Vision Sensors Eliminate Rejection of Good Parts in Inspecting Wheel Fasteners

September 2010. Cognex Corporation: One of Maclean Vehicle Systems’ (MVS’s) many automotive fastener products is 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 less than desired, at times resulting in expensive over-sort.

“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 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.”

Konieczke 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. Konieczke set up the vision sensor by dragging inspection tools and dropping them onto the features that he wanted to inspect. First, he addressed the variable placement of the part by using an edge finder tool to locate the edge of the part. Then he picked a brightness tool to look for the light reflecting off the threads.

He then set up the vision sensor to interface with the programmable logic controller (PLC) that 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 sensor receives this signal it captures an image and inspects the part. The vision sensor then sends an output to the PLC indicating that the part is either good or bad. Based on the inspection results, the PLC determines whether to send the part to the pass or fail bin.

Most recently, MVS has standardized new applications on the Cognex Checker 232 vision sensor that provides high resolution and a wide field of view to inspect small features up to 1,600 parts per minute.

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. “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.

About Cognex
Cognex Corporation designs, develops, manufactures and markets machine vision sensors and systems, or devices that can "see." Cognex vision sensors and systems are used in factories around the world where they guide, inspect, gauge, identify and assure the quality of a wide range of items during the manufacturing process. Cognex is the world's leader in the machine vision industry, having shipped more than 500,000 machine vision systems, representing over $2.5 billion in cumulative revenue, since the company's founding in 1981. Headquartered in Natick, Massachusetts, USA, Cognex has regional offices and distributors located throughout North America, Japan, Europe, Asia and Latin America. For details, visit Cognex on-line at http://www.cognex.com.