CS215087B2 - Connection of the circuit for the control of the erosion machining by electric spark - Google Patents

Abstract

1492027 Electro-erosion FRIEDRICH DECKEL AG 4 March 1975 [4 Dec 1973 23 May 1974] 56184/73 and 23145/74 Heading B3V The occurrence of arcing during electrical discharge machining is sensed by detecting the absence of a high frequency component in a discharge across the machining gap and thereupon interrupting the discharges within 20 microseconds. The gap voltage or current W is fed through a filter F whose output is connected via an amplifier A to a comparator circuit C having another input derived from a gap current detector CD. When an HF component, e.g. above 1 MHz, is absent from a discharge indicative of arcing, pulses are not supplied from the filter F to the comparator circuit C, whereupon the pulse generator G is caused to switch off for a predetermined period, e.g. below 2 sees. The electrode may also be withdrawn and the amplitude of the discharges reduced. If arcing occurs too frequently, the generator is switched off and an alarm actuated. If a short is detected across the gap by a circuit S, the discharges are interrupted for a shorter period. To test whether the monitoring circuit is functioning correctly, signals simulating the occurrence of arcing are applied randomly or regularly through contacts T 1 -T 3 whereupon a signal is applied to a gate G 2 whose other input receives a signal from the generator G upon the occurrence of a discharge therefrom. If the generator has not switched off within 20 Ásecs., a signal is supplied to an integrator I which switches it off.

Description

FIELD OF THE INVENTION The invention relates to a circuit for controlling spark erosion machining in machines operating with spark erosion, with a logic circuit for recognizing a faulty discharge from the simultaneous occurrence or absence of certain electrical characteristics in a discharge circuit, for example the absence of a high frequency component at discharge voltage. the existence of operating voltage and operating current as a criterion for the detrimental state of the arc, as well as devices for short-term interruption of the machining process when such erroneous discharges occur.

A problem with modern spark erosion machines is to recognize the occurrence of faulty discharges of any kind before the workpiece or tool has been damaged. Detection circuits have been proposed for this purpose which, when certain criteria indicating an error condition occur, emit an error signal which can then be used to indicate an error or even as a control signal to remedy the error (DE-OS 2 125 749). These detection circuits usually detect certain values of the electrical state in the working slot. Particularly suitable for this are the magnitude of the operating current and the operating voltage, as well as the existence or absence of a high-frequency component superimposed on the current or the current. voltages that are particularly useful for indicating the arc state, since they disappear at all arc states, while current and voltage generally show no appreciable deviations from their normal operating values.

In this way, it is possible in principle to use the machine also in uncontrolled operation.

However, since the probability of failure of the detection circuit and thus the risk of damage to expensive workpieces is still relatively high, in many applications, for example in the machining of turbine blades for aircraft engines, additional safety measures are required for the operation of the spark erosion machine. The redundant design of important components is a common way to increase operational safety. However, multiple embodiments of the detection circuit described above are very costly and expensive.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a device of the above-mentioned type in which a considerable increase in operational safety is achieved by simple means and without multiple detection circuitry.

This object is achieved according to the invention in that the circuit is provided with an input device for the arbitrary introduction of test signals simulating erratic discharges into the discharge circuit. If the detection circuit is working correctly, the machine first reacts as a true error, ie generates an error signal. With the additional information indicating that the error is a simulated error, the error signal is processed into a test signal that indicates the correct functioning of the detection circuit and serves as a command to continue the machining process. In the absence of an error signal, despite the introduction of a simulated error, a test signal is used, which is used to trigger a warning indication, to stop the machine or the like.

According to the invention, the input device may be a two-pole switch which introduces signals to the detection circuit corresponding to the operating current and the operating voltage when a true error occurs.

