INDUCTION-BASED FOOD HOLDING/WARMING SYSTEM AND METHOD

• US 20120294990A1
• Filed: 05/20/2011
• Published: 11/22/2012
• Est. Priority Date: 05/20/2011
• Status: Active Grant

• Current Assignee: Cooktek Induction Systems, LLC (Middleby Corporation)
• Original Assignee: Cooktek Induction Systems, LLC (Middleby Corporation)
• Inventors: Graber, Warren S., Metz, Reinhard, Visher, Robert J.
• Granted Patent: US 9,585,202 B2
• Time in Patent Office: Days
• US Class Current: 426/231
• CPC Class Codes: A47J 36/24 Warming devices
• CPC Class Codes: A47J 36/2483 with electrical heating means
• CPC Class Codes: H05B 2213/07 Heating plates with temperature control means
• CPC Class Codes: H05B 6/062 for cooking plates or the like
• CPC Class Codes: H05B 6/105 using a susceptor
• CPC Class Codes: H05B 6/12 Cooking devices
• CPC Class Codes: H05B 6/1209 induction cooking plates or the like and devices to be used in combination with them
• CPC Class Codes: H05B 6/36 Coil arrangements
• CPC Class Codes: Y02B 40/00 Technologies aiming at improving the efficiency of home appliances, e.g. induction cooking or efficient technologies for refrigerators, freezers or dish washers

Abstract

A system and method for holding and warming food held in pans or trays having a low relative magnetic permeability, such as 300-series stainless steel, using induction heating.

Claims

1. A method for holding and warming food, comprising the steps of

providing a pan or tray for holding and warming the food, the pan or tray being made of a material with a low relative magnetic permeability;

and

heating the pan or tray using an induction heating unit.

2. The method of claim 1, wherein the material has a relative magnetic permeability of less than about 20.

3. The method of claim 1, wherein the material comprises cold-worked, 303 stainless steel.

4. The method of claim 1, wherein the step of induction heating uses an induction inverter operating in a frequency range of about 40-60 kHz.

5. The method of claim 1, further comprising the step of measuring the temperature of the pan or tray using a resistive thermal device.

6. The method of claim 5, wherein the measured temperature is used in a closed loop control to limit and maintain the temperature of the pan or tray at a desired value.

7. The system of claim 6, wherein the measured temperature is used to generate a ramped inverter power profile facilitating lateral heat transfer in the pans or trays.

8. The method of claim 1, wherein the step of induction heating uses an induction coil having in the range of about 40-80 turns.

9. The method of claim 1, wherein the step of induction heating uses an induction coil having a wire gauge in the range of about 14-18 gauge.

10. The method of claim 1, wherein the step of induction heating occurs at a sufficiently low coil current to minimize internal heat generation in the induction unit, enabling induction heating without the need for a cooling fan.

11. The method of claim 8, wherein the current in the induction coil is less than about 15 amperes.

12. A system for holding and warming food, comprising:

a pan or tray for holding and warming food, the pan or tray being made of a material with a low relative magnetic permeability; and

an induction heating unit with an induction heating circuit for induction heating the pan or tray, the induction heating circuit including an induction inverter operating in a frequency range of about 40-60 kHz.

13. The system of claim 12, wherein the material has a relative magnetic permeability of less than about 20.

14. The system of claim 12, wherein the material comprises cold-worked, 303 stainless steel.

15. The system of claim 12, wherein the induction heating circuit includes an induction coil having in the range of about 40-80 turns, a wire gauge in the range of about 14-18 gauge, and a current of less than about 15 amperes.

16. The system of claim 12, further comprising a resistive thermal device for measuring the temperature of the pan or tray.

17. The system of claim 16, wherein the measured temperature is used in a closed loop control to limit and maintain the temperature of the pan or tray at a desired value.

18. The system of claim 17 wherein the measured temperature is used to generate a ramped inverter power profile facilitating lateral heat transfer in the pans or trays.

19. The system of claim 16, wherein the resistive thermal device is mounted beneath the pan or tray in a manner to facilitate maintaining contact with the pan or tray despite variations in shape or size of the pan or tray.

20. The system of claim 12, wherein the pan or tray is induction-heated in a manner that minimizes internal heat generation within the induction heating unit and enables induction heating without the need for a cooling fan.

21. A system for holding and warming food, comprising:

a pan or tray for holding and warming food, the pan or tray made of a material with a low relative magnetic permeability; and

an induction heating circuit for induction heating the pan or tray, the induction heating circuit including an induction coil having a sufficiently large number of coil turns so as to increase the magnetic field strength to a level sufficient to induce a desired heating temperature into the pan or tray.

22. The system of claim 21, wherein the material of the pan or tray has a relative magnetic permeability that is less than about 20.

23. The system of claim 21, wherein the induction coil has in the range of about 40-80 turns, a wire gauge in the range of about 14-18 gauge, and a current less than about 15 amperes.

24. The system of claim 21, further comprising a resistive thermal device for measuring the temperature of the pan or tray.

25. An apparatus for warming food in a pan or tray made of 300-series stainless steel, comprising:

an induction heating unit for heating the pan or tray by induction heating, the induction heating unit including an inverter power circuit, and power circuit controls.

26. The apparatus of claim 25, wherein the inverter power circuit includes an induction coil and a resonant capacitor.

27. The apparatus of claim 26, wherein the induction coil has about 40 or more turns when using 120 volt coils, and has about 75 or more turns when using 240 volt coils.

28. The apparatus of claim 25, wherein the inductance of the heating unit coil is about 250 μ

Henries or more when using 120 volt coils, and about 800 μ

Henries or more when using 240 volt coils.

29. The apparatus of claim 25, further comprising an inverter resonant circuit including a resonant capacitor and an induction coil, wherein the inverter resonant circuit is about 5-11 amps for 120 volts, and about 4-8 amps for 240 volts.

30. A system for warming food in a pan or tray made of 300-series stainless steel by induction heating, comprising:

an induction unit including a master controller;

one or more remote control units comprising one or more slave units, each of the one or more remote control units being associated with one of the pans or trays;

serial communication architecture including a communication bus enabling the transfer of data between the master and slave units, wherein the master controller is enabled to induction heat a series of the pans or trays in a controlled fashion using one or more of the slave units.

31. The system of claim 30, wherein the communication architecture uses at least four data lines, at least one of which is bi-directional, and at least first and second control signals.

32. The system of claim 30, wherein the communication bus uses a standard Ethernet cable to connect the master controller to each of the one or more slave units.

33. The system of claim 31, wherein the first control signal latches the address of the data being sent by the master controller to the one or more slave units.

34. The system of claim 31, wherein the second control signal latches the actual data being sent by the master controller to the one or more slave units.

35. The system of claim 31, wherein when the first and second control signals are in an opposing state, the master controller can use at least three of at least the four data lines to request that one bit of data be returned from one or more of the slave unit.

36. The system of claim 31, wherein at least three of the data lines are used to select a bit of date requested by the master controller.

37. The system of claim 30, wherein one or more of the slave units comprises a programmable device that allows discrete logic to be configured internally and combined with an integrated microprocessor.