JPH08160724A - Developing bias controller - Google Patents

Abstract

PURPOSE: To prevent the sticking of carrier when trouble is caused in a reversal developing system image forming device. CONSTITUTION: When the trouble is caused, developing bias voltage becomes off (becomes 0V) in a state where potential remains on the surface of a photoreceptor, and the sticking of carrier occurs on the photoreceptor. In the case the trouble is eliminated and power is started to be supplied so that the time when the sticking of carrier on occurs may be made as short as possible, the developing bias voltage is quickly impressed before starting processing for forming an image. The value of the developing bias voltage is properly set in accordance with the standby time from causing the trouble till eliminating it, the ambient temperature of the photoreceptor and the operating time of the photoreceptor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a charging polarity of a photoconductor,
The developing bias polarity and the toner charging polarity are all set to the same polarity, and the charging voltage of the photoconductor is set higher than the development bias voltage, and in the area where the surface voltage of the photoconductor becomes lower than the development bias voltage due to light attenuation. On the other hand, the present invention relates to an apparatus for controlling a developing bias voltage in an image forming apparatus of a reversal developing system in which the toner is attached.

[0002]

2. Description of the Related Art In recent years, contrary to a normal image forming system, an image forming apparatus of a reversal developing system, in which toner is adhered to a region of a photosensitive member exposed to light, has appeared. In the image forming apparatus of the reversal development type, for example, the charging voltage of the photoconductor is −600 V, the developing bias voltage of the developing roller of the developing device is −.
Both voltages are set to relatively close values such as 450 V, and the polarity of the toner held on the developing roller is set to the negative side, which is the same polarity as the charging voltage of the photoconductor and the developing bias voltage of the developing roller. When the surface of the photoconductor is exposed to light and the surface potential is lowered (-100 to -200 V
, The toner on the negative side is more positive than the voltage on the positive side (-10
It is used to adhere to an exposed area having 0 to -200 V).

[0003]

In a normal image forming process, the toner image is formed on the photosensitive member, the toner is transferred to the paper, and the surface of the photosensitive member is discharged to complete the image forming process. Therefore, even in the case of the reversal development type image forming apparatus, a slight decrease in the surface potential of the photoconductor is observed at the initial stage of the start of the next image formation due to the release of the trap carriers in the photoconductor during the pause, but the effect is at most. This is the extent to which some image fog occurs, and does not greatly affect the image quality.

However, if the image forming process is interrupted before the charge removal of the photosensitive member is completed due to a trouble during the image forming process, the surface potential of the photosensitive member is left as it is. Will cause problems such as. This problem will be described with reference to FIG.

FIG. 15 shows the surface potential of a dark portion (a region not exposed to light) of the photoconductor and the developing bias voltage applied to the developing roller. At the start of the image forming process, the photoconductor charging voltage and the developing bias voltage are gradually increased while being controlled so that the voltage difference between them does not open too much, and finally the target voltage (for example, charging voltage). -6
00V, developing bias voltage −450V).
As a result, the dark portion potential of the photoconductor and the developing bias voltage gradually increase as shown in the figure. The image forming process is executed with the potential of the photoconductor dark area and the developing bias voltage being set to the target voltages, but if a trouble such as a jam occurs during the image forming process, power is supplied to the entire image forming apparatus. Stops compulsorily. At this time, the dark area voltage on the surface of the photoconductor is charged to about -600 V, and in that state, the supply of the developing bias voltage is also cut off. As a result, the potential difference between the dark portion on the surface of the photoconductor and the developing device becomes as large as about 600 V, and as a result, the + charge carrier contained in the developing device (the iron powder itself is + charged to negatively charge the toner). And the like) adhere to the photoconductor side. So-called career advancement.

The phenomenon of the carrier rising disappears when the image forming process is started after the trouble such as the jam is solved and the power supply to the image forming apparatus main body is restarted.
This is because the surface of the photoconductor is first discharged at the start of the image forming process, and the charging voltage and the developing bias voltage are gradually increased as shown in FIG. 15. Conversely, the image forming process is started. Until then, career advancement will continue to occur.

The carrier attached to the photoconductor due to such carrier rising is collected and discarded by the cleaner arranged facing the photoconductor. However, unlike the toner, the carrier in the two-component developer is not always replenished, and the carrier that has been attached to the photoreceptor and discarded due to the carrier rising remains unreplenished. Therefore, when the carrier rises, the toner charge amount becomes insufficient in the subsequent image forming process.

