Centerless runout and profile inspection system and method

The runout or profile of parts is measured without the need for precision supports by rotating the part generally about an axis of rotation. The changes in position of one or more reference surfaces on the part along first and second tracking axes are measured for a plurality of rotational positions of the part. The change in position of the target surface for which the runout or profile is to be determined is measured along a third tracking axis which lies substantially in a common plane with the first and second tracking axes. The change in position of the rotational axis of the part along the third tracking axis is determined from the changes in position of the one or more reference surfaces and the distances between the tracking axes, and is subtracted from the measured change in position of the target surface along the third tracking axis to determine the runout or profile. Independent measurement devices, which can be aligned to the vertical using a level when the tracking axes are horizontal comprise a transmitter generating a plane of laser energy extending along and perpendicular to the tracking axis and a receiver which detects the change in the portion of the plane of laser energy blocked by the surface being tracked.

BACKGROUND OF INVENTION 
1. Field of Invention 
This invention relates to a method and system for measuring the runout and 
profiles of parts without the need for precision supports. 
2. Background Information 
Current methods of inspecting and measuring the runout of shafts and rotors 
or the profiles of cams, cranks, screws and other such similar parts 
require the use of precision supports for rotation of either the 
inspection part or the measurement gauge to establish the parts center or 
a reference surface. Examples of these supports include V-blocks, 
precision centers, granite inspection tables, instrument spindles, lathes, 
rotary tables or other such precision devices. Setup and use of these 
devices requires the labor of one or more highly trained and skilled 
technicians. The inspection operation can be very time consuming, labor 
intensive, expensive and tedious to perform. In some cases large objects, 
such as generator rotors and turbine assemblies, can make current methods 
of inspection impractical. 
There is a need therefore for an improved method and system for measuring 
runout or the profile of parts which eliminates the requirement for 
precision support of the measuring instrument or the part to be inspected. 
There is a related need for such a method and system which does not require 
a highly trained and skilled technician. 
There is a further need for such a method and system which reduces setup 
and inspection time. 
SUMMARY OF THE INVENTION 
These and other needs are satisfied by the invention which is directed to 
apparatus and a method of detecting and measuring the runout or profile of 
surfaces on a part which does not require precision supports. The part is 
rotated generally about a selected axis of rotation. It is not necessary 
that the part be rotated precisely about this axis. As the part is 
rotated, one or more reference surfaces are tracked along first and second 
tracking axes. The profiles of these reference surfaces are presumed to be 
precise. The surface which is to be checked for runout or profile is 
tracked along a third tracking axis as the part is rotated. All three 
tracking axes lie substantially in a common plane and are all generally 
transverse to the axis of rotation of the part. Changes in position of the 
one or more reference surfaces and the target surface are measured along 
the respective tracking axes for a plurality of angular positions of the 
part. The distances between the tracking axes are also measured. The 
runout or profile of the target surface is then determined as a function 
of the change in position of the one or more reference surfaces along the 
first and second tracking axes, the change in position of the target 
surface along the third tracking axis and the distances between the 
tracking axes. 
In determining the runout or profile for each rotational position of the 
part, the change in position of the axis of rotation along the third 
tracking axis is determined as a function of the changes in position of 
the one or more reference surfaces along the first and second tracking 
axes, and then the runout or profile is determined from the difference 
between the measured change in position of the target surface along the 
third tracking axis and this calculated change in position of the axis of 
rotation along the third tracking axis. 
In accordance with another aspect of the invention, the changes in position 
of the surfaces tracked along the respective tracking axes are measured by 
transmitting radiant energy toward the tracked surface and detecting 
interception of the radiant energy thereby. More particularly, a plane of 
radiant energy is transmitted along the tracking axis in a plane 
perpendicular to the common plane in which all of the tracking axes lie 
over the range of movement of the tracked surface. A portion of this plane 
of radiant energy is blocked by the part at the tracked surface. By 
detecting the change in the portion of the plane of radiant energy blocked 
by the tracked surface as the part is rotated, the change of position of 
the tracked surface is measured. Alternatively, other systems can be used 
for measuring the changes in position of the tracked surfaces, such as for 
instance, linear variable differential transformers (LVDTs) having a blade 
attached to the core of the LVDT and biased against the surface to be 
tracked. 
