Patent Application
20110000904
The present invention relates to an induction heat cooking device for heating an object to be heated such as a cooking container.
In recent years, induction heat cooking devices for heating cooking containers such as a pot and a frying pan with a heating coil by induction have been widely used in ordinary households and commercial-use kitchens. The induction heat cooking device includes a heat sensitive element such as a thermistor on a lower surface of a top plate to detect the temperature of the bottom surface of a cooking container with the heat sensitive element, and controls the heating coil so that the detected temperature agrees with a target temperature. For example, when the cooking container is preheated before fried food are cooked, the induction heat cooking device controls the heating coil so that the temperature detected by the heat sensitive element reaches a preheating target temperature.
When a pot contains a large amount of oil and food, for example, when fried food is cooked, (i.e., the load is large), the temperature of the bottom surface of the cooking container gradually increases. In contrast, when a frying pan contains only a small amount of oil (i.e., the load is small), the temperature increases rapidly. In this induction heat cooking device, the heat sensitive element detects the temperature of the bottom surface of the cooking container placed on the top plate by detecting the temperature transferred from the cooking container to the top plate, and therefore, the heat sensitive device has poor temperature following capability with respect to the temperature of the bottom surface of the cooking container. Accordingly, when the temperature of the bottom surface of the cooking container rapidly increases, there is a large error between the actual temperature of the bottom surface of the cooking container and the temperature detected by the heat sensitive element. As a result of this large error, even after the actual temperature of the bottom surface of the cooking container has reached the target temperature, the heat sensitive element cannot detect the actual temperature having reached the target temperature, which causes the induction heat cooking device to continue heating. Therefore, the temperature of the bottom surface of the cooking container may go far beyond the target temperature, and may reach a dangerous temperature such as an oil firing temperature. In order to solve the above problem, a conventional induction heat cooking device detects the temperature gradient of the bottom surface of the cooking container, and stops heating when the temperature gradient is determined to be steeper than a predetermined temperature gradient, thus controlling the heating coil so that the temperature of the bottom surface of the cooking container does not reach a dangerous temperature (for example, refer to Patent Document 1).
Patent Document 1: JP 64-33881 A
However, the conventional induction heat cooking device that controls and stops heating based on the temperature gradient calculated based on the temperature detected by the heat sensitive element may fail to stop heating at an appropriate time as described below, when the load is small, for example, when a cooking container having a thin bottom plate is used for cooking of stir-fried food, in which the cooking starts with a small amount of oil.
Since the heat sensitive element detects the temperature of the bottom surface of the cooking container by detecting the temperature of the lower surface of the top plate, a large clearance between the top plate and the bottom surface of the cooking container at the position at which the heat sensitive element detects the temperature would have a great affect on the relationship between the detected temperature and the actual temperature of the bottom surface of the cooking container. In particular, a large clearance is formed between the bottom of the pot and the top plate in a case where the bottom of the pot is warped. In this case, the temperature of the bottom of the pot is less likely to be transferred to the top plate. Accordingly, the temperature gradient calculated from the temperature detected by the heat sensitive element is less than the actual temperature gradient of the bottom of the pot. Therefore, the conventional induction heat cooking device may fail to stop heating at an appropriate time.
When the thickness of the bottom surface of the cooking container is thin, the temperature of the bottom surface of the cooking container rapidly increases. On the other hand, it takes some time for the heat of the bottom surface of the cooking container to be transferred to the lower surface of the top plate. Therefore, even if the heat sensitive element can detect the same slope as the actual temperature gradient of the bottom surface of the cooking container, it takes some time for the heat sensitive element to detect it, and the heat sensitive element may fail to stop heating at an appropriate time.
As described above, the conventional induction heat cooking device often fails to stop heating at an appropriate time because the conventional induction heat cooking device controls and stops heating based on the temperature gradient calculated based on the temperature detected by the heat sensitive element. If the conventional induction heat cooking device fails to stop heating at an appropriate time, the temperature of the bottom surface of the cooking container goes far beyond the target temperature, and there is a problem in that it takes a long time to thereafter stabilize the temperature to the target temperature. On the other hand, in a case where the load is small, it is necessary for the conventional induction heat cooking device to start heating the cooking container with a small heating power so that the temperature of the bottom surface of the cooking container does not go beyond the target temperature. In this case, however, there is a problem in that it takes a long time for the temperature of the bottom surface of the cooking container to reach the target temperature.
Therefore, when the conventional induction heat cooking device heats an object to be heated having a thin bottom plate, there is a problem in that the conventional induction heat cooking device cannot raise the temperature of the object to be heated to the target temperature in a short time, and cannot prevent a transitional temperature with respect to the target temperature from attaining an excessively high temperature. Therefore, while stir-fried food is cooked with a frying pan, the conventional induction heat cooking device cannot finish preheating in a short time, and cannot prevent the frying pan from reaching an excessively high temperature and deforming or getting discolored.
The present invention solves the above problems, and aims at providing an induction heat cooking device that raises the temperature of an object to be heated to a target temperature in a short time and prevents a transitional temperature with respect to the target temperature from attaining an excessively high temperature, even when the object to be heated has a thin bottom plate. More specifically, the present invention aims at providing an induction heat cooking device that can finish preheating in a short time and can prevent a frying pan from reaching an excessively high temperature and deforming or getting discolored, while stir-fried food is cooked with the frying pan. Further, the present invention provides an induction heat cooking device that continues heating to keep an object to be heated at an appropriate temperature after the preheating is finished.
