Laser thickness gauge and method including passline angle correction

摘要

A laser thickness gauge has three laser displacement sensors each transmitting a laser beam onto a target web. Two sensors are spaced along the web and face one surface of the web and the third sensor faces the opposite surface. The thickness of a web that is positioned along a passline plane between the sensor is measured even when the passline plane is not perpendicular to the beams of the sensors. A data processor computes the passline angle from the distance measurements communicated from the three sensors. During setup and calibration, data representing physical characteristics of the gauge are measured and stored and during operation are processed with currently measured data to generate correction factors that are used to correct thickness measurements determined from the three laser sensors.

主权项

1. A laser thickness gauge for detecting the thickness of a target web extending along a passline plane, the gauge comprising:
(a) a pair of laser displacement sensors each capable of transmitting a laser beam, spaced apart by an air gap distance A, and comprising a first laser sensor spaced from a first side of the passline plane and a second laser sensor spaced from a second, opposite side of the passline plane, the sensors being oriented to direct their laser beams parallel to and toward each other and intersecting a reference plane at 90°, the first laser sensor having an output providing a signal representing the distance S1 between the first sensor and the web, the second laser sensor having an output providing a signal representing the distance S2 between the second sensor and the web; (b) a third laser displacement sensor capable of transmitting a laser beam, spaced from the passline plane and located on the same side of the passline plane as the second laser sensor to have its laser beam spaced along the passline by a distance DS away from the laser beam of the second sensor, the third sensor oriented to direct its laser beam parallel to the laser beams of the pair of laser sensors and having an output providing a signal representing the distance S3 between the third sensor and the web; and (c) a digital data processor including a storage memory for storing processing instructions and a value A representing the distance between the first laser sensor and the second laser sensor, the processor having an output and having inputs connected respectively to the outputs of the three laser sensors and receiving in real time a signal representing the distances S1, S2 and S3, the processor including a stored algorithm that computes in real time a measured thickness Tm of a web positioned along the passline plane in accordance with
tan θ=(S2−S3)/DS, passline angleθ=arctan(tan θ) andTm=(A−S1−S2)cos θ,wherein θ is an angle between the reference plane and the passline plane and wherein the three laser sensors are mounted in an orientation so their parallel laser beams are oriented at an oblique angle to the passline plane.