U.S. patent application number 12/782622 was filed with the patent office on 2010-12-09 for scheme for low power strain measurement.
Invention is credited to Steven W. Arms, Christopher P. Townsend.
Application Number | 20100308794 12/782622 |
Document ID | / |
Family ID | 43126735 |
Filed Date | 2010-12-09 |
United States Patent
Application |
20100308794 |
Kind Code |
A1 |
Townsend; Christopher P. ;
et al. |
December 9, 2010 |
Scheme for low power strain measurement
Abstract
A method of determining a parameter includes providing a sensor
that provides a sensor analog voltage. The method also includes
providing a peak detecting circuit for detecting a peak voltage in
the sensor analog voltage. The method also includes providing the
sensor analog voltage to the peak detecting circuit and detecting
the peak voltage. The method also includes recording the peak
voltage.
Inventors: |
Townsend; Christopher P.;
(Shelburne, VT) ; Arms; Steven W.; (Williston,
VT) |
Correspondence
Address: |
JAMES MARC LEAS;Law Office Of James Marc Leas
37 BUTLER DRIVE
S. BURLINGTON
VT
05403
US
|
Family ID: |
43126735 |
Appl. No.: |
12/782622 |
Filed: |
May 18, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61179336 |
May 18, 2009 |
|
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|
Current U.S.
Class: |
324/103P |
Current CPC
Class: |
G01L 1/225 20130101;
G01M 5/0091 20130101; G01P 1/127 20130101; G01B 7/16 20130101; G01R
19/04 20130101; G01B 2210/58 20130101; G01M 5/00 20130101; G01P
15/123 20130101 |
Class at
Publication: |
324/103.P |
International
Class: |
G01R 19/04 20060101
G01R019/04 |
Claims
1. A method of determining a parameter, comprising: a. providing a
sensor that provides a sensor analog voltage; b. providing a peak
detecting circuit for detecting a peak voltage in said sensor
analog voltage; c. providing said sensor analog voltage to said
peak detecting circuit and detecting said peak voltage; and d.
recording said peak voltage.
2. A method as recited in claim 1, wherein after said recording
said peak voltage (d) further comprising resetting said peak
detecting circuit for detecting another peak voltage in said sensor
analog voltage.
3. A method as recited in claim 2, wherein said circuit includes a
resetting switch for resetting said peak detecting circuit.
4. A method as recited in claim 1, wherein said circuit stores a
present sensor analog voltage peak value and repeatedly compares
said sensor analog voltage with said present sensor analog voltage
peak value, wherein said present sensor analog voltage peak value
is determined to be said peak voltage when said sensor analog
voltage falls a specified amount below said present sensor analog
voltage peak value.
5. A method as recited in claim 4, wherein said circuit includes an
amplifier for storing said present analog voltage peak value.
6. A method as recited in claim 5, wherein said circuit includes a
comparator, wherein said comparator includes a first input and a
second input, wherein said first input is for said sensor analog
voltage and wherein said second input is for said present sensor
analog voltage peak value.
7. A method as recited in claim 6, wherein said circuit draws less
than 4 microamps.
8. A method as recited in claim 1, wherein said sensor is sensitive
to strain and wherein said sensor analog voltage is related to
strain.
9. A method as recited in claim 1, wherein said sensor is sensitive
to loading and wherein said sensor analog voltage is related to
loading.
10. A method as recited in claim 9, wherein said sensor measures
change in loading without power consumption.
11. A method as recited in claim 1, further comprising: e.
providing a valley detecting circuit for detecting a valley voltage
in said sensor analog voltage; f. providing said sensor analog
voltage to said valley detecting circuit and detecting said valley
voltage; and g. recording said valley voltage.
12. A method as recited in claim 11, wherein said sensor is mounted
on a component, wherein said sensor is sensitive to strain, and
wherein said sensor analog voltage is related to strain, further
comprising using said recorded peak voltage and said recorded
valley voltage to determine a parameter related to fatigue
life.
13. A method as recited in claim 12, further comprising measuring a
static strain and using both said static strain and a plurality of
recorded peak voltages and recorded valley voltages to determine
said parameter related to fatigue life.
14. A method as recited in claim 12, further comprising measuring
mean load and using both said mean load and a plurality of recorded
peak voltages and recorded valley voltages to determine said
parameter related to fatigue life.
15. A method as recited in claim 12, wherein said parameter related
to fatigue life includes at least one from the group consisting of
remaining life and fatigue life expended.
16. A method as recited in claim 1, wherein said sensor is mounted
on a component, wherein said component is for rotating.
17. A method as recited in claim 16, wherein said component
includes at least one from the group consisting of a shaft, a gear,
a wind turbine blade, a helicopter blade, a helicopter structural
component, a sporting equipment, a hand tool, an instrumented bolt,
a tire, a wheel, and a machine tool.
18. A method as recited in claim 1, wherein said sensor is
self-powering.
19. A method as recited in claim 18, wherein said sensor includes a
piezo-electric element.
20. A method of determining a parameter, comprising: a. providing a
sensor that provides a sensor analog voltage; b. providing a
circuit for detecting a feature of said sensor analog voltage; c.
providing said sensor analog voltage to said peak detecting circuit
and detecting said feature; and d. using said feature to provide
timing for when to record data from said sensor.
21. A method as recited in claim 20, wherein said feature is at
least one from the group consisting of a peak sensor analog voltage
and a valley sensor analog voltage.
22. A method as recited in claim 21, further comprising recording
at least one from the group consisting of said peak sensor analog
voltage and said valley sensor analog voltage.
23. A method as recited in claim 20, wherein said sensor provides
said sensor analog voltage without consuming power.
24. A method as recited in claim 23, further comprising providing a
power consuming sensor for providing a second measurement and
providing power for making said second measurement.
25. A method as recited in claim 24, further comprising using said
feature to provide timing for providing power to said power
consuming sensor for making said second measurement.
26. A method as recited in claim 25, further comprising recording
said second measurement and turning off power to said power
consuming sensor after said recording said measurement.
27. A method of determining a parameter, comprising: a. providing a
dynamic analog sensor; b. providing a circuit for detecting at
least one from the group consisting of peaks and valleys of data
from said dynamic analog sensor; and c. recording data from said
dynamic analog sensor only when said circuit detects at least one
from the group consisting of peaks and valleys of data from said
dynamic analog sensor.
28. A method as recited in claim 27, further comprising providing a
power consuming sensor for providing a second measurement and
providing power for making said second measurement.
