JPH02298428A - Electric discharge machine - Google Patents

Abstract

PURPOSE:To perform stable feed control against the change in machining shape through the judgment of presence of hollow portions by installing a control means which stops a servo feed control, and controls the feed at a fixed speed preset or calculated in advance if any void were detected on a work piece by a detection means. CONSTITUTION:A comparison is made to see whether an enumerated data on no-load the which is obtained in a time series by specified samples is larger than a standard value R/. A retreat control is made when smaller than the standard value R1, considering that a discharge electrode 2 and a work piece 1 are set too close to be in a state of short circuit. Next, when larger than the standard value R1, another comparison is made to see whether an enumerat ed data on no-load time sampled is larger than a standard value R2 which is larger than the standard value R1 with a comparison means 23 of a CPU23. If larger than the standard value R2, a judgment of hollow portion is made to stop a servo feed control and control the feed with the feed control means of the CPU 23 at a preset speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electric discharge machine for machining a workpiece by generating an electric discharge in a machining gap between a discharge electrode and a workpiece.

[Conventional technology]

A wire-cut electrical discharge machine winds up a thin wire made of brass or the like and uses it as an electrode to feed the contour in a predetermined shape using numerical control. This is an electric discharge machine that hollows out and processes.

This wire-cut electrical discharge machine detects machining conditions that change due to causes such as changes in the thickness of the workpiece, changes in the machined shape, and disturbances, and controls the feed rate during electrical discharge machining. Such a feed rate control device detects the no-load time from when a discharge voltage is applied to the machining gap until the discharge starts, and controls the electrode feed so that the no-load time coincides with a preset time. There was something to do.

[Problem to be solved by the invention]

By the way, electric discharge machines detect machining conditions and control the machining conditions during electric discharge machining in order to stabilize machining conditions that change due to changes in workpiece thickness, changes in machining shape, disturbances, etc., and to maintain a constant machining gap. Controlling the feed rate is being done.

However, depending on the workpiece, as shown in FIG.
Hollow part 1 of workpiece 101 when machining in one direction.
01a may exist. Hollow part like this] 0
1a, the time from applying the discharge voltage to the machining gap to starting the discharge becomes longer, so the no-load time increases, and the total value of the currently detected large no-load time,
The difference from the preset reference time becomes very large. Therefore, the feed rate commanded from the control unit is extremely large (
become faster). On the other hand, after passing through the hollow portion 101a, it is common to start electric discharge machining again on the end face 01b of the workpiece. In this case, it is natural that the feed speed needs to be made smaller (slower) again.

However, due to operational delays in the drive system that provides relative feed between the wire electrode and the workpiece, even if the commanded feed speed decreases as described above, in reality, the feed speed remains high. ing. Therefore, there is a problem that the wire electrode collides with the workpiece, resulting in a "short circuit" or the wire electrode becomes "broken."

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an electric discharge machine that can perform stable machining without causing the short circuit or disconnection when machining a hollow part. With the goal.

[Means to solve the problem]

In order to achieve this object, the electric discharge machine of the present invention relatively moves the discharge electrode and the workpiece having a space approximately in the center, and applies a voltage to the gap between the discharge electrode and the workpiece. In an electrical discharge machine that processes a workpiece while applying electrical discharge and performing servo feed control according to the state of the gap using the discharge energy, a space portion of the workpiece is moved into the gap during electrical discharge machining of the workpiece. a detection means for detecting based on the state of the workpiece, and stopping the servo feed control when the detection means detects a space portion of the workpiece;
A feed control means that controls the feed at a constant speed that is preset or calculated, and further moves the discharge electrode and a workpiece having a space approximately in the center relative to each other. Also, in an electric discharge machine that applies a voltage to a gap between the discharge electrode and the workpiece to produce a discharge and machining the workpiece with the discharge energy, a first detection means for detecting the start of application of the voltage; a second detection means for detecting the start of discharge in the gap; and a no-load time from the start of voltage application to the start of discharge based on the detection results of the first detection means and the second detection means. a measuring means for measuring, a no-load time totaling means for summing the measured values measured by the measuring means at every predetermined sampling period, and a reference value being set in advance for the combined value summed by the no-load time totaling means. and a comparison means for comparing the combined value and the reference value, and when the comparison result by the comparison means is smaller than the reference value, speed control is performed so as to achieve optimal feed control based on the total value. In addition, when the comparison result is larger than the reference value, the feed controller is configured to perform feed control at a preset or calculated constant speed.

