JP2012123069A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that prevents the occurrence of change in color tone by recovering residual toner from a moving body in a simple configuration.SOLUTION: An image forming apparatus includes a plurality of image forming units, a specific one of which Pk alone is provided with recovery means 70 for recovering residual toner. Residual toner attached on a moving body 5 is transferred from the moving body 5 to an image carrier 1k of the specific image forming unit Pk to be recovered to the recovery means 70.

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a laser printer, a copying machine, and a facsimile, and in particular, transfers a toner image from a plurality of image carriers to a transfer material carried on or on a movable body. The present invention relates to an image forming apparatus.

  Conventionally, an electrophotographic image forming apparatus generally requires a collection container for collecting toner (residual toner) remaining on an image carrier. In an in-line (tandem) type image forming apparatus that transfers toner images formed on a plurality of image carriers onto a moving body or onto a transfer material carried on the moving body, generally, the image is formed on the image carrier or on the moving body. In order to collect the residual toner, a collection container is required.

  In a monochrome image forming apparatus that forms a monochrome image using only black toner, a method of collecting residual toner on an image carrier or a moving body in a developing device and reusing it in an image forming operation is widely known. Yes. On the other hand, in a color image forming apparatus that forms, for example, a full color image using a plurality of color toners, toners of at least four colors of yellow, magenta, cyan, and black are used, and a developing device is provided for each color. In such a color image forming apparatus, the residual toner on the image carrier or the moving member exists in a state where a plurality of color toners are mixed. When such a residual toner in which a plurality of colors are mixed is collected in a specific developing device, there is a problem that color mixture occurs and the color changes when an image is formed.

  Therefore, Patent Document 1 discloses a method of collecting a residual toner mixed with a plurality of colors on a moving body in a black developing device. This utilizes the feature that when yellow, magenta, and cyan are mixed, black is developed.

  Further, Patent Document 2 discloses a method of collecting a toner image (patch) for detecting an image density made of a single color toner formed on a moving body in each color developing device.

JP 2004-279474 A JP 2001-324855 A

  However, for example, when a jam or misprint occurs, a large amount of toner remains on the image carrier or the moving body. Note that the jam refers to a state in which the operation of the image forming apparatus is stopped due to a poor conveyance of the transfer material and the transfer material stays in the image forming apparatus. In addition, misprinting means that the image forming operation is stopped due to incompatibility between the size of the formed image and the size of the transfer material, or the misalignment between the image forming timing and the transfer timing of the transfer material. This means that the toner has remained on the top.

  It is very difficult to specify the color ratio of these residual toners. If all the toner is collected in the black developing device in such a state, as a result, there is a high possibility of causing a black color variation during image formation. Also, in the case of jams, misprints, and the like, unlike patches formed at the time of image density detection, they are not formed with only single color toner, so it is very difficult to collect them in each color developer.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus that can prevent color variation from occurring by collecting residual toner from a moving body with a simple configuration.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to an image carrier that moves while carrying toner, and a plurality of image forming units each provided with a developing device that supplies toner to the image carrier and forms a toner image. An image forming unit that moves while contacting each of the image carriers, and a moving body that transfers toner of a different color from each of the image carriers onto a transfer material carried thereon or thereon. In the forming apparatus, a recovery unit that recovers toner on the image carrier is further provided only in a specific image forming unit among the plurality of image forming units, and residual toner on the moving body is In the image forming unit, an electric field in a direction in which the toner moves from the movable body to the image carrier is formed between the image carrier and the movable body, thereby moving while contacting the image carrier. Transfer from the moving body to the image carrier. It is an image forming apparatus characterized by recovering said recovery means.

  According to the present invention, it is possible to prevent color variation from occurring by collecting residual toner from a moving body with a simple configuration.

1 is a schematic longitudinal sectional view showing an overall configuration of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic control block diagram of a main part of an image forming apparatus according to an embodiment of the present invention. It is a schematic diagram showing a state of the image forming apparatus in a periodic cleaning operation according to the present invention. It is a schematic diagram for demonstrating operation | movement of the cleaning apparatus contact / separation mechanism. It is a schematic diagram for demonstrating transition of an example of the irregular cleaning operation | movement according to this invention. It is a schematic diagram for demonstrating transition of an example of the irregular cleaning operation | movement according to this invention (continuation of FIG. 5). It is a sequence diagram of an example of an irregular cleaning operation according to the present invention. It is a schematic diagram for demonstrating transition of the other example of the irregular cleaning operation | movement according to this invention. It is a schematic diagram for demonstrating the transition of the other example of the irregular cleaning operation | movement according to this invention (continuation of FIG. 8). It is a sequence diagram of the other example of the irregular cleaning operation | movement according to this invention. It is a schematic longitudinal cross-sectional view which shows the whole structure of the image forming apparatus which concerns on the other Example of this invention. It is a flowchart figure of an example of the image formation operation | movement according to this invention.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
1. First, the overall configuration of an image forming apparatus according to an embodiment of the present invention will be described. FIG. 1 is a schematic longitudinal sectional view showing the overall configuration of the image forming apparatus 100 of the present embodiment. The image forming apparatus 100 according to this embodiment is an inline (tandem) type laser beam printer that employs an intermediate transfer method capable of forming a full-color image using an electrophotographic method.

  The image forming apparatus 100 includes, as a plurality of image forming units, first, second, and second elements arranged in a line in order from the upstream side to the downstream side in the moving direction of a surface carrying a toner image of an intermediate transfer belt 5 described later. It has 3rd, 4th image formation part Py, Pm, Pc, Pk. The first, second, third, and fourth image forming units Py, Pm, Pc, and Pk respectively form yellow (Y), magenta (M), cyan (C), and black (K) images. Is to do. In the present embodiment, the configurations of the first, second, third, and fourth image forming portions Py, Pm, Pc, and Pk have many common portions. Accordingly, in the following, when no particular distinction is required, the subscripts y, m, c, and k given to the reference numerals to indicate that they are elements provided for any one of the image forming units are omitted, and the general description will be given. To do.

