RESET MECHANISM FOR A COUNTER FOR COUNTING THE NUMBER OF REVOLUTIONS OF A PHOTOCONDUCTIVE DRUM

Abstract: In a reset mechanism for resetting a counter counting the number of rotations of a photoconductive drum (1) which is employed in a laser beam printer and the like, are provided a rocking member (17) to be rocked only when the photoconductive drum (1) is primarily rotated and means for resetting the counter in response to the rocking movement of the rocking member. Thus, the counter is accurately reset in case that a new photoconductive drum is installed in the printer and the photoconductive drum is primarily rotated.

Description: Background of the Invention This invention relates to a reset mechanism according to the precharacterizing part of claim 1. Laser printers are recently coming into wide use and compact inexpensive printers utilizing semiconductor lasers in particular are increasingly put to practical use. A laser printer of that sort has been so contrived as to obtain hard copies of image data on a recording sheet by means of so-called elecrophotographic duplicating processes including exposing process for exposing a photoconductive drum charged with electricity to a laser beam modulated according to image data on graphs as well as characters and subsequently passing resulting latent images through a developing process for forming a visible image on the surface of the photoconductive drum, transferring process for transferring the visible image to a recording sheet, fixing process for fixing the transferred image on the recording sheet by pressurizing the recording sheet with the heat, and the like. In such a laser printer as an electrophotographic imaging device, the photoconductive drum is slowly wearing off as it undergoes each step of the electrophotographic duplicating processes, e.g., transfer or cleaning of the surface of the photoconductive drum. If the photoconductive drum itself is wearing off continuously, it will become poorly charged or allow the presence of an after-image on its surface This will also cause bad setting, i.e. inadequate transfer to recording sheet, etc. Consequently, the photoconductive drum is formed into a unit so that it can simply be replaced and equipped with a counter for counting pulse signals which are synchronized with a revolution of the photoconductive drum to use the count for determining the timing at which the photocondutive drum is to be replaced. In other words, the photoconductive drum is replaced at the point of time the count indicated by the counter has reached a predetermined value, i.e., a predetermined number of recording sheets corresponding to the point of time have been printed. The counter is cleared when the photoconductive drum is replaced. There is provided a microswitch, for instance, for detecting the presence or absence of the photoconductive drum and the counter is reset using presence-absence -presence signals applied by the microswitch when the photoconductive drum is replaced. However, since the power supply of the printer is turned off when the photoconductive drum is replaced, the microswitch will not be actuated and consequently the counter cannot be reset. In other words, the counter will succeed to the existing count prior to the replacement and start counting again. The counter will otherwise be reset despite the fact that the photoconductive drum is reinstalled after it is removed once for maintenance, inspection and the like. A known arrangement to solve the afore-mentioned problems is to provide the photoconductive drum unit with a pin abutting against the microswitch for detecting the presence or absence of the photoconductive drum in such a manner that the pin breaks immediately after it has come into contact with the microswitch simultaneously when the unit including the photoconductive drum is mounted. Since the pin is broken at the time the unit is initially mounted, the counter is prevented from being reset when the photoconductive drum is mounted again after it has been once removed. However, the counter is not reset while the power supply of the printer itself is turned off as in the preceding case where such a pin is not employed; the problem, in this case, remains i.e. that a mounting of a new photoconductive drum is undetected. A reset mechanism is known from DE 37 15 709 A1 which resets a counter when a container is installed. In case the container is removed for purposes of maintenance and put back there again, the count value of the counter is also reset. Furthermore, a reset mechanism is known from US-A-4,585,327 