Energy efficient appliances improve the energy efficiency in kitchens. Commercial kitchens and restaurants use gas for cooking because gas cooking tends to more efficient than use of electrical appliances for cooking. In recent years, induction cooking has received some traction, especially in hotels and airport facilities that require use of electricity to cook.
The heating element used for induction heating is a conductive coil. Current through the coil produces an oscillating magnetic field. The magnetic field is created along the axial direction of the coil. Cookware, such as a stainless steel or iron pot, or a stainless steel or iron pan, is placed in the center of the coil, oriented axially. The oscillating magnetic field produced by the coil induces eddy current within conductive material within the cookware. Due to the electrical resistance within the cookware, the induced currents will generate heat in the cookware, thereby heating up the cookware.
Induction coils are designed in a plane, typically in a donut shape, so that the magnetic field can be spread out to the bottom of the pot. Because of the donut shape, the heating area is in an annular shape leaving a cold region at the center. Currently, this effect is mitigated by using a composite base for cookware, for example, sandwiching an aluminum disc between layers of ferromagnetic material to spread the heat across the base of the cookware.
A typical induction heater set up is shown in
For an induction cooking device, the coil is arranged differently than a typical induction heater. The typical design of an induction heating coil 201 is shown in
Using a disc-shaped induction heating coil, it is difficult to create a large uniform heating area such as is needed for griddle cooking. Further, using a composite metal plate to even out the temperature across the large area required by a griddle can be expensive.
However, as described below, it is possible to design an induction heating element that will eliminates temperature hot spots and provides an even heating surface for both industrial and foodservice applications. This is done, for example, by providing a first array of parallel current-carrying wires, oriented in the same direction and sufficiently closely spaced such that the wires effectively create a flat current sheet. Current through the flat current sheet induces a uniform magnetic field above the wire array. In order to form a closed circuit, there is a second array of return current carrying wires arranged under the first array of parallel current-carrying wires. Magnetic field shielding is placed between the first array of parallel current-carrying wires and the second array of return current carrying wires so that the magnetic field of the second array of return current carrying wires does not cancel out the magnetic field of the first array of parallel current-carrying wires. The result is a strong uniform magnetic field above the first array of parallel current-carrying wires, where cookware such as a griddle can be placed to be heat up uniformly.
Although the following detailed description contains many specifics for the purpose of illustration, anyone of ordinary skill in the art will readily appreciate that many variations and alterations to the following exemplary details may be made. One skilled in the relevant art will recognize, however, that the concepts and techniques disclosed herein can be practiced without one or more of the specific details, or in combination with other components, etc. In other instances, well-known implementations or operations are not shown or described in detail to avoid obscuring aspects of various examples disclosed herein.
The magnetic field generated in area 431 below second array of return current carrying wires 420 and in area 432 above first array of parallel current-carrying wires 410 is negligible because in these areas the magnetic effects of second array of return current carrying wires 420 and first array of parallel current-carrying wires 410 tend to cancel out.
The purpose of magnetic shielding sheet 450 is to separate the magnetic field generated from current through first array of parallel current-carrying wires 410 from the magnetic field generated from current through first array of parallel current-carrying wires 410 from second array of return current carrying wires 420. Magnetic shielding sheet 450 significantly reduces or eliminates the magnetic field cancellation that resulted in a negligible magnetic field in area 431 below second array of return current carrying wires 420 and in area 432 above first array of parallel current-carrying wires 410. When magnetic shielding sheet 450 is inserted between first array of parallel current-carrying wires 410 and second array of return current carrying wires 420, induction ready cookware placed in area 431 below second array of return current carrying wires 420 and in area 432 above first array of parallel current-carrying wires 410 will receive sufficient magnetic energy for cooking. For example, magnetic shielding sheet 450 contains a heat sink for heat dissipation.
