JP4908766B2 - Engine-driven arc welding machine - Google Patents

Description

  The present invention relates to an engine-driven arc welder.

An arc welding machine for a TIG or a coated arc welding rod used mainly in the field uses an engine-driven generator so as not to select an installation location, and is required to be small and light. Thus, an engine-driven welding machine that includes a thyristor circuit that converts the AC output of the generator into a DC output and that is miniaturized by controlling the phase angle is disclosed (Patent Document 1).
By the way, when arcing during welding of TIG or coated arc welding rods, the arc length changes during normal welding, and when the arc voltage fluctuates or the cable is lengthened, the voltage drop due to the cable is added and the load state is changed. May increase. For this reason, if the engine output is designed to match the rated load during welding in order to reduce the size of the equipment, the engine becomes overloaded as the load increases due to fluctuations in the arc voltage, and the engine rotates. The speed may be greatly reduced or stopped.
Therefore, using the characteristic that the engine speed (rotation speed) decreases when the load on the generator increases and exceeds the maximum output of the engine, the engine speed or the frequency of the welding generator is detected and set in advance. A technique for avoiding an overload condition by suppressing an increase in welding output due to a difference from the reference frequency is disclosed (Patent Document 2).
Japanese Patent Laid-Open No. 3-128173 (FIG. 1) JP-A-7-80642 (Claim 1)

However, the technique of Patent Document 2 prevents an excessive decrease in engine rotation speed by suppressing an increase in welding output due to a difference from a preset reference frequency. Therefore, if output suppression is performed when the welding load increases, the engine rotation speed increases and output suppression stops. Thereby, since welding load increases again, output suppression is repeated. As a result, the welding output may pulsate up and down, making it impossible to perform good welding.
Therefore, an object of the present invention is to avoid the pulsation of the welding output current and perform good welding.

In order to solve the above problems, an engine-driven arc welder according to the present invention controls a welding output current by rectifying an AC output of a welding generator driven by the engine and an AC output of the welding generator into a DC output. An engine-driven arc welder comprising a control circuit, comprising: a frequency detection means for detecting the rotational speed of the engine or the frequency of the generator for welding, wherein the welding output current is greater than or equal to a reference value; When the value detected by the frequency detection means is less than a set value, the welding output current is suppressed so as not to exceed the current value adjusted by the welding current adjuster, while the engine is kept constant for the set value. Rotational speed control is performed.
According to said structure, the alternating current output of the welding generator driven by an engine is rectified into direct current output, and the controlled welding output current is supplied. If the engine rotational speed or the welding generator frequency is less than the set value, constant rotational speed control is performed with the set value as a target, and the welding output current is suppressed. The engine output increases as the rotational speed decreases. However, when the engine is overloaded, the engine output decreases, and the rotational speed gradually decreases at the maximum output rotational speed. That is, the suppression of the welding output current prevents the engine from being greatly decelerated or stopped. If constant rotational speed control is performed with the set value as a target, the change in the engine rotational speed is reduced, and good welding can be performed without the welding output current going up and down and pulsating. In particular, when welding is performed in the vicinity of the maximum output of the engine, the output fluctuation associated with the increase and decrease of the rotational speed is small.
Furthermore, even if a slow-down operation is performed in which the engine rotational speed is reduced during no-load operation that is not during welding, rotational speed suppression control is not performed. Thereby, a sufficient welding short-circuit current can be obtained even at the start of welding.

According to the present invention, it is possible to reduce the change in the engine rotation speed, so that not only the pulsation of the welding output current is avoided , but also a sufficient welding short-circuit current can be obtained at the start of welding during the slow-down operation. it can.

The configuration of an engine-driven arc welder as an embodiment of the present invention will be described with reference to FIG.
The engine-driven arc welder 100 of this embodiment is a control circuit that rectifies the AC output of the welding generator 2 driven by the engine 1 and the welding generator 2 to DC and phase-controls the welding output current. The thyristor circuit 3, the microcomputer 20, the zero cross detector 30, the thyristor gate driver 40, and the welding current adjuster 50 are the main parts, and the reactor 5, the current detector 9, and the commutation diode 4 are provided.