which is designed for resetting a counter in a copying apparatus. This document provides that the reset mechanism is operated by an actuating member when a photosensitive member or a magazine is installed. After the reset mechanism has been operated, the actuating member is destroyed. Summary of the Invention It is therefore an object of the invention to provide an improved reset mechanism for a photoconductive drum counter to ensure that the counter for counting the number of revolutions of a photoconductive drum is reset only when the photoconductive drum is replaced. This problem is solved by the features of claim 1. In this arrangement , the rocking member operates the control means when a new photoconductive drum is installed, so that the counter can be reset using the output signal of the control means at the time the power supply intended for the whole printer is turned on and the photoconductive drum is initially rotated. In other words, the counter can be reset whenever a new photoconductive drum is installed and therefore prevented from being reset when the photoconductive drum is detached therefrom for the purpose of maintenance to ensure that the counter is reset only when the photoconductive drum is replaced. Description of the Accompanying Drawings Fig. 1 is a schematic side view of a laser printer having a reset mechanism for a photoconductive drum counter according to one embodiment of the present invention; Fig. 2 is an enlarged side view illustrating a part of a sub-shell provided on the printer of Fig. 1; Fig. 3 is a sectional view taken along a line III-III of Fig. 2; Fig. 4 is a side view of one example of a lock mechanism of the photoconductive drum; Fig. 5 is a side view of a sub-shell incorporating the reset mechanism according to another embodiment of the present invention; Fig. 6 is a sectional view taken along a line VI-VI of Fig. 5; Fig. 7 is a plane view of the sub-shell illustrated in Fig. 5; Fig. 8 is a partial top view of the sub-shell of Fig. 5; and Figs. 9(A) and 9(B) are top and elevational views illustrating microswitch layouts included in the reset mechanism according to the present invention. Description of the Embodiments Fig. 1 is a schematic side view of a laser printer having a reset mechanism for a photoconducitve drum counter according to the first embodiment of the present invention. This laser printer is designed to print data received from a host computer or the like on a fan-folded form 10 by electrophotographing and to deliver the printed paper. A toner-cleaning station 2, a de-charging station 3 a charging staton 4, an optical scanning system 5 for leading onto a photoconductive drum 1 a laser beam modulated according to input data, a developing station 6, and a transferring station 7 are adequately disposed in the above order along the direction of rotation of the photoconductive drum 1. A fixing station 8 is disposed in a predetermined fore part in the direction of movement of the fan-folded form 10, whereas a guide mechanism 9 for carrying and guiding the fan-folded form 10 in a predetermined direction is properly disposed in the path of the fan-folded form 10 from the drum 1 to the fixing station 8, the guide mechanism 9 being simultaneously used to regulate the fan-folded form 10 moderately by applying resisting force to both ends thereof. The surface of the photoconductive drum 1 is scanned by the laser beam emitted by the optical scanning system 5 in the longitudinal direction thereof (main scanning). While the main scanning is repeated, the photoconductive drum 1 is rotated in direction of an arrow "C" so that the surface thereof is scanned in the direction opposite to the direction of rotation thereof (auxiliary scanning). A latent image is accordingly formed on the surface of the photoconductive drum 1 by the laser beam and the latent image is formed into a toner image by the developing station 6. In other words, the latent image thus formed is developed into a visible image through the electrophotographic process. The toner image is transferred from the surface of the photoconductive drum 1 onto that of the fan-folded form 10 by the transfer station 7 and the toner image thus transferred is fixed by the fixing station 8. The fan-folded form 10 is then discharged from the laser printer. The photoconductive drum 1 is installed in a sub-shell 11 as a support member in such a manner that both ends thereof are supported thereby and a simply replaceable unit is formed with the sub-shell. More specifically, the sub-shell 11 used to support the photoconductive drum 1 is