Resistance spot welding gun with weld quality detection feature
First Claim
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1. In an apparatus for detecting the quality of a resistance spot weld on workpieces using a welding gun, the improvement wherein:
- said welding gun includes a fluid activated cylinder having two opposite ends, a piston assembly within the cylinder having a piston rod extending through both ends thereof, one end of the piston rod being coupled to a first electrode for contacting a surface of one of the workpieces, said cylinder being slidably mounted on supporting structure and being connected to a second electrode for contacting an opposite surface of the other workpiece to be welded to said one workpiece, the opposite end of the piston rod being coupled to a sensor assembly having a housing mounted for movement with the cylinder, whereby said sensor assembly provides output signals for detecting the quality of the weld as a function of piston rod movement relative to the cylinder.
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Abstract
A method and apparatus are disclosed for detecting weld nugget growth on a workpiece during a welding operation using a resistance spot welding gun. In the preferred embodiment, a piston rod is slidably mounted in a cylinder and is connected at one end to an electrode of the gun. The opposite end of the piston rod extends rearwardly through the cylinder and is coupled to a sensor assembly for detecting the amount of movement of the piston rod created by weld nugget growth on the workpiece during the welding cycle.
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Citations
17 Claims
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1. In an apparatus for detecting the quality of a resistance spot weld on workpieces using a welding gun, the improvement wherein:
said welding gun includes a fluid activated cylinder having two opposite ends, a piston assembly within the cylinder having a piston rod extending through both ends thereof, one end of the piston rod being coupled to a first electrode for contacting a surface of one of the workpieces, said cylinder being slidably mounted on supporting structure and being connected to a second electrode for contacting an opposite surface of the other workpiece to be welded to said one workpiece, the opposite end of the piston rod being coupled to a sensor assembly having a housing mounted for movement with the cylinder, whereby said sensor assembly provides output signals for detecting the quality of the weld as a function of piston rod movement relative to the cylinder. - View Dependent Claims (2)
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3. Apparatus for detecting weld nugget growth on workpieces during a welding operation using a resistance spot welding gun, said apparatus comprising:
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a cylinder having a piston rod slidably mounted therein; first and second electrodes; first means for connecting the piston rod to said first electrode; second means for causing said piston rod to move under fluid pressure within the cylinder in a first direction to move at least the first electrode against a surface of one of the workpieces toward the second electrode; third means for applying power to the electrodes to begin the welding operation; and fourth means for sensing the difference between the relative spacing of the electrodes at a position of maximum penetration into the workpieces and at a position when the electrodes have subsequently separated from each other due to weld nugget growth between the workpieces, with said fourth means using at least in part a measurement of the movement of the piston rod to detect said difference. - View Dependent Claims (4, 5, 6, 7, 8)
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9. In a self-equalizing resistance spot welding gun, the improvement comprising:
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first and second electrodes adapted to squeeze opposite sides of workpieces together; at least one cylinder having a body with two ends, a fluid actuated piston assembly including a piston rod extending through both ends of the cylinder, said cylinder being slidably mounted on supporting structure; first means for connecting a forward end of the piston rod to one of said electrodes; second means for connecting the body of the cylinder to the other electrode; third means for selectively applying fluid pressure to the cylinder to cause said piston rod to slide within the cylinder in a first direction to move its associated electrode against a surface of one of the workpieces and to cause the cylinder to slide in an opposite direction to thereby move the other electrode against the other workpiece; fourth means for applying current between the electrodes to begin the welding operation; a sensor assembly having a housing attached to the rear of the cylinder and movable therewith, said sensor assembly including a shaft attached at one end to the rearward end of the piston rod, and transducer means for sensing movement of the shaft, said transducer means having a first part movable with the shaft and a second part fixed to the housing; and circuit means connected to said transducer for determining weld quality characteristics as a function of output signals from said transducer. - View Dependent Claims (10)
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11. A method for detecting the quality of a weld between two workpieces during resistance spot welding operations using apparatus having at least one movable electrode for contacting a surface of one of the workpieces, said method comprising:
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contacting opposite sides of the workpieces with two opposing electrodes, at least one of the electrodes being said movable electrode; applying power to the electrodes; generating a first signal associated with the relative spacing between the electrodes at a position of maximum penetration into the workpieces; storing said first signal; subsequently generating a second signal associated with the relative spacing between the electrodes when the electrodes have separated from each other yet remain in contact with the workpieces; and using the difference between the first and second signals to provide an indication of the quality of the weld. - View Dependent Claims (12, 13)
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14. A method for detecting the quality of a weld between two workpieces during resistance spot welding operations using a self-equalizing welding gun, said gun having first and second movable electrodes opposing each other, with at least said first electrode being movable under control of a fluid actuated cylinder, said method comprising:
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mounting a sensor assembly to an end of the cylinder opposite said first electrode, said sensor assembly including transducer means having a first part movable with a piston rod in the cylinder whose one end is connected to said first electrode, said transducer means having a second part movable with said second electrode whereby said transducer means provides signals associated with the relative movement between the two electrodes; applying fluid pressure to the cylinder to cause said electrodes to move toward each other to contact opposite surfaces of the workpieces; applying electrical power to the electrodes; monitoring the output of the transducer and storing a first signal therefrom associated with the position of the electrodes at a position of maximum penetration thereof into the workpieces; continuing to monitor the output of the transducer means and selecting a second signal therefrom associated with the position of the electrodes when the electrodes have separated from each other from the position of maximum penetration but while the electrodes are still in contact with the workpieces; and using the difference between the first and second signals to provide an indication of the quality of the weld between the workpieces. - View Dependent Claims (15)
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16. A self-equalizing welding gun including means for providing an indication of weld quality, said gun comprising:
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support means for holding a transformer for supplying power; a cylinder having a body with two ends, said cylinder being slidably mounted on said support means, the cylinder having a piston assembly therein including a piston rod extending through both ends of the cylinder; a first electrode connected to a forward end of the piston rod; a generally U-shaped arm connected at one end to said cylinder; a second electrode connected to an opposite end of said arm in opposing alignment with said first electrode; third means for selectively applying fluid pressure to the cylinder to cause said piston rod to slide within the cylinder to move the first electrode against a surface of one of the workpieces and to cause the cylinder to slide in opposite direction to thereby move the second electrode against the other workpiece; means for selectively applying power from said transformer to said electrodes; a sensor assembly having a housing attached to the rear of the cylinder and movable therewith, said sensor assembly having a first part movable with said piston rod and a second part affixed to the housing of the sensor assembly, and transducer means for generating electrical signals associated with relative movement between the first and second parts thereby providing an output associated with the relative spacing between said electrodes which can be used to determine the quality of the weld. - View Dependent Claims (17)
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Specification