EP0053523B1

EP0053523B1 - Cooking apparatus

Info

Publication number: EP0053523B1
Application number: EP81305717A
Authority: EP
Inventors: Takeshi Okuno
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 1980-12-03
Filing date: 1981-12-03
Publication date: 1987-08-26
Also published as: DE3176397D1; AU528472B2; EP0053523A1; AU7812681A; CA1172706A; JPS5795528A

Description

The present invention relates to a microwave oven.
A gas sensor element having a resistance value which changes in response to the cooking condition of foodstuff disposed in a cooking apparatus has been developed. A microwave oven including a gas sensor element is described in our U.K. Patent Application No. 7930612, "COOKING UTENSIL CONTROLLED BY GAS SENSOR OUTPUT", published on August 28, 1980, the publication number being GB-A-2,040,502.
In the above-mentioned microwave oven, the cooking sequence program is stored in a microcomputer system included in the microwave oven and, therefore, only a limited number of automatic cooking operations are performed. It was difficult to determine a suitable cooking constant, which determines the completion of cooking in combination with the output signal derived from the gas sensor element, for each of the various kinds of cooking operation.
On the other hand, a cooking apparatus has been developed which includes a cassette tape player system for audibly announcing an explanation concerning cooking. A microwave oven having a cassette tape player system is described in our European Patent Application No. 80303308.3, "CASSETTE TAPE CONTROLLED COOKING APPARATUS", published on April 1, 1981, the publication number being EP-A2-0,026,094. This specification is prior art only by virtue of Article 54(3) of the European Patent Convention.
In the above-mentioned cassette tape controlled microwave oven, the cassette tape carries digital data for controlling the cooking operation in addition to the audio information for providing the audible announcement of an explanation concerning cooking. The digital data includes time data for determining a cooking time period.
GB-A-2026726 discloses a microwave oven which is controlled in accordance with data on a card. In one arrangement, the data represents the power levels used during respective periods within the cooking operation. In another arrangement, a temperature probe is used, the output of the probe selecting the appropriate power level data.
US-A-4097707 discloses a microwave oven in which a first cooking operation proceeds until the humidity near the food being cooked reaches a predetermined value selected according to the nature of the food. Cooking is then continued for a time period calculated by multiplying the measured cooking period of the first cooking operation by a coefficient which is again set according to the nature of the food.
European published specification EP-A-0017749 discloses a sewing machine which includes a cassette player system for providing audible instructions of numerical data representing a sewing program.
It would be desirable to provide a microwave oven which permits cooking of a very large variety of foodstuffs with consistent results, which is simple to operate, and which is particularly (although not exclusively) suited for use with a gas sensor.
According to the present invention, there is provided a microwave oven comprising microwave energy generating means for cooking food in a compartment of the oven, a tape player system for reproducing audio information recorded on a magnetic tape in order to provide audible cooking instructions and for reproducing control data also recorded on said magnetic tape, and control means coupled to the tape player system for receiving the reproduced control data and for controlling the microwave energy generating means, said control means being operable also to control the tape player system in response to said control data wherein there is also provided sensing means for producing an output signal indicative of the condition of the food, and wherein the control means is also coupled to said sensing means and is responsive to said output signal reaching a value corresponding to a reference level which is set in accordance with said reproduced control data for terminating a cooking operation.
Although different types of food may require many different reference levels for proper cooking to be carried out (particularly when the desired sensor output at the end of the cooking operation varies according to the food type), all these kinds of food can be cooked without the requirement for the user to remember the various levels because the data needed to set the level for any given type of food can be derived from the magnetic tape.
In a preferred embodiment an additional cooking operation is carried out after the first mentioned cooking operation, the period of the additional cooking operation being determined by a time-representing value derived by the control means from the reproduced control data. With such an arrangement it is possible to obtain more consistent cooking results over a larger variety of foods than with the arrangement described in GB-A-2026726, wherein the cooking is carried out either solely in accordance with a predetermined timing sequence or solely in accordance with the change in temperature of the food.
In a preferred embodiment of the present invention, the microwave oven incorporates a supplementary, electric heater. A gas sensor is disposed in the oven for detecting the cooking condition of a foodstuff disposed in the compartment of the oven. The magnetic tape carries digital data related to a cooking completion condition for the first mentioned, or main cooking operation. The cooking constant data read by the cassette tape player system is stored in a control system included in the oven. The cooking constant data is used to obtain a reference level indicating the cooking completion condition, which is compared with the output signal derived from the gas sensor, whereby a cooking completion instruction signal is developed from the control system when the output signal derived from the gas sensor reaches the reference level. Thereafter, an additional cooking operation is carried out for a period determined by the product of the period of the first cooking operation and a further constant derived from the reproduced control data.
An embodiment of the invention will now be described by way of example with reference to the accompanying drawings, in which:

