The mechanical assembly dimensional measurements with the automated visual inspection system

► The presented AVI system enables quick dimensional measurements. ► The study was to determine if AVI system can be used instead of current temperature measuring method. ► The replacement can not be done, because the bimetal is not linear at high temperatures. ► It can be used as a control system in the production for elimination of poor protectors. This article describes the automated visual inspection system for dimensional measurements of a mechanical assembly, called the protector, where an USB video camera with regular lens is used. A special user software was written. It uses a linear and a polynomial approximation for defining edges of selected protector structures. A higher order polynomial approximation is also used for pixel to metric units transformation. The accuracy, the repeatability and especially the usability of automated visual inspection system was verified with protectors, previously measured with the reference measurement method. The verification procedure showed that the measurement accuracy is in the range of ±0.02 mm. The time necessary for frame capturing, image processing and displaying the measurement results is less than a second. The comparison measurements showed that this system can not be used as a replacement for the current measurement system of monitoring switch-off temperatures in a oven. However, the presented visual inspection system can be used as a dimensional measurement and control system in the company testing laboratory.