Electrophotographic image forming apparatus

Abstract: An image forming apparatus for forming an image on a recording material; an image bearing member; a rotatable developing rotary; a developing unit mounting portion, in the developing rotary, for detachably mounting a developing unit for developing an electrostatic latent image formed on the image bearing member; and a controller for executing, after exchange of the developing unit, an intermittent rotating operation wherein the developing rotary is repeatedly rotated and stopped.

Description: FIELD OF THE INVENTION AND RELATED ART The present invention relates to an electrophotographic image forming apparatus. In this specification, an electrophotographic image forming apparatus means an apparatus that forms an image on recording medium with the use of an electrophotographic image forming system. It includes, for example, an electrophotographic copying machine, an electrophotographic printer (laser beam printer, LED printer, and the like), a facsimile machine, a word processor, and the like. A typical structure of a color laser beam printer prior to the present invention is as follows. A charging roller, to which voltage is being applied, is placed in contact with a photosensitive drum, with a predetermined contact pressure, to uniformly charge the peripheral surface of a photosensitive drum so that a latent image can be formed. The charged peripheral surface of the photosensitive drum is exposed by a scanning section which comprises a laser diode. More specifically, the laser diode emits a laser beam modulated with image data signals toward a polygon mirror, which deflects the laser beam. Thereby the laser beam is caused to make a scanning movement in the direction of the generatrix of the photosensitive drum while being focused upon the peripheral surface of the photosensitive drum through an image forming lens and a deflection mirror. In this way, the scanning laser beam is projected upon the peripheral surface of the photosensitive drum. As a result, a plurality of electrostatic latent images correspondent to different primary color components of an original image, are formed on the peripheral surface of the photosensitive drum by the laser beam modulated with the image data signals. An image development rotary comprises a development unit for developing the latent image correspondent to magenta color, a development unit for developing the latent image correspondent to cyan color, a development unit for developing the latent image correspondent to yellow color, and a development unit for developing the latent image correspondent to black color. In a latent image developing operation, the latent image developing unit (hereinafter, development unit), which contains the color toner correspondent to the latent image to be developed, is stopped at a position (hereinafter, developing position) where the distance between the peripheral surface of the latent image developing roller (hereinafter, development roller) of the development unit, and the peripheral surface of the photosensitive drum 1, becomes minimum, that is, microscopic. As the development unit is moved to the developing position, the development roller is connected to a high voltage power source of the main assembly of the image forming apparatus, so that bias for developing a latent image (hereinafter, development bias) is applied to the development unit. At the same time, the development roller is engaged with a driving means linked with the driving power source on the main assembly side of the image forming apparatus. As the development roller is rotatively driven while the development bias is applied to the development roller, the latent image on the photosensitive drum is developed into a toner image. The development unit is in the form of a development cartridge which integrally comprises the development roller as a latent image developing member, and a toner storing portion. The development unit in the form of a cartridge makes it possible for a user to maintain the image forming apparatus without relying on service personnel, and therefore, the operability of the apparatus is greatly improved. Thus, the development unit in the form of a cartridge (hereinafter, development cartridge) is widely used as a development unit for the electrophotographic image forming apparatus. EP-A-0678794 discloses an image forming apparatus having a rotatable member having a cylindrical developing unit and also having a toner storing unit at one end. The developing unit has four developing sections, for performing developing operations with black, cyan, yellow and magenta toner respectively. The toner storing unit has four removable toner containers, one for each developing section. In use, the toner is fed from a toner container to the respective developing section as required. If one colour of toner is used continuously all the toner near the toner outlet of the relevant container may be supplied to the developing unit so that no further toner can be supplied even though the toner container may still contain a supply of toner elsewhere in the container. Under these circumstances, the rotary member is rotated to move toner in the containers towards the toner outlets. Black toner is stored along the axis of the rotatable member, and a black toner receptacle (from which black toner is fed to the black developing section) is replenished by rotating the rotatable member so that the receptacle passes underneath the axially located black toner supply. Toner tends to cohere near the toner container outlets, and if a container is removed in this condition the cohered container is apt to come out through the outlet and make a mess. Therefore when the apparatus detects that a toner container is empty and should be replaced, it causes the rotatable member to make one rotation thereby to loosen the toner by vibration. The loosened toner is transferred to the means for feeding it to the developing section, so that it is no longer cohered at the container outlet when the container is removed for toner replacement. When a toner container has been replaced, and the apparatus has detected that its front cover has been closed again, it performs a recovery procedure in which it drives the corresponding developing section and a toner supply roller for a predetermined period of time, to replenish the developing section with toner. SUMMARY OF THE INVENTION According to the present invention there is provided an image forming apparatus as set out in claim 1 and an image forming apparatus as set out in claim 8. Optional features are set out in the remaining claims. An embodiment of the present invention provides an electrophotographic image forming apparatus which can loosen the powder toner used for developing an electrostatic latent image, before developing the latent image. An embodiment of the present invention helps to limit the torque which the development unit driving motor of an electrophotographic image forming apparatus needs to generate to rotatively drive the development unit. An embodiment of the present invention provides an electrophotographic image forming apparatus in which an intermittent development rotary rotation sequence, in which an image developing rotary is rotated, and then, temporarily stopped, is repeated a plurality of times immediately after one or more image development units are replaced. There now follows a description of the preferred embodiments of the present invention in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a vertical section of the color laser beam printer embodying the present invention. Figure 2 is a perspective drawing which depicts a method for installing a development unit into the main assembly of the printer. Figure 3 is a perspective drawing which depicts the method for installing a development unit into the main assembly. Figure 4 is a perspective drawing which depicts the method for installing a development unit into the main assembly. Figure 5 is a perspective drawing which depicts the method for installing a development unit into the main assembly. Figure 6 is a perspective drawing which depicts the method for installing a development unit into the main assembly. Figure 7 is a perspective drawing which depicts the method for installing a development unit into the main assembly. Figure 8 is a perspective drawing which depicts the method for installing a development unit into the main assembly. Figure 9 is a perspective drawing which depicts the method for installing a development unit into the main assembly. Figure 10 is