Mechanical averaging gauge

A mechanical averaging gauge for averaging displacements at a plurality of locations along the surface of an object. The gauge includes a measuring unit which is urged into contact with the surface of the object. Several probes extend from the measuring unit and rest on the surface of the object. The probes are interconnected by means of cylindrical sliding members in contact with the rear of each of the probes. Trapezoidal sliding members are disposed between the cylindrical members so that the displacement of the measuring unit from a reference surface is the average of the various displacements of the individual probes. The arrangement also results in each probe contacting the surface of the object with substantially equal force. Therefore, the arrangement has application as a clamping device.

BACKGROUND OF THE INVENTION 
The present invention relates to a mechanical linkage which may be employed 
in a gauge to average displacements at a plurality of locations along the 
irregular surface of an object. The linkage arrangement also results in 
substantially equal force being applied to the object so that an equal 
force clamp may be constructed. 
Gauges are known having probes for contacting irregular surfaces of an 
object with an output indicating the average of the individual probe 
displacements. Such gauges are often used for classifying vane airfoils so 
that turbine wheels can be built up having appropriate vane throat areas. 
One known gauge operates on a hydraulic principle to average probe 
displacements. Generally, flexible diaphragms with an unsupported section 
provide an interface between the probe and a fluid reservoir. The 
hydraulic gauges, while quite accurate, are temperature sensitive 
potentially resulting in errors with ambient temperature changes. Other 
classification gauges are known using "whiffles" or probes whose 
orientations are utilized for object classification. 
It is therefore an object of the present invention to provide a gauge which 
eliminates the drawbacks of the known hydraulic gauges. 
A further object of the invention is such a gauge which is highly accurate 
and substantially wear resistant resulting in a high degree of measurement 
repeatability. 
A still further object of the invention is a mechanical linkage arrangement 
which provides equal force at each probe contact point for use in 
clamping. 
SUMMARY OF THE INVENTION 
The gauge apparatus of the present inveation for averaging displacements at 
a plurality of locations along the surface of an object from a reference 
surface includes a base member which supports the reference surface. A 
measuring unit is mounted on the base member for linear motion 
perpendicular to the reference surface and apparatus is provided for 
biasing the measuring unit toward the reference surface. Apparatus 
responsive to the displacement of the measuring unit from the reference 
surface is provided. The measuring unit of the present invention includes 
a plurality of probes extending from the measuring unit toward the 
reference surface and perpendicular to this surface. Contained within the 
measuring unit are a plurality of first and second sliding members, each 
of the first sliding members being in contact with a rear portion of one 
of the probes and the second sliding members being in contact with two 
adjacent ones of the first sliding members. By means of this linkage 
arrangement, the average of the displacements of the individual probes is 
equal to the amount of movement of the measuring unit and is indicated by 
a mechanical indicator or by electrical components. 
The mechanical linkage within the measuring unit also results in each probe 
contacting the reference surface with essentially the same force. Thus, 
the mechanical linkage arrangement may be used as in a clamp which applies 
substantially equal force to an object at multiple locations along an 
irregular surface of the object.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
With reference first to FIGS. 1, 2 and 3, a gauge 10 has a reference 
surface 12 mounted on a base member 14. A measuring unit 16 is supported 
on the base member 14 for linear motion in a direction perpendicular to 
the surface 12. The measuring unit 16 is attached to an arm 18 which 
passes through a slot 20 and is connected to a shaft 22 which actuates an 
indicator 24. The indicator 24 thus responds to the position of the 
measuring unit 16 with respect to a reference such as the surface 12. 
Electronic measuring apparatus such as an LVDT may be used in place of the 
mechanical indicator 24 to provide a signal responsive to the position of 
the measuring unit 16 with respect to the reference surface 12. As can be 
seen in FIGS. 2 and 3, a second arm 26 attached to the measuring unit 16 
passes through another slot 28 in the base member 14 and is attached to 
one end of spring material 30, the other end of which is wound around a 
spindle 32 creating a constant force spring mechanism which biases the 
measuring unit 16 toward the right in FIGS. 1, 2 and 3. Also connected to 
the arm 26 is a shaft 34 of a damper or dashpot 36. The damper 36 is 
rigidly affixed to the base member 14. 
The measuring unit 16 will now be described in detail with reference to 
FIGS. 1 and 4. As shown in FIG. 1, the measuring unit 16 includes five 
probes 40, 42, 44, 46 and 48. It is emphasized that the use of five probes 
is entirely exemplary and more or fewer probes may be employed within the 
scope of the present invention. Still referring to FIG. 1, the probes 
40-48 are shown in contact with a vane airfoil 50 whose characteristics 
are to be classified. It should be noted that the gauge 10 is particularly 
well suited for classifying vane airfoils such as the vane airfoil 50, but 
the gauge 10 has general application to performing measurements on other 
objects as well. 
