Abstract:
A programmable slow-cooker appliance, in which a user sets a time and temperature for cooking a food item. A programmable controller prevents the unit from being used solely as a “keep warm” appliance, and a unique design allows cooling of the controller during cooking.

Description:
This application is a continuation of application Ser. No. 09/802,174, filed Mar. 8, 2001, (pending), which is hereby incorporated by reference herein. 
     This application claims priority to Provisional Application No. 60/189,443, filed Mar. 15, 2000, and to Provisional Application No. 60/196,273, filed Apr. 5, 2000. 
     This application also claims priority to U.S. patent application Ser. No. 09/802,174, filed Mar. 8, 2001, now U.S. Pat. No. 6,573,483 the entirety of which is incorporated herein. 
    
    
     BACKGROUND OF THE INVENTION 
     Time and convenience are in short supply for homemakers wishing to supply a home-cooked meal to family members. Some appliances, such as slow-cooker appliances, attempt to meet this need by providing all-day cooking while a homemaker is absent. Such appliances, however, tend to be of the type where only one temperature and all day cooking is possible, regardless of the food item, and thus potentially subjecting the food item to over- or under-cooking. Another option may be to use a cooking unit with, a controller, where a user may set a time or temperature desired. These units, however, tend to be quite a bit larger and more expensive than slow-cooker appliances. If these units are of more reasonable size, they also suffer because the controller inevitably must be placed near the heating element. 
     What is needed is a cooking appliance in which the user retains control over the time and temperature of cooking, but which is small enough to be convenient. What is needed is a slow-cooker unit in which the controller does not become overheated and damaged by the heating element. 
     SUMMARY OF THE INVENTION 
     One embodiment of invention is a programmable slow-cooker appliance, including a heating unit, which includes upstanding sidewalls and a bottom wall. The sidewalls and bottom encompass a heating area. The appliance includes a heating element mounted on the inner surface of the interior wall of the heating unit. In one embodiment, the cooking area may also encompass a cooking unit inside the heating unit, suitable for holding food to be cooked. The appliance includes a programmable controller mounted thereto via a controller housing, which acts to insulate the controller from the heat of the appliance, preferably via a unique system of ventilation. The housing utilizes ventilation holes on its bottom and top to encourage a chimney effect, in which air from the surroundings is drawn through the housing. This air cools the controller, and the air is then exits from ventilation holes near the top of the housing, convecting heat away from the controller. 
     Another aspect of the invention is a method of using the programmable controller to ensure that food is cooked according to the desires of a user. The user provides a food item and places the food item into the slow-cooker appliance, as described above. The user sets a cooking time and temperature for the programmable slow-cooker unit, using the controls to set both the time and the temperature. The cooking time according to one embodiment may not be set less than four hours, and the temperature may not be set for less than 150 degrees Fahrenheit (66 degrees Celsius). This prevents a user from accidentally setting the cooker to a “warm” temperature, in which food would only be warmed but not cooked thoroughly before consumption. In one embodiment, if the user sets no time or temperature, but merely turns the cooker on, the cooker defaults to a particular time and temperature, set by the user or the factory, such as a default setting of four hours and 175 degrees Fahrenheit or eight hours and 150 degrees Fahrenheit. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of an embodiment of a prior art slow-cooker appliance having an oval shape that may be utilized in the present invention; 
     FIG. 2 is a perspective view of a prior art embodiment of a cooking unit  14  which may be utilized with the appliance of FIG. 1; 
     FIG. 3 is a perspective view of a prior art cooking unit  39  similar to that shown in FIG. 2, but having a circular shape; 
     FIG. 4 is a perspective view of a slow cooker appliance incorporating the present invention; 
     FIG. 5 is a detailed plan view of a portion of the control  200  of the embodiment of FIG. 4; 
     FIG. 6 is a bottom plan view of the embodiment of FIG. 4; 
     FIG. 7 is a side cutaway view of the embodiment of FIG. 4; 
     FIG. 8 is a plan view of a heat sink  256  as utilized in the embodiment of FIG. 4; 
     FIG. 9 is a side view taken along a line  9 — 9  of FIG. 8; 
     FIGS. 10 and 13 are schematic circuit diagrams showing the circuitry and components implemented in preferred embodiments; 
