Research on zero-stiffness flexure hinge (ZSFH) based on spring four-bar linkage(4BSL)

In order to overcome the spring back behavior of the conventional flexure hinge, the positive and negative stiffness matching method is used. The spring four-bar linkage(4BSL) is designed as a negative stiffness rotation mechanism, while the inner and outer ring of the flexure hinge (IORFH) is used as a positive stiffness mechanism. By coupling the 4BSL and the IORFH, a novel Zero-stiffness Flexure Hinge(ZSFH) is constructed. The negative stiffness characteristics of the 4BSL are analyzed and the spring of 4BSL is designed as linear rectangular leaf spring string. The zero-stiffness quality of the ZSFH based on 4BSL (ZSFH_4BSL) is analyzed, and the influence of structural parameters of the ZSFH_4BSL on zero-stiffness quality is explored. Samples are made and verified by experiments. The test results show that in the range of ±20°, the torque is reduced by 95% compared with the IORFH, and the relative error between the test result and the theoretical result is less than 7%, which verifies the validity of the theoretical analysis and the excellence of the design scheme.