JPH0639559A - Method and device for deciding secondary side condition of welding transformer - Google Patents

Abstract

PURPOSE:To enable deciding of a welding condition and a condition of the secondary side of welding transformer by detecting a change of the resistance value at the secondary side of welding transformer, based on the prescribed and detected electric current values. CONSTITUTION:At the electric current ratio withmetic circuit 72 of the withmetic circuit 68, to which the command welding electric current value outputted from CPU 58, is inputted, the electric current ratio between the commanded welding electric current value and secondary side current value outputed from the detecting electric current selecting circuit 54 is obtained. Based on this electric current ratio, the resistance change quantity similar to the change of the secondary side electric current value of the welding transformer circuit is obtained. The comparing circuit 78, to which this resistance change quantity is inputted, compares this resistance change quantity with the prescribed resistance value from the comparing value setting circuit 76. The compared result is outputted to CPU 58. While the differentiating circuit 80, to which the resistance change quantity is inputed, outputs the differentiating resistance change quantity obtained by differentiating computing to the computing circuit 84. The comparing circuit 84 compares this differentiating change quantity with the prescribed resistance value from the comparing value setting circuit 82 and outputs the compared result to CPU 58.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a welding transformer secondary side state determining method and apparatus, and more specifically, based on a preset reference welding current value and a detected welding current value, The present invention relates to a method and apparatus for detecting a change in resistance value on the secondary side of a welding transformer and determining the secondary side state of the welding transformer based on the detection result.

[0002]

2. Description of the Related Art In the field of welding, resistance welding devices are widely used for welding various works. In controlling the welding current in these resistance welding devices, the welding current is controlled by an open loop without using a feedback loop. In this type of resistance welding apparatus, the generation state of nuggets, the generation of spatter, the shunting of welding current, and the like are detected by the changes in the voltage between electrode tips and the welding current value.

The technical idea of detecting the generation state of a nugget by the voltage between the electrode chips is described in JP-B-2-3726.
No. 8 "Control method and control device for resistance welding machine" and JP-A-63-299871 "Resistance welding control or monitoring device".

[0004]

However, in the method of detecting the generation state of the nugget and detecting the generation of spatter in the above-mentioned prior art, the reading wire for reading the detected voltage between the electrode tips is the movable part. And the movable part is fixed to the electrode tip closest to the welded part.

For this reason, the reading wire may be broken due to the bending and stretching action, or may be damaged by the scattering of spatter generated during welding, which may reduce the reliability of the detected voltage between the electrode tips. .

Further, if a wire breakage of the reading wire occurs during the welding work, the resistance welding device in operation must be stopped to perform the repair work, which causes a problem that the line is stopped for a long time.

The present invention has been made in order to solve such a conventional inconvenience, and is set in advance without reading the voltage between the electrode tips through the reading wire provided in the electrode tip. The change in the resistance value on the secondary side of the welding transformer is detected with high accuracy from the set welding current value and the detected welding current value, and the detection result indicates that the welding transformer is composed of spatter generation and welding current shunting. An object of the present invention is to provide a secondary side state determination method and apparatus for a welding transformer that determines the state of the secondary side.

[0008]

In order to achieve the above object, the first invention is a method for determining the secondary side state of a welding transformer in a resistance welding machine in which a welding current is controlled by an open loop. A first step of detecting a welding current flowing through the primary side or the secondary side of the transformer, and a second step of comparing the detected welding current value detected in the first step with a preset command welding current value. Steps of
A third step of detecting a change in the resistance value of the secondary side of the welding transformer based on the comparison result in the second step, and a change of the detected resistance value of the secondary side of the welding transformer in the welding transformer. And a fourth step of determining the state of the secondary side of the.

Further, a second aspect of the present invention is a secondary side state determination device for a welding transformer in a resistance welding machine for controlling a welding current in an open loop, and a welding current memory for storing a preset command welding current value. Means, primary side welding current detecting means for detecting a welding current flowing through the primary side of the welding transformer, secondary side welding current detecting means for detecting a welding current flowing through the secondary side of the welding transformer, and the primary side. Detection current selecting means for selecting the primary welding current value detected by the side welding current detecting means or the secondary welding current value detected by the secondary welding current detecting means, and the detection current selecting means. Comparing means for comparing the commanded welding current value with the primary welding current value or the secondary welding current value, and the resistance value of the secondary side of the welding transformer based on the comparison result output from the comparing means. Secondary-side resistance value detecting means for detecting a change, and secondary-side state determining means for determining the secondary-side state of the welding transformer based on the detected change in the secondary-side resistance value of the welding transformer, It is characterized by including.

[0010]

In the method and apparatus for determining the secondary side state of the welding transformer according to the present invention, the welding current flowing through the primary side of the welding transformer is detected by the primary side welding current detecting means and flows into the secondary side of the welding transformer. The secondary side welding current detecting means detects the welding current.

Then, the comparing means compares the command welding current value stored in the welding current storage means with the primary side welding current value or the secondary side welding current value selected by the detected current selecting means, Based on the comparison result, the secondary side resistance detecting means detects a change in the resistance value of the secondary side of the welding transformer.
Further, the secondary side state determination means determines the state of the secondary side of the welding transformer based on the detected change in the resistance value, whereby the welding state, the maintenance time of the secondary side conductor of the welding transformer, and the welding are performed. It is possible to determine the abnormality of the secondary conductor of the transformer.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the method for determining the secondary side state of a welding transformer according to the present invention will be described in detail below with reference to the accompanying drawings, with reference to preferred embodiments in relation to an apparatus for carrying out the method. To do.

FIG. 1 is a block diagram showing the overall construction of a first embodiment of the present invention. In the figure, reference numeral 20 indicates an inverter type DC resistance welding apparatus.

