JPS583797B2 - resistance welding equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION In controlling a resistance welding process, one method proposed for determining the duration of current flowing through a welding electrode includes the following:
This is due to the electrical resistance value between the electrodes.

This resistance value drops during welding, so the quality of welding can be monitored by monitoring the resistance value between the electrodes and cutting off the welding current when this resistance value drops to a predetermined value. There is a way to do it.

Special Publication No. 55-6037 (British Patent No. 1,446,6
The control unit disclosed in No. 52) relates to such a method.

It detects and holds the voltage that develops between the welding electrodes to derive a low voltage level that is a predetermined ratio below this peak value, and then compares subsequent lower cycle peaks with said low voltage level. Welding is then terminated when the subsequent cycle peak drops to the lower voltage level.

Welding machines equipped with this type of control unit have an internal timer that operates at a predetermined period of time.

Thus, if a control unit is provided in such a welding machine, if the resistance-responsive control unit does not first terminate the welding within a predetermined time according to the decrease in resistance, i.e. the voltage drop across the electrodes, Welding is terminated by the internal timer.

The time determined by the internal timer is the limit time at which an acceptable weld is obtained.

If the welding machine's internal timer causes the welding to be terminated after such a period of time has elapsed, it is desirable to display an indication that the welding is questionable.

This means that a system that indicates suspicious welds should distinguish between welds that are terminated with a resistive response unit and those that are terminated with the welder's internal timer.

However, this is very difficult in practice because when the internal timer cuts off the welding current, the interelectrode voltage drops, which activates the resistive response unit.

In order to display the suspicious welding only when the welding is completed by the operation of the internal timer, Japanese Patent Publication No. 55-6037 provides an auxiliary timer to the control unit,
By setting this auxiliary timer to operate at the same time interval as the internal timer of the welding machine, the auxiliary timer turns on the warning light after a predetermined period of time has elapsed.

The present invention makes it possible to eliminate such an auxiliary timer.

A resistance welding device according to the present invention includes a resistance welding device including a switching means for accumulating application of an alternating current to a welding electrode, and an internal timer for driving the switching means to cut off the welding current after a predetermined number of cycles. Used in a welding machine, by detecting the voltage between the electrodes, a predetermined resistance drop of a member inserted between the electrodes is detected, and upon this detection, the switching means is operated to stop the supply of welding current to the electrodes. , a resistance response first detection means that operates once in each cycle of the welding current waveform; and a resistance response first detection means that indicates that the welding is suspicious if welding is not completed and is terminated by the internal timer. In a resistance welding device having a display means, the end of the supply waveform between the switching means and the electrode is detected, and if the resistance response first detection means is not yet operating at the time of the end, the suspicious welding is detected. In order to drive the display means to display, the second detection means is responsive to the supply current waveform between the switching means and the electrode, and the second detection means responds to the welding current waveform in order to detect the presence or absence of the supply waveform. is operated multiple times in each cycle, and this multiple operation causes the second resistive responsive first sensing means to detect the voltage drop across the electrodes caused by the termination of the supplied waveform by the internal timer.
The present invention is characterized in that detection is performed by a detection means, and the display means is driven based on the output thereof, and the display means is driven only when welding is completed by an internal timer.

Removal of the auxiliary timer from the control unit simplifies the preparation procedure when switching from one welding process to another.

In Japanese Patent Publication No. 55-6037, the welding time must be adjusted depending on the thickness and composition of the material, so both the internal timer and the auxiliary timer of the welding machine must be adjusted every time the welding process is changed.

According to the invention it is sufficient to adjust only the internal timer.

Another drawback of the prior art is that its reliability is
It depends on the accuracy of two timers.

If the internal timer is set to a shorter time than the auxiliary timer (due to inadvertence or failure), a warning light will be activated indicating a suspicious weld, even if the weld is insufficient or missing. Not done.

Therefore, by eliminating the auxiliary timer from the control unit, system reliability is improved.

Preferably, the resistive responsive first sensing means includes a ramp generator (gradient voltage generator) that is reset at each cycle of the waveform between the electrodes when the peak value of the waveform exceeds a reference level; and a comparator that operates to terminate the weld when the output exceeds another reference level (ie, when the slope is not reset).

The second sensing means also includes a further lamp generator and a second sensing means which causes the second lamp generator to operate twice in each cycle while the supply waveform is applied.
and a comparator that operates an indicator indicating a suspect weld when the output of the other lamp generator exceeds a reference level.

Therefore, the second comparator indicates a suspect weld because the first lamp generator is reset every cycle while the second lamp generator is reset every half cycle. Activate the display, and then
The output of the ramp generator reaches the reference level and provides a weld end signal later than the second comparator.

