WO1999053251A2

WO1999053251A2 - Lightwave oven and method of cooking therewith using conventional cooking recipes

Info

Publication number: WO1999053251A2
Application number: PCT/US1999/008118
Authority: WO
Inventors: Sam Adapa; William Minnear; Peggy O. Beaver; Eugene R. Westerberg
Original assignee: Quadlux, Inc.
Priority date: 1998-04-14
Filing date: 1999-04-14
Publication date: 1999-10-21
Also published as: WO1999053251A3; AU3641799A

Abstract

A lightwave oven and cooking method which allows a user to use conventional oven recipes in a lightwave cooking oven (100). In accordance with the described method, a food item is received in the oven cavity (8) and user instructions are received from a user. The user instructions specify at least one conventional cooking parameter (e.g. oven temperature and/or cook time) representing a cooking parameter for cooking the food item in a conventional oven. The oven determines at least one lightwave cooking parameter (e.g. lightwave cooking time, lamp intensity, etc.) using the at least one conventional cooking parameter, and controls the oven's lightwave cooking lamp (28) to cook the food item using the at least one lightwave cooking parameter.

Description

LIGHTWAVE OVEN

AND METHOD OF COOKING THEREWITH

USING CONVENTIONAL COOKING RECIPES

Field of the Invention

This invention relates to the field of lightwave ovens and methods of cooking therewith using radiant energy in the infrared, near- visible and visible ranges of the electromagnetic spectrum. More particularly, this invention relates to methods of using lightwave ovens to cook foods using conventional oven recipes.

Background of the Invention Ovens for cooking and baking food have been known and used for thousands of years. Basically, oven types can be categorized in four cooking forms; conduction cooking, convection cooking, infrared radiation cooking and microwave radiation cooking.

There are subtle differences between cooking and baking. Cooking just requires the heating of the food. Baking of a product from a dough, such as bread, cake, crust, or pastry, requires not only heating of the product throughout but also chemical reactions coupled with driving the water from the dough in a predetermined fashion to achieve the correct consistency of the final product and finally browning the outside. Following a recipe when baking is very important. An attempt to decrease the baking time in a conventional oven by increasing the temperature results in a damaged or destroyed product. In general, there are problems when one wants to cook or bake foodstuffs with high-quality results in the shortest times. Conduction and convection provide the necessary quality, but both are inherently slow energy transfer methods. Long- wave infrared radiation can provide faster heating rates, but it only heats the surface area of most foodstuffs, leaving the internal heat energy to be transferred by much slower conduction. Microwave radiation heats the foodstuff very quickly in depth, but during baking the loss of water near the surface stops the heating process before any satisfactory browning occurs. Consequently, microwave ovens cannot produce quality baked foodstuffs, such as bread.

Radiant cooking methods can be classified by the manner in which the radiation interacts with the foodstuff molecules. For example, starting with the longest wavelengths for cooking, the microwave region, most of the heating occurs because the radiant energy couples into the bipolar water molecules causing them to rotate. Viscous coupling between water molecules converts this rotational energy into thermal energy, thereby heating the food. Decreasing the wavelength to the long- wave infrared regime, the molecules and their component atoms resonantly absorb the energy in well-defined excitation bands. This is mainly a vibrational energy absorption process. In the near-visible region of the spectrum, the main part of the absorption is due to higher frequency coupling to the vibrational modes. In the visible region, the principal absorption mechanism is excitation of the electrons that couple the atoms to form the molecules. These interactions are easily discerned in the visible band of the spectra, where they are identified as "color" absorptions. Finally, in the ultraviolet, the wavelength is short enough, and the energy of the radiation is sufficient to actually remove the electrons from their component atoms, thereby creating ionized states and breaking chemical bonds. This short wavelength, while it finds uses in sterilization techniques, probably has little use in foodstuff heating, because it promotes adverse chemical reactions and destroys food molecules. Lightwave ovens are capable of cooking and baking food products in times much shorter than conventional ovens. This cooking speed is attributable to the range of wavelengths and power levels that are used.

There is no precise definition for the visible, near visible and infrared ranges of wavelengths because the perceptive ranges of each human eye is different. Scientific definitions of the "visible" light range, however, typically encompass the range of about 0.39 μm to 0.77 μm. The term "near- visible" has been coined for radiation that has wavelengths longer than the visible range, but less than the water absorption cut-off at about 1.35 μm. The term "infrared" refers to wavelengths greater than about 1.35 μm.

For the purposes of this disclosure, the visible region includes wavelengths between about 0.39 μm and 0.77 μm, the near- visible region includes wavelengths between about 0.77 μm and 1.35 μm, and the infrared region includes wavelengths greater than about 1.35 μm Typically, wavelengths in the visible range (.39 to .77 μm) and the near-visible range (.77 to 1.35 μm) have fairly deep penetration in most foodstuffs. This range of deep penetration is mainly governed by the absorption properties of water. The characteristic penetration distance for water varies from about 50 meters in the visible to less than about 1 mm at 1.35 μm. Several other factors modify this basic absorption penetration. In the visible region electronic absorption of the food molecules reduces the penetration distance substantially, while scattering in the food product can be a strong factor throughout the region of deep penetration. Measurements show that the typical average penetration distances for light in the visible and near-visible region of the spectrum varies from 2-4 mm for meats to as deep as 10 mm in some baked goods and liquids like non-fat milk.

The region of deep penetration allows the radiant power density that impinges on the food to be increased, because the energy is deposited in a fairly thick region near the surface of the food, and the energy is essentially deposited in a large volume, so that the temperature of the food at the surface does not increase rapidly. Consequently the radiation in the visible and near-visible regions does not contribute greatly to the exterior surface browning.

In the region above 1.35 μm (infrared region), the penetration distance decreases substantially to fractions of a millimeter, and for certain absorption peaks down to 0.001 mm. The power in this region is absorbed in such a small depth that the temperature rises rapidly, driving the water out and forming a crust. With no water to evaporate and cool the surface the temperature can climb quickly to 300° F. This is the approximate temperature where the set of browning reactions (Maillard reactions) are initiated. As the temperature is rapidly pushed even higher to above 400° F the point is reached where the surface starts to burn.

It is the balance between the deep penetration wavelengths (.39 to 1.35 μm) and the shallow penetration wavelengths (1.35 μm and greater) that allows the power density at the surface of the food to be increased in the lightwave oven, to cook the food rapidly with the shorter wavelengths and to brown the food with the longer infrared so that a high-quality product is produced. Conventional ovens do not have the shorter wavelength components of radiant energy. The resulting shallower penetration means that increasing the radiant power in such an oven only heats the food surface faster, prematurely browning the food before its interior gets hot.

It should be noted that the penetration depth is not uniform across the deeply penetrating region of the spectrum. Even though water shows a very deep penetration for visible radiation, i.e. , many meters, the electronic absorptions of the food macromolecules generally increase in the visible region. The added effect of scattering near the blue end (.39 μm) of the visible region reduces the penetration even further. However, there is little real loss in the overall average penetration because very little energy resides in the blue end of the blackbody spectrum.

Conventional ovens operate with radiant power densities as high as about 0.3 W/cm² (i.e. at 400 °F). The cooking speeds of conventional ovens cannot be appreciably increased simply by increasing the cooking temperature, because increased cooking temperatures drive water off the food surface and cause browning and searing of the food surface before the food's interior has been brought up to the proper temperature. In contrast, lightwave ovens have been operated from approximately 0.8 to 5 W/cm² of visible, near-visible and infrared radiation, which results in greatly enhanced cooking speeds. The lightwave oven energy penetrates deeper into the food than the radiant energy of a conventional oven, thus cooking the food interior faster. Therefore, higher power densities can be used in a lightwave oven to cook food faster with excellent quality. For example, at about 0.7 to 1.3 W/cm², the following cooking speeds have been obtained using a lightwave oven:

Food Cook Time pizza 4 minutes steaks 4 minutes biscuits 7 minutes cookies 11 minutes vegetables (asparagus) 4 minutes For high-quality cooking and baking, applicants have found that a good balance ratio between the deeply penetrating and the surface heating portions of the impinging radiant energy is about 50:50, i.e. , Power(.39 to 1.35μm)/Power(1.35μm and greater) ~ 1. Ratios higher than this value can be used, and are useful in cooking especially thick food items, but radiation sources with these high ratios are difficult and expensive to obtain. Fast cooking can be accomplished with a ratio substantially below 1 , and it has been shown that enhanced cooking and baking can be achieved with ratios down to about 0.5 for most foods, and lower for thin foods, e.g., pizza and foods with a large portion of water, e.g., meats. Generally the surface power densities must be decreased with decreasing power ratio so that the slower speed of heat conduction can heat the interior of the food before the outside burns. It should be remembered that it is generally the burning of the outside surface that sets the bounds for maximum power density that can be used for cooking. If the power ratio is reduced below about 0.1, the power densities that can be used are comparable with conventional cooking and no speed advantage results.