For example, magnetic shielding sheet 450 has the properties of high saturation level and low eddy current density, leading to low power loss. With the combination of the thickness of the material and the saturation of magnetic shielding sheet 450, the magnetic field in space 432 generated from current in first array of parallel current-carrying wires 410 will not be affected much by the magnetic field generated from current in second array of return current carrying wires 420. If the magnetic field in space 432 is intended for induction cooking, it is preferable that magnetic shielding sheet 450 should be placed close to second array of return current carrying wires 420. The magnetic flux conductivity of magnetic shielding sheet 450 should match the total magnetic field flux generated from total electric current from second array of return current carrying wires 420. In this way the magnetic field distribution from current in the first array of parallel current-carrying wires 410 should be minimally affected by this shielding sheet.
Alternatively, two sheets of magnetic shielding can be used, one close to first array of parallel current-carrying wires 410 and one close to second array of return current carrying wires 420, so that the magnetic field can be concentrated near first array of parallel current-carrying wires 410 and near second array of return current carrying wires 420. Nevertheless, to minimize loss it is preferable to use a single sheet to redirect the magnetic field from second array of return current carrying wires 420.
An important property of magnetic shielding sheet 450 is low loss, so that loss resulting from the presence of magnetic shielding sheet 450 does not affect the overall efficiency of the induction cooking device. The loss in magnetic shielding sheet 450 includes hysteresis losses and eddy current losses. The hysteresis loss is due to the flipping of the domains of magnetic shielding sheet 450, which causes energy to be lost as heat. With proper selection of the material used to produce magnetic shielding sheet 450, it is possible to design an induction cooking appliance with minimum loss due to magnetic shielding sheet 450. If necessary, second array of return current carrying wires 420 and magnetic shielding sheet 450 can be mounted on a heat sink that dissipates the heat generated from resistive losses in electric induction wire 401 and the heat generated from the eddy current and hysteresis losses in magnetic shielding sheet 450.
In
For example, a first array of parallel current-carrying wires can have a geometry suitable for even heating of a griddle cooking appliance. A typical griddle has a rectangular surface area such as twenty-four inches by twenty-four inches, or forty-eight inches by forty-eight inches. An array of induction cooking elements such as first array of parallel current-carrying wires 410 can be used to cover an entire griddle, resulting in a griddle appliance with uniform heating without the need for multi-ply surfaces. This is helpful as for a large griddle implemented using a tri-ply construction of the griddle surface, the layers tend to be thin, and this tends to warping in a griddle application. Using explosion bonding to obtain thicker multi-ply composite metal constructions is expensive.
A typical griddle plate is a one-half inch to one-inch thick steel plate. When using first array of parallel current-carrying wires 410 or a similar uniform heating wiring array, it is possible to use a thinner griddle plate because with the uniform heating provided by first array of parallel current-carrying wires 410, the chance of warping is reduced.
For example, first array of parallel current-carrying wires 410 is used to implement one modular element in an array of modular elements. In such an array, it is preferable to be able to control the induction power to each individual modular element. When a temperature sensor is installed in each modular element to sense the temperature of the cookware at the area of the modular element, it is possible to provide power to each modular element accordingly. For example, when a cold piece of meat is place in area of a griddle, the local temperature of the griddle metal plate will drop. The dropping of the temperature locally can contribute to warping of the metal plate. Therefore, it is desirable to for a griddle plate to increase the power to a modular element that heats that cold area, without increasing the temperature of other areas of griddle plate not loaded with cold meat. Such individual control of the modular elements improves overall energy efficiency of griddle cooking and reduces the chance of warping the griddle plate, which improves the useful life of the equipment.
In addition to cooking, another application of induction heating can be for heating up sheet metal after painting to help the paint set. Using induction to induce eddy currents within the sheet metal can lead to better finish quality than is provided by heating the paint using a heat lamp. Also, providing heat via induction to the sheet metal helps strengthen the bond between paint and metal.
