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Machine vision lighting plays a vital role in the inspection of banknotes. Today’s notes contain many security features (holograms, conductive strips, UV ink, micro print and etch features – to name a few) which complicates the inspection process often requiring several separate inspections. The print inspection examines the notes for defects (missing print, debris, spots, etc.) during production. However, with the many security features on today’s bank notes this is just the beginning of the inspection process. Automated optical inspection systems are used at each point in the production process in order to ensure the required fidelity and high standards. Identifying the correct machine vision lighting for each inspection point is critical to the inspection integrity.
Print Inspection Phase
Image quality is critical in any type of print inspection. If the quality of the captured image is poor, print errors may not be detected during inspection. In order to ensure maximum image quality, a uniform source of illumination over the entire object is required. With processing speeds of up to 40 notes per second, the intensity of the machine vision lighting is also critical. Without sufficient intensity the system will not capture an adequate image and line speed will have to be reduced to allow for image quality; reducing the throughput of the production process.
When banknotes are inspected for visual defects, including missing print, ink spots etc., a monochrome line scan camera can be used along with a monochrome LED Line Light. If, however, color information (color uniformity and consistency in color) is required, a color camera and white light source will be used.
UV Machine Vision Lighting
Anti-counterfeiting features, which are typically invisible to the naked eye, must also be examined for consistency. To inhibit counterfeiting of banknotes, selected features are printed in fluorescent ink, which is invisible to the naked eye. During the inspection process, defects in the application of fluorescent ink markings can be detected by a monochrome line scan camera with appropriate filters, which observes the banknote illuminated under UV light. UV COBRA Slim has been utilized in a number of these types of applications.
Key Considerations for an LED Line Light for Currency Inspection
As discussed, there are a number of considerations when selecting machine vision lighting for currency inspection. Considerations include: uniformity, intensity, available wavelengths and reliability.
The COBRA Slim series, with its marketing leading intensity and uniformity, provides an ideal solution in a number of currency inspection applications.
For more information visit the Cobra Slim series page.