In order to achieve the above aims, an induction heat cooking device according to the present invention includes a top plate made of a material through which an infrared light is transmitted, a heating coil for receiving a high frequency current to heat a cooking container placed on the top plate by induction, an inverter circuit for providing the high frequency current to the heating coil, an operation unit including an operation mode setting unit for setting an operation mode of the inverter circuit and a heating power setting unit for setting a heating power of the inverter circuit, an infrared sensor for detecting an infrared light that is emitted from a bottom surface of the cooking container and transmitted through the top plate, a control unit for controlling an output of the inverter circuit, based on an output of the infrared sensor and a setting inputted to the operation unit, and a notification unit, wherein the operation mode includes a preheating heating mode for performing preheating before performing heating, wherein when the operation mode is set to the preheating heating mode, the control unit starts operation in a preheating mode for heating the cooking container with a first heating output corresponding to the preheating heating mode, and wherein when an increment of an output value of the infrared sensor is more than a first predetermined increment since the heating starts with the first heating output, the control unit causes the notification unit to notify that the preheating is finished, and the operation mode is changed to a waiting mode for performing heating with a second heating output that is lower than the first heating output, and wherein when a user sets a heating power by means of the heating power setting unit in the preheating mode, change to the heating power set by the user is prohibited, and wherein when the user sets a heating power by means of the heating power setting unit in the waiting mode, change to the heating power set by the user is permitted, and the operation mode is changed to the heating mode for performing heating with a third heating output corresponding to the heating power set by the user.
The operation mode may be changed to the waiting mode when the increment of the output value of the infrared sensor with respect to a predetermined initial output value exceeds the first predetermined increment, instead of the increment of the output value of the infrared sensor since the heating starts with the first heating output. In this case, the predetermined initial value may be an output value of the infrared sensor that is obtained when the cooking container, having such a temperature that the gradient of increase in the output of the infrared sensor with respect to a change of temperature of the cooking container is equal to or less than a predetermined value, is placed on the top plate.
The induction heat cooking device may further include a timer count unit for counting a time from when the operation mode is changed to the waiting mode. In this case, when the time counted by the timer count unit reaches a first predetermined time in the waiting mode, the control unit may halt heating or change the second heating output to a heating output that is smaller than the second heating output.
When the time counted by the timer count unit reaches a first predetermined time, the notification unit may notify the user that the heating is halted or the second heating output is changed to the heating output that is smaller than the second heating output.
When the time counted by the timer count unit reaches a second predetermined time that is shorter than the first predetermined time, the notification unit may issue a notification for prompting the user to start cooking.
The operation unit may include a plurality of switches. In this case, the timer count unit stops counting when a predetermined switch in the operation unit is pressed down before the counted time reaches the first predetermined time.
The operation unit may include a plurality of switches. In this case, when a predetermined switch in the operation unit is pressed down before the counted time reaches the first predetermined time, the timer count unit may reset counting and may start counting all over again, and the timer count unit may reset the first predetermined time to a third predetermined time that is longer than the first predetermined time. When the counted time since the resetting reaches the third predetermined time, the heating may be halted, or the second heating output may be changed to a heating output that is smaller than the second heating output.
The induction heat cooking device may further include a numerical display unit for displaying a number. In this case, the numerical display unit may display how much time it takes for the time counted by the timer count unit to reach the first predetermined time.
The induction heat cooking device may further include a heating power display unit for displaying a heating power. In this case, the heating power display unit may not display the heating power in the preheating mode, and may display the heating power after the operation mode is changed to the waiting mode.
The induction heat cooking device may further include an operation mode display unit for displaying a mark representing the operation mode. In this case, in the preheating mode, the operation mode display unit may light a heating mark indicating that the heating is performed and may blink a preheating mark indicating that the preheating function is operated. When the operation mode is changed to the waiting mode, the operation mode display unit may stop blinking the preheating mark and may light the preheating mark. When the operation mode is changed to the heating mode, the operation mode display unit may light the heating mark and may turn off the preheating mark.
According to the heat cooking device of the present invention, a preheating function having an excellent usability can be achieved with an infrared sensor. In other words, the change of the output of the infrared sensor is measured, and the temperature of the bottom surface of the cooking container is detected. Accordingly, the actual temperature of the bottom surface of the cooking container can be accurately detected with high thermal responsiveness. Therefore, the heating output can be large, and the object to be heated can be brought to a target temperature in a short time. Thereafter, the output can be reduced immediately, and the object to be heated is maintained at a temperature appropriate for preheating. As a result, the transitional temperature can be prevented from reaching an abnormally high temperature with respect to the target temperature. More specifically, a preheating mode is arranged for operating the preheating function. In the preheating mode, the temperature is controlled with the infrared sensor. Therefore, even when stir-fried food is cooked with a frying pan, the heating power can be set large in the preheating mode, and the preheating can be finished in a short time without damaging the frying pan. In addition, the object to be heated can be maintained at an appropriate temperature by continuing heating after the preheating is finished.
The embodiments of the present invention will be hereinafter described with reference to the drawings.
The induction heat cooking device according to Embodiment 1 of the present invention includes a top plate 1 arranged on the top surface of the device and a heating coil 2 (an outer coil 2a and an inner coil 2b) for heating the object 10 to be heated on the top plate 1 by induction by generating high frequency magnetic field. The top plate 1 is made of an electrically insulating material such as glass. Infrared light can penetrate through the top plate 1. The heating coil 2 is arranged below the top plate 1. The heating coil 2 is concentrically divided into two parts, i.e., the outer coil 2a and the inner coil 2b. A clearance is arranged between the outer coil 2a and the inner coil 2b. The object 10 to be heated is heated by an eddy current generated by the high frequency magnetic field of the heating coil 2.
An operation unit 4 is arranged on the user side of the top plate 1. With the operation unit 4, the user gives instructions such as start/stop. A display unit 12 is arranged between the operation unit 4 and the object 10 to be heated. Below the operation unit 4 and the display unit 12, a light source 14 is arranged to illuminate the operation unit 4 and the display unit 12.
