METHOD AND APPARATUS FOR AUTOMATICALLY BALANCING ROTATING MACHINERY

Abstract: A method of and apparatus for balancing rotating machinery (20) involves the transient acquisition of transient data (100) over the operational speed range of the engine being analyzed. A spectrum of the transient data is acquired using a real time spectrum analyzer (7) capturing an RPM triggered waterfall (34, 38). Further, a computer calculates a one shot balance solution. The balance solution (44) is shown on a video display screen (850) and includes the suggested solution to the balance problem based on the acquired data and generic sensitivity coefficients (46) and the predicted vibrational behavior of the proposed solution. By acquiring a second set of data, it can be verified whether the one shot balance solution remedied the balance problem. If a problem remains, the operator may calculate engine specific sensitivity coefficients based on at least two previous data acquisition runs. A new trim balance solution is then calculated based on the immediately previous run and the calculated engine specific sensitivity coefficients.

Description: METHOD AND APPARATUS FOR AUTOMATICALLY BALANCING ROTATING MACHINERY FIELD OF INVENTION The invention generally relates to rotating machinery and, more particularly, to a method and apparatus for automatically obtaining a balance solution for balancing rotating machinery. BACKGROUND OF INVENTION Vibrational forces can result in failure or inefficient operation of rotating machinery like turbine engines. In turbine engine environments, a substantial number of close-tolerance parts rotate at high speeds in a high temperature atmosphere. Consequently, significant vibrations due to imbalance can significantly harm the engine assembly. To avoid such pitfalls, techniques have been developed which monitor vibrations and indicate when the rotating machinery is unbalanced. Reliable engine vibration monitoring typically begins with an accelerometer. An electrical output signal must be delivered from the accelerometer, often located in the depths of the engine, via specially configured cables, to signal processing electronics. The electronics are used to condition the accelerometer signals for on-board storage or cockpit displays. Once a balancing problem has been discovered, it is necessary to perform engine vibration analysis to diagnose and correct the problem. Specifically, the engine has to be taken out of service and analyzed which typically involves mounting the engine on a test stand. Mounting the engine on the test stand is time-consuming and costly. A conventional method for performing such analysis involves first conducting a vibration survey. Vibration data is sensed by an accelerometer and tachometer over a plurality of engine speeds to determine whether a vibrational limit has been exceeded. If, during the vibration survey, the limit is not exceeded, then the engine is appropriately balanced and no further steps need to be taken. When the vibrational limit has been exceeded, typically the first assumption is that a balancing problem exists and a balancing procedure is initiated. However, if the vibrations are not reduced with balancing, spectral analysis is employed to pinpoint the cause of the vibration problem. Data must be acquired to quantify the magnitude of the vibrations. In the past, a steady state dwell has been performed at approximately ten discrete points over the applicable range of engine operation to acquire the amplitude and the phase of the vibration as a function of speed. Thereafter, a trial weight is installed which could be a first guess or one shot of how to balance the system. Next, a second steady state dwell is performed at the same discrete points to measure the change in vibration that resulted form the change in balance weight. The change quantifies an imbalance sensitivity value (coefficient) which is used to calculate a new balance solution using a least squares algorithm. Assuming, as is commonplace, that the engine remains unbalanced, a new balance solution is calculated. The balance solution is ideally the best solution for the entire operating range of the engine. In another conventional method, an individual manually logs data for each steady state dwell and enters the logged numbers into a computer which calculates the balance solution. According to another balancing system in the prior art, the MTI ® PBS-4100™ available from Mechanical Technology Inc. , the specifications of engines can be stored in a computer so that the system knows where to conduct the steady state dwells. Data obtained from those dwells is processed by the computer using the least squares algorithm to determine a balance solution. After the first dwell, the PBS-4100™ system using generic sensitivity or influence coefficients stored in the computer for the engine model being tested, performs one shot balancing and then the second steady state dwell for confirming whether the system is balanced. After a balance solution has been calculated by the PBS-4100™ system, the system provides a display to show the recommended location and size of the balance weight which should be installed on the engine. One problem associated with this method is the difficulty in ensuring that the first and second steady state dwells are performed at the identical speeds. There could be differences between 10-15 RPM in the first and second steady state dwells which adversely affect the data quality. In particular, data is acquired within a tolerance band of engine speeds. For example, data can be acquired from 2950-3050 RPM for a target speed of 3000 RPM. The errors in speed result in errors in calculating engine specific sensitivity coefficients and balance calculations. Another problem which arises with the above method is that it takes a substantial period of time to balance an unbalanced engine. SUMMARY OF INVENTION The present invention provides a method and apparatus for overcoming the drawbacks associated with conventional rotating machinery balancing systems. For example, the present invention provides a method and apparatus for balancing a rotating member in a reduced amount of time over conventional methods. Automated data acquisition provides fast, accurate balance solutions in minutes, eliminating dwell or constant speed operation resulting in a fuel savings as well. Further, the present invention can more precisely estimate a balance solution for an unbalanced rotating member. One of the ways this can be accomplished is by using automatic or transient data acquisition during a slow engine acceleration or deceleration so that no dwelling at engine speeds is necessary. As a result, data can be acquired at substantially more points while reducing data acquisition time. Between 50 and 100 points may be automatically acquired using transient data acquisition with real time processing while approximately ten points are acquired according to the conventional steady state dwell method. The accuracy of the balance solution is enhanced by employing more measurement points. Accordingly, using transient data acquisition results in a more accurate balance calculation than the conventional steady state dwell method. More specifically, transient data acquisition is triggered on the measured speed of the