JPH0947883A - Inverter resistance welding controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve quality control and productivity by providing a function for monitoring the condition of current limiting control. SOLUTION: A CPU 40 starts a control pulse CA or CB at the raising edge of each clock cycle, turning on transistors (18, 24) or (20, 22). Then, in response to the output signal of a comparator circuit 56, or else to the falling edge of the clock ϕ, the CPU 40 raises the control pulse CA or CB fall, turning off the transistors (18, 24) or (20, 22). Simultaneously, the CPU 40 takes in the level of a current detection signal Si at that point of time through a sample-and- hold circuit 54 and an A/D converter 58, storing it in a prescribed address in a storage part 64 as a current measurement value. After the completion of welding energizing, the CPU 40 determines the mean value on the current measurements of all cycles stored in the storage part 64, deciding the normal/ defective condition of the welding based on this mean value of the current.

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 energization in an inverter type resistance welding machine.

[0020]

2. Description of the Related Art Recently, in an inverter type resistance welding machine, current limiter control has been used as a constant current control method for matching a primary side or secondary side current with a desired set current value in a feedback loop. There is.

The current limiter control is a method of detecting the instantaneous value or waveform of the current for each cycle of the 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 energization can be started up at high speed without causing overshoot.

However, in the current limiter control,
Even if the current peak value is maintained constant, when the pulse width fluctuates, the effective current value fluctuates, and there is a problem that resistance heating and eventually weldability become unstable. However, by sufficiently increasing the inverter frequency and shortening the cycle of each cycle, fluctuations in the pulse width or the effective current value can be suppressed, and this problem can be substantially eliminated.

[0050]

According to the limiter control as described above, in principle, the current reaches the limiter level every cycle and the current peak value should be constant. However, in reality, the current may not reach the limiter level when the current does not flow well.
For example, if the resistance value of the secondary side circuit (conductor) increases due to dirt on the electrodes or heat generation due to welding energization, or if the AC power supply voltage fluctuates and drops, even if the inverter switches on in each cycle. The current rise may be slow and the limiter level may not be reached within the cycle.

The conventional inverter-type resistance welding control device of this type does not have a function of monitoring the above-mentioned limiter control status. Therefore, welding energization is repeatedly executed without confirming the welding result,
Welding quality was left to visual inspection. For this reason, the burden on the worker is great and it is difficult to prevent the defective products from being successively produced.

Further, in the inverter resistance welding machine, when the secondary conductor or cable between the welding transformer and the welding electrode is cut or broken, or when the insulator is sandwiched between the welding electrode and the object to be welded. However, even if the inverter is operated by the control unit, no current actually flows on the secondary side. In order to detect such a non-energized abnormal situation, conventionally, it has been judged whether or not the measured current value is zero.

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

The present invention has been made in view of the above problems, and provides an inverter resistance welding control apparatus having a function of monitoring the status of current limiter control and improving quality control and productivity. Is the first purpose.

Further, the present invention provides an inverter type resistance welding control device having a function of surely detecting a non-energized abnormal state on the secondary side on the primary side, and improving quality control and productivity. The second purpose.

[0110]

In order to achieve the above-mentioned first object, a first inverter type resistance welding control apparatus of the present invention supplies a current on the primary side or the secondary side of an inverter type resistance welding machine. In an inverter-type resistance welding control device that controls the switching operation of an inverter so as to substantially match a desired set current value, a clock circuit that generates a clock pulse that defines a unit cycle of the switching operation of the inverter, and the set current value. Limiter level setting means for setting a predetermined limiter level corresponding to the above, current detection means for detecting the current during welding, and switching on of the inverter in response to the start of the clock pulse in each clock cycle. At the time when the output signal of the current detecting means reaches the limiter level or A control means for switching off the inverter at the end of a clock pulse, a current measuring means for measuring the value of the current at each time when the inverter is switched off, and a current measuring means during welding. It is configured to include a welding quality determination unit that determines the quality of welding based on the data of the current measurement value, and a determination result output unit that outputs the determination result of the welding quality determination unit.

