Semi-automatic welding control unit. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Semi-automatic welding control unit. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / welding equipment

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The control unit (hereinafter referred to as the “block”) is the main part of the semiautomatic welding machine type PDG-312-1 (PDI-304) and is designed to organize the welding cycle of the semiautomatic machine by supplying control signals to the executive bodies of the latter.

(click to enlarge)

The main parameters of the block:

Supply voltage, V.......65
Mains frequency, Hz.......50
Switched power, W, not more than.......630
Multiplicity of motor armature speed control, not less.......10
Duration of delay for turning on the welding source after turning on the gas valve (unregulated), s......0,5±0,1
Duration of delay for turning on the drive after turning on the welding source (unregulated), s, no more.......0,5
Delay duration for turning off the welding source after turning off the drive, s: no more than.......0,5
not less than ....... 2,5
Duration of delay for turning off the gas valve after turning off the welding source, s: no more than.......0,5
not less than ....... 4,5
Duration of turning on the engine when welding "dots", s: no more ....... 1,0
not less than ....... 5,0
Rigidity of the mechanical characteristics in the range of 500-600 under normal climatic conditions according to GOST 15150-69 when the load changes from 0,3In to In, no more than......+10%

The block provides: dynamic braking; electronic protection of the motor armature from overloads; turning on gas purge during commissioning; execution of “welding” and “adjustment” modes.

The unit remains operational when the supply voltage changes within the range of 0,90 to 1,05 Un.

In setup mode, the block provides:

turning on the supply of protective gas to adjust its flow rate; setting the required electrode wire feed speed;
choice of work cycle; welding with long seams; welding with short seams;
spot welding.

In welding mode, the unit provides execution of commands to start and stop welding. When giving a command to start welding, the unit must: turn on the supply of shielding gas, the welding current source; with an unregulated shutter speed (0,5 s), turn on the electrode wire feed; ensure stability of the electrode wire feed speed with an accuracy of ±10% of the set value at a simultaneous value of the supply voltage from plus 5% to minus 10% of the rated voltage and motor armature current from 0,3 In to In.

When giving a command to stop welding, the unit must: turn off and brake the armature of the electrode wire feed motor; turn off the welding current source after a certain time interval (adjustable by the adjuster); turn off the supply of shielding gas after a certain time interval (adjustable by the adjuster).

The block provides the ability to regulate the speed of rotation of the drive, feed welding wire from the feed mechanism of the semi-automatic device, as well as carry out the necessary work in the “adjustment” mode.

The device and principle of operation of the block

The block of elements controls the semi-automatic welding elements (electric motor, electric valve, welding source) to provide semi-automatic welding. The block of elements (hereinafter A3) consists of a group of elements that form the supply voltage; welding cycle control circuits; control circuits for electric motor operation.

The group of elements that generates the supply voltage consists of: diodes VD26 - VD29, providing 62 V power to the armature circuit of the feeder motor; elements R27; VD7; C7; R55; C17, providing 15-18 V power supply to the MS and circuit elements; VD10 elements; VD13; C20, compensating the influence of the EMF of the motor’s self-induction on the switching VS1; diode VD8, which provides electrical wiring between a source of stabilized voltage of 15 V and a source of pulsating voltage with a frequency of 100 Hz; elements C8;C16;C21 of the filter against impulse noise of the welding source when operating in the “welding” mode; quenching resistor R26 of the 48 V power supply winding of the feed motor electric motor; quenching resistor R30 for 48 V power supply to the solenoid valve winding.

The welding cycle control circuit is made on microcircuits D2 - D4, transistors VTZ - VT6, thyristor VS4, relay K1 and elements that provide their modes. Inverter D2.4 is a buffer cascade that controls the state of trigger D4.2, in turn, the trigger determines the duration of operation of the spot welding and long seam welding modes (in the short seam welding mode, trigger D4.2 is not involved). From output 11 of inverter D2.4, the signal goes: to inverter D2, which gives the command to turn on the circuit that controls the operating mode of the solenoid valve: D2.З; VT5; D2.3; VT4; S4; to the coincidence circuit D3.1, which gives permission for the operation of the control circuit of the electrode wire feed motor DA1; VT2; VS1; VT1; VS3. From output D3.1, the signal goes to the circuit that controls the switching mode of the welding source (VT6; D2.1; VT3; K1). Simultaneously, from output 8 of trigger D4.2, the signal is sent to the coincidence circuit D3.2, which controls the dynamic braking of the electric motor and the supply of electrode wire (VD22; R39; C19; R28; VS2). The dynamic braking mode is activated after the “End welding” command.

Consider the control scheme of the welding cycle in the "spot welding" mode.

