JPH02137677A - Direct current resistance welding equipment - Google Patents

Abstract

PURPOSE:To reduce the size and weight of a welding gun assembled body by forming circuits where plural rectifier circuits are connected in parallel and supplying a welding current from the circuits connected in parallel. CONSTITUTION:The welding current is supplied from a welding transformer to welding electrodes 48a and 48b and works Wa and Wb are subjected to resistance welding. The circuits where the plural rectifier circuits consisting of rectifiers and the welding transformers are connected in parallel are formed in a welding controller 22 and a welding transformer part 36. The welding current is then supplied from the circuits connected in parallel to the welding electrodes 48a and 48b. The rectifier circuit is constituted of the welding transformer having a secondary coil and a center tap and two rectifiers substantially. The respective rectifier circuits are driven by different inverters respectively. By this method, the size and weight of the welding gun assembled body are reduced.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a DC resistance welding device for resistance welding workpieces using direct current. This direct current is further converted into high frequency alternating current, and then converted back into direct current using a welding transformer and rectifier.
In an impark-type DC resistance welding device that welds workpieces by supplying this direct current to the welding electrode, a large current can be supplied to the workpiece by connecting the DC conversion circuit consisting of the welding transformer and rectifier in parallel. The present invention relates to a DC resistance welding device that can be made smaller and lighter at the same time.

[Background of the Invention] A resistance welding device, for example, holds a set of workpieces between a pair of electrodes, generates Joule heat by passing a welding current between the electrodes, and presses the electrodes relatively. This is a device for joining workpieces, and it is a joining method with excellent work efficiency as it does not require welding rods etc. during joining.

In this case, since the resistance welding method requires a much larger welding current than, for example, the arc welding method, the welding transformer tends to be large and heavy. Therefore, this has been pointed out as a difficulty when attaching it to the arm of a welding robot or the like.

Recently, in order to make this welding transformer more compact, direct current is first converted into high-frequency alternating current, and this high-frequency alternating current is supplied to the welding transformer to step down the voltage, and then converted to direct current again using a rectifier. Inverter-type DC resistance welding equipment that supplies the welding gun arm with 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 inversely proportional 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 it is possible to avoid the voltage drop due to the increase in high frequency impedance due to stray inductance caused by the length and shape of the welding gun arm and the voltage drop due to the skin effect, resulting in high efficiency. This is because it is possible to construct a device of

This type of inverter-type DC resistance welding device is shown in FIG. The device is composed of a converter section 2, an inverter section 4, and a welding transformer section 6, and is connected to a commercial three-phase AC power source 7.
The three-phase alternating current outputted from the converter section 2 is converted into direct current by the rectifier 8 and capacitor 10, and this direct current is converted to the frequency of the three-phase alternating current by the full-bridge inverter section 4 consisting of transistors 12a to 12d, etc. After the current is converted into high-frequency alternating current, it is again converted into direct current using a center-tapped welding transformer 14 and rectifiers 16a and 16b, and then supplied between welding electrodes 18a and 18b.

Note that the welding electrode 18a is connected to a common connection point of the rectifiers 16a and 16b, and the electrode 18b is connected to a center tap 19 of a secondary coil constituting the welding transformer 14.

With this configuration, when a pair of workpieces W, , Wb are sandwiched between welding electrodes 18a, 18b, welding current is applied to the workpieces W, , Wb.

The contact area melts and joins.

By the way, in the resistance welding apparatus configured as described above, there is always a demand for a larger supply current and a smaller size. This makes it possible to supply a large current even when welding steel plates with materials with different melting points, such as plated steel plates, or materials with high thermal conductivity, such as aluminum plates. .

However, in the conventional DC resistance welding device, if the current capacity is further increased and it is attempted to be attached to the arm of an existing robot, the weight of the welding transformer 14 itself will increase, requiring a larger robot. , it is necessary to connect the transistors 12a to 12d, etc. constituting the inverter section 4 in parallel, or to connect the rectifiers 16a, 16b in parallel, etc., and it has been pointed out that there is a concern that problems will arise in the stability and reliability of the device.

[Object of the Invention] The present invention has been made to overcome the above-mentioned disadvantages, and provides a method for supplying a large current to a workpiece by connecting a rectifier circuit consisting of a welding transformer and a rectifier in parallel in a DC resistance welding device. It is an object of the present invention to provide a DC resistance welding device that enables the above-mentioned functions to be made smaller and lighter at the same time.

[Means for Achieving the Object] In order to achieve the above object, the present invention provides a DC resistance welding device for welding workpieces by supplying welding current from a welding transformer to a welding electrode, which comprises a welding transformer and a rectifier. The present invention is characterized in that it includes a circuit in which a plurality of rectifier circuits are connected in parallel, and the welding current to be supplied to the welding electrode is supplied from the parallel-connected circuit.

