JP5445954B2 - Image forming apparatus - Google Patents

Description

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

  In recent years, there are an increasing number of electrophotographic image forming apparatuses capable of forming color images, such as color copiers and color printers. Among them, each of the plurality of photoconductors has a developing unit, and each of the photoconductors is an image formed by monochromatic toners of different colors of yellow, cyan, magenta, and black (hereinafter referred to as Y, C, M, and K). (Single color toner image) is formed, and these single color toner images are sequentially superimposed and transferred onto an intermediate transfer member to form a composite color image, and then the composite color image is collectively transferred onto paper. The number of image forming apparatuses is increasing.

  The image forming operation in such an image forming apparatus is roughly divided into two modes, that is, a monochrome mode and a full color mode. In the monochrome mode, when the apparatus receives a print request in the monochrome mode, the Y, C, and M photoconductors and the intermediate transfer member are not brought into contact with each other, and only K is formed. On the other hand, in the full color mode, the apparatus receives a print request in the full color mode, contacts the Y, C, and M photoconductors with the intermediate transfer member, and drives the photoconductors and developing units for all the colors. Form.

  Here, it is not a monochrome mode, but the formation of an image with few colors used, that is, the formation of a monochrome image other than black, the formation of a two-color image (whether or not it includes black), or the formation of a three-color image including black In the case of formation, image formation is performed in the full color mode. In this case, there is actually a color that is not used for image formation. However, if the developing unit for that color is also driven, the toner and the developer are often subjected to load due to unnecessary stirring, which often leads to deterioration. . Then, when the next image formation is performed, image quality deterioration such as blurring, density decrease, and dirt on the background occurs, so a large amount of toner is consumed and replenished, and the process unit is replaced early before the end of its life There was a risk that it would be necessary to do this.

  On the other hand, the photosensitive member is in contact with the intermediate transfer belt and must be driven. However, the toner and the developer are deteriorated due to unnecessary stirring by not driving the developing unit of the unused color. Can be prevented. However, if the developing unit is simply stopped, the developer existing in the developing nip formed by the photosensitive member and the developer carrying member is brought into contact with the surface of the photosensitive member being driven for a long time. If the surface of the photoconductor is scratched or has a mechanism for applying a lubricant to the surface of the photoreceptor, the lubricant is not only scratched by the developer stopped in the developing nip, but also in the developing unit. There is a problem in that normal charging of the toner is hindered by mixing in the toner.

In order to deal with such a problem, Patent Document 1 discloses an image forming apparatus including a separating unit that moves a photosensitive member and a developing unit away from each other. According to this image forming apparatus, in addition to stopping the driving of the developing device that does not perform image output, the developing device that does not perform image output is separated from the opposing photosensitive member, whereby the photosensitive member and the developer carrying member are separated from each other. Therefore, the above problem can be prevented.
Patent Document 2 discloses an image forming apparatus provided with contact / separation means for selectively contacting or separating an intermediate transfer member and a plurality of photosensitive members. According to this image forming apparatus, the photosensitive member of the color not used for image formation is separated from the intermediate transfer member by the contact / separation means, and the separated photosensitive member is not driven, so that the above problem can be prevented.

However, the image forming apparatus disclosed in Patent Document 1 requires an additional mechanical configuration for separating the developing device from the photosensitive member, which may increase the cost and increase the size of the apparatus.
In addition, the image forming apparatus disclosed in Patent Document 2 requires an additional mechanical configuration for separating the intermediate transfer member from the unused color photoreceptor, which increases costs and enlarges the apparatus. There is a risk of connection.

  Japanese Patent Application Laid-Open No. 2003-228561 discloses a technique for rotating the developer carrying member in reverse after image formation to separate the developer from the developer carrying member.

It is conceivable to apply the technique disclosed in Patent Document 3 in order to prevent damage to the surface of the photosensitive member and hindering normal charging of the toner while suppressing an increase in cost and an increase in size of the apparatus.
However, when the technique disclosed in Patent Document 3 is applied, it is impossible to specify in advance a color that is not used in the next image forming operation after the end of image formation. It is necessary to reversely rotate the developer carrier. In this way, if the developer carrier is reversely rotated every time after the image formation is completed, the development caused by the dropping of the agent from the developer carrier during the reverse rotation or the peeling of the toner fixed to the developer carrier in the developing unit. Inadequate pumping may occur, and an abnormal image may be generated during image formation or a large amount of toner may be consumed.

  The present invention has been made in view of the above problems, and its purpose is caused by a drop in the developer from the developer carrier and a poor pumping of the developer during image formation while suppressing an increase in cost and an increase in the size of the apparatus. It is an object of the present invention to provide an image forming apparatus capable of preventing an abnormal image and a large amount of toner consumption.

In order to solve the above problems, the invention of claim 1 is directed to an image carrier on which a latent image is formed and a plurality of developing means for developing the latent image with developers of different colors carried on the developer carrier. An image carrier driving means for driving the image carrier, a development driving means for driving the plurality of developing means, a control means for controlling the image carrier driving means and the plurality of development driving means, A transfer material carrying / conveying means for carrying and transferring the transfer material, and images formed on the image carrier by the plurality of developing means are sequentially transferred onto the intermediate transfer material or the transfer material to obtain a color image. An image forming apparatus to be formed, wherein the control unit includes a developer of a color developing unit that is not used for image formation of the color image after the input of the color image formation request and before the start of image formation of the color image. Rotate the carrier once in the opposite direction to normal image formation, After, it performs driving control so as not to drive the developer carrying member at the time of image formation of the color image, when the color of the developing unit is not used for image formation is not performed predetermined number consecutive image formation, other While the color developing means used for image formation performs image formation for a predetermined number of images, the color developing means not used for image formation is also drive-controlled .
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the driving source of the image carrier driving unit and the driving source of the development driving unit are configured by the same driving source, and the driving source Further provided is a rotation driving force transmission blocking means capable of blocking the transmission of the rotation driving force to the developer carrier of each of the plurality of developing means, and the control means is used for image formation by rotating the driving source in the reverse direction. When the developer carrying member of the developing means that does not color is once rotated in the reverse direction, the image carrier is rotated in the reverse direction, and then the drive source is rotated forward to rotate the image carrier in the forward direction. The rotational driving force transmission blocking means cuts off the transmission of the rotational driving force to the developer carrying body of the developing means, and performs drive control so as not to drive the developer carrying body of the developing means. Is.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, a plurality of the image carriers are provided in correspondence with the plurality of developing units, and development is performed for each of the plurality of image carriers. The control means rotates the developer carrier of the color developing means not used for forming a color image once in the direction opposite to that during normal image formation, and does not use it for image formation. The drive control is performed so that the image carrier rotates in the forward direction .
Also, the invention of claim 4 is the image forming apparatus according to claim 3, further comprising a charging means for charging the image bearing member, the charging means corresponds to the color which is not used for image formation at the time of color image formation The image carrier is also configured to be charged.
Further, the invention of claim 5 is the image forming apparatus of claim 4 , further comprising a developing bias applying means for applying a developing bias to the developer carrier of each of the developing means, wherein the developing bias applying means is a color image. The developer carrying member of the developing unit corresponding to the color not used for image formation at the time of formation is also configured to apply a developing bias.
According to a sixth aspect of the present invention, there is provided the image forming apparatus according to any one of the third to fifth aspects, wherein each of the plurality of transfer nips formed by each of the image carriers and the intermediate transfer member or the transfer material carrying / conveying means is predetermined. The image forming apparatus further includes a transfer bias applying unit that applies a transfer bias for forming a transfer electric field, and the transfer bias applying unit includes an image carrier of a color that is not used for image formation at the time of color image formation and the intermediate transfer member or the transfer material. The transfer bias for forming the transfer electric field in the transfer nip formed by the carrying and conveying means is reduced from the transfer bias used for image formation.
According to a seventh aspect of the present invention, in the image forming apparatus according to the first to sixth aspects, the image forming apparatus further comprises a lubricant applying means for applying a lubricant comprising a fatty acid metal salt and an inorganic lubricant to the image carrier. It is a feature.

