JPH0413076B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a current control device for a resistance welder that controls welding current to various set values. (Prior Art) Conventionally, an AC power source is connected to an inverter made of transistors via a rectifier circuit and a wave circuit, and the inverter is connected to a welding electrode via a welding transformer and a rectifier circuit, and the current flows into the input circuit of the inverter. A device has been proposed that turns off the current applied to the base of the inverter's transistor when the effective value of the welding current reaches the effective value set by the current setting device, deactivates the inverter, and controls the effective value of the welding current to the set value. has been done. In this device, the setting value of the current setting device when using a large-capacity welding transformer F and the actual welding current value can be made to correspond by using the characteristic F shown in Fig. 1 measured in advance. This can be achieved by shortening the secondary conductor of the welding gun, reducing the number of workpieces to be welded, or reducing the thickness and using a welding transformer A with a correspondingly smaller capacity. First, the characteristic becomes as shown in characteristic A in FIG. Therefore, when using a welding transformer with a different capacity, the variable resistor inserted in the base circuit of the inverter transistor is adjusted each time, so that the setting value of the current setting device corresponds to the actual welding current value. That's what I was doing. Therefore, when frequently replacing a welding transformer with a different capacity, there are inconveniences such as the time required for adjustment, which makes it impossible to use the transformer immediately, and poor welding due to adjustment errors. (Problems to be Solved by the Invention) An object of the present invention is to provide a current control device for a resistance welding machine that does not have the above-mentioned disadvantages. (Means for Solving the Problems) The present invention has a welding transformer and a control signal connected to the primary coil of the welding transformer and which sets the welding current to a predetermined value by a control signal corresponding to a set value by a welding current setting device. A current control device for a resistance welding machine equipped with an inverter to control, comprising a correction device for the control signal,
The correction device includes a welding transformer capacity setter that outputs a setting signal corresponding to the capacity of the welding transformer to be used, a memory that stores correction constants corresponding to a plurality of capacities of the welding transformer, and a welding current. The welding current of the set value flows into the welding circuit from the welding current value set in the setting device and the correction constant corresponding to the capacity of the welding transformer set in the welding transformer capacity setting device read from the memory. and an arithmetic unit that calculates a control signal value corresponding to the arithmetic unit, and the control signal outputted from the arithmetic unit is supplied to the inverter. (Function) According to the configuration of the present invention, when the welding current setting value is set in the welding current setting device and the capacity of the used welding transformer is set in the capacity setting device of the used welding transformer, the used transformer is set from the memory. A correction constant corresponding to the capacity of The welding current of the set value set in the welding current setting device flows through the welding circuit. (Example) An example of the present invention will be described with reference to the drawings. In FIG. 2, 1 is a welding transformer, and the primary coil of the welding transformer 1 is connected to transistors 2 ₁ , 2 ₂ , 2
The secondary coil was connected to an AC power terminal 5 through an inverter 2, a wave circuit ₃ , and a rectifier circuit 4 _, and the secondary coil was connected to a welding electrode 7 through a rectifier circuit 6. The bases of the transistors 2 ₁ , 2 ₂ , 2 ₃ , 2 ₄ are connected to a pulse width control circuit 1 which is energized by the clock pulse of an oscillator 9 via a base drive circuit 8.
0, and the transistor 2 ₁ , until the output of the current detection circuit 12 which detects the effective value of the welding current obtained from the current detector 11 such as a Hall sensor reaches the welding current value set by the current setting device 13. 2
Apply current to the bases of transistors ₂ , 2 ₃ , and 2 ₄ , and when it exceeds, turn off transistors 2 ₁ , 2 ₂ , 2 ₃ , and 2 ₄ ,
The welding current of the set value is now flowing. The above is not particularly different from what was proposed earlier. According to the present invention, the welding current setting device 13 and the welding transformer capacity setting device 1 output a setting signal corresponding to the capacity when the capacity of the welding transformer to be used is set.
4, a memory 15 for storing correction constants corresponding to a plurality of capacities of the welding transformer, and a welding current setting device 1
The control signal value corresponding to the welding current setting value is calculated from the welding current value set in step 3 and the correction constant corresponding to the capacity of the welding transformer 1 used and set in the setting device 14 read from the memory 15. The control signal correction device includes a CPU 16 as an arithmetic unit, and applies the control signal output from the CPU 16 to the pulse width control circuit 10 via the D/A converter 17, thereby controlling the welding current setting device 13 and the capacity. According to the setting of the setting device 14, even when the welding transformer 1 is replaced with a welding transformer 1 having a different capacity, a welding current corresponding to the welding current setting value is made to flow through the welding circuit. To further explain the stored contents of the memory 15, when welding transformers of various capacities are used, the welding setting value I set by the welding current setting device 13 in the welding transformer 1 of each capacity and the welding setting value of this setting value D/ when current actually flows through the welding circuit
The relationship with the output value S (control signal value) of the A converter 17 is, for example, as shown in the third diagram, and is expressed by the following equation. S=KI+V However, K and V are correction constants.The following formula shows an example of correction constants for welding transformers of various capacities.