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing bias control device for preventing a carrier from rising when a trouble occurs in an image forming apparatus of a reversal developing system.

[0009]

According to a first aspect of the present invention, there is provided a developing bias control device, wherein when a trouble occurs in which the power source is cut off in the state where the charge on the surface of the photoconductor remains, when the power supply is started after the trouble occurs. Until the waiting time, the voltage setting means for predicting the photoconductor surface potential after the waiting time based on the waiting time and obtaining the developing bias voltage corresponding thereto, and the trouble occurrence. And a applying unit for applying the developing bias voltage obtained before the start of the subsequent first image forming process.

According to a second aspect of the present invention, in the developing bias control apparatus according to the first aspect, the voltage setting means includes means for correcting the developing bias voltage according to the ambient temperature of the photoconductor. Is characterized by.

According to a third aspect of the present invention, in the developing bias control apparatus according to the first or second aspect, the voltage setting means includes means for correcting the developing bias voltage in accordance with the usage time of the photoconductor. It is characterized by having.

[0012]

According to the first aspect of the present invention, when a trouble such as a jam occurs and the power is cut off, the time when the power is cut off is measured as a waiting time, and an appropriate development is performed based on the waiting time. Bias voltage is required. When the power is cut off while the charges on the surface of the photoconductor remain, the developing bias voltage becomes 0 V, so that the potential difference between the residual potential on the surface of the photoconductor and the developing bias potential becomes large and carrier rise occurs. On the other hand, when the trouble is resolved and the power supply is restarted, the required developing bias voltage is applied even before the start of the image forming process, so that the carrier rise does not occur. Normally, at the start of power supply after the trouble is resolved, the image forming process is started after the temperature setting of the fixing device is in a state where the image can be formed.
The development bias voltage is applied and the carrier rise does not occur. Conventionally, the carrier rise does not occur from this point, but according to the present invention, the development bias voltage is applied before the start of the image forming process. It will be started, and you will be able to prevent career advancement as quickly as possible.

According to the second aspect of the present invention, the developing bias voltage is obtained based on the waiting time after the power is cut off and the ambient temperature of the photoconductor. The amount of attenuation of the surface potential of the photoconductor is affected not only by the waiting time but also by the temperature of the photoconductor.When the temperature of the photoconductor is low, the decay of the surface potential becomes slower, and when the temperature of the photoconductor is high, the decay of the surface potential is decreased. Therefore, the surface potential of the photoconductor after the waiting time varies depending on the photoconductor temperature. Since the photoconductor temperature substantially matches the ambient temperature of the photoconductor, the ambient temperature of the photoconductor can be regarded as the temperature of the photoconductor. In the present invention, the developing bias voltage at the start of power supply is set in consideration of the ambient temperature of the photoconductor, so that a more appropriate value can be set.

In the invention described in claim 3, the developing bias voltage is obtained based on the waiting time after the power is cut off, the ambient temperature of the photoconductor, and the usage time of the photoconductor. Usually, the photosensitive member undergoes film thickness reduction as it is used, and the film thickness of the photosensitive layer becomes thinner. As the film thickness of the photoconductor becomes thinner, the charge holding capability of the photoconductor decreases, so that the surface potential of the photoconductor decays in a shorter time when the photoconductor holding the residual potential is left unattended. In the present invention, since the developing bias voltage at the start of power supply is set in consideration of the usage time of the photoconductor, that is, the degree of attenuation of the surface potential of the photoconductor, a more appropriate value can be set.

[0015]

1 is a diagram showing a schematic construction of a digital copying machine to which a reversal developing system according to an embodiment of the present invention is applied. This digital copying machine has a scanner unit 2, a laser printer unit 3, a multi-stage paper feeding unit 4, and a sorter 5.