29. A method as recited in claim 28, further comprising using
detection of at least one from the group consisting of peaks and
valleys of data from said dynamic analog sensor to provide timing
for providing power to said power consuming sensor for making said
second measurement.
30. A method as recited in claim 29, further comprising recording
said second measurement and turning off power to said power
consuming sensor after said recording said measurement.
31. A system, comprising a device, an electronic circuit, a first
strain gauge and a second strain gauge, wherein said electronic
circuit, said first strain gauge, and said second strain gauge are
mounted on said device, wherein said first strain gauge consumes
power for its operation and wherein said second strain gauge
consumes no power for its operation, wherein said electronic
circuit is connected to receive data from said first strain gauge
and from said second strain gauge.
32. A system as recited in claim 31, wherein said first strain
gauge includes a piezoresistive strain gauge and wherein said
second strain gauge includes a piezoelectric strain gauge.
33. A system as recited in claim 31, wherein said electronic
circuit includes a processor, wherein said processor is configured
for taking data from said first strain gauge and from said second
strain gauge, wherein said processor includes a program that uses
data from both said first strain gauge and from said second strain
gauge for determining a parameter.
34. A system as recited in claim 33, wherein said processor
includes a program to sample data from said first strain gauge less
frequently than from said second strain gauge.
35. A system as recited in claim 33, wherein said device has
geometrical and material properties, wherein said parameter is a
fatigue life parameter of said device, wherein said processor has a
program to use said data along with said properties to compute said
fatigue life parameter of said device.
36. A system as recited in claim 35, wherein said fatigue life
parameter includes fatigue life expended.
37. A system as recited in claim 35, further comprising a
non-volatile display, wherein said display is mounted on said
device, wherein said processor includes a program to update said
display with said fatigue life parameter.
38. A system as recited in claim 31, further comprising an energy
harvesting device, wherein said energy harvesting device is
connected to provide power for operating said electronic
circuit.
39. A system as recited in claim 38, wherein said energy harvesting
device collects energy from one from the group consisting of strain
and vibration.
40. A method of monitoring a structure comprising: a. providing a
structure having a component; b. mounting a sensor to said
structure, wherein said sensor provides an analog voltage related
to loading; c. mounting a peak detecting circuit to said structure
wherein said peak detecting circuit is for detecting a peak voltage
in said analog voltage related to loading; d. providing said analog
voltage related to loading to said peak detecting circuit and
detecting said peak voltage; and e. using said peak voltage in
determining a parameter related to severity of usage of said
component.
41. A method as recited in claim 40, further comprising recording
data derived from said sensor related to loading.
42. A method as recited in claim 40, further comprising replacing
said component if information derived from said recorded data shows
that said component experienced a load history indicating damaging
usage.
43. A method of operating a system as recited in claim 42, wherein
said load history indicating damaging usage includes a load
exceeding a threshold.
44. A method of operating a system as recited in claim 42, wherein
said load history indicating damaging usage includes fatigue
inducing cyclic loading.
45. A method as recited in claim 40, further comprising mounting an
energy harvesting device to said structure,
46. A method as recited in claim 45, wherein said energy harvesting
device is configured to convert at least one from the group
consisting of vibration of the structure and strain of the
structure into electricity.
47. A method as recited in claim 45, wherein said peak detecting
circuit is powered solely with electricity derived from said energy
harvesting device.
48. A method of operating a system as recited in claim 45, further
comprising mounting a wireless communications device to said
structure, and further comprising transmitting data derived from
said sensor with said wireless communications device, wherein all
power for powering said wireless communications device is derived
from said energy harvesting device.
49. A method as recited in claim 40, wherein said sensor is
self-powering.
50. A method as recited in claim 40, further comprising mounting a
display to said structure and displaying said parameter related to
fatigue life of said component.
Description
PRIORITY
[0001] This application claims the benefit of U.S. Provisional
Patent Application 61/179,336, filed May 18, 2009, "Component RFID
Tag with Non-Volatile Display of Component Use," incorporated
herein by reference.
RELATED APPLICATIONS
[0002] This application is related to commonly assigned U.S. Pat.
No. 7,461,560, filed Mar. 28, 2005, "Strain Gauge with Moisture
Barrier and Self-Testing Circuit," to Steven W. Arms et al., ("the
'560 patent"), docket number 115-017, incorporated herein by
reference.
[0003] This application is related to commonly assigned U.S. Pat.
No. 7,719,416 filed Sep. 11, 2006, "Energy Harvesting, Wireless
Structural Health Monitoring System," to Steven W. Arms et al.,
("the '416 patent"), docket number 115-030, incorporated herein by
reference.
[0004] This application is related to commonly assigned U.S. patent
application Ser. No. 12/761,259 filed Apr. 15, 2010, "Wind Turbines
and Other Rotating Structures with Instrumented Load Sensor Bolts
or Instrumented Load Sensor Blades," to David Maass et al., ("the
'259 application"), docket number 115-067, incorporated herein by
reference.
[0005] This application is related to commonly assigned U.S.
Provisional Patent Application 61/293,948 filed Jan. 11, 2010,
"Wireless sensor synchronization methods," to Stephen J. DiStasi et
al., ("the '948 application"), docket number 115-071, incorporated
herein by reference.
[0006] This application is related to commonly assigned U.S.
Provisional Patent Application 61/309,767 filed Mar. 2, 2010,
"Harvesting Power from Multiple Energy Sources," to Christopher P.
Townsend et al., ("the '767 application"), docket number 115-072,
incorporated herein by reference.
[0007] This application is also related to commonly assigned U.S.
patent application Ser. No. 12/782,597, filed May 18, 2010,
"Component RFID Tag with Non-Volatile Display of Component Use,"
docket number 115-068, ("the '597 application"), incorporated
herein by reference, that also claims the benefit of the 61/179,336
provisional application.
BACKGROUND
[0008] Components on machines such as aircraft have a fatigue life
that depends on factors including number of hours used and severity
of use. A particular component may be used on one aircraft and
later installed on another, making tracking these parameters a
challenge. The present application provides several ways to
accomplish this tracking
[0009] Severity of use may be determined by measuring strain. One
way to provide a low power strain measurement for fatigue life
calculation was to turn power off, avoiding exciting strain sensors
and supporting electronics except when sampling, as described in
the '777 application. But the ability to reduce power was limited
by the substantial amount of current drawn by the strain sensors
and amplifiers during sampling. Especially in situations where the
measurement required frequent sampling or turning on power rapidly
to take a measurement, high power was needed. Not only did high
bandwidth amplifiers that turn on quickly use more power they also
introduced additional noise. And the power used by the system
increased with the rate at which data was sampled. The high power
consumption and high cost associated with providing sufficient
power restricted the use of such systems. Thus, a better system for
monitoring strain for fatigue life calculation is needed, and this
system is provided by the present patent application.