[Table] In FIG. 2, 18 is an interface. FIG. 4 shows a block diagram of an example of the pulse width control circuit 10. In the figure, 19 and 20 are flip-flops, 21, 22, 23, and 24 are AND gates, and 2
5 is a monostable multivibrator whose terminal output is at a low level for a short time with the clock pulse of oscillator 9, 26 is an OR gate, 27 is an inverter, 28
is a comparator that compares the output of the current detection circuit 12 that detects the effective value of the welding current flowing in the welding circuit with the output of the D/A converter 17, and outputs a low level signal when the two match. The pulse width control circuit 10 operates a flip-flop circuit using the clock pulse of the oscillator 9 when the effective value output from the current detection path 12 does not reach the control signal value corresponding to the welding current setting value output from the D/A converter 17. The output of the Q terminal of the flip-flop 20 remains at a high level, the output of the Q terminal of the flip-flop 20 alternately becomes a high level, and the output of the terminal of the monostable multivibrator 25 becomes a low level for a short time every time a clock pulse is input. Therefore, high level signals are alternately output from the AND gates 27 and 28 with short low level periods between them, and when the effective value reaches the set value, the AND gates 27 and 28
The output will be at a low level. Next, the operation of the circuit shown in the second diagram will be explained. Now, assume that there are two workpieces sandwiched between the welding electrodes 7,
Correspondingly, as welding transformer 1, for example
Use one with a capacity of 20KVA. Then, the welding current is set to, for example, 7000A using the welding current setting device 13, and the capacity setting device 14 is set to the aforementioned 20KVA. Since the memory 15 stores the correction constants K and V for each welding transformer 1 having a plurality of capacities as described above, the setting signals from the setting devices 13 and 14 are sent to the CPU 16 via the interface 18. When input, the correction constants K=1, V=0.3125 corresponding to the setting signal are read out by the memory 15, and the CPU
In step 16, calculation is performed according to the previous equation, and the control signal corresponding to the welding current of 7000A is converted to the D/A converter 1.
Output from 7. This control signal is thus applied to the pulse width control circuit 10, and the output of this circuit 10 is passed through the base drive circuit 8 to the transistors 2 ₁ to 2 ₄ of the inverter 2.
The inverter 2 outputs an AC voltage of, for example, 800 Hz to the primary coil of the welding transformer 1, and a welding current of 7000 A flows through the welding circuit. If the welding current can be changed without replacing the welding transformer 1, all you have to do is reset the welding current setting device 13, increase the number of workpieces, or thicken the plate material of the workpieces, and increase the capacity accordingly. When replacing the welding transformer 1, by resetting the welding transformer capacity setting device 14, the welding current set by the welding current setting device 14 flows through the welding circuit. (Effects of the Invention) According to the present invention, when replacing a welding transformer with a welding transformer of a different capacity in response to changes in workpiece welding conditions, there is no need to manually adjust the inverter, reducing the number of work steps. Since it is only set using a capacity setting device, it is effective in preventing welding defects due to adjustment errors.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the relationship between the welding current setting value and welding current with the capacity of the welding transformer as a parameter;
FIG. 2 is a block diagram of one embodiment of the present invention, FIG. 3 is a diagram showing the relationship between the welding current setting value and the output value of the D/A converter using the capacity of the welding transformer as a parameter, and FIG. 4 1 is a block diagram of an example of a pulse width control circuit. 1... Welding transformer, 2... Inverter, 7...
Welding electrode, 10... Pulse width control circuit, 13...
Welding current setting device, 14... Welding transformer capacity setting device, 15... Memory, 16... CPU, 17...
D/A converter.

Claims (1)

[Claims] 1. In a current control device for a resistance welding machine, comprising a welding transformer and an inverter connected to the primary coil of the welding transformer and controlling the welding current to a predetermined value by a control signal corresponding to a set value by a welding current setting device. , the correction device includes a welding transformer capacity setter that outputs a setting signal corresponding to the capacity of the welding transformer to be used, and a correction device each corresponding to a plurality of capacities of the welding transformer. A memory for storing constants, a welding current value set in the welding current setting device, and a correction constant corresponding to the welding transformer capacity set in the welding transformer capacity setting device read from the memory. A resistance welding machine comprising: a computing unit for calculating a control signal value corresponding to the set value welding current flowing through the welding circuit; and a control signal outputted from the computing unit is supplied to an inverter. Current control device.