JP6727767B2 - Image forming device - Google Patents

Description

The present invention relates to an electrophotographic image forming apparatus.

Conventionally, in the electrophotographic system, a colored toner is developed on an electrostatic latent image created by charging and exposing the surface of an image carrier to form a visible image, and the toner image is transferred onto a transfer paper or the like, An image is formed by fixing with a heat roll or the like. Untransferred toner, external additives, and discharge products remain on the surface of the image carrier after the transfer process. For this reason, it becomes necessary to remove them by the cleaning means prior to the image forming process.

As a cleaning means for removing the transfer residual toner and the like, various methods such as a method using a fur brush, a magnetic brush or the like and a method using an elastic cleaning blade are used. A means for scraping off the transfer residual toner by rubbing the image bearing member with a cleaning blade is generally used because it is simple and inexpensive.

With the recent increase in speed and image quality of image forming apparatuses, the toner to be used has become nearly spherical, and it has become difficult to secure cleaning performance only with a cleaning blade. Therefore, there is a cleaning assisting means for assisting the removal of the transfer residual toner. For example, a fur brush that comes into contact with the image bearing member is arranged before the cleaning blade, and the transfer residual toner before reaching the cleaning blade is removed by the fur brush. Since there is pre-cleaning with a fur brush, there is a technique for reducing the load on the cleaning blade and improving the cleaning performance.

As a specific technique using a fur brush, in Patent Document 1, the rotation speed of a fur brush, which is a charging assisting means, is controlled to be slower than that of an image carrier during image formation, and the fur brush is used during non-image formation. The rotation speed of is faster than that during image formation. This proposes a control for ejecting the transfer residual toner in the fur brush. As a result, it is said that the fur brush can be prevented from clogging.

Further, in recent years, in order to extend the life of the image carrier, there is a thermosetting image carrier in which the surface of the image carrier is irradiated with an electron beam so that the surface thereof is not easily scraped. If the surface of the image carrier is not easily shaved, the cleaning blade is likely to be rattled, the blade is reversed, and the cleaning edge is damaged or worn. Therefore, the role of a cleaning auxiliary member such as a fur brush that improves cleaning performance has become important.

JP, 10-221925, A

In Patent Document 1, the transfer residual toner in the fur brush is discharged to the image carrier by increasing the peripheral speed of the fur brush during non-image formation. However, in the fur brush in the initial state, since the transfer residual toner does not exist in the fur brush, the number of times of rubbing with the image carrier only increases.

Depending on the material of the fur brush, when the number of times of rubbing with the image carrier increases, there is a problem that the image carrier is charged with a polarity opposite to the charging potential due to frictional charging with the fur brush. If the image carrier is charged in the opposite polarity, it becomes difficult for the charging means to uniformly charge, and image unevenness occurs.

Further, when the speed of the image forming apparatus is increased, as the image forming speed becomes faster, the charging ability becomes more necessary. Therefore, when the image carrier is charged with a polarity opposite to the charging potential by the rubbing of the fur brush, it becomes necessary to increase the charging ability for charging. In order to increase the charging ability, the apparatus configuration becomes complicated by providing a plurality of charging members, and it becomes difficult to reduce the size and cost of the apparatus. That is, if the image carrier is charged with a polarity opposite to the charging potential due to the rubbing of the fur brush, it becomes difficult to increase the image forming speed.

Further, it is difficult to increase the speed of the image forming apparatus, and besides the image unevenness, since the charged potential is different from the originally intended charging potential, the potential for development is shifted, which may cause density fluctuations and fog images on a white background. There is a problem that a defective image is generated. However, if the number of times of rubbing between the fur brush and the image carrier is blindly changed, the role of the fur brush as a cleaning auxiliary member is impaired and the cleaning performance is deteriorated.

Needless to say, the same problem arises in a cleaning auxiliary member that is not a fur brush but is in contact with the image carrier and is charged with a polarity opposite to the charging potential.

The present invention solves the above-described problems, and an object of the present invention is to provide an image forming apparatus capable of both preventing image defects and preventing cleaning defects.

A typical configuration of the image forming apparatus according to the present invention for achieving the above object is to form a toner image on an image bearing member charged by a charging unit and transfer the toner image to a transfer member to form an image. An image forming unit is provided, and the image forming unit is rotatable in contact with the image carrier to clean the toner on the image carrier after transferring the toner image from the image carrier to the transfer body. In an image forming apparatus having a different brush member, the brush member and the image carrier are based on an image signal of an image formed in a predetermined number of sheets immediately before and an image signal accumulated from the start of use of the brush member. And a changing means for changing the peripheral speed difference between

According to the present invention, prevention of image defects and prevention of cleaning defects can both be achieved.

FIG. 2 is a cross-sectional explanatory view showing the configuration of the image forming apparatus according to the present invention. FIG. 3 is an explanatory cross-sectional view showing the configuration of the cleaning device of the image forming apparatus according to the present invention. It is a block diagram showing a configuration of a control system of the image forming apparatus according to the present invention. FIG. 6 is a cross-sectional explanatory view showing an example of a potential measuring means for measuring the potential of the image carrier. 7 is a flowchart illustrating an operation of changing a rubbing condition between a cleaning unit and an image carrier in a reference example of the image forming apparatus according to the present invention. FIG. 6 is a diagram showing a relationship between the cleaning performance with respect to the peripheral speed ratio of the peripheral speed of the cleaning means with respect to the peripheral speed of the image carrier, and the potential of the image carrier. FIG. 6 is a diagram showing a relationship between idle rotation time of a cleaning unit made of a new product and a durable product, a peripheral speed ratio of a peripheral speed of the cleaning unit to a peripheral speed of the image carrier, and an electric potential of the image carrier. 6 is a flowchart illustrating an operation of changing a rubbing condition between the cleaning unit and the image carrier in the embodiment of the image forming apparatus according to the present invention.

An embodiment of an image forming apparatus according to the present invention will be specifically described with reference to the drawings. Here, first, a reference example of the present invention will be described, and then an embodiment of the present invention will be described .

[Reference example]
First, the configuration of a reference example of the image forming apparatus according to the present invention will be described with reference to FIGS.

<Image forming device>
FIG. 1 is a cross-sectional explanatory view showing the configuration of the image forming apparatus according to the present invention. The image forming apparatus 13 shown in FIG. 1 includes a photosensitive drum 1Y serving as an image carrier that carries a toner image on image forming stations 14Y, 14M, 14C, and 14K for yellow Y, magenta M, cyan C, and black K, respectively. It has 1M, 1C and 1K. For convenience of description, the photosensitive drum 1 may be simply used as a representative of the photosensitive drums 1Y, 1M, 1C, and 1K. The same applies to other image forming process means.

Around each photosensitive drum 1, a charging roller 2 serving as a charging unit for uniformly charging the surface of the photosensitive drum 1 is provided. Further, the surface of the photosensitive drum 1 uniformly charged by the charging roller 2 is provided with a laser scanner 3 as a latent image forming means for irradiating a laser beam 3a according to image information to form an electrostatic latent image. There is.

Further, a developing device 4 is provided as a developing means for supplying toner to the electrostatic latent image formed on the surface of the photosensitive drum 1 by the laser scanner 3 to develop the electrostatic latent image. Further, there is provided a primary transfer roller 5 which serves as a primary transfer means for primarily transferring the toner image developed on the surface of the photosensitive drum 1 by the developing device 4 onto the outer peripheral surface of the intermediate transfer belt 8 serving as a transfer body.

Further, there is provided a fur brush 6 composed of a brush-like rotating body as a cleaning means for cleaning the transfer residual toner remaining on the surface (on the image carrier) of the photosensitive drum 1 after the primary transfer by the primary transfer roller 5. ing. Further, a cleaning device 15 serving as a cleaning means having the fur brush 6 and the cleaning blade 7 is provided.

In the present reference example , after the transfer residual toner remaining on the surface of the photosensitive drum 1 after the primary transfer is scraped off, a fur brush 6 which can be arbitrarily rotated as a brush-like rotary member for collecting and retaining the transfer residual toner. Is used. In this reference example , the fur brush 6 is used as the rotating body, but a rotatable roll-like rotating body may be used.

An intermediate transfer belt 8 is provided facing the surface of each photosensitive drum 1 so as to be rotatably stretched in a clockwise direction in FIG. 1 by stretching rollers 8a, 8b, and 8c. A secondary transfer roller 10 serving as a secondary transfer unit is provided opposite to the outer peripheral surface of the intermediate transfer belt 8. The recording material 12 is conveyed to a secondary transfer nip portion where the outer peripheral surface of the intermediate transfer belt 8 and the secondary transfer roller 10 are in contact with each other by a conveying unit (not shown).

<Image forming operation>
First, the surface of the photosensitive drum 1 rotating counterclockwise in FIG. 1 is uniformly charged by the charging roller 2 to which a charging bias voltage is applied from the charging bias power source provided in the high voltage power source 502 shown in FIG. It A laser scanner 3 scans and exposes a surface of the photosensitive drum 1 uniformly charged by the charging roller 2 with a laser beam 3a according to image information, so that an electrostatic latent image is formed on the surface of the photosensitive drum 1. A toner (developer) is supplied from the developing device 4 to the electrostatic latent image formed on the surface of the photosensitive drum 1 to develop it as a toner image.

For the toner image developed on the surface of each photosensitive drum 1, a primary transfer bias voltage is applied to each primary transfer roller 5 from the primary transfer bias power source provided in the high voltage power source 502 shown in FIG. As a result, the primary transfer is sequentially performed by superimposing on the outer peripheral surface of the intermediate transfer belt 8 rotating in the clockwise direction in FIG.

