GB1558413A

GB1558413A - Rotary drum support apparatus

Info

Publication number: GB1558413A
Application number: GB54177A
Authority: GB
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1976-01-08
Filing date: 1977-01-07
Publication date: 1980-01-03

Description

(54) ROTARY DRUM SUPPORT APPARATUS (71) We, XEROX CORPORATION, a corporation organised under the laws of the State of New York, United States of America, of Rochester, New York 14644, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to rotary drum support apparatus and more particularly to supports for photosensitive drums that prevent drum run-out.

In present reproduction machines, a problem has been encountered with photoreceptor drum radial run-out of up to .050 inches or more. The reason for such a deviation in tolerance lies with the drums and how they are handled in manufacturing and in the field. Hitting the rim of the drum deforms the counterbore, and an outof-tolerance condition occurs when endbells that interference fit with the drum are reassembled in the drum. This is especially true of the inner endbell in a number of reproduction machines which is concave by about 5 inches. A slight cock in its assembly throws its shaft support bearing off center considerably due to magnification of the error by the length of the concavity.Since in a number of reproduction machines a shaft that is journaled to the machine frame is cantilevered from the frame to support a photoconductive drum without an an exterior support, more run-out is observed on the inboard side of the photoconductive drum than on the outboard side.

A solution to the above-mentioned problem of drum run-out is required before improved reproduction machines can be marketed incorporating magnetic brush rollers in their development process instead of cascade development because reducing the radial drum run-out minimizes the effects of the drum tolerances on the spacing between the drum and the magnetic brush rollers.

According to the present invention we provide apparatus including a rotary drum and a frame within which the drum is mounted, a shaft mounted on said frame at least one end support mounted on said shaft, said end support having an outer surface thereon including a series of lobes spaced from each other around said surface, said at least one end plate being seated in and supporting the drum with said spaced lobes on the end support seated in contact with the inner surface of said drum.

A preferred embodiment of the invention includes a rotary drum support apparatus in which outboard and inboard end supports in the form of endbells are connected by tie rods and adapted to be placed on a cantilevered shaft for supporting a drum, and a series of spaced equidistant lobes are formed around the outer surfaces of the outboard and inboard endbells which are to be fitted against the inner surface of the drum, thereby reducing the contact area when the interface fit between the hub and drum occurs. A two-armed removable support is disclosed for giving rigid support to the cantilevered shaft.

Preferred embodiment of the present invention will now be described with reference to the accompanying drawings in which: Fig. 1 is an exploded partial schematic of an apparatus incorporating the present invention Fig. 2 is an enlarged partial cross-section of a second embodiment of this invention.

The present invention can be used in any device that requires support for a rotary drum. However, for the purpose of exemplary disclosure, the invention will be described within the environment of a xerographic reproduction apparatus. An example of such a xerographic reproduction apparatus is shown in U.S. Patent 3,775,008 in the name of R. A. Schaeffer and is incorporated herein by reference. Examples of prior drum support members include U. & Patent 2,089,401; 3,536,485; 3,615,603, and 3,839,722. It is generally recognized that photoreceptor drum run-out is a significant contributor to field maintenance problems, and that it degrades copy quality.

The photoreceptor drum is the heart of a xerographic copier. As each copy is reproduced, a bar of light scans the original document, and then transmits its reflective image through lenses to a revolving selenium coated drum which has been electro-statically charged. Because of the conductivity of the drum, the light discharges the electrical charges, leaving a latent image identical to that on the document. The drum then rotates through a chamber of powdered ink which coats the charged areas. A sheet of paper is then precisely applied over the image. The image is then transferred electrically to the paper.

After transfer the paper is stripped from the drum and passed through a fuser which fixes the image to the paper. To accomplish this, the drum must be (A) discharged, (B) cleaned, (C) charged, (D) exposed, (Ej developed, (F) covered with paper and (G) stripped of the paper and image for each copy made. To achieve and maintain reliably good copy quality, the radial dimensions and electrical tolerances in the cavity between the drum and the station A through G must be rigidly maintained. Any out of roundness or imperfections in the drum surface may result in copy quality variations or possible drum damage, due to interference.

One of the most prevalent methods of bringing the powdered ink or developer material into contact with an image bearing photoconductor is to pour or cascade developer material over the photoconductor, permitting the material to gravity flow downwardly in contact with the photoconductor for a sufficient period of time to affect development With this method of development it is satisfactory to support the photoconductive drum on a cantilevered support.However, in order for xerographic machines to use magnetic brush develop ment where the developer material is trans ported through a development zone adjacent the imaged photoconductor by the magnetic brushes, radial drum run-out or "walking" of the drum must be controlled because spacing between the drum and magnetic brush rollers must be maintained within allowable tolerances or degrading copy quality will result It is to curtail the "walking" of the drum along the cantilevered shaft that the two-armed end support is disclosed.

