Realization of Artificial Nonlinear Spring with Controllable Stiffness

Traditionally, nonlinear stiffness is achieved using mechanical components designed for a specific structure under certain loading conditions. In the present paper, the desired stiffness nonlinearity with various controlled stiffness values is obtained using smart materials. A prototype nonlinear spring is designed by a cantilever beam with bonded macro-fiber composite (MFC). The novel active prototype is modeled, simulated and experimentally validated to realize the artificial nonlinear spring (ANS) approach. To characterize the dynamic behavior of the proposed MFC-beam system, a dynamic linearized model is identified using a fourth order transfer function. Proportional integral (PI) controller is implemented to achieve the required spring stiffness function. According to the applied load estimation technique, three models are used to control the nonlinear stiffness. The results show precise nonlinear responses to measurable static and quasi-static external loads. Unmeasurable loads are real-time estimated and adequately responded. Both softening and hardening springs with a wide range of nonlinear stiffness values are obtained and tuned according to the demands. The proposed approach widens the application range of nonlinear springs and improves their performance.