JP3259012B2 - Inverter type resistance welding control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0010]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device for controlling welding current in an inverter type resistance welding machine.

[0020]

2. Description of the Related Art In recent years, current limiter control has been used as a constant current control method for matching a primary or secondary current to a desired set current value in a feedback loop in an inverter type resistance welding machine. I have.

The current limiter control is a method of detecting an instantaneous value or waveform of a current at each cycle of an inverter frequency and switching off the inverter when the instantaneous value of the current reaches a predetermined limiter level. Since the peak values can be made uniform, there is an advantage that welding current can be started up at high speed without causing overshoot.

However, in the current limiter control,
When the pulse width fluctuates even if the current peak value is maintained constant, the effective current value fluctuates, and there is a problem that resistance heating and, consequently, weldability become unstable. However, by increasing the inverter frequency sufficiently to shorten the cycle of each cycle, the variation in the pulse width or the effective current value can be suppressed, so that this problem can be substantially solved.

[0050]

According to the above-described limiter control, in principle, the current should reach the limiter level in each cycle and the current peak value should be uniform. However, in practice, when the current does not flow well, the current may not reach the limiter level.
For example, if the resistance of the secondary circuit (conductor) increases due to contamination of electrodes or heat generated by welding current, or if the AC power supply voltage fluctuates and drops, even if the inverter is switched on in each cycle, The rise of the current may be slow and may not reach the limiter level within a cycle.

The conventional inverter-type resistance welding control apparatus of this type does not have a function of monitoring the status of the limiter control as described above. Therefore, welding energization is repeatedly performed without confirming the welding result,
Judgment of welding quality was left to visual inspection and the like. For this reason, the burden on the worker was large, and it was also difficult to prevent the repetition of defective products.

Also, when the secondary conductor or cable between the welding transformer and the welding electrode is cut or broken in the inverter type resistance welding machine, or when an insulator is sandwiched between the welding electrode and the work to be welded. Even when the control unit operates the inverter, no current actually flows on the secondary side. Conventionally, in order to detect such a non-energized abnormal situation, it is conventionally determined whether or not the measured current value is zero.

Such a detection method may be used when directly detecting the current on the secondary side. However, when the constant current control is performed by detecting the current on the primary side, it has been difficult with the conventional detection method to reliably detect a non-energized abnormal situation. That is, while the inverter is operating, even if no current flows on the secondary side, the exciting current flows through the welding transformer, and the current measured on the primary side does not become zero due to the exciting current. For this reason, there is a possibility that it is determined that the current is not supplied.

The present invention has been made in view of the above-mentioned problems, and provides an inverter type resistance welding control device which accurately monitors a current limiter control condition to improve quality control and productivity. This is the first object.

The present invention also provides an inverter-type resistance welding control device which has a function of reliably detecting an abnormal state of non-energization on the secondary side on the primary side, and improves quality control and productivity. This is the second purpose.

[0110]

In order to achieve the first object, a first inverter-type resistance welding control device according to the present invention is configured to control a primary or secondary current of an inverter-type resistance welding machine. In the inverter-type resistance welding power supply device that controls the switching operation of the inverter so as to substantially match the set current value, a clock circuit that generates a clock pulse that defines a unit cycle of the switching operation of the inverter; Limiter level setting means for setting a corresponding predetermined limiter level, current detection means for detecting the current during welding energization, and in each clock cycle, switching on the inverter in response to the beginning of the clock, When the output signal of the current detection means reaches the limiter level or when the clock signal Graphics and inverter control means for switching off the inverter at either end of a current measuring means for measuring the value of the current at each time of switching off the inverter, than the current measuring means during welding operation It is configured to include a welding quality determination unit that determines the quality of welding based on the obtained data of the measured current value, and a determination result output unit that outputs a determination result obtained by the welding quality determination unit.

The first inverter type resistance welding control device
Now, in the current limiter control, every clock cycle
During switching off, that is, the current value at the peak point is measured.
The current measurement value (peak point current value) is
Is judged based on the data, and the judgment result is output.
Is done.

