Continuous Measurement of Aggregate Size and Shape by Image Analysis of a Falling Stream

Quality control of aggregate is very important for mining, mineral processing and aggregate production. In last decade, several authors presented a system for automatic image analysis of aggregates on a moving conveyor belt. The test results showed that the system was capable of estimating size distributions of aggregates in real time, but could not give any information about shape(s) because of the difficulties of handling overlapping aggregates. As a consequence we initiated a study using an on-line computer system to analyse aggregate in a gravitational flow, i.e. a falling stream of particles. Compared with images from a moving conveyor belt, in gravity flow both aggregates and background appear more and less afflicted by overlaps. This, apart from alleviating the problems of overlapping, implies that the size and shape of aggregates can be measured more accurately. The system hardware includes a CCD camera, mounted at the end of a conveyor belt, an image frame grabber and a PC computer. The system software consists of image acquisition and selection, grey level image binarization, splitting of touching aggregates based on polygon approximation and size and shape analysis based on an oriented Feret box. The system has been tested in a quarry for aggregate production at Vasteras, Central Sweden