JP2004268095A - Control method for arc welding machine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method to realize a stable short-circuit type welding even by using a welding machine with a small DC reactor. <P>SOLUTION: In the control method of the arc welding machine which is equipped with a current detector to detect an output current and a voltage detector to detect an output voltage, and performs welding based on the preset welding voltage value, a current change rate is calculated (S2) based on the output current value(S1) detected by the current detector during an arcking period. A welding voltage command value is corrected based on the current change rate so that the current change rate becomes small(S4, S5) and then the arc welding machine is controlled according to the welding voltage command value. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improvement in an arc welding machine that rectifies an alternating current into a direct current, converts the output into a high-frequency alternating current by an inverter circuit, appropriately transforms the output by a transformer, and then converts the output into a direct current by a rectifying circuit.
[0002]
[Prior art]
In output control of a conventional arc welding machine, a detected welding voltage value and a welding voltage set value which is a predetermined voltage value are error-amplified, and the welding output is controlled by the output signal. Will be explained.
FIG. 5 is a diagram showing a configuration of a conventional arc welding machine. An input side of a first rectifying unit 7 is connected to a power source 6, and an input side of a switching unit 8 is connected to a rectifying output side of the first rectifying unit 7. ing. The output side of the switching unit 8 is connected to the primary side of the main transformer 9, the secondary side of the main transformer 9 is connected to the input side of the second rectifier 10, and the output side of the second rectifier 10 One end of the DC reactor 11 is connected to one of the DC reactors 11, and the welding voltage detector 5 is connected in parallel between the other end of the DC reactor 11 and the other output side of the second rectifier 10.
The other end of the DC reactor 11 and the other of the output side of the second rectifier 10 are output as welding output, and the other end of the DC reactor 11 is energized to the wire 15 through the wire feeding device 13 and the torch 14, The other of the output sides of the two rectifiers 10 is connected to the base material 12, and arc welding is performed between the wire 15 and the base material 12. Note that the signal from the welding voltage detecting unit 5 is taken into the limiting unit 1 without smoothing, added to the data from the welding voltage command unit 4 by the adding unit 2, and output to the switching unit 8 (for example, see Patent Reference 1).
[0003]
[Patent Document 1]
JP 2002-248573 A
[Problems to be solved by the invention]
The conventional control method is a control method on the assumption that a large DC reactor 11 for gradually changing the welding current and the welding voltage is present in the circuit. For example, when the DC reactor of the circuit is as small as 20 μH, However, there is a problem that normal control cannot be performed.
Further, in the conventional short-circuit type arc welding machine, it is premised that a large DC reactor 11 for gradually changing a welding current and a welding voltage, for example, a DC reactor 11 of 30 μH or more is provided.
However, when the large DC reactor 11 is attached, a change in current at the time of arc start is hindered, and arc start failure is likely to occur, and pulse welding that requires a steep current change cannot be performed. Also, in normal short-circuit welding, when a large DC reactor 11 is attached, a large current stored in the DC reactor flows at the moment of switching from a short circuit to an arc. Had the problem that it was impossible.
[0005]
The present invention has been made in view of such a problem, and an object of the present invention is to provide a method for realizing stable short-circuit welding even in a welding machine having a small DC reactor of 20 μH or less.
[0006]
[Means for Solving the Problems]
To solve the above problem, the present invention controls as follows.
According to a first aspect of the present invention, there is provided a method for controlling an arc welding machine, comprising a current detector for detecting an output current and a voltage detector for detecting an output voltage, and performing welding based on a preset welding voltage value. In the method for controlling an arc welding machine, a current change rate is calculated based on an output current value detected by the current detector during an arc period, and the welding voltage is set so that the current change rate is reduced based on the current change rate. A command value is corrected, and the arc welding machine is controlled based on the welding voltage command value.
According to a second aspect of the present invention, there is provided a method for controlling an arc welding machine, wherein the welding voltage command value is not corrected based on the current change rate for a predetermined time after the short circuit is released. .
A method for controlling an arc welding machine according to a third aspect of the present invention includes a current detector for detecting an output current and a voltage detector for detecting an output voltage, and performs welding based on a preset welding voltage value. In the method for controlling an arc welding machine, as a welding voltage command value for setting an output voltage during an arc period, a welding voltage command value that changes in an exponential function curve is created, and welding is performed based on the welding voltage command value. It is a feature.
The method for controlling an arc welding machine according to claim 4 of the present invention is characterized in that the exponential function curve constant is set according to the length of the short-circuit period before the occurrence of an arc, the welding material, the type of the work, the plate thickness, and the type of the shielding gas. Is changed.
According to a fifth aspect of the present invention, there is provided a method for controlling an arc welding machine, wherein an output voltage during an arc period is sequentially feedback-controlled by PID control.
