Abstract:
A heating control system in a roller grill has means for setting a set temperature, at least one temperature sensor mounted in the region of the rollers to measure the temperature of the area surrounding the food being heated on the grill, a temperature display in communication with the temperature sensor that indicates the temperature of the food area, and a control device that monitors the temperature measured in the area of the rollers and food and adjusts the input to heating elements to minimize variation of the measured temperature from the set temperature. Another embodiment of the system includes an offset heating structure in at least one roller to allow a temperature offset between two sides of the roller; and means for adjusting the temperature offset between the two sides of the roller.

Description:
CROSS-REFERENCES  
       [0001]    This application claims the priority of provisional application Serial No. 60/373,894, filed Apr. 19, 2002. 
     
    
     
       TECHNICAL FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to assemblies for cooking human food and, more particularly, to an assembly having heated rollers mounted in a grill housing and having a heating control system.  
         BACKGROUND OF THE INVENTION  
         [0003]    Grills using heated rollers to cook certain food items with elongated shapes, such as hot dogs and sausages are commonly used in convenience stores, amusement parks and entertainment venues. These grills utilize a drive mechanism to rotate the rollers and, in turn, any food items placed on the rollers.  
           [0004]    Prior art grills generally utilize what is referred to as an infinite control. Rather than functioning as a true temperature control, an infinite control varies the percentage of time that the heating elements in the rollers are on. The design of the infinite controls used on most prior art grills is very similar in design to the control knob for an electric range top. The control dial is typically marked with an arbitrary scale, i.e., from 1 to 10. Instead of indicating a particular temperature setting, these numbers represent an input to the heating elements. For example, a setting of 1 might refer to an input in which the heating elements are on 10% of the time, while a setting of 9 might refer to an input in which the heating elements are on 90% of the time. Other prior art grills use a three heat switch having low, medium, and high settings. These grills vary the heat delivered by the rollers by selectively turning the heating elements in certain rollers on or off.  
           [0005]    The dial settings of the infinite controls used in the prior art do not directly correspond to the temperature of the food being cooked on the grill. Therefore, operators must depend on experimentation and testing to determine the appropriate infinite control setting for a desired food temperature rather than simply relying on the control setting itself. In addition, since most infinite controls can vary the heating element input from 1% to 100% and the input level has no direct relationship to the actual food temperature, an inexperienced operator may set the control at an input level that is too low, resulting in an unsafe food temperature.  
           [0006]    Environmental factors often compound this problem. Because the output of an infinite control remains constant and is not directly related to the temperature of the food being prepared, changes in the environmental conditions surrounding the grill will affect the temperature of the food. For example, when used at an outdoor sports stadium, the same prior art roller grill will require one setting on a warm day in August and a completely different setting on a colder day in November.  
           [0007]    In addition, prior art roller grills are limited to separate heating zones at the front and rear of the grill, with no means to vary heating from one side of the grill to the other. This limits the number of heating zones on the grill and, therefore, functionally limits the different food offerings an operator may prepare on a single grill. Due to the current trend for a more diverse product offering on roller grills, this represents a serious limitation of the prior art grills.  
           [0008]    The present invention is directed to overcoming one or more of the problems set forth above.  
         SUMMARY OF THE INVENTION  
         [0009]    An aspect of the present invention is to provide a roller grill with a control system that allows the operator to more directly control the temperature of the food being prepared on the grill.  
           [0010]    Another aspect of the present invention is to provide a roller grill with a larger number of separate heating areas that allow different foods to be heated to different temperatures at the same time.  
           [0011]    In accordance with the above aspects of the invention, there is provided a roller grill having means for setting a set temperature, at least one temperature sensor mounted in the region of the rollers to measure the temperature of the area surrounding the food being heated on the grill, a temperature display that indicates the temperature of the food area, and a control device that monitors the temperature measured in the area of the rollers and food and adjusts the input to the heating elements to minimize variation of the measured temperature from the set temperature.  
           [0012]    In another embodiment, the range from which an operator can select a set temperature is limited from about 140° F. to about 170° F.  
           [0013]    In yet another embodiment, the roller grill also includes a preheat switch that raises the temperature of the grill for a set amount of time to quickly heat the food before serving.  
           [0014]    In a further embodiment, the rollers of the grill are provided an offset heating structure in at least one roller, to allow a temperature offset between two sides of the roller, and means for adjusting the temperature offset between the two sides of the roller.  
           [0015]    These aspects are merely illustrative aspects of the innumerable aspects associated with the present invention and should not be deemed as limiting in any manner. These and other aspects, features and advantages of the present invention will become apparent from the following detailed description when taken in conjunction with the referenced drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    Reference is now made to the drawings which illustrate the best known mode of carrying out the invention and wherein the same reference numerals indicate the same or similar parts throughout the several views.  
         [0017]    [0017]FIG. 1 is a front view of a roller grill incorporating a heating control system according to an embodiment of the present invention.  
         [0018]    [0018]FIG. 2 is a side view of a roller grill incorporating a heating control system having temperature sensors according to an embodiment of the present invention.  
         [0019]    [0019]FIG. 3 is a section view taken along the line A-A in FIG. 2.  
         [0020]    [0020]FIG. 4 is a schematic diagram illustrating the components of a heating control system in a roller grill according to an embodiment of the present invention.  
         [0021]    [0021]FIG. 5 is a split schematic diagram showing the rollers of a prior art grill on top and showing rollers incorporating a heating control system having independent left and right heating sections according to an embodiment of the present invention on bottom.  
         [0022]    [0022]FIG. 6 is a schematic diagram showing rollers incorporating a heating control system having independent left and right heating sections according to another embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0023]    [0023]FIG. 1 illustrates a roller grill  10  with a heating control system. The grill  10  is composed primarily of a frame  12 , a plurality of rollers  14 , and a sneeze guard (not shown). The frame  12  houses a drive mechanism for the rollers (not shown) and a heating control system, which will be described in more detail below. Roller  14  contains at least one heating element  18 , which can be seen in more detail in FIG. 5. The figures illustrate embodiments of a roller grill in which each roller is provided with a heating element, but alternate embodiments in which only some of the rollers are provided with heating elements are also consistent with the claimed invention.  
         [0024]    An operator panel  20  is mounted in the front region of the frame  12 . The operator panel  20  contains a power switch  22  and a temperature control panel  24  for at least one heating section. The embodiment shown in FIG. 1 shows a roller grill having two temperature control panels  24 , one each for two separate heating sections. Each temperature control panel  24  contains a display  26  and temperature setting means  28 . In a particularly preferred embodiment, the display  26  is a three digit, seven segment with decimal point LED display. The display  26  has at least two modes: one mode indicates the preprogrammed temperature or temperature selected by the operator and another mode indicates the temperature measured by sensors  30 . The mode in which the measured temperature is displayed is referred to as the service mode. In one embodiment, switching the display to the service mode requires entry of a code so that access to the service mode is limited. In other embodiments, the display has additional modes to display a preheat temperature and time to reach preheat temperature, which are explained in more detail below. In the embodiment shown in FIG. 1, the temperature setting means  28  includes an adjustment mechanism having two buttons, one of which allows the operator to increase the temperature while the other decreases the temperature. Other suitable temperature setting means  28  include, but are not limited to, dials, rocker switches, or numerical keypads. The temperature setting means  28  may also be limited to a fixed temperature setting. Other embodiments of the temperature control panels  24  include LED indicators  29  and an audible alarm.  
         [0025]    The display  26  and temperature setting means  28  may have yet another mode in which an operator can select a temperature calibration factor. The temperature calibration factor is a programmed differential between the set temperature and the actual measured temperature. The grill can be subject to variations in temperature across the grilling area. Due to the positioning of the temperature sensors  30  (as discussed below) the actual grill temperature at a point spaced from the sensors may differ slightly from the measured temperature indicated by the sensors  30 . In such an instance, the actual grill temperature may be equivalent to the set temperature even though the measured temperature indicated by the sensors  30  is not. Selecting a temperature calibration factor provides control of any such variation. The temperature calibration factor is generally a factory setting.  
         [0026]    [0026]FIG. 2 shows the temperature sensing portion of the system. In the embodiment shown, two sensors  30  are mounted at one side of the frame  12  at the area of the rollers  14 . In a preferred embodiment, the sensors  30  are thermistors encased in stainless steel. This particular embodiment shows the sensors  30  mounted between the ends of the second and third rollers  14  from both the front and back of the grill  10 . This arrangement is advantageous in those embodiments in which the front and back of the grill  10  are separated into independent heating sections. The sensors  30  are positioned such that they are able to measure the temperature of the area immediately surrounding the rollers  14 , which includes the area in which any food items on the grill  10  are located. This positioning allows the sensors  30  to provide a close approximation of the temperature of the food. FIG. 3 provides another view of how the sensors  30  are mounted in this embodiment.  
         [0027]    [0027]FIG. 4 provides a schematic diagram of the components of the heating control system. A power cord  32  connects the grill  10  to a standard electrical wall outlet. The power switch  22  turns the unit on and off and controls the flow of electricity to the remaining elements of the system. A light  34  indicates when the power switch  22  is in the on or off position. A motor  36  powers a drive mechanism (not shown in more detail), which turns the rollers  14 . A relay  38  communicates with and adjusts the operation of the heating elements  18  associated with a particular heating section. There is one relay  38  for each heating section. A control device  40  communicates with the temperature control panels  24 , sensors  30  and the relays  38 . In a preferred embodiment, the control device  40  is a microprocessor.  
         [0028]    In operation, an operator selects a set temperature for a heating section by manipulating the temperature setting means  28  until the display  26  shows the set temperature. Alternatively, the operator may simply turn on the temperature setting means  28  if the set temperature is fixed. The temperature setting means  28  transmits the set temperature to the control device  40  as a signal or series of signals. The control device  40  compares the signal from the temperature setting means  28  with a signal sent by the sensor  30  for the relevant heating section, which indicates the temperature at the rollers  14  in that heating section. If a temperature calibration factor has been programmed into the unit, the control device  40  adjusts the signal sent by the sensor  30  based on the temperature calibration factor before comparing that signal with the signal from the temperature setting means  28 . The control device  40  then transmits a signal to the relay  38  that controls the heating elements  18  in the rollers  14  of that heating section directing the relay  38  to turn the heating elements  18  on or off as needed to reach the set temperature. Subsequently, the control device  40  continues to monitor the signal from the sensor  30 , compare that signal to the signal sent by the temperature setting means  28 , and transmit a signal to the relay  38  whenever the heating elements  18  in the heating section should be turned on or off to maintain the set temperature.  
         [0029]    In another embodiment, the set temperature can be programmed into the memory of the control device  40  so that the control device  40  automatically heats the grill  10  to the programmed set temperature when the power switch  22  is turned on. This embodiment is provided with a button  41  to initiate programming of the set temperature. In yet another embodiment, the audible alarm is activated when the set temperature is reached to notify the operator.  
         [0030]    In one embodiment, the control device  40  is provided with upper and lower limits on the range of temperatures that it will maintain regardless of the set temperature selected by the operator. In an advantageous embodiment, the temperature setting means  28  and display  26  are provided with the same limits as the control device  40  and will not allow an operator to enter a set temperature outside of those limits. In one particularly advantageous embodiment, a lower temperature limit of about 140° F. and an upper temperature limit of about 170° F. are used.  
         [0031]    In another embodiment, the temperature control panel  24  includes a preheat switch  42 . The preheat switch  42  communicates with the control device  40 . When an operator activates the preheat switch  42 , it sends a signal to the control device  40 . The control device  40  then raises the temperature of the grill  10  for a set amount of time (the preheat cycle time) to quickly heat food (for example, frozen hot dogs) placed on the grill  10  before serving. The control device sends a signal to the relays  38  to turn on and leave on the heating elements  18  until a particular temperature is measured by the sensors  30 . The rate at which the control device  40  raises the heat at the rollers  14  can be adjusted by changing the preheat temperature and the preheat cycle time. This capability is advantageous because it prevents the grill  10  from becoming too hot, which can damage certain foods, such as the casings of hot dogs. However, if the heating grill temperature is kept relatively low, the normal amount of time required to heat the rollers will be sufficiently long enough to prevent damage to the food without the need to manually adjust the time to reach the preheat temperature. In one embodiment, both the preheat temperature and the preheat cycle time may be programmed into the memory of the control device  40 . In another embodiment, the control device  40  rapidly increases the heat of the grill  10  initially and then allows the temperature of the grill to decrease to a lower setting.  
         [0032]    A schematic of a prior art roller grill is shown in the top half of FIG. 5. As is readily apparent, each roller in the prior art roller grill contains a single heating element. Each of the heating elements in the prior art grill has a resistance wire extending along the entire length of the heating element, distributing heat relatively evenly along the length of the roller. The lower half of FIG. 5 illustrates an embodiment of a roller grill  10  according to the present invention. The grill  10  is provided with rollers  14  that each have two heating elements  18  running therethrough. In contrast to the prior art, heating elements  18  contain a resistance wire  44  extending along only a portion of the length of the heating element  18 . In each roller, opposite halves of each heating element contain a resistance wire. This arrangement allows the temperature of the left and right sides of the rollers  14  to be offset. The temperature offset is adjustable. The temperature offset allows each front and rear heating section to be further divided into separate left and right heating sections, allowing the operator to provide a more diverse product offering on a single grill. This side-to-side grill temperature offset may also be achieved by using a single heating element  18  in each roller  14  as shown in FIG. 6. Each heating element contains two resistance wires  44 . One resistance wire  44  extends along a portion of one half of the heating element  18  while the second resistance wire  44  extends along a portion of the opposite half of the heating element  18 , thereby allowing independent control of the two sides of the heating element.  
         [0033]    The above described embodiments describe grills in which each roller is provided with a heating element. However, the claimed invention may also be utilized in alternate embodiments in which only some of the rollers contain heating elements.  
         [0034]    Other objects, features and advantages of the present invention will be apparent to those skilled in the art. While preferred embodiments of the present invention have been illustrated and described, this has been by way of illustration and the invention should not be limited except as required by the scope of the appended claims and their equivalents.