Patent Description:
Well-known high-frequency heating apparatuses measure the initial temperature of food using an infrared sensor to determine whether the food is at room temperature or frozen. These apparatuses control the output power of a magnetron, which is the microwave source so that the food can be heated in low power mode when it is frozen and can be heated in full power mode when it is at room temperature (e.g., Patent Literature <NUM>).

In general, when thawing food, low power mode is selected to ensure heating uniformity, whereas when heating food, full power mode is selected to reduce heating time. Frozen food is thawed and heated in the following manner. First, a thawing process is started in full power mode for food whose temperature is -<NUM>. When the food approaches <NUM>, the mode is switched to low power mode, and when the food is completely thawed, the mode is switched back to full power mode.

Furthermore, there is a known technique to determine the state of food, which is a load, based on the reflection energy coming from the heating chamber (e.g., Patent Literature <NUM>). This technique controls heating based on the fact that food produces high reflection energy when it is frozen and produces lower reflection energy as it is being thawed. This can prevent food from being overheated.

Such well-known techniques can heat food up to desired temperatures using the functions of thawing and heating. However, the temperature control is not precise enough for different types of food or cooking recipes, possibly causing variations in the mouthfeel or the quality of cooked food.

For example, when heating beef, proteins such as myosin and collagen begin to denature at <NUM> to <NUM>, making the beef tender and soft. Meanwhile, actin begins to denature at <NUM> or higher, removing moisture that is a source of meat juice from the beef, thereby extremely degrading the quality of the cooked beef.

Cooking at low temperature such as cooking roast beef requires fine control of the output power, for example, keeping a constant temperature of a little less than <NUM> for a certain time.

Patent Literature <NUM> describes the heating uniformity during thawing, but does not describe the control of the output power at a temperature higher than room temperature.

Patent Literature <NUM> describes a technique to calculate the energy required for heating and to stop the output power in order to prevent overheating during thawing, but does not describe the adjustment of the output power in order to achieve temperature changes appropriate for different types of food or cooking recipes.

<CIT> relates to an apparatus for processing objects with RF energy. The apparatus may include a display for displaying to a user an image of an object to be processed, the image including at least a first portion and a second portion of the object. The apparatus may also include an input unit and at least one processor configured to: receive information based on input provided to the input unit; and generate, based on the received information, processing information for use in processing the object to achieve a first processing result in the first portion of the object and a second processing result in the second portion of the object. <CIT> describes a method for executing heating according to property of food, in which a cooking appliance is provided with a reading device, a displaying screen, and a printing device. The cooking appliance forms a heating zone, which receives sensors and an ultrasonic scanner arranged therein. An object-to-be-heated is placed in the heating zone and the ultrasonic scanner scans and displays an outside configuration of the object on the displaying screen to allow a user to apply an automatic process or manual selection of a temperature difference between a single point or an average of multiple points for more than one or two points and another point for carrying out a heating operation. The sensors detect a temperature difference between a surface temperature and an interior temperature of the object in order to ensure that the temperature difference is kept constant.

The invention is defined by the subject-matter of independent claim <NUM>. The dependent claims are directed to advantageous embodiments.

Advantageously, there is provided a high- frequency heating apparatus capable of adjusting the output of the microwave source so that the temperature of the food being cooked changes in accordance with the temperature profile that defines the temperature change in the food.

A microwave source composed of a semiconductor device can implement finer control of output and adjust a plurality of parameters such as oscillation frequency and phase. This can improve heating efficiency and heating uniformity.

A high-frequency heating apparatus according to the present disclosure includes a heating chamber in which to accommodate a load, a microwave source, at least one radiator, a temperature detector, and a controller. The microwave source generates a microwave and adjusts the frequency and output of the microwave. The at least one radiator radiates the microwave into the heating chamber. The temperature detector detects the temperature in the heating chamber. The controller causes the microwave source to adjust the output of the microwave based on a temperature profile that defines the temperature change in the load, and the temperature in the heating chamber.

The food is heated in accordance with the temperature profile appropriate for the cooking recipe, thereby ensuring the quality of the cooked food.

The microwave output is adjusted in accordance with the programmed temperature profile to control the load temperature, thereby ensuring the quality of the cooked food.

The high-frequency heating apparatus according to the invention includes: a heating chamber in which to accommodate a load; a microwave source; at least one radiator; a temperature detector; and a controller. The microwave source generates a microwave and adjusts the frequency and output of the microwave. The at least one radiator radiates the microwave into the heating chamber. The temperature detector detects the temperature in the heating chamber. The controller causes the microwave source to adjust the output of the microwave based on a temperature profile that defines the temperature change in the load, and the temperature in the heating chamber.