  The image forming unit P includes a drum-type electrophotographic photosensitive member (photosensitive member) as a movable image carrier, that is, a photosensitive drum 1. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 (clockwise) by a drive motor (not shown) as drive means. Around the photosensitive drum 1, the following units are provided in order according to the rotation direction. First, the charging roller 2 is a charging member as a charging unit that uniformly charges the surface of the photosensitive drum 1. Next, there is a developing device 4 as a developing unit that develops a toner image by attaching toner to an electrostatic latent image (electrostatic image) formed on the photosensitive drum 1. Next, a primary transfer roller 8 serving as a primary transfer member serving as a primary transfer unit that transfers a toner image from each photosensitive drum 1 to an intermediate transfer belt 5 described later. The developing device 4 includes a developing roller 41 and a developing container 42 that stores toner as a developer supplied to the developing roller 42.

  In this embodiment, the fourth image forming unit Pm is provided with a cleaning device 70 as a collecting unit for collecting the residual toner on the photosensitive drum 1k. The cleaning device 70 includes a cleaning blade 71 as a cleaning member, and a collection container 72 that stores residual toner collected from the photosensitive drum 1k. The cleaning blade 71 is formed of a plate-like elastic body as a cleaning member that contacts the photosensitive drum 1k and scrapes off toner adhering to the surface of the photosensitive drum 1k. The collection container 72 stores the toner scraped from the surface of the photosensitive drum 1k by the cleaning blade 71. Note that such a cleaning device is not provided in the first, second, and third image forming portions Py, Pm, and Pc.

  In the present embodiment, the photosensitive drums 1y, 1m, and 1c of the first, second, and third image forming portions Py, Pm, and Pc that are not subjected to removal of residual toner by the cleaning device are the first image carrier. . The photosensitive drum 1k of the fourth image forming unit Pk that receives the removal of residual toner by the cleaning device 70 is the second image carrier.

  Further, a laser scanner as an exposure unit is formed so that each charged photosensitive drum 1 is irradiated with a laser beam based on image information to form an electrostatic latent image (electrostatic image) on each photosensitive drum 1. 3 is arranged. Further, an intermediate transfer belt 5, which is an endless belt-like intermediate transfer body as a movable body, is disposed so as to face each photosensitive drum 1. The intermediate transfer belt 5 is stretched around a driving roller 51 that rotates the intermediate transfer belt 5 and driven rollers 52 and 53 that apply appropriate tension to the intermediate transfer belt 5. The intermediate transfer belt 5 is rotationally driven in the direction of arrow R2 (counterclockwise) by a driving force transmitted to the driving roller 51 by a driving motor (not shown) as a driving means, and is driven by each primary transfer roller 8. The toner image transferred from each photosensitive drum 1 is carried and conveyed. The primary transfer rollers 8 are arranged on the inner peripheral surface side of the intermediate transfer belt 5 so as to face the photosensitive drums 1. Each primary transfer roller 8 is pressed against each photosensitive drum 1 via the intermediate transfer belt 5 to form a primary transfer portion (primary transfer nip) N1 where each photosensitive drum 1 and the intermediate transfer belt 5 are in contact with each other. Further, on the outer peripheral surface side of the intermediate transfer belt 5, a secondary transfer roller 9 that is a secondary transfer member as a secondary transfer unit is disposed at a position facing the driving roller 51. The secondary transfer roller 9 is pressed against the driving roller 51 via the intermediate transfer belt 5 to form a secondary transfer portion (secondary transfer nip) N2 where the secondary transfer roller 9 and the intermediate transfer belt 5 are in contact with each other. The secondary transfer roller 9 transfers the toner image on the intermediate transfer belt 5 to the transfer material S.

  Further, the image forming apparatus 100 includes a cassette 11 that accommodates the transfer material S, a feed roller 12 that sends the transfer material S from the cassette 11, and a transport roller that transports the transfer material S to the secondary transfer unit N2 at a predetermined timing. A pair 13, a fixing device 10 as fixing means, and the like are provided.

  In the present embodiment, in the first to third image forming units Py, Pm, and Pc, the photosensitive drum 1 and the charging roller 2 and the developing device 4 as process means that act on the photosensitive drum 1 are integrated. To form process cartridges 30y, 30m, and 30c. In the present embodiment, in the fourth image forming unit Pk, the photosensitive drum 1 and the charging roller 2, the developing device 4, and the cleaning device 70 as process means acting on the photosensitive drum 1 are integrally formed into a cartridge. Thus, the process cartridge 30k is configured. The process cartridges 30y, 30m, 30c, and 30k are detachable from the main body of the image forming apparatus 100.

  Further, the image forming apparatus 100 causes each process drum 30 of each image forming unit P to approach or retract from the intermediate transfer belt 5 to bring each photosensitive drum 1 into contact with or separate from the intermediate transfer belt 5. A contact / separation mechanism (contact / separation means) is provided. In the present exemplary embodiment, the contact / separation mechanism is a guide unit that allows each process cartridge mounted in the main body of the image forming apparatus 100 to slide in a direction in which the process cartridge approaches or retracts from the intermediate transfer belt 5. (Not shown). Further, the contact / separation mechanism is provided in each image forming unit P as a biasing unit that biases each process cartridge 30 mounted in the main body of the image forming apparatus 100 in a direction away from the intermediate transfer belt 5. It has a biasing member 15 such as a spring. In addition, the contact / separation mechanism is provided in each image forming unit P that switches the position of each process cartridge 30 with respect to the intermediate transfer belt 5 to contact or separate the intermediate transfer belt 5 of each photosensitive drum 1. It has a cam member 14 as a switching member. Each cam member 14 presses each process cartridge 30 in a direction approaching the intermediate transfer belt 5 against the urging force of each urging member 15 to bring each photosensitive drum 1 into contact with the intermediate transfer belt 5. it can. Further, each cam member 14 releases its pressing force, and each process cartridge 30 is allowed to move away from the intermediate transfer belt 5 by the urging force of each urging member 15, so that each photosensitive drum 1 is moved in the middle. It can be separated from the transfer belt 5. The cam member 14 is moved in a direction in which each photosensitive drum 1 is brought closer to the intermediate transfer belt 5 by controlling the operation of a motor (not shown) as a driving means by a CPU 61 (FIG. 2) of the control unit 60 described later. Alternatively, it is moved away from the intermediate transfer belt 5.

