Induction heating cooker

Abstract

To provide an induction heating cooker that can implement appropriate heat control in consideration of the induction heating characteristics of a cooking container which is an object to be heated when automatic cooking such as boiling ingredients is performed.SOLUTION: An induction heating cooker includes: a top plate; a heating coil for performing induction heating on a cooking container; an inverter for supplying a high-frequency voltage to the heating coil; a contact-type temperature sensor for measuring a temperature of the cooking container through the top plate; a control device for controlling the inverter based on the temperature measured by the temperature sensor; and an input device for allowing a user to set an automatic cooking menu and a heating time. The control device controls the inverter to sequentially carry out a plurality of heating power steps as the heating time elapses. The control device terminates a heating power step using large heating power when an effective integrated power value actually given to the cooking container reaches a reference power value within a predetermined determination time, and extends the heating power step using large heating power when the effective integrated power value does not reach the reference power value within the determination time.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an induction cooker having an automatic heating function for cooking food by boiling.

Background Art

[0002] As an induction cooker having an automatic heating function, the induction cooker of Patent Document 1 is known. This induction cooker has the problems described in paragraph 0010 of the same document: "When the load is small, for example, when starting stir-fry cooking with a small amount of oil, the temperature of the object to be heated cannot reach the target temperature in a short time." and paragraph 0011: "Therefore, proper preheating could not be completed during cooking such as stir-fry using a frying pan." Based on these problems, as described in paragraph 0012, it aimed to "provide an induction cooker that can complete preheating in a short time during cooking such as stir-fry using a frying pan."

[0003] And, as one of the inventions for achieving this object, in claim 1, it is described as follows: "··· a top plate, ··· a heating coil, ··· an inverter circuit, ··· an operation unit, ··· an infrared sensor, ··· a control unit and a notification unit, the control unit includes an input power integration unit for integrating the input power, ···, the operation unit has a preheating selection unit for selecting a preheating mode, when the preheating mode is selected, the cooking container is heated with a first heating output corresponding to the preheating mode, when the increase amount of the output value of the infrared sensor after starting heating with the first heating output exceeds a first predetermined increase amount, or when the integrated value of the input power after starting heating with the first heating output integrated by the input power integration unit exceeds a first predetermined value, the notification unit notifies that the preheating is completed, and shifts to a standby mode of heating with a second heating output lower than the first heating output, the shift to the standby mode is configured to prioritize the one that exceeds either the first predetermined increase amount or the first predetermined value first, before shifting to the standby mode, when the first heating output performs heating with an output lower than a predetermined output due to the output regulation by the simultaneous use of the heating coils, the first predetermined value of the integrated value is switched according to the first heating output, which is a feature of the induction cooker."

[0004] Here, in paragraph 0043 of Patent Document 1, it is described that "In the present embodiment, since the purpose is to perform preheating when high heat is required such as for stir-frying, the target temperature during preheating is high (for example, 280°C). Therefore, it is only necessary to obtain an output at a high temperature. Thus, as shown by the output characteristic 35a, the infrared sensor 3 of the present embodiment has a characteristic of outputting an infrared detection signal 35 when the bottom surface temperature of the object to be heated 10 is about 250°C or higher, and not outputting the infrared detection signal 35 when it is less than about 250°C." And in paragraph 0048, it is described that "When the menu switch 4b is operated and the 'preheating' mode is selected, the control unit 8 starts preheating with a predetermined heating power amount (first heating output, for example, 3 kW)."

[0005] Therefore, the "preheating" mode in Patent Document 1 refers to a control mode in which, prior to cooking stir-fries or the like that require high heat, the cooking container is heated at high power (e.g., 3 kW) until it reaches the target temperature (e.g., 280°C). Thus, it was possible to appropriately perform the heating control of the "preheating" mode by using the detection signal of an infrared sensor specialized for measurement at approximately 250°C or higher (a temperature sensor that cannot measure below approximately 250°C).

