example of a requirement which is parallel with
requirements in photogrammetric analysis.
The example given above is only one of many procedures
in which holography has been employed in industry.
These, and other applications of coherent optics in
measurement are categorised in Reference 2.
References
1 Burch.J M "Holographic Measurement of Displacement
and Strain — An Introduction"
J Strain Analaysis, 1974, 9, No 1,
pp 1-3.
2 Burch J M "Outlines of Optical Metrology" in
"Engineering Uses of Coherent Optics"
pp 1-22 Cambridge University Press 1976.
2 EXPERIMENTAL MEASUREMENT OF NORMAL SURFACE
DISPLACEMENT BY HOLOGRAPHY
E Archbold, A E Ennos (3,4)
An example of the type of problem in the measurement
of deformation by holography is shown in Figure 1.
Two plastic pipes are joined by fusing into an
encircling sleeves The elastic deformation and
relaxation when the pressure within the assembly is
changed can be very conveniently observed by
holographic methods, but to ensure a high sensitivity
and to simplify quantitative evaluation of the
patterns it is necessary to choose the directions of
illumination and viewing properly. As shown in the
figure, both these directions were made to lie as
close as possible to the normal to the nearest part
of the surface.
lilumination
Viewing
Figure 1 Plastic pipe joint mounted on Vee-blocks
The real-time ('"live-fringe") method of observation
with a single recorded hologram was employed as a
convenient way to establish the directions of
_ displacement in relation to the directions of
movement of the fringe pattern, for the purpose of
assigning fringe order numbers, as described in the
last section. The double exposure method ("frozen
fringe") was then used for detailed measurement.
Figure 2
Photograph of reconstruction from double-
exposure holograms of the pipe joint
= +
: /
3 ]
o
8 4
£
E /
Distance along pipe joint x—e
Figure 3 Profile change along surface generator AB
Figure 2 shows a typical reconstructed interference
pattern from a "frozen fringe" hologram and Figure 3
shows the derived profile change along the surface.
Another typical example is shown in Figure 4.
+ ce
Figure 4
Experimental arrangement to record the
surfaces of the chair.