Satellite dish inspection improved by measuring machine upgrade
Satellite dish inspection improved by measuring machine upgrade
Keywords: Satellites, Software, Aerospace
One of the more unusual uses for a co-ordinate measuring machine (CMM) may be found at Astrium, Stevenage, UK, where during the month-long build of each satellite dish it never leaves the confines of a COORD3 gantry-style CMM. The performance of this computer-controlled, 12 m × 4 m × 2 m measuring facility, installed during the mid 1990s, has now been improved following an electrical and controller refit plus a software upgrade carried out by LK Limited.
The British company, which itself builds CMMs and develops associated software, was called in by Astrium last year to cure an operational anomaly whereby if both sides of the bridge on the COORD3 were driven by independent motors, as is normally the case with large, gantry-style CMMS, the bridge carrying the measuring head tended to “crab” along the 12 metre X-axis instead of running smoothly. The short-term fix was to remove the second drive motor. This we are told worked well, but unlike in a normal production environment, Astrium had to operate the CMM at half speed to ensure very high precision inspection.
However, a more permanent solution was felt necessary, but research showed that few companies were able to take on a project of this size. LK was selected to carry out the upgrade as the LK Metre 4 CMM it manufactured and supplied to the Stevenage site over 20 years ago still operates effectively and service support is effective and prompt.
With the refit, both of the original drive motors were retained. The second,disengaged X-axis drive motor was reinstated and a new LK controller was fitted to drive the two motors in synchrony without any discernible irregularity of movement. At the same time, the opportunity was taken to rewire the CMM and fit new PCs, including a remote access terminal. The latter has reportedly resulted in considerable time savings as the operator can move it to where he is working, so no longer has to walk several metres to the end of the machine to check manual measurements.
LK also supplied its CAD-to-CMM software package, CAMIO. This is said to increase efficiency further by allowing computer-aided design information from Astrium’s CATIA CAD system to be imported into the CMM software environment where the data is operated on directly to create the measuring programs.
The quality of the LK upgrade is said to have been verified twice over. First, a mould tool for making the composite dishes was inspected on the CMM and the results were found to correlate closely with laserbased measurements made by the tool manufacturer. Second, a completed antenna dish underwent an electronic examination of its radio frequency footprint and this was checked against physical measurements on the CMM. Both tests are said to have shown volumetric accuracy to be within 12 microns per metre, with linear accuracy better than 8 microns per metre, achieved due to the way the machine is controlled by the LK system.
A visit to Astrium is an eye-opener for anyone uninitiated in satellite antenna technology. For example, far from being a regular geometric shape, the inner surface of the dish is enormously complex, comprising hundreds of localised peaks and valleys that vary the energy transmitted to take account of population distribution and geographical features, and to comply with regulatory coverage requirements. A fine contour check over a 3 m diameter dish on the LK-upgraded CMM requires over 70,000 measuring points and takes more than a day to complete.
Details available from: LK Limited. Tel: +44 (0)1332 811349; Fax: +44 (0)1332 850149; E-mail: sales@lkuk.co.uk; Web site: www.lk-cmm.com