a perspective drawing which depicts the method for installing a development unit into the main assembly. Figure 11 is a perspective drawing which depicts the method for installing a development unit into the main assembly. Figure 12 is a section of a development unit at the image developing position. Figure 13 is a side view of an interlocking switch. Figure 14 is a perspective drawing which depicts a method for positioning a development unit into a development rotary. Figure 15 is a sectional drawing which depicts the position of a development unit in a shipment package, and the same development unit after it has been installed in the main assembly of a printer. Figure 16 is a sequential drawing which depicts a rotational sequence of a development rotary in the first embodiment of the present invention. Figure 17 is a sequential drawing which depicts a rotational sequence of the development rotary in the first embodiment. Figure 18 is a flow chart for the rotational sequence of the development rotary in the first embodiment of the present invention. Figure 19 is a graph of the torque that is needed to drive a development unit. Figure 20 is a block diagram of the printing system in the first embodiment of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a color image forming apparatus embodying the present invention will be described with reference to the drawings. Embodiment 1 (General Structure of Image Forming Apparatus) First, the general structure of an electrophotographic color image forming apparatus will be described with reference to Figure 1, which is a vertical section of a color laser beam printer, that is, a typical form of a color image forming apparatus. A similar drawing appears in JP-A-9-80856. The image forming section of the color laser beam printer comprises an image bearing member 15 (for example, an electrophotographic photosensitive drum) which rotates at a predetermined constant speed, a black color development unit 21B which is fixedly disposed, and three color development units: a yellow color development unit 20Y, a magenta color development unit 20M, and a cyan color development unit 20C, which are rotative. Below the image forming section, an image transferring intermediary member 9 (hereinafter, intermediary transfer member) is disposed, which temporarily holds color toner images of different color transferred onto the intermediary transfer member in a superimposing manner, and then transfers them onto a recording medium 2 delivered from a recording medium feeding section. After the color toner images are transferred onto the recording medium 2, the recording medium 2 is conveyed to a fixing device 25, in which the color toner images are fixed to the recording medium 2. Thereafter, the recording medium 2 is discharged by discharge rollers 34, 35 and 36, into a delivery section 37 which is located on the top side of the printer. The recording medium 2 is constituted of a sheet of ordinary paper, an OHP sheet, or the like. The rotative color development units and the stationary black color development unit are rendered individually installable into, or removable from, the main assembly 18 of the printer. Next, the structures of the various sections of the image forming apparatus will be described in detail in a logical order. (Image Bearing Member Unit) A drum unit 13 integrally comprises an image bearing member 15 (hereinafter, photosensitive drum), a cleaning apparatus, a charging apparatus, and a cleaning apparatus holder 14 which doubles as the holder for the photosensitive drum 15. The drum unit 13 is removably installable in the printer main assembly 18, so that the drum unit 13 can be easily replaced as the service life of the photosensitive drum 15 expires. The photosensitive drum 15 in this embodiment is constituted of an aluminum cylinder with a diameter of 62 mm, and a layer of organic photoconductive material coated on the peripheral surface of the aluminum cylinder. It is rotatively supported by the cleaning apparatus container 14 that doubles as the photosensitive drum holder. Along the peripheral surface of the photosensitive drum 15, a cleaning blade 16, and a primary charging means 17 as a charging member, are disposed. The photosensitive drum 15 is rotated in the counterclockwise direction in synchronism with the image forming operation, by the driving force transmitted from an unillustrated motor to the one of the longitudinal ends of the photosensitive drum 15, that is, the end at the rear in Figure 1. The cleaning blade 16 is placed in contact with the peripheral surface of the photosensitive drum 15, to remove the toner particles remaining on the peripheral surface of the photosensitive drum 15 after toner image transfer. (Charging Means) The charging means 17 is such a charging means that employs a contact type charging method. It comprises an electrically conductive charging roller as a charging member, which is placed in contact with the photosensitive drum 15. The peripheral surface of the photosensitive drum 15 is uniformly charged by applying voltage to this electrically conductive roller. (Exposing Means) The photosensitive drum 15 is exposed by the scanning section 30. More specifically, an image signals are given to a laser diode, the laser diode projects a laser beam modulated with the image signals onto a polygon mirror 31. The polygon mirror 31 is being rotated at a high speed by a scanner motor, and therefore, the laser beam modulated with the image signals is moved in a scanning movement. The laser beam, which is making a scanning movement, is sent through the image forming lens 32, and is deflected by the deflecting mirror 33 toward the peripheral surface of the photosensitive drum 15, which is rotating at the predetermined constant velocity. As a result, the peripheral surface of the photosensitive drum 15 is exposed in a manner to reflect the image signals, and consequently, an electrostatic latent image reflecting the image data is formed on the peripheral surface of the photosensitive drum 15. (Latent Image Developing Mechanism) The latent image developing system (hereinafter, development system) in this embodiment comprises: three rotative latent image development units, which are a yellow image developing unit 20Y, a magenta image developing unit 20M, and a cyan image developing unit 20C, and which develop yellow, magenta, and cyan color images, correspondingly; and one stationary development unit 21B which develops a black color image. In a color image forming operation, the development rotary 23 is rotated once for each rotation of the intermediary transfer member 9, to position the yellow image developing unit 20Y, the magenta image developing unit 20M, and the cyan image developing unit 20C, in that order, at the image developing position, where the latent images are developed into the correspondent color images. (Black Image Developing Unit) The black image developing unit 21B is a stationary unit, or a nonrotative unit, and is removably installed in the printer main assembly 18 in such a manner that the peripheral surface of the development roller 21BS of the black image developing unit 21B is positioned a microscopic distance (approximately 300 µm) away from the peripheral surface of the photosensitive rum 15. The black image developing unit 21B develops a latent image correspondent to the black component of the original image into a black toner image. It comprises a black toner storing portion and the development roller 21BS. As depicted by Figure 1, in the black image developing unit 21B, the toner is delivered to the development roller 21BS by a toner delivering member 21BT disposed in the black toner storing portion. The toner having been delivered to the vicinity of the development roller 21BS is coated in a layer on the peripheral surface of the development roller 21BS which is being rotated in the clockwise direction by a development blade 21BB placed in contact with the peripheral surface of the development roller 21BS with a predetermined pressure. While the toner is coated on the development roller 21BS, the toner is triboelectrically charged. Then, as bias for developing a latent image (hereinafter, development bias) is applied to the development roller 21BS, the toner particles in the toner layer jump from the development roller 21BS to the peripheral surface of the peripheral surface of the photosensitive drum 15 in a manner to reflect the electrostatic latent image (jumping development); the latent image on the peripheral surface of the photosensitive drum 15 is reversely