  In the present invention, the developer carrying member of the developing means not used for image formation at the time of color image formation is temporarily rotated in the direction opposite to that at the time of normal image formation before the image formation, thereby developing the image carrier and the developing member. The developer present in the development nip formed with the agent carrier is removed. Even if the developer carrier of the developing means not used for the image formation is stopped without being driven, the developer in the development nip is removed. Problems due to contact with the carrier can be prevented. In addition, after the color image formation request is input, before the start of image formation, the developer carrier of the developing means of the color that is not used for image formation is rotated in the reverse direction. Compared to the configuration in which the developer carrying member is rotated in the reverse direction, the number of reverse rotations can be reduced, and the occurrence of problems associated with the reverse rotation of the developer carrying member can be reduced. Further, since it is not necessary to provide a mechanical mechanism for contacting and separating the image carrier and the developer carrier, it is possible to prevent an increase in cost and an increase in the size of the apparatus.

  According to the present invention, it is possible to prevent an abnormal image and a large amount of toner consumption due to a drop of a developer from a developer carrier or a poor pumping of a developer during image formation while suppressing an increase in cost and an increase in size of an apparatus. There is an excellent effect of being able to.

1 is a schematic configuration diagram illustrating a printer according to an embodiment. FIG. 3 is an enlarged configuration diagram illustrating a process unit for Y of the printer. The perspective view which shows the process unit. The perspective view which shows the image development unit of the process unit. FIG. 2 is an enlarged configuration diagram illustrating a fixing device of the printer. FIG. 3 is a control block diagram of the printer. 3 is a flowchart illustrating an example of a processing procedure when an image is formed by the printer. 4 is a time chart showing an example of a drive sequence when reverse rotation drive control is performed on the developing sleeve of the printer. FIG. 4 is an explanatory diagram of an operation of removing the toner and developer in the development nip by rotating the developing sleeve of the printer in the reverse direction. FIG. 4 is a control block diagram when the drive source of the developing sleeve and the photoconductor of the printer are the same. 6 is a time chart showing an example of a drive sequence in a case where reverse rotation drive control is performed on the developing sleeve when the drive source of the printer is the same. 6 is a flowchart illustrating an example of a processing procedure for alleviating a decrease in toner charge amount when there is a developing unit that is not continuously used for a predetermined number of sheets of the printer.

Hereinafter, an embodiment of an electrophotographic printer (hereinafter simply referred to as “printer”) will be described as an image forming apparatus to which the present invention is applied.
First, a basic configuration of a printer as an image forming apparatus according to the present embodiment will be described. FIG. 1 is a schematic configuration diagram illustrating a printer according to the present embodiment. The printer shown in FIG. 1 includes four process units 1Y, 1C, 1M, and 1K for generating toner images of yellow, cyan, magenta, and black (hereinafter referred to as Y, C, M, and K). These use Y, C, M, and K toners of different colors as image forming substances for forming an image, but the other configurations are the same. Taking a process unit 1Y for generating a Y toner image as an example, this has a photoconductor unit 2Y and a developing unit 7Y as shown in FIG. As shown in FIG. 3, the photosensitive unit 2Y and the developing unit 7Y are integrally attached to and detached from the printer body as a process unit 1Y. However, in a state where it is detached from the printer main body, the developing unit 7Y can be attached to and detached from a photosensitive unit (not shown) as shown in FIG.

  In FIG. 2 described above, the photosensitive unit 2Y includes a drum-shaped photosensitive member 3Y as a latent image carrier, a drum cleaning device 4Y, a static eliminator (not shown), a charging device 5Y as a charging means, a lubricant 70, and the like. doing.

  The charging device 5Y uniformly charges the surface of the photoreceptor 3Y that is driven to rotate in the clockwise direction in the drawing by a driving unit (not shown). In the figure, the charging roller 6Y that is driven to rotate counterclockwise in the drawing while a charging bias is applied by a power source (not shown) is brought close to the photosensitive member 3Y, thereby charging the photosensitive member 3Y uniformly. Device 5Y is shown. Instead of the charging roller 6Y, a roller that contacts a charging brush may be used. Further, a charger that uniformly charges the photoreceptor 3Y by a charger method, such as a scorotron charger, may be used. The surface of the photoreceptor 3Y uniformly charged by the charging device 5Y is exposed and scanned by a laser beam emitted from an optical writing unit to be described later, and carries a Y electrostatic latent image.

  The developing unit 7Y as developing means has a first agent accommodating portion 9Y in which a first conveying screw 8Y is disposed. In addition, there is also a second agent container 14Y in which a toner concentration sensor (hereinafter referred to as “toner concentration sensor”) 10Y including a magnetic permeability sensor, a second transport screw 11Y, a developing roll 12Y, a doctor blade 13Y, and the like are disposed. doing. In these two agent storage portions, a Y developer (not shown) composed of a magnetic carrier and a negatively chargeable Y toner is included. The first transport screw 8Y is driven to rotate by a driving unit (not shown), thereby transporting the Y developer in the first agent storage unit 9Y from the near side to the far side in the direction perpendicular to the drawing sheet. And it penetrates into the 2nd agent accommodating part 14Y through the communication port which is not shown in the partition wall between the 1st agent accommodating part 9Y and the 2nd agent accommodating part 14Y.

  The second transport screw 11Y in the second agent storage portion 14Y is driven to rotate by a driving means (not shown), thereby transporting the Y developer from the back side to the front side in the drawing. The toner concentration of the Y developer being conveyed is detected by the toner concentration sensor 10Y fixed to the bottom of the first agent storage portion 14Y. In this manner, the developing roll 11Y is arranged in a posture parallel to the second transport screw 11Y above the second transport screw 11Y that transports the Y developer. The developing roller 11Y includes a magnet roller 16Y in a developing sleeve 15Y made of a non-magnetic pipe that is driven to rotate counterclockwise in the drawing. A part of the Y developer conveyed by the second conveying screw 11Y is pumped up to the surface of the developing sleeve 15Y by the magnetic force generated by the magnet roller 16Y. Then, after the layer thickness is regulated by the doctor blade 13Y disposed so as to maintain a predetermined gap from the developing sleeve 15Y as a developing member, the layer thickness is regulated and conveyed to the developing area facing the photosensitive member 3Y. Y toner is adhered to the Y electrostatic latent image. This adhesion forms a Y toner image on the photoreceptor 3Y. The Y developer that has consumed the Y toner by the development is returned to the second conveying screw 11Y as the developing sleeve 15Y of the developing roll 12Y rotates. And if it conveys to the near end in a figure, it will return in the 1st agent accommodating part 9Y via the communication port which is not shown in figure.

