JPH0615112B2 - Welding secondary cable disconnection detection method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a detection method for detecting disconnection of a plurality of internal conductors forming a welding secondary cable connecting a welding gun and a transformer.

“Prior Art” The applicant of the present invention has already processed the magnetic field strength signal of the magnetic sensor by a statistical method as a method for detecting the disconnection of the secondary cable for welding, and calculated the variation amount of the magnetic intensity (statistical amount such as standard deviation and dispersion). We have proposed a method to detect the disconnection of the internal conductor that constitutes the welding secondary cable by comparing this variation amount with a preset threshold value, and it is possible to quickly and continuously detect the disconnection and to provide a continuous monitoring system. In order to prevent sudden work interruptions and reduce the inspection man-hours.

[Problems to be Solved by the Invention] However, in the above method, the variation amount of the magnetic field strength obtained by processing the magnetic field strength signals of the plurality of magnetic sensors arranged on the outer circumference of the welding secondary cable by a statistical method ( The standard deviation, the sum of squared deviations, the variance, the range, etc.) is used as the disconnection determination value. On the other hand, the strength of the magnetic field on the outer circumference of the cable is
It changes depending on the current applied during welding. For this reason, the statistic amount, which is the disconnection determination value, inevitably changes due to the amount of energizing current, and even if there is no change in the disconnection rate of the internal conductors that make up the cable, it does not exceed or exceed the preset threshold value. Therefore, there is a problem to be solved such as a risk of causing a judgment error.

"Means for Solving Problems" The present invention aims to solve the above problems and prevent deterioration of welding quality due to disconnection of an inner conductor of a welding secondary cable and sudden interruption of work. According to a specific configuration of the first invention, a plurality of positive side inner conductors connecting the welding gun and the transformer and a plurality of negative side inner conductors are arranged alternately in a ring shape with respect to the cable cross section. A plurality of magnetic sensors are arranged on the outer periphery of the welded secondary cable configured in accordance with each of the internal conductors, and the magnetic field strength signal output from each magnetic sensor is processed by a statistical method to determine the magnetic field strength. The welding secondary cable is constructed by obtaining a variation amount and comparing a characteristic value calculated by dividing the variation amount by the total sum of the plurality of magnetic sensor outputs or an average value thereof with a preset threshold value. Within each It is characterized in that the disconnection of the partial conductor is detected.

Further, a specific configuration of the second invention is that a plurality of positive side inner conductors connecting a welding gun and a transformer and a plurality of negative side inner conductors are alternately arranged in a ring shape with respect to a cable cross section. A plurality of magnetic sensors are arranged on the outer periphery of the constructed welding secondary cable so as to correspond to the respective inner conductors, and the magnetic field strength signal output from each magnetic sensor is processed by a statistical method to obtain a variation amount of the magnetic field strength. A characteristic value calculated by dividing this variation amount by the total sum of the plurality of magnetic sensor outputs or the average value thereof is stored each time, and the average value of the past N times characteristic values and a preset threshold value are stored. It is characterized in that the disconnection of each internal conductor constituting the welded secondary cable is detected by the comparison with.

"Operation" As has been clarified by the description of the specific configuration, the method of the present invention processes the magnetic field strength signal output from the magnetic sensor arranged corresponding to the internal conductor by a statistical method to cause variations in the magnetic field strength. The amount of variation is calculated quantitatively, and the value calculated by dividing this variation amount by the sum of the outputs of the multiple magnetic sensors or the average value is taken as the characteristic value of the cable breakage detection. To make sure that there is a clear significant difference in the presence or absence of disconnection of the internal conductor that constitutes the welded secondary cable.

Further, by storing the characteristic value every time and determining the disconnection based on the average value of the characteristic values of the past N times, it is possible to reduce the variation in the characteristic value due to the welding position, and it is possible to detect the disconnection with higher accuracy.

[Embodiment] An embodiment of the method and apparatus of the present invention will be described with reference to the accompanying drawings.

