Study on measurement system for non-uniform diameter spring by Machine Vision

This paper describes the establishment of a machine vision system for measurement compression spring. This kind of spring is used in the automotive suspension systems on cars. The special features for this kind spring are non-uniform diameter, non-regular helix and non-unique center line. A reverse engineering to construct spring geometry for further manufacturing becomes necessary when there is no CAD data for this spring. The reverse measurement facilities include contact stylus instrument, laser scanner and white-light grating system. These devices can be used to measure spring, but time and money consuming is a common problem with this measurement solution. In this paper, a new method with low-cost measurement developed to solve this problem. A man-machine interface for measurement by Visual Basic 6.0 has been developed which adopted a single camera mounted in a three-axis measurement frame. A fixed focal length camera and image processing technique were used to construct the object's position as well as coordinates. Therefore, the spiral of the measured spring can be constructed. By comparing the measured data to the ATOS system with Poly-works, the differences can be obtained. The largest upper deviation is about 3.3 mm and the largest lower deviation about -2.7 mm for spring geometry construction.