A machine vision-based technique for measuring the size distribution of precious ores has helped improve productivity in South African mining operations. The Lynxx Optical Particle Analyzer, developed by Stone Three Venture Technology, an advanced product development house, along with South African mining company, Anglo Platinum Research, uses vision to inspect the size of particles as the ore passes along a conveyor belt.
The ore is primarily measured for two reasons: to maximise its economic value as it is later sold on by the mining company for processing and to optimise the comminution process (reducing the particle size by crushing and grinding) in certain industries, such as the platinum and chrome industries.
The particle size varies depending on the comminution technique used or on the metal mined. Traditionally, the size of ore particles is measured using the belt-cut technique, in which the conveyor belt is stopped so that samples can be manually analysed. The Lynxx system uses cameras from Prosilica to provide a real-time and more productive alternative to the belt-cut technique. The system is capable of measuring ore particles ranging from 10-750mm and can also detect faults such as oversized particles.
The sensory rig of the Lynxx system contains four mini metal-halide floodlights to provide sufficient light, and a GC1020C camera from Prosilica looking down on the conveyor belt. The CCD colour camera has an XGA resolution (1024 x 768) with Gigabit Ethernet interface. The system images continuously, capturing between 15 to 25fps as the ore travels on the conveyor belt.
The camera is fitted inside Stone Three's custom-designed waterproof and dust-proof IP68 industrial enclosure, which is made of anodised aluminium on the outside to avoid corrosion and is designed to conduct heat away from the camera. Mining environments generally contain large amounts of dust and temperatures can reach 50°C.
The Lynxx software receives live images from the conveyor belt installation and performs various operations, such as component detection and segmentation, before calculating the ore size distribution.
The Lynxx Optical Particle Analyzer currently operates in several platinum mines in South Africa as well as iron ore and coal mines.