The inverter type DC resistance welding device 20 includes a converter circuit 22 for full-wave rectifying the alternating current output from the alternating current power source 21, an inverter circuit 24 for converting the full-wave rectified direct current into a high frequency alternating current, and the high frequency alternating current. A welding transformer circuit 26 for rectifying and rectifying, a welding gun portion 28 for sandwiching the work W, and a control circuit 30 for controlling a welding current supplied to the work W are provided.

Further, an inverter type DC resistance welding device 2
Reference numeral 0 denotes a primary side current detector 32 including a toroidal coil that detects a welding current (hereinafter referred to as a primary side current value) I ₁ on the primary side of the welding transformer circuit 26, and a secondary side of the welding transformer circuit 26. Secondary current detector 34 for detecting the welding current (hereinafter referred to as secondary side current value) I ₂ of No. _2, and a keyboard 36 for inputting welding conditions and the like to the control circuit 30.
CRT38 which is a display device as display means
And an FDD 39 which is an external storage means.

The welding gun section 28 has movable gun arms 40 and 41 for holding the work W, and the movable gun arms 4 and 4.
Electrode tips 42 and 43 fixed to 0 and 41, and a cylinder 44 that drives the movable gun arms 40 and 41 to open and close freely. An air pressure source 48 is connected to the cylinder 44 via an electromagnetic switching valve 46. To be done. The switching operation of the electromagnetic switching valve 46 is controlled by the control circuit 30.

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

The control circuit 30 includes the primary side current detector 32.
Analog / digital (hereinafter referred to as A / D) conversion circuit 50 for converting the primary side current value I ₁ output from the secondary side current value I ₁ to the digital value, and the secondary side current value I output from the secondary side current detector 34. A / D conversion circuit 52 for converting ₂ into a digital value
And a detection current selection for selecting either the primary side current value I ₁ output from the A / D conversion circuit 50 or the secondary side current value I ₂ output from the A / D conversion circuit 52. A circuit 54 and a welding current storage circuit 56 in which a preset command value of welding current (hereinafter referred to as a command welding current value) I _cmd is stored.

The control circuit 30 includes the detection current selection circuit 5
4 and an interface circuit described later (hereinafter, I / F
70) and the like, and also reads the command welding current value I _cmd from the welding current memory circuit 56 and outputs it, and a digital / converter 70 which converts the command welding current value I _cmd output from this CPU 58 into an analog value. An analog (hereinafter referred to as D / A) conversion circuit 60 and the D / A
A pulse width modulation (hereinafter referred to as PWM) circuit 62 for generating a duty pulse based on a signal output from the conversion circuit 60 is provided, and the PWM circuit 62 energizes the inverter circuit 24.

Further, the control circuit 30 includes the CPU 58.
A ROM 64 for storing a control program for controlling each of the circuits and a set value used for control;
A RAM 66 that temporarily stores a control result during the control by the CPU 58, a command welding current value I _cmd stored in the welding current storage circuit 56, and a primary side current value I output from the detected current selection circuit 54. A calculation circuit 68 for calculating the amount of change in the resistance value of the secondary side of the welding transformer circuit 26 based on ₁ or the secondary side current value I ₂ , the keyboard 36, and the CRT.
38, the FDD 39, and the I / F 70 of the electromagnetic switching valve 46.

The arithmetic circuit 68 controls the command welding current value I
A current ratio calculation circuit 72 for calculating a current ratio I _D of the primary side current value I ₁ or the secondary side current value I ₂ with respect to _cmd, and a resistance change amount calculation for obtaining a resistance change amount R _D from this current ratio I _D A circuit 74, the resistance change amount R _D and the comparison value setting circuit 7
And a comparison circuit 78 for comparing the set resistance value R1 _ref set to 6.

Further, the arithmetic circuit 68 differentiates the resistance change amount R _D output from the resistance change amount calculation circuit 74, and outputs a differential resistance change amount ΔR _D which is the result of this operation, and the differential circuit 80 described above. A comparison circuit 84 for comparing the differential resistance change amount ΔR _D with the set resistance value R2 _ref set in the comparison value setting circuit 82 is provided, and based on the comparison results output from the comparison circuit 78 and the comparison circuit 84. , C
The PU 58 determines the state of the secondary side of the welding transformer circuit 26, and outputs the determination result to the I / F 70.

FIG. 3 shows a block configuration of the PWM circuit 62.

The PWM circuit 62 includes a pulse generating circuit 86 for generating a synchronizing pulse, a triangular wave generating circuit 88 for generating a triangular wave in synchronization with the synchronizing pulse, the triangular wave and D / A.
The comparison circuit 90, which compares the command welding current value I _cmd output from the conversion circuit 60 and outputs a pulse corresponding to the comparison result, and the comparison pulse, which is synchronized with the synchronization pulse output from the pulse generation circuit 86, are compared. A pulse control circuit 94 that distributes the pulse train output from the circuit 90 to the drive circuits 96, 97, 98, 99 is included.

The drive circuits 96 to 99 energize the bases of the transistors (not shown) forming the inverter circuit 24.

In the inverter type DC resistance welding apparatus 20 configured as described above, the operation of controlling the welding current in an open loop to weld a plurality of welding points will be described with reference to FIGS. 1 to 4. .

When data indicating that the welding current is controlled, for example, based on the secondary side current value I ₂ is input from the keyboard 36 by the operator, this data is I.
Input to the CPU 58 via the / F70,
Outputs a control signal for detecting the secondary side current value I ₂ to the detection current selection circuit 54.