The toner images primarily transferred onto the outer peripheral surface of the intermediate transfer belt 8 are as follows. A primary transfer bias voltage is applied to the secondary transfer roller 10 serving as a secondary transfer unit from the secondary transfer bias power source provided in the high voltage power source 502 shown in FIG. As a result, the outer peripheral surface of the intermediate transfer belt 8 and the secondary transfer roller 10 are collectively and secondarily transferred to the recording material 12 conveyed to the secondary transfer nip portion in contact with the secondary transfer roller 10.

The recording material 12 to which the toner image is secondarily transferred is conveyed to a fixing device 11 serving as a fixing unit, and is heated and heated while passing through a fixing nip portion between a fixing roller and a pressure roller provided in the fixing device 11. The toner image is pressed and thermally fixed on the recording material 12.

After the transfer residual toner remaining on the outer peripheral surface of the intermediate transfer belt 8 after the secondary transfer is removed by being scraped off from the outer peripheral surface of the intermediate transfer belt 8 by a cleaning blade provided in a cleaning device 9 serving as a cleaning unit. , Collected in the waste toner container.

<Developer>
The developer of this reference example is configured as a two-component developer having a non-magnetic toner and a magnetic carrier. The toner is negatively charged by friction with the magnetic carrier. As the toner of this reference example, a toner having an average particle size of about 6 μm, which is obtained by pulverizing and classifying a mixture of a resin binder mainly composed of polyester and a pigment, is used. The average charge amount of the toner attached to the potential of the exposed portion of the photosensitive drum 1 is about −30 μC/g.

<Image carrier>
The photosensitive drum 1 serving as an image bearing member of this reference example has an organic photosensitive member made of a negatively chargeable OPC (Organic Photo Conductor) having an axial length of 360 mm and an outer diameter of 84 mm. Consists of In the photosensitive drum 1, a photosensitive layer having a photoconductive layer containing an organic photoconductor as a main component is formed on a conductive substrate such as aluminum.

The OPC is generally configured by laminating a charge generation layer, a charge transport layer, and a surface protection layer made of an organic material on a metal substrate as a conductive substrate. For example, each layer can be formed by using the material disclosed in JP-A-2005-43806. The photosensitive drum 1 normally rotates counterclockwise in FIG. 1 at a process speed (peripheral speed) of 300 mm/sec. The photosensitive drum 1 is rotationally driven by a motor 501, which is a drive source driven and controlled by a CPU (Central Processing Unit) 500 that is a control unit and a changing unit.

<Charging means>
The charging roller 2 serving as a charging unit in this reference example is a contact type charging roller 2 that comes into contact with the surface of the photosensitive drum 1 and is driven to rotate. The surface of the photosensitive drum 1 is uniformly charged by utilizing a discharge phenomenon that occurs in a minute gap between the photosensitive drum 1 and the photosensitive drum 1. A charging bias voltage of a predetermined condition is applied to the conductive cored bar of the charging roller 2.

For example, the direct current component (DC) bias applied to the charging roller 2 is set to −500 V, and the alternating current component (AC) bias is set to a peak-to-peak bias that is at least twice the discharge start voltage under the environmental conditions. As a result, the image forming area on the surface of the photosensitive drum 1 rotating counterclockwise in FIG. 1 is uniformly charged to about −500V. That is, the charging potential on the surface of the photosensitive drum 1 has a negative (negative electrode) (negative) polarity, and the surface of the photosensitive drum 1 is charged to the negative (negative electrode) (negative) side.

The DC component (DC) bias applied to the charging roller 2 during image formation is not limited to this value, and may be changed depending on environmental conditions, usage durability of the photosensitive drum 1 and the charging roller 2, and the like. It is appropriately set to a potential suitable for good image formation. In this reference example , an example of using the contact type charging roller 2 that comes into contact with the surface of the photosensitive drum 1 will be described, but other charging means such as a non-contact type charging roller 2 or a corona charger may be used. good.

<Latent image forming means>
The laser scanner 3 serving as the latent image forming means of the present reference example includes a semiconductor laser that performs image exposure on the surface of the photosensitive drum 1 uniformly charged by the charging roller 2 based on image information. The exposure potential on the surface of the photosensitive drum 1 irradiated with the laser beam 3a is -200V. In this reference example , an example in which a semiconductor laser is used as the image exposing means will be described, but other image exposing means using an LED (Light Emitting Diode) or the like may be used.

<Potential measuring means>
FIG. 4 is a cross-sectional explanatory view showing a configuration of a potential measuring device 16 serving as a potential measuring unit for measuring the surface potential of the photosensitive drum 1 serving as an image carrier. The potential measuring device 16 of this reference example measures the surface potential of the photosensitive drum 1 with a chopper type potential sensor.

In this reference example , a potential measuring device 16 including a chopper type potential sensor shown in FIG. 4 is used as the potential measuring means for measuring the surface potential of the photosensitive drum 1. As a result, the surface potential of the photosensitive drum 1 is measured after exposure by irradiating the surface of the photosensitive drum 1 uniformly charged by the charging roller 2 with the laser beam 3a by the laser scanner 3. This makes it possible to confirm whether the charging potential and the exposure potential on the surface of the photosensitive drum 1 are actually at predetermined potentials.

As shown in FIG. 4, the potential sensor of the chopper type provided in the potential measuring device 16 is a tuning fork type vibrator 802 which is a conductive vibrating object between the photosensitive drum 1 to be measured and the measuring electrode 801. Are arranged.

A tuning fork type vibrator 802 vibrating in the direction of arrow A in FIG. 4 increases or decreases the amount of electric force lines 807 incident on the measurement electrode 801 from the surface of the photosensitive drum 1 to make the surface of the photosensitive drum 1 to be measured. The electric field strength of is measured.

It is also possible to measure the surface potential of the photosensitive drum 1 using potential measuring means other than the chopper type potential sensor shown in FIG. For example, the measuring electrode 801 itself is physically vibrated by using a capacitance fluctuation type potential sensor, and the electric field distribution between the measuring electrode 801 and the photosensitive drum 1 as the measurement object is changed to change the electric field distribution of the photosensitive drum 1. It is possible to measure the electric field strength on the surface of.

In FIG. 4, the measurement electrode 801 receives the line of electric force 807 from the photosensitive drum 1 which is the measurement target. The tuning fork type vibrator 802 oscillates and chops the electric force line 807 that is incident on the measurement electrode 801 from the photosensitive drum 1 that is the object to be measured in the direction of arrow A in FIG. The amplification element 803 impedance-converts and amplifies the minute AC signal induced in the measurement electrode 801. The piezoelectric element 804 gives vibration to the tuning fork type vibrator 802.

805 is a circuit board. Reference numeral 806 is a connection connector. A drive signal to the piezoelectric element 804, a reception signal from the measurement electrode 801, a power source for driving these, and the like are input and output via the connection connector 806 and the circuit board 805.

As shown in FIG. 4, electric force lines 807 are incident from the surface of the photosensitive drum 1 which is the measurement target toward the measurement electrode 801 in the direction of arrow B. The shield case 808 houses the circuit board 805. On the circuit board 805, the amplification element 803 which is an impedance conversion circuit is mounted.

<Developing means>
As shown in FIG. 2, the developing device 4 serving as the developing means is rotated to a developer container 4a containing a two-component developer which is a mixture of non-magnetic toner and magnetic carrier, and an opening of the developer container 4a. And a developing sleeve 4b serving as a developer carrying member which is provided.

In this reference example , the axial length of the developing sleeve 4b is 325 mm. The developing sleeve 4b magnetically holds the developer in the developer container 4a by a magnet fixedly arranged therein, and forms a gap between the surface of the developing sleeve 4b and the surface of the photosensitive drum 1. The developer is conveyed to the developing section including the parts.

To the developing sleeve 4b, a developing bias power source for applying a developing bias voltage in which a DC voltage of -400V and an AC voltage having a peak-to-peak voltage Vpp of 1600V are superimposed is connected. By applying this developing bias voltage to the developing sleeve 4b, toner is attached to the electrostatic latent image formed on the surface of the photosensitive drum 1 to perform the developing process.

<Cleaning means>
FIG. 2 is a cross-sectional explanatory view showing the configuration of the cleaning device 15 which serves as a cleaning means. As shown in FIG. 2, each cleaning device 15 is provided with a fur brush 6 serving as cleaning means, which is rotatably supported in the housing 20 in the clockwise direction of FIG. The fur brush 6 of the present reference example serves both as a toner scraping unit that scrapes transfer residual toner remaining on the surface of the photosensitive drum 1 after the primary transfer and an image carrier polishing unit that polishes the surface of the photosensitive drum 1. ing. A cleaning blade 7 that comes into contact with the surface of the photosensitive drum 1 is provided downstream of the fur brush 6 in the rotation direction of the photosensitive drum 1.

The residual material such as the transfer residual toner remaining on the surface of the photosensitive drum 1 after the primary transfer is disturbed by the fur brush 6, so that the adhesive force to the surface of the photosensitive drum 1 is weakened. After that, the cleaning blade 7 scrapes off the surface of the photosensitive drum 1 to remove it and collects it in the housing 20 that serves as a waste toner container.

Residues such as transfer residual toner removed from the surface of the photosensitive drum 1 are once held between the fibers of the fur brush 6, and then the fur brush 6 is rotated by the clockwise rotation in FIG. Of the scraper 60 is brought into contact with the outer peripheral surface of the scraper 60.

The fur brush 6 made of fibers elastically deforms due to the contact between the tip of the scraper 60 and the outer peripheral surface of the fur brush 6. Then, due to the repulsive force of the fibers of the fur brush 6, residual substances such as transfer residual toner jump out from the fur brush 6. Then, it falls near the conveying spiral 61 having spiral blades provided in the lower part of the fur brush 6.