  The result of detecting the magnetic permeability of the Y developer by the toner concentration sensor 10Y is sent as a voltage signal to a control unit (not shown). Since the magnetic permeability of the Y developer shows a correlation with the Y toner density of the Y developer, the toner density sensor 10Y outputs a voltage having a value corresponding to the Y toner density. The control unit includes a RAM, in which a V Vref for Y which is a target value of the output voltage from the toner density sensor 10Y and a toner density sensor for C, M, and K mounted in another developing unit. The data of C Vtref, M Vtref, and K Vtref, which are target values of the output voltage, are stored. For the Y developing unit 7Y, the value of the output voltage from the toner density sensor 10Y is compared with the Y Vtref, and the Y toner supply device described later is driven for a time corresponding to the comparison result. By this driving, an appropriate amount of Y toner is supplied to the Y developer whose Y toner density has been reduced by the consumption of Y toner during development in the first agent storage unit 9Y. For this reason, the Y toner concentration of the Y developer in the second agent container 14Y is maintained within a predetermined range. Similar toner supply control is performed for the developers in the process units (1C, M, K) for other colors.

  The Y toner image formed on the photoreceptor 3Y is intermediately transferred to an intermediate transfer belt described later. The drum cleaning device 4Y of the photoreceptor unit 2Y removes the toner remaining on the surface of the photoreceptor 3Y after the intermediate transfer process. As a result, the surface of the photoreceptor 3Y that has been subjected to the cleaning process is neutralized by a neutralizing device (not shown). By this charge removal, the surface of the photoreceptor 3Y is initialized and prepared for the next image formation. In FIG. 1 described above, in the process units 1C, M, and K for other colors, C, M, and K toner images are similarly formed on the photoreceptors 3C, M, and K, and the intermediate transfer belt is formed. Intermediate transfer.

  Note that a lubricant 70 made of a fatty acid metal salt and an inorganic lubricant is applied to the surface of the photoreceptor 3Y in order to protect the surface layer of the photoreceptor and improve cleaning properties and protect the cleaning blade of the cleaning device 4Y. Examples of fatty acid metal salts include barium stearate, lead stearate, iron stearate, nickel stearate, cobalt stearate, copper stearate, strontium stearate, calcium stearate, cadmium stearate, magnesium stearate, zinc stearate , Zinc oleate, magnesium oleate, iron oleate, cobalt oleate, copper oleate, lead oleate, manganese oleate, zinc palmitate, cobalt palmitate, lead palmitate, magnesium palmitate, aluminum palmitate, palmitate Calcium acid, lead caprylate, lead caprate, zinc linolenate, cobalt linolenate, calcium linolenate, zinc ricinoleate, cadmium ricinoleate and mixtures thereof However, the present invention is not limited to this. Moreover, you may mix and use these. In the present invention, zinc stearate is most preferably used since it is particularly excellent in film formability on an image carrier. The inorganic lubricant refers to an inorganic compound that cleaves and lubricates itself or causes internal slip. Specific examples include talc, mica, boron nitride, molybdenum disulfide, tungsten disulfide, kaolin, smectite, hydrotalcite compound, calcium fluoride, graphite, plate-like alumina, sericite, and synthetic mica. However, it is not limited to this. These materials can greatly reduce the frictional force between the image carrier and the blade, and thus have a great effect on toner cleaning and cleaning blade protection. Among them, boron nitride is most preferable in the present invention because hexagonal mesh surfaces in which atoms are firmly combined overlap with each other at a wide interval, and the force acting between the layers is only weak van der Waals force, so that it is easily cleaved and lubricated. Used. These inorganic lubricants may be surface-treated as necessary for the purpose of imparting hydrophobicity. In general, the lubricity of fatty acid metal salts decreases due to the effect of charging, and toner passes through the cleaning member, resulting in poor cleaning. Further, the fatty acid metal salt itself flies to and adheres to the charging member, causing charging member contamination. Therefore, by adding an inorganic lubricant, lubricity can be assisted and toner slippage can be prevented. Furthermore, the improvement in lubricity can reduce the amount of the fatty acid metal salt permeating through, and the amount of the fatty acid metal salt flying to the charging member can be reduced.

  An optical writing unit 20 is arranged below the process units 1Y, 1C, 1M, and 1K in the drawing. The optical writing unit 20 serving as a latent image forming unit irradiates the photoconductors 3Y, C, M, and K of the process units 1Y, C, M, and K with a laser beam L emitted based on the image information. Thereby, electrostatic latent images for Y, C, M, and K are formed on the photoreceptors 3Y, 3C, 3M, and 3K. The optical writing unit 20 deflects the laser light L emitted from the light source by the polygon mirror 21 that is rotationally driven by a motor, and passes through the photosensitive members 3Y, 3C, 3M, and 3K via a plurality of optical lenses and mirrors. Is irradiated. Instead of such a configuration, it is also possible to employ one that performs optical scanning with an LED array.

  A first paper feed cassette 31 and a second paper feed cassette 32 are disposed below the optical writing unit 20 so as to overlap in the vertical direction. In each of these paper feed cassettes, a plurality of recording papers P as recording members are accommodated in a stack of recording papers. The uppermost recording paper P includes a first paper feed roller 31a, The second paper feed rollers 32a are in contact with each other. When the first paper feed roller 31a is driven to rotate counterclockwise in the figure by a driving means (not shown), the uppermost recording paper P in the first paper feed cassette 31 is vertically oriented on the right side of the cassette in the figure. The paper is discharged toward the paper feed path 33 arranged so as to extend. Further, when the second paper feed roller 32 a is driven to rotate counterclockwise in the figure by a driving means (not shown), the uppermost recording paper P in the second paper feed cassette 32 is directed toward the paper feed path 33. Discharged. A plurality of transport roller pairs 34 are arranged in the paper feed path 33, and the recording paper P fed into the paper feed path 33 is sandwiched between the rollers of the transport roller pair 34 while being fed between the paper feed paths 33. 33 is conveyed from the lower side to the upper side in the figure.

  A registration roller pair 35 is disposed at the end of the paper feed path 33. The registration roller pair 35 temporarily stops the rotation of both rollers as soon as the recording paper P fed from the conveyance roller pair 34 is sandwiched between the rollers. Then, the recording paper P is sent out toward a later-described secondary transfer nip at an appropriate timing.

