A Facility For Evaluation of Actuators Based on Giant Magnetostrictive Materials
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"**Dept. of Power
Engineering, ABB Corporate Research, 721 78 Vasterhs, Sweden
ABSTRACT The recent development of actuators based on giant magnetostrictive materials in for instance hydroacoustic transducers has caused an increase in output forces from the drive elements used. The high stress levels make testing of the actuators with well defined mechanical loads difficult. The need for standards and improved evaluation methods has therefore become evident. Based on experiences from earlier test facilities a new set-up has been designed with the intention to obtain - higher resonance frequency - facilitated assembly of test objects - increased operating forces - flexible choice of mechanical loads - computer controlled measurement procedure - controllable environmental conditions, for instance temperature. In order to achieve the specifications, the test rig involves hydraulics for prestressing and clamping of the test object and the mechanical load. A method of mechanically disconnecting the prestress device from the fixture gives lower mass to stiffness ratio in the fixture and therefore a better high frequency performance. The presented test rig is considered to have the prerequisites of serving as a platform for future evaluation and standardization of actuators.
BACKGROUND In [1] is reported some deficiencies of an earlier test rig made for magnetostrictive rods with diameters of 6 mm. With the increased power levels that follow from rods with diameters up to 30 mm, these imperfections give strains in the fixture that exceed the magnetostrictive displacements in the test object. Therefore great efforts have been made on the design of a new stiffer construction that also facilitates mounting and allows higher prestressing. BASIC DEMANDS The test rig should provide an environment where actuators can be tested under well known mechanical and other conditions, e.g. temperature. One demand of the evaluation facility is that a physical window with a fully controllable and continuously variable height is provided for the actuators with their mechanical loads. It should also be possible to clamp the actuator at an arbitrary stress level. During measurements this window should keep a fixed length. To prevent possible movements of the 273 Mat. Res. Soc. Symp. Proc. Vol. 360 01995 Materials Research Society
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Figure 1: Schematic drawing of the test rig (a) and the desired mechanical equivalent (b). actuator from influencing the loading conditions it should be fixed to a back mass. The maximum width of the test object should be 200 mm and the height of the test window should be continuously adjustable from 500 mm down to 25 mm where it should be possible to apply a compressible force of up to 70 kN. The total strain of the fixture when an actuator is stressed with 70 kN should be less than 5 % of the strain of the test object. To obtain this it is important to ensure that no part of the rig moves in r
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