In reference to Figure 1, the present invention is shown incorporated into a reproduction machine similar to the Xerox 4000.

As is shown in the Figure, a frame with a front panel 12 and a rear panel 11 for a reproduction machine is shown supporting a shaft 13 that has a cantilever mounting to the rear panel of the frame. Concaved endbells 30 and 40 are shown supported on the shaft, with the rear or inboard endbells 40 having a pronounced cavity therein that fits over bearing 60. Means are located on the surface of the outboard and inboard endbells immediately adjacent the inner surface of the drum for reducing the contact area where interface fit between the hub and the drum 10 occurs to diminish photoreceptor drum run-out. A drum in the form of a photosensitive member 20 is shown as being placeable over the inboard endbell or hub 40 and the front or outboard endbell 30 is shown as being adaptable to close the open end of the drum.Ties rods 16 extend through the openings in the inboard hub or endbells 40 through the interior of the drum and through the complementary openings in the outboard hub 30 and have threads thereon that allow nuts 18 and washers 70 to tighten the inboard and outboard endbells to the drum. A twoarmed support 50 is also shown adjacent to the outboard hub and is used to stabilize the cantilevered shaft 13 once the drum is placed thereon. End cap 19 ensures that rotation of the support shaft is transmitted to the drum through connection stub 17.

It is within the area of the endbells and the end support that the present invention resides. There is shown in the Figure a series of discretely spaced equidistant lobes 35 upon the mounting surface of the inboard hub as well as the outboard hub.

The plurality of lobes as they are incorporated into the endbells of the present invention reduce the loading torque, applied through tie rods 16, necessary to properly seat the hub against the drum. This loading torque is reduced a preferred torgue range of 35 to 55 inch-pounds, although a range of 25 to 75 inch-pounds would be satisfactory, and thereby reduces run-out and improves drum assembly and disassembly by diminishing the tapered contact surfaces between the drum and the endbells to nine equidistant half-inch wide lobes. While nine lobes are disclosed as preferable for the practice of this invention it should be understood that a range of 6 to 9 lobes will perform satisfactorily. One of the other objects of reducing the contact surfaces is to reduce assembly interference.

Hitting the rim of the drum during assembly, deforms the counterbore and therefore causes an out of tolerance condition to occur. This in turn increases the probability of run-out due to endbells cocking or bend ing as assembly. Even though the lobes could be made flat as a mating service for the interior end surfaces of the drum, it is preferred that a gradual incline or slope toward the center of the drum be included at the lead edge of each lobe to improve seating or mating of the drum and hubs and possibly reduce deburring time. If one desireds to add a heater to the drum the front hub can be redesigned to accommodate a slip ring for such purposes.

A further means of reducing drum run-out is the two-armed support 50 that is releasably mounted on capless pins 14 that are tapered for each of attachment and detachment of the support to the exterior of front frame panel 12. Maintaining the support in this manner also reduces the time necessary for removal and replacement of drums.

This support is in the form of a removable support bracket with two substantially spaced arms at approximately 90" and a central self-aligning ball bearing 51, more fully described with reference to Fig. 2, for the outboard end of the drum shaft.

The arms extend a greater distance from the drum support than the radius of the drum and provides a rigid support having two fixing points for the normally unsupported end of the drum shaft. The arms are arcuate in shape to allow connection stub 17 on the shaft 13 to be recessed in relation to a vertical plane at the outboard end of the drum. A crossbrace is located at 54 intermediately of the arms to provide reinforcement for the support bracket, as well as serves as a hand grip to assist in installing and removing the bracket. The support bracket has apertures 52 and 53 with aperture 53 being vertically elongated to allow for manufacting error in placing pins 14 on the front frame panel. The bracket 50 in conjunction to the cantilever mounting of drum supporting shaft 13 at the rear panel 11 gives support to the shaft at three fixing points.

In a second embodiment of the present invention shown in Fig. 2 in partial crosssection drum shaft 13 is shown with front hub 30 mounted thereon. The self-aligning ball bearing 51, having an inner race 80 and an outer race 81, is mounted between the connection stub 17 on the shaft and the support bracket 50. A floating collar 90 ensures that the clamping force exerted by knob 19, in order to key the drum endbell 30 to the shaft 13, is directed at the face of the inner race 80 of self-aligning bearing 51 and not through the outer race 81. It is because of the possibly poor alignment of the threaded knob in its thread that collar 90 is allowed to float on the knob and seek its own alignment onto the outside surface of the drum shaft and onto the face of the inner race of the bearing.

In present reproduction machines, drum mounting hubs provide for an interference fit between the mounting surfaces of the drum and the hub. Improper assembly of these items allows drum run-out to exceed levels compatible with proper machine operation resulting in scratched drums and copy quality problems. As can be seen from the above detailed description, the apparatus of the present invention reduces the contact area where the interference fit occurs. This is accomplished by machining pads on the hub. These pads of which nine are recommended symmetrically spaced even though other numbers of pads could be picked, locate the center of the hub/ drum combination as does current systems.