If blackbody sources are used to supply the radiant power, the power ratio can be translated into effective color temperatures, peak intensities, and visible component percentages. For example, to obtain a power ratio of about 1 , it can be calculated that the corresponding blackbody would have a temperature of 3000°K, with a peak intensity at .966 μm and with 12% of the radiation in the full visible range of .39 to .77 μm. Tungsten halogen quartz bulbs have spectral characteristics that follow the blackbody radiation curves fairly closely. Commercially available tungsten halogen bulbs have successfully been used with color temperatures as high as 3400 °K. Unfortunately, the lifetime of such sources falls dramatically at high color temperatures (at temperatures above 3200 °K it is generally less that 100 hours). It has been determined that a good compromise in bulb lifetime and cooking speed can be obtained for tungsten halogen bulbs operated at about

2900-3000 °K. As the color temperature of the bulb is reduced and more shallow-penetrating infrared is produced, the cooking and baking speeds are diminished for quality product. For most foods there is a discernible speed advantage down to about 2500° K (peak at about 1.2 μm; visible component of about 5.5%) and for some foods there is an advantage at even lower color temperatures. In the region of 2100 °K the speed advantage vanishes for virtually all foods that have been tried.

Some lightwave ovens are rectangular-shaped ovens using polished, high-purity aluminum reflective walls. It has been determined that about 4 kilowatts of lamp power is necessary for a lightwave oven of this type to have a reasonable cooking speed advantage over a conventional oven. Four kilowatts of lamp power can operate four commercially available tungsten halogen lamps, at a color temperature of about 3000°K, to produce a power density of about 0.6-1.0 W/cm² inside the oven cavity. This power density has been considered near the minimum value necessary for the lightwave oven to clearly outperform a conventional oven. Such ovens may be utilized as commercial ovens in restaurants or they may be used in homes as replacements for the conventional wall-mounted ovens or range ovens found in every kitchen.

A high efficiency lightwave oven has also been developed. Such an oven can be utilized as a kitchen counter-top lightwave oven and can be operated using a standard 120 VAC electrical outlet. This high efficiency lightwave oven can achieve a uniform time-average power density of about 0.7 W/cm² in a lightwave oven cavity using only two 1.0 KW, 120 VAC tungsten halogen quartz bulbs consuming about 1.8 KW of power at any one time and operating at a color temperature of about 2900 °K. The dramatic increase in power density is attained by making a relatively small change in the reflectivity of the oven wall materials, and by changing the geometry of the oven to provide a novel reflecting cavity. Uniform cooking of foodstuffs is achieved by using novel reflectors adjacent to the lamps. As discussed, lightwave ovens are highly beneficial in that they cook food to high levels of quality in cooking times that are much shorter than those required for conventional cooking ovens. However, it is desirable to provide the lightwave oven user with the option of cooking foods in the lightwave ovens using conventional recipes. In other words, users may wish to program the lightwave oven for the standard cooking times and cooking temperatures called for in their traditional recipes, and to have the food cooked in the standard cooking time. It is desirable to provide this capability in the lightwave oven in a manner which allows the cooked food to have the same attributes, i.e., color, texture, amount of rise, browning, and flavor, that it would have had it been cooked in a conventional thermal oven. It is further desirable to provide such a lightwave oven and cooking mode which, as with other lightwave cooking modes, requires no preheat time and maintains low oven air temperatures throughout the cooking cycle. Because lightwave oven technology is relatively new, even users desiring to use their lightwave ovens in the fast lightwave cooking mode may be required to use trial and error to determine how best to cook foods that have traditionally been cooked in a conventional oven. Thus, it is also desirable to provide a lightwave cooking oven and method which provides an easy conversion from cooking recipes for conventional ovens to cooking recipes in a lightwave oven.

Summary of the Invention

The present invention is a lightwave oven and cooking method which allows a user to use conventional oven recipes in a lightwave cooking oven.

In accordance with the described method, a food item is receied in the oven cavity and user instructions are received from a user. The user instructions specify at least one conventional cooking parameter (e.g. oven temperature and/or cook time) representing a cooking parameter for cooking the food item in a conventional oven.

The oven determines at least one lightwave cooking parameter (e.g. lightwave cooking time, lamp intensity etc.) using the at least one conventional cooking parameter, and controls the oven's lightwave cooking lamp to cook the food item using the at least one lightwave cooking parameter.

Brief Description of the Drawings

Fig. 1 is a front elevation view of a lightwave oven suitable for practicing the method according to the present invention.

Fig. 2 is a cross-sectional bottom view of the lightwave oven of Fig. 1 , showing the lower interior surface of the oven.

Fig. 3 is a cross-sectional top view of the lightwave oven of Fig. 1, showing the upper interior surface of the oven.

Fig. 4 is a cross-sectional front view of the lightwave oven of Fig. 1, taken along the plane designated 4-4 in Fig. 2. Fig. 5 is a graph showing lightwave cooking power ramps for the autopulse cooking mode. Fig. 6 A is a top cross-sectional view of a lightwave oven. Fig. 6B is a front view of the lightwave oven of Fig. 6A. Fig. 6C is a side cross-sectional view of the lightwave oven of Fig.

6A. Fig. 7 A is a bottom view of the upper reflector assembly of the oven of Fig. 6A.

Fig. 7B is a side cross-sectional view of the upper reflector assembly. Fig. 7C is a partial bottom view of the upper reflector assembly illustrating the virtual images of one of the lamps. Fig. 8 A is a top view of the lower reflector assembly of the oven of

Fig. 6A.

Fig. 8B is a side cross-sectional view of the lower reflector assembly. Fig. 8C is a partial top view of the lower reflector assembly illustrating the virtual images of one of the lamps. Fig. 9 A is a graph showing the sequential lamp activation times for the cook mode of operation.

Fig. 9B is a graph showing the sequential lamp activation times for the crisp mode of operation.

Fig. 9C is a graph showing the sequential lamp activation times for the grill mode of operation.

Fig. 10 is a graph showing the sequential lamp activation times for the cook mode of operation with a reduced oven intensity.

Fig. 11A is a graph showing the sequential lamp activation times for the cook mode of operation with a reduced oven intensity of 90% . Fig. 1 IB is a graph showing the sequential lamp activation times for the cook mode of operation with a reduced oven intensity of 80%.

Fig. 11C is a graph showing the sequential lamp activation times for the cook mode of operation with a reduced oven intensity of 70% .

Fig. 1 ID is a graph showing the sequential lamp activation times for the cook mode of operation with a reduced oven intensity of 60% . Fig. HE is a graph showing the sequential lamp activation times for the cook mode of operation with a reduced oven intensity of 50% .

Fig. 12 is a graph showing the sequential lamp activation times for the bake mode of operation.

Fig. 13 is a cross-sectional side view showing a configuration of the pan sensor useable in connection with the present invention.

Detailed Description According to one aspect of the invention, the lightwave oven operates in a "thermal emulation mode" to cook the food in the same amount of time as would a conventional thermal oven and to cook the food to the same level of quality as would be attained in the conventional thermal oven. The method includes placing the food in a lightwave oven and cooking the food at the conventional cooking time by operating the lightwave cooking lamps at reduced power. There is no requirement for preheating the oven and the oven air temperature does not exceed approximately 180° F even though the cooking effects achieved by operating a thermal oven at 325° - 475 °F are being simulated. Likewise, the oven wall temperatures stay relatively cool, and remain well below the corresponding thermal oven temperature.

Conventional ovens typically cook using calrod elements positioned in the oven cavity. These calrod elements cook at a color temperature of on the order of approximately 1050° - 1250°K, which corresponds to a radiation peak of approximately 2.8 - 2.3 μm. Before food is placed in a conventional oven, the oven is pre-heated to the desired cooking temperature (e.g. 350°F) in order to heat the oven walls and the air in the oven cavity to that temperature. Once the food is placed in the oven, cooking is accomplished using two principal energy transfer methods: convective hot air and direct radiation of heat from the calrod elements and hot oven walls onto the surface of the food. Both of these mechanisms transfer heat only to the surface of the food, and thermal conduction carries this heat into the deeper regions of the food.

To emulate the shallow surface heating effects utilized in conventional ovens, the method of the present invention operates the lamps in a lightwave oven at reduced power (approximately 4 - 40% of maximum power, depending on the oven, the cookware reflectivity, and the recipe). This shifts the radiation peak out to approximately 2.0 to 1.2 μm (corresponding to a color temperature of approximately 1400° to 2450° K) and thus limits the penetration of the radiant energy into the food. This low-penetration radiation undergoes multiple reflections from the reflective oven walls, and the resulting uniform bath of radiant energy onto the food heats the surface regions of the food and permits conduction of heat into the interior regions of the food.

According to another aspect of the invention, the oven translates a conventional recipe to a lightwave recipe and cooks the food using lamp intensities and cooking times that are typical of lightwave cooking. The oven includes a recipe translator that receives as user input the conventional cooking temperature, conventional cooking time, and the food type, and converts the user-input time and temperature into a corresponding lightwave cooking program that will cook the food in a period of time that is much shorter than the conventional cooking time. As with the thermal emulation mode, no oven pre-heat time is required for the lightwave cooking mode.

The "thermal emulation mode" and "recipe translator" for cooking using conventional recipes in lightwave ovens will be described herein with respect to lightwave oven of the types 100, 201 shown in Figs. 1 through 8C. It should be appreciated, however, that these modes may be practiced using a variety of types of lightwave ovens.

