Teleoperated multi-robots rely on communications, both between the human’s local robot and the multiple remote robots and among the remote robots themselves, to execute the remote tasks commanded by their human operator. If attacked, the communications may lead to task failure, loss of multi-robot connectivity and possibly unstable teleoperation. To render teleoperated multi-robots resilient to Denial of Service (DoS) attacks with arbitrary frequency and duration, this paper augments a passivity-based controller for normal teleoperation with: 1) a controller that stops the remote robots at safe distances from each other and from obstacles when a DoS attack starts; and 2) a controller that restores the multi-robot connectivity before resuming normal teleoperation when a DoS attack stops. The teleoperation of a simulated multi-robot system with one leader and two followers illustrates the effectiveness of the proposed distributed control strategy.Note to Practitioners—Research and industry increasingly seek to use robots in inaccessible unstructured environments Teleoperated multi-robots are ideally suited for such environments because they fuse human cognition with remote multi-robotic execution. However, they can be hindered by cyber attacks on their communications. As cyber attacks become more prevalent, resilience to them becomes increasingly important for practical teleoperated multi-robots. This paper presents a first distributed control strategy for rendering teleoperated multi-robots resilient to DoS attacks. For industrial practitioners, the proposed strategy has two key advantages: 1) it is straightforward to implement; and 2) it is effective for DoS attacks with arbitrary frequency and duration. Future work will tackle teleoperated multi-robots under malicious attacks.

A remote multirobot system (RMRS) outfitted with wireless sensors for large-scale data collection may need to be tele-driven by several human users simultaneously. The long distances between the users’ local robots and the RMRS can inject time-varying delays in their communications. This article enables such multiuser teleoperation of an RMRS through a control strategy that robustly synchronizes an RMRS with tree topology and proximity-limited one-hop communications among its robots, enables multiple users to tele-guide the RMRS and to feel the actions of the other users over time-delayed communications between the users’ local robots and the RMRS, and contains the RMRS to the stationary convex hull spanned by the local robots of all users in the steady state. A control design constrained by the connectivity of the RMRS and by the passivity of the teleoperator guarantees effective coordination, safe teleoperation, and steady-state containment. The design is a dynamic feedforward–feedback passivation strategy facilitated by a suitable decomposition of the teleoperator into interconnected subsystems. The analysis of the storage functions, and thus of the input–output relations, of all subsystems and their interconnections proves the properties of the design. Comparative experiments in a teleoperation testbed with four local and ten remote robots validate its practical efficacy.

A remote team of robots may be teleoperated by multiple users to explore unstructured environments and to tackle unforeseen emergencies therein. During a large-scale environmental search, each user may visually observe a unique hazard endangering the remote robot connected to their local robot. Therefore, each user may want to tele-drive the remote robot team to a location different than the target locations of other users. This paper resolves the possible conflicts among the multiple user commands through a distributed clustering algorithm that allocates to each user a number of remote robots proportional to the urgency of their request. A pivotal design challenge in the teleoperation context is to ensure that the remote robots allocated to each user are topologically reachable from the user’s local robot within the induced communication subnetwork. The proposed design overcomes this challenge through a reachability-constrained integer linear program that modulates the interconnections of the remote robots on the fly. A comparative experiment on a platform with 2 local and 12 remote robots validates the practical efficacy of the proposed clustering algorithm.

This paper proposes a strategy to overcome the threats posed to connectivity-preserving synchronization of Euler-Lagrange networks by time-varying delays and bounded actuation. It first introduces a suitable distributed negative gradient plus damping injection controller, based on which it establishes that the local connectivity of time-delay Euler-Lagrange networks can be preserved by appropriately regulating the interagent connections and increasing the damping injection locally. Yet, actuator saturation may impede the proper modulation of the interagent connections and the injection of sufficient damping and, thus, may threaten the maintenance of connectivity. This paper then develops an indirect coupling control framework which integrates the bounded actuation constraints into the control design. The framework endows every agent with a virtual proxy and couples initially adjacent agents through their virtual proxies. The interproxy couplings then tackle the time-varying delays while the agent-proxy couplings account for the saturation of actuators. Lyapunov-Krasovskii analysis proves that the indirect coupling strategy can drive time-delay Euler-Lagrange networks with bounded actuation to connectivity-preserving synchronization by limiting the energy of the agent-proxy and interproxy couplings according to the actuation constraints. Experiments with Geomagic Touch haptic robots validate the proposed designs compared to a conventional proportional plus damping controller.

In a distributed multi-master-multi-slave teleoperation system, the human users may compete against each other for the control of the team of slave robots. To win the competition, one operator would send the largest command to the slave group. For the sake of team cohesion, the slave group should follow the command of the winning operator and ignore the commands of the other users. To enable (i) the slave team to identify the winning operator, and (ii) each slave to determine whether to admit or discard the command it receives from its operator, this paper proposes a dynamic decision-making protocol that distinguishes the decision variable of the slave commanded by the winner from the decision variables of all other slave robots. The protocol only requires the slaves to exchange and evaluate their decision variables locally. Lyapunov stability analysis proves the theoretical convergence of the proposed decision-making algorithm. An experimental distributed winner-take-all teleoperation in a 3-masters-11-slaves teleoperation testbed validates its practical efficacy.

