JP2021023955A - Pulse arc welding control method - Google Patents

Abstract

To set a feedback control gain of a welding current in various welding conditions to a proper value in pulse arc welding.SOLUTION: According a pulse arc welding control method, a welding current Iw, which rises from a base current value Ib to a peak current value Ip during a rise period Tu, becomes the peak current value Ip during a peak period Tp, and falls from the peak current value Ip to the base current value Ib during a fall-down period Id, is electrically conducted repeatedly as one pulse cycle, and the welding current Iw is feedback-controlled on the basis of a current set value. In this method, a differential value between a current detection value of the welding current Iw and the current set value is detected, the differential value is integrated over a prescribed period during the pulse cycle to detect a difference integral value, and a feedback gain is automatically adjusted on the basis of the difference integral value. The prescribed period is the whole period of the pulse cycle.SELECTED DRAWING: Figure 1

Description

The present invention relates to a pulse arc welding control method that automatically adjusts the gain of feedback control of welding current.

Consumable electrode type pulse arc welding (hereinafter referred to as pulse arc welding) is widely used for welding various metals such as steel, stainless steel, and aluminum. In this pulse arc welding, the base current value rises from the base current value to the peak current value during the rise period, becomes the peak current value during the peak period, falls from the peak current value to the base current value during the fall period, and then falls during the base period. Inside, a welding current, which is the base current value, is energized, and these energizations are repeated as one pulse cycle to perform welding. In pulse arc welding, one pulse period and one droplet transition state are obtained. Therefore, since the droplet transition state is stable, less spatter is generated and a beautiful bead appearance can be obtained.

The welding power source used for pulse arc welding has a constant current characteristic, and the welding current is feedback-controlled based on the current setting signal. In order to stabilize the welding state of pulse arc welding, it is important that the waveform of the welding current and the waveform of the current setting signal exactly match. For this purpose, it is necessary to set the gain of the feedback control of the welding current to an appropriate value.

In the invention of Patent Document 1, the control gain is changed based on the welding impedance information obtained by dividing the welding voltage by the welding current. That is, whether the welding load state is in the arc state or the short-circuit state is determined from the welding impedance information, and the gain of the feedback control is switched to a value suitable for each welding load state.

Japanese Patent No. 5047707

The welding load state changes depending on various welding conditions. Welding conditions include a plurality of combination conditions such as the material of the base material, the type of shield gas, the diameter of the welding wire, the length of the welding cable, the protrusion length of the wire, and the feeding speed of the welding wire. In order to adjust the gain of the feedback control of the welding current to an appropriate value according to these various welding conditions, a lot of working time is required. As a result, under various welding conditions, the feedback control gain is often not set to an appropriate value.

Therefore, an object of the present invention is to provide a pulse arc welding control method capable of automatically adjusting the gain of feedback control of welding current to an appropriate value under various welding conditions.

In order to solve the above-mentioned problems, the invention of claim 1 is
The welding wire is fed and rises from the base current value to the peak current value during the rise period, becomes the peak current value during the peak period, and falls from the peak current value to the base current value during the fall period. Then, during the base period, the welding current, which is the base current value, is repeatedly energized as one pulse cycle.
In the pulse arc welding control method in which the welding current is feedback-controlled based on the current set value,
The difference value between the current detection value of the welding current and the current set value is detected, the difference value is integrated over a predetermined period during the pulse cycle to detect the difference integration value, and the difference integration value is used as the basis for the difference integration value. Automatically adjusts the feedback control gain,
This is a pulse arc welding control method characterized by the above.

In the invention of claim 2, the predetermined period is the entire period of the pulse period.
The pulse arc welding control method according to claim 1, wherein the pulse arc welding is controlled.

In the invention of claim 3, the predetermined period is a period spanning the rising period, the peak period, and the falling period.
The pulse arc welding control method according to claim 1, wherein the pulse arc welding is controlled.

According to the present invention, the gain of feedback control of welding current can be automatically adjusted to an appropriate value under various welding conditions.

It is a current waveform diagram which shows the pulse arc welding control method which concerns on Embodiment 1 of this invention. It is a block diagram of the welding apparatus for carrying out the pulse arc welding control method which concerns on Embodiment 1 of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment 1]
FIG. 1 is a current waveform diagram showing a pulse arc welding control method according to the first embodiment of the present invention. FIG. (A) shows the time change of the current setting signal Ir, and FIG. 6B shows the time change of the welding current Iw. The operation will be described below with reference to the figure.

