JP2013128941A - Resistance welding machine and control method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resistance welding machine that compensates a basic target current value by using short current due to a delay in rising of AC waveform reproduced by an inverter as correction current to achieve ideal electric current to a load.SOLUTION: The resistance welding machine 100 includes: an inverter 40 for converting direct current to alternating current and outputting AC current; a current sensor 60 for detecting a current value of the AC current output by the inverter 40; and a control section 70 for controlling the inverter 40. The control section 70 uses the current value detected by the current sensor 60 and a basic target current value preset beforehand to compute short current to the basic target current value, and computes correction target current value that the basic target current value is compensated by the short current. Then, the control section makes current having the correction target current value to be output from the inverter 40.

Description

  The present invention relates to a resistance welding machine including an inverter that converts direct current into alternating current and outputs alternating current, and a control method thereof.

  The resistance welder is connected to a commercial three-phase power source, converts three-phase alternating current into direct current, further converts direct current into alternating current, and welds the workpieces. A full-wave rectifier circuit and a smoothing circuit are provided to convert three-phase alternating current into direct current, and an inverter is provided to convert direct current into alternating current. The inverter can output an alternating current having an arbitrary waveform and an arbitrary frequency from direct current.

  As a resistance welding machine, for example, Patent Document 1 discloses one having a frequency switching means for changing an AC power supply frequency necessary for welding according to welding conditions such as a plate thickness and / or material of a workpiece and a welding speed. Has been.

  According to the resistance welding machine of Patent Document 1, the alternating current of the alternating current power source is rectified by the rectifier circuit, and the rectified direct current is converted into a smooth direct current by the smoothing circuit. The direct current obtained through the rectifier circuit and the smoothing circuit is high-frequency converted by an inverter having a plurality of switching elements, and a desired alternating current waveform is reproduced. The AC waveform current is amplified by the welding transformer and supplied to the secondary welding electrode. For this reason, a welding current having an AC waveform such as a triangular wave, a sine wave, a rectangular wave, or a trapezoidal wave having a power supply frequency necessary for welding is supplied to the welding electrode, and the workpiece is welded while being pressurized.

JP 2001-105155 A

  By the way, according to the resistance welding machine of Patent Document 1, the inverter reproduces an alternating current waveform such as a triangular wave, a sine wave, a rectangular wave, or a trapezoidal wave by PWM control. The PWM control uses the instantaneous current value of the alternating current as the basic target current value.

  However, since a load is connected to the secondary side of the inverter, the AC current rise delay depending on the time constant of the load occurs until the basic target current value is reached, and the target AC waveform cannot be obtained. Since the magnitude of the time constant of the load varies depending on the equipment and the workpiece, the rising delay of the alternating current is not constant.

  Further, as the AC waveform rises more steeply like a rectangular wave, the difference between the basic target current value and the actually measured effective current value occurs, and the rise delay occurs. Therefore, the feature of the inverter that has the advantage of current correction from the instantaneous current value becomes sparse.

  The present invention was devised in view of the above circumstances, and compensates the shortage current due to the rising delay of the AC waveform reproduced by the inverter as a correction current to the basic target current value, which is ideal for the load. An object of the present invention is to provide a resistance welding machine capable of energization and a control method thereof.

  A resistance welding machine for achieving the above object includes an inverter, a current sensor, and a control unit. The inverter converts direct current to alternating current and outputs an alternating current. The current sensor detects the current value of the alternating current output from the inverter.

  The control unit calculates a deficient current with respect to the basic target current value using the current value detected by the current sensor and a preset basic target current value, and compensates the basic target current value with the deficient current. The value is calculated and the current of the corrected target current value is output from the inverter.

  According to the resistance welding machine according to the present invention, the control unit calculates an insufficient current with respect to the basic target current value using the current value detected by the current sensor and the preset basic target current value. Further, the control unit calculates a corrected target current value obtained by compensating the basic target current value with the insufficient current, and outputs the current of the corrected target current value from the inverter.

  Thereby, the rising delay of the alternating current depending on the time constant of the load connected to the inverter can be instantaneously corrected, and a resistance welder capable of ideally energizing the load can be provided.

It is a block diagram of the resistance welding machine which concerns on this embodiment. It is a circuit diagram which shows the inverter of the resistance welding machine which concerns on this embodiment. It is a flowchart which shows the control method of the resistance welder of this embodiment. It is explanatory drawing which shows the alternating current before correction | amendment by the control method of the resistance welder of this embodiment. It is explanatory drawing which shows the alternating current after correction | amendment by the control method of the resistance welder of this embodiment.