Next, when the welding process is started, the CPU
Reference numeral 58 outputs the command welding current value I _cmd read from the welding current storage circuit 56 to the D / A conversion circuit 60. In this case, the welding current storage circuit 56 stores the respective command welding current values I _{cmd at the} respective times when the steady state is reached after the slow-up energization period, and these command welding current values I _cmd are sequentially stored. The data is read out by the CPU 58 and D /
It is output to the A conversion circuit 60. This command welding current value I
_{The cmd} is input to one input terminal of the comparison circuit 90 included in the PWM circuit 62.

On the other hand, the triangular wave generating circuit 8 of the PWM circuit 62
In 8, the triangular wave is generated in synchronization with the pulse output from the pulse generation circuit 86, and the triangular wave is input to the other input terminal of the comparison circuit 90.

Here, the comparison circuit 90 outputs the triangular wave and the command welding current value I output from the D / A conversion circuit 60.
_cmd is compared, and a HIGH (H) level signal is output to the output terminal only while the command welding current value I _cmd is larger than the triangular wave.

The pulse train output from the comparison circuit 90 is input to the pulse control circuit 94, and the pulse control circuit 9
4 distributes the pulse train to the drive circuits 96 to 99 in synchronization with the signal output from the pulse generation circuit 86. The drive circuits 96 to 99 respectively drive the bases of a plurality of transistors (not shown) that are switching elements of the inverter circuit 24, so that the inverter circuit 2
4, a welding current is output, and this welding current is supplied to the welding transformer circuit 26 and the movable gun arms 40 and 4 of the welding gun section 28.
The work W is energized via 1 to perform welding.

At this time, the command welding current value I _cmd read from the welding current storage circuit 56 by the CPU 58,
Secondary side current value I ₂ output from the detection current selection circuit 54
Based on
A method of detecting the change in the resistance value on the secondary side will be described with reference to the flowcharts of FIGS. 4 to 8.

The current ratio calculation circuit 72 of the calculation circuit 68 to which the command welding current value I _cmd output from the CPU 58 is input (step S1) is output from the command welding current value I _cmd and the detected current selection circuit 54. The current ratio I _D with the secondary side current value I ₂ is calculated (I ₂ / I _cmd =
I _D ) (step S2).

Here, as a result of earnest studies, the inventor found that
It has been found that the current ratio I _D between the command welding current value I _cmd and the secondary side current value I ₂ is in inverse proportion to the change in the secondary side resistance value of the welding transformer circuit 26.

That is, in the open loop control having no feedback loop, the welding current storage circuit 5
When a welding current based on the command welding current value I _cmd read from 6 is applied to the work W, the welding transformer circuit 2
The secondary voltage V ₂ induced on the secondary side of 6 is always proportional to the command welding current value I _cmd regardless of the change in the resistance value on the secondary side.

However, the fact that the current ratio I _D is generated between the secondary side current value I ₂ energized by the secondary voltage V ₂ and the command welding current value I _cmd means that the welding transformer circuit which is a load. This means that the resistance value of the secondary side of 26 has changed.

Here, as is clear from Ohm's law, the current value and the resistance value are in an inversely proportional relationship. Therefore, by converting the current ratio I _D by the reciprocal number, the welding transformer circuit 26 of the 2
A resistance change amount R _D similar to the change in the resistance value on the next side is obtained (step S3). This resistance change amount R _D is the comparison circuit 78.
And to the differentiating circuit 80 (step S
4).

Comparison circuit 7 to which the resistance change amount R _D is input
8 compares this resistance change amount R _D with the set resistance value R1 _ref set in the comparison value setting circuit 76, and the comparison result is C
Output to PU58. The CPU 58 determines the cause of the change in the resistance value on the secondary side of the welding transformer circuit 26 based on the comparison result (step S5).

On the other hand, the differential circuit 80 change in resistance R _D is input, and outputs a differential resistance change amount [Delta] R _D obtained by differential calculation of the amount of change in resistance R _D to the comparison circuit 84. Comparator circuit 84 compares the set resistance value R2 _{re f} which is set to the comparison value setting circuit 82 and the differential resistance change amount [Delta] R _D, and outputs the comparison result to the CPU 58. The CPU 58 determines the cause of the change in the resistance value on the secondary side of the welding transformer circuit 26 based on the comparison result (step S6).

Next, the CPU 58 determines whether or not the welding at one welding point is completed (step S7). If not completed, the steps S1 to S6 are repeatedly executed for each sampling time preset in the ROM 64. The factor of the change in the resistance value on the secondary side of the welding transformer circuit 26 is determined a plurality of times until the welding at this point is completed.

At this time, the CPU 58 reads the resistance change amount R _D output from the resistance change amount calculation circuit 74 at each sampling time and stores it in the RAM 66. Note that steps S5 and S6 are processed by the CPU 58 as multitasking.

When it is determined in step S7 that the welding of one welding point is completed, the CPU 58 causes the maximum resistance value among the plurality of resistance change amounts R _D read from the resistance change amount calculation circuit 74 to be the maximum resistance value. R _DM is extracted and R
It is stored in the pointer P _n of the AM 66 (step S8), and the cause of the change in the resistance value on the secondary side of the welding transformer circuit 26 executed each time the welding of one welding point is completed is determined (step S9).

Next, it is judged whether or not all of the planned welding points have been welded (step S1).
0), if not ended, steps S1 to S10 are executed again.

Here, the operation of determining the state of the secondary side of the welding transformer circuit 26 based on the resistance change amount R _D , which is executed in step S5, is a block diagram of the control circuit 30 shown in FIG. 2, and FIG. This will be described with reference to the flowchart of FIG.

