NOTHING OUT OF SCOPE
How stereo measurement and 3D modeling
capabilities on the latest videoscopes bring
precision and reliability to aerospace inspections
// GUAN-LU ZHANG
V ideoscopes are instrumental for
aircraft gas turbine inspections.
Modern high-end videoscopes have
moved far beyond basic imaging; stereo
imaging capability is a reliable method to
carry out accurate and repeatable complex
measurements in three dimensions. This
same stereo measurement capability also
enables a videoscope to generate 3D
models of a component or surface – a
feature that greatly increases confidence
in measuring defects.
This article takes a closer look at the
how and the why of these advanced
capabilities. It also demonstrates how these
capabilities are used in practice during
aerospace inspections, through a case
study looking at tip gap clearance
measurements inside gas turbines.
A DOUBLE-TAKE ON STEREO
For many defects, the questions as to
whether an indication found during
inspection requires repair or replacement
are its size and its location. Conventional
visual inspection can show the type of
defect, but identifying the location and
dimensions of defects using imaging data
would be much more powerful and allows
more confident decisions. In modern
videoscopes, stereo measurement with 3D
modeling provides this increased
confidence, ensuring reliability even when
124 SHOWCASE 2020 \\ AEROSPACETESTINGINTERNATIONAL.COM
1 // Expanded
on Olympus’ IPLEX NX
industrial videoscope (a)
greater distances (b).
taking measurements from farther away.
The way stereo measurement works is
similar to how we can perceive depth.
When our eyes see an object from two
slightly different angles, our brains can
calculate approximate distances based on
parallax (i.e. the change in position of
objects when seen from different angles).
Stereo measurement employs the same
fundamental principle. Videoscopes use
dual-lens optical tip adaptors with a fixed
distance from each lens and use parallax to
determine the 3-dimensional position of an
object relative to the distal end.
When using stereo measurement with
the right optics, users can benefit from a
large field of view and a more extended