Segmented 3D Scan Locates 176 Blade Root Bolts
A blade at the 100-metre class takes 176 studs at its root, on a pitch circle between 3.2 and 5.6 metres in diameter, with studs 900 to 1050 mm long. Fitting them by hand takes about 8 hours and five people per blade. This project carries a six-axis robot and an IP65 industrial 3D camera on an AGV, scans the root in segments, fuses the point clouds, locates all bolt holes at sub-millimetre level and hands each hole pose to the tightening equipment. The positioning cycle is 41 seconds. By hand, the studs are fitted one at a time on a narrow working face, several people crowd onto the same root, protrusion stays a matter of eye and rework happens.
A 900 to 1050 mm stud turns positioning into orientation
Acceptance turns on protrusion length within plus or minus 1 mm, and accurate hole position alone is not enough: with a stud 900 to 1050 mm long, a small angular error in the hole axis is amplified along that length.
What has to be output is therefore not the centre coordinate of each hole but the complete pose, position plus axis direction. With an accurate pose, the tightening equipment executes, and protrusion length is locked by hole location and tightening depth together. The difficulty is not finding circles in 2D but the 3D pose.
A 5.6 metre pitch circle does not fit in one scan
At 5.6 metres the pitch circle is larger than a single 3D scan can cover, and a fixed 3D station cannot be placed close enough or reach around it. The scheme has the six-axis robot carry the camera around the root in segments, leaving an overlap between neighbours for registration.
Segmentation is the only workable way to cover the circle, and it carries its own contradiction: error accumulates segment by segment until the sub-millimetre claim is lost. Range is bought with segmentation, precision is what it threatens.
Overlap registration plus global optimisation
The answer is registration on the overlap plus global optimisation: all segments are solved together, so one segment's deviation is constrained by its neighbours instead of adding up. Holes are identified on the fused model, with circular face and axis extracted per hole. Because recognition runs on the fused model, a seam cannot cut a hole off-centre.
41 seconds, then the tightening head takes over
The chain has four steps: point cloud capture, feature recognition, pose computation and robot guidance. Positioning takes 41 seconds; the pose of every hole is passed to the automatic tightening equipment and the studs are driven one by one with no re-clamping or manual intervention in between.
An AGV carries robot, camera and tightening head, so the system measures and tightens wherever the root is delivered, serving several stations. The camera is IP65 for blade-shop dust, and changeover recalls scan path and model parameters for circles from 3.2 to 5.6 m.
From 8 hours to 120 minutes, and the limits
Fitting 176 studs on one blade drops from 8 hours to within 120 minutes, an efficiency gain above 75 percent; operators fall from 5 to 2, saving about RMB 300,000 a year in labour; protrusion length holds within plus or minus 1 mm. All figures are subject to site acceptance results.
It suits precision guidance on oversized parts beyond a single field of view, including wind blades, large flanges and tower flanges. Buyers should check whether target accuracy and stitching error are compatible and whether the IP rating is enough; segment paths and overlap ratio decide fusion quality and need site verification.
Questions that come up on blade roots
Are all 176 holes located in a single scan?
No. The camera scans in segments, the clouds are registered and globally optimised into one pitch-circle model, and all holes are then identified on that model.
Does stitching make the error grow?
Naive stitching does. Overlap registration plus a global solution constrains accumulation back to an acceptable sub-millimetre range.
Who guarantees the plus or minus 1 mm protrusion?
Two parties: the 3D camera supplies the hole pose, the tightening equipment executes it, and protrusion is controlled by hole location and tightening depth together.