3-D true position gauging of control arm holes:

Definition of problem:

Process/operation: using Cognex Insight cameras and lasers to gauge true position of several holes punched in the control arms of a rear axle
Product: automotive rear axle assembly
Defect types:

Consequences: out of spec holes will be rejected in later assembly operations if not corrected at this point. Defects tend to occur as a trend so many products could be made out of spec before they were caught and stopped.

Solution:

General overview:
The holes in questions are the ones that are punched into the brackets that hold the bottom end of the shock absorber on a car. The Cognex cameras are moved into position by an elaborate motion control system and use optical field splitters and sensors to measure the part.

Fixturing & Lighting:
The camera is combined with a laser displacement sensor to provide X-Y data (with the camera) and Z data through with the laser. The camera/laser assembly is moved into position (and retracted) by a precision pneumatic slide. The camera assembly is rotated into a 3-axis compound angle with respect to the part’s direction of travel. The system uses optical field splitters to combine the desired field of view for measurement.

Programming:
The camera/laser acquires images on a signal from the machine’s PLC and calculates the position of the punched hole. The program transforms the camera data from the coordinate frame of the camera to the coordinate frame of the machine. The program also calibrates the pixel data into the engineering units of millimeters. The data and image of the hole is logged to a database on a dedicated PC.

Results for the customer:

The prior inspection used in this machine was with hard gauging in a large fixture with “Go / No-Go” plug gauges.. The vision approach allows 100% inspection of all parts with data rather than pass/fail information.