SUMMARY
[0010] One aspect of the present patent application includes a
method of determining a parameter that includes providing a sensor
that provides a sensor analog voltage. The method also includes
providing a peak detecting circuit for detecting a peak voltage in
the sensor analog voltage. The method also includes providing the
sensor analog voltage to the peak detecting circuit and detecting
the peak voltage. The method also includes recording the peak
voltage.
[0011] Another aspect of the present patent application includes a
method of determining a parameter that includes providing a sensor
that provides a sensor analog voltage. The method also includes
providing a circuit for detecting a feature of the sensor analog
voltage. The method also includes providing the sensor analog
voltage to the peak detecting circuit and detecting the feature.
The method also includes using the feature to provide timing for
when to record data from the sensor.
[0012] Another aspect of the present patent application includes a
method of determining a parameter that includes providing a dynamic
analog sensor. The method also includes providing a circuit for
detecting at least one from the group consisting of peaks and
valleys of data from the dynamic analog sensor. The method also
includes recording data from the dynamic analog sensor only when
the circuit detects at least one from the group consisting of peaks
and valleys of data from the dynamic analog sensor.
[0013] Another aspect of the present patent application includes a
system that has a device, an electronic circuit, a first strain
gauge and a second strain gauge. The electronic circuit, the first
strain gauge, and the second strain gauge are mounted on the
device. The first strain gauge is mounted for determining static
strain of the device. The second strain gauge is mounted for
determining dynamic strain of the device. The electronic circuit is
connected to receive data from the first strain gauge and from the
second strain gauge.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 illustrates a 2-dimensional bar code or QR code;
[0015] FIG. 2 illustrates a non-volatile display for mounting on an
aircraft part in which the display shows the QR code of the part,
the flight hours experienced by the part, the remaining life of the
part, and the date the information was last updated;
[0016] FIG. 3a is a block diagram illustrating a zero-power
consuming energy harvesting network updating sensing RFID tag with
a non-volatile display which can send and receive data wirelessly,
communicate to the internet, and display parameters;
[0017] FIG. 3b is a three dimensional view of an implementation of
circuit elements in the block diagram of FIG. 3a illustrating a
strain gauge sensor module with energy harvesting and wireless
communication;
[0018] FIG. 4 is another block diagram illustrating a zero-power
consuming energy harvesting updating sensing RFID tag with a
non-volatile display;
[0019] FIG. 5 is a graph showing the linear relationship between
piezoelectric output voltage and strain;
[0020] FIG. 6 is a simulated timing chart showing how the voltage
IN provided by the piezo strain gauge, the output PEAK held by the
peak detector, and the output PEAKCOMP of the comparator change
with time;
[0021] FIG. 7 is timing data showing how the voltage IN provided by
the piezo strain gauge, the output PEAK held by the peak detector,
and the output PEAKCOMP of the comparator changed with time during
an experiment; and
[0022] FIG. 8 is a schematic diagram of an embodiment of a circuit
that may be used to capture peak values while consuming very little
energy.
DETAILED DESCRIPTION
[0023] A non-volatile electronic ink display is used to provide a
visual indication of the health, remaining lifetime, and/or status
of a vehicle, machine, structure, component, or other item. In one
embodiment, the display is integrated with a smart RFID tag affixed
to a structural component. Usage data collected from sensors on the
component or from transmission from another source, such as a data
base, is used to update the display periodically. Maintenance
providers are then able to look at the display on the component and
immediately determine its health, remaining life and/or status (OK
or failed) from information provided on the display.
[0024] In one embodiment, the information is displayed as text. In
another embodiment, the information is displayed as a bar code. The
bar code can be a 2-D bar code, often called a QR code. An example
QR code is provided in FIG. 1.
[0025] In one embodiment QR codes are included on an external
surface of RFID tags and/or on the non-volatile display, as shown
in FIG. 2. These QR codes could thus be a permanent code printed on
the tag. Alternatively, these QR codes can be displayed on the
non-volatile display and can be dynamically changed as part of the
RFID tag's electronic ink display.
[0026] In one embodiment, the QR code allows the information
related to the particular tag (and component to which the tag is
affixed) to link to a website or to a database with more
information, such as a record of historical sensor data for the
component, the manufacturer's lot number, the serial number of the
aircraft that the part was previously installed on, etc. For
example, as described in the news article at
http://www.centernetworks.com/google-qr-codes-print-advertising,
"you can simply whip out your cell phone, take a picture of the 2D
barcode (using specific software installed on your cell phone that
recognizes/decodes the 2D barcode) and then your phone's web
browser opens and automatically takes you to a corresponding
website with more information on the product/service that you're
interested in."
[0027] In another embodiment the QR code communicates relevant
information directly accessible via the 2D barcode scan, such as
data previously stored, or data derived from a sensor or sensors on
the component on which the QR code is mounted, as opposed to data
derived from a link to a database or a URL. At the present time
each standard QR code is capable of communicating up to 2,953 bytes
of data as described at
http://www.denso-wave.com/qrcode/qrfeature-e.html.
[0028] The standard 3 KB of data available with the QR code is
itself sufficient to communicate many relevant static and dynamic
parameters, including manufacturer ID, serial ID/EPC, flight hours,
flight dates, miles driven, remaining life estimated, remaining
life calculated locally, remaining life calculated and loaded
externally, repair history, detailed, traceable pre-deployment
history for manufacture, assembly, & transport, sensor
calibration information, and summarized sensor data statistics.
[0029] Thus, the non-volatile electronic ink display of the present
patent application supports both a centralized, database driven
approach with a link to a database or URL and it also supports a
low-level distributed approach, with data directly displayed. The
former is more scalable, allowing access to vast stores of data on
line. The latter is advantageous in certain environments where
network access is unavailable, sparse or intermittent. In one
embodiment, both approaches are included, providing immediate
component information as well as a database link/URL.
[0030] Several 2D matrix barcode alternatives to the QR code can be
used, with varying sizes, data capacities, and intended markets, as
described at http://en.wikipedia.org/wiki/Barcode#2D barcodes. One
example is a 2D tag, commonly known as data matrix
http://en.wikipedia.org/wiki/Data Matrix#cite note-1, that appears
to be covered by an ISO standard and is license/royalty free.