In the figure, the period t1 to t2 is the rise period Tu, the period t2 to t3 is the peak period Tp, the period t3 to t4 is the fall period Td, and the period t4 to t5 is the base period. It becomes Tb. The period of time t1 to t5 is one pulse period Tf. The rise period Tu, peak period Tp, and fall period Td are set to predetermined values. The base period Tb changes every moment by controlling the arc length described later. As a result, the pulse period Tf also changes from moment to moment. The welding current Iw is feedback controlled based on the current setting signal Ir.

During the rise period Tu at times t1 to t2, the current setting signal Ir rises linearly from a predetermined base current set value to a predetermined peak current set value, as shown in FIG. As shown in FIG. 3B, the welding current Iw rises from the base current value Ib later than the current setting signal Ir, and converges to the peak current value Ip after overshooting.

During the peak period Tp at times t2 to t3, the current setting signal Ir becomes the above-mentioned peak current set value, as shown in FIG. As shown in FIG. 3B, the welding current Iw becomes the peak current value Ip after the overshoot.

During the fall period Td from time t3 to t4, the current setting signal Ir descends linearly from the peak current set value to the base current set value, as shown in FIG. As shown in FIG. 6B, the welding current Iw drops from the peak current value Ip later than the current setting signal Ir, and becomes the base current value Ib after undershooting.

During the base period Tb from time t4 to t5, the current setting signal Ir becomes the above-mentioned base current set value as shown in FIG. As shown in FIG. 6B, the welding current Iw becomes the base current value Ib after the undershoot.

The difference value Ei is defined as follows, where the current detection signal of the welding current Iw is Id.
Ei = | Id-Ir | ... (1) Equation Further, the differential integral value Se is defined as follows.
Se = ∫Ei · dt… (2) Equation However, the integration period is a predetermined period in the pulse period Tf. For the specified period
(1) The entire period of the pulse period Tf (the period of times t1 to t5),
(2) Rise period Tu, peak period Tp, and fall period Td (periods t1 to t4)
Is.

The above differential integral value Se serves as an index indicating the degree of coincidence between the waveform of the current setting signal Ir and the waveform of the welding current Iw. The difference integral value Se is a real number of 0 or more, and the smaller the value, the higher the degree of agreement. When Se = 0, it indicates that both waveforms are completely matched. Therefore, the gain of the feedback control can be optimized by using the difference integral value Se as an index. An example of the optimization method is shown below.

It is assumed that the feedback control circuit of the welding current is a PID control circuit. Let Gp be the proportional gain of proportional P, Gi be the integrated gain of integral I, and Gd be the differential gain of derivative D. That is, the gain of the feedback control is composed of the proportional gain Gp, the integral gain Gi, and the differential gain Gd. Set multiple values for each gain. For example, when a plurality of values are 5, Gp1 to Gp5, Gi1 to Gi5, and Gd1 to Gd5 are set in advance. Therefore, the number of gain combinations is 5 × 5 × 5 = 125. Next, welding is performed under specific welding conditions. During welding, the 125 gain combinations are automatically sequentially switched, and the difference integral value Se at that time is detected. After the welding is completed, the combination of gains in which the differential integral value Se is the smallest value is selected as the optimum gain. After that, welding is performed with this selected gain. The minimum value, maximum value, and multiple values of each gain are set in advance by an experiment so as to have a sufficient range and a step within the range. Even if the feedback control circuit is a circuit other than the PID control circuit, a plurality of gains can be optimized as described above.

FIG. 2 is a block diagram of a welding apparatus for carrying out the pulse arc welding control method according to the first embodiment of the present invention. The welding device is mainly composed of a welding power supply PS surrounded by a broken line, a robot control device RC, a robot (not shown), and the like. Hereinafter, each block will be described with reference to the figure.

The welding power supply PS is composed of the following blocks. The power supply main circuit MC receives an AC commercial power source (not shown) such as 3-phase 200V as an input, performs output control such as inverter control according to a drive signal Dv described later, and obtains a welding voltage Vw and a welding current Iw suitable for welding. Output. Although not shown, the power supply main circuit MC includes a primary rectifier circuit that rectifies an AC commercial power supply, a capacitor that smoothes the rectified DC, and an inverter circuit that converts the smoothed DC into high-frequency AC according to the drive signal Dv. It is equipped with an inverter transformer that steps down high-frequency AC to a voltage value suitable for welding, and a secondary rectifier circuit that rectifies the stepped-down high-frequency AC. The reactor WL is inserted between the + side output of the power supply main circuit MC and the welding torch 4, and smoothes the output of the power supply main circuit MC.

