Electricity: measuring and testing – Impedance – admittance or other quantities representative of... – Lumped type parameters
Reexamination Certificate
2001-01-23
2002-10-22
Karlsen, Ernest (Department: 2829)
Electricity: measuring and testing
Impedance, admittance or other quantities representative of...
Lumped type parameters
C219S069180
Reexamination Certificate
active
06469522
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electrical discharge state detecting device for an electrical discharge machining machine which detects an electrical discharge state during an electrical discharge machining operation.
BACKGROUND OF THE INVENTION
Conventionally, it is known that an electrical discharge state in an electrical discharge machining in an electrical discharge machine can be judged by detecting the magnitude of a high-frequency component of the electrical discharge voltage waveform. This electrical discharge voltage waveform is a quite complex waveform including a high-frequency component. Accordingly, it is quite important to provide a technique in which only a characteristic waveform component is detected from the electrical discharge voltage waveform without fail and at high speed.
Japanese Laid-Open Patent Publication No. 5-293714 discloses an electrical discharge state detecting device for an electrical discharge machine. Referring to
FIG. 11
, illustrating a circuit of substantially the same constitution as that of this reference, the operation of this device will be described hereunder.
In
FIG. 11
, reference numeral
2
denotes an electrode of an electrical discharge machine, reference numeral
3
denotes a workpiece, and a machining clearance is formed between the electrode
2
and the workpiece
3
. Reference numeral
1
denotes a machining power source of the electrical discharge machining machine. An electrical discharge voltage in the form of a pulse is supplied from the machining power source
1
to the machining clearance between the electrode
2
and the workpiece
3
. Reference numeral
4
denotes a high-pass filter for use in detecting a high-frequency component of the electrical discharge voltage, reference numeral
5
denotes a rectifying circuit for rectifying the high-frequency component from the high-pass filter
4
, and an output signal vrec is outputted from the rectifying circuit
5
. In addition, reference numeral
6
denotes an electrical discharge generation detecting circuit for detecting generation of the electrical discharge in the machining clearance between the electrode
2
and the workpiece
3
. The electrical discharge generation detecting circuit
6
is composed of an electrical discharge voltage detecting circuit
60
for detecting the electrical discharge voltage at the machining clearance between the electrode
2
and the workpiece
3
and of an electrical discharge current detecting circuit
61
for detecting an electrical discharge current at the machining clearance between the electrode
2
and the workpiece
3
.
An output signal
60
s
of the electrical discharge voltage detecting circuit
60
and an output signal
61
s
of the electrical discharge current detecting circuit
61
, in the electrical discharge generation detecting circuit
6
, are inputted to a logic circuit
62
. Reference numeral
7
denotes a delay circuit. The delay circuit
7
is composed of a time constant circuit
70
for measuring a time constant tH of the high-pass filter
4
and of a logic circuit
72
. An output signal
63
from the logic circuit
62
is inputted to the time constant circuit
70
and the logic circuit
72
in the delay circuit
7
. An output signal
71
from the time constant circuit
70
is inputted to the logic circuit
72
. Reference numeral
8
denotes an integrating circuit. The integrating circuit
8
is composed of an operational amplifier
80
, a capacitor C
1
connected between the inverting (−) input terminal and the output terminal of the operational amplifier
80
, and a resistor R
1
connected in series between the output terminal of the rectifying circuit
5
and the inverting (−) input terminal of the operational amplifier
80
. In addition, non-inverting (+) input terminal of the operational amplifier
80
is connected to the ground.
Reference numeral
9
denotes a reset circuit. The reset circuit
9
is comprised of a transistor of which collector-emitter terminals are connected between both terminals of the capacitor C
1
. An output signal
73
from the logic circuit
72
of the delay circuit
7
is inputted to the reset circuit
9
. Then, reference numeral
10
denotes a comparator. An integrated output value Vint as the output signal from the operational amplifier
80
of the integrating circuit
8
is inputted to the inverting (−) input terminal of the comparator
10
, and a reference voltage Vref is inputted to the non-inverting (+) input terminal of the comparator circuit
10
.
FIG. 12
shows input and output signal waveforms at main parts in FIG.
11
. Reference character A in
FIG. 12
indicates an electrical discharge voltage waveform at the machining clearance between the electrode
2
and the workpiece
3
. Reference character B in
FIG. 12
indicates an output signal waveform of the high-pass filter
4
. Reference character I in
FIG. 12
shows an output signal waveform in the logic circuit
72
. Reference character F in
FIG. 12
shows an integrated output signal waveform of the integrating circuit
8
.
The operation of this arrangement will be described referring to
FIGS. 11 and 12
.
In
FIGS. 11 and 12
, reference numeral
20
denotes an electrical discharge voltage waveform at the machining clearance between the electrode
2
and the workpiece
3
, wherein Ton denotes an electrical discharge pulse width and Toff denotes a rest time. When an electrical discharge is generated after applying a voltage to the machining clearance between the electrode
2
and the workpiece
3
, both the output signals from the electrical discharge voltage detecting circuit
60
and the electrical discharge current detecting circuit
61
become H (high) levels. These output signals are inputted to the logic circuit
62
. In the logic circuit
62
, when all these input signals become H levels, i.e., when an electrical discharge is generated at the machining clearance between the electrode
2
and the workpiece
3
, an L (low) level is outputted. Such a time is defined as an electrical discharge detecting time t
1
. t
2
denotes a time (t
2
=t
1
+tH) after the time constant tH of the high-pass filter
4
from the electrical discharge detecting time t
1
. Reference numeral
21
denotes a high-frequency component of the electrical discharge voltage. Reference numeral
22
denotes a disturbance waveform caused by a transient characteristic of the high-pass filter
4
.
In the time constant circuit
70
, the H level is outputted for the time period tH from the fall time of the output signal
63
of the logic circuit
62
. The output signal
63
of the logic circuit
62
and the output signal
71
of the time constant circuit
70
are inputted to the logic circuit
72
, and then the output signal
73
indicated at the code I in
FIG. 12
is outputted. The rise time of the output signal
73
is defined as t
2
at I in FIG.
12
. The reset circuit
9
resets the integrating circuit
8
for a period when the output signal
73
of the logic circuit
72
is the H level. That is, the output signal vrec from the rectifying circuit
5
is integrated at the integrating circuit
8
only for a period when the output signal
73
of the logic circuit
72
is the L level. In the comparator
10
, the reference voltage Vref and an integration output Vint indicated by F in
FIG. 12
are compared with each other. When the integration output Vint is higher than the reference voltage Vref at the end of the electrical discharge pulse width Ton, it judged to be a normal electrical discharge pulse. Otherwise, it is judged to be an abnormal electrical discharge pulse such as an arc electrical discharge pulse.
However, the aforesaid electrical discharge machining machine has some disadvantages as described below.
Referring to
FIGS. 13
a
and
13
b
, a first disadvantage will be described.
FIGS. 13
a
and
13
b
are timing charts respectively showing a relation between an electrical discharge voltage waveform
20
and an integration output value Vint in the case that the same machinin
Karlsen Ernest
Mitsubishi Denki & Kabushiki Kaisha
Sughrue & Mion, PLLC
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