FIGURE 1 is a perspective view of an embodiment of a microwave oven of the present invention;
FIGURE 2 is a sectional view of the microwave oven of FIGURE 1;
FIGURE 3 is a block diagram of an embodiment of a control system included in the microwave oven of FIGURE 1;
FIGURE 4 is a schematic chart for explaining a recording condition on a cassette tape which is loaded on a cassette tape player system included in the microwave oven of FIGURE 1;
FIGURE 5 is a block diagram of part of the control system of FIGURE 3; and
FIGURE 6 is a graph for explaining an example of operation performed by the microwave oven of FIGURE 1.

A microwave oven of the present invention, which combines a microwave energy generating means and a supplementary electric heater, is shown in FIGURES 1 and 2, and comprises a housing 1 and an oven compartment, or cavity, 2 surrounded by oven walls. A sheath heater 3 is disposed in the oven cavity 2 for grilling the foodstuffs, and a magnetron 4 is secured to the oven wall for microwave cooking purposes. The microwave energy generated by the magnetron 4 is supplied to the oven cavity 2 through a waveguide 5. A power supply circuit comprising a high voltage transformer 6 and a condenser 7 is secured to the housing 1 for supplying the power to the magnetron 4. A blower fan motor 8 is associated with a blower fan 9 which functions to cool the magnetron 4.
An oven door 10 and a control panel 11 are disposed at the front face of the housing 2. The control panel 11 includes a keyboard panel 12, a digital display unit 13, a tape cassette inlet 14 for accommodating a tape cassette 15, and a heater position control knob 40 for adjusting the heater location in the oven cavity 2. The keyboard panel 12 is used to introduce numerical information such as a set temperature, a set cook time period, and cooking commands. That is, the keyboard panel 12 is an input unit for performing a digitally controlled cooking operation. A typical construction of a digitally controlled microwave oven is disclosed in US-A-4,255,639, "MICROWAVE OVEN WITH A PROGRAMMABLE DIGITAL CONTROL CIRCUIT", issued on March 10, 1981. The heater position control knob 40 is used to select the heater height between "High", "Middle" and "Low". A typical construction for shifting the heater location in the oven cavity is shown and described in US-A-4.,137,442, "HIGH-FREQUENCY OVEN HAVING A BROWNING UNIT", issued on Jan. 30, 1979.
Behind the control panel 11, a cassette tape player system 18 is disposed to confront the tape cassette inlet 14. The cassette tape player system 18 comprises a tape drive motor 16, and two magnetic reproduction heads 17a and 17_b. A printed circuit board 19 is disposed behind the keyboard panel 12 for supporting the control circuit of the microwave oven. First and second relays 20 and 21 are connected to the control circuit for controlling the operation of the magnetron 4 and the sheath heater 3, respectively. A speaker system 24 is associated with the cassette tape player system 18 for providing audible instructions derived from the cassette tape player system 18. More specifically, cooking instructions are recorded on the tape in the cassette 15, and the tape drive motor 16 drives the cassette tape at a desired timing for generating the audible instructions.
FIGURE 3 schematically shows a control system of the microwave oven of the present embodiment. Like elements corresponding to those of FIGURES 1 and 2 are indicated by like numerals.
A capstan 25 is connected to the tape drive motor 16. When a pinch roller 26 is depressed toward the capstan 25, the magnetic tape 15a in the cassette 15 is driven to travel in the direction shown by arrows in FIGURE 3 for reproduction purposes. The two magnetic reproduction heads 17a and 17_b are in contact with respective tracks recorded on the magnetic tape 15a for reproducing recorded information.
FIGURE 4 shows the recording tracks on the magnetic tape 15a. A first track 151 and a second track 152 are assigned to the forward direction drive, and a third track 153 and a fourth track 154 are assigned to the reverse direction drive. On the first and fourth tracks 151 and 154, audio information is recorded through the use of analog recording techniques for providing audible cooking instructions. On the second and third tracks 152 and 153, digital information is recorded through the use of a saturation recording technique such as the phase encoding technique for providing digital data which controls the cooking operation performed by the microwave oven.
The magnetic reproduction head 17a contacts the first track 151 or the fourth track 154. The audio information output reproduced from the magnetic reproduction head 17a is applied to an audio amplifier 27 for activating the speaker system 24. The magnetic reproduction head 17_b contacts the second track 152 or the third track 153. The digital information output derived from the magnetic reproduction head 17_b is introduced into a read-out amplifier 28, whereby the digital information output is converted into a binary code signal and applied to a digital control system 29.
The digital control system 29 comprises a central processor unit 291, a read only memory 292 and a random access memory 293. The binary code signal applied to the digital control system 29 is processed in the digital control system 29, thereby providing a control signal for controlling the operation of the microwave oven in accordance with a preselected program sequence. A motor driver circuit 30 is associated with the digital control system 29 for driving the tape drive motor 16 at a desired timing. More specifically, the digital control system 29 develops a start signal for initiating the rotation of the tape drive motor 16, and a stop signal for terminating the rotation of the tape drive motor 16. A display driver circuit 31 is associated with the digital control system 29 for driving the digital display unit 13 in accordance with the digital display data derived from the magnetic reproduction head 17_b. More specifically, the digital display unit 13 is caused to display the programmed cooking period or the programmed cooking condition in a digital fashion. A buzzer driver circuit 32 and a buzzer 33 are associated with the digital control system 29.
