EP0507528B1

EP0507528B1 - Process cartridge and image forming system with it

Info

Publication number: EP0507528B1
Application number: EP92302768A
Authority: EP
Inventors: Masahiko C/O Canon Kabushiki Kaisha Yashiro
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1991-04-01
Filing date: 1992-03-30
Publication date: 1996-09-11
Anticipated expiration: 2012-03-30
Also published as: EP0507528A2; EP0507528A3; DE69213525D1; JP3200139B2; JPH0580600A; DE69213525T2; HK121297A

Description

The present invention relates to a process cartridge which can be removably mounted in an image forming apparatus, such as an electrophotographic copying machine, a laser beam printer (LBP), a facsimile system, a word processor or the like. The invention also relates to a combination of an image forming apparatus and a process cartridge.
Examples of such process cartridges are described in patent documents US-A-4,470,689, US-A-4,462,677, EP-A-0304314 and EP-A-0351894. A further example of a process cartridge is shown in Figs. 1 to 3.
Referring to Fig. 1, a photosensitive drum 4 is disposed in the process cartridge 3. The drum is sensitive to shock and frictional wear. Thus, a drum shutter 20 is provided at a transfer opening 3c of the cartridge 3 and the photosensitive drum 4 is protected by the drum shutter 20. When the cartridge is inserted into an image forming apparatus, the drum shutter 20 is shifted from a closed position to an open position (shown by the broken line 20a), thus permitting the transferring of an image formed on the photosensitive drum.
The closed position of the drum shutter is limited or regulated by abutting a projection 20b of the drum shutter against an end 7a of a cleaner 7. The reference numeral 21 denotes a shutter arm.
The width of the drum shutter 20 is long (for example, in a process cartridge capable of forming an image on a sheet of A4 size, the width L is about 270mm, and, in a process cartridge capable of forming an image on a sheet A3 size, the width L is about 350mm). Further, the drum shutter 20 is generally formed from engineering plastics. Thus, when the cartridge 3 is dismounted from the image forming apparatus 2, if an operator grasps the process cartridge 3 by his hand as shown in Fig. 2A, a central portion of the shutter 20 will be flexed as shown in Fig. 2B. Accordingly, the drum shutter 20 may contact the photosensitive drum 4 (Fig. 2B), thus damaging the latter. To avoid this, as shown in Fig. 3, a protective sheet 23 for protecting the drum could be adhered to an inner surface of the drum shutter 20. However, also in this case, it is difficult to prevent the damage to the photosensitive drum 4 completely, due to the contact between the drum and the drum shutter 20.
The present invention is concerned with the protection given to the drum by the drum shutter and more particularly with the possibility that the drum shutter may damage the drum.
In accordance with the present invention, there is provided a process cartridge which can be removably mounted in an image forming system, the cartridge comprising a casing having a front and a rear and containing an elongate, rotatable electrophotographic drum having a photosensitive surface, the drum extending across the casing, charger means extending transversely to the casing above the drum for electrically charging the surface of the drum, developer means extending transversely to the casing to the rear of the drum for developing a latent image formed on an image bearing portion of the surface of the drum, and cleaning means extending transversely to the casing in front of the drum for cleaning the surface of the drum; the casing having an elongate exposure opening extending transversely to the casing above the drum to enable the image bearing portion of the surface of the drum to be exposed to light between the charger means and the developer means for forming the latent image on the image bearing portion of the surface of the drum; the casing also having an elongate transfer opening extending transversely to the casing at the bottom of the drum, the transfer opening providing access to the surface of the drum to enable the developed image to be transferred from the image bearing portion of the surface of the drum to a transfer material beneath the casing; the cartridge further comprising an elongate protective shutter for the transfer opening, and a plurality of linkages connecting the shutter to the casing for movement between a closed position in which the shutter closes the transfer opening, underlying the drum to protect the surface of the drum, and an open position in which the transfer opening is uncovered and the shutter is disposed outside of the casing, the linkages guiding the shutter so that during initial movement of the shutter from the closed position the shutter moves generally tangentially of the surface of the drum at the transfer opening;
characterised in that:
the shutter has first and second projections which are spaced apart in the longitudinal direction of the shutter and which, when the shutter is in the closed position, abut the surface of the drum to either side of the image bearing portion thereof so that the extent of the shutter between the projections is held spaced from the image bearing portion of the drum.
The projections therefore hold the relevant portion of the shutter spaced from the image bearing portion of the drum, and the linkages provide the opening action described above. By contrast, in the case of an arrangement like that shown in Figure 3, such an opening action would be likely to cause the protective sheet to rub on the drum.
In one embodiment of the invention, when the shutter is in its closed position, the projections abut against peripheral surfaces of the drum which are not photosensitive, and in another embodiment they abut against photosensitive peripheral surfaces of the drum which are not used for image formation.
In an embodiment of the invention, there are three of said linkages, one at one side of the casing and the other two at the other side of the casing.
Specific embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings. In the drawings:

