JP4669275B2 - Image forming apparatus - Google Patents

Description

  In the present invention, an electrostatic latent image is formed on an image carrier by exposure means based on image information, and the electrostatic latent image is developed by the developer carrier contacting the image carrier, and a developed image (toner image) is developed. ).

  FIG. 5 shows an example of a color image forming apparatus 100 having a conventional process cartridge.

  In this example, each process cartridge 7 includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 1 (1a, 1b, 1c, 1d) as an image carrier. The photosensitive drum 1 is formed by forming a photosensitive material layer such as an organic photosensitive material layer on the surface of a cylindrical base made of aluminum, for example, and is driven to rotate. Around the photosensitive drum 1, there are a charging roller 2 (2a, 2b, 2c, 2d), a laser beam scanning optical system 3 (3a, 3b, 3c, 3d) as exposure means, and a development roller 40 (development means). 40a, 40b, 40c, 40d), development unit 4 (4a, 4b, 4c, 4d), transfer roller 12 (12a, 12b, 12c, 12d), cleaner 6 (6a, 6b, 6c, 6d) Be placed. Further, a recording medium conveyance belt 11 stretched around rollers 13, 14 a, 14 b, 15 is disposed facing the photosensitive drum 1.

  The image forming apparatus includes a developing roller contact / separation mechanism 8 that separates the developing roller 40 and the photosensitive drum 1 during non-image formation.

  At the time of the image forming operation, first, each of the four image forming units, that is, the photosensitive drums 1 (1a, 1b, 1c, 1d) of the stations P (Pa, Pb, Pc, Pd) are driven to develop all the stations P. The roller 40 (40a, 40b, 40c, 40d) is driven and the developing roller abutment / separation mechanism 8 operates, that is, the operating shaft 8x is moved to move the operating piece 8y (8ya, 8yb, 8yc, 8yd). By operating the protrusions 5 (5a, 5b, 5c, 5d) of the developing unit 4, the developing rollers 40 (40a, 40b, 40c, 40d) of all the stations P are brought into contact with the photosensitive drum 1 while rotating. Then, after uniformly charging the surface of the photosensitive drum 1 with the charging roller 2, from the first station Pa to the fourth station Pd, sequentially by the laser beam scanning light by the exposure means 3 (3a, 3b, 3c, 3d). An electrostatic latent image is formed on the photosensitive drum 1 and is visualized by a developer on the developing roller 40 in accordance with the electrostatic latent image.

  The recording medium fed from the cassette 17, that is, the transfer paper S, is transported by the transport belt 11, and a visible image is transferred at a substantially abutting portion between the photosensitive drum 1 and the transfer roller 12. These images are melted and fixed by the fixing device 20.

  The developing unit 4 includes a developing roller 40 as a developer carrier, a supply roller 43 that supplies non-magnetic one-component toner (negative polarity) as a developer to the developing roller 40, and a developer regulation that regulates the amount of toner on the developing roller 40. A developing blade 44 as a member is provided.

  Since the developing roller 40 is in contact with the photosensitive drum 1, it is formed of an elastic body. A predetermined potential is supplied to the developing roller 40 by a developing bias power source (not shown) in order to transfer the toner from the developing roller 40 to the photosensitive drum 1 side.

  However, when the image forming operation shown in the above example was performed, the following problems were observed.

  When the printing operation is performed for a long time and the developing roller 40 is continuously used, the toner deteriorates due to friction with the supply roller 43 and the developing blade 44, and image defects such as fogging may occur. This is because the external additive such as a charge control agent added to the toner surface layer is peeled off by the rubbing between the developing roller 40 and the supply roller 43 or the developing blade 44, and the toner becomes electrically uncontrollable and fogging occurs. It is thought to occur. Further, since the developing roller 40 is made of an elastic material, the surface layer of the developing roller is worn and deteriorated due to long-term rubbing, and image defects such as fogging and low density may occur.

  In addition, when the durable use is continued, there is a problem that the photosensitive drum is worn away by the developing roller coming into contact with the photosensitive drum for a long time and the photosensitive layer is scraped off. This particularly occurs remarkably in a portion of the developing roller where the toner is not conveyed.

  Therefore, in order to solve the above-described problem, a developing roller contact / separation mechanism is provided for each station as in Patent Document 1, and the developing roller is moved to the photosensitive member only during the period of developing the electrostatic latent image on the photosensitive drum. It is conceivable to make it abut on the surface.

  In this method, the developing roller does not need to contact the photosensitive drum even when the previous station starts the developing operation, and contacts the photosensitive drum only during the time for developing the latent image of the station. Further, when the developing period of the own station is over, the rotation can be stopped after being separated from the photosensitive drum even if the next station is still developing.

