JP5153431B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile.

  Here, the image forming apparatus is an image forming apparatus using an electrostatic process such as electrophotography or electrostatic recording. The image carrier is a photoreceptor for electrophotography, a dielectric for electrostatic recording, or the like. The image carrier is an intermediate transfer member in the form of a belt or drum in an intermediate transfer type image forming apparatus.

  In recent years, so-called intermediate transfer type image forming apparatuses have been proposed as multi-color or full-color image forming apparatuses employing an electrostatic process such as an electrophotographic system or an electrostatic recording system. In this image forming apparatus, each color toner image (developer image) formed on an electrophotographic photosensitive member or electrostatic recording dielectric as a first image carrier is used as an intermediate transfer member as a second image carrier. A color image is formed by sequentially superimposing the images on the recording material, and transferred onto a recording material at a time.

  Hereinafter, an electrophotographic / intermediate transfer type image forming apparatus using a photosensitive drum as the first image carrier and an intermediate transfer belt as the second image carrier will be described as an example.

  In this image forming apparatus, a toner image is formed on a photosensitive drum by a charging unit, an exposing unit, and a developing unit arranged around the photosensitive drum, and electrostatically transferred to an intermediate transfer belt by a transfer unit in a primary transfer unit. . In the case of forming a color image, a full color image can be formed on the intermediate transfer belt by sequentially transferring toner images of respective colors on the intermediate transfer belt. The toner image transferred to the intermediate transfer belt is conveyed to the secondary transfer unit by the rotation of the intermediate transfer belt, and is electrostatically transferred to a recording material such as paper. At this time, as a method for removing toner remaining on the intermediate transfer belt without being transferred to the recording material, a blade cleaning method in which a blade is pressed against the intermediate transfer belt, which has a high cleaning capability, is widely used. .

  The blade cleaning method can be easily cleaned when the amount of secondary transfer residual toner generated in the normal image forming process is small. However, when there is a large amount of secondary transfer residual toner, it is assumed that, for example, the toner image transferred to the intermediate transfer belt is transferred to the cleaning unit without being transferred to the recording material due to a paper jam or the like. The linear pressure at the nip portion between the transfer belt and the blade must be set large. In other words, the linear pressure must be set large in advance in order to perform complete cleaning even when the secondary transfer residual toner amount is large. Therefore, problems such as an influence on the life of the intermediate transfer belt or a load fluctuation due to a frictional resistance fluctuation occur. In particular, when the surface of the intermediate transfer belt is coated with an elastic body, the frictional force with the blade is increased, which is more remarkable.

As a method of cleaning the toner remaining on the intermediate transfer belt after the secondary transfer process while avoiding the above problem, there is an electrostatic cleaning method that electrostatically removes the toner on the intermediate transfer belt. 3 is disclosed. That is, the conductive fur brush is brought into contact with the intermediate transfer belt and rotated. Then, a voltage application member such as a metal roller to which a voltage is applied is brought into contact with the conductive fur brush. Thus, the toner on the intermediate transfer belt is electrostatically adsorbed and cleaned (electrostatic fur brush cleaning). Further, the charge polarity of the residual toner after the secondary transfer includes those charged to (+) by the secondary transfer bias and those charged to (−). For this reason, a method is disclosed in which the residual toner after secondary transfer is recovered by applying (+) and (-) biases of different polarities to a plurality of fur brushes, respectively.
Japanese Patent No. 3236442 JP 2002-229344 A JP 2002-207403 A

  Considering the characteristics of the fur brush method in the conventional fur brush method as described above, in order to clean the transfer residual toner having different polarities, two or more fur brushes are arranged and different biases are applied respectively. This is possible. However, there is a feature that is greatly affected by the transfer process due to the feature of the fur brush method. The details will be described below.

  In the fur brush method, the cleaning ability is affected by various conditions of the process of transferring the toner to paper (recording material). For example, the resistance value of the paper changes due to a change in the moisture absorption condition of the paper, or it is affected by a change in charging characteristics accompanying the durability of the toner. First, paper moisture absorption conditions will be described. When the paper is used in a high humidity environment, the resistance value decreases due to the moisture adsorbed on the paper as the paper is left for a long time. A paper having a reduced resistance value causes more current to flow in the transfer process under constant voltage control in which a voltage is constantly applied. Then, by applying a current that is greater than that required to move the toner to the paper side, the charge of the toner is inverted. By doing so, the transfer efficiency of the toner onto the paper is reduced, and the amount of residual toner is increased. As described above, the resistance of the paper is such that moisture is more easily adsorbed as the standing time is longer, and the resistance decreases.

  For this reason, for example, when the paper is set in the paper feeding cassette section at the time of mass copying, the paper on the cassette has a relatively short paper leaving time, so there is almost no fluctuation in the resistance of the paper and the transfer conditions are good. For this reason, the transfer residual toner includes a toner that remains in the normal polarity without being reversed (referred to as non-inverted toner) and a toner in which the charged polarity is reversed to the polarity opposite to the normal polarity (referred to as reverse toner). Is almost half and the amount of toner is small.

  However, the paper at the bottom of the cassette has a long standing time under high humidity before being fed. As a result, the resistance value of the paper decreases, a large amount of current flows in the transfer portion, the amount of residual toner increases as the transfer efficiency decreases, and the toner polarity is that of the reverse toner than the non-reverse toner. Will increase.

