Microprocessor controlled welding apparatus

• US 4,561,059 A
• Filed: 02/24/1983
• Issued: 12/24/1985
• Est. Priority Date: 02/24/1983
• Status: Expired due to Term

• Current Assignee: Beckworth-Davis International, Inc.
• Original Assignee: Beckworth-Davis International, Inc.
• Inventors: Davis, Clint A., Trail, Melvin P.
• Primary Examiner(s): Smith, Jerry
• Assistant Examiner(s): Harkcom, Gary V.
• Application Number:
  US06/469,519
• Time in Patent Office: 1,034 Days
• Field of Search: 364/477, 364/513, 219/121 EA, 219/121 EM, 219/124.02, 219/124.03, 219/130.1, 219/130.21, 219/130.33, 219/130.5, 219/137 R, 219/137 PS, 901/42
• US Class Current: 700/212
• CPC Class Codes: B23K 9/067 Starting the arc
• CPC Class Codes: B23K 9/073 Stabilising the arc

Abstract

A microprocessor-controlled arc welding power supply is disclosed. A silicon controlled rectifier ("SCR") bank is used to generate a direct current arc welding current under program control. Positive sychronization is provided by the microprocessor using a phase locked loop and a polarity detector, so that the gating signals applied to the SCRs are correctly timed. Optimum tradeoffs between hardware and software are accomplished by using look up tables to store correction factors that can be quickly accessed during execution, and by using timers as smart interface chips to fire the SCRs at the same angle during each cycle until changed or updated by the microprocessor. The arc welding power supply is capable of operating in a constant current or constant voltage mode without rewiring the circuit.

Claims

1. A microprocessor-controlled arc-welding apparatus, comprising:

a three-phase transformer, the three phase transformer having at least one primary winding and having three secondary windings, the primary winding being adapted for coupling to a source of alternating current ("AC") electrical energy, each secondary winding being connected to a common ground lead;

at least three silicon controlled rectifiers ("SCR'"'"'s"), each SCR being connected between a secondary winding of the three-phase transformer and a common welding lead having a common direct current ("DC") polarity, each SCR being responsive to a gating signal to rectify an AC signal applied to its associated secondary winding by conducting direct current during a portion of an AC phase when the SCR is forward biased subsequent to the point in time when the gating signal enables the SCR, the SCR'"'"'s being mutually cooperable to generate a welding signal between the common welding lead and the common ground lead, the welding signal having a DC voltage with an average magnitude which is determined by the portion of the AC phase that the SCRs are enabled by the gating signal;

a sensor coupled to the common welding lead for directly sensing the welding signal;

an input/output controller, the input/output controller being coupled to the sensor, the input/output controller being coupled to the SCR'"'"'s;

a memory; and

,

a microprocessor, the microprocessor being coupled to the input/output controller and to the memory, the microprocessor being adapted to read welding data signals from the sensor through the input/output controller, the microprocessor, in accordance with a program stored in the memory, being operable to compare the welding data signals from the sensor with control data in memory, the micro processor being operable to signal the SCRs and provide gating signals in accordance with a program stored in memory which enables the SCRs for a portion of the AC phase so that the welding signal has a DC voltage which is determined by the microprocessor;

the microprocessor-controlled welding apparatus being capable of welding in a plurality of selectable arc-welding modes by selecting an appropriate program in memory, the microprocessor-controlled welding apparatus being capable of changing between a constant current mode and a constant voltage mode without rewiring the apparatus.

2. The microprocessor-controlled welding apparatus according to claim 1, further comprising:

a table stored in memory adapted to quickly permit the microprocessor to determine a proper gating signal for the SCR'"'"'s, the table comprising a plurality of predetermined SCR gating parameters stored in memory locations;

the microprocessor being operable to read a first welding data signal and to record a first welding data parameter in memory based upon the first welding data signal;

the microprocessor being operable to read a second welding data signal at a point in time after the first welding data signal is read, the microprocessor being operable to record a second welding data parameter in memory based upon the second welding data signal;

the microprocessor being operable to compute a first derivative parameter indicating the rate of change of the welding signal by subtracting the first welding data parameter from the second welding data parameter;

the microprocessor being operable to compute a difference parameter indicating the extent to which the sensed welding signal fails to conform with program control by subtracting the second welding data parameter from a control parameter selected by the microprocessor from control data in memory;

the microprocessor being operable to look up a memory location in the table determined by the difference parameter and the first derivative parameter, such memory location containing a predetermined SCR gating parameter stored therein, the predetermined SCR gating parameter being representative of gating control to be applied to the SCR'"'"'s based upon the extent to which the sensed welding signal fails to conform with program control and the rate of change of the welding signal; and

the microprocessor being operable to signal the SCR'"'"'s and to provide gating signals determined from the predetermined SCR gating parameter.

