Patent Publication Number: US-2016245647-A1

Title: Method and system to tolerance test a component

Description:
BACKGROUND OF THE INVENTION 
     The subject matter disclosed herein relates to tolerance testing components. 
     The various components of a system, such as a rotor stub shaft, for example, often must be individually tolerance tested prior to their incorporation into the system. Specifically, various elements of the component may be checked individually for form control (e.g., circularity for a diameter, flatness for a planar surface) and also to ensure that the relative location of elements (e.g., eccentricity for a diameter) is within required tolerances. In many cases this tolerance testing requires multiple set up operations of a probing tool. For example, when a shaft is tested, different sets of measurements (circumferential and axial) are taken to determine parameters such as circularity and eccentricity each time the shaft is set up for probing to determine relative variations of different elements of the shaft. Each set of these measurements is taken by setting the part in a lathe and rotating or moving the shaft while measuring an offset (run out) of one or more probes from their initial positions. This method of measurement is prone to false positive or false negative results based on how the lathe is positioned within the shaft during the measurements. That is, for example, if the shaft is not centered within the lathe, the probe may experience offsets due to the wobble created by rotation on the un-centered shaft rather than due to variations in the form and location of the shaft. In addition, the specific verification of relative location of different parts (elements) of the shaft requires a different setup (positioning of the lathe) for each such verification. 
     BRIEF DESCRIPTION OF THE INVENTION 
     According to one aspect of the invention, a method of tolerance testing a component using data measurements from a single test setup within a test apparatus includes receiving, at a processor, the data measurements obtained with the single test setup; separating, at the processor, the data measurements from a relative positioning of an element of the test apparatus; performing, at the processor, a virtual setup of the component to obtain additional data measurements related to one or more parts of the component; and determining, at the processor, whether a parameter associated with the one or more parts meets a specified tolerance based on the additional data measurements obtained from the virtual setup. 
     According to another aspect of the invention, a system to tolerance test a component using data measurements from a single test setup within a test apparatus includes an input interface configured to receive the data measurements from the single test setup; and a processor configured to separate the data measurements from a relative positioning of an element of the test apparatus, perform a virtual setup of the component to obtain additional data measurements related to one or more parts of the component, and determine whether a parameter associated with the one or more parts meets a specified tolerance based on the additional data measurements obtained from the virtual setup. 
     According to yet another aspect of the invention, a non-transitory computer-readable medium stores instructions which, when processed by a processor, cause the processor to implement a method of tolerance testing a component using data measurements from a single test setup within a test apparatus. The method includes receiving, at a processor, the data measurements obtained with the single test setup; separating, at the processor, the data measurements from a relative positioning of an element of the test apparatus; performing, at the processor, a virtual setup of the component to obtain additional data measurements related to one or more parts of the component; and determining, at the processor, whether a parameter associated with the part meets a specified tolerance based on the additional data measurements obtained from the virtual setup. 
     These and other advantages and features will become more apparent from the following description taken in conjunction with the drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The subject matter, which is regarded as the invention, is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. 
       The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  depicts a system to tolerance test a component according to an embodiment of the invention; 
         FIG. 2  is a flow diagram of a method of tolerance testing a component according to embodiments of the invention; 
         FIG. 3  depicts the test apparatus coordinate system reference defined as part of the method described with reference to  FIG. 2 ; 
         FIG. 4  depicts the measurement data for one probe location plotted on the three-dimensional coordinate system shown in  FIG. 3 ; 
         FIG. 5  depicts a best-fit circle drawn for the measurements data plotted in  FIG. 4 ; 
         FIG. 6  additionally depicts best-fit circles for the other probe positions resulting in the measurement data; 
         FIG. 7  depicts best-fit planes viewed as the best-fit circles from the x-axis; 
         FIG. 8  depicts the best fit circles from the z-axis; 
         FIG. 9  depicts the shaft axis in the three-dimensional coordinate system; 
         FIG. 10  depicts points from the measurement data in the form of best-fit circles and the shaft axis determined via the process described with reference to  FIGS. 3-9 ; and 
         FIG. 11  depicts the points from the measurement data shifted within the three-dimensional coordinate system. 
