In this paper, we develop a generic approach for modeling a teleoperation setup, as a negative single feedback loop containing a linear time-invariant block and an uncertain time-varying delay. It is not based on specific dynamics of masters and slaves, neither on any control architecture. The main added value of the proposed approach is the possibility of deriving frequency-domain conditions for robust stability in the presence of time-varying delays and parametric uncertainties. To address stability, we choose a primitive result providing a bound of certain delay subsystem. We combine this, with input-output stability criteria and μ-analysis and synthesis techniques, to reach a procedure based on the structured singular value providing less conservative results. Finally, our approach is presented within a suggested flowchart that helps the designer to manage the control parameter ranges and facilitates the gradual achievement of stability, robust stability, and performance properties. As a case study, we consider the Internet-based teleoperation of a gantry crane by means of the position-error control architecture. We have also obtained actual delay bounds appearing with UDP protocol for different Internet locations. Simulation and experimental results confirm the robust performance of the teleoperation system in terms of stability and tracking behavior.
This paper investigates the delay-dependent stability of a teleoperation system based on the transparent Generalized Four-Channel control G-4C scheme under time-varying communication delays. To address stability we choose here a primitive result providing a Linear Matrix Inequalities LMIs approach based on Lyapunov-Krasovskii functionals. Firstly, the scheme is modeled as the neutral-type differential-delayed equation; that is, the delay affects not only the state but also the state derivative. Secondly, we apply a less conservative stability criteria based on LMIs that are delay dependent and delay's time-derivative dependent. The reason is that, for better performance in the case of small delays, we must accept the possibility that stability is lost for large delays. The approach is applied to an example, and its advantages are discussed. As a result, we propose to modify the values of standard controllers in G-4C defining the γ-4C scheme, which introduces a tuning factor γ to increase in practical conditions the stable region fixing the desired bounds on time-varying delay, with the particularity of maintaining the tracking properties provided by this transparent control scheme. The simulation results justify the proposed control architecture and confirm robust stability and performance. Mathematical Problems in EngineeringUnder this compromise, many control schemes for teleoperation have been proposed in the last years. A first comparative study among them presented by Arcara and Melchiorri can be seen in 2 . Following this work, as stability is concerned, the teleoperation schemes are classified in intrinsically stable schemes passivity based , and delay-dependent stable schemes. Therefore, in the initial works, concerning constant delay, the stability is addressed by means of frequency Laplace or passivity techniques, applied to linear time invariant master-slave two-port systems 1-5 . On the other side, related with transparency properties, the most successful control scheme in achieving a fully transparency under ideal conditions is the four-channel control one 1, 2, 4 .But also, the low cost and availability offered by Internet have opened a new line of research to establish Internet-based teleoperation 6-9 , which requires transmitting the control signal through the network, exposing the system control loop to the varying time delay of a packet-switched network. These new difficulties were already present in the historical survey presented by Hokayem and Spong in 10 about the control theoretic approaches for bilateral teleoperation.Furthermore, Chopra et al. in 11 affirm that the bilateral teleoperators designed within the passivity framework using concepts of scattering and two-port network theory provide robust stability against constant delay in the network and velocity tracking, but cannot guarantee position tracking in general. For these reasons, many recent results try to extend the passivity-based architecture to solve these problems: see 12, 13 and references therein. Concerning these techniques...
This paper proposes a new middleware solution called Network Adaptive Deadband (NAD) for long time operation of Networked Control Systems (NCS) through the Internet or any shared network based on IP technology. The proposed middleware takes into account the network status and the NCS status, to improve the global system performance and to share more effectively the network by several NCS and sensor/actuator data flows. Relationship between network status and NCS status is solved with a TCP-friendly transport flow control protocol and the deadband concept, relating deadband value and transmission throughput. This creates a deadband-based flow control solution. Simulation and experiments in shared networks show that the implemented network adaptive deadband has better performance than an optimal constant deadband solution in the same circumstances.
This paper investigates the dynamic selection of an appropriate threshold for basic Send-on-Delta (SoD) sampling strategies, given an available transmission rate to reduce the signal tracking-error. The paper formulates the error-reduction principle and proposes an algorithm that calculates, in real time, the amplitude threshold value (also called delta value) for a desired mean transmission rate. The algorithm is implemented to be computed in a Send-on-Delta driver and is tested with three signals that match the step response of a second order control system. Comparison results with a conformant periodic transmission strategy reveals that it improves deeply the tracking-error while maintaining the desired average throughput.
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