JPH0681671B2 - DC resistance welding equipment - Google Patents

Description

The present invention relates to a direct current resistance welding apparatus for resistance welding a work by using a direct current, and more specifically, for example, by rectifying three-phase alternating current into a direct current, After converting direct current into high frequency alternating current, it is converted again into direct current using welding transformer and rectifier,
In an inverter type DC resistance welding device that welds a work by supplying this DC to the welding electrode, a large current can be supplied to the work by connecting the DC conversion circuit consisting of the welding transformer and the rectifier in parallel. In addition, the present invention relates to a direct current resistance welding device that achieves reduction in size and weight at the same time.

BACKGROUND OF THE INVENTION A resistance welding apparatus, for example, clamps a set of works by a pair of electrodes, generates a Joule heat by passing a welding current between the electrodes, and relatively presses the electrodes. It is a device for joining work pieces, and since it does not require a welding rod or the like at the time of joining, it is a joining method with excellent work efficiency.

In this case, the resistance welding joining method requires a welding current having an extremely large current as compared with, for example, an arc welding joining method, and thus the welding transformer tends to be large and heavy. Therefore, this is pointed out as a difficulty in attaching to the arm part of a welding robot or the like.

Therefore, recently, in order to reduce the size of this welding transformer, direct current is once converted into high-frequency alternating current, and this high-frequency alternating current is supplied to the welding transformer to reduce the voltage, and then converted to direct current again using a rectifier. Inverter type DC resistance welding equipment for supplying to welding gun arm is beginning to be adopted. The reason for converting to high-frequency alternating current is that the welding transformer can be made relatively small and lightweight by utilizing the fact that the cross-sectional area of the transformer core constituting the welding transformer is in inverse proportion to the frequency of the high-frequency alternating current. In addition, the reason why it is converted to direct current again and supplied to the welding gun arm is that the voltage drop due to the increase in high frequency impedance due to the stray inductance due to the length and shape of the welding gun arm and the voltage drop due to the skin effect can be avoided and high efficiency is achieved. This is because the device can be constructed.

An inverter type DC resistance welding apparatus of this type is shown in FIG. The apparatus is composed of a converter unit 2, an inverter unit 4, and a welding transformer unit 6, and converts the three-phase AC output from a commercial three-phase AC power source 7 into a DC current by a rectifier 8 and a capacitor 10 which form the converter unit 2, After converting this direct current into a high frequency alternating current by comparing with the frequency of the three-phase alternating current by the full bridge type inverter unit 4 composed of transistors 12a to 12d, the welding transformer 14 with a center tap and the rectifier 16a are again provided. It is configured to be converted into direct current by 16b and supplied between the welding electrodes 18a and 18b. The welding electrode 18a is connected to the common connection point of the rectifiers 16a and 16b, and the electrode 18b is connected to the center tap 19 of the secondary coil forming the welding transformer 14. With such a configuration, when the pair of works Wa and Wb are sandwiched between the welding electrodes 18a and 18b, a welding current is applied to melt and join the contact portions with the works Wa and Wb.

By the way, in the resistance welding apparatus configured as described above, it is always required to increase the supply current and reduce the size thereof. This makes it possible to supply a large current even when welding a steel plate having a high melting point such as a plated steel plate or a steel plate having a high thermal conductivity to the welding of the steel plate. .

However, in the conventional DC resistance welding apparatus, if the current capacity is further increased and, for example, it is attempted to be attached to the arm of the existing robot, the weight of the welding transformer 14 itself becomes large and the robot needs to be upsized. It has been pointed out that parallel connection of the transistors 12a to 12d or the like forming the inverter section 4 or parallel connection of the rectifiers 16a and 16b is required, which may cause a problem in stability and reliability of the device.

[Object of the Invention] The present invention has been made in order to overcome the above-mentioned inconvenience, and in a direct current resistance welding apparatus, it is possible to stably supply a large current to a work, and the size of the direct current resistance welding apparatus is small. It is an object of the present invention to provide a direct current resistance welding device that can achieve weight reduction at the same time.

[Means for Achieving the Purpose] In order to achieve the above-mentioned object, the present invention relates to a DC resistance welding apparatus for supplying a welding current from a welding transformer to a welding electrode to join workpieces. A plurality of rectifier circuits connected in parallel, and an inverter connected to each of the rectifier circuits, the welding current supplied to the welding electrode by driving the respective rectifier circuits by the respective inverters. Is supplied from the circuit connected in parallel.

