JP2005173228A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide no unnecessary high voltage power sources to realize miniaturization and cost reduction and to prevent a developer from sticking to a developer control member in some of image forming parts where development is not performed, in an image forming apparatus where some of a plurality of image forming parts do not participate in development. <P>SOLUTION: An image forming apparatus 100 has: a plurality of developing means 13 each of which has a developer carrier 16 and a developer control member 17; and a control part 60 for controlling the operation of the developer carriers of developing means 13Y, 13M, and 13C out of the plurality of developing means 13. Some of developer carriers are operated slowly and intermittently when development is not performed in some of the developing means. A common bias is applied to each of the developer carrier and developer control member 17 of both a developing means 13Bk which is performing development and developing means 13Y, 13M, and 13C which are not performing development. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine or a laser beam printer using an electrophotographic system or an electrostatic recording system.

  In recent years, for example, image forming apparatuses using an electrophotographic method have been increased in speed, function, and color, and various types of image forming apparatuses have been proposed. From the standpoint of speeding up, research on an inline system that forms images by arranging a plurality of image forming units (image forming units) that form images of different colors in series and simultaneously driving them, Since development is progressing and such an apparatus can form a color image at high speed, it is considered to be extremely useful in, for example, business use where high-speed printing is highly demanded.

  In this in-line image forming apparatus, a plurality of color developer images (toner images) are once superimposed and transferred onto an intermediate transfer member as a transfer target, and then transferred to a transfer material such as a recording sheet. In some cases, an intermediate transfer method is used in which a final image is formed by secondary transfer onto an OHP sheet or cloth.

  FIG. 6 shows a schematic cross-sectional view of a main part of this type of conventional image forming apparatus. The image forming apparatus 200 includes, as a plurality of image forming units, for example, first to fourth images for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (Bk). It has formation parts PY, PM, PC, and PBk. A toner image formed with toner as a developer on a drum-type electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 10Y, 10M, 10C, and 10Bk as an image carrier provided in each image forming unit, The primary transfer means 26Y, 26M, 26C, and 26Bk corresponding to each primary transfer portion N1 sequentially superimposes on the intermediate transfer member 31 for primary transfer, and then the toner image on the intermediate transfer member 31 is transferred to 2 At the next transfer portion N2, the transfer is performed on the transfer material S all at once by the action of the secondary transfer means 32. At this time, the transfer material S is nipped and conveyed by the both sides so that the front side is in contact with the intermediate transfer member 31 and the back side is in contact with the secondary transfer unit 32.

  The operation of each image forming unit will be further described with reference to the image forming apparatus 200 of FIG. The configuration of each image forming unit is substantially the same except that the color of the image to be formed is different. Therefore, in the following, unless there is a particular distinction, it is an element belonging to each image forming unit. The subscripts Y, M, C, and Bk that are shown are omitted and will be generally described.

  In each image forming unit, the surface of the photosensitive drum 10 that is rotationally driven in the direction of the arrow shown in the drawing is first uniformly charged at the contact portion with the charging roller 11 as a charging unit, and then exposed to an exposure unit (not shown). ), An electrostatic latent image corresponding to the image signal is formed on the surface. Subsequently, the electrostatic latent image is developed with toner attached by the developing unit 13, and a visible image corresponding to the electrostatic latent image is formed on the surface of the photosensitive drum 10.

  The charging roller 11 uniformly charges the surface of the photosensitive drum 1 with a constant potential when a voltage is applied by a high voltage power source (not shown) through the electrode. Further, the charging roller 11 is pressed against the surface of the photosensitive drum 10 with a predetermined pressing force, and charges the photosensitive drum 10 while being driven to rotate as the photosensitive drum 10 rotates.

  For example, a laser scanner (not shown) as an exposure unit supplies an optical signal modulated by an image signal of an image signal source, gives an optical signal L to the uniformly charged surface of the photosensitive drum 10, and outputs an image signal. An electrostatic latent image corresponding to is formed.

  As the developing means 13, conventionally, development is performed by bringing a developing roller 16 as a developer carrying member that conveys the developer to the photosensitive member into contact with the photosensitive drum 10 (hereinafter, referred to as “contact developing method”). There is. In such a developing system, a predetermined amount of toner is applied to the photosensitive drum 10 based on the relationship between the light / dark portion potential of the electrostatic latent image formed on the photosensitive drum 10 and the bias voltage applied to the developing roller 16. At the contact portion (developing portion) with the developing roller 16, it is transferred and attached to the electrostatic latent image formed on the photosensitive drum 10, and a visible image corresponding to the electrostatic latent image is formed.

  Such developing means (developing device) 13 includes a contact developing roller 16 that contacts the photosensitive drum 10, a toner supply roller 18 as a developer supply member that supplies toner to the developing roller 16, and toner supplied onto the developing roller 16. A developing blade 17 as a developer regulating member to be regulated is provided in the developing container (developing apparatus main body) 20. Further, high voltage power supplies (blade bias power supplies) 22a and 22b as regulating member voltage applying means for applying a voltage to the developing blade 17, high voltage power supplies (developing voltage applying means for applying a voltage to the developing roller 16 and the toner supply roller 18) Development bias power source) 23Y, 23M, 23C, and 23Bk are provided.

