JPH0371230B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a welding condition time change monitoring device that continuously monitors the welding condition of a welding machine.

[Prior Art] One of the methods for welding metals is resistance welding.
In this method, the metals to be welded are stacked, an electrode is pressed against the stacked area, welding current is passed through the materials to be welded, and the welding materials are welded by the Joule heat generated at that time. .

Whether or not the welded parts welded in this way have the proper strength cannot be determined just by visual observation, so we detect the current or voltage during welding to determine the quality of the weld. Judging. This is the welding conditions (current, voltage, energizing time)
By determining the upper limit value and lower limit value of and monitoring the welding state, it is determined whether the voltage or current during welding is within an allowable range. The welding monitor displays this judgment result on a display, and also outputs a signal of the judgment result to the outside or records it with a built-in printer.

The above will be explained in more detail as follows.

Generally, various welding conditions (for example, welding current, interelectrode voltage, interelectrode resistance obtained by dividing welding current by interelectrode voltage, etc.) during the welding process are monitored by detecting the welding current using, for example, a toroidal coil or shunt resistor. Either restore the original welding current waveform through an integrator or amplifier, and sample only one cycle (one cycle of the power supply frequency), or measure the cumulative value of the welding current for all cycles during welding. A method is used to compare the sampled value with a predetermined welding current (or cumulative value of welding current) and determine whether the value is appropriate.

However, when a large current is used as in resistance welding, the method of sampling only one cycle is not practical because the power supply voltage fluctuates extremely rapidly and the reliability of the sample data is low.

Therefore, judgments are made based on the maximum value during welding, the cumulative value of welding current for all cycles, or the average value obtained by dividing this cumulative value by all cycles. The manner in which the value changes is unknown, and for this reason, welding defects may occur even if welding is performed normally on the monitor.

One of the methods for compensating for such low monitoring accuracy is Japanese Patent No. 1092065 (Japanese Patent Publication No. 56-37037) titled ``Welding current monitoring method and device.''
This is done by freely setting the welding current sampling interval from desired cycle to desired cycle, and comparing the cumulative average value of the welding current in this interval with a predetermined value to determine the magnitude of the welding current. There is.

According to this method, it is possible to sample the average value of the current in the energization cycle that is most relevant to the welding result, thereby improving monitoring performance.

[Problems to be Solved by the Invention] However, with such conventional monitors, a few cycles most related to the welding result are extracted from all cycles during welding and the cumulative average value for that section is calculated, which causes problems. It is difficult to identify the location of a problem during analysis, and of course it is impossible to detect problems that occur outside the set sampling period. For this reason, the voltage value as the energization time elapses,
The manner in which the current value changes is unknown. Therefore, even if welding is performed normally on the monitor, changes in voltage or current over time cannot be determined, and conditions that are out of the appropriate range cannot be tracked in half-cycle units. Therefore, no abnormality could be detected. Note that the entire cycle refers to the period of all AC waveforms from the start of welding to the end of welding.

[Means for Solving the Problems] In order to solve these problems, this invention has the following features:
Both the reference value and the tolerance value are stored from time to time, and decisions are made by comparing them with the measured values in real time.

[Operation] Temporal changes in welding conditions during welding are compared with reference values, and all states of the welding conditions that change moment by moment are judged to be good or bad.

[Embodiment] The figure is a block diagram showing an embodiment of the present invention. In the figure, 1 is a waveform shaping circuit, 2 is an A/D conversion circuit, 3 is a control circuit, 4 is a key switch, 5 is a storage section, and 6 is a display section.

In such a device, first, as a preparatory step,
Take out a sample of the metal that will actually be welded,
Test welding is performed several times to several dozen times, and the welding current value obtained at each time by this operation is supplied to the control circuit 3 via the waveform shaping circuit 1 and the A/D conversion circuit 2, and the data is The average value of the welding current for each time period (hereinafter referred to as a reference value) is calculated based on and stored in the storage unit 5.

Alternatively, if there is data on the average value of the welding current for each time period when welding was performed under the same conditions in the past, that data is inputted by the key switch 4 and stored in the storage section 5 via the control circuit 3. In the preparation stage, one of these methods is selected to store the reference value. After the above operations are completed, the allowable range of the reference value for each time is determined according to the conditions of the material to be welded, and is stored in the storage unit 5 via the control circuit 3 by the key switch 4. At this time, the reference value is automatically calculated on the stored data, and the allowable value is set by the operator. With the above operations, you have entered the necessary conditions as a preparation stage.

Next, the operation of the monitor when welding is actually performed will be explained. When the materials to be welded are welded, a welding current detection signal is detected via a toroidal coil (not shown) and is supplied to a control circuit 3 via a waveform shaping circuit 1 and an A/D converter 2. The control circuit 3 calculates the difference between the welding current corresponding to each time of the time change of the reference value stored in the storage unit 5 in the preparation stage and supplies it to the storage unit 5. The difference between the welding current corresponding to each time of the time change and the allowable range of the reference value stored in the storage section 6 in the preparation stage are read out from the storage section 5 and supplied to the display section 6.

On the display unit 6, these two signals are displayed, and if the difference between the welding current corresponding to each time of the time change of the reference value exceeds the specified tolerance range, a buzzer and a display will be activated. be warned.

Further, each data stored in the storage unit 5 may be supplied to a printer and stored therein.

The above explanation is about current, but since the targets for monitoring changes over time are current, voltage, and resistance, which of them to monitor can be selected depending on the purpose.

FIGS. 2 to 4 are flowcharts showing an example of the control operation when this operation is controlled by the CPU, and each is processed every half cycle. Steps 100 to 105 shown in FIG. 2 are processes for calculating the average of reference values, and A in step 100 is a variable, and B in step 105 is the average value. Further, in step 103, if the "input" key is pressed, it is determined as "YES". Steps 110 and 111 in FIG. 3 are a flowchart for processing the difference between the reference value and the measured value.
Steps 120 to 126 in the figure are a flowchart for determining whether the value is out of tolerance.

[Effects of the Invention] As explained above, in this invention, since the measured value is compared with the reference value from time to time, it is inconvenient that although it is good in all cycles as in the past, it deviates from the appropriate range in half cycles. This has the effect of preventing the occurrence of

[Brief explanation of drawings]

FIG. 1 is a block diagram showing one embodiment of the present invention, and FIGS. 2 to 4 are flowcharts showing the operation. 1...Waveform shaping circuit, 2...A/D conversion circuit,
3...Control unit, 4...Key switch, 5...Storage unit, 6...Display unit.

Claims (1)

[Claims] 1. In a welding condition time change monitoring device that monitors the welding state of a welding machine, a predetermined welding condition when welding is performed a plurality of times is added by the number of times for each half cycle, and then an average value calculation means for calculating an average value for each half cycle of the welding conditions by dividing the welding conditions; a storage means for storing the average value outputted from the average value calculation means as a reference; and an arbitrary allowable range for the reference value. Tolerance range setting means for setting as a deviation from the reference value and storing it in the storage means; Tolerance value calculation means for calculating upper and lower limit tolerances from the stored reference value and the set tolerance range. and error calculation means for calculating the absolute value of the difference between the measured value of the actual welding conditions corresponding to the predetermined welding conditions and the reference value every half cycle, and calculating the output of the error calculation means and the tolerance range. A temporal change in welding conditions characterized by comprising a determination means for sending an output signal when the comparison deviates from an allowable range, and a display means for displaying at least the reference value, the measured value, the upper limit value, and the lower limit value. monitoring equipment.