Abstract:
A conveyorized oven that provides uniform cooking with control of the heater and/or the conveyor belt speed. The oven includes a controller that monitors power consumption of the heater and uses the power consumption to control the heater and/or the speed of the motor that drives the conveyor belt. The power consumption is monitored by counting the on time cycles of a switch that connects and disconnects the heater to a power main. Changes in the power consumption due to changes in loading are used by the controller to reduce recovery times of the oven temperature to a set temperature by controlling the heater and/or the motor. By using a stepper motor, there is no need for a gear box.

Description:
RELATED APPLICATION 
       [0001]    This application claims priority of U.S. Provisional Application Ser. No. 60/895,308, filed on Mar. 16, 2007, the entire contents of which are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This disclosure relates to a conveyorized oven with radiant heating and a controller for uniform cooking of food products. 
       BACKGROUND OF THE INVENTION 
       [0003]    Most ovens with a radiant heat source have a load dependency that yields different cooking results depending on how many food items are cooked simultaneously and the frequency of loading the food items. A typical example is a conveyer toaster for commercial food service where the browning of the toast will vary due to the load factor (continuous use or single piece processing) as well as the age or use of the toaster itself. Manufacturers have attempted to deal with some of these issues, but the major disadvantages are that the toasters do not react quickly and accurately and do not deal with the variation in radiation that typically occurs over the lifetime of the appliance. The most common approach takes information from an oven temperature sensor and adjusts the conveyor speed as described, e.g., in U.S. Pat. No. 5,821,503 and U.S. Pat. No. 6,624,396. This approach has the disadvantage of having a long processing time when the load factor increases. 
         [0004]    One of the weakest parts of appliances having a conveyor is the gearbox that is normally required on the motor driving the conveyor. Due to the low rotational speeds required by the conveyor, it is difficult to find a motor with sufficient torque without a gearbox. If the motor has a gearbox, it is normally expensive due to the requirements of durability and side-loading of the drive shaft. 
         [0005]    Thus, there is a need for consistent cooking of food items that is independent of load factors and age of the toasting appliance. 
         [0006]    There is a need for minimization of cooking variations due to main voltage fluctuations. 
         [0007]    There is a need for consistent cooking of food items for the same cooking set point. 
         [0008]    There is a need for minimization of the variation in processing time for different load factors. 
         [0009]    There is a need for a conveyor drive without a gear box. 
         [0010]    There is need for an improved temperature control. 
       SUMMARY OF THE INVENTION 
       [0011]    A first embodiment of a conveyor oven of the present disclosure comprises a conveyor belt that is driven by a drive wheel. A stepper motor comprises an output shaft that is coupled to the drive wheel. A controller is coupled to drive the stepper motor. 
         [0012]    In one aspect of the first embodiment of the conveyor oven of the present disclosure, the stepper motor further comprises first and second windings. The controller provides first and second sinusoidal currents to the first and second windings, respectively. 
         [0013]    In another aspect of the first embodiment of the conveyor oven of the present disclosure, the first sinusoidal current is 90 degrees out of phase with the second sinusoidal current. 
         [0014]    In another aspect of the first embodiment of the conveyor oven of the present disclosure, the controller controls a speed of the stepper motor based on a load variance of food products disposed on the conveyor belt. 
         [0015]    In another aspect of the first embodiment of the conveyor oven of the present disclosure, the conveyor belt is disposed in an oven compartment. A heater is disposed in the oven compartment to provide heat to cook food products disposed on the conveyor belt. The controller determines the load variance by monitoring a power consumption of the heater and controls the stepper motor speed based on the power consumption, thereby controlling the conveyor belt speed. 
         [0016]    In another aspect of the first embodiment of the conveyor oven of the present disclosure, the heater is an electric heater connected in circuit with a power main by a switch. The controller determines the power consumption based on an amount of time the heater is connected with the power main by the switch. 
         [0017]    In another aspect of the first embodiment of the conveyor oven of the present disclosure, the controller further controls the stepper motor speed based on a member of the group consisting of: a predetermined cook speed, the stepper motor speed and a combination thereof. 