The scanner unit 2 includes a document table 21 made of transparent glass, a double-sided automatic document feeder (RDF) 22, and a scanner unit 23. The scanner unit 23 includes a lamp reflector assembly 23a that exposes a document, a photoelectric conversion element (CCD) 23b that receives a reflected light image from the document, and a CCD 23b that reflects the reflected light image from the document.
It includes a plurality of reflecting mirrors 23c for guiding the reflected light from the document and a lens 23d for forming a reflected light image from the document on the CCD 23b. The scanner unit 23 is movable along the lower surface of the document table 21, and when a document is placed on the document table 21, the scanner unit 23 moves along the lower surface of the document table 21 while the document on the document table 21 is moved. Read the reflected light image of. on the other hand,
If a document is automatically fed using RDF22, R
The reflected light image of the document fed while being stopped below the DF 22 is read. The RDF 22 sets a plurality of originals at one time, and automatically feeds the originals one by one to the facing portion of the scanner unit 23 on the original table 21. The document to be sent is also reversed so that the scanner unit 23 reads one side or both sides of the document.

The image data obtained by reading the reflected light image of the original with the CCD 23b of the scanner unit 23 is sent to an image processing unit (not shown), and is subjected to histogram processing, error diffusion processing, density conversion processing, and magnification conversion processing. After being subjected to various processes such as the above, it is temporarily stored in the memory of the image processing unit. Then, it is read at the time of image formation, given to the laser writing unit 31 of the laser printer unit 3, converted into laser light, and outputted.

The laser printer unit 3 includes a laser writing unit 31, an image forming process unit 6, a mirror 32 for guiding the laser light output from the laser writing unit 31 to the image forming process unit 6, a fixing device 33, and a multi-stage feeding. A manual feed tray 45 for accommodating sheets for image formation is provided together with the cassette of the paper unit 4.

The laser writing unit 31 emits a semiconductor laser which emits a laser beam according to image data given from a memory, a polygon mirror which deflects the laser beam at an equal angular velocity, and a laser beam which is deflected at an equal angular velocity on the image forming process unit 6. The laser light output from the laser writing unit 31 is reflected by the mirror 32 and is included in the photoconductor of the image forming process unit 6. You are led to 61. As described above, the laser writing unit 31 converts the given image data into laser light and irradiates the photoconductor 1 with the laser light. In the output laser light at this time, the black portion (toner adhering area on which toner is placed) is turned on (light irradiation), and the white portion (area on which toner is not placed) is turned off.

The image forming process unit 6 is a drum-shaped photosensitive member 61 rotatable in the direction of the arrow in the figure, and the photosensitive member 6.
1 includes a charging device 62, a developing device 63, a transfer peeling device 64, a cleaner 65, and a static eliminator 66 that are arranged to face each other. Further, the laser writing unit 31 irradiates the position between the charging device 62 and the developing device 63 with laser light.

The charger 62 is of the scorotron type,
The surface of the photoconductor 61 is charged to substantially the same potential as the grid control voltage. The developing unit 63 includes a developing tank 63a and a toner hopper 63b, and the photoconductor 6 is provided in the developing tank 63a.
The developing roller 63c and the stirring roller 63d that stir the developer in the developing tank 63b are disposed opposite to each other.
The developer contained in the developing tank 63a is a two-component developer consisting of −charged toner and a carrier which itself is charged to + to charge the toner to −, and the toner is supplied from the toner hopper 63b. Supplied as needed. The transfer peeling device 64 transfers the toner image formed on the photoconductor 61 so as to be supplied from a paper cassette or a manual feed tray 45 described later. The cleaner 65 is the photoconductor 61.
The toner, the carrier, the paper dust, etc. remaining on the upper surface are collected to keep the surface of the photoconductor 61 clean. The static eliminator 66 exposes the surface of the photoconductor 61 to a lamp exposure to remove the residual charge on the surface of the photoconductor.

The multi-stage paper feeding unit 4 includes the first cassette 4
It has the 1st, 2nd cassette 42, the 3rd cassette 43, and the 4th cassette 44 which can be added by selection. During the image forming process, the multi-stage paper feeding unit 4 uses the cassettes 41 to 4 described above.
4 or the manual feed tray 45, one of the uppermost sheets of the cassette or tray is fed toward the transfer peeling device 64 position of the laser printer unit 3.

The sorter 5 sorts and discharges the image-formed sheets into a plurality of bins.

A control procedure when the power supply to the apparatus is cut off due to a trouble such as a jam in the copying machine configured as described above will be described. First, an embodiment of claim 1 will be described. FIG. 2 is a diagram showing the state of the dark portion surface potential of the photosensitive member and the developing bias voltage when a trouble occurs, and FIG. 3 is a flowchart showing the processing procedure at that time.

