The implementation of smaller, lighter, and more agile military systems requires new actuation technologies that offer high power density in compact form factors. The Compact Hybrid Actuator Program (CHAP) is pursuing active material based, rectifying actuators to create new actuation solutions for these demanding applications. Our actuator approach is based on thin film NiTi membranes operating in parallel (high intrinsic power density, >125 kW/kg) combined with liquid rectification, MEMS passive check valves, and commercially available power electronics. Previous results demonstrated 8 micron thick membrane actuation with 150 Hz forced convection response and force output of 100N. This paper focuses on two developments critical in scaling up previous single membrane results to power levels sufficient for military applications. This first is the development of SOI MEMS fabricated microvalve arrays which exhibit high flow rate at high frequencies. The second focus area is the design, fabrication, and assembly of a form factor compact actuator. The initial prototype demonstration of this concept shows great promise for thin film NiTi based actuation both in military technologies and in other areas which demand extremely compact actuation such as embedded fluid delivery for biomedical applications.
The objective of our Compact Hybrid Actuator Device (CHAD) program is to produce a novel, ultra-compact, high force actuator to meet the aggressive requirements for navigation, guidance and control of a compact missile as well as other military and commercial applications confronted with tight volume constraints. Our approach to this challenge uses the high power density of thin film shape memory alloys coupled with fluid rectification and commercial power electronics. Phase One of our program demonstrated the performance of critical technical elements in a non-compact form factor. NiTi films were reproducibly deposited and then fabricated into bubble actuators that demonstrated ≥ 100 Hz performance when forced convection heat transfer to a liquid was optimized. Increased efficiency in thermal activation was achieved through high Joule heating rates for short duty cycles; this allowed simplification of the power electronics. These technical elements were combined to produce a thin film SMA pump which ultimately demonstrated force outputs on the order of 250 N and average power densities on the order of 50 W/kg when operated at 100 Hz. The demonstrated performance shows great promise for applications requiring ultracompact form factors with high output force.
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