JP2001239373A - Controller for resistance welding machine and its method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a controller for a resistance welding machine and its control method capable of protecting an inverter circuit without interception of current even when an anhysteretic phenomenon arises in a welding transformer. SOLUTION: The controller 10 of a resistance welding machine in which alternating current output from an inverter circuit is supplied to the primary side of a welding transformer 6, is provided with an ammeter 9 measuring a current of the primary side of the welding transformer, a frequency calculator 23 changing the frequency of the alternating current output from the inverter circuit 5 in accordance with the measured current.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for a resistance welding machine and a method thereof.

[0002]

2. Description of the Related Art Resistance welding machines are widely used, for example, as spot welding machines. Some resistance welding machines use an inverter circuit. A welding machine using an inverter circuit converts an alternating current from a commercial power supply into a direct current by an AC-DC rectifier, and converts the direct current into an alternating current having a frequency higher than the frequency of the commercial power supply by a switching operation of the inverter circuit, thereby forming a welding transformer. Supplying to the primary side. Then, on the secondary side of the welding transformer, the rectifier converts the alternating current into direct current again and supplies it to the electrode tip.

In such a welding machine, for example, magnetic bias (magnetic saturation) may occur due to hysteresis characteristics of residual magnetism generated in an iron core of a welding transformer. When the magnetizing phenomenon occurs, the amount of current flowing through the welding transformer increases,
The current may exceed the rated current of the inverter circuit on the primary side of the welding transformer, and the switching elements and the like constituting the inverter circuit may be damaged.

Conventionally, in order to prevent the inverter circuit from being damaged due to the magnetic polarization phenomenon of the welding transformer, for example, Japanese Patent Application Laid-Open Nos. 6-114569 and 8-30823.
Japanese Patent Application Laid-Open No. 9-29139 discloses a technique for detecting a current value on the primary side of a welding transformer and, when the current value exceeds a certain value, stopping the energization to protect the inverter circuit.

[0005]

However, in the prior art, the current supply is basically stopped when an overcurrent flows. For example, when a plurality of welding points are continuously welded, In a production line where the subsequent welding operation is not performed or the welding is continuously performed at once using a plurality of welding machines while continuously transferring the work, the line is stopped by stopping one welding machine. There was also a problem that it stopped and affected other manufacturing processes.

Accordingly, an object of the present invention is to provide a welding transformer which does not stop energization even when a magnetic polarization phenomenon occurs.
An object of the present invention is to provide a welding control device and a method thereof capable of protecting an inverter circuit.

[0007]

The above object is achieved by the following means.

(1) 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, and a current measurement for measuring a current value on a primary side of the welding transformer. Means, frequency changing means for changing the frequency of the alternating current output from the inverter circuit, according to the current value measured by the current measuring means,
A control device for a resistance welding machine, comprising:

(2) The frequency changing means has a storage means for storing a predetermined reference current value, and the current value measured by the current measuring means is used as a reference current value stored in the storage means. When the frequency is exceeded, the frequency is increased.

(3) A plurality of values are set as the reference current value stored in the storage means.

(4) A method for controlling a resistance welding machine in which alternating current output from an inverter circuit is supplied to a primary side of a welding transformer, wherein a current value on a primary side of the welding transformer is measured. Changing the frequency of the alternating current output from the inverter circuit according to the measured current value.

(5) The step of changing the frequency of the alternating current output from the inverter circuit includes increasing the frequency when the measured current value exceeds a preset reference current value. Features.

(6) The preset reference current value is:
It is characterized in that a plurality of values are set.

[0014]

The present invention has the following effects for each claim.

According to the first aspect of the present invention, according to the primary current value of the welding transformer measured by the current measuring means,
Since the frequency changing means changes the frequency of the AC output from the inverter circuit, when the primary maximum current value of the welding transformer changes, the frequency is changed accordingly, thereby increasing the maximum current value. And the total amount of current supplied can be kept the same as before the frequency change. For this reason, for example, even when the welding transformer is demagnetized, it is possible to prevent the inverter circuit from being damaged without stopping the welding operation. Therefore, when a plurality of welding points are continuously welded, welding can be continuously performed to a plurality of welding points to the end, and welding can be continuously performed at once using a plurality of welding machines. Even in a production line, it is possible to prevent the line itself from being stopped due to the magnetic demagnetization phenomenon of one welding machine.

According to the second aspect of the present invention, the frequency changing means is provided with a storage means for storing a predetermined reference current value, and the current value measured by the current measuring means is stored in the storage means. When the reference current value exceeds the reference current value, the frequency is increased. When the primary maximum current value of the welding transformer rises and exceeds the reference current value, this is suppressed and supplied. The total amount of current can be kept the same as before the frequency change.