The invention has particular application to determining the runout of the 
many surfaces on an electrical generator rotor. By selecting horizontal 
tracking axes for the reference surfaces and target surfaces on the rotor, 
the measuring devices are mounted on separate stands which may be 
individually aligned with the plane of radiant energy, preferably laser 
energy, oriented in the vertical using known commonly available leveling 
equipment. The measuring device for the third tracking axis may be moved 
along the rotor to measure the runout at any desired point along the 
rotor. The rotor is supported, for both assembly and measuring the runout 
on power rollers, since it is not required that the rotor be rotated 
precisely about its longitudinal axis for measuring runout. The invention 
is also useful for checking the profile of noncylindrical parts such as 
cam shafts and other irregular shapes. In addition, the invention can be 
used to determine concentricity.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1, the invention will be described as applied to 
determining the runout or profile of a roller 1 having a first cylindrical 
end section 3, a second cylindrical end section 5 and a cylindrical center 
section 7. The end sections 3 and 5 define cylindrical reference surfaces 
9 and 11, respectively, while the center section defines a target surface 
13 which is to be inspected for runout or profile. As will become evident 
as the discussion progresses, the particular configuration of the roller 1 
is not critical. What is needed is at least one reference surface and one 
target surface to be inspected. In the roller 1 these surfaces are 
cylindrical although they need not be. However, the configuration of the 
reference surfaces must be known and are considered to be precise. For 
instance, the surfaces 9 and 11 of the roller 1 are considered to be 
precisely cylindrical. 
In accordance with the invention, the roller 1 is rotated generally about 
its longitudinally axis 15. It is an advantage of the invention that the 
roller 1 need not be rotated precisely about the axis 15. While the roller 
1 is rotated, the reference surfaces 9 and 11 are tracked along spaced 
apart first and second tracking axes 17 and 19, respectively, and the 
target surface 13 is tracked along third tracking axis 21. All three 
tracking axes 17, 19 and 21 lie in a common plane 23 and are preferably 
generally perpendicular to the longitudinal axis 15 of the roller 1. 
Accuracy of measurements made along the tracking axes are not greatly 
affected if the tracking axes are not precisely parallel to each other in 
the common plane 23. Greater inaccuracies can be introduced if any of the 
surfaces do not lie in the common plane 23. 
As the roller 1 is rotated, measurements are made along the tracking axes 
17, 19 and 21 of the movement of the reference surfaces and the target 
surface. If the roller is not rotated precisely about its longitudinal 
axis 15, it will wobble as exaggerated in FIGS. 2 and 4. In these figures, 
the position of the roller 1 at the first angular position is shown in 
full line and at a second angular position in phantom. Corresponding parts 
are shown in the second position with primed reference characters. In the 
case shown in FIG. 2, the roller 1 wobbles as it is rotated so that its 
longitudinal axis 15 precesses about a point A which is intermediate the 
ends of the roller. On the other hand, FIG. 4 illustrates the case where 
the projected axis 15 of the roller precesses about a point B which is 
beyond one end of the roller. In both cases it can be seen, however, that 
since the roller 1 does not rotate precisely about this longitudinal axis, 
the reference surface 9 moves by the amount .DELTA..sub.1, as measured 
along the first tracking axis 17, the second reference surface 11 moves by 
an amount .DELTA..sub.2 along the second tracking axis 19 and the target 
surface 13 movement is .DELTA..sub.3 measured along the third tracking 
axis 21. As can be seen graphically in FIG. 3, by measuring the distance, 
X, between the first and second tracking axes 17 and 19, the tangent of 
the angle .alpha. of the longitudinal axis 15 between the two angular 
positions of the roller 1 for the case shown in FIG. 2 is determined by 
the formula: 
##EQU1## 
(in the example of FIG. 2, .DELTA..sub.1 is considered negative since it 
extends downward from the original position of the axis 15). The tangent 
of .alpha. is also determined by the following formula: 
##EQU2## 
where Y is the distance between the tracking axes 17 and 21 and J is the 
side opposite the angle .alpha.'. 