[Effect]

A spatial portion of the workpiece is detected by the detection means.

If this spatial portion is detected, the servo feed control is stopped and the feed is controlled at a preset or calculated constant speed.

Therefore, stable machining can be performed without causing a short circuit or disconnection depending on the state of the discharge electrode and the workpiece.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of the present invention, and FIG. 2 is a block diagram of this embodiment.

As shown in FIGS. 1 and 2, the workpiece 1 is movable in a horizontal plane by means of a feed motor 11, 1.2. The wire electrode 2 is stretched approximately vertically by wire guides 13, 14 and faces the workpiece 1 via the machining gap G. The positive electrode of the machining power source 15 is directly connected to the workpiece and is also grounded. Processing power source 15 is connected to wire electrode 2.
The negative electrode of is connected via a switching element (transistor) 6 and a power supply 7. A discharge detection circuit (first and second detection means) 20 that detects the start of application of the discharge voltage and the start of discharge is connected to the electric wire 18 connecting the switching element 16 and the feeder 17, and its output signal is It is input to the no-load time counting circuit (measuring means, no-load time totaling means) 22 of the control device 21. The control device 21 includes a CPU (comparison means, feed control means) 23. memory 2
4. It is equipped with a keyboard 25, etc. Said feed motor]
].

12 is connected to the CPU via a motor drive circuit 26, and the switching element 16 is connected to the CPU via a drive circuit (not shown).
23.

FIG. 3 is a circuit diagram showing detailed configurations of the discharge detection circuit 20 and the no-load time counting circuit 22.

The discharge detection circuit 20 includes a buffer amplifier 31 that receives the voltage 2a of the wire electrode 2, and a comparator 32 that compares the output voltage with a predetermined threshold voltage Vt. The no-load time counting circuit 22 includes an AND circuit 34 to which an output signal 32a from the comparator 32 and a clock signal from the clock circuit 3B are input, and a counter 35 to which the output signal 34a is input and counted. , the output signal 35a of the counter 35 is input to the CPU 2B and read there. Here, the no-load time is the voltage (discharge voltage) 2a
This is the time from when is applied until the discharge actually starts.

FIG. 4 is a waveform diagram illustrating the operation of each of the circuits 20 and 22. Voltage of wire electrode 2, that is, voltage 2 of machining gap G
As for a, a waveform repeats, which rises due to the positive voltage of the machining power source 1-5 when the switching element 6 is turned on, and returns to zero when the switching element 16 is turned off and the discharge ends. In the discharge detection circuit 20, a predetermined threshold voltage (1) is used to discriminate a state in which a voltage is applied before the start of discharge, and the output signal 32a of the comparator 32 becomes a pulse-like signal. The pulse width of this pulse-like signal 32a is equal to the no-load time of 11°t2. This corresponds to t3, etc., and the start of discharge can be detected by the fall of this signal 32a. During the no-load time 11, the AND circuit 3 is activated only while the pulse signal 32a from the comparator 32 is output.
4 is open. While this is open, a clock signal of about 1 MHz is sent from the clock circuit 33 to the counter 35.
and the number of clocks is counted.

Therefore, the output signal 34a of the AND circuit 34 and the count value 35a of the counter 35 are accumulated over time as shown. The cumulative count value 35a is read by the CPO 23 at every predetermined sampling period, and the difference from the previous count value is calculated, thereby calculating the total for each predetermined sampling period.

FIG. 5 shows a flowchart for processing in the CPO 23. Compare the no-load time count value (combined value) obtained chronologically for each predetermined sampling to see if it is larger than the reference value R1 (Step S1). If it is smaller than the reference value R1, the discharge electrode and workpiece are Since they are too close to each other, it is assumed that there is a short circuit, and backward control is performed (step S2).

Next, if it is larger than the reference value R1 (step S
1; Y), a reference value R that is larger than this reference value R1
2, the sampled no-load time count value (
In step S3), if it is larger than the reference value R2, it is determined that there is a hollow part, and the surf feed control is stopped and the feed control is stopped at a preset speed or at a calculated constant speed. An idle running process is performed to control the feed at a speed of (step S4). If the compared value is smaller than the reference value R2 (step S3; Y), the sampled no-load time count value (total value) is subjected to electrical discharge machining so that the value matches the predetermined set value. Control the feed rate during the process (step 5). Then, when the idle running process is completed and the machining part is approached, or when the feed rate during machining is being controlled and further control of the machining feed rate is required (step S6), each of the above-mentioned steps is again performed. repeat.

