JP2018045085A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately find a surface potential of a photosensitive drum and to reduce a time required for improving an image quality and a contrast adjustment.SOLUTION: An image forming device includes: a photosensitive drum 201; an exposure device 2071 having a laser beam source 207; a transfer roller 204; a high voltage power source 302; a current detection circuit 301; a control part 208 for finding a surface potential of the photosensitive drum 201 based on a discharge start voltage (S300); and the control part 208 for adjusting a light volume of the laser beam source 207 (S304 to S307) so that the value of the current flowing through the current detection circuit 301 becomes a target current value corresponding to a predetermined surface potential of the photosensitive drum 201. The control part 208 sets a target current value based on a potential difference between the surface potential of the photosensitive drum 201 obtained on the basis of the discharge start voltage and the predetermined surface potential (S301) and the value of the current detected by the current detention circuit 301 respectively when two or more different voltages are applied by the high voltage power source 302 (S302 and S303).SELECTED DRAWING: Figure 5

Description

  The present invention relates to an image forming apparatus including a light source device.

  The contrast of the image is determined by the potential difference between the surface potential (VL) of the photosensitive drum after being irradiated with the laser light and the developing voltage (Vdc). However, since the contrast of the image varies depending on the environment (temperature, humidity) and the film thickness of the photosensitive drum, correction is necessary. In the conventional control, correction is performed by estimating the surface potential of the photosensitive drum after irradiation with laser light using the photosensitive drum usage status and sensitivity information. However, the correction may not be sufficient. Therefore, as a system for detecting the surface potential of the actual photosensitive drum and correcting it with high accuracy, for example, there is a configuration in which the surface potential of the photosensitive drum is obtained based on the positive and negative discharge start voltages of the photosensitive drum ( For example, see Patent Document 1). A configuration for correcting the surface potential of the photosensitive drum obtained based on the discharge start voltage is also disclosed (see, for example, Patent Document 2). By using the surface potential of the photosensitive drum thus obtained, the contrast can be adjusted by adjusting the amount of laser light as necessary.

JP 2012-013881 A Japanese Patent Laying-Open No. 2015-094858

  However, in the conventional configuration, when the contrast is adjusted by changing the light amount, it is necessary to alternately detect the surface potential of the photosensitive drum and change the light amount. The reason for alternately detecting the surface potential of the photosensitive drum and changing the amount of light is that the surface potential of the photosensitive drum also changes when the amount of light is changed, so that the surface potential of the photosensitive drum after changing the amount of light is accurately known. This is because it is necessary to detect the surface potential of the photosensitive drum again. Therefore, it takes time to adjust the contrast. In addition, an error occurs when the amount of change in the amount of light is estimated and determined based on the detection result of the surface potential of the photosensitive drum.

  The present invention has been made under such circumstances, and an object thereof is to obtain the surface potential of a photosensitive drum with high accuracy and to reduce the time required for improving image quality and adjusting contrast.

  In order to solve the above-described problems, the present invention has the following configuration.

  (1) A photosensitive member, a light source, an exposure unit that forms a latent image on the photosensitive member by a light beam emitted from the light source, a member that acts on the photosensitive member, and a voltage is applied to the member. A first applying unit; a detecting unit configured to detect a current flowing through the photosensitive member and the member when a voltage is applied to the member by the first applying unit; and a current value detected by the detecting unit. A discharge start voltage for starting discharge between the photosensitive member and the member based on the discharge start voltage, a control unit for determining a surface potential of the photosensitive member based on the discharge start voltage, and a current flowing through the detection unit. Adjusting means for adjusting the light amount of the light source so that the value becomes a predetermined current value corresponding to a predetermined surface potential of the photoconductor, and the control means is obtained based on the discharge start voltage. The surface potential of the photoreceptor and the The predetermined current value is set based on a potential difference from a constant surface potential and a current value detected by the detecting means when two or more different voltages are applied by the first applying means. An image forming apparatus.

  According to the present invention, the surface potential of the photosensitive drum can be obtained with high accuracy, and the time required for improving the image quality and adjusting the contrast can be reduced.

