Four-Channel Teleoperation with Time-Varying Delays and Disturbance Observers

Abstract

This paper addresses the robust stability of teleoperated systems under the four-channel architecture, affected by time-varying communication delays and using disturbance observers. It is based on our previous work which provides a framework for robust stability against delays with bounded variation and a bounded time-derivative, using structured singular values (SSV). The main new feature here is the inclusion of disturbance observers (DOBs). The DOB concept is well-documented and relevant to many applications, since only position (but not force) measurements are usually available. In this paper, we adapt two DOBs (master and slave) to our generic framework, by representing them as stable, fast filters affected by the uncertainty in the plant modelling. Our main result is an SSV test to verify robust stability. The simulation results confirm the usefulness of this approach.

Fuzzy Model Based Bilateral Control Design of Nonlinear Tele-Operation System Using Method of State Convergence

“…A number of control schemes [4]- [6], using either two-channel or four-channel architectures as a baseline, have emerged after the pioneer work of channel passification to nullify the time delay effects based on the concepts of transmission line theory [7], [8]. These include time domain passivity control to make teleoperation system work in a wide variety of environments [9], adaptive control to estimate operator or environment models and teleoperation system uncertainties [10]- [12], sliding mode control for robustness against disturbances during task execution [13], [14], model-mediated control to reconstruct the slave environment at master site [15]- [17], gain scheduling to cope with uncertainties [18], model predictive control for constrained teleoperation with poorly known time delays [19], [20], H∞ control for multi-objective optimization [21], [22], frequency domain techniques to analyze stability of teleoperation system [23], [24], disturbance observes to lessen measurements [25], [26]. The developments in the control schemes have contributed to the enormous increase in the applications of teleoperation systems being developed for nuclear plants [27]- [29], underwater exploration [30]- [32], space missions [33]- [36], surgical procedures [37]- [41] and other industrial problems [42]- [46].…”

Robust Stability of Scaled-Four-Channel Teleoperation with Internet Time-Varying Delays

“…The main novelty of the present research compared to previous related research is that we have explicitly discussed the problems associated with ideal transparency and that we have rearrange previous 4C solutions [ 22 , 25 ] so that the resulting controllers are proper, that is, they do not contain single or double differentiators and so avoid problems of noise. We have also validated this research through new simulations and real-life experiments using an Internet teleoperation setup that coordinates two Omni haptic devices between remote laboratory setups in Spain (University of Vigo) and the UK (University of Manchester).…”

“…Using this generic approach, we presented preliminary results [ 22 ] on the 4C control scheme for teleoperating simulated manipulators, as more flexible than 3C [ 23 ] or 2C [ 24 ] versions. Further work [ 25 ] addressed the robust stability of simulated teleoperated systems, with the 4C architecture affected by time-varying communication delays, by using disturbance observers that are relevant when only position (but not force) measurements are available.…”

“…The main differences between our approach [ 6 , 22 , 25 ] and other delay-dependent proposals are that we look for: (a) complete stability to zero of the whole state; and (b) robustness against continuous-time time-varying delay. The first goal implies that, in the absence of external inputs, the whole state should converge to zero.…”

“…It is well-known [ 4 ] that 4C schemes with perfect transparency do not have well-posedness and complete stability to zero of the state vector. This is the reason why, starting out with the 4C architecture [ 6 , 22 , 25 ], we introduced a scaling parameter γ to achieve complete stability to zero of the whole state.…”