developed into a toner image. In consideration of toner consumption, the toner containing portion of the black image developing unit 21B is given a toner capacity equivalent to 15,000 images (in terms of A4 size, being covered four percent with toner, in JIS standard), which is approximately twice or more the toner capacity of the other development units 20Y, 20M or 20C. Giving the black image developing unit 21B such a large toner capacity as described above can reduce the f requency with which the black image developing unit 21B must be replaced by the user, as well as the cost per print. The point at which the black image developing unit 21B is disposed is between the laser scanner section 30 as an exposing apparatus, and the development rotary 23 comprising the development units 20Y, 20M and 20C. Placing the black image developing unit 21B in this manner prevents the toner from being scattered as far as optical components such as the laser scanner section, even if the toner should leak as the unit 20Y, 20M or 20C is rotated; in other words, even if the toner leaks, the leaked toner is prevented from adhering to the polygon mirror 31, the image forming lens 32, the deflecting mirror 33, and the like, and therefore, interfering with the formation of a latent image. As a result, a clear image can be outputted. (Color Developing Unit) Each of the three development units 20Y, 20M and 20C stores toner by the amount equivalent to approximately 7000 images (in terms of A4 size sheet, covered four percent with toner, in JIS standard), and is removably held by the development rotary 23, which is rotatably about an axis 22. In an image forming operation, the development units 20Y, 20M and 20C, which are supported by the development rotary 23, are rotatively moved about the axis 22, as the development rotary 23 is rotated. Then, as the development unit, which is to be immediately used for latent image development, comes to the point at which the distance between the peripheral surface of the development unit from the peripheral surface of the photosensitive drum 15 is smallest, the rotation of the development rotary is stopped. The longitudinal end portions of the development roller 20YS of the development unit, for example, the yellow image developing unit 20Y which stores the yellow toner, is fitted with a spacer ring 20YK (Figure 14), which is coaxial with the development roller 20YS. The external diameter of the spacer ring 20YK is slightly larger than that of the development roller 20YS. As the spacer roller 20YK remains in contact with the peripheral surface of the photosensitive drum 15, a microscopic gap (approximately 300 µm) is secured between the development roller 20YS and the photosensitive drum 15, to develop an electrostatic latent image on the photosensitive drum 15 into a toner image. This arrangement for maintaining a microscopic gap between the photosensitive drum 15 and the development roller 20YS also applies to the development units for other colors. Referring to Figure 12, which depicts the yellow image developing unit 20Y which is standing still after being moved to the position where the distance between the peripheral surfaces of the photosensitive drum 15 and development roller 20YS is smallest, the development unit 20Y will be described. In the development unit 20Y, yellow toner is delivered to a toner coating roller 20YR by the toner delivering member 20YT disposed within the container. After being delivered to the vicinity of the coating roller 20YR, which is being rotated in the clockwise direction indicated by an arrow mark in the drawing, the toner is coated on the peripheral surface of the development roller 20YS, by the coating roller 20YR, and a blade 20YB placed in contact with the peripheral surface of the development roller 20YS with a predetermined pressure, while being triboelectrically charged by the coating roller 20YR and the blade 20YB. Then, as development bias is applied to the development roller 20YS placed adjacent to the photosensitive drum 15 on which a latent image has been formed, a toner image which reflects the latent image is formed on the photosensitive drum 15. This latent image developing system for the yellow image developing unit 20Y also applies to the magenta image developing unit 20M and the cyan image developing unit 20C. The yellow image developing unit 20Y comprises the development roller 20YS, and a storing portion for storing yellow toner. Similarly, the magenta color image developing unit 20M comprises a development roller 20MS and a storing portion for storing magenta toner, and the cyan color image developing unit 20C comprises a development roller 20CS and a storing portion for storing cyan toner. As the development roller of the development unit arrives at the latent image developing point as the development rotary is rotated, the development roller is connected to a high voltage power source and a driving gear 38, which are provided in the printer main assembly 18, so that a voltage which is specific to each development roller is applied to the development roller, and the development roller is rotatively driven. (Image Transferring Intermediary Member) For the formation of a single color image, the image transferring intermediary member 9 (hereinafter, intermediary transfer member) receives toner images four times; four toner images (yellow, magenta, cyan and black toner images), each of which is formed by a development unit dedicated to a specific color, and therefore, is different in color f rom the other, are transferred, in a superposing manner, onto the intermediary transfer member 9. In an image transferring operation, the intermediary transfer member 9 is rotated in the clockwise direction indicated in the drawing, in synchronism with the peripheral velocity of the photosensitive drum 15. After the color toner images are transferred onto the intermediary transfer member 9 in a superposing manner, a recording medium 2 is delivered to the interface between the intermediary transfer roller 9, and the transfer roller 10 to which voltage is being applied, and then, as the recording medium 2 is conveyed through the interface, being pinched by the intermediary transfer roller 9 and the transfer roller 10, the color toner images of different color on the intermediary transfer roller 9 are transferred all at once onto the recording medium 2 in a superposing manner. The intermediary transfer roller 9 in this embodiment comprises an aluminum cylinder 12 with a diameter of 186 mm, and an elastic layer 11 which covers the peripheral surface of the aluminum cylinder 12. The material for the elastic layer 11 is sponge, rubber, or the like, with electrical resistance in a medium range. The intermediary transfer member 9 is rotatively supported, and is rotatively driven through a gear integrally formed with the intermediary transfer member 9 (unillustrated). (Cleaning Means) The cleaning means is a means for cleaning the toner (waste toner) which is remaining on the peripheral surface of the photosensitive drum 15 after the toner images, that is, the visual images formed on the peripheral surface of the photosensitive drum 15 by the developing means, are transferred onto the intermediary transfer member 9. The toner having been removed from the photosensitive drum 15 is stored in the waste toner bin 14 of the cleaning means. The waste toner bin 14 is given a capacity larger than the total amount of the waste toner which is estimated to be produced throughout the service life (equivalent to approximately 50,000 images) of the photosensitive drum 15; since the waste toner bin 14 is integral with the cleaning means holder which also holds the photosensitive drum 15, the old waste toner bin 14 is automatically replaced with a fresh one as the photosensitive drum 15 is replaced with a fresh one after reaching the end of its service life. In this embodiment, a cleaning blade 16 is used as the cleaning member. (Recording Medium Feeding Section) The recording medium feeding section is a section for delivering the recording medium 2 to the image forming section. It primarily comprises: a feeder cassette 1 which stores a plurality of recording medium; a feeder roller 3; a feeder roller 4; a retarding roller 5 for preventing recording medium from being fed by two or more; a recording medium guide 6; and a registration roller 8. In an image forming operation, the feeder roller 3 is rotatively driven in synchronism with the image forming operation, so that the recording medium 2 in the feeder cassette 1 are fed out of