In wok cooking, it is vital that the center of the wok is hot. This is the opposite to the donut pattern resulting from conventional induction cooking devices. This makes it challenging for chefs to use induction heating when cooking with a wok. Some chefs adapt to induction wok cooking by scooping oil from the center area to the ring area to heat up the oil quicker.
As described above using a first array of parallel current-carrying wires created from a helix-shaped induction coil wired as described above can provide for induction heating where a heated central area is the hot area for cooking, as is provided by a conventional gas burner wok range.
For example,
First array of parallel current-carrying wires 710 provides a uniform heating pattern that provides heat in the center area of a burner. When cookware 702 is placed closed to first array of parallel current-carrying wires 710 heating is uniform across the bottom of cookware 702.
In the examples above, electric induction wires are arranged so that the resulting first array of parallel current-carrying wires is arranged as a single layer. However, multilayer current coils can be used to increase the strength of the induction magnetic field and therefore increasing the power delivered for heating.
As illustrated
To further take advantage on the uniform magnetic field generated by the structure in
The space within the induction heating tunnel magnetic field is uniform, intense and beneficial for cooking, especially where uniform heating is required. The uniformity of the magnetic field is ensured by the large ratio of length to width of the induction heating tunnel. Preferably the ratio is larger than one. A food-heating induction cartridge 921 is constructed of induction material that heats up when placed within an alternative magnetic field. Food-heating induction cartridge 921 is loaded with food and is placed inside the induction heating tunnel to be heated up by a uniform magnetic field. The heat generated in food-heating induction cartridge 921 is transferred to cook the food inside food-heating induction cartridge 921. To reduce the magnetic field leakage external to inducting heating tunnel, it is preferable to provide a magnetic shielding layer 902 outside the current coil. For example, the magnetic shield layer can be a foil tube or can consist of an array of magnetic bars.
For example, food-heating induction cartridge 921 includes a top plate 922 and a bottom tray 923, both made of induction material such as grade 430 stainless steel. For example, top plate 922 is hinged to tray 923 and a spring clip on tray 912 holds food by a clamping force. Preferably, top plate 922 is smaller than tray 923 so that the weight of top plate will rest on food placed on tray 923. Top plate 922 and tray 923 both apply heat to food allowing the food to cook faster than a normal cooktop cooking process where heat is coming only from the bottom of a pot. Because the heat generated during the cooking goes upward, it is preferable to have better thermal insulation on the top portion of the induction heating tunnel to minimize the temperature rise in the current coil. Additionally, or alternatively, a fan is used to draw air through a gap between the food-heating induction cartridge and the ceiling of the induction heating tunnel, so that the upper coil will can be kept at a preferred operating temperature.
Alternatively, instead of using a food-heating induction cartridge, a magnetic shield plate, as mentioned above, is placed inside open cavity 903 to decouple the magnetic field generated from the two current flow sheets. Without the interference from the magnetic field from the bottom current array, the magnetic field generated from sheet current in the top current array will present in the space above the top plate 920 of the induction cooker. An induction ready cook pot can be put on top of the plate 920, to perform conventional induction cooking.
Open cavity 903 is created by winding current coil on a rectangular tube to produce the induction heating tunnel. The rectangular tunnel shape expands in a direction perpendicular to the axial direction, making the induction heating tunnel a suitable location for heating food with the rectangular block shapes. The rectangular food-heating induction cartridge configuration is suitable for holding hamburger patty, steak, bread, pan cakes, or wafer of some sort. It is also good for cooking food with less even height, such as chicken thighs. The magnetic field induced by the top and bottom uniform current array will heat up and cook the food efficiently. The weight of the top plate will ensure constant contact between the top plate and a piece of meat. It is also preferably to position a food-heating induction cartridge in the middle of the space between the top current array and the bottom current array. The design of the food-heating induction cartridge will allow the magnetic field to reach the top and bottom induction heating plates evenly.
