JP2002091095A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To discharge a specified amount of developer outside a developer only by making a fogging potential difference (a potential difference between the surface potential of a photoreceptor and the voltage applied on a developing roller) variable in a controlling system of image formation operation. SOLUTION: This image forming device is provided with the photoreceptor, an electrifying part which uniformly electrifies the photoreceptor and applies a potential on the surface of the photoreceptor, an exposing part which forms an electrostatic latent image on the photoreceptor, a developing part which develops the electrostatic latent image with the developing roller by using a two-component developer comprising toner and magnetic carriers and makes the electrostatic latent image a toner picture, a transferring part which transfers the toner picture to a transfer paper, a cleaning part which recovers the developer remaining on the photoreceptor, a supplying part which supplies the developer to the developing part, a first electric power source which applies a developing bias voltage to the developing roller, a second electric power source which applies the voltage for determining the photoreceptor surface potential to the electrifying part and a controlling part which controls at least the output of one side of the first and the second electric power sources and adjusts the potential difference between the developing bias voltage and the photoreceptor surface potential. Therein, the controlling part adjusts the potential difference at the time of non-development of the developing part, and the developer, which has the same amount with the supplied developer, is attached to the photoreceptor and is forcibly discharged from the developing part.

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 an electrophotographic copying machine, a printer, and a facsimile machine, and more particularly, to an electrophotographic image forming apparatus equipped with a developing device of a successive developer exchange type. The present invention relates to an image forming apparatus for forming.

[0002]

2. Description of the Related Art Conventionally, as one of typical image forming apparatuses using an electrophotographic method, such as a copying machine and a printer, a method for visualizing an electrostatic latent image formed on a photosensitive member is known. There is known an image forming apparatus provided with a developing device (two-component developing device) using a two-component developer in which a toner and a carrier are mixed.

In a configuration using a two-component developer, as is well known, as the image forming operation (copying or printing operation) is repeatedly performed, the developer contained in the developing device is Only the toner inside is sequentially consumed. That is, the ratio of the toner in the developer decreases over time, and the ratio of the carrier increases.

Further, in the configuration using the two-component developer, if the image forming operation is continued in a state where the ratio of the carrier is increased as described above, the carrier gradually becomes fatigued in the developing device, for example, the toner filming. Crushing, breakage of the coating applied to the surface of the carrier, and the like. As a result, there is a problem that the developing ability of the developer is greatly reduced. Therefore, a method of exchanging the developer in the developing device has been conventionally used, and the following two types are available as a method of forming an image while exchanging the developer.

[0005] 1. Sequential developer exchange method A method in which a discharge device that constantly discharges a fixed amount of developer to the outside of the developing device is provided, and an image is formed while a new developer corresponding to this amount is supplied. In this method, the developer is constantly replaced and updated in the developing device. Techniques related to this method include, for example, a developing device disclosed in Japanese Patent Publication No. 2-15991 and Japanese Patent Application Laid-Open No. 6-250524.

[0006] 2. Batch developer exchange method All the developer contained in the developing device is periodically and collectively discharged out of the device, and a new developer corresponding to this amount is supplied instead. During the period other than the periodical replacement of the developer, the replacement or renewal of the developer is not performed.

[0007]

However, such a conventional developer exchange method has the following problems. 1. Developer Sequential Exchange Method Since a constant amount of developer must be constantly discharged out of the developing device, the configuration of the discharging mechanism becomes very complicated. In addition, a separate drive mechanism must be provided for the developing device in order to drive the discharge mechanism, thereby increasing the mechanical load on the developing device. Furthermore, since the configuration of the discharge mechanism is extremely complicated, problems are likely to occur in terms of cost and manufacturing process. Conversely, when a relatively inexpensive and simple discharge mechanism is used, it is difficult to control the amount of developer discharged, that is, to control the discharge of the developer by a fixed amount with high accuracy.

[0008] 2. Developer batch replacement method All the developers contained in the developing device are replaced regularly, so the image forming device must be stopped for the period required for the replacement. Or a reduction in image forming speed. In addition, in order to smoothly discharge the developer and shorten the stop period, it is necessary to provide a relatively large opening for discharging the developer in the developing device. When such an opening having a large size is provided, it is difficult to secure the strength of the developing device itself,
Further, the configuration of the developing device is complicated, for example, it is necessary to provide an opening / closing mechanism at the discharge opening.

The present invention has been made in view of such circumstances, and efficiently and automatically replaces a developer contained in a developing device, and has a structure of an entire apparatus including a developing device. An object of the present invention is to provide an image forming apparatus capable of forming a high-quality image with a simple structure.