The lightwave oven 100 of Figs. 1-4 includes a rectangular housing 2, a door 4, a control panel 6, a power supply 7, an oven cavity 8, and a controller 9. Referring to Fig. 1, control panel 6 is connected to controller 9. The control panel contains several operation keys 16 for controlling the lightwave oven and a display 18 indicating such information as the user input, mode of operation, remaining cook time, etc.

Referring to Fig. 2, the oven cavity 8 includes interior sidewalls 10, rear wall 11, top wall 12 (Fig. 3), and bottom wall 14. The door 4 forms a front wall and is moveable between opened and closed positions.

A turntable 20 (shown in dashed lines in Fig. 2 to permit viewing of the underlying components) is mounted on a centrally located pedestal 21 extending from the bottom wall 14. Pedestal 21 is coupled to a motor 23 positioned beneath the wall 14, which causes rotation of the turntable 20 during use. The turntable 20 is preferably detachable to provide the user with turntables of differing reflectivities depending on the cooking application. For example, for thermal emulation mode without cookware compensation, the turntable is a black or other dark color pan which supports the food in the user's selected cookware during thermal emulation mode cooking. The turntable may alternatively be a radiation transparent glass or glass-ceramic pan which likewise supports the user's cookware when the oven is operated in a lightwave cooking mode and/or in thermal emulation mode using cookware reflectivity compensation. A turntable in the form of a wire grill may also be provided for certain cooking applications including cooking in a lightwave mode.

A lower reflector/lamp assembly 24 is mounted within the bottom wall 14. A pair of 1000 W lamps 28 are mounted within the assembly 24 and extend towards the side walls 10. Each lamp 28 has an overall length of approximately 7.5 inches. The lamps 28 are offset from the centrally positioned turntable 20 towards one side of the oven. This asymmetrical positioning of the lamps promotes uniform illumination of the food's surface (or the dark color turntable) during rotation of the turntable 20.

Fig. 3 shows the oven top wall 12. An upper reflector/lamp assembly 22 is mounted within the top wall 12, off to one side. A pair of

2300 W lamps 26 are mounted within the assembly 22 and extend towards the door 4 and back wall 11. These lamps have an overall length of approximately 13 inches. As with the lower lamps 28 , upper lamps 26 are asymmetrically disposed within the oven to promote uniform illumination of the food surface during rotation of the turntable 20. Upper and lower lamps 26, 28 are generally any of the quartz body, tungsten-halogen or high intensity discharge lamps that are commercially available. The lamps utilized in the lightwave oven described herein cook with approximately fifty percent (50%) of the energy in the visible and near- visible light portion of the spectrum when operated at full lamp power. Behind each lamp is a reflector 25 (shown behind upper lamps 26 in

Fig. 4) configured to optimize reflection of radiant energy into the oven cavity and, in particular, onto the surface of the food or the dark turntable when used. The reflectors may be configured to have one of many different types of geometries that will achieve this objective. For example, they may be parabolic or formed from a plurality of facets facing the interior of the oven.

Each lamp is mounted between a pair of electrodes (not shown). Power supply 7 is connected to the electrodes to operate, under the control of controller 9, each of the lamps 26, 28 simultaneously and/or individually. Referring to Fig. 4, to keep foods from splattering cooking juices onto the lamps and reflectors, transparent upper and lower shields 70 and 72 cover the upper/lower lamp/reflector assemblies 22/24 respectively. Shields 70/72 are plates made of a glass or a glass-ceramic material that has a very small thermal expansion coefficient. Glass-ceramic materials available under the trademarks Pyroceram, Neoceram and Robax, and the borosilicate available under the name Pyrex, have been successfully used. These lamp shields isolate the lamps and reflecting surfaces so that drips, food splatters and food spills do not affect operation of the oven, and they are easily cleaned since each shield 70/72 consists of a single, plate of glass or glass- ceramic material. It has been found that modest increases in the reflectivity of the oven walls leads to substantial increases in oven efficiency. In the lightwave oven described herein, the walls 10, 11, 12, 14, door inner surface 76 and reflectors 25 may be formed of polished, high-purity aluminum (such as the German brand Alanod having a reflectivity of about 90% (averaged in the wavelength range of interest from a 3000 °K quartz tungsten-halogen lamp) and good heat resistance properties.

Other highly reflective materials may also be used. For example, the oven walls may be formed of a highly reflective porcelain material which has a reflectivity of about 87% over the range of interest. Alternatively, a highly reflective material made from a thin layer of high reflecting silver sandwiched between two plastic layers and bonded to a metal sheet, having a total reflectivity of about 95% . Such a highly-reflective material is available from Alcoa under the tradename EverBrite 95, or from Material Science Corporation under the tradename Specular + SR. While the reflectivity is the way the metal surfaces are specified, a more important parameter is the absorption (which equals 100% - reflectivity), since this relates directly to the loss of radiation that strikes the walls. By increasing the reflectivity by about 5 % over highly polished aluminum, the wall absorption has dropped from 10% to 5%, which is a factor of two. This means that there can be about double the number of reflections with the same total energy losses, so that there is a much greater probability of the food intercepting a multi- bounced light ray.

A window 78 is formed in the door 4 for viewing foods while they cook. The window 78 may be formed by bonding two plastic layers surrounding a reflecting silver layer to a transparent substrate such as plastic or glass (preferably tempered). It has been discovered that the amount of light that leaks through the reflective material used to form the interior of the oven is ideal for safely and comfortably monitoring the interior of the oven cavity while food cooks. Alternately, one could make the window 78 of two borosilicate (Pyrex) glass plates (about 3 mm thick), with the inner surfaces facing each other each being coated with a thin aluminum film having an approximate 600 angstrom thickness. The window 78 ideally should transmit about 0.1 % of the incident light from the cavity 8, so that the user can safely view the food while it cooks. Water vapor management, water condensation and airflow control in the cavity 8 can significantly affect the cooking of the food inside the oven. It has been found that the cooking properties of the oven (i.e., the rate of heat rise in the food and the rate of browning during cooking) is strongly influenced by the water vapor in the air, the condensed water on the cavity sides, and the flow of hot air in the cylindrical chamber. Increased water vapor has been shown to retard the browning process and to negatively affect the oven efficiency. Therefore, the oven cavity 8 need not be sealed completely, to let moisture escape from cavity 8 by natural convection. Moisture removal from cavity 8 can be enhanced through forced convention. A fan 80 (Fig. 2), which can be controlled as part of the cooking formula, provides a source of fresh air that is delivered to the cavity 8 to optimize the cooking performance of the oven.

Fan 80 also provides fresh cool air that is used to cool the high reflectance internal surfaces of the oven cavity 8. The cooling air flows into the oven through intake vents 82 on the front of the oven (Fig. 1), and out of the oven via exhaust port 92 (Fig. 2) located at the rear of the oven housing. The airflow from fan 80 can further be used to cool the oven power supply 7 and controller 9.

The oven 100 will be primarily used to cook food in lightwave mode, which uses fast lightwave cooking technology. One lightwave mode of cooking using the above-described oven is called the autopulse mode and is one which allows a large variety of food types to be cooked using a common mode of operation.

During use of the autopulse mode, all upper and lower lamps may be pulsed on and off simultaneously, making it a particularly suitable mode for higher power, 240V, lightwave ovens such as the one described herein. The duty cycle of the lamps is varied according to a predetermined function of time to decrease the percentage of time that the lamps 26, 28 are on.

During use of the autopulse mode, the user selects beginning and ending power settings for the oven. For example, the user may enter a starting power of 75% (corresponding to 75% "on" time for the lamps at full power) and an ending power of 25% (i.e., 25% "on" time at full power). Once the cooking cycle is initiated, the oven controller ramps the duty cycle according to an embedded algorithm, which varies depending upon the design of the lightwave oven. For example, for the oven 100, the ramp may follow the modified cosine function shown in Fig. 5. In other ovens such as the high efficiency lightwave oven mentioned above, the power ramp may be approximately linear. In all cases, when the lamps are "on" they are on at full power in order to utilize the maximum color temperature afforded by the lamps. A decrease in power to the food is achieved by decreasing the duty cycle of the lamps. Ramping down the power in this way allows higher power to be applied to the food at a time when both the food and the oven are cold and can accept energy at higher rates. The power is decreased as the food heats up and the surface of the food dries out and thus cannot accept energy at high rates without burning the surface of the food.

A second, high efficiency cylindrically shaped oven 201 is illustrated in Figs. 6A-6C. Oven 201 is ideal for connection to a standard 120 VAC kitchen outlet, which can cook using different modes of lamp operation to effect cooking, crisping, grilling, defrosting, warming and baking of foodstuffs. A brief description of the oven 201 will follow. More extensive details may be found in PCT/US98/ 18472, entitled LIGHTWAVE OVEN AND METHOD OF COOKING THEREWITH HAVING MULTIPLE COOK MODES AND SEQUENTIAL LAMP OPERATION, International Filing Date September 4, 1998, which is incorporated herein by reference for all purposes. The lightwave oven 201 includes a housing 202, a door 204, a control panel 206, a power supply 207, an oven cavity 208, and a controller 209.

