Patent Application
20100326352
This invention relates to an electrophotographic system and more specifically to a Xerographic drum used in said system.
While the present invention of a coating apparatus can be effectively used in a plurality of different tube coating uses, it will be described for clarity as used in a tube or photoconductive drum used in a Xerographic system.
By way of background, in marking systems such as xerography or other electrostatographic processes, a uniform electrostatic charge is placed upon a photoreceptor belt or drum surface. The charged surface is then exposed to a light image of an original to selectively dissipate the charge to form a latent electrostatic image of the original. The latent image is developed by depositing finely divided and charged particles of toner upon the drum photoreceptor surface. The toner may be in dry powder form or suspended in a liquid carrier. The charged toner, being electrostatically attached to the latent electrostatic image areas, creates a visible replica of the original. The developed image is then usually transferred from the photoreceptor surface to an intermediate transfer belt or to a final support material, such as paper.
In some of these electrostatic marking systems, a photoreceptor belt or drum surface and an intermediate transfer belt (ITB) are generally arranged to move in an endless path through the various processing stations of the xerographic marking process. In this endless path, several xerographic-related stations are used having a plurality of photoconductive drums which become abraded and worn partly because of contact with their components in the system, such as belt configurations, such as transfer belts, pre-fuser belts, cleaning blades or belts and the like. Each of these drums is constantly exposed to friction, especially in high speed systems, the drum needs to be frequently replaced. Also, since the photoreceptor drum is reusable once the toner image is transferred, the surfaces of these belts are constantly abraded and cleaned by a blade and/or brushes and prepared to be used once again in the marking process. In U.S. Patent publication U.S. 2008/0199216 (incorporated by reference herein) a problem in drum xerographic usage is noted, i.e. “When electrostatographic drums are cleaned by doctor type cleaning blades rubbing against the imaging surface to remove residual toner particles remaining on the imaging surface after toner image transfer to a receiving member, a high pitched ringing, squealing, squeaking, or howling sound can be created which is so intense that it is sometimes intolerable for machine operators. This is especially noted in drum type imaging members comprising a hollow cylindrical substrate.
Under normal operation in a printer/copier, a drum photoreceptor can emit a noticeable and objectionable sound. The cause of this noise can be due either to the cleaning or charging mechanisms. If a BCR (bias charging roll) is utilized to charge the photoreceptor, the AC voltage applied between the BCR and a photoreceptor can produce a “forced” mechanical vibration at the AC frequency. Alternatively, slip-stick motion of the cleaning blade against the photoreceptor surface can drive a mechanical resonance at the slip-stick frequency. There are several known methods to combat this problem, each with its own disadvantages.
The application of such a compound to the interior of the P/R tube does pose some challenges both in how to apply the coating and where/when in the manufacturing process is the coating applied. Initial thoughts were to use a process similar to flow coating, but on the interior of the P/R tube wherein the P/R tube would be rotated and a continuous touching spiral of material would be applied. However, after consideration of that concept it was believed that process would take too long and would not be compatible with the current 9 second cycle time for each station on the existing P/R production facility. This invention addresses the important concern—How to apply an acoustic dampening compound to the interior of a photoreceptor tube in a time period commensurate with a total cycle time of under 9 seconds.
Internal “Silencers” have been utilized in photoreceptor P/R tubes or drums to quench noise for quite a while; there are numerous patents related to the concept. Recently, the manually internally applied acoustic dampening coating was disclosed; see Xerox earlier noted Patent Publication 2008/0199216A1—“Method for Acoustic Dampening of Photoreceptor Drums” by Steven C. Hart & Patricia Campbell (now a pending U.S. patent application). Initial examples were created in this publication using a caulk gun and spatula to apply the coating to the tubular interior of large (84 mm) diameter photoreceptors. Hand application via a spatula is not feasible as a large scale manufacturing technique; additionally, it is difficult, if not impossible, to do inside a smaller 30 mm diameter photoreceptor. Subsequently, a crude apparatus was fabricated and used to hand coat the interior of 30 mm diameter photoreceptors. Machine testing of these samples indicated that the (un-optimized) internally applied acoustic dampening coating performed equal to or slightly better than the old style non-coated “silencers.” Additionally, it is desirable to provide an assembly to accomplish the coating operation within a total cycle time of under 9 seconds so as not to slow down the P/R production line.
This invention provides a coating dispensing assembly that can uniformly coat the interior of a photoreceptor (PR) drum or tube with a high viscosity acoustic dampening compound such as silicone rubber (RTV, HTV, or UV cure), or latex caulk, or other suitable compound in a single axial stroke. The dispense head, mounted on a rigid central pipe, is tightly movably inserted into a photoreceptor tube or drum. By “tightly” is meant where the dispenser abuts the inner tube surface without any substantial space therebetween. As the dispense head is being removed (at a controlled, but not necessarily constant velocity), the coating compound is pumped down the central pipe, through the dispense head, and applied as a uniform layer on the order of about 1 mm thick to the interior surface of the photoreceptor tube (the thickness depends upon the size of the PR tube). The internal geometry of the dispense head is designed such that the highest internal impendence occurs just as the compound exit point from the head; this ensures that the coating will be circumferentially uniform around the interior of the photoreceptor tube. Fluid flow modeling of this design suggests that coating cycle times on the order of 5 seconds can be achieved for a 1 mm thick by 370 mm long coating on the inside of a 30 mm diameter photoreceptor tube.
