JP2006011482A - Image forming unit and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily and efficiently replace an image forming element of an image forming apparatus when the image forming element comes to the end of its life. <P>SOLUTION: The life of a photoreceptor 7 is made equal to the life of a two-component developer 101 for developing a visible image from an electrostatic latent image formed on the photoreceptor 7, so that when the photoreceptor 7 and the two-component developer 101 come to the end of their life, these can be replaced together. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus that visualizes an electrostatic latent image formed on an image carrier as a toner image by a developing device using a two-component developer having toner and carrier.

  An image forming apparatus of the above type configured as a copying machine, a printer, a facsimile, or a complex machine thereof has a large number of image forming elements such as the above-described image carrier and developing device. The developing device contains a two-component developer, and the developing device has elements such as a developer carrying member for carrying and carrying the two-component developer for development. Each of these elements deteriorates with time, and finally becomes unusable. For this reason, normally, when these elements become unusable or just before that, they are replaced with new ones. This replacement time is the life of each element.

  Thus, in this type of image forming apparatus, it is necessary to replace each element when it reaches the end of its life. However, if each element is replaced every time it reaches the end of its life, The replacement work must be performed frequently, which is very troublesome.

  In view of this, an image forming apparatus has been proposed which is configured such that a plurality of elements constituting the image forming apparatus have their lifetimes set at the same time and can be replaced with new ones at the same time. However, conventionally, no special consideration has been given to the relationship between the life of the two-component developer carrier and the life of other elements. Therefore, when the carrier of the developer deteriorates, this has been replaced by a new one. I had to exchange it for something.

  The present invention has been made based on the above-described novel recognition, and an object of the present invention is to propose an image forming apparatus capable of avoiding the troublesome work of exchanging carriers alone.

  In order to achieve the above object, the present invention uses an image carrier on which an electrostatic latent image is formed, and the electrostatic latent image formed on the carrier using a two-component developer having a toner and a carrier. A developing device that visualizes the toner image, and the developing device includes a developer carrying member that carries and conveys a two-component developer used for development. An image forming apparatus for obtaining a recorded image by transferring a formed toner image onto a transfer material, wherein the life of the image carrier and the life of the carrier of the two-component developer are matched. A forming apparatus is proposed.

  At that time, the image carrier and the developer carrying member are assembled in a unit case to form an image forming unit, and the two-component developer is formed in a part of the unit case. Containment is advantageous.

  In order to achieve the above object, the present invention also provides an image carrier on which an electrostatic latent image is formed, a charging device for charging the carrier to form an electrostatic latent image on the carrier, and an image carrier. A developing device that visualizes the electrostatic latent image formed on the body as a toner image using a two-component developer having toner and carrier, and transfers the toner image formed on the image carrier to a transfer material And a cleaning device provided with a cleaning member that removes toner remaining on the surface of the image carrier from the surface, and the developing device carries and conveys a two-component developer used for development. In an image forming apparatus having a developer carrying and conveying member that transfers a toner image formed on the image carrier to a transfer material to obtain a recorded image, the life of the image carrier and the life of the charging device The carrier life of the two-component developer, and We propose an image forming apparatus, characterized in that all is matched with the life of the cleaning member.

  At that time, the image carrier, the charging device, the developer carrying member, and the cleaning member are assembled in a unit case to form an image forming unit, and the two-component developer is placed in the unit case. It is advantageous to accommodate in a developer case constituted by a part of the above.

  At that time, it is particularly advantageous to provide a toner recycling device for conveying the toner removed from the image carrier by the cleaning device to the developing device so that the toner can be reused in the developing device.

  Similarly, in order to reuse the toner removed from the image carrier by the cleaning device in the developing device, a toner recycling device for transporting the toner from the cleaning device to the developing device is provided, and a toner transport path of the toner recycling device is provided. It is particularly advantageous if it is constituted by a part of the unit case.

  According to the image forming apparatus of the first aspect, since the developer carrier and the image carrier can be exchanged together, the operation can be simplified and the maintenance cost can be greatly reduced.

  According to the image forming apparatus of the present invention, when the carrier of the developer and the image carrier have reached the end of their lives, the economic burden on the user can be reduced even if the entire image forming unit is replaced with a new one. it can.

  According to the image forming apparatus of the third aspect, since the lifetimes of the image carrier, the charging device, the carrier, and the cleaning member are all the same, the replacement operation of the elements of the image forming apparatus can be performed more efficiently. It can be carried out.

  According to the image forming apparatus of the fourth aspect, when each element reaches the end of its life, even if the entire image forming unit is replaced with a new one, a great economic burden is not imposed on the user.

  According to the image forming apparatus of the fifth or sixth aspect, the above effect can be further ensured.

  Embodiments of an image forming apparatus according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a vertical sectional view of an image forming unit 1 attached to an image forming apparatus main body (not shown), and FIG. 2 is an external perspective view of the image forming unit. The image forming unit 1 is detachably attached to the image forming apparatus main body. In this example, the image forming unit 1 is pushed into the image forming apparatus main body in the direction indicated by an arrow A in FIG. 1 is loaded and set at a predetermined position in the main body of the image forming apparatus shown in FIG. 1, and the image forming unit 1 can be taken out from the main body of the image forming apparatus by pulling out the image forming unit in the direction opposite to the arrow A. . The image forming apparatus is configured as, for example, a copying machine, a printer, a facsimile, or a complex machine thereof.

  As shown in FIGS. 1 and 2, the image forming unit 1 includes a unit case 2 and various image forming elements to be described later incorporated in the unit case 2. The unit case 2 shown as an example in FIG. 3, a case cover 4 attached to the upper portion thereof, a developing case cover 5 constituting an upper wall of a developing device to be described later, an upper wall of a toner transport path of a toner recycling device to be described later, and an upper wall of the developing device The case cover 4, the developing case cover 5, and the upper cover 6 are detachably locked to the case body 3 by a snap fit (so-called patching stop). ing. The opening 102 (FIG. 2) formed in the developing case cover 5 is closed by an agent cartridge 81 (FIG. 1) not shown in FIG.

  3 is an external perspective view showing a state when the case cover 4, the developing case cover 5, and the upper cover 6 shown in FIGS. 1 and 2 are removed from the case body 3, and FIG. FIG.

  Inside the unit case 2, a drum-shaped photoconductor 7 as an example of an image carrier on which an electrostatic latent image is formed and a charging roller 8 as an example of a charging device are rotatably assembled. The charging roller 8 extends parallel to the photoreceptor 7. In FIG. 3, the charging roller 8 is shown in a state of being separated from the photoreceptor 7.

  During the image forming operation, the photoconductor 7 is rotationally driven in a clockwise direction in FIG. 1 by a driving device (not shown). At this time, the discharging light L1 from the discharging device (not shown) supported by the image forming apparatus main body is The light enters the unit case 2 through the opening 34 formed in the case cover 4 and irradiates the surface of the photoconductor 7. Thereby, the surface potential of the photoconductor 7 is averaged to a reference potential of, for example, 0 to −150V. On the other hand, the charging roller 8 is in pressure contact with the surface of the photoconductor 7 and is driven to rotate by the rotation of the photoconductor 7 to uniformly charge the photoconductor 7 so that the surface potential is about −1100 V, for example. . At this time, a predetermined voltage is applied to the charging roller 8 by a power source (not shown).

  As described above, the surface portion of the photoconductor 7 charged to a predetermined polarity is irradiated with the light-modulated laser beam L2 in the exposure unit 9. The laser light L2 is emitted from an exposure optical system (not shown) supported by the image forming apparatus main body, and enters the unit case 2 through an opening 35 formed in the case cover 4. By such exposure, a predetermined electrostatic latent image is formed on the photoreceptor 7. For example, the surface potential of the photosensitive member portion (image portion) irradiated with the laser beam L2 is 0 to −290V, and the surface potential of the photosensitive member portion (background portion) not irradiated with the laser beam L2 is −1100V described above. Maintain approximately front and back. It is also possible to illuminate a document (not shown) and form a reflected light image on the photoconductor 7 to form an electrostatic latent image.

  On the other hand, the developing sleeve 11 (not shown in FIG. 3) of the developing device 10 is rotatably supported by the unit case 2 as shown in FIGS. 1 and 4, and this sleeve 11 is shown in FIG. Is driven to rotate counterclockwise. Further, a developing case 12 of the developing device 10 is constituted by a part of the case main body 3 in the unit case 2 and the developing case cover 5 covering the upper part, and a developer chamber 90 is defined in the developing case 12. In the developer chamber 90 of the developing case 12, a powdery two-component developer 101 (FIG. 1) having toner and carrier is accommodated. A plurality of magnets are arranged immovably.

  When the developing sleeve 11 rotates as described above, the developer 101 in the developing case 12 is transported while being carried on the developing sleeve 11 by the magnetic force of the magnet 13, and is transported by the agent regulating member including the doctor blade 14. The amount of developer applied is regulated. The regulated developer is carried to the development region between the developing sleeve 11 and the photosensitive member 7, and at this time, a developing bias voltage of, for example, about −800 V is applied to the developing sleeve 11. The toner in the conveyed developer is electrostatically transferred and attached to the image portion on the photoconductor 7, and a predetermined toner image is formed on the photoconductor 7. The electrostatic latent image formed on the photoreceptor 7 is visualized as a toner image.

  As described above, the developing device 10 is used to visualize the electrostatic latent image formed on the image carrier made of the photoreceptor 7 as a toner image using the two-component developer 101 having the toner and the carrier. The developing sleeve 11 constitutes an example of a developer carrying / conveying member that carries and conveys the two-component developer 101 used for development.

  On the other hand, as shown in FIG. 1, a transfer roller 15, which is an example of a transfer device, is rotatably supported on the image forming apparatus main body so as to face the photoreceptor 7. Further, a sheet feeding device (not shown) is provided on the image forming apparatus main body side, and from this sheet feeding device, a transfer sheet 100 as an example of a transfer material is provided with a photoreceptor 7 and a transfer roller as indicated by an arrow B in FIG. 15 is conveyed toward the transfer unit 22. The transfer paper 100 passes through the transfer unit 22 between the photoconductor 7 and the transfer roller 15 in a state where the front end of the transfer paper 100 and the front end of the toner image formed on the photoconductor 7 coincide with each other. At this time, the transfer roller 15 rotates counterclockwise in FIG. 1 while being in contact with the photoconductor 7 via the transfer paper 100, and a transfer bias voltage is applied to the transfer roller 15. 7 is transferred to the transfer paper 100.

  The transfer paper 100 that has left the photoconductor 7 is conveyed to a fixing device (not shown) as indicated by an arrow B1 in FIG. 1, where the toner image is transferred onto the transfer paper 100 by the action of heat and pressure. It is fused and fixed. On the downstream side of the transfer unit 22 in the conveyance direction of the transfer paper 100, a static elimination needle 16 supported by the image forming apparatus main body is disposed. The static elimination needle 16 is made of a thin metal plate extending in parallel with the photoconductor 7, the portion of the static elimination needle 16 on the side facing the photoconductor 7 is formed in a sawtooth shape, and the tip of each tooth has an acute angle. . A voltage is applied to the charge removal needle 16 from a power source (not shown), thereby removing the charge from the transfer paper 100 to facilitate separation of the transfer paper 100 from the photoreceptor 7.

