Distributed haptic cooperation with passive multirate wave communications

Haptic interaction in slow virtual environments (VEs) can become unstable due to the phase lag introduced in the control loop by the slow update rate of the VE. Increasing the physical damping and/or limiting the contact stiffness rendered to users can mitigate the destabilizing effect of the low VE update rate. However, large physical damping and compliant virtual contacts decrease the sense of presence in VEs, especially during interaction with rigid virtual objects. To increase the maximum virtual contact stiffness that can be rendered to users without increasing the interface damping, this paper proposes a control strategy based on multirate wave communications between a haptic interface and a VE updated at a slow and fixed rate. The multirate wave communications are shown to be guaranteed passive only if the decrease of the wave sampling rate at the connection between the haptic interface and the VE does not cause aliasing. Therefore, an antialiasing low-pass filter is placed before the wave rate drop in the communications. The passivity condition is verified analytically and numerically for multirate haptic interaction in VEs with various contact stiffnesses and update rates. The transparency of haptic interaction in slow VEs to which users connect via passive multirate wave communications is investigated analytically in the frequency domain. Experiments validate that passive multirate wave communications can render stiffer contact in slow VEs than conventional direct coupling, and illustrate the destabilizing effect of the aliasing caused by the sampling rate drop in the communications.

One of the main challenges in networked closed-loop systems is that communication delays can significantly deteriorate system performance and even cause instability. A predictor-based framework was proposed previously to improve the networked closed-loop system performance by compensating constant network delays. The key feature of this prediction scheme is that it does not require a dynamic model of the remote subsystem and has only one design parameter to tune for each predictor to mitigate the communication delays. In this paper, the predictor-based framework is developed further. Specifically, previously the predictor was developed and its stability was analyzed for constant delays only. In this paper, the predictor structure is extended to the varying delay case and its stability is established for the first time for varying delays in a sufficient but not very conservative range by leveraging a Markov chain based approach from the literature. To that end, the key assumption of the approach that varying delays can be modeled using a two-time-scale Markov chain is tested using actual network delay data. Next, to test the performance of the framework on a networked closed-loop system, it is applied to a simulated networked motor-shaft-geartrain system with different constant and varying delay models, as well as a real network. Predictors are shown to be effective in significantly reducing the negative effects caused by delays and greatly improve the fidelity of the networked integration. Finally, stability of the closed-loop system with predictor-based framework is studied with constant delays using a “mixed” small gain and passivity theorem from the literature and it is demonstrated that the predictors can even help stabilize a closed-loop linear time-invariant system when the nonpredictor-based networked system is unstable due to constant delays.

This paper investigates causal consensus problem of a class of singular (descriptor) multi-agent systems with network delays, fixed topology. For the studied systems, different from traditional open-loop prediction approach, a pseudo predictor based on closed-loop artificial system is proposed to predict the future state. For the time-varying delay, a data-receiving policy is proposed to turn it into constant delay. Consensus protocol is proposed based on predicted state to synchronize the agents' states. Necessary and sufficient conditions are derived for the existence of the proposed protocol to solve the considered consensus problem. A numerical example demonstrates the effectiveness of compensation for networked delays using the provided consensus algorithm.

Network based control of remote systems has been widely tackled and numerous methods have been proposed to deal with small and or constant delays. However, on long distance network, bandwidth and network delays may notably vary (beyond hundreds of milliseconds) according to events occurring along the transmission lines. This paper presents the long distance remote control of a small mobile robot. To face important network delay variations and possible connection rupture, a supervised delay regulator based architecture is proposed. Results of experiences that have been performed from Mexico to France are given and explained.

We propose a method for estimation of a globally constant but unknown delay τ>00$$\\end{document}]]> in a negative feedback loop, where only an upper bound on the possible values of τ is given. Also the initial datum is not revealed. The method is based on detecting the decay rate of the solution throughout its evolution and guarantees that the estimate converges to the true value of τ asymptotically for large times. In a second step, the estimated delay is used to adaptively control the sensitivity (feedback gain) of the loop with the goal of reaching optimal rate of convergence towards equilibrium. We stress that our approach is distinguished from traditional feedback control methods by leveraging the system’s sensitivity as a control parameter to achieve equilibrium. In the second part of the paper we adapt the method to estimate unknown delay and control the sensitivity in a linear opinion formation model. Here the estimation of the delay is based on the decay properties of the quadratic fluctuation of the agents’ opinions, employing appropriate approximations and some heuristic arguments. In both cases we present numerical examples illustrating the performance of the method.

To address the problem of internet based communication delay in bilateral control systems, numerous methods have been proposed. This study is among the few recent studies taking a disturbance observer approach to the problem of time delay, and introduces a sliding-mode (SM) observer to overcome specifically the effects of communication delay in the feedback loop. The observer operates in combination with a PD+ controller which controls the system dynamics, while also compensating load torque uncertainties on the slave side. To this aim, an EKF based load estimation algorithm is performed on the slave side. The performance of this approach is tested with computer simulations for the teleoperation of a 1-DOF robotic arm. Experimental results are also presented to test the performance of the approach under constant and random measurement and control input delay for no load.

This technical note proposes an event-triggered quantization policy design method to stabilize a scalar continuous-time linear time-invariant (LTI) system, whose feedback loop is closed over an unreliable digital communication network. The feedback packets suffer from network delay and may be dropped in an independent and identically distributed (i.i.d.) way. In order to save quantization bit rate, we implement a periodic event-triggering strategy which periodically samples the state and only quantizes and transmits the sampled state when a predefined event is triggered. By making good use of both the information bits and the sampling time instants of the feedback packets, our policy can obtain the desired mean-square stability at a lower bit rate than the conventional time-triggered quantization policies which utilize only the information bits inside the feedback packets. Under our quantization policy, the stabilizing bit rate condition is up to the dropout rate, the processing and network delays and the unstable eigenvalue of the system, and is independent of the bounded process noise.

