Electrophotographic imaging apparatus and process cartridge

Abstract: Cartridge (1) contains a brush charger (32) and printer (40) contains a charge roller (30). Upon installation of the cartridge a top shutter (7) is moved downward and the charge roller is moved by a pivoted arm (44) through the opening left by the shutter to contact a photoconductor drum (24) in the cartridge. In operation the roller functions after charging by the brush at a potential to control the final charge on a photoconductor prior to xerographic imaging. The precharging by the brush greatly reduces deterioration of the charge roller, permitting long machine life with the accurate and uniform operation of a charge roller.

Description: This invention relates to an electrophotographic imaging device employing a replaceable toner cartridge and contact charging. Replaceable toner cartridges are widely used in electrophotographic printers and copiers. Many such cartridges include the charging device, which may be a corona wire to generate ions or may be a charge roller or other contact charging member. The cartridges sold by the present applicant for its Optra (trademark) and 4039 families of printers have a charge roller in the cartridge. Accordingly, that charge roller necessarily is replaced when the cartridge is replaced. US-A-5365315 locates its charge roller out of the cartridge, specifically in the lid, and thereby permits use of the same charge roller for the life of the machine. However, each charging operation entails some deterioration of the charge roller. With high printer usage and particularly with increased printing speeds, a single charge roller will not function for the life of the machine. Thus US-A-5365315 discloses an imaging apparatus containing a replaceable cartridge, said cartridge containing a rotatable photoconductor, toner, and a toner applicator to tone an electrostatic image on said photoconductor, and said imaging apparatus comprising a charging member mounted on a movable member in said apparatus, said movable member when in an operating position of said apparatus locating said charging member for charging said photoconductor. In one aspect the present invention is characterised in that said cartridge contains a first contact charging member arranged to charge said photoconductor during an imaging operation to a first voltage level at or near the final charge required for printing, and said charging member of said imaging apparatus being a second charging member arranged to charge said photoconductor to a second voltage of the same polarity as said first voltage at a level controlled by the voltage of said second charging member at the final charge required for printing, at a location operatively past the location of said first contact charging member. US-A-5365315 further discloses a toner cartridge for use in an imaging apparatus, said cartridge comprising a rotatable photoconductor, toner, a toner applicator, and a shutter pivotable downward into said cartridge to leave an opening in said cartridge, said cartridge having a location which is unobstructed between said opening and said photoconductor so as to be able to receive, in use, a charging member of diameter at least about 10 mm and being part of an imaging apparatus, and so as also to be able to permit optical discharge at said photoconductor charged by said charging member, by way of a path through said opening. The present invention also defines a toner cartridge for use in an imaging apparatus according to claim 5. Thus a preferred embodiment of this invention places a charging device in the toner cartridge, but one which is a low-cost device suitable to charge the photoconductor to a level near the final charge required for printing. A charge roller in the printer or copier charges the precharged photoconductor to the final charge. Deterioration of the charge roller is greatly reduced such that the charge roller can last the life of a very heavy-duty printer (or other imaging apparatus). In operation for imaging the cartridge is installed in the imaging device, and the charge roller is moved into contact with the photoconductor through a top opening created in the cartridge by pivoting of a top shutter. The voltage applied to the precharge member is slightly less or nominally identical with that of the charge roller, so that, when the precharged surface of the photoconductor reaches the charge roller, the charge roller defines the final charge on the photoconductor. Since the final charge is applied by a roller, it is much more accurate and uniform than a charge applied by a brush or other known lower cost contact charging member. Low deterioration of the charge roller is experienced, permitting its use for a full machine life of a heavy-duty printer. The cartridge is replaced periodically when each cartridge is empty of toner which necessarily includes replacement of its low-cost contact charger. An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- Fig. 