JPH028832B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for controlling the operation and energization of a welding gun in a resistance spot welding machine.

For example, it is well known that spot welding is frequently used in the assembly process of automobile bodies.
Recently, welding work has come to be automatically performed using robots and the like.

By the way, resistance spot welding involves sandwiching and pressurizing the stacked objects to be welded using electrodes, passing a large current through the areas where the contact resistance locally decreases, and creating a gossamer-shaped weld (nugget) on the contact surface. This is a method of welding. Therefore, the secondary cable that connects the welding transformer and welding gun requires several thousand to
Conventionally, water-cooled cables have been used as secondary cables because a current of 10,000 amperes flows through them, which generates heat.In recent years, cables with a water-cooled structure have been used, especially in recent years. It accounts for the majority. Although the reciprocating lines of this type of cable are electrically insulated by a rubber diaphragm, they are frequently bent, a large current flows intermittently, and the rubber hose is filled with cooling water. During use, the cable's round trip line may be damaged and cause an internal short circuit. In such a case, the welding current flows through the short circuit point and back and forth,
Since it does not flow between the electrodes, welding cannot be performed. However, in the above-mentioned stress cable, the internal condition cannot be seen from the outside, and furthermore, in an automatic welding process using a robot or the like, it is not possible to know whether welding is good or bad each time welding, so there is a risk that welding defects will occur frequently.

In order to eliminate these inconveniences, it is conceivable to conduct periodic inspections of the secondary cable frequently, but it is extremely difficult to predict internal short circuits through periodic inspections, which can lead to welding defects. Or, the secondary cable, which can still be used sufficiently, may be replaced, resulting in an increase in welding costs. Therefore, in the past, the actual situation was to increase the frequency of welding quality inspections and strive to discover welding defects, and to discover short circuits in secondary cables etc. through welding defects, which not only placed a heavy burden on the workers, but also There were problems such as extremely low efficiency.

This invention was made in view of the above circumstances, and is a control device for a resistance spot welding machine that is capable of not only controlling normal welding work but also detecting abnormal short circuits on the secondary side of a welding transformer such as a secondary cable. The purpose is to provide the following. The control device of the present invention is operable by any of a plurality of start switches, and includes a pressurizing valve drive circuit that drives a valve for closing a welding gun, and a pressurizing valve drive circuit that drives a valve for closing a welding gun, and a pressurizing valve drive circuit that drives a valve for closing a welding gun. A preload time control circuit that controls the pressurization time of the workpiece, that is, the preload time, a welding time control circuit that controls the welding time during which welding current should flow, and a holding time that continues the closing operation of the welding gun after energization ends. A holding time control circuit, a welding current control circuit that conducts current after the preload time elapses until the welding time elapses, and a current value on the primary side or secondary side of the welding transformer is set to a predetermined reference current value. The circuit is equipped with a detection circuit that outputs a signal when the pressure is exceeded, and when one of the start switches is turned on, the other circuits except the pressurizing valve drive circuit are turned on, and the other circuits are turned on. The present invention is characterized in that the circuits other than the detection circuit are turned on when any one of the starting switches is turned on.

The control device of the present invention will be explained in more detail below based on embodiments.

FIG. 1 is a block diagram schematically showing an embodiment of the present invention, and the control device shown here is configured to be able to set multiple types of welding conditions, that is, multiple energization times and multiple current values. , the welding conditions are multiple (5 in the figure) starting switches 1, 2,
3, 4, and 5 are selected.
The starting switches 1 to 5 close the circuit by manual operation or by input from another controller (not shown) such as a robot control device.
5 closes, the preload time control circuit 6 is turned on. The preload time control circuit 6 includes start switches 1 to 5.
Multiple types of preload times S1, S2, S
The preload time control circuit 6 is turned on when any of the starting switches 1 to 5 is closed, and the preload time control circuit 6 is turned on when any of the starting switches 1 to 5 are closed. 5 (contacts a1, a2, a3, a in the figure)
4, a5) is closed, any of the preload times S1 to S1 set by the setting device 7 is closed.
It is configured to output a signal after S5 has passed.

