Vision Sensors Eliminate Faulty Rejections
Pattern and brightness tools accurately inspect wheel fastener parts
Maclean Vehicle Systems (MVS) produces many automotive fastener products, including stainless steel capped wheel nuts. The nuts are assembled on an index machine that processes two parts simultaneously at each station. The fasteners must be inspected to verify the nuts are properly threaded. MVS previously performed this fastener inspection with an eddy current sensor whose accuracy was unreliable, at times resulting in expensive over-sorting.
“We looked at a number of different vision sensors,” said TJ Konieczke, Manufacturing Controls Engineer for MVS. “Some were sensitive, intimidating, and had a high learning curve like the vision systems that we have used in the past. We selected Cognex...vision sensors because they are very easy to program and operate. We simply put them in place, connect a PC to the USB port, train them on the part to be inspected, and pick tools off a menu that inspect the critical features of the part.”
MVS mounted two Cognex vision sensors at a 45 degree angle above the two parts in the inspection station of the assembly machine. The sensors look into the assembly machine and evaluate the wheel nuts so that they can appropriately sorted for shipment. The parts are presented to the inspection station in a fixture and held in position by a spring-loaded keeper, so there is some variability in the height at which they are positioned. MVS addressed the variable placement of the part by using an edge finder tool to locate the edge of the part. A brightness tool looks for the light reflecting off the threads.
The vision sensors interface with a PLC which operates the assembly machine. The PLC provides a static output that indicates when a fixture is in position with two new parts. When the vision sensors receive this signal, they capture an image and inspect the part. The vision sensors then send an output to the PLC, indicating whether the part is good or bad. Based on the inspection results, the PLC determines whether to send the part to the pass or fail bin.
The sensors’ ability to determine part position and evaluate the brightness of the entire opening of a nut has eliminated not only incorrect pass/fail decisions but associated over-sorting. Cognex vision sensors have also increased MVS’ confidence that no bad parts will be shipped to a customer. “The latest generation of vision sensors is much more reliable and accurate while being just as easy to set up and operate and not much more expensive than traditional sensors,” Konieczke concluded.