JP2012187621A - Resistance welding control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resistance welding control device 1 capable of correcting a reactive current, generated in a to-be-welded object 17 and flowing in a flow dividing circuit, by improving working efficiency.SOLUTION: In the resistance welding control device 1, a welding clearance setting unit 29 sets each welding clearance, and a current increasing degree calculating circuit 28 calculates the increasing degree of a secondary current setting value with an output signal of the welding clearance setting unit 29 as input. A secondary current setting value adding circuit 30 outputs a signal, where the increasing degree G is added to a setting value of a secondary current setting unit 22, to a current error amplifying circuit 23, with an output signal of the secondary current setting unit 22 and an output signal of the current increasing degree calculating circuit 28 as input. The current error amplifying circuit 23 calculates an error with a detection signal of a secondary current detector 21 and an output signal of the secondary current setting value adding circuit 30 as input, and an inverter drive circuit 5 controls an inverter circuit 4 with an output signal of the current error amplifying circuit 23 as input.

Description

  The present invention relates to a resistance welding control apparatus capable of correcting a current (hereinafter referred to as a reactive current) flowing in a shunt circuit generated in a workpiece.

  In spot welding, when there is a spot already welded next to the spot welding spot and the distance between the spot welding spot and the spot welded is close, a shunt circuit is generated at the spot welded and reactive current is generated. Flowing. When a shunt circuit is generated, the welding current supplied to the point to be welded is insufficient, the nugget diameter is reduced, and as a result, a welding defect is produced in which the welding strength is reduced. Therefore, in order to keep the nugget diameter constant, it is necessary to increase the set value of the secondary current in consideration of the reactive current flowing in the shunt circuit.

Conventionally, before energizing the secondary current, the pilot current is passed for each welding point to calculate the overall resistance value, and the resistance value other than the welding point is obtained from the calculated resistance value and the resistance value of the welding point, Thus, it has been proposed to obtain the shunt ratio of the secondary current and set the current increased by the reactive current as the set value of the secondary current. (For example, refer to Patent Document 1).

JP-A-9-99379

As described above, since the resistance welding control device of the prior art can flow the current obtained by increasing the set value of the secondary current by the amount of the reactive current as the secondary current, the welding current supplied to the welding point is There is no shortage of weld defects that reduce the welding strength. However, since it is necessary to calculate the entire resistance value by supplying a pilot current to each welding point, the number of welding operations is increased and the work efficiency is lowered. Moreover, the workpiece may be incompletely welded by passing a pilot current. In that case, the welding result may be different between when the pilot current is supplied before the current increased by the reactive current is supplied as the secondary current and when the pilot current is not supplied.

In addition, a means for detecting the welding current is required to calculate the resistance value of the welding point, and the resistance value changes due to oil stains on the workpiece. In such a case, a shunt circuit is generated. In some cases, it may not be possible to distinguish whether the resistance value has changed or the resistance value has changed due to oil stains, etc., so the calculation of the ratio of the reactive current flowing in the shunt circuit becomes inaccurate. was there.

An object of this invention is to provide the resistance welding control apparatus which can improve the working efficiency and can correct the reactive current which flows into the shunt circuit which generate | occur | produces in a to-be-welded object.

In order to solve the above-described problems, the invention of claim 1
An inverter circuit;
A welding transformer that steps down the output of this inverter circuit;
A secondary current detector for detecting the secondary current of the welding transformer;
A welding separation distance setting device in which each welding separation distance which is a distance between each welding point is set;
A current increase degree calculation circuit that calculates the increase degree of the secondary current with the output signal of the welding separation distance setter as an input;
A secondary current setter;
The secondary current set value addition that outputs the signal obtained by adding the increase degree to the set value of the secondary current setter with the output signal of the secondary current setter and the output signal of the current increase degree calculation circuit as inputs. Circuit,
A current error amplifying circuit for calculating an error between the detection signal of the secondary current detector and the output signal of the secondary current set value addition circuit;
An inverter drive circuit for controlling the inverter circuit with an output signal of the current error amplifier circuit as an input;
A resistance welding control apparatus comprising:

The invention of claim 2
The welding separation distance setting device according to claim 1 is a resistance welding control device that calculates each welding separation distance from data taught in teaching.

  The resistance welding control device of the present invention can flow a current obtained by increasing the set value of the secondary current by the amount of the reactive current as a secondary current without flowing a pilot current for each welding point as in the prior art. Therefore, working efficiency can be improved compared with the prior art.

