Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-02-02
2001-04-17
Mullins, Burton (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S091000
Reexamination Certificate
active
06218751
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates to bearing devices with extremely low friction for the use for instance in Theological measuring devices and other sensitive instruments.
BACKGROUND OF THE INVENTION
In a known measuring instrument a movable instrument part is suspended by means of and between vertical tapes or strings with low torsion resistance and having low starting torque. The movable instrument part is to be influenced by the power, the effect or the like to be measured. The moving coil galvanometer is one example of such an instrument. Instrument parts suspended by tapes or strings may be used for instruments where the displaceable or rotatable part is influenced or biased without physical contact, i.e. without mechanical influence from another part. For purposes where the object to be tested or otherwise analysed is to be physically attached to the movable part or where an indicating device or the like is to be mechanically connected to a transmitter the known arrangements are hardly usable.
It has been suggested to use—for bearings where low friction and low starting torque is required—different types of magnetic bearings. DE 34 37 937 discloses a such device and more in detail a device for guiding and supporting rheological measuring systems. The intention was to bring about, in a simple way, a guiding and supporting arrangement with minimum friction and based on one stationary and one mobile magnet system with a soft iron part arranged with a vertical air gap.
Already in the 19th century however it was proved by a Mr. EARNSHAW that a devices like the one according to the DE publication is functionally impossible because of their inherent instability. It is physically impossible to achieve stability both axially and radially as is maintained in the DE publication. The device according to the DE publication not only has inferior lateral stability but is also unstable which means that it will collapse and loose its position either at the upper or the lower pair of magnets immediately.
To further clarify the state of the art and to define the invention over the state of the art, it must be mentioned that the invention is based primarily on passive magnet systems including permanent magnets only. Active magnet bearings include electromagnets shaped and arranged in a way very similar with the arrangement of a stator of a synchronous motor, whereas the armature or rotor normally is formed by a circular package of transformer sheet metal. The position of the rotor is read and checked by means of a number of distance sensors the signals from which via a quick acting boost control system optimises and distributes signals to each of the amplifier each controlling an electromagnet. In this way the rotor and shaft can be easily re-set and guided to its intended position. Annular magnet bearings, often called passive magnet bearings include annular shaped permanent magnets which attract alternatively repel each other in such a way that stability is achieved in one desired direction only, radially or axially. In the other direction, however, the bearing will always be unstable, a fact which was proven more than a hundred years ago. If ever utilized, this type of bearings always is used together with an auxiliary bearing such as an active magneto bearing.
ASPECTS ON THE INVENTION
One purpose with the invention is to bring about, by utilising a passive magnet system having a minimum of frictional resistance, an axially and radially stable bearing device especially but not exclusively for instruments of rheometer type.
SUMMARY OF THE INVENTION
The invention is a bearing device for passively supporting one part movable relatively to another part by means of magnets, preferably permanent magnets in order to bring about a stable essentially friction free measuring of a torque in a range where conventional bearing systems of the instrument ball bearing type or the like have too high a friction and too high a starting torque and the characterising features of the invention lies in that at one part and at another part, the one part rotatable relatively to the other part at least part of a revolution, pairs of magnet units arranged in a repulsion or attraction state are positioned regarding their fields of force in such a way that force components hold the rotatable part in a predetermined radial position and bias the rotatable part in an axial direction and in that at least one mechanical, essentially stable positioning means is connected between the one part and the other part and acting along the axis of rotation for counterbalancing the force biasing the one part in the one axial direction.
REFERENCES:
patent: 2305416 (1942-12-01), Hansen
patent: 2747944 (1956-05-01), Baermann
patent: 3114582 (1963-12-01), Milligan
patent: 3614181 (1971-10-01), Meeks
patent: 3761148 (1973-09-01), Grosbard
patent: 4328701 (1982-05-01), Mau-Tung et al.
patent: 5506459 (1996-04-01), Ritts
patent: 3437937 A1 (1985-08-01), None
patent: 3837845 A1 (1990-05-01), None
patent: WO 9429692 A1 (1994-12-01), None
Patent Abstracts of Japan, 7:202, JP 58-99727 A (Iwamoto Seisakusho K.K.), Jun. 14, 1983.
Derwent's Abstract, 89-322952/44, Abstract Of Su, 1455282 (Tomsk Univ. Appl. Mat), Jan. 30, 1989.
Bacon & Thomas
Global Hemostasis Institute MGR
Mullins Burton
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