Residues such as transfer residual toner that have dropped near the transport spiral 61 are transported in the axial direction of the photosensitive drum 1 by the spiral blades of the transport spiral 61 extending in the rotation axis direction of the photosensitive drum 1. Further, it is collected in a waste toner collecting container (not shown) via a collected toner conveying path (not shown).

The cleaning blade 7 of this reference example is made of urethane rubber, and the axial length of the cleaning blade 7 is 340 mm. The cleaning blade 7 is in contact with the surface of the photosensitive drum 1 with a predetermined contact pressure.

<Fur brush>
The fur brush 6 composed of a brush-shaped rotating body has fibers thereof planted on its rotating shaft 6a. It is manufactured by winding a cloth material in which fibers are flocked around the surface of a metal rotating shaft 6a having an outer diameter of 12 mm. The fibers of the fur brush 6 are 6 denier (weight per unit length) acrylic bunched fibers bundled on the base material with a flocking density of 50 kF/inch ² (flocking density per single fiber). It was done. The fiber length of the fur brush 6 is 4.5 mm.

The fibrous acrylic used as the fur brush 6 in this reference example has a characteristic that it is easily negatively (negatively) charged in the triboelectric charging series. Polyester may be used as another fiber material applicable to the fur brush 6. The fur brush 6 is arranged at a position where it penetrates the surface of the photosensitive drum 1 by about 0.5 mm, and the surface of the photosensitive drum 1 is rubbed while rotating in the forward direction with respect to the rotation direction of the photosensitive drum 1. To do.

As the material of the fur brush 6, acrylic, polyester, or the like may be used as a material of a charging series that is easily charged to the opposite polarity to the charging potential of the toner and the photosensitive drum 1. The average charge amount of the transfer residual toner may be on the positive (positive electrode) side. This is an influence when the surface of the photosensitive drum 1 passes the primary transfer roller 5. The average charge amount of the transfer residual toner that has not been primarily transferred is greatly reduced, and the polarity may be reversed from negative (negative electrode) to positive (positive electrode).

Therefore, the fur brush 6 having a charge series that tends to be negative (negative) is easier to collect the transfer residual toner and the like having a positive (positive) polarity. As a result, the transfer residual toner can be easily removed from the surface of the photosensitive drum 1 to assist the cleaning operation.

Further, there is an effect that the fur brush 6 comes into contact with the surface of the photosensitive drum 1 to gradually reduce the negative (negative electrode) charged potential in the direction of returning it to zero potential. From these effects, acrylic and polyester are preferable as the material of the fur brush 6.

In addition, as the material of the fur brush 6, polytetrafluoroethylene (PTFE; polytetrafluoroethylene,), vinyl chloride, or the like can be applied.

As shown in FIG. 2, the scraper 60 is in contact with the outer surface of the fur brush 6 opposite to the surface facing the surface of the photosensitive drum 1 (left side in FIG. 2) (right side in FIG. 2). The transfer residual toner collected from the surface of the photosensitive drum 1 to the fur brush 6 by the repulsive force of the fibers of the fur brush 6 is repelled from the fur brush 6 by the scraper 60 in contact with the outer peripheral surface of the fur brush 6. As a result, the transfer residual toner collected by the fur brush 6 does not easily clog the fibers of the fur brush 6.

Further, when the cleaning device 15 is attached to the image forming device 13, the metal rotary shaft 6 a of the fur brush 6 is attached to the metal frame of the image forming device 13 so as to be grounded. The photosensitive drum 1 and the fur brush 6 rotate in the directions of arrows a and b in FIG. 2, respectively. As a result, the photosensitive drum 1 and the fur brush 6 rotate in the same direction at their contact nip portions.

The fur brush 6 is a control unit that drives and controls the motor 501 that is the drive source shown in FIG. 3, and can be arbitrarily rotated by the CPU 500 that is the changing unit. The fur brush 6 of this reference example is set so as to be rotatable at a predetermined peripheral speed ratio (for example, 140%) to the peripheral speed of the surface of the photosensitive drum 1.

<Characteristics of fur brush>
With the materials of the fur brush 6 and the photosensitive drum 1 described above, when the number of times the fur brush 6 is rubbed against the surface of the photosensitive drum 1 is too large, the surface of the photosensitive drum 1 has a potential polarity with which a toner image is developed. It will be charged to the opposite polarity potential. In the present reference example , when positive (positive) charging means that the potential polarity on which the toner image on the surface of the photosensitive drum 1 is developed is opposite (negative) to negative (negative), An example will be described.

The surface of the photosensitive drum 1 is less likely to be positively charged when the fur brush 6 is in a new initial state. This is because when the fur brush 6 is new, there is no contamination by the transfer residual toner, and the rigidity of the fibers of the fur brush 6 is strong. Further, the performance of cleaning the surface of the photosensitive drum 1 is higher when the fur brush 6 is in a new initial state.

In the case of the initial fur brush 6 which is not contaminated with the transfer residual toner, it is not necessary to rotate the fur brush 6 at a peripheral speed ratio of 140% with respect to the peripheral speed of the surface of the photosensitive drum 1. That is, since the fur brush 6 in the new initial state has ensured sufficient cleaning performance, the cleaning performance is not impaired even if the peripheral speed of the surface of the photosensitive drum 1 is slower than 140%. ..

The present inventor investigated the influence on the surface potential of the photosensitive drum 1 when the fur brush 6 in various states from the new initial state to the latter half of the durability was rubbed on the surface of the photosensitive drum 1. As a result, it was found that the surface of the photosensitive drum 1 is more likely to be positively (positively) charged as the transfer residual toner is clogged between the fibers of the fur brush 6.

Similarly, when the cleaning performance of the fur brush 6 in various states is examined, the positive (positive electrode) charging potential V1 on the surface of the photosensitive drum 1 becomes higher as the transfer residual toner is clogged between the fibers of the fur brush 6. Do you get it.

It was also found that the positive (positive electrode) charging potential V1 on the surface of the photosensitive drum 1 becomes higher as the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 becomes smaller.

The lower the positive (positive) charging potential V1 on the surface of the photosensitive drum 1, the stronger the rubbing force of the fur brush 6 on the surface of the photosensitive drum 1, and the higher the cleaning performance.

On the contrary, it was found that the higher the positive (positive electrode) charging potential V1 on the surface of the photosensitive drum 1, the weaker the rubbing force of the fur brush 6 on the surface of the photosensitive drum 1, and the lower the cleaning performance.

As described above, the positive (positive electrode) charging potential V1 on the surface of the photosensitive drum 1 and the cleaning performance have a correlation as shown in FIG. 6, and the correlation is tabulated and the image forming apparatus 13 shown in FIG. It is stored in the database 505, which is a storage means provided inside.

In order to prevent the positive (positive electrode) charging potential V1 of the surface of the photosensitive drum 1 from decreasing, the toner is supplied to the fur brush 6 and the fibers of the fur brush 6 are forcibly clogged with the toner to be exposed. A method of weakening the rubbing force of the fur brush 6 on the surface of the drum 1 can be considered. Alternatively, it is conceivable to reduce the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1.

When these measures are taken, they are carried out within a range where the cleaning performance is not impaired based on the correlation between the positive (positive electrode) charging potential V1 of the surface of the photosensitive drum 1 and the cleaning performance of the surface of the photosensitive drum 1. ..

How the surface of the photosensitive drum 1 is charged by rubbing against the fur brush 6 was determined by measuring as follows. As an environmental condition in which the image forming apparatus 13 is installed, an environmental condition in which the temperature is 20° C. and the humidity is 50% is considered. Under this environmental condition, the charging bias voltage applied to the charging roller 2 by the charging bias power source provided in the high voltage power source 502 shown in FIG. 3 is turned off. Further, the primary transfer bias voltage applied to the primary transfer roller 5 is turned off by the primary transfer bias power source also provided in the high voltage power source 502. In addition, the operations of the laser scanner 3 and the like that affect the surface potential of the photosensitive drum 1 are also turned off.

The cleaning device 15 sets the same state as the normal image forming operation of the image forming device 13, and idles the photosensitive drum 1 for about 10 minutes. The surface potential of the photosensitive drum 1 during idling was measured every 1 second by the potential measuring device 16 shown in FIG. 4, and the surface potential of the photosensitive drum 1 after 10 minutes was measured.

If the surface potential of the photosensitive drum 1 after 10 minutes from the idling start of the photosensitive drum 1 is on the negative (negative) side, it is determined to have the same polarity as the negative (negative) charging potential. It was determined that the larger the absolute value of the surface potential of the photosensitive drum 1 at that time, the greater the influence of the rubbing by the fur brush 6.

On the other hand, if the surface potential of the photosensitive drum 1 after 10 minutes from the idling start of the photosensitive drum 1 is on the positive (positive) side, it is determined that the polarity is opposite to the negative (negative) charging potential, and the photosensitive drum 1 It was determined that the surface was positively (positive electrode) charged. Similarly, it was determined that the magnitude of the surface potential of the photosensitive drum 1 at that time was the magnitude of the influence of the rubbing of the fur brush 6.

<Control of rubbing condition of cleaning means>
Next, control of the rubbing condition of the fur brush 6 serving as a cleaning unit will be described with reference to FIGS. 3, 5, and 7. FIG. 3 is a block diagram showing the configuration of the control system of this reference example . FIG. 5 is a flowchart showing how the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 is changed according to the surface potential of the photosensitive drum 1. FIG. 7 is a diagram showing the relationship between the rotation time of the fur brush 6 (idle rotation time of the photosensitive drum 1) and the positive (positive electrode) charging potential V1 of the surface of the photosensitive drum 1.

