JP2518728B2 - Inverter resistance welding power supply - Google Patents

Description

TECHNICAL FIELD The present invention relates to an inverter type resistance welding power source device,
In particular, it relates to a power supply device for mounting on a robot.

[Prior Art] An inverter-type resistance welding power supply device has excellent efficiency and power factor, and can reduce the size of the welding transformer.
In particular, it is widely used in welding robots. In this type of power supply device, a welding transformer with a rectifying element is often used. This 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, the connection cable can be significantly shortened, and impedance drop and power consumption can be reduced.

By the way, when constant current control is performed by the inverter type resistance welding power supply device equipped with such a welding transformer with a rectifying element, the welding transformer and the welding gun are directly connected as described above, so that the current detection coil is provided on the secondary side. Since it is difficult to attach the current detection coil, the current detection coil is attached to the primary side, and the output of the inverter circuit is controlled by feeding back the current on the primary side.

[Problems to be Solved by the Invention] However, in the constant current control of the primary side current feedback system as described above, there is a problem when the secondary side rectifying element of the welding transformer is short-circuited and broken. That is, if the rectifying element is short-circuited and destroyed on the secondary side of the welding transformer, the secondary side current will not flow to the welding gun side. However, since the secondary side current flows in the closed circuit formed between the secondary side coil and the rectifying element, the corresponding primary side current continues to flow. Therefore, regardless of the non-energized state on the welding gun side,
Not only the abnormality cannot be detected on the primary side, but as a result of continuing the energization operation with feedback control, there is a possibility that the product with the welding defect will continue to flow in the line, or the power supply device parts other than the rectifying element may be damaged. .

In the case of a welding transformer with a rectifying element, a structure is used in which a pair of rectifying elements are sandwiched between the conductors (coil pieces) of the secondary side coil, but the load for electrical contact applied to both rectifying elements is unbalanced. When one of the rectifying elements is apt to cause short circuit breakdown, the other rectifying element often fails to withstand overvoltage and eventually short-circuits.

The present invention has been made in view of such problems, and detects an abnormality (short-circuit breakdown state) of a secondary side rectifying element of a welding transformer at an early stage to minimize welding failure and to chain other parts. It is an object of the present invention to provide an inverter type resistance welding power supply device that prevents a failure.

[Means for Solving the Problems] In order to achieve the above object, the first inverter type resistance welding power supply device of the present invention includes means for detecting the primary side current of the welding transformer, and the current detection means In an inverter-type resistance welding power supply device in which the output of an inverter circuit is controlled according to an output signal, the inverter circuit is activated when the welding electrode is opened, and the welding transformer is operated based on the output signal of the current detection means at this time. It is configured to include means for determining the state of the rectifying element on the secondary side.

A second inverter resistance welding power supply device of the present invention is an inverter resistance welding power supply device configured to detect a current on a primary side of a welding transformer and control an output of an inverter circuit according to the detected current value. The voltage detecting means for detecting the voltage on the secondary side of the welding transformer and the inverter circuit when the welding electrode is opened, and the state of the rectifying element on the secondary side of the welding transformer based on the output signal of the voltage detecting means at this time. And a means for determining.

Further, in the case where an abnormality of the rectifying element is found, a configuration is provided in which a unit is provided that conditionally issues an alarm according to the determination result of the determination unit so that each control unit can immediately take appropriate action.

[Operation] If the inverter circuit is operated when the welding electrode is opened and separated from the material to be welded, a pulse (primary frequency) higher than the commercial frequency (for example, 600 Hz to 2 KHz) is applied to the primary coil of the welding transformer from the inverter circuit. Side voltage) is applied. On the secondary side, if the rectifying element is normal, the welding electrode is open, so that the secondary side current does not flow and the primary side current does not flow. At this time, the secondary side voltage is detected as a no-load voltage. However, if one of the rectifiers is short-circuited and broken, the current will flow even when a reverse voltage is applied to the rectifier, and the secondary current will flow in the closed circuit between the secondary coil and the rectifier. , The primary current flows accordingly. When a secondary current flows in such a closed circuit,
The secondary voltage does not appear (it becomes almost zero). in this way,
When the welding electrode is opened, the inverter circuit is activated, and the state of each rectifying element can be judged from the waveform or value of the primary side current or secondary side voltage at that time, and an abnormality can be found.

If an abnormality in the rectifying element is found by this determination, an alarm is issued to each control unit such as the robot control unit and the inverter control unit to immediately stop the welding work so that damage can be minimized. it can.

[Embodiment] FIG. 1 shows the overall configuration of an inverter type resistance welding power source apparatus according to an embodiment of the present invention.