[0010]

SUMMARY OF THE INVENTION The present invention provides a photoconductor,
A charging unit for uniformly charging the photoconductor and applying a potential to the surface of the photoconductor, an exposure unit for forming an electrostatic latent image on the photoconductor, and a two-component developer including a toner and a magnetic carrier, which is electrostatically charged by a developing roller. A developing unit that develops the latent image into a toner image,
A transfer unit for transferring a toner image onto transfer paper; a cleaning unit for collecting the developer remaining on the photoreceptor; a supply unit for supplying the developer to the development unit; and a first power supply for applying a development bias voltage to the development roller A second power supply for applying a voltage for determining the photoconductor surface potential to the charging unit; and controlling at least one output of the first and second power supplies to reduce a potential difference between the developing bias voltage and the photoconductor surface potential. And a control unit for adjusting the voltage difference when the developing unit is not developing,
An object of the present invention is to provide an image forming apparatus in which substantially the same amount of developer as replenished developer is adhered to a photoreceptor and is forcibly discharged from a developing unit.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The photoreceptor of the present invention includes, for example, a drum-shaped or belt-shaped substrate having an organic photoconductive photosensitive layer (OPC layer), a photosensitive layer such as amorphous silicon or selenium formed on the surface thereof. Can be used. For example, a corona discharger is used for a charging unit that uniformly charges the photoconductor. The exposure unit emits, for example, light obtained by exposing and scanning a document, or a beam obtained by modulating a light beam from a laser light source or an LED light source with image data, and a conventionally known one can be used. The developing unit has a configuration in which a two-component developer stored in advance is charged to charge each component with a different polarity, and is supplied to the photoconductor by a developing roller.

The two-component developer uses a powder obtained by mixing a toner and a magnetic carrier as a developer, and its mixing ratio is about 1.5 to 20% by weight of the toner. The developing roller is composed of, for example, a plurality of fixed magnets and a non-magnetic sleeve that rotates around the fixed magnets.
m) is placed. The developing roller forms a magnetic brush with a magnetic carrier on the surface of the sleeve, and adheres the toner to the electrostatic latent image on the photosensitive member via the magnetic brush. The transfer unit may be a conventional electrostatic transfer type using corona discharge or a transfer roller type.

A conventionally known contact type or non-contact type cleaning unit can be used. The replenishing unit is for replenishing the two-component developer consumed in the developing unit, and the mixing ratio of the toner and the magnetic carrier of the replenishing developer is usually 70.
About 90% by weight of toner. As the first power supply and the second power supply, for example, a variable output DC power supply including an inverter, a step-up transformer, and a rectifier can be used.

In the present invention, the control section may control the output of the first power supply to increase the potential difference between the developing bias voltage and the surface of the photoconductor, thereby forcibly discharging the developer. Thereby, the potential of the developing roller shifts in the direction of the normal charging polarity of the magnetic carrier, or is adjusted to the same polarity as the normal charging polarity. Therefore, as a force applied to the developer, an electric repulsive force (repulsive force) exceeds the magnetic attraction force of the developing roller. Therefore, the developer held by the developing roller easily moves toward the photoconductor, and the developer can be more reliably discharged out of the developing device.

Further, the control section may control the output of the second power supply to increase the potential difference, thereby forcibly discharging the developer. Thereby, the surface potential of the photoconductor is adjusted so as to have a polarity opposite to the normal charging polarity of the magnetic carrier (that is, a potential on a white background). Therefore, the force applied to the developer is greater than the magnetic attraction of the developing roller.
The electrical attraction of the photoreceptor will be greater. Therefore, the developer held by the developing roller moves more easily toward the photoconductor, and the developer can be more reliably discharged out of the developing device.

The control section may control the outputs of the first and second power supplies to increase the potential difference, thereby forcibly discharging the developer. As a result, the potential of the developing roller can be adjusted so as to have the same polarity as the normal charging polarity of the magnetic carrier, so that the force applied to the developer is higher than the magnetic repelling force of the developing roller by the electric repulsive force. become. In addition, since the surface potential of the photoreceptor can be adjusted so as to have a polarity opposite to the normal charging polarity of the magnetic carrier, the force applied to the developer is an electric attraction rather than a magnetic attraction of the developing roller. Will exceed. That is,
Electric repulsive force against the developing roller and electric attractive force against the photoreceptor act on the developer, and the synergistic effect of these causes the developer held by the developing roller to quickly move toward the photoreceptor. Moving. As a result, the developer can be more reliably discharged out of the developing device.

Further, the control section may control the output of the first and second power supplies so that the polarity of the photoconductor surface potential and the polarity of the developing bias voltage are opposite to each other, and forcibly discharge the developer. Thereby, the fog potential difference, that is, the difference value between the surface potential of the photoconductor and the potential of the developing roller can be shifted to a side lower than the fog potential difference during normal image formation. That is, the potential applied to the developing roller becomes the same polarity as the normal charging polarity of the magnetic carrier so that the magnitude relationship between the magnetic attraction force and the electric repulsion force of the developing roller is reversed. As a result, the developer held by the developing roller easily moves toward the photoconductor. Therefore, depending on the setting of the fog potential difference, the electric repulsion generated by the developing roller can be changed, and the amount of the developer discharged to the outside of the developing device can be adjusted quantitatively.

Further, the control section may adjust the potential difference during a non-developing period before or after the developing period of the electrostatic latent image to forcibly discharge the developer. As a result, the timing of forcibly discharging the developer is adjusted to the non-image forming period, so that the operation rate and the image forming speed of the image forming apparatus are not particularly reduced, and the normal image forming operation state is secured. However, it is possible to reliably discharge the developer.

