Source: http://www.google.com/patents/US20080036617?dq=5,963,646
Timestamp: 2014-03-15 16:43:26
Document Index: 560352244

Matched Legal Cases: ['art.\n6', 'art.\n50', 'art.\n51', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'Application No. 60', 'arts1', 'Application No. 60']

Patent US20080036617 - Energy harvesting, wireless structural health monitoring system - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsA method of maintaining a structure includes providing a structure having a component subject to failure. A sensor, a memory and an energy harvesting device are mounted on the structure. The sensor is used and data derived from the sensor logged in the memory, wherein the memory is powered solely with...http://www.google.com/patents/US20080036617?utm_source=gb-gplus-sharePatent US20080036617 - Energy harvesting, wireless structural health monitoring systemAdvanced Patent SearchPublication numberUS20080036617 A1Publication typeApplicationApplication numberUS 11/518,777Publication dateFeb 14, 2008Filing dateSep 11, 2006Priority dateSep 9, 2005Also published asUS7719416, US8638217, US20100164711, US20110285527Publication number11518777, 518777, US 2008/0036617 A1, US 2008/036617 A1, US 20080036617 A1, US 20080036617A1, US 2008036617 A1, US 2008036617A1, US-A1-20080036617, US-A1-2008036617, US2008/0036617A1, US2008/036617A1, US20080036617 A1, US20080036617A1, US2008036617 A1, US2008036617A1InventorsSteven W. Arms, Chris Pruyn Townsend, David Lawrence Churchill, Michael John HamelOriginal AssigneeArms Steven W, Chris Pruyn Townsend, David Lawrence Churchill, Michael John HamelExport CitationBiBTeX, EndNote, RefManReferenced by (33), Classifications (13), Legal Events (3) External Links: USPTO, USPTO Assignment, EspacenetEnergy harvesting, wireless structural health monitoring systemUS 20080036617 A1Abstract A method of maintaining a structure includes providing a structure having a component subject to failure. A sensor, a memory and an energy harvesting device are mounted on the structure. The sensor is used and data derived from the sensor logged in the memory, wherein the memory is powered solely with energy derived from the energy harvesting device. The component is replaced if information in the memory shows that the component was subject to damaging usage.
1. A method of maintaining a structure comprising,
a. providing a structure having a component subject to component failure; b. mounting a sensor, a memory and an energy harvesting device on the structure; c. using said sensor and logging data derived from said sensor in said memory, wherein said memory is powered solely with energy derived from said energy harvesting device; and d. replacing said component if information in said memory shows that said component was subject to damaging usage. 2. A structure as recited in claim 1, wherein said structure comprises a vehicle.
3. A structure as recited in claim 2, wherein said vehicle comprises an aircraft.
4. A structure as recited in claim 3, wherein said aircraft comprises a helicopter.
5. A structure as recited in claim 1, wherein said component comprises a rotating part.
6. A structure as recited in claim 5, wherein said component comprises a helicopter pitch link.
7. A structure as recited in claim 1, wherein said sensor includes at least one from the group including a strain gauge and a piezoelectric transducer.
8. A structure as recited in claim 7, further comprising providing a programmable triaxial strain gauge signal conditioner with integral self calibration.
10. A structure as recited in claim 9, further comprising providing a processor.
11. A structure as recited in claim 10, wherein said processor is connected for controlling operation of said wireless communication device.
12. A structure as recited in claim 10, further comprising providing a multiplexer connected to provide data derived from a plurality of sensors to said processor.
13. A method of operating a system as recited in claim 9, further comprising using said processor to perform calculations and further comprising transmitting results of said calculations.
14. A structure as recited in claim 1, wherein said memory includes a volatile memory portion and a non-volatile memory portion.
15. A structure as recited in claim 1, further comprising providing data directly from said sensor to said volatile memory portion and then transferring said data to said non-volatile memory.
16. A structure as recited in claim 1, further comprising providing a low power time keeper and providing a periodic signal to said processor from said low power time keeper for waking said processor from sleep mode.
17. A method of operating a system as recited in claim 16, wherein power to said processor is turned off during time between said periodic signals.
19. A method of operating a system as recited in claim 18, further comprising buffering data acquired in said burst mode sampling before transmitting said data on said wireless communication device.
21. A method of operating a system as recited in claim 1, further comprising mounting a wireless communications device to the structure and transmitting data derived from said sensor with said wireless communications device, wherein all power for operating said wireless communications device is derived from said energy harvesting device.
22. A method of operating a system as recited in claim 21, wherein said wireless communication device includes an 802.15.4 transceiver.
23. A method of operating a system as recited in claim 1, further comprising providing a wired network for connecting sensors for logging to said memory.
24. A method of operating a system as recited in claim 1, further comprising wirelessly connecting sensors for logging data to said memory.
27. A method of operating a system as recited in claim 1, further comprising providing encryption to said information before transmitting.
31. A method as recited in claim 1, further comprising a rechargeable battery connected for recharging from said energy harvesting device.
32. A method of operating a system as recited in claim 1, wherein said damaging usage includes a load exceeding a threshold.
33. A method of operating a system as recited in claim 1, wherein said damaging usage includes fatigue inducing cyclic loading.
34. A method of operating a structure comprising:
a. providing a structure having a component subject to component failure; b. mounting a sensor module to said structure for measuring a parameter related to component failure, wherein said sensor module includes a sensor, a wireless communication device and an energy harvesting device; c. acquiring data with said sensor; d. providing information derived from said data to said wireless communication device; e. powering said wireless communications device solely with energy derived from said energy harvesting device; f. transmitting said information with said wireless communication device; g. using said information to adjust operation of said structure so as to avoid damaging usage. 35. A method of operating a system as recited in claim 34, further comprising providing a warning if said information shows that said component is subject to damaging usage.
36. A method of operating a system as recited in claim 34, wherein said damaging usage includes a load exceeding a threshold.
37. A method of operating a system as recited in claim 34, wherein said damaging usage includes fatigue inducing cyclic loading.
38. A method of operating a system as recited in claim 34, further comprising using said information to set a time for maintaining said structure.
39. A method of operating a structure comprising,
a. providing a structure having a component subject to component failure; b. mounting a sensor, a memory and an energy harvesting device on the structure; c. using said sensor and logging data derived from said sensor in said memory, wherein said memory is powered solely with energy derived from said energy harvesting device; and d. using information in said memory to adjust operation of said structure so as to avoid damaging usage. 40. A system comprising, a network of sensor nodes wherein each said sensor node includes a sensor, a processor, a memory, a low power time keeper, a wireless communication device and an energy harvesting device, said processor connected to receive data derived from said sensor, said memory connected for storing data derived from said sensor, said low power time keeper connected to periodically provide a signal to wake said processor from a sleep mode, said wireless communication device connected for communicating data derived from said sensor, said energy harvesting device connected for harvesting energy to power said processor, said memory, and said wireless communications device.
a. providing a sensor node including a sensor, a processor, a memory, a low power time keeper, a wireless communication device and an energy harvesting device; b. providing a signal from said low power time keeper to the processor to power up said processor from a powered off or a low powered condition at predetermined intervals of time; c. using energy derived from said energy harvesting device to provide power for operating at least one from the group consisting of said processor, said memory, and said wireless communications device; d. providing data derived from said sensor to said processor; e. storing data derived from said sensor in said memory; and f. using said wireless communication device to externally communicate data derived from said sensor. 42. A method of operating a system as recited in claim 41, wherein power is turned off between said intervals of time.