  As described above, when the amounts of the reversed toner and the non-reversed toner change due to a large amount of jobs, the following problems exist.

1) When a large amount of non-reversing toner is present When a large amount of non-reversing toner is present, a large amount of toner is collected by the cleaning unit that applies a bias having a polarity opposite to that of the non-reversing toner. For this reason, when the toner that cannot be collected under normal cleaning conditions exceeds a certain level, the cleaning part passes through, and the non-inverted toner remains on the image carrier, resulting in poor cleaning. On the other hand, in the cleaning unit that applies a bias having the same polarity as the toner, the amount of toner to be cleaned is small, so that the cleaning property can be kept good.

2) When a large amount of reversal toner is present When a large amount of reversal toner is present, a large amount of toner is collected by the cleaning unit that applies a bias having a polarity opposite to that of the reversal toner. For this reason, when the toner that cannot be collected under normal cleaning conditions exceeds a certain level, the toner passes through the cleaning portion and the reversal toner remains on the image carrier. When the reversal toner is present on the image carrier, in most cases, the toner is transferred to the image carrier side at the primary transfer portion, so that it is difficult to reveal. However, if the toner on the next formed image is electrostatically attracted to the polarity, it becomes manifest as a cleaning failure. That is, the reverse toner that has passed through the cleaning portion of the intermediate transfer belt reaches the primary transfer portion of the image forming station on the most upstream side. In the primary transfer portion, a bias is applied in a direction in which negative toner is transferred from the image carrier side to the intermediate transfer belt side. Usually, the reached reversal toner is transferred to the image carrier side. However, when the reversal toner is transferred and overlaps with the next image formation timing, negatively charged toner exists in the primary transfer portion on the image carrier of the most upstream image forming station. . The negatively charged toner attracts the positively charged toner, and as a result, the reversal toner remains on the intermediate transfer belt without being transferred to the image carrier at the primary transfer portion. It becomes apparent as a defective cleaning image. At this time, the cleaning unit that applies a bias having the same polarity as that of the reversal toner has a small amount of toner to be cleaned, so that the cleaning property can be kept good.

  In order to satisfy the above 1) and 2), the voltage applied to each fur brush should be set high. However, if the voltage is too high, a discharge phenomenon occurs on the image carrier. The discharge phenomenon causes problems such as discharge deterioration of the surface layer of the elastic intermediate transfer member, which is an image carrier, so that the life is significantly shortened.

  That is, the state of the residual toner after transfer changes depending on the moisture absorption conditions of the paper and the charging characteristics of the toner. Both lifespan can be achieved.

  The present invention has been made in view of the technical problems as described above. The object of the present invention is to realize the above-described compatibility and optimize the cleaning property and the life of the image carrier. To do.

A typical configuration of the image forming apparatus according to the present invention for achieving the above object is as follows:
A rotating image carrier;
An image forming means for forming a toner image on the image carrier;
A first cleaning member of the first conductive predetermined polarity voltage is applied from the power supply unit and to be removed by adsorbing the toner electrostatically from the surface of the image bearing member, said first cleaning A voltage having a polarity opposite to the predetermined polarity is applied from the second power supply means to the toner from the surface of the image carrier by being disposed downstream of the member in the rotation direction of the image carrier. A conductive second cleaning member that is adsorbed to and removed from the cleaning device;
An image forming apparatus having,
A first current amount detecting means for detecting the amount of current fed to said first cleaning member from said first feeding means,
Second current amount detection means for detecting the amount of current supplied from the second power supply means to the second cleaning member;
On the basis of the detection result of Ru is detected electrostatic flow the first current amount detecting means by said second current amount detecting means predicts the polarity and amount of toner on the surface of the image bearing member during image formation, Based on the prediction result, the cleaning property of the first cleaning member is improved in comparison with the second cleaning member, the cleaning property of the second cleaning member is improved in comparison with the first cleaning member, or Control means for controlling the cleaning conditions of the first cleaning member and the second cleaning member so as to maintain the cleaning properties of the first cleaning member and the second cleaning member without changing ,
It is characterized by having.

  According to the image forming apparatus of the present invention, it is possible to optimize the cleaning property and the life of the image carrier.

[Example]
(1) Image Forming Unit FIG. 2 is a schematic diagram showing a schematic configuration of an example of an image forming apparatus equipped with a cleaning device according to the present invention. The image forming apparatus 100 is a tandem type and intermediate transfer type color digital printer using an electrophotographic process. The image forming apparatus 100 can form and output a full-color image or a monochrome image corresponding to electrical image information input from the external host device 300 to a control circuit unit (control means: CPU) 200 on a recording material. The control circuit unit 200 exchanges various kinds of electrical information with the host device 300 and the operation unit 400, and comprehensively controls the image forming operation of the image forming apparatus according to a predetermined control program and a reference table. The external host device 300 is a computer, an image reader, a facsimile machine or the like.

  UY, UM, UC, and UBk are first to fourth image forming units as image forming means, and are arranged in tandem from left to right on the drawing. Each image forming unit is a laser exposure type electrophotographic process mechanism, and has the same configuration.

