Practical Approach for Product Dimension Measurement Using Stereoscopic Vision (original) (raw)

2014, International Journal of Electrical Energy

Vision techniques have become, since many years, a relevant means for mastering product quality parameters, as dimensions, especially in on line control and in a hard working environment. This development has been reached thanks to technologic progress in equipements, sensors and data processing power. Indeed, in dimensionnal control, industrial vision allows the detection of specific points of the object, to compute the sought dimension. This latter is, in a cartesian coordinates system, the two points Euclidean distance. However, depending of the application type and in spite of their performance, used cameras present, some constraints as parallaxe error. It is due to the natural shift, at the installation, of the cameras optical axis regarding target object; or to the dynamic state of the object. This error may affect significantly the measure precision. Stereoscopic vision is a solution that allows minimizing the above error and presenting the compromise between precision, installation space and costs. Two cameras are used to observe, each one, the whole object to be measured. In the proposed practical approach, the application is highly depending of a calibrating step, that consists in creating a data base composed of a maximum image points related to the target plan and their geometric positions in a considered coordinates system. When executed, the algorithm detects, thanks to the two cameras acquired information, pixels corresponding to object edges, find their correspondance in the created data base, computes their coordinates (xi,yi) in the defined coordinates system to, finally, computes the sought dimension. 