Browsing by Subject "Time delay"

Now showing 1 - 20 of 48

Open Access
Adaptive friction compensations for mechanical systems with measurement delay
(SAGE Publications, 2021) Odabaş, Caner; Morgül, Ömer
Application performance of mechanical positioning systems might not coincide with the theory, mainly due to nonlinearities or imperfections of system models. Although it is sometimes possible to ignore these mismatches, systems generally suffer from performance degradation or even instability eventually. Especially, friction force and time delay are two major factors of these undesired effects. Hence, in this paper, Smith predictor-based controllers and an adaptive Coulomb friction observer are designed to enhance position tracking performance of a mechanical system including time delay. In fact, implemented hierarchical control scheme provides two-degree of freedom to control both velocity and position separately. The proposed observer structure is mainly motivated by the Friedland-Park observer but could be considered as an extension of it which characterizes a general class of nonlinear functions for friction estimation. To assure its functionality with delayed measurements, different velocity predictor schemes are designed and their performances are compared. As a guideline for observer design, some conditions for exponential stability and robustness analysis are presented. Simulation results demonstrate that the proposed control system enhances the tracking performance even when the actual friction is a compound of various static and dynamic terms.
Open Access
Adaptive observer designs for friction estimation in position control of simple mechanical systems with time delay
(2021-09) Odabaş, Caner
Friction force/torque is a well known natural eﬀect that can cause performance degradation or even instability in mechanical systems, although it sometimes can be disregarded in closed loop feedback design phase. Hence, friction modeling and cancellation methods can be vital to achieve desired robustness and performance criteria in position control problems. Basically, the topic of friction cancellation is divided into two main categories named model based and non-model based methods. Friction modeling is a broad area of research and there are lots of diﬀerent modeling approaches in various complexities. Among these approaches, Coulomb Model is one the simplest yet fundamental models. Nevertheless, in some cases, being a classical static model, it is inadequate to exhibit the dominant friction components occurring at diﬀerent motion stages such as break-away force, stick-slip motion, pre-sliding behavior or friction lag. Generally, dynamical models, i.e. LuGre Model, are more advanced as a result, they are better to describe such friction eﬀects. Unfortunately, for these cases, the number of friction parameters are increased. In fact, there is a trade-oﬀ between model complexity and parameter identiﬁcation. A desired system response may not be achieved when model parameters do not coincide with the existing friction coeﬃcients. In this manner, precise identiﬁcation of each parameter can be challenging when there are many of them. Besides, some of these parameters might be time varying due to environment, temperature, material properties, position, etc. Therefore, non-model based adaptive schemes are prevalent in the literature since these methods do not require any parameter identiﬁcation. In this study, we focus on adaptive observer based friction compensation techniques and provide some stability conditions. First, we consider simple second order mechanical systems with or without time delay under Coulomb friction. To estimate the Coulomb friction, we ﬁrst consider Friedland-Park observer. Then, some necessary conditions are stated to extend the estimation function in the observer structure to a larger class of functions. Especially measurement delay can be signiﬁcant since observers estimate friction based on the velocity measurements. Therefore, it is proposed to employ a velocity predictor either based on numerical diﬀerential equation solvers or inverse Pade approximant when the existing time delay is large. What is more, a new observer design that considers friction and velocity error dynamics together is proposed as a novel contribution. Extensive MATLAB simulations are conducted to investigate the performances of proposed observers in a closed loop position control system with and without delay. To this end, Smith predictor and ITAE index-based designs are considered to utilize a position controller. In some of these simulations, LuGre model is preferred to mimic the actual friction instead of Coulomb friction in order to observe the eﬀects of dynamic parameters. Moreover, some experiments are performed on DC motor platform driven by Arduino Uno microcontroller. Under the light of acquired results, observer based friction compensation improves the system performance even existing friction cannot be conﬁned to Coulomb coeﬃcient, especially when the implemented controller has low bandwidth. Also, in terms of practicability, it is an advantage that these observer structures do not require any parameter identiﬁcation.
Open Access
Computable delay margins for adaptive systems with state variables accessible
(Institute of Electrical and Electronics Engineers Inc., 2017) Hussain, H. S.; Yildiz, Y.; Matsutani, M.; Annaswamy, A. M.; Lavretsky, E.
Robust adaptive control of plants whose state variables are accessible in the presence of an input time delay is established in this paper. It is shown that a standard model reference adaptive controller modified with projection ensures global boundedness of the overall adaptive system for a range of nonzero delays. The upper bound of such delays, that is, the delay margin, is explicitly defined and can be computed a priori. © 1963-2012 IEEE.
