Spot weld quality monitoring system

• US 4,562,330 A
• Filed: 09/09/1983
• Issued: 12/31/1985
• Est. Priority Date: 09/09/1983
• Status: Expired due to Fees

• Current Assignee: Digimetrics Incorporated
• Original Assignee: Digimetrics Incorporated
• Inventors: Hamilton, Rodrick J.
• Primary Examiner(s): Shaw, Clifford C.
• Application Number:
  US06/530,754
• Time in Patent Office: 844 Days
• Field of Search: 219/109, 219/110
• US Class Current: 219/110
• CPC Class Codes: B23K 11/25 Monitoring devices

Abstract

Adjusted voltage measurements of monitored AC electrical energy supplied during a welding operation are evaluated by integration with respect to time during half cycles to develop a variable criterion each half cycle that is compared with adjusted limits to electronically make weld quality judgements. The generation of a fail signal during two consecutive half cycles as a result of such judgements, is operative through logic gating to produce a reject signal to control the marking of defective welds, interrupt the supply of energy to the welding electrodes and effect timely operation of an ejector removing articles with defective welds from a production line.

Claims

1. (Amended) In combination with apparatus for welding a seam on a product during movement along a conveyor path by applying electrical energy from an AC source across welding electrodes, a method of evaluating weld quality including the steps of:

measuring a fractional portion of said applied electrical energy consumed each half cycle of said AC source to heat weld nuggets during said movement of the product along the conveyor path;

cyclically detecting levels of the measured energy in excess of preset limits; and

generating a reject signal in response to detection of said excessive levels during at least two consecutive half cycles.

2. (Amended) The method of claim 1 wherein said step of measuring the energy consumed includes the steps of:

independently measuring voltage drops across the electrodes and circuit resistance in series therewith;

comparing the measured voltage drops to produce a differential voltage drop corresponding to the fractional portion of the applied electrical energy; and

integrating the differential voltage drop with respect to time for each of the half cycles.

3. The method of claim 2 including the step of:

interrupting supply of the energy to the welding electrodes during measurement of said excessive levels.

4. The method of claim 3 wherein said half cycles are recognized by detection of zero levels of the measured voltage drops.

5. The method of claim 2 wherein said detection half are recognized by detection of zero levels of the measured voltage drops.

6. The method of claim 1 including the step of:

interrupting supply of the energy to the welding electrodes during measurement of said excessive levels.

7. In combination with apparatus for welding a seam on a product during movement along a conveyor path by applying electrical energy from an AC source across welding electrodes, the improvement comprising means for monitoring a fractional portion of the electrical energy applied each half cycle of the AC source to the seam during said movement thereof, means connected to the monitoring means for cyclically detecting levels of the monitored fractional portion of the electrical energy in excess of preset limits, and logic means connected to the detecting means for generating a reject signal in response to detection of said excessive levels during at least two consecutive half cycles.

8. The improvement as defined in claim 7 wherein the energy monitoring means includes means for independently measuring voltage applied to the electrodes and volt drop across circuit resistance in series with the electrodes, means connected to said independent voltage measuring means for comparing the voltage measurements to develop a differential voltage signal corresponding to said fractional portion of the electrical energy applied, and means connected to one of the independent voltage measuring means and the voltage comparing means for integrating the differential voltage signal with respect to time for each of the half cycles.

9. The improvement as defined in claim 8 including spike voltage detection means connected to the voltage comparing means for interrupting supply of the AC electrical energy to the welding electrodes in response to said reject signal during measurement of peak voltage.

10. The improvement as defined in claim 9 including means connected to the logic means for ejecting the product from the conveyor path in response to said reject signal.

11. The improvement as defined in claim 10 including means responsive to said interruption of the supply of energy for marking the seam.

12. The combination of claim 11 wherein the electrodes are rotatable wheels through which the seam is spot welded.

13. The improvement as defined in claim 7 including means connected to the logic means for ejecting the product from the conveyor path in response to said reject signal.

14. In combination with apparatus for welding a seam on a product during movement along a conveyor path by applying AC electrical energy across welding electrodes, the improvement comprising means for monitoring the electrical energy applied to the seam during said movement thereof, means connected to the monitoring means for cyclically detecting levels of the monitored electrical electrical energy in excess of preset limits, logic means connected to the detecting means for generating a reject signal in response to detection of said excessive levels during a predetermined number of consecutive cycles, and spike voltage detection means connected to the monitoring means for interrupting supply of the AC electrical energy to the welding electrodes in response to said reject signal during measurement of peak voltage.