Note: Descriptions are shown in the official language in which they were submitted.
Field of the Invention - This invention relates to
inspection of contoured objects, and particularly, to the
inspection of chord shapes of blades and vanes of gas turbine
engines.
Description of the Prlor Art - Modern gas turbine
engine designs result from the intensive analytical and
empirical evaluation of complex fluid reaction surfaces.
Accurate contouring of the fluid reaction surfaces during
manufacture is requisite to the implementation of these
intricate and precise designs. Contour inspection at
manufacture insures compliance with the developed design.
Much of the apparatus developed in the past for
inspection of complex contours has been specifically directed
to the inspection of chord shapes of blades and vanes
of gas turbine enginesO The above notwithstanding,
designers and manufacturers are continuing to devo~e
substantial economic and valued personnel resources to the
development of simplified apparatus with improved image ,
resolution.
Known apparatus includes that described in U.S~
Patent 2,607,267 to Fultz et al entitled l'Optical System
for the Inspection of Curved Profiles". In Fultz et al
a light pattern is projected onto the contour to be
inspected. A plurality of lenses, having optical axes
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which are oblique to the plane of the article cross sec-
tion to be inspected, project an image of the pattern
onto a viewing screen. A plurality of mirrors and
additional lenses are employed to form a composite image
of the pattern at the viewing screen.
Other systems employ lenses having optical axes
perpendicular to the plane of the cross section. See
U.S. Patents 2,574,119 to Mottu entitled "Optical
Controlling or Inspecting Arrangement for Verifying the
Cross Sections of Pi~ces with Comple~ Profiles"; 2,737,080
to Mottu entitled "Optical Device for Examining the
Cross Section of Parts Having an Intricate Outline", and
2,741,153 to Reason et al entitled "Optical Projection
Systems". As shown, these systems require large diameter,
large relative aperture (Relative aperture is the ratio
of aperture diameter to focal length of the lens.) lenses
to collect adequate light for projection of the pattern
image. Particularly large lenses are required to "see
around" obstructions to the line of sight between the
~0 imaging lens and the inspected cross section.
SUMMARY OF THE INVENTION
A primary aim of the present invention is to
; provide methods and apparatus for inspecting the contours
o articles having complex geometries. The projection
~ of a contour image onto a dispLay screen is an ultimate
; goal and, in an intermediate step the formation of a
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composite optical path, adapted to "see around" obstructions
between a display screen and the contour to be inspected, is
sought.
According to the present invention a composite
optical path between the display screen of a contour inspection
device and the article to be inspected is formed. The composite
path comprises multidirectional views of which are joined at a
beam splitter~
The primary feature of the present invention is the
beam splitter. A pair of parallel mirrors bracket the light
pattern on the article contour to be inspected and are optically
aligned with the beam splitter to form a composite optical path
emanating from the beam splitter. In one embodiment, a plurality
of composite optical paths are formed and directed to a single -
imaging lens on the axis of the inspection apparatus.
A principal advantage of the present invention is
the enhanced ability of the inspection apparatus to "s~e around"
obstructions to the conventional line of sight. The concepts
taught are particularly well adapted to the measurement of airfoil
contours of vanes having integrally formed platforms.
In accordance with a specific embodiment of the -
invention there is provided, in a contour inspection apparatus of
the t~pe having an imaging eLement for projecting the image of
a light pattern on the article to be inspected wherein the
improvement comprises: a first forming mirror and a second forming
mirror which brac~et the light pattern on the article to be
- inspected; and a beam splitter which is optically aligned with said
first and second mirrors to form a composite optical path compris-
ing a first segment reflected from said first forming mirror and
a second segment reflected from said second forming mirror.
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In accordance with a further embodiment of the
invention there is provided, for inspecting the cross section
contour of an article, apparatus having components oriented
about an axis which is perpendicular to the plane of the cross
section to be inspected, including: a base structure for
supporting the components of the apparatus, means attached to the
base structure for projecting a light pattern onto an article
at the cross section to be inspected; a first forming mirror and
a second forming ~.nirror which bracket the plane of the cross
section to be inspected, and a beam splitter which is optically
aligned with said first and second mirrors to form a composite
optical path comprising a first segment reflected from said first
forming mirror and a second segment reflected from said second
forming mirror.
From a different aspect, and in accordance with the
. invention, a method for viewing cross section contour of an
` article~ comprisesthe steps of: projecting a light pattern onto
the article at the cross section to be inspected, viewing said
light pattern along a composite optical path, and forming an
image of the light pattern as viewed along said composite optical
path.
; The foregoing and other objects, features and
. advantages of the present invention will become more apparent
~ in the light of the following detailed
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description of the preferred embodiment thereof as shown
in the accompanying drawings.
BRIEF DESCRIPTION OF THE DR~WINGS
Fig. 1 is a simplified side elevation view of
inspection apparatus constructed in accordance with the
present invention;
Fig. 2 is a simplified illustration of a portion
of the inspection apparatus aligned to an obstructed
region of a vane;
Fig. 3 is a simplified illustration of a portion
of the inspection apparatus aligned to a second obstructed
region of the vane; and ^
Fig. 4 is a view of the cross section image on the
display screen.
