JP6950260B2 - Image forming device and control method - Google Patents

Description

The present invention relates to an image forming apparatus and a control method.

In recent years, there has been a demand for smaller particle sizes of toner particles in an electrophotographic image forming apparatus from the viewpoint of improving image quality, and examples of methods for obtaining such toner particles include an emulsion polymerization method and a suspension polymerization method. The polymerization method of is used.

Here, as a method of removing residual toner after transfer of an image carrier such as a photoconductor, a cleaning blade made of urethane rubber or the like is brought into contact with the image carrier in the counter direction to scrape off toner particles. There is. However, as the particle size of the toner particles becomes smaller, the adhesive force between the toner particles and the image carrier increases, so that it becomes difficult to remove the residual toner on the image carrier. In particular, in a cleaning blade that has been used for a long period of time, when the tip portion in contact with the image carrier is worn, the scraping force is reduced, so that toner passes through the blade, which is a so-called "slinque" cleaning defect. It becomes easy to remove the residual toner on the image carrier.

In order to assist the cleaning of residual toner, some auxiliary members such as brush rollers are provided on the upstream side of the cleaning blade. This auxiliary member rotates while abutting on the surface of the image carrier, and applies a voltage to the rotation axis to form an electric field in the direction of attracting toner to the image carrier to remove a part of the residual toner. Remove mechanically and electrostatically.

In the image forming apparatus disclosed in Patent Document 1, two brush rollers are provided, and the number of rotations of the brush rollers and the applied voltage are controlled by the average image density calculated from the image data.

Further, the image forming apparatus disclosed in Patent Document 2 superimposes a toner image formed by a plurality of image forming units on a belt-shaped intermediate transfer body to form a full-color toner image, which is then printed on paper by a batch transfer means. It has a configuration for batch transfer to. In such a configuration, a countercharged toner removing means for removing toner having a charging polarity different from that of the toner is provided on the photoconductor drum of the second and subsequent image forming units. With this reverse-charged toner, for example, when the first-color toner image is transferred and then the second-color toner image is transferred, a part of the first-color toner image is present at a position where the first-color toner image is present and the second-color toner image is not present. It occurs due to the phenomenon of reverse transfer onto the second color photoconductor drum. The reverse-charged toner removing means of Patent Document 2 includes a brush roller and an application means for applying a bias having the same polarity as the charging characteristics of the toner to the brush roller.

Japanese Unexamined Patent Publication No. 2006-276065 Japanese Unexamined Patent Publication No. 2000-242152

Even if the auxiliary member is provided on the upstream side of the cleaning blade, if the amount of residual toner reaching the cleaning blade is large, "sliding" is likely to occur. In the image forming apparatus disclosed in Patent Document 1, the number of rotations of the brush roller and the applied voltage are controlled by estimating the amount of residual toner from the image data and using the average image density calculated from the image data. Therefore, no consideration is given to the amount of reverse-transferred toner in which the toner transferred on the upstream side is reverse-transferred to the photoconductor drum on the downstream side, and the amount of toner reaching the cleaning blade cannot be controlled.

Further, the image forming apparatus disclosed in Patent Document 2 discloses a reverse-charged toner removing means for removing the reverse transfer toner, but it is premised on a configuration in which a cleaning blade is not provided, and reaches the cleaning blade. No consideration is given to the amount of toner to be used.

The present invention has been made in view of the above circumstances, and in an image forming apparatus including a plurality of image forming portions, by suppressing the amount of toner reaching the cleaning blade of the image forming portion on the downstream side, it is possible to reduce the amount of toner. An object of the present invention is to provide an image forming apparatus for preventing the occurrence of cleaning defects.

The above object of the present invention is achieved by the following means.

(1) An intermediate transfer body to which the toner image is transferred and
A plurality of image forming portions that are sequentially arranged on the intermediate transfer body along the moving direction, form toner images of different colors, and are transferred to the intermediate transfer body at the transfer position.
An image forming apparatus equipped with a control unit.
Each of the image forming parts
Image carrier and
A developing device that forms a toner image on the image carrier,
A pre-cleaning unit that removes a part of the residual toner on the image carrier after transfer to the intermediate transfer body, and
A cleaning blade that abuts on the image carrier and removes the residual toner is provided on the downstream side of the pre-cleaning unit and on the upstream side of the developing device in the rotation direction of the image carrier. ,
In the control unit, in the image forming unit second and subsequent from the upstream side in the moving direction of the intermediate transfer body, the toner image transferred on the intermediate transfer body on the upstream side is reverse-transferred to the image carrier. An image forming apparatus that determines the amount of reverse transfer toner, sets cleaning conditions for the pre-cleaning unit based on the determined amount of reverse transfer toner, and adjusts the amount of toner that reaches the cleaning blade.

(2) The pre-cleaning unit is a brush roller that comes into contact with the image carrier and rotates.
The image forming apparatus according to (1) above, wherein the control unit sets the rotation speed of the brush roller and / or the applied voltage applied to the brush roller based on the determined amount of reverse transfer toner.

(3) When the determined amount of reverse transfer toner is larger than a predetermined threshold value, the control unit sets the rotation speed of the brush roller to be higher than the normal speed at the time of image formation, and / or the application. The image forming apparatus according to (2) above, wherein the voltage is set to a voltage shifted to the same polarity side as the charging polarity of the toner from the normal voltage at the time of image forming.

(4) The control unit further determines the amount of residual transfer toner remaining on the image carrier without transferring the toner image formed by the image forming unit to be determined to the intermediate transfer body, and determines the determination. The image forming apparatus according to the above (2) or (3), wherein the applied voltage applied to the brush roller is set by comparing the transfer residual toner amount and the reverse transfer toner amount.

(5) The control unit is
When the amount of residual transfer toner is larger than the amount of reverse transfer toner, the applied voltage applied to the brush roller is set to the first voltage.
The above (4), wherein when the transfer residual toner amount is smaller than the reverse transfer toner amount, the applied voltage is set to a second voltage shifted to the same polarity side as the charging polarity of the toner from the first voltage. Image forming device.

(6) Any of the above (2) to (5), further comprising a solid lubricant solidified with a lubricant and a coating portion for supplying the lubricant scraped from the solid lubricant to the surface of the image carrier. The image forming apparatus described in.

(7) The image forming apparatus according to (6) above, wherein the coating portion is the brush roller.

(8) The image forming according to any one of (1) to (7) above, wherein the control unit determines the amount of reverse transfer toner of each image forming unit based on the image data used for image forming. Device.

(9) The control unit determines the amount of reverse transfer toner of the image-forming unit to be determined based on the image data, and the image-forming unit is the intermediate transfer body at a corresponding position in the image region. a toner image image to be transferred to the upper, performed by imaging unit upstream of the acting image portion is compared with the toner image image transferred onto the intermediate transfer member, the image forming according to (8) Device.

(10) In the image forming unit to be determined, the control unit uses the toner produced by the image forming unit on the upstream side of the image forming unit in the region of the intermediate transfer body corresponding to the white background portion that does not form the toner image. The image formation according to (8) or (9) above, wherein when the image is transferred, it is determined that the toner in the region is reverse-transferred to the image carrier of the image-forming portion to be determined. Device.

(11) The control unit refers to a region of the intermediate transfer body corresponding to a white background portion that does not form a toner image in the image-forming unit third and subsequent from the upstream side in the moving direction of the intermediate transfer body from the image-forming unit. The amount of reverse transfer toner when the toner image is transferred by a plurality of image forming portions on the upstream side, and the toner image when only one image forming portion on the upstream side of the image forming portion is transferred. The image forming apparatus according to (10) above, which determines that the amount of the reverse transfer toner is larger than the amount of the reverse transfer toner.

(12) In the image forming unit to be determined, the control unit uses the toner produced by the image forming unit on the upstream side of the image forming unit in the region of the intermediate transfer body corresponding to the white background portion that does not form the toner image. When the image is transferred, the amount of reverse transfer toner on the image carrier in the region is determined based on the amount of transfer toner on the intermediate transfer body calculated based on the image data (8). The image forming apparatus according to any one of (11) above.

(13) The control unit further determines the amount of the reverse transfer toner by using the transfer voltage applied to the transfer member provided at the transfer position of the image forming unit to be determined (8). ) To the image forming apparatus according to any one of the above (12).

(14) Further, a sensor for measuring the amount of toner on the intermediate transfer body is provided at each position on the upstream side and the downstream side of the transfer position of the image forming portion to be determined.
The control unit calculates the reverse transfer rate at which the toner of the intermediate transfer body reverse-transfers to the image carrier of the image-forming unit from the output of the sensor, and uses the calculated reverse transfer rate to perform the reverse transfer. The image forming apparatus according to any one of (8) to (13) above, which determines the amount of copy toner.

