JPS5914314B2 - Resistance welding machine control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to current control of a resistance welding machine equipped with a switching element formed by connecting thyristors in antiparallel, and particularly to controlling the firing angle of the thyristor using a microcomputer. The present invention relates to a control device for a resistance welding machine.

In general, the quality of welding in resistance welding is determined by the Joule heat applied to the welded material, that is, (welding current) 2 x (resistance between the welded material + resistance between the electrode and the welded material) f0 x (current application time) Welding current is known to be a major factor in maintaining quality.

Therefore, how to perform constant current control against variations in load impedance has become a major issue. To control this load current, a switching element with thyristors connected in antiparallel is installed on the primary side of the welding machine's Toku5 lance, and the load current is detected in terms of the primary side, and this is connected to the set value of the welding current. Current control using so-called phase control, which controls the firing angle of the switching element by comparison, is usually used. 30 Recently, devices using microcomputers have come to be used as devices for controlling this current because they have arithmetic functions and can perform program control.

As illustrated in FIG. 1, the load current of a welding transformer 101 is detected by an amplifier circuit 105 via a 35 current transformer 104 provided on the primary side, and the load current is detected by an amplifier circuit 105.
06 into an effective current value, and this effective value is converted into a digital signal by an analog-to-digital conversion circuit 107 and input into the arithmetic processing section 108.
The power factor angle of the load is measured using the program and data stored in the welding circuit, and the firing angles of the thyristors Thl and Th2 of the switching circuit 103 for the target value of the welding current are determined based on this power factor angle. When the output signal of the arc angle matches the count number of the clock pulse signal synchronized with the AC power supply 102 sent from the pulse generation circuit 110, the output signal of the counter circuit 111 causes the switching circuit 103 to be activated via the gate circuit 112. The AC power source 102 is connected between the welding chips 113 and 113, which ignites the thyristors Thl and Th2 and pressurizes the material to be welded 114.
Electric power is supplied from the welding transformer 101 through the welding transformer 101 to control the load current.

However, since the device configured in this way detects the load current on the primary side of the welding transformer,
If the turn ratio or the number of secondary circuits (the number of welding chip circuits formed by connecting a welding chip to each of the secondary coils divided into multiple parts) of the welding transformer differs, the conversion ratio will differ and the load current will be detected. However, it has the disadvantage that accurate current control is not possible and the quality of welding deteriorates, especially when welding materials with severe welding conditions, such as corrosion-resistant galvanized steel sheets, where the range of current values suitable for welding current is narrow. Furthermore, there is the problem that if the welding temperature exceeds this range, it cannot be applied to welding that would cause welding failure due to welding of welding chips. In addition, resistance welders can set the welding current over a wide range (for example, 5000A to 15000A) depending on the material to be welded, so the welding current value suitable for the material to be welded can be set to, for example, 5000A. There is a difference in the accuracy per bit of the digital signal taken into the arithmetic processing unit between when the welding current is set to 15000A and when it is set to 15000A, and the accuracy of current control varies depending on the set value of the welding current, resulting in variations in welding quality. There is a problem.

The present invention has been made in view of the above-mentioned points, and its purpose is to reduce the accuracy of current control even when the turn ratio of the welding transformer, the number of secondary circuits, and the set value of the welding current are different. The object of the present invention is to provide a device that can control the load current without causing the load current to increase.

The present invention has an amplifier circuit that is connected to a current transformer provided on the primary side of a welding transformer to detect a load current, and the amplification degree can be switched to multiple stages Gl, G2...GO. Equipped with a gain switching circuit with
...Gn is made to correspond to the welding current target value setting range, and the range of the primary current of the welding transformer is divided into multiple regions Wl, W2......WO according to the current value. Lever areas Wl, W2...... are set corresponding to WO, and the primary side current value is determined based on the data of the turns ratio of the welding transformer, the number of secondary circuits, and the target value of the welding current. The calculated current values are the areas Wl, W2...
・・・・Determine which region of Wn it is in, and determine the amplification degree (for example, G1) that corresponds to the corresponding region (for example, W1).
) is switched by the output signal of the arithmetic processing section to control the load current with a constant precision.

Embodiments of the present invention will be described below with reference to FIGS. 2 and 3.

1 is a welding transformer, and the primary side is an AC power supply 2 (for example, AC
44OV), and welding chips 6, 6 are connected to the secondary side, and between these welding chips 6, 6, for example, 5000A~
It is designed to carry a current of 15,000A.

The welding chips 6, 6 are adapted to sandwich and pressurize the workpiece 7 from above and below by energizing an electromagnet (not shown). 3 is a switching circuit in which thyristors Thl and Th2 are connected in antiparallel and inserted into the primary side of the welding transformer 1.