It is a block diagram of the resistance welding control apparatus of this invention. It is a figure which shows the relationship between the welding separation distance D [mm] (horizontal axis) and the increase degree G [%] (vertical axis) of a secondary current setting value.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on examples with reference to the drawings. FIG. 1 is a block diagram of a resistance welding control apparatus according to the present invention, which is a case of an inverter control system, in which a welding current is a direct current. In the figure, the resistance welding control apparatus 1 rectifies commercial power AC power generated by an AC power source 2 by a rectifier circuit 3. The DC power output from the rectifier circuit 3 is input to the inverter circuit 4. The inverter circuit 4 is composed of a bridge circuit made up of a plurality of switching elements (not shown), and the input DC power is converted into pulsed high-frequency AC power by a high-frequency switching operation. The switching operation of the inverter circuit 4 is controlled by a control signal from an inverter drive circuit 5 described later.

The welding transformer 6 includes a primary coil 7, a secondary coil 8, and a core 9. The primary coil 7 is connected to the output side of the inverter circuit 4. The output terminal of the secondary coil 8 is the first rectifying element 10 and the second coil. The rectifier element 11 is connected to the upper arm 12, and the center tap 14 of the secondary coil 8 is connected to the lower arm 13. A first welding tip 15 and a second welding tip 16 are attached to the distal ends of the upper arm 12 and the lower arm 13, respectively.

The high-frequency AC power output from the inverter circuit 4 is applied to the primary coil 7 of the welding transformer 6, and a high-current high-frequency AC power with a reduced voltage is generated in the secondary coil 8 of the welding transformer 6. The high-frequency AC power generated in the secondary coil 8 is alternately rectified every half cycle by the first rectifying element 10 and the second rectifying element 11, and DC power is supplied between the upper arm 12 and the lower arm 13. . A plurality of workpieces 17 are pressed by the upper arm 12 and the lower arm 13 to cause a direct current to flow, and the welds are metallurgically joined by Joule heat.

The secondary current setter 22 is set with a secondary current, and the welding separation distance setting device 29 sets a welding separation distance that is a distance between a spot welding point and an already welded point closest to the welding point. Is done. The current increase degree calculation circuit 28 stores a function indicating the relationship between the welding separation distance D [mm] and the increase degree G [%] of the secondary current set value. This function is determined by determining the degree of increase in secondary current when the desired nugget diameter is obtained by actually measuring the nugget diameter by changing the welding separation distance for various workpiece materials and plate thicknesses. The The secondary current set value addition circuit 30 receives the output signal of the secondary current setter 22 and the output signal of the current increase calculation circuit 28 as inputs, and sets the current increase calculation circuit to the set value of the secondary current setter 22. A set value obtained by adding the degree of increase calculated by 28 is output to the current error amplifier circuit 23.

The secondary current detector 21 detects a welding current that is a current on the secondary side of the welding transformer 6. The current error amplification circuit 23 receives the detection signal of the secondary current detector 21 and the output signal of the secondary current set value addition circuit 30 as input, amplifies these errors, and outputs the error signal to the inverter drive circuit 5. . The welding time setter 24 sets the welding time per time. The welding start circuit 25 outputs a signal that becomes a high level when welding is started. The starting circuit 26 receives the output signal of the welding time setter 24 and the output signal of the welding start circuit 25 as input, and only the time set by the welding time setter 24 after the output signal of the welding start circuit 25 becomes high level. A signal that is at a high level is output.

  The operation will be described below. For example, a welding torch attached to the tip of a welding robot has a set value of 10,000 [A] with two sheets of mild steel with a thickness of 1 [mm] overlapped, and the welding current is set in one direction. A case where spot welding is performed while continuously moving toward the surface will be described. In this case, for example, the function shown in FIG. 2 is used as the function stored in the current increase calculation circuit 28. FIG. 2 is a diagram showing a function of the welding separation distance D [mm] (horizontal axis) and the increase degree G [%] (vertical axis) of the secondary current set value. In the figure, when the welding separation distance D is 20 [mm], the secondary current setting value increase degree G is 15 [%], and when the welding separation distance D is 40 [mm], the secondary current setting value increase. When the degree G is 10 [%] and the welding separation distance D is 60 [mm], the increase degree G of the secondary current set value is 5 [%].

  When spot welding is performed by the welding robot, the welding separation distance between the welding points is calculated from the position of each welding point taught by teaching, and the calculated welding separation distance is set in the welding separation distance setting unit 29. The Further, the set value of the secondary current taught at each welding point is set in the secondary current setter 22. For example, in teaching, the welding separation distance is calculated as 20 [mm] from the position of the weld point between the first and second strike points, and the set value of the secondary current at the first and second strike points is 10,000 [ A]. At this time, the welding separation distance of the first and second strike points is set to 20 [mm] in the welding separation distance setting device 29, and the secondary current setting of the first and second strike points is set in the secondary current setting device 22. The value is set to 10,000 [A].