The housing 202 includes sidewalls 210, top wall 212, and bottom wall 214. The door 204 is rotatably attached to one of the sidewalls 210 by hinges 215. Control panel 206, located above the door 204 and connected to controller 209, contains several operation keys 216 for controlling the lightwave oven 201, and a display 218 indicating the oven's mode of operation. The oven cavity 208 is defined by a cylindrical-shaped sidewall 220, an upper reflector assembly 222 at an upper end 226 of sidewall 220, and a lower reflector assembly 224 at the lower end 228 of sidewall 220.

Upper reflector assembly 222 is illustrated in Figs. 7A-7C and includes a circular, non-planar reflecting surface 230 facing the oven cavity 208, a center electrode 232 disposed at the center of the reflecting surface

230, four outer electrodes 234 evenly disposed at the perimeter of the reflecting surface 230, and four upper lamps 236, 237, 238, 239 each radially extending from the center electrode to one of the outer electrodes 234 and positioned at 90 degrees to the two adjacent lamps. The reflecting surface 230 includes a pair of linear channels 240 and 242 that cross each other at the center of the reflecting surface 230 at an angle of 90 degrees to each other. The lamps 236-239 are disposed inside of or directly over channels 240/242. The channels 240/242 each have a bottom reflecting wall 244 and a pair of opposing planar reflecting sidewalls 246 extending parallel to axis of the corresponding lamp 236-239. (Note that for bottom reflecting wall 244, "bottom" relates to its relative position with respect to channels 240/242 in their abstract, even though when installed wall 244 is above sidewalls 246.) Opposing sidewalls 246 of each channel 240/242 slope away from each other as they extend away from the bottom wall 244, forming an approximate angle of 45 degrees to the plane of the upper cylinder end 226. Lower reflector assembly 224 illustrated in Figs. 8A-8C has a similar construction as upper reflector 222, with a circular, non-planar reflecting surface 250 facing the oven cavity 208, a center electrode 252 disposed at the center the reflecting surface 250, four outer electrodes 254 evenly disposed at the perimeter of the reflecting surface 250, and four lower lamps

256, 257, 258, 259 each radially extending from the center electrode to one of the outer electrodes 254 and positioned at 90 degrees to the two adjacent lamps. The reflecting surface 250 includes a pair of linear channels 260 and 262 that cross each other at the center of the reflecting surface 250 at an angle of 90 degrees to each other. The lamps 256-259 are disposed inside of or directly over channels 260/262. The channels 260/262 each have a bottom reflecting wall 264 and a pair of opposing planar reflecting sidewalls 266 extending parallel to axis of the corresponding lamp 256-259. Opposing sidewalls 266 of each channel 260/262 slope away from each other as they extend away from the bottom wall 264, forming an approximate angle of 45 degrees to the plane of the lower cylinder end 228.

Power supply 207 is connected to electrodes 232, 234, 252 and 254 to operate, under the control of controller 209, each of the lamps 236-239 and 256-259 individually. Fan 280 provides fresh cool air that is used to cool the high reflectance internal surfaces of the oven cavity 208.

To keep foods from splattering cooking juices onto the lamps and reflecting surfaces 230/250, transparent upper and lower shields 270 and 272 are placed at the cylinder ends 226/228 covering the upper/lower reflector assemblies 222/224 respectively. Upper and lower lamps 236-239 and 256-259 are generally any of the quartz body, tungsten-halogen or high intensity discharge lamps commercially available, e.g., 1 KW 120 VAC quartz-halogen lamps. The oven according to the preferred embodiment utilizes eight tungsten-halogen quartz lamps, which are about 7 to 7.5 inches long and cook with approximately fifty percent (50%) of the energy in the visible and near- visible light portion of the spectrum at full lamp power. Door 204 has a cylindrically shaped interior surface 276 that, when the door is closed, maintains the cylindrical shape of the oven cavity 208. A window 278 is formed in the door 204 (and surface 276) for viewing foods while they cook. Window 278 is preferably curved to maintain the cylindrical shape of the oven cavity 208.

In the oven 1, the inner surface of cylinder sidewall 20, door inner surface 76 and reflective surfaces 30 and 50 are formed of a highly reflective material made from a thin layer of high reflecting silver sandwiched between two plastic layers and bonded to a metal sheet, having a total reflectivity of about 95%. Such a highly-reflective material is available from Alcoa under the tradename EverBrite 95 , or from Material Science Corporation under the tradename Specular + SR.

While all eight lamps could operate simultaneously at full power if adequate electrical power were available, the lightwave oven 201 has been specifically designed to operate as a counter-top oven that plugs into a standard 120 VAC outlet. A typical home kitchen outlet can only supply 15 amps of electrical current, which corresponds to about 1.8 KW of power. This amount of power is sufficient to only operate two commercially available 1 KW tungsten halogen lamps at color temperatures of about 2900°K. Operating additional lamps all at significantly lower color temperatures is not an option because the lower color temperatures do not produce sufficient amounts of visible and near-visible light. However, by sequential lamp operation as described below and illustrated in Figures 9A- 9C, different selected lamps from above and below the food can be sequentially switched on and off at different times to provide a uniform time- averaged power density of about 0.7 W/cm² without having more than two lamps operating at any given time. This power density cooks food about twice as fast as a conventional oven.

For example, one lamp above and one lamp below the cooking region can be turned on for a period of time (e.g. 2 seconds). Then, they are turned off and two other lamps are turned on for 2 seconds, and so on. By sequentially operating the lamps in this manner, a cooking region far too large to be evenly illuminated by only two lamps is in fact evenly illuminated when averaged over time using eight lamps with no more than two activated at once. Further, some lamps may be skipped or have operation times reduced to provide different amounts of energy to different portions of the food surface.

A first mode of sequential lamp operation (cook mode) for evenly cooking all sides of the food is illustrated in Fig. 9A. In cook mode, one upper lamp 236 and one lower lamp 258 are initially turned on, so that the total operating power does not exceed twice the operating power of each of the lamps. These lamps 236/258 are maintained on for a given period of time, such as two seconds, and then are turned off (for about 6 seconds). At the time lamps 236/258 are turned off, a different upper lamp 237 and a different lower lamp 259 are turned on. These lamps 237/259 are maintained on for two seconds and are then turned off at the same time the upper lamp 238 and lower lamp 256 are turned on, to be followed in sequence by upper lamp 239 and lower lamp 257. This cook mode sequential lamp operation continues repeatedly which provides time-averaged umform cooking of the food in the oven chamber 208 without drawing more than the power needed to operate two lamps simultaneously. Preferably, the upper lamp in operation is on the opposite side of the reflector assembly 222 than the corresponding side of reflector assembly 24 containing the lower lamp in operation. Therefore, lamp operation above the food rotates among the four upper lamps 236-239 in the same direction around the cavity as the rotation of lamp operation below the food among the four lower lamps 256-

259.

A second mode of sequential lamp operation (crisp mode) for cooking and browning mainly the top side of the food is illustrated in Fig. 9B. In crisp mode, each upper lamp 236-239 is turned on for four seconds, then turned off for four seconds, with the operation of these lamps staggered so that only two lamps are on at any given time. Lower lamps 256-259 are not activated. For example, two upper lamps 236/239 are initially turned on, so that the total operating power does not exceed twice the operating power of each of the lamps. These upper lamps 236/239 are maintained on for a given period of time, such as two seconds, and then one of the lamps 239 is turned off, and another upper lamp 237 is turned on. Two seconds later, upper lamp 236 is turned off, and upper lamp 238 is turned on. Two seconds later, upper lamp 237 is turned off and upper lamp 239 is turned on. This crisp mode sequential lamp operation continues repeatedly which provides time-averaged uniform irradiation of mainly the top surface of the food in the oven chamber 208 without drawing more than the power needed to operate two lamps simultaneously.

A cook mode formula has also been developed based upon the discovery that for many foods, such as meats and pizza, the final cooked foodstuff quality is improved if a cooking sequence using cook mode is concluded in the crisp mode. The added browning effect improves most foods cooked in cook mode, while other foods that do not need any extra browning are not adversely affected. The cook mode formula simply calls for the cooking mode to be switched from cook mode to crisp mode for the last few minutes of the cooking sequence. The actual time t_c that the cook mode is converted to the crisp mode varies depending on the overall cook time T of the cooking sequence, as illustrated below:

For T = under 10 minutes, t_c should be 2 minutes. For T = 10-20 minutes, t_c should be 4 minutes. For T = 20-30 minutes, t_c should be 6 minutes.

For T = 30-60 minutes, t_c should be 8 minutes. For T = greater than 60 minutes, t_c should be 10 minutes. Therefore, as an example, a foodstuff that normally cooks well in cook mode in 40 minutes, will cook better by being cooked in cook mode for 32 minutes followed by the crisp mode for 8 minutes. It should be noted that the cook mode formula also varies depending upon higher/lower maximum power densities, cavity size, overall oven cavity reflectivity, oven cavity wall materials, and the type and color temperature of the lamps used.

