Patent Publication Number: US-7908928-B2

Title: Monitoring system

Description:
GOVERNMENT RIGHTS 
     This invention was made with U.S. Government support under cooperative agreement no. 70NANB2H3064 awarded by the National Institute of Standards and Technology (NIST). 
     The U.S. Government has certain rights in the invention. 
    
    
     CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. patent application Ser. No. 11/227,157, filed Sep. 16, 2005 entitled SYSTEMS AND METHODS FOR DETERMINING FATIGUE LIFE, U.S. patent application Ser. No. 11/227,155, filed Sep. 16, 2005 entitled CLASSIFYING A WORK MACHINE OPERATION, and U.S. patent application Ser. No. 11/227,269, filed, Sep. 16, 2005 entitled SYSTEMS AND METHODS FOR MAINTAINING LOAD HISTORIES, all of which claim priority to U.S. Provisional Patent Application No. 60/675,493, filed Apr. 28, 2005. Each of the above-listed applications are herein incorporated by reference in their entirety. 
     TECHNICAL FIELD 
     This disclosure relates generally to a monitoring system and, more particularly, to a monitoring system including wireless nodes for monitoring loads experienced by a structural component. 
     BACKGROUND 
     Machines, such as construction machines (e.g., tractors, dozers, loaders, earth movers, or other such pieces of equipment), may have any number of structural components that are subject to fatigue damage which could lead to structural failures. One method for monitoring fatigue damage on a machine structure is to perform a manual, visual inspection. However, such a method may be impractical for several reasons. First, such an inspection may not be as comprehensive as desired. This may be due, in part, to the difficulty of accessing some components of the machine, such as when the structure in question is concealed and cannot be viewed without dismantling a portion of the machine. Second, a manual inspection of structural components can only be performed on a periodic basis, yet damage and resulting catastrophic failure still can occur between inspections. Third, a manual inspection may not be able to detect how much fatigue damage may have already occurred in the machine, or predict the fatigue life of one or more machine components based on the fatigue damage. While manual inspection may provide some insight into damage that is visible to an inspector, (e.g., large visible cracks in a machine component), internal damage may not be readily apparent through manual inspection (e.g., small internal cracks in a component). 
     Some systems have been proposed utilizing various ways of monitoring structures electronically to detect fatigue damage. However, these proposed systems have not adequately addressed the monitoring of structures with rapidly changing load pictures, such as movable machines. This is due in part to the way these proposed systems collect data about the structure. These proposed systems may collect data about the structure at a relatively low sampling rate to ease the computing burden of performing analysis on the data and storing the analysis results. However, a low sampling rate may entirely miss some load states which endure very briefly. 
     Many critical load states experienced by a machine may only endure very briefly. For example, when a wheel loader is digging and the bucket hits a rock, the load state may peak for a few brief moments before the rock is broken or dug out. In structures with rapidly changing load states, the sampling rate must be high in order to capture these peak load states which may endure only very briefly. If the sampling rate is too slow to capture all or most of these critical load states, the analysis results will not accurately reflect the true condition of the structure. Therefore, high sampling rates may be more appropriate for detecting the true condition of the structure, which may facilitate an accurate fatigue evaluation. 
     In addition, some machines have structural components that are used in harsh environments. For example, a forestry machine may be operated amongst trees and bushes with branches that can damage wires that supply power to and carry data from strain sensing devices. Therefore systems have been developed that utilize wireless strain sensing devices. However, as mentioned, high sampling rates can collect large volumes of data that can be difficult to process, and/or transmit, especially wirelessly. Wirelessly transmitting high volumes of data that result from rapid sampling may not always be practical or possible. In addition, supplying power to such wireless strain sensing devices may also present a challenge. 
     Systems have been developed including wireless nodes having strain sensing devices that are configured to monitor strain and process strain data at the site of measurement to reduce the volume of data to be transmitted. For example, U.S. Patent Application Publication No. 2005/0017602 to Arms et al. (“the &#39;062 document”) discloses a system configured to monitor peak strain or strain accumulation. The system of the &#39;062 document may include a processor at the nodes for processing data acquired by the strain sensing devices. 
     Although the &#39;062 document discloses a system that may be configured to monitor various aspects of fatigue, the &#39;062 document is not configured to predict fatigue life of a structural component using the processors at the nodes. In fact, the &#39;062 document does not discuss predicting fatigue life at all. Predicted fatigue life can be utilized to plan maintenance schedules and preventative maintenance, such as replacement of parts. However, the system of the &#39;062 document does not disclose making such a prediction. 
     The present disclosure is directed to solving one or more of the problems described above. 
     SUMMARY OF THE INVENTION 
     In one aspect, the present disclosure is directed to a monitoring system including a structural component configured to undergo mechanical loading and a wireless node attached to the structural component. The node may include a strain sensing device configured to measure strain experienced by the structural component at the location of the node. The node may also include a processor configured to predict, based on the strain measurements, fatigue life of the structural component. 
     In another aspect, the present disclosure is directed to a method of evaluating fatigue in a structural component configured to undergo mechanical loading. The method may include taking measurements of strain experienced by the structural component at a node attached to the structural component. The method may also include processing data collected regarding the strain measurements with a processor located at the node. The method may further include predicting, with the processor, fatigue life of the structural component based on the strain measurements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic illustration of a machine according to consistent with certain disclosed embodiments. 
         FIG. 2  is a block diagram illustration of a monitoring system consistent with certain disclosed embodiments. 
         FIG. 3  is a diagrammatic illustration of an exemplary structural component consistent with certain disclosed embodiments. 
         FIG. 4  is a block diagram of an exemplary monitoring system consistent with certain disclosed embodiments. 
         FIG. 5  is a summary flow chart of exemplary processes performed by methods and systems consistent with certain disclosed embodiments. 
         FIG. 6  is a flow chart of an exemplary process for determining unknown loads, consistent with certain disclosed embodiments. 
         FIG. 7  is a flowchart of an exemplary strain calculation process consistent with certain disclosed embodiments. 
         FIG. 8  is a flowchart of an exemplary neural network configuration process consistent with certain disclosed embodiments. 
         FIG. 9  is a flow chart of an exemplary operation classification process consistent with certain disclosed embodiments. 
         FIG. 10  is a flow chart of an exemplary payload determination process consistent with certain disclosed embodiments. 
         FIG. 11  is a diagrammatic illustration of an exemplary body under load consistent with certain disclosed embodiments. 
         FIG. 12  is a flow chart of an exemplary load history building process consistent with certain disclosed embodiments. 
         FIG. 13  is a block diagram of an exemplary damage rate histogram consistent with certain disclosed embodiments. 
         FIG. 14  is a flow chart of an exemplary data analysis process consistent with certain disclosed embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to exemplary embodiments and illustrations. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts. While specific configurations and arrangements are discussed, it should be understood that this is done for illustrative purposes only. 
     Methods and systems consistent with the disclosed embodiments perform processes that determine, among other things, loads, health, and use of a machine or components of a machine. In one embodiment, a machine may be outfitted with a number of sensors. Some of the sensors may measure information reflecting the orientation and movement of the machine, such as inclination relative to the ground, and the positions of the movable parts of the machine. Other sensors may measure information about forces acting on the machine. Additional sensors may also measure the strain experienced by certain components of the machine. 
     Certain forces acting on the machine, however, may be difficult to directly measure using these sensors, such as ground engaging forces acting on the machine&#39;s wheels. The disclosed embodiments overcome this problem by using the measured forces and strains, along with other information, such as orientation information, to determine unmeasured forces. The unmeasured forces may be calculated using, for example, traditional Newtonian force balance and stress-strain calculations. Moreover, in certain embodiments, a neural network may be used to more quickly solve for these unknown forces. 
     Accordingly, the type of data used and determined in certain disclosed embodiments may include different types of data. One type may be measured data associated with raw measured information reflecting forces experienced by a component or structure (e.g., pressure in a cylinder, etc.). A second type of data may be measured strain data associated with actual strains experienced by a component or structure. For example, sensors on opposite ends of a component may provide measured information that reflect the strain experienced by that component. Collectively, the first and second types of data may define the constraints of the state of a given body (e.g., a component, set of components, the entire machine, etc.). Another type of data may include the unknown load data calculated using the measured data. 
     Once the measured forces are measured, and the unmeasured forces are calculated, methods and systems consistent with certain embodiments may generate a complete free body diagram of a portion (e.g., one or more components) of a machine or the entire machine. Based on the complete free body diagram and the orientation data associated with the machine, or a component thereof, the strain at any desired point on the machine may be calculated. In certain embodiments where technology is used to obtain a fast sampling rate of the free body diagram, the calculated strain at a given point on the machine may be used to continuously update a prediction of the remaining fatigue life of a structure surrounding the given point. 
     In certain embodiments, the data used in determining the remaining fatigue life of a machine may be used for other purposes. For example, the data associated with the complete free body diagram, and other data reflecting the orientation and movement of the machine, may be used to classify an operation of the machine at any given point in time into one of several discrete operating states. For example, the data may be used to determine whether the machine is digging or roading at any given point in time. As another example, the data of the free body diagram may be used to compute the weight of material in a bucket of the machine following a digging operation. As another example, the data of the free body diagram and the orientation data, along with information reflecting the current position of the machine&#39;s center of gravity at a given point in time or operation may be used to determined whether the machine is in danger of tipping. In another example, the data of the free body diagram may be used to determine historically high loading states of the machine, or individual components thereof, that are experienced during actual operation. The historical high loading state data may be used to better understand the forces experienced by the machine, or components thereof, to assist in the design or manufacture stages associated with the machine. It should be noted that the above examples are not intended to be limiting, as there are many uses for the data collected and calculated by the methods and systems disclosed herein. 
       FIG. 1  illustrates a machine  10 . Machine  10  may include a frame  12 , power source  14 , a work implement  16 , an operator station  18 , and a monitoring system  20 . 
     Although machine  10  is shown as a vehicle, machine  10  could be any type of mobile or stationary machine. In the case of a mobile machine, machine  10  may include one or more traction devices  22 . Traction devices  22  may be any type of traction devices, such as, for example, wheels, as shown in  FIG. 1 , tracks, belts, or any combinations thereof. 
     Power source  14  may be mounted to frame  12  and may include any kind of power source. For example, power source  14  may be an internal combustion engine, such as a gasoline engine, a diesel engine, a gaseous-fuel driven engine or any other exhaust gas producing engine. Alternatively, power source  14  can be an electric motor, or any other kind of power source. 
     Work implement  16  may include any type of implement or tool configured to facilitate completion of one or more tasks. For example, work implement  16  may include a construction work tool, such as a loader bucket, as illustrated in  FIG. 1 . Other possible construction work tools may include blades, drill bits, jackhammers, grapples, etc. Work implement  16  may also include other types of tools such as clamps, presses, etc. 
     System  20  may include a structural component  23  of machine  10 . Structural component  23  may be configured to undergo mechanical loading. Structural component  23  may be any structural member of machine  10 , such as, for example, frame  12 , work implement  16 , a support structure for work implement  16  (e.g., a lift arm  24 , a tilt link  25 , or a tilt lever  26 ), or any other structural member that may be subjected to mechanical loading. 
     Machine  10  may also include various other components associated with work implement  16 . For example, work implement  16  may be powered and controlled by a number of actuators, including a tilt actuator  27  and a lift actuator (not shown). 
       FIG. 2  illustrates monitoring system  20  in greater detail. System  20  may include at least one wireless node  28  attached to structural component  23 . Node  28  may include a strain sensing device  30  configured to measure strain experienced by structural component  23  at the location of node  28 . 
     Strain sensing device  30  may be configured to measure any type of strain. For example, strain sensing device  30  may be configured to measure axial strain, shear strain, torsional strain, or even multi-axial strain (e.g., using a rosette type device). 
