Position and Force Tracking in Bilateral Teleoperation

Abstract

A teleoperator is a dual robot system in which a remote slave robot tracks the motion of a master robot, which is, in turn, commanded by a human operator. To improve the task performance, information about the remote environment is needed. Feedback can be provided to the human operator by many different forms, including audio, visual displays, or tactile. However, force feedback from the slave to the master, representing contact information, provides a more extensive sense of telepresence. When this is done the teleoperator is said to be controlled bilaterally. In bilateral teleoperation, the master and the slave manipulators are coupled via a communication network and time delay is incurred in transmission of data between the master and slave site. It is well known that the delays in a closed loop system can destabilize an otherwise stable system. Time delay instability in force reflecting teleoperation was a long standing impediment to bilateral teleoperation with force feedback. The breakthrough to the bilateral teleoperation problem was achieved in [1] where concepts from Network Theory, Passivity and Scattering Theory were used to analyze mechanisms responsible for loss of stability and derive a time delay compensation scheme to guarantee stability independent of the (constant) delay. These results were then extended in [7], where the notion of wave-variables was introduced to define a new configuration for force-reflecting teleoperators. In a bilateral teleoperator, apart from the basic necessity of a stable system, there are primarily two design goals which ensure a close coupling between the human operator and the remote environment. The first goal is that the slave manipulator should track the position of the master manipulator and the second goal is that the environmental force acting on the slave, when it contacts a remote environment, be accurately transmitted to the master. It this paper we primarily address the position