Chucks or sockets – Expanding – Fluid-pressure actuator
Reexamination Certificate
1999-07-16
2001-02-06
Bishop, Steven C. (Department: 3722)
Chucks or sockets
Expanding
Fluid-pressure actuator
C242S571100, C269S022000, C279S002070, C279S004030, C403S031000
Reexamination Certificate
active
06182977
ABSTRACT:
BACKGROUND
When workpieces of different types are being machined, they have to be firmly held in a stationary manner in a specific position, or they have to be clamped to a movable or immovable machine part in a machining unit. In both cases, the clamping apparatus used for this not only has to position the workpiece but also has to absorb and transmit the forces arising from a machining operation. In the process, the shape of the workpiece must not be changed, either by the clamping forces or by the machining forces. This- applies, above all, to thin-walled workpieces. These forces are for the most part absorbed by a frictional connection.
Clamping sleeves are often used to clamp round workpieces to a machining unit. The clamping sleeves are designed to be relatively thin-walled. One side of the clamping sleeve serves as a contact surface on the workpiece, to be specific either on an external surface of the workpiece or on an internal surface of a hollow workpiece. On the other side, there is a relatively narrow annular space between the clamping sleeve and the machine part which is adjacent to it and in which the clamping sleeve is fitted. This annular space is sealed off in both axial directions. If a hydraulic or pneumatic operating medium in this annular space is pressurized, the clamping sleeve deforms elastically in the direction of the workpiece and clamps the latter firmly. Because the clamping sleeve, for its part, is connected to the machine part which accommodates it by a positive connection or a frictional connection, it is possible for the machining forces acting on the workpiece to be transmitted to the machine part, or conversely from the machine part to the workpiece.
The clamping sleeves have the disadvantage that their ability to be deformed radially is only very low and, in addition, this ability decreases further from the central longitudinal section outward to the two end sections. Clamping sleeves can therefore be used only to clamp workpieces which lie within a very small range of diameters. The consequence of this is that workpieces which are not machined in the clamping area often cannot be firmly clamped by means of clamping sleeves.
The chucks which are used for clamping workpieces with an adequately great dimensional strength and which generally have three clamping jaws cannot be used in the case of workpieces with a low dimensional strength, in particular in the case of thin-walled workpieces. The clamping tongues which are often used in addition cannot reliably clamp workpieces having large tolerances on the diameter or shape deviations, for example non-roundness. In addition, in the case of these chucks the radial clamping force is distributed to a few circumferential points, in particular when the actual diameter of the workpiece does not coincide exactly with the nominal diameter of the clamping tongues. Thin-walled workpieces are then subjected to an increased risk of deformation.
SUMMARY OF THE INVENTION
The invention is based on the object of providing a clamping apparatus with which even workpieces having large tolerances on the diameter and/or shape errors can be clamped reliably, and with which even workpieces with a low dimensional strength, in particular thin-walled workpieces, can be clamped, at least with low deformation, and can also be machined. This object is achieved by a clamping apparatus having the features described further below.
The fact that, in the clamping apparatus, the higher-strength clamping elements are embedded in the clamping surface of the clamping ring, made of an elastomer, and the fact that the clamping ring has a U-shaped cross section and is arranged in a circumferential recess, matched to it, in the clamping apparatus, means that the clamping elements are pressed against the workpiece when the internal space of the U profile is acted on by a hydraulic or pneumatic operating medium, and the workpiece is therefore firmly clamped radially. In the process, the end walls of the clamping ring are pressed against that side wall of the recess of the clamping apparatus which is in each case adjacent to it. As a result, on the one hand the internal space of the clamping ring is sealed off well to the outside, and on the other hand a good frictional connection between the end walls of the clamping ring and the clamping apparatus is achieved, which firmly clamps the clamping ring itself in the clamping apparatus. As a result, ultimately the workpiece is clamped radially to the machine part to which the clamping apparatus is fastened. At the same time, the high elasticity of the clamping ring means that relatively great tolerances on the diameter and even other shape deviations of the workpiece, such as non-roundness, can be bridged very well.
The fact that the clamping ring can be displaced within certain limits in the holding device when the operating medium is not pressurized, or at low pressures of the operating medium, and also can still be deformed after the pressure of the operating medium has been increased, because of the elasticity of the material of the clamping ring, means that the workpiece can be set to the intended radial desired position within these limits. This makes it possible, for example, to accommodate a workpiece between two points and, by means of the clamping apparatus, to absorb the torque which occurs in the case of material-removing machining or, conversely, to transmit said torque to the workpiece, even when there are relatively great tolerances on the diameter and/or relatively great deviations from the circularly cylindrical shape at the clamping point of the workpiece, or if there is a non-concentric clamping surface.
The fact that a relatively large number of higher-strength clamping elements are distributed in the circumferential direction on the circumference of the elastic clamping ring means that the radial clamping forces, which are identical to one another, are distributed to a corresponding number of circumferential points, so that the radial clamping force of the individual clamping element can be kept relatively low, and a high overall clamping force is nonetheless achieved. Because of the elasticity of the clamping ring, each clamping element can adjust to a relatively great extent to that deviation of the workpiece surface from the ideal surface which is present in its circumferential section, without the clamping force exerted by said clamping element changing.
The fact that there is a clamping device, by means of which, following the radial clamping of the workpiece by the clamping elements, the latter themselves can be axially firmly clamped, means that the clamping of the workpiece is fixed, and hence the influence of the compliance of the clamping ring is completely eliminated, and the workpiece is virtually completely rigidly clamped. It is even possible for the clamping ring to be relieved of the radial clamping force. With regard to the subsequent rigid clamping of the clamping elements, their initial radial clamping force can be kept lower. This reduces the elastic deformation, above all in the case of thin-walled workpieces, whose roundness is thus improved. This is still further assisted by the fact that use is made of clamping elements whose dimension in the circumferential direction of the clamping ring is relatively small and that for this purpose the number of clamping elements is selected to be all the greater.
In a refinement of the present invention, the clamping ring is guided relatively close to the clamping apparatus, so that the workpiece is also positioned by the clamping apparatus within certain limits. In another alternative refinement of the present invention, it is conversely possible for the workpiece, together with the clamping apparatus, to be adjusted arbitrarily to a relatively great extent within the clamping apparatus and hence within the machining unit, so that, for example, relatively great shape deviations can be compensated for, such as those which often occur with unmachined pieces.
Using a refinement of the present invention, it is als
Bishop Steven C.
Foley & Lardner
Hainbuch GmbH Spannende Technik
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