Abstract:
A method of manufacturing an interchangeable fixture is disclosed, the method comprising the steps of making components of the fixture, selecting a reference component, the reference component having a constant geometric dimensional relationship with a system for controlling movements of a tool having a tool center point, making an intermediate assembly comprising the components of the fixture and the reference component, creating a first locating feature on the intermediate assembly and creating a second locating feature on a tool support relative to the tool center point, and assembling the tool support and the intermediate assembly such that the first locating feature and the second locating feature engage correspondingly.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    This invention relates generally to manufacturing components, and more specifically to methods and interchangeable apparatus for accurately and controllably locating tools on workpieces during manufacturing operations such as polishing, deburring, materials removal and other machining and inspection operations. 
         [0002]    Complexly shaped articles, such as blisks used in aircraft engines, are manufactured by techniques using specially shaped tooling that accomplish material removal from the work piece. In an example of particular interest, an integral compressor blade/disk (BLISK) structure of a gas turbine engine is manufactured as a single piece by machining methods such as milling and electro chemical machining (ECM). Finish machining operations such as polishing and deburring of machined components such as BLISKs are needed and have to be performed so as to avoid damaging these expensive components. Due to the complex geometries involved in BLISKs, many of the finishing operations are done manually. 
         [0003]    Multi-axis robots which reproduce the motions of humans have sometimes been used for finish machining operations such as polishing and deburring. For example, for deburring of complex shaped articles such as BLISKs, conventional multi-axis robots using an air powered abrasive belt tool at the end of a robot arm have been used. However, these conventional robot arms use the same tool previously controlled by humans and reproduce the motions of a human performing this task. This approach has severely limited the use of robots for finishing operations on complex geometries such as BLISKs because the abrasive belt polishing tool must be kept away from critical geometric features that are not easily accessible. To avoid costly damage to these expensive components, the conventional abrasive belt tool must be kept away from critical geometry due to its constantly changing overall length and true position due to inherent belt stretching and belt tracking. This is especially a problem in robotic or automatic machining systems which lack the hand-eye coordination of humans. The constantly changing true position and tool conditions such as stretching and tracking of the machining tool have severely limited the use of robotic polishing and deburring of critical components such as BLISKs. Manufacturing individual components of a fixture for use in machining or inspection operations inherently involves some variations due to manufacturing tolerances and assembly stack-ups. These manufacturing tolerances and assembly stack-ups conventionally have resulted in variations in the location of the machining or inspection tool center point. In manufacturing operations a large number of tool assemblies and robots are used and conventional methods of accounting for the manufacturing variations in tools are not adequate to ensure precise location and control of tool center point within complex geometry parts such as BLISKs. 
         [0004]    Accordingly, it would be desirable to have a system for performing automated finish machining operations on complex geometries such as BLISKs without causing damage to the component. It would be desirable to have a device that maintains the true position in space of the contact point of the machining tool regardless of changes in tool conditions such as belt wear, stretching, tracking, tension changes and other causes. It is desirable to have a method of making a device for use in manufacturing and inspection operations on complex geometries that can maintain the true position in space of a tool that can be controlled automatically in robots or other automated systems. It is desirable to have a method of manufacturing a tool assembly such that various tools can be interchanged while maintaining the precision of location of the tool center point. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0005]    The above-mentioned need or needs may be met by exemplary embodiments which provide a method of manufacturing an interchangeable fixture, the method comprising the steps of making components of the fixture, selecting a reference component, the reference component having a constant geometric dimensional relationship with a system for controlling movements of a tool having a tool center point, making an intermediate assembly comprising the components of the fixture and the reference component, creating a first locating feature on the intermediate assembly and creating a second locating feature on a tool support relative to the tool center point, and assembling the tool support and the intermediate assembly such that the first locating feature and the second locating feature engage correspondingly. 
         [0006]    In another embodiment, the method described above is further developed to manufacture a robotic tool by the additional steps of mounting a drive system on the intermediate assembly such that the drive system has flexibility to move on the intermediate assembly and mounting a tool on the tool support such that the tool is capable of being driven by the drive system. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the concluding part of the specification. The invention, however, may be best understood by reference to the following description taken in conjunction with the accompanying drawing figures in which: 
           [0008]      FIG. 1  shows an exemplary embodiment of the present invention of a robotic system for deburring a gas turbine engine BLISK. 
           [0009]      FIG. 2  shows an isometric view of a partially assembled tool forming a portion of an exemplary embodiment of the present invention of a device for removing material from complex components. 
           [0010]      FIG. 3  shows an isometric view of a partially assembled tool forming a portion of an exemplary embodiment of the present invention of a device for removing material from complex components, including bearings. 
