JP3461444B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reversal development type image forming apparatus applied to a copying machine or the like.

[0002]

2. Description of the Related Art As shown in FIG. 1, an image forming apparatus of a reversal development type has a photosensitive drum 2 which is rotatable in a predetermined direction and which has conductivity, and a charger which uniformly charges the surface of the photosensitive drum 2. 3, an exposure device 4 for forming an electrostatic latent image according to an image to be formed on the surface of the charged photosensitive drum 2, and a developing device for developing the electrostatic latent image with a developer 21 containing toner and carrier. A transfer device 6 for transferring the developer 5 and the developer 21 to the recording paper 7 is provided. For such an image forming operation, power is supplied to the photoconductor drum 2, the charging device 3, the exposing device 4, the developing device 5 and the transfer device 6. When an abnormality in the image forming operation is detected during execution of the image forming operation, the power supply is interrupted in response to the abnormality detection, and the power supply is restarted after the abnormality is resolved.

In the image forming apparatus, the photosensitive drum 2,
In addition to the charger 3, the exposure device 4, the developing device 5 and the transfer device 6,
A cleaning device for removing the developer 21 remaining on the surface of the photoconductor drum 2 after transfer, a static eliminator for removing the potential remaining on the surface of the photoconductor drum 2 after transfer, and the developer 21 transferred to the recording paper 7. It is configured to include a fixing device for fixing the.

The developing device 5 adopting the so-called two-component developing system uses a metal developing sleeve 19 to which a predetermined developing bias voltage is applied, and a rotatable magnet roller 20 arranged inside thereof. Further, the developer 21 including a carrier made of magnetic particles and a toner electrostatically attached to the surface thereof is used. The carrier is attracted to the surface of the developing sleeve 19 and comes into contact with the photosensitive drum 2 during development. At this time, the toners contacting at the same time are electrostatically adsorbed on the surface of the charged photosensitive drum 2, and the carrier is attracted by the magnet roller 20 and returns to the developing device 5.

Therefore, the charging polarity of the photosensitive drum 2, the charging polarity of the developing sleeve 19 and the charging polarity of the toner are all selected to be the same, and the charging polarity of the carrier is selected to be the opposite polarity. The charger 3 is the photosensitive drum 2
Is charged to a potential higher than the charging potential of the developing device 5. The exposure device 4 irradiates the photosensitive drum 2 with light according to an image to be formed. In the photoconductor drum 2, the potential of the light-irradiated region is attenuated and becomes lower than the charging potential of the developing device 5. Toner adheres to such areas.

FIG. 11 is a timing chart showing the surface potential VS of the photosensitive drum and the developing bias voltage during the normal operation. In order to prevent carrier adhesion to the photoconductor drum 2 in the reversal development system, the potential is controlled so that the surface potential VS of the photoconductor drum becomes almost 0 (zero) from the end of the image forming operation to the restart. The developing bias voltage is controlled so that the potential difference from the surface potential VS of the photosensitive drum becomes a constant value.

FIG. 12 is a timing chart showing the surface potential VS and the developing bias voltage of the conventional photosensitive drum when the image forming operation is interrupted. When there is an abnormality in the image forming operation such as recording paper conveyance failure, the power supply is interrupted first. As a result, the developing bias voltage is almost zero.
(Zero). The photoconductor drum 2 continues to rotate due to inertial force, and its rotation stops after a delay from the time of interruption of power supply. Then, after the abnormality is resolved, the system is restarted and power is supplied. The surface potential VS of the photosensitive drum shown in FIGS. 11 and 12 indicates the potential of the dark portion, that is, the area where the light is not emitted by the exposure device 4.

[0008]

When the image forming operation is abnormal and the power supply is interrupted even though the surface potential VS of the photosensitive drum is not removed, the surface potential VS of the photosensitive drum is high. It is left as it is. That is,
Surface potential VS of photosensitive drum and surface potential VDB of developing device
And the potential difference VS-VDB is left as it is. Therefore, a phenomenon in which positively charged carriers included in the developing device adhere to the photosensitive drum, that is, a so-called carrier rising phenomenon occurs.

