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

Abstract

Several classes of weight-handling equipment with nonlinear dynamics are exactly linearisable by feedback. This implies that a controller ensuring the 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 using this method. However, the value of model parameters such as the mass of the load or the friction coefficients must be known in order to calculate the actuated inputs in closed loop. The 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∞ techniques. The procedure is applied to a SCARA-type robotic arm and to a two-dimensional overhead crane system. The simulation results show the applicability of the suggested method.