Fig. 1 is a side sectional view of a process cartridge for explaining the background art for the present invention;
Figs. 2A and 2B are views for explaining the background art for the present invention, where Fig. 2A is a side view of a process cartridge grasped by an operator's hand, and Fig. 2B shows a relation between a photosensitive member and a drum shutter;
Fig. 3 is a perspective view of a drum shutter for explaining the background art for the present invention;
Fig. 4 is an elevational sectional view of a laser beam printer according to a preferred embodiment of the present invention;
Fig. 5A is a perspective view of a process cartridge according to a first embodiment of the present invention, and Fig. 5B is a side view of the process cartridge;
Figs. 6A and 6B are views showing a process cartridge according to the present invention in a condition that it is started to be inserted into an image forming system, where Fig. 6A is a perspective view of the process cartridge and Fig. 6B is an end view of the process cartridge;
Figs. 7A and 7B are views showing the process cartridge in a condition after it is completely inserted into the image forming system, where Fig. 6A is a perspective view of the process cartridge and Fig. 6B is an end view of the process cartridge;
Fig. 8 is a side view of the process cartridge for explaining the operation thereof; and
Figs. 9A and 9B are perspective views of a drum shutter.

The present invention is applicable to an image forming system such as an electrophotographic system, an electrostatic recording system and the like which utilizes electrophotographic technique and which can be embodied as an electrophotographic copying machine, a laser beam printer and the like.
First of all, as an example of the image forming system, a compact laser beam printer as an output device for an information processing system will be explained.
As shown in Fig. 4, a laser beam printer 1 includes a process cartridge 3 removably mounted within a frame 2 of the printer. The process cartridge 3 has a frame 3a within which there are arranged a photosensitive drum 4 acting as an image bearing member, and a conventional process means comprising a charger 5, a developing device 6 (including a toner containing portion 6a and a developing sleeve 6b) and a cleaner 7 (including a cleaning blade 7a and a waste toner reservoir 7b) which are disposed around the photosensitive drum. Incidentally, the reference numerals 33a and 33b denote cartridge mounting means on which the process cartridge 3 can be mounted from a direction shown by the arrow A. Further, within the frame 2 of the printer at an upper portion thereof, there are arranged a scanner unit 8 for illuminating a laser beam 8a on a photosensitive member 4a of the drum and scanning the drum, and a reflection mirror 9. The scanner unit 8 receives image information from an information processing system (not shown) such as a computer or a word processor and emits the laser beam 8a in correspondence to the information.
When the photosensitive drum 4 uniformly charged by the charger 5 is illuminated by the laser beam 8a, a latent image corresponding to the image information is formed on the drum. The latent image is developed by the developing device 6 to form a toner image. Within a lower portion of the frame 2, there is disposed a sheet supply cassette 10 containing sheets (recording media) S therein. A sheet supply roller 11 is arranged above the sheet supply cassette 10. The sheet S contained in the sheet supply cassette 10 is supplied one by one by means of the sheet supply roller 11 to reach a pair of register rollers 12 which in turn send the sheet between the photosensitive drum 4 and a transfer charger 13 in registration with the toner image formed on the photosensitive drum 4. Then, the toner image on the photosensitive drum 4 is transferred onto the sheet S at a transfer station. The sheet to which the image was transferred is sent, by a convey belt unit 14, to a fixing device 15 (including a heat roller 15a and a pressure roller 15b), where the toner image is permanently fixed to the sheet. Thereafter, the sheet is ejected out of the frame 2. Incidentally, the frame 3a of the cartridge has an exposure opening 3b and a transfer opening 3c and supports the photosensitive drum 4, developing device 6 and cleaner 7.
In the laser beam printer 1 according to the illustrated embodiment, there are two methods for ejecting the sheet S after the image formation, one of which is a method for ejecting the sheet S with face-up, i.e., with facing an imaged surface upside. In this case, the sheet S is sent by face-up ejector rollers 16 toward a face-up ejection tray 17. The other method for ejecting the sheet is a method for ejecting the sheet S with face-down, i.e., with facing the imaged surface downside at the page order. In this case, the sheet S fed from the face-up ejector rollers 16 is guided upwardly via a switching means 31 such as a flapper and a sheet guide member 32 to invert the sheet, and then is ejected onto a face-down ejection tray 19 via face-down ejector rollers 18. Incidentally, the switching means 31 may be automatically switched by the activation of a plunger (not shown) when an operator turns a switch button (not shown) ON or may be manually switched by manipulating a manual lever (not shown).