The present invention may further comprise a charge removing section for removing charges on the surface of the photosensitive member, and the unnecessary developer on the photosensitive member from which the charges have been removed may be collected by the cleaning section. As a result, the charge eliminator charges the surface of the photoconductor before the cleaning process to improve the cleaning effect by weakening the attraction force between the residual toner and foreign matters and the photoconductor, and also forcibly discharges the developer by discharging the developer. Reduces the adsorbing power of surplus developer on the surface. Therefore, the surplus developer on the surface of the photoreceptor can be efficiently collected by the cleaning unit.

According to the present invention, in the image forming apparatus, when image formation is continuously performed on a plurality of transfer papers and the developing unit develops each image, the control unit performs development of one image and the next. The developer may be forcibly discharged by adjusting the potential difference between the developing process and the developing process. Thus, when the image forming operation is continuously performed on a plurality of sheets, the developer can be forcibly attached to the photoconductor and can be forcibly discharged out of the developing device by adjusting the bias voltage during the transfer period of the transfer sheet.
Therefore, when performing continuous copying, it is not necessary to provide a special period for forcibly discharging the developer in order to maintain the image quality. Can be maintained.

In this case, it is preferable that the control section controls the output of the first power supply to increase the potential difference, thereby forcibly discharging the developer. Thereby, in order to form a continuous image, the potential of the developing roller shifts in the direction of the normal charging polarity of the magnetic carrier or can be adjusted so as to have the same polarity as the normal charging polarity. The agent can be easily moved toward the photoreceptor.

As shown in FIG. 1, the image forming apparatus according to the present invention comprises a drum-shaped photosensitive member 1 having an organic conductive photosensitive layer and rotating in the direction of arrow A, a charger 2, an exposure unit 3, a developing device 4, a transfer device 5a, a peeling device 5b, a pre-cleaning neutralizer 6, a cleaning device 7, and an image forming unit in which a neutralizer (not shown) is provided in this order. The image forming unit may be provided with a configuration other than these.

The developing device 4 is provided with a developing roller 4a opposed to the surface of the photoconductor 1, and a developer hopper for replenishing the developing device 4 with a new developer (hereinafter referred to as a replenishing developer). 4b is provided above.
Further, the control unit 1 controls the image forming operation of the image forming unit.
0, and in particular, as shown in FIG.
Reference numeral 0 denotes a replenishing motor for replenishing the replenishing developer from the developer hopper 4b, a developing motor for driving the developing roller 4a, outputs of power supplies P1 and P2, and outputs from a developer concentration detector and a copy start switch (not shown). Control. The power supplies P1 and P2 are variable output DC high voltage power supplies.
The developing bias voltage a is determined, and the surface potential of the photoconductor 1 is determined by the output of the power supply P2. The power supply P1 can change not only the magnitude of the output but also the polarity of the output.

The image forming operation in such a configuration will be described. As shown in FIG. 2, first, the charger 2 uniformly charges the surface (in FIG. 2, the negative charge is applied) in accordance with the voltage applied from the power source P2. Photoreceptor 1 given)
Receives an exposure corresponding to the document at the exposure unit 3 such as an LSU or an LED, and forms an electrostatic latent image corresponding to the document on the front surface. Next, the developing roller 4a supplies toner to the surface of the photoconductor 1, whereby the electrostatic latent image on the surface of the photoconductor 1 is developed into a toner image (visible).

The developing roller 4a has a known structure having a magnet inside. The developer supplied to the surface of the developing roller 4a is regulated so as to always have an appropriate amount by a developer regulating member (not shown) arranged in the main body of the developing device 4. The developer is transferred and circulated to the developing roller 4a while being stirred by the stirring member, the developer guide member, the developer transfer screw, and the like in the main body of the developing device 4. The developer concentration (mixing ratio of toner and carrier) is detected by a developer concentration detector (not shown). As the developer concentration detector, a conventionally known detector for detecting the magnetic permeability of the developer is suitably used.

Next, the transfer device 5a transfers the toner image on the surface of the photoconductor 1 obtained by development onto a transfer paper (not shown) conveyed from a paper supply unit (not shown). The transfer device 5a is of an electrostatic transfer type, in which a discharge device for generating a DC corona discharge is disposed so as to face the photoreceptor 1 via the transfer paper, and a DC corona discharge is applied to the transfer paper from the back side. Thus, the toner image carried on the surface of the photoreceptor 1 is transferred onto transfer paper.

The transfer paper on which the toner image has been transferred by the transfer device 5a is separated from the photoreceptor 1 by a separation device 5b and sent to a fixing device (not shown). Here, when the fixing process is performed to form a fixed toner image on the transfer paper, the transfer paper is discharged out of the apparatus.

On the other hand, foreign matters such as toner remaining on the surface of the photoconductor 1 after the transfer process and paper dust adhering to the surface of the photoconductor 1 are cleaned and collected by the cleaning device 7. The cleaning device 7 has a cleaner blade 7a that is arranged in contact with the surface of the photoreceptor 1, and this blade 7a
The residual toner is scraped off by rubbing the surface of the photoconductor 1 with a. The cleaning device 7 is provided with a transfer screw 7b and the like in addition to the cleaner blade 7a, and foreign matters such as residual toner and paper dust scraped off from the surface of the photoreceptor 1 are transferred to a storage container (not shown) by the transfer screw 7a. Where the residual toner and paper dust are stored. Further, the surface of the photoconductor 1 whose surface has been cleaned by the cleaning device 7 is erased by an unillustrated static eliminator, and is uniformly charged again by the charger 2.