The first inverter type resistance welding control device
In a preferred aspect of the invention, the welding quality determination means
Is obtained by the current measuring means during the welding energization.
Means for calculating an average value of the measured current values;
Monitoring value setting means for setting a monitoring value for determination;
The monitoring value and the average value obtained by the average value calculation means
It may be configured to include comparison means for comparison.

In order to achieve the second object,
The second inverter-type resistance welding control device of the present invention is commercially available.
Rectify AC to DC and convert this DC to inverter
It is converted to an AC pulse of a predetermined frequency, and this AC pulse is melted.
After passing through the contact transformer, it passes through the rectifier to make it DC again,
This direct current is supplied to the workpiece through the welding electrode.
Of the inverter-type resistance welding machine
Primary to measure the current on the primary side of the resistance welding machine during energization
Current measurement means, obtained by the primary current measurement means
If the measured primary current is smaller than the set current and
A predetermined value selected to be larger than the exciting current of the
The resistance welding is compared with the monitoring value and based on the comparison result.
De-energization to detect unpowered abnormal situations on the secondary side of the machine
And a detecting means.

In the second inverter type resistance welding control device, the measured value of the primary current is compared with the monitoring value for non-energization detection in consideration of the exciting current of the welding transformer, and based on the comparison result, the non-energized value on the secondary side is determined. Is detected.

[0160]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a circuit configuration of an inverter type resistance welding control apparatus according to one embodiment of the present invention.

In the inverter type resistance welding machine to which the control device is applied, the input terminal of the three-phase rectifier circuit 12 is connected to the three-phase
A direct current is obtained at the output terminal. This DC is input to the inverter 16 after being smoothed by the capacitor 14.

The inverter 16 has, for example, giant transistors (hereinafter, referred to as GTRs) 18 to 24 as switching elements, and converts an input direct current into a pulse-like (rectangular wave) high-frequency alternating current by a high-frequency switching operation. The switching operation of the inverter 16 is performed by the driving circuit (42, 4) by the CPU 40 of the resistance welding control device.
8), (44, 46) via GTR (18, 24 ),
It is controlled by control pulses CA and CB supplied to (20, 22).

The high-frequency alternating current output from the inverter 16 is supplied to the primary coil of the welding transformer 26, and a reduced high-frequency alternating current is obtained in the secondary coil. This high-frequency alternating current is converted into direct current by a rectifier circuit comprising a pair of diodes 28 and 30, and a direct current secondary current (welding current) I 2 is applied through the welding electrodes 32 and 34 to the material 36 to be welded.
38.

In the resistance welding control apparatus according to the present embodiment, a current sensor 50 composed of, for example, a Hall current transformer is attached to a primary conductor between the primary capacitor 14 and the inverter 16. This current sensor 50
Outputs a voltage signal (current detection signal) Si representing the instantaneous value or waveform of the primary current I1.

The output terminal of the current sensor 50 is connected to the amplifier 5
2 and connected to the input terminal of the sampling and holding circuit 54 and to one input terminal of the comparison circuit 56. Sampling and holding circuit 54
Is configured to sample and hold the current detection signal Si in response to a control signal CH from the CPU 40. An output terminal of the sampling and holding circuit 54 is connected to a data input terminal of the CPU 40 via an AD converter 58.

The other input terminal of the comparison circuit 56 has a CP
Under the control of U40, the limiter level (voltage) LM corresponding to the set current value is given from the limiter level generator 60.

A clock circuit 62, a storage unit 64, an input unit 66, a display unit 68, a buzzer 70, and the like are also connected to the CPU 40 directly or via an interface circuit (not shown).

Clock circuit 62 defines a unit cycle of switching of inverter 16, for example, 4 kHz.
Are supplied to the CPU 40. The storage unit 64 includes a ROM and a RAM, and the ROM stores various programs that define the operation of the CPU 40, and the RAM stores various set value data, various measured value data, calculation data, and the like. The input unit 66 includes various keys provided on an operation panel of the control device unit and an interface circuit connected to an external device via a communication cable. The display unit 68 includes a display, a lamp, and the like provided on the operation panel of the control device unit.

