DE2313263C2 - Control arrangement for controlling a machining parameter for an electrical discharge machine - Google Patents

Description

The invention relates to a control arrangement for controlling a machining parameter for an electrical discharge machine with a sensing device that monitors the working gap status and the output of signals, which indicate its compliance or non-compliance with a desired normal state triggers a memory, the content of which varies as a function of these signals in standardized fonts and which an actuator for the digits d- ~ s operates the respective machining parameters at the working gap.

An electrical discharge machine with such a control arrangement is described in US Pat. No. 3,670,136.

When operating such a machine, on the one hand, there is an effort to set the various operating parameters for to set the working gap such as the duration and size of the machining current pulses and gap distance in each case, that the greatest possible processing progress results. On the other hand, there must also be operating conditions be avoided at the working gap, in which the machining condition is unsuitable? like for example the formation of permanent arcs can result. These two demands are in contradiction to each other, and there must always be an acceptable compromise between them.

For this purpose, the working gap is monitored by a sensor, with the help of which the Let the operational sequence distinguish between permissible and impermissible conditions in the working gap. Using these sensor readings the respective operating parameters are then changed with the aid of appropriate actuators so that a desired normal state is restored at the working gap. In practical operation has now further shown that such tracking alone is not sufficient to avoid operational disruptions, for example, by the Avoid the formation of permanent spark gaps or arcs. Namely, if the actuators for the Changes in the operating parameters can react immediately to the respective sensor signals there is always the risk of overreaction in the form of an undesirably rapid or major change in the affected person Operating parameters, which in turn cause damage to the workpiece to be machined or also to the lead to the workpiece to be machined or also to the machine parts that interact with it can.

The invention is based on the object of designing a control arrangement of the type mentioned at the outset in such a way that that they are too rapid or too strong a change in operating parameters depending on the respective operating status at the working gap with certainty excludes sensor signals.

The object set is achieved according to the invention in that with the in the form of a first bidirectional counter trained memory via a comparator to adjust its content to the sensing device connected second bidirectional counter is coupled in such a way that it eir · advancing the first bidirectional counter by one unit upwards or downwards only if the counters are the same. Advantageous refinements and developments of the invention emerge from the subclaims.

When operating the control arrangement designed according to the invention, on the one hand, the sensor detects the Occurrence of undesired states in the working gap indicating error signals and, on the other hand, compliance generated normal state signals occurring in the desired working conditions, which in turn act as control signals are used to change the individual operating parameters via the corresponding actuator. Included the actuator reacts to an error signal with a change in the respective operating parameter in the sense a cancellation of the undesired operating / .state and thus mostly also in the sense of a slowing down of the Editing. Conversely, a return of normal state signals in due to no error signal during a long period of interrupted sequence a reaction of the actuator in the sense of an adjustment of the respective operating parameters in the direction of increasing the machining speed to take effect.

The second bidirectional counter acts as a stabilizing element by preventing the the first bidirectional counter acting on the respective actuator prevents the incoming sensor signals, because the counter reading of the first bidirectional counter only after the counter reading has been updated of the second bidirectional counter can be changed further. This way the overreaction becomes the Control arrangement avoided altogether with certainty.

As a result of the control arrangement designed according to the invention when operating an electrical discharge machine The operating parameters that influence the operation are, in particular, the pause between successive processing pulses and the period and the amount of return movement of the machining electrode with respect to the To name workpiece, these parameters individually or in combination with the invention Regulation can be subjected. ι ο

The invention is explained in more detail below with reference to the drawing. It shows

F i g. 1 and 2 block diagrams of a control device according to the invention;

F i g. 3 signals that appear in different parts of the FIG. 2 occur circuit shown; and

F i g. 4 shows a graphic representation of the sequence of electrical machining with the aid of the present Invention.

In Fi g. 1 shows a counter C1, the input of which is connected to a terminal 1 which receives "OK pulse" signals from a discriminator, not shown, which detects "OK pulses" among successive pulses entering the gap between the machining electrode and fed into the workpiece. An "OK impulse" is an impulse that causes a satisfactory processing discharge. Whether or not each individual pulse at the machining gap is an "OK pulse" can be determined, for example, by measuring the scan or current level of the pulse after the start of the current flow through the gap with reference to a threshold value that distinguishes a normal discharge from a short circuit, an arc, and other undesirable impulses. The counter C1 with its assigned input circuit is used to count the "OK pulses". When it has counted a specified time of input impulses, for example eight "OK impulses", it is deleted and starts counting again. When the counter C 1 is cleared, it sends a clear signal to a second counter C 2.