  An intermediate transfer member may be used as a transfer material, and the toner image on the photosensitive member may be primarily transferred to the intermediate transfer member, and then the toner image may be secondarily transferred to a transfer sheet as a final transfer material. it can.

  Residual toner adhering to the photoreceptor 7 after the toner image is transferred is scraped off from the surface of the photoreceptor 7 by the cleaning blade 18 of the cleaning device 17 shown in FIG. In this way, the surface of the photoconductor 7 is cleaned, and the next image forming operation starts again. The cleaning device 17 has a cleaning case 19 constituted by a part of the case body 3 in the unit case 2, and the toner scraped off by the cleaning blade 18 is transferred to the toner conveying member 20 disposed in the cleaning case 19. It is discharged out of the cleaning device 17 by rotation, and is reused in the developing device 10 as will be described later. The toner conveying member 20 is configured in an appropriate form such as a toner conveying screw or a toner conveying coil. The cleaning blade 18 is an example of a cleaning member that removes toner remaining on the surface of the photoreceptor 7 from the surface and cleans the surface, and is fixedly held on the case body 3 as will be described later. ing.

  As described above, the illustrated image forming apparatus transfers the toner image formed on the image carrier made of the photoconductor 7 onto the transfer paper 100 conveyed toward the image carrier to obtain a recorded image. The image forming unit configured to be detachably attached to the main body of the image forming apparatus has at least one image forming element including the image carrier described above assembled in a unit case. In this example, the image forming unit 1 is configured by assembling the constituent elements of the photoreceptor 7, the charging roller 8, the developing device 10, and the cleaning device 17 to the unit case 2.

  Here, in order to correctly convey the transfer paper 100 toward the photoreceptor 7, it is necessary to provide a guide portion for guiding the transfer paper 100. For this reason, the image forming apparatus shown in FIG. 1 is provided with upper and lower guide parts 23 and 24 for guiding the transfer paper 100 conveyed to the transfer part 22. The lower guide portion 24 is constituted by a guide member fixed to the image forming apparatus main body, and this guide member also serves to guide the transfer paper 100 that has left the transfer portion 22 in the direction of the arrow B1.

  Here, the upper guide portion 23 can also be constituted by a guide member fixed to the image forming apparatus main body. However, in this case, in addition to the lower guide member, the upper guide portion 23 is also configured. However, it must be provided as an independent member in the main body of the image forming apparatus, which increases the number of parts and increases the cost.

  Therefore, in the image forming apparatus of this example, the lower part of the unit case of the image forming unit 1 attached to the main body of the image forming apparatus, and the lower part of the case main body 3 in the example shown in FIG. The upper guide part 23 to be regulated is configured. The unit case 2 of the image forming unit 1 is positioned with respect to the image forming apparatus main body so that the lower part of the unit case constitutes the guide portion 23. The guide portion 23 is located above and spaced apart from the lower guide portion 24, and is located at a site upstream of the transfer portion 22 in the conveyance direction of the transfer paper 100. This is used to guide the transfer paper 100 conveyed to the head.

  As described above, since the guide portion 23 for guiding the transfer paper 100 is constituted by the unit case itself, it is not necessary to provide an independent member as the upper guide portion, and the number of parts of the image forming apparatus is reduced and its cost is reduced. Can be achieved.

  FIG. 5 is a perspective view showing the case main body 3 of the unit case 2 constituting the image forming unit 1 upside down from the state shown in FIG. As can be seen from this figure, a part of the photoreceptor 7 protrudes outward from the unit case 2 from the notch 25 formed in the unit case 2, in this example, the bottom wall 21 of the case body 3. In addition, the arrow B in FIG. 5 indicates the conveyance direction of the transfer paper 100 sent toward the transfer unit 22 (FIG. 1), as with the arrow B in FIG. Further, symbol W indicates a sheet passing area through which the transfer paper 100 passes, and the transfer paper 100 having the maximum width also passes through this area W.

  In this example, as shown in FIG. 1 and FIG. 5, a guide portion 23 constituted by a lower part of the unit case protrudes from the bottom wall 21 of the case body 3 in the unit case 2 and conveys the transfer paper 100. The guide ribs 26 extend along the direction B. These ribs 26 are separated from each other in a direction orthogonal to the transfer direction B of the transfer paper 100 and are provided in a sheet passing area W through which the transfer paper 100 passes. The size of the transfer paper 100 can be reliably guided.

  Instead of the guide rib 26 described above, a guide surface for guiding the transfer paper 100 conveyed to the transfer portion 22 may be configured by a flat surface at the bottom of the unit case, for example, the lower surface of the bottom wall 21, If the surface is flat, the transfer paper 100 may be brought into close contact with the flat guide surface due to the electrostatic force of the transfer paper 100, and the transferability of the transfer paper 100 may be reduced. When such a decrease in transportability occurs, the toner image transferred onto the transfer paper 100 may be stretched or shrunk, resulting in an abnormal image. Further, when toner adheres to the guide portion formed of a flat plane, the adhesion area becomes large, so that a large amount of adhering toner may be reattached to the leading edge of the transfer paper and the transfer paper may be markedly stained.

  On the other hand, when the guide portion 23 is constituted by the guide rib 26 and the transfer paper 100 is guided by the free edge of the guide rib 26 as in the example shown in FIGS. Even if the transfer paper 100 comes into contact with the transfer paper 100, the contact area becomes extremely small, so that the transfer paper 100 can be prevented from coming into close contact with the guide portion 23 by electrostatic force, and the occurrence of an abnormal image can be prevented. Moreover, even if the toner adheres to the guide portion 23 constituted by the free edge of the guide rib 26, the contact area between the guide portion 23 and the transfer paper 100 is small, so that a large amount of toner adheres to the transfer paper 100. It is possible to prevent the transfer paper 100 from being significantly soiled by the toner.

  Further, as shown in FIGS. 1 and 5, the transfer paper 100 is placed on the lower part of the unit case 2 other than the paper passing area W through which the transfer paper 100 passes, in the example shown in the lower part of the case body 3. A protrusion 27 is provided that protrudes outward (downward in FIG. 1) from the guide portion 23. A protrusion 27 is provided at the lower portion of the unit case 2 that does not obstruct the transfer of the transfer paper 100. In the example of FIGS. 1 and 5, protrusions 27 formed integrally with the case body 3 are provided on both outer sides of the sheet passing width range of the transfer paper 100 guided by the guide portion 23, and a total of four protrusions 27 are provided. A protrusion 27 is provided. The height H at which these protrusions 27 protrude from the bottom wall 21 of the unit case 2 is higher than the height h at which each guide rib 26 protrudes from the bottom wall 21.

  Here, when the image forming unit 1 is taken out from the main body of the image forming apparatus as described above, the unit 1 is placed on a mounting surface such as a flat floor surface or a desk surface with the lower side of the unit case facing downward. Placed. At this time, since the projecting portions 27 projecting outward from the guide portion 23 are provided at the lower portion of the unit case 2, these projecting portions 27 come into contact with the placement surface. That is, the guide part 23 existing between the protrusions 27, in this example, the free edge of the guide rib 26 does not contact the placement surface.

  According to the above configuration, even if foreign matter exists on the placement surface, there is no possibility that the foreign matter adheres to the guide portion 23 or the guide portion 23 is damaged by the foreign matter. Therefore, even if the image forming unit 1 is loaded and used again in the image forming apparatus main body as it is, no foreign matter adheres to the transfer paper 100, and the guide unit 23 functions to guide the transfer paper 100 without hindrance. be able to. Even if foreign matter on the mounting surface adheres to the projection 27 or the projection 27 is slightly damaged by the foreign matter, when the image forming unit 1 is set on the main body of the image forming apparatus, the projection Since 27 is located outside the paper passing area W through which the transfer paper 100 passes, there is no possibility that the transfer of the transfer paper 100 is hindered.

  In FIG. 5, the protrusions 27 are provided on both sides of the transfer paper 100 to be conveyed. Good. FIG. 6 shows the unit case outer side of the guide portion 23 composed of the guide ribs 26 on both sides of the transfer paper to be conveyed and the portion of the unit case bottom wall 21 upstream of the sheet passing area W in the transfer paper conveyance direction. The example which provided the protrusion 27 which protruded in each is shown.

  The protrusion height H from the bottom wall 21 of the protrusion 27 shown in FIGS. 1, 5 and 6 is such that when the image forming unit 1 is placed on the placement surface, the photoconductor 7 is also placed on the placement surface. The size is set so as not to touch.

  Next, in order to understand the present invention, each apparatus constituting the illustrated image forming apparatus and each component will be described in more detail.

  First, the photoconductor 7 illustrated in FIG. 1 is composed of a laminated OPC photoconductor, and FIG. 7 is a schematic enlarged view of the cross-sectional structure thereof. 7 includes a charge generation layer (CGL) 29 having a thickness of 0.1 to 1 μm and a charge transfer layer (CTL) having a thickness of 10 to 30 μm on a conductive substrate 28. ) 30 are sequentially stacked, and the charge generation layer 29 and the charge transfer layer 30 constitute a photosensitive layer 31. The laser light L2 incident on the photosensitive member 7 is transmitted through the light-transmitting charge transfer layer 30 and absorbed by the charge generation layer 29, and carriers are generated by the excitation energy in the charge generation layer 29. The generated carriers are injected into the charge transfer layer 30 by an external field force, move through the charge transfer layer 30, reach the surface of the photoreceptor, and neutralize the surface charge. The charge transfer layer 30 shown in FIG. 7 is of a hole transport type and shows a state when it is negatively charged.

  Next, the charging roller 8 shown in FIGS. 1 and 3 constitutes an example of a charging device that charges the carrier so as to form an electrostatic latent image on the image carrier. Has a configuration in which conductive rubber is wound around the outer peripheral surface of a metal core, and contacts the surface of the photoconductor 7 when the photoconductor 7 is charged. The charging roller 8 is supported at its longitudinal ends at only one end by a bearing 33a shown in FIG. 3 so that the bearing 33a extends in parallel to the charging roller 8. Along with the charging roller 8, each end portion 33 in the longitudinal direction is supported so as to be movable within a predetermined range in a direction approaching or separating from the photoreceptor 7. A cleaning pad 32, which is an example of a charging roller cleaning member that extends long along the charging roller 8, is attached to the surface of the charging roller case 33 that faces the charging roller 8.

  A first compression spring (not shown) is press-fitted between each of the bearings 33 a described above and each end portion in the longitudinal direction of the charging roller case 33, so that each bearing 33 a approaches the photoreceptor 7. The charging roller 8 can be brought into pressure contact with the surface of the photoreceptor 7. Further, the charging roller case 33 is also formed in the case body 3 of the unit case 2 at each end in the longitudinal direction of the case 33 so that the charging roller case 33 can move in a direction approaching or separating from a predetermined range with respect to the surface of the photoreceptor 7. Each notch 36 (only one is shown in FIG. 3) is assembled. The charging roller case 33 is prevented from coming out of the case body 3 by the case cover 4 (FIGS. 1 and 2). Further, a second compression spring 37 (only one of which is shown in FIG. 3) is provided between the case main body 3 and each end portion in the longitudinal direction of the charging roller case 33. The charging roller case 33 is urged in a direction away from the surface of the photoreceptor 7.