the feeder cassette into the printer main assembly, one by one, while being separated by the feeder roller 3. Then, the recording medium 2 is guided to the conveyer roller 7 by the recording medium guide 6, and then is further conveyed by the conveyer roller 7 to the registration roller 8. The registration roller 8 is intermittently rotated with predetermined timing so that the recording medium 2 and the toner images align with each other in the following image forming step, that is, the image transferring process; in other words, the registration roller 8 is temporarily stopped to temporarily stop the forwarding of the recording medium 2, and then, is rotated again to convey the recording medium 2 toward the intermediary transfer roller 9. (Image Transferring Section) The image transferring section comprises a transfer roller 10, as an image transferring member. The transfer roller 10 is constituted of a metallic shaft, and a layer of foamed elastic material with electrical resistance in a medium range which is wrapped around the peripheral surface of the metallic shaft. It is rotatively driven, and also can be pivoted between a top position and a bottom position about the axis of the member which supports the transfer roller 10. While the four color toner images are being transferred onto the intermediary transfer member 9, that is, while the intermediary transfer member 9 is being rotated a plurality of times to receive the four toner images, the transfer roller 10 is kept at the bottom position outlined with a solid line in the drawing, being separated from the intermediary transfer member 9, so that the toner images are not disturbed. After all four toner images are transferred onto the intermediary transfer member 9, the transfer roller 10 is moved by an unillustrated member such as a cam to the top position indicated with a broken line in the drawing, in synchronism with the timing with which the color toner images are transferred onto the recording medium 2; in other words, the transfer roller 10 is pressed upon the intermediary transfer member 9, with the recording medium 2 being pinched between the transfer roller 10 and the intermediary transfer member 9. At the same time as the transfer roller 10 is moved to the top position, bias begins to be applied to the transfer roller 10, and therefore, the toner images on the intermediary transfer member 9 are transferred onto the recording medium 2. Since both the intermediary transfer member 9 and the transfer roller 10 are driven, the recording medium 2 pinched between the two members is conveyed at a predetermined speed leftward in the drawing, that is, toward a thermal fixing device 25 in which the next image forming process is carried out. (Image Fixing Device) The toner images formed on the photosensitive drum 15 by the developing means 20 and 21 are transferred onto the recording medium 2 by way of the intermediary transfer member 9. The thermal fixing device 25 is a device that fixes, with the use of heat, the toner images having been transferred onto the recording medium 2. As depicted in Figure 1, the thermal fixing device 25 comprises a fixing roller 26 for applying heat to the recording medium 2, and a pressure roller 27 for pressing the recording medium 2 upon the fixing roller 26. Both rollers are hollow, and contain heaters 28 and 29, respectively. They convey the recording medium 2 by being rotatively driven. Thus, while the recording medium 2 which is holding the toner images is conveyed by the fixing roller 26 and the pressure roller 27, heat and pressure are applied to the toner images and the recording medium 2, whereby the toner images are fixed to the recording medium 2. (Installation of Color Development Unit) At this time, a method for installing the development units in this embodiment into the printer main assembly will be described with reference to Figures 2 - 11. First, a front door 39, as the cover of the apparatus main assembly 18, is opened by a user, by pivoting it about a vertical hinge 39a. In the space behind the front door, a door 43 as a development unit cover is disposed, the bottom edge of which is attached to the apparatus main assembly 18 with the use of a hinge 43a (Figure 4). The color component development units are installed by opening this development unit cover 43. It should be noted that as the front door 39 is opened, the operation of the printer is automatically stopped; a projection 40 attached to the front door 39 releases an interlock switch 41 illustrated in Figure 13, and as a result, the power circuit of the apparatus main assembly 18, which is run on 24 V, is interrupted. Referring to Figure 13, a rod 40a which is moved by being pushed by the projection 40 is attached to the apparatus main assembly 18, and is horizontally movable. It is also under the pressure applied in the horizontal direction by a tension spring 48. The right-hand end of the rod 40a is placed in contact with one end of a lever 49 pivotally attached to the apparatus main assembly with a pin 49a. The other end of the lever 49 is pressing an actuator spring 41a of the interlock switch 41 fixed to the apparatus main assembly 18, being therefore under the pressure from the actuator spring 41a. As the operator closes the front door 39 against the force of the spring 48, the rod 40a is pushed by the projection 40 on the front door 39, and therefore, it moves rightward, pushing in turn the lever 49. As a result, the lever 49 is pivoted counterclockwise about the pin 49a, and pushes the actuator spring 41a, turning on the interlock switch 41. As a result, the apparatus main assembly begins to receive power. On the contrary, as the operator opens the front door 39, the projection 40 is moved leftward by the force of the spring 48, allowing the lever 49, which is under the pressure from the actuator spring 41a, to pivot clockwise about the pin 49a to a position outlined by a double dot chain line in Figure 13. As a result, the interlock switch 41 is turned of, and therefore, the apparatus main assembly 18 is cut off from the power source. The development unit cover 43 is provided with a transparent window 43b, so that the operator can confirm the identity of the development unit. When a desired development unit is not at a position where it can be removed through an opening 43c, a button 47 located below the development unit cover 43 is to be pushed by the operator as shown in Figure 3 so that the development rotary 23 is rotated to move the desired unit to the position where the desired unit can be removed. After waiting until the development rotary 23 stops to place the desired development unit at the position where the desired unit can be replaced, the operator opens the development unit cover 43 to expose the section of the development rotary in which the development unit is fitted, as shown in Figure 4. Then, the operator pushes down a release lever 46 in the direction indicated by an arrow mark in Figure 5. The release lever 46 is a member that prevents the development unit from moving in the direction in which the development unit is moved out of the development rotary. It is pivotally attached to the development rotary 23, and prevents the frontward movement of the development unit by being placed in contact with the rear portion of the development unit frame. It should be noted here that as the development unit cover 43 is opened to replace a development unit, the development rotary 23 is automatically locked; a projection 44 attached to the development unit cover 43 releases an interlock switch 42 illustrated in Figure 13, whereby the development rotary stopper solenoid (unillustrated) is activated. Also referring to Figure 13, a rod 44a that moves by being pushed by the projection 44 is attached to the main assembly 18 in such a manner that it is allowed to move vertically, and is under the upward pressure from a tension coil spring 55. When the rod 44a is at the topmost position, it is not pressing the actuator 42a of the interlock switch 42, whereas when it is at the bottommost position, it is pressing the actuator 42a of the interlock switch 42. As the operator closes the development unit cover 43 against the force of the spring 55, the projection 44 pushes down the rod 44a, and the interlock switch 42 is turned off. Next, as the development unit cover 43 is opened, the projection 44 is moved away from the rod 44a, allowing the rod 44a to be moved upward by the force of the spring 55, and as a result, the interlock switch 42 is turned on. The interlock switch 42 is wired to the