Gear cutting – milling – or planing – Milling – Including means to infeed rotary cutter toward work
Patent
1999-02-22
2000-08-08
Howell, Daniel W.
Gear cutting, milling, or planing
Milling
Including means to infeed rotary cutter toward work
7449003, 408234, 408237, 409211, 409216, 901 23, 901 41, B23C 112
Patent
active
060992174
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a movement device for a machine tool or a robot according to the preamble of the independent claims.
In such a device the part of the machine that is to be moved can be moved in up to three translational and rotatory degrees of freedom in respect to a base by moving several sliding carriages, each of which is connected by means of suited joints via a rigid articulated rod with the part to be moved, on at least two parallel linear tracks.
Machine tools for machining primarily have the object to provide certain relative movements between a tool and a workpiece. The most commonly used milling tools have three axes. Here, the tool can be moved, not only in its rotative cutting movement, but also in three translatory degrees of freedom in respect to the work piece. In addition to this, tools with four or five axes are used as well where the tool can additionally be moved in one or two rotatory degrees of freedom in respect to the workpiece.
Most of the conventional machine tools have a serial kinematic structure. The required number of degrees of freedom is achieved by serial arrangement of the corresponding number of linear and rotative axes. It is, however, increasingly desired that, on the one hand, the stiffness of the device is as high as possible, while, on the other hand, the masses to be moved should be as small as possible such that additionally generated mass forces remain small. Tools with serial kinematic structure are not well suited for such requirements because the bottom most axis of movement has to carry the weight of all those lying above it. In addition to this, the errors of movement of all axes are added, be they thermal, geometric or caused by the present loads.
Because of their kinematic structure machine tools with parallel kinematic structure, such as they have existed for a few years and are described in WO 92/17313, EP-A-0534 585 and U.S. Pat. No. 4,988,244 are better suited for high requirements in dynamics and accuracy. These machines are based on the so called generalized Stewart platform. The part of the machine to be moved is moved by means of six telescope like, driven legs. The masses to be moved are smaller than in serial structures and the errors of the individual axes of movement are not added. Only forces in axial direction of the legs, where they have their largest stiffness, are generated. Bending strain, as it is found in serial arrangements, does not occur.
The disadvantage of these tools lies in the fact that the available working space is small compared to the overall size of the machine. Enlarging the working space is connected with a corresponding enlargement of the whole machine and correspondingly with a lost in dynamics because the legs become larger, heavier and less stiff. A further disadvantage lies in the fact that these machines can hardly be built using conventional standard components. Yet a further disadvantage is the fact that these machines always have six axes, and therefore require six drives, guidings and measurement systems even though milling tools only require up to five axes, and even three axes are sufficient in most cases.
J. M. Herve and F. Sparacino describe in "Theory and Practice of Robots and Manipulators", A. Morecki, G. Bianchi, K. Jaworek (ed.), Springer pp. 301ff, different robot manipulators, among others also a model with three parallel lead screws, wherein a nut is moved along each lead screw. Two legs connected to a parallelogram are attached to each nut in articulated manner. This device is, however, not suited for machining tools because it does not provide sufficient stability and accuracy.
It is an object of the invention to provide a device of the type mentioned initially that substantially avoids as well as possible the above mentioned disadvantages of the machines based on the Stewart platform and, in particular, that guarantees a high stability and accuracy and/or a large working space.
These objects are achieved by the device according to the independent claims.
By using parallel tracks, a linear e
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Herve, J.M. et al., "Methodical Design Of New Parallel Robots Via The Lie Group Of Displacements," in Theory and Practice of Robots and Manipulators, Morecki et al. (Eds.), Springer pp. 301-306.
Weikert Sascha
Wiegand Alexander Konrad
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