FIELD OF INVENTION
[001] The present invention relates to a measuring apparatus for
the radial height measurement of a blade or a vane of a turbo-
machinery. More specifically the present invention provides an
apparatus for measuring radial height of an individual blade or a
stator vane of a turbo-machinery either in the bladed condition on
a rotor or in a casing as well as on standing alone condition. The
present apparatus is also enable to measure the blade-tip
clearance.
BACKGROUND AND THE PRIOR ART
[002] Due to manufacturing errors, deviation in machining
processes and material deviation there are consequent variations
in structural and geometrical properties between individual blades
in real blade-disk assemblies of the turbo machinery leading to
mistuned blades.
[003] Such deviations in geometry can heavily influence the rotor
dynamics behaviour, shaft work extraction across the rotor and
vibratory stresses in the blades. Knowing that blade tip clearance
is usually maintained less than 0.5 mm to avoid the leakage loss, a
slight bigger size of blades will lead to blades rubbing against the
casing, which potentially results into a catastrophic mechanical

failure of the blades. On the opposite scenario would open up the
tip clearance gap which will migrate more flow from pressure side
to the suction side over tip. This will be one of most degrading
aerodynamics mechanisms.
[004] Moreover, the mistuning abolishes the cyclic symmetry
(periodicity) of the structure of the blade-disk assembly resulting to
bifurcation of the tuned eigenvalue pairs and absence of free wave
propagation (nonexistence of pure traveling waves as natural
vibration modes). Such loss of cyclic symmetry has a direct
consequence on the forced response of the blade-disk mode
localization and result into increased localized vibration amplitudes
compared to the tuned blade-disk assembly.
[005] Hence, during workshop assembly, on-site routine
overhauling as well as periodic inspection throughout the life of a
rotating machine such as in axial flow compressor, steam turbine,
gas turbine, blower, fan etc. blade height and blade-tip clearance
needs to be measured. The accuracy of the measurement should be
of the order of approx. 0.02 mm. To date, there are limited ways of
measuring the direct blade height. For blade-tip clearance several
indirect ways are available, but every technique has their own
limitations.

[006] One of the well-known techniques for measuring the blade
height is using height micrometer. However the individual blade
height as is taken using a depth micrometer is not accurate
(usually is of order of approx. 0.1 mm) to meet the assembly and
machining requirement. The difficulty arises due to curvilinear
base profile of the rotor as well as slant face of the tip shroud of the
blade. This results into different readings at same place taken at
different points of time. One way to fix this problem is to locate the
mid-point of blade tip using local measurement and then marked
using markers. However, during machining process the trace made
using marker will be erased and next reading will be erroneous.
[007] Furthermore, it is important to note that the curved profile of
rotor makes it difficult to take exact readings as the stem of depth
micrometer may land anywhere on curvature and each point in
curvature has different reading.
[008]Another well-known technique for measuring blade height
and tip clearance is through dial indicator or outside micrometer
on the conventional or CNC programmed lathe machine. This
methodology provides very accurate measurement for both blade
height and blade tip clearance, however, this is a very costly
procedure, demand huge investment as well as cannot make easily
available at the remote places, in-situ application, and for various

research laboratories at University and Institute. Various contact-
less blade height measuring devices have been proposed in the
recent past.
[009] Invention US4566225A describes a process and apparatus
which used a stroboscopically controlled laser beam for the
measurement of the height of turbine rotor blades.
[0010] Invention JPH02298602A discloses a sensor based method
for measuring the dimensions of turbine blades. In this process a
measuring jig having a turn table to which a measuring sensor
movable in both horizontal and vertical directions are provided
while turbine blade will be fixed.
[0011] Invention CN108463689A discloses a device for the contact-
less three-dimensional inspection of a turbo machine blade
particularly for aircraft turbines and jet engines using the laser
technology. This device measures the blade through scanning
faces of the blade over the entire height.
[0012] Invention JPH0843064A provides another method for
detecting blade height by using sensors and setting a plurality of
distance sensors in the longitudinal direction on a blade. These
devices are accurate in measurement, but usually applicable for
workshop or laboratory application and also required specialized
technician to operate.

