STATIC SQUARE-WAVE RESISTANCE TUBE WELDING SYSTEM

• US 3,636,298 A
• Filed: 10/20/1969
• Issued: 01/18/1972
• Est. Priority Date: 10/20/1969
• Status: Expired due to Term

• Current Assignee: Blakeslee G. Wheeler, Robert L Risberg
• Original Assignee: Blakeslee G. Wheeler, Robert L Risberg
• Inventors: Risberg, Robert L., Wheeler, Blakeslee G.
• Primary Examiner(s): Truhe, J. V.
• Assistant Examiner(s): Smith, J. G.
• Application Number:
  US04/867,703
• Time in Patent Office: 820 Days
• Field of Search: 219/108,110,113,114,81,59,102,116 321/14,18,19
• US Class Current: 219/108
• CPC Class Codes: B23K 11/256 the measured parameter being the inter-electrode electrical resistance

Abstract

A resistance welder system for welding a continuous seam throughout the length of a tube or pipe having controlled thyristors for generating a square-wave current of a desired amplitude and at constant or variable frequency. The power is generated and transmitted at high voltage low current and transformed at the welder electrodes to low voltage high current. The system includes a controlled DC link for obtaining a desired voltage and current from a constant voltage source, and a static square-wave generator consisting of an inverter with forcing to generate a square-wave AC current from the DC link output. The voltage converter for controlling the DC link is regulated by a voltage regulator to maintain an average value of AC voltage at the electrode transformer, and a fast responding minor loop current regulator to maintain constant current in the presence of transient changes in resistivity or contact resistance.

Claims

1. In a resistance welding system for producing a uniform continuous weld, the combination comprising:

power supply lines adapted to be connected to an electrical supply source;

voltage converter means connected to said lines and supplied with power therefrom and being operable to provide a controlled DC voltage;

a DC bus connected to said voltage converter means for receiving said controlled DC voltage;

a welder comprising a transformer and electrodes constructed to roll or slide along the work on opposite sides of the joint to apply a welding current across the joint during relative movement between the work and electrodes for continuous seam welding purposes;

a solid state square-wave generator supplied from said DC bus and comprising means operable to provide a square-wave voltage having its leading edge shaped to provide a near square-wave current to the workpiece of controllable amplitude and frequency;

means connecting the output voltage and near square-wave current of said square-wave generator to said welder transformer to produce a uniform seam weld comparable to a DC weld;

means for controlling said voltage converter means to control the DC bus voltage thereby to control the value of the squarewave voltage applied to the welder; and

means for controlling said solid state square-wave generator thereby to control the frequency of the square-wave voltage applied to the welder.

2. The invention defined in claim 1, wherein said means for controlling said voltage converter means comprises:

a voltage comparator circuit;

means for applying a voltage reference signal to said comparator circuit;

means for applying a voltage feedback signal to said comparator circuit; and

said comparator circuit comprising means for comparing said voltage reference and said voltage feedback signals and for providing an output signal for control of said voltage converter.

3. The invention defined in claim 1, wherein said means for controlling said voltage converter means comprises:

a fast responding current regulator circuit;

means for applying a current reference signal to said current regulator circuit;

means for applying a current feedback signal to said current regulator circuit;

said current regulator circuit comprising means for comparing said current reference and current feedback signals and for providing a control voltage as a function thereof; and

means responsive to said control voltage for controlling said voltage converter means.

4. The inveNtion defined in claim 3, wherein said means for applying a current reference signal to said current regulator circuit comprises:

a voltage comparator circuit;

means for applying a voltage reference signal to said comparator circuit;

means for applying a voltage feedback signal to said comparator circuit; and

said comparator circuit comprising means for comparing said voltage reference and said voltage feedback signals and for providing an output signal which is the current reference for said current regulator circuit.

5. The invention defined in claim 4, wherein:

said voltage comparator circuit is relatively slow as compared to said current regulator circuit whereby the output of the converter is caused to respond rapidly to transient changes in resistance to maintain substantially constant power to the weld.

