JPH0158008B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electric discharge machining apparatus, and particularly to an electric discharge machining apparatus that performs electric discharge machining by moving an electrode and a workpiece relative to each other.

FIG. 1 shows the configuration of this type of electrical discharge machining apparatus.
In the figure, first, the electrode 10 and the workpiece 12 are opposed to each other with the machining fluid 16 in between. Then, electrical discharge machining is performed using electrical energy supplied by the electrical discharge machining power supply 14. The relative movement between the electrode 10 and the workpiece 12 is performed by moving the XY table 26 on which the workpiece 12 is placed and moving the electrode 10 up and down. The table 26 is connected to the X-axis drive motor 18 and the Y-axis drive motor 18.
It is driven by a shaft drive motor 20. Further, the electrode 10 is driven by a Z-axis drive motor 22. Thereby, the relative motion between the electrode 10 and the workpiece becomes a three-dimensional motion. Each drive motor 18, 2 of XY axis
0 and 22 are controlled by a control device 24. This control device is configured by, for example, an information processing device using a CPU (central processing unit).

FIG. 2 shows a portion of the control device that specifically controls the XY-axis moving motor. In the same figure,
An axis movement command issued from the CPU 30 is input to an error counter 36 via a bus line 32 and a BRM (pulse distribution circuit) 34. The error counter 36 receives the output of the BRM 34 and a feedback signal from an encoder 44 directly connected to the XY axes. In a normal servo mechanism, there is an electrical or mechanical time delay element, which causes a follow-up delay (position error) between the axis movement command value output from the CPU and the current value. The value corresponding to this follow-up delay becomes the content of the error counter 36. The contents of the error counter 42 are converted into an analog quantity by a D/A converter (digital-to-analog converter) 38, and sent to the motor 4 via an amplifier 40.
Drive 2. The contact state between the electrode 10 and the workpiece 12 is detected by the contact detection circuit 46. The detection signal V _c from this detection circuit 46 is
30. FIG. 4 shows the electrode 10
The timing charts before and after the and workpiece 12 come into close contact are shown. In this case, since there is a follow-up delay in a normal servo system, when the electrode 10 and workpiece 12 come into contact, the command value from the CPU 30 is ahead of the current value by the value e ₁ of the error counter 36. . In addition, the CPU 30 receives a contact signal.
When V _c is input, the axis movement command is immediately stopped, but since there is a calculation delay time T ₁ of the CPU 30, the axis movement pulse e ₂ from the BRM 34 is output for the delay time T ₁ minute. For this reason, electrode 1
Even after contact between 0 and workpiece 12, the
The axis will move by an amount equivalent to e ₁ + e ₂ . The amount of movement of this extra shaft, that is, the amount of thrust, is proportional to the speed of movement of that axis. For example, if the speed of movement is
In the case of 1000 mm/min, a plunge amount of about 1 mm occurs, which causes the problem that the electrode 10 and the workpiece 12 collide, causing damage to both or at least one of them.

This invention was made in view of the above-mentioned conventional problems, and its purpose is to make the movement speed relatively high when moving the electrode and the workpiece relative to each other to achieve a predetermined position. It is an object of the present invention to provide an electric discharge machining apparatus which can accurately and highly accurately determine a stop position without causing a so-called large plunge amount, and thereby can perform accurate electric discharge machining.

In order to achieve the above object, this invention makes an electrode and a workpiece face each other, applies a voltage between them to generate an electric discharge, and moves the electrode and workpiece by an axis movement command from a numerical control device. In an electrical discharge machining device that performs relative movement to machine a workpiece, a counting means for counting the amount of position error between an axis movement command value and a current value of the axis, and converting the counted value into an analog quantity. a conversion means and a contact detection means for detecting contact between the electrode and the workpiece, the shaft is moved by rotating the motor according to the analog amount, and when the electrode and the workpiece come into contact, The present invention is characterized in that it has a control circuit that resets the count value of the counting means based on the output signal of the contact detection means.

Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

First, the embodiment of the electric discharge machining apparatus according to the present invention is basically similar to the conventional apparatus described above in its basic configuration. However, the control device, especially the XY
As shown in FIG. 3, the parts that control the drive motors of the shafts are different from the conventional one described above. That is, FIG. 3 shows the main parts of the electric discharge machining apparatus according to the present invention, particularly the control device thereof. Also,
FIG. 5 shows the electrode 1 in the configuration shown in FIG.
2 shows timing charts before and after the workpiece 12 approaches and contacts the workpiece 12. In FIGS. 3 and 5, when the electrode 10 and the workpiece 12 come into contact, the contact detection circuit 46 outputs a contact detection signal V _c . This contact detection signal V _c is read into the CPU 30 .
When the CPU 30 reads the contact detection signal V _c ,
Stop the pulse distribution output from BRM34.
In this case, the contact detection signal V _c has a pulse width T ₂ that is longer than the calculation time delay T ₁ from when the CPU 30 inputs the signal V _c to when the pulse distribution output is stopped. In addition, the contact detection signal V _c is
The error counter 36 is reset during the time of the pulse width _T2 . At this time, the value _e1 of the error counter 36 that is about to be reset is set in the register 50. Also, while the contact detection signal V _c is resetting the error counter 36, the calculation delay time of the CPU 30
During _T1 , the number of movement command pulses output from the BRM 34 is counted by the counter 48.
In the case of the conventional device described above, the value e ₁ is the sum of the axis movement command pulse e ₂ output during the time T ₁ from when the CPU inputs the contact detection signal until it stops outputting the pulse distribution. _However , in the case of this invention, since the error counter 36 is reset by the contact detection signal _Vc , the value of the error counter 36 is forced to change. becomes zero, and as a result, the values of e ₁ and e ₂ above are D/A
There is no output to the transducer 38, and eventually the electrode 10 is brought to a quick stop at the position where the contact is detected. At this time, the position where the electrode 10 was rapidly stopped and
Although an error of e ₁ + e ₂ occurs between the position recognized by the CPU 30, the value e ₁ set in the register 50 and the value e ₂ counted by the counter 48 are transferred to the CPU.
30, and the current value inside CPU30
By performing an operation of adding a correction of X ₁ − (e ₁ + e ₂ ) to X ₁ , the current value of the electrode 10
The current values inside the CPU 30 match, so that no error occurs. Due to the above operation,
If the electrode 10 and the workpiece 12 come into contact while moving, there will be no error between the current value of the electrode 10 and the current value inside the CPU, and even if the axis is moved at a relatively high speed, the electrode 10 and the workpiece 12 will not touch each other during movement. There is no risk of damage due to collision with the workpiece 12, and accurate and highly accurate positioning can be performed by safely and rapidly stopping axis movement.

Note that in the above embodiment, the error counter 36,
Although the register 50, counter 48, BRM 34, etc. are configured by hardware, it is also possible to configure these in software in the CPU 30, and in this case, the same effect as described above can be obtained. Of course, it can be done.

As described above, the electric discharge machining apparatus according to the present invention is capable of accurately and reliably stopping the movement quickly at the contact detection position between the electrode and the workpiece even when the axis is moved at a relatively high speed. can. Furthermore, by having the CPU read up the value of the error counter when it is reset, the CPU can accurately know the current value that has been rapidly stopped.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the operating principle of the electric discharge machining apparatus according to the present invention, Fig. 2 is a block diagram showing a conventional example of the control device portion thereof, and Fig. 3 is a block diagram showing the control device portion of the electric discharge machining apparatus according to the present invention. FIG. 4 is a timing chart showing an example of the operation of a conventional device, and FIG. 5 is a timing chart showing an example of the operation of the device according to the present invention. The same members in each figure are given the same reference numerals, 10 is the electrode, 12 is the workpiece, 14 is the electric discharge machining power source, 1
8, 20, 22 are X, Y, and Z axis drive motors, 24
is the control device, 26 is the XY table, 30 is the CPU
(central processing unit), 34 is BRM (pulse distribution circuit), 36 is error counter, 38 is D/A converter,
42 is a motor, 44 is an encoder, 46 is a contact detection circuit, 48 is a counter, and 50 is a register.

Claims (1)

[Claims] 1. An electrode and a workpiece are opposed to each other, a voltage is applied between them to generate an electric discharge, and the relative movement of the electrode and the workpiece is controlled by an axis movement command from a numerical control device. In an electric discharge machining apparatus that processes a workpiece, the apparatus comprises: a counting means for counting a positional error amount between an axis movement command value and a current value of the axis; a converting means for converting the counted value into an analog quantity; and an electrode. contact detection means for detecting contact between the object and the workpiece; storage means for storing the positional error amount counted by the counting means; and movement of the shaft by rotating a motor using the analog quantity converted by the conversion means. The output signal of the contact detection means is inputted to the reading control terminal of the storage means, the reset terminal of the counting means, and the central processing unit of the numerical control device, respectively, to detect when the electrode and the workpiece are in contact with each other. in case of,
The count value of the counting means is stored in the storage means by the output signal of the contact detection means, and then the count value of the counting means is reset, and the position error amount stored in the storage means is processed by the central processing of the numerical control device. An electric discharge machining device characterized in that the current axis movement value is read by the device and corrected.