  This difference is schematically shown in the timing charts of FIGS. The horizontal axis is time, and the timing of each operation during image formation is shown.

  FIG. 6 is a timing chart when the developing roller contact / separation operation is simultaneously performed in all stations, and FIG. 7 is a timing chart when the development roller contact / separation operation is performed independently for each station.

  According to the method of Patent Document 1 shown in FIG. 7, it can be seen that the driving time of the developing roller and the contact time with the photosensitive drum can be shortened.

  However, if the contact time between the developing roller and the photosensitive drum is further shortened and the developing roller contact operation is performed at the timing after the preceding station starts the latent image formation, the vibration due to the developing roller contact operation will occur. May propagate and disturb the formation of the latent image in the previous station, causing image defects such as horizontal streaks. This was remarkable during the formation of a latent image of a high-print image such as a photographic image or when the process speed was high.

For this reason, in order to prevent an image defect due to the shock of developing roller contact at the adjacent station, as shown in FIG. 7, the contact operation of the developing roller at an earlier timing than the preceding station starts the latent image formation. It is necessary to do. Similarly, when performing the developing roller separation operation, the separation operation is performed so that the vibration of the separation operation propagates and the latent image formation in the subsequent station is not disturbed to cause image defects such as horizontal stripes. There is a need.
JP 2001-318506 A

  However, the conventional image forming apparatus has the following problems.

  As shown in Patent Document 1, even if an independent development contact / separation mechanism is used for each station, if the process cartridge is used for a longer period of time and the printing operation is repeated and the development roller is continuously used, The toner deteriorates due to friction with the supply roller and the developing blade, and image defects such as fogging may occur.

  Further, since the developing roller is made of an elastic material, the surface layer of the developing roller is worn and deteriorated by rubbing for a long time, and image defects such as fogging and low density may occur.

  In addition, if the durable use is continued, there is a problem in that the photosensitive drum is worn away due to the developing roller coming into contact with the photosensitive member for a long time and the photosensitive layer is scraped off. This particularly occurs remarkably in a portion of the developing roller where the toner is not conveyed.

  At this time, if a process cartridge in which the developing roller, the photosensitive drum, and the toner container are integrated is used, if the printing is continued at a low printing rate, the developing roller may be worn out before the toner is used up. The photoconductive drum is scraped and the service life is reached.

  Accordingly, an object of the present invention is to appropriately set the optimum contact and separation timing according to conditions in an image forming apparatus in which a plurality of image carriers are provided and there are a plurality of contact and separation timings of the developer carrier with respect to the image carrier. By selecting, the contact time between the image carrier and the developer carrier is shortened, and the rotation time of the developer carrier is shortened so that the developer is deteriorated, the developer carrier is deteriorated, and the image carrier is scraped. It is an object of the present invention to provide an image forming apparatus capable of suppressing the process and extending the life of the process cartridge.

  Another object of the present invention is to provide an image forming apparatus having a plurality of image forming portions each having an image carrier, and a plurality of contact and separation timings of the developer carrier with respect to the image carrier. By switching the contact and separation timing, the life of the image carrier and the developer carrier and the process can be reduced while preventing image defects due to the contact and separation shocks of the developer carrier in the adjacent image forming units. An object of the present invention is to provide an image forming apparatus capable of extending the life of a cartridge.

  Another object of the present invention is to provide an image forming apparatus in which a plurality of image carriers are provided and there are a plurality of contact and separation timings of the developer carrier with respect to the image carrier. By switching based on the printing rate of the image, it is possible to select the optimal contact and separation timing of the developer carrier, and to extend the life of the image carrier and the developer carrier, and thus the life of the process cartridge. An image forming apparatus is provided.

  Another object of the present invention is to provide an image forming apparatus using a process cartridge in which an image carrier, a developer carrier, and a developer container are integrated, and a plurality of the image carrier and developer carrier. It is an object of the present invention to provide an image forming apparatus that has contact and separation timings and can appropriately extend the life of a process cartridge by appropriately selecting optimum contact and separation timings according to conditions.

The above object is achieved by the image forming apparatus according to the present invention. In summary, according to one aspect, the present invention includes a plurality of image forming units, and each of the image forming units forms an electrostatic latent image on the image carrier based on image information and image information. Exposure means for carrying, developer means for carrying the developer and rotating contact with the image carrier to form the electrostatic latent image as a developed image, developing means, and the image carrier and developer carrier In an image forming apparatus provided with a contact / separation mechanism for contacting or separating
A first image forming mode, and a second image forming mode having a printing rate smaller than that of the first image forming mode,
In the first image forming mode, the image bearing member and the developer bearing member are brought into contact with each other by the contact / separation mechanism before an electrostatic latent image is formed by the exposure unit in an adjacent image forming unit. ,
In the second image forming mode, while the electrostatic latent image is formed by the exposure unit in the previous adjacent image forming unit, the contact / separation mechanism causes the image carrier and the developer carrier to An image forming apparatus is provided, wherein the image forming apparatus is in contact with each other .