Here, the pre-cleaning static eliminator 6 normally performs AC + DC charging on the surface of the photoconductor 1,
The cleaning device 7 is provided to reduce the attraction force between the foreign material such as residual toner and paper powder remaining on the photosensitive member 1 and the photosensitive member 1 to improve the cleaning efficiency of the cleaning device 7.
However, the pre-cleaning static eliminator 6 may not be necessary in an apparatus having a low image forming processing speed.

The developing device 4 employs a two-component magnetic brush developing system. Therefore, the developer used is a two-component developer composed of a toner and a magnetic carrier, and the mixing ratio of the toner and the magnetic carrier is usually 1.5 to 5.0.
Toner weight%. Also, the developer hopper 4b
The replenishing developer replenished from also comprises a toner and a magnetic carrier, and the mixing ratio of the toner and the magnetic carrier is:
Usually, it is 70 to 90% by weight of the toner.

In the image forming apparatus having the above structure, when a plurality of image forming operations (copy / print) progress and the toner concentration of the developer in the developing device 4 decreases, the control of the control section 10 causes the developer hopper 4b Supplies a new supply of developer. Specifically, a developer supply roller 4c provided between the developer hopper 4b and the main body of the developing device 4 is rotated by a drive motor or the like, and the developer supply roller 4c is rotated.
A fixed amount of the replenishing developer is supplied into the developing device 4 by a groove provided in a part around c. At this time, based on the detection by the developer concentration detector described above, the control unit 10
Keeps the concentration of the developer in the developing device 4 at a predetermined concentration. The supply of the replenishment developer stored in the developer hopper 4d to the developer supply roller 4c is performed by a transfer / stirring member (not shown).

In this type of image forming apparatus, as described above, as the image forming operation (copy or print) is repeatedly performed, the toner in the developer housed in the developing device 4 is discharged. The developer is sequentially consumed, and the ratio of the magnetic carrier in the developer gradually increases.
If the image forming operation is continuously performed in a state where the ratio of the magnetic carrier is increased, the carrier in the developing device 4 gradually becomes fatigued, and is subjected to, for example, toner filming, crushing, and the surface of the magnetic carrier. This causes problems such as breakage of the coated film, and the developing ability of the developer is greatly impaired.

In order to avoid the above problem and always maintain the developing ability of the developer in the developing device 4 at a predetermined level, the magnetic carrier excessively present in the developer must be removed from the developing device 4 in a timely manner. It is necessary to discharge and always supply new developer (supplementary developer). According to the present invention, in carrying out this basic principle, the surplus developer whose developing ability is being impaired is discharged from the developing device 4 to the outside of the developing device 4 without providing a special developer discharging mechanism.

More specifically, according to the present invention, the fogging potential difference indicated by the potential difference between the surface potential of the photosensitive member 1 and the developing bias voltage applied to the developing roller 4a is variably controlled by the control unit 10 for controlling the image forming operation. By,
The surplus developer in the developing device 4 and deteriorating the developing ability is adhered to the photoreceptor 1 so as to be almost the same amount as the replenishment developer, and is forcibly discharged to the outside of the developing device 4. The developer is collected by the cleaning device 7. If this method is used, a fixed amount of developer can be discharged out of the developing device 4 only by changing the fog potential difference in the control system of the image forming operation. Therefore, it is not necessary to provide a special mechanism for discharging the developer from the developing device in the image forming apparatus of the successive developer replacement type, and the existing configuration of the developing device can be used. . The method of discharging the developer will be described in more detail below.

FIG. 3 is a timing chart for explaining the image forming operation of a typical image forming apparatus. This operation represents an operation in a so-called single mode in which copying is performed on one transfer sheet. For the toner in the developer, an optimum fog potential difference for preventing the toner from unnecessarily adhering to the photoconductor 1 and a developing potential for adhering the toner to the photoconductor 1 are defined. I have. Note that the toner used in this description is a negatively charged toner, and the higher the developing potential indicated by the reference numeral VI (closer to the + side), the larger the amount of adhesion becomes. The higher the value, the more difficult it is to adhere.

However, these are toners having normal charge polarity, and in the case of a magnetic carrier charged to a positive polarity opposite to the charge polarity of the toner, undesired adhesion to the photoreceptor occurs. This may cause damage to the surface of the photoreceptor as carrier adhesion (also referred to as carrier pulling or carrier rising), and is not generally welcomed.

Therefore, as shown in FIG. 4, the adhesion of the uncharged toner and the positively charged toner when the fog potential difference which is the difference between the surface potential Vo of the photosensitive member 1 and the bias voltage Vb to the developing roller 4a is changed. , As well as the carrier adhesion. When the fog potential difference is -150 V, the adhesion of the uncharged toner and the positively charged toner is minimized, and the undesired adhesion of the magnetic carrier to the photoreceptor 1 is increased when the fog is higher than -250 V. ing. Thus, in the example of the toner shown in FIG. 3, the surface potential Vo is set to −550 V, and the bias voltage Vb
Is set to -400V.