A tape start button 34 is disposed on the control panel 11 for controlling the cassette tape drive. When the tape start button 34 is actuated, the start signal is developed from the digital control system 29. The first relay 20 is associated with a first control switch 35 which is disposed between the high voltage transformer 6 and an AC power source 37. The high voltage transformer 6 functions, in combination with the condenser 7 and a diode 38, to energize the magnetron 4. The second relay 21 is associated with a second control switch 36 which is disposed between the sheath heater 3 and the AC power source 37. The relays 20 and 21 are controlled by control signals developed from the digital control system 29.
The microwave oven of the present embodiment further comprises a gas sensor 42 of which a resistance value changes in response to the concentration of the gas developed from the foodstuff disposed in the microwave oven. A preferred gas sensor is "TSG #813" manufactured by Figaro Engineering Inc. A detection characteristic of the gas sensor 42 is described in the above copending GB-A-2040502.
The gas sensor 42 is connected to a resistance-to-frequency converter 43 implemented with an astable multi-vibrator. The frequency of an output signal derived from the resistance-to-frequency converter 43 changes in response to the variation of the resistance value of the gas sensor 42. A preferred circuit construction of the combination of the gas sensor 42 and the resistance-to-frequency converter 43 is described in our copending U.K. Patent Application No. 8123276 "SENSOR CONTROLLED COOKING APPARATUS", filed on July 28, 1981, a copy of which was forwarded to the European Patent Office when this application was filed.
The digital information recorded on the second and third tracks 152 and 153 includes cooking program data for determining the sequence of cooking operations, the cooking time period, the cooking heat source, etc., and, in addition to that, cooking constant data which is used to determine a reference level which is compared with the output signal derived from the resistance-to-frequency converter 43. The cooking constant is a particular value determined for each of the plural kinds of cooking operation.
FIGURE 5 shows an essential part of the digital control system 29. For the purpose of simplicity, FIGURE 5 only shows the digital control system related to the automatic microwave cooking operation controlled by the output signal derived from the gas sensor 42.
The digital control system 29 comprises a main processor 50 and a subprocessor 90. The subprocessor 90 controls the drive of the cassette tape player system 18 and the read out operation of the digital data recorded on the cassette tape 15_ao More specifically, the subprocessor 90 includes a first detection unit 92 for reading out a cooking constant A, a second detection unit 94 for reading out an additive cooking coefficient N, a first power detection unit 96 for reading out microwave power data for the main cooking operation, and a second power detection unit 98 for reading out microwave power data for an additional cooking operation in which additive cooking is carried out.
The main processor 50 comprises a first comparator 52 which functions to compare the output signal derived from the resistance-to-frequency converter 43 with a reference level determined in the main processor 50 and to develop a first control signal when the output signal frequency of the resistance-to-frequency converter 43 reaches the reference level. A second comparator 54 is included in the main processor 50, which develops a second control signal when the additional cooking operation is performed for a preselected period of time.
An operation mode of the digital control system 29 will be described with reference to the FIGURE 5 block diagram and an output frequency variation shown in FIGURE 6.
When the cook start instruction is developed in the microwave cooking mode, the microwave oven is first placed in a cooling period to. The gas sensor 43 detects the concentration of the gas within the oven cavity. The frequency of the output signal developed from the resistance-to-frequency converter 43 varies as shown in FIGURE 6 in response to the variation of the detected gas concentration. The main processor 50 includes a minimum frequency memory 56 for storing the minimum frequency F_o detected during the cooling period to.
As already discussed above, a detection frequency F, derived from the resistance-to-frequency converter 43 varies in response to the detected gas concentration. The cooking constant A recorded on the cassette tape 15a and read out by the first detection unit 92 included in the subprocessor 90 is introduced into a reference level calculation unit 58 included in the main processor 50. The reference level calculation unit 58 calculates a reference level A-F_o through the use of the minimum frequency F_o obtained from the minimum frequency memory 56. The thus obtained reference level A.F_a is introduced into and stored in a reference level memory 60 included in the main processor 50.
The microwave cooking is conducted at the microwave power determined by the first power detection unit 96. When the detection frequency F₁ detected by an output frequency detection unit 62 reaches the reference level A-F_o contained in the reference level memory 60, the first comparator 52 sends a first control signal to a cooking control signal generator 64 in order to terminate the main cooking operation.
A period counter 66 and a timepiece 68 are included in the main processor 50 for detecting a main cooking period T₁. The microwave oven of the present embodiment is constructed to conduct additive cooking at a microwave power read by the second power detection unit 98 for a preselected period of time T₂. More specifically, the main processor 50 includes an additive cooking period calculation unit 70 which functions to calculate the additive cooking period T₂ in response to the main cooking period T₁ obtained from the period counter 66 and the additive cooking coefficient N recorded on the cassette tape 15a and read by the second detection unit 94. In a preferred form, a modification factor AN is introduced, at an operator's choice, from the keyboard panel 12 into the additive cooking period calculation unit 70. The additive cooking period T₂ is determined in accordance with the following equation:
When the additive cooking is performed for the additive cooking period T₂, the second comparator 54 develops a second control signal to terminate the additional cooking operation.
In a preferred form, the main processor 50 is implemented with a microprocessor "IX2058YA" manufactured by Sharp Corporation, and the subprocessor 90 is implemented with a microprocessor "IX2057YA" manufactured by Sharp Corporation.