aforementioned solenoid. For example, assuming that the density of the toner in the development unit 20Y (development unit 20M or development unit 20C) has become extremely high due to the vibration that has occurred during the transportation of the development unit 20Y, then, if the development unit in this state is installed, as is, in the main assembly 18, the initial torque necessary for driving the development unit becomes rather high as indicated by a line 51 in Figure 19. If this initial torque necessary to drive the development unit exceeds the maximum allowable torque 53 of the motor of the apparatus main assembly 18, the development roller and/or the toner conveying member may not be rotated smoothly at the beginning of their rotations, although the rotation of the development roller and/or the toner conveying member eventually reaches its predetermined velocity as the toner density is reduced by its initial rotation. Thus, in order to prevent the above-described problem, the operator must shake the development unit well, as shown in Figure 6, before installing the color development unit 20Y (color development unit 20M or color development unit 20C) into the apparatus main assembly 18. Next, the toner seal 20YP of the development unit 20Y is peeled in the arrow direction in Figure 7. The shaking of the development unit 20Y and the peeling of the toner seal 20YP make the toner in the development unit 20Y ready to be supplied to the development roller 20YS. When the toner seal is peeled, the development unit 20Y must be in such a position that the development roller 20YS is on the top side. The color development unit (20Y, 20M or 20C) is inserted in the arrow direction in Figure 8. It must be inserted by holding it in such a position that the development roller 20YS comes to the top side as shown in Figure 14. The insertion of the development unit 20Y is completed as the projection 20YZ formed as a portion of the front wall of the housing of the development roller 20YS comes in contact with a flange of the development rotary 23. Next, the operator returns the lever 46 in the arrow direction in Figure 9 to prevent the development unit 20Y from accidentally coming out frontward, and closes the development unit cover 43, finishing the installation of the development unit. This installation procedure is repeated three times to install all three development units 20Y, 20M and 20C, in the development unit spaces 23A of the development rotary 23. In a factory where the development unit 20Y is manufactured, the development unit 20Y is packaged for shipment, in such a position that the development roller 20YS is on the bottom side as shown in Figure 15. If the development unit 20Y in this position is vibrated during its shipment or the like situation, the toner in the development unit 20Y is packed adjacent to the toner seal 20YP above the development roller 20YS; the density of the toner increases. However, in this embodiment, the position in which the development unit 20Y is placed to pull off the toner seal 20YP and install the development unit 20Y into the apparatus main assembly 18 is reversal, in terms of vertical direction, to the position in which the development unit 20Y is placed for shipment; the two positions are different by 180 deg. in the vertical direction. With the development unit 20Y being in the position in which the development roller 20YS is on the top side, the impacted toner in the toner chamber 20YU is likely to naturally loosen, and therefore, even if the operator forgets to shake the development unit 20Y, or does not shake well, the initial torque necessary for driving the development unit 20Y is prevented from significantly increasing. To give a supplementary description regarding the properties of the toner in this embodiment, the toner used in this embodiment has the following properties. If a certain amount of the toner used in this embodiment is placed in a bottle, and is vibrated, the density of the toner in the bottom becomes extremely high. Then, if this bottle is held upside down for a certain length of time, the toner in the bottle loosens in only three to ten seconds. In other words, the toner used in this embodiment is such toner that easily packs itself, but also easily loosens itself. This embodiment is based on this property of the toner. Therefore, the development rotary and the development units are so structured that when the operator installs a new development unit, the development unit is kept, for a predetermined length of time, in such a position that the development roller is on the top side. However, such a structural arrangement does not guarantee that the packed toner in the development unit loosens itself by 100 %. Thus, in this embodiment, the development rotary is rotated in accordance with the following sequence. (Sequence for Rotating Development Rotary) Referring to Figures 16 and 18, the sequence for rotating the development rotary will be described. The development rotary is rotated following a sequence: A - B - C - D - E - F. Figure 16, (A) depicts the development unit 20Y and the development rotary 23 in a state in which the development unit 20Y has been completely installed in the development rotary 23. When the printer is not in a sleep mode (standby mode in which the printer is not used for a predetermined length of time or longer) temperature control for the thermal fixing device 25 is started. Figure 16, (B) depicts the development unit 20Y and the development rotary 23 in a state in which the development rotary 23 has begun to be rotated to detect the home position of the development unit 20Y to confirm the position of the development unit 20Y having been installed in the development rotary 23. More specifically, the development rotary 23 is continuously rotated more than once in the clockwise direction indicated by an arrow mark in the drawing, and is stopped at the home position (position at which the development unit 20Y is stopped before it is moved to the image developing position). At the home position, the identity (color) of the development unit 20Y is checked; more specifically, the color label attached to the side wall of the development unit 20Y is detected by a sensor (unillustrated). Next, the amount of the toner in the development unit 20Y is detected. When the detected amount of the toner is smaller than a predetermined amount (Mg), the initial torque necessary for driving the development unit 20Y is small, and therefore, the following sequence is not carried out. There are two possible cases in which the detected amount of the toner is less than the predetermined amount: a case in which, for some reason, a development unit 20Y, half or more of the toner in which has been used, is installed; and another case in which a development unit 20Y has not been fully filled with the toner to begin with. The first case can be detected by detecting the amount of the toner in the development unit 20Y in advance. This can be detected by a method in which the electrostatic capacity of the toner is detected immediately after the development unit is installed in the development rotary 23, a method in which the density of the toner in the development unit 20Y is detected with a piezoelectric element, or the like method. The second case can be detected by a method in which a member that reflects the amount of the toner initially filled in the development unit 20Y is attached to the side wall of the development unit 20Y, and this member is detected by a sensor (unillustrated) of the apparatus main assembly 18. However, this step of detecting the amount of the remaining toner in the development unit 20Y may be eliminated. When this step is eliminated, the following sequence is carried out regardless of the amount of the toner in the development unit 20Y. In other words, the system for detecting the amount of the toner in the development unit 20Y to determine whether or not the following sequence should be carried out can be eliminated by eliminating the step for detecting the amount of the toner in the development unit 20Y. In this embodiment, however, a toner amount detecting system to determine whether or not the amount of the toner in the development unit 20Y is above the minimum amount necessary for forming a desirable image is provided. Next, the temperature of the thermal fixing device 25 is detected. When the detected temperature of the thermal fixing device 25 is lower than a predetermined value, the following sequence is carried out, but when the detected temperature of the thermal fixing device 