A multi-color developing device for an image forming apparatus

Abstract: A multi-color developing device for an image forming apparatus comprising: a first developing unit (31) retractable with respect to a photosensitive drum (20); a second developing unit (32) adjacent to the first developing unit and retractable with respect to the photosensitive drum; a cam mechanism (37) for bringing either one of the first or second developing units to a position remote from the photosensitive drum when the other one, either the first or second developing units is positioned adjacent to the photosensitive drum; a pair of driving gears (66,166) provided between the first and second developing units for receiving power to drive the respective developing units; a first joint gear (64) which engages one of the driving gears (66) to transmit power to the first developing unit; a second joint gear (164) which engages the other one of the driving gears (166) to transmit power to the second developing unit; a first joint member (66) which rotatably supports the first joint gear (64) and which moves the first joint gear to the position to engage with or disengage from the corresponding driving gear (66) in synchronization with the moving of the first developing unit (32) close to or away from the photosensitive drum (20); and a second joint member (163) which rotatably supports the second joint gear (164) and which moves the second joint gear to the position to engage with or disengage from the corresponding driving gear (166) in synchronization with the moving of the second developing (32) unit close to or away from the photosensitive drum (20).

Description: This invention relates to a multi-colour developing device for use in an image forming apparatus, and more particularly, it relates to a multi-colour developing device for an image forming apparatus in which a plurality of developing units are arranged to be movable towards and away from a photosensitive drum. According to US-4 710 016 a known two-colour developing device for an image forming apparatus comprises a pair of developing units arranged to be movable towards and away from a photosensitive drum, a cam mechanism for bringing either one of the developing units to a position adjacent the photosensitive drum, developer drive gears provided to drive each developing unit, and a driving unit for selectively driving the developer drive gears, the driving unit including a driving gear and intermediate gears. The intermediate gears for each developing unit are engaged with the driving gear whether the developing unit is in a developing position adjacent the photosensitive drum or in the retracted position. In the known developing device, each intermediate gear is put in the state of engagement with the corresponding developer drive gear when the corresponding developing unit is positioned in the developing position adjacent the photosensitive drum. The intermediate and developer drive gears engage with each other only when the respective developing unit is positioned adjacent the photosensitive drum. That is, the intermediate gear gradually meshes with the driving gear from a state of tooth edge disengagement into a state of engagement as the developing unit moves from a position remote from the photosensitive drum to a position closer to the developing position until the developing roller in the developing unit is positioned adjacent the photosensitive drum with a predetermined clearance. In the above-described device, the intermediate gear and the developer drive gear must be manufactured so that the correct predetermined clearance is provided between the photosensitive drum and the developing roller in the developing unit when the gears are properly engaged, thus requiring accuracy in the finished gears. Also, in the above-mentioned device, since the intermediate and driving gears are constantly engaged with each other, each developing unit can be moved only within the range of the gear engagement, thus limiting the travelling stroke of the developing units. According to the present invention there is provided a multi-coloured developing device for an image-forming apparatus comprising a first developing unit having a first drive gear and being movable, in use, towards and away from a photosensitive drum, a second developing unit having a second drive gear adjacent the first developer unit and also being movable, in use, towards and away from the photosensitive drum, a cam mechanism for selectively moving either one of the developer units into a position adjacent the drum and first and second driving gears for respectively driving the developer units located between the developer units, characterised in that each developer unit has an intermediate gear in driving connection with the particular drive gear and engageable with the particular driving gear on movement of the particular developer unit into a position adjacent the drum, each intermediate gear being carried on a mounting member which is movably mounted in the particular developer unit to enable the intermediate gear operatively to engage with the particular driving gear as the developer unit is moved, in use, towards the drum independently of the precise final position of the developer unit in relation to the drum. Preferably, first