     In some embodiments, strain sensing device  30  may utilize thin films attached to structural component  23  to detect strain. The resistance of such thin films may be altered with mechanical strain. Therefore, strain sensing devices that employ such thin films may measure strain by detecting a change in resistance of the thin film. 
     In other embodiments, node  28  may be configured to operate using power harvested from the mechanical loading that it is designed to detect. For example, strain sensing device  30  may utilize a piezoelectric transducer (PZT) material. PZT materials may generate electrical power upon experiencing strain. Therefore strain sensing devices that employ PZT materials may be able to generate power as opposed to thin film-based strain sensing devices, which consume power in order to detect the changing resistance of the film. By generating its own power, strain sensing device  30  may be configured to operate substantially or completely independent of an external power source. Such independence may facilitate wireless operation of node  28  as it may not need to be coupled to an external power source. In addition, node  28  may generate enough power with strain sensing device  30  to power other devices at node  28 , such as a processor  32  and/or a wireless transmission device  34 , both of which will be discussed in more detail below. 
       FIG. 2  is a block diagram representation of system  20 .  FIG. 2  illustrates an exemplary embodiment including a processor at node  28 . Processor  32  may be configured to predict, based on strain measurements taken by strain sensing device  30 , fatigue life of structural component  23 . Processor  32  may be mounted at any location on or in the vicinity of strain sensing device  30  (e.g., mounted to structural component  23 , attached to a component adjacent to structural component  23 , etc.). 
     Processor  32  may include any means for receiving information regarding data collected at node  28  and/or for monitoring, recording, storing, indexing, processing, and/or communicating such information. These means may include components such as, for example, a memory, one or more data storage devices, a central processing unit, or any other components that may be used to run an application. Exemplary data that may be stored at node  28  may include accumulated fatigue damage, total time spent in active data acquisition, and a histogram of strain ranges. 
     Although aspects of the present disclosure may be described generally as being stored in memory, one skilled in the art will appreciate that these aspects can be stored on or read from types of computer program products or computer-readable media, such as computer chips and secondary storage devices. 
     Node  28  may be configured to wirelessly transmit, to a location remote from node  28 , information relating to the strain measurements taken by strain sensing device  30 . Wireless transmission device  34  may include, for example, an RF module and/or a transceiver (not shown), and thus, may facilitate such transmission. The location to which node  28  is configured to wirelessly transmit may include a central processor  36  configured to receive information relating to the strain measurements. Such information may include raw resistance or strain data, calculated loads from the strain data, selected information like averages or peak values, or processed data like fatigue predictions or fatigue damage evaluations. Although data processing may take place at node  28  via processor  32 , such processed data may be transmitted to central processor  36  for further processing, sorting, and/or storage. Wireless transmission may be accomplished using any type of wireless datalink or other wireless transmission medium. Central processor  36  may be located on board machine  10  (as shown in  FIG. 2 ) or, alternatively, at a location remote from machine  10 . 
     Such information may also be retrieved from node  28  through a physical interface. For example, in some embodiments, node  28  may be configured to interface with a portable electronic device  38 . Node  28  may be configured to transfer, to portable electronic device  38 , information relating to the strain measurements. Portable electronic device  38  may include any type of device configured to store and/or process data, such as a laptop computer, personal digital assistant (PDA), or any other device suitable for downloading or otherwise retrieving such data. System  20  may be configured to interface with any available portable electronic device and/or, system  20  may include a custom portable electronic device designed specifically for such an application. 
     In some embodiments, system  20  may include more than one node  28 , as illustrated in  FIGS. 2-4 . Each node  28  may including a strain sensing device  30  configured to take strain measurements. In some embodiments more than one structural component of machine  10  may be equipped with a node. Alternatively or additionally, more than one node may be attached to a single structural component, as shown in  FIG. 2  and  FIG. 3 . In certain embodiments including more than one node, central processor  36  may be configured to receive information relating to the strain measurements from more than one of the nodes. Alternatively, or additionally, nodes  28  may be configured to communicate with one another (i.e., wirelessly). 
     System  20  may include a display  40 . Display  40  may be located at any suitable location on machine  10 , such as, for example, in operator station  18 . In some embodiments, display  40  may be configured to communicate with central processor  36 . Display  40  may be any kind of display, including screen displays, such as, for example, cathode ray tubes (CRTs), liquid crystal displays (LCDs), plasma screens, and the like. Display  40  may be configured to display information regarding system  20 . 
     In one embodiment, display  40  may include a warning indicator  42  (e.g., a warning lamp, warning message, etc.). Warning indicator  42  may be configured to activate in response to certain results of the fatigue evaluation performed by system  20 . For example, warning indicator  42  may be configured to activate in response to certain predetermined types of fatigue damage results (e.g., indications of cracking, multiple peak loads above predetermined threshold values, etc.) and/or predicted fatigue life (e.g., predicted residual fatigue life shorter than a predetermined threshold value). Warning indicator  42  may be configured to suggest a course of action in response to such fatigue evaluation results. For example, warning indicator  42  may be configured to suggest service, repair, or replacement of certain structural components. 
     In addition to providing visual feedback regarding fatigue evaluations performed by system  20 , display  40  may also be configured to display other information regarding system  20  or any other device and/or system associated with machine  10 . As an alternative or in addition to display  40 , system  20  may include one or more audible alerts for conveying information about system  20  to an operator. 
     Exemplary Monitoring System 
       FIG. 4  shows an exemplary monitoring system  200  consistent with certain disclosed embodiments. As shown in  FIG. 4 , monitoring system  200  is somewhat more comprehensive than monitoring system  20  illustrated in  FIG. 2 . However, the components and configurations included in monitoring system  20  may also be included in monitoring system  200 . For example, monitoring system  200  is shown to include a number of wireless nodes, which will be discussed in greater detail below. In certain embodiments, these nodes may include the same or similar componentry as wireless nodes  28  illustrated in  FIG. 2  (e.g., a strain sending device, a processor, a wireless transmission device, etc.). 
     In one embodiment, monitoring system  200  may be implemented on a machine that has moving parts, a rapidly changing load state, etc., such as machine  10 . Further, monitoring system  200  may be configured to perform health and usage monitoring functions associated with the operations of machine  10 . That is, monitoring system  200  may be configured to process information affiliated with the dynamic load changes experienced by machine  10 . Further, monitoring system  200  may be configured with hardware and/or software that enables it to process machine-related data in real time, as well as generate, store, and manage information related to raw data obtained from one or more machine components, such as sensors. In this regard, the monitoring system may maintain a manageable set of information for analysis and reporting. Moreover, monitoring system  200  may include wireless communication elements (e.g., wireless transmission devices  34 ) that enable moving and non-moving components of machine  10  to communicate without wired data links. Other aspects may be implemented by the disclosed embodiments and the configuration of monitoring system  200  is not limited to the examples listed above or described below. 
     Sensor Network 
     As shown in  FIG. 4 , system  200  may include a wired sensor network  202 , a wireless sensor network  204 , a central computer  206  (which may be a digital signal processor (DSP)), and a memory component, such as a vehicle database  208 . Wired sensor network  202  and wireless sensor network  204 , together may include sensors for detecting, for example, hydraulic pressures in actuators, positions of cylinder rods, implement linkage angles, velocities and accelerations, steering articulation angle, strain on bolts forming structural joints, vehicle ground speed, inclination relative to the Earth, and forces on instrumented pins in linkages and other structures. Data obtained by wired sensor network  202  and wireless sensor network  204  may be used to perform structural health and usage monitoring. 
     The sensor networks  202  and  204  may each be configured to collect data indicative of loads acting on machine  10 . Although  FIG. 4  shows a wired sensor network  202  and wireless sensor network  204 , either network may be implemented as a wireless or wired network. In one example, wired sensor network  202  may include an orientation sensor  210 , one or more hydraulic pressure sensors  212 , one or more cylinder position sensors  214 , one or more work implement position sensors  216 , one or more work implement velocity sensors  218 , load pins  220 , and bending bridges  222 . Generally, these may all be referred to as “sensors.” In addition, wired sensor network  202  may include interface electronics  224  and/or an electronic control module (ECM)  226 . In other embodiments, wired sensor network  202  of the exemplary health and usage monitoring system  200  may include additional sensors and/or different sensors or other components. 
     In general, the sensors implemented by machine  10  (e.g., sensors  210 - 228 ) may be separated into three categories: sensors that sense orientation and movement of the machine, sensors that measure loads (e.g., cylinder pressure sensors, strain gauges on the rod ends of hydraulic cylinders, etc.), and sensors that sense strain at some point, such as a sensor on a structural frame within machine  10 . The number and position of the sensors implemented within machine  10  may depend on the type of machine, the type of component(s) within machine, the desired and actual use of the machine, and other factors. For example, a certain number of sensors associated with the first two categories may be selectively positioned in order to provide adequate information to constrain the problem of generating the entire free body diagram of the machine or machine component. The sensors from the third group, however, may be positioned in locations to provide a base set of measured data to compare to calculated strains (e.g., normal strain values). Further, based on the location of certain machine components, or other sensors, a sensor positioned on these certain machine components may be wired or wireless. 
     Orientation sensor  210  may be one or more inclinometers disposed on machine  10  to measure one or both of pitch and roll of machine  10  relative to the Earth. Hydraulic pressure sensors  212  may be associated with a hydraulic system to detect fluid pressure. In one exemplary embodiment, pressure sensors  212  may be associated with a cylinder head of tilt actuator  27 . Hydraulic pressure sensors  212  may be disposed at other locations about machine  10  to measure hydraulic pressures. Pressure sensors  212  may provide information regarding one or more forces acting on the structure of machine  10  at connection points of the hydraulic actuator. 
     Cylinder position sensors  214  may be configured to sense the movement and relative position of one or more components of machine  10 . Position sensors  214  may be operatively coupled, for example, to actuators, such as tilt actuator  27 . Alternatively, position sensors  214  may be operatively coupled to the joints connecting the various components of machine  10 . Some examples of suitable position sensors  214  include, among others, length potentiometers, radio frequency resonance sensors, rotary potentiometers, machine articulation angle sensors and the like. 
     Work implement position sensors  216  may be associated with work implement  16  in a manner to detect position of work implement  16 . In one exemplary embodiment, work implement position sensors  216  may be rotary position sensors disposed at pin connections on work implement  16 . Other position sensors also may be used including, among others, radio frequency resonance sensors, rotary potentiometers, angle position sensors, and the like. Work implement acceleration sensors  218  may include an accelerometer or other type of sensor or sensors configured to monitor acceleration and may be associated with work implement  16  in a manner to properly detect acceleration of any desired point. Velocities may also be obtained based on the time-derivative of position sensors for the bucket or other similar component of machine  10 . 
     Load pins  220  may be configured to measure force in x and y-axes in inner and outer shear planes of a pin and may be instrumented with, for example, one or more strain gauges. The load pins  220  could be instrumented with strain gauges on the outer or inner surface of the pin, or they could be instrumented with some other technology designed to react to the stress state in the pin, such as magnetostriction. Load pins  220  may be disposed at joints on machine  10 . In one exemplary embodiment, load pins  220  may be disposed at joints connecting components of work implement  16  and/or connecting the actuators, such as tilt actuator  27 , to work implement  16 . Load pins  220  may be disposed at other joints about machine  10 . 
     Bending bridges  222  may be configured to measure strain in or along surfaces, such as, for example, along sides of lift arm  24 . In one exemplary embodiment, the bending bridges may include, for example, four strain gauges. In one exemplary embodiment, the strain gauges on bending bridges  222  may be configured to provide one combined output. 
     Interface electronics  224  may be in communication with the sensors, such as load pins  220  and bending bridges  222 , and may be configured to receive data signals from the sensors, process the data signals, and communicate data to computer  206 . Interface electronics  224  may include, for example, a module including, for example, a PIC 18F 258 microprocessor, 32 KB Flash, 1.5 KB RAM, 256 bytes EEPROM, CAN 2.0B interface with 12 bit external A/D sampling, and 4 strain channels. In one exemplary embodiment, monitoring system  200  may include nine interface electronics  224 , each associated with load pins  220  and bending bridges  222 . The interface electronics may be configured to communicate time-stamped and synchronized information, along with sensed values. 