When a trouble such as a jam occurs and the power supply to the copying machine is cut off, the developing bias voltage becomes 0 V, and the dark portion surface potential of the photoconductor gradually decreases with time (n1 → n2). On the other hand, as the processing of the main body of the copying machine, a timer is started at the same time when the power supply is cut off,
The standby time T until the power supply is restarted is measured (n
3 → n4 → n5). Then, the developing bias voltage is obtained based on the waiting time T, and the obtained developing bias voltage is applied to the developing roller 63c (n6 → n7).

FIG. 4 shows how the dark surface potential of the photoconductor is attenuated when the power supply to the copying machine is suddenly turned off during the image forming process. The photosensitive member used was an OPC photosensitive member having a photosensitive layer thickness of 25 μm, and the temperature around the photosensitive member was 20 ° C. As shown in the figure, the surface potential of the dark portion of the photoconductor is almost at the same level as the charging voltage (-6 when the power is turned off).
00V) and decreases with the passage of time.

On the other hand, it was examined how the amount of carriers attached to the surface of the photoconductor 61 changes depending on the potential difference between the dark portion surface potential of the photoconductor 61 and the developing roller 63c, and the results are shown in FIG. As can be seen from the figure, the potential difference between the dark surface potential of the photoconductor 61 and the developing roller 63c is approximately 350.
It can be seen that the amount of adhering carrier (carrier rising) increases from around V. Therefore, the potential difference between the surface potential of the photoconductor 61 and the developing roller 63c is approximately 3
It is desirable that the voltage is less than about 50V. The photoconductor 6
If the potential difference between the surface potential of the dark portion of No. 1 and the developing roller 63c is too small (less than about 80 V), the photoconductor 61
The repulsive force between the surface dark part potential and the −charged toner becomes small, and a phenomenon (fog) occurs in which toner adheres to the dark part on the surface of the photoconductor 61. As a result, the potential difference between the dark portion surface potential of the photoconductor 61 and the developing roller 63c is approximately 100 to 3.
It is desirable to set it to about 00V.

As can be seen from this, when the power supply to the copying machine is turned off and the surface potential remains on the photoconductor 61, the developing bias potential is set to prevent carrier rising and toner adhesion. It is desirable that the value is set to a value having a potential difference of about 100 to 300 V with respect to the current surface potential of the dark portion of the photoconductor. FIG. 6 is a table showing a specific setting example of the developing bias voltage, and the developing bias voltage to be set is determined for each waiting time T. This table is stored in advance in the memory of the main body of the copying machine and is used when the developing bias voltage is calculated in step n6 based on the waiting time T obtained in steps n3 to n5 in FIG. This prevents the carrier from rising at the same time when the power supply to the copying machine is restarted, and prevents the carrier from rising after the start of power supply until the charge removal processing on the photoconductor surface actually starts. As a result, it is possible to reduce the deterioration of the image quality due to the rising carrier.

In FIG. 2, the deviation t between the dark portion potential of the photoconductor (control timing of the photoconductor charging voltage) and the control timing of the developing bias voltage is the deviation of the phase angle between the charging device 62 position and the developing device 63 position. By shifting the control timing as shown in the figure, the timing of the step up of the dark part potential and the step up of the developing bias voltage on the surface of the photoconductor 61 coincide with each other.

Next, as an embodiment of claim 2, an example in which the developing bias voltage is corrected based on the ambient temperature of the photosensitive member will be described.

First, FIG. 7 shows the relationship between the temperature of the photoconductor and the temperature around the photoconductor. The ambient temperature of the photoconductor at this time was detected by the thermocouple at the positions of the upper part (7a) of the cleaner 65, the upper part (7b) of the charger 62, and the upper part (7c) of the static eliminator 66, respectively. From this result, it can be understood that the photoconductor temperature and the ambient temperature of the photoconductor are almost the same, and the ambient temperature of the photoconductor may be regarded as the temperature of the photoconductor, but the position of the cleaner 65 is the most sensitive. The temperature is close to the body temperature, and in this example, the thermocouple 7a is arranged above the cleaner 65 to detect the ambient temperature of the photoconductor.

