The NPL Small CMM - 3-D measurement of small features

Macro sized objects (i.e. several centimetres in size) are routinely measured using conventional CMMs, which can achieve uncertainties of the order of a few micrometres. Conversely, nanometre and micrometre sized objects or features normally fall within the measurement capabilities of the field of nanometrology, where SPM-type instruments can achieve nanometric uncertainties. However the overlap between these two fields is not so good. There are few, if any nanometrology instruments that have ranges of several centimetres, yet which retain an uncertainty of a part per million. Similarly, there are no true 3-D CMMs that can achieve significantly better than a micrometre uncertainty for complex measurands. In order to address these shortfalls, NPL has designed and built a specialised CMM. The instrument has a working volume of 50 x 50 x 50 mm and an uncertainty in the range of 50 - 150 nm. It operates as a true CMM, in full 3-D and can be programmed just like any other CMM.