6. In a resistance welding system, the combination comprising:

power supply lines adapted to be connected to an electrical supply source;

voltage converter means connected to said lines and supplied with power therefrom and being operable to provide a controlled DC voltage;

a DC bus connected to said voltage converter means for receiving said controlled DC voltage;

a solid state square-wave generator supplied from said DC bus and being operable to provide a square-wave voltage and current of controllable amplitude and frequency;

a welder comprising a transformer and electrodes constructed to roll or slide along the work on opposite sides of the joint to apply a welding current across the joint for welding purposes;

means connecting the output voltage of said square-wave generator to said welder transformer;

means for controlling said voltage converter means to control the DC bus voltage thereby to control the value of the square-wave voltage applied to the welder; and

means for controlling said solid state square-wave generator thereby to control the frequency of the square-wave voltage applied to the welder comprising;

a frequency control circuit operable to control the frequency of the output voltage and current applied to the welder;

means for controlling the frequency control circuit to set said output frequency at a selected value; and

means responsive to variation in the amplitude of said output voltage for controlling said frequency control circuit to vary the frequency to maintain constant volt-seconds per half-cycle in said output voltage.

7. In a resistance welding system, the combination comprising:

power supply lines adapted to be connected to an electrical supply source;

voltage converter means connected to said lines and supplied with power therefrom and being operable to provide a controlled DC voltage;

a DC bus connected to said voltage converter means for receiving said controlled DC voltage;

a solid state square-wave generator supplied from said DC bus and being operable to provide a square-wave voltage and current of controllable amplitude and frequency;

a welder comprising a transformer and electrodes constructed to roll or slide along the work on opposite sides of the joint to apply a welding current across the joint for welding purposes;

means connecting the output voltage of said square-wave generator to said welder transformer;

means for controlling said voltage converter means to control the DC bus voltage thereto to control the value of the square-wave voltage applied to the welder; and

means for controlling said solid state square-wave generator thereby to control the frequency of the square wave voltage applied to the welder comprising;

a frequency control circuit operable to control the frequency of the output voltage applied to the welder;

means responsive to said output voltage and current for providing a control voltage proportional thereto; and

means for applying said control voltage to control said frequency control circuit to maintain the frequency proportional to the value of saiD output voltage above a minimum bias frequency.

8. The invention defined in claim 7, wherein said means for applying said control voltage comprises:

means for adjusting the ratio of output frequency to output voltage above a minimum bias frequency.

9. In an electronic resistance type tube welding system for producing a uniform continuous weld, the combination comprising:

voltage converter means adapted to be connected to and supplied from an AC source and being operable to provide a controlled DC voltage;

a DC bus connected to said voltage converter means for receiving said controlled DC voltage;

a seam welder comprising a transformer having a primary and secondary, and electrodes connected to the secondary and constructed to engage opposite sides of the seam and to move relative thereto to apply welding current across the seam for welding purposes;

a solid state square-wave generator supplied from said DC bus and comprising means operable to provide a square-wave output voltage and a square-wave current at the workpiece having its leading and trailing edges shaped to compensate for lack of weld power during the current reversal;

means connecting the output of said square-wave generator to the primary of said transformer to produce a uniform seam weld equivalent to a DC weld;

voltage control means for controlling said voltage converter means to control the DC bus voltage thereby to control the value of said square-wave output voltage and current; and

frequency control means for controlling said square-wave generator thereby to control the frequency of the square-wave output voltage applied to the primary of said transformer to provide a square-wave current for welding purposes.

10. The invention defined in claim 9, wherein:

said voltage converter means comprises an SCR bridge; and

said voltage control means comprises a firing circuit for controlling the firing angle of the SCR'"'"''"'"'s in said bridge.

11. The invention defined in claim 10, wherein said voltage control means also comprises:

a current integrator circuit;

means for deriving a current reference signal and for applying it to said current integrator circuit;

means for deriving a current feedback signal proportional to the output current and for applying it to said current integrator circuit; and

said current integrator circuit comprises means for integrating the difference between said current reference and current feedback signals and for providing a control voltage as a function thereof for controlling said firing circuit.

12. The invention defined in claim 11, wherein said means for deriving a current reference signal comprises:

a voltage comparator circuit;

means for applying an adjustable voltage reference to said comparator circuit indicative of the selected value of output voltage;

means for deriving a voltage feedback signal proportional to the DC bus voltage and for applying it to said comparator circuit; and

said comparator circuit comprises means for providing an output signal proportional to the difference between said voltage reference and voltage feedback signals which becomes the current reference for said integrator circuit.

13. The invention defined in claim 12, wherein said means for deriving said voltage feedback signal and for applying it to said comparator circuit comprises:

first coupling means for applying a normal voltage feedback signal to said comparator circuit; and

second coupling means for applying a derivative feedback signal to said comparator circuit.