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] However, among the automatic cooking menus implemented by induction cookers, there are also automatic cooking menus for boiling ingredients such as soft-boiled eggs (i.e., automatic cooking menus that require power control to maintain the temperature of the cooking container near 100°C). To appropriately perform that type of automatic cooking, it was not possible to use the control method of Patent Document 1 that uses an infrared sensor that cannot measure below approximately 250°C.

[0008] Also, since the input power integration unit in Patent Document 1 only integrates the input power value itself and does not integrate the effective power value that actually contributes to the induction heating of the cooking container, the induction cooker in that document could not perform appropriate heating control considering the actual heat generation amount that varies according to the induction heating characteristics of the cooking container.

[0009] Therefore, an object of the present invention is to provide an induction cooker that can achieve appropriate power control in consideration of the induction heating characteristics of the cooking container, which is the object to be heated, when performing automatic cooking for boiling ingredients.

Means for Solving the Problems

[0010] An induction heating cooker comprising a top plate on which a cooking container is placed, a heating coil provided below the top plate for induction heating the cooking container, an inverter for supplying a high-frequency voltage to the heating coil, a contact-type temperature sensor for measuring the temperature of the cooking container via the top plate, a control device for controlling the inverter based on the measured temperature of the temperature sensor, and an input device for a user to set an automatic cooking menu and a heating time, wherein the control device controls the inverter to sequentially perform a plurality of heating power steps as time of the heating time elapses, and when an effective integrated power value actually applied to the cooking container reaches a reference power value within a predetermined determination time, the heating power step of high heating power is terminated, and when the effective integrated power value does not reach the reference power value within the determination time, the heating power step of the high heating power is extended.

Advantages of the Invention

[0011] According to the induction heating cooker of the present invention, when performing automatic cooking for boiling food, appropriate heating power control can be realized in consideration of the induction heating characteristics of the cooking container as the object to be heated.

Brief Description of the Drawings

[0012]

Figure 1

Figure 2A

Figure 2B

Figure 2C

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Embodiments for Carrying Out the Invention

[0013] Hereinafter, an embodiment of the induction heating cooker of the present invention will be described with reference to the drawings.

[0014] <Schematic Configuration of the Induction Heating Cooker> FIG. 1 is a diagram showing the schematic configuration and control block of the induction heating cooker 1 of this embodiment. As shown here, the induction heating cooker 1 of this embodiment includes a top plate 2, a heating coil 3, an inverter 4, an infrared sensor 5, a temperature sensor 6, an input device 7, a display device 8, and a control device 9. Each will be described sequentially below.

[0015] The top plate 2 is a heat-resistant glass plate horizontally arranged on the upper part of the induction heating cooker 1, and the cooking container 10, which is the object to be heated, is placed thereon. Hereinafter, it is assumed that the cooking container 10 is a metal pot with a diameter of about 18 cm, and about 1.0 L of water W and two eggs E are contained therein.

[0016] The heating coil 3 is a coil with a diameter of about 20 cm arranged below the top plate 2, and generates eddy currents by applying a high-frequency magnetic field to the cooking container 10 to cause self-heating.

[0017] The inverter 4 applies a high-frequency voltage to the heating coil 3 to generate a high-frequency magnetic field in the heating coil 3.

[0018] The infrared sensor 5 is a non-contact type temperature sensor that receives infrared rays radiated from the bottom surface of the cooking container 10 and transmitted through the top plate 2 through the gap 3a of the heating coil 3, and measures the bottom surface temperature of the cooking container P from the amount of received light energy. As described above, the infrared sensor 5 is a sensor specialized for measurements of about 250°C or higher.

[0019] The temperature sensor 6 is a contact-type temperature sensor that measures the bottom surface temperature of the cooking container 10 via the top plate 2, and is composed of a thermistor closely attached to the lower surface of the top plate 2. Since the thermistor can also measure temperatures below about 250°C, this temperature sensor 6 can measure low temperatures that cannot be measured by the infrared sensor 5.

[0020] The input device 7 is a device equipped with keys that the user operates when setting the device status, etc., and the display device 8 is a device such as a liquid crystal display that displays the device status set by the user. These are arranged on the front side of the upper surface of the top plate 2 where the user can easily operate and view them. Note that the functions of the input device 7 and the display device 8 may be provided by a single touch panel display.

