Optical Sensor for On-line Paper Caliper Measurement and Control, PaperCon 2013

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Papermakers have long demanded a reliable, non-marking, caliper measurement to be used as input to a caliper control system. Current methods utilize contacting buttons pressed into the sheet on both sides. The thickness of the sheet is then assumed to be the distance between the two buttons, measured by a magnetic displacement measurement. This method has inherent disadvantages, including: sheet marking, hole creation, sheet break, drift from dirt buildup, measurement error from sheet compression and high maintenance costs due to wear. In this paper we will present an online caliper measurement device which utilizes laser triangulation and eddy-current displacement measurement coupled with a novel single sided sheet stabilization device. Device features including sheet stabilization, temperature control and dust mitigation will also be discussed. The new device is simple to install and requires little maintenance. Results from production trials will be presented. Submicron profile agreement to lab and contacting sensors has been demonstrated on various light paper grades.