A Guide to the Application of CORTEX
Laser Scanning and Diffraction Gauges

General:

The DG (Scanning Laser Gauge) and WG (Laser Wire Gauge) type instruments manufactured by CORTEX Research and Development Ltd. can measure the outside diameter of cylindrical objects, such as rods, tubes, cables, wires or fibres. The measurement is fast (up to 200 measurements/sec), precise and contact-free. The diameter range spanned by these instruments is from 10 micrometer to 50 mm.

Both instrument types (DG and WG gauges) are similar in that they basically consist of a Measuring Head and an industrial PC based Control Unit with a keypad and colour LCD monitor. One control unit can handle one or two measuring heads, depending on the application. The layout of these heads is similar in that there is a sender and a receiver part, and the object to be measured is placed between them (Fig. 1).

Measuring principles:

The WG Laser Wire Gauges have a stationary laser beam. The object to be measured is placed into the laser beam and diffracts (scatters) the light beam. The diffraction pattern is detected in the receiver head via a one dimensional CCD light sensor, digitised and evaluated by the control unit to obtain the diameter of the object. This principle is especially suited for objects of small diameter, such as wires or fibres.

The sender part of the DG Scanning Laser Gauges produces a scanning (up-down moving) laser beam (vertical line) and the object to be measured is placed into this beam and its „shadow” is detected at the receiver part. This principle is used for measuring larger diameter objects.

Application of the WG1C Laser Wire Gauge :

The typical application of the WG Laser Wire Gauges is the measurement of very thin objects, such as copper, tungsten and molybdenum wires. The typical diameter ranges are 10 - 500 m but diameters up to 1 mm (optionally 2 mm) can be measured.

The basic function of these instruments is to measure and display the wire diameter and to classify it according to programmed parameters (typically nominal diameter and tolerances). This can be extended with several options, such as SPC (Statistical Process Control) evaluation, analogue outputs (e.g. for chart recorder or process control), interfacing to a drawing or spooling machine to qualify a given length (spool) of wire either during manufacture or at the Quality Control of the finished product.

Normally one measuring head is connected to a control unit, however if required two measuring heads can also be connected. This makes the following applications possible (depending on the software of the control unit):

· Two independent diameter measurements at approximately the same location (cost effective solution).

· Measurement of the same wire at two different manufacturing stages (e.g. copper wire without and with lacquer layer).

· Measurement of the same wire in two orthogonal directions to obtain ovality data.

Application of the DG Scanning Diameter Gauges

The application of the DG Scanning Diameter Gauges are very widespread.

Basically two types of gauges are available: The DG1C Gauge performs precise measurements with 0.1 m resolution and works in the 0,05 - 10 mm measuring range (20 mm on special request), while the DG50C Gauge has a resolution of 1 m and a 1 ‑ 50 mm measuring range.

The main application of the DG1C Gauge is the QC of wires and cables or small machined parts during or after the manufacturing stage.

The DG50C Gauge can be used for similar measuring purposes for diameters up to 50 mm in harsh industrial environments.

All the options mentioned before (analogue outputs, double measuring heads, interfaces etc.) can be applied in the case of the Scanning Diameter Gauges as well.

Some of the most frequent applications are:

· Continuos diameter measurement of copper, tungsten and molybdenum wires during and after manufacture

· Measurement of cables

· Measurement of plastic rods and tubes

Application of Diameter Gauges in glass tube manufacture

The DG50C device has found wide spread use in the glass industry for measuring glass tube. A special characteristic of CORTEX equipment is that a reference signal is inputted from the glass cutter, which enables the gauge to classify and sort (usually via solid state relays) the cut-up glass tubes while the measurement is performed on the continuos tube on the drawing line, before the cut is made.

A further option is a 4-20 mA Proportional and/or PID control signal output for process control.

Thus one diameter gauge placed on the drawing line can provide the following functions, usually performed by several gauges:

· Measure and display of the continuos tube diameter

· Classification and sorting of the cut up glass tubes according to several tolerance classes

· PID process control signal (for air-blow or drawing speed regulation)

· Data collection (standalone or by monitoring PC via serial line).

The measuring systems can be expanded with the following measuring options:

· Laser measuring system for sensing glass imperfections (knots and stones) in glass tubes

· Vision system for measuring the bow (curvature) of cut up glass tubes

· Measurement of wall thickness of glass tubes

Special Applications of the DG Scanning Diameter Gauges

Below we list some of the special applications developed so far for the diameter gauges:

· Measurement of cut up glass tubes for compact fluorescent lighting sources (CFL). In this special application only one head is used, but the glass tubes travel parallel to the laser scan direction and also rotate. Thus as the tube traverses the measuring range, its diameter is measured at different angles of rotation, which enables to sort the piece according to both the diameter and ovality into different tolerance classes (Fig. 2).

This system can be extended with the measurement of tube-end tilt and tube length to provide complete QC of the product.

· Measurement of several wires with one gauge (Fig. 3).

· X-Y head arrangement for the measurement of ovality of wires (DG1C), glass tubes and hot rolled iron rods (DG50C) (Fig. 4).

· Measurement and control of steel rods on the grinding machine. In this application the grinding machine step motor is directly steered with programmable parameters by the control unit according to the difference between the measured and nominal diameter.

Data Collection Option:

All diameter measuring instruments can be supplied as an option in a special version for data acquisition. The functions of the software typically include SPC data acquisition, display and data logging according to work shifts and tube types. Alternatively several WG and/or DG devices can be linked to an overhead monitoring-evaluation system (PC) by the standard serial interface (RS232 or RS485) or via local computer network (Ethernet) for similar data collection purposes. Special software for a given application can be developed on request.

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