Abstract:
A machine readable medium and a method are disclosed that determine whether a pattern of manufactured or simulated features violates a feature relating tolerance and determines acceptability of the pattern. Allowable tolerance may include feature relating tolerances and material conditions. Manufactured centers are drawn relative to a one true position. A circle drawn through or outside the manufactured centers is used to determine if there is feature relating tolerance violation. Material condition may also be used.

Description:
GOVERNMENT RIGHTS 
   This invention was made with Government support under FAR 52.227-12 awarded by Comanche EMD contract. The Government has certain rights in this invention. 

   BACKGROUND OF THE INVENTION 
   The present invention generally relates to the production of articles of manufacture in a computer simulation or in the real world, and more particularly, to a method for accurately evaluating pattern compliance for a simulated or manufactured article. 
   American, Canadian, German, and International Organization for Standardization (ISO) standards define methods for specifying multiple levels of pattern and feature related tolerances often referred to as composite positional tolerances. Composite positional tolerances include a pattern locating tolerance and a feature relating tolerance. A pattern locating tolerance is a tolerance that relates a collection of manufactured features on an object relative individually to the specified datums of the designed pattern. A feature relating tolerance can include a tolerance relating to the size of a feature, the positions of a set of features relative to each other, and the rotation of a pattern of features relative to a specified origin. 
   Another specification may include maximum material condition (MMC) and least material condition (LMC). MMC may be defined as the condition in which a feature of size contains the maximum amount of material within the stated limits of size, for example, minimum hole diameter or maximum shaft diameter. LMC may be defined as the condition in which a feature of size contains the least amount of material within the stated limits of size, for example, maximum hole diameter, or minimum shaft diameter. An allowable tolerance may be specified as the combination of the pattern-locating and feature related tolerances and a material condition. 
   Presently, the manufacturing industry does not have an efficient or effective way of determining whether or not the feature relating requirements are achieved. Inspection of manufactured articles and analyzing the resulting data are not currently evaluated in an automated and correct manner to determine whether or not combined manufactured features such as hole size and location are acceptable to the applied feature relating tolerances. For example, evaluating manufactured hole size, form, orientation, and location are all completed separately, and confidence in the accuracy of each evaluation is low. 
   Referring to  FIG. 1 , one method for documenting inspection data consists of paper gaging, where information is recorded on paper. Measurements are taken, and hole positions  92  are plotted on a grid  94  at an enlarged scale using a true position  96  as the origin. Concentric circles  90  representing tolerance zone diameters are then overlain to determine compliance with the pattern locating tolerance. This method does not consider variation in feature size easily, and does nothing to examine compliance with the feature relating tolerance. 
   As can be seen, there is a need for accurately determining inspection data. Also, there is a need for determining inspection data in a timely manner, with perhaps, using only a single iteration. Moreover, there is a need for quickly analyzing inspection data in a step of the manufacturing process so that the results of the analysis can be used in subsequent processes. 
   Variation effects within a pattern of features may also be determined when performing a variation analysis of a design prior to manufacturing that design. The variation analysis software performs hundreds or thousands of simulated build cycles, and in each cycle, varies all of the parameters randomly. Assembly variation analysis that utilizes feature patterns, such as holes, for assembly is currently reliant on approximations and iterations for the assembly of parts. Such a process may introduce error, is inefficient, and requires advanced software skills for completion. 
   In addition to the need for assessing produced parts, there is a need to accurately determine the variation effects on patterns of features during variation analysis. 
   SUMMARY OF THE INVENTION 
   The present invention provides a machine-readable medium for programming a computer to determine feature relating tolerance consumed for a plurality of manufactured features on an object, the medium including processor executable instructions comprising determining a true position for each of the plurality of manufactured features, determining a location for each of the plurality of manufactured features, organizing each of the true positions into a single association, organizing the location of each of the plurality of manufactured features relative to the single association, determining a circle that intersects or contains each location, determining the diameter of the circle, and comparing the diameter of the circle with the size of the feature relating tolerance to determine acceptability of the pattern. 
   In one aspect of the present invention, a machine-readable medium programs a computer to determine feature relating tolerance consumed for a plurality of manufactured holes on an object, the medium including processor executable instructions comprising, determining a true position for each of the plurality of manufactured holes, determining a center for each of the plurality of manufactured holes, superimposing each of the true positions to form one true position, determining the centers of each of the plurality of manufactured holes relative to the one true position, determining a circle that intersects or contains each of the centers of the circles, determining the diameter of the circle, and determining feature relating tolerance consumed from said diameter. 
