Method and apparatus for controlling resistance welding

An apparatus for controlling resistance welding, for use with workpieces to be welded, said apparatus comprising:

• a rectifier circuit operable to convert an alternating current having a commercial frequency to a direct current;
• a bi-directional switching circuit operable to convert the direct current from said rectifier circuit to pulses having a high frequency;
• a welding transformer having a primary coil operable to receive the pulses from said switching circuit and a secondary coil operable to output pulsed voltages at a high frequency;
• first and second welding electrodes connected across said secondary coil of said welding transformer operable to make pressure contact with the workpieces at spaced positions;
• a weld period setting device operable to divide a weld time of a resistance welding operation into first and second weld periods and to set the second weld period to be longer than the first weld period;
• a current setting device operable to set first and second current values, for the first and second weld periods, respectively, of a primary or secondary current of said welding transformer such that the second current is equal to or greater than the first current;
• and
• a switching controller operable to successively switch said switching circuit in a first polarity at a high frequency during the first weld period in such a manner that the primary or secondary current having a value almost equal to the first current value flows, and to successively switch said switching circuit in a second polarity at a high frequency during the second weld period in such a manner that the primary or secondary current having a value almost equal to the second current value flows, so that nuggets at the spaced positions grow to essentially the same size at the end of the second weld period.

An apparatus for controlling resistance welding for use with workpieces to be welded, said apparatus comprising:

• a rectifier circuit operable to convert an alternating current having a commercial frequency to a direct current;
• a bi-directional switching current operable to convert the direct current from said rectifier circuit to pulses having a high frequency;
• a welding transformer having a primary coil operable to receive the pulses from said switching circuit and a secondary coil operable to output pulsed voltages at a high frequency;
• first and second welding electrodes connected across said secondary coil of said welding transformer operable to make pressure contact with the workpieces at spaced positions;
• a weld period setting device operable to divide a weld time of a resistance welding operation into first and second weld periods and to set the second weld period to have a time duration almost equal to that of the first weld period;
• a current setting device operable to set first and second current values of a primary or secondary current of said welding transformer such that the second current value is greater than the first current value;
• and
• a switching controller operable to successively switch said switching circuit in a first polarity at a high frequency during the first weld period such that the primary or secondary current having a value almost equal to the first current value flows and to successively switch said switching circuit in a second polarity at a high frequency during the second weld period such that the primary or secondary current having a value almost equal to the second current value flows so that nuggets at the spaced positions grow to essentially to the same size at the end of the second weld period.

A resistance welding apparatus for use with workpieces to be welded, said apparatus comprising:

• a rectifier circuit operable to convert an alternating current having a commercial frequency to a direct current;
• a bi-directional switching circuit operable to convert the direct current from said rectifier circuit to pulses having a high frequency;
• a welding transformer having a primary coil operable to receive the pulses from said switching circuit and a secondary coil operable to output pulsed voltages at a high frequency;
• a pair of welding electrodes connected across said secondary coil of said welding transformer operable to make pressure contact with the workpieces at spaced positions;
• a switching controller operable to define a weld time of a resistance welding operation as a plurality of a weld periods, operable to successively switch said switching circuit in a first polarity at a predetermined high frequency during an odd numbered weld period in the plurality of weld periods and to successively switch said switching circuit in a second polarity at the predetermined high frequency during an even numbered weld period in the plurality of weld periods;
• a current detector operable to detect a primary or secondary current of said welding transformer so as to provide a detected current signal;
• a current monitor operable to monitor the primary or secondary current based on the detected current signal from said current detector immediately after each weld period so as to detect a timing when the primary or secondary current has reached a predetermined monitor value;
• and
• a weld period starter operable to start a next weld period in response to the timing detected by said current monitor.