FIG. 13 is a graph showing the transition of the surface potential VS of the photosensitive drum left in the dark. It can be seen that the surface potential VS of the photosensitive drum decreases with the passage of time. Further, FIG. 14 is a graph showing carrier rising characteristics. The horizontal axis shows the absolute value of the potential difference VS-VDB between the surface potential VS of the photosensitive drum and the surface potential VDB of the developing device. The vertical axis shows the number of carriers increased. It can be seen that the number of carriers rising increases as the potential difference VS-VDB increases. The carrier rising phenomenon described above continues to occur until the abnormality is resolved and power supply is restarted.

The carrier attached to the photosensitive drum is collected and discarded by the cleaning device. In the two-component developing method, the toner is always replenished, but the carrier is not replenished, so the carrier is reduced. Therefore, in the subsequent image forming operation, the charge amount of the toner becomes insufficient and the image characteristics deteriorate. Further, the adhered carrier may damage the photoconductor drum when the carrier is collected by the cleaning device.

Further, the image forming apparatus of the prior art disclosed in Japanese Patent Laid-Open No. 1-282573 develops in consideration of the photosensitive drum which continues to rotate due to inertial force even after the power supply is interrupted when the image forming operation is abnormal. The application timing of the bias voltage is delayed. However, in this publication, the potential control at the time of occurrence of an abnormality is performed, but the potential control at the time of restart after the abnormality is solved is not performed, so that the carrier rising phenomenon occurs when the apparatus is restarted immediately after the occurrence of the abnormality.

An object of the present invention is to provide an image forming apparatus capable of preventing the carrier from adhering to the photosensitive member when the image forming operation is interrupted or restarted.

[0013]

SUMMARY OF THE INVENTION The present invention is directed to a photoconductor which is rotatable in a predetermined direction and has conductivity, a charger for uniformly charging the photoconductor surface to a predetermined potential, and a charged photoconductor surface. Is exposed in accordance with the image to be formed to form an electrostatic latent image, toner charged to the same polarity as the charged photoconductor, and charged to the opposite polarity to the charged photoconductor. Power is supplied to a developing device that develops an electrostatic latent image with a developer containing a carrier, a transfer device that transfers the developer to a recording sheet, a photoconductor, a charger, an exposure device, a developing device, and a transfer device. Power supply means, abnormality detection means for detecting an abnormality in the image forming operation during execution of the image forming operation, interruption means for interrupting the power supply in response to the abnormality detection, and restart means for restarting the power supply after the abnormality is resolved In an image forming apparatus equipped with And idle time measuring means for measuring a photosensitive member of idle time to the time of stopping from the time the complete rotation of the photosensitive member, the surface potential V of the photosensitive body based on idle time
Development bias setting means for setting a development bias voltage at which the potential difference VS-VDB between S and the surface potential VDB of the development device is substantially constant, and development control means for applying the set development bias voltage to the development device when power supply is resumed. And an image forming apparatus including:

According to the present invention, the surface of the photoconductor is uniformly charged to a predetermined potential, and then an electrostatic latent image corresponding to the image to be formed is formed on the surface. The electrostatic latent image is developed with a developer. That is, when a carrier having toner electrostatically attached to its surface comes into contact with the photoreceptor during development,
The toner is electrostatically adsorbed on the surface of the charged photoreceptor, and the carrier returns to the developing device. In this way, the electrostatic latent image is visualized by the toner. The toner adhering to the photoconductor is transferred to the recording paper to form an image.

When an abnormality in the image forming operation such as a recording paper conveyance error is detected during the image forming operation in which the power is supplied to the photoconductor, the charging device, the exposing device, the developing device and the transfer device, the power supply is interrupted. . Here, the idling time of the photoconductor from the time when the power supply is stopped to the time when the rotation of the photoconductor is completely stopped is measured, and the surface potential VS of the photoconductor and the surface potential VDB of the developing device are measured based on the idling time. Potential difference VS-VD
A developing bias voltage is set so that B becomes substantially constant. When the power supply is restarted after the abnormality is resolved, the set developing bias voltage is applied to the developing device. Therefore, when the image forming operation is restarted, the potential difference VS-VDB becomes substantially constant, and it is possible to prevent the carrier from adhering to the photoconductor.

