JPS61293686A - Welding current waveform control device for resistance welding machine - Google Patents

Abstract

PURPOSE:To increase the welding quality by setting the pulse width by the sequence circuit signal and by controlling the current waveform of driving circuit and the frequency in the inverter circuit having the power rectifying, smoothing and power inverting circuits for a resistance welding machine. CONSTITUTION:The waveform of the welding current of a sequence circuit 9 is set 11 by the ON, OFF of the welding current, the pressure and release of a welding gun 7, etc. for the detecting current 14 of the inverter circuit 1 having a power rectifying circuit 2, smoothing circuit 3 and power inverting circuit 4 and driven by a modulating pulse width 13 by controlling 12 the frequency thereof, The welding current is therefore controlled freely in the waveform corresponding to the welding purpose and the welding quality is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) The present invention relates to a welding current waveform control device for a resistance welding machine.

·· of · . As for welding current waveform control in conventional resistance welding machines,
For example, upslope or downslope control is performed when welding for a relatively long time using a spot welder. Amplifier slope control is performed to prevent dust and other defects that are likely to occur at the start of energization, and down slope control is performed to prevent cracking during cooling and other purposes. The supplied current value is controlled by controlling the phase of the power supply voltage or by controlling the slope time. In such control, the upslope or downslope control time is O~
It is about 10 cycles, usually about 0 to 5 cycles, and the minimum time during which the current value can be changed is only half a cycle of the commercial frequency, that is, 8.33 to 10 m5ec.

In addition, when welding is performed for a relatively short time using a capacitor spot welder, for example, the control of the supplied current value is as follows:
This is done by controlling the peak current value or by controlling the time to reach the peak current value. They are controlled by changing the power supply voltage supplied to the welding transformer or the turns ratio of the welding transformer, but the current waveform is limited to a sinusoidal transient characteristic.

As described above, in conventional resistance welding machines, it has not been possible to freely control the waveform of the welding current depending on the purpose of welding.

The present invention was made in view of the above-mentioned problems in the conventional resistance welding machine, and its purpose is to provide a resistance welding machine that allows the waveform of welding current to be freely controlled according to the purpose of welding. An object of the present invention is to provide a welding current waveform control device for a welding machine.

. In order to achieve the above object, the welding current waveform control device of the present invention applies to a resistance welding machine in which a forward conversion circuit, a smoothing circuit, and an inverse conversion circuit are provided in the primary power supply circuit of a welding transformer. The method includes means for setting the welding current energization time, means for setting the number of divisions by which the energization time is divided into a plurality of sections, and means for setting the current value for the divided section, and the set current value for each divided section. A welding current waveform setter that emits a signal corresponding to It is characterized by being added to the drive circuit that drives the conversion circuit.

For example, the rated capacity of a welding transformer is 20kVA.

FIG. 5 shows the relationship between the frequency of the voltage on the downstream side of the transformer and the welding current in an example of a welding machine whose pocket dimensions are 120 x 240 mm. In Figure 5, frequency =
The current at 300Hz is defined as 100%. In the figure,
DC is the welding current when a rectifier circuit is installed on the secondary side of the welding transformer to make it direct current, and AC is the welding current when the welding current is alternating current, as can be seen from the power frequency vs. welding current characteristics in Figure 5. As such, due to the welder's glue actance, if the frequency is changed during energization, the welding current value will change accordingly.

The welding current value also changes by changing the pulse width of the voltage applied to the primary side of the welding transformer.

As can be seen from the above, in a resistance welding machine, the welding current can be increased by changing the frequency of the voltage applied to the primary side of the welding transformer, or changing the pulse width of the applied voltage. In other words, changing the value allows changing the welding current waveform.

FIG. 4 is a diagram schematically illustrating control of the welding current waveform using the above-mentioned methods (1) and (2) in combination. In the figure, (a) shows the waveform of the obtained welding current, with time on the horizontal axis and welding current on the vertical axis.