Open Access
Controller redesign for delay margin improvement
(Elsevier, 2020-01) Gündeş, A. N.; Özbay, Hitay
Two important design objectives in feedback control are steady-state error minimization and delaymargin maximization. For many practical systems it is not possible to have infinite delay margin andzero steady state error for unit step reference input. This paper proposes a re-design method forcontrollers initially designed to satisfy the steady-state error requirement. The objective is to makestructural changes in the controller so that a lower bound of the delay margin is improved withoutaffecting the steady-state error. The order of the new controller is (ν+1) higher than the order of theoriginal controller, whereνis the number of unstable poles of the plant.
Open Access
Design of a switched robust control scheme for drug delivery in blood pressure regulation
(Elsevier B.V., 2016) Ahmed, S.; Özbay, Hitay
A control algorithm based on switching robust controllers is presented for a Linear Parameter Varying (LPV) time-delay system modeling automatic infusion of vasodilator drug to regulate postsurgical hypertension. The system is scheduled along a measurable signal trajectory. The prospective controllers are robustly designed at various operating points forming a finite set of robust controllers and then a hysteresis switching is performed between neighboring robust controllers for a larger operating range of the LPV system. The stability of the switching LPV system for the entire operating range is ensured by providing a sufficient condition in terms of bound on the scheduling signal variation using the concept of dwell time. Simulation results are provided to verify the performance of the designed control scheme. © 2016
Open Access
Dwell time-based stabilisation of switched linear delay systems using clock-dependent Lyapunov-Krasovskii functionals
(Taylor and Francis, 2018) Koru, A. T.; Delibaşı, A.; Özbay, Hitay
Dwell time stability conditions of the switched delay systems are derived using multiple clock-dependent Lyapunov-Krasovskii functionals. The corresponding conditions are approximated by both using piecewise linear functions and sum of squares polynomials. The upper bound of the dwell time is minimised using a combination of a bisection and a golden section search algorithm. Using the results obtained in the stability case, synthesis of dwell time minimiser controllers are presented. Some numerical examples are given to illustrate effectiveness of the proposed method, and its performance is compared with the existing approaches. The resulting values of the dwell time via the proposed technique show that the novel approach outperforms the previous ones.
Open Access
Explicit time-delay compensation in teleoperation: an adaptive control approach
(John Wiley and Sons Ltd, 2016) Abidi K.; Yildiz, Y.; Korpe, B. E.
This paper proposes a control framework that addresses the destabilizing effect of communication time delays and system uncertainties in telerobotics, in the presence of force feedback. Force feedback is necessary to obtain transparency, which is providing the human operator as close a feel as possible of the environment where the slave robot is operating. Achieving stability and providing transparency are conflicting goals. This is the major reason why, currently, a very few, if at all, fully operational force feedback teleoperation devices exist except for research environments. The proposed framework handles system uncertainty with adaptation and communication time delays with explicit delay compensation. The technology that allows this explicit adaptive time-delay compensation is inspired by Massachusetts Institute of Technology (MIT)'s Adaptive Posicast Controller. We provide simulation results that demonstrate stable explicit adaptive delay compensation in a force-reflecting teleoperation set up. Copyright Â© 2016 John Wiley & Sons, Ltd. Copyright Â© 2016 John Wiley & Sons, Ltd.
Open Access
Hopf cycles in one-sector optimal growth models with time delay
(Cambridge University Press, 2017) Özbay, Hitay; Saǧlam, Hüseyin Çağrı; Yüksel, Mustafa Kerem
This paper analyzes the existence of Hopf bifurcation and establishes the conditions under which the equilibrium path converges toward periodic solutions in a one-sector optimal growth model with delay. We establish the limits and the possibilities of nonlinear dynamics (i.e., cycles) vis-à-vis delays. In particular, we formulate a new method to further comprehend the root distribution of the characteristic equation of a standard optimal growth model with delayed investment structure. We show that nonmonotonic dynamics (limit cycles, persistent oscillations) occurs when the delayed investment causes permanent adjustment failures among the economic variables in the economy. © Cambridge University Press 2016.
