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TECHNICAL BRIEFS

Networked Real-Time Control Strategy Dealing With Stochastic Time Delays and Packet Losses

[+] Author and Article Information
Won-jong Kim1

Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123wjkim@tamu.edu

Kun Ji, Ajit Ambike

Department of Mechanical Engineering, Texas A&M University, College Station, TX 77843-3123

1

Corresponding author.

J. Dyn. Sys., Meas., Control 128(3), 681-685 (Jun 21, 2005) (5 pages) doi:10.1115/1.2232692 History: Received August 18, 2004; Revised June 21, 2005

A novel model-predictive-control strategy with a timeout scheme and p-step-ahead state estimation is presented in this paper to overcome the adverse influences of stochastic time delays and packet losses encountered in network-based distributed real-time control. An open-loop unstable magnetic-levitation (maglev) test bed was constructed and employed for its experimental verification. The compensation algorithms developed in this paper deal with the network-induced stochastic time delays and packet losses in both the forward path and the feedback path simultaneously. With the p-sampling-period delay upper bound, the networked control system (NCS) can also accommodate up to p1 successive packet losses. Experimental results demonstrate the feasibility and effectiveness of this networked real-time control strategy.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

Distributed real-time control system with network-induced time delays

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Figure 2

Actual control signal U(N) adopted by the actuator node and components of the control signal packet u(n) with respect to time when different time delays or packet losses occur. Figures (a)–(d) cover all the possible cases of the time delay τca(n) up to 4h or the number of consecutive packet losses up to 3. Short vertical lines indicate sampling instants. Solid arrows indicate that new control signal packages arrive in the corresponding sampling interval. Dotted arrows indicate that the incoming control signal packages are delayed or lost.

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Figure 3

Ball position with packets losses beginning at t=12s

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Figure 4

Ball position with four successive packet losses occurring every 6s

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Figure 5

Ball position with 20% packet losses beginning at t=12s onwards

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Figure 6

Step response without packet loss

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Figure 7

Step response with 20% packet losses

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Figure 8

Tracking a sinusoidal command with packet losses beginning at t=50s

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Figure 9

System tracking response with 10% packet losses

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Figure 10

System tracking response with 20% packet losses

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