The infrared sensor 3 is arranged below the gap between the outer coil 2a and the inner coil 2b. Since the high frequency magnetic field of the heating coil 2 is strong at this position, the infrared sensor 3 can detect the approximate maximum temperature of the bottom surface of the object 10 to be heated (an output corresponding to the temperature at a position in the radius direction of the cooking container). The infrared light based on the temperature of the bottom surface of the object 10 to be heated that is emitted from the bottom surface of the object 10 to be heated passes through the top plate 1 and the clearance between the outer coil 2a and the inner coil 2b, and the infrared sensor 3 receives the infrared light. The infrared sensor 3 detects the received infrared light, and outputs an infrared light detection signal 35 based on the amount of detected infrared light.
Below the heating coil 2, a rectifying/smoothing unit 6 is arranged to convert an alternating voltage provided by a commercial power source 5 into a direct current voltage, and an inverter circuit 7 is arranged to receive the direct current voltage from the rectifying/smoothing unit 6, generate a high frequency current, and output the generated high frequency current to the heating coil 2. An input current detection unit 9 is arranged between the commercial power source 5 and the rectifying/smoothing unit 6 to detect the magnitude of the input current flowing from the commercial power source 5 to the rectifying/smoothing unit 6.
The rectifying/smoothing unit 6 includes a full-wave rectifying device 61 constituted by bridge diodes, and also includes a low pass filter connected to the output terminal of the full-wave rectifying device 61 and constituted by a choke coil 62 and a smoothing capacitor 63. The inverter circuit 7 includes a switching device 73 (in the present embodiment, IGBT), a diode 72 connected in antiparallel with the switching device 73, and a resonant capacitor 71 connected in parallel with the heating coil 2. The switching device 73 of the inverter circuit 7 turns on and off to generate high frequency current. A high frequency inverter is constituted by the inverter circuit 7 and the heating coil 2.
The induction heat cooking device according to the present embodiment further includes a control unit 8 for controlling the operation of the induction heat cooking device. The control unit 8 has a heating control unit 81 for controlling the high frequency current provided from the inverter circuit 7 to the heating coil 2 by controlling ON/OFF state of the switching device 73 of the inverter circuit 7. The heating control unit 81 controls ON/OFF state of the switching device 73 based on a signal transmitted from the operation unit 4 and a temperature detected by the infrared sensor 3.
The control unit 8 further has an input power integration unit 82 for adding up an input power. The input power integration unit 82 adds up the input power based on the input current detected by the input current detection unit 9. For example, the input power integration unit 82 calculates the integration value of the input power since the preheating has started. In a case where the input current is deemed to be approximately constant, the input power integration unit 82 may calculate the integration value of the input power based on the elapsed time. The input power can be calculated from a product of the input current and the input voltage, and accordingly, the input power may be obtained by measuring the input voltage. Alternatively, the input voltage may be deemed to be constant, and the integration value of the input power may be simply calculated from the input current and the elapsed time.
The induction heat cooking device according to the present embodiment further includes a notification unit 13. The notification unit 13 is, for example, a speaker for outputting a beep sound. More specifically, when the preheating is finished, the notification unit 13 outputs a beep sound for notifying the finish of preheating.
The display unit 12 includes an operation mode display unit 12a indicating an operation mode, a heating power display unit 12b indicating the magnitude of the output of the heating coil 2, and a timer display unit 12c indicating the remaining time of a timer. The operation mode is a mode for suitably setting the operation of the inverter circuit 7 for various kinds of cooking (for example, preheating, heating, fried food, boiling water, and cooking rice). As shown in the left column of the following Table 1, the induction heat cooking device according to the present embodiment includes five operation modes, i.e., “preheating heating mode”, “heating mode”, “fried food mode”, “water boiling mode”, and “rice cooking mode”. When the user selects “preheating heating mode”, the induction heat cooking device according to the present embodiment performs operation in “preheating mode”, “waiting mode”, and “heating mode” in order, the details of which will be described in detail later.
The operation unit 4 is arranged on the front side (user side) of the display unit 12. The operation unit 4 includes a plurality of capacitance switches 4a to 4f. The user uses the switches 4a to 4f to give instructions about cooking. The switches 4a to 4f are arranged according to the number of heating portions 11.
Particular functions are respectively assigned to the switches 4a to 4f. For example, the switch 4a is an ON/OFF switch for controlling start and stop of cooking.
The switch 4b is a menu switch for switching the operation mode to either “preheating heating mode”, “heating mode”, “fried food mode”, “water boiling mode”, “rice cooking mode”. Every time the user presses down the menu switch 4b, characters and pictures representing “heating”, “preheating heating”, “fried food”, “water boiling”, “rice cooking” blink in this order in the operation mode display unit 12a, so that the user switches the selection of the operation mode. When the user selects any one of the operations modes, i.e., “heating mode”, “preheating heating mode”, “fried food mode”, “water boiling mode”, “rice cooking mode”, and manipulates the ON/OFF switch 4a, the selected operation mode is decided. Accordingly, an indication corresponding to the decided operation mode is lighted, and indications corresponding to the undecided operation modes are turned off.
The switch 4c is a heating power setting switch for increasing the heating power. The switch 4d is a heating power setting switch for decreasing the heating power. During operation in “heating mode” or “waiting mode”, the heating power can be set by manipulating the heating power setting switches 4c and 4d.
The switches 4e, 4f are timer switches for setting a heating time.
When the control unit 8 detects that the switches 4a to 4f are pressed down, the control unit 8 controls the inverter circuit 7 based on the pressed switch, and controls the high frequency current provided to the heating coil 2.
