A recent laser-based measuring system with a 0.01-um resolution quickly measures surface flatness of fuel-injector spacer rings, up to 75,000 rings/day. The system also works more accurately than other methods such as LVDTs. Model LC-2420 laser-displacement meters from Keyence Corp., Woodcliff Lake, N.J., use a noncontact, laser-based, precision triangulation method to measure flatness. The system works on almost all surfaces including specularly reflective, highly polished finishes.


(left) Parallelism measurement of a spacer ring takes 1.7 sec. Good parts go to a bin via the triangular chute, then to another laser-inspection station for size sorting. Bad parts automatically route to a rework bin. The system operates in a temperature-controlled clean room and is mechanically isolated from the blue vibratory parts feeder located above it. Rings stack like coins in the clear vertical tube prior to inspection.

The ring manufacturer Metal Cutting Corp., Cedar Grove, N.J., uses a vibratory parts feeder to deliver rings to a special fixture housing two Model 2420s that simultaneously check top and bottom surfaces for parallelism. A mechanism rotates a ring between the beams four complete revolutions (reduces random errors). "Good" parts are parallel to within 1 um. A secondary sorting operation sizes parts into categories of 5 um total tolerance.

"Ring surfaces must be highly parallel or injectors can leak or incorrectly deliver a fuel charge," explains MCC's Larry Mesmer. "Automakers require 100% inspection." The laser system has helped MCC deliver over 75 million spacers without a single defect.