Energy recovery in time-varying delay teleoperated system using wave-variables

Abstract

While control theory for bilateral teleoperation systems under constant time communication delay is well developed, the research on time-varying communication delay systems is still ongoing. Most wave-based approaches proposed in literature to deal with time-varying delay appear too conservative resulting in high degradation from the constant time delay case.We have already proposed a bilateral control scheme with energy balance monitoring over packet switched communication networks. In the previous work, we dealt with a simplify situation where the time-varying was in the communication channel from master to the slave. However, we did not implement and test the system with a more complex scenario in which the delay was in both communication paths. The paper presents a complete bilateral teleoperation control scheme to compensate nonlinearity introduced by an Internet like communication channel. The system implements intelligent strategies to maintain the system passivity while it deals with position drift compensation, packets loss and blackouts management. Experimental results using the proposed control scheme are shown.

Passivity-Based Control over Differentiated-Services Packet Networks

“…Unfortunately passivity is not preserved by the scattering transformation when the delay is time-varying. In Section IV the solution proposed in [12] to overcome this limitation will be briefly recalled and properly included in our control architecture.…”

“…In this work we implement the technique proposed by [12] where not only the wave variables corresponding to the command and the measurement are sent through the network, but also their integrals ( t t0 (·)ds, t t0 (·) 2 ds) to guarantee the passivity (and so the stability) of the overall system. The scheme implementing this technique is shown in Figure 4.…”

“…This behavior could lead to exhaust all the available energy and then use a zero command until a new packet arrives. The authors in [12] propose to use the last command even in absence of energy for a short time, because in reality the controller generates energy at constant rate putting it into the network but the plant simply does not know. This guarantees a smoother behavior of the output.…”

“…To guarantee stability, the passivity concept and the scattering formulation have been improved following the work in [11], [12] where the stability is guaranteed also in case of time-varying delays and packet dropouts.…”