Optimization of Semi-Active Pneumatic Actuators for an Exoskeleton Robot for Running

Abstract

In running motion, human legs are often represented by a spring loaded inverted pendulum (SLIP) model. Therefore, an exoskeleton robot that helps human to run needs spring-like mechanisms. Semi-active pneumatic actuators can achieve spring-like behavior during stance by closing of an electronic solenoid valve and almost no resistive force during swing by opening the valve. In this paper, the mounting position and initial pneumatic pressure of the pneumatic actuators are optimized. In the process of optimization, simulations are conducted on one-leg hopping motion for effectiveness of pneumatic actuators instead of a more complicated running motion. To optimize pneumatic actuators, the mounting position and initial pressure are set as design variables. And the average energy consumption rate calculated from the humans joint power during the hopping motion is selected as the cost function. The constraints includes the pneumatic actuators mountable range, maximum cylinder length, minimum cylinder length, and the maximum permissible internal pressure. As a result, the energy consumption rate is reduced by 13.0%, 4.5%, and 31.8% when the actuators are used only for knee, ankle, and both, respectively, compared to the case without pneumatic actuators.