3. The microprocessor-controlled welding apparatus according to claim 2, further comprising:

an SCR control circuit, the SCR control circuit being connected between the input/output controller and the SCRs, the SCR control circuit including timers responsive to a SCR gating parameter for determining a delay for gating signals applied to the SCRs, each SCR having a timer associated therewith, the SCR control circuit being operable to signal the SCRs by generating a gating signal for each SCR after a delay determined by the time associated with each SCR.

4. The microprocessor-controlled welding apparatus according to claim 3, further comprising:

a background voltage supply coupled to the common welding lead and the common ground lead, for providing a background voltage between the common welding lead and the common ground lead during selected periods of time that a welding signal is not being generated, the background voltage supply being responsive to signals from the microprocessor to selectively provide said background voltage.

5. The microprocessor-controlled welding apparatus according to claim 4, further comprising:

a weld function control circuit coupled to the input/output controller, the weld function control circuit being adapted for selectively controlling weld functions such as wire feed, gas flow and background voltage in response to signals from the microprocessor.

6. The microprocessor-controlled welding apparatus according to claim 1, further comprising:

an input/output data port coupled to the microprocessor for providing direct communication of digital data to an external digital device.

7. The microprocessor-controlled welding apparatus according to claim 6, further comprising in combination:

a digital computer coupled to the input/output data port, the digital computer being capable of controlling the microcomputer-controlled welding apparatus.

8. The microprocessor-controlled welding apparatus according to claim 6, further comprising in combination:

a welding robot coupled to the input/output data port, the welding robot being responsive to signals from the microprocessor to perform steps in a welding sequence.

9. The microprocessor-controlled welding apparatus according to claim 3, further comprising:

a printer coupled to the input/output controller, the printer being responsive to signals from the microprocessor to print out quality control data concerning welding operations.

10. The microprocessor-controlled welding apparatus according to claim 3, further comprising:

a synchronization circuit coupled to a winding of the three-phase transformer, the synchronization circuit including a phase locked loop and a polarity detector adapted to detect the polarity of an AC signal applied to such winding, the phase locked loop being locked to said AC signal, the synchronization circuit including a timer which is initiated responsive to detection of a first zero crossing of a reference signal generated by the phase locked loop, the synchronization circuit being adapted to detect a second zero crossing of said reference signal, the synchronization circuit being operable to compute a measure of the elapsed time between cycles of the phase locked loop, by measuring the elapsed time between the first zero crossing and the second zero crossing, the synchronization circuit being operable to divide the measure of such elapsed time into equal periods corresponding to the number of SCR'"'"'s and to generate synchronization signals which are coupled to the SCR control circuit;

the SCR control circuit being operable to generate a gating signal for each SCR responsive to a corresponding synchronization signal, such gating signal being generated after a delay determined by an SCR gating parameter provided by the microprocessor; and

the synchronization circuit being operable to recompute the timing of said synchronization signals during subsequent cycles of said AC signal to synchronize the timing of gating signals for SCRs despite variations in the frequency of said AC signal.

11. The microprocessor-controlled welding apparatus according to claim 10, wherein the three secondary windings of the three-phase transformer have a center-tap connected to the common ground lead, and further comprising three additional SCRs, each additional SCR being connected to an end of a secondary winding opposite from one of the first three SCRs.

15. The microprocessor-controlled welding apparatus according to claim 2, further comprising:

an inductor, the inductor being connected in series between the SCR'"'"'s and the common welding lead, the inductor operating to tend to smooth the rectified direct current produced by the SCR'"'"'s.

16. The microprocessor-controlled welding apparatus according to claim 15, further comprising:

a diode, the diode being connected between the common ground lead and the common welding lead.

17. The microprocessor-controlled welding apparatus according to claim 16, further comprising:

a capacitor, the capacitor being connected between the common ground lead and the common welding lead.

18. The microprocessor-controlled welding apparatus according to claim 2, further comprising:

a user program interpreter stored in memory for interpreting software user program commands which may be supplied by an operator, the interpreter providing the microprocessor-controlled welding apparatus with a capability of changing between a constant current mode and a constant voltage mode under program control in response to software user program commands.