4 is a current transformer inserted into the primary side of the welding transformer 1,
The load current is derived in terms of the primary side.

5 detects the load current via the current transformer 4, and controls the firing angles of the thyristors Thl and Th2 of the switching circuit 3 so that the load current becomes the target value of the welding current to adjust the current of the resistance welding machine. This is a control device that performs control.

This will be explained. 8 is an amplifier circuit, which connects the current transformer 4
Insert resistor R1 into the secondary side of , ground one end, and connect the other end to
The non-inverting input terminal is connected to the grounded inverting input terminal of the operational amplifier A1 through the input resistor R4, and the operational amplifier A
, multiple resistors R2, R2 (...
・・・・・・R2n is inserted in series, and these resistors R2, R2
5-... Analog switches Sl, S2, which are opened and closed by input signals to the mutual connection points of R2n (i.e., voltage dividing points) Al, a2......An・・・・・・
. . . One end of Sn is connected to form the gain switching circuit 9, and the analog switches Sl, S2 . . .
...The other end of Sn is connected to operational amplifier A via negative feedback resistor R3.
Commonly connected to the inverting input terminal of 1, analog switch S
By selectively closing Sn, the operational amplifier A1 has the amplification degree Gl, G2...
. . . is switched to either GO and output.

That is, the analog switches SL, S2, . . .
...When S1 of SO is closed, the amplification degree G of operational amplifier A1 is changed to amplification degree G, and when analog switch SO is closed, operational amplifier A1
The amplification degree G is then switched to the amplification degree Gn.

Reference numeral 10 denotes an effective value conversion circuit connected to the output terminal of the operational amplifier A1 of the amplifier circuit 8, and outputs the effective value of the input.

Reference numeral 11 denotes an analog-to-digital conversion circuit (hereinafter referred to as A/D conversion circuit) connected to the output terminal of the effective value conversion circuit 10 and configured to convert an analog input into, for example, a 10-bit digital signal and output it. .

The output of this A/D conversion circuit 11 is processed by a calculation processing section (hereinafter referred to as CP).
(abbreviated as U) 12. 1
3 is a programmable read-only memory (hereinafter referred to as PR) that stores various programs for sequence control.
(abbreviated as OM) 14, the number of secondary circuits of the welding transformer 1,
It is a storage unit equipped with a random access memory (hereinafter abbreviated as RAM) 15 that stores various data such as the turns ratio, target value of welding current, and welding time.

In addition, the RAM 15 of the storage unit 13 stores target value setting ranges for welding currents of welding transformers of various resistance welders (for example,
000A to 15000A) corresponding to the primary side converted current value (range where the maximum value of the current that also takes into account the withstand capacity of thyristors Th, Th2 is, for example, 1200A) is divided into multiple regions Wl, W2, W2,・・・・・・・・・Wn
The areas Wl, W2 . ．． ．． ．． ．． ．． ．． ．． ．． W.O.
data is stored. Then, the above regions W,,W
2...Wn is the amplification degree G of the operational amplifier A1
1, G2......Gn, and from the set data of the welding transformer turns ratio, number of secondary circuits, and target value of welding current, the CPU 12 calculates the current value converted to the primary side. The values are calculated as areas Wl, W2...
・・Determine which of the WO corresponds to, for example, W,
If so, the analog switch S1 is closed by the output signal of the CPU12, and the load current is detected at the amplification level G1. The above amplification degree Gl, G2...
...The mutual relationship of Gn is the area Wl, W2...
・・・・Maximum current value in each region of Wn (for example, W1-1
200A,. W2=1000A) is selected as a range. Moreover, the A/D conversion circuit 11
is output in full scale for each range in each region, so that even if the primary-side converted current value is small, the error per bit is the same. Reference numeral 16 denotes an input/output section, which is connected from both ends of the switching circuit 3 to a zero cross detection circuit 17 which is connected between the terminals of the AC power supply 2 and detects this every time the voltage crosses the zero point and sends out an output signal. A signal from a voltage detection circuit 18 which detects and outputs the voltage between both terminals is inputted and taken into the CPU 12.

Further, this input/output section 16 is connected to a counter circuit 19 connected to an oscillation circuit 20 that oscillates a clock pulse signal.
An output signal of the firing angle is sent from Ul2, and a selected output signal from CPU I2 is sent to the analog switches Sl, S2, . . . SO. When the counter circuit 19 receives the firing angle output signal from the CPU 12 via the input/output section 16, it counts based on the clock pulse signal of the oscillation circuit 20,
An output signal is sent when the count value matches the firing angle signal. Reference numeral 21 denotes a gate circuit that sends a firing signal to the gates of the thyristors Thl and Th2 of the switching circuit 3, which sends a firing signal at the same firing angle in both positive and negative half cycles according to the output of the counter circuit 19. It's starting to force you to turn on.

