Patent Abstract:
A workpiece having at least one physical feature is placed into a workstation fixture having at least one adjustable locator. Measurement data reflecting the position of the at least one physical feature of the workpiece and measurement data reflecting the position of the at least one adjustable locator are obtained. A processor ingests and utilizes the collection of assembly data and the measurement data to define and store in memory at least one ordered pair correlating the physical feature and the adjustable locator. The processor defines a test vector that connects the position of the at least one physical feature and the position of the at least one adjustable locator. The processor to computationally discovers a best fit for adjusting the position of the adjustable locator to register with the physical feature by applying to the test vector a computational optimization process that seeks to minimize the length of the test vector to thereby generate a digital shim vector. The adjustable locator is then physically moved according to the digital shim vector, which is stored in association with the collection of assembly data.

Full Description:
FIELD 
       [0001]    The present disclosure relates to a system and method for joining workpieces to form an article. 
     
    
     
       DRAWINGS 
         [0002]    The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
           [0003]      FIG. 1  is a schematic illustration of an exemplary manufacturing system constructed in accordance with the teachings of the present disclosure; 
           [0004]      FIG. 2  is a perspective view of a portion of the manufacturing system of  FIG. 1 , illustrating an exemplary positioning fixture constructed in accordance with the teachings of the present disclosure; 
           [0005]      FIG. 3  is a schematic view depicting a portion of the positioning fixture of  FIG. 2 ; 
           [0006]      FIG. 4  is a schematic view depicting a portion of the positioning fixture of  FIG. 2 ; 
           [0007]      FIG. 5  is a schematic illustration of an exemplary process for joining workpieces in accordance with the teachings of the present disclosure; 
           [0008]      FIG. 6  is a schematic illustration of an exemplary assembly that is formed of workpieces that are to be joined in a workstation of the manufacturing system of  FIG. 1 ; 
           [0009]      FIG. 7  is an enlarged portion of  FIG. 6  that depicts a first orientation of selected features on a workpiece and a revised orientation of the selected features that is obtained through an optimization algorithm; 
           [0010]      FIGS. 8 and 9  are schematic depictions of workpieces that are to be joined in the manufacturing system of  FIG. 1 , the workpieces being depicted as having independent and dependent relationships, respectively; and 
           [0011]      FIG. 10  is a plot that depicts the propagation of variation in the fabrication of an article. 
       
    
    
       [0012]    Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
       DETAILED DESCRIPTION 
       [0013]    With reference to  FIG. 1  of the drawings, an exemplary system for manufacturing an article is generally indicated by reference numeral  10 . The manufacturing system  10  can include a plurality of workstations that are employed to form one or more potions of the article from various workpieces. The workstations can be collectively or generally designated by reference numeral  12 , or can be referred to specifically by reference numerals  12 ( a ),  12 ( b ), . . .  12 (n−1) and  12 ( n ). Each of the portions of the article can comprise two or more workpieces (e.g., W 1 , W 2 ) that have been joined together in one of the workstations  12 . In the particular example provided, the workpieces form a slip joint that is joined or secured by welding, but those of skill in the art will appreciate that each workstation  12  could employ one or more joining techniques, such as welding (e.g., arc-welding, MIG welding, TIG welding, spot welding, resistance welding), bonding, riveting, fastening, nailing, brazing, soldering, etc. Additionally, those of skill in the art will appreciate that the particular joint need not be a slip joint, but could be any type of joint, including a butt joint. Each workstation  12  can comprise a positioning fixture  20 , a measuring device  22 , and a workstation controller  24 . 
         [0014]    With reference to  FIG. 2 , each positioning fixture  20  can be configured to hold one or more workpieces (W 1 , W 2 ) so that the joining process can be conducted in the workstation  12 . The positioning fixture  20  can have a frame (jig)  30  and a plurality of locators  32  that are configured to position one or more of the workpieces relative to the frame  30 . 