According to the present invention, in the image forming apparatus, instead of the idling time measuring means, when an abnormality is detected, the rotation of the photoconductor from the time when the power supply is interrupted to the time when the rotation of the photoconductor is completely stopped. The developing bias setting means includes a slipping angle measuring means for measuring a slipping angle about an axis, and the developing bias setting means determines a potential difference VS-VDB between the surface potential VS of the photoconductor and the surface potential VDB of the developing device based on the slipping angle. It is characterized in that a constant developing bias voltage is set.

According to the present invention, when the abnormality of the image forming operation is detected and the power supply is interrupted during the execution of the image forming operation,
The idling angle of the photoconductor is measured from the time when the power supply is interrupted to the time when the rotation of the photoconductor is completely stopped, and the potential difference between the surface potential VS of the photoconductor and the surface potential VDB of the developing unit is measured based on the idling angle. The developing bias voltage is set so that VS-VDB is almost constant. When the power supply is restarted after the abnormality is resolved, the set developing bias voltage is applied to the developing device. Therefore, when the image forming operation is restarted, the potential difference VS-VDB becomes substantially constant, and it is possible to prevent the carrier from adhering to the photoconductor.

Further, the slipping angle can accurately and easily grasp the moving amount of the photosensitive member as compared with the slipping time. That is, in order to obtain an accurate amount of movement in the idling time, the load when the photoconductor idles due to inertial force needs to be constant, but in reality, the friction resistance between the cleaning device blade and the developing device, The amount of movement obtained from the idling time and the actual amount of movement will vary depending on the frictional resistance and the load on the drive gear, etc.In order to obtain an accurate amount of movement, the frictional resistance and load must be taken into consideration when calculating. There must be.
However, by using the idling angle, an accurate amount of movement of the photoconductor can be easily obtained without considering frictional resistance and load. Therefore, it is possible to further prevent the carrier from being attached to the photoconductor.

[0019]

[0020]

[0021]

[0022]

[0023]

[0024]

[0025]

[0026]

[0027]

[0028]

[0029]

[0030]

[0031]

[0032]

[0033]

[0034]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an image forming apparatus 1 of a reversal development system which is an embodiment of the present invention. The image forming apparatus 1 has a photosensitive drum 2 that is rotatable in a predetermined direction and has conductivity, a charger 3 that uniformly charges the surface of the photosensitive drum 2 to a predetermined potential, and an image to be formed by light irradiation. An exposing device 4 for forming an electrostatic latent image on the surface of the charged photosensitive drum 2, a developing device 5 for developing the electrostatic latent image with a developer 21, and a transferring device 6 for transferring the developer 21 to the recording paper 7.
Equipped with.

In the developing device 5 employing the two-component developing system,
A metal developing sleeve 19 to which a predetermined developing bias voltage is applied and a rotatable magnet roller 20 arranged inside are used. Further, the developer 21 including a carrier made of magnetic particles and a toner electrostatically attached to the surface thereof is used. The carrier is attracted to the surface of the developing sleeve 19 and comes into contact with the photosensitive drum 2 during development. At this time, the toners contacting at the same time are electrostatically adsorbed on the surface of the charged photosensitive drum 2, and the carrier is attracted by the magnet roller 20 and returns to the developing device 5.

Therefore, the charging polarity of the photosensitive drum 2, the charging polarity of the developing device 5 (the charging polarity of the developing sleeve 19) and the charging polarity of the toner are all selected to be the same, and the charging polarity of the carrier is opposite to these. Chosen for the polarity of. The charger 3 charges the photosensitive drum 2 to a potential higher than the charging potential of the developing sleeve 19. The exposure device 4 irradiates the photosensitive drum 2 with light according to an image to be formed. In the photoconductor drum 2, the potential of the light-irradiated region is attenuated and becomes lower than the charging potential of the developing sleeve 19. Toner adheres to such areas.

