MEMS Proportional Control Valves Enable Lightweight Orthoses

Ten research projects out of the Center for Compact and Efficient Fluid Power (CCEFP) were presented at the Fluid Power Innovation and Research Conference(FPIRC) last fall. The projects pertain to five sectors in fluid-power research: human-scale technologies, mobile applications, manufacturing, stationary equipment, and fluids/tribology.

The first project—a Hybrid MEMS Proportional Fluid Control Valve (PDF)—is meant to replace bulky solenoid valves for motion control in orthoses, wearables, and other human-scale technologies. Like most MEMS, which is an acronym for micro-electro mechanical systems, it contains tiny components on a lightweight chip that perform mechanical tasks as part of a larger system.

Clean-room technology allows for MEMS with microscopic actuators that open and close orifice arrays for proportional flow control. (Courtesy of Pneumatic Tips)

Designed by a multi-institutional team led by the University of Minnesota, the hybrid MEMS uses a baseplate with tiny orifices interfacing another plate containing microscopic piezoelectric actuators. (Actuator arrays are shown on the left.)  The actuators are arranged in parallel for uniform pressure drop through the orifices. The MEMS are designed to work at pressures that are sufficient to supply airflow to larger pneumatic actuators. The team works with the University of Illinois at Champaign-Urbana to power their pneumatic ankle orthosis.

The piezoelectric actuators respond to a small voltage generated by two electrodes over the actuator plate. Depending on the strength of the electrical signal, the piezoelectric material will bend to proportionally open and close the orifices. By using a more reactive piezoelectric material over the bending axis and a less responsive one below, the team could achieve higher bending strength compared to actuators that use only one material (bimorph vs. unimorph).

The research meets the CCEFP’s mission to produce streamlined fluid power actuators and systems.  Because the piezoelectric actuators are low energy, they could be powered throughout the day using only a small battery, improving the overall comfort and weight of orthoses as patients recover from injuries.