Electrophotography – Image formation – Photoconductive member
Reexamination Certificate
2000-03-08
2001-06-26
Grimley, Arthur T. (Department: 2852)
Electrophotography
Image formation
Photoconductive member
Reexamination Certificate
active
06253047
ABSTRACT:
Disclosed in the embodiments herein is a system for improving the motion quality of the drive systems used in print engines, such as xerographic printers. In particular, there is disclosed an improved, low cost, and simple system for improving the drive motion control of such printer component drive systems, with the disclosed crowned gear drive system. It has been discovered in this printing art that surprising improvements in the evenness of critical printer component motion velocities can be provided with sufficient gear tooth lead edge crowing in the printer component drive systems. It has been discovered that the disclosed system can overcome prior motion error problems in driven printer components caused by normal gear axis alignment errors between the respective axes of rotation of mating gears, such as normally occurs in manufacturing and/or assembly tolerances and errors.
By thus reducing the criticality of the required degree of parallelism of the respective axes of rotation of the gears in a gear drive train, lower cost gear sets can be used to achieve the same acceptably high degree of motion smoothness in the output of printer component drives systems. The motion quality improvement provided by the disclosed drive systems may even enable the elimination in certain printer drive applications of typical “gear boxes” having rigid enclosing gear mounting box steel plate frames to hold all the gear shafts rotatably mounted therein with fully parallel axes of rotation.
Uniform drive motion is particularly critical for the movement of the photoreceptor or other imaging surface of a printer. Even very small fluctuations in the motion of a imaging surface relative to an imager can create highly visible defects in the resultant prints. Numerous prior patents have addressed corrections in such motion fluctuation image quality problems. For example, Xerox Corp. U.S. Pat. No. 5,153,644 issued Oct. 6, 1992 to Eugene L. Yang, et al, and various other references on this subject cited therein. Also noted are Xerox Corporation U.S. Pat. Nos. 5,937,241 and 5,845,175 on gear mounts for enhanced motion quality.
The increasing demand for high resolution color printers, with their superposed plural images of different colors, and their requirements for large uniform color solid image areas, has added to printer motion control criticality. Such printers are especially prone to customer observable image defects in print quality, including those due to motion errors.
Printer drive system noise, especially for printers in office environments, is also an issue of concern to printer manufacturers. Furthermore, it is increasingly subject to various governments regulations.
The difficulty and cost of manufacturing gears with a precise desired amount of gear tooth crowning, instead of straight teeth edges, is a limiting factor in their utilization. The system of the disclosed embodiments is believed to be particularly applicable to accurately molded, relatively low cost, plastic gears. Examples of precision plastic gear molding art, especially with gas injection molding, are disclosed in co-pending Xerox Corp. U.S. provisional application No. 60/156,220 filed Sep. 27, 1999, entitled “Plastic Injection Molding with Reduced Dimensional Variations Using Gas Pressure and Secondary Plastic Injection,” by Robert E. Hildebrand, and art cited therein, including U.S. Pat. Nos. 5,707,659; 5,639,405; and 5,151,278. (An alternatives is compressed powdered metal gears.) Since, as disclosed herein, crowing of only one (or two) outer edges of each gear tooth of only one gear of a gear set need be modified to achieve the desired results, relatively little mold and/or tooling changes in manufacturing are required. In particular, with only single edge or corner crowning of the gear teeth, as disclosed herein, a simple two-part mold with a simple draw can be used to make the subject gear, and avoid any parting line flashing along the tooth center, thus providing a significant cost advantage in producing low cost crowned gears suitable for the subject substantially improved motion uniformity printer drive systems.
Various types of different gear crowning for different purposes, and manufacturing methods, are known in other arts, and need not be described herein. For example, it is known in the automobile industry to provide gear tooth crowning at magnitudes of 0 to 10 microns to control audio noise in gear meshes of automobiles. Crowning of 6-12 microns is typically standard.
There are also articles available such as: “Method for Cutting Straight Bevel Gears Using Quasi-Complementary Crown Gears”, by Koreaki Ichino, Hisashi Tamura and Kazumasa Kawasaki, available on the Internet at “http://www.gear-net.com” as Report 5 on the Japan Gear-Net website, pages 1-13 (initial publication date unknown). It discloses hobbing metal gear teeth to provide crowning.
A specific feature of the specific embodiments disclosed herein is to provide in a printing apparatus with at least one component having critical drive motion uniformity and a drive system providing drive motion to said component having said critical drive motion uniformity; the improvement wherein: said drive system comprises at least one engaged pair of rotatable first and second drive gears with substantially parallel respective first and second axes of gear rotation, said first and second axes having slight alignment variations relative to one another, and wherein at least said first drive gear has gear teeth having at least one crowned outer edge, said gear tooth outer edge crowning being sufficient to substantially increase said drive motion uniformity of said drive system in spite of said alignment variations of said first and second axes of gear rotation.
Further specific features disclosed in the embodiments herein, individually or in combination, include those wherein said gear teeth of said first drive gear have two crowned outer engagement edges; and/or wherein said rotatable first and second drive gears are oppositely lead circular half-crowned; and/or wherein said component with said critical drive motion uniformity is an imaging surface; and/or wherein said gear teeth of said first drive gear have outer edges which are substantially linear other than at said crowned outer edge; and/or wherein said component with said critical drive motion uniformity is a photoreceptor belt; and/or wherein said rotatable first and second drive gears are oppositely half-crowned, and are plastic molded gears; and/or wherein said crowning is at least approximately 75 microns; and/or wherein said crowning is in the range of approximately 75-100 microns.
As to specific components of the subject apparatus, or alternatives therefor, it will be appreciated that, as is normally the case, some such components and methods are known per se in other apparatus or applications which may be additionally or alternatively used herein, including those from art cited herein. All references cited in this specification, and their references, are incorporated by reference herein where appropriate for teachings of additional or alternative details, features, and/or technical background. What is well known to those skilled in the art need not be re-described herein.
REFERENCES:
patent: 2335504 (1943-11-01), Gazda
patent: 2682760 (1954-07-01), Shenk
patent: 4524643 (1985-06-01), Ziegler et al.
patent: 5768656 (1998-06-01), Nagasue et al.
Casella James M.
Hildebrand Robert E.
Narayan Anand
Poletto Anthony G.
Sweitzer Karl
Grimley Arthur T.
Ngo Hoang
Xerox Corporation
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