JPH05177362A - Inverter type resistance welding method - Google Patents

Abstract

PURPOSE:To improve productive efficiency by suppressing the interruption of welding work to the minimum when an abnormal situation of unenergizing is generated, in a secondary side circuit of an inverter type resistance welding machine. CONSTITUTION:At the time of normalcy, constant current control is carried out so that a welding current I2 is coincident to a set value by a secondary side feedback system. When a situation that the welding current I2 does not flow in the secondary side circuit during a welding energizing cycle is generated due to some causes, an unenergizing detection part 44 detects the abnormal situation of unenergizing and informs a system control part 42 on it. The system control part 42 interrupts or suspends welding energizing, releases a welding gun 24 and allows an inverter control part 34 to carry out test energizing. In this test energizing, when a current I1 is not carried to a primary side circuit, the system control part 42 allows the welding gun 24 to again sandwich materials to be welded and allows the inverter control part 34 to resume welding energizing to carry out welding energizing by constant current control of a primary side feedback system.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter type resistance welding method, and more particularly to a resistance welding method for performing constant current control.

[0002]

2. Description of the Related Art Inverter resistance welding methods are widely used in automatic welding machines, especially welding robots, because they have excellent efficiency and power factor and can make the welding transformer small. A welding transformer with a rectifying element is often used in this type of power supply. This welding transformer is a transformer in which all the constituent parts are made as an integral unit, and a rectifying element is integrally attached to a secondary coil and is directly connected to a welding gun. With this direct connection structure, it is possible to shorten the secondary cable and reduce impedance drop and power consumption.

In an inverter type resistance welding power source device in which such a welding transformer with a rectifying element is mounted on a robot, when so-called constant current control is performed, a current detection sensor is attached to the secondary side circuit of the welding transformer, and this current detection is performed. It is customary to feed back the output signal of the sensor and control the operation of the inverter circuit so that the secondary side current (welding current) matches the set value.

[0004]

By the way, in order to carry out welding energization, even if an object to be welded is sandwiched by a gun of a robot and an inverter circuit is operated, a welding current may not flow in a secondary side circuit. .. There are mainly three causes of this abnormal situation.

The first is a case where the rectifying element on the secondary side of the welding transformer is short-circuited and destroyed. A welding transformer with a rectifying element has a structure in which a pair of rectifying elements are sandwiched by conductors (coil pieces) of a secondary coil from both sides, but the load for electrical contact on both rectifying elements becomes unbalanced. If so, one of the rectifying elements is likely to be short-circuited and broken, and then the other rectifying element will not be able to withstand the overvoltage and will be easily short-circuited.

Secondly, the secondary side cable connecting the welding transformer and the secondary conductor or welding electrode of the gun is broken. By installing a welding transformer on the robot, the secondary side cable will be significantly shortened, but still, due to twisting during movement of the robot or fatigue over time,
It may break.

Thirdly, the output line of the current detection sensor attached to the secondary side circuit is broken due to being caught by a nearby object during movement of the robot. in this case,
Although a current actually flows in the secondary side circuit, the output signal of the current detection sensor is not fed back, so the power supply device determines that it is not energized, and stops operating.

In addition to these three causes, although the occurrence frequency is low, the welding current may not flow in the secondary side circuit even when the insulator is sandwiched between the object to be welded and the welding electrode.

Conventionally, when such a non-energized abnormal situation occurs in the secondary side circuit, the welding work is interrupted, and a worker inspects each part of the apparatus one by one to find out the cause. Then, if the cause was found, the faulty part was repaired and then the welding work was restarted. However, while the welding work is suspended in this way, the welding line stops, resulting in a drop in production efficiency.

The present invention has been made in view of the above problems, and is an inverter type that minimizes interruption of welding work to improve production efficiency when a non-energized abnormal condition occurs in the secondary side circuit. It is an object to provide a resistance welding method.

