JP2840141B2 - Method and apparatus for controlling welding current of DC resistance welding machine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is to perform suitable welding by changing the rate of increase of the welding current a plurality of times while gradually decreasing the rate of increase of the welding current during the initial period of starting the welding current. The present invention relates to a method and an apparatus for controlling a welding current of a DC resistance welding machine which can be used.

[0002]

2. Description of the Related Art In the industry, an inverter type DC resistance welding apparatus is widely used for welding various workpieces. In order to suppress excessive overshoot that occurs when the welding current reaches a preset reference welding current value, a slow-up energization by open loop control that gradually increases the welding current based on a preset change amount is performed. Done.

[0003] In the inverter type DC resistance welding apparatus, when a work is changed, a welding operation is performed by replacing a welding gun according to the shape of the work.

[0004]

In the inverter type DC resistance welding apparatus of the prior art, when the welding gun is replaced with a different type, the resistance value of the replaced welding gun is set to a predetermined reference resistance value. If it is larger than this, there is a disadvantage that the welding current cannot reach the reference welding current value within a preset slow-up time.

If the resistance value of the replaced welding gun is smaller than the reference resistance value, there is a problem that the overshoot of the welding current becomes large and the hunting period becomes long.

The present invention has been made to solve such a conventional problem. In the present invention, the welding current can quickly reach the reference welding current value during the slow-up energizing period, and the reference welding current value can be reduced. An object of the present invention is to provide a welding current control method and apparatus for a DC resistance welding machine that can suppress hunting of a welding current in the vicinity.

[0007]

According to a first aspect of the present invention, there is provided a first invention for controlling the supply of welding current according to a first rising rate until a first current supply time set in advance.
And a second step of controlling the energization of the welding current according to a rate of increase smaller than the first rate of increase until a second time of energization set after the first time of energization. It is characterized by.

[0008] Further, a third aspect of the present invention provides a base for main energization.
Until the quasi-welding current is applied,
Slow-up system that gradually increases the welding current according to excess
In the welding current control device of the DC resistance welding machine that performs control,
Energization information storage means for storing the time from the start of energization to the main energization divided into a plurality of welding current energization times and storing a current increase rate for each welding current energization time as energization information; and From the start of the energization based on the energization information stored in the means.
Comprising a welding current control means for controlling the welding current to flow through the semi-welding current, a, is stored in the current information storage means
The rate of current rise is from the start of energization to the main energization.
Between the start of the energization and the main energization side
It is set so that it becomes smaller every welding current conduction time.
It is characterized by having.

[0009]

In the method and apparatus for controlling the welding current of the DC resistance welding machine according to the present invention, the welding current control means supplies the welding current in accordance with the first increasing rate until the first current supply time stored in the current supply information storage means. Control. Next, the welding current control means controls welding current application according to a rise rate smaller than the first rise rate until the second current supply time. Therefore,
The welding current rises stepwise according to a plurality of preset rise rates, and reaches a target current.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a preferred embodiment of a method and an apparatus for controlling a welding current of a DC resistance welding machine according to the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an entire configuration of an embodiment of the present invention. In the drawing, reference numeral 20 denotes an inverter type DC resistance welding apparatus.

The inverter type DC resistance welding apparatus 20 includes a converter circuit 22 for performing full-wave rectification of three-phase AC output from a three-phase AC power supply 21, an inverter circuit 24 for converting full-wave rectified DC to high-frequency AC, A welding transformer circuit 26 for rectifying the high-frequency AC, a welding gun portion 28 for welding by energizing the work W to be welded, and a control circuit 30 for controlling the welding current by controlling the inverter circuit 24. Is provided.

Further, an inverter type DC resistance welding apparatus 2
0 is a current detector 32 for detecting a primary side current which is an output current of the converter circuit 22;
Current detector 34 connected to the welding gun unit 28 to detect a secondary current, a keyboard 36 for inputting welding conditions and the like to the control circuit 30, and a display for displaying the input welding conditions and the like A CRT 38 as an apparatus.

The welding gun section 28 includes movable gun arms 40 and 42 for holding the workpiece W, and movable gun arms 40 and 4
And a cylinder 44 for driving the cylinder 2
Is connected to a pneumatic source 48 via an electromagnetic switching valve 46.