According to another aspect of the present invention, the image forming unit includes a plurality of image forming units, and each of the image forming units includes an image carrier and an exposure unit that forms an electrostatic latent image on the image carrier based on image information. A developing means including a developer carrying member that carries the developer and rotationally contacts with the image carrying member to convert the electrostatic latent image into a developed image; and the image carrier and the developer carrying member are brought into contact or In an image forming apparatus provided with a contact / separation mechanism for separating,
A first image forming mode, and a second image forming mode having a printing rate smaller than that of the first image forming mode,
In the first image forming mode, after the electrostatic latent image is formed by the exposure unit in an adjacent image forming unit, the image carrier and the developer carrier are separated by the contact / separation mechanism,
In the second image forming mode, while the electrostatic latent image is formed by the exposure unit in the adjacent subsequent image forming unit, the image carrier and the developer carrier are formed by the contact / separation mechanism. An image forming apparatus is provided that is spaced apart from each other .

  According to the present invention, in an image forming apparatus provided with a plurality of image carriers and having a plurality of contact and separation timings of the developer carrier with respect to the image carrier, optimum contact and separation timings are appropriately selected according to conditions. By shortening the contact time between the image carrier and the developer carrier and shortening the rotation time of the developer carrier, the deterioration of the developer, the deterioration of the developer carrier, and the scraping of the image carrier are suppressed. In addition, the life of the process cartridge can be extended.

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

Example 1
First, a color electrophotographic image forming apparatus which is an embodiment of an image forming apparatus according to the present invention will be described with reference to FIG. In this embodiment, a method of selecting the timing of contact and separation of the developer carrying member with respect to the image carrying member, which constitutes a feature of the present invention, depending on the type of print image will be described.

(Overall configuration of image forming apparatus)
FIG. 1 shows the overall configuration of the color electrophotographic image forming apparatus of this embodiment.

  Referring to FIG. 1, the color electrophotographic image forming apparatus 100 includes four image forming units, that is, image forming stations P (Pa, Pb, Pc, Pd) in the vertical direction in the image forming apparatus main body 100A. Are provided side by side.

  In each image forming station P, a process cartridge mounting portion 80 (80a, 80b, 80c, 80d) is disposed, and the cartridge 7 (7a, 7b, 7c, 7d) is placed in the mounting portion 80 (80a, 80b, 80c, 80d). ) Is detachably mounted.

  The process cartridge 7 includes a drum-shaped electrophotographic photosensitive member as an image carrier, that is, a photosensitive drum 1 (1a, 1b, 1c, 1d). The photosensitive drum 1 is driven to rotate counterclockwise in FIG. 1 by a driving means (not shown).

  The photosensitive drum 1 is irradiated with a laser beam on the basis of the image information, charging means 2 (2a, 2b, 2c, 2d) for uniformly charging the surface of the photosensitive drum 1 in order according to the rotation direction. A scanner unit 3 (3a, 3b, 3c, 3d) as an exposure unit for forming an electrostatic latent image on the drum 1, and developing the electrostatic latent image using toner as a developer. Developing unit 4 (4a, 4b, 4c, 4d) as developing means for forming an image, electrostatic transfer means 12 (12a, 12b, 12c, 12d) for transferring the toner image on the photosensitive drum 1 to the recording medium S A cleaning means 6 (6a, 6b, 6c, 6d) for removing the toner remaining on the surface of the photosensitive drum 1 after the transfer is disposed.

  Here, in this embodiment, as will be better understood with reference also to FIG. 2, the photosensitive drum 1, the charging unit 2, the developing unit 4, and the cleaning unit 6 are integrally formed into a cartridge so as to form a process cartridge 7 (7a). 7b, 7c, 7d).

  The photosensitive drum 1 is obtained by applying an organic photoconductor layer (OPC photosensitive member) to an outer peripheral surface of an aluminum cylinder having a diameter of 30 mm, for example. Both ends of the photosensitive drum 1 are rotatably supported by support members (not shown). The photosensitive drum 1 is rotationally driven in a counterclockwise direction (arrow X direction in FIG. 2) by a drive motor (not shown).

  As the charging means 2 (2a, 2b, 2c, 2d), a contact charging type as shown in FIG. 2 is used in this embodiment. The charging member 2 as a charging means is a conductive roller formed in a roller shape, and the roller 2 is brought into contact with the surface of the photosensitive drum 1. Then, a charging bias voltage is applied to the roller 2. As a result, the surface of the photosensitive drum 1 is uniformly charged.