   In another aspect of the present invention, a machine-readable medium programs a computer to determine feature relating tolerance consumed for a plurality of manufactured features on an object where at least one additional feature is added to a pattern of features, the medium including processor executable instructions comprising, determining a true position for each of the plurality of manufactured features, determining a location for each of the plurality of manufactured features, organizing each of the true positions into a single association, organizing the location of each of the plurality of manufactured features relative to the single association, determining a first circle that intersects or contains each location, determining the location of the additional feature, determining if the location of the additional feature is contained within the first circle, determining a second circle that intersects or contains the plurality of manufactured features and the additional feature, if the additional feature is not contained with the first circle, determining the diameter of the second circle, and comparing the diameter of the second circle with the feature relating tolerance to determine acceptability of the pattern. 
   Another aspect of the present invention provides machine-readable medium for programming a computer to determine feature relating tolerance consumed for a plurality of manufactured features on an object, the medium including processor executable instructions comprising, determining a true position for each of the plurality of manufactured features, determining a center for each of the plurality of manufactured features, organizing each of the true positions into a one true position, organizing the center of each of the plurality of manufactured features relative to the one true position, determining a departure circle about each of the centers, and determining a circle that is tangent to or contains each of the departure circles. 
   Another aspect of the present invention provides a machine-readable medium for programming a computer to determine whether a pattern of features violates a pattern locating tolerance for a plurality of manufactured features on an object, the medium including processor executable instructions comprising, determining a true position for each of the plurality of manufactured features, determining a center for each of the plurality of manufactured features, organizing each of the true positions into a one true position, organizing the center of each of the plurality of manufactured features relative to the one true position, determining a departure circle about each of the centers, and determining where the departure circles lie relative to a pattern locating tolerance circle. 
   Another aspect of the present invention provides a system in a manufacturing site, the system comprising a computer and a coordinate measuring machine adapted to determine whether a pattern of manufactured features violate a pattern locating tolerance, and adapted to determine feature relating tolerance consumed for the pattern of features, the system adapted to perform the steps of determining a true position for each of the plurality of manufactured features, determining a center for each of the plurality of manufactured features, organizing each of the true positions into a one true position, organizing the center of each of the plurality of manufactured features relative to the one true position, determining a departure circle about each of the centers, determining if any of the departure circles lies outside a pattern locating tolerance circle to determine if the pattern locating tolerance is violated, determining a circle that is tangent to or contains each of the departure circles, and comparing a diameter of said circle to said feature relating tolerance to determine acceptability of the pattern. 
   Another aspect of the present invention provides a method for determining feature relating tolerance consumed for a plurality of manufactured features on an object comprising determining a true position for each of the plurality of manufactured features, determining a location for each of the plurality of manufactured features, organizing each of the true positions into a single association, organizing the location of each of the plurality of manufactured features relative to the single association, determining a circle that intersects or contains each location, determining the diameter of the circle, and comparing the diameter of the circle with the feature relating tolerance to determine the acceptability of the pattern. 
   In a further aspect of the present invention provides a method to determine used tolerances for a plurality of manufactured features on an object comprising determining a true position for each of the plurality of manufactured features, determining a center for each of the plurality of manufactured features, organizing each of the true positions into a one true position, organizing the center of each of the plurality of manufactured features relative to the one true position, determining a departure circle about each of the centers, determining a circle that contains each of the departure circles, and comparing the circle to the magnitude of the feature relating tolerances. 
   These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims. 