and second developing units are supported on respective support members which are movable, in use, towards and away from the photosensitive drum. Preferably, first and second urging means for urging the respective intermediate gears to engage the respective driving gear are disposed between respective mounting members and support members. Preferably, first and second abutting members are provided to disengage the respective intermediate gears from the driving gears by displacement of the respective mounting members upon retraction of the units, in use, from the photosensitive drum. Preferably, the correct engagement of each intermediate gear with its respective driving gear is determined by abutment of the respective mounting member with a part associated with the particular driving gear. Preferably, each of the first and second developing units is removably mounted in the body of the image-forming apparatus by being able to be slid, in use, in the axial direction of the photosensitive drum. Preferably, the body of the image-forming apparatus is provided with guide rails extending in the axial direction of the photosensitive drum for guiding the first and second developing units, respectively, each developing unit having a slide which engages the respective guide rail, the slide being movable with respect to the corresponding guide rail to close and widen, in use, the distance between the photosensitive drum when each of the developing units are mounted in the body of the image-forming apparatus. For a better understanding of the invention and to show how the same can be carried into effect, reference will now be made, by way of example only, to the accompanying drawings, in which: Figure 1 is a schematic diagram showing a vertical section of an image forming apparatus employing a multi-color developing device of this invention. Figure 2 is a vertical sectional view of the multi-color developing device of this invention. Figure 3 is a schematic diagram showing the construction of a driving system on the rear side of the multi-color developing device shown in Figure 2. Figure 4 is a sectional view taken along the line IV-IV of Figure 3. Figure 5 is a diagram showing the construction of the front side of the multi-color developing device shown in Figure 2. Figure 6 is a sectional view taken along the line VI-VI of Figure 2. Figure 7 is a bottom end view of a guide rail for the first developing unit of the multi-color developing device shown in Figure 2. Figure 8 is a sectional view taken along the line VIII-VIII of Figure 2. Figure 9 is a plan view of a guide rail for the second developing unit of the multi-color developing device shown in Figure 2. Figure 1 is a diagram showing the general construction of an electrophotographic copying machine having a multi-color developing device of this invention. Fixed to the top surface of the body 11 of the copying machine is an original stand 12 . Over the original stand 12 , a cover 13 is mounted which is opened and closed. Paper cassettes 14 and 15 are detachably mounted on one side of the body 11 of the copying machine. Mounted on the other side of the body 11 of the copying machine is a paper exit tray 18 for receiving sheets of paper on which an image is copied. In the upper portion of the body 11 , an optical system 19 is disposed for scanning an original document, the optical system 19 comprising a light source, a mirror, and the like. Disposed in the center of the body 11 is a photosensitive drum 20 on which an electrostatic latent image is formed. Around the photosensitive drum 20 , there are disposed a charging unit 21 for charging the photosensitive drum 20 with a given amount of charge, a multi-color developing device 22 for developing with toner the electrostatic latent image formed on the photosensitive drum 20 , a transfer unit 23 for transferring the toner image onto a copy sheet, a separating unit 24 for separating the copy sheet from the photosensitive drum 20 , and a cleaning unit 25 for removing the remaining toner on the photosensitive drum 20 . Paper feed rollers 26a and 26b are respectively disposed above the portions of the body 11 to which the paper cassettes 14 and 15 are attached. Between the paper cassettes 14 and 15 and an image forming section comprising the photosensitive drum 20 and other components, is disposed a transport path 27 on the paper feed side for transporting the copy sheet, while another transport path 28 on the paper exit side is disposed downstream of the image forming section. Disposed between the transport path 28 on the paper exit side and a paper exit roller 29 is a fixing unit 30 for fixing the transferred image on the copy sheet thereto when the sheet is transported. The multi-color developing device 22 comprises, as shown in Figure 2, a first developing unit 31 , a second developing unit 32 disposed thereunder, and a cam mechanism 37 for moving the developing units 31 and 32 . The first developing unit 31 comprises a casing 33 , and a first developing roller 34 , a delivery roller 35 and a stirring roller 36 , respectively disposed inside the casing 33 . The first developing roller 34 is used to develop the latent image formed on the surface of the photosensitive drum 20 by applying toner thereto. On the upper end of the first