detachably fitted to a predetermined region of a clamshell 12 which forms an upper cover of the laser printer and, when the sub-shell 11 is fixed in position, the photoconductive drum 1 is disposed as arranged relative to each element for the electrophotographic processing such as the developing station 6, the transferring station 7 and the like. The sub-shell 11 is readily detachable as the clamshell 12 is turned around a pivot shaft 13 and opened. Although the toner-cleaning station 2 and the charging station 4 are located in the sub-shell 11, they are not anchored thereto and therefore not detachable from the clamshell 12 as the detachment of the sub-shell 11. Fig. 2 is an enlarged side view illustrating part of the sub-shell 11 of Fig. 1 in detail. Fig. 3 is a sectional view taken along a line III-III of Fig. 2. A gear 14 is coaxially fitted to one end of the photoconductive drum 1 having both ends supported by the sub-shell 11, whereas a gear 15, a gear 16 and a doglegged lever 17 are properly disposed in the sub-shell 11 therearound. In other words, the gear 14 meshes with the gear 15, which alternatively meshes with the gear 16 as a rotary member interlocked with the rotation of the photoconductive drum 1. The lever 17 is rotatably supported by a pivot shaft 18 perpendicularly fitted to the sub-shell 11 and the perpendicular position of the pivot shaft 18 is regulated such that the extended, substantially doglegged end portion 17a of the lever 17 and a protrusion 16a formed in part of the rotary shaft of the gear 16 may abut against each other. The other end of the lever 17, i.e., what is opposite to the end portion 17a about the shaft 18 is coupled to a pivot shaft 19 perpendicularly fitted to the sub-shell 11 and a spring 20 as a bias member, and the lever 17 is biased by the tensile force of the spring 20 toward the pivot shaft 19. The end portion 17a of the lever 17 is accordingly biased such as to revolve clockwise around the pivot shaft 18. A projection 17b is formed on the end portion side 17a of the lever 17 and used to press the switch lever 21a of a microswitch 21, which will be described later. The gear 16 meshes with a rotatable lever 22 disposed close thereto and the roation of the gear 16 is retained to the extent, the lever 22 is allowed to mesh therewith. In other words, the lever 22 has one end used as a rack and is rotatably supported by a pivot shaft 23 perpendicularly fitted to the sub-shell 11, the rack portion thereof being biased by the force of a spring (not shown) in the direction in which it abuts against the gear 16. The rack portion of the lever 22 is thereby made to engage with and control the gear 16. More specifically, the lever 22 simultaneously serves as a lock mechanism for locking the rotation of the photoconductive drum 1, whereby the rotation of the photoconductive drum 1 interlocked with that of the gear 16 is retained. The locking operation implemented by the engagement of the rack portion of the lever 22 with the gear 16 is released by a pin 24 perpendicularly fitted to a predetermined position of the laser printer body while the clamshell 12 is closed ordinarily. That is, the toothless end portion of the lever 22 comes into contact with the pin 24 when the clamshell 12 is closed and is forced to move up so that the rack portion of the lever 22 is revolved and separated from the gear 16. The photoconductive drum 1, together with the sub-shell 11 supporting the photoconductive drum 1, is replaced; in other words the sub-shell 11 is replaced while the clamshell 12 is kept open after it has been turned around the pivot shaft 13. A sub-shell 11 as a substitute for the old one is of course equipped with a new photoconductive drum 1 and invariably set in such a state that the protrusion 16a of the gear 16 retains the end portion 17a of the lever 17 rotatably biased clockwise by the spring 20. The initial state of the lever 17 is hereinafter understood as one in which the protrusion 16a of the gear 16 keeps the end portion 17a of the lever 17 retained. The initial state of the lever 17, i.e., the state in which the protrusion 16a of the gear 16 ensures that the position of the end portion 17a of the lever 17 is released by a rotation of the photoconductive drum 1. Since the gear 16 is caused to rotate counterclockwise via the gear 15 correspondingly in response to the counterclokwise rotation of the photoconductive drum 1, the protrusion 16a of the gear 16 slips off the end portion 17a of the lever 17 so that the initial state is released. The microswitch 21 is secured in a predetermined