Cognex vision sensors eliminate rejects of qualified parts in wheel fastener inspection

Graphics and brightness tools accurately inspect wheel fastener parts

     McLean Automotive Systems (MVS) manufactures many automotive fastener products, including stainless steel capped wheel nuts. The nuts are assembled on indexing machines, which process two parts simultaneously at each workstation. Fasteners must be inspected to verify that the nuts are properly threaded. MVS previously used eddy current sensors for fastener inspection, whose accuracy was unreliable and sometimes resulted in costly over-sorting.

"We looked at a lot of different vision sensors," said TJ Konieczke, a manufacturing controls engineer at MVS. "Some were sensitive, intimidating, and had a high learning curve, just like the vision systems we've used in the past." We chose Cognex vision sensors because they are very easy to program and operate. We simply place them in place, connect the PC to a USB port, train them on the part to be inspected, and select a tool from a menu that inspects the key features of the part. "

MVS mounted two Cognex vision sensors at a 45-degree angle above two components at the assembly machine inspection station. Sensors inspect assembly machines and evaluate wheel nuts so they can be properly sorted for shipment. Parts are presented to the inspection station in a fixture and are held in place by spring-loaded retainers, so there is some variation in their positioning height. MVS solves the problem of variable placement of parts by using edge finding tools to locate the edges of parts. A brightness tool looks for light reflected from threads.

Vision sensors interface with the PLC that operates the assembly machine. The programmable logic controller provides a static output that indicates when the fixture is in place with the two new parts. When vision sensors receive this signal, they capture an image and inspect the part. The vision sensor then sends an output to the PLC indicating whether the part is good or bad. Based on the inspection results, the programmable logic controller decides whether to send the part to a qualified bin or a failed bin.