Resistance projection welding system and method for welding a fastener element to a workpiece

Abstract

A system and method is disclosed for monitoring and controlling a resistance projection welder for welding a projection weld nut to a workpiece. A displacement sensor measures the displacement of a welding electrode of a weld gun in real time during the welding procedure. A computer is coupled to the displacement sensor and determines whether the projection weld nut is correctly loaded between the workpiece and the welding electrode. The computer instructs a programmable logic controller (PLC) to trigger a weld controller to apply power to the welding electrode if the projection weld nut is correctly loaded onto the workpiece. The computer instructs the PLC to inhibit power if it determines the projection weld nut to be inverted, missing, or misaligned in order to allow for the removal and replacement of the projection weld nut. The computer further instructs the PLC to control and terminate the power to the welding electrode in real time in order to form a projection weld between the projection weld nut and the workpiece that is substantially similar to a predetermined projection weld. The computer processes the displacement data and provides a fault signal when the projection weld is unacceptable. A marker marks the unacceptable workpieces in response to the fault signal.

What is claimed is:  
     
       1. A welding system for welding a weld nut to a workpiece, wherein the weld nut has a first face provided with at least one projection and an opposed second face, the system comprising: 
       a power source for supplying power;  
       a weld gun having a welding electrode coupled to the power source;  
       a displacement sensor coupled to the weld gun for generating a signal responsive to an orientation of the welding electrode relative to the workpiece; and  
       a programmable logic controller (PLC) coupled to the power source and the displacement sensor, the PLC processes the displacement sensor signal to determine which face of the weld nut engages the workpiece, wherein the PLC transmits a control signal to the power source to prevent the initiation of power if the second face of the weld nut engages the workpiece.  
     
     
       2. The system of  claim 1  further comprising: 
       a vibrational weld nut feeder coupled to the PLC and the weld gun for supplying a steady stream of weld nuts to the welding electrode upon command of the PLC.  
     
     
       3. The system of  claim 1  wherein: 
       the welding electrode has an annular groove which fits over the at least one projection of the weld nut when the welding electrode engages the first face causing the distance between the welding electrode and the workpiece to be smaller than the distance between the welding electrode and the workpiece when the welding electrode engages the second face.  
     
     
       4. The system of  claim 1  wherein: 
       the displacement sensor comprises a linear variable displacement transducer.  
     
     
       5. The system of  claim 1  wherein: 
       the weld gun further comprises a ground electrode.  
     
     
       6. A welding system for welding a weld nut to a workpiece, wherein the weld nut has a first face provided with a pilot ring and a second face, the system comprising: 
       a power source for supplying power;  
       a weld gun having a welding electrode coupled to the power source;  
       a displacement sensor coupled to the weld gun for generating a signal responsive to an orientation of the welding electrode relative to the workpiece; and  
       a programmable logic controller (PLC) coupled to the power source and the displacement sensor to process the displacement sensor signal for determining which face of the weld nut engages the welding electrode, wherein the PLC transmits a control signal to the power source to prevent the initiation of power if the first face of the weld nut engages the welding electrode.  
     
     
       7. The system of  claim 6  wherein: 
       the PLC transmits a control signal to the power source to initiate power if the second face of the weld nut engages the welding electrode and the pilot ring abuts and is properly aligned with a receiving portion of the workpiece.  
     
     
       8. A welding system for welding a desired face of a weld nut to a workpiece, wherein the weld nut has first and second dissimilar faces, the system comprising: 
       a power source for supplying power;  
       a weld gun having a welding electrode coupled to the power source;  
       a displacement sensor coupled to the weld gun for generating a signal responsive to an orientation of the welding electrode relative to the workpiece; and  
       a PLC coupled to the power source and the displacement sensor to process the displacement sensor signal for determining which face of the weld nut engages the workpiece, wherein the PLC transmits a control signal to the power source to prevent the initiation of power if the welding electrode engages the first face of the weld nut.  
     
     
       9. The system of  claim 8  wherein: 
       the PLC transmits a control signal to the power source to initiate power if the welding electrode engages the second face of the weld nut.  
     
     
       10. The system of  claim 8  wherein: 
       the PLC transmits control signals to the power source to vary the power in real time based upon the displacement sensor signal such that the orientation substantially simulates a predetermined orientation sequence.  
     
     
       11. For use with a weld gun having a welding electrode, a method for welding a weld nut to a workpiece, wherein the weld nut has a first face provided with at least one projection and an opposed second face, the method comprising: 
       generating a signal responsive to an orientation of the welding electrode relative to the workpiece;  
       processing the signal to determine which face of the weld nut engages the workpiece; and  
       preventing the initiation of power if the second face of the projection weld nut engages the workpiece.  
     