The second counter C2 has its input connected to a terminal 2 which receives "NG (not good) pulse" signals from a discriminator, not shown, which detects "NG pulses" among successive pulses at the gap between the machining electrode and the workpiece. An "NG pulse" is a pulse that delivers an unfavorable result, ie a current pulse that differs from the "OK pulse". The counter C2 with its input circuit is used to count the "NG pulses". If it has counted a predetermined number of input pulses, for example four "NG pulses", before receiving the clear signal from counter C 1, then it generates a control signal at its output that identifies the state of the machining gap as "abnormal" Signal controls a monostable multivibrator or a similar timer 7Ί, which in turn generates an "O" signal at its output.

The counter Cl is then cleared. If, however, the counter C2 is cleared before the predetermined number of "NG pulses" is reached by the clear signal received from the counter CI, which indicates that the predetermined number of "OK pulses" has occurred, then no output signal becomes the timer Tl given, and this remains with a "1" output signal. In this way, the timer Ti has an "O" output indicating an abnormal gap condition. The specified number of pulses is preset, depending on the machining to be carried out, depending on the materials of the machining electrode used and the workpiece to be machined, and other machining factors.

A third input terminal 3 connected to a third counter C3 and a fourth counter C4, With this execution example: serves to count the impulses that occur when the machining electrode is returned with respect to the workpiece. If a specified number, for example eight pulses, are counted by the counter C3, it generates an output signal.

This output signal is applied to the clear input of the counter C3 via a NOT element N0T2 and a NAND element 1, the NAND element having a further input connection which is connected to the output of the timer Ti . It can be seen from this that the counter C3 is cleared when an "0" signal indicating an abnormal Upaltstatus is displayed by the timer T 1, as well as when it has reached the predetermined number of e.g. B. has counted eight returns. When this specified number is reached, the counter C3 generates a "1" output signal which designates the state of the gap as normal if the specified number of NG pulses (four NG pulses) is not passed through the counter CI during the period specified by the counter CI Counter C2 was counted. The last period is much shorter than the period in which the predetermined number of returns is counted by the counter C3.

The output signal of the counter C3 is passed through a NOR element NOR 1 and a NAND element NAND2 to the downward counter input dn 1 of a bidirectional counter UDC \ . This counts down by one unit if neither the element NOR 1 nor the element NAND2 have a blocking signal at their respective other input, which is fed in by a comparator £ and a decoder D 1, which are explained in more detail below.

In the present exemplary embodiment, the bidirectional counter UDC \ has outputs for the counts 0 to 9 which correspond to ten incrementally changed sizes of the electrical machining parameters, such as the time interval between adjacent machining pulses, the distance or the length of the relative return of the machining electrode from the machining position or the Time interval ω between adjacent tracking periods or other important processing parameters. These parameters are set by the corresponding ten positions, as described in more detail below

The bidirectional counter UDC 1 has a connection up 1 for counting up, into which the output signal of the timer 71, which indicates a detected abnormal gap condition, is fed via the element NOTi and a NAND element NAND3 in order to count up by one unit. if the timer generates an "0" signal, provided that no blocking input signal from the decoder D I is present at the NAND 3 element.

The decoder Dl, which decodes the bidirectional counter UDC \ , feeds input signals into the elements NAND2 and NANDZ in order to block the counting down command from the NOR 1 element and the counting up command from the NOT element NOT 1 when the counter UDC 1 is 0 and 9 respectively indicates.

The fourth counter C4 generates an output signal when it has counted a predetermined number of returns of the electrode, the number in this embodiment being much larger than that for the counter CZ

ίο preset number, for example 128. The output signal of the counter C4 is fed back to its clear input via the NOT element NOT3 and the NAND element NANDA . The gate NANDA has a second input terminal which leads to the timer 71, and a third input terminal which leads to a timer 74, which in turn is connected to the comparator E , which normally has an "0" output signal and and when a "1" Output signal actuates timer 74, which then outputs an "O" signal

is generated. Accordingly, the counter CA is immediately cleared and starts counting again when it has counted the predetermined number, namely 128 pulses, as soon as an "O" signal indicating an abnormal gap condition is received by the gate NANDA from the timer 71 or the gate M4 / V £? 4 the "0" off gaiigssigntii ucs r-cngcucis ι t cinpimigi, uu aiiicigi, uiu um »rtuagiingsMgiiui ucs tcigiciLiici3 c aui» Mt is switched. In other words, the counter CA starts after its previous counter status has been cleared.