(15) A plurality of image forming portions are sequentially arranged along the moving direction of the intermediate transfer body, form toner images of different colors, and are transferred to the intermediate transfer body at the transfer position. An image carrier, a developing device that forms a toner image on the image carrier, and a pre-cleaning unit that removes a part of residual toner on the image carrier after being transferred to the intermediate transfer at the transfer position. And a cleaning blade that comes into contact with the image carrier and removes the residual toner on the downstream side of the pre-cleaning portion and on the upstream side of the developing device in the rotation direction of the image carrier. It is a control method of an image forming apparatus to be provided.
In each of the image forming portions after the second from the upstream side in the moving direction of the intermediate transfer body,
A step of determining the amount of reverse-transferred toner in which the toner image transferred onto the intermediate transfer body on the upstream side is reverse-transferred to the image-bearing body.
A step of setting cleaning conditions for the pre-cleaning unit based on the determined amount of reverse transfer toner, and
A step of operating the pre-cleaning unit under the set cleaning conditions and adjusting the amount of toner reaching the cleaning blade, and
Control methods, including.
(16) An intermediate transfer body to which the toner image is transferred and
A plurality of image forming portions that are sequentially arranged on the intermediate transfer body along the moving direction, form toner images of different colors, and are transferred to the intermediate transfer body at the transfer position.
An image forming apparatus equipped with a control unit.
Each of the image forming parts
Image carrier and
A developing device that forms a toner image on the image carrier,
A pre-cleaning unit that removes a part of the residual toner on the image carrier after transfer to the intermediate transfer body, and
A cleaning blade that abuts on the image carrier and removes the residual toner on the downstream side of the pre-cleaning portion and on the upstream side of the developing device in the rotation direction of the image carrier.
A solid lubricant obtained by solidifying the lubricant, a coating portion for supplying the lubricant scraped from the solid lubricant to the surface of the image carrier, and a coating portion.
With
In the control unit, in the image forming unit second and subsequent from the upstream side in the moving direction of the intermediate transfer body, the toner image transferred on the intermediate transfer body on the upstream side is reverse-transferred to the image carrier. The amount of reverse transfer toner is determined, and based on the determined amount of reverse transfer toner, the cleaning conditions of the pre-cleaning portion are set, and the amount of toner reaching the cleaning blade is adjusted.
The pre-cleaning unit is a brush roller that comes into contact with the image carrier and rotates.
The control unit is an image forming apparatus that sets the rotation speed of the brush roller and / or the applied voltage applied to the brush roller as the cleaning condition.

According to the present invention, in the second and subsequent image-forming portions, the amount of reverse-transferred toner in which the toner image transferred onto the intermediate transfer body on the upstream side is reverse-transferred to the image-bearing body of the image-imaging portion is determined. By setting the cleaning conditions of the pre-cleaning unit based on the determined amount of reverse transfer toner, it is possible to suppress an increase in the amount of toner reaching the cleaning blade on the downstream side and prevent slippage.

It is a figure which shows the schematic structure of the image forming apparatus which concerns on one Embodiment of this invention. It is a figure which shows the structure around the image-forming part in 1st Embodiment. It is a block diagram which shows the hardware structure of an image forming apparatus. It is a figure which shows the structure of the cleaning apparatus. It is a schematic diagram which shows the output image of a vertical band chart. It is a figure which shows the structure of the bizhub modified machine 1 used for evaluation. It is a figure which shows the amount of toner after transfer at positions A to E. It is a figure which shows the recovery rate of the transfer residual toner and the reverse transfer toner by a brush roller. It is a figure which shows the measurement result of the toner charge amount distribution of transfer residual toner and reverse transfer toner. It is a figure which shows the cleaning evaluation result. It is a figure which shows the measurement result of the amount of lubricant on a photoconductor at each position. It is a figure which shows the relationship between the cleaning condition of a brush roller, and the recovery rate. It is a figure which shows the relationship between the transfer voltage and the amount of reverse transfer toner. It is a flowchart executed by the control unit 10. It is a subroutine of step S131. It is a figure which shows the structure around the image-forming part in the 2nd Embodiment. It is a flowchart which is executed in 2nd Embodiment. It is a figure which shows the structure around the image-forming part in the modification.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the description of the drawings, the same elements are designated by the same reference numerals, and duplicate description will be omitted. In addition, the dimensional ratios in the drawings are exaggerated for convenience of explanation and may differ from the actual ratios.

FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing a configuration around an image forming portion in the first embodiment. FIG. 3 is a block diagram showing a hardware configuration of the image forming apparatus.

As shown in FIGS. 1 to 3, the image forming apparatus 100 includes a control unit 10, a storage unit 20, an image forming unit 30, a paper feed transport unit 40, and an operation panel 50.

The control unit 10 is a CPU, and controls each unit of the device and performs various arithmetic processes according to a program. Further, as will be described in detail later, the control unit 10 determines the amount of reverse transfer toner based on the image data included in the received print job, and configures each device such as the image forming unit 30 including the pre-cleaning unit. Set the operating conditions of the part.

The storage unit 20 is composed of a ROM for storing various programs and various data in advance, a RAM for temporarily storing programs and data as a work area, a hard disk for storing various programs and various data, and the like. The storage unit 20 stores image data for charts used in the transfer rate measurement mode, an operating condition table of each component of the image forming unit 30 including the pre-cleaning unit, and the like.

(Image forming unit 30)
The image forming unit 30 includes an image forming unit 31, an exposure unit 32, an intermediate transfer belt 33 as an intermediate transfer body, a primary transfer unit 34, a secondary transfer unit 35, a fixing device 36, and a belt cleaning unit 37. The image-creating unit 31, the exposure unit 32, and the primary transfer unit 34 each have a configuration corresponding to each of the basic colors of yellow (Y), magenta (M), cyan (C), and black (K). The intermediate transfer belt 33 rotates and moves in the direction of the arrow. The image forming unit 31 and the primary transfer unit 34 are arranged in order along the moving direction of the intermediate transfer belt 33. The most upstream of the arrangement order is the image forming unit 31 for Y, and the second to fourth are the image forming units 31 for M, C, and K, respectively. In FIG. 1, notation of symbols other than Y is omitted for the exposed unit 32 and the primary transfer unit 34.

Each image forming unit 31 includes a photoconductor drum 311, a band electrode 312, a developing device 313, a cleaning device 314, and an eraser lamp 315.

The photoconductor drum 311 is made of an organic photoconductor in which a photosensitive layer made of a resin containing an organic photoconductor is formed on the outer peripheral surface of a drum-shaped metal substrate, and is counterclockwise as shown by an arrow in FIG. Rotate in the direction. Examples of the resin constituting the photosensitive layer include polycarbonate resin, silicone resin, polystyrene resin, acrylic resin, methacrylic resin, epoxy resin, polyurethane resin, vinyl chloride resin, melamine resin and the like.

The band electrode 312 is a scorotron charger type electrode, and charges the surface of the photoconductor drum 311 to a constant potential. A corotron charger or a charging roller may be applied as the method of the band electrode 312.

The developing device 313 contains a two-component developer composed of toners having small particles of different colors of yellow, magenta, cyan, and black, and carriers, respectively. The two-component developer consists of a carrier with ferrite as the core and an insulating resin coated around it, and a pigment or colorant such as carbon black, a charge control agent, and an external agent such as silica and titanium oxide using polyester as the main material. It consists of added toner. The carrier has a particle size of 15 to 100 μm, the saturation magnetization is 10 to 80 emu / g, the toner has a particle size of 3 to 15 μm, the charging characteristic of the toner is a negative charging characteristic, and the average charge amount is -20 to -60 μC / g. As the two-component developer, a mixture of these carriers and toner so as to have a toner concentration of 4 to 10% by mass is used. In this embodiment, as will be described later, the cleaning device 314 includes a lubricant supply unit, and a lubricant application method is adopted in which the lubricant supply unit supplies the lubricant to the surface of the photoconductor drum 311. There is. In addition, instead of the lubricant application method, a toner external addition method in which a lubricating external additive is included in the external additive added to the toner may be adopted, or a configuration in which no lubricant is applied may be adopted.

The lubricating external additive to be added to the toner is not particularly limited, and examples thereof include fatty acid metal salts, silicone oils, and fluororesins, which can be used alone or in combination of two or more. .. In particular, fatty acid metal salts are preferable. As the fatty acid metal salt, as the fatty acid, a linear hydrocarbon is preferable, for example, myristic acid, palmitic acid, stearic acid, oleic acid and the like are preferable, and stearic acid is more preferable. Examples of the metal include lithium, magnesium, calcium, strontium, zinc, cadmium, aluminum, cerium, titanium, iron and the like. Among these, zinc stearate, magnesium stearate, aluminum stearate, iron stearate and the like are preferable, and zinc stearate is most preferable. When a toner having a positive charging characteristic is used, a negatively charged lubricant is used. In that case, it is preferable to use a fluororesin-based lubricant.

The developing apparatus 313 includes a developing sleeve arranged so as to face the photoconductor drum 311 via a developing region. For example, a DC development bias having the same polarity as the charging polarity of the band electrode 312 or a development bias on which an AC voltage is superimposed is applied to the developing sleeve. The developing device 313 performs reverse development in which toner is adhered to the electrostatic latent image formed by the exposed unit 32.

The toner image formed on the photoconductor drum 311 by the developing device 313 is carried to the transfer position Pt formed between the roller-shaped primary transfer unit 34. In the primary transfer unit 34, a voltage having a polarity opposite to that of the toner is applied to the rotation shaft at the transfer position Pt by the voltage supplied from the transfer power supply 91, and the toner image on the photoconductor drum 311 is displayed on the intermediate transfer belt 33. Transcribed.

The toner images formed by the image-forming units 31 are superposed on the intermediate transfer belt 33 by the respective primary transfer units 34, and then transferred to the conveyed paper S by the secondary transfer unit 35. The paper S on which the full-color toner image is transferred is conveyed to the fixing device 36 on the downstream side, heated and pressure-treated, whereby a full-color image is formed on the paper S.

On the other hand, as various post-treatments, the transfer residual toner remaining on the photoconductor drum 311 without being transferred on the intermediate transfer belt 33 at the transfer position Pt is conveyed to the downstream side and collected by the cleaning device 314. .. Details of the configuration of the cleaning device 314 will be described later. Similarly, the transfer residual toner that remains on the intermediate transfer belt 33 without being transferred on the paper S is conveyed to the downstream side and collected by the belt cleaning unit 37. Further, the eraser lamp 315 installed between the cleaning device 314 and the band electrode 312 completely erases the latent image before the next image formation so as not to affect the image formation.

(Paper feed transport unit 40)
The paper feed transport unit 40 includes a plurality of paper feed trays 41 and a paper transport path 42. A plurality of sheets of paper S are loaded on the paper feed tray 41, and the top-level paper S is fed one by one. The paper transport path 42 includes a plurality of transport roller pairs arranged along the paper transport path 42 and a drive motor (not shown) for driving the pair of transport rollers, and the paper S fed from the paper feed tray 41 is fed by 2. It is conveyed to the transfer position of the next transfer unit 35 and the fixing device 36 on the downstream side thereof.