The image forming apparatus 1 includes, in addition to the photoconductor drum 2, the charger 3, the exposure device 4, the developing device 5 and the transfer device 6, the developer 2 remaining on the surface of the photoconductor drum 2 after the transfer.
Cleaning device for removing 1 and photosensitive drum 2 after transfer
Erasing device and recording paper 7 for eliminating the electric potential remaining on the surface of the
It is configured to include a fixing device for fixing the developer 21 transferred to the.

FIG. 2 is a block diagram of the image forming apparatus 1. The image forming apparatus 1 includes, in addition to the above-described photoconductor drum 2, charger 3, exposure device 4, developing device 5 and transfer device 6, a control unit 8, drive units 9 to 13, an abnormality detection unit 14, and idle time measurement. The unit 15, the idling angle measuring unit 16, the standby time measuring unit 17, and the power supply unit 18 are provided. The control unit 8 uses the image forming apparatus 1
Control the overall operation of. The drive unit 9 controls the rotation of the photosensitive drum 2 according to the control of the control unit 8. Further, each of the drive units 10 to 13 turns on / off the charging device 3, the exposure device 4, the developing device 5, and the transfer device 6 under the control of the control unit 8. Further, the power supply unit 18 supplies power to each unit for the image forming operation.

The abnormality detecting section 14 detects an abnormality in the image forming operation during execution of the image forming operation and gives the detection result to the control section 8.
The abnormality in the image forming operation is, for example, power shutoff or recording paper conveyance failure. In response to the abnormality detection, the control unit 8 interrupts the power supply to each unit and stops the image forming operation urgently. Further, the control unit 8 restarts the image forming operation by restarting the power supply to each unit after the abnormality is resolved.

When the abnormality detecting section 14 detects an abnormality, the idle rotation time measuring section 15 measures the idle rotation time T of the photosensitive drum 2 from the time when the power supply is interrupted to the time when the rotation of the photosensitive drum 2 is completely stopped. Then, the measurement result is given to the control unit 8.

Based on the idling time T, the control unit 8
The developing bias voltage is set so that the potential difference VS-VDB between the surface potential VS of the photosensitive drum 2 and the surface potential VDB of the developing sleeve 19 becomes substantially constant. Then, the drive unit 12 is controlled so that the set developing bias voltage is applied to the developing sleeve 19 when the power supply is restarted.

Further, the control section 8 sets the exposure time for exposing the entire surface of the photosensitive drum 2 to erase the surface potential VS based on the idle time T. Then, the drive unit 11 of the exposure device 4 is controlled so that the photosensitive drum 2 is exposed for the set exposure time.

In particular, the control section 8 compares the idling time T with the moving time required for the photosensitive drum 2 to rotate from the charging device 3 to the exposing device 4. When the idling time T is equal to or less than the moving time, the driving unit 11 of the exposure device 4 is controlled so that the entire surface of the photoconductor drum 2 is continuously exposed and the surface potential VS of the photoconductor drum 2 is erased during the idling. , Idle time T
Is larger than the moving time, the entire surface of the photoconductor drum 2 is exposed at the restart of rotating the photoconductor drum 2 from the charger 3 to the exposure device 4 and the surface potential V of the photoconductor drum 2 is exposed.
The drive unit 11 of the exposure device 4 is controlled so as to erase S.

Further, the control section 8 sets the charging time for keeping the surface of the photosensitive drum 2 at a predetermined potential based on the idling time T. Then, the drive unit 10 of the charger 3 is controlled so as to charge the photosensitive drum 2 for the set charging time.

Further, the image forming apparatus 1 includes the idle time measuring unit 1
The idle rotation angle measuring unit 16 used in place of 5 is provided.
When the abnormality detection unit 14 detects an abnormality, the idle rotation angle measurement unit 16 determines the idle rotation angle around the rotation axis of the photoconductor drum 2 from the time when the power supply is interrupted to the time when the rotation of the photoconductor drum 2 is completely stopped. D is measured and the measurement result is obtained by the control unit 8
Give to.

Based on the idling angle D, the control section 8
The developing bias voltage is set so that the potential difference VS-VDB between the surface potential VS of the photosensitive drum 2 and the surface potential VDB of the developing sleeve 19 becomes substantially constant. Then, the drive unit 12 is controlled so that the set developing bias voltage is applied to the developing sleeve 19 when the power supply is restarted.