7u is to be counted by the "O" output signal of the timer 74 which was fed into the gate NANDA. When it has counted the 128 input pulses without an "O" signal from the timer 71 indicating an abnormal gap state, the counter CA generates the "O" signal at the output of the NOT gate NOTZ and at an input terminal of the NOR 2 gate.

The other connection of the last-mentioned element is controlled by a NOT element NOTA , its

Input terminal is connected to the comparator E. From this it can be seen that the "O" signal indicating the count of 128 pulses is fed via the element NOR 2 and has a "!" Signal at its output only if the output signal of the comparator E explains its function below is explained, "1" is. The signal from N0R2 is in turn fed via a NAND gate NAND5 to the down counting input dn 2 of a bidirectional counter UDC2 . The decoder D 2 monitors the count of the Counter UDC2 and carries a signal to the element NAND5. this prevents the downward counting pulse from being fed into counter UDC2 when the latter is at zero.

The comparator E, which is provided between the first and the second counter UDC 1 or UDC2 , normally has an “O” output signal, as has already been mentioned. It has a "!" Output signal when the count of the first counter UDC \ matches the count of the: - second counter UDC2 If the "1" signal is generated, then the element NOR 1 is switched off, ie locked, so that when generating j "in £ c AKvuartcvähiimntiicoc / 4tir / * h W £ n counter C3 dsr counter UDC 1 is not counted backwards" and bsi seinsrn count remains this is the first counter UDC \ with its count never below the count of the second counter UDCZ It is also to be noted that the "1" output signal of the comparator e is the one hand fed to the timer 74 to the counter CA , and on the other hand via the NOT element NOR2. It follows that the counter CA emits counting crimp pulses in accordance with the returns of the electrode, and that the element NOR 2 is switched on, ie opened, as soon as the count of the first counter UDCX agrees with the count of the second counter UDC2 . The downward counting pulse is at the input of the second counter UDC2. after the counter CA has reached the predetermined count (128 pulses) and if there is a match between the counts of the two up-down counters

UDC \ and UDC 2 exists. In the meantime, if an abnormal gap condition is indicated by the counters Cl and C 2

is detected and the "O" signal is accordingly generated at the output of the timer 71, then the counting operation is performed terminated by the counter CA and this reset. This way the counting down becomes the second

Two-way counter precisely controlled. The counter input for up- counting up2 of the counter UDC2 is connected to the output of the NOT element

so NOTX via a NOR element NORX a NOT element NOT5. a NAND gate NAND6, a NOT gate NOT6, the timer 73 and a NAND gate NANDT connected in series. In this series circuit, one input connection of the element NAND6 is connected to the output of a timer 72, the input of which is connected to the comparator E. As long as the latter has an “O” output signal, the timer 72 remains switched off and outputs a “0” output signal to the NAND 6 element.

This means that this element is blocked from its input signals. The input signal of the timer 73 is "0", and this input signal is also fed to gate NOR 3 However, if the output of comparator m £ corresponding to the count of the first counter UDCX a "1" state is switched, because the counter UDCX with the second counter UDC2 then the timer 72 is actuated to open the element NAND 6 and to keep it open for a predetermined time interval, for example 40 s.

ω Depending on the purpose of processing and the materials of the electrode.

If, in this time interval, a signal indicating an abnormal gap is detected by the NOT element NOTX and a "!" Output signal is given to the element Λ / ΟΛ 3, then this signal is transmitted via the NOT element NOT5, the element NANDf , and the NOT element Λ / Ο76 are transmitted and form a "!" input signal for the timer 73 to activate it. The pulse generated by the timer 73 is the member NAND7 in the counter-up input up2 the counter Udc2 fed Meanwhile is also the same, an abnormal gap state indicative "" - output of the NOT element NOTX via the link NANDZ in the counter-up input upX of the first meter UDCX fed in. The first counter UDCX can then always keep its counter reading step by step

increase when it receives another "!" signal from the NOT element NOTi, indicating an abnormal gap. From the above, it can be seen, however, that the second counter UDC2 cannot increase its counter reading by more than one unit in the predetermined time interval of, for example, 40 s. If, after the start of the time interval, a single signal indicating an abnormal gap is received, the "!" Signal generated at the output of the NOT element NOTb is fed back to the element NOR 3. ■> dns is thereby blocked. The resetting of the element NANDb is blocked until the timer Γ2 ends the interval! ·, "And its output signal returns to an" O "state. After the end of the interval, the timer 72 remains switched off until it receives another"! " signal receives from Verglcicher e, indicating that the count of the counter UDC 1 coincides again with the count of the counter Udc2. If no abnormal shift condition indicating signal is received from the timer Tt during the set by the timer T2 time interval, then the bidirectional is - UDCl counter not switched forward.