43. A method of operating a system as recited in claim 41, wherein said sensor node is mounted on a structure, further comprising using data derived from said sensor to set a time for maintaining said structure.
44. A structure, comprising a wireless instrumented structural component including a first sensor, a second sensor, a processor, a transmitter, and an energy harvesting device, wherein said first sensor is for measuring a first property related to structural load in said structural component, said second sensor is for measuring a second property related to structural load in said structural component, wherein said first property differs from said second property, wherein said transmitter is connected to provide load data for said structural component, wherein all power for operating said transmitter is derived from said energy harvesting device, wherein said processor is connected to receive an output derived from said second sensor for verifying operation of said first sensor.
45. A structure as recited in claim 44, wherein said first sensor includes a strain gauge.
46. A structure as recited in claim 44, wherein said second sensor includes a piezoelectric transducer.
47. A structure as recited in claim 46, wherein said energy harvesting device includes said piezoelectric transducer.
48. A method as recited in claim 44, further comprising a rechargeable battery connected for recharging from said energy harvesting device.
49. A structure as recited in claim 44, wherein said structural component comprises an aircraft part.
50. A structure as recited in claim 44, wherein said structural component comprises a helicopter part.
51. A method of using a structure, comprising
a. providing a wireless instrumented structural component mounted to the structure, said wireless instrumented structural component including a first sensor, a second sensor, a transmitter, and an energy harvesting device, said first sensor for measuring a first property related to structural load in said structural component, said second sensor for measuring a second property related to structural load in said structural component, wherein said first property differs from said second property; b. comparing data from said first sensor with data from said second sensor to determine that said first sensor is operating properly; c. providing energy from said energy harvesting device wherein all power for operating said transmitter is derived from said energy harvesting device; and d. wirelessly transmitting data about structural load in said structural component. 52. A method as recited in claim 51, wherein said first sensor comprises a strain gauge and said second sensor comprises a piezoelectric transducer.
53. A method as recited in claim 52, wherein said comparing includes a ratio of strain gauge amplitude with piezoelectric transducer amplitude.
54. A method as recited in claim 51, wherein said strain gauge amplitude is a peak to peak amplitude and wherein said piezoelectric transducer amplitude is a peak to peak amplitude.
55. A method as recited in claim 51, further comprising providing a moisture sensor, further comprising using output of said moisture sensor to provide a check of said strain gauge data.
56. A method as recited in claim 51, further comprising providing an energy storage device connected for storing energy from said energy harvesting device.
57. A method as recited in claim 51, further comprising measuring charge on said energy storage device.
58. A method as recited in claim 51, further comprising detecting a problem with said energy harvesting device from said charge on said energy storage device.
59. A method as recited in claim 51, wherein said second sensor includes said energy harvesting device.
60. A method as recited in claim 51, further comprising providing a receiving device for receiving said data, wherein said receiving device receives data from a plurality of said wireless instrumented structural components mounted to the structure.
61. A method as recited in claim 60, further comprising determining usage of the structure from said received data.
62. A method as recited in claim 60, wherein said receiving device is located on the structure.
63. A method as recited in claim 51, further comprising providing a rechargeable battery, and charging said rechargeable battery with said energy harvesting device.
64. A sensing device, comprising an inertial sensor and a GPS, said inertial sensor integrated with said GPS wherein all power for operation of said inertial sensor is provided from energy harvesting.
65. A sensing device as recited in claim 64 wherein said inertial sensor includes a microprocessor, wherein said processor uses data from said GPS to correct data from said inertial sensor.
66. A sensing system comprising a base station, a first plurality of sensors, and a second plurality of sensors, wherein said first plurality of sensors are connected to said base station on a wired network and wherein said second plurality of sensors are connected to said base station on a wireless network.
67. A sensing system as recited in claim 66, wherein said wired network includes a CAN bus.
68. A sensing system as recited in claim 66, wherein said wireless network includes an 802.15.4 network.
69. A method of estimating time before failure of a component of a structure, comprising:
a. providing the structure having the component; b. instrumenting said structure with a sensor and a memory, said sensor to measure a parameter related to the structure, said memory for logging data derived from said sensor; c. providing an energy harvesting device on the structure, said energy harvesting device connected to provide all power for powering logging data; d. providing a model of the component subject to failure; e. entering information derived from said data into said model; and f. using said model and said information to estimate a parameter related to time before failure of said component. 70. A method as recited in claim 69, further comprising providing maintenance based on said estimated time.
71. A method as recited in claim 69, wherein said parameter related to the structure includes a parameter related to input load experienced by the structure and wherein said using said mathematical model involves estimating a parameter related to time before structural component fatigue.
72. A method as recited in claim 69, further comprising instrumenting said structure with a plurality of said sensors.
73. A method as recited in claim 69, further comprising instrumenting said structure with a plurality of said sensors.
74. A method as recited in claim 69, wherein said sensor includes a strain sensor.
75. A method as recited in claim 74, wherein said model includes empirical data relating strain and cycles to failure.
76. A method as recited in claim 74, wherein said model includes an algorithm relating strain in one location to strain in another location.
77. A method as recited in claim 74, wherein said model relates strain to load.
78. A method as recited in claim 77, wherein said model includes an algorithm relating load in one location to load in another location.
79. A method as recited in claim 69, further comprising a wireless transmitter connected for transmitting at least one from the group consisting of said data and said information.
80. A method as recited in claim 79, wherein said data includes strain.
81. A method as recited in claim 80, wherein said data includes time when a data point was logged.
82. A method as recited in claim 79, wherein said information includes peaks and valleys of cycles of strain.
83. A method of collecting information about a structure, comprising:
a. providing an instrumented component including a sensor, a memory, and an energy harvesting device, wherein said component is an integral part of a structure when installed in the structure, wherein said instrumented component includes packaging to protect said sensor, said memory, and said energy harvesting device; b. installing said component in the structure; and c. using energy derived from said energy harvesting device to provide power for logging data in said memory. 84. A method as recited in claim 83, wherein said packaging provides environmental protection.
85. A method as recited in claim 83, wherein said packaging provides shielding from electromagnetic field.
86. A method as recited in claim 85, further comprising an antenna extending outside said shielding and inside said environmental protection.
87. A method of maintaining a structure comprising,
a. providing a structure having a component subject to component failure; b. mounting a sensor, a memory and an energy harvesting device on the structure; c. using said sensor and logging data derived from said sensor in said memory, wherein said memory is powered solely with energy derived from said energy harvesting device; and d. logging data at a rate depending on amount of energy harvested by said energy harvesting device. 88. A method as recited in claim 87, wherein said rate depends on magnitude of strain experienced by the structure.
RELATED APPLICATIONS AND PRIORITY This application claims priority of Provisional Patent Application No. 60/715,987, filed Sep. 9, 2005 and Provisional Patent Application No. 60/798,570, filed May 8, 2006, both of which are incorporated herein by reference.
�Robotic system for powering and interrogating sensors,� U.S. patent application Ser. No. 10/379,224 to S. W. Arms et al, filed Mar. 5, 2003 (�the '9224 application�), docket number 115-004.
�Wireless Vibrating Strain Gauge for Smart Civil Structures,� U.S. patent application Ser. No. 11/431,194 to M. Hamel, filed May 10, 2006 (�the '194 application�), docket number 115-023.
�Sensor Powered Event Logger,� U.S. Provisional Patent Application No. 60/753,481 to D. L. Churchill et al, filed Dec. 22, 2005, (�the '481 application�) docket number 115-034.
