JPH0585265B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention includes an output control element such as a power transistor in the main circuit that can be controlled by an electric signal, and a reactor for improving welding characteristics immediately before the output terminal when viewed from the input side. The present invention relates to a DC arc welding machine that supplies DC power between a consumable electrode and a base metal to generate an arc and perform welding.

Prior Art A conventional DC arc welding machine will be described below. Figure 2 shows the configuration of a conventional DC arc welding machine. In FIG. 2, 1 is a consumable electrode, 2 is a base material, 3 is an electrode feeding motor and feeding device, 4 is a welding part, 5 is a rectifier, 6 is a smoothing capacitor, 7
is an inverter section, 8 is a transformer, 9 is a rectifier, 10
11 is a reactor for improving welding characteristics, 11 is an output control circuit, 12 is an addition/subtraction circuit, 13 is a feedback signal generation circuit, 14 is an output setting signal amplification circuit, and 15 is an output setting signal circuit.

The operation of the conventional DC arc welding machine configured as described above will be explained below. AC power input from the input terminal is rectified by a rectifier 5 and smoothed by a smoothing capacitor 6 to become DC power. Then, it is converted to AC power by an inverter section 7 made up of switching elements such as power transistors, stepped down to a voltage suitable for welding by a transformer 8, and rectified again by a rectifier 9 to become DC power, improving welding characteristics. It is supplied to the welding part consisting of the consumable electrode 1 and the base material 2 through the reactor 10. The consumable electrode 1 is fed to the base material 2 at a constant speed by the electrode feeding motor and the feed device 3, and welding is performed between the consumable electrode 1 and the base material 2. During welding, the voltage between the point immediately after the reactor 10 for improving welding characteristics and the negative side of the output terminal is detected, and a feedback signal generating circuit 13 generates a signal proportional to the detected signal as a feedback signal. Then, a smoothing circuit 16 smoothes the rapidly changing feedback signal with a time constant. Further, the output setting signal generated by the output setting signal circuit 15 is amplified by the output setting signal amplifying circuit 14 and becomes an output command signal. This output command signal is added to and subtracted from the smoothed feedback signal by an adder/subtractor 12, that is, the feedback signal is negatively fed back to the output command signal, and the resulting signal is used as an output control signal to control the output. According to the output control signal sent to the circuit 11, output control elements such as power transistors in the inverter section 7 are switched.
It controls the duty and adjusts the output. By performing such negative feedback control, the influence of fluctuations in power supply voltage and other disturbances on the output voltage during welding is reduced.

Problems to be Solved by the Invention According to the conventional DC arc welding machine as described above, the smoothing circuit for the feedback signal necessary to stabilize the feedback system does not function as described below in the transient state at the start of welding. It is having a negative impact. In other words, at the start of welding or when the arc is broken for a relatively long time, the consumable electrode and the base metal are electrically open because no arc is generated, and therefore there is no connection between the output terminals. The voltage becomes high because the no-load voltage of the welding machine is applied. When the voltage between the output terminals increases, the feedback signal generating circuit 13 also outputs a high feedback signal proportional to the voltage, and at the time of starting welding and when the arc is broken for a relatively long time, the feedback signal is output through the smoothing circuit to the addition/subtraction circuit 12.
A high feedback signal is also sent to the output voltage, and as a result, the output voltage is throttled by this feedback control. Once the output voltage is throttled, the time constant of the smoothing circuit smoothes the feedback signal, so the output voltage remains throttled even after the consumable electrode comes into contact with the base material to generate a new arc and energization begins. As a result, the arc breaks again without being able to supply the joule heat that melts the tip of the consumable electrode and transitions to a steady arc state. Due to this kind of repetition, in conventional DC arc welding machines, when starting welding or when the arc has been broken for a relatively long time, it is difficult for the arc to be generated again and to reach a stable arc state. It has drawbacks. This drawback is particularly noticeable when the feedback gain or the time constant of the smoothing circuit is large.

Means for Solving the Problems In order to solve these problems, the present invention provides an output control element such as a power transistor that can be controlled by an electric signal, and an output voltage setting that adjusts the output amount of the output control element. It has an output setting signal circuit that outputs a signal, and a reactor for improving welding characteristics immediately before the output terminal when viewed from the input side of the welding machine, and provides direct current to the arc welding load generated between the consumable electrode and the base metal. A main circuit including the output control element for supplying electric power and a reactor for improving welding characteristics is configured, and the voltage at one point between the stage immediately after the reactor for improving welding characteristics and the welding arc section when viewed from the input side is controlled. A feedback circuit that applies negative feedback to the output voltage setting signal in the circuit is provided, and a current detection circuit that detects arc breakage during welding is provided, and when the current detection circuit detects arc breakage, the feedback circuit is provided for the duration of the arc breakage. The apparatus is provided with means for inputting a signal proportional to the output voltage setting signal to the feedback circuit instead of the signal, switching to open loop control, and restarting the negative feedback when the arc breakage ends.

Effects With the above-described configuration, the present invention cancels negative feedback control and switches to open-loop control during unstable transients such as when starting welding or when an arc breaks, thereby eliminating the negative feedback effect on system stability. remove.

