Quadristability achieved by torsion-bending antagonistic action in a lamina emergent torsional joint

Multistability is the characteristic of a device can steadily stay at two or more positions without external power input, which has been employed to design surgical tools, mechanical metamaterials, logic operators, and multi-configuration robots. However, most existing multistable mechanisms with three or more stable states are created by combining several bistable mechanism units in series or parallel. This work proposes a novel quadristable compliant mechanism that achieves quadristablity utilizing the antagonistic action between torsional deflection and bending deflection in a lamina emergent torsional joint, rather than combining several bistable mechanism units. A kinetostatic model is developed based on the chained power series model to capture the load-deflection relations of this quadristable mechanism. Six design examples are presented to explore the quadristable characteristics using the kinetostatic model and nonlinear finite element model. The results are verified by the experimental results of several prototypes with varying structural parameters. The diverse stable shapes could also be useful for shape morphing mechanical metamaterials.