Measuring arm gets around to good effect

Assembly Automation

ISSN: 0144-5154

Article publication date: 1 September 2003




(2003), "Measuring arm gets around to good effect", Assembly Automation, Vol. 23 No. 3.



Emerald Group Publishing Limited

Copyright © 2003, MCB UP Limited

Measuring arm gets around to good effect

Measuring arm gets around to good effect

Keywords: Aerospace, Measuring machines, BAE SYSTEMS

While co-ordinate measuring machines (CMM) play a key role in quality and inspection, they are not the panacea to solve all inspection problems. This was brought home to BAE SYSTEMS, Aerostructures of Prestwick, following the cessation of complete aircraft production and the restructuring of its business to focus on the manufacture and assembly of major airframe structures.

John Kimm, Aerostructures Tooling and Service Manager explains: "We found we needed a more versatile and portable measuring solution which could be easily taken to a variety of work locations as and when required. So we decided to sell our existing CMM and invest in a Polar 2000 3-D articulated measuring arm which had been developed and supplied by OGP UK of Hatton in Derbyshire. One of the most important advantages in the selection of Polar was the fact it could be calibrated at any time on-site to verify its accuracy (Plate 4)".

The reason for disposing of the redundant CMM was that BAE SYSTEMS could no longer justify its installation for the type of inspection tasks it now faced which included checking components and fixture elements on major aircraft structures when any problem was found during the assembly stage. What is more, a fixed system was just no longer suitable for much of the new work as inspection often had to be carried out on-site at different hangar locations and involved checking key details on large, partly-built wing structures and leading edges.

Plate 4 OGP UK's Polar provides versatility and accuracy to BAE SYSTEMS Aerostructures of Prestwick

Prior to buying the Polar 2000 measuring arm, BAE SYSTEMS used an existing laser tracker system to check various components and sub-assemblies. But even this was far from ideal, as John Kimm explained: "The main problem with the laser was that it was fully utilised on checking jigs and fixtures and finished leading edge assemblies. This meant there was little spare capacity for our trouble shooting demands. What we needed was a quick to use cost-effective portable measuring system that was easy to set-up and simple to verify for accuracy."

After seeing a demonstration of the Polar 2000, BAE decided that this was the type of equipment, when used directly out of the box, would give the flexibility, accuracy and quick response needed for checking out potential problems during various stages of aircraft build.

Located at Prestwick International Airport, on the West Coast of Scotland, this BAE SYSTEMS site is home to a number of different activities. The aerostructures business is the largest on the Prestwick site for the manufacture, assembly and supply of leading edge wing assembly for Boeing and Airbus and the assembly of various components for Raytheon. It also manufactures parts for the new Nimrod MRA4 maritime patrol aircraft. "Here in particular, the Polar 2000 system really came into its own across a range of different projects," said John Kimm. It houses customer training facilities for in-service turboprop regional aircraft and provides engineering support and spares for regional aircraft.

As one would expect, the out-sourced components for aircraft assembly should be to specification having been inspected and audited by suppliers. However, problems can develop during build either due to slight inaccuracies in individual components from a batch, or problems relating to the alignment of build jigs which, due to their intended task, have a large number of removable parts. If a problem occurs when a certain part does not fit or line-up on its assembly jig, BAE SYSTEMS needs to know quickly and identify the cause of the error in order to minimise delay to the build programme.

Here, Polar allows both components and any relevant jig elements to be rapidly and accurately checked on site avoiding any logistics of transport, waiting for inspection availability and therefore saving valuable production time. Meanwhile, on large part-assembled structures, taking the measuring system to the appropriate bay or hangar is by far the most practical way of fault tracing without any costs or delays caused when dismantling the assembly.

The portable measuring system will easily fit in the boot of a car. Weighing just 8.5 kg, the articulated 3-D arm comes with its own special carrying case, touch-trigger probe, laptop PC, accuracy optimisation artefact and a choice of software to suit various measuring functions.

The Polar 2000 has a spherical measuring radius of 1,000 mm and a volumetric accuracy within 0.14 mm. The key differentiating feature of the Polar arm is its ability to be easily and quickly calibrated at any time on site against an artefact which is transported with the arm in its carrying case and allows the operator to zero out against the datum to confirm that everything is OK. The ability to use an artefact, which is traceable to check and calibrate the arm, is critical.

In addition, the Polar software and electronics also monitors ambient temperature and will automatically warn the operator of any changes while measuring is being performed, so he can make the decision to carry on or recalibrate.

John Kimm added: "With Polar 2000, we have a very flexible, accurate and easy to use system which can be taken to any location and is immediately ready to go." On site verification of accuracy can be performed at any time and it takes around 2 min using the built-in calibration routines in conjunction with the optimisation artefact. The software automatically computes and accounts for changes of angles and lengths as the arm is exercised around the datum points of the artefact.

John Kimm says: "As we can now perform quick measuring tasks, Polar becomes very cost-effective and also flees-up our expensive laser-based equipment." Depending on the component or fixture element to be checked, the arm is used to measure: profiles, bores, hole centres, angular faces, pockets, flanges and sections. On a jig fixing ring, for example, Polar was used to inspect the angle and section size of the main body as well as over 30 different hole centres and diameters.

After calibrating the arm and establishing a datum position on the ring, the probe was simply touched against the appropriate feature and the readings automatically stored in the laptop PC for subsequent analysis or comparison against either CAD data or a detailed drawing.

BAE SYSTEMS Aerostructures' tooling and service department currently serves the needs of seven integrated production teams (IPTs) at Prestwick which work on different aircraft assembly projects. The department is an autonomous business unit and as such, charges the relevant IPT for any inspection work that it carries out. The department needs to cover its operating costs and it is here that the introduction of the Polar arm has made on site inspection far more efficient and cost-effective.

John Kimm sums-up: "It looks as if over the coming months, Polar may well be used to perform inspection tasks for the new A380 leading edge contract which further increases our justification to purchase."

For further information, contact: Mr Andrew Fulton, Managing Director, OGP UK Limited, Station Road Industrial Estate, Hatton, Derbyshire DE65 5DU. Tel: 01283 520127.

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