Wave-Shaped Notched Compliant Joint with High Rigidity

Notched compliant joints (NCJs) have been widely used in orthopedic surgeries requiring large curvatures for a minimally invasive approach to lesions and high rigidity for cutting hard tissues. With current NCJ designs, there is a trade-off between maximizing rigidity and maximizing curvature for a specified constrained size. Considering notch geometry, larger sizes of notch gaps lead to greater curvatures, however, smaller spacing between notches decreases rigidity. Herein, we propose an NCJ with a novel notch shape, such that the gap of the spacer can be increased without changing that of the notch. Furthermore, we determined the best design parameters for achieving the maximum rigidity for a given driving force. The higher rigidity of the proposed NCJ compared with that of general NCJs is shown through a simulation and experiments. The difference in rigidities between the proposed and general NCJs was 66% with the p-value of 5.68 × 10-9 in a 95% confidence interval which was found to be a statistically significant improvement. In a cutting test, while keeping the curvature, the proposed NCJ increased the cutting amount compared with general NCJs. We verified that the proposed NCJ can achieve both high rigidity and large curvature. The main feature of this study is the development of an NCJ in which both the gap of the spacer and the gap of the notch can be independently changed without affecting each other. The proposed NCJ achieves improved rigidity without loss of curvature.