The present embodiment aims at performing preheating when high heating power is required, for example, when stir-fried food is cooked. Therefore, the preheating target temperature is high in the present embodiment (for example, 250° C. to 270° C.), and the output obtained at a high temperature is used. Accordingly, as shown by the output characteristics 35a, the infrared sensor 3 according to the present embodiment has characteristics that the infrared sensor 3 outputs the infrared light detection signal 35 when the temperature of the bottom surface of the object 10 to be heated is approximately 250° C. or more, but the infrared sensor 3 does not output the infrared light detection signal 35 when the temperature is less than approximately 250° C. In this case, “the infrared sensor 3 does not output the infrared light detection signal 35” means not only that “the infrared sensor 3 does not output the infrared light detection signal 35 at all”, but also that “the infrared sensor 3 substantially does not output the infrared light detection signal 35”, namely, “the infrared sensor 3 outputs a signal which is so weak that the control unit 8 is substantially unable to read the change of the temperature of the bottom surface of the object 10 to be heated based on the change of the magnitude of the infrared light detection signal 35”. When the object 10 to be heated has a temperature within a range in which the signal is outputted, i.e., when the object 10 to be heated has a temperature of approximately 250° C. or more, the output value of the infrared light detection signal 35 has a monotonically increasing characteristic in nonlinear manner, and increases in an exponential function manner, in which the gradient of increase becomes steeper as the object 10 to be heated has a higher temperature.
In a case where the infrared sensor 3 receives weak disturbance light, the infrared sensor 3 outputs a signal having a small value due to the disturbance light as shown by the output characteristic 35b even when the temperature is less than 250° C. In a case where the infrared sensor 3 receives intense disturbance light such as sunbeam, the infrared sensor 3 outputs a signal having a large value as shown by the output characteristic 35c even when the temperature is less than 250° C.
As mentioned above, the infrared light detection signal 35 outputted by the infrared sensor 3 is affected by the disturbance light. In order to overcome this problem, in the present embodiment, the finish of preheating, i.e., whether the object 10 to be heated has reached the target temperature or not, is determined based on whether an output increment ΔV of the voltage value V of the infrared light detection signal 35 has exceeded a first predetermined increment ΔV1 since the preheating has started. The details of the predetermined increments ΔV1, ΔV2 of
Operation of the control unit 8 of the induction heat cooking device according to the present embodiment structured as described above will be hereinafter described.
When the preheating is finished, the operation mode is changed from the preheating mode to the waiting mode. In the waiting mode, the control unit 8 accepts the manipulation of the heating power setting switches 4c, 4d by the user. In the waiting mode, the characters of “preheating”, which were blinking, are now lighting up, and the heating power bar 111 is displayed (
In a case where the object 10 to be heated is a cooking container made of glossy metal such as aluminum, the emissivity of infrared light is extremely low. As a result, even when the temperature of the object 10 to be heated increases, the output increment ΔV of the infrared sensor does not immediately increase. In order to overcome this problem, the present embodiment is configured such that the preheating is finished based on the integration value of the input power from the start of the preheating, so that the preheating can be finished accurately even when the object 10 to be heated is a metal pot. When the output increment ΔV of the infrared sensor is determined to be less than the first predetermined increment ΔV1 (No in S704), the control unit 8 determines whether the integration value of the input power from the start of the preheating has exceeded a predetermined value (S705). When the integration value of the input power is determined to have exceeded the predetermined value (Yes in S705), the finish of the preheating is notified (S706). When the integration value of the input power is determined not to have exceeded the predetermined value, the flow is returned to step S701.
The control unit 8 determines whether the output increment ΔV of the infrared sensor 3 is less than a third predetermined increment ΔV3 that is equal to or less than the second predetermined increment ΔV2 (S805). When the output increment ΔV of the infrared sensor 3 is determined to be less than the third predetermined increment ΔV3 (Yes in S805), the amount of heating electricity is returned back to the second heating output (S801). When the output increment ΔV of the infrared sensor 3 is determined not to be less than the third predetermined increment ΔV3 (No in S805), the heating continues with the third heating output.
When the heating power setting switches 4c, 4d are manipulated in the waiting mode (Yes in S802), the waiting mode is terminated, and the operation mode is changed to the heating mode.
The control unit 8 determines whether the output increment ΔV of the infrared sensor 3 has attained a value less than a fifth predetermined increment ΔV5 that is equal to or less than the fourth predetermined increment ΔV4 (S905). When the output increment ΔV of the infrared sensor 3 attains a value less than the fifth predetermined increment ΔV5 (Yes in S905), the control unit 8 changes the amount of heating electricity back to the fourth heating output (S901). When the output increment ΔV of the infrared sensor 3 is determined not to be less than the fifth predetermined increment ΔV5 (No in S905), the heating continues with the fifth heating output. When an instruction for terminating the heating is given in the heating mode (Yes in S902), the heating is terminated.
At a time t0, the user selects and decides “preheating heating mode”, and the operation starts in preheating mode. In the preheating mode, the control unit 8 starts the preheating with the first heating output (for example, 3 kW). The preheating continues with the first heating output until the output increment ΔV of the infrared sensor 3 reaches the first predetermined increment ΔV1. At a time t1, the output increment ΔV of the infrared sensor 3 reaches the first predetermined increment ΔV1. The control unit 8 determines that the object 10 to be heated has attained the target temperature of the preheating, and changes the operation mode to the waiting mode.
In the waiting mode, the control unit 8 starts the heating with the second heating output (for example, 1 kW) that is smaller than the output in the preheating mode (time t1 to time t2). When the amount of heating electricity is reduced, the distribution of the temperature of the object 10 to be heated is averaged. Accordingly, at the time t1, the output of the infrared sensor 3 temporarily decreases. It should be noted that the infrared sensor 3 is arranged at such position that the infrared sensor 3 can detect the approximate maximum temperature of the bottom surface of the object 10 to be heated. Thereafter, the output of the infrared sensor 3 increases again. At the time t2, the output increment ΔV of the infrared sensor 3 reaches the second predetermined increment ΔV2 that is larger than the first predetermined increment ΔV1. The control unit 8 changes the amount of heating electricity to the third heating output (for example, 0 kW) that is smaller than the second heating output. At a time t3, the output increment ΔV of the infrared sensor 3 attains a value less than the third predetermined increment ΔV3 that is equal to or less than the second predetermined increment ΔV2. The control unit 8 changes the amount of heating electricity back to the second heating output (for example, 1 kW).
