JPH0478409B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electric discharge machining apparatus, and more particularly to an electric discharge machining apparatus capable of controlling the peak value of machining current.

[Conventional technology]

Conventionally, this type of electric discharge machining apparatus has been shown in the block circuit diagram of FIG. 6th
In the figure, 1 is a commercial AC power supply, 3 is a machining power supply that converts the output voltage of the commercial AC power supply 1 into a DC voltage of a predetermined magnitude, 4 is a machining electrode, and 5 is a machining process performed by the machining electrode 4. 6 is an electrode drive device that raises and lowers the processing electrode 4 relative to the workpiece 5; 7 is a transformer that transforms the output voltage of the commercial AC power source 1; 8a, 8b, 8c, 8d, 8e; and 8f
1 is a rectifier that rectifies the output voltage of the transformer 7; 9 is a smoothing capacitor that removes AC components from the rectified output voltage of the transformer 7 and outputs a DC voltage; 1
0 is a switching element for applying a DC voltage between the electrodes consisting of the machining electrode 4 and the workpiece 5; 11 is a current limiting resistor that limits the peak value of the machining current flowing between the electrodes; 12 is an oscillation control circuit that controls the switching element 10 on and off.

Next, the operation of the conventional electric discharge machining apparatus will be explained. The processing power supply 3 transforms the output voltage of the commercial AC power supply 1 received by the transformer 7, converts it into a voltage of a predetermined magnitude, and outputs it, and the rectifiers 8a to 8f rectify the output voltage of the transformer 7. Further, a capacitor 9 smoothes the rectified output voltage and outputs a DC voltage of a predetermined magnitude as a machining voltage. capacitor 9
The machining voltage outputted by is applied between the electrodes via a switching element 10 and a current limiting resistor 11. At this time, the electrode driving device 6 brings the machining electrode 4 close to the workpiece 5 to generate electric discharge, and causes the workpiece 5 to be subjected to electric discharge machining by passing a machining current.

[Problem that the invention seeks to solve]

By the way, the output voltage of the commercial AC power supply 1 is V _A ,
When the proportionality constant is K, the machining voltage V _E becomes V _E =K×V _A. At this time, if the peak value of the machining current is selected as I _P , the arc voltage between the electrodes during discharge is V _D , so the resistance value R of the current limiting resistor 11 is R = V _E - V _D /I _P becomes.

When the output voltage V _A of the commercial AC power supply 1 fluctuates and becomes V _A ′=V _A ±ΔV _A , the machining voltage VE′ V _E ′=K×V _A ′. Therefore, the peak value I _P ′ of the machining current flowing between the electrodes is given by the arc voltage between the electrodes during discharge being V _D , so I _P ′=V _E ′−V _D /R=I _P ±K×ΔV _A /R.

Therefore, when the output voltage V _A of the commercial AC power supply 1 fluctuates, the peak value I _P of the machining current also fluctuates. As a result, even if electric discharge machining is performed, a predetermined surface roughness cannot be obtained, the machining speed decreases, and machining characteristics deteriorate.

FIG. 7 is a block circuit diagram of a conventional electrical discharge machining apparatus that reduces the influence of fluctuations in the output voltage V _A of the commercial AC power supply 1. In FIG. 7, parts having the same functions as those in FIG. 6 are denoted by the same reference numerals, and the explanation thereof will be omitted. In this electric discharge machining apparatus, a constant voltage device 2 is installed between a commercial AC power source 1 and a machining power source 3 to reduce the influence of fluctuations in the output voltage V _A of the commercial AC power source 1.

However, when the constant voltage device 2 is attached, the device becomes larger and more expensive.

The present invention was made to solve the above problems, and even if the output voltage of a commercial AC power supply fluctuates,
It is an object of the present invention to provide an economical electric discharge machining apparatus in which the peak value of a machining current is maintained at a selected magnitude, and the machining characteristics of electric discharge machining are not deteriorated.