rotating member. Thus, if on a first data acquisition run, data was collected starting at 1000 RPM and each 50 RPM up to 4000 RPM, data acquisition would precisely occur at those speeds. For subsequent data acquisition runs, data would also be acquired at these exact speeds in contrast to the conventional steady state dwell method. Consequently, the resultant engine specific sensitivities and balance solutions that are calculated from the acquired data are more accurate than the conventional steady state dwell method. Also, the present invention provides an estimated response of the balance solution after it has been calculated and before its implementation to allow a user to decide whether the solution is desired. Additionally, the present invention is capable of representing the balance solution for each point in the range of points from which data has been acquired so that a user can customize the balance solution according to the desired characteristics of the system. For example, a user can calculate a balance solution for a particular speed range or a particular sensor. The balancing system of the present invention does not require disconnecting the rotating member from the structure in which it has been installed, e.g., an airplane, a boat, etc. , thereby taking the engine out of service. Accordingly, the system minimizes costly engine removals and reduces unnecessary maintenance by allowing the user to test and balance the engine in place. In other words, engines do not have to removed and connected in a test stand. A method of balancing a rotating member in an interactive computer system wherein member data including characteristics of a member type is prestored in memory involves several steps. The steps include slowly changing a rotating speed of the member over a predefined speed range according to the member type, detecting transient vibrational data at a plurality of points within the speed range while changing the rotating speed of the member, determining whether the member is in an unbalanced state according to the transient data, and calculating a balance solution when the member is in an unbalanced state based on the member data and the transient data. The step of detecting transient data can include the steps of generating a waterfall file and displaying a three dimensional representation of the waterfall file data referred to as a waterfall plot. A waterfall plot is a graphical representation of data on three axes. For example, one axis is RPM, a second axis is frequency and a third axis is vibration amplitude. More specifically, the step of detecting transient data utilizes the real-time spectrum analyzer to capture and digitize both the vibration signal and the tachometer signal. The data is captured at incremental RPM values as the engine is accelerated or decelerated. For each snapshot of data, the time domain digitized waveforms are transferred to the frequency domain using the Fast Fourier Transform (FFT) Method. The resultant FFT representation of the vibration signal characterizes the spectrum of vibration components measured by the system. The step of detecting transient data includes processing the waterfall data to obtain synchronous vibration amplitude and phase data from the member at the points within the speed range at one or more locations on the member. The locations where sensing occurs can be selected by a system operator. The member data used to calculate the balance solution includes sensitivity (i.e., influence) coefficients associated with the member type. New member data may be input into the memory by an operator. The step of determining includes comparing the transient data with a predetermined vibrational limit. The method can include the step of installing at least one weight in an identified position according to the balance solution. A balance weight can be identified as installed after removal of previous balance weights, or installed without removal of previous balance weights. At least one position on the member and a correction weight to be installed at the at least one position for the balance solution can be identified and displayed. Further, a plot of a first vibration signature of the member based on the transient data can be displayed and a plot of a second vibration signature of the member based on the balance solution can be estimated and displayed. A vibration signature is a plot of the synchronous vibration amplitude as a function of the rotating speed of the member, and represents the balance condition of the rotating member. The speed range includes member speeds from an idle condition to a maximum power condition. The speed range can be selected and defined by two speeds between an idle condition speed and a maximum power condition speed according to the member type. An apparatus for balancing a rotary member according to the present invention includes sensing means, coupled to the member, for detecting transient data at a plurality of points within a speed range of the member while slowly changing a rotating speed of the member, a digital processor, coupled to the sensing means, for performing spectral analysis which produces waterfall data for detailed vibrational analysis, for producing balance data from the waterfall data, for comparing the balance data to a vibrational limit, and means, coupled to the digital processor, for calculating a balance solution based on first sensitivity coefficients and the balance data when the balance data exceeds the vibrational limit. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described in more detail with reference to preferred embodiments of the invention, given only by way of example, and illustrated in the accompanying drawings in which: Fig. 1 represents an exemplary turbine engine which can be balanced according to the present invention; Figs. 2(a)-2(c) represent exemplary configurations for interfacing aircraft engines to the engine vibration and balance analysis system according to the present invention; Fig. 3(a) is an exemplary engine vibration and balance analysis system configuration according to an embodiment of the present invention; Fig. 3(b) is a data flow diagram for the system of Fig. 3(a); Fig. 4 is an exemplary waterfall file display according to the present invention; Fig. 5 is a flow chart of an exemplary single plane balancing method according to the present invention; Figs. 6(a)-6(m) represent exemplary screens for an illustrative interactive environment according to the present invention; and Figs. 7(a) and 7(b) represent a flow chart of an exemplary dual plane balancing method according to the present invention. DETAILED DESCRIPTION A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone one of the patent disclosure, as it appears in the Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever. While the following description is in the context of aircraft engine systems, it will be understood by those skilled in the art that the present invention may be applied to other types of rotating machinery including gas turbine engines, compressors, power generators, pumps, motors, and steam turbines. Fig. 1 represents an exemplary engine for which an engine vibration and balancing analyzing system according to the present invention may be used. The engine includes a fan section