2. Next, the configuration of each part of the image forming apparatus 100 according to the present embodiment will be described in more detail.

  In this embodiment, the photosensitive drum 1 is configured by coating an organic photoconductor layer (OPC photosensitive member) on the outer peripheral surface of an aluminum cylinder having a diameter of 30 mm. In this embodiment, the charging polarity of the photosensitive drum 1 is negative. Both ends of the photosensitive drum 1 are rotatably supported by support members, and a driving force from a driving motor (not shown) is transmitted to one end thereof, thereby causing the photosensitive drum 1 to rotate in the direction of arrow R1 (clockwise). Is driven to rotate.

  The charging roller 2 is composed of a conductive roller. The charging roller 2 is brought into contact with the surface of the photosensitive drum 1. The charging roller 2 is connected to a charging power source 21 (FIG. 2) as charging voltage application means. By applying a predetermined charging voltage (charging bias) having a negative polarity and equal to or higher than the discharge start voltage by the charging power source 21, the surface of the photosensitive drum 1 is uniformly charged to the negative polarity.

  The laser scanner 3 is a laser optical unit, and is controlled by a drive circuit (not shown) to turn on the laser light L according to an image signal. The surface of the charged photosensitive drum 1 is selectively exposed by the laser light L, and an electrostatic latent image is formed on the photosensitive drum 1.

  The developing device 4 includes a developing container 42 that contains toner, and a developing roller 41 that is rotatably supported by the developing container 42. The toner stored in the developing container 42 is supplied to the developing roller 41. The toner adhering to the developing roller 41 is charged almost uniformly to the normal charging polarity (negative polarity in this embodiment) by rubbing. Further, the developing roller 41 is connected to a developing power source 22 (FIG. 2) as a developing voltage applying unit. A developing voltage (developing bias) having an absolute value smaller than the surface potential of the photosensitive drum 1 and having a negative polarity is applied to the developing roller 41 by the developing power source 22 with toner attached to the developing roller 41. As a result, toner can be attached only to the image portion of the electrostatic latent image on the photosensitive drum 1. In this embodiment, a toner charged to the same polarity as the charged polarity of the photosensitive drum 1 is attached to an exposed portion where the charge has been attenuated by exposure of the surface of the charged photosensitive drum 1, thereby static electricity on the photosensitive drum 1. The electrostatic latent image is developed as a toner image.

The primary transfer roller 8 is composed of a conductive roller. In this embodiment, the primary transfer roller 8 is a foaming elastic roller in which a layer of foaming elastic body is formed to have an outer diameter of 12 mm around a shaft having an outer diameter of 6 mm made of metal such as SUS (stainless steel). It is configured as. This foaming elastic roller has a resistance of 10 ⁶ to 10 ⁹ Ω. The primary transfer roller 8 is pressed against the photosensitive drum 1 with the intermediate transfer belt 5 interposed therebetween. The primary transfer roller 8 is connected to a primary transfer power source 23 (FIG. 2) as a primary transfer voltage application unit. The primary transfer power supply 23 applies a positive primary transfer voltage (primary transfer bias) having a polarity opposite to the normal charging polarity of the toner to the primary transfer roller 8, whereby the toner image on the photosensitive drum 1 is intermediate. Transfer (primary transfer) is performed on the transfer belt 6.

The intermediate transfer belt 5 is composed of an endless film-like member having a thickness of about 50 to 150 μm and having a volume resistivity of 10 ⁷ to 10 ¹⁴ Ωcm. The volume resistivity was obtained by applying 50-100 V at a temperature of 25 ° C. and a relative humidity of 50% with a high resistance meter R2340 manufactured by ADVANTEST, using a measurement probe in accordance with JIS method K6911. Value.

  The secondary transfer roller 9 has the same configuration and physical properties as the primary transfer roller 8. The secondary transfer roller 9 is pressed against the intermediate transfer belt 5 via the transfer material S. The secondary transfer roller 9 is connected to a secondary transfer power source (not shown) as a secondary transfer voltage application unit. The toner image on the intermediate transfer belt 5 is transferred by applying a positive secondary transfer power source (secondary transfer bias) that is a normal charging polarity of the toner to the secondary transfer roller 9 by the secondary transfer power source. Transfer (secondary transfer) onto the material S.

  The fixing device 10 includes a heating roller 10A having a built-in heating source serving as a fixing unit, and a pressure roller 10B serving as a pressing unit that presses the heating roller 10A to form a contact region (nip).

3. Image Forming Operation For example, the image forming operation by the image forming apparatus 100 will be described by taking a case of forming a full color image as an example. In this case, in each image forming unit P, each photosensitive drum 1 is uniformly charged, and then exposed according to the image information of each color by the laser scanner 3, so that each color image is formed on each photosensitive drum 1. An electrostatic latent image corresponding to the information is formed. The electrostatic latent image formed on each photosensitive drum 1 is developed as a toner image with toner of each color by each developer 4. The toner image formed on each photosensitive drum 1 is transferred by superimposing yellow, magenta, cyan, and black in this order on the surface of the moving intermediate transfer belt 5 carrying the toner image by the action of each primary transfer roller 8. (Primary transfer). On the other hand, the transfer material S stored in the cassette 11 mounted on the lower part of the main body of the image forming apparatus 100 is separated and fed one by one by the feeding roller 12 and also to the secondary transfer unit N2 by the conveying roller pair 13. It is conveyed. The multiple toner image formed of yellow, magenta, cyan and black toner formed on the intermediate transfer belt 5 is transferred to the transfer material S conveyed to the secondary transfer portion N2 by the action of the secondary transfer roller 9. (Secondary transfer). As a result, a multiple toner image composed of yellow, magenta, cyan, and black toners is formed on the transfer material. The transfer material S on which the toner image is formed is conveyed to the fixing device 10 and passed through the contact portion of the roller pair including the heating roller 10A and the pressure roller 10B, whereby the toner image is heated and fixed thereon. The Thereafter, the transfer material S is discharged to an upper discharge portion of the image forming apparatus 100.