[0031] In one embodiment, human readable information, such as text
and/or image, is written to the non-volatile display, such as the
component's remaining life in percent, assuming the component will
be operated in a manner similar to its historical record. Paper
white, non-volatile displays available from by E Ink Corporation,
Cambridge, Mass., as illustrated at http://www.eink.com/, can be
used. One example of the e-ink display used to passively indicate
how many hours a component has been flown, how much life remains,
and when the last update to the non-volatile display was made, is
shown in FIG. 2.
[0032] An e-ink display holds the last graphic image or
alphanumeric characters written to it, even if the power to the
display is shut down or has become unavailable. Thus the component
(with affixed smart RFID tag, processor and sensor) can display the
information, such as the component's remaining life or severity of
usage--or that a critical operational or environmental parameter
was exceeded, such as temperature, humidity, strain, shock,
pressure, or usage. We have shown that these non-volatile displays
will hold their graphics with no power over a temperature range of
-40 to +85 degrees C.
[0033] In one embodiment, an active RFID tag with an integral
non-volatile display uses a method such as described in a paper,
"Architecture for Dynamic Component Life Tracking in an Advanced
HUMS, RFID, and Direct Load Sensor Environment," by N. Iyyer, et
al, Sixth DSTO International Conference on Health & Usage
Monitoring, 10-12 March, 2009, Melbourne Australia, incorporated
herein by reference. The method was "developed by Technical Data
Analysis, Inc. ("the TDA method") to track usage and history of all
uniquely serialized components throughout their lifetime, so that
component life limits and applicable maintenance data are correctly
and continuously assessed." The present applicants found that the
TDA method could be used to access HUMS data or vehicle bus data.
The TDA method uses the data to compute remaining life based on
regime recognition. Remaining life so computed is then provided
back to each tag to update the information shown on the
non-volatile display. Other methods of computing remaining life can
also be used.
[0034] In another embodiment, a smart passive RFID tag with an
integral non-volatile display performs this remaining life
calculation itself. In this embodiment, data about severity of use
is written to the RFID tag with a wand or transmitted to the RFID
tag. An ultra wide band radio, such as DW4aSS1000, from decaWave,
Ltd. can be used to localize the component on the aircraft.
[0035] In another embodiment a direct loads monitoring sensor with
wireless sensing and energy harvesting is provided along with the
smart passive RFID tag with an integral non-volatile display. The
energy harvesting can be accomplished with a piezoelectric patch, a
solar cell, a dynamo or a thermoelectric generator.
[0036] In one embodiment a smart tag for aircraft is implemented
that uses only flight hours to determine remaining life. In this
case, remaining life is calculated by the tag itself. Thus, in this
embodiment, no radio link need be provided. In one scheme, the tag
uses a simple inertial motion detector, such as an accelerometer,
and a clock to record duration of time in operation. In one
embodiment, the accelerometer is used to detect vibration which is
indicative of operation. In another embodiment, the accelerometer
is used to detect orientation, as change in orientation may show
operation of an aircraft. An altimeter or pressure sensor can also
be used for determining operation of an aircraft. A temperature
sensor can be used to detect engine use. A microphone can be used
to detect noise indicative of operation. An energy harvesting
device can also serve to detect operation. For example it may be
set to harvest energy from vibration, from strain, from a turning
wheel, or with a Peltier device from a temperature gradient, all
indicative of operation. In one embodiment, electricity derived
from the energy harvesting is used to power a clock. In this
embodiment, the clock only receives energy for keeping time when
energy is being harvested. If energy is only harvested when, for
example a machine to which the energy harvester is mounted is
operating and vibrating, then the clock will record the accumulated
hours of machine operation. The integral non-volatile display is
updated with hours in use, for example flight hours, and hours of
life remaining, based on output of this clock. Time the motion
detector is producing an output or time a temperature sensor is
showing an elevated temperature can also be used for determining
accumulated hours of machine operation. For a component such as a
motor, that produces heat, a thermal energy harvester can provide
sufficient electricity for operating a circuit, including measuring
time and other functions, such as wireless communication. This
scheme is also useful for a range of applications, such as for
displaying accumulated engine hours of use in a boat, or hours of
use on car shock absorbers or bike frames.
[0037] In other embodiments using this concept, a sensor provides
data from which a parameter for display is determined and
displayed. For example, frozen food in transit could be monitored
for temperature changes and the non-volatile display updated with
the maximum temperature that occurred, along with the time (and
duration of time) at which the temperature(s) may have exceeded a
specified threshold. In other examples, another sensed parameter or
information derived from another sensed parameter, such as strain,
shock, and pressure, is displayed. In all these cases the radio
link can be eliminated, since the local sensor provides the data
for the non-volatile display.
[0038] In many of these embodiments, so little power is consumed
that a standard battery can provide sufficient power for long-term
operation. However, the present applicants recognized that in these
embodiments, as the component's sensed parameter or parameters
becomes more power hungry, such as by making measurements at a high
sample rate or where duty cycling of the sensors is not available
due to the component's particular monitoring requirements, such as
providing ever-vigilant operation, then the battery's design
capacity will increase or energy harvesting becomes an increasingly
important element in the smart tag's design.
[0039] Block diagrams of embodiments of component RFID tag 28 that
has a non-volatile display are shown in FIGS. 3a and 4. An
implementation is shown in FIG. 3b. Microprocessor 30, such as the
MSP430, available from Texas Instruments, Dallas, Tex., has
connections to a RF transmitter and receiver or transceiver 31,
non-volatile memory 32, such as FRAM or EEPROM, non-volatile
display 34 (such as e-ink), and energy storage elements 36, such as
rechargeable battery and/or a primary battery. Transceiver 31 can
be an ultra wide band radio (UWB), as shown in FIG. 3 or another
communications device. In one embodiment, precision timekeeper 38,
such as the DS3234, is used to enhance the performance and
stability over temperature of the timing information to be used by
microprocessor 30. Alternatively, microprocessor 30 can use its own
on-board low power timer 40 to calculate elapsed time. Digital
input/output (I/O) lines 46 from processor 30 are used to drive
non-volatile display 34. Sensors 48, such as absolute pressure
sensors, acoustic pressure sensors, strain sensors, load sensors,
and motion sensors, such as accelerometers and vibrometers, can be
used as inputs to microprocessor analog to digital converter (ADC)
50. Strain sensors include resistive, piezoelectric,
piezoresistive, capacitive and inductive. In one embodiment, motion
sensor input is used by microprocessor 30 to detect when the
component is in use, for example when the aircraft is flying. Many
of the components shown in FIGS. 3a and 4 can be included to
fulfill a specific purpose or they can be omitted.