A third mode of sequential lamp operation (grill mode) for cooking and browning mainly the bottom side of the food such as pizzas and for searing and grilling meats is illustrated in Fig. 9C, and is identical to the crisp mode except just the bottom lamps 256-259 are operated instead of just the top lamps 236-239. In grill mode, each lower lamp 256-259 is turned on for four seconds, then turned off for four seconds, with the operation of these lamps staggered so that only two lamps are on at any given time. For example, two lower lamps 256/259 are initially turned on, so that the total operating power does not exceed twice the operating power of each of the lamps. These lower lamps 256/259 are maintained on for a given period of time, such as two seconds, and then one of the lamps 259 is turned off, and another lower lamp 257 is turned on. Two seconds later, lower lamp 256 is turned off, and lower lamp 258 is turned on. Two seconds later, lower lamp 257 is turned off and lower lamp 259 is turned on. This grill mode sequential lamp operation continues repeatedly which provides time-averaged uniform irradiation of mainly the bottom surface of the food in the oven chamber 208 without drawing more than the power needed to operate two lamps simultaneously.

Often this grill mode of operation is used in conjunction with a special broiler pan to improve the grilling of meats and fish. This pan has a series of formed linear ridges on its upper surface which supports and elevates the food. The valleys between the ridges serve to catch the grease from the grilling process so that the food is separated from its drippings for better browning. The entire pan heats up quickly from the bottom radiant energy in the grill mode, and this heat sears the surface of the food that is in contact with the ridges, leaving browned grill marks on the food surface. The surface of the pan is coated with a non-stick material to make cleaning easier. Visible and near- visible radiation from the bottom lamps can also bounce from the sidewall 220 and upper reflecting surface 230 to strike the food from the top and sides. This additional energy aids in the cooking of the top portion of the food.

A fourth mode of operation is the warming mode, where all lamps 236-239 and 256-259 are all operated simultaneously, not sequentially, at low power (e.g. 20% of full power) so that the total power of all eight operating lamps does not exceed the full power operation of two of the lamps (i.e. about 1.8 KW). With lamps operating at such a low power, and therefore a low color temperamre, most of the radiation emitted by the lamps in warming mode is infrared radiation, which is ideal for keeping food warm

(at a stable temperature) without further cooking it.

It should be noted that the operating times of 2 seconds in cook mode or 4 seconds in grill or crisp modes for each lamp described above are illustrative, and can be lower or higher as desired. However, if the lamp operating time is set too low, efficiency will be lost because the finite time needed to bring the lamps up to operating color temperamre causes the average lamp output spectrum to shift undesirably toward the red end of the spectrum. If the lamp operating time is too long, uneven cooking will result. It has been determined that a lamp operating time of up to at least 15 seconds provides excellent efficiency without causing significant uneven cooking.

In the cook mode described above, an average cooking power density of about 0.7 W/cm² is generated in the oven cavity 208 by two lamps operating at full power (100% oven intensity). However, it is anticipated that some cooking recipes will require the oven intensity to be reduced below

100% for some or all of the cooking time. Reducing power to the lamps reduces the color temperamre of the lamps, and thus the percentage of the visible and near-visible light emitted by the lamps. Therefore, instead of individual lamp power reduction that affects the lamp output spectrum, the oven 201 includes the feature of reducing the overall oven duty cycle (reducing the average power level from one or both lamp sets) without adversely affecting the spectral output of the lamps.

The duty cycle reduction feature for reducing the (time) average power level of the upper lamps and the lower lamps is illustrated in Fig. 10 in the cook mode, however this feature is usable with any set of lamps in any mode of oven operation. The feature reduces the oven intensity by adding a time delay ΔT between the shut down of one lamp and the turn on of the next consecutive lamp so that the lamps still operate at full power but operate with a reduced overall duty cycle. For example, the first upper/lower lamps 236/256 are turned on for 2 seconds and then off, and a time delay period ΔT, such as 0.2 seconds, passes before the second upper/lower lamps 37/57 are turned on for two seconds and then off, and another 0.2 seconds pass before the third upper/lower lamps 238/258 are turned on, and so on with the fourth upper/lower lamps 239/259, for one or more cycles. In the above example, with the lamps operated for 2 seconds, separated by a time delay ΔT of 0.2 seconds, the overall time-average oven intensity (duty cycle) is about 91% of the full oven power intensity (duty cycle).

It is advantageous to have at least one of the lamps in the oven on at all times so the user can continuously view the cooking food. Therefore, the on/off cycles of the upper set of lamps 236-239 and lower set of lamps 256- 259 can be staggered so that at least one lamp is on at all times for overall duty cycles as low as 50% . Figures 11A-11E illustrate 90%, 80%, 70%, 60% and 50% time-average oven intensity (reduced duty cycle) operation in cook mode respectively, which correspond to ΔT values of 0.22, 0.50,

0.86, 1.33 and 2.0 minutes, respectively. The upper lamp cycle is shown staggered to the lower lamp cycle so that the cavity is continuously illuminated. The time delay ΔT can be different for the upper lamps 236- 239 relative to the lower lamps 256-259. Thus, upper lamps 236-239 can operate at one time-average intensity (e.g. 80%) while lower lamps 256-259 can operate at a different time-average intensity (e.g. 60%). Thus, each lamp is operated at fully power, but by reducing the duty cycle as described above, the average power level of each lamp set can be reduced without adversely affecting the lamp spectrum.

A fifth mode of lamp operation is the defrost mode, which heats food without cooking. The defrost mode is the cook mode with a highly reduced oven intensity (duty cycle). For the present described oven, operating the oven at about 30% of full oven intensity (30% duty cycle) defrosts most foods with little or no cooking effect. Intermittent full lamp power is necessary to penetrate the food interior with visible light. However, full lamp power for an extended period of time will start cooking portions of the food.

A sixth mode of lamp operation is the bake mode, illustrated in Fig. 12. Baking of foods that have to rise as well as brown (e.g. pies, breads, cookies, cakes) requires that the food interior sufficiently cooks (reaches a certain peak temperamre) and the food surface sufficiently browns. The method of baking in a conventional oven includes selecting an oven temperamre and a bake time so that the food interior peak temperamre and the ideal surface browning are achieved simultaneously at the end of the bake time. Thus, the cooking of the food interior and the browning of the food surface occur simultaneously. This baking process cannot be sped up by simply increasing the oven temperamre because that would cause the browning to occur too soon, before the food interior is fully cooked.

Likewise, in the lightwave oven 201 , many foods have to be baked in cook mode using less than the full time-average oven intensity so that the food interior cooking and the food surface browning are completed at about the same time. If the oven power is too high, then water is prematurely driven off of the food surface, and the food surface browns and burns before the food interior can be fully cooked.

The present inventors have developed the bake mode illustrated in Fig. 12 to solve the above mentioned problems. In bake mode, the lightwave oven combines varying cooking intensities in the cook mode with high intensity browning in the crisp mode to bake food. Bake mode essentially cooks the interior of the food first, and browns the food surface mostly at the end of the baking cycle. In bake mode, the oven initially operates at 100% oven intensity for a predetermined time period tj. During this initial time period, very little surface browning occurs because the food starts out cold with plenty of food surface moisture. As the food bakes, lower oven intensities are required to prevent food surface browning (which would prevent visible and near-visible light penetration needed to cook the food's interior). Therefore, after time period t_{ expires, the time-average oven intensity is reduced to 90%, for a time period tj, and then to 80% oven intensity for time period t₃, and then to 70% oven intensity for time period t₄, and then to 60% oven intensity for time period tj, and then to 50% oven intensity for time period tg. The food interior continues to cook at the reduced oven intensities without significant food surface browning. Once the food interior has nearly reached its peak temperamre (fully cooked), high oven intensity (100%) is used for a time period t₇ to brown the food's surface (and finish the interior cooking of the food). Ideally, the cook mode (upper and lower lamps) is used during time intervals t_{ to t^ for even cooking of the food's interior, and crisp mode (upper lamps only) is used during time interval t₇ to brown the food's surface from above. This bake mode operation of the present lightwave oven produces high quality baked goods in much less time than a conventional oven.

Thermal Emulation Mode

The thermal emulation mode allows the user to use a lightwave oven such as oven 100 or oven 201 for conventional recipes using the slower cooking speeds called for by the conventional recipe and available using conventional ovens. In thermal emulation mode, the lamps are operated at a fraction of maximum power (for example, between 800W - 2000W for an oven such as the oven 100 which has a maximum power of 6600 W), and at a reduced color temperamre of approximately 1400° to 2450° K (corresponding to a radiation peak of approximately 2.0 to 1.2 μm).

Table 1 lists power settings which have been developed in order to operate the oven 100, provided with Alanod aluminum walls, in thermal emulation mode. The power settings listed are percentages of maximum power. In other words, "16% " means 16% of full power, with the lamps being continuously "on" rather than being pulsed as in the autopulse mode. For a 2300W lamp, 16% of maximum corresponds to a power of approximately 368 W for that lamp.

TABLE 1:

Thermal Emulation Lamp Power Settings

For Oven 100 Having Alanod Aluminum Walls

The temperatures listed in the left hand column represent the most common oven cooking temperatures (T_C0NV) called for in conventional recipes. Thus, for a recipe calling for a 350 °F oven, the lightwave oven operates the upper lamps at 18% power and the lower lamps at 6% power. It should be noted that the listed power settings have been developed for the oven 100 and may be different for different lightwave ovens, including oven 201. For example, if the porcelain wall surfaces having 87% reflectivity are used in place of the Alanod aluminum wall surfaces, the power settings for the oven 100 are as follows.