developing unit 31 is provided a slide 42 which engages a guide rail 41 extending orthogonally to the paper transport direction. Abutting against the first developing unit 31 is a disc-shaped cam 38 of the cam mechanism 37 , the cam 38 having a diametrically extending rectangular opening in its center. The opening engages a driving shaft 39 , and the cam 38 is movable along the length of the opening. The driving shaft 39 is made to rotate in steps of 180 degrees by a control means not shown. Inside the opening of the cam 38 is provided a spring 40 for pushing the driving shaft 39 to one side of the opening. Abutting against the cam 38 is the upper end of a follower 43 the center portion of which is supported on a fulcrum 44 , the follower 43 being swingable on the fulcrum 44 . The follower 43 has its upper end abutting against the cam 38 , the upper end facing the first developing unit 31 with the cam 38 interposed therebetween. The second developing unit 32 comprises a casing 45 , and a second developing roller 46 , a delivery roller 47 and a stirring roller 48 , respectively disposed inside the casing 45 . The second developing roller 46 is used to develop the latent image formed on the surface of the photosensitive drum 20 by applying toner thereto. On the side edges of the underside of the casing 45 , there are formed a pair of slides 51 and 52 , the slides 51 and 52 engaging a pair of guide rails 49 and 50 extending orthogonally to the paper transport direction, respectively. As shown in Figure 3, on the side of the multi-color developing device 22 close to the rear end face of the body 11 , a flat supporting side plate 53 for supporting the first developing unit 31 is mounted in the upper section thereof, while in the lower section, a flat supporting side plate 54 for supporting the second developing unit 32 is mounted. The upper supporting side plate 53 is provided with a pair of horizontally elongated holes 72 in the upper corners thereof. The elongated holes 72 , respectively, are slidably engaged with a pair of pins 73 provided in a side wall 58 (Figure 4) along the rear end face of the body 11 , thus allowing the side plate 53 to move in the horizontal direction. A center shaft 55 mounted through the axis of the first developing roller 34 (Figure 2) engages the side plate 53 in a rotatable and removable way. A developing roller gear 56 is fixed to the center shaft 55 . Further, a spring 57 is disposed in a stretched state between the side plate 53 and an appropriate member of the body 11 , the spring 57 constantly exerting force to pull the side plate 53 away from the photosensitive drum 20 . As shown in Figure 4, the side plate 53 is disposed along the side wall 58 along the rear end face of the body 11 . Also, in the casing 33 of the first developing unit 31 , a supporting shaft 59 is disposed running in parallel with the center shaft 55 of the developing roller 34 and protruding through the rear side of the first developing unit 31 , the supporting shaft 59 engaging an elongated hole formed in the side plate 53 . A drive gear 60 is rotatably mounted on the supporting shaft 59 , the gear 60 engaging the developing roller gear 56 . To the side plate 53 is fixed an end of a supporting shaft 61 adjacent to the supporting shaft 59 , the supporting shaft 61 rotatably supporting a gear 62 which engages the gear 60 . Also engaged with the gear 60 is a gear 76 positioned on the side of the gear 62 nearer to the first developing unit 31 , as shown in Figure 4. The gear 76 is fixed to the delivery roller 35 . Engaged with the gear 76 is a gear 77 fixed to the stirring roller 36 . As shown in Figure 3, between the side plate 53 and the gear 62 on the supporting shaft 61 , a vertical mounting plate 63 is fitted swingably about the supporting shaft 61 . The mounting plate 63 is formed in a vertically long shape, to the lower part of which is fixed a supporting shaft 65 which rotatably supports an intermediate gear 64 . Between the upper side plate 53 and the lower side plate 54 , a driving gear 66 is disposed, being supported on a supporting shaft 68 and adjacent to the side of the lower portion of the mounting plate 63 nearer to the photosensitive drum 20 . The intermediate gear 64 is disengaged from the driving gear 66 when the lower portion of the mounting plate 63 is positioned away from the photosensitive drum 20 as shown by a solid line in Figure 3. On the other hand, the intermediate gear 64 engages the driving gear 66 when the lower portion of the mounting plate 63 is positioned close to the photosensitive drum 20 as shown by a two-dot chain line. On the lower end face of the mounting plate 63 is formed an abutting portion 67 capable of abutting against a sleeve 69 mounted on the supporting shaft 68 supporting the driving gear 66 . The abutting portion 67 is made to abut against the sleeve 69 when the intermediate gear 64 engages the driving gear 66 as shown by the two-dot chain line, thus holding the intermediate gear 64 and the driving gear 66 in a properly engaged state. The upper end portion of the mounting plate 63 is made to abut against an adjacent abutting member 70 provided on an appropriate member in the body 11 . Between the upper portion of the mounting plate 63 and the side plate 53 , a spring 71 is