Abstract:
A computer method or corresponding system for optimally balancing a rotor assembly. The computer system defines a theoretical centerline based on a mathematical model of the rotor assembly. For each disc or component of the rotor assembly, the invention system calculates rotor blade or bolt and washer distribution, based on calculated centerline deviations and angular locations of the discs and effective weights of rotor blade or bolt-and-washer sets. The rotor blade or bolt-and-washer distribution provides locations for placement of the rotor blades or bolts-and-washers so as to offset the centerline deviations and thus correct imbalance of the rotor assembly.

Description:
RELATED APPLICATION(S) 
       [0001]    This application is a continuation of U.S. application Ser. No. 11/527,033, filed Sep. 26, 2006. 
         [0002]    The entire teachings of the above application(s) are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    A bladed rotor, such as a rotor of a gas turbine engine, includes a central hub, one or more discs and a plurality of blades secured to respective discs and projecting outward from the hub. The bladed rotor having multiple rotor blades rotates about a longitudinal central axis. Because of non-uniform distribution of mass within the rotor assembly and the blades, it is difficult to achieve a perfect balance for a bladed rotor. However, minimizing imbalances within a rotor assembly is essential for minimizing vibration and noise and maximizing the efficiency and performance of the rotor (and turbine engine). 
         [0004]    Currently, rotor assemblies are balanced by separately balancing each disc or component and aligning respective individual rotor discs or components in the assembly so that the high point of one disc is offset by the low point of its adjacent disc. The blades are distributed by mass about the theoretical geometric centerline of each disc. The main drawback of this approach is that it is a trial-and-error method which does not guarantee the optimal alignment of the rotor assembly because the separate centerline of each disc or component is not aligned with the centerline of the rotor assembly. For example, alignment of two rotor discs&#39; centerlines may satisfactorily align those two discs, but introducing a third disc&#39;s high point or low point in the assembly may be impractical to align with the other two centerlines. The blades may then be redistributed about each disc in an arbitrary, trial-and-error manner in the hope of achieving some acceptable balance. A static balance machine may be used to add weights to the disc or blades to help in achieving a rudimentary balance. Consistency and repeatability is missing in this trial-and-error procedure. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention addresses the shortcomings of the prior art and provides a computer method and system for balancing engine modules (e.g., rotor assemblies of a turbine engine). 
         [0006]    A method or corresponding apparatus in an exemplary embodiment of the present invention calculates a best-fit stack of the discs and the optimal blade or bolt-and-washer distribution (for rotors with integrated blades and discs) about the centerline of rotation of the rotor assembly for a turbine engine. In particular, the present invention defines an actual centerline of a geometrical/mathematical model of a rotor assembly (module) as a whole. Based on the defined centerline, the system calculates a centerline deviation of each disc or component of the rotor assembly. Calculating the centerline deviation includes measurement characteristics of a set of rotor blades, a disc, a shaft, a hub, and/or a spacer. For each of these measurements, the following information is calculated: roundness, flatness, concentricity, concentricity angle, runout, runout angle, perpendicularity, perpendicularity angle, perpendicular plane deviation, centerline deviation, centerline deviation angle, biplane deviation, and biplane deviation angle. After calculating the best fit centerline deviation for each component, the invention system determines an angular location of the component of the turbine engine. 
         [0007]    Next, the invention system determines the centerline deviation and angle of each disc based on the centerline of both ends of the subject module as stacked and determines disc blade distribution within the turbine engine based on the calculated centerline deviation and the angular location of the disc/component of the turbine engine. Determining rotor blade distribution includes weighing of each rotor blade for the disc/component of the turbine engine by either pan weight or moment weight, as appropriate. 
         [0008]    Each rotor blade of the set of rotor blades for a given disc may be identified by a number label (indicator) and a blade weight. Further, determining the blade distribution may also include computing a rotor blade distribution in order to offset the centerline deviation. The process of offsetting the discs&#39; centerline deviation optimally balances the rotor assembly/module of the turbine engine. 
