Adaptive Control of Bilateral Teleoperation with Time Delay

1. Introduction

In teleoperation, a human operator remotely controls a robotic manipulator to carry out tasks in complex and often unstructured environments (Hokayem & Spong, 2006). Vision was the only source of feedback in early unilateral systems, which are still popular in some applications due to their simplicity and robustness to communication delay. Many modern teleoperators, however, are bilateral in the sense that position and force information are communicated in both directions between the operator (master) and the robot (slave) sites and are used for control and coordination. The force and kinesthetic feedback provided by a haptic interface and through such bilateral architecture can greatly facilitate task execution in teleoperation. The ultimate goal of teleoperation is to convey to the operator a sense of direct interaction with the task environment, a performance objective often denoted as ideal transparency in the literature (Lawrence, 1993).

From a control theory perspective, teleoperation control is complicated due to a number of fundamental challenges. The dynamics of master/slave robots are often nonlinear and subject to uncertainty. Further uncertainty is introduced into the system through interaction with unknown and widely varying environment and user dynamics. In most conventional control systems the unknown external disturbances must be suppressed. In teleoperation, however, the unknown user exogenous force is the main cause of motion and cannot be rejected. Teleoperation systems belong to the lager family of decentralized control systems since their sensing and actuation are distributed at the master and slave sites. While research in distributed control is extensive, many existing solutions attempt to weaken the interaction among the control sites rather than to coordinate their operation, as desired in teleoperation. Above all, the communication time delay between the master and slave sites poses a formidable challenge to achieving transparency while maintaining system stability in some applications of teleoperation.