JPS62148091A - Control device for resistance welding machine - Google Patents

Abstract

PURPOSE:To save an energy and to miniaturize the device by using a high frequency AC invertor circuit as the primary side AC power source and by providing the control circuit of the welding time synchronous to the invertor frequencies and a welding current control circuit as well. CONSTITUTION:A commercial power source 1 is converted into a high frequency alternating current by providing the invertor circuit 32 equipping with a rectifier 30, capacitor 31 and diode and used as the primary side AC power source. A triangular wave generator 16 generates the carrier frequency which modulates the invertor circuit 32 with the pulse width and the phase thereof is detected by a phase detecting circuit 18. Moreover, the welding time is set by a welding time setter and the welding current of an electrode 5 is controlled based on the set current of a current setter 10 and the welding current signal of a simulator 11. In this way, the energy saving and miniaturization of the device are enabled due to the invertor frequency being made optimum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a control device for an inverter-type resistance welding machine that can freely set the energizing current and energizing time.

[Technical background of the invention and its problems]

An example of a conventional control circuit for a DC resistance welding machine is shown in FIG.

In FIG. 3, the DC welding current flowing from the commercial type g1 to the welding electrode 5 via the transformer 3 and rectifiers 4a and 4b is controlled by the phase control of the thyristor 2.

In the transformer 3, the primary voltage is stepped down to several tens of kiloamperes and supplied to the secondary side, so the welding current flowing to the secondary side is from several kiloamperes to several tens of kiloamperes, and cannot be directly detected. Since it is a circuit, the primary current is detected by the current transformer 6, and the current simulator 11 outputs vTL corresponding to the secondary current.
is being converted to .

FIG. 4 shows an example of the circuit configuration of the current simulator 11, in which the primary current 6 detected by the current transformer 6 is full-wave rectified by the diode 61, resulting in a voltage drop across the resistor 62, and further into the resistor 63. .64, a diode 66°67, an operational amplifier 65, and a capacitor 68. The output voltage V is obtained through a peak charging circuit.

The discharge time constant of the peak charging circuit is the resistor 64 and capacitor 6.
Since it is determined by the product of 8, if this time constant is matched with the DC side time constant of the welding machine, the output voltage V will be a value corresponding to the welding current.

FIG. 5 shows the relationship between ■□ and V-work in FIG. 4.

Returning to FIG. 3, the welding energization time is set with the energization cycle setting device 7, and after pressing the start switch 9, the commercial power supply 1
The counter 8 counts the power supply cycles of the phase shifter 13, and the interlock circuit 14 is turned on until the count value reaches a set value, and the output of the phase shifter 13 is sent to the drive amplifier 15, thereby controlling the energization time.

The one-way W1 current is set by a current setting device 10, and the difference with the welding current detected by a current simulator 11 is amplified by an amplifier 12, and a phase shifter 13 synchronized with the commercial power supply, an interlock circuit 14, and a drive amplifier 15 The firing phase of the thyristor 2 is controlled via the thyristor 2, thereby controlling the welding current to a set value.

Recently, large-capacity self-extinguishing devices such as high-power transistors and GTOs have become economically available, and there has been a trend to apply voltage-source inverters instead of turning on and off the commercial power supply using thyristors. .

In this case as well, conventionally, the energization time has often been set by the number of cycles of the commercial power supply, but this has the following problems.

ω The energization time is set based on the cycle of the commercial power supply, so 5
It is difficult to match the welding conditions in the 0-cycle region and the 60-cycle region, and it is necessary to define two types of welding standards corresponding to the difference in energization time.

■ The inverter frequency must be an integral multiple of the commercial power supply frequency, making it impossible to optimize and variable control the inverter frequency.

■ If you use an inverter frequency that is synchronized with the commercial power supply, you can run multiple welding machines in parallel.

The chance of starting and stopping from the fixed phase of the power supply voltage increases, leading to an increase in power supply waveform distortion.

[Purpose of the invention]

The present invention is an inverter-type welding system that eliminates constraints due to power supply cycles by setting the energization period in terms of time, and also makes it possible to select the optimal frequency for the welding system by making the inverter frequency independent of the commercial power frequency. The object of the present invention is to provide a control device for a resistance welding machine.

[Summary of the Invention] The present invention provides a control device for a resistance welding machine that controls a resistance welding current on a secondary side by controlling the conduction period and conduction current of a primary side AC power source of a transformer. An energization time control circuit that uses an inverter circuit that obtains a pulse width modulated high frequency alternating current output from a commercial power source, and that starts and stops the inverter circuit in accordance with a set energization time and synchronizes with the inverter frequency. A welding current control circuit is installed that detects the resistance welding current from the primary current of the transformer via a current simulator and controls it in accordance with the set current value. In addition to keeping the conditions the same, the inverter frequency is selected to an optimal value according to the welding conditions, thereby reducing energy loss and downsizing the device.

[Embodiments of the invention]

An embodiment of the present invention is shown in FIG.

