Magnetostrictive actuator

Details Magnetostrictive actuator Magnetostrictive actuator

1997-09-12

1998-12-15

Dougherty, Thomas

Electrical generator or motor structure

Dynamoelectric

Reciprocating

H01L 4112

Patent

active

058501096

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The spontaneous length and shape change of magnetic substances in an external magnetic field which varies the magnetization direction is called magnetostriction. This effect is used in particular in so-called actuators, in order to convert electrical or magnetic energy into mechanical energy (see, for example, Janocha; Aktoren, Grundlagen and Anwendugan (Actuators, principles and applications), Springer Press (1992), pages 278-293. The magnetostrictive effect often depends in a complicated manner on the magnetization direction, but not on its mathematical sign. Magnetostrictive materials expand only to a comparatively small extent in the magnetic field. Relative length changes in the range from .DELTA.1/1.apprxeq.10.sup.-5 to 10.sup.-6 are thus observed in alloys having the components iron, nickel or cobalt. The magnetostrictive effect is considerably more evident in rare-earth metal/iron alloys, where values of up to .DELTA.1/1.apprxeq.3.multidot.10.sup.-3 are formed.
The material Tb.sub.x Dy.sub.1-x Fe.sub.2 (TERFENOL-D: x=0.3), which was developed in the United States at the start of the 1960s and is known by the trade name TERFENOL, achieved particular importance in the production of magnetostrictive actuators. Miniaturized drive elements can be developed on the basis of this material, which is characterized by the parameters quoted below (the corresponding values for PXE 52 piczo-ceramic arc quoted in brackets),


______________________________________ Relative change length .DELTA.l/l 2-3 (.ltoreq.1.5) 10.sup.-3 Energy density E.sub.v 14 . . . 25 (1) 10.sup.3 Ws/m.sup.3 Compression strength T.sub.t 700 (>600) N/mm.sup.2 Tensile strength T.sub.p 28 (.apprxeq.80) N/mm.sup.2 Thermal conductivity .lambda. 110 (1,2) W/mK Resistivity .rho..sub.el 0,6 10.sup.-6 .OMEGA.m Curie-Temperature .delta..sub.C 380 (165) .degree.C. Density .rho. 9,25 (7,8) kg/m.sup.3 ______________________________________ actuators for comparable mechanical characteristics and actuation travels.
The head of the ink jet printer which is known from U.S. Pat. No. 4,032,929, said head being opposite a roll which is covered with paper, has a multiplicity of nozzles which are arranged in a line and each of which is connected to a chamber and a reservoir for the printing medium. The nozzle plate, the reservoir and two membranes which are separated from one another by spacers form the chamber walls. The membranes are of layered construction, the outer layers each being composed of nickel, and the layers on the chamber side being composed, for example, of an Fe--Co--Ni alloy. Since these materials expand to a greatly different extent in an external magnetic field, the volume of the chambers can be varied individually by passing current through appropriately positioned conductor elements. Metallizations are used as conductor elements which are composed of copper, are sheathed in an electrical insulator and are arranged on the outer and chamber-side membrane surfaces.
A thin magnctostrictive film which is arranged on a bending element forms the active component of the electromechanical transducer which is known from German reference DE 42 20 226 A1. The external magnetic field which causes the magnetostriction is produced by a conventional air-cored coil or a conductor track system which is produced using thick-film technology. In order to reinforce the magnetic field in the region of the magnetostrictive material, the thin film is sheathed with a soft-magnetic material (Fe--Ni alloy).
U.S. Pat. No. 4,757,219 describes a magnetostrictive actuator which is of laminar construction and whose layers, which are each only about 80 .mu.m thick, are composed of an amorphous alloy containing iron.
With regard to compactness and response times, the magnetostrictive drive elements, which produce comparatively large actuation forces and are equipped with conventional coils, are considerably inferior to correspondingly designed piezo-actuators. For example, the response time of pie

REFERENCES:
patent: 3379905 (1968-04-01), Janssen
patent: 3612924 (1971-10-01), Semmelink
patent: 3701983 (1972-10-01), Franklin et al.
patent: 3783505 (1974-01-01), Schoen
patent: 4032929 (1977-06-01), Fischbeck et al.
patent: 4757219 (1988-07-01), Yamauchi et al.
patent: 5313834 (1994-05-01), Lagace
patent: 5595830 (1997-01-01), Daughton
Hartmut Janocha, Aktoren, Grundlagen und Anwendungen, Springer Verlag (1992) pp. 278-293.

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