Case Study: Glass Arissing System
When glass is toughened it is heated to over 720°C then rapidly cooled. This introduces balanced internal stresses into the glass that increase its strength and cause it to crumble into small granular chunks when broken instead of splintering into jagged shards that are much more dangerous.
The glass has to be cut to shape prior to toughening. However, cutting leaves small cracks along the edges which, if not removed, will cause the glass to shatter during the toughening process. Hence, the edges of the glass must be ground, or arrissed, to remove the cracks before the glass can be toughened.
Arrissing machines already exist but, if the glass is anything other than rectangular, have to be pre-programmed with the size and shape of the glass to be processed. We developed a machine for a customer that could handle random shapes and sizes (up to a maximum of 4.5m x 2.5m) of glass without pre-programming. The pieces travel along a series of conveyors. As the glass travels along the conveyor it is imaged using a line scan camera to produce an image of the complete piece. The image is processed to produce a robot program describing the path around the piece. Glass is transferred to a conveyor incorporating a lift pallet to lift the glass off the conveyor so that a robot mounted above the conveyor and equipped with a grinding tool, can arriss the piece. The glass is then lowered back onto the conveyor and transferred to a washing and drying station.
We developed and supplied the imaging system and algorithms for tracking the glass boundary and automatic generation of the robot program.