Energy-to-Mass Ratio—A Novel Selection Criterion of Pneumatic Motors Used for the Actuation of Wearable Assistive Devices

Abstract

The requirements to be met by a wearable assistive device are compactness, lightweight and energy efficiency. While the literature discusses the construction and performance of such devices, no information is provided as to the criteria to be applied in selecting such an actuator, capable of satisfying the mentioned conditions. Ensuring the high autonomy of a wearable assistive device requires actuators that can store a large quantity of energy in a small as possible volume, for example, actuators with a high energy density. This paper presents a comparative study of the performance of two types of pneumatic actuators: single-acting cylinders and pneumatic muscles, respectively, and offers information that will enable users to select an optimum solution. The quality indicators considered in conducting the comparative study are size, mass, the developed force and the energy-to-mass ratio. A method is proposed to determine the energy developed by the motors over the entire stroke; based on that, the energy-to-mass ratio is subsequently calculated. This indicator is a valuable tool made available to designers of wearable assistive devices. The conclusion yielded by the study asserts that while pneumatic muscles have larger radial and axial dimensions, they present benefits as to the developed forces and the energy-to-mass ratios.