Electric chuck

The present invention relates to an electric chuck as described in the preamble of Claim 1.

In particular, the inventive concept relates to applications in the field of machines for drilling printed circuits, and more generally in the field of machines for micromachining with chip removal, where the shaft rotation speeds are very high, for example 100-200,000 revolutions per minute. The printed circuit is the component which, in a modern electronic circuit, is responsible for providing the electrical connections between the various electronic components, and for providing the mechanical support for the components and the accessories.

There is a known electric chuck which is characterized in that the rotor shaft and the fixed part of the electric chuck are supported without contact, by means of a thin film of fluid, particularly precompressed air supplied constantly and under pressure. This method of support, known as pneumostatic, has considerable advantages over the conventional systems of roller bearing support, namely a capacity for very high speeds because of the low viscosity of the fluid and the absence of contact between the rotating part and the fixed part, high precision, long service life and greatly reduced vibration. The pressurized fluid which supports the chuck shaft and comes into contact with the moving surface not only supports it, but also enables it to withstand external loads caused by the mechanical machining to which it is subjected. Two pneumostatic bearings are generally provided to support the shaft radially, and to withstand the forces called radial forces, which are perpendicular to the axis of rotation of the chuck shaft. A pneumostatic

bearing is also generally provided to support the shaft in its axial direction, and to withstand the forces called axial forces, which are parallel to the axis of rotation of the chuck shaft, in both directions.

Also known in the art is the fact that the pneumostatic bearing supporting the shaft axially is positioned to the right or to the left and above or below the two bearings which support the shaft radially. Commonly, the electric motor imparting the rotary motion to the chuck shaft is positioned between the two radial bearings; in this case, the electric rotor is formed directly on the shaft. However, this construction gives rise to a number of drawbacks, including the dissipation of the heat from the motor, the rigidity of the chuck shaft, the precision of the tool rotation, and the difficulty of constructing the chuck shaft with a directly formed electrical rotor.

The object of the present invention is to overcome the aforesaid drawbacks and accordingly to develop an electric chuck with efficient dissipation of the heat from the motor and greater rigidity of the chuck shaft with a directly formed electrical rotor; these objects are achieved with the characteristics defined in Claim 1.

Advantageous developments of the device proposed by the present invention are described in the dependent claims.

The invention will now be described more fully with reference to the attached drawing which shows schematically a preferred practical embodiment, provided solely as a non-limiting example, since technical or constructional changes can be made at any time without departure from the scope of the present invention.

In the said drawing,

Figure 1 shows a longitudinal section through the said example of embodiment of the electric chuck of the invention.

Referring to Figure 1, this shows how the electric chuck 1 made according to the invention has a chuck shaft 2 which is supported by two radial pneumostatic bearings 3 and 4 and by an axial pneumostatic bearing 5 positioned centrally between the two radial bearings. The chuck shaft 2 receives the rotary motion from the motor 6 positioned at the side of the three pneumostatic bearings, and transmits it to the tool 7 which is fixed to the shaft, and which carries out the machining with chip removal.

The axial bearing 5 supports the shaft and also withstands the axial forces Fa in both directions acting on the tool during machining.

The radial bearings 3 and 4 support the shaft and also withstand the radial forces Fr over a range of 360 ° acting on the tool during machining.

The support is provided by a constant injection of precompressed fluid 8 which creates a thin film 9 between the rotating chuck shaft 2 and the pneumostatic bearings 3, 4, 5 fixed to the body of the electric chuck; the spent fluid is discharged from the electric chuck without re-use .

The central positioning of the axial bearing 5 enables the radial bearing 3 to be positioned very near the tool 7, and enables the radial bearing 4 to be positioned near the electric motor 6, thus improving the rigidity, vibration and precision of the shaft 2.

The motor 6, and more precisely the rotor 10, is positioned to the side of the bearings and can be formed separately in a simpler process and subsequently mounted so that it is fixed to the shaft 2. The phrase "positioned to the side" means that the rotor is located to the right or to the left of the set of bearings 3, 4 and 5 with which the electric chuck is provided, the reference direction for the definition of "right" and "left" being that of the axis of the shaft 2.

The use of an electric chuck according to the invention provides optimal operation while avoiding all the drawbacks encountered in the electric chucks known at present.