Schematic of the image forming apparatus of Examples 1 and 2 Schematic configuration diagram of laser drive circuit of Examples 1 and 2, schematic configuration diagram of transfer voltage application circuit The figure which shows the surface potential-current characteristic of the photosensitive drum of Example 1, The figure which shows an applied voltage-current characteristic The figure which shows the setting method of the target electric current value of Example 1. 7 is a flowchart illustrating contrast adjustment control according to the first embodiment. Timing chart showing contrast adjustment control of embodiment 1 The figure which shows the electric current value change at the time of contrast adjustment of Example 2, The figure which shows the setting method of an electric current correction amount 10 is a flowchart illustrating contrast adjustment control according to the second embodiment. Timing chart showing contrast adjustment control of embodiment 2

  Embodiments of the present invention will be described below with reference to the drawings.

[Image forming apparatus]
A laser beam printer will be described as an example of the image forming apparatus. FIG. 1A shows a schematic configuration of a laser beam printer which is an example of an electrophotographic printer. The image forming apparatus 300 includes a photosensitive drum 201 as a photosensitive member on which an electrostatic latent image is formed, and a charging roller 202 (charging unit) that uniformly charges the photosensitive drum 201. The image forming apparatus 300 also includes an exposure device 2071 (exposure unit) that forms an electrostatic latent image on the photosensitive drum 201 (photoconductor), and a developing sleeve 203 (development) that develops the formed electrostatic latent image with toner. Means). The toner image developed on the photosensitive drum 201 is transferred to a sheet (not shown) as a transfer target supplied from the cassette 316 by a transfer roller 204 (transfer means), and the toner image transferred to the sheet is fixed to the fixing device. At 314, the image is fixed and discharged onto the tray 315. The photosensitive drum 201, the charging roller 202, the developing sleeve 203, and the transfer roller 204 are image forming units. The image forming apparatus 300 is not limited to the one illustrated in FIG. 1A, and may be an image forming apparatus including a plurality of image forming units, for example. The image forming apparatus further includes a primary transfer unit that transfers a toner image on the photosensitive drum 201 to an intermediate transfer belt as a transfer target, and a secondary transfer unit that transfers the toner image on the intermediate transfer belt to a sheet. Also good.

  FIG. 1B shows a main part of the image forming apparatus according to the first embodiment. The image forming apparatus includes a photosensitive drum 201, a charging roller 202, a developing sleeve 203, a transfer roller 204, a charging voltage application circuit 205, a transfer voltage application circuit 206, and a laser light source 207. The charging roller 202 and the transfer roller 204 are members that act on the photosensitive drum 201 that is a photosensitive member. So-called image forming processes such as charging of the photosensitive drum 201 using these and exposure by the laser light source 207 are controlled by a control unit 208 that controls the image forming apparatus. The control unit 208 includes a CPU, an ASIC, and the like, and controls the image forming apparatus 300 according to various programs stored in the ROM 2081. The RAM 2082 is used as a work area for the control unit 208.

[Laser light source]
FIG. 2A shows a schematic diagram of the laser light source 207. The laser driver 404 keeps the light amount of the laser light (light beam) of the LD 405 constant while monitoring the light amount of a laser diode (hereinafter referred to as LD) 405 as a light source with a photodiode (hereinafter referred to as PD) 406. Control is in progress. A signal line for transmitting the light amount variable signal 403 is connected between the control circuit unit 401 and the laser driver 404. The laser driver 404 is configured to change the light amount of the laser light source 207 according to the light amount variable signal 403. The light quantity variable signal 403 is a PWM signal. In the LD 405, the light amount increases as the ON width of the light amount variable signal 403 increases.

  In this configuration, by changing the ON width of the light amount variable signal 403, the light amount of the laser light irradiated from the laser light source 207 to the photosensitive drum 201 can be changed. Using high voltage control, the surface potential (VL) of the photosensitive drum after the laser beam irradiation is detected. Thereafter, when the value of the surface potential (VL) of the photosensitive drum is different from a predetermined value, the value of the surface potential (VL) of the photosensitive drum can be corrected by changing the amount of laser light. The control circuit unit 401 outputs a VDO signal 402 corresponding to the image data to the laser driver 404 when performing image formation.