Next, when the ambient temperature of the photoreceptor changes,
The decay state of the dark potential of the photoconductor was examined. FIG. 8 is a diagram showing the result, and the photosensitive layer film pressure of the photoconductor 61 used here was 25 μm. As can be seen from FIG. 8, when the ambient temperature of the photoconductor becomes low, the dark part potential of the photoconductor is not easily attenuated, and the dark part potential remains high even when the standby time becomes long. On the contrary, when the ambient temperature of the photoconductor becomes high, the dark part potential of the photoconductor is apt to be attenuated, and even if there is residual charge on the surface of the photoconductor 61, the residual potential is discharged in a short time. This phenomenon is considered to be because the movement of the carrier in the photoconductor is affected by the temperature and becomes higher as the temperature becomes higher.

From the above, after the occurrence of trouble, when the ambient temperature of the photosensitive member is low, the residual potential on the surface of the photosensitive member becomes high even if the waiting time is long, so that it is necessary to apply a high developing bias voltage. On the contrary, when the ambient temperature of the photoconductor is high, even if the waiting time is short, the electric charge is released and the residual potential becomes low, so that it is necessary to apply a low developing bias voltage. FIG. 9 is a table showing an example of setting the developing bias voltage for each photosensitive member ambient temperature and waiting time.
This table is stored in advance in the memory of the control unit of the copying machine main body and used for the calculation of the developing bias voltage.

FIG. 10 is a flow chart showing the processing procedure in this embodiment, and the same parts as the processing shown in FIG. 3 are shown by the same step numbers. In the process of this example, after the trouble is resolved and the detection of the waiting time is completed, the ambient temperature of the photoconductor is detected by the thermocouple 7a (n11). Then, the developing bias voltage is calculated according to the table shown in FIG. 9 based on the photosensitive member ambient temperature and the waiting time, and the obtained developing bias voltage is applied (n12 → n7). By such processing, it is possible to set the developing bias voltage that is adapted to the actual photoconductor dark part potential at that time, and the developing bias voltage is high regardless of whether the photoconductor temperature (photoconductor ambient temperature) is high or low. Never too low or too low,
It is possible to prevent the occurrence of carrier rising and toner adhesion (fogging) on the photoconductor.

As an embodiment of claim 3, an example will be described in which the developing bias voltage is corrected according to the usage time of the photoconductor and the ambient temperature of the photoconductor.

As the photosensitive member 61 is used, the film pressure of the photosensitive layer becomes thin due to friction with the blade of the cleaner 65 and the like. Particularly in the case of an OPC photosensitive member, the film reduction phenomenon is likely to occur. FIG. 11 shows the results of examining the relationship between the usage time of the photoconductor and the film thickness of the photoconductor, and as shown in the figure, the film thickness of the photoconductor decreases with use. Here, as a guide for reducing the film thickness of the photoconductor, the use time until reaching 20 μm (approximately 250 hours) and the use time until reaching 15 μm (approximately 420 hours) are set respectively. Then, the decay state of the dark part potential was examined for three types of photoconductors, a new photoconductor (25 μm), a photoconductor used for 250 hours ((20 μm), and a photoconductor used for 420 hours (15 μm). Is a diagram showing the result, and as can be seen, the thicker the film pressure of the photoconductor (the shorter the photoconductor use time) is, the less the attenuation amount of the dark part potential is. It is understood that it is desirable to correct the developing bias voltage to be applied according to the usage time of the photoconductor.

FIG. 13 is a table showing a concrete setting example of the developing bias voltage set after the occurrence of trouble.
The developing bias voltage is set on the basis of three types of parameters, that is, the standby time, the usage time of the photoconductor, and the ambient temperature of the photoconductor. When the photoconductor is almost new (film thickness 20
9 to 25 μm), an example of setting the developing bias voltage is shown in FIG.
Is shown in. These tables are stored in advance in the memory of the control section of the copying machine main body and used for the calculation of the developing bias voltage.