The opening of open cavity 903 can be through all the way to the back side of case 901, so that a fan can be installed on one side of the case to vent out the fumes from cooking of meats. For example, a built-in fan extracts fumes from cooking. For example, a built-in filter filters unwanted contents extracted from air flow before release outside case 901. For example, an electronic control unit is built-in to control the power to the food-heating induction cartridge to cook the contents.
For example, a typical recipe to cook a hearty steak is to have a good sear on both sides of the steak to seal the flavor of the beef. The sear is performed using a frying pan over a gas or electric stove. After searing, the steak is placed in an oven to finish the cooking of the beef to the desire doneness. It is a multistep, and multi appliance cooking process.
Using an induction heating tunnel, as described above, a heating sequence can be pre-programmed to heat beef sufficiently to a provide good sear, and then to lower heating power to cook the beef a right length of time for desired doneness. Such programming allows this cooking to be done with one simple one touch of a button.
For example, a control circuit controls the current flow through induction wiring, and a sensor is used to sense the temperature of the food-heating induction cartridge. For example, the sensor is implemented using a thermal couple or infrared (IR) temperature sensor.
Often it is desirable to be able to directly sense the temperature of meat within a food-heating induction cartridge. As shown in
Power supplied to the induction cooker can be controlled by a controller according the desired temperature of the food, and time of cooking according to a recipe tailored to the type of food being cooked. For example, a power verses cooking time profile of heating is shown in
As shown in
A food-heating induction cartridge can be configured for a single food item such as a piece of steak and/or can be configured to cook multiple items. For example,
When heating meat from top and bottom in a food-heating induction cartridge, juice from the meat drips downward while the heat goes upward. To give the cooked meat a more uniform appearance, the food-heating induction cartridge can be flipped. This is similar to flipping a burger patty and steak on a frying pan or on a griddle plate.
For example,
For example, food-heating induction cartridge 1410 is made of induction ready material such as grade 430 stainless steel to allow heat up by alternating magnetic field. Because the magnetic field inside circular induction heating tunnel 1402 is uniform, the heating on the food cartridge will be uniform making it superior to the conventional donut shape of a heating element. It is especially beneficial for liquid food and food that spread out to the whole area of food-heating induction cartridge 1410. For example, food-heating induction cartridge 1410 is a pan. For solid food that does not fill the whole area in food-heating induction cartridge 1410, it is not advantageous to heat up the whole food-heating induction cartridge 1410. It is advantageous to heat up only the area within food-heating induction cartridge 1410 where the food is placed.
To improve the heat uniformity, clad metal is used where aluminum is sandwiched between two stainless steel sheets to spread heat. It is possible to make a plate with aluminum which can help spread the heat. Induction heating metal pads can be pressed on to the aluminum at the location where food is going to be placed. The induction heating metal pads can be in the shape of the food to be cooked.
The presence of a food cartridge where the magnetic heating element is magnetic in nature (For example, where the magnetic heating element is composed of stainless steel 430), will change the magnetic field distribution inside the space of the coil. It is preferable to have the all the magnetic field flux conducted in the heating element. Because the heating intensity is proportion to the magnetic field strength inside the heating element, the geometry of the magnetic heating element of the cartridge is designed to obtain temperature uniformity over the food cartridge, or more specifically, over the food contacting area of the cartridge. Besides geometric consideration, it is also important that the magnetic field saturation flux level of the magnetic heating element matches the intended heating uniformity. For example, the thickness of the heating element should not be so thick so that the magnetic field to be distribute evenly across the width of the heating pad. It is preferable to have half of the magnetic field flux pass through the top heating pad and half of the magnetic flux pass through the low heating pad and the magnetic field passes the pad evenly across the width of the pad. The magnetic field inside the tunnel is not completely uniform. That is, as measured along the length of the tunnel, the magnetic field is stronger in the middle of the tunnel. As measured along a cross section of the tunnel, the magnetic field is weaker in the center area of the tunnel.
