JPH0360928A - Electric discharging device - Google Patents

Abstract

PURPOSE:To secure the stability in an electric discharging and to enhance the working efficiency and to well perform a low consumption work by providing a signal output means which outputs a driving signal for driving a piezoelectric actuator in a voltage impressing period at the cycler shorter than the period thereof and with the necessary amplitude in response to a periodical signal. CONSTITUTION:A piezoelectric driving means 34 repeatedly performs the motion that a working electrode 28 is approached and separated from the body W to be worked along the necessary servoaxial direction with a driving signal S2 fed from an output means 4 being impressed, while the work voltage is impressed in an electric discharging gap G. Consequently, the chips collection in the electric discharging gap G is effectively prevented and a stable electric discharging is performed in the electric discharging gap G.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electric discharge machining apparatus that allows more accurate control of machining energy applied to an electric discharge machining gap.

(Prior Art) A conventional electric discharge machining apparatus is configured such that a machining electrode can move relative to a workpiece along its servo axis,
The width of the electrical discharge machining gap is servo-controlled to be maintained at a predetermined optimum value in accordance with the voltage generated in the electrical discharge machining gap formed between the machining electrode and the workpiece. Therefore, as long as the servo control is performed satisfactorily, the discharge in the discharge machining gap is stably performed in the desired state, and there is no problem. On the other hand, when the electrical discharge machining gap becomes short-circuited due to chips accumulating in the machining gap, the servo control described above will first widen the electrical discharge machining gap width, and then narrow it down to the required value. You will perform the action of being forced to move.

(Problem to be solved by the invention) By the way, the responsiveness of the above-mentioned servo control is at most 100
200 (Hz), whereas the pulse width of the machining pulse is about several tens (μSec) to 1 (msec), so once a problem occurs in the machining gap,
Due to the large number of discharge pulses generated during that time, it becomes impossible to control the machining energy applied to the machining gap.
The result is that the intended processing cannot be performed satisfactorily.

For example, in order to perform low consumption machining, the ratio of the machining current peak value and its duration must be controlled within a certain range, and if the machining gap becomes short-circuited, the servo control Therefore, there would be no problem if the short-circuit condition was resolved within a very short period of time, but due to the low response speed of the servo control, the above-mentioned machining current condition deviates from the required condition for a long period of time, causing this open wear. This results in the problem of processing. This has a large negative effect on processing quality, especially in the case of low-consumption finishing processing.

Therefore, an object of the present invention is to provide an electric discharge machining apparatus that can control machining energy in an electric discharge machining gap with extremely high responsiveness and can effectively suppress the occurrence of abnormal conditions.

(Means for Solving the Problems) The features of the present invention for solving the above problems include a moving means for imparting a required relative movement between the processing electrode and the workpiece, and the processing electrode In an electric discharge machining apparatus having a servo control system that maintains the width of the electric discharge machining gap at a required value based on an electric signal indicating the state of the electric discharge machining gap between the electric discharge machining gap and the workpiece, piezoelectric driving means for moving the machining electrode relative to the workpiece along the servo axis; and means for obtaining a period signal indicating a machining pulse voltage application period in the electrical discharge machining gap; and output means for outputting a drive signal for driving the piezoelectric drive means within the voltage application period at a cycle shorter than the period and with a required amplitude in response to the period signal. .

(Function) During the period when the machining voltage is applied to the discharge machining gap, a drive signal from the output means is applied to the piezoelectric drive means, and the machining electrode approaches the workpiece along the required servo axis direction. As a result, chips are effectively prevented from accumulating in the discharge machining gap, and stable electric discharge is performed in the discharge machining gap.

(Example) Hereinafter, the present invention will be explained in detail with reference to an illustrated embodiment.

FIG. 1 shows an embodiment of an electrical discharge machining apparatus according to the present invention. The electric discharge machining apparatus 1 shown as this embodiment is a Z-axis controlled electric discharge machining apparatus for die sinking.
The machine includes a processing machine main body 2, a processing power supply section 3 that supplies processing pulses to the processing machine main body 2, and a control unit 4 for electrode feeding servo control of the processing machine main body 2. In addition, in many cases, the control unit 4 and the power source 3 for machining are incorporated into one housing, and are called a power source device for machining.

The processing machine main body 2 includes a processing table 21 and a head portion 23 supported by a column 22 provided on the processing table 21. A processing tank 26 is provided on the processing table 21 in which a workpiece 25 placed on a bed 24 is set. The machining tank 26 is filled with a suitable electrical discharge machining fluid 27, and the workpiece 25 is filled with the electrical discharge machining fluid 27 by a machining electrode 28 attached to the head section 23 side.
It is configured to undergo electric discharge machining inside. The head portion 23 has a quill 31 that is guided by a guide member 30 fixedly provided within the casing 29 of the head portion 23 so as to be movable only in the axial direction. Quill 3
A ball screw 33 is screwed into one end 31a of the 1, and is driven to rotate by a rotary motor 32 such as a DC motor or a stepping motor.
By rotating forward and backward, the quill 31 moves forward and backward in its axial direction.