  In FIG. 1, the scanner unit 3 (3 a, 3 b, 3 c, 3 d) is arranged in a substantially horizontal direction of the photosensitive drum 1. Then, image light corresponding to the image signal is irradiated to a polygon mirror 9 (9a, 9b, 9c, 9d) rotated by a scanner motor (not shown) by a laser diode (not shown). The image light reflected by the mirror 9 selectively exposes the surface of the charged photosensitive drum 1 through the imaging lens 10 (10a, 10b, 10c, 10d). Thereby, an electrostatic latent image corresponding to the image signal is formed.

  As can be understood with reference to FIG. 2, each of the developing units 4 (4a, 4b, 4c, 4d) includes a developer storage portion storing a developer (toner), that is, a toner container 41 (41a, 41b). , 41c, 41d) and a developing frame, that is, a developing container 45 (45a, 45b, 45c, 45d).

  That is, with regard to the toner container 41, for example, the cyan developing unit 4a has a toner container 41a containing cyan toner, the yellow developing unit 4b has a toner container 41b containing yellow toner, and the magenta developing unit 4c has a magenta color. The toner container 41c containing the toner and the black developing unit 4d include a toner container 41d containing black toner. In each toner container 41, a developing roller 40 is disposed as a developer carrying member that carries and conveys the developer so as to face the photosensitive drum 1.

  In FIG. 2, the developer in the toner container 41, that is, the toner, is sent to the toner supply roller 43 by the toner conveyance stirring mechanism 42. Next, the toner is applied to the outer periphery of the developing roller 40 by the toner supply roller 43 and the developing blade 44 that is in pressure contact with the outer periphery of the developing roller 40, and charges are applied to the toner. Then, by applying a developing bias to the developing roller 40, the latent image formed on the photosensitive drum 1 is developed into a toner image.

On the other hand, as shown in FIG. 1, the image forming apparatus 100 is provided with an electrostatic transfer belt 11 that circulates and moves so as to face and contact all the photosensitive drums 1 (1a, 1b, 1c, 1d). ing. The transfer belt 11 is a film-like member having a volume specific resistance of 10 ¹¹ to 10 ¹⁴ Ω · cm and a thickness of about 150 μm. Then, the recording medium S is conveyed to the transfer position by the transfer belt 11, and the toner image on the photosensitive drum 1 is transferred.

  That is, the transfer belt 11 is stretched by four rollers, that is, the driving roller 13, the driven rollers 14a and 14b, and the tension roller 15, and rotates in the direction of the arrow in FIG. As a result, the transfer belt 11 circulates and the toner image is transferred while the recording medium S is conveyed from the driven roller 14a side to the drive roller 13 side.

  A transfer roller 12 (12a, 12b, 12c, 12d) as a transfer means is in contact with the inner side of the transfer belt 11 and faces the four photosensitive drums 1 (1a, 1b, 1c, 1d). Are arranged side by side. A positive charge is applied from the transfer roller 12 to the recording medium S via the transfer belt 11. As a result, the toner image on the photosensitive drum 1 is transferred to the recording medium S.

  The feeding unit 16 feeds and transports the recording medium S to the image forming unit. A plurality of recording media S are stored in the feeding cassette 17. At the time of image formation, the feeding roller 18 and the registration roller pair 19 are driven and rotated according to the image forming operation. Thus, the recording medium S in the cassette 17 is separated and fed one by one. The leading edge of the recording medium S hits the roller pair 19 and stops temporarily. The recording medium S is fed to the transfer belt 11 by the registration roller pair 19 in synchronization with the rotation of the transfer belt 11 and the toner image.

  The fixing unit 20 fixes the toner images of a plurality of colors transferred to the recording medium S. A heating roller 21a that rotates and a pressure roller 21b that applies pressure and heat to the recording medium S are provided. That is, the recording medium S to which the toner image on the photosensitive drum 1 is transferred is conveyed by the fixing roller pair 21 (21a, 21b) when passing through the fixing unit 20. Then, heat and pressure are applied by the fixing roller pair 21. As a result, the toner images of a plurality of colors are fixed on the surface of the recording medium S.

(Image forming operation)
First, the process cartridges 7 (7a, 7b, 7c, 7d) are sequentially driven in accordance with the timing of image formation. In response to the drive, the photosensitive drums 1 (1a, 1b, 1c, 1d) are rotationally driven, and the scanner units 3 (3a, 3b, 3c, 3d) corresponding to the cartridges 7 are sequentially driven. By this driving, the charging unit 2 (2a, 2b, 2c, 2d) applies a uniform charge to the peripheral surface of the photosensitive drum 1. The scanner unit 3 exposes the circumferential surface of the photosensitive drum 1 according to an image signal to form an electrostatic latent image on the photosensitive drum 1. The developing roller 40 develops the electrostatic latent image.