  The case cover 4 serves as a protective cover for preventing the human hand from touching the photoconductor 7 and the charging roller 8. In addition, as described above, the case cover 4 is urged by the second compression spring 37. The charged charging roller case 33 also serves as a stopper that prevents the charging roller case 33 from being detached from the case body 3. Thereby, it is not necessary to provide an independent stopper member for the charging roller case 33, and the configuration can be simplified.

  On the other hand, as shown in FIG. 1, the image forming apparatus main body is provided with an electromagnetic clutch 39 for controlling the rotation of the cam 38. The cam 38 is fixed to the rotating shaft of the electromagnetic clutch 39, and the electromagnetic clutch 39 is rotated once. It is comprised so that it may rotate 120 degree | times by operation | movement. One end 41a of a swing arm 41 swingably supported by the image forming apparatus main body via a pivot pin 40 is pressed against the cam 38 by the action of a spring (not shown). 41 b contacts the upper surface of the charging roller case 33 through the opening 34 of the case cover 4. The upper surface of the charging roller case 33 is in pressure contact with the other end 41 b of the swing arm 41 by the pressurizing action of the second compression spring 37 described above.

It occupies a rotational position in which the cam 38 is shown in FIG. 1, when the cam surface portion indicated by reference numeral a ₁ is hitting one end 41a of the swing arm 41, the charging roller case 33 is also shown in FIG. 1 position At this time, the charging roller 8 is brought into pressure contact with the surface of the photosensitive member 7 by the pressing action of the first compression spring, and the voltage applied to the core of the charging roller 8 is photosensitive as described above. The body 7 is charged to a predetermined polarity.

As described above, the charging roller 8 is kept in contact with the surface of the photoconductor 7 during the charging operation for charging the photoconductor 7, so that the charging roller 8 is soiled by the minute toner adhering to the photoconductor 7. There is a risk of uneven charging on the photoreceptor 7. For this reason, in the image forming apparatus of this example, the electromagnetic clutch 39 is actuated and the cam 38 rotates 120 ° at an appropriate time other than during the charging operation by the charging roller 8, and the cam surface portion indicated by symbol a ₂ in FIG. Is in pressure contact with one end 41 a of the swing arm 41. Thereby, the other end 41 b of the swing arm 41 presses and moves the charging roller case 33 in a direction approaching the surface of the photoreceptor 7. At this time, the charging roller 8 remains in pressure contact with the surface of the photoconductor 7, so that the cleaning pad 32 is in pressure contact with the peripheral surface of the charging roller 8. At that time, the charging roller 8 rotates following the rotation of the photosensitive member 7, and the cleaning pad 32 cleans the peripheral surface of the charging roller 8. In this way, the charging operation to the photoconductor 7 is prevented while the charging roller 8 is contaminated with toner, and uneven charging of the photoconductor 7 can be prevented.

When the operation of the image forming apparatus is stopped, the surface of the cam 38 indicated by reference numeral a ₂ in FIG. 1 is pressed against the one end 41 a of the swing arm 41 by the operation of the electromagnetic clutch 39. As a result, the other end 41b of the swing arm 41 is lifted upward from the state shown in FIG. 1, and the charging roller case 33 moves away from the photoreceptor 7 by the action of the second compression spring 37 described above. . As a result, the charging roller 8 is also separated from the surface of the photoreceptor 7. If the charging roller 8 remains in contact with the photoconductor 7 for a long time in the operation stop state of the image forming apparatus, the photoconductor 7 may be contaminated and an abnormal image may be generated. In the apparatus, as described above, when the operation is stopped, the charging roller 8 is separated from the photoconductor 7 to prevent an abnormal image from being generated during the image forming operation.

  A charging device comprising a corona discharger can be used in place of the charging roller 8, but when the charging roller 8 is employed as in this example, the ozone generation amount when the corona discharger is used is reduced to 1/100 to 1 / It is possible to suppress the number to 1000, which eliminates the need to attach an ozone processing member to the image forming apparatus main body.

Next, the charging mechanism by the charging roller 8 will be described. FIG. 8 is a charging model diagram schematically showing the photosensitive member 7 and the charging roller 8, and FIG. 9 shows an equivalent circuit of the charging model. Here, Va is a voltage applied to the core metal at the center of the charging roller 8, Vr is a voltage applied to the charging roller 8, Vg is a discharge start voltage in the gap 42 near the contact portion between the charging roller 8 and the photoconductor 7, When the surface potential of the photoreceptor 7 is Vd, these relationships are
Va = Vr + Vg + Vd (1)
It is expressed as Here, the voltage Vr applied to the charging roller 8 is represented by R as the resistance value of the charging roller 8 and I as the flowing current value.
Vr = IR (2)
The discharge start voltage Vg in the gap is expressed as follows, where d is the thickness of the photosensitive layer 31 of the photoreceptor 7 and Kd is the relative dielectric constant of the photosensitive layer 31.
Vg = 312 + 6.2 × d / Kd + √ (7737.6 × d / Kd) (3)
It is represented by The surface potential Vd of the photosensitive member is represented by Q as the charge supplied to the photosensitive member 7 and C as the electrostatic capacity of the photosensitive layer 31.
Vd = Q / C (4)
It becomes. Here, if the peripheral speed of the photosensitive member 7 is Vp, the length of the charging roller 8 is L, and its dielectric constant is Ko,
Q = I / L · Vp C = (Ko · Kd) / d
Vd = (I · d) / (Ko · Kd · L · Vp) (5)
Therefore, equation (1) is
Va = I · R + 312 + 6.2 × d / Kd + √ (7737.6 × d / Kd)
+ (I ・ d) / (Ko ・ Kd ・ L ・ Vp) (6)
It becomes. The above is the charging model type.

  Next, considering a charging control method by the charging roller 8, either a constant voltage control method or a constant current control method can be adopted as this method.

  The constant voltage control method is a control method in which Va in equations (1) and (6) is constant. In this case, it is the term of Vd that is actually used as the charging potential of the photoreceptor 7 in the equation (1). Therefore, when Vr and Vg change, Vd is affected. Here, looking at each term, the resistance value of the charging roller 8 is a variation factor in the term Vr. Accordingly, when the resistance value of the charging roller 8 increases due to environmental fluctuations, the Vr value increases and Vd decreases. Therefore, in order to suppress this influence, it is necessary to provide temperature detection means and correct Va. In addition, since the charging roller resistance value significantly increases at low temperature and humidity, it is desirable to provide a heater or the like (not shown) so as not to be below a certain temperature.

Next, in the term of Vg, it is affected by the film thickness d of the photosensitive layer 31, but when a numerical value is actually substituted and d = 28 μm at the beginning and 4 μm is decreased over time, Kd = 3.2 is calculated. Vg (28) = 626 and Vg (24) = 599, and the difference is 27V. Because of this change, the influence on the charging potential (usually 800 to 1000 V) is considered to be small. Since the value of the current flowing at the charging roller resistance value fluctuation is small, if the charging roller resistance value is suppressed to a low value (for example, 10 ⁷ Ω or less), the influence on Vd can be reduced. .

  In the case of the constant current method, it is a control method in which I is constant in equation (6), and is not affected by the terms Vr and Vg. However, the effect of the change in the photosensitive layer thickness d in the term Vd directly affects Vd, and when the initial 28 μm shown in the above example is changed by 4 μm over time, Vd becomes a value of Vd × 24/28 over time. If Vd is initially set to 850 V, it becomes 728 V over time and drops by 100 V or more, and there is a possibility that the charging performance cannot be guaranteed. In order to prevent this, a change in the film thickness of the photosensitive layer 31 may be detected and corrected. However, in practice, such a detection mechanism is expensive and cannot be mounted very much. Therefore, it is difficult to take countermeasures at present except that the surface of the photoconductor is raised and a photoconductor that does not wear is used.

  For the above reasons, in this example, the applied voltage correction for the resistance fluctuation of the charging roller 8 is required, but the constant voltage control method is adopted. As the temperature detection means of the charging roller 8, a thermistor 43 attached to the case cover 4 is used as shown in FIG. The thermistor 43 detects the surface temperature of the charging roller 8 and sends a signal to a circuit for correcting the applied voltage corresponding to the change in electrical resistance due to the temperature change of the charging roller 8. The thermistor 43 is provided at a position in contact with the charging roller 8 when the charging roller 8 is separated from the surface of the photoreceptor 7.

  As described above, since the thermistor 43 is attached to the case cover 4, it is not necessary to provide a separate attachment member for the thermistor, and the configuration of the image forming apparatus, particularly the image forming unit 1 can be simplified. . Further, when the charging roller 8 is separated from the photosensitive member 7, that is, when no voltage is applied to the charging roller 8, the thermistor 43 contacts the peripheral surface of the charging roller 8 and can detect the temperature of the roller 8. Therefore, there is no possibility that the thermistor 43 is broken due to the influence of the voltage applied to the charging roller 8.

  Next, the developing device 10 will be described. As described above with reference to FIGS. 1, 3, and 4, the developing case 12 contains a two-component developer 101 having a carrier and toner made of, for example, small iron balls, and this developer. 101 is agitated while being circulated and conveyed in the developer chamber 90 of the developing case 12 by first and second agent agitating members 44 and 45 which will be described in detail later, and is supplied to the developing sleeve 11. As described above, the layer thickness of the developer supplied to the developing sleeve 11 is regulated by the doctor blade 14 provided around the developing sleeve 11. A portion of the peripheral surface of the developing sleeve 11 that faces the photoconductor 7 is exposed from the developing case 12 to the outside.

  Here, the developing sleeve 11 is made of a non-magnetic cylindrical body made of aluminum having an outer diameter of, for example, 16 to 20 mm, and its peripheral surface is formed smoothly or in order to improve developer transportability. Concavities and convexities such as V-grooves are formed on the outer peripheral surface of 11, for example.

  As shown in FIG. 4, a shaft 46 passes through the developing sleeve 11, and the magnet 13 is fixed to the shaft 46. An end 46a on the near side of the shaft 46 is fixed and supported to the case body 3 of the unit case 2 as described later, and an end 46b on the back side is fitted and fixed to the back end of the developing sleeve 11. The sleeve end member 47 is fitted through a bearing so as to be relatively rotatable. The shaft portion 47a of the sleeve end member 47 is rotatably supported by the case body 3 of the unit case as will be described later. The front end of the developing sleeve 11 is rotatably supported on the shaft 46 via a bearing. The “back side” and “front side” referred to here are based on the direction in which the image forming unit 1 is attached to and detached from the main body of the image forming apparatus.

  As described above, the shaft 46 is supported together with the magnet 13 so as not to move with respect to the unit case 2, and the developing sleeve 11 is rotatably supported on the shaft 46. The sleeve end member 47 is rotationally driven through a coupling 48 attached thereto and a coupling 49 (FIG. 2) on the image forming apparatus main body side engaged therewith, whereby the developing sleeve 11 is illustrated. 1 is rotated counterclockwise. The bias voltage to the developing sleeve 11 is applied from the image forming apparatus main body side via the couplings 48 and 49 described above.

FIG. 10 is an explanatory diagram showing the relationship between the developing sleeve 11, the magnet 13 disposed so as not to rotate therein, and the photoconductor 7. As shown here, the individual magnets of the magnet 13, that is, the first to fifth magnets 13a to 13e are arranged in the circumferential direction of the developing sleeve 11 and are fixedly fixed to the shaft 46, respectively. It extends in the longitudinal direction. Then, in the circumferential direction of the developing sleeve 11 by the magnets 13a to 13e, magnetic field distribution _{P 1} through _{P 6} of the normal direction is formed.

