JPH0790387B2 - Inverter welding control method and device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a control method and a control device for performing welding such as seam welding in which intermittent energization is repeated in an inverter welding system.

[Prior Art] An inverter-type welding machine converts a constant DC voltage into a high-frequency AC pulse by an inverter circuit, passes the AC pulse through a welding transformer and a rectifier circuit, and welds a DC welding current obtained thereby. It is a welding machine that conducts resistance welding by pouring it into the material and has the feature that the welding transformer can be miniaturized.

Seam welding is welding in which seams or joints of metal plates are continuously joined by sewing, and is often used for processing liquid containers such as cans and tanks.

Conventionally, when seam welding is performed on a large number of works by an inverter welding machine, the waveform pattern of the AC pulse (that is, the primary current of the welding transformer) output from the inverter circuit is made the same and the energization to each work is repeated.

FIG. 4 shows an example of a waveform pattern by the conventional seam welding control. Energization time T that comes before and after the rest time ti
The waveform pattern (I1, I2, ... I6) of the inverter output pulse (welding transformer primary current) at i, Ti + 1 is the same.

[Problems to be Solved by the Invention] As described above, according to the conventional control method, the unit cycle (1
Cycle) and an integral multiple of the unit cycle (3 times in the example of FIG. 4) was defined as the energization time. Therefore, the number of pulses for each energization time was an even number (6 in the example of FIG. 4). Furthermore, each energization cycle Ti, Ti + 1, ...
The polarity of the first pulse I1 in FIG. 4 was the same (positive in the example of FIG. 4).

However, in the inverter type seam welding to which such a conventional control method is applied, a bias magnetism phenomenon often occurs in the welding transformer and the switching element in the inverter circuit is destroyed. The magnetic bias phenomenon is a phenomenon in which the welding transformer becomes magnetically saturated at either the positive or negative electrode (one side). In the case of seam welding, since the dwell time ti is relatively short, if the same pattern of current is repeated many times, the slight residual magnetization generated at each current application time gradually accumulates, resulting in a magnetic bias phenomenon. It's going to break.

FIG. 5 shows the waveform of the inverter output pulse when the magnetic bias phenomenon occurs. As shown in the figure, the peak value rises like a protrusion on one side (positive electrode). Under the conventional method, the polarity of the eccentricity phenomenon matches the polarity of the first pulse of the energization time.

The present invention has been made in view of the above problems, and provides a control method and apparatus for preventing an eccentricity phenomenon in a welding transformer in an inverter-type welding machine that performs intermittent energization such as seam welding. The purpose is to do.

[Means for Solving the Problems] In order to achieve the above-mentioned object, the inverter welding control method of the present invention provides an inverter resistance welding system in which energization is repeated with a relatively short down time, during each energization time. The number of AC pulses supplied from the inverter circuit to the primary coil of the welding transformer is set to an odd number, and the polarities of the first inverter output pulses of the energizing times preceding and following each other are reversed.

Further, in order to achieve the above object, the inverter welding control apparatus of the present invention sets an odd number of pulses for each energization time in an inverter resistance welding system in which energization is repeated with a relatively short down time. Means for setting the flag information indicating the polarity of the first or last pulse of the energization time for each energization time, and the odd pulse set value from the inverter circuit to the primary coil of the welding transformer during each energization time. Means for controlling the inverter circuit so as to supply an odd number of alternating current pulses, and the polarity of the first inverter output pulse of each energization time to the opposite polarity to that of the immediately preceding energization time based on the flag information. And means for doing so.

[Operation] In the present invention, one pulse for the positive electrode and one pulse for the negative electrode are grasped as a unit cycle, and the number of pulses given to the primary coil of the welding transformer from the inverter circuit during each energization time is set to an odd number, and they are in succession. Reverse the polarity of the first inverter output pulse during energization time. Therefore, when the first pulse of a certain energizing time is a positive pulse, the last pulse of the energizing time is a positive pulse, and in the next energizing time, it starts with a negative pulse and ends with a negative pulse.
In this way, by reversing the polarity of the pulse with each energization, even if intermittent energization is repeated many times with a relatively short rest time, the residual magnetization is re-energized for each of the positive and negative electrodes of the welding transformer. Is canceled, the magnetic flux does not accumulate in any polarity, and the magnetic bias phenomenon is prevented.