         [0009]    This rotor blade distribution per disc is displayed to a user in both a numerical and graphical format. After determining the rotor blade distribution, the rotor blades may be assembled on each disc of the turbine engine using the displayed information. The resulting rotor assembly is then verified against the computer model prediction. If the blades are integral to their discs, then the distribution is in the form of bolts and washers (bolts connect discs to each other in the assembly). It should be understood that this method or corresponding apparatus in an exemplary embodiment may be applied to a low-pressure turbine, intermediate-pressure turbine, a high pressure turbine, a low-pressure compressor, an intermediate-pressure compressor, a high pressure compressor, a combination of rotors, or a combination of rotors with their respective shafts or hubs. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention. 
           [0011]      FIG. 1  is a side view of a system embodying the present invention; 
           [0012]      FIG. 2A  is a plane view of a high pressure compressor and turbine modules; 
           [0013]      FIG. 2B  is a plane view of a low pressure compressor and turbine modules; 
           [0014]      FIG. 2C  is a plane view of a low pressure shaft and low-pressure compressor and turbine modules, including a pair of bearing housings; 
           [0015]      FIG. 2D  is a flow diagram of an example process used to determine the predicted rotor assembly and rotor blade distribution; 
           [0016]      FIG. 3  is a flow diagram of an example process of calculating rotor blade or bolt-and-washer distribution for a disc of a turbine engine rotor according to the present invention; 
           [0017]      FIG. 4  is a schematic diagram of a rotor blade or bolt-and-washer distribution about a given disc; 
           [0018]      FIG. 5  is a flow diagram of an example process of displaying rotor blade or bolt-and-washer distribution information to a user according to the present invention; 
           [0019]      FIG. 6  is a flow diagram of an example process of mounting a rotor module and verifying the straightness of the module in the present invention; 
           [0020]      FIG. 7  is a screen view diagram of a rotor disc stacking process and blade or bolt-and-washer distribution employing the present invention; 
           [0021]      FIG. 8  is a flow diagram illustrating an example process of determining a predicted vibration of a rotor module and set of rotor blades utilized in embodiments of the present invention; 
           [0022]      FIG. 9  is a schematic diagram of a rotor assembly on a balancing machine as employed by the present invention process of  FIG. 10 ; and 
           [0023]      FIG. 10  is a flow diagram illustrating an example process of balancing a rotor assembly. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    A description of preferred embodiments of the invention follows. 
         [0025]      FIG. 1  is a system  100  of the present invention for calculating a rotor blade or bolt-and-washer distribution (or disc thereof) or other component  140  that achieves optimal balance throughout a module (rotor assembly) in a turbine engine. It is useful to note that calculating the rotor blade or bolt-on-washer distribution is typically performed in such a manner as to have an optimal straight build of a rotor assembly. The system  100  uses a determination module  105  for performing calculations. Within the determination module  105 , there is a digital processing unit (with CPU)  110 , a display monitor  115 , a printer  120 , a bar code reader  122 , and input devices  125  and  130 , such as a keyboard or mouse. The determination module  105  interacts with at least one sensor or probe  145  located on a vertical gage  135 . The vertical gage  135  has a disc, disc and blade assembly, or other component  140  on a stand in such a manner as to allow at least one sensor or probe  145  to make measurements. These measurements are transmitted to the determination module  105  where they are used for calculating a best fit stack of discs and balanced module rotor blade or bolt-and-washer distribution according to the principles of the present invention. The determination module  105  having received the sensor measurement information/data from at least one sensor or probe  145 , calculates a disc or component (e.g. shafts, hub, etc.) location, with respect to a defined centerline for assembly purposes. 
         [0026]    In addition, the system  100  uses a determination module  150  for performing measurements. Within the determination module  150 , there is a digital processing unit (with CPU)  160 , a display monitor  170 , a printer  175 , and input devices  165  and  166 , such as a keyboard or mouse. The determination module  150  interacts with either a pan weight scale  180  or a moment weight scale  185 . The pan weight scale  180  determines the weight of blades, except in those instances where a moment weight is required. If the moment weight is required, the moment weight scale  185  calculates the moment weight. After calculating the weight, the CPU  160  stores the calculated/measured weight using an identification number associated to a specific disc. A bar code printer  190  identifies (produces) a barcode and the identification number that are associated with the specific disc. Bar code reader  122  reads the printed bar code as input for determination module  105 . 
