JPS6249151B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resistance welding current monitoring device, and an object of the present invention is to easily and inexpensively improve the accuracy of resistance welding current monitoring (current detection and comparison judgment with a predetermined value). With the goal.

The configuration of a conventional device of this type and its problems are as follows. An example is shown in FIG.

Here, 1 is the workpiece to be welded, 2 is a spot electrode for resistance welding, 3 is a toroidal coil that detects the resistance welding current, 4 is a waveform restoration (integration) circuit that shapes the waveform of the differential signal detected by the toroidal coil, 12
is an averaging circuit (integrator circuit) composed of a capacitor and a resistor, or a peak detection circuit composed of a capacitor and a diode, 7 is a comparison current value setting circuit, and 6 is an output of the averaging circuit 12 and a comparison current value setting. A comparison circuit 8 compares the output of the comparison circuit 7 with the output of the comparison circuit 7, and an external judgment output circuit 8 outputs a judgment output according to the output of the comparison circuit 7. With these methods, in the case of resistance welding machines that use asynchronous or semi-synchronous timer devices, an excessive inrush current may flow during the initial stage of welding due to biased magnetism in the welding transformer, as shown in Figure 7A. As a result, when the averaging circuit 12 is used, the average value of its output increases as shown in FIG. A judgment output as shown in will be output. In addition, when the peak detection circuit 12 is used, its output detects and holds the peak value of the first inrush current as shown in FIG.
The result is as shown in Figure E'.

However, these conventional methods have two problems. First, as mentioned above, judgment processing is often performed based on the current value at the initial stage of welding when inrush current flows (although this has little to do with welding quality), and it is difficult to accurately monitor welding quality. I can't do it. Second, the values to be compared are the peak value and average value of the welding current, and considering that the welding quality of resistance welding is related to resistance heat generation due to the effective value current, the comparative judgment is not made using the effective value. , poor accuracy.

For the above reasons, conventional methods and devices have been insufficient as welding current monitoring devices and have many problems.

In view of the above-mentioned conventional drawbacks, the device according to the present invention adopts an effective value-to-DC voltage conversion circuit in place of the peak hold circuit and CR averaging circuit, and also completely eliminates troubles caused by inrush current at the start of energization. In order to eliminate this problem, a switch circuit is installed somewhere between the toroidal coil output and the comparator so that the toroidal coil output signal is not transmitted to the comparator for about half a cycle to two cycles after the start of energization, or an external judgment A disabling circuit is provided to disable the output circuit for only this period. This eliminates the conventional problem of erroneous judgment due to inrush current, and furthermore, it is possible to accurately monitor welding quality by comparing the effective value current.

FIG. 1 is a block diagram of a device according to the invention, and FIG. 2 is an embodiment of the same device.

In the figure, 1 is the workpiece to be welded, 2 is a spot electrode for resistance welding, 3 is a toroidal coil for detecting resistance welding current, 4 is an AC integrating circuit as a waveform restoration circuit, 5 is an effective value-DC voltage conversion circuit, 6 is a comparison circuit, 7 is a comparison current value setting circuit, 8 is an external judgment output circuit, 9 is a switch circuit, and 10 is a switch control circuit.

In each circuit 4 to 10, R ₁ to R ₁₁ are resistors, VR is a variable resistor, C ₁ to _{C 3} are capacitors, and IC ₁
is an operational amplifier, IC ₂ is an effective value to DC voltage conversion IC, IC ₃ is an analog switch, IC ₄ is a one-shot IC, IC ₅ and IC ₆ are comparators, TR ₁ is a transistor, and LED is a light emitting diode. be.
Further, the voltages at A, B, B', C, D, D', and E are shown in A, B, B', C, D, D', and E in FIG.

Next, the operation will be explained. First, resistance welding current is detected by the toroidal coil 3. Since this detected waveform is a differential waveform, it is input to the AC integration circuit 4.

Furthermore, this is input to an effective value-to-DC voltage conversion circuit 5 (which can be constructed from an operational amplifier, but some are made into a single-chip IC). As explained earlier, Figure 3 shows the output waveforms of the main parts in Figure 2, but in this case, as seen in the output waveform A of the AC integrating circuit 4, an inrush current has occurred. Since this is the case, the effective value-DC voltage conversion circuit 5
The output B of is greatly overshot, and if this value is compared with the set output N' of the comparison current value setting circuit 7 in the comparator circuit 5, it is possible that an incorrect judgment may be made depending on the value of N'. It will be done. Also, when displaying this detected value digitally on a display, etc., the timing of A/D conversion becomes important, but if the inrush current value is A/D converted in this way, it may lead to incorrect judgments. A/D conversion should be performed in the stable region of the inrush current section. Therefore, in this example of the circuit, in order to detect the energization start point from the output of the effective value-DC voltage conversion circuit 5, a comparator in the switch control circuit 10 is used.
Using IC ₅ (this comparator IC ₅ and resistors R ₇ and R ₈ constitute a welding start point detection circuit), compare B and B' in Fig. 3, and from the output, determine the capacitor C ₃ , A trigger signal for the one-shot IC ₄ in the same circuit 10 is created using the resistor R ₆ , and the capacitor
A one-shot pulse frequency determined by the time constant of C ₂ and resistor R ₅ is obtained.

