Note: Descriptions are shown in the official language in which they were submitted.
-- 1 --
SPECIFIC.ATION
1
TITLE. Heating appliance
TECHNICAL FIEL~
This invention relates to an operational panel struc-
ture as the input unit of an electronic controller includ-
ing a microcompu-ter LSI chip or the like for controlling
the heat source of a heati.ng appliance such as an electric
oven or microwave oven.
BACKGROUND ART
The conventional heating appliance of the above de~
scribed type is in the constant danger that it could be
self-triggered due to incoming noise, a surge of lighten-
ing, noi.se static electricity, etc. and-become operative
against the user's will.
The most dangerous aspect of any heating appliance
of the above type is that it would start heating inadvert-
ently even in the absence of a heating start instructionto a controller. Under these circumstances, the tempera-
tures of the appliance body and the door rise drastically
and the user would burn himself on -those portions or the
appliance itself would catch a fire and ignite surround-
ing in~Lammables such as a curtain~
In addition, unloaded heati.ng in a microwave ovenresults in increasing the quantity of microwave radiations
9~
~==-=
~L~
-- 2 --
leaking ~rom the periphery of the door and shortelling -the
li~e of power unit components such as a magnetron.
Fig. 1 is a perspective view showing the appearance
o~ a heatin~ appliance according to an embodiment of the
presen-t invention; Fiy. 2 is a cross sectional sicle view
of the appliance; Fig. 3 is a cross sectional view o~
part of the appliance taken on the line Y~Y'; Fig. 4 is
a circuit diagram of a control circuit o~ the appliance;
Figs. 5 and 6 are cross sectional views of part of a
heating appliance according to another embodiment of the
present invention; and Fig. 7 is a cross sectional view of
part of an operational panel in a conventional heating
appliance.
With the recent remarkable advance in the electronic
controller technology using microcomputers, microcomputer-
aided appliances are in widespread use. However, the
microcomputers have the disadvantage that they are very
susceptible to static electricity and surge current. A
conventional heating appliance as shown in Fig. 7 includes
in an operational panel 2 at -the front of its main body
1 an ornamental plate 3, cook keys 4 and 5, cook ke~
switches 6 and 7 and a board A9 carrying insulating spac-
ers 8 and the cook key switches 6 and 7, and the ornamental
plate 3, the cook keys 4 and 5, the cook key switches 6
and 7, -the insulating spacers a and the board A9 together
constitute a keyboard 10. A metallic bac]c plate 11 is
disposed in contact with the board A9 and electrically
- 2a -
conneeted to a chassis 12. Another board B 15 is provicled
which earrles a microeomputer 13 responsive -to signals
from input keys sueh as the eook keys 4 ancl 5, elec-tronic
components 14 and the like. When the conventional heat-
ing applianc`e is manua~ly actuated, static charge on the
operator's body may be conveyed to the reinforcin(~ back
plate 11 so that the baek plate 11 serves as an an-tenna
to feed curren-t to the coolc switehes 6 and 7 and so forth
in the keyboard 10 and send an error signal -to the micro-
eompu-ter 13, the elee-tronie eomponen-ts 14 and the like on
the board B 15. Such error signal would lead to a danger-
ous situation such as destruc-tion of the microcomputer
13, electronic ~omponents lfi and so forth and an over-
heated condition in a variety of parts in the main body
1. While, of course, safety is usually taken into con-
sideration in the design of an e:Lectronic circuit includ-
ing the microcomputer 13 and a software con-tained in -the
microcomputer 13, the microcompu-ter 13 would perform
faulty operations or be destroyed and display tubes would
provide an erroneous display in the case of an appliance
having such display tubes. Furthermore, the appliance
would oscillate inadvertently. A more reliable fail-safe
device is an important development objective.
DISCLOSURE OF THE INVENTION
Accordingly, it is an ob~ect of the present invention
to provide a heating appliance wherein an electronic con~
troller including a microcomputer LSI chip and the li]ce
for controlling a heat source of the appliance is pre-
vented from conducting faulty operation due to static
electricity charged on the operator's body or surge cur
rent by providing an electrically conductive, metallic
thin sheet in tight contact with a component or components
constituting a keyboard mounted on a front operational
panel as an input device for the controller, the metal]ic
sheet being earthed via an appliance main body or chassis.