     Electronic control module (ECM)  226  may contain a processor and a memory device, and may be configured to receive data signals from sensors  210 ,  212 ,  214 ,  216 ,  218 , process the data signals, and communicate data to computer  206 . The processor in ECM  226  may be a microprocessor or other processor, and may be configured to execute computer readable code or computer programming to perform functions, as is known in the art. The memory device in the ECM  226  may be in communication with the processor, and may provide storage of computer programs and executable code, including algorithms and data enabling processing of the data received from sensors  210 ,  212 ,  214 ,  216 ,  218 . In one exemplary embodiment, ECM  226  may include a MPC555 microprocessor, 2 MB ROM, 256 KB RAM, and 32 KB EEPROM. 
     Wireless sensor network  204  may include a number of wireless nodes  228  and a gateway node  230 . Wireless nodes  228  may be disposed about machine  10  and may be configured to communicate data signals representative of measured strain to other wireless nodes, and ultimately to gateway node  230 . Strain gauges  232  may be configured to measure local strain on a component of machine  10 . Data collected at any of wireless nodes  228  may be communicated to other wireless nodes  228  and/or to gateway node  230  using, for example, a transceiver. 
     It should be noted that wireless node  28  and wireless node  228  are exemplary only, and may be configured in any known manner. In one exemplary embodiment, wireless node  228  may include a receiver or a transmitter instead of transceiver. In another exemplary embodiment, wireless nodes  228  may each include a processor and memory for processing signals from strain gauges  232 . Wireless nodes  228  may include other components, including a power source, such as a battery. Other configurations would be apparent to one skilled in the art. 
     In one exemplary embodiment, measurements from wireless nodes  228  may be tagged with timestamps to allow computer  206  to synchronize the measurements from the different nodes and from the wired sensor network  202 . In one exemplary embodiment, wireless nodes  228  may concatenate measurements over relatively long periods before data transmission. Means for synchronizing the measurements may be incorporated into the transmitted data. 
     Central computer  206  may be located on board machine  10  or, alternatively, at a location remote from machine  10 . In embodiments including a central processor, such as central computer  206 , data that has been processed at one or more of wireless nodes  228  may be transmitted to central computer  206  for further processing, sorting, and/or storage. In some embodiments, particularly those without a central processor, data processing may take place one or more of wireless nodes  228 . It should be understood that any of the functions for which central computer  206  may be configured, as discussed herein, may be performed by processors at one or more of wireless nodes  28  or wireless nodes  228 . As with wireless nodes  28 , wireless transmission from wireless nodes  228  may be accomplished using any type of wireless datalink or other wireless transmission medium. 
     To minimize power usage, wireless nodes  228  may compress and accumulate their data and then send the accumulated data periodically, over a programmable time interval. In one exemplary embodiment, wireless nodes  228  are programmed to send their accumulated strain data over two second intervals. This means that computer  206 , in addition to scaling the sensor data, may rebuild the time history of the actual strains. 
     The gateway node  230  may be in communication with wireless nodes  228  and may be in communication with computer  206 . Accordingly, the gateway node  230  may be configured to communicate data indicative of the strain collected by wireless nodes  228  to computer  206 . 
     It should be noted that monitoring system  200  may also be operable with a single wired network or a single wireless network, rather than simultaneously employing a wired and a wireless network. Further, the number of gauges and other instruments used to collect data may vary depending upon the application and type of machine  10 . 
     Computer  206  may be in communication with gateway node  230 , ECM  226 , and interface electronics  224 . Computer  206  may be configured to receive data signals, process the data signals, and communicate data to vehicle database  208 . Computer  206  may include one or more processors configured to execute computer readable code that perform processes consistent with certain disclosed embodiments, such as functions to determine the life of, or load on, one or more components of machine  10 . In one exemplary embodiment, computer  206  may be associated with a data transfer device (not shown) that may provide output of data from computer  206  and/or vehicle database  208 . The data transfer device could be a port connectable to a service tool, such as portable electronic device  38 . Computer  206  may include, for example, resources to process varying numbers of inputs. For instance, computer  206  may execute program code that stores data in a first-in-first-out buffer at maximum expected input sampling rates. Additionally, computer  206  may be configured to perform algorithms consistent with the health and usage monitoring embodiments disclosed herein, such as processing data through one or more neural networks, performing floating-point matrix calculations, etc. In one exemplary embodiment, computer  206  may be an MPC5200 type processor using a QNX real-time operating system. 
     Vehicle database  208  may include one or more memory devices that store data and computer programs and/or executable code, including algorithms and data enabling processing of the data received from gateway node  230 , ECM  226 , and interface electronics  224 . The memory devices may be any type of memory device(s) known in the art that is compatible with computer  206 . Vehicle database  208  also may be configured to store data calculated by computer  206  and may be configured to store computer programs and other information accessible by computer  206 . 
     In one embodiment, database  208  may store neural network software that, when executed by computer  206 , performs neural network processes consistent with the disclosed embodiments. A neural network is designed to mimic the operations of the human brain by determining the interaction between input and response variables based on a network of processing cells. The cells, commonly known as neurons or nodes, are generally arranged in layers, with each cell receiving inputs from a preceding layer and providing an output to a subsequent layer. The interconnections or links that transfer the inputs and outputs in a neural network are associated with a weight value that may be adjusted to allow the network to produce a predicted output value. Neural networks may provide predicted response values based on historical data associated with modeled data provided as independent input variables to the network. Neural networks may be trained by adjusting the data values associated with the weights of the network each time the historical data is provided as an input to allow the network to accurately predict the output variables. To do so, the predicted outputs are compared to actual response data of the system and weights are adjusted accordingly until a target response value is obtained. 
     Overview Process 
     As explained, methods and systems consistent with the disclosed embodiments collect, determine, and analyze data associated with forces experienced by machine  10 . Based on the data, embodiments may calculate unknown variables, such as unknown loads, classify machine operations, generate free body diagrams, calculate strains, determine the life of component(s) of machine  10 , and evaluate and predict the life of component(s) of machine  10  or of machine  10  itself.  FIG. 5  shows a flowchart summarizing some exemplary processes that may be performed by methods and systems consistent with certain disclosed embodiments. 
     Initially, in one embodiment, machine  10  may experience a startup stage that may include powering up machine  10  or otherwise activating monitoring system  200 . At startup, computer  206  may send one or more signals to “wake up” wireless nodes  228 . Sending the signal may include activating or commanding an intermediary component to route the wake up signal to other connected components. For example, computer  206  may issue an activation signal to gateway node  230  or a first wireless node  228 , which in turn notifies one or more remaining wireless nodes  228  to awake and begin processing. At the same time, or at a different time, computer  206  may communicate a signal to one or more wired sensors  210 - 222  in a similar manner as described above, to begin collecting and processing inputs. 
     Once awakened, one or more of sensors  210 ,  212 ,  214 ,  216 ,  218 ,  220 ,  222 ,  228  (hereinafter collectively referred to as “sensors  210 - 228 ”) may collect raw measured data from their associated components (Step  405 ). For example, sensors  210 - 228  may be disposed in different locations on machine  10  to measure one or more parameters of components such as work implement  16 . Once obtained, the raw measured data may be time-stamped and communicated to computer  206  for subsequent processing. Alternatively, in embodiments without a central processor, data processing may occur at the nodes where the data was acquired, at another wireless node, and/or at a group of wireless nodes. 
     In one embodiment, computer  206  may determine whether the data received from each sensor is reliable. In one exemplary embodiment, computer  206  may determine data reliability executing neural network software configured to recognize reliable and unreliable data for each of the types of data received from sensors  210 - 228 . For example, the neural network executed by computer  206  may receive as input data from a sensor showing a flatline channel. Based on predetermined configurations, the neural network may recognize the flatline channel as an indicator that the particular sensor has ceased functioning properly, and therefore, its data may be unreliable. In another example, the neural network may receive sensor data that is determined to include a certain threshold of reliable data (e.g., a majority of data). For example, the neural network may recognize that a majority of a sensor&#39;s data is reliable, but also includes an occasional outlier of incorrect data. The neural network may recognize this outlier as unreliable data. Therefore, based on an analysis of the data itself, the neural network may classify the data as either reliable or unreliable. 
     In other exemplary embodiments, computer  206  may use other processes to determine whether the data is reliable. For example, in one exemplary embodiment, computer  206  may perform a logic-based process that monitors the first and second time-derivatives of the incoming data signals. In this embodiment, the flatline channel may have a zero first derivative at all times, and therefore, may be identified as unreliable. In addition, an otherwise correctly functioning channel with an occasional noise spike may have unusually large higher derivatives at the times associated with the noise spike. Therefore, again, the noise spike may be identified as unreliable. 
     If computer  206  determines the raw measured data to be unreliable, the unreliable data may be discarded and substituted with a data determined using interpolation techniques known in the art (Step  410 ). Alternatively, when the unreliable data is a strain measurement for a particular component of machine  10 , the unreliable strain measurement may be substituted with a previously calculated strain for that component. In some exemplary embodiments, the unreliable data is discarded and the strain calculation process continues without substituting calculated data. In other exemplary embodiments, the processing iteration is suspended due to the unreliable data, and computer  206  resumes the strain calculation process at step  405 . In other exemplary embodiments, other components of machine  10  may screen the measured data for reliability, such as gateway node  230 , ECM  226 , electronics  224 , and/or at any of sensors  210 - 228 . In these embodiments, the gateway node  230 , the ECM  226 , the electronics  224 , and/or the sensors  210 - 228  may be configured with hardware and/or software that is capable of detecting unreliable measured data. 
     Also, in step  410 , computer  206  may determine that measured strain data is included in the measured data collected in step  405 . In certain embodiments, computer  206  may determine measured strain data based on collected measured data. For example, based on sensor data collected from sensors positioned on opposing sides of a machine component, computer  206  may determine the strain imposed on the component, or a portion thereof. Thus, in step  410 , computer  206  may produce measured data of a first category (i.e., raw measured data reflecting forces on a particular component, such as pressure, etc.) and measured data of the second category (e.g., measured strain data). 
     In one embodiment, based on the measured data provided in Step  410 , computer  206  may determine the load(s) on various structural bodies within machine  10  (e.g., one or more components of machine  10 ) (Step  415 ). Computer  206  may use the load data to determine the strain and fatigue life associated with one or more monitored components of machine  10 , as described further below. In calculating the load(s), computer  206  may convert the measured strain into a proportional quantity that reflects information that is more relevant to the actual physical strain values on the measured component than the measured strain data provided in step  410 . For example, computer  206  may convert the measured raw strain data associated with an instrumented pin located on a machine component into data representing the resultant load and local moments for the pin. In another example, computer  206  may convert measured axial strain data for a cylinder rod to load-based data, which may be then shifted in order to match load data calculated from head-end and rod-end pressure readings associated with the cylinder rod. In this example, a strain gauge may measure strain data for the cylinder. The strain gauge may provide the measured strain data to computer  206  for determining the load applied to the cylinder when it is “bottomed-out” (i.e., when a rod within the cylinder is fully extended, thus forcing the piston to the edge of one end of the cylinder). In certain embodiments, computer  206  may shift received strain data to a corrected value. Because strain gauges may sense only strain relative to the time when the gauge was activated (i.e., turned on and operational), computer  206  may execute software that performs a linear regression analysis, or similar type of analysis, on the strain data to create a best-fit expression that is used to offset the loads calculated from the rod strain so that they are in agreement with loads calculated from cylinder pressures when the cylinder is not at either of the extreme limits of displacement. The linear regression techniques performed by computer  206  may be those techniques known in the art. 
