Browsing by Author "Yousefi, Ehsan"
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Item Open Access Effects of linear filter on stability and performance of human-in-the-loop model reference adaptive control architectures(ASME, 2017) Yousefi, Ehsan; Demir, Didem Fatma; Sipahi, R.; Yücelen, T.; Yıldız, YıldırayModel reference adaptive control (MRAC) can effectively handle various challenges of the real world control problems including exogenous disturbances, system uncertainties, and degraded modes of operations. In human-in-the-loop settings, MRAC may cause unstable system trajectories. Basing on our recent work on the stability of MRAC-human dynamics, here we follow an optimization based computations to design a linear filter and study whether or not this filter inserted between the human model and MRAC could help remove such instabilities, and potentially improve performance. To this end, we present a mathematical approach to study how the error dynamics of MRAC could favorably or detrimentally influence human operator's error dynamics in performing a certain task. An illustrative numerical example concludes the study.Item Open Access An investigation of the effects of human dynamics on system stability and performance(Bilkent University, 2018-08) Yousefi, EhsanConsidered as a challenging element of closed-loop structures, the human operator, and his/her interactions with the underlying system, should be carefully analyzed to obtain a safe and high performing system. In this thesis, the interaction between human dynamics and the closed loop system is investigated for two different scenarios. The first scenario consists of a ight control system controlled by an adaptive controller. A telerobotic system where the controllers are conventional linear controllers is analyzed in the second scenario. Although model reference adaptive control (MRAC) offers mathematical design tools to effectively cope with many challenges of the real world control problems such as exogenous disturbances, system uncertainties, and degraded modes of operations, when faced with human-in-the-loop settings, these controllers can lead to unstable system trajectories in certain applications. To establish an understanding of stability limitations of MRAC architectures in the presence of humans, a mathematical framework is developed for the first scenario, whereby an MRAC is designed in conjunction with a class of linear human models including human reaction delays. This framework is then used to reveal, through stability analysis tools, the stability limit of the MRAC-human closed loop system and the range of model parameters respecting this limit. An illustrative numerical example of an adaptive ight control application with a Neal-Smith pilot model is utilized to demonstrate the effectiveness of the developed approaches. The effect of a linear filter, inserted between the human model and MRAC, on the closed loop stability is also investigated. Related to this, a mathematical approach to study how the error dynamics of MRAC could favorably or unfavorably in uence human operator's error dynamics in performing a certain task is analyzed. An illustrative numerical example concludes the study. For the second scenario, stability properties of three different human-in-the-loop telerobotic system architectures are comparatively investigated, in the presence of human reaction time-delay and communication time-delays. The challenging problem of stability characterization of systems with multiple time-delays is addressed by implementing rigorous stability analysis tools, and the results are verified via numerical illustrations. Practical insights about the results of the stability investigations are also provided. Finally, apart from these scenarios, after the observation that a simple linear transfer function model for a real force re ecting haptic device, which is used in telerobotics applications, is missing, a data-driven and first principles modeling of the Geomagic® Touch™ (formerly PHANToM® Omni® ) haptic device is considered. A simple linear model is provided for one of the degrees of freedom based on fundamental insights into the device structure and in light of experimental observations.Item Open Access Stability analysis of a human-in-the-loop telerobotics system with two independent time-delays(Elsevier B.V., 2017) Yousefi, Ehsan; Yıldıray, Yıldız; Sipahi, Rıfat; Yücelen, TanselIn this paper, stability of a human-in-the-loop telerobotics system with force feedback and communication delays is investigated. A general linear time-invariant time-delayed mathematical model of the human operator is incorporated into the system dynamics based on the interaction of the human operator with the rest of the telerobotic system. The resulting closed loop dynamics contains two independent time-delays mainly due to back and forth communication delay and human reaction time delay. Stability of this dynamics is characterized next on the plane of the two delays by rigorous mathematical investigation using Cluster Treatment of Characteristic Roots (CTCR). An illustrative numerical example is further provided in the results section along with interpretations.Item Open Access Stability analysis of human–adaptive controller interactions(American Institute of Aeronautics and Astronautics (AIAA), 2017) Yücelen, T.; Yıldız, Yıldıray; Sipahi, R.; Yousefi, Ehsan; Nguyen, N.In this paper, stability of human in the loop model reference adaptive control architectures is analyzed. For a general class of linear human models with time-delay, a fundamental stability limit of these architectures is established, which depends on the parameters of this human model as well as the reference model parameters of the adaptive controller. It is shown that when the given set of human model and reference model parameters satisfy this stability limit, the closed-loop system trajectories are guaranteed to be stable. © 2017, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.Item Open Access Stability limit of human-in-the-loop model reference adaptive control architectures(Taylor and Francis, 2018) Yücelen, T.; Yıldız, Yıldıray; Sipahi, R.; Yousefi, Ehsan; Nguyen, N.Model reference adaptive control (MRAC) offers mathematical and design tools to effectively cope with many challenges of real-world control problems such as exogenous disturbances, system uncertainties and degraded modes of operations. On the other hand, when faced with human-in-the-loop settings, these controllers can lead to unstable system trajectories in certain applications. To establish an understanding of stability limitations of MRAC architectures in the presence of humans, here a mathematical framework is developed whereby an MRAC is designed in conjunction with a class of linear human models including human reaction delays. This framework is then used to reveal, through stability analysis tools, the stability limit of the MRAC–human closed-loop system and the range of model parameters respecting this limit. An illustrative numerical example of an adaptive flight control application with a Neal–Smith pilot model is presented to demonstrate the effectiveness of developed approaches. © 2017 Informa UK Limited, trading as Taylor & Francis Group