Information
-
Patent Grant
-
6279400
-
Patent Number
6,279,400
-
Date Filed
Tuesday, March 16, 199925 years ago
-
Date Issued
Tuesday, August 28, 200123 years ago
-
Inventors
-
Original Assignees
-
Examiners
Agents
- Patnode; Patrick K.
- Stoner; Douglas E.
-
CPC
-
US Classifications
Field of Search
US
- 073 8658
- 073 116
- 073 655
- 073 656
- 356 401
- 356 403
- 356 407
- 250 55919
- 250 55938
- 348 140
- 227 321
- 227 358
- 227 359
- 227 413
- 227 416
-
International Classifications
-
Abstract
A technique for measuring and selectively adjusting a clearance between a stationary object and desirably a rotating object includes a non-contact, sensing system having a sensor attachable to the stationary object, a mask having a predetermined sized viewport or aperture that sets or limits the sensing or operation of the sensor, and a controller. The sensor is operable for sensing within a field of view a portion of the rotating object and generating a signal in response thereto. The field of view varies in response to varying the clearance between the sensor and the second object. Desirably, the portion of the second object includes a varying pattern. The controller is operable to determine the clearance between the first object and the second object in response to the signal. In another embodiment, sensing system is operable to adjust the clearance by controller providing an electrical current to a resistive heating element in the thermally expandable portion of a plurality of segmented labyrinth seals. The sensing system is also operable to measure vibration of the rotating object.
Description
BACKGROUND INFORMATION
This invention relates to measurements of clearances, and more specifically, to an apparatus and method for measuring or selectively adjusting a clearance between two objects such as a stationary object and a rotating object.
Rotating systems typically have clearances or gaps to avoid contact or rubs during operation due to manufacturing tolerances and thermal expansion or mechanical strain effects. Undesirably, clearances generally result in loss of efficiency of the system. For example, in a pressurized system, clearances cause loss in efficiency due to blowby or degradation of pressure ratios. Typically, manufacturing and design costs increase as attempts are made to reduce the size of clearances in a system.
In a jet turbine engine, for example, a clearance exists between the thin-walled casing and the tips of the rotor blades. The thin walled casing is designed so that during operation it can be heated or cooled to vary the size of the clearance between the casing and the tip of the blade particularly during start-up and shutdown. Rotating systems having a thick casing, however, can not be readily resized by heating or cooling the thick casing to adjust the clearance between the casing and a rotor blade tip.
Therefore, there is a need for a low cost, on-line apparatus and method for measuring a clearance between objects and selectively adjusting and optimizing the clearance during operation.
SUMMARY OF THE INVENTION
The above-mentioned need is met by the present invention which in one aspect relates to a technique for measuring a clearance between a surface of a first object and a surface of a second object. The system includes a sensor for sensing within a field of view a portion of the second object and generating a signal in response thereto. The field of view varies in response to varying the clearance between the sensor and the second object. A controller determines a clearance between the surface of the first object and the surface of the second object in response to the signal.
The controller is operable to determine the clearance in response to a magnitude of the signal or in response to the signal comprising a plurality of signals. Advantageously, the second object is a rotating object and the portion of the second object has a varying pattern.
In another aspect of the present invention, a system for adjusting the clearance between a first object and a second object includes a movable seal disposed between the first object and the second object. A sensor is attachable to at least one of the first object and the seal for sensing within a field of view a portion of the second object and generating a signal in response thereto. A controller is operable to adjust a position of the seal relative to the second object to selectively adjust the clearance therebetween in response to the signal. Desirably, the seal is a segmented labyrinth seal having a thermally expandable portion. Advantageously, the second object is a rotating object and the portion of the second object has a varying pattern.
In another aspect of the present invention, a system is provided for measuring vibrations of an object. Desirably, a portion of the object includes a two-dimensional pattern of spaced-apart reflective elements.
