JPH0985458A - Inverter controlled resistance welding machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain improved welding quality by accurately synchronizing energizing timing among plural power source devices for inverter controlled resistance welding and thereby flowing a set welding current in a material to be welded. SOLUTION: A plurality, for example two units, of power source devices 10, 12 for inverter controlled resistance welding are parallelly connected to welding electrodes 14, 16. Both power source devices 10, 12 are separately provided with a three-phase rectifier circuit 18A, 18B, inverter 20A, 20B, welding transformer 22A, 22B, rectifier circuit 24A, 24B and current sensor 26A, 26B, and also commonly provided with a CPU 28 and an amperometry circuit 30. A feedback type constant current control means is constituted of the current sensor 26A, 26B, ampere metry circuit 30, A/D converter 46, CPU 28 and a driving circuit 36A, 36B.

Description

Detailed Description of the Invention

[0010]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter type resistance welding machine having a plurality of inverter type resistance welding power sources.

[0020]

2. Description of the Related Art In an inverter type resistance welding machine, a plurality of inverter type resistance welding power supply devices are connected in parallel to the same welding electrode in order to increase welding capacity or current capacity.
Conventionally, a method is used in which a current obtained by combining the currents output from the respective power supply devices is supplied as a welding current to the material to be welded through the welding electrode.

FIG. 2 shows the configuration of a conventional inverter type resistance welding machine of this type. In this resistance welding machine, two inverter type resistance welding power supply devices 100 and 102 are connected to a welding electrode 10
4 and 106 are connected in parallel.

Each of the power supply devices 100 and 102 has three
Phase rectifier circuits 108A, 108B, inverter 110A,
110B, welding transformers 112A and 112B, rectification circuits 114A and 114B, control circuits 116A and 116B, current detection circuits 118A and 118B, and the like.

Each of the three-phase rectifier circuits 108A and 108B rectifies a commercial three-phase AC voltage (U, V, W) and converts it into a DC voltage. Each of the inverters 110A, 110B has a three-phase rectifying circuit 108A, 1 according to energization control pulses CPA, CPB supplied from each control circuit 116A, 116B.
The high frequency AC pulse is output by chopping the direct current from 08B by the high frequency switching. The AC pulse output from each inverter 110A, 110B is supplied to the primary side coil of each welding transformer 112A, 112B, and an AC pulse similar to the primary side is obtained on each secondary side. This secondary side AC pulse is applied to each rectification circuit 114A,
Converted to direct current by 114B. Then, the DC currents IA and I output from the rectifier circuits 114A and 114B, respectively.
The welding current IW obtained by combining B is the welding electrodes 104, 106.
Through the welded material 120, 122, the welded material 12
0, 122 are joined by resistance welding.

In each of the power supply devices 100 and 102, pulse width modulation (feedback control is applied to the pulse widths of the energization control pulses CPA and CPB so that a constant welding current IW is supplied to the materials 120 and 122 to be welded during the energization time. PWM) constant current control means is provided.

For this constant current control, for example, each inverter 110A, 110B and each welding transformer 112A,
Current sensors 124A, 12 on the primary conductor between
4B is attached. Each current measuring circuit 118A,
118B calculates | requires the electric current value of a primary electric current based on the output signal from each current sensor 124A, 124B. The control units 116A and 116B have the current measuring circuits 118A and 11B, respectively.
The current measurement value from 8B is compared with a reference value (set current value), and the energization control pulse C having a pulse width corresponding to the comparison error is compared.
PA and CPB are generated, and the energization control pulses CPA and C are generated.
PB controls the switching operation of each of the inverters 110A and 110B. That is, the energization control pulse CPA, for each one cycle or each half cycle of the inverter frequency,
Each inverter 11 for a time corresponding to the pulse width of CPB
The switching elements in 0A and 110B are turned on.

A signal ST for instructing the start of welding energization is input to each control circuit 116A, 116B from an external device such as a robot controller via an interface circuit (not shown).

[0090]

In the inverter type resistance welding machine having the plurality of inverter type resistance welding power supply devices 100 and 102 as described above, the respective control circuits 11 are provided.
6A and 116B operate with the clock having the same frequency in response to the same energization start signal ST, ideally, as shown in FIG. 3A, the inverters 110A and 110B in the respective power supply devices 100 and 102 The AC pulses IVA and IVB should be output at the same timing. However, in reality, due to variations in circuit constants or signal propagation delay times in the control circuits 116A and 116B of the power supply devices 100 and 102 and the interface circuits around them, the respective inverters 110A and 110B are different.
The output pulses IVA and IVB of the above-mentioned output have a time lag.
In particular, when constant current control is performed, each power supply device 10
Since the constant current control function works separately for 0 and 102, the pulse widths of the respective energization control pulses CPA and CPB are different, so that an additional energization timing is likely to occur.