A pair of electrode fittings 35 and 36 are provided at the other end 31b of the quill 31 via a piezoelectric actuator 34.

The electrode fixture 35 is firmly attached to the piezoelectric actuator 34 by a known flange fixing method, while the electrode fixture 36 firmly fixes the stem 37 which is fixed to the processing electrode 28. The processing electrode 28 is fixed to an electrode fixture 36. A pair of electrode fittings 35
．． 36 is positioned such that the protrusion 36a of the electrode fixture 36 is fitted into the recess 35a of the electrode fixture 35 having a shape corresponding to the protrusion 36a, and the attractive force of a magnet (not shown) provided inside these As a result, the two are firmly connected in a predetermined position, and the connection between the two can be released as desired. Since the above-described structure of the electrode fixture itself is well known, detailed explanation thereof will be omitted. Note that the piezoelectric actuator 34 and the quill 3
1 is also made by a known flange connection. In this embodiment, between the piezoelectric actuator 34 and the quill 31 and between the piezoelectric actuator 34 and the electrode fixture 3,
5 are connected by flanges as described above, but the manner of connection is not limited to this.

The piezoelectric actuator 34 moves the processing electrode 28 along its servo axis direction (that is, the axial direction of the quill 31) at a speed faster than the servo operation by the rotary motor 32.
It is provided to move a minute distance of 0 [μm], and its configuration is shown in detail in FIG.

The piezoelectric actuator 34 has a frame body 45 consisting of relatively thin flange parts 4 and 42 and support parts 43 and 44 that support and fix these flange parts 41 and 42 in a parallel state. A piezoelectric element 47 is disposed in a space 46 formed by the above.

The piezoelectric element 47 has, for example, a prismatic shape, and a pair of electrodes 48 and 49 are provided on opposing side walls, respectively, as shown. The piezoelectric element 47 is an element that expands in a predetermined direction depending on the level of the applied voltage by applying a voltage between the electrodes 48 and 49. The illustrated piezoelectric element 47 expands in its axial direction when a voltage is applied, and this expansion presses the flange portions 41 and 42 of the frame 45 in its thickness direction. In this state, the axial end surfaces 472 and 47b are respectively flange portions 4.
1. The space 4 is dimensioned to abut the inner surface of 42.
It is located within 6. In the illustrated embodiment, the end surface 47a
, 47b are bonded to the corresponding flange portions with a suitable adhesive to prevent the piezoelectric element 47 from coming off the frame 45 due to vibration or the like.

According to such a configuration, the electrode 48.4 of the piezoelectric element 47
As the level of the voltage applied between the piezoelectric elements 47 and 9 increases, the piezoelectric element 47 expands in its axial direction, and the thin flange portion 41
．． 42 is pushed outward to deform the flange portions 41 and 42 as shown by the dotted chain line in FIG. Therefore, by adjusting the level of the applied voltage, apart from the feeding operation of the processing electrode 28 due to the rotation of the rotary motor 32,
The processing electrode 28 can be sent toward the workpiece 25 or moved away from the workpiece 25 . Although the deformation of the frame body 45 is exaggerated in FIG. 2 to make the explanation easier to understand, in reality, the elongation is several tens of μm at most.
That's about it.

Next, the configuration of the electrical control system of the electrical discharge machining apparatus 1 described based on FIGS. 1 and 2 will be described with reference to FIG. 3.

The output line 3a of the processing power supply section 3 is electrically connected to the processing electrode 28 via the electrode fixture 36, and the other output line 3b is electrically connected to the workpiece 25 by being grounded. connected (see Figure 1). Therefore, the machining pulse output from the machining power source 3 is applied to the electric discharge machining gap G formed between the machining electrode 28 and the workpiece 25.
is applied, and electrical discharge machining is performed here.

The output voltage E generated at both ends of the electric discharge machining gap G is inputted to the control unit 4 and inputted to the gap state detection circuit 51 in the control unit 4, where the voltage W in the gap G of the electric discharge machining gap G is input.
It is determined whether W is wider or narrower than a required value, and a detected voltage of a level corresponding to the size of W in the gap at that time is output. The detected voltage is zero when the level of the output voltage E is at a level corresponding to the desired gap,
When the gap W becomes wider than the desired gap and the level of the output voltage E increases, the level of the detected voltage increases accordingly. On the other hand, when the gap W becomes narrower than the desired gap and the level of the output voltage E decreases, the level of the detection voltage becomes more negative accordingly.

