High frequency heating apparatus

Details High frequency heating apparatus High frequency heating apparatus

1999-08-13

2001-01-09

Leung, Philip H. (Department: 3742)

Electric heating

Microwave heating

With control system

C219S709000, C219S710000, C219S754000, C219S748000

Reexamination Certificate

active

06172348

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a high frequency heating apparatus for heating objects to be heated such as food or the like.
BACKGROUND ART
A microwave oven as a representative high frequency heating apparatus has conventionally been constructed as shown in FIGS.
1
-
7
.
A microwave oven of
FIG. 1
is of a general structure employing a turntable
1
. In this microwave oven, electromagnetic waves emitted from a magnetron
2
as an electromagnetic wave emission means are transmitted via a waveguide
3
to a heating chamber
4
, where the waves are distributed as standing waves that are determined by the shape of the heating chamber
4
and the position of an opening
5
through which the electromagnetic waves are radiated into the heating chamber
4
. A food
6
generates heat correspondingly to an electric field component of the standing waves and a dielectric loss of the food
6
. The electric power P [V/m
3
] absorbed per unit volume of the food
6
is expressed by the intensity of an applied electric field E [V/m], the frequency f [Hz], the dielectric constant &egr;r and the dielectric tangent tan&dgr; of the food
6
in an expression (1) below. The heating distribution of the food
6
is generally determined by the distribution of the standing waves of the electromagnetic waves and, hence, the heating distribution on concentric circles is uniform due to a rotating of the turntable
1
.
P=(
{fraction (5/9)})·&egr;
r·
tan&dgr;·
f·E
2
x
10
−10
[W/m
3]
  (1)
In
FIG. 1
, reference numeral
19
denotes a control means,
22
denotes a motor,
23
denotes a weight sensor, and
27
denotes a fan.
As other examples of the uniforming means, a stirrer system has been employed in which electromagnetic waves are stirred by a constant rotation of a metallic plate inside the heating chamber. Electromagnetic waves are also taken out from the waveguide
3
by a rotary waveguide (emission part)
8
having a coupling part
7
and are emitted through an emission port
9
, as shown in
FIG. 2
, in other words, the opening part itself has been rotated constantly. In this case, the rotary waveguide
8
has been built on a bottom face of the heating chamber
4
and rotated constantly at all times by a motor
10
, and the whole of a bottom part of the heating chamber
4
has been covered with a cover
11
of a material allowing the, electromagnetic waves to pass therethrough.
Actually, however, most of the apparatuses in the market are of the turntable type.
Some apparatuses are provided with a plurality of opening parts, wherein an exit for the electromagnetic waves is switched to provide a uniform a heating distribution.
FIG. 3
shows an apparatus of the kind having two openings
5
define. in a side wall of the heating chamber
4
(Japanese Patent Laid-Open Publication No. 4-319287).
A plurality of magnetrons and a plurality of waveguides are installer in some cases to constitute a plurality of opening parts (Japanese Patent Laid-Open Publication Nos. 61-181093 and 4-345788).
Alternatively, one waveguide is branched in many directions to form a plurality of waveguides while there is arranged a single magnetron, thereby constituting a plurality of opening parts (Japanese Patent Laid-Open Publication No. 61-240029 and Japanese Utility Model Laid-Open Publication No. 1-129793).
In a different constitution, end faces
14
of two sub waveguides
13
are moved at positions facing a plurality of openings
5
, as indicated in
FIG. 4
, so that the electromagnetic waves may be directed to one opening
5
which apparently is easy for the electromagnetic waves to pass through, to thereby uniform the heating distribution (Japanese Patent Laid-Open Publication No. 5-74566).
In a system of
FIG. 5
, a metallic part
12
is moved within the single waveguide
3
having a plurality of openings
5
, so that the opening
5
, which apparently is easy for the electromagnetic waves to pass through, is selected to thereby uniform the heating distribution (Japanese Patent Laid-Open Publication Nos. 3-11588 and 5-121160).
In
FIGS. 6 and 7
, a plurality of openings are formed at upper and lower parts of the heating chamber, and the openings
5
at the lower part are switched to thereby provide a uniform heating distribution (Japanese Utility Model Laid-Open Publication No. 1-129793).
A feedback control is also executed in some apparatuses by detecting the weight, shape, temperature or dielectric constant of the food
6
or the temperature, humidity or electric field in the heating chamber by sensors.
According to the above-described conventional arrangements. however, in the case where the waveguide and the heating chamber are connected to guide the electromagnetic waves into the heating chamber, all kinds of food could not be heated uniformly by a single opening part, because the position of the optimum opening part to obtain a uniform heating distribution was different for every material or shape of the food.
For example, when a flat food is heated by the conventional microwave oven, the h-eating proceeds from an edge portion of the food, resulting in a large heating irregularity with a central portion of the food left cold.
Considering the position of the opening part, if the opening part s formed near the center of the bottom face of the heating chamber and when a bottom face of the food is heated, the food is uniformly heated if it is a liquid one allowing convection, whereas only the bottom face of the food is raised in temperature if the food is a solid one allowing no convection. In this case, while the concentric heating distribution is made uniform with the use of a turntable, the heating distribution in a radial direction or a vertical direction as viewed from a rotational center of the turntable cannot be improved in spite of the rotation of the turntable.
When the stirrer or rotary waveguide is used to stir the electromagnetic waves, the electric field distribution is changed in such a manner as to switch the opening part in accordance with the rotation of the stirrer or rotary waveguide and, hence, the concentration of electromagnetic waves can be avoided to some extent in the case of defrosting or the like manner of heating requiring the avoidance of the concentration. However, due to the stirring caused by a constant rotation without regard to the kind of food, any kind of food is heated by repeating the same electric field distribution for each rotation of the stirrer or rotary waveguide, thus making it difficult to achieve a perfectly uniform heating distribution.
Even when a plurality of openings are formed, a certain fixed electric field is constituted if the openings are simply opened at the same time. Accordingly, it is hard to provide a uniform heating distribution for every kind of food. Therefore, there is actually no large difference of the heating distribution between the microwave oven of FIG.
1
and the microwave oven of
FIG. 3. A
satisfactory cooking result cannot be expected unless the optimum opening is switched or selected for each individual kind of food.
Meanwhile, in the apparatus provided with a plurality of magnetrons and a plurality of waveguides, the control of oscillation of each magnetron is followed by a switching of the waveguides and, hence, the opening through which the electromagnetic waves are to be emitted is switched. Although this arrangement is slightly effective to provide a uniform heating distribution, the increased number of magnetrons raises costs and makes the apparatus heavy and inconvenient to carry.
When a plurality of waveguides are branched in many directions from one waveguide, the opening easy for the electromagnetic waves to pass through cannot be switched perfectly, i.e., a certain amount of electromagnetic waves leak also from the openings not selected. Moreover, a large quantity of sheet metal is needed for the waveguides, causing the apparatus to be expensive and hard to manufacture.
As a solution to the above, end faces
14
of the sub waveguides
13
are moved

Affiliated with

Also associated with

Rating

High frequency heating apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with High frequency heating apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and High frequency heating apparatus will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2547115