Automated Nut Fastening

Vision systems locate nuts for automated robotic nutrunner

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Manually torqueing lug nuts that attach a wheel to a wheel hub assembly (WHA) is a difficult manual operation. Nutrunners are typically used to apply torque and tighten the nuts. Two wheels are tightened in approximately 40 seconds. Because nutrunners are typically large and heavy, this application has posed significant challenges for automation. When the vehicle arrives in the torquing area it is not always in the same position and the wheels are allowed to rotate and tilt. For automated nut fastening, a vision-enabled robot locates and fastens the nuts without the intervention of an operator.

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Find the Circles

A Cognex^® In-Sight^® vision system determines the position of the nuts in five different axes. Cognex PatMax^® pattern matching technology is used to quickly locate the wheel. An In-Sight circle finder tool is used to precisely determine the location of the center of the axle. Two laser lines generate a crosshair on each wheel and an image is acquired of each crosshair at multiple angles. The difference in position of the two crosshairs is calculated to provide the angle at which the wheels are turned and tilted.

Once the angles of the wheel are calculated, the robot moves the nutrunner to tighten the nuts. Automating this application eliminates a health and safety concern associated with repeatedly manipulating heavy nut runners.