Hexapodal machining center

A hexapodal machining center comprising a fixed frame (1) and a support (2) which are interconnected via six struts (3) of an adjustable length. The connecting points (T.sub.1, T.sub.2, T.sub.3) of three struts on the support form a first working plane, whereas a further working plane is formed by the connecting points (T.sub.4, T.sub.5, T.sub.6) of the three further struts on the support. The frame connection points (G.sub.1, G.sub.2, G.sub.3, G.sub.4, G.sub.5, G.sub.6) of the struts are also arranged in two separate working planes. The connecting points of the two working planes of the support are superimposed such that the connecting lines of the superimposed pairs of connecting points (T.sub.1, T.sub.4 ; T.sub.2, T.sub.5 ; T.sub.3, T.sub.6) extend in parallel with each other. This allows a high degree of movability of the support in all of the six degrees of freedom. In particular, the movability in the three rotational degrees of freedom and the force receiving capacity of the support are optimized.

BACKGROUND OF THE INVENTION
 The present invention relates to a hexapodal machining center having a
 fixed frame and a support which are interconnected via six struts of an
 adjustable length.
 Such hexapodal machining centers are used as machine tools. They are
 particularly suited for cutting machine tools, e.g., for milling,
 drilling, turning or grinding or for laser machining.
 In principle, hexapodal machining centers consist of a support, which is
 sometimes designated as a working platform, and of a fixed frame which are
 interconnected by six struts of an adjustable length. This allows a
 movement of the working platform in all of the six spatial degrees of
 freedom, i.e., three translational degrees of freedom and three rotational
 degrees of freedom.
 A first hexapodal machining center is known from U.S. Pat. No. 5,401,128.
 This known machine tool structure consists of an octahedral framework
 comprising twelve rigid struts. A machining unit comprising a spindle is
 arranged in the center of the framework. Furthermore, a fixed
 workpiece-receiving device is arranged in the lower part of the octahedral
 machine frame of the fixed workpiece-receiving device. The hexapod, i.e, a
 support or working platform for the machining unit, e.g., a drilling or
 milling spindle, is provided above the workpiece receiving device. Two
 respective struts of the hexapod which can be adjusted in their length are
 coupled with one end to a corner of a triangular upper frame part of the
 machine frame, the connecting points of the two struts on the machine
 frame being only slightly spaced apart with respect to their height. All
 of the connecting points of the six struts on the working platform are
 located in a joint plane. Such an arrangement limits the rotational
 movements. Moreover, the forces cannot be received in the struts in an
 optimum manner since these do not extend in the directions of the main
 load.
 A further hexapodal machining center is known from U.S. Pat. No. 5,354,158.
 In the hexapod shown in that document, two neighboring struts are coupled
 at a comer of an imaginary triangle to the working platform and two other
 neighboring struts to the comer of a further imaginary triangle on the
 frame, the two triangles arranged in parallel with each other being
 rotated relative to each other. The connecting points of the struts on the
 working platform and on the frame are each arranged in a common plane.
 Moreover, it is known from U.S. Pat. No. 5,354,158 that the connecting
 points on the frame are arranged in two spaced-apart planes. Such an
 arrangement has similar shortcomings as the arrangement according to U.S.
 Pat. No. 5,401,128 with respect to the movability of the working platform
 and the force-receiving capacity.
 SUMMARY OF THE INVENTION
 It is therefore an object of the present invention to optimize the
 movability of the support in all of the six degrees of freedom, in
 particular in the three rotational degrees of freedom, as well as the
 force-receiving capacity in a hexapodal machining center of the
 above-mentioned type.
 This object is achieved by a hexapodal machining center having a fixed
 frame and a support which are interconnected via six struts of an
 adjustable length, wherein the connecting points of three struts on the
 support form a first working plane, and the connecting points of the three
 further struts on the support form a second working plane spaced apart
 from the first working plane, wherein the connecting points of three
 struts on the frame form a first working plane and the connecting points
 of the three further struts on the frame form a second working plane
 spaced apart from the first working plane of the frame, and wherein the
 connecting points of the two working planes of the support are
 superimposed such that the connecting lines of the superimposed pairs of
 connecting points extend in parallel with each other.