The output signal of the preload time control circuit 6 is input to a welding time control circuit 8 and a welding current control circuit 9, respectively. The welding time control circuit 8 has a plurality of types of welding times W1, W2, W3, W4, W corresponding to the start switches 1 to 5.
A setting device 10 that can set 5 is connected, and these welding times W1 to W5 are set by a circuit (in the figure, contacts b1, b2, b3,
b4 and b5) are closed, and corresponding welding times W1 to W5 are input and set from the setting device 10 to the welding time control circuit 8, and a signal is sent to the welding time control circuit 8 from the preload time control circuit 6. When is input, the welding time control circuit 8 is turned on, and after the welding time W1 to W5 input and set corresponding to the activated start switches 1 to 5 have elapsed,
Welding time control circuit 8 outputs signals to welding current control circuit 9 and holding time control circuit 11.

On the other hand, the welding current control circuit 9 controls the current flowing between the electrodes (each not shown) in the welding gun, and turns on in response to a signal input from the preload time control circuit 6 to energize. , and is configured to turn on and stop energization in response to a signal input from the welding time control circuit 8. Therefore, the control device shown in FIG. The welding current is made to flow only during the set welding times W1 to W5. The current value I1,I of the welding current
2, I3, I4, and I5 are the activation switches 1 to 1;
5 (contacts c1 and c in the diagram)
2, c3, c4, and c5) are inputted to the welding current control circuit 9 from the setting device 12 connected thereto.

Further, the holding time control circuit 11 controls the welding current I1
The holding time control circuit 11 is configured to control the holding time during which the welding gun continues to clamp and press the workpiece (not shown) after the energization of I5 is completed, and the holding time control circuit 11 includes the start switch 1. ~
5 (contacts d1 and d in the diagram)
2, d3, d4, d5)
3 is connected and any of the start switches 1 to 5 is turned on, the contact d1 is interlocked with it.
~d5 is closed and activation switches 1 to 5 are turned on.
The retention times H1, H2, H3, H4, H corresponding to
5 is input and set to the retention time control circuit 11. And retention time control circuit 11
is turned on by a signal input from the welding time control circuit 8, and is configured to output a termination signal after the holding times H1 to H5 input and set from the setting device 13 have elapsed. .

Furthermore, the control device shown in FIG. 1 includes a pressurizing valve drive circuit 14. The pressurization valve drive circuit 14 includes a pressurization valve (not shown) that controls a pressure fluid such as air that opens and closes the welding gun.
The solenoid SOL is energized to operate the pressurizing valve, and the start switches 1 to 1
5, for example, the 5th activation switch.
Other starting switches 1 to 1 except starting switch 5
4 (contacts e1 and e in the figure)
2, e3, and e4) are closed to turn on and energize the solenoid SOL, and when a termination signal is input from the holding time control circuit 11, it turns on and energizes the solenoid SOL. The pressurizing valve is configured to stop and return the pressurizing valve.

Therefore, the control device shown in FIG. 1 closes the welding gun to clamp and pressurize the workpiece when the first to fourth starting switches 1 to 4 are turned on, and in this state, the preload time S1 is increased. ~ Welding current I1 ~ until welding time W1~W4 elapses after S4 elapses
I4 is energized, and after the energization ends, the holding time H1~
When the welding gun is opened after H4 has elapsed and the fifth start switch 5 is turned on,
The welding current is configured to be energized without closing the welding gun.

