Intermittent predictive control of man and machine

Lead Research Organisation: University of Glasgow
Department Name: School of Engineering

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

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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 (2012) Semi-active damping using a hybrid control approach in Journal of Intelligent Material Systems and Structures

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Gawthrop P (2009) Constrained intermittent model predictive control in International Journal of Control

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

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Gawthrop P (2009) Frequency-domain analysis of intermittent control in Proceedings of the Institution of Mechanical Engineers, Part I: Journal of Systems and Control Engineering

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

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

 
Description This project is part of a three centre project ("Intermittent Predictive Control of Man and Machine" EP/F068514/1, EP/F069022/1 and EP/F06974X/1). Together, our primary aim was to develop intermittent control theory as a new paradigm for engineering and physiological control. Intermittent control uses a sequence of parametrised open-loop control trajectories whose parameters are adjusted intermittently using feedback. We identified three objectives, corresponding to the three project parts:

- 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.

Within this project part we are addressing the last Objective: to develop the theoretical basis and system identification tools to discriminate intermittent open loop from continuous feedback control, and to develop and implement intermittent controllers that emulate natural human control, in an engineering context. Key findings are reviewed and summarised in (Gawthrop, Loram, Lakie and Gollee 2011).

We have developed descriptions for intermittent open loop control in the time and frequency domains (Gawthrop 2009) which has enabled us to implement system identification methods in both domains, and to evaluate these with simulated data and experimental recordings from humans performing a visual-manual control task (Gollee et al. 2012). This has led to the discovery of the "masquerading property" of intermittent control: for sustained control tasks an intermittent controller can appear indistinguishable from a similarly designed continuous controller, up to a certain bandwidth. This is important as it shows that sustained human control can be equally well explained by intermittent open loop control and by continuous control. This finding provides a theoretical basis for the development of the experimental methods by the project partners to distinguish intermittent from continuous control, by generalising the concept of refractoriness to higher order systems.

We have generalised intermittent control with a constant open-loop interval, to event driven intermittent control (Gawthrop and Wang, 2009). We have shown that intermittent control provides an alternative explanation for non-linear remnant which does not require an additional source of noise (Mamma et al. 2011). We have formulated intermittent control to use discretely different structural bases for trajectory construction such as an underlying continuous ("system-matched") or impulsive ("tapping") design, leading to a theoretical basis for tapping control (Gawthrop and Gollee 2012, Loram et al. 2011). In the same context we found that the separation principle remains valid if a system matched hold is used (Gawthrop and Wang 2011).

We found that intermittent control provides important advantages for engineering control system, in the context of semi-active damping (Gawthrop, Neild and Wagg 2012), power-constrained vibration control (Gawthrop, Wagg, Neild and Wang 2012), and as a way to overcome friction and other non-linearities (Gawthrop and Gollee 2012).

In summary, we have established the theoretical basis of intermittent open loop control and developed system identification tools which can differentiate intermittent from continuous control. We have demonstrated how intermittent control can be used in engineering

applications.
Exploitation Route We have shown that intermittent control can provide the basis for a range of engineering control problems such as semi-active damping, vibration control and control of application with non-linear actuators. With the outcome of this project, intermittent control can now be readily employed in these and other engineering applications.

Intermittent control is inherently variable which can be exploited in the context of adaptive control and learning. As a result, it is highly suitable for applications in robotics, in particular in the context of human machine interaction. Applications in assistive and rehabilitation systems (such as neuroprosthetics and rehabilitation robotics) or are of primary interest, since intermittent control can help to optimise the interaction with the human operator and enhance the assistive and rehabilitative outcome. The results of this research contribute to the understanding of human motor control, which can inform diagnostics and clinical intervention methods in neuromuscular dysfunction.

We are exploring how the research findings can be used in the context of clinical applications of control in rehabilitation engineering. In particular, we plan to develop systems, based on intermittent control, which make use of the open-loop interval to enhance robustness and improve rehabilitation outcome when used in neuroprosthetics or rehabilitation robotics. Our primary route to transfer these results into a clinical setting is through our established collaboration with the Queen Elizabeth National Spinal Injuries Unit, where we explore applications in spinal cord injury rehabilitation.