Note that, as the feed rate for the idle running process (step S4) of the hollow portion, the constant feed rate "during normal machining" is used. In addition, for the no-load time count value (total value) obtained chronologically at each predetermined sampling period, the "average By using a speed that is suitable for machining, control can be performed at a speed that is more suitable for machining.

Further, in the embodiment, the reference value R],
, was compared with R2. However, it is possible to add the total values of consecutive sampling periods, take the average value, and compare that value with a reference value, or step S
The result of comparison in Steps S3 and No (YES) is determined as to whether the ratio exceeds a predetermined value or not, and the process of Steps S2 and 4 (S3 and 5) is performed based on the result. control can be performed.

Furthermore, the above-mentioned discharge detection circuit may be of a type that detects "current" instead of "voltage". FIG. 6 is a circuit diagram showing a "current detection type" discharge detection circuit 2OA. A current transformer (CT) 40 is attached to the electric wire 1-8 leading to the feeder 17, and its output is insulated by a photocoupler 41 and input to a logic circuit 42. This logic circuit 42 receives an output signal 42a from the time the discharge permission signal is input until the current is detected by the current transformer 40 and the output of the photocoupler 41 is input.
Output. The output signal 42a of this logic circuit 42 corresponds to the output signal 32a of the comparator 32, and is a pulse = 13- shaped which is high level from the time when the voltage is applied to the machining gap G until the start of discharge. It becomes a signal. The pulse width corresponds to the no-load time. As described above, the no-load time counting circuit 22 counts the pulse width of its output signal.

〔Effect of the invention〕

As is clear from the detailed description above, according to the present invention, the no-load time is totaled at each predetermined sampling period and compared with a reference value prepared in advance to predict the distance between the discharge electrode and the workpiece. This makes it possible to determine the presence of a hollow portion and perform stable feed control against changes in the machining shape, thereby preventing the occurrence of a short circuit between the discharge electrode and the workpiece, for example.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the configuration of an electrical discharge machine according to the present invention, FIG. 2 is a block diagram showing an embodiment of the electrical discharge machine according to the present invention, and FIG. 3 is an electric discharge machine showing the main circuit of the embodiment. A circuit diagram, Fig. 4 is a waveform diagram showing the operation of the electric circuit diagram, Fig. 5 is a flowchart showing the processing, Fig. 6 is an electric circuit diagram showing a current detection type discharge detection circuit, and Fig. 7 is a workpiece. FIG. 3 is a plan view showing an example of a case where a hollow portion exists. DESCRIPTION OF SYMBOLS 1...Workpiece, 2...Wire electrode, 2o...Discharge detection circuit (1st and 2nd detection means), 22...No-load time counting means (measuring means, no-load time counting means) step), 23-
CPU (comparison means, feed control means), G/machining gap. Applicant's agent Yasushi Ishikawa Engraving of drawings (no changes in content) Figure 6 Figure 01a Figure 7 Procedural amendments dismissed September 27, 1989

Claims (1)

[Claims] 1. The discharge electrode and the workpiece having a space in the approximate center are moved relative to each other, and a voltage is applied to the gap between the discharge electrode and the workpiece to generate a discharge. In an electrical discharge machine that processes a workpiece while performing servo feed control using energy according to the state of the gap, the present invention is configured to detect a space portion of the workpiece based on the state of the gap during electrical discharge machining of the workpiece. A detection means, and a feed control means that stops the servo feed control when the detection means detects a spatial portion of the workpiece, and controls the feed at a preset or calculated constant speed. An electrical discharge machine characterized by the following. 2. The discharge electrode and the workpiece having a space approximately in the center are moved relative to each other, and a voltage is applied to the gap between the discharge electrode and the workpiece to generate a discharge, and the workpiece is machined by the discharge energy. An electrical discharge machine comprising: a first detection means for detecting the start of application of the voltage; a second detection means for detecting the start of electric discharge in the gap; the first detection means and the second detection means; measuring means for measuring the no-load time from the start of voltage application to the start of discharge based on the detection result of the measurement means; and no-load time totaling means for summing the measured values measured by the measuring means at each predetermined sampling period , a reference value is set in advance for the total value summed by the no-load time totaling means, a comparison means for comparing the total value and this reference value, and a comparison result compared by the comparison means is smaller than the reference value. If the comparison result is greater than the reference value, the feed control is performed at a preset or calculated constant speed. An electric discharge machine characterized by comprising a feed control means for controlling the feed speed.