[0021] The control device 9 is a microcomputer that controls the output of the inverter 4 and the display of the display device 8 according to the temperature information of the cooking container 10 measured by the infrared sensor 5, the temperature information of the cooking container 10 measured by the temperature sensor 6, the setting information input to the input device 7, etc., and also has a timer function.

[0022] <Operation Procedure until Automatic Cooking Starts> Next, the operation procedure until the automatic cooking of a boiled egg starts will be described using Fig. 2A, which is a top view of the input device 7 and the display device 8. As shown in each figure, the input device 7 is provided with keys such as a start key 71, a boiled egg key 72, a timer up key 73, and a timer down key 74, and the display device 8 displays information such as a heating time reference display 81 and a remaining timer time display 82. Note that the input device 7 is also provided with keys other than those described above (for example, a heating power setting key, etc.), and the display device 8 also displays information other than those described above (for example, the current heating power, etc.). However, in Fig. 2A, for the sake of simplicity of the figure, the illustration of keys and information that have no direct relation to the present invention is omitted.

[0023] When the user presses the soft-boiled egg key 72 of the input device 7, as shown in FIG. 2A, on the display device 8, as a rough indication of the heating time 81, "Soft-boiled: 10 minutes, Normal: 12 minutes, Hard-boiled: 15 minutes" is displayed, and as the remaining timer time display 82a, "Remaining 12 minutes", which is the initial set value, is displayed. If the user wants to change the initially set heating time (remaining timer time), the user refers to the time displayed in the rough indication of the heating time 81 and presses the timer up key 73 or the timer down key 74 to set the desired heating time.

[0024] After setting the desired heating time in the above procedure, when the user presses the start key 71, the automatic cooking of the soft-boiled egg starts. Note that in FIG. 2A, since it is a diagram explaining the case where the automatic cooking menu to be set is "soft-boiled egg", the soft-boiled egg key 72 is illustrated on the input device 7. However, the present invention can also be applied to other automatic cooking menus for cooking ingredients below the boiling point of water, such as pasta and boiled foods. When performing those automatic cookings, it goes without saying that after pressing the automatic cooking key corresponding to each menu, the same operations as above may be performed.

[0025] <Control flowchart> Next, taking the case of setting the heating time to 12 minutes and starting the automatic cooking of the soft-boiled egg (see FIG. 2A) as an example, the control flowchart of the induction heating cooker 1 of the present embodiment will be described with reference to FIGS. 3 and 4.

[0026] First, in step S1 of FIG. 3, the control device 9 receives the user's input via the input device 7 (specifically, pressing the soft-boiled egg key 72, setting the heating time, pressing the start key 71, etc.), and displays the content corresponding to the user's input and the progress of the automatic cooking in each area of the display device 8 (see FIG. 2A).

[0027] In step S2, the control device 9 starts a heating power step P1 in which a predetermined fixed power (for example, power equivalent to 2.0 kW of heating power) is supplied from the inverter 4 to the heating coil 3. The heating power step P1 is a step for rapidly increasing the temperature of the cooking container 10 at high heating power so that the water temperature in the cooking container 10 rapidly rises to 80°C or higher, the water temperature at which the eggs harden.

[0028] In step S3, the control device 9 determines whether the effective integrated power value reaches the reference power value (for example, 133 Wh) within a predetermined determination time (for example, 240 seconds) from the start of heating. If the requirements are met, the process proceeds to step S4; if the requirements are not met, the process proceeds to step S10.

[0029] Here, the effective integrated power value is, for example, the power value obtained by integrating the effective power values obtained by converting the current values of the inverter 4 detected every second. Since the current value of the inverter 4 during heating of the cooking container 10 increases or decreases according to the induction heating characteristics determined by the electrical resistance value, magnetic permeability, size, shape, etc. of the material of the cooking container 10, the effective integrated power value based on the current value also increases or decreases according to the induction heating characteristics of the cooking container 10. Therefore, if the bottom of the cooking container 10 is a magnetic metal with good induction heating characteristics, the current value of the inverter 4 tends to increase and the effective integrated power value also tends to increase. On the other hand, if the bottom of the cooking container 10 is a clad material or the like in which a thin plate of a magnetic metal with good induction heating characteristics is attached to the lower surface of a thick plate of a non-magnetic metal with poor induction heating characteristics, the current value of the inverter 4 tends to decrease and the effective integrated power value also tends to decrease.