         [0015]    Depending on the configuration of the workpieces that are to be joined in the workstation  12 , the locators  32  can be configured in one or more sets. Generally speaking, one set of locators  32  can be employed to locate a first workpiece relative to the frame  30  and another set of locators  32  can be employed to locate a second workpiece relative to the frame  30 . It will be understood, however, that one or more of the locators  32  in one set of locators  32  could be employed to position two or more workpieces relative to the frame  30 . As will be discussed in more detail below, the locators  32  will include at least one primary locator  32   p.  In some situations, a first workpiece can be positioned in a given workstation with a set of locators having no primary locators  32   p,  and each workpiece that is to be joined to the first workpiece in the given workstation can be positioned with a set of locators having two primary locators  32   p.  The locators  32  can be configured to engage one or more of the workpieces in a controlled manner to both locate the workpiece(s) in a desired manner and to eliminate translating movement along and rotational movement about X, Y and Z axes. One technique commonly employed in the design of positioning fixtures is referred to as the 3-2-1 principal of fixture design. Details regarding the design of such fixtures are beyond the scope of this disclosure, but briefly, the positioning fixture  20  is configured such that each workpiece: 
         [0016]    a) rests on three non-collinear points on a bottom surface (i.e., in an X-Y plane), which fixes the location of the workpiece in a first direction along the Z-axis, rotationally about the Y-axis, and in a first rotational direction about the X-axis; 
         [0017]    b) rests on two points on a side (X-Z plane), which fixes the location of the workpiece in one direction along the Y-axis and in a first rotational direction about the Z-axis; and 
         [0018]    c) rests on one point on an adjacent surface (Y-Z plane) to fix the location of the workpiece in one direction along the X-axis and in a second rotational direction about the Z-axis. 
         [0000]    Each locator  32  is disposed at a corresponding one of the points on which the workpiece rests. The locators  32  can comprise rest buttons or pads, concentric locators and radial locators. Clamps  38  can be employed to secure the workpiece to the positioning fixture  20  to thereby inhibit translation of the workpiece relative to the positioning fixture  20  along the X, Y and Z-axes, as well as rotationally about the X-axis in a second rotational direction. 
         [0019]    If desired, the locators  32  can be movably coupled to the positioning fixture  20  so as to be capable of being used for the production of different finished articles. For example, the locators  32  could be positionable in a first orientiation to facilitate the joining of workpieces for a first finished article (e.g., the body-in-white of a sedan) and a second orientation to facilitate the joining of workpieces for a second finished article (e.g., the body-in-white of a sport-utility vehicle). The positioning of the locators  32  can be accomplished manually, or in an automated manner via an appropriate mechanism, such as one or more linear motors (not shown). Moreover, in situations where the locators  32  are moved in an automated manner, the positioning of the locators  32  can be controlled on an as-needed basis, so that workpieces for a variety of different finished articles could be processed together through the manufacturing system  10  ( FIG. 1 ) without the need for significant down-time to re-tool the manufacturing system  10  ( FIG. 1 ). 
         [0020]    With reference to  FIGS. 2 and 3 , one or more of the locators  32 , which can be a concentric locator or a radial locator, can be a primary locator  32   p.  In the particular example provided, the primary locator  32   p  is a concentric locator and comprises a pin  40 , as well as first, second and third linear motors  42 ,  44  and  46 , that are configured to translate the pin  40  along the X, Y and Z-axes, respectively, relative to the frame  30 . As is schematically depicted in  FIG. 3 , the pin  40  can optionally be fixedly coupled the one or more other locators  32  in a given set of locators (i.e., a “first set of locators” in the particular example provided) so that operation of the first, second and third linear motors  42 ,  44  and  46  can optionally move all or a portion of the locators  32  in the particular set of locators (i.e., as a group) along the X, Y and Z-axes. The first, second, and third linear motors  42 ,  44  and  46  are depicted as employing jack- or ball-screws in the particular example provided, but it will be appreciated that any type of linear motor could be employed. 
