JP5472811B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine of these.

  In an image forming apparatus such as a copying machine, a printer, a facsimile, or a complex machine of these, a plurality of photosensitive drums as an image carrier that carries an image on a surface, and a plurality of image forming units that perform image forming processing on the photosensitive drum. A so-called tandem type that is arranged side by side is known. In this tandem type image forming apparatus, an image on each photosensitive drum is sequentially transferred to an intermediate transfer belt used as an intermediate transfer body by a primary transfer device, and then an image on the intermediate transfer belt is transferred to a secondary transfer device. There are an intermediate transfer system that batch-transfers images onto recording paper such as a sheet, and a direct transfer system that directly transfers images on each photosensitive drum sequentially onto a recording paper transported by a transfer belt by a transfer device. .

  Conventionally, in this type of image forming apparatus, in order to suppress consumption and deterioration of color toners during monochromatic image formation and wear of the color photoconductive drums, the color photoconductive drums other than black are used as a conveying belt or an intermediate. There has been proposed one configured so as to be separated from the transfer belt (see Patent Documents 1 to 4).

  However, in the above-described conventional image forming apparatus, when the toner used for image formation deteriorates with time, the toner charged to a polarity opposite to that of the normally charged toner due to a decrease in the chargeability of the toner and a broadening of the charge distribution. Adheres to the background portion (non-image portion) of the photosensitive drum, so-called background fogging occurs. When this background fog occurs, there is a problem that the toner adhering to the background portion of the photosensitive drum is transferred to the recording paper and stains the recording paper. This problem may occur in both the direct transfer method and the indirect transfer method. In particular, in the case of the direct transfer method, the toner attached to the background portion of the photosensitive drum is directly transferred to the recording paper. Therefore, it becomes remarkable. In addition, there is a method of separately providing a roller, a bias application member, and the like for collecting the background fog toner from the recording paper. However, if such a dedicated collection roller, a bias application member, and the like are provided, a large-sized image forming apparatus is provided. The problem which becomes cost and cost rise arises.

  In view of such circumstances, the present invention is intended to provide an image forming apparatus that can be reduced in size and cost, and that can suppress contamination of a recording medium due to background fogging.

According to the first aspect of the present invention, there are provided a plurality of image carriers capable of carrying an image on the surface, and an image formed on the image carrier and disposed opposite to each of the image carriers. Transfer means for transferring to an intermediate transfer body; and contact / separation means for switching the image carrier between a state in contact with the recording medium or the intermediate transfer body and a state in which the image carrier is not in contact with each other. Among these, in the image forming apparatus capable of transferring an image in a partially separated mode in which an image carrier on which an image is formed is left and the other image carrier is not in contact with the recording medium or the intermediate transfer member. Information acquisition means for acquiring quality information of toner used for an image formed on the image carrier in the separation mode, and a recording medium conveyance direction or an intermediate transfer body based on the toner quality information acquired by the information acquisition means Upstream in the direction of travel A control means for an image from said image bearing member to be location to control whether causes come in contact with the downstream side the image bearing member where no image is formed with respect to said recording medium or the intermediate transfer body transfer, When transferring an image from the image carrier disposed on the upstream side to the recording medium or the intermediate transfer member, a reversely charged toner attached to the recording medium or the intermediate transfer member from the upstream image carrier. The image is collected by the downstream image carrier in contact with the recording medium or the intermediate transfer member .

In the partial separation mode, it is possible to determine whether there is a risk of image quality deterioration due to background fogging by acquiring quality information of toner used for an image formed on the image carrier by the information acquisition unit. If there is a risk of image quality degradation, the image carrier on which no image is formed is controlled so as to come into contact with the recording medium or intermediate transfer member. The toner can be collected.
Further, the image carrier on the downstream side is brought into contact with the recording medium or the intermediate transfer member, so that the image on the image carrier is transferred to the recording medium or the intermediate transfer member, and then the recording medium is conveyed as it is, or the intermediate transfer member , The background fog toner can be collected by the downstream image carrier. In this case, since it is not necessary to reversely feed the recording medium or the intermediate transfer member upstream in order to collect the background fog toner, the control mechanism can be simplified and the printing speed can be increased.

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the recording medium after the image transfer or the intermediate transfer body is brought into contact with the recording medium based on the toner quality information acquired by the information acquisition unit. The number of the image bearing members can be controlled by the control means.

  Thus, if it is determined that the amount of background fog toner is large on the basis of the toner quality information acquired by the information acquisition means, the number of image carriers to be brought into contact with the recording medium or intermediate transfer body after image transfer is increased. As a result, it is possible to reliably collect the toner from the background fog.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, when the image carrier is brought into contact with the recording medium or the intermediate transfer member after image transfer, the image carrier is opposed to the image carrier. In this configuration, a bias having a polarity opposite to the charging polarity of the normally charged toner is applied to the transfer means.

  By applying a bias having a polarity opposite to the charging polarity of the normally charged toner to the transfer unit, an electric field for moving the toner charged to a polarity opposite to that of the normally charged toner to the image carrier side is transferred between the transfer unit and the image carrier. Thus, the background fog toner on the recording medium or the intermediate transfer member (toner charged to a polarity opposite to that of the normally charged toner) moves from the recording medium or the intermediate transfer member to the image carrier. In this manner, by applying a bias having a polarity opposite to the charging polarity of the normally charged toner to the transfer unit, the background fog toner can be moved to the image carrier and reliably recovered.