  That is, in each of the image forming units UY, UM, UC, and UBk, reference numeral 1 denotes a drum-type electrophotographic photosensitive member (hereinafter referred to as a drum) as a first image carrier, and a predetermined number of counterclockwise directions indicated by arrows. It is rotationally driven at a speed of 300 mm / second in this embodiment. 2 is a primary charger that uniformly charges the outer peripheral surface of the drum 1, and 3 is a laser exposure that scans and exposes the uniformly charged surface of the drum 1 with laser light L to form an electrostatic latent image based on a color image signal. It is a vessel. A developing device 4 visualizes the electrostatic latent image on the drum surface as a toner image. The developer 4 of the first image forming unit UY contains yellow (Y) toner as a developer. The developing device 4 of the second image forming unit UM contains magenta (M) toner as a developer. The developing device 4 of the third image forming unit UC contains cyan (C) toner as a developer. The developer 4 of the fourth image forming unit UK contains black (Bk) toner as a developer.

  Then, based on the color image signal sent from the image processing unit of the control circuit unit 200 to the laser exposure device 3 of each image forming unit, the first image forming unit UY has a Y color toner image on the surface of the drum 1. Is controlled at a predetermined control timing. The second image forming unit UM is controlled to form an M color toner image on the surface of the drum 1 at a predetermined control timing. The third image forming unit UC is controlled to form a C-color toner image on the surface of the drum 1 at a predetermined control timing. The fourth image forming unit UBk is controlled to form a Bk color toner image on the surface of the drum 1 at a predetermined control timing.

  In the image forming apparatus of the present embodiment, the drum 1 is uniformly charged to a predetermined negative polarity potential by the primary charger 2 in each image forming unit, and a negative toner having a negative charging characteristic is used as a toner as a developer. The system uses reversal development of latent images.

Each of the toner images formed on the drum surface of each image forming unit is rotated at an endless and flexible elastic intermediate transfer belt ( intermediate transfer member ) as a second image carrier in the primary transfer unit T1. : Hereafter referred to as a belt) 5 is sequentially superimposed and transferred onto the surface 5. As a result, an unfixed full-color toner image is synthesized and formed on the surface of the belt 5 by superimposing the four toner images.

  In each image forming unit, the toner remaining on the drum 1 without being transferred to the belt 5 is removed by the cleaning device 6.

  The belt 5 is suspended around a driving roller 7, a tension roller 8, and a secondary transfer backup roller 9, and is 300 mm / second, which is substantially the same as the rotational speed of the drum 1 in the clockwise direction indicated by the arrow X. Driven at speed. A primary transfer portion T1 is formed by bringing the horizontal belt portion between the driving roller 7 and the driven roller 8 into contact with the lower surface of the drum 1 of each image forming portion by the primary transfer roller 10. The primary transfer of the toner image from the drum 1 of each image forming unit to the belt 5 has a primary transfer bias of a predetermined potential opposite to the toner charging polarity (minus polarity) (plus polarity) with respect to each primary transfer roller 10. It is done by applying.

  Then, the unfixed full-color toner image synthesized and formed on the surface of the belt 5 reaches the secondary transfer portion T2 by the subsequent rotation of the belt 5. The secondary transfer portion T2 is formed by pressing the secondary transfer roller 11 with the belt 5 interposed between the secondary transfer back-up roller 9 and the secondary transfer roller T2. A nip portion between the secondary transfer roller 11 and the belt 5 is a secondary transfer portion T2. A sheet-like recording material P is separated and fed from the sheet feeding cassette 12 side through the sheet path 13 to the secondary transfer portion T2 at a predetermined control timing. A secondary transfer bias having a predetermined potential having a polarity (plus polarity) opposite to the toner charging polarity (minus polarity) is applied to the secondary transfer roller 11 at a predetermined control timing. As a result, the unfixed full-color toner image on the surface of the belt 5 is secondarily transferred in batch to the surface of the recording material P that is nipped and conveyed by the secondary transfer portion T2.

  The recording material P that has passed through the secondary transfer portion T2 is separated from the belt surface, and is introduced into the fixing device 15 by the conveyance guide 14, and the toner image is fixed on the surface of the recording material P by heat and pressure at the fixing portion. It is fixed. The recording material P exiting the fixing device 15 is discharged onto a discharge tray 16 outside the apparatus.

  Reference numeral 20 denotes a belt cleaning device according to the present invention for cleaning the image forming surface of the belt 5. In the secondary transfer portion T2, the toner remaining on the belt 5 without being transferred to the recording material P is removed by the belt cleaning device 20. The belt cleaning device 20 will be described in detail in section (2).

  In the monochrome image forming mode, only the fourth image forming unit UBk for black images performs the image forming operation. The first to third image forming units UY, UM, and UC are only driven to rotate the drum 1.

  In this embodiment, the intermediate transfer belt 5 as the second image carrier is composed of a resin layer 5a as a base layer, an elastic layer 5b as an intermediate layer, and an outer layer as shown in the layer configuration model diagram of FIG. This is an endless elastic belt having a three-layer structure of a certain surface layer 5c. The resin layer 5a is made of, for example, polycarbonate or fluorine resin. The elastic layer 5b is, for example, butyl rubber, fluorine rubber, or the like. A resistance value adjusting conductive agent such as carbon black or graphite is added to the resin layer 5a and the elastic layer 5b. The surface layer 5c is required to have a low toner adhesion and improve secondary transferability. The surface layer 5c is made of, for example, polyurethane, polyester, epoxy resin, or the like.

