This system is installed on a glass bottle production line to control the volume of glass per bottle. Glass bottles are generally moulded from "lumps" of molten glass, the glass "gobs". These gobs are formed by a variable plunger which adjusts the amount molten glass which falls downwards through an orifice. A cutter then cuts the gobs. The gobs then free-fall for some distance until they are re-directed into the moulds. In this moulding process the volume/weight of the gobs is critical for the final quality of the bottles produced. This system controls the volume/weight of the glass gobs by adjusting the height of the plunger.
Accuracy
The system was tested over an 11 hour shift and the variation in the volume of the bottles produced stayed within 0.2% rms.
Self-calibration
The cameras are mounted to the surrounding structures. These structures are subject to vibration, thermal expansion and sagging due to load changes. To compensate for any changes in the alignment of the cameras we made the system self-calibrating. The system is able to re-calibrate itself during operation. The software re-computes the camera orientation angle with every measuring cycle, automatically. It only requires operator intervention during the setup phase after changing of the moulds.
3DM Volume Measurement System
The glass gobs (temperature 1200 °C) free-fall at 3 meters per second after being cut off by the cutter. At that instant the 3 CCD cameras capture an image of the gobs. The cameras are mounted in water-cooled housings to protect them from the heat. They also contain an air purge device to ensure that the cameras lens remain clear of any airborne contaminants and remove any unwanted condensation within the camera housing.
 |  |
| Figure 1. Molten Glass Gobs in free-fall | Figure 2. Glass Gob calculated profile |
From the captured images, the system computes a 3D model of the gobs and calculates the volumes.
 |
| Figure 3. Data base display showing volume variation. |