  In the image forming apparatus 100 of this embodiment, the primary transfer and the secondary transfer achieve transfer efficiency of approximately 100%. Therefore, there is no visible residual toner (transfer residual toner) on the photosensitive drum 1 or the intermediate transfer belt 5 in the above-described image forming operation process. Therefore, in this embodiment, a special collection container for collecting the transfer residual toner on the photosensitive drums 1y, 1m, and 1c of the first to third image forming units Py, Pm, and Pc and the intermediate transfer belt 5 is provided. It is not done. However, as will be described in detail later, the fourth image forming unit Pk is provided with the cleaning device 70 as described above in order to collect residual toner or the like generated due to jamming or misprinting.

4). Control Mode FIG. 2 is a schematic control block diagram of the main part of the image forming apparatus 1 of the present embodiment. The operation of the image forming apparatus 100 is centrally performed by the CPU 61 which is a control unit of the control unit 60 provided in the image forming apparatus 100. The CPU 61 controls each part of the image forming apparatus 100 according to programs and data stored in a ROM 62 and a RAM 63 as recording means provided in the control unit 60. The CPU 61 performs various units of the image forming apparatus 100 based on an image forming signal obtained by performing predetermined processing on an image information sent from an external device such as a personal computer in an image processing unit (not shown). Are controlled to execute the image forming operation as described above. In particular, in relation to the present embodiment, the CPU 61 switches the contact or separation state of the photosensitive drums 1 with respect to the intermediate transfer belt 5 by the cam members (switching members) 14 provided in the image forming portions P. To control. Further, the CPU 61 controls the switching operation of the contact state or separation state of the cleaning device 70 with respect to the photosensitive drum 1k by a contact lever (cleaning device switching member) 73 described later in the fourth image forming unit Pk. Further, the CPU 61 controls a voltage application operation to each charging roller 2 by each charging power source 21 of each image forming unit P. Further, the CPU 61 controls a voltage application operation to each developing roller 41 by each developing power source 22 of each image forming unit P. Further, the CPU 61 controls a voltage application operation to each primary transfer roller 8 by each primary transfer power source 23 of each image forming unit P.

  Here, as will be described in detail later, each primary transfer power source 23 includes a first voltage output unit that outputs a positive voltage having a polarity opposite to the normal charging polarity of the toner, and a normal charging polarity of the toner. And a second voltage output unit that outputs a negative polarity voltage having the same polarity. The CPU 61 controls whether the voltage is output from the first voltage output unit or the second voltage output unit and applied to the primary transfer roller 8 in a cleaning operation, which will be described in detail later.

  In addition, in relation to this embodiment, the CPU 61 turns on / off driving means (a common drive motor in this embodiment) for driving the photosensitive drum 1 and the intermediate transfer belt 5.

5. 5. Cleaning of residual toner 5-1. Periodic Cleaning Operation As described above, in the image forming apparatus 100 of this embodiment, primary transfer and secondary transfer achieve transfer efficiency of approximately 100%. However, depending on the ambient temperature and humidity, the type of the transfer material S, and the like, the transfer efficiency may not be 100%, and the toner may slightly remain on the photosensitive drum 1 or the intermediate transfer belt 5. For example, when the electric resistance of the intermediate transfer belt 5, the primary transfer roller 8, the secondary transfer roller 9 and the like is increased in a low temperature and low humidity environment, an electric field required for primary transfer and secondary transfer is not formed. There can be. Further, in the case of the transfer material S having a large unevenness on the surface, there may be a difference in transfer electric field strength between the concave portion and the convex portion, and the transfer efficiency may partially decrease.

  If the image forming apparatus 100 continues to be used in such a state, the residual toner on the photosensitive drum 1 and the intermediate transfer belt 5 eventually adheres to the transfer material S and becomes toner stain (fogging). May manifest.

In order to prevent this, the cleaning operation is periodically performed in this embodiment. Referring to FIG. 3, in this embodiment, the following operations are performed in this periodic cleaning operation.
(1) The photosensitive drums 1y, 1m, and 1c of the first to third image forming units Py, Pm, and Pc are separated from the intermediate transfer belt 5. At this time, the photosensitive drum 1k of the fourth image forming unit Pk and the intermediate transfer belt 5 remain in contact with each other.
(2) In the fourth image forming unit Pk, the cleaning blade 71 of the cleaning device 70 is brought into contact with the photosensitive drum 1k, and a negative voltage which is a normal charging polarity of the toner is applied to the primary transfer roller 8k. That is, the negatively charged toner having the normal charging polarity is transferred from the intermediate transfer belt 5 to the photosensitive drum 1k in the primary transfer portion N1k (that is, between the intermediate transfer belt and the photosensitive drum) of the fourth image forming portion Pk. Create an electric field to be directed.
(3) A negative bias equal to or higher than the discharge start voltage is applied to the charging rollers 2y, 2m, and 2c of the first to third image forming units Py, Pm, and Pc.
(4) A negative voltage having an absolute value smaller than the surface potential of the photosensitive drums 1y, 1m, and 1c is applied to the developing rollers 41y, 41m, and 41c of the first to third image forming units Py, Pm, and Pc, respectively. .

  Here, in the operation (1), the negatively charged toner attached on the intermediate transfer belt 5 is applied to the photosensitive drums 1y, 1m, and 1c of the first to third image forming portions Py, Pm, and Pc. The purpose is not to transfer.

  In the operation (2), the negatively charged toner attached to the intermediate transfer belt 5 is transferred to the photosensitive drum 1k of the fourth image forming portion Pk, and further scraped from the photosensitive drum 1k by the cleaning blade 71. The final purpose is to collect in the collection container 72. At this time, the cleaning device 70 moves from the state shown in FIG. 4A to the state shown in FIG. 4B when the contact lever 73 is rotated in the direction of arrow A in the drawing by the driving means (not shown). Then, the cleaning blade 71 comes into contact with the photosensitive drum 1k. When the cleaning blade 71 is separated from the photosensitive drum 1k, the contact lever 73 is moved from the state of FIG. 4B to the state of FIG. The cleaning device 70 is moved by rotating in the direction. Usually, the cleaning blade 71 is separated from the photosensitive drum 1k during image formation.

