JPH01280260A - Foreseeing method for breaking of wire of welded secondary cable - Google Patents

Abstract

PURPOSE:To foresee the breaking of the wire without reducing a threshold value for a broken wires detection of the cable by calculating a scattered amount of a magnetic field strength after constant number of welding points from the present time by an extrapolation. CONSTITUTION:Magnetic sensors S1-S3 are arranged corresponding to each inner conductor at an outer periphery of the welded secondary cable 1. Magnetic field strength signals outputted from each magnetic sensors S1-S3 are dealed by a statistic technique, the scattered amount of a dispersion, standard deviation etc., of the obtained magnetic field strength is searched for every constant number of the welding points and stored sequentially. And, the difference between the scattered amount calculated newly and the scattered amount ccalculated in the past being retraced for the constant number of the points is searched, and after multiplying its value by a fixed magnification for the foreseeing of the broken wires, further, by adding the scattered amount calculated newly, the scattered amount of the magnetic field strength after the constant number of the welding points from the present time is calculated by the extrapolation. By comparing this value with the threshold value setting for a decision of the broken wires, the foreseeing of the breaking of the wire can be performed at an early stage before the broken wire is actually occurred.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method for predicting disconnection of a secondary welding cable that connects a welding gun and a transformer.

``Prior art'' The basic principle of detecting disconnection in welded secondary cables (hereinafter referred to as cables) is that when the thin copper wires that form each internal conductor of the cable gradually break, the resistance of the internal conductor changes, which causes the welding to occur. Since the current diversion ratio changes, this can be interpreted as a change in magnetic field strength.

For this reason, the magnetic field strength signals output from multiple magnetic sensors placed on the outer circumference of the cable corresponding to each internal conductor are processed by statistical methods to determine the amount of variation in the magnetic field strength, such as dispersion and standard deviation. A method for detecting cable breakage by comparing the amount of variation with a preset threshold value was proposed by the applicant in Japanese Patent Application No. 62-2303.
It has been proposed as 85.

``Problem to be Solved by the Invention'' In the wire breakage detection method, in order to issue a wire breakage prediction alarm in advance for the UT line of the cable, it is necessary to set a low threshold for wire breakage detection.

However, if the threshold value is set low, it may be caused by various causes such as the incorrect installation position of the magnetic sensor on the cable, variations in cable characteristics due to manufacturing reasons, and differences in welding conditions during the welding process. In some cases, the magnetic field strength signal detected by the magnetic sensor changes abnormally, and the amount of variation in the magnetic field strength calculated based on this changes exceeds the threshold value, and it is determined that the wire is disconnected even though it is not a disconnection. This caused problems in terms of cable maintenance and maintenance.

The present invention has an object to solve the above-mentioned disadvantages, and provides a method for predicting disconnection of a welded secondary cable that makes it possible to predict disconnection without lowering the threshold for detecting cable disconnection. The purpose is to

"Means for Solving the Problem J" A specific means for achieving the above object is to connect a plurality of positive internal conductors connecting a welding gun and a transformer, and the same number of negative internal conductors in a cable cross section. A plurality of magnetic sensors are arranged on the outer periphery of a welded secondary cable configured by alternately arranging them in a ring shape, corresponding to each of the internal conductors, and the magnetic field strength signals output from each magnetic sensor are statistically calculated. The amount of variation in the dispersion, standard deviation, etc. of the magnetic field strength obtained by processing the method is obtained for each fixed number of welding points and stored sequentially, and the newly calculated amount of variation and the amount of previously stored variation going back a fixed number of points are calculated. Calculate the difference between the calculated value and multiply the calculated value by a predetermined multiplier for cable breakage prediction, and then compare the value obtained by adding the newly determined amount of variation with a preset threshold value, The present invention is characterized in that disconnection of the welded secondary cable is predicted.

"Function" As clarified in the description of the specific means, the present invention provides for newly calculated variations in magnetic field strength calculated by a statistical method for each fixed number of welding strokes. By finding the difference between the amount of variation and the amount of variation calculated in the past going back a certain number of hits, multiplying that value by a predetermined multiplier for predicting wire breakage, and then adding the newly calculated variation I, By extrapolating the amount of variation in magnetic field strength after a certain number of welding points from the current point, and comparing this value with the threshold value set for wire breakage determination, wire breakage can be predicted at an early stage before wire breakage actually occurs. It can be carried out.

"Example" Embodiments of the method of the present invention will be described based on the accompanying drawings.

As schematically shown in FIG. 1, an example of the cross-sectional structure of the cable 1 includes positive internal conductors 2a whose current directions are opposite to each other.
, 2b, 2c and the negative internal conductor 3a.

3b and 3c are alternately arranged in a ring shape parallel to the cross section of the cable, each internal conductor is separated and partitioned by an insulating separator 4, and each internal conductor is twisted in the longitudinal direction of the cable in order to lower AC impedance. It is hung and stored in an exterior tube 5. In addition, three magnetic sensors Sl
, 82.33 are arranged at 120° angle intervals on the outer periphery of the cable 1 so as to be between the adjacent positive and negative internal conductors to reduce the magnetic field strength generated by energization at the welding point. To detect.