[0013] Invention CN106524865A describes a universal type steam
turbine diaphragm stator blade total length measuring device. The
device comprises a bottom plate, a blade positioning device, a blade
jacking device and a blade measuring template, a plurality of
transverse keyways and longitudinal keyways which are
perpendicular to one another. The blade jacking device and the
blade measuring template assembly connected with the transverse
key-ways and the longitudinal key ways by means of positioning
keys.
[0014] Invention US7171760B1 provides a generic height
measuring device for setting of cutting blade height on power
equipment in a workshop, The device has a support cylindrical
sleeve base with a height indicator, powered table saws and related
equipment.
[0015] Various other inventions are there related to blade
dimension measurement such as US6532678B2 which uses a
gauge to measure the pitch and rake of a blade, US7296362B2
which presents a magnetically attractable curvature-measuring,
US7681325B2 which measures the chord length of the turbine
blade, US5152070A which uses three-dimensional coordinate
position of a blade, US4265023A which presents a device

measuring the growth of turbine blades, US2737722A which
measures contours or curvatures of turbine blades or propellers.
[0016] There are devices to measure that could be used for
measuring the blade tip clearances directly. Patents pertaining to it
are US1597357 A, US1696525 A, US2238782 A, US7681325 B2.
The requirement of measuring blade and stator height is left
unaddressed.
[0017] EP2275776 A2 provide a method for measuring the blade
tip clearance using the radio frequency and ultrasonic transducer
in the assembled rotor casing condition but cannot be used during
the machining and assembly process.
[0018] As compared to the prior art, the proposed invention
pertaining to the measurement device is a cost effective, very
accurate in measurement and same time very flexible to design. No
similar device exists for measurement of radial height of blade and
stator.
[0019] It is asserted that there exists no similar patent or
published research paper in area of measuring device or apparatus
which can measure the radial height repeatedly at the same point
at different point of time, such as required during machining of
blade height to meet the blade-tip clearance.

[0020] Hence, to ensure to meet the design blade tip clearance
during in-situ or workshop blade assembly and blade tip
machining, the present invention is disclosed to measure the blade
and stator height as well as blade tip clearance with the required
degree of accuracy. The apparatus adopts a standard blade height
caliper, and has a simple structure, rapid and expedient operation
with high measuring accuracy.
OBJECTIVES OF THE INVENTION
[0021] It is therefore an object of the present invention to develop a
cost effective measuring apparatus to measure the geometrical
parameters of blades and vanes in a reproducible manner for in-
situ measurement as in assembled condition as well as for
standalone position in laboratory applications.
[0022] Another object of the present invention is to design and
develop an apparatus to measure and calculate the blade-tip
clearance accurately.
[0023] Yet another object of the present invention is to design and
develop a measuring apparatus and method for measuring the
radial height of blade and stator (vane) in an efficient, quick,
convenient and accurate way.

SUMMARY OF THE INVENTION
[0024] The proposed invention provides an apparatus for an
efficient and accurate measurement of the radial height of an
individual blades and the stator for in-situ application when blade
or vane is in bladed condition or in the laboratory for a standalone
condition within a short cycle time and method thereof.
[0025] In an aspect, the invention helps to ensure repeatability in
measurement with higher resolution. Since blade-tip clearance is
a critical factor from the point of thermodynamics performance as
well as vibratory stress, so the apparatus helps to ensure the
accuracy in blade-tip clearance during manufacturing of a rotor in
a manufacturing plant, during turbine overhauling as well as
routine periodic inspection of a bladed-rotor in the field.
[0026] In an aspect, the apparatus comprises a top plate and a
pair of vertical plates. The bottom of the vertical plates are
configured to have a convex or a concave profile for proper
engagement of the apparatus upon the rotor hub. A depth
measuring unit comprising a number of depth gauges are allowed
to pass through a number of holes on the top plate.
[0027] In an aspect, the reading at the centre gauge and the side
gauges on either sides of the centre gauge provides the