(b) shows the waveform of the voltage applied to the next side of the welding transformer. To explain the diagram, the total energization time of welding current TO
is divided into three divided sections TI, T2, and T3, and the frequency f and pulse width W of the primary voltage in each divided section are constant, and each is shown in (b). In section T1, fl and W], in section T2, f2 and W2, and in section T3, f3 and W3. As is clear from (b), the relationship between the magnitudes of each frequency is fl > f3 > f2, and the magnitude of each pulse width is w2 > w3 > wl.

As can be seen from the graph in Figure 5, the smaller the frequency, the larger the welding current, so the welding current ll-
13 is 12 >I3 >I as shown in (a)
Becomes I. Therefore, by controlling the voltage applied to the welding transformer as shown in FIG. 4(b), it is possible to control the waveform of the welding current to be as shown in FIG. 4(a).

To simplify the explanation, the waveform of the welding current is shown as a simple one, but it goes without saying that the desired current waveform can be obtained by increasing the number of divided sections depending on the required current waveform. If the number of divisions is large and the divisions are fine, a welding current waveform that changes smoothly as a whole can be obtained. Furthermore, even if the number of divisions is small and the frequency or pulse width is continuously changed, a smooth waveform can be obtained.

Fruit-”1-Yuichi An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a block diagram of an embodiment of the present invention applied to a three-phase spot welding machine. In the figure, reference numeral 1 denotes a resistance welding machine, which is constructed in the same way as a normal inverter type. The high frequency output of the inverse conversion circuit 4 is applied to the primary side of the welding transformer 5. The applied voltage is reduced to a low voltage by a welding transformer 5,
The rectifier circuit 6 converts the current into direct current, which is then applied to the welding gun 7. A CT 15 is provided on the primary side of the welding transformer 5 to detect the magnitude of the current supplied to the welding transformer 5 and feed it back via the detection circuit 14. ON/OFF% of welding current, pressurization of welding gun 7,
Commands for normal sequence control such as opening are issued by the welding sequence circuit 9, and therefore, the welding sequence circuit 9 can set the welding current energization time.

The inverse conversion circuit 4 is composed of a switching transistor, a gate turn-off thyristor, etc., and is controlled by the output signal of the drive circuit 8. By controlling the output signal, the inverse conversion circuit 4 outputs a signal. The frequency and pulse width of the pulsed voltage can be controlled, and in other words, the waveform of the welding current can be controlled as described above.

10 is a welding current waveform control device, which includes a welding current waveform setting device 11, a frequency control circuit 12, and a pulse width modulation circuit 13.

The welding current waveform setting device 11 includes a waveform indicator 111 and a memory circuit 1 consisting of a temporary memory element that can be written and read.
12. A clock circuit 113 for specifying a read timing and a counter circuit 114 for selecting data to be read are provided.

The classification number representing the welding current waveform and the current value corresponding to the number are externally designated by writing to the temporary storage element, and output to the control system described later by reading. These classification numbers and current values are processed in correspondence with the address and data of the temporary storage element, respectively.

Waveform indicator 1 for external writing (waveform settings)
11 is provided with a switch that provides a section number (address), a current value (data), a write processing mode to the temporary storage element, and a switch that can select a minute time section. A clock circuit 113 and a counter circuit 114 output a data signal of the temporary storage element, which is a waveform control signal.

The clock circuit 113 specifies the timing of reading data from the temporary storage element, and the clock circuit 113 specifies the timing of reading data from the temporary storage element.
A signal is emitted at the time interval specified in 1.

The counter circuit 114 counts the signal from the clock circuit 113 and outputs the count value to the address of the temporary storage element of the storage circuit 112.

If the counter circuit 114 starts counting the signal emitted from the clock circuit 113 in response to the energization start signal from the welding sequence circuit 9 in which the welding current energization time is set, the counter circuit 114 can be stored sequentially at specified time intervals. You can specify the address of the element and output data. The energization time may be specified for the welding sequence circuit 9 by the waveform indicator 111. When a predetermined welding current application time has elapsed, a power count reset signal is sent from the welding sequence circuit 9 to the counter circuit 114.

