Robust, Cheap and Efficient Vision System for Mechanical Thermostat Switch Sub-assembly Inspection

This paper describes the automated visual inspection system implemented in the production line for mechanical thermostat electrical switch sub-assembly full inspection. The system checks for presence of the electrical switch plates, measures the slant angle of the electrical contact plate holder and measures the contact distance as one of the most important parameters of the mechanical thermostat. The developed system consists of an USB video camera with non-telecentric fixed focal length lens, custom LED line illumination and two laser line illuminations. Also a dedicated user software was written with unique inspection and measurement algorithm. The accuracy and the repeatability of automated visual inspection system was verified with reference objects, previously measured with the reference Mitutoyo profile projector. The verification procedure showed that the measurement accuracy is in a range of ± 0.04 mm and repeatability in a range of ± 0.03 mm.