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

The AC output of 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 rectified into DC by a pair of diodes (rectifying elements) 20A and 20B. , This direct current is supplied to the welding gun 22. The welding gun 22 has a pair of welding electrodes 24
A, 24B are installed and these welding electrodes 24A, 2
By sandwiching the material to be welded (not shown) by 4B, a direct welding current is applied to the material to be welded. In addition,
The welding transformer 18 and the diodes 20A and 20B are integrally assembled in the welding transformer 16 with a rectifying element mounted on the arm (not shown) of the welding robot. Welding gun
22 is attached to the tip of the robot arm,
Under the control of the robot controller 50, which is separate from the power supply,
Each time the welding point is energized, the material to be welded is sandwiched,
It is designed to open when power is turned off.

In this power supply device, constant current control is performed by the primary power supply feedback method. For this purpose, the current detection coil 28 is attached to the conductor (primary side conductor) between the inverter circuit 14 and the rectifying element-equipped welding transformer 16. During welding, when the primary side current I1 flows, a voltage signal f1 corresponding to the primary side current I1 is generated from the coil 28, and based on this voltage signal f1, the current detection circuit 30 detects the value of the primary side current I1. The signal F1 is obtained. The current detection signal F1 is given to the inverter control unit 26 via the switch 34. The inverter control unit 26 is
The voltage detection signal F1 is compared with the current setting value, and the control signal CS corresponding to the comparison error is given to the inverter circuit 14.

The above configuration (excluding the switch 34) is the same part as the conventional one. In such a configuration, it is assumed that one diode 20A is short-circuited and broken in the welding transformer 16 with a rectifying element during welding. Then, in the half cycle in which the forward voltage is applied to the diode 20B and the secondary voltage in the reverse direction is applied to the diode 20A, the secondary current I2 does not flow to the welding gun 22 side, and instead, as shown by I2 ' A large current flows to the diode 20A side. In the half cycle in which the forward voltage is applied to the diode 20A and the secondary voltage is applied to the diode 20B in the reverse direction, the secondary current I2 normally flows to the welding gun 22 side. Therefore, although the weld is turned off at half cycle intervals, the primary side current I1 continues to flow, so the inverter controller
26 continues to drive the inverter circuit 14 by the feedback method. As a result, welding defects continue not only at this welding point but also at subsequent welding points, and the diode 20B also becomes unable to withstand overvoltage and eventually causes short circuit breakdown.In addition, switching elements in the inverter circuit 14 are also destroyed. To reach.

However, in this embodiment, an abnormality of the diode 20A is detected at an early stage by the following mechanism to prevent the above-mentioned expansion of welding failure and the chain-wise destruction of other parts.

According to this embodiment, the determination unit 32, the switch 34, the display unit 3
6, the alarm generation unit 38 is provided. The determination unit 32 is a robot controller when the welding gun 22 or the welding electrodes 24A and 24B are opened after the welding for one welding point is completed (when the welding gun 22 or the welding electrodes 24A, 24B are separated from the workpiece to move to the next welding point).
Receive the signal from 50 and start the inspection.

First, the switch 34 is switched to the determination unit 32 side, and then the inverter control unit 26 is energized for inspection. Then, the control unit 26 outputs the inverter control signal CS to the inverter circuit 14, the inverter circuit 14 is activated, and the energizing pulse (primary voltage) shown in FIG. 3 (A) is applied to the primary coil of the welding transformer 18. Is applied. However, at this time, since the welding electrodes 24A, 24B are open, if both the diodes 20A, 20B are normal, no current flows in the secondary side circuit, and therefore the primary side current I1 does not flow. However, for example, if the diode 20A has a short circuit breakdown, the diode 2
In the half cycle in which the secondary voltage is applied to 0B in the forward direction and to the diode 20A in the reverse direction, the secondary current flows as a large current to the short-circuited diode 20A side as indicated by I2 ′. Primary current of the waveform as shown in Fig. 3 (B)
I1 is obtained. When the diode 20B is short-circuited, the primary current of the same waveform is changed only by changing the polarity.
I1 is obtained. Further, when both the diodes 20A and 20B are both short-circuited, the primary side current I1 having a large current with both polarities is obtained. Thus, the waveform of the primary side current I1 differs depending on the states of the diodes 20A and 20B.

The determination unit 32 includes the current detection coil 28, the primary side current detection circuit 3
0, the state of the primary side current I1 is detected through the switch 34, and the states of the diodes 20A and 20B are determined, and the determination result is output. That is, if both the diodes 20A and 20B are normal, the determination signal is not output (the display unit may be output if necessary).
(Although 36 may be displayed as "normal"), diode 20A,
When at least one of the 20Bs has a short circuit breakdown, "abnormal" is displayed on the display unit 36 and an alarm signal is given to the alarm generation unit 38. Then, the alarm generation unit 38
The alarm signal AR is sent from the robot control device 50, the inverter control unit 26, and the like to each control unit. As a result, the robot controller 50 stops the crimping of the welding gun 22 to the next welding point, and the inverter controller 26 stops the energization to the next welding point.

