Modelling and control of a twin rotor multi-input multi-output system

A dynamic model for the characterisation of a one-degree-of-freedom (DOF) twin rotor MIMO system (TRMS) in hover is extracted using a black-box system identification technique. Its behaviour in certain aspects resembles that of a helicopter, with a significant cross-coupling between longitudinal and lateral directional motions. Hence, it is an interesting identification and control problem. Identification for a 1 DOF rigid-body, discrete-time linear model is presented in detail. The extracted model is employed for designing and implementing a feedforward/open-loop control. Open-loop control is often the preliminary step for development of more complex feedback control laws. Hence, the paper also investigates open-loop control strategies using shaped command inputs for resonance suppression in the TRMS. Digital low-pass and band-stop (Butterworth) shaped inputs are used on the TRMS testbed, based on the identified vibrational modes. A comparative performance study is carried out and the results presented. The low-pass filter is shown to exhibit better vibration reduction.