JPH09329946A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent the sticking of carriers to a photoreceptor, in turn ing on/off a power source for a developing bias, during image formation starting and completing operations and the futile consumption of toner as well. SOLUTION: The image forming device provided with a revering development system developing device 5 is provided with a controller 11 for controlling the turning on/off of high-voltage power sources for electrifying and developing biases 9 and 10, so that the application of a developing bias voltage is starred when the electrification starring end of the photoreceptor 1 faces a developing sleeve 4 and stopped when the electrification completing end faces the developing sleeve 4. The timing of turning on/off both power sources 9 and 10 is set so that the value of the surface potential of the photoreceptor 1 approaches the value of the developing bias voltage within a range where the absolute value of the surface potential of the photoreceptor 1 passing through a position facing the developing sleeve 4, while the developing bias voltage is transiently changed becomes the absolute value or below of the developing bias voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, a printer, and the like. More specifically, the surface of a uniformly charged image carrier is subjected to image exposure to form a latent electrostatic image by potential attenuation. Then, image formation using a reversal development method in which the electrostatic latent image is developed using a two-component developer containing a toner charged to the same polarity as the charging polarity and a carrier charged to the opposite polarity to the charging polarity. The present invention relates to ON / OFF control of a charging power source and a developing bias power source in an apparatus.

[0002]

2. Description of the Related Art In an image forming apparatus of this type, when charging of the surface of an image carrier by a charging means is started at almost the same time as driving of the image carrier is started at the start of image formation, when the image carrier is stopped. The surface of the image bearing member from the portion facing the charging means to the portion bearing the developer bearing member of the developing device faces the developer bearing member without being charged by the charging member. Also, at the end of image formation,
When the charging of the surface of the image carrier by the charging means is completed almost at the same time as the driving of the image carrier is completed, the uncharged surface of the surface of the image carrier does not face the developer carrier,
The charged portion on the surface of the image carrier may face the developer carrier.

By the way, in an image forming apparatus using the reversal development method, when an uncharged non-charged area on the surface of the image carrier is opposed to the developer carrier, it is opposed to the charged area on the surface of the image carrier. When a developing bias voltage having the same magnitude as the voltage applied at the time of application is applied to the developer bearing member, the direction in which toner is transferred from the developer bearing member to the image bearing member surface between the image bearing member and the developer bearing member. The electric field of is formed.
Due to this electric field, the toner adheres to the non-charged area on the surface of the image carrier, so that the toner is wasted.
The toner consumption of the entire device increases.

Further, when the developing bias power source is turned off when the non-charged area on the surface of the image bearing member reaches the developing position facing the developer bearing member, the developing bias power source is turned off between the image bearing member and the developer bearing member. , An electric field in a direction opposite to the electric field in the direction in which the toner is transferred from the developer carrier to the image carrier surface, that is, in the direction in which the carrier charged with the opposite polarity to the toner is transferred from the developer carrier to the image carrier surface. An electric field is formed, and the carrier adheres to the non-charged area on the surface of the image carrier. The electric field in the opposite direction is formed between the developer carrying member to which the developing bias voltage is applied and the non-image portion on the surface of the image carrying member even during image formation, but the electric field strength is higher than that during image formation. Since it is considerably large, the carrier easily transfers to and adheres to the image carrier. As described above, carrier adhesion occurs in the reverse electric field because when the two-component developer containing the toner and the high-resistance carrier is used, the toner and the carrier are mixed and stirred to bring the toner to the predetermined polarity. This is because the carrier is charged with the opposite polarity to the toner when the toner is triboelectrically charged.

Conventionally, in order to prevent wasteful consumption of the toner, the development start timing at which development bias voltage is applied to the developer carrying member to start development, the charged area of the image carrying member reaches the developing position. There is known an electrophotographic apparatus (image forming apparatus) which delays the delay (see Japanese Patent Laid-Open No. 54-12843).

[0006]

However, in an actual image forming apparatus, even if the control as disclosed in Japanese Patent Laid-Open No. 54-12843 is performed, the ON / OFF timing of the developing bias power source is changed. If the deviation occurs, it may not be possible to completely prevent both the adhesion of the carrier and the unnecessary adhesion of the toner. For example, when the ON timing of the developing bias power supply is earlier than a predetermined timing at the start of image formation of the image forming apparatus, useless adhesion of toner to the image carrier occurs, and when the developing bias power supply ON timing is late, an image is generated. The carrier may be attached to the carrier. Further, for example, when the image forming of the image forming apparatus is completed or when the image forming apparatus is emergency stopped, the power supply for the developing bias is turned off
If the timing is earlier than a predetermined timing, carrier adhesion to the image carrier may occur, and if the ON timing of the developing bias power source is late, wasteful adhesion of toner to the image carrier may occur.