(Operation panel 50)
The operation panel 50 includes a touch panel, a numeric keypad, a start button, a stop button, and the like, and is used for inputting various settings related to the device, displaying the state of the device, and inputting various instructions.

(Cleaning device 314)
FIG. 4 is an enlarged view of FIG. 2 and is a diagram showing the configuration of the cleaning device 314. The cleaning device 314 includes a housing 61, a brush roller 62, a lubricant supply unit 63, a flicker member 64, a transport member 65, a cleaning blade 66, and a holder 67.

The brush roller 62 functions as a "pre-cleaning unit", removes a part of the residual toner on the photoconductor drum 311 (hereinafter, also simply referred to as "on the photoconductor"), and reaches the cleaning blade 66 on the downstream side. Reduce toner. Here, the residual toner includes "transfer residual toner" and "reverse transfer toner" described later. The "transfer residual toner" is toner that has not been transferred to the intermediate transfer belt 33 at the transfer position Pt. The brush roller 62 is composed of a metal rotating shaft 62a and a large number of brush bristles 62b arranged around the rotating shaft 62a. The brush bristles 62b are planted on a base cloth (not shown) wound around a rotating shaft 62a. For example, the material of the brush bristles 62b is polyester such as 6-nylon, 12-nylon, PET, synthetic resin such as acrylic, vinylon, and aramid, or a mixture of two or more of these, and has a fineness of 2 to 15. It is denier (D), the density (planting density) is 50 to 300 kF / (inch) ² , and the hair length (height) is 2 to 8 mm. As the pre-cleaning unit, a sponge roller may be used instead of the brush roller 62.

The rotation direction of the brush roller 62 may be either a with direction (a direction in which the surface moves in the same direction) or a counter direction (a direction in which the surface moves in the opposite direction) with respect to the rotation direction of the photoconductor drum 311. However, from the viewpoint of contact-recovering the toner particles from the photoconductor drum 311 as much as possible, the counter direction is preferable, and in the present embodiment, the counter direction is set.

The rotating shaft 62a of the brush roller 62 is electrically connected to the brush power supply 92, and normally, a voltage having a polarity opposite to that of the toner is applied so that the transfer residual toner can be recovered. Further, the rotation shaft 62a is connected to a brush drive unit 93 composed of a motor, gears, etc., and the control unit 10 controls the brush drive unit 93 to change the rotation speed (rotation speed) of the brush drive unit. do.

(Lubricant supply unit 63)
The lubricant supply unit 63 includes a solid lubricant 63a, a holder 63b, and an elastic support unit 63c. One end of the elastic support portion 63c is fixed to the housing 61. The solid lubricant 63a is formed by solidifying the molten lubricant powder into a substantially rectangular parallelepiped shape. The holder 63b holds the solid lubricant 63a. The elastic support portion 63c has, for example, a compression coil spring, and presses (contacts) the solid lubricant 63a against the brush roller 62 via the holder 63b. In the present embodiment, the brush roller 62 also functions as a “coating portion”, and the brush roller 62 is rotationally driven to scrape off the lubricant (lubricant powder) from the solid lubricant 63a, which is used as a photoconductor. It is applied to the surface of the drum 311. The brush roller 62, which functions as a coating portion, also plays a role of spreading and coating the lubricant particles on the image carrier by the contact pressure at the time of coating. Further, increasing the rotation speed of the brush roller 62 increases the amount of the lubricant applied to the photoconductor drum 311, and decreasing it decreases the amount of the lubricant applied.

As the lubricant used in the solid lubricant 63a, a material that can be applied to the surface of the image carrier and can reduce the surface energy thereof to reduce the adhesive force between the toner and the image carrier is selected. Examples thereof include fatty acid metal salts, fluororesins, and the like, and these can be used alone or in combination of two or more. In particular, fatty acid metal salts are preferable. As the fatty acid metal salt, as the fatty acid, a linear hydrocarbon is preferable, for example, myristic acid, palmitic acid, stearic acid, oleic acid and the like are preferable, and stearic acid is more preferable. Examples of the metal include lithium, magnesium, calcium, strontium, zinc, cadmium, aluminum, cerium, titanium, iron and the like. Among these, zinc stearate, magnesium stearate, aluminum stearate, iron stearate and the like are preferable, and zinc stearate is most preferable. When a toner having a positive charging characteristic is used, a negatively charged lubricant is used. In that case, it is preferable to use a fluororesin-based lubricant.

The flicker member 64 is a rigid rod made of, for example, metal. It may be flat or columnar as shown in FIGS. 1, 3 and the like. Further, a voltage may be applied to the flicker member 64 so as to attract the toner or the lubricant by a power source (not shown). Further, in the case of a columnar shape, it may be configured to be rotatable. The flicker member 64 is used to separate contaminated particles such as the lubricant remaining on the brush roller 62 and the toner transferred from the photoconductor drum 311. The flicker member 64 is fixed to the housing 61 by a holder, and the tip of the flicker member 64 comes into contact with the brush roller 62. In the figure, in the rotation direction of the brush roller 62, the solid lubricant 63a, the flicker member 64, and the photoconductor drum 311 are arranged in this order, but the present invention is not limited to this. The solid lubricant 63a, the photoconductor drum 311 and the flicker member 64 may be arranged in this order so that the flicker member 64 comes into contact with the solid lubricant 63a immediately upstream.

(Cleaning blade 66)
The cleaning blade 66 is a flat plate-shaped member made of an elastic body such as urethane rubber. The cleaning blade 66 is fixed to the housing 61 by the holder 67. The surface of the photoconductor drum 311 is cleaned by the cleaning blade 66 in a state where the lubricant is supplied to the surface of the photoconductor drum 311 by the lubricant supply unit 63 and the adhesive force between the toner particles and the photoconductor drum 311 is reduced. I do. The toner collected by the cleaning blade 66 and the particles such as toner and lubricant collected by the brush roller 62 and separated by the flicker member 64 fall to the lower part of the housing 61. Particles such as toner that have fallen are conveyed to a replaceable collection box (not shown) provided at the back side of the image forming apparatus 100 by a transfer member 65 provided at the lower part of the housing 61, and are conveyed into the collection box. It is stored.

(Effect of the amount of toner reaching the cleaning blade 66)
If the amount of the lubricant on the photoconductor is small, there are problems such as quality problems related to cleaning defects such as “sliding” and “granular noise”, and problems such as increased wear on the surface of the photoconductor drum 311 and shortening of the life of the photoconductor. Here, "granular noise" means that when toner that passes through the cleaning blade 66 is generated, agglomerates of toner are formed on the photoconductor with the toner as a core, and granular white spots (granular noise) appear in the solid image printing portion. This is a phenomenon that occurs.

On the other hand, if the amount of the lubricant on the photoconductor is too large, there arises a problem that the wear of the cleaning blade 66 increases. Further, when the amount of lubricant on the photoconductor is large, the image density is high in the large part and light in the small part, and image unevenness occurs according to the amount. As described above, there is an appropriate range for the amount of lubricant on the photoconductor.

Since the lubricant on the photoconductor is reduced by the transfer to the intermediate transfer belt 33 at the transfer position Pt and the recovery by the cleaning blade 66, even if a certain amount of lubricant is supplied to the photoconductor drum 311, the lubricant on the photoconductor is on the photoconductor. The amount of lubricant varies. Therefore, in order to maintain the amount of lubricant on the photoconductor within an appropriate range, it is necessary to consider the amount of lubricant supplied and the amount recovered.

At the transfer position Pt, when the charging polarity of the lubricant is the same as that of the toner, the lubricant is transferred to the intermediate transfer belt 33 by the transfer electric field, and the amount of the lubricant on the photoconductor is reduced. The amount of decrease varies depending on the transfer electric field. On the other hand, when the charging polarity of the lubricant is opposite to that of the toner, the transfer of the lubricant to the intermediate transfer belt 33 does not occur and the amount of the lubricant does not decrease at the transfer position Pt.

On the other hand, in the cleaning blade 66, since the lubricant is recovered by the toner and the external additive particles existing on the blade edge, the amount of the recovered lubricant varies depending on the amount of toner reaching the cleaning blade 66. Therefore, if the amount of toner reaching the cleaning blade 66 is not properly controlled, the amount of lubricant may not be maintained within an appropriate range.

A brush roller 62 (pre-cleaning unit) is provided as in the present embodiment in order to suppress the problem that the lubricant is excessively recovered from the photoconductor when the amount of toner reaching the cleaning blade 66 is large. Is valid. By collecting the toner on the photoconductor in advance by the pre-cleaning unit, the amount of toner reaching the cleaning blade 66 can be suppressed, and fluctuations in the amount of lubricant and cleaning defects such as "slinking" can be prevented.

As the force for collecting toner by the pre-cleaning unit, a combination of mechanical force and electrostatic force can be used. The toner can be recovered by mechanical force by operating the surface of the pre-cleaning portion on the photoconductor that comes into contact with the toner at a speed difference with respect to the surface of the photoconductor drum 311.

Further, the surface of the pre-cleaning portion that comes into contact with or is close to the toner on the photoconductor is pre-cleaned so that the potential is opposite to the charging polarity of the toner (for example, positive potential) with respect to the surface potential of the photoconductor drum 311. By applying a bias to the cleaning portion, the toner on the photoconductor can be recovered by an electrostatic force.

Here, in order to obtain the desired toner recovery ability only by the mechanical force, it is necessary to increase the mechanical force acting on the toner from the pre-cleaning part, but in general, this mechanical force is increased. This is proportional to increasing the mechanical force acting on the photoconductor drum 311 from the pre-cleaning unit. If the mechanical force acting on the photoconductor drum 311 from the pre-cleaning part is high, the mechanical stress on the photoconductor drum 311 and the pre-cleaning part becomes strong, deterioration of these members progresses, and it is difficult to extend the service life. Is. For this reason, it is common to set the mechanical force to a certain reasonable range that is compatible with the life of the member, and to obtain the desired toner recovery ability by supplementarily combining the recovery action by the electrostatic force. Is the target.

