Surfaces that are nearly flat or spherical may be measured to nanometric accuracy using a device known as a swing-arm profilometer (SAP). There are only a handful of such machines worldwide, most of them in universities in the USA. There is only one in Britain, built in a collaboration between UK National Physical Laboratory and University College London, and adopted for further development by Leicestershire firm, Zeeko.
This one-metre capacity SAP is owned by Zeeko Ltd and is in use at the UK National Facility for Ultra Precision Surfaces, hosted within the National Facility for Ultra Precision Surfaces, OpTIC-Glyndŵr, St Asaph, North Wales. The SAP hardware is being used to create the next generation of measurement algorithms for characterising challenging meter-scale optical surfaces required for astronomy, high power laser systems and space instrumentation.
While this type of work will be a core application for SAPs, on-going tests in St Asaph have shown that the technology is scalable, permitting smaller metrology machines using the same measuring principle to be manufactured for quality control in other industries.
For example, this type of equipment would be well suited to measuring the spherical ball of a prosthetic hip. With the advent of joints in which two hard materials are used as the bearing surfaces, accurate form control is crucial to ensure longevity of the implant.
Evaluating the flatness of a high-precision machine tool's planar table is another potential application, as is inspection of lenses for high-end cameras.
The prerequisites for investment in a SAP are that the geometry of the component being inspected deviates from plano or spherical by no more than a few tens of millimetres over a metre; and that surface accuracy within a couple of hundred nanometres (nm) peak-to-valley (PV) needs to be measured. Zeeko is hopeful that advances that it is making in stitching software will bring measuring accuracy down to 10 nm PV after the exclusion of low order terms.
Hubble telescope error: Please click on the Word icon above to read the full editorial.
