xLaser trackers are polar coordinate measuring systems capable of high accuracy measurements over long distances, for example the system used by NPL can measure 40 m distances to within ± 60  μm.

The tracker makes measurements of the positions of spherically mounted retro-reflectors (SMRs) in terms of two angles (horizontal and vertical), measured using angular scales mounted in the tracker mechanics, and distance (radius) to the SMR, using a laser interferometer. Simple trigonometry converts these into the usual Cartesian coordinates people are used to dealing with (x, y, z). Special tooling fixtures allow the measurement of not just individual point locations, but also of surfaces (flatness, level), angles (squareness), surface form and alignment between parts. By combining laser trackers with other measuring systems, such as laser scanners, large objects with complex surfaces can be measured.

NPL service

The NPL service utilises the seven tests prescribed in the standard that are designed to exercise the tracker measurement systems over a wide range of angles and distances similar to those encountered in real-world use. The configurations test the horizontal and angle encoder scale errors and eccentricities, as well as the distance and displacement measuring systems. The range tests verify the accuracy of the absolute distance meter (ADM) as well as the fringe counting performance of the laser interferometer (IFM), if fitted.

ASME B89.4.19 prescribes a series of repeated length measurement tests for both IFM and ADM; two-face tests and ranging tests:

• horizontal length measurement system test (9 configurations)
• vertical length measurement system test (8 configurations)
• right diagonal length measurement system test (8 configurations)
• left diagonal length measurement system test (8 configurations)
• two-face system test measurement (12 configurations)
• ranging tests, for IFM and/or ADM up to 30 metres
• user selected volumetric tests (2 configurations)

Results from these tests are reported against the performance specification (MPE value) supplied by the laser tracker manufacturer.

• Verification to ASME B89
  • Full test available
  • Specific to trackers
  • Conformance to manufacturers specification
  • Additional calibration options
    • Laser wavelength calibration / comparison against reference interferometer
    • Weather station (temperature, humidity, pressure)

Click here for further information on NPL's large scale metrology capabilities

Contact

Customer Service tel: 020 8943 8631
E-mail: dimensional_enquiries@npl.co.uk