Patent Application
20060004499
This invention relates generally to structural health management and, more particularly, to systems, architectures, and methods for managing the structural health of mobile platforms such as aircraft.
Maintenance costs have become a key component of the life cycle costs associated with commercial and military aircraft. Further, most of the expense of maintaining a metallic aluminum aircraft is associated with corrosion prevention and control. For a typical fleet of aircraft, 70% of all structural maintenance expense is incurred inspecting the airframes during periodic (frequency-based) maintenance tasks. More particularly, the majority of the inspection expenses are associated with accessing hidden portions of the airframe. The remaining 30% of the maintenance expenses are incurred actually repairing fatigue cracks and other structural damage found during the inspections. To put these expenses in perspective, more than twice the amount spent fixing damage is spent accessing the area, and performing the inspections for finding the damage. Thus, overall maintenance costs can be reduced by replacing periodic (frequency-based) inspections with a combination of automated detection of structural damage, degradation, (and the occurrence of events that might cause the same), and maintenance based on these conditions (i.e. condition based maintenance).
The use of increasing amounts of non-traditional materials (e.g. composites) is changing the types of maintenance information desired for monitoring the health of the overall structure. For instance, less information regarding metallic corrosion will be desired while other additional types of information will be desired to ascertain the health of the composite members. Thus, the changes in the mix of desired information necessitate modifying the integrated vehicle health management (IVHM) system by adding various sensors, in particular, for monitoring the composites. These additional sensors include, but are not limited to, high bandwidth structural sensors, corrosion sensors, load, and inertial sensors.
IVHM systems allow mobile platform operators to gather, record, and analyze information describing the operational status of the active components (including electronic components that are functionally active in that they produce observable outputs—signals) of their mobile platforms. For instance, modern turbojets are instrumented with sensors to monitor the engine and to detect incipient failures thereof. Upon detection of an incipient failure, the operator can correct the incipient failure in time to avoid schedule interruptions. Before the advent of IVHM, however, the operator would have periodically removed the engine from service for extensive inspections and preventative maintenance even in the absence of a condition warranting engine removal. Whether the inspections revealed damage or degradation of the structure, the frequency-based inspection approach requires the operator to incur costs by inspecting the engine. Also, the frequency-based inspection approach forces the operator to incur opportunity costs by removing the engine from service. After implementing IVHM on the engine, though, the operator now typically waits until the IVHM system detects a condition warranting engine removal prior to removing the engine from service.
One area that IVHM systems do not address is the health of the passive structural members of the mobile platforms. The reasons that IVHM systems have failed to address structural health monitoring (SHM) include the difficulty of handling the large amounts of data and related processing that SHM entails. IVHM sensors are typically sampled at comparatively low frequencies (i.e. tens to hundreds of hertz or lower), whereas SHM sensors often require rapid sampling rates (i.e. hundreds to thousands of hertz or higher) to yield useful information. Further, an IVHM system typically monitors several hundred, to perhaps a thousand sensors, whereas an effective SHM system might have tens of thousands of structural members within its purview. Given the number of structural members and the high data rates associated with structural sensors, a completely instrumented, conventional, SHM system would overwhelm the throughput provided by today's flight-qualified processors and networks. Moreover, as with any mobile platform system, IVHM systems are constrained by the desire to conserve cost, weight, power, and space. Thus, increasing the size of the IVHM is not desirable.
Therefore, a need exists to provide a practical SHM system for mobile platforms.
It is in view of the above problems that the present invention was developed. The invention provides improved SHM systems, architectures, networks, and methods.
To address the need for structural health monitoring, the present invention provides autonomous SHM systems, architectures, networks, and methods, thereby enabling condition-based maintenance of the aircraft structure. Thus, the present invention assists maintenance personnel in their efforts to identify structural degradation and damage. Also, the present invention decreases the amount of frequency-based maintenance required for mobile platform structures.