�Slotted Bean Piezoelectric Composite,� U.S. Provisional Patent Application No. 60/739,976 to D. L. Churchill, filed Nov. 23, 2005, (�the '976 application�) docket number 115-022.
�Method for Integrating an energy harvesting circuit into a PZ element's electrodes,� U.S. Provisional Patent Application No. 60/753,679 to D. L. Churchill et al, filed Dec. 21, 2005, (�the '679 application�) docket number 115-035.
�Method for Integrating an energy harvesting circuit into a PZ element's electrodes,� U.S. Provisional Patent Application No. 60/762,632 to D. L. Churchill et al, filed Jan. 26, 2006, (�the '632 application�) docket number 115-035a.
�Structural Damage Detection and Analysis System,� U.S. Provisional Patent Application No. 60/729,166 to M. Hamel, filed Oct. 21, 2005, (�the '166 application�) docket number 115-036.
�Energy Harvesting for Wireless Sensor Operation and Data Transmission,� U.S. Pat. No. 7,081,693 to M. Hamel et al., filed Mar. 5, 2003 (�the '693 patent�), docket number 115-008.
�Shaft Mounted Energy Harvesting for Wireless Sensor Operation and Data Transmission,� U.S. patent application Ser. No. 10/769,642 to S. W. Arms et al., filed Jan. 31, 2004 (�the '642 application�), docket number 115-014.
�Wireless Sensor System,� U.S. patent application Ser. No. 11/084,541 to C. P. Townsend et al., filed Mar. 18, 2005 (�the '541 application�), docket number 115-016.
�Strain Gauge with Moisture Barrier and Self-Testing Circuit,� U.S. patent application Ser. No. 11/091,224, to S. W. Arms et al., filed Mar. 28, 2005 (�the '1224 application�), docket number 115-017.
�Miniature Stimulating and Sensing System,� U.S. patent application Ser. No. 11/368,731 to J. C. Robb et al., filed Mar. 6, 2006 (�the '731 application�), docket number 115-028.
�Miniaturized Wireless Inertial Sensing System,� U.S. patent application Ser. No. 11/446,637 to D. L. Churchill et al., filed Jun. 5, 2006 (�the '637 application�), docket number 115-029.
�Data Collection and Storage Device,� U.S. patent application Ser. No. 09/731,066 to C. P. Townsend et al., filed Dec. 6, 2000 (�the '066 application�), docket number 1024-034.
�Circuit for Compensation for Time Variation of Temperature in an Inductive Sensor,� Reissue U.S. patent application Ser. No. 11/320,559 to C. P. Townsend et al., filed Dec. 28, 2005 (�the '559 application�), docket number 1024-038.
�System for Remote Powering and Communication with a Network of Addressable Multichannel Sensing Modules,� U.S. Pat. No. 6,529,127 C. P. Townsend et al., filed Jul. 11, 1998 (�the '127 patent�), docket number 1024-041.
�Solid State Orientation Sensor with 360 Degree Measurement Capability,� U.S. patent application Ser. No. 10/447,384 to C. P. Townsend et al., filed May 2003 (�the '384 application�), docket number 1024-045.
�Posture and Body Movement Measuring System,� U.S. Pat. No. 6,834,436 to C. P. Townsend et al., filed Feb. 23, 2002 (�the '436 patent�), docket number 115-002.
FIELD This patent application generally relates to a system for structural health monitoring and for health usage monitoring. It also relates to sensor devices and to networks of sensor devices with wireless communication links. More particularly it relates to an energy harvesting system for providing power for monitoring structural health and for transmitting data wirelessly.
BACKGROUND Sensors, signal conditioners, processors, and digital wireless radio frequency (RF) links continue to become smaller, consume less power, and include higher levels of integration. The combination of these elements can provide sensing, acquisition, storage, and reporting functions in very small packages. Such sensing devices have been linked in wireless networks as described in the '127, patent and in the '9224, '194, '481, '541, '731, '637, '066, and '436 applications.
Networks of intelligent sensors have been described in a paper, �Intelligent Sensor Nodes Enable a New Generation of Machinery Diagnostics and Prognostics, New Frontiers in Integrated Diagnostics and Prognostics,� by F. M. Discenzo, K. A. Loparo, D. Chung, A. Twarowsk, 55th Meeting of the Society for Machinery Failure Prevention Technology, April 2001, Virginia Beach.
Most prior wireless structural monitoring systems have relied on continuous power supplied by batteries. For example, a paper �An Advanced Strain Level Counter for Monitoring Aircraft Fatigue�, by Weiss, Instrument Society of America, ASI 72212, 1972, pages 105-108, 1972, described a battery powered inductive strain measurement system, which measured and counted strain levels for aircraft fatigue. The disadvantage of traditional batteries, however, is that they become depleted and must be periodically replaced or recharged. This additional maintenance task adds cost and limits use to accessible locations.
A paper, �Energy Scavenging for wireless Sensor Networks with Special Focus on Vibrations,� by S. Roundy et al., Kluwer Academic Press, 2004, and a paper �Energy Scavenging for Mobile and Wireless Electronics,� Pervasive Computing, by J. A. Paradiso & T. Starner, IEEE CS and IEEE ComSoc, Vol 1536-1268, pp 18-26, 2005, describe various strategies for harvesting or scavenging energy from the environment. These sensing systems can operate truly autonomously because they do not require traditional battery maintenance.
SUMMARY One aspect of the present patent application is a method of maintaining a structure. The method includes providing a structure having a component subject to failure. A sensor, a memory and an energy harvesting device are mounted on the structure. The sensor is used and data derived from the sensor logged in the memory, wherein the memory is powered solely with energy derived from the energy harvesting device. The component is replaced if information in the memory shows that the component was subject to damaging usage.
Another aspect of the present patent application is a method of operating a structure. The method includes providing a structure having a component subject to component failure. The method also includes mounting a sensor module to the structure for measuring a parameter related to component failure, wherein the sensor module includes a sensor, a wireless communication device and an energy harvesting device. Data is acquired with the sensor and information derived from the data is provided to the wireless communication device, the wireless communications device is powered solely with energy derived from the energy harvesting device and the wireless communication device transmits the information. The information is used to adjust operation of the structure so as to avoid damaging usage.
Another aspect of the present patent application is a method of of maintaining a structure. The method includes providing a structure having a component subject to component failure; mounting a sensor, a memory and an energy harvesting device on the structure; using the sensor and logging data derived from the sensor in the memory, wherein the memory is powered solely with energy derived from the energy harvesting device; and logging data at a rate depending on amount of energy harvested by the energy harvesting device.
FIG. 15 a is a cross sectional view of the mounting of the electronics of the present patent application on a helicopter pitch link showing protection from environment and mechanical stress; and
FIG. 15 b is a side view of the pitch link of FIG. 15 a. DETAILED DESCRIPTION Mathematical models, such as finite element models of a structure can be used to provide estimates of time before structural component fatigue. Such estimates are improved when their boundary conditions and input loads are based on actual data obtained during operation of the structure that may be collected by instrumented components mounted on the structural component. Such smart components provide a significant benefit in allowing engineers and owners of vehicles to obtain better estimates of the remaining life of critical components.
A way to power each of the sensor nodes without requiring connection to a wall outlet and without having to periodically replace batteries is also provided. Integrated in each of the sensor nodes can be a device that harvests energy from an available environmental source, such as vibration or strain energy. The integrated energy harvesting wireless sensing nodes in the scaleable, wireless network provide substantial improvement to previously available structural health monitoring systems (SMS).