including a fan 1 and a booster 2 for low pressure propulsion, a core section including a high pressure gas generator or compressor 3 and a high pressure turbine 4, and a low pressure turbine section (LPT) 5. Vibration data and engine speed data are used in the engine balancing system. To obtain vibration data, sensing elements, e.g., accelerometers, must be coupled to the turbine engine to measure the appropriate data. In the exemplary engine of Fig. 1, one or more accelerometers for measuring vibration are located, among other positions, on a fan bearing (not shown) coupled to the fan 1 in the fan section, on a fan case (not shown) coupled to the fan 1 in the fan section, on a turbine rear frame (not shown) in the LPT section 5, and/or on a rear frame of the compressor 3 in the core section. The accelerometer at each position corresponds to one balance and vibration channel for measuring vibration of the engine. A wide range of accelerometers may be used to measure acceleration of the engine or to detect and measure vibrations such as compression type or shear type accelerometers. In an illustrative compression type accelerometer, a mass exerts a compressive force on a piezoelectric element. In an illustrative shear type accelerometer, a mass exerts a shear force on the piezoelectric element. General purpose type accelerometers with a sensitivity of 1 to 100 pC/g a weight of between 10 to 50 grams and a frequency range of 0 to 12 khz are suitable for use with the present invention, although the invention is not limited in this respect. Further, a miniature type accelerometer having a sensitivity of between 0.05 to 0.3 pC/g, a weight of 0.5 to 2 grams, and a frequency range of 1 to 25 khz is also satisfactory. Other types of acceptable accelerometers include those used: 1) for triaxial measurements; 2) for permanent monitoring measurements on industrial machines; 3) for use in very high temperature; 4) for calibration and other reference purposes; 5) for building and other structural vibration measurements; and 6) for very high shock measurements. In some aircraft, there are already accelerometers in place which measure the vibrations. In the event that accelerometers are not in place in the aircraft, a preferred accelerometer type is the DYTRAN ® Model 3174C high temperature accelerometer. In practical accelerometer designs, the piezoelectric element is arranged so that when the assembly is vibrated the mass of the assembly applies a force to the piezoelectric element which is proportional to the vibratory acceleration. It should be noted that direct loading of a piezoelectric output of the accelerometer output can greatly reduce the accelerometer' s sensitivity as well as limit its frequency response. To minimize these effects, the accelerometer output signal is fed through a preamplifier to a much lower impedance than that of the accelerometer, that is an impedance suitable for connection to the relatively low input impedance of typical measuring and analyzing instrumentation. Also, velocity transducers or displacement probes may also be used to detect and measure vibrations. Vibration sensors may be existing engine transducers or ground test transducers. A tachometer such as a magnetic tachometer or an optical sensor tachometer may be used to determine the speed of rotation of the engine. An eddy probe type magnetic tachometer which uses a magnetic field to count the speed of rotation can be employed in the present invention. On an aircraft equipped with an aircraft vibration monitoring (AVM) system, an exemplary magnetic tachometer senses engine RPM by picking up an intentionally machined high tooth on a gear. An exemplary optical sensor tachometer senses speed using a beam of light reflecting off a marked point. For example, the marked point is reflective tape attached to the number one blade on a fan. Aircraft engines can be classified into one of three configurations: 1) non- AVM; 2) old AVM; and 3) new AVM. In a non- AVM configuration, vibration sensors must be positioned by a technician in order to measure vibration. AVM configurations include vibration sensors. In old AVM configurations, the sensor output is accessed via an in-line connection and in new AVM configurations the sensor outputs are accessed via a front panel connector in the cockpit. Aircraft having non-AVM platforms include Boeing 727, 737-200, and 757; DC 10; and MD80. The equipment needed for a non-AVM system depends on the engine and aircraft, and may include two accelerometers; approximately 250 foot non- AVM cable package including two charge amplifiers (already in-line) and one optical sensor tachometer; bracket kits for the particular engines; and a vibration analyzer with BNC connectors and cables. Fig. 2(a) shows an exemplary non-AVM cable interface between an aircraft and a vibration analysis and balancing system of the present invention. In a non-AVM system, the engine vibration and balancing analyzer 7 is connected directly to the turbine engine 6. According to this exemplary interface, three or more data channels are coupled to three or more sensors located on the turbine. Channel 1 is coupled to the tachometer, channel 2 is coupled to a front vibration sensor on the fan bearing and channel 3 is coupled to a rear vibration sensor on the turbine rear frame. In addition, SUBSTITUTE ^ SHEET (RULE 26) power is supplied to the tachometer and accelerometer via a power line coupled to the analyzer 7 for operating the system for vibration and balancing analysis. Aircraft using old AVM platforms include the Boeing 737-300. An exemplary old AVM cable interface is depicted in Fig. 2(b). The built-in equipment typically needed includes an old AVM cable on the aircraft side 8; a tachometer conditioner box 9; and a vibration analyzer 7 with BNC connectors and cables. In the old AVM interface, channel 1 is coupled to the tachometer conditioner 9 which along with, channel 2 for front (e.g., fan bearing) vibration and channel 3 for rear (e.g., turbine rear frame) vibration, are each coupled to the AVM Box 11 and AVM receptacle 12 for obtaining vibrational data via the AVM from the aircraft side 8. The power tine is coupled to the tachometer conditioner 9. The new AVM platform is adaptable for use with all new aircraft. Fig. 2(c) represents an exemplary new AVM cable interface. The equipment typically needed includes a new AVM cable for connecting the analyzer 7 and the aircraft side 8; a tachometer conditioner box 9; and a vibration analyzer 7 with BNC connectors and cables. In the new AVM interface, channel 1 is coupled to the tachometer conditioner 9 which along with, channel 2 for front vibration and channel 3 for rear vibration, are each coupled to an AVM Box 13 located on the aircraft side 8 which acquires data. The power line is coupled to the tachometer conditioner 9. In the AVM interfaces of Figs. 2(b) and 2(c), the tachometer conditioner box 9 receives a series of pulses for engine revolution and outputs one pulse per revolution for the engine speed. An external trigger input to the vibration and balance analyzer 7 receives pulses from the tachometer, measures the time between pulses, and calculates the engine speed in RPMs. The vibration sensors measure vibration at all frequencies. For engine balancing, the vibration component