  The developing roller 16 is configured to come into contact with the surface of the photosensitive drum 10 and rotate as the photosensitive drum 1 rotates, and is arranged to be partially exposed from the developing container 20. The developing blade 17 is configured to abut against the developing roller 16, and the toner is passed between the abutting portions of the developing blade 17 and the developing roller 16 to regulate the toner, so that a thin layer of toner is formed on the developing roller 16. And a sufficient triboelectric charge (tribo) is imparted to the toner by friction at the contact portion.

  The toner supply roller 18 is provided in the developing device 13 in contact with the developing roller 16 at a position upstream of the developing blade 17 in the rotation direction of the developing roller 16. The toner is supplied to the developing roller 16 by rotating in a direction opposite to the surface movement direction of the developing roller 16 at a contact portion with the developing roller 16.

  2. Description of the Related Art Some conventional image forming units arranged in series have a process cartridge that can be attached to and detached from the apparatus main body. For example, in the laser beam printer shown in FIG. 6, the photosensitive drum 10 as a rotationally driven image carrier, the charging roller 11 as a charging means for uniformly charging the surface of the photosensitive drum 10, the electrostatic latent image. A developing device 13 as a developing unit that develops the toner with toner as a developer to form a visible image, and a cleaning device 14 as a cleaning unit that cleans the photosensitive drum 10 are integrally configured by a frame body, and this is configured as an apparatus main body. The process cartridges 1Y, 1M, 1C, and 1Bk for each color that can be attached to and detached from the printer 2 are arranged in the image forming units PY, PM, PC, and PBk. The process cartridge is not limited to this embodiment, and at least one of charging means for charging the photosensitive member, developing means for supplying a developer to the photosensitive member, and cleaning means for cleaning the photosensitive member, and the photosensitive member are integrated. Any cartridge may be used as long as the cartridge is made detachable from the main body of the image forming apparatus. According to such a process cartridge system, for example, when the developer runs out, the operator can replace the process cartridge so that other consumables such as the photosensitive member can be replaced. improves.

  In the inline method, a multicolor image (for example, a four-color full-color image) is not always formed, and, for example, a single black recording, that is, a monochrome image formation is frequently performed. In order to cope with such usage, there has also been proposed an image forming apparatus capable of switching between full-color image formation and monochrome image formation.

In addition, although not in-line, applying a bias to one developing blade is known from Patent Document 1.
JP-A-6-289703

  As described above, in the in-line method, full-color printing is not always performed, and monochrome printing may be performed.

  Further explanation will be made with reference to FIGS. FIGS. 7 and 8 show the configuration of the main parts particularly showing the photosensitive drum 10, the developing device 13, the primary transfer means 26, the intermediate transfer member 31, and the like in an example of a conventional image forming apparatus using the contact developing type developing device 13. It is a figure and other elements are omitted.

  FIG. 7 shows a full color printing operation in which the developing devices 13 of the image forming portions PY, PM, PC, and PBk for all four colors are operating. On the other hand, during monochrome printing, as shown in FIG. 8, the development cartridges 13Y, 13M, and 13C for the three color cartridges 1Y, 1M, and 1C of yellow, magenta, and cyan are stopped and the black process cartridge 1Bk is stopped. Only the developing device 13Bk is operating. At this time, in each of the yellow, magenta, and cyan image forming portions PY, PM, and PC, the primary transfer units 26Y, 20M, and 26C are moved away from the photosensitive drum 10 by the separating unit (not shown). The intermediate transfer member 31 is separated from the photosensitive drum 10 in the image forming portions PY, PM, and PC.

  On the other hand, in order to adjust the density of the four colors, four development bias power sources 23Y, 23M, 23C, and 23Bk for applying a development bias to the development roller 16 are required independently.

  Further, two or more blade bias power supplies 22a and 22b for applying a bias to the developing blade 17 are required. This is because, during monochrome printing, when the developing devices 13Y, 13M, and 13C of the three color image forming portions PY, PM, and PC other than black are stopped, the bias to the developing rollers 16Y, 16M, and 16C is stopped at the same time. This is because the bias to the developing blade 17 in the three-color image forming portions PY, PM, and PC must also be stopped. This is because when the bias is applied to the developing blade 17 even though the bias to the developing roller 16 is stopped, the toner sandwiched between the developing blade 17 and the developing roller 16 is always nipped on the developing roller 16 that is stopped. This is because it may stay inside, deteriorate the energization, and adhere to the developing blade 17. If the toner adheres to the developing blade 17, the toner coating on the developing roller 16 may be disturbed and a streak image may be generated.

  As described above, in the conventional in-line image forming apparatus capable of forming, for example, a four-color full-color image, the bias power source for the developing blade needs at least two power sources for black and the remaining three colors.

  However, when there are many power sources, there are disadvantages such as an increase in the size of the electrical equipment base and an increase in cost.

  Accordingly, an object of the present invention is to develop a developing unit for an image forming unit that operates with some of the image forming units when it is possible to stop the operation of some of the plurality of image forming units. The high-voltage power supply that applies voltage to the developer regulating member can be shared, and there is no need to provide an extra high-voltage power supply. In addition, when forming images of specific colors such as monochrome printing, the operation of some image forming units When the image forming apparatus is stopped, it is possible to provide an image forming apparatus capable of preventing the developer from adhering to the developer regulating member in a part of the image forming section that is stopped and preventing the development streaks.

