A magnetostrictive actuator enhanced by quasi-zero-stiffness preloading mechanism

Magnetostrictive actuators are a type of strain-based high-resolution actuators. With an appropriate preloading force applied on the giant magnetostrictive material (GMM), the magnetostriction can be effectively improved. Disc springs with large linear stiffness are usually adopted as the preloading mechanism. However, they lead to a fluctuation of the preloading force with the elongation of the GMM, and decreases the actuation stroke. To address this issue, a quasi-zero-stiffness (QZS) preloading mechanism is proposed, and realized through a parallel arrangement of positive-stiffness and negative-stiffness compliant mechanisms. It provides a sufficient preloading force within a limited adjustment displacement, and exhibits QZS during the actuation process, which decreases the fluctuation of the preloading force. A modified Jiles-Atherton model and a chained beam constraint model are adopted to characterize the magneto-mechanical effects in the QZS preloaded magnetostrictive actuator. The results reveal that there are coupling effects among the magnetization of GMM, the hyperelastic compression of GMM, and the deformation of the preloading mechanism. With a large linear-stiffness preloading, the fluctuation of the preloading force degrades the magnetization and increases the compression of the GMM, both contributing to the decrease of the actuation stroke. In contrast, the QZS mechanism provides a nearly constant preloading force. A prototype of the proposed isolator was manufactured, and both the QZS characteristics and the actuation performances were validated experimentally. Compared to the conventional actuator, under a harmonic applied magnetic field with the amplitude of 54 kA/m and 135 kA/m, the actuation stroke increases by 37.9% and 45.8%, and the fluctuation of the preloading force decreases by 98.3% and 96.7%, respectively. This study proposes a novel approach for the improved design of magnetostrictive actuators from the perspective of nonlinear mechanics.