(About reverse transfer toner)
The transfer residual toner that remains without being transferred is conveyed to the cleaning blade 66. Further, in the case of a color image forming apparatus including a plurality of image forming units 31, "reverse transfer" may occur in which the upstream color toner transferred on the intermediate transfer belt 33 is retransferred onto the downstream color photoconductor. be. In the following, the toner in which the toner on the upstream side is reverse-transferred onto the photoconductor of the target image-forming portion 31 is referred to as “reverse-transfer toner”. When reverse transfer occurs, the amount of reverse transfer toner that is reverse transferred by the upstream color toner is added to the amount of toner that reaches the blade portion in addition to the amount of residual transfer toner of the own color.

When the upstream color toner on the intermediate transfer body belt is reverse-transferred at the downstream image forming portion 31 (hereinafter, also referred to as “target image forming portion” or simply “self-color”), the following characteristics are exhibited. be. (The experimental data from which the following features were derived will be described later).
(Characteristic 1) The larger the amount of toner on the intermediate transfer belt 33, the larger the amount of reverse transfer toner.
(Characteristic 2) The amount of reverse transfer toner is large in the white background portion that does not form the self-colored toner image, and reverse transfer does not occur in the solid portion that forms the self-colored toner image.
(Characteristic 3) The amount of charge of the reverse transfer toner is smaller than the amount of charge of the regular toner, and the toner is weakly charged, and contains the reverse charge toner with respect to the normal polarity of the toner charge. (The transfer residue of the self-color is strongly charged with the normal toner charging polarity).

Due to the above (feature 1) and (feature 2), the amount of reverse transfer toner is extremely large compared to the amount of transfer residual toner of the own color depending on the image pattern. For example, when solid images of two or more upstream color toners overlap on a self-colored white background, the amount of reverse transfer toner increases. Therefore, the influence of the reverse transfer toner is large on the problems such as the uniformity of the amount of lubricant and the “slinching” caused by the amount of toner reaching the cleaning blade 66.

Further, due to the above (feature 3), it is difficult to suppress the amount of reverse transfer toner reaching the downstream cleaning blade 66 by collecting the reverse transfer toner in the pre-cleaning unit. That is, in the pre-cleaning section, it is common to use a combination of mechanical force and electrostatic force, but in the potential relationship between the surface of the normal photoconductor and the pre-cleaning section, the back-charged toner is used. Electrostatic force acts in the direction of being electrostatically attracted to the surface of the photoconductor (the direction in which it is difficult to collect in the pre-cleaning part). Therefore, it is difficult for the pre-cleaning unit to recover the reverse-charged toner contained in the reverse-transfer toner. Further, even if the toner is not reversely charged, since the reverse transfer toner is weakly charged, the recovery action by the electrostatic force is weak and the mechanical force cannot be sufficiently assisted, so that it is difficult to recover by the pre-cleaning part. rice field. In order to recover the weakly charged toner, it was necessary to increase the mechanical force.

Therefore, in the case of a color image forming apparatus, the uniformity of the amount of lubricant on the photoconductor of the downstream color is poor due to the influence of the reverse transfer toner of the upstream color, and "slinching" is likely to occur in the blade portion. Since the amount of lubricant on the photoconductor has an appropriate range, it is necessary to keep the amount of lubricant on the photoconductor of each color within a certain range. In addition, even if the blade wears, "slinking" must be prevented. For that purpose, in the downstream color affected by the reverse transfer toner, it is desired that the reverse transfer toner is collected by the pre-cleaning unit (brush roller) before reaching the cleaning blade 66 to reduce the amount of toner reaching the cleaning blade 66. In order to increase the recovery of reverse transfer toner by the pre-cleaning unit, it is necessary to increase the mechanical force.

However, when the mechanical force of the pre-cleaning unit is constantly increased, the problem of accelerating the progress of member deterioration occurs as described above. Even when reverse transfer toner is generated in this way, by keeping the amount of toner reaching the blade edge within a certain range, the amount of lubricant on the photoconductor of each color can be kept constant and "slinching" can be prevented. For that purpose, the presence or absence of the reverse transfer toner and the amount of the reverse transfer toner generated are determined, and when it is determined that the reverse transfer toner is generated, the control of the present embodiment described later is executed, so that the target image forming unit 31 can perform the control. It is desirable to increase the mechanical force of the pre-cleaning unit only under predetermined conditions to reduce the amount of reverse transfer toner reaching the cleaning blade 66.

(Features 1 and 2: About the amount of reverse transfer toner on the photoconductor of the target image-forming part)
FIG. 5 is a schematic diagram showing an output image of an A3 size vertical band chart used in the experiment. The output image shown in the figure is a plurality of vertical bands arranged in the width direction over the entire surface of A3 size paper. In the following, the self-color (target image forming unit 31) is described as black.
Position A: The upstream color is magenta and cyan to form a solid blue image, and the self-color (black) is a white background that does not form an image.
Position B: The upstream color forms a solid image of cyan, and the self-color (black) is a white background that does not form an image.
Position C: The upstream color does not form an image, and the self-color (black) forms a solid image.
Position D: The upstream color forms a solid blue image with magenta and cyan, and the self-color (black) also forms a solid image.
Position E: The upstream color forms a solid image of cyan, and the self-color (black) also forms a solid image.
Position F: A white background that does not form an image of any color.

As the image forming apparatus 100, bizhub PRESS C1100 (manufactured by Konica Minolta Co., Ltd.) was used. As for the cleaning device 314, the solid lubricant 63a and the like were removed, and a device modified as shown in FIG. 6 was used (hereinafter, referred to as “bizhub modification machine 1”). As the brush roller 62, the brush bristles 62b used were PET (polyethylene naphthalate) fibers. The brush roller 62 has a rotation speed of 640 mm / sec and is in the with direction.

As the flicker member 64, a metal roller made of SUS that is rotated by being driven by a motor was used. The surface of the brush roller 62 rotates with the photoconductor drum 311 at a peripheral speed (surface speed) of 640 mm / sec in the with direction. The peripheral speed of the photoconductor drum 311 is 460 mm / sec. As the developing agent, toner for bizhub PRESS C1100 was used. Further, + 200 V is applied to the rotating shaft of the brush roller 62, and + 1000 V is applied to the flicker member 64b. As a result, the transfer residual toner on the photoconductor is sucked into the brush roller 62 by the action of an electrostatic force.

The A3 size vertical band chart shown in FIG. 5 is continuously printed on 100 sheets, and the transfer residual toner (black) on the photoconductor drum 311 of the target image forming unit 31 (black) and the reverse transfer toner of the upstream color (upstream color reverse transfer toner). The amount of cyan) was examined. At this time, during the formation of the 100th image, the bizhub modification machine 1 was forcibly stopped, and the toner during image formation remained on the photoconductor drum and the intermediate transfer belt. The amount of toner was calculated by peeling the toner layer from the photoconductor on the adhesive surface of the tape and measuring the change in the mass of the tape before and after the peeling with an electronic balance. The toner layer between the transfer position Pt on the photoconductor to the intermediate transfer belt 33 and the contact position of the brush roller 62 was peeled off, and the mass of the peeled toner was defined as the amount of post-transfer toner on the photoconductor (hereinafter, "" Also called "tape peeling method"). FIG. 7 is a diagram showing the result.

Reverse transfer toner remains at positions A and B at positions downstream of the transfer position Pt on the photoconductor of the image forming portion 31 (black), and self-colored (black) transfer residual toner remains at positions C to E. bottom.

As is clear from FIG. 7, in the white background portion (positions A and B) of the self-color (black), the cyan toner on the intermediate transfer belt 33 is reverse-transferred onto the black photoconductor. Further, when the colors of M and C are overlapped, that is, when the amount of toner of the upstream color on the intermediate transfer belt 33 is large, the amount of reverse transfer toner tends to be large. At this time, since the cyan solid color was superimposed on the magenta solid on the intermediate transfer belt 33, only the upper layer cyan toner was reverse-transferred on the black photoconductor.

In the self-colored (black) solid images (positions C to E), the self-colored transfer residual toner remained, and the transfer residual toner amount did not change depending on the presence or absence of the upstream color image. That is, even if the upstream color toner is present on the intermediate transfer belt 33, if the self-colored toner is present, the self-colored toner is transferred onto the intermediate transfer belt 33, so that the intermediate transfer belt of the upstream color toner is transferred. It is considered that this is because the movement in the reverse direction from 33 to the photoconductor, that is, the reverse transcription is inhibited (feature 2).

To summarize the above, if there is an upstream color toner on the intermediate transfer belt 33 and there is no transfer of the self-colored toner in the corresponding portion (that is, a white background portion), the reverse transfer is performed on the downstream color photoconductor. At this time, the larger the amount of toner on the intermediate transfer belt 33, the larger the amount of reverse transfer toner (Feature 2). For this reason, the amount of reverse transfer toner may be larger than the amount of transfer residual toner of the own color (downstream color). On the other hand, even if there is an upstream color toner on the intermediate transfer belt 33, if there is a self-colored (downstream color) toner, the reverse transfer is hindered by this, and the self-colored transfer is performed on the downstream color photoconductor. Only the rest remains.

(Feature 3: Recovery rate of reverse transfer toner by brush roller 62)
The amount of toner after collection (removal) by the brush roller 62 on the photoconductor of the image forming unit 31 (K) is measured at five locations corresponding to positions A to E, and before and after collection by the brush roller 62. From the subsequent comparison of the amount of toner, the toner recovery rate by the brush roller 62 was calculated.