A second inverter type resistance welding control device of the present invention is the above-mentioned first inverter type resistance welding control device, wherein the welding quality determination means is obtained by the current measuring means during the welding energization. An average value calculating means for obtaining an average value of current measurement values, a monitoring value setting means for setting a monitoring value for quality judgment, and a comparison for comparing the average value obtained by the average value calculating means with the monitoring value. And a configuration including means.

In order to achieve the above second object,
A third inverter type resistance welding control device of the present invention rectifies commercial alternating current into direct current, converts this direct current into an alternating current pulse of a predetermined frequency by an inverter, passes this alternating current pulse through a welding transformer and then through a rectifier. And turn it back to direct current,
In a controller of an inverter type resistance welding machine adapted to supply this direct current to a material to be welded via a welding electrode, a primary current measuring means for measuring a primary side current of the resistance welding machine, and the primary current measuring means. The primary current measurement value obtained by the above is compared with a predetermined monitoring value which is smaller than the set current value and larger than the exciting current of the welding transformer, and based on the comparison result, the two values of the resistance welding machine are compared. A non-energization detecting means for detecting an abnormal condition of non-energization on the secondary side is provided.

[0140]

In the first and second inverter type resistance welding control devices of the present invention, the current value is measured at each clock cycle in the current limiter control, and after the energization time, the data of the measured current value, for example, the average current value is used for welding. Is judged, and the judgment result is output.

In the third inverter type resistance welding control apparatus of the present invention, 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 the comparison result shows that the secondary side An unpowered abnormal situation is detected.

[0160]

Embodiments 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 an embodiment of the present invention.

In the inverter resistance welding machine to which this control device is applied, the input terminal of the three-phase rectifier circuit 12 is connected to the three-phase commercial AC power supply terminal 10, and the three-phase rectifier circuit 12 is connected.
DC is available at the output terminal of. This direct current is smoothed by the capacitor 14 and then input to the inverter 16.

The inverter 16 has, for example, giant transistors (hereinafter referred to as GTR) 18 to 24 as switching elements, and converts the input DC into a pulsed (rectangular wave) high frequency AC by a high frequency switching operation. The switching operation of the inverter 16 is performed by the CPU 40 of the resistance welding control device by the drive circuit (42, 4).
8), (44,46) through GTR (18,20),
It is controlled by the 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 the reduced high frequency alternating current is obtained in the secondary coil thereof. This high-frequency alternating current is converted into direct current by a rectifying circuit composed of a pair of diodes 28 and 30, and a secondary current (welding current) I2 of direct current is passed through the welding electrodes 32 and 34 to the welded material 36,
38.

In the resistance welding control apparatus according to the present embodiment, the current sensor 50, which is, for example, a Hall current transformer, is attached to the primary side conductor between the primary side 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 the amplifier circuit 5
It is connected to the input terminal of the sampling and holding circuit 54 via 2 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 the control signal CH from the CPU 40. The output terminal of the sampling / holding circuit 54 is connected to the data input terminal of the CPU 40 via the AD converter 58.

CP is connected to the other input terminal of the comparison circuit 56.
Under the control of U40, a 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, etc. are also connected to the CPU 40 directly or via an interface circuit (not shown).

The clock circuit 62 defines a unit cycle of switching of the inverter 16, for example, 4 kHz.
The two-phase clocks φA and φB are supplied to the CPU 40. The storage unit 64 includes a ROM and a RAM. 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 the 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 welding quality determination and the second monitoring value for non-energization detection are set and input by the input unit 66 and stored (registered) in the storage unit 64. First
Monitoring value [Ij] of the current setting value is, for example, ± 5
You may set it to the value of%. The second monitoring value [Ik] is the exciting current of the welding transformer 26 (for example, 200 on the secondary side conversion).
It may be set to a value somewhat higher than amperes (for example, 350 amperes in terms of secondary side).

FIG. 2 shows the waveforms of the signals of the respective parts for explaining the current limiter function and the monitor function in this resistance welding control device. 3 and 4 show the main processing of the CPU 40 in this resistance welding control device. FIG.
The main screen displayed on the display of the display 68 of this resistance welding control apparatus is shown in FIG. The operation of this embodiment will be described below with reference to FIGS.