The welding wire 1 is fed in the welding torch 4 by the rotation of the feed roll 5 coupled to the feed motor WM, and an arc 3 is generated between the welding wire 1 and the base metal 2. The feed motor WM and the welding torch 4 are mounted on the robot. A welding voltage Vw is applied between the power feeding tip (not shown) in the welding torch 4 and the base metal 2, and the welding current Iw is energized.

The voltage detection circuit VD detects the welding voltage Vw and outputs a voltage detection signal Vd. The voltage averaging circuit VAV averages the voltage detection signal Vd (passes it through a low-pass filter) and outputs the voltage averaging signal Vav. The voltage setting circuit VR outputs a voltage setting signal Vr of a desired value. The voltage error amplifier circuit EV amplifies the error between the voltage setting signal Vr (+) and the voltage average signal Vav (−), and outputs a voltage error amplification signal Ev.

The V / F converter VF outputs a pulse period signal Tf, which is a trigger signal that becomes a high level for a short time at a frequency corresponding to the voltage error amplification signal Ev. The period in which the pulse period signal Tf reaches the high level for a short time is one pulse period.

The rise period setting circuit TUR outputs a predetermined rise period setting signal Tur. The peak period setting circuit TPR outputs a predetermined peak period setting signal Tpr. The fall period setting circuit TDR outputs a predetermined fall period setting signal Tdr.

The peak current setting circuit IPR outputs a predetermined peak current setting signal Ipr. The base current setting circuit IBR outputs a predetermined base current setting signal Ibr.

The current setting circuit IR includes the pulse period signal Tf, the rise period setting signal Tur, the peak period setting signal Tpr, the fall period setting signal Tdr, the peak current setting signal Ipr, and the base current. With the setting signal Ibr as an input, each time the pulse period signal Tf changes to the High level for a short time, the following processing is performed, and the current setting signal Ir and the period signal Tn are output.
1) When the pulse period signal Tf changes to the High level, the current setting that rises linearly from the value of the base current setting signal Ibr to the value of the peak current setting signal Ipr during the rise period Tu determined by the rise period setting signal Tur. The signal Ir is output, and the period signal Tn = 1 is output.
2) Subsequently, during the peak period Tp determined by the peak period setting signal Tpr, the peak current setting signal Ipr is output as the current setting signal Ir, and the period signal Tn = 2 is output.
3) Subsequently, during the falling period Td determined by the falling period setting signal Tdr, the current setting signal Ir that linearly descends from the value of the peak current setting signal Ipr to the value of the base current setting signal Ibr is output, and the period The signal Tn = 3 is output.
4)) Subsequently, during the base period Tb until the pulse period signal Tf reaches the High level again for a short time, the base current setting signal Ir is output as the current setting signal Ir, and the period signal Tn = 4 is output.

The current detection circuit ID detects the welding current Iw and outputs the current detection signal Id.

The difference value detection circuit EI takes the above-mentioned current detection signal Id and the above-mentioned current setting signal Ir as inputs, and outputs the difference value signal Ei = | Id-Ir | based on the above-mentioned equation (1).

The difference integrated value detection circuit SE uses the above-mentioned period signal Tn and the above-mentioned difference value signal Ei as inputs, and specifies a predetermined period of the pulse period by the period signal Tn based on the above-mentioned equation (2) for each pulse period. The difference integrated value signal Se = ∫Ei · dt is output.
The integration period is a predetermined period during the pulse period, and is, for example, the following period (1) or (2).
(1) The entire period of the pulse period Tf in which the period signal Tn is 1 to 4 (2) The period over the rising period Tu, the peak period Tp and the falling period Td in which the period signal Tn is 1 to 3.

The PID control circuit EA takes the above difference value signal Ei and the gain setting signal Gr described later as inputs, amplifies the difference value signal Ei by the gain determined by the gain setting signal Gr, and outputs the current feedback signal Ea.

The drive circuit DV receives the above-mentioned current feedback signal Ea and the start-up signal On from the robot control device RC described later as inputs, and when the start-up signal On is at the High level (start of welding), the above power supply is based on the current feedback signal Ea. The drive signal Dv for driving the inverter circuit in the main circuit MC is output, and when the start signal On is the Low level (welding stop), the drive signal Dv is not output.