  The first magnet 13a substantially opposes the photoconductor 7, and the magnetic force distribution has a peak above the line connecting the centers of the photoconductor 7 and the developing sleeve 11 by θ = 3 ° to 10 °. . The peak magnetic flux density is 80 to 100 (mT millitesla). If the peak magnetic flux density is too small, the developer carrier cannot be held on the developing sleeve 11 and the developer is scattered. On the other hand, if the size is too large, the toner developed on the photosensitive member 7 is likely to be traced in the circumferential direction, and the toner adhering to the low potential portion of the photosensitive member 7 is again collected by the developing sleeve 11. Sometimes. If the angle θ is too large, the developing ability is lowered.

Magnetic field distribution _{P 2} of the second magnet 13b has a peak magnetic flux density of 50 to 80 (mT) in the vicinity of the opening portion of the developing casing 12. This magnetic force has a function of transporting the developer into the developing case 12 and carrying air in the vicinity of the lower side of the developing case 12 into the developing case 12. As a result, toner scattering outside the developing case 12 can be prevented. In order to increase the efficiency of air transportability, the shape of the developing case portion 12a corresponding to the peak magnetic flux density portion may be slightly expanded in a direction away from the developing sleeve 11. As a result, the developer ears can be formed smoothly.

Third magnet 13c forms a magnetic field distribution _{P 3,} conveys the developer to the developing case 12 by the magnetic force, in cooperation with the fourth magnet 13d, magnetic field distribution _{P 4} (magnetic flux density 10mT or less ). As a result, the developer that has been subjected to development is separated from the developing sleeve 11.

  The magnetic force of the fourth magnet 13d serves to hold the developer supplied by the second agent stirring member 45 (FIG. 4), which will be described in detail later, on the developing sleeve 11. By reducing the magnetic flux density in the region of the doctor blade 14 and passing the developer in a state of being in close contact with the developing sleeve 11, the layer thickness of the developer can be regulated stably.

The fifth magnet 13e, together form a magnetic field distribution P _6, the developer held by the magnetic force of the fourth magnet 13d carrying the region of the first magnet 13a, but to stabilize the developer, the developing sleeve 11 In order to control the air flow in the vicinity, the peak magnetic flux density of the magnetic force distribution P ₆ is set so that an inlet seal 50 (described later) and the developer come into contact with each other.

The gap Gp between the developing sleeve 11 and the photosensitive member 7 is determined by the relationship between the developing sleeve 11 and the gap Gd between the doctor blade 14 and
Gp = Gd × (0.8 to 1.0) and Gp−Gd = (0 to 0.15) mm.

When the peripheral speed of the developing sleeve 11 is vs (mm / sec) and the peripheral speed of the photosensitive member 7 is vp (mm / sec), the relationship between them is as follows.
vs = (1 to 2.5) × vp

  As shown in FIGS. 4 and 11, the shaft portion 47 a of the sleeve end member 47 protruding from the back end portion of the developing sleeve 11 is rotatably fitted to the back support member 57, and the front end of the shaft 46 is The portion 46a is fitted to the front support member 58 so as not to be relatively rotatable. As shown in FIG. 11, these support members 57 and 58 are connected to the doctor blade 14 by screws 59 that are inserted into the long holes formed therein and screwed into the doctor blade 14. Therefore, if these screws 59 are loosened, the position of the doctor blade 14 can be adjusted with respect to the developing sleeve 11 in the substantially normal direction. After the adjustment, the screw 59 is tightened to fix the doctor blade 14 to the developing sleeve 11. A value obtained by moving the doctor blade 14 with respect to the developing sleeve 11 as described above and a gap between the two correspond one-to-one. Further, such adjustment work can be easily performed with the doctor blade 14 and the developing sleeve 11 removed from the developing device.

  As shown in FIGS. 3 and 4, the case body 3 of the unit case 2 has a front side outer plate 51 and a front side inner plate 52 on its front side, and a rear side outer plate 53 on its back side. A back side inner plate 54 is provided. The lower end edges of the front and rear side plates of the developing case cover 5 (FIGS. 1 and 2) are in contact with the upper end edges of the inner plates 52 and 54 of the case body 3, respectively. These inner plates 52 and 54 constitute the front and rear side plates of the entire developing case 12. As described above, the developing case 12 containing the two-component developer is constituted by a part of the unit case 2. As for the front and rear side plates of the developing case cover 5, only the side plates on the rear side are indicated by the reference numeral 5a in FIG.

  The photosensitive member 7 has flange members 86 and 87 fixed to respective ends in the longitudinal direction thereof, the front side inner plate 52 and the rear side outer side of the case body via the front side positioning plate 55 and the back side positioning plate 56. Each of the plates 53 is rotatably supported. Further, the front support member 58 fitted to the front end 46 a of the shaft 46 is also supported by the front inner plate 52 of the unit case 2 through the front positioning plate 55 so as not to rotate. Further, the shaft portion 47 a of the sleeve end member 47 is also rotatably supported by the back side outer plate 53 of the unit case 2 via the back side positioning plate 56. The back-side support member 57 is detachably fitted in the concave groove of the back-side inner plate 54.

  As described above, the photoconductor 7 and the developing sleeve 11 are supported by the unit case on the front side and the back side via the common positioning plates 55 and 56, respectively, thereby the distance between the centers of the developing sleeve 11 and the photoconductor 7. Is kept constant, and the gap Gp between the two is always kept constant.

  Further, as shown in FIG. 11, the inlet seal cover 60 is locked to the support members 57 and 58 on the rear side and the front side, and the cover 60 is also attached to the cover 60 as shown in FIGS. 1 and 10. The inlet seal 50 is attached. As shown in FIG. 1, the inlet seal cover 60 is located upstream of the developing region between the developing sleeve 11 and the photosensitive member 7, covers the upper portion of the developing sleeve 11, and regulates the developer on the developing sleeve. At the same time, the air flow is restricted. The inlet seal 50 is made of, for example, a thin resin such as PET or PUR, and prevents the toner from scattering out of the developing device 10.

  As shown in FIG. 11, side seals 61 and 62 made of a thin resin or the like are attached to the support members 57 and 58 on the back side and the near side, respectively, and these side seals 61 and 62 are attached to the developing sleeve 11. It faces the peripheral surface of each end in the longitudinal direction and prevents the toner and carrier from scattering from each end.

  Next, as shown in FIG. 4, the first and second stirring members 44 and 45 are composed of shafts 63 and 64 and a plurality of elliptic plates 65 and 66 fixed to the shafts 63 and 64. Has been. In FIG. 3, illustration of the elliptical plate is omitted for easy understanding of the drawing, but each of the elliptical plates 65 and 66 is formed in a shape in which the ellipse is partially cut out. Instead of the elliptical plate, the agitating members 44 and 45 can be configured by fixing screws to the shafts 63 and 64.

  The first agitating member 44 is rotatably supported at its ends in the longitudinal direction of the shaft 63 by the front support wall 67 and the back inner plate 54 in the case body 3 of the unit case 2, respectively. The shaft 64 of the agitating member 45 is rotatably supported at both ends in the longitudinal direction by the front inner plate 52 and the rear inner plate 54 of the unit case 2 via bearings. Further, drive gears 68 and 69 are supported at the rear end portions of the shafts 63 and 64 of the stirring members 44 and 45 so as not to rotate relative to the shafts, and are also driven by the sleeve end member 47. The gear 70 is fixed. These gears 70, 69, and 68 mesh with each other via an intermediate gear (not shown).

  Further, the case body 3 constituting the developing case 12 is provided with a partition wall 71 extending in parallel with the stirring members 44 and 45 in an area between the first and second stirring members 44 and 45. The front side and the back side of the partition wall 71 are cut out to form passages 71a and 71b, respectively.

  As described above, when the sleeve end member 47 is rotationally driven by the driving device on the image forming apparatus main body side, the developing sleeve 11 rotates, and the rotation of the sleeve end member 47 causes the drive gears 70, 69, 68 and the intermediate gear to rotate. Is transmitted to the first and second agitating members 44 and 45, and these members are rotationally driven in predetermined directions, respectively. As a result, the developer accommodated in the developer chamber 90 in the developing case 12 is conveyed while being stirred in the direction of the arrow X, and the developer is guided by the partition wall 71 and the passages 71a and 71b on both ends thereof. Circulate through. As a result, the toner and carrier of the developer are frictionally charged with different polarities. Such developer is supplied to the developing sleeve 11, and the developer from the developing sleeve 11 is returned to the stirring member side. Since each of the elliptical plates 65 and 66 has a shape in which a part of the ellipse is cut out, the developer agitating effect is enhanced by the developer hitting the edge of the cutout portion.

Here, when the pitch of the elliptic plates 65 and 66 in each of the stirring members 44 and 45 is P, and the minor axis of the ellipse is Y,
P = (1 / 3-4 / 5) × Y
It is desirable to satisfy If the pitch P is smaller than this, the developer conveying force decreases, so the number of rotations of the agitating members 44 and 45 increases, and the developer tends to deteriorate. Further, when the pitch P is larger than the above formula, the stirring performance with respect to the developer is lowered.

The rotation speeds of the first and second stirring members 44 and 45 are equal to each other, and the outer diameter Y and the pitch P of the respective elliptical plates 65 and 66 are also equal to each other. Further, the relationship between the peripheral speed v at the short diameter portion of each of the elliptic plates 65 and 66 and the peripheral speed vs of the developing sleeve 11 is as follows.
vs = (1.1 to 1.5) × v
It is desirable to satisfy.

  When the peripheral speed v of the elliptic plates 65 and 66 is higher than that expressed by the above formula, the stress on the developer increases, and conversely, when the peripheral speed v is low, it takes time to replace the developer on the developing sleeve 11. It takes a lot of time, and density unevenness occurs in the toner image formed on the photoreceptor 7.

  The gap between the elliptical plates 65 and 66 of the stirring members 44 and 45 and the partition wall 71 or the developing case wall is preferably 0.5 to 2 mm. If this gap is larger than this value, the developer cannot be reliably conveyed, and a staying developer is generated. If this gap is smaller than the above value, the developer is excessively applied to the partition wall 71 and the developing case wall. There is a risk of rubbing strongly and premature deterioration.

  Further, when the gap between the elliptical plate 66 of the second stirring member 45 and the developing sleeve 11 is set to 1.5 to 3 mm, the developer can be smoothly supplied to the developing sleeve 11, and the developer can be supplied from the developing sleeve 11. Can be collected smoothly. If the gap between the two is too large, the supply and recovery of the developer to the developing sleeve 11 are not sufficiently performed. Conversely, if the gap is too small, the developer is deteriorated due to stress and toner supply unevenness occurs.

  As shown in FIGS. 1 and 4, the developing case 12 is provided with a sensor for detecting the toner concentration of the developer 101, in this example, a magnetic permeability measuring sensor 72. Further, the toner bottle 73 shown in FIGS. 1 and 2 is detachably attached to the image forming apparatus main body.

