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The man-machine analogy in robotics and neurophysiology

Author(s): Prochazka Arthur

Journal: Journal of Automatic Control
ISSN 1450-9903

Volume: 12;
Issue: 1;
Start page: 4;
Date: 2002;
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Keywords: cybernetic actuator | finite state control | fuzzy logic

Since the time of Descartes the machine-like control of movement in animals and the animal-like control of movement in automata has fascinated and inspired scientists, engineers and philosophers alike. In 1966, Drs. Rajko Tomovic and Robert McGhee proposed the concept of a "cybernetic actuator," a new type of control system which "possesses the property of producing continuous controlled motion from an input which may assume only four distinct states". The specific application at the time was an artificial limb prosthesis. Signals from sensors monitoring joint angle and ground contact were to be continuously compared to a set of threshold values corresponding to specific moments in the step cycle. The binary signals (above or below threshold) were listed in a look-up chart which associated sensory combinations with actuator states. It was proposed that this system would provide all of the known state transitions required of an above knee prosthesis. In this and later papers Tomovic was careful to point out the differences between such "artificial reflex control" systems and neural control systems in animals. Nonetheless in the last few years it has become commonplace to see the control of locomotion and other rhythmical behaviors described in terms of "sensory rules," that is in terms of finite state systems. With the advent of neural nets and fuzzy logic control robotic devices are taking on more and more of the features of biological control systems. In turn, neurophysiologists borrow more and more from the concepts and mechanisms of modern control theory. The influence of Tomovic's simple but powerful idea continues to spread.
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