Biased transfer roll cleaner with biased shims using vacuum

Abstract: Apparatus for cleaning residual toner and paper fiber residue from a biased transfer roll (BTR) (20) in an electrophotographic apparatus, using high velocity air and substantially contactless flexible biased conductive shims (26). The high velocity air flow between the BTR and two thin conductive flex-shims is created by means of a blower (53) that evacuates the air in a vacuum chamber (22) in the apparatus. The high velocity air, in combination with the electrically biased BTR and flex-shims, removes residue from the BTR surface and carries it into the vacuum chamber and deposits the residue in a filter bag. The BTR biased shim cleaner system is low cost, efficient and significantly smaller than current BTR cleaning devices.

Description: This invention relates to an electrophotographic image forming apparatus, and more particularly to a cleaning device for removing residual toner and debris from the surface of a biased transfer roll (BTR). Typical cleaning methods in electrophotographic applications such as xerography, include wiping with a fur brush, a web, a blade and the like, a method using magnetism or a magnetic brush, a method using an air flow and/or a combination of at least several of the above. Turning now to Figures 1 and 2, cleaning apparatuses known in the art are depicted which include at least some combination of an air flow, a BTR and a brush cleaner which may be electrostatically charged. In Figure 1, an electrostatic brush cleaner 1 is depicted, including a cleaner housing 43 with upstream and downstream air inlets 40. To be effective, electrostatic brush cleaners must balance the air flows from the two sides of the housing 43. This is typically done by controlling the cleaner housing 43 spacing to the photoreceptor 16, the spacing between the brush 41 and the cleaner housing inner wall 35 and/or by adding interferences 39 between the brush 41 and the cleaner housing inner wall 35 near an air inlet 40 to create a pressure situation which will affect the air flow (air flow direction indicated at arrow 11). Additionally, positively and negatively charged detoning rolls 20a, 20b are used to assist the air flow in removing particles from the electrostatic brush 41. A flicker bar 37 is provided to help knock the toner particles free of the electrostatic brush 41 fibers. In Figure 2, a BTR cleaner 2 is depicted, using a rotating brush 3 in combination with an air system. The brush 3 removes toner from the BTR 20 and the air flow detones the brush fibers, with air flow direction indicated at arrow 11. The main disadvantages of the prior art devices discussed above include large size, insufficient component life, BTR surface abrasion and high unit manufacturing costs. Cleaning apparatuses employing an electrical bias to clean residual toner from an electrostatically charged surface in an electrophotographic device are also known. U.S. Patent No. 4,647,186, to Armstrong et al., discloses an apparatus for scavenging undesired charge particles from the surface of a recording element. The apparatus consists of a grid structure comprising a plurality of parallel, non-magnetic, electrically conductive wires. The plate is connected to an AC/DC power supply whose polarity is opposite to that of the charge particles to be scavenged. The AC grid bias functions to alternately attract the charged particles from the recording element and towards the grid, and then repel such particles from the grid itself. The grid, composed of a plurality of wires allows the scavenged particles to pass (or be pulled) through the grid by the magnetic influences of a magnetic brush applicator positioned directly beneath the grid. U.S. Patent No. 4,530,595, to Itaya et al., discloses a method and apparatus for cleaning the surface of an electrostatic image holder, where a DC voltage and/or an AC voltage whose polarity is opposite to that of the residual developer on the electrostatic image holder is impressed between an electrostatic image holder and a film member, one side of which is electrically conductive and the other side is insulated. The insulated surface of the film member is held close to the image holder and a voltage is impressed between an electrode and an electrostatic image holder. A removing means is used to remove the developer adhered on the insulating surface of the film member. U.S. Patent No. 4,479,709, to Syukuri et al., discloses a cleaning method to remove toner attached to an image retaining member of an electrophotographic copying machine, without damaging the surface of the image retaining member. An alternating electric field is applied to the surface to be charged. When applied, the toner on the photosensitive receptor drum moves to the roller and adheres thereto. The toner on the surface roller is scraped off by a blade and is collected in a recovery box. JP-A-58,196,565 describes an apparatus for cleaning rollers comprising a cleaner housing, a vacuum chamber, two flexible elastic blades, an air inlet and a means for creating and controlling air flow. It is important, for purposes of this invention, to clearly describe the BTR function in the electrophotographic apparatus. Paper, to which the image will be transferred, is fed into a nip formed by the BTR and the photoreceptor belt. The BTR is rotated at the same speed as