Image forming apparatus

Abstract: The present invention relates to an image forming apparatus for forming an image on a recording medium, comprising an image bearing member, plural development means for effecting image development by acting on said image bearing member, and drive means for enabling drive force transmission to selected one among said plural development means by rotation in a direction, and driving said selected development means by rotation in a direction opposite to the above-mentioned direction.

Description: The present invention relates to an image forming apparatus for forming an image on a recording medium, such as electrophotographic copying apparatus, laser beam printer (LBP), facsimile apparatus, word processor or the like. In an image forming apparatus in which plural developing units respectively containing toners of different colors are positioned along a running image bearing member and are activated in succession to form a color toner image, it is conceived to equip the developing units respectively with solenoid clutches and to activate said developing units in succession by on-off operations of said solenoid clutches. In such operating system, there is required a solenoid clutch for each developing unit. Thus, in case of forming a full color image with toners of four colors of cyan, magenta, yellow and black, there are required four developing units, or namely four solenoid clutches. Since such solenoid clutches are expensive, such system leads to an increased cost of the entire apparatus. Also since the solenoid clutches are relatively bulky, there is required a large space for the installation thereof. Patent Application EP-A-0410730 describes an image forming apparatus, comprising: an image bearing member; a plurality of developing means for supplying respective developing agents to the image bearing member, each of the developing means having a respective developing agent bearing member; a drive source (M) for supplying a driving force; transmitting means for transmitting the driving force to a selected one of the developing agent bearing members; and selecting means for selecting which of the developing agent bearing members is to be driven by the transmitting means. In this arrangement, each of the developing agent bearing members is driven via a respective slipping clutch, and the selecting means comprises a separate drive source which can drive a series of cams which cause all but a selected one of the clutches to slip. The present invention is characterised in that the selecting means is arranged in use to be driven by the drive source to select one of the developing agent bearing members when the drive force is not transmitted from said drive source to said plural developing agent bearing members. Thus a separate drive source for selection is not necessary, enabling compactization, and a reduction in the manufacturing cost. Specific embodiments of the present invention will now be described way of example with reference to the accompanying drawings, in which: Fig. 1 is a lateral view of a drive transmission switching mechanism for developing units, embodying the present invention; Figs. 2 and 3 are partial lateral views of a selecting mechanism for developing units, constituting an embodiment of the present invention; Fig. 4 is a lateral view of a drive transmission switching mechanism for developing units, constituting another embodiment of the present invention; Fig. 5 is a lateral view of a driving gear train; In the following there will be described an image forming apparatus provided with a driving motor, plural development units selectively driven by said motor and a switching cam mechanism for driving a selected development unit, and allowing switched drive of the plural development units with a simple and inexpensive configuration employing only one motor, by providing a transmission mechanism capable of transmitting rotation of one direction only between said motor and said switching cam mechanism and a transmission mechanism capable of transmitting rotation of the other direction only between said motor and selected development unit. This embodiment allows to securely control the selection of the development unit and the function thereof by simple mechanical means, without the use of expensive components such as solenoid clutch. More specifically a driving motor can be used for selecting the development unit, driving the selected development unit, and driving an image bearing member such as a photosensitive drum. Fig. 1 is a schematic lateral view of a preferred embodiment of the present invention, in which, for ease of understanding, the development units and the image bearing member are illustrated by double-dotted chain lines. In the illustrated apparatus, there are provided four development units 1, 2, 3, 4 respectively containing cyan (C), magenta (M), yellow (Y) and black (K) toners. In each image development, one of said development units is activated corresponding to a latent image formed on an image bearing member 30, and a developing roller (9, 10, 11 or 12) provided in said development unit supplies toner to form a toner image. Means for forming said latent image will be explained later. In the following there will be explained the switching of the development units, with reference to Figs. 1, 2 and 3, in which Figs. 2 and 3 are lateral views of an end portion of the apparatus shown in Fig. 1. As shown in these drawings, a cam 17 with a notch 17a is rotated by a driving source to be explained later. When a conical portion 13 formed on a gear 13a fits into said notch 17a, the gear 13a meshes, by the pushing force of a spring 13b, with a gear 5 which is coaxial with a gear 20 and a developing roller 9. When a gear 22, driven by a motor M (for example a stepping motor) is rotated in a direction a shown in Fig. 1, a switching gear 23a supported by a crank-shaped support member 23 assumes the illustrated position, whereby the driving force is transmitted through gears 