Technological background In the specific technical field, with reference particularly but not exclusively to machining operations performed in turning centres, it is known to provide manipulator devices, for example, in the form of gripping pincers, directly on the tool-holder slides; these manipulators provide for the loading and unloading of the workpieces, utilizing the movements of the slide along the controlled axes of movement of the machine.

A known application provides for manipulators, suitable for cooperating with corresponding workpiece loading and unloading stations, to be arranged on the respective opposed side walls of the tool-holder slide; the gripping of a machined piece from the mandrel and the gripping, in the loading station, of a piece to be machined thus take place simultaneously and, as a result of the movement of the tool-holder slide, the machined piece is deposited in an unloading station simultaneously with the loading of the piece to be machined onto the mandrel.

Description of the invention One of the main objects of the invention is to provide a machine tool equipped with manipulator devices which is designed structurally and functionally to improve the productivity of the work centre by means of a more marked reduction in workpiece loading and unloading times in relation to the working- cycle time.

Another object is to reduce, with the machine tool of the invention, dynamic stresses originating in the apparatus for gripping the pieces being machined, in particular the stresses which are generated in the mandrel during its acceleration and deceleration, at the same time achieving a reduction in the down times of the machine for maintenance and resetting of the operating conditions.

These and other objects which will become clear from the following description are achieved by a machine tool equipped with workpiece manipulator devices which is formed in accordance with the appended claims.

Brief description of the drawings.

The characteristics and the advantages of the invention will become clearer from the following detailed description of a preferred embodiment thereof which is described by way of non-limiting example with reference to the appended drawings, in which: Figures 1 to 4 are schematic front elevational views of a machine tool with a tool-holder slide provided with workpiece manipulators, at different stages of the loading of a piece onto the mandrel and of its unloading therefrom.

Preferred embodiment of the invention With reference to the drawings mentioned, a lathe, for example, a vertical lathe, shown only partially, is generally indicated 1 and comprises a tool-holder slide 2 guided transversely along a cross-member 3 in the directions of the axis marked X. The invention is intended to be suitable for applications with machine tools of various types although the type described represents a preferred selection.

The cross-member 3 is in turn movable on guides 4 of a base. 5 in the directions of the axis indicated Z. The axes X and Z are preferably perpendicular to one another.

The slide 2 is arranged for supporting a pair of tool stations 6,7 but it is intended that a different number of stations may be provided, in dependence on specific requirements for the machining of the pieces.

The lathe 1 also has a workpiece-holding apparatus 8 carrying a mandrel 9 which is driven so as to rotate about its principal axis C. The axis C is advantageously perpendicular to the axis X. The mandrel 9 has members for clamping a piece P to be machined, which may be of various types and shapes.

The turning of the piece P in accordance with predetermined working cycles is performed by the rotation of the mandrel about the axis C and the movement of the tool stations 6,7 along the controlled axes X and Z.

The lathe 1 is also provided with a manipulator device, generally indicated 10, for manipulating the workpieces P; the manipulator device is mounted directly on the tool-holder slide 2, preferably in the region of a side wall 2a thereof.

The manipulator device 10 comprises an arm 11 which is fixed to the slide 2 and on which a support 12 is mounted so as to be rotatable about a rotation axis X1.

The axis X1 is parallel to the axis C of rotation of the mandrel 9.

Two manipulator members 13,14 extend, both in the same direction, from a plate-like portion 12a of the support 12 and are constructed, for example, in the form of gripping pincers which are arranged for gripping the piece P during its movement relative to the mandrel 9, as will become clear from the following description.

The manipulators 13 and 14 have respective principal axes X2 and X3 about which they are also arranged to be rotated, with independent movements, by means of a drive transmission, not shown, disposed on the support 12. The manipulators 13,14 are advantageously arranged on diametrally opposed sides of the axis X1 of the support 12. More particularly, the axes X2 and X3 are coplanar with and equidistant from the axis X1 and are arranged angularly at 180? relative to one another.

A slide loader, indicated 15, cooperates with the lathe1 and has the function of a station for loading/unloading the workpieces in accordance with the operating cycle explained in detail below.

The operation of the machine tool is described with reference to the work stages shown in sequence in Figures 1 to 4.

In Figure 1, the piece P is being machined on the lathe. It has previously been clamped on the mandrel 9 which is rotated about the axis C and the tool station 6 has been brought to the region of the mandrel in order to perform the turning of the piece P. Upon completion of the machining in accordance with the predetermined working cycle (which may also involve the use of the tool station 7), the slide 2 is moved along the axes X and Z by numerically controlled movements to the position in which the manipulator 13 is brought to the region of the mandrel 9 (with the axes C and X1 coaxial) in order to pick up the machined piece P. Simultaneously with the movement of the slide 2,

the loader 15, on which a new, rough piece P'to be machined is disposed, is moved parallel to the axis X (arrow B) in the region of the manipulator 14 to the position in which both of the manipulators 13,14 are coaxial with the respective pieces P and P'.

After the pieces P and P'have been gripped on the manipulators 13 and 14 (Figure 2), the support 12 is raised (in the direction of the axis Z) and rotated through 180 ? about its rotation axis X1 so as to bring the manipulator 14 to the position for unloading the piece P'onto the mandrel 9 and the manipulator 13 to the position for unloading the machined piece P onto the loader 15 (Figure 3). By means of the movement of the slide 2 in the direction of the axis Z, the rough piece P'is placed on the mandrel 9 and the machined piece P is deposited on the loader 15. The loader is then moved away from the working region of the lathe in order to discharge the machined piece from the line. A new working cycle is then started on the piece P'and is completed by the cyclic repetition of the stages of Figures 1 to 4 for the loading and unloading of the pieces.

The positioning of the loader 15 is advantageously designed to optimize the travel of the slide 2, reducing the times required for supplying the mandrel 9 in comparison with the effective cycle times.

The manipulators 13 and 14 may also be arranged to be rotated at the rate of rotation of the mandrel 9. The operations to pick up the piece P from the mandrel 9 and to transfer it thereto can thus take place with the mandrel in rotation, ensuring that the relative rate of rotation between the mandrel 9 and the manipulators 13,14 is zero.

As a result, the mandrel 9 does not need to be accelerated or decelerated during the loading and unloading of the piece P and the dynamic stresses generated by its accelerations/decelerations are consequently greatly reduced, if not eliminated, reducing the times required for loading/unloading the pieces.

The manipulators 13,14 may also be capable of being driven with independent rotational movements, in dependence on specific requirements, in order to assist the gripping movements of the manipulators during operations to load/unload the mandrel 9.

The invention thus achieves the objects proposed affording the above- mentioned advantages over known solutions.