Field of the invention

This invention relates to liquid heating appliances such as electric kettles.

Background of the invention

Electric kettles used to boil water typically have an on-button which automatically switches off once the water has boiled. Because of the dedicated application of an electric kettle, i.e. to bring water to boiling point, electric kettles generally have a limited user interface consisting of a single on-button. The input and output functionality of a typical kettle interface consists of the user being able to switch the kettle on and off. Generally, a kettle will provide only a minimal indication to a user as to the operational state of the kettle, for example the physical position of the on-button.

Electric kettles typically also have a straightforward design including, for example, a simple spout, a lid that can be lifted off manually or flipped open with a button, and a conventional handle connected towards the top and bottom of the side of the kettle with which to lift and tilt the kettle. There is an ongoing need for kitchen appliances such as electric kettles to have improved ergonomics and/or improved functionality, both while at the same time providing a product that is aesthetically pleasing.

The improved functionality as mentioned above could relate to the safety and efficiency of the kettle. One problem with kettles, for example, is that switching the kettle on while there is no water in it may cause damage to the kettle.

Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art. Summary of the invention

In one aspect the present invention provides a kettle including: a heating element for heating liquid held in a chamber of the kettle; a user interface including a touch control and a display, the touch control including a transparent touch control surface through which the display is viewable, the touch control surface, when touched, activating a touch control sensor; a controller adapted to control supply of power to the heating element to control heating of the liquid held in the chamber, the controller being connected to the user interface and being further adapted to control the kettle in response to activation of the touch control sensor and to provide feedback as to a current operational state of the kettle via the display.

The kettle may further include a temperature sensor for estimating the temperature of any contents of the kettle, the controller being adapted to control the kettle in response to both the temperature estimated by the temperature sensor and the activation of the touch control sensor.

The controller may be further adapted to display the estimated temperature sensed by the temperature sensor on the display.

The controller may be further adapted to display an estimated time until a user set temperature is reached.

The display may be an LCD display. Alternatively, the display may be an LED display.

The touch control sensor and display may be provided on a printed circuit board. The printed circuit board may be coloured black.

The user interface may further include one or more additional controls, the or each additional control operable by a user to select a mode of operation of the kettle.

The or each additional control may be an additional touch control. The current operational state of the kettle may be selected from a group including a standby state, a boil state, a boiled state, a heat state, a heated state, a keep warm state, and an error state.

The user interface may be mounted to the kettle. Alternatively, the user interface may be mounted to a base on which the kettle rests.

The kettle may further include a speaker, the controller adapted to provide audible feedback as to the current operation state of the kettle via the speaker.

The chamber may be defined by a transparent or translucent body. The body may be glass.

In a second aspect the present invention provides a method of operating a kettle to heat contents of the kettle to a user defined temperature, the kettle including a heating element, a temperature sensor for estimating the temperature of the contents of the kettle, and a user interface for inputting the user defined temperature, the method including: supplying power to the heating element until a pre-defined temperature is sensed by the temperature sensor, and cutting power to the heating element on sensing of the pre-defined temperature, wherein the pre-defined temperature is less than the user defined temperature.

The method may further include pulse operating the heating element once the predefined temperature is sensed, the pulse operation of the heating element continuing until the temperature sensor senses a temperature equal to or above the user defined temperature.

In a third aspect the present invention provides a method of operating a kettle including a heating element and a temperature sensor for estimating the temperature of any contents of the kettle, the method including: supplying power to the heating element for an energised delay period; cutting power to the heating element for a de-energised delay period, and determining a thermal response of the kettle resulting from the energised delay period, the thermal response determined with respect to one or more temperatures sensed by the temperature sensor, and at the end of the de-energised delay period selectively supplying power to the hearing element or keeping power to the heating element cut off depending on the thermal response.

If the determined thermal response exceeds a reference thermal response power to the heating element may remain cut off. If the determined thermal response does not exceed the reference thermal response power may be supplied to the heating element.

The thermal response of the kettle may be the temperature sensed by the temperature sensor during or at the end of the de-energised delay period.

Alternatively, the thermal response of the kettle may be the rate of change of the temperature sensed by the temperature sensor calculated across the energised and/or de-energised delay periods, or sub-periods therein.

The energised delay period may be or be between 1 and 10 seconds, or any discrete value or sub-range therebetween.

The de-energised delay period may be or be between 1 and 10 seconds, or any discrete value or sub-range therebetween.

Also described herein is a liquid heating appliance. The liquid heating appliance may be a kettle.

The liquid heating appliance may include a frusto-conical body defining a heating chamber and a heating assembly for heating contents of the heating chamber. The body may be translucent or transparent. The body may be made of glass.

