Gain scheduler middleware: a methodology to enable existing controllers for networked control and teleoperation-part II: teleoperation

This paper is the second of two companion papers. The foundation for the external gain scheduling approach to enable an existing controller via middleware for networked control with a case study on a proportional-integral (PI) controller for dc motor speed control over IP networks was given in Part I. Part II extends the concepts and methods of the middleware called gain scheduler middleware (GSM) in Part I to enable an existing controller for mobile robot path-tracking teleoperation. By identifying network traffic conditions in real-time, the GSM will predict the future tracking performance. If the predicted tracking performance tends to be degraded over a certain tolerance due to network delays, the GSM will modify the path-tracking controller output with respect to the current traffic conditions. The path-tracking controller output is modified so that the robot will move with the fastest possible speed, while the tracking performance is maintained in a certain tolerance. Simulation and experimental results on a mobile robot path-tracking platform show that the GSM approach can significantly maintain the robot path-tracking performance with the existence of IP network delays.     

On the gain scheduling for networked PI controller over IP network

The potential use of networks for real-time high-performance control and automation is enormous and appealing. Replacing a widely used proportional-integral (PI) controller by a new networked controller for networked control capability can be costly and time-consuming. This paper proposes a methodology based on gain scheduling with respect to real-time IP traffic conditions to enhance the existing PI controller so it can be used over IP networks with a general network protocol like Ethernet. This paper first describes the gain scheduling approach based on constant network delays using a rational function approach. The formulation is extended to random IP network round-trip time (RTT) delays by using the generalized exponential distribution model. Simulation results show that the PI controller with gain scheduling provides significantly better networked control system performance.     

State feedback controller design of networked control systems

This paper is concerned with the controller design of networked control systems (NCS). A new model of the NCSs is provided under consideration of both the network-induced delay and the data packet dropout in the transmission. In terms of the given model, a controller design method is proposed based on a delay-dependent approach. The feedback gain of a memoryless controller and the maximum allowable value of the network-induced delay can be derived by solving a set of linear matrix inequalities. Two examples are given to show the effectiveness of our method.     

Remote fuzzy logic control of networked control system via Profibus-DP

This paper focuses on the feasibility of fuzzy logic control for networked control systems (NCSs). In order to evaluate its feasibility, a networked control system for servo motor control is implemented on a Profibus-DP network. The NCS consists of several independent, but interacting, processes running on two separate stations. By using this NCS, the network-induced delay is analyzed to find the cause of the delay. Furthermore, the fuzzy logic controller's performance is compared with that of conventional proportional-integral-derivative controllers. Based on the experimental results, it is found that the fuzzy logic controller can be a viable choice for an NCS due to its robustness against parameter uncertainty.     

Fault-tolerant vibration control in a networked and embedded rocket fairing system

Active vibration control using piezoelectric actuators in a networked and embedded environment has been widely applied to solve the rocket fairing vibration problem. However, actuator failures may lead to performance deterioration or system dysfunction. To guarantee the desired system performance, the remaining actuators should be able to coordinate with each other to compensate for the damaging effects caused by the failed actuator in a timely manner. Further, in the networked control environment, timing issues such as sampling jitter and network-induced delay should be considered in the controller design. In this study, a timing compensation approach is implemented in an adaptive actuator failure compensation controller to maintain the fairing system performance by also considering the detrimental effects from real-time constraints. In addition, time-delay compensation in the networked control system is discussed, which is able to reduce damaging effects of network-induced delays.     

QoS-based remote control of networked control systems via Profibus token passing protocol

This paper focuses on a quality-of-service (QoS)-based remote control scheme for networked control systems via the Profibus token passing protocol. Typically, token passing experiences random network delay due to uncertainties in token circulation, but the protocol has in-built upper and lower bounds of network delay. Thus, to ensure the control performance of networked control systems via the Profibus token passing protocol, the network delay should be maintained below the allowable delay level. As the network delay is affected by protocol parameters, such as target rotation time, we present here an algorithm for selection of target rotation time using a genetic algorithm to ensure QoS of control information. We also discuss the performance of the QoS-based remote control scheme under conditions of controlled network delay. To evaluate its feasibility, a networked control system for a feedback control system using a servo motor was implemented on a Profibus-FMS network.     