In still another aspect of the present invention, a method for measuring a clearance between a surface of a first object and a surface of second object comprises the steps of sensing within a field of view a portion of the second object and generating a signal in response thereto, the field of view varying in response to varying the clearance between the first object and the second object, and determining the clearance between the first object and the second object in response to the signal.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1
is a cross-sectional view of a compressor, which is symmetric about a center line, and to which is attached a non-contact, clearance measurement system according to the present invention;
FIGS. 2 and 3
are enlarged views of the non-contact, clearance measurement system shown in
FIG. 1
;
FIGS. 4A and 4B
are partial, perspective views of the central rotor blade shown in
FIG. 1
;
FIGS. 5A and 5B
are graphs of the signals generated by the clearance measurement sensor shown in
FIG. 1
corresponding to the field of views illustrated in
FIGS. 2 and 4A
, and
FIGS. 3 and 4B
, respectively;
FIGS. 6A and 6B
are partial, perspective views of the central rotor blade shown in
FIG. 1
;
FIGS. 7A and 7B
are graphs of the signals generated by the sensor shown in
FIG. 1
corresponding to the field of views illustrated in
FIGS. 2 and 6A
, and
FIGS. 3 and 7B
, respectively;
FIG. 8
is a cross-sectional view of a non-contact, clearance adjusting system according to the present invention operable for adjusting the magnitude of a clearance;
FIG. 9
is a sectional view taken along line
9
—
9
in
FIG. 8
; and
FIG. 10
is a top view of an alternative embodiment of a target, having a varying pattern for use in the detection of vibrations of the rotor blade, shown in
FIG. 1
, according to the present invention.
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1
illustrates a cross-sectional view of a compressor
10
such as in a gas turbine. Compressor
10
includes a shroud or casing
12
defining therein a chamber
14
and having a plurality of inwardly extending stationary blades
16
. Compressor
10
also includes a rotor
20
having a plurality of outwardly extending rotating blades
22
.
A rotor blade tip surface or portion
24
of blades
22
and an inner surface
18
of casing
12
define a gap or tip clearance
30
to avoid rubs during operation. In this exemplary compressor, air leakage or blowby through clearance
30
from a high pressure side of compressor
10
to a low pressure side of compressor
10
reduces the efficiency of compressor
10
.
With reference to
FIGS. 1-3
, a non-contact, clearance measuring system
40
is operable to determine a magnitude of clearance
30
, i.e., the size, width, or distance between rotor blade tip surface
24
and inner surface
18
of casing
12
. In this exemplary embodiment, as best shown in
FIGS. 2 and 3
, system
40
includes a sensor
50
, a mask
60
having a predetermined sized viewport or aperture
62
that sets or limits the sensing or operation of sensor
50
, and a computing environment of controller
70
connected to sensor
50
. Sensor
50
is desirably attachable to stationary casing
12
by being inserted through a bore
64
extending through casing
12
.
Depending on the distance between inner surface
16
of casing
12
and rotor blade tip surface
24
, the magnitude of clearance and the area of the field of view observable by sensor
50
varies. For example,
FIG. 2
illustrates clearance
30
having a magnitude D
1
and a field of view FV
1
, i.e., the portion or area of rotor blade tip surface
24
sensed by sensor
50
. As the magnitude of clearance
30
increases the area of the field of view increases.
FIG. 3
illustrates a clearance
30
having a magnitude D
2
and a field of view FV
2
. The relationship of the magnitude of the signal generated by sensor
50
is generally fixed (e.g., generally linearly or proportionally related) via angle A being fixed. Such an arrangement readily allows precalculation of clearances to field of views or determination of a clearance based on the field of view observed.
From the present description, it will be appreciated by those skilled in the art that for a circularly-shaped viewport, the field of view will be circularly-shaped. It is also appreciated that the viewpoint may have other configurations, e.g., square, rectangular, or other configurations depending upon the shape of the field of view desired.
