Precision for assembling large components
Assembling large structures, such as large aircraft wings or wind turbines, relies on accurately manufacturing and aligning constituent parts with precision to tenths of a micrometre. To achieve first time right assembly, component mismatches created by sagging or small temperature variations in vast assembly halls need mitigation. For example, misalignments in aircraft wing assembly can require the addition of several hundred kilograms of shim, effecting the planes fuel economy throughout its life.
In industry laser trackers are used for measuring dimensions and controlling positioning of large components using light based interferometry. This technique offers nanometre precision in well controlled labs but in industrial workshops temperature gradients and air turbulence seriously degrade its performance.
The EMRP project Large volume metrology in industry (LVM) developed measurement concepts based on interferometry techniques, for new costeffective and precise Large Volume Metrology tools, and derived strategies to compensate for measurement errors associated with industrial conditions.
- Established three approaches to compensate for refractive index effects in optical measurements due to environmental variations (temperature, humidity etc.) in real industrial environments.
- Developed proof-of concept prototypes and novel systems based on laser tracking and other optical technologies, capable of measuring distances of the order of 40-50 metres with micrometre precision.
- Validated the performance of these systems at NMI calibration facilities under very stable conditions to ensure measurement traceability in more rigorous testing.
- Assessed the performance of these new systems at the 50-metre tape bench facility at GUM, which was upgraded with additional temperature, pressure, and humidity sensors to enable provision of conditions similar to those in industrial environments.
- Demonstrated the performance of the new systems under industrial conditions at the Airbus industrial research facility in Filton, UK.
Industries manufacturing and assembling large components need new measurement systems to bridge the accuracy gap between expensive laser tracking and other cheaper methods. By stimulating innovation in optical measurement techniques, this project has initiated new end-user collaborations, redirected existing research, generated best measurement practice, and provided valuable training to the LVM community. Five patents have been submitted relating to project outcomes and these form the basis for potential industrial exploitation: two measurement systems (InPlanT and FSI) are being developed further, and a third (compensated tracking interferometer) is the subject of commercial discussions. Outputs from this EMRP project are contributing to the UK national project The Light Controlled Factory, which is further researching the enabling role of optical metrology in factories of the future. A multimillion Euro investment at Airbus in Filton, UK to develop measurement capability will use results from the project. A new calibration service using the tracking interferometer is also being established for large component measuring machines.
The follow-on EMPIR project Large Volume Metrology Applications (LAVA) enables the continuation of developments to the methods established in this project towards commercialisation and greater industrial uptake.