This prevents welding defects from spreading to subsequent welding points, and avoids a situation in which other parts in the power supply device are broken in a chain manner. It should be noted that the display section 36 may display not only "abnormal" but also which diode is in a short circuit state, and by doing so, allow the operator to perform appropriate repair / replacement work. You can

FIG. 2 shows the overall construction of an inverter type resistance welding power source device according to another embodiment. The parts having the same structures and functions as those of the above embodiment (FIG. 1) are designated by the same reference numerals. In this embodiment, a secondary side voltage detection circuit 40 is provided. Then, similarly to the above-mentioned embodiment, when the welding electrodes 24A, 24B are opened after energization to each welding point, the determination unit 3
2 causes the inverter control unit 26 to perform energization for inspection, and determines the state of the diodes 20A and 20B from the state of the secondary side voltage V2 at that time.

FIG. 4 shows the waveform of the secondary side voltage V2 when the diode 20A is causing a short circuit breakdown. When the diode 20B is short-circuited, a waveform with a phase difference of 180 ° is obtained.If both diodes 20A and 20B are short-circuited, a zero voltage is obtained over substantially the entire period. If both 20B are normal, a continuous no-load voltage is obtained instead of every other half cycle as shown. In this way, since the state of the secondary side voltage V2 differs depending on the state of the diodes 20A, 20B, the determination unit 32 can determine the state of the diodes 20A, 20B from the output signal of the secondary side voltage detection circuit 40. it can. In the illustrated example, the secondary side voltage detection circuit 40 is connected so as to detect the voltage between the welding electrodes 24A and 24B as the secondary side voltage V2.
The voltage between the taps may be detected.

[Advantages of the Invention] The present invention has the above-described configuration,
The following effects are obtained.

According to the inverter type resistance welding power source device of claim 1,
The inverter circuit is activated when the welding electrode is opened, and the state of the rectifying element on the secondary side of the welding transformer is determined based on the state of the primary side current at this time. It is possible to detect an abnormality of the element at an early stage, prevent the welding failure from expanding, and prevent the chain failure of other parts.

According to the inverter type resistance welding power source device of claim 2,
When the welding electrode is opened, the inverter circuit is activated, and the state of the secondary side rectifying element of the welding transformer is determined based on the state of the secondary side voltage at this time. It is possible to detect an abnormality of the rectifying element at an early stage and prevent the spread of welding defects and the chain failure of other parts.

According to the inverter type resistance welding power source device of claim 3,
When an abnormality of the rectifying element is detected, an alarm is generated in response to the determination result of the determination means, so that each control unit can take appropriate measures to minimize the damage.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an inverter type resistance welding power supply device according to an embodiment of the present invention, and FIG. 2 is a block diagram showing a configuration of an inverter type resistance welding power supply device according to another embodiment. FIG. 3 is a waveform diagram showing the waveform of the primary-side current when one diode is short-circuited in the power supply device of the embodiment, and FIG. 4 is one of the diodes in the power supply device of the embodiment. FIG. 6 is a waveform diagram showing a waveform of a secondary side voltage when a voltage is generated. 14 …… Inverter circuit, 16 …… Welding transformer with rectifying element, 18 …… Welding transformer, 20A, 20B …… Diode, 22
...... Welding gun, 24A, 24B ...... Welding electrode, 26 …… Inverter control unit, 28,44 …… Current detection coil, 30 …… Primary side current detection circuit, 32 …… Determination unit, 34 …… Switch, 36 …… Display unit, 38 …… Alarm generation unit 38,40 …… Secondary side voltage detection circuit, 50 …… Robot control device.

Claims (3)

(57) [Claims] 1. An inverter-type resistance welding power source apparatus comprising means for detecting a primary side current of a welding transformer and controlling an output of an inverter circuit according to an output signal of the current detecting means. Inverter resistance welding, characterized in that it comprises means for activating the inverter circuit at the time of opening and judging the state of the rectifying element on the secondary side of the welding transformer based on the output signal of the current detecting means at this time. Power supply. 2. An inverter-type resistance welding power supply device in which a primary side current of a welding transformer is detected and an output of an inverter circuit is controlled according to the detected current value, wherein a secondary side voltage of the welding transformer is controlled. Voltage detecting means for detecting, and means for activating the inverter circuit when the welding electrode is opened, and determining the state of the rectifying element on the secondary side of the welding transformer based on the output signal of the voltage detecting means at this time, An inverter-type resistance welding power supply device comprising: 3. The inverter type resistance welding power source device according to claim 1, further comprising a unit that conditionally issues an alarm according to the determination result of the determination unit.