Technical Field

The present invention relates to a machine tool for mechanical machining.

Background Art

In the mechanical machining sector, various machine tools are known designed to shape mechanical workpieces by removing shavings.

In this specific sector, the machine tools are split into:

roughing machines, designed to remove the larger residues from the workpieces being machined; and

- grinding machines which, having a fine-grain and extremely hard grinding wheel, are designed to perform the grinding operation suitable for bringing the workpiece being machined to the optimum project state of shape or surface.

Taking into account the superior degree of precision required during machining, the grinding machines are usually more sophisticated with respect to the roughing machines and require a number of solutions that allow the tools and workpieces being machined to remain stably in position without excessive vibrations or oscillations.

Traditional grinding machines consist of a base frame on which are fitted a tool- holding head and a piece-holding head.

The tool-holding head, in turn, has a grinding tool rotating around a horizontal rotation axis and is mobile along two horizontal Cartesian axes to move the tool closer to/away from the piece-holding head.

The piece-holding head, instead, consists of a supporting structure carrying a series of bearings to support a rotating shaft.

One extremity of the rotating shaft is turned towards the tool-holding head and is associated with a self-centring spindle for gripping the workpieces being machined.

The opposite extremity of the rotating shaft, on the other hand, is associated, by means of a transmission pulley and belt, to a motor for the putting into rotation of the self-centring spindle during machining.

The rotating shaft is substantially horizontal and parallel to the rotation axis of the grinding tool but, to perform particular chamfering jobs, it can be made to oscillate with respect to the tool-holding head.

For this purpose, the supporting structure of the piece-holding head is associated with the frame of the machine in a rotatable way around a vertical axis, so as to change the angle of incidence of the grinding tool with respect to the workpiece. These traditional machines do have a number of drawbacks, including the fact that the piece-holding heads made this way have rather voluminous overall dimensions, in particular along the horizontal direction defined by the rotating shaft (about 800÷1000 mm).

Such overall dimensions, besides representing a considerable limitation of the room at the disposal of the machine, prevent the piece-holding head from rotating by ample degrees of rotation (usually restricted to about 10°÷20°) inasmuch as greater rotations would carry the workpiece too far away from the grinding tool fitted on the tool-holding head.

Nor should it be forgotten that traditional grinding machines are able to efficiently operate to grind inner and outer cylindrical surfaces coaxial or parallel with the rotation axis of the tool (axial grinding), but are not equally able to machine flat surfaces at right angles to the rotation axis of the tool (front grinding), such operations requiring the grinding tool to work at the tip, with low efficiency, or for a tool-holding head able to rotate around its own axis, with consequent increase in machine cost.

It must also be pointed out that traditional machines are designed to only work the extremity of the workpieces turned towards the tool-holding head, the opposite extremity being fastened on the self-centring spindle.

In many cases however, the surfaces to be machined are arranged on both extremities of the workpiece which, therefore, needs to be fastened a first time to machine one extremity, removed from the spindle and fastened a second time to machine the opposite extremity, with consequent increase in machining times and a considerable loss of machining precision caused by the repositioning. It is further underscored that the motors usually fitted on traditional machines do not allow controlling the position of the workpiece in any way and are unable to cooperate with the tool to interpolate the relative motion of the workpiece and of the tool for the purpose of grinding complex surfaces (round or oval).

The presence of a transmission pulley and of a belt, furthermore, considerably increases the play as regards the transmission of motion, with the risk of losing precision and not satisfying the very close tolerances usually required in traditional grinding operations.

To overcome the above drawbacks at least in part, grinding machines have been designed equipped with a "brushless" motor fitted on the supporting structure on the opposite side with respect to the self-centring spindle and linked without transmissions directly to the rotating shaft.

As an alternative to the "brushless" motor, the use is known of "torque" type motors, having an outer stator associated with the supporting structure and an inner rotor keyed without transmissions to the rotating shaft.

In both cases, the rotating shaft continues to be fitted, by means of bearings, on the supporting structure and to have an extremity carrying the self-centring spindle.

The position and speed of the "brushless" or "torque" motors can be controlled electronically by means of an electronic unit which allows actively and automatically controlling the movement of the workpiece and of the tool for the purpose of interpolating them to obtain complex surfaces.

Notwithstanding this, the machines equipped with "brushless" or "torque" motors continue to be affected by the numerous drawbacks of traditional grinding machines relating to excessive overall dimensions, the difficulty in rotating the piece-holding head, the low efficiency in performing front grinding and the need to fit and remove the workpiece several times.