The system architecture of the present patent application allows for flight tests to be performed with a range of wireless and wired networked sensing nodes. The wireless nodes may be deployed to monitor the loads on the rotating components of helicopters, for example. Wired and wireless nodes may also be used for fatigue monitoring on non-rotating components, such a fixed wing aircraft. Other types of aircraft, land vehicles, and water craft could also benefit from the capability to autonomously track and assess structural damage �on the fly.�
The present applicants found that by providing data logging and data analysis capability on-board, the vehicle becomes �self-aware� and can assess and record severity of its own usage and its usage history. This information can be used for condition based maintenance on every vehicle in a fleet, providing for example, information on the fatigue rates of each vehicle's structure and rotating components. If combined with component tagging and tracking operators and maintenance and repair organizations can use the SMS data obtained from actual severity of usage and actual operating load measurements, as determined using the techniques of the present patent application, to automatically update the status of the life-limited parts1. The information can also be used in health usage monitoring systems (HUMS). 1 El-Bakry, M., Component Tagging & Tracking�An Essential Enabling Technology for Effective �Safe Life� Structural Monitoring, Proceedings of 5th Intl. Workshop on Structural Health Monitoring, Stanford, Calif., Sep. 12-14, 2005
The present applicants have created working prototypes for a wireless network of sensor nodes, each of which harvests energy from available strain energy or vibration energy. The miniature, energy harvesting wireless nodes of the present patent application allow sensors to be located in areas that are currently not instrumented, such as on rotating or moving components as well as in remote, inaccessible areas. The present applicants used both single crystal PZT and PZT fibers in their energy harvesting prototypes. One system uses a tuned flexural element for vibration energy harvesting, while the other system harvests strain energy directly from a vibrating (cyclically straining) composite beam2. In both schemes, applicants demonstrated that sufficient energy could be harvested to power a wireless strain sensor transceiver3. They also adapted their energy harvesting sensor systems for damage tracking on aboard helicopters and demonstrated that the operational strains in the helicopter's control rod (or �pitch link�) generate enough power to allow continuous, wireless operational load monitoring of this critical structure, even during conditions of straight and level flight when the least amount of strain energy is available for harvesting.4 2 Churchill, D. L., Hamel, M. J., Townsend, C. P., Arms, S. W., �Strain Energy Harvesting for Wireless Sensor Networks�, proc. SPIE's 10th Int'l Symposium on Smart Structures & Materials, San Diego, Calif., paper presented March 20033 Arms, S. W., Churchill, D. L., Townsend, C. P., Galbreath, J. H.: �Power Management for Energy Harvesting Wireless Sensors�, proc. SPIE's Symposium on Smart Structures & Materials San Diego, Calif. March 20054 Arms, S. W., Townsend, C. P., Churchill, D. L., Moon, S. M., Phan, N., �Energy Harvesting Wireless Sensors for Helicopter Damage Tracking�, accepted for presentation at AHS 2006, Health & Usage Monitoring Systems (HUMS), Phoenix, Ariz., May 9-11, 2006
Integrated inertial & magnetic sensor triaxial suite 60, called 3DM-GX1�, available from Microstrain, Inc., Williston, Vt. http://microstrain.com/3dm-Ex1.aspx is illustrated in FIG. 2. This 3DM-GX1� device combines three angular rate gyros with three orthogonal DC accelerometers, three orthogonal magnetometers, multiplexer, 16 bit A/D converter, and embedded microcontroller, to output its orientation in dynamic and static environments.
Operating over the full 360 degrees of angular motion on all three axes, 3DM-GX1� provides orientation in matrix, quaternion and Euler formats. The digital serial output can also provide temperature compensated, calibrated data from all nine orthogonal sensors at update rates of 350 Hz.
Networks of 3DM-GX1� nodes can be deployed by using the built-in RS-485 network protocol. Embedded microcontrollers relieve the host system from the burden of orientation calculations, allowing deployment of dozens of 3DM-GX1� nodes with no significant decrease in system throughput.
The miniature electronics modules are designed to support sensing and RF communications at microwatt energy levels. This enables their use with strain and vibration energy harvesting systems the present applicants have demonstrated. The present applicants have also demonstrated wireless sensing nodes that support other sensors, such as conventional strain gauges and thermocouples6. 6 Arms, S. W., Townsend, C. P., Churchill, D. L., Moon, S. M., Phan, N., �Energy Harvesting Wireless Sensors for Helicopter Damage Tracking�, accepted for presentation at AHS 2006, Health & Usage Monitoring Systems (HUMS), Phoenix, Ariz., May 9-11, 2006
The strain gauge nodes are capable of peak valley compression and fatigue calculation using embedded rainflow algorithms7. This versatility allows the wireless sensing network to be tailored to best meet an aircraft's specific monitoring requirements, and facilitates their use on aging aircraft, where it is best not to disturb the existing wiring. Furthermore, the nodes' embedded software may be wirelessly upgraded to allow enhancements to the damage detection algorithms and structural interrogation protocols in the future. 7 Arms, S. W., �Scaleable, Wireless Structural Testing System�, Aerospace Testing Expo 2005 North America, Open Technology Forum, Long Beach, Calif., Nov. 7-11, 2005
−55 to +85
On board temperature
−55 to 85 Degrees C.
Differential sensor inputs
3 bridge sensors inputs
Differential input gains
Differential input offset adjust
mV referred
DC 3.0 V/50 mA
2.450-2.490
Data acquisition resolution
Max data acquisition rate
Data Storage on standard
Power required to maintain
3.1/40
Mechanical dimensions of
Signal Wireless Data Acquisition & Logging of Sensor Data After the signal from sensor 122 has been amplified and filtered, the signal will be acquired using high speed analog to digital converter (ADC) 128 with programmable conversion rates as high as one megasample/second. The output of this converter is stored in memory using direct memory access (DMA), allowing the high speed capability of the ADC to be preserved. For the highest speed acquisition, the data is fed directly into static random access memory (SRAM) for the duration of the test. The use of SRAM is desirable as it supports high speed acquisition at relatively low power. After the test is completed, the data can be transferred to non-volatile flash memory 132 and can be downloaded via a wired or wireless interface at a later time. Alternatively, that data can be transmitted in real time over the wireless IEEE802.15.4 interface.
One embodiment uses a memory chip that integrates one megabyte of SRAM and two megabytes of flash memory into a package that measures approximately 6 mm�8 mm. The 16 bit ADC with DMA is integral to the system microcontroller (C8051F061, Silicon Labs, Austin, Tex.). The sample rate can be programmable by the user from 100 Hz to 1 MHz. The amount of time that the sensor data is acquired by the burst sampling mode can also be programmable by the user. For a triaxial rosette strain gauge and a flash size of 2 Megabyte, the present applicants found that data can be acquired and stored with burst mode sample rates of 100 kHz for up to 3.4 seconds. For a 100 Hz acquisition rate, burst mode can be continued for 3400 seconds (�56 minutes) before memory is filled and data is download.
Triggering and Time Synchronization Triggering data acquisition from the sensors can be through a command over wireless IEEE802.15.4 network 134. For applications that require time synchronization, the trigger packet can include network time synchronization data. For many embedded applications the sensed data acquired by individual structural health monitoring modules can be synchronized in time. Each wireless sensing node module has precision time clock 146 that can be periodically resynchronized over wireless network 134. The wireless synchronization method will support time synchronization between remote wireless sensing node modules 120 to a resolution of better than 1 millisecond.