  Above each of the process units 1Y, 1C, 1M, and 1K, a transfer unit 40 that is endlessly moved counterclockwise in the drawing while an intermediate transfer belt 41 that is an endless moving body is stretched is disposed. The transfer unit 40 serving as transfer means includes an intermediate transfer belt 41, a belt cleaning unit 42, a first bracket 43, a second bracket 44, and the like. Further, four primary transfer rollers 45Y, 45C, 45M, 45K, a secondary transfer backup roller 46, a drive roller 47, an auxiliary roller 48, a tension roller 49, and the like are also provided. The intermediate transfer belt 41 is endlessly moved counterclockwise in the figure by the rotational driving of the driving roller 47 while being stretched by these eight rollers. The four primary transfer rollers 45Y, 45C, 45M, 45K each sandwich the intermediate transfer belt 41 moved endlessly in this manner from the photoreceptors 3Y, 3C, 3M, and 3K to form primary transfer nips. ing. Then, a transfer bias having a polarity opposite to that of toner (for example, plus) is applied from the primary transfer rollers 45Y, 45C, 45M, 45K serving as transfer bias applying means to the back surface (loop inner peripheral surface) of the intermediate transfer belt 41. The intermediate transfer belt 41 sequentially passes through the primary transfer nips for Y, C, M, and K along with its endless movement, and on the photoreceptor 3Y, C, M, and K on the front surface. The Y, C, M, and K toner images are superimposed and primarily transferred. As a result, a four-color superimposed toner image (hereinafter referred to as a four-color toner image) is formed on the intermediate transfer belt 41.

  The secondary transfer backup roller 46 sandwiches the intermediate transfer belt 41 with the secondary transfer roller 50 disposed outside the loop of the intermediate transfer belt 41 to form a secondary transfer nip. The registration roller pair 35 described above feeds the recording paper P sandwiched between the rollers toward the secondary transfer nip at a timing at which the recording paper P can be synchronized with the four-color toner image on the intermediate transfer belt 41. The four-color toner image on the intermediate transfer belt 41 is affected by the secondary transfer electric field formed between the secondary transfer roller 50 to which the secondary transfer bias is applied and the secondary transfer backup roller 46, and the influence of the nip pressure. The secondary transfer is batch-transferred onto the recording paper P in the secondary transfer nip. Then, combined with the white color of the recording paper P, a full color toner image is obtained.

  Untransferred toner that has not been transferred to the recording paper P adheres to the intermediate transfer belt 41 after passing through the secondary transfer nip. This is cleaned by the belt cleaning unit 42. In the belt cleaning unit 42, the cleaning blade 42a is brought into contact with the front surface of the intermediate transfer belt 41, whereby the transfer residual toner on the belt is scraped off and removed.

  A fixing unit 60 is disposed above the secondary transfer nip in the drawing. As shown in FIG. 5, the fixing unit 60 includes a pressure heating roller 61 that includes a heat source 61 a such as a halogen lamp, and a fixing belt unit 62. The fixing belt unit 62 includes a fixing belt 64 serving as a fixing member, a heating roller 63 including a heat source 63a such as a halogen lamp, a tension roller 65, a driving roller 66, and the like. Then, the endless fixing belt 64 is endlessly moved in the counterclockwise direction in the drawing while being stretched by the heating roller 63, the tension roller 65, and the driving roller 66. In the process of endless movement, the fixing belt 64 is heated from the back side by the heating roller 63. A pressure heating roller 61 that is rotationally driven in the clockwise direction in the drawing is in contact with the surface of the fixing belt 64 that is heated in this manner from the front side. Thereby, a fixing nip where the pressure heating roller 61 and the fixing belt 64 abut is formed.

  Outside the loop of the fixing belt 64, a temperature sensor (not shown) is disposed so as to face the front surface of the fixing belt 64 with a predetermined gap, and the fixing belt 64 just before entering the fixing nip. Detect surface temperature. This detection result is sent to a fixing power supply circuit (not shown). The fixing power supply circuit performs on / off control of power supply to the heat source 63 a included in the heating roller 63 and the heat source 61 a included in the pressure heating roller 61 based on the detection result by the temperature sensor. Thereby, the surface temperature of the fixing belt 64 is maintained at about 140 [° C.].

  In FIG. 1 described above, the recording paper P that has passed through the secondary transfer nip is separated from the intermediate transfer belt 41 and then sent into the fixing unit 60. Then, in the process of being conveyed from the lower side to the upper side in the figure while being sandwiched between the fixing nips in the fixing unit 60, the full-color toner image is fixed by being heated or pressed by the fixing belt 64.

  The recording paper P subjected to the fixing process in this manner is discharged outside the apparatus after passing between the rollers of the paper discharge roller pair 67. A stack unit 68 is formed on the upper surface of the housing of the printer main body, and the recording paper P discharged to the outside by the discharge roller pair 67 is sequentially stacked on the stack unit 68.

  Above the transfer unit 40, four toner cartridges 100 Y, C, M, and K that store Y, C, M, and K toners are disposed. The Y, C, M, and K toners in the toner cartridges 100Y, 100C, M, and K are appropriately supplied to the developing units 7Y, C, M, and K of the process units 1Y, C, M, and K. These toner cartridges 100Y, 100C, 100M, and 100K are detachable from the printer main body independently of the process units 1Y, 1C, 1M, and 1K.

  In the printer having the above basic configuration, the process units 1Y, C, M, and K, the transfer unit 40, the belt cleaning unit 42, the secondary transfer unit having the secondary transfer roller 50, and the fixing unit 60 are combined. An image forming unit for forming an image on the recording paper P as a recording member is configured.

Next, a characteristic configuration of the printer according to the present embodiment will be described.
Forming images that are not in monochrome mode but use fewer colors, that is, forming a single color image other than black, forming a two-color image (whether or not black is included), or forming a three-color image including black In this case, image formation is performed in the full color mode. Then, there are actually colors that are not used for image formation. However, if the developing unit for that color is also driven, the toner and developer for that color are often subjected to unnecessary agitation and lead to deterioration. . If this happens, the image quality will deteriorate when the next image formation is performed, such as blurring, density reduction, and dirt on the background. There is no choice but to recover by replacing it. For this reason, in the printer according to the present embodiment, control is performed so that the photosensitive member of a color not used for image formation is driven, but the developing unit is stopped. However, in this case, there is a problem that the surface of the photosensitive member is damaged due to the developer present in the developing nip, or that the lubricant on the surface of the photosensitive member is mixed into the developing unit and hinders normal charging of the toner. . Conventionally, a technique is known in which the developing sleeve is reversely rotated after the image formation is completed, the developer is pulled away from the developing sleeve, and the developer existing in the development nip is removed, but this is used in the next image forming operation after the image is completed. Since it is impossible to specify in advance the colors that are not to be processed, it is necessary to reversely rotate the developing sleeves of all the colors each time after the end of the image. However, if the reverse rotation of the developing sleeve is performed every time after the image formation is completed, there may be a case where the developer is not pumped up due to the dropping of the agent during the reverse rotation or the peeling of the fixed toner in the developing unit. Then, there are problems that an abnormal image occurs during image formation, a large amount of toner is consumed, and the life of the process unit is shortened. Therefore, in the printer according to the present embodiment, the developing sleeve of the color that is not used for image formation is reversely rotated immediately before image formation to remove the developer present in the development nip, thereby reversing the developing sleeve more than the conventional technique. The number of rotations is reduced.