The liquid heating appliance may include a lid arrangement. The lid arrangement may include an annular void defined between an external skirt and an internal cover, the internal cover including a pouring opening, wherein on pouring the contents of the liquid heating appliance pass through the pouring opening to the skirt, the skirt acting as a spout.

The kettle may also or alternatively include a handle. The handle may be carried on a ring sized to locate around a neck of the frusto-conical body to secure the handle in place. The ring may rest on a shoulder of the body. The handle may include a lower arm which is carried adjacent to the frusto-conical body and which is oriented substantially parallel to an external surface of the frusto-conical body to which the lower arm is adjacent. The handle may include an upper arm which is carried adjacent to a lid arrangement of the kettle and which is oriented substantially parallel to an external surface of the lid arrangement to which the upper arm is adjacent. The upper and/or lower arms may be connected to the ring by a connecting arm. The connecting arm may be disposed in a substantially horizontal orientation when the kettle is in an upright position.

Brief description of the drawings

Embodiments of the invention will now be described with reference to the drawings, in which:

Figure 1 is a perspective view of an electric kettle and base according to one embodiment of the invention;

Figure 2A is a plan view of the kettle of Figure 1 ;

Figure 2B is a sectional view of the kettle of Figure 1 along section A-A of Figure 2A; Figure 3A is a bottom perspective view of the kettle of Figure 1 ; Figure 3B is a top perspective view of the base shown in Figure 1 ;

Figure 4 is a partial bottom perspective view of a heating and control assembly for the kettle of Figure 1 ;

Figure 5 is a partial bottom perspective view of a heating and control assembly for the kettle of Figure 1 showing the heat source controller;

Figures 6A and 6B show flow diagrams of two modes of operation for a kettle according to an embodiment of the invention;

Figure 7A shows a plan view of a user interface arrangement according to a first embodiment of the invention;

Figure 7B shows a cross sectional side view of the user interface of Figure 7A along section B— B;

Figure 7C shows a plan view of a user interface arrangement according to a second embodiment of the invention;

Figures 8A-8C each show a plan view of a user interface arrangement according to alternative embodiments of the invention; and

Figure 9 provides a graph showing the effect of introducing a delay on the temperature in a dry-boil scenario.

Detailed description of the embodiments

Heating vessels (such as kettles and percolators) are in common use and are often used to bring liquid contents to the boil or some other desired temperature. The rate of heating depends on factors such as the initial temperature of the liquid contents and the volume of liquid present in the vessel relative to the power available to heat. While the embodiments of the present invention are described in relation to a kettle, it will be appreciated that the various features and components described, either alone or in combination, may be used in other heating vessels or liquid heating appliances.

1. Description of kettle

Referring to Figures 1 , 2A, and 2B, an electric kettle 100 in accordance with an embodiment of the invention will be described. Kettle 100 has a frusto-conical body 104 with a relatively large base tapering to a relatively narrow neck. The body 104 defines a heating chamber 102, which in use holds water to be heated and/or boiled. The body 104 can be made from glass or another suitable heat resistant material. In this embodiment the body 104 is made of SCHOTT ^R glass and is substantially transparent.

The glass body 104 is open at the bottom end to allow assembly with a contact plate 118. When assembled, the contact plate 118 forms the base of the heating chamber 102. To facilitate assembly, the bottom of the glass body 104 terminates in a lip 202 which locates in an outer peripheral channel 203 of the contact plate 118. The body 104 is then secured to the contact plate 118 in a water-tight fashion using, for example, a food grade silicone adhesive such as Dow Corning 734 flowable silicone.

When water is held in the heating chamber 102 it is in direct contact with an upper side of the contact plate 118. The contact plate 118 is formed from stainless steel and is an uninterrupted polished plate that is easy to clean. Other materials which are suitable for contacting water and are resistant to high temperatures and oxidation may be used.

Heating of the kettle 100 can be achieved using an electronically controlled heating and control assembly 120. The heating and control assembly 120 is housed between the contact plate 118 and the lower housing 136 of the kettle. The heating and control assembly 120 is described in more detail below with reference to Figures 4 and 5.

The glass body 104 is also open at the upper end to allow water to be poured into and out of the body 104 via the neck 112. The upper end of the glass body is secured to a lid arrangement 110. The lid arrangement 110 includes an external skirt 114 surrounding a cover 111. The cover 111 includes an opening 113 through which water may be poured and an indicator 1 15 indicating the location of the opening 1 13 in the cover 11 1. An annular void 1 17 is defined between the skirt 1 14 and the cover 1 1 1.