  Still another object of the present invention is to reduce the size and cost of the apparatus by using a common high-voltage power source and to prevent the developer from sticking to the developer regulating member and developing streaks when the contact development method is adopted. In addition, an image forming apparatus capable of preventing the transfer material from being stained on the back is provided.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention provides a developer carrier for developing an electrostatic image formed on the image carrier by supplying the developer to the image carrier, and a developer supplied to the developer carrier. An image forming apparatus comprising: a plurality of developing units each including a developer regulating member that regulates the amount of the developing unit; and a switching unit configured to prevent development of some of the developing units from among the plurality of developing units. In some of the developing means, when the development is not performed, the developer carrier is operated slowly or intermittently,
A bias is commonly applied to both the developer regulating member of the developing unit that does not perform development and the developer regulating member of the developing unit that performs development. In the image forming apparatus, the developing unit that does not perform the developing and the developing unit that performs the developing have a power source that can apply a bias in common to both of the developer regulating members. .

  As described above, according to the present invention, when there is a switching means for preventing the development of some of the development means from among the development means, the development is performed with the part of the development means. A high voltage power source for applying a voltage to the developer regulating member can be shared. Therefore, there is no need to provide an extra high-voltage power source, and in the case of performing image formation of a specific color such as monochrome printing, when some image forming units are not operated, some of the stopped images It is possible to prevent the developer from adhering to the developer regulating member in the forming portion and to prevent development streaks. Furthermore, according to the present invention, when the contact development method is adopted, the apparatus can be reduced in size and cost due to the common use of the high-voltage power source, and the developer can be prevented from sticking to the developer regulating member and the development streak. Moreover, it is possible to prevent the back surface of the transfer material from being stained.

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

  In this embodiment, the present invention is embodied in an in-line image forming apparatus adopting a contact development method. The present invention is not limited to the form of the apparatus, but can be implemented in the form of a method supported by the description of the present embodiment.

  FIG. 1 shows a schematic cross section of an image forming apparatus 100 of the present embodiment. The image forming apparatus 100 according to the present exemplary embodiment is configured to transfer a material such as a recording sheet by an electrophotographic method in accordance with an image information signal from an external host device such as a personal computer that is communicably connected to the apparatus body 2. An image can be formed and output on an OHP sheet or cloth.

  The image forming apparatus 100 includes, as image forming units, first to fourth image forming units (image forming units) that form images of colors of yellow (Y), magenta (M), cyan (C), and black (Bk). Unit) PY, PM, PC, PBk. The four sets of image forming units PY, PM, PC, and PBk are arranged in parallel along an intermediate transfer belt 31 that moves around in the direction of arrow A in the figure as an intermediate transfer member. That is, by transferring the toner image to the intermediate transfer belt 31 corresponding to the yellow, magenta, cyan, and black image forming portions PY, PM, PC, and PBk arranged in a vertical row in order from the bottom in FIG. A full-color image can be formed.

  FIG. 2 shows the image forming unit in more detail. In the present embodiment, the image forming section for each color has substantially the same configuration except that the color of the image to be formed is different. The subscripts Y, M, C, and Bk indicating that the element belongs to the section are omitted, and the description will be made comprehensively.

  Each image forming unit includes a drum-type electrophotographic photosensitive member (photosensitive drum) 10 as an image carrier. The surface of the photosensitive drum 10 is uniformly charged by a charging roller 11 as charging means that rotates following the photosensitive drum 10. Next, the exposure device 12 as an exposure unit performs scanning exposure with the optical signal L in accordance with the image signal information, whereby an electrostatic latent image is formed on the surface of the photosensitive drum 10. Next, toner as a developer is attached to the electrostatic latent image by a developing device 13 as developing means, and a visible image is formed as a developer image (toner image).

  For example, during full-color image formation, each color toner image formed on the photosensitive drum 10 in each image forming unit is applied with a predetermined primary transfer bias to a primary transfer roller 26 as a primary transfer unit. In each image forming section, the photosensitive drum 10 and the primary transfer roller 26 are sequentially transferred onto the intermediate transfer belt 31 in a multiple manner at the primary transfer section N1. Thus, a full-color image is formed on the intermediate transfer belt 31.

  Next, a predetermined secondary transfer bias is applied to a secondary transfer roller 32 as a secondary transfer unit, whereby the toner image on the intermediate transfer belt 31 is secondarily transferred to the transfer material S. In synchronization with image formation on the intermediate transfer belt 31, the transfer material S is transferred from the transfer material supply unit 40 including the transfer material cassette 41, the transfer material supply roller 42 as a conveying unit, and the intermediate transfer belt 31 to the secondary transfer belt 31. The toner is supplied to the secondary transfer portion N2 facing the transfer roller 32.

  Thereafter, the recording material S to which the toner image has been transferred is conveyed to the fixing device 30 and the unfixed image is fixed to the transfer material S. Then, the transfer material S on which the image is fixed is carried out to the paper discharge tray 35, and the image formation is completed.