  FIG. 6 is a control block diagram of the printer according to the present embodiment. In this figure, the printer includes a control unit 100 as control means, a reversible AC motor 101Y as a drive source, a drive gear 102Y, a forward / reverse relay 103Y, a developing sleeve 15Y, a motor 104Y as a drive source, a drive gear 105Y, A photoconductor 3Y and a developing bias applying relay 106Y as a developing bias applying means are provided.

  The control unit 100 includes a CPU, a ROM, a RAM, an input / output contact, and the like, and is a programmable controller that can be programmed in a ladder language, for example.

  The reversible AC motor 101Y rotates and drives the developing sleeve 15Y in the forward direction, in the present embodiment, in the counterclockwise direction CCW (Counter ClockWise), and in the reverse direction, in the present embodiment, in the clockwise direction CW (ClockWise). It is a drive motor. The reversible AC motor 101Y is not limited to this as long as it is a motor capable of normal rotation and reverse rotation, and may be a stepping motor or a reversible DC motor. For example, in the case of a stepping motor, a motor controller and a motor driver may be used instead of the forward / reverse relay 103Y, and the amount and speed of reverse rotation can be freely controlled. The drive gear 102Y is a reduction mechanism that reduces the rotational driving force of the reversible AC motor 101Y and transmits it to the developing sleeve 15Y. The forward / reverse relay 103Y supplies power so as to rotationally drive the reversible AC motor 101Y in the counterclockwise direction CCW by the internal switch SW based on a control signal from the control unit 100, or in the clockwise direction CW. It is a relay that switches whether to supply power so as to be driven to rotate. The illustrated example shows a state where the power supply is OFF. The reversible AC motor 101Y, the drive gear 102Y, and the forward / reverse relay 103Y constitute a developing drive means.

  The motor 104Y is a drive motor for rotationally driving the photoreceptor 3Y in the forward rotation direction, in the present embodiment, in the clockwise direction CW. Unlike the reversible AC motor 101Y, the motor 104Y can rotate in one direction. Good. The drive gear 105Y is a reduction mechanism that reduces the rotational driving force of the motor 104Y and transmits it to the photoreceptor 3Y. The motor 104Y and the drive gear 105Y constitute image carrier driving means.

  The developing bias applying relay 106Y is connected to a developing bias power source (not shown), and is a relay for applying a developing bias to the developing sleeve 15Y by turning on an internal switch based on a control signal of the control unit 100. is there.

  The forward rotation directions of the developing sleeve 15Y and the photoreceptor 3Y are opposite to each other. That is, the forward rotation direction of the developing sleeve 15Y is the counterclockwise direction CCW, and the forward rotation direction of the photoconductor 3Y is the clockwise direction CW.

  In addition, even if the developing sleeve 15Y rotates in the reverse direction, a reverse rotation preventing means may be provided in order to prevent the first conveying screw 8Y and the second conveying screw 11Y from rotating in the reverse direction. For example, a ratchet mechanism may be provided in the drive system as the reverse rotation preventing means.

  FIG. 7 is a flowchart illustrating an example of a processing procedure during image formation of the printer according to the present embodiment. In the figure, image data in response to a print request is input from an external personal computer or the like (not shown) (step S1), and the image data is analyzed for each of Y, C, M, and K colors (step S2). If the analysis result of the image data is a monochrome image (Yes in step S3), the monochrome mode is set (step S4) and image formation is performed (step S5). On the other hand, if the analysis result of the image data is not a monochrome image (No in step S3), the full color mode is set (step S6), and it is determined whether the image data is a full color image (step S7). . If the image data is a full color image (Yes in step S7), image formation is performed (step S5). On the other hand, when the image is not a full-color image (No in step S7), since there are colors that are not used for image formation, drive control is performed to reversely rotate the developing sleeves of the unused colors (step S8). In FIG. 6, for example, when Y is not used, the control unit 100 outputs a control signal for switching the internal switch SW of the forward / reverse rotation relay 103Y in the clockwise direction CW for a predetermined time. Then, it is determined whether or not the reverse rotation drive control of the developing sleeve has been completed. If not completed, the reverse rotation drive control is continued (No in step S9), and if completed (Yes in step S9), Image formation is performed (step S5), and the process ends.

  FIG. 8 shows an example of a drive sequence in the case where the developing sleeve is controlled to rotate backward, and the drive sequence between the photosensitive member and the developing sleeve when at least one of Y, C, and M is not used in the full color mode. It is. In FIG. 8, (a) is the rotational drive of the photosensitive member of the used color, (b) is the rotational drive of the developing sleeve of the used color, (c) is the rotational drive of the photosensitive member of the unused color, and (d) is not used. Each sequence of rotation driving of the color developing sleeve is shown.

  If there is a color that is not used in the full color mode, as shown in FIG. 8D, first, the developing sleeve of the unused color is reversely rotated in the clockwise direction CW for the reverse rotation time t1. For example, when only Y is not used, the internal switch SW of the forward / reverse relay 103Y is switched in the clockwise direction CW based on the control signal of the control unit 100. And the reverse rotation time t1 preset by the timer on the sequence program programmed by the ladder language with the control part 100 is measured. For example, the reverse rotation time t1 is set to 1.0 to 2.0 seconds. When the reverse rotation time t1 is up, the internal switch SW of the forward / reverse relay 103Y is turned OFF. As a result, the Y developing sleeve 15Y can be reversely rotated by the reverse rotation time t1. When the reverse rotation of the Y developing sleeve 15Y that is not used is completed, as shown in FIGS. 8A and 8C, the driving of the photosensitive member for the used color and the photosensitive member for the unused color is started. Then, as shown in FIG. 8B, the driving of the developing sleeve for the used color is started at a timing slightly delayed from the driving of the photosensitive member.

  The timer for measuring the reverse rotation time t1 is not limited to the timer on the sequence program, and may be an external timer. In the case of an external timer, it becomes easy for the service person to change the set time. Further, the reverse rotation amount of the developing sleeve may be detected and stopped by a detection sensor such as a capacitive proximity switch or a reflective photoelectric switch without using a timer. When the detection sensor is used, for example, a rib formed at an equal angle on the flange side surface of the developing sleeve can be detected, and can be stopped by reversely rotating, for example, 30 to 180 degrees. Further, if the stepping motor is used instead of the reversible AC motor, the reverse rotation amount and the rotation speed of the developing sleeve can be controlled more accurately.

  FIG. 9 is an explanatory diagram of an operation of removing the toner and developer in the development nip by rotating the developing sleeve in the reverse direction. FIG. 9A is an explanatory view showing the state of the developer and toner in the developing nip when the developing sleeve and the photosensitive member are stopped, and FIG. 9B is the state of the developing nip after the developing sleeve is reversely rotated. It is explanatory drawing which shows.

  As shown in FIG. 9A, the developer and toner are present in the developing nip when the developing sleeve 15Y and the photoreceptor 3Y are stopped. In this state, when the developing sleeve 15Y is reversely rotated for the reverse rotation time t1, as shown in FIG. 9B, the developing sleeve 15Y is reversely rotated by about 180 degrees in the clockwise direction CW and stopped. Then, the developer and toner in the development nip move while being carried on the development sleeve 15Y, and are removed from the development nip.