         [0021]    In some situations, the positioning fixture  20  can be configured to have a quantity of primary locators  32   p  that is one less than the quantity of workpieces that are to be joined in the workstation  12 , and each of the primary locators  32   p  can be associated with a different set of locators. It will be appreciated, however, that the quantity of primary locators  32   p  employed in a particular positioning fixture  20  can be varied as desired. For example, a single primary locator  32   p  could be employed if movement of one type (e.g., translation along the X, Y and/or Z axes) was desired, while two primary locators  32   p  could be if more than one type of movement (e.g., translation and rotation) was desired. 
         [0022]    It will be appreciated that the purpose of the primary locators  32   p  is to permit the set of locators  32  that control the positioning of one workpiece to be moved relative to the set of locators  32  that control the positioning of a second workpiece. Optionally, as shown in  FIG. 4 , the primary locator  32   p  can include a pair of retractable clamping jaws  50  that are movable between a retracted position, which permits an associated workpiece W 1  to be loaded onto the primary locator  32   p,  and an extended position that can be employed to urge the workpiece W 1  against a shoulder  52  or rest button to thereby fix the workpiece W 1  against the shoulder  52  or rest button to inhibit translation along and rotation of the workpiece W 1  about (the pin  40 ) of the primary locator  32   p.    
         [0023]    Returning to  FIG. 1 , the measuring device  22  can be any type of device that is configured to collect data in real time relating to the physical positioning of various features on the workpieces when the workpieces are mounted on the positioning fixture  20  prior to the commencement of a joining operation. For example, the measuring device  22  can comprise a first device, such as a laser radar device or an optical measurement device, which is configured to collect 3-dimensional data relating to the workpieces, and an analyzing tool that can be employed to evaluate the 3-dimensional data and identify the size, shape and relative position of selected features on the workpieces. In the particular example provided, the analyzing tool employs data from the first device in conjunction with data transformation techniques and pattern recognition techniques to identify one or more of the selected features. Each of the features can comprise a surface or edge of a workpiece, a datum on a workpiece, a hole or slot in a workpiece, etc. and is selected for its ability to influence variation in the finished article. In the particular example provided, the analyzing tool is employed to a) determine the magnitude of variances between actual feature dimensions (size, location, etc.) and associated nominal feature dimensions (as determined from blueprints or CAD data), b) determine if any of the actual feature dimensions is out of tolerance, and c) statistically analyze the magnitude of the variances to determine if the actual feature dimensions are in statistical control or out of statistical control. The statistical analysis can be employed to identify instances where one or more features are being manufactured in a non-ideal manner so that corrective action can be implemented to ensure that workpieces subsequently fed into the manufacturing system  10  are less apt to add significant variation into the finished article. It will be appreciated that the non-ideal manner of manufacture could be the manufacture of the feature in an out-of-tolerance manner, or could be the positioning or forming of the feature at a position or to a size that deviates from its nominal blueprint location or size. Optionally, the measuring device  22  can be employed to identify features and/or components of the workpiece(s) and/or assembly that can be out-of-tolerance or otherwise non-conforming (e.g., incomplete or improperly assembled/fabricated) and generate an appropriate response, such as an alarm, flag or shut-down command, which can be used to prevent the out-of-tolerance/non-conforming workpiece or assembly from being used. 
         [0024]    The workstation controller  24  can receive data and information from the measuring device  22  and can employ an optimizing algorithm to re-orient one or more of the workpieces relative to the other workpieces as desired. In this regard, the results of the optimizing algorithm can be employed to operate the first, second and third linear motors  42 ,  44  and  46  ( FIG. 3 ) to move one or more of the locators  32  in a desired manner. 
         [0025]    Generally speaking, the optimization algorithm can determine two vectors that can be employed to control the movement of a workpiece to an optimized location. The two vectors can include a first vector, which relates to rotation of the workpiece about an axis, and a second vector that relates to translation of the workpiece in a plane. It will be appreciated that the two vectors could be employed in separate movements (i.e., sequentially) or may be combined in some situations so that rotation and translation corrections could be implemented simultaneously. The optimization algorithm can also coordinate the movement of the primary locators  32   p  for a given workpiece to prevent binding of a workpiece on a fixture or the breaking of one or more of the locators  32 , and can perform a mapping function that identifies the (new) position of one or more of the features after the primary locator(s)  32   p  have moved the workpiece(s). 
