KR19990038035A - Inverter Type Welding Power Supply - Google Patents

Abstract

The rising characteristic of the current in the large welding current range is improved, and the ripple component in the small welding current range is minimized.

In the inverter welding power supply device to be supplied to the object to be welded 15, a welding current setting circuit 18 for setting a welding current supplied to the object to be welded 15, and a current or a welding transformer flowing through the inverter circuit 12. The current detector 16 which detects the current flowing to the primary side and the set value of the welding current setting means 18 and the detected value detected by the current detector 16 are compared, and when the detected value reaches the set value, a coincidence signal is output. Pulse width control to turn off the current by the comparison circuit 17, the gate circuit 19 which prohibits the output of the comparison circuit 17 for a predetermined time according to the set current, and the coincidence signal passing through the gate circuit 19. The circuit 20 and the polarity inversion circuit 21 which inverts the pulse signal from the pulse width control circuit 20 and outputs it to the inverter circuit 12 were comprised.

Description

Inverter Type Welding Power Supply

The present invention relates to an inverter type welding power supply for use in resistance welding, and more particularly, to improve the rising characteristic of the current in the large welding current range, and to minimize the ripple component in the small welding current range. An inverter welding power supply device can be provided.

Inverter type welding power supply device used in conventional resistance welding machine converts commercial alternating current into direct current, and converts the direct current into high frequency pulse type high frequency alternating current by inverter to flow to the primary side of the welding transformer, The current for welding induced on the secondary side is rectified by a rectifying element and supplied to the welded object through the welding electrode.

In the conventional inverter type welding power supply device, a pulse type high frequency alternating current having a pulse width modulated by the inverter is input to the welding transformer to generate a current for welding. Since the pulse width of the high frequency current is relatively large and the rest period corresponding to the pulses is small, the ripple portion of the welding current supplied to the welded object is small.

However, when the welding current decreases, the ratio of the time for which the pulse current flows within a certain period becomes small, and the ratio of the rest period during which the pulse current does not flow becomes large. Therefore, the pulse type high frequency current having a small pulse width is used for welding transformer. Even if it inputs into and produces the electric current for welding, the ripple of this welding current is large and there exists a problem which adversely affects welding.

Fig. 9 is an explanatory waveform diagram showing a generation form of ripple in the conventional small current region, and Fig. 9A shows a current flowing to the primary side of the welding transformer by switching the inverter to a gate signal of a constant frequency. 9B shows the current waveform flowing through the inverter by switching the inverter, and FIG. 9C shows the secondary side by flowing the current of FIG. 9A to the primary side of the welding transformer. Is a welding current waveform when the welding current induced by the rectifying element is rectified, and the ripple component of the welding current becomes large as is apparent from FIG. 9 (C).

On the other hand, when the welding current is viewed from the viewpoint of waveform control, in consideration of the recent diversification of the welded object, the up-slope portion, as well as the decay control, the wave control (down slope) method, Alternatively, a resistance welding machine capable of controlling waveforms of various welding currents such as flowing a welding current with a steep rise after securing an energization path with a preheat is desired.

However, in the conventional so-called pulse width modulation type welding power supply device in which the pulse width is changed at a constant frequency as described above, the polarity continuously changes before reaching the target current, and furthermore, the time for the rise of the current from the frequency is increased. As a result, there is a limit in rapidly changing the welding current, and as described above, a resistance welding machine capable of controlling the waveform of various welding currents cannot be realized.

Fig. 10 is an explanatory waveform diagram showing the current rise situation in the conventional high current range, and Fig. 10A shows the primary side of the welding transformer by switching the inverter to a pulse width controlled gate signal of a constant frequency. 10C shows an actual welding current waveform when it takes time to raise the welding current, and FIG. 10D shows an abnormal welding current waveform.

As is apparent from this FIG. 10, the actual welding current rises slowly as shown in FIG. 10 (C), and the welding current as shown in FIG. 10 (D) does not rise sharply.

In addition, in the case of welding in which the to-be-welded material is limited and the current range is limited, an inverter power source of a constant frequency may be selected accordingly.

In recent years, however, various welded objects are mixed, and a welding transformer mounted on a robot or the like can be used in a wide range from small current to large current in response to a large number of welding conditions. In this case, however, the inverter power source is selected in accordance with the large current required by the system. Therefore, in the case of a small current, the ratio of the pulse on / off period is small and the ripple component has a large welding current.

In addition, when a welding current with a steep rise characteristic is required, there is a limit to the rise speed limited by the frequency, and the control frequency may be lowered to advance this, but in this case, the ripple component in the small current range increases. There is a conflicting problem.

The present invention has been made in view of the above circumstances, and an object of the present invention is to improve the rise characteristic of a current in a large welding current range and to minimize the ripple component in a small welding current range. The present invention provides a welding power supply device.

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a configuration diagram of an entire inverter-type welding power supply device showing a first embodiment according to the present invention.

FIG. 2 is a circuit diagram showing a specific example of the comparison circuit, gate circuit, pulse width control circuit, CPU, and welding current setting circuit in FIG. 1; FIG.

FIG. 3 is a circuit diagram showing a specific example of a comparison circuit, a polarity inversion circuit including a pulse width control circuit, and a timing signal generation circuit in FIG.

Fig. 4 is a diagram showing an example of a setting table of a prohibition time, a rest time, and a maximum allowable time for each set current value in the embodiment of the present invention.

