Work holders – With fluid means – Plural positioning means sequentially operated
Reexamination Certificate
2000-01-20
2001-08-28
Hail, III, Joseph J. (Department: 3723)
Work holders
With fluid means
Plural positioning means sequentially operated
C269S032000, C269S052000
Reexamination Certificate
active
06279886
ABSTRACT:
The present invention relates to a power clamp and in particular, but not exclusively, to a pneumatically- or hydraulically-operated power clamp.
Air-powered power clamps have for many years employed a pneumatically-driven drive rod that is connected to a pivoting clamping arm by a pivot link. As the drive rod is actuated, the clamping arm is driven through the pivot link, which causes the arm to rotate about its pivot joint with the clamp body to a closed position and then applies a clamping load. The pivot link may be driven to a centred or over-centre position, to lock the clamp. An example of such a clamp is illustrated in U.S. Pat. No. 4,458,889.
One disadvantage of clamps of the general type described above is that the force required to release the clamp is generally higher than the clamping force, owing to the high static friction forces that must be overcome to effect release. This is particularly true when the clamp is locked in an over-centre condition, since an additional force must be applied to bring the clamp back to a centred positioned before it can be released.
This difficulty is further compounded by the fact that the release force that can be applied by a pneumatically-operated drive rod is generally less than the applying force, owing to the fact that the pneumatic piston has a smaller effective area on the release side than it has on the applying side, owing to the presence on that side of the drive rod.
As a result of the foregoing, it is generally necessary to arrange the clamp so that the applied clamping force is always significantly less than the potential maximum force with the available air pressure, so that there is sufficient air pressure to release the clamp. Alternatively, the clamp may be arranged so that a centred or over-centre condition is never reached, so that the clamp is never locked in the clamped condition. However, this is not acceptable for all situations, as sometimes it is necessary to provide a self-servo locking clamp (i.e. a clamp that remains locked even after the air pressure has been removed).
It is an object of the present invention to provide a power clamp that mitigates at least some of the aforesaid disadvantages.
According to the present invention there is provided a power clamp including a body member, an arm member connected to the body member by means of a pivot joint to allow pivoting movement of the arm member between an open position and a closed position, an actuator, a first drive mechanism connecting the actuator to the arm member to control movement thereof, and a second drive mechanism connecting the actuator to the arm member to apply a clamping force to the arm member when the arm member is in a closed position.
Advantageously, said first drive mechanism and said second drive mechanism are arranged to operate sequentially when the actuator is actuated.
Advantageously, said first drive mechanism includes a lost motion mechanism, to allow limited movement of the actuator when the arm member is in a closed position without causing significant movement of the arm member.
Advantageously, the second drive mechanism includes a cam device for applying a clamping force to the arm member. The cam device may be arranged for linear movement. The cam device may be arranged for movement with the actuator. The second drive mechanism may include a roller that engages the cam device. The cam device may have a cam surface that includes a first portion of positive gradient and a second portion of zero or negative gradient.
Advantageously, the actuator includes a drive rod that is arranged for longitudinal reciprocating movement. Preferably, the pivot joint has a pivot axis that is substantially perpendicular to the longitudinal axis of the drive rod.
Advantageously, the actuator is hydraulically- or pneumatically-actuated.
REFERENCES:
patent: 4458889 (1984-07-01), McPherson et al.
patent: 4620696 (1986-11-01), Blatt
patent: 4905973 (1990-03-01), Blatt
patent: 5460358 (1995-10-01), Sendoykes
patent: 5704600 (1998-01-01), Robinson
patent: 5998984 (1999-12-01), Takahashi
patent: 6079896 (2000-06-01), Dellach
Hail III Joseph J.
HMC Brauer Limited
Merchant & Gould P.C.
Shanley Daniel
LandOfFree
Power clamps does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Power clamps, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Power clamps will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2521410