  When the sensor 72 detects that the toner concentration of the developer 101 accommodated in the developer chamber 90 in the developing case 12 is equal to or lower than a reference value, the toner bottle 73 is opened by a toner replenishment signal based on the detection signal. The toner is formed by the case main body 3 through the opening 6a (FIG. 2) formed in the upper wall of the upper cover 6 from the supply port 73a of the toner bottle 73. The toner is supplied to the toner replenishing unit 75 (FIGS. 3 and 4).

  The toner bottle 73 containing the replenished toner has a spiral projection formed on the inner wall surface thereof, and the toner inside the toner bottle 73 is sequentially sent from the back side to the replenishment port 73a and replenished to the toner replenishing portion 75. The At this time, a hopper (not shown) for guiding the replenished toner is provided between the toner bottle 73 and the toner replenishing unit 75, so that the toner from the toner bottle 73 does not scatter and enters the toner replenishing unit 75. Supplied. The drive shaft 74 that rotates the toner bottle 73 is provided with an electromagnetic clutch (not shown). When a toner supply signal is output, the electromagnetic clutch is turned on and the drive shaft 74 for the toner bottle rotates.

  As shown in FIGS. 3 and 4, a shielding plate 76 made of a thin resin sheet in which a large number of small holes are formed between the toner replenishing portion 75 and the developer chamber 90 containing the two-component developer. In the toner replenishing portion 75, a toner feeding member 78 made of a thin resin sheet having a base end portion fixed to a shaft 77 is disposed. The gear 79 fixed to the shaft 77 has a first agitation. The gear 44 is engaged with a gear 80 fixed to the shaft 63 of the member 44. The diameter of the small hole formed in the shielding plate 76 is about 0.5 to 1 mm, for example. The shaft 77 is rotatably supported by the case body 3.

  As described above, when the first stirring member 44 is rotated, the rotation is transmitted to the shaft 77 through the gears 80 and 79, the toner delivery member 78 is rotated, and the tip portion thereof is in sliding contact with the shielding plate 76. As a result, the toner in the toner replenishing section 75 is fed into the developer chamber 90 provided with the stirring member 44 through the small hole of the shielding plate 76.

  As described above, the toner from the toner bottle 73 is once accumulated in the toner replenishing unit 75 and sent to the developer chamber 90 little by little through the small hole of the shielding plate 76. In both cases, the developer chamber 90 is replenished with a certain amount of toner. The toner supplied to the developer chamber 90 is agitated and mixed with the two-component developer existing therein by the agitating members 44 and 45.

  If the sensor 72 continues to detect a decrease in toner density even after the toner replenishing operation described above, it is assumed that the toner in the toner bottle 73 has run out, and a message indicating that the toner end is near is displayed on the display unit. To the user. If the toner bottle is not exchanged even though such a display is made, the operation of the image forming apparatus is stopped when the image forming operation for 50 sheets is performed on the A4 size transfer paper after the display. To do.

  The replacement operation of the toner bottle 73 is determined based on the opening / closing time of the front door (not shown) of the main body of the image forming apparatus. After the replacement of the toner bottle 73, the toner supply operation is performed for a predetermined time, and the detection voltage of the sensor 72 is a constant value. After confirming that the image forming apparatus has reached, the prohibition of operation of the image forming apparatus is released.

  As shown in FIG. 2, an opening 102 is formed in the developing case cover 5, and the developer cartridge 81 shown in FIG. 1 is mounted in the opening 102. When a new image forming unit 1 is shipped from a manufacturing factory or a store, the lower opening of the developer cartridge 81 is covered with a flexible seal member (not shown), and toner and carrier are placed inside the cartridge 81. A two-component developer is stored. At this time, there is no developer in the developer chamber 90.

  When the image forming unit 1 is delivered to the user, by rotating a roller (not shown), the sealing member is wound around the roller and the opening of the developer cartridge 81 is opened. As a result, the internal developer falls into the developer chamber 90 in the developing case 12. As described above, since the developer is sealed and stored in the developer cartridge 81 until the image forming unit 1 is delivered to the user, the developer is deteriorated due to moisture absorption during storage of the image forming unit 1. It is possible to prevent the developer from leaking out of the developing device.

  Next, the basic concept of the development mechanism using the two-component developer, particularly the magnetic brush development with the two-component developer focusing on the force acting on the toner will be described.

Regarding the developing electric field, the developing electric field formed between the photosensitive member 7 and the developing sleeve 11 shown in FIG. 10 is generally expressed by the following equation.
E = ε (Vd−Vb) / Gp (7)
E = Developing electric field (V / mm) ε: Dielectric constant of developer Vd: Image portion potential (V) of photosensitive member Vb: Developing bias voltage (V) Gp: Developing gap (gap between photosensitive member and developing sleeve) ( mm)
From formula (7), it can be seen that the development electric field can be controlled by the development bias voltage. Therefore, image density control is performed by changing the developing bias voltage and controlling the developing electric field.

Regarding the forces acting on the toner a) Adhesive force between the carrier of the developer and the toner FIG. The toner particle T exchanges several charges with the surface of the carrier C by contact and friction several times, has a negative charge of q, and a positive charge corresponding to the charge is on the carrier side. The adhesion force Ft at the contact point between the two consists of the Coulomb force due to the charge q and the short-range van der Waals force Fv, and is expressed as follows.
Ft = Fv + αq ² / 4πε ₀ r ² (8)
Here, r is the toner particle radius, ε ₀ is the dielectric constant of vacuum, and α is a constant (1 to 1.9) depending on the dielectric constant of the toner.

b) Model of Insulating Magnetic Brush Development In the two-component development, development is performed when the development driving force (electrostatic force) (q · E) acting on the toner particles becomes larger than the adhesion force with the carrier.
q · E> Fv + αq ² / 4πε ₀ r ² (9)
Equation (9) is easy to understand when described with reference to FIG. Here, a developing electric field such as E ₁ <E ₂ is shown, and a straight line represents each developing force. Development does not occur in the electric field of E ₁ , and qE ₂ above the Ft curve is between q ₁ and q ₂ , so that any toner having a charge in this range can be developed.

  The above is the description of the developing device 10 and the configuration related thereto, but in the conventional image forming unit in which at least the photosensitive member and the developing device are assembled, the developing device does not have a carrier and is a one-component system development. The mainstream was the use of agents. In this case, when the toner particles are adhered from the developing sleeve to the photosensitive member, there is no medium such as a carrier of the two-component developing method, so the developing sleeve needs to be close to the photosensitive member, and the distance is usually 0 to 0. .3mm is very small. Therefore, when the toner recycling as will be described later used in the present embodiment is performed and parts such as a waste toner tank are to be deleted, the recycled toner once adhered to the photosensitive member and collected by the cleaning device is not treated with paper dust. Therefore, if the gap between the photoconductor and the developing roller is narrow, foreign matters such as paper dust are caught in the gap, and abnormal images such as white stripes are likely to occur. Therefore, toner recycling is not suitable for the one-component development method. In some cases, toner recycling is performed by a one-component development method. In this case, the life of the image forming unit is as short as, for example, about 10K (K = 1000) sheets.

  In contrast, in this example, the development method is a two-component development method, so that the distance between the photoconductor 7 and the development sleeve 11 can be 0.5 mm or more. There is no occurrence of foreign matter such as powder, and the life of the image forming unit can be extended to the number of copies, for example, 30K or more. Therefore, compared with the one-component development method, the cost for using the carrier is increased, but the life of the image forming unit 1 is extended more than twice, so the total cost is reduced and the replacement interval of the image forming unit 1 is increased. Maintenance costs are also reduced.

  Next, the transfer device will be described. The transfer roller 15 shown in FIG. 1 is obtained by winding a conductive resin around a metal core, and is pressed together with the bearing toward the photosensitive member by a compression spring (not shown). A constant current is passed through the transfer roller 15 to transfer the toner on the photosensitive member to the transfer paper. The transfer roller 15 can also be brought into and out of contact with the photoreceptor 7 by the same mechanism as the charging roller 8.

The transfer mechanism will be described. In FIG. 14, a charged toner layer dt having a volume charge density ρ is provided on a photoconductor 7 having a photosensitive layer 31 having a thickness dm, and a transfer paper 100 having a thickness dp is positioned therebelow. The gap between the toner layer and the transfer paper is defined as g. Further, a charge σc having a polarity opposite to that of the charged toner is applied on the transfer paper 100. In this state, the force Fe (x) in the recording paper direction acting on the toner T having the charge amount qt at x from the surface of the photoreceptor is expressed by the following equation.
Fe (x) = qt {-σc -ρ (dt-x)} / (ε 0 · Kt) (10)
Here, ε ₀ is the dielectric constant of vacuum, and Kt is the relative dielectric constant of the toner layer. The electrostatic force Fe (x) acting on the charged toner T at a distance x from the surface of the photoreceptor is balanced with the mechanical adhesion force Fa. At this point, the toner layer is divided and the thickness of (dt−x) is increased. Assuming that only the toner layer is transferred to the transfer, the transfer rate η is expressed by the following equation.
η = (dt−x) / dt
= ∫ ₀ ¹ −1 / (ρ · dt) {σc + (ε ₀ · Kt) Fa / qt} (11)
In Equation (10), the volume charge density ρ can be expressed as ρ = δ · p · Tp, where δ is the toner density, p is the filling rate of the charged toner layer, and Tp is the toner specific charge. The toner charge amount qt can be expressed as qt = Tp · m, where m is the mass of one toner. Therefore, equation (10) is
Fe (x) = {− σc · m · Tp−δ · p · m (dt−x) Tp ² } / (ε ₀ · Kt) (12)
Can also be expressed. The above is the transfer model formula.

Next, the transfer control method will be described. First, an equivalent circuit is shown in FIGS. 15 and 16 as a transfer model in the case where toner is present on the maximum copy width size paper. Thereby, the image portion transfer current Ib is obtained.
Ib = (V-Vl) / (R + Zb) (13)
However, Zb = (1 / Cd + 1 / Cp + 1 / Ct)
Cd = Ko, Kd, L, Vp / d
Cp = Ko, Kp, L, Vp / dp
Ct = Ko ・ Kt ・ L ・ Vp / dt
V: transfer voltage, Vl: image portion surface potential, R: transfer roller resistance value, Ko: dielectric constant, Kd: photosensitive layer relative permittivity, Kp: transfer paper relative permittivity, Kt: toner layer relative permittivity, d: Photosensitive layer thickness, dp: transfer paper thickness, dt: toner layer thickness, L: paper passing width, Vp: photosensitive member peripheral speed (13) Substituting each value into the equation,
V-Vl = Ib * R + (Ib * dp) / (Ko * Kp * L * Vp) + (Ib * dt) / (Ko * Kt * L * Vp) + (Ib * d) / (Ko * Kd *) L ・ Vp) (14)
From the equation (14), when the transfer control method is a constant current method, the transfer charge σc acting on the transfer described in the above transfer mechanism is the same as Ib / L · Vp in the term of the transfer paper of the equation (14). Therefore, by controlling so that Ib is constant, a stable transfer charge is always given, and the transfer conditions are stabilized.

  On the other hand, in the case of constant voltage control, when V is constant in equation (14), the resistance value R of the transfer roller 15 changes greatly due to environmental changes, and when the resistance value increases, the voltage of the transfer roller increases. As a result, the voltage value applied to the transfer paper becomes smaller, the transfer charge changes, and stable transfer conditions cannot be obtained. Therefore, constant current control is advantageous for the resistance value change of the transfer roller 15.