22, 23c, 23a, 21, 20, 13a and 5 to rotate the developing roller 9 which thus supplies toner to a latent image formed on the image bearing member 30 with a rotating shaft 30a. Said crank-shaped support member 23 supports a gear 23c at the center and gears 23a, 23b on both ends which can vibrate vertically about an axis 23d coaxial with the gear 23c, whereby either gears 21 and 23a or gears 19 and 23b come into a meshing state. When the gears 21 and 23a are in the mutually meshing state, conical portions 14, 15, 16 of gears 6, 7, 8 coaxial with the driving rollers 10, 11, 12 of other development units 2, 3, 4 are pressed by the cam 17, so that said gears 6, 7, 8 are disconnected from the gear 20 and the developing rollers 10, 11, 12 do not rotate. Also when one of other conical portions 14 - 16 fits into the notch 17a of the cam 17, only one developing roller, driven by one of the gears 14a - 16a fitted into said recess 17a, is rotated as explained above, while other three developing rollers are stopped. In the present embodiment, when the motor M is reversed by a signal from a control unit 100 to be explained later, the gear 22 starts to rotate in a direction opposite to the arrow a shown in Fig. 1, whereby the support member 23 is shifted to disengage the gears 21 and 23a and to bring the gears 19 and 23b into the mutually meshing state. Then the gear 19 rotates the cam 17 through the gear 18 whereby the notch 17a of said cam 17 selectively fits with one of the conical portions, corresponding to the signal from the control unit 100. Thus, by a signal from the control unit 100, the motor M is rotated in a predetermined direction to bring a developing roller to an operable state through the cam 17 and the intermediate gears 13a - 16a provided with conical portions 13 - 16. More specifically, the gear 20 and the selected one of the gears 14a - 16a are brought into the mutually meshing state, thereby establishing a drive transmission path between the motor M and the selected one of the developing rollers 9 - 12. Then the motor M is reversed to transmit the driving force thereof to said selected developing roller, thus effecting the development step by rotating said developing roller and the image bearing member 30. The above-explained operation is repeated for a necessary number of times in response to the signals from the control unit 100. For example, if said signals instruct the formation of a full-color image, said operation is repeated four times, whereby the developing rollers 9 - 12 rotate in succession to form a full-color image. On the other hand, if said signals indicate the formation of a monochromatic image, there is conducted development of a selected color only. In the following there will be explained another embodiment of the present invention with reference to Fig. 4, in which components corresponding to those of the foregoing-embodiment are represented by same symbols, and will not be explained further. In the present embodiment, gears 24, 25 respectively provided with one-way clutches 24a, 25a are provided respectively between the motor gear 22 and the switching gear 19 and between said motor gear 22 and the driving gear 21. Also provided are freely rotatable shafts 28, 29 and gears 26, 27 integrally rotatable with said shafts, and said gears 26, 27 respectively mesh with the gears 19, 20. Also the directions of driving force transmission from the gears 24, 25 to the shafts 28, 29 are mutually opposite. In such configuration, the motor M can select the development units by the cam 17 in the rotation in one direction, and effect the development by driving the developing roller and the image bearing member in the rotation in the other direction. As explained in the foregoing, the present embodiment is to selectively activate plural development units by utilizing the rotation of a single motor in one direction for the selection of said development units and the rotation in the other direction for the drive of the selected development unit and the image bearing member, in secure manner through an extremely simple mechanical configuration, and such embodiment is evidently effective for reducing the manufacturing cost of the apparatus of this kind. The present invention need not necessarily be applied to an image forming apparatus utilizing a process cartridge, but, in case such process cartridge is employed, it is not limited to that described in the foregoing embodiments but may include at least an image bearing member and plural development means. It may further integrally include process means acting on the image bearing member, such as charging means, cleaning means or a lens. In the multi-color image forming apparatus explained above, a color image is obtained by overlaying images on a recording material by repeating, plural times, a process of latent image formation on an image bearing member, image development and image transfer onto a recording material. However it is also possible to employ a method of forming overlaid images on an intermediate transfer member by repeating, plural times, a process of latent image formation on an image bearing member, image development and image transfer onto the intermediate transfer member, and transferring said overlaid images collectively onto the recording material, or a method of effecting latent image formation and image development plural times on an image bearing member to obtain overlaid images on said image bearing member, and collectively transferring said overlaid images onto the recording material. The formation of a multi-color image includes so-called full-color image formation and formation of so-called multi-color (two-color or three-color for example) image, by formation of plural monochromatic images. As explained in the foregoing, the present invention can provide an image forming apparatus capable of exactly transmitting the driving force to development means selected from plural development means, with a smaller space than in the conventional technology.