In the schematic block diagram of the apparatus for carrying out the method of the present invention shown in FIG. 2, reference numeral 6 denotes a sensor assembly fitted around the outer periphery of the cable 1, including three magnetic sensors Sl.

S2. S3 are arranged in a ring shape at equal intervals of 120°, and the three magnetic sensors St, S2. The magnetic field strength signals xIn xt and xt from S3 are sent to the preamplifier 7, respectively.
．． Enter in 8.9. The preamplifier 7°8.9 receives magnetic field strength signals X + , X 2 . This is to amplify X3 to a level that allows signal processing. Next is the preamp 7.8
．． The outputs of 9 are input to peak hold (or sample hold) circuits 10, 11 and 12, respectively. The circuit 1
0.11.12 is a sequence controller 14 that receives welding start and end timer signals from the welding timer 13.
The timing signal is used to hold the peak value of the magnetic field strength signal in a specific cycle of energization.

This time, each output from &'J10, 11.12 is input to the A/D conversion circuit 15 and converted into a digital signal.

16 is a microcomputer which inputs the control signal of the sequence controller 14, outputs an A/D conversion signal to the A/D converter, and also outputs the magnetic field strength signal X1 converted by the A/D converter 15. ．． X2. X
Using the digital signals of 5, calculate the amount of variation in magnetic field strength (standard deviation, deviation sum of squares 9 variance, range, etc.) using a predetermined program and internal circuit configuration, and configure cable 1 based on the calculation results. Prediction of disconnection of the internal conductor is determined based on the Good or NG ratio output. The microcomputer 16 is composed of a CPU, a RAM, a ROM, an address decoder circuit, an input/output interface (all of which are not shown), etc., and prints out each of the above-mentioned statistics using a printer 17, a CR7 display device, 1
Displayed by 8.

The cable breakage prediction function by the microcomputer 16 described above will be explained based on the block diagram of FIG. 3.

In the figure, numeral 21 is a welding point number counter, which sequentially calculates the number of welding points. 22 is a score setting circuit for setting a constant number of scores; 23 is a score comparison circuit;
The X value and the set value are compared, and when the two match, a match signal is output. 24 is a sample switch that is driven by the matching signal, and 25 to 30 are six magnetic field strength variation storage circuits arranged in series. The amount of variation (■) is input to and stored in the memory circuit 25 placed at the beginning, and the previous amount of variation stored in the circuit 25 is shifted to the next circuit 26, and this is applied to each adjacent circuit. Repeatedly transfer the memory value of the circuit 29 to the circuit 30 connected to i&sequence, and set each memory value to V,,V
, , V,2...V,-5 is updated. 31 is the stored value V Ill of the variation storage circuits 25 and 30.
A subtraction circuit 32 calls Vm-1 and calculates the difference V, -V, , , 32 is a multiplication circuit for extrapolating the amount of variation in magnetic field strength after a certain number of points, and is used for predicting disconnection. 1 magnification setting circuit 3 for calculating the product of the output value of the magnification setting circuit 33 indicating a fixed number of dots and the output value of the subtraction circuit 31 described above;
The output value of 3 is a multiple of the number of points at which the sample switch 24 is activated. Reference numeral 34 denotes an addition circuit that calculates the sum of the variation amount V newly input to the magnetic field strength variation storage circuit 25 and the output value of the multiplication circuit 32, and the added value is a constant number of strokes from the current time. This is the amount of variation in the magnetic field strength. Reference numeral 35 denotes a comparison circuit that compares the amount of variation with the output value from the judgment value setting circuit 36 that sets a threshold for determining wire breakage, and issues a wire breakage prediction alarm if the amount of variation exceeds the threshold.

Next, the operation of the wire breakage prediction function will be explained.

When the power of the apparatus is turned on, the welding point counter 21 and the magnetic field strength variation storage circuits 21 to 30 are reset to zero.

When welding work is started, the number of welding points is sequentially input to the welding point number counter 21 and integrated, and the last two digits are outputted to the number of welding points comparison circuit 23.

From the dot number setting circuit 22, the lower two digits are sent to the comparison circuit 23.
When the values of 0'', rO'' are output, and the last two digits of the number of welding points are rO'', rQ'', a match signal is output from the welding point comparison circuit 23 every 100 welding points, and the sample switch 24 is driven. Then, the variation lv of the magnetic field strength calculated for each number of welding points was inputted and stored in the variation storage circuit 25, and was also stored in the storage circuit 25 in synchronization with the output timing of the coincidence signal. The variation amount v, -1 of 100 dots before is shifted to the dispersion amount storage circuit 26, and the variation amount of magnetic field strength of 200 dots ago, stored in the memory circuit 26, is shifted sequentially downward to the storage circuit 27. Shift the memory value to update the limb position. The value stored in the mt* tail memory circuit 3o is discharged, and the amount of variation in magnetic field strength for each 1°O welding point of the maximum number of past 500 welding points is stored.