[0040] In one embodiment, strain energy harvesting is accomplished
with an energy harvesting material, such as PZT patch 52, available
from Smart Materials, Inc., Liberty, Tex. and Advanced Cerametrics,
Inc., Lambertville, N.J. In another embodiment, the strain energy
is harvested using piezo polymer films (PvDF).
[0041] In one embodiment, energy harvesting electronics 54 converts
the voltage provided by energy harvesting material 52, 64 into a
voltage suitable for storage onto one or more energy storage
elements, as described in commonly assigned U.S. Pat. No.
7,081,693, incorporated herein by reference. Energy harvesting
electronics 54 may include power level threshold detection circuit
55, such as a nanoamp comparator switch, which is connected to an
interrupt line 50a on microprocessor 30 or to ADC 50b of
microprocessor 30.
[0042] Processor 30 is powered by energy derived from energy
harvester 52, 64. For example, the energy derived from the energy
harvester can be stored in a rechargeable battery or super
capacitor 56. Processor 30 can also be powered with energy from a
primary battery. If processor 30 is powered with energy from a
primary battery, an energy harvester can be used to act as a sensor
to detect when a vehicle, such as an aircraft, or a machine, or
component is in use, and to provide an indication of the severity
of use. Additional energy harvesting or energy collecting devices
can be included, such as coil 66 which collects energy from a
source of radiation, such as a closely coupled RF source. One such
coil, part number 4513TC-404XGL is available from Coilcraft, Inc.,
Gary, Ill., and works at 125 Khz from a source generating radiation
at that frequency. Power collected by coil 66 is converted on board
to dc to provide power for operating microprocessor 30, transceiver
31, and other components of RFID tag 28. In one embodiment, power
is provided by energy harvesting devices 52, 64 when strain or
vibration is available and power is provided by coil 66 when energy
harvesting components 52, 64 are not receiving strain or vibration,
for example, when an aircraft is not in operation.
[0043] Macro Fibre Composite, available from Smart Materials, Inc.,
Sarasota, Fla., and bulk piezoelectric materials have been used to
harvest energy from a component's cyclic strain of operation to
power a wireless sensor, as described in papers by Arms et al, AHS
2006, 2007, and 2009, incorporated herein by reference (see
attached title pages for titles, authors, and publication
information).
[0044] The present inventors recognized that higher energy output
from a strain energy harvester would be a good indication that the
severity of usage has increased. This information is then used to
provide an improved estimate of fatigue life expended (FLE) as
compared to relying on flight hours alone. A load history
indicating damaging usage includes a load exceeding a threshold.
The load history indicating damaging usage includes fatigue
inducing cyclic loading. If information derived from recorded data
shows that a component experienced a load history indicating
damaging usage the component may be replaced. An operator receiving
information about a load exceeding a threshold may alter the way
the structure is being used, for example by operating in a way that
reduces the loading.
[0045] In one embodiment, when connected to interrupt line 50,
microprocessor 30 is "woken up" from sleep to record that a
threshold of energy generation has been crossed. Achieving that
energy generation threshold indicates that a sufficiently high
level of strain was experienced. If that energy generation
threshold is crossed at higher frequency this would indicate that
component usage is more severe because of increased frequency of
strain above the amount needed to reach that energy generation
threshold.
[0046] In one embodiment, once woken up, processor 30 uses ADC 50
to sample the strain energy harvesting power production level more
frequently. Sampling at a higher rate enhances the processor's
estimate of severity of usage, which allows a better estimate of
the fatigue life expended than would be available from a
determination of flight hours alone.
[0047] In some cases, while vibration may be present, the strain
level experienced by the component under test may be relatively
low. In that case, applicants have placed strain harvester 52 onto
a flexible, tuned substrate (such as a tapered cantilever beam), in
order to capture energy generated by exposure to vibration, as
described in commonly assigned U.S. patent application Ser. No.
11/604,117, "Slotted Beam Piezoelectric Composite," incorporated
herein by reference. In this embodiment, as the vibration
harvester's output increases, processor 30 uses that increased
output to estimate severity of usage, which again facilitates an
improved estimate of component remaining life than would be
available from a determination of flight hours alone.
[0048] In some cases, it is important to know both the static and
dynamic strains. The present inventors also recognized that by
including a piezoresistive strain gauge capable of detecting static
strain levels, and a piezoelectric strain gauge capable of
detecting dynamic strains they could produce a hybrid sensing
system that could monitor both static and dynamic strains, but with
lower energy consumption as compared to a piezoresistive strain
sensor alone. They recognized that if the static strains are
changing relatively slowly, this piezoresistive or foil type strain
gauge sensor can be sampled at a lower sample rate than the dynamic
strains for the purpose of fatigue life calculation. They also
recognized that the dynamic strains can be acquired from a
piezoelectric strain gauge without any external source of
excitation energy and that uses the motion being measured to
provide the energy measured. Thus, the dynamic response of the
piezoelectric energy harvesting elements is used as a sensor for
the changing component strains, with the advantage that this type
of sensor generates its own power and needs no additional
excitation current, thus, avoiding expenditure of energy for
tracking the dynamic response. This can be accomplished by adding a
piezoresistive or foil type strain gauge as a sensing element,
connected to an ADC line of the processor along with a
piezoelectric strain gauge. In this embodiment, the processor
acquires the static and dynamic strains and uses this information,
along with the component's unique geometrical and material
properties, to compute an FLE for the component and to update the
non-volatile electronic ink display.
[0049] One example of an accelerometer sensor and "shake and wake"
sensor that can be used by the MSP430 microprocessor to determine
when a machine is in operation, for example, flying, is the
ADXL346, available from Analog Devices, Norwood, Mass. The ADXL346
is a small, thin, low power, three-axis accelerometer with high
resolution (13-bit) measurement at up to .+-.16 g. Digital output
data is formatted as 16-bit twos complement and is accessible
through either a SPI (3- or 4-wire) or I2C digital interface.
Either of these digital interfaces can be used to interrupt the
MSP430 microprocessor from sleep or as a sensing line to allow the
processor to form a better estimate of the severity of component
usage.
