Work holders – Relatively movable jaws – Three coacting work grippers
Reexamination Certificate
1999-06-14
2001-03-27
Watson, Robert C. (Department: 3723)
Work holders
Relatively movable jaws
Three coacting work grippers
C269S217000, C269S233000, C269S258000, C269S266000, C269S268000, C269S902000
Reexamination Certificate
active
06206355
ABSTRACT:
The present invention relates to a clamp according to the preamble of patent claim , and in particular to a clamp for holding rigid workpieces. The invention has been developed primarily for use as a clamp in the wood-processing industry and the description hereinafter is set forth in such context. However, it should be appreciated that the invention is not limited to this particular field of use and it may be used for supporting or clamping any of a range of rigid workpieces.
In the past, various clamping devices have been proposed for clamping or supporting workpieces. For instance, the vice is a tool which is widely used and consists in essence of two steel plates which are drawn together by a lead screw. While the vice is effective for holding a single workpiece, or for holding parallel workpieces, it is not versatile in that the device cannot adequately cater to asymmetrical or irregular shaped workpieces.
U.S. Pat. No. 4,767,110 discloses a modified vice arrangement to cater for irregular shaped workpieces. This patent discloses a work table incorporating two vice jaws. Each of the two vice jaws incorporates a plurality of connection holes. At least three tension elements are removably secured to the connection holes of the vice jaws. The tension elements are arranged such that one of the tension elements is located in one of the jaws where the other two tension elements are located in the second jaw. The tension elements are secured to the connection holes via shanks and these shanks are eccentrically located on the tension elements. In this way, the respective tension elements can be independently moved out of respective connection holes and inserted at a different location to provide longitudinal adjustability of the tension elements independent of both vice jaws. The tension elements are further rotatably secured by means of the shaft, whereby an individual angular adjustment of the tension elements is made possible.
With this arrangement it is possible that a workpiece is clamped by firstly locating the tension elements in appropriate connection holes such that they are as close to the workpiece as possible. The vice jaws are then brought together and at least some of the tension elements are positioned until such time that all individual tension elements apply a force on the workpiece. To assist in rotation of the tension elements, each claw is provided with a lever.
Although this arrangement does enable greater flexibility of the type of workpieces which can be clamped, it does have the limitation that it is required to be located on a workbench and furthermore a rapid adjustment of the tension elements is not possible. Moreover, the actual handling of the workpiece is difficult in that it is necessary to bring the vice jaws together, while a pressure must be applied simultaneously on each lever at the tension elements. In order to ensure that the tension elements grip the workpiece safely, a force normal to the contact surface must be applied. This normal force is necessary if there is not sufficient frictional force between the workpiece and the tension element to prevent the workpiece from merely sliding between the two tension elements, without causing a rotation of the tension elements which would be of use for clamping.
EP-A 0 267 982 discloses a clamp, wherein the tension elements have to be manually positioned in order to reach the working position. In this working position the tension elements are exactly opposite with respect to one another. Accordingly, the user of the prior art clamp has to position the tension elements with two hands so that the user cannot simultaneously operate the clamping screw by means of the handle.
From EP-A-0 513 117 there is further known a clamp in accordance with the preamble of patent claim
1
. With this clamp the user is enabled to move out both tension elements of a clamping assembly by means of a slider in order to position a workpiece between the tension elements. Subsequently both of the tension elements are moved back as far as possible by actuating the slider. At the subsequent clamping of the workpiece by actuating the threaded spindle, a pressure must be simultaneously applied on the slider by the other hand during an initial phase.
It is the object of the present invention to increase the handling comfort for the user compared to the aforementioned clamps by reducing the number of the necessary working steps.
A further object of the present invention is the provision of a clamp with automatic self-positioning and self-adjusting tension elements.
A further object of the invention is the provision of a clamp having tension elements capable of frictionally holding a workpiece prior to the actual clamping operation, without the need for additional forces to be applied by the user.
These and further objects which will be apparent from the following description are achieved by the clamp of present invention, as set forth in claim
1
.
The clamp of the present invention comprises at least one clamping assembly having at least two tension elements which are slidably arranged in converging oblong holes, such that rotation of the tension elements from one position to a second position is not hindered.
Between the tension elements of the clamping assembly there is provided a spring means, which is tensioned by movement of the tension elements within the oblong holes. A restoration force, based on the spring means, acts on the tension elements in order to relocate the tension elements always to the initial position following a linear movement of the tension elements within the oblong hole.
Preferably each tension element is oval shaped in cross section, wherein the cross section runs perpendicular to its axis of rotation. Alternatively, each tension element is shaped as a modified three-cornered rod, wherein the cross section is of triangular shape. Also in this case the cross section runs perpendicular to the longitudinal axis of the tension element. This modified three-cornered rod has a curved peripheral face extending laterally from one edge to the opposite edge, and each of this curved peripheral faces is formed from a different material. Thereby three peripheral faces are provided, each of the faces having different hardness, flexibility or surface texture.
Furthermore, it is preferable that each tension element is conical in shape in the direction of its longitudinal axis, whereby the tapered end of the cone is positioned in close proximity to the oblong holes. The opening angle of the cone is 1-2 degrees, preferably 1.5 degrees. This cone-shape compensates for deformation of the tension elements under load.
Preferably, the clamp according to the present invention includes a second clamping assembly which is moveable in respect to the first one and which serves to exert on the workpiece the force necessary for clamping to thereby move the workpiece in the direction of convergence of both oblong holes.
Preferably the second clamping assembly according to the present invention consists of a steel plate which is connected to a threaded spindle. The threaded spindle is located in a corresponding counterpart. In this way the second clamping assembly is capable of linear movement by rotation of the threaded spindle.
Alternatively, the second clamping assembly is the same in structure as the first clamping assembly. In this arrangement, the connecting elements of the two clamping assemblies are secured at a respective end of a coupling element which enables the relative movement of the first clamping assembly towards the second clamping assembly. The coupling element may consist of a threaded spindle and a sleeve having a thread on its inner surface. In this way rotation of the sleeve relative causes linear movement of the first clamping assembly relative to the second clamping assembly.
An advantage of the preferred embodiment of the present invention is that, due to the restoration force acting between the tension elements, a fast and automatic alignment and positioning of the displaceable tension elements is possible at
Greer Burns & Crain Ltd.
Lichtenberg Wilfried
Watson Robert C.
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