The kettle 100 may be filled or partially filled with water either through the opening 113 in the lid arrangement 1 10, or directly through the neck 112 of the kettle after removing the lid arrangement 1 10. Similarly, water may be poured out of the heating chamber 102 through the lid arrangement 110. Typically the kettle 100 will be tilted, allowing water to flow through the opening 1 13 and on to the skirt 1 14, the skirt 1 14 acting as a spout to direct the water to a cup or similar. The lid arrangement 1 10 can be formed from the same glass as the glass wall 104, or can be formed from a plastic moulding, attached to the glass body 104 using a food grade adhesive such as silicone.

The kettle also includes a handle 108 which has a short arm 130 and a long arm 128. In the illustrated embodiment the short arm 130 is disposed at the same angle as the lid arrangement 1 10 (essentially vertical), and the long arm 128 is disposed at a similar angle to the slope of the body 104. The short and long arms 130 and 128 are connected to (or integral with) a connecting arm 132 which is secured to a ring 142. The ring 142 is placed around the neck 112 of the kettle 100 where it rests on a shoulder 134 formed in the glass body 104. The ring 142 is glued in place using a food grade adhesive such as silicone. The handle 108 and/or ring 142 may be integrally formed, for example from plastic or aluminium, or may be separate parts secured together to form the handle 108.

The two arms of the handle 108 allow a user to assume different holding positions for the kettle 100. For example, depending on the weight of the kettle 100 due to its contents and/or the preference of the user, the kettle may be held using only the long arm 128, or may be held using both the short arm 130 and the long arm 128.

2. Description of heating and control assembly

The heating and control assembly 120 is generally located underneath the internal chamber 102, on the opposite side of the contact plate 1 18 (which forms part of the heating and control assembly 120) to the heating chamber 102. As can be seen, the heating and control assembly 120 does not make use of a steam tube extending into the heating chamber 102. Noting that the body 104 of the present embodiment is transparent, avoiding the need for a steam tube provides for an aesthetically pleasing kettle, uninterrupted by the presence of such a steam tube.

In the illustrated embodiment the kettle 100 is a so-called "cordless" kettle and does not itself carry a cord. Rather, the kettle 100 connects to and is provided with power from a base 106. The base 106 has a base housing 308 shaped, in this instance, like a tray with an upturned lip, and is provided with an electrical connector 306. The base 106 is arranged to be connected to a power source via an electrical cord (not shown), and when the kettle 100 is in place on the base 106 power is delivered to the kettle 100 via the connector 306.

The lower housing 136 of the heating and control assembly 120 of the kettle 100 includes a hub 302. The hub 302 is electrically connected to the heating and control assembly 120 and is designed to electrically and physically interconnect with the electrical connector 306 in the base 106.

The base housing 308 and the lower housing 136 of the kettle 100 are, in the present embodiment, both circular in cross-section and the connector 306 and hub 302 are also circular. The hub 302 defines a socket 304 to accommodate the connector 306 so that the base 106 and the kettle 100 can be electrically interconnected.

One embodiment of the heating and control assembly 120 is shown in greater detail in Figures 4 and 5 and is described below.

The heat used to boil the water is generated by a heating element 122, which terminates in tails 402 carrying electrical connectors by which the heating element 122 is connected to a power source (in this instance this is via the base 106). The heating element 122 shown is a sheathed resistance element, although other types of heating elements may be used such as thick film resistance elements or "flat elements" (as described, for example, in international application PCT/GB98/01439). The heating element 122 is bonded to a heat distribution plate 124. The heat distribution plate 124 can, for example, be an aluminium billet. The bonding achieves a good thermal coupling between the heating element 122 and the heat distribution plate 124 so that heat generated by the heating element 122 is rapidly and efficiently transferred to the heat distribution plate 124. Many known bonding techniques are suitable including induction welding, flame or oven welding, impact welding, and/or mechanical fasteners.

The heat distribution plate 124 is, in turn, bonded to the contact plate 118 so as to provide a good thermal coupling between the heat distribution plate 124 and the contact plate 118. A suitable bonding method is induction brazing, however alternative bonding techniques may be used (e.g. those mentioned above).

The heat distribution plate 124 of the present embodiment is formed from aluminium, which is a good thermal conductor, and is of sufficient thickness so that heat is evenly distributed over the contact plate 118. Alternative materials for the heat distribution plate 124 include other metals and metal alloys. The heat distribution plate 124 is generally thicker than the contact plate 118 and formed from a material which is a better thermal conductor than the contact plate 118.

