Patent Publication Number: US-6987252-B2

Title: Speedcooking oven including convection/bake mode and microwave heating

Description:
BACKGROUND OF THE INVENTION 
   This invention relates generally to ovens and, more particularly, to an oven operable in speedcooking, microwave, and convection/bake modes. 
   Ovens typically are either, for example, microwave, radiant, or thermal/convection cooking type ovens. For example, a microwave oven includes a magnetron for generating RF energy used to cook food in an oven cooking cavity. Although microwave ovens cook food more quickly than radiant or thermal/convection ovens, microwave ovens do not brown the food. Microwave ovens therefore typically are not used to cook as wide a variety of foods as radiant or thermal/convection ovens. 
   Radiant cooking ovens include an energy source such as lamps which generate light energy used to cook the food. Radiant ovens brown the food and generally can be used to cook a wider variety of foods than microwave ovens. Radiant ovens, however, cook many foods slower than microwave ovens. 
   In thermal/convection ovens, the food is cooked by the air in the cooking cavity, which is heated by a heat source. Standard thermal ovens do not have a fan to circulate the hot air in the cooking cavity. Convection ovens use the same heat source as a standard thermal oven, but add a fan to increase cooking efficiency by circulating the hot air around the food. Thermal/convection ovens cook the widest variety of foods. Such ovens, however, do not cook as fast as radiant or microwave ovens. 
   One way to achieve speedcooking in an oven is to include both microwave and radiant energy sources. The combination of microwave and radiant energy sources facilitates fast cooking of foods. In addition, and as compared to microwave only cooking, a combination of microwave and radiant energy sources can cook a wider variety of foods. 
   While speedcooking ovens are versatile and cook food quickly, in at least one known speedcooking oven, the radiant energy sources are thermally separated from the cooking cavity. Waste heat from the radiant energy sources is directed out of the oven via air flow paths. In addition, such known speedcooking oven is rated for operation at 240 volts. The 240 volt rating is required in order to simultaneously operate the radiant and microwave energy sources. 
   BRIEF SUMMARY OF THE INVENTION 
   In an exemplary embodiment of the invention, an oven includes radiant cooking elements, an RF energy source (e.g., a magnetron), and convection cooking elements. The oven is operable in a speedcooking mode wherein both radiant and microwave cooking elements are utilized, in a convection/bake bode in which convection and radiant cooking elements are utilized, and in a microwave only cooking mode wherein only the magnetron is utilized for cooking. 
   In an exemplary embodiment, the oven includes a shell, and a cooking cavity is located within the shell. The oven also includes a microwave module, an upper heater module, and a lower heater module. The microwave module includes a magnetron located on a side of cavity. The upper heater module includes radiant heating elements such as a ceramic heater and a halogen cooking lamp. The upper heater module also includes a sheath heater. A convection fan is provided for blowing air over the heaters and into the cooking cavity. The lower heater module includes at least one radiant heating element such as a ceramic heater. 
   Generally, a combination of the lamps, the heaters, and the RF generation system is selected to provide the desired cooking characteristics for speedcooking, microwave, and convection/bake modes. For example, in the speedcook mode, the radiant heaters and the convection fan are used to heat the outside of the food, and microwave energy is used to heat the inside of the food. As described below in more detail, the radiant heaters and the magnetron may be cycled throughout the cooking cycle to provide the desired cooking results. 
   In the convection/bake mode, the lower ceramic heater and upper sheath heater are energized to preheat the air in the oven. During the cooking cycle, the lower ceramic heater and upper sheath heater are controlled to provide the desired energy, and the convection fan circulates air to assure even cooking. In the microwave mode, the magnetron is energized in accordance with the user selections. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a front view of an oven; 
