Quality Scan: Real-Time Inspection for Real-Time Decisions
By Tom Moran
V.P. and General Manager
Farmington Hills, MI
Machined, formed, or assembled products should be measured where they are made. To this common-sense approach, technological advances have added a new capability: Real-Time Laser Probe Surface Inspection systems (RTLSI) with instantaneous comparison to CAD data.
Manufacturers now have an unmatched set of new tools to support on-the-spot decision-making.
In today’s marketplace, there are big profit margins for those who can innovate rapidly-and big penalties for those who do not. Unfortunately, many manufacturing companies still struggle with getting new products into initial production. As production runs get shorter and product changeovers more frequent, these struggles increasingly impact time to market, returns on assets, productivity, and quality.
A change in any physical dimension of a product-a manufacturing tolerance, for example-requires dozens of decisions on product modifications and tooling adjustments. Tackling these without analysis based on surface measurements compared to the determined standard, nominal, CAD file, etc., is becoming unthinkable.
The role of the portable arm in RTLSI is to physically connect the laser probe to the real world, and deliver the probe into the measurement area. When a laser probe is interfaced to the PCMM and point-cloud processing software, every one of those millions of scanned points gets a known set of 3-D coordinates. And each can be compared to the CAD file “on the fly,” in real-time.
Feedback from the PCMM encoders establishes the 3-D coordinates of every point gathered in a surface inspection and its location in 3-D space. This is essential for measuring anything where orientation to other parts of a system is important-the forming surfaces in sheet-metal stamping dies, for example, or the mating surfaces of molded parts.
RTLSI works because data from two very different systems-laser probes and the arm’s encoders-are mathematically merged into one 3-D coordinate space. The software has to compare as many as 23,000 points/sec with the original CAD file or solid model and display any errors in the part. Contact and noncontact inspection results can be merged into the same file as RTLSI systems use contact and noncontact probes interchangeably.
Real-time laser-scanning inspection is already impacting real-time decision-making in most areas of manufacturing operations, including:
- First-article inspections, especially for formed and assembled products.
- Ad-hoc, on-the-fly dimensional measurements including what-if analyses.
- Documentation of dimensions for customers.
- Verification that part surfaces meet all applicable regulations.
- Inspection and documentation of surfaces that could be involved in warranty claims or product liability lawsuits.
Three pieces of state-of-the-art technology are common to every RTLSI system.
- A portable coordinate measuring machine (PCMM) that locates probed points in 3-D space. PCMMs can measure to ±16 µm, varying with the size of the arm. A PCMM and laser probe system can measure to ±46 µm (scanner accuracy + PCMM accuracy).
- A laser probe to gather points on a surface. The newest generation of these devices gathers more than 23,000 points/sec in 3-D space with an accuracy of 30 µm or even less (at two-sigma statistical accuracy). At the level of the RTLSI system, probing is done at rates of about 30 scan lines/sec (30 Hz). Each scan line has 768 points.
- Software to process the laser probe’s cloud of points quickly enough for real-time comparisons with the part’s original CAD data or solid model, and capable of identifying geometric features. To keep pace with today’s laser probes, the inspection software reads and processes about 1.4 million points/min in real-time (not just “later” with post-processing).
RTLSI is the key to 100% inspection.
Inspection of all aspects of all parts is now an achievable goal. No longer is there reason to question whether good parts are being shipped to customers. If RTLSI is used, there will be no question.
This article was first published in the October 2004 edition of Manufacturing Engineering magazine.