         [0026]    With reference to  FIGS. 5 , a method for performing a joining operation at a given workstation  12  ( FIG. 1 ) is schematically depicted. The method can begin at block  60 , where a first workpiece and a second workpiece are mounted on first and second sets of locators  32   a  and  32   b  ( FIG. 1 ), respectively. At this initial stage, each of the primary locators  32   p  ( FIG. 1 ) associated with the first set of locators  32   a  ( FIG. 1 ) is positioned relative to the second set of locators  32   b  ( FIG. 1 ) by an associated set of the first, second and third linear motors  42 ,  44  and  46  ( FIG. 3 ) at an initial position. Clamps (not specifically shown) can be operated to secure the first and second workpieces to the frame  30  ( FIG. 1 ). 
         [0027]    The method can proceed to block  62 , where the measuring device  22  ( FIG. 1 ) can collect and analyze 3-dimensional data regarding selected features on the first and second workpieces. In the particular example shown in  FIG. 6 , which depicts a door D for an automotive vehicle, the features comprise first and second pairs of hinge mount holes HM 1  and HM 2 , respectively, a pair of latch mount holes LM, and a datum line DL. 
         [0028]    Returning to  FIGS. 1 and 5 , the method can proceed to decision block  64  where control (e.g., the workstation controller  24 ) can determine if the several features are in their optimized location. For purposes of this methodology, an optimized location of the features is the positioning of the first and second workpieces in a manner that minimizes the effect that the features of the first and second workpieces have on the magnitude of the variation in the fabrication of the article. Note that the optimized location of the features is not necessarily the location that minimizes the variation between the nominal location of each feature and the actual location of each feature, as in a least squares regression analysis. In our experience, the several features will have differing levels of influence on the magnitude of variation in the fabrication of the article and consequently, we employ a weighting technique in addition to advanced kinematics and engineering principals. 
         [0029]    Referring to the example of  FIG. 6 , a hinge (not shown) that is to be mounted to the door D via the second pair of hinge mount holes HM 2  and a latch (not shown) that is to be mounted to the door D via the pair of latch mount holes LM are configured with a relatively large degree of compliance (e.g., the holes in the hinge and the latch that receive fasteners that are threaded into the second hinge mount holes HM 2  and latch mount holes LM are relatively larger in diameter than the fasteners), another hinge (not shown) that is to be mounted to the door D via the first pair of hinge mount holes HM 1  is configured with a relatively smaller degree of compliance, and the datum line DL is critical to the gap-and flush fit of the door D to the remainder of the body (not shown) of the automotive vehicle. In this example, the datum line DL is given a first weight (e.g., a weight of one (1.0)), the first hinge mount holes HM 1  is given a second, smaller weight (e.g., a weight of one-half (0.5)), while the second pair of hinge mount holes HM 2  and the latch mount holes LM are each given still smaller weights (e.g., a weight of one-tenth (0.1)). Accordingly, the several features can be prioritized in the optimization algorithm such that the feature or features that most influence the magnitude of variation in the article can be oriented as close as possible to their nominal positions to thereby reduce the magnitude of variation in the article. 