Embodiments of the present invention will be described below with reference to the drawings.

In FIG. 1, the supply voltage is connected to a thyristor or ignitron circuit 1 connected in series with the primary winding of a transformer 14.
2.

The firing circuits 16 and 18 control the operation of the thyristor or ignitron circuit.

The secondary winding of the welding transformer 14 has one turn and is connected to each electrode 19 via a copper rod.

The welder's internal timer 24 deactivates the thyristor or ignitron device if the resistance-responsive control unit does not terminate the weld within a predetermined number of cycles in the welding current.

FIG. 2 is a block diagram of an auxiliary control unit embodying the invention.

The interelectrode voltage (FIG. 1) is applied via a low-pass filter 26 to a main compensator 28 in the form of a divider circuit.

The purpose of this main compensator is to ensure that the subsequent circuitry provided to measure the electrode voltage drop does not malfunction due to mains voltage fluctuations.

This compensation will be made as follows.

The main voltage is passed through a transformer 20 to a low pass filter 26
is applied to a low-pass filter 22 having the same characteristics as .

At this time, the wave output is transmitted to the peak detector 24.

The peak detector 24 includes a discharge path which causes the output voltage of the peak detector 24 to drop slightly between successive cycles.

That is, when a peak is given in one cycle, this peak value drops due to the discharge path until the next cycle, and the new peak is maintained in the next cycle, and the same process is repeated.

Note that the degree of drop between cycles is approximately linear.

The peak voltage of this peak detector 24 is supplied to the division circuit 2B and is used as a divisor for the electrode voltage.

This output voltage represents the exact quotient in a given manual cycle.

The peak value of the voltage obtained by main compensation of the electrode voltage at the start of welding is detected by a peak detector 30, and its output is applied to a potentiometer 32.

The slider of this potentiometer is set to divide the peak voltage of the detector 30 at a predetermined ratio and supply it to the comparator 34.

Comparator 34 also receives the output of divider circuit 28 directly during welding.

When welding is started, each time the divider output is greater than or equal to the tap voltage of potentiometer 32 in each cycle, comparator 34 outputs a corresponding pulse.

This pulse is applied to the miss pulse detector 36 to reset the ramp generator 38.

The ramp voltage from the ramp generator is applied to a comparator 40;
It is compared to a reference voltage from potentiometer 42.

This reference level is placed above the level of the ramp voltage at which the ramp generator is reset each cycle.

If the resistance value drops to a predetermined value that compensates for the voltage drop across potentiometer 32, the divider output will no longer be greater than or equal to the output of potentiometer 32, and comparator 34 will no longer provide a reset pulse to the ramp generator. .

When this condition occurs, the output of the ramp generator rises above the reference voltage of comparator 40.

As a result, comparator 40 operates relay 48 via circuit 44 and amplifier 46.

Relay 48 opens contacts 50 and 52 (FIG. 1) of the thyristor or ignitron ignition control circuit, thereby terminating the weld.

The circuit 44 is a timer which is used to set a predetermined number of cycles, e.g. 30.
This is to prevent the welder from operating again during the cycle.

The output of the low pass filter 22 is also applied to a Schmitt trigger circuit 54 which operates on both the positive and negative input waveforms, thus providing twice the number of pulses from the circuit at the main frequency.

These pulses are applied as reset pulses to the ramp generator 56 of another missed pulse detector 58.

The output of this ramp generator is provided to a comparator 60, and the combination operates similarly to the previous ramp generator 38 and comparator 40, respectively.

However, whereas the previous ramp generator 38 is reset every 20 milliseconds (at 50 Hz), the ramp generator 56 is reset every 10 milliseconds.

Thus, if the weld is terminated by the internal timer 24 (FIG. 1), the two missed pulse detectors will "race".
The condition then occurs, but since the reset pulse is no longer supplied to the ramp generator 56 before the reset pulse is no longer supplied to the ramp generator 38, the lamp The output of generator 56 will reach the reference level of the corresponding comparator.

Therefore, before the missed pulse detector 36 operates, the missed pulse detector 58 drives the timer circuit 62 (which has the same function as the timer circuit 44), which results in an acoustic sound being emitted from the speaker 64 and a visual alarm being emitted from the light source 66. Emitted.

Timers 44 and 62 are actually two halves of a single circuit and are cross-coupled so that they are not driven simultaneously.

Therefore, when timer 44 operates with a resistive response unit, timer 62 will not indicate that the weld is suspect, and vice versa.

The output of the low-pass filter 26 is the Schmitt trigger circuit 6
8 to the four-stage shift register 70.

