Patent Application
20050214020
The present invention relates generally to electrophotographic printing and/or copying machines. More particularly, the present invention relates to a method and apparatus for cleaning the transfer roller in such machines.
In modern high-speed/high-quality electrophotographic machines, such as copiers and printers, a latent image charge pattern is formed on a dielectric member, such as an endless-loop belt. Pigmented toner particles are drawn by electrostatic attraction onto the latent image charge pattern to develop the image carried on the dielectric member. A receiver sheet or image substrate, such as, for example, a piece of paper, is then brought into contact with the image on the support member. An electric field is applied to transfer the image from the support member to the image substrate. Thereafter, the image substrate carrying the transferred image is separated from the dielectric support member and the image is fixed to the substrate, such as, for example, by fusing.
One way in which the electric field is applied to effect transfer of the image from the support member to the image substrate is the use of a roller-type transfer station or sub-system wherein a transfer roller is in engagement with the dielectric member. The transfer roller is electrostatically biased and causes the transfer of the charged toner particles from the surface of the dielectric member to the image substrate as the image substrate passes between the transfer roller and the dielectric member. During operation, however, residual toner and other particulate material, such as paper dust, is sometimes picked up by and/or attracted to the biased transfer roller. These particles can be transferred onto the back surface of the next image substrate and create undesirable marks thereon. Therefore, the transfer roller is continuously and automatically cleaned by a cleaning mechanism.
The cleaning mechanism is typically an elongate cylindrical fiber cleaning brush, and is electrically non-conductive. The cleaning brush and transfer roller are generally in relatively close proximity with parallel central axes. The fiber cleaning brush engages the surface of the transfer roller with a force that is calculated to achieve relatively efficient cleaning of the transfer roller surface. A motor drives the cleaning brush to rotate in the area of contact between the cleaning brush and the transfer roller in a direction opposite to the direction in which the transfer roller is rotated, and thereby increases the effectiveness with which the cleaning brush removes particles from the surface of the transfer roller.
Despite the above-described measures to improve the effectiveness with which the cleaning brush removes or cleans the transfer roller, a typical cleaning brush is relatively inefficient and requires multiple passes in order to clean even a moderately contaminated roller. A conventional cleaning brush may typically have a maximum cleaning efficiency of less than approximately ten percent.
Therefore, what is needed in the art is a transfer roller cleaning brush having an improved cleaning efficiency.
The present invention provides a method and apparatus for cleaning a transfer roller in an electrophotographic machine.
The invention comprises, in one form thereof, an electrophotographic machine having a dielectric member carrying a toner image. A biased transfer roller engages the dielectric member and transfers the toner image to an image substrate. A cleaning brush having a plurality of bristles, at least some of which are electrically conductive, engages the transfer roller. An electrically conductive housing encloses the cleaning brush. The bristles contact the transfer roller through an opening in the housing. At least one of the cleaning brush and the housing is biased to substantially the same electrical potential as the transfer roller.
An advantage of the present invention is that the efficiency with which the transfer roller is cleaned is improved.
Another advantage of the present invention is that a conductive cleaning brush is used to clean the transfer roller without substantially reducing image transfer current thereby maintaining efficient image transfer and image quality.
The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become apparent and be better understood by reference to the following description of one embodiment of the invention in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring now to
Generally; in use, machine 10 moves dielectric support 12 past and/or through charging station 14 wherein a uniform charge is applied thereto. Dielectric support 12 is thereafter moved past and/or through exposure station 16 wherein the uniform charge is altered to form a latent image charge pattern (not shown) corresponding to the information desired to be printed and/or reproduced. The latent image charge pattern is carried by dielectric member 12 into development station 18, wherein pigmented marking particles (i.e., toner) are brought into close association with and electrostatically drawn to the latent image charge pattern thereby creating a developed image on dielectric member 12. Transfer station 20 generates an electric charge to transfer the toner of the developed image carried on dielectric member 12 to an image substrate, such as, for example, a piece of paper, fed from hopper 22 into and through transfer station 20 along path P. Detach mechanism 24 facilitates removal of the image substrate from dielectric member 12. Fusing station 26 fixes the toner particles to the image substrate by, for example, heat and/or pressure, and delivers the image substrate to output hopper 28. The dielectric support 12 is then cleaned by cleaning station 30.
