MICROWAVE OVEN AND CONTROL METHOD THEREOF

Abstract: Method for controlling start and stop of a heating procedure in a microwave oven (1) by using an optically readable sensor (6) provided on a container or package (5) and comprising a package type field and a field changing its colour emitting properties at a desirable ready-temperature. An optical reading device (9) of the oven reads said sensor before and during the procedure, thereby providing a conditional feedback control of said start and stop, and a safe operation by the use of uncomplicated technology.

Description: MTCROWAVE OVEN AND CONTROL METHOD THEREOF FTET.D OF TECHNOLOGY This invention is directed to a method at a micro¬ wave oven for heating of a foodstuff or a beverage in a container or package, being provided with an information sensor comprising a temperature sensitive field changing its colour emitting properties at a desirable ready- temperature of said foodstuff or beverage, the oven comprising an oven cavity, a system for supplying icro- waves to the cavity, a control unit for controlling the supply of microwaves, and an optical reading device for reading said information sensor in the cavity during heating. The invention is also directed to a microwave oven for implementing the method as well as the use of an information sensor on a container in a microwave oven. TECHNICAL BACKGROUND AND PRIOR ART The invention is primarily, but not solely, concerned with start/stop-control of a heating procedure in microwave ovens which have been specifically adapted for heating of pre-cooked or instant food and beverages contained in standardized, preferably disposable packages of an approved type for direct introduction into the oven cavity and heating of the foodstuff or beverage therein. In order to optimize the transfer of microwave energy to the foodstuff or beverage the dimensions and the design of the oven cavity is preferably fitted to the exterior of said package or container, thereby substantially adjoining the cavity walls. This is a generally space saving concept by substantially reducing the external dimensions of the microwave oven, and furthermore reduces the energy loss during heating, which in turn reduces the heating time and/or allows for the use of a less powerful magnetron as microwave source. An oven of this type has been disclosed in SE patent No. 9302128-5, in the name of the applicant. The heating procedure shall be automatically inter¬ rupted when said foodstuff or beverage has reached the desirable "ready-to-use" or ready-temperature. This necessitates a closed loop control of the heating pro¬ cedure, i.e. information about the actual temperature of the foodstuff or beverage must be fed back to said control unit, which will then interrupt the microwave supply when receiving a feedback signal of a level which corresponds to said desirable temperature. JP 6094244-A2 discloses a microwave oven and a spe¬ cifically designed cooking container. When used together the same will operate substantially according to the method and microwave oven disclosed in the introduction. Said container is provided with a thermo-colour and a reflection type light sensor is provided for detecting a change of colour of said thermo-colour, thereby providing a feedback information for controlling the heating operation. A similar type of container has been disclosed in DE 38 36 424 Al directed to a baby drink or formula bottle which is provided with a thermo-colour. GB 2052731 A discloses an optical feedback sensor having a light reflective/transmissive characteristic which varies with temperature. The invention is primarily concerned with standar¬ dized package designs of the type which is or may be expected to be used for many different kinds of food- stuffs and beverages, not generally intended or adequate for heating in a microwave oven. From this follows that a user may accidentally use the microwave oven for non- intended heating purposes, running thereby the risk of spoiling the foodstuff or beverage and even the risk of consuming an unhealthy piece of food or drink. Another problem has to do with the package itself and specifi¬ cally the widely different package materials. For example, packages having the preferred external dimen¬ sions may appear as an orange juice package of which the interior is lined with aluminum foil in order to with¬ stand the aggressive character of the juice. Using a package of this kind in a microwave oven, you may risk an open fire situation with very short notice, and may as well incur serious damages on the microwave system of the oven. These problems have not been actualized in the referenced prior art, nor solved thereby. SHORT DESCRIPTION OF THE INVENTION A first object of invention is to provide a heating method and a microwave oven for implementing the same being specifically adapted for heating of pre-cooked or instant foodstuff or beverage by using the disposable package thereof as a heating vessel, alternatively by using a designed heating container, such that risks involved with use of non-approved packages and containers in the microwave oven that may end up in low and even unhealthy qualities of food and beverages which are pre¬ pared, as well as technical damage of the oven itself, are eliminated. A second object of invention is to obtain a method and oven allowing heating to be performed fully automati- cally with respect to start and stop of the heating pro¬ cedure while using fitted packages or containers together with simplified and cost effective control functions and means. Said objects of invention are obtained by a method according to the introductory part of the specification comprising the following steps: - introducing said package or container into an oven cavity having walls adjoining substantially to the exterior of said package or container, said information sensor being thereby brought into a reading position in relation to said optical reading device, - reading, by means of said reading device, on said information sensor a control information field indicating the type