According to the third aspect of the present invention, a plurality of values are set for the reference current value stored in the storage means. It can be predicted.

According to the present invention, the frequency of the alternating current output from the inverter circuit is changed according to the primary maximum current value of the welding transformer. By changing the frequency in response to a change in the maximum current value, it is possible to suppress an increase in the current value and to maintain the total amount of current supplied as before the frequency change. For this reason, even if, for example, a magnetic bias 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, when a plurality of welding points are continuously welded, welding can be continuously performed to a plurality of welding points to the end, and welding can be continuously performed at once using a plurality of welding machines. Even in a production line, it is possible to prevent the line itself from being stopped due to the magnetic demagnetization phenomenon of one welding machine.

According to the fifth aspect of the present invention, when the primary maximum current value of the welding transformer exceeds a predetermined reference current value, the frequency is increased.
When the primary maximum current value of the welding transformer rises and exceeds the reference current value, this can be suppressed and the total amount of supplied current can be kept the same as before the frequency change.

According to the present invention, since a plurality of values are set as the reference current value, it is possible to predict the occurrence of the magnetic bias of the welding transformer step by step based on the plurality of reference current values. It becomes possible.

[0021]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.
An embodiment of the present invention will be described.

FIG. 1 is a block diagram showing a schematic configuration of a welding device using a control device to which the present invention is applied.
FIG. 3 is a block diagram for explaining functions of the control device.

The welding apparatus is roughly divided into a welding machine main body 1 which receives power supplied from a power source 2 and supplies a high voltage current to a welding transformer 6 and a welding gun electrode 7 to perform a welding operation itself, and a control for controlling the welding operation. It comprises the device 10.

The welding machine body 1 comprises an AC-DC rectifier 3, a smoothing capacitor 4, and an inverter circuit 5. A voltmeter 8 for measuring voltage is connected to the power supply 2, and an ammeter 9 is connected to the output side of the inverter circuit 5 to measure the primary current of the welding transformer 6. are doing. The measurement values of the voltmeter 8 and the ammeter 9 are input to the control device 10.

The control device 10 comprises an A / D converter 11, an arithmetic device 20, and a storage device 30.
As its function, it comprises a primary current detection unit 21, an alarm level determination unit 22, a frequency calculation unit 23, and a PWM pulse output unit 24. Note that each unit in the arithmetic device 20 functions by processing performed by the arithmetic device 20 executing a predetermined program, but may be individual hardware instead of the arithmetic device.

In the storage device 30, the overcurrent alarm level 3
1 and a welding condition set value 32 are stored. Also,
The internal timer 41 outputs a reference signal for measuring time.

Next, the operation will be described.

An alternating current (for example, 50 Hz or 60 Hz) supplied from a power source 2 is supplied to the welding machine body 1 by an AC-DC.
It is converted to DC by the rectifier 3, smoothed by the smoothing capacitor 4, and supplied to the inverter circuit 5. Here, the inverter circuit 5 converts DC into AC having a high frequency under the control of the control device 10 described later, and supplies the AC to the welding transformer 6. In the welding transformer 6, the supplied AC is converted into a large current necessary for welding, and further converted into DC and supplied to the electrode 7 at the tip of the welding gun.

On the other hand, in the control device 10, the measured value signal from the ammeter 9 is converted into a digital signal by the A / D converter 11, input to the primary current detection unit 21 in the arithmetic device 20, and The primary current value of the welding transformer 6 is 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 the predetermined overcurrent alarm level flows, the alarm level determination unit 22 Instructs to change the frequency.

The frequency calculating section 23 reads the signal of the internal timer 41 and the welding condition set value 32, and changes the ratio of the ON time within one cycle after the frequency change (hereinafter, referred to as duty (Duty)). A frequency that is the same as before is calculated and transmitted to the PWM pulse output unit 24.

The PWM pulse output section 24 generates a pulse based on the command value and outputs the pulse to the inverter circuit 5. The inverter circuit 5 generates an AC by performing a switching operation according to the pulse.

Here, the determination of the overcurrent in the alarm level determination section 22 and the change of the frequency in the frequency calculation section 23 based on the determination will be described in detail.

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. FIG. Shows a case where the energization is stopped when an overcurrent is detected.

