Design of a smart tailored stiffness nonlinear spring

Assembly manipulator plays an essential role in the space structure deployment process. Current manipulators' members possess a particular load-displacement function. However, the operation in unknown environments with variable external loads requires an intelligent manipulator that responds to the load according to the assigned loaddisplacement function associated with the current task. This paper presents a novel approach to generate a tailored nonlinear stiffness spring from a linear stiffness structure using smart materials. Herein, one member of the manipulator is idealized as an elastic cantilever beam with a particular restoring force-displacement function. Due to its high flexibility and strong actuating force, a Macro-fiber composite (MFC) patch is bonded to the beam's surface and used as an actuator to secure a tailored force-displacement function. A finite element model is developed based on the linear piezoelectric constitutive equations. Modal truncation method is used to reduce the order of the dynamic model of the structure. According to the tailored restoring force-displacement function, feedforward and feedback PID control algorithms are designed to compensate the force error. Finite element model is experimentally validated and the obtained results are used to simulate the nonlinear stiffness of the cantilever beam. Both simulation and experimental results demonstrate the effectiveness of the proposed approach to design the required tailored nonlinear spring.