<Control system>
First, the configuration of the control system of this reference example will be described with reference to FIG. In FIG. 3, the following members are connected to a CPU (Central Processing Unit) 500 serving as a control unit. An environmental sensor 503 for detecting the environmental conditions in which the potential measuring device 16 and the image forming apparatus 13 shown in FIG. 4 are installed is connected. In addition, a memory 504 that serves as a storage unit that stores the conditions under which image formation is performed is connected.

In addition, the CPU 500 stores a table of the number of durable recording materials 12 for each component and the ratio of the peripheral speed of the outer surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 according to the number of durable recording materials 12. A database 505 serving as a storage means is connected. In addition, a toner amount detecting unit 506, which serves as toner amount detecting means, is connected.

The CPU 500 operates the image forming apparatus 13 in accordance with signals input in advance and stored in the database 505 and input information for image formation. Therefore, the CPU 500 is connected to a motor 501 which is a drive source for driving the photosensitive drum 1, the fur brush 6, the developing device 4, the intermediate transfer belt 8 and the like.

Further, a high-voltage power source 502 is connected to the CPU 500. The high-voltage power supply 502 is provided with a charging bias power supply that applies a charging bias voltage to the charging roller 2 during image formation. Further, a developing bias power source for applying a developing bias voltage to the developing sleeve 4b is provided. Further, a primary transfer bias power source for applying a primary transfer bias voltage to the primary transfer roller 5 is provided. Further, a secondary transfer bias power source for applying a secondary transfer bias voltage to the secondary transfer roller 10 is provided.

As a result, the CPU 500 controls the motor 501 and the high-voltage power source 502 according to the image forming signal, and applies respective bias voltages to the charging roller 2, the developing device 4, the primary transfer roller 58, and the secondary transfer roller 10. Image forming operation can be performed.

Next, drive control of the fur brush 6 will be described with reference to FIG. First, in step S1, the drive control of the fur brush 6 is started. The timing for performing the drive control of the fur brush 6 is as follows. To use the image forming apparatus 13, the power is turned on, and the image forming condition data stored in the memory 504 or the database 505, which serves as a storage unit, is referred to, and a preparatory operation for image formation is performed. At that time, the drive control of the fur brush 6 may be performed.

Alternatively, it has been found that, in a new initial state of the fur brush 6, it is difficult for the surface of the photosensitive drum 1 to be positively (positively) charged due to the rubbing of the fur brush 6. In this case, the image forming condition data stored in the memory 504 or the database 505 is referred to. Then, the control timing may be changed according to the total number of rotations J0 of the fur brush 6 or the amount of toner remaining on the surface of the photosensitive drum 1 after the primary transfer reaches the fur brush 6.

For example, the drive control of the fur brush 6 shown in FIG. 5 is performed every 1000 prints of the recording material 12 from the new initial state of the fur brush 6 to the number of prints of the recording material 12 of 10,000. Then, while the number of printed recording materials 12 exceeds 10,000 and reaches 20,000, the drive control of the fur brush 6 is performed every 2000 printed sheets of recording material 12. If the number of printed recording materials 12 exceeds 20000, the drive control of the fur brush 6 may be performed every 5000 printed recording materials 12.

It should be noted that changing the rubbing condition between the fur brush 6 and the surface of the photosensitive drum 1 increases the number of times of rubbing between the fur brush 6 and the surface of the photosensitive drum 1 as the number of images formed on the recording material 12 increases. You can also let it. The number of rubbing times between the fur brush 6 and the surface of the photosensitive drum 1 is proportional to the ratio of the peripheral speed of the fur brush 6 to the peripheral speed of the photosensitive drum 1. Therefore, the peripheral speed ratio of the fur brush 6 to the peripheral speed of the photosensitive drum 1 can be increased as the number of images formed on the recording material 12 increases. Further, as described above, the interval of the drive control timing for changing the peripheral speed ratio of the fur brush 6 with respect to the peripheral speed of the photosensitive drum 1 can be widened as the number of printed sheets of the recording material 12 increases.

When the drive control of the fur brush 6 is started, the fur brush 6 and the photosensitive drum 1 are rotationally driven by the motor 501 without driving the charging roller 2, the intermediate transfer belt 8, the primary transfer roller 5, the developing device 4, and the like. A fixed time (30 seconds in the present reference example ) elapses after the fur brush 6 and the photosensitive drum 1 start rotating. At that time, in step S2, the surface potential of the photosensitive drum 1 at that time is measured by the potential measuring device 16 shown in FIG. 4 arranged downstream of the laser scanner 3 shown in FIG. 2 in the rotational direction of the photosensitive drum 1. .. In step S2, the charging potential V1 of the surface of the photosensitive drum 1 measured by the potential measuring device 16 shown in FIG. 4 was +18V, for example.

Next, in step S3, the CPU 500 reads out the threshold value V0 stored and stored in the database 505 in advance, and the charged potential of the surface of the photosensitive drum 1 measured by the potential measuring device 16 shown in FIG. V1 is compared with the threshold V0. In this reference example , the threshold value V0 is set to +10V, although it depends on the configuration of the image forming apparatus 13. That is, if the positive (positive electrode) charging potential V1 of the surface of the photosensitive drum 1 is +10 V or less, no image defect occurs.

In step S3, the charging potential V1 of the surface of the photosensitive drum 1 measured by the potential measuring device 16 shown in FIG. 4 and the threshold value V0 have the relationship of the following mathematical formula 1. In that case, the charging potential V1 of the surface of the photosensitive drum 1 is not the positive (positive) charging potential V1 at which image unevenness occurs. Therefore, after proceeding to step S4, the fur brush 6 is rotated at a peripheral velocity ratio of 140% with respect to the peripheral velocity of the surface of the photosensitive drum 1, and then proceeding to step S5, the drive control of the fur brush 6 is completed.

[Equation 1]
V1≦V0

On the other hand, in step S3, if the charging potential V1 of the surface of the photosensitive drum 1 measured by the potential measuring device 16 shown in FIG. 4 and the threshold value V0 have the relationship of the following equation 2, the process proceeds to step S6. ..

[Equation 2]
V1>V0

In step S6, the CPU 500 controls as follows according to the values of the charging potential V1 of the surface of the photosensitive drum 1 measured by the potential measuring device 16 shown in FIG. 4 and the threshold value V0. The positive (positive electrode) charging potential V1 of the surface of the photosensitive drum 1 shown in FIG. 6 stored in advance in the database 505, the threshold value V0, and the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 are shown. Refer to the table showing the relationship. Then, the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 is changed.

The peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 is changed by the CPU 500, which serves as a changing unit, and the rotational speeds of the fur brush 6 and the photosensitive drum 1 which are rotationally driven by the motor 501 shown in FIG. Can be performed by controlling each.

In this reference example , the CPU 500, which is a changing unit, changes the sliding condition between the fur brush 6 and the surface of the photosensitive drum 1 according to the measurement result of the potential measuring device 16 shown in FIG.

Then, the steps S2 to S3 are performed again with the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 changed in step S6. In step S3, the peripheral speed of the outer peripheral surface of the fur brush 6 with respect to the peripheral speed of the surface of the photosensitive drum 1 in step S6 until the charging potential V1 of the surface of the photosensitive drum 1 and the threshold value V0 have the relationship of the above-described equation 1. The ratio change is repeated.

The charging property by frictional charging caused by the fur brush 6 rubbing the surface of the photosensitive drum 1 depends on environmental conditions such as temperature and humidity. Therefore, the threshold value V0 may be appropriately changed according to the detection result of the environment sensor 503 that detects the environmental conditions such as the temperature and humidity of the place where the image forming apparatus 13 is installed. Environmental information of temperature and humidity detected by the environmental sensor 503 is also sent to the CPU 500 and used for arithmetic control.

In FIG. 5, the positive (positive) charging potential V1 on the surface of the photosensitive drum 1 is lowered by lowering the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1. In addition to lowering the peripheral speed ratio of the outer peripheral surface of the fur brush 6 with respect to the peripheral speed of the surface of the photosensitive drum 1, toner may be forcibly supplied to the fur brush 6.

Further, the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 adjusted in the step S6 is adjusted in consideration of the cleaning performance shown in FIG. This makes it possible to achieve both positive (positive electrode) electrostatic charge prevention on the surface of the photosensitive drum 1 and ensuring cleaning performance.

Further, when the drive control of the fur brush 6 shown in FIG. 5 is performed, the measurement result by the potential measuring device 16 shown in FIG. 4 is determined in consideration of the signal from the high voltage power supply 502 shown in FIG. Then, the drive control result of the fur brush 6 shown in FIG. 5 is determined by comparing and referring to the table stored in the database 505.

FIG. 6 shows the relationship between the cleaning performance of the surface of the photosensitive drum 1 with respect to the peripheral speed ratio of the outer surface of the fur brush 6 with respect to the peripheral speed of the surface of the photosensitive drum 1, and the positive (positive electrode) charging potential V1 of the surface of the photosensitive drum 1. Show. The positive (positive electrode) charging potential V1 on the surface of the photosensitive drum 1 is measured by a potential measuring device 16 shown in FIG. The cleaning performance of the surface of the photosensitive drum 1 was determined by measuring the number of particles such as toner particles passing through the cleaning blade 7 shown in FIG. 2 on the surface of the photosensitive drum 1.

In FIG. 6, the two vertical axes represent the positive (positive electrode) charging potential V1 of the surface of the photosensitive drum 1 and the cleaning performance of the surface of the photosensitive drum 1. As the surface cleaning performance of the photosensitive drum 1, the number of particles such as toner particles passing through the cleaning blade 7 shown in FIG. 2 on the surface of the photosensitive drum 1 is counted.