The relationship between the output voltage E and the detected voltage R is shown in FIG. Note that the level of the output voltage E at which the level of the detection voltage becomes zero can be arbitrarily set by adjusting the variable resistor 52 connected to the gap state detection circuit 51. The gap adjusted by can be set to a desired value. Since the configuration of the above-mentioned gap state detection circuit 51 is well known, detailed explanation thereof will be omitted here.

The detection signal 1 is applied to the changeover switch 53 as a changeover control signal of the changeover switch 53 whose movable contact 53a is connected to a constant level DC power source +■. Fixed contacts 53b and 53c of the changeover switch 53 are connected to control terminals U and D of a motor drive circuit 54 for controlling the drive of the rotary motor 32, respectively. The motor drive circuit 54 is
When a high level voltage is applied to the control terminal U, the rotary motor 32 is rotated in the forward direction, thereby advancing the machining electrode 28 toward the workpiece 25 along the servo axis, while controlling the a first control signal for rotating the rotary motor 32 in the opposite direction when a high level voltage is applied to the terminal, thereby retracting the machining electrode 28 away from the workpiece 25 along the servo axis; This configuration outputs S1.

When the level of the detection voltage is zero or positive, the changeover switch 53 switches its movable contact 53a to the state shown by the solid line, and when the level of the detection signal is negative, the movable contact 53a changes to the state shown by the dotted line. This is a configuration that can be switched to the state shown. As a result, when the gap W in the discharge machining gap G is equal to or wider than a predetermined value, the changeover switch 53 is switched as shown by the solid line, and the motor drive circuit 5
A high level voltage of DC power supply +V is applied to the control terminal U of No. 4, the rotary motor 32 is rotated in the forward direction, and the processing electrode 28 moves forward along the servo axis.

On the other hand, when the discharge machining gap G becomes narrower than a predetermined value, the changeover switch 53 is switched as shown by the dotted line, and the DC power + level voltage is applied to the rotating motor 3
2 is rotated in the opposite direction, and the processing electrode 28 is retreated along the servo axis. As a result of the rotation control described above, servo control of electrode feeding is performed so that the gap is always maintained at an appropriate value.

In addition, in the above-mentioned embodiment, the processing electrode 28 is moved forward even when the level of the detected voltage is zero.
Since the condition of the electrical discharge machining gap is always changing at a high speed, when the level of the detected voltage becomes zero, the rotary motor 3
There is no problem at all even if the structure is not configured to stop the feeding of step 2. However, of course, when the level of the detected voltage becomes zero, the movable contact 53a of the changeover switch 53 is brought into a state in which it does not contact any of the fixed contacts 53b and 53c, thereby stopping the rotation of the rotary motor 32. You can also use it as Furthermore, the detected voltage is set to the motor drive circuit 54.
The motor drive circuit 54 may be configured such that the forward and reverse rotation speed of the rotary motor 32 changes according to the absolute value of the level of the detected voltage.

The output voltage E is also manually inputted to a level discrimination circuit 55, which outputs a gate voltage signal GS that is at a high level only during the period when the machining pulse voltage is applied to the discharge machining gap G. Ru. As can be seen from the above explanation, the period when the gate voltage signal GS is high and Q is the period corresponding to 708 hours of the processing pulse. Therefore, without providing the level discrimination circuit 55, the processing power supply Turn on the switching element used in section 3,
The pulse signal for turning off may be used as is.

Reference numeral 56 indicates the above-mentioned τ. It is a pulse generator that outputs a pulse train signal P having a period shorter than N, preferably 1/3 or less, and this pulse train signal P
is applied to the other input of the AND circuit 57, to which the gate voltage signal GS is applied. Therefore, the pulse train signal P is output from the AND circuit 57 only when the gate voltage signal GS is in a high level state, and the pulse train signal from the AND circuit 57 is transmitted to the DC amplifier 58.
The amplified output voltage signal is applied to the piezoelectric element 47 as the second control signal S2.

FIG. 5 shows a characteristic diagram showing the relationship between the applied voltage M applied to the piezoelectric element 47 and the extension amount Δl of the piezoelectric element 47. Here, what is scaled on the vertical axis is the amount of expansion relative to the length when the piezoelectric element 47 is initialized. The characteristic line (A) in FIG. 5 represents the initialized piezoelectric element 4.
This shows how the amount of extension Δl changes when the level of the voltage applied to M is gradually increased from zero, and it can be seen that the amount of extension Δ increases as the level of the applied voltage M increases. I understand. After the level of the applied voltage M reaches, for example, the maximum rated value Mm, when the level is gradually lowered, the amount of expansion decreases along the characteristic line (B) due to its hysteresis characteristic. . For this reason, the applied voltage M
Even if the level of Δl becomes zero, the amount of expansion Δl does not become zero, but becomes a predetermined value Δl. If the level of the applied voltage M is then changed within the range from zero to Mm, the amount of expansion Δl at each time will be determined according to the characteristic line (b).