As shown in FIG. 3B, such a time difference td between the inverter output pulses IVA and IVB.
As a result, the pulse shape of the synthetic pulse IVC is deformed in the direction in which the portion near the peak value decreases and the skirt portion increases accordingly. Although the current integration amount of the welding current IW per unit cycle does not change due to such a pulse shape deformation, the energy near the current peak value decreases. For this reason, even if the currents IA and IB are flowing in the respective power supply devices 100 and 102 by the PWM control of the feedback system, the maximum value or the effective value of the DC welding current IW that actually flows in the workpieces 120 and 122. The value becomes lower than the set value, which causes deterioration of welding quality.

The combined pulses IVC and IVC in (a) and (b) of FIG. 3 are virtual combined inverter output pulses for indicating the total inverter output (combined value) for each unit cycle. It does not actually appear in the device 100, 102.

The present invention has been made in view of the above problems of the prior art, and accurately synchronizes the energization timing among a plurality of inverter type resistance welding power source devices, and supplies the welding current as set to the material to be welded. It is a first object of the present invention to provide an inverter-type resistance welding machine capable of obtaining excellent welding quality.

Further, the present invention is an inverter type in which a plurality of inverter type resistance welding power supply devices perform appropriate constant current control so that a welding current as set is flown in a material to be welded to obtain good welding quality. A second object is to provide a resistance welding machine.

[0140]

In order to achieve the above object, the inverter resistance welding machine according to the first aspect of the present invention is configured such that the output terminals of a plurality of inverter resistance welding power supply devices are connected in parallel to the same welding electrode. In the inverter resistance welding machine, the welding current obtained by combining the currents respectively output from the plurality of inverter type resistance welding power supply devices is made to flow to the material to be welded through the welding electrode, and the switching of the inverter is performed. A common power supply control device for supplying a common energization control pulse for controlling the operation to the plurality of inverter type resistance welding power supply devices is provided.

The inverter type resistance welding machine of the second invention is
Output terminals of a plurality of inverter type resistance welding power supply devices are connected in parallel to the same welding electrode, and a welding current obtained by combining the currents respectively output from the plurality of inverter type resistance welding power supply devices is passed through the welding electrodes. In an inverter type resistance welding machine in which the current is supplied to the material to be welded by detecting each current in each of the plurality of inverter type resistance welding power source devices for each cycle or half cycle of the inverter frequency, the currents are detected. Comparing the total current measurement value from the current detection means with a predetermined reference value for each one cycle or each half cycle of the inverter frequency, Generating a common energization control pulse for controlling the switching operation of the inverter having a pulse width according to the comparison error And configured to and a current control means for supplying the energization control pulse to said plurality of inverter resistance welding power supply apparatus.

The inverter type resistance welding machine of the third invention is
Output terminals of a plurality of inverter type resistance welding power supply devices are connected in parallel to the same welding electrode, and a welding current obtained by combining the currents respectively output from the plurality of inverter type resistance welding power supply devices is passed through the welding electrodes. In an inverter type resistance welding machine in which the welding current is flowed to the welded material, the current measuring means for detecting the welding current flowing in the welded material for each cycle or half cycle of the inverter frequency to obtain the current value. And comparing the welding current measurement value from the current detecting means with a predetermined reference value for each cycle or each half cycle of the inverter frequency, and for the inverter having a pulse width corresponding to the comparison error. A common energization control pulse for controlling switching operation is generated, and the energization control pulse is applied to the plurality of inverter type resistance weldings. It has a configuration comprising a current control means for supplying the source device.

[0170]

1 shows the configuration of an inverter type resistance welding machine according to an embodiment of the present invention. In this resistance welding machine, a plurality of, for example, two inverter type resistance welding power supply devices 10, 12 are connected in parallel to the welding electrodes 14, 16.

The dual power supply devices 10 and 12 are the three-phase rectifier circuit 1
8A, 18B, inverters 20A, 20B, welding transformers 22A, 22B, rectifier circuits 24A, 24B and current sensors 26A, 26B are provided separately, and a common (shared) CPU (microprocessor) 28 is provided.
And a current measuring circuit 30.