Open Access
Independent estimation of input and measurement delays for a hybrid vertical spring-mass-damper via harmonic transfer functions
(IFAC, 2015-06) Uyanık, İsmail; Ankaralı, M. M.; Cowan, N. J.; Saranlı, U.; Morgül, Ömer; Özbay, Hitay
System identification of rhythmic locomotor systems is challenging due to the time-varying nature of their dynamics. Even though important aspects of these systems can be captured via explicit mechanics-based models, it is unclear how accurate such models can be while still being analytically tractable. An alternative approach for rhythmic locomotor systems is the use of data-driven system identification in the frequency domain via harmonic transfer functions (HTFs). To this end, the input-output dynamics of a locomotor behavior can be linearized around a stable limit cycle, yielding a linear, time-periodic system. However, few if any model-based or data-driven identification methods for time-periodic systems address the problem of input and measurement delays in the system. In this paper, we focus on data-driven system identification for a simple mechanical system and analyze its dynamics in the presence of input and measurement delays using HTFs. By exploiting the way input delays are modulated by the periodic dynamics, our results enable the separate, independent estimation of input and measurement delays, which would be indistinguishable were the system linear and time invariant. © 2015, IFAG.
Open Access
Integral action controllers for systems with time delays
(Springer, 2009) Özbay, Hitay; Gündeş, A. N.
Consider a stabilizing controller C 1 for a given plant P. If C 1 and P do not have any zeros at the origin, then one can use a cascade connected PI (proportional plus integral) controller C pi with C 1 and keep the feedback system stable. In this work we examine the allowable range of the integral action gain in C pi , and discuss how C 1 should be chosen to maximize this range for systems with time delays.
Open Access
Local pinning of networks of multi-agent systems with transmission and pinning delays
(Institute of Electrical and Electronics Engineers, 2016) Lu, W.; Atay, F. M.
We study the stability of networks of multi-agent systems with local pinning strategies and two types of time delays, namely the transmission delay in the network and the pinning delay of the controllers. Sufficient conditions for stability are derived under specific scenarios by computing or estimating the dominant eigenvalue of the characteristic equation. In addition, controlling the network by pinning a single node is studied. Moreover, perturbation methods are employed to derive conditions in the limit of small and large pinning strengths. Numerical algorithms are proposed to verify stability, and simulation examples are presented to confirm the efficiency of analytic results. ï¿½ 2015 IEEE.
Open Access
Low order controller design for systems with time delays
(2011-12) Gündeş, A. N.; Özbay, Hitay
Finite-dimensional controller synthesis methods are developed for some classes of linear, time-invariant, single-input single-output, or multi-input multi-output systems, which are subject to time delays. The proposed synthesis procedures give low-order stabilizing controllers that also achieve integral-action so that constant reference inputs are tracked asymptotically with zero steady-state error. © 2011 IEEE.
Open Access
Low-order controller design for haptic systems under delayed feedback
(2012) Liacu, B.; Koru, A. T.; Özbay, Hitay; Niculescu, S. -I.; Andriot, C.
In this paper, we consider PD controller design for haptic systems under delayed feedback. More precisely, we present a complete stability analysis of a haptic system where local dynamics are described by some second-order mechanical dynamics. Next, using two optimization techniques (H ∞ and stability margin optimization) we propose an optimal choice for the controller gains. The derived results are tested on a three degree of freedom real-time experimental platform to illustrate the theoretical results. © 2012 IFAC.
Open Access
A new model of cell dynamics in Acute Myeloid Leukemia involving distributed delays
(2012) Avila, J. L.; Bonnet, C.; Clairambault, J.; Özbay, Hitay; Niculescu, S. I.; Merhi, F.; Tang, R.; Marie, J. P.
In this paper we propose a refined model for the dynamical cell behavior in Acute Myeloid Leukemia (AML) compared to (Özbay et al, 2012) and (Adimy et al, 2008).We separate the cell growth phase into a sequence of several sub-compartments. Then, with the help of the method of characteristics, we show that the overall dynamical system of equations can be reduced to two coupled nonlinear equations with four internal sub-systems involving distributed delays. © 2012 IFAC.
Open Access
A new PI and PID control design method and its application to active queue management of TCP flows
(2007) Üstebay, Deniz
PID controllers are continuing to be used in many control applications due to their simple structures. Design of such controllers for unstable systems with time delays is an active research area. Recently, stabilizing PI and PD controllers for a class of unstable MIMO (multi-input multi-output) systems with input/output delays have been investigated and allowable controller gain intervals for such controllers have been maximized. Motivated by these studies, this thesis proposes a new method for tuning the parameters of PI, PD and PID controllers for integrating processes with time delays. The method is based on selecting the centers of the maximized gain intervals as the controller gains for the purpose of obtaining optimal controllers. As an application of this method, controllers for AQM (Active Queue Management) of TCP (Transmission Control Protocol) flows have been designed. AQM is a congestion control method used in computer networks to increase link utilization with less queueing delays. The fluid flow model of TCP’s congestion avoidance mode based on delay differential equations supplies the mathematical background for modelling the AQM as a feedback control system and designing different control schemes accordingly. Firstly, the proposed controller design method has been applied to AQM for the case of time invariant time delay and secondly the method has been supported with switching control technique to obtain optimum system performance in the case of time varying time delay. The performance of the designed controllers for both cases has been illustrated by packet level simulations in ns-2.
