Non-contact scanning for measurement and analysis is growing in importance every year right across the world of materials fabrication, finding exciting new applications across a widening range of industries and settings.
In many places, scanning can be the route to massively increased speed and efficiency while delivering a new type of data to solve problems that are beyond the reach of traditional touch-probing methods.
Look, Don’t Touch
High-volume scanning data can be used as a reverse
The most superficially obvious advantage of scanning over touch-probe measurement is the ability to take accurate measurements without physically touching the part being measured. The range of industries manufacturing products that require quality assurance processes applied to materials with a delicate or easily damageable finish is wide, and for such applications scanning offers a non-contact solution that traditional touch-probe CMMs cannot match.
And it is not just the point of measurement where scanners present a non-contact benefit. Readying a part to be scanned needs only a stable platform, with no clamping required, ensuring measurement accuracy. And while in the past applications for scanning were limited by the need for target markers placed on the product to be measured, the technology has by now progressed sufficiently that extremely accurate measurement results can be collected with no need to touch the component at all outside of initial placement and reorientation.
Such reduced preparation requirements for successful scanning introduce what is perhaps the key benefit of scanning over probing: vastly reduced measurement process times.
Scanners have the capacity to capture huge amounts of data very quickly. The exact speed at which a scanner can collect data varies with the exact type of scanning technology used, but compared with one-point-at-a-time touch-probe measurement, the point-cloud data collection of even the most basic scanner is on another level.
Even entry-level scanning solutions can capture up to 50,000 data points every second, while with the very latest laser scanning technology, that number rises to three quarters of a million.
What this comes down to is the potential for increased speed and efficiency in data collection. Every important data point needed to accurately map, for instance, a car door panel, can be collected in less than two minutes with the right scanning technology. Performing the same measurement process only 10 years ago would have presented a long task, requiring not only more measurement time but also a significant amount of preparation time in order to ensure all the most important measurement points were taken.
Even then, the data collected by touch probe would be a level of abstraction away from a proper representation of the part in question. Scanning on the other hand is able to produce a picture of a component, cataloguing every undulation and deviation in form.
A Different Type Of Data
That brings us to the other clear improvement that scanners deliver. The huge amount of data they have the capacity to collect has deeper implications than merely the ability to record the same old measurements at a faster rate. This quantitative increase in data actually translates to a qualitative difference as we move from a predefined set of key data points to a multi-million-point data cloud, representing a fundamental change in the way that data can be used.
The result is the potential to almost instantly create a three-dimensional model of the object or surface being scanned. This allows for geometric and dimensional part analysis that would be all but impossible to replicate through touch-probe measurement. With scanning technology, we can create two-dimensional cross section mappings and perform flush and gap inspections based on a range of useful geometrical definitions.
Going even further, high-volume scanning data can be used as a reverse engineering tool, useful from competitor product analysis through to the manufacture of spare parts for which no model exists, such as old aircraft components. Such functionality also allows for the update and re-design of existing CAD models based on real world production data—it is even possible to compare to CAD models in real-time with some technologies. Some scanners are even able to record accurate colour mapping that is ideal for reporting and documentation purposes.
The range of applications to which scanning technologies are well suited is extensive, from inspecting panels during installation processes to in-depth defect analysis of composite parts. With an accurate three-dimensional model and appropriate software solution, it is now even possible to carry out virtual assembly of prototype parts for the purposes of accurate interference analysis.
Accurate surface models and cross sections are extremely useful in the aerospace and wind power industries, where improving the efficiency of turbine blades is highly important. Portable scanners also offer an interesting solution for preventative maintenance of casting dies; a quick shop-floor “health check” with a scanner can avoid costly scrapping unless absolutely necessary.
With scanning being so easily applicable within portable measurement solutions, its benefits are not limited to controlled quality room environments. Scan data can easily be collected on the shop-floor, in-line within fabrication processes or even from within a mid-installation aircraft fuselage.
From inspecting panels during installation processes to in-depth
defect analysis of composite parts, scanners can be used
for many purposes
Portable scanning technology currently comes in several ‘flavours’, each with its own benefits and points of interest. Laser line scanning offers accurate and reliable data acquisition at high-speed across almost any surface type. This technology can be used in conjunction with a laser tracker to perform scanning tasks over large areas, and the lack of moving parts makes such laser tracker and scanner combination systems perfect for robot mounting for in-line measurement tasks.
Alternatively, laser line scanners can be found mounted on portable measuring arms for extremely fast and accurate measurement of smaller parts and surfaces, with the arm acting as a global reference system for the scanner system.
A variation on this technology is “flying dot” laser scanning, which is flexible enough to scan across multiple surface colours and materials with no settings adjustments. It is also unaffected by ambient light and offers adjustable laser line width and scan point density settings along with a larger stand-off for easier measurement.
The other major portable scanning technology comes in the form of structured light scanners, such as white light fringe projection and photogrammetry systems that offer extremely high accuracy and point-cloud resolution for small-volume measurement. While the required target markers can be slightly time consuming to position, they allow for better lines of sight by repositioning the scanner without restarting the measurement process.
With a combined fringe projection and photogrammetry system, it is now even possible to visualise the results of a measurement directly on the object being measured, offering a visceral real-world representation of your data.
The Future Of Metrology?
There are some factors that balance all these benefits when it comes to comparing scanning with traditional touch-probe measurement techniques. Perhaps the most important one is that the trade-off for increased speed and size of data collection when it comes to scanning is in terms of accuracy. This is the area in which the conventional touch-probe based CMM still wins the argument. If accuracy down to fractions of a micron is central to your measurement needs, scanning technology is not yet ready for you.
The other key argument against implementing scanning technology yesterday comes down to cost. New scanning technologies are unsurprisingly more expensive than probing solutions when controlling for equivalent levels of accuracy. As always when adopting new tools, a key part of the investment decision comes down to value, and while the benefits of scanning solutions represent a bargain for many users, for others the investment is too much—for now at least.
But for the wide range of applications that do not require data at such high accuracy levels and for which the requisite investment is justified, the benefits of scanning are absolutely clear: Scanning is the metrology technology of tomorrow.
APMEN Metrology & Design, Apr 2017