[0030] The reason for giving 133 Wh as an example of the reference power value is as follows. That is, since the reference power value in this embodiment is the power value required to boil 1.0 L of water W for boiling two eggs E, originally, it may be determined based on the heat quantity calculated by the specific heat of water (about 4.2 J / g°C) × the temperature rise (the temperature difference between normal temperature and the boiling point of water) × the water quantity (1.0 L = 1.0 kg). However, since the output power of the inverter 4 also changes according to the heat quantity for heating the cooking container 10 and the heat quantity dissipated during heating, 133 Wh taking these heat quantities into account is exemplified as the reference power value in this embodiment.

[0031] In step S4, the control device 9 starts a heating process P2 in which a predetermined fixed power smaller than the fixed power in the heating process P1 (for example, power equivalent to 1.1 kW of heating power) is supplied from the inverter 4 to the heating coil 3. Note that the heating process P2 is an auxiliary process for sufficiently raising the water temperature in the cooking container 10 even in winter when the temperature of tap water is low. Therefore, if it is summer when the temperature of tap water is high, this step and the subsequent step S5 may be omitted.

[0032] In step S5, the control device 9 determines whether the end condition of the heating process P2 is satisfied. If the requirement is met, it proceeds to step S6, and if the requirement is not met, step S5 is repeated. Note that the end condition of the heating process P2 may be that a predetermined time (for example, 60 seconds) has elapsed since the start of the heating process P2, or that the measured temperature by the temperature sensor 6 has reached a predetermined temperature (for example, 90°C).

[0033] In step S6, the control device 9 starts a heating process P3 in which a predetermined power smaller than the fixed power in the heating process P2 (for example, power equivalent to 0.6 kW of heating power) is supplied from the inverter 4 to the heating coil 3 while performing on-off control. Note that the heating process P3 is a process for maintaining a water temperature suitable for boiling eggs while preventing the eggs from colliding with each other due to over-boiling of the water in the cooking container 10.

[0034] In step S7, the control device 9 sets the measured temperature of the temperature sensor 6 at the start of the heating process P3 as the target temperature. The significance of setting the target temperature will be described later.

[0035] In step S8, the control device 9 performs the heating control of the thermal power process P3. FIG. 4 is a flowchart showing the details of step S8. As shown here, in step S8a, the control device 9 determines the magnitude relationship between the measured temperature of the temperature sensor 6 and the target temperature set in step S7. If the measured temperature is sufficiently higher than the target temperature, it proceeds to step S8b; if the measured temperature is sufficiently lower than the target temperature, it proceeds to step S8c; if neither condition is met (for example, if the difference between the measured temperature and the target temperature is less than 2°C), step S8 ends. In step S8b, the control device 9 reduces the thermal power for the next control period. On the other hand, in step S8c, the control device 9 increases the thermal power for the next control period. Note that to achieve the increase or decrease of the thermal power, the magnitude of the output power of the inverter 4 may be controlled, or the duty ratio of the output power of the inverter 4 may be controlled.

[0036] In step S9, the control device 9 determines whether the remaining timer time has reached 0. If the requirement is met, the heating is terminated and the user is notified of the end of cooking; if the requirement is not met, it returns to step S8. In this way, by repeating step S8 until the remaining timer time reaches 0, the temperature of the water W in the cooking container 10 can be maintained at a desired temperature suitable for boiling eggs.

[0037] On the other hand, when the requirement of step S3 is not met, in step S10, the control device 9 extends the heating time of the thermal power process P1 by a predetermined time (for example, 180 seconds). How much to extend the thermal power process P1 can be appropriately set according to the situation. For example, the extension time can be calculated based on the following formula 1.