     FIG. 11 is a wiring diagram showing some of the electric componentry of the preferred embodiment; and 
     FIG. 12 is an embodiment of the front panel. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, one prior art embodiment of a food-heating slow-cooker appliance  10  is shown. The appliance  10  preferably comprises a heating, unit  12  and a cooking unit  14 . An exemplary slow cooker appliance  10  may be a Crock-Pot® Slow Cooker made by The Rival Division of The Holmes Group® of Milford, Mass. The heating unit  12  preferably has a bottom  16  and a continuous outer sidewall  18 . The bottom  16  and an interior sidewall  17  define a well-like heating chamber  20  having an oval cross-section, and the interior sidewall  17  defines an annular lip  22  at an upper edge of the outer sidewall  18  and the interior sidewall  17 . The heating chamber  20  has a heating element  24  disposed therein and mounted to the heating unit  12 , either under the bottom  16  or additionally between the outer sidewall  18  and the interior sidewall  17 . A control switch  26  is conventionally used to provide electricity to the heating element  24 . The heating element  24  functions to heat the cooking unit  14  via the heating chamber  20 . 
     As shown in FIG. 2, the cooking unit  14  has a bottom  28  with preferably a continuous sidewall  30  upstanding therefrom. The continuous sidewall  30  preferably has an annular lip  38  projecting in flange-like fashion from the upper end thereof and a substantially oval cross-section. The cooking unit  14  is adapted to be at least partially received within the heating unit  12  with the annular lip  38  of the cooking unit  14  preferably engaging the annular lip  22  of the heating unit  12 , supporting the cooking unit  14  within the heating unit  12 . Preferably, the annular lip  38  further defines a pair of handle portions  38 ( a ) and  38 ( b ) to facilitate lifting the cooking unit  14 . The cooking unit  14 is preferably made of ceramic with a coating of conventional glazing compound. 
     The thermal and heat retaining properties of the ceramic cooking unit  14  allow it to conduct heat from the heating chamber  20  through the sidewall  30 . This provides even heating throughout the unit  14 . 
     As shown in FIG. 3, an alternative embodiment of the appliance  10  includes a cooking unit  39  having a sidewall  40  and a substantially circular cross-section. This embodiment is preferably adapted to fit within a heating unit having a complementary circular heating chamber. This cooking unit  39  is used in an embodiment of the present invention shown in FIG.  4 . 
     In use, the heating unit  12  is provided with a first cooking unit  39 . The heating element  24  (not shown) may be powered on and off as necessary to supply heat at a maintained temperature to the cooking unit  39  and the heating chamber via a programmable control  200 . The control  200  preferably includes a circuit board housing  210 , a control panel  220 , and an insulation shield  222  assembled together for attachment to the outer sidewall  18  of the heating unit  12 . The interior of the housing  210  contains a printed circuit board  254  (shown in FIG. 7) containing electronic components of the control. 
     As shown in FIGS. 5 and 6, the housing  210  preferably includes a control panel user interface  224  located on an inclined front surface of the housing  210 . Preferably, the housing  210  and insulation shield  222  are made from a thermoplastic material such as polypropylene. A pair of side walls  226 , a top wall  228 , and bottom wall  230  are preferably located adjacent the control panel  224  and support the control panel  224  in an inclined position away from the front of the cooking appliance  10 . This gives the user access to the control panel  224 , and also locates the controls and componentry within the housing  210  away from a significant amount of the heat generated by the appliance  10 . The printed circuit board  254  may be mounted via threaded screws  255  to rearwardly projecting screw receiving portions  258  on the rear side of the housing  210 . 
     The control panel  224  includes a plurality of indicator lights, such as LEDs  262 , spaced on the front panel  224 . As is well-known in the art, a variety of other indicator devices may be provided, including digital readouts, audible alarms, liquid crystal displays, incandescent lamps or fluorescent readouts. Preferably, the control panel  224  also includes a plurality of cantilevered portions  264  and  266  as shown in FIG.  5 . The cantilevered portions  264 ,  266  preferably include rearwardly projecting fingers  268  (shown in FIG. 7) which translate the depression of the portions  264 ,  266  toward the rear portion of the housing  210 . The fingers  268  are preferably used to depress pushbutton switch portions located on the circuit board  254 . A water-impermeable label membrane may be applied over the front of the control panel  224  to label the indicators  262  and cantilevered portions  264  and  266  for the user. The membrane may also protect the front control panel  224  from damage from spilled foods or liquids and facilitate cleaning. 