       FIG. 2  is a schematic illustration of the oven shown in  FIG. 1 ; 
       FIG. 3  is a schematic illustration of the oven shown in  FIG. 1  in speedcooking mode; 
       FIG. 4  is a schematic illustration of the oven shown in  FIG. 1  in convection/bake mode; 
       FIG. 5  is a schematic illustration of the oven shown in  FIG. 1  in microwave mode; 
       FIG. 6  is an exploded view of an oven cavity assembly; 
       FIG. 7  is an exploded view of an oven interior assembly; 
       FIG. 8  is an exploded view of additional components of an oven interior assembly; 
       FIG. 9  is an exploded view of an oven controller; 
       FIG. 10  is an exploded view of an oven door; 
       FIG. 11  is a schematic illustration of an oven control; 
       FIG. 12  is a functional block diagram of an oven; 
       FIG. 13  is a functional block diagram of a structural subsystem of an oven; 
       FIG. 14  is a functional block diagram of a control and electrical subsystem of an oven; 
       FIG. 15  is a functional block diagram of a lower heater module subsystem of an oven&#39; 
       FIG. 16  is a functional block diagram of a convection module subsystem of an oven; 
       FIG. 17  is a functional block diagram of a cooling and cooktop venting subsystem of an oven; 
       FIG. 18  is a functional block diagram of an RF generation subsystem of an oven; 
       FIG. 19  is a flow chart illustrating process steps for venting compensation; 
       FIG. 20  is a block diagram illustration of a speedcook mode; 
       FIG. 21  illustrates duty cycles for the speedcook mode illustrated in  FIG. 20 ; 
       FIG. 22  is a flow chart illustrating process steps for thermal compensation in the speedcook mode; 
       FIGS. 23 ,  24  and  25  illustrate lookup tables utilized in connection with the thermal compensation illustrated in  FIG. 22 ; 
       FIG. 26  is a graph illustrating cooking cavity temperature with and without thermal compensation; 
       FIG. 27  is a block diagram illustration of a microwave mode; 
       FIG. 28  illustrates duty cycles for the microwave mode illustrated in  FIG. 27 ; 
       FIG. 29  is a block diagram illustration of an oven/bake mode; and 
       FIG. 30  illustrates duty cycles for the oven/bake mode illustrated in FIG.  29 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention is directed, in one aspect, to operation of an oven that includes sources of radiant and microwave energy as well as at least one convection/bake heating element. Although one specific embodiment of such an oven is described below, it should be understood that the present invention can be utilized in combination with many other such ovens and is not limited to practice with the oven described herein. For example, the oven described below is an over the range type oven. The present invention, however, is not limited to practice with just over the range type ovens and can be used with many other types of ovens such as countertop or built-in wall ovens. 
     FIG. 1  is a front view of an over the range type oven  100  in accordance with one embodiment of the present invention. Oven  100  includes an outer case  102 , a plastic door frame  104 , and a control panel frame  106 . Oven  100  further includes a stainless steel door  108  mounted within door frame  104 , an injection molded grille  110 , and a bottom panel  112 . A window  114  in door  108  is provided for viewing food in the oven cooking cavity, and an injection molded plastic handle  116  is secured to door  108 . A control panel  118  is mounted within control panel frame  106 . 
   Control panel  118  includes a display  120 , an injection molded knob or dial  122 , and tactile control buttons  124 . Selections are made by rotating dial  122  clockwise or counter-clockwise and when the desired selection is displayed, pressing dial  122 . For example, many cooking algorithms can be preprogrammed in the oven memory for many different types of foods. When a user is cooking a particular food item for which there is a preprogrammed cooking algorithm, the preprogrammed cooking algorithm is selected by rotating dial  122  until the selected food name is displayed and then pressing the dial. Instructions and selections are displayed on vacuum fluorescent display  120 . The following functions can be selected from respective key pads  124  of panel. 
   