[Embodiments] Next, preferred embodiments of the DC resistance welding apparatus according to the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 2 shows a schematic configuration of a welding robot system incorporating the DC resistance welding apparatus according to the present invention. The welding robot system basically comprises a welding robot 20, a robot controller 21, and a welding controller 22. The welding robot 20 has a first arm portion 26, which is rotatable in the arrow direction, on a base 24, and the first arm portion 26 has a second arm portion 26.
One end of the arm portion 30 is pivotally attached, and the second arm portion 30 is configured to be movable up and down in the arrow direction by a cylinder 27 that is driven by hydraulic pressure or the like attached to the first arm portion 26.

On the other hand, a gun body 34 is attached to the other end of the second arm portion 30 via a rotary shaft 32. Here, the gun body 34 is supported by a welding transformer portion 36, a bracket 38 connected to the welding transformer portion 36, a cylinder 40 fixed to the upper portion of the bracket 38, and a spindle 42 provided at a substantially central portion of the bracket 38. The fixed gun arm 44 and the movable gun arm 46 are provided, and electrodes 48a and 48b are attached to the tips of the fixed gun arm 44 and the movable gun arm 46. The gun body 34 is rotatably supported by the rotating shaft 32 in the arrow direction,
The movable gun arm 46 opens and closes in the direction of arrow AB under the action of the cylinder 40 driven by air pressure or the like. The first arm portion 26, the cylinder 27, the second arm portion 30, and the rotating shaft 32 that form the welding robot 20 are connected to the robot controller 21 via a cable 41. On the other hand, the cylinder 40 and the welding transformer section 36 that constitute the gun body 34 are connected to the welding controller 22 via a cable 43, and the welding controller 22
Is connected to the three-phase AC power source 64 via the cable 45 and is also connected to the robot controller 21 via the cable 47. In this case, the robot controller 21 controls the posture of the welding robot 20 based on the teaching data and gives a welding start command to the welding controller 22. In addition, the welding controller 22 controls welding conditions such as the capacity of welding current supplied from the electrodes 48a and 48b to the works Wa and Wb and the energization time.

FIG. 3 shows a block diagram of an electric circuit relating to control of a welding state of the DC resistance welding apparatus.

As is clear from the figure, the electric circuit basically includes a welding controller 22 and a welding transformer section 36, and the welding controller 22 further includes a power conversion section 50 and a control section 52. The power conversion unit 50 is a converter unit 56 including four converters 54a to 54d for converting three-phase alternating current into direct current.
And four inverters that convert this direct current into high frequency alternating current 58
The inverter unit 60 includes a to 58d. The control unit 52 basically includes a master timer 53 which is a main control unit and sub timers 55a to 55d which are sub control units.

In the figure, a three-phase AC power supply 64 is provided on the input side of the rectifier diode stacks 62a to 62d that form the converters 54a to 54d.
Commercial alternating current is supplied from the diode stack 62a.
To 62d are rectified and smoothed to DC by DC reactors 64a to 64d and capacitors 66a to 66d. The DC voltages V _{1 to} V ₄ are connected to the input sides of the inverters 58a to 58d. The inverters 58a to 58d are, for example, full-bridge type transistor inverters.

The outputs of the inverters 58a to 58d are the primary coils 70 of the four welding transformers 68a to 68d constituting the welding transformer section 36.
connected to a to 70d. And welding transformers 68a-6
The transformer cores 73a to 73d and the electrostatic shield electrode 75 are interposed between the primary coils 70a to 70d and the secondary coils 72a to 72d forming the 8d, and rectifying diodes are provided on both ends of the secondary coils 72a to 72d. One end of 74a to 74h, for example, the anode is connected, the other end of each rectifying diode 74a to 74h side, in this case, the cathode side is common to each welding transformer 68a to 68d, as can be understood from the drawing. It is connected. Here, the respective connection points are connected in common after passing through the current detectors 76a to 76d such as a current transformer that monitors the branch currents I _{1 to} I ₄ , and are connected to one electrode 48a via the fixed gun arm 44. Is configured to.

On the other hand, a center tap 78a is provided on the secondary coils 72a to 72d.
Through 78d, and the center taps 78a through 78d are commonly connected, a current detector 80 such as a current transformer for monitoring the welding current I ₀ on the secondary side and the movable gun arm 46.
Is connected to the other electrode 48b via. This electrode 48
Work Wa and Wb are interposed between a and 48b. That is,
The welding current I ₀ supplied to the welding electrodes 48a and 48b of the welding transformer section 36 is configured to be supplied from a circuit in which single-phase center tap rectifier circuits are connected in parallel.