[Embodiment] An embodiment of the present invention will be described below with reference to FIGS. 1 to 3.

FIG. 1 shows the circuit configuration of an inverter welding system to which the control device according to this embodiment is applied.

In this system, four bridge-connected large capacity transistors (GTR) 10 to 16 constitute an inverter circuit. On the output side of this inverter circuit, the welding transformer
Rectifier circuit consisting of 18, diodes 20a, 20b, welding electrodes 22,2
4 is connected. The input terminals Na and Nb of the inverter circuit are connected to the output terminals of the rectifier 30, and a constant DC voltage Ec is applied.

The control unit of this embodiment includes drive circuits 40 to 46 for driving the GTRs 10 to 16 respectively, a CPU 48 that supplies inverter control signals Ca and Cb to those drive circuits, and a program and data necessary for the processing of the CPU 48, respectively. ROM50, RAM5 to store
2, and an interface (I / F) 54 for exchanging signals between the CPU 48 and an external device.

Prior to welding, a data input device (not shown) such as a keyboard via the I / F 54, the inverter frequency, energizing time,
The set values such as the rest time, the number of times of energization, and the current are input to the CPU 48 and stored in the RAM 52. The CPU 48 controls the switching operation of the GTRs 10 to 16 by applying the inverter control signals Ca and Cb according to the set values to the drive circuits 40 to 46.

These inverter control signals Ca and Cb are "H" level pulse signals having phases different from each other by 180 ° at a predetermined frequency. When the control signal Ca is "H", the GTR10, 16 are turned on and the inverter output terminals Ma, When a pulse current in the positive direction (positive polarity) flows from the Mb to the primary coil of the welding transformer 18 and the control signal Cb is "H", the GTR12 and 14 are turned on and the inverter output terminals Ma and Mb
As a result, a pulse current in the negative direction (negative polarity) flows through the primary coil of the welding transformer 18. In this way, the primary current IA of the AC pulse waveform is supplied to the welding transformer 18 from the inverter circuit. Then, the AC pulse generated on the secondary side of the welding transformer 18 is converted into DC by the rectifier circuits 20a and 20b, and the DC welding current I _W is passed through the welding electrodes 22 and 4 to be welded material 2
Supplied to 6,28.

Now, the number of pulses to be output from the inverter circuit during each energizing time is determined from each energizing time and the inverter frequency, but in this embodiment, it is set so that an odd number of pulses are always output. That is, the CPU 48 sets the value as the set value of the pulse number when the calculated value of the pulse number is odd, and has the odd value obtained by adding or subtracting 1 to the value when the calculated value of the pulse number is even. Use the pulse number setting value.
This pulse number set value is stored in the RAM 52. In addition, the CPU
The inverter 48 controls the inverter so that the polarities of the first pulses of the energizing times that are successive to each other are reversed. To perform this control, for example, at the end of each energization time, a flag indicating the polarity of the first or last pulse of the energization time is set in the register of the CPU 48 or the RAM 52.

Therefore, when the polarity of the first pulse in a certain energization time is positive, the number of pulses is an odd number, so that the energization time ends with a positive pulse, and the flag indicating the positive electrode is set.
Then, the next energization time is started by the pulse of the polarity (negative electrode) opposite to the polarity (positive electrode) of the flag.