The input terminal of the converter circuit 22 is connected to the three-phase AC power supply 21. One output terminal of the converter circuit 22 is connected to the control circuit 30, and the other output terminal is connected to one input terminal of the inverter circuit 24 via the current detector 32. Connected to. The input terminal of the welding transformer circuit 26 is connected to the output terminal of the inverter circuit 24, and the output terminal of the welding transformer circuit 26 is connected to the welding gun unit 28 via the current detector 34. In addition, the current detector 34
Is connected to the control circuit 30.

The control circuit 30 is connected to the electromagnetic switching valve 46 and the other input terminal of the inverter circuit 24,
Connected to the robot controller 50.

FIG. 2 is a block diagram showing the configuration of the control circuit 30.

The control circuit 30 includes an A / D conversion circuit 52 for converting a primary-side current value, which is an analog value output from the current detector 32, to a digital value, an output of the current detector 32, and an overcurrent setting device. A comparing circuit 56 for comparing the output of the comparator 54 with an output of the comparator 54;
A latch circuit 58 for temporarily storing the comparison result output from the comparison circuit 56;

The control circuit 30 integrates an output of a current detector 34 for detecting a current on the secondary side, and an A / A converter for converting an analog output of the integration circuit 60 into a digital value.
The D conversion circuit 62 is connected to the input / output terminals of the A / D conversion circuits 52 and 62 and the input terminal of the latch circuit 58.
U64.

Further, the control circuit 30 has a digital / analog (hereinafter, D / A) connected to an output terminal of the CPU 64.
A), a comparison circuit 72 for comparing the output of the D / A conversion circuit 66 with a triangular wave input from a pulse generation circuit 68 via a triangular wave generation circuit 70, the comparison circuit 72 and the latch An AND gate 74 for performing a logical OR operation with the circuit 58; and a pulse control circuit 76 for distributing a pulse train output from the AND gate 74 to the A phase and the B phase in synchronization with the synchronization pulse output from the pulse generation circuit 68. including.

Drive circuits 78, 80, 82 and 84 energize the bases of transistors (not shown) constituting inverter circuit 24 in response to a pulse signal output from pulse control circuit 76.

The CPU 64 stores a program for performing pre-energization control, main energization delay control, slow-up control, main energization control, pseudo welding stop control, and the like.
A RAM 88 for storing a value of a reference welding current;
Interface of keyboard 36, CRT 38, electromagnetic switching valve 46, and robot controller 50 (hereinafter, I / O
90 (referred to as F).

The CPU 64 further includes an energization information storage circuit 92 for storing a plurality of scheduled energization times and a plurality of rates of change of the welding current, and a timer 94 for counting the energization time of the welding current.
And the gain coefficient k ₁ used when calculating the welding current,
Lookup table (hereinafter, L ₂₎ storing k ₂ ... k _N
96 (referred to as UT).

In this case, the current detector 34 constitutes a welding current reading means, and the CPU 64 constitutes a target current computing means, a current difference computing means, and a welding current computing means.

A method for controlling the slow-up welding current in the inverter type DC resistance welding apparatus 20 configured as described above will be described with reference to FIGS.

In this embodiment, as shown in FIG. 4, a first control step of increasing the welding current by a rate of change A to a pre-stored scheduled energizing time T _S1 ,
By a second control step of increasing the rate of change B _S1 to scheduled energization time T _S2, it describes a method to reach the reference welding current value I _C.

The information indicating the reference welding current value I _C for the main energization and the information indicating that the welding current is controlled based on, for example, the secondary-side welding current value I _N are stored on the keyboard 3.
When the information is input by the operator from step 6, the information is stored in the RAM 88 via the CPU 64, and the preparation step ends.

Next, when the welding process is started, R
The control circuit 30 according to the program stored in the OM 86
The CPU 64 executes a program of the main energization control through execution of programs such as a pre-energization control, a main energization delay control, and a slow-up energization control. The estimated energizing time T _S1 of the first control step and the change rate A for increasing the welding current are read from 92, and the energization of the welding current is started in accordance with the change rate A, and the timer 94 for counting the energizing time is energized. .