  Hereinafter, the resistance welding machine according to the present embodiment will be described with reference to the drawings.

  FIG. 1 is a block diagram of a resistance welder according to this embodiment. FIG. 2 is a circuit diagram showing an inverter of the resistance welding machine according to the present embodiment.

  In the resistance welding machine according to the present invention, the control unit calculates a shortage current with respect to the basic target current value by using the current value detected by the current sensor and the preset basic target current value. Further, the control unit calculates a corrected target current value obtained by compensating the basic target current value with the insufficient current. The control unit can provide a resistance welding machine capable of ideally energizing the load by causing the inverter to output the current of the corrected target current value.

  The resistance welding machine 100 according to this embodiment performs high-frequency conversion on direct current obtained by rectifying three-phase alternating current using an inverter 40, reproduces alternating current waveforms such as rectangular waves and trapezoidal waves by PWM control, and uses a transformer 80. It is an apparatus for welding a load 90.

  As shown in FIG. 1, the resistance welder 100 of this embodiment includes a rectifier circuit 20, a smoothing circuit 30, an inverter 40, a current sensor 60, a control unit 70, and a transformer 80.

  The rectifier circuit 20 is connected to a commercial three-phase AC power supply 10 and rectifies the three-phase AC current into a DC current. The rectifier circuit 20 is configured by, for example, a rectifier element such as a diode.

  As a rectifier circuit 20 that rectifies commercial three-phase alternating current into direct current, for example, a three-phase half-wave rectifier circuit that three-phase rectifies all phases of the three-phase alternating current power supply 10 with three rectifier elements. Can be mentioned. Examples of the other rectifier circuit 20 include a six-phase rectifier circuit that rectifies all the phases of the three-phase AC power supply 10 with six rectifier elements. In this embodiment, a three-phase full-wave rectifier circuit is used.

  The smoothing circuit 30 is a circuit that is connected to the secondary side of the rectifier circuit 20 and smoothes the pulsating current of the alternating current rectified by the rectifier circuit 20 so as to approximate a smoother direct current. Examples of the smoothing circuit 30 include a smoothing circuit using a capacitor having a property of charging at a certain voltage value or more and discharging at a value less than the certain voltage value.

  The inverter 40 is connected to the secondary side of the smoothing circuit 30 and performs high-frequency conversion on the direct current input from the smoothing circuit 30, and converts the direct current from the direct current into a rectangular wave, a trapezoidal wave, a triangular wave, a sine wave, etc. by PWM control. This is a power supply circuit that reproduces AC waveforms. In the inverter 40, a basic target current value of an alternating current is set in advance, and a current waveform such as a rectangular wave or a trapezoidal wave represents a change with time of the basic target current value.

  As shown in FIG. 2, the inverter 40 includes a plurality of switching elements 51 to 54 that switch energization paths. The inverter 40 of the present embodiment includes two pairs of IGBTs 51, 52, 53, and 54 as switching elements, and alternately controls the switching of each pair of IGBTs 51, 52, 53, and 54 every certain period, An AC waveform such as a rectangular wave or a trapezoidal wave is output by switching the energization path.

  Examples of the switching element include an IGBT (Insulated Gate Bipolar Transistor), a diode, a GTO (Gate Turn Off Thyristor), and a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor).

  The current sensor 60 is a sensor that detects a current value of an alternating current that flows between the inverter 40 and the transformer 80 and is connected to the primary side (input side) of the transformer 80 that will be described later, which is the secondary side of the inverter 40. . As the current sensor 50, for example, a sensor for measuring an alternating current such as a CT (Current Transformer) is used.

  The control unit 70 is connected to the secondary side of the current sensor 60, performs arithmetic processing based on the current value detected by the current sensor 60, changes the open / close timing and open / close time of the IGBT 51-54, and turns on / off the inverter 40. This device controls the off ratio.

  The control unit 70 uses the current value detected by the current sensor 60 and the preset basic target current value to calculate an insufficient current with respect to the basic target current value. Further, the control unit 70 calculates a corrected target current value obtained by compensating the basic target current value with the insufficient current, and causes the inverter 40 to output the current of the corrected target current value.