Fig. 5 is a time chart for explaining the operation of the inverter type welding power supply device according to the first embodiment of the present invention.

Fig. 6 is a current waveform diagram obtained by automatically controlling the switching frequency of a power transistor for an inverter circuit in accordance with the magnitude of a welding current in the first embodiment of the present invention.

Fig. 7 is a timing diagram of generation of the primary side current waveform of the welding transformer in the first embodiment of the present invention.

Fig. 8 is a configuration diagram of essential parts of an inverter type welding power supply device in a second embodiment of the present invention.

Fig. 9 is an explanatory waveform diagram showing a generation form of ripple in a conventional small current region.

10 is an explanatory waveform diagram showing a situation of current rise in a conventional large current region.

<Description of Symbols for Main Parts of Drawings>

10: rectifier circuit, 12: inverter circuit, 13: welding transformer, 13A: primary winding, 13B: secondary winding, 15: welded object, 16: current detector (current detection means), 17: comparison circuit (comparative means) 18: welding current setting circuit (welding current setting means), 181: DA converter, 19: gate circuit, 20: pulse width control circuit, 21: polarity inversion circuit, 22: timing signal generating circuit, 221: prohibition time counter, 222: idle time counter, 224: maximum allowable time counter, 23: drive circuit, 24: CPU, 25: RAM, 26: current detector (current detection means), 28: welding current detector (welding current detection means), 29: Voltage detector (voltage detection means), 30, 31: waveform shaping circuit, 32: AD converter.

The invention of claim 1 for achieving the above object is an inverter circuit for converting a direct current rectified from commercial alternating current into a high frequency alternating current, and a high frequency alternating current converted from the inverter circuit flows to the primary side of the welding transformer, thereby An inverter type welding power supply for rectifying the induced welding current by a rectifying element and supplying it to a welded object through a welding electrode, comprising: welding current setting means for setting a welding current value supplied to the welded object; The current detection means for detecting the flowing current or the current flowing in the primary side of the welding transformer and the welding current value set by the welding current setting means and the detected value detected by the current detection means are compared to the set welding current value. Comparison means for outputting a coincidence signal when it arrives, the time at which the welding start command is issued, and the pulse width of the pulse width control circuit. The gate circuit prohibits the sending of the coincidence signal from the comparing means for a predetermined time set in accordance with the welding current value from the time of the falling down of the signal, and permits the sending of the coincidence signal after the predetermined prohibition time elapses. And inverts to a low level at the time of sending out the coincidence signal transmitted from the comparing means through the gate circuit, and maintains this low level state according to the welding current value to maintain a predetermined rest time and then passes the rest time. A pulse width control circuit for generating a pulse signal that is inverted to a high level and continues this high level state until the coincidence signal is sent; and a pulse signal sent from the pulse width control circuit each time the idle time elapses. Positive in the inverter circuit such that the polarity of the output of the inverter circuit is reversed by inversion. And a polarity inversion circuit alternately supplied to the negative gate.

The invention according to claim 2 further includes a timing signal generation circuit for supplying a timing signal for control to the gate circuit, the pulse width control circuit and the polarity inversion circuit.

In the present invention, the coincidence signal output from the comparing means is controlled by controlling the coincidence signal output from the comparing means by controlling the gate circuit with the gate control signal having the prohibition time from the timing signal generating circuit. The polarity of the pulse signal from the pulse width control circuit sent to the polarity inversion circuit is guaranteed, while ensuring the minimum on-time corresponding to the set current value, excluding the effect of overshoot and noise of the current detecting means to the quasi change. The idle time required for reversing can also be changed with respect to the set current value, thereby ensuring an optimum time.

Therefore, since the set value is low in the small current region of the welding current, the period during which the inverter circuit is turned on is short, and the set value is high in the large current region of the welding current, and the period during which the inverter circuit is turned on is large. As a result, the switching frequency of the inverter circuit is controlled to be high in the small current region of the welding current, and the switching frequency of the inverter circuit is controlled to be lowered in the large current region of the welding current. Thereby, the rise characteristic of the electric current in a large welding current range can be improved, and the ripple component in a small welding current range can be minimized.

The invention according to claim 3 is characterized in that the output signal of the pulse width control circuit is forcibly turned off after the maximum allowable time has elapsed when the coincidence signal is not output within the preset maximum allowable time.

In the present invention, when the maximum allowable time has elapsed, the output signal of the pulse width control circuit is forcibly turned off and the polarity is inverted. Thus, a state in which the welding current is difficult to flow due to a problem in the secondary circuit including the welded object is caused. It is not left for a long time, and steep rise of primary current can be prevented beforehand.

In the invention according to claim 4, the timing signal generation circuit is cleared by a signal at the time of falling of the pulse signal from the pulse width control circuit or at the time when the welding start command is issued, and the welding current value from the time at which the welding start command is issued. A prohibition time counter for counting a predetermined prohibition time set in accordance with the above-described method, and transmitting a gate control signal of the gate circuit that maintains an output at a low level until the count value reaches a predetermined prohibition time, and the pulse width; Cleared by a signal at the time of falling of a pulse signal from the control circuit or a signal at which a welding start command is issued, the predetermined idle time set in accordance with the welding current value is counted from the time at which the welding start command is issued, and this count value is a predetermined value. The operation timing of the pulse width control circuit and the polarity inversion circuit are controlled by the signal output when the idle time is reached. It is cleared by the idle time counter and the signal at the time of falling of the pulse signal from the pulse width control circuit or the time at which the welding start command is issued, and the maximum preset in accordance with the welding current value from the time at which the welding start command is issued. And a maximum allowable time counter which counts the allowable time, outputs a signal to be output when the count value reaches the maximum allowable time, and forcibly turns off the output signal of the pulse width control circuit. .

