JPH0215917A - Servo control method for electric discharge machine - Google Patents

Abstract

PURPOSE:To prevent the hunting phenomenon of an electric discharge machine by reducing the position command value determined according to the quantity of variation in voltage between an electrode and a work, when the position error gets greater, to accumulate no serious position error in an error register. CONSTITUTION:The voltage VD between an electrode and a work is detected by a voltage detecting circuit 12 and the quantity of variation in detected voltage VD (that is, the quantity of variation in difference between the detected voltage VD and a set voltage VS) every sampling time is calculated as a position command C. Based on a position error Er which is adifference between the position command C and a position feedback value, a motor is driven to move the electrode relatively to the work, whereby executing the electric discharge work. At this time, the position error Er is monitored by a position command reduction means 21 and when the error Er gets greater, the reduction rate of the position command C gets higher to inhibit a serious position error from being accumulated in an error register 17, whereby preventing the hunting phenomenon of an electric discharge machine.

Description

[Detailed Description of the Invention] <Industrial Field of Application> The present invention relates to a servo control method for an electric discharge machine, and in particular, the present invention relates to a servo control method for an electric discharge machine, and in particular, a method for controlling a machining electrode relative to a workpiece while maintaining a constant gap between the machining electrode and the workpiece. This invention relates to a servo control method for moving objects.

<Prior art> In an electrical discharge machine, such as a die-sinking electrical discharge machine, the electrode is moved in the depth direction relative to the workpiece while maintaining a constant gap between the machining electrode and the workpiece. The workpiece is electrically discharged according to its shape.

FIG. 3 is an explanatory diagram of the servo system in such a die sinking electrical discharge machine, in which 1 is a machining electrode, 2 is a workpiece, 3 is a motor that moves the machining electrode up and down relative to the workpiece, 4 is a servo amplifier, 5 is a voltage detection circuit that detects the voltage between the processing electrode 1 and the workpiece 2, and 6 is a comparison circuit that generates an error voltage vE according to the difference between the detected voltage v0 and the set voltage vs. Set voltage V.

is a value corresponding to the predetermined length gap between the machining electrode 1 and the workpiece 2, so if the motor 3 is driven based on the error voltage v6, the gap between the machining electrode 1 and the workpiece 2 can be maintained constant. The electrode can be moved in the vertical direction while moving.

Figure 4 is a block diagram of a software servo that realizes servo control of such an electrical discharge machine through digital processing.
1 is a motor, 12 is a voltage detection circuit that detects the voltage v0 between the processing electrode and the workpiece, and 13 is the amount of change in the detected voltage v0 every predetermined sampling time T, in other words, the detected voltage V. and the set voltage V, and 14 is an AD converter (14) that converts the analog voltage V input at each sampling time into an AD converter and outputs it as a positive control command C. ADC), 15 is a command synthesis unit, 1
6 is an arithmetic unit, 17 is an error register that stores a position error Er, and 18 is a gain setting unit in which a position gain Kp is set.

<Problem to be solved by the invention> In the conventional servo system, the amount of change (v) of the voltage between the electrode and the workpiece at each sampling time (v) is the position command, and the difference between the position command and the actual amount of movement is Servo control is performed based on the position error to maintain a constant gap between the electrode and the workpiece.

However, in conventional servo systems, when the position feedback becomes small due to the spring elements of the machine, a large position error Er accumulates in the error register, and hunting may occur in the machine.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a servo control method for an electric discharge machine that can prevent a large position error from accumulating in an error register and thus prevent hunting of the machine.

Means for Solving the Problems> FIG. 1 is a block diagram of a servo system of an electric discharge machine according to the present invention.

11 is a motor, 12 is a voltage detection circuit, and 13 is a detection voltage v
17 is an error register that stores the positive error Er, and 21 is a position command reduction means.

Function> The voltage detection circuit 12 detects the voltage vo between the electrode and the workpiece, and at each sampling time, the amount of change in the detected voltage v0 (the amount of change in the difference between the detected voltage v0 and the set voltage V) is determined. is the position command C, and the position error Er, which is the difference between the position command and the position feedback, is
The electrode is moved relative to the workpiece by driving the motor based on this. During such servo control, the position command reducing means 21 is made to monitor the position error Er, and as the position error Er increases, the rate at which the position command value C is reduced is increased, and the error register is increased. 1
7 to prevent large position errors from accumulating.

<Embodiment> FIG. 1 is a block diagram of a software servo that realizes servo control of an electrical discharge machine according to the present invention by digital processing, and the same parts as in the conventional example shown in FIG. 4 are given the same reference numerals.