The main advantage is to reduce the load required to properly seat the hub against the drum, thereby decreasing the possibility of incurring drum run-out.

WHAT WE CLAIM IS: 1. Apparatus including a rotary drum and a frame within which the drum is mounted, a shaft mounted on said frame, at least one end support mounted on said shaft, said end support having an outer surface thereon including a series of lobes spaced from each other around said surface, said at least one end plate being seated in and supporting the drum with said spaced lobes on the end support seated in contact with the inner surface of said drum.

2. Apparatus as claimed in claim 1, wherein said lobes are spaced equidistant around the outer surface of said end support.

3. Apparatus as claimed in claims 1 or 2, wherein said lobes are tapered toward the interior of said drum.

4. Apparatus as claimed in claims 1 to 3, wherein said shaft is cantilevered.

5. Apparatus as claimed in any preceding claim, wherein said drum is a hollow cylinder, and an end support on the shaft is located at each end of said drum.

6. Apparatus as claimed in claim 4, wherein said cantilevered shaft includes a removable support bracket having two substantially spaced arms for supporting the end of the drum mounting shaft remote from its cantilever mounting, whereby rigid support with three fixing points is provided for said drum mounting shaft.

7. Apparatus as claimed in claim 1 and substantially as described herein with reference to Figures 1 or Figure 2 or the accom panying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. of run-out due to endbells cocking or bend ing as assembly. Even though the lobes could be made flat as a mating service for the interior end surfaces of the drum, it is preferred that a gradual incline or slope toward the center of the drum be included at the lead edge of each lobe to improve seating or mating of the drum and hubs and possibly reduce deburring time. If one desireds to add a heater to the drum the front hub can be redesigned to accommodate a slip ring for such purposes. A further means of reducing drum run-out is the two-armed support 50 that is releasably mounted on capless pins 14 that are tapered for each of attachment and detachment of the support to the exterior of front frame panel 12. Maintaining the support in this manner also reduces the time necessary for removal and replacement of drums. This support is in the form of a removable support bracket with two substantially spaced arms at approximately 90" and a central self-aligning ball bearing 51, more fully described with reference to Fig. 2, for the outboard end of the drum shaft. The arms extend a greater distance from the drum support than the radius of the drum and provides a rigid support having two fixing points for the normally unsupported end of the drum shaft. The arms are arcuate in shape to allow connection stub 17 on the shaft 13 to be recessed in relation to a vertical plane at the outboard end of the drum. A crossbrace is located at 54 intermediately of the arms to provide reinforcement for the support bracket, as well as serves as a hand grip to assist in installing and removing the bracket. The support bracket has apertures 52 and 53 with aperture 53 being vertically elongated to allow for manufacting error in placing pins 14 on the front frame panel. The bracket 50 in conjunction to the cantilever mounting of drum supporting shaft 13 at the rear panel 11 gives support to the shaft at three fixing points. In a second embodiment of the present invention shown in Fig. 2 in partial crosssection drum shaft 13 is shown with front hub 30 mounted thereon. The self-aligning ball bearing 51, having an inner race 80 and an outer race 81, is mounted between the connection stub 17 on the shaft and the support bracket 50. A floating collar 90 ensures that the clamping force exerted by knob 19, in order to key the drum endbell 30 to the shaft 13, is directed at the face of the inner race 80 of self-aligning bearing 51 and not through the outer race 81. It is because of the possibly poor alignment of the threaded knob in its thread that collar 90 is allowed to float on the knob and seek its own alignment onto the outside surface of the drum shaft and onto the face of the inner race of the bearing. In present reproduction machines, drum mounting hubs provide for an interference fit between the mounting surfaces of the drum and the hub. Improper assembly of these items allows drum run-out to exceed levels compatible with proper machine operation resulting in scratched drums and copy quality problems. As can be seen from the above detailed description, the apparatus of the present invention reduces the contact area where the interference fit occurs. This is accomplished by machining pads on the hub. These pads of which nine are recommended symmetrically spaced even though other numbers of pads could be picked, locate the center of the hub/ drum combination as does current systems. The main advantage is to reduce the load required to properly seat the hub against the drum, thereby decreasing the possibility of incurring drum run-out. WHAT WE CLAIM IS:

1. Apparatus including a rotary drum and a frame within which the drum is mounted, a shaft mounted on said frame, at least one end support mounted on said shaft, said end support having an outer surface thereon including a series of lobes spaced from each other around said surface, said at least one end plate being seated in and supporting the drum with said spaced lobes on the end support seated in contact with the inner surface of said drum.

4. Apparatus as claimed in claims 1 to 3, wherein said shaft is cantilevered.