Design and Characterization of an Efficient Multistable Push-Pull Linear Actuator Using Magnetic Shape Memory Alloys

Magnetic shape memory alloys (MSMA) have significant potential for industrial applications, especially in fast-switching linear actuators. Besides the eponymous active magnetic shape memory effect, they are characterized by a significant hysteresis owing to the material-inherent twinning stresses. In conventional MSMA push-actuators, twinning stresses represent an energy loss. However, energy efficient concepts embrace them as a multistable holding force, which is especially beneficial for applications such as robotic grippers, clamping devices, and valves. To actively use the MSM effect in both push and pull directions, perpendicular magnetic fields are required. In this paper, we introduce a novel excitation setup using highly anisotropic pole shoes to generate the necessary fields with unprecedented efficiency. This concept allows customization to provide an inherent bias force in any direction, tailored to specific use cases. A demonstrator based on our approach is realized for a balanced push-pull actuator and analyzed extensively both simulatively as well as experimentally. Simulations were performed with COMSOL Multiphysics, integrating nonlinear magnetics and mechanics with a model based on homogenized twin bands from prior research. The nonlinear switching patterns predicted by the simulations were validated through optical investigations of the physical demonstrator using digital image correlation. The results confirm the dynamic, efficient, and multistable performance of the actuator, even under small disturbances.