The horizontal axis of FIG. 6 represents the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1. By changing the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 and confirming under each condition, the positive (positive electrode) charging potential V1 on the surface of the photosensitive drum 1 and the cleaning performance are The compatible range is stored in the database 505 shown in FIG.

As shown in FIG. 6, as the peripheral speed of the outer peripheral surface of the fur brush 6 is higher than the peripheral speed of the surface of the photosensitive drum 1 (on the right side in FIG. 6), the fur brush 6 rubs against the photosensitive drum 1. Therefore, as shown by the curve d in FIG. 6, the positive (positive) charging potential V1 on the surface of the photosensitive drum 1 becomes large.

On the other hand, as the peripheral speed of the outer peripheral surface of the fur brush 6 is higher than the peripheral speed of the surface of the photosensitive drum 1 (on the right side of FIG. 6), the cleaning performance of the surface of the photosensitive drum 1 is increased as shown by the curve e in FIG. Will improve. When the peripheral speed of the outer peripheral surface of the fur brush 6 is slower than the peripheral speed of the surface of the photosensitive drum 1 (on the left side of FIG. 6), the ability to disturb the transfer residual toner on the surface of the photosensitive drum 1 is reduced and the cleaning performance is reduced. Will fall.

In FIG. 6, the cleaning performance is evaluated by measuring the number of particles such as toner particles passing through the cleaning blade 7 on the surface of the photosensitive drum 1. Therefore, in FIG. 6, an increase in the curve e means a decrease in the cleaning performance, and a decrease in the curve e means an improvement in the cleaning performance.

For example, consider a case where the photosensitive drum 1, the fur brush 6, and the cleaning blade 7 are all new. When the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 is 30% to 105%, the positive (positive electrode) charging potential V1 on the surface of the photosensitive drum 1 and the cleaning performance can be compatible. I understood.

FIG. 7 shows the relationship between the idle rotation time of the fur brush 6 and the positive (positive) charging potential V1 on the surface of the photosensitive drum 1. The vertical axis of FIG. 7 represents the positive (positive electrode) charging potential V1 of the surface of the photosensitive drum 1, and the horizontal axis represents the idle rotation time of the fur brush 6. The conditions of the fur brush 6 plotted in FIG. 7 exemplify three conditions indicated by the curves f, g, and h in FIG. 7.

A curve f shown in FIG. 7 is obtained by idly rotating the peripheral speed of the outer peripheral surface of the new fur brush 6 at a peripheral speed ratio of 140% with respect to the peripheral speed of the surface of the photosensitive drum 1.

A curve g shown in FIG. 7 is obtained by idling the peripheral speed of the outer peripheral surface of the new fur brush 6 at a peripheral speed ratio of 100% with respect to the peripheral speed of the surface of the photosensitive drum 1.

A curve h shown in FIG. 7 is obtained by idling the peripheral speed of the outer peripheral surface of the durable (old) fur brush 6 at a peripheral speed ratio of 140% with respect to the peripheral speed of the surface of the photosensitive drum 1.

In the curve f shown in FIG. 7, when the idle rotation time of the fur brush 6 reaches 5 minutes, the positive (positive electrode) charging potential V1 on the surface of the photosensitive drum 1 exceeds +50V. Therefore, the positive (positive) charging potential V1 on the surface of the photosensitive drum 1 is high.

A curved line g shown in FIG. 7 is a peripheral velocity of the outer peripheral surface of the fur brush 6 indicated by a curved line f from 140% to 100% of the peripheral velocity of the surface of the photosensitive drum 1 according to the control shown in FIG. The positive (positive) charging potential V1 of the surface of the photosensitive drum 1 when the speed ratio is lowered is shown. In the curve g shown in FIG. 7, the positive (positive electrode) charging potential V1 on the surface of the photosensitive drum 1 is low and stable as compared with the curve f.

The curve h shown in FIG. 7 is a durable (old) fur brush 6, and thus has a lower ability to positively charge the surface of the photosensitive drum 1 than a new fur brush 6. Therefore, the curve h shown in FIG. 7 is a positive (positive) charging potential on the surface of the photosensitive drum 1 even if the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 remains 140%, which is the same as the curve f. V1 is low and stable.

The positive (positive) charging potential V1 on the surface of the photosensitive drum 1 may be measured for each sheet when the image is formed on the recording material 12. The positive (positive electrode) charging potential V1 of the surface of the photosensitive drum 1 can be measured at a timing such as rotation after the image formation is completed. Accordingly, the positive (positive electrode) charging potential V1 on the surface of the photosensitive drum 1 can be controlled to be equal to or lower than a certain level.

That is, control is performed to change the ratio of the peripheral speed of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 so that the positive (positive electrode) charging potential V1 on the surface of the photosensitive drum 1 is stabilized below a certain level.

Further, this reference example is an example in which the positive (positive electrode) charging potential V1 of the surface of the photosensitive drum 1 is measured by the potential measuring device 16 shown in FIG. Therefore, the provision of the potential measuring device 16 leads to an increase in the size and cost of the image forming apparatus 13.

Since the positive (positive electrode) charging potential V1 on the surface of the photosensitive drum 1 is directly measured using the potential measuring device 16, the detection accuracy is good. In addition, instead of the potential measuring device 16, toner is supplied to the positive (positive electrode) charging potential V1 on the surface of the photosensitive drum 1 to perform development. Then, the amount of toner developed in the charging area of the positive (positive) charging potential V1 on the surface of the photosensitive drum 1 is detected by the toner amount detecting unit 506 shown in FIG.

The fur brush 6 rubs against the surface of the photosensitive drum 1 to charge the surface of the photosensitive drum 1 to a male potential having a polarity opposite to that of the potential polarity at which the toner image is developed. The developing device 4 develops with respect to the charged potential. The toner amount of the developed toner image is detected by the toner amount detecting unit 506 which serves as a toner amount detecting means. The potential measuring means of the present reference example measures the potential of the surface of the photosensitive drum 1 based on the toner amount detected by the toner amount detecting unit 506 instead of the potential measuring device 16.

Then, based on the detection result of the toner amount detecting unit 506, the CPU 500 as a changing unit may perform control to change the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1.

The toner amount detection unit 506 shown in FIG. 3 is, for example, a patch that optically detects the density of a patch image developed by supplying toner to a positive (positive) charging potential V1 on the surface of the photosensitive drum 1. Image detection sensor can be applied. Alternatively, after the toner image is fixed on the recording material 12, the density can be measured by reading the toner image with a scanner.

The surface potential of the photosensitive drum 1 is rubbed with the fur brush 6 to detect a positive (positive electrode) charging potential V1 charged in a polarity opposite to the polarity of the charging potential on the developing side, and the photosensitive drum 1 is detected. The peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of No. 1 is changed.

The surface of the photosensitive drum 1 is rubbed against the fur brush 6 to cause the surface potential of the photosensitive drum 1 to have a polarity opposite to the polarity of the developing side. The peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of No. 1 is reduced. As a result, it is possible to prevent the surface potential of the photosensitive drum 1 from being charged to a polarity opposite to the polarity of the charging potential on the developing side.

That is, the surface potential of the photosensitive drum 1 is charged by the rubbing of the cleaning member such as the fur brush 6 to a polarity opposite to the polarity of the charging potential on the developing side. As a result, the surface potential of the photosensitive drum 1 becomes non-uniform. As a result, image defects such as image unevenness and white background fogging occur. In the present reference example , this can be prevented, and at the same time, prevention of defective cleaning of the surface of the photosensitive drum 1 can be achieved. In addition, the speed of image formation is facilitated.

[First Embodiment]
Next, the configuration of the embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. The same components as those of the reference example are designated by the same reference numerals, or the same reference numerals are given even if the reference numerals are different, and the description thereof will be omitted.

In the present embodiment, what is different from the reference example is the control flow for performing the rotation operation of the fur brush 6 shown in FIG. Therefore, the description overlapping with the reference example will be omitted. Figure 8 is a flowchart showing how to control the rotation of the fur brush 6 definitive in image forming equipment of the present embodiment.

In FIG. 8, the positive (positive) charging potential V1 on the surface of the photosensitive drum 1 differs depending on the state F0 of the fur brush 6. The state F0 of the fur brush 6 changes as the image forming operation is repeated, as described above. Specifically, the change in the state F0 of the fur brush 6 changes depending on the rotation speed of the fur brush 6, the amount of toner that enters between the fibers of the fur brush 6, and the amount of charge of the toner.

The positive (positive) charging potential V1 on the surface of the photosensitive drum 1 changes depending on the surface layer state and the film thickness of the photosensitive drum 1.

Therefore, in the present embodiment, the number of rotations of the fur brush 6 and the amount of toner reaching the fur brush 6 are integrated. The data stored in the memory 504 serving as a storage unit that stores the image forming conditions of the image forming apparatus 13 illustrated in FIG.

Repeated rubbing between the fur brush 6 and the surface of the photosensitive drum 1 causes physical deformation and brush characteristics of the fur brush 6. Therefore, the change in the state F0 of the fur brush 6 depends on the rotation speed of the fur brush 6.

Further, the positive (positive) chargeability of the surface of the photosensitive drum 1 changes depending on the presence or absence of toner between the fibers of the fur brush 6. Therefore, it is necessary to consider the amount of toner reaching the fur brush 6 in addition to the number of revolutions of the fur brush 6.

