Abstrict
An electric heater for arranging beneath a translucent cooking
plate includes at least one electrical heating means, such as a
ribbon, coil or filament lamp, in a housing comprising a base and
a peripheral wall. Light indicator means is supported peripherally
on the heater and visible, in operation, through the cooking plate.
The light indicator means comprises an elongate light-emitting device
at least partially surrounding the heater and arranged to emit light
towards the underside of the cooking plate. Mask means is provided
overlying the device and integral with the heater, the mask means
being of a material substantially opaque to light from the device.
The mask means has one or more apertures, different in configuration
to the configuration of the device, through which one or more apertures
light from the device is visible, viewed through the cooking plate.
Claims
I claim:
1. An electric heater for arranging beneath a translucent cooking
plate, the heater comprising: at least one electrical heating means
in a housing comprising a base and a peripheral wall; light indicator
means supported peripherally on the heater and visible, in operation,
through the cooking plate, the light indicator means comprising
an elongate light-emitting device at least partially surrounding
the heater and arranged to emit light towards the underside of the
cooking plate; and mask means overlying the device and integral
with the heater, the mask means being of a material substantially
opaque to light from the device and having one or more apertures
therein, different in configuration to the configuration of the
device, through which one or more apertures light from the device
is visible, viewed through the cooking plate.
2. An electric heater according to claim 1, wherein a plurality
of apertures are provided in the mask means, in spaced-apart relationship
along the length of the light-emitting device.
3. An electric heater according to claim 1, wherein the mask means
is formed of a material capable of withstanding the operating temperature
environment of the heater.
4. An electric heater according to claim 3, wherein the mask means
comprises a material selected from the group consisting of metals;
ceramics; ceramic fibre materials; glass cloth materials.
5. An electric heater according to claim 1, wherein the mask means
is formed from material selected from sheet form and strip form.
6. An electric heater according to claim 5, wherein the mask means
is of substantially L-shaped cross-section so as to provide a downwardly-directed
flange portion.
7. An electric heater according to claim 1, wherein the base and
peripheral wall of the heater comprise thermal and electrical insulation
material.
8. An electric heater according to claim 7, wherein the base and
peripheral wall are located in a supporting dish.
9. An electric heater according to claim 1, wherein the light-emitting
device is located in a recess or rebate provided in the upper surface
of the peripheral wall.
10. An electric heater according to claim 9, wherein the mask means
overlies the surface of the peripheral wall, at least in part.
11. An electric heater according to claim 9, wherein the mask means
is flush with the surface of the peripheral wall.
12. An electric heater according to claim 9, wherein the mask means
is lower than the surface of the peripheral wall.
13. An electric heater according to claim 1, wherein the mask means
serves to secure in location the light-emitting device.
14. An electric heater according to claim 1, wherein the light-emitting
device comprises an elongate light guide having a light exit region
facing the underside of the cooking plate and having at least one
light entry region arranged to receive light from a light source,
the light from the source being transmitted along the light guide.
15. An electric heater according to claim 14, wherein the light
exit region extends substantially along the length of the light
guide.
16. An electric heater according to claim 15, wherein the light
entry region is provided at one or both ends of the light guide.
17. An electric heater according to claim 16, wherein the light
source is located inside a housing which is provided with one or
more apertures therein to receive the one or both ends of the light
guide.
18. An electric heater according to claim 17, wherein the housing
has an interior surface which is light-reflective.
19. An electric heater according to claim 18, wherein the light-reflective
surface comprises a metallic, or other suitable, layer.
20. An electric heater according to claim 1, wherein the light
guide comprises a glass rod, the surface of which is adapted to
allow egress of light from a light exit region facing the underside
of the cooking plate.
21. An electric heater according to claim 1, wherein the light
indicator means comprising the elongate light-emitting device serves
as a hot warning indicator for providing a visual warning when the
translucent cooking plate is at a temperature at which it is unsafe
to be touched.
22. A cooking appliance provided with an electric heater according
to claim 1.
Description This invention relates to an electric heater, such as a radiant
electric heater, for arranging beneath a translucent cooking plate,
such as a glass-ceramic cooking plate. More particularly, the invention
relates to such a heater having at least one electrical heating
means, such as a coiled wire, elongate electrically conductive ribbon,
or tungsten-halogen lamp, in a housing comprising a base and a peripheral
wall.
