A car is fitted with all kinds of lights, from headlights to lights on the dashboard. And each and every single one of those lights requires their own specific connector. Lumileds Middelburg, borne of Philips Lighting, manufactures connectors and subjects them to the rigorous quality assurance as required by the automotive industry. Automation is starting to play an increasingly bigger role in this process by replacing human visual inspections. For many years DEMCON has been developing and implementing inspection systems for Lumileds Middelburg based on machine vision technology.
One challenging project involved a production line which assembled 75,000 connectors a day. The system positioned a metal spring and a rubber ring on a moulded part with cast contact pins and a metal ring with contact wings. Accuracy was vital; the wings have to be flat enough to ensure good electrical contact and the rubber ring must not exhibit any signs of contamination or damage. The quality assurance procedures which were in place at the time, a vision system complemented by human inspection, were no longer sufficient.
DEMCON’s task was to automate the entire inspection for a cycle time of just over one second. The new vision system had to be able to carry out fourteen control measurements; it had to check whether the spring was in place, the type of wing ring, the flatness of the wings, whether there were any burrs on the wing ring, or if the rubber ring was contaminated/damaged etc. The process was made even more complicated by the fact that placing the connector in a product holder on a turntable offered no mechanical space for an unobscured 360° side view. Lumileds approached DEMCON to see whether 3D technology would provide a solution to this problem, so we conducted a feasibility study and developed a proof-of-principle.
The new system is fitted with two cameras which can take up to a total of five shots; image processing then takes care of the fourteen measurements per product. One of the cameras captures a shot of the side of the connector with the help of an angled mirror (a conic section), which is pushed around the product from the top. Another camera covers the intricate line pattern that is projected onto the wings to determine how flat they are. Inflections are detected using a 3D reconstruction, which is accurate to 15 micrometres. DEMCON built a system that comprises standard components such as cameras, optics and pattern projector, and even designed the mirror and the system’s mechanical suspension. Due to the high demands on service life (twenty million cycles per year), the decision was made to use an electrically-driven linear slide for the positioning of the mirror.
Developing the software to control the system and for image processing and the user interface proved to be the biggest challenge. The system assesses five images a second to decide whether a part is approved or rejected. The vision system was programmed in a sophisticated way, using the Halcon library for image editing, so that it could produce the necessary speed as well as high levels of reliability. According to the principles of six sigma, the number of erroneous ratings must not be greater than thirty per million. A comprehensive user interface displays images from the two cameras and a dashboard with current measurements. If necessary, rejection statistics can alert an operator.
Synchronising the vision system with the production line was absolutely essential, since the turntable cannot continue if the mirror is not raised. This was possible due to the excellent communication which was set up between the industrial PC for vision and the PLC for production control. Similarly, the cooperation between DEMCON and Lumileds Middelburg was also excellent throughout this project.
For more information visit www.demcon.com/industrial.