         [0018]    In another aspect of the first embodiment of the conveyor oven of the present disclosure, the stepper motor further comprises first and second windings. The controller provides first and second sinusoidal currents to the first and second windings, respectively. The first and second sinusoidal currents have a frequency that is a function of the power consumption and the member of the group. 
         [0019]    In another aspect of the first embodiment of the conveyor oven of the present disclosure, the stepper motor speed is determined by the frequency. 
         [0020]    In another aspect of the first embodiment of the conveyor oven of the present disclosure, the controller controls the switch based on a temperature of the heater. 
         [0021]    A first embodiment of a method of the present disclosure operates a conveyorized cooking oven by placing food products on a conveyor belt, providing heat to cook the food products, and driving the conveyor belt with a stepper motor. 
         [0022]    In one aspect of the first embodiment of the method of the present disclosure, the method comprises further providing first and second out of phase sinusoidal currents to first and second windings, respectively of the stepper motor. 
         [0023]    In another aspect of the first embodiment of the method of the present disclosure, the method further comprises controlling a speed of the motor based on a load variance of the food products on the conveyor belt. 
         [0024]    In another aspect of the first embodiment of the method of the present disclosure, the heating step uses a heater and the method further comprises determining the load variance by monitoring a power consumption of the heater and controlling the stepper motor speed based on the power consumption, thereby controlling the conveyor belt speed. 
         [0025]    In another aspect of the first embodiment of the method of the present disclosure, the power consumption is determined by an amount of time the heater is connected with an energy source. 
         [0026]    In another aspect of the first embodiment of the method of the present disclosure, the stepper motor speed is further controlled based on a member of the group consisting of: a predetermined cook speed, the stepper motor speed and a combination thereof. 
         [0027]    In a second embodiment of the conveyor oven of the present disclosure, a conveyor belt that is driven by a drive wheel. A heater is disposed to cook food products on the conveyor belt. A motor is coupled to the drive wheel. A controller is coupled to monitor a power consumption of the heater and to control a speed of the motor based on the power consumption, thereby controlling a speed of the conveyor belt. 
         [0028]    In one aspect of the second embodiment of the conveyor oven of the present disclosure, the heater is an electric heater connected in circuit with a power main by a switch. The controller determines the power consumption based on an amount of time the heater is connected with the power main by the switch. 
         [0029]    In another aspect of the second embodiment of the conveyor oven of the present disclosure, the controller further controls the motor speed based on a member of the group consisting of: a predetermined cook speed, the motor speed and a combination thereof. 
         [0030]    In a second embodiment of the method of the present disclosure, the conveyor oven is operated by placing food products on a conveyor belt, operating a heater to cook the food products, driving the conveyor belt with a motor, monitoring a power consumption of the heater, and controlling a speed of the motor based on the power consumption. 
         [0031]    In one aspect of the second embodiment of the method of the present disclosure, the power consumption is determined by an amount of time the heater is connected with an energy source. 
         [0032]    In a third embodiment of the conveyor oven of the present disclosure, the oven comprises a conveyor belt and a heater that is disposed to cook food products on the conveyor belt. A controller is coupled to monitor a power consumption of the heater and to control a temperature of the heater based on the power consumption. 
         [0033]    In one aspect of the third embodiment of the conveyor oven of the present disclosure, a switch connects and disconnects the heater with a power main. The controller monitors the power consumption by counting an on time of the switch, and controls the switch with a deviation of the power consumption based on a predetermined power consumption with the conveyor belt unloaded. 
         [0034]    In another aspect of the third embodiment of the conveyor oven of the present disclosure, a temperature probe provides a signal indicative of a temperature of the heater. The controller uses the signal to control the switch to maintain the heater temperature in equilibrium with a set temperature despite variations of the heater temperature. 
         [0035]    In another aspect of the third embodiment of the conveyor oven of the present disclosure, the temperature probe is disposed in contact with the heater. 
         [0036]    In a third embodiment of the method of the present disclosure, the conveyor oven is operated by placing food products on a conveyor belt, operating a heater to cook the food products, monitoring a power consumption of the heater, and controlling a temperature of the heater based on the power consumption. 
         [0037]    In one aspect of the third embodiment of the method of the present disclosure, the power consumption is monitored by counting an on time of a switch that connects and disconnects the heater with a power main. The temperature is controlled by using a deviation of the power consumption based on a predetermined power consumption with the conveyor belt unloaded to control the switch. 