     Also, in addition to cylinder forces, strain gauges may be implemented within machine  10  that measure the axial force in, for example, tilt link  25 . In this example, computer  206  may execute software that converts the measured strain data obtained from the strain gauge for tilt link  25  to load-based data using strain to force conversion methods known in the art. In instances where the strain gauge does not measure absolute strain data values, computer  206  may perform correction processes that correct the measured load on tilt link  25  to represent an absolute strain value. Computer  206  may then use linear regression analysis, or similar processes, to determine the axial load in tilt link  25 . 
     In certain embodiments, tilt link  25  may experience a dump stop event during operation of machine  10 . A dump stop event is a condition when tilt link  25  impacts lift arm  24  during operation. The forces imposed on these elements during such an event may cause fluctuations in determining the load associated with tilt link  25 . As such, computer  206  may execute processes that compensate for the forces occurring during a dump stop event to accurately determine the load experienced by tilt link  25 . One process may be configured to provide an estimate of the load of tilt link  25  for non-dump stop event states (e.g., when tilt lever  26  is not in contact with lift arm  24 ). A second process may be configured to calculate tilt link load during times when tilt lever  26  is in contact with lift arm  24 . Each of these processes may be based on load determining algorithms and techniques known in the art and executed by computer  206 . 
     In certain embodiments, one or more wireless strain gauges may be employed to measure the load on a given component of machine  10 . For instance, one or more of wireless nodes  228  may be configured as a wireless strain gauge for tilt lever  26  that measures its tilt link load. It should be noted that such determinations may be performed using well-known kinematic equations. Further, to conserve the energy of wireless node  228 , each node may be configured with a “sleep” mode. For instance, a wireless tilt lever strain gauge, and its accompanying wireless node  228 , my be placed in a low power mode (i.e., “sleep” mode) whenever tilt lever  26  is not in contact with lift arm  24 . In another exemplary embodiment, computer  206  may estimate the load on a given machine component using a neural network configured to provide the output load based on known neural network programming software processes. It should be noted that component loads may be determined using other configurations and techniques, and the disclosed embodiments are not limited to the above described examples. 
     Computer  206  may also determine unknown loads (e.g., unmeasured loads) acting on or within machine  10 , such as all unknown loads for the entire machine, or certain portions of machine  10 , such as a front section, lift arms, etc. For example, unknown loads may be associated with ground interface loads that cannot be measured directly by a sensor. In certain embodiments, computer  206  may determine unknown loads using a neural network or by employing traditional deterministic software based upon the equations of motion. Embodiments involving a neural network are described further below. In some applications, it may not be necessary to employ a neural network to determine the unknown loads. In certain embodiments, if inertial loading and contributions from mechanical vibration are not significant, computer  206  may use the Newtonian equations of static equilibrium to determine the unknown loads. 
     Once computer  206  determines the unknown loads, it may execute software that coordinates system transforms to associate all of the determined loads (known and unknown) to coordinate data corresponding to one or more respective components of machine  10  (Step  425 ). This process allows computer  206  to generate a free-body diagram of one or more, or all of the respective components of machine  10 , which is described in further detail below in connection with  FIG. 6 . 
     As explained, the data collected and calculated by monitoring system  200  may be used to perform one or more processes consistent with certain disclosed embodiments. In one embodiment, the determined load data may be used to calculate strains experienced by one or more components of machine  10 . For instance, in one embodiment, computer  206  may obtain an influence coefficient matrix (A) that is stored in a memory device within machine  10  (Step  430 ). The influence coefficient matrix (A) includes data reflecting the strain response at a number of chosen locations of a particular component under the influence of a particular unit load. Using the influence coefficient matrix (A), and other information, computer  206  may calculate strain data associated with one or more components of machine  10 , or for the entire machine itself (Step  435 .) Details regarding the strain calculations performed by computer  206  are further described below in connection with  FIG. 7 . 
     In another embodiment, the load(s) determined by computer  206  in Step  415  may be used to determine a payload of machine  10  during its operations (Step  440 ). Details of the payload determination processes performed by computer  206  are further described below in connection with  FIG. 10 . 
     In another embodiment, the measured data collected and/or determined by computer  206  in Steps  405  and  410 , as well as the strain(s) calculated in Step  435 , may be used to determine the fatigue life of one or more components of machine  10 , or of machine  10  itself (Step  445 ). This information may also be used to determine damage of the one or more components of machine  10 , or of machine  10  itself (Step  450 ). 
     Also, in another embodiment, the calculations performed by monitoring system  200  may produce result data that may be used to update the information stored in database  208  (Step  460 ). For example, information reflecting the payload determined in Step  440  may be stored in database  208  for subsequent processing by computer  206  or an off-board system interfaced with machine  200  via communication network (e.g., wireline or wireless network). Further, any damage data for a particular component(s) determined in Step  460 , may be stored as information in database  208  that is also accessible for subsequent analysis and processing. Similarly, the calculated strains and fatigue life information determined in Steps  435  and  445  may be stored in database  208 . In this regard, embodiments may continuously update information reflecting the health and use of one or more components of machine  10 , or of machine  10  itself, thus providing up-to date status information reflecting the operation of machine  10 , and its components. 
     Additionally, the data collected and calculated by monitoring system  200  may be used to classify an operation of machine  10  (Step  465 ). For example, the measured and determined data produced by Steps  405  and  410 , the unknown loads determined in Step  420 , the coordinate system transforms determined in Step  425 , and the calculated strains obtained in Step  435 , may be used by computer  206  to automatically determine a current operation of machine  10 . Details regarding classifying operations of machine  10  are described below in connection with  FIG. 9 . 
     Calculating Unknown Loads to Obtain Free Body Diagram 
     As explained, methods and systems consistent with certain embodiments enable monitoring system  200  to calculate unknown loads associated with one or more components of machine  10 . In one instance, computer  206  may use a neural network to determine unknown loads during operation of machine  10 . In certain embodiments, the unknown loads may be used to generate a free-body diagram of a given component of machine  10 .  FIG. 6  illustrates an exemplary unknown load determination process consistent with certain embodiments. 
     Initially, the neural network used to determine the unknown loads should be trained. To do so, in one embodiment, a testing process may be performed before monitoring system  200  performs run-time determinations of unknown loads. The testing process may be performed for each of a fleet of machines, for each type of machine, etc. that is installed with monitoring system  200 . For exemplary purposes, machine  10  is described as being exposed to the testing process, although it should be noted that a machine similar to machine  10  may be used in lieu of testing machine  10  to train the neural network. 
     During testing, machine  10  may be operated for a predetermined time, under one or more operational conditions. During this time, measured data is collected (Step  510 ). The measured data may correspond to a specific set of measured data, and may be collected via sensors that measure forces, and/or sensors that measure strains representing forces experienced by one or more, or all, components of machine  10 . The measured data may then be used as values in, for example, Newtonian static equilibrium equations, that generate output values reflecting unknown loads of specified locations of one or more components of machine  10  (Step  520 ). These output values, along with the specified set of measured data, are fed into a neural network to train the network to provide predicted unknown loads within a predetermined threshold (e.g., unknown load values within a certain percentage value of the unknown load values calculated using the Newtonian static equilibrium equations) (Step  530 ). If the neural network does not produce results within the predetermined threshold, the weights associated with the network may be adjusted until the network produces unknown load output values that meet the predetermined threshold criteria. 
     In one embodiment, the weight values of the network may be defined based on information determined during previous training of the neural network. In one embodiment, the neural network may be trained based on calculated load values associated with areas of a machine component that are not monitored by sensors during real time operations. These calculations may be performed using a mechanism analysis software package, such as Pro/Mechanica® Motion, that simulates the operation of machine  10  using test data as input. The unknown loads would be calculated as output, and would be used to construct the neural network training set. 
     Once the neural network is trained, its may be stored in a memory device that is accessible by computer  206  for execution during operation of monitoring system  200 . Subsequently, machine  10  may perform operations (Step  540 ). During these operations, computer  206  collects measured data in a manner similar to the processes described above in connection with Steps  405  and  410  of  FIG. 4  (Step  550 ). The measured data (e.g., measured force data and strain data reflecting forces on given components) are fed into the neural network, which produces output values reflecting estimates of the unknown loads of machine  10  (Step  560 ). 
     In one embodiment, once computer  206  determines the unknown loads, it may also execute software that associates all of the determined load data to the coordinate systems corresponding to one or more respective components of machine  10 . This process allows computer  206  to generate a free-body diagram of one or more, or all of the respective components of machine  10  (Step  570 ).  FIG. 3  shows one example of lift arm  24  with its associated loads (shown as arrows without their respective load data values) in a free body form illustration. As shown, lift arm  24  may include twenty-eight externally applied loads. In some embodiments, only some of these loads may be directly measured by one or more sensors  210 - 228 . The remainder of the loads may be calculated based upon the known loads in the manner described above in connection with Step  420 . Computer  206  may resolve the load data into the appropriate coordinate system for any structural component using known algorithms, such as trigonometric calculations, that may vary for each type of machine  10  and/or each type of component of machine  10 . Alternatively, computer  206  may execute neural network software that has been trained to estimate loads in the correct coordinate system of a particular component, such as lift arm  24 . It should be noted that  FIG. 3  shows an illustration of one component of machine  10  including coordinate-based loads. The determined load data, relative to their respective coordinate data, is stored as data in a memory location that may be used to perform other processes consistent with certain disclosed embodiments. 
     Calculating Strain and Determining Fatigue Life 
     As explained, computer  206  may execute software that calculates strains acting on one or more components of machine  10 .  FIG. 7  shows a flowchart of an exemplary strain calculation process consistent with certain disclosed embodiments. Initially, computer  206  may retrieve and analyze the free body diagram(s) previously determined by computer  206 , and described above in connection with  FIGS. 3 and 6  (Step  710 ). Depending on the strains being determined, computer  206  may retrieve and analyze one or more free body diagrams. For example, to determine all strains acting upon machine  10 , computer  206  may retrieve and analyze the free body diagram data associated with all components of machine  10 . Alternatively, if computer  206  is determining the strain of a particular component, it would retrieve and analyze the free body diagram associated with that component. In certain embodiments, when determining the strains acting on machine  10 , computer  206  may process free body diagrams one at a time, to later analyze the calculated strains of each respective component. 
     As noted above in connection with  FIG. 5 , computer  206  may execute software to calculate the strains using an influence coefficient matrix (A). As such, computer  206  may retrieve and populate matrix (A) corresponding to the respective component(s) associated with the strains being calculated (Step  720 ). Each column of matrix (A) may represent the strain response at a number of chosen locations of a particular machine component (e.g., lift arm  24  shown in  FIG. 3 ) under the influence of a particular unit load, with all other loads set to zero. 
     In one embodiment, the influence coefficient matrix (A) may be determined by known unit load analysis of a finite element model of the given component, as is known in the art. In another exemplary embodiment, instead of analysis of a finite element model, computer  206  may experimentally determine data for selected rows of the influence coefficient matrix (A) for the given machine component during selected time periods of operation of machine  10 , such as initial operation time periods ranging from start-up of the machine to a certain time period thereafter (e.g., one or more minutes, hours, etc. later). During these time periods of operation, the given component for the matrix under construction may be presumed to be structurally sound (e.g., having no fatigue flaws or cracks). Thus, while the component is deemed structurally sound, the influence coefficient matrix (A) may be determined by measuring strains on the component, and performing a least squares fit between the known external loads on the component and the measured strains. Based upon the results of the least squares fit calculation, the influence coefficient matrix (A) may be populated with the correct entries. Thus, experimentally determining rows in the influence coefficient matrix (A) may be used for high-stress gradient areas in the given component that may be difficult to model using the finite element method. 
     The fundamental relationship between measured strain and applied load for a quasi-static body is given by the equation below. 
     