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

FIG. 2 shows a schematic configuration of a welding robot system incorporating a DC resistance welding device according to the present invention, and the welding robot system basically consists of a welding robot 20, a robot controller 21, and a welding controller 22.
will be accomplished. The welding robot 20 has a first arm part 26 that is rotatable in the direction of the arrow on a base 24, and one end part of a second arm part 30 is pivoted to the first arm part 26. The two-arm section 30 is configured to be movable up and down in the direction of the arrow by a cylinder 27 attached to the first arm section 26 and driven by hydraulic pressure or the like.

On the other hand, a gun body 34 is attached to the other end of the second arm section 30 via a rotating shaft 32. Here, the gun body 34 is supported by a welding transformer part 36, a bracket 38 connected to the welding transformer part 36, a cylinder 40 fixed to the upper part of the bracket 38, and a support shaft 42 provided approximately in the center of the bracket 38. It is composed of a fixed gun arm 44 and a movable gun arm 46, and electrodes 48a and 48 are provided at the tips of the fixed gun arm 44 and the movable gun arm 46.
b is attached. The gun body 34 is rotatably supported by the rotating shaft 32 in the direction of the arrow, and the movable gun arm 46 is a cylinder 400 driven by air pressure or the like.
It opens and closes in the direction of arrow AB force under the action. Note that the first arm portion 26, cylinder 27, and second
The arm portion 30 and the rotating shaft 32 are connected to the robot controller 21 via a cable 41. On the other hand, gun body 3
The cylinder 40 and the welding transformer section 36 that make up the part 4 are connected to a welding controller 22 via a cable 43, and the welding controller 22 is connected to a three-phase AC power source 64 via a cable 45, and a robot via a cable 47. It is connected to the controller 21. in this case,
The robot controller 21 controls the posture of the welding robot 20 based on teaching data, and gives a welding start command to the welding controller 22. Further, the welding controller 22 controls welding conditions such as the capacity of the welding current supplied from the electrodes 48a and 48b to the workpieces W, Wb, and the current application time.

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

As can be understood from the figure, the electric circuit basically comprises a welding controller 22 and a welding transformer section 36, and the welding controller 22 further comprises a power conversion section 50 and a control section 52.

The power conversion section 50 is composed of a converter section 56 made up of four converters 54a to 54d that convert three-phase alternating current to direct current, and an inverter section 60 made up of four inverters 58a to 58d that convert this direct current to high frequency alternating current. There is. The control section 52 basically includes a mask timer 53 which is a main control means and sub-timers 55a to 55 which are sub-control means.
5d.

In the figure, commercial AC is supplied from a three-phase AC power supply 64 to the input sides of rectifying diode stacks 62a to 62d that constitute converters 54a to 54d, and is rectified by the diode stacks 62a to 62d, and connected to DC reactors 64a to 64d and a capacitor 66a. to 6
It is smoothed and converted into DC by 6d. This DC voltage Vl
V4 through V4 are connected to the input sides of inverters 58a through 58d. The inverters 58a to 58d are, for example,
It consists of a full-bridge transistor inverter.

The outputs of the inverters 58a to 58d are supplied to the four welding transformers 68a to 68d constituting the welding transformer section 36.
are connected to the primary coils 70a to 70d. and,
Primary coil 7 forming welding transformers 68a to 68d
0a to 70d and secondary coils 72a to ? Between the transformer cores 73a to 73d and the electrostatic shield electrode 7
5 is inserted and the secondary coil? One ends of rectifier diodes 74a to 74h, for example, anodes, are connected to both end sides of rectifier diodes 2a to 72d.
The other end on the 4h side, in this case, the cathode side, is commonly connected to each of the welding transformers 68a to 68d, as can be understood from the figure. Here, each connection point is a branch current ■, or I
, through current detectors 76a to 76d such as current transformers, which are connected in common to the fixed gun arm 4.
It is configured to be connected to one electrode 48a via 4.

On the other hand, the secondary coils 72a to ? 2d is provided with center taps 78a to 78d, and each center tap 7
After 8a to 78d are commonly connected, welding current I on the secondary side. The movable gun arm 46 is connected to the other electrode 48b through a current detector 80 such as a current transformer for monitoring the current. A workpiece W is placed between the electrodes 43a and 48b.
, W, are interposed. In other words, the welding current {circle around (2)} is supplied to the welding electrodes 48a, 48b of the welding transformer section 36.

is configured to supply from a circuit in which single-phase center tap rectifier circuits are connected in parallel.