  Further, the primary transfer residual toner that is not transferred during the primary transfer and remains on the photosensitive drum 10 is obtained by a cleaning device 14 as an image carrier cleaning means having a cleaning blade 14a and a waste toner container 14b as cleaning members. The toner is collected in the waste toner container 14b and the photosensitive drum 10 is cleaned. On the other hand, the secondary transfer residual toner that is not transferred at the time of the secondary transfer and remains on the intermediate transfer belt 31 is disposed so as to be detachable from the intermediate transfer belt 31, and is an intermediate transfer member cleaning unit (not shown). The intermediate transfer belt 31 is cleaned.

  In this embodiment, the photosensitive drum 10 has a diameter of 30 mm and is driven to rotate in the direction of the arrow in the drawing at a peripheral speed of 100 mm / sec. The surface of the photosensitive drum 1 is uniformly charged by the charging roller 11.

  A DC voltage of −1150 V is applied to the charging roller 11 from a charging bias power source (not shown) which is a high voltage power source, and the surface of the photosensitive drum 10 is uniformly charged with a dark part potential of about −600 V. In this embodiment, a DC bias is used as the charging bias, but a bias in which an AC component is superimposed on a DC component may be used as the charging bias.

  The exposure device 12 scans and exposes the surface of the photosensitive drum 10 with an ON / OFF-controlled laser in accordance with image data input to the image forming apparatus, and the surface of the photosensitive drum 1 has a bright portion potential of about −80V. An electrostatic latent image is formed.

  The developing device 13 has substantially the same configuration as that of the conventional one shown in FIG. 6, and the electrostatic latent image on the photosensitive drum 10 is charged with the same charging polarity (as the charging polarity of the photosensitive drum 10) by a contact developing method. In this embodiment, reversal development is performed using toner of negative polarity.

  More specifically, as shown in FIG. 2, the developing device 13 is provided in a developing container (developing device main body) 20 containing a negatively charged nonmagnetic toner (one component toner) which is a one-component developer as a developer. A developing roller 16 as a developer carrying member, a developing blade 17 as a developer regulating member, a toner supply roller 18 as a developer supplying member, and an agitating blade 19 as a developer agitating / conveying means are configured.

  In this embodiment, the developing roller 16 is configured by providing a cored bar 16a made of a metal such as aluminum or an aluminum alloy with an elastic layer 16b made of a base layer 16b1 and a surface layer 16b2 thereon, and has an outer diameter of 16 mm. is there. The base layer 16b1 of the elastic layer 16b is made of rubber such as silicon, and the surface layer 16b2 is made of ether urethane or nylon. Of course, the structure is not limited thereto, and a structure in which a foam such as sponge is used for the base layer 16b1 and a rubber elastic layer is formed on the surface layer 16b2 is also possible. The resistance value was 1 MΩ when a total pressure of 1 kg was applied to the φ30 metal cylinder and 50 V was applied. In this embodiment, the developing roller 16 is rotationally driven by a driving means (not shown) at a peripheral speed of 160 mm / sec.

  The electrostatic latent image formed on the photosensitive drum 10 is visualized at the contact portion (developing portion) by toner carried on the developing roller 16 that is in contact with the surface of the photosensitive drum 10 during development. It is a statue. At this time, a DC voltage of −350 V is applied to the developing roller 16 from a high voltage power source (developing bias power source) 23Y, 23M, 23C, 23Bk as a developing voltage applying unit, and the negatively charged toner is transferred to the developing roller 16. To an electrostatic latent image formed on the photosensitive drum 1. A bias in which an AC component is superimposed on a DC component may be used as the developing bias.

  As described above, in the in-line method, there are four developing devices 13, and the developing bias power supplies 23Y, 23M, 23C, and 23Bk are arranged for the developing devices 13 in order to adjust the density of each color.

  Above the developing roller 16, a developing blade 17 as a developer regulating member is supported by the developing container 20. The developing blade 17 is provided so that the vicinity of the free end thereof is in contact with the outer peripheral surface of the developing roller 16 in a surface contact state.

  In this embodiment, the contact direction of the developing blade 17 is a so-called counter direction in which the tip end side is positioned upstream of the rotation direction of the developing roller 16 with respect to the contact portion. In this embodiment, the developing blade 17 abuts a phosphor bronze plate having a spring elasticity with a thickness of 0.1 mm against the surface of the developing roller 16 with a predetermined linear pressure. The developing blade 17 maintains the pressure-contact force of the developing blade 17 with respect to the developing roller 16 and is frictionally charged, so that the negatively chargeable toner 10 is charged.

  Further, the toner coating amount is stabilized by applying a DC voltage of −600 V to the developing blade 17 from a high voltage power supply (blade bias power supply) as a regulating member voltage applying means. This blade bias power source 22 is a single power source for the developing rollers 16 of the developing devices 13Y, 13M, 13C, and 13Bk in the four color image forming portions PY, PM, PC, and PBk of yellow, magenta, cyan, and black. In common, the same bias value is applied.

  The toner supply roller 18 can have a sponge structure or a fur brush structure in which fibers such as rayon and nylon are planted on a cored bar. In this embodiment, however, the urethane foam 18b provided on the metal core 18a has a diameter of 16 mm from the viewpoint of supplying the toner to the developing roller 16 and removing the toner remaining on the developing roller 16 without being used for development. An elastic roller was used.