1 is an illustrative perspective view of a replaceable toner cartridge; Fig. 2 is an illustrative sectional view of the parts of the cartridge pertinent to this invention when installed in a printer, as well as illustrating the charge roller entered into the cartridge and the optical path to the photoconductor; Fig. 3 is illustrative of the printer as a whole with particular detail of the charge roller mounted in the machine; and Fig. 4 is identical to Fig. 2 except that it shows a roller as the charging member in the cartridge. Referring to Fig. 1, a toner cartridge 1 has a toner chamber 3 holding toner 5 (Fig. 2) and a top shutter 7, which rotates into cartridge 1 upon installation. Shutter 7 has a control arm 7a, integral with shutter 7, which contacts an abutment 7b (Fig. 3) upon insertion of cartridge 1. Cartridge 1 has positioning studs 8a and 8b on opposite sides for locating cartridge 1 when installed. A link 9 (Fig. 2) connects to a bottom shutter 11 to move bottom shutter 11 upon installation in the direction away from chamber 3. As is conventional, toner cartridge 1 is replaced with an identical cartridge 1 when toner 5 in a cartridge 1 is gone. Fig. 2 illustrates cartridge 1 as installed and with the uninstalled positions of shutters 7 and 11 also shown in dashed outline. As is generally conventional toner 5 is agitated by a roller 20, termed a toner adder roller, and applied by a developer roller 22 to a photoconductor drum 24 (termed a drum because it is typically hollow). Toner 5 is metered by an electrified doctor blade 27 as it is moved to drum 24 by rotation of developer roller 22. (Arrows in the illustrations of roller 22 and drum 24 show the direction of rotation during operation). Shutter 7 is rotated downward toward a surface 26 in cartridge 1, leaving an opening 28 above photoconductor 24. Charge roller 30 moves by pivoting as will be described from a position outside opening 28 (shown in dashed lines) to within the cartridge 1 in contact with the top of photoconductor 24 (shown in solid lines). Prior (with respect to the rotation of photoconductor 24 in imaging operating) to the location of contact of roller 30, a charge wiper or brush 32 is permanently mounted in cartridge 1 in charging contact with photoconductor 24. Arrow 34 shows a path to a location past the charging of photoconductor 24 by roller 30 at which the photoconductor 24 is discharged to form latent images, as is essentially conventional, which are developed with toner 5 applied by developer roller 22, as is also essentially conventional. Charge roller 30 is preferably at least 12 mm in diameter, so the area past brush 32 under opening 28 must be unobstructed to permit roller 30 to enter opening 28 and contact drum 24 and to permit a clear optical path 34 for imaging after charging by roller 30. To complete the imaging, paper or other substrate 35 is moved by feed rollers 36 nestled beneath cartridge 1, which move paper 35 into contact with photoconductor 24 at the area opened by the movement of shutter 11. The toner image is transferred to paper 35, as is conventional, and subsequent steps of fixing the image by heat and delivery of paper 35 may also be essentially conventional. Fig. 3 illustrates a printer 40 with the cartridge 1 installed. Moveable parts are shown in solid line in the down position and dashed line in the up position. Light applied in the path of arrow 34 is generated by a laser printhead 42 which may be of a conventional nature. Charge roller 30 is mounted on arm 44, which is pivoted at a hinge 48. Front door 54 is rotated on hinge 56 upward (clockwise in Fig. 3) to provide room to insert and take out cartridge 1. Door 54 is pivoted upward on hinge 56 when cartridge 1 is inserted. Door 54 is then rotated downward to a closed position. When cartridge 1 is inserted control arm 7a encounters abutment 7b to pivot shutter 7 downward to create opening 28. At the same time charge roller 30 pivots through the opening 28 and into contact with photoconductor 24. Charge roller 30 is spring mounted (not shown) around pivot 48 to provide a constant force between charge roller 30 and photoconductor 24. Rollers 60 receive paper 35 having the final image and place it on output tray 62. In operation charge brush 32 places a substantial portion of the required negative charging current onto photoconductor 24 prior to final charging by charge roller 30. Because brush 32 applies charge from strands, it produces a somewhat non-uniform charging pattern on the photoconductor 24 that would result in print quality pattern non-uniformity if used alone. However, in accordance with this embodiment, the surface of photoconductor 24 precharged by brush 32 subsequently reaches charge roller 30 and charge roller 30 deposits the final, uniform charge onto photoconductor 24. The potential supplied to the brush 32 is -1400 volts, and the potential supplied to the charge roller 30 is -1600 volts. The aluminum core of photoconductor drum 24 is at -200 