The data output from the storage circuit 112 is sent to the frequency control circuit 12 composed of a D/A conversion circuit 121 and a V/F conversion oscillation circuit 122. Since the data sequentially read out from the memory circuit 112 is sent as a digital signal in bit format, this is first converted by the D/A conversion circuit 121 into an analog signal with a voltage value proportional to the welding current value set. . The circuit 121 further processes this signal to generate a signal with a voltage value corresponding to the welding current, and inputs the signal to the V/F conversion oscillation circuit 122. Further, this voltage value signal is also sent to the pulse width modulation circuit 13.

The V/F conversion oscillation circuit 122 is a circuit that oscillates a pulse signal with a frequency proportional to the voltage value of an input signal, and can be configured by, for example, a combination of a comparator and an integrator. Therefore, the frequency of the output signal of the V/F conversion oscillation circuit 122 is inversely proportional to the set welding current value. Note that if the pulse signal oscillated by the V/F conversion oscillation circuit 122 is a sawtooth wave or a triangular wave, pulse width modulation, which will be described later, can be performed relatively easily.

The pulse width conversion modulation circuit 13 is a circuit for controlling the pulse width of the primary side voltage of the welding transformer 5 in order to obtain a set welding current value, and as shown in FIG. The configuration may include an amplifier 131, a comparator 132, a flip-flop circuit 133, and AND circuits 134 and 135. The output of the detection circuit 14 connected to the CT 15 is input to the non-inverting input terminal of the feedback amplifier 131, and the output of the voltage proportional to the set current value from the D/A conversion circuit 121 is input to the inverting input terminal. .

The output of the V/F conversion oscillation circuit 122 is input to the non-inverting input terminal of the comparator 132, and the output of the feedback amplifier 131 is input to the inverting input terminal. V/F conversion oscillation circuit 1
The output of 22 is also sent to a flip-flop circuit 133.

The waveforms of each part ■ to ■ of the circuit 13 having such a configuration are
As shown in the figure. In the figure (■), the dotted line indicates the output voltage of the feedback amplifier 131, and shows the case where the value of the output voltage gradually decreases. As can be seen from the figure, V/
A pulse signal that is synchronized with the sawtooth waveform of the output of the F-conversion oscillation circuit 122 and has a pulse width corresponding to the output voltage of the D/A conversion circuit 121 is input to the drive circuit 8 . Drive circuit 8 drives inverse conversion circuit 4 based on this signal.

Therefore, the frequency and pulse width of the primary voltage of the welding transformer 5 correspond to the current value set by the setting device 111. Therefore, a welding current with a desired waveform is supplied to the welding gun 7.

It goes without saying that the present invention can be implemented in various forms by combining known electrical means in addition to the embodiments described above.

Light JF and Steel Frame As described above, the welding current waveform control device of the present invention makes it possible to freely control the welding current waveform in a resistance welding machine according to the purpose of welding. can improve the quality of

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an application example of an embodiment of the welding current waveform control device of the present invention, FIG. 2 is a circuit diagram of a pulse width modulation circuit used in the embodiment of FIG. 1, and FIG. FIG. 4 is an explanatory diagram of welding current waveform control, and FIG. 5 is a graph illustrating the relationship between frequency and welding current. In the figure, 1... resistance welding machine, 4... inverse conversion circuit, 8... drive circuit, 10... welding current waveform control device.

Claims (1)

[Claims] (1) In a resistance welding machine in which the primary power supply circuit of the welding transformer is equipped with a forward conversion circuit, a smoothing circuit, and an inverse conversion circuit, there is a means for setting the welding current energization time, and the number of divisions to be divided into multiple sections. a welding current waveform setter having means for setting, and means for setting the current value of the divided section and emitting a signal corresponding to the set current value of each divided section, and in response to the signal from the waveform setting device, Welding current waveform control for a resistance welding machine, comprising a pulse control circuit that changes at least one of the width and frequency of an output pulse, the output pulse being applied to a drive circuit that drives the inverse conversion circuit. Device.