  The toner supply roller 18 made of an elastic roller is in contact with the developing roller 16 and in the developing process, the peripheral speed is 100 mm / sec so as to be in the opposite direction to the developing roller 16 at the contact portion with the developing roller 16. Is driven to rotate. The penetration amount of the toner supply roller 18 with respect to the developing roller 16 was 1.5 mm.

  As described above, the toner image on the surface of the photosensitive drum 10 is transferred to the intermediate transfer belt by the transfer roller 26 to which a primary transfer bias is applied from a primary transfer bias power source (not shown) as a primary transfer voltage application unit. Then, the image is transferred to a transfer material S by a secondary transfer roller 32 to which a secondary transfer bias is applied from a secondary transfer bias power source (not shown) as a secondary transfer voltage application means, and then fixed. Is done.

  Subsequently, when the next image data is input to the image forming apparatus 100, the rotation of the photosensitive drum 10, the developing roller 16, the toner supply roller 18 and the like is not stopped, and the developing roller 16 remains at the same potential. The image forming operation is repeated.

  In the present embodiment, together with the developing device 13, the photosensitive drum 10 that is rotationally driven, the charging roller 11 that uniformly charges the surface of the photosensitive drum 10, and the cleaning device 14 are integrated together by a frame, and the process cartridge 1. Configure. The process cartridges 1Y, 1M, 1C, and 1Bk for each color are detachably attached to the image forming apparatus main body 2 via the mounting means 50 provided in the image forming apparatus main body 2. In this embodiment, the waste toner container 14b that supports the photosensitive drum 10, the charging roller 11, and the cleaning blade 17 is integrated with the developing container 16, which supports the developing roller 16, the developing blade 17, the toner supply roller 18, and the stirring blade 19. The process cartridge 1 is configured by connecting to.

  However, the aspect of the process cartridge 1 is not limited to this, and for example, a type in which only the developing device 13 is fixedly installed on the image forming apparatus main body 2 may be used. That is, the process cartridge integrally includes a photosensitive member as an image carrier, a charging unit that charges the photosensitive member, a developing unit that supplies developer to the photosensitive member, and a cleaning unit that cleans the photosensitive member. Any cartridge may be used as long as it is made into a cartridge and the cartridge is detachable from the image forming apparatus main body. On the other hand, only the developing device 13 can be a cartridge (developing cartridge) that can be attached to and detached from the image forming apparatus main body 2.

  In this embodiment, in a state where the process cartridge 1 is mounted on the image forming apparatus main body 2, a driving means (not shown) provided in the image forming apparatus main body 2 and a drive transmission means on the process cartridge 1 side are connected. The photosensitive drum 10, the developing device 13, the charging roller 11, and the like can be driven. Further, a power source for applying a voltage to the charging roller 11, the developing roller 16, the developing blade 17 and the like with the process cartridge 1 mounted on the image forming apparatus main body 2 is supplied to the process cartridge 1 side and the image forming apparatus main body 2 side. Each is electrically connected to an object through a provided contact.

  In this embodiment, the developing motor 25 for switching the peripheral speed of the developing roller 17 and the power sources (blade bias power source, developing bias power source, primary transfer bias power source, secondary transfer bias power source, charging bias provided in the image forming apparatus 100) The power source) is controlled by a CPU 60 (FIG. 3) as a control unit that controls the overall operation of the image forming apparatus main body 2. In this embodiment, the CPU 60 as the control means controls the developing bias power supply 23 at a predetermined timing based on a value preset in the storage unit of the CPU 60 as described below, and Y, M, and C developing. The developing motor 25 is controlled as means for switching the peripheral speed of the roller 17.

  Next, switching between full color printing and monochrome printing will be described.

  The image forming apparatus according to the present exemplary embodiment includes a full-color print mode (first mode) that forms a full-color image using all the image forming units, and a single-color image formation mode (monochrome) that forms a single black image as a specific color. Print mode, first mode).

  FIGS. 3 and 4 are main part configuration diagrams showing the photosensitive drum 10, the developing device 13, the primary transfer roller 26, the intermediate transfer belt 31 and the like, and other elements are omitted.

  As shown in FIG. 3, the intermediate transfer belt 31 is stretched between a driving roller 36 and a switching roller 37. The switching roller 37 is movable by a moving means (not shown) in a direction toward / away from the lowest yellow developing device 13Y in the drawing.

  FIG. 3 shows a state in the full color print mode. In this mode, the switching roller 37 is close to the lowest developing device 13Y for yellow in the drawing. Then, the four primary transfer rollers 26Y, 26M, 26C, and 26Bk all come into contact with the corresponding photosensitive drums 10Y, 10M, 10C, and 10Bk via the intermediate transfer belt 31. In all four color image forming portions PY, PM, PC, and PBk, the photosensitive drum 10, the developing roller 16, the toner supply roller 18, and the primary transfer roller 26 are rotationally driven in the directions indicated by arrows in the drawing. .