In a first preferred embodiment, the present invention provides a mobile platform comprising at least one mobile platform system that includes a processor. The mobile platform also includes a structure and an SHM system. The SHM system includes another processor and a structural sensor. The dedicated SHM processor is separate from the mobile platform system processor. In another specific embodiment, the SHM system may also process existing mobile platform parameters to determine structural loading conditions. In particular, the airplane parameters may be correlated with mobile platform loads via structural load models so that, depending on which loads are of interest, insight into the loads can be gained without the addition of structural sensors. In other preferred embodiments, the mobile platform includes flight control, maintenance information, and IVHM systems. In embodiments with a flight control system, the SHM system may receive parameters from the flight control system to determine loads on the structure therefrom. Alternatively, the sensor may be a structural load sensor, which the SHM processor uses, along with the parameters, to determine still other loads. In yet another preferred embodiment, the present invention provides a method that includes separating SHM functions from a pre-existing processor of a mobile platform system. The method also includes dedicating an SHM system to perform SHM functions and establishing communications between the SHM system and the mobile platform system.
In a preferred embodiment the SHM system will monitor multiple areas of the aircraft structure to minimize maintenance by reducing or eliminating routine inspections and by assisting in the evaluation and assessment of non-destructive inspection for incidental damage or specific mandated inspections by regulatory agencies. Ideally a low-cost low weight system will allow 100% monitoring for all types of damage. However, initially high SHM systems costs (sensors costs, SHM processor, software & network costs, SHM installation costs, and maintenance costs) will not be practical for implementation. Therefore, in a preferred embodiment, the SHM system will support monitoring in areas that have high return with low cost risk, such as areas that are difficult to access for inspection or have a high cost impact due to frequent inspections or other cost factors—such as areas near, on, under or behind, the aircraft lavatories and galleys, floor beams, door surrounds, pressure bulkheads, fuselage and wing hard landing inspection areas, vertical stabilizer attachment, pylon to wing attachment and strut, fuselage crown structure, fuselage structure under wing to body fairing, wing ribs, cockpit window sills, wing center section, fuselage structure above the wing center section and main landing gear bay, and fuselage structure in the bilge area. In the preferred embodiment the SHM system sensors in sparse (or dense) arrays can also be used to support annoyance maintenance, non-safety issues, such as for locating acoustic vibrations. Another preferred embodiment also includes provisions for adding additional monitoring equipment throughout the airplane's service life.
Further features and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings.
The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and together with the description, serve to explain the principles of the invention. In the drawings:
Referring to the accompanying drawings in which like reference numbers indicate like elements,
As shown in
By contrast, the structural members 12 to 18 comprise thousands of individual members (e.g. load carrying body panels, trusses, stringers, ribs, and the like). While many SHM sensors (e.g. strain sensors) operate at the comparatively lower sampling rates akin to the IVHM sensors, many other SHM sensors operate at much higher frequencies. For instance, shock, vibration, and ultrasonic non-destructive inspection sensors must be sampled rapidly to provide adequate insight into the phenomenon that they are intended to monitor. In contrast, corrosion sensors may be sampled infrequently (e.g. every minute, weekly, or monthly) yet still provide adequate insight into the health of the structure when analyzed on a less frequent basis (e.g. annually). Taken as a group, therefore, the SHM sensors generate a large volume (i.e. high bandwidth) of data for which existing aircraft data systems cannot economically, or practically, be configured to accommodate.
Currently, scheduled inspections of the aircraft 10 structures are driven primarily by a given element's susceptibility to environmental considerations, although fatigue and susceptibility to accidental damage also play roles in the frequency of inspection. The present invention provides systems, architectures, networks, and methods to reduce the requirement for these periodic inspections. Also, the present invention provides strategically placed sensors and an autonomous SHM system to detect events and conditions that warrant unscheduled inspections. More particularly, sensors are included at difficult to access locations to reduce the need to inspect these areas. Thus, the present invention eliminates the time and labor required to access and inspect these inaccessible areas. Also, the time and labor necessary to repair damage to the aircraft, incidental to the access effort, is likewise eliminated. Further, because many of these areas are typically sealed (or otherwise protected from the environment) at the factory, the superior factory protection seal is maintained until a condition warranting intrusion is sensed.