   What is needed is a method to evaluate manufactured objects for pattern compliance and compliance with allowable tolerance in a timely and accurate manner. This method may be hand implemented as well as being implemented as a computer program retained on a machine-readable medium. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram illustrating a prior art paper gaging technique for documenting inspection data; 
       FIG. 2  is a diagram illustrating a designed rectangular plate having three holes, according to an embodiment of the present invention; 
       FIG. 3  is a diagram illustrating a manufactured rectangular plate for the designed rectangular plate in  FIG. 2 , according to an embodiment of the present invention; 
       FIG. 4  is a diagram illustrating the centers of manufactured holes relative to a one true position, according to an embodiment of the present invention; 
       FIG. 5  is a diagram illustrating a pattern locating tolerance zone about the one true position illustrated in  FIG. 4 , according to an embodiment of the present invention; 
       FIG. 6A  is a diagram illustrating an embodiment of the rectangular plate in  FIG. 3 , with an additional manufactured hole, according to an embodiment of the present invention; 
       FIG. 6B  is a diagram illustrating an embodiment of the rectangular plate in  FIG. 3 , with an additional manufactured hole, according to an embodiment of the present invention; 
       FIG. 7  is the center of the additional manufactured hole in  FIG. 6A , shown relative to the one true position in  FIG. 5 , according to an embodiment of the present invention; 
       FIG. 8  is the center of the additional manufactured hole in  FIG. 6B , shown relative to the one true position in  FIG. 5 , according to an embodiment of the present invention; 
       FIG. 9  is a diagram illustrating a pattern related circle that includes all the centers of the manufactured holes of  FIG. 6B , according to an embodiment of the present invention; 
       FIG. 10  is a diagram illustrating hole centers relative to a one true position, according to an embodiment of the present invention; 
       FIG. 11  is a diagram illustrating the departure circles around the hole centers illustrated in  FIG. 10 , according to an embodiment of the present invention; 
       FIG. 12  is a diagram illustrating a pattern locating tolerance used for the pattern in  FIG. 11 ; 
       FIG. 13  is a diagram illustrating centers of four external features relative to a one true position; 
       FIG. 14  is a flowchart illustrating a method for determining feature relating tolerance consumed for a plurality of manufactured features on an object; and 
       FIG. 15  is a flowchart illustrating a method for determining consumed feature-relating tolerance for a plurality of manufactured features on an object. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The following detailed description is of the best currently contemplated modes of carrying out the invention. The description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention, since the scope of the invention is best defined by the appended claims. References to manufactured features may equally refer to features generated in a computer simulation or features produced in fabrication processes. 
   The present invention provides a machine readable medium, method and system for determining the size and location of manufactured features on an object, determining the translation of a pattern of features, and determining tolerance consumed. Such method may be, but is not limited to, hand-implemented or implemented by a computer program. By determining tolerance consumed for features such as holes during or shortly after a manufacturing process, mating parts can be correctly designed and efficient assembly processes chosen. The present invention may be implemented at or in close proximity to a manufacturing site where the manufactured article is produced. 
   The present invention differs from the prior art in that the present invention provides a method for accurately determining inspection information. Also, the present invention provides a method for determining inspection information in a timely manner using only a single iteration. Moreover, the present invention provides a method for quickly analyzing inspection data in a step of the manufacturing process so that the results of the analysis can be used in subsequent processes. 
   In an embodiment,  FIG. 2  is a diagram illustrating the designed features for an object such as a part. The designed part may be a rectangular plate  10  having features including three spaced-apart circular holes  12 ,  14 ,  18 . The manufactured holes may have a cross-sectional shape, including, but not limited to, circular, oval and quadrilateral. Each of the designed circular holes  12 ,  14 ,  18  has a center, referred to as the true center  19 ,  20 ,  24 , respectively, and a designed size, referred to as a true size. The designed size may be gauged using the diameter of the circle as well as the area of the circle. Each hole  12 ,  14 ,  18  may have a designed position on the rectangular plate referred to as a true position. The true centers  19 ,  20 ,  24  may be used as the true position  119 ,  120 ,  124  for each hole  12 ,  14 ,  18 , respectively. One of the true centers, for example, the true center  24  for the bottom left circle  18  may be used as the origin of a Cartesian coordinate system. A computer aided drafting (CAD) system may be used to render the diagram. The information of the circular holes  12 ,  14 , and  18  may be represented as digital data and stored on a machine-readable medium including a hard drive and an optical disk, as well as being processed on a computer. 
     FIG. 3  is a diagram illustrating a manufactured rectangular plate  28 , created from the design illustrated in  FIG. 2 . The manufactured holes  30 ,  32 , and  36  correspond to designed holes  12 ,  14  and  18 . Manufactured rectangular plate  28  may also represent a simulated manufactured plate, and manufactured holes  30 ,  32 , and  36  may represent simulated manufactured holes. The simulated holes may be generated to provide a variation analysis model of a rectangular plate. Each manufactured hole  30 ,  32 ,  36  has deviated from the true size as well as the true position. A true size deviation may comprise a hole larger than designed, or a hole smaller than designed. Each hole may have a positional error relative to its true position. The positional error may be determined by the distance between center  38 ,  40 ,  44  of each manufactured hole  30 ,  34 ,  36  and their true positions  119 ,  120 ,  124 , respectively. The deviations may extend along the depth of each hole. Data regarding the dimensions and position of the manufactured rectangular plate  28  may be acquired by many methods known in the art, including, but not limited to, examining the rectangular plate  28  with a coordinate measuring machine. 