25 is above the predetermined value, the following sequence is not carried out. The temperature of the thermal fixing device 25 is detected by a thermistor (unillustrated) placed in contact with the fixing roller 26. Figure 16, (C) depicts the development rotary 23 and the development unit 20Y in a state in which the development rotary 23 has been rotated to a referential stop position, that is, the position from which the intermittent development rotary rotation sequence in,this embodiment is started, and is being kept there for a predetermined length of time. At this referential stop position, the development unit 20Y is in the position in which the development roller 20YS is on the top side as depicted in Figure 16, (A). In other words, the development unit 20Y is at the position where the development unit 20Y can be removed from the development rotary 23. Figure 16, (D) depicts the development rotary 23 and the development unit 20Y in a state in which the development rotary 23 has been rotated 120 deg. more, and then, is being kept there for a predetermined length of time. Figure 16, (E) depicts the development rotary 23 and the development unit 20Y in a state in which the development rotary 23 has been 120 deg. more, and then, is being kept there for a predetermined length of time. Figure 16, (F) depicts the development rotary 23 and the development unit 20Y in a state in which the development rotary 23 is being rotated to the home position, that is, the position at which the development unit 20Y is stopped before being moved to the image developing position. After the sequence described above through which the development rotary 23 is rotated more than once, the driving force is transmitted to the development roller 20YS from the apparatus main assembly 18. The sequence described above is carried out according to the flow chart given in Figure 18. It was shown that in this embodiment, as long as the length of time during which development rotary 23 was kept at the referential stop position was set to six seconds or more, the toner in the development unit 20Y sufficiently loosened as depicted in Figure 15. The torque necessary for driving the development unit 20Y after the development rotary 23 was rotated following the above-described sequence is as represented by a curved line 52 in Figure 19. As is evident from the graph, the initial torque necessary for driving the development unit 20Y after the development rotary 23 was rotated following the above-described sequence never exceeds the maximum allowable torque output 53 of the motor. The curved line 52 represents the torque necessary to drive the development unit 20Y after the development unit 20Y sealed with the toner seal 20YP was manually and vigorously shaken by the operator while being held by the operator in such a position that the development roller 20YS was on the bottom side as illustrated in Figure 15, (B); the toner seal 20YP was removed; the unsealed development unit 20Y was installed in the development rotary 23; and the above-described intermittent development rotary rotation sequence was carried out. As is evident from the curved line 52, the initial torque necessary to drive the development unit 20Y was not significantly higher, compared to when the development roller 20YS was on the top side. When the development unit 20Y left in such a position that the development roller 20YS was on the bottom side as illustrated in Figure 15 was installed in the development rotary 23 without being manually shaken by the operator, that is, without being subjected to strong vibration, the torque necessary for driving the development unit 20Y was as represented by the curved line 52a. In the test represented by the curved line 52a, the above-described intermittent rotation sequence was not carried out, but the initial torque necessary for driving the development unit 20Y was relatively small. When the development unit 20Y manually shaken by the operator while being held by the operator in such a manner that the development roller 20YS was on the bottom side was installed in the development rotary 23, but the intermittent rotation sequence was not carried out, the initial torque necessary for driving the development unit 20Y exceeded the maximum allowable torque 53 of the motor, as the curved line 51 shows. Embodiment 2 Next, referring to Figure 17, the second embodiment of the present invention will be described. In the drawings, the components identical to those described in the first embodiment are designated with the same codes to avoid the repetition of the same descriptions. In the first embodiment, when the development roller 20YS passes by the photosensitive drum 15 as the development rotary 23 is rotated, the spacer rings 20YK fitted around the longitudinal ends of the development roller 20YS, one for one, come in contact with the peripheral surface of the photosensitive drum 15. Therefore, it is possible that if the impact of the contact between the spacer ring 20YK and the photosensitive drum 15 is large, the layer of the toner coated on the peripheral surface of the development roller 20YS may be partially disturbed. This second embodiment is different from the first embodiment in the location of the referential stop position. The referential stop position in this embodiment is the position illustrated in Figure 17, (C), where the distance between the peripheral surface of the development roller 20YS and the peripheral surface of the photosensitive drum 15 is smallest, that is, where a latent image on the photosensitive drum 15 is developed. In order to stop the development rotary 23 at the referential stop position, the rotational velocity of the development rotary 23 is reduced before it is stopped at the referential stop position. Therefore, the impact that occurs as the spacer rings 20YK of the development roller 20YS come in contact with the peripheral surface of the photosensitive drum 15 is also reduced. Consequently, the layer of the toner coated on the peripheral surface of the development roller 20YS is prevented from being disturbed, as described above. However, the attitude of the development unit 20Y at the referential stop position is not such that the development roller 20YS is exactly on the top side, and therefore, the development unit 20Y must be kept stationary for a longer time than in the first embodiment; in other words, the development rotary 23 must be kept stationary a longer time than in the first embodiment. In this embodiment, the eight seconds or more was necessary. As is evident from the description given above, in this embodiment, the development rotary 23 having been stopped at the home position is rotated to the referential stop position, and is stopped there for approximately eight seconds. Then, the development rotary 23 is rotated approximately 120 deg., and is stopped for approximately eight seconds. Thereafter, the development rotary 23 is rotated again approximately 120 deg., and is stopped for approximately eight seconds. Then, the development rotary 23 is rotated again approximately 120 deg., and is stopped for approximately eight seconds. This rotational sequence is carried out to loosen the toner in the development unit. Further, in the preceding embodiments, the direction in which the development unit is inserted into the development rotary was the same as the direction of the generatrix of the photosensitive drum. But, obviously, the same effects as those described above can be also obtained when the present invention is applied to an image forming apparatus, in which the development unit is inserted into the development rotary in the direction perpendicular to the generatrix of the photosensitive drum. Further, in the preceding embodiments, the present invention was described with reference to the development unit 20Y for yellow color component. But, apparently, the description given above with reference to the development unit 20Y also applies to other development units 20M and 20C. Further, the same effects as those described with reference to the development unit for yellow color component in the preceding embodiments can be obtained even if the development unit for black color component is installed in the development rotary. The development unit to which the present invention is applicable includes the black component development unit, as well as the color component development units. In order for a development unit to be compatible with the present invention, a development unit has only to comprise a toner storing portion and an image developing