The amount of toner after recovery with the brush roller 62 was measured by the tape peeling method from the photoconductor in the same manner as the amount of toner after transfer described above. FIG. 8 is a diagram showing the recovery rate of the transfer residual toner and the reverse transfer toner by the brush roller 62. Since the results were almost the same for the reverse transfer toners (positions A and B) and the transfer residual toners of their own colors (positions C to E), the recovery rate measurement results were typically obtained at the positions corresponding to positions A and C in the figure. Is shown. As is clear from FIG. 8, it can be seen that the recovery rate of the reverse transfer toner (positions A and B) is lower than that of the self-color transfer residue (positions C to E).

Further, the post-transfer toner on the photoconductor corresponding to the positions A and C (downstream from the transfer position Pt and upstream from the contact position of the brush roller 62) was collected, and the toner charge distribution was measured.

FIG. 9 shows the measurement results of the toner charge amount distribution of the transfer residual toner and the reverse transfer toner. E-SPART Analyzer MODEL EST-III (manufactured by HOSOKAWA MICRON CORPORATION) was used to measure the amount of toner charged, and two types of post-transcriptional toner, collected at position A and position C, were charged into the sample input port. ..

As shown in FIG. 9, the self-colored transfer residual toner corresponding to the position C is charged with a strong negative electrode property corresponding to the negative charge polarity of the toner, whereas most of the reverse transfer toners at the position A are charged. It can be seen that there is a tendency that there are many weakly charged toners that are reversely charged (positive electrode) and have a low charge amount (Characteristic 3).

By applying + 200V to the rotating shaft 62a of the brush roller 62, an electrostatic force that attracts the self-colored transfer residual toner (negative value) toward the brush roller 62 side is applied to the brush roller 62. The recovery rate of the transfer residual toner of its own color is increased by assisting the mechanical force of the brush. However, since the auxiliary action by the electrostatic force does not work on the weakly charged toner contained in the reverse transfer toner, the recovery rate is lowered. In particular, for back-charged toner, the potential difference between the photoconductor drum 311 and the brush roller 62 formed by the bias applied to the brush roller 62 is the repulsive force (force attracted to the photoconductor) on the brush roller 62. Therefore, it is considered that the recovery rate is decreasing.

(Issues when there is a lot of reverse transfer toner (system without lubricant))
A cleaning evaluation was carried out using a bizhub modified machine 1 (see FIG. 6), and the presence or absence of slippage was confirmed. FIG. 10 is a diagram showing a cleaning evaluation result. As the evaluation conditions, the cleaning blade 66 used was at the end of durability and had an edge wear amount of 25 μm. Here, the edge wear amount is the width (length in the moving direction) of the contact area with the photoconductor drum 311 that has expanded due to wear.

When the A3 size vertical band chart (see FIG. 5) was continuously printed with the following number of sheets, the presence or absence of slippage was confirmed at the positions corresponding to the positions A to E. In the evaluation, the edge of the cleaning blade 66 was observed, and if there was toner accumulation on the downstream side of the edge (contact position), slippage occurred (indicated by "x"), and if there was no accumulation, no slippage occurred ("○"). As shown), the evaluation was made after printing 5 sheets and printing 20 sheets, respectively. As the photoconductor drum 311 used for the evaluation, a horizontal band having a printing rate of 5% was 250 on A3 paper in advance using another device, that is, a normal bizhub PRESS C1100 (with a lubricant supply unit (see FIG. 18 described later)). A sheet was printed and the surface of the photoconductor was coated with a lubricant substantially uniformly, which was loaded into the bizhub remodeling machine 1 and used.

As shown in FIG. 10, the slip-out did not occur at the positions C to E where the self-colored transfer residual toner was present, whereas the slip-out occurred at the positions A and B where the reverse transfer toner was present. In particular, at position A where the amount of reverse transfer toner is large, slippage occurred at the time of printing 5 sheets. As shown in FIG. 7, the amount of reverse transfer toner is large at position A, and as shown in FIG. 8, the toner recovery rate of the brush roller 62 is lower than that of the self-colored transfer residual toner, and the toner reaches the cleaning blade 66. The amount of toner increases at positions A and B. Therefore, it is probable that the reverse transfer toner could not be completely cleaned at the positions A and B, and that slippage occurred.

(Issues when there is a lot of reverse transfer toner (system that supplies lubricant))
Next, the reverse transfer toner in the system that supplies the lubricant on the photoconductor, such as the device provided with the lubricant supply unit as shown in FIG. 4 or the system in which the lubricant is added to the toner, is the cleaning blade. Other issues that arise when reaching 66 will be described. FIG. 11 shows the measurement result of the amount of lubricant on the photoconductor of the most downstream color (black) after 3000 sheets of A3 size vertical band chart (see FIG. 5) are continuously printed. As the image forming apparatus 100, bizhub PRESS C1100 was used. As the cleaning device 314, a modified one as shown in FIG. 4 was used (hereinafter, also referred to as “bizhub modified machine 2”).

As the brush roller 62, one made of PET fiber was used. Further, the flicker member 64 in contact with the brush roller 62 was rotationally driven by a motor. Further, by applying + 1000 V to the flicker member 64 and + 200 V to the brush roller 62, the transfer residual toner on the photoconductor was sucked into the brush roller 62 by the action of an electrostatic force. The surface of the brush roller 62 was set to rotate with the photoconductor drum 311 at a peripheral speed of 640 mm / sec in the with direction. As the developing agent, toner for bizhub PRESS C1100 was used. For the amount of lubricant on the photoconductor, the surface of the self-colored (black) photoconductor drum 311 was replaced by the ratio of zinc in zinc stearate obtained by measurement by an X-ray photoelectron spectroscopy analyzer.

As is clear from FIG. 11, the amount of the lubricant at the position F where the toner image is not formed for both the upstream color and the self-color (black) is about 2 at%, which is large. On the other hand, the amount of the lubricant at the position C where the self-colored (black) toner image is formed is about 1.8 at%, which is decreasing. It is considered that this is because the lubricant was recovered at the edge of the cleaning blade 66 by the transfer residual toner of the self-color. At position A, the amount of lubricant is reduced to about 1.4 at% even though a black toner image is not formed. This is because the cyan toner is reverse-transferred onto the self-colored photoconductor and reaches the black cleaning blade 66 to recover the lubricant. Further, as described above, the reverse transfer toner has a larger edge arrival amount than the self-color transfer residual toner, so that it is considered that the recovery amount of the lubricant is increased. From the above results, it can be seen that the amount of lubricant on the photoconductor of the downstream color is affected by the reverse transfer toner of the upstream color. Therefore, in order to achieve the problem of keeping the amount of the lubricant within a predetermined range, not only the transfer residual toner of the own color but also the reverse transfer toner containing the reverse charge / weak charge toner is collected by the brush roller 62. It can be seen that it is preferable to reduce the amount of toner that reaches the cleaning blade 66.

(Control of brush roller 62)
As the image forming apparatus, the above-mentioned bizhub remodeling machine 2 was used. Further, in order to improve the toner recovery function of the brush roller 62, the rotation direction of the brush roller 62 is changed to a peripheral speed of 230 mm / sec in the rotation direction of the photoconductor drum 311 and the counter direction in order to improve the mechanical force. bottom. The bias voltage applied to the brush roller 62 (hereinafter referred to as “brush application bias”) was changed. The bias voltage of the flicker member 64 was changed according to the change of the brush application bias so that the potential difference between the flicker member 64 and the brush roller 62 was constant (Δ800V). After printing 100 sheets of A3 size vertical band chart (see FIG. 5), the toner recovery rate of the position A (reverse transfer toner) and the position C (self-color transfer residual toner) with the brush roller 62 was measured. The recovery rate was calculated from the mass measured by the tape peeling method from the photoconductor. The change in the recovery rate with respect to the brush application bias is shown by a dotted line (condition 1 in FIG. 12).

When the brush application bias was set to 0 V, the recovery rates of the self-colored transfer residual toner and the reverse transfer toner were both low because there was no auxiliary action due to the electrostatic force. As the brush application bias was increased to the positive electrode property, the recovery rate of the self-colored transfer residual toner charged to the negative electrode property increased. On the other hand, the recovery rate of the reverse transfer toner was further reduced. On the other hand, when the brush application bias was increased to the negative electrode property, the recovery rate of the reverse transfer toner containing the reverse charge toner increased. Therefore, in order to sufficiently increase the recovery rate of the self-colored transfer residual toner, it is necessary to set the brush application bias to a high value. For example, it is necessary to make the setting shown by P1 in FIG. On the other hand, at this time, the recovery rate of the reverse transfer toner is low and becomes P1'. On the other hand, if the brush application bias is set to the reverse polarity for the purpose of increasing the recovery rate of the reverse transfer toner, the recovery rate of the reverse transfer toner can be increased as in P4', and the reverse transfer reaches the cleaning blade 66. The amount of toner can be suppressed. On the other hand, since an electrostatic repulsive force acts on the self-colored transfer residual toner, the recovery rate of the self-colored transfer residual toner decreases (P4).

Next, when the peripheral speed of the brush roller 62 is changed to 460 mm / sec, the change in the recovery rate with respect to the brush application bias is shown by a solid line (condition 2 in FIG. 12). When the brush application bias is set to 0V (P5), although there is no auxiliary action due to the electrostatic force, the action of the mechanical force is increased due to the increase in peripheral speed, so that the self-colored transfer residual toner and the reverse transfer toner are recovered. Both rates have improved. Compared with P1 and P1'at a peripheral speed of 230 mm / sec, even with the same brush application bias, the recovery rate of self-colored transfer residual toner can be maintained by increasing the peripheral speed (P2), while the recovery rate of reverse transfer can be increased. Yes (P2'). However, even with the setting of P2', an electrostatic repulsive force acts on the reversely charged toner among the reverse transfer toners to hinder the recovery. Therefore, by setting P3 and P3'to weaken the electrostatic repulsive force in combination with the action of mechanical force due to the increase in peripheral speed, while suppressing the decrease in the recovery rate of the self-colored transfer residue, the reverse transfer toner The recovery rate can be increased.