(2) Belt cleaning device 20
FIG. 1 is a schematic diagram showing a schematic configuration of the belt cleaning device 20. The belt cleaning device 20 is an electrostatic brush cleaning device that removes secondary transfer residual toner (developer) from the surface of the rotating intermediate transfer belt 5 as a second image carrier. In this embodiment, the belt cleaning device 20 is disposed outside the belt 5 so as to face a belt winding portion of a tension roller (belt stretching roller) 8 that supports the belt 5.

  The belt cleaning device 20 includes a plurality of cleaning units inside a device housing (cleaner container) 21 having a longitudinal direction in the width direction of the belt 5 (a direction orthogonal to the belt moving direction). In the present embodiment, the first cleaning unit 22 and the second cleaning unit 23 located on the downstream side of the first cleaning unit 22 in the moving direction of the belt 5 are provided.

  The first cleaning unit 22 includes a conductive fur brush roller 24 as a belt cleaning member, a metal roller 25 in contact with the fur brush of the fur brush roller, and a cleaning blade 26 in contact with the metal roller.

  Similarly, the second cleaning unit 23 includes a conductive fur brush roller 27 as a belt cleaning member, a metal roller 28 in contact with the fur brush roller, and a cleaning blade 29 in contact with the metal roller.

Both fur brush rollers (hereinafter referred to as fur brushes) 24 and 27 are obtained by implanting a conductive fur brush on the peripheral surface of a metal roller as a core metal. In this example, the fur brush is a carbon dispersion type nylon fiber having a yarn resistance value of 0.3 M (Ω / cm) and a fiber thickness of 6 denier at a rate of flocking density of 500,000 / inch ² . The hair is planted on a metal roller. The fur brushes 24 and 27 are rotatably disposed so as to face the opening of the device housing 21 facing the belt 5. The fur brushes 24 and 27 are parallel to the tension roller 8 that supports the belt 5 and are in contact with the belt 5 while maintaining an intrusion amount of about 1 mm. The fur brushes 24 and 27 are rotationally driven by the drive mechanisms 34 and 35 in the clockwise direction of the arrow (in the direction opposite to the belt moving direction at the contact portion with the belt 5) at a speed of 50 mm / second in this embodiment. The surface of the belt 5 is rubbed by the rotating fur brushes 24 and 27, and the toner (developer) on the belt surface is collected by the fur brush. As a mechanism for electrostatically cleaning the toner, it is preferable to rotate the toner using a conductive fur brush from the viewpoint of cleaning properties.

  The metal rollers 25 and 28 are both made of aluminum, and are parallel to the fur brushes 24 and 27, respectively, and are in contact with each other while maintaining an intrusion amount of about 1 mm. The metal rollers 25 and 28 are rotated at the same speed as the fur brushes 24 and 27 in the counterclockwise direction of the arrow by the drive mechanisms 34 and 35. The toner collected by the fur brushes 24 and 27 is electrostatically transferred and attached to the surfaces of the metal rollers 25 and 28.

  The cleaning blades 26 and 29 are both made of urethane rubber and are in contact with the metal rollers 25 and 28 while maintaining an intrusion amount of 1 mm. The toner adhering to the surfaces of the metal rollers 25 and 28 is scraped off from the surfaces of the metal rollers by the cleaning blades 26 and 29 and accommodated in the apparatus housing 21.

  A negative DC voltage is applied to the metal roller 25 of the first cleaning unit 22 by a first DC power supply (power feeding means) E1. Reference numeral 31 denotes a first current amount detection means (ammeter) that detects the amount of current (cleaning current) flowing from the first DC power source E1 to the first cleaning unit 22. Electrical information relating to the detected current amount is fed back from the first current amount detection means 31 to the control circuit unit 200.

  By applying a voltage to the metal roller 25, a toner in which a potential difference is generated with the fur brush 24 and the charged polarity in the secondary transfer residual toner on the belt 5 is reversed, in this embodiment, a positive polarity toner. Is adsorbed and transferred to the fur brush 24 side. The attracted and transferred toner is further transferred from the fur brush 24 side to the metal roller 25 due to a potential difference, and is scraped off and removed from the surface of the metal roller by the cleaning blade 26.

  The toner having no polarity in the secondary transfer residual toner on the belt 5, the toner having a normal charging polarity, and the negative polarity toner in this embodiment are not electrostatically adsorbed and transferred to the fur brush 24 side. The negative polarity is applied by the negative polarity bias applied to the fur brush 24. This is considered to be charged by charge injection or discharge.

  A positive DC voltage is applied to the metal roller 28 of the second cleaning unit 23 by a second DC power source (power feeding means) E2. Reference numeral 32 denotes a second current amount detection means (ammeter) that detects the amount of current (cleaning current) flowing from the second DC power source E2 to the second cleaning unit 23. Electrical information relating to the detected current amount is fed back from the second current amount detection means 32 to the control circuit unit 200.