     
       
         
             
             
           
             
                 
             
           
          
             
                SPEEDCOOK 
               Selecting this pad enables an operator to 
             
             
                 
               perform the following speedcook functions: 
             
             
                 
               1) manually enter speed cooking time and 
             
             
                 
               powerlevels, 2) select preprogrammed 
             
             
                 
               control algorithms, or 3) store manually 
             
             
                 
               programmed algorithms as recipes 
             
             
               OVEN/BAKE 
               Selecting this pad enables an operator to 
             
             
                 
               manually enter cooking time and temperature 
             
             
                 
               for the oven/bake mode. 
             
             
               MICROWAVE 
               Selecting this pad enables an operator to 
             
             
                 
               manually enter cooking time and power level 
             
             
                 
               for the microwave mode, as well as use pre- 
             
             
                 
               programmed microwave features, such as 
             
             
                 
               sensor cooking. 
             
             
               START/PAUSE 
               Selecting this pad enables an operator to start 
             
             
                 
               or pause cooking. 
             
             
               CLEAR/OFF 
               Selecting this pad stops all cooking and 
             
             
                 
               erases the current program. 
             
             
               MICROWAVE EXPRESS 
               Selecting this pad enables an instant 30 
             
             
                 
               seconds of full-power microwave for quick 
             
             
                 
               and easy warming of a sandwich, or reheat 
             
             
                 
               of coffee. 
             
             
               BACK 
               Selecting this pad causes the oven to return 
             
             
                 
               to the previous selection. 
             
             
               WARM 
               Selecting this pad causes the oven to enter 
             
             
                 
               the warming and reheating mode. 
             
             
               POWER LEVEL 
               Selecting this pad enables adjusting the 
             
             
                 
               power levels for speed cooking and 
             
             
                 
               microwave cooking. 
             
             
               TIMER 
               Selecting this pad controls a general purpose 
             
             
                 
               timer (e.g., minutes and seconds) 
             
             
               REMINDER 
               Selecting this pad enables an operator to 
             
             
                 
               select a time at which an alarm is to sound. 
             
             
               HELP 
               Selecting this pad enables an operator to 
             
             
                 
               find out more about the oven and its features. 
             
             
               OPTIONS 
               Selecting this pad enables access to the auto 
             
             
                 
               night light, beeper volume control, clock, 
             
             
                 
               clock display, and display scroll speed 
             
             
                 
               features. 
             
             
               VENT FAN 
               Selecting this pad enables an operator to 
             
             
                 
               clear the cooktop area of smoke or steam. 
             
             
               SURFACE LIGHT 
               Selecting this pad turns ON/OFF the surface 
             
             
                 
               light for the cooktop. 
             
             
                 
             
          
         
       
     
   
