All publications by Gawthrop in 2015

The bond graph approach to modelling biochemical networks is extended to allow hierarchical construction of complex models from simpler components. This is made possible by representing the simpler components as thermodynamically open systems exchanging mass and energy via ports. A key feature of this approach is that the resultant models are robustly thermodynamically compliant: the thermodynamic compliance is not dependent on precise numerical values of parameters. Moreover, the models are reusable owing to the well-defined interface provided by the energy ports. To extract bond graph model parameters from parameters found in the literature, general and compact formulae are developed to relate free-energy constants and equilibrium constants. The existence and uniqueness of solutions is considered in terms of fundamental properties of stoichiometric matrices. The approach is illustrated by building a hierarchical bond graph model of glycogenolysis in skeletal muscle.

It is now over 70 years since Kenneth J. Craik postulated that human control systems behave in an intermittent, rather than a continuous, fashion. This chapter provides a mathematical model of event-driven intermittent control, examines how this model explains some phenomena related to human motion control, and presents some experimental evidence for intermittency. Some new material related to constrained multivariable intermittent control is presented in the context of human standing, and some new material related to adaptive intermittent control is presented in the context of human balance and reaching. We believe that the ideas presented here in a physiological context will also prove to be useful in an engineering context.

This paper investigates the use of an actuator and sensor pair coupled via a control system to damp out oscillations in resonant mechanical systems. Specifically the designs emulate passive control strategies, resulting in controller dynamics that resemble a physical system. Here, the use of the novel dynamically dual approach is proposed to design the vibration absorbers to be implemented as the controller dynamics; this gives rise to the dynamically dual vibration absorber (DDVA). It is shown that the method is a natural generalisation of the classical single-degree of freedom mass–spring–damper vibration absorber and also of the popular acceleration feedback controller. This generalisation is applicable to the vibration control of arbitrarily complex resonant dynamical systems. It is further shown that the DDVA approach is analogous to the hybrid numerical-experimental testing technique known as substructuring. This analogy enables methods and results, such as robustness to sensor/actuator dynamics, to be applied to dynamically dual vibration absorbers. Illustrative experiments using both a hinged rigid beam and a flexible cantilever beam are presented.

Intermittent control uses open-loop control punctuated with feedback at times determined by error-driven events. The open-loop trajectories are based on an underlying closed-loop strategy and are generated by a system-matched hold. The single-loop event-driven intermittent control method is extended to the multi-loop decentralised control situation. This decentralised intermittent controller is based on an underlying continuous-time decentralised design which is suitable for systems with both input and state interactions. This extension is achieved by using local models of the remote interacting subsystems. These models are used for control signal generation and they are only updated with remote information at discrete event-driven sample times thus reducing information flow. The approach is illustrated using a simulation of a five-pool irrigation channel model previously examined in the literature.

Keywords: closed loop systems;control system synthesis;decentralised control;open loop systems;closed-loop strategy;continuous-time decentralised design;control signal generation;decentralised intermittent control;feedback;five-pool irrigation channel model;multiloop decentralised control;open-loop control;open-loop trajectory;single-loop event-driven intermittent control method;Approximation methods;Bismuth;Control systems;Couplings;Integrated circuits;Mathematical model;Observers

A sensorimotor architecture inspired from biological, vertebrate control should (i) explain the interface between high dimensional sensory analysis, low dimensional goals and high dimensional motor mechanisms and (ii) provide both stability and flexibility. Our interest concerns whether single-input-single-output intermittent control (SISO_IC) generalized to multivariable intermittent control (MIC) can meet these requirements.We base MIC on the continuous-time observer-predictorstate-feedback architecture. MIC uses event detection. A system matched hold (SMH), using the underlying continuoustime optimal control design, generates multivariate open-loop control signals between samples of the predicted state. Combined, this serial process provides a single-channel of control with optimised sensor fusion and motor synergies. Quadratic programming provides constrained, optimised equilibrium control design to handle unphysical configurations, redundancy and provides minimum, necessary reduction of open loop instability through optimised joint impedance. In this multivariate form, dimensionality is linked to goals rather than neuromuscular or sensory degrees of freedom. The biological and engineering rationale for intermittent rather than continuous multivariate control, is that the generalised hold sustains open loop predictive control while the open loop interval provides time within the feedback loop for online centralised, state dependent optimisation and selection.

Keywords: biological techniques;feedback;multivariable control systems;open loop systems;optimal control;quadratic programming;sensor fusion;somatosensory phenomena;biological control;continuous time optimal control design;continuous-time observer-predictorstate-feedback architecture;event detection;feedback loop;joint impedance;motor synergies;multivariate open-loop control signal;neuromuscular;open loop instability reduction;quadratic programming;sensor fusion;sensorimotor architecture;sensory analysis;single-input-single-output intermittent control;system matched hold;unstable multivariate system intermittent control;vertebrate control;Bandwidth;Feedback loop;Joints;Microwave integrated circuits;Muscles;Optimal control;Process control