As described above, in the waiting mode, the following operations are repeatedly performed: when the output increment ΔV of the infrared sensor 3 attains a value equal to or more than the second predetermined increment ΔV2, the amount of heating electricity is reduced to the third heating output (for example, 0 kW), and when the output increment ΔV of the infrared sensor 3 attains a value less than the third predetermined increment ΔV3, the amount of heating electricity is returned back to the second heating output (for example, 1 kW). By repeating the above operations, the temperature of the object 10 to be heated in the waiting mode is maintained within a temperature range suitable for the preheating, i.e., the temperature of the object 10 to be heated does not become less than the temperature obtained at the finish of the preheating (for example, approximately 250° C.).
As described above, because the temperature of the object 10 to be heated is detected based on the output increment ΔV of the infrared sensor 3 since the start of the heating, the detected temperature is less likely to be affected by static disturbance light. Further, because the temperature of the object 10 to be heated is detected based on the output increment ΔV of the infrared sensor 3 since the start of the heating, the detected temperature is not largely affected by the temperature of the object 10 to be heated at the start of the heating. Accordingly, the preheating can be finished within a temperature range that can be tolerated from a practical point of view, and the temperature of the object 10 to be heated can be maintained at an appropriate temperature after the preheating has been finished. In other words, in a case where the temperature of the object 10 to be heated at the start of the heating is such a temperature that the output of the infrared sensor 3 can be detected, the gradient of the increasing output of the infrared sensor 3 becomes steeper as the temperature of the object 10 to be heated increases, even when the temperature is higher than approximately 250° C. in
When the user manipulates the heating power setting switches 4c, 4d at the time t4, the control unit 8 changes the operation mode to the heating mode, and starts the heating with the fourth heating output according to the set heating power. The value of the fourth predetermined increment ΔV4 and the value of the fifth predetermined increment ΔV5, which is less than the fourth predetermined increment ΔV4, are determined based on the set fourth heating output. For example, when the set fourth heating output is determined to be larger than the second heating output, the fourth predetermined increment ΔV4 is set to a value larger than the second predetermined increment ΔV2. On the other hand, for example, when the set fourth heating output is determined to be less than the second heating output, the fourth predetermined increment ΔV4 is set to the same value as the first predetermined increment ΔV1.
At a time t5, the output increment ΔV of the infrared sensor 3 reaches the fourth predetermined increment ΔV4. The control unit 8 reduces the amount of heating electricity to the fifth heating output (for example, 0 kW) that is smaller than the fourth heating output. At a time t6, the output increment ΔV of the infrared sensor 3 attains a value less than a fifth predetermined increment ΔV5 that is equal to or less than the fourth predetermined increment ΔV4. The control unit 8 changes the amount of heating electricity back to the fourth heating output.
As described above, in the heating mode, the following operations are repeatedly performed: when the output increment ΔV of the infrared sensor 3 attains a value equal to or more than the fourth predetermined increment ΔV4, the amount of heating electricity is reduced to the fifth heating output (for example, 0 kW), and when the output increment ΔV of the infrared sensor 3 attains a value less than the fifth predetermined increment ΔV5, the amount of heating electricity is returned back to the fourth heating output. By repeating the above operations, the object 10 to be heated is maintained at the temperature according to the set heating power in the heating mode. In the heating mode, after the start of the heating, the temperature of the object 10 to be heated is detected based on the output increment ΔV of the infrared sensor 3 in the same manner as the temperature of the heated object is detected based on the second predetermined increment ΔV2 as described above, and the effects obtained from this configuration are also the same. The fourth predetermined increment ΔV4 is set to the increment of the voltage outputted by the infrared sensor 3 from when the heating starts to when the temperature of the portion of the heated object measured by the infrared sensor 3 attains, for example, approximately 290° C. Therefore, the temperature is prevented from exceeding the firing temperature of the small amount of oil contained in the heated object.
In the induction heat cooking device according to the present embodiment, the infrared sensor 3 having high thermal responsiveness detects the temperature of the object 10 to be heated. Accordingly, the actual temperature of the object 10 to be heated can be accurately detected. For example, when the bottom surface of the cooking container is warped or the bottom surface of the cooking container is thin, the actual temperature of the object 10 to be heated can be accurately detected without delay in time. Therefore, even when the preheating starts with high heating power (first heating output, for example, 3 kW), the temperature of the object 10 to be heated does not greatly exceed the target temperature, the infrared sensor 3 can immediately detect that the temperature of the object 10 to be heated has reached the target temperature. As a result, the preheating can start with high heating power, and the target temperature can be reached in a short time. Thus, the preheating can be finished in a short time before the heating, even when stir-fried food is cooked, in which cooking starts with a small amount of oil but with high heating power.
Further, the finish of the preheating is accurately performed, and the heating power is reduced right after the operation mode is changed to the waiting mode. Accordingly, the temperature of the object 10 to be heated does not greatly exceed the preheating target temperature after the preheating is finished. Therefore, the object 10 to be heated such as a frying pan can be prevented from reaching an excessively high temperature and deforming or getting discolored.
Still further, in the waiting mode, the heating is performed while the heating power is reduced to the second heating output, and when the output increment ΔV of the infrared sensor 3 attains a value less than the third predetermined increment ΔV3 that is equal to or less than the second predetermined increment ΔV2, the third heating output (for example, 0 kW) is changed back to the second heating output (for example, 1 kW). In other words, the control is performed such that even when the temperature changes after the preheating is finished, the infrared sensor 3 immediately detects the change, and immediately brings the temperature back to the temperature obtained upon the finish of the preheating. Therefore, in a short time, the temperature can be stabilized to the temperature obtained upon the finish of the preheating. In other words, in the waiting mode, it is possible to maintain the temperature obtained upon the finish of the preheating. Accordingly, for example, even after many foods are put into the cooking container in the waiting mode, and the temperature of the cooking container decreases, the temperature can be immediately brought back to the temperature obtained upon the finish of the preheating. Therefore, foods in the cooking container can be sufficiently heated. In addition, efficient heating can be achieved when the operation mode is changed from the waiting mode to the heating mode.