Gain adaptation of networked DC motor controllers based on QoS variations

Connecting a complex control system with various sensors, actuators, and controllers as a networked control system by a shared data network can effectively reduce complicated wiring connections. This system is also easy to install and maintain. The trend is to use networked control systems for time-sensitive applications, such as remote DC motor actuation control. The performance of a networked control system can be improved if the network can guarantee quality-of-service (QoS). Due to time-varying network traffic demands and disturbances, QoS requirements provided by a network may change. In this case, a network has to reallocate its resources and may not be able to provide QoS requirements to a networked control application as needed. Therefore, the application may have to gracefully degrade its performance and perform the task as best as possible with the provided network QoS. This paper proposes a novel approach for networked DC motor control systems using controller gain adaptation to compensate for the changes in QoS requirements. Numerical and experimental simulations, and prototyping, are presented to demonstrate the feasibility of the proposed adaptation scheme to handle network QoS variation in a control loop. The effective results show the promising future of the use of gain adaptation in networked control applications.     

多时滞Lurie网络控制系统动态输出反馈控制器设计

针对一类具有非理想网络状况,如时变网络时滞、分组丢失和乱序等问题的基于动态输出反馈控制器的网络控制系统,建立了多时滞Lurie网络控制系统模型,应用Lyapunov-Krasovskii泛函方法,保留Lyapunov-Krasovskii泛函导数中经常被忽略的有用项,提出了一种具有更低保守性的多时滞Lurie网络控制系统时滞相关稳定条件。并通过增加一等式约束将非线性矩阵不等式转化为线性矩阵不等式表示的可解性问题,给出了一种动态输出反馈控制器的设计方法。数值实例表明该设计方法具有更低的保守性。     

Bilateral Teleoperation Over Networks Based on Stochastic Switching Approach

In this paper, new control strategies based on linear matrix inequalities and Markov jump linear systems are proposed for bilateral teleoperation systems over networks with random time delays and packet losses. The characteristics of the network are thoroughly incorporated in the design and two cases are considered: where both communication directions behave identically and where they are independent. In both cases, the tracking error is shown to be bounded by the rate of change of the external forces acting on the teleoperation system. The theoretical results are verified with simulation results using experimentally collected network data to show the performance of the proposed scheme as well as how to fine-tune the controller gain to balance the tradeoff between force and position fidelity. Experimental teleoperation results are then presented that show the practical performance of the proposed control scheme.     

Fractional delay compensated discrete-time SMC for networked control system

Time-varying network induced delay in the communication channel severely affects the performance of closed loop network control systems. In this paper, a novel idea of compensating the fractional time varying communication delay in the sliding surface is presented. The fractional time delay in the sensor to controller and controller to actuator channel is approximated using the Thiran approximation technique to design the sliding surface. A discrete-time sliding mode control law is derived using the proposed surface that compensates fractional time delay in sensor to controller and controller to actuator channels for uncertain network control systems. The sufficient condition for closed loop stability of the system is derived using the Lyapunov function. The efficacy of the proposed strategy is supported by the simulation results.     

Robustness evaluation of fractional order control for varying time delay processes

In this paper, we investigate the robustness of a methodology to design fractional order PI controllers combined with Smith Predictors, for varying time delay processes. To overcome the drawback of possible instability associated with Smith Predictor control structures, mainly due to the changes in the time delay, the design focuses on ensuring robustness of the closed loop system against time delay uncertainties. The proposed method is based on time-domain performance specifications??more accessible to the process engineer, rather than the more abstract notions related to the frequency domain. A second advantage of the proposed method relies on additional robustness to plant uncertainties, achieved by maximizing open-loop gain margin. The convergence problems associated with optimization techniques, previously used in fractional order controller designs, are eliminated by an iterative procedure in computing the gain margin. The simulation example provided demonstrates the efficiency of the proposed method, in comparison to classical integer order PI controller.     

Stabilizing network control for pneumatic systems with time-delays

This paper concerns with control design for networked pneumatic systems with uncertain communication delays. In the practical networked control systems (NCSs), there are usually unavoidable plant and communication delays. It has been known that time delays may not only deteriorate the system performance, but also destabilize the controlled plant. To alleviate the influence resulting from time delays while maintaining performance, a mixed fuzzy-PID/neural network compensating scheme is applied to the pneumatic system with communication delays. Real-world experiments verify effectiveness and superiority of our proposed approach.     

基于信息物理融合系统的紧耦合网络控制方法

从信息物理融合系统(CPS,cyber physical system)的设计理念来看,要求系统中的通信计算部分和被控制物理对象进行紧密耦合操作。遵照这种紧耦合操作原则,针对无线网络控制系统(WNCS,wireless networked control system),提出一种紧耦合自适应模糊控制方法。模拟实验数据显示这种设计方法能根据实时的NCS紧迫度和网络的拥塞度有效地调整被控系统的采样周期及网络信道占用优先级,从而优化利用了有限的网络资源,改善了整个网络控制系统的性能。     

HMM based estimation of NCS network load and its application in switching control

The analysis and design of the Networked Control System (NCS) are more challenging due to the random time delays brought by the network. And modeling the uncertain time delays has been becoming a significant focus of research. This paper modeled the network delays with Hidden Markov Model (HMM), and then on the basis of Viterbi algorithm, proposed a method to estimate the network’s current load state using random time delay sequence. In further simulation we first designed PID controllers corresponding to the network’s different load states respectively, and applied the proposed method to guide switching control of the networked closed-loop system. The results showed the effectiveness of HMM in network state estimation and switching control.     

