Leitz CMM supports search for other Earths
2 mins read
Hexagon Metrology has installed the UK's most accurate, large volume co-ordinate measuring machine in a deal designed to speed up the search for earth-like planets in outer space.
The £400,000 machine - an ultra high accuracy Leitz PMM-F - has been supplied to Bedfordshire-based Cranfield University. The CMM will be used by School of Applied Sciences to inspect optics destined for next-generation telescopes, including the James Webb space telescope, the replacement for Hubble.
The Leitz machine will also be used in research to develop mirrors for ELTs - the extra large telescopes under development by the European Southern Observatory and other leading astronomical agencies.
ELTs - made up of 1 to 2-metre segments that interlock to create mirrors of up to 100 metres in diameter - are manufactured on a high-precision grinder known as the BoX (short for Big OptiX - see web link below).
Developed by the Cranfield University Precision engineering centre, the machine is part of a four-year, £3.5 million grant-aided collaborative project designed to kick-start a revival in UK ultra-precision surface manufacturing.
Mirrors for the new 50-100 metre super telescopes will be made up of between 600 and 2,000 segments each - in contrast to the 36 segments used in their predecessors - necessitating faster, more accurate, lower-cost production technologies.
The Leitz CMM is to be used to verify the performance of the BoX machine. It will also serve as a precision motion system to move laser-based curvature sensors around the surface of machined mirror surfaces to confirm their surface accuracy and relative position to edge features.
Cranfield's functional specification stipulated a pre-determined positioning capability for the CMM's measuring probe of less than one micron when inspecting 1-metre parts. A further requirement was for the curvature sensor - a compact interferometer - to hold position with a stability of 100 nm (0.1 of a micron) in order to permit stable measurements of the concave mirror surfaces.
"Our demanding specification meant there were only two or three credible manufacturers of CMMs in the world that could meet our specification" said Paul Shore, Professor of Ultra Precision Technologies (UPT) at Cranfield. "And, of the CMMs we tested, only the Leitz PMM-F satisfied our needs.
"The Leitz engineering team was also extremely responsive to design changes we wanted to implement for our specific application. This gave us a high degree of confidence in the machine and the technical support behind it."
The CMM, which is fitted with a Leitz 3D probe head and a special interferometer adaptor, will run Hexagon's PC-DMIS CAD++ measurement software and a Quindos metrology package.
As part of the contract, Hexagon Metrology+, the company's aftermarket services division, will supply PC-DMIS and Quindos software training and an annual calibration service.
"As a result of this collaboration, the CMM in its 'Infinite' guise achieves a first term of better than 0.3µ (of a micron)," said Hexagon Metrology's sales and marketing manager, Gavin Bell.