In the present invention, the provision of the prohibition time counter facilitates the setting of the prohibition time data in accordance with the welding current value, and the provision of the rest time counter facilitates the setting of the rest time data in accordance with the welding current value and the maximum allowable time. By providing a counter, it is easy to set the maximum allowable time data according to the welding current value, and also the optimum timing can always be ensured even for the set current value that changes with time.

According to the invention described in claim 5, the comparison circuit compares only one polarity of the primary current of the welding transformer, stores the pulse width at that time, and stores the pulse on the polarity side in which the comparison circuit is not operated. The drive circuit is operated with a pulse width, so that the pulse width of the primary current of the welding transformer is positive and negative.

In the present invention, the unbalance caused by the polarity of the primary current of the welding transformer can be eliminated, and the preventive effect can also be exhibited against the horseshoe.

Invention of Claim 6 has welding current detection means which detects the welding current which flows into the secondary side of the said welding transformer, The detection value of this welding current detection means is converted into a digital signal, and it compares with the preset value, This detection And the set value of the welding current setting means is changed so that the deviation between the set value and the set value becomes zero.

In the present invention, the welding current can be controlled using the turn ratio of the welding transformer as a coefficient.

Invention of Claim 7 has voltage detection means which detects the voltage between the said welding electrodes, and converts the detected value of this voltage detection means into a digital signal, compares it with the preset value, and the deviation of this detection value and a set value is zero. Characterized in that for changing the set value of the welding current setting means to

In the present invention, the voltage between the welding electrodes can be controlled by using the turns ratio of the weld transformer and the resistance value of the welded object as coefficients.

According to the invention described in claim 8, the electric power, which is the product of the detection value of the welding current detection means and the detection value of the voltage detection means, is converted into a digital signal and compared with a preset value, and the deviation between the detection value and the setting value is zero. The setting value of the setting means is changed so that

In the present invention, the number of turns of the weld transformer and the resistance value of the welded object can be used as coefficients to control the power which is the product of the voltage and the current.

Next, embodiments of the present invention will be described with reference to the drawings.

1 is a configuration diagram of an entire inverter-type welding power supply apparatus showing a first embodiment according to the present invention. FIG. 2 is a welding including a comparison circuit, a gate circuit, a pulse width control circuit and a CPU in FIG. 3 is a circuit diagram showing a specific example of the current setting circuit, and FIG. 3 is a circuit diagram showing a specific example of the polarity inversion circuit and the timing signal generation circuit.

In Fig. 1, R, S, and T are input terminals of a three-phase AC power supply, and 10 is a rectifier circuit connected to three-phase input terminals R, S, and T. The rectifier circuit 10 provides three-phase alternating current. Full-wave rectified and converted into direct current. Denoted at 11 is a smoothing capacitor connected in parallel between the output terminals of the rectifying circuit 10, and at 12 is an inverter circuit connected at both ends of the smoothing capacitor 11 in parallel. The inverter circuit 12 converts smoothed direct current into high frequency alternating current and is configured by connecting the power transistors TR1 to TR4 to the bridge. Reference numeral 13 denotes a welding transformer, and both ends of the primary winding 13A of the welding transformer 13 are connected to the output terminal of the inverter circuit 12. One welding electrode 14A is connected to both ends of the secondary winding 13B of the welding transformer 13 via the rectifying diodes D1 and D2, and the other side of the secondary winding 13B is connected to the middle tab. Welding electrodes 14B are connected. Reference numeral 15 denotes a welded object held by the welding electrodes 14A and 14B.

In Fig. 1, reference numeral 16 denotes a current detector (current detection means) for detecting a current flowing in the inverter circuit 12 in accordance with the switching operations of the power transistors TR1 to TR4. The inverter current is converted into a voltage and input to the comparison circuit 17. 18 is a welding current setting circuit for setting a welding current supplied to the welded object 15 and generating a DC voltage proportional to the welding current, and the voltage output from the welding current setting circuit 18 is a comparison circuit. It is input to (17).

The comparison circuit 17 compares the detected voltage detected by the current detector 16 with the set voltage value set in the welding current setting circuit 18, and when the detected voltage matches the set voltage value, the matching signal is converted into a gate circuit ( Output to 19).

The gate circuit 19 prevents the coincidence signal from the current detector 16 from being transmitted from the timing signal generation circuit 22 to be described later for a predetermined time set in accordance with the welding current value. At the same time, after this predetermined prohibition time has elapsed, the constitution signal is allowed to be sent.

Numeral 20 denotes a pulse width control circuit, and the pulse width control circuit 20 inverts to a low level at the time of transmission of the coincidence signal sent out from the comparison circuit 17 through the gate circuit 19, and this low level. The state is maintained for a predetermined idle time set in accordance with the welding current value, and when the idle time elapses, the state is inverted to a high level to generate a pulse signal 20a which continues the high level state until the coincidence signal is sent out. . This pulse signal 20a is supplied to the polarity inversion circuit 21.

