The first measurement system of its type in the UK - a combination of
Geodetic Services’ photogrammetric technique and Delcam’s PowerInspect
software - has boosted helicopter manufacturer, GKN Westland’s
productivity
The photogrammetric technique uses reflective datum points and targets on
a product or tool, which are highlighted by a flash light unit and
recorded as a digital image. Now, thanks to the new generation of digital
cameras, computers and software, photogrammetry can be exploited for
precision measurement, and this is exactly what GKN Westland Helicopters
is doing to verify the engineering geometry of parts developed on its
Catia system.
The technique can be used in one of two ways. In the first procedure, the
equipment uses two cameras to photograph each point being measured. A
triangulation algorithm is then used to calculate the position of the
point from the two pictures. In this mode, termed ‘on-line’ - the results
are equivalent to those generated in real time by a conventional
co-ordinate measuring machine.
The second method uses a single camera to take a series of pictures of
the part. The points to be measured are identified again by reflective
targets, and typically around 12 pictures will be taken. These can
generate several thousand points, depending on the part size and range of
reflective targets employed. Termed ‘off-line’, this mode allows data to
be collected quickly and analysed later.
With both approaches, Westland loads the digital images into a Delcam
PowerInspect module, which is used to perform the detailed analysis and
provide reports of the product compared with the Catia model. The
software generates both pictorial and graphical summaries of the results
plus an Excel spreadsheet containing all the numerical data. Westland’s
central tooling manager, Dave Wakely picks up the story.
“The photogrammetric equipment is much more portable than our traditional
approach. that would take many hours to set up, whereas it is now
possible to complete a measurement task in less than an hour. A further
bonus is that work can continue on another section of the aircraft while
a measurement is taking place. Previously, everything had to stop as any
movement of the part affected the results. This meant either a delay in
production or waiting for the shift to end before we could start the
measurement task.
“PowerInspect has integrated well with Westland’s Catia. We regularly
take files from this system into PowerInspect and have not experienced
any data translation problems. The sophisticated surface fit software
program has also proved invaluable in determining the minimum product
deformation. Additionally, we have now loaded PowerInspect on our
co-ordinate measuring machine to exploit the benefit of a common software
package supporting two systems.”