Topic of the Month in August: The latest Software Developments for infrared inspection

The forming of glass products, especially containers, is complex and needs the careful monitoring of many parameters. These parameters include IS timings; glass viscosity and temperature; mould temperatures and vacuum pressures, and all must stay within very narrow ranges of their preset levels.

External disturbances can cause changes and even a small change in one parameter will directly affect the value of the others. Natural drift in parameters often initiates instability in forming, causing faulty products. Hollow glass manufacturers always look for more ways to establish and maintain stable forming and hot end process monitoring is a successful way.

At the hot end, containers give off infrared radiation whose intensities vary according to glass temperature, material properties and thickness. A new infrared camera system captures images of containers straight after the IS machine and changes in infrared intensity are measured, stored and compared to a "blueprint” to spot deviations and allow the operator to correct them before production is lost. Deviations can often produce out-of-tolerance containers such as leaners, sunken shoulders or bent necks which, if they escape detection and rejection, can damage cold end handlers or clients' filling operations.

Shape inspection


Now a new Shape software module has been introduced which measures very accurately, right at the hot end, the shape of a round container. Even the smallest deviation in shape is notified straight away. Glassmakers can therefore catch any problems with the forming process at an early stage of the production process, before many other containers are manufactured in the same way.

During the first test-trials, it was observed that the dimensional accuracy in detection was actually too high, in certain situations. For instance, there were many containers with deformations in the shoulder area. According to the manufacturerŽs criteria these bottles should be qualified as faulty and therefore be removed. The glass manufacturers took a different view, however. Despite the deviation of the shape in the shoulder area, which was barely visible, the bottles were still ‘sellable' to their customers.

To overcome this ‘problem' the new Shape module was modified, now allowing the user to define its own reject-criteria for shape inspection. For this purpose the bottle or jar was divided in many measuring zones. For each zone the shape tolerance can be set-up by the user.

Another area that needed to be addressed was the classification of oval products. The development team came up with a software modification to enable the user to determine the tolerance for oval ware during set-up and therefore indicate if oval ware is acceptable or not. After these modifications, the test-trials proved to be successful – all kinds of shape deformations were found. Another unexpected success was that many bottles with so-called ‘fins' were also detected.

A final application of the new Shape module makes it possible to detect the so-called ‘shifted finish' of a bottle or jar. Sometimes the position of the finish is offset from the ideal centreline, caused by a malfunction of the glass forming process. These critical defects are now identified by the software so that the bottle or jar is rejected automatically. The Shape module not only increases the quality of the bottles, but also contributes to an increase in efficiency along the production-line.

Leaners and bent necks



The company has also developed a new and more sophisticated method to measure the eccentricity of the bottle. In most cases the eccentricity is still measured manually by rotating the bottle while looking at the maximal dimensional deviation, taken from the vertical axis at the finish.

This method is not very accurate and doesn't provide the hot end operator with in-depth information on the nature of the eccentricity problem (ie leaner or bent neck). Nor does it provide details of the origin of the problem - for example which cavities have an out-of-tolerance eccentricity; do all the cavities have the same problem; how often the problem is occurring.

With new software algorithms for eccentricity it is now possible to separate the contribution of the bent neck from the total eccentricity of the container. But this new method for eccentricity has proven far more effective when deployed at the production of socalled long neck bottles. Especially in these situations, it provides the machine operator with all the necessary information - enabling the right remedial actions to be performed.

Source: OGIS GmbH, www.glassglobal.com
in cooperation with dmg World Media, www.glassmediaonline.com and
XPAR Vision Authors: Joop Dalstra and Harro Kats, www.xparvision.com