Further, the above control device has a detection circuit 15 that is turned on when the welding gun is not closed, that is, a circuit that closes in conjunction with the fifth starting switch 5 among the starting switches 1 to 5 (indicated by contact e5 in the figure). The detection circuit 15 has a detection circuit 15 that is turned on through the circuit. The detection circuit 15 outputs an alarm signal when a current value on the primary side or secondary side of a welding transformer (not shown) exceeds a predetermined reference current value. As shown in the figure. Reference numeral 16 in FIG. 2 is an integrator, which is one of the welding transformers.
The energizing current input from the current detector 17 such as a toroidal coil, Hall element, or current transformer attached to the next or secondary side is converted into a current waveform that is a differential waveform thereof, and the output is given to the waveform shaper 18. It is configured like this. The waveform shaper 18 is configured to rectify the signal input from the integrator 16 and convert it into a DC voltage according to the energizing current value, and further inputs the DC voltage to the comparator 19. On the other hand, the comparator 19 includes the reference generator 2
0 is connected, the reference generator 20 sets a reference voltage corresponding to the reference current value, and the comparator 19 compares the reference voltage with the voltage input from the waveform shaper 18. Waveform shaper 1
When the voltage input from 8, that is, the measured current value is larger than the reference current value, the alarm signal generator 21
outputs a signal to the alarm signal generator 21
is designed to output an alarm signal. Note that the reference current value is used as a standard for determining whether or not the actual measured current value is abnormal, and specifically, when the welding electrodes are turned on with mutual insulation. The value of no-load current flowing to the primary side of the welding transformer and the value of 1 when actually welding.
If the welding current flowing to the next side is set to an intermediate value, or if the configuration is configured to detect the current on the secondary side,
It is preferable to set the value to half the welding current value on the secondary side.

Next, the operation of the control device configured as described above will be explained. The selection of welding conditions and the start of welding work are performed by the first to fourth starting switches 1 to 4 among the starting switches 1 to 5.
That is, for example, when the second start switch 2 is turned on, the contacts a2, b2,
c2, d2, and e2 are closed, and as a result, the preload time S2, which is preset corresponding to the second starting switch 2,
Welding time W2, welding current I2, and holding time H2 are each transmitted from setting devices 7, 10, 12, and 13 to preload time control circuit 6, welding time control circuit 8, welding current control circuit 9, and holding time control circuit 11, respectively. Input/set. At the same time, the pressure valve drive circuit 14 is turned on to excite the solenoid SOL, and as a result, the pressure valve is switched, and the welding gun is closed, thereby clamping and pressurizing the workpiece. Further, the preload time control circuit 6 is also turned on, and the setting device 7 is turned on.
The preload time control circuit 6 outputs a signal to the welding time control circuit 8 and the welding current control circuit 9 after the preload time S2 inputted from the preload time S2 has elapsed. Correspondingly, the welding current control circuit 9 is turned on, so that the second starting switch 2 is turned on, and a welding current I2 of a predetermined current value selected flows between the electrodes of the welding gun. Further, the welding time control circuit 8 receives a signal from the preload time control circuit 6 and turns on, and then outputs a signal after the welding time W2 selected by the second start switch 2 has elapsed, and as a result, the welding current The control circuit 9 is turned off and the current supply is stopped. That is, the application of the welding current I2 continues until the welding time W2 has elapsed. After the energization is completed, that is, the holding time control circuit 11 is turned on by the output signal of the welding time control circuit 8, and the holding time control circuit 11 is turned on by the input/setting of the second starting switch. After the holding time H2 has elapsed, a termination signal is output, and as a result, the pressurizing valve drive circuit 14 is turned off and the solenoid SOL is demagnetized, so that the welding gun opens and releases the workpiece. Therefore, as shown in FIG. 3, the welding gun pressurizes the workpiece for a selected preload time S2, welding time W2, and holding time H2 when the start switch 2 is turned on. It will continue until.
The time chart is shown in Figure 3.