It is possible to use a pattern perforated feature on the heating element complementary to the magnetic field distribution to obtain a uniform thermal profile. For example, the high magnetic field area has a high density perforated feature. The perforated feature can be simple round holes, or elongated voids. The holes and voids can be filled with aluminum, ceramic and other non-magnetic materials making the heating element a composite material structure.
To create a grill mark, a preselected pattern on the heating pad can be used to show the restaurant's logo, a special message or just simple a parallel grill mark. The protruded pattern can help make scorch mark on meat such as a steak or a burger.
Hamburger is a popular modern fast food. Cooking hamburgers efficiently allows for energy savings and better service for consumers. A food-heating induction cartridge can be used to cook a burger patty similar to cooking a steak. For example, a burger patty-oriented design is used. The temperature profile of the power to cook a burger patty is similar to the power profile for cooking steak. In a restaurant setting, burger patties are typically cooked on a griddle equipment to cook in a batch. It takes a large griddle plate with a top and bottom heating element to speed up the cooking; however, it is a conventional griddle configuration with high energy consumption.
For example,
An induction heating food cartridge for a patty is composed two pieces. A first piece is a pan 1630 made of induction ready stainless steel with an induction ready metal plate. Alternatively, pan 1630 is an aluminum pan with induction pad of the same diameter of the bottom of pan 1630 embedded either inside or outside of the bottom of pan 1630. For example, the induction pad of pan 1630 consists of an array of pads. For example, the induction pad of pan 1630 has a first pattern of perforations selected to achieve uniform heating under influence of an alternative magnetic field.
A second piece is a lid plate 1620 used as induction heating element from the top. For example, lid plate 1620 is made of induction ready stainless steel with an induction ready metal plate. Alternatively, lid plate 1620 is an aluminum plate with induction pad embedded on either side. For example, the induction pad of lid plate 1620 consists of an array of pads. For example, the induction pad of lid plate 1620 has a first pattern of perforations selected to achieve uniform heating under influence of an alternative magnetic field.
Lid plate 1620 can be connected to pan 1630 by a hinge. The hinge is loosely attached so that the weight of lid plate 1620 can ensure lid plate 1620 rests on the food that is in pan 1630. The hinge can be a tong type configuration with two flat holding induction metal pieces and with a clip lock mechanism to hold the food in between the two holding pieces. A handle 1631 is connected to pan 1630.
A control unit inside case 1601, provides power to the array of induction heating tunnels. The power supplied to each induction heating tunnel has a similar profile to the temperature profile shown in
Control circuitry is used to sense the loading of a patty cartridge into an induction heating tunnel in order to automate heating time start. An operator can just keep loading the array of induction heating tunnels and the cooking is performed automatically. Sensing is done, for example, by sensing the capacity of the food-heating induction cartridge with and without food, or by using other physical parameters. LED indicators 1603 for each induction heating tunnel are used to tell the operator if the patty is done in that induction heating tunnel. When the patty is done, the LED light will turn green. The operator can take the burger patty out from the food-heating induction cartridge and put the empty food-heating induction cartridge back into the induction heating tunnel. For example, induction cooking device 1600 senses whether a food-heating induction cartridge is empty or not. When an operator places an empty patty cartridge in an induction heating tunnel, the LED light for the induction heating tunnel will be yellow and no power or minimum power is applied to the empty patty cartridge. Alternatively, to keep the patty cartridge at a suitable temperature, the patty cartridge is warmed. The ability of such system to hold temperature after the patty is cooked reduces an operation step to move the patty from a cooking station to a holding station and reduces the need for an equipment space for holding equipment.
For example, a switch 1604 at each induction heating tunnel allows an operator to switch off that induction heating tunnel when the work load of the day is low. Instead of using a switch 1604, a control panel 1605 can be used to control power to each induction heating tunnel.
For example, for each induction heating tunnel, a switch can have several positions to indicate the weight category of the food put in the induction heating tunnel. For example, if a chicken thigh sizes are categorized into three groups (heavy weight, medium weight and light weight) a switch for each induction heating tunnel includes corresponding toggle positions so that an operator can indicate the weight of the food placed in the induction heating tunnel for cooking. Alternatively, a button array by each induction heating tunnel can be used instead of a toggle switch. Alternatively, this functionality can be programmed using control panel 1605. Recipes can be stored inside the programmer for ease of use of the equipment.