As shown in FIG. 4, the probes 40-48 slide in channels in the measuring 
unit 16 with a rear portion of each of the probes coming into contact with 
right circular cylindrical members 52, 54, 56, 58 and 60. The cylindrical 
members 52-60 are slidable within a recess 62 (also see FIG. 2) in the 
unit 16. Trapezoidal members 64, 66, 68, and 70 are also slidable within 
the recess 62 and are arranged so that each one of the trapezoidal members 
64 resides between an adjacent pair of the cylindrical members. That is, 
for example, the trapezoidal member 64 resides between the cylindrical 
members 52 and 54. The recess 62 includes angled sides 72 and 74. It is 
preferred that the probes, cylindrical and trapezoidal members all be made 
of a wear-resistant material such as hardened steel. 
In order to understand fully the present invention, one must keep in mind 
that the cylindrical and trapezoidal members are freely slidable within 
the recess 62. Each trapezoidal member 64-70 includes a recessed portion 
71 to enhance sliding. If, for example, the probe 40 were pushed toward 
the left in FIG. 4, the cylindrical member 52 will be forced downwardly in 
FIG. 4 because of the sloping wall 72. The downward motion of the cylinder 
52 biases the trapezoidal member 64 downwardly which, because of the 
sloping face 76 of the trapezoidal member 64, urges the cylindrical member 
54 and the probe 42 to the right in FIG. 4. Similarly, the remaining 
probes 42-48 are also urged to the right in FIG. 4. The net effect of this 
unique linkage is that displacements of the individual probes 40-48 are 
averaged. In effect, the measuring unit 16 is a mechanical analog of the 
hydraulic gauges discussed above. 
FIG. 5 shows a top plate 80 which covers the top of the measuring unit 16. 
The top plate 80 includes raised portions 82, 84, 86 and 88 which maintain 
the cylindrical members disposed between adjacent pairs of trapezoidal 
members. 
The operation of the present invention will now be discussed in conjunction 
with all of the figures. To perform measurements on a vane airfoil 50, for 
example the measuring unit 16 is moved toward the left in FIG. 1 and the 
vane airfoil 50 is inserted. When the measuring unit 16 is released, the 
constant force spring mechanism 32 pulls the measuring unit 16 toward the 
right bringing the probes 40-48 into contact with the surface of the vane 
airfoil 50. The dashpot 36 damps the motion of the measuring unit 16. 
Because of the linkage arrangement described above in conjunction with 
FIG. 4, each of the probes 40-48 will contact the surface of the vane 
airfoil 50 regardless of surface irregularities. When the measuring unit 
16 comes to rest with the probes contacting the surface to be 
characterized, the position of the measuring unit is indicated by the 
indicator 24. Importantly, this indicated value is the average of the 
displacements of the individual probes 40-48 from a reference such as the 
reference surface 12. 
Another important feature of the present invention is the recognition that 
the linkage arrangement described above not only averages the individual 
probes' displacement, but also, the force with which each of the probes 
contacts the surface is substantially equal. That is, once the measuring 
unit 16 comes to rest against the object to be measured due to the force 
of the constant force spring spindle mechanism, each of the probes pushes 
on the surface with substantially the same force; in this case, each probe 
pushes with one fifth of the force provided by the spindle mechanism 32. 
Thus, the apparatus 10 in FIG. 1 may also be considered a clamping device 
in that the object 50 is clamped between the probes and the reference 
surface 12 with each probe providing an equal force. Of course, for 
clamping, the spring mechanism might be replaced with other force applying 
devices such as a vise-like device. Such a clamp has numerous uses where 
it is important to apply forces uniformly over an irregular surface area. 
The unique linkage arrangement of the present invention results in a gauge 
which is highly temperature insensitive and capable of highly repeatable 
measurements. Because the linkage elements are made of a wear-resistant 
material such as hardened steel, there is negligible wear, assuring 
repeatability. The present invention thus overcomes the drawbacks of known 
gauges by eliminating temperature sensitive hydraulic substances and 
deformable, stretchable diaphragms. The unique linkage also results in 
equal force application for use as a clamp. 
It is recognized that modifications and variations will occur to those 
skilled in the art and it is intended that all such modifications and 
variations be included within the appended claims. For example, it is 
recognized that sliding members having shapes other than right circular 
cylindrical and trapezoidal may be used.