Microwave ovens and methods of cooking food

• US 4,647,746 A
• Filed: 07/08/1985
• Issued: 03/03/1987
• Est. Priority Date: 07/11/1984
• Status: Expired due to Fees

• Current Assignee: Microwave Ovens Limited
• Original Assignee: Microwave Ovens Limited
• Inventors: Eke, Kenneth I.
• Primary Examiner(s): Leung, Philip H.
• Application Number:
  US06/752,592
• Time in Patent Office: 603 Days
• Field of Search: 219/10.55 B, 219/10.55 M, 219/10.55 R, 219/10.55 E, 99/325, 99/451, 99/DIG. 14, 426/243, 426/523
• US Class Current: 219/681
• CPC Class Codes: H05B 6/6411 the supports being rotated
• CPC Class Codes: H05B 6/6435 Aspects relating to the user interface of the microwave heating apparatus
• CPC Class Codes: H05B 6/645 using temperature sensors
• CPC Class Codes: H05B 6/6473 combined with convection heating H05B6/6485 takes precedence
• CPC Class Codes: H05B 6/6482 combined with radiant heating, e.g. infrared heating

Abstract

A microwave oven has a magnetron for supplying microwave power to a cavity of the oven, and an electrical resistance heating element over which air is blown by a fan to provide a forced flow of hot air through the cavity. The variation in hot air temperature is monitored, and the slope of the temperature/time variation is sensed after a predetermined time interval from the commencement of cooking with the oven in a cold condition. The sensed slope is then used to predict the time period it will take the hot air temperature to reach a predetermined threshold, and the microwave power and the hot air are discontinued after the predicted time period has elapsed.

Claims

1. A microwave oven comprising a microwave generator for supplying microwave power to a cavity of the oven, thermal heating means for supplying a forced flow of hot air to the cavity simultaneously with said microwave power, monitoring means for monitoring the variation in hot air temperature with time, said monitoring means monitoring a gradient of a curve of the temperature increase of said hot air plotted against time, sensing means which senses said gradient after a predetermined time interval between about three and eight minutes after commencement of cooking with the oven in a cold condition, processing means responsive to said sensing means which predicts the period of time it will take the hot air temperature to reach a predetermined threshold, and switching control means operative to discontinue the supply of power to the microwave generator and the thermal heating means when said predicted period of time has elapsed if such predicted period of time is shorter than a further predetermined time period or if said processing means predicts that the predicted time is longer than said further predetermined time period provides that the oven continues to operate beyond the threshold temperature but with increased power delivered by said microwave generator and decreased power delivered by said thermal heating means, said sensed gradient of the temperature/time curve after said predetermined time interval being representative of one of three major categories of foodstuff, in that a relatively steep gradient of the temperature/time curve is characteristic of baked food items, a less steep gradient of the temperature/time curve is characteristic of heavier food items such as joints of meat, and a relatively flat gradient of the temperature/time curve is characteristic of frozen foods, said switching control means being responsive to the category of foodstuff which is being cooked as so identified so that magnitude and duration of microwave power and forced hot air power appropriate thereto is automatically executed.

2. A microwave oven according to claim 1, wherein said predetermined time interval is between 4 and 6 minutes from the commencement of cooking with the oven in a cold condition.

3. A microwave oven according to claim 1, wherein the oven comprises means for altering the particular threshold temperature so that the user has the choice of selecting a well baked food item or a lightly baked food item.

4. A microwave oven according to claim 1, wherein said further predetermined time period is thirty minutes.

5. A method of cooking food in a microwave oven having a cavity supplied with microwave power simultaneously with thermal power provided by a forced flow of hot air through said cavity, comprising monitoring a gradient of a curve of hot air temperature plotted against time, sensing said gradient after a predetermined time interval between three and eight minutes from the commencement of cooking with the oven in a cold condition, identifying said sensed gradient of the temperature/time curve after said predetermined time interval as being representative of one of three major categories of foodstuffs in that a relatively steep gradient of the temperature/time curve is characteristic of baked food items, a less steep gradient of the temperature/time curve is characteristic of heavier food items like joints of meat and a relatively flat gradient of the temperature/time curve is characteristic of frozen foods, and automatically selecting and executing an appropriate magnitude of microwave power and forced hot air power in accordance with the category of foodstuff as identified, predicting on the basis of said selected magnitude by electronic processing means the time period it will take for the hot air temperature to reach a particular threshold value, and switching off said microwave power and said thermal power after said time period so predicted has elapsed.

6. A method according to claim 5, wherein the predetermined time interval is between four and six minutes from the commencement of cooking with the oven in a cold condition.

7. A method according to claim 5, comprising the further step of selecting said threshold value.