To distinguish the simulated error from the true error, the input device according to the invention is connected to a logic monitor circuit. This circuit detects when power from the generator is supplied to the working slot, for example by measuring the power, current or voltage at the generator output, and generates a corresponding signal. This signal, together with the additional signal generated by the additional switch when the error signal is input, is processed into the test signal described above. If the auxiliary signal is present and the power supply to the generator is interrupted, the detection circuit is working correctly and the machining process can resume. However, if the power supply to the generator stops, the detection circuit has not detected a - simulated - error, which can lead to a defective detector, resulting in a corresponding warning or, ultimately, shutting down the machine.

Accordingly, it is essentially the task of the monitor circuit to evaluate the different combinations of the two signals, namely, the signals that indicate whether an error is simulated or not and whether the generator is operating or not. This object can be achieved according to a further feature of the invention in that the monitor circuit consists, for example, of a summing gate connected to the integrator. The sum gate compares the two input signals and creates a new signal from them as described. The task of the integrator is first to collect a series of test signals and only after the detected detector failure has been detected for a certain period of time to signal a warning indication or a warning signal. to turn off the machine.

The entire described input circuitry with a monitor circuit can be constructed very simply in terms of design, so that its own reliability is much higher than that of the detection circuit, and hence the overall reliability is considerably higher than when doubling the detection circuit.

The introduction of the simulated error signals may be carried out automatically by means of a signal generator to relieve the operator from this task, in particular in terms of uncontrolled operation. The introduction can take place at regular intervals or even within a random distribution at different intervals, so that it cannot occur synchronously with a regularly recurring error and remain undetected in this way. For example, a range of 1 to 5 seconds has proven to be an expedient time interval.

An exemplary embodiment of the invention is illustrated in the drawing and described in more detail below. The invention is illustrated on an arc detection circuit, using current and voltage in the working slot as well as the occurrence of a high-frequency component in the working voltage as criteria for determining the machining state. In the drawings: FIGS. 1a to 1c show different shapes of the stress-strain curve in the working slot during idling, normal operating condition and arc; FIG. 2 is a block diagram of a detection circuit with an input device and a monitor circuit; FIG. 3 shows the circuit diagram of the high-pass filter F of FIG. FIGS. 4a to 4c show different shapes of the voltage waveform at the output of the high-pass filter in idle, normal operating condition and arc conditions. FIGS. .

Giant. 1A to 1C show the ^{type P} ic Ru ^{It runs} hy discharging ^h o - ^{P P} oŽadovaných EIT discrete states on the path of the spark between the tool electrode and the workpiece to different states. As can be seen from the comparison, the discharge voltage in a good operating state (Fig. 1b) is generally lower than the no-load operation (Fig. 1a), but somewhat higher than the voltage that can be detected when an arc occurs (Fig. 1c).

The voltage difference between the voltage and when the ^b Lou ^to u at ^p etime, Good operating ^¹H status is VSA ^to too small to be able to indicate an existing when within a broad range - working conditions, good operating condition, which is required for machining a workpiece in the desired way.

As noted above, the presence or absence of the high-frequency component as defined herein is detected in the discharge path between the tool electrode and the workpiece. At the same time, the current intensity in the path is checked. The presence of the operating voltage and the operating current as well as the absence of the high-frequency component leads to the occurrence of an arc.

The check is preferably performed by means of a compaction circuit. To avoid confusion of the short-circuit arc as defined above, the comparator circuit C is supplied with a third signal indicating the short-circuit condition.

In the circuit shown schematically in FIG. 2, the discharge voltage or discharge current is conducted at a location W through a high-performance filter F, one embodiment of which is shown in FIG. 3. The output of this filter circuit F- is amplified by amplifiers. as a first input signal supplied to the comparator circuit C · proved especially účelrým, ^VA obsahhujeli Preamplifier C and a frequency ^ -on ^ Tovy mmiú-C, which is the price ^y ^ vysokodfre ENCN O ^{L M} ma ^t e that when ^{Z PU} manner is reliably generated signal odppnOííajcí logic 1. the second input komptačního circuit C is derived from the detector or discharge current I-i-tract to CD. Due to the discrete and individual character of the discharges, both inputs of the circuit C show a pulse train. Suitably, the high frequency component of the charging voltage amplifier A can then be designed to provide a pulse train when good operating conditions are detected, concurrently with the pulse train which represents the current signal of the CD detector.