  An operation control signal from a robot controller (not shown) is input to the welding robot, and the tip of the welding torch attached to the welding robot reaches the first hit point on the workpiece. At that time, a welding control signal from the robot control device is input to the resistance welding control device 1, and spot welding is performed when the set value of the secondary current is 10,000 [A]. Thereafter, the tip of the welding torch is moved to the second strike point of the workpiece.

When the tip of the welding torch reaches the second strike point of the workpiece, the current increase calculation circuit 28 corresponds to the set value of the welding separation distance setting device 29 corresponding to 20 [mm] from the function shown in FIG. 15 [%] is calculated as the increase degree G of the secondary current set value. The secondary current set value addition circuit 30 receives the output signal of the secondary current setter 22 as an input, and adds the increase calculated by the current increase calculation circuit 28 to the set value of the secondary current setter 22. The set value is output to the current error amplifier circuit 23.

That is, the set value of the secondary current setter 22 is increased by 15 [%], and a set signal of 11,500 [A] is output to the current error amplifier circuit 23. The inverter drive circuit 5 receives the output signal of the current error amplification circuit 23 as an input, and the detection value of the secondary current detector 21 becomes 11, 500 [A] which is the output value of the secondary current set value addition circuit 30. The inverter circuit 4 is controlled. Thereafter, when spot welding at the final spot is completed in the same manner, the welding robot and the resistance welding control device 1 are stopped.

  As a result, the resistance welding control apparatus 1 according to the present invention uses the current obtained by increasing the set value of the secondary current by the amount of the reactive current as the secondary current without causing the pilot current to flow for each welding point as in the prior art. Since it can flow, working efficiency can be improved compared with the prior art.

In the spot welding of the resistance welding control apparatus 1 of the present invention described above, a shunt circuit is generated at the already welded point closest to the spot welding point, and a reactive current flows. The reactive current rarely flows to the welding point far from the spot welding point.

The above-described resistance welding control apparatus 1 of the present invention has been described with respect to the case where feedback control is performed by detecting the secondary current of the welding transformer 6, but the operation is also performed when feedback control is performed by detecting the primary current of the welding transformer 6. Since the effects are the same, the description thereof is omitted.

Further, the resistance welding control apparatus 1 of the present invention described above calculates the welding separation distance between the welding points from the position of each welding point taught by teaching, and the calculated welding separation distance is used as the welding separation distance setting device. The case of setting to 29 has been described. Instead, the welding operator may set individual welding separation distances with the welding separation distance setting device 29.

DESCRIPTION OF SYMBOLS 1 Resistance welding control apparatus 2 AC power supply 3 Rectifier circuit 4 Inverter circuit 5 Inverter drive circuit 6 Welding transformer 7 Primary coil 8 Secondary coil 9 Core 10 1st rectifier 11 Second rectifier 12 Upper arm 13 Lower arm 14 Center tap 15 First welding tip 16 Second welding tip 17 Workpiece 21 Secondary current detector 22 Secondary current setting device 23 Current error amplification circuit 24 Welding time setting device 25 Welding start circuit 26 Start-up circuit 28 Current increase calculation circuit 29 Welding Separation distance setter 30 Secondary current set value addition circuit D Welding separation distance G Increasing degree of secondary current set value

Claims (2)

An inverter circuit;
A welding transformer that steps down the output of this inverter circuit;
A secondary current detector for detecting the secondary current of the welding transformer;
A welding separation distance setting device in which each welding separation distance which is a distance between each welding point is set;
A current increase degree calculation circuit that calculates the increase degree of the secondary current set value with the output signal of the welding distance setting device as an input;
A secondary current setter;
The secondary current set value addition that outputs the signal obtained by adding the increase degree to the set value of the secondary current setter with the output signal of the secondary current setter and the output signal of the current increase degree calculation circuit as inputs. Circuit,
A current error amplifying circuit for calculating an error between the detection signal of the secondary current detector and the output signal of the secondary current set value addition circuit;
An inverter drive circuit for controlling the inverter circuit with an output signal of the current error amplifier circuit as an input;
A resistance welding control device comprising: The resistance welding control apparatus according to claim 1, wherein the welding separation distance setting device calculates each welding separation distance from data taught in teaching.

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