In FIGS. 1 and 2, during welding energization time, the CPU 40 alternately outputs two-phase control pulses CA and CB synchronized with the two-phase clocks φA and φB, respectively. 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 positive primary current I1 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 the above, the GTRs (18, 24) and (20, 22) are prevented from being turned on at the same time, and the short-circuit breakdown of the inverter 16 is prevented.

While the inverter 16 is operating, the 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, for example, when the clock φA is input (step A1), the CPU 40 raises the control pulse CA at the beginning of φA to turn on the GTRs 18 and 24 (step A1). Step A2).
When the GTRs 18 and 24 are turned on, the primary current I1 rises.

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

Due to a change in the resistance value of the secondary side circuit or a change in the three-phase AC power supply voltage, the rise of the primary current I1 is not good, and the current detection signal Si becomes the limiter level LM within the cycle. It may not reach. In this case, the CPU 40 controls the control pulse C at the end of the clock φA.
A is turned off and GTRs 20 and 22 are turned off (steps A4 and A5). When the GTRs 18 and 24 are turned off, the primary current I1 falls.

Simultaneously with the fall of the control pulse CA as described above, the CPU 40 gives 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 applied to the A / D converter 5
It is fetched via 8 and stored in a predetermined storage address of the storage unit 64 as a measured current value (step A6).

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

After the welding energization is completed (step A7), FIG.
As shown in FIG. 5, the CPU 40 causes the current measurement values IP1 stored in the storage unit 64 for all cycles of the current welding energization.
, IP2, ..., An average value IPM is obtained (step B1).

Then, the current average value IPM is first compared with the first monitoring value [Ij] for detecting non-conduction (step B2). In this comparison, when IPM <[Ij] (step B3), it is determined that a non-energized abnormal condition has occurred in the secondary side circuit (step B4), and, for example, FIG.
Display of non-energization as shown in "NO CURRENT !!
! Is displayed on the display of the display unit 68 (step B5
At the same time, a predetermined buzzer sound (for example, beeper sound) is output from the buzzer 70 to notify the non-conduction (step B6).

If IPM ≧ [Ij] in the first comparison (step B2) (step B3), then the current average value IPM is used as the second monitoring value [Ik] for determining the quality of welding.
(Step B7).

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

In the second comparison (step B7), the average current value IPM is in the range of the monitored value [Ik] (for example, ±
5%) (step B8), it is determined that welding is good (step B12). Then, for example, as shown in FIG. 5B, a good welding indication <GO> is displayed on the display unit 6.
Display on display 8 (step B13). In this case, no buzzer sounds because no special inspection by workers is required.

Note that FIG. 5A is a setting screen showing set values for welding energization. In the upper row of this setting screen, the leftmost number [1] is the schedule number, the rightward number [10] is the first energizing time (milliseconds), and the rightward number [05] is the cooling time. (Milliseconds) to the rightmost value [1
[0] indicates the length of the second energization time (milliseconds). Also, the numerical value [0500] on the left side of the lower row is the first
The secondary current setting value for energization (kiloamps) and the numerical value [2000] on the right side indicate the secondary current setting value (kiloamps) for the second energization.

FIGS. 5B and 5C are monitor screens showing the results of welding energization. Numerical values [0499] and [1999] in the lower row in FIG. 5B are secondary current measurement values (average values) in the first energization and the second energization, respectively. Also in FIG. 5C, the numerical values [0470] and [1890] in the lower row are secondary current measurement values (average values) in the first energization and the second energization, respectively. Since the primary current I1 and the secondary current I2 have the same proportional relation to the winding ratio of the welding transformer 26, the secondary current setting value is the primary current setting value, and the primary current measurement value is the secondary current setting value. Each measured value can be easily calculated.

As described above, in the inverter type resistance welding control apparatus of the present embodiment, the current peak value is detected in each clock cycle in the current limiter control, and the average value of the measured current values is obtained after the end of the energization time. The average current 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 result of the current limiter control in this manner, visual inspection by an operator is not required, and quality control and productivity can be improved. In addition, since the result of the welding failure is also notified by the buzzer sound, a worker in the vicinity can notice the welding failure 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 is a period in which the current peak value gradually rises, the measured current value in this period may be excluded from the average current value. The same applies to the period immediately before the end of energization.

