JP3752947B2 - Control device and method for resistance welding machine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a resistance welding machine control apparatus and method.
[0002]
[Prior art]
Resistance welders are frequently used as spot welders, for example. Some resistance welding machines use an inverter circuit. A welding machine using an inverter circuit converts an alternating current from a commercial power source into a direct current by an AC-DC rectifier, and converts the direct current into an alternating current having a frequency higher than that of the commercial power source by a switching operation of the inverter circuit. Supplying to the primary side. On the secondary side of the welding transformer, alternating current is again converted into direct current by a rectifier and supplied to the electrode tip.
[0003]
In such a welder, for example, a demagnetization (magnetic saturation) may occur due to a residual magnetic hysteresis characteristic generated in an iron core of a welding transformer. When a magnetic demagnetization phenomenon occurs, the amount of current flowing through the welding transformer increases, so that the rated current of the inverter circuit on the primary side of the welding transformer may be exceeded, and the switching elements that constitute the inverter circuit are damaged. There is a fear.
[0004]
Conventionally, in order to prevent the inverter circuit from being damaged due to such a demagnetization phenomenon of the welding transformer, for example, in Japanese Patent Laid-Open Nos. 6-114569 and 8-308239, the current value on the primary side of the welding transformer is set. A technique is disclosed in which the inverter circuit is protected by detecting and stopping energization when this exceeds a certain value.
[0005]
[Problems to be solved by the invention]
However, the conventional technique basically stops energization when an overcurrent flows. For example, when welding a plurality of welding points in succession, the subsequent welding operation is not performed. In addition, in a production line that continuously welds workpieces at a time using a plurality of welding machines while continuously conveying workpieces, the line itself stops when one welding machine stops, and other manufacturing There was also a problem that said it affected the process.
[0006]
Accordingly, an object of the present invention is to provide a welding control apparatus and method capable of protecting an inverter circuit without stopping energization even when a demagnetization phenomenon occurs in a welding transformer.
[0007]
[Means for Solving the Problems]
The above object is achieved by the following means.
[0008]
(1) A resistance welding machine control device in which the alternating current output from the inverter circuit is supplied to the primary side of the welding transformer, wherein the current measuring means measures the current value on the primary side of the welding transformer; A storage means for storing a predetermined reference current value, and the frequency of the alternating current output from the inverter circuit when the current value measured by the current measurement means exceeds the reference current value; And a frequency changing means for changing the frequency of the inverter circuit to a frequency that is the same as that before the frequency change, and the ratio of the ON time of the inverter circuit in one cycle after the frequency change is high . .
[0009]
( 2 ) The reference current value stored in the storage means is characterized in that a plurality of values are set.
[0011]
( 3 ) A resistance welding machine control method in which the alternating current output from the inverter circuit is supplied to the primary side of the welding transformer, the step of measuring the current value on the primary side of the welding transformer, and the measurement When the set current value exceeds the preset reference current value, the frequency of the alternating current output from the inverter circuit is increased , and the on-time ratio of the inverter circuit within one cycle after the frequency change Changing the frequency to the same frequency as before the frequency change , and a control method for a resistance welder.
[0012]
( 4 ) The preset reference current value is characterized in that a plurality of values are set.
[0014]
【The invention's effect】
The present invention has the following effects for each claim.
[0015]
According to the first aspect of the present invention, when the current value measured by the current measuring means exceeds the reference current value stored in the storage means, the frequency is increased. When the primary side maximum current value rises and exceeds the reference current value, this can be suppressed and the total amount of current supplied can be kept the same as before the frequency change. For this reason, for example, even when a bias magnetism occurs in the welding transformer, damage to the inverter circuit can be prevented without stopping the welding operation. Therefore, in the case of continuously welding a plurality of welding points, the welding can be continued until the end of the plurality of welding points, and the welding is continuously performed at a time using a plurality of welding machines. Even in the production line, it is possible to prevent the line itself from being stopped due to the demagnetization phenomenon of one welding machine. Moreover, since the duty after the change is the same as that before the change, the total power supply amount does not change, so that there is no possibility of welding failure or the like due to the frequency change.
[0016]
According to the second aspect of the present invention, since a plurality of values are set for the reference current value stored in the storage means, it is possible to predict the occurrence of bias magnetization of the welding transformer step by step based on the plurality of reference current values. Is possible.
[0018]
According to the third aspect of the present invention, the frequency is increased when the primary maximum current value of the welding transformer exceeds a preset reference current value. When the maximum current value increases and exceeds the reference current value, this can be suppressed, and the total amount of current supplied can be kept the same as before the frequency change. For this reason, for example, even when a bias magnetism occurs in the welding transformer, damage to the inverter circuit can be prevented without stopping the welding current, and the welding operation can be continued as it is. Therefore, in the case of continuously welding a plurality of welding points, the welding can be continued until the end of the plurality of welding points, and the welding is continuously performed at a time using a plurality of welding machines. Even in the production line, it is possible to prevent the line itself from being stopped due to the demagnetization phenomenon of one welding machine. Moreover, since the duty after the change is the same as that before the change, the total power supply amount does not change, so that there is no possibility of welding failure or the like due to the frequency change.