Claims

1. A microwave oven comprising microwave energy generating means (4) for cooking food in a compartment (2) of the oven, a tape player system (18) for reproducing audio information recorded on a magnetic tape (15a) in order to provide audible cooking instructions and for reproducing control data also recorded on said magnetic tape, and control means (29) coupled to the tape player system for receiving the reproduced control data and for controlling the microwave energy generating means (4), said control means (29) being operable also to control the tape player system in response to said control data wherein there is also provided sensing means (42, 43) for producing an output signal indicative of the condition of the food, and wherein the control means (29) is also coupled to said sensing means and is responsive to said output signal reaching a value corresponding to a reference level which is set in accordance with said reproduced control data for terminating a cooking operation.

2. A microwave oven as claimed in Claim 1, wherein the sensing means (42, 43) comprises a gas sensor (42) for detecting the concentration of reducing gas in the oven compartment (2).

3. A microwave oven as claimed in Claim 2 wherein the sensing means (42, 43) further comprises a resistance-to-frequency converter (43) responsive to the sensor (42) for providing the output signal.

4. A microwave oven as claimed in Claim 3, wherein the control means (29) is operable to derive the reference level by performing the calculation A. F_o, wherein A is a constant obtained from the reproduced control data and F_o is a frequency adopted by the output signal prior to a first cooking operation.

5. A microwave oven as claimed in any preceding claim wherein the control means (29) is arranged to derive from the reproduced control data a time-representing value which determines the period of an additional cooking operation carried out after the first-mentioned cooking operation.

6. A microwave oven as claimed in Claim 5, wherein the control means (29) is further operable to derive from the reproduced control data a value which determines the microwave energy used during the additional cooking operation.

7. A microwave oven as claimed in Claim 5 or Claim 6, wherein the control means (29) is operable to calculate the product of the period (T1) of the first-mentioned cooking operation and a constant (N) contained in the reproduced control data in order to derive the time-representing value.

8. A microwave oven as claimed in Claim 7, the oven including means (12) whereby a user can enter data to modify the time-representing value.

9. A microwave oven as claimed in any preceding claim, the oven further comprising a supplementary heater (3) controlled by the control means (29) for grilling food in the oven compartment (2).