Metal working – Method of mechanical manufacture – Gear making
Reexamination Certificate
2000-03-17
2001-09-18
Echols, P. W. (Department: 3726)
Metal working
Method of mechanical manufacture
Gear making
C029S893000, C029S893300, C074S462000, C264S328100
Reexamination Certificate
active
06289586
ABSTRACT:
Disclosed in the embodiment herein is a low cost system and method of manufacturing and assembly of an improved gear drive system providing improved motion quality. It is particularly suitable for producing a lower cost, less critical, drive system for motion uniformity critical components, such as imaging surface drives in print engines, such as a xerographic photoreceptor drive system, although not limited thereto.
In particular, there is disclosed in the embodiment herein a crowned gear set drive system which can be manufactured a low cost by common plastic molding and reverse mounting engagement of half-crowned gears, allowing for simplified, lower cost, gear molding, yet providing the improved motion uniformity of fully crowned gears to compensate for misalignment of the mating gear axes. That is, the disclosed system can overcome or greatly reduce prior motion error problems in driven components caused by normal gear axis alignment errors between the respective axes of rotation of the mating gears. Such gear axes alignment errors occur normally from 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 train, lower cost gear sets can be used to achieve the same acceptably high degree of motion smoothness in the output of the drive system. The motion quality improvement provided by the disclosed drive system may even enable the elimination in certain 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.
As noted, 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 an 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 prior difficulty and cost of manufacturing gears with a precise desired amount of gear tooth crowning, instead of straight teeth edges, has been a limiting factor in their utilization. The system of the disclosed embodiment is particularly applicable to relatively low cost but accurately molded plastic gears. It will be apparent to those skilled in the art that the same basic method may also be applicable to compressed powdered metal gears.
Examples of precision plastic gear molding art, especially with gas injection molding for enhanced conformity, 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, Attorney Docket No. D/99507P, and art cited therein, including U.S. Pat. Nos. 5,707,659; 5,639,405; and 5,151,278.)
Since, in the oppositely half-crowned gear set drive disclosed herein, crowning of only one lead edge of one side of each gear tooth need be provided to achieve the desired results, relatively little mold and/or tooling changes in manufacturing are required as compared to normal gear molding. In particular, with only single side crowning of the gear teeth, as disclosed herein, a simple two-part mold with a simple draw can be used to make the gear, and mold parting line flashing in the tooth engagement surface can be avoided, thus providing a significant cost advantage in producing low cost crowned gears suitable for the substantially improved motion uniformity 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 a method of manufacturing an improved gear drive system to provide improved drive motion uniformity with reduced manufacturing costs, said method producing a gear drive system comprising at least one pair of rotatable first and second engaged gears with respectively engaged gear teeth areas and respective first and second gear axes, said gear drive system having a drive motion tolerance to slight alignment variations of said first and second gear axes relative to one another; comprising: molding said first and second drive gears with gear teeth having outer edge crowning on only one side of said gear teeth in a mold in which the parting lines of said mold are outside of said respectively engaged gear teeth areas, said gear tooth outer edge crowning being sufficient to substantially increase said drive motion uniformity of said drive system with said alignment variations of said first and second axes of gear rotation; and assembling said first and second gears engaged into said gear drive system so that said outer edge crowning on only one side of said gear teeth of said engaged first and second gears are respectively opposite in position to one another to provide said tolerance in motion control to slight alignment variations of said first and second gear axes relative to one another.
Further specific features disclosed in the embodiments herein, individually or in combination, include said first and second gears are oppositely half-crowned plastic molded gears; and/or wherein said gear tooth outer edge crowning of said engaged gear teeth of said first and second gears is an equal but opposite lead circular half-crowning; and/or wherein said first and second gears are identically molded in the same mold but assembled inverted relative to one another in said gear drive system to provide said oppositely positioned outer edge crowning; and/or wherein said gear teeth have outer edges which are substantially linear other than at said crowned outer edge thereof.
As to specific components of the subject apparatus, or methods of manufacture, 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: 5151278 (1992-09-01), Baxi et al.
patent: 5639405 (1997-06-01), Erikson
patent: 5707659 (1998-01-01), Erikson
patent: 5802921 (19
Casella James M.
Hildebrand Robert E.
Poletto Anthony G.
Echols P. W.
Xerox Corporation
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