position of the printer body facing the clamshell 12. When the lever 17 on the sub-shell 11 is in the initial state, the microswitch 21 is fixed at a position wherein its switch lever 21a is pressed by the projection 17b of the lever 17. The microswitch 21 is designed to detect whether the switch lever 21a is pressed by the projection 17b of the lever 17, i.e., whether the lever 17 is in the initial state or not. When the switch lever 21 is free of pressure force applied by the projection 17b of the lever, i.e., when the lever 17 is released from the initial state, for that purpose, the microswitch 21 emits a detection signal. The microswitch 21 is electrically connected to a photoconductive drum counter, not shown, for counting the pulse signal synchronized with the rotation of the phothoconductive drum 1 and the detection signal is received by the photocondutive drum counter as a reset signal. The resetting of the photoconductive drum counter on the basis of the detection signal is effected on condition that the photoconductive drum counter is reset by the detection signal supplied by the microswitch 21 only when the clamshell 12 remains closed. When the clamshell 12 is left open, the photoconductive drum counter will not be reset. In other words, the power supply of the laser printer is not turned on when the clamshell 12 is left open and the photoconductive drum counter will not be reset no matter how often the microswitch 21 may produce the detection signal. With this arrangement, the photoconductive drum counter is reset upon receipt of the detection signal from the microswitch 21 only when the photoconductive drum 1 is rotated after the clamshell 12 is closed to turn on the power supply while the lever 17 in the sub-shell 11 remains in the initial state (i.e., the photoconductive drum 1 fitted to the sub-shell 11 has to be new). When the sub-shell 11 equipped with the photoconductive drum 1 is installed again after it is removed for the inspection of the photoconductive drum 1, the photoconductive drum counter is prevented from being wrongly reset since the lever 17 has been already released from the initial state. Thus, the photoconductive drum counter is reset with certainty only when the photoconductive drum 1 is replaced. Although the lock mechanism has the rack portion of the lever 22 mesh with the gear 16 to stop the photoconductive drum 1 from rotating, the present invention is not limited to this arrangement but applicable in any other way as the occasion may demand; e.g., one side of a rectangular plate 25 may be toothed as shown in Fig. 4 to mesh with the gear 14. In the lock mechanism shown in Fig. 4, slits 25a, 25b are formed in the plate 25 and pins 26, 27 perpendicularly fitted to the sub-shell 11 are slidably fitted into the slits 25a, 25b, whereas the plate 25 is biased by a spring, not shown, and by its own weight toward the gear 14, whereby the gear 14 is stopped from rotating when it meshes with the rack portion of the plate 25. The rack portion of the plate 25 is released from meshing with the gear 14 when the plate 25 is forced to move up by a pin, not shown, similar to the pin 24. Referring to Fig. 5 to 9, a second embodiment of the present invention will subsequently be described, wherein like reference numbers designate like components shown in the first embodiment. A laser printer of the second embodiment is arranged such that the sub-shell 11 supporting the photoconductive drum 1 is mounted on the laser printer body side and the open-close type clamshell presses the sub-shell 11 when it is closed so as to maintain subshell 11 in position. When the clamshell is opened, the photoconductive drum 1 is easily replaceable. The drum gear 14 formed on the periphery of the photoconductive drum 1 and a cleaner drive gear 31 for driving a cleaning device are revealed at one side end of the sub-shell 11. When the sub-shell 11 is mounted on the laser printer body, the gears 14, 31 mesh with a drive gear, not shown, disposed on the laser printer body side to make the force rotation from the photoconductive drum 1 transmitted. An idle gear 32 as a rotary member interlocked with the rotation of the photoconductive drum 1 meshes with the cleaner drive gear 31, whereas gear 33, 34 respectively fitted to a cleaner brush and a recovery roller mesh with the idle gear 32 to rotate the cleaner brush and the recovery roller via the idle gear 32 in response to a rotation of the cleaner drive gear31. The cleaner drive gear 31 is geared to the drum gear 14 and driven to rotate invariably when the photoconductive