     
    
    
     The detailed description explains embodiments of the invention, together with advantages and features, by way of example with reference to the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     As noted above, the currently used methodology to verify that a component meets specified tolerances is prone to error and requires re-setup and re-run for each verification of a different set of elements of the component. Embodiments of the system and method described herein relate to obtaining measurements using a single setup and post-processing the measurements for more accurate tolerance assessments without the need for additional measurements using different test setup configurations. As detailed below, by obtaining measurements with a part reference set by the lathe axis, analysis may also be performed for a part reference set by a part axis defined by two part diametric sets, and a part set normal to a selected axial data (face) set and centered on a selected diametric data (center) set. While a shaft is used as an exemplary component in the description of the embodiments below, alternate embodiments of the system and methods described may apply, as well, to other components being tolerance tested. 
       FIG. 1  depicts a system to tolerance test a component  114  according to an embodiment of the invention. The exemplary component  114  shown in  FIG. 1  is a shaft  115 . The exemplary parameters whose tolerances are of interest with reference to the shaft  115  are circularity (form control for the diameter) and eccentricity (location control for the diameter). As shown in  FIG. 1 , the component  114  (shaft  115 ) is set up within a test apparatus  110  that may include one or more probe devices  112  and a controller  117  that rotates the shaft (component  115 ) about a lathe  119  or moves the probe  112  along the axial length of the shaft  115  and records the displacement of the probe  112  (the run out). For example, when the shaft  115  is rotated about the lathe  119 , any displacement of the probe  112  (up or down from its original position) may indicate non-uniform circularity of the shaft  115  at the axial position at which the probe  112  is shown in  FIG. 1 . The arrangement in  FIG. 1  illustrates one of the issues resulting from relying solely on measurements taken by the controller  117 . As shown in  FIG. 1 , the lathe  119  is not perfectly centered within the shaft  115 . This creates a wobble effect when the shaft  115  is rotated about the lathe  119 , and a false reading of non-circularity is likely even if the shaft  115  were perfectly circular at the axial position shown for the probe  112 . This wobble effect may be addressed through the setup in the following way. When probes are disposed at two elements (A and B) with the lathe  119  centered within the shaft  115  at least at axial positions of the two elements (A and B), then a wobble is identifiable based on both probes being displaced at the same radial positions. That is, as the shaft  115  is rotated, the probes (at A and B) would not be displaced at all if circularity were perfect at A and B and the lathe  119  were perfectly centered within the shaft  115  at A and B. If circularity were perfect at A and B but a wobble resulted from the lathe  119  position, then both probes (at A and B) would be displaced at the same time during rotation. If circularity were not perfect at A or B, then the probes would likely be displaced independently of each other. Embodiments of the invention facilitate virtual setup of the component  114  to verify circularity (a form control parameter) and eccentricity (a location control parameter) within specified tolerances without the burden and uncertainty associated with the physical test apparatus  110 . 
     According to embodiments of the present invention, the measurement data  130  from the test apparatus  110  is provided to an analyzer  120 . The analyzer  120  includes one or more processors  122 , one or more memory devices  124 , an input interface  126 , and an output interface  128 . The analyzer  120  receives the measurement data  130  from the test apparatus  110  through the input interface  126  and provides an analysis of whether parameters at various elements (e.g., circularity at A and B) of the component  114  meet required tolerances. The measurement data  130  is provided for a single setup of the test apparatus  110 . For example, the setup may be as shown in  FIG. 1  with the lathe  119  not centered within the shaft  115 . Because the analyzer  120  separates the parameter measurement (e.g., circularity, eccentricity) from the location (relative to the lathe  119 ) in the measurement data  130 , as discussed further below, the analyzer  120  uses modeling to virtually set up the component  114 , as needed, to compare selected elements for a determination of how closely they meet specified tolerances. The analyzer  120  uses models and instructions stored in the memory device  124  to process the measurement data  130  with the processor  122  and output the result via the output interface  128 . The output may be, for example, parameter values based on the virtual setup or a determination of whether the parameter meets the specified tolerance. 
       FIG. 2  is a flow diagram of a method of tolerance testing a component  114  according to embodiments of the invention. At block  210 , the method includes obtaining measurements (measurement data  130 ) from a single setup of the component  114  in the test apparatus  110  at the analyzer  120 . Separating the form control parameters (e.g., circularity and flatness measurement data  130 ) and location control parameters (e.g., eccentricity, which is relative to the lathe  119  position for the particular test apparatus  110  setup in  FIG. 1 ) at block  220  is detailed further below. Selecting elements for comparison at block  230  may be based on a pre-programmed sequence or on user input. At block  240 , performing virtual setup based on the elements to be compared (according to block  230 ) involves the modeling discussed further below. Determining whether a parameter (e.g., circularity, flatness, eccentricity) is within the specified tolerance at block  250  is based on the virtual setup (at block  240 ). The processes detailed herein have the technical effect of tolerance testing elements of a component based on obtaining measurements data  130  from a single setup of the physical test apparatus  110 . 