[0011]

To achieve the above object, the inverter resistance welding method of the present invention performs constant current control for matching the current flowing through the secondary side circuit of the welding transformer with a set value. In the inverter type resistance welding method, detecting a non-energized abnormal state in the secondary side circuit based on an output signal of a means for detecting a current flowing through the secondary side circuit of the welding transformer, the non-energized abnormal state is detected. When detected, the welding electrode is opened from the work to be welded to operate the inverter circuit, and the non-energized abnormal situation is determined based on the output signal of the means for detecting the current flowing through the primary side circuit of the welding transformer. Perform a predetermined inspection, and when a predetermined inspection result is obtained, switch to constant current control based on the output signal of the primary side current detection means and restart welding energization. And configured to have the steps of that.

[0012]

[Operation] In a normal state, as a rule, the constant current control is performed by the secondary side feedback method. However, if for some reason there is a monitor result that the welding current did not flow in the secondary circuit during the welding energization cycle, the welding energization is immediately interrupted or stopped and the welding electrode is released from the work piece. (Separate)

In this open state, for example, the inverter circuit is operated for several cycles, and the energization state of the primary side circuit at that time is checked. As a result of this inspection, when a current flows in the primary side circuit, it is determined that, for example, the rectifying element of the secondary side circuit is short-circuited and broken, and an operator or the like is notified to prompt repair.

However, when the current does not flow in the primary side circuit in the above inspection, the current is switched to the constant current control by the primary side feedback system using the primary side current detection sensor, and the subsequent welding energization is executed. Therefore, the welding energization is restarted at the welding point where the welding energization was interrupted, and if it is performed normally, the welding energization at the next welding point is executed. As a result, if the cause of the non-energized abnormal situation in the secondary circuit is not the failure of the power supply device itself but the output line of the secondary side current detection sensor is broken, for example, it takes a little time for inspection. The welding operation can be continued substantially continuously without stopping the welding line. Therefore, the productivity of the welding line can be improved.

Immediately after switching to the constant current control by the primary side feedback system, it is monitored whether welding energization is normally performed or is still unenergized. By interrupting the welding energization again and issuing a predetermined alarm, it is possible to take early measures against an abnormal situation such as disconnection of the secondary side cable.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows the configuration of an inverter type resistance welding power source apparatus for carrying out the method according to one embodiment of the present invention.

This power supply device is a three-phase inverter type, which inputs three-phase commercial AC voltages S, T, and U to a three-phase rectifier circuit 12 through a breaker 10, and the DC output voltage of this rectifier circuit 12 is applied to an inverter circuit 14. Supply to. The inverter circuit 14 is composed of a GTR, an FET, or the like, and the input direct current has a frequency higher than the commercial frequency (eg, 600).
The pulsed alternating current is output by chopping with switching of Hz to 2 KHz). The operation of the inverter circuit 14 is controlled by the control signal CS from the inverter control unit 26.

The AC output voltage from the inverter circuit 14 is supplied to the primary coil of the welding transformer 18, and the secondary voltage obtained in the secondary coil of the welding transformer 18 is a pair of diodes (rectifying elements) 20A, 20B. Is rectified into a direct current by this, and this direct current is supplied to the welding gun 24 via the secondary cables 22, 22. A pair of welding electrodes 26 is attached to the tips of the pair of rotatable conductor arms of the welding gun 24.
A and 26B are attached respectively, and at the time of welding, a welding current (secondary side current) I2 of direct current is made to flow under the condition that these welding electrodes 26A and 26B sandwich a workpiece (not shown). ing.

The welding transformer 18 and the diodes 20A and 20B are connected to an arm (not shown) of a welding robot.
The welding transformer 16 with a rectifying element mounted on is assembled integrally. The welding gun 22 is a robot
It is attached to the tip of the arm and is pinched or released from the object to be welded under the control of the robot controller 50 which is separate from the power supply device.