of package or container, - supplying to said control unit, as a condition for starting the heating, said package or container type control information, - starting the heating if said read-out information indicates an approved type of package or container, and preventing start of the oven if such a field is missing alternatively not indicating an approved type of package or container, and - interrupting the heating at said ready-temperature when reading said change of colour emitting properties. A microwave oven implementing the method according to the invention and designed for heating/cooking a foodstuff or a beverage in its package or a fitted con¬ tainer, being provided with an information sensor com¬ prising a temperature sensitive field and a field which indicates an approved type of package or container, said oven comprising an oven cavity, a system for supplying microwaves to the cavity, a control unit for controlling the supply of microwaves, and an optical reading device for reading said information sensor and supplying a read signal to the control unit, is featured in accordance with the disclosure of the appended claims. Preferred embodiments of the invented method and microwave oven are evident from the subclaims. The invention is also directed to a use, namely using, in a microwave oven, a package type indicator provided on a disposable foodstuff or beverage package for starting a heating procedure of said foodstuff or beverage in said package, and a temperature sensitive indicator thereof for interrupting said heating at a desirable ready-temperature. The invention, primarily focusing problems which may be expected with an increased future use of disposable packages of foodstuffs and beverages together with special purpose microwave ovens for heating the same and which have to be solved in order to avoid serious user security risks, is based on the recognition that these problems may be solved by a mutual adaption of the package, alternatively a fitted container, and the control system of the oven, by providing the package with an optically readable characteristic which, by feed-back to the oven control unit, will unambigously sort out non- approved packages or containers from approved ones, thereby effectively prohibiting use of non-approved packages or containers, providing as well a user-friendly operation of the oven. In the foregoing as well as in remaining parts of this specification "optical reading" and "colour" have been used, implicating thereby the use of light wave¬ lengths within the optical range. However, also other wavelengths as well as different changes of radiation emitting properties may be used. The information sensor may for example comprise fields having crystallized substances, which may be stimulated by a reading radia¬ tion to release its contained information on descrete wavelengths or within defined wavelength ranges. Tempera¬ ture feedback may be obtained by bringing said substances to generate radiation of a temperature sensitive wave- length. SHORT DESCRIPTION OF DRAWINGS The invention will be described more in detail in the following in connection with a non-limitative embodi- ment of a microwave oven according to the invention and by reference to the drawing, in which: Fig. 1 shows a perspective view of a microwave oven according to the invention with oven door thereof in open position and with a package positioned in the oven cavity; Fig. 2 discloses the oven in Fig. 1 without said package; Fig. 3 discloses the oven in Fig. 1 in a front view in which the oven door and the front plate of the oven have been eliminated; and Fig. 4 shows a package to be used according to the invention. DESCRIPTION OF PREFERRED EMBODIMENT Fig. 1 discloses a microwave oven which is specifi¬ cally adapted for heating of beverages or foodstuff in their packages. The adaption of the oven means that the oven cavity thereof has dimensions which have been adapted to the size of the package in such a way that the cavity is substantially filled out by the same. The oven comprises a housing 1, an oven door 2, an oven front 3, to which the oven door 2 adjoins in its closed position, and an oven cavity 4. Inside the cavity is shown a bottle-shaped package 5 to which the shape of the cavity 4 has been adapted. At the bottom of the cavity there is a position means 7 for a defined positioning of the package 5 in the cavity. On two sides of the package 5 optically readably control information fields 6 have been provided. Alternatively, the package may carry such fields on one side only. Inside the housing 1 the oven is provided with an ordinary magnetron for microwave generation, a microwave feeding system for feeding the microwaves into the cavity 4, a fan arrangement for cooling the magnetron, an elec¬ tronic control unit which is usually microprocessor based, and a power supply for supplying high voltage to the magnetron and other operation voltages to the oven. Because said parts of the oven have no importance for a closer understanding of the invention, the same will not be described herein. Instead may be referred to SE patent No. 902128-5, describing a microwave oven of the actual type, and further to the numerous microwave oven types which have been brought into the market by the applicant during several years, specifically the ovens of the type designations VIP20 and VIP27. Fig. 2 discloses the microwave oven in Fig. 1 in the same view but without the package 5. From Fig. 2 is clear that said positioning means 7 has the design of a tray- shaped carrier which has been fitted to the bottom part of the package 5. On the left sidewall of the cavity 4 two holes 8 have been provided, forming openings for optically reading the control information sensor exempli- fied by two circular control information fields 6 on the package. Reading is obtained by an optical reading device 9 disclosed in Fig. 3. The size of the holes 8 have been adapted to the wavelength of the microwaves such that leaking of microwaves from the cavity 4 through the holes 8 is prevented. The control information