volts DC. Since the second voltage is larger than the first and of the same polarity, it dominates the final charge, and the charge roller 30 controls the uniformity and level of the final charge. The final surface charge on photoconductor 24 immediately after leaving roller 30 is very uniform at approximately -1040 volts. To attain a 250,000 page life, the charge roller 30 has an uncoated or powder-coated epichlorohydrin resin body. The diameter is designed as relatively large (i.e., 12 or 15 mm, at least in the order of magnitude of 10 mm) to also increase life. Alternatively, the charge roller 30 can be coated with selected semiconductive material such as carbon-loaded Nylon® 6-6 to control final electrical characteristics, as is conventional. The charge brush 32 is 4 mm conductive, carbon-loaded nylon fiber woven into a cloth of 60,000 to 250,000 fibers per square inch. This is commercially available as a contact charging member at relatively low cost. Any low cost contact charger is an alternative as the charge applied to photoconductor 24 need not be precise or uniform at this precharge location. A low cost charge roller 32a is illustrated in Fig. 4 as the cartridge-mounted charging member. The foregoing printer 40 will operate with paper feed up to at least 5.4 inches per second, which can be considered 24 pages per minute. Printer 40 can function normally for 250,000 pages without replacing charge roller 30. Possible variations will be apparent. Some charging systems apply AC and DC to the charge roller 30. In such a system, two alternatives are available, applying DC only to the charge brush 32 or applying combined AC and DC to both brush 32 and charge roller 30. Typical combined potentials for the charge roller 30 would be -1040 volts DC combined with 1500 volts peak to peak AC sine wave at 600 Hz, which achieves a final charge of -1040 volts. Where both the brush 32 and the charge roller 30 have combined AC and DC voltages, they would be identical.

Claims: An imaging apparatus containing a replaceable cartridge (1), said cartridge containing a rotatable photoconductor (24), toner (5), and a toner applicator (22) to tone an electrostatic image on said photoconductor, and said imaging apparatus comprising a charging member (30) mounted on a movable member (44) in said apparatus, said movable member when in an operating position of said apparatus locating said charging member for charging said photoconductor (24), characterised in that said cartridge contains a first contact charging member (32;32a) arranged to charge said photoconductor during an imaging operation to a first voltage level at or near the final charge required for printing, and said charging member (30) of said imaging apparatus being a second charging member arranged to charge said photoconductor to a second voltage of the same polarity as said first voltage at a level controlled by the voltage of said second charging member at the final charge required for printing, at a location operatively past the location of said first contact charging member. An imaging apparatus as claimed in claim 1, in which said first contact charging member is a wiper (32) and said second charging member is a contact charging roller (30). An imaging apparatus as claimed in claim 2, in which said wiper (32) is a cloth of woven filaments. An imaging apparatus as claimed in claim 1, in which said first contact charging member is a contact charging roller (32a). A toner cartridge (1) for use in an imaging apparatus, said cartridge comprising a rotatable photoconductor (24), toner (5), a toner applicator (22), and a shutter (7) pivotable downward into said cartridge to leave an opening in said cartridge, said cartridge having a location which is unobstructed between said opening and said photoconductor so as to be able to receive, in use, a charging member (30) of diameter of at least about 10 mm and being part of an imaging apparatus, and so as also to be able to permit optical discharge at said photoconductor charged by said charging member, by way of a path through said opening, characterised in that said cartridge also contains a first contact charging member (32;32a) at a first charging position arranged to charge said photoconductor, and said unobstructed location being downstream of said first charging position in the direction of rotation of said photoconductor, whereby, in use in the imaging apparatus, said first contact charging member (32;32a) is arranged to charge said photoconductor (24) at or near the final charge required for printing and said charging member (30) of said imaging apparatus is arranged to charge said photoconductor (24) of the same polarity as said first contact charging member (32;32a) at the final charge required for printing at said unobstructed location.

Inventors: REAM GREGORY LAWRENCE, REAM,GREGORY LAWRENCE
Applicants: LEXMARK INT INC, LEXMARK INTERNATIONAL, INC.
Application year: 1996
Main classification: G03G15
IPC codes: G03G15, G03G21