Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-10-05
2004-03-02
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S254100, C310S268000, C310S156010
Reexamination Certificate
active
06700278
ABSTRACT:
DESCRIPTION
1. Field of the Invention
The invention relates to a disk motor with an armature disk (
3
), which is rotatably mounted and provided with permanent magnets, and with a stator comprising a stator plate which is equipped with coils.
2. Background of the Invention
Such disk motors are used as direct drives for turntables, for example. A basic explanation of disk motors can be found in H.-D. Stölting, A. Beisse, Elektrische Kleinmaschinen, Verlag Teubner, 1987, p. 169ff and p. 186ff.
DE 34 25 805 A1 discloses a DC motor realized as a disk motor to rotate a mirror. The stator comprises a coil-insulating frame and a stator flange connected thereto, which flange completely encloses the rotor and protects it from external influences. The rotor has a shaft which is attached to the mirror and which has on its lower end a magnet holder equipped with a two-pole permanent magnet. The rotor shaft ts punted in two ball bearings secured in the stator flange. To minimize axial play, the outer rings of the ball bearing must be prestressed against the associated inner rings. To achieve this, the citation teaches that the stator flange fixes both outer rings, which are arranged one above the other, whereas the associated inner rings are stressed in the opposite direction by the dimensions of the rotor. The disadvantage of this arrangement, however, is that there are two ball bearings arranged one above the other and separated by some distance. A single bearing is desirable to reduce the overall height.
To achieve high torques, disk motors are usually equipped with a soft-magnetic flux-return element, i.e. a closed magnetic circuit to increase the flux density in the air gap. The magnetic lines of electric flux are guided through ferromagnetic material with only small air gaps between the individual components. As explained in Stölting/Beisse, for example, this is realized by providing the circumference of the armature disk with an annular skirt, attached to which skirt is an annular flux-return element with which the flat coils of the stator are supported from underneath. The magnetic lines of electric flux run outward from the permanent magnets through the armature disk, down through the annular skirt and back to the permanent magnet through the annular flux-return element and the active region of the coil (cf. Stölting/Beisse, p. 186).
A disk motor of similar design is disclosed in German utility model DE-GM-75 419 11. The armature disk has at its center a bell-shaped spacer to which the annular flux-return element is fastened. The rotor housing is equipped with a bearing type in which two porous bearings and an intermediary felt ring for the storage of oil are arranged for the radial bearing of the rotor shaft. For axial bearing, the housing has a floor plate with a tube-like extension, on the lower edge of which is attached a supporting member for a thrust bearing for the rotor shaft. The bottom end face of the rotor shaft is crowned and rests on the thrust bearing. The overall height of this motor is significantly greater that that of the motor disclosed in DE 34 25 805 A1 because it has a total of three bearings.
Another variant of a disk motor with two ball bearings and a magnetic annular flux-return element is disclosed in DE 35 28 303 A1, which strives for a low overall height. The armature disk has a tube-like hub in which two ball bearings are arranged. The ball bearings are fixed at a defined distance to one another on a shaft stub attached to the stator plate. The function of the annular flux-return element is served by the stator plate, which must be manufactured of a suitable ferromagnetic material.
This disk motor has the following disadvantages: first there are two ball bearings with the associated additional assembly/installation costs; and second, the flux-return circuit does not run exclusively through the active region of the coils and thus does not contribute wholly to the generation of torque. Because the entire stator plate is involved in magnetic flux return, significant eddy currents are created which have a braking effect on the armature disk. Furthermore, attractive force is exerted on the armature disk in both the skirt region and the hub region, thus very large forces are exerted on the armature disk and in turn the bearings; significant bearing loads can result which under certain circumstances can lead to premature bearing failure. In addition, the entire bearing plate must be manufactured of ferromagnetic material and be of the same diameter as the armature disk. The motor is heavy as a result.
SUMMARY OF THE INVENTION
The object of the current invention is to provide a disk motor that is characterized by a flat design, good smoothness of running and high torque.
To achieve this object, the current invention teaches that an annular soft-magnetic prestressing device is arranged concentrically on the stator plate in such a manner that at least one section of the prestressing device is located below the coil window of the coils in the axial direction.
The advantage of the current invention lies in the fact that the magnetic prestressing eliminates the axial play of the armature disk bearing, so that an appropriate smoothness of running can also be achieved using only a single bearing, e.g. a ball bearing or a plain bearing. If a single bearing is sufficient, overall height is significantly reduced, yet there is still enough space for the bearing that commercially available ball bearings can be used.
If the disk motor is realized as a micromotor, commercially available bearings are understood to be those having an overall height of 1 mm or more. The advantage of commercially available bearings is that overall manufacturing costs are lower than if two custom bearings with extremely low overall heights must be used. The magnetic prestressing as taught by the current invention thus permits optimization of running characteristics with a lower overall height.
It has been demonstrated that providing the stator plate with a closed ring, or at least a ring segment, of a soft-magnetic, in particular a ferromagnetic, material is sufficient for the magnetic prestressing. The magnitude of the magnetic prestressing can be set via the width of the prestressing ring or ring segment with no change in the overall height, thus enabling adaptation to the geometry of the armature disk and the bearing used. This avoids unnecessarily large bearing loads, and thus can significantly extend the service life of the motor.
It is preferred that the radial width of the prestressing device be less than or equal to the corresponding width of the coil window.
By arranging at least one section of the prestressing device below the coil window of the coils in the axial direction, whereby the inner regions of the coil where the magnetic lines of electric flux run parallel to the coil axis are understood, the magnetic prestressing circuit also contributes to the generation of torque.
It is advantageous if the prestressing device includes a material with high ohmic resistance to prevent eddy currents.
Because the prestressing device is arranged on the stator plate, in particular on the top of the stator plate, there is no housing between the prestressing device and the coil window to adversely affect the magnetic field. The advantage of this is that the stator material can be freely chosen.
As taught by another embodiment, the armature disk can support an annular flux-return element which extends below the coils. In this case, the prestressing device is arranged as to be opposite the annular flux-return element in the radial direction. By locating the prestressing device below the coil window, the prestressing device becomes an element of the magnetic flux return and thus all of the magnetic lines of electric flux are used wholly for the generation of torque.
It is also advantageous that the prestressing device has a contour that guides the magnetic lines of electric flux from the annular flux-return element to the coil window.
The prestressing device preferably becomes wider in the direction
Ehrfeld Wolfgang
Kleen Stephan
Michel Frank
Nienhaus Matthias
Stölting Hans-Dieter
Hudak, Shunk & Farine Co. LPA
Institute fur Mikrotechnik Mainz GmbH
Mullins Burton
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