As described in Figure 4, the heat distribution plate 124 defines a void 404 in the vicinity of the cold tails 402. The void 404 forms a thermally insulating zone, insulated from the heat distribution plate 123. Heat which is transmitted from the heating element 122 to the heat distribution plate 124 is not readily transmitted across the void 404. The region of the contact plate 118 located in the void 404 does not conduct significant amounts of heat when compared to the aluminium heat distribution plate because the contact plate 118 is formed from stainless steel, which is not as good a thermal conductor as aluminium.

Mounted in the void 404 is an electronic temperature sensor 406, which is thermally insulated from the heat of the heat distribution plate 123 by the void 404. Heat from the heat distribution plate 124 is not readily transmitted to the electronic temperature sensor 406. As a result, the electronic temperature sensor 406 is thermally insulated from the heating element 122 and heat distribution plate 124.

Preferably, though not essentially, the thermally insulating zone and the temperature sensor 406 are located between the cold tails 402 of the heating element 122. The cold tails do not generate significant amounts of heat, so the electronic temperature sensor 406 is further insulated from the heat generated by the heating element 122. The void 404 may be left empty (i.e. an air gap) or may be filled, either partially or wholly, with an insulating material, for example silicone or rubber. An example of this is shown in Figure 4 where a silicone plug 204 has been used to partially fill the void. The temperature sensor 406 is mounted in the silicone plug 204 which provides further thermal and electrical insulation to the temperature sensor 406. The silicone plug 204 is also resilient, which (when mounted) results in the plug 204 (and hence the temperature sensor 406) being pressed against the stainless steel contact plate 118 in the region of the void 404. The silicone plug 204 includes a flange (hidden from view by the mounting bracket 412) and two channels passing through the plug 204 to accommodate the temperature sensor 406.

The plug 204 and temperature sensor 406 are maintained in place by the mounting bracket 412 which is mechanically fastened to the heat distribution plate 124. The bracket 412 is preferably formed from a relatively rigid material, such as a plastic, metal or metal alloy. The bracket 412 is shaped to fit around the top of the plug 204 and rest on the flange of the plug 204. The bracket 412 locates the silicone plug 204 in the centre of the void 404 so the sensor 406 is insulated and may press the silicone plug 204 against the contact plate 118, providing a good thermal connection between the sensor 406 and the contact plate 118. The temperature sensor 406 may be mounted in a number of alternative ways which minimise the influence of heat from the heat distribution plate 124.

As described above, the temperature sensor 406 is mounted so as to touch the contact plate 118, This improves the thermal coupling between the electronic temperature sensor 406 and the contact plate 118. The thermal coupling may be further improved using known techniques, such as applying a heat transfer paste. In alternative embodiments, however, the sensor 406 may be mounted such that it is in close proximity to the contact plate 118 without actually touching the contact plate 118.

The temperature sensor 406 is in thermal communication with the contact plate 118 in a contact region. When water contained in the heating chamber 102 of the kettle 100 heats up, the contact plate 118 will heat to a similar temperature. Due to the void 404, the region of the contact plate 118 located within the void is insulated from the heat distribution plate 124 and will more accurately reflect the temperature of the water (rather than the temperature of the heat distribution plate which may, as will be appreciated, be different). This allows the water temperature to be sensed with greater accuracy and responsiveness.

In the present embodiment the temperature sensor 406 is a thermistor. NTC thermistors formed from metal oxides are suitable. A thermistor has a number of advantages over other types of temperature sensors. A thermistor senses the temperature of water in the kettle within a continuous range. This provides significantly more information on the temperature of the water than, for example, a bimetallic actuator. A bimetallic actuator is typically activated only when the water reaches a threshold temperature value and is deactivated when the water falls below a threshold temperature value. As a result, a bimetallic actuator only senses whether the water temperature is above or below a threshold value. The thermistor provides responsive and accurate readings because it is mounted in a thermally insulating zone in direct thermal communication with the contact plate 118.

While the heating and control assembly 120 shown in Figure 4 and described above has a single void 404 in which the temperature sensor 406 is located, it would be possible to have multiple voids around the temperature sensor with each void forming a thermally insulating region. By positioning a number of the thermally insulating regions around the sensor 406, a thermally insulating zone is formed.

In the illustrated embodiment, the contact plate 118 is free of indentations in order to improve the accuracy of the temperature sensor 406. Because the contact plate 118 is free of indentations, water contained in the heating chamber 102 of the kettle 100 is able to readily and rapidly mix. This means the temperature of water located immediately above the temperature sensor 406 is more likely to accurately reflect the average temperature of the water contained in the kettle 100. Other configurations of contact plate 118 may also be used. For example, the contact plate may be concave or convex, or may include a dome-shaped protrusion in the vicinity of the temperature sensor 406.

