JP2981289B2 - Output overcurrent protection device for arc welding power supply - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an output overcurrent protection device for an arc welding power supply, and more particularly to an improvement in reset means after output is stopped by detecting output overcurrent.

[0002]

2. Description of the Related Art FIG. 3 shows a main circuit configuration of a conventional arc welding power supply using a consumable electrode and a circuit configuration of an output overcurrent protection device. In FIG. 3, 1 is a three-phase AC power supply, 2 is an input-side rectifier circuit that converts a three-phase AC input into DC, 3 is a smoothing capacitor, 4 is an inverter that converts DC smoothed by the capacitor 3 into high-frequency AC, 5 Is a welding transformer, 6 is an output-side rectifier circuit for converting high-frequency alternating current stepped down by the transformer 5 to DC again, 7 is a DC reactor for smoothing output current, 8 is a shunt resistor for detecting output current, and 9 is a welding wire. A contact tip 10 is energized, 11 is an arc load, 12 is a base material, and 1 to 12 constitute a main circuit.

The output overcurrent protection device shown in FIG. 3 is configured as follows. Reference numeral 13 denotes a control circuit which normally controls the output of the welding power source by driving or stopping the inverter 4 by turning on and off a start signal from a start switch 14. In connection with this output control, wire feed control and the like are also performed according to commands from the control circuit 13. Reference numeral 15 denotes an overcurrent detection circuit, which outputs the output of the shunt resistor 8 to an amplifier 15-1.
The signal amplified in (1) is input to the (−) input, and the overcurrent setting unit 15-2
Is applied to an integrating circuit consisting of a resistor 15-4, a capacitor 15-5, and an operational amplifier 15-6 as a (+) input, so that the value of the output current I flowing through the shunt resistor 8 exceeds the overcurrent set value. If this happens, the output voltage Va of the integration circuit is reduced in proportion to the time, and the output voltage Va of this integration circuit is compared with the output voltage Vb of the overcurrent time setting device 15-3 by the comparator 15-7. When the output current I equal to or greater than the overcurrent set value continues to flow for the overcurrent set time or longer, the output of the comparator 15-7 is changed from a low level to a high level, and is output as an abnormality determination signal. When an output overcurrent flows due to a short circuit between a chip, a base material or a chip or a nozzle due to sputtering, an abnormality determination signal output from the overcurrent detection circuit 15 enters the set input terminal S of the latch circuit 16 and 16 is operated. Once the latch circuit 16 operates, the output of the latch circuit 16
Stops the output of the welding power source irrespective of whether the start signal is on or off (the wire feed is also stopped at the same time), and keeps stopping the output until the latch circuit 16 is reset. In this case, in order to restart the arc, it was necessary for a person to go to the installation location of the welding power source, to turn off the control power source or the input power source and then turn it on again to reset the latch circuit 16.

[0004]

In the prior art described above, after detecting an overcurrent, a person must go to the installation location of the welding power source to reset the latch circuit once operated. Is far from the work site,
(2) When the welding power source is installed at a higher place than the work site, or (3) When the work site is narrow or at a high place, it takes a long time to reset, and the work efficiency is reduced.

Also, in an automatic machine such as a welding robot, when the latch circuit is reset, if the start signal is kept on, an unexpected irregular operation such that welding is started simultaneously with the resetting is performed. And there is a safety problem.

An object of the present invention is to solve such problems of the prior art.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention detects an output current of a welding power source and detects an abnormality when the value of the output current is equal to or more than a predetermined value and this state continues for more than a predetermined time. An overcurrent detection circuit that outputs a determination signal, a latch circuit that operates based on the abnormality determination signal, and a welding power supply that is normally turned on or off by a startup signal from a startup switch separate from a control power supply or an input power supply of the welding power supply A control circuit for controlling the output and stopping the output of the welding power source by the output of the latch circuit when the overcurrent is detected, regardless of whether the start signal is on or off, and maintaining this state until the latch circuit is reset. In the output overcurrent protection device of the arc welding power supply, the state of the start signal after a predetermined pause time required for preventing overheating of the welding power supply after the output of the abnormality determination signal is determined. If the start signal is off at the end of the predetermined pause time, reset means for sending a reset signal to the latch circuit when the start signal changes from on to off if the start signal is on if it is on. It is a feature.

[0008]

[Function] The purpose of the arc welding power supply to stop output by detecting overcurrent is (a) to avoid overheating of the welding power supply due to overcurrent, and (b) to inform the operator of output side abnormalities such as chip short circuit. And if it can fulfill its purpose,
Since it is not necessary to keep the output stopped, in the present invention, a reset signal is output from the reset means to the latch circuit under the following conditions to release the output stop latch.

(1) After the detection of the overcurrent, the output is continuously stopped until a predetermined pause time elapses regardless of whether the start signal is on or off. Thus, overheating of the welding power source is avoided and an abnormality on the output side is notified.

(2) If the activation signal is off at the end of the predetermined pause time, the latch is immediately released. If the activation signal is on, the latch is not released until the activation signal is once turned off. That is, after the elapse of the predetermined pause time, the arc restart cannot be performed unless the start signal is intentionally turned from off to on.

By performing the latch release under the above conditions (1) and (2), one of the problems of the prior art is that a person does not need to go to the welding power source installation site for resetting. Another problem is that irregular operation such that welding is started at the same time as resetting is not performed.

