Intermittent predictive control of man and machine

Lead Research Organisation: Manchester Metropolitan University
Department Name: Exercise and Sports Science

Abstract

For fifty years, the servo mechanism, a simple, reactive, continuous feedback system, has been used as a model of human neural control systems. The PID servo is the most well known example which uses positional and velocity feedback to stabilise the variable of importance. It has always been known that the nervous system is more sophisticated than this. We are all aware that we anticipate: sometimes the error in our expectations catches us out, such as when we use too much force to lift a suitcase that is lighter than we expected. There has been increasing acceptance that the nervous system predicts our world and predicts how neural signals will be converted into bodily movement. As a model of motor control, the servo paradigm has been increasingly replaced by the optimal control or continuous predictive control paradigm which is founded on the engineering control methodology of internal models, prediction and optimisation. While it is more sophisticated and richer in its expression, the continuous predictive control paradigm is still inconsistent with several aspects of biological behaviour. Biological control is inherently variable. For humans, the temporal response to stimuli is inconsistent, the reformulating of immediate goals is highly flexible, and the bandwidth, i.e. frequency limit, of meaningful control is rather low. These neural features are not natural outcomes of the continuous control paradigm derived from engineering insight, which has been designed precisely to negate these limitations of human control and produce control which is temporally consistent, with high bandwidth, highly specified function and hence minimal goal flexibility. This proposal's power derives from a new type of engineering control methodology known as Intermittent predictive control . Intermittent predictive control provides a spectrum of possibilities between the two extremes of continuous-time and discrete-time control: the control signal consists of a sequence of (continuous-time) parameterised trajectories whose parameters are adjusted intermittently. It is different from discrete-time control in that the control is not constant between samples; it is different from continuous-time control in that the trajectories are reset intermittently. As a class of control theory, intermittent predictive control is more general than continuous control and provides a new paradigm incorporating continuous predictive and optimal control with intermittent, open loop (ballistic) control. This new intermittent predictive control paradigm has important technological applications. Consequently there is a need to develop the concept, theory and system identification of these controllers. This new paradigm is also intuitively similar to human physiological control systems in that low bandwidth, flexible, variable control is a natural product of the mechanism. We intend to discover whether human postural mechanisms are best explained by a continuous PID type of controller or an intermittent control process. The powerful corrective responses that occur when posture is perturbed can be explained on the basis of high bandwidth continuous feedback. However, we question whether such mechanisms dominate in the exquisitely fine control of unperturbed, skilled and learned postural activities such as standing. If the intermittent predictive control paradigm is applicable, then natural postural balance is correctly reinterpreted as centrally modulated, voluntary control like any other form of movement. Clarification of this issue will have important implications for diverse healthcare topics including the rehabilitation of spinally injured patients who are no longer able to stand and the diagnosis of risk factors in elderly patients with a history of falling.We aim to incorporate our biological insights into the design of engineering controllers that mimic the real-time flexibility of the human nervous system.

Publications

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Gawthrop P (2013) Human stick balancing: an intermittent control explanation. in Biological cybernetics

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Gawthrop P (2012) Intermittent tapping control in Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering

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Gawthrop P (2009) Event-driven intermittent control in International Journal of Control

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Gawthrop P (2011) The system-matched hold and the intermittent control separation principle in International Journal of Control

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Gawthrop P (2010) Act-and-Wait and Intermittent Control: Some Comments in IEEE Transactions on Control Systems Technology

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Gawthrop P (2011) Intermittent control: a computational theory of human control. in Biological cybernetics

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Gawthrop P (2013) Power-constrained intermittent control in International Journal of Control

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Gawthrop P (2010) Intermittent redesign of continuous controllers in International Journal of Control

 
Description This project provides the lead to a wider three centre project (Intermittent Predictive Control of Man and Machine). Together, our primary aim is to develop intermittent predictive control theory as a new paradigm for engineering and physiological control. We identify three specific objectives.

• Control of balance: to provide physiological evidence discriminating intermittent open-loop from continuous feedback mechanisms in human balance.

• Control of posture: to provide physiological evidence of intermittent open loop control of posture in general.

• System identification and control: to develop the theory and system identification methods that will discriminate intermittent from continuous control and to develop intermittent controllers that emulate natural human control.



Within this project part we are accumulating evidence to meet our main objective which is to provide physiological evidence discriminating (or not) intermittent open loop from continuous feedback mechanisms in human visual manual control and balance.



We have developed a rigorous methodology for distinguishing time-variant intermittent control from linear-time-invariant continuous control (Loram et al., 2012).



