JPH0644542Y2 - Inverter resistance welding machine control or measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of use] The present invention relates to a control or measuring device for an inverter resistance welding machine having a function of detecting the occurrence of splash.

[Prior Art] In resistance welding, welding conditions such as welding current, energizing time, and welding voltage are controlled during welding so that desired welding quality can be obtained. From this, the conventional resistance welding control or measuring device detects and measures the welding conditions and outputs the angle measurement value as it is, or calculates the error of the angle measurement value with respect to the set value and calculates the error. The output of the display or the lighting of a specific lamp is used to judge whether the welding result is acceptable or not.

[Problems to be solved by the invention] By the way, when the resistance heat generated by resistance welding is excessive, a splash (explosion) is generated from the workpiece. When such a splash occurs, welding often fails in precision welding of electronic components and the like.

However, even if the measured values of various welding conditions are given by the conventional resistance welding control or measuring device, those measured values do not indicate or reflect the presence or absence of the splash occurrence. Therefore, conventionally, an operator visually inspects an object to be welded after welding to determine a welding result, but such a visual inspection causes a decrease in productivity and a burden on the operator. .

The present invention has been made in view of these problems, and provides a control or measuring device for an inverter resistance welding machine having a function of automatically and accurately determining whether or not a splash has occurred for each resistance welding. The purpose is to provide.

[Means for Solving Problems] In order to achieve the above object, the control or measuring apparatus for an inverter resistance welding machine of the present invention rectifies a commercial AC voltage into a DC voltage, and converts the DC voltage into an inverter circuit. The pulsed high frequency AC voltage of a predetermined frequency is converted by the above, the high frequency AC voltage is passed through a welding transformer and then passed through a rectifier to be converted into a DC voltage again, and this DC voltage is applied between welding electrodes sandwiching the material to be welded. In the control or measuring device of the inverter type resistance welding machine, which controls the inverter circuit by the feedback type constant current control circuit so that a constant welding current flows, the welding current is synchronized with the inverter frequency. And a voltage applied to the welding electrode at a timing synchronized with the inverter frequency. Voltage detecting means for detecting, and resistance value calculating means for calculating a resistance value between the welding electrodes at a timing synchronized with an inverter frequency based on a voltage value and a current value respectively obtained from the voltage detecting means and the current detecting means. When the time change rate of the resistance value exceeds the reference value by sequentially calculating the time change rate of the resistance value obtained by the resistance value calculating means in a certain section of the energization time and comparing it with a predetermined reference value. A splash detecting means for determining that a splash has occurred is provided.

[Operation] During the energization time of resistance welding, the resistance value between the welding electrodes sandwiching the material to be welded changes like the characteristic curve RQ shown in FIG.

That is, immediately after the start of energization, the contact resistance between the welding electrode and the material to be welded acts and the resistance value becomes high. Although the resistance value of this contact resistance component decreases in a short time, the specific resistance value increases from around time t1 due to the temperature rise, and reaches the maximum resistance value around time t2. The generation of the nugget starts from this point, and the resistance value gradually decreases as the nugget is generated.

Splash is likely to occur near the maximum resistance value, that is, near the start of nugget formation. When a splash occurs, the resistance value drops abruptly, and the characteristic curve of the resistance value change rate becomes like a dotted line RQ '.

According to the present invention, the voltage detection means, the current detection means, and the resistance value calculation means, which operate at the timings synchronized with the inverter frequency, respectively, determine the inter-electrode resistance value which changes like the characteristic curve of FIG. When the resistance value changes, the sudden drop in the resistance value change rate is detected by the splash detection means, and the occurrence of splash is determined. By displaying and outputting the determination result, a worker or the like can know whether or not a splash has occurred.

Further, since the splash occurs near the middle of the energization time, a predetermined section of the energization time (for example, ta to tb in FIG. 2) may be set as the monitoring period, which allows the resistance value that normally occurs immediately after the start of energization or at the end of energization to be monitored. A sudden drop is not mistaken for a splash.

[Embodiment] FIG. 1 shows an overall circuit configuration of an embodiment in which the present invention is applied to an inverter type resistance welding machine.