In this case, S4 is in the upper position according to the diagram, S2 is in an open state - the “work” mode. When you press the button on the burner (the duration of pressing the button does not affect the operation), a positive potential corresponding to the log. "1" (hereinafter "1") is supplied to input 12 D2.4. In this case, at 13 D2.4 there is a logic “1” from pin 8 of D4.2 (initial state of trigger D4.2) through the connected contacts of switch S4.

A log appears at the input of inverter D2.4. zero (“0”), which changes the state of trigger D4.2 with a delay, the duration of which is determined by the discharge time of capacitor C12 through resistors R36; R35 to voltage less than 7V.

While the “point” is being worked out, any manipulations with the button on the burner do not change the state of the circuit, because At pin 13 of D2.4 there is no prohibiting (zero) signal taken from direct output 8 of trigger D4.2.

At the same time, from output 11 of inverter D2.4, the signal is supplied to inverter D2.2, which gives a command to elements D2.3; VT4; VS4 to turn on transistor VT4. This signal also goes to the coincidence circuit D3.1, from the output of which a “1.4” is sent through D1, opening the transistor VT6 and forming a “2.1” at the output of D0, which opens the “switch” VT3. Current will flow through the winding of relay K1, the relay is activated and turns on the welding source with its contacts.

A “25” is sent through VD1, allowing the operation of the circuit that controls the electrode wire feed motor.

According to the cyclogram, when you press the “START” button on the torch, the electrovalve is turned on, then the welding source and the electrode wire feed motor are turned on.

The duration of spot welding is set by resistor R35. At the end of welding, the engine is turned off, dynamic braking is turned on, then the welding source is turned off with a delay, which is set by resistor R31, and at the end of the cycle, with a delay, which is set by resistor RXNUMX, the solenoid valve is turned off.

Let's take a closer look at the end of the spot welding cycle. At the end of welding, the “STOP” command is received at input 10 of trigger D4.2 (due to the discharge of capacitor C12 to a voltage of 7V -''0"), the trigger switches to its original state, i.e. at pin 8 of D4.2 -"1 ", on pin 9 of D4.2 - "0".

From output 9 of trigger D4.2, through the switched contacts SA "0" is supplied to the coincidence circuit D3.1, which prohibits the motor control circuit, the power circuit of the armature winding is de-energized, but the engine rotates by inertia.

Almost simultaneously, the dynamic braking circuit is activated. Delay duration 40 ms t= 0,5 (R53,C15). Log. “1” from 9 of output D4.2 through contacts S4 goes to the input of the coincidence circuit D3.2, which turns on the dynamic braking thyristor VS2, the armature winding is closed, and the engine stops abruptly.

From output D3.1, “14” is sent through VB0, which gives the command to turn off the welding source. Turning off occurs with a delay, the duration of which is determined by the value of R31, "0" closes transistor VT6, which forms a "2.1" at output D1, which closes the "switch" VT3 and de-energizes relay K1. The welding source will turn off.

Log "1" at output D2.1 also gives a command to turn off the solenoid valve. While charging, the voltage C13 through RЗЗ, R34 (t=0,5 (R33-R34) C13) will open transistor VT5. A “2.3” will appear at the “input D1”, a “0” generated at the output of the inverter D2.3 will turn off the transistor VT4 and the thyristor VS4. The winding of the solenoid valve will be de-energized. The duration of switching off the gas shut-off valve is determined by the value of RЗЗ.

When working with “SHORT SEAMS”, the positive potential through the “START” button located on the torch holder is supplied to the input of inverter D2.4, the output is formed “1”, which, through the connected contacts of switch S4, is supplied to the cycle control circuit in the “SPOT WELDING” mode ". The duration of welding is determined by the duration of the ON state of the "START" button. When it is released, the circuit returns to its original state, while trigger D4 does not participate in the operation.

When welding with “LONG SEAMS”, the welding duration is determined by the time interval between the first and subsequent presses of the “START” button on the torch holder.

When a positive potential is applied through the "START" button, the buffer stage D2.4 will switch the trigger D4, and the trigger remembers this state by self-locking at input 13 of D4.2 through the inverter D2.4.

Signals taken from trigger D4 and inverter D2.4 through the connected contacts of switch S4 are supplied to the welding cycle control circuit and the electric drive control circuit, similarly in the "SPOT WELDING" mode.

The control circuit for the electric drive for feeding the electrode wire consists of the following functional units: summing amplifier DA1, control pulse generator VT2; R17; R18; C4; a power amplifier assembled on a thyristor VS3, a current protection circuit (R3; R5; VT1, VD4), a dynamic braking thyristor VS2, an optothyristor VS1 that supplies the armature winding of the electric motor.

