Quantitative analysis and evaluation of bilateral control schemes applied to electro-hydrostatic actuators

A bilateral teleoperator allows operators to use a master manipulator to interact with the environment via a slave manipulator. It can be used in remote, hazardous or inaccessible situations. Although numerous bilateral teleoperation studies have been conducted on electrical actuators, research on hydraulic actuators, especially research on electro-hydrostatic actuators (EHAs), a class of pump-controlled systems, is currently limited. In bilateral teleoperation, one issue concerns how to tune the controller parameters with regard to stability and transparency in the presence of uncertainty. In this paper, an approach based on quantitative feedback theory (QFT) that provides guidance on controller parameter selection during the bilateral teleoperation of EHAs is introduced. Parametric uncertainties in dynamics of human operators, master manipulators and environments are described in templates to compute bounds quantitatively, and trade-offs between stability and transparency are visualized. Four commonly used bilateral control schemes are exemplified using this method: force reflection (FR), position error (PE), shared compliant control (SCC) and force reflection with passivity (FRP). The bilateral controllers are tuned through simulations and are validated through contact experiments involving both soft and hard environments. Given its simple structure and excellent level of transparency, FR is found to be the most suitable scheme of the four for teleoperations of EHAs.