[0007] Further, the reason why it is not possible to completely prevent both the carrier adhesion and the toner wasteful adhesion is that a potential change area is generated at the boundary between the charged area and the non-charged area on the surface of the image carrier. , Development bias power ON /
It can also be mentioned that a transient change occurs in the developing bias voltage when it is OFF. If there is such a potential change region on the image carrier or a transient change in the developing bias voltage, the developing bias power source is turned on even if the control as disclosed in Japanese Patent Laid-Open No. 54-12843 is performed. Depending on the magnitude relationship between the developing bias voltage and the potential on the surface of the image carrier which are transiently changed by turning on / off, an electric field for transferring to the image carrier side such as a carrier on the developer carrier is generated, There is a possibility that it is not possible to completely prevent both the adhesion of the carrier and the unnecessary adhesion of the toner.

Here, the carrier is attached to the surface of the image carrier mainly by electrostatic attraction, but since the carrier is heavier than the toner, centrifugal force due to gravity and rotation of the developer carrier acts strongly, If the gravity or centrifugal force becomes larger than the electrostatic attractive force, it falls from the surface of the image carrier. Even if the number of carriers attached to the surface of the image carrier is small, the carriers dropped from the surface of the image carrier while the image forming apparatus is used for a long time may cause a transfer charger or a transfer device located below the image carrier in the apparatus. There is a risk that the material transportation path will be contaminated.

On the other hand, since the toner adhering to the surface of the image carrier is sufficiently charged to a predetermined polarity, the force of adhering to the image carrier by electrostatic attraction is stronger than that of the carrier. Further, since the toner is lighter than the carrier and weak in the action of gravity and centrifugal force, the electrostatic attraction force is overwhelmingly stronger than that of gravity and centrifugal force, and the toner does not separate from the surface of the image carrier by gravity or centrifugal force. . Most of the toner that falls off the image carrier in an actual image forming apparatus causes the image to be generated in a short time when the separation claw that separates the tip of the transfer medium separates the transfer medium from the image carrier to rub the surface of the image carrier. The toner image at the tip of the area is peeled off from the surface of the image carrier.

From the viewpoint of contamination in the apparatus, the carrier adhesion is not desirable, but the toner adhesion does not cause much trouble. If it is difficult to achieve both toner adhesion to the image carrier and carrier adhesion so as not to occur at the same time, prioritize prevention of wasteful toner consumption or priority of prevention of carrier contamination within the device. Or
Will be the choice. Here, if the inside of the device is contaminated by the carrier, the service life of the contaminated component or unit may be shortened or it may cause a failure. On the other hand, wasteful toner consumption is not desirable, but if it is included in the amount of toner consumed by the image forming apparatus, the overall cost of toner will be slightly higher, which will shorten the life of the unit and cause malfunctions. There is no such thing.

The present invention has been made under the above background, and an object thereof is to turn on / off the developing bias power source or switch the developing bias voltage in the image forming start operation and the image forming end operation. An object of the present invention is to provide an image forming apparatus capable of reliably preventing carrier adhesion to an image carrier and suppressing toner adhesion to the image carrier as much as possible to prevent wasteful toner consumption.

[0012]