         [0027]      FIG. 2A  shows a high-pressure spool  210  of a gas turbine. The high-pressure spool  210  includes a high-pressure compressor  220 , a high-pressure turbine  230 , and a high-pressure shaft  240 . The high-pressure compressor  220  includes a plurality or rotor blades  220   a  . . .  220   n , each set of blades being carried by a respective disc  213   a  . . . n. The high-pressure turbine  230  includes a plurality of rotor blades  230   a  . . .  230   n , each set of blades being carried by a respective disc  230   a  . . . n. 
         [0028]      FIG. 2B  shows a low-pressure spool  250  of a gas turbine. The low-pressure spool  250  includes a low-pressure compressor  260 , a low-pressure turbine  270 , and a low-pressure shaft  280 . The low-pressure shaft  280  rotates within the high-pressure shaft  240 . In some engine designs, the high-pressure shaft  240  and the low-pressure shaft  280  is the same shaft. It is useful to note that in some engine designs an intermediate shaft compressor (not shown) and discs may also be used. 
         [0029]      FIG. 2C  generally shows a low-pressure shaft  240  and a low-pressure compressor  260  extending through a pair of bearing housings  245 . The proper alignment of a rotor assembly with the centerline through the bearings can reduce the vibration and imbalance of the rotor assembly and turbine engine. One such useful component to align is the disc  213   n  carrying the plurality of rotor blades  220  or rotor blade fan  24 . An oil circulation system delivers lubricating oil to lubricate the bearings (not shown) within the respective bearing housings  245 , wherein the oil flows through the bearings for drainage to a sump, not shown, within a lower region of the bearing housing  245 . As will be readily understood, proper alignment of components of each bearing housing  245  will substantially reduce the onset of oil leakage. Further, proper alignment of the dynamic and static structures of each bearing can reduce rapid wear of the seal structures. Alignment of the disc  213   n  carrying the plurality of rotor blades  220  or blade fan  24  is as follows: 
         [0030]    Characteristic information of each part (e.g., disc  213 , rotor blades  220 , etc.) is measured and input to a software program (e.g., “SuperStack” by AXIAM, Incorporated of Gloucester, Mass.) of the determination module  105  of  FIG. 1 . The software program uses the input characteristic measurements to generate output characteristic measurements for aligning discs  213  and the plurality of rotor blades  220 . In particular, the software program outputs correct balancing information in the form of a rotor blade or bolt-and-washer distribution. The rotor blade or bolt-and-washer distribution is computed by 1) calculating a centerline deviation of each rotor disc with respect to the centerline of the rotor assembly (module) as a whole (from end to end); 2) calculating an angular location of each rotor disc; and 3) determining the rotor blade or bolt-and-washer distribution based on the centerline deviation and angular location of each rotor disc. 
         [0031]    Referring now to the centerline deviation, the measurement characteristics include those of a set of rotor blades, a disc, a shaft, a hub, and a spacer. For each part measurement, the software program mathematically levels and centers the part. The software program builds a mathematical model for the parts as hypothetically placed together to form a rotor assembly or module. The software program defines from end to end (including bearings or journals) an assembly model theoretical centerline. Using the theoretical centerline, the software program calculates geometric measurements of each part including: roundness, flatness, concentricity, concentricity angle, runout, runout angle, perpendicularity, perpendicularity angle, perpendicular plan deviation, centerline deviation, centerline deviation angle, biplane deviation and biplane deviation angle. Using these measurement characteristics, a rotor blade or bolt-and-washer distribution for the plurality of rotor blades in the subject rotor assembly (module) is calculated. In particular, the software program calculates the location of each part in space. Using a known weight of each part (user input data such as gross weight, moment weight or manufacturing weight, e.g., from bar code reading in  FIG. 1 ) and the foregoing measurement characteristics (calculated geometric measurements), the software program calculates a blade or bolt-and-washer distribution which offsets centerline deviations and balances the overall subject rotor assembly. In a preferred embodiment, this is accomplished using Applicants&#39; mathematical formula/process which is illustrated in  FIG. 2D . 