Open Access
A new PI and PID control design method for integrating systems with time delays: applications to AQM of TCP flows
(World Scientific and Engineering Academy and Society (WSEAS), 2007-02) Üstebay, Deniz; Özbay, Hitay; Gündeş, N.
Allowable PI and PD controller gains for a class of unstable MIMO systems with input/output delays have been investigated in [5, 12]. Using the results of these studies, we propose a new method for tuning the parameters of PI and PID controllers for integrating processes with time delays. As an application of this method, we design PI and PID controllers for Active Queue Management,of TCP flows and illustrate performance,of these controllers by packet level simulations in ns-2. Key‐Words: PID Controllers, Time Delay, Integrating Processes, Active Queue Management
Open Access
A new technique for direction of arrival estimation for ionospheric multipath channels
(ELSEVIER, 2009) Guldogan, M. B.; Arıkan, Orhan; Arikan, F.
A novel array signal processing technique is proposed to estimate HF channel parameters including number of paths, their respective direction of arrivals (DOA), delays, Doppler shifts and amplitudes. The proposed technique utilizes the Cross Ambiguity Function (CAF), hence, called as the CAF-DF technique. The CAF-DF technique iteratively processes the array output data and provides reliable estimates for DOA, delay, Doppler shift and amplitude corresponding to each impinging HF propagated wave onto an antenna array. Obtained results for both real and simulated data at different signal to noise ratio (SNR) values indicate the superior performance of the proposed technique over the well known MUltiple SIgnal Classification (MUSIC) technique.
Open Access
Numerical computation of H∞ optimal controllers for time delay systems using YALTA
(Elsevier B.V., 2016) Yeğin, M. O.; Özbay, Hitay
Numerical computation of H∞ controllers for time delay systems has been a challenge since 1980s. Even though significant techniques are developed to obtain direct optimal controllers, application of these methods may require manual computation depending on the plant. In this paper, an alternative computational technique is proposed for direct optimal controllers originally obtained by Toker and Özbay (1995). The new controller expression contains finite dimensional transfer functions and an infinite dimensional term, which is stable. Thus it is suitable for finite dimensional approximations and practical non-fragile implementations. In this method, in order to eliminate manual computation of the plant factorization for neutral and retarded delay systems YALTA (a tool developed at INRIA) is used. The new controller computation is implemented in Matlab, and it is illustrated on an example. © 2016
Open Access
Observer based friction cancellation in mechanical systems
(IEEE, 2014-10) Odabaş, Caner; Morgül, Ömer
An adaptive nonlinear observer based friction compensation for a special time delayed system is presented in this paper. Considering existing delay, an available Coulomb observer is modified and closed loop system is formed by using a Smith predictor based controller as if the process is delay free. Implemented hierarchical feedback system structure provides two-degree of freedom and controls both velocity and position separately. For this purpose, controller parametrization method is used to extend Smith predictor structure to the position control loop for different types of inputs and disturbance attenuation. Simulation results demonstrate that without requiring much information about friction force, the method can significantly improve the performance of a control system in which it is applied. © 2014 Institute of Control, Robotics and Systems (ICROS).
Open Access
On dwell time minimization for switched delay systems: Time-Scheduled Lyapunov Functions
(Elsevier B.V., 2016) Koru, A. T.; Delibaşı, A.; Özbay, Hitay
In the present paper, dwell time stability conditions of the switched delay systems are derived using scheduled Lyapunov-Krasovskii functions. The derivative of the Lyapunov functions are guaranteed to be negative semidefinite using free weighting matrices method. After representing the dwell time in terms of linear matrix inequalities, the upper bound of the dwell time is minimized using a bisection algorithm. Some numerical examples are given to illustrate effectiveness of the proposed method, and its performance is compared with the existing approaches. The yielding values of dwell time via the proposed technique show that the novel approach outperforms the previous ones. © 2016