For example, exhaust fans are installed at the back of the induction heating tunnels to draw out the fumes created in the cooking process. Also, a filter system is used to clean out the exhaust flow before discharge to the environment. The speed flow of the exhaust system can be controlled according the number of burger patties being cooked and the stage of the cooking of the burger patty so as to optimize the energy consumption of the system.
Different temperature profiles can be programmed to optimize cooking for different recipes to vary the amount a burger patty is cooked or the crunchiness of the bread and so on. In order to take into account different degrees of the softness of cheeses the temperature holding profiles can be varied. This can allow induction cooking device 1600 to both cook and hold burger patties. This improves the energy efficiency on cooking a burger patty and eliminates the need to move a patty from a cooking station to a warming cabinet, eliminating the requirement to have warming cabinet and to have space for the warming cabinet. Because real estate in any restaurant establishment is a premium, it is a great help to eliminate the amount of required equipment.
The design of such a multi-tunnel cooking system can be modular. For example, multi-tunnel cooking system can include a basic four-tunnel model for a restaurant where burgers are not the major selling items on the menus. For restaurants where burgers are more substantially sold modularity can be increased, for example to a four by eight tunnel cooking system. A floor standing unit can be used. Such multi-tunnel cooking stations can also employ the traditional induction donut shape coils to work with induction heating food cartridges.
In a burger cooking operation, there is also a need to warm up bread used as a burger bun. Induction heating tunnel depth can be lengthened to hold a long food-heating induction cartridge that has a place for a burger and a bun. For example,
For example, pointy stubs on an induction heating pad on a food-heating induction cartridge and/or on a lid can be used to push into the meat to allow faster heat up of thicker portions of meet. The plates on the food-heating induction cartridge can be coated with non-stick coating for easy use.
A pizza-heating induction cartridge can use a conveyor belt induction oven as shown in
A conveyor belt induction oven can also be able cook flat bread and taco bread and pan cake type of food using a simple cartridge composed of two flat plates.
For example, a bread cartridge 1910 is used to hold a slice of bread or a bagel. For example, bread cartridge 1910 includes a pair of induction metal plates, a gap between the plates is designed to be adjustable so that in operation the gap is set to be slightly smaller than the thickness of the bread so that the plates are in contact with the bread during cooking. The pair of metal plates can be, for example, hinged steel plates. The gap between the plates is designed to the thickness of the bread or slightly smaller than the thickness of the bread so that the plates are in contact with the bread during cooking. Alternatively, bread cartridge 1910 is designed to be spring loaded to ensure contact with the bread. Because the induction heating plates are in contact with bread, it is possible to have engraving of graphic, text message on the plates so that the message or pattern will be toasted on the bread. The metal plates can be stamped to some patterned protrusions from the flat surface to make strong contact with the bread. Alternatively, a patterned cut out or recession can be used that results in a pattern on the cooked food item. For example, the pattern can be a logo of the hotel where a toaster is used for the continental breakfast. Or a greeting message to someone when making toast in the morning. It is a great gift product to offer personalized messages or images on toaster plates.
A sensing control is used to sense when a food-heating induction cartridge is inserted into an induction heating tunnel, so that the heating power is automatically on. Alternatively, power to an induction heating tunnel is switched on manually.
The foregoing discussion discloses and describes merely exemplary methods and implementations. As will be understood by those familiar with the art, the disclosed subject matter may be embodied in other specific forms without departing from the spirit or characteristics thereof. Accordingly, the present disclosure is intended to be illustrative, but not limiting, of the scope, which is set forth in the following claims.
Number | Date | Country | |
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Parent | 15942528 | Apr 2018 | US |
Child | 16011898 | US |