The CPU64 current detector 34 reads the welding current value I _N integrating circuits 60 and via the A / D converter circuit 62 secondary from (step S1), the read energization time T from the timer 94 (step S2 It is determined whether the energization time T is equal to or less than the scheduled energization time T _S1 of the first control process read from the energization information storage circuit 92 (step S3). If T ≦ T _S1 , the first control process is performed. (Step S
3 to step S8) are executed. In the first control step, an ideal welding current value I at the energizing time T is obtained from the calculation of the energizing time T and the change rate A of the welding current read from the energizing information storage circuit 92 (T × A = I) (step S
4). Then, substituting the gain coefficient K ₁ in the first control step read from LUT96 the gain coefficient K _n to be used in the calculation of the pulse width P _W (step S5).

[0030] Then, CPU 64 is determined by calculating the error [Delta] I of the welding current I _N of the secondary side with respect to the ideal welding current value _{I (I-I N = ΔI} ) ( step S6), and the the error [Delta] I a gain coefficient k _n, the calculation for obtaining the pulse width P _W immediately from the immediately preceding pulse width P _WB performed by the following equation (step S7).

[0031] _{P W = P WB + (ΔI} × k n) switching elements of the inverter circuit 24 by the pulse width P _W obtained by this calculation is biasing, the pulse width P _W is immediately before under the control of the CPU64 Pulse width P _WB
Is stored in the RAM 88.

Next, the pulse width P _W is converted to a D / A conversion circuit 66.
(Step S8), and the control routine of the first control process consisting of steps S1 to S8 is repeated again until the scheduled energization time T _S1 ends.

In step S3, if the energizing time T exceeds the scheduled energizing time T _S1 , the control in the second control step is performed assuming that the first control step has been completed.

In the second control step, it is determined whether or not the energization time T is less than or equal to the scheduled energization time T _{S2 in} the second control step (step S9). If T ≦ T _S2 , the energization information storage circuit 9 is determined.
2 and the estimated energizing time T
_From the welding current value I _{TS1 at S1} and the planned energizing time T _S1 , an ideal welding current value I at the energizing time T is obtained from the following equation (step S10).

[0035] Next _{I = (T-T S1)} × B + I TS1, substituting the gain coefficient K ₂ in the second control step gain coefficient K _n (step S11), and similarly followed first control step, step S6 Steps S8 to S8 are executed. When the energization time T exceeds the scheduled energization time T _S2 of the second control step, the second control step ends, the slow-up control step ends, and then the main energization step.

[0036] In this case, to correct the first control step and the second control step, the welding current of the read secondary value I _N ideal welding current value I determined as a function of the energization time T, the proper A high welding current.

Furthermore, the rate of change B in the second control step when for is smaller than the change rate A of the first control step, the slow-up welding current reaches the reference welding current value I _c for the current The rate of change becomes small, and overshoot of the welding current can be suppressed, and hunting of the welding current for a long time can be prevented.

In step S7, the D / A signal is sent from the CPU 64.
The pulse width P _WB for controlling the welding current output to the conversion circuit 66 is converted into an analog voltage by the D / A conversion circuit 66 and input to one input terminal of the comparison circuit 72 (see FIG. 5).

On the other hand, the triangular wave generated by the triangular wave generation circuit 70 in synchronization with the pulse output from the pulse generation circuit 68 is input to the other input terminal of the comparison circuit 72 (see FIG. 5). The comparison circuit 72 compares the analog voltage output from the D / A conversion circuit 66 with the analog voltage (see FIG. 5), and the D / A conversion circuit 6
6 is high, the output terminal HI
A GH (H) level signal is output (see FIG. 5).

In this case, it can be understood from FIG. 6D that the pulse width output from the comparison circuit 72 depends on the magnitude of the analog voltage output from the D / A conversion circuit 66. That is, when the output voltages of the D / A conversion circuit 66 have different voltage values X1, Y1, and Z1, respectively, the comparison circuit 72
Output from the D / A conversion circuit 6
6 are X, Y, and Z according to the output voltage.

The value X output from the comparison circuit 72,
The pulse train having the pulse widths of Y and Z is distributed by the pulse control circuit 76, and the drive circuits 78, 80, 8
2, 84, and these drive circuits 78, 8
0, 82 and 84 drive the bases of the transistors which are the switching elements of the inverter circuit 24,
The welding current value output from the inverter circuit 24 is corrected, and the corrected welding current is supplied to the work W via the welding transformer circuit 26 and the movable gun arms 40 and 42 of the welding gun unit 28 to perform welding.