Testing synchronization can be accomplished by providing the same input to each node 120 of multiple wireless sensing node breadboard nodes using a function generator producing a 10 Hz sine wave. Data acquisition is triggered using the trigger data packet, and data collected and stored locally along with a time stamp for each data point. The time stamp is initialized to zero on detection of the synchronization packet. The data is downloaded, and phase lag and synchronization between channels can be documented. The time stamp can include the calendar date and time. The present applicants found that they could provide this information while maintaining extremely low average quiescent currents.
Micropower Timekeeper & Timed Burst Mode Sampling Capabilities Micropower time keeper 146 is included in the wireless sensing node systems to provide scheduled sampling of sensor data (or scheduled wake up) during conditions of low vibration (or machine downtime). Micropower time keeper 146 (Maxim DS1390, Sunnyvale, Calif.) draws less than 800 na. A small button cell battery may be included to power micropower time keeper 146 to ensure its operation after extended periods of low vibration where energy storage elements may be completely discharged. Thus, timing can be preserved even under such conditions. Alternatively, time can be broadcast to each wireless sensing node. A serial interface for this component for connection to a processor is well known.
(1) The wake up may initiate a �sniff� for the presence of the 802.15.4 carrier. If the carrier is present the wireless sensing node program will cause the system to enter into communication mode. The system can then, depending on the communicated commands, cause one or more of the following to happen; the wireless sensing node system will send previously stored data via the 802.15.4 radio link to the requesting base station, and/or the system will accept and self program new parametric data from the requesting base station which can include parameters for the number of data points to be acquired during each sampling, the sampling rate, how many channels to sample, the interval between sampling sessions or the times of day to sample (scheduled sampling), and new gain or offset parameters for the programmable signal conditioners.
After any of the above sequences are completed, wireless sensing node module 120 will power off the acquisition circuitry and then enter sleep mode itself until the next scheduled interrupt occurs. During sleep mode the energy storage elements shall be background recharged by energy harvesting system 148.
b) �burst� mode sampling and storage at very high sample rates (up to 1 MHz) at scheduled time intervals, to be downloaded at a later time.
For an application such as the pitch link, strain readings can easily be converted to loads through a prior calibration step applying static loads to the the pitch link and measuring its strain response. A mathematical relationship between strains and loads can also be used.
Energy Harvesting and Background Recharging for Wireless Sensing Modules Vibration or strain energy may also be harvested using low cost piezoelectric (PZT) materials. A custom, tapered mechanical structure described in commonly assigned copending U.S. Provisional Patent Application No. 60/739,976, �Slotted Beam Piezoelectric Composite,� to David Churchill, incorporated herein by reference, efficiently converts low level vibrations to high strains, and serves as the carrier for the PZT material that converts the strains into electricity.
The harvester's resonant frequency can be tuned in the field using external adjustment 150 by moving location of the proof mass or by adjusting a magnetic field in proximity to a ferrous material or a permanent magnet located on the mass, as shown in FIG. 9 and as described in the '976 application. The PZT material was epoxy bonded to the tapered flexure element, which provided a uniform strain field to the PZT material as described and illustrated in the '976 application. During tests of this element, a strain gauge was bonded to the PZT material to facilitate documentation of the strain levels that were present within the PZT. Adjustment of the (240 gram) proof mass location relative to the fixed end of the flexure allowed us to mechanically �tune� the harvester's resonant frequency. Resonance could be readily adjusted from about 38 Hz to about 55 Hz.
U = m � ζ   e � A 2 � ( ω   n ω ) � ω 3 [ ( ω   n ω ) 2 - 1 ] 2 + [ 2 � ( ζ   m + ζ   e ) � ω   n ω ] 2 where m is the proof mass, ζe is the electrical damping, ζm is the mechanical damping, and ωn is the natural frequency of the harvester's resonant structure. Thus, the power output is proportional to the magnitude of the proof mass and to the square of the vibration amplitude.
The electrochemical battery stack was background charged when sufficient charge had been accumulated on the input capacitor8. In a laboratory test of vibration energy harvesting simulating low level vibrations that might be found on a ship or aircraft, the PZT harvester produced from 2.2 to 2.8 milliwatts of output power at input vibration levels of only 0.1 to 0.13 G's and at relatively low strain levels (150 to 200 microstrain). At these low vibration levels the vibrations were barely perceptible to human touch. FIG. 10 plots strain input vs. power output for both resonant flexure and non-resonant harvester types. Our wireless relative humidity and temperature demonstration node, programmed for a one second wireless update rate, may be powered perpetually with about 100 milliG's of input vibration energy. 8 Arms, S. W., Townsend, C. P., Hamel, M. J., Churchill, D. L., �Vibration Energy Harvesting for Wireless Health Monitoring Sensors�, Proceedings Structural Health Monitoring 2005, pages 1437-1442, Stanford, Calif., September 2005
A charge controller circuit was demonstrated that periodically checks the state of the battery and, if appropriate, disconnects the load from the battery, thereby protecting the battery from damage which can be sustained if the battery voltage drops below a prescribed voltage (2.0 volts). This was accomplished by using a micropower comparator and a low �on� resistance switch. The quiescent current of this switch was less then 350 nanoamperes on average.
Inertial Sensing Suite Integrated with GPS In one embodiment, a micro-electromechanical system (MEMS) inertial and magnetic sensing suite, called 3DM-GX1�, is combined with a Global Positioning System (GPS) unit & antenna as shown in FIGS. 3, 4, and 8. 3DM-GX1 combines three angular rate sensors with three orthogonal DC accelerometers, three orthogonal magnetometers, a multiplexer, a 16 bit AID converter, and an embedded microcontroller, to output its orientation in dynamic and static environments. Operating over the full 360 degrees of angular motion on all three axes, 3DM-GX1 provides orientation in matrix, quaternion and Euler formats. The digital serial output can also provide temperature compensated, calibrated data from all nine orthogonal sensors at update rates of 350 Hz. Output modes and software filter parameters are user programmable. Programmed parameters and calibration data are stored in nonvolatile memory. Further description is provided in the '384 and '637 applications.
Inertial & Magnetic MEMS Sensing Suite 3DM-GX1 includes sensors 156 connected to signal conditioners and multiplexer 158 for feeding data to microprocessor 160 which can run embedded software algorithms, as shown in FIG. 11 to compute orientation in Euler, matrix, and quaternion formats on board. Microprocessor 160 is able to store data on associated EEPROM 162. Also stored there are sensor calibration coefficients, orthogonality compensation coefficients, temperature compensation coefficients, and digital filter parameters. The microprocessor can calculate Euler angles, quaternion and matrix as shown in box 164 and can provide output through RS 232, RS 485, or CAN bus 166 to computer or host system 168 or to multidrop RS 485 network 170. It can also provide 4 channel programmable analog outputs.