In this power supply device, in a steady state, as a general rule, the constant current control is performed by the secondary side feedback method. For this control, a current detection sensor, for example, a toroidal coil 28 is attached to the secondary side circuit so as to be wound around one conductor arm of the welding gun 24 as shown in the figure. When the secondary side current I2 flows through the secondary side circuit during welding, the toroidal coil 28 outputs a voltage signal f2 corresponding to the secondary side current I2, and the secondary side current detection circuit 30 is based on the voltage signal f2. As a result, the current detection signal F2 representing the value of the secondary side current I2 is obtained. This current detection signal F
2 is given to the inverter control unit 34 via the switching circuit 32. The inverter control unit 34 uses the current detection signal F2
Is compared with the secondary side current set value [I2] from the setting section 36, and the control signal CS corresponding to the comparison error is given to the inverter circuit 14.

The above configuration (excluding the switching circuit 32)
Is a part common to the conventional power supply device of this kind. According to the present embodiment, in addition to the above configuration, the switching circuit 32, the primary side current detection sensor such as the current transformer 38,
A primary side current detection circuit 40, a system control section 42, a non-energization detection section 44, a display section 46, and an alarm generation section 48 are provided, and only a secondary side current set value [I2] is set from the setting section 36 to the inverter control section 34. Not the primary side current setting value [I
1] is also given.

The current transformer 38 is mounted on the primary side between the inverter circuit 14 and the welding transformer 18, and when the primary side current I1 flows through the primary side circuit, a voltage signal f1 corresponding to the primary side current I1 is applied. Output.
The primary side current detection circuit 40 outputs a current detection signal F1 representing the value of the primary side current I1 based on this voltage signal f1 and supplies this current detection signal F1 to the other input terminal of the switching circuit 32. Then, as will be described later, when a non-energized abnormal condition occurs in the secondary side circuit, the secondary side current detection circuit 30
The current detection signal F1 from the primary side current detection circuit 40 is sent to the inverter control section 34 via the switching circuit 32 instead of the current detection signal F2 from the.

The non-energization detector 44 monitors the secondary side current detection signal F2 or the primary side current detection signal F1 obtained at the output terminal of the switching circuit 32, and based on the state of the signal, during the energization cycle, It is monitored whether or not the current I2 flows through the secondary side circuit or whether or not the current I1 flows through the primary side circuit, and the monitoring result is transmitted to the system control unit 42 by the signal RE.

The system control unit 42 is composed of a microcomputer, and gives a required control signal to each unit in the power supply device and exchanges a required control signal with an external robot control unit 50. That is, the switching control signal S for instructing the switching circuit 32 which one of the secondary side current detection signal F2 and the primary side current detection signal F1 should be selected.
Give W. A timing signal ST indicating the monitoring time is given to the non-energization detection unit 44. The display unit 46 is supplied with the data SD and the display control signal VD for displaying the inspection result, the message from the system side and the like on the screen. The alarm generation unit 48 is provided with a control signal SA for instructing the generation of an alarm signal when a failure is found by inspection. The inverter control unit 34 is supplied with a control signal SJ for instructing the start and end timings of energization, and the secondary side current set value [I2] from the setting unit 36 is supplied.
Alternatively, a selection control signal SE for instructing which of the primary side current set value [I1] should be selected is given.

In addition, between the system control unit 42 and the robot control unit 50, from the robot control unit 50 to the system control unit 42, the state of the welding robot, particularly the state in which the welding gun 24 is opened, or A status signal GA indicating whether or not the object to be welded is sandwiched is given, and the robot controller 50 is controlled by the system controller 42.
Is supplied with a gun control signal GB for instructing opening or pinching of the gun 26.

Next, the operation of this embodiment will be described.
During normal operation, constant current control is performed by the secondary side feedback method as described above. When the welding current I2 flows in the secondary side circuit during the welding energization cycle, the current detection signal F2 representing the measured current value is supplied to the inverter control unit 34 via the switching circuit 32, and the inverter control unit 34 causes the welding current I2 to flow.
The inverter circuit 14 is switched so that 2 becomes equal to the set value [I2].

