Cortex Technical R&D Ltd.

Knot Detector

Real-Time Electro-Optical System for Detecting Knots and Stones in Lead Glass Tubes

A real-time laser based electro-optical system has been developed and implemented at a glass plant of the GE-Tungsram company at Vác, Hungary to detect knots and stones in lead glass tubes.

Knot detector

The differently sized and shaped knots and stones cause serious quality problems to lead glass manufacturing. The melted glass coming from the furnace proceeds its way as a continuous flow of hot tube along the drawing line towards the cutting machine. The knot detecting system is located at the end of the drawing line close to the cutting mechanism. The system contains a specially designed laser based sensor head connected to Cortex's Visual Signal Processor (VSP), which is a multi-DSP based visual microcomputer designed for stand-alone industrial image and signal processing tasks. The optical sensing head contains two special diode laser sources, which are perpendicular to each other. The optical head is built around the drawing line in a way that the continuous glass tube is situated at the cross section of the two laser lines. Each laser source has an optical detector opposite to it. The lens system of the detectors has been designed to enhance the light disturbances caused by knots and stones in the glass tube. The output waveforms of the detectors are continuously sampled at a very high rate and analysed by the VSP. The output of the system is a GO/NoGO signal (for each tube) to the sorting and rejecting mechanism. The system also provides statistical data for the host computer containing information about the number and size of detected knots and stones for each tube. The LabWindows CVI (TradeMark of National Instruments) based user interface running on the host PC provides straightforward user programming (i.e. parameter setting) of the system and easy access to the generated statistical data.

Four knot detecting systems has been put into practice at Vác Lighting Plant. The four systems are connected in network configuration and a single PC acts as the host computer.

(C) 1999. Cortex Ltd.