FIG. 2B shows a schematic configuration of the transfer voltage application circuit 206 according to the first embodiment. A current detection circuit 301 serving as a detection unit is a circuit that detects a current I1 obtained by adding a current I2 flowing through a feedback circuit (hereinafter referred to as an FB circuit) 303 and a current I3 flowing through a load 304. The current I1 is expressed by the following formula (1).
I1 = I2 + I3 (1)

  A high voltage power supply 302 as a first application unit is a power supply that generates a transfer positive voltage and a transfer negative voltage. The FB circuit 303 is a circuit provided so that the output voltage becomes a predetermined voltage value. The load 304 is a total of loads from the output circuit (transfer voltage application circuit 206) through the transfer roller 204 to the ground of the photosensitive drum 201.

  The first embodiment includes a transfer voltage application circuit 206 that applies a transfer voltage, which is a DC voltage, to the transfer roller 204. The transfer voltage application circuit 206 is a constant voltage power source capable of generating a positive DC voltage and a negative DC voltage and capable of switching between a positive DC voltage and a negative DC voltage. When a DC voltage is applied from the high voltage power supply 302 to the transfer roller 204, the current detection circuit 301 serving as detection means detects the current value (I1) flowing through the photosensitive drum 201 via the transfer roller 204.

  The control unit 208 serving as a control unit performs the following operation in a period during which image formation is not performed (hereinafter, referred to as a non-image area), such as before image formation, between sheets, and after image formation. The control unit 208 applies different DC voltages to the transfer roller 204 from the high voltage power supply 302, and detects each current I1 when a different DC voltage is applied from the current detection circuit 301. The control unit 208 determines a voltage at which discharge is started between the photosensitive drum 201 and the transfer roller 204 (hereinafter referred to as a discharge start voltage) based on each current I 1 detected by the current detection circuit 301. A known method is used as a method for determining the discharge start voltage. That is, the control unit 208 detects the current value detected by the current detection circuit 301 by applying a positive voltage from the high voltage power supply 302 and the current detection circuit 301 when a negative voltage is applied by the high voltage power supply 302. The discharge start voltage is determined based on the current value. The control unit 208 calculates the surface potential of the photosensitive drum 201 based on the determined discharge start voltage, and corrects an error generated in the calculation result. A known method is used as a method for correcting an error occurring in the calculation result of the surface potential of the photosensitive drum 201 based on the discharge start voltage. The control unit 208 sets a target value of the value of the current I1 detected by the current detection circuit 301 by contrast adjustment according to the surface potential of the photosensitive drum 201 whose error has been corrected. The control unit 208 changes the amount of laser light via the control circuit unit 401 so that the value of the current I1 flowing through the current detection circuit 301 becomes a set target value. Note that the contrast of the image is determined by the surface potential (VL) of the photosensitive drum 201 after the laser light irradiation and the developing voltage (not shown) applied to the developing sleeve 203 by the developing voltage power source (not shown) as the second applying means. Vdc) and the potential difference.

[Setting method of target value of current in contrast adjustment]
Next, a method for setting the target value of the current value in contrast adjustment will be described. In the first embodiment, the DC voltage applied to the transfer roller 204 will be described by taking positive polarity as an example, but it may be negative. A transfer voltage application circuit 206 applies a positive voltage (hereinafter referred to as a positive voltage), for example, 500 [V] to the transfer roller 204. When the surface potential of the photosensitive drum 201 is changed in this state, the current I1 detected by the current detection circuit 301 exhibits a linear characteristic as shown in FIG. FIG. 3A shows the surface potential (−V) of the photosensitive drum 201 on the horizontal axis and the value (detected current value) of the current I1 (μA) detected by the current detection circuit 301 on the vertical axis. For example, when the surface potential of the photosensitive drum 201 is −100 V in a state where a positive transfer voltage of 500 V is applied to the transfer roller 204, the value of the current I1 detected by the current detection circuit 301 is 4 μA.