Further, by setting the brush application bias to 0V (P5), the recovery rate of the reverse transfer toner can be further increased. On the other hand, the recovery rate of the self-colored transfer residual toner is slightly lowered because the auxiliary action due to the electrostatic force disappears. From this, it is determined which toner amount is larger depending on which area ratio is higher, the reverse transfer toner amount or the self-colored transfer residual toner amount, according to the image pattern to be printed, and priority is given to the recovery of the reverse transfer toner. Then, it is possible to switch between the setting of P5 and the setting of P3 and P3'with priority given to the recovery of the self-colored transfer residual toner. The determination of which of the reverse transfer toner amount and the self-color transfer residual toner amount is larger will be described later.

However, the self-colored transfer residual toner has a higher charge amount than the reverse transfer toner and is greatly affected by the action of electrostatic force. Therefore, when the brush application bias is set to the negative electrode property, the recovery rate of the self-color transfer residual toner is remarkable. It is more preferable to set the brush application bias between P5 and P3 because it is considered to decrease. By controlling the mechanical force and electrostatic force of the brush roller 62, the recovery rate of both the self-colored transfer residual toner and the reverse transfer toner can be increased, and the amount of toner reaching the cleaning blade 66 can be reduced.

(Issues when changing the setting of the brush roller 62 in the constant / upstream color)
The fiber state of the brush roller 62 was observed after 500,000 A4 size charts having an image area ratio of 10% for each color were endured. As the setting of the brush roller 62, 230 mm / sec (P1 (P1') in FIG. 12) and 460 mm / sec (P3 (P3') in FIG. 12) were compared. Compared with P1, the fibers of the brush bristles 62b of the brush roller 62 of P3 showed frayed hair bundles and frayed fibers. In the brush roller 62 of P3 in which the deterioration of the fiber was observed, the mechanical force of the fiber acting on the toner was reduced due to the deterioration of the fiber, and the recovery rate was lowered. When such a situation occurs, the life of the cleaning device 314 or the unit life of the image forming unit 31 including the cleaning device 314 is shortened, which causes a problem. In order to prevent this, it is preferable that the setting of the brush roller 62 is not changed for the yellow unit of the most upstream color (first) in which the reverse transfer toner is not generated. Further, even in the downstream color (second and subsequent colors), the setting change of the brush roller 62 is limited to when the amount of reverse transfer toner is large, and it is preferable to use the brush roller 62 in the P1 setting in normal times.

(About the judgment of the amount of reverse transfer toner)
By referring to the relationship shown in FIG. 7 above, it is possible to calculate (estimate) the amount of reverse transfer toner and the amount of self-color transfer residual toner on the photoconductor. Here, the amount of toner for each color to obtain the desired concentration is 5 g / m ² , the transfer efficiency for each color is 95% (5% remains on the photoconductor), and the reverse transfer rate is 5% (95% is intermediate transfer). Residual on the belt, 5% transferred as reverse transfer toner). From the image pattern to be printed, the area ratio of the transfer residual toner of the own color (for example, black) is obtained. Residual toner amount is 0.25 g / ^{m 2} with 5% 5 g / ^{m 2.} In the present specification, the term "transfer efficiency" is used for the transfer ratio of the self-colored toner, and the term "reverse transfer rate" is the self-colored upstream toner (upstream color toner) on the intermediate transfer belt. It is used for the transfer ratio of reverse transfer to the photoconductor drum 311.

From the image pattern, the amount of toner on the intermediate transfer belt of the upstream color of each part is obtained. The yellow toner of the intermediate transfer belt 95% 5 g / ^{m 2} on 4.75 g / ^{m 2} is present as a solid part of. After that, if there is further color superimposition of magenta in the transfer portion of the next color (magenta), the amount of toner on the intermediate transfer belt increases. For example, if there is a solid yellow ^{color and a solid magenta color (5 g / m 2} on the photoconductor), the amount of toner on the intermediate transfer belt will be ^{9.5 g / m 2.} 5% an is 0.238 g / ^{m 2} is reverse transcribed magenta photoconductor for yellow transfer toner amount 4.75 g / ^{m 2} if the white portion is no color superimposition of magenta, yellow toner amount on the intermediate transfer belt 4 .Reduces to 513 g / m ² .

In this way, the toner on the intermediate transfer belt repeatedly increases and decreases by transfer / reverse transfer from the next color to the next color to reach the transfer part of its own color. By repeating the above calculation procedure of yellow to magenta, The amount of toner on the intermediate transfer belt that reaches the transfer portion of its own color (black) can be estimated. Furthermore, if there is a self-colored (black) color overlap, reverse transfer is not performed, but in the part (white background) where there is no self-colored (black) color superimposition, 5% of the toner amount on the intermediate transfer belt is on the self-colored photoconductor. Reverse transcription. For example, if the above-mentioned magenta toner passes through the cyan transfer position on the entire white background, the amount of toner on the intermediate transfer belt that reaches the black transfer position is the yellow solid portion (4.287 g / m ² ), yellow and magenta colors. It is estimated to be the overlapped portion (9.025 g / m ² ), whereas if there is no black color overlap, the amount of reverse transfer toner to the black photoconductor is 0.214 g / m ^{2 for} the yellow solid portion and yellow / magenta color. It can be calculated as 0.451 g / m ^{2 of the overlapped portion.}

Here, the total amount of self-colored transfer residual toner CN can be calculated from the image area ratio of the self-colored transfer residual toner of 0.25 g / m ^2.

Next, the amount of reverse transfer toner Bn1 obtained from the area ratio of 0.214 g / m ² yellow solid (no image for magenta, cyan, and black) and the yellow / magenta color layered portion (cyan, black ^{) of 0.451 g / m 2} The total amount of reverse transfer toner BN can be calculated from the sum of the amount of reverse transfer toner Bn2 obtained from the area ratio (without image). Here, the case where the printing is a solid portion (100% density) has been described as an example, but when the image density is low and the amount of toner on the photoconductor is small, the intermediate transfer belt is based on the density information obtained from the image pattern. The above toner amount and the reverse transfer toner amount may be calculated. The amount of toner, transfer efficiency, and reverse transfer rate on the photoconductor of the image forming apparatus may be measured and grasped in advance.

From the comparison between the self-colored transfer residual toner amount CN and the total reverse transfer toner amount BN estimated for each color in this way, the cleaning condition of the brush roller 62 can be switched to P1, P3, or P5. This P1 is advantageous for collecting the self-colored transfer residual toner and causes less stress on members such as brush rollers. In P3, the recovery of the self-colored transfer residual toner and the recovery of the reverse transfer toner can be compatible. P5 is more advantageous for recovering the reverse transfer toner and disadvantageous for recovering the self-colored transfer residual toner.

(Modification example)
(When estimating the reverse transfer rate from the transfer voltage)
In the above description, the method of estimating the amount of reverse transfer toner based on a constant reverse transfer rate estimated in advance from the image pattern has been described, but the reverse transfer rate in consideration of the transfer voltage is obtained as in the modification described below. The amount of reverse transfer toner may be estimated based on this.

It is generally known that the higher the transfer voltage, the greater the amount of reverse transfer toner. FIG. 13 is a diagram showing the relationship between the transfer voltage in the magenta image forming unit 31 and the amount of reverse transfer toner of yellow toner on the photoconductor drum 311. From FIG. 13, it can be seen that the amount of yellow reverse transfer toner increases as the transfer voltage increases.

Reverse transfer toner is considered to be generated as follows. When the transfer voltage applied to the primary transfer unit 34 becomes high, the current flowing through the photoconductor drum 311 via the intermediate transfer belt 33 at the transfer position Pt becomes large. If toner is present in that region, the toner charge is attenuated, and toner that is charged to a polarity opposite to the original charging characteristics of the toner is generated. As a result, toner (reverse transfer toner) that moves from the intermediate transfer belt 33 to the photoconductor drum 311 is generated due to the transfer electric field, contrary to the toner having the original charging characteristics.

Generally, the surface potential of the photoconductor before transfer is about −600 V in the background portion (white background portion) and about -50 V in the solid portion. As the transfer voltage, a voltage suitable for transferring the toner existing in the solid portion (surface potential of −50 V) on the photoconductor drum 311 onto the intermediate transfer belt 33 is applied to the primary transfer portion 34. For example, when a transfer voltage is applied to the primary transfer portion 34 so that the surface of the intermediate transfer belt becomes 500 V as a voltage suitable for transfer, the potential difference between the intermediate transfer belt 33 and the photoconductor drum 311 in the solid portion is 550 V. However, in the background portion, a potential difference of 1100 V is generated due to the influence of the surface potential of the photoconductor. When transferring the toner of its own color (for example, magenta) to the intermediate transfer belt 33, the potential difference in the background part does not matter because the toner is present in the solid part, but the toner of the upstream color (for example, yellow) is transferred to the background part. May exist. In that case, the potential difference between the photoconductor drum 311 and the intermediate transfer belt 33 becomes large, and the excess current flowing by the potential difference causes the charge of the yellow toner to have the opposite polarity. As a result, toner that is reverse-transferred from the intermediate transfer belt 33 to the photoconductor drum 311 is generated. Therefore, the generation rate of the reverse transfer toner (reverse transfer rate) can be estimated from the transfer voltage applied to the primary transfer unit 34. As described above, the reverse transfer toner is likely to be generated in the background portion because the potential difference from the surface of the photoconductor is large, but when the transfer voltage is increased, the reverse transfer toner is also generated in the solid portion. On the other hand, even if the transfer voltage is high, if the upstream color toner does not exist on the intermediate transfer belt 33, the reverse transfer toner does not occur in the downstream color.

