This invention relates to a double-rotatable spindle head for machine tools.

Double-rotatable heads for machine tools are known for machining three-dimensional surfaces, in particular for preparing light alloy moulds and models. They generally comprise two parts or half-heads, one of which (the first half-head) is able to rotate with respect to the machine structure about an axis, the other (second half-head) being able to rotate with respect to the first about a second axis at an angle to the preceding. Coordinated rotation of the two half-heads, generally by electric motors via a gear transmission system, enables the toot axis to be orientated in the desired direction in space.

In a known type of double-rotatable head, the first half-head is of fork shape with its axis of rotation (first axis) perpendicular to the transverse arm thereof, and the second half-head, which supports the tool spindle, is hinged to the two parallel arms of the first half-head about an axis (second axis) parallel to the transverse arm thereof. This known type of double-rotatable head, in which rotating the second half-head with respect to the first half-head about the second axis results in movement of the tool axis in a vertical plane, with a range which can even reach 110°, i. e. suitable for machining undercuts, presents a serious limitation related to the fork shape of the first half-head.

In effect, this shape results in a substantial bulk to the sides of the spindle and hence a difficulty in making the tool approach the surface of the workpiece, and in particular a difficulty in inserting the tool and its spindle into cavities present in said workpiece.

In another type of double-rotatable head, the first half-head is of substantially cylindrical shape with its axis coinciding with the first axis, the second half-head being positioned to the side of the first half-head, with the second axis perpendicularly cutting the first axis. In this case rotating the second half-head with respect to the first half-head about the second axis causes the tool axis to again move in a vertical plane but practically without any limitation.

By virtue of this lateral position of the second half-head with respect to the first half-head a reduction in the minimum distance between the spindle and surface of the workpiece is obtained, and hence a greater approach of the tool to said surface. However the loss of structural symmetry of the head results in a reduction in operative accuracy compared with the previous fork type.

In another known type of double-rotatable head the second half-head is coupled to the first half-head on a flat surface inclined at 45° to the first axis, the second axis being perpendicular to said flat surface.

By rotating the second half-head with respect to the first half-head about the second axis, the tool axis describes a conical surface having an angle of 90° at its vertex, and can pass in particular from the vertical position, parallel to the first axis, to the horizontal position.

This construction has proved more valid than the preceding, both with regard to the approachability of the tool to the surface of the workpiece, its penetrability into cavities present therein when required, and an accentuated reduction in the Pivot effect, which can result in a substantial reduction in the maximum machinable dimension of the workpiece for equal machine tool

dimensions. However because of the limited range of the tool axis, it cannot do undercut work.

An object of the invention is to eliminate all the drawbacks jointly or separately encountered in known double-rotatable heads for machine tools, and in particular to provide a double-rotatable head which besides being able to work in close proximity to the three-dimensional surface to be machined, can also penetrate into cavities present in the workpiece and can also machine undercuts.

Another object of the invention is to provide a double-rotatable head practically without slack and friction, which generally exist in traditional heads and are the cause of positioning inaccuracies and the need for frequent adjustments for their reduction.

These and further objects are attained according to the invention though a double-rotatable spindle support head for a machine tool as described in claim 1.

A preferred embodiment of the invention is described in detail hereinafter with reference to the accompanying drawings, in which: Figure 1 is a side view of a double-rotatable head of the invention in a configuration with the tool axis parallel to the first axis; Figure 2 is a vertical section therethrough in the same configuration as Figure 1; Figure 3 is a side view thereof in a configuration with the tool axis at an angle of 110° to the first axis; and Figure 4 is a vertical section therethrough in the same configuration as Figure 3.

As can be seen from the figures, the double-rotatable head of the invention comprises, in traditional manner, a first half-head 2 applied to the machine tool structure (not shown) via a connection element 4, and a second half-head 6 supporting the tool spindle 8. The first half-head 2 can rotate with respect to the machine structure, and hence to the connection element 4 about a first axis 10 by virtue of the presence of guide bearings 12 applied to said connection element 4 and engaging a circumferential groove 14 provided in the casing of the first half-head 2.

The first half-head 2 is rotated with respect to the connection element 4 by a direct motor, the stator 16 of which is rigid will said connection element 4 and the rotor 18 of which is rigid with said first half-head 2.

The second half-head 6 and the first half-head 2 are coupled together on a flat surface, the representation of which in the plane of the drawing is indicated by the line 20. This surface forms an angle of 35° with the first axis 10.

The second half-head 6 can rotate with respect to the first half-head 2 about a second axis 22, by virtue of the presence of guide bearings 24 applied to said first half-head 2 and engaging a circumferential groove 26 provided in the casing of the second half-head 6.

The second half-head 6 is rotated with respect to the first half-head 2 by a direct motor, the stator 28 of which is rigid with said first half-head 2 and the rotor 30 of which is rigid with said second half-head 6.

Both the direct motors, i. e. that interposed between the connection element 4 and the first half-head 2 and that interposed between the first half- head 2 and the second half-head 6, can be either permanent magnet synchronous motors or induction motors. The angular position of the first half-

head 2 to the connection element 4 and the angular position of the second half-head 6 to the first half-head 2 are controlled by respective position transducers 32,34.

In operation, while the rotation of the direct motor interposed between the connection element 4 and the first half-head 2 causes both the half-heads 6 and 2 to rotate about the first axis 10 and hence cause the tool axis to describe a conical surface, which becomes cylindrical when the two axes are parallel, rotation of the direct motor interposed between the first half-head 2 and the second half-head 6 causes this latter to rotate about the second axis 22 to hence vary the angle between the first axis 10 and the spindle axis.

More specifically, this angle can vary from 0° to 110° and assume all intermediate values between these two end values.

Consequently, by suitably controlling the two direct motors the spindle axis can be made to assume any spatial direction within a cone having a vertex angle of 220°.

From the aforegoing it is apparent that the double-rotatable head of the invention is particularly advantageous compared with traditional double- rotatable heads, and in particular : -it enables the tool to be positioned in strict proximity to the surface of the workpiece, -it ensures good penetrability of the tool and its spindle into any cavities in the workpiece, -it enables undercuts to be machined, -it practically eliminates slack and friction between parts in mutual movement, to obtain high precision in positioning the tool with respect to the workpiece, without the need for frequent adjustments.