     FIG. 2  is a schematic illustration of oven  100  shown in FIG.  1 . As shown in  FIG. 2 , and in an exemplary embodiment, oven  100  includes a shell  126 , and a cooking cavity  128  is located within shell  126 . Cooking cavity  128  is constructed using high reflectivity (e.g., 72% reflectivity) stainless steel, and a turntable  130  is located in cavity  128  for locating food. Oven  100  includes a microwave module, an upper heater module  132 , and a lower heater module  134 . Microwave module includes a magnetron located on a side of cavity. Magnetron, in an exemplary embodiment, delivers a nominal 900 W into cavity according to standard IEC (International Electrotechnical Commission) procedure. Upper heater module  132  includes radiant heating elements illustratively embodied as a ceramic heater  136  and a halogen cooking lamp  138 . In the exemplary embodiment, ceramic heater  136  is rated at 600 W and halogen cooking lamp  138  is rated at 500 W. Upper heater module  132  also includes a sheath heater  140 . In the exemplary embodiment, sheath heater  140  is rated at 1100 W. A convection fan  142  is provided for blowing air over heating elements and into cooking cavity  128 . Lower heater module  134  includes at least one radiant heating element illustrated as a ceramic heater  144  rated at 375 W. 
   The specific heating elements and RF generation system (e.g., a magnetron) can vary from embodiment to embodiment, and the elements and system described above are exemplary only. For example, the upper heater module can include any combination of heaters including combinations of halogen lamps, ceramic lamps, and/or sheath heaters. Similarly, lower heater module can include any combination of heaters including combinations of halogen lamps, ceramic lamps, and/or sheath heaters. In addition, the heaters can all be one type of heater. The specific ratings and number of lamps and/or heaters utilized in the upper and lower modules can vary from embodiment to embodiment. Generally, the combinations of lamps, heaters, and RF generation system is selected to provide the desired cooking characteristics for speedcooking, microwave, and convection/bake modes. 
     FIGS. 3 ,  4 , and  5  schematically illustrate operation of oven  100  in various modes. Oven  100  may, of course, operate in fewer or more modes than as illustrated in  FIGS. 3 ,  4 , and  5 , and the descriptions set forth below are exemplary only. In addition, operation and use of oven  100  is not limited to the specific order of steps described below. Various steps can be performed in orders different from the exemplary order described below. 
     FIG. 3  is a schematic illustration of oven  100  in speedcooking mode. Generally, for the speedcook mode, a user places food in cavity on turntable  130  and selects “Speedcook” from control panel  118 . The user then uses dial  122  to select a food type and then selects “Start”. Radiant heaters  136  and  138  and convection fan  142  are used to heat the outside of the food, and microwave energy is used to heat the inside of the food. As described below in more detail, the radiant heaters and the magnetron are preferably cycled throughout the cooking cycle to provide the desired cooking results. 
     FIG. 4  is a schematic illustration of oven  100  in a convection/bake mode. Generally, for the convection/bake mode, a user selects “Convection/Bake” from keypad  118 , and then uses dial  122  to select a temperature and cook time. Lower ceramic heater  144  and upper sheath heater  140  are then energized to preheat the air in oven. The food is then placed in cavity  128  and cooking begins. During the cooking cycle, convection fan  142  circulates air to assure even cooking. 
     FIG. 5  is a schematic illustration of oven  100  in a microwave mode, sometimes referred to herein as the microwave only mode. Generally, for the microwave mode, the user places food in oven on turntable  130 . The user then selects “Microwave” or “Express” from keypad  118 . Dial  122  is utilized to select a food type and once the food type is selected, the user selects “Start” from keypad  118 . The magnetron is then energized in accordance with the user selections. 
   Set forth below is a description of one specific embodiment of an oven  200  that is operable in speedcooking, convection/bake, and microwave modes. Many variations of such specific embodiment are possible, and the present invention is not limited to the specific embodiment described below. 
   More specifically,  FIG. 6  is an exploded view of an oven cavity assembly  200 . As shown in  FIG. 6 , cavity assembly  200  includes a cavity subassembly  202  that defines a cooking cavity  204 . A turntable motor mount  206  and motor  208  are assembled to cavity subassembly  202 , and a mica sheet  210  insulates motor  208  from motor mount  206 . A turntable rack  212  is mounted on a turntable surface  214  defined within cavity  204 . In one embodiment, rack  212  includes three circumferentially spaced wheels so that rack  212  rotates under the control of motor  208  and within cavity  204 . Various trays, such as a black metal tray  216  and a glass tray  218 , are mountable on rack  212 . Oven  200  contains a 12V 10 W halogen lamp for illuminating cooking cavity  204  and making the food easily visible to the user. 