The gain optimization start switch SW is provided on the front panel of the welding power supply PS, and outputs a gain optimization start signal Sw that becomes a high level when the switch is turned on and a low level when the switch is turned off. The gain optimization start signal Sw may be output from the robot control device RC.

The gain setting circuit GR receives the above-mentioned gain optimization start signal Sw and the above-mentioned difference integrated value signal Se as inputs, performs the following processing, and outputs the gain setting signal Gr. Here, since the feedback control circuit is the case of the PID control circuit EI, the gain setting signal Gr is composed of the proportional gain Gp, the integrated gain Gi, and the differential gain Gd as described above.
1) Gp1 to Gp5, Gi1 to Gi5 and Gd1 to Gd5 are set in advance. Therefore, there are 125 combinations of gains.
2) When the gain optimization start signal Sw reaches the High level during welding, the 125 gain combinations are automatically sequentially switched and output as the gain setting signal Gr. At the same time, the value of the differential integrated value signal Se in each gain combination is stored.
3) The gain combination in which the difference integral value signal Se is the smallest value among the 125 gain combinations is stored as the optimum gain combination and output as the gain setting signal Gr.

The feed rate setting circuit FR outputs a predetermined feed rate setting signal Fr. The feed control circuit FC receives the above feed speed setting signal Fr and the start signal On from the robot control device RC described later as inputs, and when the start signal On is the High level (start of welding), the feed speed setting signal Fr. To output the feed control signal Fc for feeding the welding wire 1 to the above feed motor WM at the feed speed determined by, and to stop the feed when the start signal On is the Low level (welding stop). Outputs the feed control signal Fc.

The robot control device RC moves the robot (not shown) according to a work program taught in advance, and outputs a start signal On instructing welding start or welding stop.

According to the first embodiment described above, the difference value between the current detection value of the welding current and the current set value is detected, the difference value is integrated over a predetermined period during the pulse period, the difference integration value is detected, and the difference integration value is detected. The gain of feedback control is automatically adjusted based on the value. The above-mentioned predetermined period is the entire period of the pulse period, or the period over the rising period, the peak period, and the falling period. In the present embodiment, the gain of the feedback control of the welding current can be automatically adjusted to an appropriate value under various welding conditions. Therefore, a stable welding state can always be obtained under various welding conditions.

1 Welding wire 2 Base material 3 Arc 4 Welding torch 5 Feeding roll DV Drive circuit Dv Drive signal EA PID control circuit Ea Current feedback signal EI Difference value detection circuit Ei Difference value signal EV Voltage error amplification circuit Ev Voltage error amplification signal FC Feed control circuit Fc Feed control signal FR Feed speed setting circuit F Feed speed setting signal GR Gain setting circuit Gr Gain setting signal Ib Base current value IBR Base current setting circuit Ibr Base current setting signal ID Current detection circuit Id Current detection signal Ip Peak current value IPR Peak current setting circuit Ipr Peak current setting signal IR Current setting circuit Ir Current setting signal Iw Welding current MC Power supply Main circuit On Start signal PS Welding power supply RC Robot control device SE Difference integrated value detection circuit Se Difference integrated value ( signal)
SW Gain optimization start switch Sw Gain optimization start signal Tb Base period Td Fall period TDR Fall period setting circuit Tdr Fall period setting signal Tf Pulse period (signal)
Tn Period signal Tp Peak period TPR Peak period setting circuit Tpr Peak period setting signal Tu Rise period TUR Rise period setting circuit Tur Rise period setting signal VAV Voltage averaging circuit Vav Voltage averaging signal VD Voltage detection circuit Vd Voltage detection signal VF V / F Converter VR Voltage setting circuit Vr Voltage setting signal Vw Welding voltage WL Reactor WM Feed motor

Claims (3)

The welding wire is fed and rises from the base current value to the peak current value during the rise period, becomes the peak current value during the peak period, and falls from the peak current value to the base current value during the fall period. Then, during the base period, the welding current, which is the base current value, is repeatedly energized as one pulse cycle.
In the pulse arc welding control method in which the welding current is feedback-controlled based on the current set value,
The difference value between the current detection value of the welding current and the current set value is detected, the difference value is integrated over a predetermined period during the pulse cycle to detect the difference integration value, and the difference integration value is used as the basis for the difference integration value. Automatically adjusts the feedback control gain,
A pulse arc welding control method characterized by this. The predetermined period is the entire period of the pulse period.
The pulse arc welding control method according to claim 1. The predetermined period is a period spanning the rise period, the peak period, and the fall period.
The pulse arc welding control method according to claim 1.

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