The polarity inversion circuit 21 inverts the pulse signal 20a transmitted from the pulse width control circuit 20 each time the idle time elapses so that the polarity of the output of the inverter circuit 12 is inverted. The transistors 12) are alternately supplied to the bases of the transistors TR1, TR4, TR2, and TR3.

The timing signal generation circuit 22 controls the gate circuit 19, the pulse width control circuit 20, and the polarity inversion circuit 21 at the optimum timing for welding, and is generated from the timing signal generation circuit 22. Power transistors TR1 to TR4 of the inverter circuit 12 by supplying the respective timing signals to the gate circuit 19, the pulse width control circuit 20, and the polarity inversion circuit 21, and controlling them at optimum timings. The signal for driving X is output to the driving circuit 23.

In Fig. 2, the comparison circuit 17 is composed of an operational amplifier. The detection voltage VIN of the current detector 16 is input to the non-inverting input terminal of the operational amplifier 17, and the set voltage VF output from the DA converter 181 is input to the inverting input terminal of the operational amplifier 17. do.

The gate circuit 19 is constituted by an AND gate having one input of the coincidence signal from the comparison circuit 17, and the gate control signal sent from the timing signal generation circuit 22 to the other input terminal of the AND gate. 22a is input. The gate control signal 22a is for holding the AND gate in the OFF state for a predetermined time set in accordance with the welding current value from the time when the welding start command is issued. The overshoot of the current detector 16 is started in accordance with the start of welding. (B) The transmission of the coincidence signal due to a malfunction when a current exceeding the set value of the welding current setting circuit 18 is detected by noise momentarily is prohibited, and the welding current is not turned off in a very short time. After the predetermined time elapses, the AND gate is opened, and the coincidence signal from the comparison circuit 17 is output to the pulse width control circuit 20 when the welding current reaches the set value.

The pulse width control circuit 20 is constituted by a D flip flop, which is set by a preset signal 22b transmitted from the timing signal generation circuit 22, and the Q of the D flip flop from this point in time. Inverts the output to a high level, and generates a pulse signal 20a that inverts the Q output to a low level when the coincidence signal sent from the comparison circuit 17 through the gate circuit 19 is input as a clock. Output This D 'flip-flop is cleared every time the welding start signal 22c transmitted from the timing signal generation circuit 22 is applied.

The CPU 24 controls the inverter circuit 12. The CPU 24 has a function of the timing signal generation circuit 22, and the CPU 22 includes a drive circuit 23 for driving the power transistors TR1 to TR4. Waveform control of various welding currents, such as being connected, and the upslope portion is supplied with two-stage energization, decay control or phasing control (downslope) method, or a preheating current flow path, and then a steeply rising welding current flows. RAM 25 for storing welding current setting data is connected, and the welding current setting data read out from the RAM 25 by the welding current setting command is input to the DA converter 181 via the CPU 24. do.

The D-A converter 181, the CPU 24, and the RAM 25 constitute the welding current setting circuit 18. As shown in FIG.

In Fig. 3, the polarity inversion circuit 21 has a D flip-flop 211 whose clock is the preset signal 22a transmitted from the timing signal generation circuit 22, and a Q output of the D flip-flop 211. Is one input, the AND gate 212 having the pulse signal 20a from the pulse width control circuit 20 as the other input, and the NOT gate for inverting the Q output of the D flip-flop 211. And an AND gate 214 which uses the output of the 213 as one input and the pulse signal 20a from the pulse width control circuit 20 as the other input.

The timing signal generation circuit 22 is cleared by the signal at the time when the pulse signal 20a from the pulse width control circuit 20 falls or when the welding start command is issued, and the welding is started from the time when the welding start command is issued. A prohibition time counter 221 for counting a predetermined prohibition time set in accordance with the current value, and outputting a gate control signal 22a for keeping the output at a low level until the count value reaches a predetermined prohibition time, and a pulse; The predetermined pause time is cleared by the falling time of the pulse signal 20a from the width control circuit 20 or by the signal at the time when the welding start command is issued, and set according to the welding current value from the time at which the welding start command is issued. When the count value reaches a predetermined idle time, the idle time counter 222 which outputs a signal and the signal from the idle time counter 222 are inverted to obtain a pulse width as a preset signal. To the NOT gate 223 output to the control circuit 20 and the polarity inversion circuit 21, and to the signal at the time when the pulse signal 20a from the pulse width control circuit 20 falls or when a welding start command is issued. The maximum allowable time counter 224 and the maximum allowable time are cleared by counting the maximum allowable time set in accordance with the welding current value from the time when the welding start command is issued and outputting a signal when the count value reaches the maximum allowable time. And a NOR gate 225 for inverting the signal from the counter 224 and outputting it to the pulse width control circuit 20 as a clear signal 22c and forcibly turning off the output signal of the pulse width control circuit 20. have.

Further, the timing signal generation circuit 22 includes a differential circuit 226 for detecting the fall of the welding start command signal, a differential circuit 227 for detecting the fall of the pulse signal of the pulse width control circuit 20, and the differential circuit. A NOR gate 228 is provided which inverts the output signals of 226 and 227 and supplies them to the counters 221, 222 and 224 as clear signals.

The prohibition time setting data of the prohibition time counter 221, the rest time setting data of the rest time counter 222, and the maximum allowable time setting data of the maximum allowable time counter 224 are from the RAM 25 to the CPU 24 and the like. The counters 221, 222, and 224 are preset via the data bus 241.