Further, the maintenance of the laser beam printer 1 according to the illustrated embodiment (for example, the jam treatment or the replacement of the process cartridge) is effected from a direction shown by the arrow A after an upper portion 2a of the frame 2 is rotated upwardly with respect to a lower portion 2b around a pivot P to expose the interior of the printer. Incidentally, the process cartridge 3 is mounted on the upper portion 2a.
Next, the process cartridge according to a first embodiment will be explained. Incidentally, in the embodiment described hereinbelow, the constructural elements having the same functions as those in the aforementioned embodiment are designated by the same reference numerals.
Figs. 5A and 5B show the process cartridge according to the first embodiment of the present invention, where Fig. 1 is a perspective view of the process cartridge and Fig. 5B is a side view of the cartridge.
In this embodiment, two ribs 20c are formed on an inner surface 20e of a drum shutter 20 as a cover (surface facing a photosensitive drum 4 when the shutter is in a closed position) near both ends thereof along a width thereof (i.e., along an opening/closing direction of the shutter), so that the ribs are abutted against the photosensitive drum (image bearing member) 4 when the shutter is closed. In this case, the position of the ribs 20c is so selected that they are abutted against non-imaging areas or non-photosensitive surfaces (cylindrical peripheral surfaces) 4b disposed on both ends of the drum, thus preventing the ribs from contacting with a photosensitive surface (imaging area) 4a of the drum. That is to say, according to this embodiment, the ribs 20c are protruded from the drum shutter 20 toward the drum at areas out of the photosensitive surface or imaging area 4a. Incidentally, the ribs 20c have semi-cylindrical surfaces 20d adapted to be smoothly abutted against the photosensitive drum 4. Further, the areas of the photosensitive drum 4 against which the ribs 20c are abutted are not limited to the non-photosensitive surfaces, but may be photosensitive surfaces on which an image is not formed. Furthermore, the ribs 20c are protruded from the inner surface 20e of the drum shutter 20 by about 3 - 7 mm, preferably about 4 - 6 mm and most preferably about 5.5 mm.
In Fig. 5B, when a flexed amount of the process cartridge 3 at loading points (normally, load of about 2 Kg) generated by forces F due to the operator's grasp of the process cartridge 3 is δ, the height d of each rib 20c may be selected so that the height d becomes greater than the flexed amount δ (d > δ). With this arrangement, even if the drum shutter 20 is flexed, it does not contact with the photosensitive surface 4a, thus preventing the damage of the photosensitive surface 4a. Further, in the illustrated embodiment, although the ribs 20c on both ends of the drum shutter 20 are abutted against the non-photosensitive surfaces 4b, since such surfaces are out of the image forming area, if such surfaces are damaged, the image to be formed is not influenced upon such damage. Furthermore, the ribs 20c may be abutted against the portions of the photosensitive surface 4a so long as such portions are non-imaging areas. Also in this case, the image to be formed is not influenced badly.
Further, because of d > δ, any protection sheet is not required, thus reducing the cost of the cartridge. Furthermore, since the drum shutter are directly positioned with respect to the photosensitive drum 4, the positioning accuracy of the drum shutter is improved, thus enhancing the protecting ability of the drum shutter 20 regarding the photosensitive drum 4.
Incidentally, in the above-mentioned conditions shown in Figs. 5B, the drum shutter 20 covers the exposed area (transfer area) of the photosensitive drum 4; whereas, when the process cartridge 3 is inserted into the printer, the drum shutter 20 is retracted from this position.
In this embodiment, the drum shutter 20 is integrally formed from high impact plastic resin such as polystyrol, and a thickness thereof is about 0.5 - 3 mm, preferably about 1 - 2 mm and most preferably about 1.5 mm.
Next, an opening/closing mechanism for the drum shutter 20 during the mounting and dismounting of the process cartridge 3 with respect to the frame 2 of the printer will be explained with reference to Figs. 6 and 7. Incidentally, Figs. 6A and 6B show a condition that the process cartridge 3 is started to be inserted into the frame 2 of the printer, where Fig. 6A is a perspective view of the process cartridge and Fig. 6B is a side view of the cartridge. Further, Figs. 7A and 7B show a condition that the process cartridge 3 is completely inserted into the frame 2 of the printer, where Fig. 7A is a perspective view of the process cartridge and Fig. 7B is a side view of the cartridge. Incidentally, the reference numeral 3b denotes an exposure opening through which the light corresponding to the image information is illuminated onto the photosensitive member 4a.
First of all, the frame 3a of the process cartridge 3 is inserted from the position shown in Figs. 6A and 6B toward a direction shown by the arrow V. As a result, a projection 40c of a movable link 40 for releasing the drum shutter (protection member) 20 is abutted against a fixed member 41 formed on the frame 2 of the printer. When the process cartridge 3 is further inserted into the frame 2, the link 40 is rotated around a pivot 40a, with the result that the drum shutter 20 is opened while being guided by links 42a, 42b disposed on both sides of the shutter. As shown in Figs. 7A and 7B, when the process cartridge 3 is mounted in a predetermined mounting position, the shutter 20 is maintained in the open condition in the vicinity of the frame 3a near the cleaner 7.