Desirably, sensor
50
is a light sensor, for example, a photodiode, for observing and sensing reflected light from rotor blade tip surface
24
, and generating a signal in response thereto to controller
70
. Controller
70
includes, for instance, at least one central processing unit
72
, a memory or main storage
74
, and one or more input/output devices
76
. Memory or main storage
74
of controller
70
is operable to store a predetermined database of signal measurements to clearance measurements. Controller
70
includes suitable computer programming for comparing the signal generated by sensor
50
to the predetermined database to determine a magnitude of clearance
30
. Alternatively, memory or main storage
74
may include programming code for computing the clearance directly from the magnitude of the signal.
Desirably, rotor blade tip surface
24
includes a reflective pattern or target
80
having a varying pattern. As best shown in
FIGS. 4A and 4B
, in one embodiment, target
80
comprises a liner pattern of reflective elements
82
which are mounted on rotor blade tip surface
24
and aligned with an axis of rotor shaft
21
(
FIG. 1
) of rotor
20
(FIG.
1
). In this exemplary embodiment, target
80
includes five micron sized glass reflecting beads on a bed of 400C Polyamide which is then attached to rotor blade tip surface
24
. The Polyamide both absorbs light and holds the beads in correct orientation during a vacuum sealing process. The target may alternatively include chemical, mechanical, or laser etching, adding or removing of material to the rotor blade tip surface (e.g., by photolithography) to provide an optical pattern of varying density. In addition, the target may be a sealed high temperature glass vacuum impregnated optical disc. Desirably, target
80
is affixed to the rotor blade tip
24
by being mounted into a recess
26
(
FIGS. 2 and 3
) so that the target is shielded from the flow of blowby gas and protected should a contact or a rub occur between rotor blade tip surface
24
and inner surface
16
(FIGS.
2
and
3
).
With reference to
FIGS. 4A and 5A
, as target
80
passes through field of view FV
1
, one of reflective elements
82
is observed or detected so that sensor
50
(
FIG. 2
) generates a signal having a magnitude of V
1
which corresponds to clearance D
1
(see also FIG.
2
). With reference to
FIGS. 4B and 5B
, as target
80
passes through field of view FV
2
, three of reflective elements
82
are observed or detected so that sensor
50
(
FIG. 3
) generates a signal having a magnitude of V
2
which corresponds to clearance D
2
(see also FIG.
3
).
From the present description, it will be appreciated by those skilled in the art that target
80
may comprise a single elongated strip wherein the magnitude of the signal varies in response to the size of the field of view. Desirably, the use of reflective elements
82
allows a signal to have a discrete level or magnitude which can be readily and accurately correlated to a clearance measurement by controller
70
. While the exemplary target includes five reflective elements, it will be appreciated that the target may have more or less that five reflective elements.
In another aspect of the present invention, clearance measuring system
40
may further comprise a light emitter
52
, as shown in
FIGS. 2 and 3
, connected to controller
70
for selectively emitting light as target
80
passes through a field of view. For example, in a gas turbine electrical generating plant connected to a 60 H
z
grid the speed will be maintained at a generally constant 3,600 rpms so that the rotation of the shaft of the compressor can be synchronized to the passing of target
80
through a field of view. Desirably, an encoder (not shown) on the rotor shaft is operable to determine the position of the rotor shaft, and a synchronizer or a phase-locked loop circuit operably incorporated into controller
70
allows light to be pulsed or strobed as target
80
passes through the field of view. From the present description, it will be appreciated by those skilled in the art that the clearance measuring system may include a bifurcated fiber optic assembly for emitting radiation and receiving the reflection thereof. It will also be appreciated that the emitter and sensor may be operable to emit and detect visible light or nonvisible radiation including coherent electromagnetic radiation from a laser.