member (for example, development roller); the development unit may comprise any one, or all, of an electrophotographic photosensitive member, a charging member, and a cleaning member, in addition to a toner storing portion and an image developing member. The development unit means a unit that integrally comprises these components, and is removably installable in the development rotary of the main assembly of an image forming apparatus. In other words, structures to which the present invention is applicable are not limited to the structure described in the preceding embodiments. Next, referring to Figure 20 which is a block diagram, the general operational sequence of the structures in the preceding embodiments will be described. In the diagram, a reference figure 100 designates a control section that controls the entirety of the apparatus. The control section 100 comprises: a CPU such as a microprocessor; ROMs which store the control programs for the CPU, such as the one depicted by the flow chart in Figure 18; RAMs which are used as the work areas for the CPU, and temporarily store various data; and the like components. The control section 100 receives electrical signals from a group 101 of sensors; the interlock switch 41 for detecting the opening or closing of the front door 39 (Figure 2); the interlock switch 42 for detecting the opening or closing of the development unit cover 43 (Figure 3); a sensor S3 for detecting the temperature of the thermal fixing device 25 (Figure 1); a sensor (jam sensor) for detecting the recording medium jam that occurs during recording medium conveyance (unillustrated); and the like sensors. The control section 100 also receives image data or the like from a host 102 such as a computer or a word processor. Based on these electrical signals and image data, and the like, the control section 100 controls, as described before, the rotation of the photosensitive drum 15, and various image forming processes: conveying 102 of the recording medium 2; exposing 103; charging 104; developing 105; transferring; and fixing 107, as well as the rotation of the development rotary 23. The following is the summary of the preceding embodiments. An image forming apparatus for forming an image on recording medium comprises: an image bearing member (for example, the electrophotographic photosensitive drum 15); a rotatable development rotary (23); development unit installation spaces (23A) in which development units (for example, color component development units 20Y, 20M and 20C) for developing latent images formed on the image bearing member are removably installed; and a control section (100) which carries out an intermittent development rotary rotation sequence, in which the development rotary (23) is temporarily stopped after it is rotated by a predetermined angle, is repeated a predetermined number of times immediately after the development unit is replaced. Before carrying out the intermittent development rotary rotation sequence, the control section carries out a sequence in which the development rotary (23) is rotated until it reaches the referential stop position. The aforementioned referential stop position is a position at which the distance between the development roller of a development unit and a photosensitive drum (15) as the image bearing member becomes smallest. When the temperature of a thermal fixing device (25) is lower than a predetermined temperature, the control section (100) carries out the intermittent rotation sequence, whereas when the temperature of the thermal fixing device (25) is higher than the predetermined temperature, the intermittent rotation sequence is not carried out. The thermal fixing device (25) is a device for thermally fixing the toner image having been transferred onto a recording medium (2), to the recording medium (2). After a development unit.desired to be replaced is replaced, the control unit first rotates the development rotary (23) to the referential stop position, and then, carries out the intermittent development rotary rotation sequence. The control section recognizes the completion of the development replacement process by sensing that a cover (for example, the development unit cover 43) for covering the opening (43c) through which the development unit in the development unit space (23A) is replaced is opened, and closed, and then, the front door (39) is closed. After recognizing the completion of the development unit replacement process, the control section carries out the nonintermittent development rotary rotation sequence. A development unit is replaced in the following manner; first, the front cover is opened; next, the cover (43) which covers the opening through which a development unit in the development installation space (23A) is replaced is opened; and then, the desired development unit is replaced. The control section (100) recognizes that all of the desired development units have been replaced by detecting the closing of the front door (39) Then, the control section (100) carries out the nonintermittent development rotary rotation sequence, in which the predetermined point of the development rotary (23) is rotated to the referential point. Thereafter, the control section (23) carries out the intermittent development rotary rotation sequence. Further, the main assembly of an image forming apparatus is provided with a button (47). As the button (47) is pressed, the development rotary (23) is rotated by a predetermined angle, so that the one of the plurality of the development units installed in the development rotary (23) is moved to the position where the development unit can be removed through the opening (43c). The effects of the preceding embodiments are as follows: (1) Even when an operator installs a development unit into the main assembly of an image forming apparatus without sufficiently shaking the development unit, the initial torque necessary to drive the development unit can be prevented from becoming significantly high. Therefore, the driving system is not subjected to sudden increase of the torque, and as a result, image formation is stably carried out. In addition, it is unnecessary to switch the currently used development unit motor, or the driver, to larger ones, and therefore, it is possible to prevent the size of the main assembly, and the cost of the apparatus, from increasing. (2) When the temperature of the thermal fixing device is higher than a predetermined temperature, the intermittent development rotary rotation sequence is not carried out. For example, immediately after an operator turns off, by mistake, the power switch of the apparatus main assembly, or unplugs the main assembly f rom the power source, during the malfunctioning, such as a paper jam, the thermal fixing apparatus is sufficiently high, and therefore, the intermittent development rotary rotation sequence is not carried out. As a result, the standby state can be reached in a shorter time. On the other hand, it is possible that an operator replaces the development unit after the operator has turned off the power switch, or unplugs the apparatus from the power source, by mistake. This is a rather unusual case. However, even in such a case, the intermittent development rotary rotation sequence is carried out if the temperature of the thermal fixing device is lower than the predetermined one, and therefore, the initial torque necessary for driving a development unit can be prevented from significantly increasing. (3) When the amount of the toner in a development unit is smaller than a predetermined amount, the intermittent development rotary rotation sequence is not carried out. Therefore, an image forming apparatus can reach the standby state in a shorter time. (4) The position at which a development unit is stopped is the image developing position, and the speed of the motor which drives a development rotary can be sufficiently reduced before the development unit is stopped at the image developing position. Therefore, the impact that occurs when a development roller and an electrophotographic photosensitive drum come in contact with each other can be reduced. Consequently, the layer of toner coated on the development roller is not disturbed. As a result, an image forming apparatus is prevented from forming abnormal images at the beginning of an image forming operation. As described above, according to the present embodiments, the aggregated toner in a development unit can be loosened by the intermittent development rotary rotation. While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth.