  By this control, there is no possibility that even a small amount of dirt toner is input to the photosensitive member 3Y facing the stopped developing sleeve 15Y, which may increase the coefficient of friction of the photosensitive member and cause the cleaning blade to sag. Conceivable. However, since it has a mechanism for applying the lubricant 70 composed of the fatty acid metal salt and the inorganic lubricant to the photoconductor 3Y, the photoconductor friction coefficient can be kept low regardless of the amount of input toner on the photoconductor. Can do.

  As described above, the toner and developer in the developing nip can be removed by rotating the developing sleeve of the unused color in the direction opposite to that during normal image formation and then stopping it before driving the photoreceptor. it can. As a result, even if a photosensitive member that is not used for development thereafter is driven to rotate, it is possible to avoid problems caused by contact with the photosensitive member when toner and developer are present in the development nip. That is, it is possible to avoid problems such as the surface of the photoconductor being damaged, or the lubricant on the surface of the photoconductor being mixed in the developing unit and hindering normal charging of the toner. In addition, after specifying a color that is not used after receiving a print request, the developing sleeve of the corresponding color is reversely rotated immediately before printing the image. The number of rotations can be reduced, and the occurrence of problems associated with the reverse rotation of the developing sleeve can be reduced.

  In the control block diagram shown in FIG. 6, the configuration in which the driving source for driving the developing sleeve and the driving source for driving the photosensitive member are separately provided has been described. However, the developing sleeve and the photosensitive member can be combined with one driving source. It can also be set as the structure driven.

  FIG. 10 is a control block diagram of this configuration. In the figure, a control unit 100, a reversible AC motor 101Y as the same drive source, a drive gear 107Y, a photoreceptor 3Y, a forward / reverse relay 103Y, an electromagnetic clutch 108Y as a rotational drive force transmission blocking means, a developing sleeve 15Y, A developing bias application relay 106Y is provided.

  The drive gear 107Y is a reduction mechanism that decelerates the rotational driving force of the receivable AC motor 101Y and transmits it to the photoreceptor 3Y and the developing sleeve 15Y. The rotational output of the drive gear 107Y is such that the photoreceptor 3Y and the developing sleeve 15Y rotate in opposite directions.

  The electromagnetic clutch 108Y is a rotational driving force transmission interruption device that operates an internal electromagnetic coil based on a control signal of the control unit 100 to transmit or interrupt the rotational driving force of the driving gear 107Y to the developing sleeve 15Y. is there. By providing this electromagnetic clutch 108Y, even if there is only one drive source, if Y is not used during image formation, the rotation of the developing sleeve 15Y can be stopped while the photoreceptor 3Y is rotated. .

  FIG. 11 is an example of a drive sequence in the case where the developing sleeve is controlled to rotate backward, and the driving sequence between the photosensitive member and the developing sleeve in the case where at least one of Y, C, and M is not used in the full color mode. It is. FIG. 11A shows the rotational driving of the photosensitive member of the used color, FIG. 11B shows the rotational driving of the developing sleeve of the used color, FIG. 11C shows the rotational driving of the photosensitive member of the unused color, and FIG. Each sequence of the rotation driving of the developing sleeve is shown.

  When there is a color that is not used in the full color mode, as shown in FIGS. 11C and 11D, first, together with the photosensitive member of the unused color, the developing sleeve of the unused color is reversely rotated in the clockwise direction CW. Reverse rotation is performed for time t1. At this time, the photosensitive member rotates in the counterclockwise direction opposite to the developing sleeve. For example, when only Y is not used, the internal switch SW of the forward / reverse relay 103Y is set to the clockwise direction CW based on the control signal of the control unit 100 in FIG. Further, the electromagnetic clutch 108Y is turned on to transmit the rotational driving force to the developing sleeve 15Y.

  Then, the controller 100 measures the preset reverse rotation time t1, and when the time is up, the internal switch SW of the forward / reverse relay 103Y is switched to the counterclockwise direction CCW and the electromagnetic clutch 108Y is turned OFF to develop the developing sleeve. The transmission of the rotational driving force to 15Y is cut off. As a result, as shown in FIGS. 11D and 11C, the developing sleeve 15Y stops, and the photoreceptor 3Y rotates in the forward rotation direction (clockwise direction CW). In addition, as shown in FIG. 11A, the driving of the photoconductors of the used colors is started at the same timing as the rotation of the photoconductor 3Y in the normal rotation direction. Then, as shown in FIG. 11B, the driving of the developing sleeve for the used color is started at a timing slightly delayed from the driving of the photosensitive member for the used color.

  As shown in the example of FIG. 11, by providing the electromagnetic clutch 108Y, the rotational drive of the photoreceptor 3Y and the developing sleeve 15Y can be controlled by the same drive source, and the photoreceptors and developing sleeves of the unused colors are imaged. Before the forming operation, the toner and developer in the developing nip can be removed by rotating in the direction opposite to that during normal image formation and then stopping. Further, the cost and size of the apparatus can be reduced as compared with the configuration in which the drive source is provided separately.

  When the photosensitive member 3Y is rotated in reverse, the intermediate transfer belt 41 is separated from the photosensitive member 3Y or the intermediate transfer belt 41 is also used in order to avoid sliding with the intermediate transfer belt 41 in the primary transfer nip. It is desirable to rotate them together.

  Here, image formation may be performed in which printing that does not use a specific color among Y, C, M, and K continues, and printing that uses that color is rarely performed. In this case, since the charge amount of the toner of the color that has been stopped without being used is reduced, the start-up of the charge is not in time for the next use, and the image density may increase unintentionally. is there. This problem can be prevented by alleviating the decrease in the toner charge amount.

  FIG. 12 is a flowchart illustrating an example of a processing procedure for forcibly driving a developing unit when a predetermined number of developing units are not continuously used to alleviate a decrease in toner charge amount. . On the sequence program, there are set continuous unused number measurement counters CT, CC, CM, and CK for measuring the number of continuous unused sheets of color developing units that are not used during the image forming operation. These continuous non-use sheet count counters CY, CC, CM, and CK are used to cumulatively count the number of unused color development units that are not continuously used for image formation during the image forming operation. Yes, if it is used for image formation before counting up, the measured cumulative continuous unused number is reset to zero, and the measurement of the continuous unused number is resumed from the next unused time. The set number of sheets to be counted up by the continuous unused number measurement counters CY, CC, CM, and CK is set to 100, for example, in A4 conversion.

  In FIG. 12, image data in response to a print request is input from an external personal computer (not shown) or the like (step S10), and the image data is analyzed for each of Y, C, M, and K colors (step S11) to form an image. Do. Then, for the colors that are not used during the image forming operation, the cumulative continuous unused number of sheets is measured by the continuous unused number counting counters CY, CC, CM, and CK (step S12). While the continuous non-use number counting counters CY, CC, CM, and CK are not counted up, the continuous non-use number is continuously counted (No in step S13). Here, when the continuous unused number counting counters CY, CC, CM, and CK are used for image formation before counting up, the accumulated continuous unused number of the color is reset to zero and the next unused time is not used. The counting of continuous unused sheets is restarted from. On the other hand, when any one of the continuous unused sheet count counters CY, CC, CM, and CK is counted up (Yes in step S13), the counter is not used until a predetermined number of pages in which image formation is continuous is reached. Control is performed to drive all color development units including the development units for the colors used (step S14). For example, the development units for all colors are driven until the fifth page is reached in A4 conversion. After this drive control, the continuous unused sheet counts of the continuous unused sheet count counters CY, CC, CM, and CK are all reset to zero (step S15). The counting of the number of unused sheets is resumed (Yes in step S16). On the other hand, if this control is not continued, the process ends (No in step S16).