In the present embodiment, the first monitoring value for judging the quality of welding and the second monitoring value for detecting non-energization are set and input by the input unit 66 and stored (registered) in the storage unit 64. First
Monitoring value [Ij] is, for example, ± 5
It may be set to a value of%. The second monitored value [Ik] is the exciting current of the welding transformer 26 (for example, 200
Ampere) may be set to a somewhat higher value (for example, 350 amperes on the secondary side).

FIG. 2 shows signal waveforms of respective parts for explaining the current limiter function and the monitor function in the resistance welding control device. 3 and 4 show main processing of the CPU 40 in the resistance welding control device. FIG.
7 shows a main screen displayed on the display of the display unit 68 of the resistance welding control device. Hereinafter, the operation of this embodiment will be described with reference to FIGS.

In FIGS. 1 and 2, the CPU 40 alternately outputs two-phase control pulses CA and CB synchronized with the two-phase clocks φA and φB during the welding energization time. One control pulse CA is supplied to the control terminals of the GTRs 18 and 24 of the inverter 16 via the drive circuits 42 and 48, and turns on the GTRs 18 and 24 for the pulse duration. When the GTRs 18 and 24 are on, a primary current I1 having a positive polarity flows through the primary coil of the welding transformer 26. The other control pulse CB is supplied to the control terminals of the GTRs 20 and 22 of the inverter 16 via the drive circuits 44 and 46, and turns on the GTRs 20 and 22 for the pulse duration. When the GTRs 20 and 22 are on, a negative primary current I1 flows through the primary coil of the welding transformer 26.

A time gap G is provided between the two-phase clocks φA and φB. As a result, the control pulses CA and CB do not overlap in time, and the inverter 16
In this case, the GTRs (18, 24) and (20, 22) are not turned on at the same time, and the short-circuit breakdown of the inverter 16 is prevented.

While the inverter 16 is operating, a pulse current I1 flows through the current sensor 50. Current sensor 5
0 outputs an analog current detection signal Si representing the instantaneous value or waveform of the primary current I1.

As shown in FIG. 3, when, for example, the clock φA is input (step A1), in that cycle, the CPU 40 raises the control pulse CA at the beginning of φA and turns on the GTRs 18 and 24 (FIG. 3). Step A2).
When the GTRs 18 and 24 are turned on, the primary current I1 rises.

When the primary current I1 rises normally, the current detection signal Si reaches the limiter level LM in the cycle, at which point the output voltage of the comparator 56 changes from L level to H level. In response (step A3)
The CPU 40 causes the control pulse CA to fall, causing the GTR 18,
24 is turned off (step A5).

Due to fluctuations such as an increase in the resistance value of the secondary circuit or a drop in the three-phase AC power supply voltage, the rise of the primary current I1 is not good, and the current detection signal Si falls to the limiter level LM in the cycle. May not be reached. In this case, the CPU 40 controls the control pulse C at the end of the clock φA.
A is dropped, and the GTRs 18 and 24 are turned off (steps A4 and A5). When the GTRs 18 and 24 are turned off, the primary current I1 falls.

At the same time as the control pulse CA falls as described above, the CPU 40 supplies a control signal to the sampling and holding circuit 54 to hold the level IPn of the current detection signal Si at that time. Then, the held current peak value IPn is output to the AD converter 5.
8 and stored as a current measurement value in a predetermined storage address of the storage unit 64 (step A6).

In the cycle of the clock φB, the control pulse CB is supplied from the CPU 40 to the GTRs 20 and 22 of the inverter 16, and the same operation as in the cycle of the clock φA is performed. In this way, the current limiter control for one cycle and the measurement of the current peak value IPn are performed in each clock cycle.

After the end of the welding current (step A7), FIG.
As shown in FIG. 7, the CPU 40 calculates the current measurement values IP1 for all the cycles of the current welding energization stored in the storage unit 64.
, IP2,... (Step B1).

Then, the current average value IPM is first compared with a second monitoring value [ Ik ] for non-energization detection (step B2). In this comparison, when IPM <[ Ik ] (step B3), it is determined that an abnormal state of non-energization has occurred in the secondary circuit (step B4), and for example, (D) in FIG.
"NO CURRENT !!"
! Is displayed on the display of the display unit 68 (step B5).
) At the same time, a predetermined buzzer sound (e.g., a beep sound) is output from the buzzer 70 to inform of no power supply (step B6).

