Induction compensating method and apparatus for weld nugget resistance sensing leads of spot welders

• US 4,403,132 A
• Filed: 07/20/1981
• Issued: 09/06/1983
• Est. Priority Date: 07/31/1980
• Status: Expired due to Fees

• Current Assignee: ARO Machinery Company Limited
• Original Assignee: ARO Machinery Company Limited
• Inventors: Sugimoto, Nobuo
• Primary Examiner(s): Shaw, C. C.
• Application Number:
  US06/284,874
• Time in Patent Office: 778 Days
• Field of Search: 219/109, 219/110
• US Class Current: 219/109
• CPC Class Codes: B23K 11/258 the measured parameter being a voltage
• CPC Class Codes: G01R 15/18 using inductive devices, e.g. transformers

Abstract

In an electrical spot welding machine having sensor leads for monitoring weld nugget resistance connected to the electrodes or to the welding current conductors, the voltage component induced in the sensor leads due to inductive coupling is cancelled out by inducing a substantially equal and opposite compensating voltage in the sensor leads. For this purpose an inductance coil may be connected into one of the sensor leads and appropriately positioned on one of the welding current conductors. A core-less coil can be employed, and correct adjustment of the compensating voltage can be achieved by adjusting the coil angularly with respect to the axis of the welding current conductor.

Claims

1. In an electrical spot-welding machine having a welding head including a pair of relatively movable electrodes for gripping the work to be welded and main welding current conductors, a method of compensating for inductive coupling between the main welding current conductors and the electrical sensor leads that monitor weld nugget resistance across the work to be welded, said method comprising the steps of:

(a) temporarily connecting the sensor leads to the welding electrodes and positioning said sensor leads along paths away from said current conductors so that there is no inductive coupling therebetween;

(b) performing a welding cycle and recording the instant during the cycle at which the weld nugget voltage drop as represented by the sensor lead signal indicates the weld termination point, when there is no inductive coupling between the sensor leads and the current conductors;

(c) re-positioning the sensor leads so that they are connected to the current conductors at desired final points of connection and laid along desired final paths such as are appropriate when the machine is in commercial use;

(d) connecting into one of said leads an inductive compensating coil that is mounted on the welding head close to at least one main current conductor in an angularly adjustable manner; and

(e) performing welding cycles and adjusting the angular position of the compensating coil until an angular orientation of the coil is achieved at which the weld termination point as indicated by the sensor lead signal representing weld nugget voltage drop occurs at the same instant in a welding cycle when said sensor leads are repositioned as when said sensor leads are temporarily positioned along paths away from said conductors.

2. A method as in claim 1 comprising the further step of:

fixing the compensating coil on the welding head in said angular orientation to which it has been adjusted.

3. A method according to claim 2, wherein the compensating coil has an inductive core.

4. A method according to claim 2, wherein the compensating coil is a core-less coil.

5. A method according to claim 2 wherein the compensating coil is mounted on one of the welding current conductors.

6. An electrical spot-welding machine comprising:

a welding head including a pair of relatively movable electrodes for gripping the work to be welded and a pair of main welding current conductors extending to said electrodes along longitudinal axes that are about parallel to one another;

a welding current supply circuit connected to said current conductors;

a pair of electrical sensor leads connected each to a respective one of said current conductors to provide a signal representative of the voltage drop between said electrodes for use in machine control;

an inductive compensating coil; and

means for adjustably coupling said compensating coil along one of said sensor leads, said coil being mounted on one of said current conductors;

the axis of said coil being adjusted to and fixed at a determined non-perpendicular angular orientation with respect to the plane containing the longitudinal axes of said current conductors such as to compensate for such undesirable inductive component as would otherwise appear in the sensor lead signal.

7. A method according to claim 6, wherein the sensor leads are connected at or close to the welding electrodes and are led back along the welding current conductors.

8. A machine according to claim 6, wherein the sensor leads are connected to the ends of the welding current conductors remote from the welding electrodes.

9. A machine according to claim 8, wherein the welding electrodes are carried on hinged jaws which also constitute the welding current conductors, and the compensating coil is mounted on one of the jaws at a position remote from the electrodes.