As shown in FIG. 4, the prohibition time setting data of the prohibition time counter 221, the rest time setting data of the rest time counter 222, and the maximum allowable time setting data of the maximum allowable time counter 224 are various types of welding. It is configured in a table set according to the current value, and is preset in the respective counters 221, 222 and 224 by selectively reading out each set data from the table in accordance with the welding current value.

Next, operation | movement of this embodiment comprised as mentioned above is demonstrated with reference to FIG.

First, a set value of a welding current required for welding the object to be welded 15 is set in the welding current setting circuit 18. In this case, a welding current setting command is input by operating an input device (not shown) of the CPU 24, and the welding current setting data according to the setting command is read out from the RAM 23 and input to the DA converter 181. From the DA converter 181, the DC voltage VF for the set value of the waveform shown in FIG. 2, which is proportional to the welding current, is output and input to the comparison circuit 17.

In the initial state in which no current flows in the inverter circuit 12, the output of the current detector 16 is 0V, and the output of the comparison circuit 17 is also 0V, that is, the "L" level.

In this state, when the welding start command signal (see FIG. 5 (A)) is input by operating the input device (not shown), the pulse width control circuit (B) by the clear signal 22c from the timing signal generation circuit 22 is performed. The D flip-flop of 20) is cleared, and the counters 221, 222, and 224 are cleared by the clear signal from the differential circuit 226 (see Fig. 5B), and the count is started by the clock. . Accordingly, when the count value of the idle time counter 222 reaches the idle time set value T2 as shown in Fig. 5C, the preset signal 22b shown in Fig. 5D is sent out, and this preset is performed. The signal 22b is preset by being applied to the D flip flop of the pulse width control circuit 20, so that the Q output of the D flip flop, i.e., the pulse signal 20a of the pulse width control circuit 20 is shown in FIG. As shown in Fig. 1), the level is set to the "H" level. The pulse signal 20a is output to the drive circuit 23 through the polarity inversion circuit 21, and drives the inverter circuit 12 by this drive circuit 23.

On the other hand, the prohibition time counter 221 counts the predetermined prohibition time T3 set in accordance with the welding current value from the time point cleared by the welding start command, and outputs it until this count value reaches the predetermined prohibition time T3. From the time point at which the prohibition time T3 has elapsed (see Fig. 5C), the coincidence signal is sent, and the Q output of the pulse width control circuit 20 is inverted to a low level. Gate control signal 22a shown in Fig. 5F is outputted, and the gate control signal 22a is input to the gate circuit 19 until the output remains high level until?

After the prohibition time T3 has elapsed, when the inverter current reaches the set value of the DA converter circuit 181 as shown in Fig. 5G, the matching signal shown in Fig. 5H is output from the comparison circuit 17. . When this coincidence signal is input to the pulse width control circuit 20 through the gate circuit 19, the pulse signal 20a is inverted to a low level as shown in Fig. 5E. Accordingly, the inverter current is also turned off as shown in Fig. 5G. At the same time, when the pulse signal 20a is inverted to the low level, the counters 221, 222, and 224 are cleared by the signal from the differential circuit 227 that differentiates the fall, and the count is started again by the clock. Accordingly, when the count value of the idle time counter 222 reaches the idle time T2 as shown in Fig. 5C, the preset signal 22b shown in Fig. 5D is sent out, and this preset signal 22b Is applied to the D flip flop of the pulse width control circuit 20, and the Q output of the D flip flop, i.e., the pulse signal 20a of the pulse width control circuit 20 is shown in FIG. As shown, it goes back to the "H" level. Next, the same operation is repeated.

By the above operation, when the pulse signal 20a from the pulse width control circuit 20 shown in FIG. 5E is applied to the polarity inversion circuit 21, the Q output of the D flip-flop 211 is shown in FIG. As shown in Fig. 5J, the output of the AND gate 212 is shown in Fig. 5K, and the output of the AND gate 214 is shown in Fig. 5L.

As a result, the signals shown in FIGS. 5 (K) and 5 (L) are outputted to the drive circuit 23, so that the power transistors TR1 and TR4 and the power transistors TR2 and TR3 of the inverter circuit 12 are alternately turned on. The inverter current is turned off so that the path of the primary winding 13A, the power transistor TR4 rectifier circuit 10 of the rectifier circuit 10, power transistor TR1 welding transistor 13, or the rectifier circuit 10, power transistor TR3 The primary winding 13A of the welding transformer 13 flows in the path of the power transistor TR2 rectifier circuit 10, and when this current starts to flow, the output voltage of the current detector 16 rises.

Here, the circuit including the welding transformer 13, the welding electrodes 14A and 14B, and the object to be welded 15 can be approximated by the RL series circuit of the resistance R and the inductance L, so that the inverter circuit 12 The inverter current flowing in the flow rises to the time constant at L / R. When the output voltage VIN of the current detector 16 matches the DC voltage VF of the D-A converter 181, the matching signal is output from the comparison circuit 17, and the above-described operation is repeated. In addition, such operation | movement is repeatedly performed until reaching the electricity supply time set according to the to-be-welded object 15. FIG.

In addition, since the snubber circuits not shown are added to the power transistors TR1, TR4, TR2, and TR3, the spike voltages when these power transistors are turned off are absorbed by the snubber circuit, and a steady off state is obtained. It becomes

Next, the comparison circuit 17 is operated only for one polarity according to claim 5, the output pulse width at that time is stored, and the other polarity side will be described in the manner of driving with the same pulse width.

