Abstract:
A method for testing a unit is described where the unit includes one or more of electrical, electronic, mechanical, and electromechanical components. The described method includes applying at least one stimulus to the unit, receiving sound emissions from the unit, converting the sound emissions into one or more acoustic signatures, comparing the acoustic signatures based on the received emissions to stored acoustic signatures expected as a result of the at least one stimulus, and determining a status for the unit based on the comparisons.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This invention relates generally to testing of equipment, and more specifically to, acoustic signature fault detection for and within electronic, electromechanical, and mechanical equipment.  
         [0002]     Currently electronic, electromechanical, and mechanical equipment, for example, equipment for aircraft and for other vehicles including navigation, tactical and other systems, are tested using measurements of voltage, current, and temperature. More specifically, such systems, sometimes referred to in the testing environment as a unit under test (UUT), are typically tested using automated test equipment. In such automated test equipment (ATE) the UUTs are subjected to a set of stimuli (applied electrical signals or mechanical inputs) that are typically experienced under operating conditions. The ATE is configured to measure one or more output conditions, electrical or mechanical, that result due to the applied stimuli. Output conditions (measurements) that are different than expected output conditions are utilized to try to determine which portion, for example, a removable circuit card, is the source of the different than expected output conditions (e.g., the failed test or fault).  
         [0003]     However, there is still sometimes ambiguity with such testing methods. Sometimes one or more circuit cards or other subassemblies have to be removed and replaced until the source of the failed test is isolated. Some components and combinations of components emit an audible sound when operating. Others emit a sound when not operating correctly. Still others emit a frequency when one or more components or subassemblies have failed that is different than a frequency emitted when all components are operating correctly. Such audible frequency emissions are sometimes collectively referred to as acoustic signatures.  
       BRIEF SUMMARY OF THE INVENTION  
       [0004]     In one aspect, a method for testing a unit, the unit including one or more of electrical, electronic, mechanical, and electromechanical components is provided. The method comprises applying at least one stimulus to the unit, receiving sound emissions from the unit, and converting the sound emissions into one or more acoustic signatures. The method further comprises comparing the acoustic signatures based on the received emissions to stored acoustic signatures expected as a result of the at least one stimulus, and determining a status for the unit based on the comparisons.  
         [0005]     In another aspect, a unit configured to allow acoustic signature testing of the unit during operation of the unit. The unit comprises at least one microphone located within the unit and a processor configured to receive and process signals originating from the microphone. The processor is programmed to communicate with an external system regarding the processed signals.  
         [0006]     In still another aspect, a method for configuring a unit for acoustic signature testing is provided. The method comprises embedding one or more microphones within the unit, configuring a processing device within the unit to receive inputs from the one or more microphones, and programming the processing device to communicate data regarding received inputs to an external system. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0007]      FIG. 1  is a block diagram illustrating test equipment connected to a unit under test (UUT) for testing of the UUT.  
         [0008]      FIG. 2  is a block diagram of the test equipment of  FIG. 1  incorporating acoustical testing.  
         [0009]      FIG. 3  is a graph illustrating certain acoustic signatures for a known good inertial measurement unit.  
         [0010]      FIG. 4  is a graph illustrating the same acoustic signatures as illustrated in  FIG. 3  for a suspect inertial measurement unit.  
         [0011]      FIG. 5  is a block diagram of an inertial measurement unit configured for acoustic signature testing. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0012]      FIG. 1  is a block diagram illustrating a connection between automated test equipment (ATE)  10  and a unit under test (UUT)  12 . ATE  10  typically includes a microcomputer  20  or other processing device which is bussed to control operation of and receive data from input/output circuits. Examples of input/output circuits include digital input and output  22 , analog input and output  24 , timing circuits  26 , and other input and output circuits  28 . As an example, other input and output circuits  28  may include specialized circuits providing an interface to unique circuits within a particular UUT  12 . Examples of specialized circuits includes synchros and resolvers. While not shown, ATE  10  and microcomputer  20 , depending upon the requirements for testing a particular UUT  12 , may also incorporate and control operation of a mechanical interface which exists on a particular UUT  12 . An example of such an interface may include an interface to a gear assembly extending from UUT  12 .  