However, if the welding current I2 does not flow in the secondary side circuit during the welding energization cycle for some reason, that is, the state of non-energization occurs, the non-energization detecting unit 44 determines the non-energization abnormal condition. It is detected and notified to the system control unit 42 by the signal RE. Then, the system control unit 42
Immediately interrupts or suspends the welding energization to the inverter control unit 34 and gives the robot control unit 50 a gun control signal GB to open the welding gun 24. When the gun 24 is opened, the welding electrodes 24A and 26B are released (separated) from the object to be welded.

Next, the system control unit 42 switches the switching circuit 32 to the primary side current detection circuit 40 side by the switching control signal SW, and then causes the inverter control unit 34 to perform the test energization. This test energization is performed by the inverter circuit 14
May be switched for only a few cycles. In this test energization, when the current I1 flows through the primary side circuit, the system control unit 42 recognizes this through the non-energization detection unit 44, and from this inspection result, the cause of non-energization in the secondary side circuit this time is rectification. It is determined that one or both of the diodes 20A and 20B of the element-equipped welding transformer 16 are short-circuited and destroyed. That is, for example, when one diode 20A is short-circuited and destroyed, the secondary current I2 does not flow to the welding gun 24 side in the half cycle in which the forward voltage is applied to the diode 20B and the secondary voltage is applied to the diode 20A in the reverse direction. , I2 ′, a large current flows to the short-circuited diode 20A side. Therefore, the primary side current I1 'corresponding to the secondary side current I2' flows in the primary side circuit. Also, both diodes 20
When A and 20B are short-circuited, the short-circuit current continues to flow during each half cycle, that is, the entire cycle.

When such an inspection result is obtained, the diodes 20A and 20B must be replaced and repaired.
The system control unit 42 causes the alarm generation unit 48 to generate an alarm, displays the cause of the current non-energization on the display unit 46, and prompts the worker to perform repair work.

In the test energization, when the current I1 does not flow in the primary side circuit, the system control unit 42 then gives the robot control unit 50 a gun control signal GB to sandwich the welding object in the welding gun 24 again. Let As a result, the welding electrodes 26A and 26B again come into pressure contact with the workpiece.
In this state, the system control unit 42 causes the inverter control unit 34 to restart welding energization. However, this time, welding current is carried out by the constant current control of the primary side feedback method. Therefore, the system control unit 42 causes the inverter control unit 34 to set the primary side current setting value [I1] from the setting unit 36.
To select.

As a result, the inverter controller 34 determines that the current I1 flowing through the primary side circuit is the primary side current set value [I1].
The inverter circuit 14 is switched so as to coincide with. This primary side current set value [I1] is selected as a value obtained by multiplying the secondary side current set value [I2] by a predetermined value (such as the winding ratio of the welding transformer 18). By performing the current control, the secondary side current I2 that matches the secondary side current set value [I2] flows in the secondary side circuit. In this way, the welding current is re-applied to the previously interrupted welding point.

The system controller 42 monitors whether or not the welding current is normally supplied through the non-energization detector 44,
If it is normal, it is determined that the current non-energized in the secondary side circuit this time is due to the failure of the current detection sensor (toroidal coil) 28 on the secondary side, or the sensor output line 29 is normally broken, and the welding energization is continued. To do.

In this way, while switching to the constant current control of the primary side feedback system to continue welding energization, the system control unit 42 displays the cause of the current non-energization on the display unit 46, and further, if necessary. Then, an alarm is issued to the alarm generation unit 48 to prompt the worker to inspect and repair around the secondary side current detection sensor. When the worker completes the recovery work and operates a predetermined switch, the system control unit 42 causes the switching circuit 32 to switch the secondary side current detection circuit 3 in response to the operation.
At the same time as switching to the 0 side, the inverter control unit 34 is made to select the secondary side current set value [I2] to return from the primary side feedback system to the secondary side feedback system.