         [0030]    In some situations, the weighting could cause one or more of the features to be moved away or further away from their nominal position(s). In the example of  FIG. 7 , the latch mount holes LM are originally located at their nominal locations, but due to the priority associated with the location of the datum line DL, the workpiece W 1  can be moved somewhat to re-orient the datum line (depicted in broken line), which can move the hinge mount holes HM (as shown in broken line) away from their nominal positions. In severe instances, one or more lower weighted features could actually be moved into a position that is actually considered out-of-tolerance but which nevertheless permits the first and second workpieces to be joined and functionally integrated into the article. For example, if second pair of hinge mount holes HM 2  were to be positioned within +/−0.5 mm from their nominal position, but were positioned +0.6 mm from their nominal position due to the prioritization of the datum line DL, the optimization algorithm would permit the configuration if there was sufficient compliance between the hinge and the second pair of hinge mount holes HM 2  to permit the door D to be mounted to the remainder of the vehicle body such that the door D opened, closed and latched properly and all criteria associated with the gap-and-flush fitting of the door D to the remainder of the vehicle body could be satisfied. One key to obtain the maximum benefit of the optimization algorithm is to appreciate that some tolerances may be somewhat arbitrary and that an out-of-tolerance situation for one feature does not necessarily render the article defective or inoperative. It will be appreciated, however, that limits could optionally be placed on the optimization algorithm that would not permit the location of one or more features to be positioned at an out-of-tolerance position. 
         [0031]    With reference to  FIGS. 8 and 9 , another key to maximizing the benefit of the optimization algorithm concerns identifying or determining whether the workpieces that are to be joined are “independent”, which is shown in  FIG. 8 , or “dependent”, which is shown in  FIG. 9 . In both examples, two sets of locators (not specifically shown) are employed, with a first set of the locators being employed to position a first workpiece W 1  and a second set of the locators being employed to position a second workpiece W 2 . In these situations only one primary locator (not shown) is required, but it will be appreciated that one or more additional primary locators could be integrated into the first set of locators and/or the second set of locators. 
         [0032]    With reference to  FIG. 8 , an independent situation is depicted in which the features on one workpiece (e.g., the features Fa, Fb, Fc and Fd on the first workpiece W 1 ) are able to be positioned relative to the features on a second workpiece (e.g., the features Fg, Fh, Fi, Fj and Fk on the second workpiece W 2 ) without causing movement of the second workpiece W 2 . In the example provided, a portion of the first workpiece W 1  overlies a portion of the second workpiece W 2  and the two workpieces W 1 , W 2  are joined together via a lap weld. The first workpiece W 1  can be positioned independently of the second workpiece W 2  so that the features Fa, Fb, Fc and Fd can be collectively oriented in a desired manner without movement of the second workpiece W 2  or the features Fg, Fh, Fi, Fj and Fk. 
         [0033]    With reference to  FIG. 9 , a dependent situation is depicted in which independent movement of the features on one workpiece (e.g., the features Fa, Fb, Fc, Fd, Fe and Ff on the first workpiece W 1 ) relative to the features on a second workpiece (e.g., features Fg, Fh, Fi, Fj, Fk, Fl and Fm on the second workpiece W 2 ) is limited by an interaction between at least one of the features on the first workpiece W 1  and at least one of the features on the second workpiece W 2 . In the example provided, a portion of the first workpiece W 1  overlies a portion of the second workpiece W 2  and the first and second workpieces W 1 , W 2  are secured to one another via a lap weld. Unlike the prior example, however, the features Fe and Ff on the first workpiece W 1  and the features Fl and Fm on the second workpiece W 2  are holes that are to be aligned to one another to receive threaded fasteners (not shown) therethrough that permit the joined first and second workpieces W 1  and W 2  to be mounted to a portion of the vehicle body. In this situation, movement of the first workpiece W 1  relative to the second workpiece W 2  is limited by a number of factors, including the amount of clearance between the holes and the threaded fasteners and the location of the holes in the vehicle body that receive the threaded fasteners. 
         [0034]    Returning to  FIGS. 1 and 5 , if the features are not in their optimized locations, the method can proceed to block  66  where the primary locator  32   p  (with the associated set of locators  32 ) can be moved by the first, second and third linear motors  42 ,  44  and  46  ( FIG. 3 ) as required to position the first workpiece at a location that positions the features on the first and second workpieces at their optimized locations. The method can loop back to block  62 , which permits the measuring device  22  to confirm the positioning of the features in their optimized locations (within predefined limits) and to permit the workstation controller  24  to confirm that the optimized locations have not changed. 
