WO2002060302A2

WO2002060302A2 - Smart toaster

Info

Publication number: WO2002060302A2
Application number: PCT/GB2002/000410
Authority: WO
Inventors: Richard Geoffrey Woodham; Michael Black; Timothy Sweyn Norris; Stephen W. Mahon; Michael C. Stevens
Original assignee: Sentec Limited
Priority date: 2001-01-30
Filing date: 2002-01-30
Publication date: 2002-08-08
Also published as: AU2002229893A1; WO2002060302A3

Abstract

There is described a smart toaster (10; 100) comprising: (a) a toasting chamber (30, 110, 230) for receiving one or more slices of bread (430); (b) heater arrays (210) for generating radiation for toasting the one or more slices (430) in the toasting chamber (30, 110; 230); (c) an optical interrogation apparatus (240) for monitoring the one or more slices of bread (430) during toasting and providing one or more corresponding reflectivity signals; (d) a microcontroller unit (250) processing for receiving the one or more reflectivity signals, and for de-energizing the heater arrays (210) when the one or more reflectivity signals indicate that the one or more slices (430) are toasted to a desired degree. The toaster (10, 100) is distinguished in that the interrogation apparatus (240) is arranged to emit strobed radiation to optically interrogate the one or more slices of bread (430), and to demodulate strobed radiation reflected from the one or more slices (430) with respect to the strobe to generate the one or more reflectivity signals. The toaster (10; 100) is of advantage in that the use of strobed radiation renders the toaster (10, 100) relative to ambient quasi-constant ambient illumination and enables exterior surfaces of the one or more slices of bread (430) to be optically monitored to provide precise and accurate toasting control.

Description

SMART TOASTER

Technical field of the invention

The present invention relates to smart toasters for intelligently toasting slices of bread. Moreover, the present invention also relates to a method of intelligently toasting slices of bread.

Background to the invention

Toasters for toasting slices of bread are known consumer products. Such products are often sold through electrical retailers and department stores.

Conventional toasters each include one or more arrays of heating elements, for example arrays of nichrome wire elements wound onto mica formers, and a mechanism for maintaining one or more slices of bread in spatial proximity to the one or more arrays. In operation, the one or more slices are maintained in proximity to the one or more arrays energized so that their elements glow to red/orange heat, for example in the order of 1000 °C. The one or more arrays are energized for a sufficient duration for superficially charring external surfaces of the one or more slices, namely toasting the one or more slices. A degree of bread slice browning is controlled by the duration of element array energization. In many conventional toasters, an externally-accessible knob is provided for adjusting the duration of array energization. Moreover, the mechanism is often provided with a spring arrangement for ejecting the one or more slices on completion of toasting.

In such conventional toasters, many factors can influence toasting characteristics of the one or more slices of bread, for example moisture content, bread flour colour and type, bread age, and slice thickness influencing slice spatial proximity to the one or more arrays.

Attempts have been made to improve the performance of conventional toasters. For example, in a published United States patent no. US 5, 672, 288, there is described a toaster which is constructed so that the duration of its toasting cycle can be varied. In the toaster, an RC network provides an oscillating signal to a counter. In operation, when the counter has counted a required number of oscillations from the network, the counter triggers a transistor switch which activates a main solenoid for terminating toasting action. The RC network of the system comprises a variable resistor which may be manually operated to adjust the degree of toasting. Moreover, the network additionally comprises a heat sensitive resistor for monitoring toasting temperature, and a light sensitive resistor to measure toaster heating element temperature. The RC network and the counter are of advantage in that they provide the toaster with more accurate and precise toasting time duration control based on heating element temperature.

In a published United States patent no. US5, 702, 957, there is described an improved toaster comprising a user control panel for receiving and displaying user selections corresponding to a desired toast darkness setting. In the improved toaster, a toaster shade display includes a linear array of light emitting diodes (LEDs) for indicating to a user a selected toast darkness setting. The LEDs are sequentially turned on and off to indicate to the user selected toast darkness setting. The improved toaster does not monitor the toasted state of bread slices within the toaster.

In a published United States patent no. US 5, 960, 702, there is described a toasting apparatus for bread products. The apparatus comprises a frame provided with an insertion slot communicating with a toasting chamber. The chamber is arranged to receive one or more slices of bread and is located between heating elements combined with heat reflectors for directing thermal energy generated by the heating elements towards the one or more slices of bread, the thermal energy being especially in the form of infrared radiation. The apparatus is equipped with an observation system for visually monitoring the degree of toasting of the one or more slices of bread in the toasting chamber. The observation system comprises an illumination device, for example an incandescent bulb, for illuminating the toasting chamber in such a way that an accurate indication of the reflectivity of the one or more slices of bread being prepared is provided.

In a published United States patent no. US 4, 245, 148, there is described an optically sensitive circuit for a food browning device, for example a toaster, which utilizes a radiant energy source to brown food. The circuit comprises a light sensitive variable resistor or photocell which is optically coupled to light reflected from the food being browned in the device. A voltage generated by a voltage divider including the light sensitive resistor therein is compared with a preselectable voltage generated by a second voltage divider to determine whether or not the heat source should be turned off. The circuit includes an appropriate solid state control to ensure that a start-up delay is provided at the beginning of each browning cycle and to reset the circuit for future operation when the desired browning of the food is achieved. In a published German patent application no. DE 2, 152, 927, there is described a toaster comprising optical components for optically interrogating a surface of a slice of bread being toasted within the toaster. The optical components comprise an incandescent bulb for providing optical radiation to illuminate the surface of the slice, first and second photosensitive resistors for monitoring reflected light from the surface and liglit directly emitted from the bulb respectively and a release solenoid for terminating toasting when activated. The photosensitive resistors are connected in a bridge configuration together with two additional resistors.

In a published United Kingdom patent application no. GB 2, 199, 733, there is described an electrical toaster comprising a light detector arranged to receive light reflected from slices of bread being toasted and to develop a signal representative of the amount of light reflected, and means responsive to the detected signal indicating that the amount of reflected light has dropped to a predetermined proportion of an initial value thereof to produce an output signal indicative as such.

The inventors have appreciated that the known toasters and toasting apparatus described in the foregoing exhibit one or more problems in operation, for example:

(a) the toasters are not capable of automatically, namely intelligently, distinguishing between bread types, for example between white bread and brown bread; (b) the toasters are not capable of adequately coping with partially toasted bread being reinserted into the toasters;

(c) the toasters are adversely affected by long term deposits on optical surfaces which disturbs calibration and accurate operation of the toasters;

(d) the toasters are potentially susceptible to optical interference from ambient light sources, for example domestic fluorescent light sources.

The inventors have therefore devised a smart toaster capable of addressing one or more of the problems described in (a) to (d) above.

Summary of the invention

According to a first aspect of the present invention, there is provided a smart toaster comprising: (a) a toasting zone for receiving one or more slices of bread; (b) toasting means for generating radiation for toasting the one or more slices in the toasting zone;

(c) optical interrogating means for monitoring the one or more slices of bread during toasting and providing one or more corresponding reflectivity signals; (d) processing means for receiving the one or more reflectivity signals, and for de-energizing the toasting means when the one or more re lectivity signals indicate that the one or more slices are toasted to a desired degree, characterised in that the interrogating means is arranged to emit strobed radiation to optically interrogate the one or more slices of bread, and to demodulate strobed radiation reflected from the one or more slices with respect to the strobe to generate the one or more reflectivity signals.

The invention is of advantage in that the use of the strobed radiation is capable of rendering the toaster less sensitive to quasi-constant ambient illumination and/or enables the toaster to monitor more precisely and accurately exterior surfaces of the one or more slices during toasting.

It is to be appreciated that the term strobed radiation encompasses both strobed radiation visible to the naked eye, and strobed infrared radiation.

Preferably, the processing means is arranged to de-energize the toasting means when the one or more reflectivity signals are less than one or more threshold values. Use of the reflectivity signals to control toasting end-point is capable of improving toasting repeatability from slice to slice.

Preferably, the toaster includes user-adjustable controls coupled to the processing means for adjusting the one or more threshold values. Such controls enable the user to select a desired degree of toasting.

Preferably, the controls and the processing means are arranged to set the one or more threshold values ratiometrically based on an initial strobed radiation reflectivity of the one or more slices and a ratio set by the user on the user-adjustable controls. Ratiometric control is capable of providing more accurate toasting repeatability and is capable of rendering the toaster less susceptible to degradation in performance due to long-term contamination and deposits on its optical surfaces.

- A - Preferably, the processing means comprises first analysing means for determining whether the one or more slices are brown bread or white bread, and for adjusting the threshold values according to whether the one or more slices are white bread or brown bread. The first analyzing means is of advantage in that the ratiometric control provides best results when account is taken of bread type. The first analyzing means is conveniently at least partially software-based.

Preferably, the processing means comprises second analysing means for determining rate of slice toasting when the toasting means is initially energized, and thereby determining whether the one or more slices are initially un-toasted or at least partially toasted. The second analyzing means is of benefit in that it enables the toaster to select between ratiometric control and threshold level control as appropriate depending upon the condition of the one or more slices. More preferably, the processing means is arranged to select non-ratiometric control when the one or more slices are initially at least partially toasted.

Preferably, the toasting zone comprises a plurality of toasting slots. More preferably, the interrogating means is arranged to interrogate the slots using strobed radiation of mutually different strobe frequencies for reducing optical cross-talk from slot to slot. Reduction of crosstalk between slots is of advantage to ensure superlatively accurate toasting control.