  On the other hand, when the voltage applied to the transfer roller 204 is changed by the transfer voltage application circuit 206 in a state where the surface potential of the photosensitive drum 201 is −100 [V], the value of the current I1 detected by the current detection circuit 301 is A linear characteristic as shown in FIG. FIG. 3B shows the applied voltage (transfer voltage) (V) applied by the transfer voltage application circuit 206 on the horizontal axis and the value of the current I1 (μA) detected by the current detection circuit 301 on the vertical axis (detection current). Value). For example, when a transfer voltage of 500 V is applied to the transfer roller 204 with the surface potential of the photosensitive drum 201 being −100 V, the current I1 detected by the current detection circuit 301 is 4 μA.

  3A and 3B, if the value of the current I1 detected by the current detection circuit 301 is equal, the potential difference between the photosensitive drum 201 and the transfer roller 204 is equal. For example, when the value of the current I1 detected by the current detection circuit 301 is 4 μA, the potential difference between the photosensitive drum 201 and the transfer roller 204 is 600V. This indicates that if the potential difference between the photosensitive drum 201 and the transfer roller 204 is equal, the value of the current I1 detected by the current detection circuit 301 becomes equal.

  FIG. 4 shows the surface potential (V) of the photosensitive drum 201 on the horizontal axis, and the value of the current I1 (detected current value) (μA) detected by the current detection circuit 301 on the vertical axis. The control unit 208 calculates the potential difference between the characteristic expression (linear characteristic) indicating the relationship shown in FIG. 3A or 3B, the detection result of the surface potential of the photosensitive drum 201 corrected for the error, and a predetermined surface potential. Ask. If the characteristic equation and the potential difference are known, the control unit 208 determines the value of the current I1 detected by the current detection circuit 301 when the detection current value becomes a predetermined surface potential as the surface potential when the detection current value becomes equal to the target current value. Can be calculated.

For example, it is determined that the relationship between the surface potential of the photosensitive drum and the value of the current I1 detected by the current detection circuit 301 is a characteristic (hereinafter referred to as a characteristic equation) as indicated by a straight line as shown in FIG. The Here, it is assumed that the detection result of the surface potential of the photosensitive drum 201 whose error has been corrected is −100 V, and the predetermined surface potential when the image contrast is to be set to a predetermined contrast is −150 V. The potential difference between the surface potential of the photosensitive drum 201 corrected for the detection result error and a predetermined surface potential is 50 V (= −100 − (− 150)). If the predetermined surface potential of the photosensitive drum 201 is a potential corresponding to a target value of the current value (hereinafter referred to as a target current value (predetermined current value)), the control unit 208 can calculate from the characteristic formula and the potential difference (50 V). A target current value can be calculated. The characteristic equation is the value of the current I1 detected by the current detection circuit 301 when two or more predetermined transfer voltages are applied to the transfer roller 204 during the detection of the surface potential of the photosensitive drum 201 or before the contrast adjustment. Is required. In FIG. 4, when the surface potential of the photosensitive drum is 0 [V], the detected current value is α [μA], the slope of the characteristic equation is β, and the surface potential is X [V]. 2).
I1 = βX + α (2)

  The control unit 208 monitors the value of the current I1 detected by the current detection circuit 301 based on the characteristic formula and the potential difference, and monitors the ON width of the light quantity variable signal 403 so that the value of the current I1 becomes the target current value. The amount of laser light is changed by changing. Thereby, a predetermined surface potential of the photosensitive drum 201 can be obtained. Further, since the amount of laser light is changed so as to be the target current value, the time required for contrast adjustment can be reduced.

[Target current setting]
FIG. 5 is a flowchart illustrating processing for detecting the surface potential of the photosensitive drum 201 and adjusting the contrast according to the first exemplary embodiment. FIG. 6 is a diagram showing a timing chart of the processing from step (hereinafter referred to as S) 304 to S305 in FIG. In S300, the control unit 208 detects the surface potential of the photosensitive drum 201 based on the discharge start voltage by a known method. An error in the detected surface potential of the photosensitive drum 201 is corrected by a known method. In S301, the control unit 208 obtains a potential difference between the predetermined surface potential (VL) of the photosensitive drum 201 corresponding to the contrast to be obtained and the surface potential of the photosensitive drum 201 detected in S300. A predetermined surface potential (VL) of the photosensitive drum 201 corresponding to the contrast to be obtained is a target surface potential, and a current value corresponding to the target surface potential is a target current value.