As described above, according to the present embodiment, an appropriate welding current value I is obtained by calculation from the energization time T read during the slow-up control period and a preset change rate. the error ΔI like the welding current value I _N read and, to determine the pulse width P _W immediately after, it is possible to obtain an appropriate welding current in conformity to the set change rate a or rate of change B.

Further, since the change rate B is smaller than the change rate A, the pulse width P _W obtained by the above calculation is obtained.
A proper until it reaches the vicinity of the reference welding current value I _C generates a welding current of sharp change amount reference welding current value I _C
Since the gradual change amount in the vicinity, it is possible to suppress the hunting of the welding current generated in the reference welding current value I _C vicinity.

Accordingly, it is possible to prevent the welding dust from being generated due to the overcurrent due to the overshoot of the welding current, and to improve the welding quality.

Further, in the above embodiment, the welding current is controlled by the welding current value I detected by the secondary-side current detector 34.
_Although performed based on _N , it is also possible to control the welding current based on information on the primary side current value detected by the current detector 32.

[0046]

According to the method and apparatus for controlling a welding current of a DC resistance welding machine according to the present invention, the welding current rises according to a plurality of preset rise rates, and thus reaches the reference welding current value as quickly as possible. This makes it possible to suppress hunting of the welding current in the vicinity of the reference welding current value with respect to a change in load due to replacement of the welding gun or the like.

Therefore, it is possible to suppress the occurrence of dust in the welding caused by the overshoot, and to achieve the effect of performing high quality welding.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an entire configuration of an embodiment of a method and an apparatus for controlling a welding current of a DC resistance welding machine according to the present invention.

FIG. 2 is a block diagram showing a configuration of a control circuit in FIG.

FIG. 3 is a flowchart showing an operation of the embodiment shown in FIG. 1;

FIG. 4 is a diagram for explaining the operation of the embodiment shown in FIG. 1;

FIG. 5 is a timing chart for explaining an operation of generating a pulse for controlling a welding current in the embodiment shown in FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 20 ... Inverter type DC resistance welding apparatus 22 ... Converter circuit 24 ... Inverter circuit 26 ... Welding transformer circuit 28 ... Welding gun part 30 ... Control circuit 32,34 ... Current detector 52,62 ... A / D conversion circuit 64 ... CPU 66 ... D / A conversion circuit 70 ... triangle wave generation circuit 72 ... comparison circuit 76 ... pulse control circuit 78,80,82,84 ... drive circuit 92 ... energization information storage circuit 94 ... timer 96 ... LUT

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) B23K 11/24

Claims (4)

(57) [Claims] 1. A first step of controlling the welding current to flow according to a first rising rate until a first current flowing time set in advance, and a second current flowing time set after the first current flowing time. A second step of controlling the energization of the welding current in accordance with an increasing rate smaller than the first increasing rate until the first increasing rate. 2. The method according to claim 1, wherein the first or second step comprises one or more steps of controlling the application of the welding current according to a rate of rise set to gradually decrease. A welding current control method for a DC resistance welding machine. 3. Until the reference welding current for the main current is applied
In addition, the welding current is
DC resistance welding with slow-up control to gradually increase
In the welding current control device of the welding machine, the time from the start of energization to the main energization is stored separately for a plurality of welding current energization times , and the current increase rate for each welding current energization time is stored as energization information. Storage means, based on the energization information stored in the energization information storage means
From the start of the energization, the reference welding current for the main energization is
Comprising a welding current control means for controlling the welding current to flow, and the current rise rate which is stored in the current information storage means,
During the time from the start of the energization to the main energization,
The welding current energizing time on the main energizing side from the energizing start side
A welding current control device for a DC resistance welding machine, wherein the welding current control device is set to be smaller each time . 4. The apparatus according to claim 3, wherein said welding current control means reads a welding current, reads a welding current, a timer which counts a current flowing time of said welding current, and said welding time and a preset welding current. Target current calculation means for calculating a target welding current from the amount of change, current difference calculation means for calculating the difference between the target current and the read welding current, and the current difference and the immediately preceding welding current. And a welding current calculating means for calculating a welding current immediately after the welding current control device.