Redundancy in the control of robots with highly coupled mechanical structures

This paper investigates the hypothesis that robots based on highly coupled mechanical structures can give rise to redundancy in control. Highly coupled mechanical structures have the property that actuation at one location can translate into movement at multiple locations, and conversely, movement at one location can be caused by multiple actuators. Due to this property, multiple control strategies may exist for a single behavior. Tensegrity structures which have recently been shown to form the basis for successful locomotor robots (Paul et al., 2005), have highly coupled mechanical structures. Thus, as a case study, it was of interest to investigate whether these new tensegrity based robots could offer a high degree of redundancy of control. This was investigated on two robots, based on three and four strut tensegrity prisms. Control strategies for locomotion were evolved using a genetic algorithm in simulation, and the evolved behaviors were compared. It was found that multiple control strategies existed for forward locomotion in both structures, and that qualitatively similar behavior could be obtained with significantly different control strategies. This indicated that a considerable degree of redundancy could exist in the control of robots based on highly coupled mechanical structures.