An operating unit receives a selection by a user. The controller determines the temperature profile to be implemented based on the selection by the user.

The controller causes the microwave source to change a cycle of adjusting the output of the microwave.

According to the invention, the controller causes the microwave source to adjust the frequency of the microwave at a cycle shorter than a cycle of adjusting the output of the microwave.

first power detector may detect transmission energy transmitted from the microwave source to the heating chamber, and a second power detector that detects reflection energy that returns from the heating chamber to the microwave source. The controller causes the microwave source to adjust the frequency of the microwave based on the transmission energy and the reflection energy.

The at least one radiator can include a plurality of radiators, and the microwave source adjust the relative phase of the plurality of microwaves radiated from the plurality of radiators.

According to the invention, the controller causes the microwave source to adjust the relative phase of the microwaves at a cycle shorter than the cycle of adjusting the output of the microwave.

A first power detector can detect transmission energy transmitted from the microwave source to the heating chamber, and a second power detector that detects reflection energy that returns from the heating chamber to the microwave source. The controller causes the microwave source to adjust the relative phase of the plurality of microwaves based on the transmission energy and the reflection energy.

Embodiments of the present disclosure will now be described as follows with reference to the drawings.

<FIG> is a structural block diagram of high-frequency heating apparatus <NUM> according to a first exemplary embodiment of the present disclosure.

As shown in <FIG>, high-frequency heating apparatus <NUM> includes: microwave source <NUM>; heating chamber <NUM> where food <NUM> is placed as a load; antenna <NUM>, which is a radiator; temperature sensor <NUM>, which is a temperature detector; control board <NUM>, which is a controller; and operating unit <NUM>.

Temperature sensor <NUM> detects the temperature of food <NUM>. Control board <NUM>, which is a circuit board including a microprocessor, adjusts the output of microwave source <NUM> based on the temperature of food <NUM>. Operating unit <NUM> enables the user to select a cooking recipe.

Microwave source <NUM> includes a microwave oscillator and a variable gain amplifier, which are composed of a semiconductor device. The oscillator included in microwave source <NUM> generates a microwave having a frequency of <NUM> to <NUM>. The variable gain amplifier included in microwave source <NUM> amplifies the microwave generated by the oscillator to an arbitrary output value within a permissible range.

The microwave from microwave source <NUM> is radiated into heating chamber <NUM> by antenna <NUM>. The radiated microwave heats food <NUM>. Temperature sensor <NUM>, which is a food probe, is inserted into food <NUM> to detect the internal temperature.

When the user selects a desired cooking recipe using operating unit <NUM>, control board <NUM> determines the temperature profile appropriate for the recipe. The temperature profile defines the temperature change in food <NUM> suitable for the cooking recipe, and the entire cooking time of the recipe.

Control board <NUM> causes microwave source <NUM> to generate the microwave having the frequency and the output such that the temperature change in food <NUM> from the beginning of the cooking process agrees with the temperature change that is defined in the programmed temperature profile. Hence, the selected recipe is implemented.

<FIG> is a control flowchart of high-frequency heating apparatus <NUM>. As shown in <FIG>, when the user selects a cooking recipe with operating unit <NUM> in Step S31, control board <NUM> refers to the data table and determines the temperature profile to be implemented based on the selected recipe.

In Step S32, control board <NUM> causes microwave source <NUM> to operate under specified initial output conditions that are appropriate for the predetermined temperature profile. Microwave source <NUM> outputs a microwave appropriate for the initial output conditions. The initial output conditions of the microwave in the temperature increasing process (a) can be, for example, a frequency of <NUM> and an output value of <NUM> W.

In Step S33, control board <NUM> monitors the temperature of food <NUM> based on the signal detected by temperature sensor <NUM>, for example, every one second. In Step S34, control board <NUM> determines whether the temperature of food <NUM> agrees with that defined in the temperature profile.

If the temperature of food <NUM> fails to agree with that defined in the temperature profile (No in Step S34), the process returns from Step S34 to Step S32. For example, when the temperature of food <NUM> is lower than the temperature defined in the temperature profile, control board <NUM>, for example, increases the output of microwave source <NUM> to <NUM> W in Step S32 so as to accelerate the heating of food <NUM>. If food <NUM> easily absorbs a microwave having a frequency of <NUM>, control board <NUM> may change the microwave frequency to <NUM>.

