Control Strategy of a Pneumatic Artificial Muscle for an Exoskeleton Application

Abstract

Numerous studies in the field of service robotics have been done. The use of wearable robots or exoskeletons has rapidly increased in the last decade, primarily focused on rehabilitation. Wearable robots use many type of actuators such as hydraulic, electric, pneumatic, among others; and different control strategies that determine its performance. This paper focuses on the design and experimental evaluation of a control strategy of a pneumatic artificial muscle (PAM) for an exoskeleton application. The main advantage of this actuator is its high strength to weight ratio, however it has a low control accuracy. An incremental adaptive Proportional-Integral-Derivative (PID) and a Proportional-Integral (PI) cascade controls were implemented in order to manipulate the degree of rotation of the joints of an exoskeleton limb and to overcome PAMs nonlinearity, hysteresis, and time varying characteristics. The relay experiment method was used to determine the PI and PID parameters in each working point.