The stored values V, 2, and -5 of the first circuit 25 and the circuit 30 connected to the last of the storage circuits are input to a subtraction circuit 31 to calculate V, -V, . This value is the degree of change in magnetic field strength every 100 points, and if = V, -V, then V, V, -s = D-+ D, -1+ D-t+
D-3+D-4, which ultimately becomes S, the sum total of the degree of change for each 100 welding points of the past 500 welding points.

Inputting this sum S into the multiplication circuit 32 and calculating the product with the output value of the magnification setting circuit 33 for wire breakage prediction When the multiplication factor is set to α times, the number of welding points is 500 x α after the welding point The increase in the amount of variation in magnetic field strength is calculated, and by adding the amount of variation V, which is input to the variation amount storage circuit 25 in the adding circuit 34, the variation in magnetic field strength after 500xα points from the current time jlQ itself is , can be calculated by extrapolation, and is inputted to the comparison circuit 35 and compared with the disconnection determination threshold value inputted to the comparison circuit 35 from the determination value setting circuit 36. If Q exceeds the disconnection determination threshold, it is assumed that a disconnection will occur after 500×α points from the current point, and a disconnection alarm is issued to predict a cable disconnection. In addition, this disconnection prediction judgment is performed when the number of welding points is 50.
After the 0 welding point is exceeded, the number of welding points is sequentially calculated every 100 welding points.6 Figure 4 is an explanatory diagram showing the concept of wire breakage prediction by the method of the present invention, and is calculated when the number of welding points is 20 and P6-2. The difference in the amount of variation in magnetic field strength is vn-V. Find -9,
By multiplying this by 2 to the magnification α for wire breakage prediction, the extrapolated value Q7 is calculated for the number of welding points P Th, Io after 1000 points from the current time, that is, the variation 1, that is, the number of welding points P. .

In addition, in the same way, the difference between the variation amount v1 of the magnetic field strength and V, □ when the number of welding points P, and P, □, is calculated, and the above α
When multiplied by , an extrapolated value Q is calculated for the number of points P1, and the limb position Q exceeds the wire breakage determination threshold. Therefore, a breakage of the cable is expected after 1000 points (P, 1°) from the current point, so a breakage prediction alarm is issued.

In the conventional method, a wire breakage cannot be predicted because a wire breakage is determined by comparing the amount of variation in magnetic field strength calculated every 100 points with a wire breakage determination threshold, but the method of the present invention can predict a wire breakage in advance by using an extrapolated value. It becomes possible to do so.

"Effects of the Invention J As clarified in the explanation of the above-mentioned specific means and effects, the present invention is based on the amount of variation in magnetic field strength calculated by a statistical method for each fixed number of welding strokes. Find the difference between the amount of variation calculated in the past and the amount of variation calculated in the past going back a certain number of hits, multiply that value by a predetermined multiplier for predicting wire breakage, and then add the newly calculated amount of variation. By extrapolating the amount of variation in magnetic field strength after a certain number of welding points from the current point, and comparing this value with the threshold value set for wire breakage determination, it can be detected at an early stage before wire breakage actually occurs. By predicting wire breakage, unlike the method of lowering the wire breakage determination threshold for wire breakage prediction, there is no erroneous determination of wire breakage, and the amount of variation in magnetic field strength that indicates a wire breakage condition can be reached. Since it is possible to issue a wire breakage prediction warning in advance,
This has the effect of making it possible to properly maintain and maintain the cables, thereby preventing accidents such as production line stoppages.

[Brief explanation of the drawing]

The accompanying drawings show embodiments of the present invention; FIG. 1 is a schematic cross-sectional view of a cable and also shows the arrangement of magnetic sensors; FIG. 2 is a schematic block diagram of an apparatus for carrying out the method of the present invention; FIG. 3 is a block diagram showing a cable breakage prediction/judgment function, and FIG. 4 is an explanatory diagram showing the concept of cable breakage prediction. 1... Cable, 16, Microcomputer, 25-30. ,,Variation amount storage circuit, 31,
,,subtraction circuit, 32,,,multiplication circuit, 33. ,. Magnification setting circuit, 34, Addition circuit, 35. ,,
Comparison circuit, 36. ,,judgment value setting circuit.

Claims (1)

[Claims] a plurality of positive internal conductors connecting the welding gun and the transformer;
A plurality of magnetic sensors are arranged on the outer periphery of the welded secondary cable, which is constructed by alternately arranging the same number of negative internal conductors in a ring shape with respect to the cross section of the cable, in correspondence with each of the internal conductors. The amount of variation such as the dispersion and standard deviation of the magnetic field strength, which is obtained by processing the magnetic field strength signal output from the magnetic sensor using a statistical method, is obtained for each fixed number of welding points and stored sequentially, and the newly determined amount of variation is A value obtained by adding the newly determined amount of variation to a value obtained by calculating the difference between the amount of variation and the amount of variation stored in the past going back a certain number of hits, and multiplying the calculated value by a predetermined multiplier for predicting cable breakage; A method for predicting disconnection of a welded secondary cable, comprising predicting disconnection of the welded secondary cable by comparing with a preset threshold value.