disposed in a stretched state, the resilience of the spring 71 constantly exerting pulling force to make the upper portion of the mounting plate 63 abut against the abutting member 70 . As shown in Figure 4, the supporting shaft 68 supporting the driving gear 66 is connected via a spring clutch 74 to a gear 75 which is driven by a driving source (not shown) disposed in the body 11 . The spring clutch 74 disengages the transmission of power from the driving source to the driving gear 66 when the side plate 53 or 54 moves in the horizontal direction, thus facilitating the movement of the side plate 53 or 54 . The second developing unit 32 has essentially the same construction in the supporting side plate 54 as that of the first developing unit 31 . The supporting side plate 54 is provided with a pair of horizontally elongated holes 172 in the upper corners thereof. The elongated holes 172 respectively, are slidably engaged with a pair of pins 173 provided in the side wall 58 (Figure 4) along the rear end face of the body 11 , thus allowing the side plate 54 to move in the horizontal direction. A center shaft 155 mounted through the axis of the second developing roller 46 (Figure 2) engages the side plate 54 in a rotatable and removable way. A developing roller gear 156 is fixed to the center shaft 155 . Further, a spring 157 is disposed in a stretched state between the side plate 54 and an appropriate member of the body 11 , the spring 157 constantly exerting force to pull the side plate 54 away from the photosensitive drum 20 . The side plate 54 is disposed on substantially the same vertical plane as the upper side plate 53 . To the side plate 54 is fixed an end of a supporting shaft 161 adjacent to the developing roller gear 156 , the supporting shaft 161 rotatably supporting a drive gear 162 which engages the developing roller gear 156 . As shown in Figure 3, between the side plate 54 and the gear 162 on the supporting shaft 161 , a vertical mounting plate 163 is fitted swingably about the supporting shaft 161 . The mounting plate 163 is formed in a vertically long shape, to the upper portion of which is fixed a supporting shaft 165 which rotatably supports an intermediate gear 164 . Between the upper side plate 53 and the lower side plate 54 and upwardly of the mounting plate 163 , a driving gear 166 is disposed which is supported on a supporting shaft 168 . The intermediate gear 164 is disengaged from the driving gear 166 when the upper portion of the mounting plate 163 is positioned away from the photosensitive drum 20 as shown by a two-dot chain line in Figure 3. On the other hand, the intermediate gear 164 engages the driving gear 166 when the upper portion of the mounting plate 163 is positioned nearer to the photosensitive drum 20 as shown by a solid line. On the upper end face of the mounting plate 163 is formed an abutting portion 167 capable of abutting against a sleeve 169 mounted on the supporting shaft 168 supporting the driving gear 166 . The abutting portion 167 is made to abut against the sleeve 169 , as shown by the solid line, when the intermediate gear 164 engages the driving gear 166 , thus holding the intermediate gear 164 and the driving gear 166 in a properly engaged state. The lower end portion of the mounting plate 163 is made to abut against an adjacent abutting member 170 provided on an appropriate member in the body 11 . Between the lower portion of the mounting plate 163 and the side plate 54 , a spring 171 is disposed in a stretched state, the resilience of the spring 171 constantly exerting pulling force to make the lower portion of the mounting plate 163 abut against the abutting member 170 . The driving gear 166 , engaged with the adjacent driving gear 66 , is connected to the driving source (not shown) disposed in the body 11 , the power from the driving source being transmitted via the spring clutch 74 . The spring clutch 74 may be eliminated if proper urging force is provided by the springs 57 and 157 . On the side of the multi-color developing device 22 close to the front side of the body 11 , a side wall 78 is disposed which is fixed to the body 11 , as shown in Figure 5. The side wall 78 is provided with an insertion opening 79 in the center thereof, through which the first developing unit 31 and the second developing unit 32 are inserted from the front side of the body 11 into the interior of the body 11 . The side wall 78 is also provided with four pins 80 protruding toward the front side of the body 11 . The pins 80 respectively engage the holes provided in side plates 81 and 82 disposed on the side of the first developing unit 31 and second developing unit 32 close to the front side of the body 11 , thus allowing the first developing unit 31 and the second developing unit 32 to be mounted in position in the body 11 by the side plates 81 and 82 . The side plate 81 is provided with a pair of horizontally elongated holes 83 . The elongated holes 83 respectively engage a pair of pins 84 provided on the side of the casing 33 (Figure 2) of the first developing unit 31 close to the front side of the body 11 , the first developing unit 31 thus being supported movably in the horizontal and parallel direction. The other side plate 82 is also provided with a pair of horizontally elongated holes 