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Laser scanners on CMM's capture thousands of points every second and enable to digitize objects with complex surfaces in a rapid and accurate way. The resulting data from a laser scanner is a 3D pointcloud that can be further processed for part to CAD inspection where the 3D pointcloud is compared to the original CAD model or for reverse engineering purposes.
When it comes to measuring features - one of the main applications in metrology- the single laser stripe scanner has some limitations compared to the traditional touch probes. To accurately measure the features, many scanner re-orientations are required to digitize the holes from various directions.
A recent technological evolution is the Cross Scanner, a patented high-speed, multi-stripe laser sensor that digitizes features from different directions without the need for a C-axis re-orientation. The optimal distribution of measured points enables the Cross Scanner to efficiently scan features such as holes, slots and gap & step with many more points than a touch probes.
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Changing the way feature scanning is done…
Laser scanners have already proven their uses and benefits in areas of quality control such as first article inspection, off-line inspection and troubleshooting. Compared to traditional touch probe testing, laser scanning enables fast acquisition of accurate 3D pointcloud models that can be subsequently used for full part inspection or reverse engineering applications. However fast and accurate inspection of features such as holes, slots, gap & step remains to be an inspection challenge. The cross scanner introduces a patented technical paradigm that measures holes and features in one fast single scan by combining 3 laser stripe scanners whose planes are rotated by 120 degrees and slightly tilted. Each camera has its own laser field and is scanning in an alternating way. The total throughput speed of the scanner is as such 3 times 6400points per second, meaning 19200 points per second.
The single laser stripe scanning method measures the intersection of a laser plane with an object from a single view direction. This approach cannot capture information outside areas that are not viewable by both the laser plane and the viewing direction. This characteristic of single laser stripe scanners requires that multiple scans be taken from different directions. Objects having several features require at least three scans to obtain a sufficiently detailed digitized surface.
Main advantages
The patented cross sensor, introduces a number of advantages that represent a breakthrough for laser digitizing. A higher speed and increased flexibility is obtained for real 3D measurement by avoiding the use of a (expensive) motorized sixth axis (C axis) that can introduce errors. Compared to a traditional laser stripe scanner mounted on a Renishaw PH10, the cross sensor has an even higher speed and flexibility, avoiding the discrete repositioning of the sensor head.
Another important advantage is the better resolution of the XC scanner since the object is digitized with an optimal density in all directions.
The most important benefit is achieved by having a real 3D measurement resulting in an accurate representation of the measured feature. The cross scanner can look into feature by the 3 camera’s that are distributed over 120 degrees and slightly tilted.
Typical applications
While the cross scanning technology applies to general digitizing applications, it is particularly suited for sheet metal quality control containing features.
The following examples show the working and benefits of the cross scanner.
Feature detection on a sheet metal piece
A piece of sheet metal (50cm x 20cm) from a car is scanned using the cross scanner. The total scan time was less than 4 minutes resulting in a pointcloud of 1,6 million data points. Using a traditional scanner the same detailed scanning job would require at least 12 to 15 minutes. The better resolution is clearly visible when zooming in on a detail of the pointcloud.
Edge detection on windows encapsulation
This case study shows the advantages of the cross scanner when scanning curved contours like e.g. a car window. With the traditional laser stripe scanner at least 8 PH10 reorientations are necessary to complete the scan. The cross scanner simply does not need any re-orientation of the indexing probe head. The scanning time with the single laser stripe scanner for this object is about 1min30 seconds while the cross scanner only needs 8 seconds.
Another advantage is that the teaching time for automated scanning drastically reduces since there is no need to teach all the different PH10 orientations. Beside the timesavings the cross scanner also guarantees a better accuracy since the PH10 avoids the extra orientation. A higher resolution at the edge is also accomplished as indicated on the figure.
Scanning of complete engine block
The cross scanner is also suited for surface measurements of engine blocks, cylinder heads, gearbox covers and other casted parts. As it scans into the pockets and holes, it gives a detailed 3D view of the part.
Traditional touch trigger measurements often take several days or even week to inspect a complete engine block. Using the XC50 this is reduced to 1 or 2 hours. As the XC50 is scanning from 3 directions, a single PH10 orientation suffices to measure all details. Another advantage is the straightforward programming of the scan path, reducing programming time and avoiding measurement errors.
When comparing the measured data to the nominal CAD model, you gain insight in the full 3D information by a clear deviation color map. This is valuable information that is not available when using the touch probes, where the number of measured points is limited.
Finally the results are presented in customizable report where flyouts indicate the hot spots.
Conclusions
The cross scanner is a revolution in laser scanning applications. Beside the enhanced resolution and real 3D scanning capabilities, it also saves a considerable amount of scanning time by avoiding the re-orientation of the head when scanning curves.
Typical applications are found in automotive industry where features, holes, slots and pockets in sheet metal pieces or casted parts are inspected. Other applications comprise gap and flush measurements of fitting parts.
Download: XC50 Cross Scanner (PDF file)
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