Fig. 1 shows the welding secondary cable 1 (hereinafter referred to as the cable)
1 shows an example of the cross-sectional structure of the positive side inner conductors 2a, 2b, 2c and the negative side inner conductors 3a, 3b, 3c whose current directions are opposite to each other, and are alternately parallel to the cable cross section in a ring shape. The inner conductors are separated from each other by the insulating separator 4, and the inner conductors are twisted in the cable longitudinal direction in order to reduce the AC impedance, and the inner conductors are housed in the outer tube 5. When the cable 1 is used, cooling water is passed through the void 6 in the outer tube 5 to cool it.

FIG. 2 shows a method of measuring the magnetic field in the vicinity of the cable 1 which is the basis of the method of the present invention. When each inner conductor is energized as indicated by the arrow in the figure, radiation is emitted from the center of the cable 1. The strength of the magnetic field formed by the magnetic force lines g generated in the direction is measured by the Gauss meter G.

Further, the principle by which the disconnection of the internal conductor that constitutes the cable 1 can be detected by this measuring method will be briefly described.

When currents are applied to two conductors placed in parallel in opposite directions, a magnetic field is generated around each conductor with the lines of magnetic force in opposite directions, and the magnetic field strength at the intermediate position between the two conductors is Shows the strength of superposition. When the magnetic sensor is arranged at this intermediate position, a change in the amount of electricity flowing through the two conductors can be grasped as a change in magnetic field strength. Furthermore, when this is applied to the three sets of inner conductor bundles that form the cable 1, it becomes possible to capture the change in the amount of current flowing through each of the three sets of conductor bundles by the three magnetic sensors, and to form each inner conductor. Since the thin copper wire is gradually broken and the resistance of the inner conductor changes and the shunt ratio of the current changes, it is possible to detect this as a change in the magnetic field strength and detect the disconnection of the inner conductor.

Figures 3 (a) and 3 (b) show the results of measuring the disconnection modes of the internal conductors that make up the cable and the distribution of the magnetic field strength of the magnetic field in the vicinity thereof along the circumference of the cable, according to the measurement method and measurement principle. Indicates.

In FIG. 3A, the vertical axis represents the magnetic field strength, and the horizontal axis represents the internal conductors arranged in the order of arrangement. The number attached to the conductor on the horizontal axis is
As shown by A in the same figure (b), the internal conductors shown in FIG. 1 are numbered in a clockwise order, and those not numbered in B, C, and D are broken internal conductors. Show. According to FIGS. 3 (a) and 3 (b), in a normal cable with no disconnection in the inner conductor, in the middle of each inner conductor, a periodic pattern in which the magnetic field strength is equal and the maximum is shown,
In the case of a cable with a broken internal conductor, the strength of the magnetic field does not change and a periodic pattern is not exhibited, and there is a big difference between the two.

It should be noted that as a disconnection pattern of the cable, it is usual that one or two internal conductors are gradually disconnected without disconnecting all of the internal conductors at the same time. Therefore, the disconnection of the internal conductor of the cable can be detected by quantitatively capturing the disturbance of the magnetic field strength.

FIGS. 4 (A) and 4 (B) show the arrangement positions of the magnetic sensors arranged in the cable 1 having the structure shown in FIG. 1. The positive side inner conductor and the negative side inner conductor, for example, 2a, 3a and 2b. And 3b, 2
A magnetic sensor is arranged in the middle of each pair of three inner conductors c and 3c. In the case of FIG. 1 (A), three magnetic sensors are arranged on the same circumference of the outer tube 5 of the cable 1 at 120 ° angular intervals. The magnetic sensors Sa, Sb, and Sc are arranged so as to capture the maximum magnetic flux in the radial direction generated when each inner conductor is energized. In the case of FIG. Since the twist is applied along the longitudinal direction as described above, considering the cross section in the longitudinal direction at one point on the circumference, the internal conductors are arranged in a line as shown in the figure, so that three magnetic sensors are provided. Sa, Sb, and Sc are arranged on the straight line in the longitudinal direction outside the exterior tube 5 so as to capture the maximum vertical magnetic flux generated when each internal conductor is energized.