[0050] The ADXL346 accelerometer is well suited for mobile
component applications. It measures the static acceleration of
gravity in tilt-sensing applications, as well as dynamic
acceleration resulting from motion or shock. Its high resolution (4
mg/LSB) enables measurement of inclination changes as little as
0.25.degree.. Several special sensing functions are provided.
Activity and inactivity sensing detect the presence or lack of
motion and if the acceleration on any axis exceeds a user-set
level. Tap sensing detects single and double taps. Free-fall
sensing detects if the component is falling. These functions can be
mapped to one of two interrupt output pins. An integrated 32-level
first in, first out (FIFO) buffer can be used to store data to
minimize host processor intervention. Both 4- and 6-position
orientation sensing are available for 2- and 3-D applications. Low
power modes enable intelligent motion-based power management with
threshold sensing and active acceleration measurement at extremely
low power dissipation.
[0051] One disadvantage of the ADXL346 accelerometer is that it
requires power to operate. Applicants found that they could
overcome this disadvantage by using passive sensors that require no
external source of power for operation. Passive sensors, such as
the SQ-SEN-200 series sensor, available from SignalQuest, Inc.,
Lebanon, N.H., act like a normally closed switch that chatters open
and closed as it is tilted or vibrated. Unlike other rolling-ball
sensors, the 200 is truly an omnidirectional movement sensor. It
will function regardless of how it is mounted or aligned. When at
rest, it normally settles in a closed state. When in motion, it
will produce continuous on/off contact closures. It is sensitive to
both tilt (static acceleration) and vibration (dynamic
acceleration). The sensor can be easily used to produce a series of
CMOS or TTL level logic level or pulse train using a single
resistor to limit current. In one embodiment the signal level is
read directly by a digital input and used to interrupt, or wake up
a microcontroller. In another embodiment, the number of signal
levels above a threshold is counted to estimate the amount and
duration of activity. The sensor is fully passive, requires no
signal conditioning, and the microcontroller interrupt interface
draws as little as 0.25uA of continuous current.
[0052] In another embodiment, the energy harvesting element is
separate and distinct from the sensing elements. As described
herein above, the output from the energy harvester alone can also
be used to compute an estimate of FLE.
[0053] The present applicants also recognized that individual RFID
tag 28 with non-volatile display 34, battery backed timekeeper 36,
38, and an on-board database of its component and aircraft serial
numbers, can display its remaining life on its non-volatile display
34 in an embodiment that does not necessarily include motion
sensors integrated with RFID tag 28. This embodiment is
accomplished by relating the component's flight hours on each
specific aircraft on which it served to another data set collected
by that aircraft's flight computer and/or its health and usage
monitoring system (HUMS) 68, and/or any other data collection
system such as wireless sensor data aggregater (WSDA) 70. These
on-aircraft monitoring systems can estimate the severity of vehicle
usage through characterization of various flight regimes ("regime
recognition") experienced. For each flight regime experienced, such
as straight and level, pull-ups, and gunnery turns, there is
available a related estimate of the fatigue life expended for each
component on the aircraft, based on an instrumented flight test for
that aircraft. The paper, "Fatigue Life Reliability Based on
Measured Usage, Flight Loads and Fatigue Strength Variations," by
Dr. Suresh Moon, et al., ("the Moon paper") presented at the
American Helicopter Society 52.sup.nd Annual Forum, Washington,
D.C., Jun. 4-6, 1996, incorporated herein by reference, provides
further information. Thus, since the time and date that each of
these regimes was flown are known to the on board monitoring system
on each aircraft, the communication of the stored data about each
permits on-board microprocessor 30 to add up the lifetime effects
of each lifetime detractor and update non-volatile display 34 on
tag 28 for each component to be updated with its individual FLE
estimate.
[0054] WSDA 70 for the structural health monitoring system 68
supports data recording and remote access from wireless transceiver
31, as shown in FIG. 3. WSDA 70 serves as the data aggregation
engine for the system. It can also acquire data from cell phone,
satellite, and internet, as shown in FIG. 3. It can also acquire
data from hardwired, high speed networked sensors, such as the
aircraft bus, as also shown in FIG. 3. WSDA 70 may aggregate data
from other sources, as described in commonly assigned and
co-pending U.S. patent application Ser. No. 11/518,777,
incorporated herein by reference, such as an inertial sensing
subsystem (ISS) as well as data from a wireless sensing network or
wireless sensing node. It may receive data from an energy
harvesting and load sensing component, such as the pitch link of a
helicopter. In one embodiment, WSDA 70 includes components
integrated within its enclosure, including IEEE 802.15.4
transceiver, cellular connectivity, flash EEPROM for data logging,
an on board DSP with structural usage algorithms, a cockpit
notification display, a can bus and a vehicle bus. WSDA 70 can be
located on the aircraft or it can be located on a ground vehicle
that communicates with the aircraft or it could be in a hand held
device where it could be used to query the wireless network.
[0055] This embodiment illustrates a scheme for a component's
remaining life to be computed externally but does not require
sensor data to be provided by sensors on the component itself. In
this embodiment, time data is used and data from a sensor on the
component is optional. From information about when a component was
flying, and information about what the aircraft using that
component was doing during that time--information readily available
from standard systems on the aircraft--models are used to estimate
what type of life limiting usage that part experienced and to
estimate the corresponding reduction in component life. In this
embodiment, all of this is computed externally and periodically
pushed back onto the component's tag 28 and displayed on its
non-volatile display 34.
[0056] In one embodiment real time timekeeper 38 provides date and
time for time stamping sensor-provided data related to operation of
the aircraft or the machine. Microprocessor 30 periodically wakes
up from sleep to see if the aircraft is flying and records the
number of hours flown and time and date of each flight. When the
aircraft lands a data base queries tag 28 to record the hours it
flew and download the logbook with the time stamped sensor data.
The data may also include information regarding severity of flight.
This information may be obtained from a separate system on the
aircraft that takes pitch, roll, and yaw, stick position, and other
measured parameters along with the aircraft's identification. Then
the severity of flight regimes is computed based on that data, as
described in the Moon paper. Hours, dates and time recording can
then be related to severity of usage.
[0057] The present applicants also designed a device that combines
several features to allow measuring strain at very high data rate
and at very low power. The device allows continuous monitoring of
both static and dynamic loading and yet uses little power. In one
embodiment, such low power is consumed for the measurements that
the life of a battery used for powering the device approaches the
shelf life of the battery. Alternatively, power requirement is so
low that energy harvesting can be used to provide power from an
ambient source, such as the varying strain itself, vibration, or
light, eliminating the need for replacing a battery.