Accordingly, in the normal image forming operation, as shown in FIG. 3, the surface potential Vo of the photosensitive member 1 which is a high potential on the minus side is started (timing a), and then the surface potential Vo is increased. Rises to -150 V (timing b), application of the developing bias Vb is started while maintaining the fog potential difference of -150 V. Vo = -5
50V, Vb = -400V is reached (timing c),
After a lapse of a predetermined time, an image area is formed. In this image area, the original image is irradiated on the photoconductor 1, a portion to which toner is to be attached rises to the developing potential VI, and when the image area ends, the fog potential difference is reduced. While maintaining this, the surface potential Vo and the bias voltage Vb of the photoreceptor 1 are both increased until they reach zero level (timings e and f).

On the other hand, in the present invention, the developer is forcibly discharged by reversing the method of preventing the carrier from adhering to the photosensitive member 1. That is, when the developer is forcibly discharged, the uncharged toner, the oppositely charged toner, and the magnetic carrier are efficiently removed from the photosensitive member 1 in a manner opposite to the normal image forming operation.
It needs to be attached to the surface. Therefore, as shown in FIG. 4, the fog potential difference is −300 V or more, preferably −30 V or more.
When the voltage is set to 0 V, all of the uncharged toner and the oppositely charged toner magnetic carrier can be efficiently attached to the surface of the photoconductor 1.

As a specific method of forcibly adhering the surplus (fatigue) developer existing in the developing device 4 to the photoreceptor 1,
(1) A method in which the magnetic carrier in the developer is repelled from the developing roller 4a to make it easier to separate, and the carrier is pushed into the photoconductor 1 side. (2) A method in which the magnetic carrier in the developer is easily attracted to the photoconductor 1 side. , And the like.

(1) The method of setting the developing bias of the developing roller 4a to a bias that easily separates the magnetic carrier in the developer from the developing roller 4a and pushing the carrier from the developing roller 4a toward the photosensitive member 1 is performed by the control unit 10 By changing the voltage applied to the developing roller 4a in the direction of the normal charge polarity of the magnetic carrier (in this case, the plus direction) or by completely switching the voltage to the same polarity (in this case, the plus polarity), the developing roller 4a Of the photoconductor 1
Is controlled so as to be higher than the surface potential.

As a result, when viewed from the developing roller 4a side, the electric repulsive force (repulsive force) exceeds the magnetic attraction force of the developing roller 4a as a force applied to the developer. As a result, the developer held by the developing roller 4a, in particular, the magnetic carrier having a positive polarity repels, so that the entire developer is easily moved toward the photoreceptor 1 and the developer is more reliably moved out of the developing device 4. Can be discharged.

Further, the above-described pre-cleaning static eliminator 6
Operates to reduce the attraction force between the residual toner and foreign matters and the photoconductor 1 by charging the surface of the photoconductor 1, but it is preferable to use this also for forcibly discharging the developer. That is, the developer is forcibly discharged, and the photosensitive member 1
In the state where the surplus (fatigue) developer is attached to the surface, the attraction force between the photoreceptor 1 and the surplus developer is weakened by the pre-cleaning neutralizer 6. As a result, the surplus developer on the surface of the photoconductor 1 can be efficiently collected by the cleaning device 7.

When a transfer roller is used as the transfer device 5a instead of the electrostatic transfer system, the excess developer is forcibly attached to the surface of the photosensitive member 1 and then collected by the cleaning device 7. At this time, it is preferable to separate the transfer roller from the photoconductor 1. by this,
Adhesion of the surplus developer on the surface of the photoconductor 1 is not hindered by the transfer roller, and conversely, the developer does not adhere to the transfer roller. Therefore, the reliability of the operation of collecting the surplus developer can be further improved.

As a specific control of the method (1), the developing bias amount of the developing roller 4a is set at the time of normal image formation and at the time of collecting the developer (at the time of forcibly attaching the developer to the photoconductor).
And can be changed. Specifically, while the developing bias amount during normal image formation is set to about −100 to −400 V, the developing bias amount during developer collection is set to −
The voltage is set to 100 V or higher, or the polarity of the developing bias is switched to reverse polarity (positive polarity).

(2) In the technique of increasing the potential of the electrostatic latent image on the photosensitive member 1 before development to attract magnetic carriers in the developer to the photosensitive member 1 side, the control section 10 develops the developer. When the photoconductor 1 is discharged to the outside of the apparatus 4, the surface potential of the photoconductor 1 is maintained at the potential after the exposure is attenuated, or the surface potential is changed in a direction opposite to the normal charging polarity of the magnetic carrier (that is, a direction of the potential on the white background side). To control. That is, the potential of the photoconductor 1 is maintained in the opposite polarity direction to the charging polarity of the magnetic carrier.

As a result, when viewed from the photosensitive member 1 side, the force applied to the developer is greater than the magnetic attraction force of the developing roller, that is, the electric attraction force of the photosensitive member. Therefore, the developer held by the developing roller, particularly the magnetic carrier having a positive polarity, is easily sucked.
Becomes easier to move toward the photoconductor, and the developer can be more reliably discharged out of the developing device.

As a specific control of the above method (2), a bias amount (charging potential) of a charging bias of the photosensitive member 1 is used.
Can be changed between normal image formation and developer collection (when the developer is forcibly attached to the photoconductor 1). In particular,
The charging bias amount during normal image formation is -600 to
While the voltage is set to about -800 V, preferably -700 to -800 V, the charging bias amount at the time of collecting the developer is set to-
Set to about 850-1100V.

