Wheel Fastener Inspection
Vision sensors compare many different features, eliminate incorrect decisions
Automotive wheel fasteners must be inspected to verify the nuts are properly threaded. A good part is threaded on the inside diameter, while a bad part has a smooth inside diameter. In the past, eddy-current sensor technology was the typical choice for this application. Applying an eddy-current sensor on this application is difficult since it does not detect small differences between a threaded and an unthreaded part. The eddy-current sensor has to be set to a very high level of sensitivity to ensure that it does not pass any unthreaded parts. This setting has the unintended consequence of rejecting a significant number of good parts, which would have to be sorted. Even a 0.5% false-positive rate in a day’s production run of 80,000 parts results in 400 rejected parts.
Inspection Technology of ChoiceMachine vision has become the technology of choice for wheel fastener inspection. The Cognex® Checker® vision sensor is capable of understanding what a good part should look like and can compare as many different features as needed to make a pass or fail decision. The Cognex Checker is very compact, has self-contained lighting and lens and is rugged enough to withstand tough factory conditions.
The Checker vision sensor determines the position of the part and evaluates the brightness of the nut opening compared to a specific point evaluated by an eddy-current sensor. Since a Checker sensor inspects a larger area and is able to adapt to variation in part appearance, it eliminates incorrect pass and fail decisions. The elimination of sorting costs quickly pays for the new vision sensor. The vision sensor also increases confidence and prevents bad parts from shipping to the final customer.