drum 1 is rotated and the cleaner brush and the recovery roller both mechanically connected to the drive gear 31, are driven to rotate. The lever 17 as a lever member is pivotally supported by the case 11a of the sub-shell 11 in such a manner as to be capable of horizontally rocking above the idle gear 32 as shown in Fig. 6, which is a sectional view taken along a line VI-VI of Fig. 5. The lever 17 has a retaining part 17b at one end of a horizontal lever portion 17a, the retaining part 17b extending in a vertical direction. A shaft 17c is protruded upward and downward substantially in the center of the lever portion 17a and can be rotatated by the shaft 17c in the case 11a. A torsion spring 35 as a bias means is externally fitted to the upper side of the shaft 17c and used to bias the lever 17 in a direction in which the retaining part 17b is separated from the idle gear 32. The relative position of the lever 17 is set up so that, when the retaining part 17b is revolved in a direction close to the idle gear 32, the lowermost end of the retaining part 17b interferes with the addendum but not with the bottom of the idle gear 32. The retaining part 17b is thus made revolvable up to a position closest to the idle gear 32 when the lowermost end of the retaining part 17b is inserted in between the teeth of the idle gear 32. When the retaining part 17b has moved closest to the idle gear 32, moreover, the lever portion 17a is, as shown in Fig. 7, substantially vertically protruding to the required extent relative to a side case plate 11b out of a slit 11c provided with the case plate 11b. The side case plate 11b of the sub-shell 11 is provided with an operating protrusion 11d adjacent to the protruding lever portion 17a. In the laser printer thus constructed, the photoconductive drum 1, together with the sub-shell 11, is replaced. With a new photoconductive drum 1, the retaining part 17b is revolved in a direction in which it moves close to the idle gear 32 while resisting the bias force of the torsion spring 35 and set in such a state that the retaining part 17b is held in between the teeth of the idle gear 32 and retained therein. In other words, the sub-shell 11 of the new photoconductive drum 1 is arranged in such a manner that the lever portion 17a of the lever 17 is protruding from the side case plate 11b. The revolving force of the lever 17 biased by the torsion spring 35 is not adapted to drive and rotate the idle gear 32 and the cleaning station 4 connected to the idle gear 32. A microswitch 36 as a switch means is disposed in a position corresponding to the position wherein the lever 17 is located on the sub-shell 11. The lever portion 17a protruding from the side case plate 11b is caused to press the microswitch 36. As shown in Fig. 8 and 9, an operating arm 41 having an inclined elastic portion 41a which is movable close to a side surface of the sub-shell 11 and an operating presser portion 41b formed with the lower end outwardly bent is disposed in a position corresponding to the lever portion 17a protruding from the side case plate 11b, whereas the microswitch 36 is disposed in such a manner that a switch button 36a corresponds as to its position to the operating presser portion 41b of the operating arm 41. The operating arm 41 is normally set free from pressing the switch button 36a of the microswitch 36. When the sub-shell 11 is mounted on the laser printer body, the lever portion 17a protruding from the side case plate 11b of the sub-shell 11 abuts against the inclined portion 41a, thus causing elastic deformation thereof and thereby the switch button 36a is pressed by the operating presser portion 41b. The operating arm 41 is formed as a part of an operating fitting 40, which is fitted with an operating arm 42 similar in shape to the operating arm 41 and disposed in parallel to and a predetermined space apart from the operating arm 41. A microswitch 37 fixedly superposed on the microswitch 36 is disposed in a position corresponding to the operating arm 42. The operating arm 42 corresponds to the operating protrusion lid protruding from the side case plate 11b of the sub-shell 11 and adjacent to the lever portion 17a and is caused to press a switch button 37a a provided on the microswitch 37 whenever the sub-shell 11 is fitted into the laser printer body. In the laser printer thus constructed, the lever portion 17a and the operating protrusion 11d, each protruding from the side case plate 11d, are adapted to press the microswitches 36, 37 via the respective operating arms 41, 42 when the sub-shell of a new