3DM-GX1 Detailed Specifications Parameter
Range: Pitch, Roll, Yaw (�)
360, all axes
Matrix & Quatemion Modes
+/−90, +/−180, +/−180
Euler Angles Mode
Static Accuracy (�)
Dynamic Accuracy (� rms)
Typical, application dependent
Repeatability (�)
Resolution (�)
Turn on time (sec)
4 channels, user configurable
Update Rate (Hz maximum)
Orientation outputs
65 � 90 � 25
42 � 40 � 15
5.2 to 12 DC
−40� C. to +70
−40� C. to +85
Vibration (g rms)
20-700 Hz, white
Operational Shock (g)
10 msec halfsine
Survival Shock (g)
RS-485 networking optional
Serial Communications speed (kBaud)
19.2, 38.4, 115.2
Range (�/sec)
+/−300
Turn-on to turn-on repeatability (�/sec)
25� C. fixed temperature
In-Run stability, fixed temp. (�/sec)
After 15 minute warm up
In-Run stability, over temp. (�/sec)
Over −40� C. to +70� C. range
Short term stability (�/sec)
15 second Allan variance floor
Angle random walk, noise (�/√hour)
Allan variance method
Scale Factor Error (%)
Resolution (�/sec)
G-sensitivity (�/sec/g)
Std w/ g-sensitivity compensation
Alignment (�)
Std w/ alignment compensation
−3 dB Nominal
Turn-on to turn-on repeatability (mg)
In-Run stability, over temp. (mg)
Short term stability (mg)
Noise (mg/√Hz rms)
+/−1.2
In-Run stability, over temp. (mGauss)
Noise (mGauss/√Hz)
GPS Enhancement Commercially available GPS units and antennas are available from a wide variety of sources. GPS antenna with external mount for external mount on an aircraft are environmentally sealed and are available from Navtech, Model 12700 Antenna.
GPS data is used to compensate for inertial errors that can occur during sustained aircraft turns. GPS input is relatively low cost to implement (from a parts perspective), and provides benefits, including very precise velocity data, ground speed, altitude, latitude, longitude, and timing information9. The velocity data is used to correct 3DM-GX1 orientation errors due to centrifugal forces. 9 El-Sheimy, N: Report on Kinematic and Integrated Positioning Systems, FIG XXII International Congress, Washington, D.C. USA, Apr. 19-26 2002 (htt)://www.fig.net/nub/fig�2002/TS5-1/TS5�1_elsheimv.pdf)
Microprocessor engine DSP 104 can be a low power PC 104 compatible single board computer based on the Intel� IXP425 XScale� network processor, as shown in FIG. 12. The IXP425 is an implementation of the ARM compliant, Intel XScale microarchitecture combined with communication peripherals including, 2 high speed Ethernet MACs, hardware accelerated cryptography, 2 high speed serial ports, a local PCI interface and DMA controller. Table III provides a set of specifications for the gateway.
Microprocessor Engine
PC104 IXP425
DES, 3DES, AES, with
Hardwired Bus Interface
Alternate Hardwired Network
Ethernet (TCP/IP)/
Wireless Sensor RF Data
Power (Full operating mode)
Power (Sleep Mode)
PC/104 from factor
3.8″ � 3.6″
Timing & Communications Protocols Two communication interfaces allow transmission of real time sensor data or downloading of previously recorded data. The first communications interface is hardwired controller area network (CAN) bus 90. This CAN bus may support the inertial sensing suite (ISS) interface to base station 102. Alternatively a low power wireless interface can be used to support the many applications where it is difficult to impossible to embed lead wires for data communication from the system under test. A low power IEEE802.15.4 bidirectional direct sequence spread spectrum radio link 108 and an embedded protocol stack that can support ad hoc multi-hop communications may be used in each of the wireless sensing nodes for these applications.
CAN Bus Hard-Wired Network The wired bus network uses automotive grade, commercial off the shelf (COTS) CAN transceivers to provide a multidrop distributed communication bus that allows up two 32 individual inertial sensing nodes to be located on the network. The CAN bus is a broadcast type of bus. This means that all nodes can �hear� all transmissions. There is no way to send a message to just a specific node; all nodes will invariably pick up all traffic.
The CAN hardware, however, provides local hardware filtering so that each node may react only to messages intended for the particular node. The network uses a 2 wire communication topology with a maximum data rate of 1.0 Mbps. The CAN bus may be converted into the aircraft standard 1553 network protocol in the future. Note that when the wired bus is used for the hardware communications architecture, then power for these sensing nodes would also be provided on the network, which eliminates the need for energy harvesting on these nodes. The CAN network can also support future nodes, which may include both sensing and actuation capabilities. Actuators can be used in concert with piezoelectric materials for active damping and/or for providing signal for non-destructive material testing (such as acoustic crack detection), as described in commonly assigned copending U.S. patent application Ser. No. 11/368,731, �Miniature Stimulating and Sensing System,� (�the '731 application�) to John Robb et al, filed Mar. 6, 2006, incorporated herein by reference. Actuators may also be used for damping vibration.
IEEE802.15.4 Wireless Network The IEEE802.15.4 network is a standard for low power data communication networks. These radio systems use extremely low power relative to radio networks such as Bluetooth (IEEE802.15.1) and WiFi (IEEE802.11), and such are very suitable for use in distributed sensor network applications. The 802.15.4 radios use low power (1 mW) direct sequence spread spectrum (DSSS) radios at 2.4 GHz for the physical communication layer. The radio standard also incorporates AES128 data encryption standard for its security layer, which allows for secure transfer of over the air data. The over the air data transfer rate is 250 kbps which is adequate for transfer of stored data in this application.
The 802.15.4 standard does not specify the network topology to be used. However, since the radios are very low power, mesh network topologies, as shown in FIG. 13, are often implemented using this technology. A mesh network allows for any node in the network to transmit to any other node in the network within its radio transmission range. This allows for what is known as multihop communications, that is, if node 180 a wants to send a message to another node 180 e that is out of radio communications range, it can use an intermediate nodes 180 b, 180 c, and 180 d to forward the message to the desired node 180 e. This network topology has the advantage of redundancy and scalability. If an individual node fails, such as 180 b, a remote node such as 180 a can still communicate to any other node in its range, which in turn, can forward the message to the desired location by routing, for example, through nodes 180 f and 180 g. In addition the range of the network is not necessarily limited by the range in between single nodes, it can simply be extended by adding more nodes to the system. This multihop capability can be used in embedded instrumentation applications, where radio range can be degraded due to fading losses and multipath interference when radios are embedded in equipment.
Alternatively, when higher packet rates are desired, a star network topology is more desirable, as shown in FIG. 13. The wireless nodes of the present patent application will support both a star and mesh network topology. FIG. 13 shows a combination of star and mesh topology. Single hop node 182 a and 182 b communicate only to multihop node 180 a for example. The specific use will determine which topology is most appropriate.
System Time Synchronization With multiple physical interfaces for communications employed in the same network, time synchronization is maintained between all nodes on the network. Maintaining time synchronization between the gateway and the CAN inertial nodes is relatively simple, as the busses are wired together and synchronization can be easily maintained using the wired bus. However, the wireless network nodes are more difficult to keep synchronized because they are very low power devices that cannot afford the energy to constantly listen for a synchronization packet. Therefore, it is desirable to only periodically send a timing packet to the wireless node for synchronization. For this to be effective, a highly stable local time reference is provided at each wireless node. The present applicants found that a stable real time clock with temperature compensation for the clock achieves a timing stability of approximately 2 parts per million (ppm). A 2 ppm error would result in a timing error accumulation of 2 microseconds per second. The present applicants found for a star network that the desired network timing synchronization of 1 millisecond can be achieved by broadcasting a synchronization byte with a time synchronization update just once every 500 seconds.
The system architecture of the present patent application allows for flight tests to be performed with a range of wireless and networked sensing nodes. The wireless nodes may be deployed to monitor the loads on the rotating components of helicopters, for example, but they may also be used for fatigue monitoring on fixed wing aircraft. Unmanned vehicles could also benefit from the capability to autonomously track and assess structural damage �on the fly�.
