The present invention relates to systems for monitoring and diagnosing structural health conditions, and more particularly to diagnostic network patch (DNP) systems for monitoring structural health conditions.
As all structures in service require appropriate inspection and maintenance, they should be monitored for their integrity and health condition to proling their life or to prevent catstrophic failure. The diagnostics and monitoring of structures, as that carried out in structural health monitoring (SHM), are often accomplished by the network of active sensors. The active sensors, such as diagnostic network patches and piezoelectric transducers, are often used as both actuators transmitting stress wave within a structure, and sensors developing the sensor signal in response to the stress wave. When damage occurs the associated actuator-sensor paths become affected. But the minimum distance of the transmission paths of the diagnostic network is limited by the electromagnetic interference, or crosstalk, of actuation signals to the sensor signals.
Also, the general tend is that existing wired SHM systems are changed to wireless SHM systems that can diagnose the structural elements of infrastructure, without the structural system being dismantled or the ground being excavated for inspection and monitoring. Wireless SHM systems, deployed scalably in the structural elements of infrastructure, need in-situ compact small electronic platforms for multiplexing the diagnostic patches attached to the structure, actuating the actuator patches and receiving the sensor signals from the the sensor patches. But the size of a high-voltage power-supply component included in each electronic platform, and the power consumption during actuating actuator patches, often hindered the scalable deployment of wireless SHM systems.
Accordingly, there is a need for a system that can improve the performance of SHM systems by reducing the electromagnetic interference, the power consumption and the size of the electronic platform, so that SHM systems can be smaller and more compact with longer usage life, and to be reliable in the interpretation of structural health conditions.
According to one embodiment of the present invention, a method of monitoring structural health conditions by use of a plurality of patch sensors attached to an object is provided, where each of the patch sensors is capable of at least one of transmitting a stress wave upon receipt of actuation signals and developing a sensor signal in response to said stress wave. The method includes: generating the first and second actuation signals, the second actuation signal being approximately identical to the inverted signal of the first actuation signal; applying the voltage difference between the first and second actuation signals across two electrical terminals of a transmitter patch, by initiating the first actuation signal to one electrical terminal and at same time the second actuation signal to the other electrical terminal, so as to facilitate the generation of said stress wave within a structure; and receiving the sensor signals from the sensor patches to monitor the health conditions of the structure. The health conditions include at least one selected from the group consisting of damage, impact, cavity, corrosion, local change of internal temperature and pressure, degradation of material, and delamination of a structure.
According to another embodiment of the present invention, a computer readable medium may carry one or more sequences of instructions for monitoring structural health conditions by use of a plurality of patch sensors attached to an object, where each of the patch sensors is capable of at least one of transmitting a stress wave upon receipt of actuator signals and developing a sensor signal in response to said stress wave. The execution of one or more sequences of instructions by one or more processors cause the one or more processors to perform the steps of: generating the first and second actuation signals, the second actuation signal being approximately identical to the inverted signal of the first actuation signal; applying the voltage difference between the first and second actuation signals across two electrical terminals of a transmitting patch, by initiating the first actuation signal to one electrical terminal and at same time the second actuation signal to the other electrical terminal, so as to facilitate the generation of said stress wave within structure; and receiving the sensor signals from the sensor patches to monitor the health conditions of a structure.
According to yet another embodiment of the present invention, a system for monitoring structural health conditions by use of a plurality of patch sensors attached to an object, each of the patch sensors being capable of at least one of transmitting a stress wave upon receipt of actuation signals and developing a sensor signal in response to said stress wave, includes a transmitter patch configured to receive the actuation signals of inverted polarities and to generate a stress wave from the actuation signals. The system also includes a sensor patch configured to receive the stress wave and to generate a sensor signal having a first portion corresponding to an electromagnetic interference cancelled out by accumulating the interferences of the actuation signals, and a second portion corresponding to the stress wave. The system also includes a processor in communication with the actuator patch and the sensor patch, wherein the processor is configured to provide the actuation signals and receive the sensor signal.
Although the following detained description contains many specifics for the purposes of illustration, those of ordinary skill in the art will appreciate that many variations and alterations to the following detains are within the scope of the invention. Accordingly, the following embodiments of the invention are set forth without any loss of generality to, and without imposing limitation upon, the claimed invention.
In one embodiment of the present invention, methods of reducing the electromagnetic interference and lowering the high-voltage level of a power supply component in a structural health monitoring system are described.
