Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2000-03-21
2003-01-07
Picard, Leo (Department: 2121)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S176000, C219S069160
Reexamination Certificate
active
06505091
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electric discharge machining control method and an electric discharge machining control device in which an electrode and a workpiece are placed in a machining liquid, a voltage is applied between the electrode and the workpiece, and the workpiece is machined with the generated electric discharge.
BACKGROUND ART
In an electric discharge machine, an electrode and a workpiece are placed in a machining liquid, a voltage is applied between the electrode and the workpiece, and the workpiece is machined with the generated electric discharge. A gap distance control system for adjusting the distance between the electrode and the workpiece is provided in the electric discharge machine that maintains a stable machining state.
FIG. 16
shows the configuration of a machining control system including the conventional gap distance control system. This configuration is described, for example, on p88 to p90 of “Mechanism of Electric Discharge Machining and How to Make Full Use of It” (published by Gijutsu Hyoron-sha). As shown in this figure, designated at the reference numeral
101
is an electric discharge machining process, at
102
a machining-state detecting section, at
104
a reference-value setting section, at
105
an error-signal computing section, at
106
a control variable computing section, at
107
a machining-trajectory setting section, at
108
a rotational condition setting section, at
109
an electrode driving unit, at
110
a machining-pulse condition setting section, and at
111
a machining power unit. Designated at the reference sign y is a quantity of state in the electric discharge machining process
101
, at ym a detected value of the quantity of state y detected by the machining-state detecting section
102
, at r a reference value of a machining state set in the reference-value setting section
104
, at e an error signal computed from the detected value ym and the reference value r by the error-signal computing section
105
, at Rv a machining-trajectory instruction value set in the machining-trajectory setting section
107
, at Rr a rotation instruction value set in the rotational condition setting section
108
, at Up is a control variable computed from the error signal e and the machining-trajectory instruction value Rv by the control variable computing section
106
, at Mp an electrode moving quantity operated according to the control variable Up and the rotation instruction value Rr by the electrode driving unit
109
, at Rs a machining-pulse condition instruction value set in the machining-pulse condition setting section
110
, and at Ms a machining pulse quantity operated according to the instruction value Rs by the machining power unit
111
. It should be noted that the machining-trajectory instruction value Rv and the control variable Up are a vector variable corresponding to XYZ axes, the rotation instruction value Rr is a vector variable corresponding to a rotating speed and direction around a C axis. The electrode driving unit
109
consists of an XYZ-axial driving unit and a C-axial rotating unit, and controls a gap distance in the XYZ-axial direction while rotating the electrode in the C-axial direction according to the electrode moving quantity Mp. In addition, the machining-pulse condition instruction value Rs consists of an open voltage, a peak current, a pulse-ON time, and a pulse-OFF time, or the like.
FIG. 17
shows the operation of the conventional gap distance control system. A gap distance control algorithm is generally executed through software-processing by a microcomputer, and this figure shows a k-th processing. The processing in Step S
201
is performed in the machining-state detecting section
102
and in this step a machining state of the electric discharge machining process as, for instance, an average gap voltage ym (k) is detected. The processing in Step S
401
is performed in the error-signal computing section
105
and in this step an error signal e (k) from the reference value r and the detected value ym (k) of the average gap voltage is computed. The processing in Step S
1701
is performed in the control variable computing section
106
and in this step a control variable Up (k) from the machining-trajectory instruction value Rv set in the machining-trajectory setting section
107
and the error signal e (k) is calculated. Further, the control variable computing section
106
gives the control variable Up (k) to the electrode driving unit
109
. Here, Kp is a proportional gain and Ki is an integral gain. The electrode is then moved in such a manner that the detected value ym (k) coincides with the reference value by using the well-known PI compensation (proportional & integral compensation).
FIG. 18
shows a power spectrum of a detected value indicating a machining-state in the conventional gap distance control system. Namely, this figure shows the power spectrum P of an average gap voltage ym (k) detected by the machining-state detecting section
102
when machining is executed by the electric discharge machine having the conventional gap distance control system. As can be seen in this figure, the power spectrum shows peaks at frequencies f
1
, f
2
, and f
3
. These peaks correspond to rotational frequencies of the electrode and the harmonic of the frequencies. The peaks in the power spectrum are derived from eccentric of the electrode to be rotated as well as from fluctuations in electric characteristics at the feeding brush section.
FIG. 19
shows a power spectrum of a machining-state detected value in another electric discharge machine using the conventional gap distance control system. Namely, this figure shows a power spectrum P of an average gap voltage ym (k) detected by the machining-state detecting section
102
when machining is executed by another electric discharge machine having the conventional gap distance control system. When compared with
FIG. 18
, a new peak appears at the frequency f
4
. This is a resonance frequency of the mechanical system of the XYZ-axial driving unit. Therefore, if the mechanical system has many resonance frequencies then peaks corresponding to each resonance frequency appear in the power spectrum. As described above, the presence of peaks in the power spectrum of the detected average gap voltage indicates the fact that there exists disturbance to the gap distance control system at the frequency corresponding to each peak. A stable machining state cannot be maintained at such frequencies where a peak is present.
As described above, for machining using a rotated electrode, eccentric of the electrode varies a gap distance, which disturbs the gap distance control system and deteriorates the machining speed. In addition, rotation of the electrode fluctates the electric characteristics at feeding brush sections, because machining current is fed from a machining power unit to the electrode through the feeding brush sections, which disturbs the gap distance control system and deteriorates the machining speed. Further, when there is mechanical resonance in the electrode driving unit, a control variable to the driving unit and an actual movement of an electrode are different, which results into an inappropriate control of the gap distance and deteriorates the machining speed.
DISCLOSURE OF THE INVENTION
A first electric discharge machining control method according to the present invention comprises the steps of detecting a machining state, filtering a detected value indicating the machining state with a notching frequency, computing an error signal from an output value by means of filtering and a set value of a machining state, computing a control variable for controlling movement of an electrode from the error signal and a set movement value of the electrode, and moving the electrode in a specific direction and at the same time rotating the electrode vertical to the opposite surface to a workpiece according to the control variable. With those operations, disturbance to a gap distance control system can be suppressed. Therefore, machining spe
Imai Yoshihito
Nakagawa Takayuki
Yuzawa Takashi
Garland Steven R.
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
Picard Leo
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