Hybrid Monolithic SMA Actuators

Shape memory alloy (SMA) actuators are an attractive solution for many mechatronics applications. Compared to traditional actuation solutions, they provide scalable, linear motion with lower part counts. Low actuation voltages mean they can be readily integrated electrically with control electronics. Their high energy density makes them ideal for applications where actuation volume is restricted, and scaling actuators down has the benefit of increasing their potential bandwidth. Traditionally, the design and manufacture of an SMA actuator is done from stock wire or spring forms of NiTi, with a discrete bias mechanism to provide the required reset force. Reducing the size of SMA actuators increases the difficulty of fixturing this bias mechanism. To address this problem, others have introduced the concept of a monolithic actuator, machined from planar SMA and using local annealing to selectively impart the shape memory effect (SME) to portions of the structure. This paper proposes an alternative approach to monolithic SMA actuator fabrication, using powder fabrication techniques. Several advantages of this approach are described, including the potential for fabrication of so-called "hybrid" monolithic actuators with functionally graded areas. Finite element model (FEM) results are presented demonstrating the advantages of the hybrid approach over more traditional monolithic construction.