Dimensional accuracy is a critical factor in the manufacture of industrial glass, which is often used for demanding technical applications, including the production of photovoltaic modules. Here, even a small deviation from the required geometry or thickness can adversely affect the function of the glass at a later date. Because it is transparent, glass is a difficult material to measure, but technologies are now available that are capable of reliably and accurately inspecting glass geometry (format, thickness and evenness) as well as surface quality.
The German glass manufacturer, Schott is currently using two different optical methods supplied by precision sensor specialist, Micro-Epsilon, including confocal chromatic sensors and the light intersection technique. At Schott’s production line, a robot places a glass pane on a transport system, which feeds it into the measuring station. Here, the pane is deposited on a solid block of granite in order to isolate it from factory floor borne vibrations. Six Micro-Epsilon optoNCDT 2401 confocal chromatic sensors are located on a traversing beam directly above the pane, and these measure the thickness and planarity in six tracks.
The desired distance or thickness data for the confocal principle is obtained from polychromatic white light, provided by a conventional LED. The sensors have a measuring range of 10mm and only measure the thickness from one side; the granite slab is also used as the reference surface.
Meanwhile, a Micro-Epsilon scanCONTROL 2800 series laser profile sensor circumnavigates the pane during the traversing process. The edge is therefore inspected for flaking (small defects, chips or cracks) while simultaneously measuring the edge geometry of the pane. In this way, the surface profile of the edge of the pane can be accurately reproduced.
Schott is actually using the two new measuring stations in its goods inwards and goods issued areas. This ensures that only 100% intact panes are further processed and despatched.