Further, the control section 8 sets the exposure time for exposing the entire surface of the photosensitive drum 2 to erase the surface potential VS based on the idling angle D. Then, the drive unit 11 of the exposure device 4 is controlled so that the photosensitive drum 2 is exposed for the set exposure time.

In particular, the control section 8 compares the idling angle D with the moving angle required for the photosensitive drum 2 to rotate from the charging device 3 to the exposing device 4. When the idling angle D is equal to or smaller than the movement angle, the drive unit 11 of the exposure device 4 is controlled so that the entire surface of the photoconductor drum 2 is continuously exposed and the surface potential VS of the photoconductor drum 2 is erased during the idling. , Idling angle D
Is larger than the movement angle, the entire surface of the photoconductor drum 2 is exposed at the restart of rotating the photoconductor drum 2 from the charger 3 to the exposure device 4, and the surface potential V of the photoconductor drum 2 is exposed.
The drive unit 11 of the exposure device 4 is controlled so as to erase S.

The control unit 8 also sets the charging time for keeping the surface of the photosensitive drum 2 at a predetermined potential based on the idling angle D. Then, the drive unit 10 of the charger 3 is controlled so as to charge the photosensitive drum 2 for the set charging time.

Further, the image forming apparatus 1 is provided with a waiting time measuring unit 17 for measuring the waiting time from the time of detecting the abnormality to the time of eliminating the abnormality and giving the measurement result to the control unit 8. The control unit 8
Is based on the standby time, and is based on the waiting time.
Of the surface potential VS, and a developing bias voltage corresponding to the surface potential VS is set. Then, the drive unit 12 is controlled so that the set developing bias voltage is applied to the developing sleeve 19 when the power supply is restarted.

First, the first control operation when the image forming apparatus 1 detects an abnormality will be described. From FIG. 13, the surface potential VS of the dark portion of the photosensitive drum left in the dark is almost the same level as the charging voltage of the photosensitive drum at the time of power-off (time when the elapsed time is 0 (zero)). It is decreasing over time. Further, from FIG. 14, the number of carriers that have risen increases as the potential difference VS-VDB increases, and when the potential difference VS-VDB exceeds 300 V, the number of carriers that rises remarkably increases. Therefore, the potential difference VS-VDB is 3
It is preferably smaller than 00V. However, if the potential difference VS-VDB is made too small, for example, about 80 V or less, the repulsive force between the photoconductor drum 2 and the toner becomes small, and the toner adheres to the dark portion of the photoconductor drum 2.
So-called fogging occurs.

Therefore, the potential difference VS-VDB is 100.
The range of V to 300 V is preferable, and when the image forming operation is urgently stopped when an abnormality is detected and the surface potential VS of the photoconductor drum 2 is left without being neutralized, carrier adhesion to the photoconductor drum 2 is prevented. In order to achieve this, it is preferable that the developing bias voltage applied to the developing sleeve 19 at the time of restart is set so as to have a potential difference of 100 V to 300 V with respect to the surface potential VS of the photosensitive drum 2.

FIG. 3 is a diagram showing the distribution of the surface potential VS on the photosensitive drum when an abnormality is detected. 3A shows a state immediately after the emergency stop of the image forming operation, FIG. 3B shows a state after a predetermined time T1 from the emergency stop, and FIG. 3C shows a state after a predetermined time T2 (T2 from the emergency stop. The state after> T1) is shown. Immediately after the emergency stop, it can be seen that the potential VS remains between the position facing the charger 3 of the photosensitive drum 2 and the position facing the developing device 5. After the time T1, the position where the potential VS remains is moved to the downstream side in the rotational direction, that is, to the position facing the developing device 5, because the photosensitive drum 2 idles due to inertial force after the emergency stop. I understand. It can be seen that after the time T2, the position where the potential VS remains moves further to the downstream side in the rotation direction. As described above, since the photosensitive drum 2 idles due to the inertial force even after the emergency stop, the distribution of the surface potential VS moves.