Description of the Invention

The main aim of the present invention is to provide a machine tool for mechanical machining which has compact overall dimensions, is highly manoeuvrable with great freedom of movement and which can be used in a practical and efficient way.

A further object of the present invention is to provide a machine tool for mechanical machining which allows positioning the workpieces being worked in a practical, easy and functional way without any loss of time or precision. Another object of the present invention is to provide a machine tool for mechanical machining that allows overcoming the mentioned drawbacks of the state of the art in the ambit of a simple, rational, easy and effective to use as well as low cost solution.

The above objects are achieved by the present machine tool for mechanical machining, comprising:

at least a supporting frame;

at least a tool-holding head associated with said supporting frame and having at least a machining tool;

at least a piece-holding head having:

at least a base element which is mounted on said supporting frame by interposition of a first motorised rotation device around a first axis; at least a gripping device for gripping at least a workpiece to be machined which is mounted on said base element by interposition of a second motorised rotation device around a second axis substantially transversal to said first axis, for the putting into rotation of said workpiece during the machining;

characterised by the fact that said second motorised rotation device comprises an annular motor having a statoric tubular element associated with said base element and a rotoric tubular element associated with said gripping device, said tubular elements being arranged one inside the other coaxially to said second axis and being motorised to rotate one with respect to the other, inside said annular motor being defined a compartment housing at least a portion of said gripping device.

Brief Description of the Drawings

Other characteristics and advantages of the present invention will become more evident from the description of some preferred, but not sole, embodiments of a machine tool for mechanical machining, illustrated purely as an example but not limited to the annexed drawings in which:

figure 1 is an axonometric view of the machine according to the invention;

figure 2 is an exploded and cross-section view of a portion of the machine of figure 1 ;

figure 3 is an axonometnc and cross-section view of a portion of the machine of figure 1;

figures from 4 to 8 are axonometnc, partially cross-section views of the machine of figure 1, which show some possible machining operations which can be performed using the machine according to the invention;

figure 9 is an axonometric, partially cross-section view of an alternative embodiment of the machine according to the invention.

Embodiments of the Invention

With particular reference to such figures, globally indicated by 1 is a machine tool for mechanical machining.

The machine 1 comprises a supporting frame 2 for resting on the ground and on which is fitted a tool-holding head 3 and a piece-holding head 4.

The tool-holding head 3 has at least a machining tool 3 a.

The piece-holding head 4 has a base element 5, 6 which is fitted on the supporting frame 2 by interposition of a first motorised rotation device 7, 8, for the putting into rotation of the base element 5, 6 around a first axis B, arranged substantially vertically.

The piece-holding head 4 also comprises a gripping device 9, 10 for the grip of a workpiece P to be machined.

The gripping device 9, 10 is fitted on the base element 5, 6 by interposition of a second motorised rotation device 11, 12, for the putting into rotation, during machining, of the gripping device 9, 10 and of the workpiece P around a second axis C substantially transversal to the first axis B.

More in detail, the second axis C is substantially horizontal.

At least one between the first motorised rotation device 7, 8 and the second motorised rotation device 11, 12 is an annular motor of the "torque" type.

Usefully, the second motorised rotation device 11, 12 is made up of an annular motor of the "torque" type having a statoric tubular element 11 associated with the base element 5, 6 and a rotoric tubular element 12 associated with the gripping device 9, 10.

The tubular elements 11, 12 are arranged one inside the other coaxially to the second axis C and are motorised to rotate one with respect to the other.

The tubular elements 11, 12, furthermore, are of round-section cylindrical shape, with the same axial overall dimensions and coinciding radial sizes.

More in detail, the statoric tubular element 1 1 comprises an outer surface 1 la associated with the base element 5, 6, and an inner surface l ib on which the rotoric tubular element 12 slides.

The rotoric tubular element 12, in turn, has an outer surface 12a sliding inside the statoric tubular element 11 and an inner surface 12b supporting the gripping device 9, 10.

The particular ring conformation of the tubular elements 11, 12 allows defining a compartment 13 inside the annular motor 11, 12.

Advantageously, the compartment 13 is open at both the axial extremities for fitting the workpiece P to be machined from side to side.

For this purpose, it must be specified that by axial extremities are meant the circular openings 13 a, 13b of the tubular elements 11, 12 which are arranged on opposite sides along the second axis C.

The gripping device 9, 10 comprises a self-centring spindle 9 having at least two gripping jaws 10 radially mobile with respect to the second axis C.

