ILLUMINATION g
implement in an industrial environment, and that hasn’t happened yet. Tat’s the push that we’re making.’ Advanced Illumination is working with
Matrox Imaging to bring all the components required for photometric stereo into an accessible, robust and flexible system. Advanced Illumination’s wide range of lights – including ring lights, bar lights and line lights among others – multi-channel controllers and mounting accessories will be combined with Matrox Imaging’s smart cameras, vision controllers and MIL software to develop the system. Trailkill emphasised the need for the
system to be flexible because of the high level Gone in a flash
Researchers at the Austrian Institute of Technology (AIT) have developed what they say is the world’s fastest LED strobing system, capable of operating at 600kHz light switching frequency. The system, called
Xposure:flash, was developed to complement the institute’s 600kHz multi-line scan Xposure:camera, which was first demonstrated at the Vision 2016 trade fair. The researchers say that, together, the two solutions address the demand for both faster inline inspection – to match increasing production process speeds – and the ability to acquire multiple types of data from objects using a single camera. Xposure:flash simultaneously
provides high illuminance and high homogeneity, not only for one object plane, but also within a given 3D volume. Two LED panels with white LEDs and LEDs in the
near-infrared wavelengths are positioned around the object and are flashed in sequence, synchronous with the Xposure:camera triggering. The camera is therefore able to capture lines in both visible and NIR wavelengths. The system can also be fitted with white LED panels in a way that enables it to be used for casting shadows around the 3D structures on an object’s surface, as is required to perform photometric stereo imaging. The researchers have shown
Visible and near infrared data stream captured while inspecting a banknote with the Xposure:camera
how the camera can be used to inspect banknotes. ‘This is a high-speed printing process, and from this came the demand for developing this high-speed camera and high- speed flashing technology,’ said Petra Thanner, senior research engineer at the AIT’s Centre for Vision, Automation and Control. ‘The notes have to be inspected at several wavelengths – visible, NIR or UV. Our 600kHz camera achieves this by capturing one line in the visible and one line in the NIR sequentially, enabling two types of image to be created for each bank note at incredibly high speeds.’ The photometric stereo capabilities can also be used to image the textured intaglio print on a banknote. With the rate of both the LED strobing and line scanning in
32 IMAGING AND MACHINE VISION EUROPE JUNE/JULY 2020
‘We’ve got to walk before we can run, and we are definitely still at the walking stage’
of customisation required for photometric stereo applications: ‘Depending on the application, you may need a very different controller, different lights or a different mounting setup; it’s staggering how much customisation can be required,’ Trailkill continued. ‘If you don’t make this all easy to
understand, or write the application notes
explaining it, people just aren’t going to use it.’ Advanced Illumination is therefore working on a section of its website that will contain all the information required for implementing the different components required for photometric stereo imaging. Trailkill concluded by reiterating that while photometric stereo is a very practical application with a lot of promise, until all the pieces are brought together, explained and made easy to understand, its uptake in industry will be limited. ‘It’s a lot of work to get it out onto the
factory floor,’ he said. ‘We’ve got to walk before we can run, and we are definitely still at the walking stage.’ O
Print inspection of a banknote, capturing a high-resolution colour image (top), a photometric stereo image of the intaglio print (middle), and an OVD image of the hologram
the set-up, it’s important that there is no overlap between the flashing cycles of the different LED panels. As one LED panel switches off before another switches on, its light level must decrease fast enough so that no residual light from it is captured in the next line scan, and that the only light being captured is from the next panel switching on. This created a challenge for the researchers, because when developing the Xposure:camera, the fastest lighting controller available could only operate at 20kHz, rather than at the hundreds of kilohertz required. This meant that the LED panels would only dim over 20µs, whereas the Xposure:camera captures lines every 1-2µs. A dimming time in the range of hundreds of nanoseconds was needed. The researchers developed an ultrafast light switching
technology, and together with an Austrian firm, built a prototype controller capable of operating at 600kHz. This was achieved by positioning the switching transistors closer to the LEDs, according to Ernst Bodenstorfer, another scientist on the Xposure:flash team at the AIT’s Centre for Vision, Automation and Control. The prototype has a dimming time of 300ns, making it suitable for the ultrafast line scanning of the Xposure:camera. The Xposure:flash controller
measures 93 x 55mm; the LED panels have a footprint of 140 x 17mm. ‘Thanks to it’s small size, the Xposure:flash would be very good for integrating into small spaces, such as in cameras,’ Thanner said. ‘We’d be happy to integrate our technology with cameras from vendors if there is a demand; we are open to collaborations.’
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