Articulated arm verification service
1 min read
The National Physical Laboratory (NPL is offering the UK's first service for the verification of articulated arm co-ordinate measurement machines (CMMs) to the ASME B89 standard used by arm manufacturers.
Articulated arm (or portable) CMMs can achieve uncertainties of a few 10s of microns. NPL's Engineering Measurement team designed a specialised calibration facility for these devices. It comprises a unique and highly stable precision-engineered granite structure, weighing around four tonnes.
The granite supports both the instrument being tested and a pair of calibrated length artefacts made from carbon-fibre tubes, selected for their lightness, stiffness and low coefficient of thermal expansion. These artefacts are 2.4 m long and sit on kinematic mounts bolted to the granite structure. Each artefact has 19 magnetic nests defining all possible measurement positions for articulated arms that can range in size from about 1 to 4 m in length. NPL manufactured and assembled the artefacts, including bonding the nests to the tubes.
As articulated arm CMMs are used on the shop floor, the service has to be fast to avoid production downtime. A target turnaround of five working days from delivery to return is offered. In support of that, NPL produced specially written software for guiding the operator through the test process, recording and analysing the measurements and then automatically generating the certificate.