In the present invention, the reason why the welding transformer section 36 is composed of four welding transformers 68a to 68d is that the electrical specifications such as the current capacity of the rectifying diodes 74a to 74h for supplying the welding current and the inverters 58a to 58d are configured. This is because the electrical specifications such as the current capacity of the power transistors connected in the full bridge type and the mechanical specifications such as the weight of the gun body 34 that can be held by the second arm portion 30 of the welding robot 20 are comprehensively taken into consideration. . In this case, the welding transformer can be divided into smaller semiconductors such as transistors and diodes as compared with the case where one welding transformer is configured, and the primary coil related to the transformer core and the magnetic field between the secondary coils can be used. It is extremely effective in reducing the size and weight of the transformer itself because of the shortened path and the expansion of the heat dissipation area of the transformer core.

The output signals of the current detectors 76a to 76d are sub-control means and the inverters via sub-timers 55a to 55d each having a base drive circuit of a timer means and full-bridge type transistors constituting the inverters 58a to 58d.
58a-58d. The sub timers 55a to 55d are master timers having main control means and timer means.
53 are connected to the master timer 53, and
A feedback signal is provided from a current detector 80 which monitors the secondary welding current I ₀ . The master timer 53 has a condition setter 82 for setting welding conditions such as welding current and energizing time.
Is connected to the robot controller 21 via the interface 84 and is connected to the robot controller 21.
Performs operations such as interlocking in collaboration with 21.

The DC resistance welding apparatus according to the present invention is basically configured as described above. Next, regarding the action and effect thereof, the master timer 53 and the sub-timers 55a to 55d, which form the welding controller 22, have a ROM or the like. Description will be made based on the flowchart shown in FIG. 4 showing the algorithm of the recorded program.

First, in FIG. 2, the cylinder 40 is urged by the driving action of the welding controller 22, the movable gun arm 46 moves in the direction of arrow A, and the electrodes 48a and 48b are opened. Next, the first arm 26, the second arm portion 30 urged by the cylinder 27, and the rotating shaft 32, which constitute the welding robot 20, are respectively swung and moved up and down based on teaching data set in advance in the robot controller 21. Then, the fixed gun arm 44 and the movable gun arm 46 rotate to rotate the workpieces Wa and Wb.
Move to the position to clamp (STP1).

In this state, the welding start command from the robot controller 21 is an interface that constitutes the welding controller 22.
It is introduced into the master timer 53 via 84. Therefore, the workpieces Wa, Wb corresponding to the welding start command from the condition setter 82
A predetermined welding command relating to the welding current and energizing time according to the plate thickness, material, etc. is input to the master timer 53 (STP2). In this case, the master timer 53 operates the workpiece based on the welding command.
Data corresponding to the welding currents I ₀ of Wa and Wb are read from a memory (not shown) that constitutes the master timer 53, and the welding branch currents I _{1 to} I ₄ are to be taken up by the inverters 58a to 58d.
Corresponding set current values i _{1 to} i ₄ , in this case the welding current I ₀
Calculate 1/4 of the value of (STP3). Then, the cylinder 40 is actuated to move the movable gun arm 46 in the direction of the arrow B to bring the works Wa and Wb into contact between the electrodes 48a and 48b, and the initial pressurization read from the memory is started. Wb is pressurized (STP4). Then the master timer
Reference numeral 53 indicates a conduction time t ₀ read from a memory (not shown), and the set welding current values i _{1 to} i ₄ are read from the sub-timers 55a to 55d.
And energization start command are output at the same time (STP5, STP6).

Therefore, the energization is controlled by the sub timers 55a to 55d (STP7), that is, the sub timers 55a to 55d simultaneously drive the inverters 58a to 58d based on the set welding current values i _{1 to} i ₄ . That is, the inverters 58a to 58d driven by the sub timers 55a to 55d are the master timer 53
Thus, the energization start timing is synchronized. The output of the inverters 58a to 58d, for example, a high frequency alternating current of 800 Hz, is applied to the primary coil 70a of the welding transformers 68a to 68d.
Through 70d to the secondary coils 72a through 72d.
After being rectified by the diodes 74a to 74h connected to both ends of each of the next coils 72a to 72d, they are added and the electrodes are added.
It is supplied as a welding current I ₀ between 48a to 48d. In this case, the branch currents I _{1 to} I ₁ introduced from the current detectors 76a to 76d
Sub timers 55a to 55d having feedback control means such as a comparator based on the signal corresponding to I ₄ are master timers.
53 as compared to the welding current value i ₁ to i ₄ is set by perform feedback control by pulse width modulating the base drive current of the inverter 58a to 58d, the set current value i ₁ to i ₄ This set Constant current branch currents I _{1 to} I ₄ corresponding to the same current value as the current detectors 76a to 7
It flows through 6d and is supplied to the works Wa and Wb.