         [0032]      FIG. 2D  is an information flow diagram  282  that represents the mathematical formulas used in rotor assembly and blade or bolt-and-washer distribution of the present invention. More specifically, the process calculates a straight rotor assembly against a centerline between bearing journals. At step  284 , the process inputs data that relates to part and other information. The part information includes height, diameter, weight, center of gravity location, probe location, number of bolt holes, bolt hole radius, and individual blade weight whereas other information includes rotor speed, part with bearing journal, number of blades, bolt weight, and washer weight. After receiving the data input, step  286  calculates the best fit centerline for each part in the assembly. The calculation uses Homogeneous Transformation Matrix (HTM) mathematics for each part from established datum to predict a straight assembly. In particular, the HTM uses probe locations and number of bolt holes data received in step  284  allowing the process to calculate the centerline deviation and angular location of each component of the assembly in step  288 . After calculating the centerline and angular location, the process creates a new centerline and angle of each part at step  290  using the probe locations and number of bolt holes. The process mathematically translates the centerline of the assembly to two bearing journal centerlines in such a manner as to create a new centerline and angle for each part. At step  292 , the process mathematically calculates balance and angle for each part based on a computed deviation of each part from the journal centerline. In calculating the balance and angle, the process uses the following data: centerline deviation, centerline deviation angle, center of gravity location, weight, height, and diameter. Next, at step  294  the process computes a blade distribution or bolt and washer distribution based on the part centerline, center of gravity and weight. In computing the blade or bolt and washer distribution, the process uses the following data: centerline deviation, centerline deviation angle, center of gravity location, part weight, and blade weight. Next, the process computes the balance of the assembled rotor (step  296 ) and then a projected rotor vibration (step  298 ). In computing the rotor balance and vibration, the process uses the following data: balance deviation of each plane, rotor weight and rotor speed. In this way, the process predicts rotor assembly and rotor blade distribution. 
         [0033]    It should be understood by one skilled in the art that the alignment of a plurality of rotor blades or bolts-and-washers  220   n  may be applied to a low-pressure turbine, an intermediate-pressure turbine, a high-pressure turbine, a low-pressure compressor, an intermediate-pressure compressor, or a high-pressure compressor. 
         [0034]      FIG. 3  is a flow diagram  300  illustrating an example process of computing a blade or bolt-and-washer distribution for a disc of a turbine engine according to the present invention. After defining the model centerline, the blade or bolt-and-washer distribution process  300  calculates a centerline deviation and an angular location of each rotor disc or component of the turbine engine (step  305 ). Further, the process computes a blade distribution for each rotor blade in a set of rotor blades of a given disc (steps  310   a ,  310   b  and  315 ). Next, the process calculates the weight distribution based on the centerline deviation and angular location of the given disc (as calculated in  305 ) and the weight effects of each blade or bolt-and-washer in the set. 
         [0035]      FIG. 4  is a schematic diagram of a rotor blade or bolt-and-washer distribution  400  for a given disc  213  of  FIG. 2A . A turbine engine rotor disc  405  is seen in such a manner as to view the location of rotor blades or bolts-and-washers  410 ,  415 , and  420 . Rotor blade  410  is labeled or identified as blade number  26  and is shown in slot or blade location number  1  of the subject disc. Rotor blade  415  is shown in blade location number  2  and has identifier number  42 . Similarly rotor blade  420  is shown in slot/blade location  3  and identified as blade number  6 . The placement of each rotor blade is based on the rotor blade distribution described above. In particular, the rotor blades  410 ,  415 , and  420  are positioned (assigned a slot/blade position) in such a way as to geometrically balance the given rotor component or disc to the theoretical centerline of the rotor assembly by offsetting the disc&#39;s calculated centerline deviation and angular location with the weight of each rotor blade. 
         [0036]      FIG. 5  is a flow diagram  500  illustrating an example displaying process of blade or bolt-and-washer distribution information. Before displaying blade or bolt-and-washer distribution information, the distribution information is calculated as described above. At step  505 , the process calculates a centerline deviation and angular location for each rotor disc or component of a turbine engine. For each rotor disc of a rotor assembly, the process computes a blade distribution (loop  510   a  through  510   b ). Next, at step  515 , the process computes blade or bolt-and-washer distribution based on (a) the centerline deviations and angular locations of components/discs of the turbine engine as calculated in step  505 , and (b) weight effects of the blades or bolts-and-washers per blade or bolt position. From the results of step  515 , the process  500  displays numerical and graphical results illustrating blade position per disc on a display monitor (step  520 ). 