           [0011]      FIG. 4  shows an isometric view of a partially assembled tool forming a portion of an exemplary embodiment of the present invention of a device for removing material from complex components, including a motor carriage. 
           [0012]      FIG. 5  shows an isometric view of a partially assembled tool forming a portion of an exemplary embodiment of the present invention of a device for removing material from complex components, including a motor. 
           [0013]      FIG. 6  shows an isometric view of an exemplary embodiment of the present invention of a device for polishing a component. 
           [0014]      FIG. 7  shows a cross sectional view of the exemplary embodiment of the present invention shown in  FIG. 6 . 
           [0015]      FIG. 8  shows a side view with a partial cross section of the exemplary embodiment of the present invention shown in  FIG. 6 . 
           [0016]      FIG. 9  shows a method of manufacturing interchangeable robotic tool assemblies. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0017]    Referring to the drawings wherein identical reference numerals denote the same elements throughout the various views,  FIG. 1  shows an exemplary embodiment of the present invention of a robotic system for deburring a gas turbine engine BLISK. A conventional robot  14 , having a conventional robotic arm  14 , is shown in  FIG. 1 . The Robot  14  is mounted conventionally to the ground or a suitable platform. The robot  14  has a stationary coordinate system  17  for use as a reference for programming the location of the tool point in space, represented by the tool point coordinate system  19 . A fixture  20  that holds a machining device  100  is mounted using a mount system  22  on the robotic arm  16 . The machining device  100  and the mount system  22  are shown in more detail in  FIGS. 2-8 . The component  12  to be machined is mounted on a suitable fixture  13 , having a component coordinate axis  18  suitably located with respect to the robot coordinate axis  17 . The robotic arm typically has multiple degrees of freedom to translate and rotate with respect to the robot coordinate system  17 . Similarly the component  12  being machined may be conventionally mounted with multiple degrees of freedom with respect to the coordinate system  18 . 
         [0018]    In the exemplary embodiment shown in  FIG. 1 , a drive system  30  that drives a machining tool, such as a polishing tool  40 , is mounted on the fixture  20 . In order to effect material removal from the component  12 , the machining tool, such as the polishing tool  40 , contacts the component at a point of contact  43 . The path in space that the tool traverses during machining or inspection is programmed using conventional methods. However for finishing operations on complex geometries such as a BLISK, this normal tool path programming is not sufficient due to the changes in the true position of the tool contact point arising from contact forces and from wear of the tool during machining. This is especially true in polishing operations where the amount of material removed from the component is small. The risk of a tool mark or mis-machining in intricate geometries in complex parts such as BLISK is high unless the true position of the contact point is absolutely controlled regardless of the tool conditions. In the exemplary embodiment of the present invention shown in  FIG. 1-8 , the spatial location of the true position of the point of contact  43  of the tool has a fixed relationship with respect to the coordinate system  17  of the robot or other machining center regardless of the variations that might occur due to tool wear, tool belt tracking, tool belt tension changes or other reasons. This enables the programming of the location of the point of contact  43  in an automated machining system, such as a robot  14  or machining center (not shown), such that it can predictably follow, in a controlled way, and maintain a constant relationship with the intricate geometries of complex parts such as a BLISK. In a further aspect of the invention, as described subsequently herein, safety mechanisms to avoid damaging the component  12  during incidents such as tool breakage or belt tension loss or break are incorporated. 
         [0019]    In the exemplary embodiment of a system for polishing shown in  FIG. 1 , a polishing tool  40  using a polishing belt  41  contacts a BLISK (shown as item  12 ) at a contact point  43  that is programmed to follow the contours of the BLISK surfaces and edges for removing burrs. The polishing belt  41  is driven by a drive system  30 . The drive system  30  is mounted flexibly in a fixture  20  such that the spatial location of the contact point  43  has a constant relationship with the local geometry of component  12  and is maintained constant during the polishing operation. Any machining induced forces or tool wear or other sources that tend to change the tool path geometry during machining are accommodated by the flexibility that is designed into the unique mounting system for the drive system  30 . A flexible mounting system that can be used as above is described in detail subsequently herein. 
