Electric heating – Inductive heating – With heat exchange
Reexamination Certificate
2002-09-18
2003-12-09
Leung, Philip H. (Department: 3742)
Electric heating
Inductive heating
With heat exchange
C219S624000, C219S627000, C219S663000, C219S667000, C219S506000, C099S325000
Reexamination Certificate
active
06660981
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an induction-heating cooking device incorporating an inverter for household or business use.
BACKGROUND ART
In a conventionally developed induction-heating cooking device, as a structure for indicating a portion of the cooking device which is to be heated by a heating coil, light emitting elements, such as LEDs, are installed in the vicinity of the outer perimeter of the heating coil. The LEDs are lighted according to need, such that the portion to be heated is indicated through an insulating plate having light transmissivity.
A conventional heating cooking device
1000
is described with reference to FIG.
10
. The heating cooking device
1000
includes: a heating coil table
101
; a heating coil
102
provided on the heating coil table
101
; a light-transmissive insulating plate
103
provided above the heating coil
102
; and output control means
104
which controls electrical conduction to the heating coil
102
. The heating cooking device
1000
further includes display means
106
provided at the outer perimeter of the heating coil
102
. The display means
106
includes light emitting elements
105
. The light emitting elements
105
indicates the position of the heating coil
102
through the insulating plate. As shown in
FIG. 10
, a plurality of LEDs, which are provided as the light emitting elements
105
, are connected by wirings
1001
so as to form an electric serial circuit. The wirings
1001
are provided along the outer perimeter of the heating coil
102
.
Heating cooking devices developed in recent years, which use an inverter and to which the principles of induction heating and dielectric heating are applied, have good heating responsivity and heating controllability. In such a cooking device, a temperature detecting element, a weight sensor, and the like, are provided in the vicinity of a position where a pan or food (load) is to be placed, for detecting the temperature of the pan or food and the weight of the food. Adjustment of the power of heat and adjustment of the cooking time are performed according to the detected temperatures and weight, whereby elaborate cooking can be achieved. Further, although fire is not used, a high thermal efficiency is still obtained, and additionally such a cooking device does not substantially pollute air in a room, but can be used safely and maintained to be clean. Such characteristics have received attention, and the demand for such cooking devices has been sharply increasing.
Furthermore, in such a heating cooking device using an inverter, electrical and thermal stresses imposed on a switching element are reduced, whereby the price of the cooking device is decreased, and the reliability of the cooking device is increased. Especially in a multiple-burner induction-heating cooking device, in order to avoid the generation of interference noise generated between pans placed on adjacent burners, the same, constant operation frequency is used for both these burners, and an inverter which operates based on a system, where a plurality of switching elements in one burner are alternately driven, is used.
Hereinafter, an operation of a heating cooking device is described with reference to the drawings.
FIG. 11
is a block diagram showing a structure of a conventional heating cooking device
1100
. Parts (a) through (f) of
FIG. 12
show waveforms in respective sections of this conventional example.
FIG. 13
is a load to heating power characteristic graph.
In
FIG. 11
, reference numeral
31
denotes a commercial power source, and reference numeral
32
denotes a rectifying circuit. Reference numeral
33
denotes an inverter circuit. The inverter circuit
33
includes first switching means
33
a
and second switching means
33
b
, a load coil
33
c
, and a resonant capacitor
33
d
. The inverter circuit
33
applies a high frequency current to the load coil
33
c
so as to inductively heat a load pan
34
which is magnetically coupled to the load coil
33
c
. A control circuit
35
includes: driving means
36
for driving the first switching means
33
a
and second switching means
33
b
; level setting means
37
for outputting a digital signal wherein an input current to the inverter circuit
33
becomes a predetermined value; D/A conversion means
38
for converting an output of the level setting means
37
to an analog value; reference oscillation means
39
for outputting a rectangular wave with a fixed High/Low ratio at a constant frequency; signal conversion means
41
for converting an output of the reference oscillation means
39
to a predetermined triangular wave; driving signal generation means
42
for receiving outputs of the D/A conversion means
38
and the signal conversion means
41
and outputting a signal which allows the driving means
36
to output driving signals to the first switching means
33
a
and second switching means
33
b
. Furthermore, in this conventional example, a microcomputer
40
includes the level setting means
37
and the reference oscillation means
39
. Reference numeral
43
denotes input current detection means. The input current detection means
43
detects an input current to the inverter circuit
33
and outputs the detected value to the microcomputer
40
. The microcomputer
40
changes an output value of the level setting means
37
based on this value, thereby controlling an input current to the inverter circuit
33
so as to be a desired value.
An operation of the above structure is described with reference to parts (a) through (f) of FIG.
12
and FIG.
13
. The parts (a) through (f) of
FIG. 12
show a timing chart illustrating: an output of the reference oscillation means
39
; an output of the D/A conversion means
38
; an output of the signal conversion means
41
; an output of first comparison means
42
a
; an output of second comparison means
42
b
; and outputs of first non-conduction time addition means
42
c
and second non-conduction time addition means
42
d
.
FIG. 13
shows a relationship between a driving time ratio T
31
/T
32
, which represents a ratio between a driving time T
31
of the first switching means
33
a
and a driving time T
32
of the second switching means
33
b
, and an input P to the load pan
34
.
An operation of the above structure is described. The inverter circuit
33
converts a direct current, which is obtained by rectifying a current from the commercial power source
31
by the rectifying circuit
32
, into a high frequency alternating current. The high frequency current is allowed to flow through a resonant loop formed by the load coil
33
c
and the resonant capacitor
33
d
, whereby an eddy current is generated in the load pan
34
which is magnetically coupled to the load coil
33
c
. Joule heat generated due to the eddy current inductively heats the load pan
34
.
The microcomputer
40
outputs to the signal conversion means
41
by the reference oscillation means
39
a rectangular wave with a constant High/Low ratio (“1” in this example) at a constant frequency at a constant frequency T
0
and having a constant amplitude as shown in part (a) of FIG.
12
. The signal conversion means
41
converts this rectangular wave to a triangular wave as shown in part (b) of FIG.
12
. On the other hand, the microcomputer
40
increases or decreases a digital value output of the level setting means
37
such that an output of the input current detection means
43
becomes a desired value, whereby an analog output level Vo of the D/A conversion means
38
can be set to any voltage between Vl and Vh as shown in part (b) of FIG.
12
.
In this conventional example, a case where the output voltage Vo of the D/A conversion means
38
is Vm shown in part (b) of
FIG. 12
, at which the driving time ratio T
31
/T
32
is X, is considered. The first comparison means
42
a
compares the output voltage Vo(=Vm) of the D/A conversion means
38
with an output of the signal conversion means
41
. The first comparison means
42
a
outputs High if the output of the signal conversion means
41
is greater t
Fujii Yuuji
Hattori Kenji
Ogata Taizo
Leung Philip H.
Matsushita Electric - Industrial Co., Ltd.
Snell & Wilmer LLP
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