   A first bottom panel  220  is secured to a lower surface  222  of cavity subassembly  202 , and bottom panel  220  includes an opening  224  for securing turntable motor  208 . A second bottom panel  226  also is secured to cavity subassembly  202 , and second bottom panel  226  includes vent openings  228 , or inlets, as well as a reflector  230 , a cooktop light panel  232  and cover  234 . Filters  236  are positioned between second bottom panel  226  and cavity subassembly  202  for filtering air drawn therethrough. 
   Side panels  238  are mounted to opposing sides of cavity subassembly  202 , and insulation panels  240  are positioned between each side panel  238  and subassembly  202 . A magnetron mount  242  is mounted on a side of subassembly  202 , and side panel  238  and insulation panel  240  include openings  244  for magnetron mount  242 . Side panel  238  and insulation panel  240  also include vent openings  246 . A back panel  248 , including an insulation panel  250 , is mounted to a back surface  252  of subassembly  202 . Outer case  254  also mounts over subassembly  202 , and a top plate  256  for a vent fan is mounted to outer case  254 . A front grille  260  is mounted over cavity subassembly  202  and between subassembly  202  and an outer case top surface  262 . A screen  264  secured to cavity includes a blocking portion  266  having a pattern that matches the shape of the sheath heater to reduce the amount of radiant energy from the sheath heater in the cavity. 
     FIG. 7  is an exploded view of an oven interior assembly  300 . As shown in  FIG. 7 , a magnetron  302  mounts to magnetron mount  242  on a side surface of cavity subassembly  202 . In addition, a high voltage transformer  304 , low voltage transformers  306 , and a thermal cut-out (TCO)  308  mount to a base plate  309  that is secured to a bottom surface of subassembly  202 . Also, reflector  310 , having a ceramic heater  312  secured therein, is mounted to a bottom surface of subassembly  202 . A damper assembly  314  including a damper door  316 , motor  318 , and mount  320  are arranged to mount over opening  246  in a side of subassembly  202 . In addition, a fan assembly  324  for cooling magnetron  302  includes a fan housing  326 , fan  328 , a motor  330 , a capacitor  332  and a capacitor bracket  334 . A control board  336  having heater relays secured thereto also is mounted by mount  338  to cavity subassembly  202 . 
     FIG. 8  is an exploded view of additional components of oven interior assembly  300 . An insulation panel  340  is located over cavity subassembly  202 , and a top plate  342  is located over panel  340 . A sheath heater  344  is secured to top plate  342 , as well as a heater/lamp assembly  346 . Heater assembly  346  includes a ceramic heater  348  and a halogen lamp  350  secured within a mount  352 . A reflector  354  is secured to mount  352  for directing energy into cavity  204 . An air chamber housing  356  is located over reflector  354 , and an insulation panel  358  and a housing plate  360  are secured over air chamber housing  356 . A thermistor  362  is located within the air chamber defined by housing  356 . 
   A convection fan assembly  364  including a convection fan  366 , a lower casing  368 , an insulation pad  370 , an upper casing  372 , and a motor  374 , are secured in flow communication with air chamber housing  356 . A top cover  376  extends over motor  374 , and a cover plate  378  mounts over convection fan assembly  364 . An access panel  380  for access to the cavity light is secured to cover plate  378 . A vent fan  382  is secured to a fan mount  384  that secures to top plate  342 . 
   A plastic housing  386  defining an air flow path and having a damper therein (not shown) also is secured to top plate  342 . Housing  386  includes a chamber  388  for air flow which facilitates the removal of moisture from oven cavity  204  during microwave cooking. The damper door is open during microwaving to allow moisture to escape the cooking cavity and it is closed during cooking modes that employ the heaters to ensure heat remains in the cooking cavity. A front grill protruder  390  also mounts to top plate  342 . 
     FIG. 9  is an exploded view of oven controller  118 . Controller  118  includes an exterior panel  400 . Rotary  124  dial extends from panel  400  and is rotatable relative to panel  400 . A grounding plate  402  is located behind exterior panel  400  and between exterior panel  400  and a key panel  404 . A push button assembly  406  mounts to key panel  404 , and push buttons  408  extend through openings  410  in grounding plate  402  and exterior panel  400 . Key panel  404  also includes a display  412  as well as light emitting diodes (LEDs)  414 . A shield  416  mounts to key panel  404  and over LEDs  414 . Ribbon connectors  418  extend from key panel  404  to a control board  420 . A microprocessor  422  as well as other components as described below in more detail are mounted to control board  420 . 
     FIG. 10  is an exploded view of oven door  108 . Door  108  includes an injection molded door frame  430  and handle  116  secured thereto. A microwave choke  432  including glass window  114  is secured to door frame  430  by a choke cover  434 . Door  108  is mounted to cavity subassembly  202  by a latch  436 . 