In the present invention, more preferably, both of the above methods (1) and (2) are used. As a result, two effects, an electric repulsive force on the developing roller and an electric attractive force on the photoconductor, act on the developer, and the developer held by the developing roller is directed toward the photoconductor by a synergistic effect of the two. Move quickly. As a result, the developer can be more reliably discharged out of the developing device.

As described above, in the present invention, the control unit 1
By the control of 0, the developer substantially the same amount as the newly supplied replenishment developer is forcibly attached to the surface of the photoconductor 1 and is forcibly discharged out of the developing device. Therefore, the developer can be easily discharged out of the developing device 4 only by changing the fog potential difference. In addition, since the developer held over substantially the entire length of the developing roller 4a can be uniformly attached to the surface of the photoconductor 1, the amount of the developer forcedly discharged from the developing device 4 can always be quantified. Will be possible. Therefore, the developer can be quantitatively discharged only by changing the control of the control system. Further, since there is no need to separately drive a mechanism such as a constant-rate discharging mechanism, the mechanical load associated with the operation of the developing device 4 can be minimized.

In the present invention, the control unit 10
However, when the developer is discharged to the outside of the developing device 4, it is preferable to control so that a fog potential difference lower than that during image formation is set. That is, the fog potential difference, that is, the difference value between the surface potential of the photosensitive member and the potential of the developing roller, is shifted to a lower side than the fog potential difference during normal image formation. In other words, the potential applied to the developing roller is set to the same polarity as the normal charging polarity of the magnetic carrier in order to reverse the magnitude relationship between the magnetic attraction force and the electric repulsive force of the developing roller.

As a result, the developer held by the developing roller easily moves toward the photosensitive member. Therefore, depending on the setting of the fog potential difference, the electric repulsion generated by the developing roller can be changed, and the amount of the developer discharged to the outside of the developing device can be adjusted quantitatively.

Further, in the present invention, the control unit 10 controls the timing of forcibly discharging the developer to the outside of the developing device 4 so as to coincide with the non-image forming period of the pre-rotation or post-rotation of the photosensitive member. Is preferred. As a result, the timing of forcibly discharging the developer is synchronized with the non-image forming period, so that the operating rate and the image forming speed of the image forming apparatus are not particularly reduced, and the normal image forming operation state is secured. However, it is possible to reliably discharge the developer. As the non-image forming period, the photosensitive member 1
During pre-rotation or post-rotation.

[Embodiment 1] An embodiment 1 in which the developer is forcibly discharged using the above methods (1) and (2) will be described. As described above, in the present invention, the developer is forcibly discharged at the time of non-image formation. Therefore, the control for forcibly discharging the developer at the time of the front rotation of the photoreceptor 1, at the time of the post rotation, and both of them is performed. The control by the unit 10 will be described. The description of this embodiment all refers to an operation in a so-called single mode in which copying is performed on one transfer sheet.

First, as shown in FIG. 5, a case where the developer is forcibly discharged at the time of the pre-rotation of the photosensitive member 1 (immediately before the copying operation) will be described. Main switch (power switch of image forming apparatus), charging bias (photoconductor surface potential),
Development motor and development bias (development bias voltage)
Comparing the respective timing charts, after the main switch is turned on, the charging bias of the photoconductor 1 is set to -850 to -1100 V, which is a value for forced discharge.
become. At this point, the developing motor is in the OFF state, and the developing bias of the developing roller 4a also remains at ± 0.

Thereafter, the charging bias is changed to the forced discharge value (−8).
The developing bias is also a value for forced discharge while the pulse of 50 to -1100 V) is shown. It becomes -100 V or more, or its polarity is switched from minus to plus. Then, the developing bias is changed to the forced discharge value (−100).
V or higher polarity)
The charging bias becomes ± 0, and the pulse of the forced discharge value disappears.

Then, when the copy is started, that is, when the image forming operation is turned on, the charging bias is reduced to a normal value of -700.
On the other hand, the developing bias shows a normal value of -100 to -400 V from the forced discharge value. At this time, the developing motor is also turned on. Then, when the copy end, that is, when the image forming operation is completed, the charging bias becomes ± 0, and after a short delay, the developing motor is turned off and the developing bias becomes ± 0.

As described above, before the copy starts,
By setting the charging bias to -850 to 1100 V (that is, the method (2)) and setting the developing bias to -100 V or more or a positive polarity (that is, the method (1)), the developer is supplied from the developing device 4 during non-image formation. Can be forcibly discharged.

Next, as shown in FIG. 6, the case where the developer is forcibly discharged at the time of post-rotation of the photosensitive member 1 (immediately after the copying operation) will be described. As shown in FIG. 6, even after the main switch is turned on, until the copy starts,
Both the charging bias and the developing bias are ± 0,
The developing motor is also in the OFF state. Then, when the copy is started, that is, when the image forming operation is turned on, the charging bias shows the normal −700 to −800 V, the developing bias also shows the normal −100 to −400 V, and the developing motor also turns on.