In FIG. 1, a commercial power supply 1 is converted into a smooth DC voltage through a rectifier 30 and a capacitor 31, and an inverter bridge 3 using transistors and diodes.
2, the AC power is converted into AC power having a frequency higher than the commercial power supply frequency (generally 500 Hz to IKHz), and is supplied to the electrode 5 via a transformer 3 and rectifiers 4a and 4b.

The energization time is set by the energization time setter 71, and when the start switch 9 is pressed, the timer counter 81 starts counting the energization time, and continues to send the energization command signal vll□ to the synchronization circuit 19 until the count value reaches the set value. are doing.

The triangular wave generator 16 generates a carrier frequency that pulse width modulates (PWM) the inverter bridge 32, the phase of which is detected by the phase detection circuit 18, and the phase detection signal v1.
is output.

The energization command signal v,1 is generated by the synchronization circuit 19 as a signal v0.1 synchronized with the phase detection signal vl. converted to
The signal is input to the interlock circuit 14.

On the other hand, the set current set by the current setting device 10 is determined by the welding current signal VX obtained by the current simulator 11.
and the difference is determined by the amplifier 12 and the V
is compared with the output signal VΔ of the triangular wave generator I6, and is input to the PWM generator 17 together with the phase detection signal V1s, and the PWM output signal v1□ayVi7b is input to the drive amplifier 15 through the interlock circuit 14. ,
As a result, during the energization period of the inverter bridge 32, the PW
The welding current flowing through the electrode 5 is controlled to the current set value by M control.

FIG. 2 is a time chart of signals of various parts showing the above-mentioned operation, and shows the case where the start switch 9 is pressed at time t1, thereby the timer counter 81 starts counting, and counts up at time t.

In this case, the setting value of the energization time is 1. -11, and is usually set in units of 10m5.

VΔ is a carrier triangular wave voltage, and the phase detection signal V1
e is a signal synchronized with this, and the energizing time t2 to t4 of the inverter bridge is determined by the signal v1s which synchronizes the counter signals t to t3 with the rising edge of vllI.

The rise of V□8 occurs every two cycles of VΔ and corresponds to one cycle of the output V of the inverter bridge 32, so the voltage applied to the transformer always has the same number of positive and negative pulses, and the voltage applied to the transformer always has the same number of positive and negative pulses. The device 3 does not produce DC bias.

The PWM generator 17 generates a PWM output signal divided every half cycle of vl by ``1'' and 0'' of the phase detection signal v11 obtained by comparing the output V, 3 of the amplifier 12 and the triangular wave voltage VΔ. Vi?ay Vxtb is obtained, and the transistors of the inverter bridge 32 connected in an H-type are made conductive alternately to obtain an AC output V, and as in the case of Fig. 3, welding is performed via the transformer 3. Current can be obtained.

C Effects of the Invention As explained above, according to the present invention, the energization time of the welding machine can be set regardless of the inverter frequency, so unlike setting based on the number of cycles, the energization time of the welding machine can be set regardless of the power supply frequency or the inverter frequency. Therefore, it is possible to unify the welding conditions in the 50 cycle region and the 60 cycle region.

Also, the inverter bridge is cycle by cycle.

Since the transformer is energized alternately, the transformer is not subject to DC bias magnetization, and the energization time and inverter frequency can be separated, so the inverter frequency can be selected at the optimal value taking into account the characteristics of the transformer and secondary rectifier. becomes possible.

In other words, in general, increasing the inverter frequency makes the transformer smaller, but the switching loss of the rectifier increases, so there is an optimal value that includes both, and the present invention can freely select the optimal inverter frequency corresponding to this. Therefore, it is advantageous in terms of energy saving and resource saving.

Especially in resistance welding machines where the robot is equipped with a welding gun and a transformer, by appropriately selecting the frequency of the inverter, it is possible to minimize the load on the robot.
Particularly effective.

Furthermore, since the inverter frequency can be selected independently of the commercial power supply frequency, current distortion with respect to the commercial power supply when operating a large number of welding machines can be reduced.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention, a second circuit diagram,
FIG. 4 is a circuit diagram showing an example of the current simulator in FIG. 3, and FIG. 5 is a time chart showing its operation. 1... Commercial power supply 2... Thyristor 3...
・Transformer 4a, 4b... Rectifier 5...
Electrode 6... Current transformer 7... Energization cycle setting device 8... Counter 9... Starting switch 10
... Current setting device 11 ... Current simulator 30 ... Rectifier 31 ... Capacitor 3
2... Inverter bridge 71... Energization time setting device 81... Timer counter No. 1 Figure 2 Figure 3 Figure 4 Figure 5r5! J

Claims (1)

[Claims] In a resistance welding machine control device that controls the energization period and current of the primary side AC power source of a transformer to control the secondary side resistance welding current, a high frequency pulse width modulated pulse width modulated source from a commercial power source is used as the primary side AC power source. an inverter circuit that obtains an alternating current output of A control device for a resistance welding machine, comprising a welding current control circuit that detects the primary current of a transformer and controls it in accordance with a set current value.