Product category:
Coordinate Measurement systems
News Release from: Hexagon Metrology | Subject: Leitz PMM-F CMM
Edited by the Manufacturingtalk Editorial
Team on 13 August 2007
CMM checks telescope mirrors to under 1
micron
Research and designcentre stipulated a pre-determined positioning capability for a CMM's measuring probe of less than one micron when inspecting 1m parts.
What is believed to be the UK's most accurate, large volume coordinate measuring machine (CMM) has been installed by Hexagon Metrology has installed in the Bedfordshire-based Cranfield University Worth GBP 400,000, the ultra high accuracy Leitz PMM-F CMM will be used by the academic institute's School of Applied Sciences to inspect optics
This article was originally published on Manufacturingtalk on 2 Aug 2006 at 8.00am (UK)
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The optics will be used for next generation telescopes, including the replacement for Hubble orbiting telescope - the James Webb space telescope.
Cranfield will also use the Leitz CMM in research to develop mirrors for ELTs - the extra large telescopes under development by the European Southern Observatory and other leading astronomical interests.
The ELTs are made up of one to 2m segments that interlock to create mirrors of up to 100m in diameter.
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A high-precision grinder, known as the BoX (short for Big OptiX), produces the components.
Cranfield University Precision engineering centre developed the BoX using part of a four-year, GBP 3.5 million grant-aided collaborative project designed to revive UK ultra-precision surface manufacturing.
Mirrors for the new 50-100m 'super telescopes' will be made up of between 600 and 2,000 segments each - necessitating faster, more accurate, lower-cost production technologies.
"Earth-like planets, unlike stars, are extremely difficult to see, which is why a new breed of telescope is needed to detect them," said Paul Shore, Professor of Ultra Precision Technologies (UPT) at Cranfield.
"A significant stumbling block has been the time it takes to manufacture the mirror segments.
Prior to the development of the Cranfield BoX machine, and large scale polishing systems developed by University College London, available manufacturing technologies for large ultra-precision mirror production were slow and costly," said Prof Shore.
"Processing would have taken hundreds of hours for each segment meaning the time taken to manufacture the mirrors for an ELT mirror would have been many years.
But now the Cranfield and UCL-developed machines have removed that obstacle, reducing mirror processing from days to hours," he added.
The Hexagon-supplied 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 1m parts.
A further requirement was for the curvature sensor - a compact interferometer - to hold position with a stability of 100nm (0.1 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 Prof Shore.
"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 is fitted with a Leitz 3D probe head and a special interferometer adaptor and will run Hexagon's PC-DMIS CAD++ measurement software and a Quindos metrology package.
Hexagon's factory-trained engineers installed and calibrated the in July, 2007.
Hexagon Metrology+, the company's aftermarket services division, is supplying PC-DMIS and Quindos software training and an annual calibration service.
"We're delighted to be a part of this exciting project," said Hexagon Metrology's sales and marketing manager, Gavin Bell.
"We worked long and hard with Professor Shore's UPT group both at Cranfield and over at our Leitz HQ in Wetzlar, Germany, to ensure the PMM system met all the group's requirements.
As a result of this collaboration the CMM in its 'Infinite' guise achieves a first term of better than 0.3 micron," said Bell.
"The fact that we won the order against some of the stiffest competition in the world clearly demonstrates our ability to work closely with clients to meet their precise needs and timescales.".
Hexagon has also installed ultra high accuracy Leitz PMM CMMs for Cummins, Ricardo, Rolls Royce, BAE Systems, Alstom and Bosch.
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