CONTROL SYSTEMS WITH NETWORK DELAY Asif Šabanović 1 , Kouhei Ohnishi 2 , Daisuke Yashiro 2 , Merve Acer 1 , Nadira Š.-Behlilović 1 1 Sabanci University, Orhanli, Istanbul, Turkey, 2 Keio University, Yokohama, Japan {asif,nadira@sabanciuniv.edu }, merveacer@su.sabanciuniv.edu , ohnishi@sd.keio.ac.jp , yasshi@sum.sd.keio.ac.jp Abstract. In this paper motion control systems with delay in measurement and control channels are discussed and a new structure of the observer-predictor is proposed. The feature of the proposed system is enforcement of the convergence in both the estimation and the prediction of the plant output in the presence of the variable, unknown delay in both measurement and in the control channels. The estimation is based on the available data – undelayed control input, the delayed measurement of position or velocity and the nominal parameters of the plant and it does not require apriori knowledge of the delay. The stability and convergence is proven and selection of observer and the controller parameters is discussed. Experimental results are shown to illustrate the theoretical predictions. Keywords. Control, Time-Delay, Motion Control, Disturbance observer. 1. INTRODUCTION ontrol of system with delay in measurement and/or in control channel, due to the wide use of the network and teleoperation, is becoming very interesting research topics. Such systems are encountered in remotely controlled systems. Ideal bilateral control allows extension of a person’s sensing to a remote environment. It has been paid considerable attentions in the recent and is expected to be an emerging point of modem developments in robotics, micro-parts handling, control theory and virtual reality systems. The potential applications of the teleoperation include network robotics, tele-surgery, space and seabed tele-manipulation, micro-nano parts handling, inspection and assembly. In recent years many interesting solutions ranging variation of the classic Smith predictor [1,2], control based on sliding modes [3], μ-Synthesis [4], Oboe and Fiorini proposed a design strategy of Internet-based telerobotics [5], Uchimura and Yakoh described bilateral robot system on hard realtime networks [6]. Passivity based approaches like scattering theory and wave variables have predominated the research field [7][8][9][10]. Those approaches assure the passivity as well as stability and are valid for constant delay. However, those are not able to be directly applied to time-varying delay cases. Among the proposed methods the communication disturbance observer (CDOB) based control of systems with delay [11] stands on its own as a simple design procedure based on well known disturbance observer method. It offers a framework for the application of the disturbance observer for the systems with constant and/or time-varying delay. Experimental results has confirmed applicability but at the same time revealed problem related to the convergence of the estimated- predicted value to the plant’s output, especially in the case of the time-varying delay. In this paper problems in control of motion systems with time delay in both measurement and the control channels will be discussed. The solution will be proposed in the general framework of disturbance observer method with additional compensation selected to guaranty the convergence of the estimated plant variables in the presence of unknown possibly time varying time delay in both measurement and the control channels. This additional compensation terms are shown to be essential improvement of the CDOB guarantying the convergence and the stability. The paper is organized as follows. In section II the plant and the problem statement are given. In section III the solution for systems with time delay and the dynamic distortion in the measurement channel are discussed. In section IV the solution for systems with delay in both measurement and the control channels are presented. In section V the closed loop behavior and the experimental results of the system with time delay in both measurement and the control channels are presented. 2. PLANT AND PROBLEM STATEMENT Assume known one dof motion control system exposed to unknown time delay in control channel and unknown dynamics and delay in the measurement channel. The error in measurement may consist of time delay, dynamical distortion, and nonlinear gain in any combination. Due to the fact that it appears in the measurement channel it can be treated as a block in series with system output as depicted in Fig. 1. At the same time the transmission of the control signal is assumed to be distortion free except for the time- delay. Fig. 1. Single dof system with distortion and delay in measurement and control channels C EDPE 2009, October 12-14, 2009, Dubrovnik, Croatia