Method for immobilizing a frame structure in its free state to establish a net datum position

Abstract

An apparatus and method for immobilizing a vehicle chassis frame in its free state atop a frame fixture so as to establish a net datum position of the chassis frame for enabling a net datum feature to be fabricated in a location net to the fixture and in design-intent position on the chassis frame. The apparatus does not compressingly clamp any portion of the chassis frame in order to avoid deforming or displacing the chassis frame and to avoid building stress into the chassis frame or incurring springback of the chassis frame. The chassis frame is interposed between a pair of opposed pads used for contacting opposite portions of the chassis frame. A work support connects to each of the opposed pads for advancing the opposed pads from a retracted position to an advanced position to find opposite portions of the chassis frame. The advancing device advances the pair of opposed pads into contact with the chassis frame without measurably displacing the chassis frame despite the tolerance variations. Once the opposed pads find their respective opposite reference contact surfaces on the chassis frame, a locking mechanism is provided for locking the pair of opposed pads in place in the advanced position so as to immobilize the chassis frame therebetween. Subsequently, a forming and piercing mechanism may be used to fabricate locating features net to the frame fixture and in design-intent position on the chassis frame.

What is claimed is:  
     
         1 . An apparatus for finding and immobilizing a workpiece in its free state so as to establish a net datum position of said workpiece, said apparatus comprising: 
 at least one pair of opposed pads;    means for advancing said at least one pair of opposed pads from a retracted position to an advanced position in contact with opposite portions of said workpiece so as to find said workpiece without measurably displacing said workpiece; and    means for locking said at least one pair of opposed pads in said advanced position, whereby said at least one pair of opposed pads lock in place so as to immobilize said workpiece in its free state.    
     
     
         2 . The apparatus as claimed in  claim 1 , further comprising: 
 unlocking means for unlocking said at least one pair of opposed pads so as to release said workpiece; and    retracting means for retracting said at least one pair of opposed pads from said advanced position to said retracted position clear of said workpiece.    
     
     
         3 . The apparatus as claimed in  claim 2 , wherein said advancing means and said retracting means comprises: 
 a spring for biasing each pad of said at least one pair of opposed pads toward said retracted position; and    means for pneumatically actuating each pad of said at least one pair of opposed pads toward said advanced position.    
     
     
         4 . The apparatus as claimed in  claim 3 , wherein said locking means and said unlocking means comprises a hydraulic locking device associated with each pad of said at least one pair of opposed pads to lock each pad of said at least one pair of opposed pads in said advanced position.  
     
     
         5 . The apparatus as claimed in  claim 4 , wherein said advancing means, said retracting means, said locking means, and said unlocking means comprise a work support device of the pneumatic-advance, hydraulic-lock, and spring-retract type.  
     
     
         6 . The apparatus as claimed in  claim 5 , wherein: 
 each pad of said at least one pair of opposed pads comprises a workpiece contact side and a locking side opposite said workpiece contact side; and    said advancing means and said retracting means comprise a pair of fluidic cylinder devices mounted between said at least one pair of opposed pads in contact with said workpiece contact sides of said at least one pair of opposed pads, and said locking and unlocking means comprise a pair of locking fluidic cylinder devices in contact with said locking sides of said at least one pair of said opposed pads.    
     
     
         7 . An apparatus for finding and immobilizing a chassis frame in its free state, despite within-tolerance variations in size or location of said chassis frame, so as to establish a net datum position of said chassis frame to enable net datum features to be fabricated net to a fixture and in design-intent position on said chassis frame, said apparatus comprising: 
 a pair of opposed hydraulic units, each hydraulic unit of said pair of opposed hydraulic units being disposed on opposite sides of a portion of said chassis frame such that said portion of said chassis frame is between said pair of opposed hydraulic units, each hydraulic unit of said pair of opposed hydraulic units comprising: 
 a plunger mounted displaceably therein and terminating in a pad, said plunger being normally biased toward a retracted position clear of said chassis frame;  
 means for advancing said plunger from said retracted position to an advanced position, such that said pad contacts said chassis frame without measurably displacing said chassis frame; and  
 means for locking said pad in said advanced position, so as to immobilize said chassis frame in its free state between said pair of opposed hydraulic units.  
   
