Tool-holder turrets of the type indicated above are known in the art and are commonly used to carry out turning and/or milling operations on workpieces, with the turret being mounted on the machine tool in conventional positions.

An example of such a turret is illustrated in document US-A- 5,787, 767.

In accordance with the abovementioned known art, the rotating disk bearing the working tools is operated by control means comprising a motor shaft which is coaxial and concentric with the longitudinal axis of the turret, which is connected to the disk at one end and to the electric motor at the other end, with suitable gearwheels in-between.

The electric motor is commonly mounted outside the base body of the turret.

Positioning the motor outside the turret body gives rise to cost problems making it necessary to use gear mechanisms to provide the connection between the motor shaft and the shaft of the rotating tool-holder disk, as well as dimensional problems when mounting the turret on the machine tool.

It has been suggested in the art that the electric motor driving the tool-holder disk should be housed directly within the body of the said disk, which in this way lies in a position concentric with the rotor, with a significant reduction in the axial dimensions of the turret.

An example of such a connection is illustrated in US-A- 2002/0170397.

Although reducing the problems of the axial dimensions of the turret body, direct connection between the rotor of the motor and the tool-holder disk in accordance with the solution in the abovementioned known art nevertheless gives rise to a number of appreciable disadvantages, the most important of which is that tool-holders with a radial tang of the standard type, for example DIN69880, cannot be fitted

onto the disk unless the radial dimensions of the tool- holder disk are unacceptably increased, and also tool- holders having a radial tang of the rotating type cannot be fitted.

The functioning of the latter in fact requires that devices for the transmission of motion, which are also positioned in a radial direction with respect to the axis of the turret, for which there is no room in the situation illustrated in the said document, have to be housed.

In the illustrated example of the known art the said devices must in fact pass through the rotor of the motor in a radial direction in order to reach the periphery of the disk where the members which connect and transmit motion to the rotating tools are commonly housed.

Another solution in the known art relating to the mounting of the electric motor within the hollow body of a turret with direct connection between the rotor and the tool-holder disk is illustrated in document US-A 5, 664, 470.

In accordance with the technical solution illustrated in the abovementioned document the electric motor is housed within the stationary base body of the turret with the stator fixed to the latter through a flexible wall located at the end of the stator and positioned transversely to the axis of the turret.

Similarly the part of the rotor facing the tool-holder disk is axially connected to the latter through the flexible flange of a tubular member which is concentric with the axis of the turret, transverse to the said turret.

It follows that in the known art both the stator and the rotor are free to float to follow the axial movements imposed on the rotor as a consequence of the axial movements of the tool-holder disk when it is immobilised and released within the confines of the stationary body of the turret.

This is a technical solution which is subject to possible frequent breakages of the flexible members through which the motor is connected to the tool-holder disk and to the body of the turret, hot'to mention the disadvantages which may occur as a consequence of loss of coaxiality between the stator and rotor of the motor which may also give rise to jamming of the motor and render the turret unusable.

The purpose of this invention is therefore to provide a solution in which the tool-holder disk is connected directly to the rotor part of the electric drive motor to bring about angular movements between the working positions of the tools, thus overcoming the disadvantages incurred in the known art.

Another object of the invention is to make it possible to position tools of the rotating type, such as, for example, tools for drilling, milling and the like, as well as tools of the fixed type, on the tool-holder disk so as to ensure a high degree of versatility.

These objects are accomplished by the mechanism according to the invention as described in claim 1.

Other advantages and characteristics of the present invention will become clear from the following detailed

description which is given with reference to the appended drawings which are provided purely by way of non-limiting example and in which: - Figure 1 shows a view in longitudinal cross-section of a turret according to the invention designed for the fitting of radial tool-holders for tools of the fixed type, - Figure 2 shows a detail of a tool-holder disk for a turret of the type illustrated. in Figure 1 suitable for the fitting of axial tool-holders for tools of the fixed type, - Figure 3 shows a front view of the tower in Figure 1 from the side of the tool-holder disk, - Figure 4 shows a rear view of the turret in Figure 1, - Figure 5 shows a longitudinal cross-section of a turret according to the invention designed for the fitting of radial tang tool-holders for tools of the rotating type.

With reference to the aforesaid figures, 1 indicates the stationary base body of the turret which is provided with axial cavity 2 extending along longitudinal axis X-X. Tool- holder disk 3 is rotatably mounted about an axis of rotation which is coaxial with and coincides with axis X-X. A first annular member 4, rendered of one piece with body 1 through bolts as indicated by 5, is mounted in a position concentric with axis X-X. This annular member 4 has a crown of teeth 6 which are therefore of one piece with body 1. A second annular member 7 with a corresponding crown of teeth 8 is positioned concentrically with first annular member 4.