First, the primary current of the welding transformer in which the magnetic demagnetization phenomenon has occurred gradually rises by energization, for example, as shown in FIG. 3A. Therefore, any pulse D1 (D1
Indicates the time of the pulse, and the time of one cycle at this time is T1
), The overcurrent alarm level may be exceeded at the next pulse Derr even if the overcurrent alarm level has not been exceeded. In such a case, in the control device 10 of the present embodiment, the alarm level determination unit 22
It is determined that the current of err has exceeded the current alarm level, and the frequency calculator 23 is instructed to change the frequency.

The frequency calculator 23 calculates the duty ratio D1 / T1 for the pulse time D1 and the duty ratio D2 / T2 after the frequency change (where D2 is the time of the pulse after the frequency change, and T2 is 1 at that time). The frequency is calculated such that the period time is the same (D1 / T1 = D2 / T2).

In 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 obtained. Is determined to be the same as before the change, and the reciprocal thereof is obtained as the frequency f2 after the change.

This can be expressed by the following equation (2).

D2 = Derr × const (1) f2 = 1 / T2 = D1 / (T1 × Derr × const) (2) where D1 / T1 = D2 / T2.

When the frequency is determined in this manner, the 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
Output a pulse that becomes the switching timing of the inverter circuit 5.

Here, the constant const is, for example, Der
0.9 may be set as a value that is about 10% smaller than the pulse width of r.

As a result, as shown in FIG. 3A, after the frequency is changed, the time of one pulse D2 is shorter than before the change, so that the supply of current in that cycle is stopped before reaching the overcurrent alarm level. Since the duty after the change is the same as that before the change, the total power supply amount does not change. Therefore, there is no possibility that a welding failure or the like is caused by the frequency change.

On the other hand, when such control is not performed,
As shown in FIG. 3B, the power supply is stopped at the time when Derr is reached, and all subsequent operations are stopped.

Further, for example, a plurality of overcurrent alarm levels may be provided in advance, and an optimum alarm level may be selected in accordance with conditions unique to each welder.

Next, the flow of the operation of the control device will be described with reference to the flowchart shown in FIG.

First, a predetermined pulse is output from the PWM pulse output unit 24 at the same time as the energization is started (S1). The pulse output at this time is a pulse previously determined based on the welding condition set value 32.

Subsequently, it is determined whether or not the primary maximum current value of the welding transformer has exceeded an overcurrent alarm level (S).
2). Here, if the primary-side maximum current value does not exceed the overcurrent alarm level, it is determined whether or not the energization has ended (S3).
If the energization has been completed, the process ends (the energization ends). If the energization has not ended, the process returns to step S1, and the processing is continued until the energization ends.

On the other hand, if the primary-side maximum current value exceeds the overcurrent warning level in step S2, the pulse time at which 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.

Subsequently, D2 is calculated based on Derr (S5). The frequency f2 after the change is calculated from D1, T1, and Derr (S6).

Then, the obtained D2 and f2 are converted to PW
Set to the M pulse output unit 24 (S7), step S1
Return to Thereafter, in the process, a pulse is output by the newly set D2 and f2 (S1), and the welding operation is continued.

As described above, in the present embodiment,
When an overcurrent is detected by the primary current of the welding transformer 6,
By changing the frequency, the maximum current value is prevented from further increasing. Therefore, even when the welding transformer is demagnetized, the welding operation can be continued without stopping the energization. Further, since the increase in the maximum current value is suppressed by changing the frequency, the duty within one cycle can be matched before and after the frequency change, so that 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 device 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 a 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 unit 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 (6)

[Claims] 1. 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, wherein current measuring means for measuring a current value on a primary side of the welding transformer. And a frequency changing means for changing the frequency of the alternating current output from the inverter circuit in accordance with the current value measured by the current measuring means. 2. The frequency changing means has a storage means for storing a predetermined reference current value, wherein the current value measured by the current measuring means exceeds the reference current value stored in the storage means. 2. The control device for a resistance welding machine according to claim 1, wherein the frequency is increased when the control signal is applied. 3. The control device for a resistance welding machine according to claim 2, wherein a plurality of values are set as the reference current value stored in said storage means. 4. A method for controlling a resistance welding machine in which alternating current output from an inverter circuit is supplied to a primary side of a welding transformer, comprising: measuring a current value on a primary side of the welding transformer; Changing the frequency of the alternating current output from the inverter circuit according to the measured current value. 5. The method according to claim 1, wherein changing the frequency of the alternating current output from the inverter circuit increases the frequency when the measured current value exceeds a preset reference current value. The method for controlling a resistance welding machine according to claim 4, wherein 6. The control method for a resistance welding machine according to claim 5, wherein a plurality of values are set as the preset reference current value.