  In step S <b> 302, the control unit 208 derives a characteristic equation indicating the relationship between the surface potential of the photosensitive drum 201 and the detected current value as illustrated in FIG. 4. The control unit 208 obtains a detected current value of 2 or more during detection of the surface potential of the photosensitive drum 201 in S300 or in S302. For example, the control unit 208 detects the detected current value with the current detection circuit 301 when a predetermined transfer voltage is applied, and detects the detected current value with the current detection circuit 301 when a transfer voltage different from the predetermined transfer voltage is applied. Is detected. The control unit 208 derives a characteristic equation based on these two values. Note that a value (for example, −100 V, 4 μA) obtained when the surface potential of the photosensitive drum 201 is detected in S301 for one of the two points may be used. In step S303, the control unit 208 calculates a target current value from the characteristic equation derived in step S302 (for example, the straight line graph in FIG. 4) and the potential difference obtained in step S301 (for example, 50 V).

  When the target current value is calculated, the control unit 208 performs contrast adjustment after S304. The control unit 208 also functions as an adjustment unit that adjusts the amount of light in contrast adjustment. In step S304, the control unit 208 compares the target current value calculated in step S303 with the value of the current I1 detected by the current detection circuit 301 (hereinafter referred to as a detected current value), and determines whether the current value is within the tolerance. To do. The tolerance is, for example, 0.01 μA. If the control unit 208 determines in step S304 that the target current value is within the tolerance as a result of comparing the target current value and the detected current value, the contrast adjustment control ends. If the control unit 208 determines in S304 that it is not within the tolerance, the process proceeds to S305. In S305, the control unit 208 determines whether or not the detected current value is larger than the target current value, and if it is determined that the detected current value is larger than the target current value, the light amount value (PWM value) of the laser beam is stepped in S306. Up and the process returns to S304. Step-up is to increase the amount of laser light. When the amount of laser light is increased, the detected current value decreases. When a negative transfer voltage is applied, the detection current value increases when the amount of laser light is increased.

  If the control unit 208 determines in S305 that the detected current value is equal to or smaller than the detected current value, the control unit 208 steps down the light amount value (PWM value) of the laser beam in S307, and returns the process to S304. Step down is to reduce the amount of laser light. When the amount of laser light is reduced, the detection current value increases. Note that when a negative transfer voltage is applied, the detection current value decreases as the amount of laser light is reduced. The amount (step width) by which the amount of light is changed in S306 and S307 is determined according to the characteristics of the photosensitive drum 201.

  When the detected current value falls within the tolerance, the surface potential of the photosensitive drum 201 falls within the tolerance of the surface potential corresponding to the desired contrast. The control unit 208 stores the laser light amount at this time, that is, the ON width of the light amount variable signal 403 in the RAM 2082. The control unit 208 can obtain a predetermined contrast by performing image formation using the ON width of the light quantity variable signal 403 stored in the RAM 2082.

  FIG. 6A is a graph in which the horizontal axis represents time and the vertical axis represents the detected current value (μA). In FIG. 6A, the target current value calculated in S303 is indicated by a two-dot chain line. FIG. 6B is a graph showing time on the horizontal axis and the amount of laser light on the vertical axis. In [1] and [2], since the detected current value is equal to or less than the target current value, the amount of laser light is stepped down. In [3], since the detected current value is larger than the target current value, the amount of laser light is stepped up. In [4], the detected current value is within the tolerance of the target current value.