When the start command is input from the input device, the CPU 24 inputs a preset signal to the D flip flop of the pulse width control circuit 20, and simultaneously starts a pulse width measurement counter (not shown) as an up count. . The drive circuit 23 outputs signals for turning on the power transistors TR1 and TR4 and turning off the power transistors TR2 and TR3. As a result, current begins to flow in the primary winding of the welding transformer 13, and when the current value reaches a set value, a coincidence signal is output from the comparison circuit 17.

At this time, since the gate circuit 19 is opened by the gate control signal from the CPU 24, the coincidence signal from the comparison circuit 17 is input to the D flip flop of the pulse width control circuit 20. The signal of the pulse width determined by inverting the Q output from the high level to the low level is output to the CPU 24.

When the pulse signal is inverted to the low level, the pulse width measuring counter stops, and the operation proceeds to the operation of the timing signal generation circuit 22, and the power transistors TR1 and TR4 are turned off. After the rest time T2 for stably inverting the inverter circuit 12 is secured, a signal for turning on the power transistors TR2 and TR3 is output to the drive circuit 23. At the same time, the previously used pulse width measuring counter is set to a down count, and then down counted sequentially from the count value in which the signal of the previous pulse width is measured, and the power transistors TR2 and TR3 are turned off at the time of zero.

After the rest time T2 for stably inverting the inverter circuit 12 is secured, the D flip-flop of the pulse width control circuit 20 is preset, the gate circuit 19 is opened, and the pulse width measurement is performed again. Start the counter as an up counter, and turn on the power transistors TR1 and TR4.

Next, the same operation is repeatedly performed until the energization time set in accordance with the object to be welded 15 is reached.

Next, the case where the inverter current does not rise to the specified welding current value within a predetermined time due to an abnormality on the secondary side including the to-be-welded material 15, and the coincidence signal is not output from the comparison circuit 17 will be described. do.

In this case, as shown in the abnormal period on the secondary side in Fig. 5, the maximum allowable time counter 224 is provided with the falling time or welding start command of the pulse signal 20a from the pulse width control circuit 20. Cleared by the signal at the time point, the preset maximum allowable time T4 is counted according to the welding current value from the time when the welding start command is issued, and when the count value reaches the maximum allowable time T4, the signal shown in Fig. 5 (I) is obtained. Send it out. By applying this signal to the pulse width control circuit 20 as a clear signal 22c, the output signal of the pulse width control circuit 20 is forcibly turned off.

As a result, the state in which the welding current becomes difficult to flow for a long time due to the problem of the secondary circuit including the to-be-welded material can be prevented from being left for a long time, and a sudden rise in the primary current can be prevented in advance.

FIG. 7 compares the set voltage VF proportional to the welding current and the detection voltage VIN proportional to the inverter current from the current detector 16 with the comparison circuit 17, and the power transistors of the inverter circuit 12 at the same time point. The timing of generation of the primary side current waveform of the welding transistor 13 obtained by turning off the power transistors TR2 and TR3 after turning off the TR1 and TR4 and leaving the idle time T2.

In Fig. 7, T1 is an on period of the power transistor, and T2 is an off period (rest period). In addition, T3 prevents the transmission of the coincidence signal even when the coincidence signal is transmitted because the current value detected by the current detector 16 exceeds the set value due to an overshoot or noise during the rise of the weld current. By applying the gate control signal having this prohibition time T3 to the gate circuit 19, the overshoot and the malfunction caused by noise are prevented when the welding current rises, and the minimum on time for each polarity is prevented. Secure.

In addition, when such a substantially rectangular current flows to the primary side of the welding transformer 13, the welding current of the same waveform is induced on the secondary side of the welding transformer 13, and this current is rectified by the diodes D1 and D2 and welded. The to-be-welded object 15 is supplied through the electrodes 14A and 14B, and the to-be-welded object 15 is welded.

Next, the case where the welding current changes with the passage of time will be described.

In this case, the welding current setting command is input by operating the input device (not shown) of the CPU 24, and the welding current setting data which changes with the passage of time according to this setting command is read out from the RAM 25. It inputs to DA converter 181, and outputs DC voltage VF for the set value of the waveform which is proportional to the welding current which changes with the passage of time from this DA converter 181, and inputs it to the comparison circuit 17. As shown in FIG.

In the comparison circuit 17, the set voltage VF of the waveform proportional to the welding current which changes with the passage of time and the detection voltage VIN proportional to the inverter current from the current detector 16 are compared, and the detection voltage VIN is set. When the voltage VF coincides, the coincidence signal is output from the current detector 16 to the gate circuit 19 and the pulse width control circuit 20. As a result, the drive circuit 23 is operated by outputting the pulse signal generated by the pulse width control circuit 20 to the polarity inversion circuit 21 to operate the inverter circuit 12. When the detection current VIN reaches the set voltage VF, the output current of the inverter circuit 12 is in a state where the idle time T2 is secured from the positive polarity to the negative polarity, or from the negative polarity to the positive polarity. Invert

Therefore, since the set voltage VF is low in the low current range of the welding current, the period T1 during which the power transistors TR1, TR4 or TR2, TR3 of the inverter circuit 12 are turned on becomes small, and in the high current range of the welding current, Since the voltage VF is high, the period T1 during which the power transistors TR1, TR4 or TR2, TR3 of the inverter circuit 12 turns on becomes large.

