An investigation of the effects of human dynamics on system stability and performance

Abstract

Considered 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 flight 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 flight 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 influence 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 reflecting haptic device, which is used in telerobotics applications, is missing, a data-driven and first principles modeling of the Geomagic extsuperscript{ extregistered} Touch extsuperscript{TM} (formerly PHANToM extsuperscript{ extregistered} Omni extsuperscript{ extregistered}) 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.