Preferably, the slots are disposed in an "in-line" configuration or in a "transverse" configuration with respect to end regions of the toaster.

In some situations, where the toaster comprises a plurality of slots, the user will insert slices of different types of bread into the slots. Therefore, in order to ensure that all the different slices are toasted to a repeatable degree, the toaster is preferably provided with mutually independent toasting monitoring control for each of the slots.

Alternatively, to render the toaster cheaper and simpler to manufacture, the toaster is preferably provided with a single average toasting monitoring control for the plurality of slots.

Preferably, the interrogating means is arranged to generate the strobed radiation at a strobe frequency in a range of 500 Hz to 500 kHz. Such a range renders the interrogating means and the processing means readily implementable using standard electronic devices whilst substantially avoiding interference from quasi-static ambient illumination sources, for example fluorescent strip lighting often found in kitchen environments. More preferably, the strobe frequency is substantially 1 kHz.

Preferably, the interrogating means is optically coupled through optical interfacing means to the toasting zone, the interfacing means adapted to withstand elevated toasting temperatures induced by the toasting means in the toasting zone. In order to toast the one or more slices of bread, the toasting means has to be heated to a temperature in the order of 1000 °C which heats toaster component parts neighbouring thereto to temperatures of several hundred degrees Centigrade.

Preferably, the interfacing means comprises a thermal break for shielding the interrogating means from elevated temperatures generated by the toasting means in the toasting zone.

In order to further reduce temperature increase of sensitive components within the toaster, the toasting zone preferably comprises reflecting means for reflecting radiation generated by the toasting means towards the toasting zone and away from the interrogating means.

In order to simplify toaster mechanical construction, the interrogating means is preferably disposed adjacent to the toasting zone with the interfacing means interposed between the toasting zone and the interrogating means.

More preferably, the interrogating means comprises one or more sensor printed circuit boards bearing optical components to generate the strobed radiation and to receive the reflected strobed radiation to generate the reflectivity signals, and the toasting zone preferably comprises a plurality of slots for receiving the one or more slices of bread, the one or more circuit boards disposed substantially parallel to their respective slots. Such substantially parallel implementation is of advantage in that it is capable of rendering the toaster spatially compact and substantially of similar size to conventional toasters.

Conveniently, the processing means is disposed on one or more processor printed circuit boards at one or more end regions of the toaster, the one or more sensor circuit boards being coupled directly to the one or more processor circuit boards by way of circuit-board connectors.

Preferably, the processing means is disposed on one or more processor printed circuit boards at one or more end regions of the toaster, the one or more sensor circuit boards being coupled to the one or more processor circuit boards by way of one or more flexible interconnect circuit boards. Use of flexible circuit boards renders the toaster less sensitive to manufacturing tolerances in its various components.

More preferably, the one or more flexible interconnect circuit boards comprise Kapton-based circuit boards. Kapton is of advantage on account of its desirable high- temperature characteristics in comparison to other plastics materials.

Preferably, the interfacing means comprises one or more optically transmissive inserts for coupling the strobed radiation to and from the one or more slices. More preferably, the inserts are fabricated from a heat tolerant glass. Yet more preferably, the inserts are fabricated from a soft Pyrex-type glass; such glass is relatively inexpensive and susceptible to mass-production glass molding processes..

Preferably, at least one of said one or more inserts comprises obliquely angled optical surfaces directed towards the slots for directing and receiving strobed radiation at a non-normal angle to the one or more slices of bread within the slots. The oblique surfaces assists to direct strobed radiation to the one or more slices so that the strobed radiation is effectively reflected.

Preferably, the one or more inserts are elongate defining an elongate axis and their optical surfaces are angled in a range of 15° to 60° relative to a perpendicular to said elongate axis. Such a range of angle ensures best strobed radiation reflection from the one or more slices.

More preferably, the obliquely angled surfaces are cleaved, molded and/or ground.

Conveniently, the obliquely angled surfaces are provided with a scattering finish to improve strobed radiation scatter within the toasting zone.

Preferably, the interrogating means is disposed remotely from the toasting zone with the interfacing means optically coupling the strobed radiation between the remote interrogating means and the toasting zone. Such remote location assists to isolate the interrogating means from relatively elevated temperatures experienced around and in the toasting zone. Preferably, the interfacing means comprises one or more light guides for coupling the strobed radiation between the remote interrogating means and the toasting zone. More preferably, to improve manufacturability and reduce cost, the one or more light guides are fabricated from a substantially optically transparent plastics material.

Alternatively, the interrogating means is preferably disposed adjacent to the toasting zone, and the interfacing means is arranged to couple strobed radiation between the interrogating means and the toasting zones by way of reflection in the interfacing means. Such reflection is capable of thermally shielding the interrogating means from the toasting zone, and also enables effectively larger optical surfaces to presented towards the toasting zone, the larger optical surface susceptible to user cleaning to remove long-term contamination and deposits thereon.

More preferably, the interfacing means is additionally arranged to reflect radiation generated by the toasting means towards the toasting zone for toasting thereat the one or more slices of bread. Such reflection of toasting means radiation is of advantage in maintaining the interrogating means at a moderate temperature.

Preferably, the interfacing means comprises a plurality of curved mirror-like surfaces for reflecting the strobed radiation and radiation emitted by the toasting means.

With regard to the interrogating means, the toasting zone preferably comprises a plurality of slots for receiving the one or more slices of bread, and the interrogating means is preferably grouped into a plurality of sensor units, each unit capable of generating the strobed radiation and receiving reflected strobed radiation form the one or more slices of bread, the sensor units disposed so as to interrogate sites within each slot, the sites disposed in a spatially linear manner.

Alternatively, the toasting zone preferably comprises a plurality of slots for receiving the one or more slices of bread, and the interrogating means is preferably grouped into a plurality sensor units, each unit capable of generating the strobed radiation and receiving reflected strobed radiation form the one or more slices of bread, the sensor units disposed so as to interrogate sites within each slot, the sites spatially disposed along diagonal axes and/or orthogonal axes.

More preferably, the interrogating means comprises one or more light emitting diodes (LEDs) for generating the strobed radiation, and one or more photodetectors for detecting reflected strobed radiation from the toasting zone. LEDs are capable of providing strobed radiation merely by providing them with strobed excitation current; moreover, they also are capable of exhibiting long operating life-times in the order of 100000 hours.

Preferably, the one or more photodetectors comprises one or more photodiodes and/or one or more phototransistors. More preferably, such photodiodes and phototransistors are silicon-based devices.

Preferably, in order to further improve toaster toasting performance, the interrogating means is arranged to interrogate the one or more slices of bread using strobed radiation whose wavelength is temporally switched between a plurality of colours for enabling the processing means to determine colour of the one or more slices in addition to their optical reflectivity, the processing means arranged to use slice colour information for enhancing toasting accuracy.

According to a second aspect of the present invention, there is provided a method of monitoring toasting within a smart toaster, the toaster comprising:

(a) a toasting zone for receiving one or more slices of bread;

(b) toasting means for generating radiation for toasting the one or more slices in the toasting zone; (c) optical interrogating means for monitoring the one or more slices of bread during toasting and providing one or more corresponding reflectivity signals;

(d) processing means for receiving the one or more reflectivity signals, and for de-energizing the toasting means when the one or more reflectivity signals indicate that the one or more slices are toasted to a desired degree, the method characterized in that it comprises the steps of:

(e) arranging for the interrogating means to emit strobed radiation to optically interrogate the one or more slices of bread; and

(f) demodulating strobed radiation reflected from the one or more slices with respect to the strobe to generate the one or more reflectivity signals.

Preferably, the method further comprises the step of arranging for the processing means to de- energize the toasting means when the one or more reflectivity signals are less than one or more threshold values. Preferably, the toaster includes user-adjustable controls coupled to the processing means for adjusting the one or more threshold values.

Preferably, the method further comprises the step of arranging for the controls and the processing means to set the one, or more threshold values ratiometrically based on an initial strobed radiation reflectivity of the one or more slices and a ratio set by the user on the user-adjustable controls.

Preferably, the method further comprises the steps of:

(a) arranging for the processing means to comprises first analysing means for determining whether the one or more slices are brown bread or white bread; and

(b) for adjusting the threshold values according to whether the one or more slices are white bread or brown bread. .

Preferably, the processing means comprises second analysing means for determining rate of slice toasting when the toasting means is initially energized, and thereby determining whether the one or more slices are initially un-toasted or at least partially toasted.

Preferably, the method further comprises the step of arranging for the processing means to select non-ratiometric control when the one or more slices are initially at least partially toasted.

According to a third aspect of the present invention, there is provided a smart toaster comprising:

(a) a toasting zone for receiving one or more slices of bread;

(b) toasting means for generating radiation for toasting the one or more slices in the toasting zone; (c) optical interrogating means for monitoring the one or more slices of bread during toasting and providing one or more corresponding reflectivity signals; (d) processing means for receiving the one or more reflectivity signals, and for de-energizing the toasting means when the one or more reflectivity signals indicate that the one or more slices are toasted to a desired degree, characterised in that the processing means is arranged to operate in a ratiometric mode wherein the desired degree is determined from an initial reflectivity of the one or slices of bread and a ratiometric setting specified by a user of the toaster on controlling means coupled to the processing means. It will be appreciated that features of the invention described in the foregoing can be combined in any combination without departing from the scope of the invention.