Next, the operation will be explained.

The control sequence for resistance welding is basically divided into four stages: pressurization, welding, holding, and pausing. First, by applying the AC power source 2, a control power source (not shown) is supplied to the control device 5. In this state, a target value of welding current suitable for welding is set based on the turn ratio of the welding transformer 1, the number of secondary circuits, the material of the material to be welded 7, the plate thickness, the number of stacked sheets, etc. using a data table (not shown). CP this set up data
Read by Ul2 and write to RAMl5,
Based on these data, the target value of welding current
The current value converted to the primary side is calculated by the arithmetic processing of CPU12. This calculated current value is R
Write to AMl5. Next, each time period for pressurization, welding, holding, and rest suitable for welding the material to be welded 7 is set using a data table, and these are written in the RAM 15 by the CPU 12. After setting these welding conditions, welding is performed according to the processing flow shown in FIG. First, by turning on a start button (not shown) (201), an electromagnet (not shown) is energized to operate the welding chips 6, 6, and the workpiece 7 sandwiched between the welding chips 6, 6 is pressurized ( 202). Then, when the set pressurization time ends (203), the RAM
The target value of the welding current written in l5 is converted into the primary side current value (hereinafter referred to as target value), and the value (hereinafter referred to as target value) is taken in (204
), this target value is the area Wl taken in from RAMl5,
W2・・・・・・・・・Determine which area of Wn it corresponds to (205′, 20da5・・・・・・・・・
・205n). Then, the CPU 12 sends an output signal to the analog switch via the input/output section 16 to close the analog switch, for switching to an amplification degree corresponding to a region one step higher in current value than the corresponding region. For example, when the corresponding region is W2 (205), in order to switch to the amplification G1 corresponding to the region W1, an output signal is sent to analog switch S1 to close it (206
o As a result, at the initial stage of energization, even if a current that exceeds the range determined by the above target value flows due to the material, plate thickness, surface condition, etc. of the workpiece 7, the operational amplifier A1 is saturated and accurate load current is maintained. This prevents the current from becoming undetectable (that is, detecting less current due to saturation). After that, welding time begins.

First, the thyristors Thl and Th2 of the switching circuit 3
is fired at a firing angle of 900 (207). This is a zero cross detection circuit 17 that detects the zero point of the first positive half cycle of the voltage of the AC power supply 2 when welding time begins.
and the detection signal of the voltage detection circuit 18 that detects that voltage is applied to the switching circuit 3,
When input via the input/output unit 16, the CPU 12 sends a command for 900 firings to the counter circuit 19 via the input/output unit 16, and upon receiving this command, the counter circuit 19 receives the first cycle of the voltage of the AC power supply 2. When the clock pulse signal of the oscillation circuit 20 is counted from the zero point of the positive half cycle of the voltage and both input signals match (when the count value becomes the same as the ignition command of 90 points), that is, the clock pulse signal of the oscillation circuit 20 is counted from the zero point of the positive half cycle of the voltage. 90
At the same time point (c), an ignition signal is sent to the gate of the thyristor (for example, Th2) of the switching circuit 3 via the gate circuit 21 to cause it to ignite (the same applies to the negative half cycle of the voltage). Thyristor with a firing angle of 900 (
For example, ignite Thl). The load current flowing to the secondary side of the welding transformer 1 due to this 900 ignition is input to the operational amplifier A1 of the amplifier circuit 8 via the current transformer 4 provided on the primary side. The operational amplifier A1 amplifies the input by the amplification degree G1 by closing the analog switch S1, converts this into an effective value by the effective value conversion circuit 10, and sends it to the A/D conversion circuit 11. A/D conversion circuit 1 that received this
1 converts the effective value into, for example, a 10-bit digital signal (208) and causes the CPU 12 to take it in. CPU12 is A
The current delay from when the voltage across the switching circuit 3 (positive half cycle) becomes zero until the load current becomes zero is caused by the signal taken from the /D conversion circuit 11 and the signal taken from the voltage detection circuit 18. The angle θ is measured, and the power factor angle φ is measured based on the data of the correlation between the current delay angle and the power factor angle of the load stored in RAM15 using this current delay angle θ. Difference △I between the output signal of the A/D conversion circuit 11 (effective value of detected load current) and target value
Calculate the firing angle increment Δa for the second cycle from
The firing angle of the cycle is determined (209). As can be seen from the above, the determination of the firing angle for the second cycle is performed after the positive half cycle of the voltage of the AC power supply 2 is completed. After the negative half cycle is completed (210), it is determined which of the regions Wl, W2...Wn the target value is in (211', 21f... ...21
1n-1) Analog switch S of the gain switching circuit 9 for switching to the amplification degree G2 corresponding to the corresponding level
2, sends an output signal through the input/output unit 16 to close it (212''), and at the firing angle of the second cycle determined by the positive half-cycle energization of the first cycle (209),
As described above, a firing signal is sent from the gate circuit 21 via the counter circuit 19 in response to the firing angle signal of the CPU12 to fire the thyristors Thl and Th2 (213). Then, as described above, the load current is detected in the positive half cycle of the second cycle, converted to an effective value, and the digital signal of the effective value is taken into the CPU12 from the A/D conversion circuit 11 (214
), the firing angle for the third cycle is determined from the power factor angle, effective value, and target value as described above (215). Then, until the welding time ends (216), the firing angle is determined based on the positive half-cycle energization result of the previous cycle and the firing is performed (21).
3 to 216) are repeated. Therefore, the firing angle from the second cycle onward is determined by calculating the firing angle increment Δa from the effective value of the load current detected in the positive half cycle of the previous cycle, and calculating the firing angle at the point of the previous cycle (n-1 times). If the arc angle is AO-, the firing angle An of the next cycle (n times) is determined by An-1-Δa, and the firing angle is set to 1 so that the load current reaches the target value. Constant current control of the welding current is performed by controlling the firing angle every cycle. Then, the end of the welding time is determined by CPUl2 (216), and when the welding time has ended, CPUl2 stops sending out the firing angle signal, and the thyristors Thl and Th2
is turned off and entered into a holding time (217). At this time, the material to be welded 7 remains under pressure by the welding tips 6, 6. When the holding time ends (217), the above-mentioned electromagnet (not shown) is de-energized and the welding chips 6, 6 are removed.
are operated to separate them from each other and release the pressure on the workpieces 7 to be welded, thereby entering a rest period and ending the welding operation (END). Next, when welding different parts of the material to be welded 7, the turns ratio of the welding transformer, the number of secondary circuits,
The primary side current value is calculated from the target value of the welding current, and welding is performed using this value while controlling the load current to the target value according to the process flow shown in FIG. 3, as described above.