Annular member 7 is fixed, through bolt members 9 to tool-

holder disk 3 and can therefore rotate together with the latter. A third annular member 10, provided with a corresponding toothed crown 11, facing crowns of teeth 6 and 8, is housed within cavity 2. This can be moved axially between a first position in which crown of teeth 11 simultaneously engages both crowns 6 and 8, consequently immobilising tool-holder disk 3, and a second position in which said crown of teeth 11 is disengaged from the teeth in the first and second crowns with the consequent possibility that tool-holder disk 3 can rotate.

The aforesaid first, second and third crowns of teeth as a whole constitute immobilising means for immobilising and releasing tool-holder disk 3. These means, indicated as a whole by lla, can in a further embodiment be constructed in different ways, for example using coupling means of the multiple disk brake type.

Axial displacement of third annular member 10 which immobilises and releases disk 3 is brought about by a first tubular member 12 with corresponding actuator means 12a housed in cavity 2 in a position which is concentric with axis X-X, with interposed annular seals 13. These actuator means behave like a hydraulic piston within cavity 2 and are fed with hydraulic fluid in a conventional way, and for this reason are not described in detail.

As an alternative, the said actuator means may comprise a pneumatic control system of the type described in US-A- 5,787, 767.

The activation of tool-holder disk 3 when in the released position to make the necessary angular movements between

working positions is brought about by an electric motor, indicated as a whole by 14, the casing 15 of which is axially secured to base body 1 of the turret and is therefore stationary together with the latter. The inside of housing 15 represents an extension of cavity 2 of the stationary body and is regarded as being an integral part of that cavity.

In the embodiment illustrated in Figure 1, motor 14 has its stator 16 fixed to housing 15 and rotor 17 positioned within the stator.

As an alternative electric motor 14 may also be of the type with an external rotor and a stator located concentrically within.

In both cases the outside diameter of electric motor 14 is designed to be less than or at most equal to the maximum outside diameter of third annular member 10 with teeth 11.

In accordance with this invention rotor 17 is in the form of hollow shaft with a through cavity 18 which is open at both ends 19 and 20.

A second tubular member 21 provided with a through axial cavity 22 opening at both ends 23 and 24 is positioned within cavity 2, concentrically with axis X-X and inside first tubular member 13.

Cavity 22 of said second tubular member 21 is defined by its circular crown having a predetermined constant radial thickness S over its entire axial extent. The amount of thickness S depends on both the magnitude of the torsional

forces which have to be transmitted and the amount of radial space which is necessary to receive both bolt members 25 fixing end 24 to end 19 of rotor 17 and bolt members 26 fixing end 23 to tool-holder disk 3.

The latter is provided with a cavity 27 and in the embodiment illustrated in Figure 1 can receive a tool-holder 28 of the type with a radial tang 29 for fitting tools 30 of the fixed type.

In the alternative illustrated in Figure 2, tool-holder disk 3a has no internal cavity and is designed to receive tool- holder 28a of the type with an axial tang 29a for mounting tools 30a of the fixed type.

In accordance with the embodiments in Figure 1 and Figure 2, because axial cavities 18 and 22 are not used, end 23, which faces tool-holder disk 3 or 3a, is closed off by a removable transverse cover 31.

Likewise, end 20 of hollow rotor shaft 17 is closed off by a removable cap 32 which is axially fixed to housing. 15 of the motor.

In accordance with a preferred embodiment electric motor 14 is a servo motor which is associated in a conventional way with a position transducer 33 keyed onto rotor shaft 17.

Servo motor 14 and transducer 33 are controlled by electronic devices which are located within housing 34 fitted onto or within the edge of the turret as described in EP 0 768 585.

With reference to Figure 5, the structural members of the turret corresponding to those described with reference to Figure 1 are indicated by the same reference numbers.

It will be seen that the turret is designed to operate with tools 35 of the rotating type mounted on mandrel 36 of tool- holder 37 inserted radially on tool-holder disk 3 with tang 38.

A drive unit, indicated as a whole by 39, which is of a conventional type, and which is housed in cavity 27 of disk 3, is provided for the rotation of tools 35. Rotatory motion of unit 39 is brought about through a drive shaft 40 which is caused to rotate by auxiliary motor 41 fixed to the stationary base of the turret and connected by a conventional series of transmission gears 42,43 and 44.

Shaft 40 is housed within a supporting tube 45 which passes axially through adjacent cavities 18 and 22 of rotor 17 and second tubular member 21 from which cap 32 and correspondingly cover 31 have been removed.

Contiguous cavities 18 and 22 can also be used for the passage of pipes for fluids or electrical connections.

As indicated in Figure 5, in addition to tool-holder 37 for rotating tools 35, disk 3 may be equipped with a tool-holder 28 for fixed tools 30.

The turret according to the invention can therefore be adapted to operate with a tool-holder for fixed tools or with a tool-holder for tools of the rotating type while

continuing to have very small axial and transverse dimensions.

Naturally, the principle of the invention remaining the same, the forms of embodiment and details of construction may be varied widely with respect to those described and illustrated, which have been given purely by way of example, without thereby departing from the scope of the invention.