Abstract:
An oven for cooking with light having wavelengths in the visible, near visible, and infra-red spectral ranges uses one or more quartz halogen tungsten lamps or quartz arc bulbs positioned above and below the food item. Uniform cooking of the food item is achieved by positioning the lamps asymmetrically with respect to the midline of the oven and by rotating the food item on a rack during the cooking cycle.

Description:
RELATED APPLICATIONS 
     This is a continuation of application Ser. No. 08/065,802 filed on May 21, 1993, now abandoned, which is a continuation-in-part of application Ser. No. 07/738,207, filed Jul. 30, 1991, now abandoned, which was a continuation-in-part of application Ser. No. 07/350,024, filed May 12, 1989, now U.S. Pat. No. 5,036,179 which was in turn a continuation-in-part of application Ser. No. 07/195,967, filed May 19, 1988, now abandoned. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to the field of radiant source ovens. More particularly, this invention relates to ovens having a rotating rack and an array of linear radiation sources typically shorter than the transverse dimension of the cooking location and which are arranged to maximize uniform cooking of a food item. 
     BACKGROUND OF THE INVENTION 
     Ovens following the present invention and having linear sources of visible and infra-red radiant energy are disclosed and described in U.S. Pat. No. 5,036,179 and U.S. patent application Ser. No. 07/738,207 which are incorporated herein by reference. These ovens provide high-speed, high-quality cooking and baking of food items by impinging high-intensity visible, near-visible, and infrared radiations onto a food item. The ovens cook the food items within the short periods of time normally found in microwave cooking while maintaining the browning of infrared cooking and the quality of conduction-convection cooking. When food is exposed to a sufficiently intense source of visible, near-visible, and infrared radiation, the food absorbs low levels of visible and near-visible radiation, thereby allowing the energy to penetrate the foodstuff and heat it deeply. The longer infrared radiation does not penetrate deeply but acts as an effective browning agent. 
     Ordinarily, the source of the visible, near-visible and infrared radiation for this invention is in excess of two elongated quartz-halogen tungsten lamps, or equivalent means such as quartz arc lamps. Typical quartz-halogen lamps of this type operate at 3000 degrees Kelvin and convert electrical energy into black body radiation having a range of wavelengths from 0.4 μm to 4.5 μm with a peak intensity at 0.965 μm. Each lamp can generally provide about between 1.5 and 2 kW of radiant energy with a significant portion of the energy in the visible light spectrum. 
     The ovens can use a plurality of these lamps or an array of several lamps either operated in unison or selectively operated in varying combinations as necessary for the particular food item sought to be cooked. These radiation sources are ordinarily positioned above and below the food item. The walls of the surrounding food chamber are preferably made from highly reflective surfaces. The visible and infrared waves from the radiation sources impinge directly on the food item and are also reflected off the reflected surfaces and onto the food item from many angles. This reflecting action improves uniformity of cooking. 
     The intensity of radiant energy received by an object decreases with the increase in distance between the object and the radiant energy source. Despite the improved uniformity of cooking provided by the reflective interior surfaces of the oven, the areas of the food item that are positioned directly above or below the radiation sources receive more direct energy and therefore cook more quickly than their surrounding areas. 
     FIGS. 1A and 1B show an end view and a longitudinal side view, respectively, of a single linear radiation source 100 and further show the distributions of light intensity measured at the surface of a food item positioned underneath the radiation source. As shown in both figures, the regions of the food item which are positioned directly below the light source are exposed to the maximum intensity received by the food item, while the surrounding areas are exposed to significantly lower intensities. 
     FIG. 2A shows a lamp configuration under which a food item 104 is cooked under an array of elongate radiation sources 100 that are shorter than the length of the food item and that are arranged in parallel. The food item is cooked to the desired degree in the regions of the food item that are close to the lamps, designated by shading in FIG. 2B. The unshaded regions remain uncooked or undercooked. 
     Rotating the food item relative to the stationary radiation sources also yields a non-uniformly cooked end product. FIG. 3A shows a circular food surface 104, such as a pizza, positioned underneath a single radiation source 100a having a length l. The radiation source is parallel to and shorter than diameter d of the pizza. Referring to FIG. 3B, when the pizza is rotated about its center C, the radiation source cooks a circular region AA having diameter equal to the length l of the radiation source 100a. Moreover, cooked portion AA is itself non-uniformly cooked: the regions that are closer to the center C spend more time under the radiation source and therefore are cooked more thoroughly than those regions that are further away from it. 
     As shown in FIGS. 4A and 4B, positioning a single source 100b parallel to a diameter d of the rotating pizza will cook only an annular path BB, leaving the remainder of the pizza uncooked. 
     Combining the concepts described with respect to FIGS. 3B and 4B partially solves the problem of non-uniform cooking. FIG. 5A shows five equally spaced radiation sources 100c, 100d, 100e fixed over a pizza 104 which is positioned on a rotating rack (not shown). The sources are equal in length, and their length l is less than the diameter d of the pizza 104. The center source 110c lies above the diameter of the pizza, and the outer radiation sources are positioned parallel to it. 
     When the pizza is rotated about the center C, the energy generated by radiation sources 100d and 100e creates partially cooked annular paths similar to region BB in FIG. 4B. These paths are also exposed by the center source 100c, although their exposure time is minimal as explained with respect to FIG. 3B. 
     Designing an oven having radiation sources that extend beyond the outer boundaries of the food location in the oven would allow uniform cooking of the food region even where the sources are arranged as in FIG. 5A. However, there are limits to the size of radiation sources that can be manufactured for use in ovens of the present type, making it often impractical to utilize radiation sources that are longer than the area of food sought to be cooked. To attempt to do so would unnecessarily limit the size of the food items which could be cooked using combined visible and infra-red radiation. A lamp configuration is therefore needed that will provide uniform cooking even where the size of the cooking surface exceeds the dimensions of the lamps. 
