Welding control using fuzzy logic analysis of video imaged puddle dimensions

Abstract

A welding system includes an imaging system that takes frame by frame pictures of a weld puddle. The imaging system is located in the weld torch. From the images puddle length and width are determined. The length and width are applied against stored membership functions that cover a range of different weld current characteristics and the degree of membership of each dimension in those functions is determined, producing an alpha factor for each membership function. This provides a fuzzy current requirement. Stored values for moment and area for each membership function are multiplied by the alpha for the respective function. The total of the moments is divided by the total of the areas to produce a desired weld current. The weld head includes a weld wire feeder that is driven by a servo by which the wire can be feed along either side of the weld joint. The wire feeder is gear driven in such a way that it does not interfere with the optics in the weld torch. The optics include a strobe to illuminate the puddle. Signal processing includes a process for interpolating the puddle centerline from the range in puddle widths over successive strobed images of the puddle. The head is positioned automatically over the centerline.

We claim: 
     
       1. A welder comprising a welding torch on a controlled robotic arm, imaging means in the torch, a wire feeder on the torch and a weld controller for controlling the position of the torch and electric current supplied by the torch, characterized in that: the weld controller comprises signal processing means for producing a first signal indicating a weld dimension in response to an output signal from the imaging means produced by the weld puddle; for providing from a plurality of stored logic sets and in response to the first signal a second signal indicating a degree of membership in a first set calling for a first current change and a third signal indicating a degree of membership in a second set calling for a laser change in current; for providing a fourth signal that represents the product of the second signal and a first stored area value .[.associated with said fist set.].; for providing a fifth signal that represents the product of the third signal and a second stored area value .[.associated with the second set.].; for providing a sixth signal that represents the product of the second signal and a .Iadd.first .Iaddend.moment value .[.for the first set.].; for providing a seventh signal that represents the product of the third signal and a .Iadd.second .Iaddend.moment value .[.for the second set.].; and for providing an eighth signal that represents the .[.value.]. .Iadd.sum .Iaddend.of the sixth signal .Iadd.and the seventh signal .Iaddend.divided by .Iadd.the sum of .Iaddend.the .[.seventh.]. .Iadd.fourth .Iaddend.signal .Iadd.and the fifth signal .Iaddend.to initiate a change in the electric current.   
     
     
       2. The welder described in claim 1, further characterized in that: there are five of said stored logic sets, a first set defining an increase in current of a first level for a first range of puddle dimensions, a second .Iadd.set .Iaddend.defining an increase in current of a second level, less than the first level, for a second range in puddle dimensions including some of the dimensions in said first range, a third .[.range.]. .Iadd.set .Iaddend.indicating no change in current for a third range of dimensions including some of the dimensions in said second range, a fourth set defining a decrease in current of said second level for a fourth range of puddle dimensions including some of the dimensions in said third range; and a fifth set defining .[.an.]. .Iadd.a .Iaddend.decrease in current of said first level for a fifth range of puddle dimensions include some dimensions in said fourth range. 
     
     
       3. The welder described in claim 1, further characterized in that the dimension is puddle width. 
     
     
       4. The welder described in claim 1, further characterized in the wire feed is rotatable about the axis of the weld torch and includes a servo drive responsive to signals from the signal control to index the wire feed to locations on opposed sides of the puddle. 
     
     
       5. The welder described in claim 1, further characterized in that the imaging means providing successive video frames of the puddle and the signal processing means comprises means for determining the centerline of the puddle from said images to provide a first centering signal for centering the weld torch over the puddle. 
     
     
       6. A welder comprising a welding torch on a controlled robotic arm, imaging means in the torch, a wire feeder on the torch and a weld controller for controlling the position of the torch and electric current supplied by the torch, characterized in that: the weld controller comprises signal processing means for producing a first signal indicating a weld puddle length and width in response to an output signal from the imaging means from the weld puddle, for providing from a plurality of stored logic sets and in response to the first signal a second signal indicating a degree of membership in a first set calling for a first current change and a third signal indicating a degree of membership in second set calling for a lesser change in current; for providing a fourth signal that represents the product of the second signal and a first stored area value associated with the first set, and for providing a fifth signal that represents the product of the third signal and a second stored area value associated with the second set; for providing a sixth signal that represents the product of the second signal and a stored moment value for the first set; for providing a seventh signal that represents the product of the third signal and a stored moment value for the second set; for providing an eighth signal that represents the .[.value.]. .Iadd.sum .Iaddend.of the sixth signal .Iadd.and the seventh signal .Iaddend.divided by .Iadd.the sum of .Iaddend.the .[.seventh.]. .Iadd.fourth .Iaddend.signal .Iadd.and the fifth signal .Iaddend.to indicate a change in the electric current; for storing said logic sets for different wire feed rates for different changes in current level, and for controlling the electric current in response to said eighth signal and the wire feed according to said logic sets.   
     