(Control method)
Next, a control method of the image forming apparatus 100 according to the present embodiment will be described with reference to FIGS. 14 and 15. FIG. 14 is a flowchart showing a control procedure executed by the control unit 10. FIG. 15 is the subroutine. These controls are used for setting the cleaning conditions of the brush roller 62 of the image forming unit 31 of the second and subsequent (M, C, K) in the order of arrangement. By setting the cleaning conditions, the amount of toner reaching the cleaning blade 66 of the image forming unit 31 of each color is adjusted, that is, the amount of lubricant supplied (coating amount) to the photoconductor drum 311 is stabilized.

(Step S110)
First, accept the print job.

(Step S120)
By accepting the print job, the job start signal is input to the image forming unit 30, and the image forming conditions are set. This image forming condition includes a set value of the transfer voltage applied to the primary transfer unit 34. This setting is an appropriate value obtained by actually changing the transfer voltage at the start-up of the image forming apparatus 100 or at the start of a job, or an appropriate value obtained from a table stored in the apparatus main body based on atmosphere conditions and image information. It is set based on.

Since the set value set in step S120 is stored in the storage unit 20, the reverse transfer rate can be calculated based on the set value of the transfer voltage. The relationship between the transfer voltage and the reverse transfer toner rate may be stored in the storage unit 20 in advance as a reference table in the apparatus main body.

(Loop processing (S130 to S137))
Next, the cleaning condition setting loop is executed in order for the target colors from the second (magenta) to the final color (black).

(Step S131)
In this procedure, the total reverse transfer toner amount BN is determined. Hereinafter, the process of step S131 will be described based on the subroutine shown in FIG.

(Step S210)
First, the image area ratio of each color is calculated. This can be calculated from the image data included in the print job.

(Step S220)
Next, the toner amounts A1, A2 ... An on the intermediate transfer belt immediately before each transfer position are obtained from the transfer voltage of the target color (magenta in this case), the image area ratio, and the information of color overlap. Specifically, the amount of toner on the intermediate transfer belt A1, A2, based on the number of pixels in which the toner image of the upstream color is on the white background of the target color (magenta), that is, the number of pixels in yellow (no image in magenta) and its density information.・ ・ Find An. For example, in the case of a pixel having a solid yellow portion, toner adheres to the intermediate transfer belt at ^{4.75 g / m 2, and this may be multiplied by the area of the pixel.} The numbers 1 to n indicate the respective regions in which the image region is divided into n in the main scanning direction.

(Step S230)
When the amount of toner A1 ... An on the intermediate transfer belt is calculated, the reverse transfer rate is derived from the information of the transfer voltage of the own color set in step S120 using the reference table, and the reverse transfer toner is derived using this. The amounts B1 ... Bn are calculated.

(Step S240)
The total reverse transfer toner amount BN for each color is calculated from B1 ... Bn, and the process is returned to the control shown in FIG.

(Step S132)
Here, it is determined whether or not the total reverse transfer toner amount BN calculated in step S131 is equal to or greater than the predetermined threshold value B0. If the total reverse transfer toner amount BN is equal to or greater than the threshold value B0, the process proceeds to step S133, and if it is less than the threshold value B0, the process proceeds to step S137.

(Step S133)
Here, the total transfer residual toner amount CN of the own color is calculated from the transfer efficiency of the own color and the area ratio of the own color. The self-colored transfer efficiency may be derived from the transfer voltage information set in step S120 using a reference table stored in the storage unit 20, and a predetermined transfer efficiency (for example, 95%) set in advance may be used. You may. The value calculated in step S210 is used as the area ratio of the self-color. Then, the total transfer residual toner amount CN can be calculated by obtaining the total toner amount for image formation from the area ratio of the own color and multiplying this by the transfer residual ratio (= 1-transfer efficiency) obtained from the transfer efficiency.

(Step S134)
Next, the total reverse transfer toner amount BN obtained in step S131 and the total transfer residual toner amount CN obtained in step S133 are compared. If the total reverse transfer toner amount BN is greater than or equal to the total transfer residual toner amount CN, the process proceeds to step S135, and if the total reverse transfer toner amount BN is less than the total transfer residual toner amount CN, the process proceeds to step S136.

(Step S136)
The cleaning condition of the brush roller 62 is set to the reverse transfer toner priority condition, that is, the P5 condition.

(Step S137)
The cleaning condition of the brush roller 62 is set to the transfer residual toner priority condition, that is, the P3 condition.

(Step S138)
The cleaning condition of the brush roller 62 is set to the normal condition, that is, the P1 condition.

Here, the cleaning conditions of P1, P3, and P5 are as described with reference to FIG. Reprinted below.
P1 (transfer residual toner priority condition): brush application bias high (third voltage), rotation speed low,
P3 (intermediate condition): During brush application bias (first voltage), high rotation speed,
P5 (reverse transfer toner priority condition): brush application bias low (second voltage), rotation speed high.

(S138)
The above loop processing (S130-S138) is repeated in order until the final color (black). When the setting of the cleaning condition of the final color image forming unit 31 is completed, the process proceeds to step S140.

(S140)
Under the cleaning conditions set so far, the cleaning device 314 of the image forming unit 31 of each color is operated to execute printing and end the control. If unfinished printing remains, the process of step 120 or less may be repeated.

As described above, in the present embodiment, by performing the above control, it is possible to suppress an increase in the amount of toner (residual transfer toner and reverse transfer toner) reaching the cleaning blade of the downstream color according to the amount of reverse transfer toner. Therefore, it is possible to prevent the cleaning blade from slipping. Further, in the case of a system in which a lubricant is applied, the fluctuation range of the amount of the lubricant on the photoconductor can be reduced, and the coating amount can be kept within a certain range.

As described above, the degree of influence of the image area ratio differs depending on the order of the image forming portions. Only yellow toner affects the magenta, which is the second color image area, but yellow toner and magenta toner affect the cyan image area, and yellow toner, magenta toner, and cyan toner affect the black image area. do. Therefore, in order to more accurately control the amount of toner reaching the cleaning blade and the amount of lubricant on the photoconductor, the image area ratio of all colors on the upstream side of the self-coloring unit is used as in the present embodiment. It is preferable to determine the amount of reverse transfer toner.

(Second Embodiment)
In the above-described embodiment, the amount of reverse transfer toner is calculated by using a predetermined constant reverse transfer rate, the reverse transfer rate obtained from the transfer voltage setting information and the reference table, and the image data. In the second embodiment shown below, the amount of reverse transfer toner is calculated using the reverse transfer rate obtained by measurement.

FIG. 16 is a diagram showing a configuration around an image forming unit 31 of the image forming apparatus 100 according to the second embodiment. In the image forming apparatus 100 shown in the figure, two sensors 94 and 95 are arranged so as to face the intermediate transfer belt 33. In the moving direction of the intermediate transfer belt 33, the sensor 94 is arranged on the upstream side of the transfer position Pt, and the sensor 95 is arranged on the downstream side. The sensors 94 and 95 are optical sensors including a light emitting unit and a light receiving unit, respectively, and measure the density of the toner image on the intermediate transfer belt 33.

FIG. 17 is a flowchart showing a control for obtaining the reverse transcription rate executed by the control unit 10 of the second embodiment.

(Step S310)
Wait for an instruction to start executing the reverse transcription rate measurement mode. The reverse transcription rate measurement mode is executed every predetermined period (for example, every day) or when a predetermined trigger (for example, when the power supply of the image forming apparatus is turned on) is input. Alternatively, when printing is executed, it may be performed between the sheets of the continuously conveyed sheets or at the front-rear position of the sheets. In this case, the start of execution of the print job is the trigger. Alternatively, the execution may be started by the user's operation on the operation panel 50. When the execution start instruction is input, the process proceeds to step S320.

(S320)
A toner image is formed based on the image data for the evaluation patch stored in the storage unit 20 in advance. For example, if the reverse transfer rate of the image forming unit 31 of the second color is to be calculated, a solid yellow toner image (no image for magenta) is formed.

(S330)
The sensor 94 on the upstream side measures the optical density of the toner image on the intermediate transfer belt 33 on the upstream side of the transfer position Pt, and the toner amount M1 is calculated from the measured value. The amount of toner can be calculated by converting the obtained optical density into the amount of toner using a conversion table stored in the storage unit 20 in advance.

(S340)
Similarly, the sensor 95 on the downstream side calculates the toner amount M2 on the intermediate transfer belt 33 on the downstream side of the transfer position Pt.

(S350)
The reverse transfer rate (M2 / M1) is calculated from the toner amounts M1 and M2 calculated in steps S340 and S350, and this is stored in the storage unit 20 to end the process.

As described above, in the second embodiment, the same effect as that of the first embodiment is obtained, and the reverse transfer rate is measured, so that the amount of toner reaching the cleaning blade 66 can be determined more accurately. It becomes possible. Even when measuring the reverse transfer rate, the cleaning conditions of the pre-cleaning section as shown in FIGS. 14 and 15 are set in consideration of the amount of reverse transfer toner reaching the cleaning blade 66 and the amount of toner. You may do so.

(Modification example)
FIG. 18 is a diagram showing a configuration around an image forming portion of the image forming apparatus according to the modified example. In the figure, the housing of the cleaning device 314 and the transport member are not shown. In the modified example shown in FIG. 18, two brush rollers 621 and 622 are provided as compared with the image forming portion according to the embodiment shown in FIG.

The brush roller 621 on the upstream side exclusively cleans the surface of the photoconductor drum 311 and functions as a pre-cleaning unit. The brush roller 622 on the downstream side is exclusively used for applying the lubricant and functions as a coating portion. The brush roller 622 scrapes the lubricant from the lubricant supply unit 63 and applies it to the surface of the photoconductor drum 311. Further, a lubricant fixing member 69 is provided on the downstream side thereof. The lubricant immobilizing member 69 has a function of further spreading and applying a lubricant onto the photoconductor by a brush roller 622 and a function of eliminating excess lubricant particles. As the lubricant fixing member, for example, like the cleaning blade 66, a flat plate-shaped blade made of an elastic body such as urethane rubber is used.

