JP2789361B2 - Capacitor type spot welding machine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a condenser type spot welder, and more particularly to a condenser type spot welder having an improved capacitor charging voltage control function.

[Conventional technology]

As a conventional condenser type spot welding machine, for example,
There is one as shown in FIG. In the figure, an AC power supply 1 is connected to a primary winding of a transformer 11, and its voltage is boosted by a secondary winding and connected to a control rectifier circuit 2. The control rectifier circuit 2 includes thyristors 21 and 22 and diodes 23 and 24 connected in a bridge. The DC output voltage of the control rectifier circuit 2 can be controlled according to the drive pulse of each gate of the thyristors 21 and 22. The energy charged in the capacitor 3 connected thereto via the resistor 31 is transmitted to the primary winding of the transformer 5 via the thyristor 4. The secondary winding is connected to the welding electrode 51, and when the thyristor 4 is turned on, the charging energy of the capacitor 3 is discharged and a current flows through the primary winding of the transformer 5, and the primary and secondary windings A large current having an inverse ratio of the turns ratio flows through the welding electrode 51, heat is generated by power consumption, and the workpiece is spot-welded.

In order to stabilize the voltage of capacitor 3, capacitor 3
Is detected and connected to the inverting input terminal of the operational amplifier 61. The non-inverting input terminal of the operational amplifier 61 is connected to the reference voltage source 61.
Is connected, and the output of the operational amplifier 61 is connected to the base of the transistor 71 via the resistor 63. The collector of the transistor 71 is connected to the positive terminal 12 of the control power supply through the resistor 75.
Connected to. One end of the resistor 75 is a Zener diode 86
Is connected to the base of the NPN transistor 85, and a current corresponding to the error signal flows from the collector to the emitter of the NPN transistor 85. This current flows through switch 93 to U
It is connected to a relaxation oscillator composed of JT 91, capacitor 92, pulse transformer 94 and resistor 95. A pulsating voltage synchronized with the AC power supply 1 is supplied to the resistor 95 via the terminal 13. When the switch 93 is turned on, the capacitor 92 is charged and the potential rises to a certain potential. Turns on, and a pulse current flows through the pulse transformer 94. This pulse current flows from the secondary winding of the pulse transformer 94 to the diode 9
It is supplied to each gate of thyristors 21 and 22 via 6,97.

[Problems to be solved by the invention]

However, in such conventional charge control of a capacitor-type spot welding machine, a capacitor oscillation voltage is detected by a capacitor circuit, a comparison circuit that compares the voltage with a reference voltage, and a signal for controlling the charge voltage is supplied to a relaxation oscillation circuit. When sending to
Since the transistor was unnecessarily saturated and had non-linear characteristics, quick response and smooth characteristics could not be obtained when the charging voltage control fluctuated. An object of the present invention is to obtain a stable and fast response charging voltage control.

[Means for solving the problem]

In order to solve the above-mentioned problems, the present invention provides a transistor amplifier having a non-saturation characteristic obtained by comparing a charging voltage with a reference voltage, and having a non-saturation characteristic in series between an input terminal of the amplifier and a base of the transistor. A relaxation oscillator controlled by a constant current characteristic is connected via a non-saturation amplifier having a diode connected and a second diode connected between the input terminal of the amplifier and the collector of the transistor.

[Action]

Therefore, with this simple configuration, it is possible to avoid a nonlinear characteristic due to saturation and a delay in response speed, and it is possible to achieve a fast response speed and smooth control together with a relaxation oscillator using constant current characteristics.

Embodiment FIG. 1 is a view showing an embodiment of the present invention. First, the configuration will be described. The AC power supply 1 is connected to the primary winding of the transformer 11, and its voltage is boosted to about 400 V by the secondary winding and connected to the control rectifier circuit 2. The control rectifier circuit 2 includes a thyristor 21 and diodes 23 and 24 connected in a bridge. The DC output voltage of the control rectifier circuit 2 can be controlled from almost zero to the maximum value according to the drive pulse of each gate of the thyristor 21. Therefore, the capacitor 3 connected thereto via the resistor 31 is charged with a controllable DC voltage. The energy charged in the capacitor 3 is connected to the primary winding of the transformer 5 via the thyristor 4. The secondary winding is connected to the welding electrode 51. When the thyristor 4 is turned on, the charging energy of the capacitor 3 is discharged and a current flows through the primary winding of the transformer 5, and a large current having an inverse ratio of the turns ratio of the primary and secondary windings (usually 60: 1) is generated. It flows to the welding electrode 51 and generates heat due to power consumption, so that the workpiece is spot-welded.

