Electricity: magnetically operated switches – magnets – and electr – Electromagnetically actuated switches – Radio frequency switch
Patent
1995-12-08
1997-12-02
Donovan, Lincoln
Electricity: magnetically operated switches, magnets, and electr
Electromagnetically actuated switches
Radio frequency switch
333235, 333 241, 310 26, H01H 5300
Patent
active
056940971
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a force and/or motion generating arrangement, comprising a body of magnetostrictive material, which may be utilized for applying a force on and/or imparting a motion to another object, and means for feeding a magnetic flux through said body in order to cause an elastic deformation thereof.
In practice, such arrangements are utilized for various different purposes. For instance, they are utilized as clamping arrangements or striking arrangements in which the magnetostrictive body may be caused to generate clamping forces or impact forces, respectively. Moreover, they are also used as micropositioning arrangements, in which case the magnetostrictive body is connected to a movable object to set the position of said object. Additionally, they are utilized as vibrating arrangements in which the magnetostrictive body serves to impart a vibrating motion to an object connected thereto. However, there exist also many other applications in addition to those above mentioned.
In the prior art, said body of magnetostrictive material has usually been formed as an elongate straight rod. Further, said means for feeding a magnetic flux through said body have usually been formed by an electric winding, consisting of a coil, which has been mounted on the rod extending round the same and which has been capable of generating a magnetic flux passing through the rod in the longitudinal direction thereof.
Due to the high reluctance of the closed path for the magnetic flux formed by the rod and the long air gap between the two ends of the rod, a comparatively high ampere-turn is required to generate a sufficiently high magnetic flux through the rod. This means that a relatively high current has to be fed through the coil and that the number of winding turns of the coil has to be comparatively large which, in its turn, results in that, during operation, the coil will be significantly heated. As a consequence of the high thermal coupling between the coil and the rod, said heating of the coil results in a significant heating of the rod as well, which will hereby experience a considerable thermally induced change in its length. This thermal change in the length of the rod often causes severe problems, which are especially troublesome in connection with an intermittent operation as any temperature balance will then never be reached. Apart from the problems occurring as a consequence of the thermally induced change in the length of the rod, the heating of the rod also causes additional problems following from the fact that the magnetostrictive properties of the rod are dependent on the temperature.
In order to overcome the above problems at least to some degree, in some cases, the coil has been provided with means for water-cooling the same. However, such a water-cooling involves considerable costs while simultaneously offering large practical difficulties, especially if the available space is restricted or if the arrangement in question should be movable. Naturally, as an alternative to a water-cooling of the coil, it is conceivable to utilize a direct water-cooling of the rod by feeding cooling water through one or more passages provided therein. However, in this case, apart from substantially the same disadvantages as in the case of water-cooling the coil, disadvantages will also occur as a consequence of the fact that the material in the rod may be corrodible and have a tendency to hydrogen embrittleness.
In GB-A 874 659, which not even hints at the problem above discussed, there is disclosed an arrangement which however may be said to represent a better solution of the problem of obtaining a reduction in the heating of an elongate body of magnetostrictive material which may be elastically deformed by feeding a magnetic flux therethrough. Said patent specification discloses an ultrasound generator in which a U-shaped yoke of soft magnetic material is utilized to feed a magnetic flux, produced by means of a winding mounted on said yoke, in the longitudinal direction through a body of magnetostrictive
REFERENCES:
patent: 4651116 (1987-03-01), Schloemann
patent: 5070316 (1991-12-01), Engdahl et al.
Donovan Lincoln
Oenico AB
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