         [0037]      FIG. 6  is a flow diagram  600  of an example process of verifying a subject module (e.g., rotor assembly of a turbine engine) against the initial predictive mathematical model. The process mounts the subject module on a gage (step  610 ). Next, as measured by the gage, the process compares location and orientation of the module to that of the mathematical model. Based on the comparison, the process verifies the straightness of the subject module to the predictive mathematical model (step  615 ). 
         [0038]      FIG. 7  is a schematic diagram of a rotor disc stacking and balancing (blade distribution) output  700  of a preferred embodiment. A set of rotor discs  705 ,  715 , and  725  are shown with their respective individual or part center  710 ,  720 , and  730 , respectively. The rotor assembly as a whole has a defined centerline shown at  735 . The centerline  735  depicts a theoretical model centerline, a centerline deviation, and an angular location of each rotor disc  705 ,  715 , and  725 . Rotor blade or bolt-and-washer distribution are indicated by balance points (shaded dots) which result from the above described computation relating to calculated centerline deviations and the angular locations of discs to weight effects of rotor blades or bolts-and-washers at blade locations of the disc. The rotor blade or bolt-and-washer distribution allows for an aligned stacking of each rotor disc  705 ,  715  and  725 . 
         [0039]    It is useful to note that using the foregoing output  400 ,  700 , (e.g., blade or bolt-and-washer distribution information of  FIG. 4  and rotor disc stacking and balancing of  FIG. 7 ) one is able to optimally assemble a module (e.g., rotor assembly) of the turbine engine. 
         [0040]      FIG. 8  is a flow diagram  800  illustrating an example process of determining a predicted vibration of a module assembled according to the above. The process  800  receives input of a manufacturer-specified operating speed of the rotor. Receiving the specified operating speed allows one to adjust for vibration using known techniques given the results of process  800  such as the weight distribution of disc  213 , associated blade sets or bolts-and-washers and other rotor components (resulting from the output  700  of  FIG. 7 ). Step  805  measures and calculates a centerline deviation and an angular location for each rotor disc of the assembled engine. Next, the process makes a computation of the blade or bolt-and-washer distribution and a determination of the predicted vibration for each rotor disc (steps  810  through  820 ). In particular, step  815  computes a blade or bolt-and-washer distribution based on the centerline deviation and angular location of the disc and/or component with respect to the measured centerline of the turbine engine (as calculated in step  805 ) and offset weight effects of the blades in terms of displacement and velocity. After the last iteration of step  820 , the process determines a predicted imbalance of a set of rotor blades or bolts-and-washers for each rotor disc  213 . It is useful to note the rotor vibrations may be determined while the turbine is in an operational state (.i.e., test cell). Next, the process determines the predicted vibration of a module assembly (step  825 ). That is, predicted vibration enables one to determine in advance of operation if the subject rotor assembly does not meet vibration threshold/criteria. 
         [0041]      FIG. 9  is a schematic diagram of a balancing machine assembly  900 . Specifically, a balancing machine  905  contains a module  910  for balance testing. More specifically, the module  910  is installed in the balancing machine  905  for verification of an initial unbalance in two different planes (e.g., left and right plane). Verification is performed using the mathematical model described above. 
         [0042]      FIG. 10  is a flow diagram illustrating an example process  1000  of balancing a rotor assembly. After beginning (step  1005 ), the process installs a completed rotor assembly onto a balancing machine (step  1010 ) such as that illustrated in  FIG. 9 . Next, the process measures a left plane and a right plane of the rotor assembly to check for any unbalances or imbalances (step  1015 ). After measuring the planes, the process verifies the actual balance by comparing the actual values with previously computed predicted balance values (step  1020 ). After verifying the actual balance, the process  1000  completes a final trim balance on the left and right planes as indicated by the verification process (step  1025 ). 
         [0043]    While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.