Friction identification in a sight stabilisation system at low velocities

Abstract

A friction model is derived based upon rigorous experiments on a sight stabilisation system at low velocities. The model covers both stiction and, to some extent, one slip region. The stiction model was identified from many frequency response functions between angular displacement and motor torque by the describing function approach, where the amplitude of angular vibration is constant. Experimental results show that the combination of constant stiffness and structural damping is appropriate for the stiction force modeling and that these parameters decrease with increase of the response amplitude, but the structural damping was replaced with a viscous damping and a lag compensator for control applications. In the slip region, Coulomb friction force was obtained by observing the angular displacement as well as angular velocity while the motor torque was increased slowly in the open loop control. The suggested friction model would be very useful practically for enhancement of the sight tracking and image stabilisation performance by friction compensation. (C) 1997 Academic Press Limited.