Next, consider the case where the transfer paper exists but the area where the toner exists is narrow, or the transfer paper size is small and the area where the photoconductor 7 and the transfer roller 15 are in direct contact is wide. 17 and 18 show the case where the transfer paper 100 is present but no toner layer, and FIGS. 19 and 20 show the case where the photoconductor 7 and the transfer roller 15 are in direct contact. Here, if the currents flowing are Iw and Id,
Iw = (V−Vd) / (R + Zw) (15)
However, Zw = (1 / Cd + 1 / Cp)
Id = (V−Vd) / (R + Zd) (16)
However, Zd = (1 / Cd)
Vd: the surface potential of the non-image portion of the photoreceptor. Here, in the case of constant current control, when a small size (A6, etc.) transfer paper is passed, most of the applied current flows into the photoconductor 7, and the result Ib does not become a sufficient value, and the transfer charge becomes small and transfer is performed. It becomes defective. As a means for preventing this, there is a method of measuring the resistance value of the transfer roller once and then applying a voltage suitable for this resistance value so that an appropriate transfer charge can be obtained. When this is described, when the voltage across the current I ₁ in the non-image-forming and V _1,
I ₁ = (V ₁ −Vd) / (R + Zd) (17)
From this relationship, the resistance value R of the transfer roller is obtained. That is,
R = 1 / I ₁ · {V ₁ −Vd− (I ₁ · Id) / Cd} (18)
Here, Vd is a charging potential, Cd is a capacitance of the photosensitive layer, and this value is a known value.

Then, a voltage value Ib is the appropriate current value I ₂ at the time of image formation When V _{2,
I 2 = (V 2 -Vl)} / (R + Zb) (19)
Substituting equation (18) into equation (19) to obtain V ₂ ,
_{V 2 = (I 2 / I} 1) × (V 1 -Vd) + I 2 (Zb-Zd) + Vl (20)
Thus, by applying a constant voltage at the time of image formation with the voltage value V ₂ derived by the equation (20) with respect to V ₁ obtained at the time of non-image formation, an appropriate value always corresponding to the resistance value R of the transfer roller is obtained. Transfer is possible with the voltage V.

Consider the influence of linear velocity. In order to see the relationship between the photosensitive member peripheral speed Vp and the transfer roller resistance R, when the equations (13), (14), and (15) are solved for R,
R = (V-Vl) / (Qb.L.Vp) -Yb / Vp (21)
R = (V−Vd) / (Qw · L · Vp) −Yw / Vp (22)
R = (V−Vd) / (Qd · L · Vp) −Yd / Vp (23)
However, Yb / Vp = 1 / Cd + 1 / Cp + 1 / Ct
Yw / Vp = 1 / Cd + 1 / Cp
Yd / Vp = 1 / Cd
Here, Qb, Qw, and Qd are the charge amounts per unit area of the image portion, the non-image portion, and the non-sheet passing portion, respectively. That is, Qb = Ib / L · Vp, Qw = Iw / L · Vp, Qd = Id / L · Vp. Therefore, it can be seen that when the photosensitive member peripheral speed is changed, the transfer roller resistance value may be changed in inverse proportion to the peripheral speed.

  In the equation (16), the term of the discharge start voltage (Vg) entered in the charging mechanism of the charging roller is omitted. This is because the equation of Vg is Vg = 312 + 6.2 × d / Kd + √ (7737.6 × d / Kd), d: omitted because it can be regarded as a substantially constant value determined by the film thickness of the photosensitive layer and Kd: the relative dielectric constant of the photosensitive layer.

  Next, the cleaning device 17 shown in FIG. 1 will be described. The cleaning blade 18 of the cleaning device 17 is made of an elastic body such as a flat polyurethane rubber, and is fixed to a metal blade holder 82 with an adhesive or a double-sided tape. As shown in FIG. 3, the position of the blade boulder 82 in a direction parallel to the inclined surface 84 is regulated by two positioning pins 83 provided on the inclined surface 84 formed on the case body 3. It is fixed to the case main body 3 with screws 85 in a so-called counter direction opposite to the rotation direction of the photoconductor 7. The screws 85 are in the same direction as the attachment surface of the cleaning blade 18 and the blade holder 82 is brought into close contact with the inclined surface 84 formed on the case main body 3 so as to follow the inclined surface 84. The position of the cleaning blade 18 in the direction perpendicular to the inclined surface 84 is restricted.

  As described above, the contact angle and pressure of the cleaning blade 18 against the photosensitive member 7 are completely guaranteed, and problems such as defective cleaning and generation of abnormal noise are prevented. Further, the thrust direction position of the screw 85 for fixing the blade holder 82 to the case body 3 can be set further outside both ends including the flange members 86 and 87 of the photoconductor. There is an advantage that only the cleaning blade can be replaced without taking off.

  Next, the toner recycling apparatus will be described.

  The toner scraped off from the photoreceptor 7 by the cleaning blade 18 of the cleaning device 17 shown in FIGS. 1 and 3 is transported to the front side in the cleaning case 19 by the toner transporting member 20, and projects into the case 19 integrally. It is discharged outside through the pipe 88 provided. A gear (not shown) is fixed to the back end of the toner conveying member 20, and this gear meshes with a gear formed integrally with the flange member 87 on the back side of the photoconductor 7, so that the photoconductor 7 rotates. Is transmitted to the toner conveying member 20, and the toner conveying member 20 is driven to rotate.

  As shown in FIGS. 3, 21, and 22, a roller portion 91 and a pair of pins 89 projecting from the roller portion 91 are provided at the front end portion of the toner conveying member 20 that protrudes outside the cleaning case 19. The toner recycling belt 92 is wound around the roller portion 91. The belt 92 is formed with a large number of long holes 93 of equal length along the circumferential direction, and each pin 89 described above enters one of the long holes 93. As shown in FIG. 3, the toner recycling belt 92 is located in the toner conveyance path in the bowl-shaped portion 94 formed by a part of the case body 3, and the upper portion of the toner conveyance path is the upper cover 6 (see FIG. 2).

  As shown in FIGS. 3 and 22, a driven roller 95 is rotatably supported on the bowl-shaped portion 94, and the above-described toner recycling belt 92 is wound around the roller 95. When the toner conveying member 20 is rotationally driven as described above, the roller portion 91 integrated therewith rotates, and at this time, the pins 89 are successively engaged with the long holes 93 of the toner recycling belt 92, As a result, the toner recycling belt 92 is driven in the direction indicated by the arrow in FIG. In addition, a large number of elastic fins 96 arranged in the circumferential direction protrude from the outer surface of the toner recycling belt 92, and when the toner recycling belt 92 is driven, the elastic fins 96 are arranged inside the hook-shaped portion 94 and the upper cover 6. Touch the wall.

  The toner discharged to the outside of the cleaning case 19 of the cleaning device 17 by the toner conveying member 20 passes through the elongated hole 93 of the belt 92 while moving in an unstable manner in the vicinity of the transfer portion with the toner recycling belt 92. Then, it falls onto the inner wall surface of the bowl-shaped portion 94. Then, the toner is transported through the toner transport path by the elastic fins 96 of the driven toner recycling belt 92 and is fed into the developer chamber 90 of the developing device 10. At this time, since the elastic fin 96 is pressed against the inner wall surface of the bowl-shaped portion 94, the toner is not transported to the developing device 10 without remaining, and a problem that excessive stress is applied to the toner can be prevented.

  An inclined surface 94a is formed by a protrusion on the inner wall surface portion of the bowl-shaped portion 94 in the vicinity of the driven roller 95. When the elastic fins 96 rub against the inclined surface 94a, the elastic fins 96 are elastically bent. When the elastic fin 96 is deformed and passes through the inclined surface 94a, each elastic fin 96 is elastically restored to its natural state. For this reason, the toner conveyed by the elastic fins 96 is blown to the second stirring member 45 shown in FIG. In this way, the toner can be reliably conveyed to the developer chamber 90. The toner conveyed to the developer chamber 90 is agitated and mixed with the developer 101 existing therein and reused.

As shown in FIG. 21, when the thickness of the toner recycling belt 92 is t ₁ and the thickness of each elastic fin 96 integrated therewith is t ₂ , t ₁ <t ₂ is set. As a result, the waist strength of the elastic fin 96 becomes stronger than the waist strength of the toner recycling belt 92, and the elastic fin 96 presses against the inner wall surface of the bowl-shaped portion 94 as shown in FIG. When transported, the elastic fin 96 itself is not greatly bent and deformed. When the elastic fin 96 starts to contact the inclined surface 94a, the fin 96 is greatly bent and deformed, and then when the elastic fin 96 is elastically restored, the toner is blown out vigorously.

  By using the toner recycling apparatus as described above, the waste toner tank for storing the toner collected from the photoreceptor 7 can be eliminated, and the collected toner can be efficiently reused in the developing device 10.

  Further, since the bowl-shaped portion 94 constituting the toner conveyance path is constituted by a part of the case main body 3, as in the case where the bowl-shaped portion 94 and the other case main body portion are configured separately, It is possible to prevent the toner from leaking through the gap between them, and it is not necessary to provide a sealing material such as a sponge for preventing the toner leakage. Further, since the bowl-shaped portion 94 and the other case main body are integrated, the assembling property of the image forming unit 1 is improved.

  By the way, as described above, the shafts 63 and 64 of the first and second stirring members 44 and 45 rotatably supported by the unit case 2 are connected to the drive gears 68 and 64 at the end portions on the back side. 69 is fitted to the shafts 63 and 64 so as not to rotate relative to each other. When such a gear is supported on a shaft, conventionally, in order to prevent the gear from shifting and detaching from the shaft in the axial direction, a locking ring such as an E ring or a C ring is fitted to the shaft. However, the locking ring prevents the gear from being detached from the shaft. The locking ring was used as a stopper to prevent gear disengagement. However, if such a locking member is used, the number of parts increases and the cost increases.

  On the other hand, in the configuration example shown in FIGS. 3 and 4, the back side outer plate 53 of the unit case 2 is located outside the above-described drive gears 68 and 69, A stopper is configured to prevent the drive gears 68 and 69 from detaching from the shafts 63 and 64 in the axial direction. That is, the case body 3 of the unit case 2 includes a back side inner plate 54 that rotatably supports the shafts 63 and 64, and a back side outer plate 53 that is positioned on the outer side, and between the plates 53 and 54. The drive gears 68 and 69 are arranged on the rear side, and the back side outer plate 53 constitutes a stopper that prevents the drive gears 68 and 69 from being detached from the shafts 63 and 64. The upper part of the space where the gears 68 and 69 are located is covered with a part of the developing case cover 5.

  In this way, the outer plate 53 is configured so as to function as a stopper for the gears 68 and 69 in addition to its original function, so that a conventionally required locking ring can be omitted. The number of parts can be reduced and the cost can be reduced.

  Furthermore, since the gears 68 and 69 are located in a sealed space between the outer plate 53 and the inner plate 54 on the back side, it is possible to eliminate the possibility that a person touches the gears 68 and 69. Further, since the case body 3 has a double wall structure of the inner plate 54 and the outer plate 53, it is possible to more reliably prevent the developer of the developing device 10 from leaking to the outside of the image forming unit 1. Even if the developer slightly leaks out of the developer chamber 90 from the inner plate 54 and the side plate 5a (FIG. 1) on the back side of the developing case cover 5, the outer plate 53 causes this to leak out of the image forming unit. Can be prevented.