As the magnetic sensor, the Hall element is used in the present embodiment, but a magnetoresistive element, a magnetoelectric conversion element such as a coil can also be used.

FIG. 5 shows a block diagram of an apparatus to which the method of the present invention is applied.

Reference numeral 10 denotes a preamplifier, which receives magnetic field strength signals from three magnetic sensors Sa, Sb, Sc arranged in the sensor ring 7 fitted in the cable 1 as shown in FIG. 4 (A).
It amplifies to a signal processable level, and has three amplifiers 10a, 10b, 10c corresponding to each magnetic sensor. Reference numeral 11 is a sample switch for passing only a signal of a specific welding current cycle, and three switch 11a, 11
It consists of b and 11c. A peak hold circuit 12 stores the maximum value of the magnetic field intensity signal that has passed through the sample switch 11, and is composed of three circuits 12a, 12b and 12c. 1
Reference numeral 3 denotes an A / D conversion circuit that converts the analog voltage stored in the peak hold circuit into a digital signal that can be easily processed by the microcomputer 14, and 14 uses a digital signal from the A / D converter 13 to calculate a statistical amount (standard Deviation, deviation sum of squares, variance, range, etc.), and the presence or absence of disconnection of the internal conductors of the cable 1 based on the result of the calculation.
M, an address decoder circuit 15 and an input / output interface 16. Reference numeral 17 is a pulsing circuit, which produces a signal for operating the integrating circuit 21 for integrating the welding current cycle by the amplified signal of the preamplifier 10, so that the maximum value selector circuit 18, the comparing circuit 19 and the threshold voltage And a setting circuit 20. The integrating circuit 21 is composed of a first integrating circuit 21a and a tenth integrating circuit 21b. Two
Reference numeral 2 is a sample cycle number setting circuit, and reference numeral 23 is a comparison circuit which determines from the signal from the circuit 22 and the signal from the integrating circuit 21a at the first place that the set number of cycles has been reached.
Reference numeral 24 is a sample switch drive signal generation circuit and a comparison circuit 2
The sample switch 11 is turned on / off by receiving the signal No. 3 and the sample switch 11 is turned on / off to pass the signal indicating the magnetic field strength generated by the current for one specific welding current cycle. Reference numeral 25 is a pressurizing valve signal input circuit, which inputs information on the start and completion of the welding process from the welding machine as a pressurizing valve signal and sends a signal to the welding end signal generating circuit 26 and the reset signal generating circuit 27. The welding end signal generation circuit 26 sends a reset signal to the non-energization determination flip-flop circuit 29 which determines non-energization. The reset signal generation circuit 27 sends a reset signal for resetting the peak hold circuit 12, the integrating circuit 21, etc. at the start of welding. Reference numeral 28 denotes a determination start determination flip-flop circuit, which sends timing information for starting the arithmetic processing and the disconnection determination processing to the microcomputer 14. Other 30
Is a lamp lighting circuit that lights the lamps 31 and 32 that display the result of disconnection determination, and 33 is a power supply circuit that supplies a predetermined voltage to each circuit.

The operation of the device of the present invention will be described below with reference to the block diagram of FIG. 5 and the timing chart of the device of the present invention of FIG.

