A new spring actuator composing of two parts: driving unit and ferromagnetic shape memory alloy (FSMA) spring, is designed based on hybrid actuation mechanism. The driving unit, which is based on hybrid magnet, consists of coil, yoke, and ring shape permanent magnet (PM); the FSMA spring can be either composite material, which is made of shape memory alloy of superelastic grade, and soft ferromagnetic material, or FSMAs such as FePd. In this design, driving units are inserted in between ferromagnetic springs. This will provide the actuator with larger force and stroke. FEM analysis under axis symmetric model has been used to optimize the driving components. According to the numerical results, the iron blocks, both on the top and the bottom, can provide larger magnetic forces facing downwards and upwards respectively due to the gradient of magnetic flux density. Advantages of this design are simple, robust, and compact yet providing relatively large force (20N) and stroke (30mm).
Design of ferromagnetic shape memory alloy (FSMA) based spring actuators is discussed where a variety of design parameters are included, design of FSMA and FSMA composite, that of compact electromagnet, and the mode of deformation of a helical spring. Advantages of FSMA and FSMA composite are simple design, faster actuation speed large axial stroke and magnetic force.