In this case, the computation circuit can perform the function of a logic product, so that in the case of good operating conditions, its output also has a pulse train. But as there arc not the High Pass Filter £ supplied to the comparator circuit C no imppusy so there is no - the output signal of the commutation circuit C ⁱⁿ this zero ýstu ^p may ^b YT suitable way to identify ^{the causes} of ^{KLA-pyrimidin n} pros ^^ means of ZPO áovací ^{f h} o ^s i of the integration mechanisms. It is used in a known manner, for example, to pass a signal to a generator G, which then causes an interruption of the energy supply to the discharge path within a predetermined period of time.

In the absence of the high-frequency component, the input of the computational circuit C from the amplifier circuit A may show a logic 1 signal, for example above 1.5 MHz in the discharge voltage or discharge current, such as a logic 0 signal if the high-frequency component příoomna. This can best be achieved by logically opening the above-mentioned logical output of circuit A. The current signal from the CD detector can then, as previously described, have a logic 1 signal whose start and end practically coincide with the start and end of each individual operating process. Otherwise, it is a logic 0, whereby the compaction circuit C, which again acts as a product circuit, can be designed to provide an output signal to each of the two inputs - only after a response to the current input signal. This arrangement would then provide the output signal of the compaction circuit C, but only if the state of the arc is naatta (provided that it cannot be confused with any other clear state, see below). Such an output signal can then be used to control the switching device and interrupt the power supply to the discharge path.

A servo system can also be commissioned to retract the tool electrode

The short circuit can be eliminated by providing a third input signal from the short circuit circuit S to the comparator circuit C. This circuit provides a logic 0 and otherwise a logic ”1 if a short circuit exists.

It can easily be seen that the mode of operation of the comparator circuit C may be a function of the product gate, the sum gate, or a combination of both, as desired. Therefore, the above-described control circuit provides an arc indication, so that the electroerosion process can be controlled or modified so that it is virtually immediately interrupted when the arc occurs, by interrupting the required operating discharges. This interruption may take 0.5 seconds, so that a normal servo system can pull the electrode back if it is not a DC servo system. The retraction itself will cause sufficient mixing of the flushing liquid, thereby increasing slagging to the extent that the cause of the arc is eliminated.

The short circuit detector S is preferably designed and arranged to interrupt the power supply to the discharge path when it detects a short circuit. In this way, retraction of the tool electrode can be performed while controlling the servo system. Typically, if a short reaction time (8 milliseconds) for a short-circuit condition takes precedence over a longer reaction time (0.5 seconds) for an arc condition, for example when one of the above-described methods of distinguishing between these two states is applied, which can be extremely important in many applications, for example, if the occurrence of short-circuit states 100 times more often than the occurrence of arc states.

In some cases, the control circuit may be selectively wired to respond to and distinguish between arc states and short-circuit states in one of three ways, namely by:

(a) responds differently to them;

(b) responds only to earlier; and

(c) responds only at a later stage.

In this way, the use of existing special control devices may be dispensed with in a specific manner, or may be supplemented to detect a short-circuit condition.

The high-pass filter of FIG. 3 is designed based on the choice of components and connection method to block all frequencies below 1.5 MHz. It is further provided with two diodes D1. D2 in order to limit the output voltage to a predetermined maximum value, for example to 1 V, in particular in terms of switching on peaks of maybe 80 V and peak offs of several tens of V. In this way, the output waveform of the high-pass filter is shown. 4b, in the presence of good operating conditions, and of the shapes shown in FIGS. 4a and 4c, in the presence of idling and arcs. The signal transmitted under the latter two conditions has only occasionally sharp peaks, which can be very easily distinguished, for example by means of a voltage limiter and an integration device or some other delay circuit, from much longer-lasting high-frequency pulses that are transmitted at good operating conditions. conditions.