  The shortage current is a current for compensating for a shortage due to a follow-up delay with respect to the basic target current value when the alternating current rises depending on the time constant of the load connected to the inverter 40 in a half cycle of the alternating current.

  The transformer 80 is a welding transformer that can output a large current for welding, and is a device that is connected to the secondary side of the inverter 40 and amplifies the magnitude of the alternating current output from the inverter 40 and supplies it to the load 90. is there.

  Next, with reference to FIGS. 3 to 5, a control method of the resistance welding machine 100 of the present embodiment configured as described above will be described together with its operation. FIG. 3 is a flowchart showing a control method of the resistance welder of the present embodiment. FIG. 4 is an explanatory diagram showing an alternating current before correction by the control method of the resistance welder of the present embodiment. FIG. 5 is an explanatory diagram showing the AC current after correction by the control method of the resistance welder of the present embodiment.

  The resistance welding machine 100 is controlled using a current value detected by the current sensor 60 and a preset basic target current value in the resistance welding machine 100 including the inverter 40, the current sensor 60, and the control unit 70. The unit 70 is a method for controlling the output current of the inverter 40.

  The control method of the resistance welder 100 first includes a step of detecting the current value of the alternating current by the current sensor 60. Specifically, as illustrated in FIG. 3, when the resistance welding machine 100 of the present embodiment is turned on and energization is started, the control unit 70 starts energization for a half cycle of the AC waveform reproduced by the inverter 40. (S1).

  When energization is started, as shown in FIG. 4, an alternating current rises, and for example, a trapezoidal current waveform is supplied to the load 90. Although the basic target current value P of the rectangular AC current is set in the inverter 40 in advance, the current that actually flows through the load 90 does not become a rectangular wave. The trapezoidal wave in FIG. 4 represents the change over time of the current that actually flows through the load 90.

  As described above, since the load 90 is connected to the secondary side of the inverter 40, the AC current rise delay depending on the time constant of the load 90 occurs until the basic target current value P is reached, and the target AC is reached. The waveform is not obtained. Since the magnitude of the time constant of the load varies depending on the equipment and the workpiece, the rising delay of the alternating current is not constant. Further, as the AC waveform rises more steeply like a rectangular wave, the difference between the basic target current value P and the actually measured effective current value occurs, and the rise delay occurs. Note that T in FIG. 4 is a rise delay time.

  Therefore, in the control method of the resistance welder 100 of the present embodiment, the control unit 70 performs cumulative processing of the measured effective value of the current value detected by the current sensor 60 during the rising of the AC waveform (S2 / YES) ( S3), obtaining an insufficient current for the rising delay of the alternating current. That is, the control method of the resistance welding machine 100 according to the present embodiment calculates the deficient current with respect to the basic target current value using the current value detected by the current sensor 6 and the basic target current value preset in the inverter 40. Includes stages.

  Specifically, when the rising of the AC waveform is completed (S2 / NO), the control unit 70 calculates an insufficient current (area of the hatched triangle in FIG. 4) of the rising delay from the accumulated measured effective value current (S4). ). Here, shortage current = target effective value current−measured effective value current is a value obtained by time integration.

  Next, the control method of the resistance welder 100 according to the present embodiment includes a step of calculating a corrected target current value obtained by compensating the basic target current value with an insufficient current. That is, the control unit 70 calculates a corrected target current value in which the basic target current value is compensated with the insufficient current based on the insufficient current calculated in step 4, and the basic target current value P is calculated as shown in FIG. Is corrected (S5).

  The calculation of the corrected target current value R by the control unit 70 is performed by increasing the peak value of the flat part F of the current waveform such as a rectangular wave or a trapezoidal wave reproduced by the inverter 40 according to the magnitude of the shortage current U. . In the correction section S in which the peak value of the flat portion F of the current waveform is increased according to the shortage current U, the current value detected by the current sensor 60 reaches the basic target current value and then the basic target current value falls. It is a section. In FIG. 5, the portion of the current waveform flat portion F where the peak value rises D corresponds to the shortage current U due to the rising delay of the alternating current. Therefore, the shortage current U = (R−P) × S can be expressed.

  And the control method of the resistance welding machine 100 of this embodiment includes the step which outputs the electric current of correction | amendment target electric current value from the inverter 70. FIG. That is, the control unit 70 continues the peak control (S6) and causes the inverter 70 to output the current having the corrected target current value. This peak control is performed during half-cycle flow (S7 / NO). In this way, after the current value detected by the current sensor 60 reaches the basic target current value, the load is compensated for the shortage current with respect to the basic target current value until the basic target current value falls. 90 can be energized ideally.