In order to achieve the above object, a charging member for uniformly charging the surface of an image carrier and a charging unit having a charging power source for applying a voltage to the charging member, Exposure means for forming an electrostatic latent image on the image carrier by image-exposure-damping the surface of the image carrier charged by the charging means, and toner charged to the same polarity as the charging polarity of the charging means. And a developer carrying member carrying a two-component developer containing a carrier charged to a polarity opposite to the charging polarity, and a developing bias power source for applying a developing bias voltage having the same polarity as the charging polarity to the developer carrying member. An image forming apparatus of a reversal developing system, comprising: a developing unit having:
In the invention, the application of the developing bias voltage to the developer carrying member is started when the charging starting end of the image carrying member faces the developer carrying member, and the charging end end of the image carrying member is A control means for controlling ON / OFF of the charging power source and the developing bias power source is provided so that the application of the developing bias voltage is stopped when facing the developer carrying member, and the developing bias power source is turned on. The absolute value of the potential of the surface of the image carrier passing through the position facing the developer carrier when the developing bias voltage is transiently changed by / OFF is
ON / OFF of the charging power source and the developing bias power source so that the value of the potential on the surface of the image carrier and the developing bias voltage value are close to each other under the condition that the absolute value of the developing bias voltage is not more than the absolute value. According to a second aspect of the invention, the developing bias power source applies the developing bias power source when the developer carrier faces the charged area on the surface of the image carrier. The voltage and the developing bias voltage applied when the developer bearing member faces the non-charged area of the image bearing member surface are constituted so that the polarity can be switched and applied. The charging power source and the charging power source are switched so that the developing bias voltage is switched when the charging start end faces the developer carrier and when the charging end end of the image carrier surface faces the developer carrier. The developing bias charge A control unit for controlling the developing bias voltage, and the potential of the surface of the image carrier passing through the position facing the developer carrier when the developing bias voltage is transiently changed by the switching of the developing bias voltage. The charging power source and the developing bias power source so that the value of the potential on the surface of the image carrier and the developing bias voltage value are close to each other under the condition that the absolute value is equal to or less than the absolute value of the developing bias voltage. O
It is characterized in that N / OFF timing is set.

In the invention of claim 1, the control means controls ON / OFF of the charging power source and the developing bias power source,
In the image forming start operation of the apparatus, when the charging start end of the surface of the image carrier is opposed to the developer carrier, application of the developing bias voltage to the developer carrier is started, and thus the charging start end of the image carrier is started. By the time the toner reaches the position facing the developer carrying member, the non-charged area on the surface of the image carrying member is prevented from facing the developer carrying member to which the developing bias voltage is applied, and the same polarity as the developing bias voltage is applied. The electric field in the direction in which the toner is transferred to the surface of the image carrier is prevented from being formed between the image carrier and the developer carrier.

Further, when the charging end end of the surface of the image bearing member faces the developer bearing member in the image forming termination operation of the apparatus, the application of the developing bias voltage to the developer bearing member is stopped, so that the image bearing member is stopped. After the charging end end of the body has passed the position facing the developer carrying member, the non-charged area of the image carrying member is prevented from facing the developer carrying member to which the developing bias voltage is applied, and the same as the developing bias voltage. An electric field in which polar toner is transferred to the surface of the image carrier is prevented from being formed between the image carrier and the developer carrier.

Then, the developing bias power source is turned ON / OF.
When the development bias voltage is transiently changed by F, the absolute value of the potential of the surface of the image carrier passing through the position facing the developer carrier is set to be equal to or less than the absolute value of the development bias voltage. Turn on the charging power supply and the developing bias power supply
By setting the ON / OFF timing, the carrier charged with the opposite polarity to the charging potential on the image carrier transfers from the developer carrier to the surface of the image carrier while the developing bias voltage changes transiently. An electric field directed in the direction of turning is prevented from being formed between the image carrier and the developer carrier.

Further, under the condition that the absolute value of the potential on the surface of the image bearing member is not more than the absolute value of the developing bias voltage,
By setting the ON / OFF timings of the charging power source and the developing bias power source so that the potential value on the surface of the image carrier and the developing bias voltage value are close to each other, the toner having the same polarity as the developing bias voltage is generated. An electric field that transfers to the surface of the image carrier shortens the time during which it is formed between the image carrier and the developer carrier.

According to the second aspect of the present invention, the control means controls ON / OFF of the charging power source and the developing bias power source, and in the image forming start operation of the apparatus, the charging start end of the surface of the image carrier is the developer carrier. The voltage applied to the developer carrying member is switched from a voltage having a polarity opposite to that of the developing bias voltage to the developing bias voltage so that the charging start end of the image carrying member faces the developer carrying member. By the time it reaches, the non-charged area on the surface of the image carrier should not face the developer carrier to which the developing bias voltage is applied, and the toner of the same polarity as the developing bias voltage should be transferred to the surface of the image carrier. An electric field directed in the direction of turning is prevented from being formed between the image carrier and the developer carrier.

