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Triangulation is key to paint depth measurement
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01/04/2007
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A new type of non-contact sensor that attaches directly to a robot arm is being used to measure and control the thickness of coatings on vehicle instrument systems and airbag claddings during the spraying process while the paint is still wet, writes Roger Bishop.
The Micro-Epsilon system uses an eddy current sensor in combination with a laser-based optical triangulation sensor. The eddy current sensor measures the distance to the spray mould. The sensor has an opening in the centre, through which the laser sensor measures the distance to the sprayed component.
The eddy currents pass through the sprayed skin to the nickel-coated spray mould. The laser sensor supplies the reference distance to the skin surface. These processed signals are then subtracted from one another to provide an accurate measurement of the thickness of the applied paint skin.
Paint coatings are normally sprayed in a heated mould using robot-guided nozzles. Tight tolerances are required, particularly for safety-critical parts such as airbag claddings, on in-process measurement is highly desirable. Up to now, users have had to use single eddy current sensors. These would normally be positioned to touch the paint skin which require the paint to be dry and could also damage the surface.
The system was developed initially for Belgian company Recticel, which manufactures automotive components such as vehicle dashboards, HVAC systems, seating, head and arm rests and under-bonnet systems. It is now also being used by Poland’s leading tyre manufacturer Debica for measuring and controlling in real-time, the thickness of automotive tyre material as it is being applied to the metal/fabric former.
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Author
Roger Bishop
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