The comparison circuit 78 outputs the resistance change amount R _D output from the resistance change amount calculation circuit 74 in step S4.
And the set resistance value R1 set in the comparison value setting circuit 76.
comparing the _ref, judges whether R _D = R1 _ref (step S5-1), if R _D = R1 _{re f,} and outputs a coincidence signal to the CPU 58. The CPU 58 determines whether or not the energization of the point during welding has ended (step S5-
2) If the energization is not completed, step S5-1
At, the process determines whether the resistance change amount R _D input at the next sampling time matches the set resistance value R1 _ref .

If it is determined in step S5-2 that the energization has ended, the process returns to the main processing routine.

In step S5-1, if the resistance change amount R _D does not match the set resistance value R1 _ref , R _D
<R1 _ref is determined (step S5-3), R _D
If <R1 _ref , the comparison circuit 78 outputs data indicating that R _D <R1 _ref to the CPU 58.

Based on the above data, the CPU 58 determines that a shunt current has occurred or a short circuit has occurred on the secondary side of the welding transformer circuit 26 (step S5-4), and sets an abnormality detection flag (step S5-4). S5-5), I /
Dividing on the secondary side of the welding transformer circuit 26 via F70,
Alternatively, data indicating that a short circuit has occurred is displayed on the CRT.
Then, the CRT 38 displays it (step S5-6).

The waveforms of the respective parts when it is determined in the step S5-4 that a shunt or a short circuit has occurred are shown in FIG.
5 shows.

Next, the CPU 58 causes the step S5-
In 2, it is determined whether or not the energization of the point during welding has ended.

In step S5-3, R _D <R1
_When it is not _ref , the comparison circuit 78 outputs data indicating that R _D > R1 _ref to the CPU 58 (step S5-7).

Based on the above-mentioned data, the CPU 58 determines that the mating surface abnormality of the work to be welded or the disconnection of the secondary side conductor is detected (step S5-8), and sets an abnormality detection flag in the RAM 66 (step S5-8). S5-
9), through the I / F 70, data indicating that the secondary conductor is disconnected on the secondary side of the welding transformer circuit 26 is output to the CRT 38, and the CRT 38 displays it (step S5-10). ).

FIG. 16 shows the waveforms of the respective parts when it is determined in step S5-8 that a workpiece mating surface abnormality or a disconnection of the secondary side conductor has been detected.

Next, the CPU 58 causes the step S5-
In 2, it is determined whether or not the energization of the point during welding has ended.

In this way, until the welding of one welding point is completed, the resistance change amount R _D output from the resistance change amount calculation circuit 74 at each preset sampling time.
Is compared with the set resistance value R1 _ref , the cause of the change in the resistance value on the secondary side of the welding transformer circuit 26 is determined based on the comparison result, and this is displayed on the CRT 38.

Then, in step S6,
The operation of determining the secondary side state of the welding transformer circuit 26 based on the differential resistance change amount ΔR _D will be described with reference to the block diagram of the control circuit 30 shown in FIG. 2 and the flowchart of FIG. 6.

The differentiating circuit 80 differentiates the resistance change amount R _D output from the resistance change amount calculating circuit 74 (step S
6-1), the calculated differential resistance change amount ΔR _D is compared with the comparison circuit 84.
Output to. The comparison circuit 84 uses the differential resistance change amount ΔR _D and the set resistance value R set in the comparison value setting circuit 82.
It is determined whether or not 2 _ref matches (step S6-
2), if [Delta] R _D = R2 _ref, judges whether the current point in the weld has been completed (step S6-
3).

If the energization is not completed, step S6
At -1, the differential calculation of the resistance change amount R _D input at the next sampling time is performed, and if the energization is completed, the process returns to the main processing routine.

In step S6-2, when the differential resistance change amount ΔR _D and the set resistance value R2 _ref do not match, it is determined whether or not ΔR _D <R2 _ref (step S6-
4), if ΔR _D <R2 _ref , the comparison circuit 78 outputs ΔR
Data indicating that _D <R2 _ref is output to the CPU 58. Based on the above data, the CPU 58 determines that spatter is occurring on the secondary side of the welding transformer circuit 26 (step S6-5), and outputs data indicating that spatter is occurring via the I / F 70 to the CRT 38. Output to
The CRT 38 displays this (step S6-6). Next, in step S6-3, the CPU 58 determines whether or not the energization of the point during welding has ended.

17 and 18 show the waveforms of the respective parts when it is determined that the spatter is generated in the step S6-5 and are compared with the waveforms of the respective parts when the welding without the spatter is performed. .

If the result determined in step S6-4 is not ΔR _D <R2 _ref , the comparison circuit 78
Is the data indicating that ΔR _D > R2 _ref
8 (step S6-7). The CPU 58 determines that the inspection time of the secondary side conductor of the welding transformer circuit 26 is detected based on the data (step S6-8), sets an abnormality detection flag (step S6-9), and
The data indicating that the secondary conductor of the welding transformer circuit 26 has deteriorated through the I / F 70 and the inspection time has come is CR.
The data is output to T38, and the CRT 38 displays it (step S6-10).

FIG. 19 shows the waveform of each part when it is determined in step S6-8 that the inspection time of the secondary conductor has been detected.

Next, the CPU 58 causes the step S6-3 to be executed.
At, it is determined whether or not the energization of the point during welding is completed.

In this way, the comparison circuit 84 compares the differential resistance change amount ΔR _D and the set resistance value R2 _ref output from the differentiation circuit 80 at each preset sampling time until the welding of one welding point is completed. Are compared, and the comparison result is output to the CPU 58. The CPU 58 determines the cause of the change in the resistance value of the secondary side of the welding transformer circuit 26 based on the comparison result, and displays it on the CRT 38.

