Proceedings of SPIE
A variable resolution video machine vision system has been built which will determine the 3-D shape of a firing pin from the dent it has made in the primer of a shell. The system can also compare primer dents in different shells and determine if a 3-D match exists. A real time optical 3-D shape recognition feature allows the operator to align the shells, determine if there is a match, and quantify the quality of the 3-D match. The system uses a laser interferometer to project variable spatial frequency structural illumination on the shells which are viewed by video cameras. A computer determines the 3-D shape of the primer dent and predicts the shape of the firing pin. Optical shape recognition and alignment is achieved by mixing the video data with a computer generated mask and using this signal in a spatial light modulator to diffract a laser beam onto a detector. The magnitude and shape of the detector output indicates in real time the quality of the match or can be used to align the shells. A demonstration of the validity of the 3-D shape prediction has been carried out with large scale firing pin and shell-primer models, and the shape of a real firing pin has been determined from an actual fired shell. The result is a mixed video-optical processing system that could be used for real-time shell and firing pin matching in the forensic laboratory. Limitations and improvements in the current system are discussed.
Dawson, Donald W.; Hart, Chris; Gilbert, Bernard S. III; Andrade, Rafael A.; and Blatt, Joel H., "Prediction Of Firing Pin Shape And 3D Matching Of Shells And Firing Pins Based On Firing Pin Impressions In Primers" (1997). Aerospace, Physics, and Space Science Faculty Publications. 75.