  According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the quality information of the toner is used as a travel distance of the image carrier on which an image is formed using the toner. It is acquired by detecting.

  By detecting the travel distance of the image carrier, it is possible to acquire toner quality information.

According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, a yellow image is used as the image carrier to be brought into contact with the recording medium or the intermediate transfer body after image transfer. At least the image carrier capable of being carried is used.

  The yellow toner is not noticeable even if it adheres to the recording medium. Therefore, by using an image carrier capable of carrying at least a yellow image, the ground fog toner on the image carrier adheres to the non-image area of the recording medium. Even if it does, the fall of an image quality can be suppressed.

According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, one of the image carrier and the transfer unit facing each other is changed to the other by the contact / separation unit. In contrast, the image carrier can be switched between a state in contact with the recording medium or the intermediate transfer member and a state in which the image carrier is not in contact with each other.

  As the contact / separation means, it is possible to adopt a configuration in which one of the image carrier and the transfer means facing each other is contacted / separated from the other.

According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect , the contacting / separating means includes a moving member provided with a convex portion or a concave portion and configured to be reciprocally movable. Accordingly, the image carrier or the transfer means is relatively moved between a portion where the convex portion or the concave portion is provided and a portion where the convex portion or the concave portion is not provided, thereby providing an image carrier. Alternatively, the transfer means is configured to be brought into contact with and separated from.

  As the contacting / separating means, the moving member configured as described above can be used.

According to an eighth aspect of the present invention, in the image forming apparatus according to the seventh aspect , the moving member is configured to be reciprocally movable by a gear member that can be rotated by a driving means.

  In this way, the movable member can be reciprocated by the rotatable gear member.

According to a ninth aspect of the present invention, in the image forming apparatus according to the seventh aspect , the moving member is configured to be reciprocally movable by an eccentric cam that can be rotated by a driving means.

  In this way, the movable member can be reciprocated by the rotatable eccentric cam.

According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the seventh to ninth aspects, a position detecting unit that detects a moving position of the moving member is provided, and based on information detected by the position detecting unit. Thus, the movement of the moving member is controlled.

  By detecting the moving position of the moving member by the position detecting means, the movement of the moving member can be controlled with high accuracy.

  According to the present invention, when there is a risk of image quality deterioration due to background fogging in the partially separated mode, an image carrier on which an image is not formed is brought into contact with a recording medium or an intermediate transfer member, and the background fogging is caused by the image carrier. Since the toner can be collected, contamination of the recording medium can be suppressed and a high-quality image can be provided.

  On the other hand, in the initial stage where the chargeability and fluidity of the toner are not lowered or in a low-humidity environment where the chargeability of the toner is high, there is little background fog toner. By keeping the recording medium or the intermediate transfer member out of contact with the recording medium or the intermediate transfer member, it is possible to suppress the wear of the image carrier and the consumption and deterioration of the toner.

  In addition, as described above, by using an image carrier on which an image is not formed as a member for collecting the background fog toner, it is not necessary to separately provide a dedicated roller or the like for collecting the background fog toner. Therefore, size reduction and cost reduction can be achieved.

1 is a schematic configuration diagram of a direct transfer type tandem type image forming apparatus according to an embodiment of the present invention. FIG. 4 is a diagram for explaining a contact / separation operation of a photosensitive drum provided in the image forming apparatus. It is a figure which shows the structure of the contact / separation means of the said photoreceptor drum. It is a figure which shows other embodiment of the said contact / separation means. 4 is a flowchart for explaining a monochrome image forming operation in the present invention. FIG. 3 is a diagram illustrating a state in which two photosensitive drums of yellow and magenta are brought into contact with a conveyance belt during monochrome image formation. 1 is a schematic configuration diagram of an image forming apparatus configured to make a transfer roller contact and separate. 1 is a schematic configuration diagram of an image forming apparatus that does not include a conveyance belt. 1 is a schematic configuration diagram of an indirect transfer type image forming apparatus.

  Hereinafter, embodiments according to the present invention will be described with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified or abbreviate | omitted suitably.

  FIG. 1 is a schematic configuration diagram of a direct transfer type tandem type image forming apparatus according to an embodiment of the present invention. However, the configuration of the present invention is not limited to the image forming apparatus shown in FIG. 1, and can also be applied to other copiers, printers, facsimiles, or multifunction peripherals thereof.

  In the image forming apparatus 100 shown in FIG. 1, four process units 1Y, 1M, 1C, and 1Bk as image forming units are detachably attached to the image forming apparatus main body 99. The process units 1Y, 1M, 1C, and 1Bk have the same configuration except that they contain toners of different colors of yellow, magenta, cyan, and black corresponding to the color separation components of the color image.

  Specifically, the process units 1Y, 1M, 1C, and 1Bk respectively charge the photosensitive drums 2Y, 2M, 2C, and 2Bk as image carriers and the surfaces of the photosensitive drums 2Y, 2M, 2C, and 2Bk. Charging rollers 3Y, 3M, 3C, 3Bk as means, developing devices 4Y, 4M, 4C, 4Bk as developing means for developing electrostatic latent images on the photosensitive drums 2Y, 2M, 2C, 2Bk, A cleaning unit (not shown) for cleaning the surfaces of the photosensitive drums 2Y, 2M, 2C, and 2Bk is provided.