At the end of copying, that is, when the image forming operation is completed, the charging bias once becomes ± 0, and shortly thereafter, the value for forced discharge is −850 to −1100.
V. On the other hand, the developing bias and the developing motor maintain the state at the time of image formation for a short time even after the copy end. That is, the developing motor remains ON and the developing bias remains at the normal value.

Thereafter, while the charging bias indicates the pulse of the forcible discharge value, the developing motor is turned off, and at the same time, the developing bias becomes -100 V or more, which is the forcible discharge value, or its polarity changes from minus to plus. Is switched to. Thereafter, while the charging bias further indicates the pulse of the forced discharge value, the developing bias becomes ± 0, and shortly thereafter, the charging bias also becomes ± 0.

As described above, immediately after the copy end, the charging bias is set to −850 to 1100 V (that is, the method (2)), and the developing bias is set to −100 V.
The developer can be forcibly discharged from the developing device 4 at the time of non-image formation by making the above or the positive polarity (that is, the method (1)).

Next, a case will be described in which the developer is forcibly discharged during the pre-rotation of the photosensitive member 1 immediately before and after the copying operation. As shown in FIG. 7, when the main switch is turned on, the charging bias of the photoconductor 1 soon becomes -850 to -1100 V, which is a value for forced discharge. At this time, the developing motor is in the OFF state, and the developing roller 4a
Also remain at ± 0.

Thereafter, the charging bias is changed to the forced discharge value (−8).
While a pulse of (50 to -1100 V) is shown, the developing bias also becomes -100 V or more, which is the value for forced discharge, or its polarity is switched from minus to plus. Then, the developing bias is changed to the forced discharge value (−100 V
While the pulse of the above (or positive polarity) is shown, the charging bias becomes ± 0, and the pulse of the forced discharge value in the developing bias disappears. Then, when the copy is started, that is, when the image forming operation is turned on, the charging bias indicates the normal −700 to −800 V, while the developing bias indicates the normal −100 to −400 V from the forced discharge value. At this time, the developing motor is also turned on.

At the end of copying, that is, when the image forming operation is completed, the charging bias once becomes ± 0, and shortly thereafter, the value for forced discharge, −850 to −1100.
V. On the other hand, the developing bias and the developing motor maintain the image forming state for a short time even after the copy end. That is, the developing motor remains ON and the developing bias remains at the normal value.

Thereafter, while the charging bias indicates the pulse of the forced discharge value, the developing motor is turned off, and at the same time, the developing bias becomes -100 V or more, which is the forced discharge value, or the polarity thereof changes from minus to plus. Is switched to. Thereafter, while the charging bias further indicates the pulse of the forced discharge value, the developing bias becomes ± 0, and shortly thereafter, the charging bias also becomes ± 0.

As described above, before the copy starts,
The charging bias is set to −850 to 1100 V (that is, method (2)), and the developing bias is set to −100 V or more or a positive polarity (that is, method (1)).
Further, immediately after the copy end, the charging bias is set to −850 to 1100 V (that is, the method (2), and the developing bias is set to −100 V or more or positive polarity (that is, the method (1) is used). In some cases, the developer can be forcibly discharged from the developing device 4 more reliably.

[Embodiment 2] Embodiment 2 using the above-mentioned methods (1) and (2) will be described. The following explanation is
This represents an operation in a so-called multi-mode, such as copying a plurality of single documents or continuous copying of a plurality of documents.

As shown in FIG. 8, in this embodiment, since a continuous image forming operation is performed, comparing the respective timing charts of the main switch, the charging bias, the developing motor, and the developing bias, It is assumed that the state in which is turned ON is continued. Therefore, this is the most basic operation in the image forming operation. The charging bias relating to the process of forming an electrostatic latent image on the surface of the photoconductor 1 is not a value for forced discharge but always a normal value of -700 to -800 V. Of course, the developing motor is always ON.

Thereafter, when performing the image forming operation continuously for a plurality of sheets, the control unit 10 changes the fog potential difference at a timing corresponding to the interval between the transfer sheets conveyed in each image forming operation (the sheet interval in FIG. 8). Control. In other words, in the continuous image formation in which the charging bias is always at the normal value, in the state where the normal image formation is performed (the image area in FIG. 8), the developing bias shows the normal −100 to −400 V, but the paper interval is reached. At the timing, the developing bias is -100V which is a value for forced discharge.
Otherwise, the polarity is switched from minus to plus. Then, when the timing between the sheets is switched to the timing of the image area, the pulse of the forced discharge value (−100 V or more or positive polarity) indicated by the developing bias disappears and returns to the normal value.

As described above, when an image forming operation is continuously performed on a plurality of sheets, the developing bias is instantaneously set to −100 V in accordance with the timing between the transfer sheets.
With the above or the positive polarity (that is, the method (1)), the developer can be forcibly discharged from the developing device 4 at the time of non-image formation, and at the time of performing continuous copying, the developer is maintained in order to maintain image quality. Since it is not necessary to provide a period for forcibly discharging, the operation rate or image forming speed of the image forming apparatus in continuous image formation does not decrease,
It is possible to efficiently form a plurality of images.