The pulse width of this pulse is about half a cycle to 2 or 3 cycles of energization, and this circuit 10
The output is used as a control signal for the switch circuit 9 or a disabling signal for an external determination output circuit 8, which will be described later.

Here, an analog switch IC ₃ is configured between the effective value-DC voltage conversion circuit 5 and the comparison circuit 6,
A switch circuit 9 controlled by a switch control circuit 10 is provided, and the switch circuit 9 is configured to open only when the output of the switch control circuit 10 is at a high level. Therefore, comparison and determination are not performed while the output of the switch control circuit 10 is at a high level from the start of energization. In other words, D is a low level. On the other hand, when the output C becomes low level,
D becomes higher than N', and the output E of the comparator circuit 6 is obtained. Therefore, it is possible to prevent factors such as inrush current that would disturb the measurement from entering, and it is possible to make extremely simple and highly accurate determinations.

In FIGS. 1 and 2, the switch circuit 9 is inserted between the circuits 5 and 6, but this is of course not limited to this, and for example, the switch circuit 9 is inserted between the circuits 4 and 5.
It is also possible to do this by changing the trigger circuit of the one-shot IC ₄ in the circuit 10.

Further, as shown in FIG. 4, this switch circuit 9
may be inserted between the circuit 6 and the external determination output circuit 8 (here, this is an example configured to output the determination result to the outside using an LED).

Further, FIG. 5 shows an example of a circuit in which the external output determination circuit 8 is disabled only while the C signal is at a high level. Note that TR ₂ is a transistor and R ₁₂ is a resistor. The embodiments shown in FIGS. 4 and 5 are included in claim 2 of the present invention.
Further, the switch circuit 9 and the switch control circuit 10 in the embodiment of FIG. 2 are collectively referred to as a switch circuit in the first claim.

According to the monitoring device of the present invention having the above-described configuration, an effective value-to-DC voltage conversion circuit is used in place of the peak hold circuit and CR averaging circuit conventionally used in this type of device, and furthermore, an energization In order to completely eliminate troubles caused by inrush current, etc. at the start, the switch circuit is connected to the effective value - DC voltage conversion circuit so that the output signal of the toroidal coil is not transmitted to the comparator circuit for about half a cycle to two cycles after the start of energization. A circuit is installed on the input side or output side of the power source, or a circuit is installed that disables the external judgment output circuit for this period to prevent detection of the unstable current peculiar to welding that occurs when energization starts, making it extremely easy to detect. Moreover, the resistance welding current can be monitored with high precision.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an embodiment of the monitor device according to the present invention, FIG. 2 is a circuit diagram of the same, FIG.
5 is a circuit diagram of another embodiment of the main parts of the apparatus of the present invention, FIG. 6 is a block diagram of a conventional monitor apparatus, and FIG. 7 is a voltage waveform diagram of each main part of the apparatus. 3... Toroidal coil, 4... AC integrating circuit, 5
... Effective value - DC voltage conversion circuit, 6... Comparison circuit, 7
... Comparison current value setting circuit, 8... External judgment output circuit,
9...Switch circuit, 10...Switch control circuit,
IC ₃ ...analog switch, IC ₄ ...one shot circuit (one shot IC), IC ₅ ...comparator.

Claims (1)

[Claims] 1. A toroidal coil for detecting a resistance welding current, an AC integrating circuit for restoring the output of the toroidal coil to the original resistance welding current waveform, and converting the effective value of the output of the AC integrating circuit into a DC voltage. an effective value-DC voltage conversion circuit to be converted; a comparison current value setting circuit; a comparison circuit that compares the output of the effective value-DC voltage conversion circuit with the output of the comparison current value setting circuit; and an output of the comparison circuit. The switch circuit is equipped with an external judgment output circuit that notifies the outside, a welding start point detection circuit that is open for a certain period of time after the resistance welding current starts flowing, a one-shot circuit, and an analog switch. A resistance welding current monitor device characterized by being inserted into the input side or output side of a conversion circuit. 2. A toroidal coil that detects the resistance welding current, an AC integrating circuit that restores the output of the toroidal coil to the original resistance welding current waveform, and an effective value-DC that converts the effective value of the output of the AC integrating circuit into a DC voltage. a voltage conversion circuit, a comparison current value setting circuit, a comparison circuit that compares the output of the effective value-DC voltage conversion circuit and the output of the comparison current value setting circuit, and an external determination that notifies the output of the comparison circuit to the outside. A resistance welding current monitoring device comprising: an output circuit; and a circuit that disables the external determination output circuit for a certain period of time after the resistance welding current starts flowing.