Patent Application
20070063456
The present invention refers to a clamping apparatus for clampingly retaining a work piece having a shaft with polygonal cross section in a well defined position. It comprises a clamping body member with a clamping chamber adapted to receive the shaft of the work piece, clamping means for clampingly retaining the shaft of the work piece in the clamping chamber, and reference surface means provided on the clamping body member for defining the position of the shaft clampingly retained in the clamping chamber in X-direction and/or in Y-direction.
Clamping apparatuses of the kind referred to herein serve for clampingly retaining work pieces in a well defined position, preferably in the operating region of a machine tool, whereby the expression “work piece” is used in its broadest meaning; in other words, besides conventional work pieces, that expression shall cover also for example machining tools.
The document EP-A-0,248,116 discloses an apparatus for clamping non-rotating work pieces which have a shaft or a portion with a polygonal cross section. The apparatus comprises a clamping body member, provided with a clamping chamber having also a polygonal cross section. This clamping chamber serves for receiving the afore mentioned shaft or portion of the work piece. The clamping chamber is provided with three reference surfaces, serving for exactly aligning the work piece both in Y- and X-directions as well as with regard to its angular orientation around the Z-axis. For fixing the work piece, a clamping screw is provided, adapted to engage a chamfered thrust portion of the above mentioned shaft or portion of the work piece, in order to press the shaft or the portion of the work piece against the three reference surfaces. Even if this apparatus is rigid and stable and provides for a high repetitional accuracy, its production is very time consuming and costly.
It is an object of the present invention to provide a clamping apparatus for clampingly retaining a work piece having a polygonal shaft in a positionally well defined manner that can be manufactured easily, quickly and particularly at very low costs without affecting the positional accuracy of clamping of the work piece to be clampingly retained in the apparatus to a noteworthy degree.
In order to meet this and other objects, the present invention provides a clamping apparatus for clampingly retaining a work piece having a shaft with polygonal cross section in a well defined position. The apparatus comprises a clamping body member with a clamping chamber adapted to receive the shaft of the work piece, clamping means for clampingly retaining the shaft of the work piece in the clamping chamber, and reference surface means provided on the clamping body member for defining the position of the shaft clampingly retained in the clamping chamber in X-direction and/or in Y-direction.
The reference surface means comprises stop pin members provided in the clamping body member, whereby the stop pin members consist of a material that is harder than the material the clamping body member consists of.
Thus, one of the fundamental ideas of the invention is to manufacture the clamping body member of a base material that can be machined quickly, easily and, thereby, a low costs, while the few elements required for an accurate positioning in X- and/or Y-directions are made of a substantially harder material.
Preferably, the stop pin members are of cylindrical shape; thus, commercially available already finished round blanks can be used for manufacturing the stop pin members. A further advantage of cylindrical stop pin members may be seen in the fact that a work piece having flat lateral surfaces rests on the stop pin members along a line only, thus providing a high degree of immunity against contamination.
In the following, embodiments of the apparatus according to the invention will be further described, with reference to the accompanying drawings, in which:
A clamping chamber 8 is provided in the interior of the clamping body member 2, having a polygonal cross section. In the present example, the cross section of the clamping chamber 8 is substantially square. The clamping chamber 8 serves for receiving the work piece 27 which has a portion or shaft 28 with a cross sectional shape corresponding to the cross sectional shape of the clamping chamber 28. The front portion of the work piece 27 is designated by reference numeral 29. The work piece 27 is provided with a chamfered edge 30 adapted to be engaged by a clamping mechanism 10 of the clamping apparatus 1. In the region of three corners of the clamping chamber 8, free spaces in the form of recesses 9a, 9b, 9c are machined into the clamping body member 2. These recesses 9a, 9b, 9c ensure that the work piece 27 to be clampingly retained in the clamping apparatus 1 rests on the interior walls of the clamping chamber 8 with its lateral surfaces of its shaft 28 only and not with its edge portions. In the region of the fourth edge of the clamping chamber 8, the clamping mechanism 10 is located, as will be further explained herein after.
Along the one interior wall 11 of the clamping chamber 8, two bores 13, 14 are provided in the clamping body member 2, extending in Z-direction. Along the adjacent interior wall 12, located opposite to the clamping mechanism 10, a further bore 15 is provided in the clamping body member 2, extending in Z-direction as well. The position of these bores 13, 14, 15 refers to a reference point or a reference system, which is determined, in the present example, by the centering elements located on the base plate 4. These bores 13, 14, 15 are located within the clamping body member 2 such that they are open to the clamping chamber 8 along a strip-shaped portion. Inserted in each of these three bores 13, 14, 15 is a stop pin member 16, 17, 18, made of a material that is harder than the material of which the clamping body member 2 is made. For example, the clamping body member can be made of aluminum, while the stop pin members 16, 17, 18 are made preferably of hardened steel. Such stop pin members 16, 17, 18 are commercially available at a reasonably low price.