This regime recognition may be performed on the Gateway itself so that the vehicle becomes �self-aware� and can assess and record severity of usage, and usage history. This information can be used for enhanced condition based maintenance, by providing important information on the fatigue rates of the vehicle's structure and rotating components. Combined with component tagging & tracking, operators and maintenance and repair organizations can use the SMS to automatically update the status of the life-limited parts according to FAR 121.380 (a)11. The information can also be used in health usage monitoring systems (HUMS). 11 El-Bakry, M., Component Tagging & Tracking�An Essential Enabling Technology for Effective �Safe Life� Structural Monitoring, Proceedings of 5th Intl. Workshop on Structural Health Monitoring, Stanford, Calif., Sep. 12-14, 2005
Piezoelectric Energy Harvesting Strain Measurement System A schematic diagram of the system is shown in FIG. 14. One or more piezoelectric material is connected to Conn2. When piezoelectric material is subjected to dynamic (changing) strain, an AC voltage is generated at connectors JH1 and JH2. This AC voltage is rectified and filtered by full wave diode rectification bridges. Charge provided by this voltage is stored in capacitors ch7 and ch8. The voltage (Vbat) on the capacitors is then regulated and supplied as system power to the rest of the circuit. Alternatively, if more power is available then required by the circuit, the extra charge can be stored in battery BT2 by switching on the battery charging regulator, UH1. Once the voltage on Vbat is reduced to a value that is lower then that required to charge the battery the regulator is turned off by the microprocessor. The microcontroller U3 controls the basic operation of the application circuit. Periodically, the microcontroller wakes up and samples data from the strain gauges and transmits or logs the sampled data to flash memory, U6.
Health Monitoring of the Strain Gauge Using Built in Test (BIT) The magnitude of the voltage produced by the piezoelectric patch increases as the amplitude of the dynamic strain level increases (referred to as the PZT peak to peak amplitude, or Apzt. This signal can be used as a reference to compare to the dynamic component (referred to as the strain gauge peak to peak amplitude, or Asg) of the strains measured by foil strain gauges. One way to track the health of the strain gauges is to form a ratio of these two amplitudes:
Ratio=Asg/Apzt This ratio may be recorded by the on board processor and recorded locally (or logged on an on-board machine) during typical operating conditions, such as straight and level flight. The ratio will tend to remain the same during operation if the health of the PZT and strain gauge elements does not change. In the case of the strain gauge output degrading because of delamination (or debonding of the strain gauge from the component substrate), the ratio would tend to decrease. In the case of the PZT elements debonding from the component substrate, or should some of the PZT fibers start to fail, this ratio would increase.
The instrumented component could be calibrated for static and dynamic load measurement. Known loads would be applied through a dynamic actuator (such as a hydraulic ram) through a �gold standard� such as a pre-calibrated load cell. The loads as reported by the load cell would be monitored simultaneously with outputs of amplitude from the PZT elements as well as the strain gauges. This information would be stored in order to facilitate conversion of digital output from the electronics that condition the PZT and strain gauges into separately measured loads (dynamic for the PZT, and both static and dynamic for the strain gauges). A static load calibration can be used to derive load both static and dynamic information from the output of the strain gauges, while the PZT cannot be calibrated statically.
One method of calibrating the PZT output would be to use the dynamic strain gauge output as the �gold standard� for strain measurement to calibrate the PZT. This has the advantage of eliminating the need for a dynamic load calibration. It may be advantageous to perform this calibration method early in the installation process, when the strain gauges and the PZT have not been subjected to potential degradation from exposure to the environment and from cyclic strain.
Piezoelectric materials can be used as strain gauges when the static loads are not important or do not need to be measured. In the case of the pitch link, the static and the dynamic loads are significant, and both need to be measured in order to obtain a reliable estimate of fatigue of that structure. However, one could use a piezoelectric strain gauge (as opposed to a foil strain gauge) to measure dynamic structural strains. The advantage of the piezoelectric strain gauges in systems which use energy harvesting systems is that no power is required for the sensing element. A separate piezoelectric element can be used to measure strain, as opposed to using the PZT energy harvesting element to provide both power and sensing functions. The reason for this is that the PZT used to provide power is generally a larger element, because it is designed to capture as much strain energy as is practical in the application, and therefore, is not well suited to discrete strain measurement locations. Furthermore, the PZT used for energy harvesting is loaded by other elements in the circuit, which may introduce some error in the strain measurement. Therefore, in the case where dynamic strain measurement only is required, an accurate and low power method of accomplishing this would be to substitute a piezoelectric strain gauge for the foil strain gauge at the input to the amplifier (pins 2 & 3 of connector JP2)
Moisture ingress into the strain gauge, PZT, and electronics elements can also be detected using a thin, integrated capacitive moisture sensor, such as we have described in our previous patent application, incorporated herein by reference, and entitled �Strain gauge with moisture barrier and self testing circuit�, by Arms et al., U.S. patent application Ser. No. 11/091244 filed 28 Mar. 2005.
Another strategy for built-in-test would be to �ping� the PZT elements mounted on the component with enough electrical energy to create mechanical response in the component and a measurable strain response from the strain gauge. This response of the strain gauge could be characterized and any significant reduction in its magnitude would reflect strain gauge debonding. The advantage of this method is that it could be performed while the vehicle is not in operation. The disadvantage of this method is that energy must be supplied to to the PZT in order to create a mechanical response (strain) in the component. Methods for exciting or �pinging� a piezo element have been previously described in the U.S. patent application Ser. No. 11/368,731, �Miniature Stimulating and Sensing System,� (�the '731 application�) to John Robb et al, filed Mar. 6, 2006, incorporated herein by reference.
Measuring Loads in Rotating Components Strain gauges can be used to convert a structural element into a load or moment sensing element. In the case of the pitch link, four strain gauges may be arranged around the pitch link's cylindrical shaft to amplify tension & compression while cancelling out thermal effects and bending loads. These techniques for instrumenting a column element as a longitudinal force sensing element are well known (reference: Measurements Group, Inc., �Strain Gage Based Transducers, Their Design and Construction�, pages 25-28, 1988).
Application of Load Measurement for Condition Based Maintenance The working pitch link loads during helicopter flight are very useful to acquire. These data can provide insight not only into fatigue of the pitch link, but to the overall severity of usage of the entire helicopter. Previous work, using strain gauges bonded to the pitch link, and slip rings to power and acquire data from the rotating components, have shown that pitch link loads increase significantly depending of the helicopter's flight regime. Since the pitch link is pinned to other structures (the pitch horn and the swash plate), the pitch link loads also provide insight into the loads borne by other structures on the machine. These connecting structures are also subject to cyclic fatigue, and their rate of fatigue depends on the severity of usage.
Packaging for the Energy Harvesting Wireless Pitch Link Sart Component Our approach is to electromagnetically shield and environmentally protect our electronics assembly after direct epoxy bonding to pitch link 200. Polyurethane materials have been used to surround and protect by providing a tacky, conformal seal for our microelectronics, which prevents moisture ingress. Polyurethane material 202 is protected by a thick overcoat of elastomeric shrink tubing 204. This method is ideally suited to the pitch link application, as it secures the conformal polyurethane sealant material and provides excellent mechanical protection of our electronics module 206, RF antenna 52, strain sensing elements 32, and energy harvesting elements 50 after mounting to a slender cylindrical element, pitch link 200, as shown in FIGS. 15 a, 15 b. The injectable polyurethane sealant (part number HT 3326-5, Aviation Devices and Electronic Components, AV-DEC, Fort Worth, Tex.) was originally designed for environmental sealing of electrical connectors. We determined that this type of conformal coating would be useful for environmental protection of the micro-electronics module, battery, and PZT harvester materials (after bonding of these elements to the pitch link).