The control method of an arc welding machine according to claim 6 of the present invention is characterized in that, in the PID control, the control speed when increasing the output voltage is increased, and the control speed when decreasing the output voltage is decreased. Things.
According to a seventh aspect of the invention, there is provided a method for controlling an arc welding machine, wherein a short circuit or an arc period is determined based on a constant of the exponential function curve and the output voltage.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
2 and 3 show block diagrams of the present invention. FIG. 2 is a configuration diagram of the arc welding machine, and FIG. 3 is an explanatory diagram of the current control circuit 17 of the configuration diagram of the present invention. The configuration will be described based on FIG. The AC current input from the AC power supply 6 is rectified by the rectifier circuit 7 into a DC current. The DC current is converted into high-frequency AC by the inverter circuit 8, and the transformer 9 converts the DC current into a voltage suitable for arc welding. Next, the configuration of the current control circuit 17 will be described with reference to FIG. The current value of the output at the time of the arc is detected by the current detector 16 and read into the digital signal processor 18. The digital signal processor 18 converts an analog input welding current value into a digital value via an A / D converter 20. Normally, the welding current value is converted to a constant percentage of analog value by a Hall element or a shunt. For example, 1000 A is converted to an analog voltage of 10 V and input to the A / D converter 20. The A / D converter 20 buffers the output of the A / D converter 20 by a predetermined period of interrupt processing according to a program preset in the digital signal processor 18.
[0008]
As described above, the current value converted into the digital value is stored in the memory 22. Thus, the converted current value can be processed in time series by the timer function of the digital signal processor 18. Here, a current value change per time α = (In−I (nt)) / t is obtained from the converted current value In and the current value I (nt) detected t times before. In order to reduce the change α in the current value, a negative voltage is added to the welding command voltage when α is positively large, and a positive voltage is applied when α is negatively large.
That is, welding command voltage = command voltage−a * α.
a is a constant that is experimentally obtained, and a large constant is set when the change in the current value is made gentle. When the voltage (−a * α) is added to the command voltage at the time of the arc, the current value changes gently, but a short circuit occurs at the time of the arc, and immediately after the short circuit is released, the voltage (−a * α) is applied. It takes time to return from the high current at the moment when the short circuit is released to the current at the time of normal arc, and the operation becomes oscillating. For a predetermined time (several hundred microseconds), this -a * α voltage is Do not add.
The processing described above is shown in the flowchart of FIG.
In S1 of FIG. 1, an output current is input. In S2, a current change rate is obtained from the time-series data of the output current input in S1. In S3, the magnitudes of the change rates are compared. In S4, if the current change rate is positive, a negative voltage is added. In S5, when the current change rate is negative, a positive voltage is added.
[0009]
(Second embodiment)
The digital signal processor 18 issues a command using a curve using an exponential function as the command voltage during the arc period.
Exponential function can be expressed by Y (command voltage ^{value) = a x · b + c} 0 <a <1. The command voltage represented by an exponential function is superimposed on the -a * α for reducing the current change, and becomes a welding command voltage. The command voltage represented by the exponential function has different values for a, b, and c depending on the length of the short circuit period before the occurrence of an arc, the type of the welding material, and the type of the shielding gas.
For example, if the short-circuit period before the occurrence of an arc is long, the amount of heat is insufficient, so that large values are set for a, b, and c to increase the heat input. However, if a, b, and c are simply changed in proportion to the short circuit period before the occurrence of the arc, the arc length always fluctuates and becomes unstable. Therefore, in the same welding section, a and c are almost fixed. However, b is changed so as to have a strong correlation with the short-circuit period before the occurrence of the arc. When stainless steel is used as a welding material, stainless steel is likely to be formed in a convex bead. Therefore, it is necessary to form heat as soon as possible by applying heat immediately after an arc is formed from a short circuit. As described above, in order to apply heat instantaneously from the short-circuit to the arc, a is decreased, b is increased, the voltage is increased just after the short-circuit becomes an arc, and the voltage is rapidly decreased thereafter. .
[0010]
Further, when performing welding on an ultra-thin plate, it is necessary to stabilize the welding by increasing the number of short circuits as much as possible without applying the arc heat, so that a is increased, b is decreased, and c is decreased. The angle of the arc voltage is low and the arc voltage promotes a short circuit. For example, when CO2 gas is used as the shielding gas, the arc is likely to break when the arc length is increased particularly in a low current range. Therefore, the voltage a at the moment when a short-circuit becomes an arc is increased by increasing a and decreasing b. Keep the arc length short by not setting it high. For example, when Ar gas is used as a shielding gas and a state like a spray transfer is used to reduce spatters, a is reduced, b is increased, and the voltage at the moment when a short-circuit becomes an arc is increased. , Keep the arc length long.