On the other hand, when detecting a short circuit, the fifth starting switch 5 among the starting switches 1 to 5 is turned on. Accordingly, each contact a5, b5, c5, d5 linked to the fifth starting switch 5 closes, so that the preload time S5, welding time W5, and welding current I are set in advance in correspondence with the fifth starting switch 5.
5 and holding time H5 are set by setting devices 7, 10,
12 and 13 are input and set to each of the preload time control circuit 6, welding time control circuit 8, welding current control circuit 9, and holding time control circuit 11. Further, since the other contact e5 linked to the fifth starting switch 5 is closed, the detection circuit 15 is turned on. In that case, there is a fifth valve on the pressure valve drive circuit 14 side.
Circuit (contact) that closes in conjunction with start switch 5
Since the pressurizing valve drive circuit 14 is not turned on, the welding gun remains open. After the preload time S5 has elapsed, the welding current control circuit 15 operates to flow the welding current I5 inputted in advance until the welding time W5 elapses. In that case, unless there is a particular short circuit on the secondary side of the welding transformer, the circuit is open, so no overall current flows through the secondary side, and a few amperes to several tens of amperes flows through the primary side. Only current flows, but if there is a short circuit on the secondary side of the secondary cable or welding gun, a welding current I5 of several thousand to tens of thousands of amperes will flow on the secondary side, and the A current of several hundred amperes flows through the The current on the primary or secondary side of the welding transformer is detected by the current detector 17 shown in FIG. The voltage is converted into a voltage according to the current flowing through the waveform shaper 18, and further compared with a reference voltage in the comparator 19. In that case, if a short circuit occurs on the secondary side of the welding transformer, a large current as described above will flow to the primary and secondary sides even though the welding gun is open. The current value significantly exceeds the reference current value preset by the reference generator 20, so that the comparator 19 outputs a signal. Since the alarm signal generator 21 is turned on by the output signal of the comparator 19, the alarm signal lights up a lamp or sounds an alarm, thereby preventing a short circuit on the secondary side of the welding transformer. can be easily known. Note that the holding time control circuit 11 outputs a termination signal after the holding time H5 has elapsed after the end of energization, but if a short circuit occurs on the secondary side of the welding transformer as described above, an appropriate reset operation is performed. It is preferable to interlock so that activation switches 1 to 5 do not function until then.

As explained above, according to the control device of the present invention, by turning on one of the predetermined start switches among the start switches, the welding gun is energized with the welding gun open, and one of the welding transformers at that time is turned on. Since the current value on the next side or secondary side can be detected and compared with the reference current value, if a short circuit occurs on the secondary side of the welding transformer, the short circuit can be directly known, and therefore this According to the device of the invention, two
Next, you can deal with abnormal short circuits by replacing the cable, etc.
Inconveniences such as welding defects and their rework can be eliminated before they occur.

[Brief explanation of drawings]

Fig. 1 is a block diagram schematically showing an embodiment of the present invention, Fig. 2 is a block diagram showing an example of the detection circuit, and Fig. 3 shows the relationship between pressurization and energization during welding and short circuit detection. This is a time chart showing timing. 1, 2, 3, 4, 5... Start switch, 6... Preload time control circuit, 7, 10, 12, 13... Setter,
8... Welding time control circuit, 9... Welding current control circuit,
11... Holding time control circuit, 14... Pressure valve drive circuit, 15... Detection circuit.

Claims (1)

[Claims] 1. By closing the welding gun electrically connected to the secondary side of the welding transformer, the object to be welded is clamped and pressurized by a pair of electrodes provided on the welding gun,
In this state, a current is passed through the primary side of the welding transformer to close the plurality of start switches and the welding gun in a resistance spot welding machine that welds the workpiece by passing a welding current between the electrodes. a pressurization valve drive circuit that drives a valve for welding, a preload time control circuit that controls a preload time until current flows to the primary side of the welding transformer after one of the start switches is turned on, and a preload time control circuit that controls the welding current. a welding time control circuit that controls the welding time during which current is applied to the primary side of the welding transformer in order to conduct the welding process; a holding time control circuit that controls the holding time that continues the closing operation of the welding gun after the energization is completed; A welding current control circuit that conducts current until the time elapses, and a detection circuit that outputs a signal when the current value on the primary side or secondary side of the welding transformer exceeds a predetermined reference current value. When any of the starting switches is turned on, the circuits other than the pressurizing valve drive circuit are turned on, and when any of the other starting switches is turned on, the circuits other than the pressurizing valve drive circuit are turned on. A control device for a resistance spot welding machine, wherein the circuits other than the detection circuit are turned on.