[0038] Extension time = (Reference power value - Effective integrated power value at the determination time point) × Correction coefficient K ··· (Formula 1) For example, if the reference power value is 133 Wh, the effective integrated power value at the time when the determination time (for example, 240 seconds) has elapsed is 103 Wh, and the correction coefficient K is 6, the extension time calculated by formula 1 is 180 seconds (3 minutes). Therefore, combined with the standard heating time of 240 seconds (4 minutes) of the thermal power process P1, the heating time of the thermal power process P1 becomes 7 minutes.

[0039] At this time, in order to match the extended heating time and the remaining timer time, the control device 9 appropriately corrects the remaining timer time display 82 of the display device 8. For example, if the heating time set in step S1 is 12 minutes and the heating power process P1 is extended by 180 seconds (3 minutes) in step S10 after 240 seconds (4 minutes) from the start of heating, the remaining timer time display 82b "remaining 8 minutes" in FIG. 2B before the extension is corrected to the remaining timer time display 82c "remaining 11 minutes" in FIG. 2C after the extension. Thereby, the user can correctly grasp the remaining timer time after the extension from the remaining timer time display 82.

[0040] In step S11, the control device 9 determines whether the time extended in step S10 (for example, 180 seconds) has elapsed. If the requirements are met, the process proceeds to step S4, and if the requirements are not met, step S11 is repeated. Thereby, even when using the cooking container 10 with poor induction heating characteristics, the water temperature in the cooking container 10 can be raised to 80°C or higher, which is the water temperature at which the eggs solidify, with high heat.

[0041] Next, with reference to FIGS. 5 to 7, the above-described heating power control will be described more specifically.

[0042] <When using a cooking container 10 with standard induction heating characteristics> FIG. 5 is a graph showing the heating power control when using the cooking container 10 with standard induction heating characteristics (for example, a cooking container 10 made of magnetic stainless steel) assumed in this embodiment, and is an example in which a hard-boiled egg is completed in the set heating time of 12 minutes.

[0043] The upper graph in FIG. 5 is a graph showing the time change of the actual temperature (water temperature) of the water W in the cooking container 10, the time change of the bottom surface temperature of the cooking container 10 measured by the temperature sensor 6, and the time change of the effective integrated power value. The lower graph is a graph showing the time change of the output of the inverter 4. The dashed-dotted line in the upper graph is the target temperature set in step S7.

[0044] In this example, at the determination time 240 seconds after the start of heating, the effective integrated power value actually applied to the cooking container 10 is the same as the reference power value (for example, 133 Wh). Therefore, in the situation of FIG. 5, since the requirements of step S3 described above are satisfied at the determination time, the step S10 of extending the heating power step P1 is not carried out, and the process proceeds to the heating power step P2 of step S4.

[0045] <When using a cooking container 10 with poor induction heating characteristics> FIG. 6 is a graph showing the heating power control when using a cooking container 10 (for example, a cooking container 10 made of aluminum or non-magnetic stainless steel) with induction heating characteristics worse than the standard, and is an example in which a hard-boiled egg is completed in 15 minutes, which is longer than the set heating time of 12 minutes.

[0046] In this example, since the induction heating characteristics of the cooking container 10 are poor, even if the power of 2.0 kW, which can be obtained when heating a cooking container 10 with standard induction heating characteristics, is supplied to the heating coil 3, only a smaller heating power (for example, 1.55 kW) can be obtained. Therefore, at the determination time 240 seconds after the start of heating, the effective integrated power value applied to the cooking container 10 remains at 103 Wh, which does not reach the reference power value (for example, 133 Wh), and as a result, the water temperature also remains at about 70 °C, which does not reach about 100 °C.

[0047] Therefore, in the situation of FIG. 6, since the requirements of step S3 described above are not satisfied at the determination time 240 seconds after the start of heating, step S10 is carried out and the heating power step P1 is extended. As a result, the high-heating-power heating power step P1 can be continued until the water temperature reaches near 100 °C. After the end of the extended heating power step P1, the heating power steps P2 and P3 equivalent to those in FIG. 5 are executed.