  On the other hand, FIG. 4 shows a state in the monochrome print mode. At this time, the developing motor 24 rotates the Bk developing roller. In this mode, the switching roller 37 moves away from the lowest yellow developing device 13Y in the drawing (in the direction of the arrow in the drawing). Then, since the primary transfer rollers 26Y, 26M, and 26C for yellow, magenta, and cyan are separated from the photosensitive drums 10Y, 10M, and 10C, in the three-color image forming portions PY, PM, and PC, the intermediate transfer belt 31 is No contact with the photosensitive drum 10. In the three-color image forming portions PY, PM, and PC, the photosensitive drum 10, the developing roller 16, the toner supply roller 18, and the primary transfer roller 26 are stopped.

  In this embodiment, the CPU 60 as the control unit is a switching unit that switches the movement of the switching roller 37 and the driving / stopping of the photosensitive drum 10, the developing roller 16, the toner supply roller 18, and the primary transfer roller 26 in the image forming unit. It has the function of. The CPU 60 turns ON / OFF the moving means of the switching roller 37 at a predetermined timing, and turns ON / OFF the driving means of the photosensitive drum 10, the developing roller 16, the toner supply roller 18, and the primary transfer roller 26 in some image forming units. The switching is performed by controlling the ON / OFF of the drive transmission means such as OFF or the clutch by a general method that is easily understood by those skilled in the art.

  Here, as shown in FIG. 8, conventionally, in the monochrome print mode, as the regulating member voltage applying means, yellow, magenta, and cyan image forming portions PY, PM, and blades in development blades 17Y, 17M, and 17C in PC are used. A first blade bias power supply 22a for applying a bias and a second blade bias power supply 22b for applying a blade bias to the developing blade 17Bk in the black image forming unit PBk are provided. In the monochrome print mode, in the three color image forming portions PY, PM, and PC of yellow, magenta, and cyan, the power sources for both the developing roller 16 and the developing blade 17 are stopped.

  As described above, when both the developing roller 16 and the developing blade 17 are powered down to 0 V, the toner does not adhere to the stopped developing roller 16 as described above.

  However, as shown in FIG. 8, the provision of the first blade bias power source 22a and the second blade bias power source 22b has disadvantages such as an increase in the size of the electrical board and an increase in cost as described above.

  From this point of view, in this embodiment, the blade bias power source 22 is shared by the four color image forming units, thereby realizing downsizing and cost reduction of the apparatus. However, when the blade bias power supply 22 is single as described above, when the developing roller 16 is stopped in the yellow, magenta, and cyan image forming portions PY, PM, and PC in the monochrome print mode, A bias is applied to both of the developing rollers 16.

  That is, when all the image forming units have a single power supply for the developing blade 17, the developing roller 16 stops in the image forming units PY, PM, and PC of three colors of yellow, magenta, and cyan in the monochrome print mode. In spite of this, a bias is applied to the developing blade 17.

  Therefore, the toner sandwiched between the developing blade 17 and the developing roller 16 always stays in the nip on the stopped developing roller 16, and there is a possibility that the current is deteriorated and is fixed to the blade.

  More specifically, in the monochrome print mode, it is necessary to apply a bias of −600 V to the developing blade 17Bk of the black image forming unit PBk. As a result, the potential of the developing blade 17Bk is increased to the same polarity as the toner, and the toner is directed toward the developing roller 16Bk. However, if the developing bias applied to the developing rollers 16Y, 16M, and 16C of the remaining three color (yellow, magenta, and cyan) image forming portions PY, PM, and PC is reduced to 0V, the developing rollers 16Y, 16M, and 16Bk Then, a potential difference of 600 V is generated between the developing blades 17Y, 17M, and 17C, and the toner sandwiched between the developing rollers 16Y, 16M, and 16C and the developing blades 17Y, 17M, and 17C is deteriorated by energization.

  Therefore, in this embodiment, according to the present invention, the developing rollers in the developing devices 13Y, 13M, and 13C when developing is not performed are slowly rotated.

In this embodiment, the peripheral speed ratio between the developing rollers 16Y, 16M, and 16C and the photosensitive drum 10 is changed in the three color image forming portions PY, PM, and PC of yellow, magenta, and cyan. For example, the speed is reduced to 150% when development is being performed, and is reduced to 1% when development is not being performed. Since the peripheral speed of the photosensitive drum 10 is 100 mm / s, the peripheral speed of the developing roller 17 is reduced from 150 mm / s to 1 mm / s.
Bias applied to the developing roller 16 and the developing blade 17 in the black image forming portion PBk and the other three colors (yellow, magenta, cyan) image forming portions PY, PM, and PC in the full color print mode and the monochrome print mode. The values and are summarized in Tables 1 and 2. Table 1 shows this example, and Table 2 shows a conventional example.

いままで上述した説明を、上記表にまとめて示す。

The above description is summarized in the above table.

When developing is not performed, the bias of the developing roller 16 is lowered to 0V.
In the embodiment, since the power supply is common to Bk in the monochrome print mode, the blade bias applied to the unused development blades 17Y, 17M, and 17C of three colors (yellow, magenta, and cyan) is −600V of Bk. It becomes equal.