On the other hand, when the cartridge 3 is dismounted from the frame 2 of the printer, the cartridge is drawn in a direction opposite to the direction V. Meanwhile, when the movable link 40 is disengaged from the fixed member 41, the drum shutter 20 is returned to the closed position covering the transfer opening 3b of the frame 3a, by a biasing force of a spring 43 disposed on the pivot 40a. In this position, the shutter 20 is maintained in the closed position by abutting a portion 40d of the movable link 40 against the frame 3a by the biasing force of the spring 43.
Incidentally, in this embodiment, the movable link 40 is rotatably mounted on the frame 3a via the pivot 40a, and the other end of the movable link is rotatably connected to a lateral edge 20f of the shutter 20 via a pin 40b. Further, the links 42a, 42b are rotatably mounted at their one end 42c on the frame 3a, and are also rotatably connected at their other end 42d to the lateral edge 20f of the shutter 20.
Now, the details of the process cartridge are shown in Fig. 8 as a side view. Incidentally, in Fig. 8, several positions of the drum shutter 20 transited from the closed position to the open position are also illustrated. The reference numeral 50 denotes a guide disposed outside the frame 3a for guiding the cartridge 3 in the mounting direction during the insertion of the cartridge.
As clearly seen in Fig. 8, the movable link 40 has a "convex" shape so that it encircles a right half of the photosensitive drum 4 and is pivotally mounted on the frame 3a via the pivot 40a, and the end of the link is rotatably connected to a central portion of the lateral edge 20f of the shutter 20 via the pin 40b. On the other hand, the link 42a has an end portion bent at a right angle, and a distal end of the bent portion is rotatably connected to the lateral edge 20f of the shutter 20 at a corner 20g of the end thereof to be opened. The end 42c of this link is pivotally mounted on the frame 3a. Incidentally, the attachment end 42c of the link 42a is disposed between the photosensitive drum 4 and the pin 40a for the movable link 40c in the vertical direction. Further, in the horizontal direction, the end 42c is disposed on the frame 3a outside the peripheral surface of the photosensitive drum 4 and the pivot 40a for the movable link 40.
By properly selecting the lengths of the movable link 40 and the links 42a, 42b, as shown in Fig. 8, the drum shutter 20 is opened along the proximity of the frame 3a near the cleaner 7. Thus, in the process cartridge according to this embodiment, since the opening/closing movement of the shutter 20 is effected along the proximity of the frame 3a, it is possible to further reduce the cartridge mounting space in the frame 2 of the printer in comparison with the conventional case.
Figs. 9A and 9B are perspective views of which may be used in the arrangements of shutters 20 Figs. 6, 7 and 8. Incidentally, Fig. 9B is a perspective view of the shutter to which the links are attached.
In the shutters 20 of Figures 9A and 9B, vertical projections 20h are formed on lateral edges of a cover portion 20a of the shutter 20. In Figure 9A, each projection 20h has a semi-cylindrical surface 20i which is adapted to be abutted against the drum 4, and a flat surface 20j. In this embodiment, when the shutter 20 is shifted from the open position to the closed position, the flat surfaces 20j of the projections 20h are firstly abutted against the peripheral surface of the drum 4. Then, the semi-cylindrical surfaces 20i of the projections 20h reach the peripheral surface of the drum 4 while being guided by the flat surfaces 20j, with the result that the shutter 20 is in the closed condition with the semi-cylindrical surfaces 20i of the projections mated with the peripheral surface of the drum 4. Now, the drum shutter 20 is molded from polystyrol resin similar to the frame 3a. Accordingly, also in this embodiment, the drum shutter 20, when closed, is positioned with respect to the peripheral surface of the drum 4 with high accuracy, and, thus, when the operator grasps the cartridge 3, even if the shutter 20 is flexed (normally, the shutter is subjected to the load of about 2 Kg), it is possible to prevent the surface of the photosensitive member 4a from being damaged by the flexed shutter 20. Further, when the shutter 20 is closed, since the projections 20h mate with the peripheral surface of the drum, the protection ability for the photosensitive member 4a can be further improved.
Now, the concrete dimension of the shutter will be described hereinbelow. Incidentally, the following example is a case where the shutter 20 is used with a process cartridge capable of recording an image on a sheet having A4 size:
According to the above-mentioned embodiment, since the cover portion of the drum shutter for protecting the image bearing member, i.e. the photosensitive drum, is abutted against the non-imaging area of the photosensitive drum, even if the drum shutter is subjected to the excessive load, the image bearing surface of the photosensitive drum can be protected effectively.