FIG. 4 is a graph showing the surface potential VS at the position facing the developing device 5 of the photoconductor drum 2 with respect to the idling time T of the photoconductor drum 2. The idling time T of the photosensitive drum 2 is the time from the time when the power supply is interrupted to the time when the rotation of the photosensitive drum 2 is completely stopped when the abnormality is detected by the abnormality detecting unit 14 as described above. When the idling time T is relatively short, the surface potential VS is substantially the same as the charging potential, but when the idling time T is long, the surface potential VS decreases to almost zero (0).

FIG. 5 is a diagram showing an example of setting the developing bias voltage at the time of restart. The developing bias voltage applied to the developing sleeve 19 at the time of restart is set to the surface potential V of the photosensitive drum 2.
The relationship between the idle rotation time T of the photosensitive drum 2 and the developing bias voltage at the time of restarting for setting so as to have a potential difference of 100 V to 300 V with respect to S is shown. Idle time T
The developing bias voltage at the time of restart is set in association with each other, and the control unit 8 stores a table storing such a relationship.
Has Therefore, the control unit 8 controls the idling time measuring unit 15
The developing bias voltage corresponding to the idling time T measured by can be selected from the table and set.

FIG. 6 is a flow chart showing the first control operation when the abnormality of the image forming apparatus 1 is detected. When the image forming operation is started and the abnormality detecting unit 14 detects an abnormality in the image forming operation in step a1, the process proceeds to step a2,
The control unit 8 interrupts the power supply from the power supply unit 18 and urgently stops the image forming operation. Next, in step a3, the idling time measuring unit 15 measures the idling time T, and gives the measurement result to the control unit 8. Further, in step a4, the control unit 8 refers to the table and selects and sets the developing bias voltage corresponding to the measured idling time T. Next, in step a5, the controller 8 drives the drive unit 1 to apply the set developing bias voltage to the developing sleeve 19 at the time of restart.
Control 2 Then, the first control operation at the time of abnormality detection is ended, and the process proceeds to the step of executing a normal image forming operation.

FIG. 7 is a timing chart showing the surface potential VS of the photosensitive drum and the developing bias voltage when an abnormality is detected. When an abnormality in the image forming operation is detected, the power supply is interrupted first. As a result, the developing bias voltage applied to the developing sleeve 19 becomes 0 (zero).
Since the photoconductor drum 2 continues to rotate due to inertial force, its rotation stops after a delay from the point of interruption of power supply. Then, after the abnormality is resolved, the image forming operation is restarted and the power supply is restarted.

At the time of restart, the developing bias voltage set based on the idling time T as described above is applied to the developing sleeve 19, so that the carrier is attached to the photosensitive drum 2 at the same time when the power supply is restarted. It will not occur. Therefore, it is possible to prevent the phenomenon of carrier rising that occurs after the power supply is resumed and before the surface potential of the photosensitive drum 2 is removed and the charging process is performed.

Next, the second control operation when the image forming apparatus 1 detects an abnormality will be described. The first control operation uses the idling time T, while the second control operation uses the idling angle D.

FIG. 8 is a graph showing the surface potential VS at the position facing the developing device 5 of the photoconductor drum 2 with respect to the idling angle D of the photoconductor drum 2. The idling angle D of the photoconductor drum 2 is the angle from the time when the power supply is interrupted to the time when the rotation of the photoconductor drum 2 is completely stopped when the abnormality detection unit 14 detects the abnormality as described above. When the idling angle D is relatively narrow, the surface potential VS is almost the same as the charging potential, but when the idling angle D increases, the surface potential VS decreases to almost zero (0).

FIG. 9 is a diagram showing an example of setting the developing bias voltage at the time of restart. The developing bias voltage at restart is 100 V to 300 with respect to the surface potential VS of the photosensitive drum 2.
The relationship between the idling angle D of the photosensitive drum 2 and the developing bias voltage at the time of restart for setting so as to have a potential difference of V is shown. The developing bias voltage is set in association with each idling angle D, and the control unit 8 has a table storing such a relationship. Therefore, based on the idling angle D measured by the idling angle measuring unit 16, the control unit 8 can refer to the table and select and set the corresponding developing bias voltage.