  On the other hand, in the conventional example, since the power supply is individually provided, the blade bias applied to the developing blades 17Y, 17M, and 17C of three colors (yellow, magenta, and cyan) that are not used is set to 0 V, and the developing blade 17 and the developing blade are developed. The potential difference between the roller 16 and the roller 16 can be eliminated. As a result, the power is not supplied, so that the toner is not deteriorated and the toner can be prevented from sticking in the nip between the developing roller 16 and the developing blade 17.

  As a result of intensive studies by the present inventors, in the developing device 3 that is stopped in the monochrome print mode, when the difference between the bias applied to the developing blade 17 and the bias applied to the developing roller 16 is 200 V or more, the toner is fixed. Was found to occur. In the test, the image forming apparatus 100 of the present embodiment, which is the same except for this bias difference, was evaluated by observing the toner adhesion of the developing blade 17 and drawing it out. The case where the streak image was not good (◯) and finely fixed but the streak image did not appear was slightly bad (Δ). The results are shown in Table 3, Table 4, and Table 5.

現像ローラを停止したまま、通電すると、通電時間が長いほうがトナー固着が悪化する傾向にある。６０分程度のモノクロ連続プリントを想定すると、現像ローラ１６と現像ブレード１７との電位差は３００Ｖ以上になる場合は、現像ローラ１６を停止させるより、ゆっくり回転させた方がよい。

When the developing roller is stopped and energized, the longer the energization time, the worse the toner fixation. Assuming monochrome continuous printing of about 60 minutes, if the potential difference between the developing roller 16 and the developing blade 17 is 300 V or more, it is better to rotate the developing roller 16 slowly than to stop it.

  At this time, the same toner does not always stay between the developing roller 16 and the developing blade 17. The nip width between the developing roller 16 and the developing blade 17 is 1.0 mm, and the toner is sandwiched in this width. In the conventional example, since the operation is stopped, only the 1.0 mm width toner is constantly deteriorated in energization. On the other hand, in this embodiment, since the toner is rotated slowly, the individual toner is energized only for a moment between the toner and the nip. Moreover, in the roller having an outer diameter of 16.0 mm, the outer periphery is 16 × π = 50.0 mm, and the accumulated time for energization is reduced to 1/50 compared to 1.0 mm when stopped.

  As described above, according to the present exemplary embodiment, during monochrome printing, the developing roller 16 that does not perform development is slowly rotated to reduce energization deterioration of the toner sandwiched in the nip between the developing roller 16 and the developing blade 17. It can be reduced and the development blade 17 can be prevented from sticking, and development streaks can be prevented. In addition, since a bias can be applied to the developing blade 17 of the developing device 13 that is not developing in monochrome printing, the high voltage power supply of the developing blade 17 is made one even though there are a plurality of developing devices 13. Can do.

  In this embodiment, as shown in FIG. 4, in the monochrome print mode, the developing rollers 16Y, 16M, and 16C are set in the yellow, magenta, and cyan image forming portions PY, PM, and PC in accordance with the sequence described below. As indicated by an arrow in the figure, the photosensitive drum 10 is separated. This is to prevent the toner of the developing 16 that is slowly rotating from being rubbed against the stopped photosensitive drum 10.

  FIG. 5 shows a sequence of such a separation operation. The developing roller 16 in the yellow, magenta, and cyan image forming portions PY, PM, and PC rotates at a peripheral speed of 150% during development. A developing bias of −350 V is applied. Next, the developing roller 16 is moved away from the photosensitive drum 10 so that development is not performed. Immediately after the separation, the peripheral speed is gradually reduced from 150% to 1%, and the developing roller 16 rotates slowly. At the same time, the developing bias is dropped from -350V to 0V. Further, since the power supply is common to the developing blade 17, a bias of −600 V is also applied to the developing blade 17 that does not perform development. Thereafter, when returning from the monochrome print mode to full color printing, the bias applied to the developing roller 16 is returned to −350 V, and then the developing roller 16 is brought into contact with the photosensitive drum 10. At this time, since the surface potential of the photosensitive drum 10 is maintained at a predetermined −600 V, the toner does not move onto the photosensitive drum 10.

  In order to separate the developing roller 16 from the photosensitive drum 10, for example, the developing container 20 that is swingably joined to the waste toner container 14 b that supports the photosensitive drum 10 and integrally forms the process cartridge 1 is connected to the image forming apparatus main body. 2 is oscillated around an oscillating shaft 71 by a separating means 70 reciprocally moved by a driving means (not shown) provided in FIG. In the present embodiment, the operation of the separation means 70 is controlled by the CPU 60 as the control means. However, the present invention does not limit the separation means of the developing roller 16, and any separation means conceivable by those skilled in the art can be employed for the same purpose. Such changes are within the scope of the design changes of the present invention.

  By performing the above-described separation contact operation, the toner moves linearly to the photosensitive drum 10 even when a bias having the same potential as the blade bias applied to the developing blade 17 during the stop is applied to the developing roller 16. As a result, it was possible to prevent the back of the transfer material S from being stained via the intermediate transfer belt 31.

  As described above, in this embodiment, by rotating the developing roller slowly, for example, when the image forming unit of another color is not developed in order to form a single color image of a specific color, the specific color and Without providing an extra high voltage power source, such as providing a blade bias power source for each of the other color image forming portions, the toner is prevented from sticking to the developing blade 17 in the other color image forming portion, and developing streaks are avoided. Can be prevented.