Guaranteed Cost Networked Control for T–S Fuzzy Systems With Time Delays

This paper develops a guaranteed cost networked control (GCNC) method for Takagi-Sugeno (T-S) fuzzy systems with time delays. The state feedback controller is designed via the networked control system (NCS) theory. The stability of the overall fuzzy system using GCNC is also established. Network-induced delay in network transmission and packet dropout are analyzed. Some deductions are also extended to uncertain systems. Simulation results show the validity of the present control scheme     

Nonlinear bilateral teleoperators with non-collocated remote controller over delayed network

Remote robots in bilateral teleoperation systems are utilized to accomplish various missions in different locations, which are generally far away from local robots collocated with a human operator. In order to enhance flexibility of teleoperators with extensive applicability, this paper proposed a novel control framework, where the remote controller is non-collocated with the robot in the environment. In contrast to traditional teleoperation systems, the remote robot only needs to send out sensory information and receive control commands from the local side. Stability and transparency of the proposed teleoperators are studied for PD-like controller with fixed time delays, and P-like controller with time-varying delays. If the control gains are contingent to upper bounds of time delays, then the system is stable with guaranteed position tracking and force reflection. Numerical simulations and experiments were conducted to demonstrate the effectiveness of the proposed control algorithms in bilateral teleoperation.     

时延网络控制系统控制方法研究综述

本文介绍了网络控制系统的基本概念,分析了网络控制系统的优缺点,并主要针对网路控制系统中的时延问题,论述了6种时延网络控制系统控制方法:增广状态离散时间模型法、缓冲队列法、摄动法、随机最优控制方法、鲁棒控制方法、模糊逻辑调节法.本文对6种控制方法各自的特点和适用范围进行了较为详细地讨论,并对各自的优缺点进行了对比分析,对进一步研究适合于时延网络控制系统自身特点的控制方法进行了展望.本文研究的内容是当今控制领域研究的热点问题之一,无论对网络控制系统的研究与应用,还是对网络控制系统中时延问题的解决都具有一定的意义和参考价值.     

Optimizing controller location in networked control systems with packet drops

In networked control, there is locational freedom in choosing the node at which to locate the controller, so as to mitigate the effects of packet losses in the network. What is the optimal location for the placement of the control logic? Second, what is the optimal control law in that position? The difficulty in answering these two questions is that analysis of optimality in networked control systems subject to random packet drops suffers from Witsenhausen's 'non-classical information pattern'. Thus, the general problem is considered intractable. We make headway on this problem by using a "Long Packet Assumption", LPA, which allows packets to be arbitrarily long. This is not intended for implementation, but only to develop a lower bound on the cost. In particular, under this assumption the optimal controller location can be shown to be collocated with the actuator. For this position, under the LPA, we can also calculate the optimal cost, which is then a lower bound on the optimal cost for the original problem for all locations. Despite the apparent strength of the LPA, we have found that this lower bound is often close to currently realizable upper bounds. This establishes the near optimality of currently implementable controllers in such instances. Using the lower bound on cost we obtain a necessary condition for stabilizability over all controller locations. This condition matches known sufficient conditions for some special cases, thus establishing a necessary and sufficient condition for location optimized stabilizability of networked control systems with packet loss.     

具有时延和丢包的不确定性NCS的稳定性

研究了同时具有网络时延和数据丢包的不确定网络化控制系统的稳定性.将数据丢失看成一种特殊的时延,利用动态反馈控制器设计提高系统的动态性能,得到了总时滞(包括传感器与控制器之间的时滞,控制器与执行器之间的时滞)的表达式,建立了不确定网络化控制系统模型.通过构造李亚普诺夫函数,采用线性矩阵不等式技巧,给出了系统稳定的判定定理.仿真结果表明了该方法的有效性.     

Quantized Observer-Based Sliding Mode Control for Networked Control Systems Via the Time-Delay Approach

This paper investigates the sliding mode control problem for networked control systems, which are influenced by the non-ideal network environment, such as network-induced delays, packet dropouts and quantization errors. The states of the system are assumed to be unavailable, and an observer is designed to estimate the state of the system, based on which a sliding mode controller is given to guarantee the closed-loop system to be stable. Furthermore, it is shown that the proposed control scheme ensures the reachability of the sliding surfaces in both the state estimate space and the estimation error space. Finally, a numerical example is given to illustrated the effectiveness of the proposed methodology.