     FIG. 4  is a diagram illustrating the centers  38 ,  40 ,  44  of each manufactured hole relative to a one true position  46 . The one true position  46  represents the true positions of each manufactured holes  30 ,  32 ,  36  as a single point. The one true position  46  may be a superimposition of true positions  119 ,  120 ,  124 . The centers  38 ,  40 ,  44  of each manufactured hole are drawn relative to the one true position  46  as they would be drawn relative to their true positions  119 ,  120 ,  124  ( FIG. 3 ), respectively. The one true position  46  may be represented as the arbitrarily-positioned origin of a coordinate system, including an x, y coordinate system and in this coordinate system, the centers  38 ,  40 ,  44  of each manufactured hole are drawn with respect to the one true position  46 . 
     FIG. 5  is a diagram illustrating a circle  50  that represents the pattern locating tolerance zone (PLTZ) about the one true position  46 . A PLTZ is a tolerance zone that may be specified in the design data. The PLTZ specifies the positional tolerance for features in a group. The diameter D 1  of the circle  50  represents the PLTZ. A feature relating circle  52  may be drawn that intersects or includes each of the centers  38 ,  40 ,  44 . The feature relating circle  52  may represent the magnitude of the feature relating tolerances. The feature relating circle  52  provides a range of how the existing holes  30 ,  32 ,  36  ( FIG. 3 ) deviate from the one true position  46 , and thus, feature relating circle  52  provides an accurate indicator of the deviations of the manufactured holes  30 ,  32 ,  36  from the designed pattern. The diameter of the feature relating circle  52  indicates the maximum deviation of the manufactured holes  30 ,  32 ,  36  ( FIG. 3 ) and the amount of tolerances consumed. The region  56  outside of feature relating circle  52  would indicate a positional error relative to the pattern of features that is greater than any of the positional errors of manufactured holes  30 ,  32 ,  36 . The region  57  inside of feature relating circle  52  would indicate a positional error relative to the pattern of features that is smaller than the combined positional errors of manufactured holes  30 ,  32 ,  36 . 
     FIG. 6A  is a diagram illustrating an embodiment of a rectangular plate  28  in  FIG. 3 , with an additional manufactured hole  58 . In an embodiment,  FIG. 7  is a diagram illustrating the center  60  of a fourth manufactured hole  58  ( FIG. 6A ) shown relative to the one true position  46  of  FIG. 5 . The one true position  46  in  FIG. 7  includes the true position  74  ( FIG. 6A ) of manufactured hole  58 . In this embodiment, the center  60  of manufactured hole  58  lies within the feature relating circle  52 , and thus manufactured hole  58  does not have a relative positional error greater than the deviation of manufactured holes  30 ,  32 ,  36 . Feature relating circle  52  remains a valid indicator of the range of the relative positional errors of all manufactured holes,  30 ,  32 ,  36 ,  58  on the rectangular plate  28 . 
     FIG. 6B  is a diagram illustrating an embodiment of the rectangular plate  28  in  FIG. 3 , with an additional manufactured hole  70 . In another embodiment,  FIG. 8  is a diagram illustrating a manufactured center  62  of the fourth manufactured hole  70  from  FIG. 6B  shown relative to the one true position  46 . The one true position  46  includes the true position  75  of manufactured hole  70 . In this embodiment, the center  62  of manufactured hole  70  lies outside of feature relating circle  52 , and thus manufactured hole  70  has a positional error that is greater than the deviation of manufactured holes  30 ,  32 ,  36 . Feature relating circle  52  is no longer a valid indicator of the range of the relative positional errors of all manufactured holes,  30 ,  32 ,  36 ,  70  on the rectangular plate  28 . Thus, a new feature relating circle must be drawn that includes all of the centers. 
     FIG. 9  is a diagram illustrating a feature relating circle  76  that includes all the centers  38 ,  40 ,  44  and  62  of the manufactured holes  30 ,  32 ,  36  and  70  of  FIG. 6B , respectively. The feature relating circle  76  may be derived by including manufactured center  72 , of manufactured hole  70  which was not included in feature relating circle  52  of  FIG. 8 . Feature relating circle  76  includes manufactured centers  38 ,  40  and  44  as well as manufactured center  62 . Feature relating circle  76  may be used as a gauge to determine the relative positional errors of manufactured holes  30 ,  32 ,  36 ,  70  for the rectangular plate  28  in  FIG. 6B . 
   In an embodiment, the used or consumed tolerance for any object having a pattern of features may be determined.  FIG. 10  is a diagram illustrating manufactured centers  102 ,  104  and  106  relative to a one true position  100  for an object, such as a rectangular plate having internal features such as holes.  FIG. 11  is a diagram illustrating the size departure  112 ,  114  and  116  as departure circles for each of hole centers  102 ,  104  and  106 , respectively. The departure for an internal feature such as a hole may be the difference in diameter from the minimum hole diameter allowable for a feature in a pattern. This difference could be positive or negative. A positive difference in diameter is considered to be a positive diameter of the departure circle. A negative difference in diameter means that the feature relating circle should pass to the outside of that departure circle. The center for the departure circle is the still the manufactured center of the feature relative to a one true position. The departure for an external feature such as a pin may be the difference in diameter from the maximum pin diameter. A positive difference in diameter of an external feature means that the feature relating circle should pass to the outside of that departure circle. 
