Patent ID: 6802995
Filing Date: 2004-10-12
Classification: B29C

Abstract:
In an extrusion system having a die for receiving molten plastic and for providing from the die a bubble that exits the die in molten form and that solidifies above a frost line, the system providing cooling air on the bubble as it exits the die, the system comprising:a plurality of acoustic bubble sensors each arranged to provide a sound pulse to a bubble and to sense the sound pulse after it bounces off the bubble, the bubble sensors for providing data to indicate a position of the bubble; and a controller responsive to data from the plurality of bubble sensors for controlling a flow of cooling air to the bubble, the controller disregarding data from a sensor that is blocked so that the sensor cannot sense the sound pulse after it bounces off the bubble, and continuing to use data from at least one other bubble sensor to determine a position of the bubble.