FIG. 10 is a flow chart showing the second control operation when the abnormality of the image forming apparatus 1 is detected. The image forming operation is started, and in step a1, the abnormality detection unit 14
Detects an abnormality in the image forming operation, the process proceeds to step a2, and the control unit 8 interrupts the power supply from the power supply unit 18 and urgently stops the image forming operation. Then proceed to step a6,
The idling angle measuring unit 16 measures the idling angle D and gives the measurement result to the control unit 8. Further proceeding to step a7, the control unit 8 refers to the table and selects and sets the developing bias voltage corresponding to the measured idling angle D. Next, in step a5, the control unit 8 controls the drive unit 12 to apply the set developing bias voltage to the developing sleeve 19 at the time of restarting. Then, the second control operation at the time of abnormality detection is ended, and the process proceeds to the step of executing a normal image forming operation.

At the time of restart, the developing bias voltage set on the basis of the idling angle D as described above is applied to the developing sleeve 19, so that as shown in FIG. 7, as in the case of the first control operation. As soon as the power supply is restarted, the carrier does not adhere to the photosensitive drum 2.
Therefore, it is possible to prevent the phenomenon of carrier rising that occurs after the power supply is resumed and before the surface potential of the photosensitive drum 2 is removed and the charging process is performed.

Further, the idling angle D used in the second control operation can accurately and easily grasp the moving amount of the photosensitive drum 2 as compared with the idling time T. That is, the idle time T
In order to obtain an accurate movement amount, the load when the photoconductor drum 2 idles due to inertial force must be constant, but in reality, the friction resistance with the blade of the cleaning device and the friction with the developing device 5 Due to the resistance and the load of the drive gear, the amount of movement obtained from the idling time T and the actual amount of movement will vary, and in order to obtain an accurate amount of movement, these frictional resistances and loads should be taken into consideration when calculating. There must be. However, by using the idling angle D, an accurate movement amount can be easily obtained without considering frictional resistance and load. Therefore, the carrier rising phenomenon can be further prevented.

[0065]

[0066]

[0067]

[0068]

[0069]

[0070]

[0071]

[0072]

[0073]

[0074]

[0075]

[0076]

[0077]

[0078]

[0079]

[0080]

[0081]

[0082]

[0083]

[0084]

[0085]

[0086]

[0087]

[0088]

[0089]

[0090]

[0091]

[0092]

[0093]

[0094]

[0095]

[0096]

[0097]

[0098]

[0099]

[0100]

[0101]

[0102]

[0103]

[0104]

[0105]

[0106]

[0107]

[0108]

[0109]

As described above, according to the present invention, the power supply is interrupted when an abnormal operation is detected during the image forming operation. Here, the idling time from the interruption of the power supply to the complete stop of the rotation of the photoconductor is measured, and the potential difference VS-VDB between the surface potential VS of the photoconductor and the surface potential VDB of the developing device is calculated based on the idling time. Since the developing bias voltage that is almost constant is set and the developing bias voltage that is set when the power supply is restarted after the abnormality is resolved is applied to the developing device, when the image forming operation is restarted, the carrier to the photoreceptor is Adhesion can be prevented.

According to the present invention, instead of the idling time, the idling angle from the interruption of the power supply to the complete stop of the rotation of the photosensitive member is measured, and the developing bias voltage is set and applied based on the idling angle. Since this is done, it is possible to prevent the carrier from adhering to the photoconductor when the image forming operation is restarted. Further, by using the idling angle, it is possible to easily obtain an accurate movement amount of the photoconductor without considering frictional resistance and load, and it is possible to further prevent the carrier from adhering to the photoconductor.

[0111]

[0112]

[0113]

[0114]

[0115]

[0116]

[0117]

[Brief description of drawings]

FIG. 1 is a diagram showing an image forming apparatus 1 of a reversal development type which is an embodiment of the present invention.

FIG. 2 is a block diagram of the image forming apparatus 1.

3A and 3B are diagrams showing a distribution of a surface potential VS on a photosensitive drum when an abnormality is detected, FIG. 3A shows a state immediately after an emergency stop of an image forming operation, and FIG. 3B shows an emergency stop. 3C shows a state after a predetermined time T1 from FIG. 3, and FIG. 3C shows a state after a predetermined time T2 (T2> T1) from the emergency stop.

