Optical Testing of Bolt-Type Screws

The handling of standard components, for example screws. In automatic assembly lines often leads to trouble and, thus, to the stop of the assembly line due to the permitted fault rate of 2%. A 100-% inspection of the screws before assembly is desirable to reduce these stop periods. Studies showed that faults in assembly are 70% geometrical faults. The inspection jobs derived from fault analysis can preferrably be carried out with optical sensors by the silhouette procedure. Because of this trend, an electro-optical measuring system, composed of a process control computer directing a line scan camera and a linear guide driven by a step motor for axial translation of the screw, was built for fundamental examination. With this installation the geometry of the screw can be measured in meridional section, and the data can be stored in the computer. The developed information-processing programs permit, after an adjustment of the screw position according to software, a comparison of the stored sample and the measured object to be made. Because of this comparison and after a calculation of the parameters of the screw thread an appraisal of the fault is possible.