Claims

A process cartridge which can be removably mounted in an image forming system, the cartridge comprising a casing (3) having a front and a rear and containing an elongate, rotatable electrophotographic drum (4) having a photosensitive surface, the drum extending across the casing, charger means (5) extending transversely to the casing above the drum for charging the surface of the drum, developer means (6) extending transversely to the casing to the rear of the drum for developing a latent image formed on an image bearing portion of the surface of the drum, and cleaning means (7) extending transversely to the casing in front of the drum for cleaning the surface of the drum; the casing having an elongate exposure opening (3b) extending transversely to the casing above the drum to enable the image bearing portion of the surface of the drum to be exposed to light between the charger means and the developer means for forming the latent image on the image bearing portion of the surface of the drum; the casing also having an elongate transfer opening (3c) extending transversely to the casing at the bottom of the drum, the transfer opening providing access to the surface of the drum to enable the developed image to be transferred from the image bearing portion of the-surface of the drum to a transfer material beneath the casing; the cartridge further comprising an elongate protective shutter (20) for the transfer opening, and a plurality of linkages (40, 42a, 42b) connecting the shutter to the casing for movement between a closed position in which the shutter closes the transfer opening, underlying the drum to protect the surface of the drum, and an open position in which the transfer opening is uncovered and the shutter is disposed outside of the casing, the linkages guiding the shutter so that during initial movement of the shutter from the closed position the shutter moves generally tangentially of the surface of the drum at the transfer opening;
characterised in that:
the shutter has first and second projections (20c) which are spaced apart in the longitudinal direction of the shutter and which, when the shutter is in the closed position, abut the surface of the drum to either side of the image bearing portion thereof so that the extent of the shutter between the projections is held spaced from the image bearing portion of the drum.
A cartridge according to claim 1, wherein, when the shutter is in its closed position, the projections abut against peripheral surfaces of the drum which are not photosensitive.
A cartridge according to claim 1, wherein, when the shutter is in its closed position, the projections abut against photosensitive peripheral portions of the drum which are not used for image formation.
A cartridge as claimed in any preceding claim, wherein there are three of said linkages, one at one side of the casing and the other two at the other side of the casing.
A cartridge according to claim 4, wherein a pair of the linkages (42a, 42b) each have one point (42d) pivotally connected to the shutter adjacent a front edge (20g) thereof and at a respective end thereof, and each have another point (42c) pivotally connected to the casing, said one points (42d) of the pair of linkages being below said other points (42c) of the pair of linkages when the shutter is in its closed position; and the further linkage (40) has one point (40b) pivotally connected to one end of the shutter between the front and rear edges thereof and has another point (40a) pivotally connected to the casing above the drum and to the rear of said other points of the pair of linkages.
A cartridge according to claim 5, wherein the further linkage is curved so that, when the shutter is in its closed position, the linkage extends from said one point thereof upwardly and forwardly and then upwardly and rearwardly to said other point thereof.
A cartridge according to claim 5 or 6, wherein the further linkage extends past said other point thereof to form a projection (40c) for engagement with the image forming system to open the shutter.
A cartridge as claimed in any preceding claim, wherein the shutter, when in its open position, is disposed in front of the casing.
A cartridge as claimed in any preceding claim, wherein the drum is disposed closer to the front than the rear of the casing.
A combination of an image forming system and a cartridge as claimed in any one of the preceding claims removably mounted in the system.
A combination as claimed in claim 10, wherein the image forming system has a cavity in which the cartridge can be mounted in an operative position, the combination having means (50) for guiding the cartridge for insertion, front first, into the cavity towards the operative position, and the image forming system having means (41) for operating the shutter, as the cartridge is guided towards the operative position, to move the shutter from its closed position to its open position.