Drum mounting apparatus

Abstract: An apparatus for mounting a photoreceptor drum (22) so that the imaging surface (23) thereof remains at a substantially constant distance from an imaging source (84) to minimize image distortion caused by drum runout. The photoreceptor drum (22) is mounted on a rotatable supports (70) and is resiliently urged against a guide (76). By urging the imaging surface (23) of the photoreceptor drum (22) against a rotatable guide (76), the imaging surface (23) is maintained a substantially constant distance (D) from the imaging source (84) thereby minimizing lateral magnification error caused by drum runout.

Description: This invention relates generally to a photoreceptor drum mounting apparatus, and more particularly concerns a photoreceptor drum runout control for multiple imaging stations in a tandem architecture electrophotographic printing machine. With the advent of multicolor electrophotographic printing, it is desirable to use the so-called tandem architecture which comprises a plurality of image forming stations. This tandem architecture offers a high potential for throughput and image quality. One choice of photoreceptors in this tandem engine architecture is a drum based photoreceptor architecture used in combination with an intermediate transfer belt. To provide durability, it is desirable to use a larger diameter drum which affords more than a single pitch so as to increase drum life, number of copies per minute and copy volume. A problem with a larger drum is that the total indicated runout (being runout caused by the eccentricity of the drum) of the drum becomes larger as the diameter of the drum increases. This total indicated runout causes image registration error at each photoreceptor drum and between the multiple photoreceptor drums. It is desirable that the multiple drum surfaces in a tandem printing machine remain at a constant distance from the imaging source. Photoreceptor drum runout causes a change in the conjugate length between the imaging source and the photoreceptor surface. This variation in conjugate length due to the drum runout can cause a lateral magnification error which precludes proper image registration when printing color copies. US-A-4,120,576 discloses a drum support apparatus including an outbound and inbound hub, having outer surfaces adapted for interface fitting with the inside surface of a drum. The hubs, while being supported on a cantilevered shaft from a frame, have provisions to be secured by the tightening of a single nut at the center of a drum. The assembly creates an equal distribution of force on the hubs, thus diminishing circular runout of the drum. US-A-3,490,841 discloses a photocopying drum apparatus which is detachably mounted for rotation on a cantilevered shaft comprising two sections, an inner section and an outer section, connected together endwise by a universal joint. One end of the drum is supported by a sleeve and the other end is supported by a chuck having three pivotal segments, the pivotal segments allowing removal of the drum from the shaft. Both the sleeve and the chuck are fixed to the outer section of the cantilevered shaft. The inner section of the shaft is mounted in a pivot arm which is pivotally connected to a pivot support, the pivot arm being resiliently biased towards a fixed support. The pivot arm is hollow and the inner section of the shaft is supported therein by means of a pair of bearings located in the walls of the pivot arm, the inner shaft being driven via a pulley mounted thereon and positioned between the bearings. The surface of the drum is maintained a fixed distance from a lens as the resilient biasing of the pivot arm towards the fixed support brings the drum surface into contact with guide rollers positioned to define the fixed distance. In accordance with one aspect of the present invention, there is provided a drum mounting apparatus according to claim 1 of the appended claim. Pursuant to another aspect of the present invention, there is provided an electrophotographic printing machine according to claim 9 of the appended claims. Other features of the present invention will become apparent as the following description proceeds and upon reference to the drawings, in which: Figure 1 is an end elevational view depicting the photoreceptor drum runout control apparatus of the present invention; and Figure 2 is a side elevational view of Figure 1. An illustrative electrophotographic printing machine incorporating the photoreceptor drum runout control apparatus of the present invention is shown in Fig. 3 of USSN 07/906,181 published as US-A-5 218 405. Since such machines are well known in the art, the description of the features thereof has been omitted from the present disclosure. For a general understanding of the features of the present invention references are made to the drawings. In the drawings, like reference numerals have been used throughout to designate identical elements. Referring now to the specific subject matter of the present invention, Figures 1 and 2 depict the photoreceptor drum runout control apparatus in greater detail. With reference to Figure 1, there is shown a single photoreceptor drum 22 illustrative of each of the four drums illustrated in Figure 3 of USSN 07/906,181. A typical imaging unit, generally indicated by reference numeral 80, including a laser 82, a polygon 84 and a modulator (not shown) is also illustrated. It is critical that the conjugate length (represented by "D") between the polygon 84 and the photoreceptor surface 23 remains constant. A change in the conjugate length of the distance between the polygon 84 and the photoreceptor surface 23, causes a lateral magnification error to be introduced to the image. This is especially critical in the foregoing type of multicolor printing machine as the four different color toner images must be positioned superimposed in registration with one another. The lateral magnification error introduced by even a small amount of drum runout, which causes the conjugate length between the polygon 84 and the photoreceptor surface 23 to vary, can cause unacceptable lateral magnification error. The photoreceptor drum 22 is supported axially by bearings 70. Each of these bearings 70 is spring-biased by spring 72 so as to urge the photoreceptor drum 22 in a direction toward the scanning beam reflected by the polygon 84. Photoreceptor surface 23 is urged against guide bearings 76 mounted to the frame 78 of the machine. The photoreceptor drum 22 is constantly spring-biased so that the surface 23 is constantly riding against the guide bearings 76, causing the conjugate length "D") between polygon 84 and photoreceptor surface 23 to remain constant. By utilizing this configuration for each photoreceptor drum in the machine, the change in lateral magnification error on each and between successive drums is minimized. In recapitulation, it is evident that there is provided a drum runout control apparatus which maintains a substantially constant conjugate distance between a polygon and the drum surface so as to minimize lateral magnification error. The photoreceptor drum is mounted on a rotatable supports and is resiliently urged against a guide. By urging the imaging surface of the photoreceptor drum against a rotatable guide, the imaging surface is maintained a substantially constant distance from the imaging source thereby minimizing lateral magnification error caused by a drum runout period.

Claims: A drum mounting apparatus for mounting a drum (22) for rotation, the drum (22) having a shaft and a surface (23) which is maintained at a substantially constant distance (D) from a pre-selected reference location, the apparatus comprising: supporting means (70) located on the shaft for rotatably supporting the drum (22) and located at either end thereof; guiding means (76) positioned at a fixed location to define the distance (D) from the pre-selected reference location; and biasing means (72) for resiliently urging the drum (22) toward the guiding means (76) to position the surface (23) of the drum (22) in contact therewith; characterised in that the biasing means (72) comprises a frame and spring means (72) mounted therein, the spring means (72) acting directly on the supporting means (70) to urge the surface (23) of the drum (22) into contact with the guiding means (76). The apparatus of Claim 1, wherein the supporting means (70) comprises a pair of rotatable bearings. The apparatus of Claims 1 or 2, wherein the guiding means (76) comprises at least one member which is adapted to be in rolling contact with the surface (23) of the drum (22). The apparatus of Claim 3, wherein each member comprises a plurality of rotatable bearings. An electrophotographic printing machine having at leeast one drum which is mounted using apparatus according to any of the preceding claims.

Inventors: WONG LAM F, WONG, LAM F.
Applicants: XEROX CORP, XEROX CORPORATION
Application year: 1993
Main classification: G03G15
IPC codes: G03G15, G03G21