     To further protect the electronic componentry within the housing  210  from the heat generated by the appliance  10 , the annular shield member  222  is preferably sized for interposition between the heating unit  12  and the housing  210 . In particular, as shown in FIGS. 5 and 6, the shield  222  includes a top wall  232 , a pair of side walls  234 , and a bottom wall  236 . The shield  222  acts as a ventilated spacer to hold the electronic components and the housing  210  at a distance away from sidewall of the cooking unit  12 . 
     In order to dissipate heat that may otherwise be retained between the cooking unit  12  and the rear of the housing  210 , an air circulation space is provided within the shield. In particular, as shown in the side cutaway view of FIG. 7, the air space  240  behind the shield  222  may vent warmer air out through an upper elongated slot  242  defined within the top wall  232  of the shield  222 . Likewise, an elongated slot  244  is defined into the air space  240  in the bottom wall  236  of the shield  222 . Heated air may thus escape through the top elongated slot  242  and cooler air may enter the air space  240  through the bottom elongated slot  244 . As shown in FIG. 7, the shield  222  also preferably defines a rearwardly projecting cylindrical flange  246  that extends into the outer wall  18  to allow passage of control and power wiring between the interior of the heating unit  12  and the interior of the housing  210 . 
     In a similar fashion, air circulation is promoted through the housing  210  through a set of openings, preferably defined between the upper portion and, the bottom of the housing  210 . In particular, a plurality of openings  250  are defined within the bottom wall  230  of the housing  210 . An elongated upper slot  252  is provided on the front face  224  of the housing  210 . This allows air to freely circulate behind the control panel  224  and assist in the dissipation of heat from the circuit board  254  and its electronic componentry within the housing  210 . Preferably, a heat sink  256  is provided as shown in FIG.  7  and positioned between the circuit board  254  and the front panel  224  inside the housing  210 . The sink  256  preferably includes a plurality of openings defined therein to allow air to circulate between the openings  250  and  252  and through and around the heat sink  256  to dissipate additional heat therefrom. Also shown is the relative position of cooking unit  14 . 
     FIGS. 8 and 9 show a detailed view of the heat sink  256 . Preferably, the heat sink is machined from 0.063 inch thick 3003-0 anodized aluminum. The heat sink  256  is preferably bent at a 160 degree angle between a bottom flange portion  256   a  and an upper portion  256   b . A centrally located retaining tab portion  256   c  is bent parallel with the lower portion  256   a , and the portions  256   a  and  256   c  are used for attachment of the heat sink  256  to the rear side of the housing  210  interior via the rearwardly projecting screw receiving portions  258 . To maximize the dissipation of heat, a plurality of winged sections  257  and  259  are provided on the heat sink  256  and extend outwardly from a center portion  256   a  of the heat sink  256 . A plurality of openings are defined through the heat sink  256  to allow the fingers  258  of the control panel cantilevered portions  264 ,  266  to project through the heat sink and contact the circuit board  254  at the rear of the housing  210 . The openings  251  also facilitate cooling air flow through and past the heat sink  256  to further dissipate heat therefrom. 
     The circuit board  254  mounts circuitry and logic allowing the user of the appliance  10  to electronically control and program cooking cycles and temperature. A schematic diagram of the electronic circuitry and components is shown in FIG.  10 . The diagram shows a preferred exemplary circuit incorporating preferred components as utilized in the preferred embodiment of the present invention. One skilled in the art will recognize that the componentry illustrated herein is exemplary only and that many other components may be substituted to achieve the functions described herein. FIG. 10 includes labels for each of the components of the circuit, and only major components will be described herein. 
     First, as shown in the diagram, the preferred circuit  300  is preferably built around an EPROM/ROM-based CMOS microprocessor controller  302 , such as the PIC16CR54C RISC CPU manufactured by Microchip Technology, Inc. The chip output preferably includes circuited drivers for  6  LED indicators  262  (labeled D 3 -D 8 ) as shown. These LED indicators may be assigned labels as follows: 
     