The amount of toner that reaches the fur brush 6 is calculated as follows. The transfer efficiency of the toner image measured from time to time at the primary transfer nip portion between the surface of the photosensitive drum 1 and the surface of the primary transfer roller 5 which are in contact with each other via the intermediate transfer belt 8 shown in FIG. It is stored in the database 505 shown. Then, it is calculated by calculating the image information input at the time of image formation and the transfer efficiency stored in the database 505 shown in FIG.

It is known that the toner charge amount changes when passing through the primary transfer roller 5. Therefore, the charge amount of the transfer residual toner remaining on the surface of the photosensitive drum 1 is measured when the transfer conditions such as the primary transfer bias voltage applied to the primary transfer roller 5 are changed, and the storage means shown in FIG. 3 is obtained. It is stored in the database 505.

Then, based on the charge amount data of the transfer residual toner remaining on the surface of the photosensitive drum 1 stored in the database 505, it can be predicted as follows. To calculate and predict the toner amount reaching the fur brush 6 and the charge amount of the toner by referring to the transfer conditions such as the primary transfer bias voltage applied to the primary transfer roller 5 and the image information to be printed. Can be done.

When the toner reaching the fur brush 6 is calculated and predicted, if the toner distribution in the axial direction of the photosensitive drum 1 is also included in the calculation, uneven charging due to positive (positive electrode) charging on the surface of the photosensitive drum 1 occurs. It can be prevented.

On the other hand, it is known that the surface layer state of the photosensitive drum 1 that affects the positive (positive electrode) charging characteristics of the surface of the photosensitive drum 1 and the change in the film thickness are related to the rotation speed of the photosensitive drum 1. Therefore, the CPU 500 integrates the number of rotations of the photosensitive drum 1 and stores the total number of rotations N0 of the photosensitive drum 1 in the database 505 shown in FIG.

The surface layer state and film thickness of the photosensitive drum 1 are more accurately predicted. For that purpose, charging conditions such as a charging bias voltage applied to the surface of the photosensitive drum 1 by the charging roller 2 shown in FIG. 2 are considered. Furthermore, transfer conditions such as the primary transfer bias voltage applied to the primary transfer roller 5 are considered. Further, it is desirable to consider the contact condition of the fur brush 6 and the cleaning blade 7 provided in the cleaning device 15 with the surface of the photosensitive drum 1.

In the present embodiment, for the surface layer state and the film thickness (photoconductor) state change of the photosensitive drum 1, only the total rotation number N0 of the photosensitive drum 1 is used as a parameter for predictive calculation. Further, the change in the state F0 of the fur brush 6 uses the integrated value of the number of rotations of the fur brush 6 and the history of image information as parameters because the fur brush 6 is driven to rotate during image formation.

FIG. 8 shows a flowchart for controlling the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 for each number of recording materials 12 when forming an image on the recording material 12.

In step S11 of FIG. 8, control of the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 is started. Next, in step S12, the CPU 500 refers to the total rotation number N0 of the photosensitive drum 1, the total rotation number J0 of the fur brush 6, and the image information L0 stored in the database 505 shown in FIG. 3 as needed. The database 505 is configured as a storage unit that stores the conditions for performing image formation.

Next, in step S13, the state F0 of the fur brush 6 is calculated from the image information L0 acquired by the CPU 500 in step S12 and the total rotation number J0 of the fur brush 6.

In step S13, the state F0 of the fur brush 6 is calculated by a numerical value from 0% to 100% indicating how much the surface of the photosensitive drum 1 is positively (positively) charged by rubbing.

In this embodiment, the larger the state F0 of the fur brush 6 is, the stronger the positive (positive) charging force on the surface of the photosensitive drum 1 due to the friction of the fur brush 6 is defined.

The image information L0 is used to calculate the amount of the transfer residual toner remaining on the surface of the photosensitive drum 1 after the primary transfer reaches the fur brush 6 shown in FIG. 2 and the charge amount of the toner. In step S13, the state F0 of the fur brush 6 is calculated. At that time, as the image information L0, the image information P printed on the X recording materials 12 immediately before calculating the state F0 of the fur brush 6 is used. Further, the image information (including the control patch image) Q which has been flown from the time when the fur brush 6 is replaced and started to be used is used.

The image information L0, P, and Q referred to here means not only normal image formation but also the image formed for control and the toner amount used when troubles such as jam (JAM) are calculated. To do.

Therefore, the integration method may be based on the image information, but the image information may be calculated based on the history of toner replenishment from the toner bottle (not shown) to the developing device 4 or the toner remaining amount in the toner bottle.

The image information P printed on the X recording materials 12 immediately before the calculation of the state F0 of the fur brush 6 is as follows. Even if the fur brush 6 is in a state of being almost new, cleaning is performed without transferring the control patch image or the like formed on the surface of the photosensitive drum 1 to the X recording materials 12 immediately before calculating the state F0 of the fur brush 6. It may be collected by the blade 7. Further, it is used to calculate the state F0 of the fur brush 6 on the assumption that the fur brush 6 is used in a state where the transfer efficiency is low and a large amount of toner reaches the fur brush 6.

Therefore, the state F0 of the fur brush 6 takes into consideration the influence on the state F(P) of the fur brush 6 by the image immediately before using the image information P and Q. Furthermore, the influence on the state F(Q) of the fur brush 6 from when the fur brush 6 is replaced and started to be used until now is considered. Then, the above F(P) and F(Q) are multiplied by the coefficients α and β, respectively, and added up to be calculated by the following formula (3). Note that F(P) and F(Q) in the following formula 3 are the change in the outer diameter of the fur brush 6 due to the total number of rotations J0 (endurance) of the fur brush 6 and the amount of toner coming to the fur brush 6 ( Image information).

[Equation 3]
F0=α×F(P)+β×F(Q)

Thereby, the state F0 of the fur brush 6 and the state of the surface of the photosensitive drum 1 can be known. Further, the current peripheral speed (rotational speed) of the fur brush 6 can be known. As a result, the positive (positive electrode) charging potential V1 of the surface of the photosensitive drum 1 and the cleaning performance are calculated and predicted by the table stored in the database 505 according to the number of times the fur brush 6 and the photosensitive drum 1 are rubbed. can do.

In other words, the setting range of the peripheral speed of the fur brush 6 that can balance the positive (positive electrode) charging potential V1 of the surface of the photosensitive drum 1 and the cleaning performance becomes clear. The respective thresholds N1, F2 and F1 shown in steps S14, S15 and S18 of FIG. 8 are set based on the setting range where the positive (positive electrode) charging potential V1 of the surface of the photosensitive drum 1 and the cleaning performance are compatible with each other. There is. The thresholds N1, F2 and F1 are appropriately changed according to the peripheral speed (rotational speed) of the fur brush 6.

Next, in step S14, the CPU 500 compares whether or not the total rotation number N0 of the photosensitive drum 1 accumulated and stored in the database 505 at any time is equal to or greater than a preset threshold value N1. If the total number N0 of rotations of the photosensitive drum 1 is equal to or larger than the threshold value N1 in step S14, the process proceeds to step S15.

In step S15, the CPU 500 compares whether or not the state F0 of the fur brush 6 calculated by the equation 3 is less than or equal to a preset threshold value F2. When the state F0 of the fur brush 6 is equal to or smaller than the threshold value F2 in step S15, the CPU 500 determines that the possibility that the surface of the photosensitive drum 1 is positively (positively) charged by the rubbing of the fur brush 6 is low. Then, proceeding to step S16, the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 is not changed. Then, it progresses to step S17 and ends control.

If the total number N0 of rotations of the photosensitive drum 1 is less than the threshold value N1 in step S14, the process proceeds to step S18. In step S18, the CPU 500 determines whether or not the state F0 of the fur brush 6 is greater than or equal to a preset threshold F1.

The positive (positive) tendency of the surface of the photosensitive drum 1 changes depending on the surface state of the photosensitive drum 1. Therefore, the total number of rotations N0 of the photosensitive drum 1 is confirmed in step S14. When the total rotation number N0 of the photosensitive drum 1 is smaller than the threshold value N1, the surface of the photosensitive drum 1 tends to become positive (positive). Therefore, the threshold value F1 of the state F0 of the fur brush 6 is set in step S18 in accordance with the positive (positive) tendency of the surface of the photosensitive drum 1.

On the other hand, when the total number N0 of rotations of the photosensitive drum 1 is equal to or greater than the threshold value N1, the surface of the photosensitive drum 1 is difficult to become positive (positive). In consideration of the state, the threshold F2 of the state F0 of the fur brush 6 is set in step S15. The threshold value F1 in step S18 is a threshold value in a state where the surface of the photosensitive drum 1 is likely to become positive (positive), so that the threshold value F1 is allowable as positive (positive) in the fur brush 6 as compared with the threshold F2 in step S15. Becomes narrower. That is, the relationship of {threshold F1<threshold F2} is set. The tendency of the surface of the photosensitive drum 1 to become positive (positive) at the beginning is different depending on the material of the surface layer or the photosensitive layer of the photosensitive drum 1.

When the state F0 of the fur brush 6 is equal to or more than the threshold value F1 in step S18, the process proceeds to step S19. In step S19, the CPU 500 refers to the table stored in the database 505 based on the state of the photosensitive drum 1 and the fur brush 6 so that the peripheral speed (rotation speed) of the fur brush 6 becomes the optimum rotation speed. Change to.

Then, the process proceeds to step S17 to end the control. If the state F0 of the fur brush 6 is larger than the threshold value F2 in step S15, the process proceeds to step S19 and the peripheral speed (rotation speed) of the fur brush 6 is determined by referring to the table stored in the database 505. change. Then, the process proceeds to step S17 to end the control.