         [0038]    In another aspect of the third embodiment of the method of the present disclosure, the method further measures the temperature of the heater. The switch is controlled to maintain the heater temperature in equilibrium with a set temperature despite variations of the heater temperature. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]    Other and further objects, advantages and features of the present disclosure will be understood by reference to the following specification in conjunction with the accompanying drawings, in which like reference characters denote like elements of structure and: 
           [0040]      FIG. 1  is a front view of an oven of the present disclosure; 
           [0041]      FIG. 2  is a cross-sectional view along line  2  of  FIG. 1 ; 
           [0042]      FIG. 3  is a cross-sectional view along line  3  of  FIG. 1 ; 
           [0043]      FIG. 4  is a schematic diagram of the oven of  FIG. 1 ; and 
           [0044]      FIG. 5  is a view of a heater element and temperature probe of the oven of  FIG. 1 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0045]    Referring to  FIGS. 1-3 , an exemplary oven  20  of the present disclosure comprises side walls  22  and  24 , a top wall  26 , a bottom wall  28 , a back wall  30  and a front wall  32 . Front wall  32  comprises a food entry port  34  and a food exit slot  36  near bottom wall  28 . Food items to be toasted or cooked are inserted via food entry port  34  and after cooking are retrieved from food exit port  36 . A partition  38  (shown in  FIGS. 1 and 3 ) divides oven  20  into an oven compartment  40  (shown in  FIG. 2 ) and a control compartment  42  (shown in  FIG. 3 ). 
         [0046]    A conveyor belt  44  is disposed in oven compartment  40  and is supported by a framework (not shown) that is attached, for example, to bottom wall  28 . Conveyor belt  44  is disposed on an idler wheel  46  and a drive wheel  48  for clockwise rotation. One end of conveyor belt  44  is disposed near food entry port  34  so that upon entry food items land on conveyor belt  44  and are conveyed through oven compartment  40 . At the opposite end of conveyor belt  44  the cooked food items fall by gravity onto a chute  50  that guides them to a tray  52  located adjacent food exit port  36 . 
         [0047]    A plurality of radiant heater elements  60  is disposed in oven compartment  40  above and below conveyor belt  44  to provide radiant heat toward the tops and bottoms of food items on conveyor belt  44 . Manually operable cook temperature set buttons  54  and manually operable conveyor belt speed set buttons  56  are located on front wall  37 . 
         [0048]    Referring to  FIGS. 2 and 3 , drive wheel  48  comprises an axle  72  that extends through partition  38  into control compartment  42 . Axle  72  is coupled via a pulley  74  and a belt  76  to a drive pulley drive pulley  78 . Drive pulley  78  is driven by a motor  80 , which is also disposed in control compartment  42 . 
         [0049]    Referring to  FIG. 4 , oven  20  further comprises a controller  100  that controls radiant heating elements  60  to provide a consistent temperature in oven compartment  40  despite variations due to food item loading, power main variations and cooling due to heat loss to ambient via food entry port  34 . A temperature probe  64  is embedded in heater elements  60 , preferably in association with upper radiant heater element  62  (also shown in  FIGS. 2 and 5 ) that is located near food entry port  34 . Temperature probe  64 , for example, may be a resistor temperature detector (RTD). In an alternate embodiment, temperature probe  64  may comprise a combination of a thermocouple and an ambient temperature probe. 
         [0050]    Controller  100  also receives a set point temperature Tset based on a setting of cook temperature buttons  54  and a conveyor belt speed set point Sset based on a setting of conveyor speed buttons  56 . 
         [0051]    Radiant heating elements  60  are connected in circuit with an ac source  90  and contacts  92  of a relay  94 . Relay  94  may be a solid state relay, such as a triac. Controller  100  processes signals received from temperature probes  64  and  66  and modulates relay  94  to maintain a nearly constant radiation from radiant heating elements  60 . 
         [0052]    Controller  100  comprises a microprocessor  102 , a memory  104 , an analog to digital (A/D) converter  106  and digital to analog converters  108  and  110 . A heater program  112  and a motor program  114  are stored in memory  104 . A/D converter  106  converts an analog signal from temperature probe  64  to digital values that are input to microprocessor  102 . 