In this case, the set resistance value R1 _ref set in the comparison value setting circuit 76 and the set resistance value R2 _ref set in the comparison value setting circuit 82 are 2 of the welding transformer circuit 26 obtained by calculation in advance. It is possible to input from the keyboard 36 based on the resistance value on the next side,
The set resistance value R1 _ref and the set resistance value R2 _ref used in the present embodiment are the resistance change amount R read by welding performed immediately after the movable gun arms 40 and 41 and the electrode tips 42 and 43 are replaced with new ones. It is set based on _D and the differential resistance change amount ΔR _D.

Next, regarding the operation for determining the factor causing the change in the resistance value on the secondary side, which is executed in step S9, the block diagram showing the configuration of the control circuit 30 in FIG. 2 and the flowcharts in FIG. 7 and FIG. Will be described with reference to.

This operation is executed every time welding of one welding point is completed.

In step S7, it is determined that the welding of one welding point is completed, and in step S8, the presence or absence of an abnormality detection bit which is the welding result of the welding point n and the maximum resistance value R _{DMn at} this welding point n are determined. When stored in the pointer P _n of the RAM 66, the CPU 5
8 sets A to 1 (A ← 1) (step S9-
1), 1 is assigned to A of the pointer P _nA , and the data stored in the pointer P _n-1 of the RAM 66 is read (step S9-2).

In this case, the pointer P _n-1 of the RAM 66 stores the data regarding the abnormality detection bit which is the welding result of the immediately preceding point n-1 and the maximum resistance value R _DMn-1 .

Therefore, the CPU 58 determines whether or not the abnormality detection bit is stored in the pointer P _n-1 (step S9-3).

If the abnormality detection bit is stored in the pointer P _n-1 , it is determined that an abnormality has occurred in the welding at the point n-1, and A is incremented (A = 2) (step S9-4). , A pointer P storing the welding result of point n-2 performed immediately before point n-1.
The contents of _n-2 are read to determine whether or not the abnormality detection bit is stored.

In this way, the newest point n-A in the past where the abnormality detection bit is not stored is searched for, and the maximum resistance value R _DMA which is the welding result at this point n-A is read.

[0073] Then, by subtracting the maximum resistance value R _DMA from the maximum resistance value R _DMn at point n of the latest welding obtain the maximum resistance difference _{R DF (R DMn -R DMA =} R DF) ( step S9- 5) It is determined whether or not this maximum resistance value difference R _DF matches the set resistance value R3 _ref input from the keyboard 36 (step S9-6), and if R _DF = R3 _ref , the point n It is determined whether or not the abnormality detection flag is set during welding (step S9-7). If the abnormality detection flag is not set, the maximum resistance value R at point n is determined.
Stored in the pointer P _n of RAM66 and _DMn (step S9-8).

In step S9-6, the maximum resistance value difference R_DF
Is the set resistance value R3_refR does not match_DF<R3
_refOr not (step S9-9), R_DF
<R3 _refIf so, set the abnormality detection flag
(Step S9-10), split flow or wear of electrode tip
Is determined to have occurred (step S9-11), and
Is displayed on the CRT 38 (step S9-12).

Next, the CPU 58 reads the abnormality detection flag (step S9-7) and sets the abnormality detection bit to "1".
And (step S9-13), said this abnormality detection bit "1" by adding the maximum resistance value R _DMn (step S9-14), and stores the pointer P _n of RAM 66 (step S9-8).

In step S9-9, the
Large resistance value R_DMnAnd the maximum resistance value R _DMAMaximum resistance value of
Difference R_DFIs the set resistance value R3_refR is less than_DF
> R3_ref(Step S9-15), the
As with Step S9-10, if you set the abnormality detection flag
Both (step S9-16), abnormality in the work mating surface
Has occurred, or an abnormality has occurred in the secondary conductor
It is determined (step S9-17) and displayed on the CRT 38.
(Step S9-18), the above-mentioned step S9
-7 Perform the processing below.

Regarding the abnormality of the secondary side conductor determined in the step S9-17, the waveform of each part when it is determined that it is the deterioration of the electrode tip or the inspection time of the secondary side conductor which shows the content thereof is shown in FIG. 21 shows the waveform of each part when deterioration of the electrode tip occurs.

In this case, the deterioration of the electrode tip means that when a zinc-plated work is welded, zinc or foreign matter is attached to the tip of the electrode tip, and the resistance value of the electrode tip is 5 or less.
It means an increase of about 0 μΩ.

As described above, the maximum resistance value R _DMn obtained by welding the latest welding point is subtracted by subtracting the newest maximum resistance value R _DMA from the past welding data in which welding is normally performed. determine the maximum resistance difference R _DF, by comparing the maximum resistance difference R _DF and setting the resistance value R3 _ref, welding shunt generated in the secondary side of the transformer circuit 26, the workpiece mating surface abnormalities, or 2 Anomalies in the secondary conductor can be detected.

When R _DF <R3 _ref in the determination in step S9-9, the reason why the resistance value on the secondary side of the welding transformer circuit 26 is decreased is that the welding current is applied due to shunting or wear of the electrode tip. It can be determined that the cross-sectional area of the route has increased.

Further, when it is determined in step S9-9 that R _DF <R3 _ref is not R _DF <R3 _ref , and R _DF > R3 _ref is determined in step S9-15, the work W to be welded due to insufficient pressurization or the like is detected. It can be determined that the resistance value on the secondary side of the welding transformer circuit 26 has increased because the degree of adhesion of the mating surfaces has decreased.