TABLE 2:

Thermal Emulation Lamp Power Settings

For Oven 100 Having Porcelain Walls

It is desirable to adjust the power settings listed on the above tables to compensate for the initial thermal load of the food and oven components which can increase the needed power equivalents in recipes having short cooking times, and for the buildup of heat that occurs in the oven walls and other components during long cooking times. Although, as stated, the internal oven air and wall temperamre remains cool relative to the conventional oven temperatures that are emulated in thermal mode, slight heating of the oven's interior components does occur. Radiation of heat from these components onto the food can accelerate the cooking process.

It has been found that these effects can be compensated for by adjusting the powers listed in Tables 1 and 2 in accordance with the following table.

TABLE 3: POWER SETTING MODIFICATIONS BASED ON COOKING TIME

Adjustments to the power settings to the power equivalent settings are made by the system software.

The following three examples illustrate application of the constraints set forth in Table 3 to conventional recipes specifying various cooking times. Assume for the purposes of the examples that the oven 100 has Alanod aluminum walls. Example 1

Conventional Recipe: 14 minute cooking time at 350°F

Thermal Mode Equivalent Settings: Use power settings from Table 1 corresponding to a (350°F + 50°F) = 400°F oven. Lamp powers are thus set to 22% top and 8% bottom for the duration of the cooktime.

Example 2

Conventional Recipe: 30 minutes cooking time at 350°F

Thermal Mode Equivalent Settings: Use power settings which correspond to a 350°F conventional oven temperamre (e.g. 18% top and 6% bottom).

Example 3

Conventional Recipe: 60 minute cooking time at 350° F

Thermal Mode Equivalent Settings: For minutes 0 - 30:00, use power settings which correspond to a 350°F conventional oven temperamre (e.g. 18% top and 6% bottom). For the last 30:00 minutes, use power settings corresponding to a (350° - 25 °F) = 325 °F conventional oven temperamre (e.g. 16% top and 6% bottom).

A preferred method of cooking using the thermal emulation mode in oven 100 includes the following steps. First, without preheating the oven, the user places the food in user-selected cookware (e.g. on a baking sheet or in a casserole dish) and places the cookware (or the food itself if no cookware is used) onto the black or dark color turntable 20. Next, the user selects "thermal mode" using one of the input keys 16 and is then prompted to input the time and temperamre called for in the conventional recipe being followed. The controller 9 determines which of the power equivalents listed at Table 3 applies to the entered cooking time, and obtains the upper and lower lamp power settings associated with the entered temperamre (as modified in accordance with Table 3) from a lookup table corresponding to Table 1 or 2. The oven then cooks the food for the user-specified duration using the obtained power settings. It should be pointed out that the power equivalents for thermal mode are not food-specific and so the user need not be prompted to input the food type.

It is significant that operation of the lightwave oven in cooking mode requires no pre-heat time. This is because the lightwave oven, even when operated in thermal mode, cooks primarily by impinging radiant energy onto the food surface rather than by heating the surface of the food using heated air and radiated heat from the oven walls. Thus, when the user places the food into the oven to begin cooking, the oven air and walls are at room temperamre. It is also important to note that the internal air temperamre of the oven air never exceeds approximately 180°F, even though the cooking effect being attained is equivalent to cooking with a conventional oven having an air temperamre of 325° F or higher. This facilitates oven cleaning in that it prevents spilled food from burning or hardening onto the wall surfaces. The food surface and interior, however, reach approximately the same final temperamre as they would in a conventional oven.

Because the above-described thermal mode does not compensate for variations in cookware reflectivities, it is important for the user to use the black/dark turntable when this cooking mode is utilized. It may therefore be desirable to equip the oven with a sensor that looks for the dark turntable before initiating the thermal mode cooking cycle. The sensor may be an optical sensor (see sensor 200 which is described below) or a mechanical sensor that is tripped by a corresponding member at the base of the dark turntable. If the dark turntable is not detected, a warning signal may be given to alert the user that the dark turntable should be installed. Alternatively, the absence of the dark turntable pan may have the effect of causing the controller 9 to operate the oven using the thermal mode with cookware reflectivity compensation that is described below.

Thermal Emulation Mode Using Cookware Reflectivity Sensor

In a conventional oven, the reflectivity of cookware used to support the foodstuff can have a noticeable effect on the cooking process. For example, cookies that properly bake on an aluminum cooking sheet at 350° F may burn slightly on the bottom if baked on a dark steel pan. To compensate, the baking temperamre might have to be reduced to 325 °F.

Some manufacturers of very dark, non-reflective cookware include instructions to lower the oven temperamre by 25 degrees for certain food recipes. The effect of cookware reflectivity on conventional oven baking/cooking is not terribly significant, however, because conventional baking/cooking results from a combination of radiation and convection.

In a lightwave oven, however, most of the heat transfer is by radiation, even when operated in thermal emulation mode. It has been discovered that the amount of radiation absorbed by cookware supporting the foodstuff in a lightwave oven greatly varies depending upon the reflectivity of the cookware. Cookware with low reflectivity, thus high absorption of the lightwave oven radiation, can reach temperatures that are hundreds of degrees greater than highly reflective cookware used at the same lightwave oven intensity. Since the cookware bottom surface is usually in direct contact with the foodstuff, and is usually the closest cookware surface to the lightwave oven lamps, cookware reflectivity is one of the largest variables in the cooking (and/or baking) process in a lightwave oven. When food is present on the cookware, the energy that would increase cookware temperamre by hundreds of degrees is coupled to the food, whereby the food temperamre rises faster and higher resulting in enhanced cooking, browning and burning of the food. Further, highly absorbing cookware can affect the average power density inside the oven cavity.

There are countless different types of cookware available for use in a lightwave oven, each with their own reflectivity characteristics. The cookware temperamre differentials from varying reflectivities make it very difficult to estimate power and cook time settings in a lightwave oven without burning the foodstuff bottom or end up with undercooked food.

Further, some cookware have reflectivity characteristics that change as the cookware ages, gets tarnished, is not cleaned well, or conceivably even as the cookware heats up.

Use of the black or dark colored turntable 20 eliminates the variations the cookware can cause during operation in thermal mode by eliminating reflections of the radiant energy emitted by the lower lamps. It should be appreciated that the effect of variations in cookware types can be compensated for in alternative ways, as well.

For example, the user may visually inspect the cookware before use, estimate the effect of its reflectivity on the cooking sequence, and then adjust the lightwave cooking recipe accordingly. However, this would involve much trial and error with very little precision. Further, the naked eye is not good at measuring the reflectivity of any given material for the visible, near visible and infrared light produced by the lightwave oven. Moreover, in the age of automation, it is not desirable for the user of a lightwave oven, especially users in the home, to have to take into account the reflectivity characteristics of their cookware each time they operate their lightwave oven.

Another method for compensating for variations in cookware reflectivity during use of the thermal emulation mode involves using a optical sensor within the oven 100 to measure an amount of the radiant energy produced by at least one of the lower lamps that is reflected by cookware in the cooking region. The thermal mode power settings of the lower lamps (and, if necessary, the upper lamps) listed on Table 1 would be correlated to various cookware reflectivities. For thermal mode use, the oven software may include a number of lookup tables similar to Table 1 , each of which gives conventional temperamres and lamp settings for a given range of reflectivities.

Thermal emulation cooking with cookware reflectivity compensation eliminates the need for the black or dark colored turntable 20. The dark turntable is replaced with an alternate turntable which includes a food support formed of a radiation transparent glass or glass-ceramic material such as those described with respect to the lamp shields 70, 72, or with a turntable having a wire rack or grill. The user's cookware is positioned on the alternate food support during cooking in thermal mode with cookware reflectivity compensation.

Referring again to Fig. 2, cookware reflectivity compensation is accomplished by using an optical sensor 200 mounted below a small hole 202 formed in the bottom lamp reflector assembly 24 of the oven cavity. The sensor is preferably a silicon photo transistor or diode that measures visible and near visible radiation. Typical devices have a spectral sensitivity of about 0.4 to 1.1 microns. Alternately, for greater spectral response, the sensor can be a radiation sensitive thermopile, preferably with a differential sensing element to reduce sensitivity of thermal drift. Sensor 200 is electrically coupled to the controller 9. The sensor 200 is positioned to receive light from the lower lamps 28 that is reflected off of the bottom of cookware placed on the alternate food support. The reflectivity of the cookware dictates the amount of light from the lower lamps 28 that is reflected by the cookware to sensor 200. The sensor output is a measure of the relative power level of light impinging on it, which is proportionate to the reflectivity of the cookware placed on the turntable. The sensor output is also a function of the geometric orientation of the sensor, the oven cavity, and the placement of the cookware therein. Once the reflectivity of the cookware is measured, the controller 9 selects the intensity of the lower lamps 28 based on the measured reflectivity of the cookware in the oven. It should be noted that cookware reflectivity compensation can be utilized during lightwave cooking modes (including autopulse) and may operate in real time to continuously monitor reflectivity and adjust lamp output.