As in this embodiment, the following is predicted from the total number N0 of rotations of the photosensitive drum 1, the number of rotations of the fur brush 6, the peripheral speed (rotational speed), and the image ratio. It is predicted under what conditions the cleaning performance and the positive (positive electrode) charge on the surface of the photosensitive drum 1 can be prevented. Thereby, the peripheral speed (rotational speed) of the fur brush 6 can be changed.

Further, by positively supplying toner to the fur brush 6 in addition to changing the peripheral speed (rotational speed) of the fur brush 6, positive (positive electrode) charging of the surface of the photosensitive drum 1 can be prevented.

As described above, the method for preventing positive (positive electrode) electrification on the surface of the photosensitive drum 1 may be appropriately selected depending on the state of the image forming apparatus 13 and the usage state.

In the reference example , the positive (positive) charging potential V1 on the surface of the photosensitive drum 1 was measured by providing the potential measuring device 16 and the patch image detection sensor shown in FIG. In the present embodiment, the positive (positive) charging potential V1 on the surface of the photosensitive drum 1 is predicted without providing the potential measuring device 16 and the patch image detecting sensor shown in FIG. ) Control can be optimized.

As the control timing of the peripheral speed (rotational speed) of the fur brush 6, an operation immediately after calculating the state F0 of the fur brush 6 before and after image formation and calculating the state F0 of the fur brush 6 is performed. Therefore, the peripheral speed (rotational speed) of the fur brush 6 may be changed.

The CPU 500 only refers to the data in the table stored in the database 505 and compares the state F0 of the fur brush 6 with the threshold values F1 and F2. For this reason, the down time of the image forming apparatus 13 does not occur, so that the image forming apparatus 13 can be executed at short intervals.

<When changing from monochrome printing to color printing>
FIG. 1 shows a tandem type full-color image formation in which four color image forming stations 14Y, 14M, 14C, and 14K are arranged in a straight line along the stretching direction of the intermediate transfer belt 8 (left-right direction in FIG. 1). The device 13. In such an image forming apparatus 13, the bias voltage is not applied to the charging roller 2 and the primary transfer roller 5 during monochrome printing of black K color or the like. Then, in the state where only the photosensitive drum 1 idles, only the image forming station 14K for black K carries out the image forming operation.

During monochrome printing of black K or the like, the fur brush 6 and the photosensitive drum 1 in the color image forming stations 14Y, 14M, and 14C are continuously idle.

In this case, in step S13 of FIG. 8, the image information L0 acquired in step S12 is continuous in solid white, and image formation is not performed in the color image forming stations 14Y, 14M, and 14C. Therefore, since there is no transfer residual toner remaining on the surface of each photosensitive drum 1 after the primary transfer, almost no transfer residual toner is supplied to each fur brush 6.

Therefore, the CPU 500 detects that the amount of toner that has entered between the fibers of the fur brush 6 has decreased, and the numerical value of the state F0 of the fur brush 6 increases. That is, the CPU 500 determines that the positive (positive) chargeability of the surface of the photosensitive drum 1 which is rubbed by the fur brush 6 during monochrome printing is increased. Then, in step S19, CPU 500 changes the peripheral speed (rotational speed) of fur brush 6.

That is, during monochrome printing, the surface of the photosensitive drum 1 is likely to be positively (positively) charged by the rubbing of the fur brush 6 in each of the color image forming stations 14Y, 14M, and 14C. Therefore, the peripheral speed (rotational speed) of the fur brush 6 is reduced. This prevents positive (positive electrode) charging of the surface of the photosensitive drum 1.

On the other hand, monochrome printing is completed and color printing is started. At that time, if the peripheral speed (rotational speed) of the fur brush 6 is too low, the cleaning performance of the surface of the photosensitive drum 1 may be insufficient. Therefore, the control shown in FIG. 8 is performed again, and the peripheral speed (rotation speed) of the fur brush 6 is increased as necessary.

In the tandem type color image forming apparatus 13, the surface of each photosensitive drum 1 of the color image forming stations 14Y, 14M and 14C is moved so as to be separated from the outer peripheral surface of the intermediate transfer belt 8 during monochrome printing. Some are provided with transportation means. In that case, the color image forming stations 14Y, 14M, and 14C are stopped. Therefore, the above-described consideration is not necessary, and the state F0 of the fur brush 6 may be appropriately determined according to the driving conditions of the fur brush 6 and the photosensitive drum 1.

<For monochrome printing>
In the color image forming stations 14Y, 14M and 14C for monochrome printing such as black K, it is not necessary to apply the charging bias voltage to the charging rollers 2Y, 2M and 2C. In that case, the surface potential of the photosensitive drum 1 is approximately 0V. Therefore, the surface of the photosensitive drum 1 is likely to be positively (positively) charged by the rubbing of the fur brush 6.

Therefore, a small charging bias voltage is applied to each of the charging rollers 2Y, 2M and 2C of the color image forming stations 14Y, 14M and 14C during monochrome printing of black K or the like. As a result, the surface of the photosensitive drum 1 is not as surface potential as in color printing, but may be charged so as to have a small surface potential.

In Steps S11 to S14 of FIG. 8 shown in the case of "changed from monochrome printing to color printing" described above, the state F0 of the fur brush 6 is calculated from the image information L0 and the total rotation number N0 of the photosensitive drum 1. There is. Alternatively, the peripheral speed (rotation speed) of the fur brush 6 may be adjusted based on the setting of the charging bias voltage applied to the charging roller 2 that charges the surface of the photosensitive drum 1.

According to the study by the present inventor, it has been found that the larger the absolute value of the surface potential of the photosensitive drum 1 is, the more difficult it is for the surface of the photosensitive drum 1 to be positively (positively) charged by the rubbing of the fur brush 6. Moreover, even if the photosensitive drum 1 has the same surface potential (for example, −100 V), the positive (positive electrode) of the surface of the photosensitive drum 1 when the fur brush 6 is rubbed by the setting of the charging bias voltage applied to the charging roller 2. It was also found that the charging potential V1 was different.

As in the present embodiment shown in FIG. 1, the peak-to-peak voltage Vpp is 800V as an AC component (AC) bias of the charging bias voltage applied to the charging roller 2 of the contact charging type, and the surface potential of the photosensitive drum 1 is set to -100V. Consider when charged. Further, consider a case where the peak-to-peak voltage Vpp is 2000V as an AC component (AC) bias and the surface potential of the photosensitive drum 1 is charged to -100V.

In this case, when the peak-to-peak voltage Vpp of 800 V as the AC component (AC) bias of the charging bias voltage applied to the charging roller 2 is 800 V, the surface of the photosensitive drum 1 is more likely to be positively (positively) charged by the rubbing of the fur brush 6. I know that.

Therefore, the peripheral speed (rotation speed) of the fur brush 6 may be changed based on the image information L0, the total rotation number J0 of the fur brush 6 and the total rotation number N0 of the photosensitive drum 1. Alternatively, the peripheral speed (rotation speed) of the fur brush 6 may be changed according to the AC component (AC) bias voltage of the charging bias voltage applied to the charging roller 2.

The AC component (AC) bias voltage of the charging bias voltage applied to the charging roller 2 is a parameter that has a correlation with the amount of discharge current from the charging roller 2. If the amount of discharge current from the charging roller 2 is small, the surface of the photosensitive drum 1 is likely to be positively (positively) charged by the rubbing of the fur brush 6.

A non-contact corona charging method is considered for the charging roller 2 instead of the contact charging method as in the present embodiment. When the amount of discharge current applied to the discharge electrode of the corona charger is reduced, the surface of the photosensitive drum 1 is likely to be positively (positively) charged by the rubbing of the fur brush 6.

In consideration of these, the AC component bias of the charging bias voltage applied to the charging roller 2 during color printing is as follows. With the peak-to-peak voltage Vpp of 2000 V applied, a DC component (DC) bias is applied to set the surface potential of the photosensitive drum 1 to −800 V.

On the other hand, in the color image forming stations 14Y, 14M, and 14C during monochrome printing, the AC component bias of each charging roller 2 is as follows. With the peak-to-peak voltage Vpp of 500 V applied, a DC component (DC) bias is applied to set the surface potential of the photosensitive drum 1 to −100 V.

The black K image forming station 14K is as follows as an AC component (AC) bias of the charging bias voltage applied to the charging roller 2. With the peak-to-peak voltage Vpp of 2000 V applied, a DC component (DC) bias is applied to set the surface potential of the photosensitive drum 1 to −800 V.

No image formation is performed in the color image forming stations 14Y, 14M, and 14C during monochrome printing. Therefore, the alternating-current component (AC) bias of the charging bias voltage applied to each charging roller 2 of the color image forming stations 14Y, 14M, and 14C during monochrome printing is as follows. The surface of the photosensitive drum 1 is charged by applying a peak-to-peak voltage Vpp having a magnitude of 1/4 of the AC component (AC) bias of the charging bias voltage applied to each charging roller 2 during color printing.

If the charging roller 2 is not a contact charging type but a non-contact corona charging type, the discharge current amount applied to the discharge electrode of the corona charger is smaller in monochrome printing than in color printing.

As described above, the color image forming stations 14Y, 14M, and 14C for monochrome printing in which the surface of the photosensitive drum 1 is charged using the contact charging type charging roller 2 with a small discharge current amount are as follows. is there. The surface of each photosensitive drum 1 is likely to be positively (positively) charged by the rubbing of the fur brush 6.

Therefore, a parameter corresponding to the discharge current amount of the charging roller 2 is stored in advance in the memory 504 and the database 505, and the peripheral speed (rotational speed) of the fur brush 6 is uniformly reduced in monochrome printing as compared with color printing. The control may be performed.