  Each of the photosensitive drums 2Y, 2M, 2C, 2Bk is rotated at a linear speed of 50 mm / s counterclockwise by a driving device (not shown). Each charging roller 3Y, 3M, 3C, 3Bk is in contact with the surface of the photosensitive drum 2Y, 2M, 2C, 2Bk, and the charging roller 3Y, 3M, 3C is rotated by the rotation of the photosensitive drum 2Y, 2M, 2C, 2Bk. , 3Bk is driven to rotate. Further, the charging rollers 3Y, 3M, 3C, and 3Bk are configured to be applied with DC or a bias in which AC is superimposed on DC by a high voltage power source (not shown). Each of the developing devices 4Y, 4M, 4C, and 4Bk is a one-component contact type developing device in which one-component toner as a developer is initially stored. Each developing device 4Y, 4M, 4C, 4Bk is configured to be supplied with a predetermined developing bias from a high voltage power source (not shown).

  Further, in the image forming apparatus main body 99, an exposure device 5 as an exposure unit that exposes the surface of each of the photosensitive drums 2Y, 2M, 2C, and 2Bk, a paper feed cassette 6 that stores a sheet-like recording medium, and the like. A transfer belt 7 as a transfer means for transferring the recording medium, and four transfer rollers 8Y, 8M, as transfer means for transferring the toner images on the photosensitive drums 2Y, 2M, 2C, 2Bk onto the recording medium. 8C and 8Bk and a fixing device 9 as a fixing unit for fixing the toner image transferred to the recording medium are provided.

  The exposure device 5 is configured to irradiate each photosensitive drum 2Y, 2M, 2C, 2Bk with laser light corresponding to image information. As this exposure apparatus 5, a laser beam scanner using a laser diode or the like can be used.

  The paper feed cassette 6 accommodates recording paper P as a recording medium. Here, the recording medium accommodated in the paper feed cassette 6 includes not only plain paper generally used for copying and the like, but also OHP sheets, cardboard, postcards and other thick paper, envelopes, and the like. The paper feed cassette 6 is provided with a paper feed roller 10 for feeding the stored recording paper P. A registration roller pair 11 for correcting skew of the recording paper P and adjusting the conveyance timing is disposed in the middle of the conveyance path for conveying the recording paper P from the paper feed cassette 6 to the conveyance belt 7.

  The conveyor belt 7 is an endless belt stretched by a driving roller 12, a tension roller 13, and four transfer rollers 8Y, 8M, 8C, and 8Bk. The driving roller 12 is rotated clockwise in the figure by a driving device (not shown), and the conveyance belt 7 is rotated in the direction of arrow A in the figure by the rotation of the driving roller 12. Both ends of the tension roller 13 are urged toward the transport belt 7 by springs (not shown). Further, flanges are press-fitted at both ends of the tension roller 13, thereby restricting meandering of the conveyor belt 7. Each roller that stretches the conveyor belt 7 is supported by a side plate of a conveyor belt unit (not shown).

  As the drive roller 12, for example, a roller made of polyurethane rubber having a surface layer portion of 0.3 to 1 mm or a roller having a thin layer coating of 0.03 to 0.1 mm on a metal roller can be used. However, in the present embodiment, a urethane coating roller having a wall thickness of 0.05 mm and a diameter of 19 mm, in which the diameter change due to temperature is small, is used. Further, the tension roller 13 in the present embodiment is constituted by an aluminum pipe having a diameter of 19 mm and a width of 231 mm.

The transfer rollers 8Y, 8M, 8C, and 8Bk are in contact with the conveyor belt 7 at positions facing the photosensitive drums 2Y, 2M, 2C, and 2Bk. A transfer nip as a transfer portion is formed at a position where the conveyance belt 7 is sandwiched between the photosensitive drums 2Y, 2M, 2C, and 2Bk. A predetermined transfer bias (+400 to +2500 V) is applied to each transfer roller 8Y, 8M, 8C, 8Bk from an unillustrated high-voltage power supply for each color. As the transfer rollers 8Y, 8M, 8C, and 8Bk, a conductive sponge roller, a conductive solid roller, or the like can be used. The conductive sponge roller is configured by, for example, covering a metal core such as SUS with an elastic body adjusted to a resistance value of 10 ⁴ to 10 ¹³ Ω with a conductive material.

  Further, a toner mark sensor (TM sensor) 14 is disposed at a position facing the conveying belt 7. The toner mark sensor 14 is composed of a regular reflection type or diffusion type sensor, and detects toner on the conveyor belt 7 to measure the density of each toner image and each color position. Thus, the image density and alignment are adjusted.

Hereinafter, the basic operation of the image forming apparatus will be described with reference to FIG. 1 taking a case of forming a color image as an example.
When the image forming operation is started, the photosensitive drums 2Y, 2M, 2C, and 2Bk are rotationally driven counterclockwise by a driving device (not shown), and the charging rollers 3Y, 3M, 3C, When a predetermined bias is applied to 3Bk, the surfaces of the photosensitive drums 2Y, 2M, 2C, and 2Bk are uniformly charged to a predetermined polarity. Next, a laser beam is irradiated from the exposure device 5 onto the surface of each of the charged photosensitive drums 2Y, 2M, 2C, and 2Bk to form an electrostatic latent image. At this time, the image information exposed on each of the photosensitive drums 2Y, 2M, 2C, and 2Bk is single-color image information obtained by separating a desired color image into color information of yellow, magenta, cyan, and black. The toner is supplied to the electrostatic latent images formed on the photosensitive drums 2Y, 2M, 2C, and 2Bk as described above by the developing devices 4Y, 4M, 4C, and 4Bk. To be visualized (visualized image).