3. Heat source controller

Referring to Figure 5, the heating and control assembly 120 further includes a controller 502 mounted on a printed circuit board (PCB) 504. The controller is electronically connected to the temperature sensor 406, the heating element 122 and the user interface 116. The controller 502 controls the operation of the heating element 122 with reference to the temperature sensed by the temperature sensor 406 and user input (received via the user interface 116). Preferably, the controller 502 is made up of an electronic circuit or number of electronic circuits including a microprocessor. These circuits may be designed in a number of ways to provide the functionality described below.

In the present embodiment, the controller 502 provides for both a boil function and a keep warm function, both of which rely on feedback signals from the temperature sensor 406 for operation.

Using the user interface 116 (as described below) a user may decide on the particular mode of operation desired, e.g. to heat water to a particular temperature and/or to keep the water warm at or about a particular temperature. The user interface 116 is connected to the controller 502 and, when operated by a user, sends signals to the controller 502. While the user interface 116 is shown as being situated towards the base of the kettle 100 it could, of course, be situated in alternative locations such as on the handle 108 of the kettle 100 or on the base 106. When power is supplied to the kettle 100 (i.e. the kettle is plugged into a wall socket (via the base) which is turned on) the controller 502 maintains the kettle 100 (as a default) in a standby mode.

The user interface 116 includes at least a command button 704 which, when activated submits a user command to the controller 502. The precise command submitted on activation of the command button will, as described below, depend on the current mode of the kettle. For example, if in a standby mode the command button may cause the controller 502 to enter an active mode as set by the user (e.g. boil, heat, keep warm). Alternatively, if the kettle is currently in an active mode (such as boil) the command button may turn the kettle off/return the kettle to standby mode.

Figure 6A shows a flow diagram of the standby mode 600 of the kettle 100. In this mode no power is supplied to the heating element 122. During this mode, however, the temperature sensor 406 is monitored by the controller 502 (step 602) in case an over heating error occurs. If an overheating error is detected (in step 604) an error signal 604 is communicated. The error signal may, for example, be a flashing red light and/or a series of audible beeps. If a user command is received (at step 605) via the user interface 116 (such as boil, keep warm, or heat to a certain temperature) the controller 502 enters the relevant active mode (step 606).

By way of general overview, if the active mode started by the user is a boil or heat mode, the controller 502 causes power to be supplied to the heating element 122 in order to heat water in the kettle 100. As described below, when causing power to be supplied to the heating element 122 the controller may introduce a delay in order to reduce the likelihood of a boil-dry event occurring where there is little or no water in the kettle 100. As is also described further below, the controller 502 also displays on the user interface 116 an indication (for example a particular colour, graphic or similar) to indicate to the user that the kettle is being boiled or heated.

During operation, the temperature sensor 406 senses the temperature of the water (via the contact plate 118). If a predetermined upper heating limit is reached, the controller 502 ceases operation of the heating element 122. The predetermined upper limit will vary depending on the mode of operation selected by the user. For example, if the user has selected to boil the water in the kettle, the relevant pre-determined upper limit may be set at 97°C (the reason this is not set at 100°C is due to the time lapse between ceasing operation of the heating element 122 and the peak temperature of the water/contact plate 118 that will be reached in time, as described in further detail below). Alternatively, if a user uses the user interface 116 to select to heat water to a user-defined temperature, the predetermined upper limit will be set with reference to that user-defined temperature (e.g. at a few degrees below the user-defined temperature or at a percentage of the user-defined temperature).

Once the upper heating limit has been reached, the controller 502 enters a standby mode indicated by an audio-visual output from the user interface 116 as shown in Figure 6 and described below. In the standby mode, the controller 502 causes power to be cut from the heating element 122 and may change the display of the user interface 116 to indicate that the water has boiled (in the event of a boil operation) or that the water has reached the user-defined temperature (in the event of heating to a specific temperature).

More specifically, figure 6B provides a flow chart 610 illustrating the boil mode of operation of the kettle 100 - i.e. where a user has selected to boil the contents of the kettle. In the boiling mode 610 the controller 502 operates the heating element 122 (step 612).

If the user voluntarily elects to cancel the boil operation by activation of the command button (step 614) the controller 502 stops power to the element 122 (step 615) and communicates this to the user via the user interface 116 (step 616), e.g. by displaying a red light and providing an audible beep. Power is also cut if the user lifts the kettle from the base 106 (step 617). In the illustrated embodiment where the user interface 116 is mounted on the kettle, removal of the kettle from the base also cuts power to the user interface 116 which is disabled (step 618).

In the active mode the controller 502 monitors the temperature of the water in the kettle (via the temperature sensor 406) (step 619). If the temperature has reached the upper heat limit (which in this instance is 97°C) and the boil gradient has been detected (step 620, described below) the controller 502 cuts power to the heating element 122 (step 621), provides user feedback (step 622), and enters standby mode (step 623).

