Temperature-pressure characteristics of SMH actuator system using hydrogen-absorbing alloys

This paper presents the temperature-pressure characteristics of a newly developed SMH actuator using hydrogenabsorbing alloys. The new special metal hydride(SMH) actuator is characterized by its small size, low weight, noiseless operation, and compliance similar to that of human bodies. The simple SMH actuator, consisting of plated hydrogenabsorbing alloys as a power source, Peltier modules as a thermal source, and a cylinder with metal bellows as a mechanical functioning part, has been developed. An assembly of copper pipes has been constructed to improve the thermal conductivity of the hydrogen-absorbing alloys. It is well known that hydrogen-absorbing alloys can reversibly absorb and desorb a large amount of hydrogen, more than about one thousand times of their own volume. By heating the hydrogen-absorbing alloys, the hydrogen equilibrium pressure increases due to desorption of hydrogen, whereas, by cooling the alloys, the hydrogen equilibrium pressure drops due to absorption of hydrogen by the alloys. The new SMH actuator utilizes the reversible reaction between the thermal energy and mechanical energy of the hydrogen absorbing alloys. To be able to use the SMH actuator in medical and rehabilitation applications, the desirable characteristics of the actuator have been studied. For this purpose, the detailed characteristics of the new SMH actuator for different temperature, pressure, and external loads were explored.