  As shown in the example of FIG. 12, when there is a color that is not used in an image that has been requested to be printed, and that color is not used continuously for a predetermined number of times, until the image formation reaches a certain predetermined number of pages that is continuous. By driving the development units 7Y, C, M, and K of all colors including the development unit 7 of the unused color and then stopping the development unit 7 of the unused color, the toner of that color is stopped. Reduction in charge amount can be mitigated.

  In the above-described example, when any one of the continuous non-use number counting counters CY, CC, CM, and CK is counted up, all the colors including the development unit of the non-use color are included until the predetermined number of pages is reached. Although the control for driving the developing unit is performed, it may be controlled to forcibly drive only the developing unit of the counted up color. In this case, thereafter, only the continuous unused sheet count counter of the incremented color developing unit is reset to zero.

  In the printer according to the present embodiment, the unused photoreceptor 3 is driven during the image forming operation. At this time, if a charging bias is not applied, a blade or a brush for cleaning the photoreceptor 3 is used. In some cases, the photosensitive member 3 may be charged abnormally, such as positively charged, due to frictional charging with the toner. Therefore, in the printer according to the present embodiment, when the unused color photoconductors are driven three times, the charging bias is applied in the same manner as in the image formation to prevent the above-described problem.

  Further, when a charging bias is applied to the photoreceptor 3 of an unused color, if a developing bias is not applied, a small amount of developer remaining on the developing sleeve 15 is developed on the photoreceptor, and image formation is performed. It may cause trouble. Therefore, in the printer according to the present embodiment, the above-described problems are prevented by applying a developing bias to the developing unit 7 of a color that is not used during image formation.

  As for the transfer bias of the unused color, the transfer bias to be applied is reduced compared to the image formation in order to reduce the reverse transfer of the toner carried on the belt from the upstream in the rotation direction of the intermediate transfer belt 41. It is preferable to keep it.

The printer according to the above embodiment is a printer including an intermediate transfer unit. However, the present invention does not include an intermediate transfer unit, and an image that forms a color image by sequentially transferring an image directly from a photoconductor to a transfer material. The present invention can also be applied to a forming apparatus.
The printer according to the above embodiment is a printer including a plurality of photoconductors, but the present invention is an image forming apparatus that forms a color image by disposing a plurality of developing units around one photoconductor. Can also be applied.

As described above, according to the printer of this embodiment, the photosensitive member 3 as an image carrier on which a latent image is formed and the different colors carried on the developing sleeves 15Y, 15C, 15M, and 15K as developer carriers. Developing units 7Y, C, M, K as a plurality of developing means for developing the latent image with the developer, motors 104Y, C, M, K as an image carrier driving means for driving the photosensitive member 3, and a driving gear 105Y , C, M, K and receivable AC motors 101Y, C, M, K as driving means for driving the developing units 7Y, 7C, 7M, 7K, driving gears 102Y, 102C, 102M, 102K, positive Control unit 100 as a control means for controlling the reverse relays 103Y, 103C, 103M, and 104K, the motors 104Y, 104C, and 104K, and the receivable AC motors 101Y, 101C, 101M, and 101K, and recording as a transfer material Carry paper P And a conveying roller pair 34 such as a transfer material carrying and transporting means for. An image formed on the photosensitive member 3 by a plurality of developing units 7Y, 7C, 7M, and 7K is sequentially transferred onto an intermediate transfer belt 41 or a recording paper P as an intermediate transfer member to form a color image. After the input of the color image formation request, the control unit 100 sets the developing sleeve 15 of the developing unit 7 of the color not used for image formation of the color image before the start of image formation of the color image during normal image formation. Then, it is rotated once in the opposite direction, and then drive control is performed so that the developing sleeve 15 is not driven when the color image is formed.
Further, the driving source of the photosensitive member 3 and the driving source of the developing units 7Y, C, M, and K are configured by the same reversible AC motors 101Y, 101C, 101M, and 101K, and the reversible AC motors 101Y, 101C, 101M, and 101K are provided. Electromagnetic clutches 108Y, C, C as rotational driving force transmission blocking means capable of blocking transmission of the rotational driving force to the developing sleeves 15Y, C, M, K of the plurality of developing units 7Y, C, M, K. M and K are further provided. The controller 100 reversely rotates the photosensitive member 3 when the developing sleeve 15 of the developing unit 7 of the color not used for image formation is rotated in the reverse direction by rotating the reversible AC motor 101 in the reverse direction. When the reversible AC motor 101 is rotated forward to rotate the photosensitive member 3 forward, the electromagnetic clutch 108 interrupts transmission of the rotational driving force to the developing sleeve 15 of the developing unit 7, and Drive control is performed so as not to drive the developing sleeve 15. By providing the electromagnetic clutch 108, the rotational drive of the photosensitive member 3 and the developing sleeve 15 of the developing unit can be controlled by the same driving source. In addition, the toner and developer in the development nip are removed by rotating in the opposite direction to that during normal image formation and then stopping. By not driving the color developing unit 7 that is not used for image formation, it is possible to prevent the toner and developer from being deteriorated due to useless stirring. In addition, the possibility of occurrence of a problem due to the reverse rotation of the developing unit 7 is minimized, and an abnormal image is suppressed without increasing the cost and the size of the apparatus without damaging the photoreceptor 3 that is not used for image formation. Can be prevented and the life of supplies and units can be extended.
Further, a plurality of the photoreceptors 3Y, 3C, 3M, and 3K are provided so as to correspond to the plurality of developing units 7Y, 7C, 7M, and 7K, and development corresponding to each of the plurality of photoreceptors 3Y, 3C, 3M, and 3K. Development is performed by the units 7Y, C, M, and K. The control unit 100 once rotates the developing sleeve 15 of the developing unit 7 of the color not used for color image formation in the direction opposite to that during normal image formation, and then sets the photoreceptor 3 not used for image formation to the normal direction. Drive control is performed to rotate. Thus, even in a printer having a plurality of photoreceptors 3Y, C, M, and K corresponding to each of the plurality of developing units 7Y, C, M, and K, photoreceptors of colors that are not used for image formation during color image formation. 3 and the developing sleeve 15 formed between the developing sleeve 15 can be removed.
In addition, when the predetermined number of developing units 7 of colors not used for image formation have not been continuously formed, the control unit 100 determines that the developing units 7 of colors used for other image formation are predetermined. During the image formation for the number of sheets, the development units 7 for the colors not used for the image formation are also driven and controlled. By forcibly driving the developing unit 7 of the color in which the image formation is not continuously performed for a predetermined number of sheets and the charge amount of the toner is decreased, the decrease in the charge amount of the toner of the color can be alleviated. In this way, by always performing control to stir and charge the toner in the developing units 7Y, 7C, 7M, and 7K to some extent, it is possible to reduce a decrease in charge amount with time.
Further, charging devices 5Y, 5C, 5M, and 5K as charging means for charging the photoreceptors 3Y, 3C, 3M, and 3K are further provided, and the charging devices 5Y, 5C, 5M, and 5K form an image when forming a color image. The photosensitive member 3 corresponding to the color not used in the above is also charged. If the photosensitive member 3 is not charged, frictional charging with a blade, a brush, or the like for cleaning the photosensitive member 3 may cause the photosensitive member 3 to be charged abnormally such as positively charged, which may cause problems in image formation. Therefore, these problems can be prevented by controlling the charged state of the photoreceptor 3 corresponding to the unused color.
The image forming apparatus further includes a development bias application relay 106 as a development bias application means for applying a development bias to the development sleeves 15Y, C, M, and K of the development units 7Y, 7C, 7M, and 7K. The relay 106 also applies a developing bias to the developing sleeve 15 of the developing unit 7 corresponding to a color not used for image formation during color image formation. Here, when charging the photosensitive member 3 corresponding to an unused color, if a developing bias is not applied, a small amount of developer remaining on the developing sleeve 15 is developed on the photosensitive member 3 and is not intended. Development with a developer may cause problems in image formation. Therefore, this problem can be prevented by controlling the development bias to be applied in accordance with the charged state of the photoreceptor 3.
Further, as transfer bias applying means for applying a transfer bias for forming a predetermined transfer electric field to each of a plurality of transfer nips formed by the respective photoreceptors 3Y, 3C, 3M, and 3K and the intermediate transfer belt 41. Primary transfer rollers 45Y, 45C, 45M, 45K are further provided. The primary transfer rollers 45Y, 45C, 45M, 45K are formed by the photosensitive member 3 and the intermediate transfer belt 41, which are not used for image formation during color image formation. A transfer bias for forming a transfer electric field in the formed transfer nip is reduced as compared with a transfer bias used for image formation. Regarding the intermediate transfer bias of the color that is not used, the reverse transfer of the toner carried on the belt from the upstream in the rotation direction of the intermediate transfer belt 41 is reduced by reducing the bias applied compared to the time of image formation. Can do. As described above, it is possible to reduce reverse transfer and prevent the occurrence of abnormal images, and to prevent an increase in the amount of wasted waste toner.
Further, a lubricant 70 is provided as a lubricant application means for applying a lubricant composed of a fatty acid metal salt and an inorganic lubricant to the photoreceptors 3Y, 3C, 3M, and 3K. By applying a lubricant 70 composed of a fatty acid metal salt and an inorganic lubricant to the photoreceptor 3, the coefficient of friction of the photoreceptor can be kept low regardless of the amount of input toner on the photoreceptor, and the cleaning blade can be bent. Can be prevented.