         [0020]      FIGS. 2 ,  3  and  4  show partial assemblies of an exemplary embodiment of a fixture  20  for flexibly mounting a drive system  30  as described previously.  FIG. 5  shows a motor  60  mounted in the fixture  20 .  FIG. 6  shows an assembled view of a device  100  which comprises a motor  60  and a polishing tool  40  mounted in the fixture  20 . The exemplary embodiment of the fixture comprises a conventional tool mount system  22  that is used to attach the entire assembly  100  quickly to the robotic arm  16  of a conventional robot system  14  or a machining center (not shown). Adaptor plates  27  may be optionally used as necessary to attach a conventional rotary actuator  26  to the tool mount system  22 . The rotary actuator  26  enables a rotational degree of freedom to the machining tool assembly, such as for example, the polishing tool  40  shown in  FIG. 1 . The rotary actuator is powered by a conventional pneumatic motor (not shown) powered by air supplied by a pneumatic supply line  114 . Alternatively, the rotary actuator  26  may be powered by a conventional electrical motor (not sown). 
         [0021]    A base  25  is attached using conventional attachment means to the top of the rotary actuator such that the entire base  25  and other components attached to can be rotated as needed during machining using the rotary actuator  26 . The base comprises a centrally located channel  96  that has a number of tapped holes for receiving attachment screws. A bumper block  88  is attached on top of the base  25  near the rear side of the base  25 . A rail  92  is attached to the channel  96  using conventional means. A forward bearing  93  and a rear bearing  94  are slidably mounted on the rail such that the bearings  93  and  94  can slide along the length of the rail  92 . The bearings  93  and  94  have tapped holes on their top that can receive attachment screws. A motor carriage  62  is attached using conventional attachment means to the top of the forward bearing  93  and to the top of the rear bearing  94 . The entire motor carriage  62 , and all other components attached to it, can be moved linearly forward and rearward on the rail  92 . A proximity sensor system is attached to the bumper block  88  such that the location of the motor carriage is sensed when it moves beyond a certain specified location towards the rear side, such as might happen when there is a tool breakage during machining. This is a safety feature to cut off the machining operation to prevent damage to the component  12 . The proximity sensor system comprises a bracket  81  attached to the bumper block  88  and an electrically operated conventional proximity sensor  82  having a plunger  83  which activates the cut off system when needed. The electrical system is housed in an electrical module  116 . 
         [0022]    The motor carriage  62  has a cavity for receiving a motor housing  64  partially located within it. The motor housing  64  is pivotably attached to the motor carriage  62  using a pair of motor housing mounts  90 . The motor housing mounts  90  are firmly attached near their lower end to the motor carriage  64  using conventional attachment means. The motor carriage  62  has a pivot  71  on each side that is supported by the motor housing mounts  90 . In the exemplary embodiments shown herein, the pivots  71  are shown in the form of screws attached to the housing mounts  90  near their top that engage with corresponding holes on the sides of the motor carriage  62 . Other suitable pivoting means may also be used alternatively. A motor  60  is located within the motor housing  64  and held within the motor housing conventional means, such as attachment screws.  FIGS. 5 and 6  show a pneumatic motor  60 , driven by air supplied through an air line  112 . The air supply line  112  is connected to the pneumatic motor  60  using a quick-connect attachment  110 . Any other suitable type of powering system such as an electric motor or hydraulic actuator may also be used instead of a pneumatic motor. A spring block  50  is attached using conventional means to the carriage base  95  which is located at the forward end of the motor carriage  62 . The spring block  50  has a compression spring  52  attached to it and has a spring post located inside the spring and attached to the spring block  50 . The spring post guides the spring and prevents buckling when the spring exerts a force on the spring block  50  and the motor carriage  62 . In the exemplary embodiment shown in  FIGS. 5 and 7 , the spring  52  is attached within a slot in the spring block  50 . The components of the system described herein may be manufactured using any suitable material which is light weight, preferably using Aluminum. 
         [0023]    An exemplary embodiment of the present invention for absolutely locating the true position of a machining tool contact point  43  with respect to the tool mount system  22  and flexibly mounting the drive system  30  in the fixture  20  is shown in  FIGS. 6-8 . Referring to these Figures, riser gussets  56  are located at the forward end of the base  25  attached to the sides of the base plate  25  using conventional attachment means. A vertical frame  54  having an arch-type shape is attached to the riser gussets  56  such that the riser gussets provide lateral support to the vertical frame  54 . The vertical frame may also be attached at its lower end to the forward end of the base  25 . 
         [0024]    Referring to  FIG. 6 , a spring base  51  is attached to the forward end face of the vertical frame  54 . As described before, the aft end the spring  52  is attached to the spring block  50 . The forward end of the spring  52  is attached to the spring base  51 . This is shown in cross sectional view in  FIG. 7 . The forward end of spring fits within to a cavity located near the middle of the spring base  51  and is held in place by an adjustment screw  53 . During the machining operations, as explained subsequently herein, the spring  52  exerts a force on the spring block  50  attached to the carriage  62  and pushes the carriage aft, away from the vertical frame  54 . The adjustment screw can be adjusted to control the magnitude of the force generated in the spring. 