Description of the diagrams

Embodiments of the invention will now be described, by way of example only, with reference to the following diagrams in which:

Figure 1 is an external view of two smart toasters according to the invention;

Figure 2 is a schematic diagram of principal functional parts of the smart toasters of Figure 1;

Figure 3 is a schematic diagram of toasting characteristics of white and brown bread;

Figure 4 is an illustration of a first optical configuration for use in the toasters of Figure 1;

Figure 5 is a schematic diagram of an interrogation apparatus of the toaster of Figure 4;

Figure 6 is an illustration of a heater wire and its associated mica material former of the toaster of Figure 4;

Figure 7 is an illustration of sensor unit spatial configurations for the toaster of Figure 4;

Figure 8 is an illustration of a second optical configuration for use in the toasters of Figure 1;

Figure 9 is an illustration of a part of the second optical configuration of Figure 8;

Figure 10 is an illustration of a third optical configuration for use in the toasters of Figure 1;

Figure 11 is an illustration of the third optical configuration of Figure 10 in greater detail;

Figure 12 is a front view of a reflector assembly of the optical configuration of Figure 11 ; Figure 13 is a schematic diagram of an optical circuit employed in interrogation apparatus of the toasters of Figure 1;

Figures 14a, 14b, 14c are a depiction of an algorithm suitable for controlling operation of the toasters in Figure 1 ; and

Figure 15 is a schematic diagram of the spatial disposition of component parts to implement a four-slot transverse toaster of a type illustrated in Figure 1.

Description of embodiments of the invention

Referring to Figure 1, two smart toasters according to the invention are shown; the toasters are indicated generally by 10, 100.

The smart toaster 10 comprises a molded plastics-material body 20, two slots 30a, 30b for receiving slices of bread to be toasted, first and second internal printed circuit boards (PCBs) 40a, 40b, and user adjustable controls 50, for example for selecting a degree of browning required and for selecting manual/automatic bread type selection. The body 20 is generally elongate with the PCBs 40a, 40b included at end regions of the body 20 as illustrated; in operation, the end regions are generally coolest parts of the toaster 10 and therefore most appropriate for accommodating electronic devices. The slots 30a, 30b are substantially parallel to an elongate axis X-X' of the toaster 10 as shown, namely the toaster 10 is referred to as being in an "in-line" configuration. If required, one of the PCBs 40a, 40b can be omitted to simplify toaster construction and manufacturing cost.

The smart toaster 100 is similar to the toaster 10 except that it comprises a plastics-material body 105 which is less elongate than the body 20. Moreover, the toaster 100 comprises four slots 110a, 110b, 110c, llOd disposed transversely to an elongate axis Y-Y'of the toaster 100 as illustrated, namely the toaster 100 is referred to as being in a "transverse" configuration.

In the following, optical components, and control methods and algorithms described are equally applicable to both of the toasters 10, 100. Referring to Figure 2, there is shown a network of principal functional parts in each of the toasters 10, 100; the network is indicated generally by 200. The network 200 includes a mains electricity supply (for example a cable and plug for connecting into a mains electricity wall socket), one or more heater arrays 210 for toasting slices of bread, a release mechanism 220 for ejecting slices of bread from the toasters 10, 100 when toasted, a toasting chamber 230, an optical interrogation apparatus 240, a microcontroller unit 250, and finally a low-voltage power supply 260 for providing power to one or more electronic devices included in the microcontroller unit 250. The chamber 230 is sub-partitioned into one or more slots as illustrated in Figure 1 for accommodating one or more slices of bread to be toasted.

Interconnection within the network 200 will now be described.

The network 200 is connected together as illustrated in Figure 2. The mains supply is connected to the one or more heater arrays 210 and also to the low-voltage power supply 260. The one or more arrays 210 are in close spatial proximity to the toasting chamber 230 so that infrared radiation generated by the one or more arrays 210 when energized is communicated to one or more slices of bread in the chamber 230. The low-voltage power supply 260 is connected to the microcontroller unit 250. The microcontroller unit 250, in turn, is coupled to the interrogation apparatus 240 and also to the release mechanism 220; in operation, the microcontroller unit 250 is capable of energizing the release mechanism 220 to terminate bread toasting and thereby eject one or more toasted slices of bread. The apparatus 240 is in optical communication with the chamber 230 for injecting strobed light thereinto and to receive reflected and/or transmitted strobed radiation therefrom. Moreover, the apparatus 240 is arranged to demodulate reflected and/or strobed radiation with respect to the strobe for generating toasting indicative signals for the microcontroller unit 250.

As will be elucidated later, the apparatus 240 is preferably coupled via one ore more light guides to the chamber 230 so that the apparatus 240 can be shielded from thermal effects, for example long term thermal degradation, resulting from relatively high operating temperatures experienced at peripheral boundaries of the chamber 230 whereat the heater arrays 210 are situated. More preferably, the light guides are at least partially fabricated from low-cost substantially-transparent plastics materials such as one or more of polycarbonate, acrylic, Perspex and substantially transparent PVC. Alternatively, the light guides can be fabricated from an inexpensive glass, for example Pyrex, which is capable of withstanding higher temperatures than plastics materials. Shielding the apparatus 240 from thermal exposure potentially improves reliability and long-term toasting accuracy of the toasters 10, 100

As an alternative to employing light guides, the apparatus 240 can be mounted in relatively close proximity to the chamber 230 provided that adequate thermal shielding and insulation is provided, for example by using metallic reflectors and high-temperature mechanical coupling, for example silicone and/or fibre-glass sleeving and woven insulating sheets. If required, the apparatus 240 can be provided with one or more temperature sensors therein coupled to the microcontroller unit 250 so that unit 250 can apply signal compensation to reduce thermal effects experienced by the apparatus 240 from influencing toaster 10, 100 operation.

Operation of the network 200 will now be described with reference to Figure 2.

STEP 1: One or more slices of bread are inserted into the toasting chamber 230 thereby latching the release mechanism 220. Preferably, the release mechanism 220 is sprung loaded so that the user stores mechanical energy in the mechanism 220 for subsequently ejecting the one or more slices from the mechanism 220 when toasting has been completed.

STEP 2: The microcontroller unit 250 scans the controls 50 to read in user settings, for example degree of browning desired, and/or manual or automatic selection of bread type.

STEP 3: The unit 250 scans the one or more slices of bread using the interrogation apparatus 240 to determine their initial reflectivity characteristics; this provides the unit 250 with an initial indication of bread type when the one or more slices have not been pre-toasted. The unit 250 stores this initial indication in its memory.

STEP 4: If the initial reflectivity characteristics determined in STEP 3 indicate that the one or more slices of bread are more browned than specified in the user settings selected on the controls 50, the network 200 immediately activates the release mechanism 220 to eject the one or more slices of bread; in such a situation, the heater arrays 210 are preferably not energised.

Conversely, if the initial reflectivity characteristics determined in STEP 3 indicate that the one or more slices of bread are less browned that selected in the user settings on the controls 50, the unit 250 then connects the heater arrays 210 to the mains supply whilst repeatedly monitoring, by using the apparatus 240, subsequent optical reflectivity characteristics of the one or more slices of bread. The unit 250 thereby determines rate of change of reflectivity of the one or more slices of bread and therefore is capable of distinguishing whether the one or more slices are un-toasted slices of bread or partially toasted slices of bread which have been reinserted into the toasters 10, 100.

If the rate of change of reflectivity is greater than a predetermined level, the microprocessor unit 250 thereby determines that the one or more slices have previously been toasted and have been reinserted; in such a situation, the unit 250 does not have a measure of the initial (un-toasted) reflectivity characteristics of the one or more slices of bread. The unit 250 then assumes a final degree of browning dependent on the user settings selected on the controls 50; the final degree of browning is an approximate average between final browning states for brown and white bread. The unit 250 maintains power applied to the heater arrays 210 until the final degree of browning is achieved, whereafter the unit 250 disconnects the heater arrays 210 from the main supply and then activates the release mechanism 220 to eject the one or more slices of bread from the toasters 10, 100.

If the rate of change of reflectivity is less than a predetermined level, the unit 250 thereby determines that the one or more slices have not been pre-toasted; in such a situation, the unit 250 maintains power applied to the heater arrays 210 until the reflectivity characteristics of the one or more slices are a fractional ratio of the original reflectivity characteristics, the ratio dependent on the specified settings on the controls 50 and also whether the initial reflectivity characteristics indicate that white or brown bread is being toasted. If required, the unit 250 can have a look-up table stored in its memory defining suitable relationships for brown and white bread. When the aforesaid ratio is finally reached, the unit 250 de-energizes the heater arrays 210 and causes the release mechanism 220 to eject the one or more slices of bread.

STEPS 1 to 4 describe operation of the toaster 10, 100 in overview. An algorithm appropriate for the processor unit 250 will be described in more detail later with reference to Figures 14a, 14b, 14c.

The network 200 can be operated to monitor the toasting condition of each slice individually, and to eject each slice individually when toasted; although such a degree of independence and flexibility is often desirable, it does render the interrogation apparatus 240 and the mechanism 220 more complex. Alternatively, the network 200 can be configured to derive an average degree of toasting for the one or more slices and eject them simultaneously when a pre-selected degree of average toasting has been achieved; such an arrangement results in a simple interrogation apparatus 240 and a simple mechanism 220, thereby reducing smart toaster manufacturing cost.