[Means for solving problems]

The electric discharge machining apparatus according to the present invention rectifies and smoothes the output voltage of a commercial AC power supply and converts the DC voltage into a machining pulse voltage consisting of a repetitive pulse waveform via a switching element that is controlled on and off by an oscillation control circuit. In electrical discharge machining equipment that applies this converted machining pulse voltage between opposing machining electrodes and the workpiece to generate electrical discharge and perform electrical discharge machining on the workpiece, the output voltage of the commercial AC power supply is detected. a commercial power supply voltage detector, a current limiting variable resistor that is connected in series with the switching element and limits the peak value of the machining current flowing between the machining electrode and the workpiece; It is connected to the output side of the power supply voltage detector, and when a fluctuation occurs in the detected voltage of the commercial power supply voltage detector, the peak value of the machining current, which is set in advance by the resistance value of the current limiting variable resistor, is maintained. It is equipped with a resistance control circuit that changes the resistance value.

[Effect]

In the present invention, a commercial power supply voltage detector detects the output voltage of a commercial AC power supply, and a resistance control circuit connected to the output side of the commercial power supply voltage detector changes the detected voltage of the commercial power supply voltage detector. When this occurs, the resistance value of the current limiting variable resistor that limits the peak value of the machining current is changed to a value that maintains the preset peak value of the machining current.

〔Example〕

Hereinafter, one embodiment of the present invention will be described in detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of an electric discharge machining apparatus according to the present invention. In Fig. 1, 1 is a commercial AC power supply, 3 is a processing power supply that converts the output voltage of the commercial AC power supply 1 into a DC voltage of a predetermined magnitude, 4 is a processing electrode, and 5 is a processing device using the processing electrode 4. the workpiece to which
Reference numeral 6 denotes an electrode drive device that raises and lowers the processing electrode 4 relative to the workpiece 5; 7 a transformer that transforms the output voltage of the commercial AC power supply 1; 8a, 8b, 8c, 8d, 8;
e and 8f are rectifiers that rectify the output voltage of the transformer 7, 9 is a smoothing capacitor that removes the AC component of the rectified output voltage of the transformer 7 and outputs a DC voltage, and 10 is a DC voltage processing capacitor. A switching element for applying voltage between the electrodes consisting of the electrode 4 and the workpiece 5, 12 an oscillation control circuit for controlling the switching element 10 on and off, and 13 limiting the peak value of the machining current flowing between the electrodes. 14 is an analog-to-digital conversion circuit that converts the output voltage of the commercial AC power supply into a digital voltage; 15 is a current-limiting variable resistor 13 that converts the output voltage of the analog-to-digital conversion circuit 14; This is a resistance control circuit that controls the resistance value of .

FIG. 2 is a circuit diagram of the current limiting variable resistor 13 shown in FIG. 1. Current limiting variable resistor 13
has a plurality of resistors R1, R2,..., RN connected in parallel, and each resistor R1, R2,..., RN has a switching element S1, S2,..., which is controlled on/off by the resistance control circuit 15. SN are connected in series.

Next, the overall operation of the electrical discharge machining apparatus according to the present invention will be explained. The processing power source 3 transforms the output voltage of the commercial AC power source 1 received by the transformer 7, converts it into a voltage of a predetermined magnitude, and outputs the voltage, and rectifiers 8a to 8a.
8f rectifies the output voltage of the transformer 7, and a capacitor 9 smoothes the rectified output voltage to output a DC voltage V _E of a predetermined magnitude. Note that, when the output voltage of the commercial AC power supply ₁ is V _A and the proportionality constant is K, the DC voltage V E becomes V _E =K×V _A. The DC voltage output from the capacitor 9 is transferred to a switching element 10 and a current limiting variable resistor 13.
is applied between the electrodes via. At this time, the electrode drive device 6 brings the machining electrode 4 close to the workpiece 5 to generate an electric discharge, and passes a machining current to the workpiece 5.
Perform electrical discharge machining.