  By applying a voltage to the metal roller 28, a potential difference is generated between the metal roller 28 and the fur brush 27, and the negative toner which is not removed by the first cleaning unit 22 and is carried to the second cleaning unit 23 is on the fur brush 27 side. Adsorbed and transferred to. The attracted and transferred toner is further transferred from the fur brush 27 side to the metal roller 28 due to a potential difference, and is scraped off and removed from the surface of the metal roller by the cleaning blade 29.

  Therefore, the toner having the reversed polarity of the secondary transfer residual toner on the belt 5 is removed by the first cleaning unit 22, and the non-inverted toner is removed by the second cleaning unit 23. All the transfer residual toner remaining on the toner can be removed.

  Depending on the transfer conditions, the non-reversing toner and the reversing toner having both positive and negative charges are mixed depending on the transfer conditions. Therefore, by applying a plurality of fur brushes 24 and 27 with voltages having different polarities. It is possible to keep good cleaning ability.

(3) State detection of residual toner on belt 5 In the above cleaning configuration, a mode for detecting the state of secondary transfer residual toner on the belt 5 will be described below. FIG. 4 is a control flow based on detection of the cleaning current.

  Here, in the following description, the first cleaning is an operation of removing the secondary transfer residual toner on the belt 5 by the first cleaning unit 22. The second cleaning is an operation of removing the secondary transfer residual toner on the belt 5 by the second cleaning unit 23.

  The control circuit unit 200 includes first and second DC power supplies E1 when the image forming apparatus starts copying (before image formation), that is, before the secondary transfer residual toner on the belt 5 is cleaned by the belt cleaning device 20. The output voltage value of E2 is corrected. That is, the output voltage values of the first and second DC power supplies E1 and E2 are corrected so that the set current values are optimum for the first cleaning unit 22 and the second cleaning unit 23, respectively. Here, the set current value for the first cleaning unit 23 is It1, and the set current value for the second cleaning unit 23 is It2.

  This operation is called CVC (Cleaning Voltage Control). That is, even if the resistance values of the brush rollers 24 and 27 and the belt 5 change, the first and second direct currents are set so that the cleaning currents flowing through the first and second cleaning units 22 and 23 are always constant. The output voltages of the power supplies E1 and E2 are changed. The optimum set current values It1 and It2 mentioned above indicate areas where the cleaning conditions are the best when the transfer conditions are good.

  FIG. 5 shows an image diagram of CVC control taking the first cleaning unit 22 as an example. Different voltages V1 and V2 are applied to the first cleaning unit 22 and the second cleaning unit 23 by the first DC power supply E1 and the second DC power supply E2, respectively. Then, the current values I1 and I2 flowing in the first cleaning unit 22 and the second cleaning unit 23 at that time are detected by the first and second current amount detection units 31 and 32, respectively. By linearly complementing these two points a and b with a straight line c, it is possible to derive the voltage Vt of the cleaning current It which is the optimum cleaning characteristic under the optimum transfer conditions. The output voltages of the first DC power supply E1 and the second DC power supply E2 at this time are defined as Vt1 and Vt2, respectively. The setting of the cleaning current It is changed for each use environment (absolute water amount in the apparatus) of the image forming apparatus. The control circuit unit 200 sets the cleaning current It according to the value of the absolute moisture amount (electrical signal related to the absolute moisture amount) in the image forming apparatus which is detected and input by the environmental sensor 33 provided in the image forming apparatus. .

  When image formation starts (during image formation), the first and second current amount detection units 31 and 32 are synchronized with the timing at which the belt 5 is cleaned by the first and second cleaning units 22 and 23. The amount of current detected by changes. The change information is transferred to the control circuit unit 200. If the detected current values of the first and second current amount detection means 31 and 32 at this time are defined as I = Im1 and I = Im2, the first and second cleaning units 22 and 23 each have a fixed time. The toner amounts Mc1 and Mc2 that are cleaned are estimated as follows.

Mc1∝ | Im1-It |
Mc2∝ | Im2-It |
The control circuit unit 200 detects the toner amounts Mc1 and Mc2 in the first and second cleaning units 22 and 23, respectively, so that the state of the transfer residual toner on the belt 5 is the following three types A and B: , C classification.

Type A: A lot of reversal toner Type B: A lot of non-reversal toner Type C: The transfer conditions are suitable and the amount of residual toner itself is small The specific detection flow of types A, B, and C will be described below. The transfer residual toner generally increases in proportion to a large amount of image information (image data amount) formed on the recording material P, that is, a large amount of toner used. In the image forming apparatus of the present embodiment, an image signal is transferred from the image processing unit of the control circuit unit 100 to the laser exposure device 3 of each image forming unit. When the image signal is transferred as described above, the information amount of the image is stored as a video counter value in the video counter unit 100a of the control circuit unit 100 for each color image signal of Y, M, C, and Bk. FIG. 6 shows the relationship between the video count value Cv of Y + M + C + Bk and the untransferred toner Me. At this time, Me is the total amount of the secondary transfer residual toner obtained by adding the reverse toner and the non-reverse toner.

  The control circuit unit 200 stores the Me value from the relationship shown in FIG. 6 every time image data is added to the video count 100a one by one. The control circuit unit 200 calculates the Cv value and the Me value from the average values of the image data of 50 sheets of recording material in order to accurately detect the transfer residual toner amount. At this time, the control circuit unit 200 determines, based on the detected Me value, whether the transfer residual toner on the belt 5 is classified into the above three types A, B, and C as follows. Control.

