Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
1999-11-08
2002-05-07
Picard, Leo P. (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C219S069160, C200S041000
Reexamination Certificate
active
06385501
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a discharge machining control method and a discharge machining control apparatus in which an electrode and a workpiece are located in a machining liquid and machining is executed by applying a voltage between the electrode and the work to generate electrical discharges.
BACKGROUND ART
In a discharge machining apparatus for executing machining by applying a voltage to a section between an electrode and a workpiece located in a machining liquid to generate discharges for machining the workpiece, a gap distance control system for adjusting a distance between the electrode and the work is provided for maintaining stable machining conditions.
FIG. 11
shows configuration of a machining control system including a gap distance control system based on the conventional technology described, for instance, on pages 88 to 90 in “Mechanism of Discharge Machining and Method for Full Utilization of the Same” (Gijutsu Hyoron-sha). In this figure, designated at the reference numeral
101
is a discharge machining process, and at
102
a machining state detecting section. Designated at the reference numeral
103
is a reference value setting section, and at
104
an error signal computing section. Designated at the reference numeral
109
is a machining trajectory setting section, at
110
an electrode driving unit. Designated at the reference numeral
111
is a machining pulse condition setting section, at
112
a machining power supply. Designated at the reference numeral
1101
is a controlled variable computing section. Further, y is a value indicating a state of the discharge machining process
101
, and ym is a detected value of y by the machining state detecting section
102
. r is a reference value for a machining state set in the reference value setting section
103
, and e is an error signal obtained from the detection value ym and the reference value r by the error signal computing section
104
. Rv is a machining trajectory instruction value set in the machining trajectory setting section
109
, and Up is a controlled variable set obtained from the error signal e and the machining trajectory instruction value set Rv by the controlled variable computing section
1101
. Mp is an electrode moving quantity for operation according to the controlled variable set Up by the electrode driving unit
110
. Rs is a machining pulse condition instruction value set in the machining pulse condition setting section
111
. Ms is a machining pulse quantity operated by the machining power supply
112
according to the instruction value set Rs. It should be noted that the machining trajectory instruction value set Rv and controlled variable set Up are vector values corresponding to X, Y, and Z axes and the electrode driving unit
110
is a X, Y, Z-axial driving unit. The gap distance is controlled according to the electrode moving quantity Mp in the X, Y, Z-axial directions. The machining pulse condition instruction value set Rs comprises such parameters as an open voltage, a peak current, a pulse-ON time, and a pulse-OFF time.
FIG. 12
is a view schematically showing the discharge machining process
101
. In this figure, designated at the reference numeral
1201
is an electrode, at
1202
a work, at
1203
a machining liquid, at
1204
discharge occurring between the electrode
1201
and the work
1202
, and at
1205
a machined surface by means of electric discharges. In the discharge machining apparatus, a gap distance control system as described below is provided for satisfying required machining precision and machining surface roughness and also for optimizing a machining speed.
FIG. 13
is a view showing contents of operations of a gap distance control system based on the conventional technology. Execution of a gap distance control algorithm is generally carried out by means of software processing utilizing a computer, and the k-th time processing is shown in this figure. Step S
201
indicates the processing in the machining state detecting section
102
, and herein a machining state in a discharge machining process is detected as an average gap voltage ym(k) Step S
202
indicates the processing in the error signal computing section
104
, and herein an error signal e(k) is computed from a reference value r of the average gap voltage and the detected ym(k). Step S
1301
indicates the processing in the controlled variable computing section
1101
, and herein a controlled variable set Up(k) is computed from the machining trajectory instruction value set Rv in the machining trajectory setting section
109
and the error signal e(k), and the controlled variable set Up(k) is instructed to the electrode driving unit
110
. Kp is a proportion gain, while Ki is an integration gain, and an electrode is controlled so that the detected ym(k) is equalized to the reference value r by means of the technique of PI compensation (proportion+integration compensation).
In recent years, there has been proposed a machining method in which an electrode having a simple form is used and discharge machining having a three-dimensional form is executed by numerically controlling the electrode. Also cases of performing micro machining utilizing the discharge machining are increasing. In the machining method as described above, an area subjected to discharge machining is smaller as compared to that in the conventional technology, and as a result the moving speed of the machining surface becomes higher, so that it becomes difficult to match the detected value to the reference value without any steady state error in the conventional type of gap distance control system. Namely, a state in the discharge machining process is deviated from the optimal state, so that the machining speed becomes disadvantageously lower.
The present invention was made to solve the problems as described above, and it is an object of the present invention to provide a discharge machining control method as well as a discharge machining apparatus in which it is possible to match the detected value to the reference value without any steady state error even when the discharge machining area is small and to improve the machining speed by keeping a discharge machining process in an optimal state.
DISCLOSURE OF THE INVENTION
In the discharge machining control method according to the present invention, an error signal is obtained from a reference value and a value indicating a detected state of machining; a first controlled variable is obtained by adding a value obtained by multiplying the error signal by a proportion gain to a value obtained by multiplying the error signal by a first integration gain for integration; a second controlled variable is obtained by multiplying an instruction value by a second integration gain for integration; and a controlled variable for a driving unit for adjusting a distance between an electrode and a work is obtained by adding the first controlled variable to the second controlled variable and multiplying the sum by a machining trajectory vector.
Further, in the discharge machining control method according to the present invention, the instruction value is previously registered in a data table in correspondence to at least one of the machining pulse conditions, discharge area, or material of the electrode or work, and the instruction value can be changed during machining.
Further, in the discharge machining control method according to the present invention, process parameters are identified with a signal indicative of a position of the electrode or the work and a value indicative of a detected machining state, or with a signal indicative of the speed of the electrode or the work and a value indicative of a detected machining state, and the instruction value is automatically adjusted during machining depending upon the identified process parameters.
Further, in the discharge machining control method according to the present invention, the second integration gain can freely be adjusted by the operator during machining.
Further, in the discharge machining control method acco
Imai Yoshihito
Nakagawa Takayuki
Yuzawa Takashi
Gorland Steven R.
Leydig , Voit & Mayer, Ltd.
Mitsubishi Denki & Kabushiki Kaisha
Picard Leo P.
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