Browsing by Author "Sipahi, R."

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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, Yıldıray
Model 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.
Open Access
Human-in-the-loop systems with inner and outer feedback control loops: adaptation, stability conditions, and performance constraints
(American Institute of Aeronautics and Astronautics, 2019) Arabi, E.; Yücelen, T.; Sipahi, R.; Yıldız, Yıldıray
In this paper, we focus on human-in-the-loop physical systems with inner and outer feedback control loops. Specifically, our problem formulation considers that inner loop control laws use a model reference adaptive control approach to suppress the effect of system uncertainties such that the overall physical system operates close to its ideal behavior as desired in the presence of adverse conditions due to failures and/or modeling inaccuracies. Moreover, we consider that the outer loop control laws exist owing to employing either sequential loop closure and/or high-level guidance methods. As it is true in practice, in addition, humans are considered to inject commands directly to the outer loop dynamics in response to the changes in the physical system, where the outer loop commands affect inner loop dynamics in response to the commands received from the humans as well as in response to the changes in the physical system.
Open Access
Set-theoretic model reference adaptive control for performance guarantees in human-in-the-Loop systems; a pilot study
(American Institute of Aeronautics and Astronautics, Inc., 2020-01) Koru, Ahmet Taha; Doğan, K. M.; Yücelen, T.; Arabi, E.; Sipahi, R.; Yıldız, Yıldıray
Control design that achieves high performance in human-in-the-loop machine systems still remains a challenge. Model reference adaptive control (MRAC) is well positioned for this need since it can help address issues of nonlinearities and uncertainties in the machine system. Moreover, given that human behavior is also nonlinear, task-dependent, and timevarying in nature, MRAC could also offer solutions for a highly synergistic human-machine interactions. Recent results on set-theoretic MRAC further our understanding in terms of designing controllers that can bring the behavior of nonlinear machine dynamics within a tolerance of the behavior of a reference model; that is, such controllers can make nonlinear and uncertain dynamics behave like a “nominal model.” The advantage of this argument is that humans can be trained only with nominal models, without overwhelming them with extensive training on complex, nonlinear dynamics. Even only with a training on simple nominal models, human commands when supplemented with set-theoretic MRAC can help control complex, nonlinear dynamics. In this study, we present a computer-based simulator that our research team tested under various conditions, as preliminary results supporting the promise of a simpler yet more effective means to train humans and to still achieve satisfactory performance in human-machine systems where humans are presented with complex, nonlinear dynamics.
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.
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