In the present invention, the welding transformer section 36 is composed of four welding transformers 68a to 68d because of the electrical specifications such as the current capacity of the rectifier diodes 74a to 74h that supply the welding current, and the configuration of the inverters 58a to 58d. This is because we comprehensively considered electrical specifications such as the current capacity of the power transistors connected in a full bridge configuration, and mechanical specifications such as the weight of the gun body 34 that can be held by the second arm 30 of the welding robot 20. . In this case, dividing the welding transformer allows the use of smaller semiconductors such as transistors and diodes compared to when the welding transformer is composed of one piece, and the magnetic field between the primary coil and secondary coil of the transformer core. This is extremely effective in reducing the size and weight of the transformer itself because the path is shortened and the heat dissipation area of the transformer core is expanded.

The output signals of the current detectors 76a to 76d are sub-control means, and are used as timer means and inverters 58a to 58.
The signals are introduced into the inverters 58a to 58d via subtimers 55a to 55d having full-bridge type transistor base drive circuits constituting 8d. The sub-timers 55a to 55d are each connected to a mask timer 53 which is a main control means and has a timer means, and this mask timer 53 receives the welding current 1 on the secondary side.
A feedback signal is provided from a current detector 80 that monitors o. A condition setter 82 for setting welding conditions such as welding current and energization time is connected to the mask timer 53, and is also connected to the robot controller 21 via an interface 84 to control the robot controller 21.
performs interlock operations in collaboration with

The DC resistance welding device according to the present invention is basically constructed as described above, and the operation and effects thereof will be explained below with reference to the mask timer 5 that constitutes the welding controller 22.
3 and the sub-timers 55a to 55d will be explained based on the flowchart shown in FIG.

First, in FIG. 2, the cylinder 40 is energized under the driving action of the welding controller 22, and the movable gun arm 46 moves in the direction of the arrow, opening the gap between the electrodes 48a and 48b.

Next, the first arm part 26 that constitutes the welding robot 20,
The fixed gun arm 44 and the movable gun arm 46 rotate, move up and down, and rotate, respectively, based on teaching data set in advance in the robot controller 21, so that the second arm section 30 and the rotating shaft 32, which are energized by the cylinder 27, rotate, move up and down, and rotate, respectively. Move to the position where the workpieces W, , and W are held (STPI).

In this state, a welding start command is input from the robot controller 21 to the mask timer 53 via the interface 84 that constitutes the welding controller 22. Therefore, from the condition setter 82, a predetermined welding command regarding the welding current and energization time according to the plate thickness, material, etc. of the workpieces W, , Wb corresponding to the welding start command is manually inputted to the mask timer 53 (SrF2). . In this case, the mask timer 53 controls the welding current of the workpieces W, , W, based on the welding command.
. The inverters 58a to 58d read the data corresponding to the mask timer 53 from a memory (not shown) and set the current values 11 to 9 corresponding to the welding skill flows 11 to I4, in this case, the welding current I
. Calculate the value of 1/4 of (SrF3). Next, by operating the cylinder 40 and moving the movable gun arm 46 in the direction of arrow B, the workpieces W- and Wb are moved to the electrodes 48a148.
At the same time, the initial pressure read from the memory is started, and the works W6, W are pressurized (S
rF4>. Next, the mask timer 53 receives the energization time t from a memory (not shown).

The set welding current values 11 to 14 and the energization start command are simultaneously output to the sub-timers 55a to 55d (SrF2.5TP6).

Therefore, the energization is controlled by the sub-timers 55a to 55ti (SrF2), that is, the sub-timers 55a to 55d simultaneously drive the inverters 58a to 58d based on the set welding current values 1 to 14. That is, the inverters 58a to 58d driven by the sub-timers 55a to 55d have their energization start timings synchronized by the mask timer 53. Inverter 5
For example, the high frequency alternating current of 800 Hz, which is the output of the welding transformers 8a to 58d, is transmitted from the primary coils 70a to 70d of the welding transformers 68a to 68d to the secondary coils 72a to 72d.
This secondary coil? 2a to? After being rectified by diodes 74a to 74h connected to both ends of each electrode 2d, the welding current I is summed and applied between electrodes 48a to 48a. Supplied closed. In this case, sub-timers 55a to 55d having feedback control means such as comparators are set to the welding current value set by mask timer 53 based on signals corresponding to branch currents 11 to I introduced from current detectors 76a to 76d. 11 to 14, the base drive currents of the inverters 58a to 58d are pulse width modulated to perform feedback control, and thereby the set current value 1. Constant current branch currents 11 to I corresponding to the same current values as those of 14 to 14
, passes through the current detectors 76a to 76d to generate the workpiece Wa.
It is supplied to SWb.