It should now be assumed that the counter UDC2 now has the nth count of 10 possible (0 to 9), while the control counter UDCX is counted up and down depending on the signals fed in, in a range of counts that are above the η-th level, and that the control counter UDC \ controls adjusting devices according to its counter reading, the size of a processing parameter being determined by the adjusting devices. In such a condition, the control counter UDC \ can lower its counter reading "if it matches the n / th counter reading of the Bc?> J ^ff S7äh!? Rs IJV) CTl . This happens in accordance with the gap signal arriving at the down-counting input, which indicates that the machining in the machining gap has improved. A new size of the machining parameters is then set in the setting device so that it agrees with the nth count of the counter UDC 1, and this is used for the following machining is actually suitable for a satisfactory progress of the machining, then during the time interval set by the timer T2 no signal indicating an abnormal gap condition must be delivered, which requires that the value of the machining parameter is set to the previous value. The device ensures that the nth count and thus the nth P parameter size are retained until the allocated time interval ends.

It is important to note that after the counter reading of the control counter UDCX coincides with the counter reading of the reference counter UDC 2, a signal indicating a normal gap state occurs again and again at the output of the counter C3 and at the input of the element NOR 1, which is sent to the counter via the element NAND2 -Low input of the control counter UDCX leads. In the device described, however, the transmission of this signal is blocked by the "1" output signal of the comparator £, so that the control counter UDCX is blocked for a relatively long time interval with respect to each down-counting pulse, namely until a predetermined number of pulses, for example 128 pulses, were counted by the counter C4. In this way, it is only after the completion of this counting, in which a downward counter pulse is given to the reference counter UDC2, that the control counter UDC X increases its control counter reading by one unit, depending on a signal indicating a normal gap state, whereby at this point in time the counter readings of the two bidirectional counters match again. This actually reduces the premature down counting of the control counter UDC X and excludes an excessive change in the size of the machining parameters which would have a destructive effect on the workpiece. This also avoids too great a change in the parameter value in the opposite direction and thus swaying back and forth.

After the counter readings between the control counter UDCX and the reference counter UDC2 match, it is possible that the newly set size of the machining parameter, if it is used, is not suitable for ensuring satisfactory machining. But such premature countdown is detected and corrected immediately. After the match at the nth count between the two counters, the timer Tl immediately begins the monitoring period, for example 40 seconds. During this period, an abnormal gap condition signal if such a signal occurs, by the timer TX to the up-counting input of the Control counter UDCX to reset its counter reading to the previously set value, the (n + l) -th reading. At the same time, the signal indicating an abnormal gap condition also increases the count of the reference counter UDC 2 by such a unit. In this way, the new reference level, the (n + I) -Ie level, is set, which prevents the count of the control counter UDCX from falling below this value. Another signal which occurs during the above-mentioned monitoring period and which indicates an abnormal gap condition can be detected and processed by the timer Π. This increases the control counter UDCX to the (n + 2) th counter reading, which in turn corrects the size of the machining parameters accordingly in order to prevent a further anomalous state of the gap. However, the count of the reference counter UDC2 remains at the (n + l) -th status and waits until the count of the control counter UDC X drops to this reference status

The coincidence of the two counters UDC X and UDC 2 at the / i-th count results in a situation that requires the taxpayer UDC X to count up from time to time. If no signal indicating an abnormal gap condition is detected during the test period, which begins with the coincidence of the two counts and ends after the time period set by the timer T2 (40 s), then the two counters keep UDCX and UDC 2 after the end of the test period the matching n-th counter reading, the control counter UDC X determining the size of the machining parameters determined thereby. If an abnormal condition then occurs in the machining gap, then the timer TX generates a signal indicative of the abnormal gap state in order to cause the counter reading of the Control counter UDCX the value (n + 1) increases while the counter status of the reference counter UDC2 remains at the nth value. The value (n + 1) of the control counter UDCX supplies the new size of the processing parameter. When the abnormal gap condition is thereby eliminated, the counter Ci counts the predetermined number of times

