Design, Construction and Testing of a Single-axis Servomechanism for Control Experiments involving Coulomb Friction, Backlash and Joint Compliance

SUMMARY An investigation of the effects of system non-linearities, such as Coulomb friction and backlash, and undesirable structural dynamics, such as joint compliance, on the dynamic modeling and control of mechanical positioning systems is presented. These effects are often neglected in dynamic system analysis and control studies. An innovative, computer-controlled, mechanical positioning test bed was designed and constructed to facilitate investigations of these effects. The test bed allows fully adjustable, quantified and well-defined measurements of Coulomb friction, backlash, joint compliance and inertia. System identification and parameter estimation techniques are used to estimate and verify linear system parameters. Open-loop and closed-loop simulations of the system, incorporating the undesirable effects which can be exhibited by the test bed, are presented and compared with experimental results. The positioning performance of the servomechanism is shown to degrade with increases in Coulomb friction, backlash and joint compliance. Candidate control strategies to compensate for the above-mentioned adverse phenomena are described and their effectiveness is evaluated. Future experimental and theoretical work is described.