measurement of the height of the blade or vane and also the blade
tip clearance.
[0028] In an aspect, the present invention can also offer a quick
verification of blade height measured using exiting processes.
Hence, in allusion to challenges of existing blade measurement
technologies, the proposed invention is very simple to implement,
highly flexible to design and easy to scale to suit the different types
of blade and vane used in various rotating machineries such as of
used in axial flow compressor, gas turbine, blower, fan, steam
turbine etc.
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
[0029] The present subject matter would be described in greater
detail with reference to the following figures. It should be noted
that the description merely illustrates the principles of the present
subject matter. It will thus be appreciated that those skilled in the
art will be able to devise various arrangements that, although not
explicitly described herein, embody the principles of the present
subject matter and are included within its scope. The present
invention will now be described more specifically with reference to
the following specification, as illustrated in the accompanying
drawings, in which like reference characters refer to the same parts

throughout the different figures and subsequently incorporated in
the subjoined claims. The drawings are not necessarily to scale,
emphasis instead being placed upon illustrating the principles of
the invention and in which:
[0030] Figure 1a illustrates the schematic perspective view of
measuring apparatus (1) with concave stand (80) for measuring the
radial height of an individual blade which is mounted on a rotor.
[0031] Figure 1b illustrates the schematic perspective view of
measuring apparatus (1) with convex stand (90) for measuring the
radial height of an individual stator which is fixed inside a casing.
[0032] Figure 2 illustrates the rotor-apparatus assembly.
[0033] Figure 3 illustrates the blade tip clearance at a particular
stage of a rotating engine.
[0034] Figure 4 illustrates the blade height measurement using
the apparatus (1).
[0035] Figure 5 illustrates a pictorial representation of
experimental data of blades mistuning in terms of the blade radial
height and its natural frequencies having Mean = 86.068 mm, S.D
= 0.1703 mm.

DETAIL DESCRIPTION OF THE PREFERRED EMBODIMENTS
OF THE PRESENT INVENTION WITH REFERENCE TO THE
ACCOMPANYING DRAWINGS
[0036] While the embodiments of the disclosure are subject to
various modifications and alternative forms, specific embodiment
thereof have been shown by way of example in the figures and will
be described below. It should be understood, however, that it is not
intended to limit the disclosure to the particular forms disclosed,
but on the contrary, the disclosure is to cover all modifications,
equivalents, and alternative falling within the scope of the
disclosure.
[0037] The terms “comprises”, “comprising”, or any other
variations thereof used in the disclosure, are intended to cover a
non-exclusive inclusion, such that a device, system, assembly that
comprises a list of components does not include only those
components but may include other components not expressly
listed or inherent to such system, or assembly, or device. In other
words, one or more elements in a system or device proceeded by
“comprises… a” does not, without more constraints, preclude the
existence of other elements or additional elements in the system or
device.

[0038] It should be observed that the present invention resides
primarily in a novel and non-obvious combination of hardware
elements and method steps. Accordingly, these elements and steps
have been represented by conventional elements and steps in the
drawings, showing only those specific details that are pertinent to
the present invention so as not to obscure the disclosure with
details that will be readily apparent to those skilled in the art
having the benefit of the description herein.
[0039] The proposed invention relates a measuring apparatus
which measures the height of a blade or stator with a fixed
reference.
[0040] In an embodiment of the present disclosure, the apparatus
(1) referring Figure 1(a, b) comprises of three plates differentiated
as primary or guiding top plate (10) and a pair of identical
secondary or supporting plates (20). Both secondary vertical plates
(20) are conjoined with guiding plate (10) through a plurality of
screws (50) making a space (S) between the vertical plates (20).
[0041] In an embodiment, referring Figure 1a, the bottom of the
pair of vertical plates (20) are designed curvilinear concave (80) for
the apparatus (1).

[0042] In another embodiment of the present disclosure, referring
Figure 1b, the bottom of the pair of vertical plates (20) are
designed curvilinear convex (90) for the apparatus (1).
[0043] The guiding top plate (10) of the apparatus (1) comprises of
three holes (30, 40) arranged in a straight line such that centre
hole (30) is located just above the mid-point of the blade (100) tip
and another two side holes (40) on either side of the centre hole
(30) coincide above either side on the rotor curvature.
[0044] In the embodiments of the present invention, the assembly
and arrangement of apparatus (1) along with a depth measuring
unit (2) for measurement of the height (H) of the blade (100) is
illustrated in figure 2. The depth measuring unit (2) comprises
three depth gauges (60, 70) (referring Figure 1) extended
downward towards the rotor or stator body, for measuring the
height (H) of the blade (100) or stator vane (110).
[0045] The surface finish of the mating surfaces of the apparatus
(1) with rotor or casing as well as with depth gauge being an
important variable over the facets in the design of the proposed
invention. Therefore, to improve the flatness of surfaces of the
apparatus (1) the upper surface of the top plate (10) of the
apparatus (1) is blue matched with a glass surface using engineer’s
blue—the pigment Prussian Blue in an oil base. The resulting