Still further, the temperature obtained upon the finish of the preheating can be maintained. Therefore, the object 10 to be heated can be prevented from being excessively heated. For example, even when a small amount of oil in a pot is heated, the temperature of the pot does not increase rapidly in the waiting mode. Therefore, safe induction heat cooking device can be provided.
In the preheating mode, the setting of the heating power is disabled, and the control is performed so that an appropriate temperature is automatically attained. Accordingly, the preheating is not performed at a temperature that is different from the target temperature of the preheating. Further, after the finish of the preheating is notified, the setting of the heating power is enabled. Therefore, the user can start cooking with the foods kept at an appropriate temperature. In addition, after the preheating is finished, the user can optionally change the heating power according to the foods.
In the preheating, the heating power bar 111 is hidden, which enables the user to easily, visually understand that the heating power cannot be changed. Moreover, after the preheating is finished, the heating power bar 111 is displayed, which enables the user to visually understand that the preheating is finished and that the setting of the heating can be performed. Therefore, the operability is improved.
On the operation mode display unit 12a, the characters of “heating” and the characters of “preheating” are turned on, blinked, or turned off. Accordingly, the user can easily, visually understand the mode in which the operation is currently performed. Therefore, the operability is improved. For example, in the preheating mode, the characters of “heating” are turned on, and the characters of “preheating” are blinked, so that the user is notified that the preheating operation is performed. After the preheating is finished, the character of “preheating” is switched from blinking to continuous lighting, so that the user is notified that the preheating is finished and that the temperature is maintained. When the operation mode is changed from the waiting mode to the heating mode, the characters of “preheating” are turned off, and only the characters of “heating” are lighted, so that the user is notified that the waiting mode is terminated and that the operation mode is changed to the heating mode.
The light receiving device of the infrared sensor 3 employs the photodiode 31 made of silicon. Therefore, the infrared sensor 3 is inexpensive.
The infrared sensor 3 is arranged at a position in the radius direction of the coiled wire of the heating coil 2, i.e., at a position between the outer coil 2a and the inner coil 2b, so that the infrared sensor 3 measures the portion of the bottom surface of the object 10 to be heated located above the position between the coiled wires of the outer coil 2a and the inner coil 2b, at which the heating coil 2 generates the most intense high frequency magnetic field. Accordingly, the infrared sensor 3 can measure the high temperature close to the highest temperature of the object 10 to be heated. Therefore, while the infrared sensor 3 has high detection sensitivity with respect to the high temperature portion of the object 10 to be heated, the power supply to the heating coil 2 can be controlled. Therefore, excessive heating can be prevented.
Further, the preheating control is performed based on the output increment ΔV of the infrared sensor 3. Therefore, the preheating can be performed without being affected by disturbance noise such as light.
Still further, the preheating is finished based on not only the output increment of the infrared sensor 3 but also the integration value of the input power. Therefore, even when a cooking container has extremely low emissivity, excessive heating can be prevented, and appropriate preheating control can be performed.
According to the present embodiment, there are operation modes including “heating mode” for going into “heating mode” without performing preheating and “preheating heating mode” for performing preheating before performing heating. Accordingly, the user can select whether preheating is performed or not. Therefore, the operability can be further improved.
When the degree of adverse effect exerted on the infrared sensor 3 by disturbance light can be sufficiently reduced by improving or adding an optical filter and a light shielding structure, the operation mode may be changed to the waiting mode based on the increment of the output value of the infrared sensor 3 with respect to a predetermined initial output value, instead of the increment ΔV of the output value of the infrared sensor 3 from when the heating starts with the first heating output. For example, the predetermined initial output value may be obtained as follows: the cooking container 10 having a low temperature (for example, 35° C. or less) at which the gradient of increase in the output of the infrared sensor 3 with respect to the change of the temperature of the bottom surface of the cooking container 10 is approximate zero or equal to or less than a predetermined value is placed on the top plate 1, and an output value of the infrared sensor 3 (predetermined initial output value) is measured and stored in advance while the cooking container 10 covers the infrared sensor 3. The predetermined initial output value may be, for example, an increment ΔV of the output value of the infrared sensor 3 with respect to the above output value of the infrared sensor 3 (predetermined initial output value). In other words, the predetermined initial output value may be about the same value as the output value of the infrared sensor 3 that is obtained when the cooking container 10 having a low temperature at which the gradient of increase in the output of the infrared sensor 3 with respect to the change of the temperature of the cooking container 10 is equal to or less than a predetermined value is placed on the top plate 1. In another example, the output value of the infrared sensor may be measured when an object having about the same emissivity as others is used as the cooking container 10 to prevent visible light from entering into the infrared sensor 3. It may be an output value of the infrared sensor 3 under the condition where the infrared sensor 3 does not output the value corresponding to the amount of received light. In this case, the first predetermined increment ΔV1 to the fifth predetermined increment ΔV5 represents the increments ΔV of the output values of the infrared sensor 3 with respect to the predetermined initial output value. The control unit 8 stores the predetermined initial output value to a storage unit (not shown) of the control unit 8, and calculates the difference between the output value of the infrared sensor 3 and the predetermined initial output value, thus easily calculating the increment ΔV of the output value of the infrared sensor 3.
In Embodiment 1, the increment ΔV of the output value of the infrared sensor 3 is the increment of the output value of the infrared sensor 3 with respect to the start of the heating. In this case, when the temperature of the cooking container 10 is high at the start of the heating, the infrared sensor 3 has high output sensitivity. Accordingly, as the temperature comes close to the target temperature, the temperature of which output is actually suppressed and controlled becomes higher than the target temperature. As a result, the error with respect to the target temperature increases. As described above, however, the increment ΔV of the output value of the infrared sensor 3 is the increment of the output value of the infrared sensor 3 with respect to the output value of the infrared sensor 3 that is measured and stored in advance at such a temperature at which the gradient of increase in the output of the infrared sensor 3 with respect to the change of the temperature of the bottom surface of the cooking container 10 is approximate zero or equal to or less than a predetermined value. Therefore, the error is prevented from increasing when the temperature is controlled and adjusted to the target temperature of the cooking container 10.