the photoreceptor so that no relative motion between the paper and the untransferred toner image occurs. The BTR consists of an aluminum core with a slightly conductive urethane rubber coating. A high bias is applied to the core which creates an electric field at the paper which causes the charged toner particles to transfer from the photoreceptor surface to the paper. The advantage of using a BTR over corona transfer is that the pressure created in the BTR nip flattens out any ripples, etc., in the paper which create gaps between the paper and the photoreceptor. These gaps decrease the strength of the field needed to transfer toner to the paper and cause deletions in the resulting copies. The same gaps can be caused by large particles, such as carrier beads or toner agglomerates from the developer housing. These create "tent" deletions which appear as white circles around the large particles. BTRs can improve the appearance of copies by greatly decreasing the diameter of the "tent" deletions. Consequently, there is a need to clean the BTR surface because paper fibers from the backside of the copy can be attracted to the biased roll and toner which occurs on the photoreceptor between the copy regions will transfer to the roll. This toner consists of low level "background" toner, toner developed as a control patch used in maintaining the proper toner concentration and development field in the developer housing, and toner which accumulates on the lapped seam of the belt. If these materials are not cleaned from the BTR surface, they may retransfer to the back of copy sheets, appearing as spots and smudges, and if duplexed copies are being run, the spots and smudges will appear on both sides of the copies. It is an object of the present invention to provide an improved apparatus for cleaning a biased transfer roll in electrophotographic apparatuses having particularly stubborn or large toner cleaning requirements. Hereinafter, the terms 'shim' and 'blade member' are used interchangeably. The invention as defined in claim 1 is intended to achieve this object. The shims flutter during operation as a result of the air flow and, although they may intermittently touch the BTR surface, they remain substantially contactless. In the invention, the conductive disturber fabric is fixedly attached to the shims and will lightly contact the BTR surface to disturb the toner and assist the electrostatic and air current means removal of the residual toner. In a preferred embodiment, the conductive shims are made of a conductive synthetic resin or plastic and, for a transfer current of -50µA, a bias range of -2.1kV to -3.3kV above the BTR bias applied to the shims results in good BTR surface cleaning for all environments, even under stressed conditions. In another preferred embodiment, for a transfer current of -75µA, a bias range of -2.6kV to -3.4kV above the BTR bias applied to the shims results in equally good BTR surface cleaning for all environments, even under stressed conditions. Alternatively, various other DC voltage options are possible. Additionally, AC bias voltage may also be possible, for example, bias voltages of -3kV and -5kV may be applied to the BTR and shims respectively, with a DC rider signal of ± 500 volts riding on the -5kV shim voltage. As the air passes over and between the BTR and shims, the shims will tend to flutter, to at least some extent, dependent upon the air flow. Therefore, the shims may intermittently touch the BTR surface, thereby further enhancing BTR surface cleaning, but remain substantially contactless due to the air flow. By way of example only, embodiments of the invention will be described with reference to the accompanying drawings, in which:- Figures 1 and 2 (already described) are schematic plan views of prior art cleaning apparatuses; Figure 3 is a schematic plan view showing cleaning apparatus (not covered by the present invention); Figure 4 is a schematic plan view depicting the BTR and biased shims of Figure 3 in operation (i.e., fluttering); Figure 5 is an enlarged schematic plan view of the circled area of Figure 3 showing the shims in operation (i.e., fluttering); Figure 6 is a schematic plan view depicting other elements of the cleaning apparatus; Figures 7 and 8 are schematic views depicting electrical relationships within the apparatus; and Figures 9 and 10 are schematic plan views similar to Figures 4 and 5 depicting an embodiment of the invention. A BTR air cleaner with biased shims will be described in combination with a copier or xerographic device that uses a BTR. However, the cleaning apparatus may be used with any printing apparatus that includes a toner retentive imaging surface and a BTR. Turning now to Figures 3-8, a first embodiment (not covered by the present invention) is depicted. Shown is an apparatus for cleaning toner and paper fiber residue (see Figure 3) from the surface 21 of a BTR 20 in an electrophotographic apparatus using high velocity air and substantially contactless, flexible, electrically biased conductive shims 26. A high velocity, preferably 0.0045m 3 /s (9.5 cubic feet per minute), air flow 12 between the BTR 20 and two thin conductive flex-shims 26 is created and controlled by means of a blower 53 that evacuates the air in the cleaner housing vacuum chamber 22. The high velocity air 12, in combination with the electrically biased