  As described above, the toner images on the photosensitive drums 1 are sequentially transferred to the recording medium S by the electric field formed between the photosensitive drums 1 and the transfer rollers 12. The recording medium S to which the four color toner images are transferred is separated from the transfer belt 11 by the curvature of the driving roller 13. Then, it is carried into the fixing unit 20. After the toner image is heat-fixed by the fixing unit 20, the recording medium S is discharged from the discharge unit 24 to the outside of the main body by the discharge roller pair 23.

(Process cartridge)
Next, the process cartridge 7 (7a, 7c, 7d, 7d) used in the present embodiment will be described with reference to FIG. FIG. 2 is a main cross section of the process cartridge 7 containing toner.

  In this embodiment, the process cartridge 7a containing cyan toner, the process cartridge 7b containing yellow toner, the process cartridge 7c containing magenta toner, and the process cartridge containing black toner are used. 7d has the same configuration.

  The process cartridge 7 is divided into a photosensitive drum unit 50 as a first frame having a photosensitive drum 1, a charging unit 2 and a cleaning unit 6, and a developing unit 4 as a second frame having a developing unit. ing. The developing unit 4 is attached to the photosensitive drum unit 50 so as to be swingable by a support shaft (fulcrum) Po, and the developing roller 40 is in contact with the photosensitive drum 1 by the pressing force of the spring 55.

  In the photosensitive drum unit 50, the photosensitive drum 1 is rotatably attached to the cleaning frame 51 via a bearing (not shown). As described above, the primary charging means 2 for uniformly charging the surface of the photosensitive drum 1 and the developer (toner) remaining on the photosensitive drum 1 are removed on the circumference of the photosensitive drum 1. Further, the residual toner removed from the surface of the photosensitive drum 1 by the cleaning blade 60 is sequentially sent to a waste toner chamber 51a provided behind the cleaning frame by the toner feeding mechanism 52. Then, the photosensitive drum 1 is rotationally driven in the X direction (counterclockwise) in accordance with the image forming operation by a driving force of a driving motor (not shown).

  In FIG. 2, the developing unit 4 includes a developing roller 40 as a developer carrying member that contacts the photosensitive drum 1 and rotates in the direction of arrow Y, a developing container (developing frame) 45 in which the developing roller 40 is disposed, and And a toner container 41 containing toner.

  The developing roller 40 is rotatably supported by the developing container 45, and on the circumference of the developing roller 40, a developer supply member that contacts the developing roller 40 and rotates in the arrow Z direction, that is, a toner supply roller 43, Developing blades 44 as developer regulating members are respectively disposed. Further, in the toner container 41, a toner transport stirring mechanism 42 for stirring the stored toner and transporting it to the toner supply roller 43 is provided.

  At the time of development, when the stored toner is transported to the toner supply roller 43 by the toner transport agitating mechanism 42, the toner supply roller 43 that rotates in the direction of the arrow in the figure is the development roller that rotates the toner in the direction of the arrow in the figure. The toner is supplied to the developing roller 40 by rubbing with the developing roller 40 and is carried on the developing roller 40. The toner carried on the developing roller 40 reaches the developing blade 44 as the developing roller 40 rotates, and the developing blade 44 regulates the toner to form a predetermined toner thin layer. The regulated toner reaches the charging roller 70 as the developer charging means as the developing roller 40 rotates, and is given a desired charge amount.

  Further, the toner thin layer on the developing roller 40 is conveyed to a developing unit where the photosensitive drum 1 and the developing roller 40 are in contact with each other, and in the developing unit, the toner is sensitized by a DC developing bias applied to the developing roller 40 from a power source (not shown). The latent image is developed by attaching to the electrostatic latent image formed on the surface of the body drum 1. The toner remaining on the surface of the developing roller 40 without contributing to the development is returned to the developing container 45 as the developing roller 40 rotates, and is peeled off and collected from the developing roller 40 at the rubbing portion with the toner supply roller 43. The The collected toner is stirred and mixed with the remaining toner by the toner transport stirring mechanism 42.

  As in this embodiment, in the contact development method in which development is performed by contact between the photosensitive drum 1 and the developing roller 40, the photosensitive drum 1 is preferably a rigid body, and the developing roller 40 is preferably a roller having an elastic body. . As this elastic body, a solid rubber single layer or a solid rubber layer coated with a resin coating in consideration of charge imparting property to toner is used.

