Antagonistic drive mechanism to increase impulsive force inspired by exoskeleton spring system of mantis shrimp

Abstract

In this paper, a mechanism for generating an impulsive force by using the distortion of an exoskeleton is described. Pneumatic artificial muscles not only have a high power to weight ratio, but also have a high affinity with the human body due to their use of air pressure. However, pneumatic artificial muscles have a slow stretch response rate due to their viscous properties. Therefore, earthworm type mobile robots and wearable assistive devices using artificial muscles move slowly and have difficulty assisting human movements. We focus on the mechanism of force generation using the distortion of the exoskeleton, similar to what is seen in the punching of a mantis or the jumping of a grasshopper, as a countermeasure against the delay in the response rate of the artificial muscle. In this study, we propose a new mechanism to generate a shooting force by incorporating an element similar to an exoskeleton spring into the antagonistic drive mechanism of an artificial muscle. We designed and developed a prototype then operated it and measured the impulsive force. It was found that the developed mechanism showed similar joint movements through muscle contraction to those of mantis shrimp and grasshoppers. Furthermore, it was shown that the time constant for the maximum strike force was 6.6 N and 63.2 % of the maximum impulsive force was 0.183 s.