Principles and Properties of Various Applications

2 Principles and Properties of Various Applications Linear Actnators and Drivers 

Many linear actuators have been built [43-50]. For example, Etrema [43] has a wide range of products of different sizes, aU of which are adapted for quasi-static use. The 50/6MP, for instance, [43] is based on a 50 mm-long by 6mm-diameter Terfenol-D rod. It is biased with a field Ho of about 

The MAS type of driver is an interesting example, both from the results obtained and the modeling point of view. It has the smallest coupling factor, due to the series magnets that introduce magnetic reluctances, uncoupled 

The curve of the absolute maximum strain against the frequency of the unloaded MAS (Fig. 6.38) has been calculated and tested taking into account both the field limit and the stress limit at each frequency. It defines a law of current that depends on frequency. This new strain curve is above the classical curve of strain at constant current, based on the maximum current acceptable at resonance. It possesses a large pass band, which might be used in several applications such as active damping, low frequency projectors, etc. 

Following a principle used in piezoelectric ultrasonic motors [60], T. Aku-ta [61] has built the first magnetostrictive friction motor. This stator is made of pairs of orthogonal actuators excited with sinusoidal 90° phase-shift currents, which produce an elliptical vibration. The modeling of such magnetostrictive stators [42] has shown that in quasi-static operation a good elliptical motion is produced. It has also been shown that there are many coupled modes, but none of them provides a satisfactory elliptical motion. Therefore, unlike piezoelectric motors, this motor cannot operate at resonance. As a consequence and in relation to the previous analysis of power (Fig. 6.34), the efficiency is comparatively weak. Its other characteristics are a speed of 40°/s and a torque of 1.8 Nm [62]. 

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