  When the image forming operation is started, the sheet feeding roller 10 starts rotating, and the recording sheet P stored in the sheet feeding cassette 6 is sent out by the sheet feeding roller 10. The recording paper P sent out by the paper supply roller 10 is temporarily stopped by the registration roller pair 11 and the skew is corrected here. Thereafter, the driving of the registration roller pair 11 is resumed at a predetermined timing, and the recording paper P is sent to the transport belt 7. Further, a predetermined transfer bias (+400 to +2500 V) is applied to each transfer roller 8Y, 8M, 8C, 8Bk from a high voltage power source (not shown), and each transfer roller 8Y, 8M, 8C, 8Bk and each photosensitive drum 2Y, 2M, A transfer electric field is formed in the transfer nip between 2C and 2Bk. Then, the recording paper P carried on the transport belt 7 is transported in the direction of the arrow A in the figure as the transport belt 7 rotates, and when the recording paper P passes through each transfer nip, each photosensitive drum 2Y. , 2M, 2C, and 2Bk, the toner images are transferred so as to overlap on the recording paper P in the order of black, cyan, magenta, and yellow. Thus, a color image is carried on the recording paper P. The toner remaining on the photosensitive drums 2Y, 2M, 2C, and 2Bk is removed by a cleaning device (not shown) to prepare for the next image formation. Thereafter, the recording paper P onto which the toner image has been transferred is conveyed to the fixing means 9, where the recording paper P is heated and pressurized to fix the toner image, and then the recording paper P is discharged out of the apparatus. .

  The operation when forming a color image has been described above, but the image forming apparatus according to the present embodiment can form a monochrome image using only black toner in addition to the color image. However, when forming a monochrome image, it is necessary to form a monochrome image if all the photosensitive drums 2Y, 2M, 2C, and 2Bk are in contact with the transport belt 7 as in the color image formation shown in FIG. Even the photosensitive drums 2Y, 2M, and 2C having no color must be driven. In this case, compared with the case where the driving of the color photosensitive drums 2Y, 2M, and 2C is stopped, the color toner is consumed and deteriorated, and the color photosensitive drums 2Y, 2M, and 2C are worn. For this reason, in the image forming apparatus according to the present embodiment, as shown in FIG. 2B, when a monochrome image is formed, the color photosensitive drums 2Y, 2M, and 2C are connected by a contact / separation unit (not shown). They are separated from the conveyor belt 7 and their driving is stopped. In this way, when performing monochrome image formation, a toner image is formed only on the black photosensitive drum 2Bk in the partially separated mode in which the color photosensitive drums 2Y, 2M, and 2C are separated from the transport belt 7. It is transferred to the recording paper P on the conveyor belt 7. In the partial separation mode, the photosensitive drum brought into contact with the conveyance belt 7 is not limited to the black photosensitive drum 2Bk. It is also possible to adopt a configuration in which a partly separated mode can be obtained by contacting other photosensitive drums or two or more photosensitive drums.

  By the way, as the quality of toner, such as chargeability and fluidity, deteriorates with time, the amount of toner charged in the toner to a polarity opposite to the normal charge polarity increases, and the background portion of the photosensitive drum (non-image) Part)) may occur. In particular, when this background fog occurs when forming a monochrome image, the black toner attached to the background portion of the photosensitive drum is transferred onto the recording paper, and the stain on the recording paper is noticeable and the image quality is deteriorated. .

  Therefore, in the present embodiment, when a background fog occurs during monochrome image formation, as shown in FIG. 2C, one of the color photosensitive drums 2Y, 2M, and 2C (in the drawing, a yellow photosensitive member). The drum 2Y) is brought into contact with the conveyor belt 7 so that the toner adhered to the non-image portion of the recording paper is collected by the photosensitive drum. Hereinafter, a configuration for collecting the toner on the non-image part will be described in detail.

  FIG. 3 is a diagram showing the configuration of the contacting / separating means for the photosensitive drum. In FIG. 8, (a) is a color image forming mode in which all the photosensitive drums 2Y, 2M, 2C, and 2Bk are brought into contact with the conveying belt 7, and (b) is a case in which only the black photosensitive drum 2Bk is brought into contact with the conveying belt 7. (C) is a monochrome image forming mode in which the color photosensitive drums 2Y, 2M, and 2C are separated from the conveyance belt 7, and (c) is a toner collection in which the yellow photosensitive drum 2Y is in contact with the conveyance belt 7 in the monochrome image formation mode. Indicates the mode.

  As shown in FIG. 3, the contact / separation means 20 includes a moving member 21 that can reciprocate in the horizontal direction (lateral direction in the figure), a gear member 22 that moves the moving member 21, and the like. The gear member 22 meshes with the tooth row of the rack portion 21a provided on the moving member 21, and the moving member 21 moves in the horizontal direction when the gear member 22 rotates forward or backward by a driving unit (not shown). It is supposed to be. The moving member 21 is provided with three convex portions 21y, 21m, and 21c for pushing up the color photosensitive drums 2Y, 2M, and 2C upward.