Pulses, for example eight pulses, as already mentioned above, so that the control counter UDCX returns to the nth count. If the abnormal gap condition is not eliminated or a further abnormal gap count occurs, then a further signal indicating this is generated by the timer TX in order to increase the control counter UDCX to the (n + 2) th count. If the machining gap assumes a suitable discharge or favorable machining conditions, then the increased count is immediately reduced step by step depending on signals which indicate the normal gap condition and which are generated by the counter C3, until it returns to the η-th value.

On the right side of Fig. 1 is a display device with a display decoder D 3 and a Tube display device V is provided, which is connected to the output connection of the control counter LOC1

,: ίο are to enable a visible display of its output signal, the control counter reading, whereby

#! this signal is also fed into the parameter setting device via an output connection OLT, which

on the basis of FIG. 2 will be explained in more detail.

ß; In FIG. Furthermore, a digital switch DS is provided, which allows the counter readings to be set from

jl; each of the two counters UDC 1 and UDC2 by hand. The digital switch DS is a selector switch

C, 15 ter 5W assigned, which is used to selectively connect an "automatic" connection A UT and a "manually ] ■ operated «connection MANUT with the counters UDC \ and UDC2 via a NOR element NOR 4 and a

ψ Connect NOT member NOT8. This arrangement ensures that a change in the digital switching

H ters Ds me then on rfie counter UDC ! and UDC2 is effective when the manually operated connection MANUT'ir.

p a switch position is set so that it is ineffective if the AUT connection is in this switch position

ment, whereby the counters are locked against the operation of the digital switch DS. The use of the Ij digital switch DS is necessary for certain types of processing, which are advantageous for an initial

ii | start borrowed reference counter reading that is greater than the "O" word. These operations are different

J; initial reference values desirable or necessary, depending on the type of training of the machining M processing electrode and the shape in which the workpiece is to be brought, as well as depending on whether from one Ig 25 rough machining is switched to fine machining with a single workpiece.

Furthermore, an input connection CLT is provided for a clear signal for the counters UDC 1 and UDC2 in order to reset the counts of these counters to "0" if this is desired, for example, at the end of a given processing. The clear signal from the connection CLT is fed into the counters via the NOT element NOT1 and the element NAND 8, the latter element having a further input connection CWT connected to it. The input terminal CWT generates a clear signal when the electrical power supply is switched on, so that the previously stored counter content, if such is stored, is automatically cleared at the start of the new processing.

From the above description it can be seen that the counters CX to C 4 controlled by the sensing elements, together with the timers TX to Γ 4, form a sensing device which monitors the state of the working gap. The sensing device is designed so that it detects both short-term and long-term changes in the working gap. The duration of the acquisition interval can be determined by presetting the counters C1 to C4.

In FIG. 2 shows an exemplary embodiment of a machining parameter setting device. The output signal of the bidirectional control counter UDC 1, which appears at its output terminal OLT, is fed to a decoder D 4 which generates the control command to control the size of one of several processing parameters in accordance with the counter The decoder D4 specified in the exemplary embodiment is provided with ten output stages corresponding to the ten count values of the control counter UDC 1. It can optionally be actuated by the corresponding counter readings in order to select and set one of the ten different values for each of the electrical machining parameters (one or more) For the sake of clarity, the figure shows only the nth output stage connected to the nth output of the decoder D 4. It goes without saying that the corresponding nine output stages are each connected to the other nine outputs of the decoder D 4. As already mentioned above was to include the most important electrical machining parameters the time interval between adjacent discharge machining pulses, the length of the path of the machining electrode from the workpiece so in the return, which is used and set independently of the gap setting servo mechanism, the time interval between the returns, i.e. the length of time in which the electrode and the workpiece is held in a machining position to allow discharges, the reference voltage or control level for the servo feed control, and the speed of the circulated dielectric fluid through the machining gap.In the following description, the control device for the two parameters of the feedback is explained in more detail.