       
         
           
             
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     where r=no. of measured strain channels on a body, and n=no. of external loads on a body. The influence coefficient matrix (A) may be populated row-by-row. In one embodiment, the first row of the above equation may be written in a time-dependent column vector form, for k time steps into the future, as shown below. 
     
       
         
           
             
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     The least-squares best-fit solution for the unknown elements in the first row of the influence coefficient matrix is given by the following equation.
 
 a   1   ′=[F   T   F]   −1   F   T   s   1 
 
     The above calculations may be repeated for the remaining rows of the influence coefficient matrix (A). In one embodiment, the number of iterations (i.e., k) that may be necessary for computer  206  to generate an influence coefficient matrix (A) that is satisfactory for all time periods of operation may be dependent on the amount of load data to be obtained. For example, the number of iterations k may continue until test data for each of the different loads has been obtained. 
     Once the influence coefficient matrix (A) has been fully populated, computer  206  calculates the strain using, for example, known matrix multiplication techniques (Step  730 ). For example, computer  206  may calculate the strain by multiplying a column vector including data reflecting the external loads experienced by the given component by the influence coefficient matrix (A). The results of the matrix multiplication representing the calculated strain for the given component may be stored in a memory location for subsequent processing. In one embodiment, computer  206  calculates the strain for each of the monitored components of machine  10  to provide a representation of the strains experienced by machine  10  during operation. 
     In accordance with certain embodiments, computer  206  may also execute software that performs fatigue life calculation processes to estimate the life of a given machine component and/or machine  10 . The fatigue life calculation process may accept strain values that are calculated from the multiplication of the external loads on the component by the influence coefficient matrix as input, or directly measured strain values may serve as input. In this manner, an additional measure of system robustness can be attributed to monitoring system  200 . 
     In certain embodiments, fatigue life calculations may be performed based on the measured data collected and determined in Steps  405  and  410  of  FIG. 5 . Additionally, as noted above, fatigue life calculations may be performed using the calculated strains determined in Step  435  of  FIG. 5 , and further described in  FIG. 7 . 
     Computer  206  may execute a software process that performs fatigue life algorithms to estimate the life of one or more components of machine  10 . Computer  206  may calculate the fatigue life of components having associated with them one or more strain gauges, such as strain gauges configured in the form of a wireless node  228 . This measured strain data, or the strain data calculated in Steps  435  of  FIG. 4 , may be used to estimate the accumulated damage in these areas. In one embodiment, estimated fatigue damage may be determined using rainflow analysis followed by an application of Miner&#39;s rule. Rainflow analysis is a method to count the cycles in complex, random loading of components. Miner&#39;s rule may then be used to sum the resulting damage at each point of interest of a component. This information, may provide an assessment of the structure of machine  10 . The fatigue damage estimated by Miner&#39;s rule effectively provides an estimate of remaining structural life. 
     For example, to determine the fatigue life of a component, a stress-life curve may be used for the welded joints, while a stress-life curve with Goodman mean stress correction may be used for other remaining structures associated with a component. In addition, separate strain-life curves may be used as desired for certain locations, such as a strain-life curve with Morrow mean stress calculation. As known in the art, computer  206  may execute software that performs the following equation to determine fatigue life based on applied stresses.
 
log  N =log  a+d ·log σ− m ·log  S  
 
     N: number of cycles 
     a: life intercept; constant for each curve 
     d: d=0 for B50 curve, d=−1.28 for B10 curve 
     σ: standard deviation; constant for each curve 
     m: slope of the curve; constant for each curve 
     S: stress range=2*Sa (Data) 
     A Goodman mean stress correction may be conducted using the equation shown below. 
     
       
         
           
             
               
                 
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     S a : stress amplitude with S m  (Data) 
     S a0 : modified stress amplitude for 0 mean stress 
     S m : mean stress (Data) 
     S u : ultimate strength=material constant 
     The fatigue damage estimated by Miner&#39;s rule effectively provides an estimate of remaining structural life. Fatigue life calculations utilizing a strain-life approach may be carried out using one of the equations below. 
     
       
         
           
             
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     ε α : strain amplitude (Data) 
     Δε: strain range (Data) 
     N: number of cycles 
     σ ƒ ′: fatigue strength coefficient; material constant 
     E: Young&#39;s modulus; material constant 
     b : fatigue strength exponent; material constant (negative value) 
     ε ƒ ′: fatigue ductility coefficient; material constant 
     c: fatigue ductility exponent; material constant (negative value) 
     Morrow mean stress (S m ) correction may be incorporated as in the equation below. 
     
       
         
           
             
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     The fatigue life may also be calculated from strain obtained by using the influence coefficient matrix (A) and the external loads as described above. In such embodiments, flags associated with the rows of the influence coefficient matrix (A) associated with the location of interest of a component may be activated by a user or software process executed by computer  206 . For example, if an unexpected fatigue problem develops at some location that is not equipped with a strain gage, the rows of the influence coefficient matrix (A) associated with that location could be activated by altering the value of a flag associated with those rows. 
     The results of the fatigue life calculations may reflect estimated fatigue life for one or more components of machine  10 , as well as an estimate for the fatigue life of the entire structure of machine  10 , or portions thereof. Computer  206  may store the fatigue life calculation results in a memory, such as vehicle database  208 , for subsequent access and analysis. 
     As the machine  10  continues to perform operations, the present age of the machine (designated below as t now ) may creep into the probability density function associated with the distribution of fatigue life, ƒ(t). In one embodiment, computer  206  executes software processes to determine an altered fatigue life distribution for that component based on Bayes theorem. For example, the probability that the fatigue life will be less than some arbitrary time in the future, t*, is given by the following equation. 
     
       
         
           
             
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     The updated probability density function may then be calculated as in the following equation. 
     
       
         
           
             
               
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                 up 
               
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     The new expected life (i.e. the mean value of the updated probability density function) is given by the following equation. 
     
       
         
           
             
