Control System Development for Pneumatic Artificial Muscle Driven Active Rotor Systems

An active trailing edge flap system for helicopter rotor blades is under development in this study. The system uses Pneumatic Artificial Muscles (PAMs) as the driving actuation technology and is intended to generate flap deflections suitable for both vibration mitigation and primary control of the helicopter. Previous work has shown the ability of these actuators to develop large flap deflections under full-scale loading over a wide range of operating frequencies. The current work aims to develop a feedback control system that will allow the actuation system to track the complex waveforms required for vibration reduction and primary control. Tracking of single frequency sine waves over a range of frequencies was used to develop the control algorithm. Initially, proportional control alone was implemented with a commercially available pneumatic spool valve using output feedback from an angle sensor and provided good tracking at low frequency, though phase lag increased with frequency. The addition of a fixed dead-time compensator (FDTC) significantly reduced the tracking error and increased closed-loop bandwidth by compensating for the lag time between controller commands and the system response. For further improvement, a variable dead-time compensator (VDTC) to cope with changes in the system dead-time due to changing operating conditions was introduced in this study. Testing of this controller on single sine waves and with several complex waveforms composed of representative 1/rev, 3/rev, 4/rev and 5/rev components shows good magnitude and phase tracking over a wide range of loading conditions, with relatively low error.