The first predetermined increment ΔV1 to the fifth predetermined increment ΔV5 may be changed according to the material and the emissivity of the object 10 to be heated. Therefore, appropriate temperature control can be achieved.
In the present embodiment, the waiting mode is a mode for maintaining the temperature obtained at the finish of the preheating. Alternatively, the temperature maintained in the waiting mode may be a predetermined appropriate temperature that is less than the temperature obtained at the finish of the preheating. In this case, the second predetermined increment ΔV2 may be set within the range equal to or less than the first predetermined increment ΔV1.
When the object 10 to be heated is maintained at a high temperature for a long period, the bottom surface of the object 10 to be heated may be discolored. In order to cope with such case, the second heating output may be reduced to, for example, approximately 500 W after the preheating is finished. In this case, after the preheating is finished, the temperature may not return back to the temperature obtained at the finish of the preheating (for example, 180° C. to 200° C.). In this case, however, this preheating process can still serve as the preheating function. Accordingly, the second heating output may be set appropriately.
It should be noted that the fourth predetermined increment ΔV4 and the fifth predetermined increment ΔV5 equal to or less than the fourth predetermined increment ΔV4 may be decided regardless of the magnitude of the set fourth heating output. In this case, the fourth predetermined increment ΔV4 is also set larger than the second predetermined increment ΔV2. When the set fourth heating output is larger than the second heating output, the fourth predetermined increment ΔV4 is set larger than the second predetermined increment ΔV2, and as the set fourth heating output becomes larger, the fourth predetermined increment ΔV4 may be set smaller. When the fourth heating output is extremely large, the heated object is prevented from reaching an excessively high temperature by increasing the responsiveness in the temperature suppression.
When the preheating mode is terminated, and the operation mode is changed to the waiting mode, the characters of “preheating” may be turned off.
The notification unit 13 may be a speaker for outputting voice guide, LEDs, a liquid crystal, and the like.
In the present embodiment, the infrared sensor 3 outputs the infrared light detection signal 35 when the temperature is approximately 250° C. or more. However, this value is not limited to approximately 250° C. For example, this value may be a temperature less than or higher than 250° C. However, in order to make the infrared sensor 3 inexpensively and in view of variation of the circuit of the control unit 8, the output of the infrared light detection signal 35 preferably starts when the temperature is within the range between 240° C. and 260° C.
The light receiving device of the infrared sensor 3 may be other types of photodiodes and phototransistors, and the infrared sensor 3 may be a quantum infrared sensor. In addition, the infrared sensor 3 may be not only the quantum infrared sensor but also other types of infrared sensors such as a thermopile.
In the description of Embodiment 2, the first predetermined increment ΔV1 is set according to the material of the object 10 to be heated. In a case where the cooking container is made of glossy metal such as aluminum, the emissivity of infrared light is extremely low. As a result, even when the temperature of the object 10 to be heated increases, the output increment ΔV of the infrared sensor does not immediately increase. In order to overcome this problem, the present embodiment is configured such that even when the object 10 to be heated is a metal pot, the first predetermined increment ΔV1 is set according to whether the cooking container is made of aluminum or not, so that the preheating can be finished more accurately.
When the value of the heating coil current is compared with the value of the input current, and the cooking container made of aluminum is heated, the hating coil current has a larger value, compared with a case where other metal materials such as iron and stainless are heated. Therefore, it can be determined whether the cooking container is made of aluminum or not based on the detected input current and the detected heating coil current. The heating control unit 81 determines whether the material of the cooking container identified by the material determination unit 83 is aluminum or not (S1202). When the material is determined to be aluminum, the first predetermined increment ΔV1 is set to an increment α (S1203). When the material is determined not to be aluminum, the first predetermined increment ΔV1 is set to an increment β (S1204). It should be noted that α is less than β.
The first predetermined increment ΔV1 thus set is used in step S704 of
The emissivity of infrared light emitted from the cooking container made of aluminum is smaller than the emissivity of infrared light emitted from other metal materials such as iron. When the radiant quantity is the same, the temperature of the cooking container made of aluminum is higher than the temperature of the cooking container made of other metal materials. Accordingly, when the first predetermined increment ΔV1 is kept constant, and the material of the cooking container is aluminum, the cooking container may be excessively heated. Therefore, the present embodiment is configured such that the material of the cooking container is determined, and when the determined material is aluminum, the first predetermined increment ΔV1 is set smaller, compared with a case where the determined material is other metal materials such as iron. As a result, even when the cooking container is made of aluminum, excessive heating can be prevented, the cooking container is prevented from reaching an excessively high temperature. In other words, as shown in
In the present embodiment, the first predetermined increment ΔV1 is changed according to whether the material is aluminum or not (for example, whether aluminum or iron). Likewise, this can also be applied to other materials. According to the emissivities of materials, the first predetermined increment ΔV1 may be changed such that the first predetermined increment ΔV1 for a material having high emissivity may be set smaller than the first predetermined increment ΔV1 for a material having low emissivity. In such case, similar effects can be obtained.
It should be noted that the increments α, β set as the first predetermined increment ΔV1 may be changed. Accordingly, even when the material of the cooking container to be heated and the degree of warpage of the bottom surface of the cooking container are beyond the scope of assumption, appropriate temperature control can be performed. In addition, the safety can be improved, and efficient heating can be achieved.