         [0053]    Although motor  80  can be any suitable type, motor  80  is preferably a sine wave driven stepper motor that has first and second windings  82  and  84  and an armature  86 . Armature  86  is coupled to drive pulley  78  ( FIG. 3 ) so as to provide drive to drive wheel  48  via belt  76  to drive conveyor belt  44 . This avoids the troublesome gear box required by other types of motors. 
         [0054]    Microprocessor  102  executes heater program  112  to process the signal TC with a set temperature Tset to modulate relay  94  to control radiant heating elements  60  to provide a nearly constant radiation from the heating elements. The set point temperature is entered by a user or a cook program. Heater program  112  causes microprocessor  102  to compare or algebraically subtract TC with Tset to produce a difference value or signal that controls the switching on and off of relay  94 . Heater program  112  evaluates temperatures Tset and TC at a predetermined rate, e.g., 40 times per second. The reaction time between applied power and measured temperature increase is somewhat slower than desired. To improve the temperature regulation some random noise is added to the measured heater temperature TC before comparison with the set point temperature Tset. 
         [0055]    Due to noise from the ac source  90 , a passive filter (not shown) can be used at the output of temperature probe  64  and a notch filter can be implemented in software and used by heater program  112  as well. 
         [0056]    As food product is placed into oven  20 , controller  100  increases the power level to heating elements  60  to maintain the temperature Tset from cook temperature set buttons  54 . In an alternate embodiment, the power consumption of heater elements  60  is used to compensate for the load factor instead of or in combination with changing the belt speed. In this embodiment, heater program  112  includes instructions, which are executed by microprocessor  102  to monitor the power consumption and to use the monitored power consumption to adjust the value of Tset. The power consumption is monitored by counting the power cycles of on-time versus off-time of relay  94 . This procedure is performed to calibrate the predetermined base power consumption level without a load (food items) on conveyor belt  44 . This calibration may be performed, e.g., at the place of manufacture and stored in EPROM (not shown). In a cooking mode, heater program  112  causes microprocessor  102  to again perform the above procedure. Heater program  112  causes microprocessor  102  to compare the measured power consumption level with the predetermined base of the two dimensional Tset vs. power consumption level, to determine a deviation in power consumption. This deviation is used to change the value of Tset to achieve a more consistent heat treatment of the food products as the loading factor varies, i.e., continuous loading vs. single pieces. 
         [0057]    Starting with an unloaded conveyor belt  44 , TC and Tset are substantially the same and relay  94  is operated to control its on time and off time to maintain this equilibrium or state. When food product is loaded on to conveyor belt  44 , TC begins to fall resulting in a negative delta (difference) between Tset and TC. Microprocessor  102  uses the negative delta to increase the on time of relay  94 , thereby resulting in an increase in power consumption and, therefore, a deviation value as described above. Microprocessor  102  uses the power consumption deviation value to increase the value of Tset, thereby increasing the negative temperature delta, which in turn increases the on time of relay  94 . With heaters  60  having more on time, TC begins to rise. This reduces the value of the negative delta, which is used to reduce the value of Tset and eventually bring TC and Tset back into equilibrium at the correlating Tset temperature. 
         [0058]    In some embodiments it is not sufficient to maintain the temperature of the heating elements for a consistent browning of the food products between single and continuous runs. Accordingly, controller  100  also adjusts the speed of conveyor belt  44  in order to maintain uniform or consistent cooking of the food items. Controller  100  monitors power consumed by radiant heater elements  60  and, based on a predetermined or calibrated power consumption without loading, adjusts the conveyor belt speed accordingly. 
         [0059]    Controller  100  measures the power consumption of heating elements  60  by counting power cycles of on-time versus off-time of relay  94  for a series of predetermined time periods or windows, e.g., each window being about two seconds. In an alternative embodiment, the count of power cycles is compensated by the deviation of actual mains voltage compared to nominal mains voltage. Controller  100  compares the current power consumption level with a pre-known (predetermined) power consumption level that corresponds with the base power consumption without any load. The difference of power consumption levels is used to calculate a corresponding change of speed of conveyor belt  44 , where an increase of power consumption slows down conveyor belt  44  and prolongs the cooking time. However, the cooking time will not be as long as with the aforementioned common approach that increases the power level and maintains the radiating energy from the heating elements to the load. 
