Stability in Haptic Teleoperation Literature Review

摘要

Teleoperation is the indirect manipulation of an object using a robotic manipulator. The term haptic teleoperation is used to indicate the presence of force feedback. Haptic teleoperation can be very valuable, because it can help to perform a task more time effectively and more reliably. Stability is an important issue in haptic teleoperation, because the creating of a perfect transparent teleoperator leads to stability problems. This report discusses techniques to analyse the stability, the relationships between them, influences on stability and stabilising techniques. To analyse the stability, the teleoperator is modelled as a linear system consisting of a master device, a communication channel and a slave device. It is augmented with models of the human operator and the environment to yield the complete teleoperation system. If it is assumed that the operator and environment are passive then the stability of the teleoperation system can be analysed by looking at the teleoperator part only. One concept is the absolute stability criterion. The other one is the passivity criterion, which is also applicable to nonlinear systems and very easy to apply. Both concepts can be conservative, however. As an alternative, analysis tools based on the whole teleoperation system can be used. With Routh’s stability criterion the stability can be analysed without actually solving for the poles of the system. With the root-locus method the location of the poles can be plotted as a parameter varies. With the Nyquist stability concept the stability of a teleoperation system can be analysed using the open-loop transfer function. Lyapunov stability is also applicable to nonlinear systems and with the small gain theorem and μ-analysis the robust stability of a teleoperation system can be analysed. Based on the analysis techniques, influences on the stability can be investigated. Influences on stability can originate from any part in the system. Important influences on the stability are time delays, digital implementation of the controllers and a phase transition from free air to hard contact. Frequently used techniques to stabilise a teleoperation system are: H∞ control, adaptive control and addition of damping. Damping could be added by designing a passive communication channel or it could be added in an adaptive way, that is to say, by adding damping when the teleoperator becomes active.