BACKGROUND TO THE INVENTION
It is known to provide light indicator means supported peripherally
on a heater and visible in operation through the cooking plate,
the indicator comprising an elongate light-emitting device at least
partially surrounding the heater and arranged to emit light towards
the underside of the cooking plate. In the case of a circular heater,
the elongate light-emitting device is arranged to be correspondingly
circular, or part-circular.
Such light indicator means serves particularly as a hot warning
indicator for providing a visual warning when the translucent cooking
plate is at a temperature at which it is unsafe to be touched.
DESCRIPTION OF PRIOR ART
Electric heaters having light indicating means of this type are
described, for example, in EP-A-0 359 028, EP-A-0 438 656, and GB-A-2
271 840. The light indicating means may, for example, comprise an
elongate filament lamp or an elongate gas discharge lamp, such as
an elongate neon lamp. Of particular interest, however, is an indicating
means comprising an elongate light guide, such as an appropriately-shaped
glass rod, having a light exit region facing the underside of the
cooking plate, and preferably extending substantially along the
length of the light guide, and having at least one light entry region,
such as one or both ends of the glass rod, arranged to receive light
from a light source. The light from the source is transmitted along
the light guide and the source suitably comprises a filament lamp,
such as a tungsten-halogen lamp.
In operation, the light indicating means, viewed through the cooking
plate, is observed as a ring of light surrounding the heater. Such
a ring may be continuous or may take the form of a series of bright
spots, the latter being achieved by means such as providing a series
of spaced-apart notches in the surface of the light guide.
In practice, however, the observed ring of light, whether continuous
or in the form of bright spots, may not be sharply defined or of
uniform brightness and stray light may be visible through the cooking
plate. This is aesthetically undesirable.
Furthermore, there is a requirement to be able to provide sharply-defined
patterns of illumination which can readily be varied from one heater
to another, if required, to meet specific visual requirements in
different cooking appliances, without requiring modification to
a basic elongate light-emitting device. Such specific visual requirements
may also include patterns of illumination incorporating designs
or logos.
OBJECT OF THE INVENTION
It is an object of the present invention to fulfill these requirements
and overcome or minimise the disadvantages of the prior art.
SUMMARY OF THE INVENTION
The present invention provides an electric heater for arranging
beneath a translucent cooking plate, the heater comprising: at least
one electrical heating means in a housing comprising a base and
a peripheral wall; light indicator means supported peripherally
on the heater and visible, in operation, through the cooking plate,
the light indicator means comprising an elongate light-emitting
device at least partially surrounding the heater and arranged to
emit light towards the underside of the cooking plate, wherein mask
means is provided overlying the device and integral with the heater,
the mask means being of a material substantially opaque to light
from the device and having one or more apertures therein, different
in configuration to the configuration of the device, through which
one or more apertures light from the device is visible, viewed through
the cooking plate.
The apertures are selected with regard to number, size, shape and
position to provide any particular desired visual effect with good
uniformity of brightness.
In a particular embodiment, a plurality of apertures are provided
in the mask means, in spaced-apart relationship along the length
of the light-emitting device.
The mask means is formed of a material capable of withstanding
the operating temperature environment of the heater. It suitably
comprises an appropriately opaque material selected from the group
consisting of metals; ceramics; ceramic fibre materials; glass cloth
materials.
The mask means may suitably be formed from material in sheet or
strip form and may optionally be provided of substantially L-shaped
cross-section whereby a downwardly-directed flange portion, preferably
unapertured, provides screening of light radiating laterally from
the light-emitting device and/or provides a means for securing the
mask means to the heater.
The base and peripheral wall of the heater may comprise thermal
and electrical insulation material suitably located in a supporting
dish, such as of metal.
The light-emitting device may be located in a recess or rebate
provided in the upper surface of the peripheral wall. The mask means
may overlie the surface of the peripheral wall, at least in part,
or may be flush with, or lower than, the surface of the peripheral
wall.
Preferably the light-emitting device substantially surrounds the
heater.
The mask means may serve to secure in location the light-emitting
device.