Network delay in haptic-based CVEs (collaborative virtual environments) severely deteriorates the haptic interaction quality (e.g., larger force feedback than real). In order to compensate this delay effect, existing studies dynamically change spring and damper coefficients according to the network delay. However, it is difficult to choose proper coefficients to offset the delay effect by precisely reflecting virtual object characteristics. In this paper, a new delay-compensation scheme based on the force feedback prediction is proposed to improve the force feedback experience. By predicting the virtual object movements and force feedback, the proposed scheme in client side provides timely force feedback to a user. Then, it gradually converges to real (but delayed) information from the server in order to maintain the consistency of virtual environment. According to the experiment results, the proposed scheme can improve the haptic interaction quality by providing more realistic force feedback similar to that of no network delay.

This chapter introduces and surveys bilateral (master-slave) control methods and system architectures for telerobotics known in the literature. The discussion takes a focus most relevant to subsequent chapters, see [1, 2, 3] for complementary and more complete surveys. Firstly, an introductory example of a control-oriented block diagram formulation for a typical two-channel force-velocity architecture is presented, where the human system interface (master) is force controlled and the teleoperator (slave) is velocity controlled. Then a network theoretic view using n-ports is taken and the basic concept of passivity is explained meaning that an interconnection of passive subsystems results in an overall passive system. Transparency is defined, meaning that the human operator should ideally feel as if directly acting in the remote environment (is not able to feel the technical systems/communication network at all). The well known and for ideal transparency required four-channel architecture is presented. The important discussion of time delay in the communication network, which impairs or might threaten stability properties of the closed loop teleoperation system, is then discussed. The most successful approach using the scattering (wave variable) transformation approach is presented, which guarantees that the communication two-port is lossless (passive) for arbitrary constant time delay. Finally, we mention the key challenges in the design of bilateral teleoperation systems and give a short preview of the subsequent chapters addressing some of these challenges.

This work proposes the use of a Smith predictor with jitter transport delay adaptation to feedback control systems on which control loops are closed through an IP network. The well know Smith predictor is efficient to compensate constant transport delay but IP networks presents jitters which disturb the performance of the predictor. Therefore, together to the predictor it is implemented a new compensation way to this typical jitter of these networks. This compensation has a data structure in order to store values from the output of the predictor, in order to the right value be read to from it to compare with to the value from the system feedback. The value is chosen based in the last delay in the control loop. The proposed approach was validated via simulation and experimental results are presented in the paper.

This paper addresses the problem of steady-state position and force tracking in bilateral teleoperation. Passivity-based control schemes for bilateral teleoperation provide robust stability against network delays in the feedback loop and velocity tracking, but do not guarantee steady-state position and force tracking in general. Position drift due to data loss and offset of initial conditions is a well-known problem in such systems. In this paper, we introduce a new architecture, which builds upon the traditional passivity-based configuration by using additional position control on both the master and slave robots, to solve the steady-state position and force-tracking problem. Lyapunov stability methods are used to establish the range of the position control gains on the master and slave sides. Experimental results using a single-degree-of-freedom master/slave system are presented, showing the performance of the resulting system

This article investigates the input-to-state stability (ISS) of continuous-time networked control systems with model uncertainty and bounded noise based on event triggering. The feedback loop is closed over an unreliable digital communication network. Feedback packets suffer from network delay and may be dropped in an independent and identically distributed (i.i.d.) way, which may harm to the concerned stability. This article focuses on a Lyapunov-based event-triggered control design scheme with the consideration of i.i.d. packet dropouts. By designing a state-dependent event-triggering threshold and updating methods, it can still ensure ISS for the concerned multidimensional system in the presence of i.i.d. packet dropouts and model uncertainty without exhibiting the Zeno behavior. Simulations are done to verify the effectiveness of the achieved results.

Low‐frequency electromagnetic (EM) waves are essential in underwater, deep‐earth, and other communication environments due to their minimal attenuation. The magnetoelectric (ME) antenna, a novel mechanical antenna, provides a promising solution for low‐frequency EM wave communication, overcoming the limitations of conventional designs in terms of size and efficiency. To address the low transmission rate in low‐frequency EM wave communication, this paper proposes a multi‐key tunable antenna array based on an ME cantilever beam design. Each antenna array element consists of Metglas/0.7Pb(Mg1/3Nb2/3)O3–0.3PbTiO3 (PMN‐PT) ME composite. Simulations identified a structure that significantly lowers the resonant frequency, allowing the ME antenna array to operate within the ultra‐low frequency (ULF, 300 Hz‐3000 Hz) band. Furthermore, the resonant frequency can be tuned over a range of 500 Hz, enabling multi‐frequency‐shift keying (MFSK) communication. Using quaternary FSK (4FSK) modulation, a 40 baud color image transmission is successfully demonstrated in a 5 S m−1 saline environment. Compared to binary FSK (2FSK) at the same baud rate, the transmission speed is increased by 100%. This approach achieves both low attenuation and high transmission rates, offering a promising new direction for ocean communications.

Multi-Pulse Oscillations in Relay Systems

Networked control systems (NCSs) are significant and foremost multidisciplinary research areas for many decades. This paper is mainly oriented toward recent developments and challenges of network-induced delays due to inclusion of data network in NCSs. Network delays deteriorate the control performance and stability of the NCSs. The time-varying delays can be measured in real time by calculating the time difference of sending and receiving control packets. Various compensation techniques are reviewed to mitigate the effect of constant, time-varying, and stochastic delay. Lastly, some conclusions are drawn and the future research scope is directed.