  As described above, in this embodiment, the image forming apparatus 100 causes the cleaning device 70 to contact or separate from the photosensitive drum 1k by moving the cleaning device 70 close to or away from the photosensitive drum 1k. It has a separation mechanism (contact / separation means). In this embodiment, the cleaning device abutment / separation mechanism includes a contact lever 73 as a cleaning device switching member that enables the cleaning device 70 to move in a direction in which the cleaning device 70 approaches or retracts from the photosensitive drum 1k. The contact lever 73 is controlled by the CPU 61 (FIG. 2) of the control unit 60 to control the operation of a motor (not shown) that is a driving unit thereof, so that the cleaning device 70 approaches the photosensitive drum 1k or the photosensitive drum. Swing away from 1k.

  In the operation (3), the surfaces of the photosensitive drums 1y, 1m, and 1k of the first to third image forming units Py, Pm, and Pc are uniformly charged negatively, and each photosensitive drum 1y, The object is to charge the toner adhering to 1 m and 1 c to a negative polarity. At this time, in order to more uniformly charge the toner, an AC voltage obtained by superimposing a negative DC voltage on the charging rollers 2y, 2m, and 2c of the first to third image forming units Py, Pm, and Pc is used. You may apply. In this case, the AC voltage is set so that the amplitude of the AC voltage is equal to or higher than the discharge start voltage.

  The operation (4) has the following object. That is, the negatively charged toner adhered on the photosensitive drums 1y, 1m, and 1c of the first to third image forming units Py, Pm, and Pc is transferred to the developing rollers 41y, 41m, and 41c, and finally. It is to collect | recover to each developing container 42y, 42m, 42c. The collected toner is reused at the next and subsequent image formation.

  The operations (1) to (4) are started almost at the same time, and are continuously performed for at least one turn of the intermediate transfer belt 5. Preferably, when the toner on the intermediate transfer belt 5 reaches the primary transfer portion N1k next in the primary transfer portion N1k at the start of the operation, the toner can reach the contact portion between the cleaning blade 71 and the photosensitive drum 1k. Continue until. Thereby, almost all of the negative-polarity residual toner on the intermediate transfer belt 5 and the negative-polarity residual toner on the photosensitive drum 1k of the fourth image forming unit Pk are transferred to the process cartridge 30k of the fourth image forming unit Pk. It is possible to collect in the provided collection container 72. Further, the negative residual toner on the photosensitive drums 1y, Pc, and Pk of the first to third image forming units Py, Pm, and Pc is collected in the developing containers 42y, 42m, and 42c.

  An appropriate peripheral speed difference may be provided between the intermediate transfer member 5 and the photosensitive drum 1k in order to promote toner transfer from the intermediate transfer member 5 to the photosensitive drum 1k.

  Further, after the series of operations described above, an operation for collecting the positive toner remaining on the intermediate transfer belt 5 in the collecting container 72 may be performed. In this case, in the operation (2), the polarity of the voltage applied to the primary transfer roller 8k of the fourth image forming unit Pk is set to be positive with the polarity opposite to the polarity. That is, an electric field is formed in the primary transfer portion N1k of the fourth image forming portion Pk to direct the toner charged to the positive polarity having the opposite polarity to the normal charging polarity from the intermediate transfer belt 5 to the photosensitive drum 1k. The operations similar to the above (1) to (4) are continued for at least one turn of the intermediate transfer belt 5. Preferably, when the polarity of the voltage is changed, the toner on the intermediate transfer belt 5 in the primary transfer portion N1k next reaches the primary transfer portion N1k and then reaches the contact portion between the cleaning blade 71 and the photosensitive drum 1k. Continue until you get it.

  In this embodiment, the toner adhered on the photosensitive drum 1 and the intermediate transfer belt 5 can be collected in the developing containers 42y, 42m, and 42c or the collecting container 72 by periodically performing the above-described operation. Therefore, it becomes possible to prevent the toner smear image from becoming obvious. In this embodiment, this periodic cleaning operation is performed during non-image formation other than during image formation in which an image is formed on the transfer material S and output. Examples of non-image formation include the following. During a preparatory operation before entering the standby state when the image forming apparatus 100 is turned on (pre-multi-rotation operation). During the preparatory operation (pre-rotation operation) from the standby state until the actual image formation starts. During the preparation (arrangement) operation (after the post-rotation operation) until the image forming apparatus 100 enters the standby state after outputting the image. A period (between sheets) corresponding to the interval between the transfer material S and the transfer material S during the continuous image output operation for a plurality of transfer materials S

5-2. Irregular Cleaning Operation As described above, in the image forming apparatus 100 of the present embodiment, substantially no residual toner is generated on the photosensitive drum 1 and the intermediate transfer belt 5 during normal image formation. However, in the image forming apparatus 100 according to the present embodiment, the transfer efficiency is lowered due to the above-described environment and the unevenness of the transfer material S, and also on the photosensitive drum 1 and the intermediate transfer belt 5 due to jam or misprint. A large amount of toner may adhere.

  In the present exemplary embodiment, the jam refers to an image forming operation halfway due to a poor conveyance of the transfer material S between the time when the transfer material S is fed from the cassette 11 and discharged from the image forming apparatus 100. Says the state of being censored. Further, in this embodiment, the misprint means a state in which the image forming operation is interrupted halfway for the following reason, and the toner remains on the photosensitive drum 1 or the intermediate transfer belt 5. . That is, this is because the size of the image formed on the intermediate transfer belt 5 and the size of the transfer material S are incompatible, or the image formation timing and the transfer timing of the transfer material S are shifted. If the image forming operation is terminated halfway, the operation of the image forming apparatus 100 is stopped.

  As described above, if all the toner is collected in the black developing device in a state where a jam or a misprint has occurred, there is a high possibility of causing a change in black color during image formation. Further, in the case of jamming or misprinting, the residual toner on the intermediate transfer belt 5 does not necessarily consist of a single color toner, so that it is very difficult to collect it in each color developer.