On the other hand, a signal corresponding to the welding current I ₀ is introduced to the master timer 53 from the current detector 80 that monitors the welding current I ₀ flowing between the workpieces Wa and Wb, and should an abnormal current be detected. If it is, the master timer 53 to the sub timers 55a to 55d
An energization end command is output to the robot controller 21 and a welding abnormality signal that is an interlock signal is output to the robot controller 21 via the interface 84 (STP8). When the determination result of step 8 is satisfied, that is, when the welding current I ₀ is within the predetermined range corresponding to the command value of the welding current I ₀ , the predetermined energization time t ₀ is reached. Is monitored (STP9), and when the energization time t ₀ is reached, the master timer
An energization time end command is output from 53 to the sub-timers 55a to 55d (STP10). In this case, the sub-timers 55a to 55d simultaneously stop the supply of the base current to the transistors forming the inverters 58a to 58d (STP11). That is, the master timer 53 synchronizes the energization end timing of the inverters 58a to 58d driven by the sub timers 55a to 55d. By this, the work Wa, Wb
The supply of the welding current I ₀ to is cut off.

Next, the works Wa and Wb are held and held for a predetermined time under the action of the fixed gun arm 44 and the movable gun arm 46 in a state where the supply of the welding current I ₀ is cut off. During this time, the nugget (not shown) generated between the works Wa and Wb is almost completely solidified
Wa and work Wb are joined (STP12). After that, when the welding end command signal is supplied from the master timer 53 to the gun body 34, the movable gun arm 46 again moves open in the direction of arrow A under the action of the cylinder 40, and the workpieces Wa and Wb retreat. The welding work is completed (STP13).

In this case, according to the present invention, since the inverters 58a to 58d and the welding transformers 68a to 68d are connected in parallel, the size and weight of the gun can be reduced and the gun body 34 can be connected to the second arm portion of the welding robot 20. When attached to 30, the durability of the welding robot 20 does not decrease. In addition, the restrictions on the mutual interference between the works Wa and Wb and the gun body 34 are alleviated, and the operation range of the gun body 34 is expanded.

Moreover, since the weight of the second arm portion 30 is reduced, the moving speed of the entire arm portion of the welding robot 20 is improved, and the welding cycle time can be shortened.
In addition, since the transistors composing the inverters 58a to 58d can reduce the current capacity per transistor, it is not necessary to connect the transistors in parallel. Therefore, the selection work such as the current balance of each transistor when the transistors are connected in parallel Therefore, it is possible to provide an inverter unit having excellent stability. Further, when any one of the inverter units fails, each inverter can be replaced by configuring each inverter unit, and the recovery from the failure state can be performed in a short time.

In the above embodiment (hereinafter referred to as the first embodiment), the sub-timers 55a to 55d feed back the branch currents I _{1 to} I ₄ to perform the constant current control, but the feedback detection point, that is, the current detection. The insertion points of the devices 76a to 76d are not limited to the output side of the welding transformers 68a to 68d, but as shown in FIGS. 5 and 6, the input side (second embodiment) or the output side (second embodiment) of the inverters 58a to 58d. Of course, the third embodiment) may be adopted. Inverter
When it is inserted into the input side of 58a to 58d (FIG. 5), it is preferable to use a Hall element capable of detecting a direct current as the current detectors 76a to 76d. In the second and third embodiments, the error with respect to the set value of the welding current I ₀ is slightly large, but the wiring process can be performed in the welding controller 22, which is advantageous in manufacturing.

In the first to third embodiments, the sub timer 55
Each of a to 55d has a feedback control means such as a comparison amplifier, and the master timer 53 monitors an abnormality in the welding current I ₀ , but does not perform feedback control. Therefore, the sum of the branch currents I _{1 to} I ₄ and the magnitude of the welding current I ₀ do not necessarily match due to stray capacitance or the like existing in the gun arms 44, 46 and the like. Therefore, when more accurate control is required, feedback control means such as a comparison amplifier is added to the master timer 53 shown in FIGS. 3 to 5 (fourth embodiment), and the welding current I By performing feedback control between ₀ and the command value, the welding current I ₀ can be controlled extremely accurately.

Furthermore, as another embodiment (fifth embodiment), a seventh embodiment
As shown in the figure, the feedback control by the sub-timers 55a to 55d is not performed, and the feedback control means may be added only to the master timer 53 to control the welding current I ₀ . In this case, the currents flowing through the transistors that form the inverters 58a to 58d and the currents flowing through the rectifier diodes 74a to 74h are not equal in the normal case, but the specifications and characteristics have a margin or the specifications and characteristics are equal. It can be realized by selecting and adopting various parts.

