SU1355409A1 - Method of stabilizing welding current in resistance welding under thyristor control - Google Patents

Abstract

The invention relates to welding production, in particular, to contact welding with alternating current with thyristor control. The invention makes it possible to improve the quality of the welded joint. The goal is achieved by stabilizing the current in each half-period, starting from the second, by setting the thyristor switching angle ot in accordance with the expression "t be Uc-b, b, where U is the mains voltage; N is the value of the welding current specified for this half-period, referred to the full-phase switching current at a mains voltage equal to OPS bg ,, bj-parameters of the adjustment ® characteristics. In this case, the value of WB in the first half period is fixed. The values of bd and b depend only on the power factor of the full phase at the coscp welding circuit. 2 Il, 2 tab. cl with SP cl

Description

The invention relates to the welding industry,

 The aim of the invention is to improve the quality of the welded joint.

Figure 1 shows the adjustment characteristics of the welding machine; Fig. 2 is a diagram of the device for implementing the proposed method.

Current stabilization by the method is carried out as follows.

It is known that the adjustment characteristic of an AC contact machine during phase regulation can be represented as

 b

de

oi.

B, 1

II 1 „

o b, oi, thyristor switching angle;

adjustment factors, depending on the power factor of the full-phase activation of the welding circuit cos cf;

the ratio of the effective value of the welding current to the current of the full phase switch on. cheni at oi. 9 In accordance with Ohm’s law, for an AC circuit, the effective value of the welding current at full-phase switching is defined as

T hsl

 KZ

where Ug is the effective value of the network voltage; K - transformation ratio; Z is the total resistance of the welding circuit, -

those. for the effective value of the welding current, the expression

WK K Z

(bo + b, about).

(one)

The stabilization of the welding current should ensure the equality of the welding current at different values of the mains voltage, i.e.

Uc

.

KZ

(B,

Vby) | f- (b,

+ b, oi), (2)

and

on

- reference network voltage, arbitrarily selected from the allowed range of network voltages;

2

is the firing angle at which, in the case of a mains voltage equal to the reference voltage, a welding current of I a is obtained,

To set the welding value, use the heating level, which is the ratio of the set current to the full-phase current with a certain reference voltage, i.e.

N

II

Uerj.

KZ

(3)

Compared (3) and the right-hand side of equality (2), we obtain the stabilization condition in the form

(BUT)

Thus, with known

BREEDS, ai, - it is possible to maintain a given level of heating N by setting the switching angle in each half-period in accordance with formula (4).

35 It is known that the values of b and b depend only on the power factor of the full-phase switching on of the welding circuit cos cp, which can be determined from the values of the angles of incl. 140 and the conductivity about and.

The quantities bd and b are known at discrete values of costf ,. however, for the purpose of stabilizing the current, subject to fluctuations

45 by formula (4) it is necessary to be able to determine b and b, for any value of costf. For this, approximate polynomials are defined:

(five)

, 562-2.189cosif + 0.9642cos2q; b, -1.029 + 0.9184cos (pO, 3631cos2q)

which are in the range of change cosif, 2; 0.8 provides high accuracy of correspondence (see tab. O, Thus, by measuring the previous half period and knowing oi in the same half-period, you can determine the power factor costp, which is used to calculate the current values of b. And b., Then in accordance with of

measures with the magnitude of the mains voltage for the next half-period the switching angle ci is determined from formula (4).

As a reference voltage, it is best to choose the smallest possible network voltage, i.e. nominal value - 10%. At any other network voltage, N 1 has a physical meaning from the permissible range. Thus, at a nominal supply voltage of 380 V, UQ is chosen to be 340 V.

Mathematical modeling and experimental testing (see Table 2 showed that the proposed method allows the welding current to be stabilized with allowable mains voltage fluctuations with an error not exceeding 1% where N is a predetermined heating percentage.

The method can be implemented using a device whose block diagram is shown in FIG. 2. The device includes a synchronization unit 1, a conduction angle sensor 2; three arithmetic units 3, -5, 6; analog-to-digital converter (ADC) 4; setpoint register 7, thyristor contactor 8, comparison circuit 9, binary counter 10, pulse generator 11.- I

Conductor Angle Sensor 2

on arithmetic unit 3, the value of the conduction angle in a digital form, in which the value of the power factor of the welding circuit, which is fed to the input of the arithmetic unit 5, is calculated from this value and the angle & C from the arithmetic unit 6. Here cos (f, in accordance with formulas (5), the values of b and b are calculated, which are then fed to the inputs of the arithmetic unit 6. The synchronization unit 1 generates two signals. One of them is the pulse generated at wives che rez zero. The second signal is analogue, corresponding in magnitude to the actual value of the mains voltage. This signal goes to .DCP 4, the output of which generates a digital value of the mains voltage. The last goes to the third input of the arithmetic unit 6,

355409

which by b

15

20

Yu

) 25 ". Q. 35

40 45. 50 gg

B, uc calculates the new value of the angle ot and gives it to the output. This value goes to the arithmetic unit 3 and the digital phase shifter consisting of blocks 7, 9, 10, 11. The parallel setpoint register stores the value coming from the arithmetic unit 6 corner eb. Binary counter 10 counts the pulses from generator 11, whereby the counting starts each time from zero to the moment of the beginning of the next; 1 cycle, which is ensured by applying to the reset input of an impulse counter generated by synchronization unit 1. The value entered in register 7 and the current value of counter 10 are compared in comparison circuit 9, which generates a pulse if these values are equal, i.e. at the time point corresponding to “6. This pulse includes one of the thyristors in the thyristor contactor 8.

The method is especially easy to implement if blocks 3, 4, 5, 6 are single crystal micro-electronics, for example, Electronics C5-31M.

The application of the method allows to improve the quality of the welded joint by increasing the accuracy of stabilization and simplification of the control equipment,

Claims (1)

Invention Formula The method of stabilization of welding current in contact welding with thyristor control, which consists in changing the switching angle of the thyristors in each half-period of alternating current to compensate for fluctuations of the mains voltage in accordance with the control characteristic depending on the switching angle and conductivity of the thyristors in the previous half-period of the mains voltage characterized in that in order to improve the quality of the welded joint, the turn-on angle of the thyristors al / is set in accordance with the expression "G NU and. B. b where n  J2 UU-L KZ 1355A09 network reference voltage selected from the allowed range of network voltages; . the effective value of the welding current when wired1 and network equal to and he 340 2.92 2.00 1, 49 2.62 1.81 1.33 2.27 1.65 1.17 1.68 1.26 0.90 t 380 2.92 2.01 1.50 .2.6 1.82 1.35 2.30 1.65 1.18 1.70 1.26 0.90 400 2.90 2.02 1.50 2.62 1.81 1.36 2.30 1.65 1.18 1.70 1.26 0.90 6 coefficient 4) The factors of the adjusting characteristic, depending on the coefficient ({) of the power of the full-phase connection of the welding circuit, determined by the values of the switching angles and carried out. Table 2 A, 3/1. 200 .100 .0.1 0,2 0,3 44 FIG. 2 Editor M.Kelemes Compiled by V. Gribov Tehred L. Oleinik Order 5745/14 Circulation 970 ... Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk: ab. 4/5 Production and printing company, Uzhgorod, st. Project, 4 0.7 0.8 coff Oi5 0.6 Figure 1 Corrector Y. Erdeyi