Spot welding control system and control method

• US 6,232,572 B1
• Filed: 04/20/1999
• Issued: 05/15/2001
• Est. Priority Date: 04/20/1998
• Status: Active Grant

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Kanjo, Mitsunori
• Primary Examiner(s): Shaw, Clifford C.
• Application Number:
  US09/294,330
• Time in Patent Office: 756 Days
• Field of Search: 219/110, 219/109, 219/86.41, 219/86.24, 219/86.7
• US Class Current: 219/110
• CPC Class Codes: B23K 11/115 by means of two electrodes placed opposite one another on both sides of the welded parts
• CPC Class Codes: B23K 11/253 the measured parameter being a displacement or a position
• CPC Class Codes: B23K 31/125 Weld quality monitoring

Abstract

Paired electrodes, of which a wear amount is detected, press workpieces to be welded, conducting a current therethrough, and have an inter-electrode displacement amount varying during the current conduction, which displacement amount is detected continuously from a reference position (a). Detected inter-electrode displacement amounts are corrected in dependence on the detected wear amount, and corrected inter-electrode displacement amounts (h) are based on to make a decision of a welding state of the workpieces.

Claims

1. A spot welding control system comprising:

a pair of electrodes pressing a welding object, conducting a current through the welding object;

an inter-electrode displacement amount detector substantially continuously detecting an inter-electrode displacement amount of the pair of electrodes;

a regression line calculator calculating a regression line from inter-electrode displacement amounts detected by the inter-electrode displacement amount detector;

a reference regression line memory having stored therein a reference regression line based on a reference inter-electrode displacement amount;

a comparator comparing the regression line calculated by the regression line calculator with the reference regression line stored in the reference regression line memory;

a welding condition setter setting a welding condition of the welding object in accordance with a result of comparison by the comparator; and

a current conduction controller controlling a current conducting state of the pair of electrodes in dependence on the welding condition set by the welding condition setter.

2. The spot welding control system of claim 1, wherein the welding condition setter sets the welding condition so that a regression line calculated by the regression line calculator coincides with the reference regression line stored in the reference regression line memory.

3. The spot welding control system of claim 1, wherein the welding condition comprises one of a welding current between the pair of electrodes and the welding object, the welding current being variable, a conduction time of the welding current, the conduction time being variable, and a pressing force acting on the welding object from the pair of electrodes, the pressing force being variable.

4. The spot welding system of claim 3, wherein the one of the welding current, the conduction time, and the pressing force of the welding condition has an order of priority therebetween and a weighting set thereamoung.

5. A spot welding control system comprising:

a pair of electrodes for pressing a welding object, conducting a current through the welding object;

inter-electrode displacement amount detection means for substantially continuously detecting an inter-electrode displacement amount of the pair of electrodes;

regression line calculation means for calculating a regression line from inter-electrode displacement amounts detected by the inter-electrode displacement amount detection means;

reference regression line storage means for storing therein a reference regression line based on a reference inter-electrode displacement amount;

comparison means for comparing the regression line calculated by the regression line calculation means with the reference regression line stored in the reference regression line storage means;

welding condition setting means for setting a welding condition of the welding object in accordance with a result of comparison by the comparison means; and

current conduction control means for controlling a current conducting state of the pair of electrodes in dependence on the welding condition set by the welding condition setting means.

6. A spot welding control system comprising:

a pair of electrodes pressing a welding object, conducting a current through the welding object;

a wear amount detector detecting a wear amount of the pair of electrodes;

an inter-electrode displacement amount detector substantially continuously detecting an inter-electrode displacement amount of the pair of electrodes;

a regression line calculator correcting inter-electrode displacement amounts detected by the inter-electrode displacement amount detector in dependence on the wear amount detected by the wear amount detector and calculating a regression line from corrected inter-electrode displacement amounts;

a reference regression line memory having stored a reference regression line based on a reference inter-electrode displacement amount;

a comparator comparing the regression line calculated by the regression line calculator with the reference regression line stored in the reference regression line memory;

a welding condition setter setting a welding condition of the welding object in accordance with a result of comparison by the comparator; and

a current conduction controller controlling a current conducting state of the pair of electrodes in dependence on the welding condition set by the welding condition setter.