Substituting and rearranging: 
##EQU3## 
The change in position, dev, of the axis 15 along the tracking axis 21 is 
then: 
EQU dev=.DELTA..sub.1 +J Eq. (4) 
(again .DELTA..sub.1 is considered negative in the example of FIG. 2 as is 
dev while J is positive). Substituting equation 3 in equation 4: 
##EQU4## 
The runout or profile, .epsilon., is then the difference between the 
change in position of the tracking axis along the third tracking axis 21 
and the measured change in position of the target surface 13 along the 
axes 21, or: 
EQU .epsilon.=.DELTA..sub.3 -dev Eq. (6) 
Similarly as shown graphically in FIG. 5, equations 5 and 6 can be used to 
determine the change in position of the axis of rotation and the runout or 
profile where the axis of rotation rotates about a point outside of the 
part. In the above ,equations, the tracking axis 17 is considered to be 
the origin so that, if the tracking axis 21 tracking the target surface is 
to the left of the axis 17 as viewed in FIGS. 2 and 4, the sign of the 
distance, Y, between the axes 17 and 21 is negative. 
Similar measurements and calculations are made for a plurality of angular 
positions of the roller 1 through 360 degrees of rotation. The maximum 
difference between the change in position of the axis of rotation and 
measured movement of the target surface along the third tracking axis is 
the run out of the target surface. If desired, these deviations can be 
plotted to generate a visual representation of the runout. 
It should be noted that the technique for measuring the runout does not 
require the measurement of the diameter of any of the cylindrical sections 
of the rotor. In addition, the various sections may be of different 
diameters. It is also not necessary to have two distinct reference 
surfaces if the first and second tracking axes can be spaced far enough 
apart on a single reference surface as shown in FIG. 1 where the axial 
length of the reference surface 9 is sufficient that the second tracking 
axis 19' can also be used to track the reference surface 9. The greater 
the distance between the first and second tracking axes, the greater is 
the accuracy of the calculations made by equations 1 and 2. 
The technique of the invention can also be applied for checking the profile 
of noncylindrical surfaces such as the camming surface 25 on the cam 27 
shown in FIG. 6. Here, the changes in position of reference surfaces 29 
and 31 on opposite ends of shaft 33 on which cam 27 is mounted for 
rotation are measured along first and second tracking axes 35 and 37, 
respectively, while movement of the camming surface 25 is measured along 
the third tracking axis 39. The calculation using equation (5) establishes 
movement of the axis of rotation at the third tracking axis 39. The 
differences between the movement of the axis of rotation at each angular 
position of the rotor 1 and the measured movement of he camming surface 25 
along the third tracking axis 39 calculated using equation (6) represent 
the actual profile of the cam surface. This actual profile can be compared 
with the design profile to determine any errors in the profile. 
An example of an application of the invention is the use of the technique 
for determining the runout of the various surfaces of the rotor of a large 
electric power generator. Such a rotor 41 as shown in FIGS. 7A and 7B can 
typically be 35 to 40 feet long. The rotor is machined from a forging and 
has a number of elements such as blower hubs contact rings, etc., shrink 
fit onto the machined forging. The runout of the machined surfaces and 
accessories added to the rotor are checked during initial manufacture and 
assembly, and also during overhaul. The practice has been to mount an 
accessory on the rotor in an assembly area, and then transport the entire 
rotor to a precision lathe for checking and correcting runout. The rotor 
is then returned to the assembly area for mounting of the next accessory. 
This procedure is very time consuming and therefore costly. 
In accordance with the invention, the rotor 41 is supported for both 
assembly and checking of runout on a pair of spaced-apart power rollers 
43. Each of the power rollers 43 comprise pairs of rollers 45 laterally 
spaced apart on a frame 47. The rollers 45 are driven by an electric motor 
49 through a chain 51, gear boxes 53 and shaft 55. Power for the roller 
motor is provided through power supply 57. 
The rotor 41 is supported by the spaced-apart pairs of rollers 45 and the 
roller supports 43. As the large center section of the rotor 58 is slotted 
longitudinally for receiving the rotor windings, bellybands 59 are used to 
provide a smooth rotational surface for rotating the rotor. 
Bearing surfaces 61 and 63 adjacent the ends of the rotor 41 are used as 
the reference surfaces for measuring runout in accordance with the 
invention. Changes in position of the reference surfaces 61 and 63 due to 
the fact that the rotor is not precisely rotated about longitudinal axis 
65 by the power rollers 43 are measured by laser gauges 67a and 67b. The 
change in position of a selected target surface on the rotor 41 as the 
rotor rotates is measured by a mobile laser gauge 67c. As shown in phantom 
in FIG. 7A, this laser gauge 67c can be moved to successively measure the 
runout of each of the various surfaces of the rotor 41. A rotary encoder 
68 tracks the angular position of the rotor 41. 