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     Applying the Bayesian approach by computer  206 , may avoid user confusion that may result when the machine hours exceed an original estimated time for crack initiation with no visible crack present at the component location under analysis. The results of the Bayesian calculation process are also stored in a memory device, such as database  208 , for subsequent access and use by other processes consistent with the disclosed embodiments. 
     Damage Detection 
     In certain embodiments, computer  206  may also be configured to execute software that performs a damage detection process for machine  10 . The damage detection process may include performing a linear regression analysis between the calculated strains determined at step  435  of  FIG. 5  and the measured strain data obtained at step  410 . For example, computer  206  may perform software processes that generate a function reflecting the linear regression analysis of the strains calculated in step  435  of  FIG. 5  and the measured strain data determined in step  410  of  FIG. 5 . The function may be generated based on a graph bounded on the X-axis by the calculated strains and on the Y-axis by the measured strains. By analyzing the slope and/or correlation coefficient of the of the linear regression analysis within this graph, computer  206  may determine whether damage exists in the component associated with the strains under analysis. For example, if the slope of the function generated by the regression analysis is not within a certain threshold of “1,” computer  206  may determine damage exists in the component. The damage detected may be a fatigue crack, a loose bolted joint or other type of failing joint, and any other form of structural failure associated with a component of machine  10 . 
     This embodiment may be further explained based on the influence coefficient matrix used to calculate strains. In certain embodiments, the influence coefficient matrix (A) is populated early in the machine&#39;s life. Thus, strains calculated during this time frame using matrix (A) may be not be different from the actual measured values. Later in machine  10 &#39;s life, the strain values measured and determined by monitoring system  200  may change values. Thus, when calculating strains at this stage of machine  10 &#39;s life, matrix (A) does not accurately reflect the strain response of machine  10  at that time. Therefore, comparing the calculated strains with the measured strains using the linear regression analysis may result in a function having a slope different from “1,” reflecting the difference in strain values between the calculated and measured strains. This difference may reflect a crack, bend, or similar damage to an analyzed component. Computer  206  may use rules or other forms of intelligence to determine the level of damage based on the difference of the resulting function&#39;s slope to the target value of slope “1.” For example, the amount of detected damage may be proportional to the difference in the function&#39;s slope from “1.” That is, larger differences between the function&#39;s slope from the target value may represent more damage in the analyzed component. 
     The results of the damage detection process may be stored in a memory device, such as database  208 , for subsequent access and use by processes consistent with the disclosed embodiments. In certain embodiments, computer  206  may report the damage to the operator of machine  10  via a display device or similar warning indicator. Further, computer  206  may generate a damage report and store the information in database  208 . An off-board system, such as a laptop, server computer, another machine&#39;s computer, etc., may access database  208  via a communication network interconnecting the off-board system and machine  10 , such as a wireline or wireless network. Alternatively, computer  206  may receive a request from an off-board system to send damage reports. In response to the request, computer  206  may retrieve the damage report stored in database  208  and send the report to the requesting off-board system. In another embodiment, computer  206  may perform the damage detection process in response to the request from the off-board system. Alternatively, computer  206  may perform software processes that automatically direct computer  206  at periodic times to perform the damage detection process and report the results of the process to predetermine target systems, such as a particular off-board system. It should be noted that the damage detection results may be accessed and processed by any type of on-board or off-board system, and the above examples are not intended to be limiting to the disclosed embodiments. 
     Operation Classification 
     As explained, methods and systems consistent with certain embodiments may determine the operation being performed by machine  10  based on different types of information. For instance, in certain embodiments, computer  206  may execute software that classifies a current operation being performed by machine  10 . Classification of the current operation may include an analysis of the loads acting on machine  10 , as well as any other sensed or derived parameters, including, for example, inclination relative to the earth; ground speed velocity and/or acceleration; positions, velocities, and accelerations of the implement; and/or pressures. One method of classifying the operation would be to use traditional deterministic software programming techniques. Alternatively, these parameters may be fed into a neural network for analysis to classify the current operation. In one example, the neural network may classify the current operation into one of the following operations: (1) roading with no load; (2) digging; (3) roading with a load; (4) dumping; (5) idling; (6) bulldozing; (7) back-dragging; and (8) other. Additional or alternative classifiable operations may be used. Further, while the exemplary operations may be appropriate when machine  10  is a wheel loader, they may not be appropriate for a different type of machine, such as, for example, a motor grader or hauling machine. Thus, computer  206  may execute software that classifies operations that are specific to the type of machine  10 , which may perform the same or different types of classified operations as other types of machines. 
     In embodiments implementing a neural network for operation classification, database  208  may be installed with a neural network that is configured to produce output values reflecting certain operations associated with the type of machine  10 .  FIG. 8  shows a flowchart of an exemplary neural network configuration process consistent with certain disclosed embodiments. To configure the neural network to perform operation classification functions, actual operational data associated with the operation classifications are first recorded in a memory device during operation of machine  10  (Step  810 ). For instance, sensor data may be collected by computer  206 , or another device configured to collect operational data from machine  10 . The recorded data may also include time stamp information that reflects when particular data values for each sensor data is obtained during machine operations. The recorded sensor data values (e.g., data values reflecting the measured parameter, such as strain, ground speed velocity, etc.) are designated as inputs, which are assigned to time periods associated with the operation of machine  10  during data collection. Thus, each data input may include a set of data inputs arranged as a function of time (e.g., input  1 (t 1 ), input  2 (t 2 ), . . . , input I (tI), where I may be any positive integer). Based on this information, a user or computer-executed process may assign an operation classification to each of the time periods associated with the input data (Step  820 ). For example, minimal forces or strains may be applied to certain components of machine during idle time periods. Accordingly, the user or software process may assign an idle operation classification to the time periods having data input values reflecting these minimal forces or strains. 
     Once operation classes are assigned to the data inputs for the measured time periods, the classified data inputs are fed into a neural network as inputs in order to train the network to accurately classify operations during real time operation of machine  10  (Step  830 ). For instance, in one embodiment, the data inputs are applied to the neural network to produce, as output data, a predicted set of classified operations for each time period (e.g., time periods  1 -I). Further, machine  10  may be exposed to real operations associated with each of the classified operations. During these operations, computer  206 , or another internal or external machine device, may collect actual sensor data. Computer  206 , or a testing system, may then compare the predicted output classification data values with the actual classification of the operations performed during the real time operations of machine  10  to determine whether the neural network predicts the operations of machine  10  during each of the time periods within a predetermined criteria. The predetermined criteria may be associated with a threshold value that reflects a maximum acceptable difference between the actual and predicted classification output values. One skilled in the art would recognize that a number of different conditions, thresholds, etc. may be applied as the predetermined criteria by the disclosed embodiments. If the neural network does not meet the predetermined criteria, the network may be adjusted and re-tested until the predetermined criteria is met. Once the neural network produces accurate predicted classifications, the network may be stored in database  208  for subsequent use in classifying operations of machine  10  during later real time operations. 
     In another embodiment, a process may be implemented that allows a user to classify operations of a machine under test conditions. In this exemplary embodiment, a machine (e.g., machine  10 ) may perform one or more operations over a predetermined period of time. During operation, sensors on the machine may collect measured data associated with one or more components of the machine. Further, the operation of the machine may be videotaped or monitored in some form. Subsequently, a user may view a time stamped video clip of the machine during the recorded operations and assign operations to certain time periods of the operation. This time stamped operation data and the collected measured data is correlated as classification data as a function of time. The classification data may be fed as the inputs into the neural network for training the network in a manner similar to that described above (e.g., train the network until the predetermined threshold criteria is met). 
     In one embodiment, when the neural network does not meet the predetermined criteria, a user or computer executed process, such as program code executed by computer  206 , may adjust the weights associated with links corresponding to the nodes within the neural network to compensate for previous inaccurate predictions of operation classification output values. For example, if the neural network includes more than one level of nodes, the weights associated with each link interconnecting the layered nodes may be adjusted to train the network to produce more accurate output values. The weight adjustments may be performed by any number of known algorithms used for training neural networks, such as algorithms associated with radial basis function approximations. One skilled in the art would recognize that certain embodiments of the present invention may employ different algorithms that affect the learning process of the neural network. 
     Although the above exemplary embodiment describes the neural network being stored in database  208 , the network may also be trained after it is stored in a memory device located in machine  10 . Further, the neural network (trained or untrained) may be stored in a memory device internal to computer  206  or any other electronic component within machine  10 . As such, embodiments are not limited to the above examples. 
     Once the neural network is trained and provided in machine  10 , computer  206  may perform an operation classification process that determines the type of operation performed by machine  10  during certain time periods of operation.  FIG. 9  is a flowchart of an exemplary operation classification process consistent with certain disclosed embodiments. In addition to strain data, computer  206 , or another component of machine  10 , may receive sensor data as inputs from sensors  210 - 228  (Step  910 ). The received sensor data may reflect operational parameters associated with operations of machine  10  over a period of time. Accordingly, the received parameter data may be time stamped by sensor  210 - 228  or computer  206 . The received parameter data may be checked for reliability, in a manner similar to the processes described below in connection with steps  420  of  FIG. 5 . 
     The received data may then be fed as inputs into the trained neural network stored in database  208  (or elsewhere) (Step  920 ). Additionally, computer  206  may feed other information as inputs to the neural network. For example, unknown load data, free body diagram data, and calculated strain data may be used as inputs to the network. The neural network processes the inputs using known neural network processes and produces output values. Based on the output values, computer  206  may determine the classification of an operation performed during certain periods of time of operation of machine  10  (Step  930 ). For instance, based on parameter data values associated with one or more machine components, computer  206  may determine at time t 1 , machine  10  was roading with no load, digging, roading with a load, dumping a load, etc. The operation classification information may be stored in a memory location within a memory device (e.g., database  208 , local memory within computer  206 , etc.) for subsequent processing consistent with certain disclosed embodiments. 
     It should be noted that computer  206  may execute more than one neural network to perform any of the neural network processes described above. For example, one neural network may be used to classify the current operation, while a second neural network may be used to determine the unknown loads of a machine component. 
     Payload Determination 
     As described, methods and systems consistent with certain embodiments enable computer  206  to execute software that estimates the payload carried by machine  10  based on the measured data. Some payload determination systems may require that the operator pause the machine and then request an estimate from the system just before dumping the load. Pausing the machine ensured that inertial forces would not corrupt the payload determination. The disclosed embodiments enable payload determinations to take place without pausing the machine during dump operations. 
       FIG. 10  shows a flowchart of an exemplary payload determination process  1000  consistent with certain embodiments. At step  1002 , measured data and calculated loads (i.e., the results of the operation classification process described above in connection with  FIG. 9 ) may be received by computer  206  as inputs. At a step  1004 , based on these inputs, computer  206  may determine whether the current operation is classified as a certain type of operation, such as a dump operation. If the current operation is not classified as a dump operation (Step  1004 ; No), then the payload determination process returns to step  1002 . The payload determination process may continue to loop until the current operation is classified as a dump operation. It should be noted that the dump operation is an exemplary operation used by computer  206  during the payload determination process. The disclosed embodiments contemplate using other types of classified operations to determine whether to calculate the payload of machine  10 . 
     When the current operation is classified as a dump operation (Step  1004 ; Yes), computer  206  may perform a kinematics analysis to determine and consider the motion of machine  10  and/or one or more of its components, such as work implement  16  (Step  1006 ). Further, computer  206  may perform a kinetics analysis to calculate and determine the payload mass (Step  1008 ). The kinetics analysis may include determining the mass M from a derived expression for the payload, M=f(q i ). In the expression for the payload, time derivatives of measured quantities q appear. These may be calculated via numerical differentiation using a three-point central difference method, shown in the equation below. 
     
       
         
           
             
               
                 
                   ⅆ 
                   q 
                 
                 
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                   t 
                 
               
               ⁢ 
               
                 ( 
                 
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                   n 
                 
                 ) 
               
             
             ≈ 
             
               
                 
                   q 
                   
                     n 
                     + 
                     1 
                   
                 
                 - 
                 
                   q 
                   
                     n 
                     - 
                     1 
                   
                 
               
               
                 2 
                 ⁢ 
                 Δ 
                 ⁢ 
                 
                     
                 