12. A method of controlling a welding apparatus, comprising the steps of:

sensing a first welding sample using a circuit that produces a signal indicative of welding current or voltage;

sensing a second welding sample at a later time using the circuit that produces a signal indicative of welding current or voltage;

computing a first derivative parameter using a processor by subtracting the first welding sample from the second welding sample;

computing a difference parameter using a processor by subtracting the second welding sample from a predetermined control parameter;

looking up an adjustment parameter from a table of predetermined parameters where the table of predetermined parameters contains a predetermined parameter corresponding to each of a range of first derivative parameters and to each of a range of difference parameters; and

,

adjusting elements controlling welding current or voltage, responsive to the adjustment parameter obtained from the table.

13. The method according to claim 12, further comprising the step of:

synchronizing with an alternating current used to supply power for welding by determining the frequency of the alternating current using a phase locked loop, and by determining the phase error of the phase locked loop using a zero crossing detector.

14. The method according to claim 13, wherein the step of adjusting elements controlling welding current or voltage is performed by firing silicon controlled rectifiers, each at a time delay offset from the beginning of the cycle of an alternating signal produced by the phase locked loop by a time determined by the adjustment parameters, connected by the amount equal to the phase error that the alternating signal produced by the phase locked loop is offset from the alternating current used to supply power for welding, the phase error being determined by a zero crossing detector.

19. A microprocessor-controlled welding apparatus, comprising:

a three-phase transformer, the three-phase transformer having at least one primary winding and having three secondary windings, the primary winding being adapted for coupling to a source of alternating current ("AC") electrical energy;

at least three solid state switching devices, each solid state switching device being connected between a secondary winding of the three-phase transformer and a first common welding lead, each switching device being responsive to a gating signal to rectify an AC signal applied to its associated secondary winding by conducting direct current during a portion of an AC phase after the gating signal fires the switching device, the switching device being mutually cooperable to generate a welding signal between the first common welding lead and a second welding lead coupled to the secondary windings of the three-phase transformer, the welding signal having a direct current voltage with an average magnitude which is determined by the portion of the AC phase that the switching devices are fired by the gating signal;

a sensor coupled to the first common welding lead for directly sensing the welding signal;

an input/output controller, the input/output controller being coupled to the sensor, the input/output controller being coupled to the switching devices;

a memory;

a microprocessor, the microprocessor being coupled to the input/output controller and to the memory, the microprocessor being adapted to lead welding data signals from the sensor through the input/output controller, the microprocessor, in accordance with a program stored in memory, being operable to compare the welding data signals from the sensor with control data in memory, the microprocessor being operable to signal the switching devices and to provide gating signals in accordance with a program stored in memory which fire the switching devices for a portion of the AC phase so that the welding signal has a direct current voltage which is determined by the microprocessor;

the microprocessor being operable to read a first welding data signal and to record a first welding data parameter in memory based upon the first welding data signal;

the microprocessor being operable to read a second welding data signal at a later point in time, the microprocessor being operable to record a second welding data parameter in memory based upon the second welding data signal;

the microprocessor being operable to compute an error parameter indicating the extent to which the sensed welding signal fails to conform with program control by subtracting the second welding data parameter from a control parameter selected by the microprocessor from control data in memory;

the microprocessor being operative to compute a first derivative parameter indicating the rate of change of the welding signal by subtracting the first welding data parameter from the second welding data parameter;

the microprocessor being operative to look up a memory location in a table stored in memory containing a plurality of predetermined gating parameters stored in memory locations, the table being adapted to quickly permit the microprocessor to determine a proper gating signal for the switching devices, the memory location in the table being determined by both the error parameter and the first derivative parameter, the memory location containing a predetermined gating parameter representative of gating control to be applied to the switching devices based upon the extent to which the sensed welding signal fails to conform with program control and the rate of change of the welding signal; and

,

the microprocessor being operative to signal the switching device and to provide firing signals determined from the predetermined gating parameter obtained from the table.

20. The microprocessor-controlled welding apparatus according to claim 19, further comprising:

a synchronization circuit coupled to a winding of the three-phase transformer, the synchronization circuit including a phase locked loop and a zero crossing detector, the phase locked loop being operative to prove an indication of the frequency of the source of AC electrical energy, the zero crossing detector being operative to detect the phase error of the phase locked loop compared with the source of AC electrical energy, the synchronization circuit being operative to compute a measure of the elapsed time between cycles of the phase locked loop which may be divided into equal periods corresponding to the number of solid state switching devices, the synchronization circuit being operative to generate signals which may be used for firing the switching devices in synchronization with the source of AC electrical energy.