Prime-mover dynamo plants – Electric control
Reexamination Certificate
2000-02-10
2001-10-30
Ponomarenko, Nicholas (Department: 2834)
Prime-mover dynamo plants
Electric control
C322S095000, C318S434000, C310S06800R
Reexamination Certificate
active
06310405
ABSTRACT:
This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application for NDFG SPARK PREVENTION APPARATUS FOR AN AC/DC MICROWAVE OVEN earlier filed in the Korean Industrial Property Office on Sep. 21, 1999 and there duly assigned Ser. No. 40529/1999.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a non-directional frequency generator, and more particularly to a non-directional spark prevention apparatus for preventing sparks generated from a non-directional frequency generator.
2. Description of the Related Art
Generally, electronic appliances such as microwave ovens, etc., are designed to be driven solely by an alternating current (hereinafter called AC) power source, and accordingly have a shortcoming in that the electronic appliances can not be used in the places such as the outdoors, in vehicles such as ships, airplanes, etc., where the AC power source is not available. In order to solve such a problem, a non-directional frequency generator (hereinafter called NDFG) has been used to convert direct current (hereinafter called DC) into AC in the places where the AC power source is not available.
The NDFG usually uses relays or semiconductor elements for its converting operation into AC. The conventional semiconductor type NDFG circuit, however, has some problems of increasing manufacturing cost due to the expensive semiconductor elements, output loss of the semiconductor elements due to the switching operation, and excessive heat generation due to the output loss, etc.
In order to solve the above problems, the same applicant disclosed a NDFG utilizing a rotational AC converter to convert DC into AC in the Korean Patent Application Nos. 98-18589 (filed May 22, 1998) and 98-21117 (filed Jun. 8, 1998), which have not been opened to the public yet.
Hereinafter, the above NDFG will be briefly described as a related art with reference to the accompanying drawings.
FIG. 1
is a schematic view for showing the NDFG of a microwave oven driven by the DC power source according to the related art of the present invention.
FIG. 2
is a view for showing the waveforms of the AC power source generated by the rotation of the NDFG, in which (a), (b), and (c) refer to the output waveforms of a first relay RY
1
, a second relay RY
2
, and a non-directional frequency generator.
Referring to
FIG. 1
, the NDFG
100
includes a motor
110
driven by the DC power source for generating rotational force, a commutator
130
rotated by the motor
110
, and a plurality of brushes such as first, second, third, and fourth brushes
121
-
124
as shown in
FIG. 1
, which are in contact with the outer circumference of the commutator
130
. The commutator
130
includes a conductive part which is divided into at least two parts
132
a
and
132
b
as shown in
FIG. 1
, but into an even number of parts. The commutator
130
includes an insulating part
133
of a predetermined width formed between the conductive parts
132
a
and
132
b
. The conductive parts
132
a
and
132
b
are in simultaneous contact with at least two neighboring brushes
121
-
124
. The DC is applied to input sides of the first to fourth brushes
121
-
124
, while the output sides of the first to fourth brushes
121
-
124
are connected with a high voltage transformer (hereinafter called HVT). The first and second relays RY
1
and RY
2
switch on/off the operation of the NDFG
100
.
The operation of the NDFG
100
is as follows: The first and second relays RY
1
and RY
2
are in the on-state, and the commutator
130
is rotated by the DC. Accordingly, the brushes
121
-
124
in contact with the commutator
130
come in contact with the conductive part
132
a
, the insulating part
133
, the conductive part
132
b
, and the insulating part
133
which are formed on the outer circumference of the commutator
130
, sequentially.
More specifically, as the first brush
121
on the upper side of the commutator
130
comes in contact with the conductive part
132
a
, the electric current from the positive (+) terminal of the DC power source is inputted into the first brush
121
, and flows through the conductive part
132
a
of the commutator
130
and the fourth brush
124
, and to the upper portion of the primary coil
202
of the HVT downwardly to the lower portion of the primary coil
202
of the HVT. Then, the electric current is inputted into the second brush
122
, and circulates through the conductive part
132
b
, the third brush
123
, and to the negative (−) terminal of the DC power source.
Next, as the commutator
130
is further rotated and as the first brush
121
accordingly comes in contact with the insulating part
133
, the electric current can not flow through the commutator
130
.
Then the commutator
130
is further rotated to 90°, the electric current from the positive (+) terminal of the DC power source is inputted into the first brush
121
, flows through the conductive part
132
b
of the commutator
130
and the second brush
122
, reverses its direction, and flows from the lower portion of the primary coil
202
of the HVT to the upper portion of the primary coil
202
of the HVT. Then, the electric current is inputted into the fourth brush
124
, flows through the conductive part
132
a
, and the third brush
123
, and then circulates to the negative (−) terminal of the DC power source.
By the constant rotation of the commutator
130
of the NDFG, AC is generated at the primary coil
202
of the HVT in a manner as described above, then the AC is transmitted to a secondary coil of the HVT through the primary coil
202
thereof. Then, the HVT converts the normal voltage into a high voltage, and the magnetron MGT is driven by the high voltage stepped-up by the HVT.
While the AC power is generated as above, there are two periods that alternate with each other, i.e., a brush-on period in which the conductive part
132
a
or
132
b
of the commutator
130
comes in contact with the brushes
121
-
124
so that the electric current flows through the commutator
130
, and a brush-off period in which the insulating part
133
of the commutator
130
comes in contact with any of the brushes
121
-
124
so that the electric current can not flow through the commutator
130
. Meanwhile, during the brush-off period, the energy stored in the secondary coil of the HVT and a capacitor during the brush-on period is induced to the primary coil of the HVT. Accordingly, the voltage is induced during the brush-off period, generating backward current. Referring to
FIGS. 2A through 2C
, voltage waveforms VW and current waveforms CW induced from the secondary coil to the primary coil of the HVT during the brush-off period are shown. In
FIGS. 2A and 2B
illustrate direct current waveforms inputted while the first and second relays of the NDFG
100
are switched on, while
FIG. 2C
illustrates alternating current waveforms detected at the output side of the NDFG
100
.
In addition to the voltage and current waveforms shown in
FIGS. 2A through 2C
, spark waveforms are also shown which are steeply falling at the beginning of the brush-off period. The spark waveforms suddenly fall when the brush-on period is changed over to the brush-off period during the operation of the circuit, which means the excessive spark is produced between the commutator
130
and the brushes
121
-
124
at the beginning of the brush-off period, i.e., when the brush-on period is changed over to the brush-off period.
Such a generation of sparks destabilizes the operation of the NDFG, and shortens the life time of the NDFG.
SUMMARY OF THE INVENTION
The present invention has been developed to overcome the above problems of the related art, and accordingly it is an object of the present invention to provide a non-directional frequency generator spark prevention apparatus for preventing a spark production at the beginnings of brush-on/off periods of the non-directional frequency generator which is for converting direct current into alternatin
Han Yong-Woon
Jang Seong-deog
Kang Kwang-Seok
Sung Han-Jun
Bushnell , Esq. Robert E.
Ponomarenko Nicholas
Samsung Electronics Co,. Ltd.
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