Electricity: magnetically operated switches – magnets – and electr – Magnets and electromagnets – Magnetostrictive-type device
Patent
1993-04-07
1995-05-09
Picard, Leo P.
Electricity: magnetically operated switches, magnets, and electr
Magnets and electromagnets
Magnetostrictive-type device
310 26, 73668, 73576, 367168, 367156, 381190, H01F 700, H01L 4106, G01N 2900, G01H 100
Patent
active
054143977
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an elastic clamping device for use in linear motors and actuators where a pressure means presses the clamping device with a predetermined force against a body having magnetostrictive properties located on the inside.
Magnetostrictive bodies change their geometry under the influence of a magnetic field. A rod, for example, becomes thinner and longer. Such rod may be used as an advancing element. In the art of linear motors or actuators using magnetostrictive bodies, various mechanisms and methods have been employed to utilize the change in the geometry of such bodies under the influence of a magnetic field. In patent application SE 8700219-2, dated Jan. 21, 1987 (PCT/SE88/00010, dated Jan. 19, 1988), a linear motor is described in which a magnetostrictive rod is kept within a stator tube surrounding it with a press fit. The amount of the press fit, which is dependent on the tolerance between the rod and stator tube, determines the frictional force between the inner surface of the stator tube and the outer surface of the magnetostrictive rod, and consequently, determines the output force of the linear motor. The rod moves within the tube in a worm-like manner by being exposed to a magnetic field travelling in the longitudinal direction. The rod expands longitudinally and contracts radially in the respective region influenced by the magnetic field causing the rod to be released from the pressure of the stator tube and performing a step-like motion in the longitudinal direction. Magnetostrictive rods are also described with several short sections in series.
A prestress, beyond the provision or secure clamping, has other effects. It does not only eliminate the influence of mechanical hysteresis in the direction of expansion of the magnetostrictive body referred to on page 3, lines 20 pp in the above cited SE-patent application. It also causes a reorientation of the grains of the magnetostrictive material and leads to an enhancement of the longitudinal expansion and consequently, the radial contraction. The amount of the prestress influences the extent of this effect within certain limits. A prestress in the direction of contraction enhances this effect. Therefore, it is very important to keep the prestress within the predetermined limit so as to achieve the desired performance of the linear motor.
Various problems are inherent in the latter linear motor. Even if the motion in the longitudinal direction of such a rod substantially takes place only after the magnetostrictive rod is released from the inner surface of the stator tube wear and tear still occurs. This leads to a change in the dimensions of both the rod and stator tube and thus a pressure exerted by the stator tube onto the rod and the radial prestress in the magnetostrictive rod. In the extreme this wear can lead to such a change in the diameter conditions that the stator tube no longer securely clamps the non-contracted portion of the magnetostrictive rod and thus the basis for a defined advancement of the rod relative to the stator tube is lost. Since the predetermined radial pressure is unadjustable, then it is not possible in this actuator to compensate for wear or any change in load. Also, the only way to adjust the predetermined radial pressure is to change the tolerance between the stator tube and the rod which is very difficult. Furthermore, in the same linear motor, both the magnetostrictive body and the stator tube have to be machined to narrow tolerances, so as to generate the desired press fit. This makes the fabrication of the two bodies complicated and expensive and the linear motor becomes very sensitive to wear between the two bodies.
Therefore, the object of this invention consists in developing a method or respectively an elastic clamping device for at least one body with magnetostrictive properties facilitating release of the contracting body, causing a prestress therein in the direction of the contraction and making this predetermined pressure causing this prestress, adjustable.
SUMMARY OF THE INVENTION
REFERENCES:
patent: 1750124 (1930-03-01), Pierce
patent: 1882400 (1932-10-01), Pierce
patent: 2506141 (1950-05-01), Drouin
patent: 2843974 (1958-07-01), Butterworth
patent: 4432080 (1984-02-01), Wardle
patent: 5020036 (1991-05-01), Petermann
patent: 5039894 (1991-08-01), Teter
patent: 5281875 (1994-01-01), Kiesewetter
patent: 5317223 (1994-05-01), Kiesewetter
"The AIL Inchworm Motor", Airborne Instruments Laboratory, Advertisement, Proceedings of the IRE, Aug. 1957.
Dynamotive Corp.
Picard Leo P.
Ryan Stephen T.
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