Further, in the inverter type resistance welding control apparatus of the present embodiment, the monitoring value for non-energization detection in consideration of the exciting current of the welding transformer 26 is set, and the average current value is set in the primary side feedback type current limiter control. An abnormal state of non-energization on the secondary side is detected from the comparison result by comparing with the monitoring value for non-energization detection. This makes it possible to reliably detect a non-energized abnormal state on the secondary side even from the primary side without being disturbed by the exciting current of the welding transformer 26. Further, since such a non-energized abnormal situation is displayed and outputted, the worker in the vicinity is notified by a predetermined buzzer sound, so that workability can be improved.

In the above-mentioned embodiment, the non-energized inspection is carried out after the welding energization is finished, but the same inspection can be carried out during the energization. In that case, the energization may be stopped immediately at the time of detecting the non-energized abnormal situation.

Besides, various modifications of the above-mentioned 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 that case, since the primary current detection signal Si of the AC waveform is output from the current sensor 50, the signal waveform having the same polarity as shown in FIG. 2 is obtained by passing through the absolute value circuit. For monitoring the current limiter function, the secondary current I2 can be detected by a current sensor such as a toroidal coil.

Further, an AD converter is connected after the amplifier 52 to digitize the primary current detection signal Si so that the signal processing by the sample and hold circuit 54 and the comparator 56 can be performed digitally or by software. You may

[0500]

As described above, according to the inverter type resistance welding control apparatus of the present invention, the condition of the current limiter control is monitored, the quality of welding is judged, and the judgment result is output. It is possible to improve quality control and productivity by eliminating the need for visual inspection by workers.

Further, according to the inverter type resistance welding control apparatus of the present invention, by comparing the measured value of the primary current with the monitoring value in consideration of the exciting current of the welding transformer, the abnormal state of non-energization on the secondary side is detected. Since the primary side is surely detected, the current control function on the primary side can be guaranteed, and the quality control and the productivity can be improved.

[Brief description of drawings]

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

FIG. 2 is a diagram showing waveforms of signals of respective parts for explaining a current limiter function and a monitor function in the inverter resistance welding control apparatus of the embodiment.

FIG. 3 is a diagram showing main processing during welding energization of a CPU in the inverter resistance welding control apparatus of the embodiment.

FIG. 4 is a diagram showing the main processing of the CPU in the inverter type resistance welding control apparatus of the embodiment immediately after welding energization.

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

[Explanation of symbols]

 16 Inverter 18-24 Giant Transistor 26 Welding Transformer 32,34 Welding Electrode 36,38 Welding Material 40 CPU 50 Current Sensor 54 Sample and Hold Circuit 56 Comparison Circuit 62 Clock Circuit 64 Storage Section 66 Input Section 68 Display Section 70 Buzzer

Claims (3)

[Claims] 1. An inverter type resistance welding control apparatus 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, a current detection unit that detects the current during welding energization, In each clock cycle, the inverter is switched on in response to the start of the clock pulse, and the inverter is switched at the time when the output signal of the current detection means reaches the limiter level or at the end of the clock pulse. Inverter control means for turning off, and the inverter Current measuring means for measuring the value of the current at each time when the power is switched off, and the quality of welding for judging the quality of welding based on the data of the current measured value obtained by the current measuring means during welding energization. An inverter-type resistance welding control device comprising: a determination unit; and a determination result output unit that outputs the determination result of the welding quality determination unit. 2. The welding quality determination means sets an average value calculation means for obtaining an average value of the current measurement values obtained by the current measurement means during the welding energization, and a monitoring value for quality determination. 2. The inverter type resistance welding control device according to claim 1, further comprising a monitoring value setting means and a comparing means for comparing the average value obtained by the average value calculating means with the monitoring value. 3. A commercial alternating current is rectified into a direct current, and this direct current is converted into an alternating current pulse having a predetermined frequency by an inverter,
In the controller of the inverter type resistance welding machine, the AC pulse is passed through the welding transformer and then passed through the rectifier to be turned into direct current, and this direct current is supplied to the material to be welded through the welding electrode. Primary current measuring means for measuring the current on the primary side, a primary current measured value obtained by the primary current measuring means is smaller than a set current value, and a predetermined value selected to be larger than the exciting current of the welding transformer. Compared with the 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.