The circuit according to FIG. 2 further comprises a clock mechanism to enable it by means of the input device T1. T2. formed by clocked switches, and switches TJ to supply signals that simulate the presence of an arc, more specifically, a logic state of 1 for T1 and a logic state of 0 for T2. The terms logical 1 and logical 0 ”refer to two different logical states of the signal, for example two voltages that differ by 12 V.

If the switches forming the input device T1 are clocked. T2, closed, are supplied to the detection circuit with signals having the same value as the signals that the circuit would detect if an arc condition occurred. The circuit should respond, for example, by interrupting the power supply to the discharge path.

This can be checked by detecting if the power supply to the discharge path ceases after the clocked switches forming the input device 11, T2 have been closed. However, it is advantageous to automate this process. The switch TJ is used for this purpose. When the generator G starts to discharge, a corresponding signal is applied to the main summing gate G ^ with an inverted output via the equalizing network M and the invert gate G ^.

Normally, the second gate input G ^ receives a logic signal "1" through a resistor R. However, if the switch TJ is closed, a logical "0" signal is applied to this second gate input G ^. Thus, if generator G is still on and produces the required shocks after the test state has been reached by closing the switches constituting the input device Τχ, TJ, and the switch TJ, then a logical "0" signal is present at each gate input G ^ The output of this gate is connected to the integrator I by a logic 1 ”signal. If the power supply to the discharge path is not interrupted before the predetermined time interval has elapsed, this will provide a logic 1 signal to the integrator I during a time interval sufficient for the integrator I to produce an output signal that turns off the generator G. This is achieved by means of a main switch (not shown), and an alarm, which may be of an optical and / or acoustic nature, is also generated. However, if the actual detection circuit is operating correctly, then the power supply to the discharge path will cease in a very short time and then will start again. This may be a normal interrupt, which is, for example, less than 0.5 seconds when an arc occurs. Advantageously, however, it is designed to be much shorter, in order to be tested by means of a modulating component, which switches the power supply to the discharge path again after a few milliseconds.

In the case of the circuitry of FIG. 2, it is preferred to use the COSIOS circuitry, which is exemplified in various manuals of the Radio Corporation of America because of its insensitivity to noise. This circuit, for example, does not respond to 6V noise, but to 12V signals. If this logic COSIAOS is used in conjunction with an electromagnetic relay having a plurality of contacts, then it is necessary to use a delay device. This device is designed to prevent the response of the CUSI408 logic from switching all relay switches and to indicate incorrectly the arc status in this way. The delay device may conveniently also be designed to function as an integrator clock.

As used herein, the term " electrode " is understood to mean, for example, an abrasive wheel, wherein the discharge of electrical energy occurs between the wheel and the workpiece.

Claims (4)

1. Circuit for erosion control of spark erosion machining of machines operating with spark erosion, with a logic circuit for recognizing a faulty discharge in the presence or absence of certain electrical characteristics in the discharge circuit, for example from the absence of a high frequency component at the discharge voltage at discharge the simultaneous existence of operating voltage and operating current as a criterion for a harmful arc condition, as well as a device for short-term interruption of the machining process in the presence of such erratic discharges, characterized in that it is provided with an input device (T, T ^) into the discharge circuit. Circuit connection according to Claim 1, characterized in that the input device (1 ', 1') is a two-pole switch. 3. Circuit arrangement, the circuit according to claim 1 or 2, characterized in that the input device (Tp ₂ ^{T e} 3 monitorovým associated with a logical circuit. 4. The circuit according to claim 3, wherein the monitor circuit comprises, for example, a summing gate (Gg) connected to the integrator (I). .