  One of the purposes of the present embodiment is a simple configuration that causes jamming, misprinting, and the like, and even if a large amount of residual toner exists on the photosensitive drum 1 or the intermediate transfer belt 5, it remains from the intermediate transfer belt 5. It is to prevent the color variation from occurring by collecting the toner.

  Therefore, the present embodiment generally has the following configuration. That is, the cleaning device 70 as a collecting unit that collects toner from the image carrier is provided only in the specific image forming unit Pk. After processing such as jamming or misprinting, each photosensitive drum 1 is operated in a state in which each photosensitive drum 1 and the intermediate transfer belt 5 are separated from each other, whereby residual toner on each photosensitive drum 1 is transferred to each developing device 4. In the developing container 42. Further, the residual toner on the intermediate transfer belt 5 is collected by the cleaning device 70 as the collecting unit in the specific image forming unit Pk. This will be described in more detail below.

  Next, the irregular cleaning operation in the present embodiment will be described in more detail with a specific example. 5 and 6 show the residual toner and the intermediate transfer belt 5 accompanying the irregular cleaning operation (from state I to IV) after the image forming operation is stopped due to the occurrence of jam or misprinting. The state of the main elements around is schematically shown.

  Here, as an example, an untransferred toner image is placed on all the photosensitive drums 1, and at least a part of all color toner images is already primary-transferred onto the intermediate transfer belt 5. The operation when the forming operation is stopped will be described. In this case, the following toner area exists on the intermediate transfer belt 5. That is, the area where only the yellow toner is transferred between the primary transfer portions of the first and second image forming portions Py and Pm, and the colors of yellow, magenta, cyan and black on the leading end side in the transport direction from the regions. In this area, two or more colors of toner are mixed and transferred.

  First, a state I in FIG. 5A shows a state immediately after an image forming operation is stopped due to a jam or a misprint.

  Next, as shown in the state II of FIG. 5B from the state I of FIG. 5A, all the photosensitive drums 1 and the intermediate transfer belt 5 are once separated from each other, and then each of the photosensitive drums 1 and the intermediate transfer are transferred. Each of the belts 5 is rotated. At this time, a negative voltage equal to or higher than the discharge start voltage is applied to each charging roller 2 of each image forming unit P. Alternatively, at this time, an AC voltage (amplitude is equal to or greater than the discharge start voltage) on which a negative DC voltage is superimposed may be applied. This is intended to uniformly charge the surface of each photosensitive drum 1 to the negative polarity and to charge the toner attached to each photosensitive drum 1 to the negative polarity. At this time, a negative voltage having an absolute value smaller than the surface potential of each photosensitive drum 1 is applied to each developing roller 41 of each image forming unit P. This is intended to transfer the negatively charged toner adhering to each photosensitive drum 1 to each developing roller 41 and finally collect it in each developing container 42. As a result, the non-mixed residual toner on each photosensitive drum 1 is collected by each developing device 4 and reused.

  On the other hand, as shown in the state III of FIG. 6A, the fourth image is formed before the tip of the toner area on the intermediate transfer belt 5 reaches the primary transfer portion N1k of the fourth image forming portion Pk. The photosensitive drum 1k of the forming portion Pk and the intermediate transfer belt 5 are brought into contact with each other. Similarly to the operation (2) in the periodic cleaning operation, in the fourth image forming unit Pk, the cleaning blade 71 is brought into contact with the photosensitive drum 1k, and a negative voltage is applied to the primary transfer roller 8k. To do. That is, an electric field is formed in the primary transfer portion N1k of the fourth image forming portion Pk to direct the negatively charged toner having the normal charging polarity from the intermediate transfer belt 5 to the photosensitive drum 1k. This is intended for the following effects, as shown in state IV of FIG. That is, the negatively charged toner adhering to the intermediate transfer belt 5 is transferred to the photosensitive drum 1k of the fourth image forming unit Pk, and further scraped off from the photosensitive drum 1k by the cleaning blade 71, and finally the recovery container. 72 is an effect of collecting. This operation is performed at least for one round of the intermediate transfer belt 5 with reference to the time when the rear end of the toner area on the intermediate transfer belt 5 first passes through the primary transfer portion N1k of the fourth image forming portion Pk. Continue. Preferably, the toner on the intermediate transfer belt 5 at the primary transfer portion N1k at the reference time next reaches the primary transfer portion N1k and then continues until the toner can reach the contact portion between the cleaning blade 71 and the photosensitive drum 1k. And do it. As a result, the toner on the intermediate transfer belt 5, particularly the residual toner mixed in color, can be finally collected in the collection container 72.

  7 shows the contact state between the intermediate transfer belt 5 and the photosensitive drum 1, the ON / OFF state of the voltage applied to the charging roller 2 and the developing roller 41, and the primary transfer roller 8 in the above-described series of sequence operations. Indicates the ON / OFF state of the voltage. In the figure, the periods indicated by bands indicate the contact state and the voltage ON state, respectively, and the periods not indicated by the band indicate the separated state and the voltage OFF state, respectively. In the figure, 1st, 2st, 3st, and 4st indicate the first, second, third, and fourth image forming units Py, Pm, Pc, and Pk, respectively.

  As in the case of the periodic cleaning operation, an appropriate peripheral speed difference may be provided between the intermediate transfer belt 5 and the photosensitive drum 1k in order to promote toner transfer.

  Further, after the series of operations described above, an operation for collecting the positive toner remaining on the intermediate transfer belt 5 in the collecting container 71 may be performed. In this case, as shown in FIG. 7, the polarity of the voltage applied to the primary transfer roller 8k of the fourth image forming unit Pk in the same manner as in the states III and IV of FIGS. 6 (a) and 6 (b). Is performed as a positive polarity having a polarity opposite to the above polarity.