If the temperature of food <NUM> agrees with that defined in the temperature profile (Yes in Step S34), the process proceeds from Step S34 to Step S35. In Step S35, control board <NUM> determines whether the time elapsed since the start of the cooking has reached the cooking time defined in the temperature profile. If the result in Step S35 is "No", the process returns to Step S33. If the result is "Yes", control board <NUM> ends the cooking.

Thus, in Steps S32 to S35, control board <NUM> controls microwave source <NUM> so that the temperature of food <NUM> changes as defined in the temperature profile during the heating time defined in the temperature profile.

<FIG> shows an example of the temperature profile. The temperature profile shown in <FIG> is for cooking roast beef. The profile defines performing the following sequential processes: a temperature increasing process (a), a constant temperature process (b), and a temperature decreasing process (c).

In the temperature increasing process (a), control board <NUM> allows food <NUM> to be heated for <NUM> minutes to increase its temperature from room temperature to <NUM>. When the temperature of food <NUM> reaches <NUM> after the <NUM> minutes, the process proceeds to the constant temperature process (b).

In the constant temperature process (b), control board <NUM> causes microwave source <NUM> to decrease the output of the microwave or to change the frequency of the microwave. Thus, food <NUM> is kept at a comparatively low temperature of <NUM> for <NUM> minutes.

When food <NUM> is kept at a constant temperature as in the constant temperature process (b), microwave source <NUM> may repeat operating and stopping. This method, however, may increase the error from the target temperature of <NUM>, making it difficult to achieve fine temperature control, which influences the quality of cooked food. Therefore, the output of microwave source <NUM> is preferably set at a low level to reduce temperature variations in the constant temperature process (b).

When <NUM> minutes have passed since the start of the cooking, the process proceeds to the temperature decreasing process (c). In this process (c), control board <NUM> decreases the temperature of food <NUM> to <NUM> in <NUM> minutes.

The gradual temperature change in the temperature decreasing process (c) is achieved not by simply stopping microwave source <NUM> but by setting the output of microwave source <NUM> at a low level. For example, to absorb liquid seasoning into food <NUM>, heating is stopped to reduce convection. In general, however, liquid seasoning is more easily absorbed into food <NUM> as food <NUM> is at higher temperature. For this reason, microwave source <NUM> preferably continues to generate a microwave having the output that is low enough to avoid convection.

The temperature profile may define that when food <NUM> is at high temperature, the output of microwave source <NUM> is stopped to let food <NUM> rest until cool enough to be taken out safely.

As described above, the present exemplary embodiment programs a temperature profile appropriate for the cooking recipe selected by the user, and adjusts the output of microwave source <NUM> according to the temperature of food <NUM>. This enables the temperature of food <NUM> to change in accordance with the temperature profile, thereby ensuring the quality of the cooked food.

In the present exemplary embodiment, a food probe as temperature sensor <NUM> is used to detect the internal temperature of food <NUM>. Alternatively, however, an infrared sensor may be used to detect the surface temperature of food <NUM>.

In the temperature increasing process (a), when the volume of food <NUM> is large, food <NUM> may fail to be heated to the temperature defined in the temperature profile even if microwave source <NUM> is operated at maximum output power. In such a case, control board <NUM> may extend the temperature increasing process (a) until food <NUM> is heated to the temperature defined in the temperature profile.

Similarly, in the temperature decreasing process (c), food <NUM> may not be cooled to the temperature defined in the temperature profile even if the output of microwave source <NUM> is stopped. In such a case, control board <NUM> may extend the temperature decreasing process (c) until food <NUM> is cooled to the temperature defined in the temperature profile.

A temperature profile may define a plurality of temperature change processes such as the temperature increasing process (a) and the constant temperature process (b) shown in <FIG>. In such a case, control board <NUM> may extend the cycle of adjusting the output of microwave source <NUM> in the temperature increasing process (a) by giving priority to the heating rate. Control board <NUM> may reduce the cycle of adjusting the output of microwave source <NUM> in the constant temperature process (b) by giving priority to the precision of the temperature control of food <NUM>. This can reduce the cooking time and further ensure the quality of the cooked food.

<FIG> show other examples of the temperature profile. The temperature profile shown in <FIG> is for cooking a stew in a pot, such as pot-au-feu. This profile defines performing the following sequential processes: a temperature increasing process (d) and a constant temperature process (e).

In the temperature increasing process (d), control board <NUM> allows food <NUM> to be heated for <NUM> minutes to increase its temperature from room temperature to <NUM>. In the constant temperature process (e), control board <NUM> allows food <NUM> to be stewed at <NUM> for <NUM> minutes.

