The National Physical Laboratory (NPL), the UK's National Measurement Institute, has developed a new range of three dimensional standards for verifying coordinate measurement machines (CMMs) for freeform tasks.
The standards are complex reference artifacts that provide traceability routes for a range of diverse measuring techniques.
The standards allow the verification of portable and fixed non-contact coordinate measuring systems, taking in systems employing laser scanning and fringe projection technologies, as well as those employing tactile sensors. They also help evaluate the surface measurement capabilities of new scanning measurement technologies.
Each NPL FreeForm standard bears several geometrical forms that are blended to form a single surface that tests various aspects of a scanning instrument's performance. Ceramic tooling balls or hemispheres on each corner of the standards aid registration. The precise nature of the surface employed by the standard allows traceability to be transferred to the freeform measurement technology. It is also possible to incorporate designed deformation to the surface, typically 100 µm in size.
The FreeForm standards are available to buy directly from NPL and are each supplied with a calibration certificate, the relevant CAD model and traceable measurement data files. It also forms part of NPL's calibration consultancy offer, which can be carried out onsite or at NPL.
The NPL FreeForm standards are available in various sizes. They have linear base dimensions nominally 37.5 mm, 75 mm, 150 mm and 300 mm and bearing four ceramic tooling balls.