The resistor that regulates the feed speed of the electrode wire, which is located on the feeder, is supplied with a stabilized voltage from VD8, and the reference voltage U1 is removed from the slider of this resistor and supplied to the input of the summing amplifier DA3.

The divider on resistors R2, R7 is connected in parallel to the motor armature, and the feedback voltage Uoc is removed from the output of resistor R2 and supplied to the inverting input of amplifier DA1. This voltage is proportional to the motor armature voltage.

A voltage Uoc is removed from resistor R9, proportional to the current flowing through the motor armature and resistor R29. This voltage is summed through resistors R11, R12 with the reference voltage to the non-inverting input of summing amplifier D1.

Therefore, at the output of the amplifier we get the mismatch voltage Up

Ur \uXNUMXd Uz-Uos.

The mismatch voltage is supplied to the input of a comparator made on a unijunction transistor VT2. When the voltage on capacitor C4 reaches the threshold for turning on transistor VT2, the latter opens, and a control pulse appears on resistor R18, which opens thyristor VS3, turning on thyristor VS1. Due to the fact that base 2 of transistor VT2 is powered by a voltage in-phase with the supply voltage, the leading edge of the control pulse moves in phase depending on the value of Up.

In steady state, with a constant position of the resistor motor for setting the feed speed of the electrode wire, the motor armature rotates at a constant speed; the voltage at the armature terminals and across resistor R29 does not change, and therefore the value of Uр is constant.

If the load on the motor shaft has increased, the rotation speed of its armature and the voltage on it decrease, and the armature circuit current increases. Accordingly, the negative feedback voltage Uos decreases, and the positive feedback voltage Uos increases.

From the above voltage (I), it is obvious that the voltage Up increases. An increase in Up causes a corresponding phase shift in the control pulse at the output of the comparator, and the thyristor turns on earlier, which leads to an increase in the voltage at the motor armature, and therefore the rotation speed, to the previous level.

The action of positive feedback Uos is most effective at low armature rotation frequencies, i.e. when the absolute value of this voltage is commensurate with the value of the reference voltage, and the voltage at the motor armature is small.

The DC amplifier KR140UD1B (DA1) was used as a summing amplifier. The amplifier is covered by frequency-dependent feedback (C5, C6, R16).

A voltage setting the electrode wire feed speed is supplied to the non-inverting input 11 of the amplifier through resistor R14, and an integrated signal proportional to the armature current is supplied through resistor R12.

A signal proportional to the voltage at the motor armature is supplied to the inverting input 10 of the amplifier from the divider R2, R7.

To the same input through resistors R15; R20 is supplied with a stabilized voltage to set output 5 of the amplifier, a voltage equal to the switching threshold of the unijunction transistor VT2 at zero value of the reference voltage.

Resistor R20 sets the minimum armature speed of the motor.

To compensate for the scatter in the parameters of unijunction transistors and ensure the identical output characteristics of the drives, base 2 of transistor VT2 is connected to the parametric stabilizer R24, VD9 through a divider R25.

By moving the slider of resistor R25 in each instance of the drive based on 2 transistors VT2, a voltage is established at which the voltage at the emitter, measured by an oscilloscope, will be equal to 3,5 V.

The current feedback voltage in the armature circuit is removed from the divider R9. A diode limiter VD1, VD2, R4 is connected in parallel to the divider to limit the maximum feedback voltage.

The engine of the resistor R3 sets the required threshold for switching on the current protection.

Diodes VD3, VD4 serve to limit the signal in the base circuit of transistor VT1 and for temperature compensation of the operating mode of this transistor.

Relay K2 is turned on by a toggle switch located on the feed mechanism in the “ADJUSTMENT” mode to feed the electrode wire into the channel of the welding torch.

Relay contacts K2 turn on the drive and turn off dynamic braking and the welding source.

When the load on the motor shaft does not exceed the permissible value, the current cut-off transistor VT1 is closed. The voltage from the collector of this transistor and output 9 of DD4.2 is supplied through S4 to the input of the coincidence circuit D3.1. As the armature current increases, the voltage across resistor R29 and across resistor R3 connected in parallel to it increases. The resistor R3 motor is connected to the base of the transistor VT1 and is installed in such a way that when the armature current reaches a value of 1,5 In, the transistor VT1 opens.

The voltage at one of the inputs of the circuit of element D3.1 becomes close to zero, therefore, the output stage of amplifier D3.1 is closed, the signal at input 11DA1 is canceled, the generator at VT2 is turned off, and the thyristor VS1 turns off the main thyristor that controls the motor, while the current in There is no motor armature circuit, transistor VT1 closes, “3.1” appears at output D1, allowing the engine to turn on - the drive turns on again.

Thus, a certain average current value is maintained in the armature circuit, not exceeding the permissible value.

Author: V.E.Tushnov

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