Area Scan Inspection of Banknote Production
Verifying invisible images at 12 feet per second.
The challenge was to detect and evaluate the quality of an anti-counterfeiting, covert diffractive image embedded into polymer (paperless) banknotes as they were being printed on a high-speed web press. The security feature on each note, which appears transparent and undetectable to the human eye, needed to be identified and evaluated as the web moved at over 12 ft. (3.7 m) per second. Additionally, the polymer stock on the web could vary in width from 24 in. (600 mm) to 49 in. (1250 mm).
Newton engineers developed a solution that incorporated six rows of synchronized area scan cameras arrayed along the front face of the web and matched them with custom developed, structured light illuminators on the backside of the web. The illuminators projected light through the currency and onto opposing beam splitter screens where the hidden features were revealed. The area scan cameras observed the screens and made pass-fail determinations based upon pattern match and image quality. Each banknote on the web was encoded, allowing for rejects to be logged. Later, these notes were identified using the encoded data and removed from production.