Metal hydride alloys can compactly store larger amounts of hydrogen than that possible when hydrogen is stored in a liquid state. These alloys alter the equilibrium pressure of hydrogen by changing its temperature. We developed novel actuation devices, called metal hydride (MH) actuators, and we adopted these MH alloys as thermally controllable pressure generators. The MH actuators provide several unique properties, including a high power-to-weight ratio, softness, noiselessness, and eco-friendliness, that are different from other conventional actuators, such as electric motors, pneumatic actuators, and hydraulic actuators. The purpose of this research is threefold: First, we provide an overview of the properties of MH alloys for human-friendly actuators. Second, we describe the basic structure and characteristics of the MH actuators and their applications to wheelchairs with seat lifters, transfer equipment for toilets, continuous passive motion machines for joint rehabilitation, and portable rescue tools for disaster prevention and preparedness. Finally, we discuss designs to further improve the MH actuators in the future to obtain more suitable devices for assistive technologies and disaster rescue operations.
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