JPS6158255B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrode positioning method for an electric discharge machining apparatus.

As is well known, in an electric discharge machining apparatus, in order to machine a desired position of a workpiece, it is necessary to position a machining electrode with respect to the workpiece in advance.

For this reason, in the past, the center of the electrode and the processing center of the workpiece were marked, a prism or lens was placed between the electrode and the workpiece, and the workpiece was placed so that both marks coincided. was moved to determine the desired position.

However, in such conventional methods, prisms etc. must be placed on the electrode and the workpiece,
Moreover, the optical axis needs to maintain a parallel relationship with the axis of the spindle on which the electrode is attached, and if this is not satisfied, errors will occur in positioning. Therefore, with such a configuration, highly accurate positioning is extremely difficult.

Further, as a conventional electrical electrode positioning method, there is a method of electrically detecting the contact between the electrode and the workpiece, and thereby knowing the relative position between the end face of the electrode and the end face of the workpiece. This type of device is shown in Figure 1.
is an electrode for processing, 2 is a workpiece, 3 is a main column, 4 is a bed, 5 is a servo feed head of electrode 1, 6 is a table feed motor, 7 is a feed screw driven by the table feed motor 6, It engages with the female thread of the processing table 8 on which the workpiece 2 is placed, and
is driven in a direction perpendicular to the electrode 1. A short circuit detection circuit 9 is electrically connected to the electrode 1 and the workpiece 2, electrically detects whether or not there is contact between the two, and sends a signal to the drive control circuit 10. The drive control circuit 10 is generally composed of a numerical control device or the like, and drives the table feed motor 6 in a desired direction using a paper tape or the like as an input command.

Next, to explain this operation, when the drive control circuit 10 receives a positioning command, it drives the feed motor 6 until it is informed by a signal from the short circuit detection circuit 9 that the electrode 1 and the workpiece 2 have contacted each other. The processing table 8 is driven. The feed motor 6 is configured to stop at the same time when the contact between the electrode 1 and the workpiece 2 is notified by a signal from the short circuit detection circuit 9, so that the electrode 1 slightly contacts the workpiece 2. It will be positioned as shown. In addition, in the above description, only the end face positioning in the X-axis direction was explained, but the end face positioning in the Y-axis direction is also possible in exactly the same way. Therefore, the end faces can be positioned on the X and Y axes, and the electrode can be positioned by specifying the dimensions of the machining shape with reference to the end faces of the electrode 1 and the workpiece 2.

However, in general, the electrode 1 and the workpiece 2 are designed to have extremely high rigidity in order to improve accuracy, and if the feed motor 6 is driven while the electrode 1 and the workpiece 2 are in contact, the electrode 1 may be damaged. ,
This will cause trouble to the entire electrical discharge machine. Therefore, there was a problem in that such electrode positioning had to be carried out with the feed motor 6 running at an extremely low speed.

As described above, in conventional electrode positioning methods, it is difficult to achieve high precision positioning when positioning is performed using an optical method, and when using an electrical contact detection circuit, even if the feed motor 6 is stopped at the same time as contact is made, The problem of overshooting occurs due to the inertia of the mechanical system, which causes the feed motor 6 to run at an extremely low speed, resulting in the disadvantage that positioning takes time and cannot be called a practical electrode positioning method.

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and it applies a high voltage of about 1000 V or more between the electrode and the workpiece, and removes air as the electrode and workpiece approach. The approach is detected by a minute corona discharge current inside, and the positioning is performed by reducing the speed of the feed motor before the electrode and workpiece come into mechanical contact, without damaging the electrode and workpiece due to discharge. It is an object of the present invention to provide an electrode positioning method that accurately positions an electrode and a workpiece within an extremely short period of time.

An embodiment of the present invention will be described below with reference to the drawings. In Fig. 2, the same or corresponding parts as in Fig. 1 are indicated by the same reference numerals, so the explanation will be omitted.
1 is a high-voltage power supply with a voltage of about 1000 V or more, 12 is a resistor for detecting current of corona discharge, and 13 is a circuit for detecting the voltage generated in the current detecting resistor 12, for example, corona discharge consisting of an operational amplifier, etc. It is a detection circuit.

Next, the operation of the present invention will be described. When positioning the electrode, a high voltage is applied between the electrode 1 and the workpiece 2 from the high voltage power supply 11. A voltage of about 1000V or more is applied from the high voltage power supply 11,
When the distance between the electrode 1 and the workpiece 2 is large, no corona discharge occurs. Therefore, the processing table 8 is moved at high speed by the feed motor 6, and the electrode 1 is moved to the workpiece 2.
However, by designing the internal impedance of the high-voltage power supply 11 to be extremely high, the discharge current can be suppressed to about 10 μA, and arc discharge will not occur. There is no transition and corona discharge occurs. Since the current value of the corona discharge is extremely small, the electrode 1 and the workpiece 2 will not be damaged, and even if you touch the electrode 1 or the like and receive an electric shock, you will not feel any electric shock. When a minute current flows through the resistor 12 due to the occurrence of corona discharge, a voltage is generated across the resistor 12, which is input to the drive control circuit 10 via the corona discharge detection circuit 13, which is comprised of an operational amplifier or the like. Based on this signal, the drive control circuit 10 stops the feed motor 6 or decelerates its drive to lower the voltage of the high voltage power supply 11 in order to further reduce the distance between the electrode 1 and the workpiece 2. It acts to stop the feed motor 6 when corona discharge occurs again or when the electrode 1 and the workpiece 2 come into contact.

As described above, this invention detects the approach of the electrode and the workpiece using a minute corona discharge current, and the feed motor is activated before the electrode and the workpiece come into contact without damaging the electrode or the workpiece. Since it is possible to perform positioning at a reduced speed, the electrode can be moved at high speed initially, and the distance for final positioning at low speed can be extremely short, so the time required to complete positioning is extremely short. This results in shortened and highly accurate positioning.

In addition, in order to achieve more precise positioning, at the same time that corona discharge occurs, the drive of the feed motor 6 is decelerated and the voltage of the high-voltage power supply 11 is lowered, so that the point at which corona discharge occurs again or when the electrode and workpiece are slightly This is obtained by bringing the electrode close to the workpiece until contact is made and then stopping.

In addition, if a high frequency power source of approximately 10 KHz or more is used as a high voltage power source, corona discharge will occur stably even at a relatively low voltage, making it possible to perform highly accurate positioning and to prevent the human body from accidentally touching the electrode. Due to the skin effect caused by the high frequency, the current flows only on the surface of the human body, making it an extremely safe device. Also, if a capacitor or the like is accidentally inserted between the electrode and the workpiece, it will be charged to a high voltage with a DC voltage power source, creating the possibility of electric shock, but capacitors have low impedance against high-frequency power sources. Therefore, it is extremely safe as it does not charge to high voltage.

[Brief explanation of the drawing]

FIG. 1 is a diagram explaining a conventional electrode positioning method, and FIG. 2 is an explanatory diagram showing an embodiment of the present invention. Note that the same symbols in the figures indicate the same or equivalent parts, 1 is the processing electrode, 2 is the workpiece, 5 is the servo feed head, 6 is the feed motor, 10 is the drive control circuit, 11 is the high voltage power supply, and 12 is the corona current. The detection resistor 13 is a corona discharge detection circuit.

Claims (1)

[Claims] 1 A high-frequency, high-voltage voltage is applied between the electrode and the workpiece, the occurrence of corona discharge due to the proximity of the electrode and the workpiece is detected, and the detection signal is used to reduce the positioning speed of the electrode to move the workpiece A method for positioning an electrode in an electrical discharge machining device.