BEST MODE FOR CARRYING OUT THE INVENTION
Referring -to Figs. 1 to 4, there is illustrated a
heating appliance constructed according -to an embodiment
of the presen-t inventlon, wherei.n a metallic thin shee-t
17 is bonded between a~ insu:Lating sheet 16-and an
ornamental plate 3 which are componen-ts of a keyboard 10
and is provided wi-th a grounding conductor 18 ex-tending
from its one end and leading -to the ground via a chassis
12.
In Figs. 1 and 2, a door 19 is provided to freely
open across a frorlt opening in the main body 1~ A heat-
ing chamber 20 is defined within the main body 1. An
operational panel 2 is disposed at the front of the
main body 1 and on one side of the door, 19 which
.1!
'.~ ''
-- 5
panel is made of an insulating material such as plastic
and environed by~ an operational panel f:ramework 21. As
seen in Fig. 3, -the keyboard 10 is disposed at the back
of the ope.ra-tional panel 2 to extend o~er an aperture 22.
5 Within keyboard 10 there are provided a plurality of in
put keys comprised of conductive material typicall.y carbon
peast, that is, cook keys 4 and 5 and a cook start key
23. The above-mentioned keyboaxd 10 comprises said orna-
mental plate 3 which is exposed to the operator's fingers,
the electrically conductive me-tallic sheet 17 typically
made of aluminum foil or stainless steel foil, pre:Eerably
a material of high tensile strength, and adhesively se-
cured between the ornamental plate 3 and the insulating
sheet 16, the insulating sheet 16, the plurality of input
keys bonded to the insulating sheet 16, a plastic board
A9 carrying switches 6 and 7 disposed in juxtaposition
with said input keys~ for example, cook keys 4 and 5, and
an insulating spacer 8 for spacing the board A9 from the
insulating sheet 16. The grounding conductor 18 extend-
ing from the one end of the metallic thin sheet 17 as anintegral unit is bent around the board A9 and electrical-
ly connected to the board A9 and a stepped portion 24 of
a me-tallic back plate 11 disposed behind the board A9 and
leading to the chassis 12 in the main body 1.
The shape of said electrically conductive metallic
sheet 17 will be described in further detail. I-t is de-
sirable from safe points oE view tha-t the bonding area
~"'`'" ~ =~
-- 6
oE the sheet 17 be greater -than the area of -the aper-ture
~2 in the opera-~ional panel 21 as seen in Fig. 3. In
other words, the width of the sheet is larger than Ql in
Fig. 3 and the ver-tical leng-th thereof is larger -than Q2
in Fig. 1. It is necessary that the sheet 17 be positioned
closer to the operation surface than the cook keys 4 and
5. These area and position relationships obvia-te the
possibility oE faulty operation because the coo]c keys 4
and 5 are e]ectrically isolated from the exposed surface
of the sheet 17 even when part of the operator's body
comes into contact with the operational panel framework
21 or the ornamental plate 3 in actuating the keyboard
manually from the front.
In cases where the operational panel framework 21
is not used, safety can be guaranteed by bonding the
sheet 17 having an area greater than the area of the
board A5 in the above specified position.
Although in the embodiment of Fig. 3 the sheet is
sandwiched between the stepped portion 24 of the back
plate 11 and the board A9, it is obvious that it may be
interposed directly between the back plate 11 and the
board without using the stepped portion.
Further, provided that as in the above embodiment,
the ornamental plate 3 and the insulating sheet 16 are
substantially equal in size and the sheet 17 is equal
in size to these components as well, the sheet may be
bonded more easily and lends itself better to mass
~, S',~ ' i S
-- 7
production.
Unlike the~above illus-trated embodimen-t, the sheet
17 may be bonded betwen the insulating sheet 16 and the
cook keys 4 and 5.
The reference numeral 25 represents a pad on which
wires connected to the switches 6 and 7 associated with
the cook keys 4 and 5 are concentrated, and lead wires
26 leading from the pad 25 are connected to the electron-
ic control device including the microcomputer 13~ elec-
tronic components 14 and so forth mounted on a board s 15.
When a food is put in the heating chamber 20 in the
main body 1 of the above described and illustrated heat-
ing appliance and the door 19 is closed, the door switches
27 and 28 shown in Fig. 4 are closed. Then, as the cook
key 4 or 5 and the cook start key 23 in the keyboard 10
are actuated, the microcomputer 13 operates so that a
contact 30 of a relay 29 is closed and a high frequency
generator 31 oscillates to generate high frequency waves.