In contrast to the scheduled inspections discussed above, unscheduled inspections are currently driven primarily by a structural member's susceptibility to accidental damage. Thus, the present invention also provides systems, architectures, networks and methods useful for detecting and assessing accidental damage. The present invention also reduces the occurrence of unscheduled inspections to only those inspections necessary to respond to actual damage and degradation. “Hard landings” represent an example of events that might cause such accidental damage. These hard landings currently require time-consuming, invasive, unscheduled inspections of the landing gear and other structures exposed to hard landings induced forces. Yet, on average, 98 to 99% of hard-landing inspections reveal no damage. Thus, in accordance with the principles of the present invention, it is desirable to conduct only a sufficient number of unscheduled inspections to reveal the results of the 1 to 2% of hard landings for which the SHM system indicates the desirability of inspecting an affected area. Because of these advantages, the present invention reduces aircraft down time and maintenance expenses.
With reference now to
The “systems” discussed herein with typically include combinations of software applications, firmware, neural networks, algorithms, networks, processors, sensors, data concentrators, signal conditioners, and other hardware as will be further described. Further, those skilled in the art will recognize that the functions performed by the systems may be distributed in various manners depending on the specific application of the invention involved. Thus, phrases such as “the system performs a function” will be recognized to mean that some, or all, of the system may be involved in performing the function. For instance, because a system can include a “network,” a system can communicate with other systems via the system's network. Of course, a network typically consists of various nodes (or points), the communications paths there between, and the related software. For clarity, therefore, when the primary function involved in a particular discussion of a system includes communications, the term “network” will usually be used to designate the portion of the “system” performing the function. Therefore, because the optional systems data system 106 primarily provides communications between systems, the systems data system 106 will usually be referred to as a network. Moreover, since the other systems discussed (e.g. the SHM system 110) typically perform functions in addition to communications, these other systems will usually be referred to as systems instead of networks.
Turning now to the SHM system 110, the dedicated SHM system 110 includes a dedicated SHM processor 134, structural data modules or concentrators 136 (e.g. multiplexer/demultiplexers), as many SHM sensors 142 as the operator desires for monitoring the aircraft structure, and a dedicated network 110A allowing communications there between. The data modules 136 communicate with the sensors 142 to signal condition, gather, record, pre-process, and process the sensor data in accordance with the distribution of functions selected for a given application. The SHM processor 134 receives the sensor data from the data module 136 and manipulates it to ascertain the health of the monitored structures. The SHM processor 134 may also receive data from sensors 144 in other systems 115 (including the flight controls system 112) via the overall system data network 106. Further, to allow the SHM system 110 to be independent of the aircraft power system, a battery may power the SHM system 110 hardware, or some portion thereof. Of course, the SHM system 110 may also draw power from the onboard power system.
The SHM system may also rely on the other systems 115 in other ways. One way the SHM system can rely on these other systems 115 is the SHM system 110 may receive data (or information) pertaining to the conditions sensed by the sensors 144 associated with the other systems 115. Avionic unit and hydraulic line temperatures are specific examples of the sensors 144 that the SHM system 110 may receive data and SHM related information from. Additionally, it may sometimes occur that an SHM sensor 142 may be located in an area of the aircraft remote from the SHM system 110 or any portion thereof. In such situations, it may be impractical to connect the SHM sensor 142 directly to the SHM system 110. Thus, the SHM sensor 142 may be connected to one of the other systems 115 that, in turn, communicates data and information from the sensor 142 to the SHM system 110. Moreover, it may sometimes be preferable to duplicate a sensor 144 of one of the other systems 115 with a separate sensor 142 dedicated to the SHM system 110. For instance, the SHM system 110 may include an aircraft pitch rate sensor 142 rather than relying on the flight control system 112 for such data or information.
Moreover,
The overall SHM system associated with a fleet of aircraft includes the ground SHM system 138 and each of the SHM systems 110 associated with the fleet of individual aircraft. Thus, the overall SHM system includes the ground SHM system 138 (preferably common to all aircraft in the fleet), and the crew and maintenance terminals 130A and 130B, the SHM processor 134, the structural data modules 136, the sensors 142, and the other portions of the SHM system 110 associated with each of the aircraft.