     
       12. A welding system for welding a fastener element to a workpiece, wherein the fastener element has a first face provided with at least one projection and an opposed second face, the fastener element further having a central fastening portion for receiving a cooperating threaded member, the system comprising: 
       a power source for supplying weld power;  
       a weld gun having a welding electrode coupled to the power source, the welding electrode having a contact face configured to engage a face of the fastener element;  
       a displacement sensor coupled to the weld gun for generating a signal responsive to an orientation of the welding electrode relative to the workpiece; and  
       a processor coupled to the power source and the displacement sensor, the processor processes the displacement sensor signal to determine if the spacing between the welding electrode and the workpiece falls within an acceptable spacing region when a face of the fastener element engages the workpiece prior to welding, wherein the processor transmits a control signal to the power source to prevent the initiation of weld power if the spacing falls outside of the acceptable spacing region.  
     
     
       13. The system of  claim 12  wherein: 
       the weld gun further comprises a ground electrode configured to engage the workpiece.  
     
     
       14. The system of  claim 12  wherein: 
       spacing between the welding electrode and the workpiece falling within the acceptable spacing region prior to welding is indicative of the first face of the fastener element engaging the workpiece.  
     
     
       15. The system of  claim 12  wherein: 
       the processor transmits a control signal to the power source to enable the initiation of weld power if the spacing falls within the acceptable spacing region.  
     
     
       16. For use with a weld gun having a welding electrode, a method for welding a fastener element to a workpiece, wherein the fastener element has a first face provided with at least one projection and an opposed second face, the fastener element further having a central fastening portion for receiving a cooperating threaded member, the method comprising: 
       generating a signal responsive to an orientation of the welding electrode relative to the workpiece when the welding electrode engages a face of the fastener element;  
       processing the signal to determine if the spacing between the welding electrode and the workpiece falls within an acceptable spacing region when a face of the fastener element engages the workpiece prior to welding; and  
       preventing the initiation of weld power if the spacing falls outside of the acceptable spacing region.  
     
     
       17. The method of  claim 16  further comprising: 
       transmitting a control signal to the power source to enable the initiation of weld power if the spacing falls within the acceptable spacing region.  
     
     
       18. A welding system for welding a projection fastener to a workpiece, wherein the projection fastener has a first face provided with a projection and an opposed second face, the system comprising: 
       
         a pair of welding electrodes one of which cooperating with the projection fastener to be welded;  
       
       
         a displacement sensor operable with at least one of the welding electrodes for generating a signal responsive to an orientation of the welding electrode cooperating with the projection fastener and the workpiece; and  
       
       
         a processor operable with the displacement sensor for processing the displacement sensor signal to determine which face of the projection fastener engages the workpiece;  
       
       
         wherein the processor generates a control signal output indicative of an orientation of the projection fastener which terminates welding power to the welding electrode if the second face of the projection fastener engages the workpiece so that the projection fastener is not improperly welded.  
       
     
     
       19. The system of  claim 18  wherein: 
       
         the control signal output causes welding power to be supplied to the welding electrode only if the first face of the projection fastener engages the workpiece.  
       
     
     
       20. The system of  claim 18  wherein: 
       
         the control signal output causes welding power to the welding electrode to be inhibited if the second face of the projection fastener engages the workpiece.  
       
     
     
       21. The system of  claim 18  wherein: 
       
         the projection fastener is a weld nut.  
       
     
     
       22. The system of  claim 18  wherein: 
         the processor includes a programmable logic controller  ( PLC ).  
     
     
       23. The system of  claim 18  wherein: 
       
         the processor includes a computer.  
       
     
     
       24. A method for welding a fastener element to a workpiece using a pair of welding electrodes coupled to a weld power source, wherein the fastener element has a first face provided with a projection to be welded to the workpiece and an opposed second face which cooperates with one of the weld electrodes, the fastener element further having a central fastening portion for receiving a cooperating fastener member, the method comprising: 
       
         generating a signal indicative of the spacing between the welding electrode cooperating with the fastener and the workpiece when the fastener engages both the workpiece and an electrode; and  
       
       
         processing the signal to determine if the first face of the fastener provided with a projection is properly oriented relative to the workpiece; and  
       
       
         terminating the application welding power by the weld power source to the welding electrodes if the first face of the projection fastener is not properly oriented to the workpiece so that the projection fastener is not welded if the fastener is misoriented.  
       
     
     
       25. The method of  claim 24  wherein terminating the application welding power comprises providing a fault signal inhibiting the application welding power to the welding electrodes by the weld power source if the first face of the projection fastener is not properly oriented to the workpiece.  
     
     
       26. The method of  claim 24  wherein terminating the application welding power comprises providing a weld signal causing the application welding power to the welding electrodes by the weld power source only if the first face of the projection fastener is properly oriented to the workpiece.