The light-emitting device may be provided of various forms. It
may comprise an elongate filament lamp or an elongate gas-discharge
lamp such as a neon lamp. It may advantageously comprise an elongate
light guide having a light exit region facing the underside of the
cooking plate, and preferably extending substantially along the
length of the light guide, and having at least one light entry region
arranged to receive light from a light source, the light from the
source being transmitted along the light guide.
The light entry region(s) may comprise one or both ends of the
light guide.
The light source suitably comprises a filament lamp, such as a
tungsten-halogen lamp.
The filament lamp may be located inside a housing, suitably of
metal or ceramic material, which is provided with one or more apertures
therein to receive the one or both ends of the light guide. The
housing may have an interior surface which is light-reflective such
as by provision thereon of a metallic, or other suitable, layer.
The light guide suitably comprises a glass rod which may have a
substantially circular cross-section, although other cross-sections
such as rectangular, oval, or triangular, could be considered.
The surface of the glass rod is adapted to allow egress of light
from the light exit region facing the underside of the cooking plate.
In this regard, at least an elongate surface strip of the rod constituting,
and/or diametrically opposite, the light exit region may be frosted
or etched or micro-roughened. Such frosted or etched or micro-roughened
surface strip may be graded in degree such that the degree of frosting,
etching or micro-roughening increases with increasing distance along
the rod from the light entry region or regions, for example as described
in GB-A-2 271 840. By this means, facility of egress of light from
the light exit region increases with increasing distance along the
rod from the light entry region or regions and light emitted towards
the underside of the cooking plate is of substantially uniform intensity
along the rod.
As an alternative to a frosted or etched or micro-roughened elongate
surface strip, a corresponding elongate surface strip of the rod
opposite the light exit region may be coated with a light-reflective
paint, enamel or lacquer, preferably of a light colour such as white.
The coated strip may be tapered in width, such that the width increases
with increasing distance from the light entry region or regions,
whereby substantially uniform density of emitted light along the
rod is obtained.
In a particular embodiment, the electric heater is of substantially
circular shape and the elongate light-emitting device is of corresponding
circular, or particular, shape.
The light indicator means comprising the elongate light-emitting
device is particularly suitable for use as a hot warning indicator
for providing a visual warning when the translucent cooking plate,
which is usually of a glass-ceramic material, is at a temperature
at which it is unsafe to be touched.
The invention is now described by way of example, with reference
to the accompanying drawings in which:
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an exploded perspective view of one embodiment of an
electric heater according to the invention;
FIG. 2 is a cross-sectional view of the heater of FIG. 1 in unexploded
form, located beneath a translucent cooking plate;
FIG. 3 is a partial cross-sectional view of a second embodiment
of an electric heater according to the present invention; and
FIG. 4 is a partial cross-sectional view of a third embodiment
of an electric heater according to the present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
A radiant electric heater, for use in a cooking appliance having
a translucent glass-ceramic cook top, is constructed as follows.
A circular metal dish 1 contains a base layer 2 of thermal and electrical
insulation material, such as microporous thermal and electrical
insulation material, which is well known to the skilled person.
A heating element 4, in the form of a corrugated metal alloy strip
5, whose corrugations are not shown for simplicity, is secured to
the base layer 2 by embedding therein to part of its height. If
desired, the strip 5 of the element 4 may be profiled along that
edge thereof which is embedded, for example by providing downwardly-extending
integral spaced-apart tabs (not shown) which are embedded in the
insulation material of the base layer 2.
Instead of, or additional to, the strip-form heating element 4,
other well-known forms of heating element may be provided, for example
a coiled wire heating element and/or a bright radiating element
such as a quartz-halogen lamp or a molybdenum disilicide element.
A terminal connector 6 is provided for electrically connecting
the heating element 4 to an electrical supply for operation thereof.
Against the side of the dish 1 is located a peripheral wall 3 of
thermal insulation material whose top surface 8 is arranged in use
to contact directly, or indirectly, the underside of a translucent
glass-ceramic cooking plate 9 in a cooking appliance.
A well-known form of thermal cut-out device 7 is provided, extending
over the heating element 4. The cut-out device 7 has two sets of
switch contacts. One set of contacts is connected to, and arranged
to switch off, the heating element 4 to prevent over-heating when
the heater is installed and operating in a cooking appliance.