  By performing such control, a constant surface potential of the photosensitive drum 201 that is not influenced by the environment, the film thickness of the photosensitive drum 201, and the surface state of the transfer roller 204 can be obtained, and high quality image quality can be formed. Become. Further, since the amount of laser light is changed according to the value of the current I1 detected by the current detection circuit 301, the time required for contrast adjustment can be reduced. In Example 1, a transfer voltage is used. However, the same effect can be obtained by using a charging voltage instead of the transfer voltage and detecting a current value flowing when the charging voltage is applied. In this case, the charging voltage application circuit 205 has a current detection circuit, and the surface potential of the photosensitive drum 201 is adjusted by changing the amount of laser light according to the result of detecting the current flowing through the charging roller 202 and the photosensitive drum 201. To do. As described above, according to the first embodiment, the surface potential of the photosensitive drum can be obtained with high accuracy, and the time required for improving the image quality and adjusting the contrast can be reduced.

  The second exemplary embodiment includes a transfer voltage application circuit 206 that applies a transfer voltage, which is a DC voltage, to the transfer roller 204. The transfer voltage application circuit 206 is a constant voltage power source capable of generating a positive or negative DC voltage. The current detection circuit 301 detects the value of the current I1 that flows to the photosensitive drum 201 via the transfer roller 204 when the transfer voltage application circuit 206 applies a DC voltage to the transfer roller 204. The current detection circuit 301 applies a different DC voltage to the transfer roller 204 in the non-image area. The control unit 208 determines a discharge start voltage between the photosensitive drum 201 and the transfer roller 204 based on each current value detected by the current detection circuit 301. The control unit 208 calculates the surface potential of the photosensitive drum 201 using the determined discharge start voltage, and corrects an error occurring in the calculation result. The control unit 208 sets a target current value detected by the current detection circuit 301 by contrast adjustment according to the surface potential of the photosensitive drum 201 whose error has been corrected, and the detected current value flowing through the current detection circuit 301 becomes the target current value. The amount of laser light is adjusted so that In the second embodiment, errors that occur during contrast adjustment are corrected.

[Error in contrast adjustment]
An error that occurs during contrast adjustment will be described. The contrast adjustment is controlled so as to obtain a predetermined surface potential by monitoring the detection current value detected by the current detection circuit 301 and adjusting the amount of laser light so that the detection current value becomes the target current value. However, the environment (for example, temperature and humidity) in the vicinity between the photosensitive drum 201 and the transfer roller 204 and the load characteristics of the photosensitive drum 201 and the transfer roller 204 themselves may change while the amount of laser light is being changed. There is. These changes may change the detection current value of the current detection circuit 301. Therefore, even if the potential difference between the photosensitive drum 201 and the transfer roller 204 is the same, there is a case where an error occurs in the light amount value of the laser light determined by the contrast adjustment because it differs from the characteristics when the target current value is calculated.

  FIG. 7A shows the amount of laser light on the horizontal axis and the detection current value (μA) of the current detection circuit 301 on the vertical axis. At the time when the target current value is obtained, the light quantity and current characteristics are shown by broken lines, and the light quantity value required for the target current value is a predetermined light quantity value. However, the characteristics of light quantity and current change to a graph indicated by a solid line due to a change in environment. At this time, if the light quantity value is adjusted so as to be the target current value in the solid line graph, the obtained light quantity value is deviated from the predetermined light quantity value as indicated by an asterisk.

[Error correction during contrast adjustment]
Next, a method for correcting errors that occur during contrast adjustment will be described. The control unit 208 calculates the current value increased or decreased with respect to the time required to change the light amount of the laser light once, and corrects the error by reflecting the calculated current value on the target current value. Note that the amount of change (predetermined amount) in the amount of laser light per time is determined according to the characteristics of the photosensitive drum 201. Further, the predetermined time required for changing the light amount by a predetermined amount (change amount per time) is obtained in advance through experiments or the like.

  Specifically, the control unit 208 measures the value of the current I1 by the current detection circuit 301 in a state where the potential difference between the photosensitive drum 201 and the transfer roller 204 is constant. The control unit 208 measures the value of the current I1 again with the current detection circuit 301 after the time required for changing the amount of laser light once has elapsed. The control unit 208 obtains the difference between the current values before and after the time necessary for changing the amount of laser light once, and uses the obtained difference as the correction amount of the target current value. When determining the correction amount of the target current value, the light quantity is not changed, and the apparatus waits for the predetermined time described above.