That is, the switching frequency of the power transistor for the inverter circuit is increased in the low current region of the welding current, and the switching frequency of the power transistor is controlled in the high current region of the welding current.

6 shows an example of the current waveform diagram obtained by automatically controlling the switching frequency of the power transistor for inverter circuit according to the magnitude of the welding current.

In FIG. 6, (A) shows the current waveform flowing to the primary side of the welding transformer, (B) shows the current waveform flowing through the inverter by switching the inverter, and (C) shows the current of (A) welding transformer. It is a welding current waveform when the current for welding induced in the secondary side is rectified by the rectifying element by flowing to the primary side of the.

As shown in Fig. 6C, the ripple component of the welding current in the small current region after rectification becomes very small, and a high quality welding current can be supplied.

In addition, even when the welding current is increased or decreased to a gentle slope type or the welding current is changed to a steep stepped shape, these welding currents can be freely set, and welding is also performed on these set values. The current can be reliably followed-controlled.

In the embodiment shown in FIG. 1, the case where the current detector 16 is arranged on the input side of the inverter circuit 12 has been described. However, the primary side current of the welding transformer 13 is applied to the output side of the inverter circuit 12. The current detector 26 to be detected is disposed, the current detected by the current detector 26 is rectified by the rectifier circuit 27, and a voltage proportional to the rectified current is input to the comparison circuit 17, thereby performing the above-mentioned. The same can be done with.

Next, the second embodiment of the present invention will be described with reference to FIG. 8.

It is a block diagram of the principal part of the inverter type welding power supply apparatus in 2nd Embodiment of this invention. In FIG. 8, the same code | symbol is attached | subjected to the same component as FIG. 1, the description is abbreviate | omitted, and a different part from FIG. 1 is demonstrated mainly.

In this second embodiment, the feature is that the welding current is controlled by using a voltage value that is the product of the welding current and the resistance of the welded object or a power that is the product of the voltage value and the welding current. .

Therefore, a voltage or power is set as a set value in the RAM 25 connected to the CPU 24. Then, by arranging the welding current detector 28 in the secondary transformer of the welding transformer 13 and connecting to the welding electrodes 14A and 14B, a voltage detector for detecting a voltage multiplied by the welding current and the resistance of the welded object ( 29), waveform welding circuits 30 and 31 are connected to the welding current detector 28 and the voltage detector 29, respectively, and detected by the welding current detector 28 by the waveform shaping circuit 30. Waveform shaping one welding current, waveform shaping the voltage detected by the voltage detector 29 by the waveform shaping circuit 31, and converting each welding current and voltage into a digital signal by the AD converter 31. Input to the CPU 24. This CPU 24 compares the setting voltage of the RAM 25 set in advance by arithmetic processing with the setting voltage or setting power, and sets the setting data to the DA converter 181 constituting the welding current setting circuit so that this deviation becomes zero. Change. Thereby, welding current can be controlled similarly to the said 1st Embodiment.

In this case, the direct control is the current of the inverter circuit 12, but the welding current or the voltage between the welding electrodes 14A and 14B is determined by counting the turn ratio of the welding transformer 13 and the resistance value of the welded object 15 as coefficients. Can be controlled. Moreover, the electric power which is the product of a voltage and a current can be controlled.

As described above, according to the present invention, the matching signal output from the comparing means is controlled by controlling the gate circuit with the gate control signal having the prohibition time from the timing signal generating circuit. The pulse signal from the pulse width control circuit sent to the polarity inversion circuit is guaranteed while ensuring the minimum on time corresponding to the set current value by eliminating the effect of overshoot and noise of the current detecting means to the steep change in the current rise. Since the idle time required for inverting the polarity is also changed with respect to the set current value, the optimum time can be ensured. Therefore, since the set value is low in the small current range of the welding current, the period during which the inverter circuit is turned on is small. In addition, since the set value is high in the large current range of the welding current, the period during which the inverter circuit is turned on is increased. . As a result, the switching frequency of the inverter circuit is controlled to be higher in the small current region of the welding current, and the switching frequency of the inverter circuit is reduced to be lower in the large current region of the welding current, thereby improving the rise characteristic of the current in the large welding current region. In addition, the ripple component in the small welding current range can be minimized.

In addition, according to the present invention, when the maximum allowable time elapses, the output signal of the pulse width control circuit is forcibly turned off and the polarity is inverted, so that the welding current is less likely to flow due to the problem of the secondary circuit including the welded object. The state is not left for a long time, and the steep rise of the primary current can be prevented in advance.

According to the present invention, the timing signal generation circuit is composed of a prohibition time counter, an idle time counter and a maximum allowable time counter, and the prohibition time counter is provided, whereby the prohibition time data can be easily set according to the welding current value. The provision of the idle time counter facilitates the setting of the idle time data according to the welding current value, and the provision of the maximum allowable time counter facilitates the setting of the maximum allowable time data according to the welding current value and changes with time. The optimum timing can always be ensured even for the set current value.

Further, according to the present invention, the comparison circuit compares only one polarity of the primary current of the welding transformer to store the pulse width at that time, and on the polarity side where the comparison circuit is not operated, the driving circuit is operated at the stored pulse width. Since the furnace is operated to make the pulse width of the primary current of the welding transformer positive and negative, the unbalance due to the polarity of the primary current of the welding transformer can be eliminated, and the prevention effect can be exerted on the horseshoe.

