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A new dimension of 3D capturing
Chromasens GmbH Posted 03/20/2012Chromasens GmbH has developed a new kind of process for colour 3D surface measurement based on its self-developed, trilinear CCD line scan camera technology. The system, that can be used in a variety of areas, is based on stereoscopic capturing and supports the capturing of almost any size object. Through the fusion of high-quality line scan camera systems and state-of-the-art graphic processor technology, altitude values can be captured and displayed with the highest precision in real-time using an image correlation process.
A wide spectrum of applications have already existed in the past for capturing surface shapes and to recognise surface flaws and these have been covered by a plethora of different processes. Important system parameters, particularly in applications in the industrial construction process, are the speed and resolution of 3D measurement in relation to the size of the surface to be measured. The established measurement methods normally based on the use of matrix cameras had so far been of limited use.
"Our engineers, in close cooperation with the Otto von Guericke University in Magdeburg, were able to develop a process based on the use of high-performance, trilinear line scan sensors and which significantly increased the speed and resolution of optical 3D measurement," explains Markus Schnitzlein, Managing Director of Chromasens.
Movement creates new perspectives
Problems such as illumination fall-off at the edge of the surface, multiple measurements in the case of large measurement areas and low lateral resolution do not occur in the use of line scan sensors. Line scan sensors, optical systems and high-intensity illumination modules, that were also developed by Chromasens and modified for this purpose, are arranged on a level (planar) in the 3D measurement system by Chromasens.
In contrast to static image capturing with matrix cameras, a line scan camera image only occurs through the movement of the line scan sensor during capturing. The movement process, described as 'scanning', is generally linear but can also follow other patterns. The dynamic 3D measurement of the line sensor system takes place independently of the scanning principle in the process developed by Chromasens.
Through the description of the arrangement of the sensors, which is determined in advance by a calibration process, a 3D scatter plot can be calculated in the world coordinates system. Thus, the object surface is digitalised and is available for further evaluation in the form of spatial coordinates and RGB colour values.
The altitude measurement precision is around 1/10 of the object pixel size. If the optical resolution has 100 μm per pixel, for example, then the attainable altitude resolution is approx. 10 μm. The mathematical calculation of the altitude data takes place in real-time. The use of graphic processors of the latest generation operated in parallel for hardware acceleration currently allows calculations of up to 200 million colour 3D points per second.
"Classic line scan cameras have long offered very high spatial resolution, even allow multispectral colour capturing and are therefore often used for routine inspections for quality assurance on production lines. The expansion of the wide application spectrum by the still missing channel for depth data is a logical advance," explains Markus Schnitzlein.
In his opinion, the new measurement system for industrial use combines the advantages of customer-specific line scan cameras with proven 3D evaluation methods known from 3D matrix camera systems.
Processes for the non-contact optical surface measurement of three-dimensional objects are increasingly important given the rapidly progressing technological development. An obvious application for the colour 3D process presented here is the matching of colour impression and shape on a 3D shape embossed and printed on the surface, e.g. in high-quality cosmetic packaging, toys or membrane keypads.
Further applications for 3D surface measurement include wood and wooden products, tiles, flagstones or veneered surfaces. Processed metallic surfaces can also be holohedrally measured with this solution.
The first projects, e.g. in the quality control of leather, have already been achieved. "Customers can turn to us with their measurement tasks. By an analytical pre-evaluation of the respective object surface, Chromasens can suggest a suitable camera system with the right sensors, lenses and illumination that is optimally suited to that measurement task," says Markus Schnitzlein, inviting interested parties to try out the new 3D surface measurement process.