85 . The elongated holes 85 respectively engage a pair of pins 86 provided on the side of the casing 45 (Figure 2) of the second developing unit 32 close to the front side of the body 11 , the second developing unit 32 thus being supported movably in the horizontal and parallel direction. Description is now given of the guide mechanism used at the time of mounting and removing the first developing unit 31 . As shown in Figure 2, the slide 42 provided on the upper end of the casing 33 of the first developing unit 31 comprises a connecting portion 87 in the lower part thereof, and an engaging portion 88 integrally formed with and on top of the connecting portion 87 . The engaging portion 88 has a shape extending outwardly of the sides of the connecting portion 87 . Also, as shown in Figure 6, the side of the engaging portion 88 nearer to the photosensitive drum 20 is provided in its innermost portion to the rear of the body 11 with a protruding portion 89 (the lower end in Figure 6) protruding to one side. On the other hand, the guide rail 41 shown in Figure 2 is fixed to the body 11 . The guide rail 41 has a C-shaped cross section with a downwardly open end, and extends in the axial direction of the photosensitive drum 20 . The hollow space of the guide rail 41 is provided with an appropriate size to allow the engaging portion 88 of the slide 42 to be slidably engaged, while the open end in the lower portion of the guide rail 41 is provided with an appropriate width to allow the connecting portion 87 to pass therealong with appropriate play. The engaging portion 88 and the protruding portion 89 engage the lower surface of the guide rail 41 for sliding thereon. As shown in Figure 7, the lower surface and side surface of the guide rail 41 nearer to the photosensitive drum 20 are cut out in the innermost portion thereof to the rear of the body 11 to form a cut-out portion 90 . The cut-out portion 90 is provided with an appropriate size to allow the protruding portion 89 of the slide 42 to protrude outwardly when the entire slide 42 is fully engaged with the entire guide rail 41 . The guide mechanism used at the time of mounting and removing the second developing unit 32 is now described. The slides 51 and 52 formed on the side edges of the underside of the second developing unit 32 extend in such a way that they can guide the casing 45 of the second developing unit 32 in the axial direction of the second developing roller 46 . As shown in Figure 8, the slide 51 is provided only on the innermost inner portion of the casing 45 , and is formed in a crook shape, the lower edge thereof extending toward the photosensitive drum 20 (Figure 2). As shown in Figure 2, the crooked portion of the slide 51 engages the upper portion of the guide rail 49 having a U-shaped cross section. The guide rail 49 is fixed to the body 11 , and, as shown in Figure 9, has a cut-out portion 91 formed in the side thereof nearer to the photosensitive drum 20 and to the innermost portion of the body 11 . The cut-out portion 91 engages the slide 51 when the second developing unit 32 is set in the body 11 . As shown in Figure 8, the slide 52 formed on the remote side of the casing 45 of the second developing unit 32 from the photosensitive drum 20 extends in a straight line, the lower end thereof slidably engaging a guide groove 92 of the guide rail 50 shown in Figure 2. As shown in Figure 9, the guide groove 92 is provided with a width that approximately matches that of the slide 52 along the portion thereof nearer to the front side of the body 11 , and the inside wall of the guide groove 92 is eliminated inwardly of that portion. Thus, when the second developing unit 32 is set in the body 11 , the slide 52 is movable sideward of the guide groove 92 where the inside wall is eliminated. The following will describe the operations of the electrophotographic copying machine of the above-mentioned construction. When a copy command is given, the photosensitive drum 20 starts to rotate, and the surface thereof is uniformly charged by means of the charging unit 21 . Next, the original document placed on the original stand 12 is scanned by the optical system 19 , the light reflected from the original document being projected onto the photosensitive drum 20 to form a latent image thereon. The latent image is then developed into a toner image on the photosensitive drum 20 by means of the multi-color developing device 22 . The operations of the multi-color developing device 22 will be described later in detail. In the meantime, the copy sheet accommodated in the paper cassette 14 or 15 is passed through the transport path 27 on the paper feed side, and is fed to the image forming section comprising the photosensitive drum 20 and other components, where the toner image is transferred onto the predetermined position on the copy sheet. The copy sheet with the toner image transferred thereon is transported through the transport path 28 on the paper exit side to the fixing unit 30 where the toner image is fixed onto the copy sheet. The copy sheet with the toner image fixed thereon is discharged onto the paper exit tray 18 by means of the paper exit roller 29 . In the multi-color developing device 22 , the following operation is performed when switching over between the first