  Further, by causing the developing roller 16 in the image forming section to stop as described above to be separated / abutted with respect to the photosensitive drum 10, the intermediate transfer belt 31 is not developed on the photosensitive drum 10 with toner in a straight line. Thus, the risk of the backside contamination of the transfer material S can be eliminated.

  Next, another embodiment of the present invention will be described. Since the basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the first embodiment, elements having the same configuration and function are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the second embodiment, unlike the first embodiment, the developing rollers 16Y, 16M, and 16C are intermittently rotated instead of slowly rotating. By intermittent rotation, the same toner is always prevented from being deteriorated by energization.

表7に示すように、実施例２では、モノクロで連続プリント中に、回転を停止していた現像ローラ１６Ｙ、１６Ｍ、１６Ｃを、一旦回転させ、再び停止させる。例えば、17ppmの画像形成装置においては、約50枚に相当する3分ごとに、現像ローラを少しだけ間欠回転させる。回転させる量は、なるべく停止位置が重ならないほうが望ましい。そこで、回転させる量として、例えば、外径16mmの現像ローラの外周50mmに対し、43mm程回転させる。ニップ幅1mmなので、43/50回転となり、同一の場所に重なるのは、50回後である。すなわち、３分×50回で、150分後であり、これほど長く、モノクロプリントをし続けるユーザーは、ほぼいないと考えられる。

As shown in Table 7, in Example 2, the developing rollers 16Y, 16M, and 16C that had stopped rotating during monochrome continuous printing are temporarily rotated and then stopped again. For example, in a 17 ppm image forming apparatus, the developing roller is slightly rotated intermittently every 3 minutes corresponding to about 50 sheets. The amount of rotation is preferably such that the stop positions do not overlap as much as possible. Therefore, for example, the rotation amount is about 43 mm with respect to the outer periphery 50 mm of the developing roller having an outer diameter of 16 mm. Since the nip width is 1mm, it becomes 43/50 rotations, and the same place overlaps after 50 times. That is, it is considered that there are almost no users who continue monochrome printing for 3 minutes × 50 times and 150 minutes later.

  When the developing rollers 16Y, 16M, and 16C are temporarily rotated, it is desirable that the developing rollers 16Y, 16M, and 16C be separated from the photosensitive drum 10. This is to prevent the toner of the development 16 from being rubbed against the stopped photosensitive drum 10 during intermittent rotation.

  In each of the above embodiments, the image forming apparatus is described as an intermediate transfer system. However, as is well known to those skilled in the art, a transfer material carrier is provided instead of the intermediate transfer body, and this transfer material carrier is used. After transferring the toner images from the respective image forming units on the transfer material carried on the body and transported to the respective image forming units, the transfer material is separated from the transfer material carrying member and transferred to the unfixed toner image. For example, there is an image forming apparatus that obtains a full color image. The present invention is equally applicable to such an image forming apparatus.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic sectional view showing an image forming unit of the image forming apparatus in FIG. 1 in more detail. FIG. 2 is an explanatory diagram illustrating a state during full color printing of the image forming apparatus of FIG. 1. FIG. 2 is an explanatory diagram illustrating a state during monochrome printing of the image forming apparatus of FIG. 1. FIG. 6 is a sequence diagram for explaining an embodiment of an operation for switching between a full color print mode and a monochrome print mode. It is a principal part schematic sectional drawing of an example of the conventional image forming apparatus. FIG. 7 is an explanatory diagram illustrating a state during full color printing of the conventional image forming apparatus illustrated in FIG. 6. FIG. 7 is an explanatory diagram illustrating a state during monochrome printing of the conventional image forming apparatus illustrated in FIG. 6.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Process cartridge 2 Image forming apparatus main body 10 Photosensitive drum (image carrier)
11 Charging roller (charging means)
12 Exposure equipment (exposure means)
13 Developing device (Developing means)
16 Development roller (developer carrier)
17 Development blade (developer regulating member)
18 Toner supply roller (developer supply member)
22 Blade bias power supply (regulator member voltage application means)
23 Development bias power supply (development voltage application means)
24 Bk developing roller motor 25 Y, M, C developing roller motor 26 primary transfer roller (primary transfer means)
36 Driving roller 37 Switching roller 31 Intermediate transfer belt (intermediate transfer member)
60 Control means 70 Separation means

Claims (3)

A developer carrying member for supplying a developer to the image carrying member to develop the electrostatic image formed on the image carrying member; a developer regulating member for regulating the developer to be fed to the developer carrying member; A plurality of developing means each comprising:
Switching means for preventing development of some of the plurality of developing means; and
In an image forming apparatus having
An image forming apparatus characterized in that, in some of the developing units, the developer carrying member is operated slowly or intermittently when development is not being performed.   2. A bias is applied to each of the developer carrying member and the developer regulating member in both a developing unit that does not perform development and a developing unit that performs development. The image forming apparatus described in 1.   A developer restricting member of a developing unit that does not perform development, and a developer restricting member of a developing unit that performs development, each having a power source that can apply a bias in common The image forming apparatus according to claim 2.

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