This temperature profile can maintain a nearly boiling temperature to prevent the pot from boiling over or the ingredients falling apart into pieces in the pot.

The temperature profile shown in <FIG> is for baking dough for cake, for example. This profile defines performing the following sequential processes: a temperature increasing process (f), a temperature increasing process (g), and a temperature decreasing process (h).

In the temperature increasing process (f), control board <NUM> allows food <NUM> to be heated for <NUM> minutes to increase its temperature rapidly from room temperature to <NUM>. In the temperature increasing process (g), control board <NUM> allows food <NUM> to be heated for <NUM> minutes to increase its temperature gradually from <NUM> to <NUM>. In the temperature decreasing process (h), control board <NUM> allows food <NUM> to be cooled to <NUM> in <NUM> minutes.

The cooking defined in this temperature profile is performed using not only microwave source <NUM> but also an unillustrated radiant heater. This temperature profile can ensure the rising of dough.

When implementing the temperature control of food <NUM> corresponding to these temperature profiles, control board <NUM> may change the oscillation frequency of microwave source <NUM> at a timing different from the timing of adjusting the output of microwave source <NUM>.

An example according to the invention: assume that the cycle of adjusting the output of microwave source <NUM> is one second, and that the oscillation frequency of microwave source <NUM> is changed in steps of <NUM> from <NUM> to <NUM> every <NUM> second. In this case, food <NUM> can be heated at ten different oscillation frequencies in one cycle of adjusting the output of microwave source <NUM>.

In general, when a microwave is radiated into a closed space such as heating chamber <NUM>, the microwave multi-reflected in the closed space becomes a standing wave, creating a strong electric field region and a weak electric field region. This electric field distribution changes depending on the frequency of the applied microwave.

Hence, according to the invention, the microwave frequency is adjusted at a cycle shorter than the cycle of adjusting the output of microwave source <NUM> to equalize the time averages of the electric field distribution. This reduces uneven heating of food <NUM>, thereby improving the quality of cooked food.

In the present exemplary embodiment, the microwave generated by microwave source <NUM> is radiated into heating chamber <NUM> through antenna <NUM>. However, antenna <NUM> may be replaced by a waveguide.

High-frequency heating apparatus <NUM> according to a second exemplary embodiment of the present disclosure will now be described as follows. <FIG> is a structural block diagram of high-frequency heating apparatus <NUM>. In <FIG>, components identical to those in the first exemplary embodiment are denoted by the same reference numerals, and the description thereof will be omitted.

In the present exemplary embodiment, the microwave generated by microwave source <NUM> is radiated into heating chamber <NUM> through antennas 102a and 102b. In the present exemplary embodiment, antennas 102a and 102b correspond to radiators.

As shown in <FIG>, microwave source <NUM> of the present exemplary embodiment includes: oscillator <NUM>; phase shifter <NUM>; amplifiers 403a and 403b; wave detectors 404a and 404b; and control board <NUM>.

Oscillator <NUM> is the oscillator that is composed of a semiconductor device and that generates the microwave having an adjustable oscillation frequency. Phase shifter <NUM> controls the microwave phase. Amplifiers 403a and 403b are variable gain amplifiers for amplifying the microwave generated by oscillator <NUM> to an output value in a permissible range.

Heating chamber <NUM> includes antenna 102a connected to amplifier 403a, and antenna 102b connected to amplifier 403b.

In the present exemplary embodiment, the microwave generated by oscillator <NUM> is divided into two parts: one is amplified by amplifier 403a and is radiated into heating chamber <NUM> by antenna 102a, whereas the other passes through phase shifter <NUM>, is amplified by amplifier 403b, and is radiated into heating chamber <NUM> by antenna 102b.

The microwave radiated by antenna 102b is adjusted in phase by phase shifter <NUM>, thereby having a different phase from the microwave radiated by antenna 102a.

Wave detector 404a separately detects transmission energy Pfa transmitted from amplifier 403a to antenna 102a and reflection energy Pra returning via antenna 102a. Wave detector 404b separately detects transmission energy Pfb transmitted from amplifier 403b to antenna 102b and reflection energy Prb returning via antenna 102b.

Wave detector 404a functions as a first power detector when detecting the transmission energy Pfa, and functions as a second power detector when detecting the reflection energy Pra. Similarly, wave detector 404b functions as a first power detector when detecting the transmission energy Pfb, and functions as a second power detector when detecting the reflection energy Prb.

