Dynamic characteristics of the SMH actuator using hydrogen-absorbing alloys

Abstract

The dynamic characteristics of the special metal hydride(SMH) actuator using hydrogen absorbing alloys has been studied through the experiments on the characteristics of the temperature-pressure relation using a Peltier module. The SMH actuator uses the reversible reactions between thermal energy and mechanical energy inside hydrogen-absorbing alloys. It is well known that hydrogen-absorbing alloys can reversely absorb and desorb a large volume of hydrogen gas, more than about 1000 times of their own volume. By using Peltier element, we can actively control the energy conversion through hydrogen-absorbing alloys through hydriding and dehydriding reactions. Heating hydrogen-absorbing alloys using Peltier element will increase the equilibrium pressure of hydrogen gas resulting in the desorption of hydrogen gas by the alloys. Whereas, by cooling the alloys, the equilibrium pressure of hydrogen gas will decrease and hydrogen gas will be absorbed. In the present study, a simple special metal hydride (SMH) actuator, consisting of plated hydrogen-absorbing alloys as a power source, Peltier elements as a heat source, and a cylinder with metal bellows as a mechanical functioning part, has been developed. An electro-less copper plating has been used to improve the thermal conductivity of the hydrogen-absorbing alloys. To study the effects of the electro-less copper plating and the dynamic characteristics of the newly developed SMH actuator, a series of experiments has been performed and analyzed. The experiment demonstrated that the SMH actuator, which contains only 14.5 g of hydrogen-absorbing alloys, was able to easily lift 40 kg of weight with the displacement of 35 mm. The displacement of the cylinder was controlled in the periodic movement. The developed SMH actuator has merits in its small size, light weight, noiseless operation, and compliances similar to those of human bodies. Therefore, the SMH actuator is suitable for uses in medical and rehabilitation applications.