We have shown that intermittent control can provide a wider explanation of human motor control than continuous control (Gawthrop et al., 2011).



Using visual, manual sustained control of stable and unstable loads we have shown



• that continuous control is not necessary, that explicitly intermittent control is natural, effective, and soundly physiological in nature, and is particularly robust and effective for control of uncertain changing systems (Loram et al., 2011).

• that using conventional periodic and random disturbance stimuli and both nonparametric and parametric methods of analysis, sustained human control is compatible with an intermittent control model as well as linear, continuous control(Loram et al., 2009; Gollee et al., 2011)

• that sustained control contains substantial refractoriness which distinguishes it from time-invariant continuous control and which is naturally explained using intermittent control (Van de Kamp et al., 2011, 2013)

• that, unlike continuous control paradigms, the intermittent control paradigm can explain non-linear remnant without additive noise (Mamma et al., 2011)





Using somato-sensory, visual and vestibular feedback to balance and control the whole body as an unstable load we are conducting the same experiments and analysis as above. The results are yet to be published.
Exploitation Route Clarification of these issues will have important implications for diverse healthcare topics including the rehabilitation of spinally injured patients who are no longer able to stand and the diagnosis of risk factors in elderly patients with a history of falling.

We aim to incorporate our biological insights into the design of engineering controllers that mimic the real-time flexibility of the human nervous system.
The methods, and results and insights gained are being exploited through the development of artificial controllers that incorporate the real-time flexibility and adaptability of the human nervous system. These controllers are being applied to the development of assistive technology for rehabilitation in Spinal Cord Injury.



The techniques for measuring human control are being developed for the diagnosis of risk factors and development of human motor control throughout the life span.
Sectors Healthcare

URL http://www.icmm.org.uk/home
 
Description This demonstrates the relevance of intermittent control as a paradigm for interpreting human control. It demonstrates that human intermittent control is natural, is as or more effective than continuous control, that intermittent control is soundly physiological, that intermittent contorl allows more robust, successful adaptation to changing systems. Beneficiaries: All who develop, use or benefit from artifical or biological control systems Contribution Method: This research demonstrates the relevance of intermittent control as a paradigm for understanding human adaptive control. This Impact is a new methodology allowing system identification of intermittent control. Intermittent control is a powerful, general paradigm which encompasses continuous control as a special case and which incorporates a hybrid of event triggered and continuous processes. The intermittent control paradigm, initially proposed 60 years ago, is applicable to machine and biological control, but lacks a system identification methodology. The paradigm is particulalry relevant to low bandwidth and adaptive systems. This publication provides the first methodology for disciminating intermittent from continuous control in sustained control by biological or machine systems. This new methodology will promote widespread use of intermittent control in machine applications and will allow identification of intermittent control in biological systems. Intermittent control is a powerful, general paradigm which encompasses continuous control as a special case and which incorporates a hybrid of event triggered and continuous processes. The intermittent control paradigm, initially proposed 60 years ago, is applicable to machine and biological control, but lacks a system identification methodology. The paradigm is particulalry relevant to low bandwidth and adaptive systems. This publication provides the first methodology for disciminating intermittent from continuous control in sustained control by biological or machine systems. This new methodology will promote widespread use of intermittent control in machine applications and will allow identification of intermittent control in biological systems. Beneficiaries: Control Engineering, Human motor control and rehabilitation engineering communities Contribution Method: This research allows the development of intermittent control as a powerful, general paradigm for control engineering, rehabilitation engineering, assistive technology.
Sector Aerospace/ Defence and Marine,Digital/Communication/Information Technologies (including Software),Healthcare
Impact Types Cultural,Societal

 
Description robotICs
Amount € 200,000 (EUR)
Funding ID FP7-627959 
Organisation European Commission 
Sector Public
Country European Union (EU)
Start 04/2014 
End 03/2016
 
Description Partnership with IIT 
Organisation Italian Institute of Technology (Istituto Italiano di Tecnologia IIT)
Country Italy 
Sector Academic/University 
PI Contribution Contributing expertise of intermittent control Contributing lab facilities and resources to further experiments.
Collaborator Contribution Contributing time of Dr Jacopo Zeneri as collaborator and co-author. Contributing time of PhD studentship to conduct experimental studies at MMU.
Impact One publication so far. DOI 10.1109/EMBC.2016.7590629
Start Year 2015
 
Description Partnership with University of Manchester research group 
Organisation University of Manchester
Country United Kingdom 
Sector Academic/University 
PI Contribution Intellectual contribution to Academic collaboration
Collaborator Contribution Intellectual contribution to Academic collaboration
Impact Publication 10.1063/1.4871880
Start Year 2012