Friction Compensation of Harmonic Drive Actuators

Friction models and methods of friction compensation as app lied to harmonic drive servo-actuators are investigated. In the absence of output torque measurements and output shaft encoder data nearly complete friction compens ation is achieved. Simulation and experimental results showing the application of the friction compensation are given. Introduction Because of the absence of backlash and high gear ratios servo -actuators with harmonic drive gearing are commonly used for space manipulator s. One of their major drawbacks is their high levels of internal friction. In addi tion to the friction caused by the DC-motor brushes and the bearings, the harmonic drive gearing in the actuators causes a major part of the total friction due to the flex-s pline and the large gear tooth area. The friction is nonlinear and is dependent on the s ate of the motor and its environment. A wide range of friction models have been th oroughly reviewed by Armstrong-H́elouvry et al.[1] and Olssonet al.[2]. The ubiquitous Coulomb friction model and its simple extensions have difficulties when t he velocity is near zero because of the jump discontinuity in that region. A more gene ral model of friction is