Each setting stage comprises two transistor switches Tr 1 and Tr 2, which are each connected to monostable multivibrators (monoflops) MX and M 2. As already mentioned above, each setting stage receives an input signal from the decoder DA, which is optionally fed into it. In this way, the nth setting stage receives such a signal from the nth output of the decoder D 4 when the bidirectional control counter is at the nth count, during which time there is no output signal at the other nine outputs of the decoder D 4 The transistor switches Tr X and Tr 2 are kept conductive when they receive an input signal and cause the monosiabile multivibrators MX and M 2 to be operational. If, in this case, the first monostable multivibrator M 1 is activated, then at its connection UP it delivers a pulse of a duration which corresponds to a predetermined length of the electrode return with respect to the workpiece. When the second nrsnostable multivibrator M 2 is activated, it delivers a pulse to the same connection UP , the duration of which corresponds to a predetermined time between the returns, i.e. defines the processing time interval, i.e. the time between the point in time at which the electrode moves to the processing position, and the time at which the electrode is subsequently withdrawn

ϊ \ ζ to interrupt processing. A circuit for controlling the / wide monostable multivibrator M 2 is provided with the reference symbol COT and comprises a connection C, which is connected to the machining gap in order to tap the average gap voltage, and a Schmitt trigger SM, which sets the average gap voltage with a threshold value compares and supplies a control signal to the multivibrator M 2 via a NAND element NAND9 and a NOT element NOT9 when the gap voltage falls below this comparison value. The first multivibrator M \ begins its timer function after being controlled by the second monostable multivibrator M 2. The element NAND 9 is controlled at the second input by the first multivibrator Mi in order to block the second multivibrator M 2 during the operating time of the first multivibrator. The signals appearing at the connection UP are supplied to a control circuit of an associated electrode drive device, for example in the control coils in a hydraulic servo feed device.

In FIG. 3 are those in the circuit of FIG. 2 occurring signals are shown. The amplitude of the signals is plotted on the ordinate and the time on the abscissa. The signal A represents the mean switching voltage which occurs at the connection G. The signal B represents the output signal of the Schmitt trigger SM . The signal C represents the output signal of the monostable multivibrator M2. The signal D represents the output signal of the monostable multivibrator M 1.

It should be assumed that the transistors TrI and Tr 2 according to the output signal of the

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it can also be assumed that the machining electrode has then already been withdrawn from the workpiece. The machining electrode then sews the workpiece to narrow the gap between them. As shown, the first sequence of electrical machining discharges occurs at time / 1. The occurrence of electrical discharges is initially sporadic. With the further decrease in the gap distance, their number in the unit of time approaches the number of electrical pulses that are fed into the machining gap, accompanied by a gradual decrease in the mean gap voltage, as shown. At time r 2, the gap distance reaches an optimal value at which processing should continue, and the Schmitt trigger SM generates a digital "!" Output signal that the monostable multivibrator M2 sends depending on the reduction in the average gap voltage below a predetermined level Actuation controls. The previously set-. The time constant in the multivibrator M 2 determines the machining time or the length of time in which the machining electrode and the workpiece are held in a machining position. At time 1 3 after the completion of this time period of the multivibrator M 2 is the multivibrator M 1 is driven by the switch-off, which provides a signal at the output UP to drive back to the machining electrode from the workpiece. At the time f 4, in which, as shown, the signal pulse for the retraction of the electrode ends, or shortly thereafter, the electrode reaches its extreme position. The servo signal then enables the electrode to automatically approach the workpiece again by repeating the above-mentioned period from time 1 5 on and the fixed machining time period starting again at 1 6. The time interval between f 4 and i5 or iS, which indicates the time required for the automatic return of the electrode to the machining control by the servo signal, is obviously proportional to the length or extent of the return of the electrode, which is determined by the time interval between times j3 and f4 is determined. However, a suitable means can be used by the time interval ί4-f 4- f 5 or 1 6 to reduce or independently set, so that the interrupt processing or the remaining time / 3-f 5 f or 3-16 or reduced in can be controlled as desired.

It should be noted that the use of the designation "interrupt processing" or "editing remaining time" is not necessarily true for the time interval between f 3 and 1 5 since not exclude the possibility of some electrical discharges in a machining during this time interval shall be. Indeed, if the length of the return is about 0.01-0.02 mm, then some of the applied electrical pulses may cause electrical discharges across the spread gap during the time interval in question, although the frequency of the discharges will then decrease sharply.