     SUMMARY OF THE INVENTION 
     The present invention utilizes an array of light sources asymmetrically placed with respect to the diameter of a rotating rack. The lamps have a length that is shorter than the width or diameter of a cooking area. Rotation of a food item beneath the asymmetrically placed lamps causes substantially all of the food surface to be exposed to substantially the same radiation for a substantially equal period of time and therefore results in substantially uniform cooking of the food item. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B are an end view and a side view, respectively, of a lamp and with its associated intensity distribution measured at the surface of a food item positioned underneath the lamp. 
     FIGS. 2A through 5B are schematic representations showing four different lamp arrays and the regions of a food item that are cooked by each of the respective arrays. 
     FIG. 6 is a front section view of an oven according to the present invention. 
     FIG. 7 is a side section view of a preferred embodiment of an oven according to the present invention. 
     FIGS. 8A, 8B, and 8C are a perspective view, a top plan view, and a side elevational view, respectively, showing the preferred means for rotating the rack of the present invention. 
     FIG. 9 is a schematic representation of the preferred lamp configuration according to the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention is comprised generally of an oven 10, a rotating circular rack 31, and upper and lower arrays 18, 16 of radiant energy sources, or lamps. 
     FIG. 6 is a front section view of the oven. The energy for cooking is supplied by lower heating lamps 16 and upper radiation heating lamps 18. The lamps are preferably quartz-halogen tungsten lamps which are capable of producing approximately 2 kW of radiant energy with a significant portion of the light energy in the visible light spectrum. When illuminated, the lighted portion of a preferred lamp has a length of approximately 10 inches. 
     The inner surface of the inner wall 12 is preferably a highly polished metal, such as aluminum or stainless steel, which is very reflective to the wide spectrum of wavelengths from the radiant lamps. The oven has a door 40 (FIG. 7) which also has a reflective inner surface. 
     Two radiation transparent plates 20 and 24 are used to isolate the cooking chamber from the radiant lamps, making the oven easier to clean. These plates can be formed from materials, such as high quality heat-resistant glasses and ceramics that are transparent to visible, non-visible and infrared radiations. The lower transparent plate 20 is supported by brackets 22a and 22b and is positioned above the lower lamps 16. The upper transparent plate 24 is supported by brackets 26a and 26b and is positioned below upper lamps 18. 
     Shelf 28 is mounted between the transparent plates inside the oven chamber. As shown in FIG. 8A, the shelf 28 has a circular cut out portion 27 which is lined at its perimeter by a track 29. A circular rack 31, comprised of a grid of small diameter metallic bars 33, rests loosely on the track 29 as shown in FIG. 8B. During use, a heat-resistant glass dish which holds the food is placed on top of the rack for cooking. The rack has a diameter of preferably 12 to 14 inches and is capable of rotating around an axis of rotation, designated r. Rollers 35 are positioned such that when one of them is rotated by a motor (not shown), they engage with the perimeter portion of the rack, causing the rack to rotate within the track 29. 
     FIG. 7 shows a side section of the preferred oven according to the present invention. In the preferred embodiment, there are 5 lower lamps 16a through 16e and 5 upper lamps 18a though 18e. By appropriately selecting the lateral spacing between the lamps relative to the food, even cooking can be achieved over the entire surface. This is accomplished by rotating the food item using the rack 31 and by arranging the lamps such that during the cooking cycle all regions of the food surface receive equivalent amounts of energy from the lamps. As described above, this requires arranging the lamps such that all regions of the food surface are positioned directly underneath a lamp for substantially equivalent periods of time. 
     This desired result is most readily accomplished by positioning the lamps asymmetrically with respect to the midline m of the lamp array. Asymmetry is achieved by positioning unequal numbers of lamps on either side of the midline, and/or by positioning the lamps at unequal distances from the midline such that the lamp arrangements on either side of the midline are not &#34;mirror images&#34; of one another. 
     Alternatively, an equal number of equally spaced lamps may be positioned on either side of the midline, and asymmetrical configurations of lamps may be selectively illuminated depending on the size and of the food item sought to be cooked and its ability to absorb visible light. Because different food types will be capable of absorbing different amounts of energy, a configuration of this type would be particularly helpful when, for example, a dish containing various foods is positioned on the rack for cooking. 
     A top view of the preferred lamp array is shown in FIG. 9. In the preferred oven, the lamps in the upper and lower arrays are identically arranged. Positioning of the lamps will be described with respect to a midline m which bisects the array and which intersects the axis of rotation r (FIGS. 6 and 7) of the rack 31. Three of the lamps, 18a, 18b, and 18c, are positioned on one side of the midline and are respectively 5.5 inches, 4.5 inches and 1 inch from the midline. The remaining two lamps, 18d, 18e, are positioned on the opposite side of the midline and are positioned 3.5 inches and 5.9 inches from the midline, respectively. The lamps are positioned approximately 3 inches above the rack 31. The lateral positions of the lamps from the midline can be varied plus or minus one-eighth inch from their stated positions while still maintaining substantially uniform radiation across the food location. 
     Using the preferred dimensions given above, the lamp configuration may be reduced to a mathematical expression which will yield alternative lamp configurations that will likewise achieve uniform cooking. Assuming the diameter of the food location &#34;d&#34; is 12 inches and the lamp filament length &#34;L&#34; is 10 inches as stated above, it can be seen that L=(10/12)×d. A general formulation of the distance of each lamp from the midline &#34;m&#34; may be calculated in terms of L as follows: 
     D n  =x n  L, where D n  is the distance from the midline of the lamp having reference numeral &#34;n&#34; in FIG. 7. For example, for lamps 18c and 18b the respective multiplier x 18c  and x 18b , may be calculated using the distances used in the preferred embodiment: 
     