FIGS. 6A and 6B
illustrate a target
90
which is mounted on rotor blade tip surface
24
and aligned parallel to a circumference of the shaft. Emitter
52
(
FIGS. 2 and 3
) may be strobed five times with each time corresponding to one of the five reflective elements
92
being aligned under sensor
50
(
FIGS. 1-3
) so that a varying signal can be generated by sensor
50
in response to the reflected light from target
90
. For example, with a field of view FV
1
(FIG.
6
A), sensor
50
generates a varying signal having five equal spikes, as shown in
FIG. 7A
, with each spike having a magnitude corresponding to the reflection from one of reflective elements
92
. With a field of FV
2
(FIG.
6
B), sensor
50
generates a varying signal having five spikes with the first and last having a magnitude corresponding to two of reflective elements
92
and the middle three spikes having a magnitude corresponding to three of reflective elements
92
. In this aspect of the invention, memory or main storage
74
of controller
70
is operable to store a predetermined database of varying signal measurements Or patterns to clearance measurements and controller
70
includes suitable computer programming for comparing the signal generated by sensor
50
to the predetermined database to determine a magnitude of clearance
30
. Alternatively, the various spikes may trigger a counter which can be correlated to a clearance measurement or memory, or main storage
74
may include suitable programming code for computing the clearance directly from the number and magnitude of the spikes of the signal.
In another aspect of the present invention, as shown in
FIGS. 8 and 9
, a non-contact, clearance adjusting system
100
is operable to selectively adjust a clearance
130
during operation between rotating rotor blade tip surface
24
and a surface
118
of a labyrinth seal
110
attached to a casing
12
in response to an observed field of view FV
3
.
For example, clearance
130
is desirably adjusted and optimized during start-up when rotor blades
22
heat up faster than casing
12
(to avoid rubs), during steady state operation (to reduce the gap to increase the efficiency), and during shut down when casing
12
cools down faster than blades
22
(to avoid rubs). Desirably, clearance adjusting system
100
allows a reduction in the cost of manufacture, an increase in efficiency, and an increase in the life of the rotating system.
In this exemplary embodiment, clearance adjusting system
100
includes a clearance measuring system
40
, and labyrinth seal
110
comprising a plurality of labyrinth seal segments
113
having a thermally expandable portion
115
attachable to casing
12
. Thermally expandable portion
115
is operably attached to a controller
170
which is operable to feed an electrical current to a resistive heating element
117
in thermally expandable portion
115
to heat thermally expandable portion
115
causing labyrinth seal surface
118
to move inwardly toward rotor blade tip surface
24
to reduce clearance
130
. By stopping the electrical current to resistive heating element
117
, labyrinth seal surface
118
moves away from rotor blade tip surface
24
. As shown in
FIG. 9
, notches or overlaping portions
114
accommodate circumferential expansion and contraction between adjacent segments
113
. A single system
100
may be employed or two or more seal. segments
113
may each include a system
100
. A temperature sensor
178
may also be used in the monitoring and adjusting of the expansion of labyrinth seal
110
as well as clearance measuring system
40
.
In still another aspect of the present invention, vibrations (e.g., axial oscillations along the length of a longitudinal axis of the shaft or torsional oscillations of the shaft) of the rotor blade may be detected. Desirably, for detecting vibrations, a target
200
attachable to a rotor blade tip
24
includes a two-dimensional pattern of reflective elements
202
as illustrated in FIG.
10
.
Vibrations of rotor blade tip surface
24
cause target
200
to move relative to field of view FV
3
. By aligning and sensing target
200
at, e.g., top dead center, of each rotation of the rotor, and by monitoring the changing signal detected, and selectively strobing the target, vibrations of the blade can be detected. For example, in this embodiment, memory or main storage of a controller (e.g., controller
70
in
FIGS. 2 and 3
) is operable to store a predetermined database of the magnitude of signal measurements to a field of view. A controller is operable to compare the changing magnitude of the signal over time (the clearance and the field of view being generally constant) as target
200
moves relative to field of view FV
4
. During operation, axial vibrations, i.e., motion of the blade forward and aft, will cause reflective elements
202
, or a portion thereof, of target
200
to move in the direction of double-headed arrow X and out of field of view FV
4
which reduces the magnitude of the signal detected and analyzed. Over a period of time, the varying or changing signal can be related and determined by the controller to a frequency of vibration of the rotor blade. Similarly, torsional oscillation may be detected and determined by a varying or changing signal due to target
200
moving in the direction of double-headed arrow Y.