According to the present invention, the present invention has a welding current detecting means for detecting a welding current flowing in the secondary side of the welding transformer, and the detected value of the welding current detecting means is converted into a digital signal and compared with a preset value. By changing the set value of the welding current setting means so that the deviation between the and set value becomes zero. The welding current can be controlled by using the turn ratio of the welding transformer as a coefficient.

According to the present invention, the present invention has a voltage detecting means for detecting a voltage between welding electrodes, converts the detected value of the voltage detecting means into a digital signal, compares it with a preset value, and the deviation between the detected value and the set value is zero. By changing the set value of the welding current setting means as much as possible, the voltage between the welding electrodes can be suppressed by making the number of turns ratio of the weld transformer and the resistance value of the welded object a coefficient.

Further, according to the present invention, the power which is the product of the detected value of the welding current detecting means and the detected value of the voltage detecting means is converted into a digital signal and compared with a preset value, and the deviation between the detected value and the set value is zero. By changing the set value of the welding current setting means as much as possible, the power which is the product of the voltage and the current can be controlled by making the number of turns ratio of the weld transformer and the resistance value of the welded object a coefficient.

Claims (8)

An inverter circuit for converting a direct current rectified from commercial alternating current into a high frequency alternating current, and a high frequency alternating current converted by the inverter circuit flows to the primary side of the welding transformer, whereby a current for welding induced in the secondary side is induced. Inverter-type welding power supply for rectifying by the rectifying element and supplying to the welded object through the welding electrode, Welding current setting means for setting a welding current value supplied to the welded object; Current detecting means for detecting a current flowing in the inverter circuit or a current flowing in a primary side of the welding transformer; Comparison means for comparing a welding current value set by the welding current setting means with a detection value detected by the current detecting means and outputting a coincidence signal when the detected value reaches the set welding current value; During the predetermined time set in accordance with the welding current value from the time when the welding start command is issued and the pulse signal falling time of the pulse width control circuit, the coincidence signal from the comparing means is prohibited from being sent out, and this predetermined prohibition time elapses. And a gate circuit for allowing the transmission of the coincidence signal. When the coincidence signal sent out from the comparison means is sent out through the gate circuit, it is inverted to a low level, and the low level state is maintained according to the welding current value, so that this idle time has elapsed. A pulse width control circuit which inverts to a high level at this point in time and generates a pulse signal which continues this high level state until the coincidence signal is sent; A polarity inversion circuit for supplying alternatingly to the positive and negative gates of the inverter circuit such that the pulse signal transmitted from the pulse width control circuit is inverted and the polarity of the output of the inverter circuit is inverted each time the idle time elapses; Inverter type welding power supply characterized in that it comprises a. The inverter welding power supply according to claim 1 or 2, further comprising a timing signal generating circuit for supplying a timing signal for control to said gate circuit, said pulse width control circuit, and said polarity inversion circuit. The inverter welding power supply according to claim 1, wherein when the coincidence signal is not output within a preset maximum allowable time, the output signal of the pulse width control circuit is forcibly turned off after the maximum allowable time has elapsed. Device. The timing signal generating circuit is cleared by the signal at the time when the pulse signal from the pulse width control circuit falls or when the welding start command is issued, and the welding is performed from the time at which the welding start command is issued. A prohibition time counter that counts a predetermined prohibition time set in accordance with the current value, and sends a gate control signal of the gate circuit that maintains the output at a low level until the count value reaches a predetermined prohibition time; and the pulse Cleared by a signal at the time when the pulse signal from the width control circuit descends or when a welding start command is issued, the predetermined idle time set in accordance with the welding current value is counted from the time at which the welding start command is issued, and the count value is predetermined. Operation of the pulse width control circuit and the polarity inversion circuit by the signal output when the idle time is reached Is cleared by a down time counter for controlling the control signal and a signal at the time when the pulse signal from the pulse width control circuit falls, or when a welding start command is issued, and preset according to the welding current value from the time at which the welding start command is issued. And a maximum allowable time counter that counts the maximum allowable time, outputs a signal to be output when the count value reaches the maximum allowable time, and forcibly turns off the output signal of the pulse width control circuit. Inverter type welding power supply, characterized in that. The pulse width stored in claim 1, wherein the comparison circuit compares only one polarity of the primary current of the welding transformer, stores the pulse width at that time, and does not operate the comparison circuit. The drive circuit is operated so that the pulse width of the primary current of the welding transformer is made equal to plus and minus the same width. The method according to claim 1, further comprising a welding current detecting means for detecting a welding current flowing to the secondary side of the welding transformer, converting the detected value of the welding current detecting means into a digital signal and comparing the preset value with a preset value. And a setting value of the welding current setting means so that the deviation of the setting value becomes zero. The method according to claim 1, further comprising a voltage detecting means for detecting a voltage between the welding electrodes, converting the detected value of the voltage detecting means into a digital signal and comparing it with a preset setting value so that the deviation between the detected value and the setting value becomes zero. Inverter type welding power supply, characterized in that for changing the set value of the welding current setting means. The method according to claim 1, wherein the electric power, which is the product of the detection value of the welding current detection means and the detection value of the voltage detection means, is converted into a digital signal and compared with a preset setting value so that the deviation between the detection value and the setting value becomes zero. Inverter type welding power supply, characterized in that for changing the set value of the setting means.