Electric heating – Metal heating – Cutting or disintegrating
Utility Patent
1998-09-08
2001-01-02
Evans, Geoffrey S. (Department: 1725)
Electric heating
Metal heating
Cutting or disintegrating
C219S069160, C219S069180
Utility Patent
active
06169262
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to electric discharging machines, and more particularly, to an apparatus and method for use on an electric discharging machine to enhance the working efficiency of the electric discharging machine.
2. Description of Related Art
FIG. 1
is a schematic block diagram of a conventional electric discharging machine. As shown, the electric discharging machine includes a discharging circuit
1
, a discharging feedback control circuit
2
, and a CNC (computer numerical control) unit
6
. In more detail, the feedback control circuit
2
includes a voltage detector
3
, an RC voltage averaging circuit
4
, and an ADC (analog-to-digital converter)
5
. The voltage detector
3
is coupled to the discharging circuit
1
to detect the voltage drop between the electrode and the workpiece. The output of the voltage detector
3
is then transferred to the RC voltage averaging circuit
4
to be averaged thereby. Then, the output of the RC voltage averaging circuit
4
is transferred to the ADC
5
to be converted into digital form. The digital output from the ADC
5
is then transferred to the CNC unit
6
for the CNC unit
6
to accordingly control the feedrate of the electric discharging machine.
FIG. 2
is a schematic diagram showing the waveform of the voltage drop between the electrode and the workpiece under various conditions. As shown, during the period T
d
, the voltage V
i
is applied to the workpiece; during the period T
on
, the voltage V
d
is applied; and during the period T
off
, no voltage is applied; where
V
i
is ignition voltage;
V
d
is discharge voltage;
T
d
is ignition delay time;
T
on
is the on-time of the discharge voltage; and
T
off
is the off-time of the discharge voltage.
The average discharge voltage V
g
is then:
V
g
=(
V
i
*T
d
+V
d
*T
on
)/(
T
d
+T
on
+T
off
)
Fundamentally, the feedrate of the electric discharging machine is related to the average discharge voltage V
g
. Therefore, the technician can adjust for the desired feedrate by adjusting the average discharge voltage V
g
.
One drawback to the foregoing servo feedrate control method for the electric discharging machine is that all the discharging parameters, including discharging current, discharging on-time, and discharging off-time, are fixed after being set, making the average discharging voltage also fixed after being set, so that the feedrate will not be adaptively adjustable in response to any variations in the discharging conditions.
Therefore, in the conventional electric discharging machine, the average discharging voltage should be carefully set in advance. As indicated by the foregoing equation, the average discharging voltage V
g
is related to the ignition voltage V
i
, the ignition delay time T
d
, the discharging voltage V
d
, the discharging on-time T
on
, and the discharging off-time T
off
. Moreover, the discharging voltage will be varied according to the different materials that make up the electrode and the workpiece. For example, in the case of the combination of copper and steel, the average discharging voltage is within the range from 17 V (volt) to 25 V; and in the case of the combination of graphite and steel, the average discharging voltage is from 20 V to 33 V.
In the RC voltage averaging circuit
4
of
FIG. 1
, the RC constant is also an important parameter. A large RC constant would allow a short-pulse discharging to be more stable, but may cause the servo response to be more sluggish. Moreover, poor sampling would degrade the working efficiency of the servo control, resulting in an increase in the ignition delay time or in the number of useless discharges.
If the technician adjusts the discharge parameters for some desired results, it would then affect the average discharge voltage. Therefore, a tradeoff exists between the working efficiency of the servo control and the discharge parameters. This makes the working efficiency of the servo control not always optimal.
SUMMARY OF THE INVENTION
It is therefore an objective of the present invention to provide an apparatus and method for use on an electric discharging machine to enhance the working efficiency of the electric discharging machine.
In accordance with the foregoing and other objectives of the present invention, an apparatus and method are provided for use on an electric discharging machine to enhance the working efficiency of the electric discharging machine.
The method of the invention includes the following steps:
(1) detecting the average discharge voltage;
(2) determining the average ignition delay time of the discharges to accordingly adjust the gain of the servo control loop of the discharging;
(3) detecting the ignition delay time to accordingly adjust the magnitude of the ignition voltage and the length of the discharging off-time,
(4) detecting whether the number of consecutive occurrences of arcing reaches a preset number; and, if yes, performing a residue cleaning process; and
(5) detecting whether a short-circuit occurs; and, if yes, stopping the machining process immediately.
The apparatus of the invention includes the following constituent parts:
a voltage detector for detecting the voltage drop between the workpiece and the electrode;
a discharging waveform comparison circuit, responding to the output of the voltage detector, to check whether the detected voltage by the voltage detector is an ignition voltage;
an ignition delay time computation circuit that, in the event that the discharge waveform comparison circuit determines that the detected voltage by the voltage detector is ignition voltage, detects the length of the ignition delay time of the ignition voltage;
a discharging counter, that responds to the output of the voltage detector, for counting the number of occurrences of discharges; and
a CNC unit that in response to the output of the ignition delay time computation circuit and the output of the discharge counter, determines the average ignition delay time obtained from dividing the total time of a series of discharges by the total number of these discharges and accordingly controls the ignition delay time of the subsequent discharges within the average discharge voltage.
The apparatus of the invention further comprises: an ignition delay time detector for detecting whether the ignition delay time is greater than a preset reference value; and, if yes, the ignition delay time detector generates a trigger signal; and a high-voltage ignition circuit, responding to the trigger signal generated by the ignition delay time detector, for applying a high voltage to help the ignition. The apparatus of the invention further comprises: a counter, coupled to the ignition delay time detector, for counting the number of occurrences of discharges for reference by the CNC unit to set the next feedrate.
The apparatus of the invention further comprises: an ignition delay time detector for detecting whether the ignition delay time is less than a preset reference value; and, if yes, the ignition delay time detector generates a trigger signal; and a discharge off-time extending circuit responding to the trigger signal generated by the ignition delay time detector, for extending the discharge off-time.
The apparatus of the invention further comprises: an ignition delay time detector for detecting whether the ignition delay time is less than a preset reference value; and, if yes, the ignition delay time detector generates a trigger signal; and a counter, responding to the trigger signal generated by the ignition delay tine detector, for counting the number of consecutive occurrences of arcing; and, if the ignition delay time detector reaches a preset value, the counter generates an actuating signal to actuate the CNC unit to perform a residue cleaning process.
The apparatus of the invention further comprises: a short-circuit detector, coupled to the output of the voltage detector, for detecting whether the detected voltage by the voltage detector is below a preset short-circuit value; and, if yes, the short-circuit
Lee Chao Hsiu
Lin Jui-Kuan
Nien Yung-Feng
Su Hsin Chaun
Evans Geoffrey S.
Industrial Technology Research Institute
Smith , Gambrell & Russell, LLP
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