 A great freedom of movement of the support and the working platform,
 respectively, is thereby achieved because the joints of the struts at the
 connecting points on the support do not interfere with one another. In
 particular, a greater freedom of movement is thereby achieved with respect
 to the rotational degrees of freedom. Therefore, the hexapodal machining
 center can also be used for more compact supports or smaller machines.
 Moreover, the superimposed configuration of the connecting points on the
 support improves the stiffness of the backing of the support, thereby
 ensuring a greater manufacturing accuracy.
 A machining unit and/or sensor system for sensing the position may be
 mounted on the support. The machining unit may carry a spindle, with a
 desired spatial position of the spindle being provided depending on the
 respective requirements, e.g., horizontal or vertical. The structure of
 the frame is adapted accordingly.
 The struts are suspended within the frame in such a manner that the
 connecting points of three respective struts on the frame form a total of
 two separate working planes. Such an arrangement of the struts will
 enhance movability, in particular with respect to the rotational degrees
 of freedom, and result in a more uniform force-receiving capacity.
 Moreover, a particularly economic arrangement of the constructional space
 is thereby made possible because the distribution of the connecting points
 on the support and on the frame will provide more space for the design of
 the respective joints at the connecting points. On the whole, the
 constructional freedom of design is increased and a more compact
 construction is made possible, so that the ratio of the space available
 for machining to the space required by the machining center is increased.

DETAILED DESCRIPTION OF THE INVENTION
 The hexapodal machining center illustrated in the figures of the embodiment
 is designed as a machine tool used for machining. The machine tool
 comprises a frame 1 which requires a substantially triangular base. At the
 corner points of the triangular base, three columns 4 extend upwards from
 a frame bed 5 at the floor side. The columns 4 are interconnected at their
 upper end via a joint frame yoke 6 and form a machine tool frame or frame
 1 together with the frame bed 5.
 A support or working platform 2 is suspended on said frame 1 via six struts
 3 having an adjustable length. The supports 2 receive the tool proper, for
 instance a drilling or milling tool, to machine a workpiece in a machining
 room inside the frame 1, i.e., between the frame bed 5 and the support 2.
 For the protection of the operating personnel, the frame openings which
 remain between the columns 4 are closed by way of panels 10 which have
 arranged therein viewing openings for controlling the manufacturing
 process. Moreover, there are closable access openings for providing access
 to the working area, in particular to a workpiece table 8 mounted on the
 frame bed 5. A machining area which is as large as possible is obtained in
 that the workpiece table 8 is movable in two directions in the plane of
 the frame bed 5, so that workpieces whose machining dimensions exceed the
 maximum motional range of the support 2 can also be machined on the whole.
 As becomes especially apparent from FIGS. 2 and 3, the support 2 has a
 basic shape which is substantially cylindrical relative to the
 longitudinal axis A thereof, with the longitudinal axis A in the
 inoperative state or the normal position of the support 2, extending in a
 direction perpendicular to the plane of the frame bed. In the illustrated
 embodiment as a cutting machine tool, the support 2 has provided thereon a
 main spindle 9, which is coaxial to the longitudinal axis A thereof and is
 driven by a drive device, for instance by an electric motor which is also
 arranged on the support 2.
