JPS5810176B2 - Electric discharge machining equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrical discharge machining device that electrically erodes a workpiece by means of a spark discharge obtained by periodically applying pulse current to a machining gap between an electrode and a workpiece, and particularly relates to The present invention relates to an abnormal continuous discharge detection device that detects when abnormal discharge occurs continuously during machining.

As this type of device, one that detects abnormal continuous discharge by detecting the presence or absence of no-load time has been generally used.

This is done when a voltage is applied to the machining gap and a pulse with a no-load time appears, or when there is no no-load time (hereinafter referred to as abnormal discharge).

) refers to a short circuit or pseudo short circuit (the state immediately before transitioning to a short circuit).

) etc. Therefore, when a certain number of pulses in this state continue, it is determined to be a normal state, and when a pulse with no-load time does not appear for more than the above-mentioned certain number, the state is shifted to an arf state. This system determines that there is an abnormal condition and generates an abnormal signal.

That is, if a voltage is applied to the machining gap and an abnormal discharge occurs, this is counted by a counter and N pulses (for example, 25
If the discharge continues (6 pulses), an abnormal signal is output, and if no-load time is detected before the abnormal discharge continues for N pulses, the counter is reset and starts counting again from 1 pulse.

However, in the conventional method described above, when the pulse width and pause width are short, or when both are short at the same time, the number of pulses of abnormal discharge N during a short circuit or pseudo short circuit due to machining debris. (For example, the above-mentioned 256 pulses) voltage pulses are applied, and as a result, the above-mentioned abnormal discharge continues for more than N pulses, and an abnormal signal is output.

For example, when the pulse width is 2 μsec and the pause width is 2 μsec, if a pulse with no no-load time continues for 256 pulses or more, a pulse with no no-load time occurs and then 102
An abnormal signal will be output after 4 μsec. For example, if the pulse width is 500 μsec and the pause width is 500 μsec, the abnormal signal will be output after 256 m5 sec.

In this way, when the pulse width and pause width are changed greatly, for example from about 1 μsec to several thousand μsec, it is difficult to configure the system to detect this at a certain number of counts and issue an abnormal signal. When the pause width is shortened, an abnormal signal is issued even though abnormal continuous discharge has not occurred, reducing machining efficiency.

It is also well known that a certain period of time is set and an abnormal signal is issued when abnormal discharge continues for a certain period of time.
If this is done, when the pulse width and pause width are long, or when both are long at the same time, it will be determined that abnormal continuous discharge is occurring after just a few pulse discharges.

That is, as in the above example, if the set time for determining abnormal discharge is 1024 μsec after the generation of a pulse with no no-load time, then the pulse width is 2 μsec.
c. If the machining condition is a pause width of 2 μsec, an abnormal discharge state will be determined only after 256 pulses with no no-load time occur consecutively, but for example, if the pulse width is 64 μsec,
sec and a pause width of 64 μsec, 8 pulses with no no-load time occur consecutively, and it is determined that an abnormal discharge state is occurring.

To further explain the above matter using drawings, the number of abnormal discharge pulses in the machining gap is set, and when the number of abnormal discharge pulses exceeds the set value, the abnormal signal is generated.
By determining the abnormal state and the normal state using the line La as the boundary as shown in Fig. If so, an abnormal signal will be generated even during a short circuit or a pseudo short circuit caused by machining debris when the period is short.

In addition, in the case where a certain time is set and an abnormal signal is output when the abnormal discharge continues for a certain period of time, the abnormal state is determined by determining the abnormal state with line Lb as the boundary as shown in Figure 1.
As mentioned above, when the pulse width or rest width is long, or both are long, in other words, when the cycle is long, it is determined that an abnormal continuous discharge occurs after just a few pulse discharges, and an abnormal signal is generated. will occur.

Therefore, as shown in Fig. 2, it is necessary to judge the abnormal state and normal state using the line Lo as the boundary, that is, when the pulse width and pause width are long, the judgment is made with a sufficient number of pulses, and the pulse width
When the pause width is short, it is desirable to determine after a sufficiently long period of time and issue an abnormality signal.This makes it possible to distinguish between short circuits or pseudo-short circuits caused by machining debris and abnormal continuous discharge, and to detect them accurately. Abnormal machining can be detected.

This invention has been made in view of the above points, and will be described in detail below with reference to FIG. 3 of the drawings.

That is, FIG. 3 is a block diagram showing this invention device,
In the figure, 1 is an electrode, 2 is a workpiece that faces the electrode 1 through a machining gap, and 3 is an on/off pulse voltage that is supplied between the electrode 1 and the workpiece 2 via a switching element 4. A machining power source consisting of a DC power supply; 5 an oscillator for driving the switching element 4 on and off; 6 a detection resistor for detecting the machining gap voltage; That is, it is provided with a terminal 8 that outputs one pulse every time a discharge without a no-load time occurs, and a terminal 9 that outputs one pulse every time a discharge with a no-load time occurs.