  As described above, in this embodiment, the residual toner on the moving body is transferred from the moving body 5 to the image carrier 1k while being in contact with the image carrier 1k of the specific image forming unit Pk, and is collected by the collecting unit 70. to recover. At this time, an electric field in the direction in which the toner moves from the moving body 5 to the image carrier 1k is formed between the image carrier 1k and the movable body 5 in the specific image forming portion Pk. In the present exemplary embodiment, when the residual toner on the moving body is collected by the collecting unit 70, each of the image forming units Py to Pc other than the specific image forming unit among the plurality of image forming units Py to Pk is supported. The body 1 is separated from the moving body 5. Further, in this embodiment, prior to collecting the residual toner on the moving body by the collecting unit 70, the image carriers 1 of the plurality of image forming portions Py to Pk are separated from the moving body 5. Then, in each of the plurality of image forming units Py to Pk, the residual toner on the image carrier 1 is collected in the developing device 4 as the image carrier 1 moves.

  FIG. 12 shows a schematic flow of an image output operation of the image forming apparatus 100 of the present embodiment. First, when the CPU 61 detects an image formation request from the external device 200 (S101), the CPU 61 starts a pre-rotation operation and performs the above-described periodic cleaning operation during the pre-rotation operation (S102). When the pre-rotation operation is completed, an image forming operation for forming an image to be transferred and output to the transfer material S is started (S103). The CPU 61 monitors the occurrence of a jam, misprint, or the like by a signal input from a top sensor or the like provided in the conveyance path of the transfer material S in the image forming apparatus 100 (S104). If no jamming or misprinting occurs, the CPU 61 outputs a specified number of images for the normal image forming operation (S105), and performs a post-rotation operation (S106). Thereafter, the operation of the image forming apparatus 100 ends. On the other hand, when the CPU 61 determines that a jam or a misprint has occurred (S104), it confirms that a predetermined jam processing (removal of a jammed transfer material, etc.) has been performed, and the above-mentioned error is detected. A regular cleaning operation is performed (S107). Thereafter, the operation of the image forming apparatus 100 ends.

  As described above, according to this embodiment, when a large amount of toner adheres to the photosensitive drum 1 or the intermediate transfer belt 5 due to jamming or misprinting, residual toner that is not mixed color on each photosensitive drum 1. Can be collected in the developing container 42 of each color and reused. Further, when a large amount of toner adheres to the photosensitive drum 1 or the intermediate transfer belt 5 due to jamming or misprinting, the residual toner on the intermediate transfer belt 5, particularly the mixed residual toner, is transferred to a specific image forming unit Pk. It collects in the provided collection container 72. For this reason, it is possible to prevent the color variation from occurring as compared with the case where the residual toner is collected in the black developer and reused.

Example 2
Next, another embodiment of the image forming apparatus according to the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the image forming apparatus of the first embodiment. Accordingly, elements having the same or corresponding functions and configurations as those of the image forming apparatus of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted, and characteristic points of the present embodiment will be described.

  In this embodiment, the cleaning blade 71 is always in contact with the photosensitive drum 1k in the fourth image forming portion Pk. That is, in this embodiment, the image forming apparatus 100 does not have the cleaning device contact / separation mechanism described in the first embodiment. Further, as will be described later, in this embodiment, the photosensitive drum 1 and the intermediate transfer belt 5 of each image forming unit P are not separated in the irregular cleaning operation. For this reason, in this embodiment, the contact / separation mechanism between each photosensitive drum 1 and the intermediate transfer belt 5 described in the first embodiment may not be provided in relation to the operation.

  Next, the irregular cleaning operation in the present embodiment will be described in more detail with a specific example. FIGS. 8 and 9 show the residual toner and the intermediate transfer belt 5 accompanying the transition of the irregular cleaning operation (from state I to IV) after the image forming operation is stopped due to the occurrence of jam or misprint. The state of the main elements around is schematically shown.

  Here, as an example, as in the first embodiment, untransferred toner images are placed on all the photosensitive drums 1, and at least some of the toner images of all colors are already primary on the intermediate transfer belt 5. The operation when the image forming operation is stopped in the transferred state will be described.

  First, a state I in FIG. 8A shows a state immediately after the image forming operation is stopped due to a jam or a misprint.

  Next, from the state I in FIG. 8A to the first transfer rollers 8y, 8m, and 8c of the first to third image forming units Py, Pm, and Pc as shown in the state II in FIG. 5B. A positive voltage is applied. This is intended to transfer the negatively charged toner attached to the photosensitive drums 1y, 1m, and 1c of the first to third image forming portions Py, Pm, and Pc to the intermediate transfer belt 5. is there. On the other hand, a negative voltage is applied to the primary transfer roller 8k of the fourth image forming unit Pk. This is intended to: That is, the residual toner on the photosensitive drum 1k of the fourth image forming unit Pk is scraped off by the cleaning blade 71 and collected in the collection container 72. Further, the negatively charged toner attached to the intermediate transfer belt 5 is transferred to the photosensitive drum 1k of the fourth image forming portion Pk, scraped off by the cleaning blade 71, and collected in the collection container 72. As shown in state III of FIG. 9A, this operation is performed with reference to the position on the intermediate transfer belt 5 that was in the primary transfer portion N1k of the fourth image forming portion Pk when the image forming operation is stopped. At least one turn of the intermediate transfer belt 5 is continuously performed. Preferably, the toner on the intermediate transfer belt 5 at the primary transfer portion N1k at the reference time next reaches the primary transfer portion N1k and then continues until the toner can reach the contact portion between the cleaning blade 71 and the photosensitive drum 1k. And do it. As a result, as shown in state IV of FIG. 9B, the toner on the intermediate transfer belt 5 can be finally collected in the collection container 72.

  In the states III and IV shown in FIGS. 9A and 9B, the primary transfer rollers 8y, 8m, 8c, and 8k of the first to fourth image forming units Py, Pm, Pc, and Pk are shown in FIG. The voltage applied in the state II of (b) is continuously applied. Thus, the toner on the intermediate transfer belt 5 passes through the primary transfer portions N1y, N1m, and N1c of the first to third image forming portions Py, Pm, and Pc. Then, the toner image is transferred to the photosensitive drum 1k in the primary transfer portion N1k of the fourth image forming portion Pk, scraped off by the cleaning blade 71, and finally recovered in the recovery container 72.

