SU854645A1 - Apparatus for commutation and current control - Google Patents

Description

The invention relates to electrical engineering, in particular to contact electric welding, and can be used in current control circuits of contact welding machines. 5

A device is known for deflating and regulating current, comprising a welding transformer, two controlled valves connected in parallel, a protection trigger and emergency shutdown of the device in case of a malfunction of one of the valves and a control circuit. The secondary winding of the welding transformer is connected to the counting input of the trigger through a single-phase bridge rectifier, as a result of which, during welding, the trigger switches twice during the voltage period of the supply network [1].

Frequent switching of the trigger leads to 20 failures in its work. In addition, when the welding current passes around the secondary winding of the welding transformer, a powerful alternating magnetic field appears, 25 which creates interference comparable to the level of the signal taken from this winding. The interference signal enters the counting stroke of the trigger, which also leads to malfunctions in its operation. With this construction of the device circuit 30, there is no galvanic isolation between the power circuits of the welding machine and the control circuit.

The purpose of the invention is to increase the reliability of the device.

This goal is achieved due to the fact that an additional transformer with a secondary winding is introduced into the device for switching and regulating current, containing a welding transformer, controlled valves connected in opposite parallel, a control circuit and a trigger for protecting and emergency shutdown of the device in case of a malfunction of one of the valves made of two symmetric sections, an AND element, two delay elements and two rectangular pulse shapers, while the inputs of the latter are connected to the corresponding section additional transformer, the outputs of the formers of rectangular pulses are connected to the corresponding inputs of the element And, the control circuit is connected through (the first element of the delay d to the third input of the element And, and the output of the latter through the second ele

The delay is connected to the control input of the protection trigger.

Figure 1 shows a diagram of a device? figure 2 - plot of stresses characterizing the operation of the device;

a - plot of the voltage applied to the primary winding of the welding transformer, and flowing through it under the influence of this voltage of the welding current (ψ is the angle of the controlled valve);

b - voltage plot at the output of the first pulse shaper;

in - plot of the voltage at the output of the second pulse shaper;

d is a plot of the voltage at the output of the control circuit, which, through a time delay, enters the input of the element AND the time by which the signal from the output of the control circuit is delayed);

d - plot of the voltage at the output of the protection trigger the time by which the signal from the output of the protection trigger is delayed.

A device for switching and regulating current comprises a welding transformer 1, controlled valves 2 and 3, transformer 4, first and second valves 5 and 6, first and second formers of rectangular pulses 7 and 8, element 9, the first delay element 1.0, and the second element 11 delays, protection trigger 12, and control circuit 13.

The device operates as follows.

In the initial state, the outputs of the drivers 7 and 8 of the rectangular pulses present the signal `` Logical 1 ''. At the time of starting work, from the output of the protection trigger 12 to the input of the control circuit 13 a signal <sup>1</sup> 'Logic 1''(ohm. 2d) is received, allowing the passage of Ignition pulses to controlled valves 2 and 3. Signal *' Logic 1 '* of the start of welding (see FIG. 2d) from the control circuit 13 through the delay element 10 is supplied to the input of the element And 9. At the same time, the first ignition pulse opens a controlled valve, the anode of which is currently receiving a positive half-wave of the mains voltage. In this case, a current pulse passes through the primary winding of the welding transformer 1 under the action of the applied voltage (see Fig. 2a), and from one of the sections of the secondary winding of the transformer 4, a signal, through a corresponding valve, for example S3, is supplied to a square-wave pulse former, for example 7 , at the output of which appears a logical “0 '''(see Fig. 26). At the output of the second rectangular pulse shaper, there is still a logical 'Ί' (see Fig.2c). At the inputs of the element And 9 there are two logical "1" and one logical "O", therefore, at the output of the element And 9 there is a logical "O" <sup>1</sup> and the trigger 12 of the protection remains in the same state. The delay element 10 delays the signal from the control circuit 13 to prevent false triggering of the protection trigger 12 before the passage of the first pulse of the welding current (see figure 2d). Second, the ignition pulse from the output of the control circuit 13 ^ opens the second controllable valve and the signal from the transformer 4 goes to another square-wave pulse shaper 8, at the output of which a logical `` 0 '' appears (see Fig. 2c). The combination of logical signals at the inputs of the element And 9 does not change, since t logical `` .1 ' ¹ (see Fig. 26) appears at the output of the rectangular pulse shaper 7, and the protection trigger 12 does not change its state.

If, for some reason, one of the controlled gates 2 or 3 does not open (see Fig. 2a by a dotted line), then the logical trigger 12 of the protection appears at the inputs of the And 9 element, (see Fig. Zd); to the input control circuit 13 receives a signal `` Logical 0 '', prohibiting the passage of ignition pulses. Welding stops. The delay element 11 prevents false triggering of the protection trigger 12 from the moment of the end of one pulse of the welding current until the start of the second pulse of the welding current (see fig.2d).

'A new welding cycle can only begin after resetting the trigger 12 protection in its original position. This ensures reliable protection of the controlled valves from overload, and the welding transformer from one-sided magnetization, arising in the welding mode when only one of the two controlled valves is turned on.

Connecting the transformer parallel to the primary winding of the welding transformer provides galvanic isolation of the control circuit from the power circuits of the welding machine, and also eliminates the influence of interference from the secondary winding of the welding transformer on the operation of the control circuit of the welding machine. The protection trigger in this circuit is triggered only at the time of an emergency in the operation of the welding machine,, and therefore failures in its operation are practically eliminated.

Claims (1)

1. USSR author's certificate 356072, cl. At 23 K 11/24, 03/17/71. U2,1 9ig.2