In addition, as still another embodiment (sixth embodiment),
Similar to the fifth embodiment, the components of the inverter units 58a to 58d and the welding transformer unit 36 are selected, for example, to reduce variations in performance specifications or increase margins in performance specifications. Therefore, the current detectors 76a to 76d and 80, the feedback control means (not shown) forming the master timer 53 and the sub timers 55a to 55d are omitted, and the welding current I ₀ is supplied only by the feedforward command without performing feedback control. It goes without saying that it is okay.

[Effects of the Invention] As described above, according to the present invention, when obtaining the welding current to be supplied to the welding electrode, the rectifier circuit including the welding transformer and the rectifier is connected in parallel to form the current supply circuit. Therefore, the welding current to the work can be made relatively large, and the welding gun assembly can be reduced in size and weight, and a DC resistance welding apparatus excellent in maintainability can be realized.

Furthermore, a signal proportional to the welding current supplied to the work from each rectifying circuit is detected, and the welding current is feedback-controlled on the basis of this signal to make the welding current a constant current for stable welding. The effect that the current can be supplied to the work is obtained.

Although the present invention has been described with reference to the preferred embodiment, the present invention is not limited to this embodiment,
It goes without saying that various improvements and design changes can be made without departing from the scope of the present invention.

[Brief description of drawings]

FIG. 1 is a block diagram of an electric circuit of a DC resistance welding apparatus according to the prior art, FIG. 2 is a schematic configuration diagram of the DC resistance welding apparatus according to the present invention, and FIG. 3 is a main part of the DC resistance welding apparatus shown in FIG. FIG. 4 is a flow chart for explaining the operation of the DC resistance welding apparatus according to the present invention, and FIGS. 5 to 7 are other embodiments of the main part of the DC resistance welding apparatus according to the present invention. It is an electric circuit block diagram concerning. 20 …… Welding robot 21 …… Robot controller 22 …… Welding controller, 44 …… Fixed gun arm 46 …… Movable gun arm, 48a, 48b …… Electrode 50 …… Electrode conversion unit, 52 …… Control unit 53 …… Master timer 55a to 55d …… Sub timer 56 …… Converter section, 60 …… Inverter section 58a to 58d …… Inverter 62a to 62d …… Rectifier diode stack 68a to 68d …… Welding transformer

Front Page Continuation (72) Inventor Hitoshi Saito 1-10-1 Shin Sayama, Sayama City, Saitama Prefecture Honda Engineering Co., Ltd. (72) Nobuo Kobayashi 1-10-1 Shin Sayama, Saiyama City, Saitama Honda Engineering Co., Ltd. In-house (56) References JP-A-61-279375 (JP, A)

Claims (5)

[Claims] 1. A DC resistance welding apparatus for joining a work by supplying a welding current from a welding transformer to a welding electrode, wherein a circuit in which a plurality of rectifying circuits each including a welding transformer and a rectifier are connected in parallel and each of the rectifying circuits are provided. DC resistance welding, characterized in that a welding current supplied to a welding electrode is supplied from the circuits connected in parallel by driving the respective rectifier circuits by the respective inverters. apparatus. 2. The apparatus according to claim 1, wherein each inverter is connected to a main control means having a feedback control means, and the main control means is supplied with welding current from the circuit connected in parallel to a welding electrode. The DC resistance welding apparatus is characterized in that a signal proportional to is introduced via current detection means, and the welding current is made constant by feedback control. 3. The apparatus according to claim 1, wherein each inverter is connected to a sub-control unit having a feedback control unit corresponding to the respective inverter, and the sub-control unit is connected to each of the rectifier circuits. A direct current resistance welding apparatus, characterized in that a signal proportional to the outputted welding branch current is introduced via a current detecting means, and the welding branch current is made constant by feedback control. 4. The DC resistance welding device according to claim 3, wherein the main control means is connected to the sub control means. 5. The device according to claim 1, wherein each inverter is connected to a sub-control unit having a feedback control unit corresponding to each inverter, and the sub-control unit is connected to each of the rectifier circuits. A current proportional to the output welding branch current is introduced through the current detection means and is connected to the main control means having at least the timer means, and the main control means is such that each of the inverters is based on the welding current command value. A command value corresponding to the welding branch current to be taken up is calculated and given to the sub control means, and the sub control means converts the welding branch current into a constant current by feedback control based on the welding branch current. The DC resistance welding apparatus is characterized in that the timer means synchronizes the energization timing of the welding branch current.