         [0060]    Microprocessor  102  executes motor program  114  to provide the motor control. Motor program  114  includes a sine wave routine that is used by microprocessor  102  to generate two sine waves that are  90  degrees out of phase with one another. Motor program  114  causes microprocessor  102  to count the power cycles of on-time versus off-time of relay  94 . This procedure is performed to calibrate the predetermined base power consumption level without a load (food items) on conveyor belt  44 . This calibration may be performed, e.g., at the place of manufacture and stored in EPROM (not shown). In a cooking mode, motor program  114  causes microprocessor  102  to again perform the above procedure. Motor program  114  causes microprocessor to compare the measured power consumption level with the predetermined base power consumption level to determine a deviation in power consumption. The deviation is translated to a conveyor belt speed value and added algebraically to the speed set point Sset to provide a deviation speed value. The speed deviation value is used by microprocessor  102  to modify the frequency of the two sine waves by microprocessor  102 . The frequency modified sine waves are fed to two digital to analog (D/A) converters  108  and  110  that convert the digital sine waves into analog sine waves that are filtered by low pass filters (not shown) to condition the wave shapes by smoothing. The sine waves are then fed by two amplifiers  116  and  118  that are connected to windings  82  and  84 , respectively, of motor  80 . Motor control program  114  causes microprocessor  102  to repeat this process at a high rate, e.g., 10,000 times per second) to generate two sine-wave currents separated in phase by 90° in windings  82  and  84 , the frequency of which varies with the power consumption of heater elements  60 . In an alternate embodiment, the speed deviation value can be sent to the digital to analog converters to modify the frequency. 
         [0061]    In an alternate embodiment, motor program  114  causes microprocessor  102  to algebraically sum the deviation speed value and the conveyor belt speed set point Sset and process the sum with an actual motor speed value to provide a feedback control. The actual motor speed value is determined by the frequency of the sine wave current that is fed to stepper motor  80 . 
         [0062]    The two 90° phase shifted sinusoidal currents are applied to bipolar windings  82  and  84  to eliminate vibration and noise of stepper motor  80 . This configuration results in a near vibration free motor that has a very smooth movement. Another advantage of the present disclosure is that it provides controlled torque that allows drive wheel  48  to have sufficient torque to run conveyor belt  44  without destroying the belt or motor when the belt stops due to interference with some object. 
         [0063]    The heating element with a heat sensor is the weakest link in the toaster in terms of life and so when the heating element fails, the control will send out an error message and will provide an fixed power level regulation so the toaster can sill be used (assuming that the other heating elements are still working). That fixed power level will change dependent of the heat setting of buttons  54 . 
         [0064]    The conveyorized oven of the present disclosure provides a unique multiple heater configuration that provides cavity cooking uniformity. The conveyorized oven of the present disclosure also provides a unique voltage identifier feature in which the controller identifies the incoming voltage and pulses the correct power to the heater elements. The conveyorized oven of the present disclosure provides a unique stepper motor and motor drive for driving the conveyor belt. The conveyorized oven of the present disclosure also provides a unique speed adjustment to compensation for power consumption variations of heater elements  60 , i.e., conveyor belt  44  slows down or speeds up to create uniform toasting of the bread. 
         [0065]    A preferred embodiment of the conveyorized oven of the present disclosure is a toaster that includes upper and lower infrared heating elements that are controlled independently, a digital display, stainless steel construction, capability of toasting up to 800 buns per hour, a 10″ wide conveyor belt big on volume, small in space, can accommodate 2 buns, or toast slices, can also toast bagels, Cibatta rolls, English muffins and more, and comes complete with NEMA 6-30 cord &amp; plug. 
         [0066]    While we have shown and described several embodiments in accordance with our disclosure, it is to be clearly understood that the same may be susceptible to numerous changes apparent to one skilled in the art. Therefore, we do not wish to be limited to the details shown and described but intend to show all changes and modifications that come within the scope of the appended claims.