FIG. 2 is a waveform pattern of the output pulse of the inverter circuit according to this embodiment, that is, the primary current I of the welding transformer 18.
The waveform pattern of A is shown. As shown in the figure, the number of pulses output at each successive energizing time Ti, Ti + 1 is an odd number (7 in this example), and the charge energizing time Ti, Ti
The polarity of the first pulse of +1 is opposite. In this way, the number of pulses supplied to the primary coil of the welding transformer during each energization time is set to an odd number, and the polarity of the first pulse is reversed at each energization time. Also, since the residual magnetization is canceled at each of the positive and negative electrodes of the welding transformer at each energization time, magnetic flux does not accumulate in either polarity, and as shown in FIG. Pulse waveform is maintained.

In this embodiment, a current sensor 56 is provided in the primary circuit of the welding transformer 18, and the primary current detection signal output from this sensor 56 is amplified by the amplification circuit 58 and then the A / D converter 6
At 0, it is converted into a digital signal and sent to the CPU 48. CPU48
Controls the primary current IA to match the set value by a feedback method based on the current detection data, and determines whether the number of pulses during each energization time is an odd number as set, or whether it is the first or last pulse. It is possible to confirm whether or not the polarity of the pulse is the desired polarity.

[Effect of the Invention] The present invention has the following effects by having the above-described steps or configurations.

According to the inverter welding control method of claim 1, the number of pulses given from the inverter circuit to the primary coil of the welding transformer during each energization time is set to an odd number, and the polarities of the first pulses of the energization times before and after are reversed. By doing so, the pulse pattern is reversed at each energization, and the residual magnetization of the welding transformer is canceled at each energization for both polarities.Therefore, as in seam welding, there are intermittent short intervals with a relatively short down time. Even if the energization is repeated many times, the magnetic flux does not accumulate in any polarity, and the magnetic bias phenomenon can be prevented.

According to the inverter welding control apparatus of claim 1, an odd number of pulses is set for each energization time, and flag information indicating the polarity of the first or last pulse of the energization time is set for each energization time. , During each energization time, the inverter circuit supplies an odd number of AC pulses corresponding to the pulse set value to the primary coil of the welding transistor, and based on the flag information, sets the polarity of the first inverter output pulse at each energization time. Since the polarity is set to be opposite to that of the immediately preceding energization time, the inverter welding control method of the present invention can be carried out to prevent the demagnetization phenomenon of the welding transformer.

[Brief description of drawings]

FIG. 1 is a block diagram showing the overall circuit configuration of an inverter welding system to which an embodiment of the present invention is applied, and FIG. 2 is a waveform of an inverter output pulse (welding transformer primary current waveform) pattern according to the embodiment. FIG. 3 is a waveform diagram showing an example, FIG. 3 is a waveform diagram showing a waveform of an inverter output pulse according to an embodiment in which a magnetic bias phenomenon does not occur, and FIG. 4 is a waveform of an inverter output pulse according to a conventional method (welding transformer primary current waveform). FIG. 5 is a waveform diagram showing an example of a pattern, and FIG. 5 is a waveform diagram showing a waveform of an inverter output pulse when a magnetic bias phenomenon occurs under the conventional method. 10 to 16 …… Large capacity transistor (GTR), 18 …… Welding transformer, 22,24 …… Welding electrode, 48 …… CPU, 50 …… ROM, 52 …… RAM, 54 …… Interface (I / F) .

Claims (2)

[Claims] 1. In an inverter resistance welding system in which energization is repeated with a relatively short dwell time, the number of AC pulses supplied from an inverter circuit to a primary coil of a welding transformer during each energization time is an odd number, and An inverter welding control method, characterized in that the polarities of the first inverter output pulses of successive energization times are reversed. 2. An inverter-type resistance welding system in which energization is repeated with a relatively short dwell time, means for setting an odd number of pulse machines for each energizing time, and the first or the energizing time of each energizing time. Means for setting flag information indicating the polarity of the last pulse; and the inverter circuit so as to supply an odd number of AC pulses corresponding to the odd pulse set value from the inverter circuit to the primary coil of the welding transformer during each energization time. And a means for controlling the polarity of the first inverter output pulse of each energizing time to be opposite to that of the immediately preceding energizing time based on the flag information. apparatus.