On the other hand, the resistance control circuit 15 initializes the resistance value of the current limiting variable resistor 11 to R when the power is turned on.
The peak value of the machining current flowing between the electrodes during electrical discharge machining is selected as I _P. The arc voltage between the electrodes during discharge is V _D
Then, the peak value of the machining current I _P is I _P =V _E −V _D /R. Further, the analog-to-digital conversion circuit 14 converts the output voltage V _A of the commercial AC power supply 1 into a digital voltage and outputs the digital voltage, which is constantly monitored by the resistance control circuit 15. That is, the analog-to-digital conversion circuit 14 functions as a commercial power supply voltage detector that detects the output voltage V _A of the commercial AC power supply 1.
Based on the output of the analog-to-digital conversion circuit 14 as a commercial power supply voltage detector, the resistance control circuit 15 performs the selected processing when the output voltage V _A of the commercial AC power supply 1 changes to V _A '=V _A ±ΔV _A. In order to maintain the current peak value I _P , the resistance value of the current limiting variable resistor 11 is changed from R to R'. Here, the resistance value
Since the arc voltage during discharge is V _D , R'=K×V _A ′−V _D /I _P =R±K×ΔV _A /I _P . As a result, the peak value I _P ′ of the machining current becomes I _P ′=K×V _A ′−V _D /R′=I _P and is maintained at the selected peak value of the machining current.

Next, FIGS. 3, 4, and 5 show other embodiments of the electrical discharge machining apparatus according to the present invention, and only the main parts are shown. In FIGS. 3, 4, and 5, the same reference numerals are given to the parts that perform the same functions as in FIG. 1, and the explanation thereof will be omitted. . In the above example, analog
The digital conversion circuit 14 converts the output voltage V _A of the commercial AC power supply 1 into a digital voltage. In the embodiment shown in FIG. 3, the output voltage of the transformer 7 is converted into a digital voltage, and in the embodiment shown in FIG. In the embodiment shown in FIG. 5, the output voltage of the current limiting variable resistor 13 is converted into a digital voltage.

〔Effect of the invention〕

According to the present invention, the commercial power supply voltage detector detects the output voltage of the commercial AC power supply, and the resistance control circuit connected to the output side of the commercial power supply voltage detector detects the detected voltage of the commercial power supply voltage detector. When fluctuations occur, the resistance value of the current limiting variable resistor that limits the peak value of the machining current is changed to a value that maintains the preset peak value of the machining current, so the voltage of the commercial AC power supply will fluctuate. However, the peak value of the machining current is kept constant, and an electrical discharge machining apparatus with improved machining characteristics for electrical discharge machining can be economically obtained.

[Brief explanation of drawings]

Fig. 1 is a block circuit diagram of an electric discharge machining apparatus according to the present invention, Fig. 2 is a circuit diagram of a current limiting variable resistor shown in Fig. 1, and Figs. FIGS. 6 and 7 are block circuit diagrams showing other embodiments of the electric discharge machining apparatus according to the present invention. FIGS. 6 and 7 are block circuit diagrams of conventional electric discharge machining apparatuses. In each figure, 1 is a commercial AC power supply, 3 is a processing power supply, and 4
is a processing electrode, 5 is a workpiece, 6 is an electrode drive device, 7 is a transformer, 8a, 8b, 8c, 8d, 8
8f are rectifiers, 9 is a capacitor, 10 is a switching element, 12 is an oscillation control circuit, 13 is a current limiting variable resistor, 14 is an analog-to-digital conversion circuit, and 15 is a resistance control circuit. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (1)

[Claims] 1. A DC voltage obtained by rectifying and smoothing the output voltage of a commercial AC power source is converted into a pressurized pulse voltage consisting of a repetitive pulse waveform through a switching element controlled on and off by an oscillation control circuit, and this In an electric discharge machining apparatus that generates electric discharge by applying a converted machining pulse voltage between an opposing machining electrode and a workpiece to perform electric discharge machining on the workpiece, the output voltage of the commercial AC power source is a commercial power supply voltage detector for detecting; a current limiting variable resistor that is connected in series with the switching element and limits the peak value of the machining current flowing between the machining electrode and the workpiece; , connected to the output side of the commercial power supply voltage detector,
and a resistance control circuit that changes the resistance value of the current limiting variable resistor to a value that maintains a preset peak value of the machining current when a fluctuation occurs in the detected voltage of the commercial power supply voltage detector. An electrical discharge machining device characterized by: 2. The electric discharge machining apparatus according to claim 1, wherein the resistance control circuit has a function of initially setting the resistance value of the current limiting resistor.