       
         
               
               
               
             
           
               
                   
                   
               
               
                   
                 LED 
                 Indicates 
               
               
                   
                   
               
             
             
               
                   
                 D3 
                 On 
               
               
                   
                 D4 
                 WARM 
               
               
                   
                 D5 
                 4 HOUR 
               
               
                   
                 D6 
                 6 HOUR 
               
               
                   
                 D7 
                 8 HOUR 
               
               
                   
                 D8 
                 10 HOUR  
               
               
                   
                   
               
             
          
         
       
     
     Two momentary pushbutton contact switches S 1  and S 2  are used to trigger the “Off” and “Cook” features, respectively, as will be described in the cooking procedure below. Of course, other indicators and switches may be substituted. Note that while examples are given, the circuitry may be implemented in numerous ways, as is well-known in the art, to accomplish the varying programming modes described below. 
     The temperature of the cooking appliance is measured using a thermistor  310 , which is connected externally of the circuit board to the underside of the bottom of the heating chamber. A retention clip  320 , shown in FIG. 7, is utilized to hold the thermistor in thermal contact with the bottom  16 . In a preferred embodiment, the appliance uses a model USX1732 thermistor manufactured by U.S. Sensor, Inc. 
     Triac  304 , which is preferably a logic Triac Model L4008L6-ND manufactured by Digi-Key, Inc., is utilized to switch the power supplied to the heating elements of the appliance. Preferably, the Triac is of an isolated tab type and includes a heat sink tab that is fastenable to the heat sink  256  shown in FIGS. 8 and 9. Preferably, the Triac is mounted separately to one of the mounting holes on the center portion  256   a  of the heat sink  256  so that the tab is in thermal contact with the heat sink  256  to dissipate heat generated from its current controlling function. Most of the other components of the circuit  300  are mounted on a conventional printed circuit board  254 . 
     FIG. 11 shows the wiring of the external Triac  304  in relation to the circuit board  254  and heating elements  24 . As shown in the Figure, the heating elements  24  are in thermal contact with and wrapping around the interior sidewall  17  of the heating unit. 
     The operation of the appliance  10  is as follows. The programmable circuitry  300  allows the user to set both the temperature and desired time for cooking. The functions of the switches Si and S 2 , which are activatable via the cantilevered portions  264  and  266  of the control panel  224 , are as follows: 
     S 1 . OFF pushbutton—turns the appliance  10  off. 
     S 2 . COOK pushbutton—subsequent pushes of the button cycle through 4 hour, 6 hour, 8 hour and 10 hour cook times. 
     When the unit is plugged in, the power “on” indicator flashes. The user then pushes the COOK button (switch S 2 ) to set the temperature and cooking time. As the user pushes the COOK switch S 2 , the LED&#39;s D 5 -D 8  illuminate to indicate the corresponding time setting as follows. 
     LEDs 
     D 3 . POWER—on when appliance  10  is in cook or warm modes. 
     D 5 . 4 HOUR—on when appliance is in 4-hour cook mode 
     D 6 . 6 HOUR—on when appliance is in 6-hour cook mode 
     D 7 . 8 HOUR—on when appliance is in 8-hour cook mode 
     D 8 . 10 HOUR—on when appliance is in 10-hour cook mode 
     D 4 . WARM—on when appliance is in half-power mode 
     Thus, subsequent pushes of the COOK switch S 2  activate different cooking modes, as shown by the 6 HOUR, 8 HOUR and 10 HOUR LEDs  262  on the control panel  224 . If the COOK switch S 2  is pressed in the 10 HOUR mode, the control  200  recycles to the 4 HOUR cooking mode, and its indicator. 