[0019]
According to the fourth aspect of the present invention, since a plurality of values are set as the reference current value, it is possible to predict the occurrence of the demagnetization of the welding transformer step by step with the plurality of reference current values. .
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings.
[0022]
FIG. 1 is a block diagram showing a schematic configuration of a welding apparatus using a control device to which the present invention is applied, and FIG. 2 is a block diagram for explaining functions of the control device.
[0023]
The welding apparatus is roughly divided into a welding machine main body 1 that receives power supply from the power source 2 and supplies a high-voltage current to the welding transformer 6 and the welding gun electrode 7 to perform a welding operation itself, and a control device 10 that controls the welding machine. Become.
[0024]
The welding machine body 1 includes an AC-DC rectifier 3, a smoothing capacitor 4, and an inverter circuit 5. Further, a voltmeter 8 for measuring voltage is connected to the power source 2, and an ammeter 9 is connected to the output side of the inverter circuit 5 to measure the primary side current of the welding transformer 6. is doing. The measured values of the voltmeter 8 and the ammeter 9 are input to the control device 10.
[0025]
The control device 10 includes an A / D converter 11, a calculation device 20, and a storage device 30, and the calculation device 20 includes, as its functions, a primary current detection unit 21, an alarm level determination unit 22, a frequency calculation unit 23, And a PWM pulse output unit 24. Each unit in the arithmetic device 20 functions here by processing performed by the arithmetic device 20 executing a predetermined program, but may be individual hardware instead of the arithmetic device.
[0026]
In the storage device 30, an overcurrent alarm level 31 and a welding condition set value 32 are stored. The internal timer 41 outputs a reference signal for measuring time.
[0027]
Next, the operation will be described.
[0028]
In the welding machine body 1, alternating current (for example, 50 Hz or 60 Hz) supplied from the power source 2 is converted into direct current by the AC-DC rectifier 3, smoothed by the smoothing capacitor 4, and supplied to the inverter circuit 5. Here, the inverter circuit 5 converts the direct current into an alternating current having a high frequency under the control of the control device 10 described later, and supplies the alternating current to the welding transformer 6. In the welding transformer 6, the supplied alternating current is converted into a large current necessary for welding, further converted into direct current, and supplied to the electrode 7 at the tip of the welding gun.
[0029]
On the other hand, in the control device 10, the measurement value signal from the ammeter 9 is converted into a digital signal by the A / D converter 11 and input to the primary current detection unit 21 in the arithmetic device 20, and the current welding transformer 6 primary-side current values are detected. The detected current value is input to the alarm level determination unit 22. The alarm level determination unit 22 reads the overcurrent alarm level in the storage device 30 and compares it with the detected current value. When a current equal to or higher than a predetermined overcurrent alarm level flows, the alarm level determination unit 22 returns to the frequency calculation unit 23. Instruct to change frequency.
[0030]
The frequency calculation unit 23 reads the signal of the internal timer 41 and the welding condition set value 32, and the ratio of the ON time within one cycle after the frequency change (hereinafter referred to as duty) is the same as before the change. Is calculated and transmitted to the PWM pulse output unit 24.
[0031]
The PWM pulse output unit 24 generates a pulse based on the command value and outputs it to the inverter circuit 5. The inverter circuit 5 generates an alternating current by performing a switching operation according to this pulse.
[0032]
Here, the determination of the overcurrent in the alarm level determination unit 22 and the change of the frequency in the frequency calculation unit 23 based on the determination will be described in detail.
[0033]
FIG. 3 is a diagram showing a time change of the primary current absolute value, FIG. 3A shows a case where the frequency is changed by the control device, and FIG. 3B is an overcurrent without changing the frequency as in the prior art. The case where energization is stopped at the time of detecting is shown.
[0034]
First, the primary current of the welding transformer in which the demagnetization phenomenon has occurred gradually increases due to energization, as shown in FIG. 3A, for example. Therefore, in the case of an arbitrary pulse D1 (D1 indicates the pulse time, and the time of one cycle at this time is T1), even if the overcurrent alarm level is not exceeded, the next pulse Derr In addition, the overcurrent alarm level may be exceeded. In such a case, in the control device 10 of the present embodiment, the alarm level determination unit 22 determines that the current of Derr has exceeded the current alarm level, and instructs the frequency calculation unit 23 to change the frequency.
[0035]
In the frequency calculation unit 23, D1 / T1 which is the duty at the time of the pulse time D1, and D2 / T2 which is the duty after the frequency change (where D2 is the time of the pulse after the frequency change, T2 is the time of one cycle at that time) ) Is matched (D1 / T1 = D2 / T2).
[0036]
For this calculation, for example, as shown in the following equation (1), first, D2 is obtained by multiplying the pulse time Derr when the alarm level is reached by a predetermined constant const, and the duty at that time is before the change. By obtaining a period T2 that is the same as the above, the reciprocal thereof is obtained as the changed frequency f2.