  When the gear member 22 is rotated from the state shown in FIG. 3A and the moving member 21 is moved to the left side of the figure, as shown in FIG. 3B, the convex portions 21y and 21m are moved along with the movement. , 21c pushes up the bearings of the color photosensitive drums 2Y, 2M, 2C so that the photosensitive drums 2Y, 2M, 2C are separated from the transport belt 7. In this state, when the gear member 22 is further rotated to move the moving member 21 to the left side of the drawing, the yellow photosensitive drum 2Y falls from the convex portion 21y and is conveyed as shown in FIG. Contact the belt 7. Note that the magenta and cyan photoconductive drums 2M and 2C are on the convex portions 21m and 21c, respectively, and are maintained in a state of being separated from the transport belt 7. As described above, according to the present embodiment, as the moving member 21 moves, the color photosensitive drums 2Y, 2M, and 2C have a portion where the convex portions 21y, 21m, and 21c are provided and a portion where the convex portions are not provided. The color photosensitive drums 2Y, 2M, and 2C are configured so as to be able to come into contact with and separate from the conveyor belt 7 by being relatively moved. Although not shown, the moving member 21 is provided with a recess, and the color photosensitive drums 2Y, 2M, and 2C are relatively moved between a location where the recess is provided and a location where no recess is provided. In addition, the color photosensitive drums 2Y, 2M, and 2C can be brought into and out of contact with the conveyor belt 7.

FIG. 4 is a view showing another embodiment of the contact / separation means 20.
The contact / separation means 20 shown in FIG. 4 has a moving member 21 as in the embodiment shown in FIG. 3, but the mechanism for moving the moving member 21 is different from the embodiment shown in FIG. . Specifically, the contacting / separating means 20 shown in FIG. 4 has an eccentric cam 23 that contacts the moving member 21. The eccentric cam 23 has three cam surfaces 23a, 23b, and 23c having different distances from the rotation center. Accordingly, when the eccentric cam 23 is rotated by receiving a driving force from a driving means (not shown), the position of the moving member 21 is changed according to the cam surfaces 23a, 23b, 23c contacting the moving member 21 in FIG. (B) It changes to three stages (c). As the moving member 21 moves, the convex portions 21y, 21m, and 21c provided on the moving member 21 push up the bearings of the color photosensitive drums 2Y, 2M, and 2C. , 2M, 2C are separated from the conveyor belt 7. The contact / separation operation of the color photosensitive drums 2Y, 2M, 2C in FIGS. 4A, 4B, and 4C is the same as the contact / separation operation described in FIGS. 3A, 3B, and 3C. Since it is the same, description is abbreviate | omitted here.

  Although not shown, a position detecting unit that detects the position of the moving member 21 may be provided, and the movement of the moving member 21 may be controlled based on information detected by the position detecting unit. By detecting each position of the moving member 21 shown in FIG. 3 or 4 by this position detecting means, the movement of the moving member 21 can be controlled with high accuracy. As the position detection means, for example, a transmission type optical sensor, a reflection type optical sensor, or a sensor that detects the position by detecting the presence or absence of conduction is applicable.

  In addition, the image forming apparatus according to the present embodiment is based on the information acquisition unit that acquires the quality information of the toner used for the black photosensitive drum 2Bk, and the quality information of the black toner that is acquired by the information acquisition unit. And a control means for controlling whether or not the yellow photosensitive drum 2Y is brought into contact with the conveyor belt 7. The quality information of the toner can be grasped by obtaining information such as the travel distance of the photosensitive drum, the toner consumption, the waste toner amount, the rotation time of the motor that drives the photosensitive drum, and the like. In the present embodiment, an ID chip (not shown) provided in the process unit is used as the information acquisition means in order to obtain information used for new detection of the process unit, toner end detection, and other various controls. In the information obtained by the ID chip, the travel distance information of the black photosensitive drum is obtained as information relating to quality such as a decrease in chargeability and fluidity of the toner.

  The control means includes a CPU (not shown) for controlling various operations of the image forming apparatus. The travel distance information of the black photosensitive drum as the toner quality information acquired by the IC chip is transmitted to the control unit, and the control unit travels the black photosensitive drum based on the received information. It is determined whether or not the distance exceeds a predetermined travel distance. Then, based on the determination result, it is configured to control whether or not the yellow photosensitive drum 2Y is brought into contact with the transport belt 7. The “predetermined mileage” here is a threshold value for the mileage estimated to be a quality (degraded state) in which the quality of the toner produces a background fog that may cause a reduction in image quality.

Hereinafter, the monochrome image forming operation will be described with reference to the flowchart shown in FIG.
When monochrome image formation is started, the control means determines whether or not the travel distance of the black photosensitive drum exceeds a predetermined travel distance based on the information received from the IC chip. If the travel distance of the black photosensitive drum does not exceed the predetermined travel distance, it is determined that there is no risk of image quality deterioration due to background fogging, and the state moves to the state shown in FIG. 3B or 4B. The member 21 is moved so that all the color photosensitive drums 2Y, 2M, and 2C are separated from the transport belt 7. Then, a toner image is formed only on the black photosensitive drum 2 </ b> Bk, and is transferred to the recording paper P on the conveyance belt 7.