That is, if a voltage of level Mm is applied to the piezoelectric element 47 only once, unless a voltage of a level higher than Mm is applied thereafter, the difference between the applied voltage level at that time and the amount of expansion will change according to the characteristic line (b). The relationship will be uniquely defined.

The second control signal S2 is a pulse signal whose level changes between zero and Mo. Therefore, when the second control signal S2 is applied to the piezoelectric element 47, the electric discharge machining gap length is
It changes by the length Ll with the period of the pulse signal P.

According to such a configuration, when electrical discharge machining is performed in the electrical discharge machining gap G, the machining electrode 28 is moved forward or backward along the servo axis by the rotary motor 32 to maintain the required value in the electrical discharge machining gap. Servo control is performed to do this. Then, the period during which the machining pulse voltage is applied to the discharge machining gap, that is, τ. In state 8, the piezoelectric actuator 34 is responsively driven by the second control signal S2, which is a pulse signal, so that the machining electrode 28 reliably expands and contracts along its servo axis, and the machining gap G is To effectively prevent chips, etc. from accumulating.

Therefore, since the discharge in the discharge machining gap is reliably executed, for example, even in cases where the discharge time must be maintained at a predetermined length such as in so-called low consumption machining, the discharge of the specified length can be carried out reliably. The discharge time can be reliably secured, and the required machining can be performed reliably. As can be seen from the above explanation, the stability of the discharge increases significantly, so
For example, when performing finishing machining under low consumption machining conditions, the planned machining can be performed satisfactorily.

In the above embodiment, the piezoelectric actuator 34 shown in FIG. 2 is used as an example to move the electrode by a minute distance with good response, but the present invention is limited to a device using this piezoelectric actuator 34. For example, the piezoelectric element 47 can be directly connected to the quill 3 and the electrode fitting 35.
For example, each end surface of the piezoelectric element 47 may be fixed to the quill 31 and the electrode fixture 35 using an adhesive. Furthermore, the mounting position of the piezoelectric actuator 34 or the piezoelectric element 47 is not limited to the position of the embodiment shown in FIG. , which is easily understood from the above explanation.

Further, in the above embodiment, the case where the present invention is applied to a die-sinking electric discharge machining apparatus with only Z-axis control has been described as one example, but the present invention is limited only to this type of electric discharge machining apparatus. It goes without saying that the present invention can be similarly applied to all types of electrical discharge machining equipment that performs servo control of the electrical discharge machining gap, such as multi-axis electrical discharge machining equipment and various types of wire-cut electrical discharge machining equipment. be.

(Effects of the Invention) According to the present invention, as described above, the stability of the electric discharge can be ensured by changing the width of the electric discharge machining gap by a minute amount at high speed while applying the electric discharge machining pulse. This not only improves machining efficiency, but also provides excellent effects such as low consumption machining.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing one embodiment of the present invention, and FIG.
Figure 3 is an enlarged detailed view of the piezoelectric actuator shown in Figure 1, Figure 3 is a circuit diagram of the electrical system of the electrical discharge machine shown in Figure 1, Figure 4 shows the voltage relationship of each part shown in Figure 3. The characteristic diagram shown in FIG. 5 is a characteristic diagram of the piezoelectric element shown in FIG. 2. 1... Electrical discharge machining device, 2... Processing machine main body, 4...
'Control unit, 25... Workpiece, 28... Machining electrode, 32... Rotating motor, 34... Piezoelectric actuator, 47... Piezoelectric element, 51... Gap state detection circuit, 55... Level discrimination circuit, 56... Pulse generator, 57... AND circuit, S2... Second control signal. Figure Figure Level of applied voltage M □

Claims (1)

[Claims] 1. Electric discharge generated in the electrical discharge machining gap between the machining electrode and the workpiece, including a moving means for providing relative movement along a predetermined servo axis between the machining electrode and the workpiece. In the electric discharge machining apparatus configured to control the driving of the moving means based on a machining voltage to maintain the width of the electric discharge machining gap at a required value, the machining electrode is moved along the servo axis to the target. a piezoelectric actuator for moving the workpiece relative to the workpiece; a means for obtaining a period signal indicating a machining pulse voltage application period in the discharge machining gap; An electric discharge machining apparatus comprising: signal output means for outputting a drive signal for driving at a period shorter than the period and with a required amplitude within an application period.