  Further, as shown in FIG. 23 or FIG. 24, a protrusion 97 having a rib shape or a cylindrical shape is formed on the surface of the back side outer plate 53 facing each drive gear 68, 69, and If the end faces of the drive gears 68 and 69 are in contact with each other, the area where each of the drive gears 68 and 69 is in contact with the back outer plate 53 can be reduced, thereby reducing the frictional force acting between them. The driving torque of the gears 68 and 69 can be reduced. In addition, the wear of the gears 68 and 69 and the unit case 2 can be reduced and the service life thereof can be extended.

  As described above, the case portion that contacts the gear is provided adjacent to the outside of the gear, and the configuration that prevents the gear from being removed from the shaft by the case portion is widely applied to various machines and devices other than the image forming unit. Applicable.

  Various configurations for preventing the drive gears 68 and 69 from shifting inward in the axial direction with respect to the shafts 63 and 64 can be employed. For example, as shown in FIG. The gears 68 and 69 can be prevented from moving inward in the axial direction of the shafts 63 and 64 by at least one of 54 and the bearing 154 attached thereto. Alternatively, as shown in FIG. 26, step portions 163 may be formed on the shafts 63 and 64, and the step portions 163 may prevent the gears 68 and 69 from moving inward in the axial direction. Further, as shown in FIG. 27, the locking ring 164 made of an E ring or a C ring may prevent the gears 63 and 64 from shifting inward in the axial direction.

  As described above, the image forming apparatus shown in the figure has an image carrier formed of the photosensitive member 7 on which an electrostatic latent image is formed, and the electrostatic latent image formed on the photosensitive member 7 is divided into two components having toner and a carrier. A developing device 10 that visualizes a toner image using a system developer, and the developing device 10 includes a developing sleeve 11 that carries and conveys a two-component developer 101 used for development. A developer carrying / conveying member is provided, and a toner image formed on the photoreceptor 7 is transferred to a transfer material made of transfer paper 100 to obtain a recorded image. In addition, in order to form an electrostatic latent image on the photoreceptor 7, a charging device configured as a charging roller 8 that charges the photoreceptor 7 and a toner image formed on the photoreceptor 7 are transferred to the transfer paper 100. And a cleaning device 17 having a cleaning member comprising a cleaning blade 18 for removing toner remaining on the surface of the image carrier from the surface.

  As described above, the illustrated image forming apparatus includes a large number of elements, and the two-component developer 101 is accommodated in the developer chamber 90 and used. Each of these elements deteriorates with time, and finally becomes unusable. Normally, these elements are replaced with new ones when they can no longer be used or at a time just before that. This replacement time is the life of each element. At that time, if each element is configured to have a lifetime that is completely different, each element must be replaced every time the lifetime is reached, which makes the replacement work extremely complicated. . If each element is configured so that a plurality of components of the image forming apparatus have a lifetime almost at the same time, the plurality of components that have reached the end of their lifetime can be replaced in a batch, thereby simplifying the work. .

  However, conventionally, no consideration has been given to the relationship between the carrier life of the two-component developer and the life of other imaging elements. Therefore, normally, when the carrier deteriorates, the developer should be replaced. I had to do it alone.

  In this example, from such a viewpoint, these are configured so that the photoconductor 7 which is an example of the image carrier and the carrier life of the two-component developer 101 coincide. According to such a configuration, when the photoconductor 7 and the developer 101 have reached the end of their lives, they can be exchanged together, and the workability can be greatly improved.

  In the illustrated image forming apparatus, an image carrier made of a photosensitive member 7 and a developer carrying / conveying member made of a developing sleeve 11 are assembled to a unit case 2 to form an image forming unit 1, and two-component development is performed. Since the agent 101 is accommodated in the developing case 12 constituted by a part of the unit case 2, as described above, when the photoconductor 7 and the carrier having the same lifetime reach the lifetime, the image forming unit 1 Even if the whole is replaced with a new one, the economic burden on the user is not excessive. If the entire image forming unit 1 is replaced, the replacement work can be remarkably simplified. Moreover, since the developing case 12 of the developing device 10 is constituted by the unit case 2, the cost of the entire image forming unit can be reduced, and the economic burden on the user can be further reduced.

  Further, not only the life of the photoconductor 7 and the life of the carrier but also the life of the charging roller 8 constituting the charging device and the life of the cleaning blade 18 constituting the cleaning member are all matched. Sometimes, these can be exchanged together, and the workability can be further improved.

  In this case, in this example, an image carrier made up of the photoconductor 7, a charging device made up of the charging roller 8, a developer carrying / conveying member made up of the developing sleeve 11, and a cleaning member made up of the cleaning blade 18 are provided in the unit case 2. Since the image forming unit 1 is assembled and the two-component developer 101 is accommodated in the developing case 12 configured by a part of the unit case 2, the image forming unit 1 is formed when these components reach the end of their service life. Even if the entire unit 1 is replaced with a new one, the economic burden on the user can be further reduced.

  Further, in the image forming apparatus of this example, the toner removed from the image carrier made of the photosensitive member 7 by the cleaning device 17 is reused in the developing device 10 from the cleaning device 17 to the developing device 10. A toner recycling device is provided for transporting the toner to the user, so that the toner can be reused. Therefore, the economic burden on the user can be reduced, and even if the entire imaging unit that has reached the end of its life is replaced with a new one, On the other hand, there is no excessive economic burden.

  Further, in the image forming apparatus of this example, the toner removed from the image carrier made of the photoreceptor 7 by the cleaning device 17 is transported from the cleaning device 17 to the developing device 10 so that the toner can be reused in the developing device 10. And a toner transport path of the toner recycling device is constituted by a part of the unit case 2, so that it is possible to reduce the economic burden on the user by reusing the toner. Even if a toner recycling device is provided, the toner conveyance path is constituted by the unit case 2, so that an increase in the cost of the image forming unit 1 can be effectively suppressed, and the entire image forming unit that has reached the end of its life can be renewed. Even if it is replaced with a thing, the burden on the user can be further reduced.

  Here, the lifetime of each component of the image forming unit 1 can be set as follows, for example. Here, it is assumed that the lifetime of each element when it is in a state immediately before it cannot withstand use.

  First, the lifetime of the developer, more precisely, the lifetime of the carrier is due to the fact that the coating layer on the surface of the carrier is peeled off over time due to stirring and circulation of the developer, and the triboelectric charging characteristics of the carrier deteriorate. It is determined. That is, by selecting the thickness of the carrier coating layer and the total amount of the developer 101 accommodated in the developer chamber 90 of the developing device 10, the approximate lifetime of the developer 101 can be determined.

  The lifetime of the photoreceptor 7 is determined mainly by the fact that the photosensitive layer 31 is scraped over time by the cleaning blade 18, the film thickness is reduced, and an appropriate charging potential cannot be obtained. That is, by selecting the film thickness of the photosensitive layer 31, the approximate lifetime of the photoreceptor 7 can be set.

  The life of the cleaning blade 18 is determined by the contact pressure with respect to the photoconductor 7 and the wear amount of the blade edge that is in contact with the photoconductor 7. Generally, when the amount of wear increases, the cleaning performance for residual toner on the photoreceptor deteriorates. However, the higher the contact pressure of the cleaning blade 18 with respect to the photoconductor 7, the greater the amount of wear of the cleaning blade 18, but the higher the cleaning performance, so the life of the cleaning blade 18 is extended. However, when the contact pressure is high, the load torque of the photoconductor 7 increases. For this reason, the approximate life of the cleaning blade 18 can be set by selecting the contact pressure of the cleaning blade 18 against the photosensitive member 7.

  The service life of the charging roller 8 depends on the pressure with which the cleaning pad 32 (FIG. 1) for cleaning the minute toner adhering to the surface of the charging roller is pressed against the charging roller 8. If the pressing pressure is large, the cleaning performance with respect to the charging roller 8 is increased. Although it is good, scratches occur on the surface of the charging roller over time, and image unevenness occurs. Further, when the pressing pressure is small, the cleaning property with respect to the charging roller 8 is deteriorated. For this reason, the approximate life of the charging roller 8 can be set by selecting the pressing force of the cleaning pad 32 against the charging roller 8.

  The above is a factor for determining the lifetime of each element constituting the image forming unit 1. Next, a more specific example when the lifetimes of the carriers of the photoconductor 7 and the developer 101 are matched will be shown.

  First, when an image is formed on S sheets of transfer paper after starting to use a new image forming unit 1, the photoconductor 7 and the developer 10 reach the end of their lives when the number of copies reaches S. Assume that the entire image forming unit 1 is replaced.

  When the developer 101 is used until it becomes deteriorated and cannot be used, the carrier coating layer is formed so that the triboelectric charging characteristic of the carrier deteriorates immediately after the image formation of the S sheets is finished. Determine the thickness and amount of developer. The triboelectric charge polarity of the carrier can be expressed by toner specific charge (charge amount Q / M per unit weight), and FIG. 28 shows the relationship between the toner specific charge and the number of copies. If the toner specific charge (Q / M) is lower than the allowable range, the background stains and the image density are lowered. Therefore, immediately before this state, the coating layer thickness of the carrier is set so that the number of copies becomes S. The amount of the developer is set.

  For example, when the above-described S sheet is 30K sheet, 40K sheet, or 50K sheet (K = 1000), the life of the developer is the toner specific charge (Q which is a substitute value of the frictional charging characteristic of the carrier as described above. / M), but this value is within the range of 10 to 40 μc / g even after each number of 30K, 40K, or 50K sheets is passed, and immediately after reaching each copy number. If the carrier coating layer thickness and the amount of developer are selected so that the toner specific charge is lower than this value, the lifetime of the developer can be set correctly. Specifically, the coating layer thickness is selected from the range of 0.5 μm to 1.5 μm, for example, and the developer amount (weight) is selected from the range of 2.45 N to 4.41 N. Since the cost can be reduced if the amount of the developer 101 is small, the combination with the thickness of the coating layer of the carrier should be used in the direction of reducing the developer amount when the lifetime copy number is 30K sheets than when it is 50K sheets. It is desirable to set.