[0037]
This is expressed by the following equation (2).
[0038]
D2 = Derr × const (1)
f2 = 1 / T2 = D1 / (T1 × Derr × const) (2)
However, D1 / T1 = D2 / T2.
[0039]
When the frequency is determined in this way, this frequency f2 and the time D2 of one pulse at that time are output to the PWM pulse output unit 24, and the PWM pulse output unit 24 outputs a pulse that becomes the switching timing of the inverter circuit 5. To do.
[0040]
Here, the constant const may be set to 0.9, for example, as a value that decreases by about 10% from the pulse width of Derr.
[0041]
As a result, as shown in FIG. 3A, after the frequency is changed, the time of one pulse D2 is shorter than that before the change, so that the current supply in that cycle is stopped before the overcurrent alarm level is reached. Since the duty after the change is the same as that before the change, the total power supply amount does not change, so that there is no possibility of welding failure or the like due to the frequency change.
[0042]
On the other hand, when such control is not performed, as shown in FIG. 3B, energization is stopped at the time when Derr is reached, and all subsequent operations are stopped.
[0043]
Further, for example, a plurality of overcurrent alarm levels may be provided in advance, and an optimal alarm level may be selected according to conditions unique to each welder.
[0044]
Next, the flow of operation by this control apparatus will be described with reference to the flowchart shown in FIG.
[0045]
First, when energization is started, a predetermined pulse is output from the PWM pulse output unit 24 (S1). The pulse output at this time is a pulse determined in advance based on the welding condition set value 32.
[0046]
Subsequently, it is determined whether or not the primary-side maximum current value of the welding transformer has exceeded the overcurrent alarm level (S2). Here, if the primary maximum current value does not exceed the overcurrent alarm level, it is determined whether or not energization is terminated (S3), and if energization is terminated, the process is terminated (energization is terminated). If the energization is not completed, the process returns to step S1 and the process is continued until the energization is terminated.
[0047]
On the other hand, when the primary maximum current value exceeds the overcurrent warning level in step S2, the pulse time when the overcurrent warning level is exceeded, that is, the Derr is calculated (S4). The calculation of Derr is performed based on the value of the internal timer 41.
[0048]
Subsequently, D2 is calculated based on Derr (S5). The changed frequency f2 is calculated from D1, T1, and Derr (S6).
[0049]
Then, the obtained D2 and f2 are set in the PWM pulse output unit 24 (S7), and the process returns to step S1. Thereafter, a pulse is output by the newly set D2 and f2 (S1), and the welding operation is continued.
[0050]
As described above, in the present embodiment, when an overcurrent is detected with the primary current of the welding transformer 6, the maximum current value is prevented from increasing further by changing the frequency. Therefore, the welding operation can be continued without stopping energization even when the magnetizing of the welding transformer occurs. Further, since the increase in the maximum current value is suppressed by changing the frequency, the duty within one cycle can be made to match before and after the frequency change, so the total power supply amount does not change. Therefore, even if the frequency is changed, welding failure does not occur.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a schematic configuration of a welding apparatus using a control device to which the present invention is applied.
FIG. 2 is a block diagram for explaining functions of the control device.
FIG. 3 is a drawing showing a time change of a current waveform on the primary side of a welding transformer.
FIG. 4 is a flowchart showing an operation procedure of the control device.
[Explanation of symbols]
2 Power supply 3 AC-DC rectifier 5 Inverter circuit 6 Welding transformer 7 Electrode 10 Control device 11 A / D converter 20 Arithmetic device 21 Primary current detection unit 22 Alarm level determination unit 23 Frequency calculation unit 24 PWM pulse output unit 30 Storage device 31 Overcurrent alarm level 32 Welding condition set value 41 Internal timer

Claims (4)

A control device for a resistance welding machine in which alternating current output from an inverter circuit is supplied to a primary side of a welding transformer,
Current measuring means for measuring a current value on a primary side of the welding transformer;
A storage means for storing a predetermined reference current value, and the frequency of the alternating current output from the inverter circuit when the current value measured by the current measurement means exceeds the reference current value; And a frequency changing means for changing the frequency of the inverter circuit to a frequency that is the same as that before the frequency change, and the ratio of the ON time of the inverter circuit in one cycle after the frequency change is high . .   2. The resistance welding machine control device according to claim 1, wherein a plurality of values are set as the reference current value stored in the storage means. A control method for a resistance welding machine in which alternating current output from an inverter circuit is supplied to a primary side of a welding transformer,
Measuring a current value on a primary side of the welding transformer;
When the measured current value exceeds a preset reference current value, the frequency of the alternating current output from the inverter circuit is increased , and the on-time of the inverter circuit within one cycle after the frequency change Changing the frequency to the same frequency as before the frequency change , and a control method for the resistance welder. The resistance welding machine control method according to claim 3 , wherein a plurality of values are set as the preset reference current value.

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