RU1816580C - Service current pulse generator for electroerosion machine - Google Patents

Abstract

Usage: the invention relates to the field of electrical discharge machining of metals and can be used as a source of technological current pulses for powering electrical discharge machining machines. SUMMARY OF THE INVENTION: To increase productivity and processing quality, the generator is additionally equipped with two low-pass filters, a dividing device, and an additional resistor. In this case, the master oscillator is made controllable, and the first filter is made in the form of a double winding circuit with a ferromagnetic core and a shunt resistor. As the resistance of the erosion gap increases, the frequency of the pulses of the technological current increases. 1 ill.

Description

The invention relates to the field of EDM of metals and can be used as a source of pulsed technological current for powering EDM machines.

The purpose of the invention is to increase the productivity and quality of workpiece processing.

The invention is illustrated in the drawing, which shows a block diagram of the proposed generator.

The generator contains a bridge inverter 1, made in the form of thyristors 2, 3, 4. 5 connected to each other and a capacitor 6, and the anode group of thyristors (thyristors 2 and 4) is connected to inductor 7

positive pole + at the power source (not shown in the diagram). The control electrodes of the thyristors 2, 3, 4,5 are connected to the corresponding outputs of the master oscillator 8 and, in addition, the control electrodes of the thyristors 3 and 5 are connected to the inputs of the OR9 circuit. The cathodes of the third thyristor 3 and the fourth thyristor 5 are connected to the anodes of the first diode 10 and the second diode 11 connected to each other. The cathode of the first diode 10 is connected through the primary winding of the saturating throttle 12 to the midpoint О of the power source, the cathode of the second diode 11 is connected to the cathode the third diode 13. The anode of the diode 13 is connected to the first output of the control key 14 and one of the taps of the secondary winding of the saturable throttle 12. The second tap of this winding is connected to the cathode of the erosion gap 15. one of the taps

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a ballast resistor 16 and a first input terminal of a second low-pass filter 17. The cathodes of the diodes 11 and 13 are connected to one of the taps of the additional resistor 18 and the first input terminal of the third low-pass filter 19. The second tap of the resistor 18 is connected to the anode EP15, one of the taps of the ballast resistor 16 and the second input terminals of the filters 17 and 19, the outputs of the filters 17 and 19 are connected respectively to the first and second inputs of the dividing device

20. The primary winding of saturating throttle 12 is made with intermediate taps, the number of which is equal to the number of switching keys (in the given example of the generator implementation there are three such keys:

21. 22 and 23), the second outputs of these keys being connected to the cathodes of thyristors 3, 5 and the anodes of the diodes 10.11, and the first outputs of these keys being connected to the said intermediate taps. The inputs of the keys 21, 22, 23 are connected to the corresponding outputs of the extremum search unit 24, the input of which is connected to the output of the first low-pass filter 25, which is the point of connection of one of the taps of the primary winding of the double-winding drossel 26 with a ferromagnetic core and one of the taps of the shunt resistor 27 The second branch of this resistor is connected to the second branch of the secondary winding of the throttle 26 and the common wire of the electrical circuit, and the first branch of the secondary winding of the throttle 26 is connected to the output of the dividing device 20 and the input of authorizing generator 8. The first tap of the primary winding of choke 26 is combined with the input filter 25 and connected to the second output of the control key 14. Enter key 14 is connected to the output of the 28 rectangular pulse shaper 28 and the input connected to the output circuit ILY9.

Technical implementation of the device.

Thyristors 2,3,4,5 can be types of PM, PM or other, and capacitor 6 - type KSG, KSO.

The OR9 circuit is a two-type resistive-diode cell. Resistor 27 can be of the type MLT, ULI, ULM, etc. Resistor 18 is a low-resistance resistor and several Ohms, made in the form of a plate of manganin, nichrome, constantan. Resistor 16 is a high-resistance resistor such as PEV, PE V Ril and others. Inductors 12 and 26 are made on toroidal or U-shaped ferrite cores. The inductor 7 is made on a U- or W-shaped core made of transformer steel and

has an air gap. Low-pass filters 17 and 19 can be implemented on the basis of transistors or integrated circuits, for example, K140 series according to the standard

scheme. In this case, the input part of the filters contains, in addition to the filter itself, a voltage divider and a resistive-diode voltage limiter (implemented according to any known scheme) to protect the operational amplifier (or transistors) from breakdown by high voltage. The dividing device 20 can be implemented on the basis of operational amplifiers with an output power amplifier.

