Ilia G. Polushin

A Force-Reflection Algorithm for Improved Transparency in Bilateral Teleoperation With Communication Delay

The problem of stable force-reflecting teleoperation with time-varying communication delay is addressed in this paper. A new force-reflection (FR) algorithm is presented, where the environmental force reflected on the master side can be altered depending on the forces applied by the human operator. This alteration is not felt by the human operator; however, it makes the FR safe in the sense it does not destroy the stability of the teleoperator system. In particular, using input-to-output stability small gain approach, it is shown that the overall stability in the teleoperator system with the force-reflecting algorithm proposed can be achieved theoretically for arbitrarily low damping on the master side and arbitrarily high FR gain. The simulation results presented confirm that the proposed FR algorithm significantly improves the stability/performance characteristics of the force-reflecting teleoperator system in the presence of time-varying communication delays.

Attitude Synchronization of Multiple Rigid Bodies With Communication Delays

We consider the attitude synchronization problem of multiple rigid bodies (or spacecraft) in the presence of communication delays. Specifically, we propose a virtual systems-based approach that removes the requirement of the angular velocity measurements. First, we present a solution to the leaderless and leader-follower problems in the case of time-varying communication delays and undirected communication topology. Second, we present an attitude synchronization scheme that solves the leaderless problem under directed interconnection between rigid bodies in the presence of constant communication delays. Finally, we show that the proposed schemes can be extended in a straightforward manner to solve the cooperative attitude tracking control problem.

A Multichannel IOS Small Gain Theorem for Systems With Multiple Time-Varying Communication Delays

A version of the input-to-output stability (IOS) small gain theorem is derived for interconnections where the subsystems communicate asynchronously over multiple channels, and the communication is subject to multiple time-varying possibly unbounded communication delays. It is shown that a ldquomulti-dimensionalrdquo version of the small gain condition guarantees the stability of the interconnection of IOS subsystems under certain mild assumptions imposed on communication process. The fulfillment of these assumptions does not depend on characteristics of the communication channels, but can always be guaranteed by implementation of certain features of the underlying communication protocol. This result is applicable to a wide range of dynamical systems whose parts communicate over networks, such as Internet-based teleoperators.

Control schemes for stable teleoperation with communication delay based on IOS small gain theorem

The problem of stabilization of a force-reflecting telerobotic system in presence of time delay in the communication channel is addressed. We introduce an approach that is based on application of the input-to-output stability (IOS) small gain theorem for functional differential equations (FDEs). A version of the stabilization algorithm as well as its two adaptive extensions are proposed. For all these control schemes, the input-to-state stability (ISS) of the overall telerobotic system is guaranteed in the global, global practical, or semiglobal practical sense for any constant communication delay under the assumption that the environmental dynamics satisfy a weak form of finite-gain stability property. As an intermediate step, we formulate and prove a general IOS (ISS) small gain result for FDEs.

Synchronization of Lagrangian Systems With Irregular Communication Delays

The synchronization problem of networked Euler-Lagrange systems with unknown parameters is addressed. The information flow in the network is represented by a directed communication graph and is subject to unknown and possibly discontinuous time-varying communication delays with unknown upper bounds. We propose a control scheme that achieves position synchronization, i.e., all the positions of the systems converge to a common final position, provided that the directed communication graph contains a spanning tree. The convergence analysis of the proposed scheme is based on the multidimensional small-gain framework. Simulation results on a network of ten robot manipulators are given to illustrate the effectiveness of the proposed control scheme.

A small gain framework for networked cooperative force-reflecting teleoperation

For cooperative force-reflecting teleoperation over networks, conventional passivity-based approaches have limited applicability due to nonpassive slave-slave interactions and irregular communication delays imposed by networks. In this paper, a small gain framework for stability analysis design of cooperative network-based force reflecting teleoperator systems is developed. The framework is based on a version of weak input-to-output practical stability (WIOPS) nonlinear small gain theorem that is applicable to stability analysis of large-scale network-based interconnections. Based on this result, we design a cooperative force-reflecting teleoperator system which is guaranteed to be stable in the presence of multiple network-induced communication constraints by appropriate adjustment of local control gains and/or force-reflection gains. Experimental results are presented that confirm the validity of the proposed approach.

Projection-Based Force Reflection Algorithm for Stable Bilateral Teleoperation Over Networks

The problem of stable force-reflecting teleoperation is addressed where the communication between the master and the slave is subject to multiple time-varying, discontinuous, and possibly unbounded communication delays. A new force reflection algorithm is proposed which improves the stability of the system without decreasing its transparency. Based on an estimate of the human forces provided by a high-gain input observer, the proposed algorithm restricts the reflected force in such a way that it eliminates the motion of the master induced by the force reflection signal without changing the human perception of the environmental force. It is shown that the force reflection algorithm proposed allows to achieve stability of the system for arbitrarily high force-reflection gain and arbitrarily low damping/stiffness of the master manipulator.

Stability of bilateral teleoperators with generalized projection-based force reflection algorithms

A general stability result for bilateral teleoperator systems with projection-based force reflection algorithms from a broad class is presented. It is shown that the overall stability of a teleoperator system can be achieved under mild assumptions on subsystem stability, properties of the communication channel, dynamics of the human operator, and the human force measurement/estimation process. In particular, the stability is achieved under a new general assumption on human dynamics which allows for both passive and nonpassive behaviour of the human operator. It is demonstrated that the use of projection-based force reflection algorithms effectively removes the constraints on subsystem gains that are typical for direct application of the small-gain design, thus solving the trade-off between stability, manoeuvrability, and high force reflection gain in bilateral teleoperation over communication networks.

Networked teleoperation with non-passive environment: Application to tele-rehabilitation

In master-slave teleoperator systems used for tele-rehabilitation purposes, the passivity can be violated because of the assistive actions of a therapist; moreover, any type of passivation approach to the design of such a system would defeat the purpose of the assistive therapy. In this paper, a design framework is presented that does not rely on passivity considerations. A number of results are given that deal with stability and transparency properties of the tele-rehabilitation system in the case of intrinsically non-passive behaviour of the therapist. In particular, a stabilization scheme for the networked tele-rehabilitation system is proposed which guarantees stability regardless of the specific actions of the therapist. Simulation results are presented which confirm the theoretical developments.

Force reflection algorithm for improved transparency in bilateral teleoperation with communication delay

The problem of stable force-reflecting teleoperation with time-varying communication delay is addressed. A new force reflection algorithm is presented, where the environmental force reflected on the master side can be altered depending on the forces applied by the human operator. This alteration is not felt by the human operator, however, it makes the force reflection safe in the sense it does not destroy the stability of the teleoperator. In particular, using IOS small gain approach, it is shown that the overall stability in the teleoperator system with the force-reflecting algorithm proposed can be achieved theoretically for arbitrarily low damping on the master side and arbitrarily high force-reflection gain. The simulation results are presented that confirm that the proposed scheme allows to decrease master damping significantly, and thus improve the transparency of force-reflecting teleoperation, without sacrificing the overall stability