Machine element or mechanism – Control lever and linkage systems – Elements
Reexamination Certificate
1999-07-30
2001-11-13
Green, Mary Ann (Department: 3682)
Machine element or mechanism
Control lever and linkage systems
Elements
C074S523000
Reexamination Certificate
active
06314832
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to frictional resistance to relative displacement of members, and more particularly to controlled frictional resistance to cyclic displacement of one member relative to another.
There is need for improvements in devices which provide frictional resistance to relative displacement of members, considering the difficulty of controlling transitions between static friction (existent before the members are relatively displaced) and sliding friction (existent while the members are undergoing relative displacement). Such transitions occur, for example, during cyclic (back and forth) movement of such members. Experience has shown that the force needed to effect cyclic back and forth movement between frictionally interengaged members tends to increase and then decrease over a range of cycling, under the static and sliding friction conditions occurring during each cycle, as referred to. Such force increases and decreases transmitted through associated mechanism can and do increase the wear, and reduces the lives, of such mechanism.
What is needed is a means to reduce or substantially eliminate such force increase and decrease, needed to cyclically displace one member relative to another over a large number of cycles, which the members are frictionally interengaged.
SUMMARY OF THE INVENTION
It is a major object of the invention to provide a solution to the above described problems. The present invention meets the need referred to, and is embodied in apparatus to provide controlled frictional resistance to cyclic displacement of a member, comprising
a) a base
b) a friction part remaining frictionally and slidably engaged with said base, in response to cyclic displacement of said member,
c) at least one spring element transmitting force acting to hold said part in frictional engagement with said base,
d) one of said friction part and base having a friction surface engaged with the other of said part and base, and characterized in that the force to overcome friction between the base and part remains substantially the same over a large number of displacement cycles of said member, for example up to 300,000 minimum.
Accordingly, the solution to the problem as described is embodied in a friction surface on at least one of the part and base that will maintain substantially constant the force required to overcome static and sliding friction, over a large number of cycles of the part relative to the base.
Another object is to provide the friction surface on the movable part, and which has an associated coefficient of friction less than 0.15, and which will maintain friction constant, in use.
Yet another object is to provide the friction surface to consist of a DELRIN related thermoplastic material, as for example the material known commercially as FULTON 404, a product of LNP Corporation, Malvern, Pa.
A further object is to provide the spring element to comprise a stack of BELLEVILLE washers operating to provide constant force holding the part in engagement with the base.
An additional object is to provide a pivot mounting the movable part to pivot relative to the base, and a thrust bearing between at least one of the spring and the pivot. The thrust bearing, for example includes a series of anti-friction needle bearings spaced about an axis defined by the pivot. A spring force adjustment component may be provided, and may comprise a nut threadably engaging a shaft on which the pivot, spring or springs, and thrust bearing are carried.
These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification and drawings, in which:
REFERENCES:
patent: 2542423 (1951-02-01), Metzger
patent: 2552726 (1951-05-01), Larson
patent: 3987687 (1976-10-01), Bland et al.
patent: 4018104 (1977-04-01), Bland et al.
patent: 4833938 (1989-05-01), Reinwall et al.
patent: 5394767 (1995-03-01), Hoblingre et al.
Graber Stephen P.
Harris Stephen A.
Adams Rite Manufacturing Co.
Green Mary Ann
Haefliger William W.
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