Measurement in Aerospace
Laser trackers guided by additional LEDs are providing six- degrees-of-freedom guidance to aerospace manufacturers.
also drill holes. Both are operations where knowing position and direction of the tool is vital.
“The big advantage here is that those six-axis robots do not need to be calibrated,” said Martin. Robot calibration is a time-consuming process, performed in special calibra- tion cells. Robots also need to be recalibrated periodically to ensure absolute accuracy. Giving them “senses” via metrol- ogy devices like laser trackers and LED mountings means the robot system can figure out accurately for itself its position relative to the part it is cutting, drilling, or fastening, to a typi- cal accuracy of 50 µm, according to Martin. Fusing metrology data from different sensors and turn- ing it into guidance for a robot is provided by software from New River Kinematics, the company that became a Hexagon brand in January 2013. This is done through Spatial Analyzer along with a newer package called SA Machine. “SA Machine provides that needed interface for the robot,” said Martin, who reports that it currently operates KUKA robots. More brand- name robot modules are on the way.
Not Just for Assembly
Metrology has migrated into not only airframe assembly, but also original fabrication of those parts. Metrology devices are helping machine both airframe and engines, according to Leo Somerville, president and CEO of Renishaw (Hoffman Estates, IL). Airframe parts include large monolithic stringers, wings, and ribs while precise jet engine parts include blades, disks, blisks, and stators.
The challenge in larger airframe parts is the need to machine them in temperature uncontrolled environments. On machine, in-process metrology is the only practical approach, since at- tempting to machine and then move a 10 or 20' (3.1–6.1-m) piece represents quite a challenge, according to Somer- ville. “On these large CNC machines, aircraft manufacturers have developed some clever techniques to re-establish datums and perform metrology checks on the parts,” he said. Since they are using CNC machines as metrology devices, they periodically calibrate them
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ManufacturingEngineeringMedia.com | February 2014
Photo courtesy Hexagon Metrology
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