In this resistance welding machine, the inverter circuit 14 outputs a pulsed (rectangular) high frequency AC voltage by chopping the DC voltage E input from the input terminals 10 and 12 by high frequency switching. The switching frequency of the inverter circuit 14, and thus the pulse width of its high-frequency AC output, is variably controlled by the pulse width control circuit 36 via the inverter drive circuit 40. The high frequency AC voltage output from the inverter circuit 14 is applied to the primary coil of the welding transformer 16,
The stepped down high frequency AC voltage obtained from the secondary coil is rectified into a DC voltage by the rectifier circuit 20 including the diodes 18a and 18b. Then, this DC voltage is supplied to the objects to be welded 24a, 24b via the pair of welding electrodes 22a, 22b, whereby the welding current I is applied to the objects to be welded 24a, 24b.

This resistance welding machine is provided with a foot-back type constant current control circuit for controlling the welding current I constant.
In this constant current control circuit, a toroidal coil 26 is provided on the secondary conductor of the welding machine as a current sensor for detecting the welding current I, and an output voltage representing a differential waveform of the current I is obtained from this coil 26. . The output voltage of the coil 26 is converted into a signal representing the waveform of the welding current I by the waveform restoring circuit 28 including an integrating circuit, and based on the current waveform signal, the current average value computing circuit 30 synchronizes with the inverter frequency f, for example, at a constant cycle. A voltage signal SI indicating the average value of the welding current I is obtained for each ΔT. This voltage signal SI is applied to one input terminal of the current comparison circuit 32. To the other input terminal of the current comparison circuit 32, the voltage signal SI ₀ from the current setting circuit 34 representing the welding current setting value is applied. The comparator circuit 32 outputs both signals S
The pulse width control circuit 36 is provided with an output signal er representing the error by comparing I and SI ₀ . The pulse width control circuit 36 controls the high frequency AC output of the inverter circuit 14 by pulse width modulation (PWM), and inputs, for example, a sawtooth signal of a constant high frequency (inverter frequency) f as a modulated wave from the frequency generator 38. , And a pulsed PWM signal P _PWM having a binary level of “H” and “L” is generated by comparing this with the error signal er, and each transistor of the inverter circuit 14 is turned on / off by this. According to such a constant current control circuit,
Feedback-type constant current control is performed so that the error output er of the comparison circuit 32 becomes zero, that is, the welding current I matches the set value.

Now, in this embodiment, in order to measure the resistance value between the welding electrodes 22a, 22b, the voltage average value calculation circuit 42 between these welding electrodes.
Are connected. The arithmetic circuit 42 calculates, for example, the average value of the inter-electrode applied voltage V at every constant period ΔT synchronized with the inverter frequency f, and outputs the voltage signal SV representing the voltage average value. This voltage signal SV is converted into a digital signal by the A / D converter 44, and then the CPU (microprocessor) 48
Given to. In addition, the voltage signal SI indicating the average value of the welding current I output from the current average value calculation circuit 30 is A / D
The signal is converted into a digital signal by the converter 46 and then given to the CPU 48.

The CPU 48 performs the following arithmetic processing for a certain section (for example, ta to tb in FIG. 2) during the energization time according to the arithmetic program stored in the ROM 50.

First, the resistance value between the welding electrodes is divided by dividing the digital value (voltage measured value) from the A / D converter 44 by the digital value (current measured value) from the A / D converter 46 at every constant time Δt. Figure out Ri. As a result, as shown in FIG. 3, the resistance value change curve RQ
The resistance values R1, R2, ... Corresponding to the above positions are obtained.

Next, the CPU 48 sequentially calculates the time change rate ΔRi for several combinations of resistance values (for example, [R ₁ , R ₂ , R ₃ ], [R ₂ , R ₃ , R ₄ ], ...). Then, it is judged whether or not some of them exceed the reference value MR. When a splash occurs, resistance values R ₈ , R ₉ , R ₁₀ , on the curve RQ ′ are obtained, and the rate of change ΔRi between R _{7 and} R ₉ is the maximum value Max ΔRi, which exceeds the reference value MR. . If no splash occurs, resistance values R ₈ ′, R ₉ ′, R ₁₀ ′, ... On the curve RQ ′ are obtained, but there is no change rate ΔRi exceeding the reference value MR. The data obtained by the above arithmetic processing is stored in the RAM 52.