If IPM ≧ [ Ik ] in the first comparison (step B 2) (step B 3), the current average value IPM is then used as the first monitoring value [ Ij ] for judging the quality of welding.
(Step B7).

In the second comparison, the current average value IPM
Is out of the range of the monitored value [ Ij ] (for example, ± 5%) (step B8), it is determined that the welding is defective (step B9). Then, as shown in FIG. 5 (C), a display <NG> of the good or bad contact is displayed on the display of the display unit 68 (step B10), and at the same time, a predetermined buzzer sound (for example, a buzzer 70) notifies the welding failure. Bit sound)
Is sounded (step B11).

In the second comparison (step B7), the current average value IPM is in the range of the monitored value [ Ij ] (eg ±
5%) (step B8), it is determined that the welding is good (step B12). Then, for example, as shown in FIG.
8 (step B13). In this case, no buzzer sound is emitted since there is no particular need for inspection by the operator.

FIG. 5A is a setting screen showing the set values of the welding current. In the upper row of this setting screen, the numerical value [1] on the left end is the schedule number, the numerical value [10] on the right is the first energization time (millisecond), and the numerical value [05] on the right is the cooling time. (Milliseconds) with the rightmost number [1
0] indicates the length (millisecond) of the second energization time. The numerical value [0500] on the left side of the lower row is the first number.
The energized secondary current set value (kilo amps) and the numerical value [2000] on the right side indicate the second energized secondary current set value (kilo amps), respectively.

FIGS. 5B and 5C are monitor screens showing the results of welding energization. In FIG. 5B, the numerical values [0499] and [1999] in the lower row are secondary current measured values (average values) in the first and second energizations, respectively. Similarly, in FIG. 5C, the numerical values [0470] and [1890] in the lower row are the measured secondary current values (average values) in the first and second energizations, respectively. Since there is a proportional relationship between the primary current I1 and the secondary current I2 equal to the winding ratio of the welding transformer 26, the primary current set value is calculated from the secondary current set value, and the secondary current set value is calculated from the measured primary current. The measured values are each easily obtained by calculation.

As described above, in the inverter-type resistance welding control apparatus according to the present embodiment, the current peak value is detected at each clock cycle in the current limiter control, and the average value of the measured current values is obtained after the end of the energizing time. The current average value is compared with a predetermined monitoring value for welding quality determination to determine welding quality, and the determination result is displayed and output together with the measured current value.

By displaying and outputting the status or the result of the current limiter control in this way, visual inspection of the operator becomes unnecessary, and quality control and productivity can be improved. In addition, since the result of the poor welding is also notified by a buzzer sound, the nearby worker can notice the poor welding without looking at the operation panel of the control device unit, and the workability can be improved.

Since several cycles immediately after the start of energization are periods during which the current peak value gradually rises, the measured current value during this period may be excluded from the current average value. The same applies to the period immediately before the end of energization.

Also, in the inverter type resistance welding control apparatus of this embodiment, a monitoring value for non-energization detection is set in consideration of the exciting current of the welding transformer 26, and the average current value in the current limiter control of the primary feedback system is set. An abnormal state of non-energization on the secondary side is detected from the comparison result with the monitoring value for non-energization detection. Thus, it is possible to reliably detect a non-energized abnormal situation on the secondary side even from the primary side without being disturbed by the exciting current of the welding transformer 26. Furthermore, since such a non-energized abnormal condition is displayed and output to a nearby worker with a predetermined buzzer sound, workability can be improved.

In the above-described embodiment, the non-energization test is performed after the end of the welding energization, but a similar inspection may be performed during the energization. In such a case, the energization may be stopped immediately upon detecting a non-energized abnormal situation.

In addition, various modifications of the above-described embodiment are possible. For example, the current sensor 50 can be mounted between the inverter 16 and the welding transformer 26 on the primary side of the resistance welding machine. In this case, since the primary current detection signal Si of the AC waveform is output from the current sensor 50, a signal waveform having the same polarity as shown in FIG. 2 can be obtained by passing through the absolute value circuit. Regarding the monitoring of the current limiter function, the secondary current I2 can be detected by a current sensor such as a toroidal coil.

