During the development of Australia’s Next Generation Banknote series, Note Printing Australia’s (NPA) design and creation of the large top-to-bottom window containing holographic security feature elements has created a stunning aesthetic that makes its easier than ever for the Australian public to authenticate a genuine banknote.
That window area – the largest of its kind in the world to date – created technical challenges that needed to be addressed, particularly in the area of quality control and being able to inspect the application of the foil that is used to create the holographic feature effects.
NPA uses high-speed single note inspection machines that have a range of sensors and cameras that ensure the quality of every note manufactured before it is despatched to the central bank for issuance.
The machines however, were not manufactured to inspect foil in such a large window area, and so David Mann, NPA’s Control Systems Engineer, commenced a project on how a high-resolution image could be captured on these machines that could identify any imperfections in the application of the foil on the clear polymer surface.
“We needed to come up with a solution in which the machine’s camera could detect any tiny scratches, creases, missing pieces, or out-of-registration foil. This is on a machine that is processing 40 notes per second,” says David. “The existing machinery couldn’t do it, and while the supplier had some ideas we found that those possible solutions couldn’t satisfy other inspection requirements.”
The challenge was around illumination of the foil elements in such a way that didn’t interfere with the inspection of other printed features on the note that also require inspection. The complication was that ‘dark field’ illumination is used to inspect printed features, while ‘bright field’ illumination was needed to inspect foil.
In essence, David and his team developed and tested an independent source of ‘bright field’ light that was built in to the machine. Initially, computer simulations showed David’s proposed solution to be promising – a first prototype was built on the basis that the machine’s algorithms could manage this new image. As they went deeper into the project, David would assemble various prototypes, assess results, and continue modifying the kit. Over time, the team worked to combine the bright and dark field light in perfect synchronicity to enable the full inspection of the note.
“Some key challenges included the physical size of the kit as it had to fit into a narrow space, the angle of light, the diffusion of that light, the pulsing levels of the light, and the timing of the light’s exposure to the note such that the camera could capture the image perfectly,” says David. “The notes move at 10 metres per second which is 36 kilometres an hour, so at that speed the light had to switch within microseconds to achieve a location accuracy to about one-tenth of a millimetre.”
The final piece of the puzzle involved the camera not being able to capture the light source perfectly evenly, which resulted in window images that were darker at one end of the note. David’s last prototype involved the creation of a radial array of lights that were all aimed directly at the camera’s lens.
In addition, the machine operator can adjust the intensity being emitted from the light array to optimise the image. The technology also allows the timing of the illumination to be tweaked to accommodate different window positions, which is the case for different denominations across the NGB series.
Says David, “The resulting image now shows a note that appears completely consistent in appearance across the note with each feature clearly visible and able to be inspected in high resolution. I termed it ‘hybrid illumination’ because the image is a combination of dark field and bright field illumination.”
David credits collaboration between his technical team and NPA’s production team as the key to success.
NPA CEO Malcolm McDowell says the development of this solution was vitally important to the overall success of the NGB project.
“They say necessity is the mother of invention, and I don’t underestimate how daunting the initial challenge was when David and his team first contemplated a solution,” says Malcolm. “But through their expertise, discipline, persistence, and a sense of urgency, a remarkable result was achieved. David deserves credit for this invention, and I am delighted to say that David Mann’s Hybrid Illumination technology is operating perfectly across all our single note inspection systems.”