By using the image forming apparatus of the modified example as shown in FIG. 18, the cleaning condition of the pre-cleaning portion can be controlled regardless of the amount of the lubricant supplied on the photoconductor. On the other hand, in the image forming apparatus according to the first and second embodiments, one brush roller 62 has a function of a pre-cleaning member and a function of applying a lubricant, and the number of parts is as compared with the modified example of FIG. There is a merit that the cost can be reduced and the cost increase can be prevented.

(Other variants)
The configuration of the image forming apparatus described above is not limited to the above configuration, as the main configuration has been described in explaining the features of the above-described embodiment and modification. Further, the configuration provided in the general image forming apparatus is not excluded.

For example, in the above-described embodiment, in order to more accurately control the amount of toner reaching the cleaning blade and the amount of lubricant on the photoconductor, the color is reversed based on the image area ratio of all colors on the upstream side of the self-coloring unit. I was looking for the amount of copy toner, but it is not limited to this. It may be simplified to avoid complication of processing. For example, since the yellow toner of the most upstream color affects all the image forming portions of the downstream color, only the image area ratio of the upstream color may be considered in the calculation of the image forming portion of cyan or black.

Further, in the above-described embodiment, both the rotation speed of the brush roller and the brush applied voltage are controlled based on the determined amount of reverse transfer toner, but only one of them may be controlled.

Further, the control program for operating the image forming apparatus may be provided by a computer-readable recording medium such as a USB memory, a flexible disk, or a CD-ROM, or may be provided online via a network such as the Internet. good. In this case, the control program recorded on the computer-readable recording medium is usually transferred to and stored in a memory, storage, or the like. Further, this control program may be provided as a single application software, or may be incorporated into the software of each device as a function of the image forming device.

100 Image forming device 10 Control unit 30 Image forming unit 31 Image forming unit 311 Photoreceptor drum (image carrier)
312 Band electrode 313 Developer 314 Cleaning device 61 Housing 62 Brush roller (pre-cleaning part)
62a Brush bristles 62b Rotating shaft 63 Lubricant supply unit 63a Solid lubricant 63b Holder 63c Elastic member 64 Flicker member 65 Transport member 66 Cleaning blade 67 Holder 315 Eraser lamp 32 Exposure unit 33 Intermediate transfer belt (intermediate transfer body)
34 Primary transfer unit (transfer member)
35 Secondary transfer unit 36 Fixing device 37 Belt cleaning unit 40 Paper feed transfer unit 50 Operation panel

Claims (16)

An intermediate transfer body to which the toner image is transferred, and
A plurality of image forming portions that are sequentially arranged on the intermediate transfer body along the moving direction, form toner images of different colors, and are transferred to the intermediate transfer body at the transfer position.
An image forming apparatus equipped with a control unit.
Each of the image forming parts
Image carrier and
A developing device that forms a toner image on the image carrier,
A pre-cleaning unit that removes a part of the residual toner on the image carrier after transfer to the intermediate transfer body, and
A cleaning blade that abuts on the image carrier and removes the residual toner is provided on the downstream side of the pre-cleaning unit and on the upstream side of the developing device in the rotation direction of the image carrier. ,
In the control unit, in the image forming unit second and subsequent from the upstream side in the moving direction of the intermediate transfer body, the toner image transferred on the intermediate transfer body on the upstream side is reverse-transferred to the image carrier. An image forming apparatus that determines the amount of reverse transfer toner, sets cleaning conditions for the pre-cleaning unit based on the determined amount of reverse transfer toner, and adjusts the amount of toner that reaches the cleaning blade. The pre-cleaning unit is a brush roller that comes into contact with the image carrier and rotates.
The image forming apparatus according to claim 1, wherein the control unit sets the rotation speed of the brush roller and / or the applied voltage applied to the brush roller based on the determined amount of reverse transfer toner. When the determined amount of reverse transfer toner is larger than a predetermined threshold value, the control unit sets the rotation speed of the brush roller to be higher than the normal speed at the time of image formation, and / or sets the applied voltage to an image. The image forming apparatus according to claim 2, wherein the voltage is set to a voltage shifted to the same polarity as the charging polarity of the toner from the normal voltage at the time of formation. The control unit further determines the amount of residual transfer toner remaining on the image carrier without transferring the toner image formed by the image forming unit to be determined to the intermediate transfer body, and determines the transfer. The image forming apparatus according to claim 2 or 3, wherein the applied voltage applied to the brush roller is set by comparing the amount of residual toner and the amount of reverse transfer toner. The control unit
When the amount of residual transfer toner is larger than the amount of reverse transfer toner, the applied voltage applied to the brush roller is set to the first voltage.
The fourth aspect of claim 4, wherein when the transfer residual toner amount is smaller than the reverse transfer toner amount, the applied voltage is set to a second voltage shifted to the same polarity side as the charging polarity of the toner from the first voltage. Image forming device. The image according to any one of claims 2 to 5, further comprising a solid lubricant obtained by solidifying the lubricant and a coating portion for supplying the lubricant scraped from the solid lubricant to the surface of the image carrier. Forming device. The image forming apparatus according to claim 6, wherein the coating portion is the brush roller. The image forming apparatus according to any one of claims 1 to 7, wherein the control unit determines the amount of reverse transfer toner of each of the image forming units based on image data used for image forming. Based on the image data, the control unit transfers the determination of the amount of reverse transfer toner of the image forming unit to be determined by the image forming unit onto the intermediate transfer body at a corresponding position in the image region. a toner image image for, carried out by the imaging unit upstream of the acting image portion is compared with the toner image image transferred onto the intermediate transfer member, the image forming apparatus according to claim 8. In the image forming unit to be determined, the control unit transfers the toner image by the image forming unit on the upstream side of the image forming unit to the region of the intermediate transfer body corresponding to the white background portion that does not form the toner image. The image forming apparatus according to claim 8 or 9, wherein it is determined that the toner in the region is reverse-transferred to the image carrier of the image forming portion to be determined. The control unit is on the upstream side of the image forming unit with respect to the region of the intermediate transfer body corresponding to the white background portion that does not form the toner image in the image forming unit third and subsequent from the upstream side in the moving direction of the intermediate transfer body. The amount of reverse transfer toner when the toner image is transferred by a plurality of image-forming parts is the reverse transfer when the toner image is transferred by only one image-forming part on the upstream side of the image-forming part. The image forming apparatus according to claim 10, wherein the amount of toner is determined to be larger than the amount of toner. In the image forming unit to be determined, the control unit transfers the toner image by the image forming unit on the upstream side of the image forming unit to the region of the intermediate transfer body corresponding to the white background portion that does not form the toner image. 8 to 11 claim that the amount of reverse transfer toner on the image carrier in the region is determined based on the amount of transfer toner on the intermediate transfer body calculated based on the image data. The image forming apparatus according to any one of. The control unit further determines the amount of the reverse transfer toner by using the transfer voltage applied to the transfer member provided at the transfer position of the image forming unit to be determined, claim 8 to claim 8. 12. The image forming apparatus according to any one of 12. Further, a sensor for measuring the amount of toner on the intermediate transfer body is provided at each position on the upstream side and the downstream side of the transfer position of the image forming portion to be determined.
The control unit calculates the reverse transfer rate at which the toner of the intermediate transfer body reverse-transfers to the image carrier of the image-forming unit from the output of the sensor, and uses the calculated reverse transfer rate to perform the reverse transfer. The image forming apparatus according to any one of claims 8 to 13, which determines the amount of copy toner. Are sequentially arranged along the moving direction of the intermediate transfer body, the different color toner images respectively formed, comprises a plurality of image forming portions to be transferred to said intermediate transfer member at the transfer position, the imaging unit, the image bearing member A developing device that forms a toner image on the image carrier, a pre-cleaning unit that removes a part of residual toner on the image carrier after being transferred to the intermediate transfer at the transfer position, and the above. An image including a cleaning blade that abuts on the image carrier and removes the residual toner on the downstream side of the pre-cleaning portion and on the upstream side of the developing device in the rotation direction of the image carrier. It is a control method of the forming device.
In each of the image forming portions after the second from the upstream side in the moving direction of the intermediate transfer body,
A step of determining the amount of reverse-transferred toner in which the toner image transferred onto the intermediate transfer member on the upstream side is reverse-transferred to the image-bearing body.
A step of setting cleaning conditions for the pre-cleaning unit based on the determined amount of reverse transfer toner, and
A step of operating the pre-cleaning unit under the set cleaning conditions and adjusting the amount of toner reaching the cleaning blade, and
Control methods, including. An intermediate transfer body to which the toner image is transferred, and
A plurality of image forming portions that are sequentially arranged on the intermediate transfer body along the moving direction, form toner images of different colors, and are transferred to the intermediate transfer body at the transfer position.
An image forming apparatus equipped with a control unit.
Each of the image forming parts
Image carrier and
A developing device that forms a toner image on the image carrier,
A pre-cleaning unit that removes a part of the residual toner on the image carrier after transfer to the intermediate transfer body, and
A cleaning blade that abuts on the image carrier and removes the residual toner on the downstream side of the pre-cleaning portion and on the upstream side of the developing device in the rotation direction of the image carrier.
A solid lubricant obtained by solidifying the lubricant, a coating portion for supplying the lubricant scraped from the solid lubricant to the surface of the image carrier, and a coating portion.
With
In the control unit, in the image forming unit second and subsequent from the upstream side in the moving direction of the intermediate transfer body, the toner image transferred on the intermediate transfer body on the upstream side is reverse-transferred to the image carrier. The amount of reverse transfer toner is determined, and based on the determined amount of reverse transfer toner, the cleaning conditions of the pre-cleaning portion are set, and the amount of toner reaching the cleaning blade is adjusted.
The pre-cleaning unit is a brush roller that comes into contact with the image carrier and rotates.
The control unit is an image forming apparatus that sets the rotation speed of the brush roller and / or the applied voltage applied to the brush roller as the cleaning condition.

Images