On the other hand, the mask timer 53 receives the welding current ■ flowing between the workpieces WaSWb. Welding current I from a current detector 80 that monitors the welding current I. If an abnormal current or the like is detected, the mask timer 53 outputs an energization termination command to the sub-timers 55a to 55d, and also sends a signal to the robot controller 21 via the interface 84.
A welding abnormality signal, which is an ink clock signal, is output (
SrF2). If the judgment result of step 8 is satisfied,
That is, the welding current ■. is the relevant welding current■. If the value is within a predetermined range corresponding to the command value of
), gt when energized. When the current supply time is reached, an energization time end command is output from the mask timer 53 to the sub-timers 55a to 55d (STPIO). In this case, the sub-timers 55a to 55d simultaneously stop supplying base current to the transistors constituting the inverters 58a to 58d (S
TPII). That is, the inverters 58a to 58d driven by the sub-timers 55a to 55d have their energization end timings synchronized by the mask timer 53. As a result, the supply of welding current Io to the workpieces W, , W is cut off.

Next, the workpiece WaSWb has a welding current ■. The gun is held and held for a predetermined period of time under the action of the fixed gun arm 44 and the movable gun arm 46 in a state where the supply of gun is cut off. During this time, a nugget (not shown) generated between the works W- and Wb is almost completely solidified, and the works Wa and Wb are joined (SrF
12>.

Thereafter, when a welding end command signal is supplied from the mask timer 53 to the gun body 34, the movable gun arm 46 moves open again in the direction of arrow A under the action of the cylinder 40, and the workpiece W
, , the welding work ends when Wb leaves work (SrF13).

In this case, according to the invention, the inverters 58a to 58
d, welding transformers 68a to 68d, etc. are connected in parallel, making it possible to reduce the size and weight of the gun body 34. Therefore, when the gun body 34 is attached to the second arm portion 30 of the welding robot 20, the welding robot 20 Durability does not decrease. Moreover, restrictions on mutual interference between the workpieces Wa, W and the gun body 34 are relaxed, and the gun body 34
This has the advantage of expanding the operating range.

Furthermore, since the weight borne by the second arm section 30 is reduced, the movement speed of the entire arm section of the welding robot 20 is improved, and the welding cycle time can be shortened. In addition, since the transistors constituting the inverters 58a to 58d can reduce the current capacity per transistor, there is no need to connect the transistors in parallel, so it is necessary to select the current balance of each transistor when connected in parallel. Therefore, it is possible to provide an inverter section with excellent stability. Further, in the event that any of the inverter sections breaks down, by configuring each impark unit, each unit can be replaced, and recovery from a faulty state can be accomplished in a short time.

In the embodiment described above (hereinafter referred to as the first embodiment), the sub-timers 55a to 55d perform constant current control by feeding back the branch currents 1 to 1. The insertion points of the inverters 76a to 76d are not limited to the output sides of the welding transformers 68a to 68d, but can also be inserted on the input sides (second embodiment) or output sides (in the second embodiment) of the inverters 58a to 58d, as shown in FIGS. Of course, it is also possible to adopt the third embodiment). Note that when inserted into the input side of the inverters 58a to 58d (FIG. 5), the current detectors 76a to 7
It is preferable to use a Hall element that can also detect direct current as 6d. In the second and third embodiments described in 11t1, although the error with respect to the set value of the welding current ■o becomes a little large, it is possible to carry out wiring processing within the welding controller 22, so there is an advantage in manufacturing.

In the first to third embodiments described above, the sub-timer 5
5a to 55d have feedback control means such as comparison amplifiers, and the mask timer 53 controls the welding current ■. monitors for abnormalities, etc., but does not perform feedback control. Therefore, due to stray capacitance existing in the gun arms 44, 46, etc., the sum of the branch currents 11 to I4 and the welding current I. The sizes of are not necessarily the same. Therefore, if more accurate control is required, a third
A feedback control means such as a comparator amplifier is also added to the mask timer 53 shown in FIGS.
, welding current■.

Welding current machining by performing feedback control between the command value and the command value. can be controlled extremely precisely.

Furthermore, as another embodiment (fifth embodiment), the seventh
As shown in the figure, welding current I is controlled by adding feedback control means only to mask timer 53 without performing feedback control using sub-timers 55a to 55d. The control may be performed. In this case, the currents flowing through the transistors constituting the inverters 58a to 58d and the currents flowing to the rectifier diodes 74a to 74h are not equal in normal cases, but the components have sufficient specifications and characteristics, or the specifications and characteristics are equal. This can be achieved by selecting and selecting suitable parts.