         [0025]    The true position of a machining tool contact point  43  is absolutely located in space using a tool contact arm  42 , arm locator pins  47 , and an arm mount  49 . The arm mount  49  is rigidly attached to the top of the vertical frame  54  using conventional means. The arm mount provides support to the machining tool, such as the polishing tool  40 , during machining and transmits the reaction forces from the tool to the motor carriage  62  which can slide along the rail  92 . 
         [0026]      FIGS. 6 ,  7  and  8  show a device for polishing and deburring a component, having a polishing and deburring tool  40 . The tool  40  comprises a roller  44  attached to the forward end of a contact arm  42  that is clamped to the arm mount  49  using an arm clamp  46 . The roller is capable of rotating around a roller axis of rotation  45 . The arm clamp  46  is located on the arm clamp using arm locator pins  47 , as described herein. The tool  40  has an abrasive belt  41  that is supported by the roller  44  at the forward end and by a belt drive wheel  63  at the aft end. The belt drive wheel  63  is attached to the drive motor  60  and rotates around an axis of rotation  61 . The abrasive belt  41  is driven by the motor  60  and the belt drive wheel  63  around the roller  44 . For polishing and deburring, removal of material from the component  12  is accomplished by contacting the moving abrasive belt  41  on the component  12  surfaces and edges. The contact point  43  forces during machining between the abrasive belt  41  and the component  12  are transmitted by the contact arm  42  to the arm mount  49  and the vertical frame  54 . These forces are transmitted to the motor carriage  62  which can move along the rail  92 . The abrasive belt has a tension which tends to pull the two axes of rotation  45  and  61  toward each other. This is opposed and reacted by the compressive force that is set in the spring  52  using the adjustment screw  53 . The tension in the abrasive belt  41  is set using the adjustment screw  52 . It is noted that because of the unique way of mounting the contact arm  42  and machining tool such as  41 , the machining forces or other tool conditions do not alter the spatial location of the tool contact point  43  which is absolutely located at the specified locations in space at all times during machining. These factors which change the true location of tool contact points in conventional machining systems are accommodated in the present invention by automatically changing the position of the flexibly mounted drive motor carriage  62  on the rail  92  due to the compressive forces from the spring  52  exerted on the carriage  62  through the spring block  50 . 
         [0027]    In one aspect of the invention, the exemplary embodiments described herein incorporate a proximity sensor system  80  which can detect tool failure or tool wear conditions during machining and provide a means for safely shutting down the machining operations without damaging the component  12  being machined. The proximity sensor system  80  comprises a proximity target  84  attached to the bumper block  88  that is located near the aft end of base  25 , and a proximity sensor  82  mounted on the motor carriage near its aft end. Referring to  FIG. 7 , during machining, if there is a significant loss of tension in the abrasive belt  41  such as from wear, track jump, or breakage, the energy stored in the compressed spring  52  will apply a force on the spring block and eject motor carriage rearwards along the rail  92 . The proximity sensor  82  will sense the position of the motor carriage  62  and send an electrical signal to the robot or machining center to safely shut down the system or take other appropriate actions to prevent damage to the component  12 . Bumpers and plungers are provided on the bumper block  84  and proximity sensor to absorb any shock load that may be induced due to the sudden ejection of the motor carriage  62 . 
         [0028]    In belt driven systems, belts can jump the track from the pulleys or other drives if the drive system axis is not properly aligned. In an aspect of the present invention, the exemplary embodiments described herein incorporate means for adjusting the orientation of the motor axis of rotation  61  and adjust tracking of the polishing belt in the belt drive wheel  63 . An exemplary implementation of this feature is shown in  FIG. 8 . As explained previously herein, the drive motor  60  is located within a motor housing  64  which is pivotably attached to the mounts  90  using motor housing pivots  71 . In addition, a motor housing alignment pin  72  is inserted into a corresponding recess in the wall of motor housing  64  and the motor housing mount  90 . An alignment set screw  76  and a locking set screw  74  are provided within the motor housing mount  90 . By appropriately adjusting the alignment set screw  76  and the locking set screw  74 , the orientation of the axis of rotation  61  of the motor  60  can be changed as necessary for proper alignments of the drive system  30 . Belt tracking within the belt groove of the belt drive wheel  63  may change as the belt  41  wears during operation. The means described above can be used to adjust belt tracking to ensure that the polishing belt remains within the groove and on the roller  44 . 