     
       7. The welder described in claim 6, further characterized in that the wire feed is rotatable about the axis of the weld torch and includes a servo drive responsive to signals from a signal control to index the wire feed to locations on opposed sides of the puddle. 
     
     
       8. The welder described in claim 6, further characterized in that the imaging means providing successive video frames of the puddle and the signal processing means comprises means for determining the centerline of the puddle from said images to provide a first centering signal .[.to.]. for centering the weld torch over the puddle. 
     
     
       9. A welder comprising a torch contains a camera that provides sequential snapshots of a weld paddle and a controller for increasing and decreasing weld current as a function of puddle dimensions, characterized in that the controller comprises: means, responsive to .[.an.]. a puddle dimension signal from the camera indicating a puddle dimension, for summing two values for desired current change from two adjacent fuzzy logic sets defined by respective puddle dimensions and current change levels, and for changing the weld current as a function of said sum, said two fuzzy logic sets being selected from a plurality of fuzzy logic sets for possible puddle dimensions ranging from a minimum to a maximum and said two values being determined as .Iadd.a .Iaddend.proportional function of the degree of membership in each of said two adjacent fuzzy logic sets for the puddle dimension signal.   
     
     
       10. A welder as described in claim 9, further characterized by a wire feeder mounted on the torch and rotatably moveable about an axis of the torch normal to the puddle. 
     
     
       11. The welder described in claim 10, further characterized by a motor, a shaft rotated by the motor and a transmission coupling the shaft to the feeder, the motor being operable to rotate the shaft to move the feeder. 
     
     
       12. The welder described in claim 9, further characterized in that the controller comprises means for generating a signal indicating a puddle centerline from a plurality of successive puddle dimensions produced in response to successive outputs from the camera and for providing a control signal to reposition the torch over said centerline. 
     
     
       13. An inert electric gas welder comprising an electric current torch containing means for providing an image of a weld puddle, characterized by: signal processing means operating in successive computing cycles for determining from the image a dimension of the weld puddle, for determining from stored functions the degree of membership of said dimension in a plurality of fuzzy logic functions indicating discrete changes in weld current, said degree of membership being an alpha value, for storing a moment and area for each fuzzy logic function, for providing for each alpha value greater than a set minimum a current .[.temp.]. moment value that is the product of the alpha for the function and the moment for the membership function, for providing a current .[.temp moment.]. .Iadd.area .Iaddend.value that is the product of the alpha for the membership function and the area for the membership function, for providing, in a discrete signal processing cycle, a first value that is the sum of each of said current .[.temp.]. moments and a second value that is the sum of each of said .Iadd.current .Iaddend.areas, for providing, during a computing cycle, a third signal that is the value of the first value divided by the second value, and for providing a signal to the electric current torch to modify the current through the electric current torch as a function of the magnitude of said third signal.   
     
     
       14. The welder described in claim 13, further characterized in that there are five of said fuzzy logic functions for titanium wire welding said discrete changes comprising a big increase in current, a big decrease in current, an increase in current, a decrease in current and no change in current. 
     
     
       15. The welder described in claim 13, further characterized in that there are twenty-five of said fuzzy logic functions for stainless steel wire welding, said discrete changes comprising .Iadd.a big increase in current, .Iaddend.a big decrease in current, an increase in current, a decrease in current and no change in current. 
     
     
       16. A welder comprising imaging means for producing image signals indicating the length and width of a weld puddle beneath the torch, characterized by: signal processing means for providing length and width values from the image signals, for storing moment and area values for different discrete ranges of puddle length and puddle width that identify fuzzy membership functions associated with weld current levels, for selecting the membership functions associated with said length and width values, for providing a membership signal indicating the degree of membership of the length and width values in each of said selected associated membership functions, for selecting among a pair of said length and width values the one with the lowest degree of membership, for providing a moment value that is the product of said lowest degree of membership and one of the stored moment values; for providing in area signal that is the product of said lowest degree of membership and one of the stored area values, and .Iadd.for .Iaddend.providing a current signal that represents the sum of all moment signals divided by the sum of all area signals, said current signal controlling weld current.   
     
     
       17. A welding method characterized by: illuminating a weld puddle with a strobe light during welding;   providing signals indicating a weld puddle dimension based on individual video frames of the weld puddle produced from the strobe light on a video camera in a weld torch above the puddle;   storing N membership functions, each identifying a discrete change in weld current for a range of said dimensions and storing a moment value and an area value for each membership function;   providing an alpha signal for each membership function in which said puddle dimension falls, the alpha signal indicating the degree of membership of said dimension in the membership function, based on a stored value for the function and the dimension;   providing for each membership function for which an alpha value is produced, a pair of signals indicating the product of said alpha value and a moment and area stored for said membership function;   changing weld current as a function of the sum of all said pair of signals for which alpha signals are produced.   
     