     FIG. 11  is a schematic illustration of oven control. Power is provided to oven  100  via lines L 1 , G, and N. Thermal cut outs  450  and a fuse  452  also are provided to protect oven components, e.g., from overheating or an overcurrent condition. A primary interlock switch  454  is located in the oven door and prevents energization of cooking elements unless door is closed. Relays R 1 , R 2 , R 5 , R 9 , R 10 , R 14 , and R 15  are secured to a main printed circuit board (PCB)  456  and relays R 3 , R 4 , R 7 , R 8 , R 11 , R 12 , R 13 , and R 16  are mounted on a sub PCB  458 . Relays R 1 -R 16  are coupled to a micro computer on main PCB which is programmed to control the opening and closing thereof. Relays R 1 -R 16  are electrically connected in series with thermal cut out (TCO)  450 . 
   Energization of halogen lamp  460  is controlled by relays R 3  and R 4 . To increase reliability of the halogen lamp, a soft start operation can be used. Particularly, in accordance with the soft start operation, a triac connected in series with lamp  460  delays lamp turn-on. For example, lamp  460  may be delayed for one second from commanded turn-on to actual turn-on. 
   Energization of sheath heater  462  is controlled by relay R 7 . Energization of upper ceramic heater  464  is controlled by relay R 8 . Energization of lower ceramic heater  466  is controlled by relay R 9 . 
   Oven  100  also includes a magnetron fan (MF) and a turn table motor (TM) controlled by relay R 16 . Convection fan motor (CM) is controlled by relay R 6 , and vent motor (VM) is controlled by relays R 11 , R 12 , and R 13 . Damper motor (DM) is controlled by relay R 10 . Oven light (OL) and cooktop light (CL) are controlled by relays R 1 , R 15 , and R 14 . 
   Relays R 5  and R 2  control energization of the microwave module which includes a high voltage transformer  338  which steps up the supply voltage. As also shown in  FIG. 11 , oven  100  includes a door sensing switch  468  for sensing whether door is opened, a humidity sensor  470  for sensing the humidity in cooking cavity, a thermistor  472 , a base thermostat  474 , and a damper switch  476 . 
     FIG. 12  is a functional block diagram of oven  100 . As shown in  FIG. 12 , oven  100  includes a structural subsystem  500 , a controls and electrical subsystem  502 , a lower heater module subsystem  504 , a convection module subsystem  506 , a cooling and cooktop venting subsystem  508 , and an RF generation subsystem  510 . Various features of each system are indicated in FIG.  12 . In addition,  FIG. 13  illustrates additional functional details on structural subsystem  500 ,  FIG. 14  illustrates additional functional details on controls and electrical subsystem  502 ,  FIG. 15  illustrates additional functional details on lower heater module subsystem  504 ,  FIG. 16  illustrates additional functional details on convection module subsystem  506 ,  FIG. 17  illustrates additional functional details on cooling and cooktop venting subsystem  508 , and  FIG. 18  illustrates additional functional details on RF generation subsystem  510 . 
   As explained above, a thermistor  362  is located within the air chamber defined by housing, i.e., in the vent airflow path from the vent fan. Output from the thermistor is representative of a temperature in the cooking cavity. A temperature sensed by the thermistor can be affected, however, by the vent fan airflow. Specifically, when the vent fan is on, it is possible that a signal generated by the thermistor will represent a lower temperature than the actual temperature in the cooking cavity.  FIG. 19  is a flow chart  550  illustrating process steps executed by micro computer to adjust for inaccuracies that may result from sampling the output signal from the thermistor when vent fan air is flowing over, and therefore cooling, the thermistor. 
   Specifically, during a thermal cook cycle and after a user selects “Start”  552  on the keypad, the micro controller determines whether the vent fan is ON  554 , e.g., by checking the state of vent fan relay. If the vent fan is not on, then the temperature represented by the thermistor output signal is adjusted in accordance with the values in look-up Table A  556 , below. For example, and in one specific embodiment, if the thermistor output signal represents a temperature of 223 degrees and if the fan is not on, then the actual cooking cavity temperature is 250 degrees. After sampling the thermistor, then a 30 second delay  558  is entered. If cooking time has not ended  560 , micro computer once again determines whether the vent fan is on  554 . 
   If the vent fan is on  554  at the time of sampling thermistor, then look-up Table B  562 , below, is utilized. For example, if the thermistor output signal represents a temperature of 214 degrees and if the fan is on, then the actual cooking cavity temperature is 250 degrees. Every thirty seconds  558  the control checks to see if the vent fan is on. The target thermistor reading is adjusted accordingly throughout the cooking time until cooking stops  564 . 
   Of course, the specific values for the thermistor readings and the corresponding oven cavity temperatures can vary depending on the specific configuration of the oven, the type of thermistor utilized, and the amount of impact vent fan airflow has on the thermistor. The values set forth below in Tables A and B are, therefore, exemplary only. 
   