With regard to the boil gradient (as detected in step 620), the controller 502 continually measures the change in temperature sensed by the temperature sensor 406 over time (for example 10 times a second, every second). These measurements allow an estimation as to the volume of water in the kettle 100 to be made. For example, a slow change temperature may indicate a large amount of water, while a fast temperature change may indicate a small amount of (or no) water in the kettle.

To further increase the accuracy of this measurement, the initial/ambient temperature of any water in the kettle may be estimated by the temperature sensor 406 in a delay period (as discussed below).

The estimation of the amount of water in the kettle (and the initial/ambient temperature of that water) allows a boil gradient to be estimated - i.e. how long the water should take to reach the desired temperature (which may be 100°C in a boil operation, or may be less as defined by the user).

If the time to reach the desired temperature as estimated by the boil gradient is exceeded (i.e. the estimated time period has elapsed but the temperature sensor 406 has not sensed the relevant temperature) this may indicate a thermistor fault and may trigger an error condition.

During operation, the controller 502 also provides some error detection/fault prevention. For example:

• if the kettle has been operating for over a set period of time (in this instance 10 minutes) without reaching the pre-determined temperature, the controller 502 will communicate an alert (step 624) and cut power to the element 122 (step 625). • if the temperature has exceeded an upper temperature limit (in this case 120°C) (step 626) the controller 502 will communicate an alert (step 624) and cut power to the element 122 (step 625).

• if the temperature has exceeded the upper limit, a temperature sensor fault has been detected (discussed below) (step 627), and the kettle has been operated for a predetermined time period (in this instance 10 minutes) (step 628), the controller 502 will cut power to the element 122 (step 629), report an error condition (step 630) and enter the standby mode (step 621).

A temperature sensor fault may be detected where there is no change in signal from the sensor over time under certain conditions, such as:

• open circuit

• short circuit

• no response when to there is power to the element

As is described below, a user can select to operate the kettle to boil water, to keep water warm at or about a specific temperature, or to heat water to or near a specific temperature by using the user interface 116. To give effect to a user's selected operation mode, the controller 502 of the present embodiment can operate the heating element 122 in two modes: a full power on mode, and a full power off mode. In the full power on mode, the heating element provides 2400W of power. When a certain temperature is selected, for example 75°, the controller 502 switches the heating element 122 to the full power on mode providing 2400W until the upper heating limit is reached. If the upper heating limit is set to the actual temperature requested by the user (e.g. 75° in this instance) it is likely that overshoot will occur. This is due to the fact that the heating element 122 or the contact plate 118 retain heat after power to the element is shut off and continue to transfer that heat to the water in the kettle 100.

As such, the controller 502 only operates the heating element 122 until the upper heating limit is sensed. For example, if the desired temperature is 75°C, the upper heating limit may be 65°C. Once the temperature sensor 406 senses a temperature of 65°C the controller 502 will cease operation of the heating element 122, relying on the overshoot (i.e. the heat that continues to be transferred to the water after cutting power to the heating element 122) to raise the water temperature to the desired temperature.

In addition to the above (or alternatively), the controller 502 may also be configured to operate the heating element 122 in pulses in certain circumstances (this will be referred to as pulse operation). By pulsing the heating element 122 the likelihood of the desired temperature being overshot is reduced. In pulse operation, the controller 502 operates the heating element 122 until a predetermined temperature (lower than the desired temperature) is reached. This predetermined temperature may, for example, be set to 80% of the desired temperature. Once the predetermined temperature is reached, the heating element 122 is turned off, and is then "pulsed" (i.e. switched on for small periods of time) until the desired temperature is reached. This pulsing allows the water to "creep up" to the desired temperature, i.e. 75° in this example, which again reduces the likelihood of overshooting the desired temperature.

4. Additional functionality supported by the heating and control assembly and heat source controller

Heating assemblies suitable for use with the current invention are described in WO 2008/052276 and WO 2007/131271 , which are incorporated herein in their entirety by reference. Other functionality that can be provided by the heating and control assembly 120, as described in WO 2008/052276, includes a method for predicting the time required to boil the water in the kettle, and a pulsed mode of operation for the heating element 122 that would reheat the water in the kettle to a threshold temperature.

