JPH0732955B2 - Resistance measuring device in resistance welding machine - Google Patents

Description

The present invention relates to a resistance measuring device for calculating a substantial resistance value of a secondary cable in a resistance welding machine.

[Prior Art] It is necessary to calculate a substantial resistance value in order to know deterioration of a cable or wear of a tip in a resistance welding machine.
Therefore, the voltage is detected between both ends of the cable or between the chips, the welding current is detected, and the resistance value is calculated from these measured values (see, for example, JP-A-61-189882).

[Problems to be Solved by the Invention] By the way, in the above-mentioned prior art, it is possible to calculate the resistance value of the cable or the like from this measured value by detecting the voltage and current, but this calculation is performed. The issue is whether the cable deterioration can be determined within a practical range based on the resistance value. That is, the electric resistance of the conductor (generally copper wire) used for the cable naturally varies depending on the temperature. The conductor temperature varies depending on the season of cooling water such as cables, time of day, or location of use. Further, the conductor temperature rises due to energization, and the magnitude of the change is related to the current value, the flow rate of the cooling water, the cooling water temperature, etc., and varies depending on the timing of measurement.

Therefore, in the above method of detecting only the voltage and current and calculating the resistance value of the cable from this measured value, the resistance value is affected by the resistance change due to cable deterioration and the temperature change of the conductor. There is probably a problem in determining deterioration.

The present invention has been made in view of the above problems of the conventional technique, and an object of the present invention is to substantially calculate an increase in resistance due to deterioration of a cable to an accuracy within a practical range and to calculate the resistance. An object of the present invention is to provide a resistance measuring device in a resistance welding machine capable of displaying a value or outputting a judgment result.

[Means for Solving the Problem] In order to achieve the above object, a resistance measuring device in a resistance welding machine according to the present invention is provided with a means for detecting a cooling water outlet temperature of a secondary cable end or a temperature of a part of a cable conductor. , A means for detecting the secondary side or primary side voltage of the transformer and a means for detecting the secondary side or primary side current of the transformer, and these detected temperatures,
From the voltage and the current, the resistance value at the reference temperature after the point where the voltage is detected is calculated.

Further, the above device is provided with a means for judging deterioration of a conductor such as a cable when the calculated resistance value exceeds a preset value.

Further, the above device is provided with a means for judging deterioration of a conductor such as a cable when the calculated resistance value exceeds a preset value.

[Operation] Basically, first, the temperature, voltage and current are detected, the resistance value of the cable at that temperature is calculated from this measured value, and this resistance value is corrected to the resistance value at the reference temperature. Therefore, the corrected resistance value becomes a substantial value that is not affected by changes in temperature. In addition, deterioration of the conductor of the cable can be accurately determined by the corrected range of increase in resistance value.

[Embodiment] An embodiment of the present invention will be described with reference to FIGS. 1 to 3.

In FIG. 1, 1 is a lead wire for detecting the voltage when the cable is energized, 2 is a toroidal coil for detecting the welding current, and 3 is a temperature detecting sensor for detecting the outlet temperature of the cooling water. is there. Reference numeral 4 denotes an antiparallel thyristor in the primary circuit of the transformer 5 connected to the commercial power source, and the resistance welding machine 7 is arranged on the secondary side of the transformer 5. The lead wires 1, 1 ... Are connected to the respective arms of the resistance welding machine 7 by the respective ends of the cables 8, 9 and the differential voltage detection circuit 10, 11.
The temperature detecting sensor 3 is arranged at the outlet of the cooling water at the end of the cable 8 to guide the temperature of the detected cooling water to the temperature detecting circuit 12, and the toroidal coil 2 is a secondary conductor. The current detected by the sensor is placed in the current detection circuit 13. 14 is an analog-digital converter, 15
Is a digital arithmetic unit. And the differential voltage detection circuit
The voltage from 10, 11 and the temperature from the temperature detection circuit 12 and the current from the current detection circuit 13 are input to the analog-digital converter 14, where they are digitally converted, and the converted data is further digitalized. It is input to the calculation unit 15. In the digital arithmetic unit 15, the degree of upper and lower limits (%) recognized as deterioration (abnormal) when a resistance value recognized as a preset arbitrary cable deterioration (abnormality) or resistance value immediately after replacement is used as a reference (%) Data and the temperature already detected,
Data for calculating the resistance value at the temperature used as the reference for setting from the voltage and current values is input from the setting unit 16.