  After obtaining the correction amount of the target current value, the control unit 208 corrects the target current value by the number of times the amount of laser light has been changed by a predetermined amount for contrast adjustment, and thus occurs during contrast adjustment. The error can be corrected. The corrected target current value is expressed by the following equation (3).

Target current value after correction = target current value− (correction amount × (number of times of change + 1)) (3)
FIG. 7B shows time (s) on the horizontal axis and the detected current value (μA) of the current detection circuit 301 on the vertical axis. A black circle indicates a point where a current value is detected by the current detection circuit 301. The time between the two points is the time required to change the amount of light once. For example, when the current increases within the time required for one light amount change (current increase amount), the environment or the like has changed since the target current value was obtained. In the second embodiment, it is possible to perform contrast adjustment with higher accuracy by correcting an error that occurs during contrast adjustment. The schematic configuration of the image forming apparatus of the second embodiment and the schematic configuration of the transfer voltage applying circuit 206 are the same as those of the first embodiment. The same components are denoted by the same reference numerals, and description thereof is omitted.

[Error correction processing during contrast adjustment]
FIG. 8 is a flowchart for explaining processing for correcting an error during contrast adjustment according to the second embodiment. FIG. 9 shows a timing chart of S404 to S408 in FIG. The control of the second embodiment will be described using the flowchart of FIG. The same steps as those described in the flowchart of FIG. In the second embodiment, the control unit 208 advances the process to S404 after the process of S306 or S307.

  When the control unit 208 calculates the target current value in S303, the control unit 208 proceeds to a sequence for correcting an error that occurs during contrast adjustment. In step S <b> 401, the control unit 208 measures the value of the current I <b> 1 using the current detection circuit 301 while maintaining a constant potential difference between the photosensitive drum 201 and the transfer roller 204. The control unit 208 resets and starts a timer (not shown). In step S <b> 402, the control unit 208 refers to the timer without changing the laser light amount, and determines whether or not the time required to change the laser light amount once (predetermined time) has elapsed. To do. If it is determined in S402 that the predetermined time has not elapsed, the control unit 208 returns the process to S402, and if it is determined that the predetermined time has elapsed, the control unit 208 proceeds to S403. The control unit 208 monitors changes in the environment or the like within a predetermined time in the process of S402. In step S403, the control unit 208 measures the value of the current I1 again using the current detection circuit 301. The control unit 208 obtains a difference between the detected current value measured in S401 and the detected current value measured again in S403, and uses the difference as a correction amount. In addition, the control unit 208 initializes (0) a variable for counting the number of times the amount of light has been changed. The control unit 208 obtains a corrected target current value from Expression (3). That is, the control unit 208 obtains a corrected target current value based on the target current value obtained in S303, the correction amount obtained in S403, and the number of times the amount of light has been changed.

  The control unit 208 performs contrast adjustment after S304. In step S304 to step S307, the control unit 208 compares the target current value before correction with the detected current value, adjusts the amount of laser light (S306, S307), and advances the process to step S404. When the control unit 208 determines that the detected current value is within the tolerance of the target current value before correction (YES in S304), the contrast adjustment control ends.

  In S404, the control unit 208 compares the corrected target current value obtained in S403 with the detected current value, and determines whether or not the detected current value is within the tolerance of the corrected target current value. If the control unit 208 determines in S404 that the detected current value is within the tolerance of the corrected target current value, the contrast adjustment control ends. If the control unit 208 determines in S404 that the detected current value is not within the tolerance of the corrected target current value, the process proceeds to S405. In step S405, the control unit 208 determines whether the detected current value is greater than the corrected target current value. If the control unit 208 determines in S405 that the detected current value is larger than the corrected target current value, the control unit 208 increases the light amount value (PWM value) of the laser beam in S406, and advances the process to S408. If the control unit 208 determines in S405 that the detected current value is less than or equal to the corrected target current value, the control unit 208 steps down the light amount value (PWM value) of the laser beam in S407 and advances the process to S408. Note that the case where a negative transfer voltage is applied is the same as in the first embodiment. In S408, the control unit 208 adds 1 to the variable for counting the number of times the amount of light has been changed, recalculates the corrected target current value from Expression (3), and returns the process to S404.