         [0035]    Returning to decision block  64 , if the features are in their optimized locations, the method can proceed to block  68  where the workpieces can be secured together. In the example provided, the workpieces are joined via a MIG welding process, but as noted above, other joining processes could be employed in the alternative. The method can proceed to block  70 . 
         [0036]    In block  70  the measuring device  22  can be employed to determine the locations of the features. The method can proceed to decision block  72 . 
         [0037]    In decision block  72 , control determines whether the features are in their optimized locations within predefined tolerances. If the features are not in their optimized locations within the predefined tolerances, the method proceeds to block  74  where the assembly (i.e., the joined workpieces) are identified as being non-compliant. Such pieces may be scrapped or reworked as necessary. 
         [0038]    Returning to decision block  72 , if the features are in the optimized locations with the predefined tolerances, the method proceeds to bubble  76  where the method ends. The assembly is considered to be compliant with tolerances and can be fed into a subsequent workstation as part of the subsequent steps for fabricating the article. It will be appreciated that the positions of the primary locators  32   p  can be returned to a “home” or “nominal position” after the joined assembly has been removed from the fixture. Optionally, the positions of the primary locators  32   p  can be left at their current positions. 
         [0039]    With reference to  FIG. 10 , a first plot P 1  and a second plot P 2  are employed to illustrate variation created in a prior art multi-step fabrication process and a multi-step fabrication process in accordance with the teachings of the present disclosure, respectively. A prior art system for fabricating an article is configured in a manner that seeks to position each pair of workpieces that are to be joined at predefined positions (e.g., their nominal positions) prior to the joining operation. Fabrication of the article in this manner produces variation (due to deviations in the tooling that is employed to fixture and orient the workpieces, as well as deviations in the workpieces themselves) that is compounded at each subsequent step of the fabrication process as depicted by the first plot P 1  and as such, the magnitude of the variation that is possible in the finished article can be relatively large if there are many steps to the fabrication process and/or if the article is relatively complex in its configuration, such as a body-in-white. In contrast, the fabrication system of the present disclosure seeks to position each pair of workpieces that are to be joined in a manner that minimizes the magnitude of variation in article. In this regard, the several workpieces in a workstation can be positioned in optimized locations to eliminate variation caused by deviations in the tooling that is used to fixture and orient the workpieces, as well as to reduce variation caused by deviations in the workpieces themselves. Accordingly, variation created in one workstation can be attenuated in a subsequent station as shown in the second plot P 2  and consequently, the magnitude of variation that is possible in the finished article is significantly reduced as compared to the prior art multi-step fabrication process. 
         [0040]    It will be appreciated that the location optimizing technique that is employed in the workstations of the manufacturing system  10  ( FIG. 1 ) can eliminate the effect of tooling wear on the fixturing that is used to position the workpieces, can eliminate the production of assemblies that are not fit for use in the finished article through real-time monitoring of the features of the workpieces before the joining operation, can reduce scrap by permitting the use of some workpieces having one or more out-of-tolerance features, and can improve the overall quality of the finished article relative to a conventional joining operation that seeks to orient workpieces in their nominal positions prior to joining the workpieces. 
         [0041]    While the manufacturing system  10  ( FIG. 1 ) has been described as employing a plurality of workstations  12  ( FIG. 1 ), each having a positioning fixture  20  ( FIG. 2 ) that includes a jig or a frame  30  ( FIG. 2 ) and at least one primary locator  32   p  ( FIG. 2 ), it will be appreciated that a portion of the jig or frame  30  ( FIG. 2 ) could be coupled to or integrated with a robot (i.e., the end effector of a robot) and the robot could be employed to vary the position of an associated workpiece in 3-dimensional space as needed. Configuration in this manner essentially integrates a set of the locators  32  ( FIG. 2 ) with portion of the jig or frame  30  ( FIG. 2 ) so that the motors that are employed to position the robot are substituted for the linear motors and move (as a group) the portion of the jig or fixture and an associated set of locators. 
         [0042]    The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.

Technology Classification (CPC): 8