The basic concept of intermittent open-loop control marks a departure from traditional engineering control principles which have been based on continuous actuation and sensing. The theoretical framework developed in this project provides the basis for future fundamental new developments in engineering control, adaptation and learning.
Sectors Digital/Communication/Information Technologies (including Software),Healthcare

URL http://www.icmm.org.uk
 
Description An important aspect of intermittent control is that it can provide an explanation and theoretical framework for adaptation and learning, and for the role which variability plays in this context. We are developing methods to apply this understanding in the context of rehabilitation following neurological injury, e.g. in spinal cord injury, where re-learning of function plays an important role. This leads to better rehabilitation outcome, with associated reduced health-care costs.
First Year Of Impact 2013
Sector Healthcare
Impact Types Economic

 
Description CONACyT International Scholarships
Amount £76,698 (GBP)
Funding ID 314429 
Organisation National Council on Science and Technology (CONACYT) 
Sector Public
Country Mexico
Start 10/2013 
End 09/2016
 
Description Standard proposal
Amount £2,998,222 (GBP)
Funding ID EP/R018634/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Academic/University
Country United Kingdom
Start 05/2018 
End 04/2022
 
Description Multivariable intermittent control for learning and adaptation 
Organisation Delft University of Technology (TU Delft)
Department Robotics Institute
Country Netherlands 
Sector Academic/University 
PI Contribution - Develop new control engineering approaches to extend intermittent control to adaptation and learning - implement and evaluate multi-variable intermittent control
Collaborator Contribution Collaboration in all related areas, including robotics, human movement control, and control theory
Impact Multi-disciplinary collaboration, involving engineering, human physiology and robotics. Outputs include software implementations of algorithms and simulation methods.
Start Year 2014
 
Description Multivariable intermittent control for learning and adaptation 
Organisation Manchester Metropolitan University
Department School of Healthcare Science
Country United Kingdom 
Sector Academic/University 
PI Contribution - Develop new control engineering approaches to extend intermittent control to adaptation and learning - implement and evaluate multi-variable intermittent control
Collaborator Contribution Collaboration in all related areas, including robotics, human movement control, and control theory
Impact Multi-disciplinary collaboration, involving engineering, human physiology and robotics. Outputs include software implementations of algorithms and simulation methods.
Start Year 2014
 
Description Multivariable intermittent control for learning and adaptation 
Organisation University of Melbourne
Country Australia 
Sector Academic/University 
PI Contribution - Develop new control engineering approaches to extend intermittent control to adaptation and learning - implement and evaluate multi-variable intermittent control
Collaborator Contribution Collaboration in all related areas, including robotics, human movement control, and control theory
Impact Multi-disciplinary collaboration, involving engineering, human physiology and robotics. Outputs include software implementations of algorithms and simulation methods.
Start Year 2014
 
Description robotICs: do autonomous robots benefit from an Intermittent Control (IC) implementation? 
Organisation Delft University of Technology (TU Delft)
Department Robotics Institute
Country Netherlands 
Sector Academic/University 
PI Contribution - provide control theory knowledge and expertise - 6 months research placement by PhD student in Delft to transfer intermittent control implementation to robotic device
Collaborator Contribution - access to robotic systems to implement intermittent control algorithms - expertise in the area of robotics
Impact - PhD training - knowledge transfer
Start Year 2014
 
Description robotICs: do autonomous robots benefit from an Intermittent Control (IC) implementation? 
Organisation Manchester Metropolitan University
Department School of Healthcare Science
Country United Kingdom 
Sector Academic/University 
PI Contribution - provide control theory knowledge and expertise - 6 months research placement by PhD student in Delft to transfer intermittent control implementation to robotic device
Collaborator Contribution - access to robotic systems to implement intermittent control algorithms - expertise in the area of robotics
Impact - PhD training - knowledge transfer
Start Year 2014