In addition, as yet another embodiment (sixth embodiment),
Impark parts 58a to 58d and welding transformer part 3
6 components in the same way as in the fifth embodiment, e.g.
The current detector 76
Feedback control means (not shown) constituting a to 76d and 80, mask timer 53, and sub-timers 55a to 55d are omitted, and the welding current I is controlled only by the feedforward command without performing feedback control. Needless to say, it is also possible to supply

[Effects of the Invention] As described above, according to the present invention, when obtaining a welding current to be supplied to a welding electrode, a current supply circuit is constructed by connecting a rectifier circuit including a welding transformer and a rectifier in parallel. Therefore, it is possible to apply a relatively large welding current to the workpiece, and it is also possible to realize a DC resistance welding device that has a small and lightweight welding gun assembly and is excellent in maintainability.

Although the present invention has been described above with reference to preferred embodiments, the present invention is not limited to these embodiments.
Of course, various improvements and changes in design are possible without departing from the gist of the present invention.

[Brief explanation of the drawing]

Fig. 1 is an electric circuit block diagram of a DC resistance welding device according to the prior art, Fig. 2 is a schematic configuration diagram of a DC resistance welding device according to the present invention, and Fig. 3 is a main part of the DC resistance welding device shown in Fig. 2. FIG. 4 is a flowchart explaining the operation of the DC resistance welding device according to the present invention, and FIGS. 5 to 7 are other embodiments of the main parts of the DC resistance welding device according to the present invention. FIG. 2 is an electric circuit block diagram according to the present invention. 20... Welding robot 21... Robot controller 22... Welding controller 44... Fixed gun arm 46... Movable gun arm 48a, 48b.
...Electrode 50... Electrode converter 52... Control section 53... Mask timer 55a-55d... Sub-timer 56... Converter B 60... Impark section 58a-58d... Inverter 628 ~62d... Rectifier diode stack 68a~
68d...Welding transformer

Claims (7)

[Claims] (1) A DC resistance welding device that supplies welding current from a welding transformer to a welding electrode to join workpieces, including a circuit in which a plurality of rectifier circuits each consisting of a welding transformer and a rectifier are connected in parallel, and supplies the welding current to the welding electrode. A DC resistance welding device characterized in that the welding current is supplied from the circuits connected in parallel. (2) In the device according to claim 1, the rectifier circuit is substantially connected to a welding transformer having a center tap in the secondary coil.
rectifiers, the center tap is formed as one output terminal, one pole side of one of the two rectifiers is connected to one terminal of the secondary coil, and one of the two rectifiers is connected to one terminal of the secondary coil. One pole side of the other of the two rectifiers is connected to the other terminal of the next coil, and the other pole sides of the respective rectifiers are connected to each other to form the other output terminal. The circuit connected in parallel is configured such that the one output terminal, which is the center tap of the plurality of rectifier circuits configured as described above, and the other output terminal are connected to each other. A DC resistance welding device characterized by: (3) A DC resistance welding apparatus according to claim 1 or 2, wherein each rectifier circuit is configured to be driven by a different inverter. (4) In the apparatus according to claim 3, a main control means having a feedback control means is connected to each inverter, and the main control means has a welding current proportional to the welding current supplied to the welding electrode from the parallel connected circuit. A direct current resistance welding device characterized in that the welding current is made constant by feedback control, and the welding current is made constant by feedback control. (5) In the device according to claim 3, each inverter is connected to a sub-control means having a feedback control means corresponding to each inverter, and this sub-control means receives the output from each of the rectifier circuits. A DC resistance welding device characterized in that a signal proportional to a welding branch current is introduced via a current detection means, and the welding branch current is made constant by feedback control. (6) In the apparatus according to claim 5, a main control means having a feedback control means is further connected to the sub-control means, and the main control means is connected to the welding current supplied to the welding electrode from the parallel-connected circuit. A direct current resistance welding device characterized in that it is configured such that a proportional signal is introduced through a current detection means, and the welding current is made constant by feedback control. (7) In the apparatus according to claim 3, each inverter is connected to a sub-control means having a feedback control means corresponding to each inverter, and this sub-control means receives the output from each of the rectifying circuits. a current proportional to the welding branch current is introduced through the current detection means and connected to the main control means having at least timer means;
The main control means calculates a command value corresponding to the welding branch current to be handled by each of the inverters based on the welding current command value and gives it to the sub-control means. A direct current resistance welding apparatus, wherein the welding branch current is made constant by feedback control based on the above, and the timer means is configured to synchronize the timing of application of the welding branch current.