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Portable arm increases productivity.

Technicians at the Engineering Prototype Division of the Naval Air Warfare Center (NAWC) in China Lake, Calif., formerly needed a crane for inspecting or reverse-engineering very large parts. Now a portable measurement arm (a device that moves measurement instrumentation around an object) is brought to the task - whether the job is inspecting a part in process on a nearby computer numerical control (CNC) machine, or verifying a vendor's work a thousand miles away.

The division tackles jobs such as designing and producing a new warhead for the SLAM ER missile, retrofitting test aircraft with new antenna mounts, and reverse-engineering parts that are no longer being manufactured. Often, the new part must fit on another part or platform that cannot be brought to a coordinate measuring machine (CMM), and the project may start without benefit of any computer-aided design (CAD) drawings. The portable measurement arm and AnthroCAM 3-D CAD-based measurement, reverse-engineering, and analysis software - all from FARO Technologies, Inc. of Lake Mary, Fla. - have boosted speed and accuracy.

"We previously used a crane to lift the warhead, bring it to a granite table, and measure 150 features with a vertical height gauge, each with a different starting point," explained Mike Rivers, a materials engineering technician at the NAWC Weapons Division facility. "Then we'd lift it again, rotate it, place it on a rotary CMM table, make radial measurements, and finally remount the part for further machining. That took about nine hours."

By contrast, the measurement arm allows the staff to test larger sizes and weights. Both size and weight can be measured at the same time, and the inspection can be done right at the CNC machine. The total work time is now two hours. "Portability is the key" Rivers said. "Often the parts either would take two people to move them, or they're attached to an aircraft in need of a retrofit. For jobs involving ordinance or rockets, they may even be kept in a restricted area. In the past, we had to go in and take hand measurements with calipers, or we found ourselves limited in the shop by what would fit on our traditional CMM's."

The arm is an articulated measuring arm made of aircraft-grade aluminum, with precision bearings and rotary transducers at each of its six joints. At the arm's base is a mounting plate for direct attachment to either a fixed surface or a portable tripod. Rivers tends to use the tripod in his own facility. At a customer's site, he attaches the baseplate either to a table top or directly on a milling machine - anywhere there is a six-inch flat spot available. The arm's freedom of movement provides a basic spherical measurement-envelope of up to 8 feet. This range can be extended indefinitely as the user moves the arm to a new location and realigns to target data affixed on large bodies.

To take individual or continuous streams of data points, the user grasps a handle containing one of several probe styles and pushes a button as the tip touches each desired location. The probe sends the data to a PC-based on-board controller that translates each recorded location in three-dimensional space. Calibration of the probe takes less than one minute, and even then it is only needed when the user changes probes.

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Title Annotation:Naval Air Warfare Center's Engineering Prototype Division's use of a portable measurement arm for inspecting very large machinery
Author:Paula, Greg
Publication:Mechanical Engineering-CIME
Date:Jul 1, 1998
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