It is evident from the foregoing description con-
cerning the embodiment that, even if the keyboard 10 is
actuated with the finger of the operator carrying static
electri.city, any error signal is never conveyed to the
microcomputer 13, the electronic components 14 and so
forth mounted on the board B 15 by way of the operational
panel framewor:k 21 because the operational panel frame-
work 21 .is made of an electrically insulating material.
In addition, i:n the event that static electricity is
~ , F = ~ =~_~
~ 8 --
discharged frorn the opera-tor's body, an error siynal i.s
not fed to the ~icrocomputer 13, -the electronic components
14 and so forth on the board B 15 and the appliance is
free from any safety problern because the groundlng con-
ductor 18 ex-tending from the metallic shee-t 17 made of
the aluminum or stainless foil and constituting the key-
board 10 is in electric contact with the back plate 11
grounded via the chassis 12 in the main body 1.
It is further possible to reduce the overall thick-
ness of the keyboard 10 because the grounding conductor
18 extending from the sheet 17 and so forth is a metallic
sheet such as an aluminum foil or a stainless steel sheet
rather than a conductive rubber member or the like. The
respective sheets constituting the keyboard 10, for exam
ple, the sheet 17 and the insulating sheet 16~ are more
desirable for mass production than those made of rubber
because the former may be roll-shaped and can be easily
printed and bonded. This of course leads to low profile
and compactness of the operational panel region.
The operator may depress the input keys on the key-
board 10 almost as lightly as in the case where the key-
board is not provided with the sheet 17 and more lightly
than in the case o a rubber-made keyboard, as if the
keyboard were not provided with the sheet 17. Thus, the
ease of operati.on is not affected in the least.
It is generally known that static electricity which
may be charged on the human body is as high as of the
- 9
order of abou-t 10 to 15 KV, -thouyh it depends on weather
conditions~ the ~o-tential at the human body with respect
to the ground, kinds of clothes, etc. While an aluminum
deposited film does not perform its duty for this reason,
5 the thin metallic sheet made of aluminum foil or stainless
steel foi] as in the embodiment achieves its purpose suc~
cessfully even in the presence of such high voltage.
In the case where an electrically conductive metal
layer is vacuum~deposited on each of the insulating sheet
10 16 and the ornamental plate 3, the problem occurs that
the deposited conductive layer is strained OIl repeated
operation of the input keys in the keyboard 10 and is
eventually cracked or broken, thus failing to ensure satis-
factory conductivity. However, the sheet 17 of metal foil
15 has a high tensile strength and is thus excellent in du-
rability and shock resistance.
Moreover, in the event that the ornamental plate 3
is damaged for any reason, the provision of the sheet 17
prevents low voltage electric shocks in advance and as-
20 sures a greater degree of safety~
The above described advantages are also available in
an alternative embodiment as illustrated in Fig. 5, where-
in a grounding conductor 18 extending from one end of the
sheet 17 lies sandwiched between a rib 32 of the opera
25 tional panel 2 and a bent portion 33 of the back plate 11
and held in electric contact with the back plate 11 for
grounding purposes. This structure is easier to assemble
~ ~.R ~
~ A
-- 10 --
and more sui-table for mass production than the e~bodiment
shown in Fig. 3.~
As seen in Fig. 6, the grounding conductor 18 of the
sheet 17 may be forced against the back pla-te ll and held
in electric contact wi-th the back plate ll for grounding
purposes by means of a resilient leaf spring 34 spot-
welded to the back plate 11, in whlch case the above de-
scribed advantages may be similarly expec-ted. With -this
arrangement, the leaf spring 34 abso:rbs erros in assembl-
ing the keyboard so that the grounding conductor 18 issecured more tightly in electric contact with the back
plate ll.
INDUSTRIAI, APPLICABILITY
As described hereinbefore, the heating appliance
embodying the present invention is such that the elec-
trically conductive me-tallic thin sheet is dispoed at
the keyboard of the operational panel actuatable by the
human body or the like and is grounded via the chassis
or a portion of the main body. This arrangement pre-
vents a faulty operation of the electronic contro].ler
including the microcomputer due to the static electricity
accumulated on the human body or the like or a suxge cur-
rent and assures an increased degree of safety.
O ~ ~ r ~
