Slave Manipulators Analysis of Control Architectures for Teleoperation Systems with Impedance

A large number of bilateral teleoperation control architectures in the literature have been designed based on assumed impedance models of the master and slave manipulators. However, hydraulic or heavily The International Journal of Robotics Research Vol. 20, No. 6, June 2001, pp. 419-445, ©2001 Sage Publications © 2001 SAGE Publications. All rights reserved. N at P http://ijr.sagepub.com Downloaded from Teleoperation Systems with Impedance/ Admittance Master and Slave Manipulators Canada K7L 3N6 [email protected] Septimiu E. Salcudean Department of Electrical and Computer Engineering University of British Columbia Vancouver, British Columbia Canada V6T 1Z4 [email protected] better accuracy. Teleoperation has found applications in many areas including space technologies, underwater explorations, military/fire-fighting operations, mining, nuclear/toxic waste handling and disposal, surgery, rehabilitation, training, education, and entertainment (Sheridan 1989; Melchiorri and Eusebi 1996). Besides stability, which is the fundamental requirement for every control system, transparency or telepresence is the principal goal in bilateral teleoperation controller design. Transparency, interpreted as the accurate rendering of the environment to the operator, is technically achieved if the slave position and force follow the master position and force faithfully. Toward this end, several bilateral control architectures have been developed. A survey of most of the proposed architectures can be found in Brooks (1990), Melchiorri and Eusebi (1996), and Salcudean (1998). These architectures can be categorized based on the number and the type of signals transmitted between master and slave. In theory, fourchannel (and even three-channel) control architectures that incorporate both master and slave position and force information exchange can offer perfect transparency (Lawrence 1993; Yokokohji and Yoshikawa 1994; Hashtrudi-Zaad and Salcudean 1999). However, in practice, the dynamics of the operator and especially the environment vary drastically, compromising both performance and stability. Moreover, delays in the data transmission channels further complicate the design problem (Lawrence 1993; Salcudean et al. 1995; Daniel and McAree 1998). Therefore, there is a need for guidelines in adjusting the control parameters for a good trade-off between stability robustness and performance. A majority of the control architectures proposed are taigeared and many other manipulators cannot be properly described by impedance models. In this paper, a common four-channel bilateral control architecture designed for the above impedance models is extended to teleoperation systems with master and slave manipulators of either the admittance or impedance type. Furthermore, control parameters that provide perfect transparency under ideal conditions are found for each type of teleoperation system. Because in practice such parameters may not lead to systems that are robust to time delays and model uncertainties, an analysis of the stability and performance robustness of this very general architecture and two-channel architectures is also presented. The analysis uses the passivity-based Llewellyn two-port network absolute stability criterion, as well as bounds on the minimum and range of values of the impedance transmitted to the operator. The results of these evaluations provide design guidelines on choosing a particular control architecture and its parameters given different master and slave manipulator structures. KEY WORDS—absolute stability, bilateral control, two-port network, teleoperation, transparency