The pair of actuation signals 166 and 168 is sent concurrently to an actuator patch 104 by initiating the first actuation signal 166 to one electrical terminal and at same time the second actuation signal 168 to the other electrical terminal of the actuator patch, which results in applying the time-varying voltage difference of the actuation signals 166 and 168 across two electrical terminals of the actuator patch. The actuator patch 104 provides a vibratory motion according to the waveform of the applied voltage difference, so as to generate a stress wave 1616 when attached to a host structure. That is, the actuator patch 104 converts the applied voltage difference of two actuation signals 166 and 168 with opposite polarities to a stress wave 1616 that propagates through the structure, resulting in the transmission of the stress wave 1616 to at least one sensor patch 106. The actuation signal may be any suitable waveform signal, such as a toneburst signal and a bipolar pulse train with several peaks. The sensor patch 106 converts the transmitted stress wave to a sensor signal 1612. If only one actuation signal is used, a noise, or “crosstalk”, signal of electromagnetic interference may occur in the sensor signal when the actuator patch is energized by high voltage pulses. Concurrent positive and negative actuation makes the crosstalk signal be cancelled out because their noise signal components are accumulated in the sensor signal.
In one embodiment of the invention, methods of increasing clearability of the sensor signals of stress wave in concurrent positive and negative actuation are provided. In each sequence of concurrent positive and negative actuation, the actuator patch 104 alternatively employs the non-inverted waveform 164a and the inverted waveform 164b, so that the sensor patch 106 provides the senor signals generated by the corresponding waveform signals 164a and 164b. Then the sensor signals corresponding to the waveform signals 164a and 164b, which are alternatively switched between inverted and non-inverted, are accumulated to provide an averaged sensor signal of stress wave. Accumulating the sensor signals, alternatively generated by the non-inverted waveform signal 164a and the inverted waveform signal 164b, provides a high clearability of the sensor signals of stress wave, causing to filter out nuisance signals.
In the case where only one actuation signal is used, the voltage difference is equal to the amplitude of the actuation signal. But concurrent positive and negative actuation makes the voltage difference be approximately twice as large as the single actuation signal amplitude, resulting in the increase of the propagation distance of the stress wave by a factor of two compared to when only one actuation signal is applied. That is, given the distance between the actuator patch and the sensor patch, the actuator energized by two actuation signals, with the half of the signal amplitude of single actuation signal, can generate the same amount of elastic wave energy as that of the actuator energized by the single actuation signal. Thus we can lower by half the high-voltage level of the power supply component of high-voltage amplifiers or pulse generators included in a structural health monitoring system, allowing the form factor of the SHM system to be reduced.
In one embodiment of the invention, methods of monitoring the health conditions of a host structure by use of receiving “crosstalk-immune” sensor signals are described. Before processing the concurrent positive and negative actuation, a SHM system may form a diagnostic network including the patch sensors and a plurality of stress wave transmission paths, each said transmission path being a signal link between a transmitter patch and a sensor patch. The patch sensors may be attached to the host structure. The SHM system may cause the designated actuator patch to transmit the stress wave and the sensor patch to receive the crosstalk-immune sensor signals, and then analyze the crosstalk-immune sensor signals to determine the health conditions of the host structure. Based on the analysis of the crosstalk-immune sensor signals, the SHM system may optimize the diagnostic network for robust damage detection by routing the stress wave transmission paths of high sensitivity to damage. The methods of networking the diagnostic patches and optimizing their network are described in, for example, U.S. Pat. No. 7,286,964 to Kim, and U.S. patent application Ser. No. 11/509,198, filed on Aug. 23, 2006, which are hereby incorporated by reference in their entirety and for all purposes.
When the SHM system analyzes the crosstalk-immune sensor signal, the system may compare the received crosstalk-immune sensor signal to a crosstalk-immune baseline signal to determine a deviation therebetween, the crosstalk-immune baseline signal being measured by use of the diagnostic network in the absence of structural anomaly. Then the SHM system may perform a diagnostic data processing, such as generating a structural condition index and a tomographic image, with the crosstalk-immune sensor signals. In the procedure of performing diagnostic data processing, the SHM system may perform at least one of the steps of: extracting the first arrival wave packet from each sensor signal; generating damage probability-of-detection curves of the diagnostic network; optimizing the gain and frequency operating condition of the patch sensors; and compensating sensor signals for dynamic environmental change, which are also described in the previously referenced U.S. Pat. No. 7,286,964 to Kim. The derivation, applications, and limitations of damage Probability of Detection (POD) curves can be found in Health & safety Executive Research Report 454, 2006, by Jacobi Consulting Limited, entitled “Probability of Detection (POD) curves.”
Referring back to
It is noted that the actuator patch 104 and the sensor patch 106 may be attached to a host structure. The noise signal 1614, which is generated by the electromagnetic interference of the actuation signal 166, is received before the sensor signal 1612. As the distance between the actuator patch and the sensor patch decreases, or the flight time of the stress wave between them becomes shorter, the noise signal 1614 and the sensor signal 1612 move close to each other. In some cases, two signals of 1612 and 1614 may overlap each other. In such cases, if the concurrent positive and negative actuation described above were not used in the system 100, the electromagnetic interference noise 1614 overlapping the sensor signal 1612 might cause false indication of damage by altering the sensor signal 1612 and resulting in invalid sensor readings. Thus, the concurrent positive and negative actuation technique enhances the reliability of the structural health monitoring systems by canceling the crosstalk signal 1614.
