White light leaps forward
A UK company has developed a technology that could revolutionise 3D scanning.
3D scanning is changing, and that will radically alter the way we use 3D data in product development. This, at least, is the message from Phase Vision, a UK company that has recently launched a highly innovative series of new generation, white light scanners that it believes could revolutionise the future of 3D measurement.
White light scanners are not new of course. However, like laser scanners, early white light scanners had a fixed 'stand-off distance'. That meant that, while the scanner had the potential to measure large objects, they had to be square on to the scanner and in just the right place or the lenses became defocused and distorted the images.
Another challenge facing all triangulation-based systems was the ability to see into holes. Triangulation works by sending a ray of light onto the object and measuring the reflection on the scanner's camera. There has to be an angle between the two beams – which limits the depth of holes which can be measured. The greater the angle, the more accurate the system – but the more difficult it becomes to see into holes.
Shiny surfaces are also a challenge for any optical scanner as reflections cause 'noise', which can confuse the scanner, Composite components are also challenging, with light-absorbing surfaces which make it hard to see the projected light. That lack of contrast introduces yet more noise into the system – but the alternative to optical measurement (using mechanical probes) is impractical.
Recognising that all these problems stemmed from the 'signal to noise ratio', Phase Vision decided to develop better software algorithms to separate the signal from the noise. While this greatly increased software complexity, it was also a lot cheaper than the alternative of using more and/or better expensive, high-end CCD cameras. Equally, sophisticated software eliminated the need for a second camera and allowed the triangulation angle (between the camera and projector) to be reduced. It even allows the scanner to operate in brighter lighting and to cope with a range of standoff distances. The angle between the optical devices defines how usable the system is. With a single camera, the required angle is reduced – giving a deeper usable volume in which components can be measured. It also gives a greater ability to see into holes and a greater ability to measure objects at oblique angles. By enabling use of a single camera and smaller angles, the Quartz system has reaped huge benefits in usability.
Central to the system is that, rather than using 'black and white stripes', the Quartz system uses sine waves – smooth sweeping transitions. These images do not have sharp edges, so are relatively unaffected by most of the sources of noise. This allows complex software to distinguish between the noise and the object, and provides a massive improvement in accuracy.
By using complex algorithmic software to eliminate noise, the Quartz designers also enabled the use of high-power digital projectors – traditional structured light systems have used old-fashioned 'slide' projectors for the highest possible quality images. By using the most powerful projector available in a 3D scanner, Quartz has the power to measure large objects in normal working environments; while digital image control allowed the use of an even more sophisticated projection technique, where the projected sequence is repeated twice – once for each polarisation. This allows two measurements to be made via independent optical paths – giving extensive cross-checking within the system and eliminating spurious data introduced by highly reflective surfaces.
Finally, the ability to work accurately with de-focused optics enables the Adaptive Range Technology, which is integrated into Quartz scanners. This allows the scanner to take advantage of the very deep measurement volume the single-camera architecture enables.
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