  As shown in FIGS. 1 and 2, the process cartridge 7 is mounted on the image forming apparatus main body 100A along the process cartridge guide (not shown) provided on the apparatus main body 100A from the arrow direction. This is done by guiding the inside of the main body, inserting it into the mounting part 80 (80C, 80Y, 80M, 80Bk) and positioning it at a predetermined position.

  On the other hand, in this embodiment, as shown in FIG. 1, a developing roller abutment / separation mechanism is provided adjacent to the process cartridge 7 mounted on the mounting portion 80 (80C, 80Y, 80M, 80Bk) of the image forming apparatus main body 100A. That is, the contact / separation mechanism 8 (8A, 8B, 8C, 8D) is arranged.

  According to the present embodiment, the contact / separation mechanism 8 (8A, 8B, 8C, 8D) is integrally formed with the operation shaft 8x (8xa, 8xb, 8xc, 8xd) extending in the vertical direction and the operation shaft 8x. And an operating piece 8y (8ya, 8yb, 8yc, 8yd) that engages with the protruding member 5 (5a, 5b, 5c, 5d) provided on each process cartridge 7 (7a, 7b, 7c, 7d). Accordingly, by operating the contact / separation mechanism 8 and moving the operation shaft 8x up and down, the operation piece 8 engages with the protruding member 5 of the process cartridge, and the contact or separation operation of the photosensitive drum 1 and the developing roller 40 is performed. I do.

  As described above, the image forming apparatus according to the present exemplary embodiment includes the plurality of process cartridges 7 (7a, 7b, 7c, and 7d) each including a plurality of colors of toner and arranged in a tandem manner. Includes a photosensitive drum 1 capable of forming an electrostatic latent image by the exposure means 3 (3a, 3b, 3c, 3d), and a developing roller 40 (40a, 40a) that develops the electrostatic latent image on the photosensitive drum 1 with toner. 40b, 40c, 40d). In addition, the image forming apparatus includes a contact / separation 8 that causes the photosensitive drum 1 and the developing roller 40 to perform a contact / separation operation independently for each color.

  Here, in order to develop the electrostatic latent images formed on the photosensitive drums 1a, 1b, 1c, and 1d with toners of various colors, the developing rollers 40a, 40b, 40c, and 40d are moved to the photosensitive drums 1a, 1b, and 1c. 1d is brought into contact with the toner. At this time, if the developing rollers 4a, 4b, 4c, and 4d are always in contact with the photosensitive drums 1a, 1b, 1c, and 1d, as described above, wear is greatly generated and the durability is deteriorated. It also causes toner deterioration.

  Therefore, the developing rollers 40a, 40b, 40c, and 40d are moved to the photosensitive drums 1a, 1b, 1c, and 40d only during the time required for the image forming period by the developing roller contact / separation mechanism 8 (8A, 8B, 8C, 8D) for each color. It is driven to rotate by being brought into contact with 1d, and after completion of the development, the contact is removed and the rotation of the developing rollers 40a, 40b, 40c and 40d is stopped. At this time, the photosensitive drum 1 and the developing roller 40 perform the abutting operation at a predetermined timing, considering at least a time when the developing roller 40 can be stably developed after the abutting. Further, it is necessary to perform the developing roller contact operation before starting the latent image formation at the station P that performs the contact operation so that the latent image formation is not affected by the vibration caused by the contact operation.

  In order to prevent an image defect due to a shock at the developing roller contact at the adjacent station P, the contact operation is performed at a timing before the adjacent process cartridge 7 starts the latent image formation.

  In this embodiment, the image forming apparatus has a plurality of timings for contacting and separating the developing rollers 40a, 40b, 40c, and 40d with the photosensitive drums 1a, 1b, 1c, and 1d, that is, a plurality of contact and separation sequences. The contact or separation timing can be selected so that the contact time can be minimized without causing image defects.

  In this embodiment, there are two contact and separation sequences, and the contact and shortening time is shortened while preventing image defects due to the developing roller contact and separation shock at the adjacent station P according to the image information. A method for selecting a separation sequence is shown.

(First developing roller contact and separation sequence)
With reference to FIG. 3, the operation of the image forming apparatus in the first developing roller contact and separation sequence will be described in order according to the time series.

  When the image forming operation starts, the photosensitive drums 1 (1a, 1b, 1c, 1d) for all colors are rotationally driven, and the first color developing roller 40a is driven to contact the photosensitive drum 1a. Subsequently, the developing roller 40b for the second color is driven to come into contact with the photosensitive drum 1b. A latent image of the first color component of the image information is formed on the photosensitive drum 1a by the exposure means 3a on the first color process cartridge 7a. This latent image is visualized by the developing roller 40a having the first color toner.