imprints having any high spot of surface roughness, allowing the
hand scraper to improve the surface texture so that the top surface
of the apparatus (1) can properly mate with the depth gauges (60,
70) during the measurement process. Similarly the other mating
surfaces such as concave profile (80) or convex profile (90) are blue
matched with rotor or stator curvature respectively. The suitable
concave profile (80) or convex profile (90) also ensures the
matching of the base portion of the apparatus (1) with the diameter
of compressor hub.
[0046] In the present invention, the materials of both the plates
(10, 20) are of mild steel and the thickness of plates are kept
around 15 mm to meet the stiffness requirement.
[0047] During inspection of height (H) of the blade (100) such as
required during machining, grinding, finishing of blade tip at the
time of blade assembly, periodic overhauling and inspection, the
apparatus (1) is mounted over the rotor blade (100) or stator (110)
(referring Fig 2 and Fig 4). Once the apparatus (1) is firmly
assembled, the depth gauges (60, 70) embedded in the depth
measuring unit (2) are inserted through the holes (30, 40) of the
guiding top plates (10). The position of the rotor blade (100) or the
stator vane (110) with casing is illustrated in figure 3.

[0048] In the present invention, the first radial depth (X1) of tip at
the mid-point of blade (100) is measured with the help of depth
gauge (60) and the second radial depth (Y1, Y2) of rotor surface at
the opposite adjacent sides of the blade (100) is measured with the
help of pair of depth gauge (70). In order to verify the accuracy, the
measurement taken on the rotor or casing at the adjacent side of
blade (100) or stator vane (110) are compared. Either side of the
gauges (70) inserted within the holes (40) enables a comparison of
both values (Y1, Y2) and thus ensures the accuracy of
measurement.
[0049] In the embodiments disclosed herein, all the three holes
(30, 40) are designed to ensure accurate radial positioning of depth
gauges (60, 70). For each blade (100) three readings are taken: first
two readings (Y1, Y2) on rotor surface (by gauge 70) and third
reading (X1) on blade tip (by gauge 60). The blade tip reading (X1)
obtained from centre gauge (60) is subtracted from the average of
rotor reading (Y1, Y2) from two side gauges (70), which gives the
blade height (H) reading (referring figure 4). This removes the
human measurement error.
[0050] The radial height (H) of the rotor blade (100) or the stator
vane (110) can be computed using the relation


[0051] wherein, Y1 and Y2: Measurement for depth of rotor hub on
either side of blade (100) or vane (110) from top plate (10).
[0052] and X1: Measurement for depth of the rotor blade (100) or
vane(110) tip from top plate (10).
[0053] The dimensions of the proposed apparatus (1) is generic
and can be easily modified based on the requirement for the use of
different shaped blade (100) or Vane (110). In general basic
dimension of different elements of the apparatus as shown in
figure 1a and figure 1b will be chosen as
[0054] Height of apparatus (1), h = Blade height (H) + (10-15) mm;
[0055] Thickness of side plate (20), T1 = (10-12) mm;
[0056] Thickness of top plate (10), T2= (5-8) mm;
[0057] Width of apparatus (1), B = Blade axial chord + (40-50) mm;
[0058] Length of apparatus (1), L = nD/N mm;
[0059] wherein, ‘D’ is the diameter of rotor shaft or casing in mm,
‘N’ is the number of blades (100) or vanes (110) used per stage and
‘n’ is a constant.