fields 6 are pro¬ vided at the level of said holes 8, which means that the fields 6 will automatically be brought into correct reading position relative to said holes 8 by positioning the package 5 on the tray 7. Fig. 3 discloses a front view of the oven in Fig. 1 and Fig. 2, in which the oven door 2 and the oven front 3 have been eliminated. Outside the cavity 4 there is an optical reading device 9 comprising one upper and one lower pair of light transmitters/light receivers of a kind which is wellknown to the skilled man. Said pairs of light transmitters/light receivers communicate with the cavity via an upper 8' respectively a lower 8' ' hole in the cavity wall 10 (see also Fig. 2) . The light trans¬ mitter of each pair comprises a light emitting diode, and the light receiver comprises a photo transistor. The reading device 9 is connected to the control unit of the oven for communicating the read control information to the control unit. The detailed manner in which this control information is allowed to influence the control of the oven via the control unit microprocessor complies with common skills and knowledge in this field, and cor¬ responds with the manner in which information from humi- dity, temperature or weight sensors may be used. Also in this case may be referred to above mentioned oven types. In order to improve the security of reading a suitable lense device may be provided in the holes 8' , 8' ' . Fig. 4 discloses a package of a disposable type and built from a microwave transmitting material, which is suitable for the intended use. The bottom of the bottle has a substantially quadratic shape. In this embodiment two of the substantially plane side surfaces of the package have been provided with optically readable information sensors, each of which comprising an upper and a lower, substantially circular control information field 6' and 6'', respectively. By the use of said information fields, alternatively of rectangular shape, it is among other things possible to separate approved packages from others which are not fitted for microwave oven use. The field 6'' is covered by a temperature sensitive colour showing a change of its colour, more pecisely its colour or radiation emitting properties, at the desirable final or "ready-to-use" temperature (ready-temperature) of the beverage which is heated in its package, said properties depending on both illuminating wavelength and temperature, e.g. reflection/emission for green light changing from high to low when temperature goes from low to high. By using a temperature sensitive colours having a reversible change of colour, which means that the field recovers its initial colour at cooling of the package, the same may be reheated to said temperature. The field 6' is used as a package type indicator and is covered by a colour which will not change with temperature. The reading device is arranged to establish the change of colour of the field 6' ' based on the reflected light from this field. The corresponding fields 6' and 6' ' on the other side of the package may have the same design with the difference that the colour of the field 6'' may be selected so as to change colour at a different, higher or lower temperature. Thereby, it is possible to heat the package to different ready-temperatures. The choice of a desirable ready-temperature is simply done by turning the side showing the change of colour at the desirable ready- temperature towards the holes 8, which means the reading device 9. Preferably the actual colour change or ready- temperatures are as well disclosed by numerals on the respective sides of the package. In similar manner said fields may be carried by a reusable container or vessel. The field β ' ' may, alternatively, be covered by a layer of a fluorescent colour and a coating of a trans¬ parent, temperature sensitive colour showing a change of colour by going from a transparent to a non-transparent state, or the reverse, at a selected ready-temperature. The light from an oven lighting arrangement activates the fluorescent layer, which will then transmit fluorescent light of a wavelength which is different from other appearing wavelengths in the oven and may be separated in the reading device 9 in simple manner. When the trans- parent coating changes the fluorescent light is extin¬ guished. Temperature sensitive colours which are trans¬ parent as well as non-transparent and showing reversible or irreversible change of colour at different tempera¬ tures are generally known and used, as well as fluores- cent colours showing fluorescence when stimulated by different light wavelengths. The provision of said colours on a package is obvious to the skilled man and therefore not disclosed in detail herein. Heating of a beverage to a desirable ready-tempera- ture by using a microwave oven according to Fig. 1, 2, 3 and by using the package of Fig. 4 having a lower control information field 6'' showing a change of colour at the desirable ready-temperature and an upper package type field 6', proceeds by the following steps: - introducing the package into the oven cavity 4 closing the oven door 2 sensing the closed oven door by means of a so called door switch of the oven (not disclosed) sensing a change of condition of said door switch by the oven control unit, thereby activating the reading device 9 - establishing, by the reading device 9 reading the control information field 6', that the package 5 is positioned in the cavity and is of a type which is approved supplying said information from the reading device 9 to the oven control unit, thereby starting the heating procedure sensing and establishing the change of colour of the field 6' ' by the reading device supplying the colour change information to the control unit, thereby interrupting the heating procedure at the desirable temperature. Obviously, the heating control concept of using a sensor providing package type and ready-temperature control information may be implemented by arbitrarily shaped containers, not necessarily of a disposable type, and general purpose ovens.