An A / D converter is connected downstream of the amplifier 52 to digitize the primary current detection signal Si, and the signal processing by the sample / hold circuit 54 and the comparator 56 is performed digitally or by software. It may be.

[0500]

As described above, according to the inverter type resistance welding control apparatus of the present invention, the current limiter control status is monitored accurately , the welding quality is determined, and the determination result is output. As a result, visual inspection by an operator is not required, and quality control and productivity can be improved.

Further, according to the inverter type resistance welding control device of the present invention, by comparing the measured value of the primary current with the monitored value in consideration of the exciting current of the welding transformer, the abnormal situation of non-energization on the secondary side can be solved. Since the detection is reliably performed from the primary side, the current control function on the primary side is guaranteed, and quality control and productivity can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a circuit configuration of an inverter type resistance welding control device according to one embodiment of the present invention.

FIG. 2 is a diagram showing signal waveforms of respective parts for describing a current limiter function and a monitor function in the inverter type resistance welding control device of the embodiment.

FIG. 3 is a diagram illustrating main processing during welding energization of a CPU in the inverter-type resistance welding control device according to the embodiment.

FIG. 4 is a diagram illustrating main processing immediately after welding energization by a CPU in the inverter-type resistance welding control device according to the embodiment.

FIG. 5 is a diagram showing a main screen displayed on a display of a display unit in the inverter-type resistance welding control device of the embodiment.

[Description of Signs] 16 Inverters 18 to 24 Giant transistors 26 Welding transformers 32, 34 Welding electrodes 36, 38 Material to be welded 40 CPU 50 Current sensor 54 Sample and hold circuit 56 Comparison circuit 62 Clock circuit 64 Storage unit 66 Input unit 68 Display 70 Buzzer

Continuation of front page (56) References JP-A-2-284776 (JP, A) JP-A-5-329660 (JP, A) JP-A-5-177362 (JP, A) JP-A-4-94879 (JP) JP-A-3-57569 (JP, A) JP-B-53-40177 (JP, B2) JP-B-3-71230 (JP, B2) JP-B-54-36133 (JP, B2) (58) Field surveyed (Int. Cl. ⁷ , DB name) B23K 11/24

Claims (3)

(57) [Claims] 1. An inverter-type resistance welding power supply device for controlling a switching operation of an inverter so that a current on a primary side or a secondary side of an inverter-type resistance welding machine substantially matches a desired set current value. A clock circuit that generates a clock pulse that defines a unit cycle of operation, a limiter level setting unit that sets a predetermined limiter level corresponding to the set current value, and a current detection unit that detects the current during welding energization. In each clock cycle, the inverter is switched on in response to the beginning of the clock, and the inverter is switched either when the output signal of the current detection means reaches the limiter level or at the end of the clock pulse. An inverter control means for turning off; Current measuring means for measuring the value of the current at each point in time when the data is switched off, and welding for judging the quality of welding based on the data of the current measured value obtained from the current measuring means during welding energization. An inverter-type resistance welding power supply device comprising: a quality judgment unit; and a judgment result output unit that outputs a judgment result obtained by the welding judgment unit. 2. The welding quality judgment means sets an average value calculation means for calculating an average value of the current measurement values obtained by the current measurement means during the welding energization, and sets a monitoring value for quality judgment. 2. The inverter-type resistance welding control device according to claim 1, further comprising: a monitoring value setting unit; and a comparing unit that compares the average value obtained by the average value calculation unit with the monitoring value. 3. A commercial AC is rectified to DC, and this DC is converted into an AC pulse of a predetermined frequency by an inverter.
The AC pulse to DC again through the rectifier after passed through a welding transformer, a control device of the inverter resistance welding machine which is adapted to supply the DC through the welding electrodes to the material to be welded, during said welding operation A primary current measuring means for measuring the current on the primary side of the resistance welding machine, and a primary current measurement value obtained by the primary current measuring means selected to be smaller than a set current value and larger than an exciting current of the welding transformer. Compared with the specified monitoring value
An inverter-type resistance welding control device, comprising: non-energization detecting means for detecting an abnormal state of non-energization on the secondary side of the resistance welding machine based on the comparison result.