The other set of switch contacts in the cut-out device 7 is arranged
for connection to a light indicator means, described hereinafter,
which is visible in operation through the translucent glass-ceramic
cooking plate 9 and serves to provide a visual warning that the
surface of the cooking plate is too hot to touch and/or to provide
a visual delimitation of that area of the cooking plate beneath
which the heater is positioned. The light indicator means may be
arranged to be illuminated, for example, when the temperature of
the cooking plate reaches about 40.degree. C.
The light indicator means comprises an elongate light guide in
the form of a circular light-transmitting glass rod 10 which is
located in a rebate in the peripheral wall 3 of the heater and substantially
surrounds the heater. The light-transmitting rod 10 has ends 11,
12 which locate in apertures in a housing 13 which encloses a light
source in the form of a halogen lamp 14. The housing 13 is suitably
of ceramic or metal material and preferably has a light-reflective
inner surface to enhance illumination of the ends of the light transmitting
rod 10. the light-reflective inner surface may suitably comprise
a metallic layer on the housing. The lamp 14 is connected to a suitable
electrical supply through one of the sets of switch contacts in
the cut-out device 7 and becomes illuminated when the cooking plate
9 reaches a predetermined temperature, such as 40.degree. C.
Light from the lamp 14 is transmitted along the rod 10 and is arranged
to exit radially from the rod, towards the glass-ceramic cooking
plate 9. This is achieved by providing an etched, frosted or micro-roughened
surface strip 15 along the length of the rod on that region of the
rod either adjacent to, or diametrically opposite, the cooking plate
9, as described for example in GB-A-2 271 840. The etched, frosted
or micro-roughened surface strip 15 is preferably graded such that
there is an increasing degree of etching, frosting or micro-roughening
with increasing distance from the ends 11, 12 of the rod where the
lamp 14 is provided. By this means, substantially uniform brightness
of light exiting from the rod 10 towards the cook top 9 is achieved
along the length of the rod 10.
A mask means 16 is provided overlying the light transmitting rod
10 and integral with the heater. The mask means in its simplest
form comprises a ring-shaped thin strip 17 of substantially light-opaque
material provided with a pattern of apertures 18 therein different
in configuration to the configuration of the light transmitting
rod 10. The thin strip 17 suitably comprises a metal, although other
substantially light-opaque materials such as ceramics, ceramic fibre
materials or glass cloth materials could be considered. Preferably,
a downwardly-directed flange portion 19 is provided on the ring-shaped
strip 17 so that the resulting mask means is of substantially L-shaped
cross-section. As shown in FIG. 2, the mask means locates the light
transmitting rod 10 in position, the flange portion 19 being suitably
secured to the metal dish 1 of the heater by forming an interference
fit therewith or by means 20, such as threaded fasteners or spot
welds. The upper surface of the strip 17, which is provided with
the apertures 18 is arranged to be level with, or slightly below,
the top surface 8 of the peripheral wall 3 of the heater, but may
be arranged to overlie, at least in part, the top surface 8 of the
wall.
In operation, light exiting radially from the light transmitting
rod 10 passes through the apertures 18 in the mask means 16 and
is visible as a sharply defined substantially uniformly bright circular
pattern through the cooking plate 9. The mask means 16, particularly
with its flange portion 19, prevents stray light from the rod 10
escaping in undesirable directions, particularly laterally.
It may be advantageous for the interior of the mask facing the
light-transmitting rod 10 to be light-reflective, at least in part.
Any desired number, shape and pattern of apertures may be selected
to provide a particular required visual effect. One or more apertures
may be shaped in conformance with a logo identifying, for example,
the manufacturer or supplier of the heater or cooking appliance.
By a straightforward change of apertured mask, different visual
patterns may be provided from one cooking appliance to another.
Instead of the light transmitting rod 10 and lamp source 14, a
ring-shaped discharge lamp, such as a neon lamp, could be used,
or a ring-shaped filament lamp, the mask means 16 being equally
suitable for use with these alternative arrangements. In this respect,
FIG. 3 illustrates a ring-shaped filament lamp 10a in conjunction
with a mask that is substantially flush with the upper surface of
the peripheral wall 3 and FIG. 4 illustrates a ring-shaped discharge
lamp 10b in conjunction with a mask that is at a level lower than
the upper surface of the peripheral wall 3. |