Next, assuming that the photoconductor 7 continues to be used until it deteriorates, the film thickness of the photoconductive layer 31 is set so that an appropriate charging current cannot be obtained immediately after the number of copies reaches S. To do. As an example, considering the case where the width of change in the charging potential due to the change in the film thickness of the photosensitive layer 31 over time is 20 V or less, in the equation shown above in the charging mechanism of the charging roller 8, The film thickness of the photosensitive layer 31 may be selected so that the variation in the term of the discharge start voltage (charging start voltage) Vg affected by the film thickness of the layer 31 is 20 V or less. Since the amount of wear of the photosensitive layer after copying S sheets is known in advance, this is set to l. If the initial photosensitive layer thickness is d, the relative dielectric constant is Kd, the initial charging start voltage is Vgs, and the charging start voltage after copying S sheets is Vge,
Vgs = 312 + 6.2 × d / Kd + √ (7737.6 × d / Kd)
Vge = 312 + 6.2 × (dl) / Kd + √ {7737.6 × (dl) / Kd}
Vgs−Vge = 1.931 + 49.17 {√d−√ (dl)}
Here, if l is 3 μm,
Vgs−Vge = 5.79 + 49.17 {√d−√ (d−3)}
If the change width is 20 V or less,
Vgs−Vge = 5.79 + 49.17 {√d−√ (d−3)} ≦ 20
√d−√ (d−3) ≦ 0.289
It becomes. Here, √d = D and d-3 = D ² −3,
D-√ (D ² -3) ≦ 0.289
√ (D ² −3) ≦ D−0.289
And when both sides are squared,
D ² −3 ≦ D ² −0.578 D + 0.0835
0.578D ≦ 3.0835
∴D ≦ 5.33
√ From d = D, d = D ²
∴d = 5.33 ² = 28.4 μm

  Therefore, if the photosensitive layer 31 is worn by 3 μm after copying S sheets, it is possible to make the fluctuation range 20 V or less by selecting a photosensitive layer having a thickness of 28.4 μm.

  For example, in order to make the photoconductor 7 have a lifetime with the number of copies of 30K sheets, the potential decrease due to the change in the film thickness of the photosensitive layer after passing 30K sheets is set to 20 V or less, and the photoconductor is further provided. When the film is used as it is, the film thickness of the photosensitive layer 31 is set so that the potential drop becomes larger than 20V immediately after that. Assuming that the wear amount of the photosensitive layer 31 after copying 30K sheets is 2 μm, the initial film thickness is about 13 μm from the above formula.

  Similarly, when the photosensitive member 7 has a lifetime of up to 40K sheets, the wear amount of the photosensitive layer 31 is 2.5 μm, and the initial film thickness may be set to around 20 μm.

  Further, when the photoconductor 7 reaches the end of its life with 50K sheets, the wear amount of the photosensitive layer 31 is 3 μm, so the initial film thickness is set to around 28.4 μm.

  As described above, the lifetimes of the developer and the photosensitive member can be matched, and the image forming unit in which the photosensitive member and the developing device are integrated can be replaced at once. As a result, the maintenance cost can be greatly reduced compared to the case where individual parts are replaced by service personnel at different times.

  Further, in order for the cleaning blade 18 to have a lifetime with S copies, it can be seen from the graph of FIG. 29 showing the relationship between the contact pressure of the blade 18 to the surface of the photosensitive member and the amount of wear of the cleaning blade 18. Thus, for example, when the contact pressure of the cleaning blade 18 is small, no defective cleaning has occurred yet at the end of copying S sheets, and when the cleaning blade 18 continues to be used as it is, immediately after copying S sheets. In addition, the contact pressure is set so that defective cleaning occurs. The same applies when the contact pressure of the cleaning blade 18 increases.

  When the contact pressure is set to a high value, the amount of wear of the cleaning blade 18 increases, but the number of copies that can be cleaned with the cleaning blade 18 in a good cleaning state increases, and the life of the cleaning blade 18 can be extended. FIG. 29 can be understood well. However, if the contact pressure is large, the load torque of the photosensitive member increases as described above, and a large load is applied to the drive motor, and the capacity of the drive motor must be increased. Cost increases. Therefore, it is more economical not to set the contact pressure of the cleaning blade 18 to the photoconductor 7 too high.

  As described above, the life of the cleaning blade 18 can be set, and by matching the life of the cleaning blade 18 with that of the photoconductor 7 and the developer, they can be replaced at the same time, and the maintenance cost can be further reduced.

  For example, as described above, when the life of the developer and the photoconductor 7 is 30K, the contact pressure of the cleaning blade 18 with respect to the photoconductor 7 is about 0.1176 N / cm, and the life is 40K. In the case of the number of sheets, the contact pressure of the cleaning blade 18 with respect to the photoconductor 7 is set in the vicinity of 0.1568 N / cm. Further, when the number of copies to be used is 50K, the lifespan of the respective elements can be substantially matched by setting the contact pressure of the cleaning blade 18 in the vicinity of 0.196 N / cm.

  Further, the charging roller 8 reaches the end of its service life with the number of S copies, and the roller 8 may be configured to be replaced at this time as follows.

  30 and FIG. 31 show a pressure contact force (pad pressure) at which the cleaning pad 32 that cleans the fine toner adhering to the surface of the charging roller 8 abuts against the surface of the charging roller 8, the cleaning performance by the pad 32, and charging. The relationship of image unevenness due to scratches generated on the surface of the roller 8 is shown. A range indicated by “OK” in these drawings is a range in which the cleaning property of the charging roller 8 by the cleaning pad 32 is good and image unevenness is small.

  30 and 31, even after copying S sheets, the cleaning performance by the cleaning pad 32 is good, image unevenness does not occur, and the charging roller 8 is used as it is. In addition, the pad pressure is selected so that the cleaning property and the image unevenness are poor. In this way, the lifetimes of the developer 101, the photoconductor 7, the cleaning blade 18 and the charging roller 8 can all be matched.

  For example, when the number of copies S up to the end of its life is 30K, the pressing force (pad pressure) of the pad 32 against the charging roller 8 is set in the vicinity of 5.88N, and when the number of copies S is 40K, Is set in the vicinity of 7.84N. Similarly, when the life copy number S is 50K, the pad pressure is set in the vicinity of 9.8N.

  The pad pressure is also preferably set to a low value if the cleaning performance of the charging roller 8 by the pad 32 can be satisfied. This can reduce the driving load of the photoconductor 7, so that the driving motor has a small capacity. Can be used and the cost can be reduced.

  As described above, replacement elements to be assembled in the unit case 2, that is, the photosensitive member 7, the developer 101, the cleaning blade 18, and the charging roller 8 are copied to a predetermined number of times. By selecting the material and setting the characteristic value, it is possible to configure a unit that is more economical and less wasteful than before, and when replacing the parts, the replacement work is completed by replacing one imaging unit, Maintenance is greatly improved, and maintenance costs can be significantly reduced.

  On the other hand, if it is possible to use low-cost, highly durable parts, it is possible to change the lifetime of the individual parts.

  As described above, the image forming unit is configured by assembling the image forming elements of the photosensitive member, the developing device, the cleaning device, and the charging roller to the unit case. However, these image forming elements or other image forming elements are appropriately combined, and at least 1 An image forming unit can be configured by assembling two image forming elements in a unit case. Usually, at least a photoconductor and a developing device are assembled in a unit case to constitute an image forming unit. By assembling at least one image forming element and the unit case in this manner to form the image forming unit, the assemblability is improved and the operability at the time of replacement of the image forming unit is improved. The present invention can also be applied to an image forming apparatus that does not constitute an image forming unit by assembling a plurality of image forming elements.

2 is a vertical sectional view of an image forming unit mounted on the image forming apparatus main body. FIG. FIG. 2 is a schematic external perspective view showing an image forming unit and a toner bottle not equipped with a developer cartridge. FIG. 5 is a perspective view showing the image forming unit in a state where a case cover, a developing case cover, and an upper cover are removed. FIG. 4 is a partial cross-sectional plan view in the same state as FIG. 3. It is a perspective view which shows the state which reversed the case main body. It is a perspective view similar to FIG. 5 which shows another example. 2 is an enlarged schematic cross-sectional view of a photoreceptor. FIG. It is a schematic diagram of a photoconductor and a charging roller. It is a figure which shows the equivalent circuit of a charging roller, a photoreceptor, and a power supply. FIG. 4 is an explanatory cross-sectional view showing a relationship between a developing device and a photoconductor. It is a disassembled perspective view of a doctor blade, a developing sleeve, a support member, and an inlet seal cover. It is explanatory drawing which shows a development model. 6 is a graph showing an example of a relationship between toner charge and force acting on toner. It is explanatory drawing which shows a transcription | transfer model. It is explanatory drawing which shows the relationship between a photoconductor and a transfer roller. It is a figure which shows the equivalent circuit of FIG. It is explanatory drawing which shows the relationship between a photoconductor, a transfer roller, and transfer paper. It is a figure which shows the equivalent circuit of FIG. It is explanatory drawing which shows the relationship between a photoconductor and a transfer roller. It is a figure which shows the equivalent circuit of FIG. FIG. 3 is an enlarged perspective view of a toner recycling belt. FIG. 3 is a vertical sectional view of a toner recycling belt. It is a perspective view which shows the other example of the back side outer plate of a unit case. It is a perspective view which shows the further another example of the back side outer plate of a unit case. It is a horizontal sectional view showing one structural example which prevents a drive gear from shifting in the direction of an axis of a shaft. It is a horizontal sectional view showing another example of composition which prevents a drive gear from shifting in the direction of an axis of a shaft. FIG. 10 is a horizontal sectional view showing still another configuration example for preventing the drive gear from shifting inward in the axial direction of the shaft. 6 is a graph illustrating an example of a relationship between the number of copies and a toner specific charge. It is a graph which shows an example of the relationship between the number of copies and the amount of wear of the cleaning blade. 6 is a graph showing an example of the relationship between the number of copies and the cleaning property of the charging roller. It is a graph which shows an example of the relationship between the number of copies and image unevenness.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming unit 2 Unit case 10 Developing device 12 Developing case 17 Cleaning device 100 Transfer paper 101 Two-component developer

Claims (6)

An image carrier on which an electrostatic latent image is formed, and a developing device that visualizes the electrostatic latent image formed on the carrier as a toner image using a two-component developer having toner and a carrier. And the developing device has a developer carrying member that carries and conveys a two-component developer to be developed, and transfers the toner image formed on the image carrier to a transfer material. In an image forming apparatus that obtains a recorded image by
An image forming apparatus characterized in that a life of the image carrier and a life of a carrier of the two-component developer are matched. The image carrier and the developer carrying member are assembled in a unit case to form an image forming unit, and the two-component developer is accommodated in a developing case constituted by a part of the unit case. Item 2. The image forming apparatus according to Item 1. An image carrier on which an electrostatic latent image is formed, a charging device for charging the carrier to form an electrostatic latent image on the carrier, and an electrostatic latent image formed on the image carrier, And a developing device that visualizes a toner image using a two-component developer having a carrier, and a toner that remains on the surface of the image carrier after the toner image formed on the image carrier is transferred to a transfer material A cleaning device having a cleaning member for removing the toner from the surface, and the developing device has a developer carrying and conveying member that carries and conveys a two-component developer to be developed, and the image In an image forming apparatus for obtaining a recorded image by transferring a toner image formed on a carrier to a transfer material,
An image forming apparatus comprising: a life of the image carrier, a life of the charging device, a life of the carrier of the two-component developer, and a life of the cleaning member. An image forming unit is configured by assembling the image carrier, the charging device, the developer carrying member, and the cleaning member in a unit case, and the two-component developer is part of the unit case. The image forming apparatus according to claim 3, wherein the image forming apparatus is housed in a developer case constituted by: The image forming apparatus according to claim 4, further comprising a toner recycling device that transports the toner removed from the image carrier by the cleaning device to the developing device from the cleaning device so that the toner can be reused in the developing device. In order to reuse the toner removed from the image carrier by the cleaning device in the developing device, a toner recycling device for transporting the toner from the cleaning device to the developing device is provided, and the toner transport path of the toner recycling device is connected to the unit case. The image forming apparatus according to claim 4, comprising a part.

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