required for balance calculations is the fundamental or synchronous vibration component. The frequency of this component is at the frequency of the engine rotational speed. The RPM value calculated from the external trigger is used to locate the frequency component in a magnitude and phase waterfall to obtain the balance vibration magnitude and phase. During engine operation, an aircraft vibration monitor will indicate or sensors will sense a vibration. To analyze the vibration, a flight line mechanic connects a breakout cable to the AVM or installs sensors (e.g., accelerometers) and a tachometer. Several elements form an illustrative engine vibration and balance analyzer as shown in Fig. 3(a). The vibration data and engine speed are received from the sensors and, via the external trigger input, supplied to a transient data acquisition circuit 100 which includes an analog to digital (A/D) converter 150 (e.g., a 16 bit A/D converter) for converting acquired data into digital form. Each vibration sensor corresponds to a balance channel. Data can be acquired in either 1) the conventional steady state speed method where vibration amplitude, phase and speed (RPM) information are collected at selected constant speed operating conditions; or 2) in a slow transient engine accelerations or decelerations in which on-line vibration amplitude, phase, and RPM data is collected. The pre-processed digital vibration data is forwarded to a digital signal processor (DSP) memory 250 in a signal processing circuit 200. According to an exemplary embodiment, DSP memory 250 is an 8 megabyte RAM, but may be larger according to the number of channels (sensor locations) on the engine. In the signal processing circuit 200, a DSP processing section 350 processes the vibration and tachometer signals (i.e., acquired transient data) using real time spectrum analyzer functions. In an illustrative implementation, the signal processing circuit 200 includes a 32 bit DSP microprocessor which runs at 50 MHz. At predetermined incremental RPM changes (e.g., 50 RPMs), the vibration and the tachometer data are averaged, processed, and stored into the waterfall file located in the DSP memory 250. The incremental changes in engine speed for signal processing are selected in consideration of the ability of the analyzer to acquire data. Thus, to achieve the best resolution the selected increment is preferably as small as the analyzer will permit. At the conclusion of the data acquisition process, the waterfall file data is written to a disk from the memory 250. The waterfall data is then post-processed to extract the balance amplitude and phase signature. The signal processing section 200 is controlled by a user interface 400 including a host interface 450 which downloads DSP software to the DSP processing section 350. The DSP memory 250 forwards displayable traces, e.g., graphically displayable information, including time and waterfall files and amplitude, phase, and speed information to the host interface 450. The displayable traces, in addition to representing the data, also show a vibrational limit on the data plots either input by the user or prestored in a hard drive 500. Thus, the DSP processing section 350 compares the data with the vibrational limit. In an exemplary embodiment, the user interface includes a MICROSOFT ® compatible graphic users interface which guides the user through the balancing procedure. An exemplary host interface may be a standard 80386 or optional 80486, with companion coprocessor operating at 33 MHz. The host interface 450 is coupled to a digital input/output (I/O) card 550 and downloads spectrum analysis software for digital signal processing operations (i.e., FFT algorithm 32) to the digital I/O card 550. The digital I/O card 550 may be coupled to function keys on a keyboard, a mouse, a printer, etc. The user interface 400 is coupled to a disk drive controller 600 and stores and receives data from both an internal hard drive 500 (i.e., a 50 megabyte hard disk drive, 120 megabyte optional) and a floppy 700 (e.g., 1.44 megabyte 3.5 inch floppy disk). The balancing software 650 for leading the user through the steps to balance an engine is stored in the hard drive 500. Other information typically stored in the hard drive 500 includes the software for the spectrum analyzer, data acquisition program, the data for each engine type, engine run data and waterfall data following completion of data acquisition, and balance solution data. The data for each engine type includes setup information for how the data is acquired and the balance characteristics of the particular engine. Information exported from the hard drive 500 to the floppy 700 usually includes the engine run and waterfall data and a balance file. The balance file contains the vibration data acquired in a previous run and can be used to calculate a balance solution when combined with engine sensitivity file at any time for the engine to which it applies. Also, the user interface 400 is coupled to a video graphics adapter (MT) 750 which can send video data to a gas plasma display 800 and/or an external MT display 850 for displaying the balance solution, the waterfall file, etc. An exemplary waterfall file display is shown in Fig. 4. A data flow diagram is shown in Fig. 3(b) for the system described Fig. 3(a). From the rotating member 20, vibration data and engine speed data are detected by a plurality of vibration sensors 22 and a speed sensor 25, respectively. The sensors correspond to balance channels. The data information from the vibration sensors 22 and speed sensors 25 is input to a spectrum analysis portion of the balance analyzer. More particularly, the vibration data from the vibration sensors 22 is transformed from the time domain into the frequency domain using the FFT 32. The parameters needed to perform this transform can be modified by the user with the typical values set up as follows: Fmax=500 MHz, N=200 lines and overlap=max. The FFT 32 result is transformed into a magnitude spectrum at a magnitude waterfall section 34. Also, a cross correlation spectrum section 36 calculates a cross correlation spectrum that is input to a phase waterfall section 38 which determines the phase response of a vibration sensor 22 with respect to the speed sensor 25 (i.e., tachometer). The acquisition of each magnitude and phase spectrum is triggered by the tachometer. The balance amplitude from the magnitude waterfall section 34 can be used to perform spectrum analysis diagnostics in a diagnostics section 40. The balance amplitude and phase signature data from magnitude waterfall section 34 and phase waterfall section 38, respectively, are saved into a balance vibration data file 42. The data in the balance data file 42 is used to calculate a balance solution 44 with a sensitivity file 46 which includes the sensitivity coefficients associated with the engine being balanced. A high performance real-time spectrum analyzer designed to diagnose vibrational problems, including at least balance related problems, may be used as a digital signal processing device. An exemplary analyzer for implementing the present invention is the Dynamic Signal Analyzer Model SA390 manufactured by Scientific-Atlanta, Inc. An analyzer which can identify balance as well as non-balance related problems