developing unit 31 and the second developing unit 32 for changing toner colors, etc. Figure 2 shows the state in which the lower second developing unit 32 is in the developing position while the upper first developing unit 31 is in the retracted position. From the state of Figure 2, to change the first developing unit 31 to the developing position and the second developing unit 32 to the retracted position, the spring clutch 74 is disengaged to allow the driving shaft 39 to rotate by 180 degrees. This makes the cam 38 rotate to move the first developing unit 31 into the developing position shown by the two-dot chain line, thus bringing the first developing roller 34 of the first developing unit 31 in the predetermined position with respect to the photosensitive drum 20 . When the first developing unit 31 is positioned in the predetermined developing position with respect to the photosensitive drum 20 , the spring 40 disposed inside the cam 38 is compressed to absorb the force acting on the first developing unit 31 . Also, since the protruding portion 89 of the slide 42 is allowed to pass through the cut-out portion 90 of the guide rail 41 , there arises no possibility of the guide rail 41 interfering with the movement of the first developing unit 31 . In the meantime, since the pressing force of the cam 38 is released, the second developing unit 32 is moved away from the photosensitive drum 20 into the retract position shown by the two-dot chain line by means of the spring force of the spring 157 . When the first developing unit 31 and the second developing unit 32 are thus moved as shown in Figure 2, the upper mounting plate 63 disengages from the abutting member 70 , and is swung by the spring force of the spring 71 so that the lower portion thereof moves closer to the photosensitive drum 20 , as shown by the two-dot chain line in Figure 3, thereby causing the intermediate gear 64 to engage the driving gear 66 and the abutting portion 67 of the mounting plate 63 to abut against the sleeve 69 . Thus, the intermediate gear 64 is made to properly engage the driving gear 66 in the proper position. As a result, the rotating force of the driving gear 66 is transmitted to the developing roller gear 56 via the intermediate gear 64 , the gear 62 , and the gear 60 , thus putting the first developing unit 31 into an operating condition with the first developing roller, etc. rotating. On the other hand, when the second developing unit 32 is moved away from the photosensitive drum 20 , the lower end portion of the lower mounting plate 163 is brought to abut against the abutting member 170 . As a result, the mounting plate 163 is swung about the supporting shaft 161 so that the upper portion thereof moves away from the photosensitive drum 20 , and is positioned as shown by the two-dot chain line in Figure 3. This causes the intermediate gear 164 to disengage from the driving gear 166 , thereby disabling transmission of the rotating force of the driving gear 166 to the center shaft 155 and putting the second developing unit 32 into non-operating condition with the developing roller 46 , etc. at rest. In this case, since the intermediate gear 164 becomes completely disengaged from the driving gear 166 , it is possible to provide a sufficient stroke for travelling of the second developing unit 32 . Next, from the state in which the first developing unit 31 is in an operating condition and the second developing unit 32 is in non-operating condition, to change the first developing unit 31 to non-operating condition and the second developing unit 32 to an operating condition, the spring clutch 74 is disengaged to allow the driving shaft 39 to rotate by 180 degrees once again. This makes the first developing unit 31 move away from the photosensitive drum 20 into the retracted position shown by the solid line in Figure 3, which movement causes the upper end portion of the upper mounting plate 63 to abut against the abutting member 70 . As a result, the mounting plate 63 is swung about the supporting shaft 61 so that the lower portion thereof moves away from the photosensitive drum 20 , and is positioned as shown by the solid line in Figure 3. This causes the intermediate gear 64 to disengage from the driving gear 66 , thereby disabling transmission of the rotating power of the driving gear 66 to the center shaft 55 and putting the first developing unit 31 into a non-operating condition. In this case, since the intermediate gear 64 becomes completely disengaged from the driving gear 66 , it is possible to provide a sufficient stroke for travelling of the first developing unit 31 . In the meantime, since the second developing unit 32 is moved toward the photosensitive drum 20 by the action of the cam mechanism 37 , the lower mounting plate 163 is released from the control of the abutting member 170 . As a result, the mounting plate 163 is swung by the spring force of the spring 171 so that the upper end portion thereof moves closer to the photosensitive drum 20 , and is positioned as shown by the solid line in Figure 3. This causes the intermediate gear 164 mounted on the mounting plate 163 to engage the driving gear 166 , and the abutting portion 167 of the mounting plate 163 to abut against the sleeve 169 . Thus, the intermediate gear 164 is made