The conductor on the secondary side of the welding transformer circuit 26 and serving as a welding current energizing path is composed of a wiring member for energizing the welding current, the movable gun arms 40 and 41, the electrode tips 42 and 43, and the like. However, since these conductors are composed of different metals from each other, different expansion and contraction are repeated due to supply and release of Joule heat generated by energization or non-energization of welding current. Therefore, an abnormal state occurs in which the conductors are relaxed and the contact resistance value between the conductors is increased. Again, 2
It is determined that a secondary conductor abnormality has occurred.

Then, the welding is performed immediately after the electrode tips 42 and 43 are polished (dressed) by grinding or the like, or the welding performed immediately after the electrode tips 42 and 43 are exchanged is detected and stored in the RAM 66. The CPU 58 reads the stored maximum resistance value R _DM1 (step S9-1).
9) the latest resistance value R _DMn from the maximum resistance value R _DMn detected by welding at the welding point n
_DM1 is subtracted to obtain the time-dependent resistance change value R _DT (R _DMn −
R _DM1 = R _DT ) (step S9-20).

The CPU 58 determines whether or not the aged resistance change value R _DT is larger than the set resistance value R4 _ref input from the keyboard 36 (step S9-21), and R _DT
If> R4 _ref , a warning indicating that it is time to polish the electrode tips 42, 43 or replace the electrode tips 42, 43 is displayed on the CRT 38 (step S9).
-22), and returns to the main processing routine.

FIG. 22 shows the state of comparison between the resistance change value R _DT with time and the set resistance value R4 _ref in step S9-21.

In step S9-21, R _DT > R
If it _becomes 4 _ref , step S1 of the main processing routine
Return to 0.

As described above, the maximum resistance value R stored in the RAM 66, which is detected by the welding performed immediately after the electrode tips 42, 43 are polished or replaced, is stored.
_DM1 and the maximum resistance value R detected by the latest welding
Deterioration of the electrode tips 42 and 43 is detected by comparing with _DMn .

As described above, in the first embodiment,
In the inverter type DC resistance welding device 20 controlled by the open loop, the secondary side current value I ₂ is read, and the current ratio I between the secondary side current value I ₂ and the command welding current value I _cmd is read.
A change in the resistance value of the secondary side of the welding transformer circuit 26 is detected by _D , and an abnormality factor on the secondary side of the welding transformer circuit 26 is determined based on the detected change data of the resistance value.

Next, the inverter type DC resistance welding device 2
Another embodiment of the arithmetic circuit 68 in 0 will be described with reference to FIG. In the following examples,
The same components as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

In the figure, reference numeral 100 indicates a control circuit, and reference numeral 102 indicates an arithmetic circuit. The arithmetic circuit 102 is shown in FIG.
The triangular wave P _tg output from the triangular wave generating circuit 88 of the PWM circuit 62 shown in FIG.
6, the pulse width-modulated pulse P _w output from the comparison circuit 104 for comparing the command welding current value I _cmd output and output from the comparison circuit 90, and the pulse output from the comparison circuit 104. duty calculation circuit 106 for outputting data P _D corresponding to the change ratio of the duty of P _ref, the data P _D is output from the duty computing circuit 106 converts the resistance change amount R _D, the amount of change in resistance R _And a resistance change amount calculation circuit 108 for outputting _D to the comparison circuit 78.

Further, the calculation circuit 102 differentiates the resistance change amount R _D output from the resistance change amount calculation circuit 108 and outputs a differential resistance change amount ΔR _D which is the calculation result, and the differential circuit 80. The comparison circuit 84 compares the differential resistance change amount ΔR _D with the set resistance value R2 _ref set in the comparison setting circuit 82.

The operation of the arithmetic circuit 102 thus configured will be described with reference to the timing chart of FIG.

Comparison from the triangular wave generating circuit 88 shown in FIG.
Triangular wave P output to circuit 104_tgIs shown in FIG.
Command welding current output from the welding current storage circuit 56
Value I _cmdWaveform is shown in FIG. The triangular wave P_tg
And the command welding current value I_cmdComparison circuit 1 to which and are input
04 is the triangular wave P_tgAnd the command welding current value I_cmdAnd
Compare (see FIG. 11C), P_tg<I_cmdWhen
High-level pulse P_refDuty calculation circuit 1
It outputs to 06 (refer to FIG. 11 (D)).

The comparison circuit 78 and the comparison circuit 84.
The CPU 58 determines the state of the secondary side of the welding transformer circuit 26 based on the comparison result output from the same as in the first embodiment.

Next, as a second embodiment, a case of a thyristor type resistance welding apparatus will be described with reference to FIGS. 12 to 14.

FIG. 12 is a block diagram showing the structure of a thyristor resistance welding apparatus. In the figure, reference numeral 130 indicates a thyristor resistance welding apparatus. The thyristor resistance welding apparatus 130 includes a thyristor circuit 132 and a control circuit 134 that controls the thyristor circuit 132, and the thyristor circuit 132 includes a power supply waveform detector 136.

FIG. 13 shows a block configuration of the control circuit 134.

The control circuit 134 is the thyristor circuit 13 described above.
A phase control circuit 138 for generating a signal for energizing the power supply waveform detector 1 is provided in the phase control circuit 138.
The waveform of the power source detected by 36 is input.

FIG. 14 shows a block diagram of the configuration of the phase control circuit 138.

The phase control circuit 138 is a thyristor circuit 13
Conduction angle control circuit 1 for generating a gate signal applied to 2
40, a power supply waveform detection circuit 142 that detects a power supply waveform from the output of the power supply waveform detector 136, and a synchronization signal generation circuit 144 that generates a synchronization signal based on the power supply waveform output from the power supply waveform detection circuit 142. And a trigger signal generation circuit 150 which outputs a signal indicating the conduction angle output from the conduction angle control circuit 140 to the drive circuits 146 and 148 in synchronization with the synchronization signal.

