A framework of designing compliant mechanisms with nonlinear stiffness characteristics

This paper proposes a general framework to design nonlinear compliant mechanisms, taking advantage of the knowledge of rigid-body and compliant mechanisms. Stiffness-softening and stiffness-hardening mechanisms are discussed in this paper. Combining with adjusting the stiffness of the joints, the PRRP and RRRP mechanisms are used to design the 1-DOF translational and rotational mechanisms with nonlinear stiffness characteristics, respectively. It is presented that when designing a stiffness-softening mechanism the initial position is off the limb singularity position, and that when designing a stiffness-hardening mechanism the initial position should start from the limb singularity position. A compliant bistable translational mechanism is also designed and analysed in order to demonstrate the design approach. This paper can lay down a theoretical foundation for further optimizing compliant mechanisms, which can also be used for designing rigid-body mechanisms with nonlinear stiffness characteristics.