DEVELOPMENT OF A HYBRID PNEUMATIC-ELECTRIC ACTUATOR

Abstract

This thesis presents the development of a novel hybrid pneumatic-electric actuator which combines the advantages of both pneumatic and electrical actuator. The hybrid actuator consists of a pneumatic cylinder and a DC motor. They are connected in parallel using gears. The components are sized to provide the torque required to rotate a single-link robot arm vertically upwards. On/off solenoid valves are used rather than servo valves to keep the hardware cost low. A mathematical model of the nonlinear actuator dynamics is derived using a combination of physical laws and empirical curve fitting. The dynamics of the mechanical, electrical and pneumatic elements are included. Then a novel discrete-valued model-predictive control plus integral compensator algorithm is created for controlling the position of the pneumatic cylinder using the on/off valves. The control algorithm for the hybrid actuator is completed by using a conventional PD algorithm to control the electric motor. Experiments shows the hybrid actuator outperform pneumatic actuator in every aspect. Conversely, the DC motor added a faster acting and finer quantized force to the pneumatic cylinder force, which greatly improved the dynamic position control performance of the hybrid actuator. In experiments, the mean root-mean-square error and the maximum absolute error improved by 84% and 77%, respectively.