Through the above-described arithmetic processing, the CPU 48 determines that the splash has occurred when the rapid resistance value change rate is recognized, and determines that the splash has not occurred when the rapid resistance value change rate is not recognized. Then, the judgment result is displayed on the screen of the display 54. Accordingly, when the determination result of the splash occurrence is obtained, the worker may treat the work to be welded as a defective welding product, and does not have to perform a visual inspection one by one.

In addition, the CPU48 will send I / 0 when a splash occurs.
Correction data for reducing the welding current setting value by an appropriate value is given to the current setting circuit 34 via 56. As a result, in the next resistance welding, the set value signal SI ₀ supplied from the setting circuit 34 to the comparison circuit 32 decreases, so that the welding current I is slightly corrected, and splash is prevented or suppressed.

If an automatic sorter is installed on the processing line, the CPU48 sends a command signal to remove defective welding products from the line.
Alternatively, it may be sent to the automatic sorter via I / 056.

[Advantages of the Invention] The present embodiment has the above-described configuration,
It has the following effects.

Focusing on the phenomenon that the resistance value between welding electrodes drops abruptly when a splash occurs during the current-carrying time of resistance welding, the resistance value between electrodes is dynamically monitored and the presence or absence of a splash is automatically and accurately determined. Since this is done, it is possible to improve productivity by eliminating the need for visual inspection by workers.

Further, by monitoring the inter-electrode resistance value only in a predetermined section where splash can occur, it is possible to eliminate erroneous recognition or erroneous determination.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall circuit configuration of an embodiment in which the present invention is applied to an inverter type resistance welding machine, and FIG. 2 is a temporal change of resistance value between welding electrodes during energization time of resistance welding. FIG. 3 is a characteristic curve diagram showing the above, and FIG. 3 is a diagram for explaining the action of splash detection according to the embodiment. In the drawing, 22a, 22b ... Welding electrodes, 24a, 24b ... Workpiece to be welded, 26 ... Current sensor (toroidal coil), 28 ... Waveform restoration circuit, 30 ... Current average value calculation circuit, 32 ... Current Comparison circuit, 34 …… Current setting circuit, 42 …… Voltage average value calculation circuit, 44,46 …… A / D converter, 48 …… CPU, 50 …… ROM, 52 …… RAM, 54 …… Display unit , 56 …… I / O.

Claims (2)

[Scope of utility model registration request] 1. A commercial AC voltage is rectified into a DC voltage, the DC voltage is exchanged with a pulsed high frequency AC voltage of a predetermined frequency by an inverter circuit, and the high frequency AC voltage is passed through a welding transformer and then passed through a rectifier. A DC voltage is applied again, and this DC voltage is applied between welding electrodes sandwiching the material to be welded, and the inverter circuit is controlled by a feedback constant current control circuit so that a constant welding current is caused to flow. In a control or measuring device of an inverter type resistance welding machine, a voltage detection means for detecting a voltage applied to the welding electrode at a timing synchronized with an inverter frequency, and a means for detecting the welding current at a timing synchronized with an inverter frequency Current detecting means, voltage values obtained from the voltage detecting means and the current detecting means, and A resistance value calculating means for calculating the resistance value between the welding electrodes at a timing synchronized with the inverter frequency based on the current value, and a time change rate of the resistance value obtained by the resistance value calculating means in a certain section of the energization time sequentially. An inverter comprising: a splash detecting unit that calculates and compares with a predetermined reference value, and determines that a splash has occurred when the time rate of change of the resistance value exceeds the reference value. Type resistance welding machine control or measuring device. 2. The inverter resistance welding machine according to claim 1, wherein the splash detecting means is provided with means for displaying a determination result regarding the presence or absence of splash and / or outputting a signal. Control or measuring device.