         D.sub.18c =1=x.sub.18c (10) 
    
     
         x.sub.18c =1/10 
    
     
         D.sub.18b =4.5=x.sub.18b (10) 
    
     
         x.sub.18b =4.5/10 
    
     The multipliers for the all of the lamps 18a through 18d, which were calculated in the manner shown above, are included in the following chart: 
     
         ______________________________________  Lamp No.         x.sub.n______________________________________  18a    5.5/10  18b    4.5/10  18c      1/10  18d     3.5/100  18e    5.9/10______________________________________ 
    
     In similar fashion, the distance D n  between the midline &#34;m&#34; and each of the respective lamps may be expressed in terms of the relationship (L/d) (where L/d is approximately between 10/12 and 1) of the length &#34;L&#34; of the lamp filaments to the diameter &#34;d&#34; of the food location: 
     
         D.sub.n =y.sub.n (L/d) 
    
     The multiplier y n  for each of the respective lamps is thus calculated using the preferred distances between each of those lamps and the midline 
     
         D.sub.18c =1=y.sub.18c (10/12) 
    
     
         y.sub.18c =12/10=1.2 
    
     
         D.sub.18b =4.5=y.sub.18b (10/12) 
    
     
         y.sub.18b =5/4 
    
     The multipliers for the all of the lamps 18a through 18d, which were calculated in the manner shown above, are included in the following chart: 
     
         ______________________________________  Lamp No.         y.sub.n______________________________________  18a    6.6  18b    5.4  18c    1.2  18d    4.2  18e    7.08______________________________________ 
    
     In the embodiment of FIG. 7 the positions of the lower lamps 16a-16e are the same as the upper lamps 18a-18e but obviously the position of one of these two sets can be reversed with respect to the other. 
     To use the oven of the present invention, the food item sought to be cooked is positioned on the rack 31 and the door 40 is closed. The motor is switched on, causing the roller to engage and rotate the rack. The lamps are illuminated for a predetermined cooking time, causing the food item to cook uniformly. 
     The present invention is described in relation to the preferred embodiment but is limited only in terms of the language of the appended claims.