  Here, as shown in the engine output-engine rotational speed characteristic of FIG. 2A, the engine 1 has a lower engine rotational speed as the load (output) of the engine 1 increases than the no-load rotational speed a. Then, it passes through the rated output rotation speed b and reaches the maximum output rotation speed c. Furthermore, when the load is increased to an overload state, the engine speed decreases from the maximum output speed c and the engine output also decreases. Further, since the maximum output region in the vicinity of the maximum output rotation speed c is a boundary region where the output increases and decreases, the output fluctuation is small relative to the rotation speed fluctuation.

  The welding generator 2 is an AC generator driven by the engine 1 and has a drooping characteristic with a constant field magnetic flux having voltage-current characteristics as shown in FIG. Further, an AC generator having a constant voltage characteristic in which the field magnetic flux as shown in FIG. 2B and 2B, the vertical axis represents the output voltage e, and the horizontal axis represents the output current i.

  The AC output of this AC generator is rectified to DC, and the welding output current is controlled to output a drooping characteristic or constant current characteristic suitable for TIG or coated arc welding. FIG. 2 (c) shows the welding output power supply characteristic when the output of the AC generator with the power supply characteristic having the drooping characteristic is controlled to the constant current characteristic. Min and Max in the figure are the values when the welding output current is set to the minimum and maximum, and the solid line b in the figure only rectifies the output of the AC generator to DC, and the output characteristics when the current is not controlled It is. A broken line c in FIG. 2C is a voltage-current characteristic when the maximum output of the engine 1 is constant, and shows a constant power characteristic.

The thyristor circuit 3 is a mixed bridge circuit composed of three thyristors 3a, 3b, 3c and three diodes 3d, 3e, 3f. The thyristor circuit 3 rectifies the AC output of the welding generator 2 and sets the ignition timing. The DC output is increased or decreased by controlling.
Here, the configuration of the thyristor circuit 3 will be specifically described. The anode end of the thyristor 3a and the cathode end of the diode 3d are connected to the U phase of the welding generator 2, and the anode end of the thyristor 3b and the cathode end of the diode 3e are connected to the V phase. Are connected to the anode terminal of the thyristor 3c and the cathode terminal of the diode 3f. Each cathode terminal of each thyristor 3a, 3b, 3c is a positive output, and each anode terminal of each diode 3d, 3e, 3f is a negative output.

  The + side output converted into the DC output by the thyristor circuit 3 is connected to the cathode terminal of the commutation diode 4 and is connected to the output terminal (+) via the reactor 5. The negative output is connected to the anode end of the commutation diode 4 and is connected to the output terminal (−) via the current detector 9.

  The reactor 5 has functions for smoothing the output current of the thyristor circuit 3 and performing welding stably. The microcomputer 20 is for performing detection and control of each part.

  The zero cross detector 30 detects a zero potential of each line voltage of the welding generator 2 and is used to control the ignition timing of the thyristors 3a, 3b, 3c. The microcomputer 20 counts this zero potential falling or rising timing interval, whereby the power generation frequency of the welding generator 2 can be calculated.

  A specific circuit diagram is shown in FIG. 3A, and each phase, for example, the U phase of the welding generator 2 is connected to the anode end of the photodiode inside the photocoupler 11 via the resistor 12, and the cathode The end is connected to another phase of the welding generator 2 such as a V phase. The collector end of the phototransistor in the photocoupler 11 is pulled up to the power supply potential (+5 V) by the resistor 13, and the collector potential is monitored by the microcomputer 20.

  As a result, as shown in FIG. 3B, if the line voltage between the U phase and the V phase of the welding generator 2 is a positive potential, the collector potential becomes a LOW level, and if it is a negative potential, The collector potential goes high. The zero cross point is detected by this level change, and the microcomputer 20 calculates the power generation frequency. In addition, the same circuit is configured for both the V phase-W phase and the W phase-U phase, and the microcomputer 20 controls the phase of the thyristor of each phase.

  The thyristor gate drive unit 40 supplies a gate trigger current necessary for the thyristors 3a, 3b, and 3c, and is driven by the microcomputer 20.

  The welding current adjuster 50 is a variable resistor for adjusting to a current suitable for welding work, and is adjusted (set) between the maximum value Max and the minimum value Min.

  The current detector 9 detects the welding output current flowing through the load using a shunt resistor or a current transformer, and transmits the signal to the microcomputer 20. Further, the microcomputer 20 detects the adjustment value adjusted by the welding current adjuster 50, and the microcomputer 20 performs constant current control of the welding output current in accordance with the adjustment value.