to properly engage the driving gear 166 in the proper position. This engagement of the gears allows the rotating force of the driving gear 166 to be transmitted from the driving gear 166 to the developing roller gear 156 via the intermediate gear 164 and the gear 162 , thus putting the second developing unit 32 into an operating condition. Also, when the second developing unit 32 is moved to the predetermined developing position, the spring 40 disposed inside the cam 38 is compressed to absorb the force acting on the second developing unit 32 , thus providing the predetermined clearance between the photosensitive drum 20 and the second developing roller 46 . In the above-described movement, since the slide 51 is allowed to pass through along the cut-out portion 91 of the guide rail 49 while the slide 52 moves sideward of the guide groove 92 , there arises no possibility of the guide rails 49 and 50 interfering with the movement of the second developing unit 32 . To remove the first developing unit 31 , the first developing unit 31 is placed in the retracted position remote from the photosensitive drum 20 so that the protruding portion 89 of the slide 42 is engaged with the guide rail 41 . Then, by pulling the side plate 81 shown in Figure 5 toward the front side, the entire first developing unit 31 is drawn out toward the front side with the slide 42 sliding while being guided by the guide rail 41 . On the other hand, to mount a fresh first developing unit 31 in the body 11 , the slide 42 is made to engage the guide rail 41 , and the first developing unit 31 is inserted through the insertion opening 79 provided in the side wall 78 . As the first developing unit 31 is further inserted, the center shaft 55 and supporting shaft 59 of the first developing unit 31 engage the respective holes provided in the side plate 53 to fit the first developing unit 31 onto the side plate 53 and, thus, position the first developing unit 31 with respect to the side plate 53 . Next, the holes provided in the side plate 81 which is mounted on the front side of the first developing unit 31 fit into the pins 80 provided on the side wall 78 , thus positioning the first developing unit 31 with respect to the side wall 78 . After that, the protruding portion 89 of the slide 42 is engaged with the cut-out portion 90 of the guide rail 41 to complete the setting of the first developing unit 31 in the body 11 . Thus, the first developing unit 31 is mounted so that it is movable with respect to the photosensitive drum 20 by the action of the cam mechanism as previously described. To remove the second developing unit 32 , the second developing unit 32 is first placed in the retracted position. Then, by pulling the side plate 82 shown in Figure 5 toward the front side, the entire second developing unit 32 is drawn out toward the front side with the slides 51 and 52 being guided respectively by the guide rails 49 and 50 . On the other hand, to mount a fresh second developing unit 32 in the body 11 , the slide 51 is made to engage the insertion guide rail 49 while engaging the slide 52 with the guide rail 50 , and then, the fresh second developing unit 32 is inserted through the insertion opening 79 provided in the side wall 78 . When the second developing unit 32 is inserted, the slide 51 engages the cut-out portion 91 of the guide rail 49 , while the slide 52 slides on the guide groove 92 of the guide rail 50 to be positioned in the innermost portion of the guide groove 92 where the inside wall is eliminated, thus completing the setting of the second developing unit 32 in the body 11 . Thus, the second developing unit 32 is mounted so that it is movable with respect to the photosensitive drum 20 by the action of the cam mechanism 37 as previously described. Thus, the device described herein makes possible the objectives of (1) providing a multi-colour developing device for an image forming apparatus in which only the selected developing unit can be driven without using a clutch for each developing unit, thereby simplifying the construction of the driving system; (2) providing a multi-colour developing device for an image forming apparatus in which the intermediate gear provided in the developing unit becomes completely disengaged from the corresponding driving gear when the developing unit is positioned in a retracted position away from the photosensitive drum travel; (3) providing a multi-colour developing device for an image forming apparatus in which, when the developing unit is positioned in the developing position adjacent to the photosensitive drum, the intermediate gear is put in the proper state of engagement with the driving gear, so that the positional relationship between the intermediate gear and the driving gear can be set independently of the clearance between the developing roller in the developing unit and the photosensitive drum, thereby permitting accurate setting of the gear engagement as well as of the clearance between the developing roller and the photosensitive drum; and (4) providing a multi-color developing device for an image forming apparatus in which the developing unit is easily removable from the body of the image forming apparatus, so that the developing unit can be readily replaced, for example, with one of a different color.