7. The spot welding control system of claim 6, wherein the welding condition setter sets the welding condition so thus a regression line calculated by the regression line calculator coincides the reference regression line stored in the reference regression line memory.

8. The spot welding control system of claim 6, wherein the welding condition comprises one of a welding current between the pair of electrodes and the welding object, the welding current being variable, a conduction time of the welding current, the conduction time being variable, and a pressing force acting on the welding object from the pair of electrodes, the pressing force being variable.

9. The spot welding system of claim 8, wherein the one of the welding current, the conduction time, and the pressing force of the welding condition has an order of priority and a weighting set thereamoung.

10. A spot welding control system comprising:

a pair of electrodes for pressing a welding object, conducting a current through the welding object;

wear amount detection means for detecting a wear amount of the pair of electrodes;

inter-electrode displacement amount detection means for substantially continuously detecting an inter-electrode displacement amount of the pair of electrodes;

regression line calculation means for correcting inter-electrode displacement amounts detected by the inter-electrode displacement amount detection means in dependence on the wear amount detected by the wear amount detection means and calculating a regression line from corrected inter-electrode displacement amounts;

reference regression line storage means for storing therein a reference regression line based on a reference inter-electrode displacement amount;

comparison means for comparing the regression line calculated by the regression line calculation means with the reference regression line stored in the reference regression line storage means;

welding condition setting means for setting a welding condition of the welding object in accordance with a result of comparison by the comparison means; and

current conduction control means for controlling a current conducting state of the pair of electrodes in dependence on the welding condition set by the welding condition setting means.

11. A spot welding control method comprising:

pressing a welding object by a pair of electrodes, conducting a current through the welding object;

substantially continuously detecting an inter-electrode displacement amount of the pair of electrodes during the conducting;

calculating a regression line from detected inter-electrode displacement amounts;

comparing the calculated regression line with a preset reference regression line;

setting a welding condition of the welding object in accordance with a result of comparison; and

controlling a current conducting state of the pair of electrodes in dependence on the set welding condition.

12. The spot welding control method of claim 11, wherein the welding condition comprises one of a welding current between the pair of electrodes and the welding object, the welding current being variable, a conduction time of the welding current the conduction time being variable, and a pressing force acting on the welding object from the pair of electrodes, the pressing force being variable.

13. A spot welding control method conspiring:

detecting a wear amount of a pair of electrodes;

pressing a welding object by the pair of electrodes, conducting a current through the welding object;

substantially continuously detecting an inter-electrode displacement amount of the pair of electrodes during the conducting;

correcting detected inter-electrode displacement amounts in dependence on the detected wear amount;

calculating a regression line from corrected inter-electrode displacement amounts;

comparing the calculated regression line with a preset reference regression line;

setting a welding condition of the welding object in accordance with a result of comparison; and

controlling a current conducting state of the pair of electrodes in dependence on the set welding condition.

14. The spot welding control method of claim 13, wherein the welding condition comprises one of a welding current between the pair of electrodes and the welding object, the welding current being variable, a conduction time of the welding current, the conduction time being variable, and a pressing force acting on the welding object from the pair of electrodes.

15. A spot welding control method comprising:

controlling a pressure exerted on a welding tip, using a servo motor;

setting a reference position for detection of a displacement amount to be a position for the welding up to contact on a workpiece without pressure

lowering the welding tip from the reference position by a movement amount to press the workpiece together with the electrode tip;

setting a reference pressing position to be an end position of the electrode tip calculated from the reference position and the movement amount;

calculating a plate thickness of the workpiece and an allowance for the workpiece to be welded, relative to the reference pressing position; and

changing a welding condition with a decision for presence of a gap in the workpiece or of an inadequate welding angle, when the end position of the welding tip exceeds a range of the allowance.