Non-contact laser scanning is an increasingly common process. It offers the opportunity to rapidly measure large areas of parts and automate inspection, but the technology is not trusted sufficiently for product sign-off, due to lack of validation, differences between tactile and scan results and the risk of customer-supplier disagreements. So its uptake in product verification is, suggests NPL Huddersfield (www.npl.co.uk), held back because of this.
Laser scanning, in the same way as other non-contact measurement, can be more challenging, as it is disproportionately affected by environmental and other factors when compared to tactile measurement systems, explains the metrology expert. These include: ambient lighting conditions; laser power settings; reflectivity or absorbency of surfaces to be scanned; and laser angle of incidence etc. The effect is generally to increase the measurement uncertainty, sometimes by many times the equivalent tactile system uncertainty.
PROJECT TO BOOST CONFIDENCE
This being the case, NPL Huddersfield undertook a project to try and establish enhanced confidence in methods. Among the laser scanning systems it employs in house is the Nikon LD15Dx laser, which is used in conjunction with a Nikon CMM (01332 811349).
NPL undertakes research into a wide range of areas of measurement in support of UK industrial requirements, with knowledge gained passed onto potential beneficiaries. In Huddersfield, the laboratory has been involved in a number of projects where customers have wanted to consider implementing laser scanning within their measurement processes – usually to speed up the measurement process, and/or to gather a lot more data about the part to be measured in a short space of time. In general, the parts to be scanned were either freeform surfaces or quite complex components that would usually require a lot of effort and time to be analysed.
The NPL project was set up to establish the feasibility of using dimensional scanning systems as 'comparators' for carrying out high volume and in-process inspection of products. Objectives were to evaluate the possibility of using a laser scanner in conjunction with a CMM to measure components to the required uncertainty levels, as defined by the customer. The laser scanning process also had to be relatively easy to implement and to perform.
Current research is looking at ways to implement laser scanning for customers that have a requirement to measure large numbers of the same type of component. The aim is to identify, relatively easily, the possibility of using tactile measurement data for a component, comparing this to laser scanned data and using offsets/corrections to improve the accuracy of the laser measurements. This research is ongoing and kicked off with simple components having well-defined features.
Research in the Huddersfield laboratory on a range of laser scanning projects has undertaken over about 18 months and will continue on the current project until the end of this year. Most of the work undertaken so far has used Taguchi Design of Experiment (DoE) techniques to optimise the measurement process. NPL reports that this appears to have been the most efficient approach so far and has led to relatively quick results.
In general, the organisation has been able to provide results that give potential end users the ability to decide if laser scanning is appropriate for their own particular requirements. Sometimes the result can be a bit grey, in that the data cannot strongly suggest one method or another, and so the final decision has then to be made by the end user, based on other factors, such as cost of implementation, training or other factors.
But NPL Huddersfield says that inspecting parts by scanning "has the potential to significantly improve product verification capabilities in the UK advanced manufacturing supply chain by speeding up inspection and allowing whole part inspection". Visual inspection for defects is still widely used within even the most high-tech companies and the potential to perform this activity automatically would lead to quicker inspection with greater consistency, it adds.
And the measurement specialist additionally says that it hopes that the current research will give potential users another measurement option to be used alongside current techniques, and also to offer a possible high speed measurement option that can support inspection of many features in a short space of time.
SPREADING THE WORD
The findings from the organisation's current work and case study will be promoted through the NPL Product Verification Network (PVN) and through Sharing in Growth interventions (where NPL will engage with over 50 companies in the aerospace and civil nuclear supply chains). The wider vision is to develop guidance and procedures for introducing scanning into product verification activities at manufacturing sites.
Thereafter, it is expected that new services to train and support operators in applying scanning techniques will be introduced and made available through PVN. The development of skills and sharing of knowledge will enable NPL to offer improved component inspection and consultancy.
Potentially, all companies who use or wish to use non-contact laser scanning will benefit from this current research. In addition, businesses who desire to speed up introduction of this technology within their own organisation can interact directly with NPL on a commercial and confidential basis, with results being specific to their own application.
NPL Huddersfield says follow-up research will hopefully include expanding the laser-scanning research into more complex components, where it is currently unable to achieve sufficiently small measurement uncertainty values to meet customer requirements.
NIKON GIVES BOOST TO LASER SCANNING PRODUCTIVITY
Nikon Metrology (01332 811349) pioneered non-contact laser scanning on a CMM 20 years ago and has now introduced the new Nikon InSight L100 scanner, featuring superior optics and innovative camera technology that offers measurement productivity that, until now, was not achievable on a scanning CMM, says Nikon. Offering speed, accuracy and ease-of-use on a CMM, it is ideal for high accuracy inspection of larger components where productivity is key.
Suitable for measurement of both surfaces and features, even shiny or multi-material parts, the equipment quickly delivers accurate data and intuitive part-to-CAD comparison reports.
The 100 mm wide field of view (FOV), combined with data acquisition speed of 200,000 points per second, delivers rapid measurement not previously achievable on a scanning CMM, the company highlights. And to facilitate manual scan path programming, a new FOV projector ensures good part coverage.
A high quality glass Nikon lens, optimised for laser scanning, combines with the high definition camera to give a point resolution of 42 microns, enabling the capture of fine detail and measurement of sharp edges. The InSight L100 has a small probing error of 6.5 microns, which is a measure of the scanner's low noise level, resulting in smooth meshes having high levels of detail. Combined with the high point resolution, feature measurement accuracy approaches that of a touch-probe, Nikon says.
A greater range and mix of surface materials, finishes, colours and transitions can be measured more efficiently without user interaction for manual tuning or treatment of the component surface. Nikon Metrology's fourth-generation Enhanced Scanner Performance (ESP4) technology adapts the laser intensity to varying colours or materials for each point in the scan line faster than ever.
The InSight L100 scanner can be combined with tactile probes and a change rack to create a versatile, automated multi-sensor CMM, too.
First published in the Machinery June 2015 Quality and Metrology Supplement