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Journal of Experimental Biology 120,369-385 (1986)
Published by Company of Biologists 1986

A Biological Feedback Control System with Electronic Input: The Artificially Closed Femur-Tibia Control System of Stick Insects

G. WEILAND 1, U. BÄSSLER 1, and M. BRUNNER 1

1 Fachbereich Biologie der Universität D-6750 Kaiserslautern, F.R.G.

An experimental arrangement was constructed which is based on the open-loop femur-tibia control system of two stick insect species (Carausius morosus and Cuniculina impigra). It could be artificially closed in the following way: the position of the tibia was measured by an optical device and this value was used to drive a penmotor which moved the receptor apodeme of the femoral chordotonal organ in the same way as in intact animals. This arrangement allows direct comparison of the behaviour of the open-loop and the closed-loop system as well as introducing an additional delay.

The Carausius system has a phase reserve of only 30°-50° and the factor of feedback control approaches 1 between 1 and 2 Hz. This agrees with the observation that an additional delay of 70-200 ms produces long-lasting oscillations of 1-2 Hz. The Cuniculina system has a larger phase reserve and consequently a delay of 200 ms produced no oscillations. All experiments show that extrapolation from the open-loop system to the closed-loop system is valid, despite the non-linear characteristics of the loop. Consequences for servo-mechanisms during walking and rocking movements are discussed.

Key words: femur-tibia control system, feedback oscillations, stability and gain of feedback loops

Accepted on September 4, 1985






© The Company of Biologists Ltd 1986