[0058] The present applicants found a way to measure dynamic strain
continuously while completely avoiding power consumption while
taking the strain measurement. Thus, they were able to capture
dynamic change in loading at the equivalent of a high data rate
without power consumption. In one embodiment, the present
applicants used a low power amplifier and a method of recording
data that vastly reduces current draw for taking and analyzing data
for an application, such as determining fatigue life of a component
or structure.
[0059] In addition, the present applicants found an extremely low
power method of periodically measuring the mean load, whose value
is also used in determining fatigue life. Thus, this patent
application provides various embodiments of ways to monitor dynamic
strain at very high data rate, monitoring static strain, and
determine fatigue life while consuming orders of magnitude less
power than has otherwise been achievable.
[0060] In one embodiment, piezoelectric strain gauges are used in
combination with conventional resistive strain gauges and an
improved sampling and data analysis technique. The present
applicants found that piezoelectric strain gauges generate a
voltage proportional to the applied strain. As shown in FIG. 5,
piezoelectric output voltage v. strain shows a linear relationship.
Thus, the piezoelectric strain gauges continuously supply a voltage
proportional to strain, providing a steady stream of changing
strain data while avoiding current draw and energy consumption for
operating the strain gauges. Since they generate their own power,
their operation does not require drawing energy from an external
source of power or from an energy storage device, eliminating one
power consumption issue.
[0061] However, piezoelectric strain gauges only provide a dynamic
response. That is, they only provide strain information while
strain is changing. When strain is constant the piezoelectric
strain gauge reading goes to zero.
[0062] The present applicants also provided an embodiment that uses
information from the piezoelectric strain gauges not just for their
high data rate dynamic strain information but also for providing
timing for when to record data coming from the piezoelectric strain
gauges. In one embodiment, the time for recording is at peaks of
the data. Because the data is recorded only at intervals and
because those intervals are just where needed for determining
fatigue life, little energy is consumed for the dynamic strain
measurement even at the equivalent of a high data rate because only
one sample is taken to record each peak and each valley.
[0063] In one embodiment, peak indicator circuit 80 includes peak
detector 82 and comparator U5. Peak detector 82 includes op amps U1
and U2, diodes D1 and D3, capacitor C1, and resistors. Op amp U1
charges capacitor C1 to a voltage equal to the maximum voltage seen
on input waveform IN obtained from the piezoelectric sensor 83.
Diode D3 prevents any discharge of capacitor C1 when the voltage on
IN later declines from its peak value. Op amp U1 sets its output
connected to D3 at a value so its negative input connected to R2 is
equal to its positive input connected to IN. With diode D1
providing feedback, op amp U1 must set its output one diode drop
above IN. With D3 in series, C1 will therefore be charged to a
voltage equal to IN.
[0064] Op amp U2 has its negative input and its output tied
together at PEAK. Therefore PEAK follows the voltage applied to the
positive input of U2, which is also the voltage across capacitor
C1. Thus, PEAK is equal to the voltage on capacitor C1 and PEAK is
solidly maintained by the high impedance of op amp U2. Thus PEAK
retains a latched value of the maximum voltage provided at IN. This
PEAK voltage and IN are provided to the input terminals of
comparator U5 for comparison.
[0065] The voltage IN provided by the piezo strain gauge, the
output PEAK of peak detector 82 and the output PEAKCOMP of
comparator U5 are shown for a simulation in FIG. 6. The voltage IN,
the output VALLEY of valley detector 84 and the output VALLEYCOMP
of comparator U6 are shown for actual data in FIG. 7. It is seen
that VALLEY tracks with IN while IN is decreasing toward its
minimum value. Then VALLEY remains at that minimum value while IN
increases from the minimum value.
[0066] Comparators U5, U6 are a type that uses very low power to
check the difference between what was most recently captured as a
peak or valley of the input voltage and the present reading of
piezoelectric strain sensor 83. This comparison is made
continuously by the analog circuit elements, as shown in FIGS. 6
and 7. Once the present reading IN falls a specified amount below
the most recent PEAK, comparator U5 determines that a peak has been
reached; voltage output of comparator U5 drops; and this output of
comparator U5 is fed to awaken microprocessor 86 and to command
microprocessor 86 to sample and record the magnitude of PEAK. This
specified amount is set at a level sufficient to ensure that noise
does not trigger a peak detection. In one embodiment detection
level is hardware programmable. Thus, microprocessor 86 remains in
sleep mode until just the moment it is actually needed to receive
and record peak data. Microprocessor 86 records that PEAK voltage
and goes back to sleep.
[0067] In one experiment a circuit as shown in FIG. 8 was built and
tested. In this schematic voltage source V3 simulates the voltage
IN provided by piezoelectric sensor 83 which in this experiment was
assumed to provide a sinusoidal signal. Voltage source V3 provides
the voltage labeled IN coupled into op amp based peak detection
circuit 80 that includes op amps U1 and U2, as shown in the
schematic of FIG. 8.
[0068] The output of this op amp based peak detection circuit,
labeled PEAK in the schematic is fed to comparator U5. When PEAK is
greater than input signal IN from piezoelectric sensor 83 and the
difference between PEAK and IN is greater than a pre-specified
fixed amount, output PEAKCOMP of comparator U5 changes state
indicating that a peak was detected, as shown in FIGS. 6 and 7.
This state change is used to "wake up" sleeping microprocessor 86.
Once awake, microprocessor 86 samples the voltage on the PEAK line
and stores the value as a detected peak.
[0069] On the right hand side of the schematic of FIG. 8 a similar
circuit is provided that detects valleys. In this case output
VALLEYCOMP from comparator U6 is used to awaken the microprocessor
to sample the voltage on the VALLEY line and store its value as the
detected valley voltage.
[0070] Once a peak or valley is detected, the peak or valley
detector is reset by the microprocessor by applying a pulse to the
base of the transistor Q1 (Peak) or Q2 (valley). Turning on
transistor Q1 allows the voltage on C1 to discharge through R1, and
Q1, and that causes the voltage on PEAK to discharge through R2,
D1, D3, R1, and Q1. Similarly turning on Q2 allows the voltage on
C2 to discharge through Q2 and R5, and that causes allows the
negative voltage on VALLEY to discharge through R4, D2, D4, Q2, and
R5.