         [0013]     ATE  10  further includes power supplies  30  configured to provide the various voltages and currents needed to operate microcomputer  20 , the input/output circuits, and user interface  32 . User interface  32  provides the interface that allows a user to operate ATE  10  for the testing of UUT  12 . A wiring harness  40  is utilized to connect ATE  10  to UUT  12 . Certain UUTs have additional operating requirements, for example, forced air cooling. For such UUTs, a holding fixture  50  is configured to mate with wiring harness  40 . Holding fixture  50  is configured to provide the forced air cooling (not shown) to UUT  12  and further provides an enclosure that may be utilized for UUT specific interfaces (not shown), controlled by ATE  10 , that are not included within ATE  10 .  
         [0014]     While ATE  10 , wiring harness  40 , and holding fixture  50  provide most of the parametric testing for most UUTs, certain UUTs exhibit characteristics during operation that may provide information as to whether there is an operational problem or the potential for a future operational problem therein. Specifically, certain UUTs emit sounds, which are sometimes audible, during start up sequences and/or during operation. A change to the frequency or volume of such sound may provide information as to what portion of the UUT is, or is not, operating properly. Further, certain UUTs do not emit an audible sound when properly operating. Emission of sound by such UUTs may be an indication that a portion of the UUT is not operating properly. Still further, for UUTs that emit a sound during operation, a lack of sound emissions may also provide information as to which portion of the UUT is not operating properly.  
         [0015]      FIG. 2  is a block diagram of ATE  100  that adds an acoustic signature diagnostic tool to the testing functionality provided by known ATE, for example, ATE  10 . ATE  100  is configured to provide evaluation of auditory characteristics, for example, amplitude, length of time, and frequency, not currently evaluated by ATE systems testing UUTs. As such, ATE  100  may use an acoustic signature of the equipment under test, for example UUT  12 , to aid in the diagnostics of the equipment or unit under test. In one embodiment, a microcomputer  102  within ATE  100  is additionally configured with one or more routines to detect anomalies in the acoustic signatures emanating from UUTs that are indicative of a failure within the UUT. Similarly, an acoustic signature can also be utilized, at least partially, to determine that the UUT is operating properly.  
         [0016]     ATE  100  also incorporates all of the previously described functionality of ATE  10  and similar components are illustrated using the same reference numerals utilized in  FIG. 1 . ATE  100  further incorporates a sound interface  104  that communicates with microcomputer  102 . In one embodiment, sound interface  104  communicates with microcomputer  102  utilizing the same bus structure as does the previously described input and output circuits. One example of a sound interface  104  is a digital computer sound card input. Extending from sound interface  104  is a portion of a wiring harness  106 . Wiring harness  106  additionally provides an interface between the input and output circuits, including power supplies  30 , of ATE  100  and holding fixture  50 . As previously described, holding fixture  50  is configured for attachment of UUT  12  and to provide connection to the input and output circuits of ATE  100 .  
         [0017]     In the embodiment illustrated, extending from holding fixture  50  (and electrically connected to wiring harness  106 ) is a microphone  110 . In an alternative embodiment, for example for retrofitting to existing ATE, a connection between sound interface  104  and microphone  110  may be separate from wiring harness  106 .  
         [0018]     In one example embodiment, UUT  12  is an inertial measurement unit (IMU). In the example embodiment, microphone  110  is a sensitive microphone placed near the IMU under test. Microphone  110  is placed in close proximity to the IMU and attached to a digital computer sound card input. ATE  100  is configured with a software program used to capture a resulting acoustic signature, for example, created during a power up sequence of the IMU. In addition, ATE  100  may be further configured to measure acoustic outputs of UUT  12  during specific portions of the test program as the operating capabilities of UUT  12  are tested.  