The output of the third stage, Q3, operates a switch circuit connected to the peak detector, which prevents the detector from operating during the first two cycles, thereby causing false peak values given during transient conditions. avoids detection.

The output Q4 of the fourth stage drives timer circuits 44 and 62.

When the miss pulse detector 58 detects termination of the welding power source, a reset signal is sent from the detector 58 to the shift register 7.
Applied to 0.

The second stage of shift register 70 feeds an amplifier 72 connected to light source 74 .

If the light source 74 does not turn on after the second cycle, it means that the electrodes are connected in the wrong phase.

The four-role shift register has three information lines: data, clock, and reset.

Data is provided by Schmitt trigger circuit 54 and clock is provided by Schmitt trigger circuit 68.

Therefore, the shift register operates only when the data is high during the presence of a clock pulse and when a reset is applied.

These conditions allow the shift register to operate correctly.

If a control unit such as that described in FIG. This will be done by a timer.

If the welder is cut off by the internal timer, the missed pulse detector 58 will detect this and indicate that the weld is questionable.

Figures 3A and 3B are operation time charts for the configuration shown in Figure 2. Figure 3A shows the case where welding is terminated by a resistance response between the electrodes, and Figure 3B shows the case where welding is terminated by the internal timer of the welding machine. Indicates the case where it will be terminated.

First, the waveforms of each part of the configuration shown in FIG. 2 will be explained with reference to FIG. 3A.

Waveform a shows the output voltage of the low-pass filter 26.

Further, the waveform a can be seen as the output waveform of the main compensation division circuit 28.

That is, the circuit 28 simply adjusts the voltage amplitude to compensate for variations in the supply voltage, as described above.

This voltage amplitude represents the resistance value between the electrodes.

Note that for purposes of illustration, the number of cycles in the AC waveform is reduced, and the initial resistance drop is shown over a longer period of time than usual.

The reason for the resistance fluctuation is as follows.

First, when two metals to be bonded are placed between electrodes, their surfaces are not completely flat, and therefore uniform contact cannot be obtained over the entire surface between the electrodes.

During the first part of the alternating current (usually no more than one cycle) the surface irregularities are smoothed out to give a good contact;
This reduces the resistance between the electrodes.

Over several cycles the metal is heated and this causes a slight increase in resistance.

Thereafter, the contact resistance decreases over the remainder of the welding process due to the larger contact area as the welding process progresses.

Waveform C shows the output of low-pass filter 22, ie, the filtered mains (supply) voltage.

The main supply voltage is shown slightly ahead of the electrode voltage (waveform a).

The reason for this is related to the operation of the main compensation divider and shift register, which are not so relevant to the essential requirements of the invention.

The filtered mains voltage at the output of the low-pass filter 22 is applied directly to a Schmitt trigger circuit 54, which outputs waveforms d and e.

Waveform d is applied to data input D of shift register 70.

Clock input C of shift register 70 is provided by a Schmitt trigger circuit 68 which receives a filtered electrode voltage.

The output of Schmitt trigger circuit 68 is shown by waveform b.

The voltages at each stage of the shift register are indicated by f, g, h, and i.

Returning to the electrode voltage, waveform a is provided to the peak detector 30.

Detector 30 is prevented from operating during the first two cycles of the AC waveform by the shift register (output Q3).

The output of peak detector 30 is shown as a solid line in waveform j and rises to that value after two cycles of waveform a.

In waveform j, the peak value increases during the next two cycles due to the increase in resistance as the metal is heated.

In the waveform j, a value decreased to a predetermined value by the slider of the potentiometer 32 is shown by a broken line.

This dashed output goes to comparator 34 where it is compared with waveform a.

The comparison result output of the comparator 34 is shown by a waveform K.

This waveform K includes pulses until the peak value of waveform a becomes equal to or less than the value of the broken line of waveform j.

Waveform l shows the output of ramp generator 38 and the potentiometer 420 reference level.

The ramp generator 38 is reset by the output k of the comparator 34 and reaches the reference level only when the pulses of the comparator 34 disappear, ie when the electrode voltage falls below a predetermined voltage.

If this condition occurs, the miss pulse detector 36 will drop as shown by waveform m, thereby stopping the welding machine.

In the above example, the welding machine is switched off with a decrease in resistance, resulting in a better weld.

As a result of the reduction in resistance, the circuits shown at 56-66 are not used.

A missed pulse detector 58 with a ramp generator 56 and a comparator 60 is similar to the previous missed pulse detector 36 except that the ramp generator 56 is reset at each waveform d and e, i.e. twice the frequency of the supply voltage. It works in the same way.

The output n of the ramp generator 56 does not reach the reference voltage until the supply voltage is turned off.