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     In the equation, Δt is the time increment between each sampled value. Determining the mass of the load may be performed by solving for the necessary unmeasured variables, such as, for example, loads at non-instrumented pins and other unknowns. In one exemplary embodiment, computer  206  may execute software that solves, for example, a 10×10 system for ten variables that contribute to determining the payload of machine  10 . In one exemplary embodiment, the 10×10 system may be combined into a single, derived analytical expression to determine the payload using methods known in the art. The derived expression for the payload, M=f(q i ) may account for all inertial effects during the loading and dumping process. The expression M=f(q i ) is derived from a set of Newtonian equations of motion for the front linkage of machine  10 . Algebraic manipulations are performed to reduce all of the equations to a form M=f(q i ). The Newtonian equations of motion involve variables related to inertial effects so that these effects can be accounted for in the payload calculation. Accordingly, an operator may no longer need to pause machine  10  to allow the machine to calculate its payload. Further, computer  206  may be configured with software that, based on the operation classification of machine  10 , automatically determines payload at predetermined times, such as when machine is about to perform a dump operation, during roading with load, etc. 
     In one exemplary embodiment, computer  206  may execute software that determines different stages of a dump operation once this operation is classified. For instance, computer  206  may execute software that determines different stages of a dump operation based on the positions and load data of one or more components of machine  10  during a classified dump operation. Accordingly, computer  206  may detect when machine  10  is beginning, performing, and ending a dump operation. Based on this knowledge, computer  206  may perform the above described kinematics and kinetic analysis processes at both the beginning and end of the determined dump operation. In this regard, computer  206  may determine the mass of the delivered material by determining the difference between the mass of the payload at the beginning of the dump operation and at the end of the dumping operation (Step  1010 ). Therefore, the payload calculation may reflect the mass of delivered material, even when only a part of the payload is dumped. 
     In one exemplary embodiment, the determined payload may be optionally displayed in an operator interface (e.g., display  40 ) located in operator station  18  (Step  1012 ). This may allow an operator to track the weight of material being dumped by machine  10 . In addition to the payload amount, display  40  may convey additional information to the operator (e.g., with warning indicator  42 ). Such information may include, for example, an impending tip-over alert and a maximum load scenario, both of which may be determined by computer  206  based on determined load and strain data, as well as other measured parameters, such as inclination relative to the Earth. Display  40  and/or warning indicator  42  may include, for example, an audible noise, lights, a liquid-crystal display, etc. 
     Computer  206  may store data reflecting the calculated payload in a memory device, such as vehicle database  208 . To this end, computer  206  may perform a process that determines a cumulative payload for a given time period based on previously calculated and stored payload information. The cumulative payload information may be maintained in database  208 , and displayed by display  40 . Such payload information may also be downloaded off-board machine  10  for subsequent processing. 
     In one embodiment, computer  206  may execute neural network software that is trained to determine payload of machine  10  based on measured stress data, determined load data, and other collected parameter information. In another embodiment, monitoring system  200  may interface with some other pre-existing payload determination system rather than rely on the processes for payload determination described here. 
     INDUSTRIAL APPLICABILITY 
     The disclosed monitoring system may be applicable to any structural component configured to be subjected to mechanical loading. The disclosed system may be configured to evaluate fatigue in structural components of machines. The disclosed system may be applicable to stationary machines, such as power generation sets, cranes, lifts, etc., as well as mobile machines, such as construction equipment like loaders, track type tractors (e.g., bulldozers), hauling vehicles, excavators, earthmovers, etc. The disclosed system may be applicable to machines of any size and configured for any task. In some embodiments, the disclosed system may be configured to evaluate fatigue in machines having moving parts. In other embodiments, the disclosed system may be used to evaluate fatigue in mechanically loaded structures without moving parts. 
     An exemplary method of using the disclosed monitoring system may include taking measurements of strain experienced by structural component  23  at node  28  attached to structural component  23 . The method may further include processing data collected regarding the strain measurements with processor  32  located at node  28 . The method may also include predicting, with processor  32 , fatigue life of structural component  23  based on the strain measurements. In addition, the method may include evaluating fatigue damage based on the strain measurements. 
     An exemplary method of using the disclosed system may also include transferring recorded and, in some embodiments, processed data. For example, the method may include wirelessly transmitting, to a location remote from node  28 , information relating to the strain measurements. In some embodiments, the method may include taking strain measurements at two or more nodes  28 , and wirelessly transmitting, to central processor  36  information relating to the strain measurements from nodes  28 . In other embodiments, the method may include interfacing node  28  with portable electronic device  38  and transferring, to portable electronic device  38 , information relating to the strain measurements. 
     An exemplary method of using the disclosed system may further include operating node  28  using power harvested from the mechanical loading being monitored by strain sensing device  30 . Such power harvesting may be accomplished using a piezoelectric transducer material. 
     Methods and systems consistent with the disclosed embodiments may use fatigue data, including collected strain data, calculated strains, loads, operational information, etc. to provide estimates of fatigue life and/or fatigue damage for one or more components of machine  10 , as well as payload of machine  10 . This information may be used to provide insight regarding the health of machine  10  and to gather information useful for future design improvements of machines. In certain embodiments, the information determined by system  20  may be useful to design future machines, operate machines, to determine resale values based on known wear of machine  10 , and/or to determine when to perform maintenance and/or repair. In addition, system  20  may provide health information that is relevant and useful to a number of entities, including, for example, machine owners, machine operators, machine purchasers, service mechanics, and machine developers and engineers. Such relevant information may include, 1) fatigue damage data, 2) fatigue life predictions, 3) extreme load cases for one or more components, 4) load histories at various severity levels, 5) damage rate data, and 6) crack detection. 
     Information regarding fatigue data may be stored at node  28  and may be made accessible to one or more users. In certain embodiments, system  20  may continuously update the stored data that is representative of the structural health of the structural component  23  and/or of machine  10 . Processor  32  may be configured to utilize the fatigue data to estimate the residual life and/or value of a particular component, set of components, or machine. Alternatively or additionally, users may access the fatigue data and may perform their own fatigue evaluation based on the data. Information about fatigue damage and/or predicted fatigue life may be relevant to those purchasing and/or selling machines that have been previously operated. 
     In one exemplary embodiment, instead of continuously storing damage related data for all locations of each of the monitored components, monitoring system  200  may track accumulated damage only at discrete locations, such as at the locations where one or more sensors are actively sending signals to computer  206 . Further, health and usage monitoring system  200  may optionally accumulate damage data via the calculated strain at a number of desired component locations, as determined by a user. In one exemplary embodiment, the cumulative damage may be partitioned into portions attributable to each of the various machine operations. For example, in a wheel loader machine monitoring system may store cumulative damage data in matrix form. Each row of the matrix may correspond to a particular location of a wireless node  228  and a data value associated with an amount of damage. The matrix may be configured in any form, such as a designated set of columns storing accumulated damage data for each of the classified operations for that machine. A related column may also store the total damage data for a particular wireless node  228 . The damage data may include directional information corresponding to the most likely-orientation of a fatigue crack. 
     Information regarding the different classifiable operations may be stored within vehicle database  208  and made available to one or more users or computer systems, such as computer  206 . The types of operations that may be classified by the disclosed embodiments may vary based on the type of machine to machine. For example, a wheel loader may have associated classifiable operations such as, for example, roading with no load, digging, roading with a load, dumping, idling, bulldozing, back dragging, and “other.” The classification of these operations may be performed either by a neural network or via deterministic software. 
     Once classified into a specific operation, computer  206  may execute software that determines the amount of time spent performing an operation in real-time. In one example, computer  206  may store this information in vehicle database  208  as data indicative of a total amount of time that machine  10  operates in a particular operation. For example, based on collected sensor data, and determined load and other parameter information, computer  206  may determine that machine  10  is entering a digging operation at a time t 1 . The operation may continue until computer  206  determines that an operation other than digging is being performed. At that time, computer designates the end of the digging operation at a time t 2 . The time period between t 1  and t 2  may be summed with the time periods of other digging operations to maintain a total time period that machine  10  is operating in a digging operation. Computer  206  may perform software that forms this information in a histogram. Alternatively, computer  206  may download this information to an off-board system that forms the histogram. The histogram also may include information showing a total operation time for each of the other classifiable operations. Alternatively, embodiments may form separate histograms for the other classified operations, or selected combinations of operations. Further, the operation information maintained by health and usage monitoring system  200  may be customized or configured based on desired characteristics. For example, the total time spent working in a classifiable operation need not reflect a total time over the lifetime of machine  10 . Instead, the total time data for the classified operation may reflect the amount of time working in the classifiable operation since a last maintenance job was performed on the machine, the total amount of time working in the classifiable operation at a specific worksite, etc. 
     Computer  206  also may be configured to execute software that determines in real-time the amount of fatigue of at least one component of machine  10  over a period of time due to a specific operation. Again, referring to the digging operation as an example, when determining the fatigue, computer  206  may determine that the machine is entering a digging operation at time t 1 . The operation may continue until computer  206  determines that the digging operation has ended at time t 2 . Using any fatigue life calculation processes described above, computer  206  may determine the component&#39;s fatigue life by calculating the amount of fatigue that occurred during the time period between t 1  to t 2 . Summing the determined fatigue with the total lifetime fatigue that occurred while performing the operation may provide a total amount of fatigue due to the classifiable operation. Further, the total amount of fatigue may be reflective of fatigue during the machine&#39;s entire operational lifetime, since the machine&#39;s last maintenance, since initiating work at a specific worksite, etc. This information may be displayed in a histogram showing the fatigue for each operation separately, collectively, or for sets of selected operations. 
     In another embodiment, health and usage monitoring system  200  may store information regarding the extreme (e.g., maximum or minimum) instantaneous load scenarios over a machine&#39;s or component&#39;s lifetime. For example, referring to  FIG. 11 , a body  1100  is shown under the influence of any number of external loads ƒ i  (i=1 to n). The body  1100  may be a portion of any of the structures comprising machine  10 . When any one of the external loads ƒ i  complies with a pre-established factor, such as surpassing a previously stored lifetime maximum or minimum load value, then computer  206  may update vehicle database  208  with the new lifetime maximum or minimum value. By storing both the lifetime maximum load and the lifetime minimum load, a total range of loading is captured and available for analysis and display on a display device in any format. 
     In one exemplary embodiment, health and usage monitoring system  200  may store a snapshot of all load values acting on body  1100  at a particular point in time. For example, when any one load value exceeds a pre-established factor of a lifetime maximum or minimum value, computer  206  stores data regarding all the applied load values for body  1100 . In one exemplary embodiment, each of the external loads ƒ i  may be considered an element in a column vector f(t). To save the data regarding all the applied loads, the complete column vector f(t) may be saved. It should be noted that each body and each load being monitored by health and usage monitoring system  200  may have its own “extreme load case matrix.” The extreme instantaneous load scenario provides information regarding the most devastating instantaneous load applied to the body  1100  for each applied load. 
     In addition, health and usage monitoring system  200  may associate the lifetime maximum and minimum load values with the machine&#39;s current operation classification in memory. The load data and corresponding operation classification information may be used in designing and developing components for avoiding yield or buckling failures. Thus, in certain embodiments, computer  206 , or another machine system, may send the stored load and operation classification information to an off-board computer system for subsequent analysis, such as design, manufacturing, and diagnostic analysis. 
     In certain embodiments, computer  206  may execute software that stores in database  208  information associated with the load histories at various severity levels for each classified operation over one or more selected time periods (e.g., t 1  to t 2 ). This information may be provided to the operator of machine  10  or to off-board systems for analysis by computer-executed software or a user. For example, the stored information may include data reflecting the loads applied to a given component determined at time t 1 (e.g., the beginning of a classified operation) to time t 2  (e.g., the end of the classifiable operation) for a desired severity level. A desired severity level may be represented as a percentage value reflecting a level of damage experienced by a given component(s). For example, a 100% severity level may reflect the most damaging example experienced by the component or machine during a given operation. A 50% severity level may represent the average damage experienced by the component or machine during the operation. Accordingly, for example, a user or software process may direct computer  206  to store the load history of the component at the 90 th  percentile severity level for a digging operation. Computer  206  collects and stores all the loads that occur during the digging operation when the loads amount to a severity level at the 90th percentile. The determination as to whether a particular loading history is at a 90 th  percentile severity level may be made by comparing the damage rate for that particular operation with a known 90 th  percentile damage rate obtained from the damage rate histogram (contained in database  208 ) associated with some component of machine  10 . In one exemplary embodiment, when a newly collected load history is associated with a severity level that is closer in value to a pre-selected severity level (e.g., a desired level set by a user) than that of a previously saved load history associated with the same severity level, the newly collected load history may replace the previously stored history in database  208 . 
     To better illustrate this exemplary embodiment,  FIG. 12  shows a flowchart for storing load history information in vehicle database  208 . Initially, machine  10  performs an operation. During the current operation, computer  206  collects measured data and load data in a manner consistent with the process steps described above in connection with  FIG. 5  (Step  1205 ). Computer  206  collects the measured data associated with a given component of machine  10  at a time t 1 . Recording may be based on a pre-established first triggering event. In one exemplary embodiment, the triggering event may be associated with the initiation of a classified operation, as determined in a manner consistent with the above disclosed embodiments. For instance, referring to the above mentioned digging operation as an example, computer  206  may detect a first triggering event when it determines machine  10  has begun a digging operation. 
     At some point, computer  206  stops recording load data at a pre-established second triggering event at time t 2 . The second triggering event may be an indication that a classified operation has ended, as determined by computer  206  in a manner consistent with the above disclosed embodiments. 
     Computer  206  may also determine the current operation performed by machine  10  during the monitored time period t 1 &lt;t&lt;t 2  (Step  1207 ). In one embodiment, computer may execute a neural network to classify the current operation in a manner similar to that described above in connection with  FIG. 9 . Additionally, computer  206  may collect load data determined by computer  206  in a manner consistent with the disclosed embodiments. The load data may be used to populate a candidate load matrix (Step  1208 ). The candidate load matrix reflects a data structure including the load history for the component or machine  10  during the current operation for the given time period t. Thus, the stored load data in the matrix may include all the loads applied to the analyzed component over the time period t 1 &lt;t&lt;t 2 . 
     Computer  206  may also determine a target damage rate for one or more components of machine  10  for the time period t. The target damage rate corresponds to the desired severity level percentile. Accordingly, if the desired severity level is the 90th percentile for the exemplary digging operation, computer  206  may select the target damage rate to correspond to the 90th percentile damage rate. In certain embodiments, computer  206  may access and analyze a damage rate histogram to determine the target damage rate. For example, the body  1100  of  FIG. 11  is shown under the influence of any number of external loads ƒ i  (i=1 to n). The load history for the i th operation, f i (t) may give rise to a corresponding damage field, D i (r,t), which is increasing with time. Accordingly, for each of the different operations performable by machine  10 , a complete finite time history (of length t 2 −t i ) of f(t) may be selected by monitoring the residual of the following equation. 
     
       
         
           
             
               
                 
                   
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     As explained above, the target damage rate is the damage rate corresponding to the desired percentile of severity. The damage field, D i (r,t), is the amount of damage that exists on the component at time t at a particular surface location r (a position vector in the body&#39;s local coordinate system) attributable to the i th  operation. A weighting function, w(r), is a measure of the relative importance of failure at various locations on the surface of the body being monitored. For example, a weld failure at one location on a body might be more damaging, and more expensive to repair, than a similar failure on another part of the body. The time interval, t 2 −t 1 , for the load history f i (t) may be equal to the duration of one instance of that operation that most closely satisfies the target damage rate equation. In the target damage rate equation above, the quantities are shown in integral form in order to conveniently convey the concept. In another exemplary embodiment, however, the surface integrals may be approximated in the form of a weighted summation. A total damage field, D total (r,t), may be determined using the following equation. 
     