flex- shims 26, removes the residue from the BTR surface 21 and carries it into and through the vacuum chamber 22 and deposits the residue in a filter bag 51 (see Figure 6). The BTR biased shim cleaner 10 system as described herein, is low cost, smaller and will have longer component life with significantly less BTR surface abrasion than prior devices. In Figure 3, portions of an electrophotographic apparatus are shown, including the image forming surface of a moving photoreceptor 16 which is in contact with an electrically biased BTR 20. Also shown is a belt drive roll 18, stripper roll 14, and paper guide 24. Figure 4 shows the structural relationship between the BTR surface 21, the flexible conductive shims 26 and the vacuum chamber 22 of the cleaner housing 43. As air flows between the flexible conductive shims 26 and the BTR surface 21, the shims 26 will tend to flutter, to at least some extent, dependent upon air flow 12. Therefore, the shims 26 will disturb the toner and paper fiber residue, yet remain substantially contactless with respect to the BTR surface 21, to further enhance cleaning. In Figure 5, an enlarged view of a portion of the circled area in Figure 3 is shown in order to more clearly show the conductive flex-shims 26 during flutter. Figure 6 shows the BTR biased shim cleaner 10 system arrangement (BTR and BTR power supply not shown), wherein the BTR biased shim cleaner 10 is connected to a shim power supply 49 and the cleaner housing 43 is connected to a blower 53 by means of an air hose 47, the evacuated air and toner passing through a toner filter 51, where scavenged toner is collected. Figures 7 and 8 depict the BTR 20 and shim 26 power supplies and bias relationships. In particular, Figure 7 shows the BTR and biased shim circuit 54, wherein BTR current 55 and shim current 57 are indicated. In Figure 8, the relationship between BTR and shim current 55, 57 is shown, wherein transfer current 71 equals BTR current 55 plus shim current 57. In the circuit diagram 54, transfer current 71 is a function of BTR current 55 and shim current 57 which provides BTR voltage 67 and shim voltage 63 respectively. Further, the difference in voltage 69 (i.e. V shims) is a function of the resistance 65 (between shims 26 and BTR core 20), while BTR resistance is indicated at 73. As discussed above, an electrical bias is applied between the shims 26 and the BTR 20 which helps to detach the residue from the BTR surface 21. This is a substantially contactless cleaner because the shims only intermittently touch the BTR surface 21 due to flutter caused by the air flow between the flexible conductive shims 26 and the surface of the BTR 21. Results have shown that for a transfer current of -50µA, a DC bias voltage range from -2.1 kV to -3.3kV (preferred value -2.5kV for a BTR current of -15µA) above the BTR bias on the shims 26 produces good cleaning for all environments even under stressed conditions. Additionally, for a transfer current of -75µA, a DC bias voltage range from -2.6kV to -3.4kV (preferred value -3kV for a BTR current of -30µA) above the BTR bias on the shims 26 also produces good cleaning for all environments under stressed conditions. However, various other DC voltage combinations are possible. Additionally, AC bias voltages may also be possible, for example, bias voltages of -3kV and -5kV may be applied to the BTR and shims respectively, with a DC rider signal of ± 500 volts riding on the -5kV shim voltage. In another embodiment (see Figures 9 and 10), the use of conductive disturber fabric 26a is shown. This embodiment is useful with electrophotographic apparatuses having particularly stubborn or large toner cleaning requirements. The apparatus shown in Figures 9 and 10 would operate in the same basic manner as described with respect to the first embodiment. However, the conductive disturber fabric 26a would lightly contact the BTR surface 21 to disturb the toner and assist the electrostatic and air flow means of removing the residual toner. Abrasion of the BTR surface 21 and wear of the fabric material 26a is less of a concern in this embodiment since contact is very light, again due to the air flow 12. However, BTR and fabric materials not sensitive to wear may be selected if high volume uses are envisioned. The performance of the BTR air cleaners with biased shims, described above, has been predicted through testing over a range of BTR and cleaner shim biases. As known in the art, cleaning performance necessarily depends on the charge of toner entering the transfer nip, the mass density of toner input and the efficiencies of pressure transfer and cleaning of toner by air flow alone. The biased shim BTR cleaners described herein have been shown to work over a reasonable range of currents and biases. However, additional operating latitude could be gained by increasing the cleaner air flow above the 0.0045m 3 /s (9.5 cubic feet per minute) previously mentioned. The BTR air cleaners with biased shims, described above, can be significantly smaller (e.g., 60% smaller) than the cleaner in Figure 2, inexpensive to manufacture with substantially increased component life (e.g., roughly three times greater than the cleaner in Figure 2) and offer low BTR surface abrasion, and are cost effective to operate. Power savings alone could reduce costs by one third (again, relative to the cleaner in Figure 2).