Claims: CLAIMS 1. A method at a microwave oven (1) for heating a food stuff or a beverage in a container or package, being provided with an information sensor (6) comprising a temperature sensitive field (6") changing its colour emitting properties at a desirable ready-temperature of the food stuff, said oven comprising an oven cavity (4) , a system for supplying microwaves to the cavity, a control unit for controlling the microwave supply, and an optical reading device (9) for reading said information sensor in said cavity during heating, c h a r a c t e r i z e d by the following steps: - introducing said package or container into an oven cavity having walls adjoining substantially to the exterior of said package or container, said information sensor being thereby brought into a reading position in relation to said optical reading device, - reading, by means of said reading device, on said information sensor a control information field indicating the type of package or container, - supplying to said control unit, as a condition for starting the heating, said package or container type control information, - starting the heating if said read-out information indicates an approved type of package or container, and preventing start of the oven if such a field is missing alternatively not indicating an acceptable type of package or container, and - interrupting the heating at said ready-temperature when reading said change of colour emitting properties. 2. A method as claimed in claim 1 for heating a food piece or beverage in its package or in a fitted container to one ready-temperature of a number of selectable ready- temperatures, c h a r a c t e r i z e d by - introducing said package or container with the side thereof carrying the temperature sensitive colour field of a selected ready-temperature in said reading position. 3. A microwave oven (1) for heating/cooking a foodstuff or a beverage in its package or a fitted container, being provided with an information sensor (6) comprising a temperature sensitive field (6') and a field which indicates an approved type of package or container, said oven comprising an oven cavity (4) , a system for supplying microwaves to the cavity, a control unit for controlling the supply of microwaves, and an optical reading device for reading said information sensor and supplying a read signal to the control unit, c h a r a c t e r i z e d in that said oven control unit is programmed to prevent start of the oven when the read signal from said reading device indicates that at least one of the following conditions is fulfilled: - said information sensor is lacking on the package or container, - the information does not indicate a package or container which is approved for heating in the oven, said oven control unit being furthermore programmed to start heating when the read signal indicates an approved type of package or container, and to interrupt heating at the desirable ready-temperature when the read signal indicates a change of colour emitting properties of said temperature sensitive field. 4. A microwave oven as claimed in claim 3, c h a r a c t e r i z e d in that said optical reading device (9) comprises: - a first pair of a cooperating light transmitter and light receiver for reading said package type information field (6' ) , - a second pair of a cooperating light transmitter and light receiver for reading said temperature sensitive field (6") . 5. A microwave oven as claimed in claim 3 or 4 , c h a r a c t e r i z e d by - positioning means (7) provided in said cavity (4) for defining the position of the package when introduced into the cavity, thereby bringing said information sensor (6) into a reading position relative to the reading device (9) . 6. Using, in a microwave oven, an optically readable package type indicator provided on a disposable foodstuff or beverage package for starting a heating procedure of said foodstuff or beverage in said package, and an optically readable temperature sensitive indicator thereof for interrupting said heating at a desirable ready-temperature.

Inventors: BRAUNISCH ECKART, GINDAHL KRISTER, OHLSSON MAGNUS, BRAUNISCH, ECKART, GINDAHL, KRISTER, OHLSSON, MAGNUS
Applicants: BRAUNISCH ECKART, GINDAHL KRISTER, OHLSSON MAGNUS, WHIRLPOOL EUROP, BRAUNISCH, ECKART, GINDAHL, KRISTER, OHLSSON, MAGNUS, WHIRLPOOL EUROPE B.V.
Application year: 1996
Main classification: H05B6
IPC codes: F24C7, H05B6