Each of the three-phase rectifier circuits 18A and 18B rectifies a commercial three-phase AC voltage (U, V, W) and converts it into a DC voltage. This DC voltage is smoothed by a smoothing circuit including coils 32A and 32B and capacitors 34A and 34B, and then input to the inverters 20A and 20B. Each of the inverters 20A and 20B has a drive circuit 36 from the CPU 28.
Common energization control pulse C supplied via A and 36B
According to PO, the high-frequency AC pulse is output by chopping the DC from each of the three-phase rectifier circuits 18A and 18B by high-frequency switching.

The AC pulse output from each inverter 20A, 20B is supplied to the primary side coil of each welding transformer 22A, 22B, and an AC pulse similar to the primary side is obtained on each secondary side. This secondary side AC pulse is a pair of diodes (38A, 40A), (38B, 40B).
Is converted into direct current by each rectifying circuit 24A, 24B. Then, a welding current IW, which is a combination of the DC currents IA and IB output from the rectifier circuits 24A and 24B, flows into the materials 42 and 44 to be welded through the welding electrodes 14 and 16, and the materials 42 and 44 to be welded resist. It is joined by welding.

In this inverter type resistance welding machine, a pulse width for feedback control is applied to the pulse width of the energization control pulse CP0 so that the welding current IW maintained at the set current value during the energization time flows to the workpieces 42 and 44. Modulation (PW
M) type constant current control means is provided. The constant current control means includes current sensors 26A and 26B and a drive circuit 3 which are separately provided in both power supply devices 10 and 12.
6A, 36B and a current measuring circuit 30, an AD converter 46, and a CPU 28 which are common to both power supply devices 10, 12.

For each unit cycle (1 cycle or half cycle) of the inverter frequency, each inverter 20A,
The switching element 20B is turned on for a time corresponding to the pulse width of the energization control pulse CP0 from the CPU 28.

Each of the current sensors 26A and 26B is, for example, a Hall current transformer, and the primary currents iA and i output from the inverters 20A and 20B in each unit cycle.
Sensor output signal (current detection signal) DiA that represents the waveform of B
, DiB are generated and applied to the current measuring circuit 30. The current measuring circuit 30 adds the current detection signals DiA and DiB for each unit cycle, and based on the combined value, the total primary current effective value S for both power supply devices 10 and 12
Find I. The total primary current effective value SI from the current measuring circuit 30 is converted into a digital signal by the AD converter 46 and then given to the CPU 28.

The CPU 28 has a built-in memory for storing programs and data, respectively, and stores (setting registration) the current setting value or reference value converted into the primary current in the memory in advance. For each unit cycle, the CPU 28 compares the total primary current effective value SI from the current measuring circuit 30 with the reference value and obtains the pulse width of the energization control pulse CP0 for energizing the next cycle from the comparison error. Then, in the next cycle, the energization control pulse CP0 having the obtained pulse width is output in synchronization with the start end of the clock φ, and the inverter 2 is driven through the drive circuits 36A and 36B.
Supply to 0A and 20B. The clock φ from the clock circuit 48 defines the inverter frequency.

The CPU 28 inputs a signal ST instructing the start of welding energization from an external device such as a robot controller via the interface circuit 50.

As described above, in the inverter type resistance welding machine of this embodiment, the two inverter type resistance welding power supply devices 1 are used.
The CPUs 0 and 12 commonly use the energization control CPU 28, and the common CPU 28 responds to the energization start signal ST to control the energization of both power supply devices 10 and 12 with a common energization control pulse CPO. According to such a common control system, the energization timing is accurately synchronized between the two power supply devices 10 and 12 without being affected by the circuit constants, the signal processing time, the signal propagation delay time, etc. in the interface circuit 50 and the CPU 28. be able to.

Further, in the inverter type resistance welding machine of this embodiment, the common current measuring circuit 30 and the common CPU 2 are used.
A constant current control feedback loop is constituted by 8 and a common energization control pulse CPO is applied to both power supply units 10 and 12 so that the effective value of the inverter output or the total primary current of the entire welding machine matches the reference value (set value). Inverter 2
It is given to 0A and 20B. As a result, the dual power supply 1
The timing of the constant current control at 0 and 12 is exactly the same, and the maximum value or effective value of the welding current IW, which is the sum of the output currents (secondary currents) IA and IB, can be made to exactly match the reference value. . Therefore, stable and good welding quality can be guaranteed.