Each of the stop pin members 16, 17, 18 is inserted into and fixed in the assigned bore 13, 14, 15 by means of a press fit. Thereby, the stop pin members 16, 17, 18 protrude with a fraction of their diameter into the clamping chamber 8. The bores 13, 14, 15 as well as the stop pin members 16, 17, 18 preferably extend through the clamping body member 2 into the base plate 4; thereby, the position of the stop pin members 16, 17, 18 is well defined not only with regard to the clamping body member 2, but also with regard to the base plate 4 provided with the centering elements.
In the region of the forth corner of the clamping chamber 8, located on the bisecting line of the angle between the two interior walls 11, 12 provided with the stop pin members, the clamping mechanism 10 is situated. The clamping mechanism 10 comprises a thrust plate 20 in the form of a clamping jaw which can be moved forth and back by means of a set screw 21. For this purpose, the end of the set screw 21 is provided with a turntable-like protrusion in the form of a T-shaped end portion 22, rotatably engaging a corresponding recess of the thrust plate 20. The direction of action of the thrust plate 20 is chosen such that a work piece 27 received in the clamping chamber 8 is pressed against the reference surfaces constituted by the three stop pin members 16, 17, 18 upon tightening the set screw 21. It is understood that, instead of providing three stop pin members 16, 17, 18, for example four stop pin members could be provided; in such a case, the interior wall 12 of the clamping chamber opposite to the clamping mechanism 10 would be provided with two stop pin members.
Since the stop pin members 16, 17, 18 are of cylindrical shape, the reference surface is constituted by a line contact area between the stop pin members 16, 17, 18 and the flat lateral surfaces of the shaft 28 of the work piece 27. These line contact areas are shown in the drawing by means of dash-dotted lines 16a, 17a, 18a. As soon as the shaft 28 of the work piece 27 rests on the three stop pin members 16, 17, 18, the work piece is positioned in X- and Y-directions as well as with regard to its angular position around the Z-axis. Instead of the clamping mechanism shown in the drawings, it is possible to provide two clamping mechanisms offset to each other by 90°, one being located opposite to the lateral wall 11 provided with two stop pin members 16, 17, and the other one being located opposite to the lateral wall 12 provided with one stop pin member 18.
Preferably, the shaft 28 of the work piece 27 is provided with a chamfered edge portion 30 to be engaged by the thrust plate 20 in non-positive or, if appropriate in positive manner. By means of this chamfered portion 30, also the correct angular orientation of the shaft 28 with regard to the clamping body member is determined; in other words, the shaft 28 cannot be inserted into the clamping body member 2 in a position rotated by 90°, 180° or 270° with regard to the correct orientation.
The bottom of the clamping chamber 8 is provided with a screw 25 serving as a Z-direction stop member. This screw 25 is screwed into a bore running through the base plate 4 and provided with a corresponding female thread. For exactly determining the height of the screw 25 above the bottom of the clamping chamber 8, i.e. for exactly determining the Z-reference position, the head of the screw 25 at the bottom of the clamping chamber 8 is ground down to the desired height.
Furthermore, the clamping body member 2 is provided with a ball thrust screw 23 for loosely fixing a work piece received in the clamping chamber 8.
Instead of the embodiments shown in the drawings, in which the clamping body member is attached to a base plate, and in which the base plate comprises centering elements and a draw bar, it is possible to attach the clamping body member for example to an arbitrary base plate or a similar element which, in turn, is provided with a defined reference point. In some cases, it may even be sufficient to provide the clamping body member itself with one or several reference elements, such that the clamping body member can be attached to an arbitrary base body member in a well defined position. Finally, also multiple clamping apparatuses could be realized, in which a number of clamping body members are attached to a common base plate.
Due to the fact that the clamping body member 2 is made of a inexpensive, relatively light and easily to machine base material, and further that it is provided with stop pin members 16, 17, 18 constituting the reference surfaces 16a, 17a, 18a and made of a material that is substantially harder than the material of the clamping body member 2, the clamping apparatus of the invention can be manufactured quickly, easily and at low costs. By providing cylindrical sop pin members, 16, 17, 18 as reference surfaces, a line contact between work piece and stop pin members is ensured; this has a positive effect as far as the immunity against contamination is concerned. With a clamping apparatus according to the invention, both work pieces and machinining tools can be clampingly fixed in a well defined position, with high repetitional accuracy, in the proper orientation and also in a reference oriented manner.
| Number | Date | Country | Kind |
|---|---|---|---|
| 01536/05 | Sep 2005 | CH | national |