including acoustic problems may also be employed. The spectrum analyzer must be capable of performing engine vibration surveys across the entire engine speed range and preferably includes versatile time domain (oscilloscope) and spectrum displays to aid in identifying sources of vibration. Such a device eliminates unnecessary engine removals and solves vibrational problems with significant time and cost savings. By employing a spectrum analyzer which can process a data spectrum or waterfall data in real time, the engine vibration and balance analysis system may carry out transient data acquisition in which an engine can be accelerated from idle to full power for multi-speed, multi-plane balancing. The device acquires a multitude of vibrational data including amplitude, phase, and frequency over an engine's power range. More data increases accuracy and results in better predicted balance solutions. Real time transient data acquisition avoids the dwelling associated with conventional balancing systems while providing substantially more data points. Further, the engine need only run on the order of two to five minutes to obtain data which not only is less than conventional methods, but also results in increased fuel savings and shorter time to obtain a balance solution. The engine vibration and balance analysis system of the present invention is further adaptable to receiving vibration data from an on-flight engine vibration monitoring system such as the ENDEVCO ® MICROTRAC II™. Accordingly, the data on-flight may be entered into the engine vibration and balance analyzer as a data run and a balance solution can be calculated. The steps involved in an exemplary balancing operation for a single plane balancing solution used with the engine vibration and balance analysis system described above are shown in the flow diagram of Fig. 5. In step ST1, the hardware for connecting the engine and the analyzer is hooked up. Control passes to step ST2 where the engine run information is collected concerning the engine speed and vibration level. After data has been collected, in step ST3 it is determined whether the engine vibrations exceed a predefined vibrational limit. If the vibrational limit is not exceeded, no balance problem is detected in ST3. Then control shifts to step ST4 where the hardware is removed and the operation is complete at ST5. Otherwise, if the vibrational limit is exceeded, a balance problem has been detected and control shifts to step ST6 where a first shot or one shot balance solution to the problem using generic sensitivity coefficients is calculated. Thereafter, control shifts to step ST7 where correction weights are installed according to the one shot balance solution calculated in step ST6. After installing correction weights in step ST7, the engine is run again at step ST8 to acquire vibrational data. Next at step ST9 it is determined whether a vibration problem still exists. Consequently, in step ST9 the acquired data is again compared to the vibrational limit to determine if a balance problem still exists. If no balance problem is detected in ST9, then control shifts to step ST 10 where the hardware is removed and the operation is complete at ST11. If a problem exists at step ST9, new engine specific sensitivities are calculated based on the previous two runs at step ST12. Control shifts to step ST13 where a new balance solution is calculated based on the new engine specific sensitivities and the data acquired during the previous engine run. The steps ST7, ST8, ST9 are again conducted. If a balance problem remains, steps ST12, ST13, ST7, ST8, and ST9 are carried out until the problem has been eliminated. Once a desired solution has been obtained, the various cabling and hardware connected to the engine are removed at STIO, the operation is complete at step STll, and the engine can be normally operated. Figs. 7(a) and 7(b) represent the flow diagram of the balancing operation necessary to obtain a dual plane balancing solution. Similar steps depicted in Fig. 5 are represented with the same labels in Figs. 7(a) and 7(b). If a user desires to calculate a dual plane solution, after a balance problem is detected at step ST9, a second shot solution is calculated with generic sensitivities at step ST14. Thereafter, balance weights are installed and the engine is run again at steps ST15 and ST16, respectively. At step ST17 the acquired data is compared with vibrational limit to determine whether a balance problem remains. If not, steps STIO and STll are carried out. Otherwise control passes to step ST18 where new sensitivities are calculated based on data acquired during the three previous engine runs (ST2, ST8, and ST16). In step ST19, the new sensitivities are used with the data from the last run to calculate a balance solution. Subsequently, weights are installed and the engine is run again at steps ST15 and ST16, respectively. Another comparison is made at step ST17 to determine whether further balancing is required. If a problem remains, steps ST18, ST19, ST15, ST16, and ST17 are carried out until the problem has been solved. Once it is determined that a balancing problem no longer exists, steps STIO and STl l are executed and the operation is complete. It is to be understood that the system can be adapted to perform balancing for more than two planes by modifying the above process based on the number of planes desired. An open architecture MICROSOFT ® WINDOWS™ operating system with full internal spectrum analysis may be employed for interactive user/system communication. The system is designed for PC compatibility. Other operating systems known in the art such as DOS, OS/2™ and the like can be adapted to employ the present invention. However, WINDOWS™ is preferred. In an illustrative implementation of the present invention, various operation modes may be accessed by a user in a WINDOWS™ environment where a user inputs data and selects operations to be performed. The system user after hooking up the appropriate cabling and connecting the necessary hardware as described with reference to Figures 2(a)-2(c) enters the WINDOWS™ environment and is presented with a main menu of alternatives on a screen of the engine vibration and balance analyzer as shown in Fig. 6(a). If the user selects the SETUP push button by, for example, using a trackball to position the pointer on the SETUP push button and clicking, a Select Engine type screen as shown in Fig. 6(b) is presented. The Select Engine Type screen includes a list field 300 which lists various pre-stored data files containing specifications regarding a plurality of engine types. The files are preferably stored in hard drive 500 of Fig. 3(a). The user then selects the appropriate engine type corresponding to the engine to be balanced. Alternatively, a user may identify an engine type not stored in memory in which case the engine vibration and balance analyzer will prompt the user to enter data concerning the specifications of the engine to be balanced. The Select Engine Type screen also includes list field 310 and drop-down fields 320 and 330 to change drives and directories and vary the list of files, respectively, appearing in list field 300 in a manner well-known in the art. After selecting the file corresponding to the desired engine, the Main