FIG. 14 is a flow chart showing the processing procedure in this embodiment, and the same portions as the processing shown in FIG. 3 are indicated by the same step numbers. In the process of this example, after the trouble is resolved and the detection of the waiting time is completed, the ambient temperature of the photoconductor is detected by the thermocouple 7a (n21), and the usage time of the photoconductor 61 is obtained (n22). It should be noted that the usage time of the photoconductor 61 can be easily obtained by previously disposing a timer for integrating the time during which the photoconductor 61 is in use. Then, the developing bias voltage is calculated according to the tables shown in FIGS. 9 and 13 based on the standby time, the ambient temperature of the photosensitive member, and the usage time of the photosensitive member, and the obtained developing bias voltage is applied (n23 → n7). By such processing, it becomes possible to set the developing bias voltage that is adapted to the actual dark potential of the photoconductor at that time, and the carrier rises regardless of the photoconductor temperature (photoconductor ambient temperature) and the photoconductor use time. It is possible to prevent toner adhesion (fogging) on the photoconductor.

In this embodiment, the actual use time of the photoconductor is detected by the timer, and the developing bias voltage is set based on the detected time. In order to correspond to the time, these may be detected instead of the usage time of the photoconductor, and the developing bias voltage may be set based on the detection.

[0040]

According to the first aspect of the present invention, it is possible to eliminate the carrier rise immediately after the power supply is restarted after a trouble occurs, and the carrier loss in the developing device due to the carrier rise can be minimized. Can be suppressed to As a result, it is possible to suppress the deterioration of the image quality due to the loss of the carrier that cannot be normally supplied.

According to the second aspect of the present invention, since the setting of the developing bias voltage at the time of starting the power supply after the trouble comes to correspond more to the actual state of the surface potential of the photosensitive member at that time, the carrier rises. It is possible to more reliably prevent toner adhesion to the photoconductor and the photoconductor.

According to the third aspect of the present invention, since the setting of the developing bias voltage at the time of starting the power supply after the trouble comes to correspond more to the actual state of the surface potential of the photosensitive member at that time, the carrier rises. It is possible to more reliably prevent toner adhesion to the photoconductor and the photoconductor.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a digital copying machine to which a developing bias control device according to an embodiment of the present invention is applied.

FIG. 2 is a diagram showing an example of a rising state of a developing bias voltage after a trouble is cleared.

FIG. 3 is a flowchart showing a processing procedure when a trouble occurs (corresponding example of claim 1).

FIG. 4 is a diagram showing a state in which a dark portion potential is attenuated depending on a photoconductor leaving time.

FIG. 5 is a diagram showing the relationship between the potential difference between the dark portion of the photoconductor and the developing bias voltage, and the amount of carrier adhered to the photoconductor.

FIG. 6 is a table showing a specific setting example of the developing bias voltage after the trouble is cleared (corresponding example of claim 1).

FIG. 7 is a diagram showing a relationship between a photosensitive member temperature and a temperature around the photosensitive member.

FIG. 8 is a diagram showing the influence of the ambient temperature of the photoconductor on the attenuation of the dark portion potential.

FIG. 9 is a table showing a specific setting example of the developing bias voltage after the trouble is cleared (corresponding example of claim 2).

FIG. 10 is a flowchart showing a processing procedure when a trouble occurs (corresponding example of claim 2).

FIG. 11 is a diagram showing a relationship between a photoconductor use time and a photoconductor film thickness.

FIG. 12 is a diagram showing the influence of the photoconductor film thickness on the attenuation of the dark potential.

FIG. 13 is a table showing a specific setting example of the developing bias voltage after the trouble is cleared (corresponding example of claim 3).

FIG. 14 is a flowchart showing a processing procedure when a trouble occurs (corresponding example of claim 3).

FIG. 15 is a diagram showing a state of a photoconductor dark portion potential and a developing bias voltage when a trouble occurs in the conventional technique.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Motoyuki Itoyama 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation

Claims (3)

[Claims] 1. When a trouble occurs in which the power is shut off while electric charges remain on the surface of the photoconductor, the time means for measuring the time until the start of power supply after the trouble occurs as a waiting time, and the waiting time. Voltage setting means for predicting the surface potential of the photosensitive member after the waiting time based on the above, and for obtaining a developing bias voltage corresponding to the potential, and the obtained developing before the start of the first image forming processing after the occurrence of the trouble. A developing bias control device comprising: an applying unit that applies a bias voltage. 2. The developing bias control apparatus according to claim 1, wherein the voltage setting means includes means for correcting the developing bias voltage according to the ambient temperature of the photoconductor. 3. The developing bias control apparatus according to claim 1, wherein the voltage setting means includes means for correcting the developing bias voltage according to the usage time of the photoconductor.