The controller 9 uses a lookup table and/or an algorithm that relates cookware reflectivity to the intensity of the lower lamps to compensate for highly reflective or highly absorbing cookware. Then, the lamp intensity is selected by the controller. If, for example, cookware with a relatively high reflectivity is detected, a relatively higher intensity is used for the lower lamps to bring the cookware to its proper temperamre and fully cook the food. Conversely, if cookware with a relatively low reflectivity is detected, the intensity of the lower lamps is set at a relatively lower level to prevent the cookware from getting too hot and burning or overcooking the foodsmff. In addition, in order to maximize cooking efficiency for most foods, the upper lamp output power can be increased when the lower lamp power is decreased for cookware reflectivity compensation, and vice versa. The lookup table and/or algorithm is established empirically through experimentation and/or power density calculations based upon the particular lightwave oven design.

Control of the lower lamps depending upon the cookware reflectivity is important for several reasons. First, the bottom surface of the cookware usually has the most contact with the foodstuff and therefore the temperamre thereof greatly affects the cooking of the foodsmff through conduction of heat. Secondly, the bottom surface of the cookware has the closest proximity to the lightwave oven lamps, and tends to absorb a lot of energy from these lamps. In order to accurately measure the cookware 's reflectivity, the sensor of the preferred embodiment preferably only detects light incident thereon within a small cone angle (acceptance angle), and is positioned off-center relative to the pedestal 21 but near the center of the mmtable. Also, the sensor acceptance angle should be oriented so that as much of the light rays as possible that are incident within the acceptance angle are first reflection light rays, which are rays that originate from the lower lamps and are reflected only once off of the bottom surface portion of the cookware (near the center of the mmtable) and to the sensor 200. This preferred orientation provides the best and most consistent measurement of cookware reflectivity for the following reasons. First, the center of the mmtable is the place most likely to be covered by cookware placed in the lightwave oven. Second, limiting the acceptance angle at or near the center of the mmtable means that the size of the cookware shouldn't significantly affect the reflection measurement. Third, the small acceptance angle minimizes the effects of cookware height, food size and color, and cookware position on the reflection measurement. Fourth, the sensor is using the actual energy generated by the lamps during the cooking/baking sequence to measure the cookware reflectivity. Thus, it accurately measures reflectivity in real time from the energy actually used to cook the foodsmff, and any changes in reflectivity during the cooking/baking sequence can be automatically detected and compensator for if desired.

Forming an optimal acceptance angle for sensor 200 can be accomplished in several ways. One way is using a sensor that has internal apertures to result in a small acceptance angle. Another way is to use hole

202 itself as an aperture, and back the sensor 200 from hole 202 to achieve a small acceptance angle. Still another way is to use an optical fiber with an input end thereof at hole 202. The optical fiber has a small acceptance angle, and use of an optical fiber also allows the sensor to placed away from the reflector assembly where the heat emanated therefrom may cause erroneous readings (i.e. especially in thermopile sensors that can be sensitive to ambient heat). It should be noted that there is an optical range of acceptance angle values for sensor 200 to minimize errors in reflectivity determination. The acceptance angle needs to be large enough so that contaminated spots on the mmtable or the cookware do not significantly change the amount of light measured by sensor 200, but small enough to prevent significant amounts of second reflected light rays or rays that have not reflected off of the cookware from being detected by sensor 200.

Fig. 6 illustrates an arrangement for mounting sensor 200 under hole 202. Hole 202 is positioned within the lower reflector assembly 24. The sensor 200 is mounted inside a mounting tube 208, with a diffuser 210 immediately above the sensor 200, and an aperture member 212 above the diffuser 210. The diffuser 210 ensures that the sensor is evenly illuminated by the incoming light. The aperture 212, along with the open end 214 of tube 208 act to define the acceptance angle for the sensor 200. Depending upon the optical orientation of mounting tube 208 and sensor 200, either or both the diffuser and aperture could be eliminated.

For increased accuracy, the sensor 200 should have a peak spectral sensitivity near the peak spectral output of the lamps. Therefore, if the sensor has a wide spectral sensitivity, and/or a peak spectral sensitivity significantly different from the peak spectral output of the lamps, a filter 216 can be added to change the overall spectral sensitivity of the sensor/filter combination to better match that of the lamps.

Glass cookware does not reflect light well like opaque cookware does, so measuring energy absorption by glass cookware is not best performed by trying to measure reflected light from the lower lamps.

Instead, glass cookware absorption can be measured by measuring light transmission from the upper lamps. For glass cookware compensation, the sensor acceptance angle is aligned with one of the upper lamps. The sensor can then be used in several ways to compensate for the use of glass cookware. One way is for the user to calibrate the lightwave oven by placing the glass cookware in the oven without any food thereon. The oven controller then operates the one opposing upper lamp and measures how much light is transmitted through the glass cookware and to the sensor. This level of transmitted light is then compared to the amount of light that reaches the sensor without any cookware or food therein. The difference indicates how much energy is being absorbed by the glass cookware. The controller then controls the lower (and/or upper) lamps accordingly once food on the glass cookware is placed in the oven and the cooking sequence begins.

Alternately, glass cookware compensation can utilize that fact that almost all foodstuffs allow at least some light to pass therethrough. Therefore, if sensor 200 detects that any light from the upper lamps is being transmitted through the food, then that indicates that either a glass pan or no pan is being used. Alternately, if no light from the upper lamps is transmitted through the food, then that indicates that an opaque metal pan is being used. The controller then operates the lamps accordingly. Cookware significantly larger than the foodsmff placed thereon may also warrant special cooking sequence modifications. With relatively small foodsmff s, the upper lamps significantly contribute to cookware heating. The solution is a special cook mode where the user inputs to the controller that the cookware is significantly larger than the food. Then, the controller can control both the upper and lower lamps appropriately based on the bottom surface reflectivity measured by sensor 200 and the fact that the cookware is much larger than the foodsmff.

It should be noted that if glass cookware, or no cookware, is used to support the foodsmff, then sensor 200 measures the reflectivity of the foodsmff itself when the lower lamps are operated. If sensor 200 detects low food reflectivity, lower lamp powers are reduced to prevent the bottom of the foodsmff from burning. If sensor 200 detects high food reflectivity, then lower lamp powers are increased to properly cook the bottom surface of the foodsmff. A preferred method of cooking using the thermal emulation mode with cookware reflectivity compensation includes the following steps. First, the alternative mmtable having a glass, glass-ceramic, or wire rack food support is installed in the oven. Without preheating the oven, the user places the food in user-selected cookware and places the cookware (or the food itself if no cookware is used) onto the radiation mmtable. Next, the user selects "thermal mode with cookware compensation" using one of the input keys 16 and is then prompted to input the time and temperamre called for in the conventional recipe being followed. The sensor 200 measures the reflectivity of the cookware holding the food. If a wire rack is used to support the food, the sensor senses the wire positions and measures intermediate signals lying between the sensed wires as the reflectivity of the cookware. If desired, rotation of the rack may be sensed in this way.

The controller 9 looks to a lookup table having upper and lower lamp power settings for use with cookware of the measured reflectivity, and it obtains the upper and lower lamp power settings associated with the user- specified temperamre. The oven then cooks the food for the user-specified duration using the obtained power settings.

Although thermal emulation and emulation with pan compensation have been described with respect to the oven 100, it should be appreciated that similar emulation schemes may be utilized for ovens such as the oven 201.

Recipe Translator

A user wishing to use conventional recipes in a lightwave cooking mode may alternatively do so by making a straightforward conversion of conventional cooking recipes into lightwave cooking recipes. Using the lightwave oven's recipe translator, the user can input the conventional recipe cooking time and temperamre, and the oven will convert those variables to a corresponding lightwave cooking time and a lightwave power setting. One recipe translator has been developed for use in connection with the autopulse mode for the oven 100. Although the recipe translation factors will vary between lightwave oven designs, correlation has been established between conventional oven temperamre settings and the beginning and ending autopulse power settings for the oven 100.

TABLE 4: RECIPE TRANSLATOR POWER SETTINGS

The starting and ending power settings represent the percentage of time that the pulsing lamps are on. It should be noted that when the lamps are on they are on at full lamp power and reductions in power are achieved with duty cycle reductions.

Correlation has also been established between the conventional cooking time and the lightwave cooking time for various food groups. In many instances, cooking time translation involves simply multiplying the conventional oven cooking time called for in a particular recipe by a conversion factor. For certain food groups, such as baked goods, the lightwave cooking time is obtained by multiplying the conventional cooking time by a multiplier from approximately 0.3 (or slightly below) to 0.35, whereas a cooking time multiplier for certain meats is approximately 0.5. To utilize the recipe translator using the autopulse mode, the user inputs the conventional oven temperamre and cooking time called for by the recipe, as well as the food type (e.g. baked good, meat etc.). Using the conventional temperamre, the controller obtains the starting and ending power settings from a first lookup table corresponding to Table 4. The cooking time conversion factor corresponding to the specified food type is obtained from a second look up table, and the cooking time is converted by multiplying the conversion factor by the conventional cooking time (this step may alternatively be performed manually in which case the user would simply input the lightwave cooking time). Intermediate power settings (i.e. , the powers between the starting and ending powers) as well as the length of time the oven operates at each determined power are established in accordance with the algorithm for the autopulse ramp. The cooking program begins with the obtained starting power, ramps down to the ending power in accordance with the autopulse function, and ends after the calculated lightwave cooking time has elapsed.

