Metrology: measuring products shape or the correct alignment of machines and parts
Metrology is a high-precision technology that SGS experts use to proof geometrical properties on industrial products. It doesn’t matter if a part has a size of 160 millimetres or the assembly line has a length of more than 160 metres. Thereby SGS achieves accuracies (addicted to devices size) up to a few 1/100mm. The whole equipment is mobile so the measurement can be taken where it is needed – e.g. directly within the production – worldwide.
This mobility sometimes makes quality controls possible in the first place or reduces times and costs. Automation of measurement and analysis is the future of quality inspection within the production – a process that metrology supports step by step. SGS measures if a device is located at its nominal Position or if a plant is working (geometrically) correct. SGS also provides metrology services to determine if intermediate and end products have their exact dimensions and shapes or if parts can be assembled accurately. Thereby SGS does not only analyse – we do also help adjusting the specimen.
How does metrology work?
Simply said: we do measure points. The bases for our work are points measured directly at the part / machine to be inspected. There are a lot of different methods how to do this but after all every system collects points. These so called clouds of points can be analysed in different ways. Using these points some regular geometries like circle, cylinder, cylinder axis can be calculated and analysed. It is also possible to measure free formed surfaces. In this case the clouds of points are measured and compared to a CAD-model. The so called Colormapping generates an easily interpreted graphic image of the part to be inspected.
Metrology: The different Systems
Depending on the measurement location, the aspired accuracy and the part to be inspected a broad variety of different measurement systems can be used:
- Polar Systems - Using Polar Systems like Laser Tracker, Total Stations or Laser Radar a horizontal angle, a vertical angle and a distance is measured between the instrument and (mostly) a reflector that is located directly at the device. The connected software is transforming these polar coordinates to Cartesian ones and is supporting the user doing the analysis. The advantages of these systems are the broadest field of application and the high accuracy over a long distance.
- Photogrammetry - This is a technique of measuring 3D-coordinates of targeted objects by the use of photos. A bundle adjustment is extracting the coordinates of a whole series of photos taken by special cameras. This method is especially applicable when the floor or the part to be inspected is unstable supported. It is also the most portable measuring solution.
- Fringe Projection - This kind of measurement bases on photogrammetry. Instead of photographing targeted points a projected grid is being filmed by two cameras. The grid is shifted several times and after the shifting-procedure the connected software is analysing the distinctions between the grey scale value of the different pictures. Using these method millions of points can be measured very quickly – not only single points.
- Measuring Arms - These Measuring Arms combines exactly known lengths (arm tubes) with precision angular encoders within the hinges. A tip for punctual measurements or a scanner can be located at the end of the measuring arm.
Metrology within aviation
Since aviation started it has always been essential that technical parts work and fit together at its best. The more complex a plane becomes the more challenging is its realisation – and the more has to be proofed and measured. In the very beginning Metrology is required within research and development. Only one example: the behaviour of materials (e.g. CFRP) and techniques within the autoclave-process has to be figured out. How big is the shrinking-effect of CFRP or how does CFRP yield using big layer structured in coincidence with steeply inclined moulds? Afterwards Metrology is needed for the building of every single facility.
From building and adjusting plants over the teaching of robots up to approval of machines there is a broad variety of measurements that have to be taken before one single part can be produced. In the next step Metrology helps evaluating quality of single parts machining and flexion. This is especially important in aviation where the tolerances of very complex parts have to be proofed and documented. After that Metrology supports the process of assembling parts – another very important task especially in building aircrafts.