         [0019]     To illustrate capabilities of ATE  100 ,  FIG. 3  is a graph  150  illustrating a portion of an audible output for a known good IMU. Graph  150  illustrates an amplitude of sound over time emitted by the IMU during the power up sequence and the beginning of communications with external systems. However,  FIG. 4  is a graph  200  illustrating the same audible outputs as illustrated in  FIG. 3  for a suspect IMU. In this particular IMU, a five volt power supply is not operational. After about 30 seconds, a dither motor within the IMU becomes saturated and begins to oscillate. The audible sound created by this oscillation is shown in graph  200  as a 875 Hz signal. By receiving the 875 Hz signal through microphone  110 , ATE  100  is capable of determining that the five volt power supply has failed without having to make a series of signal measurement as is done utilizing current testing methods.  
         [0020]     While described in terms of an ATE application, the acoustic signature testing methods described herein may also be implemented within the various products, for example IMUs, themselves.  FIG. 5  is a block diagram of an IMU  300  which incorporates the above described acoustic signature sampling capabilities. IMU  300  includes a microprocessor  302 , memory  304 , gyroscopes  306 , accelerometers  308 , gyro and accelerometer excitation and control circuits  310 , serial input/output (I/O) circuits  312 , and discrete input/output (I/O) circuits  314 . In one embodiment, discrete I/O circuits  314  includes circuitry dedicated to a built in test (BIT) for IMU  300 .  
         [0021]     Gyroscopes  306 , accelerometers  308 , gyro and accelerometer excitation and control circuits  310 , serial I/O circuits  312 , and discrete I/O circuits  314  communicate with microprocessor  302  over a bus  320 . IMU  300  further includes power supply circuits  322  which provide the various power sources utilized by the other components of IMU  300 . In the embodiment illustrated, IMU  300  further includes a microphone sensor  330  located in proximity to gyroscopes  306  and accelerometers  308 . Microphone sensor  330  is configured to provide signals to an analog-to-digital (A/D) converter  332  which digitizes the analog signals received from microphone sensor  330  and outputs those signals to bus  320  for receipt by microprocessor  302 . After analysis of such signals, microprocessor  302  is configured to provide a result of such analysis to external systems, for example, by communicating the analysis through serial I/O  312 . As used herein, the term microprocessor is understood to include all devices capable of processing programmed instructions. In a specific embodiment, microprocessor  302  is a microcontroller which incorporates the functions of A/D converter  332  internally.  
         [0022]     Incorporation of microphone  330  and A/D converter  332  provide another testing function that can be incorporated into a prognostic health management system stored in memory  304  and running on microprocessor  302 . Such an embodiment might include, for example, measurements of sound levels and frequencies for a known good IMU that are stored within IMU  300 . Comparison of the acoustic signature for the known good IMU are then compared to measurement taken within IMU  300 , for example, during power up sequences and may include periodic measurements of sound levels during operation. If the sound levels and frequencies vary from expected levels and frequencies stored within IMU  300 , microprocessor  302  is programmed to communicate those measurements to an external system for either storage or further analysis (by either a user or the external system). Upon completion of the analysis, it is communicated to the proper persons, for example, those who provide maintenance for the systems which employ IMUs  300 . The communication may also include the possible causes for the uncharacteristic levels and/or frequencies generated within the IMU  300 .  
         [0023]     While microphone  330  is described herein as being in proximity to gyroscopes  306  and accelerometers  308 , it is to be understood that such an embodiment is only one example. Microphones providing signals to A/D converters might be utilized in several places within an IMU to provide information regarding failed, or likely to fail components. As such, operators, for example those familiar with IMU designs, can use the acoustic signature, perhaps in graphical form, (i.e., amplitude, time, frequency) to determine the failure mode within the IMU and act accordingly.  
         [0024]     While described herein in terms of a microphone receiving audio signals, other embodiments utilize devices other than microphones to determine the presence of an acoustic signature or other vibrational characteristics. Specifically, and in one embodiment, a low level laser beam is reflected from a surface, for example, a gimbal in an inertial measurement unit. The reflection is demodulated, which exposes any changes in vibration.  
         [0025]     While described in terms of an example IMU, the above descriptions should not be construed as being so limited. Many other products and subassemblies are configurable to allow the incorporation of microphones, vibration measurement devices, and A/D converters for implementation of the above described acoustic testing methods, including, but not limited to, sensor products such as ring laser gyroscopes and accelerometers, printing wiring boards, power supplies, electronic products, and mechanized products.  
         [0026]     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.