Eddy current tool positioning system

A method for positioning a tool relative to a first surface of a workpiece, the first surface being opposite to a second surface whereon a member is to be joined to the workpiece, comprising the steps of:

• controllably positioning a discontinuity detection means relative to the first surface of the workpiece, the workpiece having a discontinuity between the member and the second surface, the discontinuity being detectable by the discontinuity detection means;
• moving the detection means relative to the workpiece such that the detection means intersects the discontinuity at a plurality of points for producing an output signal from the detection means at each of the points;
• determining a position of the discontinuity from the detection means output signals;
• and
• controllably positioning a tool along the first surface relative to the determined position of the discontinuity.

A welding system comprising:

• means for welding;
• means for engaging a workpiece during the welding of a member to the workpiece, the workpiece being welded from a first surface along a discontinuity between the member and the workpiece, the discontinuity being disposed along a second surface of the workpiece, the second surface being opposite the first surface;
• means for translating said welding means along the first surface relative to the discontinuity, said translating means being responsive to a controlling means for being translated in accordance with predetermined position coordinates;
• eddy current probes means having an output signal responsive to the presence of the discontinuity;
• and
• means for controllably translating said eddy current probe means over the second surface relative to the discontinuity, said eddy current probe translating means being responsive to said output signal for determining the position coordinates of the discontinuity.

In a welding system, a method of determining the position of a discontinuity between a first member and a second substantially planar member which are to be welded together along the discontinuity, the first member being disposed substantially adjacent to a top surface of the second member, comprising the steps of:

• controllably translating a discontinuity detecting means over a bottom surface of the second member such that the detecting means intersects the discontinuity at a plurality of points;
• detecting an output signal from the detecting means, the signal being generated by the detecting means in response to the detecting means intersecting the discontinuity;
• recording the position of the detecting means relative to the bottom surface each time the output signal is detected, each recorded position defining a point on the bottom surface;
• connecting a set of two or more substantially adjacent points with a line element drawn through the substantially adjacent points;
• extending each of the line elements such that line elements from adjacent sets of points intersect, the intersection defining the position of a critical point;
• and
• determining the position of the discontinuity as being defined by that portion of the intersecting line elements between the critical points.