Shaper 28 can be made in the form of a standby blocking generator. Between the output of the driver 28 and the input of the key 14, it is advisable to have transformer or optocoupler isolation.

The control key can be implemented, for example, on the transistor KT604 (A, B), while the input of the node 14 is the base of the transistor, the second output is the emitter of the transistor (between the base and the emitter

a resistor is turned on with a resistance of several kilograms), and the collector of the transistor is the first output.

Switching keys 21-23 can be performed on transistors KT805A,

KT848 or other sufficiently powerful high-voltage transistors. In this case, the key inputs are transistor bases, and the outputs are the emitter and collector electrodes. The extremum search block 24 consists of

interconnected differentiator, half-wave rectifier, rectangular pulse shaper, countable trigger, search pulse generator, two AND elements, reversible

counter and decoder according to the same scheme as in the prototype. This block can be implemented on microcircuits of the 155.176, 511 or other series. The input of block 24 is the input of the differentiator, and the outputs are the outputs of the decoder. To match the power between the outputs of block 24 and the inputs of the keys 21 ... 23, power amplifiers are included, not shown in the generator block diagram. For the purpose of galvanic isolation of block 24 and

of these keys, these amplifiers may contain optocoupler pairs or transformers.

The master oscillator 8 can be made, for example, in the form of a magnetotransistor multivibrator (see Fig. 10, 31; 10.32 in the aforementioned work of V.V. Gusev and others) or a multivibrator with a collector-base coupling and emitter capacitance (see Fig. 35 in the work of V.N.Yakovlev Pulse

transistor generators, Kiev, Tekhnika, 1968 - 443 s.), in this case, in the first case, the magnetotransistor multivibrator must have four output windings (according to the number of inverter thyristors) having the corresponding phasing, and in the second case to the collectors of each multivibrator transistor Two additional pulse amplifiers with transformer output must be connected. The connection of these output circuits to the thyristors of the inverter 1 should be such that the pulses simultaneously appear on the control electrodes first of one pair of thyristors (2.5), and then simultaneously appear on another pair of thyristors (3.4). In series with the input circuit of node 8, a stable voltage source consistent with the output signal of block 20 can be turned on.

The generator operates as follows.

When supplying control pulses to the control electrodes of two thyristors, included in the opposite arms of inverter 1, for example, thyristors 2 and 5, the latter are also unlocked by a circuit: inductor 7 - thyristor 2 - capacitor 6 - thyristor 5 - diode 1G primary dc interconnector 12 - midpoint O power supply - a current flows, soldering a voltage pulse across the secondary winding of the interconnector 12. The windings of saturating throttle 12 are phased so that the positive potential of this voltage is applied to the anode of the diode 13 and the first output terminal of the control key 14, and the negative one is applied to the cathode of the EDM 15, one of the taps of the ballast resistor 16, the first input terminal of the second lower filter 17 frequencies and

negative pole-1 at the power source. Since the number of turns of the secondary winding of the throttle 12 is greater than the number of turns of its primary winding, even when the switching keys are closed 21, 22, 23, the voltage on the secondary winding is increased and through the diode 13 and additional resistor 18 breaks through the erosion gap 15, which in the initial state is current I didn’t. The voltage of the erosion gap 15 falls on the input terminals of the filter 17, and the voltage drop on the resistance 18 corresponding to the current EP15 falls on the input terminals of the third low-pass filter 19. The current flows through EP15 due to its breakdown and now the charge current of the capacitor 6 flows through the diode 11, the resistor 18 and the resistor 16 and the erosion gap 15 connected in parallel,

As the capacitor 6 charges, the voltage rises on it, the current drops, and when this voltage coincides with the voltage between the positive pole and the midpoint of the power supply, the charge current drops to zero and the thyristors 2, 5 close. At the end of the charge capacitor b pulse

0, the current of the EDM 15 ends.

