Work holders – Relatively movable jaws – Means to actuate jaw
Reexamination Certificate
2000-03-17
2001-06-05
Hail, III, Joseph J. (Department: 3723)
Work holders
Relatively movable jaws
Means to actuate jaw
Reexamination Certificate
active
06241231
ABSTRACT:
The invention relates generally to a device for clamping workpieces and more particularly to a novel and improved clamping device which incorporates a shape memory alloy to clamp and/or unclamp a workpiece.
INCORPORATION BY REFERENCE
U.S. Pat. No. 5,197,720 illustrates the use of a super elastic alloy used in a non-positive clamping device and is incorporated herein by reference.
BACKGROUND OF THE INVENTION
Clamps for releasably holding materials during a manufacture process or the releasable locking of tooling such as dies, fixtures or molding plates are known in the art. Such self-locking clamping devices are illustrated in U.S. Pat. Nos. 4,721,293, RE 32,704 and 5,197,720. In U.S. Pat. Nos. 4,721,293 and RE 32,704, non-positive locking clamping devices are designed to use a fluid such as air or water to move a piston to clamp a workpiece. In U.S. Pat. No. 5,197,720, a non-positive clamping device is shown which incorporates the use of a super elastic alloy. The '720 patent incorrectly uses the term “shape memory alloy” to identify the super elastic alloy. As discussed below, shape memory alloys are a special class of alloys that have shape memory characteristics when heated, whereas super elastic alloys exhibit shape memory characteristics when physical stresses are applied to the alloys. The super elastic alloy in the '720 patent is designed to be mechanically moved by the use of a fluid to thereby lock a workpiece in position. When the workpiece is to be released, the fluid pressure is reduced thereby allowing the super elastic alloy to revert to its original shape and position thereby unclamping the workpiece.
Non-positive clamping tools can provide adequate clamping when properly operated. However, if a failure occurs which would result in a loss of fluid pressure, the clamping forces dissipate thereby allowing the workpiece to be inadvertently released from the clamp. Furthermore, the non-positive clamping device is typically complex in design and requires sophisticated pumps, seals and overall design to operate. The inherent complexity of this design subjects the design to an increased possibility of failure, i.e. pump, valve fitting or line failures. Positive clamping devices overcome the problems associated with non-positive clamping devices; however, such positive clamping devices have typically required complex designs resulting in a clamp that is difficult to repair when it fails.
In view of the prior art of clamping devices, there is a demand for a clamping device which is easy to manufacture, simple in design, reliable in operation and can clamp and unclamp a wide variety of workpieces.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a novel clamping device for the clamping of a workpiece in position. Preferably, the clamp device is designed for positive clamping; however, the clamp can be alternatively designed for non-positive clamping applications. The clamping device includes a clamping element such as a clamping surface, clamping pin, clamping lock, clamping clip, etc. which is designed to secure and unsecure a workpiece to and from a clamp surface. The clamping element is preferably made of a material strong enough to secure a workpiece in position for a particular type of operation. In addition, the clamping element preferably has flexible properties which allow the clamping element to be moved between a clamp and unclamped position. The clamping device also preferably includes a mechanism for moving the clamping element into a clamped state or unclamped state to provide for positive clamping or non-positive clamping, respectively. As can be appreciated, the clamping device has a wide variety of applications due to the positive nature or non-positive nature of clamping and further provides a mechanism for easily clamping or unclamping of a workpiece.
In accordance with another aspect of the present invention, the clamping element includes a super elastic alloy. Super elastic alloys are alloys which exhibit super elastic/pseudo elastic shape recovery characteristics. These alloys are characterized by their ability to be transformed from an martensitic crystal structure to a stress induced martensitic structure and return elastically to the austenitic shape when the stress is removed. These alternating crystalline structures provide the alloy with its super elastic properties. Such alloys may include an alloy comprising primarily of In—Ti, Fe—Mn, Ni—Ti, Ag—Cd, Au—Cd, Au—Cu, Cu—Al—Ni, Cu—Au—Zn, Cu—Zn, Cu—Zn—Al, Cu—Zn—Sn, Cu—Zn—Xe, Fe, Be, Fe
3
Pt, Ni—Ti—V, Fe—Ni—Ti—Co, Cu—Sn and Ni—Ti—Cu. These alloy systems may include small amounts of other metals which improve the super elastic characteristics of the alloy. These alloys are especially suitable for use in clamping devices in that their capacity to elastically recover almost completely to their initial configuration once stress has been removed on the alloy. In accordance with yet another aspect of the present invention, the super elastic alloy preferably is a separate component of the clamping device and is shaped to provide a force on the clamped element to force the clamped element into a clamped state for positive clamping. Alternatively, or in addition to, the clamping element may be made up of or include a super elastic alloy which is shaped for positive clamping of the workpiece. By designing the clamping element to be or include a super elastic alloy, the clamping element will position itself into a clamped state for positive clamping. An external force is used to move the clamping element into an unclamped state. Once the external force is reduced or removed, the clamping element will elastically move into its original clamped position.
In accordance with still another aspect of the present invention, the clamping device includes a super elastic alloy which is shaped to provide a force on the clamped element to force the clamped element into an unclamped state for non-positive clamping. Alternatively, or in addition to, the clamping element may be made up of or include a super elastic alloy which is shaped for non-positive clamping of a workpiece. By designing the clamping element to be or include a super elastic alloy, the clamping element will position itself in an unclamped state for non-positive clamping. An external force is used to move the clamping element into a clamped state. Once the external force is reduced or removed, the clamping element will elastically move into its original unclamped position.
In accordance with still yet another aspect of the present invention, the mechanism for moving the clamping element into an unclamped state includes the use of a fluid such as gas or liquid to apply a force to the clamping element to cause the clamping element to move into an unclamped state. Preferably, the fluid is at least partially encapsulated in a super elastic alloy. The pressurization of the fluid causes, the super elastic alloy to move thereby causing the clamping element to move into an unclamped state. When the pressure of the fluid is reduced, the force on the clamping element is also reduced thereby allowing the clamping element to return to the clamped state. The clamping element may include and/or be the super elastic alloy or be a separate component. Preferably, the clamping element is or includes a super elastic alloy that is shaped in a natural unclamped position.
In accordance with another aspect of the present invention, the mechanism for moving the clamping element into a clamped state includes the use of a fluid such as a gas or liquid to apply pressure to the clamping element and to cause the clamping element to move into its clamped state. Preferably, the fluid is a compressible fluid sealed in the body of the clamping device. The fluid is pressurized to constantly apply a force to the clamping element to force the clamping element into a clamped state. The fluid is compressible so as to allow the clamped element to be moved out of its clamped state when the mechanism for moving the clamping element out of its clamped st
Schron, Jr. Jack H.
Summers Jeff L.
Hail III Joseph J.
Jergens, Inc.
Vickers Daniels & Young
Wilson Lee
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