[0048] <When using a cooking container 10 with good induction heating characteristics> FIG. 7 is a graph showing the heating power control when using a cooking container 10 (for example, a cooking container 10 made of iron) with induction heating characteristics better than the standard, and is an example in which a hard-boiled egg is completed in 12 minutes, which is the set heating time.

[0049] In this example, since the induction heating characteristics of the cooking container 10 are good, even if power corresponding to a heating power of 2.0 kW is supplied to the heating coil 3 for a standard cooking container 10, the actual heating power generated will be greater than 2.0 kW (for example, 2.2 kW). Therefore, the effective integrated power value reaches the reference power value (for example, 133 Wh) before 240 seconds have elapsed since the start of heating. This means that the water temperature rises to approximately 100°C before 240 seconds have elapsed since the start of heating.

[0050] Therefore, in the situation of FIG. 7, in order to satisfy the requirements of step S3 described above before 240 seconds have elapsed since the start of heating, the process proceeds to the heating power step P2 of step S4 without performing the step S10 of extending the heating power step P1. After the completion of the heating power step P1, a heating power step P2 equivalent to that of FIG. 5 and a heating power step P3 that is longer than that of FIG. 5 by the amount by which the heating power step P1 is shortened are executed.

[0051] Note that the reason for shifting from the high-heating-power heating power step P1 to the medium-heating-power heating power step P2 when the effective integrated power value reaches the reference power value is as follows. That is, if heating is continued at high power even after boiling, there is a risk that the eggs will collide with each other or the eggs will collide with the inner surface of the cooking container 10 due to intense convection, resulting in cracks in the eggs. Therefore, in this embodiment, by immediately reducing the heating power after boiling, the convection inside the cooking container 10 is weakened, and cracking of the eggs can be prevented.

[0052] <Effects of this Embodiment> According to the induction heating cooker of this embodiment described above, when performing automatic cooking for boiling food, appropriate heating power control can be achieved in consideration of the induction heating characteristics of the cooking container, which is the object to be heated.

Explanation of Reference Numerals

[0053] 1 Induction heating cooker 2 Top plate 3 Heating coil 4 Inverter 5 Infrared sensor 6 Temperature sensor 7 Input device 71 Cut start key 72 Boiled egg key 73 Timer up key 74 Timer down key 8 Display device 81 Approximate time display 82 Remaining timer time display 9 Control device 10 Cooking container

Claims

1. A top plate on which a cooking container is placed, A heating coil provided below the top plate for inductively heating the cooking container, An inverter that supplies a high-frequency voltage to the heating coil, A contact-type temperature sensor that measures the temperature of the cooking container via the top plate, A control device that controls the inverter based on the measured temperature of the temperature sensor, An induction heating cooker comprising an input device for a user to set an automatic cooking menu and a heating time, The control device controls the inverter to sequentially perform a plurality of heating power steps as time elapses for the heating time, When the effective integrated power value actually applied to the cooking container within a predetermined determination time reaches a reference power value, the high-heating-power heating step is terminated, An induction heating cooker characterized in that when the effective integrated power value does not reach the reference power value within the determination time, the high-heating-power heating step is extended.

2. In the induction heating cooker according to Claim 1, When the effective integrated power value does not reach the reference power value within the determination time, the heating time of the high-heating-power heating step is extended according to the difference between the reference power value and the effective integrated power value at the time of the determination time. An induction heating cooker characterized by this.

3. In the induction heating cooker according to Claim 1, When the effective integrated power value does not reach the reference power value within the determination time, the cooking container is heated longer than the heating time set by the user by the extended heating time of the high-heating-power heating step. An induction heating cooker characterized by this.

4. In the induction heating cooker according to Claim 1, Furthermore, it is provided with a display device for displaying the remaining heating time, An induction heating cooker characterized in that when the effective integrated power value does not reach the reference power value within the determination time, the remaining heating time for the extended heating time is displayed on the display device.

5. In the induction heating cooker according to Claim 1, The control device performs a low-heating-power heating step after the high-heating-power heating step, An induction heating cooker characterized in that during the low-heating-power heating step, the inverter is controlled to maintain the measured temperature of the temperature sensor at the start of the low-heating-power heating step.

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