When control pulses are applied to the control electrodes of thyristors 3,4, the latter open and the row 5 of the capacitor 6 is restarted. In this case, when the keys are closed, 21,22,23 current flows through the circuit: inductor 7-thyristor 4 - capacitor 6 - thyristor 3- diode 10-primary winding drossel 12 - midpoint of the source

0 power. The resulting increased voltage pulse on the secondary winding of the throttle 12 through the diode 13 and the resistance 18 punches EP15, as a result of which the latter becomes electrically conductive.

5 Thanks to this, further recharging of the capacitor 6 occurs along the circuit: inductor 7 - thyristor 4 - capacitor 6 - thyristor 3 - diode 11 - resistor 18 - resistor 16 connected in parallel and

0 EP15. At the end of the recharging of the capacitor 6, the thyristors 4 and 3 are closed and the current pulse of the erosion gap 15 stops. The voltage drop at the additional resistor 18, proportional to the total current of EP15 and the resistor

16. is applied to the input terminals of the filter 19, and the voltage at the erosion gap 15 is applied to the input of the filter

17.

0 Thus, when pulses are fed alternately to the control electrodes of thyristors 2-5.3-4, voltage pulses appear on the electroerosion gap 15 and pulses flow through EP15

5 of the current. As a result, sequences of voltage pulses act on the inputs of the filters 17 and 19, the constant components of which are extracted by these filters. Therefore, the first entrance

0 of the dividing device 20, a signal is proportional to the average value of the voltage in the erosion gap, and a signal proportional to the current of the erosion gap is received at the second input. At the same time, a voltage proportional to the average value of the resistance of EP15 arises at the output of the dividing device 20. This voltage controls the pulse repetition rate generated by the master oscillator B:

the higher this voltage, the higher the pulse frequency of the generator 8, the lower the specified voltage, the lower the pulse frequency of the generator 8. This means that with increasing resistance of the discharge line, the repetition rate of the process current pulses flowing through the electric field increases (such an increase in resistance can be caused, in particular, by the pollution of EP by erosion products).

The pulses from the two outputs of the master oscillator 8 through the OR9 circuit are fed to the input of the rectangular pulse shaper 28, which generates rectangular pulses of calibrated duration and amplitude. These pulses are fed to the input of the control switch 14, which opens under the influence of these pulses and provides a resistance close to zero between the first and second output terminals thereof. When the key 14 is open, the voltage from its first output terminal (equal to the voltage in the erosion gap 15) passes without change to its second output terminal, and from it to the input of the first low-pass filter 25. The time constant of the filter 25 is determined by the inductance of the primary vol. coils of drossel 26 and the resistance of resistor 27. The indicated inductance depends on the current flowing in the secondary winding of the drossel 26 and the magnetic field strength created by it. Since the magnetic permeability of ferromagnets usually decreases with increasing magnetic field strength, the inductance of its primary winding and, as a consequence, the time constant of the filter 25 decrease with increasing current in the secondary winding of the throttle 26. As a result, the time constant of the first filter decreases with increasing frequency of the current pulses 25 is reduced.

The extremum search unit 24 works in exactly the same way as in the prototype device (USSR author's certificate M 1505696), that is, it sends a control pulse alternately to each key 21, 22, 23, under which the key is opened and connects one or another intermediate the primary winding of the throttle 12 with the cathodes of thyristors 3, 5. After several procedures for switching on the keys 21, 22, 23 (as well as others not shown in the figure), the block 24 produces control pulses only for those keys, when the closed state of which the pulse amplitude wives and the erosion gap 15 is close to the maximum possible, and the change of this amplitude is minimal when changing keys. In other words.

block 24, in the same way as in the prototype, provides the search for the extremum (maximum) of the amplitude of the voltage pulses on the EP15, i.e. the most acceptable transformation ratio of throttle 12.

