This study aims at developing a triple loop based sliding mode controller that defines a switching function. The controller is based on a triple loop controller that utilizes a vane type pneumatic motor servo drive to provide feedback on the state variables (position, velocity, acceleration) and feedforward at a desired position.
The benefit of the proposed method is the design flexibility of the controller, possessing superior capability in position tracking control when applied to systems with strong non-linearity (such as a position servo system adopting vane type pneumatic motor). Additionally, it uses only the required performance of the system control (settling time and percent over shoot) without a system model.
Simulations and experimental validation were performed to evaluate the performance of the proposed controller.
The results show that the robust control with the non-chattering phenomenon is achieved by converting the switching function into a triple loop controller in the boundary layer when the system enters the boundary layer introduced to the sliding mode design.
Experimental results obtained by applying the designed controller in the vane type pneumatic motor servo drive indicate that the maximum drive velocity of approximately 1500mm/s can be controlled to a steady state error within 0.2mm.
In addition, the controller facilitates precise and robust position control over various changes in the start position and the desired position. When the sinusoidal wave reference input had amplitude 400mm and frequency 0.2Hz, the trajectory of the target value varied by time resulted in the tracking error being within 1.5mm in 0.1 seconds.
The pneumatic motor servo drive incorporating the proposed controller would be a great alternative to electric and hydraulic servo motor drives in a wide range of industrial heavy duty applications that require high speed control accuracy (such as robotics and automation systems).
It is expected that the triple loop based sliding mode controller would be highly efficient for hydraulic servo systems that have significant non-linear characteristics.