The power supply 260 can be one or more of a transformer coupled supply, for example a simple switch mode supply including a miniature ferrite transformer, a switched capacitor isolated supply, or a resistive step-down supply; for example, when the supply is a resistive step-down supply, it can beneficially be derived from the heater arrays 210.

Referring to Figure 3, in a graph indicated by 300, there is illustrated toasting characteristics of white and brown bread. The graph 300 comprises a time abscissa axis 310 and a bread exterior exposed surface reflectivity coefficient ordinate axis 320. Toasting characteristics presented on the graph 300 correspond to actual measurements acquired whilst toasting slices of bread.

Toasting characteristics for different types of white bread are denoted by 330a, 330b. Different types of white bread, for example depending on the grade and density of flour employed to manufacture the bread, give rise to different rates of toasting for similar toasting radiative energy input from the heater arrays 210. The characteristics are denoted by an initial pseudo-plateau region corresponding substantially to a reflectivity coefficient of a value W₀ which later temporally relatively abruptly changes to a slope region which traverses a target degree of reflectivity of a value Wi corresponding to desired toasting browness; during operation, the microcontroller unit 250 terminates toasting and activates the release mechanism 220 when the value Wi is attained. The user preferably selects a ratio WJWo using the controls 50 to set a desired degree of toasting. Alternatively, the controls 50 and the microcontroller unit 250 can be selectively configured so that the user selects the value Wx only.

When partially toasted bread is inserted in the toasters 10, 100, it is often not possible for the microcontroller unit 250 to determine the value W₀ and must therefore switch to using the value Wi selected by the user. When the microcontroller unit 250 is switched by the user via the controls 50 to automatically identify bread colour and to toast according to the ratio Wι/W₀, a potential ambiguity arises where partially-toasted white bread re-inserted into the toaster 10, 100 can appear substantially identical to un-toasted brown bread; in such an ambiguous situation, the microcontroller unit 250 can only distinguish bread type of the basis of rate of toasting. In general, from empirical measurements, it is found that the slope region for brown bread has a steeper temporal gradient in comparison to white bread. However, different bread types vary in toasting rate and hence there is a potential susceptibility of the network 200 to deliver inconsistent results from slice to slice in a situation where partially toasted bread is reintroduced into the toasters 10, 100. In practice, such problems are rarely encountered.

For comparison, toasting characteristics for different types of brown bread are denoted by 340a, 340b. Different types of brown bread, for example depending on the grade and density of flour employed to manufacture the bread, give rise to different rates of toasting for similar toasting radiative energy input. The characteristics are denoted by an initial pseudo-plateau region corresponding substantially to a reflectivity coefficient of a value B₀ which later temporally relatively abruptly changes to a slope region which traverses a degree of reflectivity of a value Bi corresponding to desired degree of toasting; during operation, the microcontroller unit 250 terminates toasting and activates the release mechanism 220 when the value Bi is attained. The user preferably selects a ratio Bi/Bo using the controls 50 to set a desired degree of toasting. Alternatively, the controls 50 and the microcontroller unit 250 can be configured so that the user selects the value Bi only.

Conveniently, the values B_b Wi can be made mutually identical and variable in response to the user adjusting the controls 50. Such an approach is preferably adopted when initial values of W₀ and B₀ are not available.

An advantage of operating the microcontroller unit 250 in a ratiometric mode as described in the foregoing is that effects of interrogating light attenuation caused by long-term buildup of contamination and/or deposits on optical surfaces of the interrogation apparatus 240 does not significantly influence toasting performance. However, such deposits and/or contamination can influence the determination of Wo and B₀ and, if not accounted for over a long period of time (for example ten years of heavy toaster use) can potentially result in the toaster 10, 100 misinterpreting white bread to be brown bread. The deposits and/or contamination can arise from volatile components in bread being vapourized during repeated toasting operations or from general cooking in a kitchen environment, for example fat deposits arising from frying food products in oils such as sunflower oil. For example, some users may attempt to repeatedly toast bread which has already been impregnated with garlic butter, resulting in interior surfaces of the slots 30a, 30b, 110a, 110b, 110c, llOd becoming progressively coated in wax-like deposits.

As will be described later, the interrogation apparatus 240 preferably includes features to enable the microcontroller unit 250 to determine optical performance of the apparatus 240. The features preferably include optical surfaces which are susceptible to contamination in a similar manner to optical surfaces of the apparatus 240 interfacing to the one or more slices of bread within the chamber 230. The microcontroller unit 250 is capable of interrogating the features and thereby determining degradation in optical performance over time.

In calculating rate of toasting, the microcontroller unit 250 is programmed to take into account an initial warm-up period corresponding to the heater arrays 210 attaining red heat (circa 1000 °C); on account of nichrome wire on a mica former preferably being employed, this initial period is in the order of 10 seconds. Other types of heating technology potentially useable in toasters, for example ceramic heating elements, tend to exhibit a relatively longer initial warm-up period. Such alternative types of heating technology can be employed in the toasters 10, 100 and their microcontroller units 250 programmed accordingly.

Referring to Figure 4, there is shown a plan view of an upper surface of the toaster 10. Included within the toaster 10, and not illustrated in Figure 1, is a right- angle electrical connector 400 and a sensor printed circuit board (PCB) 410. The sensor PCB 410 is disposed with its plane substantially orthogonal to that of the PCB 40a. Moreover, the sensor PCB 410 is disposed with its plane substantially parallel to the slots 30a, 30b as illustrated.

The sensor PCB 410 comprises six sensor unit, for example a sensor unit 420, each sensor unit 420 operable to generate strobed interrogation radiation and to receive reflected radiation from one or more slices of toast in the slots 30a, 30b. The reflected strobed radiation is converted at the sensor units 420 to corresponding reflectance signals for processing in the microcontroller unit 250 included on the PCB 40a.

Although only a single sensor PCB 410 is shown in Figure 4, it will be appreciated that three such sensor PCBs with associated connectors can be included coupled to the PCB 40a; such an arrangement enables all sides of slices of bread inserted into the toaster 10 to be monitored to achieve superlative toaster performance, for example to avoid any risk of toast charring (blackening). In practice, it would be preferable to include only one sensor PCB to render the toaster 10 more economical to manufacture; this assumes both sides of slices of bread brown in a similar manner when toasted.

In Figure 4, details of the interrogation apparatus 240 are omitted for clarity. However, such details are illustrated in Figure 5.

In Figure 5, there are shown component parts of the interrogation apparatus 240. The apparatus 240 comprises the sensor PCB 410 and its associated sensor units 420. The chamber 230 includes radiation heat reflectors 500a, 500b for example fabricated from tin-plated steel sheet exhibiting a shiny mirror-type finish; the heat reflectors 500a, 500b are associated with the slots 30a, 30b respectively as illustrated. Interposed between the slots 30a, 30b and their associated reflectors 500a, 500b are the heater arrays 210 comprising heater formers 510a, 510b respectively; the formers 510a, 510b are preferably fabricated from mica composite material capable of withstanding temperatures in the order of 1500 °C. Onto each of the formers 510a, 510b is wound a nichrome heater wire 520 capable of glowing to red heat when energized by the mains supply. The wire 520 is supported in notches at lateral peripheral edges of the formers 510a, 510b and is meandered on sides of the formers 510a, 510b facing towards their associated slots 30a, 30b as illustrated. The reflectors 500a, 500b serve to reflect heat generated by the wire 520 away from the sensor PCB 410 towards the slots 30a, 30b, namely away from the sensor units 420. Each sensor unit 420 comprises input and output optical inserts 600, 610 respectively attached by spring steel circlips into holes punched into the reflectors 500a, 500b. The inserts 600, 610 project through over-sized holes in the formers 510a, 510b as illustrated slightly beyond the heater wire 520 towards the slots 30a, 30b. Beneficially, end surfaces of the inserts 600, 610 are formed obliquely, for example at an angle in a range of 15° to 60°, more preferably substantially 45°, to assist guiding strobed light to one or more slices of bread in the slots 30a, 30b and receiving reflected radiation therefrom. Such oblique surfaces can be generated by fabricating the inserts 600, 610 from lengths of glass rod which are cleaved at an oblique angle. Alternatively, the inserts 600, 610 can be molded components. As a further alternative, the oblique surfaces can be formed by a grinding process.

The inserts 600, 610 are beneficially fabricated from a heat-resistance glass material capable of coping with rapid thermal gradients, for example fabricated from Pyrex glass. If required, the oblique surfaces can be left with a frosted finish to help scatter strobed light onto the one or more slices of bread in the slots 30a, 30b and receive scattered reflected strobed light therefrom.

Each sensor unit 420 of the apparatus 240 comprises a light emitting diode (LED) 630 and a photodetector 640 soldered onto the sensor PCB 410. Thermally resistant sleeves 650 associated with each LED 630 and each photodetector 640 confine light to corresponding inserts 600, 610 respectively as illustrated. The sleeves 650 are preferably fabricated from opaque silicone rubber capable of withstanding temperatures up to 250 °C or, alternatively, woven fiberglass capable of withstanding temperatures up to 800 °C. Importantly, the LEDs 630 and photodetectors 640 are separated by a gap region from their respective inserts 600, 610 to provide a thermal break within the sleeves 650 as illustrated. Such gap regions maintain the LEDs 630 and the photodetectors 640 cooler in operation and hence less susceptible to thermal drift effects which can be detrimental to toaster 10 operation.