     FIG. 12  is a diagram illustrating the PLTZ  121  and used tolerance for the object in  FIG. 11 . A PLTZ  121  may be represented by circle and is centered about the one true position  100 . The PLTZ  121  is not violated if a portion of each of the departure circles  112 ,  114 , and  116  lies within the PLTZ circle  121 . The departure circle  112 ,  114  and  116  for each hole center  102 ,  104  and  106  may be drawn relative to the one true position  100 . 
   Still referring to  FIG. 12 , the used tolerance of the holes corresponding to hole centers  102 ,  104  and  106  may be derived by a used feature relating circle  122  that is tangent to the near side of each departure circle  112 ,  114  and  116 . Typically, when circle  122  is drawn to the near side of each departure circle  112 ,  114  and  116 , each departure circle  112 ,  114  and  116  lies outside of circle  122 . The diameter D 3  of consumed tolerance circle  122  may be compared with the diameter D 4  of an allowable tolerance circle  160  that represents allowable feature relating tolerance. If diameter D 3  is greater than diameter D 4  then the pattern of internal features having centers  102 ,  104  and  106  and size departures exceeds the allowable tolerances. 
     FIG. 13  is a diagram illustrating centers  132 ,  134 ,  136 ,  138  of four external features relative to a one true position  130 . External features may include, but are not limited to, pins. Departure circles  142 ,  144 ,  146   148  are drawn about the centers  132 ,  134 ,  136 ,  138  of each external feature, respectively. Similar to the method described in  FIG. 12 , a PLTZ may be represented by circle  164  and may be centered about the one true position  130 . The PLTZ is not violated if each of the departure circles  142 ,  144 ,  146   148  lies entirely within the PLTZ circle  164 . 
   Still referring to  FIG. 13 , a used tolerance circle  150  may be drawn that is the smallest circle that contains all of the departure circles  142 ,  144 ,  146   148 . Typically, the used tolerance circle  150  may be tangent to the outside of some of the departure circles, for example, departure circles  142 ,  144 , and  146 . The diameter D 2  of the used tolerance circle  150  may be compared to with the diameter D 5  of an allowable tolerance circle  162 . If the diameter D 2  of the used tolerance circle  150  is smaller than the diameter D 5  of the allowable tolerance circle  162 , then the pattern of external features does not exceed the allowable tolerance. The diameter D 2  of used tolerance circle  150  may be compared with the diameter D 5  of an allowable tolerance circle  162  to determine the remaining allowable tolerance. 
     FIG. 14  is a flowchart illustrating an embodiment of the method illustrated in  FIGS. 2–5 , for determining feature relating tolerance consumed for a plurality of manufactured features on an object. One step for determining remaining pattern related tolerance for a plurality of manufactured features on an object may comprise determining  168  a true position for each of the plurality of manufactured features. Another step for determining remaining pattern related tolerance for a plurality of manufactured features on an object may comprise determining  170  a location for each of the plurality of manufactured features. Another step may comprise organizing  172  each of the true positions into a single association. Another step may comprise organizing  174  the location of each of the plurality of manufactured features relative to the single association. Another step may comprise determining  176  a circle that intersects or contains each location. Another step may comprise determining  178  the diameter of the circle. Another step may comprise comparing  180  the diameter of the circle with the pattern related tolerance to determine the acceptability of the pattern. 
     FIG. 15  is a flowchart illustrating an embodiment of the method illustrated in  FIGS. 10–13 , for determining consumed tolerances for a plurality of manufactured features on an object. One step for determining used tolerances for a plurality of manufactured features on an object may comprise determining  182  a true position for each of the plurality of manufactured features. Another step for determining used tolerances for a plurality of manufactured features on an object may comprise determining  184  a center for each of the plurality of manufactured features. Another step may comprise organizing  186  each of the true positions into a one true position. Another step may comprise organizing  188  the center of each of the plurality of manufactured features relative to the one true position. Another step may comprise determining  190  a departure circle about each of the centers. Another step may comprise determining  192  a circle that is tangent to or contains each of the departure circles. Another step may comprise comparing  194  the circle to the tolerances. 
   It should be understood, of course, that the foregoing relates to preferred embodiments of the invention and that modifications may be made without departing from the spirit and scope of the invention as set forth in the following claims.