Further, in the image forming end operation of the apparatus, when the charging end of the surface of the image carrier faces the developer carrier, the voltage applied to the developer carrier is changed from the developing bias voltage to the developing bias voltage. Is switched to a voltage of opposite polarity, so that after the charging end of the image carrier passes the position facing the developer carrier, the non-charged region of the image carrier carries the developer carrying the developing bias voltage. The toner is not opposed to the body and an electric field in the direction in which the toner having the same polarity as the developing bias voltage is transferred to the surface of the image carrier is not formed between the image carrier and the developer carrier.

Then, the developing bias power source is turned ON / OF.
When the developing bias voltage is transiently changed by F, the absolute value of the potential of the surface of the image carrier passing through the position facing the developer carrier is set to be equal to or less than the absolute value of the developing bias voltage. By setting the ON / OFF timing of the charging power source and the switching timing of the developing bias voltage, the carrier charged to the opposite polarity to the charging potential on the image carrier while the developing bias voltage is transiently changed. Is an electric field in the direction of transfer from the developer carrier to the image carrier surface,
It is prevented from being formed between the image carrier and the developer carrier.

Further, under the condition that the absolute value of the potential on the surface of the image bearing member is not more than the absolute value of the developing bias voltage,
By setting the ON / OFF timing of the charging power source and the switching timing of the developing bias voltage so that the potential value of the surface of the image carrier and the developing bias voltage value are close to each other, the polarity of the developing bias voltage is the same. The electric field that causes the toner to transfer to the surface of the image carrier shortens the time formed between the image carrier and the developer carrier.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the present invention is applied to an electrophotographic image forming apparatus will be described below. First, the schematic configuration of the image forming apparatus according to the present exemplary embodiment will be described with reference to FIG. This image forming apparatus is provided with a drum-shaped photosensitive member 1 as an image bearing member which is rotationally driven in the direction of an arrow at a predetermined linear velocity, and around the photosensitive member 1, the photosensitive member 1 is set to a predetermined negative potential. A charging device 2 as a charging means for uniformly charging, an image exposure device 3 for irradiating a uniformly charged surface on the photoconductor 1 with light corresponding to an image to perform image exposure, a negatively charged toner and a positive polarity. A developing device 5 as a developing means having a developing sleeve 4 as a developer carrying member carrying a two-component developer containing a carrier charged in a negative direction, and a photoreceptor 1.
A transfer device 6 for transferring the above toner image onto a transfer sheet (not shown) as a transfer material, a cleaning device 7 for removing the toner remaining on the photoconductor 1 after the transfer, and a residual charge on the photoconductor 1 are removed. A static eliminator 8 and the like are provided.

The charging device 2 has a charging member (not shown) facing the surface of the photoconductor 1, and a predetermined voltage is applied to this charging member from a high voltage power source 9 as a charging power source. A developing bias voltage having the same polarity as the charging voltage is applied to the developing sleeve 4 of the developing device 5 from a high voltage power source 10 as a developing bias power source. These two high-voltage power supplies 9 and 10 are a control device 1 as a control means including a CPU, a RAM, a ROM, an I / O interface and the like.
ON / OFF control is performed at 1.

During normal image formation in the image forming apparatus having the above-described structure, the photosensitive member 1 is rotationally driven in the direction of the arrow, and the surface of the photosensitive member 1 is uniformly charged by the charging device 2 to a predetermined negative potential, for example. Light corresponding to the image is irradiated by the image exposure device 3, whereby the potential of the portion corresponding to the image is attenuated and an electrostatic latent image is formed on the photoconductor 1. The electrostatic latent image on the photoconductor 1 is developed with the negative polarity toner supplied from the developing sleeve 4 to form a toner image. The toner image on the photoconductor 1 is transferred to a transfer sheet (not shown) by the transfer device 6. The toner remaining on the photoconductor 1 after the transfer is removed by the cleaning device 7 and the residual charge is removed by the charge removing device 8, and then the toner is prepared for the next image formation.

Next, with reference to the time chart of FIG. 2, the control of the image forming apparatus having the above-described structure at the start of image formation and at the end of image formation will be described. At the start of image formation of this image forming apparatus, the start button is pressed to start the rotational driving of the photoconductor 1, and then the high voltage power source 9 for charging is turned on.
Then, uniform charging of the surface of the photoconductor 1 is started. Then, the developing bias voltage is applied to the developing sleeve 4 when the charging start end of the surface of the photosensitive member (the leading end of the charging area in the moving direction of the peripheral surface of the photosensitive member) faces the developing sleeve 4. The high voltage power supply 10 for bias is turned on.