The photodetectors 640 are preferably photodiodes or phototransistors. Phototransistors are preferred as they provide a degree of amplification directly at the sensor PCB 410, and hence render the toaster 10 less prone to 50 Hz interference resulting from electrical currents flowing through the heater wire 520..

On account of light guiding properties of the inserts 600, 610, they are not susceptible to guiding therethrough thermal radiation received directly laterally thereat from the nichrome wire 520. Moreover, the oversized holes through which the inserts 600, 610 project ensure that direct thermal contact of the inserts 600, 610 to the former 510 is substantially avoided. Moreover, the circlips 620 and the reflector 500 assist to ensure that thermal radiation conducted down the inserts 600, 610 is diverted away from the sleeves 650 and their associated LEDs 630 and photodetectors 640. As the sleeves 650 are relatively poor heat conductors, the LEDs 630 and photodetectors 640 are maintained at a relatively cool temperature, for example 60 °C during toaster 10, 100 operation, for example even when the toasters 10, 110 are used continuously with negligible cooling period between slices of bread being inserted.

The sleeves 650 are also preferably substantially opaque so that the photodetectors 640 are protected from receiving strobed light directly from their associated LEDs 630. Referring to Figure 6, there is shown the former 510 in plan view together with its associated heater wire 520. Positions of the oversized holes for the inserts 600, 610 are indicated along a central widened region along an axis D-D'. There are three sensor units 420 accommodated. Preferably, the central widened region is sufficiently narrow to avoid noticeable spatial variations in toasting colour. However, the central region is of benefit to maintain radiative heat emitted from the wire 520 away from the inserts 600, 610. The wire 520 is wound in a meandered pattern and supported on peripheral edge notches punched into the former 510 so that substantially most of the heater wire 520 faces towards slices of bread inserted into the slots 30a, 30b.

Although Figures 5 and 6 illustrate a simple spatial arrangement of the sensor units 420, it will be appreciated that other spatial arrangements for the sensor units 420 are possible to provide more comprehensive monitoring of slices of bread inserted into the slots 30a, 30b. In Figure 7, first, second and third alternative sensor unit 420 spatial configurations are indicated generally by 700, 710, 720 respectively. In the first configuration 700, there are four sensor units 420 arranged along mutually orthogonal axes. Conversely, in the second configuration 710, there are six sensor units 420 disposed along both orthogonal and diagonal axes as illustrated. In the third configuration 720, there are four sensor units 420 disposed along diagonal axes. In general, more sensor units 420 improves repeatability of toasting whereas fewer sensor units 420 reduces toaster 10, 100 manufacturing costs. In the second configuration 710, it is desirable to spatially dispose windings of the heater wire 520 closer together at peripheral regions of the former 510 relative to a central region of the former, because the central region is generally hotter than the peripheral regions in operation when toasting slices of bread. A similar approach is adopted for the first configuration 700. If required, the third configuration 720 can be modified to more closely spatially dispose the wire 520 at the peripheral regions of the former 510.

The inventors have identified during experiments that the sensor units 420, despite thermal shielding as described in the foregoing, can be influenced by temperature increase. For example, light emission efficiency of the LEDs 630 diminishes as LED temperature increases. Similarly, background leakage currents in the photodetectors 640 tends to increase with temperature which can result in an effective reduction in light sensing sensitivity. If required, one or more temperature sensors can be included on the sensor PCB 410 to sense temperature of the sensor units 420 and to generate a temperature indicative signal for the microcontroller unit 250; the microcontroller unit 250 is thereby capable of applying appropriate signal compensation so that characteristics as presented in Figure 3 are achieved. In order to reduce thermal effects in the sensor units 420, they can be moved to reside on the PCB 40a and optical communication between the PCB 40a and the slots 30a, 30b provided by way of light guides. As the PCB 40a remains relatively cool during toaster 10, 100 operation, thermal effects in the sensor units 420 when located on the PCB 40a are substantially circumvented.

Referring to Figure 8, there is shown a second optical configuration for use in the toasters 10, 100 of Figure 1. The sensor units 420 are all clustered together in an optical unit 800 on the PCB 40a. Bundles of light pipes indicated by 810 are included to couple strobed interrogation radiation from the optical unit 800 to the slots 30a, 30b and reflected strobed interrogation radiation from the slots 30a, 30b back to the optical unit 800. Such a second configuration is of advantage in that the number of LEDs and photodetectors required can be potentially reduced, and cost savings can be made by avoiding the need for the sensor PCB 410 and its associated connector 400; however, fabrication of the bundles 810 adds to cost.

The bundles 810 are preferably fabricated from a substantially optically-transparent plastics material, for example from one or more of polycarbonate, clear PVC and/or acrylic plastics materials. Alternatively, the bundles 810 can be fabricated from glass, for example from Pyrex glass.

The bundles 810 can be molded as unitary components; such unitary optical components potentially require complex and expensive molding tools for their manufacture. Alternatively, they can be fabricated from several straight light pipes which are fused together and subsequently thermally treated to form ends of the light pipes through right angle bends as illustrated in Figure 8. If the bundles 810 are fabricated from plastics materials, the inserts 600, 610 are preferably employed at the reflectors 500a, 500b and the formers 510a, 510b with thermal breaks to avoid the bundles 810 being melted during toaster 10, 100 operation. The bundles 810 are preferably optically mutually isolated, for example by coating them in reflective silvered and/or opaque material except in the vicinity of the optical unit 800 and bent ends of the bundles 810 facing onto the slots 30a, 30b.

Referring to Figure 9, an end section of the bundles 810 is indicated generally by 900. The bundles 810 comprise light pipes, for example a light pipe 910, which is bent through substantially a right angle indicated by 920 a short distance of circa 6 mm before its optical port indicated by 925. The glass inserts 600, 610 affixed by way of the steel circlips 620 to the reflector 500 are arranged to protrude through oversized punched holes in the former 510 as illustrated. The heater wire 520 on the former 510 is not shown for clarity. Each light pipe is coupled at its optical port by way of the sleeves 650 with an air gap between the optical port and its associated glass insert to provide thermal isolation. When the bundles 810 are fabricated from glass, the inserts 600, 610 can be omitted and ends of the glass light pipes circlipped directly onto the reflector 500, thereby simplifying toaster 10, 100 construction.

Referring to Figure 10, there is shown a third optical configuration for use in the toasters 10, 100. The third configuration comprises the PCB 40a, the connector 400 and the sensor PCB 410 as for the first configuration as illustrated in Figure 4. In the third configuration, the slots 30a, 30b are provided with mutually similar reflector assemblies 1000a, 1000b as illustrated. Strobed radiation generated by LEDs on the sensor PCB 410 is conveyed by way of reflection within the assemblies 1000a, 1000b to one or more slices of bread within the slots 30a, 30b, and reflected strobed radiation from the one or more slices is conveyed by way of reflection within the assemblies 1000a, 1000b back to photodetectors on the sensor PCB 410. Such reflection within the reflector assemblies 1000a, 1000b is of benefit in that the LEDs and photodetectors are thereby substantially isolated from radiation generated at the assemblies 1000a, 1000b for toasting the one or more slices of bread. Preferably, each slot 30a, 30b is surrounded on both sides thereof by such assemblies, although only those assemblies 1000a, 1000b neighbouring onto the sensor PCB 410 preferably need to be operable to optically interrogate slices of bread within the slots 30a, 30b as illustrated in Figure 10.

In Figure 11, the assembly 1000a is shown in greater detail. The assembly 1000a comprises a tin- plated reflector 1010 having a shiny mirror-like reflective finish. The reflector 1010 is fabricated from sheet material into which perforations having bendable tabs are punched, after which the reflector 1010 is pressed in shaping dies to assume a cross-sectional profile as illustrated in Figure 11. The reflector 1010 is formed into a series of cylindrical reflector units, each unit including a central raised projection ridge as shown. The aforesaid perforations are arranged to correspond to lateral walls of the projections. Front faces of ridges facing towards the slice of bread 430 to be toasted are provided with corresponding mica composite material thermal strips 1060. The heater wire 520 is routed in front of the strips 1060 and is secured at regular intervals using alumina ceramic insulation tubes 1050 which are affixed by bending metal tabs 1070 associated with the aforesaid perforations over the ceramic tubes 1050. Due to thermal cycling, the heater wire 520 will in general naturally distort to be slightly spatially isolated from the strips 1060, especially if the tubes 1050 are of significant diameter, for example 2.5 mm in diameter with 1 mm diameter central hole therethrough.

The sensor PCB 410 is provided with several spacer plates 1020 fabricated from relatively thin shiny tin-plated steel sheet, for example of 300 μm thickness. The plates 1020 exhibit mirror-like lateral surfaces. Preferably, the plates 1020 are provided with edge tabs which are inserted into the sensor PCB, twisted and then soldered to attach the plates 1020 onto the sensor PCB 410. Edges of the plates 1020 remote from the sensor PCB 410 are arranged to centrally align with centers of the ridges but only occasionally spatially contact therewith. Such an arrangement results in a relatively poor thermal conduction from the reflector 1010 along the plates 1020 to the sensor PCB 410. Moreover, the plates 410 are capable of dissipating thermal energy propagating therealong by convection and/or radiation and/or conduction to air behind the reflector 1010.

The sensor PCB 410 further includes LEDs 1030 for generating strobed interrogating radiation for interrogating the slice of bread 430 and photodetectors 1040 for receiving reflected strobed radiation from the slice 430.