The reflection energies Pra and Prb are loss energies not contributing to the heating of food <NUM>. The reflection energies Pra and Prb can be reduced by adjusting the oscillation frequency of oscillator <NUM> and the amount of phase adjustment of phase shifter <NUM>, thereby improving the efficiency of the energies contributing to the heating.

<FIG> shows the frequency characteristics of transmission energy Pf and reflection energy Pr in the frequency range of <NUM> to <NUM>. In the graph, (Pf - Pr)/Pf in the vertical axis represents the efficiency of the energies contributing to the heating. The larger the index, the higher the heating efficiency.

As shown in <FIG>, the frequency range of <NUM> to <NUM> contains comparatively highly efficient frequencies such as <NUM> and <NUM>, and comparatively inefficient frequencies such as <NUM> and <NUM>.

Therefore, in Step S32 of <FIG>, control board <NUM> adjusts the oscillation frequency of oscillator <NUM> before cooking so as to sweep the frequency range of <NUM> to <NUM> in steps of <NUM>, thereby checking the heating efficiency at each frequency. After this, control board <NUM> allows cooking to be performed at a microwave whose frequency has the highest heating efficiency. This can reduce the power consumption during cooking.

Selecting a plurality of frequencies with comparatively high heating efficiencies and sequentially using these frequencies during cooking can further improve the heating efficiency and the heating uniformity.

In the case of using a plurality of antennas, the phase difference having the highest heating efficiency can be checked before cooking in the same manner as frequency. To be more specific, control board <NUM> can control phase shifter <NUM> to sweep the phase difference between the microwave radiated by antenna 102a and the microwave radiated by antenna 102b from <NUM>° to <NUM>° in steps of <NUM>°, thereby checking the heating efficiency at each phase difference. After this, control board <NUM> allows cooking to be performed at the phase difference having the highest heating efficiency. This can further reduce the power consumption during cooking.

In the temperature control of food <NUM> in accordance with the temperature profile, control board <NUM> may change the amount of phase adjustment of phase shifter <NUM> at a timing different from the timing of adjusting the output of microwave source <NUM>.

In particular, adjusting the relative phase of two microwaves at a cycle shorter than the cycle of adjusting the output of microwave source <NUM> will equalize the time averages of the electric field distribution in heating chamber <NUM> in the same manner as frequency. This reduces uneven heating of food <NUM>, thereby improving the quality of cooked food.

Changing both frequency and phase during cooking can further reduce uneven heating of food <NUM>.

The relation between heating efficiency and oscillation frequency shown in <FIG> is one example. This relation not only changes depending on the shape and size of heating chamber <NUM> and the material and volume of food <NUM>, but also is affected by the temperature change in food <NUM> during cooking. Hence, the oscillation frequency is preferably reset regularly as well as before starting cooking.

In the first and second exemplary embodiments, food <NUM> is cooked by microwave heating alone. Alternatively, however, the microwave heating may be combined with radiant heating using, for example, an infrared heater or with convection heating using hot air.

The output value of microwave source <NUM> can be determined by proportional-integral-differential (PID) control. P control means proportional control. When the difference between the temperature defined in the temperature profile and the actual temperature of food <NUM> is ΔT, the P control adjusts the output value of microwave source <NUM> according to the value of ΔT.

I control means integral control. The I control adjusts the output value of microwave source <NUM> according to the cumulative value of ΔT. D control means differential control. The D control adjusts the output value of microwave source <NUM> according to the amount of change in ΔT.

To be more specific, the control index is calculated by the formula shown in Mathematical Formula <NUM>. In this formula, Kp, Ki, and Kd are predetermined coefficients. These coefficients should be set suitable for each cooking recipe.

Claim 1:
A high-frequency heating apparatus (<NUM>) comprising:
a heating chamber (<NUM>) configured to accommodate a load (<NUM>);
a microwave source (<NUM>) configured to generate a microwave, and to adjust a frequency and an output of the microwave;
at least one radiator (<NUM>) configured to radiate the microwave into the heating chamber (<NUM>);
a temperature detector (<NUM>) configured to detect a temperature in the heating chamber (<NUM>); and
a controller (<NUM>) configured to cause the microwave source (<NUM>) to adjust the output of the microwave, the adjustment being based on a temperature profile defining a temperature change in the load (<NUM>), and the temperature in the heating chamber (<NUM>),
characterized in that:
the controller (<NUM>) causes the microwave source (<NUM>) to change a cycle of adjusting the output of the microwave, and causes the microwave source (<NUM>) to adjust the frequency of the microwave at a cycle shorter than a cycle of adjusting the output of the microwave.