can be written as Vacts (i) = 2Vpa (1 + C (i) / Cd (i)) as in the first embodiment. Therefore, Vacts (i) = 2 (Vacts'(i)-| Vl | + | Vt |) ... Satisfies the relational expression of the equation (6).

Assuming that the average of the discharge start voltage Vacts'(i) is Vacts' (ave) and the average of the AC bias discharge start voltages is Vacts (ave), the equation (7) can be obtained from this relational expression.
Vacts (i) -Vacts (ave) = 2 (Vacts'(i) -Vacts' (ave)) ... Equation (7)

From this equation (7), the AC bias discharge start voltage in the measurement region D (i) can be detected. In this embodiment, the partially measured region is the exposed portion, but it may be the non-exposed portion as in the third embodiment.

When the same effect as in Example 1 was confirmed for this example, the same result as in Table 1 of Example 1 was obtained. From this, it was found from this example that the same effect as in Example 1 can be obtained even if the discharge current control circuit 33 is used for detecting the partial discharge start voltage.

The configuration of this embodiment is not limited to this. The speed, exposure amount, etc. are only examples for carrying out this embodiment. Further, in this embodiment, the discharge start voltage is detected as the discharge information and the partial discharge start voltage is measured as the partial discharge information. However, the present invention is not limited to this, for example, the discharge current is detected as the discharge information and the partial discharge current is measured. You may.

1: Image forming device, 3: Photosensitive drum, 4: Laser scanner, 6: Charging roller, 19: Engine controller, 20: CPU, 33: Discharge current control circuit, 34: DC bias discharge start voltage detection circuit

Claims (10)

A rotatable image carrier that carries a latent image and
An exposure means for exposing the image carrier and
A charging member that charges the image carrier and
Bias application means for applying a bias voltage to the charging member, and
A discharge amount detecting means for detecting the amount of current discharged between the charging member and the image carrier, and a discharge for determining a bias voltage applied to the charging member from the amount of discharge current detected by the discharge amount detecting means. Current control means and
It has a discharge information detecting means for detecting discharge information which is information about discharge between the charging member and the image carrier.
The discharge information detecting means sets a part of the in-plane printable area of the image carrier whose width in the direction perpendicular to the rotation direction is smaller than the width of the printable area as a partial measurement area. Then, when the image carrier is charged to a constant potential by the charging member and then different potentials are formed between the partial measurement region and the region other than the partial measurement region by the exposure means, the partial measurement region and the partial measurement region are formed. The partial discharge information regarding the discharge with the charging member is detected, and the discharge information is detected.
The discharge current control means is an image forming apparatus that corrects a bias voltage in image forming applied to the charging member based on the partial discharge information. The image forming apparatus according to claim 1, wherein the discharge information is a discharge start voltage. The image forming apparatus according to claim 1, wherein the discharge information is a discharge current. The partial measurement area and the partial measurement area are divided by forming the partial measurement area as an exposed portion exposed by the exposure means and the region excluding the partial measurement area as a non-exposure portion not exposed by the exposure means. The image forming apparatus according to any one of claims 1 to 3, wherein the partial discharge information is detected by setting the regions to be excluded to different potentials. The partial measurement area and the partial measurement area are divided by using the partial measurement area as a non-exposed area that is not exposed by the exposure means and the area excluding the partial measurement area as an exposed area that is exposed by the exposure means. The image forming apparatus according to any one of claims 1 to 3, wherein the partial discharge information is detected by setting the regions to be excluded to different potentials. The image forming apparatus according to any one of claims 1 to 5, wherein the discharge information detecting means detects discharge information when a DC bias voltage is applied to the charging member. The discharge information detecting means according to any one of claims 1 to 5, wherein the discharge information detecting means detects discharge information when an AC bias voltage is superimposed on a DC bias voltage on the charging member. Image forming device. The image forming apparatus according to claim 7, wherein the discharge current control means detects discharge information when an AC bias voltage is superimposed on a DC bias voltage on the charging member. The image forming apparatus according to any one of claims 1 to 8, wherein the partial measurement area is set according to the width of the recording material. A rotatable image carrier that carries a latent image and
An exposure means for exposing the image carrier and
A charging member that charges the image carrier and
Bias application means for applying a bias voltage to the charging member, and
Discharge amount detecting means for detecting the amount of current discharged between the charging member and the image carrier, and
Discharge current control means for determining the bias voltage applied to the charging member from the amount of discharge current obtained by the discharge amount detecting means, and
It is an image forming method in an image forming apparatus which has.
The image is provided by the charging member with respect to a partial measurement region in which the width in the direction perpendicular to the rotation direction is set to be smaller than the printable region in a part of the printable region in the plane of the image carrier. The process of charging the carrier to a constant potential and
A step of setting the partial measurement region and the region excluding the partial measurement region to different potentials by the exposure means, and
A step of detecting partial discharge information regarding a discharge between the partial measurement region and the charging member, and
An image forming method comprising a step of correcting a bias voltage in image forming applied to the charging member based on the partial discharge information.

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