  On the other hand, when the travel distance of the black photosensitive drum exceeds a predetermined travel distance, it is determined that there is a risk of image quality deterioration due to the background fog, and the state shown in FIG. 3C or FIG. The moving member 21 is moved to separate the magenta and cyan photosensitive drums 2M and 2C except yellow from the conveying belt 7. Then, a toner image is formed only on the black photosensitive drum 2 </ b> Bk, and is transferred to the recording paper P on the conveyance belt 7. Thereafter, when the recording paper P is conveyed downstream and reaches the position of the yellow photosensitive drum 2Y, a predetermined bias (+400 to +400 to the transfer roller 8Y facing the yellow photosensitive drum 2Y is applied to the transfer roller 8Y. + 2500V) is applied. The bias applied at this time is a bias having a polarity opposite to the charging polarity of the normally charged toner. As a result, an electric field is formed between the transfer roller 8Y and the yellow photosensitive drum 2Y to move the toner charged to a polarity opposite to that of the normally charged toner toward the yellow photosensitive drum 2Y. The background fog toner (toner charged to a polarity opposite to that of the regular charged toner) adhering to the non-image area moves from the recording paper to the yellow photosensitive drum 2Y and is collected. Thereafter, the toner collected by the yellow photosensitive drum 2Y is removed by a cleaning unit (not shown).

  In the above-described example, among the color photosensitive drums 2Y, 2M, and 2C, only the yellow photosensitive drum 2Y is controlled to come into contact with the conveyance belt 7. However, the photosensitive drum to be brought into contact with the conveyance belt 7 is controlled. The larger the number, the more reliable it is possible to collect more of the background fog toner. For example, as shown in FIG. 6, two photosensitive drums 2Y and 2M of yellow and magenta may be brought into contact with the conveyor belt 7 when forming a monochrome image. Further, at the time of monochrome image formation, as shown in FIG. 2A, it is possible to bring all the color photosensitive drums 2Y, 2M, and 2C into contact with the conveying belt 7.

  Further, the number of color photosensitive drums 2Y, 2M, and 2C to be brought into contact with the conveyance belt 7 may be configured to be changeable based on the black toner quality information over time. As a result, when the amount of deteriorated toner is large, a large number of color photosensitive drums can be brought into contact with each other to reliably collect the background fog toner.

  Further, since the chargeability and fluidity of the toner also change depending on the temperature and humidity, an environmental condition detection sensor for detecting the temperature and humidity in the image forming apparatus or the surrounding environment is provided, and the temperature or the temperature detected by the environmental condition detection sensor is provided. When the humidity exceeds a predetermined value, control may be performed so that at least one of the color photosensitive drums is brought into contact with the conveyance belt 7. It is also possible to control the contact / separation operation of the color photosensitive drum by using the toner quality information obtained by the IC chip and the detection information of the environmental condition detection sensor in combination.

  Further, the background fog toner can be collected by selecting any of the plurality of color photosensitive drums 2Y, 2M, and 2C and bringing them into contact with the conveying belt 7, but the yellow photosensitive drum 2Y is given priority. It is desirable to select it. This is because yellow toner is not noticeable even if it adheres to the recording paper. Therefore, by using at least the yellow photosensitive drum 2Y, even if the background fog toner on the yellow photosensitive drum 2Y is non-imaged on the recording paper, This is because deterioration in image quality can be suppressed even if it adheres to the portion.

  Further, as in the present embodiment, the color photosensitive drums 2Y, 2M, and 2C used for collecting background fog toner are more transported in the recording paper conveyance direction (arrows in FIG. 2) than the black photosensitive drum 2Bk. It is desirable that it is disposed downstream of (A direction). If the color photoconductor drums 2Y, 2M, and 2C are disposed upstream of the black photoconductor drum 2Bk, the recording paper must be fed back to the upstream side in order to collect background fog toner. This is because the control mechanism becomes complicated and the printing speed also decreases.

  The embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention. For example, the direct transfer type image forming apparatus according to the present invention may be configured as shown in FIG. In this image forming apparatus, as shown in FIG. 7A, the transfer belts 8Y, 8M, and 8C are brought into contact with and separated from the color photosensitive drums 2Y, 2M, and 2C, so that the transport belt 7 is moved to the color belt. The photosensitive drums 2Y, 2M, and 2C are configured to be able to contact and separate. In this case, as shown in FIG. 7B, at the time of monochrome image formation, at least one of the transfer rollers 8Y, 8M, 8c facing the color photosensitive drums 2Y, 2M, 2C (yellow in the figure). By bringing the transfer roller 8Y) facing the photosensitive drum 2Y into contact with the photosensitive drum, it is possible to collect the background fog toner on the recording paper as in the above-described embodiment.