When a welding command signal is applied to the welding control device 40 from an automatic welding machine (robot, dedicated machine, etc.) or a welding operator,
When the welding operation is started and the pressurizing valve signal shown in FIG. 6A is
It is emitted to a control valve that controls a cylinder for welding the members to be welded by the welding electrode. Further, the pressurizing valve signal applied to the disconnection detecting device (hereinafter simply referred to as a device) of the device of the present invention is slightly delayed in the pressurizing valve signal input circuit 25 in order to prevent malfunction due to squeeze operation (first). 6B), the reset signal generation circuit 27 issues a reset signal (FIG. 6D). This reset signal is supplied to the peak hold circuit 12, the integrating circuit 21, the determination start determination flip-flop circuit 28, the gate control flip-flop circuit 34, etc. of the device to initialize these circuits. Subsequently, when the energization time is entered after the completion of the initial pressurization time, a welding current flows in the cable 1 and a magnetic field is generated in the vicinity of the cable 1, and this is detected by the magnetic sensor S arranged on the sensor ring 7.
a, Sb, Sc detect and output the sixth sensor output signal.
A signal similar to the signal shown in FIG.
b, 10c. Depending on the disconnection mode of the cable 1, almost no output signal may be obtained by any of the magnetic sensors, so the three preamplifiers 10
The maximum value selector circuit 18 selects the maximum value among the amplified signals a, 10b, and 10c, and the comparison circuit 19 compares the signal with the threshold voltage set by the threshold voltage setting circuit 20 in advance. The sensor output pulse signal is used (FIG. 6G). This pulse signal is integrated by the integration circuit 21, and compared with the number of sample cycles set by the sample cycle number setting circuit 22 by the comparison circuit 23. If they match, a match signal is sent to the sample switch drive signal generation circuit 24. send.

Since the sample cycle used in the comparison circuit 23 is a decimal 1-digit numerical value, the integration circuit 21b in the tenth place is arranged so that a pulse signal of 11 cycles or more is not applied to the integration circuit.
The gate circuit 35 is closed after the least significant bit of is turned on (when the pulse of the 10th cycle is counted).

Upon receiving the coincidence signal, the sample switch drive signal generation circuit 24 supplies the sample switch drive signal having a time width of one cycle synchronized with the welding power supply frequency to the sample switch 11 (FIG. 6H). Receiving the signal, the sample switches 11a, 11b, 11c are closed for the time width of one cycle, and the amplified output signals of the preamplifier 10 are closed by the circuits 12a, 1 of the peak hold circuit 12, respectively.
Send to 2b and 12c. As shown in FIG. 6I, the peak hold circuit 12 holds the maximum value of the amplified output signal received within the above time width even after the sample switch 11 has stopped operating.

At the same time, the sample switch drive signal sets the judgment start judgment flip-flop circuit 28 to notify the microprocessor CPU of the start of the signal processing and judgment processing (FIG. 6J), and also the non-conduction judgment flip-flop circuit 2
9 is set, and the fact that the welding current is supplied while the pressure valve signal is being input is stored. The microprocessor CPU notified of the determination start drives the analog-digital conversion circuit 13 via the address decoder circuit 15, takes in the sensor output voltage held in the peak hold circuit 12 as a digital value, and outputs each digital output. The signals x ₁ , x ₂ , x ₃ are arithmetically operated based on the following equations (i, ii, iii) to calculate the standard deviation s, and the standard deviation s is used as a characteristic value as a parameter for detection of disconnection and each output signal is output. It is calculated by dividing by the sum of x ₁ , x ₂ and x ₃ .

Since the expressions (i), (iii), and (iv) have the above relationship, the numerator of the characteristic value is not limited to the standard deviation, and may be the variance or the sum of squared deviations.

Note that the variance shown here is exactly called an unbiased variance, but the variance and the standard deviation divided by the number of data 3 are also the same.

Furthermore, between the range R determined by the difference between the maximum value S _max and the minimum value S _{min in} the statistical data and the standard deviation s, s = R / k (where k is a constant defined by the number of data) Since there is a relationship, the range R may be used as the numerator of the characteristic value. Further, the denominator of the characteristic value may use the average value of the formula (i).