  The engine-driven arc welder 100 of the present embodiment is configured by the above components, and welding work is performed using the space between the output terminal (+) and the output terminal (−).

  Next, the operation of the engine-driven arc welder 100 will be described with reference to FIG. The welding generator 2 is driven by the engine 1, and the welding generator 2 outputs a three-phase alternating current. The three-phase AC output is converted into a DC output by the thyristor circuit 3. Further, if the rotational speed is controlled to be slightly lower than the engine rated load rotational speed, it can be controlled in the vicinity of the engine maximum output.

  When the welding operation is started between the output terminals (+) and (−), the phase is controlled so that the current detected by the current detector 9 becomes the current value adjusted by the welding current adjuster 50, and the constant current Welding work is performed. Then, in an overload state in which the engine rotation speed is reduced to a rotation speed equal to or lower than a predetermined set value, the welding output current is suppressed so that the engine rotation speed is set to a constant rotation speed. Further, when the welding current adjuster 50 is adjusted to a reference value or more and the welding output current is detected by the current detection unit 9, this current suppression is performed.

  Here, a method of suppressing the welding output current when the engine 1 is overloaded from the normal welding output state will be described with reference to the flowchart of FIG.

  In step SP10, it is determined whether or not the adjustment value of the welding current adjuster 50 is greater than or equal to a reference value. If it is equal to or greater than the reference value, it is determined as “YES”, and the process proceeds to step SP20 to determine whether or not the welding output current flowing through the load is detected. In step SP20, if the welding output current is not detected, it is determined as “NO”. If it is determined that either step SP10 or SP20 is “NO”, the process proceeds to step SP50 where constant current control is performed so that the target current adjusted by the welding current adjuster 50 is obtained by phase control of the thyristor, Return to the routine.

  On the other hand, if “YES” is determined in step SP20, the process proceeds to step SP30, and it is determined whether or not the frequency of the zero cross detection unit 30 is less than the set value. Here, if the arc length increases during welding or the voltage drop due to the welding cable increases, the frequency becomes less than the set value, and “YES” is determined, and the process proceeds to step SP40. In step SP40, a certain amount is reduced from the target current adjusted by the welding current adjuster 50. As long as the condition up to step SP40 is continued, the decreased target current value continues to decrease by a certain amount in a stepwise manner. And a process progresses to step SP50 and welding output current is suppressed so that it may become target current. As a result, the engine load is suppressed, and the engine speed is restored to the set value.

On the other hand, if “NO” is determined in step SP30, the process proceeds to step SP60, where the adjustment value of the welding current adjuster 50 is set to the maximum value, and the target current value is increased by a certain amount to obtain the target current. That is, the value decreased by a certain amount stepwise in step SP40 is increased again. If that is continued determination of "NO", the target current is increased stepwise to a maximum adjustment value set in the welding current regulator 50. If step SP60 is executed before executing step SP40, the adjustment value is set and no increase is made.

  However, in an actual welding machine, constant rotation speed control is performed so that step SP30 balances with the value set by repeating the determination of “YES” and “NO”. Thereby, favorable welding can be performed without the welding output current pulsating up and down. When the welding output voltage further increases and the load increases, a constant output operation, that is, a constant power operation is performed by constant rotation speed control, and the output of the welding machine moves on the broken line c in FIG. It will be.

  FIG. 2D shows the welding output characteristics when the welding current adjuster 50 is adjusted to the maximum value Max and the welding voltage changes during welding. A dash-dot line passing through the point a in FIG. 2D represents a welding resistance line (a line having a characteristic of E = 20 + 0.04I where E is a welding voltage and I is a welding output current). When the arc length is extended during welding at the point a in the figure, the welding voltage rises and reaches the point b, the engine speed decreases and the suppression of the output current starts. When the arc length is further increased and the welding voltage E is increased, the welding output current is further reduced by constant rotation speed control (constant power control), and is balanced at the point c. However, microscopically, the engine speed is slightly increased and decreased and the welding output current I is also slightly increased and decreased, but the current does not change so as to affect the weld bead and no pulsation is felt.