The invention includes a PR and dispenser assembly that comprises this dispenser positioned in the PR tube or drum with a material inlet at its rear portion and a material outlet at its front portion. The dispenser is configured to be removed from the PR once the coating process is completed.
An idealized cross section of the dispense head inside of a photoreceptor tube of the PR and dispenser assembly is illustrated in
In
In order to apply a (uniform) layer of material 8 to the interior of the photoreceptor tube 2, the dispense head 1 is inserted into the PR tube 2 such that the dispensing point is in one embodiment on the order of 20 mm from the end of the PR tube. Of course, this distance will vary depending upon the size of the tube 2. Next, a “spool” valve 5 is activated (opened). This allows the acoustic dampening compound 3 to be pumped down the central support pipe, through the dispense head 1 and to be extruded onto the interior of the tube 2. Simultaneously, the assembly 1 is withdrawn from the PR tube 2 at a controlled velocity, until the dispense point is on the order of 20 mm from the other end of the PR tube 2. At this time/point, the “spool” valve 5 is deactivated (closed) as the dispense head 1 continues to be extracted from the inside of the tube. “Spool” valves 5 have by design a “suck back” of the material being applied; this results in a “clean” break of the material flow and a well-defined edge to the applied material 3.
Assume that the pressure used to pump the compound into the dispense head 1 is constant, i.e. the flow rate is constant. Then the coating 8 thickness should be approximately inversely linear with the extraction velocity. Thus, if a uniform coating 8 thickness is desired, the extraction velocity will be constant. On the other hand, if one desires a coating thickness that is thicker in the center of the tube than at the ends, then the extraction velocity will be lower in the central region of the tube than the ends.
It is highly desirable to ensure that the layer of material coating 8 is circumferentially uniform. By “circumferentially uniform” is meant a uniformity around a point on the circumference of the inner surface of the PR. Failure to do so could lead to a rotational imbalance that could in turn cause motion quality defects in any image. Furthermore, a circumferentially uniform layer 8 should provide the most efficient acoustic dampening for any given quantity of dampening material 3.
In order to achieve a circumferentially uniform layer 8, it is important that the compound 3 is extruded out of the dispense head 1 in a uniform fashion all the way a round the head 1. To achieve this, the highest flow impedance should occur just at the exit gap 9 where the material 3 leaves the dispense head 1. This is accomplished by appropriate design of the material flow channel. The cross sectional area of the channel perpendicular to the flow stream should smoothly and continuously decrease as the material 3 moves out from the central support pipe 10 to the dispensing point 9 having the smallest area at the dispense point 9.
Several different flow channel geometries can be used, if suitable. If one were to attempt to utilize a design similar to that shown in
In
In summary, embodiments of the present invention provide: a photoconductor (PR) and dispenser assembly comprising: a PR having a tubular form with an outer photoconductor's surface and a hollow inner portion. The dispenser is configured to tightly slide into the PR inner tubular surface. The dispenser has a rear end portion being a material inlet and having at a front end portion an acoustical dampening material outlet. This material outlet is configured to apply a substantially circumferentially uniform coating of this sound or acoustic dampening material to the PR inner surface. The dispenser is configured to be totally removable from the hollow inner portion of the PR after the coating of a sound dampening material is completed.
The rear end portion of the dispenser is in flow connection to a source of the acoustic dampening material. The front end portion of the dispenser comprises an outlet gap, this outlet gap is in flow relationship to a material conduit that extends through the dispenser from the rear end portion to the front end portion.
Specifically, an embodiment of the dispenser comprises a tubular-shaped housing having a central core in an interior portion and a material flow path extending around said core. The flow path extends through substantially an entire length of the housing.
One end of the housing comprises a coating material inlet opening, and an opposite end of the housing comprises a coating material dispensing section with a material dispensing gap.
The material inlet opening is configured to receive the acoustic dampening coating material, this material dispensing section is configured to apply an acoustic dampening material as a uniform coating in an inside portion of the drum. A source of said acoustic dampening material is in flow connection with the coating material inlet opening. This source has a connecting valve which is configured to turn a material flow on and turn off to said inlet opening.
The housing has a central core, an exterior portion surrounding the central core, between the exterior portion and said central core is a material flow path that is configured to transport the material from the inlet opening to a material exit gap. The housing has a material exit gap in the material dispensing section, this gap is configured to be adjustable to provide for coatings of various thicknesses.
In one preferred embodiment the adjuster is an adjustable or removable washer, both configured to adjust the gap. The dispenser also has at least one dowel pin to support the central core of the dispenser.
In one other preferred embodiment the dispenser is configured to accept a different size spacer washer, the washer is configured to adjust a width of the exit gap and the spacer is also configured to not obstruct the material flow through said housing.
The invention also comprises dispenser system useful in coating an interior of a xerographic drum or tube, said dispenser comprising a tubular-shaped housing having a central core in an interior portion and a material flow path extending around said core. The flow path extends through substantially an entire length of the housing.
One end of the housing comprising a coating material inlet opening and an opposite end of the housing comprising a coating material dispensing section with a material dispensing gap. The inlet opening is in flow connection with a source of an acoustical dampening material.
It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