For example, in Japanese Patent Application Laid-Open No. Hei 9-311541, when the toner is excessively charged, the excessively charged toner is forcibly adhered to the photosensitive member as a black solid image. A technique has been disclosed in which the developer is removed and charged by driving the developer carrier when there is a large amount of poorly charged toner. However, this technique does not replace the developer successively, but is a technique for coping with the case where toner with poor charging is generated until it gets tired, and furthermore, as in the present invention, the toner and magnetic properties are determined by using the fog potential difference. Since the technical idea of forcibly discharging both carriers is not disclosed at all, the present invention cannot easily correspond to the technique disclosed in the above publication.

[0073]

According to the present invention, in the control system of the image forming operation, the fog potential difference (the potential difference between the surface potential of the photoreceptor and the voltage applied to the developing roller) can be changed to a fixed amount outside the developing device. Of the developer can be discharged. Therefore, in the developer forming apparatus of the successive developer exchange method,
It is not necessary to provide a special configuration for discharging the developer from the developing device (for example, a fixed-quantity discharging mechanism or a discharge opening), and an existing configuration of the developing device can be used.

Further, since the developer held by the developing roller can be uniformly attached to the surface of the photoreceptor,
It is possible to quantify the amount of the developer that is forcibly discharged from the developing device. Therefore, the developer can be quantitatively discharged only by changing the control of the control system. Further, since there is no need to separately drive a mechanism such as the above-described fixed discharge mechanism that is not directly involved in the image forming operation, the mechanical load involved in operating the developing device can be minimized.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view showing an image forming apparatus of the present invention.

FIG. 2 is an explanatory diagram showing the operation of FIG.

FIG. 3 is an explanatory diagram showing a relationship between a developing bias voltage and a photoconductor surface potential of the image forming apparatus of the present invention.

FIG. 4 is a graph showing a relationship between a potential difference between a developing bias voltage and a photoconductor surface potential and the amount of toner and carrier adhered.

FIG. 5 is a time chart showing the operation of the first embodiment of the present invention.

FIG. 6 is a time chart showing the operation of the first embodiment of the present invention.

FIG. 7 is a time chart showing the operation of the first embodiment of the present invention.

FIG. 8 is a time chart showing the operation of the second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charger 3 Exposure part 4 Developing device 4a Developing roller 4b Developer hopper 4c Developer supply roller 5a Transfer device 5b Peeling device 6 Static eliminator before cleaning 7 Cleaning device P1 Power supply P2 Power supply

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Keiji Kato 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Hiroshi Kubota 22-22, Nagaikecho, Abeno-ku, Osaka-shi, Osaka (72) Inventor Yasuyuki Ishiguro 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation (72) Inventor Yu Wakabayashi 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Sharp Corporation F Terms (reference) 2H027 DA02 DA04 DE07 EA01 EA05 EC06 EC17 ED09 ED30 EF08 EF12 2H077 AB02 AC02 AD06 AD13 AD35 CA19 DA10 DA42 DA54 DB08 DB12 DB14 DB25 EA03

Claims (9)

[Claims] 1. A photoconductor, a charging unit for uniformly charging the photoconductor and applying a potential to the photoconductor surface, an exposure unit for forming an electrostatic latent image on the photoconductor, and a toner and a magnetic carrier.
A developing unit that develops the electrostatic latent image with a developing roller using a component developer to form a toner image, a transfer unit that transfers the toner image to transfer paper, and a cleaning unit that collects the developer remaining on the photoconductor, A replenishing unit for replenishing the developing unit with a developer, a first power supply for applying a developing bias voltage to the developing roller, and a second power supply for applying a voltage for determining the photoconductor surface potential to the charging unit
A power supply; and a control unit for controlling at least one of the first and second power supplies to adjust a potential difference between the developing bias voltage and the photoconductor surface potential. An image forming apparatus that adjusts the amount of developer, adheres substantially the same amount of developer to the photoreceptor, and forcibly discharges the developer from the developing unit. 2. The image forming apparatus according to claim 1, wherein the control unit controls the output of the first power supply to forcibly discharge the developer by increasing the potential difference. 3. The image forming apparatus according to claim 1, wherein the control unit controls the output of the second power supply to increase the potential difference to forcibly discharge the developer. 4. The image forming apparatus according to claim 1, wherein the control unit controls the outputs of the first and second power supplies to increase the potential difference, thereby forcibly discharging the developer. 5. The control unit according to claim 1, wherein the first and second polarities of the photosensitive member surface potential and the developing bias voltage are opposite to each other.
2. The method according to claim 1, wherein the developer is forcibly discharged by controlling an output of a power supply.
The image forming apparatus as described in the above. 6. The image forming apparatus according to claim 1, wherein the control unit adjusts the potential difference and forcibly discharges the developer during a non-developing period before or after a developing period of the electrostatic latent image. 7. The image forming apparatus according to claim 1, further comprising a charge removing section for removing charges on the surface of the photoreceptor, wherein the unnecessary developer on the charged photosensitive member is collected by the cleaning section. 8. The image forming apparatus according to claim 1, wherein
When image formation is continuously performed on a plurality of transfer sheets and the developing unit develops each image, the control unit adjusts the potential difference between the development of one image and the development of the next image. Image forming apparatus for forcibly discharging the developer. 9. The image forming apparatus according to claim 8, wherein the control unit controls the output of the first power supply to forcibly discharge the developer by increasing the potential difference.