If the kettle 100 is operated with little or no water, a boil-dry event may occur. While the temperature sensor 406 will, eventually, detect that the temperature exceeds the limit and will shut off the heating element 122, this may be too late to prevent the heat distribution plate 124, electronic components in the controller 502, and user interface 116 from reaching excessively high temperatures. In order to reduce the likelihood of a boil dry event occurring, a delay process is implemented. The delay process is implemented in order to keep the components of the heating and control assembly 120 (including the controller 502 and the circuit board 504) and the user interface 116 within operational temperature tolerances. This increases the safety of the kettle 100 as well as the accuracy provided by the temperature sensor.

Figure 9 provides a graph 900 showing the temperatures reached when a kettle is operated without any water.

Line 902 shows the temperature reached in a normal dry-boil situation - i.e. relying solely on a bi-metallic mechanism to detect the dry boil and cut power to the kettle. In this instance the maximum temperature sensed is approximately 251 °C (at a time of approximately 55 seconds).

Line 904 shows the temperature reached when the power to the element is cut after 20 seconds. At 20 seconds the temperature sensed is approximately 122°C, yet at approximately 53 seconds the sensed temperature reaches approximately 91 °C.

Line 906 shows the temperature reached when the power to the element is cut after 15 seconds. At 15 seconds the temperature sensed is approximately 80°C, yet at approximately 50 seconds the sensed temperature reaches approximately 163°C.

Line 908 shows the temperature reached when the power to the element is cut after 10 seconds. At 10 seconds the temperature sensed is approximately 56°C, yet at approximately 47 seconds the sensed temperature reaches approximately 125°C.

Line 910 is a reference line showing the ambient temperature over time.

To limit any damage done to the PCB 504, the delay process includes the following steps when the kettle 100 is operated:

• Energising the kettle (i.e. providing the heating element 122 with power) for an energised delay period. This period may be selected as desired, however a period of between 2 to 7 seconds has been found appropriate; • De-energising kettle (cutting power to the heating element 122) after the energised delay period for a de-energised delay period (e.g. between 6 and 10 seconds). During this de-energised delay period, the temperature imparted to the heat distribution plate 124 by the heating element 122 will have had sufficient time to reach the temperature sensor 406 (primarily via the contact plate 118).

• After and/or during the de-energised delay period, the thermal response of the kettle as a result of the energised delay period is determined. This thermal response may, for example, be the rate of change of temperature as sensed by the temperature sensor 406. Alternatively, the thermal response may be the actual temperature sensed at the end (or partway through) the de-energised delay period.

If the determined thermal response exceeds (or equals) a reference thermal response (i.e. a reference rate of change or temperature), this may be taken as an indication that there is insufficient water in the kettle to absorb the heat being generated and to protect the kettle power should not be re-supplied to the element 122 (or, in the case that power has automatically been supplied, that the power should be cut).

Alternatively, if the determined thermal response does not exceed the reference thermal response, this may be taken as an indication that there is sufficient water in the kettle and power can be re-supplied to the element 122.

As will be appreciated, the reference thermal response against which the actual thermal response is measured will be set so as to reduce the likelihood of the kettle/kettle components reaching damaging temperatures. In one embodiment the reference thermal response is based on the temperature sensed and is the predetermined upper heating limit for the particular mode of operation of the kettle as described above. In this case if, after the de-energised delay period, the predetermined upper heating limit is sensed then power is not resupplied to the element. The above process can be performed during any of the operational states of the kettle. By introducing the delay the risk of overshooting the desired (and/or safe) temperature is reduced.

By way of example, and referring again to figure 9, line 908 may be considered as operation of a kettle (without water in this instance) with a 10 second energised delay period. At a time of 20 seconds (i.e. having operated the kettle for the energised delay period of 10 seconds and then delayed in figure 9, when kettle without water had been operated for 10 seconds (i.e. an energised delay period of 10 seconds) and then had power cut, the approximate temperature sensed at 20 seconds (i.e. at the end of a de- energised delay period of a further 10 seconds) was 110°C.

In contrast, were the kettle operated without the 10 second energised delay period (as shown by line 902), the temperature sensed at 20 seconds has reached approximately 135°C.

The delay process is, for example, useful as a safety feature to avoid or reduce the likelihood of overheating of the electronic components in the controller 502 and the user interface 116 during re-boiling. If the water in the kettle has already boiled, and re- boiling of the water is selected, most of the heat generated by the heating element 122 in addition to the approximately 100° will be dissipated somewhere other than in the water. This may result in the overheating of the electronic circuitry in the kettle. To counter this the controller 502 implements energised and de-energised delays as described above to give the temperature sensor 406 time to read the temperature of the water accurately. If the water temperature is very high and close to boiling temperature, for example 95°, then the time that the heating element 122 is switched to full power mode (and therefore the heat generated) will be limited.