Microprocessor CPU whose characteristic value is calculated as described above
Stores the characteristic value in the successive internal memory, calculates the average value of the characteristic values of the past N times, compares the average value with a predetermined determination threshold value, and if it exceeds Warning of cable replacement (NG signal), lamp drive circuit 3
When it is 0, the NG lamp 32 is turned on to notify. If it goes down, a normal display (GOOD signal) will be displayed in the same manner.
The OD lamp 31 is turned on and a notification is given.

After the above determination, the microprocessor CPU sends a determination end signal (K in FIG. 6) to the non-energization determination flip-flop circuit 29 to reset the circuit 29, and a set signal to the determination start determination flip-flop circuit 28 is passed. The signal gate 36 is closed.

When the energization time and the holding time are finished, the welding end signal is generated by the welding end signal generating circuit 26 at the off edge of the pressurizing valve signal.

If the welding current is normally applied, the set signal gate 36 to the determination start determination flip-flop circuit 28 is closed as described above, so the microphone CPU is not activated and the non-conduction determination flip-flop circuit 29 is not activated. It only resets. However, when the welding current is not supplied, the gate 36 is open, and as shown in J'of FIG.
8 is set, the microprocessor CPU starts signal processing, and it is read through the input circuit of the input / output interface 16 that the non-energization determination flip-flop circuit is not set. As a result, the non-energization determination is performed, and the NG lamp 32 warns as in the case of the cable disconnection detection.

The operation of the device of the present invention is as described above, and the repulsive force between the inner conductors forming the cable 1 generated during energization causes the inner conductor to vibrate, and as a result, the external magnetic field strength fluctuates, and the magnetic sensor Even when an error occurs in the sensor output signal of the above, since the intensity signal of the magnetic field generated by the current for one cycle of the welding current set in advance is taken in, not only the error caused by the vibration can be removed but also the non-energization determination By providing the flip-flop circuit 29, connecting the output of the flip-flop circuit 29 to the input circuit of the input / output interface 16, and reading the output with the microprocessor, it is possible to detect the non-conduction of the welding current. Furthermore, due to the structural characteristics of the welded secondary cable, the mounting of the magnetic sensors is not limited to equiangular spacing around the cable, but can be linearly arranged in the longitudinal direction of the cable.

FIG. 7 (I) shows digital output signals x ₁ , x ₂ , x _{3 obtained} by digitizing the outputs of the three magnetic sensors Sa, Sb, Sc.
This shows the relationship between the sum x _{s of the above} and the energized current, and it can be seen that the two have a substantially proportional relationship.

Further, FIG. 7 (II) shows the digital output signals x ₁ , x ₂ ,
The relationship between the standard deviation s of x ₃ and the energizing current is shown, and it can be seen that the two have a substantially proportional relationship. This result indicates that by dividing the standard deviation s by x _s , the standard deviation calculated based on the magnetic field strength signal output from the magnetic sensor corresponding to each energization current value can be averaged to eliminate the error. Show the possibilities. FIG. 7 (III) shows the relationship between s / x _s and the energizing current. For each energizing current value, s / x
It can be seen that x _s is approximately constant.

FIGS. 8 (I) and (II) show the relationship between the normalized standard deviation s and the characteristic value s / x _s and the energization current, respectively. For comparison of both, s and s / x _s Average value Is normalized as 100. With these results,
The change in the values of s and s / x _s due to each energizing current value is about 1/8 of s / x _s compared to s, and the effect of the change in energizing current can be made very small.

Further, FIGS. 9 (I) and (II) show the relationship between the s and s / x _s and the disconnection rate. As is clear from FIG. 9 (I), the standard deviation depends on the energizing current value. The relationship between s and the wire breakage rate is clearly different, and the range of wire breakage rates that exceed the judgment threshold value, that is, the range in which a judgment error due to the applied current is large, is s /
For x _s, the value of s / x _s as shown in FIG. (II) is possible without being affected by the electric current value, therefore there is little scope to produce decision error.