     
       
         
             
             
             
           
             
                 
               TABLE A 
             
             
                 
                 
             
             
                 
                Cavity Temp. 
               Plug-in (no fan) 
             
             
                 
                 
             
           
          
             
                 
                250 
               223 
             
             
                 
               275 
               242 
             
             
                 
               300 
               261 
             
             
                 
               325 
               281 
             
             
                 
               350 
               300 
             
             
                 
               375 
               319 
             
             
                 
               400 
               338 
             
             
                 
               425 
               357 
             
             
                 
               450 
               376 
             
             
                 
                 
             
          
         
       
     
   
   
     
       
         
             
             
             
           
             
                 
               TABLE B 
             
             
                 
                 
             
             
                 
                Cavity Temp. 
               Plug-in (with fan) 
             
             
                 
                 
             
           
          
             
                 
                250 
               214 
             
             
                 
               275 
               232 
             
             
                 
               300 
               251 
             
             
                 
               325 
               270 
             
             
                 
               350 
               288 
             
             
                 
               375 
               306 
             
             
                 
               400 
               324 
             
             
                 
               425 
               343 
             
             
                 
               450 
               362 
             
             
                 
                 
             
          
         
       
     
   
     FIG. 20  is a block diagram illustration of a speedcook mode. In the speedcook mode, sheath heater  140  is off, upper ceramic heater  136  is on, halogen lamp  138  is on, lower ceramic heater  144  is on, and RF system  302  is on. Control  118  energizes and de-energizes the upper and lower ceramic heaters, the halogen lamp, and the RF system to heat the air and also radiate energy directly to the food on turntable  130 . 
   More specifically, and as shown in  FIG. 21 , in an exemplary embodiment, control  118  operates the cooking elements on a 32 second duty cycle. The length of time each component is on during a particular cycle varies depending on the power level selected. In addition, and as shown in  FIG. 21 , during the speedcooking mode, while the halogen lamp and ceramic heaters are energized, the RF system is not energized. Similarly, when the RF system is energized, the halogen lamp and ceramic heaters are not energized. Such control of the duty cycle enables use of the 120V source. 
   The ratio of the heater on time and microwave on time can be precisely controlled. Different foods will cook best with different ratios. The oven allows control of these power levels through both pre-programmed cooking algorithms and through user-customizable manual cooking. 
   In addition, and for the speedcook mode, it is possible that the speedcook operations follow a previous cooking operation. As a result, the cooking cavity may be heated rather than cool. If the cooking cavity is heated, then to achieve the desired cooking, it may be necessary to adjust the cooking algorithm to compensate for energy already present in the cooking cavity at the time speedcooking is initiated. 
   An algorithm  600  for performing such compensation is illustrated in FIG.  22 . Specifically, once “Speedcook” is selected  602 , the cooking cavity temperature is determined  604  by the micro controller. The micro controller samples the thermistor and determines whether the thermistor sample value is less than 150 degrees F.  606  or greater than or equal to 150 degrees F.  608 . If the temperature is less than 150 degrees F., then the normal cooking algorithm and time are used  610 , i.e., no adjustment is made. If, however, the temperature is greater than or equal to 150 degrees F., then a thermal compensation is performed  612 . 
   For thermal compensation, a thermal compensation time (TCT) is determined in accordance with:
 
 TCT =( TM −31.25)/56.25,
 
and a compensation level U* is determined in accordance with:
 
 U *=(⅓) U. 
 