       
         
           
             
               
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     It should be noted that the direction of damage used for the summation in the above equation must be the same for all of the classifiable operations. Also, it should be noted that an amount of total damage may be different on every plane. Accordingly, the plane having the highest amount of total damage must be the plane utilized when solving for the target damage rate. Again, the location of each wireless node  228  may potentially have a different plane of maximum damage. The target damage rate may be determined prior to or during the current operation of machine  10 . 
     Computer  206  may also calculate the current damage rate for the component over a time period t of the single digging operation, where t 1 &lt;t&lt;t 2  (Step  1210 ). Computer  206  may determine the total damage using the equations for determining the target damage rate described above, based on the measured data associated with the current operation of the machine. 
     Once the target damage amount is obtained, and the current damage rate is determined, computer  206  may evaluate a residual of the current damage rate (Step  1215 ). A residual represents a degree to which the target damage rate (determined above) is not satisfied. In one embodiment, computer  206  may determine the current residual of the current damage rate by calculating a damage factor residual based upon the target damage rate. The target damage factor residual reflects a difference between the desired target damage rate (in this example, the 90 th  percentile) and the actual damage rate determined by computer  206 . It may be expected that some small amount of residual may exist, as any externally applied load history may not exactly give rise to the target damage rate (in this example, the 90 th  percentile). 
     Once the current residual is determined, computer  206  may collect a previously stored residual from a memory device within machine  10 , such as database  208  (Step  1220 ). The previous residual corresponds to a residual that was previously determined by computer  206  based on a previous operation similar to the current operation of machine  10 , determined in Step  1207 . Also, computer  206  may previously have generated and stored in database  208  a previous load matrix associated with the previous residual. 
     At step  1225 , computer  206  may compare the current residual with the previously stored damage residual. Based upon the comparison, computer  206  may determine whether the new load history (i.e., candidate load matrix) more closely corresponds to the desired target damage rate by determining whether the current residual is less than the previous residual. If the current residual is not less than the previous residual (Step  1225 ; No), then computer  206  determines the previously stored residual, with its associated load history, is closer to the target severity level (such as the 90th percentile) than the newly calculated residual with its load history (i.e., the candidate load matrix). Accordingly, computer  206  flushes the current residual and candidate matrix ( 1245 ), and the may return to step  1205  to monitor the next operation. 
     If, however the current residual is less than the previous residual (Step  1225 ; Yes), computer  206  may determine the newly calculated residual with its associated new load history (i.e., candidate load matrix), is closer to the target severity level (such as the 90th percentile) than the previously stored residual with its associated load history (i.e., previously stored load matrix). Accordingly, computer  206  replaces the previously stored residual with the current residual, and the load history associated with the previous residual (i.e., previous load matrix) is replaced with the current load history (i.e., candidate load matrix) in database  208  (Step  1250 ). In this manner, health and usage monitoring system  200  may continuously monitor for a load history that most closely matches the desired load severity. The process may return to Step  1205  to monitor for the next operation. 
     Although in the example described, the desired severity level was the 90 th  percentile, it is contemplated that the disclosed embodiments may store the load history for a classified operation at any desired percentile. In one example, computer  206  is configured to execute software that stores the load histories for each operation at the lifetime maximum (i.e., 100th percentile). Alternatively, computer  206  may store load histories for sets of severity levels, such as the 90th, 50th, and 10th percentile for each component and each operation. Storing the load history between time t 1  and t 2  for each operation at a desired severity level provides a manageable amount of data for analysis, thus reducing the amount of memory space used to store load history data. Accordingly, a user or software executed process may access database  208  to view and/or analyze the load histories for each desired severity level and thus obtain operation profiles of machine  10 . 
     Additionally, as mentioned above, information for generating a damage rate histogram may be stored in vehicle database  208  and made accessible to a user or computer system, such as computer  206  or an off-board computer system. For example,  FIG. 13  shows a damage rate histogram  1300  for an exemplary operation of machine  10 . In this exemplary embodiment, histogram  900  may be developed to represent the damage rate over the lifetime of machine  10  for the single classified operation, such as the digging operation. 
     As shown in  FIG. 13 , the x-axis of histogram  1300  may represent damage rates with increasing severity. The y-axis may represent percentage of hours spent at each damage rate while performing the respective classified operation. Computer  206 , or other system components of machine  10 , may collect the information for generating the histogram. For example, sensors  210 - 228  may measure and collect certain types of data, such as strain data values. Computer  206  may use the collected data to perform the fatigue life calculations described above consistent with certain disclosed embodiments. Therefore, computer  206  may determine the length of time for a single classified operation time interval (e.g., t 1 &lt;t&lt;t 2 ). The change in determined damage may be divided by the time period, and the quotient will determine the damage rates, which computer  206  (or another computer-based system) may format into data that may be provided to display  40  for display. Computer  206  may use the result of the calculated weighted integral damage rate, determined using the target damage equation described above, to update the histogram  1300 . After the histogram has been populated, a damage rate of any severity level (e.g., 10th, 50th, 90th, or 100th percentile) for any operation may be obtained for use in selecting the load history of corresponding severity. 
     In another embodiment, computer  206  may store information in database  208  reflecting the detection of a crack or loosely fitted part associated with a component of machine  10 . As explained above, methods and systems of the disclosed embodiments may detect a crack based on a comparison/cross-plot of calculated and measured strain for the component. For instance, computer  206  may consider the slope and correlation coefficient derived from a cross-plot and least-squares linear fit of calculated vs. measured strain for any given strain channel of the component. Computer  206  may use this information as an indication of crack initiation in the given component and provide a warning to a user or other computer system. Thus, a user may be warned of pending cracks in a machine component. For example, computer  206  may provide a warning of crack initiation for a given component to the operator or owner of machine  10 , via display  40  and/or warning indicator  42 . Alternatively, or additionally, computer  206  may provide the warning to a software process executing in another computer system, such as an ECM controlling engine operations. In response to the warning, the computer system may perform a process to avoid further damage to the component, such as reducing engine idle speed, stopping the engine, etc. 
     It should be noted that the information contained in vehicle database  208  may be used to extrapolate accumulated damage associated with one or more components of machine  10 , or of machine  10  itself, even if one or more of sensors  210 - 228  have ceased to function. For example, consider a situation where all of the instrumented pins and wireless strain gages implemented on machine  10  have ceased to function, and only vehicle speed, cylinder displacement, and cylinder force sensors remain operational. Computer  206  may still be able to determine the classified operation of machine  10  based on the available parameters obtained from the operational sensors. For instance, during a particular operation, computer  206  may match the average power expended by the cylinders to the appropriate “damage-rate bin” in the damage rate histogram  1300  for that operation, based upon previous correlations made by computer  206 . In this manner, computer  206  may estimate an additional amount of damage without any fatigue life calculations based upon strain, either calculated or measured. 
     As explained, methods and systems consistent with the disclosed embodiments enable a user or off-board system to collect health and usage information from machine  10 .  FIG. 14  shows a flow chart  1450  of an exemplary data analysis process consistent with certain embodiments. In one example, computer  206 , or another computer system, may transfer information from vehicle database  208  to an off-board system, such as an external database (Step  1452 ). In one embodiment, the off-board system may be configured to receive and analyze information from a plurality of machines. 
     At step  1454 , the off-board system may perform statistical analysis of the information. For example, when information from multiple machines has been downloaded to an off-board database, the off-board system, a user, or another computer system, may access the database to compare and analyze the machine information for structural integrity of one or more components of machine  10 , and the other machines. The information may be analyzed for, among other things, abusive use of the analyzed machine. Further, the off-board system may rank the remaining fatigue life of one or more machines (Step  1456 ). 
     Steps  1458  to  1468  show a number of possible uses of the information downloaded from machine  10 . For example, at step  1458 , a service contract may be priced based on the fatigue life evaluated at step  1456 . The service contract may be priced to take into account the remaining fatigue life, as well as any rough handling due to heavy loading that may have been applied to machine  10 . 
     At step  1460 , the data may be screened for condition-based maintenance that should be performed. This may include evaluating the health related data for machine  10  to determine which components are most in need of maintenance based upon their remaining life or their condition. Accordingly, components having a short remaining fatigue life may be maintained or replaced to ensure efficient and continuous operation of machine  10 . 
     At a step  1462 , sales forecasts may be created by dealers based upon the remaining fatigue life of the machines. Accordingly, dealers may be able to predict the future needs of a customer and thereby create sales forecasts. At a step  1464 , engineers may design or generate new designs for machine  10  based upon the evaluated fatigue life and the information obtained from machine  10 . For example, using the information obtained from machine  10 , engineers may be able to remove excess material from components or areas of components that may not receive high stress. In one exemplary embodiment, new designs may be based upon the downloaded health information. 
     In step  1466 , efficiencies of a work site including one or more machines that include health and usage monitoring system  200  may be evaluated. In one exemplary embodiment, an off-board system may review and analyze the amount of time a machine, or a set of machines, perform a specific operation. For example, if an inordinate amount of time is spent roading without a load, then that efficiency may be noted and corrected to create a more efficient work site. 
     In step  1468 , the efficiency of specific operators may be evaluated using the information obtained from vehicle database  208 . For example, the information may indicate that one operator is more efficient than another operator in performing certain operations of a type of machine at a work site. Using such information, work site managers may be able to recommend additional training or additional operators to maintain an efficient work site. Other uses for the information obtained from monitoring system  200  may also be available. 
     Although monitoring system  200  is described with reference to a machine, it should be noted that methods and systems consistent with the disclosed embodiments may be used with structures and components other than machines. For example, monitoring system  200  may be used to monitor any structural system subject to fatigue life. In some embodiments, monitoring system  200  may be used to monitor any structural system that may be used to perform a plurality of operations. Some examples of other structures that may incorporate monitoring system  200  disclosed herein may include civil structures, aircraft, and automobiles. Other structures may equally benefit from the system described herein. 
     Methods and systems consistent with the disclosed embodiments provide useful information that allows operators, user, and computer systems to assess the health of a machine and perform further analysis based on this information. For instance, because monitoring system  200  gathers data related to structural mechanics and estimates structural life in near real-time, it may be used to monitor the structural integrity of a structure, such as, for example a machine, throughout the structure&#39;s lifespan. Moreover, as mentioned above, monitoring system  200  also may be useful for providing information to assist the design, manufacture, operation, resale, and repair of components and machines. For example, over time, the information obtained by monitoring system  200  may be used to more efficiently design and more accurately analyze components of a machine. The structures may then be redesigned and manufactured with, for example, different materials and dimensions that may be lighter, less expensive, stronger, etc., while still providing acceptable performance in the field. 
     It will be apparent to those skilled in the art that various modifications and variations can be made in the disclosed embodiments without departing from the scope of the invention. Other embodiments of the disclosed embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed embodiment. For example, the process steps shown in the disclosed figures may be performed in different order, and are not limited to the sequences illustrated therein. Also, additional or fewer process steps may be implemented during these processes. Further, although the disclosed embodiments describe computer  206  executing software associated with neural networks to perform specific processes, methods and systems consistent with the disclosed embodiments may allow computer  206  to request another system to execute this software and report its results to computer  206 . Further, computer  206  may download neural network software from off-board systems prior to, or subsequent to, the network being trained. In another embodiment, the payload determination process may be performed for operations other than dump operations. For instance, computer  206  may perform payload determination processes when machine  10  is roading with a load, etc. 
     Further, an off-board system, as the term is used herein, may represent a system that is located remote from machine  10 . An off-board system may be a system that connects to the machines through wireline or wireless data links. Further, an off-board system may be a computer system including known computing components, such as one or more processors, software, display, and interface devices that operate collectively to perform one or more processes. Alternatively, or additionally, an off-board system may include one or more communication devices that facilitate the transmission of data to and from the machines. In certain embodiments, an off-board system may be another machine remotely located from machine  10 . 
     Additionally, although the disclosed embodiments are described as being associated with data and software programs stored in memory and other storage mediums, one skilled in the art will appreciate that these embodiments may also be stored on or read from other types of computer-readable media, such as secondary storage devices, like hard disks, floppy disks, optical storage devices, DVDs, or CD-ROM; a carrier wave from a communication link or network, such as the Internet; or other forms of RAM or ROM. 
     It is intended that the specification and examples be considered as exemplary only, with a true scope of the invention being indicated by the following claims and their equivalents.