Specifically, in the case of the contact charging type charging roller 2, the smaller the alternating-current component (AC) bias or the direct-current component (DC) bias of the charging bias voltage applied to the charging roller 2, the smaller the fur brush 6 becomes. Controls to reduce the peripheral speed (rotational speed).

In the case of the non-contact corona charging method, the peripheral speed (rotation speed) of the fur brush 6 is controlled to be lower as the amount of discharge current applied to the discharge electrode of the corona charger is smaller. In this case, the CPU 500, which is a changing unit, changes the rubbing condition between the fur brush 6 and the surface of the photosensitive drum 1 according to the amount of discharge generated by the charging bias applied to the corona charger that is a charging unit.

During color printing, the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 is 120%. During monochrome printing, the peripheral speed (rotational speed) of the fur brush 6 may be controlled so that the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 is 100%.

By reducing the amount of discharge current from each charging roller 2 of the color image forming stations 14Y, 14M, and 14C during monochrome printing, damage to each photosensitive drum 1 can be minimized. Furthermore, as described above, it is possible to prevent positive (positive electrode) charging of the surface of each photosensitive drum 1 by the rubbing of the fur brush 6.

<When changing from color printing to monochrome printing>
In the tandem-type full-color image forming apparatus 13 shown in FIG. 1, during color printing, the image forming operation is performed in each of the color image forming stations 14Y, 14M, and 14C. Therefore, the peripheral speed (rotation speed) of the fur brush 6 may be changed according to the image information L0 for each of the image forming stations 14Y, 14M, and 14C. Depending on the conditions, the fur brushes 6 of the image forming stations 14 for all colors may have the same peripheral speed (rotational speed).

When the color printing is changed to the monochrome printing, the same as the above-described “when the monochrome printing is changed to the color printing” is as follows. The fur brush 6 and the photosensitive drum 1 are kept idle, and the transfer residual toner remaining on the surface of each photosensitive drum 1 after the primary transfer is not supplied between the fibers of the fur brush 6. Therefore, the positive (positive electrode) charging property of the surface of the photosensitive drum 1 due to the rubbing of the fur brush 6 becomes high.

According to the state F0 of the fur brush 6 during color printing, the peripheral speed (rotation speed) of the fur brush 6 is appropriately reduced during monochrome printing. During monochrome printing, the peripheral speed (rotational speed) of each fur brush 6 may be uniformly reduced. Further, the peripheral speed (rotational speed) of each fur brush 6 may be uniformly reduced when performing monochrome printing from the start of printing other than when the color printing is changed to monochrome printing.

<When only the photosensitive drum 1 is replaced>
The fur brush 6 is in a durable state by repeatedly forming an image, but a case will be described in which only the photosensitive drum 1 is replaced when the photosensitive drum 1 has some trouble or reaches the end of its life.

When only the photosensitive drum 1 is replaced, when the data is retrieved from the table stored in the database 505 in step S12 of FIG. 8, the total rotation number N0 of the photosensitive drum 1 becomes zero.

Here, the photosensitive drum 1 itself has a characteristic that the surface of the photosensitive drum 1 is more likely to be positively (positively) charged by rubbing the fur brush 6 when a new one is used. Therefore, in step S14 of FIG. 3, the CPU 500 determines whether or not the photosensitive drum 1 is new by referring to the data in the table stored in the database 505.

This makes it possible to consider the case where only the photosensitive drum 1 is replaced. In the new photosensitive drum 1, the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 is reduced. As a result, even if only the photosensitive drum 1 is replaced with a new one, it is possible to prevent the occurrence of positive (positive electrode) charging on the surface of the photosensitive drum 1 due to the rubbing of the fur brush 6.

As the durability of the photosensitive drum 1 progresses, the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 is increased. This makes it possible to prevent positive (positive electrode) electrification on the surface of the photosensitive drum 1 due to rubbing of the fur brush 6 and to secure cleaning performance at the same time.

<When toner is forcibly consumed>
For example, when images having a low image ratio such as a white solid image are continuously formed, the developing device 4 is in an idle rotation state, and the developer contained in the developer container 4a is deteriorated. Therefore, when a predetermined number of images of the recording material 12 having a low image ratio are continuously formed, the developer contained in the developer container 4a of the developing device 4 may be forcibly consumed.

When the toner forcibly consumed the developer contained in the developer container 4a of the developing device 4 is carried on the surface of the photosensitive drum 1 and reaches the cleaning device 15 without being primarily transferred, a large amount of toner is collected in the fur brush 6 To reach.

Alternatively, the amount of toner reaching the fur brush 6 may temporarily increase due to troubles such as continuous formation of solid images and jamming (JAM). In step S12 of FIG. 8, of the image information L0, the image information P printed on the X recording materials 12 immediately before the state F0 of the fur brush 6 is calculated is considered. Further, the image information (including the control patch image) Q which has been passed from the time when the fur brush 6 is exchanged and the use is started to the present is considered. Then, the state F0 of the fur brush 6 is calculated in consideration of the image information P.

Based on the state F0 of the fur brush 6, the CPU 500 determines whether the peripheral speed (rotation speed) of the fur brush 6 needs to be changed. This makes it possible to prevent the positive (positive electrode) charge on the surface of the photosensitive drum 1 due to the rubbing of the fur brush 6 and achieve the cleaning performance at the same time.

According to the present embodiment, it is detected that the surface potential of the photosensitive drum 1 is charged by the rubbing of the fur brush 6 in the opposite polarity to the polarity of the charging potential on the developing side, and the fur speed relative to the peripheral speed of the surface of the photosensitive drum 1 is detected. The peripheral speed ratio of the outer peripheral surface of the brush 6 is changed.

The outer peripheral surface of the fur brush 6 with respect to the peripheral speed of the surface of the photosensitive drum 1 according to the charging potential V1 charged to the opposite polarity of the charging potential on the developing side of the surface potential of the photosensitive drum 1 by the rubbing of the fur brush 6. Reduce the peripheral speed ratio of. As a result, it is possible to prevent the surface potential of the photosensitive drum 1 from being charged to a polarity opposite to the polarity of the charging potential on the developing side.

That is, the surface potential of the photosensitive drum 1 becomes non-uniform due to the charging potential V1 that is charged by the rubbing of the cleaning member such as the fur brush 6 on the surface of the photosensitive drum 1 opposite to the developing side. As a result, image defects such as image unevenness and white background fogging occur. The prevention of such image defects and the prevention of cleaning defects can both be achieved. In addition, it is easy to increase the image forming speed.

In the present embodiment, the CPU 500, which is the changing unit, changes the rubbing condition between the fur brush 6 and the surface of the photosensitive drum 1 according to the image forming conditions stored in the memory 504 serving as the storage unit and the database 505. Other configurations are the same as those of the reference example, and similar effects can be obtained.

In each of the above-described embodiments, as an example of changing the sliding condition between the fur brush 6 and the surface of the photosensitive drum 1, the peripheral speed ratio of the outer peripheral surface of the fur brush 6 to the peripheral speed of the surface of the photosensitive drum 1 is changed. An example has been described.

In addition, the number of times of rubbing between the fur brush 6 and the surface of the photosensitive drum 1 per unit time is changed. Alternatively, the relative movement direction between the fur brush 6 and the surface of the photosensitive drum 1 is changed. Alternatively, the contact pressure between the fur brush 6 and the surface of the photosensitive drum 1 is changed. Alternatively, the penetration amount of the fur brush 6 on the surface of the photosensitive drum 1 is changed. The rubbing condition between the fur brush 6 and the surface of the photosensitive drum 1 can be changed by changing at least one of them.

1, 1Y, 1M, 1C, 1K... Photosensitive drum (image carrier)
5, 5Y, 5M, 5C, 5K... Primary transfer roller (transfer means)
6, 6Y, 6M, 6C, 6K... Fur brush (cleaning means)
500... CPU (change means)
504... Memory (storage means)

Claims (4)

An image forming unit that forms a toner image on the image bearing member charged by a charging unit and transfers the toner image to a transfer member to form an image is provided, and the image forming unit transfers from the image bearing member to the transfer member. In an image forming apparatus having a brush member that is rotatable in contact with the image carrier for cleaning the toner on the image carrier after transferring the toner image,
Changing means for changing the peripheral speed difference between the brush member and the image carrier based on the image signal of the image formed on the immediately preceding predetermined number of sheets and the image signal accumulated from the start of use of the brush member. An image forming apparatus comprising: The changing unit obtains from an image signal of an image formed in a predetermined number of sheets immediately before stored in a storage unit and an image signal accumulated from the start of use of the brush member, by rubbing the brush member. The peripheral speed difference between the brush member and the image carrier is changed according to the value of the force for charging the surface of the image carrier and the value of the total number of rotations of the image carrier. The image forming apparatus according to claim 1. The changing unit has an image signal of images in which the total number of rotations of the image carrier is smaller than a first threshold value and the predetermined number of images immediately before is formed, and an image signal accumulated from the start of use of the brush member. When the value of the force obtained by charging the surface of the image carrier by the friction of the brush member is equal to or greater than the second threshold value, the peripheral speed difference between the brush member and the image carrier is reduced. The image forming apparatus according to claim 2, wherein the image forming apparatus is changed. The changing unit is configured such that the value of the total number of rotations of the image carrier is equal to or more than a first threshold value, the image signal of the image formed in the predetermined number of sheets immediately before, and the image accumulated from the start of using the brush member. When the value of the force for charging the surface of the image carrier by the rubbing of the brush member, which is obtained from the signal, is greater than or equal to a third threshold value that is greater than the second threshold value, the circumference of the brush member and the image carrier member is increased. The image forming apparatus according to claim 3, wherein the image forming apparatus is changed so as to reduce the speed difference.