Drives and Controls Magazine

Robot arms scan bearings for signs of stress

01 February, 2002

Robot arms scan bearings for signs of stress

AEA Technology and NSK`s European Technology Centre have jointly developed what they claim is the world`s first NDT (non-destructive testing) machine that can measure residual stresses in the surfaces of bearing raceways. The technique, which is said to be 1,000 times faster to traditional methods based on X-ray diffraction, could help to prolong bearing lives.

The aim of the system, called BeSt, is to determine the nature and size of stresses in raceways. While compressive stresses can prevent surface cracks from growing, tensile stresses can accelerate the growth of cracks, leading to premature bearing failures.

Conventional X-ray measurements are expensive - the diffraction machines typically cost round £300,000 - and time-consuming, limiting the amount of data that can be collected.

The BeSt method exploits the fact that residual stresses in a material cause small changes in its magnetic permeability. A four-axis, servo-controlled robot arm carries electromagnetic probes across the raceway surface analysing its electromagnetic behaviour, and thus any stresses. It takes less than a second to take a measurement with a spatial resolution of ±3mm.

This means that a stress map of a complete raceway can be collected in about an hour, compared to the several weeks it would take using X-ray diffraction. The new system can measure stresses to a depth of around 18mm. AEA and NSK are now looking at ways of delving deeper into the material. The system may eventually be integrated into NSK`s production lines.