  Further, the direct transfer type image forming apparatus according to the present invention may be an image forming apparatus that does not include a conveying belt as shown in FIG. In the image forming apparatus shown in FIG. 8, a conveyance guide 30 is disposed between the transfer rollers 8Y, 8M, 8C, and 8Bk, whereby the recording paper is guided and conveyed. The conveyance guide 30 is made of a conductive material such as a SUS plate and is grounded via a predetermined electric resistance. Thereby, it is possible to prevent electric charges from being accumulated in the conveyance guide 30 due to rubbing between the conveyance guide 30 and the recording paper, and the conveyance guide 30 is controlled to have a predetermined potential. Thus, by preventing the charge from being accumulated in the conveyance guide 30, the toner image held on the recording sheet mainly by electrostatic force is prevented from being adversely affected by the charge accumulated in the conveyance guide 30. It is possible. Further, the color photosensitive drums 2Y, 2M, and 2C and the transfer rollers 8Y, 8M, and 8C facing them are configured to be able to contact and separate from each other. In the image forming apparatus configured as described above, at the time of forming a monochrome image, at least one of the color photosensitive drums is brought into contact with the transfer roller, so that the background fog toner on the recording paper is removed as in the above embodiment. It can be recovered.

The configuration of the present invention is not limited to the direct transfer type image forming apparatus shown in FIG. 1 but can be applied to the indirect transfer type image forming apparatus shown in FIG.
An indirect transfer type image forming apparatus 200 shown in FIG. 9 includes an image forming unit having a plurality of photosensitive drums 2Y, 2C, 2M, 2Bk and the like as an image carrier, an exposure device 5 as an exposure unit, and an intermediate transfer. An endless intermediate transfer belt 33 as a body, a plurality of primary transfer rollers 31Y, 31C, 31M and 31Bk as primary transfer means, a secondary transfer roller 32 as secondary transfer means, and a fixing device as fixing means 9 and a plurality of paper feed cassettes 6 for storing the recording paper P. Around each of the photosensitive drums 2Y, 2C, 2M, and 2Bk, a charging roller 3 as a charging unit, a developing device 4 as a developing unit, and the like are disposed. In FIG. 9, only the charging roller 3 and the developing device 4 arranged around one photosensitive drum 2Y are denoted by reference numerals, and the other photosensitive drums 2C, 2M, and 2Bk are omitted. doing.

  Each primary transfer roller 31Y, 31C, 31M, 31Bk is in contact with each photosensitive drum 2Y, 2C, 2M, 2Bk via the intermediate transfer belt 33, and each primary transfer roller 31Y, 31C, 31M, 31Bk and each A primary transfer nip as a transfer portion is formed at a position where the intermediate transfer belt 33 is sandwiched between the photosensitive drums 2Y, 2C, 2M, and 2Bk. The secondary transfer roller 32 is in contact with the intermediate transfer belt 33 at a position facing one of the rollers (secondary transfer counter roller 34) that supports the intermediate transfer belt 31, and at the contacted position, the transfer section As a secondary transfer nip.

The basic operation of the image forming apparatus 200 will be briefly described.
First, when the image forming operation is started, the surfaces of the photosensitive drums 2Y, 2C, 2M, and 2Bk are uniformly charged to a predetermined polarity by the charging roller 3, and then the charged photosensitive drums 2Y, 2Y, The surface of 2C, 2M, and 2Bk is irradiated with laser light from the exposure device 5 to form an electrostatic latent image. The toner is supplied by the developing devices 4 to the electrostatic latent images formed on the photosensitive drums 2Y, 2C, 2M, and 2Bk as described above, whereby the electrostatic latent images are visualized as toner images ( Visible image).

  Each primary transfer roller 31Y, 31C, 31M, 31Bk is applied with a constant voltage or a constant current-controlled voltage opposite to the toner charging polarity, and a transfer electric field is formed in the primary transfer nip. The toner images of the respective colors formed on the photosensitive drums 2Y, 2C, 2M, and 2Bk are sequentially transferred onto the intermediate transfer belt 33 that rotates in the direction of the arrow in the drawing by the transfer electric field formed in the primary transfer nip. The toner images are superimposed and transferred, and a color toner image is carried on the intermediate transfer belt 33.

  When the image forming operation is started, the recording paper P stored in the paper feed cassette 6 is sent out. The fed recording paper P is temporarily stopped by a registration roller pair (not shown). Thereafter, the driving of the registration roller pair is resumed, and the recording paper P is sent to the secondary transfer nip in synchronization with the toner image on the intermediate transfer belt 33. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 33 is applied to the secondary transfer roller 32, thereby forming a transfer electric field in the secondary transfer nip. When the recording paper P and the toner image on the intermediate transfer belt 33 reach the secondary transfer nip, the toner image on the intermediate transfer belt 33 is transferred onto the recording paper P by the transfer electric field formed in the secondary transfer nip. Are collectively transferred. Then, the recording paper P is conveyed to the fixing unit 9 and the toner image is fixed, and then discharged outside the apparatus.

  The indirect transfer type image forming apparatus uses the color photosensitive drums 2Y, 2C, and 2M when forming a monochrome image in order to suppress wear and the like of the color photosensitive drums 2Y, 2C, and 2M. It is configured to be separated from the intermediate transfer belt 33 and stop driving thereof.

  Even in such an indirect transfer type image forming apparatus, when the quality of the toner such as chargeability and fluidity deteriorates with time and background fogging occurs, the background portion of the photosensitive drum is not as good as the direct transfer type. The toner adhering to the toner may be transferred onto the recording paper via the intermediate transfer belt. For this reason, even in the indirect transfer type image forming apparatus, when there is a risk of image quality deterioration due to background fog during monochrome image formation, at least one of the color photosensitive drums 2Y, 2C, and 2M on which no image is formed is placed in the middle. By bringing it into contact with the transfer belt 33, the background fog toner adhering to the intermediate transfer belt 33 can be collected, and contamination of the recording paper can be suppressed.