The plates 1020 subdivide a region between the sensor PCB 410 and the reflector 1010 into optically isolated compartments, namely LED compartments and photodetector departments. Such an arrangement assists to reduce direct strobed radiation coupling from the LEDs 1030 to their corresponding photodetectors. Avoidance of such direct coupling enhances optical signal- to-noise ratio provided by the reflector 1000 and its associated components. .

Preferably, the LEDs 1030 are yellow and/or red LEDs; they can be bi-colour, and can be periodically switched so that the microcontroller unit 250 can compute a colour quality of the slice 430 in addition to merely receiving a measure of its reflectivity. Moreover, the photodetectors 1040 are preferably photodiodes and/or phototransistors. Phototransistors are of advantage in that they provide in-situ amplification which assists to reduce 50 Hz cross-talk within the toasters 10, 100.

In operation, the LEDs 1030 are soldered in an orientation into the sensor PCB 410 so that they emit strobed interrogation light predominantly towards the ridges of the reflector 1010. The light is reflected from lateral sides of the plates 1020 and is concentrated in the ridges whereat it is reflected out through the lateral perforations in the ridges to reflect from curved surfaces of the reflector 1010 facing towards the slice of bread 430. The reflected radiation from the curved surfaces propagates to the slice 430. The slice 430 reflects a proportion of strobed radiation incident thereat. The reflected radiation propagates back to curved surfaces of the reflector 1010 whereat it is reflected towards the lateral perforations of the ridges. The reflected radiation passes through the perforations to the plates 1020 whereat it is reflected towards the photodetectors 1040. The photodetectors 1040 receive the reflected radiation and generate corresponding received radiation signals which are conveyed back via the sensor PCB 410 back to the microcontroller unit 250 situated on the PCB 40a.

The third configuration illustrated in Figures 10 and 11 is of benefit in that LEDs 1030 and the photodetectors 1040 are shielded from the heater wire 520 and therefore less susceptible to exhibiting thermal drift characteristics as described in the foregoing. Moreover, the sensor PCB 410 is preferably fabricated from resin impregnated paper and/or impregnated fiberglass which are substantially thermal insulators. As the LEDs 1030 and photodetectors 1040 are free-standing components mechanically supported from the sensor PCB 410, they are thermally isolated from the plates 1020 and the reflector 1010. However, after prolonged continuous use, the compartments behind the reflector 1010 can experienced elevated temperatures; in order to cope with such a situation, the sensor PCB 410 can be provided with one or more temperature sensors, for example one or more thermistors, so that the micocontroller unit 250 can apply appropriate correction to remove the influence of such thermal effects on the LEDs 1030 and the photodetectors 1040.

Additionally, the LEDs 1030 and photodetectors 1040 of the third configuration are shielded from direct contamination resulting from volatile components being evaporated from slices of bread being toasted. The curved surfaces of the reflector 1010 facing towards the slice 430 are accessible to the user of the toasters 10, 100 for cleaning purposes; such cleaning does not require a high degree of skill and, if properly attached, the heater wire 520 will be relatively robust against damage during such cleaning.

Referring to Figure 12, a view of reflector assembly 1000 facing towards the slice 430 is shown. This view would be seen by the user looking down the slots 30a, 30b. The mica strips 1060 preferably extend beyond end of the ridges to prevent the heater wire 520 electrically shorting onto the reflector 1010. Moreover, between ridges, the heater wire 520 is formed into a loop 2000 provided with alumina ceramic tubelets 2010 to provide electrical insulation and reduce risk of electrical shock to the user.

Referring to Figure 13, components parts included within the interrogation apparatus 240 and the microcontroller unit 250 will now be described in further detail.

As described in the foregoing, the interrogation apparatus 240 comprises strobed light sources, namely the LEDs 630 and the photodetectors 640 in the case of the toaster 10, and the LEDs 1030 and the photodetectors 1040 in the case of the toaster 100. The microcontroller unit 250 includes a microcontroller 2500, for example an inexpensive PIC processor, connected to a clock quartz crystal (Xtal) to provide clocking signals to clock the microcontroller 2500; the crystal is preferably arranged to resonate at a frequency in the order of 20 MHz. The unit 250 further comprises a current buffer 2510 whose input is connected to a S_T output of the microcontroller 2500 and whose output is connected to the LEDs 630, 1030. The output S is a strobe provided by the microcontroller 2500. The unit 250 further includes a preamplifier 2520 connected to the photodetectors 640, 1040 for receiving therefrom in operation signals corresponding to reflected strobed radiation from one or more slices of bread being toasted; the preamplifier 2520 is configured as a current-to-voltage converter with a feedback impedance corresponding to a parallel connection of a capacitor C and a feedback resistor R_f. An output of the preamplifier 2520 is connected to a signal input of a synchronous demodulator 2530 whose switching control input is connected to the S_T output. The demodulator 2530 provides a low pass signal filtration characteristic by virtue of capacitor C_c included therein; the demodulator 2530 thereby provides a quasi-constant d.c. signal at its output for the microcontroller 2500. The output of the demodulator 2530 is connected to a detector signal input Sj of the microcontroller 2500. The microcontroller 2500 includes integrally therein circuits for digitizing analogue signals presented at the input S_{. The preamplifier 2520 is preferably a.c. coupled and arranged to amplify effectively at the strobe frequency but to block d.c. signals from the photodetectors 640, 1040; such blocking is provided by a blocking capacitor C_B. The buffer 2510 can be implemented as a switching metal oxide semiconductor field effect transistor (MOSFET) or equivalent switching bipolar transistor for modulating current to the LEDs 630, 1030 at the strobe frequency. Likewise, the amplifier 2520 can be implemented using operational amplifiers, for example an LM358 device or equivalent, or implemented using discrete a.c. coupled bipolar and/or MOSFET transistors. The demodulator 2530 is preferably implemented using a MOS switch and an associated operational amplifier, for example an LM358 device or equivalent. It will be appreciated that Figure 13 is schematic representation of the unit 250 and the apparatus 240. In practice, the unit 250 can include a plurality of outputs S_τ, buffers 2510, preamplifiers 2520, and demodulators 2530 when individual independent monitoring is provided for each slot 30a, 30b, 110a, 110b, 110b, llOd of the toasters 10, 100. Where individual independent monitoring is provided for each slot, the outputs S_τ are preferably strobed at mutually substantially different frequencies to reduce cross-talk from interrogation used in each slot.

In operation, the microcontroller 2500 outputs one or more strobed signals at its one or more outputs S_τ which causes the one or more buffers 2510 connected thereto respectively to provide strobe-modulated current to their associated LEDs 630, 1030 which, in turn, emit strobed interrogation radiation. Strobed radiation reflected from one or more slices for toasting and received at the one or more photodetectors 640, 1040 is converted thereat into one or more corresponding reflected strobe signals which are amplified in the one or more preamplifiers 2520 whereat d.c. components in the reflected strobe signals are removed. The one or more amplified reflected strobe signals are demodulated and filtered in associated demodulators 2530 to provide one or more demodulated input signals for the microcontroller 2500 which digitizes these signals to generate corresponding data for use in software executing within the microcontroller 2500.

Use of strobed radiation for interrogating one or more slices of bread during toasting thereof is of considerable benefit in the toasters 10, 100 as it enables the effects of quasi-static ambient illumination, for example fluorescent strip lighting, sunlight and visible radiation emitted from the heater array 210 to be substantially excluded from measurement of bread reflectivity made by the microcontroller unit 250 in combination with the interrogation apparatus 240. The LEDs 630, 1030 are preferably strobed in a frequency range of 500 Hz to 500 kHz, although a frequency in the order of 1 kHz is especially preferred. The strobe frequency selected is preferably not at a harmonic of mains supply 50 Hz as the apparatus 240 can then potentially be influenced by fluorescent lighting frequently employed in kitchen environments.

An algorithm for use in controlling the toasters 10, 100 is described in the foregoing in the context of the network 200 illustrated in Figure 2. In practice, software executing within the microcontroller 2500 can be configured according to several possible algorithms. An example of a suitable algorithm for controlling the toasters 10, 100 is illustrated in Figures 14a, 14b, 14c. When electrical power is applied to the toasters 10, 100, their microcontroller 2500 starts at a START step 2900 at the top of Figure 14a and proceeds to a step 3000. In the step 3000, the microcontroller 2500 reads the controls 50, for example to read a degree of browning required, whether or not the user has selected fully automatic operation, and/or whether or not the user has specified the colour of the bread to be toasted. Moreover, the microcontroller 2500 also detects via the apparatus 240 whether or not any slices of bread have been inserted into the slots 30a, 30b, 100a, 110b, 110c, llOd. Furthermore, the microcontroller 2500 evaluates a number of parameters V_TO> Nπ, Vτ₂ as well as the aforementioned ratios WJWo, BJBo.

After executing the step 3000, the microcontroller 2500 proceeds onto a decision step 3010 whereat the microcontroller 2500 switches to a STOP state if no slices of bread have been inserted into the slots 30, 110, or proceeds to a step 3020 if one or slices are present in the slots 30, 110. After a preset time duration in the STOP state, the microcontroller 2500 proceeds to the START step 2900 again. In the step 3020, the microcontroller 2500 applies power to the heater arrays 210; power applied to the heater arrays 210 can alternatively be hard-wire linked to the release mechanism 220. After the step 3020, the microcontroller 2500 proceeds to a step 3030 whereat the microcontroller 2500 scans via the apparatus 240 the one or more slices of bread and receives back reflected strobed radiation which is demodulated, digitized and corresponding data stored in a memory location Qi.