     In general, full power will be applied to the heating element  24  until the time corresponding to the illuminated LED elapses, after which the power to the heating element  24  is reduced by half, the WARM indicator illuminates and all cook time indicators extinguish. The choices of operation are: 4 or 6 hours on a HI temperature, and 8 to 10 hours on a lower temperature setting. Once the user selects the desired setting, the appliance  10  starts the cooking operation. Once the time setting has expired, the appliance  10  automatically reduces power to the heating element  24  to put the unit in a WARM setting. The unit will stay in the WARM setting until the user pushes the OFF button or unplugs the unit. Of course, other programming schemes are possible. 
     Preferably, the user cannot set the unit initially in the WARM setting. The system will only go to WARM after one of the time functions has expired. This avoids possible food safety problems that may be associated with cooking food only on the WARM setting. Pressing the OFF switch Si any time the unit is on preferably removes power from the heating element  24  and extinguishes all indicator LEDs  262 . 
     In another embodiment, the slow-cooker appliance utilizes four push-button switches, rather than two, to set times and temperatures for cooking. An exemplary control panel is depicted in FIG. 12, with control circuitry in FIG.  13 . Four momentary pushbutton contact switches  227 ,  229 ,  231 ,  233  are used to trigger various power and setting functions as will be described in the cooking procedure below. Of course, other numbers or types of indicators and switches may be substituted as well. FIG. 13 shows circuitry applicable to such an embodiment, incorporating controller  302 , external temperature element  310 , digital readout  57 , and Power LED  263  and Timer LED  265 . The Power LED indicates power is present at the microprocessor controller and the Timer LED indicates that the Timer function is on and working. 
     The operation of the appliance is as follows. The programmable circuitry allows the user to set both the temperature and the desired cooking time. The functions of the switches  227 ,  229 ,  231 ,  233  on an alternative embodiment of a control panel user interface  225 , are as follows: 
       227 . ON/OFF power pushbutton—turns the appliance on and off. 
       229 . TIMER pushbutton—activates stepped timer. 
       231 . UP pushbutton—increases displayed numerical value. 
       233 . DOWN pushbutton—decreases displayed numerical value. 
     When the unit is plugged in, the unit defaults to 150-degrees F. as shown on the digital display  57 . The user may adjust the desired cooking temperature in 25-degree increments using the UP  231  button or the DOWN button  233 , with 150 degrees Fahrenheit as a minimum temperature. Once the user has selected the specific temperature, the appliance will start the cooking process. 
     The user may also select the TIMER mode by pressing the TIMER button  229 . In TIMER mode, the controller defaults to 4 hours. The user can use the UP or DOWN controls to increase or decrease the time in 15-minute increments. Once the time is set, the controller  302  will count down the time remaining for cooking in 1 minute increments until the unit “times out”. At that time, the power is shut off from the heating element. 
     In all modes, the temperature is read periodically by the thermistor or other temperature element and relayed to the controller. The reading is checked at 4-second intervals. If the temperature is above or equal to the set point, power is removed. If it is below the set point, power is applied to the heating element  32 . Of course, the circuitry can be modified as desired to achieve various program methods and modes. 
     Another embodiment of the slow cooker appliance adds a piezobuzzer to the circuitry. A piezobuzzer is simply an electrically-activated buzzer that can be programmed to emit a sound at desired moments. In one embodiment, a piezobuzzer may be installed as an output  315 , controlled by the microprocessor controller  302 , as shown in FIG. 13, and programmed to emit a sound when desired. In one embodiment, the buzzer may beep to provide feedback to a user when a pushbutton is pushed. The slow cooker may also be programmed to emit a sound to indicate the end of the cooking time. The buzzer may also be used to emit sounds at other desired times. 
     It is intended that the foregoing description illustrates rather than limits this invention, and that it is the following claims, including all equivalents, which define this invention. Of course, it should be understood that a wide range of changes and modifications may be made to the embodiments described above. Accordingly, it is the intention of the applicants to protect all variations and modifications within the valid scope of the present invention. It is intended that the invention be defined by the following claims, including all equivalents.