Menu screen in Fig. 6(c) is presented. This screen provides an indication of the engine type, any comments about the engine, and indications of the connections of the vibration sensors to the data channels of the analyzer. Other engine information may be displayed and the invention is not limited in this respect. Following verification that the correct engine type has been selected, the uses actuates the ACQUIRE DATA push button and the Engine Run Setup screen of Fig. 6(d) is presented. At this time, the user may enter a serial number for a specific engine in the engine serial number field. If the user enters a serial number, the number is saved so that transient data acquired concerning this engine will be automatically saved at the end of the run for future reference. The weight and angle fields in the Engine Run Setup screen allow the user to enter weight information for existing weights in either the front plane or the rear plane. The ACQUISITION buttons permit the user to select the desired type of run, manual or automatic. In a manual mode of operation, non-transient data is acquired for specific rotating speeds, as is done in the conventional steady state dwell methods. In an automatic mode of operation, data is automatically collected when the engine is gradually accelerated. Data will be acquired at preprogrammed rotating speed intervals. For example, an exemplary data acquisition period according to the present invention can be on the order of two to five minutes where data is collected for between 50 and 100 points over that time. Selecting the CANCEL push button returns the system to the screen of Figure 6(c) without initializing the entries made. Selecting the OK push button sets the system up for acquiring data. If a tachometer signal is not present at this time, a screen is presented which informs the user that an improper RPM has been detected and prompts the user to check the tachometer connected to the balancing system. The user is also queried as to whether it is desired to continue data acquisition. In response to this query, the user may abort the test. If the tachometer signal is detected, the user may respond affirmatively to the query to continue the test. If the test is continued, a screen such as in Figure 6(d) is presented. While the engine run information is collected concerning the engine speed and vibration level, the screen in Fig. 6(e) is simultaneously presented. In one embodiment, a spectrum analyzer may be employed which displays the data information in a waterfall display (e.g., Fig. 4) typically after data acquisition, although it is possible to display the waterfall data while data acquisition is occurring. With the engine operating below the minimum engine RPM, the user can select the START push button. When the START push button is actuated, the engine speed gradually increases to the maximum speed. Upon reaching the maximum engine speed, the engine has run its course. At this time, the STOP push button should be actuated to cease data acquisition. When the STOP push button is actuated the Main Menu screen of Fig. 6(c) is presented and the user may now calculate the balance solution. When the BALANCE SOLUTION push button in Fig. 6(c) has been actuated, a Balance Menu screen is presented displaying information concerning the run and indicating whether the engine vibrations exceed a predefined limit stored in the hard drive 500 of Fig. 3(a). Thus, the data acquired is compared to the vibrational limit stored in the memory 250 of the user interface 400 to determine if a balance problem exists. An illustrative Balance Menu screen is shown in Fig. 6(f). When a balance problem is detected, the CALCULATE BALANCE SOLUTION push button may be actuated to calculate a first shot or one shot balance solution to the problem. Complex values referred to as generic sensitivity or influence coefficients are part of the data prestored in the engine vibration and balance analyzer memory 250 for each engine model type. Each stored generic sensitivity coefficient represents a value which relates to how the engine vibration of a particular engine model typically behaves as a result of a change in balance weight. By combining the acquired vibration data with the generic sensitivity data, the analyzer can calculate a one shot balance solution. When the user actuates the CALCULATE BALANCE SOLUTION push button from the Balance Menu screen, a Balance Solution screen such as that shown in Fig. 6(g) is presented. When the one shot balance solution is calculated, a diagram representing the engine balance flange is displayed showing the recommended sizes, part numbers, and hole locations of the weights to be installed. The balance solution is preferably calculated according to a least squares algorithm over all engine speeds and active vibration and balance channels. One such algorithm is disclosed in "A Least Squares Method for Computing Balance Corrections" by Thomas P. Goodman in Journal of Engineering for Industry. Aug. 1965, pp. 273-279. Also, the predicted vibrational data for the prescribed one shot balance solution is calculated and displayed along with the vibration data from the last run. After every run and without calculating a balance solution first, the user can view the data and may determine by analyzing the spectrum vibration signature that the vibration problem is not a balancing problem. Thus, for each balance solution calculated a plot of the current (i.e., associated with the preceding run) vibration signature may be displayed along with the estimated resultant vibration signature after installation of the balance weights corresponding to a calculated balance solution. Conventional systems limit the ability to troubleshoot because the amount of data is most often, if not always, inadequate to analyze the vibration data signature in the manner required to draw such a conclusion. To analyze the vibration data prior to calculating a balance solution, the user actuates Vibration Data from the menu bar of the Balance Menu screen of Fig. 6(f). A sub menu (not shown) appears under Vibration Data and includes the options of Select New Data File and Plot Vibration Data. The Select New Data File option should first be selected which allows the user to identify the desired file to be analyzed. Thereafter, the user actuates the Plot Vibration Data option and the system displays a plot of the vibration signature for the selected file. The balance weights can be identified as installed after removal of previous balance weights, or installed without removal of previous balance weights. After installing correction weights, the user can run the engine again and acquire data as described above to determine whether a vibration problem still exists. Consequently, the acquired data is again compared to the vibrational limit to determine if a balance problem still exists. If a problem exists or to insure that a proper balance is derived, the user should calculate new engine specific sensitivities after a weight has been changed. Thus, after acquiring data for a new run according to a weight change, new engine specific sensitivity coefficients, as opposed to a new balance solution, should be calculated. Engine specific sensitivity coefficients differ from generic sensitivity coefficients in that they are