     
     
         8 . The apparatus as claimed in  claim 7 , further comprising: 
 a stationary support positioned on one side of said chassis frame, one hydraulic unit of said pair of opposed hydraulic units being mounted to said stationary support; and    a movable support positioned opposite said stationary support on an other side of said chassis frame, the other hydraulic unit of said pair of opposed hydraulic units being mounted to said movable support.    
     
     
         9 . The apparatus as claimed in  claim 8 , wherein said movable support moves between a home position and a work position, said home position being distal said chassis frame to permit said chassis frame to be loaded in position with respect to said apparatus, said work position being proximate said chassis frame to permit said pair of opposed hydraulic units to find and immobilize said chassis frame.  
     
     
         10 . The apparatus as claimed in  claim 9 , wherein each hydraulic unit of said pair of opposed hydraulic units further includes a spring therein biased against said pad to retract said pad toward said retracted position.  
     
     
         11 . An apparatus for finding and immobilizing a chassis frame in its free state, despite tolerance variations in size or location of said chassis frame, so as to establish a net datum position of said chassis frame to enable net datum features to be fabricated net to a fixture and in design-intent position on said chassis frame, said apparatus comprising: 
 a pair of fixed platens comprising one platen and an opposite platen mounted opposite said one platen, said opposite platen being spaced a predetermined distance apart from and substantially parallel to said one platen;    a plurality of guide bars extending between said pair of fixed platens;    a pair of displaceable pads mounted about said guide bars between said pair of fixed platens, said pair of displaceable pads comprising one pad and an opposite pad mounted opposite said one pad, said opposite pad being mounted about said guide bars a spaced predetermined distance apart from and substantially parallel to said one pad, said pair of displaceable pads being displaceable from a retracted position distal from said chassis frame to an advanced position in contact with said chassis frame;    displacing means, positioned between said pair of displaceable pads, for displacing said pair of displaceable pads between said retracted position and said advanced position into contact with opposite reference surfaces on said chassis frame without measurably displacing said chassis frame so as to find said chassis frame; and    locking means, positioned between said pair of fixed platens and said displaceable pads, for locking said pair of displaceable pads in said advanced position so as to immobilize said chassis frame in said free state.    
     
     
         12 . An apparatus as claimed in  claim 11 , further comprising: 
 a base structure; and    a support displaceably mounted to said base structure and being displaceable between a home position distal said chassis frame and a work position proximate said chassis frame, said pair of fixed platens mounting to and extending from said support.    
     
     
         13 . An apparatus as claimed in  claim 12 , wherein said locking means comprises a pair of locking cylinders positioned between said pair of fixed platens and said pair of displaceable pads, said displacing means comprising a pair of finding cylinders positioned between said pair of displaceable pads.  
     
     
         14 . An apparatus as claimed in  claim 13 , wherein said pair of locking cylinders comprises hydraulic work supports and said pair of finding cylinders comprise hydraulic cylinders.  
     
     
         15 . An apparatus as claimed in  claim 13 , wherein said pair of locking cylinders comprises hydraulic work supports and said pair of finding cylinders comprise pneumatic cylinders.  
     
     
         16 . A method of finding and immobilizing a workpiece in its free state despite within-tolerance variations in size or location of said workpiece so as to establish a net datum position of said workpiece to enable net datum features to be fabricated net to a fixture and in design-intent position on said workpiece, said method comprising the steps of: 
 mounting said workpiece in its free state atop said fixture;    advancing an opposed pair of pads from a retracted position to an advanced position in contact with opposite portions of said workpiece without measurably displacing said workpiece despite said tolerance variations, such that said opposite portions of said workpiece are between said opposed pair of pads; and    locking said opposed pair of pads in said advanced position against said opposite portions of said workpiece so as to immobilize said workpiece in said free state.    
     
     
         17 . The method as claimed in  claim 16 , further comprising the steps of: 
 unlocking said opposed pair of pads; and    retracting said opposed pair of pads from said advanced position to said retracted position such that said workpiece may be withdrawn from said fixture.