  Next, the developing roller 40c for the third color is rotationally driven and comes into contact with the photosensitive drum 1c. The second color component latent image is formed on the photosensitive drum 1b at the second color image forming station, and then the second color latent image is visualized by the developing roller 40b. Thereafter, image formation is similarly performed for the third color image and the fourth color image.

  The toner image formed on the photosensitive drum 1 is sequentially transferred onto a sheet when the recording medium S picked up from the cassette 17 of the feeding unit 16 passes between the photosensitive drum 1 and the transfer roller 12. . The transferred toner image is heat-fixed on the paper by the fixing device 20 to form a full-color image.

  As can be seen from FIG. 3, the developing roller contact operation is performed before the latent image formation is started at the adjacent station. It can also be seen that the developing roller separation operation is performed after the latent image formation is completed at the adjacent station.

  However, in order to further extend the durable life of the process cartridge, it is desirable to further shorten the contact time between the developing rollers 40a, 40b, 40c, and 40d and the photosensitive drums 1a, 1b, 1c, and 1d.

(Second developing roller contact and separation sequence)
Next, with reference to FIG. 4, each operation sequence in the second developing roller contact and separation sequence will be described.

  At the image forming operation timing according to the second contact and separation sequence, when the image forming operation is started, the photosensitive drums of all colors are rotationally driven, the first color developing roller 40a is driven, and the photosensitive drums are driven. Contact la.

  Then, a latent image of the first color component of the image information is formed on the photosensitive drum 1a by the exposure unit 3a on the process cartridge of the first color. This latent image is visualized by the developing roller 40a having the first color toner.

  On the other hand, before the first color latent image is formed, the second color developing roller 40b is driven, and the first color latent image is formed at the previous first color image forming station. It contacts the body drum 1b.

  A second color component latent image is formed on the photosensitive drum 1b at the second color image forming station, and then the second color latent image is visualized by the developing roller 40b.

  Further, the third color developing roller 40c is rotationally driven before the second color latent image is formed, and the second color latent image is formed at the previous second color image forming station. It contacts the body drum 1c. Thereafter, image formation is similarly performed for the third color image and the fourth color image.

  The toner image formed on the photosensitive drum is sequentially transferred to the recording medium S when the recording medium S picked up from the cassette 17 passes between the photosensitive drum 1 and the transfer roller 12. The transferred toner image is heat-fixed on the paper by the fixing device 20 to form a full-color image.

  As shown in FIG. 4, in the second developing roller contact and separation sequence, when the first color latent image formation is completed, the separation operation of the developing roller 40a is performed, and the developing roller 40a is moved from the photosensitive drum 1a. Separate. At this time, the second color of the subsequent image forming station is still forming a latent image.

  Subsequently, when the formation of the latent image of the second color is completed, the separating operation of the developing roller 40b is performed, and the developing roller 40b is separated from the photosensitive drum 1b. At this time, the third color of the subsequent image forming station is still forming a latent image. Thereafter, the third color and the fourth color and the separation operation are repeated.

  In the second developing roller contact and separation sequence, the process cartridge 7 in the adjacent previous image forming station performs the contact operation of the developing roller during the latent image formation, and the process in the adjacent subsequent image forming station. Since the cartridge 7 separates the developing roller during the latent image formation, an image defect due to the developing roller contact and separation shock at an adjacent station may be seen depending on the image type.

  Further, since the developing roller 40 is an elastic body, the contact becomes unstable immediately after the contact operation due to vibration, so there is a minimum time required until the vibration converges and the development operation can be stably performed. It is not preferable to shorten the contact timing with the photosensitive drum 1 beyond this time. This time is defined as a necessary minimum contact time t0.

  In the image forming apparatus of this embodiment, the interval between the stations is 70 mm, the process speed is 140 mm / second, and in this embodiment, the necessary minimum contact time t0 is about 0.3 seconds. The developing roller contact operation was performed about 0.3 seconds ago. Further, the distance between the latent image forming position on the photosensitive drum and the developing position is about 20 mm, and the time from the start of latent image formation to the start of development is about 0.14 seconds, which is shorter than t0. Image defects due to roller contact shock are not visible.

  The image forming apparatus according to the present embodiment uses the ratio of the intermediate density portion detected by the detection unit that detects the ratio of the intermediate density portion in the image signal used for image formation, that is, the printing rate as the image forming mode. Based on text mode and photo mode.

  When the photo mode is selected, it can be determined that the width or ratio of the intermediate density portion in the print image, that is, the ratio of the intermediate density portion is very large. In the case of such an image, an image defect due to a shock at the developing roller contact and separation at the adjacent station is easy to be seen. Therefore, the development at the adjacent station is performed by using the first developing roller contact and separation sequence. It is possible to obscure image defects caused by roller contact and separation shocks.

