Systems Able To Track Damage On Rotating Helo Parts

MicroStrain, Inc. announced Tuesday it performed a successful flight test of next generation wireless strain sensors for damage tracking of rotating helicopter parts and other dynamic components. The flight test coincided with the release of the company's energy harvesting wireless strain sensing modules into the market.

The miniaturized energy harvesting sensing nodes, called ESG-LINK, have a precision time keeper, non-volatile memory for on-board data logging, and a frequency agile transceiver. Sampling rates, sample durations, sensor offsets, sensor gains and on-board shunt calibration are all wirelessly programmable.

According to the Vermont-based company, these sensing systems will operate indefinitely -- without the need for batteries, by converting the component's cyclic strains into DC power using piezoelectric materials.

Piezoelectric materials is defined by the Heritage Dictionary as: "The generation of electricity or of electric polarity in dielectric crystals subjected to mechanical stress, or the generation of stress in such crystals subjected to an applied voltage."

Recent flight tests on a Bell 412 has shown the nodes will, indeed, operate continually, without batteries, even under low energy generation conditions of straight and level helicopter flight. By continuously monitoring the strains on rotating components, the nodes can record operational loads, compute metal fatigue, and estimate remaining component life.

The critical component instrumented on the Bell M412 was the pitch link. The pitch link's controls the rotor blade's angle of attack during rotation. Pitch link loads vary strongly with aircraft flight regimes, reaching much higher loads, as much as six times, during pull ups and gunnery turns as compared to straight and level flight. Therefore the pitch link is an excellent indicator of vehicle usage severity, and can provide critical data for improved condition based maintenance.

Strain gauges bonded to the pitch link were arranged to cancel thermal and bending effects and to amplify tension/compression loads. Bench calibrations allowed the strain gauge bridge to provide load data during flight. While spinning at five revolutions per second, data were logged within the wireless node's non-volatile memory and also periodically transmitted to a small mobile base station located in the helicopter's cabin. Flight test data from MicroStrain's wireless nodes were compared to data collected by from hard wired strain gauges, using slip rings, with close agreement.

Reducing power consumption is a key requirement when energy harvesting, because the energy "checkbook" must be balanced to support continuous operation. The company's engineers have recently reported on smart wireless sensor nodes that adapt their operating modes in accordance with the amount of energy available.

The latest adaptive energy harvesting wireless sensors can sample pitch link static and dynamic loads at a rate of 32 samples per second, then communicate these wireless data into the helicopter cabin, while consuming only 250 microwatts; compared to conventional Wheatstone bridge signal conditioning electronics, which draw 72 milliwatts.

"We're delighted to release our energy harvesting wireless sensing technology at Sensors Expo 2007. Our first successful flight test, performed in concert with Bell Helicopter, has demonstrated that our technology works. The potential of energy harvesting combined with wireless sensing will now begin to be fully realized, not only on rotating helicopter components, but on a wide range of machines, structures, and systems", said MicroStrain president Steven Arms.

FMI: www.microstrain.com