Also in the thyristor resistance welding apparatus 130 configured as described above, the command welding current value I stored in the welding current storage circuit 56 by the current ratio calculation circuit 72.
The current ratio I _D between _cmd and the secondary current value I ₂ detected by the secondary current detector 34 is calculated, and the resistance change is calculated by reciprocal calculation of this current ratio I _D by the resistance change calculation circuit 74. Find the quantity R _D.

Next, the resistance change amount R _D and the set resistance value R1 _ref are compared by the comparison circuit 78, and the result of this comparison changes the resistance value on the secondary side of the welding transformer circuit 26 and the shunt current that causes the change. A short circuit, disconnection of the secondary conductor, or the like is determined.

Further, the resistance change amount R _D output from the resistance change amount calculation circuit 74 is differentiated by the differentiating circuit 80,
The differential resistance change amount ΔR _D becomes, and this differential resistance change amount ΔR
_D is compared with the set resistance value R2 _ref, and the occurrence of spatter or the inspection time of the secondary side conductor is detected based on the comparison result.

Furthermore, by detecting the change in resistance at each welding point, shunting, abnormality in the work mating surface, or abnormality in the secondary side conductor is detected, and the electrode tip 4 is detected.
The maximum resistance value R _DM1 obtained by welding conducted in such immediately after replacing the 2, 43, by comparing the maximum resistance value R _DMn obtained by latest welding, grinding of the electrode tip 43 The determination of the timing or the timing of chip replacement is the same as in the first embodiment.

As described above, according to this embodiment,
In the inverter type DC resistance welding device 20 and the thyristor type resistance welding device 130 which are controlled by the open loop, the secondary side current value I ₂ is read and the command welding current value I is read.
The change in the secondary side current value I ₂ with respect to _cmd detects the change in the secondary side resistance value of the welding transformer circuit 26,
The state of the secondary side of the welding transformer circuit 26 can be determined based on the detected change data of the resistance value.

Furthermore, the inverter type DC resistance welding device 2
At 0, the triangular wave P _tg output from the triangular wave generating circuit 88 forming the PWM circuit 62 and the command welding current value I _cmd
And the change in the resistance value on the secondary side is detected by the comparison result, and the welding transformer circuit 2 is detected by the detection result.
The state of the secondary side of 6 can be determined.

In this embodiment, the state of the secondary side of the welding transformer circuit 26 is judged based on the secondary side current value I ₂ , but the same effect can be obtained by the primary side current value I ₁ . it can.

[0108]

According to the method and apparatus for determining the secondary side state of the welding transformer according to the present invention, the welding transformer is determined by the preset welding current value and the welding current command value without detecting the voltage between the electrode tips. The change in the resistance value on the secondary side of the workpiece is detected with high accuracy, and from the detected change in the resistance value, spattering, welding current shunting, short circuit between electrode tips, and workpiece matching surface abnormality occur. Since the welding state can be determined, it is possible to prevent a decrease in the reliability of the detected voltage due to the breakage and disconnection of the voltage reading wire between the electrode tips.

Further, since it is possible to determine the maintenance time such as the inspection time of the secondary conductor and the replacement time of the electrode tip from the change of the detected resistance value, the failure of the resistance welding device can be prevented. There is an effect that it becomes possible.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of an inverter type DC resistance welding apparatus for carrying out the present invention.

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

FIG. 3 is a block diagram showing a configuration of a PWM circuit of the embodiment shown in FIG.

FIG. 4 is a flowchart showing a main processing routine of the embodiment shown in FIG.

5 is a flow chart showing an operation of determination based on a resistance change amount in the flow chart shown in FIG.

FIG. 6 is a flowchart showing a determination operation based on a differential resistance change amount of the flowchart shown in FIG.

FIG. 7 is a flowchart showing a determination operation based on a resistance change amount, which is executed at each end of one welding point in the flowchart shown in FIG.

8 is a flowchart showing a determination operation based on a resistance change amount, which is executed each time one welding point ends in the flowchart shown in FIG. 4;

9 is a block diagram showing a configuration of another embodiment of the control circuit shown in FIG.

FIG. 10 is a block diagram showing a configuration of a PWM circuit of the embodiment shown in FIG.

11 is a timing chart illustrating the operation of the control circuit shown in FIG.

FIG. 12 is a block diagram showing the overall configuration of a thyristor resistance welding apparatus for carrying out the present invention.

13 is a block diagram showing a configuration of a control circuit of the thyristor resistance welding device shown in FIG.

14 is a block diagram showing a configuration of a phase control circuit of the thyristor resistance welding apparatus shown in FIG.

15 is a diagram showing waveforms of respective parts when it is determined that a shunt or a short circuit occurs in the determination flowchart based on the resistance change amount shown in FIG.

16 is a diagram showing waveforms of respective parts when it is determined in the flowchart of determination based on the resistance change amount shown in FIG. 5 that a workpiece mating surface abnormality or a disconnection of a secondary side conductor occurs.

FIG. 17 is a flowchart of the determination based on the amount of change in differential resistance shown in FIG. 6, in which the waveform of each part when it is determined that spatter is generated is compared with the waveform of each part when welding without spatter is performed. FIG.

18 is a flowchart for comparing the waveform of each part when it is determined that spatter is generated with the waveform of each part when welding without spatter is performed in the flowchart of the determination based on the differential resistance change amount shown in FIG. FIG.

FIG. 19 is a diagram showing waveforms of respective parts when it is determined that an abnormality has occurred in the secondary side conductor in the determination flowchart based on the differential resistance change amount shown in FIG. 6.

