Abstract: Zero stiffness flexural pivot (ZSFP) has approximately zero rotational stiffness, doesn't require driving moment to function compared to general flexural pivots, and can be applied to fields like compliant grippers. By implementing inner and outer ring flexural pivot (IORFP) under pure torque as positive stiffness sub-system, studying negative stiffness mechanism and matching positive and negative stiffness, ZSFP can be modeled. The study proposes a negative stiffness rotation mechanism-spring-crank mechanism (SCM), and the negative stiffness characteristics of SCM is analyzed with models. Through matching of positive and negative stiffness, how the structural parameters of SCM affect the quality of zero stiffness for ZSFP is further analyzed. The study further proposes a stiffness and size specified spring-string of diamond leaves, which can be used in SCM, and finite element analysis (FEA) is applied to the stiffness models. Thus realizes the design, manufacture and test of a compact structure ZSFP. Test results indicate that under pure torque and ±18° rotational angle, the stiffness of ZSFP decreases 93% on average compared to that of IORFP. The proposed ZSFP has advantages in high structure compactness and quality of zero stiffness; the proposed SCM model and stiffness specified string of diamond leaves possess considerable value to the study of complaint mechanisms.

Key words: inner and outer ring flexural pivot, negative stiffness rotation mechanism, spring-crank mechanism, string of diamond leaves, zero stiffness flexural pivot