[0060] The length ‘L’ of the secondary plate (20) is an important
design parameter and has to be fixed as per pitch of blade (100) on
rotor shaft or pitch of vane (110) on casing.
[0061] In the present invention, to view the extent of mistuning
during blade manufacturing and machining process, a sequence of
finished blades as received at the workshop are measured in terms
of the deviations in their radial height. The blade radial height is
measured in a laboratory set up. The deviation in blades height (H)
measurement observed with respect to the mean height of the
blades sample is shown in figure 5, where the mean values and
the standard deviation (s.d) are as mean = 86.068 mm, s.d =
0.1703 mm respectively. Knowing the acceptable tolerance is
normally in the range of ±0.02 mm, particularly for the high speed
rotating machinery as well as in aero engine, it is perhaps obvious
these blades cannot be acceptable with present level of finishing
because it will lead to aerodynamically degrading and rubbing
phenomena either due to closing down or open the tip-to-casing
clearance gap as shown in figure 3.
[0062] The advantages are ease in design and manufactured, cost
effective solution, high accuracy in measurement, and more
important that the apparatus or device disclosed herein can also be
used in manufacturing plant, laboratory or even in remote place

such as during overhauling as well as routine maintenance and
also doesn’t require any specialized technician to operate the
proposed invention.
[0063] Furthermore, all examples recited herein are principally
intended expressly to be only for pedagogical purposes to aid the
reader in understanding the principles of the invention and the
concepts contributed by the inventor(s) to furthering the art, and
are to be construed as being without limitation to such specifically
recited examples and conditions. Also, the various embodiments
described herein are not necessarily mutually exclusive, as some
embodiments can be combined with one or more other
embodiments to form new embodiments.
[0064] Although the present subject matter have been described in
language specific to package features, it is to be understood that
the present subject matter is not necessarily limited to the specific
features described. Rather, the specific features and methods are
disclosed as embodiments for the present subject matter.
Numerous modifications and adaptations of the method of the
present invention will be apparent to those skilled in the art, and
thus it is intended by the appended claims to cover all such
modifications and adaptations which fall within the scope of the
present subject matter.

[0065] It will be understood by those within the art that, in
general, terms used herein, and especially in the appended claims
(e.g., bodies of the appended claims) are generally intended as
“open” terms (e.g., the term “including” should be interpreted as
“including but not limited to,” the term “having” should be
interpreted as “having at least,” the term “includes” should be
interpreted as “includes but is not limited to,” etc.). It will be
further understood by those within the art that if a specific number
of an introduced claim recitation is intended, such an intent will be
explicitly recited in the claim, and in the absence of such recitation
no such intent is present. For example, as an aid to
understanding, the following appended claims may contain usage
of the introductory phrases “at least one” and “one or more” to
introduce claim recitations. However, the use of such phrases
should not be construed to imply that the introduction of a claim
recitation by the indefinite articles “a” or “an” limits any particular
claim containing such introduced claim recitation to inventions
containing only one such recitation, even when the same claim
includes the introductory phrases “one or more” or “at least one”
and indefinite articles such as “a” or “an” (e.g., “a” and/or “an”
should typically be interpreted to mean “at least one” or “one or
more”); the same holds true for the use of definite articles used to
introduce claim recitations. In addition, even if a specific number

of an introduced claim recitation is explicitly recited, those skilled
in the art will recognize that such recitation should typically be
interpreted to mean at least the recited number (e.g., the bare
recitation of “two recitations,” without other modifiers, typically
means at least two recitations, or two or more recitations).
[0066] It will be further appreciated that functions or structures of
a plurality of components or steps may be combined into a single
component or step, or the functions or structures of one-step or
component may be split among plural steps or components. The
present invention contemplates all of these combinations. Unless
stated otherwise, dimensions and geometries of the various
structures depicted herein are not intended to be restrictive of the
invention, and other dimensions or geometries are possible. In
addition, while a feature of the present invention may have been
described in the context of only one of the illustrated embodiments,
such feature may be combined with one or more other features of
other embodiments, for any given application. It will also be
appreciated from the above that the fabrication of the unique
structures herein and the operation thereof also constitute
methods in accordance with the present invention. The present
invention also encompasses intermediate and end products
resulting from the practice of the methods herein. The use of

“comprising” or “including” also contemplates embodiments that
“consist essentially of” or “consist of” the recited feature.
ADVANTAGE OF INVENTION
[0067] The advantage of the present invention is that it measures
the geometrical parameters of blades and vanes in a reproducible
manner for in-situ measurement as in assembled condition as well
as for standalone position in laboratory applications.
[0068] Another advantage of the present invention is that it
develops an apparatus to measure and calculate the blade-tip
clearance accurately.
[0069] Yet another advantage of the present invention is that it
develops a cost effective measuring apparatus for measuring the
radial height of rotor blade and stator vane in an efficient, quick,
convenient and accurate way.