Claims: An image forming apparatus for forming an image on a recording material (2), comprising; an image bearing member (15); a rotatable member (23) for detachably mounting a plurality of developing units (20Y,20M,20C) for developing electrostatic latent images formed on said image bearing member with different colour toners; and heat fixing means (25) for fixing a toner image on the recording material after the toner image has been transferred onto the recording material from the image bearing member, characterised by control means (100) arranged to effect intermittent rotation of the rotatable member, wherein the rotatable member is repeatedly rotated and stopped, before the image forming apparatus enters a stand-by state, if it is detected that a temperature of the heat fixing means (25) is lower than a predetermined level. Apparatus according to claim 1 having an opening (43c) permitting mounting and demounting of the development units to and from the rotatable member (23) and a unit cover (43) for closing the said opening, and in which the control means is arranged to effect the intermittent rotation before the apparatus enters a stand-by state after an operation of closing the unit cover has been detected. Apparatus according to claim 2 in which the control means is arranged to effect the intermittent rotation after detection of the operation of closing the unit cover (43) and before the apparatus enters a stand-by state, irrespective of the detected temperature of the heat fixing means (25). Apparatus according to claim 2 or claim 3 in which the control means is arranged not to effect the intermittent rotation before the apparatus enters a stand-by state if the operation of closing the unit cover (43) is not detected and it is not detected that the temperature of the heat fixing means (25) is higher than the predetermined level. Apparatus according to claim 1 in which the control means is arranged to effect the intermittent rotation after exchange of a developing unit ( 20Y, 20C, 20M) mounted on the rotatable member (23). Apparatus according to claim 5 in which the control means is arranged to stop the rotary member (23) at a reference position. Apparatus according to claim 6 in which the control means is arranged to start the intermittent rotation after the rotary member (23) has stopped at the reference position. An image forming apparatus for forming a multicolour image on a recording material (2), comprising: an image bearing member (15); a rotatable member (23) for detachably mounting a plurality of developing units (20Y,20M,20C) for developing, with different colours of toner, electrostatic latent images formed on said image bearing member; a heat fixing means (25) for fixing a toner image on the recording material after the recording material has received the toner image from said image bearing member; a main assembly cover (39); and an open/close detecting means (41) for detecting opening and closing of said main assembly cover (39); characterised by a unit cover (43) for closing an opening (43c) for permitting mounting-and-demounting of one of said developing units relative to said rotatable member (23); an open/close detecting means (42) for detecting opening and closing of said unit cover (43); a control means (100) arranged to effect rotation of said rotatable member (23), after said main assembly cover (39) is closed, through a predetermined degree to a reference position, if said unit cover (43) has been opened and closed, and a temperature of said heat fixing means (25) is lower than a predetermined temperature, and arranged to effect intermittent rotation of said rotatable member (23), wherein it is repeatedly rotated and stopped for a predetermined duration, after said rotatable member is rotated through the predetermined degree. An apparatus according to any one of claims 2 to 4 and 8, having a switch (47) for rotating said rotatable member (23) to a position where a developing unit mounted on it is demountable from said opening (43c). Apparatus according to any one of claims 6 to 8 in which the rotatable member (23) is for mounting developing units (20Y,20M,20C) each having a developing roller (20YS,20MS,20CS), and the image bearing member (15) is an electrophotographic photosensitive member, and the reference position is a position where the developing roller of a developing unit mounted on the rotatable member is opposed to the image bearing member. Apparatus according to any one of claims 6 to 8 in which the rotatable member (23) is for mounting developing units (20Y,20M,20C) each having a developing roller (20YS,20MS,20CS), and the reference position is a position in which the developing roller of a developing unit mounted on the rotatable member is uppermost. Apparatus according to any one of the preceding claims in which the rotatable member (23) is for mounting a plurality of developing units, the plurality comprising: a yellow developing unit (20Y) having a yellow developing device for developing the electrostatic latent image with yellow toner and a yellow toner accommodating portion (20YU) for accommodating yellow toner; a cyan developing unit (20C) having a cyan developing device for developing the electrostatic latent image with cyan toner and a cyan toner accommodating portion (20CU) for accommodating cyan toner; and a magenta developing unit ( 20M) having a magenta developing device for developing the electrostatic latent image with magenta toner and a magenta toner accommodating portion (20MU) accommodating magenta toner. Apparatus according to any one of the preceding claims in which the control means (100) is arranged not to effect the intermittent rotation if it is detected that the amount of toner in a developing unit mounted on the rotatable member is less than a predetermined amount. Apparatus according to any one of the preceding claims in which the intermittent rotation of the rotatable member comprises repeatedly performing the sequence of: rotating the rotatable member; and temporarily stopping it after it has rotated by a predetermined angle. Apparatus according to claim 14 in which the predetermined angle is 120°. Apparatus according to any one of the preceding claims comprising a plurality of said developing units (20Y,20M,20C) mounted on the rotatable member (23).

Inventors: ISOBE HIRONOBU, KOBAYASHI KAZUNORI, ISOBE, HIRONOBU, KOBAYASHI, KAZUNORI
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1998
Main classification: G03G15
IPC codes: G03G15, G03G21