In a preferred embodiment, the usage monitor 202 includes an intelligent load monitoring algorithm, a neural network, or a lookup table derived from the results of an algorithm or neural network used to develop the usage monitor. The algorithm, neural network, or lookup table monitors strain sensors, accelerometers, and various flight parameters (that might include, but are not limited to, sink rate, roll rate, pitch, pitch rate, airspeed, control surface positions, fuel weight and distribution, stores, and cargo configurations) and transforms the data into information regarding the loads experienced by structural members throughout the aircraft. If the usage monitor 202 includes a neural network, the neural network is trained to determine the loads experienced by structural members that are not instrumented from more directly sensed loads experienced by instrumented structures. Thus, the intelligent load monitor (of the usage monitor 202) enables a reduction in the number of load sensors required to monitor the health of the aircraft structure.
In contrast to the usage reasoner 202 of
Using the information developed by the damage reasoner 204 (and the usage reasoner 202), the damage diagnostic and prognostic reasoner 208 triggers inspection and maintenance actions. The damage reasoner 208 also generates reports regarding the prognosis for repairing the damage and degradation detected by the damage reasoner 204. Importantly, because the current invention provides for detection of incipient damage, the inspection and assessment of the structure occurs earlier than would otherwise be the case. As a result, most resulting repairs will be relatively minor compared to than the repairs that would be called for by current practice. Another advantage provided by the present invention arises because much SHM related data may be collected while the aircraft is on the ground. For instance, the crack sensors 220, the corrosion sensors 222, and the active damage interrogators 224 may be interrogated only by the ground-based SHM data-network 138, thereby relieving the flight portion of the SHM system 110 of the associated data throughput and processing otherwise required on the aircraft.
In still another preferred embodiment of the damage reasoner 204, an impact detection algorithm, neural network, or lookup table (derived from the results produced by an algorithm or neural network used to develop the damage reasoner 204) is included in the damage reasoner 204. Strain sensors 214 in communication with the damage reasoner 204 are placed on, and around, structures likely to be subject to impact damage. Exemplary structures exposed to impact include the fuselage 12 (of
Corrosion sensors 222 may also be located in inaccessible areas of the aircraft to detect incipient corrosion therein. For example, the corrosion sensors 222 of
The fleet-wide database 210 illustrated in
In summary, the SHM application 200 of
In another preferred embodiment, the SHM processor 134 communicates with a removable memory device (e.g. an EEPROM, a floppy disk, or any storage device) to store SHM data and information thereon. Upon landing, the gate crew removes the memory device, reads the SHM data and information therefrom, and uses the ground based SHM data network 138 to analyze the SHM data and information collected during the most recent flight. Because no SHM network 110A data access (e.g. connecting an external computer to the SHM network, logging on, and initiating a transfer) is required, less time is required for the gate crew to analyze the SHM data and information. Of course, the removable memory device (or another portion of the ground-based SHM network) may be employed to reconfigure the SHM network 110A. Yet another embodiment provides a wireless interface to the SHM network 110A so that users may efficiently and securely access SHM data and information, and maintain software and data tables, accessible via the SHM system 110A.
In view of the foregoing, it will be seen that the several advantages of the invention are achieved and attained. The SHM architectures, systems, networks, and methods provided by the present invention reduce the time required for scheduled and unscheduled inspections. The present invention also ensures that inspections occur at optimal times while reducing the extent of repairs. Further, by placing the SHM related functions in a separate processor, network, or system, the present invention provides for a large degree of flexibility in expanding, modifying, and adapting the SHM functions for a particular mobile platform. For instance, a particular mobile platform operator (e.g. an airline) may specify different SHM functionality over that otherwise offered without impacting the flight worthiness of the other onboard systems. Nor would tailoring a mobile platform to specific desires consume resources that other systems would have to compete for. Thus, the present invention provides an open SHM architecture that is unencumbered by many of the restraints imposed on the other onboard systems. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use comptemplated.
As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.