Therefore, in the digital arithmetic unit 15, the analog
This is calculated as a resistance value at the reference temperature based on the temperature, voltage, and current values obtained from the input signal from the digital converter 14, and this value is displayed on the input / output unit 17. Further, the calculated resistance value is deteriorated (abnormal) in the digital calculation unit 15.
And the result of the determination is output to the determination output unit 182. Although the lead wires 1, 1 ... Which detect the voltage are connected to the respective ends of the cable,
This may be connected at both ends of the chip, both ends of the secondary side of the transformer, or the primary side of the transformer, and the toroidal coil 2 for detecting the current is also provided on the secondary side of the transformer. However, this detection may be performed by the primary of the transformer, or may be applied to the inverter circuit instead of the thyristor circuit.

FIG. 2 shows another embodiment, and the same members as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In FIG. 2, lead wires 1 and 1 for detecting voltage are connected to both ends of the secondary side of the transformer. Therefore, in this embodiment, the resistance value of the entire secondary side of the transformer (the entire welding machine including the cable and the gun) can be measured. In addition, the setting unit 16
The data for constant current control is also set in this, and since this is input to the digital arithmetic unit 15, in the digital arithmetic unit 15, a signal for constant current control is provided in addition to the operation in the first embodiment. This signal is input to the thyristor gate pulse generator 19 to control the thyristor 4 by the thyristor gate pulse generator 19 to automatically make the welding current constant.

FIG. 3 is a general relational diagram between the temperature of the cooling water of the cable and the temperature of the conductor, which is related to the welding current.

When N cycles are energized, one welding is completed and energization is stopped, and when N cycles are energized to perform the next welding, the conductors that make up the cable are proportional to the magnitude of welding current and energization time. The temperature rises, and the temperature drops sharply due to cooling when the energization is stopped. The temperature of the cooling water that cools this conductor follows the temperature of the conductor, but due to the difference in thermal conductivity (Cu and H2O), the temperature difference between the conductor and the cooling water is small at the beginning of energization (at point A). When the temperature of the cooling water is detected at, this temperature is close to the temperature of the lead wire.

Therefore, it is preferable that the temperature detection in the present invention is performed at the initial stage of energization.

[Effect of the Invention] According to the present invention, basically, the temperature, voltage, and current are first detected, and the resistance value of the cable at that temperature is calculated from this measured value, and this resistance value is corrected to the resistance value at the reference temperature. Therefore, the corrected resistance value becomes a substantial value that is not affected by the temperature change, so that the increase in resistance due to the deterioration of the conductor of the cable can be substantially calculated within the practical range of accuracy.

Further, by knowing the range of increase in the corrected resistance value, deterioration of the cable can be accurately determined, useless replacement of parts can be avoided, and optimum parts can be used.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of a resistance welding device equipped with a resistance measuring device according to the present invention, FIG. 2 is a block diagram of another embodiment, and FIG. 3 is a diagram of a cable related to energization of welding current. A general relationship diagram of the temperature of the cooling water and the temperature of the conductor is shown. 1 ... Voltage detection lead wire, 2 ... Current detector, 3 ... Temperature detection sensor, 5 ... Transformer, 7 ... Welding gun, 8 ... Secondary cable, 15 ... Digital operation part, 16 ... Setting device, 17 ... Input / output Section, 18 ... Judgment output section.

Claims (2)

[Claims] 1. A means for detecting a cooling water outlet temperature of a secondary cable end or a temperature of a part of a cable conductor, a means for detecting a secondary side or primary side voltage of a transformer, and a secondary side or primary side of a transformer. A resistance measuring device in a resistance welding machine, comprising: a means for detecting a side current; and calculating a resistance value at a reference temperature after the point where the voltage is detected from the detected temperature, voltage and current. 2. A resistance measuring apparatus for a resistance welding machine according to claim 1, further comprising means for judging deterioration of a conductor when the calculated resistance value exceeds a preset value.