It has also been discovered that a user wishing to employ the various cooking modes described herein with respect to high efficiency oven 201 may do so by making a straightforward conversion of conventional cooking recipes into lightwave cooking recipes. In many instances, recipe translation involves multiplying the conventional oven cooking time called for in a particular recipe by a conversion factor.

For example, the bake mode operation described above provides an effective translation between conventional oven recipes (which are well known for most foods) and the total bake mode time T (which is t, to t₇) for the lightwave oven. More specifically, a single formula for the time values tj to t₇ in bake mode can be used to bake most foodsmffs in a lightwave oven having a known maximum power density, where the only variable is the conventional oven baking time. Therefore, the user need only enter into the lightwave oven a bake mode time T that is a certain fraction of the conventional oven bake time, and the oven will automatically bake the food in bake mode.

For example, for the 1.8 KW lightwave oven described herein, which produces a maximum power density of about 0.7 W/cm², it has been determined that the following formula in bake mode quickly bakes most foodsmffs and produces a high quality baked food product:

t] through tj each = 1 minute, t_<5 = T - 6 minutes, t₇ = 1 minute, and T = conventional oven baking time.

2 where T is the total lightwave cooking time. This formula would change for lightwave ovens having a higher or lower maximum power density, and can also vary depending upon cavity size, overall oven cavity reflectivity, oven cavity wall materials, and the type and color temperamre of the lamps used. It should also be noted that the conventional oven baking temperamre need not be factored into the formula for bake mode operation. This formula works exceptionally well for foods with conventional baking times greater than about 14 minutes. For conventional bake times of less than 14 minutes,

T is not long enough to execute all times periods t through t₇. However, the above formula still works well for conventional bake times less than 14 minutes, where the bake sequence completes as many of the time periods tj through t_<5 as possible in time T so that the bake sequence can skip to and end with full crisping (t₇).

The use of the above formula is a tremendous advantage for those users who only know the conventional baking recipe for a given foodsmff (e.g. from the food's packaging). The user can simply enter in the conventional baking time using operation keys 16, and the controller 9 will calculate the time values ti to t₇. Alternately, if the time conversion is easy (e.g. the one half value for the 1.8 KW oven), the user can input the appropriate bake mode time T that is a certain percentage (e.g. one half) of the known conventional oven baking time, and the controller 9 will calculate the time values t, to t₇.

It should be noted that other bake formulas that vary the time in one or more of the time periods or even skip one or more time periods have also been shown to bake foodsmffs with quality results. For example, the following formula has been successfully used to bake food:

t, = 1 minute, t₂ = 1 minute, t₃ = 2 minute, t₄ = 3 minute, t₅ = T - 8 minutes, t₇ = 1 minute, and

T = conventional oven baking time, 2

where the 80% and 70% intensity time periods (t₃,t₄) are increased, and the

50% intensity time period (tg) is eliminated.

There are certain foods that may need a little more or a little less browning time than called for in the bake formula used by the lightwave oven. For these foods, the user need only visually monitor the lightwave bake mode operation during the last time interval t₇. If browning is completed before time interval t₇ expires, the user can simply stop the bake mode operation. If browning was not completed by the bake mode operation, then crisp mode can be activated to further brown the food as needed. The controller 209 can be programmed to sound an audible warning that indicates when the browning interval (t₇) begins, or after a certain portion of the browning interval has been completed, so the user can be alerted to visually monitor the baking food. Simple multipliers likewise allow users to convert conventional recipes to recipes using the cook mode. Cook mode multipliers for recipe translation lie within a range of approximately 0.5 to 0.7. For example, to translate a conventional recipe for roast pork into a lightwave cooking recipe, the user multiplies the conventional cook time by a multiplier of approximately 0.65. As with the bake mode, the multiplier will vary between lightwave oven designs.

Similar translator multipliers are applicable to others of the cooking modes described herein, such as the grill mode. The conversion from a conventional to a lightwave recipe may occur in a number of ways. For example, the user may enter the food type and conventional cooking time using the oven's user interface, and press a "convert" button which will cause the oven controller to obtain the appropriate multiplier from a lookup table, perform the time conversion calculation to obtain the lightwave cooking time, and fit the cooking mode algorithm (e.g. grill mode, cook mode, etc.) to the determined lightwave cooking time. The oven would then cook food using the appropriate lightwave cooking mode and time. Alternatively, the oven may be provided with an instmction card which lists the multipliers for various food types. The user would then multiply the conventional cooking time by the multiplier to obtain the lightwave cooking time, and then input the lightwave cooking time and food type (or desired cooking mode) using the oven's user interface. A small calculator may be embedded in the instmction card to assist the user in making the conversion.

Claims

We Claim:

1. A method of cooking in a lightwave oven using a conventional oven recipe, comprising the steps of: providing an oven housing enclosing a cooking region therein, and further providing at least one high power lamp within the oven housing that provides radiant energy in the visible, near- visible and infrared ranges of the electromagnetic spectrum; receiving a food item in the oven cavity; receiving user instructions from a user, the user instructions specifying at least one conventional cooking parameter representing a cooking parameter for cooking the food item in a conventional oven; determining at least one lightwave cooking parameter using the at least one conventional cooking parameter; and controlling the lamp to cook the food item using the at least one lightwave cooking parameter.

2. The method of claim 1, wherein the at least one conventional cooking parameter includes conventional cooking time and wherein the at least one lightwave cooking parameter includes lightwave cooking time, the lightwave cooking time being shorter than the conventional cooking time.

3. The method of claim 1, wherein the at least one conventional cooking parameter includes conventional cooking oven temperamre and wherein the at least one lightwave cooking parameter represents at least a lightwave cooking power for the lamp.

4. The method of claim 3 wherein the step of controlling the lamp to cook the food is performed without pre-heating the oven to the conventional cooking oven temperature.

5. The method of claim 4 wherein the at least one conventional cooking parameter includes conventional cooking time and wherein the at least one lightwave cooking parameter includes lightwave cooking time, the lightwave cooking time being approximately equal to the conventional cooking time.

6. The method of claim 4 wherein the at least one conventional cooking parameter includes conventional cooking time and wherein the at least one lightwave cooking parameter includes lightwave cooking time, the lightwave cooking time being shorter than the conventional cooking time.

7. The method of claim 1 wherein, in the step of receiving user instructions, the user instructions further specify a food type, and wherein the dete╧Çnining step includes determining at least one lightwave cooking parameter using the specified food type and the at least one conventional cooking parameter.

8. The method of claim 7, wherein the at least one conventional cooking parameter includes conventional cooking time and the at least one lightwave cooking parameter includes lightwave cooking time, and wherein the determining step includes selecting a scaling factor using on the specified food type and applying the scaling factor to the conventional cooking time to obtain the lightwave cooking time.

9. The method of claim 1, wherein the receiving step includes receiving a food item on a pan, wherein the method further includes the steps of measuring the reflectivity of the pan, and determining the at least one lightwave cooking parameter using on the measured reflectivity of the pan.

10. The method of claim 2 wherein the determining step includes applying a scaling factor to the cooking time.

11. A lightwave oven for use in cooking food using a conventional oven recipe, comprising: an oven housing enclosing a cooking region therein; at least one high power lamp within the oven housing that provides radiant energy in the visible, near-visible and infrared ranges of the electromagnetic spectrum to the cooking region; and a controller for receiving user instructions specifying at least one conventional cooking parameter representing a cooking parameter for cooking the food item in a conventional oven, for determining at least one lightwave cooking parameter using the at least one conventional cooking parameter, and for controlling the lamp to cook the food item using the at least one lightwave cooking parameter.

12. The lightwave oven of claim 11 wherein the at least one conventional cooking parameter includes conventional cooking time and wherein the at least one lightwave cooking parameter includes lightwave cooking time, the lightwave cooking time being shorter than the conventional cooking time.

13. The lightwave oven of claim 11, wherein the at least one conventional cooking parameter includes conventional cooking oven temperamre and wherein the at least one lightwave cooking parameter represents at least a lightwave cooking power for the lamp.

14. The lightwave oven of claim 13 wherein the controller is further for controlling the lamp to cook the food without pre-heating the oven to the conventional cooking oven temperamre.

15. The lightwave oven of claim 14 wherein the at least one conventional cooking parameter includes conventional cooking time and wherein the at least one lightwave cooking parameter includes lightwave cooking time, the lightwave cooking time being approximately equal to the conventional cooking time.

16. The lightwave oven of claim 14 wherein the at least one conventional cooking parameter includes conventional cooking time and wherein the at least one lightwave cooking parameter includes lightwave cooking time, the lightwave cooking time being shorter than the conventional cooking time.

17. The lightwave oven of claim 11 wherein, the controller is further for receiving user instmctions specifying a food type, and for determining the at least one lightwave cooking parameter using the specified food type and the at least one conventional cooking parameter.

18. The lightwave oven of claim 17, wherein the at least one conventional cooking parameter includes conventional cooking time and the at least one lightwave cooking parameter includes lightwave cooking time, and wherein the controller is further for selecting a scaling factor using on the specified food type and applying the scaling factor to the conventional cooking time to obtain the lightwave cooking time.

19. The lightwave oven of claim 11 , further including a pan sensor within the oven housing, wherein the controller is further for receiving input representing pan reflectivity from the pan sensor and determining the at least one lightwave cooking parameter using the measured reflectivity of the pan.