  When the above half cycle is completed (S7 / YES), the control unit 70 determines whether there is a next half cycle (S8). When there is a next half cycle (S8 / YES), a series of processing from Step 1 is performed, and when there is no next half cycle (S8 / NO), energization is terminated.

  As shown in FIG. 5, in the next half cycle, after the peak value of the flat part F of the previous half cycle is passed, the peak value of the flat part F of the next half cycle is reached. The shortage current U is calculated for the rising delay of the slope section L and compensated for the basic target current value P of the next half cycle.

  As described above, in the resistance welding machine 100 according to the present embodiment, the control unit 70 uses the current value detected by the current sensor 60 and the basic target current value preset in the inverter 40 to be insufficient with respect to the basic target current value. Calculate the divided current. Further, the control unit 70 calculates a corrected target current value obtained by compensating the basic target current value with the insufficient current, and performs peak control for outputting the current of the corrected target current value from the inverter 40.

  Therefore, the resistance welding machine 100 and the control method thereof according to the present embodiment can correct the rising delay of the alternating current depending on the time constant of the load 90 connected to the secondary side of the inverter 40 every half cycle. There is an advantageous effect that ideal energization for generating the amount of heat initially planned for the load is possible. In addition, the resistance welding machine 100 and the control method thereof according to the present embodiment do not need to consider the state of the load 90 connected to the secondary side of the inverter 40, and can cope with a wide range of equipment and workpieces. Become.

  The preferred embodiments of the present invention have been described above, but these are examples for explaining the present invention, and the scope of the present invention is not intended to be limited to these embodiments. The present invention can be implemented in various modes different from the above-described embodiments without departing from the gist thereof.

10 Three-phase AC power supply,
20 rectifier circuit,
30 smoothing circuit,
40 inverter,
50 switching elements,
60 current sensor,
70 control unit,
80 transformer,
90 load,
100 resistance welding machine,
F Flat part of half cycle.

Claims (8)

An inverter that converts direct current to alternating current and outputs alternating current;
A current sensor for detecting a current value of an alternating current output from the inverter;
A corrected target current value obtained by calculating an insufficient current with respect to the basic target current value using a current value detected by the current sensor and a preset basic target current value, and compensating the basic target current value with the insufficient current. A control unit that outputs the current of the corrected target current value from the inverter;
A resistance welding machine comprising:   The shortage current calculated by the control unit is insufficient due to a follow-up delay with respect to the basic target current value when the alternating current rises depending on a time constant of a load connected to the inverter in a half cycle of the alternating current. The resistance welding machine according to claim 1, wherein the resistance is compensated.   The current waveform representing the change over time of the basic target current value is a rectangular wave or a trapezoidal wave, and the calculation of the corrected target current value by the control unit is insufficient for the peak value of the flat part of the rectangular wave or trapezoidal wave. The resistance welder according to claim 2, wherein the resistance welder is raised according to the magnitude of the divided current.   In the section in which the peak value of the flat part of the rectangular wave or trapezoidal wave is increased according to the shortage current, the basic target current value is obtained after the current value detected by the current sensor reaches the basic target current value. The resistance welding machine according to claim 3, wherein the resistance welding machine is a section until falling.   The inverter includes a plurality of switching elements that switch energization paths, and the control unit outputs the current of the corrected target current value from the inverter by changing an opening / closing timing and an opening / closing time of the switching element. The resistance welder according to any one of claims 1 to 4, wherein   A rectifier circuit that converts an alternating current output from an alternating current power source into a direct current is connected to the input side of the inverter, and the magnitude of the alternating current output from the inverter is changed on the output side of the inverter. A resistance welding machine according to claim 1, wherein a transformer for supplying the load is connected.   The resistance welding machine according to claim 6, wherein the current sensor detects a current value of an alternating current flowing between the inverter and the transformer. A control method for a resistance welding machine comprising: an inverter that converts direct current into alternating current and outputs alternating current; and a current sensor that detects a current value of alternating current output from the inverter,
Detecting a current value of the alternating current by the current sensor;
Calculating a shortage current for the basic target current value using the detected current value and a preset basic target current value;
Calculating a corrected target current value obtained by compensating the basic target current value with the shortage current;
Outputting the current of the corrected target current value from the inverter;
A control method for a resistance welder comprising:

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