photoconductive drum 1 is mounted on the laser printer body. In this state, it is primarily detected that the sub-shell 11 is mounted on the printer body by means of a signal from the microswitch 37. When the power supply is turned on to start operation, the photoconductive drum counter, on receiving the signal form the microswitch 36, is reset. When the idle gear 32, being interlocked with the rotation of the photoconductive drum 1 as described above, is driven to rotate after the operation is started, the retaining part 17b of the lever 17 slips off the gap between the teeth of the idle gear 32 as it rotates. As a result, the retaining part 17b is caused by the energizing force of the torsion spring 35 to rock and revolve away from the idle gear 32, whereas the lever portion 17a is withdrawn through the slit 11c into the side case plate 11b. The microswitch 36 is thus released from being pressed. Once the photoconductive drum 1 is actuated, the lever portion 17a thus protruding retracts and stops pressing the switch button 36a of the microswitch 36. Therefore, the photoconductive drum counter will never be reset even if the sub-shell 11 is detached for maintenance and the like. On the other hand, the other microswitch 37 is pressed and operated whenever the sub-shell 11 is fitted into the printer and the presence or absence of the sub-shell 11 is detected by the output signal of the microswitch 37. In other words, the output signal from the microswitch 37 is used to determine operability of the printer.

Claims: A reset mechanism for resetting a counter for counting the number of rotations of a first rotary member (14), comprising a rocking member (17) and control means for controlling said counter and for resetting the counter when said rocking member (17) is rocked, the rocking member (17) being biased in a predetermined direction by an urging member (20) and being movable in said direction, characterized in that said control means comprises a stopping member (16a) provided on a second rotary member (16) arranged to rotate in response to a rotation of said first rotary member (14) and that said stopping member (16a) is arranged to retain said rocking member (17) in an initial state and to release it from this initial state after rotation of the first rotary member (14), such that the rocking member (17) is separated from the stopping member (16a) by the bias of the urging member (20). The reset mechanism according to claim 1 wherein said first rotary member is a photoconductive drum (14) used in a printer, said photoconductive drum (14) being exposed to light to form a latent image on the circumferential surface thereof. The reset mechanism according to claim 2, wherein a part of said control means is provided between said photoconductive drum (14) and said rocking member(17). The reset mechanism according to any one of claim 1 to 3, wherein said stopping member comprises a contact element (16a) brought into contact with a predetermined portion (17a) of said rocking member (17) for stopping a rocking operation against the bias force supplied to said rocking member (17) and a switch member (21) for resetting said counter in case that said contact element (16a) and said predetermined portion (17) are brought out of contact by means of a rocking operation of said rocking member (17). The reset mechanism according to claim 4 wherein said rocking member comprises a lever member (17) arranged to be revolvable about a shaft (18) in a predetermined direction by the bias force supplied from a spring member (20) connected to one end of said lever member (17) and said contact element (16a) comprises a projection portion on a shaft of said second rotary member (16). The reset mechanism according to claim 4 wherein said rocking member comprises a lever (17) arranged to be horizontally movable about a shaft (17c) in a predetermined direction by the bias force supplied from a torsion spring member (35) wound around said shaft (17c) and wherein said predetermined portion is a projection portion (17a) provided on said lever member (17) and said contact element comprises a teeth portion of an idle gear (32) brought into contact with said projection portion (17a) of said lever member (17), said idle gear (32) rotates in response to the rotation of said first rotary member (14).

Inventors: KITA, MASAHIRO, NEGORO, IKUO C/O ASAHI KAAGAKU KOGYO K.K., KITA, MASAHIRO, C/O ASAHI KOGAKU KOGYO K.K.,
Applicants: ASAHI KOGAKU KOGYO KABUSHIKI KAISHA
Application year: 1989
Main classification: G03G15
IPC codes: G03G21, G06M7, G06M3, G06M1, G03G15