  10 shows the contact state between the intermediate transfer belt 5 and the photosensitive drum 1, the ON / OFF state of the voltage applied to the charging roller 2 and the developing roller 41, and the primary transfer roller 8 in the above-described series of sequence operations. Indicates the ON / OFF state of the voltage. In the figure, the periods indicated by bands indicate the contact state and the voltage ON state, respectively, and the periods not indicated by the band indicate the separated state and the voltage OFF state, respectively. In the figure, 1st, 2st, 3st, and 4st indicate the first, second, third, and fourth image forming units Py, Pm, Pc, and Pk, respectively.

  As in the case of the periodic cleaning operation, an appropriate peripheral speed difference may be provided between the intermediate transfer belt 5 and the photosensitive drum 1k in order to promote toner transfer.

  Further, after the series of operations described above, an operation for collecting the positive toner remaining on the intermediate transfer belt 5 in the collecting container 72 may be performed. In this case, as shown in FIG. 10, the same operations as those in the states II, III, and IV of FIGS. 8B, 9A, and 9B are performed as the primary transfer rollers 8y, 8m, The polarity of the voltage applied to 8c and 8k is set to be opposite to the above polarity.

  Thus, in this embodiment, when the residual toner on the moving body is collected by the collecting unit 70, each of the image forming units Py to Pc other than the specific image forming unit among the plurality of image forming units Py to Pk. The image carrier 1 is brought into contact with the moving body 5. At that time, an electric field in a direction in which the toner moves from the image carrier 1 toward the moving body 5 is applied between the image carrier 1 and the moving body 5 in the image forming portions Py to Pc other than the specific image forming portion. Form.

  As described above, according to the present exemplary embodiment, it is not necessary to separate the photosensitive drums 1 and the intermediate transfer belt 5 during irregular cleaning operations. The present invention can be executed even when a separation mechanism for the intermediate transfer belt 5 is not provided. Therefore, it is advantageous for simplifying the configuration of the image forming apparatus 100. Further, in this embodiment, since a separation mechanism between the cleaning blade 71 and the photosensitive drum 11k is not necessary, this is also advantageous in simplifying the configuration of the image forming apparatus 100.

Other Embodiments Although the present invention has been described based on the specific embodiments, the present invention is not limited to the above-described embodiments.

  For example, in each of the embodiments described above, the cleaning device 70 serving as a collecting unit that collects residual toner is installed as a specific image forming unit in the black image forming unit. It is not limited to those for use. Even if the image forming section for other colors is provided as the specific image forming section, the same effects as those in the above embodiments can be obtained.

  Further, in each of the above embodiments, the order of colors of the toner images formed on the intermediate transfer belt by a plurality of image forming units is described as yellow, magenta, cyan, and black. The order may be Also, the number of colors is not limited to four, and may be smaller or larger. The specific image forming unit including the collecting unit that collects the residual toner may be an image forming unit that forms the toner image on the intermediate transfer belt.

  In each of the above embodiments, the image forming apparatus 100 is described as performing both a regular cleaning operation and an irregular cleaning operation. However, the image forming apparatus 100 performs only an irregular cleaning operation. It may be said.

  Further, in each of the above embodiments, the image forming apparatus 100 has been described as being of the intermediate transfer type. However, the present invention is not limited to this. The present invention can also be applied to a direct transfer type image forming apparatus having a conveying belt which is, for example, an endless belt-like transfer material carrier as a moving body. FIG. 11 shows a schematic configuration of an example of a direct transfer type image forming apparatus. In the image forming apparatus 300 in FIG. 11, elements having the same functions or configurations as those of the image forming apparatus 100 in FIG. For example, as shown in FIG. 11, a direct transfer type image forming apparatus 300 includes, for example, a transport belt 301 as a transfer material carrier instead of the intermediate transfer body in the intermediate transfer type image forming apparatus. The toner image formed on each photosensitive drum 1 of each image forming portion P is sequentially transferred directly onto the transfer material S while carrying the transfer material S on the transport belt 301 and transporting it. Even in such a direct transfer type image forming apparatus 300, residual toner may adhere to the conveyance belt 301 when the transfer material S is not conveyed due to conveyance failure. Therefore, the present invention can also be applied to such a direct transfer type image forming apparatus 300. In this case, the intermediate transfer belt 5 in the above-described embodiment may be replaced with the transport belt 301, and a series of operations in the above-described embodiment may be performed.

1 Photosensitive drum (image carrier)
2 Charging roller 4 Developer 5 Intermediate transfer belt (moving body)
8 Primary transfer roller 9 Secondary transfer roller 41 Developing roller 42 Developing container 70 Cleaning device (collecting means)
71 Cleaning blade 72 Collection container 73 Contact lever (cleaning device switching member)

Claims (4)

A plurality of image forming units each including an image carrier that carries toner and moves, and a developer that supplies toner to the image carrier to form a toner image; and each of the images of the plurality of image forming units An image forming apparatus having a moving body that moves while in contact with the carrier and from which toner of a different color is transferred onto or onto a transfer material carried on the image carrier.
A collecting unit that collects toner on the image carrier is further provided only in a specific image forming unit among the plurality of image forming units,
The residual toner on the moving body is formed between the image carrier and the moving body by forming an electric field in the direction in which the toner moves from the moving body to the image carrier in the specific image forming unit. An image forming apparatus, wherein the moving body that moves while contacting the image carrier is transferred to the image carrier and collected by the collecting means.   When the residual toner on the moving body is collected by the collecting unit, the image carriers of the image forming units other than the specific image forming unit among the plurality of image forming units are separated from the moving body. The image forming apparatus according to claim 1.   Prior to collecting the residual toner on the moving body by the collecting unit, the image carriers of the plurality of image forming units are separated from the moving body, and the image forming units 3. The image forming apparatus according to claim 1, wherein residual toner on the carrier is collected by the developing unit as the image carrier is moved.   When the residual toner on the moving body is collected by the collecting unit, the image bearing members of the image forming units other than the specific image forming unit among the plurality of image forming units are brought into contact with the moving body, An electric field in a direction in which the toner moves from the image carrier toward the moving body is formed between the image carrier and the moving body in an image forming section other than the specific image forming section. The image forming apparatus according to claim 1.

Images