Circuit resistance measuring device

Abstract

To provide a technique capable of highly accurately measuring a circuit resistance.SOLUTION: A circuit resistance measurement device in spot welding of welding an object comprises: an acquisition unit which acquires a measurement resistance value being each resistance value measured when performing plural times of electric conduction using a current value that is used in actual spot welding of the object and is equal to or greater than a predetermined threshold; a calculation unit which calculates any of an average value, a central value and a most frequent value of the plurality of measurement resistance values as a correction value; and a determination unit which determines a value obtained by correcting the resistance value measured in the actual spot welding of the object using the correction value as a circuit resistance value.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present disclosure relates to a circuit resistance measuring device. [Background technology]

[0002] In spot welding, there is a technique for adjusting the welding current based on the circuit resistance. Patent Document 1 describes a technique for adjusting the current according to the amount of change in resistance calculated by measuring the current value and voltage value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 6-71457 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technology described in Patent Document 1 does not adjust the current in accordance with the precise resistance value of the workpiece, and therefore there has been a demand for a technology that can measure circuit resistance with high accuracy. [Means for solving the problem]

[0005] The present disclosure has been made to solve the above-mentioned problems, and can be realized in the following forms.

[0006] According to one embodiment of the present disclosure, there is provided a circuit resistance measuring device for spot welding an object, the circuit resistance measuring device including: an acquisition unit that acquires measured resistance values, which are resistance values ​​measured when current is applied multiple times using a current value equal to or greater than a predetermined threshold value, which is a current value used in actual spot welding of the object; a calculation unit that calculates one of an average value, a median value, and a mode value of the multiple measured resistance values ​​as a correction value; and a determination unit that determines, as a circuit resistance value, a value obtained by correcting the resistance value measured in the actual spot welding of the object using the correction value. Resistance values ​​measured when a current used in actual spot welding is applied are less likely to vary than resistance values ​​measured when a current lower than the current used in actual spot welding is applied. Furthermore, with this form of circuit resistance device, a value determined by a statistical method from resistance values ​​measured by applying current multiple times is calculated as the correction value, so that it is possible to prevent the use of abnormal values ​​compared to when a resistance value measured simply once is determined as the correction value. As a result, the circuit resistance can be measured with high accuracy.

[0007] The present disclosure can be realized in various forms, for example, in the form of a circuit resistance measuring method in spot welding, a correction value calculating device, or the like. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing a schematic configuration of a circuit resistance measuring device. [Diagram 2] 6 is a graph showing an example of measured resistance values ​​acquired by an acquisition unit. [Diagram 3] 1 is a graph showing the relationship between current and resistance value. [Figure 4] 13 is a graph showing a resistance waveform when correction is performed using a correction value in a comparative example. [Diagram 5] 13 is a graph showing a resistance waveform when correction is performed using a correction value. [Figure 6] 13 is a graph showing the relationship between resistance value and the number of measurements in a comparative example. [Figure 7] 1 is a graph showing the relationship between resistance value and the number of measurements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] A. First embodiment: 1 is a schematic diagram showing a schematic configuration of a circuit resistance measurement device 100 in an embodiment of the present disclosure. The circuit resistance measurement device 100 is connected to a welding device 200 that performs spot welding, and measures a circuit resistance value during spot welding. The circuit resistance value measured by the circuit resistance measurement device 100 is used for various analyses such as estimating the nugget diameter of an object welded by spot welding performed by the welding device 200. The welding device 200 can control the current and voltage using the circuit resistance value measured by the circuit resistance measurement device 100.

[0010] The circuit resistance measuring device 100 includes an acquiring unit 10, a calculating unit 20, and a determining unit 30. The circuit resistance measuring device 100 is made up of a computer configured with a central processing unit (CPU), RAM, and ROM, and realizes the functions of the acquiring unit 10 and the calculating unit 20 by the computer executing a program installed in advance. However, some or all of the functions of these units may be realized by a hardware circuit.

[0011] The acquisition unit 10 acquires a measured resistance value, which is a resistance value when the welding device passes current. More specifically, the acquisition unit 10 acquires a current measured by an ammeter and a voltage measured by a voltmeter, and calculates a resistance value. The acquisition unit 10 acquires each measured resistance value measured when passing current multiple times using a current value equal to or greater than a predetermined threshold, which is a current value used in actual spot welding of a certain object. In this embodiment, the acquisition unit 10 acquires the resistance value when passing current at 8 kA.

[0012] The calculation unit 20 calculates, as the correction value, a value obtained by a statistical method from the multiple measured resistance values ​​acquired by the acquisition unit 10. More specifically, the calculation unit 20 calculates, as the correction value, any one of the average value, the median value, and the mode value of the multiple measured resistance values ​​acquired by the acquisition unit 10.

[0013] The determination unit 30 determines, as the circuit resistance value, a value obtained by correcting a resistance value measured during actual spot welding of an object using the correction value calculated by the calculation unit 20. The determination unit 30 may determine the circuit resistance value by correcting a resistance value measured during spot welding using the correction value, or may determine the circuit resistance value by correcting a resistance value measured during spot welding using the correction value after the completion of spot welding.

[0014] 2 is a graph showing an example of measured resistance values ​​acquired by the acquisition unit 10. The graph on the upper left shows the change in current, the graph on the lower left shows the change in voltage, and the graph on the right shows the change in resistance value calculated from these currents and voltages. In this embodiment, the acquisition unit 10 acquires, as the measured resistance value, the resistance value at time t1, which is a predetermined time after the start of current flow.