Referring now to
Transfer roller 42 engages dielectric member 12. An electrical bias is applied to the conductive core (not referenced) of transfer roller 42 by a power supply (not shown), such as, for example, a voltage-limited constant current source power supply. The electrical bias establishes the above-described electrical transfer field that will efficiently transfer a developed image from the dielectric member to a receiver member passing between dielectric member 12 and the semi-conductive surface (not referenced) of transfer roller 42. When the outer surface of transfer roller 42 contacts dielectric member 12 with no image substrate in between, transfer roller 42 tends to pick up and/or attract residual toner and/or paper dust/particles from dielectric member 12. Transfer roller 42 may be more severely contaminated when a misfeed of an image substrate occurs. In such an instance, virtually the entire developed toner image will be transferred from the dielectric member 12 to the outer surface of transfer roller 42. The residual toner and other contaminant particles can be transferred from transfer roller 42 onto the back side/surface of the next image substrate to be processed through roller transfer station 20 and thereby form undesirable marks thereon. Therefore, transfer roller 42 is cleaned by cleaning mechanism 44 which removes the residual toner and/or paper dust particles and thereby prevents the deposition thereof onto the back sides of the image substrates.
Cleaning mechanism 44 includes an elongated, cylindrical, fiber brush 52 having fiber bristles 54. Brush 52 is disposed within and supported by housing 40 such that the longitudinal axis (not referenced) of brush 52 is parallel to and spaced a predetermined distance apart from the longitudinal axis (not referenced) of transfer roller 42. Bristles 54 engage transfer roller 42 with a predetermined amount engagement that, dependent at least in part upon the density of brush 52 and its speed of rotation, is intended to maximize the efficiency with which brush 52 cleans transfer roller 42. Motor 56 is coupled to housing 40 and rotates brush 52 in a direction such that brush 52 and transfer roller 42 are rotating in opposite directions in the area of contact. Vacuum 62 is associated with brush 52 to remove cleaned particles from the fibers/bristles thereof, the particles being deposited in a downstream collection container (not shown).
Cleaning mechanism 44 also includes brush housing 64. Brush housing 64 is in communication with a vacuum-generating blower (not referenced), and forms an air-flow-directing chamber in close proximity to a portion of the periphery of brush 52. Brush housing 64 defines an opening 66 to brush 52 through which bristles 54 thereof engage transfer roller 42. Brush housing 64 is typically formed of a conductive plastic in order to prevent the build up of static electrical charge from the rotating brush therein and the air flow therethrough.
The foregoing is a general description of one embodiment of a conventional electrophotographic machine having one embodiment of a roller transfer station or sub-system. A more detailed description thereof is provided in U.S. Pat. Nos. 5,101,238 and 6,381,427, the disclosures of which are incorporated herein by reference.
Referring now to
Transfer roller 142, much like transfer roller 42 described above, has an electrically-conductive inner core (not referenced) and a semi-conductive outer surface (not referenced), typically polyurethane, that engages dielectric member 12. The outer surface of transfer roller 142 may be coated, as described in U.S. Pat. No. 6,074,756, or uncoated. An electrical bias is applied to the conductive core of transfer roller 142 by transfer roller power supply 143, such as, for example, a voltage-limited constant current source. The electrical bias establishes the above-described electrical transfer field that transfers the developed image from dielectric member 12 to a receiver member passing between dielectric member 12 and transfer roller 142. When the outer surface of transfer roller 142 contacts dielectric member 12 with no image substrate there between, transfer roller 142 tends to pick up and/or attract residual toner and/or paper dust/particles from dielectric member 12 in much the same manner as described above in regard to transfer roller 42. These particles are removed from transfer roller 142 by cleaning mechanism 144.
Cleaning mechanism 144 includes an elongated, cylindrical, transfer roller cleaning brush 152 having, as best shown in
Cleaning mechanism 144 also includes brush housing 164. Brush housing 164, much like brush housing 64, is in communication with a vacuum-generating blower (not referenced), and forms an air-flow-directing chamber in close proximity to a portion of the periphery of brush 152. Brush housing 164 defines an opening 166 to brush 152 through which bristles 154 contact transfer roller 142. Brush housing 164 is electrically conductive and has a resistivity of, for example, from approximately 103 to approximately 105 ohms-cm. Generally, and as will be more particularly described hereinafter, brush housing 164 is electrically charged to the same potential as transfer roller 142.
Fibers or bristles 154 engage transfer roller 142 through an opening 166 in brush housing 164 and engage transfer roller 142 with a predetermined amount engagement that is dependent at least in part upon the density of brush 152 and its speed of rotation, and is intended to substantially maximize the efficiency with which brush 152 mechanically cleans transfer roller 142. Motor 56 is coupled to housing 140 and rotates brush 152 in a direction such that brush 152 and transfer roller 142 are rotating in opposite directions in the area of contact. A vacuum (not shown) is also associated with brush 152 and brush housing 164 to remove cleaned particles from the fibers/bristles 154, the particles being deposited in a downstream collection container (not shown).