  FIG. 9A is a graph in which the horizontal axis represents time and the vertical axis represents the detected current value (μA). FIG. 9 (a9 shows the corrected target current value calculated in S403 or S408 by a two-dot chain line. FIG. 9B is a graph showing time on the horizontal axis and the amount of laser light on the vertical axis. In [1] and [2], since the detected current value is equal to or smaller than the corrected target current value, the light amount of the laser beam is stepped down and the corrected target current value is recalculated. In [3], since the detected current value is larger than the target current value, the light amount of the laser beam is stepped up and the corrected target current value is recalculated. Is within the tolerance of the corrected target current value.

  By performing such a sequence, errors that occur during contrast adjustment are corrected, and a constant surface potential of the photosensitive drum 201 that is not affected by the environment, the film thickness of the photosensitive drum 201, the surface state of the transfer roller 204, or the like is obtained. High quality image quality can be realized. Although the transfer voltage is used in the second embodiment, the same effect can be obtained by detecting the value of the current that flows when the charging voltage is applied using the charging voltage instead of the transfer voltage, as in the first embodiment. Can be obtained. As described above, according to the second embodiment, the surface potential of the photosensitive drum can be obtained with high accuracy, and the time required for improving the image quality and adjusting the contrast can be reduced.

201 Photosensitive drum 204 Transfer roller 207 Laser light source 208 Control unit 301 Current detection circuit 302 High voltage power supply

Claims (8)

A photoreceptor,
An exposure unit that has a light source and forms a latent image on the photosensitive member by a light beam emitted from the light source;
A member acting on the photosensitive member;
First application means for applying a voltage to the member;
Detecting means for detecting a current flowing through the photosensitive member and the member when a voltage is applied to the member by the first applying unit;
Control means for obtaining a discharge start voltage at which discharge is started between the photoconductor and the member based on the current value detected by the detection means, and for obtaining a surface potential of the photoconductor based on the discharge start voltage. When,
Adjusting means for adjusting the light amount of the light source so that the value of the current flowing through the detection means becomes a predetermined current value corresponding to a predetermined surface potential of the photoconductor;
With
The control means detects the potential difference between the surface potential of the photoreceptor and the predetermined surface potential obtained based on the discharge start voltage, and the detection means when two or more different voltages are applied by the first application means. The predetermined current value is set based on the current value detected by each of the image forming apparatuses.   The adjusting means increases the light amount of the light source when the current value detected by the detecting means is larger than the predetermined current value, and the current value detected by the detecting means is the predetermined current value. The image forming apparatus according to claim 1, wherein the light amount of the light source is decreased in the following cases.   The image forming apparatus according to claim 1, wherein the control unit corrects the predetermined current value when the light amount of the light source is adjusted by the adjustment unit.   The control means includes a current value detected by the detection means before the time required for changing the light amount of the light source by a predetermined amount, and a current value detected by the detection means after the time has elapsed. The image forming apparatus according to claim 3, wherein the predetermined current value is corrected based on a difference between the predetermined current value and the predetermined current value.   The control means applies a negative voltage to the member by the first application means and a current value detected by the detection means when a positive voltage is applied to the member by the first application means. 5. The image forming apparatus according to claim 1, wherein the surface potential of the photoconductor is obtained based on a value of the current detected by the detecting unit. Developing means for developing a latent image formed on the photoreceptor with toner to form a toner image;
Second application means for applying a voltage to the developing means;
With
The predetermined surface potential of the photoconductor is a photoconductor when a contrast, which is a potential difference between the surface potential of the photoconductor and a voltage applied to the developing unit by the second applying unit, becomes a predetermined contrast. The image forming apparatus according to claim 1, wherein the surface potential of the image forming apparatus is any one of the following. A transfer means for transferring the toner image formed on the photoreceptor to a transfer target;
The image forming apparatus according to claim 1, wherein the member is the transfer unit. Charging means for charging the surface of the photoreceptor before forming a latent image by the exposure means;
The image forming apparatus according to claim 1, wherein the member is the charging unit.

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