 On its outer surface, the cylindrical support 2 further comprises three
 connecting portions 7 that extend in the direction of the longitudinal
 axis A and are each flattened. Each of the connecting portions has
 provided thereon two joint attachments which are spaced apart in the
 direction of the longitudinal axis A and via which the struts 3 are
 coupled to the support 2. The three connecting portions 7 are uniformly
 distributed on the circumference of the cylindrical support 2. The joint
 attachments on the individual connecting portions are always at the same
 height. On the whole, there are two groups of connecting points for the
 struts 3, with the connecting points forming a respective equilateral
 triangle. The upper connecting points T.sub.1, T.sub.2, T.sub.3 in FIGS. 2
 and 3 define a first working plane of the struts 3 on the support 2, and
 the lower connecting points T.sub.4, T.sub.5, T.sub.6 in these figures
 define a second parallel working plane that is spaced apart from the first
 working plane. The working planes extend in a direction perpendicular to
 the longitudinal axis A of the support 2 and thus also to the rotational
 axis of the main spindle 9.
 The congruence, i.e., the superimposed configuration of the connecting
 points T.sub.1 to T.sub.6 of the support can in particular be seen in FIG.
 4. For instance, the "upper" connecting point T1 of the support is
 positioned above the "lower" connecting point T4 of the support. As can
 further be seen in FIG. 4, all of the connecting lines of such
 superimposed pairs of connecting points of the support extend in parallel
 with one another. This is also the case whenever, although the connecting
 points of the support are superimposed on the respective connecting
 portions, the points are spaced apart from one another at different
 distances, so that in such a case the first and second working planes of
 the support may also be bent with respect to each other.
 The respectively upper struts 3, i.e., those that are coupled to the
 support 2 at the support connection points T.sub.1, T.sub.2, T.sub.3 of
 the first working plane, extend towards a respective column 4 of the
 frame. The connecting points G.sub.1, G.sub.2, G.sub.3 on the frame 1
 define a first connecting plane of the frame at the yoke end of the
 columns 4. The three remaining struts are coupled to the columns 4 below
 the first working plane in a second working plane of the frame in FIGS. 2
 and 3.
 The struts 3 are here arranged such that two struts extending away from a
 connecting portion 7 of the support 2 extend towards different columns 4.
 As can be seen from FIG. 4, the arrangement is further chosen such that
 the struts coupled to the connecting points T.sub.1, T.sub.2, T.sub.3 of
 the first working plane of the support are operative in a rotational
 direction based on the longitudinal axis A of the support 2, i.e.,
 counterclockwise in FIG. 4, whereas the remaining struts at the second
 working plane of the support are operative in the opposite rotational
 direction, i.e., clockwise in FIG. 4.
 The support connection points T.sub.1, T.sub.2, T.sub.3 of the first
 working plane of the support are connected to the connecting points
 G.sub.1, G.sub.2, G.sub.3 of the first working plane of the frame.
 Likewise, the connecting points of the two second working planes are
 coupled with each other.
 As can further be learnt from FIG. 4, a column 4 has provided thereon a
 respective strut 3 which connects the connecting points of the first
 working plane, e.g., T.sub.1 and G.sub.1, and a strut 3 which connects the
 connecting points, e.g., T.sub.6 and G.sub.6 of the second working plane.
 The coupling operation is here performed at opposite sides of the
 respective column, with the type of arrangement being identical for each
 of the three columns 4. The struts 3 which extend from a column 4 to the
 support 2 are operative on said support in tangential direction on
 neighboring connecting portions 7, so that said struts when viewed from
 the top, as shown in FIG. 4, spatially cross each other. Such a crossing,
 however, does not impair the motional freedom of the support, 2, because
 these two struts are coupled in two different working planes to the
 support. The distance of the working planes on the support is here chosen
 to be greater than the diameter of the individual struts 3.
 The struts may be designed as hydraulic or pneumatic cylinders or also, as
 shown in the embodiment, as motor-driven screw drives. The struts are
 coupled to the support 2 and also to the frame 3 by way of universal
 joints, such as ball or cardan joints, which allow a rotational movement
 about all of the three spatial axes at the same time.
 It will be appreciated by those skilled in the art that changes could be
 made to the embodiment(s) described above without departing from the broad
 inventive concept thereof. It is understood, therefore, that this
 invention is not limited to the particular embodiment(s) disclosed, but it
 is intended to cover modifications within the spirit and scope of the
 present invention as defined by the appended claims.