Inverter type resistance welding machine

• US 5,072,090 A
• Filed: 07/27/1990
• Issued: 12/10/1991
• Est. Priority Date: 02/21/1989
• Status: Expired due to Fees

• Current Assignee: Obara Corporation (Obara Group, Inc.)
• Original Assignee: Obara Corporation (Obara Group, Inc.)
• Inventors: Morita, Tatsuo
• Primary Examiner(s): Shaw, Clifford C.
• Application Number:
  US07/558,803
• Time in Patent Office: 501 Days
• Field of Search: 219/108, 219/110
• US Class Current: 219/108
• CPC Class Codes: B23K 11/243 Multiple welding installations fed by one source
• CPC Class Codes: B23K 11/252 using digital means

Abstract

There is described an inverter type resistance welding machine comprising one rectifier, one inverter connected in series to the rectifier, and a plurality of welding current elements connected in series between a plurality of welding transformers and an output of one inverter. It is possible to reduce the space of installation of the resistance welding machine and cost involved in the installation thereof and reduce a weld time.

Claims

1. An inverter type resistance welding machine, comprising:

rectifier means for receiving a relatively low frequency AC power input and converting the AC power input into a DC power output;

inverter means connected to said rectifier means for receiving said DC power output therefrom and converting said DC power output into a relatively high frequency AC power output, said inverter means having an output terminal which provides access to said AC power output;

first and second welding units which respectively include first and second sets of openable and closable welding jaws which are closable to apply clamping pressure to a workpiece positioned therebetween and which are openable to remove the clamping pressure, said first and second welding units also respectively including first and second welding transformers for transforming said AC power output into an operative welding current for use by the corresponding welding jaws;

selectively actuable switching means for selectively applying said AC power output exclusively to each one of said welding transformers, including means for selectively connecting said output terminal of said inverter means exclusively to each one of said welding transformers;

selectively actuable pressure applying means for selectively causing each set of said welding jaws to close and apply clamping pressure to a workpiece; and

control means for effecting selective actuation and deactuation of said switching means and said pressure applying means in a predetermined sequence, including means for actuating said pressure applying means and closing said first set of welding jaws at a first point in time, means for maintaining said first set of welding jaws closed for at least a first pressure application time, means for prohibiting application of said AC power output to said first welding transformer throughout said first pressure application time, means for actuating said pressure applying means and closing said second set of welding jaws at a second point in time which is one of simultaneous with and subsequent to said first point in time at which said first set of welding jaws is closed, means for maintaining said second set of welding jaws closed for at least a second pressure application time which overlaps said first pressure application time, means for prohibiting application of said AC power output to said second welding transformer throughout said second pressure application time, means for actuating said switching means immediately after said first pressure application time has expired and applying said AC power output exclusively to said first welding transformer for a first welding time which overlaps said second pressure application time, means for prohibiting application of said AC power output to said second welding transformer until said first welding time has elapsed, and means for actuating said switching means to remove said AC power output from said first welding transformer and apply said AC power output exclusively to said second welding transformer immediately after said first welding time has elapsed.

2. An inverter type resistance welding machine according to claim 1, further comprising a current transformer connected to an output of the inverter means, a plurality of toroidal cores each connected between secondary windings of the welding transformers and the welding jaws, the current transformer and the toroidal cores respectively detecting welding current, a current detection circuit connected to the current transformer and the toroidal cores for receiving a resultant detected analog value therefrom, an analog to digital converter connected to the current detection circuit for converting the resultant analog values to digital values and supplying the same digital values to the control means.

3. An inverter type resistance welding machine according to claim 1, wherein the switching means comprises a plurality of pairs of inversed parallel thyristers connected in series respectively between said output terminal of said inverter means and said welding transformers.

4. An inverter type resistance welding machine according to claim 1, wherein the switching means comprises semiconductor switches.

5. An inverter type resistance welding machine according to claim 1, wherein the switching means comprises electromagnetic switches.

6. An inverter type resistance welding machine claim 1, wherein said second pressure application time is shorter than a sum of said first pressure application time and said first welding time.

7. An inverter type resistance welding machine claim 6, wherein said second pressure application time is longer than said first pressure application time.

8. A method for performing a welding operation, comprising the steps of:

providing a rectifier means for receiving a relatively low frequency AC power input and converting the AC power input into a DC power output;

providing an inverter means for receiving said DC power output from said rectifier means and converting said DC power output into a relatively high frequency AC power output, and providing said inverter means with an output terminal which permits access to said AC power output;

providing first and second welding units which respectively include first and second sets of openable and closable welding jaws which are closable to apply clamping pressure to a workpiece positioned therebetween and which are openable to remove the clamping pressure, and respectively providing said first and second welding units with first and second welding transformers for transforming said AC power output into an operative welding current for use by the corresponding welding jaws;

providing a selectively actuable switching means for selectively applying said AC power output exclusively to each one of said welding transformers, and providing said switching means with a means for selectively connecting said output terminal of said inverter means exclusively to each one of said welding transformers;

closing said first set of welding jaws at a first point in time;

maintaining said first set of welding jaws closed for at least a first pressure application time;

prohibiting application of said AC power output to said first welding transformer throughout said first pressure application time;

closing said second set of welding jaws at a second point in time which is one of simultaneous with and subsequent to said first point in time at which said first set of welding jaws is closed;

maintaining said second set of welding jaws closed for at least a second pressure application time which overlaps said first pressure application time;

prohibiting application of said AC power output to said second welding transformer throughout said second pressure application time;

determining that said first pressure application time has expired, and immediately thereafter applying said AC power output exclusively to said first welding transformer throughout a first welding time which overlaps said second pressure application time;

removing said AC power output from said first welding transformer when said first welding time elapses;

prohibiting application of said AC power output to said second welding transformer until said first welding time has elapsed; and

applying said AC power output exclusively to said second welding transformer immediately after said first welding time has elapsed.

9. A method according to claim 8, wherein said second pressure application time is shorter than a sum of said first pressure application time and said first welding time.

10. A method according to claim 8, wherein said second pressure application time is longer than said first pressure application time.