High-speed vision system inspects high technology web

03 February 2015

A bespoke high-speed vision inspection system has been developed for a manufacturer of high technology web that is fabricated for use in green energy projects. 

The system, which was designed, developed and installed Optimal Industrial Automation, uses Cognex VisionPro software to process critical dimensional and physical attributes of the web while the line is running at high speed. The whole 500mm width of the web is inspected to a resolution of 125µm while the web is running at 1.5m/sec.

Initially, the client investigated the use of a vision inspection system from a standard supplier. However, due to the complexity of the task, no standard product was found to be suitable. Optimal, however, was able to create a bespoke solution. 

Part of the inspection task was to detect very small surface contaminants, these often being black. On a high contrast surface this should not be an issue, however for this project the target substrate was dark in colour and provided a low contrast, which made the task much more challenging.

A further part of the project related to the dimensional verification of key surface details, and these too had to be measured to a high level of accuracy with the web running at high speed. 

A further complication is that the web has to be inspected on both sides, before another operation is carried out on the product, and it is then inspected a third time. This requires the inspection system to have three inspection stations which means that, with the resolution requirement across the whole web, the amount of data that has to be continuously read and then processed in real time is huge.

A three-pronged approach
Optimal adopted a three-pronged approach to the project. The first stage involved developing vision inspection techniques that suited the challenging application – both from a data (image) acquisition point of view and a physical point of view. Various camera systems were tested, from multiple area scan through to individual and multiple line scan systems, but each had their issues. The company had to overcome problems such as camera frame rate, physical space aspects, and how the system would work in combination with the computers that had to process the data.

After testing all these types of camera, a state–of-the-art Contact Image Sensor used in combination with Cognex VisionPro software was chosen as the best solution, even though it had to be configured in a specific way.

Optimal also had to develop special lighting techniques, which were critical to the success of the project.

The third project stage was to develop a high-level software application and networking techniques which are able to handle and process the huge amounts of data in real-time. The data processing requirements of the system were such that multiple computers were required to provide decentralised processing; and this necessitated extensive data exchange between all of these machines and the cameras; this having to be in real time. This took a huge amount of development and testing work before the best solution was finalised.

After testing and the development of the necessary image processing algorithms it became clear that the computing power demands were going to be much higher than originally anticipated, the computing requirements necessitating the use of four powerful machines with one being dedicated to each inspection task and another carrying out user interface functions. This computer ‘array’ necessitated the development and testing of various data exchange techniques that would keep up with the system’s real time requirements. Finally, a method was developed that coped with the required speeds and was robust enough to ensure that no data was lost.

Optimal designed a test rig that enabled the end product to be tested in real time outside of the production facility. The whole system was brought together and tested in real time. 

After extensive testing the system was installed at the client’s plant, where it is now running on a continuous production line. Since installation, which was achieved on time and to budget, the manufacturer has reported no faults in downstream products resulting from defects that the Optimal system is inspecting. The success of this first system has resulted in another order from the same client for a second identical system. 

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