Flexible sealants 202 can also be silicone rubber or the HT 3326-5 polyurethanes, and can provide good moisture protection, however, they remain soft and tacky after curing, and therefore, they require mechanical protection. Mechanical protection can be realized by subsequent application of heat shrinkable tubing (or cold shrink tubing). Heat shrink tubing 204 may be obtained with an integral conductive electromagnetic interference (EMI) screening (or �shielding�) and/or hot melt adhesive (The Zippertubing Co., Los Angeles, Calif.). Zippertubing possesses an advantage over traditional heat shrink tubing because the pitch link rod ends 208 a, 208 b would not need to be removed to provide environmental protection for pitch link electronics.
An alternative for EMI protection (to using heat shrink tubing with integral EMI conductive screening) would be to use a pre-formed gasket 210 of tacky polyurethane (also from AV-DEC) which includes an integral EMI shield 211. Printed circuit board (PCB) 206 may be designed to accept this electrically conductive gasket 210 at an area where a ground reference may be made, and the pre-formed gasket 210 would be placed over this area, but with a layer of electrically insulative material 212 (such as thin polyimide sheet) to prevent electrical shorting in those areas of the PCB that need to be insulated from shield 210. In this way, the PCB and other sensitive electrical components may be shielded from EMI without shielding the radio antenna (which would be part of the PCB) and without causing electrical shorting to occur.
An alternative to heat shrink tubing has also been procured, this is termed �cold shrink� tubing (3M Aerospace & Aircraft Maintenance Division, St. Paul, Minn.). Cold shrink tubing possesses the advantage of maintaining a constant compressive load over time (i.e., the material exhibits less creep and stress relation compared to heat shrink tubing). Cold shrink tubing, combined with the injectable polyurethane sealant, can provide excellent long term protection of the final pitch link load sensing assembly, including the strain/load sensors, microelectronics module with radio link, and energy harvester.
Referenced byCiting PatentFiling datePublication dateApplicantTitleUS7747415Dec 22, 2006Jun 29, 2010Microstrain, Inc.Sensor powered event loggerUS7781943Jan 23, 2008Aug 24, 2010Micro Strain, Inc.Capacitive discharge energy harvesting converterUS7839058Jan 29, 2008Nov 23, 2010Microstrain, Inc.Wideband vibration energy harvesterUS7860664Feb 13, 2009Dec 28, 2010Spirit Aerosystems, Inc.System and method for self-contained structural health monitoring for composite structuresUS7890236 *Aug 21, 2007Feb 15, 2011Clark Equipment CompanyAutomated control module for a power machineUS7911379Aug 18, 2008Mar 22, 2011Trimble Navigation LimitedConstruction equipment component location trackingUS8024980Jan 26, 2009Sep 27, 2011Microstrain, Inc.Independently calibrated wireless structural load sensorUS8080920Mar 21, 2008Dec 20, 2011The University Of Vermont And State Agricultural CollegePiezoelectric vibrational energy harvesting systems incorporating parametric bending mode energy harvestingUS8116940Jun 18, 2008Feb 14, 2012The Boeing CompanySystems and method for collecting data in a vehicleUS8131420 *Feb 27, 2008Mar 6, 2012Simmonds Precision Products, Inc.Vehicle health and usage monitoring system and methodUS8203332Jun 24, 2008Jun 19, 2012Magic Technologies, Inc.Gear tooth sensor (GTS) with magnetoresistive bridgeUS8269399 *May 13, 2010Sep 18, 2012General Electric CompanySystems and apparatus for harvesting energyUS8325030Sep 7, 2007Dec 4, 2012Lord CorporationHeat stress, plant stress and plant health monitor systemUS8402844Feb 27, 2008Mar 26, 2013Simmonds Precision Products, Inc.Roving wireless sensor and method for use in a vehicle health and usage monitoring systemUS8489255 *Mar 17, 2008Jul 16, 2013Airbus Operations GmbhMethod and device for compensation of mechanical stresses in an aircraft structureUS8527374Mar 21, 2008Sep 3, 2013Rochester Institute Of TechnologyMethod and apparatus for data acquisition in an asset health management systemUS8570152 *Jul 23, 2009Oct 29, 2013The Boeing CompanyMethod and apparatus for wireless sensing with power harvesting of a wireless signalUS8571835 *Jun 2, 2010Oct 29, 2013New Jersey Institute Of TechnologyVibration powered impact recorder (VPIR)US8593291May 18, 2010Nov 26, 2013Lord CorporationComponent RFID tag with non-volatile display of component use including the use of energy harvestingUS8607057May 15, 2009Dec 10, 2013Microsoft CorporationSecure outsourced aggregation with one-way chainsUS20100210169 *Feb 2, 2010Aug 19, 2010Ulrich R�hrModel Helicopter Control and Receiving MeansUS20110004444 *Jun 2, 2010Jan 6, 2011Reginald Conway FarrowVibration powered impact recorder (vpir)US20110018686 *Jul 23, 2009Jan 27, 2011The Boeing CompanyMethod and Apparatus for Wireless Sensing with Power Harvesting of a Wireless SignalUS20110264310 *Feb 18, 2011Oct 27, 2011Sikorsky Aircraft CorporationMethod Of Determining A Maneuver Performed By An AircraftUS20120143436 *Nov 30, 2011Jun 7, 2012Albert CornetMonitoring Device for Aircraft EquipmentUS20120166372 *Jan 6, 2012Jun 28, 2012Primal Fusion Inc.Systems and methods for applying statistical inference techniques to knowledge representationsEP2461296A1 *Dec 2, 2010Jun 6, 2012Techspace Aero S.A.Device for monitoring aeronautical equipmentEP2500267A1 *Mar 8, 2012Sep 19, 2012Airbus Operations (Soci�t� par actions simplifi�e)Monitoring of a flight control actuator of an aircraftWO2009137170A2 *Mar 20, 2009Nov 12, 2009Rochester Institute Of TechnologyMethod and apparatus for data acquisition in an asset health management systemWO2010008465A1 *Jun 23, 2009Jan 21, 2010Magic Technologies, Inc.Gear tooth sensor (gts) with magnetoresistive bridgeWO2010092152A1 *Feb 12, 2010Aug 19, 2010Airbus Operations GmbhSensor and sensor network for an aircraftWO2010135379A2 *May 18, 2010Nov 25, 2010Microstrain, Inc.Component rfid tag with non-volatile display of component use and scheme for low power strain measurementWO2012104539A1 *Jan 31, 2012Aug 9, 2012EurocopterDevice for monitoring the integrity and soundness of a mechanical structure, and method for operating such a device* Cited by examinerClassifications U.S. Classification340/679, 340/686.1, 340/693.1International ClassificationG01M99/00, G08B21/00, G08B23/00Cooperative ClassificationB64C2027/002, G01M5/00, B64C27/006, G07C5/085European ClassificationG01M5/00, B64C27/00D, G07C5/08R2Legal EventsDateCodeEventDescriptionOct 23, 2013FPAYFee paymentYear of fee payment: 4Oct 17, 2012ASAssignmentOwner name: LORD CORPORATION, NORTH CAROLINAEffective date: 20120914Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:MICROSTRAIN, INCORPORATED;REEL/FRAME:029141/0227Mar 10, 2010ASAssignmentOwner name: MICROSTRAIN, INC.,VERMONTFree format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:ARMS, STEVEN W;TOWNSEND, CHRIS PRUYN;CHURCHILL, DAVID LAWRENCE AND OTHERS;US-ASSIGNMENT DATABASE UPDATED:20100310;REEL/FRAME:24056/477Effective date: 20100302Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:ARMS, STEVEN 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