@article{GawLorLakGol11,
author = {Peter Gawthrop and Ian Loram and Martin Lakie and Henrik Gollee},
title = {Intermittent Control: A Computational Theory of Human Control},
journal = {Biological Cybernetics},
year = 2011,
volume = 104,
number = {1-2},
pages = {31-51},
doi = {10.1007/s00422-010-0416-4},
note = {Published online: 17th February 2011},
abstract = {Human motor control is often explained in terms of engineering ″servo″ theory. Recently, continuous, optimal control using internal models has emerged as a leading paradigm for voluntary movement. However, these engineering paradigms are designed for high bandwidth, inflexible, consistent systems whereas human control is low bandwidth and flexible using noisy sensors and actuators. By contrast, engineering intermittent control was designed for bandwidth-limited applications. Our general interest is whether intermittent rather than continuous control is generic to human motor control. Currently, it would be assumed that continuous control is the superior and physiologically natural choice for controlling unstable loads, for example as required for maintaining human balance. Using visual manual tracking of an unstable load, we show that control using gentle, intermittent taps is entirely natural and effective. The gentle tapping method resulted in slightly superior position control and velocity minimisation, a reduced feedback time delay, greater robustness to changing actuator gain and equal or greater linearity with respect to the external disturbance. Control was possible with a median contact rate of 0.8±0.3 s-1. However, when optimising position or velocity regulation, a modal contact rate of 2s-1 was observed. This modal rate was consistent with insignificant disturbance-joystick coherence beyond 1-2 Hz in both tapping and continuous contact methods. For this load, these results demonstrate a motor control process of serial ballistic trajectories limited to an optimum rate of 2 s-1. Consistent with theoretical reasoning, our results suggest that intermittent open loop action is a natural consequence of human physiology. }
}
@inproceedings{MamGolGawLor11,
author = {Mamma, A. and Gollee, H. and Gawthrop, P.J. and Loram, I.D.},
booktitle = {Control Automation (MED), 2011 19th Mediterranean Conference on},
title = {Intermittent control explains human motor remnant without additive noise},
year = 2011,
month = {june},
pages = {558 -563},
abstract = {Early work on modelling the human motion control system showed that only a part of the corresponding motion signals could be described in terms of a deterministic linear continuous-time model of the human control system. It was suggested that the unexplained part, called the remnant, could be modelled by adding a noise signal with a carefully chosen frequency spectrum. Intermittent control provides an alternative description of the human controller which includes a sampling mechanism. This paper suggests that the remnant can be explained by assuming that this sampling mechanism is not uniform; the addition of a noise signal is not required using this assumption. The approach of this paper is to compare the remnant frequency spectrum derived from experimental data with that from equivalent simulated data using each of the two models of the human controller in turn. It is found that both of the simulated models give similar remnant spectra to that of the experimental data. Further work is required to show which of the two models provides the best physiological explanation of remnant.},
keywords = {deterministic linear continuous time model;frequency spectrum;human motion control system;human motor remnant;intermittent control;continuous time systems;motion control;predictive control;},
doi = {10.1109/MED.2011.5983113}
}
@incollection{GawRiz11,
author = {Gawthrop, P.J. and Rizwi, F.},
affiliation = {School of Engineering, University of Glasgow, Scotland, UK},
title = {Coaxially Coupled Inverted Pendula: Bond Graph-Based Modelling, Design and Control},
booktitle = {Bond Graph Modelling of Engineering Systems},
editor = {Borutzky, Wolfgang},
publisher = {Springer New York},
isbn = {978-1-4419-9368-7},
keyword = {Engineering},
pages = {179-194},
doi = {10.1007/978-1-4419-9368-75},
abstract = {A bond graph method is used to examine qualitative aspects of a class of unstable under-actuated mechanical systems. It is shown that torque actuation leads to an unstabilisable system, whereas velocity actuation gives a controllable system which has, however, a right-half plane zero. The fundamental limitations theory of feedback control when a system has a right-half plane zero and a right-half plane pole is used to evaluate the desirable physical properties of coaxially coupled inverted pendula. An experimental system which approximates such a system is used to illustrate and validate the approach.},
year = 2011
}
@article{GawWan11,
author = {Gawthrop, Peter and Wang, Liuping},
title = {The system-matched hold and the intermittent control separation principle},
journal = {International Journal of Control},
volume = 84,
number = 12,
pages = {1965-1974},
year = 2011,
doi = {10.1080/00207179.2011.630759},
abstract = { An intermittent controller is a form of hybrid controller which adds a generalised sample and hold mechanism to an underlying continuous-time feedback control system. The sampling may be non-uniform or event driven. One particular form of the hold, termed the system-matched hold (SMH) mimics the behaviour of the closed-loop feedback control signal during the intermittent intervals. It is shown in this article that this choice of hold leads to an intermittent separation principle. In particular, this simple analytical result ensures that when using the SMH, the separation properties of the underlying state-estimate feedback control system carry over to the intermittent control system. This separation principle for the SMH has the important consequence that, unlike the zero-order hold case, the stability of the closed-loop system in the fixed sampling case is not dependent on sample interval. It is therefore suggested that the SMH should replace the conventional zero-order hold in circumstances where the sample interval is unknown, time-varying or determined by events. }
}
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