In a subsequent decision step 3040, the microcontroller 2500 compares the value Qi with the parameter V_To to determine whether the one or more slices are already thoroughly toasted. The parameter Vτo is calculated by the microcontroller 2500 to correspond to the darkest the one or more slices can be toasted irrespective of bread type based on the browness setting selected by the user on the controls 50. If the one or more slices are found in the step 3040 to be thoroughly toasted, the microcontroller 2500 promptly proceeds to a step 3050 whereat the microcontroller 2500 deactivates the heater arrays 210 , activates the release mechanism 220 to eject the one or more slices of bread and finally proceeds to a STOP state; after a preset duration in the STOP state, the microcontroller proceeds to the START step 2900 as illustrated.

If the one or more slices are found in the step 3040 to be un-toasted and/or lightly toasted (for example corresponding to partially toasted slices of bread being reinserted into the toasters 10, 100), the microcontroller 2500^' proceeds from the step 3040 to execute a step 3060. The step 3060 causes the microcontroller 2500 to pause for a period DELAY 1 sufficient for the heaters 210 to attain red heat and start to cause slight browning or additional browning of the one or more slices of bread. The microcontroller 2500 then rescans the one or more slices of bread using the apparatus 240 and stores a corresponding reflected strobed radiation reading in a memory location Q₂.

After execution of the step 3060, the microcontroller 2500 proceeds to execute a step 3070 whereat the microcontroller 2500 calculates rate of browning dQ/dt. If dQ/dt is relatively low, namely less than the parameter V_T1 preprogrammed into microcontroller 2500, there is indicated thereby that un-toasted slices of bread were inserted into the toasters 10, 100. Conversely, if dQ/dt is relatively high, namely greater than the parameter V_Tι, there is indicated thereby that partially toasted slices of bread were inserted into the toasters 10, 110.

After the step 3070, the microcontroller 2500 proceeds to execute a decision step 3080 whereat the comparison with the parameter Nπ as described above is performed. If dQ/dt is greater than V_Tι, the microcontroller 2500 is not capable of implementing ratiometric control as Wo or B₀ will not be known; in such a situation, the microcontroller 2500 proceeds to a routine as illustrated in Figure 14c. Conversely if dQ/dt is less than V_Tι, the microcontroller 2500 proceeds from the step 3080 to execute a decision step 3090 whereat the microcontroller 2500 compares the value Qi, namely the initial reflectivity reading, with a pre-calculated parameter V_T2 which sets a level at which brown bread is distinguished from white bread. If Q_x is greater than V_T2, namely a relatively high reflectivity, the microcontroller 2500 determines thereby that it is required to toast white bread where the ratio Wι/W₀ can be used, Wo corresponding to Qi. Conversely if Qx is less than V_τ2, the microcontroller 2500 determines thereby that it is required to toast brown bread where the ratio B]/Bo can be used, B₀ corresponding to Qi. From the step 3090, the microcontroller 2500 proceeds to a step 4010 where white bread pertains, or to a step 4000 where brown bread pertains. In these steps 4000, 4010, the microcontroller 2500 calculates end points Vτ₃ at which toasting is deemed to be completed for brown and white bread respectively.

After executing the step 4000 or the step 4010, the microcontroller 2500 proceeds to a step 4020 whereat the microcontroller 2500 scans the one or more slices using the apparatus 240 and stores a reflected strobed radiation measurement thereby obtained in a memory location Q . On completing the step 4020, the microcontroller 2500 proceeds to execute a decision step 4030 whereat the microcontroller 2500 compares Q₄ with the parameter V_τ3. If Q₄ is less than V_T3, the one or more slices are sufficiently toasted and the microcontroller 2500 proceeds to execute a step 4040 whereat the microcontroller 2500 deactivates the heaters 210, activates the release mechanism 220 to eject the one or more slices of bread and then proceeds to a STOP state; after a pause in the STOP state, the microcontroller 2500 proceeds back to the START step 2900. Conversely if Q₄ is greater than V_T3, the one or more slices are not sufficiently toasted; the microcontroller 2500 proceeds to a pause step 4050 after which it proceeds back to the step 4020.

When the toasters 10, 100 are presented with re-entrant toast, namely when dQ/dt is greater than Nri in the step 3080, the microcontroller 2500 proceeds to execute a step 4100 on Figure 14c. This step 4100 causes the microcontroller 2500 to set the parameter V_T2 to an average browness depending on the user selection on the controls 50 irrespective of bread type. The microcontroller 2500 proceeds from the step 4100 to execute a step 4110 whereat the microcontroller 2500 scans the one or more slices of bread using the apparatus 240 to receive a measure of reflected strobed radiation therefrom. The measure is stored by the microcontroller 2500 in a memory location Q₃. The microcontroller 2500 then proceeds from the step 4110 to a decision step 4120 whereat the microcontroller 2500 compares the value of Q₃ with the parameter V_τ2. If Q is less than Vτ₂, the one or more slices are sufficiently toasted; the microcontroller 2500 then proceeds from the step 4120 to a step 4130 whereat it deactivates the heaters 210, activates the release mechanism 220 to eject the one or more slices of toasted bread, executes a STOP state and, after a pause delay, finally proceeds to the START step 2900 in Figure 14a. Conversely, if Q₃ is greater than V_T2, the microcontroller 2500 proceeds from the decision step 4120 to a step 4140 whereat the microcontroller 2500 pauses for a period of DELAY 2 after which it proceeds to execute the step 4100.

The DELAY 2 is preferably in a range of 0.5 seconds to 5 seconds to allow the one or more slices of bread to toast further. As described in the foregoing, the DELAY 1 is somewhat longer than DELAY 2 because sufficient time has to be allowed for the heater arrays 210 to attain red heat and for exterior surfaces of the one or more slices of bread to reach a sufficient temperature at which further browning can occur.

Referring to Figure 15, there is illustrated a mechanical implementation for the transverse toaster 100 of Figure 1. The PCBs 40a, 40b are preferably provided with an interconnecting circuit board 4300, for example a flexible Kapton-strip circuit board, linked to plurality of sensor PCBs 4310, 4320, 4330 so that each of the slots 110a, 110b, 100c, lOOd is provided with optical interrogation for monitoring toasting. Kapton is a desirable material for interconnection on account of its ability to cope with elevated temperatures; for example, Kapton is routinely employed for coil ormers of high-power loudspeakers capable of being driven at several hundred Watts power. The flexible board 4300 makes tolerance control easier when constructing the toaster 100 as the board 4300 can be folded slightly to accommodate mechanical errors in manufacture. Preferably, the board 4300 is disposed on a side J2 of the toaster to render a side Jl of the toaster 100 available for accommodating the release mechanism 220, for example user- depressible resiliently-biased levers. The controls 50 are conveniently placed on the Jl side of the toaster 100 so that switches and/or potentiometers of the controls 50 can be directly mounted on the circuit board 40b or mounted on a local circuit board with Kapton ribbon-cable 4340 connection to the PCB 40b. It is thereby possible to conveniently position mechanical and electrical components around one another in this complex transverse toaster 100 for easing design and manufacture.

It will be appreciated that embodiments of the invention described in the foregoing can be modified without departing from the scope of the invention.

The LEDs 630, 1030 can be bi-colour, for example switchable between yellow and green light emission, so that the microcontroller 2500 can strobe the one or more slices of bread with different coloured light; a ratio of the measures of reflected strobed radiation for the two colours can provide the microcontroller 2500 with an indication of the colour of the one or more slices of bread during toasting rather than purely a measure of reflectivity in response to monochrome illumination. Such colour determination is of advantage to assist the toasters 10, 100 to distinguish between partially-toasted white bread and un-toasted brown bread which can have superficially similar strobed radiation reflectivity characteristics when interrogated with monochrome strobed radiation. Preferably, switching between colours should be performed at a frequency in a range of 0.2 to 5 Hz, more preferably substantially 1 Hz, to provide an aesthetically pleasing visual appearance to the user whilst ensuring a sufficiently frequent sampling interval to track toast browning and enable the interrogation apparatus 240 to settle in response to changes in strobed illumination colour. The controls 50 can be implemented to be "minimalistic", for example a single knob for adjusting toasting browness; alternatively, the controls 50 can be implemented to provide the user with full control of manual or automatic bread-type selection, whether or not the toasters 10, 100 attempt to operate in ratiometric mode, and whether or not re-entrant toast is being applied to the toaster 10, 100. If required, the controls 50 can also include visual indicators, for example bar LED displays or back-lit LCDs to indicate a stage of toasting reached by the toasters 10, 100.

In Figures 14a, 14b, 14c, the microcontroller 1500 can be arranged between the STOP state and progressing to the START step 2900, when toast has been removed from the toasters 10, 100, to scan using the apparatus 240 the slots 30a, 30b, 110a, 110b, 110c, llOd devoid of slices of bread therein. This provides the microcontroller 2500 with an indication of contamination build-up, for example on exposed ends of the inserts 600, 610 or on reflective surfaces of the reflectors 1010 so that the microcontroller 2500 can scale the values of V_Tι, V_T2, V_T3 employed to account for the optical effects of such contamination buildup. Such correction for contamination is of benefit because it can render the toasters 10, 100 susceptible to providing accurate and reliable toasting operation overlong periods of heavy use in kitchen environments.