Embodiment An embodiment of the present invention will be described with reference to FIG. In Figure 1, 1, 2, 3, 4, 5, 6,
7, 8, 9, 10, 11, 12, 13, 14, 1
5 and 16 are consumable electrodes, base material, electrode feeding motor and feeding device, welded parts,
These are a rectifier, a smoothing capacitor, an inverter section, a transformer, a rectifier, a reactor, an output control circuit, an addition/subtraction circuit, a feedback signal generation circuit, an output setting signal circuit, and a smoothing circuit. 17 is a proportional voltage generation circuit, 18 is an analog switch, 19 is a shunt resistor, and 20 is a current detection circuit.

The operation of the DC arc welding machine configured as described above will be explained below. AC power input from the input terminal is rectified by a rectifier 5 and smoothed by a smoothing capacitor 6 to become DC power.
Then, it is converted to AC power by an inverter section 7 made up of switching elements such as power transistors, stepped down to a voltage suitable for welding by a transformer 8, and rectified again by a rectifier 9 to become DC power, which improves welding characteristics. It is supplied to the welding part consisting of the consumable electrode 1 and the base material 2 through the reactor 10. The consumable electrode 1 is fed to the base material 2 at a constant speed by the electrode feeding motor and the feed device 3, and welding is performed between the consumable electrode 1 and the base material 2. During welding, the voltage between the point immediately after the reactor 10 for improving welding characteristics and the negative side of the output terminal is detected, and a feedback signal generating circuit 13 generates a signal proportional to the detected signal as a feedback signal. Then, a smoothing circuit 16 smoothes the rapidly changing feedback signal with a time constant. The smoothed feedback signal enters analog switch 18.
At the same time, the output setting signal generated by the output setting signal circuit 15 is converted by the proportional voltage generating circuit 17 into a signal proportional to the output setting signal and sent to the analog switch 18. The analog switch 18 detects the difference between the smoothed feedback signal and the signal proportional to the output setting signal in accordance with a current detection signal from a current detection circuit 20 which receives a signal from a shunt resistor 19 and performs current detection. It is decided whether to send it to the addition/subtraction circuit 12. When the current detection signal is output, that is, the arc is stable, the smoothed feedback signal is output as an analog signal, and when the current detection signal is not output, that is, when welding is started or arc breakage occurs, the signal proportional to the output setting signal is output as an analog signal. Supplied to switch 18. Further, the output setting signal generated by the output setting signal circuit 15 is amplified by the output setting signal amplifying circuit 14, and the output command signal, which becomes the output command signal, is selected by the adder/subtracter 12 and the analog switch 18. is added to and subtracted from the signal sent to
That is, the signal sent from the analog switch 18 is negatively fed back to the output command signal, and the resulting signal is used as the output control signal and the output control circuit 1
1, and according to the output control signal, the switching duty of output control elements such as power transistors in the inverter section 7 is controlled and the output voltage is adjusted. At this time, the welding output voltage is adjusted by the output setting signal determined by the output setting signal circuit 15, and therefore the welding output voltage and the output setting signal are in a proportional relationship, and are also in a proportional relationship with the feedback signal. By generating a proportional voltage in the proportional voltage generating circuit 17 that is approximately equal to the feedback voltage when a stable arc is generated, the system is kept stable even during transitions such as when starting welding or when an arc breaks. be able to.

Effects of the Invention According to the present invention, by providing negative feedback to the output voltage of a welding machine, it is possible to reduce the influence of fluctuations in the power supply voltage on the output voltage, fluctuations in various constants due to temperature, etc., and at the same time, it is possible to reduce the adverse effects when performing closed-loop control. This DC arc welding machine has the excellent effect of overcoming the instability of the system, and can re-arc in a short time even in the case of irregular arc disturbances such as when starting the arc or breaking the arc. can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a DC arc welding machine showing an embodiment of the present invention, and FIG. 2 is a block diagram of a conventional DC arc welding machine. DESCRIPTION OF SYMBOLS 1...Consumable electrode, 2...Base material, 3...Electrode feeding motor and feeding device, 4...Welding part, 5...
... Rectifier, 6 ... Smoothing capacitor, 7 ... Inverter section, 8 ... Transformer, 9 ... Rectifier, 10 ...
...Reactor, 11...Output control circuit, 12...
Addition/subtraction circuit, 13... Feedback signal generation circuit, 14...
... Output setting signal amplification circuit, 15 ... Output setting signal circuit, 16 ... Smoothing circuit, 17 ... Proportional voltage generation circuit, 18 ... Analog switch, 19 ... Shunt resistor, 20 ... Current detection circuit.

Claims (1)

[Claims] 1. An output control element such as a power transistor that can be controlled by an electric signal, an output setting signal circuit that outputs an output voltage setting signal that adjusts the output amount of the output control element, and an output terminal when viewed from the input side of the welding machine. The main circuit includes a reactor for improving welding characteristics immediately before the output control element and the reactor for improving welding characteristics, which supplies DC power to the arc welding load generated between the consumable electrode and the base metal. death,
A feedback circuit is provided that applies negative feedback to the output voltage setting signal in the control circuit by applying a negative feedback to the voltage at one point between the stage immediately after the reactor for improving welding characteristics and the welding arc section when viewed from the input side, so as to reduce the arc during welding. A current detection circuit for detecting arc breakage is provided, and when the current detection circuit detects arc breakage, a signal proportional to the output voltage setting signal is input to the feedback circuit instead of the feedback signal for the period of the arc breakage, thereby creating an open loop. A DC arc welding machine characterized by comprising means for switching to control and restarting the negative feedback when the arc breakage ends.