As already mentioned above, each of the ten setting stages, which are each connected to the ten outputs of the decoder DA , has the same design and operating mode, as explained in more detail above, with the exception of the time settings of the multivibrators Mi and M 2, which are progressively and gradually change from one setting level to the next in order to effect different sizes of the length of the return of the electrode and the processing time. In a typical example, the multivibrator M1 thus generates in the nth setting stage a variable for the length of the return of the electrode which is greater by a predetermined amount than the variable provided for the (n - \) - le stage of the multivibrator Mi, and which is smaller by the same or a different predetermined amount than the size provided for the (n + 1) -th stage of the multivibrator M 1. Similarly, the multivibrator M 2 in the n-th setting stage generates the amount of machining time (ie, the time in which the electrode and the workpiece are kept closely spaced from each other in a desired machining position) shorter than a predetermined amount the size provided for the (n- l) -th stage of the multivibrator Λ / 2, and which is longer than the size provided for the (n + 1) -th stage of the multivibrator M2 by the same or a different predetermined amount.

Although one of the two time dividing devices Mi and M 2 can be provided in each setting stage for the control of either the return of the electrode or the processing time according to the novel sensing and operating device described here, tests have shown that it is particularly advantageous is to use both devices and these two parameters at the same time and together with each control in the manner described, in particular to increase the length of the return path of the electrode and to reduce the processing time when the number of setting steps increases effective destruction by arcing on the workpiece and the elec-

trode can be prevented and processing can be optimally designed. An example of these parameter settings is given in the following table:

Table 1 R feedback pulse duration Return length Machining I. Setting levels Cf3-t4: ras) (mm) duration (Decoding outputs) Cf 2-ί 3: ms) Ü 14th 0.00 450 I. 10 0 40 0.10 400 1 65 0.20 355 P. 2 90 0.26 310 3 115 033 260 fei 4th 145 0.40 215 1 15 5 170 0.46 170 6th 195 032 120 7th 220 038 73 8th 250 0.65 25th 9

The time interval between adjacent individual electrical discharge pulses can be regulated in a similar manner in accordance with the present invention. In this case, the pulse generator, which generates signal pulses for the formation of these discharge pulses, can be designed so that it has different time settings, each of which can be actuated by the output signals of the decoder DA , and that it

delivers various previously set sizes of this time interval in accordance with the various counter readings of the control counter UDC \. In this case, the various time setting devices can each have a capacitor or resistor, which form a component that determines a period of time, which is optionally switched on and actuated in the circuit depending on the corresponding output signal of the decoder DA when the counter UDC 1 has reached the specified count.

It should be noted that the input signal at terminal 3 (Fig. 1) is not limited to pulses related to the above-mentioned electrode return. As an alternative, “OK signal pulses” can be used as the output signals of the counter C1, which indicate the normal state of the gap, as input signals for the connection 3. The use of the "OK signal pulses" as input signals to the counters C3 and CA is particularly advantageous if the processing parameter to be controlled is the time interval between adjacent discrete discharge pulses.

example Kerosene or paraffin oil is used as the dielectric processing fluid and is not "circulated".

A workpiece made of S55C is immersed in this liquid. A cylindrical copper electrode with a diameter of 20 mm is used for electrical processing. The electrical processing impulses between the electrode and the workpiece have a pulse duration of 650 μς. Furthermore, a pulse interval or a remaining time of 90 μ5 and a current amplitude (short-circuit current) of 70 A are used. A Gap detector and the above with reference to FIGS. 1-3 described control devices are used to to control the intermittent return of the electrode with respect to the workpiece during machining with the ten setting values for the length of the return and the processing time between adjacent returns, which are listed above in Table 1. In FIG. 4, the execution of the electrical machining is shown graphically, with the time on the abscissa and the progress in the machining through the depth of the recess (mm) which is formed in the workpiece (solid curve L). and changing the

so counter readings (0 to 9) of the two-direction control counter UDC 1 (curve C) are plotted on the ordinate. In

Reference symbols placed in brackets on curve (1), (2), (3), (4), (5) show the count values c of the counter UDC 1

which, as shown, increase gradually as the processing progresses.