These operations are performed by CPU12 according to a program stored in PROM14.

According to the present invention, the turns ratio of the welding transformer, the number of secondary circuits,
Since the load current is detected by switching the amplification degree according to the setting of the target value of the welding current, current control can be performed with constant accuracy even if the target value of current changes over a wide range, and the quality of welding can be improved. Stabilization can be achieved.

In addition, even if the welding transformer turns ratio, number of secondary circuits, and target value of welding current differ, it can be handled simply by setting the data, and this means that even when combined with various resistance welding machines, the same It has the advantage of being able to perform accurate and stable current control, and has the remarkable effect of expanding the range of application and further improving reliability.

[Brief Description of the Drawings] Fig. 1 is a block diagram showing an example of a conventional device, Fig. 2 is a block diagram showing an embodiment of the present invention, and Fig. 3 is a processing flow diagram explaining the operation of Fig. 2. It is. 1: Welding transformer, 3: Switching circuit, 4: Current transformer, 8: Amplifying circuit, 12: Arithmetic processing section.

Claims (1)

[Claims] 1 Connect the primary side of the welding transformer to an AC power source via a switching circuit in which thyristors are connected in antiparallel, and connect the load current on the secondary side of the welding transformer to the gate of the thyristor to the primary side of the transformer. an amplification circuit that detects the current through a current transformer; an effective value conversion circuit that converts the detected output of the current transformer into an effective value and sends it out; and a storage section for storing data, and transmits the output of the arithmetic processing section that calculates the firing angle based on the power factor angle measured from the data and the detection output to control the load current by phase angle control. In the amplifier circuit, the other end of the resistor inserted into the secondary side of the current transformer is connected to the inverting input terminal of the operational amplifier whose non-inverting input terminal is grounded via the input resistor. A resistor with multiple voltage dividing points is inserted between the output terminal of this operational amplifier and ground, one end of each of the analog switches is connected to each of the multiple voltage dividing points, and the other end is connected to a negative feedback resistor. The welding current target is commonly connected to the inverting input terminal of the operational amplifier through the circuit so that the amplification degree can be switched to multiple stages, and the welding current target is divided and set into multiple regions corresponding to the multiple stages of amplification degree of this amplifier circuit. The value data, the turns ratio of the welding transformer, and the number of secondary circuits are stored in the storage unit, and from the stored data, the plurality of analog switches are selectively closed using the output of the arithmetic processing unit to switch the amplification degree. A control device for a resistance welding machine, characterized in that it is configured as follows.