Claims

1. A smart toaster comprising:

(a) a toasting zone for receiving one or more slices of bread;

(b) toasting means for generating radiation for toasting the one or more slices in the toasting zone;

(c) optical interrogating means for monitoring the one or more slices of bread during toasting and providing one or more corresponding reflectivity signals;

(d) processing means for receiving the one or more reflectivity signals, and for de-energizing the toasting means when the one or more reflectivity signals indicate that the one or more slices are toasted to a desired degree, characterised in that the interrogating means is arranged to emit strobed radiation to optically interrogate the one or more slices of bread, and to demodulate strobed radiation reflected from the one or more slices with respect to the strobe to generate the one or more reflectivity signals.

2. A toaster according to Claim 1, wherein the processing means is arranged to de-energize the toasting means when the one or more reflectivity signals are less than one or more threshold values.

3. A toaster according to Claim 2, wherein the toaster includes user-adjustable controls coupled to the processing means for adjusting the one or more threshold values.

4. A toaster according to Claim 3, wherein the controls and the processing means are arranged to set the one or more threshold values ratiometrically based on an initial strobed radiation reflectivity of the one or more slices and a ratio set by the user on the user-adjustable controls.

5. A toaster according to Claim 4, wherein the processing means comprises first analysing means for determining whether the one or more slices are brown bread or white bread, and for adjusting the threshold values according to whether the one or more slices are white bread or brown bread.

6. A toaster according to Claim 1, 2, 3, 4 or 5, wherein the processing means comprises second analysing means for determining rate of slice toasting when the toastmg means is initially energized, and thereby determining whether the one or more slices are initially un-toasted or at least partially toasted.

7. A toaster according to Claim 6, wherein the processing means is arranged to select non- ratiometric control when the one or more slices are initially at least partially toasted.

8. A toaster according to any one of the preceding claims, wherein the toasting zone comprises a plurality of toasting slots.

9. A toaster according to Claim 8, wherein the interrogating means is arranged to interrogate the slots using strobed radiation of mutually different strobe frequencies for reducing optical cross-talk from slot to slot.

10. A toaster according to Claim 8 or 9, wherein the slots are disposed in an "in-line" configuration or in a "transverse" configuration with respect to end regions of the toaster.

11. A toaster according to Claim 8, 9 or 10, wherein the toaster is provided with mutually independent toasting monitoring control for each of the slots.

12. A toaster according to Claim 8, 9 or 10, wherein the toaster is provided with a single average toasting monitoring control for the plurality of slots.

13. A toaster according to any one of the preceding claims, wherein the interrogating means is arranged to generate the strobed radiation at a strobe frequency in a range of 500 Hz to 500 kHz.

14. A toaster according to Claim 13, wherein the strobe frequency is substantially 1 kHz.

15. A toaster according to any one or the preceding claims, wherein the interrogating means is optically coupled through optical interfacing means to the toasting zone, the interfacing means adapted to withstand elevated toasting temperatures induced by the toasting means in the toasting zone.

16. A toaster according to Claim 15, wherein the interfacing means comprises a thermal break for shielding the interrogating means from elevated temperatures generated by the toasting means in the toasting zone.

17. A toaster according to Claim 15 or 16, therein the toasting zone comprises reflecting means for reflecting radiation generated by the toasting means towards the toasting zone and away from the interrogating means.

18. A toaster according to any one of the preceding claims, wherein the interrogating means is disposed adjacent to the toasting zone with the interfacing means interposed between the toasting zone and the interrogating means.

19. A toaster according to Claim 18, wherein the interrogating means comprises one or more sensor printed circuit boards bearing optical components to generate the strobed radiation and to receive the reflected strobed radiation to generate the reflectivity signals, and the toasting zone comprises a plurality of slots for receiving the one or more slices of bread, the one or more circuit boards disposed substantially parallel to their respective slots.

20. A toaster according to Claim 19, wherein the processing means is disposed on one or more processor printed circuit boards at one or more end regions of the toaster, the one or more sensor circuit boards being coupled directly to the one or more processor circuit boards by way of circuit-board connectors.

21. A toaster according to Claim 19, wherein the processing means is disposed on one or more processor printed circuit boards at one or more end regions of the toaster, the one or more sensor circuit boards being coupled to the one or more processor circuit boards by way of one or more flexible interconnect circuit boards.

22. A toaster according to Claim 21, wherein the one or more flexible interconnect circuit boards comprise Kapton-based circuit boards.

23. A toaster according to any one of Claims 15 to 22, wherein the interfacing means comprises one or more optically transmissive inserts for coupling the strobed radiation to and from the one or more slices.

24. A toaster according to Claim 23, wherein the inserts are fabricated from a heat tolerant glass.

25. A toaster according to Claim 24, wherein the inserts are fabricated from a soft Pyrex-type glass.

26. A toaster according to Claim 23, 24 or 25, wherein at least one of said one or more inserts comprises obliquely angled optical surfaces directed towards the slots for directing and receiving strobed radiation at a non-normal angle to the one or more slices of bread within the slots.

27. A toaster according to Claim 26, wherein the one or more inserts are elongate defining an elongate axis and their optical surfaces are angled in a range of 15° to 60° relative to a perpendicular to said elongate axis.

28. A toaster according to Claim 26 or 27, wherein the obliquely angled surfaces are cleaved, molded and/or ground.

29. A toaster according to Claim 26, 27 or 28, wherein the obliquely angled surfaces are provided with a scattering finish to improve strobed radiation scatter within the toasting zone.

30. A toaster according to any one of Claims 1 to 17, wherein the interrogating means is disposed remotely from the toasting zone with the interfacing means optically coupling the strobed radiation between the remote interrogating means and the toasting zone.

31. A toaster according to Claim 30, wherein the interfacing means comprises one or more light guides for coupling the strobed radiation between the remote interrogating means and the toasting zone.

32. A toaster according to Claim 31, wherein the one or more light guides are fabricated from a substantially optically transparent plastics material.

33. A toaster according to any one of Claims 1 to 17, wherein the interrogating means is disposed adjacent to the toastmg zone, and the interfacing means is arranged to couple strobed radiation between the interrogating means and the toasting zones by way of reflection in the interfacing means.

34. A toaster according to Claim 33, wherein the interfacing means is additionally arranged to reflect radiation generated by the toasting means towards the toasting zone for toasting thereat the one or more slices of bread.

35. A toaster according to Claim 33 or 34, wherein the interfacing means comprises a plurality of curved mirror-like surfaces for reflecting the strobed radiation and radiation emitted by the toasting means.

36. A toaster according to any one of the preceding claims, wherein the toasting zone comprises a plurality of slots for receiving the one or more slices of bread, and the interrogating means is grouped into a plurality of sensor units, each unit capable of generating the strobed radiation and receiving reflected strobed radiation from the one or more slices of bread, the sensor units disposed so as to interrogate sites within each slot, the sites disposed in a spatially linear manner.

37. A toaster according to any one of the preceding claims, wherein the toasting zone comprises a plurality of slots for receiving the one or more slices of bread, and the interrogating means is grouped into a plurality sensor units, each unit capable of generating the strobed radiation and receiving reflected strobed radiation from the one or more slices of bread, the sensor units disposed so as to interrogate sites within each slot, the sites spatially disposed along diagonal axes and or orthogonal axes.

38. A toaster according to any one of the preceding claims, wherein the interrogating means comprises one or more light emitting diodes (LEDs) for generating the strobed radiation, and one or more photodetectors for detecting reflected strobed radiation from the toasting zone.

39. A toaster according to Claim 38, wherein the one or more photodetectors comprises one or more photodiodes and/or one or more phototransistors.

40. A toaster according to any one of the preceding claims, wherein the interrogating means is arranged to interrogate the one or more slices of bread using strobed radiation whose wavelength is temporally switched between a plurality of colours for enabling the processing means to determine colour of the one or more slices in addition to their optical reflectivity, the processing means arranged to use slice colour information for enhancing toasting accuracy.

41. A method of monitoring toasting within a smart toaster, the toaster comprising:

(a) a toasting zone for receiving one or more slices of bread;

42. A method according to Claim 41, further comprising the step of arranging for the processi inngg mmeeaannss ttoo de-energize the toasting means when the one or more reflectivity signals are less than one or more threshold values

43. A method according to Claim 42, wherein the toaster includes user-adjustable controls coupled to the processing means for adjusting the one or more threshold values.

44. A method according to Claim 43, further comprising the step of arranging for the controls and the processing means to set the one or more threshold values ratiometrically based on an initial strobed radiation reflectivity of the one or more slices and a ratio set by the user on the user-adjustable controls.

45. A method according to Claim 44, further comprising the steps of:

(b) for adjusting the threshold values according to whether the one or more slices are white bread or brown bread.

46. A method according to Claim 41, 42, 43, 44 or 45, wherein the processing means comprises second analysing means for determining rate of slice toasting when the toasting means is initially energized, and thereby determining whether the one or more slices are initially un- toasted or at least partially toasted.

47. A method according to Claim 46, further comprising the step of arranging for the processing means to select non-ratiometric control when the one or more slices are initially at least partially toasted.

48. A smart toaster comprising:

(a) a toasting zone for receiving one or more slices of bread;

(d) processing means for receiving the one or more reflectivity signals, and for de-energizing the toasting means when the one or more reflectivity signals indicate that the one or more slices are toasted to a desired degree, characterised in that the processing means is arranged to operate in a ratiometric mode wherein the desired degree is determined from an initial reflectivity of the one or slices of bread and a ratiometric setting specified by a user of the toaster on controlling means coupled to the processing means.