       FIGS. 3-11  detail processes involved in separating the form control parameters and location control parameters in measurement data  130  and performing virtual setup. These processes apply known techniques to the measurement data  130  to achieve the virtual setup, as detailed below.  FIG. 3  depicts the test apparatus  110  coordinate system reference defined as part of the method described with reference to  FIG. 2 . A three-dimensional coordinate system  310  is defined based on the test apparatus  110  that was used to obtain the measurement data  130 .  FIG. 4  depicts the set of points  410  in the measurement data  130  for one feature (e.g., element of the shaft such as a radial probe position or face) plotted on the three-dimensional coordinate system  310  shown in  FIG. 3 .  FIG. 5  depicts a best-fit circle  510  drawn for the measurements data  130  plotted in  FIG. 4 . The best-fit circle  510  may be obtained using known curve fitting techniques. The radial data sets shown in  FIG. 5  include both form control and location control parameters.  FIG. 6  additionally depicts best-fit circles  510  for sets of points in the measurement data  130  for the other features.  FIG. 7  depicts best-fit planes  710  viewed as the best-fit circles  510  from the x-axis. As with the best-fit circles  510 , the process of determining the best-fit plane  710  is repeated for each set of points in the measurement data  130  associated with a feature. Like the best-fit circles  510  shown in  FIG. 5 , the axial data sets shown in  FIG. 7  include both form control and location control parameters. The best-fit circles  510  and best-fit planes  710  facilitate the separation of the forms of each of the elements (e.g., circularity, flatness) from the location (e.g., eccentricity, parallelism) relative to the lathe  119  ( FIG. 1 ) and the other elements. 
       FIG. 8  depicts the best fit circles  510  from the z-axis. The centers of each of the best-fit circles  510  determine the shaft  115  axis  810 . To be clear, regardless of the setup of the shaft  115  in the test apparatus  110  (relative to the lathe  119 ) to obtain the measurement data  130 , the process described above may be used to determine the shaft  115  axis  810 . This shaft axis  810  is shown in the three-dimensional coordinate system  310  in  FIG. 9 . The lathe  119  axis lines up with the z-axis of the three-dimensional coordinate system  310 . Once the shaft  115  axis  810  is determined, the points of the measurement data  130  may be moved to perform virtual set ups in the following way. Because the shaft  115  axis  810  is fixed (parts of the shaft do not move relative to each other), the points of the measured data  130  are moved altogether. A virtual setup means that the points of the measured data  130  are moved (together) so that the shaft  115  axis  810  points corresponding with features of interest are on the z-axis of the three dimensional coordinate system  310 . This is shown with reference to  FIGS. 10 and 11 . 
       FIG. 10  depicts points from the measurement data  130  in the form of best-fit circles  510  and the shaft  115  axis  810  determined via the process described above. As noted above, the lathe  119  axis is along the z-axis. The features (points among the measurement data  130 ) of interest correspond with the best-fit circles  510   a  and  510   b  having centers  1010  and  1020 , respectively.  FIG. 11  shows the points from the measurement data  130  (shown as best-fit circles  510 ) shifted within the three-dimensional coordinate system  310 . The shaft  115  axis  810  is maintained while the centers  1010  and  1020  corresponding to the features of interest are moved onto the z-axis. The points corresponding to best-fit circles  510   a  and  510   b  may be used to determine compliance with specified tolerances based on the shift (virtual setup) shown in  FIG. 11 . For example, circularity of best-fit circle  510   a  may be determined based on the relative distance of the points used to make up the best-fit circle  510   a  from the z-axis. Eccentricity may be determined by comparing the distance of the points corresponding with best-fit circle  510   a  from the center  1010  with the distance of the respective points corresponding with best-fit circle  510   b  from the center  1020 . In this way, the virtual setup achieved by shifting the shaft  115  axis  810  facilitates tolerance testing without multiple runs of the test apparatus  110 . 
     While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.