Case Studies: Sensors Provide Continuous Quality Control

March 1, 2005
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Selcom SLS 5006/50-RU noncontact laser measurement sensors measure the thickness of calendered sheets. Photo: LMI Technologies

Vredestein Banden BV (Enschede, The Netherlands) is a medium-sized independent tire manufacturer whose strategy is to produce quality tires at an attractive price. Tires at the Enschede plant range from passenger tires for summer and winter weather conditions to all-season sports tires, vans and light truck tires, and bicycle tires. Vredestein Banden has made large investments in production equipment in recent years in order to gear itself up for the complex task of producing a wide range of tires at a single production site.

The Vredestein Banden tire plant was looking for an instrument to measure the thickness of calendered sheets. The company had been manually inspecting the surface using a caliper, but found that the method was prone to employee interpretation and did not provide continuous quality control. Also, the method lacked direct or continuous feedback to control the thickness.

Vredestein Banden chose LMI Technologies AB (Goteborg, Sweden) to help solve their problem. Four of LMI's Selcom laser measurement sensors were installed at the tire plant for calendered-sheet inspection. The four Selcom SLS 5006/50-RU sensors are mounted in a dual-head set up on two tracks on both sides of the sheet to measure the true shape and dimensions of the web. The material measured is fresh and uncured and can be characterized as hot and sticky with a black or shiny surface that evaporates as smoke or fume.

Since installing the sensors, accurate and reliable continuous thickness measurements can be made for improved quality control. Surface quality of the rollers can also be read from the Selcom Signal Processor signal, a measurement previously not possible.

The sensors consist of a semi-conductor laser diode that projects a 0.070-millimeter, 0.0028-inch, spot on the target surface. Measurement range is 6 millimeters, 0.24 inch, and stand-off distance is 50 millimeters, 1.97 inches. Resolution is 0.0015% of the measuring range. The sensor uses a visible laser light for added safety and easy spot positioning.

Since the tire plant has a two-track set up, two sets of thickness measurements are reported back to the calendered PLC for real-time control of the roller gap. This ensures that the thickness of the rubber sheet will be in tolerance, with minimum fluctuations. Measurements are not affected by surface texture, color, brightness, speed or temperature of the material.

"The SLS sensors are based on optical triangulation principles and are the most flexible sensor type available from LMI for this type of application," says Martin Sanden, business area manager for LMI Technologies.

LMI Technologies AB

(248) 359-2409



sidebar: Benefits

• The laser measurement sensors eliminate the problems of manual inspection and employee interpretation of measurements.

• The sensors provide continuous feedback to control the thickness of tires.

• The Selcom Signal Processor allows the surface quality of the rollers to be read, something previously not possible.

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