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Latching valve control using ferromagnetic shape memory alloy actuators

Ferromagnetic Shape Memory Alloys (FSMA) are a class of active materials based on nickel alloys which offer controllable, large mechanical straining based on applied mechanical stress and magnetic fields. Actuation is based on crystallographic switching between meta-stable martensite phases. The high speed, binary switching, and no power hold behavior of the FSMA material are particularly well suited for latching valve applications such as hydraulic valves, optical switches, and electromechanical relays. This paper describes the design, development, and testing of a FSMA based actuator system to drive an industrial, hydraulic, latching valve. An opposing actuator configuration is used to switch the valve spool between spool positions, as well as to reset the opposing actuator element. Specific issues addressed in the design include FSMA material strain modeling, spool movement modeling, magnetic driving coil design and circuit controller design. A prototype system, based on a commercially available latching valve platform, was constructed and tested. Size of the complete system, including two FSMA actuators, valve body, and spool is 19 × 19 × 89 mm. Maximum valve actuation frequency of the prototype system is 133Hz in a 1000 psi hydraulic test bed.