5. User interface

As noted above, the kettle 100 has a user interface 116 which is connected to the controller 502. The user interface 116 allows a user to control the kettle and also communicates information to the user on the operation of the kettle. User interface 116 includes a display by which operational information is displayed to the user. The display may, for example, make use of light-emitting diodes (LEDs) or a liquid crystal display (LCD). Superimposed on the display is a touch control which can be implemented using either a capacitive sensor (such as a QMatrix™ touch sensor IC implemented, for example, using an AT42QT2160 integrated touch and slide control panel IC) or a resistive sensor. The touch control is transparent, allowing the LED or LCD display to be visible through the touch control surface.

In addition, or by way of alternative, the user interface can incorporate a speaker for emitting audible feedback sounds to provide the user with information regarding the operation of the kettle 100. This can, for example, be implemented using piezoelectric speakers in the user interface which are controlled by the controller 502 to emit a customised series of beeps, such as:

• a single beep indicating receipt of user input (e.g. when the touch control has been operated);

• 2 beeps indicating an operation such as boil has completed, or that a set temperature has been reached;

• 3 beeps indicating an error, such as dry boil, that the desired temperature has been exceeded, or that the sensor is at its operational limit.

Various embodiments of the user interface are shown in Figures 7 and 8.

Figure 7A shows a user interface 700 that includes an interface 702 to the controller 502 and a command button 704. As shown in Figure 7B, the command button 704 includes a touch control surface 706 and a display 708. The sensor used for the touch control surface 706 and the element used for the display 708 (LED or LCD) are provided on a black printed circuit board (PCB) 709. The touch control surface 706 is transparent, which provides the user interface with a black appearance (when no information is being displayed). Figure 7C shows a user interface 710 with the display 708 controlled by the controller 502 to display a temperature reading 712. As the kettle boils, the display 708 shows the currently sensed water temperature.

Figure 8A shows a user interface 800 with a temperature touch control 804 that is used to scroll through the available water temperatures. The currently active temperature is indicated by an LED display showing the available temperatures to be 75°C at 806, 85°C at 808 and 100°C at 810. The user interface 800 then includes a command button 802 which is pressed after the temperature has been selected, and which initiates the heating process up to the selected temperature. The interface 812 between the user interface 800 and the controller 502 is adapted to the size and configuration of the user interface 800.

Figure 8B shows a user interface 814 that includes a water temperature display 816 that shows the water temperature as sensed by the sensor 406. It also includes a display of the water temperature 824 that the user has selected would like the water to be heated to. The user interface 814 includes an up scroll button 818 and a down scroll button 820 that are used to scroll through the available temperatures of 75°, 85° and 100°. In Figure 8B the selected temperature is shown to be 50° at 824.

Once the desired temperature has been selected using the scroll buttons 818 and 820, the activate button 822 is pressed to initiate heating of the water to the selected temperature. During the heating process, the water temperature display 816 shows the actual water temperature as it increases.

Figure 8C shows a user interface 826 that includes a water temperature display 830 showing the actual water temperature. The user interface 826 includes a touch control slider 828 which a user can use to select a desired water temperature. The selected temperature can be indicated either by lighting up a proportion of the touch control slider 828, or by displaying the selected temperature similar to the display shown in figure 8B at 830. Once the desired temperature has been selected with the user of the touch control slider 828, pressing the command button 832 initiates a heating or cooling process:

• if the selected temperature is above the temperature displayed at 830 then the kettle starts to heat the water;

• if the selected temperature is below the temperature displayed at 830 the water will be allowed to cool naturally until it reaches the selected temperature, and the water is then held at that temperature.

For all user interfaces described above with reference to Figures 7 and 8 a quick boil button can also be included (not shown) to heat the contents of the kettle to the boiling point of water, or a quick boil operation can be implemented with the available buttons. In one embodiment of a quick boil operation the command button (802 or 822 in Figures 8A and 8B) is touched for longer than the touch time required to switch the kettle on or off, for example for 2 seconds. This overrides the selected temperature and quick boil is selected. This quick boil operation can be stopped by touching the command button again.

All configurations can be adapted to support keep warm functionality whereby the selected water temperature is maintained for a predetermined time. For example, once the kettle has reached the selected temperature, the kettle then enters a keep warm mode for 10 minutes. After 10 minutes of no use the keep warm function will switch off, and the display on the user interface will dim, for example to 50% brightness.

Any one of the user interfaces described can also include a display of the predicted time to boil and/or the current water temperature. The user interface may also include a sleep mode which is implemented by a low power setting for the user interface.

The brightness of the user interface displays may have a perceivable rise- and fall-time. The rise- and fall-time may, for example, be between 0.5 and 2 seconds, which will allow the user to see the display gradually dimming and lighting up. It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention.