System and device for grilling food

A grill plate for grilling food, and in particular, frozen meat patties, is coated with a mixture of polytetrafluoroethylene (PTFE) and a far-infrared radiation substance. The PTFE, being an abherent, prevents food from sticking to the grill plates, while the far-infrared radiation substance facilitates heating the inner portion of the food by the far-infrared radiation emitted from the far-infrared radiation substance. The entire piece of food is cooked evenly before the outer portion is overcooked.

BACKGROUND 
This invention relates to a device for cooking (heating, baking, grilling, 
roasting, broiling and the like) food. In particular, the present 
invention relates to a device for grilling frozen meat patties (thin 
pieces of ground or minced meat, such as hamburger patties). 
One type of grilling device is disclosed in Japanese Laid-Open Patent 
Application No. 2-174816. An upper heat plate is hinged at its edge to a 
lower grill plate. A gap adjusting device controls the spacing between 
facing surfaces of the upper heat plate and the lower grill plate 
according to the thickness of the material to be grilled. The lower grill 
plate is heated with a gas burner from beneath. The upper heat plate 
contains a heater. The upper heat plate presses downward on the food, thus 
heating the food between the upper and lower plates. Since both the sides 
of the food are heated directly, baked or grilled simultaneously, the food 
is cooked to a desired preference. 
However, when frozen food material is cooked by this device, cooking is 
uneven and imperfect. A long grilling time cooks the inner portion of the 
food moderately, but overcooks the outer portion. A short grilling time 
cooks the outer portion as desired while leaving the inner portion only 
partly cooked. 
The uneven cooking problem is compounded when the meat being cooked is 
frozen initially. Before cooking of the interior can even begin, the ice 
contained therein must be melted. The ice at the surface melts soon after 
heat is applied, but melting and heating progresses from surface to 
interior. 
The internal temperature of food, especially meat, must be raised 
sufficiently high to kill harmful bacteria such as salmonella and e. coli 
sp. For instance, salmonella die after a few minutes exposure at 
59.degree. C. (138.degree. F.). Pathogenic forms of e. coli, such as e. 
coli 0157:H7, die at approximately 71.degree. C. (160.degree. F.). Cooking 
frozen meat patties using a conventional grilling device fails to raise 
the temperature inside the meat patty high enough to kill harmful bacteria 
without overcooking the outer portion. 
OBJECTS AND SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a device 
for grilling food by which the food can be cooked evenly as desired in a 
short time. 
It is a further object of the present invention to make use of the thermal 
effects of far-infrared radiation in heating or cooking an object. 
The device of the present invention includes coating a metal plate or a 
pair of metal plates with a mixture of a polytetrafluoroethylene (PTFE), 
such as is sold under the registered trademark "TEFLON", and a 
far-infrared radiation substance, such as alumina titania. The coated 
metal plate is used as a heating surface which makes contact with food. In 
other words, the coated metal plate is used as a grill plate. Food is 
pressed and heated between the coated surfaces of the pair of grill 
plates. It is also possible to place a layer of far-infrared radiation 
substance between the coating and the metal plate to enhance the thermal 
effects of the far-infrared radiation. 
Food easily separates from the grill plate since PTFE is an abherent. Even 
if a PTFE coating is relatively thick (for example, about 100 .mu.m), the 
amount of the far-infrared radiation from the PTFE coating does not 
seriously decrease. Instead of a coating, a sheet of the PTFE mixture can 
be affixed to the metal plate. The PTFE sheet is easily removed from the 
metal plate and replaced with a new sheet when necessary. When a 
far-infrared radiation substance layer is added between the PTFE sheet and 
the metal plate, increased thermal benefit from far-infrared radiation 
results. 
Briefly stated, the present invention provides a grill plate for grilling 
food, and in particular, frozen meat patties, coated with a mixture of 
polytetrafluoroethylene (PTFE) and a far-infrared radiation substance. The 
PTFE, being an abherent, prevents food from sticking to the grill plates, 
while the far-infrared radiation substance facilitates heating the inner 
portion of the food by the far-infrared radiation emitted from the 
far-infrared radiation substance. The entire piece of food can be evenly 
cooked before the outer portion is overcooked. 
According to an embodiment of the invention, there is provided an apparatus 
for heating an object, comprising: means for storing a plurality of the 
objects, a first grill plate having a first grilling surface thereon, a 
second grill plate having a second grilling surface thereon, the first 
grilling surface being aligned with, and facing, the second grilling 
surface, means for moving one of the plurality of objects from the means 
for storing to a position between the first grilling surface and the 
second grilling surface, a layer on at least one of the first grilling 
surface and the second grilling surface, the layer including a mixture of 
polytetrafluoroethylene and a far-infrared radiation substance, and means 
for moving the layer into contact with a surface of the object. The means 
for moving said layer can further include pressing the object between the 
first and second grilling surfaces. 
According to a feature of the invention, there is provided a grill plate 
for heating an object, comprising: a metal plate, a layer on the metal 
plate, the layer including a mixture of polytetrafluoroethylene (PTFE) and 
a far-infrared radiation substance, a heater in thermal contact with the 
metal plate for heating the metal plate to a heating temperature, and 
means for contacting the layer with the object. 
According to a further feature of the invention, there is provided a grill 
plate for grilling a food material, comprising: two metal plates, a heater 
between the two metal plates, and at least one of the metal plates having 
a layer of a far-infrared radiation substance. 
According to a still further feature of the invention, there is provided a 
grill plate for grilling a food material, comprising: a metal box, a 
resistive heating element inside the metal box, a layer of a far-infrared 
radiation substance on a surface of the metal box, and the layer being 
positioned for contact with the food material. 
The above, and other objects, features and advantages of the present 
invention will become apparent from the following description read in 
conjunction with the accompanying drawings, in which like reference 
numerals designate the same elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
Referring to FIG. 1, a frozen meat patty grilling system, shown generally 
at 100, includes a patty grilling device 2 having a lower grill plate 
facing an upper grill plate 1 across a gap. An elevating cylinder 20 
displaces upper grill plate 1 upward for insertion of material to be 
cooked, and downward to a predetermined spacing from lower grill plate 4 
for cooking. In this embodiment, the spacing is such that the material is 
pressed between upper grill plate 1 and lower grill plate 4. 
A slide table ST is positioned between patty grilling device 2 and a 
freezer stocker 5. Freezer stocker 5 includes a box casing 50 for 
containing a magazine 78. Magazine 78 is a removable and replaceable 
device for restocking a stack of items to be stored, and later cooked such 
as, for example, meat patties P. Meat patties P are supported on a patty 
tray 60. An elevation of patty tray 60, and thus of meat patties P, is 
controlled by a motor 62 which rotates a nut (not shown) engaging a screw 
rod 61. 
A patty discharge port 52 in a top surface 50a of box casing 50, has a size 
and shape slightly larger than the size and shape of meat patties P. The 
interior of box casing 50 is refrigerated, to keep meat patties P chilled 
or frozen. The close match between the sizes of patty discharge port 52 
and meat patties P prevents substantial leakage of heat into box casing 
50, and thereby conserves refrigeration energy. A hinged lid 51 is 
controlled by a torque actuator TA between a closed position, in which it 
covers patty discharge port 52, and an open position shown, in which it 
uncovers patty discharge port 52. 
For convenience, meat patties P may be installed in box casing 50 using 
magazine 78. Thus, when meat patties P in one magazine 78 become depleted, 
a filled magazine 78 may be substituted quickly. Alternatively, a stack of 
meat patties P may be stacked onto patty tray 60 manually. 
A conveyor device 7 moves a top patty P from freezer stocker 5, sliding it 
along slide table ST and onto a position centered on lower grill plate 4. 
Conveyor device 7 includes a pushing arm 73 having a curved part 73a 
facing freezer stocker 5. Pushing arm 73 is connected to a holder 75 
connected to a run of a belt 71. Belt 71 is reeved over a driven pulley 
70a and an idler pulley 70. Driven pulley 70a is affixed to a shaft of a 
motor 72. A plate guide 74 extends alongside, and parallel to, belt 71. 
Holder 75 includes an arm extending therefrom engaging plate guide 74. The 
engagement of the arm of holder 75 with plate guide 74 ensures that holder 
75 travels in a substantially straight path. 
A completion table KT extends beyond patty grilling device 2. 
A control device 80 controls and coordinates the activation of motor 60, 
motor 72, torque actuator TA, and elevating cylinder 20, as well as the 
heating functions, to be explained, to control the movement and heating of 
frozen meat patty grilling system 100 through its cycles. 
In operation, torque actuator TA rotates hinged lid 51 into the open 
position. Motor 62 drives the nut (not shown) engaging screw rod 61 a 
rotational amount sufficient to advance screw rod 61 upward by a distance 
substantially equal to the thickness of one meat patty P. At this 
position, the bottom of the uppermost meat patty P is slightly higher than 
top surface 50a. Elevating cylinder 20 raises upper grill plate 1 an 
amount sufficient to permit clearance for entry of meat patty P. Motor 72 
is energized to move pushing arm 73 toward the left in the figure. Curved 
part 73a engages the edge of the uppermost meat patty P, thereby pushing 
it toward the left, and sliding it along the surface of slide table ST 
until it is centered between lower grill plate 4 and upper grill plate 1. 
Motor 72 moves pushing arm 73 rightward a slight distance to clear patty 
grilling device 2. Finally, elevating cylinder 20 moves upper grill plate 
1 downward to a position contacting the upper surface of meat patty P 
located between it and lower grill plate 4. 
Upon completion of a grilling time, whose end may be determined by a 
temperature sensor or by time, elevating cylinder 20 raises upper grill 
plate 1 to its upper position. Motor 72 moves pushing arm 73 leftward 
again to push the now-cooked meat patty P from between lower grill plate 4 
and upper grill plate 1 onto completion table KT. The cooked meat patty P 
may be removed by a spatula from completion table KT, or otherwise 
prepared for its final use. 
If pushing arm 73 is made of a heat-resistant material, such as a metal, 
and is thin enough to avoid interference with the operation of upper grill 
plate 1, the intermediate step of moving pushing arm 73 from between upper 
grill plate 1 and lower grill plate 4 during cooking may be omitted. That 
is, pushing arm 73 may push the top patty P between upper grill plate 1 
and lower grill plate 4, and may remain stationary in that position while 
cooking proceeds. After cooking is completed, pushing arm 73 may then 
resumes its pushing action to push the cooked meat patty P onto completion 
table KT. 
Hinged lid 51 is raised by torque actuator TA to permit clearance for 
pushing arm 73 to travel over patty discharge port 52 to its starting 
position to the right of patty discharge port 52. Motor 62 is actuated to 
raise patty tray 60 a distance equal to the thickness of one meat patty P. 
Thus the starting conditions for the next operation is set up. 
Referring now to FIG. 2, the starting condition of cooking a meat patty is 
shown. The uppermost meat patty P is raised until its bottom surface is 
just higher than top surface 50a. Thus, when pushing arm 73 is moved 
toward the left, the uppermost meat patty P is slid off its next lower 
neighbor, which is restrained from motion by the close fit of patty 
discharge port 52. 
Upper grill plate 1 and lower grill plate 4 are preferably heated by 
embedded electric resistance heaters although any heat source may be used. 
A relatively large difference in power consumption exists between times 
when cooking is being conducted and when cooking is not being conducted. 
Control device 80 controls the energy fed to the electric resistance 
heater so as to maintain a desired temperature. In one embodiment of the 
invention, the electric energy is varied by pulse-width modulating a 
fixed-voltage power source to the resistance heaters. Referring to FIG. 
11, when cooking is not being conducted, the surfaces of upper grill plate 
1 and lower grill plate 4 are maintained at the desired temperature by 
relatively narrow pulses PLS from a fixed voltage source. 
Referring now to FIG. 10, when cooking is being conducted, more energy is 
required to overcome evaporative cooling, and to supply the heat necessary 
to thaw the meat patty, and to raise its temperature the desired amount. 
The extra energy is supplied from the same fixed voltage source by wider 
pulses PLS. 
In one embodiment of the invention, described as an open-loop embodiment, 
fixed values of pulse width are used for the cooking and non-cooking 
operations. In a more preferred embodiment, at least one conventional 
temperature sensor provides a temperature signal to control device 80. 
Control device 80 thereupon controls the pulse width over a range of 
values to maintain the temperature in commanded range. 
Several additional conventional feedback signals may be generated to assist 
control device 80 in controlling the operation of frozen meat patty 
grilling system 100. For example, an electro-optical or electrical device 
may be used to determine the open/closed status of hinged lid 51. 
Similarly, such devices may be used to sense the arrival of the upper 
surface of the leading meat patty P in the proper elevation position, the 
arrival of meat patty P in a position centered between upper grill plate 1 
and lower grill plate 4, the arrival of meat patty P in a desired end 
position on completion table KT and the arrival of pushing arm 73 back at 
the starting position in preparation for the next cooking operation. Since 
such feedback devices, and the manner in which feedback signals therefrom 
are used to control a sequence of operations are well known, detailed 
illustration and description thereof is omitted. 
Referring now to FIG. 3, upper grill plate 1 and lower grill plate 4 are 
shown facing each other. In the preferred embodiment, upper grill plate 1 
and lower grill plate 4 are identical, thus only upper grill plate 1 will 
be described in detail. 
Referring now to FIG. 5, upper grill plate 1 includes a heat reserving 
plate 3. A metal plate 10 is affixed to a surface of heat reserving plate 
3. A plate heater 11 is sandwiched between heat reserving plate 3 and 
metal plate 10. First and second terminals 1p of plate heater 11 extend 
through penetration holes 30 of heat reserving plate 3 to permit 
connection to a power source (not shown). 
A layer 9 is sprayed or otherwise affixed to the outer surface of metal 
plate 10. Layer 9 consists of a far-infrared radiation substance such as 
Al.sub.2 O.sub.3 +TiO.sub.2 (alumina titania). Far-infrared radiation has 
significant thermal effects and the far-infrared radiation band covers the 
wavelengths from 15 .mu.m-1,000 .mu.m. A PTFE (TEFLON) coating 8 is coated 
over layer 9. Coating 8 includes a powder of far-infrared radiation 
substance mixed therein. The mixing ratio of far infrared radiation 
substance to PTFE material in coating 8 is preferably about 10%. Instead 
of a coating, a sheet of such mixture may be affixed. Coating 8 makes 
contact with a surface of patty P during cooking. 
Metal plate 10 is made of any metal having a high heat conductivity such as 
copper or aluminum and is approximately 5 mm thick. 
Heat reserving plate 3 is made of copper or other metal and is about 5 mm 
in thickness. An outside surface of heat reserving plate 3 preferably 
includes an insulating layer on its outer surface (not shown) to reduce 
heat loss. 
In the preferred embodiment, heat reserving plate 3 includes a recess 
therein for accepting plate heater 11. 
Referring now to FIG. 4, one embodiment of plate heater 11 takes the form 
of a disk having resistance heating elements incorporated therein. 
Referring now to FIG. 6, a further embodiment of an upper grill plate 1' 
includes a metal box 12 into which a heating element 13 is inserted or 
molded. Coating 8, covering layer 9 (not shown in FIG. 6), is coated on a 
surface of metal box 12. As in the previous embodiment, coating 8 faces 
its companion lower grill plate (not shown). Heating element may be, for 
example, a ceramic element cast in place over a metallic resistance 
heating elements to form a unitary heater in the manner of a resistance 
heater sold under the trademark CERMET. 
Referring now to FIG. 7, a still further embodiment of an upper grill plate 
1" includes metal plates 16 sandwiching first and second plates of 
insulators 15 between them. A resistive heating element (not shown in FIG. 
7) between insulators 15 provides the heat required for cooking. 
Insulators 15 may be of any convenient material such as, for example, 
ceramic or mica. 
Referring now to FIG. 8, a resistor pattern TP, is coated by any convenient 
method onto an inner surface of one of insulators 15. A serpentine 
pattern, as shown, is convenient for providing a long resistance path, as 
well as for providing uniform distribution of heat. Coating may be 
performed by silk screening a suitable resistive slurry onto insulator 15. 
After coating, the pattern is dried and cured. Alternatively, resistor 
pattern TP may be formed by applying a solid layer of a resistive material 
to the surface of insulator 15, and chemically etching away unwanted 
portions. 
Instead of the printed or etched resistor pattern TP of FIG. 8, a 
serpentine pattern of nickel-chromium wires may be sandwiched between 
insulator 15. 
In this embodiment, the food to be heated and grilled is a circular frozen 
meat patty. The invention is not limited to meat patties, or to frozen 
articles. Various other types of foods and food material, frozen or 
unfrozen, can be similarly grilled evenly in a short time. 
The PTFE sheet in this embodiment is formed by diffusing and mixing a 
powder of a far infrared radiation substance such as alumina titania 
(Al.sub.2 O.sub.3 +TiO.sub.2) and affixing it to both upper grill plate 1 
and lower grill plate 4. However, in some embodiments only one of the 
plates may require such a PTFE sheet. 
Moreover, the present invention may be used with a griddle for single sided 
cooking. Only one grill plate, as for example shown in FIG. 5, would be 
used to form a griddle or frying pan. 
Having described preferred embodiments of the invention with reference to 
the accompanying drawings, it is to be understood that the invention is 
not limited to those precise embodiments, and that various changes and 
modifications may be effected therein by one skilled in the art without 
departing from the scope or spirit of the invention as defined in the 
appended claims.