     
       18. The method described in claim 17, further characterized in that: a pair of alpha signals are produced for puddle length and width respectively and the alpha signal with the lowest degree of membership is selected to produce said product. .Iadd.   
     
     
       19.  A welder comprising a torch, an imaging means and a controller for controlling the weld current to the torch, characterized in that the controller comprises signal processing means for: receiving signals from the imaging means for determining one or more dimensions of a weld puddle produced by the welder;   determining degrees of membership of said one or more dimensions in a plurality of adjacent fuzzy logic sets covering possible puddle dimensions ranging from a minimum to a maximum;   determining from said fuzzy logic sets for which said degrees of membership are non-zero, a plurality of possible current change amounts using a plurality of fuzzy rules; and   determining a current change signal from the possible current change amounts by summing current values of said rules, the current values being determined as a proportional function of said determined degrees of membership. .Iaddend..Iadd.20. The welder of claim 19, wherein a width dimension of the weld puddle is determined. .Iaddend..Iadd.21. The welder of claim 20, including a wire feeder which feeds titanium wire, and wherein there are five fuzzy logic rules corresponding with five puddle width fuzzy sets and providing five possible current change amounts of a big current increase, a current increase, no current change, a current   
     
     
        decrease and a big current decrease. .Iaddend..Iadd.22.  The welder of claim 19, wherein both a width dimension and a length dimension of said weld puddle are determined, and wherein degrees of membership are determined for said width dimension in a plurality of width fuzzy logic sets, and wherein degrees of membership are determined for said length dimension in a plurality of length fuzzy-logic sets. .Iaddend..Iadd.23. The welder of claim 22, including a wire feeder which feeds stainless steel wire, and wherein there are twenty five fuzzy logic rules corresponding with five puddle length fuzzy sets and five puddle width fuzzy sets and providing five possible current change amounts of a big current increase, a current increase, no current change, a current decrease and a big current decrease. .Iaddend..Iadd.24. The welder of claim 19, wherein said current values of said rules include current moment values and current area values, said current moment values and said current area values being determined from a multiplication of at least one of said degrees of membership of said one or more puddle dimensions and a moment value or area value, respectively, associated with said possible current change amounts, and wherein said current moment values are summed together, said current area values are summed together, and said summed current moment values are divided by said summed current area values to 
     
     
        provide said current change signal. .Iaddend..Iadd.25.  The welder of claim 24, wherein the current moment value and said current area value of a rule are determined by taking the minimum of the degree of membership of said width dimension in the width fuzzy set associated with the rule and the degree of membership of said length dimension in the length fuzzy set associated with the rule, and by multiplying this minimum by the moment value and current area value, respectively, associated with the current change amount of the rule. .Iaddend..Iadd.26. The welder of claim 19, including a wire feeder mounted on the torch, the feeder being rotatably moveable about the axis of the torch normal to the weld puddle. .Iaddend..Iadd.27. The welder of claim 26, wherein the feeder is coupled to a shaft by a transmission coupling, and wherein the feeder is driven in rotation by a motor rotating the shaft. .Iaddend..Iadd.28. The welder of claim 26, and including a servo drive responsive to signals from the signal processing means to index the wire feed to locations on opposed sides of the weld puddle. .Iaddend..Iadd.29. The welder of claim 19, wherein the imaging means provides successive video frames of the weld puddle, and the signal processing means comprises means for determining the centerline of the puddle from said images to provide a first centering 
     
     
        signal for centering the torch over the puddle. .Iaddend..Iadd.30.  A welding method comprising the steps of: illuminating a weld puddle with a strobe light during welding; and   providing signals indicating at least one weld puddle dimension based on individual video frames of the weld puddle produced from the strobe light on a video camera in a weld torch above the puddle;   characterized by the steps of:   storing N membership functions, each identifying a degree of membership of said one or more puddle dimensions in a plurality of fuzzy sets;   relating said fuzzy sets with weld current change amounts using fuzzy rules, and storing a moment value and an area for each of these current change amounts;   providing an alpha signal for each rule which fires, the alpha signal of a rule indicating the degree of membership of said one or more dimensions in said fuzzy sets associated with that rule;   providing for each rule for which an alpha value is produced, moment and area signals indicating the product of the alpha value for the rule with respectively the moment value and area value of the current change amount associated with that rule; and   changing the weld current as a function of the sum of said moment signals divided by the sum of said area signals. .Iaddend..Iadd.31. The method of claim 30, wherein the puddle width and length dimensions are determined, and wherein said alpha signal of a rule is the lowest of the degrees of membership of the width and length puddle dimensions in the width and length fuzzy sets associated with that rule. .Iaddend.