JPS5840227A - Pulse generator for discharge cutter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention includes a low current source for starting electric discharge, a large current source for supplying machining current, and a method for starting the operation of the low current source during the first phase. , a synchronization and monitoring circuit 40 that detects the start of discharge during a second phase and causes the operation of the large current source to start, and causes the operation of the large current source to stop during a third phase. The present invention relates to a pulse generation device for an electrical discharge cutting machine that cuts a workpiece by cutting a workpiece. This known 7e
A lus generator is described in US Pat. No. 7,633.

As is well known, in order to cut a workpiece with high processing efficiency,
It is necessary to apply a short duration, large amplitude pulse with a steep leading edge between the wire and the workpiece. Since self-induction inevitably exists in the wiring between the pulse generator and the processing area, it is difficult to obtain 74 pulses with a steep rise.

The device described in DE 21 10 1 173 has a condenser-shaped capacitor placed in the immediate vicinity of the processing area on one support arm of the wire guide. This device is advantageous in that a firing voltage is applied progressively between the wire and the workpiece, and the discharge current level decreases in the same direction as the level of the firing voltage, but the support arm of the wire A large-capacity storage battery is installed in the machine, and it is necessary to install a brush that comes into contact with the workpiece, and there are inherent disadvantages due to the movable contacts being immersed in the machining fluid.

The purpose of the present invention is to eliminate the shortcomings of the conventional devices and to combine only their advantages. The master pulse generator according to the present invention generates a second pulse whose value changes according to an increasing function of the duration of the first phase while keeping the machining discharge time constant.
It is characterized in that it comprises an adjustment unit for applying a respective discharge current level during the phases. Because of K, each discharge energy changes in the same direction as the discharge start time.

Another advantage of the novel device according to the invention is that it is possible to select the law of variation of the current level as a function of the discharge start time that gives the best results. - By way of example, it has been found to be advantageous to provide the pulse current with a minimum level that is determined when the discharge start time is zero. It has also been found to be advantageous if it is desired to limit the time for the start of operation of the current source.

Next, the embodiments of the present invention shown in the drawings will be described in more detail.

Figure 1a=/C is a diagram for explaining the present invention,
FIG. 1a shows the variation over time of the voltage U between the wire and the workpiece, and FIG. 1b shows the variation over time of the discharge current 1. Cycles of variable duration T1, T2, T3
, ■4 are shown side by side. Each cycle consists of three phases:

b) Under the action of the first generator, the voltage increases according to a predetermined time curve, for example the exponential charging curve of a capacitor. The discharge starts abruptly after a suitable discharge start time TD and the current io=! set by the first generator. The discharge current at is first set.

In response to the detection of this start of discharge, operation of a second generator, which is more powerful than the first generator, is initiated. However, the switching time of semiconductor output devices is relatively slow (0,
7-0, j μ seconds), so that the pulse 4/~ before the discharge current is established at the new current value IP.
The minimum delay seen in 3 occurs. The main feature of the present invention is to make this peak current value IP an increasing function of the discharge start time TO measured during the first phase. 11)
The figure shows ≠ current pulses that become increasingly smaller in magnitude in response to shorter discharge onset times. Noe
The pulse duration TA is preset to a constant value of several microseconds. Particular attention should be paid to the pulse At. Since at the beginning of the first phase the voltage rises according to the gradient, it is necessary to introduce a period of time between the moment when the voltage or current is observed and the beginning of the gradient in order to determine whether the onset of discharge occurs or not. Become. The time for this observation and determination is TR, which is valid for the discharge start time TD which is shorter than the time TR. In this way, from the start of the first phase, the duration TA
The time until the pulse is generated is always longer than the critical time TR.

c) No current is supplied by the one or more generators during this predetermined time TB.

FIG. 1C represents the variation of the terminal voltage of the pulse generator over time. The voltage E during the discharge start period (first phase) is approximately the same as the voltage applied between the electrodes. During the second phase following the initiation of the discharge at small current values, the voltage E reaches a voltage value Ep much higher than the discharge start voltage.
1, which overcomes the self-induction of the wiring and produces a sharp edge pulse current. Due to the same steep edge during the pulse decay, a reverse voltage EP2 occurs at the end of the pulse current. As will be appreciated, the duration of the Jarls current is constant and is independent of the variable level of current.

