Pre-filter design for exact linearization-based tracking controllers for variable-load systems

Abstract

Several classes of weight handling equipment with nonlinear dynamics are exact linearizable by feedback. This implies that a controller ensuring exponential decay of the tracking error along a reference trajectory can be also designed. The control of both fully actuated robotic arms and underactuated crane-like systems can be addressed through this method. However, the value of model parameters such as the mass of the load or the friction coefficients must be known to calculate the actuated inputs in closed-loop. Uncertainty of these parameters may result in unstable closed-loop dynamics or in the deterioration of the tracking performance. This paper presents a design procedure to take into consideration such uncertainties using a serial pre-filter which is determined using H_infty techniques. The procedure is applied for a SCARA type robotic arm and for a two-dimensional overhead crane system. Simulation results show the applicability of the suggested method.