Claims: An image forming apparatus, comprising: an image bearing member (30); a plurality of developing means (1, 2, 3, 4) for supplying respective developing agents to the image bearing member, each of the developing means having a respective developing agent bearing member (9, 10, 11, 12); a drive source (M) for supplying a driving force; transmitting means (22, 23c, 23a, 21, 20) for transmitting the driving force to a selected one of the developing agent bearing members; and selecting means (22, 23c, 23b, 19, 18, 17) for selecting which of the developing agent bearing members is to be driven by the transmitting means; characterised in that: the selecting means is arranged in use to be driven by the drive source to select one of the developing agent bearing members when the drive force is not transmitted from said drive source to said plural developing agent bearing members (9, 10, 11, 12). An apparatus as claimed in claim 1, wherein the transmission means responds to rotation of the drive source in one direction to transmit the driving force to the selected developing agent bearing member, and the selecting means responds to rotation of the drive source in the opposite direction to change the selection of developing agent bearing member. An apparatus according to claim 2, and including a gear arrangement (23) which engages by rocking either with the selecting means or with the transmitting means, depending on the rotating direction of the drive source. An apparatus as claimed in any preceding claim, further comprising discrimination means for discriminating defective drive transmission between the drive source and the selected developing agent bearing member. An apparatus according to claim 4, wherein said discrimination means comprises a drive sensor which is adapted to discriminate defective connection by directly detecting the presence or absence of rotation of the selected developing agent bearing member. An apparatus according to claim 4, wherein said discrimination means comprises a sensor which is adapted to discriminate defective connection by detecting whether a member of said selecting means is not disposed in a proper position. An apparatus according to claim 4, wherein said discrimination means is adapted to discriminate defective connection by detecting the current in a motor for driving the developing agent bearing member. An apparatus according to claim 4, wherein said discrimination means is adapted to discriminate defective connection by detecting a development bias current. An apparatus according to any preceding claim, wherein the developing agents produce mutually different developed colours. An apparatus according to claim 9, wherein the developed colours are yellow, magenta, cyan and black. An apparatus according to any preceding claim, wherein said drive source comprises a stepping motor. An apparatus according to any preceding claim, wherein the selecting means includes a cam (17) serving to connect a gear of the selected developing means with a gear in a main body of said apparatus. An apparatus according to any preceding claim, wherein the image bearing member is an electrophotographic photosensitive member, and the electrophotographic photosensitive member and the development means are formed as constituent parts of a process cartridge which is detachably loaded in a main body of the image forming apparatus. An apparatus according to claim 13, wherein said process cartridge further includes charging means and/or cleaning means for acting on the electrophotographic photosensitive member.

Inventors: INOMATA MITSUGU, INOMATA, MITSUGU, INOMATA, MITSUGU, C/O CANON KABUSHIKI KAISHA
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1992
Main classification: G03G15
IPC codes: G03G15