[0071] Peak and valley indicator circuits 80, 88 provide digital
signals PEAKCOMP and VALLEYCOMP that drive separate interrupt lines
on microprocessor 86. Each interrupt wakes microprocessor 86 from
an extremely low power sleep mode state. Having a separate
interrupt line for the peak and the valley interrupts facilitates
discrimination of peaks from valleys which facilitates rainflow
analysis of the data.
[0072] By only waking microprocessor 86 to sample the one data
point when each peak is reached and the one data point when each
valley is reached while avoiding waking processor 86 to record data
at other points in between, a tremendous amount of power is saved
as compared with sampling at a high data rate and analyzing the
stored data to detect the peaks and valleys. The power savings is
proportional to the ratio of the expected number of peaks per
second to the sample rate that would otherwise be required to
collect data without a peak detection circuit, such as the one
shown in FIG. 8.
[0073] Since op amps U1, U2, U3, and U4 each draw less than one
microamp of current and since comparator U5 and U6 also draw less
than one microamp, since Q1 and Q2 are both off except to clear
PEAK and VALLEY for a short time, and since IN is provided by
piezoelectric sensor 83, entire circuit 80, 88 draws little
power.
[0074] Current for peak and valley detector circuit 80, 88 of FIG.
8 is less than 4 microamps. Because power is generated by
piezoelectric sensor 83, and no power is consumed for activating
piezoelectric sensor 83 for its measurements, circuit 80, 88 allows
continuous detection of the dynamic waveform provided by
piezoelectric sensor 83, and it is not bandwidth limited. The
present applicants found that power consumption is approximately 75
times less than if a static strain gauge sampled at 500 Hz and
detected the peaks and valleys from the wave forms using firmware.
Because the embodiment consumes no power for continuously tracking
piezoelectric sensor 83 and because microprocessor 86 samples only
once for each peak and each valley, an ultra low power tag 28 is
enabled that can perform embedded rainflow analysis on an
individual component.
[0075] The combination of a self-generating piezoelectric patch
along with nano-power operational amplifiers and comparators
provides for a system that accurately tracks dynamic strains with a
total system power consumption that is lower than 5 microamps.
[0076] While this work focused mainly on piezoelectric strain
sensors, the circuit will work with any sensor that produces an
analog voltage output. Those that are self-generating could be
substituted to achieve that portion of the energy savings. Thus,
it's benefits are most realized when used with a sensor that is
extremely low power, zero power, or self-generating. The peak
detection circuit would also be effective to provide energy savings
with any sensor that generates a relatively high output voltage
(>100 mV) even if it requires power to operate, such as thin
film or semiconductor strain gauges. For example, it can be used to
determine maximum and minimum values of output voltage from a wide
range of sensors that provide a voltage output, including
conventional strain gauges, torque cells, load cells,
accelerometers, magnetometers, and pressure transducers. Voltage
output can vary continuously or have a pulsed voltage shape.
[0077] For example using the circuit with a load cell allows
detecting the maximum load measured on a bridge. If a car goes over
the bridge a peak load provided by the car can be measured,
allowing the weight of the car and the load on the bridge to be
recorded. If a truck then goes over the bridge another peak load
provided by the truck can be measured, allowing the weight of the
truck and the loading on the bridge to be recorded. The set of peak
loads determined over time as vehicles pass over the bridge is then
used to determine the remaining lifetime of the bridge or to
schedule inspection to determine whether cracks are developing.
[0078] The techniques for achieving low power consumption also
enable the use of small, low profile, energy harvesters as the
primary power source. They also enable batteries to be used where
such low power is drawn that the battery provides power for almost
as many hours as the battery's normal shelf life.
[0079] The present applicants also provided an embodiment that
includes a regular resistive strain gauge in combination with the
piezoelectric strain gauges. The resistive strain gauges provide
the static load that escapes detection by the piezoelectric strain
gauges. However, unlike the piezoelectric strain gauges, resistive
strain gauges do not generate their own voltages when subjected to
strain. When a current from an external power supply is applied the
magnitude of the voltage drop measured across the resistive strain
gauges is proportional to the strain experienced by the part to
which they are attached. Thus, resistive strain gauges consume
energy. In one embodiment, resistive strain gauges are configured
in a Wheatstone Bridge arrangement to minimize temperature
effects.
[0080] The present applicants recognized that data from the
piezoelectric strain gauges could also be used to set the timing
for operation of the resistive strain gauges so they are also only
drawing current and consuming power just when most needed. For
example, the resistive strain gauges may be set to provide a
measurement at each peak as determined by the piezoelectric strain
gauges. When the microprocessor is "woken up" by the digital
interrupt signal, signifying a peak or valley, it would command
sampling of the DC sensor by turning on provision of power to the
circuitry for sampling the resistive strain gauges. It would then
wait for the circuitry to settle and sample the output of the DC
sensor and circuitry and record the value. Then the microprocessor
would turn off the circuitry, go back to sleep mode, and wait until
the next interrupt occurs. Circuitry for sampling the resistive
strain gauges is shown in the '777 application, incorporated herein
by reference.
[0081] Structures that could be instrumented with
strain/load/moment measurement sensors and that use the peak/valley
detection circuits to save power include: engine drive shafts,
gearbox shafts, spinning gears, generator shafts, rotating wind
turbine blades, rotating helicopter blades, rotating helicopter
structural components, sporting equipment (bats, clubs, racquets),
Handheld tools (such torque wrenches), instrumented bolts,
car/truck/aircraft tires, car/truck/aircraft wheels, earth moving
equipment, mining machines, milling machines and rotating cutters
used for cutting metals/wood/plastics/ceramics, aircraft landing
gear, aircraft structural bolts and shear pins, drill string in oil
exploration, oil rig platforms, pipelines (on land and undersea),
moving platforms/conveyances for mass production, implanted medical
devices, such as cardiac stents (with pressure sensors), orthopedic
implants with embedded strain/load/moment sensors, and wearable
sensors such as knee braces and accelerometers to monitor
human/animal range of motion and/or levels of activity.
[0082] For example, a torque wrench, weigh scale, or smart
suspension that includes the strain/load/moment measurement sensors
and that use the peak detection circuit could have an output that
provides the peak torque, weight, or force measurement. Providing
this output to the non-volatile display would make a self powered
torque wrench, weigh scale or suspension.
[0083] While the disclosed methods and systems have been shown and
described in connection with illustrated embodiments, various
changes may be made therein without departing from the spirit and
scope of the invention as defined in the appended claims.
* * * * *
References