  As described above, according to the present embodiment, when the welding output current is equal to or higher than the reference value and the engine rotation speed decreases to near the maximum output during welding, the welding output current is suppressed and constant rotation speed control is performed. Is called. Thereby, it is avoided that the engine rotational speed is greatly decelerated or stopped. Further, good welding can be performed without the welding output current pulsating up and down.

  Further, by controlling to the maximum output rotational speed, the output of the engine and the generator can be utilized to the maximum. In addition, even if there is a slight decrease in output due to weather conditions where the engine output decreases and the use of the engine for many years, the maximum engine output at that time can be used effectively, and the engine does not decelerate or stop significantly.

  Furthermore, according to the configuration in which the constant rotation speed control is performed when the welding output current is equal to or higher than the reference value, the welding output current is not suppressed in the case of slowdown that reduces the rotation speed during no-load operation that is not during welding. A sufficient short-circuit current can be obtained at the start. In addition, it is possible to smoothly start the arc from the slowdown, and furthermore, since unnecessary suppression is not performed in the welding output current region where the constant rotation speed control does not operate, it is determined whether or not the engine is malfunctioning. Can do.

(Modification)
The present invention is not limited to the above-described embodiments, and various modifications can be made as follows, for example.
In the above embodiment, an AC generator having a drooping power supply characteristic is used. However, constant current control can also be performed by thyristor phase control using an AC generator having a constant voltage characteristic that does not have a drooping characteristic. In the above embodiment, the current detection unit 9 is provided in order to make the welding output current have a constant current characteristic. However, if the welding voltage can be detected, it can be determined that welding is in progress, and the drooping characteristic can be obtained by adjusting the phase control angle to a constant value according to the welding current adjuster 50. The detection unit 9 is not necessary. In this case, the function of step SP10 that performs the suppression control only when the welding output current is equal to or greater than the reference value is that the voltage value in the welding state is detected when the value of the welding current adjuster 50 is set to be equal to or greater than the reference value. If it is detected that the engine has fallen to the set rotational speed, the same control can be performed by increasing or decreasing the arbitrarily fixed phase control angle. Of course, the present invention can also be applied to a circuit that detects and controls both the welding output current and the welding voltage.

  Further, although the above embodiment uses a phase control circuit including a thyristor, it can also be configured by a chopper control circuit or an inverter control circuit using a self-extinguishing element such as an IGBT, and the engine rotational speed or power generation The target effect can be obtained by providing a circuit for detecting the machine frequency. In the above embodiment, each phase of the three-phase output of the welding generator is rectified and switched by a mixed bridge circuit to obtain a three-phase full-wave rectified waveform, but a pure bridge circuit is configured using six thyristors. May be. In the above embodiment, the condition is that the adjustment value adjusted by the welding current adjuster 50 is greater than or equal to the reference value. However, it is also conceivable that the condition is when the welding current detection unit 9 detects more than the reference value. .

It is a lineblock diagram of the engine drive arc welding machine which is one embodiment of the present invention. The figure (a) which shows the relationship between engine speed and engine output, the figure (b) (b ') which shows the voltage-current characteristic of the generator in normal time, the welding output voltage-current characteristic (c), and the welding current value to Max This is the welding output characteristic (d) when the welding voltage is changed when welding is performed. It is a figure which shows the circuit diagram of a zero cross detection part, and its operation | movement. It is a flowchart which sets a thyristor ignition timing.

Explanation of symbols

1 Engine 2 Welding generator 3 Thyristor circuit (control circuit)
3a, 3b, 3c Thyristors 3d, 3e, 3f Diode 4 Commutation diode 5 Reactor 9 Current detection unit 20 Microcomputer 30 Zero cross detection unit 40 Thyristor gate drive unit 50 Welding current regulator 100 Engine drive arc welder

Claims (1)

An engine-driven arc welder comprising a welding generator driven by an engine, and a control circuit that rectifies the AC output of the welding generator into a DC output and controls the welding output current,
Comprising a frequency detection means for detecting the rotational speed of the engine or the frequency of the welding generator;
When the welding output current is greater than or equal to a reference value and the value detected by the frequency detection means is less than a set value, the welding output current is suppressed so as not to exceed the current value adjusted by the welding current adjuster. However, an engine-driven arc welding machine that performs constant rotation speed control of the engine with the set value as a target.

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