At the end of image formation, the high-voltage power source 9 for charging is turned off to end the uniform charging of the photoconductor 1,
The high voltage power source 10 for the developing bias is turned off so that the application of the developing bias voltage is stopped when the charging end end of the surface of the photosensitive member (the rear end of the charging area in the moving direction of the peripheral surface of the photosensitive member) faces the developing sleeve 4. . After that, when the entire surface of the photoconductor 1 is discharged, the rotation drive of the photoconductor 1 is turned off. (Hereinafter, margin)

As shown in FIG. 2, by controlling ON / OFF of a high voltage power source for charging and developing bias, the non-charged area on the surface of the photoconductor is almost opposed to the developing sleeve 4 to which the developing bias voltage is applied. Since it does not occur, it is possible to reduce wasteful toner consumption due to the toner on the developing sleeve 4 transferring to and adhering to the non-charged area on the surface of the photoconductor.

Next, the high voltage power source 10 for the developing bias described above.
Change of the developing bias voltage when turning on / off the photoconductor 1 and the photoconductor 1 by turning on / off the high voltage power source 9 for charging.
ON / OF of the two high-voltage power supplies 9 and 10 set in consideration of the potential gradient at the charging start end and the charging end end
The F timing will be described.

Turning on the high-voltage power supply 10 for the developing bias
While the developing bias voltage applied to the developing sleeve 4 is changing during the transient response due to ON / OFF, the developing sleeve 4
The distance on the surface of the photoconductor that faces is generally several mm to 20.
mm. Here, the linear velocity of the photoreceptor 1 of the image forming apparatus is 10 mm / sec for the slow one and 500 mm / sec for the fast one. Further, the transient response time of the output voltage (development bias voltage) due to the ON / OFF of the high voltage power source 10 for the development bias is 10 when the output time changes from 10% to 90% of the final development bias voltage.
It is about msec to 100 msec. Photoconductor 1
Of the high voltage power supply 10 such that the distance on the photoconductor 1 facing the developing sleeve 4 does not become longer while the developing bias voltage applied to the developing sleeve 4 is transiently changed. Since the transient response time of the output voltage is designed to be short, the distance is within 20 mm even if the photosensitive member linear velocity is high.

On the other hand, the width in which the potential of the transition between the uniformly charged area and the non-uniformly charged area on the photosensitive member 1 is inclined is the high voltage power source 9 for charging. Is determined by the transient response time of the output signal depending on the ON / OFF state and the charge distribution on the photoconductor 1 by the charging device 2. The distance over which the surface of the photoconductor moves while the output signal is transiently changed by turning ON / OFF the high-voltage power supply 9 is generally several mm to 20 mm, as in the case of the developing bias. On the other hand, the charging distribution on the photoreceptor 1 by the charging device 2 is different between the contact type charging device using a charging roller or the like as a charging member and the charging device using a corona wire as a charging member. In the case of the contact type charging device, since the corona discharge is performed in a narrow area near the contact point with the photoconductor 1, the width of the charge distribution on the surface of the photoconductor 1 is narrow, about several mm. Also, in the case of a charging device in which a plurality of corona wires are arranged in the moving direction of the photoconductor surface, the width of the charge distribution on the photoconductor surface tends to be wider than the distance between the corona wires at both ends. The corona wire on the downstream side in the moving direction of the photoconductor surface is for increasing the uniformity of the electric potential by charging the corona wire to a considerable potential, and the charge distribution by the first corona wire becomes dominant. . Therefore, the width in which the charging potential is inclined is
In many cases, it is about 10 mm or less, which is almost the same as the case of a charging device equipped with one corona wire. Therefore, the width in which the charging potential at the transition between the charged area and the non-charged area on the surface of the photoconductor is inclined is several mm to 30 m.
m.

Further, the transient response of the output voltage of the high-voltage power supplies 9 and 10 varies among devices. For example, the changing speed of the developing bias voltage applied to the developing sleeve 4 during the transient response due to the ON / OFF of the high voltage power source 10 for the developing bias depends on individual variations of the high voltage power source 10 used in the apparatus,
It fluctuates due to the operating environment and temperature changes due to self-heating of the power supply.