Claims: A multi-coloured developing device for an image-forming apparatus comprising a first developing unit (31) having a first drive gear (60) and being movable, in use, towards and away from a photosensitive drum (20), a second developing unit (32) having a second drive gear (162), adjacent the first developer unit (31) and also being movable, in use, towards and away from the photosensitive drum (20), a cam mechanism (37) for selectively moving either one of the developer units (31, 32) into a position adjacent the drum (20) and first and second driving gears (66, 166) for respectively driving the developer units (31, 32) located between the developer units (31, 32), characterised in that each developer unit (31, 32) has an intermediate gear (64, 164) in driving connection with the particular drive gear (60, 162) and engageable with the particular driving gear (66, 166) on movement of the particular developer unit (31, 32) into a position adjacent the drum (20), each intermediate gear (64, 164) being carried on a mounting member (63, 163) which is movably mounted in the particular developer unit (31, 32) to enable the intermediate gear (64, 164) operatively to engage with the particular driving gear (66, 166) as the developer unit (31, 32) is moved, in use, towards the drum (20) independently of the precise final position of the developer units (31, 32) in relation to the drum (20). A device as claimed in claim 1, characterised in that the first and second developing units (31, 32) are supported on respective support members (53, 54) which are movable, in use, towards and away from the photosensitive drum (20). A device as claimed in claim 1 or 2, characterised in that at least one mounting member (63) is provided with a further intermediate gear (62) disposed between the drive gear (60) and the intermediate gear (64). A device as claimed in claim 1, 2 or 3, characterised in that the first and second mounting members (63, 163) are rotatably mounted on respective support members (53, 54). A device as claimed in claim 4, characterised in that first and second urging means (71, 171) for urging the respective intermediate gears (64, 164) to engage the respective driving gears (66, 166) are disposed between respective mounting members (63, 163) and support members (53, 54). A device as claimed in any preceding claim, characterised in that first and second abutting members (70, 170) are provided to disengage the respective intermediate gears (64, 164) from the driving gears (66, 166) by displacement of the respective mounting members (63, 163) upon retraction of the units (31, 32), in use, from the photosensitive drum (20). A device as claimed in any preceding claim, characterised in that the correct engagement of each intermediate gear (64, 164) with its respective driving gear (66, 166) is determined by abutment of the respective mounting member (63, 163) with a part (69, 169) associated with the particular driving gear (66, 166). A device as claimed in any preceding claim, characterised in that each of the first and second developing units (31, 32) is removably mounted in the body of the image-forming apparatus by being able to be slid, in use, in the axial direction of the photosensitive drum (20). A device as claimed in claim 8, characterised in that the body of the image-forming apparatus (11) is provided with guide rails (49, 50) extending in the axial direction of the photosensitive drum (20) for guiding the first and second developing units (31, 32), respectively, each developing unit (31, 32) having a slide (51, 52) which engages the respective guide rail (49, 50), the slide being movable with respect to the corresponding guide rail to close and widen, in use, the distance between the photosensitive drum (20) when the developing units (31, 32) are mounted in the body of the image-forming apparatus.

Inventors: MIZUNO MASAYUKI, MIZUNO, MASAYUKI
Applicants: MITA INDUSTRIAL CO LTD, MITA INDUSTRIAL CO., LTD.
Application year: 1989
Main classification: G03G15
IPC codes: G03G15