  When the character mode is selected, it can be determined that the width or ratio of the intermediate density portion in the print image, that is, the ratio of the intermediate density portion in a single word is very small. In the case of such an image, image defects due to shocks caused by contact and separation of the developing roller at the adjacent station are hardly visible, so by using the second developing roller contact and separation sequence, the developing roller driving time, It is possible to shorten the contact time.

  Therefore, it is possible to improve the life of the process cartridge 7 by preventing the toner from being deteriorated and suppressing the occurrence or wear of contact friction scratches between the photosensitive drum 1 and the developing roller 40.

  In addition, when the printing is continued at a low printing rate using the process cartridge 7 in which the developing roller 40, the photosensitive drum 1, and the toner container are integrated, the developing roller 40 and the photosensitive drum 1 have a lifetime. The toner can be used up without any trouble.

  According to the above embodiment, the contact sequence and the separation sequence described in the above embodiment have been described as being executed at the same time, but only either the contact sequence or the separation sequence described in the above embodiment is employed. It is also possible to do. That is, for example, only the contact sequence may be employed, and the separation sequence may be performed simultaneously in each image forming unit.

  That is, according to another embodiment of the present invention, one of the contact sequence and the separation sequence described in the above embodiment can be performed simultaneously in each image forming unit.

1 is a schematic configuration diagram of a color electrophotographic image forming apparatus according to an embodiment of the present invention. FIG. 6 is a cross-sectional explanatory view of a process cartridge. It is a figure explaining operation | movement of the image forming apparatus in the 1st developing roller contact and separation sequence according to this invention. It is a figure explaining operation | movement of the image forming apparatus in the 2nd developing roller contact and separation sequence according to this invention. It is a schematic block diagram of the conventional color image forming apparatus. It is a diagram for explaining the operation of the image forming apparatus in a conventional developing roller contact and separation sequence. It is a diagram for explaining the operation of the image forming apparatus in a conventional developing roller contact and separation sequence.

Explanation of symbols

P (Pa, Pb, Pc, Pd) Image forming station (image forming unit)
1 (1a, 1b, 1c, 1d) Photosensitive drum (image carrier)
2 (2a, 2b, 2c, 2d) Charging roller (charging means)
3 (3a, 3b, 3c, 3d) Scanner device (exposure means)
4 (4a, 4b, 4c, 4d) Development unit 8 Development roller contact / separation mechanism (contact / separation mechanism)
40 (40a, 40b, 40c, 40d) Developing roller (developer carrier)

Claims (4)

A plurality of image forming units, and each image forming unit includes an image carrier, an exposure unit that forms an electrostatic latent image on the image carrier based on image information, and a developer carrying the image carrier. The image forming apparatus includes a developing unit including a developer carrier that rotates and contacts the electrostatic latent image to develop the electrostatic latent image, and a contact / separation mechanism that contacts or separates the image carrier and the developer carrier. In the forming device,
A first image forming mode, and a second image forming mode having a printing rate smaller than that of the first image forming mode,
In the first image forming mode, the image bearing member and the developer bearing member are brought into contact with each other by the contact / separation mechanism before an electrostatic latent image is formed by the exposure unit in an adjacent image forming unit. ,
In the second image forming mode, while the electrostatic latent image is formed by the exposure unit in the previous adjacent image forming unit, the contact / separation mechanism causes the image carrier and the developer carrier to an image forming apparatus characterized in that abutting the. A plurality of image forming units, and each image forming unit includes an image carrier, an exposure unit that forms an electrostatic latent image on the image carrier based on image information, and a developer carrying the image carrier. The image forming apparatus includes a developing unit including a developer carrier that rotates and contacts the electrostatic latent image to develop the electrostatic latent image, and a contact / separation mechanism that contacts or separates the image carrier and the developer carrier. In the forming device,
A first image forming mode, and a second image forming mode having a printing rate smaller than that of the first image forming mode,
In the first image forming mode, after the electrostatic latent image is formed by the exposure unit in an adjacent image forming unit, the image carrier and the developer carrier are separated by the contact / separation mechanism,
In the second image forming mode, while the electrostatic latent image is formed by the exposure unit in the adjacent subsequent image forming unit, the image carrier and the developer carrier are formed by the contact / separation mechanism. An image forming apparatus characterized by separating the two . The image forming apparatus according to claim 1, wherein the first image forming mode is a photographic mode, and the second image forming mode is a character mode . The image forming apparatus according to any one of claims 1-3, wherein said image bearing member and developing means characterized in that it is a process cartridge that is configured integrally.

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