The inclination of the charging potential at the transition between the charged area and the non-charged area on the surface of the photoconductor is different from that due to the high voltage power source 9 as in the case of the developing bias voltage, and the individual dispersion of the charging device. It also changes due to environmental changes and deterioration over time.

In addition, variations in the relative positions of the charging device 2 and the developing device 5 with respect to the photoconductor 1 caused by mechanical variation factors such as variations in layout position and parallelism are the circumferential distances on the photoconductor 1. There is about 1 mm, and the control variation by the CPU of the control device 11 is 1 mm.
There is a degree.

There are such variations in the inclination of the charging potential, variations in the inclination of the amount of developing toner on the photoconductor 1, variations in the relative positions of the charging device 2 and the developing device 5, and variations in the control. Since the variations have environmental and temporal changes, the ON / OFF timing of the high voltage power supply 9 for charging and the ON / O of the high voltage power supply 10 for the developing bias.
It is almost impossible to eliminate both toner adhesion (development) and carrier adhesion to the photoconductor 1 by adjusting the FF timing.

Therefore, in the image forming apparatus of this embodiment,
Considering the variation, these variations sacrifice toner adhesion to the photoconductor 1 to some extent, and an electric field in a direction in which carriers are not transferred and adhered to the photoconductor 1 between the photoconductor 1 and the developing sleeve 4 is generated. The ON / OFF timings of the high-voltage power supplies 9 and 10 are set with a predetermined margin so as to ensure formation. ON / OFF with too much margin
When the timing is set, toner is developed on the photoconductor 1 so that the width of a black band becomes wide, and wasteful toner consumption increases. On the contrary, the margin is calculated too small to turn ON / OFF.
If the timing is set, carrier adhesion will occur on the photoconductor 1. Therefore, it is desirable to evaluate the variations and fluctuations and set the ON / OFF timing of the high-voltage power supplies 9 and 10 with a proper margin according to the evaluation result.

3 (a) and 3 (b) respectively show the settings in which the ON timings of the high voltage power supplies 9 and 10 are set by evaluating variations and fluctuations of the transient response of the developing bias voltage and the inclination of the charging potential. It is explanatory drawing which shows an example. In the figure, the horizontal axis represents the coordinates of the surface moving direction on the photoconductor 1, and the vertical axis represents the potential (charging potential and developing bias voltage). The solid line A in the figure represents the charging potential on the photoconductor 1, and the broken line B represents the developing bias voltage when facing the photoconductor surface at each coordinate. Further, t1 and t2 on the horizontal axis are O of the high voltage power source 9 for charging and the high voltage power source 10 for developing bias, respectively.
It corresponds to N operation.

In FIG. 3A, the transient response of the developing bias voltage is relatively gradual, and the photosensitive member 1 when the high-voltage power supply 9 is turned on.
This is a setting example in the case where the width of the inclined portion of the above charging potential is wide and the above-mentioned variations and fluctuations are small. FIG. 3 (b)
Unlike the case of FIG. 3A, the transient response of the developing bias voltage is relatively steep, the width of the sloped portion of the charging potential on the photoconductor 1 when the high-voltage power supply 9 is turned ON is relatively narrow, and This is a setting example in the case where the above variations and fluctuations are large. These two
In the setting examples of the two drawings, in consideration of the above variations and fluctuations, the developing sleeve 4 is changed when the developing bias voltage is transiently changed by turning on the high voltage power source 10 for the developing bias.
Under the condition that the absolute value of the charging potential of the photoconductor 1 passing through the position opposite to the absolute value of the developing bias voltage is less than or equal to
To bring the value of the charging potential close to the value of the developing bias voltage,
The ON timing of the high voltage power supplies 9 and 10 is set.

As described above, according to the present embodiment, by appropriately evaluating the transient response of the developing bias voltage, the variation and fluctuation of the inclination of the charging potential, etc., and setting the ON timing of the high-voltage power supplies 9 and 10. While the developing bias voltage is transiently changed at the start of image formation, an electric field in which the positive carrier is transferred from the developing sleeve 4 to the surface of the photosensitive member 1 is formed between the photosensitive member 1 and the developing sleeve 4. Therefore, the carrier on the developing sleeve 4 does not adhere to the photoconductor 1 and the inside of the apparatus can be prevented from being contaminated by the carrier. Further, as shown in the above example, the high voltage power supplies 9 and 10 are turned on.
By setting the timing, it is difficult to form an electric field such that the negative polarity toner is transferred from the developing sleeve 4 to the surface of the photosensitive member 1 between the photosensitive member 1 and the developing sleeve 4, and therefore the toner to the photosensitive member 1 is prevented. Adhesion can be suppressed as much as possible to prevent wasteful toner consumption. Actually, when the width of the black band image formed by developing the negative polarity toner on the developing soot 4 on the photoconductor 1 was measured, it was about several mm to 20 mm.