FIG. 2 shows one implementation of the rosy generator according to the present invention.

At the beginning of the first phase (or first operating mode), the synchronization device 40 starts the operation of the discharge initiation generator 10 by means of a signal supplied via the signal line 100. This signal causes the transistor 13 to change from the conductive state to the cut-off state, and the capacitor 12 connected in parallel with the transistor 13 begins to charge rapidly under the action of the power source E1. The charging time constant is adjusted by a variable resistor 11, for example. The power-law voltage increase is transferred to the transistor 14 (of the FET type), which provides the same form of voltage increase on the wire 1 via the signal line 101. The workpiece 2 and all ground points are connected to a common signal line 102. Since the saturation value of this voltage affects the machining speed, it is adjusted to the optimum value using the Zener diode device [16]. After a suitable discharge start time TD has elapsed, a discharge occurs suddenly, and the current limited by the variable resistor 15 is immediately set to the initial peak current value 1o.

During this first phase, the peak current value IP adjusting device 20 is 1
The voltage rise is caused by the group comparators 22^, 22B1...22N, and the potentiometers 21A, 121B,...
...Compare and observe with the reference level adjusted by 21N. As the voltage increases, the comparators 22A, 22
B,...22N output changes from "high" state to "low"
state and these signals are NANDed”-)
23A, 23B, ... 23
N.

24A, 24B, . . . , 24N. These flip-flops, set by the signal TBK supplied by line 104 from the synchronizer 40, are set for use during the second phase in which a discharge voltage of about isv is set.
It remembers the voltage level reached by wire 1 during the phase. Stored voltage level dAND)25^,
25B, . . . , 25N are transferred to the first input section. The second power section of these y-ts is kept at a low level during the first phase by the signal T^ supplied by the signal line 103 under the control of the synchronizer 40.

If it is advantageous to modulate the current value lp as a function of the time TD at which the voltage reaches its saturation or plateau value, an integrator 26 is arranged together with the switch. Thereby the level device can still operate at the saturation voltage. Integrator 26 must of course be reset to zero after each noggle. This reset is performed by the signal TB supplied through the signal line 100.

The synchronizer 40 monitors the voltage on the wire 1 via the signal line 101 and shifts the signal line 103 from a low level state to a high level state in response to a discharge start period.

This state change is NO gate 25A, 25B.

. . . a number f- of 25N), representing the start of the second phase (second operating mode). ^NDr-)25^, 25B, 25
The output of N is a preamplifier (driver) 31A which itself controls the switching transistors 32^, 32B, . . . 32N of the output generator 30.

31B,...31N. Conducted.

The number of transistors is the comparator 22A of the regulator 1120 whose output was at a high level at the start of discharge.

The numbers are 22B and 22N. In other words, this number is a measure of the voltage achieved at the start of the discharge, and since the voltage rises according to a predetermined time curve, it is also a measure of the time of the start of the discharge. In conclusion, the second phase is characterized by the generation of a pulsing current with a peak current value IP that is a function of the discharge onset time measured during the first phase.

This output pulse lasts for a time TA set by the synchronizer 40, and the synchronizer 40
When A is completed, the signal line 103 is raised to a high level, and the state is changed from the low level state to the low level state, and the signal line 103 is shut off. At the same time, the pressure of the capacitor 12 as 10
A short circuit command is given to the discharge start generator 10 via the signal line 100.

This is the third period of time T8 during which any generator is dormant.
It represents the start of a phase.

At the end of time T8, the above-described cycle of three phases is restarted.

Recall now the important points discussed above with respect to FIG. Due to the limitations inherent in the output transistors of the output generator 30, the current must be 0.0. / -0.18 seconds delay occurs. On the other hand, a weak current of several amperes is already being circulated by the discharge initiation generator 10, which maintains the discharge below approximately 2.9V. Because of this delay, the power supply E2 of the output generator 30 does not apply its full voltage to the air gap (the space between the wire 1 and the workpiece 2). Therefore, the voltage to the discharge start generator 10 is set to a normal value below OOv, and the power source E of the output generator 30 is
The voltage No. 2 (air gap voltage) can be set to, for example, Hiroshi OOV. This utilizes the advantage of starting the discharge at a low voltage while using a high voltage to rapidly ramp up the current, resulting in a short, powerful lasing that is favorable for wire discharge cutting. means to be Thereby,
The parasitic inductance that resists the rapid rise of the current is no longer critical compared to conventional equipment, and the relatively long signal lines between the generator and the air gap are no longer unsatisfactory, making the equipment easier to use and easier to use in high-speed machining. This provides advantages such as no reduction in operating efficiency.