1Y, C, M, K: Process units 2Y, C, M, K: Photosensitive unit 3Y, C, M, K: Photosensitive member (latent image carrier)
7Y, C, M, K: Development unit (development means)
15Y: Development sleeve (developer carrier)
34: Pair of conveyance rollers (transfer material carrying / conveying means)
40: Transfer unit 41: Intermediate transfer belt (intermediate transfer member)
45Y, C, M, K: primary transfer roller (transfer bias applying means)
60: Fixing unit 70: Lubricant 100: Control unit (control means)
101Y: Reversible AC motor (development drive means)
102Y: Drive gear (development drive means)
103Y: Forward / reverse relay (development drive means)
104Y: Motor (image carrier driving means)
105Y: Drive gear (image carrier driving means)
106Y: Development bias application relay (development bias application means)
107Y: Drive gear 108Y: Electromagnetic clutch (rotation drive force transmission blocking means)
CY, CC, CM, CK: Continuous non-use sheet count counter P: Recording paper (transfer material)

JP 2001-343809 A JP 2006-171233 A Japanese Patent Laid-Open No. 2005-043586

Claims (7)

An image carrier on which a latent image is formed;
A plurality of developing means for developing the latent image with different color developers carried on a developer carrying member;
Image carrier driving means for driving the image carrier;
Development driving means for driving the plurality of development means;
Control means for controlling the image carrier driving means and the plurality of development driving means;
A transfer material carrying and conveying means for carrying and transferring the transfer material,
An image forming apparatus for forming a color image by sequentially transferring an image formed on the image carrier by the plurality of developing means onto an intermediate transfer member or the transfer material,
After the input of the color image formation request, the control means sets the developer carrier of the color developing means not used for image formation of the color image before normal image formation. Is rotated once in the opposite direction, and then drive control is performed so that the developer carrier is not driven when the color image is formed, and a predetermined number of color developing means not used for image formation are continuously formed. In the case where the image forming device is not used, the developing device for the color not used for the image formation is also driven and controlled while the developing device for the color used for the other image formation performs image formation for a predetermined number of images. Image forming apparatus. The image forming apparatus according to claim 1.
The drive source of the image carrier drive means and the drive source of the development drive means are constituted by the same drive source,
A rotation driving force transmission blocking means capable of blocking transmission of rotation driving force from the driving source to the developer carrier of each of the plurality of developing means;
The control means reversely rotates the image carrier to reversely rotate the developer carrier of the color developing means not used for image formation by reversely rotating the drive source, and then driving the drive When the image carrier is rotated in the forward direction by rotating the source forward, the rotational driving force transmission blocking means blocks transmission of the rotational driving force from the developing means to the developer carrying body, and the developing means develops. An image forming apparatus that performs drive control so as not to drive the agent carrier. The image forming apparatus according to claim 1 or 2,
A plurality of the image bearing members corresponding to each of the plurality of developing means,
Development is performed by developing means corresponding to each of the plurality of image carriers,
The control means once rotates the developer carrier of the developing means of the color not used for color image formation in the direction opposite to that during normal image formation, and then forwardly rotates the image carrier not used for image formation. An image forming apparatus that performs drive control as described above . The image forming apparatus 請 Motomeko 3,
A charging means for charging the image carrier,
An image forming apparatus, wherein the charging unit is configured to charge an image carrier corresponding to a color not used for image formation when forming a color image. The image forming apparatus according to claim 4 .
A developing bias applying means for applying a developing bias to the developer carrying member of each of the developing means;
An image forming apparatus, wherein the developing bias applying unit is configured to apply a developing bias to a developer carrying member of a developing unit corresponding to a color not used for image formation when forming a color image. The image forming apparatus according to claim 3 to 5,
A transfer bias applying means for applying a transfer bias for forming a predetermined transfer electric field to each of a plurality of transfer nips formed by each of the image carriers and the intermediate transfer member or the transfer material carrying and conveying means;
The transfer bias applying means applies a transfer bias for forming the transfer electric field to a transfer nip formed by an image carrier of a color not used for image formation at the time of color image formation and the intermediate transfer member or the transfer material carrying / conveying means. An image forming apparatus characterized in that the transfer bias is lower than a transfer bias when used for image formation. The image forming apparatus according to claim 1 to 6,
An image forming apparatus, further comprising a lubricant application unit that applies a lubricant comprising a fatty acid metal salt and an inorganic lubricant to the image carrier.

Images