From the above, the value calculated by dividing the standard deviation s of the sensor outputs of the magnetic sensors Sa, Sb, Sc by the sum x _s of the sensor output signals x ₁ , x ₂ , x ₃ is used as the characteristic value of the cable disconnection detection. By capturing this, it is possible to almost eliminate the influence of the energized current, and it is possible to accurately detect the disconnection of the internal conductor that constitutes the cable even in the welding process in which the welding energized current changes greatly.

FIG. 10 shows an example of actual measurement values of the spot welding position and the disconnection detection characteristic value s / x _s for one vehicle of one welding spot gun. As shown in the figure, the characteristic value has a considerable variation depending on the spot welding position.
It can be seen that if the welding mode (cable twist, bend, etc.) per table does not change, the reproducibility is high. It is considered that the variation in the characteristic value is caused by the twist of the cable 1 depending on the spot position and the positional relationship between the inner conductor and the magnetic sensor fixed on the outer circumference of the outer tube 5 covering the inner conductor. Since the characteristic values vary in this way, it is highly risky to make an erroneous determination if the disconnection of the cable is immediately determined from the characteristic value collected and calculated in one welding process.

Therefore, by the internal processing of the CPU of the microcomputer 14, the characteristic values of the past N times are stored in the memory,
The average of the characteristic values obtained by always going back to the past N times is calculated to reduce the variation of the characteristic values, and the disconnection is determined by comparing the average value with a preset threshold value.

FIG. 11 is an explanatory diagram showing how to obtain the average value of the characteristic values of the past N times, and shows the case of N = 8. Same figure
(A) shows the welding current supplied to the cable 1 during spot welding, and the digital output signals (x _{1, n + 1} , x _{2, n + 1)} obtained by processing and detecting the welding current by the magnetic sensors Sa, Sb, Sc. ，
x _{3, n + 1} ), (x _{1, n + 2} , x _{2, n + 2} , x _{3, n + 2} ) ... (x
_{1, n + i} , x _{2, n + i} , x _{3, n + i} ) to (i), (ii), (ii)
The characteristic value s / x _s is calculated from i), (iv), and (v) by Q _{n + 1} , Q _{n + 2} , ...
Qn _{+ i} is obtained, and the average value of the past eight characteristic values is sequentially obtained as follows.

Average value Here, there are two possible methods for determining N appropriately,
One method is preset as a fixed value inside the microcomputer (however, N ≧ 2), and the other method is the vehicle 1
The number of points the spot welder hits the table is N, and it is set by an external switch. According to the former,
This can be performed by the internal processing of the CPU. According to the latter, the variation of the characteristic value described above for each vehicle has a periodicity, so that the influence of the variation can be eliminated.

The present embodiment is a case where it is applied to a portable spot welder or an automatic spot welder, and a magnetic field strength signal output from each magnetic sensor is processed by a statistical method to obtain a variation amount of the magnetic field strength. , The characteristic value calculated by dividing this variation amount by the total sum of a plurality of magnetic sensor outputs or the average value thereof is stored each time, and the average value of the characteristic values of the past N times is compared with a preset threshold value. Although the disconnection of the welding secondary cable is detected, in the stationary spot welder where the welding position (posture) does not change,
It is not always necessary to use the average value of the characteristic values of the past N times, and in this case, the disconnection may be detected by comparing the characteristic value with a preset threshold value.

Of course, even if it is a portable spot welder or an automatic spot welder, the same method as in the case of the stationary spot welder can be adopted when there is little change in the welding position (posture).

[Effect] As has been clarified in the above description of the specific configuration and operation, the method of the present invention arranges a plurality of magnetic sensors corresponding to each internal conductor, and outputs the magnetic intensity signal output from each magnetic sensor. While calculating the variation amount of the magnetic field strength by a statistical method, the variation amount is a sum of the plurality of magnetic sensor outputs, or a characteristic value calculated by dividing the average value and a preset threshold value. By detecting the disconnection of each inner conductor constituting the welding secondary cable, and the characteristic value is hardly affected by the change in the welding energizing current, the welding process in which the welding energizing current greatly changes. In addition to being able to detect disconnection of internal conductors reliably and with high accuracy, a constant monitoring system is adopted, which leads to deterioration of welding quality due to disconnection, and during sudden work. The disconnection can be prevented and the inspection man-hour can be reduced.