11 is a motor, 12 is a voltage detection circuit that detects the voltage v0 between the processing electrode and the workpiece, and 13 is RT at a predetermined sampling time.
This is a set value comparison circuit that calculates and outputs the amount of change in the detected voltage v0, in other words, the amount of change V in the difference ΔV between the detected voltage v0 and the set voltage V, at each time. That is, the set value comparison circuit 13
If the difference one sampling time ago (the difference between the detected voltage v, -1 and the set voltage vs) is ΔV + -t, and the difference at the current sampling time (the difference between the detected voltage V and the set voltage v0) is Δv1, then V is calculated using the following formula (1), and the V is output as a position command for each sampling time.

14 is an AD conversion word that AD converts the analog positive control command V output from the set value comparison port l1s13 at each sampling time and outputs it as a digital position command C. 21 is an AD conversion word that converts the position command C based on the position error Er. This is a position command reducing means for reducing the position command. 15
is the command synthesis section, 16 is the calculation section, and 17 is the position error E.
Error register that stores r, 18 is position gain K
This is a gain setting section in which P is set.

When positioning the machining electrode at a predetermined position using an NC command, the synthesizing unit 15 outputs the NC command, and when maintaining a constant gap between the machining electrode and the workpiece through constant gap control, outputs an output signal from the AD converter 14. command C is output. Further, the calculation unit 16 calculates the difference ΔE between the position command (position command reduction means output) C' and the position feedback F for each sampling time, and accumulates the calculation result ΔE in the error register 17 (Er+ΔE-4Er).

As shown in FIG. 2(a), the position command reducing means 21 changes the ratio η (%) of outputting the position command according to the value (MIN-MAX) of the position error Er, and calculates the ratio η (%) of outputting the position command according to the following formula % formula % ( 2) C' is calculated by the following and outputted as a position command.

Therefore, as shown in the table below, each time T,, T2. T,, T4. The position commands C at T, are all 10, and the positive cylinder error Er at each time is 0. More than ErMAX, Er.

8/2.0, if ErMAXx or more, η and the position command C′ output from the position command reduction means 21
is as shown in the right column of the same table, and the cumulative value of C' becomes the commanded movement amount.

When performing servo control to keep the gap between the electrode and the workpiece constant from the position command C position error position ν or more, the set value comparison diagram l513 shows the voltage detection circuit 12.
The voltage v between the electrode and the workpiece at every predetermined sampling time from
0 is read, calculation is performed using equation (1) to find the amount of change in the detected voltage v0 (the amount of change in the difference between the detected voltage v0 and the set voltage V), and the AD converter 14 converts the amount of change V into an AD It is converted and inputted to the position command reduction means 21 as a digital position command C.

The position command reducing means 21 is configured as shown in FIG. 2(a).
The rate at which the position command C is output is determined according to the r-η characteristic, the position command C is corrected to C' according to equation (2), and C' is output as the position command.

The calculation unit 16 calculates the position command C' for each sampling time.
The difference ΔE between the
-4Er), the motor is driven based on the position machining error, and the machining electrode is moved while maintaining a constant distance with respect to the workpiece.

Note that the position control in the depth direction is performed by the position command reduction means 2.
It is sufficient to count the commands C' output from 1 and stop the commands when the counted value reaches a predetermined value.

Also, the relationship between the position error Er and the ratio l is shown in Figure 2 (a).
The configuration is not limited to the one shown in FIG. 12, but can also be configured as shown in FIG.

<Effects of the Invention> According to the present invention, the voltage between the electrode and the workpiece is detected, and the amount of change in the detected voltage is determined at predetermined time intervals to be used as a position command, and the difference between the position command and position feedback is determined. Since the electrode is moved relative to the workpiece based on the position error, and the position command value determined according to the amount of change is decreased as the position error increases, it is possible to prevent large position errors from accumulating in the error register. Therefore, the hunting phenomenon of the machine can be prevented.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a servo system of an electrical discharge machine according to the present invention, FIG. 2 is an Er-η characteristic diagram, and FIGS. 3 and 4 are explanatory diagrams of a servo system of a conventional electrical discharge machine. 11...Motor, 12...Voltage detection circuit, 13...Set value comparison circuit, 17...Error register, 21...Position command reduction means Patent applicant: Fanuc Co., Ltd. Agent Patent attorney Chiki Saito Figure 2 transformation

Claims (1)

[Claims] The voltage between the electrode and the workpiece is detected, and the amount of change in the detected voltage is calculated at predetermined intervals as a position command, and the electrode is moved relative to the workpiece based on the position error, which is the difference between the position command and position feedback. 1. A servo control method for an electrical discharge machine that moves the electrical discharge machine in a fixed manner, the method comprising: reducing a position command value determined according to the amount of change as the position error increases.