Achieving robust performance for electrohydraulic servo systems: An H-infinity/mu-synthesis solution for manipulation and contouring

Methods for achieving robust performance for unconstrained and constrained contouring and manipulation task are investigated in this thesis.; Due to their large power to weight ratios electrohydraulic systems play a large role in many manipulation and contouring operations. However, due to the presence of the nonlinearities, electrohydraulic servo systems are difficult to control. The source of these nonlinearities can be traced to either the actuators or the load. Both of these effects were addressed in this thesis and their solutions were experimentally verified.; Nonlinearities in the actuation system include asymmetric actuation, nonlinear pressure/flow gain characteristics, variations in the trapped fluid volume and nonlinear transmission ratios. The effects of these nonlinearities were modelled and a method based on the dynamic inversion (or dynamic feedback linearization) principle was used for improving the linearity of electro-hydraulic servo systems operating over a wide range of conditions.; To deal with load nonlinearities, a more general class of nonlinearly coupled dynamic systems was introduced. A method was then introduced for estimating the nonlinear coupling effects using measurements. The use of H{dollar}sbinfty{dollar} and {dollar}mu{dollar}-synthesis based techniques was then proposed as a way to design feedback control systems for achieving robust performance by measurement and attenuation of such nonlinear coupling effects. The developed theory was applied to electrohydraulic robots and validated experimentally on a 2 degree of freedom electrohydraulic robot.; To deal with dynamically constrained maneuvering tasks such as robot machining operations (i.e. grinding and deburring) the concept of impedance design was introduced. We proposed a general methodology (based on H{dollar}sbinfty{dollar} control theoretic concepts) for specifying (or designing) robot end-effector impedance requirements to meet performance and robustness criteria during dynamically constrained tasks. The performance criterion can be characterized by (frequency based) weights on the force and position tracking errors. This impedance design procedure takes the environmental dynamics and its uncertainties into account and is capable of handling non-minimum phase and dynamically coupled multi-degree-of-freedom environments.