DEIAII~IL~'olLL~ll9
Detailed description of apparatus embodying the
inventive concepts follows. Although the concepts are
described in combination with inspection means employing
a lens as an image focusing elemen~, the concepts are
not restricted to such a combination and are equally
useful with other apparatus capable of processing a
composite image.
Apparatus 10 for inspecting the cross section contour
of an article 12 is shown in Fig. 1. The apparatus has
great utility for inspecting the complex contours of gas
turbine airfoils and is illustrated with respect thereto.
~le apparatus and methods of the present invention, how-
ever, are equally applicable to other contoured articles.
The components of the inspection apparatus 10 are
oriented about an axis 14 which is perpendicular to the
plane of an article cross section to be inspected. A base
plate 16 is the reference structure to which the components
are aligned. A fixture 18 for holding the arti~le 12 is
moveable in known relationship to the base plate to enable
inspection of multiple cross sections.
One or more lighting systems 20 are adapted to project
a light pattern 22 onto the article 12 at the cross
section to be inspected. An imaging lens 30 is positioned
on the axis 14 of the apparatus, the optical axis of the
lens being coincident with the axis 14. The light pattern
22 is viewed by the lens along a composite optical path
40 which is reflected to the lens by an offset pattern
mirror 32. The composite path is formed of a first seg~
ment 42 and a second segment 44 which are optically com-
; bined by a mirror system 46. Within the mirror system
the light pattern 22 is reflected along the path 40 to
the mirror 32 by a first forming mirror 48. The ligh~
pattern 22 is also reflected along the path~40 to the
mirror 32 by a second forming mirror 50 and the reflective
surface 52 of a beam splitter 54. At the beam splitter
the light pattern 22, as reflected by the first forming
mirror 48, and the light pattern 22, as reflected by the
second forming mirror 50 and the reflecting surface 54
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of the beam splitter, emanate in coincidence along the
composite path 40.
In the embodiment shown, the pattern mirrors 32 are
planar mirrors and are parallel to the axis 14. A
dimensionally proportional image, as viewed along the
composite path 40, is projectable directly from the lens
30 to a display screen 34, or as shown in Fig. 1, is
redirected by one or more image mirrors 36 to the display
screen at the axis 14. Redirection of the image to the
axis 14 forms a composite image 38 which is representative
in true dimensional proportion of the article cross section
contour. Various known magnification techniques are
employable with the described methods and apparatus with-
out destroying the true proportional relationship of the
cross section d~mensions.
The article 12 illustrated is a stator vane of a
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gas turbine engine and has, integrally formed at the ends
thereof, platorms 12A which comprise a portion of the
flow path wall extending through an engine. The platforms
12A are an obstruction to conventional cross section
viewing and, as such, impede normal inspection o the
article. As is viewable in Figs. 2 and 3, continuity of
the optical path 40 to the imaging lens 30 is maintained
notwithstanding interruptions in the first (42) or
second (44~ segments forming the composite path. Viewing
of the cross section closely adjacent either platform
12A is enabled.
The beam splitter 54 is a key element of the system
46. Beam splitters are well known in the optic field
and conventionally comprise a partially transmissive,
partially reflective material sandwiched between a pair
of protective glass sheets. In a preferred embodiment
the material is fifty percent (50%) reflective and
fifty percent (50~/O) transmissive. Accordingly, fifty
percent (50%) of the light energy traveling along the
first segment 42 transmits through the material to the
composite path 40 and fifty percent (50%) of the light --
energy traveling along the second segment 44 reflects to
the composite path 40. The ~eflected portion from the
segment 42 and the t~ansmitted portion from the segment
44 are not utilized in the embodiment shown and are not
illustrated. The light energy traveling along the com-
posite path 40 has an intensity approximate to the
intensity of conventional viewing techniques. In the
partially obstructed regions 9 as illustrated in Figs~ 2
and 3, the intensity of the light energy is reduced;
however, the image remains on the display screen.
The lens viewing angle ~, via the offset pattern
mirrors 32 is preferably within the range of five (5)
to forty-five (45) degrees. A viewing angle of twenty
(20) degrees is considered optimum. A greater viewing
angle increases the ability of the apparatus to see around
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obstructions on the article inspected. A lesser viewing
angle improves the sensitivity of the apparatus to minute
contour variations. The imaging lens is optimized for
acceptance of incident light energy at an angle ~ to
the optical axis. Accordingly, for maximized resolution -~
in each system the offset distances (b and bi) of all the
pattern mirrors 32 are equaL. -
The inspection device described is known as an
"on-axis system". "Off-axis" viewing systems, including
those employing imaging mirrors, may equally benefit from
the use of the composite viewing apparatus and method
described.
Although the invention has been shown and described
with respect to preferred embodiments thereof, it should
be understood by those skilled in the art that various
changes and omissions in the form and detail thereof
may be made therein without departing from the spirit
and the scope of the invention.