   For example, and referring to the tables illustrated in  FIGS. 23 ,  24  and  25 , if the temperature is 150 degrees F., then the thermal compensation time (TCT) is equal to 2 minutes and 7 seconds. If the total cooking time is, for example, 5 minutes, then the time during which the thermal compensation is performed is from 0 seconds to 2 minutes and 7 seconds. The thermal compensation amounts to ⅓ of the power level under which normal cooking was scheduled to occur, i.e., Phase 1. For example, if normal cooking is for the lower and upper heaters to be on for a full duty cycle, i.e., for 32 seconds, then during Phase 1, the upper heaters are on for 11 seconds (i.e., about ⅓ of 32 seconds). The lower heater is not on at all during Phase 1. At 2 minute and 8 seconds until the end of the cooking cycle, then normal cooking as scheduled is performed, i.e., Phase 2. The Phase 1 and Phase 2 duty cycles illustrated in  FIGS. 24 and 25  are, of course, exemplary only. 
   Generally, an objective of the thermal compensation described above is to provide a temperature curve as illustrated in FIG.  26 . Specifically, at time 0, if speedcooking is initiated with the cooking cavity fully cooled, then the temperature in the cooking cavity rises as indicated by the “Normal Cooking” line. If, however, the cooking cavity is at 400 degrees if speed cooking were to be initiated without thermal compensation, then the temperature of the cooking cavity would follow the non-compensated line. That is, the temperature in the cooking cavity would rise to much higher temperatures much faster than if the cooking cavity is cooled down when speed cooking is initiated. As a result, more energy is input to the food and the food may be more cooked than planned. 
   Rather than instructing a user to wait for the cooking cavity to cool, the thermal compensation algorithm allows the cooking cavity to cool down from 400 degrees and may actually fall below the temperature that would be achieved by “Normal Cooking” during Phase I to compensate for the initially higher cooking cavity temperature. During Phase 2, the control algorithm is no longer adjusted and the cooking cavity temperature tracks with the temperature that would be provided with Normal Cooking. 
     FIG. 27  is a block diagram illustration of a microwave mode. In the microwave mode, only the RF system is on during the cooking cycle. Microwave energy from the magnetron heats the food. As shown in  FIG. 28 , the RF system can be energized for 100% of the duty cycle, or can cycle on and off for an amount of time based on the selected power level during each duty cycle. 
     FIG. 29  is a block diagram illustration of an oven/bake mode, and  FIG. 30  illustrates duty cycles for the oven/bake mode. During the oven/bake mode, sheath heater  140  and lower ceramic heater  144  are energized. Specifically, during the pre-heat cycle, both the sheath heater and the lower ceramic heater are energized. Once the oven cavity temperature reaches the pre-heat temperature, then control  118  causes the sheath heater and the lower ceramic heater to be energized in accordance with a predetermined control. 
   Although many alternatives are possible, in one specific embodiment, the general control objective is to prevent the lower portion of the food from cooking at a faster rate than other portions of the food. Specifically, the lower ceramic heater is closer to the food than the sheath heater and therefore, unless a control is employed, the lower ceramic heater may cause the lower portion of the food to cook faster than other portions of the food. 
   Many control approaches can be used to achieve the desired result, i.e., even cooking of the food. In an exemplary embodiment, the lower ceramic heater is energized to be on for a shorter period of time than the sheath heater. For example, the lower ceramic heater can be controlled to be on for about 63% of the time that the sheath heater is on. Such control of the ceramic heater and the sheath heater facilitates maintaining the oven cavity temperature near a target temperature without over-shoot and under-shoot that may result in over or under cooking foods. 
   Rather than controlling the lower ceramic heater as described above, the lower ceramic heater could be controlled to operate to output a lower wattage than normal operation. For example, if the lower ceramic heater normally operates at 375 watts, the lower ceramic heater could be controlled to output 275 watts. As yet another alternative, the lower ceramic heater can be energized on every other ½ cycle, i.e., cycle skipping, to reduce the energy supplied to such heater and consequently, the energy output by the heater. Again, many alternatives are possible. 
   During operation, an operator may adjust the power level of the upper heater module, the lower heater module, and the microwave module. To change the power level, the operator selects the POWER LEVEL pad and a select icon flashes on display. A message “Select UPPER POWER” then is displayed. Rotation of dial then enables an operator to select the upper power level (clockwise rotation increases the power level and counter clockwise rotation decreases the power level). In the speedcook mode, selection of the upper power level inherently determines the microwave power level as well, since the duty cycle is defined such that the microwave runs whenever the upper heaters (ceramic and halogen) are off. When dial is pressed to enter the selection, a short beep sounds and “Select LOWER POWER” is displayed. Dial rotation then alters the current lower power level, and when dial is pressed, a short beep is sounded. “Press START” is then displayed. The oven will wait until the START pad is pressed before beginning cooking. If the power level pad is pressed when it is not allowed to change/enter or recall the power level, a beep signal (0.5 seconds at 1000 hz) sounds and the message “POWER LEVEL MAY NOT BE CHANGED AT THIS TIME” scrolls on display. After the scroll has completed, the previous foreground features return. If the power level pad is pressed at a time when a change/entry is allowed, but no dial rotation or entry occurs within 15 seconds, the display returns to the cooking countdown. 
   Cook time may also be adjusted during cooking operations. During cooking operations, a main cooking routine COOK is executed. If dial is not moved, the main cooking routine continues to be executed. If dial is moved, then the microcomputer determines whether dial was moved clockwise. If no (i.e., dial was moved counterclockwise), then for each increment that dial is moved, the cook time is decremented by one second. If yes, then for each increment that dial is moved, the cook time is incremented by one second. 
   Oven may also be operated in a warming mode. Specifically, if a user select “Warm”, then the lower ceramic heater and the sheath heater are energized to a selected target temperature, e.g., a temperature in a range of about 140 to 220 degrees F. Such operation facilitates maintaining food warmth. In addition, it is contemplated that a moist/crisp selection could be provided for a user in the warming mode so that user can select whether the food to be warmed should be moist or crisp. Specifically, if a user selects moist, then damper is maintained closed to maintain moisture in the cavity whereas if the user selects crisp, the damper is opened to allow moisture to flow out of the cooking cavity. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.