Advantageously, target
200
is not symmetrical so that the varying signal due to axial vibrations and torsional vibrations will cause different changes in the magnitude of the signals detected.
While only certain features of the invention have been illustrated and described, many modifications and changes will occur to those skilled in the art. It is therefore to be understood that the appended claims are intended to cover all such modifications and changes as fall within the scope of the invention.
Claims
- 1. A system for measuring a clearance between a surface of a first object and a surface of a second object, said system comprising:a sensor attachable to the first object for sensing within a field of view a portion of the second object having a varying pattern and generating a signal in response thereto, said field of view varying in response to varying the clearance between said sensor and the second object; and a controller for determining a clearance between the surface of the first object and the surface of the second object in response to said signal wherein the second object is a rotatable object.
- 2. The system according to claim 1, wherein said controller is operable to determine the clearance in response to a magnitude of said signal.
- 3. The system according to claim 2, wherein the clearance varies substantially proportionally to said magnitude of said signal.
- 4. The system according to claim 1, wherein said controller is operable to determine the clearance in response to said signal comprising a plurality of signals.
- 5. The system according to claim 1, wherein the varying pattern comprises a linear pattern of spaced-apart reflective elements.
- 6. The system according to claim 1, wherein said signal comprises a plurality of signals generated in response to the portion of the second object passing through said field of view.
- 7. The system according to claim 1, further comprising an emitter for radiating the portion of the second object.
- 8. The system according to claim 7, wherein said controller is operable to synchronize radiation emitted from said emitter as the portion of the second object passes through said field view.
- 9. The system according to claim 1, wherein said sensor comprises a mask having a viewport.
- 10. The system according to claim 1, wherein said sensor comprises a photodiode.
- 11. A system for adjusting the clearance between a first object and a second object, said system comprising:a movable seal disposed between the first object and the second object; a sensor attachable to the first object for sensing within a field of view a portion of the second object and generating a signal in response thereto; and a controller operable to adjust a position of said seal relative to the second object having a varying pattern to selectively adjust the clearance therebetween in response to said signal.
- 12. The system according to claim 11, wherein said seal comprises a labyrinth seal.
- 13. The system according to claim 11, wherein said seal comprises a plurality of segments.
- 14. The system according to claim 11, wherein said seal comprises a thermally expandable portion.
- 15. The system according to claim 14, further comprising a temperature sensor for monitoring a temperature of said thermally expandable portion.
- 16. The system according to claim 14, wherein the second object is a rotatable object.
- 17. A method for measuring a clearance between a surface of a first object and a surface of second object, said method comprising the steps of:sensing within a field of view a portion of the second object having a varying pattern and generating a signal in response thereto, said field of view varying in response to varying the clearance between the first object and the second object; and determining the clearance between the first object and the second object in response to said signal; wherein the second object is a rotatable object.
- 18. The method according to claim 17, wherein said step of determining the clearance comprises the step of comparing a magnitude of said signal to a predetermined magnitude corresponding to the clearance.
- 19. A system for adjusting the clearance between a first object and a second object, said system comprising:a movable seal disposed between the first object and the second object; a sensor attachable to said seal for sensing within a field of view a portion of the second object and generating a signal in response thereto; and a controller operable to adjust a position of said seal relative to the second object having a varying pattern to selectively adjust the clearance therebetween in response to said signal.
US Referenced Citations (6)
Foreign Referenced Citations (2)
Number |
Date |
Country |
354058047 |
May 1979 |
JP |
3 632 22213 |
Sep 1988 |
JP |