We claim
1. An apparatus (1) for measurement of height of a blade and a
stator vane in turbo machinery, said apparatus (1)
comprises:
a pair of vertical plates (20) arranged in a spaced
apart configuration, thereby defining a space (S)
therewithin, wherein the bottom of the vertical plates
(20) configures a curvilinear concave (80) or a
curvilinear convex (90) profile for ensuring the
engagement of the apparatus (1) with the diameter of
compressor hub of the turbo machine;
a top plate (10) fitted atop the pair of vertical
plates (20) with the aid of a plurality of screws (50),
thereby defining a top surface of the apparatus (1);
a depth measuring unit (2) configured to fit atop
the top plate (10), wherein the depth measuring unit
(2) configures three depth gauges, a centre gauge (60)
at centre of said unit (2) and two side gauges (70) on
either side of the centre gauge (60); and
a three number of holes, arrayed in a straight
line on the top plate (10), a centre hole (30) at the
centre of the top plate (10) and two side holes (40) on

either side of the centre hole (30) for receiving the
gauges (60, 70) therewithin extended in the space (S),
wherein the centre hole (30) coincides above the mid-
point of the blade (100) tip and the two side holes (40)
coincides above either side on the rotor curvature,
wherein, the apparatus (1) is configured to measure the
height of the blade (100) on a rotor hub or the vane (110) in a
casing and the blade tip clearance from the measurement of
reading at the center gauge (60) and the side gauges (70).
2. The apparatus as claimed in claim 1, wherein the reading
(X1) at the center gauge (60) engaged vertically downward in
the center hole (30) measures the blade (100) tip clearance
and the reading (Y1, Y2) at the side gauges (70) engaged
vertically downward in the holes (40) measures the
apparatus height (h) from the rotor hub.
3. The apparatus as claimed in claim 1, wherein the blade tip
clearance reading (X1) when subtracted from the average of
rotor reading (Y1, Y2) provides the measurement of height (H)
of the blade (100).
4. The apparatus as claimed in claim 1, wherein the holes (30,
40) ensures proper radial positioning of the depth gauges
(60, 70).

5. The apparatus as claimed in claim 1, wherein the length of
the vertical plates (20) is fixed as per pitch of the blade (100)
on rotor hub or pitch of the vane (110) inside the casing.
6. A method for measurement of height of a blade and a stator
vane in turbo machinery using an apparatus (1), said
method comprising:
mounting the apparatus (1) atop the blade (100) or the
stator vane (110) ensuring proper engagement atop the
diameter of compressor hub of the turbo machine with a
curvilinear concave (80) or a curvilinear convex (90) profile at
the bottom of a pair of vertical plates (20) of the apparatus
(1);
inserting three depth gauges (60, 70) embedded in a
depth measuring unit (2) through a plurality of holes (30, 40)
on a guiding top plates (10) of the apparatus (1);
measuring a first radial depth (X1) of tip at the mid-
point of blade (100) or the vane (110) with the help of the
centre depth gauge (60) and a pair of second radial depths
(Y1, Y2) of rotor surface on either adjacent sides of the blade
(100) or the vane (110) with the help of pair of side depth
gauges (70); and

estimating the height (H) of the blade (100) or the
stator vane (110) from the first (X1) and second (Y1, Y2) radial
depth readings.
7. The method as claimed in claim 6, wherein the measurement
of the first (X1) and the second (Y1, Y2) radial depth readings
provide the estimation of blade tip clearance.
8. The method as claimed in claim 6, wherein blue matching of
the upper surface of the top plate (10) of the apparatus (1)
with a glass surface improves the flatness of surfaces of the
apparatus (1).
9. The method as claimed in claim 6, wherein the radial height
measurement of the individual blade (100) or the stator vane
(110) of a turbo-machinery works either in the bladed
condition on a rotor or in a casing as well as on standing
alone condition.