As shown in FIG. 4, processing begins like this. that the taxpayer UDC 1 and the reference counter VDC 2 are both initially set to "0". The reference number remains during the period from / 0 to ti ler UDC2 on meter country "0". During this period, a single upward counting took place four times in the counter UDC 1, which is indicated by the reference symbol P 1 and is based on the detection of an abnormal condition in the machining gap by the counter Ti and the associated circuit, each upward counting switches the decoding output (setting levels) from "0" to "I" (Table 1). With each of these changes, the counter reading obviously goes back to "0" immediately. This shows that when counting up further, no another abnormal signal is detected while the counter C 3 counts eight subsequent returns of the electrode. Shortly before time f 1, the counter UDCi increases its counter value from "0" to "1" and from "0" to "2" in two steps. The incremented counter value indicated by the reference character P2 . then drops immediately to "0". but the counter value is then reset to "1" at time 1 1. This increase shows that abnormal Spaltbcdingung was acquired during the period in which the timer T2 is in operation. Through this the reference counter value increases, the counter status of I / DC2. also to "1".

In the second step (1), the counter reading drops to 0 at ΡΛ. This reflects the fact that the counter CA 128 has counted successive returns of the electrode and in the meantime has not received a signal for an abnormal gap condition, which causes the reference value to drop to "0". The count of the

Control counter UDC 1 also drops to "0" because the counter CZ has counted eight consecutive returns of the electrode. The downward counting to “0” is immediately followed by an upward counting to “1” at the count of the two counters UDCX and UDC2, which is due to the occurrence and the detection of an abnormal gap condition is effected. Similar counting down and up occurs twice thereafter at P4 . However, such repeated, intermittent countdowns have advantages and are important. As a result, the machining efficiency is kept in the best possible state, since an unnecessary upward counting is excluded, which would otherwise occur under certain conditions of the gap and clearly cause a decrease in the efficiency of the machining. Nevertheless, it can be seen from Fig. 4 that at P5 an upward counting in the counter UDC 1 is necessary, and that afterwards the counter value of the reference level UDC 2 increases to "2". This means that stable processing can no longer continue with the counter reading " 1 «can be maintained.

It should be emphasized that the reference meter is a powerful and advantageous device which is a stable one and, if necessary, an almost sequential shift of the count of the control counter with the The electrical machining progresses causes the control level of the parameter setting means to fluctuate up and down without the superimposed level. This will result in better efficiency in The machining is also free from the risk of thermal arcing, which can destroy the workpiece and the electrode.

While the invention has been described above essentially in terms of controlling the return of the machining electrode with respect to the workpiece in order to remove the machined pieces and other products from the To remove machining area, the present invention can be applied to one or more in the same way important parameters in the machining, such as the time interval between adjacent machining pulses, are used. For this purpose, only minor modifications of the illustrated embodiments are required.

From the above description it can be seen that the present invention provides an improved control apparatus relates to a processing parameter that regulates a possibly occurring undesired processing condition immediately eliminated and such a condition is prevented with the ongoing control, by adapting to the changing condition of the machining gap and efficiently monitoring the condition of the gap. The present invention not only enables an improved one Processing efficiency, but also a given and desired processing on automatic Basis without the need for operator supervision by shifting the type of processing to a destructive thermal arc and other dangerous conditions is prevented.

3 sheets of drawings 35

Claims (4)

Patent claims: 1. Control arrangement for regulating a machining parameter for an electrical discharge machining machine with a sensing device that monitors the working gap condition and triggers the output of signals indicating its agreement or non-agreement with a desired normal status to a memory, the content of which is dependent on these signals in Unit steps varies and which operates an actuator for setting the respective machining parameters at the working gap, characterized in that with the memory in the form of a first bidirectional counter (UDCi) via a comparator (E) a for setting its content to the sensing device (counter C 1 to CA, timer ίο Π to TA) connected second bidirectional counter (UDC2) is coupled in such a way that it allows the first bidirectional counter (UDC 1) to be switched up or down by one unit only when the counts are the same 2. Control arrangement according to claim 1, characterized in that between the sensing device (counter Cl to CA, timer Π to TA) on the one hand and the most and the second bidirectional counter (UDC \ or UDC2) on the other hand logic elements (NOR i, NOR 3, NAND 1 to NAND3 or NOR 2, NOR 3. NAND4 to NAND7) are inserted for a detection of the working gap state with a relatively short or with a relatively long period, one of these logic elements (NOR 1 and NOR 2) being used to control it the comparator (E) is connected. 3. Rege arrangement according to claim 1 or 2, characterized in that at least one counter (C ί to C 4) with a preselected count for determining at least one time interval is provided in the sensing device, which emits a signal when its preselected count is reached and is deleted at the same time. 4. Control arrangement according to claim 3, characterized in that at least one counter (Ci to CA) in the sensing device is coupled to a pulse source influenced by the working gap.