FIG. 20 is a diagram for explaining the operation of determining the tip dress or the replacement time of the electrode tip due to wear of the electrode tip in the flow chart of the determination based on the resistance change amount executed at the end of each welding point shown in FIGS. 7 and 8; Is.

FIG. 21 is a diagram showing the waveform of each part when it is determined that it is the inspection time of the secondary side conductor in the flow chart of the determination based on the resistance change amount executed at the end of each welding point shown in FIGS. 7 and 8. .

FIG. 22 is a flow chart of the judgment based on the resistance change amount executed at each end of one welding point shown in FIGS. 7 and 8, in the case where it is judged that the tip dress or the replacement time of the electrode tip is due to deterioration of the electrode tip. It is a figure which shows the waveform of each part.

[Explanation of symbols]

 20 ... Inverter type DC resistance welding device 24 ... Inverter circuit 26 ... Welding transformer circuit 28 ... Welding gun section 30 ... Control circuit 32 ... Primary side current detector 34 ... Secondary side current detector 40, 41 ... Movable gun arm 42, 43 ... Electrode chip 50, 52 ... A / D conversion circuit 54 ... Detection current selection circuit 56 ... Welding current storage circuit 58 ... CPU 60 ... D / A conversion circuit 62 ... PWM circuit 64 ... ROM 66 ... RAM 68 ... Arithmetic circuit 72 Current ratio calculation circuit 74 ... Resistance change amount calculation circuit 76, 82 ... Comparison value setting circuit 78, 84 ... Comparison circuit 80 ... Differentiation circuit

Claims (11)

[Claims] 1. A method for determining a secondary side state of a welding transformer in a resistance welding machine in which a welding current is controlled by an open loop, the first method detecting a welding current flowing through a primary side or a secondary side of the welding transformer. Step, a second step of comparing the detected welding current value detected in the first step with a preset command welding current value, and 2 of welding transformers based on the comparison result in the second step. A third step of detecting a change in the resistance value of the secondary side, and a fourth step of determining the state of the secondary side of the welding transformer by the change in the detected resistance value of the secondary side of the welding transformer, A method for determining a secondary side state of a welding transformer, comprising: 2. The method according to claim 1, wherein in the fourth step, a change in the detected resistance value of the secondary side of the welding transformer is equal to or less than a preset set value while the welding current is being supplied. At this time, it is determined that a shunt or short circuit has occurred on the secondary side of the welding transformer. 3. The method according to claim 1, wherein in the fourth step, a change in the detected resistance value of the secondary side of the welding transformer is equal to or more than a preset value while the welding current is being supplied. At this time, the secondary side state determination method of the welding transformer is characterized in that it is determined that the mating surface of the work is abnormal or the conductor on the secondary side of the welding transformer is broken. 4. The method according to claim 1, wherein in the fourth step, a value obtained by differentiating a change in the detected resistance value on the secondary side of the welding transformer during welding current is set in advance is set. A secondary-side state determination method for a welding transformer, which determines that spatter has occurred between the electrode tips when the value is less than or equal to the value. 5. The method according to claim 1, wherein in the fourth step, a value obtained by differentiating a change in the detected resistance value on the secondary side of the welding transformer during welding current is set in advance is set. When it is not less than the value, it is judged that it is time to replace the secondary side conductor of the welding transformer because it has deteriorated, and the secondary side state judging method of the welding transformer. 6. The method according to claim 1, wherein the fourth step is that when the change in the maximum resistance value on the secondary side of the welding transformer detected for each welding point is equal to or less than a preset value. A method for determining the secondary side state of a welding transformer, characterized in that it is determined that the electrode tip has worn. 7. The method according to claim 1, wherein the fourth step is when the change in the maximum resistance value on the secondary side of the welding transformer detected at each welding point is equal to or more than a preset set value. A method for determining the secondary side state of a welding transformer, characterized in that it is determined that the electrode tip has deteriorated. 8. A secondary side state determination device for a welding transformer in a resistance welding machine for controlling a welding current in an open loop, comprising: welding current storage means for storing a preset command welding current value; Primary side welding current detecting means for detecting a welding current flowing to the primary side, secondary side welding current detecting means for detecting a welding current flowing to the secondary side of the welding transformer, and the primary side welding current detecting means The detected primary welding current value or 2 detected by the secondary welding current detection means
A detection current selecting means for selecting a secondary welding current value; a comparing means for comparing the primary welding current value or the secondary welding current value selected by the detection current selecting means with the command welding current value; Secondary side resistance value detecting means for detecting a change in the resistance value of the secondary side of the welding transformer based on the comparison result output from the comparing means; and a change in the detected resistance value of the secondary side of the welding transformer. A secondary side state determination device for a welding transformer, comprising: a secondary side state determination means for determining the state of the secondary side of the welding transformer based on the above. 9. The apparatus according to claim 8, wherein the comparing means compares the preset command welding current value and the primary welding current value or the secondary welding current value selected by the detection current selecting means. A secondary-side state determination device for a welding transformer, which is provided with a calculation unit that calculates a ratio. 10. A welding transformer according to claim 8, wherein the secondary side resistance value detecting means includes a converting means for converting the comparison result output from the comparing means into a change in resistance value. Secondary state determination device. 11. The apparatus according to claim 8, wherein the secondary side state of the welding transformer judged by the secondary side state judging means is
Welding state consisting of spatter generation, welding current shunt, short circuit between electrode tips, and workpiece mating surface abnormality,
Check the secondary conductor maintenance time, which includes the secondary conductor inspection time and the electrode tip replacement time, and the secondary condition of the welding transformer abnormal condition, such as the secondary conductor disconnection. Characteristic welding transformer secondary side state determination device.