[0011]
In FIG. 2 of the hardware configuration diagram of the present invention, the DC reactor 11 is set to 20 μH or less in consideration of the pulse weldability, the arc startability, and the controllability. If the DC reactor 11 is small and the influence on the output voltage of the DC reactor is small, the command voltage waveform and the output voltage waveform become almost the same as shown in FIG. In order to change the output voltage waveform with an exponential function curve by the hardware, the output voltage during the arc period is sequentially fed back by PID control. The PID control is a control for equalizing a command voltage and an output voltage during an arc period based on P: proportional gain, I: integral gain, and D: differential gain.
In addition, when the arc voltage is fed back by the PID control, the tip of the wire flies due to gas explosion in the molten pool or the like, and when the arc length suddenly becomes abnormally long, the feedback arc voltage increases. The voltage will be lower. At this time, if the command voltage is rapidly lowered, the arc voltage with respect to the arc length becomes insufficient and the arc breaks. For this reason, in the PID control, when the arc voltage is controlled to be low, the control speed is reduced, and when the arc voltage is controlled to be high, the control speed is increased. As this method, for example, normally, the width of the command voltage is set to 0 V to 40 V, and the PID control is performed. The control voltage is set to 12 V to 40 V. By doing so, it is prevented that the voltage becomes small enough to cut off the arc. In the present invention in which the arc voltage is controlled by an exponential function curve in the arc welding in which the short circuit and the arc are repeated, it is important to determine the short circuit state and the arc state.
[0012]
In the present invention, Y (command voltage value) = ax ^× b + c (0 <a <1) ≒ output voltage. When the output voltage decreases, fast PID control is performed to control the output voltage to be constant. Therefore, a voltage state lower than c is a short-circuit state. A short circuit is determined when the feedback voltage is Vf <c-3V (usually, since c is 20 V to 30 V, the offset voltage for determining that the voltage is clearly lower is 2 V to 10 V).
【The invention's effect】
As described above, the arc welding machine control method of the present invention has an effect that high-performance welding can be performed by a welding machine having a small DC reactor of a main current circuit, and the small DC reactor has an effect of arc start. There is also an effect that the improvement and the pulse welding can be realized by one welding machine.
[Brief description of the drawings]
FIG. 1 is a flowchart of the present invention. FIG. 2 is a block diagram of the present invention. FIG. 3 is a diagram showing details of a control unit 17. FIG. 4 is a current, voltage, and waveform command curve.
REFERENCE SIGNS LIST 1 limiter 2 adder 3 short circuit / arc determiner 4 welding voltage commander 5 welding voltage detector 6 commercial power supply 7 first rectifier 8 switching (inverter)
9 Main transformer 10 Second rectifier 11 DC reactor 12 Base material 13 Wire feeder 14 Torch 15 Wire 16 Current detector 17 Controller 18 Digital signal processor 19 Voltage A / D
20 Current A / D
Reference Signs List 21 arithmetic unit 22 memory 23 command generation to driver 24 inverter driving driver 25 host CPU

Claims (7)

A method for controlling an arc welding machine that includes a current detector that detects an output current and a voltage detector that detects an output voltage, and performs welding based on a welding voltage value set in advance.
Calculate the current change rate based on the output current value detected by the current detector during the arc period,
Correcting the welding voltage command value so that the current change rate is reduced based on the current change rate,
An arc welding machine control method, comprising controlling an arc welding machine based on the welding voltage command value. 2. The control method for an arc welding machine according to claim 1, wherein the welding voltage command value is not corrected based on the current change rate for a predetermined time after the short circuit is released. A method for controlling an arc welding machine that includes a current detector that detects an output current and a voltage detector that detects an output voltage, and performs welding based on a welding voltage value set in advance.
As a welding voltage command value to set the output voltage during the arc period, create a welding voltage command value that changes in an exponential function curve,
A method for controlling an arc welding machine, wherein welding is performed based on the welding voltage command value. The arc welding machine according to claim 3, wherein the constant of the exponential function curve is changed according to the length of a short circuit period before the occurrence of an arc, a welding material, a type of a work, a plate thickness, and a type of a shielding gas. Control method. A method for controlling an arc welding machine that includes a current detector that detects an output current and a voltage detector that detects an output voltage, and performs welding based on a welding voltage value set in advance.
A method for controlling an arc welding machine, wherein an output voltage during an arc period is sequentially feedback-controlled by PID control. The method according to claim 5, wherein in the PID control, the control speed when increasing the output voltage is increased and the control speed when decreasing the output voltage is decreased. 7. The control method for an arc welding machine according to claim 5, wherein a short circuit or an arc period is determined based on a constant of the exponential function curve and the output voltage.

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