GB2226967A - Workpiece clamp - Google Patents

Abstract

The clamp, for holding the driver mechanism of a flextensional transducer during the machining of its end faces 2a, 3a, the driver mechanism comprising a stack of ceramic blocks 1 with a metal block 2, 3 at each end of the stack, the stack being encapsulated and held together by an epoxy resin, comprises a backing member 4 and a clamping member 10 between which the drive mechanism is clamped during machining, both members having their clamping faces shaped to have protruding lips 7, 11 in those opposed regions which in use will contact only the metal end portions so that the ceramic blocks lying between are not clamped. <IMAGE>

Description

CLAMPING TOOL This invention relates to a clamping tool for the clamping of an article to enable a machining process to be carried out in which opposed end faces of the article are formed to be both flat and parallel to one another and also to be at a desired distance apart.

Although the invention has uses in respect of a wide range of articles, it is particularly suitable for use in the manufacturing of flextensional tranducers of the type having a shell of elliptical cross section enclosing a driver mechanism lying generally along its major axis. The driver mechanism comprises a stack of piezo electric (i.e.

ceramic) blocks held together and encapsulated by a plastics resin. The end blocks, on which the opposed end faces of the stack are formed, are of metal. It is the machining of these metallic faces which is facilitated by the present invention; they require to be accurately formed since the assembled stack must be inserted between opposed faces within the shell such that changes in length of the stack along the major axis due to piezo electric action are faithfully transmitted to the shell.

One embodiment of a clamping tool is described by way of example and with reference to the accompanying drawing.

A driver mechanism for a flextensional transducer comprises a stack of ceramic blocks 1 lying between two similar end blocks 2, 3 of metal, the whole being held together as a unit by an epoxy or similar plastics resin.

The driver mechanism unit is of rectangular form both in plan and in side-elevation. As before mentioned, the metal end blocks 2, 3 provide end surfaces 2a, 3a which engage oppositely facing surfaces (not shown) formed within the shell of the transducer when the whole is assembled for use.

Thus the surfaces 2a, 3a require to be accurately formed, both in distance apart and in flatness and parallelism.

This seemingly easy task, has proved difficult because the ceramic portions of the stack were difficult to hold without damage and repeatability was difficult to achieve.

A tool has been developed which takes the form of a clamp. It comprises a backing member 4 of rectangular form having a shoulder 5 extending the length of one side edge.

The shoulder has an inwardly directed face Sa which is machined to form a planar datum against which a datum face 6 of the driver mechanism unit rests during machining. At an upper edge of the backing member is formed a narrow support lip 7 extending the width of the backing member, and at a lower edge is formed a further, similar support lip 8. The distance that these lips 7, 8 are set apart is chosen so that during machining, the metal end blocks 2, 3 of the driver mechanism unit are held against them.

The lips 7, 8 are proud of the remainder of the surface 9 of the backing member so that no portion of the ceramic blocks can be contacted by the backing member.

To hold the driver mechanism unit against the datum surface 5a and the lips 7, 8, there is provided a clamping member 10. This is of similar form to the member 4 (without the shoulder 5) and has similar support lips 11, 12 which face the support lips 7, 8 respectively and contact the other side of the blocks 2, 3 to them. The lips 11, 12 are formed proud of the remainder of the surface 13 similarly to the arrangement of the backing member 4 and for the same purpose.

The backing member 4 is of steel for rigidity whilst the clamping member 10 is of aluminium to allow some slight flexibility.

In use, the driver mechanism unit is placed against the backing member 4 with its datum face 6 located closely against the face 5a, and the side faces of its metal end blocks 2,3 against the lips 7, 8. It is then clamped in this position by the clamping member 10 whose lips 11, 12 contact the opposite sides of the blocks 2, 3 and clamp the blocks against the lips 7, 8. The clamping member 10 can be clamped by any suitable means providing it is not allowed to vibrate loose during machining. It is to be noted that the end faces of the driver mechanism unit to be machined lit above and below the upper and lower edges of the backing member 4 to give machining clearance.

Conveniently, the backing member 4 is itself accurately machined with reference to the datum surface 5a so that it can be readily and accurately mounted upon a work table of a machine tool. For example, it can be mounted upon the vertical face of a 900 L-shaped location member itself clamped to the work table. To get a correct height for machining, assuming one surface 2a, 3a is presented to the machine tool cutter or grinder at any one time, then a highly accurate block 15 (known as a slip gauge) of desired thickness is placed between the bottom face of the backing member 4 and the work table before the clamping tool is mounted on the L-bracket. To machine the other surface 2a, 3a the clamp tool is removed from the L-bracket and inverted using the block 15 as height location before re-mounting.

Claims (5)

1. A clamping tool for holding an article during a machining operation, which article has end portions with opposed end faces requiring to be machined both flat and parallel, the end portions being capable of being clamped, and has between the end portions a region of material which cannot be clamped, the clamping tool comprising a backing member and a clamping member between which the article can be clamped, both members having their clamping faces shaped to have protruding lips in those opposed regions which will in use contact only the end portions of the article so that the material lying between the end portions is not clamped.

2. A clamping tool according to Claim 1 wherein the backing member includes a shoulder portion with a datum face against which the article to be machined can be located during clamping.

3. A clamping tool according to Claim 2 wherein the backing member has at least one exterior surface accurately machined with reference to the datum face so that. it can be accurately mounted upon a work table.

4. A clamping tool according to any one of the previous claims wherein the backing member is made of a more rigid material than the clamping member.

5. A clamping tool substantially as described with reference to the accompanying drawing.