1) Type A: Mc1> 2Me
When Mc1> 2Me, the control circuit unit 200 determines that the first cleaning unit 22 has collected toner twice as much as the residual toner amount Me assumed under the optimum transfer condition. That is, the amount of toner collected by the first cleaning unit 22 is large. Since the first cleaning unit 22 has a negative polarity applied voltage, it can be seen that the amount of residual toner after transfer is mostly reverse toner having a positive polarity. Based on this detection, the control circuit unit 200 shifts to a control operation in the reverse toner cleaning mode. This threshold value can be varied depending on the use environment and the durability life of the cleaning member.

2) Type B: Mc2> 2Me
When Mc2> 2Me, the control circuit unit 200 determines that the second cleaning unit 23 has collected toner twice as much as the residual transfer toner amount Me assumed under the optimum transfer condition. That is, the amount of toner collected by the second cleaning unit 23 is large. Since the second cleaning unit 23 has a positive polarity applied voltage, it can be seen that the amount of residual toner is mostly non-reversed toner having a negative polarity. Furthermore, since the toner threshold amount (2Me) at which the non-inverted toner cleaning mode is activated is exceeded, the control circuit unit 200 shifts to the operation in the non-inverted toner cleaning mode based on this detection.

3) Type C: Mc1 = Mc2 <2Me
When Mc1 = Mc2 <2Me, the control circuit unit 200 determines that the transfer efficiency is optimized because both the first and second cleaning units 22 and 23 are below the set threshold. That is, since the residual toner amount itself is small, the image formation is continued without changing the cleaning conditions.

  According to the flow as described above, the cleaning conditions can be optimized even if the transfer conditions change and the charge polarity and amount of the transfer residual toner change.

  In short, the control circuit unit 200 predicts the polarity and amount of toner on the surface of the belt 5 from the current amount detection results detected by the current amount detection units 31 and 32 during image formation, and the cleaning device based on the prediction results. This controls the cleaning conditions. When the current when an image is not formed is I1, and the current during cleaning during image formation is I2, the total charge amount Qc of toner cleaned per unit time is Qc = I2−I1. If the cleaning toner amount is Mc, then Mc∝Qc. Therefore, the cleaning toner amount can be detected by detecting the cleaning current during image formation and the cleaning current during non-image formation. At this time, since the toner of reverse polarity is not cleaned, it passes only through the cleaning section and is not detected by the current change. Strictly speaking, the resistance value of the toner is detected as a current change, but it may be treated as an error because it is smaller than the resistance values of the image carrier and the cleaning unit. Therefore, even if the state of the secondary transfer residual toner changes due to the change in the moisture absorption condition of the recording material (paper) and the charging characteristics of the toner as described above, the change can be directly detected by the cleaning unit. . Then, by feeding back the result, it becomes possible to correct to an appropriate cleaning condition.

(4) Optimization of cleaning conditions 1) As one of the means for optimizing the cleaning conditions, control by a cleaning applied voltage will be described.

  FIG. 7 shows a correlation diagram of the cleaning property when the set currents in the first and second cleaning units 22 and 23 are independently applied. As a cleaning test method, the applied voltage (secondary transfer bias) to the secondary transfer roller 11 in the secondary transfer process of the toner image from the belt 5 to the recording material P is greatly swung from −1000 V to −3000 V, and the transfer residual The cleaning property when the polarity / amount of the toner was changed was evaluated.

  When satisfactory transfer conditions are satisfied in the secondary transfer portion T2, the set central value of the cleaning current is −20 μA for the first cleaning portion 22 and +20 μA for the second cleaning portion 23.

  When the detected current exceeded the threshold value for the reverse toner cleaning mode, the first cleaning current was −30 μA, and the second cleaning current was +8 μA. As described above, since the transfer residual toner is often positively charged, it is sufficient to increase the first cleaning current. Conversely, since the negative transfer residual toner is less than usual, the second residual current is second. On the other hand, the cleaning performance was better when the cleaning current was set weaker.

  When the detected current exceeded the threshold value for the non-inverted toner cleaning mode, the first cleaning current was −10 μA, and the second cleaning current was +30 μA. As described above, since the transfer residual toner is negatively charged in many cases, the second cleaning current may be increased. Conversely, since the positive transfer residual toner is smaller than usual, the first cleaning current is lower. On the other hand, the cleaning performance was better when the cleaning current was set weaker.

  Based on the above, 5000 continuous durability tests were performed. Table 1 shows set values of the first cleaning and the second cleaning.

  Each Me value was 3 μA. The test environment was 30 ° C./80% high temperature and high humidity, and the recording material P (paper) used was taken out of the environment controlled at 25 ° C./50%. Up to 1000 recording materials P can be set in the paper feed cassette 12, and the recording material P (paper) was taken out from the management environment for every 1000 sheets and a durability test was performed.