Further, by storing the characteristic value every time and determining the disconnection by the average value of the characteristic values of the past N times, it is possible to reduce the variation in the welding position of the characteristic value, and to detect the disconnection with higher accuracy. Is possible.

[Brief description of drawings]

Attached Drawings Fig. 1 is a cross-sectional structural view of the welded secondary cable 1, Fig. 2 is a perspective view showing a method of measuring the magnetic field in the vicinity of the welded secondary cable 1, and Figs. 3 (a) and 3 (b) are welded secondary The figure which showed the measurement result of the disconnection mode of the cable 1, and its vicinity magnetic field, FIG.
(A) and (B) are cross-sectional views showing the arrangement of the magnetic sensors, where (A) shows the circumferential arrangement and (B) shows the longitudinal arrangement of the cable. FIG. 6 is a block diagram of the device of the present invention, FIG. 6 is a timing chart of the operation of the device of the present invention, FIG. 7 (I) shows the relationship between the sum X _s of the digital output signals and the energization current, and FIG. Shows the relationship between the characteristic value s / x _s and the energizing current, and FIG. 8 (I) shows the normalized standard deviation s and the energizing current. 8 (II) shows the relationship between the normalized characteristic value s / x _s and the energizing current, and FIG. 9 (I) shows the relationship between the standard deviation s and the wire breakage rate. FIG. 9 (II) is a diagram showing the relationship between the characteristic value s / x _s and the disconnection rate, and FIG. 10 is a diagram showing the relationship between the spot welding position and the measured value of the characteristic value s / x _s . Figure 11 shows how to calculate the average value. It is an explanatory diagram showing. 1 ... Welding secondary cable, 2a-2c, 3a-3c ...
Inner conductor, Sa, Sb, Sc ... Magnetic sensor, 7 ... Sensor ring, 10 ... Preamplifier, 11 ... Sample switch, 12 ... Peak hold circuit, 13 ... Analog digital circuit, 14 ... Micro Computer, 17
...... Pulsing circuit, 21 ・ ・ ・ Integration circuit, CPU ・ ・ ・ Microprocessor, 30 ・ ・ ・ Lamp drive circuit.

Claims (2)

[Claims] 1. A welded secondary cable comprising a plurality of positive side inner conductors for connecting a welding gun and a transformer and a plurality of negative side inner conductors arranged alternately in a ring shape with respect to a cable cross section. A plurality of magnetic sensors are arranged on the outer periphery corresponding to each of the inner conductors, and the magnetic field strength signal output from each magnetic sensor is processed by a statistical method to obtain the variation amount of the magnetic field strength. Is divided by the sum of the outputs of the plurality of magnetic sensors or an average value thereof, and a characteristic value calculated by comparison with a preset threshold value detects a disconnection of each inner conductor forming the welding secondary cable. A method for detecting a disconnection of a welded secondary cable, which is characterized in that 2. A welding secondary cable comprising a plurality of positive side inner conductors connecting a welding gun and a transformer and a plurality of negative side inner conductors arranged alternately in a ring shape with respect to a cable cross section. A plurality of magnetic sensors are arranged on the outer periphery corresponding to each of the inner conductors, and the magnetic field strength signal output from each magnetic sensor is processed by a statistical method to obtain the variation amount of the magnetic field strength. Is stored every time, and a characteristic value calculated by dividing the output by the sum of the plurality of magnetic sensor outputs or an average value thereof is stored, and the welding is performed by comparing the average value of the characteristic values of the past N times with a preset threshold value. A method for detecting a disconnection of a welded secondary cable, which is characterized by detecting a disconnection of each internal conductor which constitutes the secondary cable.