  As described above, according to the present invention, in the partially separated mode in which the image carrier on which an image is formed is left and the other image carrier is not in contact with the recording medium or the intermediate transfer member, When there is a risk of image quality degradation, recording is performed by the image carrier by bringing at least one of the image carriers on which an image is not formed into contact with a recording medium or an intermediate transfer member (hereinafter referred to as “recording medium or the like”). The toner attached to the non-image part such as a medium can be collected. As a result, the recording medium can be prevented from being soiled, and a high-quality image can be provided.

  On the other hand, in the initial stage where the chargeability and fluidity of the toner are not low or in a low humidity environment where the chargeability of the toner is high, there is little toner with a background fog. By not contacting the recording medium or the like, it is possible to suppress the wear of the image carrier, the consumption and deterioration of the toner, and the like.

  In addition, as described above, by using an image carrier on which an image is not formed as a member for collecting the background fog toner, it is not necessary to separately provide a dedicated roller or the like for collecting the background fog toner. Therefore, size reduction and cost reduction can be achieved.

  Further, when collecting the background fog toner attached to the recording medium or the like, it is possible to collect a little by simply bringing the image carrier on which an image is not formed into contact with the recording medium or the like. As described above, by applying a bias having a polarity opposite to the charging polarity of the normally charged toner to the transfer unit, it is possible to reliably collect the background fog toner. As a result, the contamination of the recording medium can be suppressed to a higher degree, and higher image quality can be realized.

2Y, 2M, 2C, 2Bk photoconductor drum (image carrier)
8Y, 8M, 8C, 8Bk transfer roller (transfer means)
20 Contacting / separating means 21 Moving member 22 Gear member 23 Eccentric cam 31Y, 31C, 31M, 31Bk Primary transfer roller (transfer means)
33 Intermediate transfer belt (intermediate transfer member)
P Recording paper (recording medium)

JP 2007-286287 A Japanese Patent No. 3934778 Japanese Patent No. 3968238 JP 2008-233196 A

Claims (10)

A plurality of image carriers that can carry an image on the surface, and a transfer that is arranged to face each of the image carriers and that transfers an image formed on the image carrier to a recording medium or an intermediate transfer member And contact / separation means for switching the image carrier to a state in contact with the recording medium or the intermediate transfer member and a state in which the image carrier is not in contact with each other, and an image is formed among the plurality of image carriers. In an image forming apparatus capable of transferring an image in a partially separated mode in which the image carrier is left in contact with the recording medium or the intermediate transfer member while leaving another image carrier.
Wherein in some separation mode, and information acquisition means for acquiring quality information of toner used in an image formed on said image bearing member, based on the quality information of the toner by the information acquisition means has acquired, the recording medium conveying direction, or whether causes come in contact with the image bearing member on which an image of the downstream is not formed against the intermediate transfer member the recording medium image from said image bearing member which is disposed on the upstream side is transferred in the running direction or the intermediate transfer member a control means for controlling whether,
When transferring an image from the image carrier disposed on the upstream side to the recording medium or the intermediate transfer member, a reversely charged toner attached to the recording medium or the intermediate transfer member from the upstream image carrier. An image forming apparatus configured to be collected by the downstream image carrier that contacts the recording medium or the intermediate transfer member .   The number of the image carrier to be brought into contact with the recording medium or the intermediate transfer body after image transfer is configured to be controllable by the control means based on the toner quality information acquired by the information acquisition means. The image forming apparatus described in 1.   When the image carrier is brought into contact with the recording medium or the intermediate transfer member after image transfer, a bias having a polarity opposite to the charge polarity of the normally charged toner is applied to the transfer unit facing the image carrier. The image forming apparatus according to claim 1 or 2.   4. The image forming apparatus according to claim 1, wherein the quality information of the toner is acquired by detecting a travel distance of the image carrier on which an image is formed using the toner. 5. . 5. The image carrier according to claim 1, wherein at least the image carrier capable of carrying a yellow image is used as the image carrier to be brought into contact with the recording medium or the intermediate transfer member after image transfer. Image forming apparatus. The image carrier is brought into contact with the recording medium or the intermediate transfer member by bringing one of the image carrier and the transfer unit facing each other into contact with and separated from the other by the contact / separation unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured to be switchable between a state in which the contact is made and a state in which the contact is not made . The contact / separation means includes a moving member provided with a convex portion or a concave portion and configured to be reciprocally movable. As the moving member moves, the image carrier or the transfer means is moved to the convex portion or the The image according to claim 6 , wherein the image carrier or the transfer unit is configured to be brought into contact with and separated from each other by relatively moving between a portion provided with a concave portion and a portion where the convex portion or the concave portion is not provided. Forming equipment. The image forming apparatus according to claim 7, wherein the moving member is configured to be reciprocally movable by a gear member that is rotatable by a driving unit . The image forming apparatus according to claim 7 , wherein the moving member is configured to be reciprocally movable by an eccentric cam rotatable by a driving unit . Said position detecting means for detecting the moving position of the moving member is provided, according to any one of claims 7 configured to control the movement of the moving member 9 on the basis of the information the position detection unit detects Image forming apparatus.

Images