Here, the voltage of the capacitor 3 is detected and connected to the operational amplifier 61 in the detection error amplifier 6 and the inverting input terminal. A reference voltage source 62 is connected to a non-inverting input terminal of the operational amplifier 61. The output terminal of the detection error amplifier 6 having such a connection relation is sent to an amplifier 7 having a non-saturation characteristic via a resistor 63. Amplifier 7 with non-saturation characteristics
Is connected to the base of the transistor 71 via the diode 72 and at the same time, to the collector of the transistor 71 via the diode 73. A resistor 74 is connected between the base and the common terminal. Transistor
The collector of 71 is also connected via resistor 75 to the positive terminal 12 of the control power supply. In the amplifier circuit 7 configured as described above, when the input signal becomes larger than a certain level and the current flowing through the diode 72 increases to saturate the transistor 71, the diode 73 conducts and the current flowing through the diode 72 is suppressed. Therefore, the saturation of the transistor 71 is prevented.

That is, when the state where both diodes 72 and 73 are conducting is expressed by an equation, V73 + VCE = V72 + VBE where V72 is the voltage drop of diode 72 V73 is the voltage drop of diode 73 VCE is the collector-emitter voltage VBE of transistor 71 Indicates the base-emitter voltage of the transistor 71.

When the diodes 72 and 73 are conducting, V73 = V72, so that VCE = VBE. Therefore, VBE becomes the voltage of the diode junction (= 0.6 V), and the transistor 71 operates in the unsaturated region.

Without the circuit by diodes 72 and 73, saturation cannot be prevented in this way.

Then, the output of the amplifier 7 is sent to the constant current circuit 8. The constant current circuit 8 includes a PNP transistor 81, a resistor 82, a resistor 83, and a resistor 84. The principle of operation is that a constant current flows from the emitter of the transistor 81 so that the voltage drop of the resistor 82 due to the emitter current of the transistor 81 becomes substantially equal to the output voltage of the amplifier 7, that is, the voltage appearing across the resistor 75. Runs to the collector. This current is connected to the relaxation oscillator 9 via the switch 93. The switch 93 is closed in synchronization with the welding operation. The relaxation oscillator 9
It comprises a UJT 91, a capacitor 92, a pulse transformer 94, and a resistor 95. A pulsating voltage synchronized with the AC power supply 1 is supplied to the resistor 95 via a terminal 13. When the switch 93 is turned on, the capacitor 92 is charged from the constant current circuit 8, and when its potential rises to a certain potential, the UJT 91 turns on and a pulse current flows through the pulse transformer 94. This pulse current flows from the secondary winding of the pulse transformer 94 to the diode.
It is supplied to each gate of thyristors 21 and 22 via 96 and 97. In this figure, connection lines to the gates of the thyristors 21 and 22 are omitted.

With such a configuration, in the charging voltage control, the charging operation has a quick response to the signal from the comparison amplifier circuit at a constant current and performs a smooth operation.

Although the present embodiment is configured for a single-phase AC power supply, a multi-phase AC input may be similarly configured if provided in correspondence with the number of relaxation oscillator phases. it can. The relaxation oscillator is not limited to a circuit using UJT.
A type in which energy is stored and released repeatedly can be similarly configured.

〔The invention's effect〕

Since the present invention has the features described above, the responsiveness and stability of the charging voltage are improved, and smooth charging characteristics can be obtained. In particular, when the welding energy is varied in a wide range, a stable capacitor voltage is obtained and the finish of the welded article is improved.

[Brief description of the drawings]

FIG. 1 shows an embodiment of a condenser type spot welder according to the present invention, and FIG. 2 shows an example of a conventional condenser type spot welder. 1 ... AC power supply, 11 ... Transformer, 12 ... Positive terminal 13 ... Ripple voltage terminal, 2 ... Control rectifier, 21, 22 ... Thyristor, 23, 24 ... Diode 3 ... Capacitor, 31 ... resistor, 4 ... thyristor 5 ... transformer, 51 ... welding electrode, 6 ... detection error amplifier 61 ... operational amplifier, 62 ... reference voltage source, 63 ... resistor 7 ... amplifier, 71 ... Transistors 72, 73 ... Diodes, 74, 75 ... Resistors 8 ... Constant current circuits, 81 ... Transistors 82, 83, 84 ... Resistors, 85 ... Transistors 9 ... Relaxation oscillators, 91 …… UJT, 92 …… Capacitor 93 …… Switch, 94 …… Pulse transformer, 95 …… Resistor 96,97 …… Diode

Claims (1)

(57) [Claims] 1. A control rectifier circuit energized from an AC power supply, a capacitor charged by an output of the control rectifier circuit, and a transformer energized by discharging charging energy of the capacitor via a control switch. A welding electrode connected to the secondary winding of the transformer and holding the work to be welded; a circuit for detecting a voltage across the capacitor and obtaining a difference voltage from a reference voltage; A transistor amplifier having an unsaturated characteristic for receiving an output signal of a circuit obtained by connecting a diode in series between an input terminal of the amplifier and a base of the transistor, and having a diode connected between an input terminal of the amplifier and a collector of the transistor. A non-saturation amplifier having a second diode connected thereto, a constant current circuit corresponding to the output of the non-saturation amplifier, and the control rectifier circuit energized by the constant current circuit and connected to the control rectifier circuit. Capacitive spot welder comprising a relaxation oscillator circuit that drives.