As illustrated in FIG. 8 and in more detail in FIG. 9, the laser gauges 67 
comprise a laser source 69 which projects a plane of radiant energy 71 
perpendicular to the tracking axis 73 for the surface such as 61 being 
tracked. This plane of radiant energy 71 is also perpendicular to the 
common plane containing the tracking axes of the other laser gauges which 
in turn is perpendicular to the plane of FIG. 9. The laser gauge 67 is 
positioned so that the surface 61 of the rotor 41 intersects and partially 
blocks the plane radiant energy generated by the source 69 for all 
rotational positions of the rotor 41. Radiant energy from the source 69 is 
detected by the detector 75. The detector 75 measures the position of the 
surface 61 along the tracking axes 73 by determining the portion edge 77 
of the plane of radiant energy that is not blocked by the surface 61 
measured from the edge 77. Thus, for the position of the surface 61 shown 
in full line in FIG. 9 radiant energy of a width R is sensed by the 
detector 75. As the rotor 41 rotates and the surface 61 moves to the 
position shown in phantom in FIG. 9, the detector measures radiant energy 
of a width S. The difference between the measured widths R and S is the 
amount that the surface 61 has moved along the tracking axes 73 as the 
rotor 41 is rotated between the two positions shown in FIG. 9. Suitable 
laser gauges 67 are available from the Laser-Mike Company. 
In accordance with the invention, there is no need to precisely mount the 
rotor for rotation or to precisely position the laser gauges 67 relative 
to one another. The only alignment required is that the tracking axes 73 
for all of the laser gauges 67 lie in a common plane and are substantially 
parallel to one another. For measuring the runout of the horizontally 
supported generator rotor, this alignment can be easily made by mounting 
the laser gauges 67 on stands 81 which are leveled with respect to the 
earth. This alignment can easily be accomplished with conventional 
leveling devices. 
While it is possible for an operator to read out the measurements R and S 
from the laser gauge 67 to calculate the .DELTA. for each change in 
position of the rotor 41, it is preferable to have these calculations 
performed by a computer 79 which can correlate the measurements with the 
angular position of the rotor which is tracked by the rotary encoder 68. 
A flow chart for a suitable computer program for the computer 79 is shown 
in FIG. 10. Initially, the operator inputs to the computer the distances 
between the lasers and the number of angular positions of the shaft to be 
measured as indicated at 85 and 87 respectively. As the rotor is rotated 
by the power rollers 43, measurements taken by the laser gauges 67 at each 
of the angular positions determined by the optical encoder 68 are read 
into the computer as indicated at 89. For each set of laser measurements 
taken at each angular position, the set of laser data for the first 
angular position is subtracted from the set of data for each subsequent 
angular position to generate the .DELTA.(s) as indicated in 91. The 
movement of the rotational axis at the laser C is then calculated at 93 
from the laser data for the A and B lasers. This movement of the 
rotational axis is then subtracted from the .DELTA. calculated for laser C 
to determine the runout/profile on the target surface as indicated at 95. 
These calculations are repeated for each angular position of the rotor, as 
indicated at 97. The runout results are then displayed at 99. 
Other types of gauges for measuring reference and target surface movement 
could be utilized. For instance, linear variable differential transformers 
(LVDTs) could be utilized with blades attached to their movable cores 
biased against the surfaces to be tracked. 
As has been demonstrated, the invention provides accurate measurement of 
runout and the profile of part surfaces without the need for precision 
mounts for the part or the measurement gauges to establish parts centers 
or a reference surface. The invention is suitable for inspecting and 
measuring the runout of shafts and rotors or the profiles of cams, cranks, 
screws and other similar parts. 
While specific embodiments of the invention have been described in detail, 
it will be appreciated by those skilled in the art that various 
modifications and alternatives to those details could be developed in 
light of the overall teachings of the disclosure. Accordingly, the 
particular arrangements disclosed are meant to be illustrative only and 
not limiting as to the scope of the invention which is to be given the 
full breadth of the appended claims and any and all equivalents thereof.