The extremum search unit 24 removes a control signal from one switch key (its key and generates a control signal from another switch key with a given

. periodicity determined by the operating frequency of the search signal generator and the size of the counter included in this unit. When, when the next switching key is turned on, a change in the transformation coefficient of the throttle 12 leads to an increase in the voltage on EP15, block 24 opens the next one of the keys 21, 22, 23, the inclusion of which does not change the sign of the increment of the transformation coefficient of the throttle 12. If the switch is 21, 22 and 23) leads to a decrease in the voltage across the ЭП15, the output signal of the filter 25 drops and the block 24 together with the indicated keys provides

changing the sign of the increment of the specified transformation ratio. The aforementioned dependence of the time constant of the filter 25 on the frequency of current pulses EP15 leads to an increase (in comparison with

prototype) the absolute values of the rate of change of the output voltage of the filter 25 when changing the transformation coefficient of the throttle 12, whereby the block 24 and the keys 21-23 provide

more accurate setting close to the optimum of the mentioned coefficient.

When the resistance of the erosion gap 15 is changed when it is contaminated with erosion products, the extremum search unit 24 maintains the amplitude of the voltage pulses at this interval close to the maximum possible value (which is provided in the prototype). In addition, with increasing resistance of EP15

due to its pollution in the proposed generator provides an increase in the frequency of voltage pulses and current of the erosion gap (in contrast to the prototype, where this frequency is constant), due to which

the average current value increases. EP15 also improves processing productivity compared to the prototype. Increasing the frequency of technological current pulses also provides an increase in purity

processing compared to the prototype.

Thus, the proposed generator in comparison with the known provides an increase in productivity and quality of processing of workpieces (parts).

Claims (1)

SUMMARY OF THE INVENTION A process current pulse generator for EDM machines comprising a master oscillator, a bridge inverter with capacitor switching, control electrodes of the inverter thyristors connected to the corresponding outputs of the master oscillator, the anodes of the first and second thyristors of the inverter are connected via the inductor to the positive pole of the power source, and the cathodes of the third and fourth thyristors of the inverter are connected to the anodes of the first and second diodes, the cathode of the first diode through the primary winding a saturated dasel is connected to the midpoint of the power source, the cathode of the second diode is connected to the cathode of the third diode, the anode of which is connected through the secondary winding of the saturated dross to the cathode of the erosion gap, the negative pole of the power source and the first tap of the ballast resistor, the second tap of which is connected to the anode erosion gap, OR element, rectangular pulse shaper, control key, first low-pass filter, extremum search unit, the input of which is connected with the output of the first fil low-pass filter, the input of the first low-pass filter is connected to the second output of the control key, the control electrodes of the cathode group of the inverter thyristors are connected to the inputs of the OR element, the output of which is connected through the square-wave pulse generator to the control key input, the first control output the supply key is connected to the anode of the third diode, and the primary winding of the saturated throttle is made with intermediate taps, the number of which is equal to the number of switching keys, the switching key inputs are connected to the outputs of the extremum search unit, the first switching key outputs are connected to the primary winding taps of a saturable throttle, the second switching key outputs are connected to the anodes of the first and second diodes, characterized in that, in order to increase productivity and processing quality blanks, the second and third low-pass filters, a dividing device and an additional resistor are introduced into it, and the first low-pass filter is made in the form of interconnected a shunt resistor and a double-winding throttle with a ferromagnetic core, the first tap of the primary winding of the throttle with a ferromagnetic core is combined with the input of the first low-pass filter, the second tap of the primary winding of the throttle with a ferromagnetic core is combined with the output of the first low-pass filter and is connected through the shunt resistor to a common circuit wire and a second branch of the secondary winding of this throttle, while the master oscillator is made controllable and its input is connected to the first branch of the secondary throttle windings with a ferromagnetic core and the output of the dividing device, the first and second inputs of the dividing device are connected to the outputs of the second and third low-pass filters, an additional resistor is connected between the anode of the erosion gap and the cathode of the third diode, the input terminals of the second low-pass filter are connected to the terminals of the ballast resistor and the input terminals of the third low-pass filter are connected to the taps of the additional resistor.