In the particular embodiment shown in the illustrations, three gripping jaws 10 are provided, but alternative embodiment solutions are possible wherein different numbers of gripping jaws are fitted.

The gripping device 9, 10 and particularly the gripping jaws 10 are at least partially arranged inside the compartment 13.

In particular, the self-centring spindle 9 is fitted on the inner surface 12b of the rotoric tubular element 12 and is completely housed inside the compartment 13. In the same way, the gripping jaws 10 are fully arranged inside the compartment 13, as shown in the illustrations, to allow a considerable compacting of the longitudinal overall dimensions of the piece-holding head 4 along the second axis C, with consequent reduction of the vibrations and increase in machining precision.

Similarly to the second motorised rotation device 11, 12, the first motorised rotation device 7, 8 is also preferably made up of an annular motor of the "torque" type able to rotate by 360°.

More in detail, the first motorised rotation device 7, 8 comprises a statoric tubular body 7 and a rotoric tubular body 8, with round-section cylindrical shape, which are arranged one inside the other coaxially to the first axis B and are motorised to rotate one with respect to the other.

The statoric tubular body 7 is housed in a containment seat 14, with round- section cylindrical shape, which is associated with the supporting frame 2, while the rotoric tubular body 8 supports the base element 5, 6.

The base element 5, 6 comprises an attachment basement 5, fitted on the first motorised rotation device 7, 8, and an annular bracket 6, fitted on the attachment basement 5 and containing the statoric tubular element 11.

The outer surface 1 la of the statoric tubular element 11 is made integral to the inner surface of the annular bracket 6.

The machine 1 equipped with the piece-holding head 4 with the features indicated above is ideal for performing precision machining operations, such as grinding, in which case the machining tool 3 a consists of a grinding tool, of the type of a grinding wheel, a mill cutter or the like, specifically designed for precision removal operations.

In the particular embodiment of the invention shown in the illustrations from 1 to 8, for example, the machining tool 3a consists of a mill cutter that can be operated in rotation around an axis at right angles to the first axis B.

For the correct reciprocal positioning of the machining tool 3a and of the workpiece P, the tool-holding head 3 is fitted on the supporting frame 2 in a mobile way along:

- a first direction X, horizontal, to move closer to and away from the piece- holding head 4, which is substantially at right angles to the first axis B and parallel to the rotation axis of the machining tool 3a;

a second direction Y, horizontal, which is substantially at right angles to the first axis B and to the first direction X.

The mobility of the tool-holding head 3 along the first direction X and along the second direction Y is enough to perform most machining operations, the machining tool 3a being substantially arranged at the same height as the second axis C.

Alternative embodiments are however possible wherein the tool-holding head 3 is also mobile along a third direction Z substantially parallel with the first axis B (vertical).

By exploiting the freedom of movement of the piece-holding head 4 around the axes B, C and of the tool-holding head 3 along the above-mentioned directions X, Y, Z a single bracketing can be performed of the workpiece P on the gripping device 9, 10 and the machine 1 can be used to perform different machining operations including, by way of example only, the following:

- axial internal grinding (figure 4);

axial external grinding (figure 5);

internal grinding with chamfer or union (figure 6);

external grinding with chamfer or union (figure 7);

front grinding (figure 8).

In this respect, it must be stressed that the use of "torque" type motors allows controlling, moment by moment, the position of the workpiece P with respect to the machining tool 3a and interpolating the movement of the workpiece P with that of the machining tool 3a to make round surfaces such as unions or the like. At the same time, it must be emphasised that the particular solution of providing an open and through compartment 13, in which the workpiece P being machined can be inserted from one side to the other, allows performing the above- mentioned operations on both extremities of the workpiece P without having to remove and reposition it on the piece-holding head 4 as instead occurs with traditional machines; the 360° rotation of the first motorised rotation device 7, 8, in fact, allows turning the side of the workpiece P which has to be machined towards the tool-holding head 3.

Alternative embodiments are also possible wherein the machine 1 has a machining tool 3a different from that shown in the figures from 1 to 8, as in the case of the solution in figure 9 wherein the machining tool 3 a consists of a grinding wheel designed to grind the outside of a conical surface of the workpiece P.

In this respect, it is emphasised that the machine 1 can be equipped with a single piece-holding head 4, wherein the machining tool 3 a is changed according to the operation to be performed, or can be equipped with several piece-holding heads 4 on which different machining tools 3 a are fitted.

Finally, it should be noticed that, although the machine 1 according to the invention is ideal for carrying out grinding jobs, its use for roughing operations or the like cannot be ruled out.