Claims: A cleaning apparatus, for an electrophotographic apparatus, for removing residual toner particles and paper fibers from the surface of a rotating biased transfer roll of said electrophotographic apparatus, said cleaning apparatus comprising: a cleaner housing (43)mounted adjacent to said biased transfer roll (20), said housing further comprising a vacuum chamber (22) fixedly arranged adjacent said biased transfer roll with two flexible conductive blade members (26) fixedly mounted on opposite sides of an air inlet of said vacuum chamber, said blade members stretched along said air inlet without touching each other, and said air inlet facing said biased transfer roll; a means (53) for creating and controlling air flow across and through said air inlet; characterised in that said apparatus further comprises a means for applying an electrical bias voltage to and between said blade members and said biased transfer roll; and a conductive disturber fabric (26a) fixedly attached to each of said blade members (26). An apparatus as claimed in claim 1, wherein said air flow creating and controlling means comprises a blower connected to said vacuum chamber. An apparatus as claimed in claim 2, further comprising a toner filter (51) disposed between said vacuum chamber and said blower in communication therewith, such that removed toner particles are deposited in said toner filter. An apparatus as claimed in claim 1, wherein said residual toner and paper fibers are removed from said biased transfer roll by combined action of said electrical bias between said blade members and said biased transfer roll, said air flow between said blade members and said biased transfer roll causing said blade members to flutter and acting to carry said removed toner and paper fibers through said air inlet into said vacuum chamber to a toner filter (51) where said removed toner and paper fibers are deposited. An apparatus as claimed in any one of the preceding claims, wherein, for a particular transfer current (71), a first DC current (55) is applied to said biased transfer roll and a second DC current (57) is applied to said blade members creating an electric field between said biased transfer roll and said blade members. An apparatus as claimed in claim 5, wherein said transfer current is -50µA, said first DC current is -15µA and said second DC current is -35µA, thereby rendering said electrical bias voltage to be -2.5kV DC. An apparatus as claimed in claim 5, wherein said transfer current is -75µA, said first DC current is -30µA and said second DC current is -45µA, thereby rendering said electrical bias voltage to be -3kV DC. An apparatus as claimed in any one of the preceding claims, wherein an air flow rate between 0.0026m 3 /s (5.5 cubic feet per minute) and 0.0064m 3 /s (13.5 cubic feet per minute) is created between said blade members and said biased transfer roll. An apparatus as claimed in claim 8, wherein an air flow rate of 0.0045m 3 /s (9.5 cubic feet per minute) is created between said blade members and said biased transfer roll. An apparatus as claimed in any one of the preceding claims, wherein said blade members are made from a conductive synthetic resin material.

Inventors: FIORAVANTI ALEXANDER J, LINDBLAD NERO R, MANCINE GREGORY J, THAYER BRUCE E, FIORAVANTI, ALEXANDER J., LINDBLAD, NERO R., MANCINE, GREGORY J., THAYER, BRUCE E.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1993
Main classification: G03G15
IPC codes: G03G21, G03G15