         [0029]    In another aspect of the invention, a complete interchangeability of the different fixtures  20  and different tool contact arms  42  is attained while maintaining substantially the same true position of the tool center point with respect to the robot. This is accomplished using an embodiment of the present invention of a sequence of manufacturing and assembly steps, as shown in  FIG. 9 . Conventional manufacturing of individual components and their assembly inherently involves variations due to manufacturing tolerances and assembly stack-ups. These manufacturing tolerances and assembly stack-ups in conventional methods result in variations in the location of the tool center point, such as for example, represented by the tip of the contact arm  120 . The tool center point is the location point in space that the robot  14  controls during robotic movements. The robot  14  controls the position, velocity and rotation of this tool center point  120  to be what is necessary to accomplish the specified goals in manufacturing, inspection, and other robotic uses. 
         [0030]    An exemplary embodiment of the present invention of a method  200  of manufacturing a tool assembly, such as for example shown in  FIG. 6 , is shown in  FIG. 9  as a series of steps identified by numerals  202 - 224 . In the first step, numeral  202 , the individual components such as base  25 , riser gussets  56 , vertical frame  54  etc. shown in  FIGS. 2-8  are manufactured using conventional means. All the characteristics of the individual components except the arm mount locating holes  122  for the locating pins  47  (see  FIG. 7 ) and the arm locating holes  132  (see  FIG. 6 ) are generated. These individual components are then assembled (numeral  204 ) as described previously herein. The fixture assembly is attached (numeral  206 ) to the tool plate  21  of the robot or other machining center or another appropriate component that is located relative to the coordinate system  17  (see  FIG. 1 ). Alternatively, an equivalent tool plate such as a slave tool plate which has the same locational characteristic dimensions with respect to the coordinate system  17  can also be used. The entire assembly is then set up (numeral  208 ) on a conventional machine tool, such as a milling machine or a drilling machine, for drilling the locating holes  122  in the arm mount  49 . During this set up, the robot tool plate  21  (or the equivalent slave tool plate if used) is used to set the machine origin. This feature of the exemplary embodiment  200  of the present invention ensures that, regardless of any stack-up of tolerances due to the individual component machining and assembly process, the true position location of the locating holes  122  and locating pins  47  with respect to the robot coordinate axis  17  is substantially the same on each fixture  20  that is manufactured. Once the set up as described is complete, the locating holes  122  on the arm mount  49  are drilled (numeral  210 ). Reaming of the holes is optionally performed. The attachment holes  124  are then drilled (numeral  212 ) on the arm mount  49 , for later use for attaching an arm clamp  46 . The locating pins  47  are pressed fit into the locating holes  122  (numeral  214 ). Alternatively, locating pins may be pressed fit into the locating holes  132  on the contact arm, described below. Because of the set up described herein to create the locating holes  122 , the locating pins  47  will be in substantially the same spatial location, with respect to the robot coordinate axis  17 , on every fixture  20  that is manufactured using this method  200 . 
         [0031]    The points at which the locating holes  132  are to be drilled on the contact arm  42  are then located (numeral  216 ). These locations of the holes on the contact arm  42  are dimensioned from the tool center point  120  located at the tip of the contact arm  42 . The locating holes  132  are then drilled in the contact arm  42  (numeral  218 ). Attachment holes  134  may also be drilled in the contact arm  42  (numeral  220 ). The contact arm locating holes  132  are then aligned with the locating pins  122  on the arm mount  49  (numeral  222 ). The contact arm  42  is then attached to the arm mount  49  (numeral  224 ) using the attachment holes  124  and  134  and cap head screws  48  or other conventional attachment means. 
         [0032]    As described before herein, in the case of robot  14 , the only point the space that the robot absolutely must control is the tool center point  120 . The robot  14  controls the position, velocity and rotation of this tool center point  120 . Because of the unique way of locating the locating holes  132  on the contact arm  42  as described herein, on every contact arm  42  manufactured, the geometric relationship from the tool center point  120  to the locating holes  132  is substantially the same. For every fixture  20  manufactured according to the method  200 , the locating pins  47  and the contact arm  42  and the contact arm tool center point  120  are substantially at the same spatial location with respect to the robot coordinate system  17 , and are interchangeable during manufacturing because the geometric relationship of the tool center point  120  to the robot or other machining center is substantially the same. 
         [0033]    Although the embodiments of the present invention are described herein in the context of machining tools, such as the polishing tool  40 , it is understood that the components, assemblies, features and methods disclosed herein are similarly applicable in other contexts as well, such as for example, non-destructive evaluations and dimensional inspections of complex components such as BLISKs. This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.