Sensing Without Wires

Wireless Sensors Can Streamline Production and Improve Reliability and Safety, but Still Need a Few Improvements

By Hank Hogan

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For manufacturers large and small, wireless sensors solve problems. In applications where their wired brethren pose installation problems, they can streamline and speed up part production by providing valuable data and even improve worker safety. They also help to ensure that parts are manufactured correctly and reliably.

However, reports from the field indicate that cost remains an issue, as do power consumption and data rates. System integration and spectrum conflicts also can be challenging.

In the end, though, what matters is that wires literally can hold manufacturing down. Thus, there's a great benefit to using wireless sensors.

Look, Up in the Sky
"What the wireless buys you is reducing things like cables getting in the way or wrapping around engine hardware," says Ryan Huth, manager of the assembly special process engineering team at GE Aviation in Evendale, Ohio.

In 2012, GE Aviation and its partners expect to deliver more than 3,350 jet engines for a mix of commercial and military customers. The company also will refurbish a percentage of the 24,000 engines currently on wing that it had a hand in manufacturing. Each engine can contain as many as 25,000 parts, some of which must be secured using fasteners.

Huth's team develops processes and practices that make this assembly more efficient and cost-effective. Years ago, they investigated and GE implemented wireless sensor-equipped torque wrenches. These wrenches transmit such parameters as torque value, running torque, torque angle, torque rate, fastener location and fastener count. The measurements must be accurate and repeatable to fractions of a lb-in. or fractions of a degree.

Going wireless made the assembly process easier and safer for GE's workers. There are no wires to become entangled or to cause a tripping hazard. In their work, GE mechanics continuously walk around modules and the engine is flipped through several orientations during assembly (Figure 1).

"It reduces the number of touches an operator makes to a computer interface," Huth adds as another wireless advantage. "In an assembly shop, anywhere between 30–40% of the touches by an operator actually are interfacing with a PC. So eliminating those steps really is leaning your process."

GE's products are subject to U.S. Federal Aviation Administration (FAA) rules. Every part and assembly step must be tracked, and this history must be available. Wireless sensors transmit digital data, thereby enabling remote quality assurance checks. This data also enables retrieval of the torque parameters for a given fastener in a particular engine.

Wireless torque wrenches have come a long way, particularly when it comes to batteries, Huth says. Although expensive, the tools are ergonomic, lightweight, and easily handle data transmission needs.

The same can't be said for other GE applications. In particular, there's a need for significant improvement in wireless digital metrology tools. GE performs a series of measurements on sub and full assemblies, checking that they meet flatness, roundness or other dimensional specifications.

Engine tolerances are tight, so the metrology equipment must make accurate and repeatable measurements at a number of locations to 0.1 mil. GE would like to handle this chore wirelessly but can't for two reasons, Huth says.

One reason is that both contact and non-contact wireless metrology tools are too power-hungry for current battery technologies. Another is that wireless data rates are too limited and latency too high for meaningful measurements of what can be rapidly moving or rotating assemblies. "We collect real-time data at high sampling rates, and we're collecting a lot of information about surfaces," Huth says. "We need to collect it to a very fine resolution."

GE's experience in actually implementing wireless sensors on a plant floor has uncovered various integration challenges. These have included interference between industrial and office wireless networks, with mobile phones and other gear also in the mix. There also have been issues incorporating the collected data into planning and enterprise software.

For wireless sensor products on the shop floor, all of these matters have been resolved, Huth says. But help from wireless sensor suppliers in tackling integration problems going forward would be appreciated.

Some Solutions

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