National Physical Laboratory

Mini robot builds NPL probe

Micro CMM
The micro-scale CMM probe was designed at NPL
and built in Germany at TU Braunschweig

Precision engineering requires accurate measurements and these are often made using co-ordinate measuring machines, or CMMs.

The measurements need to be, at the very least, of equal accuracy to machining capabilities, especially when working with small components with functional micro-scale features. While some new micro-CMMs are capable of making such accurate measurements, many existing probing systems lack the functionality to do so.

To address this, NPL has developed a novel micro-scale CMM probe that aims to reduce the measurement uncertainty of micro-CMMs to below 100 nanometres (or 0.0001 millimetres). The probe consists of a three-legged flexure device and a micro stylus with a spherical tip.

Each flexure is 2 mm long, 0.2 mm wide and around 0.02 mm thick. The stylus is 2 mm long and 0.2 mm in diameter with a 0.07 mm diameter spherical tip.

The probe is a MEMS device (micro-electrical mechanical system). It has built-in piezoelectric film coated onto the flexures so they act as sensors and actuators, allowing the device to vibrate away from measurement surfaces and counteract surface forces that are very strong at these tiny distances. The vibration also allows the probe to operate in non-contact mode.

To assemble such a device there is a need for high-precision, repeatability, flexibility and low cost, as well as a workspace that takes up as little room as possible. In order to meet these demands, a miniaturised assembly setup using a robot called Parvus (which is Latin for 'small') was constructed. The robot was built at the Technische Universität Braunschweig, Germany, to function as a mini industrial production robot, to demonstrate the possibility of reducing the size of assembly lines and realising a 'desktop factory'.

The video below, put together by TU Braunschweig, shows the assembly process:

Four micro-CMM probes were successfully assembled using the process which took 30 minutes per probe. This time could be reduced to around five minutes if an automated system was put in place to feed the parts into the system, as would happen on an industrial-scale assembly line. This is just one potential improvement to the system that will be investigated in future work.

View a poster on the CMM probe

More on NPL's work on Dimensional Measurement

For more information, please contact James Claverley

Last Updated: 18 Nov 2013
Created: 30 Aug 2012

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