As best shown in
U.S. Pat. No. 6,549,747, the disclosure of which is also incorporated herein by reference, discloses a conductive cleaning brush that is associated with a biased intermediate transfer member (ITM). As described therein, the conductive brush is biased to a voltage of the same polarity as but a greater magnitude than the voltage to which the intermediate transfer member is biased, and to a polarity opposite the polarity of the toner/marking particles, in order to electrostatically draw toner and other particles from the ITM to the cleaning brush. The brush housing that encloses the conductive cleaning brush is permitted to electrically float or accumulate the charge carried by the toner/marking particles (i.e., the same magnitude and polarity), and thereby repels additional toner/marking particles.
In contrast, and as is more particularly described hereinafter, the conductive transfer roller cleaning brush of the present invention is associated with a biased transfer roller (rather than an intermediate transfer roller). Use of a conductive cleaning brush with a biased transfer roller has heretofore been problematic because contacting the transfer roller with a conductive brush creates a path through which current intended to accomplish image transfer is instead bled off from the biased transfer roller to ground thereby undesirably reducing the current available to accomplish image transfer and adversely impacting image quality. Although the amount of current sourced to transfer roller 142 can be increased to compensate for the bleed off of transfer current, doing so is an imperfect solution since the electrical load presented by transfer roller 142 and the transfer current required for quality image transfer both vary widely due to various operating conditions and parameters, such as, for example, temperature, humidity, thickness of the image substrate or paper being used, etc.
Generally, the present invention charges the conductive transfer roller cleaning brush and/or the conductive brush housing that encloses the conductive transfer roller cleaning brush to the same electrical polarity and substantially the same magnitude to which the transfer roller is charged (and to the opposite polarity as the marking particles/toner). By charging the conductive transfer roller cleaning brush and/or brush housing to substantially the same magnitude and polarity as the transfer roller the present invention substantially reduces and/or eliminates the image-degrading flow of transfer current away from the transfer roller.
Referring again to
In either of the embodiments described above and shown in
More particularly, a certain amount of transfer current ITRANS is required to achieve a high-quality and efficient transfer of the developed image from dielectric member 12 to the image substrate. Transfer current ITRANS is, for example, typically from approximately 40 to approximately 60 microamperes. However, engaging and/or cleaning biased transfer roller 142 with conductive transfer roller cleaning brush 152 will cause transfer current ITRANS to be reduced by a cleaning current ICLEAN that flows from transfer roller 142 through conductive transfer roller cleaning brush 152. Cleaning current ICLEAN can be as high as, for example, 30-40 microamperes. Transfer current ITRANS is thus reduced by the cleaning current ICLEAN, and poor-quality image transfer may therefore result. Biasing brush housing 164 to substantially the same magnitude and polarity as transfer roller 142 substantially reduces the magnitude of cleaning current ICLEAN and thereby acts to maintain transfer current ITRANS at an acceptable level.
Referring now to
The resistance value of discharge resistor 184, such as, for example, from approximately one to three gigaohms, is chosen to enable the conductive brush housing 164 to electrically discharge in an acceptable period of time and at an acceptable/safe level of current in emergency shut down situations. In the embodiment of
Referring now to
It should be particularly noted, however, that power supply 193 must be slaved to or closely follow the power output of transfer roller power supply 143 in order to ensure that conductive transfer roller cleaning brush 152 and transfer roller 142 are maintained at the same potential.
It should further be particularly noted that in the configuration wherein each of conductive brush housing 164 and transfer roller cleaning brush 152 are electrically floating and/or isolated they may each be biased to the same potential as transfer roller 142 by the same power supply or separate power supplies, and/or by transfer roller power supply 143.
In all the above-described embodiments of transfer station 120, biased transfer roller 142, conductive transfer roller cleaning brush 152 and conductive brush housing 164 are charged to substantially the same polarity and magnitude thereby preventing the image-degrading affects of the flow of transfer current from transfer roller 142 to conductive transfer roller cleaning brush 152 and/or conductive brush housing 164.
Alternatively, i.e., rather than charging brush housing 164 to substantially the same magnitude and polarity as transfer roller 142, conductive transfer roller cleaning brush 152 is connected to ground or left electrically floating with a path to ground through conductive housing 164, and the transfer current ITRANS provided by transfer roller power supply 143 is increased by an amount approximately equal to the expected cleaning current ICLEAN in order to maintain transfer current ITRANS at a sufficient level and thereby ensure quality image transfer. However, as discussed above, such an approach is less preferred due to the variation in the magnitude of transfer current ITRANS necessary to achieve high-quality image transfer under various operating conditions.
While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the present invention using the general principles disclosed herein. Further, this application is intended to cover such departures from the present disclosure as come within the known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.
This application claims the benefit of U.S. Provisional Patent Application No. 60/XXX,XXX, filed Mar. XX, 2004.
| Number | Date | Country | |
|---|---|---|---|
| 60556144 | Mar 2004 | US |
