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Vision system reduces false rejects in wheel nut manufacture

Maclean Vehicle Systems (MVS), a company manufacturing automotive fastener products, among other components, is using machine vision to verify wheel nuts are properly threaded.

The nuts are assembled on an index machine that processes two parts simultaneously at each station. MVS previously performed the fastener inspection with an eddy current sensor, the accuracy for which was not high enough and at times resulted in expensive over-sort.

MVS mounted two Cognex Checker 101 vision sensors looking down at a 45 degree angle about five inches from the two parts in the inspection station of the assembly machine. 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.

The variable placement of the part was addressed by using an edge finder tool to locate the edge of the part. Then a brightness tool was used to look for the light reflecting off the threads.

'We looked at a number of different vision sensors,' said TJ Konieczke, manufacturing controls engineer for MVS. 'We selected Cognex Checker 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.'

The ability of the vision sensor to determine the position of the part and evaluate the brightness of the entire opening of the nut as opposed to an individual point evaluated by a traditional sensor has eliminated incorrect pass/fail decisions. The elimination of sorting costs quickly paid for the new vision sensor. The vision sensor has also increased confidence that not a single bad part will be shipped to the customer.

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