Although FIGS. 3A and 3B show an example of setting the ON timing of the high voltage power supplies 9 and 10 at the start of image formation, the high voltage power supplies 9 and 10 are turned off at the end of image formation.
When the FF is performed, similarly to the ON timing, the OFF timing of the high voltage power sources 9 and 10 is set by evaluating the transient response of the developing bias voltage, the variation and fluctuation of the inclination of the charging potential and the like. More specifically, the absolute value of the charging potential of the photoconductor 1 passing through the position facing the developing sleeve 4 when the developing bias voltage is transiently changed by turning off the high voltage power source 10 for developing bias is: The high voltage power supplies 9, 10 are set so as to be smaller than the absolute value of the developing bias voltage.
Set the OFF timing of. As a result, when the high-voltage power supplies 9 and 10 are turned off, the carrier on the developing sleeve 4 does not adhere to the photoconductor 1 and the inside of the device can be prevented from being contaminated by the carrier.

Further, in the image forming apparatus of the above embodiment, when the developing sleeve 4 is at the ground potential when the high voltage power source 10 for the developing bias is turned off, the potential slightly becomes 0V or a residual potential causes a slight potential. A small amount of toner may be developed on the surface of the photosensitive body 1. In order to prevent the development of the toner, the potential difference between the surface potential of the photoconductor 1 and the potential of the development sleeve 4 is equal to that of the photoconductor 1 when the non-charged region of the photoconductor 1 faces the development sleeve 4. A voltage having a polarity opposite to the charging potential may be applied to the developing sleeve 4 so that the polarity and size are the same as when the charging region faces the developing sleeve 4.

FIG. 4 is a time chart of image forming control in the image forming apparatus in which when the non-charged area of the photosensitive member 1 faces the developing sleeve 4, the voltage is switched to a voltage having a polarity opposite to the charging polarity. At the start of image formation of this image forming apparatus, the start button is pressed to start the rotational driving of the photoconductor 1, and at the same time, the developing bias high-voltage power supply 10 is turned on.
The first developing bias voltage V1 having a polarity opposite to the charging potential
Is applied to the developing sleeve 4. After that, the high voltage power source 9 for charging is turned on to start uniform charging of the surface of the photoconductor 1. Then, when the charging start end of the surface of the photoconductor faces the developing sleeve 4, the voltage applied to the developing sleeve 4 is switched from the first developing bias voltage V1 to the normal second developing bias voltage V2. At the end of image formation, the high-voltage power supply 9 for charging is turned off to finish uniform charging of the photoconductor 1, and then applied to the developing sleeve 4 when the charging end of the surface of the photoconductor faces the developing sleeve 4. The voltage for switching is switched from the second developing bias voltage V2 to the first developing bias voltage V1. After that, when the entire surface of the photoconductor 1 is discharged, the rotation drive of the photoconductor 1 is turned off, and at the same time, the high voltage power source 10 for the developing bias is turned off.

Even when the developing bias voltage applied to the developing sleeve 4 is switched in this way, the surface of the photoconductor passing through the position facing the developing sleeve 4 when the developing bias voltage is transiently changed by the switching. Under the condition that the absolute value of the potential of is less than the absolute value of the developing bias voltage,
To bring the value of the charging potential close to the value of the developing bias voltage,
The ON / OFF timing of the high voltage power supplies 9 and 10 is set. As a result, it is possible to reliably prevent the carrier from being attached to the photoconductor 1 when the voltage is switched, and it is possible to prevent the toner from being attached to the photoconductor 1 as much as possible and prevent wasteful toner consumption.

In the above embodiment, the image forming apparatus adopting the reversal developing method in which the charge potentials of the photoconductor 1 and the toner are negative has been described, but the present invention is limited to those charge polarities. Can be applied without. For example, the present invention can be applied to the case where the reversal development method in which the charging potentials of the photoconductor 1 and the toner are positive is adopted, and the same effect can be obtained.