As shown by the object 10 to be heated in
It should be noted that the predetermined electric power integration value in S705 of
The heating coil current detection unit 15 can detect the magnitude of the heating coil current. For example, the heating coil current detection unit 15 can detect a voltage or a current in proportional to the magnitude of the heating coil current, such as the voltage of the resonant capacitor 71 and the voltage or the current of the switching device 73. In Embodiments 1 and 2, the input current detection unit 9 is a current transformer, but is not limited thereto. For example, a shunt resistor having a very small resistance of 0.1 to 10 milliohms may be connected to the input current path, and the magnitude of the input current may be measured based on the voltage drop thereof. Further, the material determination unit 83 is not limited to the above configuration. The material determination unit 83 can be anything as long as it can determine the material of the cooking container.
As described above, the induction heat cooking device according to the present embodiment can properly detect the temperature of the cooking container, and can maintain the temperature of the cooking container at an appropriate temperature, without being affected by the difference in emissivity of the infrared light due to the material of the cooking container, the temperature of the buoyancy reduction plate at the start of the heating, or the warpage of the bottom surface of the cooking container. Accordingly, the excessive temperature increase can be prevented. Therefore, the induction heat cooking device according to the present embodiment is useful for an induction heat cooking device used in ordinary households and commercial-use kitchens.
In the description of Embodiment 3, an induction heat cooking device can perform heating without causing problems in a cooking container. When a cooking container is heated for a long time, the cooking container is discolored or deteriorated (for example, deterioration of coated fluorine resin). In order to solve this problem, when the switch is not manipulated for a long time, for example, when the user does not cook or forgets to turn off the switch, the heating is halted in Embodiment 3. More specifically, in the waiting mode, when a predetermined time passes without the switch being manipulated by the user, the heating is halted. Therefore, the cooking container is prevented from being discolored and damaged.
When the heating power setting switches 4c, 4d are determined not to be manipulated (No in S1602), the control unit 8 determines whether or not the timer time measured by the timer count unit 20 exceeds the first predetermined time (for example, five minutes) (S1604). When the timer time is determined to exceed the first predetermined time, the control unit 8 causes the notification unit 13 to output a voice message for notifying that the heating is halted (S1605). For example, the notification unit 13 outputs a voice message “heating will be halted”. Thereafter, the control unit 8 stops heating (S1606). When the timer time is determined not to have exceeded the first predetermined time (for example, five minutes), the control unit 8 determines whether or not the timer time exceeds the second predetermined time (for example, three minutes) that is shorter than the first predetermined time (S1607). When the timer time is determined to have exceeded the second predetermined time, the control unit 8 causes the notification unit 13 to output a voice message for prompting the user to cook. For example, the notification unit 13 outputs a voice message “please start cooking”. When the timer time is determined not to have exceeded the second predetermined time, the flow is returned to step S1602.
When the user does not perform any operation after the preheating is finished, the heating is halted. Accordingly, the cooking container is prevented from problems. More specifically, the cooking container is prevented from being discolored and damaged.
Further, a voice message for prompting the user to start cooking is outputted before the heating is halted. Accordingly, the voice message can prompt the user to put foods into the cooking container and start cooking before the heating is halted. Therefore, this provides greater convenience for the user. Further, when the heating is halted, a voice message for notifying the halt of the heating is outputted. Accordingly, the voice message can notify the user that the heating is halted.
When the heating power setting switches 4c, 4d are manipulated in the waiting mode, the counting of the timer time is halted, and the heating is continued. Accordingly, the user can continue cooking when the user wants to cook. Therefore, this provides greater convenience for the user.
In the waiting mode, the timer display unit 12c displays the remaining time until the heating is automatically halted, which allows the user to visually, easily understand the remaining time until the termination of the heating. Therefore, the user can be prompted to do cooking.
In the present embodiment, the heating is halted in step S1606. Alternatively, instead of halting the heating, the heating output may be switched to a heating output that is smaller than the current heating output. Even in such case, the same effects as the present embodiment can be obtained.
In the foregoing description of the present embodiment, the heating power setting switches 4c, 4d are pressed down in step S1602. Alternatively, any switch other than the heating power setting switches 4c, 4d may be pressed down instead. For example, if the timer switches 4e, 4f is pressed down in S1602, the same operation as that of the present embodiment may be performed.
In S1608, the voice message for prompting the user to do cooking may be outputted only once after the timer time exceeds the second predetermined time. Alternatively, the voice message may be repeatedly outputted with a predetermined interval (for example, every 30 seconds).
When the user presses down a predetermined switch arranged within the operation unit 4 until the timer time reaches the first predetermined time, the count value of the timer time may be reset, and the count may be started all over again. When the timer time reaches a third predetermined time (for example, 10 minutes) that is longer than the first predetermined time (for example, 5 minutes), the heating may be halted. With this configuration, even when the user manipulates the switch so as to do cooking but thereafter forgets to turn off the heating, the heating can be automatically halted, and the safety can be improved.
In the present embodiment, the operation in the waiting mode has been described. Further, when the user does not manipulate the switch for a long time in the heating mode, the heating output may be reduced to a heating output that is smaller than the current heating output, or the heating may be halted. For example, the timer count unit 20 may measure a time from when the operation mode is changed to the heating mode, and between step S901 and step S902 of
In a case where the user does not perform any operation after the preheating is finished, the induction heat cooking device according to the present embodiment can stop heating before the cooking container is discolored and damaged, and can perform heating without causing problems in the cooking container. Therefore, the induction heat cooking device according to the present embodiment is useful for an induction heat cooking device used in ordinary households and commercial-use kitchens.
The induction heat cooking device according to the present invention can finish preheating in a short time when the load is small, and can maintain the temperature after the finish of the preheating. Therefore, the induction heat cooking device according to the present invention is useful for an induction heat cooking device used in ordinary households and restaurants in which stir-fried food and the like are cooked.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-036828 | Feb 2008 | JP | national |
| 2008-061303 | Mar 2008 | JP | national |
| 2008-086059 | Mar 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/000711 | 2/19/2009 | WO | 00 | 8/18/2010 |