specific to the engine being tested as opposed to an estimate for the behavior of the engine model type identified. To recalculate sensitivities, the user actuates the Sensitivity Data from the menu bar when in the Balance Menu screen and the screen in Fig. 6(h) is presented. To calculate new sensitivities, the user selects the Calculate New Sensitivities option and the Sensitivity Menu screen of 6(i) is presented. The user can now select the type of balance desired, i.e., for one or multiple planes (balance locations on the engine). For example, as shown in Fig. 6(i), a front plane, rear plane, or dual plane can be selected. If either a front or rear plane balance is desired, only two data acquisition files are needed to calculate new engine specific sensitivities. However, if a dual plane balance is desired, three data files with weight changes for both planes are needed. If a user actuates the CALCULATE FRONT PLANE push button, a first data file screen (not shown) with a list of the acquired data files stored in the system memory appears from which the user selects a first data file. Then, a second data file screen (not shown) with the same list appears for the user to select a second data file. After both data files have been selected, a Sensitivity Menu screen such as that shown in Fig. 6(j) is presented and displays a summary of the selections. At this time, the user should select the Save Sensitivities option on the menu bar to save the information just selected. After the sensitivities have been saved, they are automatically loaded for use with the next balance solution. If the user selects an arbitrary sensitivity to be used for the calculation, the user can access the file with the Select New Sensitivity File option from the screen shown in Fig. 6(h). A list of the files is presented on the screen from which the user selects the new sensitivity file (not shown) for which a solution is desired. The user should then again select the Sensitivity Data option from the menu bar (i.e., a screen like that of 6(h) is presented) and this time select the Plot Sensitivity Data option to plot data for the selected plane. A Plot Sensitivity screen such as that of Fig. 6(k) is presented displaying the current sensitivity of the selected file. Thereafter, the user should request the engine vibration and balance analysis system to calculate a new trim balance solution. The new trim balance solution calculated will be based on the newly acquired data and the engine specific sensitivities calculated rather than the generic sensitivities. Again, it is prudent for the user to test the selected trim balance solution to ensure vibrational problems have been eliminated. If such problems remain, the user should instruct the engine vibration and balance analysis system to calculate new engine specific sensitivities based on all data acquisition runs conducted for the engine and continue in the manner described above until an acceptable trim balance solution has been obtained. Each trim balance further allows the user to fine tune the balance solution. After calculating a one shot or trim balance solution, a screen (not shown) with the balance menu bar of Fig. 6(g) is presented providing the user with several options including a Select Plane option not shown on the balance menu bar of Fig. 6(g). The Return option sends the user back to the previous screen or window. The Print option, assuming the engine vibration and balance analyzer is connected to a compatible printer, permits the user to send a copy of the data to a printer. Further, the Save option saves the balance solutions and recommendations to a file on the floppy disk. All balance vibration data is automatically saved after each engine run. The user may also remove, add, or consolidate weights in the various planes via the Adjust Weights option. Also, the user may set the maximum number of weights that will be allowed for a balance solution. A new run may be conducted with or without the weights removed from the last run at the user's discretion. Also, if a weight was in a plane prior to weight installation, the system can compensate for the weight found by calculating a new solution based on the removal of the old weight. The Select Plane option lets an user select the plane for which a balance solution is desired. A sub menu under Select Plane provides plane options. Thus, the user may, for example, request the analyzer to display a front or rear plane balance solution, or recalculate a front plane solution or rear plane solution when data was taken in a dual plane mode. The Customize option allows the user to specify particular balance and vibration channels to be considered when determining a balance solution. For example, the user can customize the balance weights for specific sensors or RPM ranges. If the desired solutions are modified when the Customize option is selected, the system will recalculate the weight recommendations (i.e., the balance solution) for the customized data. Data comparison, weight versatility, and the ability to externally store data can be very important. The Data Management push button in the Main Menu (Fig. 6(c)) provides these capabilities. When the Data Management push button is actuated, the screen in Fig. 6(1) is presented. Actuation of the Sum Weights push button allows the user to manually enter a weight type and location and calculate the net weight and vector sum of the weights entered. Actuation of the Plot Data push button lets the user compare two vibration signatures of differing runs or the vibration between two different engine serial numbers (e.g. , runs). When the Plot Data push button is actuated, the user is prompted to select first and second engine serial numbers for comparison. Then, the data for each engine run can be plotted side by side as shown in Fig. 6(m). Actuating the Export data to Floppy push button lets the user externally store all information concerning the current engine serial number selected on a floppy disk. The waterfall data is used for both determining the vibration amplitude and phase for balance calculations, and to troubleshoot and diagnose non-balance related vibration problems. For example, the waterfall file can be analyzed using the spectrum analyzer functions to troubleshoot non-balance related problems. Each record in the waterfall file can be post-processed to identify vibrational frequencies and trends. This file also indicates the validity of vibration signals helping to pinpoint instrumentation problems. Conventional methods of balance data acquisitions use analog tracking filters to obtain synchronous (1/rev.) vibration levels at a steady state speed condition. Sometimes transient data is acquired during an engine acceleration or deceleration for diagnostic purposes, but no attempt in the art has been made to balance this data due to acquisition limitations associated with non-real time spectrum analyzers. While particular embodiments of the present invention have been described and illustrated, it should be understood that the invention is not limited thereto since modifications may be made by persons skilled in the art. The present application contemplates any and all modifications that fall within the spirit and scope of the underlying invention disclosed and claimed herein.