If the welding machine is switched off by a decrease in resistance, then the switch. Since the off is done by the missed pulse detector 36, waveform 0 representing the output of another missed pulse detector 58 is of no relevance.

Shift register 70 prevents operation of peak detector 30 until the third cycle of AC voltage a, as described above, and prevents circuits 30-40 from operating for resistance drops during the first two cycles. There is.

Output Q4 of shift register 70 prevents timer circuits 44 and 62 from operating before the fourth cycle of AC voltage.

Output Q2 also provides an indication if the electrodes are coupled out of phase, as discussed above.

FIG. 3B shows a case where the resistance value between the electrodes does not decrease to a predetermined value within a predetermined time.

In this case, an internal timer (waveform q) of the welding machine turns off the supply voltage after a predetermined time has elapsed.

Since the ramp generator 56 is reset every half cycle, its output waveform n is compared with the ramp reference voltage, and before the ramp voltage waveform 1 of the previous ramp generator 38 exceeds that reference voltage, the ramp generator The waveform n of the ramp voltage 56 exceeds the reference voltage.

This causes the output of miss pulse detector 58 to drop (waveform o), and before circuits 44 to 48 are activated, circuits 62 to 66 (waveform p), which indicate that welding is suspicious, are activated.

As a result, 64 and 66 indicate that the welding may have failed.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a supply circuit of a welding machine to which a control device of the present invention is connected, FIG. 2 is a circuit diagram of a control unit according to the present invention, and FIGS. 3A and 3B are operation of the circuit of FIG. 2. A time chart is shown. 19...Welding electric steel 24...Internal timer, 38...First lamp generator, 40...First comparator, 56...Second lamp generator, 60...Second comparator.

Claims (1)

[Scope of Claims] 1. Resistance welding comprising a switching means for controlling application of an alternating current to a welding electrode, and an internal timer for driving the switching means to cut off the welding current after a predetermined number of cycles. In order to detect a predetermined resistance drop of a member inserted between the electrodes by detecting the voltage between the electrodes, and operate the switching means upon this detection to stop the supply of welding current to the electrodes. , a resistance response first detection means operating once in each cycle of the welding current waveform;
A resistance welding apparatus comprising: display means for displaying a suspicious weld when the welding is not completed by the resistance response first detection means and is terminated by the internal timer, the supply waveform between the switching means and the electrode; supplying current between said switching means and the electrode for detecting the termination of said switching means and said electrode for driving said indicating means for indicating said suspicious welding if said resistively responsive first sensing means is not yet activated at said termination; a second detection means responsive to the waveform, the second detection means operating a plurality of times during each cycle of the welding current waveform to detect the presence or absence of the supply waveform; The voltage drop across the electrodes caused by the termination of the waveform is expressed as the first resistive response.
The second detection means detects the welding device before the detection means detects it, and the display means is driven by the output thereof, and the display means is driven only when the welding is completed by an internal timer. Resistance welding equipment. 2 Used in a resistance welding machine equipped with a switching means for controlling the application of alternating current to the welding electrode, and an internal timer for driving the switching means to cut off the welding current after a predetermined number of cycles; By detecting the voltage between the electrodes, a predetermined resistance drop of the member inserted between the electrodes is detected, and upon this detection, the switching means is operated to stop supplying the welding current to the electrodes. a resistance-responsive first detection means that operates once per cycle;
A resistance welding apparatus comprising: display means for displaying a suspicious weld when the welding is not completed by the resistance response first detection means and is terminated by the internal timer, the supply waveform between the switching means and the electrode; supplying current between said switching means and the electrode for detecting the termination of said switching means and said electrode for driving said indicating means for indicating said suspicious welding if said resistively responsive first sensing means is not yet activated at said termination; a second sensing means responsive to the waveform, said second sensing means operating a plurality of times during each cycle of the welding current waveform to detect the presence or absence of a supply waveform; Before the resistance response first detection means detects the voltage drop between the electrodes caused by the termination of the supply waveform, the second detection means detects the voltage drop between the electrodes caused by the termination of the supply waveform, and the output thereof drives the display means to indicate the end of welding using an internal timer. activating said indicating means only when the resistive responsive first sensing means is connected to a ramp generator, once for each cycle of said electrode voltage waveform if the peak of said electrode voltage waveform exceeds a reference level; means for resetting the lamp generator; and a comparator for indicating that the lamp generator is not reset to terminate welding when the output of the lamp generator exceeds another reference level; 2 sensing means drive another lamp generator, a circuit for resetting said another lamp generator twice in each cycle while a supply waveform is applied, and an indicating means for indicating said suspicious weld. and a comparator for driving the display means in response to the output of the another lamp generator exceeding a reference level.