Laser length measurement
By Clarence Klassen
On several recent projects, we measured web length on a roll using a laser measurement system. This was instead of the more common measuring wheel, which rides on the web.
Initial results required no calibration and produced a 100-ft roll within an inch. Nice job.
A unique pattern is projected onto the web. This is distorted by variations in the web surface. Doppler effects in the reflection can be interpreted to determine the speed or length of the web.
For good accuracy, the laser sensor must be carefully aligned to the specified tolerances. The sensor must be in an area free of wrinkles.
I wrote an article on this topic in Converting Quarterly 2018 Quarter 2, Achieving precise roll-length measurement and control.