The operation of the synchronization device 40 is also illustrated in FIG. The synchronization device 40 includes another monostable multivibrator 42 that determines the time T8, a comparator 43 that monitors the voltage on the signal line 101 to detect the start of discharge, and a comparator 43 that monitors the voltage on the signal line 101 to detect the start of discharge. Potentiometer 44 to fix the level and ORke.

45, and a monostable multivibrator for setting time TA. The input and output parts of these three monostable multivibrators are covered by the first German patent!
6322s and US 2-32 Itt Jr. to form a TD-TA-T8 cycle very similar to that described in U.S. Pat. Since the voltage cannot be established at the start of the time TD, it is necessary to observe this voltage and prepare a time TR before it is determined whether the discharge is restarted or started. When the discharge start time is zero, the TR-TA-TB cycle is set. In other words, the first time TR between the start of the first phase and the start of the second phase is always observed.

The output generator 30 may be - e.g.
;-10, it can be formed so that the dissipated energy is as low as possible. In this case, the resistor 33 of FIG. 2 is replaced by a circuit that maintains the level of current circulating in the coil within predetermined limits. The high voltage EP in FIG. 1C then depends on the slope of the current change at the terminals of the coil.

FIG. 3 shows the discharge current 1 as a function of the discharge start time TD.
λ shows two aspects of the change in λ.

The curve ■ shows a continuous function from the minimum value of 1°, and the curve I
represents a discontinuous function with two steps, each step corresponding to a predetermined limit of the discharge start time or a predetermined value of the discharge start voltage.

[Brief explanation of drawings]

Figure 1a11b is a waveform diagram showing the waveforms of the voltage and current pulses applied between the electrodes, Figure 1C is a waveform diagram showing the waveforms of the voltage and pulses supplied by the seven pulse generators;
FIG. 2 shows t? shown in FIG. 1C? FIG. 3 is a circuit diagram of a pulse generating device that generates slow pulses, and is a diagram showing how the discharge pulse current changes with respect to the discharge start time. Explanation of symbols

Claims (1)

[Claims] (1) A low current source (10) for starting electric discharge, a large current source (30) for supplying machining current, and a first
The low current source starts operating during the second phase, the start of discharge is detected and the high current source starts operating during the second phase, and the high current source starts operating during the second phase.
Nuclear force 1 is generated by wire electrical discharge machining, with a synchronizing and monitoring circuit (40) for terminating the operation of the high current source during the phase.
A Noculus generator for an electric discharge cutting machine for cutting workpieces, the Noculus generator generating a value varying according to an increasing function of the duration of the first phase while keeping the duration of the machining discharge constant during the second phase of each discharge. (adjustment units) (20
) A /4' rus generator. q) means for gradually increasing the firing voltage during the first phase and a logic circuit (2) for determining the firing voltage threshold;
at least two comparators (22) combined with
9 pulse generator according to claim 1, characterized in that it has means for making a predetermined level of the current supplied by the large current source (30) correspond to the discharge starting voltage threshold. A Noyalus generator. (3) The main pulse generation according to claim 1, characterized in that the large current source (30) is equipped with a current generator that supplies a minimum pulse current when the duration of the second phase is zero. Device. (II) A monitoring circuit (42) that synchronizes the time-pace (42) to prevent the large current source (3a) from starting operation before a predetermined time period consisting of the point at which the discharge starting voltage is applied between the two electrodes. 40) The pulse generator according to claim 1, characterized in that the pulse generator comprises: 40). (b) The adjustment unit (20) is equipped with a circuit (26) for calculating the time integral value of the discharge starting voltage applied between the two electrodes during the first phase. The pulse generator according to scope 1.