[0015] FIG. 3 is a graph showing the relationship between current and measured resistance value. The horizontal axis of the graph shown in FIG. 3 indicates the current during current flow, and the vertical axis indicates the measured resistance value. FIG. 3 shows the relationship between current and measured resistance value for each of six welding devices. As shown in FIG. 3, the larger the current, the smaller the variation in circuit resistance. The measured resistance value when current is passed at 8 kA, which is a current used in actual spot welding, is less likely to vary than the measured resistance value when current is passed at 2.5 kA, which is a current lower than the current used in actual spot welding. However, if the current is too large, the circuit resistance will vary due to resistance heating.

[0016] FIG. 4 is a graph showing the resistance waveform of the circuit resistance value when correction is performed with the correction value in the comparative example, and FIG. 5 is a graph showing the resistance waveform of the circuit resistance value when correction is performed with the correction value in the present embodiment. FIG. 4 shows the measured resistance value when a resistance value measured by applying a current of 2.5 kA is adopted as the correction value as a comparative example. FIG. 4 and FIG. 5 show the resistance waveforms in three welding devices that perform spot welding under the same conditions. Since spot welding is performed under the same conditions, it is preferable to obtain an approximate resistance waveform by correction even if the welding devices are different. By using the approximate resistance waveform, various analyses can be easily performed. As shown in FIG. 4, in the comparative example, the resistance waveforms are significantly different depending on the welding device. As shown in FIG. 5, the resistance waveforms in the present embodiment are similar to each other compared to the comparative example shown in FIG. 4. Therefore, it is easy to perform various analyses to compare the welding devices using the resistance waveform.

[0017] According to the circuit resistance measuring device 100 of the present embodiment described above, the correction value is calculated using the resistance value measured when current is passed using the current used in actual spot welding. The resistance value measured when current is passed using the current used in actual spot welding is less likely to vary than the resistance value measured when current is passed using a current lower than the current used in actual spot welding. In addition, since the correction value is calculated as a value obtained by a statistical method from the resistance values ​​measured by passing current multiple times, it is possible to suppress the use of abnormal values ​​compared to the case where the resistance value measured simply once is determined as the correction value. Therefore, the circuit resistance value can be measured with high accuracy.

[0018] B. Second embodiment: The second embodiment differs from the first embodiment in that the calculation unit 20 calculates the average value of the measured resistance values ​​after a predetermined number of repeated energizations from the start of energization as the measured resistance value. Since the configuration of the circuit resistance measurement device 100 of the second embodiment is the same as the configuration of the circuit resistance measurement device 100 of the first embodiment, a description of the configuration of the circuit resistance measurement device 100 will be omitted.

[0019] FIG. 6 is a graph showing the relationship between the resistance value and the number of measurements in a comparative example, and FIG. 7 is a graph showing the relationship between the resistance value and the number of measurements in this embodiment. FIG. 6 shows the resistance value when a current of 2.5 kA is applied as a comparative example. The horizontal axis of the graphs shown in FIG. 6 and FIG. 7 shows the number of measurements, and the vertical axis shows the resistance value. When the electrode attached to the tip of the gun in the welding device is new, the surface of the electrode may have a large surface roughness, which is an irregularity caused by processing during manufacturing. Therefore, at the initial stage of starting the measurement of the resistance value, the surface of the electrode is not familiar, and the contact state may be unstable. As shown in FIG. 6 and FIG. 7, the resistance value of the first time is significantly different from the resistance value after the fifth time.

[0020] According to the circuit resistance measuring device 100 of the second embodiment described above, the calculation unit 20 calculates the average value of the measured resistance values ​​after a predetermined number of times of current flow from the start of current flow as a correction value. The resistance value immediately after the start of current flow may be significantly different from the resistance value after several times of current flow from the start of current flow. Therefore, it is possible to prevent the use of an abnormal value. Therefore, the circuit resistance value can be measured with high accuracy.

[0021] C. Other embodiments: In the above-described embodiment, the acquiring unit 10 acquires the resistance value at a point in time when a predetermined time has elapsed since the start of energization as the measured resistance value. However, the acquiring unit 10 may acquire any one of the average value, median value, and mode value of the resistance value per unit time during a predetermined time period from the start of energization as the measured resistance value.

[0022] The present disclosure is not limited to the above-mentioned embodiment, and can be realized in various configurations without departing from the spirit of the present disclosure. For example, the technical features in the embodiments corresponding to the technical features in each form described in the Summary of the Invention column can be appropriately replaced or combined in order to solve the above-mentioned problems or to achieve some or all of the above-mentioned effects. Furthermore, if the technical feature is not described as essential in this specification, it can be appropriately deleted. [Explanation of symbols]

[0023] 10...acquisition unit, 20...calculation unit, 30...determination unit, 100...circuit resistance measuring device, 200...welding device

Claims

[Claim 1] A circuit resistance measuring device for spot welding an object, comprising: an acquisition unit that acquires a measured resistance value, which is each resistance value measured when current is applied a plurality of times using a current value that is equal to or greater than a predetermined threshold value, which current value is used in the actual spot welding of the target; a calculation unit that calculates one of an average value, a median value, and a mode value of the plurality of measured resistance values ​​as a correction value; a determination unit that determines, as the circuit resistance value, a resistance value measured during actual spot welding of the target and corrected using the correction value.

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