ELECTRIC MACHINE PROVIDED WITH MAGNETIC MEANS FORMING A STAGE

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Electric machine provided with magnetic means forming a bearing.

The invention relates to an electric machine comprising

-a chassis which is secured to a stator,

-a rotor shaft on which is fixed a rotor electromagnetically cooperating with the stator, and

-a bearing for supporting the rotor shaft and having a pivot bearing can Ôtre screwed into the frame, the bearing comprising first and second magnetic means which cooperate with each other to apply a bearing portion, participating in the rotation of the rotor shaft, against a bearing surface of the bearing, the jacket surrounding the first means while the rotor shaft is provided with the second magnetic means.

As a form of an electric motor, such a machine is known to the Japanese document Kokai no. 57-1 603k6 . In this known engine, the rotor shaft is supported by ball-bearings, while one end of the rotor shaft is applied against one face bearing a pivot bearing. The force effecting the application is provided by a magnetic force which is active between a first annular permanent magnet which is secured to the rotor shaft and a second annular permanent magnet that supports the

centreplate.

A disadvantage of said known engine is that following to the use of two magnets, a relatively expensive construction is used for creating said force application. Further in addition, it is that the magnets are annular, which pointed of the manufacturing process, has the disadvantage that the said magnet is difficult. It is especially and when the magnets are made of magnetic material of high value, for example, a compound of samarium-cobalt.

Or, the purpose of the invention is to provide an electric machine which belongs to the genus referred to in the preamble but is not affected by said disadvantages, while however the use of simple means and inexpensive the machine is thus for its support the rotor shaft axially, very stable and reproducible.

To this end, the electrical machine according to the invention is characterized in that the first magnetic means is in the form of a bearing member carrying the bearing face. In this way, the rotor shaft has a support bearing very efficient and compact because a portion of the bearing, in other words a portion already provided in particular said bearing member, is used as first magnetic means.

In the electric machine responsive to the invention, the first and second magnetic means are separated by an invariable distance that is independent of the position that the rotor in relative to the frame.

When as a result of a screwing movement, the bearing is moved relative to the frame thereby axially displace the rotor shaft to accurately position relative to a reference face, the attachment force with which the bearing part of the rotor shaft is applied to the bearing surface of the axial bearing does not vary.

By measuring provided by the invention, a simple and inexpensive method, it is possible to make in a reproducible manner any desired application force for the rotor shaft.

A preferred embodiment wherein the second magnetic means is a ring secured to the rotor shaft, has the feature that the first magnetic means is a permanent magnet axial magnetization, while said second magnetic means is made of ferromagnetic material.

Another preferred embodiment according to which the magnetic bearing is used in an optimum fashion, is characterized in that the rotor shaft is of ferromagnetic material,

" For cost considerations, there is an advantage that the bearing is obtained by soft-r lage by injecting a synthetic material, during which the bearing element is surrounded completely of the plastic, The pivot bearing formed thereby has the further advantage that that the bearing element is anchored securely.

The following description, facing the accompanying single drawing, all example, will well understand how the invention may be implemented.

The figure unique drawing shows by a cross section one embodiment. the electrical machine according to the invention.

On said figure, the reference 1 indicates a DC motor and brushless, the engine is used in an optical disk not shown, such as a disk drive portable "Compact Disc", said motor to drive the turntable 3^of the apparatus. The motor 1 comprises a frame 5 with a stator 7 which is provided with a laminated assembly 7a and coils Tjo.

In the chassis 5, it is fixed by suitable interference fit a bearing sleeve 9 which is provided with a journal bearing 9a. In said frame 5, it is further provided a ball bearing 11. The journal bearing 9, a and the ball bearing 11 are provided for support in the radial direction by a, rotor shaft 15 rotatable about an axis of rotation 13" on the rotor shaft 15, the tray-rotating 3 foregoing, as well as a cylindrical rotor 17 are fixed for participate in the movement of the shaft 15;

in this embodiment, the rotor 17 is attached to said shaft 15 via the tray-rotating 3 · Against its inner face, the rotor 17 is provided with a cylindrical permanent magnet rotor 17a, with radial magnetisation.

Axially To support the rotor shaft 15, it is used a pivot bearing 19 which encloses an element of b

bearing 19a and is the result of a injection-moulding a wear-resistant synthetic, e.g. nylon with molybdenum sulphide. The bearing element 19a which together with a ferromagnetic plate 19aa is surrounded by plastic, door, to^its side facing the rotor shaft 15, a thin layer of plastic with a bearing surface 19b which cooperates with a bearing surface 15a at one end 15b of the rotor shaft 15 · The pivot bearing 19 is provided with a external thread and can be screwed into a cylindrical portion 5a of the metal frame 5, provided with an internal thread.

The rotor shaft 15 is applied against the pivot bearing 19 under the influence of a force of magnetic application. The force acts between the bearing element 19a, which is embodied as a permanent magnet axially magnetized, and a ferromagnetic ring 23 clamped upon the end 15b of the rotor shaft 15. As the magnet material, it is used, for example, magnetic materials of high value, for example, a compound of samarium-cobalt. The magnitude of said force application can be set according to the purpose for which the engine 1 is used. The desired magnitude can be achieved by a suitable dimensioning and the choice of the material of the bearing element 19a and of the ring 23, and by the proper choice of the axial distance d between these components 19a and 23.

The figure which allows to clearly that the axial distance d selected between the bearing member 19a and the ring 23, does not vary during axial displacement of the pivot bearing 19 as a result of rotating the boom relative to the chassis 5 · This therefore means that during the positioning of the rotor shaft 15 with its disks 3 with respect to a reference plane of the frame 5 not shown, the force of application, predetermined, with which the rotor shaft 15 acts on the bearing, does not change.

At frame 5" it sst further provided a plate 25 carrying a printed pattern with electronic components involved in the electrical switch and in the set of the operation of the engine. There is plugs 27 which pass through said platinum and 25 which are electrically fixed to the printed pattern and 7b to the coils.

Naturally the invention is in no way limited to the single example of the present disclosure. Therefore, instead of being designed as a motor, the electrical machine is also feasible as dynamo.