  The details of the specific control are as follows. When the detected current exceeds the threshold value, the cleaning set current values I = It1 (−20 μA) and It2 (20 μA) change to It1 ′ = − 30 μA and It2 ′ = + 8 μA, respectively, and the CVC control is performed again. The cleaning property was optimized. FIG. 8 shows the change in the cleaning setting current with respect to the actual durable number at that time. It can be seen that the set current value changes every 1000 sheets. This is because the resistance value of the paper set in the lower part of the feeding cassette 12 under high temperature and high humidity decreases due to the moisture absorption phenomenon. As a result, most of the secondary transfer residual toner becomes the reversal toner, and Mc> 6 μA is exceeded, so that the reversal toner cleaning mode is entered and the respective cleaning setting current values are changed. When the charge distribution was examined for the polarity of the residual toner when Mc> 6 μA, 90% was the reversal toner. It can be seen that the cleaning setting values return to the initial setting values of −20 μA and +20 μA each time in order to set again the paper that has not absorbed moisture after passing 1000 sheets. When the control is not used, the cleaning performance at this time was 900, 1900, 2900, 3900, 4900, and every 1000 sheets. However, when the control of Example 2 was used, The cleaning property was good throughout the durability.

  As described above, the cleaning property largely depends on the voltage, but each has a harmful effect whether the voltage is too high or too low. As described above, when the voltage is low, cleaning failure occurs, and when the cleaning voltage is high, the charge of the toner is reversed, and cleaning failure is likely to occur, and the life of the image carrier is increased as the amount of discharge current increases. There is a harmful effect of lowering.

[Example 2]
As another example of the cleaning condition optimizing means, control by the rotation speed of the fur brush rollers 24 and 27 will be described.

  FIG. 9 shows a correlation diagram of the cleaning performance when the rotation speeds of the fur brush rollers 24 and 27 in the first and second cleaning units 22 and 23 are independently swung. When satisfactory transfer conditions are satisfied in the secondary transfer portion T2, the set center value for cleaning is 50 mm / s for the first and second cleanings, respectively.

  When the detected current exceeded the threshold value for the reverse toner cleaning mode, the rotation speed of the fur brush roller 24 in the first cleaning was 75 mm / s. Although the cleaning performance was good even when the rotation speed of the fur brush roller 27 for the second cleaning was 50 mm / s, the amount of toner to be cleaned by the second cleaning unit 23 is small, so that the life of the fur brush is considered and 25 mm / s. It was set as.

  When the detected current exceeded the threshold value for the non-inverted toner cleaning mode, the rotation speed of the fur brush roller 24 in the second cleaning was 75 mm / s, and the cleaning property was good. The rotation speed of the fur brush roller 24 for the first cleaning was good even at 50 mm / s. However, since the amount of toner to be cleaned by the first cleaning unit 22 is small, it is set to 25 mm / s in consideration of the life of the fur brush. did.

  Based on the above, 500,000 durability tests were performed in the same evaluation mode under the same conditions as in Example 1. The cleaning performance was good, and when the control was not performed, the life of the fur brush was 300,000 sheets. However, when the above control is performed, the life of the fur brush may be extended to 500,000 sheets. did it.

  Generally, the cleaning ability is improved by increasing the rotation speed of the fur brush. However, there is a concern that the life of the fur brush may be shortened due to the hair sleeping from the root due to an increase in energy with which the fur brush hair collides with the belt 5. Therefore, by optimizing the rotation speed of the fur brush according to the result of current detection, it becomes possible to achieve both cleaning ability and the life of the fur brush.

[Example 3]
As another example of the cleaning condition optimizing means, control for changing the contact area of the fur brush with the belt 5 will be described. In this case, the contact area is changed by changing the amount of penetration of the fur brush into the belt 5. At this time, increasing the contact area (increasing the amount of penetration) improves the cleaning ability. However, there is a concern that the life of the fur brush may be reduced due to the hair sleeping from the root due to an increase in energy of the fur brush hair colliding with the image belt 5. Therefore, by optimizing the penetration amount of the fur brush into the belt 5 based on the result of current detection, it becomes possible to achieve both cleaning ability and the life of the fur brush.

  In FIG. 10, the first cleaning portion 22 and the second cleaning portion 23 are assembled to first and second shift members 41 and 42 that are movable with respect to the device housing 21 of the belt cleaning device 20, respectively. . The first and second shift members 41 and 42 are respectively movable in a direction approaching the belt 5 and a direction away from the belt 5. When the first shift member 41 is moved in the direction approaching the belt 5, the contact area of the fur brush roller 24 of the first cleaning unit 22 with the belt 5 increases (the amount of penetration increases). On the contrary, when the first shift member 41 is moved away from the belt 5, the contact area of the first cleaning unit 22 with the fur brush roller 24 with respect to the belt 5 decreases (the amount of intrusion decreases). In addition, when the second shift member 42 is moved in the direction approaching the belt 5, the contact area of the fur brush roller 27 of the second cleaning unit 23 with the belt 5 increases (the amount of intrusion increases). On the contrary, when the second shift member 42 is moved away from the belt 5, the contact area of the fur brush roller 27 of the second cleaning unit 23 with respect to the belt 5 decreases (the amount of intrusion decreases).

  The first and second shift members 41 and 42 are driven to be shifted by first and second shift mechanisms 43 and 44 controlled by the control circuit unit 200, respectively. The first and second shift members 41 and 42 are, for example, a stroke motion mechanism using a motor and a cam, a stroke motion mechanism using a solenoid, a stroke motion mechanism using a forward / reverse motor and a rack and pinion, and the like.