However, even if the welding current is supplied by switching to the constant current control of the primary side feedback system as described above, the current I1 may still not flow in the primary side circuit. When the system control unit 42 confirms this through the non-energization detection unit 44, the cause of the non-energization in the secondary side circuit this time is probably the disconnection of the secondary side cables 22 or 22, or the welded object in some cases. It is determined that insulating foreign matter has adhered to the surface of the.

In this case, the secondary cables 22, 22 must be replaced and repaired, or the insulating foreign matter must be removed from the surface of the workpiece. Therefore, the system controller 42 must
An alarm is generated by the alarm generation unit 48, and the display unit 4
The cause of the current non-energization is displayed in 6 and the worker is urged to perform the repair work. In order to confirm whether the cause of non-energization is an insulating foreign substance, the welding electrodes should be re-executed several times at the same welding point or by moving the welding electrodes 26A and 26B to another welding point. May be. When the current I1 starts to flow in the primary side circuit due to the re-execution of the welding energization, it may be determined that the insulating foreign matter is attached.

As described above, in the present embodiment, when an abnormal state of non-energization occurs in the secondary side circuit at the start of or during the execution of welding energization, the system is inspected to find the cause. Then, the output is displayed. As a result, the worker can immediately repair / replace the defective / failed portion and immediately restart the welding process without inspecting each part. If the cause of the non-energization is not the failure of the power supply itself but the disconnection of the output wire of the secondary side current detection sensor, the system automatically switches to the primary side feedback method Since constant current control similar to that is performed, the welding line does not need to be stopped unnecessarily, and the production efficiency can be improved.

[0037]

As described above, according to the inverter type resistance welding method of the present invention, when a non-energized abnormal condition is detected in the secondary side circuit, an inspection for investigating the cause is performed, When a predetermined inspection result is obtained, the secondary side feedback method is automatically switched to the constant current control of the primary side feedback method to continue the welding work, so that the welding line is not stopped wastefully. In addition, the production efficiency in the welding process can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an inverter type resistance welding power source device according to an embodiment of the present invention.

[Explanation of symbols]

 14 Inverter circuit 16 Welding transformer with rectifying element 22 Secondary side cable 24 Welding gun 28 Toroidal coil (secondary side current detection sensor) 30 Secondary side current detection circuit 32 Switching circuit 34 Inverter control section 36 Setting section 38 Current transformer ( Primary-side current detection sensor) 40 Primary-side current detection circuit 42 System control unit 44 De-energization detection unit 50 Robot control unit

(72) Inventor Nobuo Kobayashi 1-10-10 Shin-Sayama, Sayama-shi, Saitama Prefecture Honda Engineering Co., Ltd. (72) Inventor Kazuo Isogai 1-10-1 Shin-Sayama, Sayama City, Saitama Prefecture Engineering Co., Ltd.

Claims (2)

[Claims] 1. An inverter-type resistance welding method for performing a constant current control for matching a current flowing through a secondary side circuit of a welding transformer with a set value, the means for detecting a current flowing through a secondary side circuit of a welding transformer. Detecting a non-energized abnormal situation in the secondary side circuit based on the output signal, and when the non-energized abnormal situation is detected, open the welding electrode from the work piece to operate the inverter circuit. ,
Performing a predetermined inspection for the non-energized abnormal condition based on the output signal of the means for detecting the current flowing through the primary side circuit of the welding transformer, when the predetermined inspection result is obtained in the inspection, the primary side An inverter-type resistance welding method, which comprises the steps of switching to constant current control based on the output signal of the current detection means and restarting welding energization. 2. It is monitored whether or not welding energization is normally performed immediately after switching to constant current control based on the output signal of the primary side current detection means, and if abnormal, welding energization is interrupted and predetermined. The alarm resistance welding method according to claim 1, wherein the alarm is generated.