FIG. 4 is a surface potential V at a position of the photosensitive drum 2 facing the developing device 5 with respect to the idle rotation time T of the photosensitive drum 2.
It is a graph which shows S.

FIG. 5 is a diagram showing an example of setting a developing bias voltage at restart.

FIG. 6 is a flowchart showing a first control operation at the time of detecting an abnormality in image forming apparatus 1.

FIG. 7 is a surface potential V of the photosensitive drum when an abnormality is detected.
6 is a timing chart showing S and a developing bias voltage.

8 is a surface potential V at a position facing the developing device 5 of the photoconductor drum 2 with respect to the idling angle D of the photoconductor drum 2. FIG.
It is a graph which shows S.

FIG. 9 is a diagram showing an example of setting a developing bias voltage at restart.

FIG. 10 is a flowchart showing a second control operation when the abnormality of the image forming apparatus 1 is detected.

FIG. 11 is a timing chart showing the surface potential VS of the photosensitive drum and the developing bias voltage during normal operation.

FIG. 12 is a timing chart showing the surface potential VS and the developing bias voltage of the conventional photosensitive drum when the image forming operation is interrupted.

FIG. 13 is a surface potential VS of a photosensitive drum left in the dark.
It is a graph which shows the change of.

FIG. 14 is a graph showing carrier rising characteristics.

[Explanation of symbols]

1 Image forming device 2 photoconductor drum 3 charger 4 Exposure device 5 Developer 6 transfer device 7 Recording paper 8 control unit 9-13 Drive unit 14 Abnormality detector 15 Idling time measurement unit 16 Idling angle measurement unit 17 Standby time measurement unit 18 power supply 21 developer

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Motoyuki Itoyama 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Masato Asanuma 22-22 Nagaike-cho, Abeno-ku, Osaka, Osaka Sharp Corporation (72) Inventor Koichi Takenouchi 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (56) Reference JP-A-5-165287 (JP, A) JP-A-1-297270 (JP, A) JP-A-9-311607 (JP, A) JP-A-8-160724 (JP, A) JP-A-7-114319 (JP, A) JP-A-7-253693 (JP, A) JP-A-4-220663 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G03G 21/00 370-540 G03G 21/14 G03G 15/00 303 G03G 15/06

Claims (2)

(57) [Claims] 1. A photosensitive member which is rotatable in a predetermined direction and has conductivity, a charger which uniformly charges the surface of the photosensitive member to a predetermined potential, and an image to be formed on the charged surface of the photosensitive member. A developer including an exposure device that exposes to form an electrostatic latent image, a toner charged to the same polarity as the charged photoconductor, and a carrier charged to the opposite polarity to the charged photoconductor, A developing device for developing the electrostatic latent image, a transfer device for transferring the developer to the recording paper, a power supply means for supplying power to the photoconductor, charging device, exposing device, developing device and transfer device, and image forming operation An image forming apparatus comprising: an abnormality detecting unit that detects an abnormality in an image forming operation during execution; an interrupting unit that interrupts power supply in response to the abnormality detection; and a resuming unit that restarts power supply after the abnormality is resolved. When an abnormality is detected, the photoconductor Of the photoconductor until the time when the rotation of the photosensitive drum is completely stopped, and the potential difference VS-VDB between the surface potential VS of the photoconductor and the surface potential VDB of the developing device based on the idle time. An image forming apparatus comprising: a developing bias setting unit that sets a constant developing bias voltage; and a developing control unit that applies the set developing bias voltage to a developing device when power supply is resumed. 2. The image forming apparatus, in place of the idling time measuring means, has a rotation axis of the photoconductor as a center from a time when power supply is interrupted to a time when rotation of the photoconductor is completely stopped when abnormality is detected. The idling angle measuring means for measuring the idling angle is set, and the developing bias setting means makes the potential difference VS-VDB between the surface potential VS of the photoconductor and the surface potential VDB of the developing device substantially constant based on the idling angle. The image forming apparatus according to claim 1, wherein a developing bias voltage is set.