10 is a first counter that counts pulses from the terminal; 11 is a first flip-flop circuit that is set to a predetermined count (for example, N pulses) of the counter 10; 12 is an independent oscillator; and 13 is the oscillator 12. 10 is a second flip-flop circuit set to a predetermined count number of the counter 13; 15 is a second flip-flop circuit set to a predetermined count value of the counter 13; This is an AND element that outputs an abnormal signal when the

Note that the first and second counters 10 and 13 are configured to be reset by an output signal from the terminal 9.

Furthermore, the first and second counters 10 and 13 are configured to be able to change their count numbers, and the independent oscillator 12 to change the oscillation frequency in multiple stages depending on the set values of the pulse width and pause width. There is.

This inventive device is constructed as described above, and its operation will be explained next.

That is, when an abnormal discharge occurs due to a short circuit or a pseudo short circuit caused by machining debris, the first counter 10 starts counting.

Then, the first flip-flop circuit 11 is set at a predetermined count (for example, N pulses).

If a pulse with no-load time appears during this time, the counter 10 is reset by the output signal from the terminal 9.

On the other hand, when there is an output signal from the terminal 8, that is, when there is an abnormal discharge, there is no output signal from the terminal 9, so the counter 13 currents the pulse from the independent oscillator 12.

When the count reaches a predetermined value, the second flip-flop circuit 14 is set and an abnormality signal is generated via the AND element 15.

That is, when a predetermined number of abnormal discharge pulses occur,
When the period in which the predetermined number of pulses are generated continues for a predetermined time, counters 10 and 13 set flip-flop circuits 11 and 14, respectively, and generate an abnormal signal via AND element 15.

If a pulse with a no-load time is generated in the machining gap before the count number of the naori counter 13 reaches a predetermined value, that is, before the flip-flop circuit 14 is set, the output signal from the terminal 9 causes the first and second The counters 10 and 13 and the first and second flip-flop circuits 11 and 14 are reset.

As mentioned above, for example, when both the pulse width and pause width are short, if a short circuit or pseudo short circuit due to machining debris occurs and a discharge without no-load time continues for more than a predetermined pulse (i.e., abnormal discharge), The flip-flop circuit 11 is set, but if no-load voltage appears within the time counted by the counter 13, the first and second counters 10, 13 and the first flip-flop circuit 11 are reset and an abnormal signal is generated. It doesn't appear.

As explained above, according to the present invention, the number of pulses of abnormal discharge in the machining gap is counted, and at the same time, the duration of the abnormal discharge is counted, and abnormal continuous discharge is detected by the AND signal of each count value. Therefore, depending on the length of the pulse width or pause width, for example, when the pulse width or pause width is short, the detection frequency increases if the number of abnormal pulses is used to determine the number of abnormal pulses, and an abnormal state can be detected during a short circuit or pseudo short circuit. Therefore, detection focuses on the duration of abnormal pulse generation, and when the pulse width or pause width is long, it is possible to identify a short circuit or pseudo-short circuit by determining the duration of abnormal pulse generation. Since not only an abnormal state in a state but also a normal state may sometimes be determined to be an abnormal state, detection focuses on the number of abnormal pulses generated.

This makes it possible to detect abnormal continuous discharges in both long and short pulse width and pause width regions, and therefore, electric discharge machining equipment capable of detecting abnormalities can be used in practical applications in both rough machining and finishing machining regions. Can be provided.

Furthermore, since the pulse width and pause width vary over a very wide range, more detailed detection can be achieved by switching the oscillation frequency of the independent oscillator or the count numbers of the first and second counters in multiple stages depending on the set values of the pulse width and pause width. It is also possible to do this.

Furthermore, in this embodiment, a discharge with no no-load voltage is determined to be an abnormal discharge, but the detection of an abnormal discharge is not limited to this method. For example, the detection of an abnormal discharge is not limited to this method. There is also a method of detecting the machining voltage during processing, and there is no technical difficulty in implementing the present invention in combination with such a detection method.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating a conventional detection method, FIG. 2 is a diagram illustrating a detection method using an apparatus according to the present invention, and FIG. 3 is a block diagram illustrating an embodiment of the apparatus according to the present invention. 1... Electrode, 2... Workpiece, 3... Processing power source,
4... Switching element, 5... Oscillator, 6...
Detection resistor, 7... Discrimination device, 8, 9... Terminal, 10
, 13...first and second counters, 11, 14...
- First and second flip-flop circuits, 12... independent oscillator, 15... AND element.

Claims (1)

[Claims] 1. An electrode that faces the workpiece through a machining gap, a machining power source that supplies current to the machining gap formed by the electrode and the workpiece through a switching element, and an electric current in the machining gap formed by the machining power source. A detection device for detecting abnormal discharge, a counting device for counting the number of abnormal discharge pulses detected by the detection device, a device for counting the duration of the abnormal discharge detected by the detection device, and a count value obtained from each of the counting devices. An electrical discharge machining device equipped with a device that determines abnormal continuous discharge when both exceed respective set values.