Robot actuation using air motors

Air motors, having inherently low cost, good pot-ver to weight ratio and intrinsically safe operation, can be utilised to control industrial robots. This paper describes the research carried out on the characterisation and control of a pneumatic system to provide actuation for a three-degrees-of-freedom (3DOF) robot. The actuator which is used as a drive is a mechanically robust piston air motor constructed of aluminium, utilising a proportional spool valve to allow air-flow control. The dynamics of the air motor in conjunction with a solenoid valve have been experimentally determined using a single-degree-of-freedom robot system. A microprocessor, combined with a position sensor and a sensitive proportional valve allows the pneumatic robot system to be controlled. Numerous control strategies have been proposed recently to control a 3DOF revolute robot arm. As such systems are nonlinear and result in coupled equations of motion it has been found necessary to employ advanced adaptive control theory to achieve satisfactory control. These approaches involve considerable on-line computation which can restrict the applicability of the control algorithm and requires the use of high powered (and expensive) computers. Four adaptive strategies have been extended to a 3DOF robot system and compared to a relatively simple modified PID approach which is not computationally intensive. From simulations the performance of the modified PID approach was found to be almost as good as the adaptive strategies considered.