During swarm teleoperation, the operator may threaten the distance-dependent inter-robot communications and, with them, the connectivity of the slave swarm. To prevent the operator from disconnecting the swarm, this paper develops a constructive strategy to dynamically modulate the interconnections of, and the local damping injections at, all slave robots. Lyapunov-based set invariance analysis shows that the strategy preserves all interaction links in the tree network while synchronizing the slave swarm. By properly limiting the impact of the user command rather than rejecting it entirely, the proposed explicit gain update law enables the operator to guide the motion of the slave swarm to the extent to which it does not endanger swarm connectivity. An experiment illustrates that the proposed strategy can maintain the tree network connectivity of a teleoperated swarm.

Proportional-derivative (PD) control is often used to coordinate the two copies of the virtual environment in distributed two-users networked haptic cooperation. However, a distributed PD controller designed for force interactions between two users may destabilize the haptic cooperation among multiple users because the effective coordination gain for each local copy of the virtual environment increases with the participant count. This paper proposes the average position (AP) strategy to upper bound the effective stiffness for the shared virtual object (SVO) coordination and, thus, to increase the stability of distributed multi-user haptic cooperation. The paper first motivates the AP strategy via continuous-time analysis of the autonomous dynamics of an SVO distributed among N users connected across a network with infinite bandwidth and no communication delay. We then investigate the effect of AP coordination on distributed multi-user haptic interactions over a network with limited bandwidth and constant and small communication delay via multi-rate stability and performance analyses of cooperative manipulations of an SVO by up to five operators. The paper shows that AP coordination: (1) has bounded effective coordination gain; (2) increases the stability region of distributed multi-user haptic cooperation compared to conventional PD coordination; and (3) renders less viscous SVO dynamics to operators than PD coordination. Three-users experimental manipulations of a shared virtual cube validate the analysis.

The wave variable transformation cannot be exploited for the control of sampled-data and discrete-time systems without precaution. This paper shows that connecting a haptic interface to a discrete time virtual environment through a wave variable controller can inject energy into the haptic feedback loop and thus jeopardize the stability of the haptic interaction. The connection involves a one step computational delay when the virtual environment is not known prior to starting the interaction. Using the Jury-Marden stability criterion, the paper investigates the effect of this computational delay on the stability of wave variable control of haptic interaction with a virtual wall. It also develops a time domain passivity analysis to compute the energy injected in the wave variable transformation by the computational delay. Then, it proposes an algorithm for dissipating the extra energy and restoring the passivity of the wave variable transformation. The paper concludes with the experimental validation of the energy dissipating algorithm.

Networked haptic cooperation entails direct interaction among users as well as joint manipulation of virtual objects. To increase the realism of both types of interactions, this paper introduces remote dynamic proxies. Remote dynamic proxies are second order dynamic representations of users at the remote peer sites. They are generated according to dynamics laws and are controlled by the user whom they represent through a virtual coupler. Hence, they move in a physically intuitive manner and do not suffer from position discontinuities due to network packet transmission limitations. The remote dynamic proxies are integrated into a distributed control architecture for networked haptic cooperation. An experimental comparison of the new controller to two recently proposed controllers demonstrates smoother rendering of contact between users, as well as stable cooperation for larger network delays.

Forbidden-region virtual fixtures (FRVFs) are traditionally imposed on users via proportional-derivative (PD) control. To reduce user penetration into the forbidden region, this paper proposes a new controller, hereafter called continuous impulsive force (CIF) controller. The CIF controller generates passive impulsive forces throughout users' motion into the forbidden region. These impulsive forces annihilate users' velocity into the forbidden region. Superimposed on typical PD control forces, the CIF control forces reduce users' incursion into the forbidden region, and render the feel of fully plastic collisions.

This paper presents an approach for haptic rendering of topological constraints to users operating serial virtual linkages. In the proposed approach, a haptic device controller is designed to penalize users’ departure from the configuration manifold of the virtual linkage. This manifold is locally approximated through the range space of the Jacobian of the virtual linkage computed at the user’s hand. Simulations and controlled experiments performed using a planar haptic interaction system demonstrate that the proposed approach successfully constrains the users’ motion as required by the topology of the virtual linkage that they manipulate.

A new simulation approach is proposed to improve the stability and the perceived rigidity of contacts during haptic interaction with multirigid body virtual environments. The approach computes impulsive forces upon contact and penalty and friction forces during contact. The impulsive forces are derived using a new multiple collision resolution method that never increases the kinetic energy of the system. When new contacts arise, the impulsive forces generate large hand accelerations without requiring increased contact stiffness and damping. Virtual objects and linkages are regarded as points in the configuration space, and no distinction is made between them in the proposed approach.

We present a system for rendering planar rigid-body motion by means of a redundant parallel mechanism. The device design, the control architecture and the passive virtual environment simulation are presented. The system is used to compare various virtual walls and friction models proposed for haptic applications. In addition, the reset-integrator dry friction model proposed by Haessig and Friedland (1991) is implemented in a haptic interface for the first time.