By Alex Lucas
Business Development Manager/Scanning Products
Nikon Metrology Inc.
New product development is a powerful force in expanding manufacturing’s impact on the global economy. Concurrently, the focus on improving production efficiency and part quality while meeting stringent production schedules is unrelenting. Measurement and inspection is benefitting from advances in laser-scanning technology, and retrofitting CMMs or articulated arms with new laser scanners is an affordable option many manufacturers are considering.
Given the right choices, many advances are possible:
- Where many touch probes might achieve input rates of one point per second, laser-scanning stripes can range from 50 to 200 mm in width and scan tens of thousands of data points per second.
- With laser scanning, even complex castings, dies and blades can be scanned in minutes.
- Reserving a CMM or articulated arm for measuring and inspection, and transferring data to PC-based reporting software can cut inspection time and speed time to market.
- A range of laser-scanning options are compatible with many existing CMMs and articulated arms.
- Integrated software packages are available that can handle gathering data, measuring, comparing scanned data to CAD models, and generating reports with both visual representations and tabular data into a single automated process.
- New technologies such as cross-scanning combine multiple scanners and digital cameras for scanning complex parts and features without re-orientation.
- Incorporating color-coded visuals and tabular data can speed approval processes and make sharing information easier.
On the entry level, numerous companies make single-stripe laser scanners that provide approximately a 50-mm stripe width, generate 20–25 stripes per second, and input something in the ballpark of 20,000 points per second while maintaining an error tolerance of 20–25 µm. For more demanding inspection tasks, Nikon Metrology manufactures a laser scanner featuring a 60-mm stripe width while scanning at 75 stripes-per-sec scan rate that can maintain an error tolerance of 9 µm. Scanners are also available with smaller fields of view for digitizing small, detailed objects with higher point densities and tolerances down to 4 µm.
For scanning large objects, laser scanners are available in hand-held models or for attaching to articulated arms, making walk-around scanning easier. Depending on the type of scanner, stripe widths can vary between 50 and 200 mm, and digital cameras capture more than a thousand points per stripe. This provides optimum resolution for efficiently scanning freeform surfaces and features. Cross-scanners are also available, that incorporate multiple scanners and multiple cameras for measuring or reverse-engineering large parts.
In the past laser scanning had difficulty dealing with highly reflective surfaces. This would necessitate spraying the object with a matte spray coating to eliminate obtaining reflective data and other extraneous noise. Today’s laser scanners feature automatic real-time adjustment of sensor settings for each individual point along the laser stripe, effectively handling highly reflective surfaces or those with varying colors.
Software compatibility is another important point to keep in mind. Nikon Metrology maintains partnerships with a number of inspection software providers and also provides its own point-cloud-processing solution. Laser scanning can input tens of thousands of points per second, so effective inspection software should be able to handle a large volume of inspection data (up to 100 million points) and provide the following tools: automated feature-detection algorithms; full part comparison to CAD or STL files; complete set of 2-D and 3-D features; geometric dimensioning and tolerancing (GDT) ability; specialized measuring capability, such as wall thickness, flush and gap, and directional comparisons; dedicated inspection modules, such as turbine-blade inspection; and off-line modules, enabling use of CMMs or articulated arms for inspection, and personal computers for creating or modifying reports and models.
Every manufactured part has its own range of inspection or reverse-engineering issues. Advancing technology could provide a solution for yours. ME
This article was first published in the September 2012 edition of Manufacturing Engineering magazine. Click here for PDF.