On Comparison of Neural Observers for Twin Rotor MIMO System

This paper presents a comparative study of neural observers for TRMS. These are Chebyshev neural network based observer (CNN) and Multi-layer feedforward neural network (MLFFNN) observer. TRMS is a highly non-linear system having mutual interference between two rotors, it is trivial to design an effective controller for the TRMS to reach the desirable yaw and pitch angles. All the states are not available for the measurement, so to estimate the inaccessible states of TRMS these non-linear state observers are designed. On Comparing Performance MLFFNN found to be better than CNN observer. KeywordsTwin rotor multi input multi output system (TRMS), Chebyshev neural network (CNN) and Multi-layer feed-forward neural network (MLFFNN), Degree of freedom (DOF). Introduction Many real physical systems are nonlinear in nature. Controlling nonlinear systems is a difficult problem due to their complex nature. This problem becomes more acute when the system’s parameters are uncertain. Uncertainty affects decision-making and appears in a number of different forms. It is an inherent part of real world systems and the observers designed for such uncertain systems are required to act in an appropriate manner and eliminate the effect of imprecise information. Model description TRMS is a laboratory prototype of a flight control system. It is a multi-input-multioutput (MIMO) nonlinear system, with substantial cross coupling between main rotor and tail rotor with degrees of freedom on the pitch and yaw angle denoted by ψ and φ 988 Shobhit kumar and Smriti Srivastava respectively. The main rotor produces a lifting force allowing the beam to rise vertically (pitch angle), while the tail rotor is used to control the beam to turn left or right (yaw angle). Both motors produce aerodynamic forces through the blades. The mechanical and electrical units provide a complete control system setup. The TRMS mechanical unit consists of two rotors which are perpendicular to each other and joined by a beam pivoted on its base, so that it can rotate freely in both horizontal and vertical planes. To make the TRMS stabilized a counterbalance arm with a weight at its end is fixed to the beam at the pivot. At both ends of the beam there are rotors driven by two independent similar DC motors and the angular velocities of the rotors is measured by Tacho generators, attached with the DC motors. TRMS can work with both 1-DOF and 2-DOF using nylon screws. The whole unit is attached to the tower allowing for safe helicopter control experiments. Another important unit is the electrical unit (placed under the tower) plays a vital role for TRMS control which allows the measured signals to be transferred to the PC and control signals to be applied to the system via a PCI-1711 I/O card. The working principle of TRMS is similar to a helicopter with two degrees of freedom (2-DOF) Modelling of trms The complete dynamics of the TRMS system can be represented in the statespace form as follows: