As part of an effort by NIST’s Physical Measurement Laboratory to produce an international performance evaluation standard for these instruments, scientists at the Engineering Physics Division (EPD) designed and constructed a calibration facility to evaluate proposed tests in a draft ASTM International standard, which is being developed under the EPD’s leadership. In May 2016, major manufacturers of 3D laser scanners from all over the world converged at NIST to put their scanners through the paces.
This laser scanner “runoff” was orchestrated by EPD’s Bala Muralikrishnan, Meghan Shilling, and Prem Rachakonda, with key assistance from Gerry Cheok of the Engineering Laboratory at NIST and Luc Cournoyer from the National Research Council (NRC) of Canada.
An invitation was sent to all leading manufacturers of 3D laser scanners to visit NIST and run the approximately 100 tests specified in the draft standard. Four of the manufacturers traveled to NIST (one each from Germany and France) to participate in the runoff. Another sent an instrument during the week for testing. Two other manufacturers who could not attend in May have expressed interest in visiting NIST soon to try out the tests.
These seven manufacturers represent about four-fifths of the entire market for large volume laser scanners. Additional participants included representatives from a company interested in entering the 3D scanner market and a company manufacturing precision spheres that are used as targets.
The draft standard specifying the test procedures was the product of three years of work by a standards committee led by Muralikrishnan that met biweekly.
“With large volume 3D laser scanners, you basically put them in the center of the room, and they sweep across the room, producing 3D point clouds,” Muralikrishnan explains. “The only current standard for these types of instruments evaluates the instrument only along one axis. That standard was released in 2015.
“The standard released in 2015 was envisioned to be one of several standards. Thus, we decided that we should extend this so that it covers the entire volumetric space. We started work in the summer of 2013 to come up with test procedures that would evaluate the performance of these instruments over the work volume.”
Once performance testing was completed, the manufacturers met with NIST and NRC staff to provide feedback on the process. While the manufacturer’s overall experience was extremely positive, the clear consensus was that the number of tests needed to be reduced in order for the standard to become more practical to use. This will be a key consideration as the draft standard is revised.
Cournoyer elaborates: “We want the test to be useful, but we also want it to be feasible. It shouldn’t take a day. It should be done within a few hours at the most, without sacrificing too much of the performance evaluation. We think we can accommodate most of the concerns that the manufacturers were discussing. We will revise the document and discuss again.”
Along with the important next step of revising the draft standard, the NIST scientists will be spending many hours perusing the vast quantity of data acquired during the runoff.