One of ordinary skill in the art will realize that a different embodiment of the present invention can employ different types of the actuator patch 104 and the sensor patch 106. For example, in the embodiments described above, the actuator patch 104 and the sensor patch 106 may include piezoelectric transducers. When affixed to a structure, these patches are capable of both converting the stress wave back to a voltage so that the prosperities of the stress wave propagated through the structure can be analyzed to monitor the health conditions of the structure. Also the actuator patch 104 and the sensor patch 106 can be actuators and sensors that are placed on a flexible dielectric substrate to form a diagnostic layer. However, a person of ordinary skill in the art will realize that the invention is not limited to these embodiments, and can encompass the use of any suitable type of actuator and sensor, such as magnetic actuators, fiber optic sensors and the like, which can be used to generate signals that can be combined so as to reduce the electromagnetic interference and lowering the high-voltage level of a power supply component.
The logic circuit 222, preferably including a field-programmable-gate-array (FPGA) or a complex-programmable-logic-device (CPLD), provides the clock and control signals to the pulse generator 224 through the control lines 264. The pulse generator 224, operated by the logic circuit 222, generates a bipolar pulse train, which is predetermined according to the wave parameters of time period or frequency, number of pulse-train peaks, and its amplitude. The SHM system 200 may employ other suitable kinds of the bipolar pulse trains generated by the logic circuit 222, such as a plain pulse signal, a pulse-width-modulated (PWM) pulse signal, a frequency-modulated pulse signal, a phase modulated pulse signal, a return-to-zero (RZ) binary signal and a non-return-to-zero binary (NRZ) signal. The pulse generator 224 may be a monolithic single channel, high speed and high voltage pulser, whose circuitry, packaged in a small electronic chip, consists of controller logic circuits, level transistors, gate driving buffers and a high current and high voltage MOSFET output stage. Any suitable pulse generators can be employed, regardless of whether the SHM system 200 is incorporated into a pulse generator based on high voltage MOSFET technology.
According to an embodiment of the present invention, the structural health monitoring system 200 further includes another pulse generator 226, also controlled by the logic circuit 222 through the control lines 262. The positive and negative pulse generators 224 and 226 generate the bipolar pulse train 266 and the inverted bipolar pulse train 268, and then transmit two actuation signals of opposite polarities to the actuator patch 204 through their corresponding electrical terminals. The actuator patch 204 converts the combined bipolar pulse train 2610 to a stress wave 2616 that propagates through a structure to the sensor patch 206. Then the sensor patch 206 converts the stress wave 2616 to the sensor signal 2612. However the crosstalk signal 2614 is also cancelled out due to concurrent positive and negative actuation.
The switch array module 346 controlled by a processor 302 is configured to select a predetermined transmission path in a diagnostic network of the stress wave 3612, by multiplexing the actuator patches and the sensor patches. In the case where the actuator patches 304a-c work as a sensor patch, the actuation line 368 connected to the high voltage negative amplifier 326 is switched to be wired to a ground 3464. Also, in the case where the sensor patches 306a-c work as an actuator patch (not shown in the
The invention can also include the switch array module 446 that is incorporated into an electronic platform for wired and wireless SHM systems capable of multiplexing the actuator and sensor patches, so as to interrogate the damage of a structure by networking the transmission paths of a diagnostic stress wave. Such SHM systems and their operations are further described in, for example, U.S. Pat. No. 7,281,428 to Kim, which is hereby incorporated by the reference in its entirety and for all purposes. Electronic platforms and their operations for wireless SHM are also explained in U.S. patent application Ser. No. 12/214,896, filed on Jun. 23, 2008, which is also incorporated by reference in its entirety and for all purposes. However it should be noted that the present invention is not limited to the wired or wireless SHM systems described in the aforementioned U.S. Pat. No. 7,281,428, and U.S. patent application Ser. No. 12/214,896. Rather, any other suitable electronic modules and power supply sources to these SHM systems can be employed, regardless of whether the modules shown in the
While the present invention has been described with reference to the specific embodiments thereof, it should be understood that the foregoing relates to preferred embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.
This application claims the benefit of U.S. Provisional Applications No. 61/127,458, entitled “Method and apparatus for reducing actuator interference in sensor singnals”, filed on May 12, 2008, which is hereby incorporated herein by reference in its entirety.
Number | Date | Country | |
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61127458 | May 2008 | US |