Handling: hand and hoist-line implements – Grapple – Swing dampener
Reexamination Certificate
1999-12-29
2001-03-27
Cherry, Johnny D. (Department: 3652)
Handling: hand and hoist-line implements
Grapple
Swing dampener
C188S083000, C188S266000, C403S031000
Reexamination Certificate
active
06206440
ABSTRACT:
FIELD OF THE INVENTION
The field of the present invention relates to mechanical joints incorporating braking and/or damping mechanisms. In particular, a mechanical joint is described producing varying damping torque in response to motion of the joint.
BACKGROUND
For purposes of the present specification, “mechanical joint assembly” shall denote an assembly which allows two members to be mechanically joined while allowing rotation of one member with respect to the other about at least one rotation axis. “Universal joint” shall denote a mechanical joint assembly providing rotation about at least two substantially orthogonal axes. Such a joint may be useful in applications in which two members must be mechanically joined but must be allowed to assume an arbitrary relative angle.
In some applications it is desirable for the motion of the moving members about the universal joint to be restricted by damping and/or braking. For example, such a universal joint is useful in situations wherein a first joined member is a boom with a second joined member suspended therefrom being some load carrying means, wherein motion of the load carrying means must be restricted, particularly when not loaded. One particular application of a braked universal joint is suspension of a grappler from a boom of a logging skidder. Several previous designs for a braked universal joint used in this way (also referred to as a swivel link) are described in U.S. Pat. Nos. 4,335,914; 4,417,759; 4,572,567; 4,573,728; 4,679,839; 4,715,641; 4,717,191; 4,723,639; 4,810,020; 5,096,247; 5,110,169; 5,451,087; and 5,601,161, each of said patents being incorporated by reference as if fully set forth herein. A much improved design for a swivel link incorporating frusto-conical surfaces for braking and load-bearing is disclosed in U.S. Pat. Nos. 5,713,688 and 5,779,383 issued to the applicant of the present application, both of said patents being incorporated by reference as if fully set forth herein. Another improved design for a swivel link employing rotational position-dependent braking torque is described in co-pending application Ser. No. 09/087,719, now U.S. Pat. No. 6,119,824 filed in the name of the applicant of the present application, said application being incorporated by reference as if fully set forth herein. The design and construction of swivel link assemblies, many drawbacks of previous swivel link designs, and improvements resulting from the use of frusto-conical braking and load-bearing surfaces are fully disclosed in these patents and application, and need not be reiterated herein.
A primary figure-of-merit for a swivel link is the number of hours of use in the field before replacement of the friction members of the joint (friction discs in older designs, friction cones in the frusto-conical design). Anything that reduces wear of the braking/friction members (and therefore reduces concomitant down time, maintenance time, and maintenance costs) is highly desirable.
During use of a swivel link, and many other braked mechanical joints, it is often the case that slow motions about the joint are insignificant and can be tolerated, while faster motions are undesirable and must be reduced or prevented (for example, to prevent injury and/or equipment damage). However, previous joints provide a constant braking torque relatively independent of the speed of motion. Reduction of the braking torque for slow rotations would reduce unnecessary wear on the braking/friction members, “saving” the braking/friction members for suppression of faster rotations.
In addition, earlier braked joint assemblies have relied on friction for generating braking torque. Mating surfaces are thrust together to generate this friction, and these surfaces must necessarily wear during use of the joint. Obviously, these surfaces could not be lubricated to reduce wear. A joint in which braking torque was not generated by friction would not be subject to such wear, could be thoroughly lubricated to reduce wear of moving surfaces, and would therefore have a longer operational lifetime before requiring maintenance or replacement.
It is therefore desirable to provide a damped mechanical joint assembly in which a relatively smaller damping torque is applied during slower motions of the joint, while a relatively larger damping torque is applied during faster motions of the joint. It is be desirable to provide a damped mechanical joint assembly in which the damping torque is generated without the use of friction members.
SUMMARY
Certain aspects of the present invention may overcome one or more aforementioned drawbacks of the previous art and/or advance the state-of-the-art of braked and/or damped mechanical joint assemblies, and in addition may meet one or more of the following objects:
To provide a damped mechanical joint assembly wherein the damping torque varies with angular velocity of rotation around the joint;
To provide a damped mechanical joint assembly wherein the damping torque increases with increasing angular velocity of rotation around the joint;
To provide a damped mechanical joint assembly wherein the damping torque decreases with decreasing angular velocity of rotation around the joint;
To provide a damped mechanical joint assembly wherein the wear of damping members is reduced;
To provide a damped mechanical joint assembly wherein the wear of damping members is reduced during slower rotation around the joint;
To provide a damped mechanical joint assembly wherein damping torque is generated with little or no concomitant friction;
To provide a damped mechanical joint assembly wherein damping torque is generated with little or no concomitant frictional wear;
To provide a damped mechanical joint assembly with a longer useful field life than previous joint assemblies; and
To provide a damped mechanical joint assembly with reduced maintenance requirements.
One or more of the foregoing objects may be achieved in the present invention by a damped mechanical joint assembly comprising: a) first and second damping members adapted for non-rotatably engaging one of two joined members; b) a joint body positioned therebetween and rotatable relative thereto; and c) a retainer for maintaining engagement of the first and second damping members with opposite damping surfaces of the joint body. The joint body is provided with a plurality of damping cylinders positioned around the joint rotation axis in a uniformly angularly spaced circular pattern, and each damping cylinder comprises a pair of piston chambers, each opening onto opposite damping surfaces, and a constricted passage connecting the piston chambers. Each of the piston chambers is provided with a piston assembly slidably positioned therein, and each damping cylinder is filled with fluid between the piston assemblies. Each damping member is provided with a circular groove comprising a plurality of uniformly angularly spaced ramped depressions separated by groove barriers. The number of damping cylinders preferably differs from the number of depressions. The fluid in the damping cylinders urges each piston assembly into engagement with the groove of the corresponding damping member, and the damping members are positioned so that when a piston assembly is located within a ramped depression of the groove of one damping member, the corresponding piston assembly is located at a groove barrier of the groove of the other damping member, thereby resulting in reciprocating motion of the piston assemblies and concomitant flow of the fluid though the constricted passage of the damping cylinders as the joint body rotates relative to the damping members. Viscous resistance to flow of the fluid through the constricted passage as the joint body rotates causes the piston assembly to be urged more strongly into engagement with one of the ramped depressions, thereby producing a damping torque opposing rotation of the joint body, the damping torque increasing with increasing angular velocity of the joint body.
Additional objects and advantages of the present invention may become apparent upon referring to the pref
Alavi David S.
Cherry Johnny D.
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