Next, the predetermined pause time after the detection of the overcurrent will be described. Detection of output overcurrent is usually performed so that the latch circuit does not operate in the event of a short circuit caused by a wire when the arc is started.
The determination is based on the fact that the maximum output current (output short-circuit current) has continued to flow for approximately one second. Here, since the maximum output current is approximately 2 to 2.5 times the rated current, the amount of heat generated by the main circuit conductor at the time of overcurrent detection is (2.5) times the rated current, that is, approximately ² times. It is sufficient to consider the total amount of heat generated when about seven times of heat is generated for approximately one second. Therefore, in order to prevent overheating due to overcurrent, approximately 1
It is only necessary to prevent overcurrent from flowing only once.
After the output is stopped by the overcurrent detection, the latch is released after a pause of approximately 7 seconds or more, so that the welding power supply does not overheat even if an overcurrent flows again thereafter.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing a main circuit configuration of an arc welding power supply using a consumable electrode and a circuit configuration of an output overcurrent protection device. FIG. 2 is a flowchart for explaining the operation of a reset circuit.

In FIG. 1, reference numerals 1 to 16 indicate portions corresponding to the same reference numerals in FIG. 3, the overcurrent detection circuit 15 detects the output current I of the welding power source with the shunt resistor 8, and outputs an output current equal to or more than the set value of the overcurrent setter 15-2. When the flow continues for the set time of -3 or more, the comparator 15-7 outputs an abnormality determination signal (high-level signal). This abnormality determination signal enters the set input terminal S of the latch circuit 16 and operates the latch circuit 16. Once the latch circuit 16 operates,
Based on the output, the control circuit 13 sends an output stop signal to the inverter 4 regardless of whether the start signal from the start switch 14 is on or off, and stops the output. Even if the output of the overcurrent detection circuit 15 returns from the high level to the low level due to the stop of the output of the welding power source, the latch circuit 16 maintains the operating state until a reset signal is input to the reset input terminal R. Remains stopped.

Next, a reset circuit 17 newly provided as reset means will be described. The reset circuit 17 shown in FIG. 1 includes a timer 17-1 and a condition determination unit 17-2, and operates as shown in FIG. The timer 17-1 is set by an abnormality determination signal from the overcurrent detection circuit 15, and when a timer set time (here, a predetermined pause time) elapses,
The timer output is turned on, and the timer 17-1 is reset simultaneously with the reset of the latch circuit 16. When the timer output is turned on, the condition determination unit 17-2 determines the state of the start signal from the start switch 14, and immediately outputs a reset signal to the latch circuit 16 if the start signal is off at the end of the timer set time. When the output stop of the welding power source is released and the start signal is then turned on from off, the control circuit 13 operates as usual and the welding can be started. If the activation signal is on at the end of the timer set time, the reset signal will not be output until the activation signal changes from on to off. Therefore, if the start signal remains on even after the elapse of the timer set time, the output of the welding power supply will continue to be stopped, and it will be necessary to turn the start signal off and then on again to resume welding. is there.

If the start signal is turned on again after the timer set time has elapsed and the output is generated without removing the output side abnormality such as a chip short circuit, the output overcurrent protection device operates in the same manner as described above. However, if the timer setting time (predetermined pause time) is set to approximately 7 seconds or more as described in the section of the operation, the welding power supply will not be overheated even if the output overcurrent flows again.

FIG. 1 shows an example in which the reset circuit 17 is composed of discrete components. However, the functions of the timer 17-1 and the condition determination unit 17-2 can be realized by software of a microcomputer. Further, in the welding power supply using the microcomputer for the control circuit 13, the addition of parts is not required by executing the latch release function shown in FIG. 2 as a part of the interrupt processing by the latch circuit output.

Although the above embodiment is directed to a welding power source of the inverter control type, it can be similarly applied to a welding power source of the thyristor control type.

[0019]

According to the present invention, after the operation of the output overcurrent protection device, it is not necessary for a person to go to the place where the welding power source is installed in order to release the latch of the output stop. Since the latch can be released only after a predetermined pause time has elapsed since the detection of the current, the purpose of overcurrent protection can be sufficiently achieved.

Further, if the start signal remains on even after the predetermined pause time has elapsed, the latch circuit is not reset, and no output is generated unless the start signal is turned off and then turned on again. If the start signal is kept on after the operation of the output overcurrent protection device, the unexpected irregular operation such as starting welding at the same time as resetting of the latch circuit will not be performed, and safety will be reduced. Can be enhanced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration according to an embodiment of the present invention.

FIG. 2 is a flowchart for explaining the operation of a reset circuit 17;

FIG. 3 is a block diagram showing a circuit configuration of a conventional technique.

[Explanation of symbols]

 4 Inverter for output control 8 Shunt resistor for output current detection 13 Control circuit 14 Start switch 15 Overcurrent detection circuit 16 Latch circuit 17 Reset circuit

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-62-107867 (JP, A) JP-A-1-122322 (JP, A) JP-A-52-31942 (JP, A) JP-A-63-63 115680 (JP, A) JP-A-1-155410 (JP, A) JP-A 60-20362 (JP, U) JP-A 50-36167 (JP, Y1) (58) Fields investigated (Int. Cl. ⁶ , DB name) B23K 9/10 B23K 9/073

Claims (1)

(57) [Claims] An overcurrent detection circuit for detecting an output current of a welding power source and outputting an abnormality determination signal when the output current value is equal to or greater than a predetermined value and this state continues for a predetermined time or more; A latch circuit that operates by the control of the welding power supply, or the control signal of the welding power supply or the start signal from a separate start switch from the input power supply, the output of the welding power supply is controlled by turning on and off, and when an overcurrent is detected, the output of the latch circuit is used. A control circuit for stopping the output of the welding power source irrespective of whether the start signal is on or off and maintaining this state until the latch circuit is reset, the output overcurrent protection device for an arc welding power source, The state of the start signal after the predetermined pause time necessary for preventing overheating of the welding power source has been output since the output of the power supply is determined. An overcurrent protection device for an arc welding power supply, comprising: reset means for sending a reset signal to the latch circuit when the start signal changes from on to off if the start signal is on at that time.