Claims: WHAT IS CLAIMED IS: 1. A method of balancing a rotating member in an interactive computer system wherein member data including characteristics of a member type is prestored in memory, said method comprising the steps of: changing a rotating speed of the member over a predefined speed range according to the member type; detecting transient data at a plurality of points within the speed range while changing the rotating speed of the member; determining whether the member is in an unbalanced state according to the transient data; and calculating a balance solution when the member is in the unbalanced state based on the member data and the transient data. 2. The method of claim 1 wherein the step of detecting further includes the step of generating waterfall data based on the transient data. 3. The method of claim 2 wherein the step of detecting further includes processing the waterfall data to obtain vibration amplitude and phase data of the member at the points within the speed range. 4. The method of claim 3 further including the steps of: displaying the processed waterfall data; and analyzing the processed waterfall data when the member is in the unbalanced state to determine whether a balancing problem exists. 5. The method of claim 1 wherein said step of determining includes comparing the transient data with a predetermined vibrational limit. 6. The method according to claim 1 wherein said step of detecting data includes sensing amplitude and phase of vibrations of the member at the points within the speed range at one or more locations on the member. 7. The method according to claim 6 wherein said step of sensing includes selecting the one or more locations on the member. 8. The method according to claim 6 further including the steps of: generating waterfall data based on the transient data; and processing the waterfall data to obtain vibration amplitude and phase data of the member at the points within the speed range. 9. The method according to claim 1 wherein the member data used in said step of calculating includes sensitivity coefficients associated with the member type. 10. The method according to claim 1 further comprising the step of inputting new member data into the memory. 11. The method according to claim 1 further comprising the step of installing at least one weight in an identified position according to the balance solution. 12. The method according to claim 1 further comprising the step of identifying a weight to be installed at one position on the member for the balance solution. 13. The method according to claim 12 further including the steps of: displaying a first vibration signature of the member based on the transient data; estimating a second vibration signature of the member based on the balance solution; and displaying the second vibration signature of the member. 14. The method according to claim 1 wherein the speed range includes member speeds from an idle condition to a maximum power condition. 15. The method according to claim 1 further including the step of selecting the speed range to be defined by two speeds between an idle condition speed and a maximum power condition speed according to the member type. 16. The method according to claim 1 wherein the member data includes characteristics of a plurality of member types, and the method further includes the initial step of selecting the member type from the plurality of memory types. 17. A method of balancing a rotating member comprising the steps of: changing a rotating speed of the member over a member speed range according to a member type; detecting transient data at a plurality of points within the speed range while changing the rotating speed of the member in a first run; determining whether the member is in an unbalanced state according to the transient data detected in the first run; calculating a first balance solution when the member is in the unbalanced state based on first sensitivity coefficients of the member type and the transient data; changing a first weight amount of the member according to either the first balance solution or a user input weight change; changing the rotating speed of the member, the member including the changed first weight amount, over the speed range; detecting transient data at a plurality of points within the speed range while changing the rotating speed of the member in a second run; and determining whether the member is in the unbalanced state according to the transient data in the second run. 18. The method according to claim 17 further comprising the steps of: calculating second sensitivity coefficients based on the transient data detected in the first and second runs; and calculating a second balance solution based on the transient data detected in the second run and the second sensitivity coefficients. 19. The method according to claim 17 further including the step of selecting the speed range to be defined by two speeds between an idle condition speed and a maximum power condition speed according to the member type. 20. The method according to claim 17 wherein said step of changing the first weight amount further includes the step of installing a weight based on the first balance solution. 21. The method according to claim 17 wherein said step of changing the first weight amount further includes the steps of inputting a user desired weight change and installing and/or removing a weight based on the user desired weight change. 22. The method according to claim 17 wherein said steps of detecting transient data each include sensing amplitude and phase of vibrations of the member at the points within the speed range at one or more locations on the member. 23. The method according to claim 22 wherein said step of sensing includes selecting the one or more locations on the member. 24. The method according to claim 17 further including selecting a plane for which the first balance solution is desired and displaying the first balance solution for the selected plane. 25. The method according to claim 24 wherein the selected plane includes one of a single plane and a multi-plane. 26. The method according to claim 17 further including the step of selecting the member type associated with the member from a plurality of member types. 27. The method according to claim 17 further including the steps of: calculating a second balance solution when the member is in the unbalanced state based on second sensitivity coefficients of the member type and the transient data detected in the second run; changing a second weight amount of the member according to either the second balance solution or a user input weight change; changing the rotating speed of the member, the member including the changed second weight amount, over the speed range; detecting transient data at a plurality of points within the speed range while changing the rotating speed of the member in a third run; and determining whether the member is in the unbalanced state according to the transient data in the third run; calculating third sensitivity coefficients based on the transient data detected in the first, second, and third runs; and calculating a third balance solution based on the transient data detected in the third run and the third sensitivity coefficients. 28. An apparatus for balancing a rotary member comprising: sensing means, coupled to the member, for detecting transient data at a plurahty of points within a speed range of the member while changing a rotating speed of the member; a digital processor, coupled to said sensing means, for performing spectral analysis on the transient data to generate waterfall data; for producing balance data from the waterfall data, and for comparing the balance data with a vibrational limit; and means, coupled to said digital processor, for calculating a first balance solution based on first sensitivity coefficients and the balance data when the balance data exceeds the vibrational limit. 29. The apparatus according to claim 28 further comprising means for displaying the waterfall data. 30. The apparatus according to claim 28 further comprising means for displaying the balance solution. 31. The apparatus according to claim 28 wherein said sensing means includes means for sensing amplitude and phase of vibrations of the member at the points within the speed range at one or more locations on the member. 32. The apparatus according to claim 31 further comprising input means, coupled to said sensing means, for inputting the one or more locations on the member. 33. The apparatus according to claim 28 wherein said sensing means detects transient data during two separate runs and said calculating means calculates second sensitivity coefficients according to at least two transient data detection runs and calculates a second balance solution based on the transient data detected in the most recent transient data detection run and the second sensitivity coefficients. 34. The apparatus according to claim 28 wherein said rotating member is an engine mounted on an aircraft. 35. The apparatus according to claim 28 further including: memory for storing member data including sensitivity coefficients associated with each of a plurality of member types and storing the transient data; input means, coupled to said memory, for receiving a selection signal for selecting a member type which identifies the first sensitivity coefficients of a member to be balanced. 36. The apparatus according to claim 35 wherein said input means further includes means for inputting data detection operating data including either specified speeds or range of speeds for which the balance solution is to be calculated, said sensing means detecting transient data in accordance with the operating data. 37. The apparatus according to claim 35 wherein said input means further includes means for inputting a specified speed or range of speeds for which the balance solution is to be calculated.

Inventors: GRABILL PAUL JOHN, GRABILL, PAUL, JOHN
Applicants: SCIENTIFIC ATLANTA, SCIENTIFIC-ATLANTA, INC.
Application year: 1995
Main classification: G06F19
IPC codes: F01D25, G01M1