[0043]

According to the first and second aspects of the invention, the developing bias voltage is transient when the developing bias power source is turned on / off or the developing bias voltage is switched in the image forming start operation and the image forming end operation. While changing, the electric field in the direction in which the carrier charged with the opposite polarity to the charging potential on the image bearing member is transferred from the developer bearing member to the surface of the image bearing member is generated between the image bearing member and the developer bearing member. Since it is not formed during this period, the carrier on the developer carrying member does not adhere to the image carrying member, and there is an effect that contamination of the inside of the apparatus by the carrier can be prevented.

Further, when the developing bias power source is turned ON / OFF or the developing bias voltage is switched in the image forming start operation and the image forming end operation, the toner having the same polarity as the developing bias voltage is transferred to the surface of the image carrier. Since the time during which such an electric field is formed is shortened, there is an effect that toner adhesion to the image carrier can be suppressed as much as possible and wasteful toner consumption can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment.

FIG. 2 is a time chart of control of the image forming apparatus.

3A and 3B are explanatory diagrams showing a relationship between a change in charging potential of a photoconductor of the image forming apparatus and a change in developing bias voltage.

FIG. 4 is a time chart of control of the image forming apparatus according to the modified example.

[Explanation of symbols]

 1 Photoreceptor 2 Charging Device 4 Developing Sleeve 5 Developing Device 9 High Voltage Power Supply for Charging 10 High Voltage Power Supply for Development Bias 11 Control Device

Claims (2)

[Claims] 1. A charging member having a charging member for uniformly charging the surface of the image bearing member, a charging power source for applying a voltage to the charging member, and a surface of the image bearing member charged by the charging unit. Exposure means that forms an electrostatic latent image on the image carrier by image-exposure-damping the potential, toner charged to the same polarity as the charging polarity of the charging means, and carrier charged to the opposite polarity to the charging polarity. An image forming apparatus provided with a developer carrying member carrying a two-component developer containing a and a developing means having a developing bias power source for applying a developing bias voltage having the same polarity as the charging polarity to the developer carrying member, When the charging start end of the image carrier surface faces the developer carrier, application of a developing bias voltage to the developer carrier starts, and the charging end end of the image carrier surface is the developer carrier. The developing bias when facing the body Turn on the charging power source and the developing bias power source so that the voltage application is stopped.
A control means for controlling ON / OFF of the image carrier is passed through a position facing the developer carrier when the developing bias voltage is transiently changed by ON / OFF of the developing bias power source. Under the condition that the absolute value of the surface potential is equal to or less than the absolute value of the developing bias voltage, the charging power source and the charging power source and the charging power source are set so that the surface potential value of the image carrier and the developing bias voltage value are close to each other. An image forming apparatus characterized in that an ON / OFF timing of a developing bias power source is set. 2. A charging member having a charging member for uniformly charging the surface of the image carrier and a charging power source for applying a voltage to the charging member, and a surface of the image carrier charged by the charging device. Exposure means that forms an electrostatic latent image on the image carrier by image-exposure-damping the potential, toner charged to the same polarity as the charging polarity of the charging means, and carrier charged to the opposite polarity to the charging polarity. An image forming apparatus provided with a developer carrying member carrying a two-component developer containing a and a developing means having a developing bias power source for applying a developing bias voltage having the same polarity as the charging polarity to the developer carrying member, The developing bias voltage applied to the developing bias power source when the developer carrier faces the charged area of the image carrier surface, and the developer carrier body faces the uncharged area of the image carrier surface. The development applied when A voltage having a polarity opposite to that of the bias voltage is switched and applied, and when the charging start end of the surface of the image carrier faces the developer carrier and the charging end end of the surface of the image carrier is the developing device. A control means for controlling the charging power source and the developing bias power source is provided so that the developing bias voltage is switched when facing the agent carrier, and the developing bias voltage is changed by switching the developing bias voltage. Under the condition that the absolute value of the potential of the surface of the image carrier passing through the position facing the developer carrier when changing is equal to or less than the absolute value of the developing bias voltage,
An image forming apparatus characterized in that the ON / OFF timing of the charging power source and the switching timing of the developing bias voltage are set so that the value of the potential on the surface of the image carrier and the developing bias voltage value are close to each other. .