It should be noted that instead of providing the current sensors 26A and 26B in the two power supply devices 10 and 12, respectively, the welding current I
Even if the current sensor 52 for detecting W is attached to the common secondary conductor and the output signal (welding current detection signal) of the current sensor 52 is given to the current measuring circuit 30, the same effect as above can be obtained. .

When the current capacities of both power supply devices 10 and 12 are equal, the CPU 28 can perform signal processing by dividing the total current measurement value SI from the current measurement circuit 30 into two equal parts as the current measurement value for one unit. . When the current capacities of both power supply devices 10 and 12 are different, the total current measurement value SI from the current measurement circuit 30 is divided by a ratio according to the current capacity of both power supply devices 10 and 12 to obtain the respective current measurement values. Signal processing is sufficient. In this case, the reference value is set to both power supply units 10 and 12.
It will be set separately according to the ratio of the current capacity.

In the above embodiment, two power supply units 10,
Although 12 are connected in parallel, it goes without saying that three or more power supply devices may be connected in parallel.

[0310]

As described above, according to the inverter type resistance welding machine of the present invention, a plurality of inverter type resistance welding power source devices connected in parallel to the same welding electrode are energized from a common power source control device. Since the control is performed by the common energization control pulse, the energization timing is accurately synchronized between the power supply devices, and the welding current according to the setting can be applied to the material to be welded to obtain good welding quality.

In particular, when the feedback constant current control method is used, the total current value obtained by adding the currents in all the power supply devices is obtained by the common current measuring means, and the common current control means is used to obtain the total current value and the reference value. Since a common energization control pulse is generated according to the comparison error with and the switching operation of the inverter of each power supply device is controlled by this common energization control pulse, proper constant current control can be performed at the current value and timing. Can be carried out and a stable and good welding quality can be guaranteed.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an inverter type resistance welding machine according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of a conventional inverter type resistance welding machine.

FIG. 3 is a current waveform diagram showing a deviation of energization timing in a conventional inverter type resistance welding machine.

[Explanation of symbols]

 10, 12 Inverter resistance welding power supply device 14, 16 Welding electrodes 20A, 20B Inverter 26A, 26B Current sensor 28 CPU 30 Current measuring circuit 42, 44 Welding material

Claims (3)

[Claims] 1. The output terminals of a plurality of inverter type resistance welding power sources are connected in parallel to the same welding electrode,
In an inverter resistance welding machine in which a welding current obtained by combining the currents respectively output from the plurality of inverter type resistance welding power supply devices is made to flow to the material to be welded through the welding electrode, in order to control the switching operation of the inverter An inverter type resistance welding machine, comprising: a common power supply control device that supplies the common energization control pulse to the plurality of inverter type resistance welding power supply devices. 2. Output terminals of a plurality of inverter-type resistance welding power source devices are connected in parallel to the same welding electrode,
In an inverter type resistance welding machine in which welding currents obtained by combining currents respectively output from the plurality of inverter type resistance welding power supply devices are made to flow to a material to be welded through the welding electrode, every one cycle of an inverter frequency or Current measuring means for detecting each current in each of the plurality of inverter type resistance welding power source devices for each half cycle and obtaining a total current measurement value obtained by combining the current values, and for each cycle of the inverter frequency, or Common energization control for comparing the total current measurement value from the current detection means with a predetermined reference value every half cycle and controlling the switching operation of the inverter having a pulse width according to the comparison error. Energization control means for generating a pulse and supplying the energization control pulse to the plurality of inverter type resistance welding power source devices , Inverter resistance welding machine, characterized by comprising. 3. Output terminals of a plurality of inverter type resistance welding power source devices are connected in parallel to the same welding electrode,
In an inverter type resistance welding machine in which welding currents obtained by combining currents respectively output from the plurality of inverter type resistance welding power supply devices are made to flow to a material to be welded through the welding electrode, every one cycle of an inverter frequency or Current measuring means for detecting the welding current flowing through the material to be welded for each half cycle to obtain a measured current value, and current measuring means for each one cycle or each half cycle of the inverter frequency. The welding current measurement value is compared with a predetermined reference value to generate a common energization control pulse for controlling the switching operation of the inverter having a pulse width according to the comparison error, and the energization control pulse is the An inverter type resistance welding machine, comprising: an energization control means for supplying a plurality of inverter type resistance welding power supply devices. Machine.