  When the contact area of the fur brush rollers 24 and 27 with respect to the belt 5 is increased in the first cleaning unit 22 and the second cleaning unit 23, the ability of the fur brush to oyster is improved and the toner remaining on the belt 5 is collected. Ability improves.

  Therefore, in the reverse toner cleaning mode, for example, the control circuit unit 200 first increases the intrusion amount setting of the fur brush roller 24 with respect to the belt 5 of the first cleaning unit 22 from the normal intrusion amount 1 mm to 2 mm. The shift mechanism 43 is controlled. That is, the first shift member 41 is moved in a direction approaching the belt 5 to obtain an optimum cleaning setting. On the other hand, in the non-reversing toner cleaning mode, the control circuit unit 200 sets the second brush unit 27 so as to increase the penetration amount of the fur brush roller 27 with respect to the belt 5 from the normal penetration amount 1 mm to 2 mm. The shift mechanism 44 is controlled. That is, the second shift member 42 is moved in the direction approaching the belt 5 to obtain an optimum cleaning setting.

  The belt cleaning device 20 in FIG. 10 also has first and second DC power sources E1 and E2, current amount detection means 31 and 32, and drive mechanisms 34 and 35, as in the device 20 in FIG. Is omitted.

[Other matters]
1) The cleaning condition optimizing means (control of the cleaning conditions) may be an appropriate combination of the optimizing means of the first to third embodiments and an appropriate combination with other optimizing means.

  2) In the first to third embodiments, the cleaning of the intermediate transfer belt 5 as the second image carrier has been described. The same effect can be obtained by applying the present invention to the cleaning of the electrophotographic photosensitive member or the electrostatic recording dielectric as the first image carrier. The image carrier can be a drum type or a belt type.

  3) The fur brush as the cleaning member is not limited to the roller type. It can also be a belt type.

  4) The cleaning member is not limited to the fur brush. A conductive elastic roller or elastic belt can also be used.

  5) One or more cleaning units may be provided.

Model drawing which showed schematic structure of belt cleaning apparatus in Example 1. Model diagram showing schematic configuration of image forming apparatus in Embodiment 1 Intermediate transfer belt layer structure model diagram Control flow diagram of first and second cleaning units Image of CVC control taking the first cleaning unit 2 as an example Relationship diagram between video count value Cv of image data (Y + M + C + Bk) and untransferred toner Me Correlation diagram of the cleaning performance when the set currents in the first and second cleaning units are independently swung. Change diagram of cleaning set current in durability test Correlation diagram of cleaning performance when the rotation speed of the fur brush roller in each of the first and second cleaning units is swung independently. Model drawing which showed schematic structure of belt cleaning apparatus in Example 3.

Explanation of symbols

  UY, UM, UC, UBk, first to fourth image forming units (image forming means), first image carrier (electrophotographic photosensitive member), second image carrier ( Intermediate transfer belt), 20 ... Cleaning device 24 ... 27 Cleaning member (conductive fur brush), E1, E2, Power supply means 31, 32 ... Current detection means 34, 35 ... Drive Means, 200 ·· Control means

Claims (6)

A rotating image carrier;
An image forming means for forming a toner image on the image carrier;
A first cleaning member of the first conductive predetermined polarity voltage is applied from the power supply unit and to be removed by adsorbing the toner electrostatically from the surface of the image bearing member, said first cleaning A voltage having a polarity opposite to the predetermined polarity is applied from the second power supply means to the toner from the surface of the image carrier by being disposed downstream of the member in the rotation direction of the image carrier. A conductive second cleaning member that is adsorbed to and removed from the cleaning device;
An image forming apparatus having,
A first current amount detecting means for detecting the amount of current fed to said first cleaning member from said first feeding means,
Second current amount detection means for detecting the amount of current supplied from the second power supply means to the second cleaning member;
On the basis of the detection result of Ru is detected electrostatic flow the first current amount detecting means by said second current amount detecting means predicts the polarity and amount of toner on the surface of the image bearing member during image formation, Based on the prediction result, the cleaning property of the first cleaning member is improved in comparison with the second cleaning member, the cleaning property of the second cleaning member is improved in comparison with the first cleaning member, or Control means for controlling the cleaning conditions of the first cleaning member and the second cleaning member so as to maintain the cleaning properties of the first cleaning member and the second cleaning member without changing ,
An image forming apparatus comprising: 2. A fur brush that rubs the surface of the image carrier by the first cleaning member and the second cleaning member being in contact with the image carrier and being rotationally driven by a driving unit. The image forming apparatus according to 1. The control of the cleaning condition is a control for changing a voltage applied from the first power supply unit to the first cleaning member and a voltage applied from the second power supply unit to the second cleaning member. The image forming apparatus according to claim 1, wherein: Control of the cleaning condition, the rotational speed of the fur brush said a first cleaning member, to claim 2, characterized in that the control for changing the rotational speed of the fur brush is a second cleaning member The image forming apparatus described. The cleaning condition is controlled by changing the contact area of the fur brush that is the first cleaning member with the image carrier and the contact area of the fur brush that is the second cleaning member with the image carrier. The image forming apparatus according to claim 2, wherein the image forming apparatus is provided.   6. The image forming apparatus according to claim 1, wherein the image bearing member is an intermediate transfer member that receives a primary transfer of a toner image and secondarily transfers the toner image to a recording material. .